233 research outputs found
Phonon-drag effects on thermoelectric power
We carry out a calculation of the phonon-drag contribution to the
thermoelectric power of bulk semiconductors and quantum well structures for the
first time using the balance equation transport theory extended to the weakly
nonuniform systems. Introducing wavevector and phonon-mode dependent relaxation
times due to phonon-phonon interactions, the formula obtained can be used not
only at low temperatures where the phonon mean free path is determined by
boundary scattering, but also at high temperatures. In the linear transport
limit, is equivalent to the result obtained from the Boltzmann equation
with a relaxation time approximation. The theory is applied to experiments and
agreement is found between the theoretical predictions and experimental
results. The role of hot-electron effects in is discussed. The importance
of the contribution of to thermoelectric power in the hot-electron
transport condition is emphasized.Comment: 8 pages, REVTEX 3.0, 7 figures avilable upon reques
Self-induced and induced transparencies of two-dimensional and three- dimensional superlattices
The phenomenon of transparency in two-dimensional and three-dimensional
superlattices is analyzed on the basis of the Boltzmann equation with a
collision term encompassing three distinct scattering mechanisms (elastic,
inelastic and electron-electron) in terms of three corresponding distinct
relaxation times. On this basis, we show that electron heating in the plane
perpendicular to the current direction drastically changes the conditions for
the occurrence of self-induced transparency in the superlattice. In particular,
it leads to an additional modulation of the current amplitudes excited by an
applied biharmonic electric field with harmonic components polarized in
orthogonal directions. Furthermore, we show that self-induced transparency and
dynamic localization are different phenomena with different physical origins,
displaced in time from each other, and, in general, they arise at different
electric fields.Comment: to appear in Physical Review
Oscillatory nonlinear differential magnetoresistance of highly mobile 2D electrons in high Landau levels
We examine the current-induced magnetoresistance oscillations in
high-mobility two-dimensional electron systems using the balance-equation
scheme for nonlinear magnetotransort. The reported analytical expressions for
differential magnetoresistivity at high filling factors in the overlapping
Landau-level regime, which show good agreement with the experimental
observation and the numerical calculation, may be helpful in extracting
physical information from experiments.Comment: 4 pages, 2 figure
Thermoelectric power of nondegenerate Kane semiconductors under the conditions of mutual electron-phonon drag in a high electric field
The thermoelectric power of nondegenerate Kane semiconductors with due regard
for the electron and phonon heating, and their thermal and mutual drags is
investigated. The electron spectrum is taken in the Kane two-band form. It is
shown that the nonparabolicity of electron spectrum significantly influences
the magnitude of the thermoelectric power and leads to a change of its sign and
dependence on the heating electric field. The field dependence of the
thermoelectric power is determined analytically under various drag conditions.Comment: 25 pages, RevTex formatted, 3 table
Generalized drift-diffusion model for miniband superlattices
A drift-diffusion model of miniband transport in strongly coupled
superlattices is derived from the single-miniband Boltzmann-Poisson transport
equation with a BGK (Bhatnagar-Gross-Krook) collision term. We use a consistent
Chapman-Enskog method to analyze the hyperbolic limit, at which collision and
electric field terms dominate the other terms in the Boltzmann equation. The
reduced equation is of the drift-diffusion type, but it includes additional
terms, and diffusion and drift do not obey the Einstein relation except in the
limit of high temperatures.Comment: 4 pages, 3 figures, double-column revtex. To appear as RC in PR
Ac-cotunneling through an interacting quantum dot under a magnetic field
We analyze inelastic cotunneling through an interacting quantum dot subject
to an ambient magnetic field in the weak tunneling regime under a non-adiabatic
time-dependent bias-voltage. Our results clearly exhibit photon-assisted
satellites and an overall suppression of differential conductance with
increasing driving amplitude, which is consistent with experiments. We also
predict a zero-anomaly in differential conductance under an appropriate driving
frequency.Comment: Phys. Lett. A (in press
Elementary operations for quantum logic with a single trapped two-level cold ion beyond Lamb-Dicke limit
A simple alternative scheme for implementing quantum gates with a single
trapped cold two-level ion beyond the Lamb-Dicke (LD) limit is proposed. Basing
on the quantum dynamics for the laser-ion interaction described by a
generalized Jaynes-Cummings model, one can introduce two kinds of elementary
quantum operations i.e., the simple rotation on the bare atomic state,
generated by applying a resonant pulse, and the joint operation on the internal
and external degrees of the ion, performed by using an off-resonant pulse.
Several typical quantum gates, including Hadamard gate, controlled-Z and
controlled-NOT gates , can thus be implemented exactly by using these
elementary operations. The experimental parameters including the LD parameter
and the durations of the applied laser pulses, for these implementation are
derived analytically and numerically. Neither the LD approximation for the
laser-ion interaction nor the auxiliary atomic level is needed in the present
scheme.Comment: 5 pages, no figure, to appear in Opt. Com
Frictional drag between non-equilibrium charged gases
The frictional drag force between separated but coupled two-dimensional
electron gases of different temperatures is studied using the non-equilibrium
Green function method based on the separation of center-of-mass and relative
dynamics of electrons. As the mechanisms of producing the frictional force we
include the direct Coulomb interaction, the interaction mediated via virtual
and real TA and LA phonons, optic phonons, plasmons, and TA and LA
phonon-electron collective modes. We found that, when the distance between the
two electron gases is large, and at intermediate temperature where plasmons and
collective modes play the most important role in the frictional drag, the
possibility of having a temperature difference between two subsystems modifies
greatly the transresistivity.Comment: 8figure
Hot air drying characteristics and nutrients of apricot armeniaca vulgaris lam pretreated with Radio Frequency(RF)
[EN] Apricot pretreated with RF and then dried with convective hot air at 65℃, 3.0m/s in this research. RF pretreatment time of 20, 30, 40 and 50min were chosen. Results showed that, there is only falling rate period during apricot hot air drying, and the drying rate of apricot is improved significantly; Herdenson and Pabis model is suitable for apricot hot air drying; retentions of flavonoids, polyphenols and Vc in dried apricot were higher than those of fresh apricot; when RF treating time was chosen 30mins, nutrients retentions of Vc, flavonoid and polyphenols were 0.9543mg/100g, 5.4089mg/100g and 7.3382mg/100g, separately.The work was financially supported by the Fundamental Research Funds for the Central Universities of China (NO. GK201503072 and GK201601007).Peng, M.; Liu, J.; Lei, Y.; Yang, X.; Wu, Z.; Huang, X. (2018). Hot air drying characteristics and nutrients of apricot armeniaca vulgaris lam pretreated with Radio Frequency(RF). En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 1583-1590. https://doi.org/10.4995/IDS2018.2018.7524OCS1583159
Radiation induced oscillatory Hall effect in high mobility GaAs/AlGaAs devices
We examine the radiation induced modification of the Hall effect in high
mobility GaAs/AlGaAs devices that exhibit vanishing resistance under microwave
excitation. The modification in the Hall effect upon irradiation is
characterized by (a) a small reduction in the slope of the Hall resistance
curve with respect to the dark value, (b) a periodic reduction in the magnitude
of the Hall resistance, , that correlates with an increase in the
diagonal resistance, , and (c) a Hall resistance correction that
disappears as the diagonal resistance vanishes.Comment: 4 pages text, 4 color figure
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