Aperture Position Research Articles

B11-O-13A New Atomic Scale EMCD Measurement Scheme by STEM-EELS under 3-beam Diffraction Condition

Electron magnetic circular dichroism (EMCD) in the transmission electron microscope (TEM) is a relatively immature technique, though it has already demonstrated quantitative results with a spatial resolution superior to what can be achieved with X-rays [ 1 ]. The main obstacles for widely sharing the method for routine use are (i) low SNR because of off-axis EELS detection, (ii) requiring a very thin sample for quantitative analysis and (iii) unstable pre- and post-edge backgrounds by subsequent measurements in changing the aperture positions. There have been a number of attempts to overcome those difficulties, such as collecting hundreds of data and applying statistical/information data processing methods [ 2 , 3 ]. In the present study we found a novel experimental condition that allowed us to solve almost all these difficulties and even applicable to atomic resolution EMCD measurements. The present scheme proposed is based on a symmetrical three-beam diffraction condition in a Fe film at STEM mode with the EELS aperture placed slightly off-axis on either side of the systematic row of the reflections. A focused electron probe is scanned on the sample to find 1-dimensional lattice fringes as the ADF-STEM image. The chiral ± EMCD signals appear at the both sides of the atomic column fringes, with the EMCD signal of the opposite sign appearing on the opposite sides of a lattice fringe. This method requires only a single scan to obtain the chiral ± EMCD signals and also exhibits stable signal fractions with the change in sample thickness. We show the first experimental results based on this concept, which can solve the most of difficulties existing and be a novel breakthrough in the quantitative atomic scale EMCD measurements.

Comparison of Four X-Band TE111 Cavities for In Vivo ESR Tooth Dosimetry

Four X-band TE111 electron spin resonance cavities which were different in dimensions and detection apertures were developed. Comparison of performance and characteristics of these cavities was carried out to investigate the influences of the cavity geometry, detection aperture position and geometry, aiming to optimize the design and capability of TE111 cavity for in vivo tooth dosimetry. The characteristics of the cavities were evaluated by finite elements calculation, DPPH sample measurement and intact tooth measurement. The results suggested that (1) expanded geometry of the aperture made it easier for teeth biting into the aperture; (2) the detection aperture position and size could introduce obvious influence to resonant quality factor Q; (3) the cavity dimension influenced the resonant factor Q, microwave distribution and in vivo detection implement; (4) lower diameter-height ratio brought more convenience for placement in inner oral. These results provided the references for future TE111 mode cavity design in aperture and cavity geometry.

A New Species ofChthonerpetonPeters 1880 (Amphibia: Gymnophiona: Typhlonectidae) from the State of Piauí, Northeastern Brazil

Abstract Gymnophionan amphibians are characterized mainly by having elongated bodies and lack of limbs and are poorly known because of their secretive life habits. Most species are fossorial, although some are aquatic or semiaquatic. We describe a new species of semiaquatic caecilian, genus Chthonerpeton, from a transition area between the Caatinga and Cerrado biomes, along the coastal vegetation of the State of Piaui, northeastern Brazil. The new species is very similar to Chthonerpeton perissodus and Chthonerpeton noctinectes in annular counts but differs in number of cloacal denticles, color pattern, position of tentacle aperture, and number of teeth.

Evolution of Angiosperm Pollen. 2. The Basal Angiosperms1

Recently, evolutionary relationships among the five major lineages of the basal angiosperms, i.e., Amborellanae, Nymphaeanae, Austrobaileyanae, Magnolianae, and Ceratophyllanae, still remain incompletely or controversially resolved. This study reviews and reevaluates the origin, evolution, and systematic significance of pollen morphology in basal angiosperms. Pollen grains from 34 species of 31 genera in 23 families of the basal angiosperms are investigated, using light microscopy (LM) and scanning electron microscopy (SEM), to illustrate the pollen diversity across the grade. Pollen data for 57 genera, representing all nine orders and 28 families of the basal angiosperms, were obtained from previous work and new investigations and were used to optimize character states onto recent molecular phylogenetic estimates. Two 18-character datasets were generated: a comprehensively coded dataset optimized with Fitch parsimony onto 12 recent phylogenies with differing topologies to evaluate the degree of pollen systematic significance of each topology, and a democratically coded dataset optimized by using Fitch parsimony, maximum likelihood, and hierarchical Bayesian inference onto a single recent phylogeny based on molecular data from Soltis et al. to evaluate the disparity of pollen evolutionary patterns among the three methods. Pollen morphology of the basal angiosperms is highly diverse, particularly in terms of pollen size, aperture number, aperture position, ectoaperture shape, tectum sculpture, and infratectal structure. Based on both datasets, the plesiomorphic pollen type for angiosperms was inferred to comprise monads of heteropolar, spheroidal, mono-apertural grains, with distal, colpate apertures, sculptured aperture membranes, and an infratectum and foot layer. Of the basal angiosperm phylogenies considered, when taxon sampling is taken into account, pollen characters provide greatest support for the topology represented in the three-mitochondrial-gene study from Qiu et al., in terms of number of synapomorphies plus what we term “likely synapomorphies” in which the subtending node is ambiguous and, therefore, the exact position of the synapomorphy is ambiguous. Thirty-six various lineages above family level are supported by pollen morphological synapomorphies or likely synapomorphies. We discuss the systematic significance of pollen morphology in basal angiosperm clades including the ANITA group (Amborellaceae, Nymphaeaceae, Schisandraceae, Trimeniaceae, and Austrobaileyaceae), Ceratophyllales, Chloranthales, and magnoliids, as well as in related lineages, i.e., monocots and basal eudicots. We also discuss present limitations in inferring the evolutionary history of pollen morphology in basal angiosperms.

