Stochastic vortex dynamics in two-dimensional easy-plane ferromagnets: Multiplicative versus additive noise

We study how thermal fluctuations affect the dynamics of vortices in the two-dimensional classical, ferromagnetic, anisotropic Heisenberg model depending on their additive or multiplicative character. Using a collective coordinate theory, we analytically show that multiplicative noise, arising from fluctuations in the local field term of the Landau-Lifshitz equations, and Langevin-like additive noise both have the same effect on vortex dynamics (within a very plausible assumption consistent with the collective coordinate approach). This is a non-trivial result, as multiplicative and additive noises usually modify the dynamics quite differently. We also carry out numerical simulations of both versions of the model finding that they indeed give rise to very similar vortex dynamics.Comment: 10 pages, 6 figure

Finite temperature dynamics of vortices in the two dimensional anisotropic Heisenberg model

We study the effects of finite temperature on the dynamics of non-planar vortices in the classical, two-dimensional anisotropic Heisenberg model with XY- or easy-plane symmetry. To this end, we analyze a generalized Landau-Lifshitz equation including additive white noise and Gilbert damping. Using a collective variable theory with no adjustable parameters we derive an equation of motion for the vortices with stochastic forces which are shown to represent white noise with an effective diffusion constant linearly dependent on temperature. We solve these stochastic equations of motion by means of a Green's function formalism and obtain the mean vortex trajectory and its variance. We find a non-standard time dependence for the variance of the components perpendicular to the driving force. We compare the analytical results with Langevin dynamics simulations and find a good agreement up to temperatures of the order of 25% of the Kosterlitz-Thouless transition temperature. Finally, we discuss the reasons why our approach is not appropriate for higher temperatures as well as the discreteness effects observed in the numerical simulations.Comment: 12 pages, 8 figures, accepted for publication in European Physical Journal B (uses EPJ LaTeX

Structural analysis of the GH43 enzyme Xsa43E from Butyrivibrio proteoclasticus

The rumen of dairy cattle can be thought of as a large, stable fermentation vat and as such it houses a large and diverse community of microorganisms. The bacterium Butyrivibrio proteoclasticus is a representative of a significant component of this microbial community. It is a xylan-degrading organism whose genome encodes a large number of open reading frames annotated as fibre-degrading enzymes. This suite of enzymes is essential for the organism to utilize the plant material within the rumen as a fuel source, facilitating its survival in this competitive environment. Xsa43E, a GH43 enzyme from B. proteoclasticus, has been structurally and functionally characterized. Here, the structure of selenomethionine-derived Xsa43E determined to 1.3 Å resolution using single-wavelength anomalous diffraction is reported. Xsa43E possesses the characteristic five-bladed β-propeller domain seen in all GH43 enzymes. GH43 enzymes can have a range of functions, and the functional characterization of Xsa43E shows it to be an arabinofuranosidase capable of cleaving arabinose side chains from short segments of xylan. Full functional and structural characterization of xylan-degrading enzymes will aid in creating an enzyme cocktail that can be used to completely degrade plant material into simple sugars. These molecules have a range of applications as starting materials for many industrial processes, including renewable alternatives to fossil fuels

Wer den Kodex nicht einhält, den bestraft der Kapitalmarkt?

Seit der Einführung des Deutschen Corporate Governance Kodex (Kodex) im Jahr 2002 sind deutsche börsennotierte Unternehmen zur Abgabe der Entsprechenserklärung gemäß § 161 AktG verpflichtet (Comply-or-Explain-Prinzip). Auf der Basis dieser Information soll durch den Druck des Kapitalmarkts die Einhaltung des Kodex überwacht und gegebenenfalls sanktioniert werden. Dabei wird regelmäßig postuliert, dass bei überdurchschnittlicher Befolgung bzw. Nichtbefolgung der Kodex-Empfehlungen eine Belohnung durch Kurszuschläge bzw. eine Sanktionierung durch Kursabschläge erfolgt. Die Ergebnisse einer Ereignisstudie zeigen, dass die Abgabe der Entsprechenserklärung keine erhebliche Kursbeeinflussung auslöst und die für das Enforcement des Kodex angenommene (und erforderliche) Selbstregulierung durch den Kapitalmarkt nicht stattfindet. Es wird daher kritisch hinterfragt, ob der für den Kodex gewählte und grundsätzlich zu begrüßende flexible Regulierungsansatz im System des zwingenden deutschen Gesellschaftsrechts einen geeigneten Enforcement-Mechanismus darstellt. This paper studies the short-run announcement effects of compliance with the German Corporate Governance Code (‘the Code’) on firm value. Event study results suggest that firm value is unaffected by the announcement, although such market reactions to the first time disclosure of the declaration of conformity were widely assumed by the private and public promoters of the Code. This result from acceptance of the German Code add evidence to the hypothesis that regulatory corporate governance initiatives that rely on mandatory disclosure without monitoring and enforcement are ineffective in civil law countries.This paper studies the short-run announcement effects of compliance with the German Corporate Governance Code (‘the Code’) on firm value. Event study results suggest that firm value is unaffected by the announcement, although such market reactions to the first time disclosure of the declaration of conformity were widely assumed by the private and public promoters of the Code. This result from acceptance of the German Code add evidence to the hypothesis that regulatory corporate governance initiatives that rely on mandatory disclosure without monitoring and enforcement are ineffective in civil law countries

Dermatoglyphics in childhood leukaemia: a guide to prognosis and aetiology?

The results of analysis of the dermatoglyphics of 152 children with acute lymphoblastic leukaemia (ALL) (and the first-degree relatives of 54 of them) contrast with those of 31 children with acute myeloblastic leukaemia (AML) (and the first-degree relatives of 25 of them). In ALL our findings suggest that neither genetic susceptibility nor an environmental factor, effective during the early antenatal period, is of aetiological importance; but the response to treatment, assessed as length of first remission, was found to be related to the amount of fingertip pattern. This may have clinical application. In AML there is evidence of a genetically determined factor carrying a high risk of the development of the disease, in that a member of each of 5 different families of the 25 studied bore a rare hypothenar pattern, compared with none in 75 control families. No dermatoglyphic features were of prognostic significance in AML

Influences of gender and socioeconomic status on motor Proficiency of Primary School Children in the UK

As the development of movement skills are so crucial to a child's involvement in lifelong physical activity and sport, the purpose of this study was to assess the motor proficiency of children aged 4-7years (range=4.3-7.2years), whilst considering gender and socioeconomic status. 369 children (176 females, 193 males, aged=5.96±0.57years) were assessed for fine motor precision, fine motor integration, manual dexterity, bilateral co-ordination, balance, speed and agility, upper-limb co-ordination and strength. The average standard score for all participants was 44.4±8.9, classifying the participants towards the lower end of the average score. Multivariate analysis of covariance identified significant effects for gender (p<0.001) and socioeconomic status (p<0.001). Females outperformed males for fine motor skills and boys outperformed girls for catch and dribble gross motor skills. High socioeconomic status significantly outperformed middle and/or low socioeconomic status for total, fine and gross motor proficiency. Current motor proficiency of primary children aged 4-7years in the UK is just below average with differences evident between gender and socioeconomic status. Teachers and sport coaches working with primary aged children should concentrate on the development of movement skills, whilst considering differences between genders and socioeconomic status