Global Analysis of the Flows of Fluids with Pressure-Dependent Viscosities

 To describe the flows of fluids over a wide range of pressures, it is necessary to take into account the fact that the viscosity of the fluid depends on the pressure. That the viscosity depends on the pressure has been verified by numerous careful experiments. While the existence of solutions local-in-time to the equations governing the flows of such fluids are available for small, special data and rather unrealistic dependence of the viscosity on the pressure, no global existence results are in place. Our interest here is to establish the existence of weak solutions for spatially periodic three-dimensional flows that are global in time, for a large class of physically meaningful viscosity-pressure relationships. (Accepted May 1, 2002) Published online November 15, 2002 Communicated by S. S. ANTMAN     

Physical,chemical and immunological characteristics of continuous-density lipoproteins isolated by single-spin gradient ultracentrifugation

The isolation of various lipoproteins of very low, intermediate, low and high density from 5 ml of serum was obtained by single-step ultracentrifugation in a potassium bromide density gradient obtained by smoothing a discontinuous gradient during the run (120 000g, 48 h, 4°C; Beckman SW27 rotor). The density profiles were reproducible. The lipoproteins were characterized by electron microscopy, fluorescence polarization, polyacrylamide gel electrophoresis and complete chemical assays. The composition of the entire lipoprotein spectrum was in accordance with previous results. The lipoprotein molecular mass, particle size distribution, Apo AI/AII ratio and microviscosity varied according to the density range.     

Optimal control of a birth and death epidemic process

We employ a birth and death process to describe the spread of an infectious disease through a closed population. Control of the epidemic can be effected at any instant by varying the birth and death rates to represent quarantine and medical care programs. An optimal strategy is one which minimizes the expected discounted losses and costs resulting from the epidemic process and the control programs over an infinite horizon. We formulate the problem as a continuous-time Markov decision model. Then we present conditions ensuring that optimal quarantine and medical care program levels are nonincreasing functions of the number of infectives in the population. We also analyze the dependence of the optimal strategy on the model parameters. Finally, we present an application of the model to the control of a rumor.     

Acrylate nanolatex via self‐initiated photopolymerization

The use of UV light to initiate emulsion polymerization processes is generally overlooked, whilst extensive literature exists on photocuring of monomer films. In this study, the unique potential of UV light to produce at ambient temperature polyacrylate latexes without initiator was exploited. Although radical initiators are utilized at low concentration, their cost, toxicity, and odor provide incentives for finding alternatives. Starting with concentrated (30 wt %) and low scattering acrylate miniemulsions (droplet diameter <100 nm), it was demonstrated that acrylate self‐initiation can promote an efficient and fast photopolymerization in micrometer‐scale reactor (spectrophotometric cell) and lab‐scale photoreactor. Herein, all kinetic, colloidal, and mechanistic aspects involved in the self‐initiation of acrylate miniemulsion were extensively examined to provide a complete picture. In particular, the effects of droplet size, initiating wavelength, optical path, and irradiance on the course of the polymerization were thoroughly discussed. A diradical self‐initiation pathway is the most likely mechanism. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1843–1853     

Large‐Scale Synthesis of Enantiopure Molecular Cages: Chiroptical and Recognition Properties

A convenient and efficient gram‐scale synthesis for enantiopure hemicryptophane–tren (tren=tris(2‐aminoethyl)amine) derivatives has been developed. The four‐step synthesis is based on the optical resolution of a key intermediate, cyclotriveratrylene, for which the energy barrier for racemization has been measured to ensure that no racemization occurs during the two last steps of the synthetic pathway. The assignments of the absolute configurations have been performed by electronic circular dichroism and the enantiopurity was determined by NMR spectroscopy in the presence of enantiopure camphor sulfonic acid. To highlight the interest of such compounds, the recognition of norephedrine neurotransmitter was investigated and showed a remarkable enantioselectivity towards the C₃ symmetrical hosts. Finally, this highly modular synthetic pathway was used to provide eight enantiopure hemicryptophanes with different sizes, shapes, and functionalities. These results underline the high potential of this approach, which could lead to many applications in chiral recognition or asymmetric supramolecular catalysis.     

