bluuebunny/crossref_metadata_2025_split huggingface dataset:
Complicated Left-Sided Native Valve Endocarditis in Adults
Authors: Hasbun Rodrigo , Vikram Holenarasipur R. , Barakat Lydia A. , Buenconsejo Joan , Quagliarello Vincent J. 
Published: April 2003

ContextComplicated left-sided native valve endocarditis causes significant morbidity and mortality in adults. Lack of valid data regarding estimation of prognosis makes management of this condition difficult.ObjectiveTo derive and externally validate a prognostic classification system for adults with complicated left-sided native valve endocarditis.Design, Setting, and PatientsRetrospective observational cohort study conducted from January 1990 to January 2000 at 7 Connecticut hospitals among 513 patients older than 16 years who experienced complicated left-sided native valve endocarditis and who were divided into derivation (n = 259) and validation (n = 254) cohorts.Main Outcome MeasureAll-cause mortality at 6 months after baseline.ResultsIn the derivation and validation cohorts, the 6-month mortality rates were 25% and 26%, respectively. Five baseline features were independently associated with 6-month mortality (comorbidity [P = .03], abnormal mental status [P = .02], moderate to severe congestive heart failure [P = .01], bacterial etiology other than viridans streptococci [P&amp;lt;.001 except Staphylococcus aureus, P = .004], and medical therapy without valve surgery [P = .002]) and were used to create a prognostic classification system. In the derivation cohort, patients were classified into 4 groups with increasing risk for 6-month mortality: 5%, 15%, 31%, and 59% (P&amp;lt;.001). In the validation cohort, a similar risk among the 4 groups was observed: 7%, 19%, 32%, and 69% (P&amp;lt;.001).ConclusionsAdults with complicated left-sided native valve endocarditis can be accurately risk stratified using baseline features into 4 groups of prognostic severity. This prognostic classification system might be useful for facilitating management decisions.
Variability in reproductive success viewed from a life‐history perspective in baboons
Authors: Altmann Jeanne , Alberts Susan C. 
Published: April 2003

AbstractNonhuman primates, like humans, mature slowly and have low fertility during a relatively long life. As data have accumulated on life‐history patterns of nonhuman primates, comparative studies have yielded important insights into the evolution of this slow life‐history style of primates. However, in order to understand selection pressures and evolutionary potential within species, it is important to complement comparative studies with detailed studies of life‐history variability within species and to identify sources of this variability. Here we present a summary of how foraging environment, social status, and group size (a measure of population density) contribute to within‐population variance in reproductive success for savannah baboons. We also discuss the extent to which savannah baboons, with their highly flexible and adaptable behavior, change their foraging environments by shifting home ranges and seeking rich food sources and how low‐ranking females, which disproportionately bear the costs of social life, may mitigate those costs. Am. J. Hum. Biol. 15:401–409, 2003. © 2003 Wiley‐Liss, Inc.
The effect of solvents on high molecular weight, stable acetal resins
Authors: Alsup R. G. , Punderson J. O. , Leverett G. F. 
Published: April 2003

AbstractHigh molecular weight polyoxymethylenes are not soluble at room temperature in any of the hundreds of solvents or solvent systems tested. However, solutions can be obtained at elevated temperatures with a wide variety of solvents. Phenolic compounds are the most effective at temperatures of 50–100°C. At the other extreme of solubility, solvents are absorbed by the acetal polymer in varying amounts, depending on the crystallinity of the polymer and the cohesive energy density of the solvent. The absorption is concentrated entirely in the noncrystalline region of the polymer.
The kinetics of the thermal degradation of the synthetic styrenated polyester, laminac 4116
Authors: Anderson David A. , Freeman Eli S. 
Published: April 2003

