Increasing Aperture Size Research Articles

A large-aperture, high-power ultrawideband radiation system with beam broadening capacity.

Due to the limited maximum output power of the pulsers based on avalanche transistors, high-power ultrawideband (UWB) radiation systems usually synthesize plenty of modules simultaneously to achieve a high peak effective potential (rEp). However, this would lead to an increased aperture size as well as a narrower beam, which would limit their applications in intentional electromagnetic interference fields. In this paper, a high-power UWB radiation system with beam broadening capacity is developed. To achieve beam broadening in the time domain, a power-law time delay distribution method is proposed and studied by simulation, and then the relative excitation time delays of the modules are optimized to achieve higher rEp and avoid beam splitting in the beam broadening mode. In order to avoid false triggering of the pulser elements when implementing the beam broadening, the mutual coupling effect in the system is analyzed and suppressed by employing onboard high-pass filters, since the mutual coupling effect is much more severe in the low-frequency range. Finally, a radiation system with 36 modules is developed. Measuring results indicate that in the high-rEp mode, the developed system could achieve a maximum effective potential rEp of 313.6kV and a maximum pulse-repetition-rate of 20kHz. In the beam broadening mode, its half-peak-power beam width in the H-plane is broadened from the original value of 3.9° to 7.9°, with a maximum rEp of 272.9kV. The polarization direction of the system could be flexibly adjusted by a built-in motor.

Particle Behavior and Aperture Optimization of Variable Vibration-Amplitude Screening Based on Discrete Element Method Simulation.

Recently, some novel screens were proposed based on the improved understanding of screening processes from particle-scale studies, one of which is the novel variable amplitude equal thickness vibration screen (VAETVS). This paper presents an investigation of using different aperture sizes to further optimize the VAETVS by the discrete element method (DEM). The screen was divided into three panels, and the aperture size of each panel was varied in the simulation. The particles' dynamics and spatial distribution were investigated to better understand the effects of varied amplitudes and aperture sizes on the screening efficiency. The results showed that the VAETVS can be effectively optimized by varied amplitude as well as varied aperture size for different screen panels. The amplitude variance is more effective for hard sieve particles and hindrance particles. It is also found that from the feed end to the discharge end, the difference in the distribution of particle mass between the coarse particles and the fine particles increases. Generally, such a difference can be increased with increasing aperture sizes. However, the effects of the apertures of the different panels were not the same. The simulated data were further analyzed by the Box-Behnken response surface method, which gave a mathematical model to predict the screening efficiency η with the varied apertures. From the model, the optimal aperture sizes are 7.5, 7.58, and 6.81 mm, yielding the maximum screening efficiency of 86.35%, and the optimal opening areas for the three panels are 35, 40, and 40%, respectively, yielding the maximum screening efficiency of 87.82%.

Design studies of a far-field plasmonic superlens with an enlarged field of view

Based on our previous studies, we numerically demonstrate imaging capability of a cascaded plasmonic superlens with an enlarged field of view for directly imaging subwavelength objects with magnification in the far field at a visible wavelength. The superlens consists of two plasmonic slabs. One is a plasmonic cavity lens for near-field coupling, and the other one is a planar plasmonic lens for phase retardation and thus image magnification is enabled. First, we investigate the superlens with an inverted plasmonic cavity structure (with respect to our previous design), which simplifies the nano-fabrication process. Then we design the planar plasmonic lens with an increased aperture size. Simulation results show that the superlens with the inverted structure can still achieve subwavelength imaging. Furthermore, a lateral resolution of 180 nm at the wavelength of 640 nm is manifested by the superlens with a larger field of view. When the aperture size of the planar plasmonic lens is doubled from 2.1 μm to 4.2 μm, the field of view of the superlens is increased by a factor of 1.4. The results provide a profound physical insight into the design of a cascaded plasmonic superlens system and pave the way for further experimental investigations.

