White light generation by resonant nonradiative energy
transfer from epitaxial InGaN/GaN quantum wells to colloidal
CdSe/ZnS core/shell quantum dots
Sedat Nizamoglu, Emre Sari, Jong-Hyeob Baek, In-Hwan Lee
and Hilmi
Volkan Demir
2008 New J. Phys. 10 123001 (10pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123001
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We propose and
demonstrate white-light-generating nonradiative energy
transfer (ET) from epitaxial quantum wells (QWs) to
colloidal quantum dots (QDs) in their close proximity. This
proof-of-concept hybrid color-converting system consists of
chemically synthesized red-emitting CdSe/ZnS core/shell
heteronanocrystals intimately integrated on epitaxially
grown cyan-emitting InGaN/GaN QWs. The
white light is generated by the collective luminescence
of QWs and
QDs, for which the dot emission is further increased by
63% with
nonradiative ET, setting the operating point in the
white region of
CIE chromaticity diagram. Using cyan emission at 490 nm
from the
QWs and red emission at 650 nm from the nanocrystal (NC)
luminophors, we obtain warm white light generation with
a
correlated color temperature of Tc = 3135 K and
tristimulus
coordinates of (x,y) = (0.42, 0.39) in the white region.
By
analyzing the time-resolved radiative decay of these NC
emitters in
our hybrid system with a 16 ps time resolution, the
luminescence
kinetics reveals a fast ET with a rate of (2 ns)-1 using
a
multiexponential fit with χ 2 = 1.0171.
Fingering
instabilities on reaction fronts in the CO oxidation
reaction on Pt(100)
D Bilbao and J Lauterbach
2008 New J. Phys. 10 123002 (10pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123002
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Fingering
instabilities arising from local perturbations to planar
reaction fronts in the CO oxidation reaction on Pt(100)
are
presented. CO oxidation represents a heterogeneous
nonlinear system
with the necessary kinetic and diffusive transport
properties to
support the development of fingered wave fronts.
External forcing
was utilized to create CO wave fronts on an otherwise
monostable,
O-covered surface, which, upon destabilization, gave
rise to
fingers of adsorbed CO extending into the O adlayer
ahead of the
reaction front. Finger spreading and tip-splitting were
observed as
the finger pattern evolved towards an intrinsic
wavelength,
independent of the length of the reaction front,
calculated to be
approximately 40 um. Our data also show the presence of
a shielding
process, where at wavelengths less than twice the
observed
intrinsic value, additional fingers were created on the
reaction
front through a tip-splitting bifurcation of an existing
finger. At
wavelengths greater than twice the intrinsic value,
additional
fingers formed in the troughs between adjacent fingers,
apparently
unaffected by the presence of the larger surrounding
fingers.
Superconductivity at 34.7 K in the iron arsenide
Eu0.7Na0.3Fe2As2
Yanpeng Qi, Zhaoshun Gao, Lei Wang, Dongliang Wang,
Xianping Zhang and
Yanwei Ma
2008 New J. Phys. 10 123003 (6pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123003
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EuFe2As2 is a member
of the ternary iron arsenide family. Similar to
BaFe2As2 and SrFe2As2, EuFe2As2 exhibits a clear anomaly
in
resistivity near 200 K. Here, we report the discovery of
superconductivity in Eu0.7Na0.3Fe2As2 by partial
substitution of
the europium site with sodium. ThCr2Si2 tetragonal
structure, as
expected for EuFe2As2, is formed as the main phase for
the
composition Eu0.7Na0.3Fe2As2. Resistivity measurements
reveal that
the transition temperature Tc as high as 34.7 K is
observed in this
compound. The rate of Tc suppression with the applied
magnetic
field is 3.87 T K−1, giving an extrapolated
zero-temperature
upper critical field of 100 T. It demonstrates a very
encouraging
application of the new superconductors.
Magnetization
dynamics in optically excited nanostructured nickel films
Georg M Mu"ller, Gerrit Eilers, Zhao Wang, Malte Scherff,
Ran Ji,
Kornelius Nielsch, Caroline A Ross and Markus
Mu"nzenberg
2008 New J. Phys. 10 123004 (9pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123004
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In this work, the
laser-induced magnetization dynamics of
nanostructured nickel films is investigated. The
influence of the
nanosize is discussed considering the timescale of
hundreds of
femtoseconds as well as the GHz regime. While no
nanosize effect is
observed on the short timescale, the excited magnetic
mode in the
GHz regime can be identified by comparison with
micromagnetic
simulations. The thickness dependence reveals insight
into the
dipole interaction between single nickel structures.
Also,
transient reflectivity changes are discussed.
Creation
of three-species 87Rb-40K-6Li molecules: interfering for the
best
Hui Jing, Yajing Jiang, Weiping Zhang and Pierre Meystre
2008 New J. Phys. 10 123005 (11pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123005
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An ultracold
three-species Bose-Fermi-Fermi degenerate atomic mixture
87Rb-40K-6Li was realized very recently (Tagliber M et
al 2008
Phys. Rev. Lett. 100 010401). Here, we study the
creation of
heteronuclear triatomic molecules in this mixture, and
show that a
constructive triple-path interference can lead to an
almost ideal
conversion rate, in comparison with the single- or
double-path
cases. The important effect of the initial population
imbalance on
the atom-molecule dark state is also investigated.
Subtracting
photons from arbitrary light fields: experimental test of
coherent state invariance by single-photon annihilation
A Zavatta, V Parigi, M S Kim and M Bellini
2008 New J. Phys. 10 123006 (10pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123006
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The operator
annihilating a single quantum of excitation in a bosonic
field is one of the cornerstones for the interpretation
and
prediction of the behavior of the microscopic quantum
world. Here
we present a systematic experimental study of the
effects of
single-photon annihilation on some paradigmatic light
states. In
particular, by demonstrating the invariance of coherent
states by
this operation, we provide the first direct verification
of their
definition as eigenstates of the photon annihilation
operator.
Vector
frequency-comb Fourier-transform spectroscopy for
characterizing
metamaterials
T Ganz, M Brehm, H G von Ribbeck, D W van der Weide and
F Keilmann
2008 New J. Phys. 10 123007 (14pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123007
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We determine
infrared transmission amplitude and phase spectra of
metamaterial samples at well-defined incidence and
polarization
with a vector ('asymmetric') frequency-comb
Fourier-transform
spectrometer (c-FTS) that uses no moving elements. The
metamaterials are free-standing metallic hole arrays; we
study
their resonances in the 7-13 um and 100-1000 um
wavelength regions
due both to interaction with bulk waves (Wood anomaly)
and with
leaky surface plasmon polaritons (near-unity
transmittance,
coupling features and dispersion). Such complex-valued
transmission
and reflection spectra could be used to compute a
metamaterial's
complex dielectric function directly, as well as its
magnetic and
magneto-optical permeability functions.
Spatial and temporal development of the plasma
potential in differently
configured pulsed magnetron discharges
Th Welzel, Th Dunger, B Liebig and F Richter
2008 New J. Phys. 10 123008 (16pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123008
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Time-resolved
emissive probe measurements have been performed to study
the spatio-temporal development of the plasma potential
in an
asymmetric bipolar pulsed magnetron discharge. The
influence of the
substrate potential as well as of the substrate position
has been
investigated while the further conditions were the same.
To access
the entire potential range which was between -100 V and
+ 400 V and
to obtain sufficient time-resolution of the emissive
probe,
different heating currents had to be used. The plasma
potential has
been found to be typically close to zero in the 'on'
phase, about +
40 V in the stable 'off' phase and up to + 400 V at
the beginning
of the 'off' phase, which is in agreement with the
results of other
authors. However, the positive values in the 'off' phase
are
generally lower than those reported and stay mostly
below the
target potential. This is explained by macroscopic
considerations
of the quasineutrality of the plasma taking into account
a magnetic
and geometrical shielding of the target, acting as an
anode in the
'off' phase, and the potential and position of the
substrate holder
and environment.
Illustration
of quantum complementarity using single photons interfering
on a grating
V Jacques, N D Lai, A Dre'au, D Zheng, D Chauvat, F
Treussart, P
Grangier and J-F Roch
2008 New J. Phys. 10 123009 (11pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123009
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A recent experiment
performed by Afshar et al (2007 Found. Phys. 37
295-305) has been interpreted as a violation of Bohr's
complementarity principle between interference
visibility and
which-path information (WPI) in a two-path
interferometer. We have
reproduced this experiment, using true single-photon
pulses
propagating in a two-path wavefront-splitting
interferometer
realized with a Fresnel's biprism, and followed by a
grating with
adjustable transmitting slits. The measured values of
interference
visibility V and WPI, characterized by the
distinguishability
parameter D, are found to obey the complementarity
relation
V2+D2⩽1. This result demonstrates that the
experiment can be
perfectly explained by the standard interpretation of
quantum
mechanics.
A
stochastic theory for temporal fluctuations in
self-organized
critical systems
M Rypdal and K Rypdal
2008 New J. Phys. 10 123010 (11pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123010
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A stochastic theory
for the toppling activity in sandpile models is
developed, based on a simple mean-field assumption about
the
toppling process. The theory describes the process as an
anti-persistent Gaussian walk, where the diffusion
coefficient is
proportional to the activity. It is formulated as a
generalization
of the Ito^ stochastic differential equation with an
anti-persistent fractional Gaussian noise source and a
deterministic drift term. An essential element of the
theory is
rescaling to obtain a proper thermodynamic limit. When
subjected to
the most relevant statistical tests, the signal
generated by the
stochastic equation is indistinguishable from the
temporal features
of the toppling process obtained by numerical simulation
of the
Bak-Tang-Wiesenfeld sandpile.
Laser
heating of large noble gas clusters: from the resonant to
the relativistic interaction regimes
E T Gumbrell, A S Moore, J A Lazarus, E L Clark, P M
Nilson, W J
Garbett, A J Comley, J S Robinson, M Hohenberger, R D
Edwards, R E
Eagleton, R J Clarke, D R Symes and R A Smith
2008 New J. Phys. 10 123011 (19pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123011
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Wide-ranging
measurements of sub-picosecond laser interactions with
large noble gas cluster targets have been conducted in
order to
help clarify the nature and extent of the underlying
laser-plasma
heating. Within the sub-relativistic vacuum irradiance
range of
1016-1017 W cm-2, we find that electron temperatures
measured with
continuum x-ray spectroscopy exhibit a pronounced
multi-keV
enhancement. Analysis indicates this behaviour to be
consistent
with collisional or collisionless resonant heating
mechanisms. We
also present the first measurements of laser-to-cluster
energy
deposition at relativistic vacuum irradiances, our data
demonstrating absorption fractions of 90% or more.
