17,889 research outputs found
Gravitational energy from a combination of a tetrad expression and Einstein's pseudotensor
The energy-momentum for a gravitating system can be considered by the tetard
teleparalle gauge current in orthonormal frames. Whereas the Einstein
pseudotensor used holonomic frames. Tetrad expression itself gives a better
result for gravitational energy than Einstein's. Inspired by an idea of Deser,
we found a gravitational energy expression which enjoys the positive energy
property by combining the tetrad expression and the Einstein pseudotensor,
i.e., the connection coefficient has a form appropriate to a suitable
intermediate between orthonormal and holonomic frames.Comment: 5 page
Designing nanophotonic structures using conditional deep convolutional generative adversarial networks
Data-driven design approaches based on deep learning have been introduced in nanophotonics to reduce time-consuming iterative simulations, which have been a major challenge. Here, we report the first use of conditional deep convolutional generative adversarial networks to design nanophotonic antennae that are not constrained to predefined shapes. For given input reflection spectra, the network generates desirable designs in the form of images; this allows suggestions of new structures that cannot be represented by structural parameters. Simulation results obtained from the generated designs agree well with the input reflection spectrum. This method opens new avenues toward the development of nanophotonics by providing a fast and convenient approach to the design of complex nanophotonic structures that have desired optical properties.11Ysciescopu
Gravitational energy in a small region for the modified Einstein and Landau-Lifshitz pseudotensors
The purpose of the classical Einstein and Landau-Lifshitz pseudotensors is
for determining the gravitational energy. Neither of them can guarantee a
positive energy in holonomic frames. In the small sphere approximation, it has
been required that the quasilocal expression for the gravitational
energy-momentum density should be proportional to the Bel-Robinson tensor
. However, we propose a new tensor
which is the sum of certain tensors
and , it has certain properties
so that it gives the same gravitational "energy-momentum" content as
does. Moreover, we show that a modified Einstein
pseudotensor turns out to be one of the Chen-Nester quasilocal expressions,
while the modified Landau-Lifshitz pseudotensor becomes the Papapetrou
pseudotensor; these two modified pseudotensors have positive gravitational
energy in a small region.Comment:
Neural Network Model for Apparent Deterministic Chaos in Spontaneously Bursting Hippocampal Slices
A neural network model that exhibits stochastic population bursting is
studied by simulation. First return maps of inter-burst intervals exhibit
recurrent unstable periodic orbit (UPO)-like trajectories similar to those
found in experiments on hippocampal slices. Applications of various control
methods and surrogate analysis for UPO-detection also yield results similar to
those of experiments. Our results question the interpretation of the
experimental data as evidence for deterministic chaos and suggest caution in
the use of UPO-based methods for detecting determinism in time-series data.Comment: 4 pages, 5 .eps figures (included), requires psfrag.sty (included
Molecular transistor coupled to phonons and Luttinger-liquid leads
We study the effects of electron-phonon interactions on the transport
properties of a molecular quantum dot coupled to two Luttinger-liquid leads. In
particular, we investigate the effects on the steady state current and DC noise
characteristics. We consider both equilibrated and unequilibrated on-dot
phonons. The density matrix formalism is applied in the high temperature
approximation and the resulting semi-classical rate equation is numerically
solved for various strengths of electron-electron interactions in the leads and
electron-phonon coupling. The current and the noise are in general smeared out
and suppressed due to intralead electron interaction. On the other hand, the
Fano factor, which measures the noise normalized by the current, is more
enhanced as the intralead interaction becomes stronger. As the electron-phonon
coupling becomes greater than order one, the Fano factor exhibits
super-Poissonian behaviour.Comment: 11 pages, 11 figure
New positive small vacuum region gravitational energy expressions
We construct an infinite number of new holonomic quasi-local gravitational
energy-momentum density pseudotensors with good limits asymptotically and in
small regions, both materially and in vacuum. For small vacuum regions they are
all a positive multiple of the Bel-Robinson tensor and consequently have
positive energy.Comment: 4 page
Excited D-branes and Supergravity Solutions
We investigate the general solution with the symmetry ISO(1,p)xSO(9-p) of
Type II supergravity (the three-parameter solution) from the viewpoint of the
superstring theory. We find that one of the three parameters (c_1) is closely
related to the ``dilaton charge'' and the appearance of the dilaton charge is a
consequence of deformations of the boundary condition from that of the boundary
state for BPS D-branes. We give three examples of the deformed D-branes by
considering the tachyon condensation from systems of D-\bar{D}p-branes,
unstable D9-branes and unstable D-instantons to the BPS saturated Dp-branes,
respectively. We argue that the deformed systems are generally regarded as
tachyonic and/or massive excitations of the open strings on Dp-\bar{D}p-brane
systems.Comment: 29 pages, 6 figures, LaTeX2e, typos corrected, references adde
Numerical estimation on free electrons generated by shielded radioactive materials under various gaseous environments
We report simulation results on generation of free electrons due to the presence of radioactive materials under controlled pressure and gases using a general Monte Carlo transport code (MCNPX). A radioactive material decays to lower atomic number, simultaneously producing high energy gamma rays that can generate free electrons via various scattering mechanisms. This paper shows detailed simulation works for answering how many free electrons can be generated under the existence of shielded radioactive materials as a function of pressure and types of gases.open0
Nonequilibrium quantum criticality in open electronic systems
A theory is presented of quantum criticality in open (coupled to reservoirs)
itinerant electron magnets, with nonequilibrium drive provided by current flow
across the system. Both departures from equilibrium at conventional
(equilibrium) quantum critical points and the physics of phase transitions
induced by the nonequilibrium drive are treated. Nonequilibrium-induced phase
transitions are found to have the same leading critical behavior as
conventional thermal phase transitions.Comment: 5 pages, 1 figur
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