Influence of preferential solvation on the interpolymer complex formation between methacrylic acid–methacrylamide copolymer and poly(vinyl pyrrolidone)

Interpolymer complex formation has been studied between methacrylic acid–methacrylamide copolymer and poly(vinyl pyrrolidone) in acetone–water mixtures of different compositions. At a specific composition of the solvent (e.g., 70% water + 30% acetone by volume), the intrinsic viscosity of the copolymer and the reduced viscosity of 1:1 interpolymer complex had minimum values. Preferential solvation coefficients (λ/C) have been calculated for the various compositions of the solvent mixtures. An excellent coincidence could be obtained between the maximum (λ/C) and the minimum in the viscosity of the polymer solutions. Interpretations have been sought in terms of conformational change of the copolymer at the specific composition of the solvent mixture.     

Catecholamine release from cultured bovine adrenal medullary chromaffin cells in the presence of 60-Hz magnetic fields

Effects of powerline frequency (50/60 Hz) electric and magnetic fields on the central nervous system may involve altered neurotransmitter release. This possibility was addressed by determining whether 60-Hz linearly polarized sinusoidal magnetic fields (MFs) alter the release of catecholamines from cultured bovine adrenal chromaffin cells, a well-characterized model of neural-type cells. Dishes of cells were placed in the center of each of two four-coil Merritt exposure systems that were enclosed within mu-metal chambers in matched incubators for simultaneous sham and MF exposure. Following 15-min MF exposure of the cells to flux densities of 0.01, 0.1, 1.0 or 2 mT, norepinephrine and epinephrine release were quantified by high-performance liquid chromatography (HPLC) coupled with electrochemical detection. No significant differences in the release of either norepinephrine or epinephrine were detected between sham-exposed cells and cells exposed to MFs in either the absence or presence of Bay K-8644 (2 microM) or dimethylphenylpiperazinium (DMPP, 10 microM). Consistent with these null findings is the lack of effect of MF exposure on calcium influx. We conclude that catecholamine release from chromaffin cells is not sensitive to 60-Hz MFs at magnetic flux densities in the 0.01-2 mT range.     

Studies on ceric–thiol-initiated aqueous vinyl polymerization with particular reference to end groups in poly(methyl methacrylate)

Ceric-thiol systems are good initiators for the acid aqueous polymerization of some water-soluble Vinyl monomers although not for styrene (in aqueous emulsion) and vinyl acetate. Thiols used are 2-mercaptoethanol, thioglycolic acid, 2-mercaptoethylamine hydrochloride, and L -cysteine hydrochloride. The polymerization proceeds through a radical mechanism. End-group analysis of poly(methyl methacrylate) obtained by initiation with various ceric-thiol systems has been carried out using Palit's dye testes. Hydroxyl, carboxyl, and amine end groups (to the extent of about one per polymer molecule) were incorporated in poly(methyl methacrylate)s obtained by initiation with 2-mercaptoethanol, thioglycolic acid, and 2-mercaptoethylamine hydrochloride, respectively, each in combination with Ce⁴⁺ ions; both amine and carboxyl end groups were obtained using C⁴⁺/L -cysteine hydrochloride initiator system. From the end-group results, the initiating species have been identified and the initiation mechanism prooposed. The probable termination mechanism also has been discussed.     

Crotocaudin; a rearranged labdane type norditerpene from Croton caudatus geisel

The structure and stereochemistry of crotocaudin, a new norditerpene occurring as a minor constituent in Crotoncaudatus Geisel (Euphorbiaceae) have been established as ent-8S,10S-15,16-epoxy-19-norcleroda-4,11,13(16), 14-tetraene 18,6S: 20,12-diolactone 7 from the detailed studies of ¹H NMR spectra using lanthanide shift reagents, decoupling experiments and chemical reactions. The congener, teucvidin, ent-10S-15,16-epoxy-19-norcleroda-4,13(16), 14-triene-18,6S: 20,12R-diolactone 1 was obtained as a major component besides several triterpenoids viz taraxerone 2, taraxerol 3 and taraxeryl acetate 4. ¹³C NMR and ¹H NMR spectra and a few novel reactions of teucvidin and its conversion to teucvin, ent-(6R,12R)-15,16-epoxy-19-nor-9,4-friedolabda-4,13(16),14-triene-18,6:20, 12-diolactone 6 are also reported.     