Optical probing
was used to resolve the onset of a supersonic ionization
front
resulting from this very high absorption, and shows that
despite
significant pre-focus heating, the greatest plasma
energy densities
can be generated about the vacuum focus position.
Electron energy
spectra measurements confirm that laser-plasma
super-heating
occurs, and together with ion data establish that
relativistic
laser-plasma coupling in atomic clusters can take place
without
significant MeV particle beam production. In conjunction
with
optical self-emission data, the optical probing also
indicates
laser pre-pulse effects at peak vacuum irradiance of 5 x
1019 W
cm-2. Laser absorption, plasma heating and energy
transport data
are supported throughout with analytical and numerical
modelling.
Coherent
exciton transport on scale-free networks
X P Xu and F Liu
2008 New J. Phys. 10 123012 (9pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123012
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The coherent exciton
transport on a class of deterministic and random
scale-free networks (DSFNs and RSFNs) generated by
simple rules is
studied in this paper. The coherent exciton dynamics is
modeled by
continuous-time quantum walks, and we calculate the
transition
probabilities between two nodes of the networks. We find
that the
transport depends on the initial nodes of the
excitation. For
DSFNs, the probabilities of finding the excitation at
the initial
central nodes are nearly periodic, in contrast to the
flat behavior
found for RSFNs. In the long time limit, the transition
probabilities on DSFNs show characteristic patterns with
identical
values. For RSFNs, we find that the excitation is most
likely to be
found at the initial nodes with high connectivity. All
these
features of quantum transport are significantly
different from
those of the classical transport modeled by
continuous-time random
walks.
Coupled quantum electrodynamics in photonic crystal
cavities towards
controlled phase gate operations
Y-F Xiao, J Gao, X-B Zou, J F McMillan, X Yang, Y-L
Chen, Z-F Han, G-C
Guo and C W Wong
2008 New J. Phys. 10 123013 (13pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123013
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In this paper, a
scalable photonic crystal cavity array, in which
single embedded quantum dots (QDs) are coherently
interacting, is
studied theoretically. Firstly, we examine the spectral
character
and optical delay brought about by the coupled cavities
interacting
with single QDs, in an optical analogue to
electromagnetically
induced transparency. Secondly, we then examine the
usability of
this coupled QD-cavity system for quantum phase gate
operation and
our numerical examples suggest that a two-qubit system
with
fidelity above 0.99 and photon loss below 0.04 is
possible.
Vacuum
fluctuations induced entanglement between two mesoscopic
systems
H T Ng and K Burnett
2008 New J. Phys. 10 123014 (8pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123014
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We study the
dynamics of a pair of molecular ensembles trapped inside a
superconducting resonator through which they are
strongly coupled
via a microwave field mode. We find that entanglement
can be
generated via 'vacuum fluctuations' even when the
molecules and
cavity field are initially prepared in their ground
state. This
entanglement is created in a relatively short time and
without the
need for further manipulation of the system. It
therefore provides
a convenient scheme to entangle two mesoscopic systems,
and may
well be useful for quantum information processing.
Fluid
acceleration in the bulk of turbulent dilute polymer
solutions
Alice M Crawford, Nicolas Mordant, Haitao Xu and
Eberhard Bodenschatz
2008 New J. Phys. 10 123015 (10pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123015
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We studied the
effects of long-chain polymers on the small scales of
turbulence by experimental measurements of Lagrangian
accelerations
in the bulk of turbulent flows of dilute polymer
solutions.
Lagrangian accelerations were measured by following
tracer
particles with a high-speed optical tracking system. We
observed a
significant decrease in the acceleration variance in
dilute polymer
solutions as compared with in pure water. The shape of
the
normalized acceleration probability density functions,
however,
remained the same as in Newtonian water flows. We also
observed an
increase in the turbulent Lagrangian acceleration
autocorrelation
time with polymer concentration. The decrease of
acceleration
variance and the increase of acceleration
autocorrelation time are
consistent with a suppression of viscous dissipation,
and cannot be
explained by a mere increase of effective viscosity due
to the
polymers.
Anomalous
compressive behavior in CeO2 nanocubes under high pressure
M Y Ge, Y Z Fang, H Wang, W Chen, Y He, E Z Liu, N H Su,
K Stahl, Y P
Feng, J S Tse, T Kikegawa, S Nakano, Z L Zhang, U
Kaiser, F M Wu,
H-K Mao and J Z Jiang
2008 New J. Phys. 10 123016 (12pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123016
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High-pressure
angle-dispersive x-ray diffraction measurements have been
performed on bulk and nanocrystalline cubic CeO2 with
mean sizes of
4.7 and 5.6 nm. It is found that the compressibility of
the
nanocrystals is lower than the bulk when a threshold
pressure is
reached. This critical pressure is found to be 10 GPa
for 4.7 nm
and 16 GPa for 5.6 nm CeO2 nanocubes. The particle size
dependence
of the threshold pressure for the hardening of CeO2
nanoparticles
is quite unusual. First-principles electronic
calculations show
that the increased bulk modulus of the nanocrystal is
due to the
strengthening of the surface Ce-O bonds resulting in a
much larger
shear modulus than in the bulk and consequently
hardening the shell
surface.
Controlling
molecular broadband-emission by optical confinement
Mathias Steiner, Antonio Virgilio Failla, Achim
Hartschuh, Frank
Schleifenbaum, Clemens Stupperich and Alfred Johann
Meixner
2008 New J. Phys. 10 123017 (23pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123017
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We investigate
experimentally and theoretically the fluorescence
emitted by molecular ensembles as well as spatially
isolated,
single molecules of an organic dye immobilized in a
quasi-planar
optical microresonator at room temperature. The
optically excited
dipole emitters couple simultaneously to on- and
off-axis cavity
resonances of the microresonator. The multi-spectral
radiative
contributions are strongly modified with respect to free
(non-confined) space due to enhancement and inhibition
of the
molecular spontaneous emission (SpE) rate. By varying
the mirror
spacing of the microresonator on the nanometer-scale,
the SpE rate
of the cavity-confined molecules and, consequently, the
spectral
line width of the microresonator-controlled broadband
fluorescence
can be tuned by up to one order of magnitude. Stepwise
reducing the
optical confinement, we observe that the
microresonator-controlled
molecular fluorescence line shape converges towards the
measured
fluorescence line shape in free space. Our results are
important
for research on and application of broadband emitters in
nano-optics and -photonics as well as
microcavity-enhanced (single
molecule) spectroscopy.
Role of particle interactions in the Feshbach
conversion of fermionic atoms to bosonic molecules
Jie Liu, Li-Bin Fu, Bin Liu and Biao Wu
2008 New J. Phys. 10 123018 (12pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123018
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We investigate the
Feshbach conversion of fermionic atom pairs to
condensed bosonic molecules with a microscopic model
that accounts
for the repulsive interactions among all the particles
involved. We
find that the conversion efficiency is enhanced by the
interaction
between bosonic molecules, while it is suppressed by the
interactions between fermionic atoms and between atoms
and
molecules. In the adiabatic limit, the combined effect
of these
interactions can lead to a ceiling of less than 100% on
the
conversion efficiency for a narrow Feshbach resonance.
Our theory
agrees with the recent Rice experiment on 6Li.
Quantum-state
engineering using nonlinear optical Sagnac loops
Jun Chen, Joseph B Altepeter and Prem Kumar
2008 New J. Phys. 10 123019 (18pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123019
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The Kerr
nonlinearity of an optical-fibre Sagnac loop can be utilized
to engineer a variety of two-photon quantum states.
These include
correlated, identical photon pairs as well as
degenerate, maximally
entangled states - both of which are used in quantum
information
processing. In fact, their underlying principle - the
reverse
Hong-Ou-Mandel effect - can also be applied to
free-space,
down-conversion-based analogues of either identical or
entangled
photon-pair sources. Due to their simple structure, such
versatile
devices are expected to find widespread applications in
quantum-state engineering.
Cubic
nonlinear Schro"dinger equation with vorticity
M Caliari, M I Loffredo, L M Morato and S Zuccher
2008 New J. Phys. 10 123020 (17pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123020
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In this paper, we
introduce a new class of nonlinear Schro"dinger
equations (NLSEs), with an electromagnetic potential (\mathcal
A,\Phi) , both depending on the wavefunction Ψ. The
scalar
potential Φ depends on |Ψ|2, whereas the vector
potential
\mathcal A satisfies the equation of
magnetohydrodynamics with
coefficient depending on Ψ. In Madelung variables,
the velocity
field comes to be not irrotational in general and we
prove that the
vorticity induces dissipation, until the dynamical
equilibrium is
reached. The expression of the rate of dissipation is
common to all
NLSEs in the class. We show that they are a particular
case of the
one-particle dynamics out of dynamical equilibrium for a
system of
N identical interacting Bose particles, as recently
described
within stochastic quantization by Lagrangian variational
principle.
The cubic case is discussed in particular. Results of
numerical
experiments for rotational excitations of the ground
state in a
finite two-dimensional trap with harmonic potential are
reported.
Electronic
relaxation and vibrational dynamics in a thiophene oligomer
studied under the same experimental condition with a
sub-5 fs laser
Zhuan Wang and Takayoshi Kobayashi
2008 New J. Phys. 10 123021 (13pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123021
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123021/njp8_12_123021.pdf
Full text HTML: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123021/njp8_12_123021.html
Using a sub-5 fs
pulse laser, the pump-probe experiment was performed
on a quinoid thiophene derivative and both electronic
relaxation
and vibrational dynamics were clarified with the same
experimental
data. From the data, two population decay times of the
lowest
electronic excited state were determined to be 200 fs
and 1.8 ps,
which can be explained by the assumption that the 21Ag
state lies
below the exciton 11Bu state together with the very low
fluorescence quantum efficiency. The relaxation process
after
excitation by the pump pulse was studied to be
11Bu→11B*u→21Ag→11Ag. According to
the
experimental data, the location of the energy level was
also
discussed. The electronic dephasing time was determined
to be 64
± 4 fs by utilizing the data in the 'negative time'
range. The
vibrational dephasing time constant of the most strongly
coupled
mode with frequency of 1466 cm-1 was determined to be
520 ± 20
fs from the widths of the corresponding Fourier power
spectra.
