Rigid body translation in the (\bar 211) twin boundary in silicon

The rigid body translation accompanying a ( 11) twin boundary in silicon has been studied by transmission electron microscopy. From a detailed analysis of theα-type fringe systems in the 111, 311 and 2 0 common reflections, the following translation vector is deduced: [011], which is equivalent to [411] in the other crystal element. A slight deviation of this orientation is possible.     

Stability analysis of a low energy vortex configuration

Recent work using the London theory of anisotropic superconductivity has shown that, for small values ofB and large values of the anisotropy, a lattice of vortex lines parallel to is not necessarily the minimum energy configuration. When is not parallel to a symmetry axis, the “double lattice”—a lattice of lines parallel to plus a lattice of lines parallel to —can have a lower energy. The question arises, however, of whether some other configuration can have a yet lower energy. To investigate this question, we perform a stability analysis of the double lattice. We find that its energy can indeed be lowered by certain deformations of the vortex lines.     

Anisotropic flow and fracture in beryl [Be3Al2(SiO3)6]

Flow and fracture resulting from Vickers indentation testing on {0 0 0 1} and {10 0 } planar orientations have been examined. Flow characterized by indent shape differentiation was analysed to belong to the slip system with planes of the types { 10 0} and {11 0}. The ensuing fracture paths were resolved to propagate along {1 0 0} and {1 1 } cleavage planes whileK _c values obtained for them were 0.196 and 0.248 MPam^1/2, respectively.     

Détermination des contraintes maximale et minimale en valeur algébrique résultant d'un effort normal et d'un moment de flexion dans une section quelconque d'un profil, à partir de trois mesures de déformations superficielles

Résumé Les contraintes maximale et minimale en valeur algébrique engendrées dans une section quelconque d'un profil, par un effort normal et un moment de flexion quelconque , peuvent être déterminées à partir de trois mesures de déformations superficielles effectuées au niveau de cette section. De plus, il est possible de calculer l'effort normal et le moment de flexion ainsi que ses composantesM _GY ,M _GZ sur les axes principaux d'inertie , et de définir la position de l'axe neutre de flexion ainsi que celle de l'axe neutre de flexion et d'effort normal.

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Summary The determination of the maximum and minimum stresses in algebraic value generated in an arbitrary section of a profile by a normal force and an arbitrary bending moment is an important problem that frequently arises. Before showing that 3 measurements of surface deformations effected on the level of the section studied suffice completely to solve this problem some theoretical considerations are recalled. These concern the establishment of the formula giving the bending stress. For this we can attach to the section either arbitrary central axes or the main central inertia axes; this latter possibility leading to a simpler formula. The formulae needed for the determination of the maximum and minimum stresses due to and are then established, for arbitrary coordinates of measurement points. Simpler formulae may be obtained when it is possible practically to choose simple ratios between the coordinates. Next it is shown that one can compute not only but and its componentsM _GY ,M _GZ , on the main intertia axes , and determine the position of the neutral bending axis as well as that of the neutral bending and normal force axis. Finally, the practical utilization of the method is indicated and a concrete case treated.

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Eine Erweiterung der Analogie zwischen der Gasdynamik und Flachwasserströmungen auf rotierende Systeme mit konservativen Massenkräften

Zusammenfassung Die bekannte Analogie zwischen den Theorien reibungsfreier flacher Wasserströmung und der isentropen idealen Gasdynamik wird im zweidimensionalen instationären Fall durch Zulassung rotierender Bezugssysteme und konservativer Massenkraftfelder erweitert. Damit kann man in einem rotierenden Wasserbehälter mit geeignet gestaltetem Boden u. a. atmosphärische Probleme näherungsweise studieren.

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Summary The well known analogy of the theories of nonviscous shallow water flows and isentropic ideal gasdynamics is generalized in the two-dimensional nonstationary case to apply to rotating systems with conservative body forces. This enables one, in particular, to simulate atmospheric problems by use of a rotating water tank with suitable bottom shape.

