25,447 research outputs found
Effective generation of Ising interaction and cluster states in coupled microcavities
We propose a scheme for realizing the Ising spin-spin interaction and atomic
cluster states utilizing trapped atoms in coupled microcavities. It is shown
that the atoms can interact with each other via the exchange of virtual photons
of the cavities. Through suitably tuning the parameters, an effective Ising
spin-spin interaction can be generated in this optical system, which is used to
produce the cluster states. This scheme does not need the preparation of
initial states of atoms and cavity modes, and is insensitive to cavity decay.Comment: 11pages, 2 figures, Revtex
On Mitigation of Side-Channel Attacks in 3D ICs: Decorrelating Thermal Patterns from Power and Activity
Various side-channel attacks (SCAs) on ICs have been successfully
demonstrated and also mitigated to some degree. In the context of 3D ICs,
however, prior art has mainly focused on efficient implementations of classical
SCA countermeasures. That is, SCAs tailored for up-and-coming 3D ICs have been
overlooked so far. In this paper, we conduct such a novel study and focus on
one of the most accessible and critical side channels: thermal leakage of
activity and power patterns. We address the thermal leakage in 3D ICs early on
during floorplanning, along with tailored extensions for power and thermal
management. Our key idea is to carefully exploit the specifics of material and
structural properties in 3D ICs, thereby decorrelating the thermal behaviour
from underlying power and activity patterns. Most importantly, we discuss
powerful SCAs and demonstrate how our open-source tool helps to mitigate them.Comment: Published in Proc. Design Automation Conference, 201
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Graphene-polyelectrolyte multilayer membranes with tunable structure and internal charge
One great advantage of graphene-polyelectrolyte multilayer (GPM) membranes is their tunable structure and internal charge for improved separation performance. In this study, we synthesized GO-dominant GPM membrane with internal negatively-charged domains, polyethyleneimine (PEI)-dominant GPM membrane with internal positively-charged domains and charge-balanced dense/loose GPM membranes by simply adjusting the ionic strength and pH of the GO and PEI solutions used in layer-by-layer membrane synthesis. A combined system of quartz crystal microbalance with dissipation (QCM-D) and ellipsometry was used to analyze the mass deposition, film thickness, and layer density of the GPM membranes. The performance of the GPM membranes were compared in terms of both permeability and selectivity to determine the optimal membrane structure and synthesis strategy. One effective strategy to improve the GPM membrane permeability-selectivity tradeoff is to assemble charge-balanced dense membranes under weak electrostatic interactions. This balanced membrane exhibits the highest MgCl2 selectivity (∼86%). Another effective strategy for improved cation removal is to create PEI-dominant membranes that provide internal positively-charged barrier to enhance cation selectivity without sacrificing water permeability. These findings shine lights on the development of a systematic approach to push the boundary of permeability-selectivity tradeoff for GPM membranes
Earth matter density uncertainty in atmospheric neutrino oscillations
That muon neutrinos oscillating into the mixture of tau neutrinos
and sterile neutrinos has been studied to explain the
atmospheric disappearance. In this scenario, the effect of Earth
matter is a key to determine the fraction of . Considering that the
Earth matter density has uncertainty and this uncertainty has significant
effects in some neutrino oscillation cases, such as the CP violation in very
long baseline neutrino oscillations and the day-night asymmetry for solar
neutrinos, we study the effects caused by this uncertainty in the above
atmospheric oscillation scenario. We find that this uncertainty
seems to have no significant effects and that the previous fitting results need
not to be modified fortunately.Comment: 7 pages, 1 figure, to appear in Phys. Rev.
