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Search Results: 1 - 10 of 298053 matches for " J. Rasmussen "
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Applications of Free Fields in 2D Current Algebra
J. Rasmussen
Physics , 1996,
Abstract: In this thesis steps are taken in the direction of formulating non-critical strings in the framework of the $G/G$ approach. A major part of the thesis is concerned with conformal field theory based on affine $SL(2)$ current algebra, in particular for admissible representations which are relevant in the $SL(2)/SL(2)$ description of coupling conformal minimal matter to 2D gravity. By virtue of fractional calculus, free field realizations are made applicable of producing integral representations of chiral blocks, even in the case of admissible representations where ghost fields raised to fractional powers are inherent. The famous work on minimal models by Dotsenko and Fateev is then generalised, working out monodromy invariant 4-point Greens functions and the operator algebra coefficients. Furthermore, the fusion rules are re-derived within the context of free field realizations by introducing the notion of over-screening. For higher groups an explicit Wakimoto free field realization is presented of affine current algebras based on simple Lie groups. Furthermore, a study is undertaken of primary fields in the framework of extra $x$ variables, and screening currents of both kinds are discussed. Several new and definite results are presented. A quantum group structure relying on both kinds of screening currents is discussed along the lines of Gomez and Sierra.
Free Field Realizations of Affine Current Superalgebras, Screening Currents and Primary Fields
J. Rasmussen
Physics , 1997, DOI: 10.1016/S0550-3213(97)00693-7
Abstract: In this paper free field realizations of affine current superalgebras are considered. Based on quantizing differential operator realizations of the corresponding basic Lie superalgebras, general and simple expressions for both the bosonic and the fermionic currents are provided. Screening currents of the first kind are also presented. Finally, explicit free field realizations of primary fields with general, possibly non-integer, weights are worked out. A formalism is used where the (generally infinite) multiplet is replaced by a generating function primary operator. The results allow setting up integral representations for correlators of primary fields corresponding to integrable representations. The results are generalizations to superalgebras of a recent work on free field realizations of affine current algebras by Petersen, Yu and the present author.
Screening Currents in Affine Current Algebra
J. Rasmussen
Mathematics , 1997,
Abstract: In this paper screening currents of the second kind are considered. They are constructed in any affine current algebra for directions corresponding to simple roots with multiplicity one in a decomposition of the highest root on a set of simple roots. These expressions are precisely of the form previously conjectured to be valid for all directions in general affine current algebras. However, by working out explicitly the screening currents in the case of SO(5) based on the Lie algebra B_2, it is demonstrated that much more complicated structures appear in the general case. In the distinguished representation of affine OSp(2|2) current superalgebra, the screening current of the second kind in the bosonic direction is also provided.
Explicit Decompositions of Weyl Reflections in Affine Lie Algebras
J. Rasmussen
Mathematics , 1997, DOI: 10.1016/S0550-3213(98)00092-3
Abstract: In this paper explicit decompositions are provided of the Weyl reflections in affine Lie algebras, in terms of fundamental Weyl reflections.
Screening Current Representation of Quantum Superalgebras
J. Rasmussen
Mathematics , 1997, DOI: 10.1142/S021773239800156X
Abstract: In this letter a screening current or contour representation is given of certain quantum superalgebras. The Gomez-Sierra construction of quantum groups in conformal field theory is generalized to cover superalgebras and illustrated using recent results on screening currents in affine current superalgebra.
Negative Screenings in Conformal Field Theory and 2D Gravity: The Braiding Matrix
J. Rasmussen,J. Schnittger
Physics , 1999, DOI: 10.1016/S0550-3213(99)00799-3
Abstract: We consider an extension of the Coulomb gas picture which is motivated by Liouville theory and contains negative powers of screening operators on the same footing as positive ones. The braiding problem for chiral vertex operators in this extended framework is analyzed. We propose explicit expressions for the R-matrix with general integer screening numbers, which are given in terms of 4F3 q-hypergeometric functions through natural analytic continuations of the well-known expression for positive integer screenings. These proposals are subsequently verified using a subset of the Moore-Seiberg equations that is obtained by simple manipulations in the operator approach. Interesting new relations for q-hypergeometric functions (particularly of type 4F3) arise on the way.
