4,193 research outputs found
Intermittent permeation of cylindrical nanopores by water
Molecular Dynamics simulations of water molecules in nanometre sized
cylindrical channels connecting two reservoirs show that the permeation of
water is very sensitive to the channel radius and to electric polarization of
the embedding material. At threshold, the permeation is {\emph{intermittent}}
on a nanosecond timescale, and strongly enhanced by the presence of an ion
inside the channel, providing a possible mechanism for gating. Confined water
remains surprisingly fluid and bulk-like. Its behaviour differs strikingly from
that of a reference Lennard-Jones fluid, which tends to contract into a highly
layered structure inside the channel.Comment: 4 pages, 4 figure
Formation energy and interaction of point defects in two-dimensional colloidal crystals
The manipulation of individual colloidal particles using optical tweezers has
allowed vacancies to be created in two-dimensional (2d) colloidal crystals,
with unprecedented possibility of real-time monitoring the dynamics of such
defects (Nature {\bf 413}, 147 (2001)). In this Letter, we employ molecular
dynamics (MD) simulations to calculate the formation energy of single defects
and the binding energy between pairs of defects in a 2d colloidal crystal. In
the light of our results, experimental observations of vacancies could be
explained and then compared to simulation results for the interstitial defects.
We see a remarkable similarity between our results for a 2d colloidal crystal
and the 2d Wigner crystal (Phys. Rev. Lett. {\bf 86}, 492 (2001)). The results
show that the formation energy to create a single interstitial is
lower than that of the vacancy. Because the pair binding energies of the
defects are strongly attractive for short distances, the ground state should
correspond to bound pairs with the interstitial bound pairs being the most
probable.Comment: 5 pages, 2 figure
Влияние стандартных схем противоязвенной терапии на клинико-лабораторные показатели у пациентов с язвенной болезнью двенадцатиперстной кишки
При изучении влияния стандартных схем квадритерапии второй линии на динамику клинико−лабораторных показателей у пациентов с язвенной болезнью двенадцатиперстной кишки установлено, что схемы с омепразолом, де−нолом, амоксициллином, тетрациклином и омепразолом, де−нолом, тетрациклином, метронидазолом одинаково влияют на динамику клинических симптомов и частоту эрадикации H. рylori. Однако первая схема более эффективно воздействует на нарушенные механизмы синтеза защитного слизистого барьера и процессы регенерации, что способствует более высокой частоте рубцевания язвы.При вивченні впливу стандартних схем квадрітерапії другої лінії на динаміку клініко−лабораторних показників у пацієнтів із виразковою хворобою дванадцятипалої кишки встановлено, що схеми з омепразолом, де−нолом, амоксициліном, тетрацикліном та омепразолом, де−нолом, тетрацикліном, метронідазолом однаково впливають на динаміку клінічних симптомів і частоту ерадикації H. рylori. Однак перша схема ефективніше впливає на порушені механізми синтезу захисного слизового бар'єру і процеси регенерації, що сприяє більш високій частоті рубцювання виразки.The investigation of the effect of standard schemes of second−line quadritherapy on the dynamics of clinical and laboratory parameters in patients with duodenal ulcer disease revealed that the scheme with Omeprazole, De−Nol, Amoxicillin, Tetracycline and Omeprazole De−Nol, Tetracycline, Metronidazole influence equally the dynamics of clinical symptoms and frequency of eradication of H. pylori. However, the first scheme more effectively influenced the disorders in the mechanism of synthesis of protective mucus barrier and regeneration processes, which contributed to the high frequency of ulcer cicatrisation
Magnetic friction due to vortex fluctuation
We use Monte Carlo and molecular dynamics simulation to study a magnetic
tip-sample interaction. Our interest is to understand the mechanism of heat
dissipation when the forces involved in the system are magnetic in essence. We
consider a magnetic crystalline substrate composed of several layers
interacting magnetically with a tip. The set is put thermally in equilibrium at
temperature T by using a numerical Monte Carlo technique. By using that
configuration we study its dynamical evolution by integrating numerically the
equations of motion. Our results suggests that the heat dissipation in this
system is closed related to the appearing of vortices in the sample.Comment: 6 pages, 41 figure
A Potential Energy Landscape Study of the Amorphous-Amorphous Transformation in HO
We study the potential energy landscape explored during a
compression-decompression cycle for the SPC/E (extended simple point charge)
model of water. During the cycle, the system changes from low density amorphous
ice (LDA) to high density amorphous ice (HDA). After the cycle, the system does
not return to the same region of the landscape, supporting the interesting
possibility that more than one significantly different configuration
corresponds to LDA. We find that the regions of the landscape explored during