Compact dual ports handheld RFID reader antenna with high isolation

A compact dual ports antenna with high isolation is proposed for handheld radio frequency identification (RFID) reader, which is rarely reported in open literatures. Different with conventional handheld RFID reader antenna with single port, the proposed antenna transmits and receives signal separately. The proposed antenna operating with full duplex mode can enhance effectively sensitivity of reader, as the strong transmitting signal of reader with single port is usually highly coupled with weak receiving backscatter signal of tag. The antenna utilizes aperture coupled patch structure that occupies less volume and provides further space-saving efficiency. The height of the proposed antenna is only 5.1 mm and the volume of that is 80 ×80 × 5.1 mm3, which is easy to integrate in handheld RFID readers. The antenna uses four symmetric coupling apertures to excite two orthogonal modes for dual polarized operation. High isolation of around −35 dB is obtained by proper arrangement of the length and position of the coupling apertures. The maximum measured return loss is −39 dB at 2.4 GHz and isolation is −47 dB at 2.4 GHz. The antenna is suitable for applications in handheld RFID readers. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:548–555, 2015.

Action can amplify motion-induced illusory displacement.

Local motion is known to produce strong illusory displacement in the perceived position of globally static objects. For example, if a dot-cloud or grating drifts to the left within a stationary aperture, the perceived position of the whole aperture will also be shifted to the left. Previously, we used a simple tracking task to demonstrate that active control over the global position of an object did not eliminate this form of illusion. Here, we used a new iPad task to directly compare the magnitude of illusory displacement under active and passive conditions. In the active condition, participants guided a drifting Gabor patch along a virtual slalom course by using the tilt control of an iPad. The task was to position the patch so that it entered each gate at the direct center, and we used the left/right deviations from that point as our dependent measure. In the passive condition, participants watched playback of standardized trajectories along the same course. We systematically varied deviation from midpoint at gate entry, and participants made 2AFC left/right judgments. We fitted cumulative normal functions to individual distributions and extracted the point of subjective equality (PSE) as our dependent measure. To our surprise, the magnitude of displacement was consistently larger under active than under passive conditions. Importantly, control conditions ruled out the possibility that such amplification results from lack of motor control or differences in global trajectories as performance estimates were equivalent in the two conditions in the absence of local motion. Our results suggest that the illusion penetrates multiple levels of the perception-action cycle, indicating that one important direction for the future of perceptual illusions may be to more fully explore their influence during active vision.

Analysis of the clear aperture of Savart plates in polarization interference imaging spectrometer

The principle of beam splitting of interference imaging spectrometer based on Savart plates is presented. The propagation track of light wave in crystal and the exit aperture is analysed by combining wave normal-tracing method with ray-tracing method at random incidence angle and azimuth angle. The relationship among exit aperture, incident angle, incident position and azimuth angle is deduced in detail. The requirements that the propagation track of light remains in Savart plates and would not exit from the top surface, bottom surface and side are discussed in detail. The area and the position of exit aperture are simulated by computer, which proves the correctness of the deduction for normal incidence of light. It is shown that the lateral shear of single Savart plate restricts the boundary of clear aperture, and the area of the clear aperture is only 85.73% against the total incident surface. The parameter of experimental prototype is introduced and the clear aperture is in detail analysed and discussed by the method mentioned above. The results show that the accurate and the approximate values of exit aperture area of experimental prototype are greatly different, and the position of exit aperture are shifted into the lower right, which may reduce the image quality and even cannot generate the double-beam interference fringes in some specific areas. The effective clear aperture as a function of azimuth angle is also presented. It shows that the used clear aperture area is between 0.8005 and 0.8547 while changes from 0 to 2, in order to match the conditions that the value of area availability decreases to 0.6976 when the light always propagates inside the Savart plates. The article shows that the change of clear aperture caused by crystal birefringence phenomenon cannot be ignored when selecting the instrument aperture stop and parameter of interference imaging spectrometer. The clear aperture of the two beams, o-light and e-light, which propagate in Savart plates should be calculated respectively and then they are used to determine the last clear apertures of plates. This study provides a theoretical and practical guidance for study, design, modulation, experiment and engineering of interference imaging spectrometers.

