A Pinned Polymer Model of Posture Control

A phenomenological model of human posture control is posited. The dynamics are modelled as an elastically pinned polymer under the influence of noise. The model accurately reproduces the two-point correlation functions of experimental posture data and makes predictions for the response function of the postural control system. The physiological and clinical significance of the model is discussed.Comment: uuencoded post script file, 17 pages with 3 figure

Soft-gluon effects in WW production at hadron colliders

We consider QCD radiative corrections to WW pair production in hadron collisions. We perform a calculation that consistently combines next-to-leading order predictions with soft-gluon resummation valid at small transverse momenta ptWW of the WW pair. We present results for the ptWW distribution at the LHC up to (almost) next-to-next-to-leading logarithmic accuracy, and study the effect of resummation on the charged-lepton distributions. Soft-gluon effects are typically mild, but they can be strongly enhanced when hard cuts are applied. The relevant distributions are generally well described by the MC@NLO event generator.Comment: 15 pages, 12 postscript figures. Error corrected in NLO plot for WW transverse-mass distribution. Results unchange

Study of the Linked Dipole Chain Model in heavy quark production at the Tevatron

We present calculations of charm and beauty production at Tevatron within the framework of kT-factorization, using the unintegrated gluon distributions as obtained from the Linked Dipole Chain model. The analysis covers transverse momentum and rapidity distributions and the azimuthal correlations between b and bbar quarks (or rather muons from their decay) which are powerful tests for the different unintegrated gluon distributions. We compare the theoretical results with recent experimental data taken by D0 and CDF collaborations at the Tevatron Run I and II.Comment: 16 page

Stochastic Resonance in Ion Channels Characterized by Information Theory

We identify a unifying measure for stochastic resonance (SR) in voltage dependent ion channels which comprises periodic (conventional), aperiodic and nonstationary SR. Within a simplest setting, the gating dynamics is governed by two-state conductance fluctuations, which switch at random time points between two values. The corresponding continuous time point process is analyzed by virtue of information theory. In pursuing this goal we evaluate for our dynamics the tau-information, the mutual information and the rate of information gain. As a main result we find an analytical formula for the rate of information gain that solely involves the probability of the two channel states and their noise averaged rates. For small voltage signals it simplifies to a handy expression. Our findings are applied to study SR in a potassium channel. We find that SR occurs only when the closed state is predominantly dwelled. Upon increasing the probability for the open channel state the application of an extra dose of noise monotonically deteriorates the rate of information gain, i.e., no SR behavior occurs.Comment: 10 pages, 2 figures, to appear in Phys. Rev.

Towards Combining Individual and Collaborative Work Spaces under a Unified E-Portfolio

Proceedings of: 11th International Conference on Computational Science and Applications (ICCSA 2011). Santander, Spain, June 20-23, 2011E-portfolios in learning environments have been attributed numerous benefits and their presence has been steadily increasing. And so has the variety of environments in which a student participates. Collaborative learning requires communication and resource sharing among team members. Students may participate in multiple teams throughout a long period of time, sometimes even simultaneously. Conventional eportfolios are oriented toward showcasing individual achievements, but they need to also equally reflect collaborative achievements. The approach described in this paper has the objective of offering students an e-portfolio as a local folder their personal computer containing a combined view of their individual and collaborative work spaces. The content of this folder can be synchronized with a remote server thus achieving resource sharing and publication of a clearly identified set of resources.Work partially funded by the Learn3 project, “Plan Nacional de I+D+I TIN2008- 05163/TSI”, the Consejo Social - Universidad Carlos III de Madrid, the Acción Integrada Ref. DE2009-0051, and the “Emadrid: Investigación y desarrollo de tecnologías para el e-learning en la Comunidad de Madrid” project (S2009/TIC-1650).Publicad

A renormalization group invariant scalar glueball operator in the (Refined) Gribov-Zwanziger framework

This paper presents a complete algebraic analysis of the renormalizability of the $d=4$ operator $F^2_{\mu\nu}$ in the Gribov-Zwanziger (GZ) formalism as well as in the Refined Gribov-Zwanziger (RGZ) version. The GZ formalism offers a way to deal with gauge copies in the Landau gauge. We explicitly show that $F^2_{\mu\nu}$ mixes with other $d=4$ gauge variant operators, and we determine the mixing matrix $Z$ to all orders, thereby only using algebraic arguments. The mixing matrix allows us to uncover a renormalization group invariant including the operator $F^2_{\mu\nu}$. With this renormalization group invariant, we have paved the way for the study of the lightest scalar glueball in the GZ formalism. We discuss how the soft breaking of the BRST symmetry of the GZ action can influence the glueball correlation function. We expect non-trivial mass scales, inherent to the GZ approach, to enter the pole structure of this correlation function.Comment: 27 page

