3,073 research outputs found
Particle interactions and lattice dynamics: Scenarios for efficient bidirectional stochastic transport?
Intracellular transport processes driven by molecular motors can be described
by stochastic lattice models of self-driven particles. Here we focus on
bidirectional transport models excluding the exchange of particles on the same
track. We explore the possibility to have efficient transport in these systems.
One possibility would be to have appropriate interactions between the various
motors' species, so as to form lanes. However, we show that the lane formation
mechanism based on modified attachment/detachment rates as it was proposed
previously is not necessarily connected to an efficient transport state and is
suppressed when the diffusivity of unbound particles is finite. We propose
another interaction mechanism based on obstacle avoidance that allows to have
lane formation for limited diffusion. Besides, we had shown in a separate paper
that the dynamics of the lattice itself could be a key ingredient for the
efficiency of bidirectional transport. Here we show that lattice dynamics and
interactions can both contribute in a cooperative way to the efficiency of
transport. In particular, lattice dynamics can decrease the interaction
threshold beyond which lanes form. Lattice dynamics may also enhance the
transport capacity of the system even when lane formation is suppressed.Comment: 25 pages, 17 figures, 2 table
Chaotic properties of systems with Markov dynamics
We present a general approach for computing the dynamic partition function of
a continuous-time Markov process. The Ruelle topological pressure is identified
with the large deviation function of a physical observable. We construct for
the first time a corresponding finite Kolmogorov-Sinai entropy for these
processes. Then, as an example, the latter is computed for a symmetric
exclusion process. We further present the first exact calculation of the
topological pressure for an N-body stochastic interacting system, namely an
infinite-range Ising model endowed with spin-flip dynamics. Expressions for the
Kolmogorov-Sinai and the topological entropies follow.Comment: 4 pages, to appear in the Physical Review Letter
Intersection of two TASEP traffic lanes with frozen shuffle update
Motivated by interest in pedestrian traffic we study two lanes
(one-dimensional lattices) of length that intersect at a single site. Each
lane is modeled by a TASEP (Totally Asymmetric Exclusion Process). The
particles enter and leave lane (where ) with probabilities
and , respectively. We employ the `frozen
shuffle' update introduced in earlier work [C. Appert-Rolland et al, J. Stat.
Mech. (2011) P07009], in which the particle positions are updated in a fixed
random order. We find analytically that each lane may be in a `free flow' or in
a `jammed' state. Hence the phase diagram in the domain
consists of four regions with boundaries
depending on and . The regions meet in a single point on the
diagonal of the domain. Our analytical predictions for the phase boundaries as
well as for the currents and densities in each phase are confirmed by Monte
Carlo simulations.Comment: 7 figure
Multiple primary cancers in the Vaud Cancer Registry, Switzerland, 1974-89.
Data collected by the Cancer Registry of the Swiss Canton of Vaud (whose population in 1980 was about 530,000 inhabitants) were used to estimate the incidence of second metachronous primary cancers following any specific neoplasm. Among 34,615 cases of incident neoplasms registered between 1974 and 1989 and followed through integrated active follow-up to the end of 1989, for a total of 118,241 person-years at risk, there were 2,185 second primaries (1,280 males, 905 females). For both sexes, the standardised incidence ratios (SIR) were significantly elevated by about 20%. Overall significantly elevated ratios were registered for cancers of the oral cavity and pharynx (SIR = 1.6 for males, 2.0 for females), oesophagus in males (SIR = 1.5), lung in males (SIR = 1.4), skin melanoma (SIR = 1.7 for males, 1.5 for females), non-melanomatous skin cancers (SIR = 1.6 for males, 1.5 for females), female breast (SIR = 1.3), kidney (SIR = 1.5 for males, 1.9 for females), and thyroid in males (SIR = 2.4). When specific first cancer sites were considered, the SIR following a cancer of the oral cavity and pharynx was around 3 in both sexes, mainly on account of a substantial excess of second primaries of the oral cavity, oesophagus, larynx and lung. The overall SIR following laryngeal cancer was 3.0, and significant excesses were observed for oral cavity and pharynx, oesophagus and lung. After lung cancer, the overall SIR was 1.7 for males and 2.6 for females, and significantly elevated SIRs were observed for oral cavity, lung and oesophagus. Following non-melanomatous skin cancers, elevated SIRs were observed in both sexes for skin melanoma and non-melanomas. The incidence of any cancer after breast cancer was significantly elevated (SIR = 1.2), mainly on account of an elevated risk of subsequent breast cancer (SIR = 1.7). With reference to cervical cancer, there was a significant excess for any subsequent primary (SIR = 1.6), and for lung cancer (SIR = 7.8). Significantly elevated SIRs were observed for kidney following bladder cancer, and for bladder after kidney cancer. In both sexes, the incidence of cancers of any site was elevated following leukaemias (SIR = 1.7 for males, 2.5 for females), and a significant excess was registered for lung in males and non-melanomatous skin cancers in both sexes.(ABSTRACT TRUNCATED AT 400 WORDS
