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1
Fu, Hao, und Rui Yu. „LIDAR Scan Matching in Off-Road Environments“. Robotics 9, Nr. 2 (15.05.2020): 35. http://dx.doi.org/10.3390/robotics9020035.
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Accurately matching the LIDAR scans is a critical step for an Autonomous Land Vehicle (ALV). Whilst most previous works have focused on the urban environment, this paper focuses on the off-road environment. Due to the lack of a publicly available dataset for algorithm comparison, a dataset containing LIDAR pairs with varying amounts of offsets in off-road environments is firstly constructed. Several popular scan matching approaches are then evaluated using this dataset. Results indicate that global approaches, such as Correlative Scan Matching (CSM), perform best on large offset datasets, whilst local scan matching approaches perform better on small offset datasets. To combine the merits of both approaches, a two-stage fusion algorithm is designed. In the first stage, several transformation candidates are sampled from the score map of the CSM algorithm. Local scan matching approaches then start from these transformation candidates to obtain the final results. Four performance indicators are also designed to select the best transformation. Experiments on a real-world dataset prove the effectiveness of the proposed approach.
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Marzo, John M., Melissa A. Kluczynski, Anthony Notino und Leslie J. Bisson. „Measurement of Tibial Tuberosity–Trochlear Groove Offset Distance by Weightbearing Cone-Beam Computed Tomography Scan“. Orthopaedic Journal of Sports Medicine 5, Nr. 10 (01.10.2017): 232596711773415. http://dx.doi.org/10.1177/2325967117734158.
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Background: Computed tomography (CT) scans are useful for objectively measuring bone alignment because they show bone detail particularly well, and these scans have been used extensively to assess patellar orientation. The tibial tubercle–trochlear groove (TT-TG) offset distance has been shown to be influenced by knee flexion and weightbearing, yet conventional CT scans are obtained with the subject relaxed, supine, and with the knee in full extension. A new cone-beam CT scanner has been designed to allow for weightbearing images, potentially providing a more physiologically relevant assessment of patellofemoral alignment. Purpose/Hypothesis: The purpose of this study was to measure the TT-TG offset in healthy individuals without any history of knee complaints when CT scans were obtained while fully weightbearing on a flexed knee. Our hypothesis was that the TT-TG offset measurement in these healthy knees would be reproducible and less than the historically reported normal range. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Twenty healthy volunteers without any history of knee complaint were recruited to undergo a weightbearing cone-beam CT scan of the knee flexed at 30°. The scans were reviewed by a radiologist and an orthopaedic surgeon, and TT-TG offset was measured using the digital tools of a picture archiving and communication system. Paired t tests were used to compare TT-TG offset on 2 separate occasions for both raters. Inter- and intrarater reliability were assessed using a 2-way mixed-effects model intraclass correlation coefficient with corresponding 95% confidence intervals for TT-TG offset. Results: The mean TT-TG offset was 2.7 mm. There were no statistically significant differences in TT-TG offset between raters ( Prater1 = .70; Prater2 = .49) and time of read ( Ptime1 = .83; Ptime2 = .19). Good to moderate interrater reliability was found at the time of both reads, and good intrarater reliability was found for both raters. Conclusion: When measured by CT scan and obtained from a subject while weightbearing on a flexed knee, the TT-TG offset is reproducible and the distance is less than that obtained via a conventional CT scan.
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Yin, Zhye, Bruno De Man und Jed Pack. „3D Analytic Cone-Beam Reconstruction for Multiaxial CT Acquisitions“. International Journal of Biomedical Imaging 2009 (2009): 1–11. http://dx.doi.org/10.1155/2009/538389.
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A conventional 3rd generation Computed Tomography (CT) system with a single circular source trajectory is limited in terms of longitudinal scan coverage since extending the scan coverage beyond 40 mm results in significant cone-beam artifacts. A multiaxial CT acquisition is achieved by combining multiple sequential 3rd generation axial scans or by performing a single axial multisource CT scan with multiple longitudinally offset sources. Data from multiple axial scans or multiple sources provide complementary information. For full-scan acquisitions, we present a window-based 3D analytic cone-beam reconstruction algorithm by tessellating data from neighboring axial datasets. We also show that multi-axial CT acquisition can extend the axial scan coverage while minimizing cone-beam artifacts. For half-scan acquisitions, one cannot take advantage of conjugate rays. We propose a cone-angle dependent weighting approach to combine multi-axial half-scan data. We compute the relative contribution from each axial dataset to each voxel based on the X-ray beam collimation, the respective cone-angles, and the spacing between the axial scans. We present numerical experiments to demonstrate that the proposed techniques successfully reduce cone-beam artifacts at very large volumetric coverage.
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Guoding, Li, R. Nan und B. Peng. „Extending the Observable Zenith Angle of FAST Using an Offset Feed“. International Astronomical Union Colloquium 182 (2001): 255–59. http://dx.doi.org/10.1017/s025292110000107x.
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AbstractThe five hundred meter aperture spherical radio telescope is will use an active spherical reflector. When the zenith scan angle is changed, the illuminated part of the reflecting surface is made to fit a paraboloid of revolution in real time by active control. The maximum zenith scan angle | ψmax | of FAST is 30° under conditions of the geometry selected in order that the feed does not illuminate the ground. The result of this paper shows that the maximum zenith scan angle | ψmax | can be extended to 69° by offsetting the feed.
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Yan, Hui, Liwei Zhang und Fang-Fang Yin. „A Phantom Study on Target Localization Accuracy Using Cone-Beam Computed Tomography“. Clinical medicine. Oncology 2 (Januar 2008): CMO.S808. http://dx.doi.org/10.4137/cmo.s808.
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The purpose of this study is to evaluate the 3-dimensional target localization accuracy of cone-beam computed tomography (CBCT) using an on-board imager (OBI). An anthropomorphic pelvis phantom was used to simulate a range of offsets in the three translational directions and rotations around each of the three axes. After a translational or rotational offset was applied, a CBCT scan of the phantom was followed by image registration to detect the offsets in six degrees. The detected offsets were compared to the offset actually applied to give the detection error of the phantom position. Afterwards, the phantom was positioned by automatically moving the couch based on the detected offsets. A second CBCT scan followed by image registration was performed to give the residual error of the phantom positioning. On the average the detection errors and their standard deviations along the lateral, longitudinal and vertical axis are 0.3 ± 0.1, 0.3 ± 0.1 and 0.4 ± 0.1 mm respectively with respect to translational shifts ranging from 0 to 10 mm. The corresponding residual errors after positioning are 0.3 ± 0.1, 0.5 ± 0.1 and 0.3 ± 0.1 mm. For simulated rotational shifts ranging from 0 to 5 degrees, the average detection error and their standard deviation around lateral, longitudinal, and vertical axes are 0.1 ± 0.0, 0.2 ± 0.0, and 0.2 ± 0.0 degrees respectively. The residual errors after positioning are 0.4 ± 0.1, 0.6 ± 0.1, and 0.3 ± 0.1 mm along the lateral, longitudinal and vertical directions. These results indicate that target localization based on CBCT is capable of achieving sub-millimeter accuracy.
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Lin, Yulan, Adonis Lupulescu und Lucio Frydman. „Multidimensional J-driven NMR correlations by single-scan offset-encoded recoupling“. Journal of Magnetic Resonance 265 (April 2016): 33–44. http://dx.doi.org/10.1016/j.jmr.2015.11.018.
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7
Qin, Jianwei, Moon S. Kim, Walter F. Schmidt, Byoung-Kwan Cho, Yankun Peng und Kuanglin Chao. „A line-scan hyperspectral Raman system for spatially offset Raman spectroscopy“. Journal of Raman Spectroscopy 47, Nr. 4 (05.10.2015): 437–43. http://dx.doi.org/10.1002/jrs.4825.
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8
Kroodsma, Rachael, Stephen Bilanow und Darren McKague. „TRMM Microwave Imager (TMI) Alignment and Along-Scan Bias Corrections“. Journal of Atmospheric and Oceanic Technology 35, Nr. 7 (Juli 2018): 1457–70. http://dx.doi.org/10.1175/jtech-d-17-0221.1.
