16,108 research outputs found
Optical phonon scattering and theory of magneto-polarons in a quantum cascade laser in a strong magnetic field
We report a theoretical study of the carrier relaxation in a quantum cascade
laser (QCL) subjected to a strong magnetic field. Both the alloy (GaInAs)
disorder effects and the Frohlich interaction are taken into account when the
electron energy differences are tuned to the longitudinal optical (LO) phonon
energy. In the weak electron-phonon coupling regime, a Fermi's golden rule
computation of LO phonon scattering rates shows a very fast non-radiative
relaxation channel for the alloy broadened Landau levels (LL's). In the strong
electron-phonon coupling regime, we use a magneto-polaron formalism and compute
the electron survival probabilities in the upper LL's with including increasing
numbers of LO phonon modes for a large number of alloy disorder configurations.
Our results predict a nonexponential decay of the upper level population once
electrons are injected in this state.Comment: 10 pages, 23 figure
Bistability of an In Vitro Synthetic Autoregulatory Switch
The construction of synthetic biochemical circuits is an essential step for developing quantitative understanding
of information processing in natural organisms. Here, we report construction and analysis of an in vitro circuit with
positive autoregulation that consists of just four synthetic DNA strands and three enzymes, bacteriophage T7 RNA
polymerase, Escherichia coli ribonuclease (RNase) H, and RNase R. The modularity of the DNA switch template allowed
a rational design of a synthetic DNA switch regulated by its RNA output acting as a transcription activator. We verified
that the thermodynamic and kinetic constraints dictated by the sequence design criteria were enough to experimentally
achieve the intended dynamics: a transcription activator configured to regulate its own production. Although only
RNase H is necessary to achieve bistability of switch states, RNase R is necessary to maintain stable RNA signal levels and
to control incomplete degradation products. A simple mathematical model was used to fit ensemble parameters for the
training set of experimental results and was then directly applied to predict time-courses of switch dynamics and sensitivity
to parameter variations with reasonable agreement. The positive autoregulation switches can be used to provide constant
input signals and store outputs of biochemical networks and are potentially useful for chemical control applications
Hamming Compressed Sensing
Compressed sensing (CS) and 1-bit CS cannot directly recover quantized
signals and require time consuming recovery. In this paper, we introduce
\textit{Hamming compressed sensing} (HCS) that directly recovers a k-bit
quantized signal of dimensional from its 1-bit measurements via invoking
times of Kullback-Leibler divergence based nearest neighbor search.
Compared with CS and 1-bit CS, HCS allows the signal to be dense, takes
considerably less (linear) recovery time and requires substantially less
measurements (). Moreover, HCS recovery can accelerate the
subsequent 1-bit CS dequantizer. We study a quantized recovery error bound of
HCS for general signals and "HCS+dequantizer" recovery error bound for sparse
signals. Extensive numerical simulations verify the appealing accuracy,
robustness, efficiency and consistency of HCS.Comment: 33 pages, 8 figure
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