Analysis and design of ring-resonator integrated hemi-elliptical lens antenna at terahertz frequency

In this paper, a novel lens integrated ring-resonator microstrip antenna is analyzed and simulated at 600 GHz. A mathematical model to compute the directivity of this kind of the antenna has been developed and the directivity of the antenna has been computed which is 18 dBi. The proposed model has been simulated by using CST Microwave Studio a commercially available simulator based on finite integral technique and similar result has been obtained. Further, the directivity of the antenna has also been computed by using the techniques reported in the literature and in this case also we have obtained the similar result. Later, a probe-fed patch integrated lens antenna has also been investigated to validate the correctness of the numerical method. To find the potential advantages of this kind of the structure, the ? 10 dB impedance bandwidth of the antenna has been compared to a lens-integrated probe-fed microstrip patch antenna and a significant enhancement in the bandwidth has been observed.     

Use of ultrasonics in shear layer cavitation control

In this paper we report results from some investigations on the use of ultrasonics in controlling hydrodynamic cavitation in the shear layer downstream of a sudden expansion. Control of this type of cavitation has been achieved by modulating the local pressure that was experienced by a nucleus present in the shear layer. This modulation was made possible by using a piezoelectric device, termed as Ultrasonic Pressure Modulator (UPM). The performance of UPM has been studied at different dissolved gas concentrations with electrolysis bubbles as nuclei. Control of cavitation due to natural nuclei has also been attempted. Efficiency of UPM, in reducing cavitation, was seen to be dependent on the driving frequency employed. Experimental and numerical studies have been conducted to bring out the physics behind this approach of cavitation control. Different measures of cavitation control have been identified and some possible applications of this method have also been outlined.     

Aspects of the crystal growth of the intergrowth tungsten bronzes

The crystal growth of a few of the members of the family of the rubidium intergrowth tungsten bronzes has been investigated as part of a program to study the compositionally induced metal to insulator transition in this bronze system. Progress in the study of this nonstoichiometric material has been made possible by successful growth of large single crystal samples. Application of vapor-assisted seeded crystal growth has led to an increase of the product crystal size by two orders of magnitude, from 0.1 mm on an edge to about 2 cm on an edge. Scanning electron microscopy has been used to characterize cracks, voids and intergrowths in this material. Transmission electron microscopy has been used to image the lattice of this quasi-two dimensional material in order to observe the frequency and amplitude of stacking defects.     

制作铊玻璃自聚焦透镜的两步离子交换工艺分析

本文分析了用一次离子交换工艺制备的自聚焦透镜的径向折射率分布规律,讨论了所能获得的最佳分布工艺条件。在此基础上提出了两步离子交换的新方法。计算表明用两步离子交换工艺制备的自聚焦透镜的折射率分布可以更接近理想分布.     

Study of the interaction of a palladium nanocontact with a hydrogen molecule

The interaction of a palladium nanocontact with a hydrogen molecule has been studied using molecular static method. The influence of impurity on the atomic structure and mechanical properties of the palladium nanocontact has been demonstrated. The characteristic interatomic distance has been determined in this contact. It has been found that the hydrogen molecule dissociates by interaction with nanocontact atoms.     

Numerical investigation of heat transfer augmentation through geometrical optimization of vortex generators

In this paper a two-dimensional numerical simulation of a steady incompressible and turbulent model has been carried out to study the effects of vortex generators in a compact heat exchanger in a curvilinear coordinate system. The mesh which is applied in this study is boundary fitted and has been smoothed by a Laplace operator. Experimental data of a former study has been applied to validate the numerical results. The effects of geometrical variation are studied by adjusting vortex generators’ inclination and relative cross location. The major issue of this study is the optimal trade-off by selecting an optimal geometric, considering the opposite influences of geometrical variation on Nusselt number and pressure drop.     

Effect of a terahertz cavity on the conductivity of short-period GaAs/AlAs superlattices

The miniband conductivity in short-period GaAs/AlAs superlattices with a terahertz cavity has been studied. A stepwise decrease in the current caused by the formation of the electrical domains has been observed in current–voltage characteristics at a certain threshold voltage. It has been found that this threshold voltage changes considerably under the variation of the cavity parameters. The shift of the threshold has been explained by the excitation of high-amplitude oscillations in the cavity.     

Mean-field approximation for the potts model of a diluted magnet in the external field

The Potts model of a diluted magnet with an arbitrary number of states placed in the external field has been considered. Phase transitions of this model have been studied in the mean-field approximation, the dependence of the critical temperature on the external field and the density of magnetic atoms has been found, and the magnetic susceptibility has been calculated. An improved mean-field technique has been proposed, which provides more accurate account of the effects associated with nonmagnetic dilution. The influence of dilution on the first-order phase transition curve and the magnetization jump at the phase transition has been studied by this technique.     

表面波型微波感耦常压氖等离子体的激发温度研究

用光学多道分析仪研究表面波型常压微波感耦氖等离子体。采用“多线法”测定了ＮｅＭＩＰ的激发温度，研究了实验参数对激发温度的影响；讨论了该等离子体的发生成机制；推算了亚稳态原子浓度随实验参数的变化情况。     

Ferrite films with enhanced stability of ferromagnetic resonance frequency

The problem of providing the frequency stability of magnetic vibrations of a ferrite film upon simultaneous changes in two magnetic parameters has been stated. The method of stabilizing the frequency of uniform ferromagnetic resonance at small deviations of the effective magnetization and the field of crystallographic magnetic anisotropy of the ferrite from initial values has been proposed. The equation that relates the frequency variation with variations in the magnetic parameters within a linear approximation has been derived. The possibility of the coefficients at the variations in the magnetic parameters to turn to zero has been investigated. It has been shown that this possibility can be implemented via the proper choice of the crystallographic film orientation and the strength and direction of the magnetizing field. In this case, the frequency shift has been determined by quadratic form over the variations in the magnetic parameters. An example of calculating the quadratic form has been given. The optimized film is compared with a film, the frequency shift of which is determined by a linear dependence on the variations in its magnetic parameters.     

