Non-Reversibility of Molecular Dynamics Trajectories

We study the non-reversibility of molecular dynamics trajectories arising from the amplification of rounding errors. We analyse the causes of such behaviour and give arguments, indicating that this does not pose a significant problem for Hybrid Monte Carlo computations. We present data for pure SU(3) gauge theory and for QCD with dynamical fermions on small lattices to illustrate and to support some of our ideas.Comment: 3 pages LATEX, 4 color figures included using epsf. Talk presented at LATTICE96(algorithms

Influential Article Review - Examining the Nature of German Retail and Commercial Customers

This paper examines retail. We present insights from a highly influential paper. Here are the highlights from this paper: Based on a unique data set of 909 defaulted retail and commercial (self-employed and SMEs) credit customers in Germany, whose original loans were made by 123 different banks, our article confirms a significant positive influence of collateral, and of amicable agreements between the debtor and the bank (redemption), on the recovery rate [1 − loss given default (LGD)]. In a further analysis of collateral, systematic biases between the realized market price and the expected market values of real estate are revealed, even though the appraisal reports should have already considered all factors influencing the value. Using valuations that were adjusted for these recognized biases, we can increase the explanatory power of the underlying models. Moreover, we compare these models to models that apply, as is common practice in the banking industry, flat haircuts to collateral values and show the superior performance of our proposed approach. For our overseas readers, we then present the insights from this paper in Spanish, French, Portuguese, and German

Participation with online recovery specific groups - findings from the UK Life in Recovery survey 2015

As the concept of recovery has expanded, and become embedded in drug and alcohol policy, so too has the proliferation of online recovery support. This article explores data from the UK Life in Recovery survey, focusing on online recovery methods categorized as online groups, websites, and smartphone applications. Although 301 people (39.30%) reported involvement with at least one online recovery method, chi-squared tests reveal significant associations between people in stable recovery (5 years or more) and the use of recovery applications (Cramer’s V = .114), as well as between people in full-time employment and the use of online recovery websites or recovery applications. Having dependent children was not associated with use of any online recovery method, yet gender was (Cramer’s V = .088). This study extends the relatively limited literature and knowledge base of online recovery methods. Although the evidence points to higher engagement of recovery websites and apps for people in stable recovery, encouraging online recovery methods for individuals in early recovery may support recovery efforts when the risk of returning to substance misuse and active using social networks remains high. Further research should investigate the mechanisms of recovery change, with a focus on gender differences

Recovery capital pathways : modelling the components of recovery wellbeing.

In recent years, there has been recognition that recovery is a journey that involves the growth of recovery capital. Thus, recovery capital has become a commonly used term in addiction treatment and research yet its operationalization and measurement has been limited. Due to these limitations, there is little understanding of long-term recovery pathways and their clinical application. We used the data of 546 participants from eight different recovery residences spread across Florida, USA. We calculated internal consistency for recovery capital and wellbeing, then assessed their factor structure via confirmatory factor analysis. The relationships between time, recovery barriers and strengths, wellbeing and recovery capital, as well as the moderating effect of gender, were estimated using structural equations modelling. The proposed model obtained an acceptable fit (χ(2) (141, N=546)=533.642, p<0.001; CMIN/DF=3.785; CFI=0.915; TLI=0.896; RMSEA=0.071). Findings indicate a pathway to recovery capital that involves greater time in residence ('retention'), linked to an increase in meaningful activities and a reduction in barriers to recovery and unmet needs that, in turn, promote recovery capital and positive wellbeing. Gender differences were observed. We tested the pathways to recovery for residents in the recovery housing population. Our results have implications not only for retention as a predictor of sustained recovery and wellbeing but also for the importance of meaningful activities in promoting recovery capital and wellbeing. [Abstract copyright: Copyright © 2017 Elsevier B.V. All rights reserved.

Two Simple Approaches to Sol-Gel Transition

We represent a theory of polymer gelation as an analogue of liquid-glass transition in which elastic fields of stress and strain shear components appear spontaneously as a consequence of the cross-linking of macromolecules. This circumstance is explained on the basis of obvious combinatoric arguments as well as a synergetic Lorenz system, where the strain acts as an order parameter, a conjugate field is reduced to the elastic stress, and the number of cross-links is a control parameter. Both the combinatoric and synergetic approaches show that an anomalous slow dependence of the shear modulus on the number of cross-links is obtained.Comment: 10 pages, LaTe

