Hemispherical Pattern Research Articles

The seismological picture of the inner core: structure and rotation

Abstract This paper presents a review of recent results concerning the structure and the rotation of the inner core, as inferred from seismological observations. We first focus on the apparent hemispherical pattern of the inner core structure, observed in both the anisotropy and the heterogeneity of the uppermost layers, whereas isotropic velocities seem to be homogeneous in a broad wavelength domain. Then we present results on the radial variations of the attenuation and its possible anisotropy, for which viscoelasticity and wave scattering provide complementary explanations. Linked to these results is a discussion about the detection of the PKJKP phase, which propagates as S-wave inside the inner core. Finally, the seismological observations of a possible inner core rotation are discussed; recent results seem to favour rotation rates below 0.2° yr −1 .

THE ROLE OF VEGETATION DYNAMICS IN CHOCTAWHATCHEE SAND PINE INVASION OF LONGLEAF PINE FORESTS

The expansion of Choctawhatchee sand pine (Pinus clausa) into longleaf pine forests (Pinus palustris) has been widespread on the Florida Panhandle since the early 1900s. This study examines the population-level processes of this sand pine invasion. Expansion of sand pine started by 1920, but rapidly increased in the 1940s. Population establishment and growth in invasive stands has been rapid, with establishment of many sand pine pioneer individuals followed by rapid infilling as these individuals reached reproductive maturity. Both noninvasive and invasive stands had numerous sand pine seedlings and saplings. Sand pine will likely persist in these communities in the near future. Analyses of hemispherical canopy photographs and regeneration patterns illustrate the ability of sand pine to establish under a variety of light conditions. Radial growth analysis of incremental tree cores highlights the importance of episodic wind disturbances in maintaining these sand pine populations. [Key words: sand pine, longleaf pine, Pinus clausa, Florida, pine invasion, Pinus palustris.]

Structure of Si atomic chains grown on the Si/Cu(110)c(2×2)surface alloy

The surface atomic structure of Si atomic chains grown on the Si/Cu(110) surface alloy has been investigated by a combination of different experimental techniques. For Si coverages below 0.5 monolayers the low-energy electron diffraction (LEED) pattern shows a $c(2\ifmmode\times\else\texttimes\fi{}2)$ reconstruction, corresponding to the formation of a surface alloy. Upon further Si deposition, the LEED pattern evolves toward a (2\ifmmode\times\else\texttimes\fi{}2)-like structure with streaks along the [001] direction. Scanning tunneling microscopy (STM) images show the presence of linear atomic Si chains on top of the surface alloy layer. We present an atomic model for the surface termination based on the STM images and on the main atomic directions of the (2\ifmmode\times\else\texttimes\fi{}2)-like phase found by a simple analysis of the $\mathrm{Si}2p$ full hemispherical x-ray photoelectron diffraction patterns. This model consists of linear atomic Si chains running along the [110] surface direction formed on top of the surface alloy. The chains present small (2\ifmmode\times\else\texttimes\fi{}2) domains, which are not in phase with respect to each other. After heating the (2\ifmmode\times\else\texttimes\fi{}2)-like phase up to 250 \ifmmode^\circ\else\textdegree\fi{}C, a quasi-(3\ifmmode\times\else\texttimes\fi{}4) structure is developed. This structure consists of similar chains exhibiting a different periodicity. Furthermore, we have used synchrotron radiation photoemission (x-ray and ultraviolet photoemission spectroscopy) to gather information about the electronic structure of the atomic chains.

電解コンデンサ用高純度アルミニウム箔の直流エッチング挙動に及ぼす表面形態の影響

The pit growth behavior of high purity aluminum foil in electrolytic capacitors used for DC etching in a hot HCl solution has been studied using grained foil. Hemispherical patterns with diameters of about 1∼3μm and cubic patterns with widths and lengths of 7∼15μm were formed by electrolytic grainings in HNO3 and HNO3/HCl solutions, respectively. By using cubic or hemispherical patterns, uniform distributions of pits were obtained for a surface that was untreated and one that was pre-treated during the early stage of DC etching. Tunnel pits were distributed most uniformly on hemispherical patterns grained at 1C/cm2. Surface dissolution occurred as clusters of tunnel pits at the intersection of hemispherical patterns above a graining charge of 10C/cm2. For cubic patterns grained at up to 30C/cm2, the distribution of tunnel pits became uniform with an increase in the charge for graining. As a result, grainings affected the expansion of the surface area as measured by capacitance after DC etching. Cubic patterns are more effective for an increase in capacitance than hemispherical patterns.

