1,720,982 research outputs found
Boltzmann equation and hydrodynamic fluctuations
No full textWe apply the method of invariant manifolds to derive equations of generalized hydrodynamics from the linearized Boltzmann equation and determine exact transport coefficients, obeying Green-Kubo formulas. Numerical calculations are performed in the special case of Maxwell molecules. We investigate, through the comparison with experimental data and former approaches, the spectrum of density fluctuations and address the regime of finite Knudsen numbers and finite frequencies hydrodynamics
Particle transport and finite-size effects in Lorentz channels with finite horizons
No full textParticle transport is investigated in a finite-size realization of the classical Lorentz gas model. We consider point particles moving at constant speed in a 2D rectangular strip of finite length, filled with circular scatterers sitting at the vertices of a triangular lattice. Particles are injected at the left boundary with a prescribed rate, undergo specular reflections when colliding with the scatterers and the horizontal boundaries of the channel, and are finally absorbed at the left or the right boundary. Thanks to the equivalence with give Correlated Random Walks, in the finite horizon case, we show that the inverse probability that a particle exits through the right boundary depends linearly on the number of cells in the channel. A non-monotonic behavior of such probability as a function of the density of scatterers is also discussed and traced back analytically to the geometric features of a single trap. This way, we do not refer to asymptotic quantities and we accurately quantify the finite size effects. Our deterministic model provides a microscopic support for a variety of phenomenological laws, e.g. the Darcy's law for porous media and the Ohm's law in electronic transport
Canonical distribution functions in polymer dynamics. (II). Liquid- crystalline polymers
No full textThe quasi-equilibrium approximation is employed as a systematic tool for solving the problem of deriving constitutive equations from kinetic models of liquid-crystalline polymers. It is demonstrated how kinetic models of liquid-crystalline polymers can be approximated in a systematic way, how canonical distribution functions can be derived from the maximum entropy principle and how constitutive equations are derived therefrom. The numerical implementation of the constitutive equations based on the intrinsic dual structure of the quasi-equilibrium manifold thus derived is developed and illustrated for a particular example. Finally, a measure of the accuracy of the quasi-equilibrium approximation is proposed that can be implemented into the numerical integration of the constitutive equation
Nonequilibrium phase transitions in feedback-controlled three-dimensional particle dynamics
Full text linkWe consider point particles moving inside spherical urns connected by cylindrical channels whose axes both lie along the horizontal direction. The microscopic dynamics differ from that of standard 3D billiards because of a kind of Maxwell's demon that mimics clogging in one of the two channels, when the number of particles flowing through it exceeds a fixed threshold. Nonequilibrium phase transitions, measured by an order parameter, arise. The coexistence of different phases and their stability, as well as the linear relationship between driving forces and currents, typical of the linear regime of irreversible thermodynamics, are obtained analytically within the proposed kinetic theory framework, and are confirmed with remarkable accuracy by numerical simulations. This purely deterministic dynamical system describes a kind of experimentally realizable Maxwell's demon, that may unveil strategies to obtain mass separation and stationary currents in a conservative particle model
From hyperbolic regularization to exact hydrodynamics for linearized Grad's equations
No full textInspired by a recent hyperbolic regularization of Burnett's hydrodynamic equations [A. Bobylev, J. Stat. Phys. 124, 371 (2006)], we introduce a method to derive hyperbolic equations of linear hydrodynamics to any desired accuracy in Knudsen number. The approach is based on a dynamic invariance principle which derives exact constitutive relations for the stress tensor and heat flux, and a transformation which renders the exact equations of hydrodynamics hyperbolic and stable. The method is described in detail for a simple kinetic model-a 13 moment Grad system
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Cloning, expression and activation of a truncated 92-kDa gelatinase minienzyme
No full textKroger M, Tschesche H. Cloning, expression and activation of a truncated 92-kDa gelatinase minienzyme. GENE. 1997;196(1-2):175-180.The matrix metalloproteinases (MMPs) are a family of highly homologous zinc-endopeptidases that degrade extracellular matrix components. Human 92-kDa gelatinase (MMP-9) represents one of the MMPs that cleaves native collagen type IV. As a basis for structural investigations, the short form (catalytic domain, amino acid residues 113-450) of the 92-kDa gelatinase cDNA was cloned and expressed in E. coli as a minienzyme. By combination of reverse transcription (RT) and polymerase chain reaction (PCR), the truncated 92-kDa gelatinase-cDNA was amplified from the corresponding mRNA derived from ovarian carcinoma cells. The cDNA fragment obtained was cloned in E. coli and sequenced. With the exception of one nucleotide inversion at position 745 (gt-->tg) the cDNA sequence was identical to the nucleotide sequence of the 92-kDa gelatinase as has been previously reported. The protein was expressed in E. coli using the vector pET-12b. The recombinant protein was stored in inclusion bodies and extracted as a 38 kDa species from the inclusion bodies by solubilization in 8 M urea. The product was purified by affinity chromatography and gel filtration. Amino-terminal sequence analysis confirmed the identity with the catalytic domain of 92-kDa gelatinase. The recombinant protein was refolded in the presence of Ca2+ and Zn2+ and yielded an active minienzyme with gelatinolytic activity. It degrades the native substrate collagen type IV and the synthetic substrate Mca-Pro-Leu-Gly-Leu-Dpa-Ala-Arg-NH2 x AcOH like the full-length 92-kDa gelatinase. The catalytic activity could be inhibited by the specific MMP inhibitors TIMP-1 and TIMP-2. (C) 1997 Elsevier Science B.V
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