On Kolmogorov-Smirnov-type tests for symmetry

Summary For a set of independent but not necessarily identically distributed random variables, a simple Kolmogorov-Smirnov-type test is proposed for testing the hypothesis of symmetry (about a common and specified point). The exact and asymptotic (null hypothesis) distributions of some allied statistics are obtained, and the Bahadur-efficiency of the test is studied. Work of the second author was supported by the U.S. National Institutes of Health, Grant GM-12868.     

Evolution of dislocation substructure in vapour-deposited lead films on glass substrates

Systematic variation of anisotropic X-ray line broadening in vapour-deposited Pb films of various thicknesses on glass substrates is studied using dislocation model of strain anisotropy incorporated into a modified Williamson-Hall and modified Warren-Averbach procedure. For smaller film thicknesses in the range of about 100-200 nm, the dislocation network is less correlated and contains substantial screw component and twin or growth faults. The films of larger thicknesses (greater than 500 nm), on the other hand, consist mostly of edge dislocations with a more regular and correlated dislocation structure. The present study reveals the inadequacy of applicability of conventional Warren-Averbach analysis in regular and correlated dislocation structures.     

Frequency Dependent Conductivity of Thin ZnO Films Prepared by R.F. Sputtering Technique

AC conductivity of different thin zinc oxide films measured in the frequency range of 10 Hz to 2 MHz in the temperature interval of 300 K to 575 K is reported. ZnO films were prepared by reactive r.f. magnetron sputtering from ZnO target. The experimental data reveal that a.c. conductivity is proportional to ^s . The value of s was found to be temperature dependent, decreases with increasing temperature. These observations suggest that correlated barrier hopping model is the most likely mechanism. The temperature dependence of a.c. Conductivity is expressed in power law form as () T ⁿ . The temperature exponent n is found to be increasing with increasing temperature and decreasing frequency in accordance with the narrow band limit. At high temperature the conductivity variation with frequency is comparatively small. The polaron binding energy (W _m), the height of Coulomb barrier (W) and the characteristic relaxation time (₀) have been calculated. The values of W _m and W increase as the thickness decreases whereas the values of ₀ decrease with decreasing thickness.     

Metastability and inverse magnetocaloric effect in doped manganite (Nd(0.25)Sm(0.25)Sr(0.5)MnO(3)) and ferromagnetic shape memory alloy (Ni(2)Mn(1.36)Sn(0.64)): a comparison

The manganite Nd(0.25)Sm(0.25)Sr(0.5)MnO(3) (NSSMO) shows a first-order metal to insulator transition on cooling, which is concomitant with a magnetic transition from the ferromagnetic to antiferromagnetic state. In some respect the sample shows a striking similarity with Ni-Mn-Sn based ferromagnetic shape memory alloys (FSMAs) undergoing a first-order magneto-structural transition, and efforts have been made to highlight the similarities and dissimilarities of the studied manganite with one such FSMA of composition Ni(2)Mn(1.36)Sn(0.64). From our transport and magnetic investigations, the region of transition in the NSSMO is found to be highly metastable, with a clear indication of a magnetically arrested state which persists even when the sample is cooled down to the lowest temperature of measurement. Interestingly, the studied manganite shows an inverse magnetocaloric effect similar to the FSMA. However, a striking difference between the two compositions is evident in the low-temperature magneto-transport behavior: while a clear signature of tunneling magnetoresistance is present in NSSMO due to the coexisting metallic and insulating clusters of nanometer dimension, the studied FSMA do not show such behavior due to the absence of any insulating phase in the intermetallic alloy.     

