87 research outputs found
The nonlinear effects in 2DEG conductivity investigation by an acoustic method
The parameters of two-dimensional electron gas (2DEG) in a GaAs/AlGaAs
heterostructure were determined by an acoustical (contactless) method in the
delocalized electrons region (2.5T). Nonlinear effects in Surface
Acoustic Wave (SAW) absorption by 2DEG are determined by the electron heating
in the electric field of SAW, which may be described in terms of electron
temperature . The energy relaxation time is determined
by the scattering at piezoelectric potential of acoustic phonons with strong
screening. At different SAW frequencies the heating depends on the relationship
between and 1 and is determined either by the
instantaneously changing wave field (), or by the
average wave power ().Comment: RevTeX, 5 pages, 3 PS-figures, submitted to Physica Status
Sol.(Technical corrections in PS-figs
Squeezing as the source of inefficiency in the quantum Otto cycle
The availability of controllable macroscopic devices, which maintain quantum
coherence over relatively long time intervals, for the first time allows an
experimental realization of many effects previously considered only as
Gedankenexperiments, such as the operation of quantum heat engines. The
theoretical efficiency \eta of quantum heat engines is restricted by the same
Carnot boundary \eta_C as for the classical ones: any deviations from
quasistatic evolution suppressing \eta below \eta_C. Here we investigate an
implementation of an analog of the Otto cycle in a tunable quantum coherent
circuit and show that the specific source of inefficiency is the quantum
squeezing of the thermal state due to the finite speed of compression/expansion
of the system.Comment: 17 pages, 5 figure
Two-qubit parametric amplifier: large amplification of weak signals
Using numerical simulations, we show that two coupled qubits can amplify a
weak signal about hundredfold. This can be achieved if the two qubits are
biased simultaneously by this weak signal and a strong pump signal, both of
which having frequencies close to the inter-level transitions in the system.
The weak signal strongly affects the spectrum generated by the strong pumping
drive by producing and controlling mixed harmonics with amplitudes of the order
of the main harmonic of the strong drive. We show that the amplification is
robust with respect to noise, with an intensity of the order of the weak
signal. When deviating from the optimal regime (corresponding to strong qubit
coupling and a weak-signal frequency equal to the inter-level transition
frequency) the proposed amplifier becomes less efficient, but it can still
considerably enhance a weak signal (by several tens). We therefore propose to
use coupled qubits as a combined parametric amplifier and frequency shifter.Comment: 6 figure
Estimates for parameters and characteristics of the confining SU(3)-gluonic field in an -meson
The confinement mechanism proposed earlier by the author is applied to
estimate the possible parameters of the confining SU(3)-gluonic field in an
-meson. For this aim the electric form factor of an
-meson is nonperturbatively computed in an explicit analytic form.
The estimates obtained are also consistent with the width of the
electromagnetic decay . The corresponding estimates of
the gluon concentrations, electric and magnetic colour field strengths are also
adduced for the mentioned field at the scales of the meson under consideration.Comment: 20 pages, LaTe
Terahertz Josephson plasma waves in layered superconductors: spectrum, generation, nonlinear, and quantum phenomena
The recent growing interest in terahertz (THz) and sub-THz science and
technology is due to its many important applications in physics, astronomy,
chemistry, biology, and medicine. We review the problem of linear and
non-linear THz and sub-THz Josephson plasma waves in layered superconductors
and their excitations produced by moving Josephson vortices. We start by
discussing the coupled sine-Gordon equations for the gauge-invariant phase
difference of the order parameter in the junctions, taking into account the
effect of breaking the charge neutrality, and deriving the spectrum of
Josephson plasma waves. We also review surface and waveguide Josephson plasma
waves. We review the propagation of weakly nonlinear Josephson plasma waves
below the plasma frequency, which is very unusual for plasma-like excitations.
In close analogy to nonlinear optics, these waves exhibit numerous remarkable
features, including a self-focusing effect, and the pumping of weaker waves by
a stronger one. We also present quantum effects in layered superconductors,
specifically, the problem of quantum tunnelling of fluxons through stacks of
Josephson junctions. We discuss the Cherenkov and transition radiations of the
Josephson plasma waves produced by moving Josephson vortices. We also discuss
the problem of coherent radiation (superradiance) of the THz waves by exciting
uniform Josephson oscillations. The effects reviewed here could be potentially
useful for sub-THz and THz emitters, filters, and detectors
High-Sulfurous Argentinian Asphaltites and Their Thermal Liquefaction Products
The results of profound chemical studies of asphaltites from the Rafaelita and Toribia fields (Mendosa and Neuquén provinces, Argentina) and prospects for their processing are presented. The composition and structural features of maltenic, asphaltene-carbenic and carboid components of these natural coal-like substances were investigated. Laboratory experiments on thermal liquefaction of asphaltites were performed, including: 1) destructive distillation (pyrolysis) at temperatures gradually rising up to 600°C; 2) thermal destruction under conditions of programmed temperature increase from 25 up to 350 or 450°C with a rate of 5°C/min and with simultaneous dilution of reaction products by straight-run diesel petroleum distillate; 3) thermal treatment of the studied sample under stationary conditions (at 350°C for one hour in water, tetraline or n-decane); and 4) thermal destruction of asphaltite samples under flow conditions (continuous ablution of reactor with water or decane, temperature rising from 25 up to 500°C, with periodical sampling at different temperature levels). The largest yields of liquid fuels were obtained when the thermal destruction process was performed in hydrocarbon medium at temperatures not lower than 400-450°C, with continuous removal of products from the reaction zone. The yield of desirable hydrocarbon products reached 25 wt.% of asphaltite organic mass, when decane served as reaction medium, and could be increased up to 70 wt.% by substituting this solvent with real petroleum (diesel) distillate
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