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Dirichlet Process Gaussian Mixture Models:Choice of the Base Distribution

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Journal of Computer Science & Technology 2010年第4期25卷 653-664页

作者： Dilan Grür Carl Edward rasmussen Gatsby Computational Neuroscience Unit University College London Department of Engineering University of Cambridge Max Planck Institute for Biological Cybernetics.D-72076 Tubingen

In the Bayesian mixture modeling framework it is possible to infer the necessary number of components to model the data and therefore it is unnecessary to explicitly restrict the number of components. Nonparametric mixture models sidestep the problem of finding the ＂correct＂ number of mixture components by assuming infinitely many components. In this paper Dirichlet process mixture （DPM） models are cast as infinite mixture models and inference using Markov chain Monte Carlo is described. The specification of the priors on the model parameters is often guided by mathematical and practical convenience. The primary goal of this paper is to compare the choice of conjugate and non-conjugate base distributions on a particular class of DPM models which is widely used in applications, the Dirichlet process Gaussian mixture model （DPGMM）. We compare computational efficiency and modeling performance of DPGMM defined using a conjugate and a conditionally conjugate base distribution. We show that better density models can result from using a wider class of priors with no or only a modest increase in computational effort.

关键词： Bayesian nonparametrics Dirichlet processes Gaussian mixtures

Towards fully automated GW band structure calculations:What we can learn from 60.000 self-energy evaluationsTowards fully automated GW band structure calculations:What we can learn from 60.000 self-energy evaluations

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npj Computational Materials 2021年第1期7卷 189-197页

作者： Asbjørn rasmussen Thorsten Deilmann Kristian SThygesen CAMD Department of PhysicsTechnical University of Denmark2800 Kongens LyngbyDenmark Center for Nanostructured Graphene(CNG) Technical University of Denmark2800 Kongens LyngbyDenmark Institut für festkörpertheorie Westfälische Wilhelms-Universität Münster48149 MünsterGermany

We analyze a data set comprising 370 GW band structures of two-dimensional(2D)materials covering 14 different crystal structures and 52 chemical *** band structures contain a total of 61716 quasiparticle(QP)energies obtained from plane-wavebased one-shot G0W0@PBE calculations with full frequency *** investigate the distribution of key quantities,like the QP self-energy corrections and QP weights,and explore their dependence on chemical composition and magnetic *** linear QP approximation is identified as a significant error source and we propose schemes for controlling and drastically reducing this error at low computational *** analyze the reliability of the 1/N basis set extrapolation and find that is well-founded with a narrow distribution of coefficients of determination(r^(2))peaked very close to ***,we explore the accuracy of the scissors operator approximation and conclude that its validity is very *** work represents a step towards the development of automatized workflows for high-throughput G0W0 band structure calculations for solids.

关键词： structure approximation weights

Analysis of synchronization in a supermarket refrigeration system

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Control Theory and Technology 2014年第2期12卷 154-162页

作者： Rafael WISNIEWSKI John LETH Jakob G. rasmussen Department of Electronic Systems Aalborg University Eredrik Bajers Vej 7C 9220 Aalborg Denmark Department of Mathematical Sciences Aalborg University Fredrik Bajers Vej 7G 9220 Aalborg Denmark

In a supermarket refrigeration, the temperature in a display cases. This leads to a synchronous operation of all display cases, case, surprisingly, influences the temperature in other display in which the expansion valves in the display cases turn on and off at exactly the same time. This behavior increases both the energy consumption and the wear of components. Besides this practical importance, from the theoretical point of view, synchronization, likewise stability, Zeno phenomenon, and chaos, is an interesting dynamical phenomenon. The study of synchronization in the supermarket refrigeration systems is the subject matter of this work. for this purpose, we model it as a hybrid system, for which synchronization corresponds to a periodic trajectory. To examine whether it is stable, we transform the hybrid system to a single dynamical system defined on a torus. Consequently, we apply a Poincare map to determine whether this periodic trajectory is asymptotically stable. To illustrate, this procedure is applied for a refrigeration system with two display-cases.

