Nonexponential Relaxations in a Two-Dimensional Electron System in Silicon

The relaxations of conductivity have been studied in a strongly disordered two-dimensional (2D) electron system in Si after excitation far from equilibrium by a rapid change of carrier density n_s at low temperatures T. The dramatic and precise dependence of the relaxations on n_s and T strongly suggests (a) the transition to a glassy phase as T->0, and (b) the Coulomb interactions between 2D electrons play a dominant role in the observed out-of-equilibrium dynamics.Comment: 5 pages, 5 figure

The glass transition and the Coulomb gap in electron glasses

We establish the connection between the presence of a glass phase and the appearance of a Coulomb gap in disordered materials with strongly interacting electrons. Treating multiparticle correlations in a systematic way, we show that in the case of strong disorder a continuous glass transition takes place whose Landau expansion is identical to that of the Sherrington-Kirkpatrick spin glass. We show that the marginal stability of the glass phase controls the physics of these systems: it results in slow dynamics and leads to the formation of a Coulomb gap

Electroreflectance spectroscopy in self-assembled quantum dots: lens symmetry

Modulated electroreflectance spectroscopy $\Delta R/R$ of semiconductor self-assembled quantum dots is investigated. The structure is modeled as dots with lens shape geometry and circular cross section. A microscopic description of the electroreflectance spectrum and optical response in terms of an external electric field (${\bf F}$) and lens geometry have been considered. The field and lens symmetry dependence of all experimental parameters involved in the $\Delta R/R$ spectrum have been considered. Using the effective mass formalism the energies and the electronic states as a function of ${\bf F}$ and dot parameters are calculated. Also, in the framework of the strongly confined regime general expressions for the excitonic binding energies are reported. Optical selection rules are derived in the cases of the light wave vector perpendicular and parallel to $$. Detailed calculation of the Seraphin coefficients and electroreflectance spectrum are performed for the InAs and CdSe nanostructures. Calculations show good agreement with measurements recently performed on CdSe/ZnSe when statistical distribution on size is considered, explaining the main observed characteristic in the electroreflectance spectra

Analysis of nonperturbative fluctuations in a triple-well potential

We consider the quantum tunneling phenomenon in a well-behaved triple-well potential. As required by the semiclassical approximation we take into account the quadratic fluctuations over the instanton which represents as usual the localised finite-action solution of the euclidean equation of motion. The determinants of the quadratic differential operators at issue are evaluated by means of the Gelfang-Yaglom method. In doing so the explicit computation of the conventional ratio of determinants takes as reference the harmonic oscillator whose frequency is the average of the individual frequencies derived from the non-equivalent minima of the potential. Eventually the physical effects of the multi-instanton configurations are included in this approach. As a matter of fact we obtain information about the energies of the ground-state and the two first excited levels of the discrete spectrum at issue.Comment: 12 pages, RevTe

The sources of the deep water of the Eastern Mediterranean Sea

The deep water in the two basins of the eastern Mediterranean Sea, the Levant and the Ionian Sea, is identical in temperature and salinity though differing slightly in oxygen content. Contrary to Nielsen\u27s thesis, none of this water is formed in the southern Aegean Sea...

Notes on determining the depths of sampling in serial oceanographic observations

In order to interpolate between thermometrically determined depths of sampling in serial oceanographic observations it ha.s been customary to plot a curve of depth to wire length ratio against wire length. It is shown that a simpler and probably more accurate method consists of plotting wire length minus depth against wire length. In this method the surface wire angle is converted into a line of tangency to the curve which always terminates at the zero point of the graph. Furthermore, the limiting slope of this curve is more readily defined and utilized

The use of electrical conductivity measurements for chlorinity determination

Limitations in our knowledge of the electrical conductivity of sea water are discussed. An empirical equation is presented which gives chlorinity aa a function of specific conductance and temperature at atmospheric pressure

Units for specific volume of sea water

Considerable confusion has developed in oceanographic literature concerning the appropriate units to be used in reporting specific volume and its ancillary parameters, specific-volume anomaly and thermosteric anomaly (specific-volume anomaly at in situ temperature and salinity and atmospheric pressure). The problem revolves around the question, should specific volume and its anomalies be given in terms of liters or cubic centimeters as the unit of volume...

Static stability parameters in oceanography

The use of static vertical stability criteria in oceanography is discussed and two basic types of such stability parameters are derived. It is shown how these can be determined by using sound velocity as one of the variables. Computation can be simplified by means of a graph

ASR Systems in Noisy Environment: Analysis and Solutions for Increasing Noise Robustness

This paper deals with the analysis of Automatic Speech Recognition (ASR) suitable for usage within noisy environment and suggests optimum configuration under various noisy conditions. The behavior of standard parameterization techniques was analyzed from the viewpoint of robustness against background noise. It was done for Melfrequency cepstral coefficients (MFCC), Perceptual linear predictive (PLP) coefficients, and their modified forms combining main blocks of PLP and MFCC. The second part is devoted to the analysis and contribution of modified techniques containing frequency-domain noise suppression and voice activity detection. The above-mentioned techniques were tested with signals in real noisy environment within Czech digit recognition task and AURORA databases. Finally, the contribution of special VAD selective training and MLLR adaptation of acoustic models were studied for various signal features