Negative hopping magnetoresistance of two-dimensional electron gas in a smooth random potential

We show that the tunnel coupling between semiclassical states localized in different minima of a smooth random potential increases when magnetic field is applied. This increase originates from the difference in gauge factors which electron wave functions belonging to different electron ``lakes'' acquire in the presence of the field. We illustrate the increase of coupling by a model calculation of tunneling through a saddle point separating two adjacent lakes. In the common case, when the barrier between two lakes is much narrower than their size, the characteristic magnetic field is determined by the area of the lakes, and thus may be quite small. The effect of the field on coupling constants leads to a negative magnetoresistance in low-temperature conduction.Comment: 9 pages RevTe

Adaptive Precision Floating Point LLL

Adaptive precision floating point LLL The LLL algorithm is one of the most studied lattice basis reduction algorithms in the literature. Among all of its variants, the floating point version, also known as L2, is the most popular one, due to its efficiency and its practicality. In its classic setting, the floating point precision is a fixed value, determined by the dimension of the input basis at the initiation of the algorithm. We observe that a fixed precision overkills the problem, since one does not require a huge precision to handle the process at the beginning of the reduction. In this paper, we propose an adaptive way to handle the precision, where the precision is adaptive during the procedure. Although this optimization does not change the worst-case complexity, it reduces the average-case complexity by a constant factor. In practice, we observe an average 20 % acceleration in our implementation

Allyl Isothiocyanate that Induces GST and UGT Expression Confers Oxidative Stress Resistance on C. elegans, as Demonstrated by Nematode Biosensor

Electrophilic xenobiotics and endogenous products from oxidative stresses induce the glutathione S-transferases (GSTs), which form a large family within the phase II enzymes over both animal and plant kingdoms. The GSTs thus induced in turn detoxify these external as well as internal stresses. Because these stresses are often linked to ageing and damage to health, the induction of phase II enzymes without causing adverse effects would be beneficial in slowing down ageing and keeping healthy conditions. for use as a nematode biosensor. With the nematode biosensor, we found that AITC induced GST expression and conferred tolerance on the nematode against various oxidative stresses. We also present evidence that the transcription factor SKN-1 is involved in regulating the GST expression induced by AITC.We show the applicability of the nematode biosensor for discovering and evaluating functional food substances and chemicals that would provide anti-ageing or healthful benefits

Luminescence spectra and kinetics of disordered solid solutions

We have studied both theoretically and experimentally the luminescence spectra and kinetics of crystalline, disordered solid solutions after pulsed excitation. First, we present the model calculations of the steady-state luminescence band shape caused by recombination of excitons localized in the wells of random potential induced by disorder. Classification of optically active tail states of the main exciton band into two groups is proposed. The majority of the states responsible for the optical absorption corresponds to the group of extended states belonging to the percolation cluster, whereas only a relatively small group of “radiative” states forms the steady-state luminescence band. The continuum percolation theory is applied to distinguish the “radiative” localized states, which are isolated in space and have no ways for nonradiative transitions along the tail states. It is found that the analysis of the exciton-phonon interaction gives the information about the character of the localization of excitons. We have shown that the model used describes quite well the experimental cw spectra of CdS(1−c)Sec and ZnSe(1−c)Tec solid solutions. Further, the experimental results are presented for the temporal evolution of the luminescence band. It is shown that the changes of band shape with time come from the interplay of population dynamics of extended states and spatially isolated “radiative” states. Finally, the measurements of the decay of the spectrally integrated luminescence intensity at long delay times are presented. It is shown that the observed temporal behavior can be described in terms of relaxation of separated pairs followed by subsequent exciton formation and radiative recombination. Electron tunneling processes are supposed to be responsible for the luminescence in the long-time limit at excitation below the exciton mobility edge. At excitation by photons with higher energies the diffusion of electrons can account for the observed behavior of the luminescence

Sub-micron quantum cascadetransistors

International audienc

Adaptive precision floating point LLL

The LLL algorithm is one of the most studied lattice basis reduction algorithms in the literature. Among all of its variants, the floating point version, also known as L2, is the most popular one, due to its efficiency and its practicality. In its classic setting, the floating point precision is a fixed value, determined by the dimension of the input basis at the initiation of the algorithm. We observe that a fixed precision overkills the problem, since one does not require a huge precision to handle the process at the beginning of the reduction. In this paper, we propose an adaptive way to handle the precision, where the precision is adaptive during the procedure. Although this optimization does not change the worst-case complexity, it reduces the average-case complexity by a constant factor. In practice, we observe an average 20% acceleration in our implementation