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Im, Sungjin, et Benjamin Moseley. « Fair Scheduling via Iterative Quasi-Uniform Sampling ». SIAM Journal on Computing 49, no 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, no 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, no 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, no 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, no 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, no 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, no 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, no 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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Norouzi, Lida, et Behnam Makvandi. « The Effectiveness of Pilates in Resiliency and Psych-asthenia of the Housewives ». Asian Social Science 12, no 4 (19 mars 2016) : 195. http://dx.doi.org/10.5539/ass.v12n4p195.
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<p>This study aimed to investigate the effect of Pilates on resiliency and psych-asthenia of the housewives in Tehran. The most common problems of the housewives included decreased resilience and uniform life that led to increased psych-asthenia. Using the knowledge of Contrology, measuring the effect of Pilates on resiliency and psych-asthenia of the housewives was considered. Quasi-experimental research design included the control groups (pre-test, post-test). The statistical population consisted of 40 housewives (20 in Pilates group and 20 in control group) that were selected using the available sampling by referring to a sports club in District 2, Tehran. Data were analyzed using analysis of variance and multivariate analysis of covariance, and the adjusted comparison was conducted at the significance level of 5%.The results showed that the adjusted mean of the scores of resiliency and psych-asthenia for the intervention group are significantly different (p>5.0) and there is a significant difference between the mean scores of resiliency and psych-asthenia of the treatment and control groups. Pilates exercises increase resiliency and decrease psych-asthenia of the housewives. Thus, it is recommended that psychologists and psychiatrists consider Pilates as a supplementary treatment in their prescriptions.</p>
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Bashir, H. A. « Diversity Control in Evolutionary Computation using Asynchronous Dual-Populations with Search Space Partitioning ». Nigerian Journal of Technological Development 17, no 3 (29 octobre 2020) : 175–88. http://dx.doi.org/10.4314/njtd.v17i3.4.
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Diversity control is vital for effective global optimization using evolutionary computation (EC) techniques. This paper classifies the various diversity control policies in the EC literature. Many research works have attributed the high risk of premature convergence to sub-optimal solutions to the poor exploration capabilities resulting from diversity collapse. Also, excessive cost of convergence to optimal solution has been linked to the poor exploitation capabilities necessary to focus the search. To address this exploration-exploitation trade-off, this paper deploys diversity control policies that ensure sustained exploration of the search space without compromising effective exploitation of its promising regions. First, a dual-pool EC algorithm that facilitates a temporal evolution-diversification strategy is proposed. Then a quasi-random heuristic initialisation based on search space partitioning (SSP) is introduced to ensure uniform sampling of the initial search space. Second, for the diversity measurement, a robust convergence detection mechanism that combines a spatial diversity measure; and a population evolvability measure is utilised. It was found that the proposed algorithm needed a pool size of only 50 samples to converge to optimal solutions of a variety of global optimization benchmarks. Overall, the proposed algorithm yields a 33.34% reduction in the cost incurred by a standard EC algorithm. The outcome justifies the efficacy of effective diversity control on solving complex global optimization landscapes.
Keywords: Diversity, exploration-exploitation tradeoff, evolutionary algorithms, heuristic initialisation, taxonomy.
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Temme, F. P. « Geodesic and re–coupling–induced limits to S 2 n group invariants of uniform ( k 1 ⋯ k 2 n ) dual tensorial sets in spin physics, or NMR : SR dynamical structure on {ℍ v } via polyhedral re–coupling and time–reversal invariance ». Proceedings of the Royal Society A : Mathematical, Physical and Engineering Sciences 461, no 2054 (8 février 2005) : 321–46. http://dx.doi.org/10.1098/rspa.2004.1323.