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AbstractThe Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) dataset released by the Precipitation Processing System (PPS) has been updated to a final version following the decommissioning of the TRMM satellite in April 2015. The updates are based on increased knowledge of radiometer calibration and sensor performance issues. In particular, the Global Precipitation Measurement (GPM) Microwave Imager (GMI) is used as a model for many of the TMI updates. This paper discusses two aspects of the TMI data product that have been reanalyzed and updated: alignment and along-scan bias corrections. The TMI’s pointing accuracy is significantly improved over prior PPS versions, which used at-launch alignment values. A TMI instrument mounting offset is discovered as well as new alignment offsets for the two TMI feedhorns. The original TMI along-scan antenna temperature bias correction is found to be generally accurate over ocean, but a scene temperature-dependent correction is needed to account for edge-of-scan obstruction. These updates are incorporated into the final TMI data version, improving the quality of the data product and ensuring accurate geophysical parameters can be derived from TMI.
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Jian, Fu, Lu Hongnian, Li Bing, Zhang Lei und Sun Jingjing. „X-CT imaging method for large objects using double offset scan mode“. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 575, Nr. 3 (Juni 2007): 519–23. http://dx.doi.org/10.1016/j.nima.2007.03.008.
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Bird, T. S., und M. A. Sprey. „Scan limitations of shaped dual-offset reflector antennas for multiple satellite access“. Electronics Letters 26, Nr. 4 (1990): 228. http://dx.doi.org/10.1049/el:19900154.
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Bramstedt, K., S. Noël, H. Bovensmann, M. Gottwald und J. P. Burrows. „Precise pointing knowledge for SCIAMACHY solar occultation measurements“. Atmospheric Measurement Techniques 5, Nr. 11 (27.11.2012): 2867–80. http://dx.doi.org/10.5194/amt-5-2867-2012.
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Abstract. We present a method to precisely determine the viewing direction for solar occultation instruments from scans over the solar disk. Basic idea is the fit of the maximum intensity during the scan, which corresponds to the center of the solar disk in the scanning direction. We apply this method to the solar occultation measurements of the satellite instrument SCIAMACHY, which scans the Sun in elevation direction. The achieved mean precision is 0.46 mdeg, which corresponds to an tangent height error of about 26 m for individual occultation sequences. The deviation of the derived elevation angle from the geolocation information given along with the product has a seasonal cycle with an amplitude of 2.26 mdeg, which is in tangent height an amplitude of about 127 m. The mean elevation angle offset is −4.41 mdeg (249 m). SCIAMACHY's sun follower device controls the azimuth viewing direction during the occultation measurements. The derived mean azimuth direction has an standard error of 0.65 mdeg, which is about 36 m in horizontal direction at the tangent point. We observe also a seasonal cycle of the azimuth mispointing with an amplitude of 2.3 mdeg, which is slightly increasing with time. The almost constant mean offset is 88 mdeg, which is about 5.0 km horizontal offset at the tangent point.
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Bramstedt, K., S. Noël, H. Bovensmann, M. Gottwald und J. P. Burrows. „Precise pointing knowledge for SCIAMACHY solar occultation measurements“. Atmospheric Measurement Techniques Discussions 5, Nr. 3 (31.05.2012): 3797–835. http://dx.doi.org/10.5194/amtd-5-3797-2012.
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Abstract. We present a method to precisely determine the viewing direction for solar occultation instruments from scans over the solar disk . Basic idea is the fit of the maximum intensity during the scan, which corresponds to the center of the solar disk in the scanning direction. We apply this method to the solar occultation measurements of the satellite instrument SCIAMACHY, which scans the sun in elevation direction. The achieved precision is in most case below 0.6 mdeg, which corresponds to an tangent height error of about 34 m for individual occultation sequences. The deviation of the derived elevation angle from the geolocation information given along with the product has a seasonal cycle with an amplitude of 2.02 mdeg, which is in tangent height an amplitude of about 114 m. The mean elevation angle offset is −4.7 mdeg (266 m). SCIAMACHY's sun follower device controls the azimuth viewing direction during the occultation measurements. The mean azimuth direction has an error of about 1.5 mdeg, which is about 84 m in horizontal direction at the tangent point. We observe also a seasonal cycle of the azimuth mispointing with an amplitude of 2.4 mdeg, which is slightly increasing with time. The almost constant mean offset is 88 mdeg, which is about 5.0 km horizontal offset at the tangent point.
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Pasquier, G., G. Ducharne, E. Sari Ali, F. Giraud, A. Mouttet und E. Durante. „Total hip arthroplasty offset measurement: Is C T scan the most accurate option?“ Orthopaedics & Traumatology: Surgery & Research 96, Nr. 4 (Juni 2010): 367–75. http://dx.doi.org/10.1016/j.otsr.2010.02.006.
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Lohumi, Santosh, Hoonsoo Lee, Moon S. Kim, Jianwei Qin und Byoung-Kwan Cho. „Through-packaging analysis of butter adulteration using line-scan spatially offset Raman spectroscopy“. Analytical and Bioanalytical Chemistry 410, Nr. 22 (22.06.2018): 5663–73. http://dx.doi.org/10.1007/s00216-018-1189-1.
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Isaac, J. Helen, und Don C. Lawton. „A practical method for estimating effective parameters of anisotropy from reflection seismic data“. GEOPHYSICS 69, Nr. 3 (Mai 2004): 681–89. http://dx.doi.org/10.1190/1.1759454.
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The location of any event imaged by P‐wave reflection seismic data beneath a tilted transversely isotropic (TTI) overburden is shifted laterally if isotropic velocities are used during data processing. The magnitude of the shift depends on five independent parameters: overburden thickness, angle of tilt, symmetry‐axis velocity, and the Thomsen anisotropy parameters and δ. The shift also varies with source–receiver offset. We have developed a procedure to estimate these five parameters when the tilt of the symmetry axis from the vertical is equal to the dip of the TTI layer (except in the special cases transverse isotropy with vertical or horizontal axis of symmetry). We observe three attributes of seismic data processed using isotropic velocities: the zero‐offset arrival time of a selected reflection, the difference in arrival time between a near‐offset and a far‐offset arrival, and the difference in imaged location (smear) of this target event between the same offsets. We then perform a cascaded scan of the five parameters to determine those combinations of the five that result in calculated attributes equivalent to the observed attributes. The multiple solutions are averaged to give the parameter estimates. Application of this method to synthetic and physical model reflection data results in multiple solutions, which are constrained and averaged to obtain the effective imaging parameters. These effective parameters are close estimates of the true model parameters in both cases. For field seismic data this procedure requires that there be a suitable observable event below the TTI overburden and assumes that the measured times and shifts are reasonably accurate.
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Résibois, Maxime, Philippe Verduyn, Pauline Delaveau, Jean-Yves Rotgé, Peter Kuppens, Iven Van Mechelen und Philippe Fossati. „The neural basis of emotions varies over time: different regions go with onset- and offset-bound processes underlying emotion intensity“. Social Cognitive and Affective Neuroscience 12, Nr. 8 (11.04.2017): 1261–71. http://dx.doi.org/10.1093/scan/nsx051.
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Fan, Chuanmao, und Gang Yao. „Single camera spectral domain polarization-sensitive optical coherence tomography using offset B-scan modulation“. Optics Express 18, Nr. 7 (24.03.2010): 7281. http://dx.doi.org/10.1364/oe.18.007281.
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Schaude, Janik, Andreas Christian Gröschl und Tino Hausotte. „Stitched open-loop measurements with a focal-distance-modulated confocal sensor“. tm - Technisches Messen 88, Nr. 9 (05.05.2021): 544–55. http://dx.doi.org/10.1515/teme-2021-0036.
