130,548 research outputs found
Viscosity and viscosity anomalies of model silicates and magmas: a numerical investigation
We present results for transport properties (diffusion and viscosity) using
computer simulations. Focus is made on a densified binary sodium disilicate
2SiO-NaO (NS2) liquid and on multicomponent magmatic liquids (MORB,
basalt). In the NS2 liquid, results show that a certain number of anomalies
appear when the system is densified: the usual diffusivity maxima/minima is
found for the network-forming ions (Si,O) whereas the sodium atom displays
three distinct r\'egimes for diffusion. Some of these features can be
correlated with the obtained viscosity anomaly under pressure, the latter being
be fairly well reproduced from the simulated diffusion constant. In model
magmas (MORB liquid), we find a plateau followed by a continuous increase of
the viscosity with pressure. Finally, having computed both diffusion and
viscosity independently, we can discuss the validity of the Eyring equation for
viscosity which relates diffusion and viscosity. It is shown that it can be
considered as valid in melts with a high viscosity. On the overall, these
results highlight the difficulty of establishing a firm relationship between
dynamics, structure and thermodynamics in complex liquids.Comment: 13 pages, 8 figure
On the composition dependence of the microscopic structure, thermodynamic, dynamic and dielectric properties of water-dimethyl formamide model mixtures. Molecular dynamics simulation results
Isothermal-isobaric molecular dynamics simulations have been performed to
examine an ample set of properties of the model water-N,N-dimethylformamide
(DMF) mixture as a function of composition. The SPC-E and TIP4P-Ew water models
together with two united atom models for DMF [Chalaris M., Samios J., J. Chem.
Phys., 2000, 112, 8581; Cordeiro J., Int. J. Quantum Chem., 1997, 65, 709] were
used. Our principal analyses concern the behaviour of structural properties in
terms of radial distribution functions, and the number of hydrogen bonds
between molecules of different species as well as thermodynamic properties.
Namely, we explore the density, excess mixing molar volume and enthalpy, the
heat capacity and excess mixing heat capacity. Finally, the self-diffusion
coefficients of species and the dielectric constant of the system are
discussed. In addition, surface tension of water-DMF mixtures has been
calculated and analyzed.Comment: 15 pages, 11 figure
Dynamics of Laterally Propagating Flames in X-ray Bursts. I. Burning Front Structure
We investigate the structure of laterally-propagating flames through the
highly-stratified burning layer in an X-ray burst. Two-dimensional
hydrodynamics simulations of flame propagation are performed through a rotating
plane-parallel atmosphere, exploring the structure of the flame. We discuss the
approximations needed to capture the length and time scales at play in an X-ray
burst and describe the flame acceleration observed. Our studies complement
other multidimensional studies of burning in X-ray bursts.Comment: Submitted to Ap
State Differentiation by Transient Truncation in Coupled Threshold Dynamics
Dynamics with a threshold input--output relation commonly exist in gene,
signal-transduction, and neural networks. Coupled dynamical systems of such
threshold elements are investigated, in an effort to find differentiation of
elements induced by the interaction. Through global diffusive coupling, novel
states are found to be generated that are not the original attractor of
single-element threshold dynamics, but are sustained through the interaction
with the elements located at the original attractor. This stabilization of the
novel state(s) is not related to symmetry breaking, but is explained as the
truncation of transient trajectories to the original attractor due to the
coupling. Single-element dynamics with winding transient trajectories located
at a low-dimensional manifold and having turning points are shown to be
essential to the generation of such novel state(s) in a coupled system.
Universality of this mechanism for the novel state generation and its relevance
to biological cell differentiation are briefly discussed.Comment: 8 pages. Phys. Rev. E. in pres
Zipf's Law in Gene Expression
Using data from gene expression databases on various organisms and tissues,
including yeast, nematodes, human normal and cancer tissues, and embryonic stem
cells, we found that the abundances of expressed genes exhibit a power-law
distribution with an exponent close to -1, i.e., they obey Zipf's law.
Furthermore, by simulations of a simple model with an intra-cellular reaction
network, we found that Zipf's law of chemical abundance is a universal feature
of cells where such a network optimizes the efficiency and faithfulness of
self-reproduction. These findings provide novel insights into the nature of the
organization of reaction dynamics in living cells.Comment: revtex, 11 pages, 3 figures, submitted to Phys. Rev. Let
Robust and Irreversible Development in Cell Society as a General Consequence of Intra-Inter Dynamics
A dynamical systems scenario for developmental cell biology is proposed,
based on numerical studies of a system with interacting units with internal
dynamics and reproduction. Diversification, formation of discrete and recursive
types, and rules for differentiation are found as a natural consequence of such
a system. "Stem cells" that either proliferate or differentiate to different
types stochastically are found to appear when intra-cellular dynamics are
chaotic. Robustness of the developmental process against microscopic and
macroscopic perturbations is shown to be a natural consequence of such
intra-inter dynamics, while irreversibility in developmental process is
discussed in terms of the gain of stability, loss of diversity and chaotic
instability.Comment: 17 pages with 3 ps figures. submitted to Physica A as a proceeding
paperfor Paladin Memorial Con
Horizontal and vertical networks for innovation in the traditional food sector
The locus of innovation is not the individual firm anymore but increasingly the network in which the firm is embedded. Hence, in this paper innovation is investigated in the broader context of networks and applied to the traditional food sector. Networking refers to a process of identifying and acting on complementary interests with or without formal means of cooperation and plays an important role for the diffusion and adoption of innovations, because they increase the flow of information. Two main types of networks exist. Vertical networks relate to cooperation of partners belonging to the same chain. Meanwhile, horizontal networks refer to coopereation among firms which are primarily competitors. Data were collected during focus groups and in-depths interviews in three European contries: Belgium, Hungary, and Italy.
In each country, data are collected from retailers/wholesalers, food manufacturers and suppliers in the beer, hard and half hard cheese, ham, sausage, or white paprika chain. In the investigated countries both vertical and horizontal networks exist. However, the intensity of using the network differs. On the one hand vertical networks are well developed based on quality assurance schemes and traceability, though these networks often face difficulties due to high lack of trust. On the other hand, horizontal networks are well developed when a producer consortium is involved. However, these networks can be inhibited through strong competition. The partners in traditional food networks focus mainly on innovation related to product characteristics such as new size, form and packaging without changing the traditional character of the product. The main barriers for innovation in the traditional food networks are the lack of understanding the benefits of networking activities for innovation, the lack of trust, the lack of knowledge of appropriate methods and skills, and the lack of financial and physical resources. Our study points out that successful SMEs use their networks to overcome lacks of knowledge and information and to create possibilities of joint use of resources
Flame fronts in Supernovae Ia and their pulsational stability
The structure of the deflagration burning front in type Ia supernovae is
considered. The parameters of the flame are obtained: its normal velocity and
thickness. The results are in good agreement with the previous works of
different authors. The problem of pulsation instability of the flame, subject
to plane perturbations, is studied. First, with the artificial system with
switched-off hydrodynamics the possibility of secondary reactions to stabilize
the front is shown. Second, with account of hydrodynamics, realistic EOS and
thermal conduction we can obtain pulsations when Zeldovich number was
artificially increased. The critical Zeldovich numbers are presented. These
results show the stability of the flame in type Ia supernovae against
pulsations because its effective Zeldovich number is small.Comment: 12 pages, 11 figure
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