bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermokinetics of formation of polymeric mesomorphous phases in block copolymers and polymer mixtures
Authors: Frenkel S.
Published: June 2010

An attempt is made to treat the formation of supercrystalline lattices in solution of melts of block copolymers on the macromolecular level using the effective flexibility parameters appearing in the equivalence principle of thermokinetics. All known data are in accord with the assumption which proposes an extremal dependence of the interaction of χ and χAB parameters on composition (χAB attaining its maximal value at A/B molar ratios close to unity). Therefore, the effective flexibility parameters fA and fB characterizing the corresponding blocks should pass through a minimum close to the χ maxima, the lines for fA and fB being, however, somewhat shifted along the composition axis. At first sight this type of behavior fits the experimental data, but closer consideration shows that the assumption of chain extension due to segreation inherently appearing in the whole concept does not hold.

Therefore the situation is reconsidered, and it is shown that if the units (i.e., spheres, cylinders, and lamellae) occupying the sites of the superlattice are treated as “supermacromolecules” (or structons, following a somewhat improved definition of Huggins) the earlier theory holds.

Moreover, it is shown that the supercrystals can be treated in terms of the kinetic theory of liquids and real crystals which leads to a understandable explanation of their unusual properties, especially their high thermal stability. Probably a general theory starting from ideal supercrystals may be developed by means of a stepwise introduction of paracrystalline defects (in the manner of Hosemann) in the lattice. The most disordered paracrystalline lattices will then correspond to polymer blends.

Special attention is given to the formation of ordered structures from extended (or extruded) binary melts, the segregation parameter ϕAB being high, but where no junctions between A and B components occurs. This corresponds to the so‐called Yudin effect, and a catastrophic deliberation of the excess enthalpy of mixing on elimination of the noncrystallizable component (matrix) leads to an annihilation of the nematic units on annealing, thus showing the influence of the ϕAB parameter on the thermodynamic and morphologic properties of the structon forming component.

Finally, something of the nature of ϕAB in phase equilibria during polymerization and its influence on the molecular‐weight distribution of branches during the course of graft copolymerization are considered.
The adsorption of macromolecules on solid/liquid interfaces
Authors: Killmann Erwin , Eisenlauer Josef , Korn Milan
Published: June 2010

Ellipsometric results obtained from the adsorption of polystyrene, poly(methyl methacrylate) and poly(ethylene glycol) on chrome, gold, and platinum surfaces out of different solutions are reported and the influences of the different interactions are discussed. From the IR spectrometric and calorimetric results for the adsorption of poly(ethylene glycol)s and for low molecular weight model substances, the fractions of adsorbed segments and binding enthalpies are deduced. With the aid of conformation models for the adsorbed macromolecules, the measured values and their dependence upon concentration, molecular weight, and type of polymer, as well as the kind of solvent and the condition of the adsorbent's surface, are discussed. Sedimentation and viscosity measurements and results concerning Aerosil suspensions are discussed and compared with the adsorption data.
Effect of shear on the crystallization kinetics of poly(ethylene oxide) and poly(e‐caprolactone) melts
Authors: Sherwood C. H. , Price F. P. , Stein R. S.
Published: June 2010

The effect of shear on polymer crystallization kinetics has been studied for three materials at several shear rates and degrees of supercooling. Two poly(ethylene oxide) samples, with molecular weights of 72, 200 and 12, 600, and a poly(e‐caprolactone) material, with a molecular weight of 9, 400, were investigated. The apparatus used was a concentric cylinder viscometer, which also functions as a dilatometer, capable of detecting very small volume changes on crystallization. The shear‐rate range of the experiments was 0 to 60 sec−1. Avrami kinetics were used to describe the transformation process and the exponent was found to increase from the quiescent value of 3 to a value greater than 5 with increasing shear rate for all materials studied. The acceleration in the transformation process was associated with a reduction in induction time. The value of induction time at high shear rates did not significantly decrease with increasing shear rate, indicating a saturation effect with shear. This was most pronounced in the low molecular weight samples. The value of induction time for the high molecular weight poly(ethylene oxide) sample, under identical experimental conditions, was substantially less than that of the low molecular weight material in all cases. Nuclei formation measurements were made for the crystallizing melt in a separate instrument. Nuclei formation under shear was very different from quiescent behavior and increased substantially with increasing shear rate. These experimental observations lead to the conclusion that accelerated crystallization is due to increased molecular chain extension and orientation under shear. This orientation greatly enhances the nucleation process, which is thought to be the rate controlling step in the crystalline transformation. This enhancement results in shorter induction times and more rapid crystallization.
The differential scanning dilatometer and phase transitions in liquid crystals
Authors: Armitage D. , Price F. P.
Published: June 2010

The performance of a differential scanning dilatometer is described in terms of the volume changes recorded near the isotropic to cholesteric transition for cholesteryl laurate. The instrument is also applied to a study of crystallization kinetics. The isotropic–nematic phase transition in p‐azoxyanisole was also examined by optical microscopy. An instability in the phase boundary is observed at increasing transformation rates. Size effects on this transition are investigated by absorbing the sample in porous silica. The transition is depressed 0.3°K in a 300 Å diameter pore.
A method for obtaining high modulus polyethylene from the melt: The influence of crystal nucleation
Authors: Keller A. , Odell J. A.
Published: June 2010