On
mechanisms of interaction in electrosurgery
Daniel Palanker, Alexander Vankov and Pradeep Jayaraman
2008 New J. Phys. 10 123022 (15pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123022
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123022/njp8_12_123022.pdf
Full text HTML: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123022/njp8_12_123022.html
Electrosurgery is
broadly used in a wide variety of surgical
procedures, yet its underlying mechanisms of interaction
are poorly
characterized. Fundamentals of electrosurgery have not
changed much
since the 1930s - cutting is still performed using
continuous RF
waveforms, leaving a collateral damage zone of hundreds
of
micrometers in depth. Pulsed waveforms with variable
duty cycle are
used mostly for tissue coagulation. Recently, we have
demonstrated
that electrosurgery with microsecond bursts applied via
microelectrodes can provide cellular precision in soft
tissue
dissection. This paper examines dynamics of pulsed
electrical
discharges in conductive medium, and accompanying
phenomena, such
as vaporization, cavitation and ionization. It is
demonstrated that
ionization of the vapor cavity around the electrode is
essential
for energy delivery beyond the vaporization threshold.
It is also
shown that the ionization threshold voltage and
resistance of the
plasma-mediated discharge are much lower in the negative
phase of
the discharge than in the positive one. Capacitive
coupling of the
ac waveform to the electrode compensates for this
asymmetry by
shifting the medium voltage on the electrode, thus
increasing the
positive and decreasing the negative amplitudes to
achieve charge
balance in the opposite phases. With planar insulated
electrodes
having exposed edges of 12.5 um in width and bursts of
40 us in
duration even tough biological tissues can be dissected
with
cellular precision. For example, cartilage dissection is
achieved
with pulse energy of 2.2 mJ per millimeter of length of
the blade,
and leaves a thermal damage zone of only 5-20 um in
width.
Detecting
groups of similar components in complex networks
Jiao Wang and C-H Lai
2008 New J. Phys. 10 123023 (26pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123023
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123023/njp8_12_123023.pdf
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We study how to
detect groups in a complex network each of which
consists of component nodes sharing a similar connection
pattern.
Based on the mixture models and the exploratory analysis
set up by
Newman and Leicht (2007 Proc. Natl. Acad. Sci. USA 104
9564), we
develop an algorithm that is applicable to a network
with any
degree distribution. The partition of a network
suggested by this
algorithm also applies to its complementary network. In
general,
groups of similar components are not necessarily
identical with the
communities in a community network; thus partitioning a
network
into groups of similar components provides additional
information
of the network structure. The proposed algorithm can
also be used
for community detection when the groups and the
communities
overlap. By introducing a tunable parameter that
controls the
involved effects of the heterogeneity, we can also
investigate
conveniently how the group structure can be coupled with
the
heterogeneity characteristics. In particular, an
interesting
example shows a group partition can evolve into a
community
partition in some situations when the involved
heterogeneity
effects are tuned. The extension of this algorithm to
weighted
networks is discussed as well.
Controlling
irreversibility and directionality of light via atomic
motion: optical transistor and quantum velocimeter
C H Raymond Ooi
2008 New J. Phys. 10 123024 (17pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123024
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123024/njp8_12_123024.pdf
Full text HTML: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123024/njp8_12_123024.html
The Doppler effect
of moving atoms can create irreversibility of light.
We show that the laser field in an electromagnetic
induced
transparency (EIT) scheme with atomic motion can control
the
directional propagation of two counter-propagating
output probe
fields in an atomic gas. Quantum coherence and the
Doppler effect
enable the system to function like an optical transistor
with two
outputs that can generate states analogous to the Bell
basis.
Interference of the two output fields from the gas
provides useful
features for determining the mean atomic velocity and
can be used
as a sensitive quantum velocimeter. Some subtle physics
of EIT is
also discussed. In particular, the sign of the
dispersive phase in
EIT is found to have a unique property, which helps to
explain
certain features in the interference.
The
stochastic dance of circling sperm cells: sperm chemotaxis
in the plane
B M Friedrich and F Ju"licher
2008 New J. Phys. 10 123025 (19pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123025
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123025/njp8_12_123025.pdf
Full text HTML: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123025/njp8_12_123025.html
Biological systems
such as single cells must function in the presence
of fluctuations. It has been shown in a two-dimensional
experimental setup that sea urchin sperm cells move
toward a source
of chemoattractant along planar trochoidal swimming
paths, i.e.
drifting circles. In these experiments, a pronounced
variability of
the swimming paths is observed. We present a theoretical
description of sperm chemotaxis in two dimensions which
takes
fluctuations into account. We derive a coarse-grained
theory of
stochastic sperm swimming paths in a concentration field
of
chemoattractant. Fluctuations enter as multiplicative
noise in the
equations for the sperm swimming path. We discuss the
stochastic
properties of sperm swimming and predict a
concentration-dependence
of the effective diffusion constant of sperm swimming
which could
be tested in experiments.
Fundamental
statistical features and self-similar properties of tagged
networks
Gergely Palla, Ille's J Farkas, Pe'ter Pollner, Imre
Dere'nyi and
Tama's Vicsek
2008 New J. Phys. 10 123026 (20pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123026
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123026/njp8_12_123026.pdf
Full text HTML: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123026/njp8_12_123026.html
We investigate the
fundamental statistical features of tagged (or
annotated) networks having a rich variety of attributes
associated
with their nodes. Tags (attributes, annotations,
properties,
features, etc) provide essential information about the
entity
represented by a given node, thus, taking them into
account
represents a significant step towards a more complete
description
of the structure of large complex systems. Our main goal
here is to
uncover the relations between the statistical properties
of the
node tags and those of the graph topology. In order to
better
characterize the networks with tagged nodes, we
introduce a number
of new notions, including tag-assortativity (relating
link
probability to node similarity), and new quantities,
such as node
uniqueness (measuring how rarely the tags of a node
occur in the
network) and tag-assortativity exponent. We apply our
approach to
three large networks representing very different domains
of complex
systems. A number of the tag related quantities display
analogous
behaviour (e.g. the networks we studied are
tag-assortative,
indicating possible universal aspects of tags versus
topology),
while some other features, such as the distribution of
the node
uniqueness, show variability from network to network
allowing for
pin-pointing large scale specific features of real-world
complex
networks. We also find that for each network the
topology and the
tag distribution are scale invariant, and this
self-similar
property of the networks can be well characterized by
the
tag-assortativity exponent, which is specific to each
system.
Evolution
of the Internet and its cores
Guo-Qing Zhang, Guo-Qiang Zhang, Qing-Feng Yang, Su-Qi
Cheng and Tao
Zhou
2008 New J. Phys. 10 123027 (11pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123027
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123027/njp8_12_123027.pdf
Full text HTML: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123027/njp8_12_123027.html
In this paper, we
empirically study the evolution of large scale
Internet topology at the autonomous system (AS) level.
The network
size grows in an exponential form, obeying the famous
Moore's law.
We theoretically predict that the size of the AS-level
Internet
will double every 5.32 years. We apply the k-core
decomposition
method on the real Internet, and find that the size of a
k-core
with larger k is nearly stable over time. In addition,
the maximal
coreness is very stable after 2003. In contrast to the
predictions
of most previous models, the maximal degree of the
Internet is also
relatively stable versus time. We use the edge-exchange
operation
to obtain the randomized networks with the same degree
sequence. A
systematical comparison is drawn, indicating that the
real Internet
is more loosely connected, and both the full Internet
and the
nucleus are more disassortative than their randomized
versions.
How to
make large, void-free dust clusters in dusty plasma under
micro-gravity
V Land and W J Goedheer
2008 New J. Phys. 10 123028 (15pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123028
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123028/njp8_12_123028.pdf
Full text HTML: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123028/njp8_12_123028.html
Collections of
micrometer-sized solid particles immersed in plasma are
used to mimic many systems from solid state and fluid
physics, due
to their strong electrostatic interaction, their large
inertia, and
the fact that they are large enough to be visualized
with ordinary
optics. On Earth, gravity restricts the so-called dusty
plasma
systems to thin, two-dimensional (2D) layers, unless
special
experimental geometries are used, involving heated or
cooled
electrons, and/or the use of dielectric materials. In
micro-gravity
experiments, the formation of a dust-free void breaks
the isotropy
of 3D dusty plasma systems. In order to do real 3D
experiments,
this void has somehow to be closed. In this paper, we
use a fully
self-consistent fluid model to study the closure of a
void in a
micro-gravity experiment, by lowering the driving
potential. The
analysis goes beyond the simple description of the
'virtual void',
which describes the formation of a void without taking
the dust
into account. We show that self-organization plays an
important
role in void formation and void closure, which also
allows a
reversed scheme, where a discharge is run at low driving
potentials
and small batches of dust are added. No hysteresis is
found this
way. Finally, we compare our results with recent
experiments and
find good agreement, but only when we do not take
charge-exchange
collisions into account.
Efficient
emission of positronium negative ions from Cs deposited
W(100) surfaces
Yasuyuki Nagashima, Toshihide Hakodate, Ayaka Miyamoto
and Koji
Michishio
2008 New J. Phys. 10 123029 (7pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123029
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123029/njp8_12_123029.pdf
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The emission of
positronium negative ions from Cs deposited W(100)
surfaces has been studied. A dramatic change in the
emission
efficiency was observed upon coating a W(100) surface
with Cs. The
conversion efficiency (the fraction of incident slow
positrons
yielding the ions) of the W(100) target with a 2.2x1014
atoms cm- 2
Cs coverage, measured over a time interval of 3x103 s
immediately
after deposition, was found to be 1.25%, which is two
orders of
magnitude higher than that obtained for the clean,
uncoated W(100)
surface and 45 times greater than the highest efficiency
reported
thus far.
