1,573 research outputs found
Localization and transport in a strongly driven Anderson insulator
We study localization and charge dynamics in a monochromatically driven
one-dimensional Anderson insulator focussing on the low-frequency,
strong-driving regime. We study this problem using a mapping of the Floquet
Hamiltonian to a hopping problem with correlated disorder in one higher
harmonic-space dimension. We show that (i) resonances in this model correspond
to \emph{adiabatic} Landau-Zener (LZ) transitions that occur due to level
crossings between lattice sites over the course of dynamics; (ii) the
proliferation of these resonances leads to dynamics that \emph{appear}
diffusive over a single drive cycle, but the system always remains localized;
(iii) actual charge transport occurs over many drive cycles due to slow
dephasing between these LZ orbits and is logarithmic-in-time, with a crucial
role being played by far-off Mott-like resonances; and (iv) applying a
spatially-varying random phase to the drive tends to decrease localization,
suggestive of weak-localization physics. We derive the conditions for the
strong driving regime, determining the parametric dependencies of the size of
Floquet eigenstates, and time-scales associated with the dynamics, and
corroborate the findings using both numerical scaling collapses and analytical
arguments.Comment: 7 pages + references, 6 figure
Effectiveness of Hub and Spoke Model for Dissemination of Innovative Farm Technologies to the Farming Community
Hub and Spoke Model was established for dissemination of the innovative farming technologies at farmersâ doorstep. The study was conducted to measure the Effectiveness of Hub and Spoke Model for dissemination of innovative farm technologies at Tiruvannamalai district of Tamil Nadu. The respondents were selected by adopting purposive random sampling technique. A sample of 75 respondents from five villages of Polur block was selected for this study. The hub and spoke model was established and the knowledge gain of the subjects both at the pre and post exposure stages were collected using teacher made knowledge tests respectively. The data were collected using a well structured and pre-tested interview schedule. The data were analyzed by using appropriate statistical tools. The percentage of knowledge gained before the exposure to treatment was 40.20 per cent and after exposed it was 76.70 per cent. The mean knowledge gain is 36.50 per cent. The âtâ value 19.93 per cent indicates that the knowledge gained by the respondents was found to be significant at one per cent level. It was identified that there existed a significant differences in the effectiveness of the hub and spoke services in imparting knowledge
Investor Behavior in the Mutual Fund Industry: Evidence from Gross Flows
Using a large sample of monthly gross flows from 1997 to 2003, we uncover several previously undocumented regularities in investor behavior. First, investor purchases and sales produce fund-level gross flows that are highly persistent. Persistence in fund flows dominates performance as a predictor of future fund flows. More importantly, failing to account for flow persistence leads to incorrect inferences with respect to the relation between performance and flows. Second, we document that investors react differently to performance depending on the type of fund, and that investor trading activity produces meaningful differences in the persistence of fund flows across mutual fund types. Third, at least some investors appear to evaluate and respond to mutual fund performance over much shorter time spans than previously assessed. Additionally, we document differences in the speed and magnitude of investorsâ purchase and sales responses to performance
Investors Do Respond to Poor Mutual Fund Performance: Evidence from Inflows and Outflows
Abstract
We examine the relation between mutual fund performance and gross flows for a large sample of actively managed U.S. mutual funds. Unlike previous studies that have only examined periods of generally increasing net flows, our sample includes periods of both increasing and decreasing net flows. We find that outflows are related to performance, with investors withdrawing money from poor performers. We also find that outflows and inflows respond asymmetrically to performance, outflows increase more aggressively following poor performance, and inflows increase more aggressively following good performance. Additionally, we find a symmetric performance net flow relation
Robust multivariate association and dimension reduction using density divergences
In this article, we introduce two new families of multivariate association measures based on power divergence and alpha divergence that recover both linear and nonlinear dependence relationships between multiple sets of random vectors. Importantly, this novel approach not only characterizes independence, but also provides a smooth bridge between well-known distances that are inherently robust against outliers. Algorithmic approaches are developed for dimension reduction and the selection of the optimal robust association index. Extensive simulation studies are performed to assess the robustness of these association measures under different types and proportions of contamination. We illustrate the usefulness of our methods in application by analyzing two socioeconomic datasets that are known to contain outliers or extreme observations. Some theoretical properties, including the consistency of the estimated coefficient vectors, are investigated and computationally efficient algorithms for our nonparametric methods are provided. (C) 2013 Elsevier Inc. All rights reserved
Electrical Properties of Atomic Layer Deposited Aluminum Oxide on Gallium Nitride
We report on our investigation of the electrical properties of
metal/Al2O3/GaN metal-insulator-semiconductor (MIS) capacitors. We determined
the conduction band offset and interface charge density of the alumina/GaN
interface by analyzing capacitance-voltage characteristics of atomic layer
deposited Al2O3 films on GaN substrates. The conduction band offset at the
Al2O3/GaN interface was calculated to be 2.13 eV, in agreement with theoretical
predications. A non-zero field of 0.93 MV/cm in the oxide under flat-band
conditions in the GaN was inferred, which we attribute to a fixed net positive
charge density of magnitude 4.60x1012 cm-2 at the Al2O3/GaN interface. We
provide hypotheses to explain the origin of this charge by analyzing the energy
band line-up.Comment: 8 pages, 4 figures, Applied Physics Letter
The Kelvin Formula for Thermopower
Thermoelectrics are important in physics, engineering, and material science
due to their useful applications and inherent theoretical difficulty,
especially in strongly correlated materials. Here we reexamine the framework
for calculating the thermopower, inspired by ideas of Lord Kelvin from 1854. We
find an approximate but concise expression, which we term as the Kelvin formula
for the the Seebeck coefficient. According to this formula, the Seebeck
coefficient is given as the particle number derivative of the entropy
, at constant volume and temperature ,
. This formula is shown to be competitive compared to other
approximations in various contexts including strongly correlated systems. We
finally connect to a recent thermopower calculation for non-Abelian fractional
quantum Hall states, where we point out that the Kelvin formula is exact.Comment: 6 pages, 2 figure
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