Diagenesis, compaction strain and deformation associated with chert and carbonate concretions in organic‐rich marl and phosphorite; Upper Cretaceous to Eocene, Jordan

ABSTRACTThis paper presents an integrated petrographic–geochemical–geomechanical study of the growth mechanisms of carbonate and chert concretions observed at outcrop and core from the Upper Cretaceous to Eocene organic‐rich carbonate mudrocks, central Jordan. It provides evidence for displacive and replacive concretion growth from the analysis of primary lithological characteristics, compaction strain and deformation structures associated with concretion growth. Concretions were analysed to determine the primary lithological controls on their development and the measurement of strain in the host rock to develop a method for constraining the growth mode and their paragenesis. Concretions exhibit either a replacive or displacive growth mode largely dependent on the original host lithology. Displacive concretions exhibit irregular shapes and semi‐fibrous internal structures in contrast to regular shapes and microcrystalline textures observed for replacive concretions. Cement fraction is high in both carbonate concretion types, indicating early formation in high‐porosity sediments at shallow burial depths. The strain field around displacive concretions is vertically asymmetrical. Conversely, it is symmetrical with uniform differential compaction for the replacive concretions. Evidence for displacive growth comes from triangular areas of chert at the lateral margins of some carbonate concretions, interpreted as areas of reduced strain. Another indicator is the forced asymmetrical folding of heterolithic host rocks around displacive concretions, with displacive carbonate units separated by trace laminae of the original (chert) beds. Enveloping chert beds exhibit early‐formed radial silica fractures with increased aperture size in the areas of maximum curvature. Carbon isotopic signatures of carbonate concretions show a strong correlation between concretion centres and host rock, suggesting a relatively shallow depth (first few tens of metres) of initial growth. Carbonate concretions are interpreted to have formed at shallow depths in the presence of alkaline pore waters rich in dissolved organic carbon in the presence of Mg2+ ions, available organic matter and redox‐sensitive metals such as U and Mo. A paragenetic history for the different concretion types is presented.

The Relative Importance of Thermal Gas, Radiation, and Magnetic Pressures around Star-forming Regions in Normal Galaxies and Dusty Starbursts

In this paper, an investigation on the relative importance of the thermal gas, radiation, and (minimum-energy) magnetic pressures around ≈200 star-forming regions in a sample of nearby normal and luminous infrared galaxies is presented. Given the range of galaxy distances, pressure estimates are made on spatial scales spanning ∼0.1–3 kpc. The ratio of thermal gas-to-radiation pressures does not appear to significantly depend on star formation rate surface density (ΣSFR), but exhibits a steady decrease with increasing physical size of the aperture over which the quantities are measured. The ratio of magnetic-to-radiation pressures appears to be relatively flat as a function of ΣSFR and similar in value for both nuclear and extranuclear regions, but, unlike the ratio of thermal gas-to-radiation pressures, exhibits a steady increase with increasing aperture size. Furthermore, it seems that the magnetic pressure is typically weaker than the radiation pressure on subkiloparsec scales, and only starts to play a significant role on few-kiloparsec scales. When the internal pressure terms are summed, their ratio to the (ΣSFR-inferred) kiloparsec-scale dynamical equilibrium pressure estimates is roughly constant. Consequently, it appears that the physical area of the galaxy disk, and not necessarily environment (e.g., nuclear versus extranuclear regions) or star formation activity, may play the dominant role in determining which pressure term is most active around star-forming regions. These results are consistent with a scenario in which a combination of processes acting primarily on different physical scales work collectively to regulate the star formation process in galaxy disks.

CLASSY V: The Impact of Aperture Effects on the Inferred Nebular Properties of Local Star-forming Galaxies

Strong nebular emission lines are an important diagnostic tool for tracing the evolution of star-forming galaxies across cosmic time. However, different observational setups can affect these lines, and the derivation of the physical nebular properties. We analyze 12 local star-forming galaxies from the COS Legacy Spectroscopy SurveY (CLASSY) to assess the impact of using different aperture combinations on the determination of the physical conditions and gas-phase metallicity. We compare optical spectra observed with the Sloan Digital Sky Survey Data Release aperture, which has a 3″ diameter similar to COS, IFU, and long-slit spectra, including new LBT/MODS observations of five CLASSY galaxies. We calculate the reddening, electron densities and temperatures, metallicities, star formation rates, and equivalent widths (EWs). We find that measurements of the electron densities and temperatures, and metallicity remained roughly constant with aperture size, indicating that the gas conditions are relatively uniform for this sample. However, using IFU observations of three galaxies, we find that the E(B − V) values derived from the Balmer ratios decrease (by up to 53%) with increasing aperture size. The values change most significantly in the center of the galaxies, and level out near the COS aperture diameter of 2.″5. We examine the relative contributions from the gas and stars using the Hα and [O iii] λ5007 EWs as a function of aperture light fraction, but find little to no variations within a given galaxy. These results imply that the optical spectra provide nebular properties appropriate for the far-UV CLASSY spectra, even when narrow 1.″0 long-slit observations are used.