Spin state
and orbital moments across the metal-insulator-transition
of REBaCo2O5.5 investigated by XMCD
M Lafkioti, E Goering, S Gold, G Schu"tz, S N Barilo, S
V Shiryaev, G L
Bychkov, P Lemmens, V Hinkov, J Deisenhofer and A Loidl
2008 New J. Phys. 10 123030 (9pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123030
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123030/njp8_12_123030.pdf
Full text HTML: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123030/njp8_12_123030.html
DyBaCo2O5.5 has
shown a complex phase diagram, which is based on the
interplay of different energy scales, related to
magnetism, orbital
ordering and for example Co spin-state transitions. For
a detailed
understanding of these fascinating materials it is
therefore
necessary to identify the order of the different energy
scales.
Small changes in the corresponding energy relations
strongly
influence the electronic structure and ground state
properties,
like low and high spin configurations, which have been
controversially discussed in order to interpret the
metal-to-insulator (MIT) transition in REBaCo2O5.5 (RE =
rare
earths). To clarify unambiguously the microscopic nature
of the
spin-state evolution associated with this MIT, we
performed
detailed temperature and angular dependent x-ray
magnetic circular
dichroism measurements in DyBaCo2O5.5 single crystals
above and
below the MIT and at the onset of the ferromagnetic
phase.
Anisotropic contributions of spin and orbital moments
have been
observed with an extremely high signal-to-noise ratio.
We can
identify a higher-spin- to lower-spin-state change
across the MIT,
which is in contrast to previous macroscopic
experimental findings.
Only the Co ions in octahedral environment are found to
be in a
reduced spin configuration in the high-temperature
metallic state.
Thermodynamic
properties of Ba1[?]xKxFe2As2 and Ca1[?]xNaxFe2As2
J K Dong, L Ding, H Wang, X F Wang, T Wu, G Wu, X H Chen
and S Y Li
2008 New J. Phys. 10 123031 (7pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/123031
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/123031/njp8_12_123031.pdf
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The specific heat
C(T) of a BaFe2As2 single crystal and hole-doped
superconducting Ba0.5K0.5Fe2As2 and Ca0.5Na0.5Fe2As2
polycrystals
were measured. For the undoped BaFe2As2 single crystal,
a very
sharp specific heat peak was observed at 136 K. This is
attributed
to the structural and antiferromagnetic transitions
occurring at
the same temperature. For the superconducting
Ba0.5K0.5Fe2As2
polycrystal, a clear peak of C/T was observed at Tc=36
K, which is
the highest peak seen at a superconducting transition
for
iron-based high-Tc superconductors so far. For the
superconducting
Ca0.5Na0.5Fe2As2 sample with lower Tc=18 K, there is no
obvious
anomaly in C/T below Tc, which may be due to its low
superfluid
density. The electronic specific heat coefficients
γ and
Debye temperatures ΘD of these compounds were
obtained from
the low-temperature data.
FOCUS ON
VISUALIZATION IN PHYSICS
Barry C Sanders, Tim Senden and Volker Springel
2008 New J. Phys. 10 125001
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125001
Advances in physics
are intimately connected with developments in a new
technology, the telescope, precision clocks, even the
computer all
have heralded a shift in thinking. These landmark
developments open
new opportunities accelerating research and in turn new
scientific
directions. These technological drivers often correspond
to new
instruments, but equally might just as well flag a new
mathematical
tool, an algorithm or even means to visualize physics in
a new way.
Early on in this twenty-first century, scientific
communities are
just starting to explore the potential of digital
visualization.
Whether visualization is used to represent and
communicate complex
concepts, or to understand and interpret experimental
data, or to
visualize solutions to complex dynamical equations, the
basic tools
of visualization are shared in each of these
applications and
implementations. High-performance computing exemplifies
the
integration of visualization with leading research.
Visualization
is an indispensable tool for analyzing and interpreting
complex
three-dimensional dynamics as well as to diagnose
numerical
problems in intricate parallel calculation algorithms.
The
effectiveness of visualization arises by exploiting the
unmatched
capability of the human eye and visual cortex to process
the large
information content of images. In a brief glance, we
recognize
patterns or identify subtle features even in noisy data,
something
that is difficult or impossible to achieve with more
traditional
forms of data analysis. Importantly, visualizations
guide the
intuition of researchers and help to comprehend physical
phenomena
that lie far outside of direct experience. In fact,
visualizations
literally allow us to see what would otherwise remain
completely
invisible. For example, artificial imagery created to
visualize the
distribution of dark matter in the Universe has been
instrumental
to develop the notion of a cosmic web, and for helping
to establish
the current standard model of cosmology wherein this (in
principle
invisible) dark matter dominates the cosmic matter
content. The
advantages of visualization found for simulated data
also hold for
real world data as well. With the application of
computerized
acquisition many scientific disciplines are witnessing
exponential
growth rates of the volume of accumulated raw data,
which often
makes it daunting to condense the information into a
manageable
form, a challenge that can be addressed by modern
visualization
techniques. Such visualizations are also often an
enticing way to
communicate scientific results to the general public.
This need for
visualization is especially true in basic science, with
its
reliance on a benevolent and interested general public
that drives
the need for high-quality visualizations. Despite the
widespread
use of visualization, this technology has suffered from
a lack of
the unifying influence of shared common experiences. As
with any
emerging technology practitioners have often
independently found
solutions to similar problems. It is the aim of this
focus issue to
celebrate the importance of visualization, report on its
growing
use by the broad community of physicists, including
biophysics,
chemical physics, geophysics, astrophysics, and medical
physics,
and provide an opportunity for the diverse community of
scientists
using visualization to share work in one issue of a
journal that
itself is in the vanguard of supporting visualization
and
multimedia. A remarkable breadth and diversity of
visualization in
physics is to be found in this issue spanning
fundamental aspects
of relativity theory to computational fluid dynamics.
The topics
span length scales that are as small as quantum
phenomena to the
entire observable Universe. We have been impressed by
the quality
of the submissions and hope that this snap-shot will
introduce,
inform, motivate and maybe even help to unify
visualization in
physics. Readers are also directed to the December issue
of Physics
World which includes the following features highlighting
work in
this collection and other novel uses of visualization
techniques:
  'A feast of visualization' Physics World
December 2008
pp 20-23   'Seeing the quantum world' by Barry
Sanders
Physics World December 2008 pp 24-27   'A
picture of the
cosmos' by Mark SubbaRao and Miguel Aragon-Calvo Physics
World
December 2008 pp 29-32   'Thinking outside the
cube' by
César A Hidalgo Physics World December 2008 pp
34-37 Focus
on Visualization in Physics Contents Visualization of
spiral and
scroll waves in simulated and experimental cardiac
tissue E M
Cherry and F H Fenton Visualization of large scale
structure from
the Sloan Digital Sky Survey M U SubbaRao, M A
Aragón-Calvo,
H W Chen, J M Quashnock, A S Szalay and D G York How
computers can
help us in creating an intuitive access to relativity
Hanns Ruder,
Daniel Weiskopf, Hans-Peter Nollert and Thomas
Müller
Lagrangian particle tracking in three dimensions via
single-camera
in-line digital holography Jiang Lu, Jacob P Fugal,
Hansen
Nordsiek, Ewe Wei Saw, Raymond A Shaw and Weidong Yang
Quantifying
spatial heterogeneity from images Andrew E Pomerantz and
Yi-Qiao
Song Disaggregation and scientific visualization of
earthscapes
considering trends and spatial dependence structures S
Grunwald
Strength through structure: visualization and local
assessment of
the trabecular bone structure C Räth, R Monetti, J
Bauer, I
Sidorenko, D Müller, M Matsuura, E-M
Lochmüller, P Zysset
and F Eckstein Thermonuclear supernovae: a multi-scale
astrophysical problem challenging numerical simulations
and
visualization F K Röpke and R Bruckschen
Visualization needs
and techniques for astrophysical simulations W Kapferer
and T Riser
Flow visualization and field line advection in
computational fluid
dynamics: application to magnetic fields and turbulent
flows Pablo
Mininni, Ed Lee, Alan Norton and John Clyne Splotch:
visualizing
cosmological simulations K Dolag, M Reinecke, C Gheller
and S
Imboden Visualizing a silicon quantum computer Barry C
Sanders,
Lloyd C L Hollenberg, Darran Edmundson and Andrew
Edmundson
Colliding galaxies, rotating neutron stars and merging
black holes
- visualizing high dimensional datasets on arbitrary
meshes Werner
Benger A low complexity visualization tool that helps to
perform
complex systems analysis M G Beiró, J I
Alvarez-Hamelin and
J R Busch Visualizing astrophysical N-body systems John
Dubinski
Visualizing
astrophysical N-body systems
John Dubinski
2008 New J. Phys. 10 125002 (22pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125002
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125002/njp8_12_125002.pdf
Full text HTML: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125002/njp8_12_125002.html
I begin with a brief
history of N-body simulation and visualization and
then go on to describe various methods for creating
images and
animations of modern simulations in cosmology and
galactic
dynamics. These techniques are incorporated into a
specialized
particle visualization software library called MYRIAD
that is
designed to render images within large parallel N-body
simulations
as they run. I present several case studies that explore
the
application of these methods to animations in star
clusters,
interacting galaxies and cosmological structure
formation.
A low
complexity visualization tool that helps to perform complex
systems analysis
M G Beiro', J I Alvarez-Hamelin and J R Busch
2008 New J. Phys. 10 125003 (18pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125003
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125003/njp8_12_125003.pdf
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In this paper, we
present an extension of large network visualization
(LaNet-vi), a tool to visualize large scale networks
using the
k-core decomposition. One of the new features is how
vertices
compute their angular position. While in the later
version it is
done using shell clusters, in this version we use the
angular
coordinate of vertices in higher k-shells, and arrange
the highest
shell according to a cliques decomposition. The time
complexity
goes from O(n\sqrt n) to O(n) upon bounds on a
heavy-tailed degree
distribution. The tool also performs a
k-core-connectivity
analysis, highlighting vertices that are not
k-connected; e.g. this
property is useful to measure robustness or quality of
service
(QoS) capabilities in communication networks. Finally,
the actual
version of LaNet-vi can draw labels and all the edges
using
transparencies, yielding an accurate visualization.