X-Ray Photoelectron Diffraction in the Backscattering Geometry: A Key to Adsorption Sites and Bond Lengths at Surfaces

For a well-characterized s2 3 1d-1O adsorbate phase of oxygen on rhodium (111) we have identified photoelectron interference fringes in the backscattering geometry for O 1s adsorbate emission at 723 eV kinetic energy. Although these features are weak, they show up as characteristic rings covering large regions of the full hemispherical photoelectron diffraction pattern. They represent the situation of a simple two-atom electron interferometer and yield directly the most relevant information on the adsorbate geometry such as the adsorption site, the adsorbate-substrate bond length, and the bond angle. [S0031-9007(98)06936-1]

STRUCTURAL DETERMINATION OF THE Si/Cu(110) INTERFACE BY PHOTOELECTRON DIFFRACTION

Deposition of 0.5 Si monolayer (ML) on a Cu (110) surface at room temperature (RT) leads to the formation of a c(2×2) LEED pattern. In order to find out the surface atomic structure of this ordered phase, X-ray photoelectron diffraction (XPD) azimuthal scans at different photon energies and full hemispherical XPD patterns of the Si 2 p core level have been measured using both synchrotron radiation and a laboratory source. We present an atomic model for the surface structure based on the examination of forward scattering and first order interference XPD features. Refinement of the structural parameters was achieved by performing single scattering cluster (SSC) calculations. In the proposed model Si atoms replace Cu atoms at the surface along the [Formula: see text] atomic rows.

A chemical state resolved x-ray photoelectron diffraction study: Initial stages in diamondlike carbon film deposition

The structural sensitivity of x-ray photoelectron diffraction is greatly enhanced by the acquisition of a full hemispherical diffraction pattern of chemically shifted core levels. Complex systems can be studied resolving the local order per element and per chemical environment. This technique is applied to study the earliest stages of hydrogenated diamondlike carbon film deposition on Si(001). Effects of the sample temperature and ion dose on the structure of deposited layers are discussed.

Boundary-layer microphone

First Page

Characterization of Cd1-yZnyTe(111) and Hg1-xCdxTe(111) real surfaces by x-ray photoelectron diffraction.

The surfaces of ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Zn}}_{\mathit{y}}$Te(111) substrates and of lattice-matched ${\mathrm{Hg}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Cd}}_{\mathit{x}}$Te epilayers have been investigated with use of x-ray photoelectron diffraction (XPD) to assess their crystalline properties, in particular termination, reconstruction, and relaxation, as well as structural imperfections induced by various etch treatments. In this context, we also explore the general analytical potential of XPD for the characterization of the surface structures of compounds. The azimuthal- and polar-angle-resolved photoemission recorded as a complete hemispherical pattern for the core levels of Cd 3${\mathit{d}}_{5/2}$, Te 3${\mathit{d}}_{5/2}$, and Hg 4${\mathit{f}}_{7/2}$ photoelectrons clearly revealed the phenomenon of photoelectron diffraction for the investigated surfaces. Modeling results indicate that the structure observed in the diffraction patterns can be interpreted simply in terms of zeroth-order interference or forward-direction focusing. Thus XPD is a powerful technique for imaging atoms in real space, and provides a complete description of the symmetry of the three-dimensional crystal lattice within the volume analyzed. The terminations of the examined (111)A and (111)B surfaces are easily differentiated and are found surprisingly to be almost perfect. We find no evidence for any reconstruction or relaxation of the (111) surfaces of ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Zn}}_{\mathit{y}}$Te and ${\mathrm{Hg}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Cd}}_{\mathit{x}}$Te.

Generation of nearly hemispherical and high gain azimuthally symmetric patterns with printed circuit antennas

Pattern shaping techniques are discussed for printed circuit antennas such as microstrip dipoles and slot elements. Crossed printed circuit dipoles or a combination of a printed circuit dipole and a slot are employed. It is demonstrated that with the proper choice of substrate or substrate-superstrate parameters it is possible to generate: 1) nearly hemispherical patterns, 2) high-gain azimuthally symmetric patterns, and 3) nearly \sec \theta patterns.

