Similar Aperture Research Articles

Fast acquisition aperture correction in prestack depth migration using beamlet decomposition

Wave-equation-based acquisition aperture correction in the local angle domain can improve image amplitude significantly in prestack depth migration. However, its original implementation is inefficient because the wavefield decomposition uses the local slant stack (LSS), which is demanding computationally. We propose a faster method to obtain the image and amplitude correction factor in the local angle domain using beamlet decomposition in the local wavenumber domain. For a given frequency, the image matrix in the local wavenumber domain for all shots can be calculated efficiently. We then transform the shot-summed image matrix from the local wavenumber domain to the local angle domain (LAD). The LAD amplitude correction factor can be obtained with a similar strategy. Having a calculated image and correction factor, one can apply similar acquisition aperture corrections to the original LSS-based method. For the new implementation, we compare the accuracy and efficiency of two beamlet decompositions: Gabor-Daubechies frame (GDF) and local exponential frame (LEF). With both decompositions, our method produces results similar to the original LSS-based method. However, our method can be more than twice as fast as LSS and cost only twice the computation time of traditional one-way wave-equation-based migrations. The results from GDF decomposition are superior to those from LEF decomposition in terms of artifacts, although GDF requires a little more computing time.

A multi-directional tracer test in the fractured Chalk aquifer of E. Yorkshire, UK

A multi-borehole radial tracer test has been conducted in the confined Chalk aquifer of E. Yorkshire, UK. Three different tracer dyes were injected into three injection boreholes and a central borehole, 25 m from the injection boreholes, was pumped at 330 m 3/d for 8 days. The breakthrough curves show that initial breakthrough and peak times were fairly similar for all dyes but that recoveries varied markedly from 9 to 57%. The breakthrough curves show a steep rise to a peak and long tail, typical of dual porosity aquifers. The breakthrough curves were simulated using a 1D dual porosity model. Model input parameters were constrained to acceptable ranges determined from estimations of matrix porosity and diffusion coefficient, fracture spacing, initial breakthrough times and bulk transmissivity of the aquifer. The model gave equivalent hydraulic apertures for fractures in the range 363–384 μm, dispersivities of 1 to 5 m and matrix block sizes of 6 to 9 cm. Modelling suggests that matrix block size is the primary controlling parameter for solute transport in the aquifer, particularly for recovery. The observed breakthrough curves suggest results from single injection-borehole tracer tests in the Chalk may give initial breakthrough and peak times reasonably representative of the aquifer but that recovery is highly variable and sensitive to injection and abstraction borehole location. Consideration of aquifer heterogeneity suggests that high recoveries may be indicative of a high flow pathway adjacent, but not necessarily connected, to the injection and abstraction boreholes whereas low recoveries may indicate more distributed flow through many fractures of similar aperture.

Effects of different immersion media in multiphoton imaging of the epithelium and dermis of human skin

In this work, we compared the performance of objectives with similar numerical aperture of 0.75 but different immersion media of air, water, glycerin, and oil in the imaging of human skin epithelium and dermis. In general, we found that the oil immersion objective recorded the strongest intensity at the same mechanical depth. We also characterized the focal shifts and found that with decreasing refractive index, the focal shift becomes increasingly more negative (for both the epithelium and dermis). In imaging the dermis, we estimated the image resolution at the depths of 18.8 and 30.2 microm, and found that the image resolution were comparable at these depths under the four types of immersion conditions. Our results demonstrate that by changing the immersion media, the main microscopic imaging effects are the recorded axial intensities and the focal shifts. The effects on the image resolution are negligible.

P-13: New Design of Advanced H-IPS(AH-IPS) Panel for High Aperture Ratio

We designed the new pixel layout of the AH-IPS, which has similar aperture ratio to the IPS with organic insulator. To improve the aperture ratio without organic insulator, we positioned the pixel electrode over the preceding gate on the base of the H-IPS structure and minimized the width of pixel and common electrodes. Additionally, we used a TCO (Transparent Conducting Oxide) as the common electrode. This AH-IPS can provide high aperture ratio and flexible design.

