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Search Results: 1 - 10 of 21250 matches for " Kim ?. Rasmussen "
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Statistical mechanics of general discrete nonlinear Schr{?}dinger models: Localization transition and its relevance for Klein-Gordon lattices
Magnus Johansson,Kim O. Rasmussen
Physics , 2004, DOI: 10.1103/PhysRevE.70.066610
Abstract: We extend earlier work [Phys.Rev.Lett. 84, 3740 (2000)] on the statistical mechanics of the cubic one-dimensional discrete nonlinear Schrodinger (DNLS) equation to a more general class of models, including higher dimensionalities and nonlinearities of arbitrary degree. These extensions are physically motivated by the desire to describe situations with an excitation threshold for creation of localized excitations, as well as by recent work suggesting non-cubic DNLS models to describe Bose-Einstein condensates in deep optical lattices, taking into account the effective condensate dimensionality. Considering ensembles of initial conditions with given values of the two conserved quantities, norm and Hamiltonian, we calculate analytically the boundary of the 'normal' Gibbsian regime corresponding to infinite temperature, and perform numerical simulations to illuminate the nature of the localization dynamics outside this regime for various cases. Furthermore, we show quantitatively how this DNLS localization transition manifests itself for small-amplitude oscillations in generic Klein-Gordon lattices of weakly coupled anharmonic oscillators (in which energy is the only conserved quantity), and determine conditions for existence of persistent energy localization over large time scales.
Severity of self-reported diseases and symptoms in Denmark
Kim Iburg, Niels Rasmussen, Kirsten Avlund
Population Health Metrics , 2006, DOI: 10.1186/1478-7954-4-3
Abstract: The 1994 Danish Health and Morbidity Survey collected data from 5,472 Danes older than 16 years of age. Interviews (response frequency: 79%) gave information on diseases and symptoms; a self-administered SF-36 questionnaire (response frequency: 64%) provided information on health-related quality of life. The severity of diseases and symptoms was represented by the health-related quality of life scores that individuals suffering from particular diseases and symptoms obtained on the single dimensions of the SF-36 and on a combined sum of all dimensions. We applied logistic regression to control for the influence of sex, age and socio-economic status on the SF-36 score. We also analysed the interaction between socio-economic status and diseases on the SF-36 score.Females, more frequently than males, reported on all symptoms and all disease groups except injuries. People with relatively low levels of education reported most diseases, especially musculoskeletal and cardiovascular diseases, more frequently than people with higher education. Age-adjusted mean SF-36 scores for all dimensions combined showed that the symptoms of melancholy/depression and breathing difficulties, psychiatric disorders and respiratory diseases scored lowest (i.e. were most often associated with worse health). Females had lower SF-36 combined scores (worse health) than males on all symptoms. We found interaction between socio-economic status and respiratory diseases and musculoskeletal diseases on the SF-36 score. SF-36 scores also indicated significantly worse health among Danes with low education and income levels compared to those with higher education and income.In 1994 the Danes most frequently reported musculoskeletal symptoms and diseases. Psychiatric disorders and respiratory diseases were identified as the most severe reported diseases. Due to the interaction between socio-economic status and some diseases, severity estimates should be interpreted with caution or stratified by socio-eco
Network Effects on Scientific Collaborations
Shahadat Uddin, Liaquat Hossain, Kim Rasmussen
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0057546
Abstract: Background The analysis of co-authorship network aims at exploring the impact of network structure on the outcome of scientific collaborations and research publications. However, little is known about what network properties are associated with authors who have increased number of joint publications and are being cited highly. Methodology/Principal Findings Measures of social network analysis, for example network centrality and tie strength, have been utilized extensively in current co-authorship literature to explore different behavioural patterns of co-authorship networks. Using three SNA measures (i.e., degree centrality, closeness centrality and betweenness centrality), we explore scientific collaboration networks to understand factors influencing performance (i.e., citation count) and formation (tie strength between authors) of such networks. A citation count is the number of times an article is cited by other articles. We use co-authorship dataset of the research field of ‘steel structure’ for the year 2005 to 2009. To measure the strength of scientific collaboration between two authors, we consider the number of articles co-authored by them. In this study, we examine how citation count of a scientific publication is influenced by different centrality measures of its co-author(s) in a co-authorship network. We further analyze the impact of the network positions of authors on the strength of their scientific collaborations. We use both correlation and regression methods for data analysis leading to statistical validation. We identify that citation count of a research article is positively correlated with the degree centrality and betweenness centrality values of its co-author(s). Also, we reveal that degree centrality and betweenness centrality values of authors in a co-authorship network are positively correlated with the strength of their scientific collaborations. Conclusions/Significance Authors’ network positions in co-authorship networks influence the performance (i.e., citation count) and formation (i.e., tie strength) of scientific collaborations.