A method is presented by which polyethylene filaments of exceptionally high modulus (500–1000 kbar) can be prepared from flowing melts. The method relies on the formation of fibrous crystals which are directly flow–induced, but are present in sufficiently small quantities not to block the flow of the melt. If the rest of the still uncrystallized material is induced to crystallize onto these fibers, which then serve as nuclei, under enhanced hydrostatic pressure, the ultrahigh moduli are obtained. In addition to their relevance to mechanical behavior these observations point to some novel aspects of crystal nucleation by fibrous substrates and to the way such nucleation can influence the modulus.
Problems with the popular theory of linear viscoelasticity
Authors: Farris Richard J.
Published: June 2010

The popular theory of linear viscoelasticity based upon representations using distributions of relaxation or retardation times is shown to be a subset of admissible response functions for these materials. The essential missing feature in the popular theory is that it cannot yield a zero energy dissipation rate at short times or high frequencies. Consequently, truly elastic response from an energy point of view cannot be contained in such models of viscoelastic behavior. It is shown that this limitation can be removed if models which include molecular inertial effects are included. It is also shown that the free‐energy functional and the energy‐dissipation functional cannot be uniquely determined from the stress‐strain response and that popular constraints placed on the relaxation functions are overly restrictive and limit otherwise admissible response.
Nucleation and crystal growth in sheared poly(1‐butene) melts
Authors: Wolkowicz Michael D.
Published: June 2010

The nucleation and growth behavior of a poly(1‐butene) melt has been measured as a function of undercooling and shear rate. Experiments were conducted using a parallel‐plate rotary shearing device with polarized light microscopy as the measuring technique. An exponential increase of nuclei with time at constant undercooling and shear rate was found. Growth rates of the crystalline bodies showed no significant change in a shear field. Nucleation and growth rate data were analyzed using expressions of the form I = I0 exp [‐ΔE/RT ‐ UTm/TΔT] G = G0 exp [‐ΔE/RT ‐ UTm/TΔT] where ΔT is the undercooling, Tm is the equilibrium melting temperature, and U contains lateral s̀ and end‐surface s̀e free energies. The value of s̀s̀e calculated from U for crystallization under shear differed from that calculated for the quiescent case by a factor of two. This difference is tentatively explained in terms of an entropy loss in the sheared system.
Some aspects regarding the structure and the mechanism of the PVC synthesis
Authors: Caraculacu A. , Buruiană E. , Robilă Gabriela
Published: June 2010

The behavior of models of PVC‐unsaturated end groups subjected to radical reactions indicates the important role some of these groupings play in the after‐polymerization processes. As a result the respective groups lead to new types of abnormal structures in PVC. The PVC head‐to‐head macroradical is thought to play an essential role in the branching formation and the occurring of the interruption processes leading to labile unsaturated end groups. Based on these results correlated with direct measurements of unsaturated structures in PVC, a reaction mechanism is suggested to explain these phenomena.
Preparation of poly amides via the phosphorylation reaction. I. Wholly aromatic polyamides and polyamide‐hydrazides
Authors: Preston J. , Hofferbert W. L.
Published: June 2010

Aromatic polyamides of the AB, AA–BB, and ordered copolyamide types plus aromatic hydrazide and amide–hydrazides were prepared via the phosphorylation reaction. The relationship of the molecular weight, as evidenced by the inherent viscosity values obtained, of the several polymers to the structural features and properties of the monomers used and the polymers obtained is discussed in detail. Some salient observations are that poor solubility of the rodlike polymers definitely appears to set limits to obtaining high molecular weight and strongly basic groups, e.g., —CO—NH—NH2, in monomers, prevent the attainment of high molecular weight because such groups coordinate more strongly with the phosphite complex than does the pyridine catalyst in the phosphorylation reaction. Fibers were spun from two aromatic polyamides prepared via the phosphorylation reaction. Excellent tensile properties were achieved for fiber from poly–p–benzamide (PPB) and the polyisophthalamide of 4, 4′‐methylenedianiline despite the relatively low molecular weight of these polymers (?7inh 1.6 and 1.1, respectively). The PPB fiber was spun from both isotropic and anisotropic spinning solutions. Fiber obtained from the anisotropic dope had moderately high tensile strengths (8–12 gpd) and remarkably high initial modulus values (435–745 gpd). These results indicate that polymers made by the phosphorylation route would give fibers with as high tensile properties as polymer made by the diacid chloride‐diamine polycondensation route providing that the inherent viscosities of polymer prepared by the former process could be increased to equal those by the latter process.
The polymerization of phenylacetylene in the presence of ferric acetylacetonate and triethylaluminum
Authors: Nguyen H. X. , Amdur S. , Ehrlich P. , Allendoerfer R. D.
Published: June 2010

The polymerization of phenylacetylene initiated by ferric acetylacetonate and triethylaluminum was studied over the temperature range −30°−70°, in bulk as well as in the presence of diluents, and over a range of catalyst compositions and concentrations. The product consisted of four major fractions: crystalline polymer of molecular weight about 7000 and a very narrow molecular‐weight distribution (MWD), (fraction I); somewhat lower‐molecular‐weight amorphous polymer with a broader MWD (fraction II); linear oligomer (fraction III); and the asymmetric cyclic triphenyl‐benzene (fraction IV). The average degree of polymerization, of fraction I (65–70) is independent of all polymerization variables, that is, temperature from −30° to 70°C, the presence or absence of diluent (tetralin or benzene), and catalyst concentration and composition. The MWD is narrow with M̄w/M̄n equal to 1.05 or less. The results suggest that thermodynamic rather than kinetic factors limit the size of the polymer. A possible mechanism is proposed.
Ultrahigh‐modulus fibers from rigid and semirigid aromatic polyamides
Authors: Alfonso Gian Carlo , Bianchi Estella , Ciferri Alberto , Russo Saverio , Salaris Franco , Valenti Barbara
Published: June 2010

