Effects of molecular weight distribution in drag reduction and shear degradation

A reduction of frictional drag in turbulent flow was obtained in benzene by using three monodisperse polystyrene samples having weight-average molecular weights of 1.8, 4.1 and 7.1 × 10⁶. By testing these polymers individually and in mixtures, data were obtained for samples with known molecular weight distributions. The drag reduction of these samples was studied as a function of polymer concentration and flow rate so that a generalized picture of the effects of polydispersity could be obtained. These results are used to help explain much of the behavior that was observed for polystyrene and other polymers. This includes the fact that the polystyrene samples exhibit a remarkably high resistance to the loss of drag reduction via degradation in turbulent flow. Such experiments indicate that drag reduction and degradation depend strongly on molecular weight distribution. Thus a molecular level interpretation of experimental results cannot be made unless the effects of the distribution are considered.     

Differential inhibition of postnatal brain,spinal cord and body growth by a growth hormone antagonist

Background  

Growth hormone (GH) plays an incompletely understood role in the development of the central nervous system (CNS). In this study, we use transgenic mice expressing a growth hormone antagonist (GHA) to explore the role of GH in regulating postnatal brain, spinal cord and body growth into adulthood. The GHA transgene encodes a protein that inhibits the binding of GH to its receptor, specifically antagonizing the trophic effects of endogenous GH.     

17O nuclear magnetic resonance studies of some enriched amino acids

The ¹⁷O NMR chemical shifts of five enriched amino acids have been measured under strictly controlled conditions of concentration, ionic strength, pH and temperature. The α, β and α, γ carboxyl resonances of aspartic and glutamic acid, respectively, have been resolved. Line widths were examined as a function of solution viscosity.     

On the origins of sudden adhesion loss at a critical relative humidity: examination of bulk and interfacial contributions

The origins for abrupt adhesion loss at a critical relative humidity (RH) for polymeric adhesives bonded to inorganic surfaces have been explored using a model poly(methyl methacrylate) (PMMA) film on glass. The interfacial and bulk water concentrations within the polymer film as a function of D 2O partial pressure were quantified using neutron reflectivity. Adhesion strength of these PMMA/SiO 2 interfaces under the same conditions was quantified using a shaft loaded blister test. A drop in adhesion strength was observed at a critical RH, and at this same RH, a discontinuity in the bulk moisture concentration occurred. The moisture concentration near the interface was higher than that in the bulk PMMA, and at the critical RH, the breadth of the interfacial water concentration distribution as a function of distance from the SiO 2/PMMA interface increased dramatically. We propose a mechanism for loss of adhesion at a critical RH based upon the interplay between bulk swelling induced stress and weakening of the interfacial bond by moisture accumulation at the PMMA/SiO 2 interface.     

Transfer measurements for the Ti+Ni systems at near barrier energies

Large enhancements have been observed in the sub-barrier fusion cross sections for Ti+Ni systems in our previous studies. Coupled channel calculations incorporating couplings to 2⁺ and 3⁻ states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer were carried out for ^46,48Ti+⁶¹Ni systems. The present paper gives the results of these studies.     

Synthesis of 2′-deoxy-5-fluoro-5′-O-1″,3″,2″-oxazaphosphacyclohexa-2″-yluridine 2″-oxide and related compounds

2′,3′-O-Isopropylidene-5′-O-1″,3″,2″-oxazaphosphacyclohex-2″-yl-uridine 2″-oxide has been obtained by the action of phosphoryl chloride and N-methylmorpholine, followed by 3-aminopropan-1-ol, on 2',3'-O-isopropy-lidineuridine. A similar reaction carried out on 3'-O-acetylthymidine, followed by removal of the acetyl group gave 5′-O-1″,3″,2″-oxazaphospha-2″-yl-thymidine 2″-oxide. Both of these compounds were obtained more conveniently by treatment of 2',3'-O-isopropylideneuridine and thymidine respectively with 2-chloro-1,3,2-oxazaphosphacyclo-hexane 2-oxide in pyridine. Similar treatment of 2′-deoxy-5-fluorouridine gave 2′-deoxy-5-fluoro-5′-O-1″,3″,2″-oxazaphosphacyclohex-2″-yluridine 2″-oxide. The latter compound was tested for activity against S 180 Crocker sarcoma and L 1210 mouse leukaemia. Only a marginal activity against the S 180 sarcoma was detected. However inactivity of the compound in inducing leukopenia indicated that it might be of low toxicity and that further testing of the compound would be justified.     

Using FTIR spectroscopy to detect sericin on historic silk

Silks represent some of the most precious ancient and historic textile artefacts in collections worldwide.Their optimum preservation demands an appreciation of their characteristics.One important concern,especially with regard to ancient Chinese silks,is whether the fabrics have been degummed.Silks with remnant sericin gum coating the fibroin fibres would require different conservation protocol.In previous research on aged silks,the presence of sericin has been inferred from amino acid analysis of hydrolysa...     

Iron-catalyzed Doyle-Kirmse reaction of allyl sulfides with (trimethylsilyl)diazomethane

[formula: see text] Iron salts efficiently catalyze the Doyle-Kirmse reaction of allyl sulfides with (trimethylsilyl)diazomethane and ethyl diazoacetate in dichloroethane at 83 degrees C. Competitive dimerization is less of a problem with (trimethylsilyl)diazomethane than with ethyl diazoacetate. Good results are obtained using only 1.5 equiv of (trimethylsilyl)diazomethane, even without slow addition. Phosphine ligands affect the kinetics, but not the diastereoselectivity. Dppe and BINAP lead to higher yields than dppp, but no enantioselection was detected with R-(+)-BINAP.