Compressive properties and energy absorption of honeycomb filled square tubes produced by selective laser melting

Honeycomb core structure used as filling material requires high out-of-plane compression stiffness and good energy absorption performance. The regular honeycomb core structure can be produced by selective laser melting (SLM) and can offer better compressive performance than that of most traditional methods, and the square tube filled with honeycomb core structure may have good performance. In order to study the properties of honeycomb filled square tube, 316 L stainless steel powder was selected as raw material to prepare honeycomb filled square tube with different aperture sizes by SLM. The compression performance and energy absorption efficiency were studied by compression experiments. The collapse mode was analyzed by both experiments and simulation. The results show that the honeycomb filled square tubes have regular structures and no obvious defects. Compression experiments agree well with the simulation results. Comprehensive behavior presents three stages: elastic stage I, yield (platform) stage Ⅱ and densification stage Ⅲ. With the increase of porosity, Young's modulus and yield strength decrease. The honeycomb filled square tube produced by SLM has a higher relative Young's modulus in comparison to other topological structures. When the porosity increases from 73.5% to 87.9%, the energy absorption efficiency in the yield stage is higher than 70%, and the energy absorption per unit volume varies from 13.44 MJ/m3 to 76.41 MJ/m3 at 50% strain. Increasing aperture size of honeycomb single tube will results in the collapse mode changing from global to progressive buckling.

Wave Dissipation and Energy-Absorption Characteristics of Wave-Absorbing Metal Plates with Different Aperture Sizes and Thicknesses under True-Triaxial Static-Dynamic-Coupling Loading

Deep rock masses exist in a complex environment with multi-field coupling; therefore, it is necessary to develop a true-triaxial static-dynamic-coupling loading test machine to explore their characteristics and mechanical response mechanism. To meet the test requirements of true-triaxial loading and strong disturbance, a wave-absorbing metal plate was selected as the boundary material between the granite and transmission end, and the modified SHPB was used to perform static-dynamic-coupling loading tests. In this study, two series of experiments on wave- absorbing metal plates were conducted, which were fixed aperture sizes with different thicknesses and fixed thicknesses with different aperture sizes. The static-dynamic-coupling loading tests on each aperture size and plate thickness were carried out under the condition of equal energy impact. The effects of the aperture size and plate thickness on the incident- and reflection-stress curves, reflectivity, energy consumption law, energy evolution, and other mechanical properties of the wave-absorbing metal plate materials were studied. The results show that the peak stress and reflectivity decrease with increasing aperture size and plate thickness, and the influence of the thickness is greater than that of the aperture size. The energy-absorption rate of the wave-absorbing metal plate increased with increasing thickness and aperture size and was maximized when the aperture size and thickness were 6–7 mm and 3–4 mm, respectively. The variation trend of the energy reflectance is opposite to that of the energy absorption and reaches a minimum when the aperture size is 6–7 mm and plate thickness is 3–4 mm. The energy transmittance of the wave-absorbing metal plate fluctuated in a stable range, but the variation range was less obvious compared to that of the energy-absorption rate.

Comparison of probability density functions for aperture-averaged irradiance fluctuations of a Gaussian beam with beam wander.

Over the years, there has been much interest in the use of optical wavelengths for communication because of the potential for high data rates. However, the performance of these systems can become significantly degraded due to turbulence-induced signal fluctuations. These fluctuations can be minimized by enlarging the receiving aperture, thereby averaging the fluctuations. There is extensive interest in developing probability density functions (PDFs) describing these intensity fluctuations so as to accurately predict system performance. This work examines several PDF models that have been suggested to represent fluctuations by comparing them to simulations of realistic propagation scenarios of a collimated Gaussian beam with centroid wander. Unlike with an infinite plane or spherical wave, the empirical PDF shape in these simulations changed significantly with increased aperture, going from a positively skewed to a negatively skewed distribution; therefore, the PDF model that describes it also must change. This change in skew can have serious consequences on the metrics of an optical communication system, e.g., number of fades and bit-error rate. In this work, we examine the evolution of the empirical PDF with aperture size and the fit of potential PDF models under various strengths of turbulence. We show that the change in skew with increasing aperture size occurred for all strengths of turbulence and that the currently used PDF models do not adequately characterize this for realistically sized apertures where beam wander is present.

