35,291 research outputs found
Electric welding torch Patent
Development of electric weeding torch with casing on one end to form inert gas shiel
Analysis and application of digital spectral warping in analog and mixed-signal testing
Spectral warping is a digital signal processing transform which shifts the frequencies contained within a signal along the frequency axis. The Fourier transform coefficients of a warped signal correspond to frequency-domain 'samples' of the original signal which are unevenly spaced along the frequency axis. This property allows the technique to be efficiently used for DSP-based analog and mixed-signal testing. The analysis and application of spectral warping for test signal generation, response analysis, filter design, frequency response evaluation, etc. are discussed in this paper along with examples of the software and hardware implementation
Effect of surface roughness on rate-dependent slip in simple fluids
Molecular dynamics simulations are used to investigate the influence of
molecular-scale surface roughness on the slip behavior in thin liquid films.
The slip length increases almost linearly with the shear rate for atomically
smooth rigid walls and incommensurate structures of the liquid/solid interface.
The thermal fluctuations of the wall atoms lead to an effective surface
roughness, which makes the slip length weakly dependent on the shear rate. With
increasing the elastic stiffness of the wall, the surface roughness smoothes
out and the strong rate dependence is restored again. Both periodically and
randomly corrugated rigid surfaces reduce the slip length and its shear rate
dependence.Comment: 15 pages, 5 figures; submitted to J. Chem. Phy
Paraelectric and ferroelectric order in two-state dipolar fluids
Monte Carlo simulations are used to examine cooperative creation of polar
state in fluids of two-state particles with nonzero dipole in the excited
state. With lowering temperature such systems undergo a second order transition
from nonpolar to polar, paraelectric phase. The transition is accompanied by a
dielectric anomaly of polarization susceptibility increasing by three orders of
magnitude. The paraelectric phase is then followed by formation of a nematic
ferroelectric which further freezes into an fcc ferroelectric crystal by a
first order transition. A mean-field model of phase transitions is discussed.Comment: 5 pages, 4 figure
A New Waveform Consistency Test for Gravitational Wave Inspiral Searches
Searches for binary inspiral signals in data collected by interferometric
gravitational wave detectors utilize matched filtering techniques. Although
matched filtering is optimal in the case of stationary Gaussian noise, data
from real detectors often contains "glitches" and episodes of excess noise
which cause filter outputs to ring strongly. We review the standard \chi^2
statistic which is used to test whether the filter output has appropriate
contributions from several different frequency bands. We then propose a new
type of waveform consistency test which is based on the time history of the
filter output. We apply one such test to the data from the first LIGO science
run and show that it cleanly distinguishes between true inspiral waveforms and
large-amplitude false signals which managed to pass the standard \chi^2 test.Comment: 10 pages, 6 figures, submitted to Classical and Quantum Gravity for
the proceedings of the Eighth Gravitational Wave Data Analysis Workshop
(GWDAW-8
Determination of the chemical potential using energy-biased sampling
An energy-biased method to evaluate ensemble averages requiring test-particle
insertion is presented. The method is based on biasing the sampling within the
subdomains of the test-particle configurational space with energies smaller
than a given value freely assigned. These energy-wells are located via unbiased
random insertion over the whole configurational space and are sampled using the
so called Hit&Run algorithm, which uniformly samples compact regions of any
shape immersed in a space of arbitrary dimensions. Because the bias is defined
in terms of the energy landscape it can be exactly corrected to obtain the
unbiased distribution. The test-particle energy distribution is then combined
with the Bennett relation for the evaluation of the chemical potential. We
apply this protocol to a system with relatively small probability of low-energy
test-particle insertion, liquid argon at high density and low temperature, and
show that the energy-biased Bennett method is around five times more efficient
than the standard Bennett method. A similar performance gain is observed in the
reconstruction of the energy distribution.Comment: 10 pages, 4 figure
Broadband sum frequency generation via chirped quasi-phase-matching
An efficient broadband sum frequency generation (SFG) technique using the two
collinear optical parametric processes \omega 3=\omega 1+\omega 2 and \omega
4=\omega 1+\omega 3 is proposed. The technique uses chirped quasi-phase-matched
gratings, which, in the undepleted pump approximation, make SFG analogous to
adiabatic population transfer in three-state systems with crossing energies in
quantum physics. If the local modulation period %for aperiodically poled
quasi-phase-matching first makes the phase match occur for \omega 3 and then
for \omega 4 SFG processes then the energy is converted adiabatically to the
\omega 4 field. Efficient SFG of the \omega 4 field is also possible by the
opposite direction of the local modulation sweep; then transient SFG of the
\omega 3 field is strongly reduced. Most of these features remain valid in the
nonlinear regime of depleted pump
Decoherence in an exactly solvable qubit model with initial qubit-environment correlations
We study a model of dephasing (decoherence) in a two-state quantum system
(qubit) coupled to a bath of harmonic oscillators. An exact analytic solution
for the reduced dynamics of a two-state system in this model has been obtained
previously for factorizing initial states of the combined system. We show that
the model admits exact solutions for a large class of correlated initial states
which are typical in the theory of quantum measurements. We derive exact
expressions for the off-diagonal elements of the qubit density matrix, which
hold for an arbitrary strength of coupling between the qubit and the bath. The
influence of initial correlations on decoherence is considered for different
bath spectral densities. Time behavior of the qubit entropy in the decoherence
process is discussed.Comment: 10 pages, 5 figure
Electronic thermal conductivity at high temperatures: Violation of the Wiedemann-Franz law in narrow band metals
We study the electronic part of the thermal conductivity kappa of metals. We
present two methods for calculating kappa, a quantum Monte-Carlo (QMC) method
and a method where the phonons but not the electrons are treated
semiclassically (SC). We compare the two methods for a model of alkali-doped
C60, A3C60, and show that they agree well. We then mainly use the SC method,
which is simpler and easier to interpret. We perform SC calculations for Nb for
large temperatures T and find that kappa increases with T as kappa(T)=a+bT,
where a and b are constants, consistent with a saturation of the mean free
path, l, and in good agreement with experiment. In contrast, we find that for
A3C60, kappa(T) decreases with T for very large T. We discuss the reason for
this qualitatively in the limit of large T. We give a quantum-mechanical
explanation of the saturation of l for Nb and derive the Wiedemann-Franz law in
the limit of T much smaller than W, where W is the band width. In contrast, due
to the small W of A3C60, the assumption T much smaller than W can be violated.
We show that this leads to kappa(T) \sim T^{-3/2} for very large T and a strong
violation of the Wiedemann-Franz law.Comment: 8 pages, 4 figure
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