Shape analysis based critical Eotvos numbers for buoyancy induced partial detachment of oil drops from hydrophilic surfaces

Removal of oil drops from solid surfaces immersed in an aqueous medium is of interest in many applications. It has been shown that drop shape analysis can be used to predict conditions at which the stability limit of a lighter than water oil drop on a solid surface immersed in an aqueous bath is reached (Adv. Colloid Interface Sci. 98 (2002) 265). However the above analysis is restricted to cases where the contact angle made by the drop is below 90degrees and when the surface conditions result in a 'pinned' contact line. In this paper, it is shown that drop shape analysis can be used to predict the critical conditions at which drop stability limit is reached for drop contact angles of 90degrees and above, which is encountered with 'hydrophilic' surfaces. This critical condition can predict the occurrence of partial oil drop detachment, before complete removal due to 'roll-up', which occurs when the hydrophilic surface is adequately smooth which prevents 'pinning' of the contact line. The critical conditions at which partial drop detachment occurs can also be approximately predicted from simple force balances. It has been shown (Adv. Colloid Interface Sci. 98 (2002) 265) that for contact angles less than 90degrees, the critical limit based on shape analysis appears to resolve the differences that arise due to alternate expressions for capillary retention force. This paper shows that even for contact angles above 90degrees, the critical conditions predicted from the shape analysis resolves the differences in the predictions from the alternate force balances. Drop shape analysis used in this paper is based on the 'Arc-length' form of Young-Laplace or 'drop shape' equation, which is different from the 'Y vs X' form of the above equation that is used in Adv. Colloid Interface Sci. 98 (2002) 265. The above drop shape equation is solved by a fourth order Runge-Kutta technique and it is shown that for angles less than 90degrees, the two forms of the drop shape equation, predict almost identical values of the critical Eotvos number. This paper highlights the competing effects of interfacial tension lowering induced drop instability and 'roll-up', a term that is used to describe the retraction of the contact line of an oil drop on a surface, in being the primary c ause for drop detachment.     

Effects of Added Surfactant on the Dynamic Interfacial Tension Behavior of Acidic Oil/Alkaline Systems

The effects of a ready-made surfactant (sodium dodecyl sulfate) on the dynamic interfacial tension between a model acidic oil (linoleic acid dissolved in paraffin oil) and various aqueous alkaline (NaOH) systems have been studied using pendant drop tensiometry at surfactant concentrations both below and above the critical micelle concentration (CMC). Below the CMC the added surfactant contributes significantly to a further reduction of interfacial tension of the reacting acid/alkaline system, whereas above the CMC the added surfactant plays an important role in damping the dynamic trends observed for the reactive system alone. Copyright 2001 Academic Press.     

Near-barrier fission of the system12C+232Th

The fission fragment angular distributions for the system¹²C +²³²Th have been measured in the energy range 0.97<>_c.m./V_B<1.22. the=" measured=" anisotropies=" have=" been=" compared=" with=" the=" predictions=" of=" the=" standard=" saddle=" point=" statistical=" model,=" using=" the=" second=" moment=" of=" the=" compound=" nucleus=" spin=" distribution=">l² deduced from a Wong model fit to the fission excitation function. While the measured anisotropies agree with the standard saddle point statistical model for E_c.m./V_B>1.05, they are abnormally large at lower energies. This is also true for the existing measurements of¹⁶O and¹⁹F +²³²Th systems. Since for this system pre-equilibrium fission contributions are not expected, this anomaly indicates strong channel coupling effects leading to an increase in l² at sub-barrier energies.The authors thank Drs. R.K. Choudhury and A. Saxena for useful discussions, Dr. R.J. Singh for making the thorium target and the Pellectron operation staff for excellent operation of the machine.     

Effects of final-state interaction and screening on strange- and heavy-quark production

Final-state interaction and screening have a great influence on $q\bar q$ production cross sections, which are important quantities in many problems in quark-gluon plasma physics. They lead to an enhancement of the cross section for a $q\bar q$ color-singlet state and a suppression for a color-octet state. The effects are large near the production threshold. The presence of screening gives rise to resonances for $q\bar q$ production just above the threshold at specific plasma temperatures. These resonances, especially $c\bar c$ and $b\bar b$ resonances, may be utilized to search for the quark-gluon plasma by studying the temperature dependence of heavy-quark pair production just above the threshold.     

Extended inflation in higher-dimensional spacetime with a Brans-Dicke scalar field

Starting from an assumption of homogeneity of matter-energy tensor and Brans-Dicke (BD) scalar field we obtain a Robertson-Walker type of metric form in five-dimensional spacetime with the essential difference that our model is spatially inhomogeneous. The model exhibits an interesting feature in that as we approach the centre of symmetry the compact dimension becomes very large, with the implication that the Kaluza-Klein excitations become very light when located there and that the origin may represent a singular concentration of matter with motion in the extra dimension. Following Wesson the effective 4D properties of matter from the 5D vacuum solutions are also briefly discussed. Assuming particular functional relationships between and as also between the scale factor and scalar field, we obtain exact solutions which may be of relevance to the early universe and its extended inflation in the BD type of theory. We also discuss very briefly rollover time immediately after tunneling to the true vacuum state to explore if dimensionality has any marked influence on the situation.