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Littérature scientifique sur le sujet « Quasi-uniform sampling »

Auteur : Grafiati

Publié le 4 juin 2021

Mis à jour le 2 février 2022

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Articles de revues sur le sujet "Quasi-uniform sampling"

Im, Sungjin, et Benjamin Moseley. « Fair Scheduling via Iterative Quasi-Uniform Sampling ». SIAM Journal on Computing 49, n^o 3 (janvier 2020) : 658–80. http://dx.doi.org/10.1137/18m1202451.

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Sun, Wei-Hsin, Chris R. Shrader, Tracey J. Turner, Matthew A. Malkan, Bradley M. Peterson, Paul M. N. Hintzen, Yoji Kondo, Sung-Nan Lin, Ting-Chang Lin et Remington P. S. Stone. « Two Year UV-Optical Monitoring of the Seyfert 1 Galaxy Markarian 335 ». Symposium - International Astronomical Union 159 (1994) : 408. http://dx.doi.org/10.1017/s0074180900175965.

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We report on the results of a UV-Optical spectral monitoring of the bright Seyfert 1 galactic nuclei Mkn 335. This campaign began in June, 1989, and ended in June, 1991. Ultraviolet spectra of fourteen epochs at nearly uniform sampling of 30-day intervals, except when the object was inaccessible from the IUE satellite, have been obtained, of which twelve were coordinated with quasi-simultaneous ground-based optical observations made at Lick Observatory.

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Stagnaro, M., et M. Bolla Pittaluga. « Velocity and concentration profiles of saline and turbidity currents flowing in a straight channel under quasi-uniform conditions ». Earth Surface Dynamics 2, n^o 1 (25 mars 2014) : 167–80. http://dx.doi.org/10.5194/esurf-2-167-2014.

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Abstract. We present a series of detailed experimental observations of saline and turbidity currents flowing in a straight channel. Experiments are performed by continuously feeding the channel with a dense mixture until a quasi-steady configuration is obtained. The flume, 12 m long, is characterized by a concrete fixed bed with a uniform slope of 0.005. Longitudinal velocity profiles are measured in ten cross sections, 1 m apart, employing an ultrasound Doppler velocity profiler. We also measure the density of the mixture using a rake of siphons sampling at different heights from the bottom in order to obtain the vertical density distributions in a cross section where the flow already attained a quasi-uniform configuration. We performed 27 experiments changing the flow discharge, the fractional excess density, the character of the current (saline or turbidity) and the roughness of the bed in order to observe the consequences of these variations on the vertical velocity profiles and on the overall characteristics of the flow. Dimensionless velocity profiles under quasi-uniform flow conditions were obtained by scaling longitudinal velocity with its depth averaged value and the vertical coordinate with the flow thickness. They turned out to be influenced by the Reynolds number of the flow, by the relative bed roughness, and by the presence of sediment in suspension. Unexpectedly, the densimetric Froude number of the current turned out to have no influence on the dimensionless velocity profiles.

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Stagnaro, M., et M. Bolla Pittaluga. « Velocity and concentration profiles of saline and turbidity currents flowing in a straight channel under quasi-uniform conditions ». Earth Surface Dynamics Discussions 1, n^o 1 (18 novembre 2013) : 817–53. http://dx.doi.org/10.5194/esurfd-1-817-2013.

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Abstract. We present a series of detailed experimental observations of saline and turbidity currents flowing in a straight channel. Experiments are performed by continuously feeding the channel with a dense mixture until a quasi-steady configuration is obtained. The flume, 12 m long, is characterized by a concrete fixed bed with a uniform slope of 0.005. Longitudinal velocity profiles are measured in ten cross sections, one meter apart, employing an Ultrasound Doppler Velocimeter Profiler. We also measure the density of the mixture using a rake of siphons sampling at different heights from the bottom in order to obtain the vertical density distributions in a cross sections where the flow already attained a quasi-uniform configuration. We performed 27 experiments changing the flow discharge, the fractional excess density, the character of the current (saline or turbidity) and the roughness of the bed in order to observe the consequences of these variations on the vertical velocity profiles and on the overall characteristics of the flow. Dimensionless velocity profiles under quasi-uniform flow conditions were obtained by scaling longitudinal velocity with its depth averaged value and the vertical coordinate with the flow thickness. They turned out to be influenced by the Reynolds number of the flow, by the relative bed roughness, and by the presence of sediment in suspension. Unexpectedly the densimetric Froude number of the current turned out to have no influence on the dimensionless velocity profiles.

