Influence of different band masses on ballistic charge transport in ferromagnet–superconductor–ferromagnet trilayers

We study transport properties of clean FISIF double-barrier junctions consisting of metallic or semiconducting ferromagnets (F), a superconductor (S), and insulating interfaces (I). We solve the scattering problem based on the Bogoliubov–de Gennes equation and calculate differential conductance for arbitrary interface transparency, different effective band masses and Fermi wave vectors in the conductors. We analyze size and coherence effects that characterize ballistic transport: subgap transmission and geometrical oscillations of the conductance. We find that different band masses, as well as different Fermi wave vectors, affect the transport properties in a way similar to interfaces of a finite transparency. In all these cases, charge transport is reduced to resonant tunneling through the quasi-bound states in the superconducting film.     

Destabilizing Heegaard splittings of knot exteriors

We give a necessary and sufficient condition for Heegaard splittings of knot exteriors to admit destabilizations. As an application, we show the following: let K₁ and K₂ be a pair of knots which is introduced by Morimoto as an example giving degeneration of tunnel number under connected sum. The Heegaard splitting of the exterior of K₁#K₂ derived from certain minimal unknotting tunnel systems of K₁ and K₂ is stabilized.     

A thin and compact compound-eye imaging system incorporated with an image restoration considering color shift, brightness variation, and defocus

A compact system of the thin observation module by bound optics (TOMBO) imager based on compound-eye imaging has been constructed to demonstrate its advantages over single-eye imaging systems such as thinner hardware. To reconstruct a high-resolution image from low resolution images captured by the compound-eye optics, we propose an image restoration scheme based on the iterative back-projection algorithm with depth map estimated from the disparities on the captured image. The scheme includes suppression of unit-by-unit color shift caused by the offset microlenses and the color filters on the commercial image sensors and deblurring of defocus by geometrical optics using the depth map. In the experiment, three-dimensional objects were captured by the TOMBO imager and reconstructed with the scheme. After the processing, the power spectrum of the captured image was improved by up to 19 dB, and the power spectrum of the effect of the color shift was reduced by 7 dB.     

Absorption-free superluminal light propagation in a quantum-dot molecule

The propagation of a weak probe field in a three-level quantum-dot molecule is investigated by employing the tunnel coupling. It is shown that in the absence of tunnel coupling, the propagation of light pulse is superluminal, similar to a simple two-level system. A high-resolution dip appears in optical spectra due to the presence of tunnel coupling. We show that this narrow dip leads to the subluminal light propagation with doublet absorption, so the group velocity of a light pulse can be controlled by interdot tunnel coupling. It is also demonstrated that by applying an indirect incoherent pumping field to the probe transition, the absorption doublet switches to the gain doublet and then the absorption-free superluminal light propagation is appeared.     

A note on the use of Frobenius map and D-modules in local cohomology

The Frobenius depth denoted by F-depth is defined by Hartshorne-Speiser in 1977 and later by Lyubeznik in 2006, in a different way, for rings of positive characteristic. The first aim of the present paper is to compare the F-depth with formal grade and reprove some results of Lyubeznik using formal local cohomology. Then the endomorphism rings of local cohomology modules will be considered. As an application, we reprove the results due to Huneke–Koh in positive characteristic and Lyubeznik in characteristic zero on the annihilators of local cohomology modules.     

Low temperature magnetoresistance in La1.32Sr1.68Mn2O7 layered manganite under hydrostatic pressure

The La_1.32Sr_1.68Mn₂O₇ layered manganite system has been studied by the low temperature electrical resistance and magnetoresistance under hydrostatic pressure up to 25 kbar. We have observe both, a Curie temperature (T_C) and a metal-insulator transition (T_MI) at 118 K in the ambient pressure. The applied pressure shifts the T_MI to higher temperature values and induces a second metal-insulator transition (T²_MI) at 90 K, in the temperature dependence of resistivity measurements. Also, the pressure suppresses the peak resistance abruptly at T_C. When an external field of 5 T is applied, we have observed a large negative magnetoresistance of 300% at the transition temperature and a 128% at 4.5 K. However, the increased pressure decreases the magnetoresistance ratio gradually. When the pressure reaches its maximum available value of 25 kbar, the magnetoresistance ratio decreases at a rate of 1.3%/kbar. From our experimental results, the decrease of magnetoresistance ratio with pressure is explained by the pressure induced canted spin state which is not favor for the spin polarized intergrain tunneling in layered manganites.     

湍流边界层流动结构研究用低Re数水洞试验台的设计及测试

自行设计制造了一台低Re数循环水洞试验台,收缩段采用维辛斯基(Witozinsky)曲线设计。变频电机调速,试验段流速范围0 2～1.0 m/s。用一维LDV系统测量了水洞试验段入口中心处的流速和湍流度随电机频率的变化,和来流速度为U_∞=0.26 m/s的平板湍流边界层速度和湍流度分布;并用PIV系统检测边界层内层低速条带结构。试验结果表明,试验段入口湍流度随着流速增大而下降,放置于试验段的平板其边界层已达到充分发展状态,并且检测到其底层低速条带结构,试验台可用于湍流边界层流动结构测试研究。     

不同载气下气体相对电离度的光谱诊断

利用速度调制光谱技术,以N2+为分子探针,研究了N2在不同缓冲气体(氦和氖)下的电离行为.N2+某一振转吸收谱线的强度与速度调制的调制度和N2+浓度成正比,因而通过测量两种缓冲气体下光谱强度,即可推算出相对电离度.     

浅海中水平线列阵深度对匹配场定位性能的影响

以浅海声传播模型为基础,通过计算机仿真观察到以下物理现象：浅海中海底水平线列阵的匹配场定位性能优于其他深度水平线列阵.利用简正波建模方法揭示了这一现象的物理机理.按照简正波理论,各号模式的形状是海水深度的函数.通过比较不同深度上各号模式幅度的变化,发现海底模式幅值接近零的模式号数明显小于其他深度.这说明海底水平线列阵可以对更多号模式进行采样,进而获得更多的目标声源信息,取得更好的匹配场定位效果. 关键词： 水平线列阵 匹配场定位 基阵深度