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1
Sun, Shujie, Dong Yu, Changhui Wang und Chuanning Xie. „A smooth tool path generation and real-time interpolation algorithm based on B-spline curves“. Advances in Mechanical Engineering 10, Nr. 1 (Januar 2018): 168781401775028. http://dx.doi.org/10.1177/1687814017750281.
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In the machining progress of free-form surface, tool path is presented as continuous small line segments. To achieve high machining speed and fine machining quality, the tool path needs to be smoothed. This study presents a smooth tool path generation algorithm based on B-spline curves for small line segments machining. The algorithm includes two modules: smooth tool path generation module and real-time look-ahead interpolation module. In the smooth tool path generation module, the tool path is divided into non-fitting regions and fitting regions by three conditions: the length of small line segments, the angle of adjacent small line segments, and the change rate of the length and angle. To control contour error and get fine machining quality, the fitting regions are corrected by circle correction method and fitted into B-spline curves, while the non-fitting regions are smoothed with B-spline curves. In this module, the gained tool path has continuous curvature. In the interpolation module, the seven-phase jerk-limited look-ahead planning is adopted to generate smooth machining velocity, while the calculation accuracy of interpolation point generated by the interpolation period crossing two adjacent tool path is controlled. Simulations and experimental results demonstrate that the proposed algorithm is able to reduce the amount of numerical control codes, achieve high machining speed, and improve machining quality.
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Belchior, Jérémy, Dominique Guines, Lionel Leotoing und Eric Ragneau. „Force Prediction for Correction of Robot Tool Path in Single Point Incremental Forming“. Key Engineering Materials 554-557 (Juni 2013): 1282–89. http://dx.doi.org/10.4028/www.scientific.net/kem.554-557.1282.
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In this work, an off-line compensation procedure, based on an elastic modelling of the machine structure coupled with a Finite Element Analysis (FEA) of the process is applied to Robotized Single Point Incremental Forming (RSPIF). Assuming an ideal stiff robot, the FEA evaluates the Tool Center Point (TCP) forces during the forming stage. These forces are then defined as an input data of the elastic robot model to predict and correct the tool path deviations. In order to make efficient the tool path correction, the weight of three numerical and material parameters of the FEA on the predicted forces is investigated. Finally, the efficiency of the proposed method is validated by the comparison between numerical and experimental geometries obtained with or without correction of the tool path.
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Frehlich, Rod, Robert Sharman, Charles Clough, Michael Padovani, Kelly Fling, Ward Boughers und W. Scott Walton. „Effects of Atmospheric Turbulence on Ballistic Testing“. Journal of Applied Meteorology and Climatology 47, Nr. 5 (01.05.2008): 1539–49. http://dx.doi.org/10.1175/2007jamc1775.1.
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Abstract The effects of atmospheric turbulence on munition target scatter are determined from numerical simulations of ballistic trajectories through many realizations of realistic simulated turbulent wind fields. A technique is evaluated for correcting for the effects of turbulence on ballistic testing procedures by using a line of sonic anemometer measurements taken along the trajectory path. The metric used to evaluate the correction is the difference between the target impact scatter produced with and without the use of the anemometers in the trajectory calculations. The improvement in the testing procedure as measured by this metric is determined as a function of the number of sonic anemometers in the line and the sonic averaging time interval. The performance of the simulations is also compared with data from a field test for a standard small-caliber munition, and the predicted and observed target scatter are in good qualitative agreement, supporting the feasibility of the approach.
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Qiu, Changwu, Qixin Cao und Shouhong Miao. „An on-line task modification method for singularity avoidance of robot manipulators“. Robotica 27, Nr. 4 (Juli 2009): 539–46. http://dx.doi.org/10.1017/s026357470800492x.
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SUMMARYIn this paper, we present an on-line task modification method (OTMM) to realize singularity avoidance for nonredundant and redundant manipulators at the velocity level. The method introduces a correction vector, constructed from the task velocity and the singular vector corresponding to the minimum singular value, into the task velocity. The performance is simply affected by the choice of the lower limit of the minimum singular value and a scalar adjusting function, which is monotone with respect to the minimum singular value. The method makes unnecessary avoiding the singularity point by off-line path planning for nonredundant or redundant manipulators, and the effort to check whether the singularity is escapable for redundant manipulators. The simulation results show the effectiveness of the OTMM for on-line singularity avoidance in manipulator motion control.
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Li, Meng, Kanhua Su, Shuli Hu, Lifu Wan und Weiqing Chen. „Displacement vectors control method for orienter ribs during path correction in coiled tubing drilling“. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 233, Nr. 10 (12.12.2018): 3531–46. http://dx.doi.org/10.1177/0954406218819036.
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The well path easily deviates from the original design trajectory during coiled tubing drilling, which needs to be corrected with an orienter. A three-segment correction trajectory with two arc segments and a line segment is constructed based on the differential geometry principle, and the direction at the target is consistent with the direction of the original borehole. Based on the parameters of the design correction trajectory, a mathematical relationship between trajectory parameters and the displacement vectors of orienter ribs is established by using the vector analysis method. According to the principle of minimum energy, the problem of multisolvability in mathematics is avoided. Then, the control model of the displacement vectors of orienter ribs with the parameters' variation of the designed correction trajectory is established. The similarly periodic variation rule of displacements of orienter ribs with the variation of tool face angle is obtained, and the closed-loop control scheme for correction trajectory while drilling is made. The results of field test show that by using coiled tubing drilling, during the circular arc section of the designed three-segment correction trajectory, the displacement vectors of orienter ribs vary similarly periodically, which is called the directional drilling mode. During drilling in the slanted segment, the displacements of each rib are equal, which is called the keeping drilling mode. The design method of correction trajectory and the displacement vector control method of the orienter ribs are practicable during path correction in coiled tubing drilling, which is helpful to improve the efficiency of coiled tubing drilling.
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Sahni, Narinder Singh, Tomas Isaksson und Tormod Næs. „Comparison of Methods for Transfer of Calibration Models in Near-Infared Spectroscopy: A Case Study Based on Correcting Path Length Differences Using Fiber-Optic Transmittance Probes in In-Line Near-Infrared Spectroscopy“. Applied Spectroscopy 59, Nr. 4 (April 2005): 487–95. http://dx.doi.org/10.1366/0003702053641522.
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This article addresses problems related to transfer of calibration models due to variations in distance between the transmittance fiber-optic probes. The data have been generated using a mixture design and measured at five different probe distances. A number of techniques reported in the literature have been compared. These include multiplicative scatter correction (MSC), path length correction (PLC), finite impulse response (FIR), orthogonal signal correction (OSC), piecewise direct standardization (PDS), and robust calibration. The quality of the predictions was expressed in terms of root mean square error of prediction (RMSEP). Robust calibration gave good calibration transfer results, while the other methods did not give acceptable results.
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Guo, Yan, Aiguo Song, Jiatong Bao, Tang Hongru und Jianwei Cui. „A Combination of Terrain Prediction and Correction for Search and Rescue Robot Autonomous Navigation“. International Journal of Advanced Robotic Systems 6, Nr. 3 (01.01.2009): 24. http://dx.doi.org/10.5772/7229.
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This paper presents a novel two-step autonomous navigation method for search and rescue robot. The algorithm based on the vision is proposed for terrain identification to give a prediction of the safest path with the support vector regression machine (SVRM) trained off-line with the texture feature and color features. And correction algorithm of the prediction based the vibration information is developed during the robot traveling, using the judgment function given in the paper. The region with fault prediction will be corrected with the real traversability value and be used to update the SVRM. The experiment demonstrates that this method could help the robot to find the optimal path and be protected from the trap brought from the error between prediction and the real environment.
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García-Botella, Angel, Lun Jiang und Roland Winston. „Flowline Optical Simulation to Refractive/Reflective 3D Systems: Optical Path Length Correction“. Photonics 6, Nr. 4 (28.09.2019): 101. http://dx.doi.org/10.3390/photonics6040101.
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Nonimaging optics is focused on the study of techniques to design optical systems for the purpose of energy transfer instead of image forming. The flowline optical design method, based on the definition of the geometrical flux vector J, is one of these techniques. The main advantage of the flowline method is its capability to visualize and estimate how radiant energy is transferred by the optical systems using the concepts of vector field theory, such as field line or flux tube, which overcomes traditional raytrace methods. The main objective this paper is to extend the flowline method to analyze and design real 3D concentration and illumination systems by the development of new simulation techniques. In this paper, analyzed real 3D refractive and reflective systems using the flowline vector potential method. A new constant term of optical path length is introduced, similar and comparable to the gauge invariant, which produces a correction to enable the agreement between raytrace- and flowline-based computations. This new optical simulation methodology provides traditional raytrace results, such as irradiance maps, but opens new perspectives to obtaining higher precision with lower computation time. It can also provide new information for the vector field maps of 3D refractive/reflective systems.
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Min, J. E., S. K. Lee und J. H. Ryu. „ADVANCED SURFACE-REFLECTED RADIANCE CORRECTION FOR AIRBORNE HYPERSPECTRAL IMAGERY IN COASTAL RED TIDE DETECTION“. ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences V-3-2021 (17.06.2021): 73–80. http://dx.doi.org/10.5194/isprs-annals-v-3-2021-73-2021.
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Abstract. Red tides are among the most common coastal hazards, causing serious damage to the coastal environment. Many satellite sensors can detect red tide blooms, but are limited in their detection of the exact area of the bloom and biological abundance in terms of spatial and spectral resolution. The high spatial and spectral resolutions of hyperspectral airborne remote sensing data may help overcome these limitations to analyze red tide blooms more effectively. To identify potential applications of hyperspectral airborne data in red tide detection, an integrated field campaign was performed in September 2016 off the coast of Tongyeong, South Korea. An AisaEAGLE sensor was installed on a Cessna 208B crewed aircraft to obtain hyperspectral images of an 18 km × 18 km coastal area. To assess the atmospheric correction of the hyperspectral data, in situ optical data and water samples were measured on two vessels concurrent with the flight path. Advanced surface-reflected radiance (Lr) correction and basic atmospheric path radiance (La) correction were performed on the hyperspectral images. Of these, Lr correction comprised a large proportion of the atmospheric correction. The atmosphere-corrected remote sensing reflectance data of the hyperspectral images closely matched the in-situ measurements. The data were assessed for red tide events using ratio analysis and the fluorescence line height technique; the ratio analysis more effectively detected regions with suspected red tides.