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Wen, Xiu Lan, Dong Xia Wang, Li Fang et Yi Bing Zhao. « Sampling Strategy for Free-Form Surface Inspection Using Coordinate Measuring Machines ». Applied Mechanics and Materials 532 (février 2014) : 106–12. http://dx.doi.org/10.4028/www.scientific.net/amm.532.106.

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Due to the complexity and non-rotational symmetry of free-form surface, it is difficult to achieve accurate and efficient inspection method. In order to solve this problem, three types of sampling sequences are proposed to specify a set of measuring points of free-form surface. For comparing the results of different sampling strategies, the profile errors of free-form surface are calculated based on a quasi particle swarm optimization (QPSO) searching the transformation parameters to implement localization and surface subdivision method finding the closest points on the design model corresponding to measured points. In order to obtain effective sampling strategies, four design models are generated by non-uniform rational basis spline (NURBS) and parts are manufactured on two machining centers to obtain surfaces of different roughness and measured on CMMs by selecting different sampling methods and sample sizes. The profile errors of parts are calculated by the proposed method and CMMs software, respectively. The results show that randomized Hammersley sampling sequence and medium sample size are preferred for the profile error inspection of given parts if accuracy and time are all considered. The research provides a method for free-form surface accurate inspection while minimizing the sampling time and cost.

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BENTH, FRED ESPEN, MARTIN GROTH et PAUL C. KETTLER. « A QUASI-MONTE CARLO ALGORITHM FOR THE NORMAL INVERSE GAUSSIAN DISTRIBUTION AND VALUATION OF FINANCIAL DERIVATIVES ». International Journal of Theoretical and Applied Finance 09, n^o 06 (septembre 2006) : 843–67. http://dx.doi.org/10.1142/s0219024906003810.

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We propose a quasi-Monte Carlo (qMC) algorithm to simulate variates from the normal inverse Gaussian (NIG) distribution. The algorithm is based on a Monte Carlo technique found in Rydberg [13], and is based on sampling three independent uniform variables. We apply the algorithm to three problems appearing in finance. First, we consider the valuation of plain vanilla call options and Asian options. The next application considers the problem of deriving implied parameters for the underlying asset dynamics based on observed option prices. We employ our proposed algorithm together with the Newton Method, and show how we can find the scale parameter of the NIG-distribution of the logreturns in case of a call or an Asian option. We also provide an extensive error analysis for this method. Finally we study the calculation of Value-at-Risk for a portfolio of nonlinear products where the returns are modeled by NIG random variables.

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Castro, Belmiro Mendes de, et Luiz Bruner de Miranda. « Hydrographic properties in the São Sebastião Channel : daily variations observed in March 1980 ». Revista Brasileira de Oceanografia 46, n^o 2 (1998) : 111–23. http://dx.doi.org/10.1590/s1413-77391998000200002.

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A four-day quasi-synoptic survey of hydrographic properties sampled from March 4 to March 7, 1980 was used for a physical description of the daily variations in the thermohaline and mass structures in the São Sebastião Channel. Temperature and salinity were sampled down the water column during events of non-tidal along channel current reversals. The observed temperature decrease and density increase in the southern channel bottom layer were mainly due to cold water transported northward by a subsurface current. The northward bottom current opposed the southward main flow in the upper layer. The low temperature and salinity of the water advected northward by the bottom current indicated influences of the South Atlantic Central Water (SACW), inducing a near bottom thermocline-like structure. By the end of the sampling period, the vertical temperature gradient intensified near the bottom and the salinity distribution reached almost uniform conditions.

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D’Agostino, Francesco, Flaminio Ferrara, Claudio Gennarelli, Rocco Guerriero, Massimo Migliozzi et Giovanni Riccio. « Reconstruction of the Far-Field Pattern of Volumetric AUTs from a Reduced Set of Near-Field Samples Collected along a Planar Spiral with a Uniform Step ». Sensors 21, n^o 5 (26 février 2021) : 1644. http://dx.doi.org/10.3390/s21051644.

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An efficient near-to-far-field transformation (NTFFT) technique, wherein the near-field (NF) measurements are acquired along a planar spiral with a uniform step to make the control of the involved positioners easier, is developed in this article. Such a technique is tailored for quasi-spherical, i.e., volumetric, antennas under test and makes use of a reduced number of NF data. An effective two-dimensional sampling interpolation algorithm, allowing the accurate reconstruction of the input NF data for the standard NTFFT with plane-rectangular scan, is obtained by setting the spiral step equal to the sample spacing required for interpolating along a radial line according to the spatial bandlimitation properties of electromagnetic fields, and by properly developing a non-redundant representation along such a spiral. Tests results are reported to demonstrate that the proposed NTFFT technique retains the same accuracy as the standard plane-rectangular one.

