Samples Of Different Geometries Research Articles

Terahertz magneto-spectroscopy of a point contact based on CdTe/CdMgTe quantum well

To understand a terahertz (THz) response of a point contact device, a number of samples based on CdTe/CdMgTe quantum wells grown by a molecular beam epitaxy were investigated at low temperatures and high magnetic fields. The experiments involved magneto-transport, photocurrent, and transmission measurements carried out with monochromatic THz sources or a Fourier spectrometer. Samples of different geometry with and without gate metallization were used. We observed excitations of a two-dimensional electron plasma in the form of optically induced Shubnikov-de Haas oscillations, cyclotron resonance transitions, and magneto-plasmon resonances. A polaron effect was observed at magnetic fields higher than 10 T. A point contact device processed with an electron beam lithography was investigated as a detector of THz radiation. It was shown that the main mechanism responsible for a THz performance of the point contact was excitation of magneto-plasmons with a wavevector defined by geometrical constrictions of the device mesa.

On the NiTi wires in dampers for stayed cables

Recent studies were dedicated to the realization of measurements on stay-cable samples of different geometry and static conditions as available at several facilities. The elaboration of the acquired data showed a a satisfactory efficacy of the dampers made of NiTi wires in smoothing the cable oscillations. A further attempt to investigate the applicability of the achieved results beyond the specific case-studies represented by the tested cable-stayed samples is herein pursued. Comparative studies are carried out by varying the diameter of the NiTi wire so that similar measurements can be taken also from laboratory steel cables of reduced size. Details of the preparation of the Ni-Ti wires are discussed with particular attention being paid to the suppression of the creep phenomenon. The resulting shape of the hysteretic cycle differs according to the wire diameter, which affects the order of the fitting polynomial to be used when trying to retrieve the experimental results by numerical analyses. For a NiTi wire of given diameter, an estimate of the amount of dissipated energy per cycle is given at low levels of maximum strain, which correspond to a fatigue fracture life of the order of millions of cycles. The dissipative capability is affected by both the temperature and the cycling frequency at which the tests are performed. Such effects are quantified and an ageing process is proposed in order to extend the working temperature range of the damper to cold weathers typical of the winter season in Northern Europe and Canada. A procedure for the simulation of the shape memory alloy behavior in lengthy cables by finite element analysis is eventually outlined.

Study of the Angular Distribution of Scintillation Photons

This paper presents a characterization method to experimentally determine the angular distribution of scintillation light. By exciting LYSO crystals with a radioactive source, we measured the light angular profiles obtained with samples of different geometries in different conditions of wrapping. We also measured the angular distribution of light emitting in glue and compared it with the one emitting in air. Angular distribution of light output of photonic crystals is also provided. Consistency of the measurements is verified with conventional light output measurements.

Modeling the temperature rise in high-pressure torsion

Experiments and finite element modeling were used to estimate the temperature rise during high-pressure torsion. The results show the temperature rise is dependent upon the material strength, the rotation rate, the sample radius, the heat capacity and the volume of the anvils. A general relationship is derived which predicts the temperature rise in samples of different geometries processed using different anvil sizes. A simplified version of the equation is presented for general use.

Measuring the three-photon self-annihilation fraction of positronium in and above thin films: A tool for determining film morphology

A technique is described for evaluating the fraction of positrons F incident on thin film samples which form ortho-positronium and subsequently decay into three gamma photons. The method involves the measurement of two linked phenomena: the decrease in the number of annihilation events involving the emission of two gamma photons with approximately 511 keV in the germanium detector photopeak, and the increase in the number of decays into three gamma photons with energies in the range 395-505 keV. After the application of a number of systematic corrections to the raw data, these measurements allow the determination of the absolute value of F without the need for calibration on a sample with known F values, thereby avoiding problems with changing samples of different geometries measured under different conditions.

An experimental-finite element analysis of the plane stress local torsion

The plane stress local torsion (PSLT) is an attractive method to strengthen the material in the areas of interest. A closed form solution of the problem is complex and an interpretation of the measured raw torque–twist data into the effective stress and strain is not straightforward. These hinder the optimization and control of the technique. In this study, the PSLT test was performed using Ti-IF steel specimens and their torque–twist response and radial distortion were compared with those obtained from an elastic–plastic model of the PSLT developed by the commercial finite element software, ABAQUS. The resultant microstructure in the samples as a result of large local shear strains and the extent of deformation were studied using SEM and a grid distortion technique, respectively. Mechanical property changes after the PSLT processing were characterized in samples of different geometry using a dedicated formulation based on the similarity theory. The micro shear punch tests allowed characterizing the gradient of the reinforcement in the radial direction of the samples.

