638 research outputs found
CO diffusion and desorption kinetics in CO ices
Diffusion of species in icy dust grain mantles is a fundamental process that
shapes the chemistry of interstellar regions; yet measurements of diffusion in
interstellar ice analogs are scarce. Here we present measurements of CO
diffusion into CO ice at low temperatures (T=11--23~K) using CO
longitudinal optical (LO) phonon modes to monitor the level of mixing of
initially layered ices. We model the diffusion kinetics using Fick's second law
and find the temperature dependent diffusion coefficients are well fit by an
Arrhenius equation giving a diffusion barrier of 300 40 K. The low
barrier along with the diffusion kinetics through isotopically labeled layers
suggest that CO diffuses through CO along pore surfaces rather than through
bulk diffusion. In complementary experiments, we measure the desorption energy
of CO from CO ices deposited at 11-50 K by temperature-programmed
desorption (TPD) and find that the desorption barrier ranges from 1240 90
K to 1410 70 K depending on the CO deposition temperature and
resultant ice porosity. The measured CO-CO desorption barriers demonstrate
that CO binds equally well to CO and HO ices when both are compact. The
CO-CO diffusion-desorption barrier ratio ranges from 0.21-0.24 dependent on
the binding environment during diffusion. The diffusion-desorption ratio is
consistent with the above hypothesis that the observed diffusion is a surface
process and adds to previous experimental evidence on diffusion in water ice
that suggests surface diffusion is important to the mobility of molecules
within interstellar ices
Characterisation of aged HDPE pipes from drinking water distribution : investigation of crack depth by Nol ring tests under creep loading
International audienceHDPE pipes are used for the transport of drinking water. However, disinfectants in waterseem to have a strong impact on their mechanical behaviour, limiting their lifetime inoperation. Indeed, oxidation occurs when they are in contact with disinfectants leading to theformation of a thin oxidised layer coupled to the cracks initiation of cracks of different lengthsfrom the inner wall surface. An original method is proposed here to characterise the ageingeffect of the pipe mechanical behaviour. Inspired from the ASTM D 2290-04 standard, NolRing tests have been performed under tensile and creep loadings on smooth rings. Aconstitutive equation has been determined from these tests using a finite element (FE)modelling. FE simulations have been performed to study the influence of the thin oxidised PElayer. Precracked specimens with different crack depth ratio have also been modelled. Thecrack depth ratio is an important parameter to quantify pipe ageing
Interoperability between Heterogeneous Federation Architectures: Illustration with SAML and WS-Federation
International audienceDigital identity management intra and inter information systems, and, service oriented architectures, are the roots of identity federation. This kind of security architectures aims at enabling information system interoperability. Existing architectures, however, do not consider interoperability of heterogeneous federation architectures, which rely on different federation protocols.In this paper, we try to initiate an in-depth reflection on this issue, through the comparison of two main federation architecture specifications: SAML and WS-Federation. We firstly propose an overall outline of identity federation. We furthermore address the issue of interoperability for federation architectures using a different federation protocol. Afterwards, we compare SAML and WS-Federation. Eventually, we define the ways of convergence, and therefore, of interoperability
Phase fluctuations in the ABC model
We analyze the fluctuations of the steady state profiles in the modulated
phase of the ABC model. For a system of sites, the steady state profiles
move on a microscopic time scale of order . The variance of their
displacement is computed in terms of the macroscopic steady state profiles by
using fluctuating hydrodynamics and large deviations. Our analytical prediction
for this variance is confirmed by the results of numerical simulations
Long range correlations and phase transition in non-equilibrium diffusive systems
We obtain explicit expressions for the long range correlations in the ABC
model and in diffusive models conditioned to produce an atypical current of
particles.In both cases, the two-point correlation functions allow to detect
the occurrence of a phase transition as they become singular when the system
approaches the transition
The compensation approach for walks with small steps in the quarter plane
This paper is the first application of the compensation approach to counting
problems. We discuss how this method can be applied to a general class of walks
in the quarter plane with a step set that is a subset of
in the interior of . We
derive an explicit expression for the counting generating function, which turns
out to be meromorphic and nonholonomic, can be easily inverted, and can be used
to obtain asymptotic expressions for the counting coefficients.Comment: 22 pages, 5 figure
The grand canonical ABC model: a reflection asymmetric mean field Potts model
We investigate the phase diagram of a three-component system of particles on
a one-dimensional filled lattice, or equivalently of a one-dimensional
three-state Potts model, with reflection asymmetric mean field interactions.
The three types of particles are designated as , , and . The system is
described by a grand canonical ensemble with temperature and chemical
potentials , , and . We find that for
the system undergoes a phase transition from a
uniform density to a continuum of phases at a critical temperature . For other values of the chemical potentials the system
has a unique equilibrium state. As is the case for the canonical ensemble for
this model, the grand canonical ensemble is the stationary measure
satisfying detailed balance for a natural dynamics. We note that , where is the critical temperature for a similar transition in
the canonical ensemble at fixed equal densities .Comment: 24 pages, 3 figure
Phase diagram of the ABC model with nonconserving processes
The three species ABC model of driven particles on a ring is generalized to
include vacancies and particle-nonconserving processes. The model exhibits
phase separation at high densities. For equal average densities of the three
species, it is shown that although the dynamics is {\it local}, it obeys
detailed balance with respect to a Hamiltonian with {\it long-range
interactions}, yielding a nonadditive free energy. The phase diagrams of the
conserving and nonconserving models, corresponding to the canonical and
grand-canonical ensembles, respectively, are calculated in the thermodynamic
limit. Both models exhibit a transition from a homogeneous to a phase-separated
state, although the phase diagrams are shown to differ from each other. This
conforms with the expected inequivalence of ensembles in equilibrium systems
with long-range interactions. These results are based on a stability analysis
of the homogeneous phase and exact solution of the hydrodynamic equations of
the models. They are supported by Monte-Carlo simulations. This study may serve
as a useful starting point for analyzing the phase diagram for unequal
densities, where detailed balance is not satisfied and thus a Hamiltonian
cannot be defined.Comment: 32 page, 7 figures. The paper was presented at Statphys24, held in
Cairns, Australia, July 201
Stochastic Dynamics of Discrete Curves and Multi-type Exclusion Processes
This study deals with continuous limits of interacting one-dimensional
diffusive systems, arising from stochastic distortions of discrete curves with
various kinds of coding representations. These systems are essentially of a
reaction-diffusion nature. In the non-reversible case, the invariant measure
has generally a non Gibbs form. The corresponding steady-state regime is
analyzed in detail with the help of a tagged particle and a state-graph cycle
expansion of the probability currents. As a consequence, the constants
appearing in Lotka-Volterraequations --which describe the fluid limits of
stationary states-- can be traced back directly at the discrete level to tagged
particles cycles coefficients. Current fluctuations are also studied and the
Lagrangian is obtained by an iterative scheme. The related Hamilton-Jacobi
equation, which leads to the large deviation functional, is analyzed and solved
in the reversible case for the sake of checking.Comment: Short version of Inria Reasearch Report, 33 pages, 6 figures.
submited to J.Stat.Phy
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