Models of granular ratchets

We study a general model of granular Brownian ratchet consisting of an asymmetric object moving on a line and surrounded by a two-dimensional granular gas, which in turn is coupled to an external random driving force. We discuss the two resulting Boltzmann equations describing the gas and the object in the dilute limit and obtain a closed system for the first few moments of the system velocity distributions. Predictions for the net ratchet drift, the variance of its velocity fluctuations and the transition rates in the Markovian limit, are compared to numerical simulations and a fair agreement is observed.Comment: 15 pages, 4 figures, to be published on Journal of Statistical Mechanics: Theory and Experiment

Protein accumulation in the endoplasmic reticulum as a non-equilibrium phase transition

Several neurological disorders are associated with the aggregation of aberrant proteins, often localized in intracellular organelles such as the endoplasmic reticulum. Here we study protein aggregation kinetics by mean-field reactions and three dimensional Monte carlo simulations of diffusion-limited aggregation of linear polymers in a confined space, representing the endoplasmic reticulum. By tuning the rates of protein production and degradation, we show that the system undergoes a non-equilibrium phase transition from a physiological phase with little or no polymer accumulation to a pathological phase characterized by persistent polymerization. A combination of external factors accumulating during the lifetime of a patient can thus slightly modify the phase transition control parameters, tipping the balance from a long symptomless lag phase to an accelerated pathological development. The model can be successfully used to interpret experimental data on amyloid-\b{eta} clearance from the central nervous system

Noise Rectification and Fluctuations of an Asymmetric Inelastic Piston

We consider a massive inelastic piston, whose opposite faces have different coefficients of restitution, moving under the action of an infinitely dilute gas of hard disks maintained at a fixed temperature. The dynamics of the piston is Markovian and obeys a continuous Master Equation: however, the asymmetry of restitution coefficients induces a violation of detailed balance and a net drift of the piston, as in a Brownian ratchet. Numerical investigations of such non-equilibrium stationary state show that the velocity fluctuations of the piston are symmetric around the mean value only in the limit of large piston mass, while they are strongly asymmetric in the opposite limit. Only taking into account such an asymmetry, i.e. including a third parameter in addition to the mean and the variance of the velocity distribution, it is possible to obtain a satisfactory analytical prediction for the ratchet drift velocity.Comment: 6 pages, 5 figures, to be published on Europhysics Letters; some references have been adde

EAPC task force on education for psychologists in palliative care

It is argued that psychological aspects of care and psychosocial problems are essential components of palliative care. However, the provision of appropriate services remains somewhat arbitrary. Unlike medical and nursing care, which are clearly delivered by doctors and nurses respectively, psychological and psychosocial support in palliative care are not assigned exclusively to psychologists. It is generally expected that all professionals working in palliative care should have some knowledge of the psychological dynamics in terminal illness, as well as skills in communication and psychological risk assessment. On the one hand, palliative care education programmes for nurses and doctors comprise a considerable amount of psychological and psychosocial content. On the other hand, only a few palliative care associations provide explicit information on the role and tasks of psychologists in palliative care. Psychologists’ associations do not deal much with this issue either. If they refer to it at all, it is in the context of the care of the aged, end-of-life care or how to deal with grief

A longer XMM-Newton look at I Zwicky 1: Distinct modes of X-ray spectral variability

The short-term spectral variability of the narrow-line Seyfert 1 galaxy I Zwicky 1 (I Zw 1) as observed in an 85 ks XMM-Newton observation is discussed in detail. I Zw 1 shows distinct modes of variability prior to and after a flux dip in the broad-band light curve. Before the dip the variability can be described as arising from changes in shape and normalisation of the spectral components. Only changes in normalisation are manifested after the dip. The change in the mode of behaviour occurs on dynamically short timescales in I Zw 1. The data suggest that the accretion-disc corona in I Zw 1 could have two components that are co-existing. The first, a uniform, physically diffuse plasma responsible for the "typical'' long-term (e.g. years) behaviour; and a second compact, centrally located component causing the rapid flux and spectral changes. This compact component could be the base of a short or aborted jet as sometimes proposed for radio-quiet active galaxies. Modelling of the average and time-resolved rms spectra demonstrate that a blurred Compton-reflection model can describe the spectral variability if we allow for pivoting of the continuum component prior to the dip.Comment: 8 pages, 9 figures. Accepted by MNRA

The fungal etiology of gout and hyperuricemia: the antifungal mode of action of colchicine

The concept of a fungal/mycotoxin etiology of gout/hyperuricemia in humans was first reported by Costantini in 1989. Gout and/or hyperuricemia have been induced in animals by the fungal species Ustilago maydis, Chaetomium trilaterale, Saccharomyces cerevisiae, and by the mycotoxins, aflatoxin, ochratoxin, oosporein, oxalic acid. Gout and/or hyperuricemia have been induced in humans by the yeast Candida utilis and by the fungal metabolites cyclosporin, ergotamine and penicillin. Gout is documented to be etiologically linked to beer, a Saccharomyces fermented beverage. Beers contain significant amounts of ochratoxin and large amounts (7 to 9 mg/dl of uric acid, a metabolite produced by the brewer's yeast Saccharomyces cerevisiae. Consistent with the fungal etiology of gout and hyperuricemia, the mode of action of colchicine in the treatment of gout is antifungal. Colchicine shares antitubulin activity with griseofulvin, a potent antifungal antibiotic. Griseofulvin is as equally effective in the treatment of gout as colchicine. Similarly, another antitubulin drug, vinblastine is also antifungal and effective in the treatment of gout. All of the other drugs used to treat gout and/or hyperuricemia possess antifungal activity.Biomedical Reviews 1992; 1: 47-52

Abstraction and Refinement in Configuration Structures

An abstraction operator for configuration structures is defined and it is proven that it is left inverse to the traditional refinement operator. The abstraction operator describes how concrete behaviour looks when observed from a more abstract level, where the difference between concrete and abstract is given by a transformation mapping. This generates a notion of implementation: L is said to implement H iff L is mapped to H by the abstraction operator. The implementation relation generated by the abstraction operator is strictly more general than the implementation function defined by a refinement operator, thus allowing a more flexible design process for distributed systems