5,687 research outputs found
A numerical and symbolical approximation of the Nonlinear Anderson Model
A modified perturbation theory in the strength of the nonlinear term is used
to solve the Nonlinear Schroedinger Equation with a random potential. It is
demonstrated that in some cases it is more efficient than other methods.
Moreover we obtain error estimates. This approach can be useful for the
solution of other nonlinear differential equations of physical relevance.Comment: 21 pages and 7 figure
Multifractals Competing with Solitons on Fibonacci Optical Lattice
We study the stationary states for the nonlinear Schr\"odinger equation on
the Fibonacci lattice which is expected to be realized by Bose-Einstein
condensates loaded into an optical lattice. When the model does not have a
nonlinear term, the wavefunctions and the spectrum are known to show fractal
structures. Such wavefunctions are called critical. We present a phase diagram
of the energy spectrum for varying the nonlinearity. It consists of three
portions, a forbidden region, the spectrum of critical states, and the spectrum
of stationary solitons. We show that the energy spectrum of critical states
remains intact irrespective of the nonlinearity in the sea of a large number of
stationary solitons.Comment: 5 pages, 4 figures, major revision, references adde
Echoes and revival echoes in systems of anharmonically confined atoms
We study echoes and what we call 'revival echoes' for a collection of atoms
that are described by a single quantum wavefunction and are confined in a
weakly anharmonic trap. The echoes and revival echoes are induced by applying
two, successive temporally localized potential perturbations to the confining
potential, one at time , and a smaller one at time . Pulse-like
responses in the expectation value of position are predicted at $t
\approx n\tau$ ($n=2,3,...$) and are particularly evident at $t \approx 2\tau$.
A novel result of our study is the finding of 'revival echoes'. Revivals (but
not echoes) occur even if the second perturbation is absent. In particular, in
the absence of the second perturbation, the response to the first perturbation
dies away, but then reassembles, producing a response at revival times $mT_x$
($m=1,2,...$). Including the second perturbation at $t=\tau$, we find
temporally localized responses, revival echoes, both before and after $t\approx
mT_x$, e.g., at $t\approx m T_x-n \tau$ (pre-revival echoes) and at $t\approx
mT_x+n\tau$, (post-revival echoes), where $m$ and $n$ are $1,2,...$ . Depending
on the form of the perturbations, the 'principal' revival echoes at $t \approx
T_x \pm \tau$ can be much larger than the echo at $t \approx 2\tau$. We develop
a perturbative model for these phenomena, and compare its predictions to the
numerical solutions of the time-dependent Schr\"odinger Equation. The scaling
of the size of the various echoes and revival echoes as a function of the
symmetry and size of the perturbations applied at $t=0$ and $t=\tau$ is
investigated. We also study the presence of revivals and revival echoes in
higher moments of position, , , and the effect of atom-atom
interactions on these phenomena.Comment: 33 pages, 13 figures, corrected typos and added reference
3-D GRMHD and GRPIC Simulations of Disk-Jet Coupling and Emission
We investigate jet formation in black-hole systems using 3-D General
Relativistic Particle-In-Cell (GRPIC) and 3-D GRMHD simulations. GRPIC
simulations, which allow charge separations in a collisionless plasma, do not
need to invoke the frozen condition as in GRMHD simulations. 3-D GRPIC
simulations show that jets are launched from Kerr black holes as in 3-D GRMHD
simulations, but jet formation in the two cases may not be identical.
Comparative study of black hole systems with GRPIC and GRMHD simulations with
the inclusion of radiate transfer will further clarify the mechanisms that
drive the evolution of disk-jet systems.Comment: 3 pages, 1 figure, Proceedings of the Eleventh Marcel Grossmann
Meeting on General Relativity, edited by H. Kleinert, R.T. Jantzen and R.
Ruffini, World Scientific, Singapore, 200
Invalidity of Classes of Approximated Hall Effect Calculations
In this comment, I point out a number of approximated derivations for the
effective equation of motion, now been applied to d-wave superconductors by
Kopnin and Volovik are invalid. The major error in those approximated
derivations is the inappropriate use of the relaxation time approximation in
force-force correlation functions, or in force balance equations, or in similar
variations. This approximation is wrong and unnecessary.Comment: final version, minor changes, to appear in Phys. Rev. Let
Relativistic Particle-In-Cell Simulation Studies of Prompt and Early Afterglows from GRBs
Nonthermal radiation observed from astrophysical systems containing
relativistic jets and shocks e.g. gamma-ray bursts (GRBs) active galactic
nuclei (AGNs) and microquasars commonly exhibit power-law emission spectra.
Recent PIC simulations of relativistic electron-ion (or electron-positron) jets
injected into a stationary medium show that particle acceleration occurs within
the downstream jet. In collisionless relativistic shocks particle (electron,
positron and ion) acceleration is due to plasma waves and their associated
instabilities (e.g. the Weibel (filamentation) instability) created in the
shock region. The simulations show that the Weibel instability is responsible
for generating and amplifying highly non-uniform small-scale magnetic fields.
These fields contribute to the electron's transverse deflection behind the jet
head. The resulting ``jitter'' radiation from deflected electrons has different
properties compared to synchrotron radiation which assumes a uniform magnetic
field. Jitter radiation may be important for understanding the complex time
evolution and/or spectra in gamma-ray bursts, relativistic jets in general and
supernova remnants.Comment: 19 pages,7 figures, contributed talk at Seventh European Workshop on
Collisionless Shocks, Paris, 7- 9 November 2007. High resolution version can
be obtained at http://gammaray.nsstc.nasa.gov/~nishikawa/shockws07.pd
Arnol'd Tongues and Quantum Accelerator Modes
The stable periodic orbits of an area-preserving map on the 2-torus, which is
formally a variant of the Standard Map, have been shown to explain the quantum
accelerator modes that were discovered in experiments with laser-cooled atoms.
We show that their parametric dependence exhibits Arnol'd-like tongues and
perform a perturbative analysis of such structures. We thus explain the
arithmetical organisation of the accelerator modes and discuss experimental
implications thereof.Comment: 20 pages, 6 encapsulated postscript figure
Knowledge Graph Completion to Predict Polypharmacy Side Effects
The polypharmacy side effect prediction problem considers cases in which two
drugs taken individually do not result in a particular side effect; however,
when the two drugs are taken in combination, the side effect manifests. In this
work, we demonstrate that multi-relational knowledge graph completion achieves
state-of-the-art results on the polypharmacy side effect prediction problem.
Empirical results show that our approach is particularly effective when the
protein targets of the drugs are well-characterized. In contrast to prior work,
our approach provides more interpretable predictions and hypotheses for wet lab
validation.Comment: 13th International Conference on Data Integration in the Life
Sciences (DILS2018
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