Synthesis by FVT and Characterization of Unhindered Silanethiones

The retro-ene reaction of allylthio- and propargylthiosilanes led, under flash vacuum thermolysis (FVT) conditions, to unhindered silanethiones, characterized by their derivatives, and also directly by coupling of the FVT with gas-phase spectrometries. Monomeric silicon oxysulfide has been generated similarly. The unsubstituted silanethione was not obtained, but dehydrogenated into silicon monosulfide during FVT.     

Non-equivalence Magnetique en Resonance Nucleaire—IV. Influence de Plusieurs Types de Dissymetries sur les Deplacements Chimiques et les Couplages Relatifs a des Systemes ?O?CH2?CH3 et ?S?CH2?CH3

Magnetic non-equivalence of methylenic protons in A? CH₂? CH₃ groups were studied for several types of compounds. Results are compared with respect (1) to the nature of heteroatom A:A = O and A = S and (2) to the structure of the local dissymmetry element: asymmetric carbon, ketal group and allenic system. Influence of substitution is discussed in relation to conformational problems. Furthermore a variation of the methylene geminal coupling constant with substituents of carbon α to OEt is observed.     

Temperature-rise fractionation of poly(3-alkyl thiophenes)

In this article, we have investigated a temperature-rise fractionation procedure for poly(3-hexyl thophene) (P3HT) and poly(3-octyl thophene) (P3OT) that provides well-defined molecular weight (MW) fractions with improved molecular weight distributions (MWD) when compared with Soxhlet extraction. This process involves dispersing the material over C18-boned silica stationary phase in a jacketed column and using incremental rises in column temperature (T_col) to gradually improve solvent quality and selectively dissolve higher molecular weight samples with a narrow polydispersity (PDI). Fractionation of P3HT with ΔT_col = 5 °C in methylene chloride (MC) yielded 7 fractions ranging from M_p of 20 to 53 kg/mol with an average PDI of 1.80 compared with a mother sample of 3.10. Predominant recovery of P3HT was acquired for fractions with T_col > 20 °C (30 wt %). Subsequent separation of P3OT in methylene chloride, with a reduced ΔT_col of 3 °C per fraction, due to increased solubility from the longer alkyl chain, generated 8 fractions with a weight range of M_n = 22 to 57 kg/mol with an mean PDI of 1.23 with the mother sample having PDI = 2.34, demonstrating the tunability of this method. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2547–2555, 2009     

Multicomponent reactions studies: Yonemitsu-type trimolecular condensations promoted by Ti(IV) derivatives

We have developed a Ti(IV)/Et₃N-promoted trimolecular condensation of aromatic heterocycles (furan, pyrrole, imidazole, indole) with aldehydes and active methylene compounds. In the case of indole and methyl acetoacetate the reaction afforded three-component products or tricyclic cyclopenta[b]indole derivative, depending on the reaction conditions. In both cases, NMR analysis evidenced that titanium enolate is the reactive species involved in the reaction.     

Magnetic dilution of the iron sublattice in CoFe2−xScxO4 (0≤x≤1)

Substitution of Fe for Sc in CoFe₂O₄ spinel structure is presented. All CoFe_2−xSc_xO₄ compounds crystallize in the spinel type structure (space group Fd3?m). By using X-ray diffraction studies, magnetic measurements and in-field ⁵⁷Fe Mössbauer spectrometry, the limit of substitution has been determined to be equal to x=0.56. An increase in the cell parameter and the strains and a decrease in the apparent crystallites size are observed. For x>0.3, a partial oxidation of cobalt is evidenced and Co³⁺ is stabilized in the structure. A ferromagnetic behavior has been observed for all investigated compounds. As x increases, the Curie temperature and the hyperfine fields decrease. Following the Stephenson model, the diminution of T_C is ascribed to a decrease of the main J_AB interaction.