Lateral Coordinates Research Articles

Minisubbands in electron excitation spectra of layered short-coherence-length superconductors.

Quasiparticle excitation spectra of short-coherence-length layered superconductors ($\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{S}$) are considered as-suming a periodic alternation of the superconducting order parameter $\ensuremath{\Delta}(x)$ versus the lateral coordinate $x$ in the $c$ direction. The found self-consistent solution suggests that the electron-hole Andreev scattering in such a periodic $\ensuremath{\Delta}(x)$ causes the appearance of minisubbands in the electron spectrum of $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{S}$, in a "clean" limit manifested as periodic spikes in the density of electron states at energies ${E}_{n}=(2n+1){\ensuremath{\Delta}}_{0}$ (${\ensuremath{\Delta}}_{0}$ is the energy gap amplitude; $n$ is a natural number).

Analyses of multi-irradiation film for system alignments in stereotactic radiotherapy (SRT) and radiosurgery (SRS)

In stereotactic radiosurgery, a seven-irradiation film was used to define any discrepancy between the beam and target centres. A mathematical model based on the linac alignment and target set-up was developed to diagnose the discrepancies of the seven-irradiation film between the beam and simulation target centres. From the measured data of the multi-irradiation film, this mathematical model leads to five parameters in seven equations. Twin computer codes were employed to solve the five parameters from the seven equations. By feeding the discrepancy data into the two computer codes, the sources of the target-to-beam discrepancy were revealed. From these decoded sources, the target coordinates were adjusted and then the seven-irradiation film procedure was repeated. This discrepancy thus obtained was found to be drastically reduced. Some decoded parameters were consistently verified by direct measurements. This demonstrates that the present mathematical model and computer code do reveal the causes of the target-to-beam misalignment and gantry sag. In a further effort to test the feasibility of the mathematical model and the computer codes, the target's lateral coordinate was deliberately offset by 1.5 mm and then another seven-irradiation film was taken. By inserting these discrepancies into the computer codes, it was found that the deviation was consistent with the intentional offset. In addition, the mathematical model and computer codes are applicable to any multi-irradiation technique.

Dissociative Adsorption of O2 on Cu(110) and Cu(100): Three-Dimensional Quantum Dynamics Studies

The dynamics of dissociative chemisorption of oxygen on Cu(110) and Cu(100) has been studied using a time-dependent quantum wave-packet approach. Dissociation probabilities for O2 on both (110) and (100) surfaces of copper are calculated for ground state as well as rovibrationally excited oxygen molecules. The present calculation simulates O2 dissociation on nascent copper surfaces with no consideration for surface reconstruction. The dynamics calculation is based on a flat-surface model in which three molecular degrees of freedom are explicitly included while the lateral coordinates of the molecule are neglected. The interaction potential energy surface (PES) for the dynamics calculation is constructed using the LEPS (London−Erying−Polyni−Sato) PES form with potential parameters fitted to some available experimental and theoretical data. The barrier of the LEPS PES for oxygen dissociation on copper is 0.11 eV for Cu(110) and 0.08 eV for Cu(100). Relatively speaking, the saddle point of the O2/Cu(110) PES is located near the entrance channel, while that of the O2/Cu(100) is near the product channel. This feature is primarily responsible for the difference in calculated dissociation probabilities of oxygen on two surfaces. Specifically, the dissociation probability of O2 on Cu(110) is large and less sensitive to the vibrational excitation of the molecule, while that of O2 on Cu(100) is much smaller and more sensitive to vibrational excitation of the molecule.