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Surmick, David M., und Christian G. Parigger. „Tracking Temporal Development of Optical Thickness of Hydrogen Alpha Spectral Radiation in a Laser-Induced Plasma“. Atoms 7, Nr. 4 (04.11.2019): 101. http://dx.doi.org/10.3390/atoms7040101.
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In this paper, we consider the temporal development of the optical density of the H α spectral line in a hydrogen laser-induced plasma. This is achieved by using the so-called duplication method in which the spectral line is re-imaged onto itself and the ratio of the spectral line with it duplication is taken to its measurement without the duplication. We asses the temporal development of the self-absorption of the H α line by tracking the decay of duplication ratio from its ideal value of 2. We show that when 20% loss is considered along the duplication optical path length, the ratio is 1.8 and decays to a value of 1.25 indicating an optically thin plasma grows in optical density to an optical depth of 1.16 by 400 ns in the plasma decay for plasma initiation conditions using Nd:YAG laser radiation at 120 mJ per pulse in a 1.11 × 10 5 Pa hydrogen/nitrogen gas mixture environment. We also go on to correct the H α line profiles for the self-absorption impact using two methods. We show that a method in which the optical depth is directly calculated from the duplication ratio is equivalent to standard methods of self-absorption correction when only relative corrections to spectral emissions are needed.
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Torres, Elizabeth B., und David Zipser. „Reaching to Grasp With a Multi-Jointed Arm. I. Computational Model“. Journal of Neurophysiology 88, Nr. 5 (01.11.2002): 2355–67. http://dx.doi.org/10.1152/jn.00030.2002.
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The generation of goal-directed movements requires the solution of many difficult computational problems. Among these are transformations from extrinsic to intrinsic reference frames, specifying solution paths, removing under-specification due to excess degrees of freedom and path multiplicity, constraint satisfaction, and error correction. There are no current motor-control computational models that address these issues in the context of realistic arm movement with redundant degrees of freedom. In this paper, we conjecture there is a geometric stage between sensory input and physical execution. The geometric stage determines movement trajectories independently of forces. It uses a gradient technique that relies on the metric of the space of postures to resolve endpoint path selection, posture-change specification, error correction, and multiple constraint satisfaction on-line without preplanning. The model is instantiated in an arm with seven degrees of freedom that moves in three-dimensional space. Simulated orientation-matching movements are compared with actual human movement data to assess the validity of several of the model's behavioral predictions.
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Saeed Al-khayyt, Saad Zaghlul. „Creating Through Points in Linear Function with Parabolic Blends Path by Optimization Method“. Al-Khwarizmi Engineering Journal 14, Nr. 1 (09.04.2018): 77–89. http://dx.doi.org/10.22153/https://doi.org/10.22153/kej.2018.10.005.
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The linear segment with parabolic blend (LSPB) trajectory deviates from the specified waypoints. It is restricted to that the acceleration must be sufficiently high. In this work, it is proposed to engage modified LSPB trajectory with particle swarm optimization (PSO) so as to create through points on the trajectory. The assumption of normal LSPB method that parabolic part is centered in time around waypoints is replaced by proposed coefficients for calculating the time duration of the linear part. These coefficients are functions of velocities between through points. The velocities are obtained by PSO so as to force the LSPB trajectory passing exactly through the specified path points. Also, relations for velocity correction and exact velocity solution are derived. Simulation results show that the engagement of modified LSPB trajectory with PSO to work well on the tested cases. This proposed method is very simple which can be used for on-line path planning, and not necessarily to use high acceleration magnitude.
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Liu, Xinjie, Jian Guo, Jiaochan Hu und Liangyun Liu. „Atmospheric Correction for Tower-Based Solar-Induced Chlorophyll Fluorescence Observations at O2-A Band“. Remote Sensing 11, Nr. 3 (11.02.2019): 355. http://dx.doi.org/10.3390/rs11030355.
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Solar-induced chlorophyll fluorescence (SIF) has been proven to be an efficient indicator of vegetation photosynthesis. To investigate the relationship between SIF and Gross Primary Productivity (GPP), tower-based continuous spectral observations coordinated with eddy covariance (EC) measurements are needed. As the strong absorption effect at the O2-A absorption bands has an obvious influence on SIF retrieval based on the Fraunhofer Line Discrimination (FLD) principle, atmospheric correction is required even for tower-based SIF observations made with a sensor tens of meters above the canopy. In this study, an operational and simple solution for atmospheric correction of tower-based SIF observations at the O2-A band is proposed. The aerosol optical depth (AOD) and radiative transfer path length (RTPL) are found to be the dominant factors influencing the upward and downward transmittances at the oxygen absorption band. Look-up tables (LUTs) are established to estimate the atmosphere transmittance using AOD and RTPL based on the MODerate resolution atmospheric TRANsmission 5 (MODTRAN 5) model simulations, and the AOD is estimated using the ratio of the downwelling irradiance at 790 nm to that at 660 nm (E790/E660). The influences of the temperature and pressure on the atmospheric transmittance are also compensated for using a corrector factor of RTPL based on an empirical equation. A series of field measurements were carried out to evaluate the performance of the atmospheric correction method for tower-based SIF observations. The difference between the SIF retrieved from tower-based and from ground-based observations decreased obviously after the atmospheric correction. The results indicate that the atmospheric correction method based on a LUT is efficient and also necessary for more accurate tower-based SIF retrieval, especially at the O2-A band.
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Dewi, Esthi Kurnia, und Bambang Trisakti. „COMPARING ATMOSPHERIC CORRECTION METHODS FOR LANDSAT OLI DATA“. International Journal of Remote Sensing and Earth Sciences (IJReSES) 13, Nr. 2 (02.06.2017): 105. http://dx.doi.org/10.30536/j.ijreses.2016.v13.a2472.
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Landsat data used for monitoring activities to land cover because it has spatial resolution and high temporal. To monitor land cover changes in an area, atmospheric correction is needed to be performed in order to obtain data with precise digital value picturing current condition. This study compared atmospheric correction methods namely Quick Atmospheric Correction (QUAC), Dark Object Subtraction (DOS) and Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes (FLAASH). The correction results then were compared to Surface Reflectance (SR) imagery data obtained from the United States Geological Survey (USGS) satelite. The three atmospheric correction methods were applied to Landsat OLI data path/row126/62 for 3 particular dates. Then, sample on vegetation, soil and bodies of water (waterbody) were retrieved from the image. Atmospheric correction results were visually observed and compared with SR sample on the absolute value, object spectral patterns, as well as location and time consistency. Visual observation indicates that there was a contrast change on images that had been corrected by using FLAASH method compared to SR, which mean that the atmospheric correction method was quite effective. Analysis on the object spectral pattern, soil, vegetation and waterbody of images corrected by using FLAASH method showed that it was not good enough eventhough the reflectant value differed greatly to SR image. This might be caused by certain variables of aerosol and atmospheric models used in Indonesia. QUAC and DOS made more appropriate spectral pattern of vegetation and water body than spectral library. In terms of average value and deviation difference, spectral patterns of soil corrected by using DOS was more compatible than QUAC.
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Volkova, Tamara A., Yulia E. Balykina und Alexander Bespalov. „Predicting Ship Trajectory Based on Neural Networks Using AIS Data“. Journal of Marine Science and Engineering 9, Nr. 3 (28.02.2021): 254. http://dx.doi.org/10.3390/jmse9030254.
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To create an autonomously moving vessel, it is necessary to know exactly how to determine the current coordinates of the vessel in the selected coordinate system, determine the actual trajectory of the vessel, estimate the motion trend to predict the current coordinates, and calculate the course correction to return to the line of the specified path. The navigational and hydrographic conditions of navigation on each section of the route determine the requirements for the accuracy of observations and the time spent on locating the vessel. The problem of predicting the trajectory of the vessel’s motion in automatic mode is especially important for river vessels or river-sea vessels, predicting the trajectory of the route sections during the maneuvering of the vessel. At the moment, one of the most accurate ways of determining the coordinates of the vessel is by reading the satellite signal. However, when a vessel is near hydraulic structures, problems may arise connected with obtaining a satellite signal due to interference and, therefore, the error in measuring the coordinates of the vessel increases. The likelihood of collisions and various kinds of incidents increases. In such cases, it is possible to correct the trajectory of the movement using an autonomous navigation system. In this work, opportunities of the possible application of artificial neural networks to create such a corrective system using only the coordinates of the ship’s position are discussed. It was found that this is possible on sections of the route where the ship does not maneuver.
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Roychoudhuri, Lopamudra, und Ehab S. Al-Shaer. „Autonomic QoS Optimization of Real-Time Internet Audio Using Loss Prediction and Stochastic Control“. International Journal of Adaptive, Resilient and Autonomic Systems 1, Nr. 3 (Juli 2010): 81–107. http://dx.doi.org/10.4018/jaras.2010070105.
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Quality of Internet audio is highly sensitive to packet loss caused by congestion in links. Packet loss for audio is normally rectified by adding redundancy using Forward Error Correction (FEC). Alternatively, path diversity mechanisms are used to improve reliability and thus session quality. To achieve optimized receiver audio quality for transmissions using single or multiple paths, the authors propose a self-adaptive joint Error and Rate Control framework based on packet loss prediction and on-line quality assessment. The Error Control chooses appropriate FEC proactively to preserve quality with optimal bandwidth, using a Markov Decision Process (MDP) and a stochastic inventory control, a novel approach for multimedia error recovery. The Rate Control uses a quality optimization model to determine the optimal dispersion over single or multiple paths. This paper will present results using simulation and Internet experiments to show the superiority of this mechanism over other similar techniques.
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Moga, Nikolay. „MUSCLE SPASTICITY AND ITS INTERACTION WITH MYOFASCIAL SYSTEM OF CHILDREN WITH CENTRAL PARESIS“. EUREKA: Health Sciences 4 (31.07.2019): 35–41. http://dx.doi.org/10.21303/2504-5679.2019.00954.
