Diagnostic evaluation of the mean meridional circulation-II

Summary We evaluate the mean meridional circulation for the Northern and Southern Hemispheres, working with the dry-static-energy and mass conservation equations. We derive an equation for the mass streamfunction on lines at constant dry static energy and we numerically integrate this equation using the annual mean data related to the period 1963 through 1973, as published by Oort in 1983. In both Hemispheres we find a rather intense Ferrel cell and a weaker Hadley cell; we do not find any polar cell. Cells strengths are accurately computed in the upper part of the troposphere; we are less confident on their numerical values in the lower part of the troposphere, for the presence of boundary layer. Comparisons with previous calculations are discussed.     

Studies of iron in deep-sea sediments by Mössbauer spectroscopy

The distribution of the forms of Fe in the solid phases in core samples of sediments from the Peru Basin has been investigated by Mössbauer spectroscopy with special attention to the cause of the sharp color transition between an upper green colored and a lower tan colored part. An important part of sample handling includes strict exclusion of oxygen during preparation of absorbers and measurements at cryogenic temperatures. The measurement strategy includes measurements between 77 K and 300 mK in zero external magnetic field, supplemented by measurements in external magnetic fields at 4.2 and 300 mK (up to 6.2 and 1 T, respectively). The temperature scans allow detection, identification and quantification of superparamagnetic iron oxides (goethite and hematite). The oxides are only present in samples from the upper tan-colored part of the core. The major part of the Fe(II) and Fe(III) (>80%) is present in a magnetic structure similar to that of layer silicates. The relative Fe(II) content of the layer silicates is practically identical to that determined from the paramagnetic components measured at liquid nitrogen temperature. This shows that the color transition in the sediment coincides with a change in the relative Fe(II) content in layer silicates from 11 to 37%. The color change can thus be explained by an increase in occurrence of Fe(II)–Fe(III) pairs exhibiting absorption bands due to intervalence electron transfer.     

Inversion layer resistance in silicon inversion layer solar cells

The inversion layer resistance is very important for metal-insulator-semiconductor inversion layer (MIS/IL) solar cells, and usually it is the main part of the series resistance. It is found that the inversion layer resistance and the junction depth are determined by the operating voltage for an MIS/IL solar cell. On the basis of MIS theory, a general relationship between the operating voltage and the inversion layer resistance (and the junction depth) has been investigated. Practical computations have been done for MIS/IL solar cells with a silicon nitride insulator layer. It is found that the inversion layer resistance has a minimum value for operating voltage near 0.4 V, and the junction depth decreases monotonically with the increase of the operating voltage.     

用于双层存储的SIL近场分析

固体浸没透镜 (SIL)用于光存储光学系统增大了光学头物镜的数值孔径 ,利用近场倏逝波读写 ,减小了光斑的直径 ,提高了存储密度。文中建议 :(1)将半球SIL分割成两部分 ,其中一部分由存储媒质的保护层充当 ,避免直接污染记录层 ;(2 )在半球SIL单层读写的基础上 ,再将第一层记录媒质作为SIL的一部分形成超半球齐明SIL ,以实现双层存储。并对此时的近场进行了解析分折     

Secure Physical Layer Network Coding versus Secure Network Coding

When a network has relay nodes, there is a risk that a part of the information is leaked to an untrusted relay. Secure network coding (secure NC) is known as a method to resolve this problem, which enables the secrecy of the message when the message is transmitted over a noiseless network and a part of the edges or a part of the intermediate (untrusted) nodes are eavesdropped. If the channels on the network are noisy, the error correction is applied to noisy channels before the application of secure NC on an upper layer. In contrast, secure physical layer network coding (secure PLNC) is a method to securely transmit a message by a combination of coding operation on nodes when the network is composed of set of noisy channels. Since secure NC is a protocol on an upper layer, secure PLNC can be considered as a cross-layer protocol. In this paper, we compare secure PLNC with a simple combination of secure NC and error correction over several typical network models studied in secure NC.     

Theory of spin-polarized low-energy electron diffraction from ferromagnetics

A theory of elastic scattering of low-energy electrons is outlined, in which the electron-solid interaction contains two spin-dependent contributions: an elastic exchange-correlation part in the real ion-core potential and an inelastic imaginary part describing electron-hole excitation. Numerical calculations for the Fe(110) surface predict, for an unpolarized primary beam, large spin polarization effects (up to 60%), which are highly sensitive to the magnetization of the topmost stomic layer.     

A theoretical study of the evaporation induced by a pulsed laser in a finite slab

The two-dimensional integral Laplace transform technique has been applied to get the temperature distributions in the molten layer, the solid part and in the backward surface of a finite target irradiated with a pulsed laser. Formulas for the time dependence of the evaporated part and the molten layer thicknesses of the target were found. This is accomplished by considering the temperature dependence of the absorption coefficient of the irradiated surface as well as the chemical reaction. As an illustrative example computations were carried out on an aluminum (Al) target.     

