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Cross-Validation, Shrinkage and Variable Selection in Linear Regression Revisited

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Open Journal of Statistics 2013年第2期3卷 79-102页

作者： Hans C. van Houwelingen willi sauerbrei Department of Medical Statistics and Bioinformatics Leiden University Medical Center Leiden The Netherlands Institut fuer Medizinische Biometrie und Medizinische Informatik Universitaetsklinikum Freiburg Freiburg Germany

In deriving a regression model analysts often have to use variable selection, despite of problems introduced by data- dependent model building. Resampling approaches are proposed to handle some of the critical issues. In order to assess and compare several strategies, we will conduct a simulation study with 15 predictors and a complex correlation structure in the linear regression model. Using sample sizes of 100 and 400 and estimates of the residual variance corresponding to R2 of 0.50 and 0.71, we consider 4 scenarios with varying amount of information. We also consider two examples with 24 and 13 predictors, respectively. We will discuss the value of cross-validation, shrinkage and backward elimination (BE) with varying significance level. We will assess whether 2-step approaches using global or parameterwise shrinkage (PWSF) can improve selected models and will compare results to models derived with the LASSO procedure. Beside of MSE we will use model sparsity and further criteria for model assessment. The amount of information in the data has an influence on the selected models and the comparison of the procedures. None of the approaches was best in all scenarios. The performance of backward elimination with a suitably chosen significance level was not worse compared to the LASSO and BE models selected were much sparser, an important advantage for interpretation and transportability. Compared to global shrinkage, PWSF had better performance. Provided that the amount of information is not too small, we conclude that BE followed by PWSF is a suitable approach when variable selection is a key part of data analysis.

关键词： Cross-Validation LASSO Shrinkage Simulation Study Variable Selection

Optimizing laser coupling,matter heating,and particle acceleration from solids using multiplexed ultraintense lasers

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Matter and Radiation at Extremes 2024年第4期9卷 16-28页

作者： Weipeng Yao Motoaki Nakatsutsumi Sébastien Buffechoux Patrizio Antici Marco Borghesi Andrea Ciardi Sophia N.Chen Emmanuel d’Humières Laurent Gremillet Robert Heathcote Vojtech Horny Paul McKenna Mark N.Quinn Lorenzo Romagnani Ryan Royle Gianluca Sarri Yasuhiko Sentoku Hans-Peter Schlenvoigt Toma Toncian Olivier Tresca Laura Vassura Oswald willi Julien Fuchs LULI-CNRS CEASorbonne UniversitéEcole PolytechniqueInstitut Polytechnique de ParisF-91128 Palaiseau CedexFrance Sorbonne Université Observatoire de ParisUniversité PSLCNRSLERMAF-75005 ParisFrance INRS-EMT 1650 BoulLionel-BouletVarennesQuebec J3X 1S2Canada Center for Plasma Physics School of Mathematics and PhysicsQueen’s University BelfastBelfast BT71NNUnited Kingdom “Horia Hulubei”National Institute for Physics and Nuclear Engineering 30 Reactorului StreetRO-077125 Bucharest-MagureleRomania University of Bordeaux Centre Lasers Intenses et ApplicationsCNRSCEAUMR 5107F-33405 TalenceFrance CEA DAMDIFF-91297 ArpajonFrance Université Paris-Saclay CEALMCE91680 Bruyères-le-ChatelFrance Central Laser Facility STFC Rutherford Appleton LaboratoryDidcotUnited Kingdom SUPA Department of PhysicsUniversity of StrathclydeGlasgow G40NGUnited Kingdom Department of Physics University of NevadaRenoNevada 89557USA Institute of Laser Engineering Osaka University2-6 YamadaokaSuitaOsaka 565-0871Japan Institut fur Laser und Plasmaphysik Heinrich Heine Universitat DusseldorfDusseldorfGermany

Realizing the full potential of ultrahigh-intensity lasers for particle and radiation generation will require multi-beam arrangements due to technology ***,we investigate how to optimize their coupling with solid ***,we show that overlapping two intense lasers in a mirror-like configuration onto a solid with a large preplasma can greatly improve the generation of hot electrons at the target front and ion acceleration at the target *** underlying mechanisms are analyzed through multidimensional particle-in-cell simulations,revealing that the self-induced magnetic fields driven by the two laser beams at the target front are susceptible to reconnection,which is one possible mechanism to boost electron *** addition,the resistive magnetic field generated during the transport of the hot electrons in the target bulk tends to improve their *** simulations also indicate that such effects can be further enhanced by overlapping more than two laser beams.