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Traditionally, the problem of muscle spasticity was considered by experts as a kind of local problem associated with the inhibition or traumatisation of the central motor neuron in a certain part of its path. According to this approach, only the first stage of the causal relationship of the two systems was reflected: the nervous and the muscular systems. In the following, intrasystem relations of the muscle and muscle complex appeared according to the type of harmonization or destructivization of the activity of this system. To resolve this problematic situation, the article examines the original theory of Thomas V. Myers about “anatomical trains” or “myofascial meridians” as an integral musculoskeletal system of the human body, which forms the basis of its anatomy and motor activity. Key ideas of tensegrity as a structure of balanced compression-tension of the musculoskeletal system are identified, and it is necessary to rush to the targets, carrying out the correction of motor disorders of the tender age children with paresis of central type by means of physical education. For deeper understanding of the activities of these mechanisms of children myofascial status harmonization, the main myofascial lines were briefly characterized: surface back line, surface frontal line, lateral line, spiral line, arm lines. On this basis, working hypothesis was formulated as for using the holistic myofascial system capabilities of the child’s body to correct both the tonic state of individual spastic muscles and to improve the general children motor status. To check the formulated hypothesis, the directions of the implementation of correctively directed physical education of tender age children with central paresis of different localization levels were indicated. An attempt was made to use the basic knowledge of the myofascial meridians functioning to increase the efficiency of diagnosing the state of musculoskeletal formations of children with spastic paresis, developing strategies and tactics for correcting their tonic state, methods and techniques for adjusting the balance of compression and tension of these structures to improve children motor activity and to improve the efficiency of their basic motor regimes mastering. There was made a fundamental conclusion that the correctional work by means of physical education should be preceded by preparatory work aimed at normalization of the whole myofascial system of a child with a spastic type of movement disorders, which can be carried out using purely medical techniques and the techniques based on the means of children physical education. Prospects of the scientific and practical development of the problem indicated in this article are highlighted separately.
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Sutisna, Setya Permana, I. Dewa Made Subrata und Radite Praeko Agus Setiawan. „SISTEM PENGENDALI KEMUDI TRAKTOR OTOMATIS EMPAT RODA PADA PENGUJIAN LINTASAN LURUS (Tracking Control System of Autonomous Four Wheel Tractor on Straight Path)“. Jurnal Agritech 35, Nr. 01 (04.05.2015): 106. http://dx.doi.org/10.22146/agritech.9425.
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This research is the development of autonomous tractor. Although research for automatic tractor have been carried out, but it is still developed to get more precision and optimal method. The purpose of this research is to develop a trajectory control system tractor to follow a straight-line when the working soil tillage. Model that was developed tobe able calculate steering angle correction of the tractor position so that the tractor will run on a reference trajectory. Tractor position is determined from RTK DGPS. Tractor direction is calculated from two position of tractor. Control algorithm consists of the arrangement of commands to control the tractor move the reference trajectory. Simulations were performed to determine controlling algorithm ability the tractor to follow reference trajectory. The algorithm ability is tested in real conditions on a straight- line path along 30 m with a speed of tractor 0.5 m/s in a field. Thetest results obtained in the field of performance accuracy rate is 97.13% control and average deviation with reference trajectory is 8.62 cm.Keywords: Autonomous tractor, tracking control system, soil tillage ABSTRAKPenelitian ini merupakan penelitian pengembangan traktor otomatis. Meskipun penelitian mengenai traktor otomatis telah banyak dilakukan, namun pengembangan masih terus dilakukan untuk mendapatkan presisi yang lebih tinggi dan metode yang optimal. Tujuan penelitian ini adalah mengembangkan sistem pengendali kemudi traktor agar dapatmengikuti jalur kerja lintasan lurus ketika melakukan kegiatan pengolahan tanah. Model yang dikembangkan harus mampu menghitung sudut setir koreksi dari posisi traktor agar traktor mampu berjalan pada lintasan lurus yang telah ditentukan. Arah pergerakan traktor diketahui dari perbandingan dua posisi traktor yang diperoleh dari RTK DGPS.Algoritma pengendalian terdiri dari susunan perintah-perintah untuk mengendalikan traktor bergerak mengikuti lintasan acuan. Simulasi dilakukan untuk mengetahui kemampuan algoritma yang telah dibuat untuk mengendalikan traktor agar dapat berjalan mengikuti lintasan acuan. Kemampuan algoritma tersebut kemudian diuji dalam kondisi riildilapangan pada lintasan lurus sepanjang 30 m dengan kecepatan traktor 0.5 m/s. Hasil pengujian di lapangan diperoleh tingkat akurasi kinerja kontrol sebesar 97.13% dan besar simpangan rata-rata terhadap lintasan acuan sebesar 8.62 cm.Kata kunci: Traktor otomatis, sistem pengendali kemudi, pengolahan tanah
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Peltola, Olli, Toprak Aslan, Andreas Ibrom, Eiko Nemitz, Üllar Rannik und Ivan Mammarella. „The high-frequency response correction of eddy covariance fluxes – Part 1: An experimental approach and its interdependence with the time-lag estimation“. Atmospheric Measurement Techniques 14, Nr. 7 (28.07.2021): 5071–88. http://dx.doi.org/10.5194/amt-14-5071-2021.
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Abstract. The eddy covariance (EC) technique has emerged as the prevailing method to observe the ecosystem–atmosphere exchange of gases, heat and momentum. EC measurements require rigorous data processing to derive the fluxes that can be used to analyse exchange processes at the ecosystem–atmosphere interface. Here we show that two common post-processing steps (time-lag estimation via cross-covariance maximisation and correction for limited frequency response of the EC measurement system) are interrelated, and this should be accounted for when processing EC gas flux data. These findings are applicable to EC systems employing closed- or enclosed-path gas analysers which can be approximated to be linear first-order sensors. These EC measurement systems act as low-pass filters on the time series of the scalar χ (e.g. CO2, H2O), and this induces a time lag (tlpf) between vertical wind speed (w) and scalar χ time series which is additional to the travel time of the gas signal in the sampling line (tube, filters). Time-lag estimation via cross-covariance maximisation inadvertently accounts also for tlpf and hence overestimates the travel time in the sampling line. This results in a phase shift between the time series of w and χ, which distorts the measured cospectra between w and χ and hence has an effect on the correction for the dampening of the EC flux signal at high frequencies. This distortion can be described with a transfer function related to the phase shift (Hp) which is typically neglected when processing EC flux data. Based on analyses using EC data from two contrasting measurement sites, we show that the low-pass-filtering-induced time lag increases approximately linearly with the time constant of the low-pass filter, and hence the importance of Hp in describing the high-frequency flux loss increases as well. Incomplete description of these processes in EC data processing algorithms results in flux biases of up to 10 %, with the largest biases observed for short towers due to the prevalence of small-scale turbulence. Based on these findings, it is suggested that spectral correction methods implemented in EC data processing algorithms are revised to account for the influence of low-pass-filtering-induced time lag.
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Wang, Jingjing, und Joongoo Park. „An Enhanced Indoor Positioning Algorithm Based on Fingerprint Using Fine-Grained CSI and RSSI Measurements of IEEE 802.11n WLAN“. Sensors 21, Nr. 8 (14.04.2021): 2769. http://dx.doi.org/10.3390/s21082769.
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Received signal strength indication (RSSI) obtained by Medium Access Control (MAC) layer is widely used in range-based and fingerprint location systems due to its low cost and low complexity. However, RSS is affected by noise signals and multi-path, and its positioning performance is not stable. In recent years, many commercial WiFi devices support the acquisition of physical layer channel state information (CSI). CSI is an index that can characterize the signal characteristics with more fine granularity than RSS. Compared with RSS, CSI can avoid the effects of multi-path and noise by analyzing the characteristics of multi-channel sub-carriers. To improve the indoor location accuracy and algorithm efficiency, this paper proposes a hybrid fingerprint location technology based on RSS and CSI. In the off-line phase, to overcome the problems of low positioning accuracy and fingerprint drift caused by signal instability, a methodology based on the Kalman filter and a Gaussian function is proposed to preprocess the RSSI value and CSI amplitude value, and the improved CSI phase is incorporated after the linear transformation. The mutation and noisy data are then effectively eliminated, and the accurate and smoother outputs of the RSSI and CSI values can be achieved. Then, the accurate hybrid fingerprint database is established after dimensionality reduction of the obtained high-dimensional data values. The weighted k-nearest neighbor (WKNN) algorithm is applied to reduce the complexity of the algorithm during the online positioning stage, and the accurate indoor positioning algorithm is accomplished. Experimental results show that the proposed algorithm exhibits good performance on anti-noise ability, fusion positioning accuracy, and real-time filtering. Compared with CSI-MIMO, FIFS, and RSSI-based methods, the proposed fusion correction method has higher positioning accuracy and smaller positioning error.
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Stuik, Remko, Laurent Jolissaint, Sarah Kendrew, Stefan Hippler und Bernhard Brandl. „Extreme adaptive optics in the mid-IR: The METIS AO system“. Proceedings of the International Astronomical Union 5, H15 (November 2009): 531. http://dx.doi.org/10.1017/s1743921310010549.
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METIS, the Mid-infrared ELT Imager and Spectrograph, is currently in its phase A study as one of the candidate first-light instruments for the European Extremely Large Telescope. METIS will feature several observational modes, ranging from diffraction limited imaging in L, M and N-bands to high-resolution Integral Field spectroscopy for the L and M-bands. METIS in its current design gives sensitivities similar to Spitzer in imaging and low-resolution spectroscopy and with its high-resolution spectrograph will provide unprecedented line sensitivity. The design of METIS is optimized for both galactic science cases (e.g. conditions in the early solar system, formation and evolution of proto-planetary disks and properties of exoplanets) and extragalactic science cases (e.g. the growth of Supermassive Black Holes). METIS will require a high-order adaptive optics (AO) system to meet its scientific goals, both to provide correction for atmospheric turbulence as well as reduce the impact of wind shake, leading to a residual image motion of 3 - 5 mas rms. METIS is expected to feature both an internal Single Conjugate AO system as well as an external Laser Tomography AO system. The challenges for the METIS AO system are mainly in the broad correction range, an excellent image stability required for coronagraphy and in providing a high sky coverage to be available for as many science targets as possible. An additional challenge for METIS is the need to compensate for composition turbulence, mainly in the form of fast fluctuations in water vapor concentration. Water vapor fluctuations impact the performance of METIS in several ways: Atmospheric dispersion causes a broadening of the point-spread function, both in the science channel and the wavefront channel, but can be corrected using a Atmospheric Dispersion Corrector. Variations in the water vapor composition cannot be corrected this way and are currently estimated to give a residual image motion of ≤10 mas rms. This effect can, especially for coronagraphy, not be neglected. Chromatic optical path difference errors, caused by changes in the index of refraction along the path through the atmosphere were found to be negligible in the case of METIS due to attenuation by the outer scale (at typical values of 25 m). Chromatic anisoplanatism is the effect that the light at different wavelengths travels through a slightly different light path through the atmosphere and can be–at least partly–corrected. The last effect is composition turbulence, mainly caused by fast (> 1 Hz) fluctuations in the water vapor content. Based on data for ALMA and radiometer probes, this leads to a maximum loss in Strehl ratio between 5 and 10%. This mainly has an impact on coronagraphy and the METIS AO team is actively investigating ways to compensate also water vapor turbulence. The main challenge is currently obtaining reliable data on the distribution and magnitude of precipitable water vapor fluctuations.