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Liste der verwendeten Symbole spezifische Wärme des Gases bei konstantem Druck - Fr in (2) definierteFroude-Zahl - Gravitationsbeschleunigung - H ortsabhängige Ruhetiefe bei Drehung des Wassers als starrer Körper - Druck - atmosphärischer Druck auf der freien Wasseroberfläche - Bezugslänge - Zeit - absolute Temperatur - Geschwindigkeitskomponenten parallel zu den Achsen - kartesische Koordinaten - durch Abweichung von der Drehung des Wassers als starrer Körper verursachte orts-und zeitabhängige Änderung der Wassertiefe - Verhältnis der spezifischen Wärmen des Gases - zu gehörende Wellenlänge - Dichte - Winkelgeschwindigkeit Mit 1 Textabbildung1 Boden des Wasserbehälters 2 freie Wasseroberfläche II freie Wasseroberfläche bei einer Drehung des Wassers als starrer KörperEin oberer Querstrich gibt an, daß die betreffende Größe eine physikalische Dimension hat; Größen ohne einen solchen Querstrich sind dimensionsfrei.     

Laminar thermal boundary layer on a continuous accelerated sheet extruded in an ambient fluid

Summary Exact boundary layer similarity solutions are developed for flow, friction and heat transfer on a continuously accelerated sheet extruded in an ambient fluid of a lower temperature.Melt-spinning, polymer and glass industries and the cooling of extruded metallic plates are practical applications of this problem.Results for skin-friction and heat-transfer coefficients are given. Larger acceleration is accompanied by larger skin-friction and heat-transfer coefficients. Rapid cooling of the sheet is accompanied by a larger Nusselt number.Nomenclature sheet width - c dimensionless constant - c _f local skin friction coefficient - F dimensionless transformed stream function - G dimensionless transformed temperature - local heat transfer coefficient - fluid thermal conductivity - length of deformation zone - m exponent of surface speed variation - q exponent of surface temperature variation - T dimensionless temperature - sheet surface temperature - solidification temperature - ambient temperature - sheet thickness - u velocity component along the sheet - u _s sheet surface velocity - wind up velocity - v velocity component normal to the sheet - x dimensionless coordinate along the sheet - y dimensionless coordinate normal to the sheet - Nu Nusselt number, - Pr Prandtl number, - Re Reynolds number, - =Re^–0.5 - dimensionless similarity coordinate - dynamic viscosity - kinematic viscosity - fluid mass density - sheet mass density - wall shear stress - dimensionless stream function With 3 Figures     

Textures in3He-A: Magnetic deformation in a narrow slab

A variational technique is used to analyze the deformed texture of superfluid³He-A in a narrow slab subject to a perpendicular magnetic field. Specific predictions are made for the anisotropy parameters and , averaged across the width.     

On primitive and free roots in a finite field

In this paper them-dimensional extension of the finite field of orderq is investigated from an algebraic point of view. Looking upon the additive group as a cyclic module over the principal ideal domain , we introduce a new family of polynomials over which are the additive analogues of the cyclotomic polynomials. Two methods to calculate these polynomials are proposed. In combination with algorithms to compute cyclotomic polynomials, we obtain, at least theoretically, a method to determine all elements in of a given additive and multiplicative order; especially the generators of both cyclic structures, namely the generators of primitive normal bases in over , are characterized as the set of roots of a certain polynomial over .     

Fermi surface and extended van Hove singularity in the non-cuprate layered perovskite superconductor Sr2RuO4

With high-resolution (22 meV) angle-resolved photoemission spectroscopy, the Fermi surface of the first copper free layered-perovskite superconductor, Sr₂RuO₄, was determined. We observed three bands to cross the Fermi energy in qualitative agreement with LDA band structure calculations; one electron-like surface encircling the point in the projected Brillouin zone, and two hole-like surfaces around the point. The most striking aspect of the measurements is the observation of an extended van Hove singularity. It is located 17 meV below the Fermi energy and extends around the point for about 0.2 Å^–1 along both the — — and the — — directions.These observations demonstrate that van Hove singularities near the Fermi surface are a more generic feature of layered oxides, and call for a clarification of their exact role in oxide superconductivity.We are grateful to D. Singh for making available his band structure calculations. D. H. Lu thanks the VW Foundation for financial support.     