Design Analysis of a Passive Buffer System for Space-Assembled Segmented Mirrors

This paper presents a passive buffer system of connection mechanism for space-assembled segmented mirrors. The purpose of assembling telescope in space is to overcome the limits of launch volume and mass to support ever increasing aperture sizes. Using this buffer system, the docking impact between two mirror segments can be alleviated effectively. In this paper, first, a design methodology called “double-elastic contact model” is developed. Then, the design details and operation principle of the connection mechanism, are presented to validate the passive buffer system. Finally, by comparing the traditional docking system, the simulated results of dynamic performance show that the proposed buffer system can absorb the impact energy effectively and is considerably suitable for assembling the space optical system.

Spatially Resolved Spectroscopic Study of nearby Seyfert Galaxies: Implications for a Population of “Missed” Seyferts at High-z

Abstract We present mosaicked long-slit spectral maps of 18 nearby Active Galactic Nuclei (AGNs), 2 LINERs, and 4 star-forming galaxies. With the resulting data cubes taken using the Kast dual spectrograph on the 3 m Shane telescope of the Lick Observatory, we measure the aperture effects on the spectroscopic classification of AGNs. With more starlight included in a larger aperture, the nuclear spectrum that is Seyfert-like may become contaminated. We generated standard spectroscopic classification diagrams in different observing apertures. These show quantitatively how the ensemble of Seyferts migrates toward the H ii region classification when being observed with increasing aperture sizes. But the effect ranges widely in individual active galaxies. Some of the less luminous Seyferts shift by a large amount, while some others barely move or even shift in different directions. We find that those Seyfert galaxies with the fraction of nuclear Hα emission lower than 0.2 of the host galaxy, 2–10 keV hard X-ray luminosity lower than 1043 erg s−1, and the observed nuclear [O iii] luminosity lower than 1040.5 erg s−1, are more likely to change activity classification type when the entire host galaxy is included. Overall, 4 of our 24 galaxies (18 Seyferts) change their spectral activity classification type when observed with a very large aperture.

A Study of mm-Wave Communications With Noncontiguous Aperture

Current millimeter wave (mm-wave) communications research is focused on large scale antenna with contiguous aperture. On the contrary, in this paper, we present a study of mm-wave communications between transmit and receive antennas based on noncontiguous aperture. Our design aims to form shaped beams with high spatial isolation. We first study the beam shaping feasibility in mm-wave communications with reduced transmit antenna element spacing. We then introduce active scatters, a class of active devices that stimulates scattering effect, to sustain the interference rejection capability of shaped beams. The composition of active scatters forms a (virtual) noncontiguous aperture that is larger than transmit and receive antennas in size. To form multiple orthogonal beam (OB) radiation patterns that have peaks and nulls at designated locations, which enable frequency reuse, we consider slightly increased aperture size of transmit antenna and noncontiguous aperture that is comprised of active scatters. In addition to beamforming via noncontiguous aperture, we also simulated QPSK-modulated signal streams transmitted via OBs and justified the simulated system by inspecting the bit error rate performance at the receiver.

