Electron-phonon scattering at the intersection of two Landau levels

We predict a double-resonant feature in the magnetic field dependence of the phonon-mediated longitudinal conductivity $\sigma_{xx}$ of a two-subband quasi-two-dimensional electron system in a quantizing magnetic field. The two sharp peaks in $\sigma_{xx}$ appear when the energy separation between two Landau levels belonging to different size-quantization subbands is favorable for acoustic-phonon transitions. One-phonon and two-phonon mechanisms of electron conductivity are calculated and mutually compared. The phonon-mediated interaction between the intersecting Landau levels is considered and no avoided crossing is found at thermal equilibrium.Comment: 13 pages, 8 figure

Microwave Photoconductivity in Two-Dimensional Electron Systems due to Photon-Assisted Interaction of Electrons with Leaky Interface Phonons

We calculate the contribution of the photon-assisted interaction of electrons with leaky interface phonons to the dissipative dc photoconductivity of a two-dimensional electron system in a magnetic field. The calculated photoconductivity as a function of the frequency of microwave radiation and the magnetic field exhibits pronounced oscillations. The obtained oscillation structure is different from that in the case of photon-assisted interaction with impurities. We demonstrate that at a sufficiently strong microwave radiation in the certain ranges of its frequency (or in certain ranges of the magnetic field) this mechanism can result in the absolute negative conductivity.Comment: 3 pages, 1 figur

Electric-Field Breakdown of Absolute Negative Conductivity and Supersonic Streams in Two-Dimensional Electron Systems with Zero Resistance/Conductance States

We calculate the current-voltage characteristic of a two-dimensional electron system (2DES) subjected to a magnetic field at strong electric fields. The interaction of electrons with piezoelectric acoustic phonons is considered as a major scattering mechanism governing the current-voltage characteristic. It is shown that at a sufficiently strong electric field corresponding to the Hall drift velocity exceeding the velocity of sound, the dissipative current exhibits an overshoot. The overshoot of the dissipative current can result in a breakdown of the absolute negative conductivity caused by microwave irradiation and, therefore, substantially effect the formation of the domain structures with the zero-resistance and zero-conductance states and supersonic electron streams.Comment: 5 pages, 4 figure

Absolute Negative Conductivity in Two-Dimensional Electron Systems Associated with Acoustic Scattering Stimulated by Microwave Radiation

We discuss the feasibility of absolute negative conductivity (ANC) in two-dimensional electron systems (2DES) stimulated by microwave radiation in transverse magnetic field. The mechanism of ANC under consideration is associated with the electron scattering on acoustic piezoelectric phonons accompanied by the absorption of microwave photons. It is demonstrated that the dissipative components of the 2DES dc conductivity can be negative ($\sigma_{xx} = \sigma_{yy} < 0$) when the microwave frequency $\Omega$ is somewhat higher than the electron cyclotron frequency $\Omega_c$ or its harmonics. The concept of ANC associated with such a scattering mechanism can be invoked to explain the nature of the occurrence of zero-resistance ``dissipationless'' states observed in recent experiments.Comment: 7 pager, 2 figure

Circular Polarization Induced by Scintillation in a Magnetized Medium

A new theory is presented for the development of circular polarization as radio waves propagate through the turbulent, birefringent interstellar medium. The fourth order moments of the wavefield are calculated and it is shown that unpolarized incident radiation develops a nonzero variance in circular polarization. A magnetized turbulent medium causes the Stokes parameters to scintillate in a non-identical manner. A specific model for this effect is developed for the case of density fluctuations in a uniform magnetic field.Comment: 16 pages, 1 figure, Phys. Rev. E, accepte

Stochastic Faraday Rotation

Different ray paths through a turbulent plasma can produce stochastic Faraday rotation leading to depolarization of any linearly polarized component. Simple theory predicts that the average values of the Stokes parameters decay according to , $\propto\exp(-\delta_l)$, with $\delta_l\propto\lambda^4$. It is pointed out that a definitive test for such depolarization is provided by the fact that remains constant while $^2+^2$ decreases $\propto\exp(-2\delta_l)$. The averages to which this effect, called polarization covariance, should apply are discussed; it should apply to spatial averages over a polarization map or temporal averages over a data set, but not to beamwidth and bandwidth averages that are intrinsic to the observation process. Observations of depolarization would provide statistical information on fluctuations in the turbulent plasma along the line of sight, specifically, the variance of the rotation measure. Other effects that can also cause depolarization are discussed.Comment: 15 pages, Accepted for publication in Ap

Reduction of Plasma Gelsolin Levels Correlates with Development of Multiple Organ Dysfunction Syndrome and Fatal Outcome in Burn Patients

BACKGROUND: Depletion of the circulating actin-binding protein, plasma gelsolin (pGSN) has been described in critically ill surgical patients. We hypothesized that the extent of pGSN reduction might correlate with different outcome of burn patients. The study was performed to evaluate the prognostic implications of pGSN levels on the development of multiple organ dysfunction syndrome (MODS) and fatal outcome in a group of severely burn patients. METHODS AND FINDINGS: 95 patients were included, and they were divided into three groups with different burn area: group I (n = 33), group II (n = 32) and group III (n = 30). According to whether there was development of MODS or not, patients were divided into MODS group (n = 28) and none-MODS group (n = 67); then the patients with MODS were further divided into non-survivor group (n = 17) and survivor group (n = 11). The peripheral blood samples were collected on postburn days (PBD) 1, 3, 7, 14, and 21. The levels of pGSN were determined and T cells were procured from the blood. The contents of cytokines (IL-2, IL-4 and IFN-γ) released by T cells were also measured. The related factors of prognosis were analyzed by using multivariate logistic regression analysis. The results showed that pGSN concentrations, as well as the levels of IL-2 and IFN-γ, decreased markedly on PBD 1-21, whereas, the levels of IL-4 increased markedly in all burn groups as compared with normal controls (P<0.05 or P<0.01), and there were obviously differences between group I and group III (P<0.05 or P<0.01). The similar results were found in MODS patients and the non-survivor group as compared with those without MODS and the survival group on days 3-21 postburn (P<0.05 or P<0.01). Moreover, as the pGSN levels decreased, the incidence of septic complication as well as MODS remarkably increased. CONCLUSIONS: pGSN levels appear to be an early prognostic marker in patients suffering from major burns