Observation of valley splitting in (lll) n-type silicon inversion layers

An additional splitting of Shubnikov-de Haas oscillations in (lll) n-type silicon inversion layers in observed. We attribute it to valley splitting, analogous to that previously observed on (100) surface layers, and point out that theoretical explanations of valley splitting, restricted to the valley configuration in (100) inversion layers, are not applicable.     

CdO—SnO2复合氧化物的组成与性能

通过控制共沉淀时溶液中Ｃｄ／Ｓｎ摩尔比的方法，合成了物相组成不同的ＣｄＯ－ＳｎＯ２复合氧化物粉料，探讨了相组成与材料电导及气敏性能之间的关系。     

Is the dynamics of polystyrene films consistent with their glass transition temperature?

Experiments in the past 1.5 decades have found that the glass transition temperature of polymer films can be noticeably different from the bulk when the film thickness is decreased below ∼100  nm. On the other hand, many dynamic measurements have found results inconsistent with the observed change in the glass transition temperature. One frequently cited reason is that the dynamic properties being probed may not be directly related to the glass transition. Viscosity is a property traditionally used to characterize the dynamic slowing down occurring to a material at the glass transition. In this paper, we report experimental result showing that the viscosity of polystyrene films supported by oxide-coated silicon decreases with decreasing film thickness, consistent with the observed glass transition temperature of the films.     

Low temperature electronic transports in the presence of a density gradient

In this paper, we review low temperature electronic transport results in high quality two-dimensional electron systems. We discuss the quantization of the diagonal resistance, R_xx, at the edges of several quantum Hall states. Each quantized R_xx value turns out to be close to the difference between the two adjacent Hall plateaus in the off-diagonal resistance, R_xy. Moreover, peaks in R_xx occur at different positions in positive and negative magnetic fields. All three R_xx features can be explained quantitatively by a ∼1% cm electron density gradient. Furthermore, based on this observation, the well known but still enigmatic resistivity rule, relating R_xx to , finds a simple interpretation in terms of this gradient. In another sample, at 1.2 K, R_xx we observe a strongly linear magnetic field dependence. Surprisingly, this linear magnetoresistance also originates from the density gradient. Our findings throw an unexpected light on the relationship between the experimentally measured R_xx and the diagonal resistivity ρ_xx.     

A miniaturized HTS microwave receiver front-end subsystem for radar and communication applications

This paper presents a miniaturized high performance high temperature superconducting (HTS) microwave receiver front-end subsystem, which uses a mini stirling cryocooler to cool a high selective HTS filter and a low noise amplifier (LNA). The HTS filter was miniaturized by using specially designed compact resonators and fabricating with double-sided YBCO films on LAO substrate which has a relatively high permittivity. The LNA was specially designed to work at cryogenic temperature with noise figure of 0.27 dB at 71 K. The mini cryocooler, which is widely used in infrared detectors, has a smaller size (60 mm × 80 mm × 100 mm) and a lighter weight (340 g) than the stirling cryocoolers commonly used in other HTS filter subsystem. The whole front-end subsystem, including a HTS filter, a LNA, a cryocooler and the vacuum chamber, has a size of only φ120 mm × 175 mm and a weight of only 3.3 kg. The microwave devices inside the subsystem are working at 71.8 K with a consumed cooling power of 0.325 W. The center frequency of this subsystem is 925.2 MHz and the bandwidth is 2.7 MHz (which is a fractional bandwidth of 0.2%), with the gain of 19.75 dB at center frequency and the return loss better than ?18.11 dB in the pass band. The stop band rejection is more than 60 dB and the skirt slope is exceeding 120 dB MHz^?1. The noise figure of this subsystem is less than 0.8 dB. This front-end subsystem can be used in radars and communication systems conveniently due to it’s compact size and light weight.     

Flexible sliced designs for computer experiments

Sliced Latin hypercube designs are popularly adopted for computer experiments with qualitative factors. Previous constructions require the sizes of different slices to be identical. Here we construct sliced designs with flexible sizes of slices. Besides achieving desirable one-dimensional uniformity, flexible sliced designs (FSDs) constructed in this paper accommodate arbitrary sizes for different slices and cover ordinary sliced Latin hypercube designs as special cases. The sampling properties of FSDs are derived and a central limit theorem is established. It shows that any linear combination of the sample means from different models on slices follows an asymptotic normal distribution. Some simulations compare FSDs with other sliced designs in collective evaluations of multiple computer models.     

Determinant Forms for Extended Heat Functions and Expansions of Solutions of Associated Cauchy Problems

We briefly review series solutions of differential equations problems of the second order that lead to coefficients expressed in terms of determinants. Derivative type formulas involving a generating function with several parameters are developed for these determinant coefficients in first order problems. These permit constructing determinant forms for the heat polynomials and their Appell transforms. Hadamard's theorem for bounding determinants and conical regions are used to deduce simplified versions of expansion theorems involving these polynomials and associated Appell transforms. Extended versions of the heat equation are also considered.     

Fundamental groups of positively curved manifolds with symmetry

We obtain a classification for the fundamental groups of closed $n$ -manifolds of positive sectional curvature which admit an isometric $T^k$ -action with $k \ge \frac{n}{6}+1 (n \ne 11, 15)$ .     

使无穷小等价成为一个等价关系

修订等价无穷小的定义,可使无穷小量的等价真正成为一种等价关系,即满足自反性,对称性和传递性。     

Regioselective α-benzylation of 3-iodoazetidine via Suzuki cross-coupling

An efficient protocol for the synthesis of α-benzyl azetidines starting from benzylboronic acid pinacol ester derivatives and 3-iodoazetidine was developed. A wide range of α-benzyl azetidine derivatives were obtained in moderate to good yields with high regioselectivity (>99%).