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Airyprime beam: From the non-truncated case to truncated one
摘要： The present paper investigates the spatial proprieties of a novel beam introduced recently known as Airyprime beam, its on-axis and transverse intensities are studied numerically. It is shown that the focused Airyprime beam exhibits two focuses corresponding to two intensities maxima limiting an Optical Bottle Beam (OBB), the latter is characterized by its length where numerical examples show that we can adjust and change it by changing the scale parameter w x0 which is related directly to the input width of the Airyprime beam. The spatial proprieties of the truncated Airyprime beam are also studied; by acting on the aperture diameter one can modify the on-axis intensity to choose between a mono focus beam and dual focus beam. Depending on the aperture diameter the Airyprime beam is transformed into other interesting laser beam patterns such as, a ?attop beam, Gaussian beam, and tune Optical Bottle Beam. The Airyprime beam could be interesting tool of trapping and guiding microparticles.
关键词： Flat top beam,Airyprime beam,Propagation and focusing,Optical bottle beam
更新于2025-09-23 15:23:52
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Electromagnetic waves' self-focusing in metamaterials having both LHM and RHM behavior: an application to filter design
摘要： Self-focusing, also known as Talbot’s effect had been widely studied by the scientific community. In this paper we show self-focusing as a coherence propagation phenomenon, in particular we studied self-focusing for a pulse propagating in a metamaterial with both behaviors: left handed material (LHM) and right handed material (RHM). These dual behaviors allow the construction of frequency filters in the range of frequency in which the metamaterial stops behaving as a LHM (negative refraction index) and begins an RHM behavior (positive refraction index). The coherence length (CL) for pulses propagating in these metamaterials seems to be larger when its frequencies are in the LHM region. Finally, we show that the cell’s size turns out to be critical in designing the filter, and as an example we present here four metamaterial cells.
关键词： metamaterials,filters,self-focusing,Coherence propagation
更新于2025-09-23 15:23:52
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Controlling the relativistic self-focusing of Hermite-cosh-Gaussian beams in plasma
摘要： The purpose of current study was to find the effects of Hermite-cosh-Gaussian (HChG) beam characteristics on the relativistic self-focusing. The Self-focusing Parameter (SFP), for mode indexes of m=0, 1, and 2 is proposed which provides a basis for achieving the nonlinear self-focusing dependencies on the beam characteristics. The dissimilar nonlinear self-focusing dependencies of different mode indexes on the initial intensity and decentered parameter of HChG beam are founded. The predictions of SFP model are then validated by investigating the beam focusing/diverging along the propagation axis and the exact conformity is observed. The results of introduced model can by applied for HChG beams with higher mode indexes, the Hermite Gaussian and cosh-Gaussian beams.
关键词： Hermite-cosh-Gaussian beam,mode indices,Decentered parameter,Plasma,Relativistic self-focusing
更新于2025-09-23 15:23:52
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[IEEE 2018 China International SAR Symposium (CISS) - Shanghai (2018.10.10-2018.10.12)] 2018 China International SAR Symposium (CISS) - Extended Map-Drift Algorithm for Spaceborne Sliding Spotlight SAR Data
摘要： For flexibly steering antenna in along-track direction, space-borne synthetic aperture radar (SAR) can achieve high resolution with wide swath conveniently, especially in sliding spotlight mode. In order to overcome azimuth folding effects in this mode, the three-step focusing algorithm was been proposed. However it is difficult to perform fine focus of image due to Doppler rate errors. In this paper, a kind of auto-focusing approach based on Map-Drift (MD) is proposed, which is compatible with the three-step imaging algorithm and efficient. Firstly, the Doppler-rate error transfer mechanism in de-ramp operation (the third step of the three-step focusing algorithm) is illustrated. Secondly, the accurate images draft due to Doppler-rate error is conduced based on this mechanism. Thirdly, a new efficient strategy of iteration is present. Finally, the validness and efficiency of the proposed approach is tested by simulation data and real SAR data.
关键词： synthetic aperture radar (SAR),Map-Drift,auto-focusing,sliding spotlight,focusing algorithm,three-step approach
更新于2025-09-23 15:22:29
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Effect of Non-Uniform Azimuth Sampling on Sar Image Formation Evaluated at 79Ghz
摘要： Conventional synthetic aperture radar (SAR) image formation requires uniform sampling along the azimuth direction. These image formation relies on frequency domain algorithms including the Range-Doppler Algorithm (RDA), Chirp-Scaling Algorithm (CSA) [1] etc, that make use of azimuth Fast Fourier Transform, hence the requirement of uniform sampling. While uniform sampling in space is not always achievable, the samples can be interpolated onto a uniform grid given the sampling rate is Nyquist. This paper studies the effect of SAR image formation when the azimuth sampling is not uniform, and not Nyquist in some interval. The results showed that even if there is a wide interval in the middle of the synthetic aperture with no samples, an image can still be formed. This result could be useful when the SAR antenna is a phased array, or when the hardware is generating bursts of pulses followed by a quiet window.