3-D image-based numerical computations of snow permeability: links to specific surface area, density, and microstructural anisotropy
We used three-dimensional (3-D) images of snow microstructure to carry out numerical estimations of the full tensor of the intrinsic permeability of snow (<b>K</b>). This study was performed on 35 snow samples, spanning a wide range of seasonal snow types. For several snow samples, a significant anisotropy of permeability was detected and is consistent with that observed for the effective thermal conductivity obtained from the same samples. The anisotropy coefficient, defined as the ratio of the vertical over the horizontal components of <b>K</b>, ranges from 0.74 for a sample of decomposing precipitation particles collected in the field to 1.66 for a depth hoar specimen. Because the permeability is related to a characteristic length, we introduced a dimensionless tensor <b>K</b>*=<b>K</b>/<i>r</i><sub>es</sub><sup>2</sup>, where the equivalent sphere radius of ice grains (<i>r</i><sub>es</sub>) is computed from the specific surface area of snow (SSA) and the ice density (&rho;<sub>i</sub>) as follows: <i>r</i><sub>es</sub>=3/(SSA&times;&rho;<sub>i</sub>. We define <i>K</i> and <i>K</i>* as the average of the diagonal components of <b>K</b> and <b>K</b>*, respectively. The 35 values of <i>K</i>* were fitted to snow density (&rho;<sub>s</sub>) and provide the following regression: <i>K</i> = (3.0 &pm; 0.3) <i>r</i><sub>es</sub><sup>2</sup> exp((&minus;0.0130 &pm; 0.0003)&rho;<sub>s</sub>). We noted that the anisotropy of permeability does not affect significantly the proposed equation. This regression curve was applied to several independent datasets from the literature and compared to other existing regression curves or analytical models. The results show that it is probably the best currently available simple relationship linking the average value of permeability, <i>K</i>, to snow density and specific surface area
Presence and geodynamic significance of Cambro-Ordovician series of SE Karakaram (N. Pakistan)
New geological, geochemical and geochronological data from the Southern Karakoram (NE Pakistan) indicate the presence of several unexpectedly old and well preserved units along the Asian margin: (1) a Precambrian basement, displaying a minimum amphibole Ar-Ar age of 651 Ma; (2) a thick Cambro-Ordovician platform-type sedimentary unit overlying the Precam-brian basement. These series are dated by graptolite and crinoid faunas, and are confirmed by concordant 87Sr/86Sr and 13C “ages” of the marbles; (3) a dismembered ophiolitic series formed by slices of metagabbros and metabasalts separated by ultramafic lenses (the Masherbrum Greenstone Complex). The occurrence of such Cambro-Ordovician series overlying a Precambrian basement in south-eastern Karakoram similar to the south-western Karakoram shows that the Karakoram constitutes a continuous tectonic block. The petrology and geochemistry of the Masherbrum Greenstone Complex (mineral chemistry, major and trace element and Sr-Nd isotopic data) are indicative of a supra-subductive environment. The presence of LREE-enriched calc-alkaline rocks [(La/Yb)N = 4.45.6; (Nb/La)N = 0.2-0.3; eNd565 = 5.1-7.1] and LREE-depleted tholeiitic rocks [(La/Yb)N =0.5-1.3; (Nb/La)N = 0.6-0.9; eNd565 = 5.6-7.8] are consistent with arc and back-arc settings, respectively. A high-Mg andesitic dolerite and an OIB-type metabasalt, with lower eNd ratios (eNd565 = 0.5 and 4.5) are in accordance with source heterogeneity beneath the arc. The Masherbrum Greenstone Complex, along with other Cambro-Ordovician central-eastern volcanic series give evidence of a tectonic situation governed by micro-plate convergent-divergent systems with occurrence of arc - back-arc settings during the Lower Palaeozoic, comparable to that of the current SW Pacific area
Sarcopenia and cognitive impairment in elderly women: results from the EPIDOS cohort
BACKGROUND: common pathophysiological pathways are shared between age-related body composition changes and cognitive impairment.
OBJECTIVE: evaluate whether current operative sarcopenia definitions are associated with cognition in community-dwelling older women.
DESIGN: cross-sectional analyses.
SUBJECTS: a total of 3,025 women aged 75 years and older.
MEASUREMENTS: body composition (assessed by dual energy X-ray absorptiometry) and cognition (measured by short portable mental status questionnaire) were obtained in all participants. Multivariate logistic regression models assessed the association of six operative definitions of sarcopenia with cognitive impairment. Gait speed (GS, measured over a 6-meter track at usual pace) and handgrip strength (HG, measured by a hand-held dynamometer) were considered additional factors of interest.
RESULTS: a total of 492 (16.3%) women were cognitively impaired. The prevalence of sarcopenia ranged from 3.3 to 18.8%. No sarcopenia definition was associated with cognitive impairment after controlling for potential confounders. To proof consistency, the analyses were performed using GS and HG, two well-established predictors of cognitive impairment. Low GS [odds ratio (OR) 2.42, 95% confidence interval (CI) 1.72-3.40] and low HG (OR: 1.81, 95% CI: 1.33-2.46) were associated with cognitive impairment.
CONCLUSION: no significant association was evidenced between different operative sarcopenia definitions and cognitive impairment. The study suggests that the association between physical performance and cognitive impairment in not mediated by sarcopenia
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