Quantum adsorption dynamics of a diatomic molecule on surface: Four-dimensional fixed-site model for H2 on Cu(111)

We presented a detailed quantum dynamics study for dissociative adsorption of H2 at different sites of Cu(111) surface to investigate the effect of surface corrugation and site specificity. The theoretical study employed a four-dimensional (4-D) ‘‘fixed-site’’ model, in which the lateral coordinates (X,Y) of the center of mass of the diatom are fixed at the impact site, but the remaining four degrees of freedom are explicitly treated in quantum calculations. The inclusion of the azimuthal angle φ in the present 4-D model is a significant step forward in theoretical studies beyond the 3-D ‘‘flat surface’’ model. This 4-D ‘‘fixed-site’’ model allows us to investigate explicitly the local corrugation effect that was not possible using the 3-D flat-surface model. We incorporated the latest ab initio data of Hammer et al. in constructing the LEPS potential energy surface, which gives the lowest dissociation barrier over the bridge site. 4-D dynamics calculations are performed in the present study to mimic a normal incidence of H2 at three symmetric sites on Cu(111): bridge, atop, and center sites with the corresponding rotation symmetries. Our results show that a hydrogen impact at a high symmetry site (six-fold atop site) shows little corrugation effect while impact at low symmetry site (two-fold bridge site) shows a large corrugation effect. In particular, our calculation shows that the inclusion of surface corrugation preserves the strong rotational orientation effect observed in flat-surface model calculations. The effect of homonuclear symmetry persists at high symmetry atop site, and to a lesser degree at a low symmetry bridge site. The contour plot of the wavefunction in the current 4-D model shows explicitly that hydrogen atoms following the dissociation of H2 over the bridge site do not settle at the neighboring center site, but migrate to the next available center site. Our study demonstrated that the 4-D fixed-site model is very useful in investigating surface corrugation and molecule site specificity in model-surface reactions.

Three-coordinate measurement of an object surface with a combined two-wavelength and two-source phase-shifting speckle interferometer

In a two-wavelength phase-shifting speckle interferometer for object contouring one usually obtains only the height coordinate of the object surface which is parallel to the viewing direction (here denoted as z-coordinate). In order to measure the lateral surface coordinates x and y by the same technique the light source is shifted in two directions (denoted as u and v) perpendicular to the optical axis. Two additional phase maps of parallel fringes are generated which are then used to assign the lateral coordinates x and y to the corresponding pixels of the camera. All the other advantages of two-wavelength interferometry remain unaffected.

Development of Shuttle Type AUV “ALBAC” and Sea Trials for Oceanographic Measurement

The ALBAC designed by the authors and constructed in 1992 is a prototype of shuttle type autonomous underwater vehicles. The ALBAC was developed for the oceanographic measurement of water column on the way and from the seabed.The vehicle does not have a propeller thruster but moves aside by gliding. To carry out the mission, the software includes three simple fuzzy controllers for longitudinal and lateral motion. The longitudinal motion controller displaces the longitudinal coordinate of the location of the center of gravity (C. G.) and controls the gliding angle, respectively of the vehicle. Two lateral motion controllers also displace the lateral coordinate of C. G. and control azimuth and yaw rate. The parameters of the fuzzy rules were optimized by using the Evolution Strategies on the simulator, and examined based on the motion data of every trial. 300-meter depth sea trials were successfully conducted in April of 1995 at the Suruga Bay of Japan.Consequently, the ALBAC is highly reliable and can be easily operated to carry out the mission to measure the profile of scientific data.

Minimally Invasive Neurosurgery Using CRW-3 Stereotaxy

The Cosman-Roberts-Wells (CRW-3) scanner independent stereotactic system is a recent arc-radius design developed from the Brown-Roberts-Wells system. The results of 74 supratentorial non-basal tumor suspect cases treated with this second generation computed tomography (CT) guided stereotactic apparatus are presented. Using a simple stereotactic target classification coupled with biopsy, trephine or mini-craniotomy, it has been possible to biopsy, excise and develop new strategies using microneurosurgical techniques with extremely low morbidity.

Ordering of amorphous silicon during solid-phase epitaxy studied by scanning tunneling microscopy.

