5,314 research outputs found
An empirical Bayes mixture method for effect size and false discovery rate estimation
Many statistical problems involve data from thousands of parallel cases. Each
case has some associated effect size, and most cases will have no effect. It is
often important to estimate the effect size and the local or tail-area false
discovery rate for each case. Most current methods do this separately, and most
are designed for normal data. This paper uses an empirical Bayes mixture model
approach to estimate both quantities together for exponential family data. The
proposed method yields simple, interpretable models that can still be used
nonparametrically. It can also estimate an empirical null and incorporate it
fully into the model. The method outperforms existing effect size and false
discovery rate estimation procedures in normal data simulations; it nearly
acheives the Bayes error for effect size estimation. The method is implemented
in an R package (mixfdr), freely available from CRAN.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS276 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Thermoelectric study of dissipative quantum dot heat engines
This paper examines the thermoelectric response of a dissipative quantum dot
heat engine based on the Anderson-Holstein model in two relevant operating
limits: (i) when the dot phonon modes are out of equilibrium, and (ii) when the
dot phonon modes are strongly coupled to a heat bath. In the first case, a
detailed analysis of the physics related to the interplay between the quantum
dot level quantization, the on-site Coulomb interaction and the electron-phonon
coupling on the thermoelectric performance reveals that an n-type heat engine
performs better than a p-type heat engine. In the second case, with the aid of
the dot temperature estimated by incorporating a {\it{thermometer bath}}, it is
shown that the dot temperature deviates from the bath temperature as
electron-phonon interaction becomes stronger. Consequently, it is demonstrated
that the dot temperature controls the direction of phonon heat currents,
thereby influencing the thermoelectric performance. Finally, the conditions on
the maximum efficiency with varying phonon couplings between the dot and all
the other macroscopic bodies are analyzed in order to reveal the nature of the
optimum junction.Comment: 10 pages, 9 figures, To be published in Phys Rev.
Quantum thermoelectrics based on 2-D Semi-Dirac materials
We show that a gap parameter can fully describe the merging of Dirac cones in
semi-Dirac materials from - and -points into the common -point
in the Brillouin zone. We predict that the gap parameter manifests itself by
enhancing the thermoelectric figure of merit as the chemical potential
crosses the gap followed by a sign change in the Seebeck coefficient around the
same point. Subsequently, we show that there is also a trade-off feature
between the maximum power delivered and the efficiency when the chemical
potential crosses the gap parameter. An optimal operating point that minimizes
the power-efficiency trade-off is consequently singled out for the best
thermoelectric performance. Our work paves the way for the use of 2D semi-Dirac
materials for thermoelectric applications.Comment: 5 pages, 5 figure
Role of dual nuclear baths on spin blockade leakage current bistabilities
Spin-blockaded electronic transport across a double quantum dot (DQD) system
represents an important advancement in the area of spin-based quantum
information. The basic mechanism underlying the blockade is the formation of a
blocking triplet state. The bistability of the leakage current as a function of
the applied magnetic field in this regime is believed to arise from the effect
of nuclear Overhauser fields on spin-flip transitions between the blocking
triplet and the conducting singlet states. The objective of this paper is to
present the nuances of considering a two bath model on the experimentally
observed current bistability by employing a self consistent simulation of the
nuclear spin dynamics coupled with the electronic transport of the DQD set up.
In doing so, we first discuss the important subtleties involved in the
microscopic derivation of the hyperfine mediated spin flip rates. We then give
insights as to how the differences between the two nuclear baths and the
resulting difference Overhauser field affect the two-electron states of the
DQD, and their connection with the experimentally observed current hysteresis
curve.Comment: 9 pages, 5 figure
Optimized Fabry-P\'erot cavity engineered nanoscale thermoelectric generators
In this work, we aim to design a heterostructure based nanoscale
thermoelectric generator that can maximize the waste-heat conversion efficiency
at a given output power. The primary objective to be achieved for this is to
realize a boxcar-shaped (bandpass) electronic transmission function (R. S.
Whitney, Phys. Rev. Lett. 112, 130601 (2014)). In order to achieve that, we
propose the use of an electronic analog of optical Fabry-P\'erot cavity over a
central resonant tunneling structure. We further explore the optimum design
possibilities by varying the geometry of the cavity wall to ensure a nearly
perfect bandpass energy filtering of electrons. Based on our findings, we
propose a general design guideline to realize such transmission and demonstrate
that such devices can be excellent thermoelectric generators compared to the
existing proposals in terms of boosting the output power without a cost in
efficiency. It is theoretically demonstrated using the non-equilibrium Green's
function technique coupled with self-consistent charging effects that an
enhancement in the maximum output power up to can be achieved through
this scheme at a higher efficiency as compared to resonant tunneling
based devices. Furthermore, an elaborate comparative study of the linear
response parameters is also presented and explained in terms of the physical
transport properties. This study suggests an optimal device design strategy for
an improved thermoelectric generator and sets the stage for a new class of
thermoelectric generators facilitated via transmission lineshape engineering
Combined monitoring, decision and control model for the human operator in a command and control desk
A report is given on the ongoing efforts to mode the human operator in the context of the task during the enroute/return phases in the ground based control of multiple flights of remotely piloted vehicles (RPV). The approach employed here uses models that have their analytical bases in control theory and in statistical estimation and decision theory. In particular, it draws heavily on the modes and the concepts of the optimal control model (OCM) of the human operator. The OCM is being extended into a combined monitoring, decision, and control model (DEMON) of the human operator by infusing decision theoretic notions that make it suitable for application to problems in which human control actions are infrequent and in which monitoring and decision-making are the operator's main activities. Some results obtained with a specialized version of DEMON for the RPV control problem are included
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