Samples Of Various Shapes Research Articles

Development of an atomic force microscope closed fluid cell for tribological investigations of large samples in chemically aggressive environments

Many atomic force microscopes (AFM) are nowadays equipped with closed fluid cells. Most of these closed fluid cells have small volume, limiting the maximum sample size, and, furthermore, do not allow for investigations in chemically aggressive environments such as solvents. The closed fluid cell for MFP-3D, the atomic force microscope from Asylum Research, Santa Barbara, CA, has a glass base and is mainly intended for investigations of flat transparent biological samples. Starting from the MFP-3D closed fluid cell, a fluid cell tailored for investigations in tribologically relevant environments, e.g. at extreme mechanical and chemical conditions which may vary with time, was developed. Samples of various shapes and sizes can thus be investigated in controlled environments, be they fluid (e.g. solvents) or gaseous (e.g. corrosive gases). First results of AFM nanotribology experiments using this fluid cell are presented. Among the systems of interest are additives diluted in solvents adsorbing to surfaces and spreading and persistence of ionic liquids on tribologically stressed surfaces.

Topological magnetic irreversibility in superconducting Pb samples of various shapes

The magnetic-field dependence of the magnetization of cylinders, disks, and spheres of pure type-I superconducting lead was investigated by means of isothermal measurements of first magnetization curves and hysteresis cycles. Depending on the geometry of the sample and the direction and intensity of the applied magnetic field, the intermediate state exhibits different irreversible features that become particularly highlighted in minor hysteresis cycles. The irreversibility is noticeably observed in cylinders and disks only when the magnetic field is parallel to the axis of revolution and is very subtle in spheres. When the magnetic field decreases from the normal state, the irreversibility appears at a temperature-dependent value whose distance to the thermodynamic critical field depends on the sample geometry. The irreversible features in the disks are altered when they are submitted to an annealing process. These results agree well with very recent high-resolution magneto-optical experiments in similar materials that were interpreted in terms of transitions between different topological structures for the flux configuration in the intermediate state. A discussion of the relative role of geometrical barriers for flux entry and exit and pinning effects as responsible for the magnetic irreversibility is given.

Equilibrium Topology of the Intermediate State in Type-I Superconductors of Different Shapes

A high-resolution magneto-optical technique was used to analyze flux patterns in the intermediate state of bulk Pb samples of various shapes - cones, hemispheres, and discs. Combined with the measurements of macroscopic magnetization, these results allowed studying the effect of bulk pinning and geometric barrier on the equilibrium structure of the intermediate state. Zero-bulk pinning discs and slabs show hysteretic behavior due to topological hysteresis - flux tubes on penetration and lamellae on flux exit. (Hemi)spheres and cones do not have a geometric barrier and show no hysteresis with flux tubes dominating the intermediate field region in both regimes. It is concluded that flux tubes represent the equilibrium topology of the intermediate state. Real-time video is available in the EPAPS Document No. E-PRLTAO-98-024726..

English

The IEEE standard on piezoelectricity recommends methods to determine the coefficientsof piezoelectric ceramics and the sizes of the samples to be used. A method to determine thedifference between the actual coefficients and the coefficients determined using the IEEE standardis presented. The difference or error for samples of various shapes and sizes is presented. Theseerrors and manufacturing considerations are used to make recommendations of the actual sizesof piezoceramics in various shapes to be used for material characterisation. Often, the IEEEstandard cannot be used to determine the coefficients of piezoceramics used in underwatertransducers and other devices because of their shapes and sizes. Radially polarised tubesand axially polarised rings used in hydrophones and projectors, respectively, are theexamples. A method to determine some of the complex coefficients of tubes used for qualitycontrol during production is presented. Finally, an analytical model that can be used todevelop a similar method for rings is presented. Several numerical results are presented toillustrate the methods.

Homogeneity of Ceramics: Correlation with Molding Method and Geometrical Parameters of Articles

The effect of the method of molding an intermediate ceramic article on its homogeneity is investigated considering samples of various shapes. A correlation is established between the degree of inhomogeneity of an intermediate article and its geometrical characteristics and molding conditions.

