Transverse Geometry Research Articles

A study of slotline leaky-wave antennas

The results of an experimental investigation of several millimeter-wave slotline leaky-wave antennas at 94 GHz are given. The experimental results show how variations in the transverse slot geometry affect the radiation pattern. Additionally, slot geometry variations also change the polarization performance of the antenna. The narrow transverse slot array was more sensitive to a perpendicularly (E/sub y/-E/sub z/) polarized electric field than the wide slot case. Also, the change in the effective phase constant along the antenna with changing slot dimensions caused a noticeable shift in the angle of the main beams. However, the beamwidths for all cases remained about the same. A simple model is presented to explain this. For designing an antenna of this form, the effective phase constant, beta , can be approximately determined using a numerical analysis of the uniform slot problem. Given beta and the operating frequency and the scanning ranges, the element spacing can be determined. The attenuation constant does not change much when the transverse slot widths are varied. If greater sensitivity to an E/sub y/-E/sub z/ polarized wave is desired, the transverse slots should be narrow. >

Magneto-optical phenomena in magnetic fluids: The influence of orientation of anisotropic scatterers

The optical anisotropy, induced in a magnetic fluid by a magnetic field, is usually explained invoking either orientation by the applied magnetic field of anisotropic scatterers already present in the fluid, or formation of such scatterers through field-induced aggregation of the constituent particles. In this paper we will discuss the orientation of anisotropic scatterers, within a general framework due to Van de Hulst. The case where the optical properties of an individual scatter centre can be represented by a diagonal second-rank polarisability tensor has been discussed in the literature. In this paper, we will show that incorporation of off-diagonal elements, such as due to the permanent magnetic moment of the scatterer, will lead to a new description of the Faraday rotation and the circular dichroism, while the well-known results for linear birefringence and linear dichroism in the transverse geometry are not affected.

A possibility of sharp tuning in a linear transversally inhomogeneous cochlear model

Considerable sharpening of basilar membrane frequency selectivity and simultaneous decreasing of phase lag can be obtained in a linear (‘passive’) hydromechanical three-dimensional cochlear model, if the transverse geometry of the cochlea is taken into account. Both the tuning qualities, Q 10, and the phase angles at CF of some transversally inhomogeneous linear models can be set into the range of experimental data [Sellick et al. (1983) Hear. Res. 10, 93–108; Robles et al. (1986) J. Acoust. Soc. Am. 80, 1364–1379.] The calculations are developed on the base of WKB-approximation. The integral coefficients of eiconal equation are the transversally averaged means of basilar membrane surface mass density and stiffness: ∝ b(x) o μ(x,y)η 2(y) dy, ∝ b(x) o D(x,y)( δ 2η δy 2 ) 2 dy , where η(y) is the major eigenfunction of basilar membrane cross-sectional vibrations. The classical Ritz's method is used for calculation of the cross-sectional eigenfunctions. The size and the form of cochlear cross-section are found also to alter the tuning. The rapid increase of the model response towards the peak is due to that damping remains negligible up to the peak position. where the imaginery part of the wave-number begins to increase sharply.

Thermal Expansion of Three-Phase Composite Materials

Exact expressions are found for overall thermal expansion coefficients of a composite medium consisting of three perfectly-bonded transversely isotropic phases of cylindrical shape and arbitrary transverse geometry. The results show that macroscopic thermal expansion coefficients depend only on the thermoelastic constants and volume fractions of the phases, and on the overall compliance. The derivation is based on a decomposition procedure which indicates that spatially uniform elastic strain fields can be created in certain heterogeneous media by superposition of uniform phase thermal strains with local strains caused by piecewise uniform stress fields, which are in equilibrium with prescribed surface tractions. The procedure also allows evaluation of thermal stress fields in the aggregate in terms of known local fields caused by axisymmetric overall stresses. Finally, averages of local fields are found with the help of known mechanical stress and strain concentration factors.

