1,720,998 research outputs found
Space structures and different scales for many-component biosystems
No full textThe right scale of description, and more generally, the matching between different scales, in modelling physical or biological systems, presents a substantial interest and related difficulties.
"This applies for instance to competition/diffusion models of different species, or to the invasion process by an aggressive population against a native one, like tumor cells in a normal tissue. Under a suitable scaling the system may be described by PDE's where space structures are visible, as is shown and discussed here in a tumor growth model.
"On the other hand, the separation of scales may be not so sharp: events occurring in `microscopic' regions may affect the macroevolution considerably. This is shown here in a model of metastatic spreading which can be studied like a collection of `proliferating' random walks on the positive one-dimensional lattice
A genralization of the H-Theorem to steady nonequilibrium states. 1 . A basic decomposition and the linear case
No full textA generalized relative entropy functional is associated to the evolution of gas in a container with (generally) non-uniform boundary data. A decomposition for its rate in 'bulk' and in 'boundary' terms is given; for the linear case both have a definite sign. The relation with the strong L(1) stability is pointed out
Stationary Boltzmann equation for a degenerate gas in a slab: boundary value problem and hydrodynamics
No full textThe continuum reaction-diffusion limit of a stochastic cellular growth model
No full textA competition-diffusion system, where populations of healthy and malignant cells compete and move on a neutral matrix, is analyzed. A coupled system of degenerate nonlinear parabolic equations is derived through a scaling procedure from the microscopic, Markovian dynamics. The healthy cells move much slower than the malignant ones, such that no diffusion for their density survives in the limit.The malignant cells may locally accumulate, while for the healthy ones an exclusion rule is considered. The asymptotic behavior of the system can be partially described through the analysis of the stationary wave which connects different equilibria
Self-diffusion in a two-dimensional system of colliding vertical sticks
No full textWe consider a system of N horizontal lines where colliding vertical sticks are placed initially according to an equilibrium prescription; they move parallel to the lines and collide; the collisions take place between sticks of the same line and of the adjacent ones. The asymptotic behavior of a tagged stick is diffusive, and the self-diffusion constant is inversely proportional to N
Beyond the eye-sight: the puzzle of a Japanese manchira
No full textIn the framework of a collaboration between the Opificio delle Pietre Dure and the Stibbert Museum (both Florence, Italy), a Japanese armour from the Edo period (XVII-XIX cent.), called manchira, was subjected to a multi-analytical diagnostic campaign. Due to the multi-layered structure of the object, constituted by silk, linen or hemp, wool, leather, and metallic parts, the diagnostic campaign entailed both non-invasive and micro-destructive techniques, such as multi-spectral photography, FORS, FT-IR, XRF and HPLC-DAD analysis, prior and in parallel to restoration practice. The main goals of the study were assessing the state of conservation in order to plan a thorough cleaning and consolidation strategy; characterizing the assembly and the materials employed; dating the object and clarifying the context of its production (e.g. the social status of the owner, the quality of the constituting materials, etc.). Reference ex-novo of dyed textiles were prepared accordingly to traditional Japanese recipes, by using materials purchased in Japan. The results were interpreted with the help of Japanese costume and textile historians and allowed us to clarify the nature of the constituting materials and to characterize the object under study. In this paper, the main results obtained by micro-destructive techniques are presented. In particular, the analysis by HPLC-DAD led to the identification of a black shade
obtained by superimposing an indigoid dye to an iron-mordanted flavonoid dye (Sophora japonica) for the dark damask and of murasaki dye for the kikkō. The influence of the dyeing technique, entailing the application of an iron mordant, was fundamental in assessing the state of conservation of the object
Quantum Statistical Mechanics: Overview
No full textAn overview of the birth of quantum statistical mechanics is given;the path from the early second quantization to more recent developments is traced,with some reference to the mathematical tools and the present challenges
Mixing properties for mechanical motion of a charged particle in a random medium
No full textWe study a one-dimensional semi-infinite system of particles driven by a constant positive force F which acts only on the leftmost particle of mass M, called the heavy particle (the h.p.), and all other particles are mechanically identical and have the same mass m ( M. Particles interact through elastic collisions. At initial time all neutral particles are at rest, and the initial measure is such that the interparticle distances xi (i) are i.i.d. r.v. Under conditions on the distribution of xi which imply that the minimal velocity obtained by each neutral particle after the first interaction with the h.p. is bigger than the drift of an associated Markovian dynamics tin which each neutral particle is annihilated after the first collision) we prove that the dynamics has a strong cluster property, and as a consequence, we prove existence of the discrete time limit distribution for the system as seen from the first particle, a psi -mixing property, a drift velocity, as well af the central limit theorem for the tracer particle
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
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