Porous gallium arsenide with arsenic clusters

It is for the first time that the possibility is demonstrated of preparing gallium arsenide with arsenic clusters under conditions of annealing of its porous layers obtained by electrochemical etching. It is found that the clusters are concentrated in porous layer barriers, their size ranges from 1 to 10 nm, and the density reaches 4×10¹⁸ cm⁻³. Under conditions of annealing in the temperature range from 400 to 600°C, an improvement in the structure quality of the porous layer is observed, and the lattice parameter (reduced for this layer) increases to approach a value characteristic of a single crystal. When highly alloyed substrates of the n-type are used, the inversion of the type of conductivity is observed in the surface part of the porous layer, which is due to the emergence of deep-lying acceptor centers. Thermal annealing leads to a narrowing of the inversion layer and to a more uniform distribution of electrically active centers over the porous layer thickness.     

Mechanism of charge exchange at a liquid crystal-electrode interface

It is shown that liquid crystal-electrode charge exchange is accomplished via the mechanism of Schottky emission through a thin dielectric layer. The thin dielectric layer (several nanometers) is formed by adsorption of neutral molecules that either are introduced on purpose or occur in even well-purified liquid crystals. The main part of the barrier determining the charge exchange process is due to the ionization of the cation losing an electron and its transformation to the anion. The barrier parameters and the dielectric layer thickness are estimated for the planar and homeotropic alignments of molecules.     

Model of a Surface Liquid-Like Layer of Ice

The previously developed model of an intermediate phase of ice with a liquid system of hydrogen bonds has been applied to describe a quasiliquid surface layer. This approach leads to a two-component model of a quasiliquid ice surface layer. In the outer part of the layer, both the proton and oxygen sublattices are melted, constituting water or the Thomson sublayer. In the inner part of the layer, only the proton sublattice is melted, whereas the oxygen sublattice holds its structure (the liquid state of the system of hydrogen bonds or the Faraday sublayer). The proposed model gives correct-in-magnitude estimates of various physical characteristics of the layer, explains the contradiction between the Faraday and Thomson hypotheses, and is consistent with recent experimental results and numerical studies.     

Anomalous absorption of bulk shear sagittal acoustic waves in a layered structure with viscous fluid

It is demonstrated theoretically that the absorptivity of bulk shear sagittal waves by an ultra-thin layer of viscous fluid between two different elastic media has a strong maximum (in some cases as good as 100%) at an optimal layer thickness. This thickness is usually much smaller than the penetration depths and lengths of transverse and longitudinal waves in the fluid. The angular dependencies of the absorptivity are demonstrated to have significant and unusual structure near critical angles of incidence. The effect of non-Newtonian properties and non-uniformities of the fluid layer on the absorptivity is also investigated. In particular, it is shown that the absorption in a thin layer of viscous fluid is much more sensitive to non-zero relaxation time(s) in the fluid layer than the absorption at an isolated solid-fluid interface.     

Low temperature CEMS determination of the morphology of rust layers on an iron plate corroded in KCl solution

CEMS and X-ray diffraction of rust layers on an iron coupon corroded in a 0.02 M KCl solution show that there exists a magnetite layer below an outer lepidocrocite layer. The 10 K spectrum displays three ferric sextets in its lepidocrocite part with fields of 448, 422 and 387 kOe respectively. They are attributed to Fe³⁺ ions having zero, one and more Cl⁻ ions as first nearest neighbours. The Cl⁻ ions do not seem to be ordered.     

周期多层量子阱结构的光吸收特性与电场分布

研究周期多层量子阱(MQW)结构的线性光学吸收特性与共振入射脉冲能量宽度、结构层数以 及周期的关系.结果表明:窄共振脉冲激发下的Bragg结构在层数达到某一值后,总吸收由随层 数单调增加变为单调减少;在非Bragg排列条件下则一直单调增加.通过对结构内电磁场强度 分布情况的分析解释了以上结果的来源,并指出吸收的Bragg压缩效应的实验条件. 关键词： 多量子阱 周期结构 吸收特性     

A new structural model of bivalve ligament from Solen grandis

It is widely accepted that the structure of bivalve ligament contains two layers: outer organic lamellar and inner aragonite fibrous layer. However, by using scanning electron microscopy (SEM), X-ray diffraction (XRD), and infrared spectroscopy (FTIR), we found an additional protein fibrous layer in the Solen grandis ligament. The ligament consists of three layers: an outer layer (OL), middle layer (ML), and inner layer (IL). OL consists of lamellar protein, oriented normal to dorsal edge. ML has unique spring-like protein fibers (ca. 120 nm in diameter) structure, stretching continuously from the left to right valve. Interestingly, IL comprises of aragonite fibers (ca. 100 nm in diameter) oriented posteriorly and inclined at an angle about 26° to dorsal edge at dorsal part; then they turn gradually to ventral part, showing striking zigzag structure vertical to ventral surface (VS). The ligament presents a new three-layered structural model different from previous reports; it may inspire not only in materials synthesis and mechanical design, but also in bivalve classification and evolution.     

