4,606 research outputs found
Dynamic Magneto-Conductance Fluctuations and Oscillations in Mesoscopic Wires and Rings
Using a finite-frequency recursive Green's function technique, we calculate
the dynamic magneto-conductance fluctuations and oscillations in disordered
mesoscopic normal metal systems, incorporating inter-particle Coulomb
interactions within a self-consistent potential method. In a disordered metal
wire, we observe ergodic behavior in the dynamic conductance fluctuations. At
low , the real part of the conductance fluctuations is essentially
given by the dc universal conductance fluctuations while the imaginary part
increases linearly from zero, but for greater than the Thouless energy
and temperature, the fluctuations decrease as . Similar
frequency-dependent behavior is found for the Aharonov-Bohm oscillations in a
metal ring. However, the Al'tshuler-Aronov-Spivak oscillations, which
predominate at high temperatures or in rings with many channels, are strongly
suppressed at high frequencies, leading to interesting crossover effects in the
-dependence of the magneto-conductance oscillations.Comment: 4 pages, REVTeX 3.0, 5 figures(ps file available upon request),
#phd0
History-dependent relaxation and the energy scale of correlation in the Electron-Glass
We present an experimental study of the energy-relaxation in
Anderson-insulating indium-oxide films excited far from equilibrium. In
particular, we focus on the effects of history on the relaxation of the excess
conductance dG. The natural relaxation law of dG is logarithmic, namely
dG=-log(t). This may be observed over more than five decades following, for
example, cool-quenching the sample from high temperatures. On the other hand,
when the system is excited from a state S_{o} in which it has not fully reached
equilibrium to a state S_{n}, the ensuing relaxation law is logarithmic only
over time t shorter than the time t_{w} it spent in S_{o}. For times t>t_{w}
dG(t) show systematic deviation from the logarithmic dependence. It was
previously shown that when the energy imparted to the system in the excitation
process is small, this leads to dG=P(t/t_{w}) (simple-aging). Here we test the
conjecture that `simple-aging' is related to a symmetry in the relaxation
dynamics in S_{o} and S_{n}. This is done by using a new experimental procedure
that is more sensitive to deviations in the relaxation dynamics. It is shown
that simple-aging may still be obeyed (albeit with a modified P(t/t_{w})) even
when the symmetry of relaxation in S_{o} and S_{n} is perturbed by a certain
degree. The implications of these findings to the question of aging, and the
energy scale associated with correlations are discussed
Mixed adsorption and surface tension prediction of nonideal ternary surfactant systems
To deal with the mixed adsorption of nonideal ternary surfactant systems, the regular solution approximation for nonideal binary surfactant systems is extended and a pseudo-binary system treatment is also proposed. With both treatments, the compositions of the mixed monolayer and the solution concentrations required to produce given surface tensions can be predicted based only on the gamma-LogC curves of individual surfactants and the pair interaction parameters. Conversely, the surface tensions of solutions with different bulk compositions can be predicted by the surface tension equations for mixed surfactant systems. Two ternary systems: SDS/Hyamine 1622/AEO7, composed of homogeneous surfactants, and AES/DPCl/AEO9, composed of commercial surfactants, in the presence of excess NaCl, are examined for the applicability of the two treatments. The results show that, in general, the pseudo-binary system treatment gives better prediction than the extended regular solution approximation, and the applicability of the latter to typical anionic/cationic/nonionic nonideal ternary surfactant systems seems to depend on the combined interaction parameter, : the more it deviates from zero, the larger the prediction difference. If rarr0, good agreements between predicted and experimental results can be obtained and both treatments, though differently derived, are interrelated and tend to be equivalent
Manifestation of ageing in the low temperature conductance of disordered insulators
We are interested in the out of equilibrium phenomena observed in the
electrical conductance of disordered insulators at low temperature, which may
be signatures of the electron coulomb glass state. The present work is devoted
to the occurrence of ageing, a benchmark phenomenon for the glassy state. It is
the fact that the dynamical properties of a glass depend on its age, i.e. on
the time elapsed since it was quench-cooled. We first critically analyse
previous studies on disordered insulators and question their interpretation in
terms of ageing. We then present new measurements on insulating granular
aluminium thin films which demonstrate that the dynamics is indeed age
dependent. We also show that the results of different relaxation protocols are
related by a superposition principle. The implications of our findings for the
mechanism of the conductance slow relaxations are then discussed
JSENet: Joint Semantic Segmentation and Edge Detection Network for 3D Point Clouds
Semantic segmentation and semantic edge detection can be seen as two dual
problems with close relationships in computer vision. Despite the fast
evolution of learning-based 3D semantic segmentation methods, little attention
has been drawn to the learning of 3D semantic edge detectors, even less to a
joint learning method for the two tasks. In this paper, we tackle the 3D
semantic edge detection task for the first time and present a new two-stream
fully-convolutional network that jointly performs the two tasks. In particular,
we design a joint refinement module that explicitly wires region information
and edge information to improve the performances of both tasks. Further, we
propose a novel loss function that encourages the network to produce semantic
segmentation results with better boundaries. Extensive evaluations on S3DIS and
ScanNet datasets show that our method achieves on par or better performance
than the state-of-the-art methods for semantic segmentation and outperforms the
baseline methods for semantic edge detection. Code release:
https://github.com/hzykent/JSENetComment: Accepted to ECCV 2020, supplementary materials include
Theory of Transmission through disordered superlattices
We derive a theory for transmission through disordered finite superlattices
in which the interface roughness scattering is treated by disorder averaging.