The early stages of silicon solid-phase epitaxy (SPE) on the Si(111) surface are studied by scanning tunneling microscopy (STM). It is shown that an amorphous layer with thickness around two bilayers deposited on the silicon surface transforms in a polycrystalline layer with extremely small grain size (about 2--3 nm) after heating to 430 \ifmmode^\circ\else\textdegree\fi{}C. The atomic-resolution STM imaging of such a disordered surface allows us to extract lateral coordinates of the upper-layer atoms. The application of the pair-distribution-function formalism reveals anisotropy in the orientational order that might indicate that the SPE occurs preferably in the step direction.

General Higher-Order Beam Theory Including Effects of Transverse and Lateral Components.

In the case of conventional analysis of beams, lateral components (along the width) of the beam are neglected, but this assumption is not always suitable for the case of real beams. In this paper we propose general higher-order equations for one-dimensional static and dynamic beam theories including the effects of lateral components as well as transverse components of general anisotropic beams by expanding the displacements of double infinite-power series with respect to the transverse and lateral coordinates of the beam. Some typical examples of the general higher-order equations given by the truncation of the series are compared with the previously proposed beam theories, and the interrelations among those theories are examined. Futhermore, static and dynamic numerical examples are shown for the cases of infinite beams subjected to sinusoidal loadings and frequency spectrum of simply supported beams.

39227 Recent European work on the NDT of composite materials : Reynolds, W.N. Materials and Design, Vol. 9, No. 4, pp. 183–191 (Jul./Aug. 1988)

Scanning acoustic microscopy (SAM) is a modern, powerful technology for the visualization of the internal structure of materials of a different nature. It uses high frequency ultrasonic waves to get information from inside inhomogeneities and therefore is a sensitive, precise and safe method for materials characterization. It is successfully used in scientific and research practice but has the greatest potential as a technology for nondestructive quality evaluation. This chapter describes the methodology and different aspects of ultrasonic inspection performed on a variety of material samples using a scanning acoustic microscope working in the range of 10–400 MHz as an example. The samples come from different areas of material sciences and were intentionally chosen as containing defects specific to each case.Compared to the widely used nondestructive technique and medical ultrasound, SAM operates with higher frequencies and at relatively short distances. The acoustic beam emitted by the transducer passes through a coupling liquid and is reflected back by inhomogeneities in the sample structure. The strength of the reflected signal is determined by the change in characteristic acoustic impedance at such an inhomogeneity. The reflections captured in the digitized received signal (A-scan) represent a 1-D property distribution along the acoustical beam. The ultrasonic image is digitally constructed from a series of A-scans acquired during lateral scanning, when the acoustic microscope scans with a mechanical motion of a single acoustic lens along the sample surface and as a result generates (collects) 3-D data about the micromechanical properties of the object in this particular volume. The main types of images obtained by acoustic microscopes are B-scan and C-scan. More complex data processing algorithms produce enhanced images that can also be attributed to these two categories. A B-scan represents the 2-D distribution of amplitudes along the axial and the lateral coordinates (vertical cross-section). A C-scan represents the 2-D distribution of amplitudes in a lateral plane at a certain time delay after the initial pulse has been emitted from the transducer (horizontal cross-section). In addition to such efficient digital characterizations of internal microstructure, it was demonstrated that SAM technology can effectively detect, evaluate, and classify a wide range of different imperfections: porosity in aluminum casting, undersized and cavernous resistance spot welds, low penetration depth of laser weld seam, insufficient or damaged area of adhesive bonding of metals and fiber-reinforced composites, biocomposites and biomaterials, etc. The precision and value of the obtained acoustic images are dependent on frequency and particular methodology, and in some industrial application cases could even be proven by destructive testing. The samples come from different areas of material sciences and were intentionally chosen as containing defects specific to each case.

