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| 2. |
- Bellomo, N, et al.
(författare)
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The generalized kinetic modelling of a multicomponent "Real-Life" fluid by means of a single distribution function
- 2003
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Ingår i: Mathematical and computer modelling. - : Elsevier Science B.V., Amsterdam.. - 0895-7177 .- 1872-9479. ; 38:06-May, s. 637-659
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Tidskriftsartikel (refereegranskat)abstract
- work proposes a fully continuum stochastic model of a multicomponent fluid. It is shown that the way to this model leads to a generalized-kinetics (GK) theory. Subsequently, the model is developed as a corresponding extension of this theory. The obtained model presents the overall generalized distribution function. It is described with a nonlinear nonlocal (or "mean-field") system of two scalar equations, no matter how many components are in the fluid, and a special prescription. The system comprises (i) the generalized kinetic equation for the conditional distribution function conditioned with the values of the particle-property stochastic process, and (ii) the McKean-Kolmogorov forward equation for the probability density of this process. The aforementioned prescription determines the number of the fluid components as the number of the modes of this density. The work also includes a theorem that provides an estimation from below for this number in the generic stationary case of the corresponding multidimensional Kolmogorov equation and points out how the modes manifest themselves in the drift and diffusion functions (more specifically, in the Fichera drift function). The discussion on the model and a few directions for future research concludes the work.
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| 3. |
- Ehlers, G., et al.
(författare)
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Direct Observation of a Nuclear Spin Excitation in Ho2Ti2O7
- 2009
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:1, s. 016405-
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Tidskriftsartikel (refereegranskat)abstract
- A single nondispersive excitation is observed by means of neutron backscattering, at E-0=26.3 mu eV in the spin ice Ho2Ti2O7 but not in the isotopically enriched (Dy2Ti2O7)-Dy-162 analogue. The intensity of this excitation is rather small, less than or similar to 0.2% of the elastic intensity. It is clearly observed below 80 K but resolution limited only below similar to 65 K. The application of a magnetic field up to mu H-0=4.5 T, at 1.6 K, has no measurable effect on the energy or intensity. This nuclear excitation is believed to perturb the electronic, Ising spin system resulting in the persistent spin dynamics observed in spin ice compounds.
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| 4. |
- Magazù, S., et al.
(författare)
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Protein dynamics as seen by (quasi) elastic neutron scattering
- 2017
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Ingår i: Biochimica et Biophysica Acta - General Subjects. - : Elsevier BV. - 0304-4165. ; 1861:1, s. 3504-3512
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Tidskriftsartikel (refereegranskat)abstract
- Background Elastic and quasielastic neutron scattering studies proved to be efficient probes of the atomic mean square displacement (MSD), a fundamental parameter for the characterization of the motion of individual atoms in proteins and its evolution with temperature and compositional environment. Scope of review We present a technical overview of the different types of experimental situations and the information quasi-elastic neutron scattering approaches can make available. In particular, MSD can crucially depend on the time scale over which the averaging (building of the “mean”) takes place, being defined by the instrumental resolution. Due to their high neutron scattering cross section, hydrogen atoms can be particularly sensitively observed with little interference by the other atoms in the sample. A few examples, including new data, are presented for illustration. Major conclusions The incoherent character of neutron scattering on hydrogen atoms restricts the information obtained to the self-correlations in the motion of individual atoms, simplifying at the same time the data analysis. On the other hand, the (often overlooked) exploration of the averaging time dependent character of MSD is crucial for unambiguous interpretation and can provide a wealth of information on micro- and nanoscale atomic motion in proteins. General significance By properly exploiting the broad range capabilities of (quasi)elastic neutron scattering techniques to deliver time dependent characterization of atomic displacements, they offer a sensitive, direct and simple to interpret approach to exploration of the functional activity of hydrogen atoms in proteins. Partial deuteration can add most valuable selectivity by groups of hydrogen atoms. “This article is part of a Special Issue entitled “Science for Life” Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo”.
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| 5. |
- Mamontov, E, et al.
(författare)
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Electrochemical potentials and pressures of biofluids from common experimental data
- 2003
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Ingår i: Acta Biotheoretica. - : Springer Science Business Media. - 0001-5342 .- 1572-8358. ; 51:3, s. 173-180
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Tidskriftsartikel (refereegranskat)abstract
- Many biosystems are complex mixtures of disparate biofluids. To study contact and transport phenomena in these mixtures, one has to apply much information on the biofluids which are components of the mixtures. A lot of the corresponding data can be extracted by means of experiments. However, it is not always easy to obtain experimental results on rather deep physical characteristics of biofluids, especially if the bioparticles are complicated systems and the fluid coexists in the mixture with a large number of other fluids. In these cases, the necessary data can, in principle , be extracted from those results which are easier to obtain experimentally. The present work proposes a method to evaluate the biofluid equilibrium pressure and electrochemical potential from common experimental values of the fluid concentration and absolute temperature as well as the fluid-particle mass, volume and spin. In so doing, the nonzero values of the particle volume are accounted for. The procedure is illustrated with a numerical example of the fluid of red blood cells (or erythocytes) in human blood. The pressure values obtained are 49.1 an 38.8 micropascals for men and women respectively whereas the electrochemical-potential values are -2.124 and -2.130 electronvolts for men and women respectively.
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| 6. |
- Mamontov, E, et al.
(författare)
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Stochastic continuum mechanics - A thermodynamic-limit-free alternative to statistical mechanics : Equilibrium of isothermal ideal isotropic uniform fluid
- 2002
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Ingår i: Mathematical and computer modelling. - : Elsevier Science B.V., Amsterdam.. - 0895-7177 .- 1872-9479. ; 36:7-8, s. 889-907
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Tidskriftsartikel (refereegranskat)abstract
- We do not know how to study finite systems in any clean way; that is, the thermodynamic limit is inevitable. The lack of the clean way stressed in this sentence of Resibois and de Leener means the following. To study finite systems, statistical mechanics and kinetic theory offer nothing but the formalism based on the thermodynamic limit (TDL) which in essence disagrees with notion of finite system. The present work proposes the model (almost-equilibrium in a certain sense) enabling one to construct continuous equilibrium descriptions of fluids, discrete multiparticle systems, with no application of TDL. For simplicity, the fluids are assumed to be isothermal, (rheologically) ideal, isotropic and uniform. The core of the model is nonlinear It (o) over tilde s stochastic differential equation (ISDE) for the fluid-particle velocity. The continuous equilibrium description is based on the stationary probability density corresponding to this equation. The construction is described as a simple analytical recipe formulated in terms of quadratures and includes the velocity (or momentum) relaxation times which can be determined theoretically, experimentally, or as the results of numerical simulations and depending on the specific nature of the fluid. The recipe can be applied to an extremely wide range of fluids of the above class. It is illustrated by the derivations of the Maxwell-Boltzmann and Fermi-Dirac descriptions for the classical and fermion fluids in arbitrary space domain, bounded or unbounded. In the particular, TDL case, the derived results are in a complete agreement with those of statistical mechanics.
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