关键词： Image focusing,Back-Projection,Azimuth Sampling,Synthetic aperture radar
更新于2025-09-23 15:22:29
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - A Car-Borne SAR System for Interferometric Measurements: Development Status and System Enhancements
摘要： Terrestrial radar systems are used operationally for area-wide measurement and monitoring of surface displacements on steep slopes, as prevalent in mountainous areas or also in open pit mines. One limitation of these terrestrial systems is the decreasing cross-range resolution with increasing distance of observation due to the limited antenna size of the real aperture radar or the limited synthetic aperture of the quasi-stationary SAR systems. Recently, we have conducted a first experiment using a car-borne SAR system at Ku-band, demonstrating the time-domain back-projection (TDBP) focusing capability for the FMCW case and single-pass interferometric capability of our experimental Ku-band car-borne SAR system. The cross-range spatial resolution provided by such a car-based SAR system is potentially independent from the distance of observation, given that an adequate sensor trajectory can be built. In this paper, we give (1) an overview of the updated system hardware (radar setup and high-precision combined INS/GNSS positioning and attitude determination), and (2) present SAR imagery obtained with the updated prototype Ku-band car-borne SAR system.
关键词： azimuth focusing,Ku-band,SAR imaging,ground-based SAR system,car-borne SAR,parallelization,SAR interferometry,GPU,CUDA,interferometry,CARSAR,Synthetic aperture radar (SAR)
更新于2025-09-23 15:22:29
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Temperature Measurement of Fluid Flows by Using a Focusing Schlieren Method
摘要： A method for measuring planar temperature fields of fluid flows is proposed. The focusing schlieren technique together with a calibration procedure to fulfill such a purpose is used. The focusing schlieren technique uses an off-axis circular illumination to reduce the depth of focus of the optical system. The calibration procedure is based on the relation of the intensity level of each pixel of a focused schlieren image to the corresponding cutoff grid position measured at the exit focal plane of the schlieren lens. The method is applied to measure planar temperature fields of the hot air issuing from a 10 mm diameter nozzle of a commercial Hot Air Gun Soldering Station Welding. Our tests are carried out at different temperature values and different planes along the radial position of the nozzle of the hot air. The experimental values of temperature measurements are in agree with those measured using a thermocouple.
关键词： temperature,focusing schlieren,measurements
更新于2025-09-23 15:22:29
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Near Real-Time Sar Image Focusing Onboard Spacecraft
摘要： SAR imagery requires image focusing through successive signal processing of received data before browsing images and acquiring information. For example, the signal data records of ALOS-2/PALSAR-2 are stored in the onboard mission data storage, transmitted to the ground, and then focused to reproduce images. Apart from the power consumption, the storage volume and the transmission network speed are the two major factors that are limiting the utility of today’s spaceborne SAR systems. One of the solutions is to further compress the SAR data through onboard signal processing and information extraction from the reproduced images. This is also beneficial for event-driven observations and fast delivery of information products. The Emergence Studio of JAXA has been developing evaluation models of FPGA-based signal processing system for onboard SAR image focusing. The model, namely, “Fast L1 Processor 2 (FLIP2)” can reproduce a 3m/6m/10m-resolution single look complex image from ALOS-2/PALSAR-2 data in near real-time. Preliminary evaluation results are presented in this article.
关键词： onboard processing,FPGA,image focusing,SAR
更新于2025-09-23 15:22:29
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Method for Processing and Analysis of the Images of a Network of Thermal Fatigue Cracks on the Surfaces of Rollers of Continuous Casting Machines
摘要： We propose an algorithm for the analysis of thermal fatigue cracks on the surfaces of rollers of continuous casting machines that does not require adaptation to images of various types and individual choice of parameters. For this purpose, the images are analyzed for a sufficiently large subset of the sets of values of the parameters. The result of this classification is regarded as a fuzzy set with a membership function of each element equal to the number of sets of parameters responsible for the detection of this element as a component of the frame of the damage grid.
关键词： image processing,thermal fatigue cracks,self-focusing,fuzzy sets,classification
更新于2025-09-23 15:21:21
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Enhanced spatial focusing increases feature-based selection in unattended locations
摘要： Attention is a multifaceted phenomenon, which operates on features (e.g., colour or motion) and over space. A fundamental question is whether the attentional selection of features is confined to the spatially-attended location or operates independently across the entire visual field (global feature-based attention, GFBA). Studies providing evidence for GFBA often employ feature probes presented at spatially unattended locations, which elicit enhanced brain responses when they match a currently-attended target feature. However, the validity of this interpretation relies on consistent spatial focusing onto the target. If the probe were to temporarily attract spatial attention, the reported effects could reflect transient spatial selection processes, rather than GFBA. Here, using magnetoencephalographic recordings (MEG) in humans, we manipulate the strength and consistency of spatial focusing to the target by increasing the target discrimination difficulty (Experiment 1), and by demarcating the upcoming target’s location with a placeholder (Experiment 2), to see if GFBA effects are preserved. We observe that motivating stronger spatial focusing to the target did not diminish the effects of GFBA. Instead, aiding spatial pre-focusing with a placeholder enhanced the feature response at unattended locations. Our findings confirm that feature selection effects measured with spatially-unattended probes reflect a true location-independent neural bias.
关键词： Global feature-based attention,Attention,Spatial focusing,Magnetoencephalographic recordings,Visual processing
更新于2025-09-23 15:21:21