Intrinsic viscosity, concentrated‐solution viscosity, and fiber properties of poly(p‐benzamide) (PBA) and the polyterephthalamide of p‐aminobenzhydrazide (X‐500) are presented. PBA yields high‐modulus fibers from solution spinning of anisotropic dopes, and X‐500 yields high‐modulus fibers from isotropic solutions. Both polymers exhibit a wormlike conformation. However, with a low‐molecular‐weight PBA (10,500) an essentially rigid conformation prevails. The viscosity of both polymers goes through a maximum and a minimum on increasing polymer concentration. However, for PBA the maximum and minimum are observed at low shear stress, and for X‐500 the discontinuity is observed only at high shear rate. The initial modulus of low‐molecular‐weight PBA fibers is unaffected by LiCl concentration but increases with polymer concentration of anisotropic dopes. X‐500 (molecular weight, 41,000) is unable to form an anisotropic solution at rest. The initial modulus of X‐500 is unaffected by LiCl but depends slightly on polymer concentration. Both shear and elongational flow contributions appear to be secondary for truly stiff polymers. Orientation is controlled by polymer concentration, and the modulus of low‐molecular‐weight PBA attains the ultrahigh level even for “as‐spun” fibers. On the contrary, control of shear and elongational parameters is shown to be essential, and feasible, in order to match the as‐spun modulus of PBA, with semirigid polymers unable to form anisotropic solutions at rest.
A new technique for molding poly(hema) gels
Authors: Štol M. , Šulc J. , Stoy V. , Raab M.
Published: June 2010

A new technique for molding poly(2‐hydroxyethyl methacrylate)—poly(HEMA) is outlined which offers some advantages over existing procedures such as polymerization casting or mechanical processing of polymerized blocks. This technique also extends the possible biomedical applications of this material.
The influence of probe concentration on the determination of tg in polymers by inverse gas chromatography
Authors: Llorente M. A. , Menduiña C. , Horta A.
Published: June 2010

Retention volumes are studied as a function of probe concentration in order to establish the optimum conditions to detect the polymer glass‐transition temperature. Poly (cyclohexyl methacrylate) is used as stationary phase and the probes tested are benzene (good solvent), 4‐heptanone (moderate solvent), n‐decane, and n‐dodecane (nonsolvents). At temperatures below Tg, a diffusion limited process (probably bulk penetration of the probe in the glassy polymer) is present over a range of probe concentrations. In the case of benzene, this process persists in up to very large concentrations and is responsible for the difficulties in the determination of Tg encountered previously with such a good solvent. By properly choosing the probe concentration, it is possible to minimize the influence of such a process and to obtain Tg estimates (with all the probes tested, including benzene) which are in quantitative agreement with the value determined by differential scanning calorimetry.
Low‐temperature calorimetry of biological macromolecule solutions
Authors: Andronikashvili E. L. , Mrevlishvili G. M. , Japaridze G. Sh. , Sokhadze V. M. , Tatishvili D. A.
Published: June 2010

The thermal properties of several biopolymeric (DNA, RNAse, Folch‐Pi apoprotein)–water systems have been investigated by low‐temperature adiabatic differential scanning microcalorimetry. Determination of the heat change and temperature of fusion of the water and eutectic mixture allowed resolution of the various water states in native polymer solutions and before and after heat denaturation of the macromolecules.
Calorimetric study on the state of water in microbial cells
Authors: Shinohara A. , Nunomura K. , Fujita T.
Published: June 2010

Calorimetric studies were carried out on partly dried yeast cells and some model substances supposed to afford the major binding sites in the yeast cells. The heat of vaporization and thawing as well as the water vapor sorption isotherm of yeast cells suggest that part of the cell water is somewhat bound to dry matter components and loses some of its responses observed when it is in bulk phase. Cell water down to 25% freezes and has the same value of differential heat of vaporization as in the bulk phase (10.5 kcal/mol). The contents of unfreezable water calculated from the heat of thawing obtained with yeast mannan, yeast RNA, bovine serum albumin (BSA), and the whole yeast cells are 43, 35, 30, and 25%, respectively. The calorimetric data obtained for yeast cells and their component molecules indicate that the magnitude of their interaction with water molecules are in the order of mannan, bovine serum albumin (BSA), and the whole yeast cells. The physical properties of water in yeast cells cannot be explained from those bound to their separate components. This may in part be due to some interactions between these molecules that change their binding properties with water molecules in yeast cells.
Development of new technologies for solid‐state polymerization. A conceptual and experimental approach
Authors: Foxman Bruce M. , Jaufmann J. D.
Published: June 2010

