Showing papers on "Transverse plane published in 1995"

Light-polarization dynamics in surface-emitting semiconductor lasers.

Abstract: A four-level model which takes account of the polarization of the laser field by including the spin sublevels of the conduction and valence bands of a semiconductor allows us to introduce vector rate equations which account for the polarization degree of freedom of the laser emission. Analysis of these rate equations and their extension to include transverse degrees of freedom provides important physical insight into the nature of polarization instabilities in surface-emitting semiconductor lasers. In the absence of transverse effects the model predicts a marginally stable linearly polarized state. The type of dynamical response of the polarization degrees of freedom is linked to the relative time scale of spontaneous-emission and spin-relaxation processes. With transverse effects included, we predict the existence of stable transverse spatially homogeneous intensity outputs with arbitrary direction of linear polarization in the transverse plane. The stability of the off-axis emission solutions to long-wavelength perturbations is investigated and, in addition to an Eckhaus instability associated with a global phase, we predict a polarization instability associated with a relative phase of the complex field vector. The role of phase anisotropy in the laser cavity is explored close to threshold and we predict that it stabilizes two preferred orthogonal directions of polarization, which, however, are discriminated in their stability properties by transverse effects.

Full 2-D photonic bandgaps in silica/air structures

Abstract: Full 2-D photonic bandgaps are demonstrated for all polarisations in structures with refractive index contrast as small as that of silica and air. They occur for light propagating out of the transverse plane, with a longitudinal component of wave vector. A new type of optical fibre based on these structures is proposed.

Transverse Shear Along Myocardial Cleavage Planes Provides a Mechanism for Normal Systolic Wall Thickening

Abstract: Recent studies in humans and other species show that there is substantial transverse shear strain in the left ventricular myocardium, and others have shown transverse myocardial laminae separated by cleavage planes We proposed that cellular rearrangement based on shearing along myocardial cleavage planes could account for >50% of normal systolic wall thickening, since <50% can be explained by increases in myocyte diameter To test this hypothesis, we measured strains at two sites with different cleavage-plane anatomy in eight open-chest dogs Columns of radiopaque markers were implanted in the left ventricular anterior free wall and septum Markers were tracked with biplane cineradiography, and strains were quantified by using finite deformation techniques Hearts were perfusion-fixed with glutaraldehyde, and cleavage-plane orientations at the bead sites were measured in three orthogonal planes At subendocardial sites of the anterior left ventricular wall, where the cleavage planes approach the

Mixing and Penetration Studies of Sonic Jets in a Mach 2 Freestream

Abstract: A comparison of the penetration and mixing characteristics of three transverse/oblique injector configurations is presented. The three geometries studied include circular transverse, circular oblique, and elliptical transverse injectors, and the crossflow is at Mach 2. Planar Mie scattering images of three near-field flow planes produced substantial information about the flowfield created by each injector. In addition to global flowfield characteristics, the Mie scattering images provided transverse and lateral penetrations for each injector. Instantaneous and time-averaged information concerning the structural organization of the flowfields was obtained. Results demonstrate increasing jet penetration in the transverse direction with increasing jet-to-freestream momentum flux ratio. Penetration of the oblique jet is appreciably less in the near-field compared to the two transverse jets due to the reduced component of momentum in the transverse direction. The transverse elliptic jet appears to spread more quickly in the lateral direction than the other two jets, suggesting that some type of axis-switchin g phenomenon occurs. Large-scale structures at the interface between the jet and freestream fluids are shown for the two transversely oriented jets, while small-scale eddies are prominent in the oblique jet flowfield. Near-field mixing appears dominated by these eddies and the counter-rotating structures that develop in the streamwise direction.