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Khalifah, Peter. „Use of radial symmetry for the calculation of cylindrical absorption coefficients and optimal capillary loadings“. Journal of Applied Crystallography 48, Nr. 1 (30.01.2015): 149–58. http://dx.doi.org/10.1107/s1600576714026569.
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The problem of numerically evaluating absorption correction factors for cylindrical samples has been revisited using a treatment that fully takes advantage of the sample symmetry. It is shown that the path lengths for all points within the sample at all possible diffraction angles can be trivially determined once the angle-dependent distance distribution for a single line of points is calculated. This provides advantages both in computational efficiency and in gaining an intuitive understanding of the effects of absorption on the diffraction data. A matrix of absorption coefficients calculated for μRproducts between 0 and 20 for diffraction angles θDof 0–90° were used to examine the influence of (1) capillary diameter and (2) sample density on the overall scattered intensity as a function of diffraction angle, where μ is the linear absorption coefficient for the sample andRis the capillary radius. On the basis of this analysis, the optimal sample loading for a capillary experiment to maximize diffraction at angles of 0–50° is in general expected to be achieved when the maximum radius capillary compatible with the beam is used and when the sample density is adjusted to be 3/(4μR) of its original density.
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Chimot, J., T. Vlemmix, J. P. Veefkind, J. F. de Haan und P. F. Levelt. „Impact of aerosols on the OMI tropospheric NO<sub>2</sub> retrievals over industrialized regions: how accurate is the aerosol correction of cloud-free scenes via a simple cloud model?“ Atmospheric Measurement Techniques Discussions 8, Nr. 8 (10.08.2015): 8385–437. http://dx.doi.org/10.5194/amtd-8-8385-2015.
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Abstract. The Ozone Monitoring Instrument (OMI) instrument has provided daily global measurements of tropospheric NO2 for more than a decade. Numerous studies have drawn attention to the complexities related to measurements of tropospheric NO2 in the presence of aerosols. Fine particles affect the OMI spectral measurements and the length of the average light path followed by the photons. However, they are not explicitly taken into account in the current OMI tropospheric NO2 retrieval chain. Instead, the operational OMI O2-O2 cloud retrieval algorithm is applied both to cloudy scenes and to cloud free scenes with aerosols present. This paper describes in detail the complex interplay between the spectral effects of aerosols, the OMI O2-O2 cloud retrieval algorithm and the impact on the accuracy of the tropospheric NO2 retrievals through the computed Air Mass Factor (AMF) over cloud-free scenes. Collocated OMI NO2 and MODIS Aqua aerosol products are analysed over East China, in industrialized area. In addition, aerosol effects on the tropospheric NO2 AMF and the retrieval of OMI cloud parameters are simulated. Both the observation-based and the simulation-based approach demonstrate that the retrieved cloud fraction linearly increases with increasing Aerosol Optical Thickness (AOT), but the magnitude of this increase depends on the aerosol properties and surface albedo. This increase is induced by the additional scattering effects of aerosols which enhance the scene brightness. The decreasing effective cloud pressure with increasing AOT represents primarily the absorbing effects of aerosols. The study cases show that the actual aerosol correction based on the implemented OMI cloud model results in biases between −20 and −40 % for the DOMINO tropospheric NO2 product in cases of high aerosol pollution (AOT ≥ 0.6) and elevated particles. On the contrary, when aerosols are relatively close to the surface or mixed with NO2, aerosol correction based on the cloud model results in overestimation of the DOMINO tropospheric NO2 product, between 10 and 20 %. These numbers are in line with comparison studies between ground-based and OMI tropospheric NO2 measurements under conditions with high aerosol pollution and elevated particles. This highlights the need to implement an improved aerosol correction in the computation of tropospheric NO2 AMFs.
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Dani, Tiar, Rhorom Priyatikanto, Slamet Supriadi, Abdul Rachman und Amrullah A. Qadir. „PENGARUH AKTIVITAS MATAHARI TERHADAP KERAPATAN ATMOSFER ATAS BERDASARKAN DATA POSISI GPS SATELIT LAPAN-A2 (SOLAR ACTVITY INFLUENCE ON THE UPPER ATMOSPHERIC DENSITY DERIVED FROM GPS DATA ON LAPAN-A2 SATELLITE)“. Jurnal Sains Dirgantara 14, Nr. 2 (08.01.2018): 127. http://dx.doi.org/10.30536/j.jsd.2017.v14.a2550.
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Studies on atmospheric density were very important to obtain a correction factor for the atmospheric density model. Thus, improvement of atmospheric models accuracy, i.e. CIRA, JASCHIA, NRLMSISE, became important in its application for re-entry prediction, satellite tracking and mitigation of the collisions probability between active satellites with space debris. GPS equipment installed in LAPAN-A2 indirectly measured the upper atmospheric density variation in-situ from the satellite orbit path. Notwithstanding the measurement had a lower temporal resolution than using accelerometer, but still gives better resolution than using Two-Line Element (TLE) data. This study had successfully determined upper atmospheric density variation with a 10 second resolution using LAPAN-A2 GPS data. The LAPAN-A2 GPS data validated using In-track Radial Cross-track (RIC) had ± 2 km error compared to the TLE data. It was also found that there was influence of solar activity on atmospheric density changes obtained from the LAPAN-A2 GPS data. AbstrakStudi kerapatan atmosfer atas sangat penting untuk memperoleh faktor koreksi dari suatu model kerapatan atmosfer. Peningkatan akurasi dari model atmosfer yang telah ada (CIRA, JASCHIA, NRLMSISE) sangat penting dalam penerapannya untuk prediksi re-entry, penjejakan satelit dan prakiraan kemungkinan terjadinya tabrakan antara satelit aktif dengan sampah antariksa. Peralatan GPS yang terpasang di satelit LAPAN-A2 secara tidak langsung dapat melakukan pengukuran in-situ perubahan kerapatan atmosfer atas dari orbit yang dilaluinya, meskipun tingkat resolusi temporalnya masih lebih rendah dibandingkan menggunakan instrumen akselerometer tetapi masih jauh lebih baik dibandingkan menggunakan data Two-Line Element (TLE). Studi ini telah berhasil memperoleh variasi kerapatan atmosfer atas dengan resolusi 10 detik menggunakan data posisi GPS LAPAN-A2. Selain itu, diperoleh pula tingkat kesalahan dalam koordinat satelit (Radial Intrack Crosstrack - RIC) data TLE terhadap data posisi GPS LAPAN-A2 sebesar ± 2 km. Selain itu terlihat pula pengaruh aktivitas matahari terhadap perubahan kerapatan atmosfer atas yang diperoleh dari data posisi GPS LAPAN-A2
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Chimot, J., T. Vlemmix, J. P. Veefkind, J. F. de Haan und P. F. Levelt. „Impact of aerosols on the OMI tropospheric NO<sub>2</sub> retrievals over industrialized regions: how accurate is the aerosol correction of cloud-free scenes via a simple cloud model?“ Atmospheric Measurement Techniques 9, Nr. 2 (05.02.2016): 359–82. http://dx.doi.org/10.5194/amt-9-359-2016.
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Abstract. The Ozone Monitoring Instrument (OMI) has provided daily global measurements of tropospheric NO2 for more than a decade. Numerous studies have drawn attention to the complexities related to measurements of tropospheric NO2 in the presence of aerosols. Fine particles affect the OMI spectral measurements and the length of the average light path followed by the photons. However, they are not explicitly taken into account in the current operational OMI tropospheric NO2 retrieval chain (DOMINO – Derivation of OMI tropospheric NO2) product. Instead, the operational OMI O2 − O2 cloud retrieval algorithm is applied both to cloudy and to cloud-free scenes (i.e. clear sky) dominated by the presence of aerosols. This paper describes in detail the complex interplay between the spectral effects of aerosols in the satellite observation and the associated response of the OMI O2 − O2 cloud retrieval algorithm. Then, it evaluates the impact on the accuracy of the tropospheric NO2 retrievals through the computed Air Mass Factor (AMF) with a focus on cloud-free scenes. For that purpose, collocated OMI NO2 and MODIS (Moderate Resolution Imaging Spectroradiometer) Aqua aerosol products are analysed over the strongly industrialized East China area. In addition, aerosol effects on the tropospheric NO2 AMF and the retrieval of OMI cloud parameters are simulated. Both the observation-based and the simulation-based approach demonstrate that the retrieved cloud fraction increases with increasing Aerosol Optical Thickness (AOT), but the magnitude of this increase depends on the aerosol properties and surface albedo. This increase is induced by the additional scattering effects of aerosols which enhance the scene brightness. The decreasing effective cloud pressure with increasing AOT primarily represents the shielding effects of the O2 − O2 column located below the aerosol layers. The study cases show that the aerosol correction based on the implemented OMI cloud model results in biases between −20 and −40 % for the DOMINO tropospheric NO2 product in cases of high aerosol pollution (AOT ≥ 0.6) at elevated altitude. These biases result from a combination of the cloud model error, used in the presence of aerosols, and the limitations of the current OMI cloud Look-Up-Table (LUT). A new LUT with a higher sampling must be designed to remove the complex behaviour between these biases and AOT. In contrast, when aerosols are relatively close to the surface or mixed with NO2, aerosol correction based on the cloud model results in an overestimation of the DOMINO tropospheric NO2 column, between 10 and 20 %. These numbers are in line with comparison studies between ground-based and OMI tropospheric NO2 measurements in the presence of high aerosol pollution and particles located at higher altitudes. This highlights the need to implement an improved aerosol correction in the computation of tropospheric NO2 AMFs.
