Angular dependence of the magnetoresistivity of Pd2Si

We present the magnetoresistivity at high magnetic field measured on single crystals of Pd₂Si of very good quality. The magnetoresistance depends on the orientation of field and current directions relative to the crystallographic axis. It shows that this suicide behaves like a compensated metal (i.e. equal numbers of electrons and holes) with open orbits along the main crystallographic directions.     

Pressure dependence of the roton spectrum in liquid helium

We suggest consistency checks on neutron scattering data on liquid helium under pressure. The theoretically calculated static structure functionS(k|P) leads to pressure dependence of the roton gap, momentum, and curvature in general agreement with experiment.Work supported in part by the U.S. Atomic Energy Commission, and in part by the National Science Foundation under Grant No. GP-29130 and through the Materials Research Center of Northwestern University.Resident Student Associate at Argonne National Laboratory, Summer 1972 and 1973.Alfred P. Sloan Research Fellow.     

Functional grading of rubber tubes within the context of a molecularly inspired finite thermoelastic model

Summary. The concept of functional grading is applied to rubber-like materials within the framework of finite thermoelasticity. A phenomenological stress-strain relation is proposed to account for the finite chain extensibility, the entropic origin for the stress, as well as the graded nature of rubbers. As an application, the azimuthal shearing of a hollow rubber tube subjected to thermal loading is considered with a view toward minimizing the strain inhomogeneity, and an optimum grading for each temperature gradient is presented.     

Wavelength calibration of a fiber-optical spectrum analyzer: temperature dependence

Optical spectrum analyzers are of increasing importance in fiber-optic laboratories. To perform reliable measurements with these devices, one must calibrate them with respect to wavelength, resolution bandwidth, power, etc. and know the temperature dependence of such calibrations. We have constructed a temperature-controlled chamber that can contain a spectrum analyzer and that can be regulated to within +/-0.1 degrees C. We report the temperature dependence of wavelength calibration and compare the various calibration results performed under temperature control with those previously obtained at ambient nonregulated temperature. For these studies we have used a compact calibration artifact based on absorption spectroscopy of acetylene.     

Frequency dependence of gel time in thermosetting resins

The increasing use of thermosetting resins in fibre reinforced composites for structural and insulating applications has necessitated the need to understand the process of crosslinking and systematics of curing time of resins with and without the reinforcing fine fibre filaments. We have employed dynamical measurements of loss tangent and dielectric constant over the frequency range 1 kHz–100kHz for investigating cure characteristics of composites. After adding crosslinking agents to resinous matrices (epoxy and polyester styrenated alkyd resins) the time variation of dielectric parameters was recorded until the completion of curing. The resin flow, the onset of gelation and completion of curing were unambiguously mapped by variations in dielectric parameters. Onset of gelation coincided with precipitous fall of dielectric constant and resonant maximum of dielectric loss. Asymptotic stabilization of dielectric parameters signalled completion of curing. The gel time and curing time were found to be substantially larger for fibre reinforced resins as compared to pure resins. The variation of electrically determined gel and cure time with frequency of ac signal employed and on the libre fraction in the composite are discussed in the paper. The present study shows that if dielectric measurements are to be employed to infer the completion of curing, low frequency measurements would be needed to correctly infer onset of gelation and time for curing. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

光谱带宽变化对中性片的影响和解决方法的探讨

本文以实测结果 ,介绍了光谱带宽变化对光谱光度测量的影响。当透射式烟度计检测用标准中性滤光片的中性程度不好时 ,这种影响会影响其研制结果及实际使用。本文提出了采用积分的方法 ,用微机编程处理或手工计算 ,就能克服影响 ,得到满意的接近实际的测试结果。     

On the continuous dependence of solutions on data in finite thermoelastostatics

Equations are presented for statical solutions in finite thermoelasticity. It is shown that solutions of these equations that reside in an appropriate subset of a Sobolev space depend continuously on the data, provided two growth inequalities are satisfied.     

Frequency domain damage detection of plate and shell structures by finite element model updating

Plate- and shell-like elements are the main constituent of many engineering structures such as ships and airplanes. This paper develops a frequency domain model updating method using power spectral density function and seeks its viability in damage identification of plates and shells. The derivation of the sensitivity equation is exact and measured natural frequencies of few lower modes are used to overcome the drawbacks of incomplete measurement. The method is numerically examined in several damage cases. The robustness of method against measurement and mass modelling error is numerically assessed using Monte-Carlo analysis and numerically simulated error contaminated data. The method proves to be robust against both kind of errors and performs well, both in cases of plate and shell elements.     