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Abstract The article presents measurements with a high-speed focal-distance modulated fibre-coupled confocal sensor integrated into a nano measuring machine (NMM-1). Combined with an appropriate signal processing, this axial beam modulating sensor yields a linear characteristic curve within a range of about 600 nm. This characteristic curve enables scans in closed-loop constant distance mode, where the controller of the NMM-1 keeps the distance between the measured surface and the sensor constant. Therefore, only one lateral scan is necessary to measure a given topography. Nevertheless, it is also possible to conduct open-loop constant height measurements on discrete heights. The axial offset between the heights needs to be only slightly less than the measuring range of the sensor, leading to a great reduction of the number of needed lateral scans to measure a given topography compared to a conventional confocal sensor, where the axial offset for a similar optical system is typically about 50 nm. To combine the scans taken at different heights, it is possible to stitch them using overlapping measuring points taken at two adjacent heights. Within this article, measurements are conducted on a roughness standard in closed-loop constant distance and in open-loop constant height mode, where the latter are evaluated with and without the application of the stitching algorithm.
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Balcarek, Peter, Ali Seif Amir Hosseini, Ulrike Streit, Tobias Franz Brodkorb und Tim Alexander Walde. „Sagittal magnetic resonance imaging-scan orientation significantly influences accuracy of femoral posterior condylar offset measurement“. Archives of Orthopaedic and Trauma Surgery 138, Nr. 2 (10.11.2017): 267–72. http://dx.doi.org/10.1007/s00402-017-2838-0.
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den Boer, Willem. „6.2: A Select Line Driver for the Offset-Scan-and-Hold Dual Select Diode AMLCDs“. SID Symposium Digest of Technical Papers 32, Nr. 1 (2001): 44. http://dx.doi.org/10.1889/1.1831893.
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Qin, Jianwei, Moon S. Kim, Kuanglin Chao, Walter F. Schmidt, Sagar Dhakal, Byoung-Kwan Cho, Yankun Peng und Min Huang. „Subsurface inspection of food safety and quality using line-scan spatially offset Raman spectroscopy technique“. Food Control 75 (Mai 2017): 246–54. http://dx.doi.org/10.1016/j.foodcont.2016.12.012.
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Liu, Zhenfang, Min Huang, Qibing Zhu, Jianwei Qin und Moon S. Kim. „Nondestructive freshness evaluation of intact prawns (Fenneropenaeus chinensis) using line-scan spatially offset Raman spectroscopy“. Food Control 126 (August 2021): 108054. http://dx.doi.org/10.1016/j.foodcont.2021.108054.
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Lübcke, Peter, Johannes Lampel, Santiago Arellano, Nicole Bobrowski, Florian Dinger, Bo Galle, Gustavo Garzón et al. „Retrieval of absolute SO<sub>2</sub> column amounts from scattered-light spectra: implications for the evaluation of data from automated DOAS networks“. Atmospheric Measurement Techniques 9, Nr. 12 (29.11.2016): 5677–98. http://dx.doi.org/10.5194/amt-9-5677-2016.
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Abstract. Scanning spectrometer networks using scattered solar radiation in the ultraviolet spectral region have become an increasingly important tool for monitoring volcanic sulfur dioxide (SO2) emissions. Often measured spectra are evaluated using the differential optical absorption spectroscopy (DOAS) technique. In order to obtain absolute column densities (CDs), the DOAS evaluation requires a Fraunhofer reference spectrum (FRS) that is free of absorption structures of the trace gas of interest. For measurements at volcanoes such a FRS can be readily obtained if the scan (i.e. series of measurements at different elevation angles) includes viewing directions where the plume is not seen. In this case, it is possible to use these viewing directions (e.g. zenith) as FRS. Possible contaminations of the FRS by the plume can then be corrected by calculating and subtracting an SO2 offset (e.g. the lowest SO2 CD) from all viewing directions of the respective scan. This procedure is followed in the standard evaluations of data from the Network for Observation of Volcanic and Atmospheric Change (NOVAC). While this procedure is very efficient in removing Fraunhofer structures and instrumental effects it has the disadvantage that one can never be sure that there is no SO2 from the plume in the FRS. Therefore, using a modelled FRS (based on a high-resolution solar atlas) has a great advantage. We followed this approach and investigated an SO2 retrieval algorithm using a modelled FRS. In this paper, we present results from two volcanoes that are monitored by NOVAC stations and which frequently emit large volcanic plumes: Nevado del Ruiz (Colombia) recorded between January 2010 and June 2012 and from Tungurahua (Ecuador) recorded between January 2009 and December 2011. Instrumental effects were identified with help of a principal component analysis (PCA) of the residual structures of the DOAS evaluation. The SO2 retrieval performed extraordinarily well with an SO2 DOAS retrieval error of 1 − 2 × 1016 [molecules cm−2]. Compared to a standard evaluation, we found systematic differences of the differential slant column density (dSCD) of only up to ≈ 15 % when looking at the variation of the SO2 within one scan. The major advantage of our new retrieval is that it yields absolute SO2 CDs and that it does not require complicated instrumental calibration in the field (e.g. by employing calibration cells or broadband light sources), since the method exploits the information available in the measurements.We compared our method to an evaluation that is similar to the NOVAC approach, where a spectrum that is recorded directly before the scan is used as an FRS and an SO2 CD offset is subtracted from all retrieved dSCD in the scan to correct for possible SO2 contamination of the FRS. The investigation showed that 21.4 % of the scans (containing significant amounts of SO2) at Nevado del Ruiz and 7 % of the scans at Tungurahua showed much larger SO2 CDs when evaluated using modelled FRS (more than a factor of 2). For standard evaluations the overall distribution of the SO2 CDs in a scan can in some cases indicate whether the plume affects all viewing directions and thus these scans need to be discarded for NOVAC emission rate evaluation. However, there are other cases where this is not possible and thus the reported SO2 emission rates would be underestimated. The new method can be used to identify these cases and thus it can considerably improve SO2 emission budgets.
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Hofsäß, Martin, Andrew Clifton und Po Cheng. „Reducing the Uncertainty of Lidar Measurements in Complex Terrain Using a Linear Model Approach“. Remote Sensing 10, Nr. 9 (13.09.2018): 1465. http://dx.doi.org/10.3390/rs10091465.
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In complex terrain, ground-based lidar wind speed measurements sometimes show noticeable differences compared to measurements made with in-situ sensors mounted on meteorological masts. These differences are mostly caused by the inhomogeneities of the flow field and the applied reconstruction methods. This study investigates three different methods to optimize the reconstruction algorithm in order to improve the agreement between lidar measurements and data from sensors on meteorological masts. The methods include a typical velocity azimuth display (VAD) method, a leave-one-out cross-validation method, and a linear model which takes into account the gradients of the wind velocity components. In addition, further aspects such as the influence of the half opening angle of the scanning cone and the scan duration are considered. The measurements were carried out with two different lidar systems, that measured simultaneously. The reference was a 100 m high meteorological mast. The measurements took place in complex terrain characterized by a 150 m high escarpment. The results from the individual methods are quantitatively compared with the measurements of the cup anemometer mounted on the meteorological mast by means of the three parameters of a linear regression (slope, offset, R 2 ) and the width of the 5th–95th quantile. The results show that expanding the half angle of the scanning cone from 20 ∘ to 55 ∘ reduces the offset by a factor of 14.9, but reducing the scan duration does not have an observable benefit. The linear method has the lowest uncertainty and the best agreement with the reference data (i.e., lowest offset and scatter) of all of the methods that were investigated.
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Levy, Robert C., Shana Mattoo, Virginia Sawyer, Yingxi Shi, Peter R. Colarco, Alexei I. Lyapustin, Yujie Wang und Lorraine A. Remer. „Exploring systematic offsets between aerosol products from the two MODIS sensors“. Atmospheric Measurement Techniques 11, Nr. 7 (13.07.2018): 4073–92. http://dx.doi.org/10.5194/amt-11-4073-2018.
