Wheel–rail contact: experimental study of the creep forces–creepage relationships

The wheel–rail contact problem plays an important role in the simulation methods used to solve railway dynamics problems. As a consequence, many different mathematical models have been developed to calculate wheel–rail contact forces. However, most of them tackle this problem purely from a theoretical point of view and need to be experimentally validated. Such validation could also reveal the influence of certain parameters not taken into account in the mathematical developments. This paper presents the steps followed in building a scaled test-bench to experimentally characterise the wheel–rail contact problem. The results of the longitudinal contact force as a function of the longitudinal creepage are obtained and the divergences with respect to Kalker's simplified theory are analysed. The influence of lateral creepage, angular velocity and certain contaminants such as cutting fluid or high positive friction modifier is also discussed

ANU Radiocarbon Dating Laboratory, General Projects

The laboratory is playing an important role in a number of research projects. Indeed, there is a continuing and increasing need for laboratory generated research involving improvements in dating techniques, analysis, interpretation and reporting of results; parameters fundamental to the validity of dating such as environmental contamination and selection of applicable dating standards. Equally important is participation on a cooperative basis in research generated by other departments and institutions, often involving field work

Polymer reptation and nucleosome repositioning

We consider how beads can diffuse along a chain that wraps them, without becoming displaced from the chain; our proposed mechanism is analogous to the reptation of "stored length" in more familiar situations of polymer dynamics. The problem arises in the case of globular aggregates of proteins (histones) that are wound by DNA in the chromosomes of plants and animals; these beads (nucleosomes) are multiply wrapped and yet are able to reposition themselves over long distances, while remaining bound by the DNA chain.Comment: 9 pages, including 2 figures, to be published in Phys. Rev. Let

Nucleosome-mediated cooperativity between transcription factors

Cooperative binding of transcription factors (TFs) to cis-regulatory regions (CRRs) is essential for precision of gene expression in development and other processes. The classical model of cooperativity requires direct interactions between TFs, thus constraining the arrangement of TFs sites in a CRR. On the contrary, genomic and functional studies demonstrate a great deal of flexibility in such arrangements with variable distances, numbers of sites, and identities of the involved TFs. Such flexibility is inconsistent with the cooperativity by direct interactions between TFs. Here we demonstrate that strong cooperativity among non-interacting TFs can be achieved by their competition with nucleosomes. We find that the mechanism of nucleosome-mediated cooperativity is mathematically identical to the Monod-Wyman-Changeux (MWC) model of cooperativity in hemoglobin. This surprising parallel provides deep insights, with parallels between heterotropic regulation of hemoglobin (e.g. Bohr effect) and roles of nucleosome-positioning sequences and chromatin modifications in gene regulation. Characterized mechanism is consistent with numerous experimental results, allows substantial flexibility in and modularity of CRRs, and provides a rationale for a broad range of genomic and evolutionary observations. Striking parallels between cooperativity in hemoglobin and in transcription regulation point at a new design principle that may be used in range of biological systems

Low-level liquid scintillation spectrometer for ß-counting

A new liquid scintillation (LS) spectrometer has been developed. lt improves the signal to noise ratio of C-14 assays by an order of magnitude compared to conventional LS systems. As a result, precision for a modern sample is 0.2 % and the dating limit is 64 Ky BP for a 15 ml sample of benzene. Sophisticated MCA facilities allow the use of Multiparameter Multichannel Analysis for data validation and age evaluation. Despite the high sophistication, the spectrometer, (named QUANTULUS) is seif contained, microprocessor controlled and user friendly. lt can be used with full advantage in a normal laboratory environment

Application of Fastsim with variable coefficient of friction using twin disc experimental measurements

In the field of railway simulation, it is a general assumption to consider the coefficient of friction as a known and constant value. This hypothesis is clearly not correct as friction is a consequence of the operating conditions (an output, not an input) and many factors can cause friction coefficient to change. In this paper, numerical algorithms based on the simplified theory of Kalker (Fastsim) and capable of modelling variable friction are studied and improved to match experimental measurements. Experimental creep curves from twin disc measurements are used to extract the friction parameters required by the numerical algorithms. Different friction functions are tested to correlate the effect of the contaminants and the pressure on the coefficient of friction. Finally, two examples are shown to highlight the differences between modelling the wheel–rail contact with variable or constant coefficient of friction and their implications in the estimation of the interaction forces and wear.This research was supported by Universitat Politecnica de Valencia (Spain).Rovira Cardete, A.; Roda Buch, A.; Lewis, R.; Marshall, M. (2012). Application of Fastsim with variable coefficient of friction using twin disc experimental measurements. Wear. 274-275:109-126. doi:10.1016/j.wear.2011.08.019S109126274-27

