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In the optical communication, the choosing scanning style is important for the optical communication, because the illuminating laser beam is narrow and the communication range is long. In this study, three typical scanning styles ...
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In the optical communication, the choosing scanning style is important for the optical communication, because the illuminating laser beam is narrow and the communication range is long. In this study, three typical scanning styles of raster scan, spiral scan and square spiral scan are compared with each other. The characteristics of the scanning styles are introduced. The numerical simulation model is built. The capturing time at the same condition is computed. The capturing time is affected by the scanning interval and the scanning area. In the same scanning area and scanning interval, the capturing time of raster scan is the biggest one and the capturing time of the square spiral scan is the smallest one.
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A vector approach to tracing the path of a laser beam through an optical system containing movable plane mirrors is described, which permits a unified treatment of a number of basic mirror-scanning devices. We show that the scan f...
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A vector approach to tracing the path of a laser beam through an optical system containing movable plane mirrors is described, which permits a unified treatment of a number of basic mirror-scanning devices. We show that the scan field produced by the mirror-scanning system is a curved surface with a straight line as its generating element. The cross section of the scan field can be a circle, an ellipse, or a curve in the shape of an egg. Based on this understanding, some advanced topics are addressed, e.g., the relationship between the scan field and the scan pattern, the dependence of the scan pattern on the location and orientation of the observation surface, optical distortions in a scan pattern, spot-size enlargement caused by non-normal incidence of the scan beam on the observation plane, and so on. Design equations and curves are derived for the mirror-scanning devices that most frequently exist in linear and circular scan technology. Part II contains an analysis of the galvanometer-based optical scanner paddle scanner and the regular polygon. In Part III, X-Y scanning systems are studied. [References: 17]
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Terrestrial laser scanning has received attention as an efficient technology in the cultural heritage domain for recording the geometry of historic monuments quickly and precisely. It is important to find appropriate scanner confi...
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Terrestrial laser scanning has received attention as an efficient technology in the cultural heritage domain for recording the geometry of historic monuments quickly and precisely. It is important to find appropriate scanner configurations to make the scanning process efficient and to build reliable records. These configurations should satisfy required constraints such as full coverage, sufficient overlap, scan range limit, and laser incidence angle. This is called the view planning problem. We sought to develop a scan planning scheme for recording large monuments in the cultural heritage domain. Typical approaches to deal with the view planning problem, however, do not consider the specific requirements in this domain. In this paper, we propose an interactive scan planning approach that supports analytic computation as well as heuristic decision. It includes three supporting guides. A next scan grid supports semi-automated optimization in interactive planning, and scan geometry helps the user to intuitively decide the next best position in a feasible region. A knowledge guide, which is reasoned out by similar properties, provides the user with experts' heuristic solutions to aid practical planning. These guides support efficient scan planning in a complementary manner. We introduce the use of region of interest to obtain more accurate data for focused features. ScanPlanner is implemented on this basis. The result of tests showed that the proposed approach allows users to make efficient and reliable scan plans for heritage recording.
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Configurations for active and passive optical scanning are categorized and unified with the use of a conjugate image model. Topics include architecture of scanners whose optical apertures may be overilluminated or underilluminated...
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Configurations for active and passive optical scanning are categorized and unified with the use of a conjugate image model. Topics include architecture of scanners whose optical apertures may be overilluminated or underilluminated by flux, which is (or is not) radially symmetric, providing scan magnification and possible image rotation. A scan locus theorem is introduced. Scanner-lens configurations include flat fielding, telecentricity, double pass, and beam expansion/compression. The resolution invariant reveals beam propagation and anamorphic beam-handling consequences. (C) 1995 Optical Society of America [References: 19]
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We present a mode-optimized two-dimensional piezoelectric fiber actuator and a robust actuation scheme to establish three different scan patterns with the same device. Having multiple scan options, the operator of the actuator is ...
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We present a mode-optimized two-dimensional piezoelectric fiber actuator and a robust actuation scheme to establish three different scan patterns with the same device. Having multiple scan options, the operator of the actuator is free to choose between improved uniformity, high frame rate to image abrupt biological event, or circular field-of-view to better image cylindrical cavities (gastrointestinal tract, esophagus, etc.) that are cylindrical in nature. We demonstrate the capabilities of the device, through first presenting its mechanical frequency behavior, then offering an actuation scheme to achieve different scan patterns, and finally generating 256 pixel width or diameter raster, spiral, and Lissajous patterns at >20 frames per second. With further development, the presented actuator design and drive scheme could serve as a useful tool as part of a minimally invasive optomedical device in the clinic.
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In wireless networks, when a mobile roaming station decides to initiate a handover, it should scan multiple channels operated by neighboring base stations (BSs) (or access points (APs)) in order to find an appropriate target base ...
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In wireless networks, when a mobile roaming station decides to initiate a handover, it should scan multiple channels operated by neighboring base stations (BSs) (or access points (APs)) in order to find an appropriate target base station before the actual handover. In some wireless networks, the active base station is able to provide a list of channels operated by neighboring base stations. However, some of these candidate channels may not be accessible to the mobile station (MS); nonetheless, the MS scans the candidate channels consecutively. For this reason, it may take a relatively long time for the MS to select an adequate target base station channel. This process can degrade the quality of service (QoS) during handovers. To shorten the scanning latency efficiently, in this paper we propose a cooperative channel scanning method whereby groups of MSs scan candidate channels using a dispersive schedule. They then share the scanning results amongst themselves, which results in a fast handover channel decision. To apply the proposed method to a real network environment, we present a group scanning architecture and detailed application scenarios appropriate for IEEE 802.16e worldwide interoperability for microwave access (WiMAX) networks. Numerical analyses and simulation results show that our proposed method achieves a shorter target channel scanning latency. Our method is thus more efficient in terms of scanning time and channel selection accuracy.