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For S n –based, uniform auxiliary dual tensorial (UDT) sets, explicitly with even maximal all–alike j i ( k i ) over v ≡ ( j 1 ⋯ j 2 n ), or ( k 1 ⋯ k 2 n ), sub–rank auxiliary labelling, the specific time–reversal invariance–dependent dual group invariants and their independent cardinalities (| SI | (2 n ) ) are fundamental to understanding simply reducible (SR) dynamical spin system structure over (Liouvillian) carrier space, a quantum physics property implicit in dual quasi–particle (QP) formalisms associated with, for example, uniform identical multiple spin NMR systems . Such UDT sets stand in total contrast to the distinct j i ( k i ) of ( j 1 ⋯ j″ n )(( k 1 ⋯ k″ n )) sub–rank orthogonal tensorial sets with their Z aa′ graph invariants which for reasons discussed in the text are of restricted validity. For UDTs as operator bases related to the (spin) interaction network–based tensors of high S n permutational NMR Hamiltonians (Liouvillians), the use of QP boson (superboson) formalisms and their dual projective maps (F. P. Temme 1993 Physica A 198 , 245–261) prove invaluable. Once the independent cardinality of the multiple invariants of these UDTs (alias the SU (2) × S 2 n group invariants) (here denoted | SI | (2 n ) ) are known in terms of democratic re–coupling (DR) and polyhedral combinatorial (PC) sampling applied to the time–reversal invariance (TRI) properties of the uniform multiple spin (sub–)system, so the SR dual carrier spaces , ℍ˜, ℍ˜ v follow directly as well–defined entities. For UDTs of general (2 n > 6)–fold ensembles, the augmented models of TRI discussed here (i.e. beyond linear re–coupled Weyl forms) are essential, due to the presence of non–Abelian degeneracy. A regular geometric automorphic limit is established for sequential (2 n )–based | SI | (2 n ) total series, specific to (higher) uniform ( j 1 ⋯ j i ), ( k 1 ⋯ k i )–based dual tensors. By treating the | SI | (2 n ) obtained from the DR–based TRIs as group measures and invoking an automorphic geodesic augmentation, certain otherwise inaccessible, additional | SI | (2 n′ ) (and hence UDTs) may be established; these are based on sporadic higher (regular) (2 n ≫ 12)–fold ensemble invariants and are obtained via finite group duality properties implicit in the concept of group measures. The PC DR–based views of general (2 n ) interacting spins of UDTs expressed here give specific insight into dynamic structure over (explicit TRI invariant–defined) Liouvillian carrier spaces. This lattice point (Erdösian) view of DR shows that UDT invariants are distinct and more contracted than predicted by the earlier linear–re–coupling–based | D 0 ( U )|(⨷ SU (2)) approach. The presence of degeneracy in general high (2 n ) UDTs as non–Abelian entities ensures that the homomorphic–based, | D 0 ( U )| enumeration (with its implied linear graphical re–coupling) is invalid for high (2 n ) uniform (NMR) multi–spin systems whose TRI properties are governed by DR re–coupling. The prime focus of the report concerns the positive conceptual value of PC lattice–point–based DR, as applied to the S 2 n –invariants which define UDTs (of NMR) and their completeness. Brief contrasts with the earlier, more restricted O (2 k + 1) (overall) invariants of ( O ( n ) ⊃ ⋯ ⊃ G )–based democratic re–coupled quantum systems are given for completeness.
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Davis, Anthony B., Alexander Marshak, Robert F. Cahalan et Warren J. Wiscombe. « Interactions : Solar and Laser Beams in Stratus Clouds, Fractals & ; Multifractals in Climate & ; Remote-Sensing Studies ». Fractals 05, supp02 (octobre 1997) : 129–66. http://dx.doi.org/10.1142/s0218348x97000875.