Sequence Effects on DNA Entropic Elasticity

DNA stretching experiments are usually interpreted using the worm-like chain model; the persistence length A appearing in the model is then interpreted as the elastic stiffness of the double helix. In fact the persistence length obtained by this method is a combination of bend stiffness and intrinsic bend effects reflecting sequence information, just as at zero stretching force. This observation resolves the discrepancy between the value of A measured in these experiments and the larger ``dynamic persistence length'' measured by other means. On the other hand, the twist persistence length deduced from torsionally-constrained stretching experiments suffers no such correction. Our calculation is very simple and analytic; it applies to DNA and other polymers with weak intrinsic disorder.Comment: LaTeX; postscript available at http://dept.physics.upenn.edu/~nelson/index.shtm

Validation of multi-body models for simulation in authorisation of rail vehicles

An application of multi-body simulations is to reduce the amount of vehicle on-track testing and present an opportunity for saving the time and costs of vehicle acceptance in regard to running characteristics. One of the objectives of the EU project DynoTRAIN was to define criteria and limits for vehicle model validation. The paper presents investigations carried out by comparing simulations with measurements from a testing campaign using a test train with 4 types of vehicles and a total of 10 force measuring wheelsets and accompanied with continuous measurement of track irregularities and rail profiles. The simulations were performed by using several vehicle models, built in different simulation tools by different partners. The results of the investigations and the criteria and limits proposed for the validation of multi-body vehicle models, intended for simulations of on-track tests, in the framework of railway vehicle authorisations are presented.Une application des simulations multi-corps consiste à réduire la quantité d'essais en ligne et à offrir une opportunité pour économiser le temps et les coûts d'acceptation des Îhicules en ce qui concerne les caractéristiques de fonctionnement dynamiques. L'un des objectifs du projet de l'UE DynoTRAIN était de définir des critères et des limites pour la validation du modèle de Îhicule. Le document présente des recherches effectuées en comparant des simulations avec des mesures à partir d'une campagne de test utilisant un train d'essai avec 4 types de Îhicules et un total de 10 essieux de mesure de force roue-rail et accompagnés d'une mesure continue des irrégularités de voie et des profils de rail. Les simulations ont été réalisées en utilisant plusieurs modèles de Îhicules, construits dans différents outils de simulation par différents partenaires. Les résultats des enquêtes et les critères et limites proposés pour la validation des modèles de Îhicules multi-corps, destinés à des simulations de tests sur voie réelle, dans le cadre des autorisations de Îhicules ferroviaires sont présentés

Dose-related effects of smallpox vaccine

BACKGROUND: We conducted a double-blind, randomized trial of three dilutions of vaccinia virus vaccine in previously unimmunized adults in order to assess the clinical success rates, humoral responses, and virus-specific activity of cytotoxic T cells and interferon-gamma-producing T cells. METHODS: Sixty healthy adults were inoculated intradermally by bifurcated needle with undiluted vaccine (dose, 10(7.8) plaque-forming units [pfu] per milliliter), a 1:10 dilution (dose, 10(6.5) pfu per milliliter), or a 1:100 dilution (dose, 10(5.0) pfu per milliliter); there were 20 subjects in each group. The subjects were monitored with respect to vesicle formation (an indicator of successful vaccination), the viral titer at the time of peak lesion formation, antiviral antibodies, and cellular immune responses. RESULTS: A vaccinia vesicle developed in 19 of the 20 subjects who received undiluted vaccine (95 percent), 14 of the 20 who received the 1:10 dilution (70 percent), and 3 of the 20 who received the 1:100 dilution (15 percent). One month after vaccination, 34 of 36 subjects with vesicles had antibody responses, as compared with only 1 of 24 subjects without clinical evidence of vaccinia virus replication. Vigorous cytotoxic T-cell and interferon-gamma responses occurred in 94 percent of subjects with vesicles, and a cytotoxic T-cell response occurred in only one subject without a vesicle. CONCLUSIONS: The vaccinia virus vaccine (which was produced in 1982 or earlier) still has substantial potency when administered by a bifurcated needle to previously unvaccinated adults. Diluting the vaccine reduces the rate of successful vaccination. The development of vesicular skin lesions after vaccination correlates with the induction of the antibody and T-cell responses that are considered essential for clearing vaccinia virus infections

Dynamics of railway freight vehicles

This paper summarises the historical development of railway freight vehicles and how vehicle designers have tackled the difficult challenges of producing running gear which can accommodate the very high tare to laden mass of typical freight wagons whilst maintaining stable running at the maximum required speed and good curving performance. The most common current freight bogies are described in detail and recent improvements in techniques used to simulate the dynamic behaviour of railway vehicles are summarised and examples of how these have been used to improve freight vehicle dynamic behaviour are included. A number of recent developments and innovative components and sub systems are outlined and finally two new developments are presented in more detail: the LEILA bogie and the SUSTRAIL bogie