Tracking and finite element analysis of stripe deformation in magnetic resonance tagging

Abstract: Magnetic resonance tissue tagging allows noninvasive in vivo measurement of soft tissue deformation. Planes of magnetic saturation are created, orthogonal to the imaging plane, which form dark lines (stripes) in the image. The authors describe a method for tracking stripe motion in the image plane, and show how this information can be incorporated into a finite element model of the underlying deformation. Human heart data were acquired from several imaging planes in different orientations and were combined using a deformable model of the left ventricle wall. Each tracked stripe point provided information on displacement orthogonal to the original tagging plane, i.e., a one-dimensional (1-D) constraint on the motion. Three-dimensional (3-D) motion and deformation was then reconstructed by fitting the model to the data constraints by linear least squares. The average root mean squared (rms) error between tracked stripe points and predicted model locations was 0.47 mm (n=3,100 points). In order to validate this method and quantify the errors involved, the authors applied it to images of a silicone gel phantom subjected to a known, well-controlled, 3-D deformation. The finite element strains obtained were compared to an analytic model of the deformation known to be accurate in the central axial plane of the phantom. The average rms errors were 6% in both the reconstructed shear strains and 16% in the reconstructed radial normal strain. >

Wood - The Internal Optimization of Trees

Abstract: Summary Trees are characterized by an optimum adaptation of their inner architecture to the loads and stresses which occur 1 The wood fibres in the tree rings are aligned with the force flow The shear between the fibres is minimized in that way 2 The wood rays provide the highest radial transverse strength where the risk of cleavage is greatest 3 The wood fibres are glued best by their “lignin chimneys” where the risk of longitudinal cleavage (“banana crack”) is greatest 4 Tangentially, the wood rays are compressed most by tangential growth stresses where the risk of “banana cracking” is greatest, ie where the spindle-shaped ray cross-sections are exposed to the greatest transverse tension Quintessence: The quality of wood is highest where the tree is exposed to the greatest risks and hazards, ie where it is subjected to the highest internal stresses The wood rays and fibres are relieved through growth stresses where the risk of failure is greatest It follows that growth stresses counterac

Self-focusing of plane dark solitons in nonlinear defocusing media

Abstract: We analyze a transverse instability of plane (quasi-one-dimensional) dark solitons in the framework of the two-dimensional nonlinear Schr\"odinger (NLS) equation for beam propagation in a defocusing nonlinear medium. We show that in the vicinity of the instability threshold the exponential growth of transverse perturbations is stabilized by nonlinearity and also by the radiation emitted from the plane dark soliton to the right and left. Dynamics of the transverse instability of the plane dark soliton of arbitrary amplitude is investigated analytically by means of the asymptotic technique, and also numerically by direct integration of the two-dimensional NLS equation. In particular we show that there exist generally three different scenarios of the instability dynamics, namely, (i) generation of a chain of two-dimensional ``gray'' solitons (anisotropic solitons of the Kadomtsev-Petviashvili, or KP1, equation) from the small-amplitude plane dark soliton, (ii) long-lived large-amplitude transverse oscillations of the plane dark soliton near the instability threshold, and finally, (iii) decay of the plane dark soliton into a chain of circular symmetric ``black'' solitons (optical vortices) of alternative topological charges. We estimate the region of the instability domain for the parameters of the soliton and perturbation where the instability of the plane dark soliton ends up in the formation of pairs of vortex and antivortex solitons.

Transverse fixation device for ensuring a rigid transverse connection between two rods of a spinal osteosynthesis system

Abstract: This device comprises two fixation elements (4), each consisting of a hook (4) designed so as to be able to cover a rigid transverse bar (3) in a sliding manner and equipped with means (9, 8) for locking on the bar (3); this hook is made up of a body (5) and at least one blade. This device forms a relatively simple transverse connection device which can be positioned quickly and which has great torsional and flexural strength.

Tibial osteotomy system

Abstract: A surgical kit for performing a tibial osteotomy is provided, comprising a pair of mounting pins for attaching, an osteotomy guide in a predetermined relation to a tibia; an osteotomy guide, comprising a transverse slot, defining a transverse cutting plane, adapted to receive and guide a transverse cutting blade for making a transverse cut into the tibia, and a plurality of oblique slots angularly offset from the transverse slot, each oblique slot defining an oblique cutting plane, adapted to receive and guide an oblique cutting blade for making a selected oblique cut into the tibia, wherein the intersection of each oblique cutting plane with the transverse cutting plane defines a wedge of bone which may be removed from the tibia. Also included with the surgical kit are a compression clamp adapted to apply compressive forces to a first portion of the tibia above the transverse cut and to a second portion of the tibia below the oblique cut to draw the first and second portions together, and a fixation plate adapted to hold the portions of the tibia together during healing. A method for performing an upper tibial osteotomy is also provided which employs the osteotomy surgical kit.

