70,772 research outputs found
Crawling in Rogue's dungeons with (partitioned) A3C
Rogue is a famous dungeon-crawling video-game of the 80ies, the ancestor of
its gender. Rogue-like games are known for the necessity to explore partially
observable and always different randomly-generated labyrinths, preventing any
form of level replay. As such, they serve as a very natural and challenging
task for reinforcement learning, requiring the acquisition of complex,
non-reactive behaviors involving memory and planning. In this article we show
how, exploiting a version of A3C partitioned on different situations, the agent
is able to reach the stairs and descend to the next level in 98% of cases.Comment: Accepted at the Fourth International Conference on Machine Learning,
Optimization, and Data Science (LOD 2018
High-Order Adiabatic Approximation for Non-Hermitian Quantum System and Complexization of Berry's Phase
In this paper the evolution of a quantum system drived by a non-Hermitian
Hamiltonian depending on slowly-changing parameters is studied by building an
universal high-order adiabatic approximation(HOAA) method with Berry's phase
,which is valid for either the Hermitian or the non-Hermitian cases. This
method can be regarded as a non-trivial generalization of the HOAA method for
closed quantum system presented by this author before. In a general situation,
the probabilities of adiabatic decay and non-adiabatic transitions are
explicitly obtained for the evolution of the non-Hermitian quantum system. It
is also shown that the non-Hermitian analog of the Berry's phase factor for the
non-Hermitian case just enjoys the holonomy structure of the dual linear bundle
over the parameter manifold. The non-Hermitian evolution of the generalized
forced harmonic oscillator is discussed as an illustrative examples.Comment: ITP.SB-93-22,17 page
Non-specific cellular uptake of surface-functionalized quantum dots
We report a systematic empirical study of nanoparticle internalization into
cells via non-specific pathways. The nanoparticles were comprised of commercial
quantum dots (QDs) that were highly visible under a fluorescence confocal
microscope. Surface-modified QDs with basic biologically-significant moieties,
e.g. carboxyl, amino, streptavidin were used, in combination with the surface
derivatization with polyethylene glycol (PEG) in a range of immortalized cell
lines. Internalization rates were derived from image analysis and a detailed
discussion about the effect of nanoparticle size, charge and surface groups is
presented. We find that PEG-derivatization dramatically suppresses the
non-specific uptake while PEG-free carboxyl and amine functional groups promote
QD internalization. These uptake variations displayed a remarkable consistency
across different cell types. The reported results are important for experiments
concerned with cellular uptake of surface-functionalized nanomaterials, both
when non-specific internalization is undesirable and also when it is intended
for material to be internalized as efficiently as possible.
Published article at: http://iopscience.iop.org/0957-4484/21/28/285105/Comment: 14 pages 7 figure
Normal state resistivity of BaKFeAs: evidence for multiband strong-coupling behavior
We present theoretical analysis of the normal state resistivity in multiband
superconductors in the framework of Eliashberg theory. The results are compared
with measurements of the temperature dependence of normal state resistivity of
high-purity BaKFeAs single crystals with the
highest reported transition temperature = 38.5 K. The experimental data
demonstrate strong deviations from the Bloch-Gr\"{u}neisen behavior, namely the
tendency to saturation of the resistivity at high temperatures. The observed
behavior of the resistivity is explained within the two band scenario when the
first band is strongly coupled and relatively clean, while the second band is
weakly coupled and is characterized by much stronger impurity scattering.Comment: 4 pages, 3 figures, to be published in JETP Letters Vol.94, N
Eliashberg approach to superconductivity-induced infrared anomalies in Ba0.68K0.32Fe2As2
We report the full complex dielectric function of high-purity
single crystals
with determined by wide-band spectroscopic
ellipsometry at temperatures . We discuss the
microscopic origin of superconductivity-induced infrared optical anomalies in
the framework of a multiband Eliashberg theory with two distinct
superconducting gap energies $2\Delta_{\mathrm{A}}\approx6\
k_{\mathrm{B}}T_{\mathrm{c}}2\Delta_{\mathrm{B}}\approx2.2\
k_{\mathrm{B}}T_{\mathrm{c}}14\
k_{\mathrm{B}}T_{\mathrm{c}}$ can be ascribed to spin-fluctuation--assisted
processes in the clean limit of the strong-coupling regime.Comment: 4 pages, 4 figures; suppl. material: 3 pages, 2 figures, 1
interactive simulation (Fig. S3
Broad-band chopper for a CW proton linac at Fermilab
Requirements and technical limitations to the bunch-by-bunch chopper for the
Fermilab Project X are discussed.Comment: 3 pp. Particle Accelerator, 24th Conference (PAC'11) 2011. 28 Mar - 1
Apr 2011. New York, US
Bilayer Quantum Hall Ferromagnet in a Periodic Potential
The bilayer quantum Hall system at a total filling of has long
resisted explanation in terms of a true counterflow superfluid, though many
experimental features can be seen to be "almost" that of a superfluid. It is
widely believed that quenched disorder is the root cause of this puzzle. Here
we model the nonperturbative effects of disorder by investigating the
bilayer in a strong periodic potential. Our model assumes that fermions are
gapped and real spins are fully polarized, and concentrates on the pseudospin
variable (the layer index), with the external potential coupling to the
topological (Pontryagin) density of the pseudospin. We find that as the
potential strength increases, there are ground state transitions in which the
topological content of the pseudospin configuration changes. These transitions
are generically weakly first-order, with a new quadratically dispersing mode
(in addition to the linearly dispersing Goldstone mode) sometimes becoming
nearly gapless near the transition. We show that this leads to strong
suppressions of both the Kosterlitz-Thouless transition temperature and the
interlayer tunneling strength, which we treat perturbatively. We discuss how
these results might extend to the case of true disorder
Transport properties and the anisotropy of Ba_{1-x}K_xFe_2As_2 single crystals in normal and superconducting states
The transport and superconducting properties of Ba_{1-x}K_xFe_2As_2 single
crystals with T_c = 31 K were studied. Both in-plane and out-of plane
resistivity was measured by modified Montgomery method. The in-plane
resistivity for all studied samples, obtained in the course of the same
synthesis, is almost the same, unlike to the out-of plane resistivity, which
differ considerably. We have found that the resistivity anisotropy
\gamma=\rho_c /\rho_{ab} is almost temperature independent and lies in the
range 10-30 for different samples. This, probably, indicates on the extrinsic
nature of high out-of-plane resistivity, which may appear due to the presence
of the flat defects along Fe-As layers in the samples. This statement is
supported by comparatively small effective mass anisotropy, obtained from the
upper critical field measurements, and from the observation of the so-called
"Friedel transition", which indicates on the existence of some disorder in the
samples in c-direction.Comment: 5 pages, 5 figure
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