傅里叶望远镜激光发射系统性能分析

The performance of Fourier telescope transmitting system directly affects the image resolution and quality. The parameters and performance requirements of laser are analyzed. The design outline of fiber laser is presented. Meanwhile, the point is put forward that the laser coherence length need to be at least 1.6 times of the residual optical path. The stability of laser power and frequency is simulated. To ensure the stability of the laser, some methods are put forward from the points of design, algorithm and practice. Furthermore, combined with the results of simulation and experiment, the influences of the transmitter performance on image quality is analyzed, from the aspects of transmitting aperture layout, aperture amount, position precision and the beam pointing error. And point out that baseline redundancy, image resolution, target spectrum and image quality are the factors should be synthetically considered when arranging transmitter array. The formula for calculating the number of transmitting apertures is obtained based on the two-dimensional sampling theorem and the statistical analysis results. The transmitting aperture number is calculated for the Fourier telescope whose resolution would be 5 cm for objects in 1000 km low earth orbit. In addition, it is concluded that the transmitting aperture position error should be less than 5% of the minimum aperture spacing. ©, 2015, Chinese Optical Society. All right reserved.

Radiant exposure level comparison between Gaussian and top hat beams in various scanning patterns

The radiant exposure of optical irradiation beams with different scanning parameters has been theoretically studied. We analyzed the difference in radiant exposure introduced by Gaussian and top hat beams. Various parameters such as scanning pattern, aperture position, beam size and scan spacing were also introduced in this study. We found that Gaussian beams introduce higher calculated radiant exposure to the aperture than top hat beams for certain beam size to aperture size ratios. However, as the scan spacing decreases, the radiant exposure difference calculated from Gaussian and top hat beams diminishes.

Characithecium (Monogenoidea: Dactylogyridae) parasitic on the Neotropical fish Oligosarcus jenynsii (Teleostei: Characidae) from the Pampasic region, Argentina, with the emendation of the genus.

Presently, only 2 species of dactylogyrid monogeneans have been reported Characidae inhabiting lakes and streams from the Pampasic region (central Argentina). During a parasitological survey on the characid Oligosarcus jenynsii, from Nahuel Rucá Lake (Buenos Aires province, Argentina), dactylogyrids were found on the gills. Specimens were identified as members of Characithecium: C. chascomusensis n. comb, C. longianchoratum n. sp., C. robustum n. sp., C. quadratum n. sp. and C. chelatum n. sp. These species can be distinguished from each other mainly by differences in the shape of the accessory piece of the male copulatory organ, morphology of anchors and ventral bars as well as position of vaginal aperture. The observation of some additional features present in all species studied, such as the vaginal aperture position (as midventral, lateroventral or lateromarginal) and the variability in the morphology of ventral bar (posteromedial projection present or absent) justified an emended diagnosis of Characithecium.

Transmission-Based Imaging of an Electrically Small Aperture in a Shielded System

The possibility of imaging the position and nature of apertures in a metallic shielding is discussed. Synthetic images are obtained from signals induced at the interior of the shielding by a set of plane waves impinging on it along different directions of arrival. The proposed technique works analogously to inverse synthetic aperture radar imaging, but is based on signals related to transmitted rather than scattered waves. A theoretical analysis of the features of the images associated to electric and magnetic coupling is presented.