Superconducting critical currents in Nb-Cu-Nb sandwiches

A preparation method is presented for Nb-Cu-Nb sandwiches for proximity-effect measurements with a large junction area of about 150×150 µm and intermediate Cu layers of thicknesses between 0.2 and 1.5 µm. The thickness of the Nb layers is about 150 µm. These samples are used to study the dependence of the superconducting critical currentI _c through the Cu layer as a function of a magnetic field applied parallel and perpendicular to the layers. Furthermore, the effects of flux lines trapped in the Nb layers on the critical currentsI _c andI _c are investigated. The results are used to discuss the influence of proximity effects in microcomposite superconductors.     

Grain growth behaviour of the Al-Cu eutectic alloy during superplastic deformation

Grain growth behaviour of the Al-Cu eutectic alloy was investigated as a function of strain (ε), strain rate and deformation temperature (T) over = 10⁻² s⁻¹ and T=400 to 540°C. The grain size increases with increase in strain and temperature. Upon deformation to a fixed strain, the grain growth is generally seen to be more at lower strain rates. The rates of overall grain growth and due to deformation alone , however, increase with increasing strain rate according to and , respectively. The increase in the grain growth rate with strain rate is attributed primarily to the shorter time involved at higher strain rate for reaching a fixed strain. The activation energy for grain growth under superplastic conditions is estimated to be 79 kJ mol⁻¹.     

The fluctuation-imposed limit for temperature measurement

In experimental sciences, random processes often place a fundamental limit on the achievable measurement resolution. A well known example is the Johnson noise voltage across a resistor. In this paper, we describe observations of the spontaneous transfer of heat in two equilibrium systems: one consisting of a thermometer linked to a reservoir, the other consisting of two thermometers connected to each other and linked to a reservoir for the purpose of temperature stabilization. In the second system, we find anti-correlations between the temperature fluctuations of the two thermometers at intermediate frequencies. We also find that the low frequency temperature noise density of the thermometers, in units of , is given by , whereR is the thermal resistance of the link between the thermometer and the reservoir. This implies that for noise reduction purposes,R is the only available engineering parameter to adjust. In a recent thermometer design, we have reduced R to achieve a low frequency temperature noise density of 5×10⁻¹¹ at 2.18 K.     

Lattice dynamics,thermal expansion,and bulk modulus of ruthenium

The lattice dynamics, third-order elastic (TOE) constants, and the temperature variation of the volume Grüneisen function of ruthenium have been calculated using the nearest neighbor central interaction model for hexagonal metals proposed by Srinivasan and Ramji Rao. The TOE constants have been employed to calculate the low-temperature limit of the lattice thermal expansion, the Anderson-Grüneisen (AG) parameter , and the second Grüneisen constantq of ruthenium. has the value 2.79 for ruthenium. The high-temperature limit has the value 3.31, which agrees well with the experimental value 3.25 obtained from thermal expansion and specific heat data of ruthenium. Anderson's theory has been used to explain the temperature dependence of the bulk modulus of ruthenium up to 923 K and has been compared with the experimental values obtained from the elastic constant data of Fisher and Dever. The variation of the lattice parameters of ruthenium with hydrostatic pressure up to 400 kbar has been calculated from its TOE constant data using the extrapolation formula of Thurston and has been compared with the experimental results of Clendenen and Drickamer. The fit is remarkably good.     