A review of an extensive study on the preparation and solid‐state reactivity of squareplanar NiX2L2 complexes is presented, where X = Cl, Br, I, or NCS and L = P(CH2CH2CN)3. Physical, chemical, and crystallographic criteria have been evaluated for such complexes, from the viewpoints of the properties and reactivity of the squareplanar monomer and the analogous octahedral polymer. Factors such as nearest‐neighbor interactions, nucleation, temperature, doping, polymorphism, and crystal symmetry greatly influence the course of the thermal solid‐state reactions. The reactions per se are characterized by chemical and crystallographic specificity, stereodirectionality, highly anisotropic front motion in single crystals, and reversibility. In a series of preliminary, related experiments, the radiation‐induced polymerization of salts and complexes of β‐acryloxypropionic acid and propiolic acid has been studied; there is a great variation in reactivity among these species. Many of the reactive phases have short contacts between neighboring molecules which would appear to satisfy topochemical criteria for reaction in the solid state.
Properties of polyacetylene doped with hexachloroiridate
Authors: Rubner M. F. , Druy M. A. , Tripathy S. K. , Sichel E. K. , Georger J. , Cholewa P. , Knowles M. , Cukor P.
Published: June 2010

Polyacetylene was doped from solution with dihydrogen hexachloroiridate (H2IrCl6·6H2O), and also doped electrochemically with tetra‐n‐butylammonium hexachloroiridate(IV) (NBu4)2IrCl6·6H2O to form electrically conductive complexes. The doped polymer was characterized by ultraviolet, visible, and infrared spectroscopy, X‐ray diffraction, EPR spectroscopy, transmission electron microscopy, and electrical transport measurements. A hydrolyzed hexachloroiridate species was incorporated in the polymer during spontaneous doping with H2IrCl6·6H2O, whereas electrochemical doping with (NBu4)2IrCl6·6H2O resulted in the introduction of the expected hexachloroiridate species. Evidence suggests that, in the case of H2IrCl6·6H2O, doping occurs by a proton acid mechanism. TEM studies indicate that the hexachloroiridate dopant is not distributed homogeneously in the polymer. The stability of hexachloroiridate‐doped polyacetylene was examined in air, in an inert atmosphere, and at high temperatures. In air, the rate of decrease of the conductivity was about one order of magnitude per 28 days, whereas in an inert atmosphere, the conductivity dropped about one order of magnitude per 250 days.
Polycarbosilane precursors for silicon carbide
Authors: Schilling C. L. , Wesson J. P. , Williams T. C.
Published: June 2010

Thermoplastic polycarbosilane precursors for silicon carbide were prepared in high yield through potassium metal dechlorinations of mixtures of vinylic or chloromethyl (ClCH2 —) methylchlorosilanes with other methylchlorosilanes in tetrahydrofuran solvent. Monomer mixtures are selected to maximize formation of backbone silicon‐carbon bonds and to maximize backbone branching at silicon, while retaining high synthetic yield and tractability and high yield of silicon carbide composition on pyrolysis. These precursor polymers are nonhazardous, relatively inert, i.e., stable to air and moisture, and have been spun to fiber form for ultimate conversion to silicon carbide fibers.
Polyetherimide: A new high‐performance thermoplastic resin
Authors: Johnson Robert O. , Burlhis Harold S.
Published: June 2010

A new high‐performance amorphous thermoplastic, named polyetherimide, has been developed by the General Electric Company. This resin is characterized by high deflection temperature (200°C at 264 psi), high tensile strength and flexural modulus (480,000 psi), and very good retention of mechanical properties at elevated temperatures. In addition, the resin exhibits good electrical properties, which remain stable over a wide range of temperature and frequencies (including microwave). Polyetherimide is inherently flame resistant without the use of additives. It has a high limiting oxygen index of 47, combined with NBS smoke chamber results which show the lowest specific optical density of any unfilled thermoplastic (Dmax = 31). One synthetic method for the preparation of polyetherimides and a comprehensive property profile of the first member of this polymer family are presented.
Molecular weight dependence of the sintering‐flow behavior for particulate polystyrenes
Authors: Denny Lisa Richards , Panichella Kathleen M. , Boyer Raymond F.
Published: June 2010

A series of particulate anionic PSs having M̄n values from 1900 to 350,000 has been observed visually on a hot‐stage microscope at heating rates from 0.2 to 10 K/min. The temperature range over which the particles sinter, coalesce, and flow onto the glass slide is relatively narrow and reproducible. The temperature corresponding to a specific optical appearance is designated Tf (for flow temperature) and appears to represent an isoviscous state. It decreases as M̄n−1 below Mc, and increases as M̄n (or possibly M̄w above Mc, where Mc is the entanglement molecular weight Tf values at 10 K/min are only slightly below TII temperatures observed by DSC and by torsional braid analysis. A plot of log heating rate versus Tf−1 with only five points for M̄n = 17,100 is clearly non‐Arrhenius and appears to follow a Vogel or WLF‐type equation. Tf is greater than and distinct from Tg at all heating rates except as M̄n becomes less than about 2000 where the two processes tend to merge. Tf is independent of the several substrates tested: glass, Mylar, carbon, mica, Al, Al2O3, and PS. Globule formation which occurs just below Tf is probably a surface tension phenomenon. Its temperature, Tg1, decreases as M̄n−2/3 at M̄n > Mc. It appears to represent an iso‐surface tension state. Origins of the endothermic peak observed by DSC on powder on first heating and the endothermic slope change found with melted films on subsequent heatings are proposed. Observations of Tg1 and Tf were made on poly(p‐methylstyrene) and poly(p‐tert‐butylstyrene) but will be reported elsewhere.
Analysis and structure of dicumyl peroxide ultraviolet‐cured poly(dimethyl siloxane) rubber crosslinks
Authors: Barrall Edward M. , Hawkins Ray , Fukushima Alice A. , Johnson Julian F.
Published: June 2010

