6,883 research outputs found
Rodlike Complexes of a Polyelectrolyte (Hyaluronan) and a Protein (Lysozyme) observed by SANS
We study by Small Angle Neutron Scattering (SANS) the structure of Hyaluronan
-Lysozyme complexes. Hyaluronan (HA) is a polysaccharide of 9 nm intrinsic
persistence length that bears one negative charge per disaccharide monomer
(Mmol = 401.3 g/mol); two molecular weights, Mw = 6000 and 500 000 Da were
used. The pH was adjusted at 4.7 and 7.4 so that lysozyme has a global charge
of +10 and + 8 respectively. The lysozyme concentration was varied from 3 to 40
g/L, at constant HA concentration (10 g/L). At low protein concentration,
samples are monophasic and SANS experiments reveal only fluctuations of
concentration although, at high protein concentration, clusters are observed by
SANS in the dense phase of the diphasic samples. In between, close to the onset
of the phase separation, a distinct original scattering is observed. It is
characteristic of a rod-like shape, which could characterize "single" complexes
involving one or a few polymer chains. For the large molecular weight (500 000)
the rodlike rigid domains extend to much larger length scale than the
persistence length of the HA chain alone in solution and the range of the SANS
investigation. They can be described as a necklace of proteins attached along a
backbone of diameter one or a few HA chains. For the short chains (Mw ~ 6000),
the rod length of the complexes is close to the chain contour length (~ 15 nm)
Raviart-Thomas finite elements of Petrov-Galerkin type
The mixed finite element method for the Poisson problem with the
Raviart-Thomas elements of low-level can be interpreted as a finite volume
method with a non-local gradient. In this contribution, we propose a variant of
Petrov-Galerkin type for this problem to ensure a local computation of the
gradient at the interfaces of the elements. The shape functions are the
Raviart-Thomas finite elements. Our goal is to define test functions that are
in duality with these shape functions: Precisely, the shape and test functions
will be asked to satisfy a L2-orthogonality property. The general theory of
Babu\v{s}ka brings necessary and sufficient stability conditions for a
Petrov-Galerkin mixed problem to be convergent. We propose specific constraints
for the dual test functions in order to ensure stability. With this choice, we
prove that the mixed Petrov-Galerkin scheme is identical to the four point
finite volumes scheme of Herbin, and to the mass lumping approach developed by
Baranger, Maitre and Oudin. Finally, we construct a family of dual test
functions that satisfy the stability conditions. Convergence is proven with the
usual techniques of mixed finite elements
Coupling Linear Sloshing with Six Degrees of Freedom Rigid Body Dynamics
Fluid motion in tanks is usually described in space industry with the
so-called Lomen hypothesis which assumes the vorticity is null in the moving
frame. We establish in this contribution that this hypothesis is valid only for
uniform rotational motions. We give a more general formulation of this coupling
problem, with a compact formulation. We consider the mechanical modeling of a
rigid body with a motion of small amplitude, containing an incompressible fluid
in the linearized regime. We first establish that the fluid motion remains
irrotational in a Galilean referential if it is true at the initial time. When
continuity of normal velocity and pressure are prescribed on the free surface,
we establish that the global coupled problem conserves an energy functional
composed by three terms. We introduce the Stokes - Zhukovsky vector fields,
solving Neumann problems for the Laplace operator in the fluid in order to
represent the rotational rigid motion with irrotational vector fields. Then we
have a good framework to consider the coupled problem between the fluid and the
rigid motion. The coupling between the free surface and the ad hoc component of
the velocity potential introduces a "Neumann to Dirichlet" operator that allows
to write the coupled system in a very compact form. The final expression of a
Lagrangian for the coupled system is derived and the Euler-Lagrange equations
of the coupled motion are presented.Comment: 23 page
Tshiyembe, Mwayila et Bukasa, Mayele. LâAfrique face Ă ses problĂšmes de sĂ©curitĂ© et de dĂ©fense. Paris, Institut Panafricain de GĂ©opolitique, Coll. « Travaux et recherches de lâInstitut Panafricain de GĂ©opolitique », 1989, 263 p.
Keohane, Robert O. International Institutions and State Power; Essays in International Relations Theory. Boulder (Col.), Westview Press, 1989, 280 p.
Trajectories from public sector of research to private sector : an analysis using french data on young PhD graduates
The organisation of research is a powerful factor structuring the labour market for recent doctorate recipients. The queue for permanent research positions in the academic sector has created a specific labour market for young doctorates, characterised by a proliferation of postdoctoralprogrammes and fixed-term contracts. In that specific context, our paper deals with the way the young PhD graduates enter the labour market, the way they get a job as researcher in the private or public sector and how much the return of the job mobility from the public academic sector to the private sector is. Using a longitudinal survey provided by the Cereq, our results suggest that even if nearly the half of the cohort has a direct access to jobs in the research sector (private or public), 20% remain in trajectories dominated by under-qualifiedjobs or recurrent unemployment. Our empirical investigation show a negative or non significant returns of the job mobility from the public academic sector to the private sector.Marché du travail; Insertion professionnelle; Post Doctorant; Jeune; Mobilité professionnelle; France
A stochastic individual based model for the growth of a stand of Japanese knotweed including mowing as a management technique
Invasive alien species are a growing threat for environment and health. They
also have a major economic impact, as they can damage many infrastructures. The
Japanese knotweed (Fallopia japonica), present in North America, Northern and
Central Europe as well as in Australia and New Zealand, is listed by the World
Conservation Union as one of the world's worst invasive species. So far, most
models have dealt with how the invasion spreads without management. This paper
aims at providing a model able to study and predict the dynamics of a stand of
Japanese knotweed taking into account mowing as a management technique. The
model we propose is stochastic and individual-based, which allows us taking
into account the behaviour of individuals depending on their size and location,
as well as individual stochasticity. We set plant dynamics parameters thanks to
a calibration with field data, and study the influence of the initial
population size, the mean number of mowing events a year and the management
project duration on mean area and mean number of crowns of stands. In
particular, our results provide the sets of parameters for which it is possible
to obtain the stand eradication, and the minimal duration of the management
project necessary to achieve this latter
Musée d\u27art de Lodz (Muzeum sztuky w Lodzi) : constitution d\u27une collection d\u27art contemporain en Pologne/note de synthÚse (Le)
Synthesis and properties of lipoamino acid/fatty acid mixtures. Influence of the amphiphilic structure.
The acylation of amino acids by acid chlorides with from 8 to 12 carbon atoms,
in alkaline aqueous medium following Shotten-Baumann reaction, results in sodium salts of
Nα-acylamino acids and fatty acids mixture. These lastest are present in proportion from 40 to
60%. These compositions represent mixtures of amphiphilic anionic surfactants. They
contribute together to the properties of the formulation. Measurements of the surface-active
properties of these formulations, such as critical micelle concentration (CMC), surface tension
at the CMC (TS), foaming capacity (FC) and foaming stability (FS), show that surfactant
mixtures with the longest chain have the most desirable properties. They are comparable to
commercial petroleum-based surfactants. Thus, the CMC, TS and CM values of the
formulation obtained starting from leucine and dodecanoyl chloride (310 mg/L, 30.1 mN/m
and 200%, respectively) are similar, even better than, sodium dodecylsulfate (290 mg/L,
39.1 mN/m and 230%, respectively
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