Biodegradation and Medical Application of Microbial Poly(3-Hydroxybutyrate)

This review is designed to be a comprehensive source for biodegradable polymer: poly(3-hydroxybutyrate)—PHB research, including fundamental structure/property relationships and biodegradation kinetics for samples of different geometry. In addition to presenting the scientific framework for the advances in PHB research, this review focuses on applications of PHB in biomedicine and environment with a discussion on commercial applications and health/safety concerns for biodegradable materials.

Biodegradation and Medical Application of Microbial Poly(3-hydroxybutyrate)

This review is designed to be a comprehensive source for biodegradable polymer: poly(3-hydroxybutyrate) research, including fundamental structure/property relationships and biodegradation kinetics for samples of different geometry. In addition to presenting the scientific framework for the advances in PHB research, this review focuses on applications of PHB in biomedicine and environment with a discussion on commercial applications and health/safety concerns for biodegradable materials.

Vortex properties of mesoscopic superconducting samples

In this work we investigated theoretically the vortex properties of mesoscopic samples of different geometries, submitted to an external magnetic field. We use both London and Ginzburg–Landau theories and also solve the non-linear Time Dependent Ginzburg–Landau equations to obtain vortex configurations, equilibrium states and the spatial distribution of the superconducting electron density in a mesoscopic superconducting triangle and long prisms with square cross-section. For a mesoscopic triangle with the magnetic field applied perpendicularly to sample plane the vortex configurations were obtained by using Langevin dynamics simulations. In most of the configurations the vortices sit close to the corners, presenting twofold or three-fold symmetry. A study of different meta-stable configurations with same number of vortices is also presented. Next, by taking into account de Gennes boundary conditions via the extrapolation length, b, we study the properties of a mesoscopic superconducting square surrounded by different metallic materials and in the presence of an external magnetic field applied perpendicularly to the square surface. It is determined the b-limit for the occurrence of a single vortex in a mesoscopic square of area d 2 , for 4 ξ ( 0 ) ⩽ d ⩽ 10 ξ ( 0 ) .

Vortex lattice and matching fields for a long superconducting wire

We investigate the flux penetration patterns and matching fields of a long cylindrical wire of circular cross section in the presence of an external magnetic field. For this study we write the London theory for a long cylinder both for the mixed and Meissner states, with boundary conditions appropriate for this geometry. Using the Monte Carlo simulated annealing method, the free energy of the mixed state is minimized with respect to the vortex position and we obtain the ground state of the vortex lattice for $N=3$ up to 18 vortices. The free energy of the Meissner and mixed states provides expressions for the matching fields. We find that, as in the case of samples of different geometry, the finite-size effect provokes a delay on the vortex penetration and a vortex accumulation in the center of the sample. The vortex patterns obtained are in good agreement with experimental results.

Temperature independent relaxation of Landau domains in aluminium

We have measured the energy dissipationQ due to Landau domain movement in two aluminium samples of different geometries after a sweep of an external field fromB a >B c toB a =0 at different temperatures. We found a time dependent heat releaseQαt −α with 1≤α≤2 depending on the sample geometry. The time dependence is independent of temperature and sweep rate. Our observations indicate that this relaxation might be due to quantum creep of Landau domains.

Competition of bulk and surface processes in the kinetics of hydrogen and nitrogen release from metals into vacuum

Abstract A comprehensive description of the competition of bulk (diffusion, transition to an adsorbed state) and surface (recombination, desorption) processes in the kinetics of hydrogen and nitrogen evolution from metals into vacuum has been presented. General analytical dependences of the time behaviour of the mean, subsurface and surface concentrations have been derived for samples of different geometry. It has been found that the character of the evolution is determined unambiguously by the product of the mean concentration in the solution and the sample size, that is by the number of monolayers dissolved in the bulk. It is shown that there exists for each metal a characteristic critical number of dissolved monolayers above which the kinetics is controlled preferentially by the diffusion rate and below which by the recombination rate. The temperature dependences of this value multiplied by the sticking coefficient have been plotted enabling one to obtain a general picture of the position of the boundaries of the diffusional and kinetic regimes for several transition metals. Specific features of the kinetics of hydrogen and nitrogen evolution in systems with exo- and endothermal-type of solution are discussed.