关键词： laser acceleration particle

Vector Product and an Integrable Dynamical System

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Communications in Theoretical Physics 2011年第12期56卷 992-994页

作者： willi-Hans Steeb Yorick Hardy Igor Tanski International School for Scientific Computing University of JohannesburgAuckland Park 2006South Africa

We study an autonomous system of first order ordinary differential equations based on the vector product. We show that the system is completely integrable by constructing the first *** connection with Nambu mechanics ... 详细信息

关键词： integrable system vector product Nambu mechanics

WHYMAP and the World Map of Transboundary Aquifer Systems at the scale of 1：50 000 000（Special Edition for the 4th World Water Forum, Mexico City, March 2006）

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Episodes 2006年第4期29卷 274-278页

作者： willi Struckmeier Andrea Richts BGR （Federal Institute for Geosciences and Natural Resources） Postfach 51 01 53 30631 Hannover Federal Republic of Germany

The availability of, and access to, fresh water is an important issue on the agenda of planners, politicians and executives all over the world. Although there seems to be an abundance of water in global calculations, surface and groundwater resources are increasingly under stress at regional and local scale. A vast majority of all freshwater is found in aquifers, many of them transboundary in extent. In the semi-arid and arid regions of the world, groundwater resources constitute the only reliable water resource for drinking water supply and irrigated food production. However, in spite of the sharply increasing use of aquifers in the past decades, the knowledge about the groundwater in aquifers and its management is still weak in many places. Investments in groundwater schemes are frequently founded on inadequate aquifer information in terms of quantitative data, reliable models and poor monitoring.

关键词：地质图淡水资源地下水地表水水资源供应水资源监测

Diversity of yO T-cell antigens

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Cellular & Molecular Immunology 2013年第1期10卷 13-20页

作者： willi K Born M Kemal Aydintug Rebecca L O'Brien Integrated Department of Immunology National Jewish Health Denver CO USA University of Colorado Denver Aurora CO USACorrespondence: Dr WK Born National Jewish Health 1400 Jackson Street GB K409 Denver CO 80206 USA.

In the last two decades, it has become clear that yo T cells recognize a diverse array of antigens including self and foreign, large and small, and peptidic and non-peptidic molecules. In this respect, 78 antigens as a whole resemble more the antigens recognized by antibodies than those recognized by T cells. Because of this antigenic diversity, no single mechanism--such as the major histocompatibility complex （MHC） restriction of ap T cells--is likely to provide a basis for all observed T-cell antigen receptor （TCR）-dependent 78 T-cell responses. Furthermore, available evidence suggests that many individual 78 T cells are poly-specific, probably using different modes of ligand recognition in their responses to unrelated antigens. While posing a unique challenge in the maintenance of self-tolerance, this broad reactivity pattern might enable multiple overlapping uses of 78 T-cell populations, and thus generate a more efficient immune response.

关键词： antigen recognition ligand T-cell receptor yo T cells

Demographic Processes Linked to Genetic Diversity and Positive Selection across a Species’ Range

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Plant Communications 2020年第6期1卷 72-84页

作者： Yvonne willi Marco Fracassetti Olivier Bachmann Josh Van Buskirk Department of Environmental Sciences University of BaselSch€onbeinstrasse 6CH-4056 BaselSwitzerland Department of Evolutionary Biology and Environmental Studies University of Z€urichCH-8057 Z€urichSwitzerland Department of Ecology Environment and Plant SciencesScience for Life LaboratoryStockholm UniversitySE-10691 StockholmSweden

Demography determines the strength of genetic drift,which generally reduces genetic variation and the efficacy of ***,we disentangled the importance of demographic processes at a local scale(census size and mating system)and at a species-range scale(old split between population clusters,recolonization after the last glaciation cycle,and admixture)in determining within-population genomic diversity and genomic signatures of positive *** were based on re-sequence data from 52 populations of North American Arabidopsis lyrata collected across its entire *** mating system and range dynamics since the last glaciation cycle explained around 60%of the variation in genomic diversity among populations and 52%of the variation in the signature of positive *** was lowest in selfing compared with outcrossing populations and in areas further away from glacial *** parallel,reduced positive selectionwas found in selfing populations and in populations with a longer route of postglacial range *** signature of positive selection was also reduced in populations without *** conclude that recent range expansion can have a profound influence on diversity in coding and non-coding DNA,similar in magnitude to the shift toward *** limits may in fact be caused by reduced effective population size and compromised positive selection in recently colonized parts of the range.