Crack detection by the electric method: Uniqueness and~approximation

Let U be a bounded domain in the boundary ∂ U of which is a closed nonself-intersecting curve. Let ω be a hole (a crack) in the interior of U the boundary of which is a closed nonself-intersecting curve. Let U and ω be star-shaped. It is shown that the problem of finding a harmonic function u and its domain , subject to given Cauchy conditions on an open subset of ∂ U and to the condition ∂ u/∂n=0 on ∂ω has at most one solution. This uniqueness result shows that an insulating crack (e.g. one made up of air) can be identified by the electric method. The problem of determining ∂ω is an ill-posed problem; it is here regularized using finite dimensional approximations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal expansion and bulk modulus of cobalt

The ten third-order elastic (TOE) constants of hexagonal cobalt, which has nearly the idealc/a value, have been evaluated using the nearest-neighbor central interaction model for hexagonal materials proposed by Ramji Rao and Srinivasan. These TOE constants have been employed to evaluate the low-temperature limit of the thermal expansion, the Anderson-Grüneisen (AG) parameter , and the second Grüneisen constantq of cobalt. has the value 2.08 for cobalt. The temperature variation of the volume Grüneisen gamma of cobalt has been calculated on this model. The high-temperature limit has the value 2.13, which agrees well with the experimental value obtained from thermal expansion and specific heat data of cobalt. Anderson's theory has been used to explain the temperature dependence of the bulk modulus of cobalt and compared with the experimental values obtained from the elastic constant data of Fisher and Dever. The calculatedB _s values agree with the experimental values to within 1%.     

Transmission electron microscope study of a directionally solidified Cu-MgCu2 eutectic

The crystallography and the interface structure of a unidirectionally solidified Cu-MgCu₂ eutectic alloy have been examined by transmission electron microscopy. The microstructure of the eutectic was found to be lamellar and regularly interrupted by faults. The preference of the particular orientation relationship could not be explained by relative atomic densities of the planes comprising the interface. Based on the defect contrast observed and extinction distance calculations, it is suggested that the fine array of defects observed at the interface may be characterized as steps with step vectors parallel to or Dislocations were also observed at the interface but they were rarely regular.     

Collective-mode spectroscopy of textures in superfluid3He-B

A phenomenological theory for the propagation of the real squashing modes in superfluid³He-B is presented. This allows one to calculate the splitting of the real squashing (rsq) mode spectrum caused by the combined effects of magnetic field, dispersion, and texture in the experimentally important range of magnetic fields from 0 to 10³ Gauss. This serves to provide a tool for the rsq-mode spectroscopy of the -textures in³He-B. In particular, a new gyrosonic effect is suggested: the intensity of the rsq modes generated in textures depends on the sense of rotation—even when the axis of rotation coincides with the direction of the ultrasound propagation .     

HREM study of atomic image of single crystal indium phosphide

This paper reports some experimental results of high resolution electron microscopy (HREM) studies on single crystal indium phosphide (InP) along the [0 0 1] zone axis. Using 400 kV electrons, with defocus value about 46.0 nm, the optimum conditions for structure imaging for both In and P atoms were found to be about 26.0 nm. Decreasing the specimen thickness to about 15.0 nm, only atomic images of P remain; increasing the specimen thickness to about 37.0 nm, only atomic images of In remain. These experimental results are in good agreement with computer simulation. It was also observed that for bent crystal deviating from the [0 0 1] axis, the bright spots, corresponding to In and P atomic columns in high resolution structure imaging, are elongated at a deviation angle equal to 0.18 degrees, the two bright spots are connected together along the direction of the [1 1 0] zone axis. This phenomenon is also confirmed by computer simulation. In the experiment, a pair of dislocation waves were observed with apparent Burgers vectors of and while the actual Burgers vectors may be and .     

Hole Density in Charge Stripes and Effect of Next-Nearest-Neighbor Transfer

By applying a variational Monte Carlo method to the two-dimensional t-J model, a couple of properties of striped states are studied. In the charge domain walls vertical (or horizontal) to the lattice (VDW), the hole density is favorable in energy similarly for 0.5 , whereas in the diagonal domain walls (DDW) the stable hole density is limited to = 1. Negative next-nearest-neighbor transfer (t/t < 0) further stabilizes VDW with = 0.5 and DDW with = 1 against the -wave superconducting state.