Angular dependence of emissivity of tungsten in the infrared region of the spectrum

A procedure is described for measuring the angular dependence of the emissivity of metals in the infrared region of the spectrum.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 36, No. 2, pp, 315–319, February, 1979.     

Frequency dependence of the dielectrophoretic separation of single-walled carbon nanotubes

Dielectrophoresis on single-walled carbon nanotubes in surfactant suspensions has been demonstrated to separate metallic from semiconducting tubes by their different electric field-induced polarisabilities. Here we report that the interaction between SWNTs and the surfactant induces a nanotube surface conductance which gives rise to a unique electric field frequency dependence of the dielectrophoretic force acting on semiconducting SWNTs. We observe a surfactant concentration dependent crossover frequency enabling separation of metallic from semiconducting SWNTs at high frequency and deposition of metallic and semiconducting SWNTs at low frequency. Proof for the effectiveness of separation is given by a comparative Raman spectroscopy study on dielectrophoretically deposited tubes excited with two different wavelengths.     

Frequency domain boundary element versus time domain finite element model for the transient analysis of horizontal grounding electrode

The paper deals with two different approaches to the assessment of the transient impedance of a horizontal grounding electrode: frequency domain boundary element analysis, based on the straight thin wire antenna model (AM) and generalized telegrapher’s equations combined with inverse Fast Fourier Transform (FFT); and time domain finite element analysis based on the transmission line model (TLM) and standard telegrapher’s equations. Extensive numerical experiments have been undertaken and some of illustrative numerical results are presented in this paper.     

Angular dependence of the current-voltage characteristics and voltage fluctuation spectrum in ceramic superconductors

Measurements were made of the current-voltage characteristics and voltage fluctuation spectrum as functions of the angle between the magnetic field applied in the plane of the sample and the direction of the transport current in a YBa₂Cu₃O_7−δ ceramic superconductor. The angular dependence of the fluctuation spectrum was measured first. It is shown that the current-voltage characteristics are not described using the vortex line cutting model and the voltage fluctuations are not caused by independent motion of vortices in the bulk of the sample. The results are consistent with the model of a self-organized critical state. Pis’ma Zh. Tekh. Fiz. 25, 8–13 (February 12, 1999)     

Ion-induced interfacial mixing in Al/Pd bilayers: incident ion energy and film thickness dependence

The dependence of ion beam mixing on the incident ion energy and film thickness in the Al/Pd system are investigated through both experiment and Monte Carlo simulation based on cascade mixing. It is found that the optimum film thickness is the mean damage depth and the degree of mixing increases with increasing incident ion energy. The radiation-enhanced diffusion or thermochemical driving force is found to play an important role, even in the low-energy region (< 40 keV).     

Frequency spectrum of the bispherical hollow system: The case of the nonuniform thickness human skull

Summary In the present work we discuss the role of the thickness nonuniformities of the human dry skull on its frequency spectrum. The mathematical modelling is based on the three-dimensional theory of elasticity, the approximation of the skull by an isotropic material occupying the region bounded by two non-concentric spheres and the introduction of the bispherical coordinates system. The mathematical analysis is based on the construction of the Navier eigenfunctions of the problem and the representation of the solution in terms of them. The frequency equation is solved numerically and the role of various parameters entering the problem is extensively discussed.     

Frequency response of fiber-optic multilayer hydrophones: experimental investigation and finite element simulation

The frequency response of a fiber-optic hydrophone that uses a dielectric multilayer system as the sensing element for ultrasound detection is investigated. A primary interferometric calibration technique is applied to determine by experiment the frequency-dependent pressure-voltage transfer function up to 45 MHz. The interaction between an incident pressure wave and the fiber end is analyzed by finite element methods. The simulation yields the response of the sensor to a short Gaussian impulse in the time domain from which the transfer function is calculated. The results of the model simulations allowed the transfer function obtained to be interpreted as the result of the superposition of longitudinal, edge diffraction and lateral waves with a resonant vibration mode of the fiber body representing an elastic rod