Metodik til studiet af strategiske ledelsesprocesser i organisationer
J?rgen Gulddahl Rasmussen
Qualitative Studies , 2010,
Abstract: Denne artikel handler om at skabe viden om en hverdagspraksis, der sj ldent er sat ord p . Den behandler de ledelsesprocesser, der i virksomheder producerer strategi og oms tter s danne strategier i produktive handlinger. Det er processer, der i sm og mellemstore virksomheder er pr get af intuition og af meget uformelle samspil mellem virksomhedsledere og medarbejdere. Metodikken er en videreudvikling af de metoder til produktion af kvalitative data, som FIRM-gruppen har eksperimenteret med gennem nogle r. Artiklen kan ses som en afrapportering af et fler rigt metodeudviklingsarbejde. Da erfaringer fra s danne virksomheder viser, at strategiske processer i h j grad udvikler sig gennem uformel kommunikation, og at lederes intuition spiller en meget stor rolle, arbejder metodikken med en struktureret udviklingsdialog mellem et mindre antal virksomhedsledere med strategiske opgaver og forskere. Denne udviklingsdialog har til form l at f lge og forst de processer, der skaber ledernes egne praksisrelaterede ”teorier” for strategisk handling. Efter en pr sentation af temaet gennemg s metodikkens praktiske fremgangsm de med unders gelser i en r kke virksomheder, opbygning af cases i samarbejde med ledere fra disse virksomheder, diskussion af disse og forel bige konklusioner hen mod de n ste trin i metodikken. Artiklen er skrevet samtidigt med arbejdet p et igangv rende forskningsprojekt og vil derfor b de v re en pr sentation og en udvikling af muligheder og vanskeligheder i metodikken.
The Benefits of Supplementary Fat in Feed Rations for Ruminants with Particular Focus on Reducing Levels of Methane Production
J. Rasmussen,A. Harrison
ISRN Veterinary Science , 2011, DOI: 10.5402/2011/613172
Abstract: Methane (CH4), a highly potent greenhouse gas, has repeatedly been identified as a significant contributor to global warming. In this connection, ruminants, animals that produce large quantities of methane, have been singled out as an area for reduction with regard to their emissions to the atmosphere. In an analysis of recently published data, we identify the underlying mechanisms of methane production in ruminants and focus on the efficacy of different fat sources in terms of their ability to reduce methane production. Specific attention has been placed on in vivo studies involving cattle and sheep, as well as studies based on a large number of animals (>10), recorded over a longer period (>21 days), and employing reliable techniques for the quantification of methane production. Data clearly indicate that supplementary fat, given to ruminants inhibits methane production, with medium-chain fatty acids (laurin, myristic acid) as well as poly-unsaturated fatty acids (linoleic and especially linolenic acid) having a significant effect. It is also apparent that conflicting findings between individual published trials can largely be resolved when one takes into consideration differences in experimental design, the composition of the basic feeds, the fat sources used, and the number of animals involved. 1. Implications The addition of supplementary fat to the diet of ruminants has been reported to effectively reduce methane production. Primarily it is the medium chain (laurin and myristic acids) and polyunsaturated (linoleic and especially linolenic) fatty acids that appear to be most efficacious. In terms of the future, and alternate cost-effective sources of such fatty acids, researchers and ruminant nutritionists might consider using the n-3 alpha-linolenic acid typically found at high levels in and readily extractable from AFA aphanizomenon flos-aquae, a type of blue green algae that grows worldwide. 2. Introduction There has been considerable interest in recent years in those factors that appear to contribute to global warming, as determined by an observed increase in atmospheric temperature. Moreover, global warming has thus far been linked to an increased concentration of greenhouse gases in the atmosphere, among them carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) [1]. Methane is a very important greenhouse gas since it has been reported to have an effect that is 21-times greater than that of carbon dioxide in terms of global warming [2]. Furthermore, a rise in emission of methane is positively correlated with an increase in population
Induced Topology on the Hoop Group
J. Rasmussen,M. Weis
Physics , 1994,
Abstract: A new topology is proposed on the space of holonomy equivalence classes of loops, induced by the topology of the space $\Sigma$ in which the loops are embedded. The possible role for the new topology in the context of the work by Ashtekar et al. is discussed.
The Environmental Impact of Galaxy Evolution
Jesper Rasmussen,Trevor J. Ponman
Physics , 2009,
Abstract: Galaxy evolution reveals itself not only through the evolving properties of galaxies themselves but also through its impact on the surrounding environment. The intergalactic medium in particular holds a fossil record of past galaxy activity, imprinted on its thermodynamic and chemical properties. This is most easily discerned in small galaxy groups, where the gravitational heating of this gas renders it observable by X-ray telescopes while still leaving its properties highly susceptible to the effects of galactic feedback. X-ray observations of the hot gas in groups can therefore provide a view of galactic feedback history that can complement dedicated studies of AGN and star formation activity at low and high redshift. Based on high-quality X-ray data of a sample of nearby groups, we present initial results of such a study and discuss some implications for the AGN and star formation histories of the group members.
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