7,318 research outputs found
Effects of Control Stick Parameters on Human Controller Response
A fixed base laboratory tracking study was conducted to determine the effects of stick displacement and stick force characteristics on human tracking performance. Three different levels of control stick force/displacement characteristics and stick electrical gain were varied to observe their influence on RMS (Root Mean Square) tracking error and RMS control activity (stick output). The results indicated that both RMS tracking error and RMS control activity were influenced by the three different levels of control stick force/displacement characteristics and stick electrical gain. The human neuromotor time constant was affected by the electrical control gain of the stick while the spring stiffness of the stick influenced the time delay characteristics of the human response behavior
Acoustoelectric current and pumping in a ballistic quantum point contact
The acoustoelectric current induced by a surface acoustic wave (SAW) in a
ballistic quantum point contact is considered using a quantum approach. We find
that the current is of the "pumping" type and is not related to drag, i.e. to
the momentum transfer from the wave to the electron gas. At gate voltages
corresponding to the plateaus of the quantized conductance the current is
small. It is peaked at the conductance step voltages. The peak current
oscillates and decays with increasing SAW wavenumber for short wavelengths.
These results contradict previous calculations, based on the classical
Boltzmann equation.Comment: 4 pages, 1 figur
The status of the quantum dissipation-fluctuation relation and Langevin equation
I examine the arguments which have been given for quantum
fluctuation-dissipation theorems. I distinguish between a weak form of the
theorem, which is true under rather general conditions, and a strong form which
requires a Langevin equation for its statement. I argue that the latter has not
been reliably derived.Comment: 9 page
Adiabatic transport in nanostructures
A confined system of non-interacting electrons, subject to the combined
effect of a time-dependent potential and different external
chemical-potentials, is considered. The current flowing through such a system
is obtained for arbitrary strengths of the modulating potential, using the
adiabatic approximation in an iterative manner. A new formula is derived for
the charge pumped through an un-biased system (all external chemical potentials
are kept at the same value); It reproduces the Brouwer formula for a
two-terminal nanostructure. The formalism presented yields the effect of the
chemical potential bias on the pumped charge on one hand, and the modification
of the Landauer formula (which gives the current in response to a constant
chemical-potential difference) brought about by the modulating potential on the
other. Corrections to the adiabatic approximation are derived and discussed.Comment: 8 pages, 2 figure
Operational reliability assessment of the GEOS A spacecraft
Decision theory application to GEOS A spacecraft operational reliability assessmen
Quantum Zeno effect and parametric resonance in mesoscopic physics
As a realization of the quantum Zeno effect, we consider electron tunneling
between two quantum dots with one of the dots coupled to a quantum point
contact detector. The coupling leads to decoherence and to the suppression of
tunneling. When the detector is driven with an ac voltage, a parametric
resonance occurs which strongly counteracts decoherence. We propose a novel
experiment with which it is possible to observe both the quantum Zeno effect
and the parametric resonance in electric transport.Comment: 4 pages, 2 figure
Theory and astrophysical consequences of a magnetized torus around a rapidly rotating black hole
(Abbrev.) We analyze the topology, lifetime, and emissions of a torus around
a black hole formed in hypernovae and black hole-neutron star coalescence. The
torus is ab initio uniformly magnetized, represented by two counter oriented
current-rings, and develops a state of suspended accretion against a "magnetic
wall" around the black hole. Magnetic stability of the torus gives rise to a
new fundamental limit EB/Ek<0.1 for the ratio of poloidal magnetic field
energy-to-kinetic energy. The lifetime of rapid spin of the black hole is
effectively defined by the timescale of dissipation of black hole-spin energy
in the horizon, and satisfies T= 40s (MH/7MSun)(R/6MH)^4(0.03MH/MT) for a black
hole of mass MH surrounded by a torus of mass MT and radius R. The torus
converts a major fraction Egw/Erot=0.1 into gravitational radiation through a
finite number of multipole mass-moments, and a smaller fraction into MeV
neutrinos and baryon-rich winds. At a source distance of 100Mpc, these
emissions over N=2e4 periods give rise to a characteristic strain amplitude
\sqrt{N}hchar=6e-21. We argue that torus winds create an open magnetic
flux-tube on the black hole, which carries a minor and standard fraction
Ej/Erot=1e-3 in baryon-poor outflows to infinity. We identify this baryon poor
output of tens of seconds with GRBs with contemporaneous and strongly
correlated emissions in gravitational radiation, conceivably at multiple
frequencies. Ultimately, this leaves a black hole binary surrounded by a
supernova remnant.Comment: To appear in ApJ (44p
Cluster virial expansion for the equation of state of partially ionized hydrogen plasma
We study the contribution of electron-atom interaction to the equation of
state for partially ionized hydrogen plasma using the cluster-virial expansion.
For the first time, we use the Beth-Uhlenbeck approach to calculate the second
virial coefficient for the electron-atom (bound cluster) pair from the
corresponding scattering phase-shifts and binding energies. Experimental
scattering cross-sections as well as phase-shifts calculated on the basis of
different pseudopotential models are used as an input for the Beth-Uhlenbeck
formula. By including Pauli blocking and screening in the phase-shift
calculation, we generalize the cluster-virial expansion in order to cover also
near solid density plasmas. We present results for the electron-atom
contribution to the virial expansion and the corresponding equation of state,
i.e. pressure, composition, and chemical potential as a function of density and
temperature. These results are compared with semi-empirical approaches to the
thermodynamics of partially ionized plasmas. Avoiding any ill-founded input
quantities, the Beth-Uhlenbeck second virial coefficient for the electron-atom
interaction represents a benchmark for other, semi-empirical approaches.Comment: 16 pages, 10 figures, and 5 tables, resubmitted to PR
Exchange interaction effects in inter-Landau level Auger scattering in a two-dimensional electron gas
We consider the influence of spin effects on the inter-Landau level
electron-electron scattering rate in a two-dimensional electron gas. Due to the
exchange spin splitting, the Landau levels are not equidistant. This leads to
the suppresion of Auger processes and a nonlinear dependence of the lifetime on
the concentration of the excited electrons even at very low excitation levels.Comment: 10 pages, 3 figure
Why is the bandwidth of sodium observed to be narrower in photoemission experiments?
The experimentally predicted narrowing in the bandwidth of sodium is
interpreted in terms of the non-local self-energy effect on quasi-particle
energies of the electron liquid. The calculated self-energy correction is a
monotonically increasing function of the wavenumber variable. The usual
analysis of photo-emission experiments assumes the final state energies on the
nearly-free-electron-like model and hence it incorrectly ascribes the non-local
self-energy correction to the final state energies to the occupied state
energies, thus leading to a seeming narrowing in the bandwidth.Comment: 9 page
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