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Abstract. Long-term measurements of global aerosol loading and optical properties are essential for assessing climate-related questions. Using observations of spectral reflectance and radiance, the dark-target (DT) aerosol retrieval algorithm is applied to Moderate Resolution Imaging Spectroradiometer sensors on both Terra (MODIS-T) and Aqua (MODIS-A) satellites, deriving products (known as MOD04 and MYD04, respectively) of global aerosol optical depth (AOD at 0.55 µm) over both land and ocean, and an Ångström exponent (AE derived from 0.55 and 0.86 µm) over ocean. Here, we analyze the overlapping time series (since mid-2002) of the Collection 6 (C6) aerosol products. Global monthly mean AOD from MOD04 (Terra with morning overpass) is consistently higher than MYD04 (Aqua with afternoon overpass) by ∼ 13 % (∼ 0.02 over land and ∼ 0.015 over ocean), and this offset (MOD04 – MYD04) has seasonal as well as long-term variability. Focusing on 2008 and deriving yearly gridded mean AOD and AE, we find that, over ocean, the MOD04 (morning) AOD is higher and the AE is lower. Over land, there is more variability, but only biomass-burning regions tend to have AOD lower for MOD04. Using simulated aerosol fields from the Goddard Earth Observing System (GEOS-5) Earth system model and sampling separately (in time and space) along each MODIS-observed swath during 2008, the magnitudes of morning versus afternoon offsets of AOD and AE are smaller than those in the C6 products. Since the differences are not easily attributed to either aerosol diurnal cycles or sampling issues, we test additional corrections to the input reflectance data. The first, known as C6+, corrects for long-term changes to each sensor's polarization sensitivity and the response versus the scan angle and to cross-calibration from MODIS-T to MODIS-A. A second convolves the detrending and cross-calibration into scaling factors. Each method was applied upstream of the aerosol retrieval using 2008 data. While both methods reduced the overall AOD offset over land from 0.02 to 0.01, neither significantly reduced the AOD offset over ocean. The overall negative AE offset was reduced. A collection (C6.1) of all MODIS Atmosphere products was released, but we expect that the C6.1 aerosol products will maintain similar overall AOD and AE offsets. We conclude that (a) users should not interpret global differences between Terra and Aqua aerosol products as representing a true diurnal signal in the aerosol. (b) Because the MODIS-A product appears to have an overall smaller bias compared to ground-truth data, it may be more suitable for some applications. However (c), since the AOD offset is only ∼ 0.02 and within the noise level for single retrievals, both MODIS products may be adequate for most applications.
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Yuan, Rupeng, Fuhai Zhang, Jiadi Qu, Guozhi Li und Yili Fu. „An enhanced pose tracking method using progressive scan matching“. Industrial Robot: the international journal of robotics research and application 46, Nr. 2 (18.03.2019): 235–46. http://dx.doi.org/10.1108/ir-10-2018-0222.
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Purpose The purpose of this paper is to propose an enhanced pose tracking method using progressive scan matching, focusing on accuracy, time efficiency and robustness. Design/methodology/approach The general purpose of localization algorithms is to dynamically track a robot instead of globally locating one. In this paper, progressive scan matching is used to promote the performance of pose tracking. Rotational and translational samples are separately generated to accelerate the calculation and to increase the accuracy. Progressive iteration of sample generation can ensure localization to achieve a specific precision. The direction of localization uncertainty is taken into consideration to increase robustness. Nonlinear optimization is adopted to achieve a more precise result. Findings The proposed method was implemented on a self-made mobile robot. Two experiments were conducted to test the accuracy and time efficiency of the method. The comparison with the basic Monte Carlo localization shows the advantages of the method. Another two experiments were conducted to test the robustness of the method. The result shows that the method can relocate a robot from an inaccurate place if the offset is moderate. Originality/value An enhanced pose tracking method is proposed to promote the performance by separately processing rotational and translational samples, progressively iterating the sample generation, taking the direction of localization uncertainty into consideration and adopting nonlinear optimization. The proposed method enables a robot to accurately and quickly locate itself in the environment with robustness.
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Kaplan, Jonathan, Mark Myerson, Matthew Welck, Joseph Tracey, Adriana Avila und ShuYuan Li. „The Use of Weight-Bearing CT Scan in the Evaluation of Hindfoot Alignment“. Foot & Ankle Orthopaedics 2, Nr. 3 (01.09.2017): 2473011417S0002. http://dx.doi.org/10.1177/2473011417s000232.
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Category: Hindfoot, Diagnostic Imaging Introduction/Purpose: Multiple techniques have been described in determining the hindfoot alignment radiographically. While these studies have traditionally showed good reliability, the 2-dimensional nature of radiographs fails to consider the contribution of the remainder of the foot on the overall alignment. A new technique has been recently published in which the hindfoot alignment is calculated using the Ground Reaction Force Calcaneal Offset off radiographs. This technique accounts for the individual forefoot contributions on overall alignment, however is still limited by the 2-dimensional nature of plain radiographs. The purpose of this study is to compare two accepted radiographic measurements, the hindfoot moment arm (HMA) and the hindfoot alignment angle (HAA), with a novel technique determining the ground reaction force calcaneal offset (GRF-CT) using 3- dimensional weight bearing CT Scans. Methods: Retrospective chart review was performed over a two-year period from 2014-2016 to identify patients with weight bearing hindfoot alignment radiographs and PedCat (Curvebeam, Warrington, USA) 3-D weight bearing CT scans. The HMA, HAA, and GRF-CT were measured by three different investigators. Each of these measurements were calculated two times on separate occasions by each investigator to determine the intra- and inter-observer reliability with each of these techniques Results: One-hundred and four patients underwent weight bearing hindfoot alignment radiographs and 3-dimensional weight bearing CT scans. There were 33 patients with varus deformities and 71 patients with valgus deformities. There was excellent intra- and inter-observer reliability with all three measurement techniques, however the GRF-CT showed the best intra- and inter-observer reliability with the lowest standard deviation Conclusion: The GRF-CT technique is more reliable than traditional radiograph techniques for measuring the hindfoot alignment. While the intra- and inter-observer reliability is good for all three techniques, the GRF-CT technique resulted in the best intra- and inter-observer reliability with the lowest standard deviation. This technique provides the most accurate hindfoot alignment as it takes into account the effect of forefoot on overall alignment, preventing inaccuracies of projection and foot orientation in contrast to traditional radiographic techniques, which may be valuable in surgical decision making.
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Ferretti, Andrea, Ferdinando Iannotti, Lorenzo Proietti, Carlo Massafra, Attilio Speranza, Andrea Laghi und Raffaele Iorio. „The Accuracy of Patient-Specific Instrumentation with Laser Guidance in a Dynamic Total Hip Arthroplasty: A Radiological Evaluation“. Sensors 21, Nr. 12 (20.06.2021): 4232. http://dx.doi.org/10.3390/s21124232.
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The functional positioning of components in a total hip arthroplasty (THA) and its relationship with individual lumbopelvic kinematics and a patient’s anatomy are being extensively studied. Patient-specific kinematic planning could be a game-changer; however, it should be accurately delivered intraoperatively. The main purpose of this study was to verify the reliability and accuracy of a patient-specific instrumentation (PSI) and laser-guided technique to replicate preoperative dynamic planning. Thirty-six patients were prospectively enrolled and received dynamic hip preoperative planning based on three functional lateral spinopelvic X-rays and a low dose CT scan. Three-dimensional (3D) printed PSI guides and laser-guided instrumentation were used intraoperatively. The orientation of the components, osteotomy level and change in hip length and offset were measured on postoperative CT scans and compared with the planned preoperative values. The length of surgery was compared with that of a matched group of thirty-six patients who underwent a conventional THA. The mean absolute deviation from the planned inclination and anteversion was 3.9° and 4.4°, respectively. In 92% of cases, both the inclination and anteversion were within +/− 10° of the planned values. Regarding the osteotomy level, offset change and limb length change, the mean deviation was, respectively, 1.6 mm, 2.6 mm and 2 mm. No statistically significant difference was detected when comparing the planned values with the achieved values. The mean surgical time was 71.4 min in the PSI group and 60.4 min in the conventional THA group (p < 0.05). Patient-specific and laser-guided instrumentation is safe and accurately reproduces dynamic planning in terms of the orientation of the components, osteotomy level, leg length and offset. Moreover, the increase in surgical time is negligible.
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Dane, D. Merrill, Robert L. Johnson und Connie C. W. Hsia. „Dysanaptic growth of conducting airways after pneumonectomy assessed by CT scan“. Journal of Applied Physiology 93, Nr. 4 (01.10.2002): 1235–42. http://dx.doi.org/10.1152/japplphysiol.00970.2001.