Based on the
obtained figure, it is possible to distinguish different
sources
and types of complex networks at a glance, in a sort of
'network
iris-print'.
Colliding
galaxies, rotating neutron stars and merging black
holes--visualizing high dimensional datasets on arbitrary
meshes
Werner Benger
2008 New J. Phys. 10 125004 (24pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125004
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125004/njp8_12_125004.pdf
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Visualization of
datasets stemming from diverse sources is challenged
by the large variety of substantial differences in
topology,
geometry and nature of the associated data fields. Since
there is
no standard on how to formulate and treat data for
scientific
visualization, algorithms are frequently implemented in
a highly
domain-specific way. Here, we explore the potential of
point-wise
rendering as a generic way to represent single or
multiple fields
instantaneously on arbitrary mesh types. This approach
is discussed
within the terminology of fiber bundles as a general
mathematical
concept to model scalar-, vector- and tensorfields given
on
topological spaces (with manifolds as a particular
case). We give
application examples based on datasets originating from
astrophysics and show first results of a tensor field
visualization
of a recently produced complex dataset of colliding
black holes in
their final orbit. We finally propose a data layout
representing
the mathematical concept of a 'field' generic enough to
handle all
cases involved.
Visualizing
a silicon quantum computer
Barry C Sanders, Lloyd C L Hollenberg, Darran Edmundson
and Andrew
Edmundson
2008 New J. Phys. 10 125005 (20pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125005
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125005/njp8_12_125005.pdf
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Quantum computation
is a fast-growing, multi-disciplinary research
field. The purpose of a quantum computer is to execute
quantum
algorithms that efficiently solve computational problems
intractable within the existing paradigm of 'classical'
computing
built on bits and Boolean gates. While collaboration
between
computer scientists, physicists, chemists, engineers,
mathematicians and others is essential to the project's
success,
traditional disciplinary boundaries can hinder progress
and make
communicating the aims of quantum computing and future
technologies
difficult. We have developed a four minute animation as
a tool for
representing, understanding and communicating a
silicon-based
solid-state quantum computer to a variety of audiences,
either as a
stand-alone animation to be used by expert presenters or
embedded
into a longer movie as short animated sequences. The
paper includes
a generally applicable recipe for successful scientific
animation
production.
Splotch:
visualizing cosmological simulations
K Dolag, M Reinecke, C Gheller and S Imboden
2008 New J. Phys. 10 125006 (18pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125006
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125006/njp8_12_125006.pdf
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We present a light
and fast, publicly available, ray-tracer Splotch
software tool which supports the effective visualization
of
cosmological simulations data. We describe the algorithm
it relies
on, which is designed in order to deal with point-like
data,
optimizing the ray-tracing calculation by ordering the
particles as
a function of their 'depth', defined as a function of
one of the
coordinates or other associated parameters. Realistic
three-dimensional impressions are reached through a
composition of
the final colour in each pixel properly calculating
emission and
absorption of individual volume elements. We describe
several
scientific as well as public applications realized with
Splotch. We
emphasize how different datasets and configurations lead
to
remarkably different results in terms of the images and
animations.
A few of these results are available online.
Flow
visualization and field line advection in computational
fluid dynamics: application to magnetic fields and turbulent
flows
Pablo Mininni, Ed Lee, Alan Norton and John Clyne
2008 New J. Phys. 10 125007 (23pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125007
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125007/njp8_12_125007.pdf
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Accurately
interpreting three dimensional (3D) vector quantities output
as solutions to high-resolution computational fluid
dynamics (CFD)
simulations can be an arduous, time-consuming task.
Scientific
visualization of these fields can be a powerful aid in
their
understanding. However, numerous pitfalls present
themselves
ranging from computational performance to the challenge
of
generating insightful visual representations of the
data. In this
paper, we briefly survey current practices for
visualizing 3D
vector fields, placing particular emphasis on those data
arising
from CFD simulations of turbulence. We describe the
capabilities of
a vector field visualization system that we have
implemented as
part of an open source visual data analysis environment.
We also
describe a novel algorithm we have developed for
illustrating the
advection of one vector field by a second flow field. We
demonstrate these techniques in the exploration of two
sets of
runs. The first comprises an ideal and a resistive
magnetohydrodynamic (MHD) simulation. This set is used
to test the
validity of the advection scheme. The second corresponds
to a
simulation of MHD turbulence. We show the formation of
structures
in the flows, the evolution of magnetic field lines, and
how field
line advection can be used effectively to track
structures therein.
Visualization
needs and techniques for astrophysical simulations
W Kapferer and T Riser
2008 New J. Phys. 10 125008 (15pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125008
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125008/njp8_12_125008.pdf
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Numerical
simulations have evolved continuously towards being an
important field in astrophysics, equivalent to theory
and
observation. Due to the enormous developments in
computer sciences,
both hardware- and software-architecture,
state-of-the-art
simulations produce huge amounts of raw data with
increasing
complexity. In this paper some aspects of problems in
the field of
visualization in numerical astrophysics in combination
with
possible solutions are given. Commonly used
visualization packages
along with a newly developed approach to real-time
visualization,
incorporating shader programming to uncover the
computational power
of modern graphics cards, are presented. With these
techniques at
hand, real-time visualizations help scientists to
understand the
coherences in the results of their numerical
simulations.
Furthermore a fundamental problem in data analysis, i.e.
coverage
of metadata on how a visualization was created, is
highlighted.
Thermonuclear
supernovae: a multi-scale astrophysical problem challenging
numerical simulations and visualization
F K Ro"pke and R Bruckschen
2008 New J. Phys. 10 125009 (20pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125009
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125009/njp8_12_125009.pdf
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The numerical
modeling of type Ia supernovae is a demanding
astrophysical task. Relevant physical processes take
place on
vastly different length- and timescales. This
multi-scale character
of the object poses challenges to the numerical
approaches. We
discuss an implementation that accounts for these
problems by
employing a large eddy simulation (LES) strategy for
treating
turbulence effects and a level-set technique to
represent the thin
thermonuclear flames. It is demonstrated that this
approach works
efficiently in simulations of the deflagration model and
the
delayed detonation model of type Ia supernovae. The
resulting data
reflect the multi-scale nature of the problem.
Therefore,
visualization has to be tackled with special techniques.
We
describe an approach that enables the interactive
exploration of
large datasets on commodity hardware. To this end,
out-of-core
methods are employed and the rendering of the data is
achieved by a
hybrid particle-based and texture-based volume-rendering
technique.
Strength
through structure: visualization and local assessment of
the trabecular bone structure
C Ra"th, R Monetti, J Bauer, I Sidorenko, D Mu"ller, M
Matsuura, E-M
Lochmu"ller, P Zysset and F Eckstein
2008 New J. Phys. 10 125010 (18pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125010
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125010/njp8_12_125010.pdf
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The visualization
and subsequent assessment of the inner human bone
structures play an important role for better
understanding the
disease- or drug-induced changes of bone in the context
of
osteoporosis giving prospect for better predictions of
bone
strength and thus of the fracture risk of osteoporotic
patients. In
this work, we show how the complex trabecular bone
structure can be
visualized using uCT imaging techniques at an isotropic
resolution
of 26 um. We quantify these structures by calculating
global and
local topological and morphological measures, namely
Minkowski
functionals (MFs) and utilizing the (an-)isotropic
scaling index
method (SIM) and by deriving suitable texture measures
based on MF
and SIM. Using a sample of 151 specimens taken from
human vertebrae
in vitro, we correlate the texture measures with the
mechanically
measured maximum compressive strength (MCS), which
quantifies the
strength of the bone probe, by using Pearson's
correlation
coefficient. The structure parameters derived from the
local
measures yield good correlations with the bone strength
as measured
in mechanical tests. We investigate whether the
performance of the
texture measures depends on the MCS value by selecting
different
subsamples according to MCS. Considering the whole
sample the
results for the newly defined parameters are better than
those
obtained for the standard global histomorphometric
parameters
except for bone volume/total volume (BV/TV). If a
subsample
consisting only of weak bones is analysed, the local
structural
analysis leads to similar and even better correlations
with MCS as
compared to BV/TV. Thus, the MF and SIM yield additional
information about the stability of the bone especially
in the case
of weak bones, which corroborates the hypothesis that
the bone
structure (and not only its mineral mass) constitutes an
important
component of bone stability.
Disaggregation
and scientific visualization of earthscapes considering
trends and spatial dependence structures
S Grunwald
2008 New J. Phys. 10 125011 (15pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125011
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125011/njp8_12_125011.pdf
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Earth attributes
show complex, heterogeneous spatial patterns generated
by exogenous environmental factors and formation
processes. This
study investigates various strategies to quantify the
underlying
spatial patterns of simulated fields resembling real
earthscapes
and to compare their performance for describing them.
The approach
is to disaggregate the variability of earth attributes
into two
components, deterministic trend m(xi) and spatial
dependence
ε(xi), and determine the effects of m(xi) and
ε(xi)
on prediction accuracy under various combinations of
spatial fields
of earth attributes encountered in different
earthscapes. We
illustrate that cross-dependencies exist between spatial
and
feature accuracy. Scientific visualization is used to
transpose
quantitative results into visual space.
Quantifying
spatial heterogeneity from images
Andrew E Pomerantz and Yi-Qiao Song
2008 New J. Phys. 10 125012 (9pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125012
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125012/njp8_12_125012.pdf
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Visualization
techniques are extremely useful for characterizing
natural materials with complex spatial structure.
Although many
powerful imaging modalities exist, simple display of the
images
often does not convey the underlying spatial structure.
Instead,
quantitative image analysis can extract the most
important features
of the imaged object in a manner that is easier to
comprehend and
to compare from sample to sample. This paper describes
the
formulation of the heterogeneity spectrum to show the
extent of
spatial heterogeneity as a function of length scale for
all length
scales to which a particular measurement is sensitive.
This
technique is especially relevant for describing
materials that
simultaneously present spatial heterogeneity at multiple
length
scales. In this paper, the heterogeneity spectrum is
applied for
the first time to images from optical microscopy. The
spectrum is
measured for thin section images of complex carbonate
rock cores
showing heterogeneity at several length scales in the
range 10-10
000 um.