The alkaline fusion method for the analysis of the hydrocarbon portion of poly(dimethyl siloxane) gum stock containing pendant vinyl groups has been applied to systems crosslinked with dicumyl peroxide in the presence of near‐UV radiation. Crosslinks made of butyl and propyl chains both with and without aromatic residues were found. Under the conditions of this study the dicumyl peroxide efficiency as a crosslinking agent is slightly greater than one. Owing to the formation of three carbon‐containing crosslinks, the total chemical crosslink density of the system was greater than predicted from simple vinyl‐to‐vinyl addition.
Synthesis and polymerization of water‐soluble polydiacetylenes
Authors: Patel G. N. , Preziosi A. F. , Bhattacharjee H. R.
Published: June 2010

Synthesis of two classes of water‐soluble polydiacetylenes °CR—CC—CRx is presented. Class I has carboxylic acid [R = —(CH2)nCOOH] and their salts as the side group, while the class II has urethane–carboxylic acid [R = —(CH2)nOCONHCH2COOH] and their salts as the side group. Monomers of class I were prepared by oxidation of diacetylenes having R = —(CH2)n+1OH group, while those of class II were prepared by hydrolysis of diacetylenes having R = —(CH2)nOCONHCH2COO(CH2)nCH3 group. The monomers polymerize in the solid state either upon thermal annealing or upon exposure to high‐energy radiation. 1HAU, R = —CH2OCONHCH2COOH, polymerizes quantitatively upon thermal annealing. The heat of polymerization (130 kJ/mol) and the activation energy of polymerization (110 kJ/mol) as determined by differential scanning calorimetry are in agreement with those reported for other diacetylenes.
Development of low temperature polycondensation processes and aromatic polyamides
Authors: Morgan Paul W.
Published: June 2010

There are two principal types of low temperature polycondensation processes: the two‐phase process known as interfacial polycondensation and a single liquid phase process or solution polycondensation. Both procedures are widely used experimentally and have led to the preparation and evaluation of thousands of polymers. Types of polymers which are made commercially are polycarbonates, block elastomers, polyimides, and aromatic polyamides. Aromatic polyamides are produced commercially for two major end uses: (1) flame and heat resistant polymers in the form of fibers, films, molding powders, and papers, and (2) polymers with extended chains for high strength, high modulus fibers. The latter class of polymers give liquid crystalline solutions which make possible the direct formation of highly oriented, high strength fibers. Aramid fibers of this type are useful in cut resistant clothing, ballistics protection, asbestos replacement, ropes and cables, and reinforcement of resins and rubber. Continuing research on the low temperature procedures is leading to new variations and applications of these processes.
Theory of electrophoresis of polyelectrolytes through gels
Authors: Dejardin Phillippe , Lumpkin Oscar J. , Zimm Brunoh.
Published: June 2010

We assume that the polyelectrolyte moves through a “tube” in a neutral gel under the influence of the electrical field. The tube is random except for possible bias due to the effects of the field. We also assume a frictional coefficient proportional to contour length for longitudinal motion in the tube. When the field is small, we easily recover the inverse‐length dependence of the mobility found previously by de Gennes and by Doi and Edwards. At higher fields a new effect appears; the tube becomes oriented because the field biases the direction of the leading end of the chain as it moves to form an extension of the tube. This leads to an increase of the mobility with increasing field.
Statistics of unentangled polymer loops and primitive paths
Authors: Helfand Eugene , Pearson Dale S.
Published: June 2010

The concepts of reptation and the tube model have been successfully used to describe the dynamics of a system of entangled polymers. Attempts to apply this model have given rise to questions about the statistics of a polymer, represented by a lattice random walk, and its entanglement with an obstacle net. We have determined the number of ways such a walk can form unentangled closed loops of various types. If one reels in a general random walk from its ends, pulling out unentangled loop, one is left with the so‐called primitive path, which is taken to represent the path of the tube. The probability that an N step random walk has a K step primitive path has been calculated. Asymptotic formulas for this probability are presented.
Light‐scattering studies of polymer solution dynamics
Authors: Chu B.
Published: June 2010

Laser light scattering has been used to study the static and dynamic properties of polymers in solution. Interpretation of the intermediate scattering function S(K, t) from the center‐of‐mass diffusion to internal motions for both polymer coils and semiflexible chains is discussed. Crossover behavior of dynamic properties in dilute and semidilute solution regimes for polymers of finite molecular weight, instead of limiting scaling law exponents, is emphasized.

The complimentary nature of modern scattering techniques, as well as the use of specific probes, including anomalous scattering with synchrotron radiation, are likely to play an increasingly important role in investigating more complex interacting polymeric species, such as block copolymers, polyelectrolytes, and ionomers.