DEPENDENCY OF THE TENSILE MODULUS ON TRANSVERSE DIMENSIONS, WATER POTENTIAL, AND CELL NUMBER OF PITH PARENCHYMA

Uniaxial tensile tests of solid and hollow cylindrical plugs of pith parenchyma from potato tubers indicate the tensile modulus of elasticity, E, can vary significantly as a function of tissue transverse area and water potential. E increases from 1.2 to 19 MPa as ψw changes from ‐1.4 to ‐0.4 MPa. E increases from 5 to 19 MPa as transverse area of solid tissue sample increases from 0.2 to 2.5 cm2. Variations in E accompanying changes in transverse area appear to be related to cell number along the radii of plugs. Hollow cylindrical plugs for which wall thickness is maintained but total tissue area is changed show constant values of E. It is suggested that shear stresses within tissue samples influence E and are dependent upon cell number and tissue water content. Material with these properties would be a “poor choice” for constructing plant organs experiencing repeated stress and periodic dehydration. However, ground tissue may act as a buffer against localized ovaling of stem and leaf cross sections under loading.

Quantum beamstrahlung from ribbon pulses.

In this paper the high-energy expansion introduced in our previous paper is used to describe the problem of beamstrahlung due to an extended pulse with an elliptical cross section of arbitrary eccentricity. We show that the transverse geometry of the pulse enters in a remarkably simple scaling manner. This case is of interest because the radiative energy loss can be markedly reduced while simultaneously keeping a fixed luminosity if the beam pulses are very thin in one transverse direction, i.e., shaped like ribbons. Effects of other types of beam shaping are briefly discussed and the physics of the process is emphasized.

Superconducting critical current of Nb-Ti wire with anisotropic defect structure. II.

Anisotropy of the global pinning force Fp was inductively measured for Nb-49 wt. %Ti monofilamentary wire with highly anisotropic pinning structures in magnetic field parallel and transverse to the wire axis. According to the recent models of Evetts and Plummer [Proceedings of the International Symposium on Flux Pinning and Electromagnetic Properties in Superconductors (Matsukuma, Fukuoka, 1985)] and of Dew-Hughes [Philos. Mag. B 55, 459 (1987)], the morphology of pins is assumed to determine the flux pinning characteristic by the occurrence of plastic shear of the fluxoid lattice. The saturation characteristic of Fp as in Nb3 Sn is expected to be obtained if the field is parallel to the wire axis, while the nonsaturation one, as in commercial Nb-Ti, is expected in the transverse geometry. However, the results obtained show similar nonsaturation characteristics in both geometries and are contradictory to expectation. These results suggest that the pinning characteristic is mainly determined by the pinning parameters as the elementary pinning force and the pin concentration, but is not affected by the simple morphology of pinning centers.

THE AETIOLOGY OF SPINAL DEFORMITIES

There are two types of spinal deformity, lordosis and kyphosis, and they are mutually exclusive at the same site. Lordosis is rotationally unstable and buckles to the side with growth and spinal flexion, producing scoliosis and changes in transverse plane geometry as secondary phenomena. Kyphosis is a uniplanar deformity arising behind the axis of spinal column rotation and it does not buckle. Spinal balance in the sagittal plane is delicate and in the normal child during adolescence both idiopathic scoliosis and idiopathic kyphosis can easily develop. The development and progression of spinal deformities can be explained in biological and mechanical terms. Any condition in which the critical load to the spine is reduced will favour the production and progression of a spinal deformity. Neuromuscular factors in idiopathic scoliosis are additive and not causative.

Electron spin polarization analyzers for use with synchrotron radiation

The measurement of the spin polarization of photoelectrons emitted from a magnetic material is discussed. An important consideration is the acceptance phase space of the spin analyzer relative to the phase space of the photoemitted electrons to be measured. Other considerations include the magnetization direction relative to the extracted beam and whether the measurements are angle integrated or angle resolved. In the longitudinal geometry where the magnetization is normal to the sample surface and along the extracted photoelectron beam, conservation of canonical angular momentum adds an additional magnetic term to the beam emittance which is absent when the magnetization is in the sample plane and transverse to the extracted beam. For angle resolved measurements in the transverse geometry, the advantages of a new, low-energy (∼ 100 eV) spin analyzer which is easily movable, compact and efficient are discussed. Different spin analyzers are described and compared, and an analysis of their application to different spin polarized photoemission measurement configurations is given.