Lagrangian
particle tracking in three dimensions via single-camera
in-line digital holography
Jiang Lu, Jacob P Fugal, Hansen Nordsiek, Ewe Wei Saw,
Raymond A Shaw
and Weidong Yang
2008 New J. Phys. 10 125013 (24pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125013
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125013/njp8_12_125013.pdf
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Lagrangian particle
trajectories are measured in three spatial
dimensions with a single camera using the method of
digital in-line
holography. Lagrangian trajectories of 60-120 um
diameter droplets
in turbulent air obtained with data from one camera
compare
favorably with tracks obtained from a simultaneous
dual-camera data
set, the latter having high spatial resolution in all
three
dimensions. Using the single-camera system, particle
motion along
the optical axis is successfully tracked, allowing for
long,
continuous 3D tracks, but the depth resolution based on
standard
reconstruction methods is not sufficient to obtain
accurate
acceleration measurements for that component. Lagrangian
velocity
distributions for all three spatial components agree
within
reasonable sampling uncertainties and Lagrangian
acceleration
distributions agree for the two lateral components. An
equivalent
single-camera, imaging-based 2D tracking system would be
challenged
by the particle densities tested, but the holographic
configuration
allows for 3D tracking in the dilute limit. The method
also allows
particle size, shape and orientation to be measured
along the
trajectory. Lagrangian measurements of particle size
provide a
direct measure of particle size uncertainty under
realistic
conditions sampled from the entire measurement volume.
How
computers can help us in creating an intuitive access to
relativity
Hanns Ruder, Daniel Weiskopf, Hans-Peter Nollert and
Thomas Mu"ller
2008 New J. Phys. 10 125014 (22pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125014
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125014/njp8_12_125014.pdf
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Computers have added
many new possibilities to the tool box used for
visualizing science in general and relativity in
particular. We
present some new results from our own work: (2+1)
dimensional
Minkowski diagrams showing two spatial dimensions,
extended
wormhole visualization, and the illustration of
accretion discs by
using the approximation via a rigidly rotating disc of
dust. We
also discuss some related examples from our earlier
work, such as
interactive and immersive visualization, or the
visualization of
the warp drive metric.
Visualization
of large scale structure from the Sloan Digital Sky Survey
M U SubbaRao, M A Arago'n-Calvo, H W Chen, J M Quashnock,
A S Szalay
and D G York
2008 New J. Phys. 10 125015 (15pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125015
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125015/njp8_12_125015.pdf
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We will discuss the
challenges of visualizing large cosmological
datasets. These include observational issues such as the
masks and
incomplete nature of the survey volume, cosmological
issues such as
redshift distortions and the difficulty of visualizing
datasets
that span cosmological epochs, as well as the inherent
visualization challenges in presenting dense
three-dimensional (3D)
datasets. Two case studies will be presented. The first
will
feature the identification of filamentary structures in
the large
scale distribution of galaxies. The second case study
will feature
visualizations of the correlations between quasar
absorption line
systems and luminous red galaxies. Finally, we will give
an
overview of our visualization work-flow which features
the use of
the open-source 3D modeling program Blender.
Visualization
of spiral and scroll waves in simulated and experimental
cardiac tissue
E M Cherry and F H Fenton
2008 New J. Phys. 10 125016 (43pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125016
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125016/njp8_12_125016.pdf
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The heart is a
nonlinear biological system that can exhibit complex
electrical dynamics, complete with period-doubling
bifurcations and
spiral and scroll waves that can lead to fibrillatory
states that
compromise the heart's ability to contract and pump
blood
efficiently. Despite the importance of understanding the
range of
cardiac dynamics, studying how spiral and scroll waves
can
initiate, evolve, and be terminated is challenging
because of the
complicated electrophysiology and anatomy of the heart.
Nevertheless, over the last two decades advances in
experimental
techniques have improved access to experimental data and
have made
it possible to visualize the electrical state of the
heart in more
detail than ever before. During the same time, progress
in
mathematical modeling and computational techniques has
facilitated
using simulations as a tool for investigating cardiac
dynamics. In
this paper, we present data from experimental and
simulated cardiac
tissue and discuss visualization techniques that
facilitate
understanding of the behavior of electrical spiral and
scroll waves
in the context of the heart. The paper contains many
interactive
media, including movies and interactive two- and
three-dimensional
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All
mechanical mixing by means of orthogonally coupled
cantilevers
A Knoll, O Zu"ger and U Duerig
2008 New J. Phys. 10 125017 (19pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125017
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125017/njp8_12_125017.pdf
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An all mechanical
signal mixing device is described which uses only
linear springs as fundamental building blocks. Two input
oscillators are coupled to an orthogonally vibrating
output
oscillator via a linear spring, which results in an
effective
nonlinear multiplicative mixing function. Numerical
simulations
have been performed for studying the performance
characteristics of
the mixer. A modified version of the mixer acting as a
mechanical
modulator is also numerically investigated for
application as a
mechanical power amplifier. The viability of the concept
is
demonstrated in a centimeter scale experimental setup
and a
micromechanical scale polymer embodiment has been built
using
two-photon polymerization lithographic methods.
Nonlinear
quantum metrology using coupled nanomechanical resonators
M J Woolley, G J Milburn and Carlton M Caves
2008 New J. Phys. 10 125018 (13pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125018
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125018/njp8_12_125018.pdf
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We consider a
nanomechanical analogue of a nonlinear interferometer,
consisting of two parallel, flexural nanomechanical
resonators,
each with an intrinsic Duffing nonlinearity and with a
switchable
beamsplitter-like coupling between them. We calculate
the precision
with which the strength of the nonlinearity can be
estimated and
show that it scales as 1/n3/2, where n is the mean
phonon number of
the initial state. This result holds even in the
presence of
dissipation, but assumes the ability to make
measurements of the
quadrature components of the nanoresonators.
Cluster-based density-functional approach to quantum
transport through
molecular and atomic contacts
F Pauly, J K Viljas, U Huniar, M Ha"fner, S Wohlthat, M
Bu"rkle, J C
Cuevas and G Scho"n
2008 New J. Phys. 10 125019 (28pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125019
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125019/njp8_12_125019.pdf
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We present a
cluster-based approach to model charge transport through
molecular and atomic contacts. The electronic structure
of the
contacts is determined in the framework of density
functional
theory, and the parameters needed to describe transport
are
extracted from finite clusters. A similar procedure,
restricted to
nearest-neighbor interactions in the electrodes, has
been presented
by Damle et al (2002 Chem. Phys. 281 171). Here, we show
how to
systematically improve the description of the electrodes
by
extracting bulk parameters from sufficiently large metal
clusters.
In this way, we avoid problems arising from the use of
nonorthogonal basis functions. For demonstration, we
apply our
method to electron transport through Au contacts with
various
atomic-chain configurations and to a single-atom contact
of Al.
Ionization and excitation cross sections for the
interaction of HZE particles in liquid water and
application to Monte Carlo simulation of radiation tracks
Ianik Plante and Francis A Cucinotta
2008 New J. Phys. 10 125020 (15pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125020
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125020/njp8_12_125020.pdf
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Relativistic heavy
ions of high charge (Z) and energy (E) (HZE) in
galactic cosmic rays (GCR) are important contributors to
space
radiation risk because they cannot be shielded
completely and their
relative biological effectiveness is very high. To
understand these
risks, Monte Carlo track structure simulations by
radiation
transport codes are widely used in radiation biology to
provide
information on energy deposition and production of
radiolytic
species that damage cellular structures. In this paper,
we show
that relativistic corrections can be applied to existing
semi-empirical cross section models for the ionization
and
excitation of water molecules by ions to extend the
validity of
their energy range up to ~104 MeV amu−1.
Similarly, an
effective charge value correction is applied for Z>2
ions.
Simulations of HZE tracks have been performed by a new
C++ Monte
Carlo transport code, named RITRACKS, that uses these
cross
sections to calculate the stopping power, radial dose,
XY-plane
projections of track segments and radial distributions
of primary
radiolytic species (H•, •OH, H2, H2O2 and
e−aq) at
~10−12 s. These new data will be useful to
understand results
from experiments performed at ion accelerators by
discriminating
the role of the so-called core and penumbra of the
tracks.
Experimental optomechanics with silicon micromirrors
Olivier Arcizet, Chiara Molinelli, Tristan Briant,
Pierre-Franc,ois
Cohadon, Antoine Heidmann, Jean-Marie Mackowski,
Christophe Michel,
Laurent Pinard, Olivier Franc,ais and Lionel Rousseau
2008 New J. Phys. 10 125021 (15pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125021
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125021/njp8_12_125021.pdf
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We experimentally
demonstrate the high-sensitivity optical monitoring
of moving micromirrors, made of low-loss dielectric
coatings upon
silicon resonators of various shapes and sizes. The very
high
optical finesses obtained (\mathcal{F}\simeq 30\,000 )
have allowed
us to measure the thermal noise of the micromirrors at
room
temperature with a shot-noise limited sensitivity at the
10^{-19}\,{\rm m}/\sqrt{\rm Hz} level and to completely
characterize their mechanical behavior, in excellent
agreement with
the results of a finite-element computation.
Applications of such
optomechanical systems range from quantum optics
experiments to the
experimental demonstration of the quantum ground state
of a
macroscopic mechanical resonator.
Nanoantenna
array-induced fluorescence enhancement and reduced lifetimes
Reuben M Bakker, Vladimir P Drachev, Zhengtong Liu,
Hsiao-Kuan Yuan,
Rasmus H Pedersen, Alexandra Boltasseva, Jiji Chen,
Joseph
Irudayaraj, Alexander V Kildishev and Vladimir M Shalaev
2008 New J. Phys. 10 125022 (16pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125022
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Enhanced
fluorescence is observed from dye molecules interacting with
optical nanoantenna arrays. Elliptical gold dimers form
individual
nanoantennae with tunable plasmon resonances depending
upon the
geometry of the two particles and the size of the gap
between them.
A fluorescent dye, Rhodamine 800, is uniformly embedded
in a
dielectric host that coats the nanoantennae. The
nanoantennae act
to enhance the dye absorption. In turn, emission from
the dye
drives the plasmon resonance of the antennae; the
nanoantennae act
to enhance the fluorescence signal and change the
angular
distribution of emission. These effects depend upon the
overlap of
the plasmon resonance with the excitation wavelength and
the
fluorescence emission band. A decreased fluorescence
lifetime is
observed along with highly polarized emission that
displays the
characteristics of the nanoantenna's dipole mode. Being
able to
engineer the emission of the dye-nanoantenna system is
important
for future device applications in both bio-sensing and
nanoscale
optoelectronic integration.