Intrinsic transverse momentum and the polarized Drell-Yan process.

Abstract: In this paper we study the cross section at leading order in 1/Q for polarized Drell-Yan scattering at measured lepton-pair transverse momentum QT. We find that for a hadron with spin 1/2 the quark content at leading order is described by six distribution functions for each flavor, which depend on both the lightcone momentum fraction x, and the quark transverse momentum k 2 . These functions are illustrated for a free-quark ensemble. The cross sections for both longitudinal and transverse polarizations are expressed in terms of convolution integrals over the distribution functions.

Local measurements of velocity fluctuations and diffusion coefficients for a granular material flow

Abstract: Measurements were made of two components of the average and fluctuating velocities, and of the local self-diffusion coefficients in a flow of granular material. The experiments were performed in a 1 m-high vertical channel with roughened sidewalls and with polished glass plates at the front and the back to create a two-dimensional flow. The particles used were glass spheres with a nominal diameter of 3 mm. The flows were high density and were characterized by the presence of long-duration frictional contacts between particles. The velocity measurements indicated that the flows consisted of a central uniform regime and a shear regime close to the walls. The fluctuating velocities in the transverse direction increased in magnitude from the centre towards the walls. A similar variation was not observed for the streamwise fluctuations. The self-diffusion coefficients showed a significant dependence on the fluctuating velocities and the shear rate. The velocity fluctuations were highly anistropic with the streamwise components being 2 to 2.5 times the transverse components. The self-diffusion coefficients for the streamwise direction were an order-of-magnitude higher than those for the transverse direction. The surface roughness of the particles led to a decrease in the self-diffusion coefficients.

Sub-100- mu m depth-resolved holographic imaging through scattering media in the near infrared.

Abstract: We discuss the compromise between depth and transverse spatial resolution for photorefractive holographic imaging through turbid media. Results from an optimized geometry for a 45°-cut rhodium-doped barium titanate photorefractive crystal are presented, demonstrating two-dimensional imaging through turbid media with both sub-100-μm depth and transverse spatial resolution.

Electrophysiology catheter with pre-curved circular tip

Abstract: An electrode catheter for mapping right sided supra-ventricular accessory electrical pathways comprises an elongated tubular catheter body and a tip portion which comprises a compound curve. The compound curve has a first bend and a second bend which forms a generally circular curve. The plane of the generally circular curve lies transverse to and preferably at an angle of about 30° to the axis of the catheter body. The generally circular curve portion of the tip portion carries a plurality of electrodes. A puller wire extends through the catheter body and into the tip portion, the distal end of the puller wire being fixedly attached to the distal end of the tip portion. A handle is provided at the proximal end of the catheter for controlling longitudinal movement of the puller wire relative to the catheter body. Proximal movement of the puller wire relative to the catheter body results in the angle of the first bend becoming more acute and a decrease in the diameter of the generally circular curve of the tip portion.

Semiclassical calculations of tunneling splitting in malonaldehyde

Abstract: We have devised a semiclassical procedure based on the Makri–Miller [J. Chem. Phys. 91, 4026 (1989)] model for calculating the eigenvalue splitting in many‐atom systems and have used it to calculate the ground‐state splitting in several isotopomers of malonaldehyde. A potential‐energy surface that includes all twenty‐one vibrational degrees of freedom was constructed based on the available theoretical and experimental information. The results for calculations in which all atoms are allowed full three‐dimensional motion are in good agreement with the experimentally measured values. Restricting the molecular motion to a plane leads to an increase in the splitting due to a decrease in the average height and width of the barrier to tunneling when the molecule is not allowed to vibrate transverse to the molecular plane. Low energy mode‐specific excitations were used to study the sensitivity of the splitting to the motions of heavy atoms. The results show that the heavy atom motions have significant influence o...

