Thermodynamics and Kinetics of Folding of a Small Peptide

We study the thermodynamics and kinetics of folding for a small peptide. Our data rely on Monte Carlo simulations where the interactions among all atoms are taken into account. Monte Carlo kinetics is used to study folding of the peptide at suitable temperatures. The results of these canonical simulations are compared with that of a generalized-ensemble simulation. Our work demonstrates that concepts of folding which were developed in the past for minimalist models hold also for this peptide when simulated with an all-atom force field

Order-dependent mappings: strong coupling behaviour from weak coupling expansions in non-Hermitian theories

A long time ago, it has been conjectured that a Hamiltonian with a potential of the form x^2+i v x^3, v real, has a real spectrum. This conjecture has been generalized to a class of so-called PT symmetric Hamiltonians and some proofs have been given. Here, we show by numerical investigation that the divergent perturbation series can be summed efficiently by an order-dependent mapping (ODM) in the whole complex plane of the coupling parameter v^2, and that some information about the location of level crossing singularities can be obtained in this way. Furthermore, we discuss to which accuracy the strong-coupling limit can be obtained from the initially weak-coupling perturbative expansion, by the ODM summation method. The basic idea of the ODM summation method is the notion of order-dependent "local" disk of convergence and analytic continuation by an order-dependent mapping of the domain of analyticity augmented by the local disk of convergence onto a circle. In the limit of vanishing local radius of convergence, which is the limit of high transformation order, convergence is demonstrated both by numerical evidence as well as by analytic estimates.Comment: 11 pages; 12 figure

Tan(beta)-enhanced supersymmetric corrections to the anomalous magnetic moment of the muon

We report on a two-loop supersymmetric contribution to the magnetic moment (g-2)_mu of the muon which is enhanced by two powers of tan(beta). This contribution arises from a shift in the relation between the muon mass and Yukawa coupling and can increase the supersymmetric contribution to (g-2)_mu sizably. As a result, if the currently observed 3 sigma deviation between the experimental and SM theory value of (g-2)_mu is analyzed within the Minimal Supersymmetric Standard Model (MSSM), the derived constraints on the parameter space are modified significantly: If (g-2)_mu is used to determine tan(beta) as a function of the other MSSM parameters, our corrections decrease tan(beta) by roughly 10% for tan(beta)=50.Comment: 4 pages, 1 figur

Behavioural, Electrophysiological and Neurostimulatory Investigations into Developmental Prosopagnosia

Developmental prosopagnosia (DP) is the difficulty or inability to recognise a face and may affect up to 2.9 percent of the population. There is controversy over whether these impairments are perceptual or memorial in nature, and uncertainty about their stability over time and how to remediate symptoms. In the first stage, a battery of ten tests was assembled to assess a wide range of face recognition skills in DP (n = 11) and compared to a control group (Chapter Two). The majority of DPs showed no signs of impaired face perception but profound face memory deficits. To seek electrophysiological corroboration of these impairments, the DPs (n = 8) were given three behavioural tasks known to elicit specific event related potentials (Chapter Three), assessing face perception (N170), face familiarity (N250r) and semantic access (N400). During the experiment, caloric vestibular stimulation (CVS) was also administered to see if it could reduce symptoms. The tasks revealed intact face perception and impaired accuracy in both memory based tasks, corroborated by an atypical N400. Subtle effects of CVS were observed in all measures of the face familiarity task but not at a level that was clinically relevant. To establish, for the first time, whether the impairments in DP are consistent over time, the effects in Chapter Three were replicated (n = 7)(Chapter Four). A similar pattern emerged and test-retest correlations showed high reliability overtime in the familiarity task but not the semantic access task. This implies that reliable 'diagnosis' of developmental prosopagnosia should be based on judgements of face familiarity and not associated with semantic activity. The beneficial effects of CVS were again present in the N250r behavioural measures and were limited to familiar faces only. This implies that CVS is optimising memory recall for face representations. The source of impairments was consistently shown to be memorial in nature and future studies may wish to explore further divisions of memory in DP such as whether impairments are associated with encoding or recall. The thesis also demonstrates the potential for CVS as both a therapeutic tool and cognitive enhancer, and justify more robust trials investigation

Final spins from the merger of precessing binary black holes

The inspiral of binary black holes is governed by gravitational radiation reaction at binary separations r < 1000 M, yet it is too computationally expensive to begin numerical-relativity simulations with initial separations r > 10 M. Fortunately, binary evolution between these separations is well described by post-Newtonian equations of motion. We examine how this post-Newtonian evolution affects the distribution of spin orientations at separations r ~ 10 M where numerical-relativity simulations typically begin. Although isotropic spin distributions at r ~ 1000 M remain isotropic at r ~ 10 M, distributions that are initially partially aligned with the orbital angular momentum can be significantly distorted during the post-Newtonian inspiral. Spin precession tends to align (anti-align) the binary black hole spins with each other if the spin of the more massive black hole is initially partially aligned (anti-aligned) with the orbital angular momentum, thus increasing (decreasing) the average final spin. Spin precession is stronger for comparable-mass binaries, and could produce significant spin alignment before merger for both supermassive and stellar-mass black hole binaries. We also point out that precession induces an intrinsic accuracy limitation (< 0.03 in the dimensionless spin magnitude, < 20 degrees in the direction) in predicting the final spin resulting from the merger of widely separated binaries.Comment: 20 pages, 16 figures, new PN terms, submitted to PR