385 research outputs found
Dominant Reaction Pathways in High Dimensional Systems
This paper is devoted to the development of a theoretical and computational
framework to efficiently sample the statistically significant thermally
activated reaction pathways, in multi-dimensional systems obeying Langevin
dynamics. We show how to obtain the set of most probable reaction pathways and
compute the corrections due to quadratic thermal fluctuations around such
trajectories. We discuss how to obtain predictions for the evolution of
arbitrary observables and how to generate conformations which are
representative of the transition state ensemble. We present an illustrative
implementation of our method by studying the diffusion of a point particle in a
2-dimensional funneled external potential.Comment: 18 pages, 7 figures. Improvement in the text and in the figures.
Version submitted for publicatio
Entanglement of two delocalised electrons
Several convenient formulae for the entanglement of two indistinguishable
delocalised spin-1/2 particles are introduced. This generalizes the standard
formula for concurrence, valid only in the limit of localised or
distinguishable particles. Several illustrative examples are given.Comment: 4 page
Puckering Free Energy of Pyranoses: an NMR and Metadynamics--Umbrella Sampling Investigation
We present the results of a combined metadynamics--umbrella sampling
investigation of the puckered conformers of pyranoses described using the
gromos 45a4 force field. The free energy landscape of Cremer--Pople puckering
coordinates has been calculated for the whole series of alpha and beta
aldohexoses, showing that the current force field parameters fail in
reproducing proper puckering free energy differences between chair conformers.
We suggest a modification to the gromos 45a4 parameter set which improves
considerably the agreement of simulation results with theoretical and
experimental estimates of puckering free energies. We also report on the
experimental measurement of altrose conformers populations by means of NMR
spectroscopy, which show good agreement with the predictions of current
theoretical models
Interplay between distribution of live cells and growth dynamics of solid tumours
Experiments show that simple diffusion of nutrients and waste molecules is not sufficient to explain the typical multilayered structure of solid tumours, where an outer rim of proliferating cells surrounds a layer of quiescent but viable cells and a central necrotic region. These experiments challenge models of tumour growth based exclusively on diffusion. Here we propose a model of tumour growth that incorporates the volume dynamics and the distribution of cells within the viable cell rim. The model is suggested by in silico experiments and is validated using in vitro data. The results correlate with in vivo data as well, and the model can be used to support experimental and clinical oncology
Gender differences in the association between education and the incidence of cardiovascular events in Northern Italy.
Background: The educational differences in the incidence of major cardiovascular events are under-studied in Southern Europe and among women. Methods: The study sample includes n\u2009=\u20095084 participants to 4 population-based Northern Italian cohorts, aged 35-74 at baseline and with no previous cardiovascular events. The follow-up to ascertain the first onset of coronary heart disease (CHD) or ischaemic stroke ended in 2002. At baseline, major cardiovascular risk factors were investigated adopting the standardized MONICA procedures. Two educational classes were obtained from years of schooling. Age- and risk factors-adjusted hazard ratios of first CHD or ischaemic stroke were estimated through sex-specific separate Cox models (high education as reference). RESULTS: Median follow-up time was 12 years. Event rates were 6.38 (CHD) and 2.12 (ischaemic stroke) per 1000 person-years in men; and 1.59 and 0.94 in women. In men, low education was associated with higher mean Body Mass Index and prevalence of diabetes and cigarette smokers; but also with higher HDL cholesterol and a more favourable alcohol intake pattern. Less-educated women had higher mean systolic blood pressure, Body Mass Index and HDL cholesterol and were more likely to have diabetes. Men and women in the low educational class had a 2-fold increase in ischaemic stroke and CHD incidence, respectively, after controlling for major risk factors. Education was not associated with CHD incidence in men. Higher ischaemic stroke rates were observed among more educated women. Conclusion: In this northern Italian population, the association between education and cardiovascular risk seems to vary by gender
Optical conductivity of the Hubbard model at finite temperature
The optical conductivity, , of the two dimensional one-band
Hubbard model is calculated at finite temperature using exact diagonalization
techniques on finite clusters. The in-plane d.c. resistivity, , is
also evaluated. We find that at large U/t and temperature T, is
approximately linear with temperature, in reasonable agreement with experiments
on high-T superconductors. Moreover, we note that displays
charge excitations, a mid-infrared (MIR) band and a Drude peak, also as
observed experimentally. The combination of the Drude peak and the MIR
oscillator strengths leads to a conductivity that decays slower than
at energies smaller than the insulator gap near half-filling.Comment: 12 pages, 3 figures appended, Revtex version 2.0, preprin
Strong correlation effects in the doped Hubbard model in infinite dimensions
The density of states and the optical conductivity of the doped Hubbard model
on a Bethe lattice with infinite connectivities have been studied using an
analytic variant of the Lanczos continued fraction method. The spectral weight
of the gap states and the position of the chemical potential upon hole or
electron doping have been studied. We argue that the strong correlation effects
such as gap states and midinfrared band shown in two dimensions also appear in
infinite dimensions.Comment: 9 pages, revtex, 3 figures upon reques
Relation between the Liquid Spinodal Pressure and the Lateral Pressure Profile at the Liquid-Vapor Interface
International audienc
po 126 survival probability of human breast carcinoma cells to radiation treatment role of cell fusion and of a syncytin1 homologous protein
Introduction The success of radiotherapy depends on the ability to inhibit tumour growth, and relapse after therapy is determined by cells that retain their clonogenic potential. The radiation sensitivity of isolated tumour cell clones in vitro is routinely determined with clonogenic assays. In solid tumours, however, clonogenic cells are not isolated and we carried out experiments to measure the influences of cell-cell contact on their proliferative potential. To this end we developed a new experimental approach to measure the effects of radiation on tumour cell populations. The observations can be understood with the help of a novel stochastic model with a well-defined biological basis. Material and methods T47D cells (human breast carcinoma) were grown at various concentrations in F(flat)-bottom and V-bottom wells of 96-well culture plates. The spheroid outgrowth method was also used to obtain densely-packed tissue cell cultures. A Gammacell40 irradiator equipped with a 137Cs source was used to treat cell cultures. Cell fusion was assessed by confocal microscopy. Syncytin 1 expression was assessed by RT-PCR and by flow cytometry using an anti-HERV antibody (clone ab7115, Abcam). Results and discussions The probability of cell survival after 8 Gy radiation treatment increased ~4.7 times when the cells were grown in V-bottom wells as compared to cells grown in F-bottom wells (p(survival)=0.0113 and 0.0024, respectively). Microscopic inspections of tissue-like cultures showed that after treatment cell populations were mostly composed of giant cells with multiple nuclei. Cytoplasmic bridges joining different cells were clearly visible. Giant cells and cytoplasmic bridges disappeared at later times (>600 hours) when the cells displayed normal morphology and started to proliferate again. Sequence analysis of cloned RT-PCR products showed that cells expressed a Syncytin 1 homologous protein (Sp). Flow cytometry assays confirmed cytoplasmic expression of Sp and revealed that Sp translocated to the cell surface of irradiated cells committed to death. The fraction of cells surviving 8 Gy treatment was significantly reduced in cultures treated with anti-Sp antibodies. Conclusion Our experimental findings indicate that recovery of breast tumours from radiation is very likely to involve complex pathways that act at the cell population level and that include events of cell fusion mediated by a protein homologous to Syncytin 1
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