Filamentation and beam propagation in broad-area semiconductor lasers

Abstract: The spatio-temporal dynamics of broad-area semiconductor lasers is studied theoretically by numerically solving space-dependent coupled partial differential equations for the (complex) optical fields, the interband polarization and the density of charge carriers. The formation and longitudinal propagation of unstable transverse optical filamentary structures is analyzed in a model configuration for typical double-heterostructure broad-area lasers. Spectral and spatial holeburning in the carrier distributions is observed as a consequence of selective density depletion by the transverse laser modes. The transverse holeburning leads to complex spatio-temporal patterns. >

Vertebral instrumentation rod

Abstract: This rod comprises a first cylindrical part, being a lumbosacral part (6), which is rigid in all directions, a second part, being a dorsal part (7), which is rigid in a frontal plane, in order to prevent scoliosis, and flexible in a sagittal plane, and a dorsolumbar transition zone (8) connecting the lumbar and dorsal parts and profiled in a progressive manner so that its thickness in the sagittal plane diminishes progressively and its width in the frontal plane increases progressively: this profile is such that the second moment of area of the transition zone remains substantially constant over its entire length. The profile, thus defined, of the transition zone has the aim of avoiding, to a great extent, the risks of breaking due to the fatigue in this zone, resulting from the various movements of the patient in a chair, in particular the flexion/extension movements in a sagittal plane, promoted by the rectangular profile of the dorsal part of the rod.

Investigation of microwave π transitions in cesium beam clocks operated with U‐shaped H plane waveguide cavities

Abstract: In this article, we present the characteristics of the ΔF=±1, ΔmF=±1, π microwave transitions which appear in the response of cesium beam resonators operating with U‐shaped waveguide Ramsey cavities bent in the plane of the H field. Such resonances are due to the presence in the cavity of microwave magnetic induction perpendicular to the static field direction. It is shown that the π resonance feature is derived from a pure two‐level atomic system interacting with four spatially separated oscillating fields. Good agreement is found between experimental data and theoretical predictions when we take into account the actual transverse microwave field profile in the cavity obtained with tridimensional electromagnetic field computations.

One-particle and two-particle instability of coupled Luttinger liquids.

Abstract: It is shown that the Luttinger liquid is unstable to arbitrarily small transverse hopping. It becomes either a Fermi liquid or exhibits long-range order at zero temperature. The crossover temperatures below which either transverse coherent band motion or long-range order start to develop can be finite even when spin and charge velocities differ. Explicit scaling relations for the one-particle and two-particle crossover temperatures are derived in terms of transverse hopping amplitude, spin and charge velocities as well as anomalous exponents. The special case of infinite-range transverse hopping can be treated exactly and yields a Fermi liquid down to zero temperature, unless the anomalous exponent $\theta $ is larger than unity.

Equilibrium Displacement and Stress Distribution in a Two-Dimensional, Axially Moving Web Under Transverse Loading

Abstract: Von Karman nonlinear plate equations are modified to describe the motion of wide, axially moving web with small flexural stiffness under transverse loading. The model can represent a paper web or plastic sheet under some conditions. Closed-form solutions to two nonlinear, coupled equations governing the transverse displacement and stress function probably do not exist. The transverse forces arising from the bending stiffness are much smaller than those arising from the applied axial tension except near the edges of the web. This opens the possibility that boundary layer and singular perturbation theories can be used to model the bending forces near the edges of the web when determining the equilibrium solution and stress distribution. The present analysis is applied to two examples : (I) a web deflecting under its own uniformly distributed weight ; (II) a web deflecting under a transverse load whose distribution is described by the product of sine functions in the axial and width directions. Membrane theory and linear plate theory solutions are used to characterize the importance of the web deformation solutions.

Soft flexible catheter tip for use in angiography

Abstract: A plurality of regions of a first transverse rigidity are formed in the flexible tip portion (12) of a catheter having a second transverse rigidity along its length which is greater than the first transverse rigidity. The regions of the lesser first transverse rigidity are formed by areas of the catheter tip (12) having an average transverse cross-sectional area less than a transverse cross-sectional area of the remainder of the catheter apparatus. The plurality of first transverse rigidity regions are formed by a respective plurality of circumferential cutout regions (20-30) in the catheter tip (12).