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Rehman, N., et D. P. Mandic. « Multivariate empirical mode decomposition ». Proceedings of the Royal Society A : Mathematical, Physical and Engineering Sciences 466, n^o 2117 (23 décembre 2009) : 1291–302. http://dx.doi.org/10.1098/rspa.2009.0502.

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Despite empirical mode decomposition (EMD) becoming a de facto standard for time-frequency analysis of nonlinear and non-stationary signals, its multivariate extensions are only emerging; yet, they are a prerequisite for direct multichannel data analysis. An important step in this direction is the computation of the local mean, as the concept of local extrema is not well defined for multivariate signals. To this end, we propose to use real-valued projections along multiple directions on hyperspheres ( n -spheres) in order to calculate the envelopes and the local mean of multivariate signals, leading to multivariate extension of EMD. To generate a suitable set of direction vectors, unit hyperspheres ( n -spheres) are sampled based on both uniform angular sampling methods and quasi-Monte Carlo-based low-discrepancy sequences. The potential of the proposed algorithm to find common oscillatory modes within multivariate data is demonstrated by simulations performed on both hexavariate synthetic and real-world human motion signals.

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Natalia, Nory, Firman Firman et Daharnis Daharnis. « Efektivitas Layanan Informasi dengan Menggunakan Media Audio Visual dalam Meningkatkan Sikap Siswa terhadap Kedisiplinan Sekolah ». Jurnal Konseling dan Pendidikan 3, n^o 2 (30 juin 2015) : 40. http://dx.doi.org/10.29210/112800.

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The research based on phenomenon where students has low attitude in school discipline, such as many students who break the rules in their the absence, the uniform and learning activity, where it can be effect on learning quality and quantity. Guidance and counseling is to improve student’s attitude on school discipline, one of them is information services. The research purpose to test effectiveness of information services with using the audio visual media to improve students attitude on school discipline. This research use quantitative method. Type of this research is Quasi Experiment with Non Equivalent Control Group Design. The population are students at SMP Muhammadiyah Padang Panjang and sample selected with using purposive sampling. The instrument is questionnaire with Likert Scale and tested for validity and reliability. The validity test used Product Moment Correlation with mean correlation coefficient 0.642 and the reliability test used Cronbach's Alpha with r 0.965. Then analysis technique using Wilcoxon Signed Ranks Test and Kolmogorov Smirnov 2 Samples Independent using SPSS 20. The results showed that information service with using the audio visual media effective to improve students attitude on school discipline.

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Thèses sur le sujet "Quasi-uniform sampling"

Hörmann, Wolfgang, et Josef Leydold. « Importance Sampling to Accelerate the Convergence of Quasi-Monte Carlo ». Department of Statistics and Mathematics, WU Vienna University of Economics and Business, 2007. http://epub.wu.ac.at/284/1/document.pdf.

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Importance sampling is a well known variance reduction technique for Monte Carlo simulation. For quasi-Monte Carlo integration with low discrepancy sequences it was neglected in the literature although it is easy to see that it can reduce the variation of the integrand for many important integration problems. For lattice rules importance sampling is of highest importance as it can be used to obtain a smooth periodic integrand. Thus the convergence of the integration procedure is accelerated. This can clearly speed up QMC algorithms for integration problems up to dimensions 10 to 12. (author's abstract)
Series: Research Report Series / Department of Statistics and Mathematics

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Grant, Elyot. « Covering Problems via Structural Approaches ». Thesis, 2011. http://hdl.handle.net/10012/6317.

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The minimum set cover problem is, without question, among the most ubiquitous and well-studied problems in computer science. Its theoretical hardness has been fully characterized--logarithmic approximability has been established, and no sublogarithmic approximation exists unless P=NP. However, the gap between real-world instances and the theoretical worst case is often immense--many covering problems of practical relevance admit much better approximations, or even solvability in polynomial time. Simple combinatorial or geometric structure can often be exploited to obtain improved algorithms on a problem-by-problem basis, but there is no general method of determining the extent to which this is possible. In this thesis, we aim to shed light on the relationship between the structure and the hardness of covering problems. We discuss several measures of structural complexity of set cover instances and prove new algorithmic and hardness results linking the approximability of a set cover problem to its underlying structure. In particular, we provide: - An APX-hardness proof for a wide family of problems that encode a simple covering problem known as Special-3SC. - A class of polynomial dynamic programming algorithms for a group of weighted geometric set cover problems having simple structure. - A simplified quasi-uniform sampling algorithm that yields improved approximations for weighted covering problems having low cell complexity or geometric union complexity. - Applications of the above to various capacitated covering problems via linear programming strengthening and rounding. In total, we obtain new results for dozens of covering problems exhibiting geometric or combinatorial structure. We tabulate these problems and classify them according to their approximability.