Classical to quantum transition of a driven nonlinear
nanomechanical resonator
Itamar Katz, Ron Lifshitz, Alex Retzker and Raphael
Straub
2008 New J. Phys. 10 125023 (20pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125023
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125023/njp8_12_125023.pdf
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Much experimental
effort is invested these days in fabricating
nanoelectromechanical systems (NEMS) that are
sufficiently small,
cold and clean, so as to approach quantum mechanical
behavior as
their typical quantum energy scale \hbar\Omega becomes
comparable
with that of the ambient thermal energy kBT. Such
systems will
hopefully enable one to observe the quantum behavior of
human-made
objects, and test some of the basic principles of
quantum
mechanics. Here, we expand and elaborate on our recent
suggestion
(Katz et al 2007 Phys. Rev. Lett. 99 040404) to exploit
the
nonlinear nature of a nanoresonator in order to observe
its
transition into the quantum regime. We study this
transition for an
isolated resonator, as well as one that is coupled to a
heat bath
at either zero or finite temperature. We argue that by
exploiting
nonlinearities, quantum dynamics can be probed using
technology
that is almost within reach. Numerical solutions of the
equations
of motion display the first quantum corrections to
classical
dynamics that appear as the classical-to-quantum
transition occurs.
This provides practical signatures to look for in future
experiments with NEMS resonators.
Rapid
energy transfer in a dendrimer having p-conjugated
light-harvesting antennas
I Akai, K Miyanari, T Shimamoto, A Fujii, H Nakao, A
Okada, K Kanemoto,
T Karasawa, H Hashimoto, A Ishida, A Yamada, I Katayama,
J Takeda
and M Kimura
2008 New J. Phys. 10 125024 (22pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125024
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125024/njp8_12_125024.pdf
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We investigate rapid
energy transfer (ET) and its temperature
dependence in a star-shaped stilbenoid phthalocyanine
(SSS1Pc)
dendrimer having π-conjugated light-harvesting (LH)
antennas,
and develop an appropriate model. In SSS1Pc, an intense
core
photoluminescence (PL) band appears under the selective
excitation
of the absorption bands of the LH antenna due to highly
efficient
ET at room temperature (RT). The transient response of
core-absorption bleaching and the temporal behaviours of
the PL
intensities of the core and antenna reveal that ET from
the LH
antenna occurs rapidly prior to achieving
quasi-equilibrium in the
photoexcited state of the LH antenna. In addition, it is
also
clarified that the ET quantum efficiency in SSS1Pc
degrades at
temperatures lower than ~100 K. To understand these
results, we
develop an ET model based on a π-conjugating network
between the
LH antenna and the core that accounts for steric
hindrance between
the LH antenna and the torsional vibration of the
LH-antenna
subunit. This model reveals that highly efficient ET
occurs at RT
through the π-conjugated network mediated by the
thermally
activated torsional vibration of the LH-antenna subunit.
FOCUS ON
ADVANCES IN SURFACE AND INTERFACE SCIENCE 2008
Matthias Scheffler and Wolf-Dieter Schneider
2008 New J. Phys. 10 125025
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125025
Basic research in
surface and interface science is highly
interdisciplinary, covering the fields of physics,
chemistry,
biophysics, geo-, atmospheric and environmental
sciences, material
science, chemical engineering, and more. The various
phenomena are
interesting by themselves, and they are most important
in nearly
all modern technologies, as for example electronic,
magnetic, and
optical devices, sensors, catalysts, lubricants, hard
and
thermal-barrier coatings, protection against corrosion
and crack
formation under harsh environments. In fact, detailed
understanding
of the elementary processes at surfaces is necessary to
support and
to advance the high technology that very much founds the
prosperity
and lifestyle of our society. Current state-of-the-art
experimental
studies of elementary processes at surfaces, of surface
properties
and functions employ a variety of sophisticated tools.
Some are
capable of revealing the location and motion of
individual atoms.
Others measure excitations (electronic, magnetic and
vibronic),
employing, for example, special light sources such as
synchrotrons,
high magnetic fields, or free electron lasers. The
surprising
variety of intriguing physical phenomena at surfaces,
interfaces,
and nanostructures also pose a persistent challenge for
the
development of theoretical descriptions, methods, and
even basic
physical concepts. This second focus issue on the topic
of
'Advances in Surface and Interface Science' in New
Journal of
Physics, following on from last year's successful
collection,
provides an exciting synoptic view on the latest
pertinent
developments in the field. Focus on Advances in Surface
and
Interface Science 2008 Contents Organic layers at
metal/electrolyte
interfaces: molecular structure and reactivity of
viologen
monolayers Stephan Breuer, Duc T Pham, Sascha Huemann,
Knud Gentz,
Caroline Zoerlein, Ralf Hunger, Klaus Wandelt and Peter
Broekmann
Spin polarized d surface resonance state of fcc
Co/Cu(001) K
Miyamoto, K Iori, K Sakamoto, H Narita, A Kimura, M
Taniguchi, S
Qiao, K Hasegawa, K Shimada, H Namatame and S
Blügel Activated
associative desorption of C + O → CO from Ru(001)
induced by
femtosecond laser pulses S Wagner, H Öström, A
Kaebe, M
Krenz, M Wolf, A C Luntz and C Frischkorn Surface
structure of
Sn-doped In2O3 (111) thin films by STM Erie H Morales,
Yunbin He,
Mykola Vinnichenko, Bernard Delley and Ulrike Diebold
Coulomb
oscillations in three-layer graphene nanostructures J
Güttinger, C Stampfer, F Molitor, D Graf, T Ihn and
K Ensslin
Adsorption processes of hydrogen molecules on SiC(001),
Si(001) and
C(001) surfaces Xiangyang Peng, Peter Krüger and
Johannes
Pollmann Fermi surface nesting in several transition
metal
dichalcogenides D S Inosov, V B Zabolotnyy, D V
Evtushinsky, A A
Kordyuk, B Büchner, R Follath, H Berger and S V
Borisenko
Probing molecule-surface interactions through ultra-fast
adsorbate
dynamics: propane/Pt(111) A P Jardine, H Hedgeland, D
Ward, Y
Xiaoqing, W Allison, J Ellis and G Alexandrowicz A novel
method
achieving ultra-high geometrical resolution in scanning
tunnelling
microscopy R Temirov, S Soubatch, O Neucheva, A C
Lassise and F S
Tautz
Probing molecule-surface interactions through
ultra-fast adsorbate dynamics:propane/Pt(111)
A P Jardine, H Hedgeland, D Ward, Y Xiaoqing, W Allison,
J Ellis and G
Alexandrowicz
2008 New J. Phys. 10 125026 (20pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125026
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125026/njp8_12_125026.pdf
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3He spin echo
measurements of the atomic scale motion of propane on a
Pt(111) surface are presented. The measurements provide
both the
height of the energy barriers to diffusion and the
strength of the
frictional coupling of propane to the substrate. We show
that both
the rate and the nature of the dynamics we measure
cannot be
reproduced by an existing empirical potential. Using
numerical
simulation we derive a potential energy surface which is
capable of
reproducing the main features of our dataset.
Fermi
surface nesting in several transition metal dichalcogenides
D S Inosov, V B Zabolotnyy, D V Evtushinsky, A A
Kordyuk, B Bu"chner, R
Follath, H Berger and S V Borisenko
2008 New J. Phys. 10 125027 (10pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125027
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125027/njp8_12_125027.pdf
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By means of
high-resolution angle-resolved photoelectron spectroscopy
(ARPES), we have studied the fermiology of 2H transition
metal
dichalcogenide polytypes TaSe2, NbSe2 and Cu0.2NbS2. The
tight-binding model of the electronic structure,
extracted from
ARPES spectra for all three compounds, was used to
calculate the
Lindhard function (bare spin susceptibility), which
reflects the
propensity to charge density wave (CDW) instabilities
observed in
TaSe2 and NbSe2. We show that though the Fermi surfaces
of all
three compounds possess an incommensurate nesting vector
in the
close vicinity of the CDW wave vector, the nesting and
ordering
wave vectors do not exactly coincide, and there is no
direct
relationship between the magnitude of the susceptibility
at the
nesting vector and the CDW transition temperature. The
nesting
vector persists across the incommensurate CDW transition
in TaSe2
as a function of temperature despite the observable
variations of
the Fermi surface geometry in this temperature range. In
Cu0.2NbS2,
the nesting vector is present despite different doping
levels,
which leads us to expect a possible enhancement of the
CDW
instability with Cu intercalation in the CuxNbS2 family
of
materials.
Adsorption
processes of hydrogen molecules on SiC(001), Si(001) and
C(001) surfaces
Xiangyang Peng, Peter Kru"ger and Johannes Pollmann
2008 New J. Phys. 10 125028 (19pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125028
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125028/njp8_12_125028.pdf
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Adsorption processes
of hydrogen molecules on the Si(001)-(2x1) and
C(001)-(2x1) surfaces are discussed in light of our
previous
studies of H2 adsorption on the related SiC(001)-c(4x2)
surface.
Very amazingly, there are pathways above the latter on
which
hydrogen molecules can adsorb dissociatively at room
temperature.
One of these pathways has not been considered before for
adsorption
of H2 on the Si(001)-(2x1) or C(001)-(2x1) surface.
Therefore, we
report first-principles investigations of the reaction
of molecular
hydrogen with the Si(001)-(2x1) and C(001)-(2x1)
surfaces on this
new adsorption pathway in addition to those that have
been studied
before. In spite of a number of similarities, the three
surfaces
show distinct differences as well, giving rise to
spectacularly
different reactivities with hydrogen molecules. This is
due to the
fact that the reaction of H2 with semiconductor surfaces
depends
crucially on intricate combined effects of the
arrangement of
surface dimers, as well as the orientation of their
dangling bond
orbitals. In addition, the chemical nature of the
surface atoms has
a pronounced effect on the spatial extent of dangling
bond orbitals
which influences the adsorption behaviour markedly as
well. In
agreement with experiments, our results show that
Si(001)-(2x1) and
C(001)-(2x1) are inert to H2 adsorption at room
temperature for all
investigated pathways which exhibit substantial energy
barriers.