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In immature dogs after pneumonectomy (PNX), pulmonary viscous resistance is persistently elevated predominantly as a result of a high airway resistance (Raw). We examined the anatomical basis for this observation by using computerized tomography scans obtained from foxhounds 4–10 mo after right PNX. Airways of the left lower lobe were followed from generations z = 0 (trachea) to z = 12. By 4 mo post-PNX, airway length increased significantly relative to sham-operated dogs, but airway cross-sectional area (CSA) did not. By 10 mo post-PNX, average airway CSA was 24% above that in controls. Theoretically, the increased airway length and CSA should reduce lobar Raw by 50%. However, post-PNX airway dilatation did not normalize total CSA, and estimated resistance due to turbulence and convective acceleration increased threefold; i.e., the 50% reduction in lobar Raw would be offset by the loss of four of seven lobes. Thus the expected reduction in work of breathing in the whole animal is only ∼30%, consistent with previously measured work of breathing in pneumonectomized dogs. We conclude that airway structure adapts slowly and incompletely, resulting in limited functional compensation.
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Sharma, Satish K., und Mukund R. Thyagarajan. „Performance Comparison of Symmetric and Offset Reflector Antennas Adaptively Illuminated by Novel Triple Mode Feedhorn“. International Journal of Antennas and Propagation 2012 (2012): 1–10. http://dx.doi.org/10.1155/2012/870318.
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Parabolic symmetric and offset reflector antennas adaptively illuminated using a novel triple-mode feedhorn (TE11+TM01+TE21) with different mode combinations and impedance and radiation performances are presented. The combination of the radiating modes in a feedhorn with proper amplitude and fixed phase values helps in electronically pointing the main beam of the radiating patterns such as that obtained in a beam-steering antenna with limited beam-scan range. This type of radiation performance virtually creates a displaced phase center location for the feedhorn, which, consequently, adaptively illuminates the reflector antenna surface. Impedance-matching bandwidths are preserved for both reflector antennas similar to the case of feedhorn alone. The copolarization gain and peak cross-polarization levels are far better with the offset reflector antenna than the symmetric reflector antenna. Such reflector antennas find applications in ground moving target indicator (GMTI) and space based radars. The investigation results are solely computed using FEKO full-wave analysis tool.
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Wang, Rui, Haiou Zhang, Wang Gui-Lan und Xushan Zhao. „Cylindrical slicing and path planning of propeller in wire and arc additive manufacturing“. Rapid Prototyping Journal 26, Nr. 1 (06.01.2020): 49–58. http://dx.doi.org/10.1108/rpj-02-2019-0035.
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Purpose The wire and arc additive manufacturing (WAAM) is a promising technology, but the parts are mostly manufactured on the plane and along the vertical direction. The purpose of this paper is to propose a cylindrical slicing and manufacturing method. Design/methodology/approach For revolved parts, e.g. blades of a propeller, instead of planes, a series of cylindrical surfaces intersect with the STL model of the part. The generated slicing layers lie on the cylindrical surface, and then these spatial contours are unfolded onto the plane by the use of the cylindrical coordinate system. A deposition system based on an NC machine is established to examine deposition paths. The temperature and stress of part of two deposition orders are analyzed using the finite element method. Findings The scan parallel path and contour offset path are not suitable to fabricate blades directly. The hybrid of two types of paths and the hybrid of skeleton and contour offset paths are capable of forming blades without gaps. Deposition symmetrically can decrease the deformation of the propeller. Originality/value The slicing algorithm is simply implemented and practicable for any parts. The recognition of gaps and supplementary skeleton path can guarantee the full deposition of contour offset paths.
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Markham, J., und D. P. Schuster. „Effects of nonideal input functions on PET measurements of pulmonary blood flow“. Journal of Applied Physiology 72, Nr. 6 (01.06.1992): 2495–500. http://dx.doi.org/10.1152/jappl.1992.72.6.2495.
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Regional pulmonary blood flow (rPBF) can be measured with an intravenous infusion of 15O-labeled water and positron emission tomography (PET). The current method depends on two assumptions related to the input of activity to the lung during the scan: 1) the pulmonary arterial tracer input is constant (i.e., a “step function” in shape), and 2) the scan begins at the instant of arrival of the step function. To determine the effect that departures from these assumptions might have on the measurement of rPBF, we performed a series of mathematical simulations for three different input functions: 1) a step function that arrived either 1 or 2 s before or after scan start; 2) a dispersed input function, with activity rising during the scan period; and 3) a combination of these two errors. Calculated values, based on the standard assumptions, were compared against the “known” values used in generating the simulated data. The results show that timing errors associated with starting the scan late cause an overestimation of rPBF, whereas timing errors due to low regional flow or departures from the assumed step input function both cause an underestimation of true rPBF. Thus, in actual practice, the combined errors probably partially offset one another. Except for states of truly high rPBF and low lung density, the errors remain less than 15% of the true value. We conclude that PET measurements of rPBF are not highly sensitive to these presumably common departures from the assumed pulmonary arterial input function to lung regions of interest.
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Blomgren, L., N. Zethraeus, G. Johansson, B. Jönsson und D. Bergqvist. „Cost consequences of preoperative duplex examination before varicose vein surgery: a randomized clinical trial“. Phlebology: The Journal of Venous Disease 21, Nr. 2 (01.06.2006): 90–95. http://dx.doi.org/10.1258/026835506777304728.
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Objectives: To investigate the cost consequences of the addition of a duplex scan to the routine clinical examination prior to surgery for varicose veins (VV). Methods: Cost data are based on a prospective study, which randomized 293 VV patients for surgery either with or without a preoperative duplex scan. Costs are collected during a two-year follow-up time and include direct costs for primary surgery and reoperation. Results: The mean cost for the primary operation was SEK 12,827 (€1410) in the duplex group and SEK 9856 (€1083) in the control group ( P<0.001). A significant part of this increase was due to more extensive primary surgery. Costs for redo surgery decreased by SEK 1131 (€124) ( P = 0.011). The mean net cost increase because of duplex is estimated to be SEK 1840 (€202) ( P<0.003). Conclusion: The savings in costs for redo surgery did not offset the costs for preoperative duplex examination before VV surgery during a two-year follow-up period.
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Ameen, Wadea, Muneer Khan Mohammed und Abdulrahman Al-Ahmari. „Evaluation of Support Structure Removability for Additively Manufactured Ti6Al4V Overhangs via Electron Beam Melting“. Metals 9, Nr. 11 (11.11.2019): 1211. http://dx.doi.org/10.3390/met9111211.
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The addition of support structures is essential for the successful fabrication of overhang structures through additive manufacturing (AM). The support structures protect the overhang portion from distortions. They are fabricated with the functional parts and are removed later after the fabrication of the AM part. While structures bearing insufficient support result in defective overhangs, structures with excessive support result in higher material consumption, time and higher post-processing costs. The objective of this study is to investigate the effects of design and process parameters of support structures on support removability during the electron beam melting (EBM)-based additive manufacturing of the Ti6Al4V overhang part. The support design parameters include tooth parameters, no support offset, fragmentation parameters and perforation parameters. The EBM process parameters consist of beam current, beam scan speed and beam focus offset. The results show that both support design and process parameters have a significant effect on support removability. In addition, with the appropriate selection of design and process parameters, it is possible to significantly reduce the support removal time and protect the surface quality of the part.
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Robinson, Simon, Günther Grabner, Stephan Witoszynskyj und Siegfried Trattnig. „Combining phase images from multi-channel RF coils using 3D phase offset maps derived from a dual-echo scan“. Magnetic Resonance in Medicine 65, Nr. 6 (19.01.2011): 1638–48. http://dx.doi.org/10.1002/mrm.22753.
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Koeppe, Robert A., David M. Raffel, Scott E. Snyder, Edward P. Ficaro, Michael R. Kilbourn und David E. Kuhl. „Dual-[11C]Tracer Single-Acquisition Positron Emission Tomography Studies“. Journal of Cerebral Blood Flow & Metabolism 21, Nr. 12 (Dezember 2001): 1480–92. http://dx.doi.org/10.1097/00004647-200112000-00013.