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Zahidi, Usman A., Ayan Chatterjee und Peter W. T. Yuen. „A Radiative Transfer Model-Based Multi-Layered Regression Learning to Estimate Shadow Map in Hyperspectral Images“. Machine Learning and Knowledge Extraction 1, Nr. 3 (06.08.2019): 904–27. http://dx.doi.org/10.3390/make1030052.
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The application of Empirical Line Method (ELM) for hyperspectral Atmospheric Compensation (AC) premises the underlying linear relationship between a material’s reflectance and appearance. ELM solves the Radiative Transfer (RT) equation under specialized constraint by means of in-scene white and black calibration panels. The reflectance of material is invariant to illumination. Exploiting this property, we articulated a mathematical formulation based on the RT model to create cost functions relating variably illuminated regions within a scene. In this paper, we propose multi-layered regression learning-based recovery of radiance components, i.e., total ground-reflected radiance and path radiance from reflectance and radiance images of the scene. These decomposed components represent terms in the RT equation and enable us to relate variable illumination. Therefore, we assume that Hyperspectral Image (HSI) radiance of the scene is provided and AC can be processed on it, preferably with QUick Atmospheric Correction (QUAC) algorithm. QUAC is preferred because it does not account for surface models. The output from the proposed algorithm is an intermediate map of the scene on which our mathematically derived binary and multi-label threshold is applied to classify shadowed and non-shadowed regions. Results from a satellite and airborne NADIR imagery are shown in this paper. Ground truth (GT) is generated by ray-tracing on a LIDAR-based surface model in the form of contour data, of the scene. Comparison of our results with GT implies that our algorithm’s binary classification shadow maps outperform other existing shadow detection algorithms in true positive, which is the detection of shadows when it is in ground truth. It also has the lowest false negative i.e., detecting non-shadowed region as shadowed, compared to existing algorithms.
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Kheirfam, Behrouz. „A corrector–predictor path-following algorithm for semidefinite optimization“. Asian-European Journal of Mathematics 07, Nr. 02 (Juni 2014): 1450028. http://dx.doi.org/10.1142/s1793557114500284.
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A corrector–predictor algorithm is proposed for solving semidefinite optimization problems. In each two steps, the algorithm uses the Nesterov–Todd directions. The algorithm produces a sequence of iterates in a neighborhood of the central path based on a new proximity measure. The predictor step uses line search schemes requiring the reduction of the duality gap, while the corrector step is used to restore the iterates to the neighborhood of the central path. Finally, the algorithm has [Formula: see text] iteration complexity.
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Liu, Chao, und Hui Wang. „A real-time predictor-modification-evaluation–corrector-modification-evaluation parametric interpolator for numerical control transition curves“. Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 234, Nr. 1-2 (18.06.2019): 95–107. http://dx.doi.org/10.1177/0954405419856951.
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A real-time parametric interpolator based on a predictor-modification-evaluation–corrector-modification-evaluation algorithm is proposed in this article, which is utilized to efficiently calculate the reference points of transition curves. Meanwhile, the stable calculation is guaranteed by analyzing the convergence condition of the predictor-modification-evaluation–corrector-modification-evaluation algorithm. Under the convergence condition, the proposed parametric interpolator and traditional line interpolators are simultaneously implemented to interpolate a two-dimensional butterfly path, which consists of quintic Bézier transition curves and line segments. Simulation and experiments are carried out, and the results demonstrate that the proposed real-time predictor-modification-evaluation–corrector-modification-evaluation parametric interpolator achieves the highest accuracy and the light stripe on the tool path is further reduced and hardly observed. Compared with other parametric interpolators, the proposed real-time predictor-modification-evaluation–corrector-modification-evaluation parametric interpolator is capable of achieving a good balance between interpolation accuracy and interpolation efficiency.
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Nekrasov, R. Yu, U. S. Putilova, A. I. Starikov, I. V. Soloviev und K. V. Kuskov. „MODELING OF TECHNOLOGY PROCESSES OF DIAGNOSTICS AND CONTROL OF NC WORKING“. Oil and Gas Studies, Nr. 3 (30.06.2015): 101–6. http://dx.doi.org/10.31660/0445-0108-2015-3-101-106.
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A problem of improvement of precision of engineering products NC working is considered. A solution is offered to solve this problem through ensuring the introducing the on-line corrections into the machines actuators path motion. The necessity is proved of creating the mathematical models of the processes of diagnostics of the system «machine - attachment - tool - slug».
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Williams, R., und J. E. Phythian. „Navigating Along Geodesic Paths on the Surface of a Spheroid“. Journal of Navigation 42, Nr. 1 (Januar 1989): 129–36. http://dx.doi.org/10.1017/s0373463300015150.
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Hairawa in the Journal made the statement that there is no easy method of calculating the length of a geodesic line on the surface of a spheroid and this is true. Nevertheless, it is the purpose here to attempt to devise a method and then to leave it to the reader to judge whether or not the amount of work involved justifies the method as an alternative to the correction methods of Andoyer and Lambert and to the work of Hairawa himself.
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Qadan, Mahmoud, und Joseph Yagil. „Are international economic and financial co-movements characterized by asymmetric co-integration?“ Review of Accounting and Finance 14, Nr. 4 (09.11.2015): 398–412. http://dx.doi.org/10.1108/raf-02-2015-0026.
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Purpose – The recent economic crises have attracted attention to the issue of international equity co-movements and correlations. Using data from 1980 to 2010, the authors examine the international co-movements of both real economic activity, as reflected in industrial production and the gross domestic product (GDP), and financial activity, as reflected in equity market returns. While classic symmetric co-integration tests do not reject the hypothesis of no co-integration, the authors find evidence of asymmetric co-integration in these three variables between the USA and the rest of the Group of Seven (G7) countries. The momentum threshold autoregressive (M-TAR) model captures the nature of the asymmetry most effectively and is the most applicable model for adjustment to long-term equilibrium. This model suggests that the path of adjustment to long-run equilibrium is somewhat different when the price differential is decreasing than when it is increasing. These findings imply that the benefits of asset diversification for investors with a long horizon might be limited in scope. Design/methodology/approach – This work is based on the theory of integrated time series. The authors use symmetric and asymmetric co-integration tests to market indices, as well as to monthly industrial production statistics and quarterly data about the GDP. In line with the financial economic literature, the authors select the GDP as a proxy that reflects the real economy and share prices to mirror the financial sector of the economy. Because no monthly data exist about GDP, the authors use instead the industrial production. Both variables cover the period from January 1980 to June 2010. Findings – The overall findings demonstrate that the USA and the rest of the G7 countries are not symmetrically co-integrated with respect to the GDP. Indeed, they are asymmetrically co-integrated. These findings may explain the additional important result that the majority of equity markets are also asymmetrically co-integrated with the USA. Research limitations/implications – The co-movements of the equity markets and real economic activity imply that the benefits of asset diversification for investors with a long horizon might be limited in scope. In the short run, however, portfolio diversification can be more beneficial due to the short-term fluctuations that may derive from the asymmetric correction process. Originality/value – Prior research on co-movements has focused mainly on studying the correlations among international equity markets by analyzing conditional correlations or using symmetric co-integration methods; the authors test the existence of a long-term relationship between economic variables with respect to the USA and the rest of the G7 countries using a threshold co-integration model.
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Zhao, Biao, Nai Gang Cui, Ji Feng Guo und Ping Wang. „Trajectory Planning and Prediction Guidance Based on the Moon-Earth Return Reentry Dynamics“. Advanced Materials Research 625 (Dezember 2012): 100–103. http://dx.doi.org/10.4028/www.scientific.net/amr.625.100.
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For the lunar return mission, a concern of the entry guidance requirement is the full flight envelope applicability and landing accuracy control. A concise numeric predictor-corrector (NPC) entry guidance (NPCEG) algorithm is developed for this requirement. It plans a real-time trajectory on-line by modulating the linear parameterized bank profile. To meet the path constraint, we propose an integrated guidance strategy which combines NPC method with an analytical constant drag acceleration method. Monte Carlo analysis shows that the algorithm is sufficiently robust to allow precision landing with a delivery error of less than 2.0 km for the entire between 2,500 km and 10,000 km range.
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Gollapudi, Srikanth, G. V. S. N. Lalitanand und Angeline Ezhilarasi. „A Comparative Study on Total Harmonic Distortion of Interleaved Boost Rectifier with the other Boost Derived Topologies“. International Journal of Engineering & Technology 7, Nr. 4.24 (27.11.2018): 103. http://dx.doi.org/10.14419/ijet.v7i4.24.21866.
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Boost rectifiers find their applications in the active power factor correction and have been subject to extensive research. Further, various topologies have been introduced, studied and applied in order to make boost rectifiers more and more efficient and better. Accordingly, Bridgeless configuration and Interleaved topology are most popular among others. In this paper, a comparative study between Basic boost rectifier, bridgeless boost rectifier, interleaved boost rectifier and bridgeless interleaved boost rectifier model has been carried out. The differences analyzed are summarized to learn about the best configuration and which can be implemented. Bridgeless configuration reduces conduction losses in the system by removing one diode from line conduction path while two parallel boost converters with anti-phase conduction in a 2-interleaved topology reduces the current ripple. BLIL combines the advantages of both the system in a single circuit.
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Grant, Nolan, Mahdi Haghzadeh und Alkim Akyurtlu. „Fully Printed Static Gain Reconfigurable Conformal Patch Antenna Arrays“. International Symposium on Microelectronics 2017, Nr. 1 (01.10.2017): 000604–7. http://dx.doi.org/10.4071/isom-2017-tha44_114.
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Abstract This work presents design and fabrication processes for creating statically gain-reconfigurable conformal patch array antennas. In our previous work, a fully printable and conformal antenna array on a flexible substrate with a new Left-Handed Transmission Line (LHTL) phase shifter based on a Barium Strontium Titanate (BST)/polymer composite was computationally studied for radiation pattern correction and beam steering applications. In this work, additive manufacturing techniques were used to experimentally demonstrate the phase compensation needed to improve the degraded performance of the conformal arrays. An Aerosol Jet direct-write printer was used to print several patch antenna arrays and was tested in an anechoic chamber to establish baseline gain metrics. Once a baseline is established, a high dielectric constant material (BST nano-ink) was dispensed onto the IDCs in several configurations, to provide the necessary phase compensation. The antennas were retested and the changes in their gain profiles were investigated. The findings of this work and the proposed method allow for gain compensation of curved conformal antennas and post-production modification of the radiation pattern of antenna arrays. This work has potential applications in the automotive industry due to the low cost of production and the ability to be integrated onto curved conformal surfaces without interfering with super structure or other mechanical design related criteria.
