563,517 research outputs found
The ultimate efficiency of photosensitive systems
These systems have in common two important but not independent features: they can produce a storable fuel, and they are sensitive only to radiant energy with a characteristic absorption spectrum. General analyses of the conversion efficiencies were made using the operational characteristics of each particular system. An efficiency analysis of a generalized system consisting of a blackbody source, a radiant energy converter having a threshold energy and operating temperature, and a reservoir is reported. This analysis is based upon the first and second laws of thermodynamics, and leads to a determination of the limiting or ultimate efficiency for an energy conversion system having a characteristic threshold
Two-dimensional GaAs/AlGaAs superlattice structures for solar cell applications: ultimate efficiency estimation
We calculate the band structure of a two-dimensional GaAs/AlGaAs superlattice
and estimate the ultimate efficiency of solar cells using this type of
structure for solar energy conversion. The superlattice under consideration
consists of gallium arsenide rods forming a square lattice and embedded in
aluminium gallium arsenide. The ultimate efficiency is determined versus
structural parameters including the filling fraction, the superlattice
constant, the rod geometry and the concentration of Al in the matrix material.
The calculated efficiency of the superlattice proves to exceed the efficiency
of each component material in the monolithic state in a wide range of parameter
values.Comment: 11 pages, 7 figure
Fundamental efficiency bound for coherent energy transfer in nanophotonics
We derive a unified quantum theory of coherent and incoherent energy transfer
between two atoms (donor and acceptor) valid in arbitrary Markovian
nanophotonic environments. Our theory predicts a fundamental bound for energy transfer efficiency arising
from the spontaneous emission rates and of the donor
and acceptor. We propose the control of the acceptor spontaneous emission rate
as a new design principle for enhancing energy transfer efficiency. We predict
an experiment using mirrors to enhance the efficiency bound by exploiting the
dipole orientations of the donor and acceptor. Of fundamental interest, we show
that while quantum coherence implies the ultimate efficiency bound has been
reached, reaching the ultimate efficiency does not require quantum coherence.
Our work paves the way towards nanophotonic analogues of efficiency enhancing
environments known in quantum biological systems.Comment: 5 pages, 4 figure
Electron bombardment improves vacuum chamber efficiency
Bombardment of vacuum chamber walls by an electron gun within the chamber achieves greater efficiency with less cost. The ultimate vacuum reached using the gun is greater than the system design level
Optimum Asymptotic Multiuser Efficiency of Pseudo-Orthogonal Randomly Spread CDMA
A -user pseudo-orthogonal (PO) randomly spread CDMA system, equivalent to
transmission over a subset of single-user Gaussian channels, is
introduced. The high signal-to-noise ratio performance of the PO-CDMA is
analyzed by rigorously deriving its asymptotic multiuser efficiency (AME) in
the large system limit. Interestingly, the -optimized PO-CDMA transceiver
scheme yields an AME which is practically equal to 1 for system loads smaller
than 0.1 and lower bounded by 1/4 for increasing loads. As opposed to the
vanishing efficiency of linear multiuser detectors, the derived efficiency is
comparable to the ultimate CDMA efficiency achieved for the intractable optimal
multiuser detector.Comment: WIC 27th Symposium on Information Theory in the Benelux, 200
Detector Efficiency Limits on Quantum Improvement
Although the National Institute of Standards and Technology has measured the
intrinsic quantum efficiency of Si and InGaAs APD materials to be above 98 % by
building an efficient compound detector, commercially available devices have
efficiencies ranging between 15 % and 75 %. This means bandwidth, dark current,
cost, and other factors are more important than quantum efficiency for existing
applications. This paper systematically examines the generic detection process,
lays out the considerations needed for designing detectors for non-classical
applications, and identifies the ultimate physical limits on quantum
efficiency.Comment: LaTeX, 7 pages, 3 figure
Random distributed feedback fiber laser of ultimate efficiency
We demonstrate a random fiber laser of ultimate efficiency. More than 2 Watts are generated from 0.5W of pump excess over the generation threshold. At higher power, an optical efficiency corresponds to the quantum limit
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