516 research outputs found
Analysis of transport properties of iron pnictides: spin-fluctuation scenario
We present a phenomenological theory of quasiparticle scattering and
transport relaxation in the normal state of iron pnictides based on the
simplified two-band model coupled via spin fluctuations. In analogy with
anomalous properties of cuprates it is shown that a large and anomalous
normal-state resistivity and thermopower can be interpreted as the consequence
of strong coupling to spin fluctuations. The generalization to the
superconducting phase is also discussed.Comment: Revised version, 6 pages, 11 references adde
Local structure of liquid/vapour interfaces approaching the critical point
Investigating the structure of fluid interfaces at high temperatures is a particularly delicate task that requires effective ways of discriminating liquid from vapour and identifying the location of the liquid phase boundary, thereby allowing to distinguish intrinsic from capillary fluctuations. Several numerical approaches require introducing a coarse-graining length scale, often heuristically chosen to be the molecular size, to determine the location of the liquid phase boundary. Here, we propose an alternative rationale for choosing this coarse-graining length scale; we require the average position of the local liquid phase dividing surface to match its flat, macroscopic counterpart. We show that this approach provides additional insight into the structure of the liquid/vapour interface, suggesting the presence of another length scale beyond the bulk correlation one that plays an important role in determining the interface structure
Quantitative Protein Dynamics from Dominant Folding Pathways
We develop a theoretical approach to the protein folding problem based on
out-of-equilibrium stochastic dynamics. Within this framework, the
computational difficulties related to the existence of large time scale gaps in
the protein folding problem are removed and simulating the entire reaction in
atomistic details using existing computers becomes feasible. In addition, this
formalism provides a natural framework to investigate the relationships between
thermodynamical and kinetic aspects of the folding. For example, it is possible
to show that, in order to have a large probability to remain unchanged under
Langevin diffusion, the native state has to be characterized by a small
conformational entropy. We discuss how to determine the most probable folding
pathway, to identify configurations representative of the transition state and
to compute the most probable transition time. We perform an illustrative
application of these ideas, studying the conformational evolution of alanine
di-peptide, within an all-atom model based on the empiric GROMOS96 force field.Comment: 4 pages, 1 figur
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
The contribution of major risk factors and job strain to occupational class differences in coronary heart disease incidence: the MONICA Brianza and PAMELA population-based cohorts
Objectives We investigated the contribution of major coronary heart disease (CHD) risk factors and job strain to occupational class differences in CHD incidence in a pooled-cohort prospective study in northern Italy.
Methods 2964 men aged 25-74 from four northern Italian population-based cohorts were investigated at baseline and followed for first fatal or non-fatal CHD event (171 events). Standardised procedures were used for baseline risk factor measurements, follow-up and validation of CHD events. Four occupational classes were derived from the Erikson-Goldthorpe-Portocarero social class scheme: higher and lower professionals and administrators, non-manual workers, skilled and unskilled manual workers, and the self-employed. HRs were estimated with Cox models.
Results Among CHD-free subjects, with non-manual workers as the reference group, age-adjusted excess risks were found for professionals and administrators (+84%, p=0.02), the self-employed (+72%, p=0.04) and manual workers (+63%, p=0.04). The relationship was consistent across different CHD diagnostic categories. Adjusting for major risk factors only slightly reduced the reported excess risks. In a sub-sample of currently employed subjects, adjusting for major risk factors, sport physical activity and job strain reduced the excess risk for manual workers (relative change = -71.4%) but did not substantially modify the excess risks of professionals and administrators and the self-employed.
Conclusions In our study, we found higher CHD incidence rates for manual workers, professionals and administrators, and the self-employed, compared to non-manual workers. When the entire spectrum of job categories is considered, the job strain model helped explain the CHD excess risk for manual workers but not for other occupational classes
A Chiral Phosphine (CRC-PHOS) Derived from ( + )-Champhanic Acid. A New Ligand for Homogeneous Asymmetric Hydrogenation
The lactone of 1S,3S-1-hydroxy-1-diphenylphosphinomethyl-
2,2,3-tri-methyl-cyclopentan-3-carboxylic acid (4, CRC-PHOS) was
prepared from ( + )-camphanic acid methylester 1, and its complex
salt [Rh(CRC-PHOS)2NBD] · CI04 • THF (5) was isolated. The latter
exhibited rather a high rate, but low enantioselectivity in the first
attempt at asymmetric hydrogenation
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
Structural Evolution and Its Implication for the Emplacement of Gold Deposit in the Central Part of Burkina Faso, West Africa
In order to constrain the structural evolution in the central part of Burkina Faso and its implication for the emplacement of gold deposits, we undertook a structural mapping by coupling Landsat and aeromagnetic images interpretation to outcrop and core mapping followed by laboratory work. This approach reveals that the structural architecture in this locality mainly results from dextral transcurrent progressive deformation due to a NW-SE trending major stress. This architecture is similar to the Riedel-Tchalenko model. Initially, the dominant normal stress created an E-W constriction resulting in the development of N-S shear corridors. Subsequently, the tangential stress that took over this generated the progressive development of simple dextral shear zones with a NE-SW orientation that are locally taken up by ENE-WSW dextral shear bands associated with the Riedel's R structures. As a result of the cooling of the crust, we are witnessing the formation of sinistral NW-SE and dextral NNE-SSW strike-slip faults respectively corresponding to Riedel's R' structures and Tchalenko's P structures. The development of NW-SE pre-Eburnean shear zones and particularly the N-S shear corridors, are synchronous with the circulation of gold-bearing fluids through the zone. However, the intersections of these directional corridors create zones suitable for gold concentration. Within these zones, ductile-brittle deformation following the emplacement of the shear bands has facilitated the remobilization and concentration of gold-bearing fluids within rocks with the appropriate rheological conditions. This is the case for Toega gold deposit
Mesoscopic simulations of the counterion-induced electroosmotic flow - a comparative study
We present mesoscopic simulations of the counterion-induced electroosmotic
flow in different electrostatic coupling regimes. Two simulation methods are
compared, Dissipative Particle Dynamics (DPD) and coupled
Lattice-Boltzmann/Molecular Dynamics (LB/MD). A general mapping scheme to match
DPD to LB/MD is developed. For the weak-coupling regime, analytic expressions
for the flow profiles in the presence of partial-slip as well as no-slip
boundary conditions are derived from the Poisson-Boltzmann and Stokes
equations, which are in good agreement with the numerical results. The
influence of electrofriction and partial slip on the flow profiles is
discussed.Comment: 10 pages, 8 figures, 3 tables, additional references and minor
changes in the tex
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