259 research outputs found
Synthèse de Produits de Référence Apparentés Aux Polyphénols. EUR 31. = Synthesis of Reference Products Related to Polyphenols. EUR 31.
Cumulant ratios in fully developed turbulence
In the context of random multiplicative cascade processes, we derive
analytical solutions for one- and two-point cumulants with restored
translational invariance. On taking ratios of cumulants in ln epsilon,
geometrical effects due to spatial averaging cancel out. These ratios can
successfully distinguish between splitting functions while multifractal scaling
exponents and multiplier distributions cannot.Comment: 9th Workshop on Multiparticle Production (Torino), 9 pages latex,
incl 9 figs and espcrc2.st
Translationally invariant cumulants in energy cascade models of turbulence
In the context of random multiplicative energy cascade processes, we derive
analytical expressions for translationally invariant one- and two-point
cumulants in logarithmic field amplitudes. Such cumulants make it possible to
distinguish between hitherto equally successful cascade generator models and
hence supplement lowest-order multifractal scaling exponents and multiplier
distributions.Comment: 11 pages, 3 figs, elsart.cls include
Contraction of cross-linked actomyosin bundles
Cross-linked actomyosin bundles retract when severed in vivo by laser
ablation, or when isolated from the cell and micromanipulated in vitro in the
presence of ATP. We identify the time scale for contraction as a viscoelastic
time tau, where the viscosity is due to (internal) protein friction. We obtain
an estimate of the order of magnitude of the contraction time tau ~ 10-100 s,
consistent with available experimental data for circumferential microfilament
bundles and stress fibers. Our results are supported by an exactly solvable,
hydrodynamic model of a retracting bundle as a cylinder of isotropic, active
matter, from which the order of magnitude of the active stress is estimated.Comment: To be published in Physical Biolog
Relation between coupled map lattices and kinetic Ising models
A spatially one dimensional coupled map lattice possessing the same
symmetries as the Miller Huse model is introduced. Our model is studied
analytically by means of a formal perturbation expansion which uses weak
coupling and the vicinity to a symmetry breaking bifurcation point. In
parameter space four phases with different ergodic behaviour are observed.
Although the coupling in the map lattice is diffusive, antiferromagnetic
ordering is predominant. Via coarse graining the deterministic model is mapped
to a master equation which establishes an equivalence between our system and a
kinetic Ising model. Such an approach sheds some light on the dependence of the
transient behaviour on the system size and the nature of the phase transitions.Comment: 15 pages, figures included, Phys. Rev. E in pres
Evidence for carbonyl sulfide (OCS) conversion to CO in the lower atmosphere of Venus
The chemical regimes in the atmosphere of Venus vary from photochemistry in the middle atmosphere to thermal equilibrium chemistry in the lower atmosphere and the surface. Many chemical cycles have been proposed, but few details about these cycles are fully verified by comparison between observations and modeling. Recent high-quality data of carbonyl sulfide (OCS) and CO from ground-based and Venus Express observations provide a unique opportunity to test our understanding of chemistry and transport in the lower atmosphere of Venus. The spatial distributions of OCS and CO in the atmosphere reflect a sensitive balance between chemistry and transport. On the basis of our updated photochemical model and winds from Lee et al.'s (2007) general circulation model, we study the chemistry and transport in a simplified two-dimensional chemistry-transport model. OCS is produced by heterogeneous reactions on the surface; the middle atmosphere is a net sink for OCS. The combination of data and modeling provides strong evidence for the loss of OCS by conversion to CO. The detailed chemical mechanism is currently unknown, although a number of speculations have been proposed. The sensitivity of the distributions of OCS and CO to model parameters is reported
Detection and construction of an elliptic solution to the complex cubic-quintic Ginzburg-Landau equation
In evolution equations for a complex amplitude, the phase obeys a much more
intricate equation than the amplitude. Nevertheless, general methods should be
applicable to both variables. On the example of the traveling wave reduction of
the complex cubic-quintic Ginzburg-Landau equation (CGL5), we explain how to
overcome the difficulties arising in two such methods: (i) the criterium that
the sum of residues of an elliptic solution should be zero, (ii) the
construction of a first order differential equation admitting the given
equation as a differential consequence (subequation method).Comment: 12 pages, no figure, to appear, Theoretical and Mathematical Physic
Meromorphic traveling wave solutions of the complex cubic-quintic Ginzburg-Landau equation
We look for singlevalued solutions of the squared modulus M of the traveling
wave reduction of the complex cubic-quintic Ginzburg-Landau equation. Using
Clunie's lemma, we first prove that any meromorphic solution M is necessarily
elliptic or degenerate elliptic. We then give the two canonical decompositions
of the new elliptic solution recently obtained by the subequation method.Comment: 14 pages, no figure, to appear, Acta Applicandae Mathematica
Detecting Venus’ volcanic gas plumes with VenSpec-H
International audienceThe VenSpec-H instrument is part of the EnVision payload which is currently being evaluated by ESA for mission selection. EnVision is a medium class mission to determine the nature and current state of geological activity on Venus, and its relationship with the atmosphere, to understand how Venus and Earth could have evolved so differently. VenSpec-H is part of the VenSpec suite [1], including also an IR mapper and a UV spectrometer [2] suite. The science objectives of this suite are to search for temporal variations in surface temperatures and tropospheric concentrations of volcanically emitted gases, indicative of volcanic eruptions; and study surface-atmosphere interactions and weathering by mapping surface emissivity and tropospheric gas abundances. Recent and perhaps ongoing volcanic activity has been inferred in data from both Venus Express an
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