Electron spin orientation under in-plane optical excitation in GaAs quantum wells

We study the optical orientation of electron spins in GaAs/AlGaAs quantum wells for excitation in the growth direction and for in-plane excitation. Time- and polarization-resolved photoluminescence excitation measurements show, for resonant excitation of the heavy-hole conduction band transition, a negligible degree of electron spin polarization for in-plane excitation and nearly 100% for excitation in the growth direction. For resonant excitation of the light-hole conduction band transition, the excited electron spin polarization has the same (opposite) direction for in-plane excitation (in the growth direction) as for excitation into the continuum. The experimental results are well explained by an accurate multiband theory of excitonic absorption taking fully into account electron-hole Coulomb correlations and heavy-hole light-hole coupling.Comment: 10 pages, 4 figures, final versio

Climate model attractors: chaos, quasi-regularity and sensitivity to small perturbations of external forcing

International audienceIn this paper we discuss some theoretical results obtained for climate models (theorems for the existence of global attractors and inertial manifolds, estimates of attractor dimension and Lyapunov exponents, symmetry property of Lyapunov spectrum). We define the conditions for "quasi-regular behaviour" of a climate system. Under these conditions, the system behaviour is subject to the Kraichnan fluctuation-dissipation relation. This fact allows us to solve the problem of determining a system's sensitivity to small perturbations to an external forcing. The applicability of the above approach to the analysis of the climate system sensitivity is verified numerically with the example of the two-layer quasi-geostrophic atmospheric model

Controlling the spin orientation of photoexcited electrons by symmetry breaking

We study reflection of optically spin-oriented hot electrons as a means to probe the semiconductor crystal symmetry and its intimate relation with the spin-orbit coupling. The symmetry breaking by reflection manifests itself by tipping the net-spin vector of the photoexcited electrons out of the light propagation direction. The tipping angle and the pointing direction of the net-spin vector are set by the crystal-induced spin precession, momentum alignment and spin-momentum correlation of the initial photoexcited electron population. We examine non-magnetic semiconductor heterostructures and semiconductor/ferromagnet systems and show the unique signatures of these effects.Comment: 4 pages, 3 figures, resubmitte

Spin Orientation of Holes in Quantum Wells

This paper reviews the spin orientation of spin-3/2 holes in quantum wells. We discuss the Zeeman and Rashba spin splitting in hole systems that are qualitatively different from their counterparts in electron systems. We show how a systematic understanding of the unusual spin-dependent phenomena in hole systems can be gained using a multipole expansion of the spin density matrix. As an example we discuss spin precession in hole systems that can give rise to an alternating spin polarization. Finally, we discuss the qualitatively different regimes of hole spin polarization decay in clean and dirty samples.Comment: 14 pages, 8 figure

OwnKit: Ownership Inference for Java

Object ownership allows us to statically control run-time aliasing in order to provide a strong notion of object encapsulation. Unfortunately in order to use ownership, code must first be annotated with extra type information. This imposes a heavy burden on the programmer, and has contributed to the slow adoption of ownership. Ownership inference is the process of reconstructing ownership type information based on the existing ownership patterns in code. This thesis presents OwnKit—an automatic ownership inference tool for Java. OwnKit conducts inference in a modular way: by only considering a single class at the time. The modularity makes our algorithm highly scalable in both time and memory usage

Spin relaxation in low-dimensional systems

We review some of the newest findings on the spin dynamics of carriers and excitons in GaAs/GaAlAs quantum wells. In intrinsic wells, where the optical properties are dominated by excitonic effects, we show that exciton-exciton interaction produces a breaking of the spin degeneracy in two-dimensional semiconductors. In doped wells, the two spin components of an optically created two-dimensional electron gas are well described by Fermi-Dirac distributions with a common temperature but different chemical potentials. The rate of the spin depolarization of the electron gas is found to be independent of the mean electron kinetic energy but accelerated by thermal spreading of the carriers.Comment: 1 PDF file, 13 eps figures, Proceedings of the 1998 International Workshop on Nanophysics and Electronics (NPE-98)- Lecce (Italy

On spurious detection of linear response and misuse of the fluctuation–dissipation theorem in finite time series

Using a sensitive statistical test we determine whether or not one can detect the breakdown of linear response given observations of deterministic dynamical systems. A goodness-of-fit statistics is developed for a linear statistical model of the observations, based on results for central limit theorems for deterministic dynamical systems, and used to detect linear response breakdown. We apply the method to discrete maps which do not obey linear response and show that the successful detection of breakdown depends on the length of the time series, the magnitude of the perturbation and on the choice of the observable. We find that in order to reliably reject the assumption of linear response for typical observables sufficiently large data sets are needed. Even for simple systems such as the logistic map, one needs of the order of observations to reliably detect the breakdown with a confidence level of ; if less observations are available one may be falsely led to conclude that linear response theory is valid. The amount of data required is larger the smaller the applied perturbation. For judiciously chosen observables the necessary amount of data can be drastically reduced, but requires detailed a priori knowledge about the invariant measure which is typically not available for complex dynamical systems. Furthermore we explore the use of the fluctuation–dissipation theorem (FDT) in cases with limited data length or coarse-graining of observations. The FDT, if applied naively to a system without linear response, is shown to be very sensitive to the details of the sampling method, resulting in erroneous predictions of the response

The use of a titanium-containing drug for the prevention of severe degrees of radiation mucositis in patients with metal structures in the oral cavity

Introduction. Oral mucositis is one of the earliest and most frequent complications of radiation therapy or chemotherapy in patients diagnosed with oropharyngeal cancer. Because of this pathology, therapeutic interventions are most often used, thereby poor treatment is considered an etiological factor of oral mucositis. Now, this issue is being actively studied in the world, but a unified algorithm for treatment and prevention of oral mucositis has not been formed.The study objective – is to evaluate the effect of titanium glycerosolvate aquacomplex in reducing the intensity of radiation induced reactions and reducing the frequency of interruptions.Materials and methods. 52 patients diagnosed with oropharyngeal cancer were included in this study, treated with radiotherapy or chemotherapy. For prophylaxis of severe stages of oral mucositis, 32 patients underwent standard symptomatic therapy (group 1, control group); 20 patients took titanium glycerosolvate aquacomplex in accordance with symptomatic therapy (group 2).Results. In the group 1 only 61.7 % of patients completed treatment. In the group 2 80 % of patients completely underwent antitumor therapy. At the same time, they developed oral mucositis of the I–II degree. Also, in the group of the studied drug, in 100 % of cases, therapy was performed without interruptions.Conclusion. Using titanium glycerosolvate aquacomplex for the prophylaxis of severe stages of oral mucositis during radiotherapy or chemotherapy of oropharyngeal cancer is effective and safe. It is also convenient from the medical and economic side, thanks to the ability to use it on an outpatient basis