Numerical Study on Wind‐Induced Noise of High‐Rise Building Curtain Wall with Outside Shading Devices

Perforation metal plates with dense holes are often used as external curtain walls of high‐rise buildings. When air flow passes through these holes at a high speed, complex vortex is generated and causes a significant issue of wind‐induced noise. In this study, both Reynolds‐averaged Navier–Stokes (RANS) simulations and large‐eddy simulations (LES) were conducted to study flow around high‐rise buildings with an external sunshade curtain wall. First, wind speed distributions at the height of a typical level under 16 wind directions were acquired. Then, the maximum wind speed ratio and its corresponding azimuth were identified. Second, the sound pressure levels in the vicinity of the shading devices with two types of perforation plate schemes were calculated to evaluate the acoustic characteristics by using the FW‐H equation to simulate sound generation and propagation. The results indicate that the maximum wind speed around the buildings exists at the building corners, and the maximum wind speed ratio is 2.8 observed at 0‐degree wind direction. Under two different wind conditions, the aeroacoustic performance of perforation plate is enhanced with reducing end plate size and increasing aperture size. The overall sound pressure level (OSPL) and A‐weighted sound pressure level (ASPL) around the shading devices are 80 dB and 68 dB(A), respectively, for the improved perforation plate scheme under the 1‐year return period maximum speed, which are changed to 58dB and 45dB(A) under the annual average speed. Therefore, it is believed that perforation plates with small end plate size and large aperture size are desirable for the noise prevention design of shading devices.

Evaluation of Large-Aperture Imaging Through the ex Vivo Human Abdominal Wall

Current clinical abdominal imaging arrays are designed to maximize angular field of view rather than the extent of the coherent aperture. We illustrate, in ex vivo experiments, the use of a large effective aperture to perform high-resolution imaging, even in the presence of abdominal wall-induced acoustic clutter and aberration. Point and lesion phantom targets were imaged through a water path and through three excised cadaver abdominal walls to create different clinically relevant clutter effects with matched imaging targets. A 7.36-cm effective aperture was used to image the targets at a depth of 6.4 cm, and image quality metrics were measured over a range of aperture sizes using synthetic aperture techniques. In all three cases, although degradation compared with the control was observed, lateral resolution improved with increasing aperture size without loss of contrast. Spatial compounding of the large-aperture data drastically improved lesion detectability and produced contrast-to-noise ratio improvements of 83%–106% compared with the large coherent aperture. These studies indicate the need for the development of large arrays for high-resolution abdominal diagnostic imaging.

Effect of the intra-abdominal infection on peritoneal lymphatic stomata and regulatory mechanism of PD123319 on peritoneal lymphatic stomata

Objective To investigate the effect of the peritoneal lymphatic stomata on intra-abdominal infection and the regulatory mechanism of angiotensin Ⅱ receptor specific inhibitor PD123319 on peritoneal lymphatic stomata. Methods The experimental study was adopted. Forty rats were divided into the control group, sham operation group, intra-abdominal infection group and intra-abdominal infection drug intervention group by the random number table, every group had 10 rats. The classic appendix perforation (CLP) intra-abdominal infection model was established in the abdominal infection group. After establishing the model of abdominal infection, PD123319 solution was injected intraperitoneally immediately (0.2 g/kg) in the abdominal infection drug intervention group. Abdominal cavity of the rats in the sham operation group was opened, and then was shut after flipping the intestine. The rats in the control group, sham operation group and intra-abdominal infection group were treated with intraperitoneal injection of 1ml stroke-physiological saline solution. After 2 hours, the rats were sacrificed, and peritoneal tissue was taken for the following tests. (1) The aperture size and distribution density of peritoneal lymphatic stomata were observed by scanning electron microscope (SEM). (2) The nitric oxide (NO) concentration in the peritoneal tissues was detected using nitric oxide nitric acid reduction method. (3) The expressions of endothelial nitric oxide synthase(eNOS)and Phospho-eNOS (P-eNOS) were detected by the Western blot. (4) The intracellular Ca2+ concentration were detect by flow cytometry. Measurement data with normal distribution were presented as ±s. The comparison among groups was analyzed using the ANOVA and pairwise comparison was analyzed by the LSD test. Results (1) The aperture size and distribution density of the peritoneal lymphatic stomata in the control group, sham operation group, intra-abdominal infection group and intra-abdominal infection drug intervention group were respectively (2.3±0.4)μm, (2.5±0.5)μm, (4.7±0.5)μm, (3.8±0.5)μm and (2.0±0.8)×108/m2, (2.1±0.7)×108/m2, (6.2±1.3)×108/m2, (4.6±1.4)×108/m2, with statistically significant differences among the 4 groups (F=98.130, 56.780, P 0.05). (2) The concentrations of NO in the peritoneal tissues in the control group, sham operation group, intra-abdominal infection group and intra-abdominal infection drug intervention group were respectively (0.380±0.024)μmol/gprot, (0.450±0.020)μmol/gprot, (1.253±0.033)μmol/gprot and (0.579±0.035)μmol/gprot, with a statistically significant difference among the 4 groups (F=52.725, P 0.05). (3) The results of Western blot showed that the expressions of eNOS and P-eNOS in the control group, sham operation group, intra-abdominal infection group and intra-abdominal infection drug intervention group were respectively (0.591±0.028)U/mg, (0.603±0.007)U/mg, (0.615±0.027)U/mg, (0.626±0.026)U/mg and (0.578±0.003)U/mg, (0.603±0.071)U/mg, (0.773±0.033)U/mg, (0.710±0.012)U/mg, with no statistically significant difference in the expression of eNOS among the 4 groups (F=0.902, P>0.05) and with a statistically significant difference in the expression of P-eNOS among the 4 groups (F=205.062, P 0.05). Conclusion The intra-abdominal infection could increase aperture size and distribution density of peritoneal lymphatic stomata, and PD123319 may be through inhibiting the activation of NO synthase to decrease the concentration of NO, enhance the concentration of Ca2+ in peritoneal mesothelial cells and reduce the opening of peritoneal lymphatic stomata. Key words: Abdominal cavity infection; Peritoneal lymphatic stomata; Nitric oxide; Angiotensin Ⅱ receptor specific inhibitor