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Ma, Tian, und Yurong Li. „Improved Tooth Crown Edge Smoothing Method Based on Noise Classification and Fitting“. Journal of Medical Imaging and Health Informatics 10, Nr. 11 (01.11.2020): 2609–19. http://dx.doi.org/10.1166/jmihi.2020.3261.
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Because three-dimensional (3D) models of teeth are currently obtained via oral scanning, there are only the tooth crown and gingival surface part, lack of data on the roots of teeth, which is not conducive to the 3D reconstruction of teeth. In order to help doctors to carry out virtual tooth correction, this paper studies the edge characteristics of the tooth crown model, removes the edge noise, which can better carry out the 3D reconstruction of teeth. Therefore, this paper proposes an improved method of tooth crown edge smoothing based on noise classification and fitting. First, according to the characteristics of the tooth crown edge, the method of noise classification is proposed after fitting analysis. The noise can be divided into two types: the noise in the boundary line and the noise in the fitting curve. Then, the noise can be identified according to the Gaussian curvature. Finally, the improved Laplacian smoothing and least squares fitting methods are used to remove the two types of noise, and the denoised tooth crown model is the output. The smoothing effect of the method is verified in terms of the noise removal rate, the patch filling rate, and the patch deletion rate. Compared with the traditional Laplacian smoothig, the new method exhibited a noise removal rate increase of 86.0%, a probability of patch filling that approximately doubled, and a probability of patch deletion that basically remained the same. Compared with the least squares fitting method, the new method exhibited a noise removal rate increase of 75.9%, a patch filling reduction of 22.61%, and a patch deletion reduction of 22.14%.
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Ma, Tian, und Yurong Li. „Improved Tooth Crown Edge Smoothing Method Based on Noise Classification and Fitting“. Journal of Medical Imaging and Health Informatics 10, Nr. 11 (01.11.2020): 2609–19. http://dx.doi.org/10.1166/jmihi.2020.32612609.
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Because three-dimensional (3D) models of teeth are currently obtained via oral scanning, there are only the tooth crown and gingival surface part, lack of data on the roots of teeth, which is not conducive to the 3D reconstruction of teeth. In order to help doctors to carry out virtual tooth correction, this paper studies the edge characteristics of the tooth crown model, removes the edge noise, which can better carry out the 3D reconstruction of teeth. Therefore, this paper proposes an improved method of tooth crown edge smoothing based on noise classification and fitting. First, according to the characteristics of the tooth crown edge, the method of noise classification is proposed after fitting analysis. The noise can be divided into two types: the noise in the boundary line and the noise in the fitting curve. Then, the noise can be identified according to the Gaussian curvature. Finally, the improved Laplacian smoothing and least squares fitting methods are used to remove the two types of noise, and the denoised tooth crown model is the output. The smoothing effect of the method is verified in terms of the noise removal rate, the patch filling rate, and the patch deletion rate. Compared with the traditional Laplacian smoothig, the new method exhibited a noise removal rate increase of 86.0%, a probability of patch filling that approximately doubled, and a probability of patch deletion that basically remained the same. Compared with the least squares fitting method, the new method exhibited a noise removal rate increase of 75.9%, a patch filling reduction of 22.61%, and a patch deletion reduction of 22.14%.
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Maddahi, Y., N. Sepehri, A. Maddahi und M. Abdolmohammadi. „Calibration of wheeled mobile robots with differential drive mechanisms: an experimental approach“. Robotica 30, Nr. 6 (12.01.2012): 1029–39. http://dx.doi.org/10.1017/s0263574711001329.
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SUMMARYExact knowledge of the position and proper calibration of robots that move by wheels form an important foundation in mobile robot applications. In this context, a variety of sensory systems and techniques have been developed for accurate positioning of differential drive mobile robots. This paper, first, provides a brief overview of mobile robots positioning techniques and then, presents a new benchmark method capable of calibrating mobile robots with differential drive mechanisms to correct systematic errors. The proposed method is compared with the commonly used University of Michigan Benchmark (UMBmark) odometry method. Two sets of comparisons are conducted on six prototyped robots with differential drives. The first set of tests establishes the workability and accuracy that can be achieved with the new method and compares them with the ones obtained from the UMBmark technique. The second experiment compares the performance of a mobile robot, calibrated with either the UMBmark or the new method, for an unseen path. It is demonstrated that the proposed method of calibration is simple to implement, and leads to accuracy comparable to the UMBmark method. Specifically, while the error corrections in both methods are within ±5% of each other, the proposed method requires single straight line motion for calibration, which is believed to be simpler and less timely to implement than the square path motion required by the UMBmark technique. The method should therefore be considered seriously as a new tool when calibrating differential drive mobile robots.
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Cholifah, Latifatul, Nurul Mufidah, Eden Lazuardi, Bagus Jaya Santosa, Sungkono Sungkono und Arif Haryono. „Identification of the Grindulu Fault in Pacitan, East Java using Magnetic Method“. Jurnal Penelitian Fisika dan Aplikasinya (JPFA) 10, Nr. 1 (13.07.2020): 22. http://dx.doi.org/10.26740/jpfa.v10n1.p22-33.
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Magnetic method in geophysical surveys is common for its non-destructive use of sub-surface structure delineation. In this study, ground-based measurements of magnetic intensity were performed using a set of instruments in some regions of Pacitan, a city in the southern area of East Java province. Based on these measurements, data acquisition was used to identify the Grindulu faulting zone in the region of interest, potentially vulnerable to geohazards. The data were first corrected using the IGRF and diurnal corrections. A filtering technique of upward continuation at a height of 900 m was then applied to separate local anomalies from regional ones as the targeted sources in the present case. These separate anomalies and their corresponding reductions to the poles as further filtering processes were analyzed for predicting the location and direction of the fault. The results, extracted from data analysis and interpretation, show that the main path of the Grindulu is directed along the NE-SW fault line or N60oE. The resulting anomalies also reflect that the Grindulu is a normal fault with surrounding minor faults lying across the Grindulu, calling for increased awareness of vulnerability in the city to seismic threats.
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Mussari, Riccardo, und Daniela Sorrentino. „Italian Public Sector Accounting Reform: A Step Towards European Public Sector Accounting Harmonisation“. Accounting, Economics, and Law: A Convivium 7, Nr. 2 (26.10.2017): 137–53. http://dx.doi.org/10.1515/ael-2017-0006.
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Abstract This paper discusses post-New Public Management (NPM) approaches to current patterns of public management reforms as a path-dependent phenomenon and as proposing corrective solutions to unintended shortcomings of NPM-inspired reforms. Public sector accounting reforms are seen as developing coherently with general public managerial reforms, and as showing a shift in the prioritised purposes assigned to public accounts in line with the overall design of projected reform-making. EU public sector accounting harmonisation is interpreted in this framework, and the Italian experience of public sector accounting reform is discussed in the light of EU membership. Particular emphasis is given to the likely overlap between national and government accounting due to increasingly shared purposes, whereby the former acquires a functional supportive role to the latter. Considerations on the drivers, as well as on the technical solutions of the new Italian public sector accounting system, suggest that Italian public sector accounting has taken a step in the direction of European public sector accounting harmonisation. Finally, the Italian case provides evidence of post-NPM-like accounting reform, contributing to the scanty empirical research on this topic.
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Shreve, Ronald L. „Late Wisconsin Ice-Surface Profile Calculated from Esker Paths and Types, Katahdin Esker System, Maine“. Quaternary Research 23, Nr. 1 (Januar 1985): 27–37. http://dx.doi.org/10.1016/0033-5894(85)90069-9.
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Values of the gradient of the former ice surface can be inferred at points along a flow line from deviations of esker paths or transitions in esker type and numerically integrated to give the profile. A profile calculated in this way shows that during formation of the Katahdin esker system about 12,700 yr ago the ice thickness at distances of 10, 20, 50, 100, and 140 km from the terminus, which is about two thirds of the distance to the ice divide, was approximately 200, 300, 600, 750, and 900 m. The terminal reach was computed by assuming an unknown uniform basal drag and matching the profile to its known elevation at the terminus and known gradient 10 km upglacier. Correction for isostatic rebound based on the elevations of contemporaneous deltas and of the marine limit proved unnecessary, because the tilt due to the difference in uplift at the two ends of the profile is only 0.1 m km−1. With other plausible assumptions as to sea levels in the past, elevations of the marine limit, or exact location of the terminus the profile could be as much as roughly 100 m higher. It hits Mount Katahdin about 500 m below its summit, which is at 1600 m, in agreement with the geological evidence farther west. The steepening of the upper part of the profile suggests that the mountain dammed and diverted the ice. Basal drag computed from the profile varies from about 20 kPa (0.2 bar) near the terminus to 30 kPa (0.3 bar) at 100 km to 70 kPa (0.7 bar) at 140 km. The relatively low values away from the influence of Mount Katahdin agree with independent evidence from deep-sea cores of substantial late Wisconsin ice-sheet thinning without comparable areal reduction. The method has potential for application over wide areas that were occupied by the Laurentide and Scandinavian ice sheets.
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Bijma, P., und J. A. M. van Arendonk. „Maximizing genetic gain for the sire line of a crossbreeding scheme utilizing both purebred and crossbred information“. Animal Science 66, Nr. 2 (April 1998): 529–42. http://dx.doi.org/10.1017/s135772980000970x.