关键词： Synchronization Hybrid systems Stability Limit cycles Stochastic approximation

Dispersal behavior correlates with personality of a North American fish

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Current Zoology 2012年第2期58卷 260-270页

作者： Josh E. rasmussen Mark C. BELK U.S. fish and Wildlife Service Klamath Falls OR 97603 USA Department of Biology Brigham Young University Provo UT 84602 USA

The process of dispersal is determined by the interaction of individual （intrinsic） traits and environmental （extrinsic） factors. Although many studies address and quantify dispersal, few evaluate both intrinsic and extrinsic factors jointly. We test the relative importance of intrinsic traits （exploration tendency and size） and extrinsic factors （population density and habitat quality） on dispersal of a medium-sized western United States minnow, southern leatherside chub Lepidomeda aliciae. A generalized linear model with a binomial response was used to determine the probability of individuals dispersing one year after tagging. Medium-sized individuals that were more prone to explore novel environments were 10.7 times more likely to be recaptured outside of their original capture area after a year （dispersal） compared to non-explorer individuals of the same size class. Differences be- tween explorer classifications within the small and large size classes were negligible. Open habitat within 50 m upstream also in- creased the probability of dispersal relative to controls. Relative location within the study reach, and population density were not significantly related to dispersal probabilities of individuals. Our results indicate that understanding of personality may illuminate patterns of dispersal within and among populations

关键词： Temperament Behavioral phenotype Exploration Lepidomeda Personality-dependent

Assessing soil thickness in a black soil watershed in northeast China using random forest and field observations

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International Soil and Water Conservation Research 2021年第1期9卷 49-57页

作者： Shuai Zhang Gang Liu Shuli Chen Craig rasmussen Baoyuan Liu faculty of Geographical Science Beijing Normal UniversityBeijing 100875China State Key Laboratory of Soil Erosion and Dryland farming on the Loess Plateau Institute of Soil and Water ConservationChinese Academy of Sciences and Ministry of Water ResourcesYangling 712100China Department of Environmental Science University of Arizona1177 E.Fourth StTucsonAZ 85721-0038USA

Soil thickness determines the soil productivity in the black soil region of northeast China,which is important for national food *** information on the spatial variation of black soil thickness is *** this paper,we propose a model framework for spatial estimation of the black soil thickness at the watershed scale by integrating field observations,unmanned aerial vehicle variations of topography,and satellite variations of vegetation with the aid of random *** sampled 141 sample profiles over a watershed and identified the black soil thickness based on indices of the mollic *** variables were derived from a digital elevation model and vegetation variables were derived from Landsat 8 *** forest was used to determine the relationship between black soil thickness and environmental *** resulting model explained 61%of the black soil thickness spatial variation,which was more than twice that of traditional interpolation methods(ordinary kriging,universal kriging and inverse distance weighting).Topographic variables contributed the most toward explaining the thickness,followed by vegetation *** black soil thickness over the watershed had a clear catenary soil pattern,with thickest black soil in the low depositional areas and thinnest at the higher elevations that drain into the low *** proposed model framework will improve estimates of soil thickness in the region of our study.

关键词： Soil thickness Random forest Black soils Northeast China Soil geomorphology

CHARACTERISTICS Of MESOSCALE fLOOD-MAKING TORRENTIAL RAIN SYSTEM SIMULATED BY HIGH RESOLUTION LIMITED AREA MODEL—NUMERICAL SIMULATION Of A HEAVY RAIN PROCESS DURING MEIYU SEASON IN 1991

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Acta meteorologica Sinica 1996年第3期10卷 284-294页

作者：朱禾 E.rasmussen Beijing Meteorological College Beijing 100081 Copenhagen University Denmark

An experimental work on the transplant of high resolution limited area model(HIRLAM) is firstly introduced into *** the implementation,first of all is to adjust a new geographical coordination and to remove the instability caused by the Tibetan Plateau,the roof of the world. Then,we have applied this model to simulate a flood-making torrential rain process which occurred in the Changjiang-Huaihe River Valley in July *** revealed the formation,development and movement of a mesoseale heavy rain system which had made a disastrous flood event in the middle and lower reaches of Changjiang River Valley. The result encourages us to use the HIRLAM for the researches on the Meiyu belt,the salient feature of precipitation of East Asia,and the numerical prediction of heavy rains in China.

关键词： heavy rain of Meiyu high resolution mesoscale