The influence of biochar position in a leach bed system anaerobically digesting chicken litter

As a consequence of the rapidly growing poultry industry, chicken litter is becoming an abundant and problematic waste. Anaerobic digestion of chicken litter can mitigate environmental issues while producing valuable by-products. Recent studies have shown that leach bed reactor (LBR) systems are suitable for processing chicken litter and that anaerobic digestion can be enhanced using biochar. This study investigates the influence of biochar position within an LBR system on anaerobic digestion of chicken litter. Compared to a system without biochar, application of biochar in both the LBR (mixed in with the feedstock or as a layer below the feedstock) and coupled leachate tank (LT) increased methane yield by 6 to 8% at 51 days and accelerated VFA degradation and methane production. More significant differences in methane yield were observed at shorter solid retention times. Biochar mixed in feedstock in addition to a filter in the LT performed best in terms of both methane and hydrogen sulfide production, with a 77% reduction in hydrogen sulfide yield and hydrogen sulfide contents maintained below 500 ppm. The enhanced rates of VFA degradation and methane production when applying biochar in both reactors corresponds with observed differences in the methanogen population. Biochar application in both reactors increased the abundance of Methanobacteriales in digestate and Methanosarcinaceae in leachate compared to the control. Microbial attachment and activity on biochar also increased when mixed in feedstock. Increased diversity of the methanogen population throughout the system, as well as increased activity on biochar, may have facilitated the syntrophic relationship between acetogenic bacteria and methanogens, thus accelerating VFA degradation and methane production. These results suggest mixing biochar in feedstock, in addition to a biochar filter in the LT, to enhance anaerobic digestion of chicken litter in this system.Ben A. Collins, Cristian H. Birzer, Stephen P. Kidd, Tony Hall, Paul R. Medwel

Extragenic suppressor mutations in ΔripA disrupt stability and function of LpxA

Background: Francisella tularensis is a Gram-negative bacterium that infects hundreds of species including humans, and has evolved to grow efficiently within a plethora of cell types. RipA is a conserved membrane protein of F. tularensis, which is required for growth inside host cells. As a means to determine RipA function we isolated and mapped independent extragenic suppressor mutants in ΔripA that restored growth in host cells. Each suppressor mutation mapped to one of two essential genes, lpxA or glmU, which are involved in lipid A synthesis. We repaired the suppressor mutation in lpxA (S102, LpxA T36N) and the mutation in glmU (S103, GlmU E57D), and demonstrated that each mutation was responsible for the suppressor phenotype in their respective strains. We hypothesize that the mutation in S102 altered the stability of LpxA, which can provide a clue to RipA function. LpxA is an UDP-N-acetylglucosamine acyltransferase that catalyzes the transfer of an acyl chain from acyl carrier protein (ACP) to UDP-N-acetylglucosamine (UDP-GlcNAc) to begin lipid A synthesis. Results: LpxA was more abundant in the presence of RipA. Induced expression of lpxA in the ΔripA strain stopped bacterial division. The LpxA T36N S102 protein was less stable and therefore less abundant than wild type LpxA protein. Conclusion: These data suggest RipA functions to modulate lipid A synthesis in F. tularensis as a way to adapt to the host cell environment by interacting with LpxA

Photoproduction of J/psi mesons at high energies in parton model and k_t-faktorization approach

We consider J/psi meson photoproduction on protons at high energies at the leading order in alpha_s using conventional parton model and k_t-factorization approach of QCD. It is shown that in the both cases the colour singlet mechanism gives correct description for experimental data from HERA for the total cross section and for the J/psi meson z-spectrum at realistic values of a c-quark mass and meson wave function at the origin Psi (0). At the same time our predictions for p_t-spectrum of J/psi meson and for p_t dependence of the spin parameter alpha obtained in k_t-factorization approach are very different from the results obtained in conventional parton model. Such a way the experimental study of a polarized J/psi meson production at the large p_t should be a direct test of BFKL gluons.Comment: LaTeX2e, 11 pages plus 8 fig. using epsfig.st