Imaging the Disk around TW Hydrae with the Submillimeter Array

We present similar to2-4 aperture synthesis observations of the circumstellar disk surrounding the nearby young star TW Hya in the CO J = 2-1 and J = 3-2 lines and associated dust continuum obtained with the partially completed Submillimeter Array. The extent and peak flux of the 230 and 345 GHz dust emission follow closely the predictions of the irradiated accretion disk model of Calvet et al. The resolved molecular line emission extends to a radius of at least 200 AU, the full extent of the disk visible in scattered light, and shows a clear pattern of Keplerian rotation. Comparison of the images with two-dimensional Monte Carlo models constrains the disk inclination angle to 7degrees +/- 1degrees. The CO emission is optically thick in both lines, and the kinetic temperature in the line formation region is similar to20 K. Substantial CO depletion, by an order of magnitude or more from canonical dark cloud values, is required to explain the characteristics of the line emission.

High light field confinement for fluorescent correlation spectroscopy using a solid immersion lens

In this paper we present recent single molecule detection experiment using a solid immersion lens (SIL) for fluorescent correlation spectroscopy measurements. We compared the performance of the SIL in combination with an air objective (40×, numerical aperture (NA)=0.6) with a water immersion objective (40×, NA=1.15) in a confocal microscope system (ConfoCorr 1). Important parameters for single molecule experiments such as collection efficiency and excitation field confinement were investigated. Although the two set-ups have similar numerical aperture the measurements demonstrated higher field confinement and better collection efficiency for the SIL system in comparison to the conventional confocal set-up. Adding spherical aberrations shifts the sample volume up to 4 μm away from the plane surface of the SIL and conserves a diffraction limited focal volume. In this case the FCS autocorrelation demonstrates a free 3D diffusion of dye molecules in a highly confined light field.

BER Performance of a Uniform Circular Array Versus a Uniform Linear Array in a Mobile Radio Environment

In this letter, we present a comparison between the bit error rate (BER) performance of a uniform circular array (UCA) and a uniform linear array (ULA) assuming quadrature phase-shift keying (QPSK) and maximal-ratio-combining (MRC) in a mobile radio communication environment. The results are based on analysis, assuming a flat Rayleigh fading channel with omni-directional antennnas and considering the azimuthal plane only. The analytical BER is derived as a function of the spatial fading correlation for both types of antenna arrays. Results show that for similar aperture sizes the UCA outperforms the ULA when considering all angles-of-arrival. However, there is considerable variability over central angle-of-arrival (AOA) for low-to-moderate angle spreads. For angles-of-arrival concentrated near the broadside of the linear array, the ULA typically performs as well as or better than the UCA. A truncated Gaussian AOA (AOA) distribution is assumed to model spatial correlation and the numerical results focus on four element arrays.

Multi-reflection photometric flow cell for use in flow injection analysis of estuarine waters

A multi-reflection flow cell suitable for flow analysis is described. Light from an LED is directed through an optical fibre into a silver coated capillary through a sidewall aperture, and emerges through a similar aperture 10 mm along the capillary after undergoing an estimated 19 reflections. This process provides a sensitivity enhancement of approximately 2.5 compared with a conventional z-cell of the same nominal path length. This enhancement is due to both the increased optical path length achieved by multiple reflection of the light beam through the sample, and minimization of physical dispersion by the use of a short, small internal diameter capillary as the flow cell. The optical design of this flow cell also minimizes the Schlieren effect. Optical and hydrodynamic characteristics of this multi-reflection cell have been evaluated using a series of bromothymol blue dye studies. Application of the flow cell to the determination of reactive phosphorus in estuarine waters with wide variation in salinity and refractive index is also described.

Varietal Differences in the Morphophysiological Response to Atmospheric Humidity in Rice

High atmospheric humidity promotes vegetative growth and dry-matter production in japonica rice. In this study, the varietal differences in the response to atmospheric humidity were examined using three japonica varieties (Nipponbare, Kinmaze, Yamadanishiki), one indica variety IR24 and japonica × indica variety (Milyang 23). The indica and japonica × indica varieties are referred to as indica varieties hereafter. The growth of the japonica varieties was greatly promoted by high humidity (90%) and greatly reduced by low humidity (60%), but that of the indica varieties was less sensitive to humidity and the growth was hardly affected by low humidity. We compared the responses of the above varieties to low humidity (water stress) using the plants under high humidity as a control. Under low humidity, as compared to the indica varieties, the japonica varieties had a higher stomatal density, longer stornata and larger stomatal aperture, resulting in a lower water potential in leaf blades and lower water -use efficiency. Under high humidity, the japonica and indica varieties showed a similar transpiration rate (per unit area), stomatal aperture and water-use efficiency, but the japonica varieties had a higher water content than the indica varieties. This may be why the japonica varieties show greatly suppressed growth and dry matter production under low humidity. These differences between the japonica and indica varieties in morphophysiological characters under low humidity might cause the varietal differences in the plant growth and dry matter production in rice.