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The ability to study multiple physiologic processes of the brain simultaneously within the same subject would provide a new means to explore the interactions between neurotransmitter systems in vivo. Currently, examination of two distinct neuropharmacologic measures with positron emission tomography (PET) necessitates performing two separate scans spaced in time to allow for radionuclide decay. The authors present results from a dual-tracer PET study protocol using a single dynamic-scan acquisition where the injections of two tracers are offset by several minutes. Kinetic analysis is used to estimate neuropharmacologic parameters for both tracers simultaneously using a combined compartmental model configuration. This approach results in a large reduction in total study time of nearly 2 hours for carbon-11–labeled tracers. As multiple neuropharmacologic measures are obtained at nearly the same time, interventional protocols involving a pair of dual-tracer scans become feasible in a single PET session. Both computer simulations and actual human PET studies were performed using combinations of three different tracers: [11C]flumazenil, N-[11C]methylpiperidinyl propionate, and [11C]dihydrotetrabenazine. Computer simulations of tracer-injection separations of 10 to 30 minutes showed the feasibility of the approach for separations down to 15 to 20 minutes or less. Dual-tracer PET studies were performed in 32 healthy volunteers using injection separations of 10, 15, or 20 minutes. Model parameter estimates for each tracer were similar to those obtained from previously performed single-injection studies. Voxel-by-voxel parametric images were of good quality for injections spaced by 20 minutes and were nearly as good for 15-minute separations, but were degraded noticeably for some model parameters when injections were spaced by only 10 minutes. The authors conclude that dual-tracer single-scan PET is feasible, yields accurate estimates of multiple neuropharmacologic measures, and can be implemented with a number of different radiotracer pairs.
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Bali, Manik, Jonathan P. Mittaz, Eileen Maturi und Mitchell D. Goldberg. „Comparisons of IASI-A and AATSR measurements of top-of-atmosphere radiance over an extended period“. Atmospheric Measurement Techniques 9, Nr. 7 (27.07.2016): 3325–36. http://dx.doi.org/10.5194/amt-9-3325-2016.
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Abstract. This study examines the trustworthiness of the Advanced Along-Track Scanning Radiometer (AATSR) and the Infrared Atmospheric Sounding Interferometer (IASI-A), as on-orbit reference instruments that are useful in re-calibrating the Advanced Very High Resolution Radiometer (AVHRR) series (Mittaz and Harris, 2011). To do this, a 39-month period (1 January 2008 to 31 March 2011) of AATSR and IASI-A inter-comparisons of top-of-atmosphere (TOA) radiance measurements is examined. Our inter-comparison reveals features of the AATSR and IASI-A bias with respect to scan angle, scene temperature, time and orbital maneuvers, and gives insight into their trustworthiness as an in-orbit reference instruments. The first feature that our study reveals is that the AATSR (nadir view) and IASI-A are both stable (have no perceptible trends in the period of study). The second feature is that IASI-A is perhaps more accurate ( ∼ 0.05 K) than its stated accuracy (0.5 K). In fact the AATSR and IASI-A bias is close to the AATSR pre-launch bias (plus a small offset of +0.07 K) implying that IASI-A can get close to pre-launch levels of accuracy. Third, a very small scan angular dependence of AATSR and IASI-A bias indicates that the IASI-A response vs. scan angle algorithm is robust, while the instrument is in orbit. Inter-comparisons of AATSR with IASI-A further reveal the impact of orbital maneuvers of the ENVISAT, the platform carrying AATSR, done in October 2011 and not anticipated previously. Our study reveals that this maneuver introduced a temperature-dependent bias in the AATSR measurements for low temperatures (< 240 K) in the period following this maneuver (Cocevar et al., 2011). Our study also shows that the known AATSR 12 µm channel offset is in fact temperature dependent, grows up to 0.4 K, varies seasonally and is correlated with instrument temperature and cannot be corrected by shifting the spectral response function (SRF) of AATSR. We also present a set of recommendations to help identify the parameters under which these instruments can provide the most trustworthy observations for the AVHRR re-calibration.
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Wang, Yu-Tzu, Jian-Hong Yu, Lun-Jou Lo, Pin-Hsin Hsu und CHun-Li Lin. „Developing Customized Dental Miniscrew Surgical Template from Thermoplastic Polymer Material Using Image Superimposition, CAD System, and 3D Printing“. BioMed Research International 2017 (2017): 1–8. http://dx.doi.org/10.1155/2017/1906197.
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This study integrates cone-beam computed tomography (CBCT)/laser scan image superposition, computer-aided design (CAD), and 3D printing (3DP) to develop a technology for producing customized dental (orthodontic) miniscrew surgical templates using polymer material. Maxillary bone solid models with the bone and teeth reconstructed using CBCT images and teeth and mucosa outer profile acquired using laser scanning were superimposed to allow miniscrew visual insertion planning and permit surgical template fabrication. The customized surgical template CAD model was fabricated offset based on the teeth/mucosa/bracket contour profiles in the superimposition model and exported to duplicate the plastic template using the 3DP technique and polymer material. An anterior retraction and intrusion clinical test for the maxillary canines/incisors showed that two miniscrews were placed safely and did not produce inflammation or other discomfort symptoms one week after surgery. The fitness between the mucosa and template indicated that the average gap sizes were found smaller than 0.5 mm and confirmed that the surgical template presented good holding power and well-fitting adaption. This study addressed integrating CBCT and laser scan image superposition; CAD and 3DP techniques can be applied to fabricate an accurate customized surgical template for dental orthodontic miniscrews.
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D’Agostino, Francesco, Flaminio Ferrara, Claudio Gennarelli, Rocco Guerriero und Massimo Migliozzi. „Non-redundant Spherical Near-Field to Far-Field Transformation for a Volumetric Antenna in Offset Configuration“. Open Electrical & Electronic Engineering Journal 13, Nr. 1 (28.02.2019): 19–29. http://dx.doi.org/10.2174/1874129001913010019.
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Background: The development of fast Near-Field (NF) measurement techniques allowing the precise determination of the Far-Field (FF) radiation features of an antenna is becoming more and more challenging nowadays. Objective: The goal of the article is the development of an NF To FF Transformation (NFTFFT) with spherical scan for offset mounted volumetric Antennas Under Tests (AUTs) requiring, unlike the classical technique, a reduced set of NF data, that is of the same amount as for the onset mounting case, thus making data gathering faster. In fact, the number of NF data needed by the standard approach may considerably increase in this case, since the size of the smallest sphere surrounding the AUT and centered at the center of the measurement sphere rises. Methods: This goal has been achieved by profitably exploiting the non-redundant sampling representation of electromagnetic field and assuming a volumetric AUT as contained in a sphere. An optimal sampling interpolation algorithm is then employed to precisely reconstruct the input NF data for the traditional spherical NFTFFT from the reduced set of the collected ones. Conclusion: The numerical simulations and experimental tests demonstrate the effectiveness of the developed approach accounting for an offset mounting of the AUT.
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Vajedian, Sanaz, und Mahdi Motagh. „COSEISMIC DISPLACEMENT ANALYSIS OF THE 12 NOVEMBER 2017 MW 7.3 SARPOL-E ZAHAB (IRAN) EARTHQUAKE FROM SAR INTERFEROMETRY, BURST OVERLAP INTERFEROMETRY AND OFFSET TRACKING“. ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences IV-3 (23.04.2018): 205–9. http://dx.doi.org/10.5194/isprs-annals-iv-3-205-2018.
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Interferometric wide-swath mode of Sentinel-1, which is implemented by Terrain Observation by Progressive Scan (TOPS) technique, is the main mode of SAR data acquisition in this mission. It aims at global monitoring of large areas with enhanced revisit frequency of 6 days at the expense of reduced azimuth resolution, compared to classical ScanSAR mode. TOPS technique is equipped by steering the beam from backward to forward along the heading direction for each burst, in addition to the steering along the range direction, which is the only sweeping direction in standard ScanSAR mode. This leads to difficulty in measuring along-track displacement by applying the conventional method of multi-aperture interferometry (MAI), which exploits a double difference interferometry to estimate azimuth offset. There is a possibility to solve this issue by a technique called “Burst Overlap Interferometry” which focuses on the region of burst overlap. Taking advantage of large squint angle diversity of ~1° in burst overlapped area leads to improve the accuracy of ground motion measurement especially in along-track direction. We investigate the advantage of SAR Interferometry (InSAR), burst overlap interferometry and offset tracking to investigate coseismic deformation and coseismic-induced landslide related to 12 November 2017 Mw 7.3 Sarpol-e Zahab earthquake in Iran.
