532 research outputs found
Angular momentum dependent friction slows down rotational relaxation under non-equilibrium conditions
It has recently been shown that relaxation of the rotational energy of hot
non-equlibrium photofragments (i) slows down significantly with the increase of
their initial rotational temperature and (ii) differs dramatically from the
relaxation of the equilibrium rotational energy correlation function,
manifesting thereby breakdown of the linear response description [Science 311,
1907 (2006)]. We demonstrate that this phenomenon may be caused by the angular
momentum dependence of rotational friction. We have developed the generalized
Fokker-Planck equation whose rotational friction depends upon angular momentum
algebraically. The calculated rotational correlation functions correspond well
to their counterparts obtained via molecular dynamics simulations in a broad
range of initial non-equilibrium conditions. It is suggested that the angular
momentum dependence of friction should be taken into account while describing
rotational relaxation far from equilibrium
Cluster Expansion by Transfer Learning from Empirical Potentials
Cluster expansions provide effective representations of the potential energy
landscape of multicomponent crystalline solids. Notwithstanding major advances
in cluster expansion implementations, it remains computationally demanding to
construct these expansions for systems of low dimension or with a large number
of components, such as clusters, interfaces, and multimetallic alloys. We
address these challenges by employing transfer learning to accelerate the
computationally demanding step of generating configurational data from first
principles. The proposed approach exploits Bayesian inference to incorporate
prior knowledge from physics-based or machine-learning empirical potentials,
enabling one to identify the most informative configurations within a dataset.
The efficacy of the method is tested on face-centered cubic Pt:Ni binaries,
yielding a two- to three-fold reduction in the number of first-principles
calculations, while ensuring robust convergence of the energies with low
statistical fluctuations
Simulation of micro injection moulding with emphasis on the formulation of feedstock viscosity : use of non-equilibrium molecular dynamics for the determination of viscosity of multi-body fluid
Dans cette approche, la viscosité de cisaillement d'un fluide composé de polymère et de particules métalliques est définie en fonction de paramètres tels que : le taux de charge, la taille des particules métalliques et la température du mélange. Une étude à l'échelle mésoscopique du mélange est proposée pour améliorer la formulation, connaître les variations de la viscosité en fonctions de ses paramètres la définissant. La méthode NEMD est utilisée pour simuler un flux de Poiseuille plan d'un mélange polymère/particules avec le package de simulation ESPResSo
Effects of Three Months of Low Molecular Weight Heparin (dalteparin) Treatment After Bypass Surgery for Lower Limb Ischemia—A Randomised Placebo-controlled Double Blind Multicentre Trial
AbstractObjectivesTo test the hypothesis that long-term postoperative dalteparin (Fragmin®, Pharmacia Corp) treatment improves primary patency of peripheral arterial bypass grafts (PABG) in lower limb ischemia patients on acetylsalicylic acid (ASA) treatment.DesignProspective randomised double blind multicenter study.Materials and methodsUsing a computer algorithm 284 patients with lower limb ischemia, most with pre-operative ischemic ulceration or partial gangrene, from 12 hospitals were randomised, after PABG, to 5000IU dalteparin or placebo injections once daily for 3 months. All patients received 75mg of ASA daily for 12 months. Graft patency was assessed at 1, 3 and 12 months.ResultsAt 1 year, 42 patients had died or were lost to follow-up. Compliance with the injection schedule was 80%. Primary patency rate, in the dalteparin versus the control group, respectively, was 83 versus 80% (n.s.) at 3 months and 59% for both groups at 12 months. Major complication rates and cardiovascular morbidity were not different between the two groups.ConclusionsIn patients on ASA treatment, long-term postoperative dalteparin treatment did not improve patency after peripheral artery bypass grafting. Therefore, low molecular weight heparin treatment cannot be recommended for routine use after bypass surgery for critical lower limb ischemia
Role of the Subunits Interactions in the Conformational Transitions in Adult Human Hemoglobin: an Explicit Solvent Molecular Dynamics Study
Hemoglobin exhibits allosteric structural changes upon ligand binding due to
the dynamic interactions between the ligand binding sites, the amino acids
residues and some other solutes present under physiological conditions. In the
present study, the dynamical and quaternary structural changes occurring in two
unligated (deoxy-) T structures, and two fully ligated (oxy-) R, R2 structures
of adult human hemoglobin were investigated with molecular dynamics. It is
shown that, in the sub-microsecond time scale, there is no marked difference in
the global dynamics of the amino acids residues in both the oxy- and the deoxy-
forms of the individual structures. In addition, the R, R2 are relatively
stable and do not present quaternary conformational changes within the time