Continuous spin-reorientation phase transition in the surface region of an inhomogeneous magnetic film

A continuous spin-reorientation transition from a uniform magnetic state with the in-plane orientation of the moments of all atomic layers to a nonuniform canted state in the surface region is considered. This transition was discovered in experiments on the divergence of magnetic susceptibility in a perpendicular magnetic field at a temperature of about 240 K, which is lower than the Curie point of gadolinium, equal to 292.5 K. These experiments were carried out on an ultrathin iron magnetic film deposited on the (0001) surface of a thin gadolinium film. It is shown that, in the vicinity of the spin-reorientation transition, the thermodynamic potential has a form characteristic of the Landau theory of second-order phase transitions. The orientation angle of the moment of the surface atomic layer with respect to the plane of the film, which is chosen as an order parameter, exhibits anomalous behavior and increases with temperature. Expressions are derived for the magnetic susceptibility of each atomic layer. It is shown that, in the vicinity of the transition, the irregular part of the magnetic susceptibility of each atomic layer exhibits behavior characteristic of the susceptibility in the Landau theory: it is less by a factor of two in the low-symmetry phase and diverges at the transition point. The regular part of the magnetic susceptibility of each atomic layer makes an additional contribution to the asymmetry of the total susceptibility in the vicinity of the transition point; this result follows from the fact that the inhomogeneous magnetic system considered is semi-infinite.     

Investigation of scaling laws in a turbulent boundary layer flow with adverse pressure gradient using PIV

We present an experimental investigation and data analysis of a turbulent boundary layer flow at a significant adverse pressure gradient at Reynolds number up to Re_θ = 10, 000. We combine large-scale particle image velocimetry (PIV) with microscopic PIV for measuring the near wall region including the viscous sublayer. We investigate scaling laws for the mean velocity and for the total shear stress in the inner part of the boundary layer. In the inner part the mean velocity can be fitted by a log-law. In the outer part of the inner layer the log-law ceases to be valid. Instead, a modified log-law provides a good fit, which is given in terms of the pressure gradient parameter and a parameter for the mean inertial effects. Finally we describe and assess a simple quantitative model for the total shear stress distribution which is local in wall-normal direction without streamwise history effects.     

Zero Viscosity Limit for Analytic Solutions of the Navier-Stokes Equation on a Half-Space.¶ II. Construction of the Navier-Stokes Solution

This is the second of two papers on the zero-viscosity limit for the incompressible Navier-Stokes equations in a half-space in either 2D or 3D. Under the assumption of analytic initial data, we construct solutions of Navier-Stokes for a short time which is independent of the viscosity. The Navier-Stokes solution is constructed through a composite asymptotic expansion involving the solutions of the Euler and Prandtl equations, which were constructed in the first paper, plus an error term. This shows that the Navier-Stokes solution goes to an Euler solution outside a boundary layer and to a solution of the Prandtl equations within the boundary layer. The error term is written as a sum of first order Euler and Prandtl corrections plus a further error term. The equation for the error term is weakly nonlinear; its linear part is the time dependent Stokes equation. This error equation is solved by inversion of the Stokes equation, through expressing the solution as a regular (Euler-like) part plus a boundary layer (Prandtl-like) part. The main technical tool in this analysis is the Abstract Cauchy-Kowalewski Theorem. Received: 5 September 1996 / Accepted: 14 July 1997     

Critical concentration of hot carriers in a quasi-two-dimensional semiconductor

The critical concentration of hot carriers necessary to maintain a Maxwellian for the isotropic part of the distribution function is calculated in an asymptotic approximation. The results are applied to electrons in an inversion layer at the surface of silicon.     

Skin electric explosion in double-layer conductors with a low-conductivity deposited layer

The experiments on explosion of cylindrical conductors aimed at comparison of plasma formation during skin explosion of homogeneous and double-layer conductors with an external layer with a lower conductivity are carried out on a high-current MIG generator (current amplitude up to 2.5 MA and current rise time 100 ns). The generator is loaded with cylindrical copper conductors with a diameter of 3 mm on the cathode part of which a titanium layer of thickness 20, 50, and 80 μm is deposited in vacuum. This type of loading makes it possible to compare the behaviors of the homogeneous and double-layer conductors in identical conditions. It is shown that using the double-layer structure of the conductor with an external layer of thickness 20–80 μm with a lower conductivity, which is obtained by vacuum arc deposition, higher values of magnetic induction (as compared to homogeneous conductor) can be attained on its surface prior to plasma formation and spread.     

Study of mass transport in rotating couple stress liquid under concentration modulation

A weakly non-linear stability analysis has been performed to examine the effect of time-periodic concentration modulation on the mass transport. We consider an infinite horizontal fluid layer is rotating with angular velocity Ω₁ about Z-axis subjected to an imposed time-periodic boundary concentration (ITBC). The concentration gradient between the plates of the fluid layer consists of a steady part and a time-dependent oscillatory part. The concentration of both walls is modulated in this case. We have expanded the infinitesimal disturbances in terms of power series of amplitude of modulation, which is assumed to be small. Ginzburg–Landau equation is obtained to find the rate of mass transfer. It is found that, the effect of Taylor number is to stabilize the system. Effect of Schmidt number and Couple stress parameter on mass transfer are also discussed. Further, it is found that the mass transport can be controlled by suitably adjusting the frequency and amplitude of modulation .