Colorimetric Determination of Seleniumin Various Environmental Samples

A new reagent system using rhodamine‐B dye for the determination of selenium is described. The method is based on the reaction of selenium with acidified potassium iodide to liberate iodine. The liberated iodine bleaches the pink colour rhodamine‐B, which is measured at 555 nm. Beer's law is obeyed over the concentration range of 1–10 μg of selenium final solution volume of 25 mL (0.04–0.4 ppm) and the apparent molar absorptivity and Sandell's sensitivity was found to be 1.96× 10⁵ l mol^?1 cm^?1 and 0.0004 μg cm^?2, respectively. The method is simple, sensitive, and selective and is satisfactorily applied to micro‐level determination of selenium in various environmental and cosmetic samples.     

Mixed convection heat transfer from three heated square cylinders in cross-flow at low Reynolds numbers

This paper presents the effects of cross buoyancy and Prandtl number on the flow and heat transfer characteristics around three equal isothermal square cylinders arranged in a staggered configuration within an unconfined medium. Transient two-dimensional numerical simulations are performed with a finite volume code based on the SIMPLEC algorithm in a collocated grid system. The pertinent dimensionless parameters, such as Reynolds, Prandtl and Richardson numbers are considered in the range of 1 ≤ Re ≤ 30, 0.7 ≤ Pr ≤ 100 and 0 ≤ Ri ≤ 1. The representative streamlines, vortex structures and isotherm patterns are presented and discussed. In addition, the overall drag and lift coefficients and average Nusselt numbers are determined to elucidate the effects of Reynolds, Prandtl and Richardson numbers on flow and heat transfer. The flow is observed to be steady for all the ranges of parameters considered. The drag coefficient is found to decrease with Re (for Ri = 0) and Ri at low Pr, whereas it increases with Pr at higher Ri. The lift coefficient decreases with Ri at low Pr and increases with Pr at higher Ri. The time and surface average cylinder Nusselt number is found to increase monotonically with Re as well as Pr while it remains almost insensitive to Ri at low Pr.     

Vibration control by recursive time-delayed acceleration feedback

This paper presents a theoretical basis of time-delayed acceleration feedback control of linear and nonlinear vibrations of mechanical oscillators. The control signal is synthesized by an infinite, weighted sum of the acceleration of the vibrating system measured at equal time intervals in the past. The proposed method is shown to have controlled linear resonant vibrations, low-frequency non-resonant vibrations, primary and 1/3 subharmonic resonances of a forced Duffing oscillator. The concept of an equivalent damping and natural frequency of the system is also introduced. It is shown that a large amount of damping can be produced by appropriately selecting the control parameters. For some combinations of the control parameters, the effective damping factor of the system is shown to be inversely related to the time-delay in the small delay limit. Selection of the optimum control parameters for controlling the forced and free vibrations is discussed. It is shown that forced vibration is best controlled by unity recursive gain and smaller values of the time-delay parameter. However, the transient response can be optimally controlled by suitably selecting the time delay depending upon the gain. The delay values for the optimal forced response may be different from that required for the optimum transient response. When both are important, a suboptimal choice of the delay parameters with unity recursive gain is recommended.     

Axially symmetric stationary electrovac solutions

Perjes and Israel and Wilson have given independently a new class of solutions of the sourcefree Einstein-Maxwell equations, which can be interpreted as the external gravitational and electromagnetic fields of a spinning source with unit specific charge. Starting from Zipoy's solutions in oblate and prolate spheroidal coordinates for the source-free gravitational field we generate some axially symmetric stationary solutions of the source-free Einstein-Maxwell equations by using Perjes' method. All these solutions become Euclidean at infinity. The asymptotic behavior and the singularity of the solutions are studied in order to gain some insight into the nature of the source. The solution in prolate spheroidal coordinates is found to contain closed timelike lines.     

Dynamical symmetries and Nambu mechanics

It is shown that several Hamiltonian systems possessing dynamical or hidden symmetries can be realized within the framework of Nambu's generalized mechanics. Among such systems are the SU(n)-isotropic harmonic oscillator and the SO(4) Kepler problem. As required by the formulation of Nambu dynamics, the integrals of motion for these systems necessarily become the so-called generalized Hamiltonians. Furthermore, in most of these problems, the definition of these generalized Hamiltonians is not unique.