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AbstractA selection index procedure which utilizes both, purebred and crossbred information was developed for the sire line of a three-path crossbreeding scheme in pigs, to predict response to best linear unbiased prediction (BLUP) selection with an animal model. Purebred and crossbred performance were treated as correlated traits. The breeding goal was crossbred performance but methods can be applied to other goals. A hierarchical mating structure was used. Sires were mated to purebred dams to generate replacements and to F^ from the dam line to generate fattening pigs. Generations were discrete, inbreeding was ignored. The selection index included purebred and crossbred phenotypic information of the current generation and estimated breeding values for purebred and crossbred performance of parents and mates of parents from the previous generation. Reduction of genetic variance due to linkage disequilibrium and reduction of selection intensity due to finite population size and due to correlated index values was accounted for. Selection was undertaken until asymptotic responses were reached. The index was used to optimize the number of selected parents per generation and the number of offspring tested per litter, and to make inferences on the value of crossbred information when the breeding goal was crossbred performance. It was optimal to test a maximum number of offspring per litter, mainly due to increased female selection intensities. Maximum response reductions due to linkage disequilibrium and correlated index values were 32% and 29% respectively. Correcting for correlated index values changed ranking of breeding schemes. Benefit of crossbred information was largest when the genetic correlation between purebred and crossbred performance was low. Due to high correlations between index values in that case, the optimum number of selected sires increased considerably when crossbred information was included.
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Lançon, A., A. Gonneau, K. Verro, P. Prugniel, A. Arentsen, S. C. Trager, R. Peletier et al. „A comparison between X-shooter spectra and PHOENIX models across the HR-diagram“. Astronomy & Astrophysics 649 (Mai 2021): A97. http://dx.doi.org/10.1051/0004-6361/202039371.
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Aims. The path towards robust near-infrared extensions of stellar population models involves the confrontation between empirical and synthetic stellar spectral libraries across the wavelength ranges of photospheric emission. Indeed, the theory of stellar emission enters all population synthesis models, even when this is only implicit in the association of fundamental stellar parameters with empirical spectral library stars. With its near-ultraviolet to near-infrared coverage, the X-shooter Spectral Library (XSL) allows us to examine to what extent models succeed in reproducing stellar energy distributions (SEDs) and stellar absorption line spectra simultaneously. Methods. As a first example, this study compares the stellar spectra of XSL with those of the Göttingen Spectral Library, which are based on the PHOENIX synthesis code. The comparison was carried out both separately in the three arms of the X-shooter spectrograph known as UVB, VIS and NIR, and jointly across the whole spectrum. We did not discard the continuum in these comparisons; only reddening was allowed to modify the SEDs of the models. Results. When adopting the stellar parameters published with data release DR2 of XSL, we find that the SEDs of the models are consistent with those of the data at temperatures above 5000 K. Below 5000 K, there are significant discrepancies in the SEDs. When leaving the stellar parameters free to adjust, satisfactory representations of the SEDs are obtained down to about 4000 K. However, in particular below 5000 K and in the UVB spectral range, strong local residuals associated with intermediate resolution spectral features are then seen; the necessity of a compromise between reproducing the line spectra and reproducing the SEDs leads to dispersion between the parameters favored by various spectral ranges. We describe the main trends observed and we point out localized offsets between the parameters preferred in this global fit to the SEDs and the parameters in DR2. These depend in a complex way on the position in the Hertzsprung–Russell diagram (HRD). We estimate the effect of the offsets on bolometric corrections as a function of position in the HRD and use this for a brief discussion of their impact on the studies of stellar populations. A review of the literature shows that comparable discrepancies are mentioned in studies using other theoretical and empirical libraries.
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Ziemann, Astrid, Manuela Starke und Claudia Schütze. „Line-averaging measurement methods to estimate the gap in the CO<sub>2</sub> balance closure – possibilities, challenges, and uncertainties“. Atmospheric Measurement Techniques 10, Nr. 11 (07.11.2017): 4165–90. http://dx.doi.org/10.5194/amt-10-4165-2017.
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Abstract. An imbalance of surface energy fluxes using the eddy covariance (EC) method is observed in global measurement networks although all necessary corrections and conversions are applied to the raw data. Mainly during nighttime, advection can occur, resulting in a closing gap that consequently should also affect the CO2 balances. There is the crucial need for representative concentration and wind data to measure advective fluxes. Ground-based remote sensing techniques are an ideal tool as they provide the spatially representative CO2 concentration together with wind components within the same voxel structure. For this purpose, the presented SQuAd (Spatially resolved Quantification of the Advection influence on the balance closure of greenhouse gases) approach applies an integrated method combination of acoustic and optical remote sensing. The innovative combination of acoustic travel-time tomography (A-TOM) and open-path Fourier-transform infrared spectroscopy (OP-FTIR) will enable an upscaling and enhancement of EC measurements. OP-FTIR instrumentation offers the significant advantage of real-time simultaneous measurements of line-averaged concentrations for CO2 and other greenhouse gases (GHGs). A-TOM is a scalable method to remotely resolve 3-D wind and temperature fields. The paper will give an overview about the proposed SQuAd approach and first results of experimental tests at the FLUXNET site Grillenburg in Germany. Preliminary results of the comprehensive experiments reveal a mean nighttime horizontal advection of CO2 of about 10 µmol m−2 s−1 estimated by the spatially integrating and representative SQuAd method. Additionally, uncertainties in determining CO2 concentrations using passive OP-FTIR and wind speed applying A-TOM are systematically quantified. The maximum uncertainty for CO2 concentration was estimated due to environmental parameters, instrumental characteristics, and retrieval procedure with a total amount of approximately 30 % for a single measurement. Instantaneous wind components can be derived with a maximum uncertainty of 0.3 m s−1 depending on sampling, signal analysis, and environmental influences on sound propagation. Averaging over a period of 30 min, the standard error of the mean values can be decreased by a factor of at least 0.5 for OP-FTIR and 0.1 for A-TOM depending on the required spatial resolution. The presented validation of the joint application of the two independent, nonintrusive methods is in the focus of attention concerning their ability to quantify advective fluxes.
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Bardou, Lisa, Éric Gendron, Gérard Rousset, Damien Gratadour, Alastair Basden, Domenico Bonaccini Calia, Tristant Buey et al. „ELT-scale elongated LGS wavefront sensing: on-sky results“. Astronomy & Astrophysics 649 (Mai 2021): A158. http://dx.doi.org/10.1051/0004-6361/202038330.
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Context. Laser guide stars (LGS) allow adaptive optics (AO) systems to reach greater sky coverage, especially for AO systems correcting the atmospheric turbulence on large fields of view. However LGS suffer from limitations, among which is their apparent elongation which can reach 20 arcsec when observed with large aperture telescopes such as the European Southern Observatory 39 m telescope. The consequences of this extreme elongation have been studied in simulations and laboratory experiments, although never on-sky, yet understanding and mitigating those effects is key to taking full advantage of the Extremely Large Telescope (ELT) six LGS. Aims. In this paper we study the impact of wavefront sensing with an ELT-scale elongated LGS using on-sky data obtained with the AO demonstrator CANARY on the William Herschel telescope (WHT) and the ESO Wendelstein LGS unit. CANARY simultaneously observed a natural guide star and a superimposed LGS launched from a telescope placed 40 m away from the WHT pupil. Methods. Comparison of the wavefronts measured with each guide star allows the determination of an error breakdown of the elongated LGS wavefront sensing. With this error breakdown, we isolate the contribution of the LGS elongation and study its impact. We also investigate the effects of truncation or undersampling of the LGS spots. Results. We successfully used the elongated LGS wavefront sensor (WFS) to drive the AO loop during on-sky operations, but it necessitated regular calibrations of the non-common path aberrations on the LGS WFS arm. In the off-line processing of the data collected on-sky we separate the error term encapsulating the impact of LGS elongation in a dynamic and quasi-static component. We measure errors varying from 0 nm to 160 nm rms for the dynamic error and we are able to link it to turbulence strength and spot elongation. The quasi-static errors are significant and vary between 20 nm and 200 nm rms depending on the conditions. They also increase by as much as 70 nm over the course of 10 m. We do not observe any impact when undersampling the spots with pixel scales as large as 1.95″, while the LGS spot full width half maximum varies from 1.7″ to 2.2″; however, significant errors appear when truncating the spots. These errors appear for fields of view smaller than 10.4″ to 15.6″, depending on the spots’ elongations. Translated to the ELT observing at zenith, elongations as long as 23.5″ must be accommodated, corresponding to a field of view of 16.3″ if the most elongated spots are put across the diagonal of the subaperture.
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Montenbruck, Oliver, und Belén González Rodríguez. „NeQuick-G performance assessment for space applications“. GPS Solutions 24, Nr. 1 (19.11.2019). http://dx.doi.org/10.1007/s10291-019-0931-2.
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AbstractOther than traditional single-layer ionosphere models for global navigation satellite system (GNSS) receivers, the NeQuick-G model of Galileo provides a fully three-dimensional description of the electron density and obtains the ionospheric path delay by integration along the line of sight. While optimized for users on or near the surface of the earth, NeQuick-G can thus as well be used for ionospheric correction of single-frequency observations from spaceborne platforms. Based on slant and total electron content measurements obtained in the Swarm mission, the performance of NeQuick-G for users in low earth orbit is assessed for periods of high and low solar activity as well as different orientations of the orbital plane with respect to the sun and the region of high total electron content. A slant range correction performance of better than 70% is achieved in more than 85% of the examined epochs in good accord with the performance reported for terrestrial users. Likewise, the positioning errors can be notably reduced when applying the NeQuick-G corrections in single-frequency navigation solutions. For users at orbital altitudes, it is furthermore shown that vertical total electron predictions from NeQuick-G may be favorably combined with an elevation-dependent thick-layer mapping function to reduce the high computational effort associated with the integration of the electron density along the ray path for each tracked GNSS satellite.
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Narain, Jaya, und Amos G. Winter V. „A Hybrid Computational and Analytical Model of Inline Drip Emitters“. Journal of Mechanical Design 141, Nr. 7 (28.03.2019). http://dx.doi.org/10.1115/1.4042613.
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This paper details a hybrid computational and analytical model to predict the performance of inline pressure compensating drip irrigation emitters. Pressure compensating emitters deliver a constant flow rate over a range of applied pressures to accurately meter water to crops. Flow rate is controlled within the emitter via a fixed resistance tortuous path, and a variable flow resistance composed of a flexible membrane that deflects under changes in pressure, restricting the flow path. A pressure resistance parameter was derived using an experimentally validated computational fluid dynamics (CFD) model to describe the flow behavior in tortuous paths. The bending mechanics of the membrane were modeled analytically and refined by deriving a correction factor using finite element analysis (FEA). A matrix formulation that calculates the force applied by a line or a patch load of any shape on a rectangular membrane, along which there is a prescribed deflection, was derived and was found to be accurate to be 1%. The combined hybrid computational–analytical model reduces the computational time of modeling emitters from hours to less than 30 min, dramatically lowering the time required to iterate and select optimal designs. The model was validated experimentally using three commercially available drip emitters and was accurate to within 12% of the experimental results.
