943 research outputs found
Convective instabilities in two superposed horizontal liquid layers heated laterally
This work is devoted to the theoretical study of the stability of two
superposed horizontal liquid layers bounded by two solid planes and subjected
to a horizontal temperature gradient.
The liquids are supposed to be immiscible with a nondeformable interface.
The forces acting on the system are buoyancy and interfacial tension. Four
different flow patterns and temperature profiles are found for the basic state.
A linear perturbative analysis with respect to two and three dimensional
perturbations reveals the existence of three kind of patterns. Depending on the
relative height of both liquids several situations are predicted: either wave
propagation from cold to the hot regions, or waves propagating in the opposite
direction or still stationary longitudinal rolls. The behavior of three
different pairs of liquids which have been used in experiments on bilayers
under vertical gradient by other authors have been examined. The instability
mechanisms are discussed and a qualitative interpretation of the different
behaviors exhibited by the system is provided. In some configurations it is
possible to find a codimension-two point created by the interaction of two Hopf
modes with different frequencies and wavenumbers. These results suggest to
consider two liquid layers as an interesting prototype for the study of
propagation and interaction of waves in the context of the B\'enard-Marangoni
problem.Comment: 21 pages, 9 figures, 2 tables;accepted to be published in PR
Tsallis statistics generalization of non-equilibrium work relations
We use third constraint formulation of Tsallis statistics and derive the
-statistics generalization of non-equilibrium work relations such as the
Jarzynski equality and the Crooks fluctuation theorem which relate the free
energy differences between two equilibrium states and the work distribution of
the non-equilibrium processes.Comment: 5 page
Magnetoresistance Effects in SrFeO(3-x): Dependence on Phase Composition and Relation to Magnetic and Charge Order
Single crystals of iron(IV) rich oxides SrFeO(3-x) with controlled oxygen
content have been studied by Moessbauer spectroscopy, magnetometry,
magnetotransport measurements, Raman spectroscopy, and infrared ellipsometry in
order to relate the large magnetoresistance (MR) effects in this system to
phase composition, magnetic and charge order. It is shown that three different
types of MR effects occur. In cubic SrFeO3 (x = 0) a large negative MR of 25%
at 9 T is associated with a hitherto unknown 60 K magnetic transition and a
subsequent drop in resistivity. The 60 K transition appears in addition to the
onset of helical ordering at ~130 K. In crystals with vacancy-ordered
tetragonal SrFeO(3-x) as majority phase (x ~0.15) a coincident
charge/antiferromagnetic ordering transition near 70 K gives rise to a negative
giant MR effect of 90% at 9 T. A positive MR effect is observed in tetragonal
and orthorhombic materials with increased oxygen deficiency (x = 0.19, 0.23)
which are insulating at low temperatures. Phase mixtures can result in a
complex superposition of these different MR phenomena. The MR effects in
SrFeO(3-x) differ from those in manganites as no ferromagnetic states are
involved
Status of QCD
I have been asked to discuss the status of QCD. It seems to me that there are
three main points to be made about the present status of QCD: QCD is
right, and we can do many beautiful things with it. There are several
important concrete problems that lie just beyond the edge of our current
understanding. There are some foundational issues in QCD, and some
recent developments, that may point toward entirely new directions. These
points will, I believe, emerge quite clearly from the following more detailed
discussion. The discussion will be in three parts. I'll first discuss
elementary processes, then more complicated processes, and then finally
foundational issues.Comment: 28 pages, use Phyzzx, figures available by FAX or mail on request,
IASSNS-HEP-93/6
Detection of human bocavirus in children with Kawasaki disease
ABSTRACTHuman bocavirus (HboV) is an emerging virus that has been implicated as a cause of acute upper and lower respiratory tract infection in children. As no serological assay is available, PCR was used to screen nasopharyngeal, serum or stool samples from 16 patients with Kawasaki disease for HBoV nucleic acid. HBoV was identified by PCR in five (31.2%) patients, suggesting that this emerging virus may also play a pathogenic role in some cases of Kawasaki disease
A cohesive zone model for fracture initiation and propagation of fused silica direct bonding interface
International audienceFused silica direct bonding is of particular interest for optical system manufacturing for spatial applications. However, in order to validate the European Space Agency standards, a better understanding of the assemblies mechanical behavior is required. Therefore, it is important to develop some predictive tools to determine numerically mechanical strength of complex assemblies. In this paper, a cohesive zone model is proposed to model the direct bonding interface behavior. In order to determine the mechanical strength of the interface, a propagation test, and an initiation test on a free edge the cleavage test have been performed on direct bonded fused silica samples. The FIT test (Flexible Initiation Test) is also used to identify the properties of the direct bonding joint. At the end, a comparative analyses is proposed between experimental results and finite elements models of the propagation and initiation tests
On the use of an appropriate TdT-mediated dUTP-biotin nick end labeling assay to identify apoptotic cells.
Apoptosis is an essential cellular mechanism involved in many processes such as embryogenesis, metamorphosis, and tissue homeostasis. DNA fragmentation is one of the key markers of this form of cell death. DNA fragmentation is executed by endogenous endonucleases such as caspase-activated DNase (CAD) in caspase-dependent apoptosis. The TUNEL (TdT-mediated dUTP-biotin nick end labeling) technique is the most widely used method to identify apoptotic cells in a tissue or culture and to assess drug toxicity. It is based on the detection of 3'-OH termini that are labeled with dUTP by the terminal deoxynucleotidyl transferase. Although the test is very reliable and sensitive in caspase-dependent apoptosis, it is completely useless when cell death is mediated by pathways involving DNA degradation that generates 3'-P ends as in the LEI/L-DNase II pathway. Here, we propose a modification in the TUNEL protocol consisting of a dephosphorylation step prior to the TUNEL labeling. This allows the detection of both types of DNA breaks induced during apoptosis caspase-dependent and independent pathways, avoiding underestimating the cell death induced by the treatment of interest
Influence of surfactants on the structure of titanium oxide gels : experiments and simulations
We report here on experimental and numerical studies of the influence of
surfactants on mineral gel synthesis. The modification of the gel structure
when the ratios water-precursor and water-surfactant vary is brought to the
fore by fractal dimension measures. A property of {\em polydispersity of the
initial hydrolysis} is proposed to explain these results, and is successfuly
tested through numerical experiments of three dimensional chemically limited
aggregation.Comment: 12 pages, 4 Postscript figures, uses RevTe
Maxwell homogenization scheme for piezoelectric composites with arbitrarily-oriented spheroidal inhomogeneities
International audienc
Is there an association between wheezing and constipation in preschool children? Explanations from a longitudinal birth cohort
Objective: To assess whether wheezing and atopic dermatitis were associated with constipation in preschool children and to what extent shared risk factors contribute to this relationship. Methods: A population-based sample of 4651 preschool children was used. At the age of 24, 36 and 48 months, a parental report of functional constipation was available according to the Rome II criteria, and data on atopic dermatitis and wheezing were available using age-adapted questionnaires from the International Study of Asthma and Allergie
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