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Recent research on cloud structure and cloud-radiation interaction at NASA's Goddard Space Flight Center is presented as a show case of interdisciplinary work where fractals and multifractals play a central role. Focus has been primarily on stratocumulus because of their first-order effect on the Earth's energy balance (hence the global climate) due to their unusual horizontal extension and persistence. These cloud layers have quasi-flat upper/lower boundaries and appear to be quite uniform but are highly variable inside. The general strategy has been: utilization of spatial statistics of in situ and remotely sensed data pertaining to cloud structure to constrain stochastic cloud models used in turn for radiative transfer simulations where artificial radiation fields are generated; these fields are compared to actual measurements. and so on, until a degree of closure is achieved. The major trends have been: i) computation and understanding of cloudradiative properties from the large scales of interest to Global Climate Models (over 102 km) down to the smallest observable scales (less than 10 m); ii) from predicting the outcome of "ideal" measurements to those of "real" ones with limited accuracy, sampling and averaging; iii) from passive to active remote-sensing methods; and iv) shifting from standard to wavelet-based analysis/modeling techniques. In terms of potential for impact on geophysical research at large, the most important contributions are: a) criteria for and measures of nonstationarity and intermittency in scale-invariant data; b) so-called "bounded" multifractal cascade models having a continuously variable degree of nonstationarity: c) a parameterization of the bulk effect of fractal variability on large-scale planetary albedo; and d) the basic scaling theory of radiative "smoothing" that explains non-trivially related multiple scattering phenomena in both solar- and lidar-based remote sensing. The last item also suggests new methods of observing clouds and new ways of processing cloud radiance data to retrieve physical cloud properties.
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Stella, Nwankwo Nonyelum, et Ogbalu Anthony Ikechukwu. « Effect of Age and Parity on Knowledge of Cervical Cancer Screening Among Women of Child Bearing Age in Anambra State ». Academic Journal of Life Sciences, no 67 (24 août 2020) : 83–92. http://dx.doi.org/10.32861/ajls.67.83.92.
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Identification of characteristics of women in terms of age and parity as related to their uptake of existing screening services can give significant data to forming cervical cancer screening administrations. This study was aimed to assess the effect of age and parity on knowledge of cervical cancer screening among women of child bearing age in Anambra State. The study adopted a quasi-experimental research design.The study was conducted at Chukwuemeka Odumegwu Ojukwu University Teaching Hospital Awka and General Hospital Onitsha between June 2019 to September 2019.Using multi-stage (purposive) sampling technique, the sample size for this study consisted of one hundred and eighty four (184) women (134) subjects for experimental group and 50 subjects for control group) attending antenatal in public hospitals in Anambra State. The instrument contained five questions on demographic data of the respondents, questions on knowledge of cervical cancer and practice questions with four point response options. The reliability of the instrument was established by using Cronbach alpha for estimating the internal consistency of the instrument. Data entry and analysis were done using Statistical Package for Social Science (SPSS) and inferential statistics (ANCOVA) was used to test the null hypotheses at 0.05 level of significance.The results showed that all the women of different age groups and women of all parity levels benefitted from the exposure to health education programme. The study therefore concludes that exposing women of child bearing age to health education programme improved the practice of cervical cancer screening practice. The knowledge of cervical cancer, knowledge of cervical cancer screening and knowledge of modes of prevention of cervical cancer are critical in determining cervical cancer screening uptake among the women. It is thus concluded that exposing women of child bearing age to health education programme improved the cervical cancer screening practice than not exposing them to any treatment. With adequate knowledge of cervical cancer and a positive perception of cervical cancer screening, utilization of cervical cancer screening services is uniform among women of all parity level.
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Викторов, Дмитрий Сергеевич, Екатерина Владимировна Пластинина et Елена Валерьевна Самоволина. « Justification of requirements for digital signal synthesizers for various types of radar ». Herald of Tver State University. Series : Applied Mathematics, no 4 (23 décembre 2020) : 43–55. http://dx.doi.org/10.26456/vtpmk604.