Fast Monte Carlo Simulation for Patient-specific CT/CBCT Imaging Dose Calculation
Recently, X-ray imaging dose from computed tomography (CT) or cone beam CT
(CBCT) scans has become a serious concern. Patient-specific imaging dose
calculation has been proposed for the purpose of dose management. While Monte
Carlo (MC) dose calculation can be quite accurate for this purpose, it suffers
from low computational efficiency. In response to this problem, we have
successfully developed a MC dose calculation package, gCTD, on GPU architecture
under the NVIDIA CUDA platform for fast and accurate estimation of the x-ray
imaging dose received by a patient during a CT or CBCT scan. Techniques have
been developed particularly for the GPU architecture to achieve high
computational efficiency. Dose calculations using CBCT scanning geometry in a
homogeneous water phantom and a heterogeneous Zubal head phantom have shown
good agreement between gCTD and EGSnrc, indicating the accuracy of our code. In
terms of improved efficiency, it is found that gCTD attains a speed-up of ~400
times in the homogeneous water phantom and ~76.6 times in the Zubal phantom
compared to EGSnrc. As for absolute computation time, imaging dose calculation
for the Zubal phantom can be accomplished in ~17 sec with the average relative
standard deviation of 0.4%. Though our gCTD code has been developed and tested
in the context of CBCT scans, with simple modification of geometry it can be
used for assessing imaging dose in CT scans as well.Comment: 18 pages, 7 figures, and 1 tabl
Thermodynamic Machine Learning through Maximum Work Production
Adaptive systems -- such as a biological organism gaining survival advantage,
an autonomous robot executing a functional task, or a motor protein
transporting intracellular nutrients -- must model the regularities and
stochasticity in their environments to take full advantage of thermodynamic
resources. Analogously, but in a purely computational realm, machine learning
algorithms estimate models to capture predictable structure and identify
irrelevant noise in training data. This happens through optimization of
performance metrics, such as model likelihood. If physically implemented, is
there a sense in which computational models estimated through machine learning
are physically preferred? We introduce the thermodynamic principle that work
production is the most relevant performance metric for an adaptive physical
agent and compare the results to the maximum-likelihood principle that guides
machine learning. Within the class of physical agents that most efficiently
harvest energy from their environment, we demonstrate that an efficient agent's
model explicitly determines its architecture and how much useful work it
harvests from the environment. We then show that selecting the maximum-work
agent for given environmental data corresponds to finding the
maximum-likelihood model. This establishes an equivalence between
nonequilibrium thermodynamics and dynamic learning. In this way, work
maximization emerges as an organizing principle that underlies learning in
adaptive thermodynamic systems.Comment: 29 pages, 10 figures, 6 appendices;
http://csc.ucdavis.edu/~cmg/compmech/pubs/tml.ht
Detrended fluctuation analysis for fractals and multifractals in higher dimensions
One-dimensional detrended fluctuation analysis (1D DFA) and multifractal
detrended fluctuation analysis (1D MF-DFA) are widely used in the scaling
analysis of fractal and multifractal time series because of being accurate and
easy to implement. In this paper we generalize the one-dimensional DFA and
MF-DFA to higher-dimensional versions. The generalization works well when
tested with synthetic surfaces including fractional Brownian surfaces and
multifractal surfaces. The two-dimensional MF-DFA is also adopted to analyze
two images from nature and experiment and nice scaling laws are unraveled.Comment: 7 Revtex pages inluding 11 eps figure
Terahertz Hall Measurements On Optimally Doped Single Crystal Bi-2212
The infrared Hall angle in optimally doped single crystal was measured from 3.05 to 21.75 meV as a continuous function of
temperature from 25 to 300\,K. In the normal state, the temperature dependence
of the real part of the cotangent of the infrared Hall angle obeys the same
power law as dc measurements. The measured Hall frequency is
significantly larger than the expected value based upon ARPES data analyzed in
terms of the relaxation time approximation. This discrepancy as well as the
temperature dependence of and is well
described by a Fermi liquid theory in which current vertex corrections produced
by electron-magnon scattering are included.Comment: 10 pages, 2 figure
Charge dynamics in the phase string model for high-Tc superconductors
An understanding of the anomalous charge dynamics in the high-Tc cuprates is
obtained based on a model study of doped Mott insulators. The high-temperature
optical conductivity is found to generally have a two-component structure: a
Drude like part followed by a mid-infrared band. The scattering rate associated
with the Drude part exhibits a linear-temperature dependence over a wide range
of high temperature, while the Drude term gets progressively suppressed below a
characteristic energy of magnetic origin as the system enters the pseudogap
phase. The high-energy optical conductivity shows a resonancelike feature in an
underdoped case and continuously evolves into a 1/\omega tail at higher doping,
indicating that they share the same physical origin. In particular, such a
high-energy component is closely correlated with the \omega-peak structure of
the density-density correlation function at different momenta, in systematic
consistency with exact diagonalization results based on the t-J model. The
underlying physics is attributed to the high-energy spin-charge separation in
the model, in which the "mode coupling" responsible for the anomalous charge
properties is not between the electrons and some collective mode but rather
between new charge carriers, holons, and a novel topological gauge field
controlled by spin dynamics, as the consequence of the strong short-range
electron-electron Coulomb repulsion in the doped Mott insulator.Comment: 19 pages, 13 figures; final version to appear in Phys. Rev.
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