Optical anisotropy of Tb3+ ions in a garnet structure

Low-temperature measurements of the absorption spectra of linearly polarized light are performed by Tb3+ ions of paramagnetic Tb3Ga5O12 and magnetically ordered Tb3Fe5O12 crystals in the optical transition domains7F6−7F0,7F6−7F1 in a transverse magnetization geometry. It is shown that at T = 100 K an abrupt anisotropy of the Tb3+ ion absorption spectra is observed in a terbium ferrite-garnet depending on the orientation of the magnetization vector I relative to the crystallgraphic axes, where the strongest changes in energetic level structure are noted at 18–25° angles between I and the [110] axis. Reduction of the temperature to 30 K results in isotropization of the spectra, which is associated with a high local anisotropy of the magnetic moment of the terbium ion in the ferrite-garnet structure at low temperatures. Dispersion dependences are obtained for the absorption index κ and the contribution to the refractive index n' due to the Tb3+ optical transitions being examined.

Electron-beam-pumped lasing in epitaxial ZnSe thin films

We have observed lasing in ZnSe thin films grown epitaxially on (100) GaAs substrates under pulsed electron beam excitation in the transverse geometry. Films were grown using both molecular beam epitaxy (MBE) and organometallic vapor phase epitaxy (OMVPE). These films have been characterized using low-temperature photoluminescence (PL) and electrical transport measurements, as well as optical and electron microscopy. Lasing thresholds as low as 1 A/cm2 have been determined for MBE-grown films (films thickness 4 μm, accelerating voltage 40 kV, temperature 16 K, pulse length 100 ns). This threshold rose with increasing temperature, but lasing could be observed at temperatures as high as 295 K. In spite of many similarities between the PL and electrical properties of the MBE and OMVPE films, our measurements on the latter films indicate that the lasing thresholds are somewhat higher in these materials (≥2x), but that the differences diminish as the electron accelerating voltage increases. Correlations between the lasing thresholds and other measured properties of the two materials are discussed. We find that the higher thresholds in the OMVPE films are due to increased cavity losses resulting from scattering by the textured film surfaces.

Electron beam pumped lasing in ZnSe/ZnSSe superlattice structuresn grown by molecular-beam epitaxy

We report the first operation of molecular-beam epitaxy (MBE) grown ZnSe/ZnSxSe1−x superlattice electron beam pumped lasers in the temperature range 100–300 K and the first room-temperature operation of MBE grown ZnSe on GaAs transverse geometry electron beam pumped lasers. Threshold current densities of 2.5 A/cm2 at 100 K were achieved by both devices. At room temperature, threshold current was 5 A/cm2 for the ZnSe devices and 12 A/cm2 for the superlattice.

FLEXURAL RIGIDITY OF CHIVE AND ITS RESPONSE TO WATER POTENTIAL

The biomechanical relationship between the ability of a plant organ to resist bending and the extent to which tissues are hydrated is illustrated for the cylindrical leaves of chive (Allium schoenoprasnum var. schoenoprasnum L.). The flexural rigidity (EI), which measures the ability to resist bending, is maximum when leaves are fully turgid and decreases monotonically as a function of water potential (r2 = 0.99). Dehydration results in a reduction in the elastic modulus (E) of leaves. Reductions in E are correlated with geometric distortion in the transverse geometry of leaves which influences their second moment of inertia (I). The traditional theory of elastic stability (developed on the basis of the mechanical behavior of nonbiological systems) is shown to be inadequate to distinguish the behavior of E as plant organs geometrically distort during dehydration. This inadequacy results from the violation of a principal assumption made by the theory (= uniform cross‐sectional geometry). A derivation is presented that accommodates the localized geometric distortions in cylindrical plant organs and permits a valid estimate of reductions in E as tissues dehydrate. Based on this derivation, the Young's modulus of chive leaves just before mechanical failure due to buckling is shown to be less than 50% of that calculated for fully turgid leaves.