This procedure permits efficient calculation of the transmission thr ough
samples with large cross-sections. These calculations can be performed
utilizing either the Keldysh or the Landauer-B\"uttiker transmission
formalisms, both of which yield identical equations. For energies close to the
lowest miniband, we demonstrate the accuracy of the computationally efficient
Wannier-function approximation. Our calculations indicate that the transmission
is strongly affected by interface roughness and that information about scale
and size of the imperfections can be obtained from transmission data.Comment: 12 pages, 6 Figures included into the text. Final version with minor
changes. Accepted by Physical Review
Surface Effects on Anisotropic Photoluminescence in One-Dimensional Organic Metal Halide Hybrids
One-dimensional (1D) organic metal halide hybrids exhibit strongly
anisotropic optical properties, highly efficient light emission, and large
Stokes shift, holding promises for novel photodetection and lighting
applications. However, the fundamental mechanisms governing their unique
optical properties and in particular the impacts of surface effects are not
understood. Here, we investigate 1D C4N2H14PbBr4 by polarization-dependent
time-averaged and time-resolved photoluminescence (TRPL) spectroscopy, as a
function of photoexcitation energy. Surprisingly, we find that the emission
under photoexcitation polarized parallel to the 1D metal halide chains can be
either stronger or weaker than that under perpendicular polarization, depending
on the excitation energy. We attribute the excitation-energy-dependent
anisotropic emission to fast surface recombination, supported by
first-principles calculations of optical absorption in this material. The fast
surface recombination is directly confirmed by TRPL measurements, when the
excitation is polarized parallel to the chains. Our comprehensive studies
provide a more complete picture for a deeper understanding of the optical
anisotropy in 1D organic metal halide hybrids
-scaling and Information Entropy in Ultra-Relativistic Nucleus-Nucleus Collisions
The -scaling method has been applied to ultra-relativistic p+p, C+C
and Pb+Pb collision data simulated using a high energy Monte Carlo package,
LUCIAE 3.0. The -scaling is found to be valid for some physical
variables, such as charged particle multiplicity, strange particle multiplicity
and number of binary nucleon-nucleon collisions from these simulated
nucleus-nucleus collisions over an extended energy ranging from = 20
to 200 A GeV. In addition we derived information entropy from the multiplicity
distribution as a function of beam energy for these collisions.Comment: 4 pages, 4 figures, 1 table; to appear in the July Issue of Chin.
Phys. Lett.. Web Page: http://www.iop.org/EJ/journal/CP
Electric Field Effect in Ultrathin Films near the Superconductor-Insulator Transition
The effect of an electric field on the conductance of ultrathin films of
metals deposited on substrates coated with a thin layer of amorphous Ge was
investigated. A contribution to the conductance modulation symmetric with
respect to the polarity of the applied electric field was found in regimes in
which there was no sign of glassy behavior. For films with thicknesses that put
them on the insulating side of the superconductor-insulator transition, the
conductance increased with electric field, whereas for films that were becoming
superconducting it decreased. Application of magnetic fields to the latter,
which reduce the transition temperature and ultimately quench
superconductivity, changed the sign of the reponse of the conductance to
electric field back to that found for insulators. We propose that this
symmetric response to capacitive charging is a consequence of changes in the
conductance of the a-Ge layer, and is not a fundamental property of the physics
of the superconductor-insulator transition as previously suggested.Comment: 4 pages text, 4 figure
Geometry-controlled kinetics
It has long been appreciated that transport properties can control reaction
kinetics. This effect can be characterized by the time it takes a diffusing
molecule to reach a target -- the first-passage time (FPT). Although essential
to quantify the kinetics of reactions on all time scales, determining the FPT
distribution was deemed so far intractable. Here, we calculate analytically
this FPT distribution and show that transport processes as various as regular
diffusion, anomalous diffusion, diffusion in disordered media and in fractals
fall into the same universality classes. Beyond this theoretical aspect, this
result changes the views on standard reaction kinetics. More precisely, we
argue that geometry can become a key parameter so far ignored in this context,
and introduce the concept of "geometry-controlled kinetics". These findings
could help understand the crucial role of spatial organization of genes in
transcription kinetics, and more generally the impact of geometry on
diffusion-limited reactions.Comment: Submitted versio
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