Microfabrication of hemispherical shells for laser fusion targets

Hemispherical shells for use in laser fusion targets have been fabricated by using reactive ion etching to produce a hemispherical original master pattern from a selected glass microsphere. Then micromolding techniques using silicone rubber and positive photoresist are employed to produce a large number of final molds which are coated with the shell material (parylene or copper). The flat background film is removed by a number of etching techniques and the final molds are dissolved to give free standing hemispherical shells. The shells were found to replicate the hemispherical section of the original microsphere within the measurement accuracy of about 3%. The advantages and current limitations of this technique are also discussed.

Industrial sewing machine noise

A sewing machine manufacturer came to the College of Engineering of the University of Hartford asking for assistance in quieting their latest model of high-speed industrial sewing machines. When the machine was installed in the anechoic chamber, initial investigations using a precision sound-level meter and weighting networks showed the sound level generally to be in the 90-dB range on the A scale. Measurements were taken at 3 ft. from the unit. Noticeably lower levels were observed in the low-frequency range. Further investigation using a real-time analyzer confirmed the initial observations. Readings were taken around the machine in a hemispherical pattern while the machine was in an anechoic chamber. All data observed on the real-time analyzer was recorded on paper charts for detailed analysis. Testing is incomplete at this point, but predominant frequencies have focused attention on certain drive mechanisms. As extensive redesign is not possible at this stage of the machine's development, only minor modifications will be allowed by the manufacturer. Probe microphones and further frequency analysis will be used to determine if redesign of external linkages will be helpful or not. All possible improvements will be outlined and submitted to the designer for future consideration. These improvements will be reported in this paper. [Student Research Project.]

Hemispherical power gain pattern measurements at 7.5 GHz

A technique is described for measuring the complete hemispherical power-gain radiation pattern of a 2.44-m diameter paraboloidal reflector antenna mounted atop a mobile small earth terminal operating at 7.5 GHz. Antenna power-gain data were measured versus azimuth and elevation angles with the earth terminal centered on a heavy-duty turntable flush with test range ground.Test site illumination was achieved with airborne transmitting antennas. Conventional and statistical power-gain patterns are presented for left-hand circular polarization and cross polarization. Results indicate that similar systems cannot rely upon orthogonal polarization to provide isolation or compatibility beyond the angular region of the main lobe.

The Mechanism and Efficiency of Sound Production in Mole Crickets

ABSTRACT Sound production in the mole crickets Gryllotalpa vineae and G. gryllotalpa is compared with that in Gryllus campestris. In all species action of the plectrum of the left forewing on the file or pars stridens of the right wing causes the harp areas of both wings to vibrate in phase with each other. As the lateral and dorsal fields of the wing are coupled flexibly, the dorsal field resonates freely. The available muscular power of G. vineae is about 3·5 mW., of G. gryllotalpa about 1 mW., and of Gryllus about 1·2 mW. The mesothoracic musculature of Gryllotalpa is fairly similar to that of Gryllus. The calling song of G. vineae has a fundamental frequency of 3·5 kHz, a pulse length of 8 msec, and a pulse interval of 14 msec, at 16°C. The song is very pure with a second harmonic of —26 dB. Simulations of the song made with modulated oscillators are of similar purity; the song can be regarded as a modulated pure note. The sound distribution has been measured, and from the area of an isobar plot and calculation of the mean power of each pulse, the total mean sound power output is 1·2 mW. and the peak power 3 mW. The efficiency of conversion of muscular to acoustic power is about 35%. G. vineae builds a double-mouthed horn-shaped burrow for singing. This contains a bulb which probably tunes the horn to act as a resistive load to the vibrating wings. The double mouths act as a line source with directional properties which concentrate the sound in a disk above the length of the burrow. The probable advantage of a directed sound output in attracting mates is considered; the disk-shaped pattern will be better than a hemispherical pattern of similar power. G. gryllotalpa also builds a hom, but this is larger than that of G. vineae and the song frequency is far lower, at 1·6 kHz. Although the sound power is far lower, about 2·5 × 10−5 W., the horn appears to act as a resistive load to the wings. Gryllus produces only about 6 × 10−5 W. at 30°C. This is attributed to the small size and hence low radiation resistance of the wings. Estimates are made of inertial losses that occur in sound production and these are shown to account for a substantial part of the mechanical power in the systems of both G. vineae and Gryllus.