Faster and more accurate testing : Green, J.E. Jr. Advanced Materials and Processes, Vol. 131, No. 1, pp. 72, 75–76, 79–80 (Jan. 1987)

Scanning acoustic microscopy (SAM) is a modern, powerful technology for the visualization of the internal structure of materials of a different nature. It uses high frequency ultrasonic waves to get information from inside inhomogeneities and therefore is a sensitive, precise and safe method for materials characterization. It is successfully used in scientific and research practice but has the greatest potential as a technology for nondestructive quality evaluation. This chapter describes the methodology and different aspects of ultrasonic inspection performed on a variety of material samples using a scanning acoustic microscope working in the range of 10–400 MHz as an example. The samples come from different areas of material sciences and were intentionally chosen as containing defects specific to each case.Compared to the widely used nondestructive technique and medical ultrasound, SAM operates with higher frequencies and at relatively short distances. The acoustic beam emitted by the transducer passes through a coupling liquid and is reflected back by inhomogeneities in the sample structure. The strength of the reflected signal is determined by the change in characteristic acoustic impedance at such an inhomogeneity. The reflections captured in the digitized received signal (A-scan) represent a 1-D property distribution along the acoustical beam. The ultrasonic image is digitally constructed from a series of A-scans acquired during lateral scanning, when the acoustic microscope scans with a mechanical motion of a single acoustic lens along the sample surface and as a result generates (collects) 3-D data about the micromechanical properties of the object in this particular volume. The main types of images obtained by acoustic microscopes are B-scan and C-scan. More complex data processing algorithms produce enhanced images that can also be attributed to these two categories. A B-scan represents the 2-D distribution of amplitudes along the axial and the lateral coordinates (vertical cross-section). A C-scan represents the 2-D distribution of amplitudes in a lateral plane at a certain time delay after the initial pulse has been emitted from the transducer (horizontal cross-section). In addition to such efficient digital characterizations of internal microstructure, it was demonstrated that SAM technology can effectively detect, evaluate, and classify a wide range of different imperfections: porosity in aluminum casting, undersized and cavernous resistance spot welds, low penetration depth of laser weld seam, insufficient or damaged area of adhesive bonding of metals and fiber-reinforced composites, biocomposites and biomaterials, etc. The precision and value of the obtained acoustic images are dependent on frequency and particular methodology, and in some industrial application cases could even be proven by destructive testing. The samples come from different areas of material sciences and were intentionally chosen as containing defects specific to each case.

Interacting laminar boundary layers in quasi-two-dimensional flow

The interaction between laminar boundary layers on swept wings and inviscid external flow is investigated in the limit of large Reynolds numbers using the method of matched asymptotic expansions. It is assumed that the direction of the free stream velocity and the normal to the leading edge include a finite sweep angle and, furthermore, that the disturbances causing the interaction process are either independent of or slowly varying with the lateral coordinate. The resulting triple-deck equations are solved numerically for the cases of supersonic flow past a swept compression ramp and a swept indentation the depth of which is slowly increasing in the lateral direction.

A differential photodetector, employing photoconductivity, for subnanosecond laser beam position measurements

A novel device is described which provides the possibility for accurate sensing of laser beam or interference fringe positions, utilising a pair of photoconductive elements that differentiates the light intensity with respect to the lateral coordinate. The device consists of a microstripline T structure with an InP:Fe chip incorporated in the middle. The chip has a metallic layer divided into three parts by two narrow photoconductive gaps, separated by a distance of 350 mu m. The central part is connected to a microstripline that constitutes the output branch, while the two side parts are connected to two similar microstriplines that are biased with DC voltages of equal magnitudes but opposite polarities. The differential mode of operation gives improved resolution as compared with ordinary photodetectors. In the case of gaussian beam position measurements a lateral resolution of 10 mu m could be demonstrated experimentally, and in measurements of interference fringe positions the resolution 2 pi /60 rad was achieved. In both cases these limits were set by the mechanical translation stage used. The temporal resolution was set by the carrier lifetime of the material, 200 ps.

Role of the nucleus ambiguus in the regulation of heart rate and arterial pressure.