Measurements of time correlation function and methods of data analysis have been developed to determine the molecular weight distribution of synthetic polymers in dilute solution. In addition to center‐of‐mass diffusion studies in dilute solution from the good solvent region to the collapsed state, determinations of both cooperative and self‐diffusion coefficients in semi‐dilute solutions are within reach. Further quantitative analysis of S(K, t) awaits better theoretical models in the intermediate K range in semidilute solutions.
Diffusion and brownian motion of polymeric liquids
Authors: Baumgärtner A.
Published: June 2010

The dynamics of dense model systems of pearl‐necklace polymer chains, consisting of up to N = 98 hard spheres each, has been investigated using Monte Carlo methods. Excluded volume conditions as well as entanglement constraints have been taken into account. The time‐dependent displacement of a single monomer on the chain follows the classic Rouse equation gr(t) α t1/2 until the monomer equilibrates, whereas the diffusion constant for the center‐of‐mass motion is in agreement with the reptation law D α N−2±0.2. The equilibration time for conformational fluctuations is given by the Rouse equation Te α N2, whereas the disengagement time, after which the motion of the monomers is dominated by the center‐of‐mass motion, is given by Td, α N3.4±0.2.
Ribonuclease S‐peptide as a carrier in fusion proteins
Authors: Kim Jin‐Soo , Raines Ronald T.
Published: June 2010

S‐peptide (residues 1–20) and S‐protein (residues 21–124) are the enzymatically inactive products of the limited digestion of ribonuclease A by subtilisin. S‐peptide binds S‐protein with high affinity to form ribonuclease S, which has full enzymatic activity. Recombinant DNA technology was used to produce a fusion protein having three parts: carrier, spacer, and target. The two carriers used were the first 15 residues of S‐peptide (S15) and a mutant S15 in which Asp 14 had been changed to Asn (D14N S15). The spacer consisted of three proline residues and a four‐residue sequence recognized by factor Xa protease. The target was β‐galactosidase. The interaction between the S‐peptide portion of the fusion protein and immobilized S‐protein allowed for affinity purification of the fusion protein under denaturing (S15 as carrier) or nondenaturing (D14N S15 as carrier) conditions. A sensitive method was developed to detect the fusion protein after sodium dodecyl sulfate‐polyacrylamide gel electrophoresis by its ribonuclease activity following activation with S‐protein. S‐peptide has distinct advantages over existing carriers in fusion proteins in that it combines a small size (≥15 residues), a tunable affinity for ligand (Kd ≥ 10−9 M), and a high sensitivity of detection (≥10−16 mol in a gel).
On the diffusion coefficients and stability of van der Waals complex Hg… N2
Authors: Ilc̆in Michal , Lukeš Vladimír , Buc̆inský Lukáš , Laurinc Viliam , Biskupic̆ Stanislav
Published: June 2010

The supermolecular CCSD(T) ab initio calculations of potential energy surface for the electronic ground state of van der Waals complex formed from a mercury atom and a nitrogen molecule are presented. Our calculations indicate the bent orientation (Jacobi coordinates are rNN = 1.103 Å, R = 4.38 Å, angle θ = 64.4°) of the van der Waals (vdW) system with a well depth De = 89.1 cm−1. The physical origin of the stability of the studied vdW structure was analyzed by the Symmetry Adapted Perturbation Theory. The separation of its interaction energy shows that the dispersion interaction is approximately two‐times stronger than the induction one and approximately four‐times higher than the electrostatic energy. The theoretical coefficient of diffusion is in good agreement with the experimental value. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Arsenic exposure induces genomic hypermethylation
Authors: Majumdar Sunipa , Chanda Sarmishtha , Ganguli Bhaswati , Mazumder D. N. Guha , Lahiri Sarbari , Dasgupta Uma B.
Published: June 2010

Gene‐specific hypermethylation has previously been detected in Arsenic exposed persons. To monitor the level of whole genome methylation in persons exposed to different levels of Arsenic via drinking water, DNA was extracted from peripheral blood mononuclear cells of 64 persons. Uptake of methyl group from 3H labeled S‐Adenosyl Methionine after incubation of DNA with SssI methylase was measured. Results showed statistically significant (P = 0.0004) decrease in uptake of 3H methyl group in the persons exposed to 250–500 μg/L arsenic, indicating genomic hypermethylation. © 2009 Wiley Periodicals, Inc. Environ Toxicol, 2010.
Increased efficacy of early spinal cord stimulation in an animal model of neuropathic pain
Authors: Truinl Michiel , van Kleefl Maarten , Linderothl Bengt , Smitsl Helwin , Janssenl Sofie P.M. , Joostenl Elbert A.J.
Published: June 2010

Although spinal cord stimulation (SCS) is an established treatment for chronic neuropathic pain, pain relief is still not successful in a large group of patients. We suggest that the success of SCS may be related to the timing of SCS during the development of chronic neuropathic pain. We therefore compared the effect of SCS applied after 24 h of neuropathic pain (early SCS) and after 16 days of neuropathic pain (late SCS).

For early SCS, male Sprague—Dawley rats (n =13) were implanted with an SCS device, followed by a partial ligation of the sciatic nerve. Using von Frey monofilaments, tactile allodynia was assessed 24 h after ligation. Animals with tactile allodynia received 30 min of SCS. Withdrawal thresholds were assessed just before SCS, during SCS and until the return to pre‐stimulation withdrawal threshold. Results were compared with the data from late SCS (n =29).

