Search results for "fiber"
showing 10 items of 2343 documents
Dilute and semi dilute solutions of block copolymers in water, near-critical and super-critical CO2: a small angle scattering study of the monomer–ag…
2002
Abstract Small angle neutron (SANS) and X-ray (SAXS) Scattering measurements on aggregate formation of block copolymers in water and in near-critical and supercritical CO2 are reported here. Time Resolved SAXS (TR-SAXS) has also been performed in the supercritical region. Experiments have been carried out for a series of different thermodynamic conditions, changing the solvent density by profiling the pressure at constant temperature. A sharp transition between monomers dissolved as random coils and micelles characterized by a solvo-philic shell and a solvo-phobic core occurs when the solvent density reaches the critical micellization value. This is easily shown in the case of scCO2.
Photochemical Generation of Cyclophanes from 1,3,5-Trisubstituted Benzenes with Chalcone Chromophores
2007
(E,E,E)-1,3,5-Tricinnamoylbenzene (7a) photodimerizes in solution to the [4.4.4](1,3,5)cyclophane 8a. The process consists of three consecutive steps in which cisoid enone conformations of 7a react in regio- and stereoselective anti-head-to-head cycloadditions. (E,E,E)-1,3,5-Tris(3-oxo-3-phenylpropenyl)benzene (13a), an isomer of 7 with reversed enone units, shows a single [2π+2π] cycloaddition of the same type. Due to steric reasons, it is afterwards not capable of intramolecular processes and oligomerizes by intermolecular photocycloadditions. Photolyses in the crystalline state yield dimers by topochemically controlled syn-head-to-tail processes (7a → 10a, 13a → 15a). An efficient dimeri…
Early lanthanide organometallic hydrides: electronic and steric control of the stability
2000
Abstract Steric and electronic effects on the stability of early lanthanide, neodymium and samarium, organometallic hydrides are discussed. The instability of (tmp)2SmH (tmp=tetramethylphospholyl) is attributed to electronic factors and the low stability of (tBuC5H4)2SmH is related to steric reasons. The analogous neodymium hydride (tBuC5H4)2NdH, could not be obtained, whereas the more hindered triethylborohydride was formed. Access to bisphospholyl bridged heterobimetallic ruthenium–lanthanide hydrides is also related to the size of the lanthanide atom. The bimetallic structures are accessible for lanthanides of ionic radii smaller than 1 A. The role of organometallic hydrides versus alkyl…
The Itô Integral
2014
The Ito integral allows us to integrate stochastic processes with respect to the increments of a Brownian motion or a somewhat more general stochastic process. We develop the Ito integral first for Brownian motion and then for generalized diffusion processes (so called Ito processes). In the third section, we derive the celebrated Ito formula. This is the chain rule for the Ito integral that enables us to do explicit calculations with the Ito integral. In the fourth section, we use the Ito formula to obtain a stochastic solution of the classical Dirichlet problem. This in turn is used in the fifth section in order to show that like symmetric simple random walk, Brownian motion is recurrent …
IMPROVED PRODUCTION OF THE ANTIBIOTIC ACTINORHODIN IN STREPTOMYCES COELICOLOR IMMOBILIZED-MYCELIAL CELL CULTIVATIONS
2017
Objectives i) Evaluation of ACT production in Streptomyces coelicolor M145 mycelial cells immobilized on polycaprolactone (PCL) and polylactic acid (PLA) nanofiber membranes, modified or not by an O2- plasma treatment. ii) Identification of gene products associated with the improvement of ACT production.
"Towards a "fingerprint" of paper network; separating forgeries from genuine by the properties of fibre structure"
2014
A novel method is introduced for distinguishing counterfeit banknotes from genuine samples. The method is based on analyzing differences in the networks of paper fibers. The main tool is a curvelet-based algorithm for measuring the distribution of overall fiber orientation and quantifying its anisotropy. The use of a couple or more appropriate parameters makes it possible to distinguish forgeries from genuine samples as concentrated point clouds in a two- or three-dimensional parameter space. Furthermore, the techniques of making watermarks is investigated by comparing genuine and counterfeit €50 banknotes. In addition, the so-called wire markings are shown to differ significantly from each…
Using the fibre structure of paper to determine authenticity of the documents: analysis of transmitted light images of stamps and banknotes.
2014
A novel method is presented for distinguishing postal stamp forgeries and counterfeit banknotes from genuine samples. The method is based on analyzing differences in paper fibre networks. The main tool is a curvelet-based algorithm for measuring overall fibre orientation distribution and quantifying anisotropy. Using a couple of more appropriate parameters makes it possible to distinguish forgeries from genuine originals as concentrated point clouds in two- or three-dimensional parameter space.
(Bi,Pb)2Sr2Ca2Cu3O10+δ superconductor composites: Ceramics vs. fibers
1991
Abstract Well characterized (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O 10+δ superconductor powder has been used to prepare superconductor-glass, -metal and -alloy composites through solid state reaction method. A recently developed Laser Floating Zone (LFZ) apparatus has been used to transform the ceramic precursors into oriented fibers. The diamagnetic properties have been studied by a.c. susceptibility. The microstructure of fibers has been studied by SEM and compared with that of the original ceramic precursors. XRD has been used to study phase composition on representative composite samples and fibers. The results indicate some potential for the 2223-Ag composite, which displays improved diamagnetic p…
Supercontinuum generation in chalcogenides : application to gas spectroscopy in atmospheric band III
2023
This thesis work aims to contribute to the development of new fiber sources emitting over a wide range of wavelengths in the IR, in particular to detect greenhouse gases in the mid-infrared range. Our spectroscopy results with nitrous oxide N2O and methane CH4 are obtained in band III. To achieve this, the generation of supercontinuum (SC) covering band III was made possible by using chalcogenide optical fibers, purified and free of highly toxic elements according to REACH regulations, in particular arsenic and antimony. The fibrable vitreous composition belonging to the Ge-Se-Te ternary system fits perfectly into the context of sustainable development, it is the one that has been identifie…
A supercritical-fluid method for growing carbon nanotubes
2007
Large‐scale generation of multiwalled carbon nanotubes (MCNTs) is efficiently achieved through a supercritical fluid technique employing carbon dioxide as the carbon source. Nanotubes with diameters ranging from 10 to 20 nm and lengths of several tens of micrometers are synthesized (see figure). The supercritical‐fluid‐grown nanotubes also exhibit field‐emission characteristics similar to MCNTs grown by chemical‐vapor deposition.