Short range scattering mechanism of type-II GaSb/GaAs quantum dots on the transport properties of two-dimensional electron gas

We have studied the scattering process of AlGaAs/GaAs two-dimensional electron gas with the nearby embedded GaSb/GaAs type-II quantum dots (QDs) at low temperature. Quantum Hall effect and Shubnikov-de Haas oscillation were performed to measure the electron density n(2D), the transport lifetime tau(t) and the quantum lifetime tau(q) under various biased gate voltage. By comparing measured results of QDs sample with that of reference sample without embedded QDs, mobilities (transport mobility mu(t) and quantum mobility mu(q)) dominated by GaSb QDs scattering were extracted as functions of n(2D). It was found that the ratios of tau(t) to tau(q) were varying within the range of 1-4, implying the scattering mechanism belonging to the sort of short-range interaction. In the framework of Born approximation, a scattering model considering rectangular-shaped potential with constant barrier height was successfully applied to explain the transport experimental data. In addition, an oscillating ratio of tau(t)/tau(q) with the increasing n(2D) was predicted in the model.

Tunable parametric fluorescence using a single crystal

In this paper, we investigate the mechanism of tunable parametric superfluorescence (PS) based on the second harmonic generation and parametric processes taking place in the same nonlinear crystal (BBO). The tunable spectra of PS has been generated between 480 nm and 530 nm, which is pumped by the second-harmonic from the high-power Ti: sapphire laser system at 1 kHz repetition rate. We present the generation mechanism of PS theoretically and simulate the process of PS ring using the amplification transfer function. The experiment and the theory show that PS will appear when the phase matching angle for second-harmonic generation is close to the optimal pump angle for optical parametric generation, and then the tunable spectra of PS are generated by slightly adjusting the crystal angle. The result provides a theoretical basis for controlling the generation of PS and quantum entanglement states, which is of great significance for the development of quantum imaging, quantum communications and other applieations.

黄土坡面土壤侵蚀中溶质随径流迁移的水动力特性研究

通过对比分析坡面水流的水动力参数与径流溶质迁移量间的关系,研究了不同地表状况下黄土坡面土壤溶质随径流迁移的水动力学特性,以求深入了解和认识坡面土壤侵蚀中溶质随径流迁移的本质机理。研究结果表明:不同坡面地表状况下,糙率系数和平均水深之比(n/h)与侵蚀过程中随径流迁移的溶质存在一定的关系,径流溶质Br-平均浓度、径流溶质Br-的平均流失率以及径流溶质Br-的相对流失量均随n/h的增加而减小。径流溶质Br-的平均流失率以及径流溶质Br-的相对流失量与水流水动力学参数n/h具有指数关系。

A switch-on mechanism to activate maize ribosome-inactivating protein for targeting HIV-infected cells

Maize ribosome-inactivating protein (RIP) is a plant toxin that inactivates eukaryotic ribosomes by depurinating a specific adenine residue at the a-sarcin/ricin loop of 28S rRNA. Maize RIP is first produced as a proenzyme with a 25-amino acid internal inactivation region on the protein surface. During germination, proteolytic removal of this internal inactivation region generates the active heterodimeric maize RIP with full N-glycosidase activity. This naturally occurring switch-on mechanism provides an opportunity for targeting the cytotoxin to pathogen-infected cells. Here, we report the addition of HIV-1 protease recognition sequences to the internal inactivation region and the activation of the maize RIP variants by HIV-1 protease in vitro and in HIV-infected cells. Among the variants generated, two were cleaved efficiently by HIV-1 protease. The HIV-1 protease-activated variants showed enhanced N-glycosidase activity in vivo as compared to their un-activated counterparts. They also possessed potent inhibitory effect on p24 antigen production in human T cells infected by two HIV-1 strains. This switch-on strategy for activating the enzymatic activity of maize RIP in target cells provides a platform for combating pathogens with a specific protease.

NEW FORMATION MECHANISM OF ELECTRIC-FIELD DOMAIN DUE TO GAMMA-X SEQUENTIAL TUNNELING IN GAAS/ALAS SUPERLATTICES

We have studied the sequential tunneling of doped weakly coupled GaAs/ALAs superlattices (SLs), whose ground state of the X valley in AlAS layers is designed to be located between the ground state (E(GAMMA1)) and the first excited state (E(GAMMA2)) of the GAMMA valley in GaAs wells. The experimental results demonstrate that the high electric field domain in these SLs is attributed to the GAMMA-X sequential tunneling instead of the usual sequential resonant tunneling between subbands in adjacent wells. Within this kind of high field domain, electrons from the ground state in the GaAs well tunnel to the ground state of the X valley in the nearest AlAs layer, then through very rapid real-space transfer relax from the X valley in the AlAs layer to the ground state of the GAMMA valley of the next GaAs well.