Instabilities and Non-Reversibility of Molecular Dynamics Trajectories

The theoretical justification of the Hybrid Monte Carlo algorithm depends upon the molecular dynamics trajectories within it being exactly reversible. If computations were carried out with exact arithmetic then it would be easy to ensure such reversibility, but the use of approximate floating point arithmetic inevitably introduces violations of reversibility. In the absence of evidence to the contrary, we are usually prepared to accept that such rounding errors can be made small enough to be innocuous, but in certain circumstances they are exponentially amplified and lead to blatantly erroneous results. We show that there are two types of instability of the molecular dynamics trajectories which lead to this behavior, instabilities due to insufficiently accurate numerical integration of Hamilton's equations, and intrinsic chaos in the underlying continuous fictitious time equations of motion themselves. We analyze the former for free field theory, and show that it is essentially a finite volume effect. For the latter we propose a hypothesis as to how the Liapunov exponent describing the chaotic behavior of the fictitious time equations of motion for an asymptotically free quantum field theory behaves as the system is taken to its continuum limit, and explain why this means that instabilities in molecular dynamics trajectories are not a significant problem for Hybrid Monte Carlo computations. We present data for pure $SU(3)$ gauge theory and for QCD with dynamical fermions on small lattices to illustrate and confirm some of our results.Comment: 28 pages latex with 19 color postscript figures included by eps

Clover improvement, spectrum and Atiyah-Singer index theorem for the Dirac operator on the lattice

We study the role of the O(a)-improving clover term for the spectrum of the lattice Dirac operator using cooled and thermalized SU(2) gauge field configurations. For cooled configurations we observe improvement of the spectral properties when adding the clover term. For the thermalized case (12^4, beta = 2.4) without clover term we find a rather bad separation of physical and doubler branches making a probabilistic interpretation of the Atiyah-Singer index theorem on the lattice questionable for this beta and lattice size. Adding the clover term leads to the creation of additional real eigenvalues which come in pairs of opposite chirality thus further worsening the situation for the index theorem.Comment: Revised version, to appear in Nucl. Phys. B; discussion reworded, References update

Effects of pioneering plants on microbial structures and functions in a glacier forefield

This study investigates the small-scale spatial impact of the pioneering plant Leucanthemopsis alpina (L.) Heywood (L. alpina) on biological and chemical-physical parameters in an early successional stage of a glacier forefield. Considering the frequent occurrence of isolated patches of this pioneer plant in the forefield of the Dammaglacier (Switzerland), we hypothesized that the impact of the plant would establish gradients in nutrients, and microbial community structure and activity that may be of importance for the successional processes occurring in the forefield. Our results indicated that, in young successional soils, the rhizosphere effect of L. alpina plant patches can influence bacterial cell numbers and activities not only within the root zone, but even at 20cm distance from the plant. Microbial cell counts, active cells, and saccharase, glucosidase, and acid phosphatase activities revealed significant distance effects, decreasing from soil directly underneath the plant to soils at 20 and 40cm distance. Soil chemical and physical parameters did not exhibit significant trends. Fingerprinting analysis of amplified 16S rDNA fragments was used to characterize the microbial community. A selective effect of the plant on the microbial community could not be shown because the bacterial communities were similar regardless of distance to the plan

Size matters for single-cell C4 photosynthesis in Bienertia

Bienertia cycloptera belongs to a diverse set of plants, recently discovered to perform C4 photosynthesis within individual mesophyll cells. How these plants accomplish high photosynthetic efficiency without adopting Kranz anatomy remains unanswered. By modelling the processes of diffusion, capture, and release of carbon dioxide and oxygen inside a typical Bienertia mesophyll cell geometry, we show that a spatial separation as low as 10 μm between the primary and the secondary carboxylases, can, on its own, provide enough diffusive resistance to sustain a viable C4 pathway at 20 °C, with a CO2 leakage <35%. This critical separation corresponds to a cell diameter of 50 μm, consistent with the observed range where Bienertia’s mesophyll cells start to develop their characteristic mature anatomy. Our results are robust to significant alterations in model assumptions and environmental conditions, their applicability extending even to aquatic plants

The Analysis of Space-Time Structure in QCD Vacuum II: Dynamics of Polarization and Absolute X-Distribution

We propose a framework for quantitative evaluation of dynamical tendency for polarization in arbitrary random variable that can be decomposed into a pair of orthogonal subspaces. The method uses measures based on comparisons of given dynamics to its counterpart with statistically independent components. The formalism of previously considered X-distributions is used to express the aforementioned comparisons, in effect putting the former approach on solid footing. Our analysis leads to definition of a suitable correlation coefficient with clear statistical meaning. We apply the method to the dynamics induced by pure-glue lattice QCD in local left-right components of overlap Dirac eigenmodes. It is found that, in finite physical volume, there exists a non-zero physical scale in the spectrum of eigenvalues such that eigenmodes at smaller (fixed) eigenvalues exhibit convex X-distribution (positive correlation), while at larger eigenvalues the distribution is concave (negative correlation). This chiral polarization scale thus separates a regime where dynamics enhances chirality relative to statistical independence from a regime where it suppresses it, and gives an objective definition to the notion of "low" and "high" Dirac eigenmode. We propose to investigate whether the polarization scale remains non-zero in the infinite volume limit, in which case it would represent a new kind of low energy scale in QCD.Comment: v2: 38 pages, 12 figures, author-preferred version; v3: journal-preferred versio