scale of our simulations while the T structure is dynamically more flexible and
exhibited the T\rightarrow R quaternary conformational transition, which is
propagated by the relative rotation of the residues at the {\alpha}1{\beta}2
and {\alpha}2{\beta}1 interface.Comment: Reprinted (adapted) with permission from J. Phys. Chem. B
DOI:10.1021/jp3022908. Copyright (2012) American Chemical Societ
Ezekiel and the Covenant of Friendship
The slippery idea of "spirituality" might, with care, be put to use by biblical exegetes. Spirituality is defined in this paper as the social enactment of religious ideas. Four categories are offered to analyze the biblical witness as a record of spirituality. These categories are, first, an ultimate end; second, an ideal self-image by which this end might be achieved; third, an encoding of teachings in Scripture by which the self-image can be realized or understood; and fourth, a proposal for a way of life that makes achievement of the ultimate end a practical possibility. Accordingly, Ezekiel's "spirituality" may be understood to have, on one hand, an ultimate end of a return of the people to the land with the presence of God; and on the other, an ideal self-image of conversion of the community toward this ultimate end. Then it encodes, in oracles of judgment and deliverance, teachings that enable adherents to form the ideal self-image, and finally, as a way of life that puts these teachings into practice, it proposes a "covenant of friendship" (Ezek 34:25 and 37:36) among the exiled people and between them and their captors.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66911/2/10.1177_014610799202200402.pd
Investigation of the presence of an aliphatic biopolymer in cyanobacteria: Implications for kerogen formation
Algaenan has been suggested to be one of the main precursors of certain kerogens. It is a non-hydrolysable and insoluble biomolecule of high molecular weight. It has been found in a limited number of microalgae species. There is considerable uncertainty about its formation and preservation, as well as its role in kerogen formation and the implications for the global C cycle. We tested whether the cyanobacterium Chlorogloeopsis fritschii can synthesise a biomacromolecule similar to algaenan with potential to contribute to kerogen via selective preservation. Two freshwater green microalgae, Pseudochoricystis ellipsoidea and Scenedesmus obliquus, as well as C. fritschii, were subjected to harsh solvent extraction and hydrolysis steps to obtain an insoluble and non-hydrolysable macromolecule. The residues from all three species were analysed using pyrolysis–gas chromatography–mass spectrometry and solid-state nuclear magnetic resonance spectroscopy. The analysis revealed that C. fritschii indeed contains a resistant biomacromolecule exhibiting the characteristic aliphatic structure of algaenan, similar to the algaenan residues from the two microalgae. Due to the robust nature of Chlorogloeopsis compared with eukaryotes, it can prevail in extreme environmental conditions such as freezing, thawing, desiccation and overheating – conditions prevalent on the primeval earth. The presence of a resistant aliphatic biopolymer in Chlorogloeopsis suggests that cyanobacteria could have contributed to kerogen via selective preservation
A unified approach to the derivation of work theorems for equilibrium and steady-state, classical and quantum Hamiltonian systems
We present a unified and simple method for deriving work theorems for
classical and quantum Hamiltonian systems, both under equilibrium conditions
and in a steady state. Throughout the paper, we adopt the partitioning of the
total Hamiltonian into the system part, the bath part, and their coupling. We
rederive many equalities which are available in the literature and obtain a
number of new equalities for nonequilibrium classical and quantum systems. Our
results can be useful for determining partition functions and (generalized)
free energies through simulations and/or measurements performed on
nonequilibrium systems
A False Start in the Race Against Doping in Sport: Concerns With Cycling’s Biological Passport
Professional cycling has suffered from a number of doping scandals. The sport’s governing bodies have responded by implementing an aggressive new antidoping program known as the biological passport. Cycling’s biological passport marks a departure from traditional antidoping efforts, which have focused on directly detecting prohibited substances in a cyclist’s system. Instead, the biological passport tracks biological variables in a cyclist’s blood and urine over time, monitoring for fluctuations that are thought to indirectly reveal the effects of doping. Although this method of indirect detection is promising, it also raises serious legal and scientific concerns. Since its introduction, the cycling community has debated the reliability of indirect biological-passport evidence and the clarity, consistency, and transparency of its use in proving doping violations. Such uncertainty undermines the legitimacy of finding cyclists guilty of doping based on this indirect evidence alone. Antidoping authorities should address these important concerns before continuing to pursue doping sanctions against cyclists solely on the basis of their biological passports
- …