For the two reaction pathways that have been
investigated before,
our results are in good accord with those of previous
density
functional and quantum Monte Carlo (QMC) calculations.
As a matter
of fact, the new reaction channel studied in this work
for the
first time turns out to have the lowest energy barrier
for H2
adsorption on the diamond surface and should thus be the
most
important channel for sticking of H2 on C(001)-(2x1).
Coulomb
oscillations in three-layer graphene nanostructures
J Gu"ttinger, C Stampfer, F Molitor, D Graf, T Ihn and K
Ensslin
2008 New J. Phys. 10 125029 (10pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125029
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125029/njp8_12_125029.pdf
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We present transport
measurements on a tunable three-layer graphene
single electron transistor (SET). The device consists of
an etched
three-layer graphene flake with two narrow constrictions
separating
the island from source and drain contacts. Three lateral
graphene
gates are used to electrostatically tune the device. An
individual
three-layer graphene constriction has been investigated
separately
showing a transport gap near the charge neutrality
point. The
graphene tunneling barriers show a strongly nonmonotonic
coupling
as a function of gate voltage indicating the presence of
localized
states in the constrictions. We show Coulomb
oscillations and
Coulomb diamond measurements proving the functionality
of the
graphene SET. A charging energy of ≈0.6 meV is
extracted.
Surface
structure of Sn-doped In2O3 (111) thin films by STM
Erie H Morales, Yunbin He, Mykola Vinnichenko, Bernard
Delley and
Ulrike Diebold
2008 New J. Phys. 10 125030 (11pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125030
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125030/njp8_12_125030.pdf
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High-quality
Sn-doped In2O3 (ITO) films were grown epitaxially on
yttria stabilized zirconia (111) with oxygen-plasma
assisted
molecular beam epitaxy (MBE). The 12 nm thick films,
containing
2-6% Sn, are fully oxidized. Angle-resolved x-ray
photoelectron
spectroscopy (ARXPS) confirms that the Sn dopant
substitutes In
atoms in the bixbyite lattice. From XPS peak shape
analysis and
spectroscopic ellipsometry measurements it is estimated
that, in a
film with 6 at.% Sn, ~1/3 of the Sn atoms are
electrically active.
Reflection high energy electron diffraction (RHEED)
shows a flat
surface morphology and scanning tunneling microscopy
(STM) shows
terraces several hundred nanometers in width. The
terraces consist
of 10 nm wide orientational domains, which are
attributed to the
initial nucleation of the film. Low energy electron
diffraction
(LEED) and STM results show a bulk-terminated (1 x 1)
surface,
which is supported by first-principles density
functional theory
(DFT) calculations. Atomically resolved STM images are
consistent
with Tersoff-Hamann calculations that show that surface
In atoms
are imaged bright or dark, depending on the
configuration of their
O neighbors. The coordination of surface atoms on the
In2O3(111)-1x1 surface is analyzed in terms of their
possible role
in surface chemical reactions.
Activated
associative desorption of C + O - CO from Ru(001) induced
by femtosecond laser pulses
S Wagner, H O"stro"m, A Kaebe, M Krenz, M Wolf, A C
Luntz and C
Frischkorn
2008 New J. Phys. 10 125031 (24pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125031
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125031/njp8_12_125031.pdf
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The femtosecond
(fs)-laser-induced associative desorption of CO from a
C/O coadsorbate on Ru(001) has been investigated. The
recombination
of the atomic reactants is found to originate
predominantly from
oxidation of isolated 'reactive' carbon atoms, whereas
oxidation of
surface carbon with carbon-carbon bonds is not observed.
Due to the
excess of oxygen atoms (C coverage in the few-percent
range) the
Cads + Oads → COgas formation exhibits
first-order kinetics.
For both excitation wavelengths 400 and 800 nm, a
strongly
nonlinear fluence (F) dependence of the CO desorption
yield Y is
observed with exponents n≈4 in a power law
parametrization
Y∝⟨F⟩n. Furthermore, excitation with 400
nm pulses
leads to a significantly higher desorption yield as
compared to 800
nm laser light with cross sections and desorption
probabilities for
400 and 800 nm excitation of σeff=4.9x10−18
cm2,
Pdes=0.17 and σeff=1.1x10−18 cm2, Pdes=0.07,
respectively, at an absorbed fluence of
⟨F⟩=170 J
m−2. This wavelength dependence is attributed to
the shorter
optical penetration of 400 nm light in the Ru substrate
leading to
higher surface temperatures at the same absorbed energy
rather than
to nonthermalized hot electrons. In addition,
two-pulse-correlation
measurements show a full-width at half-maximum of ~ 20
ps excluding
a purely electron-driven reaction mechanism, which
should exhibit a
subpicosecond response time. However, careful
qualitative and
quantitative analyses based on frictional modelling of
the
adsorbate-substrate coupling reveals that the C-O
association
reaction is mediated by both substrate phonons and
electrons. The
electronic, i.e. nonadiabatic contribution with a
coupling constant
of ηel=1/500 fs−1 is responsible for the
ultrafast
activation of the reaction found in the frictional
modelling to occur within ~1 ps after excitation.
Similarities to the
associative desorption of N2 (isoelectronic with CO)
from
N/Ru(001), a system for which density-functional
calculations
exist, can be drawn. Finally, the energy transfer to
nuclear
degrees of freedom during the C-O association process on
the
Ru(001) surface has been studied with time-of-flight
measurements.
The obtained translational energies expressed by
Ttrans=⟨Etrans⟩/2kB≈700 K exhibit only
a weak
dependence on the absorbed laser fluence and are by a
factor of ~3
lower than the calculated surface temperatures present
after
fs-laser excitation. Possible origins of this
discrepancy, such as
unequal energy partitioning between the molecular
degrees of
freedom or nonadiabatic damping, are discussed.
Spin
polarized d surface resonance state of fcc Co/Cu(001)
K Miyamoto, K Iori, K Sakamoto, H Narita, A Kimura, M
Taniguchi, S
Qiao, K Hasegawa, K Shimada, H Namatame and S Blu"gel
2008 New J. Phys. 10 125032 (10pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125032
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125032/njp8_12_125032.pdf
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Spin- and
angle-resolved photoemission spectroscopy has been applied
to
the study of the surface and bulk electronic structures
of a
face-centered cubic (fcc) Co thin film. We have
experimentally
resolved a negatively spin-polarized surface resonance
state of fcc
Co/Cu(001) at 0.4 eV below the Fermi energy. Moreover,
we have
found that the surface resonance state exhibits a strong
spin-orbit
interaction through an investigation of magnetic
dichroism in the
angular distribution spectrum of Co/Cu(001).
Organic
layers at metal/electrolyte interfaces: molecular structure
and reactivity of viologen monolayers
Stephan Breuer, Duc T Pham, Sascha Huemann, Knud Gentz,
Caroline
Zoerlein, Ralf Hunger, Klaus Wandelt and Peter Broekmann
2008 New J. Phys. 10 125033 (24pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=29894/1367-2630/10/12/125033
Full text PDF: http://www.iop.org/EJ/article/-alert=29894/1367-2630/10/12/125033/njp8_12_125033.pdf
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The adsorption of
viologens (1,1'-disubstituted-4,4'-bipyridinium
molecules) on a chloride-modified copper electrode has
been studied
using a combination of cyclic voltammetry (CV), in-situ
scanning
tunneling microscopy (STM) and ex-situ photoemission
spectroscopy
(XPS). Two prototypes of viologens could be identified
with respect
to their redox behavior upon adsorption, namely those
which retain
(non-reactive adsorption) and those which change their
redox state
(reactive adsorption) upon interaction with the
chloride-modified
copper surface at given potential. The first class of
viologens
represented by 1,1'-dibenzyl-4,4'-bipyridinium molecules
(dibenzyl-viologens, abbreviated as DBV) can be adsorbed
and
stabilized on this electrode surface in their
di-cationic state at
potentials more positive than the reduction potential of
the
solution species. XPS N1s core level shifts verify that
the
adsorbed DBV molecules on the electrode are in their
oxidized
di-cationic state. Electrostatic attraction between the
partially
solvated viologen di-cations and the anionic chloride
layer is
discussed as the main driving force for the DBV
stabilization on
the electrode surface. Analysis of the N1s and O1s core
level
shifts points to a non-reactive DBV adsorption leaving
the DBVads2+
solvation shell partly intact. The laterally ordered
DBVads2+
monolayer turns out to be hydrophilic with at least four
water
molecules per viologen present within this cationic
organic film.
The analysis of the Cl2p core level reveals that no
further
chloride species are present at the surface besides
those which are
specifically adsorbed, i.e. which are in direct contact
with the
metallic copper surface underneath the organic layer.
The reduction
of these adsorbed DBVads2+ surface species takes place
only in the
same potential regime where the solvated DBVaq2+ bulk
solution
species react and is accompanied by a pronounced
structural change
from the di-cationic 'cavitand'-structure to a
'stripe'-structure
of chains of π-stacked DBV•+ mono-cation
radicals as
verified by in-situ STM. The second class of viologens
represented
by 1,1'-diphenyl-4,4'-bipyridinium molecules
(diphenyl-viologens,
abbreviated as DPV) is much more reactive upon
adsorption and
cannot be stabilized on the electrode surface in a
di-cationic
state, at least within the narrow potential window of
copper. The
N1s core level binding energy indicates only the
presence of the
corresponding mono-reduced DPVads•+ species on the
surface
even at potentials more positive than the redox
potential of the
bulk solution species. This process leads to the
formation of a
hydrophobic viologen monolayer with stacked polymeric
\left({{\rm{DPV}}_{{\rm{ads}}}^{ \bullet + } } \right)_n
chains as
the characteristic structural motif. The wet
electrochemical
reduction of viologens is further compared with a dry
reduction
under UHV conditions. The latter reaction inevitably
affects the
di-cationic viologen species in the course of the
photoemission
experiment. Slow photoelectrons and secondary electrons
are assumed
to transform the di-cationic viologens into the
corresponding
radical mono-cations upon irradiation.
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