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Tieman, Hans J. „Description of a scanless method of stacking velocity analysis“. GEOPHYSICS 58, Nr. 11 (November 1993): 1596–606. http://dx.doi.org/10.1190/1.1443375.
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Stacking velocities can be directly estimated from seismic data without recourse to a multivelocity stack and subsequent search techniques that many current procedures use. This is done as follows: (1) apply NMO to the data (over a window, for a particular common midpoint) using initial estimates for zero offset time and velocity; (2) produce two stacks by summing the data over offset after applying different weighting functions; (3) cross correlate the two stacks; and (4) translate the lag into velocity and time updates. The procedure is iterated until convergence has occurred. Referred to as ARAMVEL (U.S. Patent No. 4,813,027), the method is best implemented as an interactive continuous velocity analysis. Although very simple, both empirical studies and theoretical analysis have shown that it determines velocities more accurately than more traditional approaches based on a scan approach. Convergence is fast, with only one or two iterations usually necessary. The method is robust, as only approximate information is necessary initially. Results with real data show that the method can economically give the detailed velocity control necessary for processing data from areas with considerable lateral velocity variation, as well as provide traveltime information that can be used for sophisticated inversion into interval velocity and depth.
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Cohen, Douglas S., Jonathan H. Lustgarten, Erik Miller, Alexander G. Khandji und Robert R. Goodman. „Effects of coregistration of MR to CT images on MR stereotactic accuracy“. Journal of Neurosurgery 82, Nr. 5 (Mai 1995): 772–79. http://dx.doi.org/10.3171/jns.1995.82.5.0772.
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✓ Coregistration of different modality imaging serves to increase the ease and accuracy of stereotactic procedures. In many cases, magnetic resonance (MR) stereotaxis is supplanting computerized tomography (CT). The advantages of increased anatomical detail and multiplanar imaging afforded by MR, however, are offset by its potential inaccuracy as well as the more cumbersome and less available nature of its hardware. A system has been developed by one of the authors by which MR imaging can be performed separately without a stereotactic fiducial headring. Then, immediately prior to surgery, a stereotactic CT scan is obtained and software is used to coregister CT and MR images anatomically by matching cranial landmarks in the two scans. The authors examined this system in six patients as well as with the use of a lucite phantom. After initially coregistering CT and MR images, six separate anatomical (for the patients) and eight artificial (for the phantom) targets were compared. With coregistration, in comparison to CT fiducial scans, errors in each axis are less than or equal to 1 mm using the Cosman-Roberts-Wells system. In fact, the coregistered images are more accurate than MR fiducial images, in the anteroposterior (p = 0.001), lateral (p < 0.05), and vertical (p < 0.03) planes. Three-dimensional error was significantly less in the coregistered scans than the MR fiducial images (p < 0.005). The coregistration procedure therefore not only increases the ease of MR stereotaxis but also increases its accuracy.
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Parsons, Sean P., Maksym I. Harhun und Jan D. Huizinga. „Theory and applications of geometric scaling of localized calcium release events“. American Journal of Physiology-Cell Physiology 299, Nr. 5 (November 2010): C1036—C1046. http://dx.doi.org/10.1152/ajpcell.00034.2010.
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Geometric measures of localized calcium release (LCR) events have been used to understand their biophysical basis. We found power law scaling between three such metrics—maximum amplitude (MA), mass above half-maximum amplitude (MHM), and area at half-maximum amplitude (AHM). In an effort to understand this scaling a minimal analytic model was employed to simulate LCR events recorded by confocal line scan. The distribution of logMHM as a function of logAHM, pMHM(pAHM), was dependent on model parameters such as channel open time, current size, line scan offset, and apparent diffusion coefficient. The distribution of log[MHM/AHM] as a function of logMA, p[MHM/AHM](pMA), was invariant, reflecting the gross geometry of the LCR event. The findings of the model were applied to real LCR line scan data from rabbit portal vein myocytes, rat cerebral artery myocytes, and guinea pig fundus knurled cells. pMHM(pAHM) could be used to distinguish two populations of LCR events in portal vein, even at the scale of “calcium noise,” and to calculate the relative current of the two. The relative current was 2. pMHM(pAHM) could also be used to study pharmacological effects. The pMHM(pAHM) distribution of knurled cell LCR events was markedly contracted by ryanodine, suggesting a reduction in channel open time. The p[MHM/AHM](pMA) distributions were invariant across all cell types and were consistent with the model, underlying the common physical basis of their geometry. The geometric scaling of LCR events demonstrated here may help with their mechanistic characterization.
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Moritz, Juliane, Mirko Teschke, Axel Marquardt, Lukas Stepien, Elena López, Frank Brückner, Marina Macias Barrientos, Frank Walther und Christoph Leyens. „Electron Beam Powder Bed Fusion of γ-Titanium Aluminide: Effect of Processing Parameters on Part Density, Surface Characteristics, and Aluminum Content“. Metals 11, Nr. 7 (09.07.2021): 1093. http://dx.doi.org/10.3390/met11071093.
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Gamma titanium aluminides are very interesting for their use in high-performance applications such as aircraft engines due to their low density, high stiffness and favorable high-temperature properties. However, the pronounced brittleness of these intermetallic alloys is a major challenge for their processing through conventional fabrication methods. Additive manufacturing by means of electron beam powder bed fusion (EB-PBF) significantly improves the processability of titanium aluminides due to the high preheating temperatures and facilitates complex components. The objective of this study was to determine a suitable processing window for EB-PBF of the TNM-B1 alloy (Ti-43.5Al-4Nb-1Mo-0.1B), using an increased aluminum content in the powder raw material to compensate for evaporation losses during the process. Design of experiments was used to evaluate the effect of beam current, scan speed, focus offset, line offset and layer thickness on porosity. Top surface roughness was assessed through laser scanning confocal microscopy. Scanning electron microscopy, electron backscatter diffraction (EBSD) and energy-dispersive X-ray spectroscopy (EDX) were used for microstructural investigation and to analyze aluminum loss depending on the volumetric energy density used in EB-PBF. An optimized process parameter set for achieving part densities of 99.9% and smooth top surfaces was derived. The results regarding microstructures and aluminum evaporation suggest a solidification via the β-phase.
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White, Mark A., Stanley J. Watowich und Robert O. Fox. „Calibration of spiral-readout image-plate detectors“. Journal of Applied Crystallography 32, Nr. 1 (01.02.1999): 65–70. http://dx.doi.org/10.1107/s0021889898010474.
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An improved method for intensity-uniformity calibration of diffraction data collected on spiral-readout image-plate (IP) systems is described. This technique is applicable to all types of spiral-readout IP detectors. The procedure utilizes an attenuated direct-beam scan of the IP to generate a radial-sensitivity calibration table. Exposure and scanning of the calibration frame are done on the same time scale as typical data collections, and require no additional equipment. Specific examples are presented for use with Mac Science DIP2000 systems. The new radial calibration is shown to reduce significantly structure-basedRfactors. The improved radial calibration is also shown to lowerRmergewhen the IP is offset from the beam center. In addition to improving data quality and statistics, this method provides a quick and simple diagnostic tool to monitor changes in the sensitivity of the IP detector as a function of age.
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Nodzo, S. R., C.-C. Chang, K. M. Carroll, B. T. Barlow, S. A. Banks, D. E. Padgett, D. J. Mayman und S. A. Jerabek. „Intraoperative placement of total hip arthroplasty components with robotic-arm assisted technology correlates with postoperative implant position“. Bone & Joint Journal 100-B, Nr. 10 (Oktober 2018): 1303–9. http://dx.doi.org/10.1302/0301-620x.100b10-bjj-2018-0201.r1.