Field synergy principle analysis for reducing natural convection heat loss of a solar cavity receiver

Due to the operating temperature from 900 K to 1300 K produced by the concentrating ratio over 2000 in solar parabolic dish-engine system, the natural convection heat loss driven by the buoyancy force of air contributes an important role in the energy loss of cavity receiver. 3-D numerical simulations were performed and the results are analyzed from the novel viewpoint of field synergy principle (FSP) in order to study the heat transfer and fluid flow characteristics in natural convection heat loss of cavity receiver. The effects of geometric parameters, including the inclination angle, aperture size, aperture position and cavity geometric shape on the natural convection heat loss of cavity receiver were examined. The FSP analysis on the simulation results demonstrates that FSP can well explain the reduction mechanism for natural convection heat loss of cavity receiver because the smaller inner production of velocity vector and temperature gradient always corresponds to the lower Nusselt number occurred in the cases with lager inclination angle, smaller aperture size, lower aperture position and frustum-cylinder cavity, respectively. Therefore, the reducing natural convection heat loss attributes to the weakening synergy between velocity vector and temperature gradient. In addition, the local heat transfer performance is studied by the presented distributions of heat transferred via fluid motion, where more interesting natural convection heat loss characteristics of cavity receiver and the detailed explanations were provided. The results of this work offer benefits for the development of theory and technique about reducing natural convection heat loss of cavity receiver.

Condenser-free contrast methods for transmitted-light microscopy.

Phase contrast microscopy allows the study of highly transparent yet detail-rich specimens by producing intensity contrast from phase objects within the sample. Presented here is a generalized phase contrast illumination schema in which condenser optics are entirely abrogated, yielding a condenser-free yet highly effective method of obtaining phase contrast in transmitted-light microscopy. A ring of light emitting diodes (LEDs) is positioned within the light-path such that observation of the objective back focal plane places the illuminating ring in appropriate conjunction with the phase ring. It is demonstrated that true Zernike phase contrast is obtained, whose geometry can be flexibly manipulated to provide an arbitrary working distance between illuminator and sample. Condenser-free phase contrast is demonstrated across a range of magnifications (4–100×), numerical apertures (0.13–1.65NA) and conventional phase positions. Also demonstrated is condenser-free darkfield microscopy as well as combinatorial contrast including Rheinberg illumination and simultaneous, colour-contrasted, brightfield, darkfield and Zernike phase contrast. By providing enhanced and arbitrary working space above the preparation, a range of concurrent imaging and electrophysiological techniques will be technically facilitated. Condenser-free phase contrast is demonstrated in conjunction with scanning ion conductance microscopy (SICM), using a notched ring to admit the scanned probe. The compact, versatile LED illumination schema will further lend itself to novel next-generation transmitted-light microscopy designs. The condenser-free illumination method, using rings of independent or radially-scanned emitters, may be exploited in future in other electromagnetic wavebands, including X-rays or the infrared.

A Rotating Synthetic Aperture Radar Imaging Concept for Robot Navigation

This paper introduces a concept for robot navigation based on a rotating synthetic aperture short-range radar scanner. It uses an innovative broadband holographic reconstruction algorithm, which overcomes the typical problem of residual phase errors caused by an imprecisely measured aperture position and moving targets. Thus, it is no longer necessary to know the exact trajectory of the synthetic aperture radar to get a high-resolution image, which is a major advantage over the classical holographic reconstruction algorithm. However, the developed algorithm is not only used to compute a high-resolution 360 ° 2-D image after each turn of the radar platform while the robot is moving, but also to calculate the relative residual radial velocity between the moving radar scanner system and all targets in the environment. This allows us to determine the exact velocity of the robotic system on which the radar scanner is mounted, and thus to obtain the exact radar trajectory, if there are stationary targets like walls in the environment.

Simulation of field emission behavior from multiple carbon nanotubes in an integrated gate triode configuration

The paper investigates the simulation results of a model for Carbon Nanotube (CNT) field emitters in triode configuration with an integrated gate. Simulation studies have been carried out to analyze and evaluate the performance of a triode device with multiple CNT tips on a silicon substrate. The model has been developed using CST Particle Studio software. The modulating effect of control gate on field emission properties of the device is simulated and dc characteristics at different gate voltages are obtained. It is seen that a small change in gate voltage causes a large change in current between the anode and the cathode. The effect of gate aperture and relative position of the CNT tip with respect to the gate level on field emission is also investigated and modeled. The model helped in providing an understanding of a complete cathode device with an integrated extractor (gate) for potential applications in Vacuum Microelectronic (VME) devices.

An Extended Analytical Formulation for Fast Prediction of Shielding Effectiveness of an Enclosure at Different Observation Points With an off-Axis Aperture

In this paper, Robinson's analytical formulation is extended to calculate the shielding effectiveness of an shielding enclosure at off-axis observation points with an off-axis aperture. First, we give the procedure of extending the original analytical formulation. Then, the transmission-line matrix method (TLM) is utilized to validate the extended analytical formulation. The application range of the extended method is decided by comparing to TLM, and the good agreement between the results calculated by two methods indicates that the extended analytical formulation is efficient in predicting the shielding effectiveness of an enclosure at different observation points with an off-axis aperture. Through the intensive calculation and analysis, the distribution of SE inside the enclosure and the variation of SE with aperture position can be obtained, which may be used as a guideline for designing shielding enclosures.