Optimisation of λ= 850 nm hybrid-mirror vertical-cavity surface-emitting laser with 37 μA threshold current

A vertical-cavity surface-emitting laser (VCSEL) structure is optimised for low threshold current. The cavity comprises a GaAlAs bottom DBR with a dielectric SiO/sub 2/-Si/sub 3/N/sub 4/ output mirror on top. The asymmetrical active region consists of GaAs-QWs, emitting at 850 nm. Selective lateral oxidation is applied to the p-side AlAs layer for current confinement. With the realised structure, a record low threshold current for selectively oxidised, hybrid Ga(Al)As lasers of I/sub th/=37 /spl mu/A at an oxide-aperture diameter of O/sub ap/=4.9 /spl mu/m is achieved. The observed multimode emission spectrum is analysed using a simplified theoretical model for the transverse-mode guiding, and first experimental results of a redesigned VCSEL structure with single-mode operation at similar aperture diameters are presented.

Application of SALT to the Local Group

In collaboration with international partners, South Africa plans to construct a 9-m class telescope for optical/infrared astronomy. This Southern African Large Telescope (SALT) will be a southern hemisphere equivalent of the Hobby-Eberly Telescope at McDonald Observatory, Texas. By limiting the scientific mission to primarily spectroscopic survey studies, with some reduced imaging capability, it is possible to construct SALT for about one-fifth of the cost of a general-purpose telescope of similar aperture. The telescope will be operated in queue-scheduled mode which opens up new applications in the time-dependent domain. A description of SALT, its capabilities, and samples of the science programme are presented.

Measurement of true transmittance of samples mounted on an aperture plate

Double beam commercial spectrophotometers usually accept samples larger than a specific size. In case samples are undersized, these samples for their transmittance measurement are mounted on an aperture plate. In order to maintain the precision of the measurement and also not to disturb the optical balance between two beams, a similar aperture plate is placed in the reference beam of the spectrophotometer. In spite of all the precautions taken the measurement often leads to an erroneous result. A simple methodology to derive values of true/actual transmittance value when the samples are mounted on an aperture plate is discussed here.

A shaped single reflector offset antenna with low cross-polarization fed by a lens horn

A novel compact primary-fed offset reflector antenna with the potential of radiating circular as well as elliptical beams with low cross-polarization, is proposed. The reflector is fed by a horn with a phase-correcting lens in the aperture. Compared to the dual-reflector offset antenna, the concept is easier to assemble and mechanically more robust. The antenna has been synthesized and analyzed by computer programs resulting from modifications of corresponding PO programs for dual-reflector offset antennas. The synthesized antenna exhibits similar cross-polarization, side-lobe level, and aperture efficiency as those of dual-reflector offset antennas, although the one-to-one correspondence between zero cross-polarization and conformal mapping from the feed to the aperture, is not exactly valid for this approach.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Searching for Supernovae—Visually and Otherwise

AbstractThe main features of visual searching for supernovae in other galaxies by amateur astronomers are described, and an outline is given of the results which have been achieved so far by this method. A short comparison is made between visual searching and photographic searching. A more extensive comparison is then made between visual searching for supernovae in Australia, and the work of the Berkeley Automatic Supernova Search at Leuschner Observatory, since 1986. Among the conclusions is the claim that a competent visual observer could produce similar results to those produced by the Berkeley group if a telescope of similar aperture was used for a similar amount of observing time, and from a good observing site. Indeed, visual searching might possibly produce more results, and such a search would only cost a small fraction of what was spent on this automatic search. It would be a worthwhile project to conduct a visual search with a suitably designed 76-cm telescope, or a one metre telescope, over a period of a few years, to see if this conclusion could be supported in practice.