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В работе обосновываются требования к уровню искажений радиолокационных станций с импульсным и квазинепрерывным излучением, построенных на основе цифровых синтезаторов сигналов четырех типов: цифровых синтезаторах отсчетов напряжения и цифровых синтезаторах отсчетов фазы с равномерной дискретизацией, цифровых синтезаторах отсчетов напряжения и цифровых синтезаторах отсчетов фазы с неравномерной дискретизацией. При построении задающего устройства РЛС возникает вопрос о выборе типа цифрового синтезатора сигналов. Основными исходными критериями при этом являются максимальный рабочий диапазон цифрового синтезатора и уровень внутриполосных искажений. При выборе типа цифрового синтезатора сигналов необходимо учитывать большое количество факторов, основными из которых являются сложность исполнения формирователя цифровых отсчетов, возможность реализации формирователя цифровых отсчетов с требуемым быстродействием и количеством разрядов [1, 2]. При предъявлении требований к суммарному уровню искажений используется критерий допустимого снижения вероятности правильного обнаружения по сравнению с её потенциальным значением при фиксированной вероятности ложной тревоги. Исходя из данного критерия в импульсных РЛС максимальное относительное среднеквадратическое значение искажений взаимокорреляционной функции сигнала с угловой модуляцией, формируемого цифровым синтезатором, не должно превышать $D_{\\delta x}\\le $-(51...67) дБ. В РЛС с квазинепрерывным излучением максимальное относительное среднеквадратическое значение искажений автокорреляционной функции сигнала с угловой модуляцией не должно превышать $D_{\\delta }\\le $-(80...120) дБ. Количество разрядов квантования фазы, напряжения и компенсации временной задержки в цифровых синтезаторах сигналов зависит не только от максимального относительного среднеквадратического значения искажений взаимокорреляционной функции но и от количества отсчетов сигнала с угловой модуляцией. Поэтому первоначально необходимо выбрать эталонную частоту цифрового синтезатора сигналов, задаваясь видом модуляции и эффективной шириной спектра сигнала с угловой модуляцией исходя из ТТХ РЛС. The paper substantiates the requirements for the level of distortion of radar stations with pulsed and quasi-continuous radiation, built on the basis of digital signal synthesizers of four types: digital synthesizers of voltage counts and digital synthesizers of phase counts with uniform sampling, digital synthesizers of voltage counts and digital synthesizers of phase counts with uneven sampling. When building a radar master device, the question arises about choosing the type of digital signal synthesizer. The main initial criteria are the maximum operating range of the digital synthesizer and the level of in-band distortion. When choosing the type of digital signal synthesizer, you must take into account a large number of factors, the main of which are the complexity of the execution of the digital readout shaper, the possibility of implementing a digital readout shaper with the required speed and number of digits [1, 2]. When making requirements for the total level of distortion, the criterion of acceptable reduction of the probability of correct detection in comparison with its potential value for a fixed probability of false alarm is used. Based on this criterion, in pulse radars, the maximum relative RMS value of the distortion of the intercorrelation function of a signal with angular modulation generated by a digital synthesizer should not exceed $D_{\\delta x}\\le $-(51...67) dB. In a radar with quasi-continuous radiation, the maximum relative mean-square value of the distortion of the autocorrelation function of the signal with angular modulation should not exceed $D_{\\delta }\\le $- (80...120) dB. The number of bits of phase quantization, voltage and time delay compensation in digital signal synthesizers depends not only on the maximum relative RMS value of the distortion of the intercorrelation function, but also on the number of samples of the signal with angular modulation. Therefore, initially you need to select the reference frequency of the digital signal synthesizer, setting the type of modulation and the effective spectrum width of the signal with angular modulation based on the tactical and technical characteristics radar.
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Wells, K. C., D. B. Millet, N. Bousserez, D. K. Henze, S. Chaliyakunnel, T. J. Griffis, Y. Luan et al. « Simulation of atmospheric N<sub>2</sub>O with GEOS-Chem and its adjoint : evaluation of observational constraints ». Geoscientific Model Development Discussions 8, no 7 (8 juillet 2015) : 5367–418. http://dx.doi.org/10.5194/gmdd-8-5367-2015.
