190 research outputs found
Resolution except for minimal singularities II. The case of four variables
In this sequel to Resolution except for minimal singularities I, we find the
smallest class of singularities in four variables with which we necessarily end
up if we resolve singularities except for normal crossings. The main new
feature is a characterization of singularities in four variables which occur as
limits of triple normal crossings singularities, and which cannot be eliminated
by a birational morphism that avoids blowing up normal crossings singularities.Comment: 23 pages. Section 3 revised. Results unchange
Crowding effect on helix-coil transition: beyond entropic stabilization
We report circular dichroism measurements on the helix-coil transition of
poly(L-glutamic acid) in solution with polyethylene glycol (PEG) as a crowding
agent. Using small angle neutron scattering, PEG solutions have been
characterized and found to be well described by the picture of a transient
network of mesh size , usual for semi-diluted chains in good solvent. We
show that the increase of PEG concentration stabilizes the helices and
increases the transition temperature. But more unexpectedly we also notice that
the increase of crowding agent concentration reduces the mean helix extent at
the transition, or in other words reduces its cooperative feature. This result
cannot be accounted for by an entropic stabilization mechanism. Comparing the
mean length of helices at the transition and the mesh size of the PEG network,
our results strongly suggest two regimes: helices shorter or longer than the
mesh size
Pacman percolation: a model for enzyme gel degradation
We study a model for the gel degradation by an enzyme, where the gel is
schematized as a cubic lattice, and the enzyme as a random walker, that cuts
the bonds over which it passes. The model undergoes a (reverse) percolation
transition, which for low density of enzymes falls in a universality class
different from random percolation. In particular we have measured a gel
fraction critical exponent beta=1.0+-0.1, in excellent agreement with
experiments made on the real system.Comment: 4 pages, 7 eps figure
Magnetic nanoconstrictions made from nickel electrodeposition in polymeric bi-conical tracks: Magneto-transport behavior
International audienceSingle nanoconstriction per magnetic wire is obtained by bi-conical track etching and electrodeposition. Magnetoresistance measurements at various angles result in irreversible jumps. Resulting jumps of magnetization have been attributed to the pinning and depinning of a constrained magnetic domain wall. a b s t r a c t In a cylindrical magnetic nanowire, a magnetic domain wall (DW) can move along the wire when an applied magnetic field or a spin-polarized current is applied. We show that in a magnetic device composed of two conical nanowires connected by a nanosized constriction, a DW can be trapped and detrapped. The magnetoreistance and the relaxation processes of the DW exhibit a specific behavior. Such a device has been fabricating by Ni electrodeposition in bi-conical tracks polymer membrane made of Swift Heavy Ions bombarded poly(VDF-co-TrFE) copolymer and poly(ethylene terephtalate) PET thin films. The latter method allows to monitor the conicity of the bi-conical wires and to give access to a panel of very well-defined structures.
Bending elasticity of a curved amphiphilic film decorated anchored copolymers: a small angle neutron scattering study
Microemulsion droplets (oil in water stabilized by a surfactant film) are
progressively decorated with increasing amounts of poly ethylene- oxide (PEO)
chains anchored in the film by the short aliphatic chain grafted at one end of
the PEO chain . The evolution of the bending elasticity of the surfactant film
with increasing decoration is deduced from the evolution in size and
polydispersity of the droplets as reflected by small angle neutron scattering.
The optimum curvature radius decreases while the bending rigidity modulus
remains practically constant. The experimental results compare well with the
predictions of a model developed for the bending properties of a curved film
decorated by non-adsorbing polymer chains, which takes into account, the finite
curvature of the film and the free diffusion of the chains on the film.Comment: 30 June 200
Robust Phase Behavior of Model Transient networks
In order to study the viscoelastic properties of certain complex fluids which
are described in terms of a multiconnected transient network we have developed
a convenient model system composed of microemulsion droplets linked by
telechelic polymers. The phase behavior of such systems has two characteristic
features: a large monophasic region which consists of two sub-regions (a fluid
sol phase and a viscoelastic gel phase) separated by a percolation line and a
two phase region at low volume fraction with separation into a dilute sol phase
and a concentrated gel phase. From the plausible origin of these features we
expect them to be very similar in different systems. We describe here the phase
behavior of four different systems we prepared in order to vary the time scale
of the dynamical response of the transient network; they consist of the
combination of two oil(decane) in water microemulsions differing by the
stabilizing surfactant monolayer (Cetyl pyridinium chloride/octanol or
TX100/TX35) and of two telechelic polymers which are end-grafted poly (ethylene
oxide) chains, differing by the end-grafted hydrophobic aliphatic chains
(C12H25 or C18H37).Comment: April 9 200
Small Angle Scattering and Zeta Potential of Liposomes Loaded with Octa(carboranyl)porphyrazine
In this work the physicochemical characterization of liposomes loaded with a
newly synthesised carboranyl porphyrazine (H2HECASPz) is described. This
molecule represents a potential drug for different anticancer therapies, such
as Boron Neutron Capture Therapy, Photodynamic Therapy and Photothermal
Therapy. Different loading methods and different lipid mixtures were tested.
The corresponding loaded vectors were studied by Small Angle Scattering (SANS
and SAXS), light scattering and zeta potential. The combined analysis of
structural data at various length scales and the measurement of the surface
charge allowed to obtain a detailed characterization of the investigated
systems. The mechanisms underlying the onset of differences in relevant
physicochemical parameters (size, polydispersity and charge) were also
critically discussed
Blood Signature of Pre-Heart Failure: A Microarrays Study
International audienceBACKGROUND: The preclinical stage of systolic heart failure (HF), known as asymptomatic left ventricular dysfunction (ALVD), is diagnosed only by echocardiography, frequent in the general population and leads to a high risk of developing severe HF. Large scale screening for ALVD is a difficult task and represents a major unmet clinical challenge that requires the determination of ALVD biomarkers. METHODOLOGY/PRINCIPAL FINDINGS: 294 individuals were screened by echocardiography. We identified 9 ALVD cases out of 128 subjects with cardiovascular risk factors. White blood cell gene expression profiling was performed using pangenomic microarrays. Data were analyzed using principal component analysis (PCA) and Significant Analysis of Microarrays (SAM). To build an ALVD classifier model, we used the nearest centroid classification method (NCCM) with the ClaNC software package. Classification performance was determined using the leave-one-out cross-validation method. Blood transcriptome analysis provided a specific molecular signature for ALVD which defined a model based on 7 genes capable of discriminating ALVD cases. Analysis of an ALVD patients validation group demonstrated that these genes are accurate diagnostic predictors for ALVD with 87% accuracy and 100% precision. Furthermore, Receiver Operating Characteristic curves of expression levels confirmed that 6 out of 7 genes discriminate for left ventricular dysfunction classification. CONCLUSIONS/SIGNIFICANCE: These targets could serve to enhance the ability to efficiently detect ALVD by general care practitioners to facilitate preemptive initiation of medical treatment preventing the development of HF
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