Generalized BV diagrams for higher order transverse modes in planar vertical-cavity laser diodes

Abstract: We use a new class of complex dispersion characteristics to analyze threshold properties of gain-guided vertical-cavity lasers. The analysis gives a fundamental gain limit for single transverse mode oscillation. The general behavior of higher order transverse modes is described by rather universal diagrams that are useful as a guideline for practical device design. A comparison between gain- and index-guided devices shows differences in effective modal gains and wavelength separations between fundamental and neighboring higher order modes. For near threshold operation of gain-guided lasers, the suppression of higher transverse modes is generally improved for large mirror reflectivities. The discussion of real devices considers the important influence of the current induced parasitic temperature profile. >

A mass-produced flat multiple-beam load cell and scales incorporating it

Abstract: A flat, mass-produced, multiple-beam load cell made from a metal plate includes: a load receiving member with a transverse section (4) integral with a load receiving tongue (5); a clamping member (3) having a transverse section (7) and possibly a pair of clamping tongues (18); and two flexure beams (2) connecting the two transverse sections of the metal plate. When a load is applied to the load receiving tongue, the flexure beams bend into symmetrical double-cantilever S-shapes (14), and each pair of sensors (8 & 10, 9 & 11) mounted on the flexure beams produce electronic signals which are equal and opposite each other while rejecting the effect of lateral or eccentric loads. Also disclosed are low profile weighing scales incorporating such load cells.

Confined Columns under Eccentric Loading

Abstract: The characteristics of confined-concrete columns under strain gradient were examined. Twelve columns were tested under two different levels of end eccentricity. The test parameters included the arrangement, spacing, and volumetric ratio of confinement reinforcement. Columns with well-distributed longitudinal reinforcement, laterally supported by closely spaced transverse reinforcement, showed extremely ductile behavior, developing inelastic displacements exceeding 4% of the drift ratio without a significant loss of strength. Those with a low volumetric ratio and wide spacing of transverse steel developed strength decay immediately after the peak load. A confined concrete model, developed on the basis of column tests under concentric loading, was used to compute analytical moment-curvature relationships of the critical column section. The analytical relationships are compared with those recorded experimentally, for columns with different eccentricity of loading and parameters of confinement. The comparison...

Numerical simulation of intense helical electron beams with the calculation of the velocity distribution functions

Abstract: The method of calculation of intense helical electron beams which allows to find the distribution function of electrons with respect to their transverse (oscillatory) and longitudinal velocities is developed. The initial velocity distribution function can be arbitrary. The data obtained in numerical simulation and experimental measurements for beams with various topologies are compared. The evolution of the transverse velocity distribution function with the beam current growth is traced. It is found that the transformation of the velocity distribution function may indicate a possible instability in a real beam.

Transverse diffusion of light in Faraday-active media.

Abstract: A new effect is considered in multiple scattering of light in a disordered dielectric medium exposed to an external magnetic field: a transverse diffusive current. This current is proportional to the imaginary, antisymmetric part of the dielectric function of the effective medium.

Two-dimensional crystals and quasicrystals in nonlinear optics.

Abstract: We report the observation of two-dimensional periodic and quasiperiodic structures in the transverse profile of an optical beam circulating in a loop which contains a nonlinear medium. The symmetries of the patterns are imposed by an image rotation within the loop. We propose a simple model which shows the existence of two unstable bands of transverse wave vectors. Close to threshold, the predictions of the model are qualitatively and quantitatively confirmed by the experiment.

Transverse mode analysis of a laser beam by near- and far-field intensity measurements.

Abstract: A quantitative measurement of laser-beam quality can be performed by determination of the presence of multiple transverse modes of the laser oscillator and by calculation of their power content. Along this line of argument, we discuss a new approach that, starting from near-field and far-field intensity measurements, can evaluate the complex excitation coefficients of the transverse modes in a laser beam. The exploitation of near-field measurements sharply improves the performances of the technique in those cases in which only far-field measurements are used. The validity of the method is confirmed by several accurate numerical simulations and by some experimental results relative to a multimode Q-switched Nd:YAG laser.