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Roumeliotis, I., N. Aretakis und A. Alexiou. „Industrial Gas Turbine Health and Performance Assessment With Field Data“. Journal of Engineering for Gas Turbines and Power 139, Nr. 5 (21.12.2016). http://dx.doi.org/10.1115/1.4034986.
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The paper presents a thorough analysis of the historical data and results acquired over a period of two years through an on-line real-time monitoring system installed at a combined heat and power (CHP) plant. For gas turbine health and performance assessment, a gas path analysis tool based on the adaptive modeling method is integrated into the system. An engine adapted model built through a semi-automated method is part of a procedure which includes a steam/water cycle simulation module and an economic module used for power plant performance and economic assessment. The adaptive modeling diagnostic method allowed for accurate health assessment during base and part load operation identifying and quantifying compressor recoverable deterioration and the root cause of an engine performance shift. Next, the performance and economic assessment procedure was applied for quantifying the economic benefit accrued by implementing daily on-line washing and for evaluating the financial gains if the off-line washings time intervals are optimized based on actual engine performance deterioration rates. The results demonstrate that this approach allows continuous health and performance monitoring at full and part load operation enhancing decision making capabilities and adding to the information that can be acquired through traditional analysis methods based on heat balance and base load correction curves.
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Vlasov, V. S., V. G. Shavrov und V. I. Shcheglov. „Spectral characteristics of equilibrium position precession of magnetization in normal magnetized ferrite plate.“ Journal of Radio Electronics 2021, Nr. 3 (März 2021). http://dx.doi.org/10.30898/1684-1719.2021.3.2.
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The investigation of spectral characteristics of precession equilibrium balance position of magnetization is the main subject of this work. The geometry of task is normal magnetized ferrite plate. In this case the parametrical excitation of exchange spin waves is not possible and the angle of precession cone may be about some tens of degree. It is established that in the condition of orientational transition the switching of alternating magnetic field having circular polarization leads to precession of equilibrium position of magnetization. In this case the magnetization vector takes part in two precession motions: the first – along the large ring, the second – along the small ring. The radius of large ring is determined by the equilibrium angle between of magnetization vector direction and the external magnetic field direction. The radius of small ring is determined by the angle of deflection of magnetization vector from equilibrium position which moves along the large ring. As a result the precession portrait consist of large circular ring which is filled along its environment by small rings. The formula for specific energy which consist of interaction of magnetization with constant and alternating fields and also with demagnetization field is derived. On the basis of Landau-Lifshits equation the system of nonlinear equations of motion for three components of magnetization is derived. By the numerical solution of this system by Rounge-Cutta method the evolutions in time and corresponded precession portraits for magnetization are found. The possibility of founding the spectral characteristics of magnetization equilibrium position precession by the standard mathematical package “Matlab” which based by fast Fourier transformation is demonstrated. The program algorithm of this calculation using the evolutions in time which are found from the system of equations for magnetization is described. The evolutions in time, precession portraits and spectrums for five basis regimes are found. This regimes are: №1 – the small-amplitude circular precession; №2 – precession of equilibrium position without the envelop of centre; №3 – non-fading precession of equilibrium position with the envelop of centre; №4 – fading precession of equilibrium position with the envelop of centre; №5 – comprehensive circular precession. It is established that for the spectrum of all regimes the most typical line are on two frequencies – on the frequency of excitation which is equal to the frequency of alternate field and on the frequency of precession of equilibrium position which is more less then the frequency of excitation. The comparative investigation of amplitudes of both spectral lines shows that in the regime №1 and especially in the regime №2 the amplitude of line on the frequency of equilibrium position precession is more then the amplitude of line on the frequency of excitation. In the regime №3 and especially №4 the amplitude of line on the excitation frequency is more larger then the amplitude of line on the equilibrium position precession and in the regime №5 the line on the frequency of equilibrium position precession is absent. The dependencies of amplitude of spectrum line on the frequency of excitation from the level of alternative field in different regimes are investigated. As a control also the measuring of the same values from the evolutions in time are executed. It is found that the measuring by the spectrums in the middle part of whole interval where the equilibrium precession take place gives out the values which are a few smaller then the same values which are found from the evolutions in time. For the compensation of this divergence the correcting addition in the form of quadratic polynomial having negative sign is proposed. The dependencies of amplitude spectrum line on the frequency of precession equilibrium from the amplitude of excitation field are investigated. It is found that the using of correction slightly increases the level of dependence (about of 20%) in the whole interval of equilibrium precession presence. In this case the general character of curve is not changed. The character indication of this dependency is the initial horizontal path which occupies the most path of regime №2 and has subsequent abatement in the regime №3, №4 with decreasing to zero in the regime №5. The mechanism of formation of horizontal path is explained on the basis of vector model. It is found that by small amplitude of excitation the precession of equilibrium takes place along the cone which angle is determined by the value of equilibrium inclination of magnetization vector from the field. This motion is the reason of horizontal path of investigated dependence. The increasing of excitation level leads to the increasing of cone angle around the equilibrium position. By this reason the both cones of precession connect together and amplitude on the frequency of equilibrium precession decrease to zero. The investigation of dependence of equilibrium precession frequency from the amplitude of excitation is made. The main measuring are made by spectrum which are founded by whole five regimes. The control measuring are made by analysis of geometrical parameters (periods) of evolutions in time. The good agreement between both dependencies is found. The discrepancy was not more then 5%. The comparison of measured dependence with the analytical formula having quadratic character founded by the basis of vector model is made. It is found that in the regimes №1 and №1 analytical formula describes the measured dependencies to the approximation of 5% but in regimes №3 and №4 the quadratic increasing of explored dependencies is slowed down and the formula gives the excessive values on 20% and more. It is established that the reason of this discrepancy is the lowering the precision of formula so as by its derivation it is accepted the supposition about a small value of equilibrium precession angle. The introduction of correction into index of degree of alternating field which decreases this index when excitation level increases is proposed. Some possible questions for new investigations is proposed. In the first place it is mentioned that the large enrichment of spectrum may be expected from violation of symmetry of equilibrium precession by constant or alternate fields. In this case the evolutions in time acquire the view of pulses having complex form. In this case in the spectrum of equilibrium precession must be appear large quantity additional frequencies harmonic character. The large variety of spectrum may introduce the investigation of equilibrium precession in anisotropic media. It is mentioned that the investigation of spectrum in these conditions may demand for interpretation of results the elaboration of new models which will be different from models which applied in symmetrical case.
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Anundsen, André Kallåk, Christian Bjørland und Marius Hagen. „Location, location, location!*: a quality-adjusted rent index for the Oslo office market“. Journal of European Real Estate Research ahead-of-print, ahead-of-print (27.08.2021). http://dx.doi.org/10.1108/jerer-02-2021-0009.
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PurposeCommonly used rent indices are based on average developments or expert opinions. Such indices often suffer from compositional biases or low data coverage. The purpose of this paper is to overcome these challenges using the authors' approach.Design/methodology/approachThe authors construct a quality-adjusted rent index for the office market in Oslo using detailed data from 14,171 rental contracts.FindingsThe authors show that compositional biases can have a large impact on rental price developments. By adding building-fixed effects to a standard hedonic regression model, the authors show that the explanatory power increases considerably. Furthermore, indices excluding location-specific information, or which include less granular location controls than at the building level, portray quite a different picture of rent developments than indices that do take this into account. The authors also exploit information on contract signature date and find that a more timely detection of turning points can be achieved by using the signature date instead of the more typically used start date of the lease.Research limitations/implicationsThe study is confined to Norwegian data, and an avenue for future research would be to explore if similar results are obtained for other countries. A weakness with the paper is that authors' do not observe quality changes over time, such as renovation. Controlling for time-varying and unit-specific attributes in hedonic models for the commercial real estate (CRE) market would be useful to purge indices further for compositional effects and unobserved heterogeneity. While the authors do control for building-fixed effects, there are additional variations within a building (floor, view, sunlight, etc.) that the authors do not capture. Studies that could control for this would certainly be welcome, both in order to estimate the value of such amenities and to see how it affects estimated rent developments. Another promising avenue for future research is to link data on rental contracts in the CRE market with firm-specific information in order to explore how firm profitability and liquidity may affect rental contracts.Practical implicationsThe authors show that the hedonic index yields a sharper fall in rents after the global financial crisis and more muted developments in the period between 2013 and 2015 than the average rent index. The results show that rents have followed their estimated equilibrium closely and have re-adjusted quickly in periods of deviation. From a financial stability perspective, the risk of a sharp fall in rents is reduced because rents often are in line with their fundamentals.Social implicationsThe authors find that a more timely detection of turning points can be achieved by using information on the signature date. This is an important finding. The financial system is heavily exposed toward CRE, and timely detection of turning points is critical for policymakers.Originality/valueThe financial system is heavily exposed toward the commercial real estate market and timely detection of turning points is of major importance to policymakers. Finally, the authors use our quality-adjusted rent index as the dependent variable in an error correction model. The authors find that employment and stock of offices are important explanatory variables. Moreover, the results show that rents have followed their estimated equilibrium path.
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„Support on Demand“. Mechanical Engineering 123, Nr. 08 (01.08.2001): 60–62. http://dx.doi.org/10.1115/1.2001-aug-4.
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OMC Precision Products, a maker of spinal implant, first line of attack for smoothness is machining to minimize cusps or scallops left behind by machine tool cutters. In finishing passes, the cusps are diminished by minimizing stepovers, the distance the tool moves into the new path. OMC focuses on making implants for correcting spinal deformities. OMC has three lines of implants, all machined from stainless steel or titanium. It makes plates and screws for spines that are degenerating or have undergone trauma; hooks and rods for deformities such as scoliosis; and cages to replace damaged vertebrae. First-article inspections are done on a Primus coordinate measuring machine from Mycrona Inc. of Plymouth, Michigan. The unit is equipped with a touch probe system from Renishaw Inc. of Schaumburg, Illinois. OMC also produces 2 alternatives to plates, a spine straightening system based on titanium or stainless-steel rods several inches long. The rods are locked in place with diverse types of bone screws or spinal hooks.