Comparison of sizing small particles using different technologies

Two of the most widely used methods in sizing particulate materials are the electrical sensing zone method (ESZ) and the laser diffraction (LD). In order to deduce size information from a measurement, it is assumed in the LD technology that the particles are spheres. For real industrial materials, only rarely are the particles spherical. The effects of non-sphericity on different technologies vary, causing discrepancies in results and bias from the true characteristics of the sample. Applications in many fields require information about the shape of the particles in addition to their size. Recently, dynamic image analysis (DIA) has been shown to be able to provide both size and shape information of particulate materials. DIA is not subject to restrictions of the spherical assumption and, therefore, provides a means to study the effect of shape in the results obtained using LD and ESZ. In this study, samples of various shapes were characterized using the three technologies (LD, ESZ, and DIA). Laser diffraction yielded progressively larger mean sizes as well as broader distributions as the shape of the particles deviates more and more from that of a sphere. The ESZ and DIA experiments, on the other hand, produced compatible results much less affected by particle shape. The study suggests that DIA is a powerful tool in characterizing nonspherical particles and that caution needs to be taken when evaluating the sizing results of nonspherical particles using laser diffraction.

Magnetoelastic Acoustic Emission in Ferromagnetic Materials. I. Effect of Crystal Anisotropy

The paper considers the relation between the parameters of magnetoelastic acoustic emission (MAE) on one side and the magnitude of longitudinal magnetostriction and the behavior of magnetic domain structure on the other, i.e., effects of irreducible displacements of 90° (71° and 109°) domain walls when the magnetization is aligned with various crystal axes in crystals of siliceous iron and nickel. The MAE parameters are controlled by processes of reshaping of magnetic domains, therefore they are highly susceptible to the crystallographic orientation of the material. In samples of various shapes (strips and disks), a linear relation between the MAE parameters and the resulting magnetostriction in the region of low fields (where domain walls are displaced) was detected, but there is no linear relation in the region of higher fields, where the role of reversible and irreversible processes of magnetization rotation is greater.

Space-charge relaxation in perovskites.

We report a dielectric anomaly in several perovskites at intermediate frequencies 10\ensuremath{\le}f\ensuremath{\le}${10}^{7}$ Hz in the temperature range 400 \ifmmode^\circ\else\textdegree\fi{}C \ensuremath{\le}T\ensuremath{\le}800 \ifmmode^\circ\else\textdegree\fi{}C. We have found this dielectric maximum in more than 100 samples of various shapes and textures. This anomaly is shown to arise from a Debye dielectric dispersion that slows down following an Arrhenius law. We have established a link between this dielectric relaxation and the conductivity. We propose that it can be achieved through a space-charge model that quantitatively agrees with the experimental results in the lower temperature range.

Magnetically induced texturing during the sintering of strontium hexaferrite (abstract)

The hexaferrite SrO⋅6Fe2O3 exhibits pronounced ferrimagnetic anisotropy at room temperature, with the direction of easy magnetization lying parallel to the c axis of its hexagonal crystal structure.1–3 This magnetic anisotropy is used to produce highly aligned permanent magnets, by the application of a magnetic field during processing at room temperature. Since this material exhibits paramagnetic anisotropy at temperatures above 470 °C, it is possible that preferred orientation textures can be produced when samples of various shapes are sintered in a magnetic field4 at temperatures between 1150 and 1250 °C. The crystal structure, texture and microstructure of samples of strontium hexaferrite prepared in this manner have been determined by x-ray diffractometry and scanning electron microscopy. The significance of the observed textures is evaluated in terms of the anisotropy of the room temperature ferrimagnetic properties.

Fast inductive method for determination of macroscopic critical current density in bulk high-T c superconductors

Method for determination of j c based on detection of the penetration of low frequency magnetic field into bulk sample of high-T c superconductor at fixed temperature is described. Key instrument of the apparatus is a phase-sensitive detector. Applicability of the method on samples of various shapes is discussed. Main advantage of the method is simplicity of evaluation procedure.