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Aims The aim of this study was to evaluate the accuracy of implant placement when using robotic assistance during total hip arthroplasty (THA). Patients and Methods A total of 20 patients underwent a planned THA using preoperative CT scans and robotic-assisted software. There were nine men and 11 women (n = 20 hips) with a mean age of 60.8 years (sd 6.0). Pelvic and femoral bone models were constructed by segmenting both preoperative and postoperative CT scan images. The preoperative anatomical landmarks using the robotic-assisted system were matched to the postoperative 3D reconstructions of the pelvis. Acetabular and femoral component positions as measured intraoperatively and postoperatively were evaluated and compared. Results The system reported accurate values for reconstruction of the hip when compared to those measured postoperatively using CT. The mean deviation from the executed overall hip length and offset were 1.6 mm (sd 2.9) and 0.5 mm (sd 3.0), respectively. Mean combined anteversion was similar and correlated between intraoperative measurements and postoperative CT measurements (32.5°, sd 5.9° versus 32.2°, sd 6.4°; respectively; R2 = 0.65; p < 0.001). There was a significant correlation between mean intraoperative (40.4°, sd 2.1°) acetabular component inclination and mean measured postoperative inclination (40.12°, sd 3.0°, R2 = 0.62; p < 0.001). There was a significant correlation between mean intraoperative version (23.2°, sd 2.3°), and postoperatively measured version (23.0°, sd 2.4°; R2 = 0.76; p < 0.001). Preoperative and postoperative femoral component anteversion were significantly correlated with one another (R2 = 0.64; p < 0.001). Three patients had CT scan measurements that differed substantially from the intraoperative robotic measurements when evaluating stem anteversion. Conclusion This is the first study to evaluate the success of hip reconstruction overall using robotic-assisted THA. The overall hip reconstruction obtained in the operating theatre using robotic assistance accurately correlated with the postoperative component position assessed independently using CT based 3D modelling. Clinical correlation during surgery should continue to be practiced and compared with observed intraoperative robotic values. Cite this article: Bone Joint J 2018;100-B:1303–9.
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Fei, Weihong, und George A. McMechan. „Fast model-based migration velocity analysis and reflector shape estimation“. GEOPHYSICS 70, Nr. 2 (März 2005): U9—U17. http://dx.doi.org/10.1190/1.1884830.
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Migration velocity analysis can be made more efficient by preselecting the traces that contribute to a series of common-reflection-point (CRP) gathers and migrating only those traces. The data traces that contribute to a CRP for one reflection point on one layer are defined in a two-step procedure. First, poststack parsimonious Kirchhoff depth migration of zero-offset (or stacked) traces defines approximate reflector positions and orientations. Then, ray tracing from the reflection points for nonzero reflection angles defines the source and receiver locations of the data traces in the CRP gather. These traces are then prestack depth migrated, and the interval velocity model adjustment is obtained by fitting the velocity that maximizes the stack amplitude over the predicted (nonhyperbolic) moveout. A small number (2–3) of iterations converge to a 2D model of layer shape and interval velocity. Further efficiency is obtained by implementing layer stripping. The computation time is greatly reduced by combining parsimonious migration with processing only the salient portions of the whole seismic data set. The algorithm can handle lateral velocity variation within each layer as well as constant velocity. The computation time of the proposed algorithm is of the same order as that of the standard rms velocity scan method, but it does not have the inherent assumptions of the velocity scan method and is faster than current iterative prestack depth migration velocity analysis methods for typical field data.
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Bonnet, Céline, und Jan Philip Schain. „AN EMPIRICAL ANALYSIS OF MERGERS: EFFICIENCY GAINS AND IMPACT ON CONSUMER PRICES“. Journal of Competition Law & Economics 16, Nr. 1 (März 2020): 1–35. http://dx.doi.org/10.1093/joclec/nhaa001.
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Abstract In this article, we extend the literature on merger simulation models by incorporating its potential synergy gains into structural econometric analysis. We present an integrated approach. We estimate a structural demand and supply model dealing with two-part tariff contracts between manufacturers and retailers as in Bonnet and Dubois (2010). This model allows us to recover the marginal cost of each differentiated product. Then we estimate potential efficiency gains using the data envelopment analysis approach of Bogetoft and Wang (2005), and some assumptions about exogenous cost shifters. In the last step, we simulate the new price equilibrium post-merger by taking into account synergy gains, and derive price and welfare effects. We use a home scan data set of dairy dessert purchases in France, and show that synergy gains could offset the upward pressure on prices post. Moreover, in this market, the increase in industry profit due to the merger is more driven by its induced synergy gains than by the market power increase.
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Shuman, Christopher A., und Josefino C. Comiso. „In situ and satellite surface temperature records in Antarctica“. Annals of Glaciology 34 (2002): 113–20. http://dx.doi.org/10.3189/172756402781818003.
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AbstractAir-temperature records (TA) during 1992 from five inland Antarctic automatic weather station (AWS) sites were compared with the best available infrared temperatures (TIR) from the Advanced Very High Resolution Radiometer (AVHRR) as well as calibrated passive-microwave temperatures (TC) from the Special Sensor Microwave/Imager (SSM/I). Daily and monthly average TA, TIR, and TC data indicate that each approach captures generally similar trends at each site but each approach also has limitations. AWS TA data are considered the most accurate but represent spatially restricted areas and may have long gaps due to sensor or transmission problems. AVHRR TIR data have daily variability similar to the TA record but have numerous small gaps due to cloud cover or observation interruptions. An offset between TA and TIR (>4 K) at the South Pole site was identified that may be due to the inclusion of data with large satellite scan angles necessary to cover this area. SSM/I TC data have the most continuity but exhibit calibration problems, a significantly damped daily response and do not cover all of Antarctica. Individual daily differences between TA and TIR as well as TA and TC can exceed 17 K, but all sites have mean daily differences of about 1 Kor better, after compensating for the offset at South Pole, and standard deviations of <6K. Monthly temperature differences are typically 5 K or better, with standard deviations generally <3K. And finally, using the available data, the 1992 average temperature differences are <1 K.
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Smith, Ryan, Ilya Borukhov, Emily Hampp, Matt Thompson, Zackary O. Byrd, Nipun Sodhi, Michael A. Mont und Laura Scholl. „Comparison of Precision for Manual versus Robotic-Assisted Total Hip Arthroplasty Performed by Fellows“. Journal of Hip Surgery 4, Nr. 03 (September 2020): 117–23. http://dx.doi.org/10.1055/s-0040-1714333.
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AbstractAlthough various studies have shown that robotic-assisted total hip arthroplasty (RATHA) is associated with improved component positioning to plan and reduced intraoperative complications, there is still a learning curve for implementation even for experienced surgeons. This study assessed this learning curve for fellows during their training year, by comparing the accuracy and precision of acetabular component positioning, leg length, component offset, and center of rotation between manual THA (MTHA) and RATHA. Six fresh-frozen lower extremity specimens were utilized for surgical procedures performed by two adult reconstruction fellows who were halfway through their training year. The specimens were randomized to undergo one side with manual instrumentation and the contralateral side with RATHA. The final intraoperative surgical plan for rotation, cup orientation, leg length, and offset values were recorded and compared with the actual values measured by computed tomography (CT) scan. Using pre- and postoperative CT scans, the RATHA group was then compared with the MTHA group for accuracy and precision to plan. To assess differences in standard deviations of each measurement, 2-variances testing was performed using α = 0.05. To assess differences in central tendencies of each measurement for each group, Mann–Whitney U tests were performed using α = 0.05. RATHA exhibited significantly (p < 0.05) greater accuracy and precision to plan compared with MTHA in shell version (2.3 ± 1.2° vs. 7.8 ± 4.6°), shell inclination (2.1 ± 1.2° vs. 7.2 ± 3.2), and leg length discrepancy (0.8 ± 0.8 mm vs. 6.4 ± 3.7 mm). Center of head rotation was reported for each anatomical plane. There was no statistical difference in distance from original center of head rotation when considering the superoinferior, mediolateral, and anteroposterior planes as well as when combined as a total deviation in all three planes. The use of CT-guided preoperative planning and intraoperative robotic technology can help surgeons achieve desired implant placement. Results from this study indicate that with limited RATHA experience, surgeons in fellowship training were able to place THA components more accurately and precisely to plan for several important parameters compared with MTHA, namely shell inclination, shell anteversion, and leg length discrepancy.