The present study examined the effect of lesion of cell bodies in the nucleus ambiguus area on the development of neurogenic hypertension and further explored the cardiovascular responses produced by chemical and electrical stimulation of the nucleus ambiguus and the neighboring C1 region. Three days after chemical lesion of the nucleus ambiguus with kainic acid, arterial pressure and heart rate were unchanged; however, subsequent sinoaortic deafferentation produced a significantly greater increase of arterial pressure (157 +/- 7 vs 132 +/- 5 mm Hg) and heart rate (436 +/- 10 vs 374 +/- 10 beats/min) compared with those produced by sham lesion. Glutamate injected into the nucleus ambiguus increased arterial pressure and heart rate at 20 nmol/100 nl and decreased heart rate at 50 nmol/100 nl. Glutamate injected into the C1 area increased arterial pressure and heart rate at both doses. Gamma-Aminobutyric acid at 50 nmol/100 nl produced bradycardia and a fall in arterial pressure when injected into both the nucleus ambiguus and C1 area. The heart rate responses to gamma-aminobutyric acid and glutamate were attenuated in sinoaortic-deafferentated rats. The nucleus ambiguus and the C1 region were mapped using electrical stimulation with microelectrodes. All points stimulated in three anteroposterior sections in the nucleus ambiguus and the C1 area produced increases in arterial pressure, whereas bradycardia was restricted to the middle of three lateral coordinates associated with the center of the nucleus ambiguus and the C1 area ventral to the nucleus ambiguus.(ABSTRACT TRUNCATED AT 250 WORDS)

The optimal shape design method applied to modelling thermal thinning of the oceanic lithosphere near hot spots

Using the optimal shape design method, which is generally described, and von Herzen's et al. measurements of the heat flow, the shape of the lithosphere and its thermal field is computed in the vertical plane parallel to the hot spot source versus the plate velocity at a distance of about 250 km from the axis of the Hawaiian Island chain. The results are compared with the computations based on Crough's idea of thermal rejuvenation of the oceanic lithosphere above a hot spot source. If we assume that the lateral cross-section of the lithospheric bottom is described by the Gaussian curve Δh=Δh0exp (−y2/2σ2), we obtain Δh0≦35 km and σ≧130 km, where Δh is the value of lithospheric thinning and y the lateral coordinate. We thus obtain the lower limit of the lateral dimension of the Hawaiian anomaly.

Adsorption site ofc(2×2) O on Ni(0001): An off-normal-direction energy-dependent photoelectron-diffraction study

We have used the technique of energy-dependent photoelectron diffraction (EDPD) to study the pseudo-bridge-site model proposed by Demuth et al. for the adsorption of c(2\ifmmode\times\else\texttimes\fi{}2) O on Ni(001). Calculated EDPD curves at the normal exit direction for the pseudo-bridge site, averaged over four domains, were compared with those for the fourfold hollow site. We found no significant differences in the EDPD curves for the two different structural models. However, the calculated EDPD curves at off-normal directions, such as those along the [011] direction, or along the O--Ni bond directions, were qualitatively different for the two sites. We therefore conclude that off-normal-direction EDPD curves, when compared with measured data, can effectively determine the lateral coordinates of the oxygen overlayer on Ni(001).

Computation of wind tunnel wall effects in ducted rotor experiments

Ducted propellers and turbines operating in a square closed wind tunnel test section are analyzed. A multiple image method is used to account for tunnel wall interference effects and a detailed method of singularities model is used for the ducted rotor. The size of the rotor wake is computed, taking into account the tunnel walls. Several ducted rotor model/wind tunnel dimension ratios are examined, ranging between 0.02 and 0.50. In addition, ducted rotor disk loading coefficients, CT , between - 30 and 0.89 are considered (the negative values correspond to the rotor acting as a propeller; the positive values indicate that the rotor is a turbine). Values of ideal propeller thrust are reduced by over 30% at the highest value of propeller disk loading (CT = — 30). The tunnel wall effect for a ducted turbine is less than for a ducted propeller and is opposite in direction. For the nearoptimum condition CT. =0.89, the ideal turbine power is increased by about 8% for the largest model/tunnel ratio considered. Nomenclature CP. = ideal thrust power coefficient for DAP (diffuseraugmented propeller) or ideal power coefficient for DAWT (diffuser-augmented wind turbine) CT() = disk loading coefficient based on freestream dynamic head D = dimension of wind tunnel test section E = complete elliptic integral, Eq. (5) K = complete elliptic integral, Eq. (4) kn = function of ring vortex coordinates and field point coordinates, Eq. (3) TV = the number of images along the side of a square image array q = velocity in r direction r = radial coordinate rp = ideal power augmentation ratio R = diffuser radius at a particular value of z S = the number of vortex rings used to represent the diffuser surface T = total number of vortices used to represent both the diffuser and the wake u = velocity in x direction U0 = freestream velocity, dimensional v = velocity in y direction w = velocity in z direction (axial direction) x = lateral coordinate in plane perpendicular to mean flow y = vertical coordinate in plane perpendicular to mean