Texte intégralRésumé :
Abstract. We describe a new 4D-Var inversion framework for N2O based on the GEOS-Chem chemical transport model and its adjoint, and apply this framework in a series of observing system simulation experiments to assess how well N2O sources and sinks can be constrained by the current global observing network. The employed measurement ensemble includes approximately weekly and quasi-continuous N2O measurements (hourly averages used) from several long-term monitoring networks, N2O measurements collected from discrete air samples aboard a commercial aircraft (CARIBIC), and quasi-continuous measurements from an airborne pole-to-pole sampling campaign (HIPPO). For a two-year inversion, we find that the surface and HIPPO observations can accurately resolve a uniform bias in emissions during the first year; CARIBIC data provide a somewhat weaker constraint. Variable emission errors are much more difficult to resolve given the long lifetime of N2O, and major parts of the world lack significant constraints on the seasonal cycle of fluxes. Current observations can largely correct a global bias in the stratospheric sink of N2O if emissions are known, but do not provide information on the temporal and spatial distribution of the sink. However, for the more realistic scenario where source and sink are both uncertain, we find that simultaneously optimizing both would require unrealistically small errors in model transport. Regardless, a bias in the magnitude of the N2O sink would not affect the a posteriori N2O emissions for the two-year timescale used here, given realistic initial conditions, due to the timescale required for stratosphere–troposphere exchange (STE). The same does not apply to model errors in the rate of STE itself, which we show exerts a larger influence on the tropospheric burden of N2O than does the chemical loss rate over short (< 3 year) timescales. We use a stochastic estimate of the inverse Hessian for the inversion to evaluate the spatial resolution of emission constraints provided by the observations, and find that significant, spatially explicit constraints can be achieved in locations near and immediately upwind of surface measurements and the HIPPO flight tracks; however, these are mostly confined to North America, Europe, and Australia. None of the current observing networks are able to provide significant spatial information on tropical N2O emissions. There, averaging kernels are highly smeared spatially and extend even to the midlatitudes, so that tropical emissions risk being conflated with those elsewhere. For global inversions, therefore, the current lack of constraints on the tropics also places an important limit on our ability to understand extratropical emissions. Based on the error reduction statistics from the inverse Hessian, we characterize the atmospheric distribution of unconstrained N2O, and identify regions in and downwind of South America, Central Africa, and Southeast Asia where new surface or profile measurements would have the most value for reducing present uncertainty in the global N2O budget.
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Brocca, Luca, Paolo Filippucci, Sebastian Hahn, Luca Ciabatta, Christian Massari, Stefania Camici, Lothar Schüller, Bojan Bojkov et Wolfgang Wagner. « SM2RAIN–ASCAT (2007–2018) : global daily satellite rainfall data from ASCAT soil moisture observations ». Earth System Science Data 11, no 4 (22 octobre 2019) : 1583–601. http://dx.doi.org/10.5194/essd-11-1583-2019.
Texte intégralRésumé :
Abstract. Long-term gridded precipitation products are crucial for several applications in hydrology, agriculture and climate sciences. Currently available precipitation products suffer from space and time inconsistency due to the non-uniform density of ground networks and the difficulties in merging multiple satellite sensors. The recent “bottom-up” approach that exploits satellite soil moisture observations for estimating rainfall through the SM2RAIN (Soil Moisture to Rain) algorithm is suited to build a consistent rainfall data record as a single polar orbiting satellite sensor is used. Here we exploit the Advanced SCATterometer (ASCAT) on board three Meteorological Operational (MetOp) satellites, launched in 2006, 2012, and 2018, as part of the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Polar System programme. The continuity of the scatterometer sensor is ensured until the mid-2040s through the MetOp Second Generation Programme. Therefore, by applying the SM2RAIN algorithm to ASCAT soil moisture observations, a long-term rainfall data record will be obtained, starting in 2007 and lasting until the mid-2040s. The paper describes the recent improvements in data pre-processing, SM2RAIN algorithm formulation, and data post-processing for obtaining the SM2RAIN–ASCAT quasi-global (only over land) daily rainfall data record at a 12.5 km spatial sampling from 2007 to 2018. The quality of the SM2RAIN–ASCAT data record is assessed on a regional scale through comparison with high-quality ground networks in Europe, the United States, India, and Australia. Moreover, an assessment on a global scale is provided by using the triple-collocation (TC) technique allowing us also to compare these data with the latest, fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5), the Early Run version of the Integrated Multi-Satellite Retrievals for Global Precipitation Measurement (IMERG), and the gauge-based Global Precipitation Climatology Centre (GPCC) products. Results show that the SM2RAIN–ASCAT rainfall data record performs relatively well at both a regional and global scale, mainly in terms of root mean square error (RMSE) when compared to other products. Specifically, the SM2RAIN–ASCAT data record provides performance better than IMERG and GPCC in data-scarce regions of the world, such as Africa and South America. In these areas, we expect larger benefits in using SM2RAIN–ASCAT for hydrological and agricultural applications. The limitations of the SM2RAIN–ASCAT data record consist of the underestimation of peak rainfall events and the presence of spurious rainfall events due to high-frequency soil moisture fluctuations that might be corrected in the future with more advanced bias correction techniques. The SM2RAIN–ASCAT data record is freely available at https://doi.org/10.5281/zenodo.3405563 (Brocca et al., 2019) (recently extended to the end of August 2019).