Hitting bacteria at the heart of the central dogma: sequence-specific inhibition
Louise Rasmussen, Hans Sperling-Petersen, Kim Mortensen
Microbial Cell Factories , 2007, DOI: 10.1186/1475-2859-6-24
Abstract: The antisense RNA (asRNA) mechanism comprises all forms of sequence-specific mRNA recognition leading to reduced or altered expression of a certain transcript [1]. Naturally occurring asRNAs are found in all three kingdoms of life, although most examples are found in bacteria, and they affect messenger RNA (mRNA) destruction, repression and activation as well as RNA processing and transcription [2]. This mechanism can be exploited in engineering strategies for inhibiting protein synthesis.For the asRNA as well as other antisense compounds to be able to anneal to an mRNA or functional RNA, such as ribosomal RNA, the chosen RNA target region must be accessible. Determining target accessibility is the first step in designing antisense molecules, and both experimental and computational approaches have been applied. A brief and inexhaustive presentation will be given here.When antisense molecules anneal to a complementary mRNA, translation can be disrupted as a result of steric hindrance of either ribosome access or ribosomal read-through (Fig. 1). This inhibition mechanism is, of course, specific for mRNAs. The annealing of antisense molecules to either mRNAs or functional RNAs can result in fast degradation of duplex RNA, hybrid RNA/DNA duplex, or duplex RNA resembling precursor tRNA by ribonucleases in the cell, or by cleavage of the target RNA by the antisense compound itself. The inhibitory efficiency of these hybridization strategies depends on factors such as length and structure, binding rate, intracellular concentration, and degradation resistance of the chosen antisense molecule. Antisense molecules and methods have been developed and designed specifically to address these issues and improve the inhibitory efficiency. These antisense strategies will be presented as well as recent studies describing their application.Although the basic principle of the antisense inhibition mechanism is the same for all three kingdoms, the conditions affecting the efficiency of t
Undervisning i klynger – en artikel om erfaringer med at organisere en form for undervisning, der skaber forbindelse mellem projektarbejde og bredere faglige temaer
Thomas Gitz-Johansen,Kim Rasmussen,Trine Wulf-Andersen
Dansk Universitetspaedagogisk Tidsskrift , 2007,
Abstract: Forfatterne har p RUC arbejdet med at udvikle og beskrive den form for undervisning, som til dagligt g r under betegnelsen klynge, hvis hovedform l er at skabe sammenh ng mellem de studerendes projektarbejde og et bredere fagligt og socialt milj . Artiklen behandler forfatternes erfaringer med at gennemf re et klyngeforl b samt de p dagogiske principper, der er lagt til grund for klyngeundervisningen.
Exact Solutions of the Two-Dimensional Discrete Nonlinear Schr?dinger Equation with Saturable Nonlinearity
Avinash Khare,Kim ?. Rasmussen,Mogens R. Samuelsen,Avadh Saxena
Physics , 2010, DOI: 10.1088/1751-8113/43/37/375209
Abstract: We show that the two-dimensional, nonlinear Schr\"odinger lattice with a saturable nonlinearity admits periodic and pulse-like exact solutions. We establish the general formalism for the stability considerations of these solutions and give examples of stability diagrams. Finally, we show that the effective Peierls-Nabarro barrier for the pulse-like soliton solution is zero.