Modelling the process of moisture absorption in three dimensions by wood samples of various shapes: cubic, parallelepipedic

Modelling the process of absorption of moisture by wood samples of various shapes and dimensions: cube and parallelepipedes, has been studied. The mathematical model is based on numerical method with finite differences, and takes into account all the facts: the external resistance with the coefficient of moisture transfer at the atmosphere-wood interface, the internal resistance with the diffusion of moisture within the wood. The problem is rather complex, because the rate of diffusion varies with the direction chosen in the wood, and because of the concentration-dependent diffusivities. Not only the model is able to obtain the kinetics of absorption of moisture in good agreement with experiments done with samples of various shapes, but it is also capable of calculating the profiles of concentration of moisture developed within the sample, and so affording a further insingt on the process of moisture absorption.

A numerical model to describe freezing of foods when supercooling occurs

A universal numerical model for freezing of food materials is proposed. This model is applicable to semi-infinite and finite cases, covering the effects of supercooling and the temperature-dependence of the fraction of frozen water present. To describe supercooling, a three-step freezing model is proposed. Theoretical predictions agree well with experimental results for samples of various shapes and compositions. Duration of supercooling, the only variable which should be determined experimentally, was related statistically to coolant temperature.

Influence of the size factor on the thermal shock resistance of ceramic samples

The cracking of brittle samples having suffered thermal shocks may be calculated by using the thermoelastic theory. This theory leads to a size effect, which is not always verified by experiments. The use of acoustic methods of characterization, for samples of various shapes and sizes, shows the size effect, but the experimental ΔTc values are greater than the calculated ones. This discrepancy must be due both to an overestimation of the A coefficient and an underestimation of the R parameter.

Semi-empirical γ-ray peak efficiency determination including self-absorption correction based on numerical integration

A method of γ-ray efficiency determination for extended (plane or bulk) samples based on numerical integration of point source efficiency is studied. The proposed method is widely applicable to samples of various shapes and materials. The geometrical factor in the peak efficiency can easily be corrected for by simply changing the integration region, and γ-ray self-absorption is also corrected by the absorption coefficient for the sample matrix.

The Relation of Force to Sample Dimensions in Objective Measurement of Tenderness of Poultry Meat

SUMMARY: Relations between maximum shear resistance and cross‐sectional dimensions were established for cooked turkey meat samples of various shapes and sizes with a Warner‐Bratzler type shearing device mounted in an lnstron tensile tester. The resistance to shear was proportional to the equivalent diameter raised to a power of about 1.2, over a wide range of sizes, shapes and intrinsic toughness. Degree of compaction before shearing was significantly correlated (r= 0.65, significant at 0.1% level) with the force at first failure per unit of equivalent diameter, and the compaction naturally increased with increasing intrinsic toughness. These data will permit comparison of shear force measurements from meat samples of different sizes and shapes.

Critical Field of Thin Superconducting Shapes

Considerations of the thermodynamics pertaining to the critical field of small superconducting samples of various shapes results in an explicit relation for the ratio of the critical field of small samples to that of bulk in terms of the magnetic moment. The magnetic moment has been calculated using Miller's modification of the Bardeen-Cooper-Schrieffer kernel which includes mean free path. The critical-field ratios of various shapes in decreasing order are sphere, cylinder in parallel field, cylinder in transverse field, and plate in parallel field. The findings are compatible with the fact that dislocations (cylinder like) may be the filaments responsible for hard superconductivity. Under certain conditions the filaments could be numerous and large enough for an appreciable fraction of the sample to appear superconducting in a specific heat measurement. The size of the filaments would also account for the lack of latent heat observed in hard superconductors. Because of the relative orientation of dislocations with respect to the applied field, not all dislocations will serve equally as filaments, thus explaining the current density vs critical-field curve and accounting for an anisotropic critical field when there is a preferred orientation of dislocations.

Quantometric Determination of Trace Impurities and Alloying Elements in Lead Alloy.

Co-operative investigations of quantometric determination of trace impurities and alloying elements in Pb-Sb-Cu alloy have been carried out by Furukawa Electric Co., Yokohama Works and the Kawasaki Branch of Industrial Research Institute of Kanagawa Prefecture, by means of ARL's Industrial Research Quantometer. Point-to-plane methods have been developed for the determination of Ni, As, Sn, Bi, Ag, Cu, and Sb with an accuracy of the order of 3 per cent. High sensitivity and good precision are obtained with overdamped discharge (L 440μH, C 20μF, R 50Ω, V 1, 000V). It is found that briquette samples are very suitable to eliminate possible segregation and make possible to analyse samples of various shapes and sizes.