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Viktorov, Dmitriy S., Ekaterina V. Plastinina et Elena V. Samovolina. « Requirements Justification to Digital Signal Synthesizers for Various Types of Radar Systems ». Journal of Siberian Federal University. Engineering & ; Technologies, novembre 2020, 818–28. http://dx.doi.org/10.17516/1999-494x-0268.
Texte intégralRésumé :
The paper justifies the requirements for the level of distortion of radar stations with pulse and quasi-continuous radiation, built on the basis of digital signal synthesizers of four types: digital synthesizers of voltage counts and digital synthesizers of phase counts with uniform sampling, digital synthesizers of voltage counts and digital synthesizers of phase counts with uneven sampling. When building a radar master device, the question arises about choosing the type of digital signal synthesizer. The main initial criteria are the maximum operating range of the digital synthesizer and the level of in-band distortion. When choosing the type of digital signal synthesizer, you have to take into account a large number of factors, the main of which are the complexity of the execution of the digital readout shaper, the possibility of implementing a digital readout shaper with the required speed and number of digits [1, 2]. When making requirements for the total level of distortion, the criterion of acceptable reduction of the probability of correct detection in comparison with its potential value for a fixed probability of false alarm is used. Based on this criterion, in pulse radars, the maximum relative RMS value of the distortion of the intercorrelation function of a signal with angular modulation generated by a digital synthesizer should not exceed Dδx ≤ –(51...67) dB. In a radar with quasi-continuous radiation, the maximum relative mean-square value of the distortion of the autocorrelation function of the signal with angular modulation should not exceed Dδ ≤ –(80...120) dB. The number of bits of phase quantization, voltage and time delay compensation in digital signal synthesizers depends not only on the maximum relative RMS value of the distortion of the intercorrelation function, but also on the number of samples of the signal with angular modulation. Therefore, initially you need to select the reference frequency of the digital signal synthesizer, setting the type of modulation and the effective spectrum width of the signal with angular modulation based on the tactical and technical characteristics radar
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Krasnikov, S. V. « Features of modeling the system of turbine unit with a variable contact zone of its stator parts ». SN Applied Sciences 3, no 10 (6 septembre 2021). http://dx.doi.org/10.1007/s42452-021-04773-4.
Texte intégralRésumé :
AbstractModeling of stator parts of power units of thermal and nuclear power plants is carried out according to several standard schemes. Common methods of modeling systems with non-uniform and non-stationary contact of stator elements lead to significant errors in calculating the amplitudes of forced vibration displacement at a given external load. The object of this paper is to analyze errors in calculating the displacement amplitudes of forced oscillations in different modeling schemes according to the standard approach and developing a method for constructing a quasi-dynamic model taking into account the time-varying contact of the system’s stator parts as well as other factors. To do this, the author has developed a series of models with different degrees of sampling and considering different system factors. Particular attention is paid to the impact of factors arising from the long operation of the power plant (subsidence of foundation). The modeling was carried out taking into account the calculation method. The finite element method was used to perform calculations. The results of the calculation of forced oscillation displacement amplitudes are available to show the areas of application of different types of three-dimensional models of the steam power unit. The results of research conducted on the developed models show the impossibility of using standard simulation schemes for systems with a variable contact between its stator elements, as shown by the example of a power unit with steam turbine. The efficiency of using the models taking into account the variable contact between the stator parts and other factors to calculate the displacement amplitudes of the forced oscillations with high accuracy is likewise presented. Every specialist should be aware of the factors that influence the research results. This paper is concerned with assessment of the influence of a number of factors on the results of calculating the vibrations of a complex mechanical system.