Aperture effects in squid jet propulsion

Squid are the largest jet propellers in nature as adults, but as paralarvae they are some of the smallest, faced with the inherent inefficiency of jet propulsion at a low Reynolds number. In this study we describe the behavior and kinematics of locomotion in 1 mm paralarvae of Dosidicus gigas, the smallest squid yet studied. They swim with hop-and-sink behavior and can engage in fast jets by reducing the size of the mantle aperture during the contraction phase of a jetting cycle. We go on to explore the general effects of a variable mantle and funnel aperture in a theoretical model of jet propulsion scaled from the smallest (1 mm mantle length) to the largest (3 m) squid. Aperture reduction during mantle contraction increases propulsive efficiency at all squid sizes, although 1 mm squid still suffer from low efficiency (20%) because of a limited speed of contraction. Efficiency increases to a peak of 40% for 1 cm squid, then slowly declines. Squid larger than 6 cm must either reduce contraction speed or increase aperture size to maintain stress within maximal muscle tolerance. Ecological pressure to maintain maximum velocity may lead them to increase aperture size, which reduces efficiency. This effect might be ameliorated by nonaxial flow during the refill phase of the cycle. Our model's predictions highlight areas for future empirical work, and emphasize the existence of complex behavioral options for maximizing efficiency at both very small and large sizes.

New Optical Designs for Large Parabolic Troughs

The potential for cost reduction in parabolic troughs (PT) large collector fields is real and will be achieved in a variety of different ways. One problem certainly contributing to the costs of Solar Thermal Electricity (STE) PT fields is certainly the fact that large fields have a significant quantity of receiver lines and pipes bringing the heat transfer fluid to and off from them. The very large pipe length in large collector fields (for instance the 50MW fields in Spain) is a source of heat losses and parasitic losses due to significant pumping power, but also a source of other costs related to the number of pumps, to the amount of (costly) circulating fluid etc. In any given large field, receiver length and pipe length are determined by the aperture size of the PTs and one way to reduce these impacts on cost would be to increase aperture size. This has been the idea behind developments like the Ultimate Trough. In this paper new optical solutions are presented to obtain much larger troughs, using the same “standard” evacuated 70mm inner radius tube, which in fact amounts to a substantial increase of concentration, but without sacrificing the acceptance angle of the optic. The Simultaneous Multiple Surface (SMS) method is used and practical solutions are obtained for apertures nearly close to twice the present standard of ≈ 6m width. The case of troughs for fixed receiver tubes is also discussed in this context. The solutions developed minimize transmission losses due to the glass cover and in that sense are an improvement on previous work. They also achieve a higher optical performance than other second stage solutions, because they are designed to eliminate optical losses through large gaps, something that is associated with the fact that the outer glass envelope has a much larger diameter than the inner receiver tube. The paper presents new examples of larger troughs with second stage concentrators, characterizing and comparing them with a “conventional” PT. The comparison is done for optical properties and for the energy collected on a sunny location (Faro, Portugal). The paper ends with a similar exercise done for fixed receiver troughs, an exercise that also leads to larger troughs (since it is done for the same 70mm inner (evacuated) receiver tube) and concentration is increased. Again optical properties and energy performance are presented and compared with the conventional PT. The new solutions represent a potential reduction in field costs or even in O&M, as suggested, and this exercise will enable manufacturers the pondering of the manufacture of larger troughs (perhaps cheaper on a sqm basis) but with the extra cost of a secondary concentrator, knowing how much energy to expect from the adoption of solutions that benefit non-imaging optics design methods.