Competition of bulk and surface processes in the kinetics of hydrogen and nitrogen evolution from metals into vacuum

A comprehensive description of the competition of bulk (diffusion, transition to an adsorbed state) and surface (recombination, desorption) processes in the kinetics of hydrogen and nitrogen evolution from metals into vacuum has been presented. General analytical dependences of the time behaviour of the mean, subsurface and surface concentrations have been derived for samples of different geometry. It has been found that the character of the evolution is determined unambiguously by the product of the mean concentration in the solution and the sample size, that is by the number of monolayers dissolved in the bulk. It is shown that there exists for each metal a characteristic critical number of dissolved monolayers above which the kinetics is controlled preferentially by the diffusion rate and below which by the recombination rate. The temperature dependences of this value multiplied by the sticking coefficient have been plotted enabling one to obtain a general picture of the position of the boundaries of the diffusional and kinetic regimes for several transition metals. Specific features of the kinetics of hydrogen and nitrogen evolution in systems with exo- and endothermal-type of solution are discussed.

Thermoelastic surface deformation—time evolution

A method is reported, which allows us to measure the dynamics of the surface thermoelastic deformations. We have obtained the time evolution of amplitudes of surface deformations induced by absorption of a laser beam in Plexiglas samples of different geometry. A qualitative discussion of the obtained results is made.

Laser beam induced current measurements of minority carrier diffusion length

Laser beam induced current (LBIC) measurement has been proposed as a technique for determining various semiconductor parameters, including minority carrier diffusion length. In this work, techniques for extracting values of bulk diffusion length from experimental LBIC curves are presented for both parallel and perpendicular barrier–beam geometries and for both thick and thin samples. Experimental tests of each technique compare diffusion length results obtained for samples of different geometries with each other, with confirmation of results by measuring the minority carrier lifetime by photoconductivity decay in samples cut from the same wafers and then calculating the diffusion length. The LBIC techniques presented in this paper are shown to allow practical and meaningful determination of diffusion length, and to have significant advantages over the electron beam induced current (EBIC) techniques from which they evolved.

Influence of edge currents in the quantum Hall effect of Wigner magneto-quantum crystals

The role of edge currents around electronic Wigner magneto-quantum crystals in quasi-two-dimensional space charge layers is discussed. Quantisation of angular momentum only allows stable lattices of hexagonal symmetry with integer ( nu =hnS/(eB)=1,2, . . .) and fractional filling degrees ( nu =p/3' with p=1,2 and l=1, 2, . . .) of the quantum levels. The influence of a liquid-like motion of the edge electrons yields a current at the crystal 'surface', which by its magnetic field widens the external field ranges for the existence of the equilibrium states and contributes additional structures in the transport phenomena, e.g. in the longitudinal and transverse voltages of strip samples or in the current measured on Corbino devices. A comprehensive explanation is attained for all structures observed so far on samples of different geometry and different electron concentration. The 2/5, 3/5, 2/7 and the equivalent effects may be shown to result from the quantisation of the edge currents, their frame moving with the Hall drift velocity, and therefore represent stationary transport effects, but no equilibrium states.

Effect of magnetic properties of a composite superconductor on the losses in a variable magnetic field: Part 3 collective interaction of turns

The results obtained in Parts 1 and 2 of this paper were for a solitary conductor in an external magnetic field. However, the magnetization of the other winding turns has a considerable effect on losses in a variable magnetic field. A theoretical treatment of the phenomena associated with the collective interaction of turns is presented. The experimental results obtained on samples of different geometry are in a good agreement with theory.

Negative differential resistance in (100) n-channel silicon inversion layers

Abstract A voltage controlled negative differential resistance (NDR) in n-channel MOSFETs of (100) orientation is investigated for lattice temperatures between 1.5 and 100 K in transverse magnetic fields up to 7 Tesla. By variation of the length of the pulses and by investigating samples of different geometry it is shown, that the NDR is not caused by lattice heating. Position and magnitude of the NDR depend substantially on the magnetic field. The observed effects can be explained by cooling of the hot carriers by the magnetic field.

An experimental verification of neutron multiple scattering calculations in vanadium

A method is described for experimentally measuring the neutron multiple scattering in four vanadium samples of different geometry by means of the polarization analysis technique. The spin-dependent scattering cross section of 51V provides a much more stringent test of multiple scattering than is possible by intensity measurements, and the experimental results are shown to be in excellent agreement with theoretical calculations of the multiple scattering carried out by a Monte-Carlo procedure.

Negative differential resistance in (100) n-channel silicon inversion layers

A voltage controlled negative differential resistance (NDR) in n-channel MOSFETs of (100) orientation is investigated for lattice temperatures between 1.5 and 100 K in transverse magnetic fields up to 7 Tesla. By variation of the length of the pulses and by investigating samples of different geometry it is shown, that the NDR is not caused by lattice heating. Position and magnitude of the NDR depend substantially on the magnetic field. The observed effects can be explained by cooling of the hot carriers by the magnetic field.