1,310 research outputs found
Noise in Electron Devices
Contains research objectives.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 36-039-AMC-03200(E
Solvable glassy system: static versus dynamical transition
A directed polymer is considered on a flat substrate with randomly located
parallel ridges. It prefers to lie inside wide regions between the ridges. When
the transversel width is exponential in the
longitudinal length , there can be a large number of
available wide states. This ``complexity'' causes a phase transition from a
high temperature phase where the polymer lies in the widest lane, to a glassy
low temperature phase where it lies in one of many narrower lanes. Starting
from a uniform initial distribution of independent polymers, equilibration up
to some exponential time scale induces a sharp dynamical transition. When the
temperature is slowly increased with time, this occurs at a tunable
temperature. There is an asymmetry between cooling and heating. The structure
of phase space in the low temperature non-equilibrium glassy phase is of a
one-level tree.Comment: 4 pages revte
Electromagnetics from a quasistatic perspective
Quasistatics is introduced so that it fits smoothly into the standard
textbook presentation of electrodynamics. The usual path from statics to
general electrodynamics is rather short and surprisingly simple. A closer look
reveals however that it is not without confusing issues as has been illustrated
by many contributions to this Journal. Quasistatic theory is conceptually
useful by providing an intermediate level in between statics and the full set
of Maxwell's equations. Quasistatics is easier than general electrodynamics and
in some ways more similar to statics. It is however, in terms of interesting
physics and important applications, far richer than statics. Quasistatics is
much used in electromagnetic modeling, an activity that today is possible on a
PC and which also has great pedagogical potential. The use of electromagnetic
simulations in teaching gives additional support for the importance of
quasistatics. This activity may also motivate some change of focus in the
presentation of basic electrodynamics
Capacity of nonlinear bosonic systems
We analyze the role of nonlinear Hamiltonians in bosonic channels.
We show that the information capacity as a function of the channel energy is
increased with respect to the corresponding linear case, although only when the
energy used for driving the nonlinearity is not considered as part of the
energetic cost and when dispersive effects are negligible.Comment: 6 pages, 3 figure
Consistently Simulating a Wide Range of Atmospheric Scenarios for K2-18b with a Flexible Radiative Transfer Module
The atmospheres of small, potentially rocky exoplanets are expected to cover
a diverse range in composition and mass. Studying such objects therefore
requires flexible and wide-ranging modeling capabilities. We present in this
work the essential development steps that lead to our flexible radiative
transfer module, REDFOX, and validate REDFOX for the Solar system planets
Earth, Venus and Mars, as well as for steam atmospheres. REDFOX is a
k-distribution model using the correlated-k approach with random overlap method
for the calculation of opacities used in the -two-stream approximation
for radiative transfer. Opacity contributions from Rayleigh scattering, UV /
visible cross sections and continua can be added selectively. With the improved
capabilities of our new model, we calculate various atmospheric scenarios for
K2-18b, a super-Earth / sub-Neptune with 8 M orbiting in the
temperate zone around an M-star, with recently observed HO spectral
features in the infrared. We model Earth-like, Venus-like, as well as H-He
primary atmospheres of different Solar metallicity and show resulting climates
and spectral characteristics, compared to observed data. Our results suggest
that K2-18b has an H-He atmosphere with limited amounts of HO and
CH. Results do not support the possibility of K2-18b having a water
reservoir directly exposed to the atmosphere, which would reduce atmospheric
scale heights, hence too the amplitudes of spectral features inconsistent with
the observations. We also performed tests for H-He atmospheres up to 50
times Solar metallicity, all compatible with the observations.Comment: 28 pages, 13 figures, accepted for publication in Ap
Noise in Electron Devices
Contains research objectives.U. S. ArmyLincoln Laboratory, Purchase Order DDL B-00306U. S. Air Force under Air Force Contract AF19(604)-5200U. S. Nav
Scalar and vector modulation instabilities induced by vacuum fluctuations in fibers: numerical study
We study scalar and vector modulation instabilities induced by the vacuum
fluctuations in birefringent optical fibers. To this end, stochastic coupled
nonlinear Schrodinger equations are derived. The stochastic model is equivalent
to the quantum field operators equations and allow for dispersion,
nonlinearity, and arbitrary level of birefringence. Numerical integration of
the stochastic equations is compared to analytical formulas in the case of
scalar modulation instability and non depleted pump approximation. The effect
of classical noise and its competition with vacuum fluctuations for inducing
modulation instability is also addressed.Comment: 33 pages, 5 figure
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