4,310 research outputs found
Mesoscopic Thermovoltage Measurement Design
Quantitative thermoelectric measurements in the mesoscopic regime require
accurate knowledge of temperature, thermovoltage, and device energy scales. We
consider the effect of a finite load resistance on thermovoltage measurements
of InAs/InP heterostructure nanowires. Load resistance and ac attenuation
distort the measured thermovoltage therefore complicating the evaluation of
device performance. Understanding these effects improves experimental design
and data interpretation.Comment: 2 pages, 3 figure
Holographic data storage in a DX-center material
We report on the optical storage of digital data in a semiconductor sample containing DX centers. The diffraction efficiency and the bit-error-rate performance of multiplexed data images are shown to agree well with a simple model of the material. Uniform storage without an exposure schedule is demonstrated. The volume sensitivity is found to be ~10^3 times that of LiNBO3:Fe. The importance of coherent addition of scattered light with diffracted light in holographic data storage is discussed
Threshold feedback control for a collective flashing ratchet: threshold dependence
We study the threshold control protocol for a collective flashing ratchet. In
particular, we analyze the dependence of the current on the values of the
thresholds. We have found analytical expressions for the small threshold
dependence both for the few and for the many particle case. For few particles
the current is a decreasing function of the thresholds, thus, the maximum
current is reached for zero thresholds. In contrast, for many particles the
optimal thresholds have a nonzero finite value. We have numerically checked the
relation that allows to obtain the optimal thresholds for an infinite number of
particles from the optimal period of the periodic protocol. These optimal
thresholds for an infinite number of particles give good results for many
particles. In addition, they also give good results for few particles due to
the smooth dependence of the current up to these threshold values.Comment: LaTeX, 10 pages, 7 figures, improved version to appear in Phys. Rev.
Mechanical coupling in flashing ratchets
We consider the transport of rigid objects with internal structure in a
flashing ratchet potential by investigating the overdamped behavior of a
rod-like chain of evenly spaced point particles. In 1D, analytical arguments
show that the velocity can reverse direction multiple times in response to
changing the size of the chain or the temperature of the heat bath. The
physical reason is that the effective potential experienced by the mechanically
coupled objects can have a different symmetry than that of individual objects.
All analytical predictions are confirmed by Brownian dynamics simulations.
These results may provide a route to simple, coarse-grained models of molecular
motor transport that incorporate an object's size and rotational degrees of
freedom into the mechanism of transport.Comment: 9 pages, 10 figure
Increasing thermoelectric performance using coherent transport
We show that coherent electron transport through zero-dimensional systems can
be used to tailor the shape of the system's transmission function. This
quantum-engineering approach can be used to enhance the performance of quantum
dots or molecules in thermal-to-electric power conversion. Specifically, we
show that electron interference in a two-level system can substantially improve
the maximum thermoelectric power and the efficiency at maximum power by
suppressing parasitic charge flow near the Fermi energy, and by reducing
electronic heat conduction. We discuss possible realizations of this approach
in molecular junctions or quantum dots.Comment: 4+ pages, 4 figure
Heat flow in InAs/InP heterostructure nanowires
The transfer of heat between electrons and phonons plays a key role for
thermal management in future nanowire-based devices, but only a few
experimental measurements of electron-phonon (e-ph) coupling in nanowires are
available. Here, we combine experimental temperature measurements on an
InAs/InP heterostructure nanowire system with finite element modeling (FEM) to
extract information on heat flow mediated by e-ph coupling. We find that the
electron and phonon temperatures in our system are highly coupled even at
temperatures as low as 2 K. Additionally, we find evidence that the usual
power-law temperature dependence of electron-phonon coupling may not correctly
describe the coupling in nanowires and show that this result is consistent with
previous research on similar one-dimensional electron systems. We also compare
the strength of the observed e-ph coupling to a theoretical analysis of e-ph
interaction in InAs nanowires, which predicts a significantly weaker coupling
strength than observed experimentally.Comment: 9 pages, 6 figure
Divergence of opinion and risk : an empirical analysis of the Ex Ante beliefs of institutional investors
Bibliography: p. [24-25
Diffusion Enhancement in a Periodic Potential under High-Frequency Space-Dependent Forcing
We study the long-time behavior of underdamped Brownian particle moving
through a viscous medium and in a systematic potential, when it is subjected to
a space-dependent high-frequency periodic force. When the frequency is very
large, much larger than all other relevant system-frequencies, there is a
Kapitsa time-window wherein the effect of frequency dependent forcing can be
replaced by a static effective potential. Our new analysis includes the case
when the forcing, in addition to being frequency-dependent, is space-dependent
as well. The results of the Kapitsa analysis then lead to additional
contributions to the effective potential. These are applied to the numerical
calculation of the diffusion coefficient (D) for a Brownian particle moving in
a periodic potential. Presented are numerical results, which are in excellent
agreement with theoretical predictions and which indicate a significant
enhancement of D due to the space-dependent forcing terms. In addition we study
the transport property (current) of underdamped Brownian particles in a ratchet
potential.Comment: RevTex 6 pages, 5 figure
Quantum-dot thermometry
We present a method for the measurement of a temperature differential across
a single quantum dot that has transmission resonances that are separated in
energy by much more than the thermal energy. We determine numerically that the
method is accurate to within a few percent across a wide range of parameters.
The proposed method measures the temperature of the electrons that enter the
quantum dot and will be useful in experiments that aim to test theory which
predicts quantum dots are highly-efficient thermoelectrics.Comment: 3 pages, 4 Figure
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