Out of the 13 allodynic animals that received early SCS, 10 (77%) responded to SCS with significantly increased withdrawal thresholds, compared to 38% in the late SCS group. The increase of the withdrawal threshold in the early SCS group could still be noticed 90 min after termination of SCS. In more than half of these animals, pre‐stimulation withdrawal thresholds were reached only the next day. Early SCS resulted in an increased number of responders to SCS and furthermore an increased duration of the effect of SCS as compared to late SCS.

Early SCS treatment of neuropathic rats is more effective as compared to the late SCS treatment.
A Comparison of Excessive Postpartum Blood Loss Estimates Among Three Subgroups of Women Attending Births in Matlab, Bangladesh
Authors: Edmonds Joyce K. , Hruschka Daniel , Sibley Lynn M.
Published: June 2010

Introduction: Postpartum hemorrhage (PPH) is the leading cause of maternal death and disability worldwide. The recognition of PPH depends on subjective visual quantification. This study sought to assess and compare the thresholds for excessive postpartum blood loss reported by skilled birth attendants (SBAs), traditional birth attendants (TBAs), and laywomen in Matlab, Bangladesh.

Methods: Data from six questions asking about excessive blood loss in the postpartum period were analyzed using analysis of variance, the Hochberg test, the Kruskal–Wallis test, and standard descriptive statistics.

Results: We found that the thresholds for excessive blood loss estimated by laywomen and TBAs exceed the biomedical standards for PPH. Skilled birth attendant reports are consistent with the definition of severe acute PPH.

Discussion: Further research on locally validated blood collection devices, in birth kits, for diagnostic aid or referral indication is needed. Areas where the coverage and uptake of skilled birth attendance are low should be targeted because of the number of homebirths attended by TBAs and laywomen in such settings.
A Meta‐analysis of the Efficacy of Ocular Prophylactic Agents Used for the Prevention of Gonococcal and Chlamydial Ophthalmia Neonatorum
Authors: Darling Elizabeth K. , McDonald Helen
Published: June 2010

Introduction: Neonatal eye prophylaxis has been routine in North America for more than a century. Contextual changes justify reexamining this practice, and prompted a systematic review of the efficacy of prophylactic agents.

Methods: We searched MEDLINE (1966–2008), EMBASE (1980–2008), CINAHL (1982–2008), and the Cochrane library (the first quarter of 2008) for relevant clinical trials and hand‐searched the resulting reference lists. We independently evaluated eligibility and study quality. Meta‐analyses were performed using a random effects model.

Results: Each of the eight included studies had substantial methodologic weaknesses. Data to estimate the efficacy of prophylaxis in the prevention of gonococcal ophthalmia neonatorum (GON) were not available. One study found no differences in rates of chlamydial ophthalmia neonatorum (CON) when three agents were compared to no prophylaxis: silver nitrate (relative risk [RR] = 1.06; 95% confidence interval [CI], 0.55–2.02; 2225 newborns), erythromycin (RR = 0.93; 95% CI, 0.48–1.79; 2306 newborns), and tetracycline (RR = 0.82; 95% CI, 0.42–1.63; 2299 newborns). No statistically significant differences were found between agents in the prevention of GON. Erythromycin and povidone‐iodine both decrease the risk of CON when compared to silver nitrate (RR = 0.71; 95% CI, 0.52–0.97; 4514 newborns, and RR = 0.52; 95% CI, 0.38–0.71; 2005 newborns, respectively).

Discussion: Failure rates of universal eye prophylaxis support reexamination of this policy where the prevalence of maternal infection is low.
Barriers to Men's Participation in Antenatal and Prevention of Mother‐to‐Child HIV Transmission Care in Cameroon, Africa
Authors: Nkuoh Godlove N. , Meyer Dorothy J. , Tih Pius M. , Nkfusai Joseph
Published: June 2010

Introduction: Men's role in HIV prevention is pivotal to changing the course of the epidemic. When men participate in Prevention of Mother‐to‐Child Transmission (PMTCT) programs, their knowledge of HIV increases, their behavior becomes supportive, and their receptiveness to HIV testing increases. In Cameroon, Africa, multiple efforts have been implemented that encourage men to “follow” their wives to obstetric/PMTCT care and to undergo HIV testing. However, only 18% of men have participated in this care.

Methods: As a quality improvement initiative, a survey was administered to identify men's knowledge and attitudes regarding antenatal care (ANC), PMTCT, and HIV. The survey consisted of a questionnaire with an emphasis on identifying barriers to men's participation in PMTCT programs and obtaining HIV testing. A convenience sampling method was used, and no participant identifying information was collected.

Results: Men's participation in ANC/PMTCT is affected by sociocultural barriers centered in tribal beliefs and traditional gender roles. The barriers identified included the belief that pregnancy is a “woman's affair”; the belief that a man's role is primarily to provide financial support for the woman's care; the man's perception that he will be viewed as jealous by the community if he comes to clinic with his pregnant wife; and cultural gender‐based patterns of communication.

Discussion: Most men consider accompanying their wife to ANC/PMTCT a good practice. Yet fewer men actually do this, because they feel that the provision of finance for ANC registration and delivery fees is their most important role in supporting their wife's pregnancy. Health care workers should encourage individuals and community leaders to build upon the traditional value of financial responsibility, expanding a man's involvement to include supportive social roles in obstetric care, PMTCT, and HIV testing.