关键词： admixture-dependent selection directional selection genetic drift range expansion selfing small population size

Clinical Data-Driven Finite Element Analysis of the Kinetics of Chewing Cycles in Order to Optimize Occlusal Reconstructions Dedicated to Professor Karl Stark Pister for his 95th birthday

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Computer Modeling in Engineering & Sciences 2021年第12期129卷 1259-1281页

作者： Simon Martinez Jurgen Lenz Hans Schindler willi Wendler Stefan Rues Karl Schweizerhof Sophia Terebesi Nikolaos Nikitas Giannakopoulos Marc Schmitter Institute of Mechanics Karlsruhe Institute of Technology(KIT)KarlsruheGermany Department of Prosthodontics Dental SchoolUniversity of WurzburgWurzburgGermany Department of Prosthodontics University of HeidelbergHeidelbergGermany

The occlusal design plays a decisive role in the fabrication of dental *** and dental technicians depend on mechanical simulations of mandibular movement that are as accurate as possible,in particular,to produce interference-free yet chewing-efficient dental *** this,kinetic data must be available,i.e.,movements and deformations under the influence of forces and *** the present study,so-called functional data were collected from healthy volunteers to provide consistent information for proper *** the latter purpose,biting and chewing forces,electrical muscle activity and jaw movements were registered synchronously,and individual magnetic resonance tomograms(MRI)were *** acquired data were then added to a large complex finite element model of the complete masticatory system using the functional information obtained and individual anatomical geometries so that the kinetics of the chewing process and teeth grinding could be realistically *** allows developing algorithms that optimize computer-aided manufacturing of dental prostheses close to *** this way,a failure-free function of the dental prosthesis can be guaranteed and its damage during usage can be reduced or prevented even including endosseous implants.

关键词： Occlusal design mechanical simulations of mandibular movement finite element model of the complete masticatory system simulation of chewing process and teeth grinding

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FASER流密码的安全性分析

密码学报 2014年第4期1卷 358-367页

作者：徐超张斌 willi Meier 可信计算与信息保障实验室中国科学院软件研究所北京100190 计算机科学国家重点实验室中国科学院软件研究所北京100190 瑞士西北高等专业学院

FASER是一个由Chaza等人设计的认证加密方案并提交到CAESAR竞赛.FASER使用两个具有相同长度的状态寄存器,一个用来加密另一个用来认证.FASER的状态寄存器可以分成两个部分,一部分由线性FSR更新另一部分由非线性FSR进行更新.一个滤波布... 详细信息

FASER是一个由Chaza等人设计的认证加密方案并提交到CAESAR竞赛.FASER使用两个具有相同长度的状态寄存器,一个用来加密另一个用来认证.FASER的状态寄存器可以分成两个部分,一部分由线性FSR更新另一部分由非线性FSR进行更新.一个滤波布尔函数用来产生密钥流,这个滤波布尔函数是由MAJ和MIX两个函数组成.我们主要评估了FASER加密过程的安全性,也就是密钥流生成阶段.我们指出FASER的最大缺陷就是线性FSR和非线性FSR直接不相互影响.因此通过线性逼近MAJ函数,可能寻找到只包含密钥流比特和线性FSR状态比特的线性关系式.对于FASER128和FASER256我们寻找到了许多这样的线性逼近等式,这些逼近等式的相关系数都是2-1.利用这个缺陷我们利用相关攻击来恢复线性FSR的内部状态,在预计算阶段寻找低重量倍式的时间复杂度是2-36,在线的复杂度是可以忽略不计的,它是线性FSR长度的多项式.攻击所需的数据量不超过2-36.此外,利用MAJ函数的性质,我们利用连续两步密钥流之间的关系构造了许多区分器,对于FASER128和FASER256这些区分器都具有2-2的相关系数.因此我们分别只需要16个FASER128或者FASER256的密钥流就可区分出密钥流和随机序列.这些区分器都没有利用MIX函数的设计缺陷,即使FASER的设计者修改了MIX函数的缺陷,我们的区分攻击依然起作用.我们还给出了在假设线性逼近中包含一个非线性FSR的状态比特的条件下如何恢复的内部状态的方法.

关键词：流密码 CAESAR FASER 相关攻击区分器

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DOS＋386=4千兆字节

微型计算机 1991年第4期11卷 48-54页

作者： willi.,A 闵珍晖