Towards a statistical theory of solid dry friction

Wearless dry friction of an elastic block of weight N, driven by an external force F over a rigid substrate, is investigated. The slider and substrate surfaces are both microscopically rough, interacting via a repulsive potential that depends on the local overlap. The model reproduces Amontons's laws which state that the friction force is proportional to the normal loading force N and independent of the nominal surface area. In this model, the dynamic friction force decays for large velocities and approaches a finite static friction for small velocities if the surface profiles are self-affine on small length scales.Comment: Latex, 10 pages. Jounal reference adde

Critical behavior of interacting surfaces with tension

Wetting phenomena, molecular protrusions of lipid bilayers and membrane stacks under lateral tension provide physical examples for interacting surfaces with tension. Such surfaces are studied theoretically using functional renormalization and Monte Carlo simulations. The critical behavior arising from thermally-excited shape fluctuations is determined both for global quantities such as the mean separation of these surfaces and for local quantities such as the probabilities for local contacts.Comment: 13 pages, 17 figures; accepted for publication in The European Physical Journa

ATP binding to a multisubunit enzyme: statistical thermodynamics analysis

Due to inter-subunit communication, multisubunit enzymes usually hydrolyze ATP in a concerted fashion. However, so far the principle of this process remains poorly understood. In this study, from the viewpoint of statistical thermodynamics, a simple model is presented. In this model, we assume that the binding of ATP will change the potential of the corresponding enzyme subunit, and the degree of this change depends on the state of its adjacent subunits. The probability of enzyme in a given state satisfies the Boltzmann's distribution. Although it looks much simple, this model can fit the recent experimental data of chaperonin TRiC/CCT well. From this model, the dominant state of TRiC/CCT can be obtained. This study provided a new way to understand biophysical processes by statistical thermodynamics analysis

On the efficient numerical solution of lattice systems with low-order couplings

We apply the Quasi Monte Carlo (QMC) and recursive numerical integration methods to evaluate the Euclidean, discretized time path-integral for the quantum mechanical anharmonic oscillator and a topological quantum mechanical rotor model. For the anharmonic oscillator both methods outperform standard Markov Chain Monte Carlo methods and show a significantly improved error scaling. For the quantum mechanical rotor we could, however, not find a successful way employing QMC. On the other hand, the recursive numerical integration method works extremely well for this model and shows an at least exponentially fast error scaling

Synthesis of Low Abundant Vitamin D Metabolites and Assaying Their Distribution in Human Serum by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) as a New Tool for Diagnosis and Risk Prediction of Vitamin DRelated Diseases

This chapter provides an overview of versatile and efficient chemical syntheses of vitamin D derivatives by application of either linear or convergent synthesis approaches. Synthesis of the most relevant naturally occurring vitamin D metabolites and their deuterated counterparts to use as calibration and reference standards in LC-MS/MS assays is also shown. The chapter then summarizes the most important mass spectrometric approaches to quantify important vitamin D metabolites in human biofluids. In addition, new developments are described that are aimed at the pathobiological interpretation of the measured vitamin D metabolite distributions in various human diseases

Metabolic engineering of the purine biosynthetic pathway in Corynebacterium glutamicum results in increased intracellular pool sizes of IMP and hypoxanthine

Background: Purine nucleotides exhibit various functions in cellular metabolism. Besides serving as building blocks for nucleic acid synthesis, they participate in signaling pathways and energy metabolism. Further, IMP and GMP represent industrially relevant biotechnological products used as flavor enhancing additives in food industry. Therefore, this work aimed towards the accumulation of IMP applying targeted genetic engineering of Corynebacterium glutamicum. Results: Blocking of the degrading reactions towards AMP and GMP lead to a 45-fold increased intracellular IMP pool of 22 mumol gCDW-1. Deletion of the pgi gene encoding glucose 6-phosphate isomerase in combination with the deactivated AMP and GMP generating reactions, however, resulted in significantly decreased IMP pools (13 mumol gCDW-1). Targeted metabolite profiling of the purine biosynthetic pathway further revealed a metabolite shift towards the formation of the corresponding nucleobase hypoxanthine (102 mumol gCDW-1) derived from IMP degradation. Conclusions: The purine biosynthetic pathway is strongly interconnected with various parts of the central metabolism and therefore tightly controlled. However, deleting degrading reactions from IMP to AMP and GMP significantly increased intracellular IMP levels. Due to the complexity of this pathway further degradation from IMP to the corresponding nucleobase drastically increased suggesting additional targets for future strain optimization

Evaluation of a Mutually Coupled Diversity Receiver

A quick, reliable, and simple evaluation of mutual coupling effects is essential for the optimization of antenna arrays for small mobile communications devices. In recent papers we have proposed novel figures of merit that quantify the impact on diversity reception in terms of scattering matrix of the array and have confirmed the validity of these formulas by practical diversity measurements. The present paper provides an extended analysis of the measurement data and contrasts the benefits of this method of array characterization with existing approaches

Analysis of natural organic matter via fourier transform ion cyclotron resonance mass spectrometry: an overview of recent non‐petroleum applications

Among the different techniques for mass analysis, ultra‐high‐resolution Fourier transform ion cyclotron resonance (FTICR) is the method of choice for highly complex samples, as it offers unrivaled mass accuracy and resolving power, combined with a high degree of flexibility in hybrid instruments as well as for ion activation techniques. FTICR instruments are readily embraced by the biological and biomedical research communities and applied over a wide range of applications for the analysis of biomolecules such as carbohydrates, lipids, nucleic acids, and proteins. In the field of natural organic matter (NOM) analysis, petroleum‐related studies currently dominate FTICR‐MS applications. Recently, however, there is a growing interest in developing high‐performance MS methods for the characterization of NOM samples from natural aquatic and terrestrial environments. Here, we present an overview of FTICR‐MS techniques for complex, non‐petroleum NOM samples, including data analysis and novel tandem mass spectrometry (MS/MS) methods for structural classifications. © 2020 The Authors. Mass Spectrometry Reviews published by John Wiley & Sons Ltd.Peer Reviewe

Absence of non-trivial asymptotic scaling in the Kashchiev model of polynuclear growth

In this brief comment we show that, contrary to previous claims [Bartelt M C and Evans J W 1993 {\it J.\ Phys.\ A} ${\bf 26}$ 2743], the asymptotic behaviour of the Kashchiev model of polynuclear growth is trivial in all spatial dimensions, and therefore lies outside the Kardar-Parisi-Zhang universality class.Comment: 3 pages, 4 postscript figures, uses eps