Adsorption interaction of water with microporous adsorbents. Part 2.—Enthalpy of immersion and thermal-desorption studies

The net integral molar enthalpy of immersion, in water and CCl4, of activated carbon cloth exhibits a maximum value with increasing air or nitric acid activation. The effect is ascribed to the occurrence of optimum pore dimensions. Molecular-sieve and specific-interaction phenomenon complicate the interpretation of the data but a separation of the pore dimension effect can be achieved. Programmed thermal-desorption studies on molecular sieve are used to demonstrate kinetic effects which arise from similar aperture or pore-opening influences.

Planar acoustic microscope lens using Rayleigh to compressional conversion

A planar acoustic lens is described in which Rayleigh waves generated by a circular interdigital transducer on LiNbO3 are converted to a focused hollow conical beam in the contiguous liquid. The focal spot is comparable to that of a standard diffraction-limited lens of similar aperture; the calculated sidelobes are higher but the measured ones are comparable.

Analysis of acoustic fill time effects on cylindrical arrays

When a plane acoustic wave impinges on a cylindrical array, the leading edge insonifies the first few elements of the array. As the wave front continues past the leading edge of the cylinder, more and more elements are insonified until all elements in the array are insonified. The time between the first and last element to be insonified is called array ’’fill time.’’ For a cylindrical array with a phase-shift beamformer, in which the insonifying pulse length is long compared to the fill time, the resultant beam pattern is essentially the same as a cylindrical array with a delay line beamformer and is approximately the same as a planar array of similar aperture size. Up to this time there has been no detailed description of how the beam pattern is affected when the pulse length and the fill time are approximately the same. This article reports a thorough analysis of array fill time of a cylindrical array; a phase-shift beamformer is compared to a delay line beamformer. The conclusion from this study is that fill time has little effect on the array beam pattern as long as the fill time is no greater than the pulse length.

Growth of barley pollen tubes in vivo. I. Ultrastructural aspects of early tube growth in the stigmatic hair

Barley styles were examined with transmission electron microscopy (TEM) and scanning electron microscopy (SEM) before and after pollination. Pollen tube penetration of a stigmatic hair may follow initial missing of the hair and (or) a period of growth on the hair surface. Changes in hair cell walls occur at penetration sites. Absence of demonstrable reserve carbohydrate in hair cells and styles and its abundance in pollen tubes suggest that early tube growth is largely dependent on endogenous substrates relative to its carbohydrate requirement. The pollen tube wall has an inner, somewhat reticular region and an outer, multilayered fibrillar region. Membrane-bound pollen tube vesicles containing reticular material fuse with the pollen tube membrane, contributing to development of the pollen tube wall. Vesicles and tube wall are stained by Ruthenium Red; this staining is compared with results of periodic acid–silver proteinate treatment. Two types of tube growth anomalies are reported. In the first, a tube may grow out of a hair and discharge its cytoplasm onto the hair surface through an aperture. Discharged, naked tube cytoplasm often remains appressed to hair surfaces. In the second, a tube may grow into a hair cell and discharge its contents therein through an apparently similar aperture. Vegetative nuclei appear unaltered during early pollen tube growth, but there are minor structural alterations in sperms and vegetative cell cytoplasm.

Analysis for fill‐time effects on cylindrical arrays

When a plane wave impinges on a cylindrical array, the leading edge insonifies the first few elements of the array. As the wave front continues past the leading edge of the cylinder, more and more elements are insonified until all elements in the array are insonified. This time between the first and last element to be insonified is called array “fill time.” For a phase‐shift beamformer, where the insonifying pulse length is long compared to the fill time, the resultant beam pattern is essentially the same as from a planar array of similar aperture or a cylindrical array with a delay line beamformer. When the pulse length and the fill time are approximately the same, there has been no detailed description of how the beam pattern is affected. Accordingly a thorough analysis of array fill time has been made of a cylindrical array, phase‐shift beamformer in comparison to a delay line beamformer and to a planar array. The conclusion reached from this study is that there is little effect on the array beam pattern due to the fill time as long as the fill time is no greater than the pulse length. [Work supported by NCSL.]

Mass Spectra Stimulated by O+ and Ar+ Interacting with a Surface

Beams of O(+) and Ar(+) in the energy range from 100 to 300 eV were directed into an aperture in one face of a copper box. The mass spectrum from a similar aperture in an adjacent face was observed with the aid of a commercial RF quadrupole spectrometer. On the basis of the results obtained it is reported that O(+) beams at about 200 eV may be essentially lost after a few collisions with a surface, in agreement with similar conclusions about atomic oxygen at thermal energies.