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Chapitres de livres sur le sujet "Quasi-uniform sampling"

Bansal, Nikhil, et Kirk Pruhs. « Weighted Geometric Set Multi-cover via Quasi-uniform Sampling ». Dans Algorithms – ESA 2012, 145–56. Berlin, Heidelberg : Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-33090-2_14.

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González, Diego, et Luis Carlos Altamirano. « Quasi-invariant Illumination Recognition for Appearance-Based Models, Taking Advantage of Manifold Information and Non-uniform Sampling ». Dans MICAI 2009 : Advances in Artificial Intelligence, 268–79. Berlin, Heidelberg : Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-05258-3_24.

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Actes de conférences sur le sujet "Quasi-uniform sampling"

Im, Sungjin, et Benjamin Moseley. « Fair Scheduling via Iterative Quasi-Uniform Sampling ». Dans Proceedings of the Twenty-Eighth Annual ACM-SIAM Symposium on Discrete Algorithms. Philadelphia, PA : Society for Industrial and Applied Mathematics, 2017. http://dx.doi.org/10.1137/1.9781611974782.171.

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Varadarajan, Kasturi. « Weighted geometric set cover via quasi-uniform sampling ». Dans the 42nd ACM symposium. New York, New York, USA : ACM Press, 2010. http://dx.doi.org/10.1145/1806689.1806777.

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Chan, Timothy M., Elyot Grant, Jochen Könemann et Malcolm Sharpe. « Weighted Capacitated, Priority, and Geometric Set Cover via Improved Quasi-Uniform Sampling ». Dans Proceedings of the Twenty-Third Annual ACM-SIAM Symposium on Discrete Algorithms. Philadelphia, PA : Society for Industrial and Applied Mathematics, 2012. http://dx.doi.org/10.1137/1.9781611973099.125.

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Didem Atalay, Kumru, et Suleyman Gokhun Tanyer. « Randomness tests for the method of uniform sampling quasi-random number generator (MUS-QRNG) ». Dans 2014 22nd Signal Processing and Communications Applications Conference (SIU). IEEE, 2014. http://dx.doi.org/10.1109/siu.2014.6830280.

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Bartsch, Christian, Magnus Hölle, Peter Jeschke et Timo Metzler. « Quasi 2D Flow-Adaptive Algorithm for Pneumatic Probe Measurements ». Dans ASME Turbo Expo 2016 : Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56624.

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The subject of this paper is a flow-adaptive measurement grid algorithm developed for 1D and 2D flow field surveys with pneumatic probes in turbomachinery flows. The algorithm automatically determines the distribution and the amount of measurement points needed for an approximation of the pressure distribution within a predefined accuracy. The algorithm is based on transient traverses, conducted back and forth in the circumferential direction. The dynamic response of the pressure-measuring system is disregarded during the traverses, which serve to detect changes in the pressure field. In contrast to previous investigations by the authors, a correction of the dynamic response is applied by deconvolving the transient measurement data using the information embedded in both transient measurements. In consequence, the performance of the algorithm is — to a large extent — independent of the transient traversing speed and the geometry of the pressure-measuring system. Insertion and removal strategies are incorporated in order to reduce measurement points and increase robustness towards differing flow field conditions. By approximation of the pressure distribution, the flow-adaptive measurement data is suited for the application of post-processing corrections without any constraints. The performance of the algorithm is demonstrated for 2D flow field surveys with a pneumatic 5-hole probe in an annular cascade wind tunnel. Compared to conventional techniques for data sampling, e.g., uniform measurement grids, the measurement grid points are automatically adjusted so that a consistent resolution of the flow features is achieved within the measurement domain. Furthermore, the application of the algorithm shows a significant reduction in the number of measurement points. Compared to the measurement duration based on uniform grids, the duration is reduced by at least 7%, while maintaining a high accuracy of the measurement. The purpose of this paper is to demonstrate the performance of measurement grids adapted to local flow field conditions. Consequently, valuable measurement time can be saved without a loss in quality of the data obtained.

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