Stimulated Brillouin scattering parasitics in large optical windows

The growth of optical radiation, scattered transverse to the pump axis by stimulated Brillouin scattering (SBS) in optical windows, is considered. Basic equations are presented, and an analytic expression that determines the parasitic buildup time is derived for a transverse SBS geometry. Losses suffered by the scattered optical radiation are included in a bulk-loss term. Calculations are performed for fused-silica windows and compared with a numerical model. This parasitic process may affect the design of laser systems that will generate multinanosecond, multikilojoule, narrow-band pulses in the ultraviolet region.

Muon Spin Precession in the Hexagonal Antiferromagnet FeSn

Muon spin precession spectra are observed in transverse field geometry at all temperatures, including the antiferromagnetic state. This unique behaviour is a consequence of the chemical and magnetic structure of FeSn. The observed precession signals contain two components, one at a frequency corresponding to the external field and, in an intermediate temperature range, a second one corresponding to a field at the muon of 0.21 T extrapolated to 0 K.

Magneto-optical transverse Kerr effect in a film-substrate system

The problem of electromagnetic reflection at an oblique angle of incidence in a system consisting of an isotropic ambient, a magnetic film and a thick magnetic substrate is studied. The magnetizations in both the film and substrate are assumed normal to the plane of incidence (transverse geometry). The results are expressed in terms of the reflection matrix. The solution includes the conditions for guided wave propagation in the system. As a special case of the general formulae the reflection matrix in a system consisting of a uniaxial film and a uniaxial substrate optical axes of which are oriented normal to the plane of incidence are obtained.

CSEM-Steel Hybrid Wiggler/Undulator Magnetic Field Studies

Current design of permanent magnet wiggler/ undulators use either pure charge sheet equivalent material (CSEM) or the CSEM-Steel hybrid configuration. Hybrid configurations offer higher field strength at small gaps, field distributions dominated by the pole surfaces and pole tuning. Nominal performance of the hybrid is generally predicted using a 2-D magnetic design code neglecting transverse geometry. Magnetic measurements are presented showing transverse configuration influence on performance, from a combination of models using CSEMs, REC (Hc = 9.2 kOe) and NdFe (Hc = 10.7 kOe), different pole widths and end configurations. Results show peak field improvement using NdFe in place of REC in identical models, gap peak field decrease with pole width decrease (all results less than computed 2-D fields), transverse gap field distributions, and importance of CSEM material overhanging the poles in the transverse direction for highest gap fields.

Characteristic Classes of Transversely Homogeneous Foliations

The foliations studied in this paper have transverse geometry modeled on a homogeneous space $G/H$ with transition functions given by the left action of $G$. It is shown that the characteristic classes for such a foliation are determined by invariants of a certain flat bundle. This is used to prove that when $G$ is semisimple, the characteristic classes are rigid under smooth deformations, extending work of Brooks, Goldman and Heitsch.

Long bone torsion: II. A combined experimental and computational method for determining an effective shear modulus.

A technique is established which allows an effective torsional shear modulus to be determined for long bones, while remaining nondestructive to whole bone specimens. Strain gages are bonded to the diaphysis of the bone. Strains are then recorded under pure torsional loads. Theoretical stress predictions are combined with experimental strain recordings to arrive at a modulus value. Shear modulus calculations for four canine radii are reported using theoretical stress predictions from circular, elliptical and finite element models of the transverse bone geometry. The effective shear modulus, obtained from an average of the shear moduli determined at strain gage locations, serves to average the heterogeneous shear modulus distribution over the cross section. The shear modulus obtained is that associated with the "circumferential" direction in transverse planes.

On an Enhancement of a Critical Current of Superconductors in s Longitudinal Magnetic Field

An expression of the torque density on torsionally sheared fluxoids is derived and the torque balance is investigated for the force-free state in superconductors placed in a longitudinal magnetic field. The critical current in the force-free geometry is determined by the moment of pinning forces which prevent fluxoids from rotating to reduce the torsional shear. The ratio of this critical current density to that in the transverse field geometry is estimated for specimens pinned strongly. And the enhancement for weak pinning is also discussed qualitatively.