Atomic coherent trapping and phase property of the field in the system of two-level atoms interacting with a single-mode field

In this paper,the condition of the atomic coherent trapping in the system of twotwo-level atoms interacting with a single-mode coherent field has been obtained.And proper-ties of the light field in this case has also been analysed by means of the phase theory intro-duced by Barnett and Pegg,     

Wastewater treatment: a novel energy efficient hydrodynamic cavitational technique

A novel method of treating a dye solution has been studied by hydrodynamic cavitation using multiple hole orifice plates. The present work deals with the effect of geometry of the multiple hole orifice plates on the degradation of a cationic dye rhodamine B (rhB) solution. The efficiency of this technique has been compared with the cavitation generated by ultrasound and it has been found that there is substantial enhancement in the extent of degradation of this dye solution using hydrodynamic cavitation. Large-scale operation coupled with better energy efficiency makes this technique a viable alternative for conventional cavitational reactors.     

Transmission electron microscopy study of vertical quantum dots molecules grown by droplet epitaxy

The compositional distribution of InAs quantum dots grown by molecular beam epitaxy on GaAs capped InAs quantum dots has been studied in this work. Upper quantum dots are nucleated preferentially on top of the quantum dots underneath, which have been nucleated by droplet epitaxy. The growth process of these nanostructures, which are usually called as quantum dots molecules, has been explained. In order to understand this growth process, the analysis of the strain has been carried out from a 3D model of the nanostructure built from transmission electron microscopy images sensitive to the composition.     

Converging shock waves in metals

Study of propagation of a spherically converging shock wave has been carried out by Whitham’s method. The variation of shock velocity and pressure along the radius of curvature has been calculated numerically for a number of metals. Attempt has also been made to compare the experimental results of velocity of detonation wave with those reported elsewhere by the application of Whitham’s method. A good agreement between experimental and theoretical results has been obtained in this study.     

Investigation of various operation modes of a miniature superconducting detector of microwave radiation

Nonequilibrium electron and phonon distribution functions have been calculated for a metallic absorber of a promising miniature superconducting detector irradiated by microwave radiation. The response of this detector has been calculated, and it has been shown that this detector can operate in either the photon counter mode or bolometric mode in dependence on the degree of nonequilibrium of the phonon subsystem.     

Path integral quantization corresponding to the deformed Heisenberg algebra

In this paper, the deformation of the Heisenberg algebra, consistent with both the generalized uncertainty principle and doubly special relativity, has been analyzed. It has been observed that, though this algebra can give rise to fractional derivative terms in the corresponding quantum mechanical Hamiltonian, a formal meaning can be given to them by using the theory of harmonic extensions of function. Depending on this argument, the expression of the propagator of the path integral corresponding to the deformed Heisenberg algebra, has been obtained. In particular, the consistent expression of the one dimensional free particle propagator has been evaluated explicitly. With this propagator in hand, it has been shown that, even in free particle case, normal generalized uncertainty principle and doubly special relativity show very much different result.     

Eine Methode zur Erzeugung von Strahlen negativer Ionen

A new method for the production of beams of negative ions to be injected into a tandem Van de Graaff accelerator is presented. Negative ions of a desired species are produced by impact of noble gas ions with molecules of a gas containing this element, and are then collected and bent into a beam with high efficiency. For example, a beam of negative fluorine ions has been obtained by bombardment of boron fluoride with 30 keV krypton ions, resulting in a current of 0·5 μA of F⁺⁺⁺⁺ at the target. The original ion source of the tandem has been used with this modified procedure. The krypton gas has been fed into the duoplasmatron and the boron fluoride into the charge exchange channel. No damage to the ion source system has been observed, even in this case. This method has also been applied to nitrogen and oxygen with good results. Some measurements are reported, and a brief discussion of the basic process of the method is given.     

制作锂玻璃自聚焦透镜的离子交换工艺的研究

本文分析了用一次离子交换工艺制备的自聚焦透镜的径向折射率分布规律,计算了所能获得的最佳分布及工艺条件.并提出在熔盐中加Li~+及分阶段离子交换的新方法.计算表明,用改进后的新工艺制备的自聚焦透镜,其折射率分布可以得到明显的改善.     

Influence of an electric field on the ferromagnetic resonance in a plane-layered magnetic system

The influence of an electric field on the ferromagnetic resonance (FMR) in a multilayer magnetic system consisting of two magnetic layers separated by a thin nonmagnetic interlayer has been investigated. It has been shown that, upon the excitation of magnetization oscillations by a microwave magnetic field, the eigenfrequencies of the ferromagnetic resonance depend on the stationary electric field applied in the plane of the layers. It has also been demonstrated that, in this system, high-frequency magnetization oscillations can be excited by an electric microwave field. The results of the investigation of the polarization properties of the excitation mechanism indicate that this effect can be observed experimentally.     

紫外傅里叶变换光谱仪干涉图数据处理

阐述了干涉图数据处理方法 ,采用紫外傅里叶变换光谱仪实验测量了汞灯光谱干涉图。使用四阶Blackman Harris窗函数作为切趾函数 ,采用最小二乘法拟和多项式对光源傅里叶变换光谱进行相位校正 ,获得了高精度的Hg紫外发射光谱