SU‐D‐18A‐05: Assessing Elekta MLC Tracking Performance

Purpose:To investigate the technical feasibility of using Elekta MLCs in tracked radiotherapy, specifically to show the capability of an Agility MLC to follow model tumor trajectories using object tracking. The system performance of the MLC is to be assessed via dosimetric experiments and temporal response measures.Methods:The system observer in the tracking cascade consisted of a camera serving for this proof of concept; Images of a moving object were acquired continuously and decorrelated for the position information, which was fed forward to the RT computer controlling the MLC via an interface provided by Elekta. The 1D motion (in the direction of the leaves) was induced by a CIRS motion controller. Additionally, the aperture position was observed by means of the light field of the linac. Calculating the phase between aperture and object yielded the mean aperture lag for the current setup. The object was restricted to sinusoidal motion with a period of 10s. For dosimetry, GafChromic radiosensitive film was irradiated with a total dose of 1000MU using an aperture size of 40mm and a motion range of 30mm.Results:Object tracking can substantially reconstruct the geometric dose response of a static target. In the dynamic case, dose is smeared out into the legs of the static distribution, leading to a reduced plateau and increased FWHM of 5mm, compared to the static width of 38mm. The time‐lag between object and aperture was determined to be approximately 300ms for the current set‐up.Conclusion:We demonstrated a tracking experiment performed on a clinical Elekta linear accelator for the first time. Observed profile variations show the dosimetric impact of tracked delivery. The determined lag is a valuable descriptor for a future tracking cascade employing predictor filters. The performed experiments are generic and possible predecessors for future applications with MR‐Linac or ultrasound probes.Conflict of interest: this project is partly funded by Elekta.

Sparse models and sparse recovery for ultra-wideband SAR applications

This paper presents a simple yet very effective time-domain sparse representation and associated sparse recovery techniques that can robustly process raw data-intensive ultra-wideband (UWB) synthetic aperture radar (SAR) records in challenging noisy and bandwidth management environments. Unlike most previous approaches in compressed sensing for radar in general and SAR in particular, we take advantage of the sparsity of the scene and the correlation between the transmitted and received signal directly in the raw time domain even before attempting image formation. Our framework can be viewed as a collection of practical sparsity-driven preprocessing algorithms for radar applications that restores and denoises raw radar signals at each aperture position independently, leading to a significant reduction in the memory requirement as well as the computational complexity of the sparse recovery process. Recovery results from real-world data collected by the U.S. Army Research Laboratory (ARL) UWB SAR systems illustrate the robustness and effectiveness of our proposed framework on two critical applications: 1) recovery of missing spectral information in multiple frequency bands and 2) adaptive extraction and/or suppression of radio frequency interference (RFI) signals from SAR data records.

A fast white-beam shutter for hard x-ray topography at beamline 1-BM of the Advanced Photon Source

Beamline 1-BM at the Advanced Photon Source (APS) delivers a white beam from a bending magnet with very intense x-ray photon flux. One important application of this beamline is white-beam x-ray topography imaging for crystal-based x-ray optics development and for industrial characterization of single crystals and epitaxial materials. Due to the intense photon flux from the third-generation synchrotron source of the APS, the exposure time of the imaging process should be accurately controlled down to the millisecond level. For this purpose we have designed and implemented a fast shutter that is vacuum compatible to 10−8 torr. The aperture is a copper block with a 70 mm horizontal and 5 mm vertical opening and is water cooled. The aperture is moved vertically up and down by means of a linear voice-coil actuator. The aperture's position is controlled using encoder feedback in a servo loop running on an industrial motion controller. A shutter opening response time of 32 milliseconds was measured. In this paper, we describe the shutter mechanics and its associated electronics installed at the 1-BM, and we report example white-beam topographs of diamond type IIa crystals.

Sensitivity of edge illumination X-ray phase-contrast imaging

Recently, we developed a theoretical model that can predict the signal-to-noise ratio for edge-like features in phase-contrast images. This model was then applied for the estimation of the sensitivity of three different X-ray phase-contrast techniques: propagation-based imaging, analyser-based imaging and grating interferometry. We show here how the same formalism can be used also in the case of the edge illumination (EI) technique, providing results that are consistent with those of a recently developed method for the estimation of noise in the retrieved refraction image. The new model is then applied to calculate, in the case of a given synchrotron radiation set-up, the optimum positions of the pre-sample aperture and detector edge to maximize the sensitivity. Finally, an example of the extremely high angular resolution achievable with the EI technique is presented.