bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of new technologies for solid‐state polymerization. A conceptual and experimental approach
Authors: Foxman Bruce M. , Jaufmann J. D. 
Published: June 2010

AbstractA 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

AbstractPolyacetylene 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

AbstractThermoplastic 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

AbstractA 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

AbstractA 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

AbstractThe 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

AbstractSynthesis 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

AbstractThere 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

AbstractWe 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

AbstractThe 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

AbstractLaser 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

AbstractThe 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

AbstractS‐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

AbstractThe 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

AbstractGene‐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

AbstractAlthough 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