this transition have properties remarkably different from those explored in
thermal equilibrium in the liquid phase
Origin of entropy convergence in hydrophobic hydration and protein folding
An information theory model is used to construct a molecular explanation why
hydrophobic solvation entropies measured in calorimetry of protein unfolding
converge at a common temperature. The entropy convergence follows from the weak
temperature dependence of occupancy fluctuations for molecular-scale volumes in
water. The macroscopic expression of the contrasting entropic behavior between
water and common organic solvents is the relative temperature insensitivity of
the water isothermal compressibility. The information theory model provides a
quantitative description of small molecule hydration and predicts a negative
entropy at convergence. Interpretations of entropic contributions to protein
folding should account for this result.Comment: Phys. Rev. Letts. (in press 1996), 3 pages, 3 figure
Association of cognitive performance with clinical staging in schizophrenia spectrum disorders:a prospective 6-year follow-up study
BACKGROUND: Clinical staging has been developed to capture the large heterogeneity in schizophrenia spectrum disorders. Including cognitive performance in the staging model may improve its clinical validity. Moreover, cognitive functioning could predict transition across stages. However, current evidence of the association between cognition and clinical staging is inconsistent. Therefore, we aim to assess whether cognitive parameters are associated with clinical stages in a large sample of patients with schizophrenia spectrum disorders and to identify cognitive markers at baseline that are associated with stage-transition at three and six-year follow-up. METHODS: We applied the staging model of Fusar-Poli et al. (2017) in 927 patients with non-affective psychotic disorders, assessed at baseline, and after three and six-year follow-up. Cognitive performance was assessed with a standard test battery. Generalized linear mixed models were used to analyze associations of cognitive performance with staging and stage-transition at follow-up. RESULTS: Findings showed that higher stages of illness were significantly associated with lower processing speed (F = 3.688, p = 0.025) and deficits in working memory (F = 6.365, p = 0.002) across assessments. No associations between cognitive parameters at baseline and stage-transition at three- and six-year follow-up were found. CONCLUSION: We conclude that processing speed and working memory were modestly associated with higher stages of illness in schizophrenia spectrum disorders, thereby slightly improving its clinical validity. However, associations were small and we found no evidence for predictive validity
Molecular mode-coupling theory for supercooled liquids: Application to water
We present mode-coupling equations for the description of the slow dynamics
observed in supercooled molecular liquids close to the glass transition. The
mode-coupling theory (MCT) originally formulated to study the slow relaxation
in simple atomic liquids, and then extended to the analysis of liquids composed
by linear molecules, is here generalized to systems of arbitrarily shaped,
rigid molecules. We compare the predictions of the theory for the -vector
dependence of the molecular nonergodicity parameters, calculated by solving
numerically the molecular MCT equations in two different approximation schemes,
with ``exact'' results calculated from a molecular dynamics simulation of
supercooled water. The agreement between theory and simulation data supports
the view that MCT succeeds in describing the dynamics of supercooled molecular
liquids, even for network forming ones.Comment: 22 pages 4 figures Late
The microbial contribution to litter decomposition and plant growth
Soil and plant roots are colonized by highly complex and diverse communities of microbes. It has been proposed that bacteria and fungi have synergistic effects on litter decomposition, but experimental evidence supporting this claim is weak. In this study, we manipulated the composition of two microbial kingdoms (Bacteria and Fungi) in experimental microcosms. In microcosms that were inoculated with fungi, litter loss was 47% higher than in microcosms that were not inoculated or only inoculated with bacteria. Combined inoculation with both bacteria and fungi did not significantly enhance decomposition compared with the fungi-only treatments, and, as such, we found no evidence for complementary effects using our experimental setup. Inoculation with fungi also had a positive impact on plant growth after 4 and 8 weeks (480% and 710% growth stimulation, respectively). After 16 weeks, plant biomass was highest in microcosms where both bacteria and fungi were present pointing to fungal-bacterial complementarity in stimulating plant growth. Overall, this study suggests that fungi are the main decomposers of plant litter and that the inoculated fungi contribute to plant growth in our experimental system
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