Probe-shift error in remote diagnostic of volume radiation sources

Determination of the distribution of the emission coefficient in a volume radiation source sometimes entails mathematical analysis of an externally measured distribution of radiative flux. Through an analysis of a hypothetical source exhibiting cylindrical symmetry, it is shown that the finite aperture of the measuring device causes a probe-shift error in the results. The shift is a strong function of the size and magnitude of the second spatial derivative of the emission and increase with the aperture size. Nomenclature tw,h) = measured radiative power, W = calculated radiative flux, W/m2 — aperture height of analyzer, m = emission coefficient, W/m3 = ideal radiative flux, W/m2 = radial coordinate, m = radius of source, m — aperture width of analyzer, m = depth coordinate normal to source axis, m = lateral coordinate normal to source axis, m — effective value of lateral coordinate, m = nominal value of lateral coordinate, m = axial coordinate of source , m = standard deviation of Gauss distribution, m

Determination of temperature profiles from optically thick lines

A method for the evaluation of high-pressure discharge temperature profiles is proposed, which is based on a numerical solution of the radiative transfer equation. The measured quantities that have to be provided for the numerical evaluation are readily obtainable because only the absolute side-on intensity of a spectral line as a function of the lateral coordinate has to be measured. The method has been applied to several optically thick mercury lines. A comparison with temperatures obtained from optically thin lines shows good agreement. This method has the following two advantages: (i) temperature determination is possible in cases where no optically thin line is available, (ii) using optically thick lines of transitions with low excited states (e.g., resonance lines), the temperature profile can be determined for larger radii than from optically thin lines.

Functional validation of projection topography in the nigrostriatal dopamine system

Anatomical investigations have revealed that the nigrostriatal pathway is topographically organised. In two experiments, nigrostriatal topography was investigated with catecholamine specific procedures, using paradigms which reflect the functional activity of dopaminergic neurones. Data were analysed with the intention of discovering possible relationships between the mesencephalic location of stimulating electrodes or injection cannulae, the extent and location of dopamine histofluorescence depletion within the striatum, and the effects of amphetamine and apomorphine on rotational behaviour. In animals pretreated with 250 mg/kgα-methyl- p-tyrosine it was found that unilateral stimulation with medially-placed nigral electrodes produced maximal depletion of dopamine histofluorescence in anterior dorso-medial regions of the striatum, while laterally-located electrodes principally depleted posterior, ventro-lateral areas. In the second experiment, 2 μg of 6-hydroxydopamine in a volume of 0.5 μl was injected unilaterally at varying loci within the ventral midbrain of animals pre-treated with desmethylimipramine (25 mg/kg). It was discovered that the lateral injection coordinate was significantly associated with both the extent and location of the depletion of dopamine-related fluorescence from the ipsilateral striatum. Rotational behaviour, induced by dopamine-agonists was related firstly, to the overall extent of dopamine depletion from the striatum, and secondly, the contraversive turning induced by apomorphine in particular was related to the dorsoventral coordinate of the mesencephalic 6-hydroxydopamine injection. The results provide functional validation for the pattern of topographical projection within the nigrostriatal dopaminergic system proposed on the basis of intracellular tracing techniques.