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Network scanning is considered to be the first step taken by attackers trying to gain access to a targeted network. System and network administrators find it useful if they are able to identify the targets scanned by network attac...
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Network scanning is considered to be the first step taken by attackers trying to gain access to a targeted network. System and network administrators find it useful if they are able to identify the targets scanned by network attackers. Resources and services can be further protected by patching or installing security measures, such as a firewall, an intrusion detection system, or some alternative computer system. This paper presents a statistical 'cross-relation' approach for detecting network scanning and identifying its targets. Our approach is based on using TCP RST packets for detecting TCP sequential scanning and ICMP type 3 (port unreachable) packets for detecting UDP sequential scanning. TCP or UDP random scanning is confirmed when there is a 'cross-relation' between an ICMP type 3, code 1 (host unreachable) and the TCP RST counts per source IP address and between an ICMP type 3, code 3 (port unreachable) and an ICMP type 3, code 1 (host unreachable). We tested the proposed approach with the DARPA 1998 data set and confirmed that our method was more effective in detecting TCP and UDP scanning than the existing approaches, and it also provided better detection accuracy.
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Background: Offset scanning procedures, such as reflection scanning, allow for dual-energy x-ray absorptiometry (DXA) body composition assessment of individuals who are too broad for standard scanning dimensions. However, limited ...
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Background: Offset scanning procedures, such as reflection scanning, allow for dual-energy x-ray absorptiometry (DXA) body composition assessment of individuals who are too broad for standard scanning dimensions. However, limited information is available concerning the precision of this procedure, particularly in athletes. Methodology: Twenty-seven muscular athletes (n = 17 males, BMI: 28.8 +/- 2.0 kg/m(2), DXA body fat: 12.5 +/- 2.7%; n = 10 females, BMI: 22.8 +/- 1.6 kg/m(2), DXA body fat: 19.2 +/- 3.4%) underwent consecutive DXA scans on a GE Lunar Prodigy scanner using the reflection scanning technique. The fully automated output was obtained for each scan, and an additional version of each scan's output was saved after manual adjustment of regions of interest (ROI). Metrics of reliability and precision were calculated for total and regional body mass (BM), lean mass (LM), fat mass (FM) and bone mineral content (BMC). These metrics included the precision error (PE), least significant change, Delta Mean, technical error of measurement, intraclass correlation coefficient, smallest worthwhile effect and minimum difference considered real. Results: Reflection scanning produced small errors for BM (PE: similar to 0.5%), LM (PE < 1%) and BMC (PE: similar to 1.2%), with larger errors observed for total FM (PE: similar to 3%). Manual ROI adjustment produced lower errors for total BM, LM, FM, and BMC, as well as lower errors for most regional estimates. The utilization of automated ROI revealed concerns unique to reflection scanning, including unnecessary estimation of trunk composition, which appreciably increased error in this region. Regional estimates produced higher errors for all variables as compared to whole-body estimates, although which regions produced the highest errors differed between BM, LM, FM, and BMC. Conclusions: Reflection scanning allows DXA body composition assessment in individuals exceeding traditional scanning dimensions, including broad athletes. Although this procedure introduces error, it may be minimized through manual adjustment of ROIs and consistency of analysis methods.
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The digital reconstruction of a computer aided design model from a physical object in the case of non-existence of such models has been a great challenge to engineers. With the advent of coordinate measuring machines (CMM), topolo...
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The digital reconstruction of a computer aided design model from a physical object in the case of non-existence of such models has been a great challenge to engineers. With the advent of coordinate measuring machines (CMM), topological information of the points on the object's surface can be extracted in the form of a point cloud. However, CMM has been a very slow process with relatively low resolution which becomes a hurdle for a rapid manufacturing process. As a result, a non-contact method has been developed to provide higher speed and high resolution scanning. Therefore, the source of uncertainties for a non-contact probe, especially the laser scanner, had been reviewed to identify the potential improvement areas. Although the uncertainties are related to data acquisition capability, the surface construction effectiveness from the point clouds has similar importance to obtain the most accurate contour with minimum deviation from the actual surface. This can be achieved by eliminating the noise and by fitting the best shape according to the feature, such as a plane, cylinder or sphere, to the point cloud. The main aim of this work is to analyse and improve the performance of the laser scanner in terms of dimensional accuracy. A DIGIBOT II~(TM) 3D laser digitizer which uses a remote ranging method was examined in the present work. The triangulation scanning system of this digitizer uses a high energy light source projected on the object's surface and a detector to sense the reflection. It was found that the scanning errors consist of random errors and systematic errors. For this scanner, the scanning data are random and follow the Gaussian distribution after the outliers are eliminated from the point cloud. The random error follows a systematic pattern where it varies with the scan depth and it is at a minimum when the y-coordinate is 228 mm and where the value of the error would be -0.0642 mm. The first systematic error is caused by the difference in the efficiency of photodetectors and the second systematic error is caused by the reflected laser intensity decrement as the scan depth increases. The second systematic error changes linearly when the y-coordinate is positive. Other methods for improving the scanning accuracy of the scanner have been recommended.
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