J Midwifery Womens Health 2010;55:363–369
Findings From the Analysis of the American College of Nurse‐Midwives' Membership Surveys: 2006–2008
Authors: Schuiling Kerri Durnell , Sipe Theresa Ann , Fullerton Judith
Published: June 2010

Introduction: The American College of Nurse‐Midwives (ACNM) Core Data Survey is an annual membership survey that collects demographic and selected workforce data about certified nurse‐midwives (CNMs), certified midwives (CMs), and students enrolled in midwifery education programs accredited by the Accreditation Commission for Midwifery Education, who are members of the organization. This article presents findings from the analysis of membership data for the years 2006 to 2008.

Methods: An e‐mail invitation to participate in the online survey was sent to all ACNM members who provided ACNM with an e‐mail address. A paper copy of the survey was available upon request. The survey instrument for the years 2006 to 2008 focused on five categories: demographics, certification, education, employment, and licensure.

Results: ACNM member respondents continue to remain predominantly white and female. The average age of CNMs/CMs for 2008 is 51 years, and the majority holds a master's degree as their highest degree.

Discussion: Very few advances have been made in the effort to increase the diversity of ACNM membership. The number of CNMs earning doctoral degrees (including the doctor of nursing practice degree) is increasing. A majority of CNMs/CMs continue to identify a broad domain of clinical midwifery practice as their primary responsibility in their primary employment, and hospitals and physician practices remain the largest employers of midwives. Salaries for midwifery‐related work are rising, but it is unclear if midwives are earning more because salaries are higher or because the higher salaries reflect market wage adjustments that occur over time.
An analytic model of plasma-neutral coupling in the heliosphere plasma
Authors: SHAIKH DASTGEER , DASGUPTA B.
Published: June 2010

We have developed an analytic model to describe coupling of plasma and neutral fluids in the partially ionized heliosphere plasma medium. The sources employed in our analytic model are based on a κ-distribution as opposed to the Maxwellian distribution function. Our model uses the κ-distribution to analytically model the energetic neutral atoms that result in the heliosphere partially ionized plasma from charge exchange with the protons and subsequently produce a long tail, which is otherwise not describable by the Maxwellian distribution. We present our analytic formulation and describe major differences in the sources emerging from these two distinct distributions.
Mind the gap: why neurological plasticity may explain seasonal interruption in humpback whale song
Authors: Wright A.J. , Walsh L.A.
Published: June 2010

Much is unknown about humpback whale (Megaptera novaeangliae) song. The behaviour is limited almost exclusively to males, occurs almost exclusively on the calving grounds and is identical within a population, although it changes periodically throughout the season. Much of current thinking associates humpback whale song with breeding, although it is not clear if it is intended to attract a mate, fend off challengers, or a combination of the two. There is, however, very little information on the internal biology of these large, sea-going mammals, so the majority of hypotheses have not considered much in the way of physiological mechanisms. Nonetheless, we believe that there is enough information available to infer that a seasonal process of neurological development and atrophy similar to that found in other animals may be present in humpback whales. We believe this explains why humpback whale song is not produced between breeding seasons and also why it does not vary between seasons, while it does so within a season. It also adds additional weight to the idea that humpback whale song is an honest signal of fitness to a potential mate or competitor.
Death Becomes Her: Women, Occupation, and Terrorist Mobilization
Authors: Bloom Mia
Published: June 2010

In recent years, the relationship between foreign military occupation and the increased likelihood of violent insurgency and terrorism has been asserted (Pape 2005) but is far from proven. The actual micro-level dynamics that make the correlation between the two sufficient to warrant extended discussion is even less understood and has led a variety of researchers to examine the micro-level foundations of how the presence of foreign military personnel might exacerbate conflict or provide motivation for the local population to mobilize against the foreign troops in their midst (e.g., Downes 2008; Edelstein 2008)
Does an EMILY's List Endorsement Predict Electoral Success, or Does EMILY Pick the Winners?
Authors: Hannagan Rebecca J. , Pimlott Jamie P. , Littvay Levente
Published: June 2010

Women's political action committees (PACs)—those committees founded by women to raise money for women candidates—have been and will likely continue to be an important part of American electoral politics. In this article, we investigate the impact of EMILY's List, because it is the standard bearer of women's PACs and is commonly cited as crucial to women's electoral success. Empirical studies of EMILY's List impact to date have largely assumed causal inference by using traditional linear models. We use a propensity score–matching model to leverage on causality and find that an EMILY endorsement helps some candidates and hurts others. Our findings set the stage for further and more nuanced investigations of when, where, and how EMILY's List can enhance the likelihood of electoral success for women.
Assessing Student Learning Outcomes and Documenting Success through a Capstone Course
Authors: Sum Paul E. , Light Steven Andrew
Published: June 2010

Colleges and universities are increasingly intentional about meeting well-articulated and consistent general education goals and documenting substantive learning outcomes. Institutional imperatives to document the successful teaching of essential knowledge and skill sets frequently fall to faculty and departments, posing new challenges in an environment of time and resource constraints. A capstone course is an increasingly common method to measure student learning and assess programmatic and institutional success. We provide concrete suggestions to design a capstone course and assess student learning outcomes. After describing the structure of the course and four innovative assignments, we present the results of assessment conducted through the capstone. We further the conversation on the development of best practices and how political science departments can align institutional and programmatic goals and lead the way in university assessment.