Staggered and short period solutions of the Saturable Discrete Nonlinear Schr?dinger Equation
Avinash Khare,Kim ?. Rasmussen,Mogens R. Samuelsen,Avadh Saxena
Physics , 2010, DOI: 10.1088/1751-8113/42/8/085002
Abstract: We point out that the nonlinear Schr{\"o}dinger lattice with a saturable nonlinearity also admits staggered periodic as well as localized pulse-like solutions. Further, the same model also admits solutions with a short period. We examine the stability of these solutions and find that the staggered as well as the short period solutions are stable in most cases. We also show that the effective Peierls-Nabarro barrier for the pulse-like soliton solutions is zero.
Effective Potential Theory: A Practical Way to Extend Plasma Transport Theory to Strong Coupling
Scott D. Baalrud,Kim O. Rasmussen,Jerome Daligault
Physics , 2014, DOI: 10.1002/ctpp.201400084
Abstract: The effective potential theory is a physically motivated method for extending traditional plasma transport theories to stronger coupling. It is practical in the sense that it is easily incorporated within the framework of the Chapman-Enskog or Grad methods that are commonly applied in plasma physics and it is computationally efficient to evaluate. The extension is to treat binary scatterers as interacting through the potential of mean force, rather than the bare Coulomb or Debye-screened Coulomb potential. This allows for aspects of many-body correlations to be included in the transport coefficients. Recent work has shown that this method accurately extends plasma theory to orders of magnitude stronger coupling when applied to the classical one-component plasma model. The present work shows that similar accuracy is realized for the Yukawa one-component plasma model and it provides a comparison with other approaches.
Accurate Determination of the Shear Viscosity of the One-Component Plasma
Jerome Daligault,Kim O. Rasmussen,Scott D. Baalrud
Physics , 2014, DOI: 10.1103/PhysRevE.90.033105
Abstract: The shear viscosity coefficient of the one-component plasma is calculated with unprecedented accuracy using equilibrium molecular dynamics simulations and the Green-Kubo relation. Numerical and statistical uncertainties and their mitigation for improving accuracy are analyzed. In the weakly coupled regime, our the results agree with the Landau-Spitzer prediction. In the moderately and strongly coupled regimes, our results are found in good agreement with recent results obtained for the Yukawa one-component plasma using non-equilibrium molecular dynamics. A practical formula is provided for evaluating the viscosity coefficient across coupling regimes, from the weakly-coupled regime up to solidification threshold. The results are used to test theoretical predictions of the viscosity coefficients found in the literature.
Statistical Mechanics of a Discrete Schr?dinger Equation with Saturable Nonlinearity
Mogens R. Samuelsen,Avinash Khare,Avadh Saxena,Kim ?. Rasmussen
Physics , 2013, DOI: 10.1103/PhysRevE.87.044901
Abstract: We study the statistical mechanics of the one-dimensional discrete nonlinear Schr\"odinger (DNLS) equation with saturable nonlinearity. Our study represents an extension of earlier work [Phys. Rev. Lett. {\bf 84}, 3740 (2000)] regarding the statistical mechanics of the one-dimensional DNLS equation with a cubic nonlinearity. As in this earlier study we identify the spontaneous creation of localized excitations with a discontinuity in the partition function. The fact that this phenomenon is retained in the saturable DNLS is non-trivial, since in contrast to the cubic DNLS whose nonlinear character is enhanced as the excitation amplitude increases, the saturable DNLS in fact becomes increasingly linear as the excitation amplitude increases. We explore the nonlinear dynamics of this phenomenon by direct numerical simulations.
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