Bandwidth enhancement using gap‐coupled hexagonal microstrip antennas in L band

ABSTRACTNew configurations, involving parasitic gap coupling of identical hexagonal microstrip antennas, are investigated to enhance the bandwidth. A better coupling between the driven and the parasitic patches is realized owing to the straight sides of the hexagonal microstrip antennas. The overall configuration exhibits an enhanced gain due to the increased aperture size. Different gap‐coupled configurations, including a novel configuration of the off‐axis gap coupling of three hexagonal microstrip antennas, are presented. For this novel configuration, measured bandwidth as large as 101.2 MHz at the center frequency of 1.884 GHz has been obtained, this is almost four times as compared to that of a single hexagonal patch. Both on‐axis and off‐axis gap coupling of three hexagonal microstrip antennas are explored and the off‐axis configuration demonstrates a bandwidth enhancement of ∼1.35 times over that of the on‐axis configuration. For all the configurations, measured and simulated bandwidths are in close agreement. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2703–2709, 2013

Modeling and simulation of gravitational solid–solid separation for optimum performance

Reichert cone separators have been used for classification in the mineral processing industry for over six decades now. However, their application has always been limited to wet processing. In this paper, we assess the potential of their modification and use in gravitational dry solid–solid separation. A theoretical model was formulated, describing the motion of particles along inverted cone-shaped series of inclined screens with increasing aperture sizes under the force of gravity. A mathematical model to quantify the rate of separation was also suggested based on the theory. Three important design parameters were proposed to aid the actual engineering design of the system. The two models were test-run by numerical simulation under computer-generated, uniformly distributed random sized particles on a hypothetical 0.254 m radius cone, from which a theoretical screening rate of 32.52 g/s was achieved. The simulations were verified experimentally by designing a prototype system of equal effective screening area, and with equal input masses of glass beads, an overall screening rate of 23 g/s and a maximum separation efficiency of 66.4% was achieved. This study showed that a change in momentum of a heap of dry particulates controllably released on a perforated inclined surface is enough to cause sufficient separation of particles (~66.4%). The rates of separation achieved depend heavily on the inclination, particulate momentum, screening area, and particle sizes and shapes. ► We have described the motion of particles along inclined screens under gravity. ► Dry particles can be separated gravitationally on an inclined perforated surface. ► We suggested a mathematical model to quantify the separation rate. ► We proposed three parameters for equipment design. ► We have also tested the models experimentally and we have reported the results.

Focusing properties of aberration-free electromagnetic waves in thin dielectric slabs

We study properties of electromagnetic fields that are focused into thin dielectric slabs using an approach based on physical-optics or Kirchhoff’s approximation, making the results valid both for low and high Fresnel number focusing geometries. A variety of thin slab structures and focusing systems are studied with emphasis on the impact of the field that is due to the presence of the back interface of the slab which is critical in various fields such as optical recording, bio and material sciences. In particular, we investigate how the intensity of the focused field depends on variables such as aperture size, aperture-slab distance, slab refractive index, and slab thickness. Numerical results show that the contribution from the electric field due to the presence of the back interface of the slab is significant along the axis, which passes through the center of the spherical aperture and the focal point. With fixed focal length, the axial field inside the slab is found to increase and the focal shift to decrease as the aperture-slab distance is reduced. With increasing relative refractive index of the slab, the axial field is found to decrease, but to be more concentrated around the focus. With increasing aperture size, the axial field is found to increase, while interference effects due to the presence of the back interface of the slab are found to decrease.