AbstractThe kinetics of the thermal decomposition of the polyester, Laminac 4116, were investigated in air and argon at atmospheric pressure by means of a continuous recording thermobalance and by differential thermal analysis. Samples were heated from ambient temperature to 600°C. at rates of 5°/min. and 15°/min. In air and argon, decompostion commences at 200°C. and is complete at 550 and 450°C., respectively. Four modes of degradation in oxygen and two in argon are indicated from derivative plots of the thermogravimetric curves. The kinetics of reaction were evaluated by the method of Freeman and Carroll. In the presence of air, the initial stage of reaction appears to involve formation of an unstable hydroperoxide intermediate which undergoes rearrangement and degradation. The energy of activation was calculated to be 19 kcal./mole. An exotherm corresponding to this first stage of degradation is observed by differential thermal analysis. The second and third stages of reaction in air correspond approximately to the two stages in argon with respect to their endothermal nature and to the temperature regions over which they occur. Mass spectrometric and infrared analysis were employed for identification of gaseous and volatile products. The fourth stage of reaction in air appears to involve the oxidation of carbon to carbon dioxide. Mechanisms of reaction are proposed and discussed.
Effect of spherulites on the mechanical properties of nylon 66
Authors: Starkweather Howard W. , Brooks Richard E. 
Published: April 2003

AbstractThe presence of spherulites in nylon 66 increases the yield point and reduces the effects of variations in per cent crystallinity. Decreasing the size of the spherulites through increased nucleation results in a higher flexural modulus and yield point, a lower ultimate elongation, and a loss of ductility. These effects are markedly reduced by raising the temperature or water content. The effects of spherulite size in nylon and grain size in metals such as mild steel are compared.
The mechanism of polyethylene oxidation
Authors: Baum B. 
Published: April 2003

AbstractAs evidenced by formation of peroxides and carbonyl, reaction occurs during the oxidation induction period of polyethylene. The meaning of the term oxidation induction period is revealed by the tremendous change in melt index, carbonyl, density, color, tensile, and elongation occurring towards the end of this time period. Hydroperoxide forms long before the end of the oxidation induction period even in the presence of an antioxidant. At any temperature both chain scission and crosslinking occur simultaneously. The rate of oxidation is accelerated by increasing temperature, unsaturation, and branching. Molecular weight seems to have no effect.
Photosensitive polymers. II. Sensitization of poly(vinyl cinnamate)
Authors: Robertson E. M. , van Deusen W. P. , Minsk L. M. 
Published: April 2003

AbstractIt was reported in Part I of this series that coatings of various polymers containing cinnamic ester groups are rendered insoluble by exposure to ultraviolet radiation, and that the rate of insolubilization may be increased by the inclusion of certain organic compounds. A continued systematic examination of the behavior of several hundred organic compounds has revealed that the ability to sensitize to some degree is quite general, provided that no complicating factors are present. The sensitivity of poly(vinyl cinnamate) is decreased by the presence of reducing groups in the addend, and sensitizing activity is lowered by interaction between adjacent groups. It is enhanced by the introduction of increasing conjugation and of ketone, nitro, or amino groups. Spectrograms of polymer‐sensitizer combinations indicate that, with increasing sensitivity value, the sensitivity shifts towards, and, in some cases, into, the visible portion of the spectrum.
Mechanism of lubricant‐extrusion of teflon tfe‐tetrafluoroethylene resins
Authors: Snelling G. R. , Lontz J. F. 
Published: April 2003

AbstractFor an understanding of the phenomenon of lubricant extrusion of Teflon tetrafluoroethylene resin under nonmelt conditions, a mechanism is proposed based on observed extrusion‐hardening and dependence of flow rate on extrusion pressure. These factors can be derived from expressions in which the maximum shearing stress is equated as the sum of two components, one proportional to the maximum shearing strain (strain‐hardening component) and another proportional to the strain rate. Thus, in turn, permits the derivation of an expression for the die pressure drop which is in agreement with the experimental data related to flow rate, die dimensions, lubricant concentrations, and time of extrusion. The analysis provides some insight into aspects of commercial extrusion, particularly in wire coating, with practical consideration of the critical nature of guide tip positioning and the effect of wire coating speed on die pressure.
Interaction of cellulose with small molecules. Glycerol and ethylene carbonate
Authors: Wellisch Eric , Hagan Lamont , Marker Leon , Sweeting Orville J. 
Published: April 2003

AbstractThe equilibrium moisture content of films softened with hygroscopic glycerol or nonhygroscopic ethylene carbonate was determined as a function of softener concentration at 15, 35, 65, 81, and 93% R.H. and compared to the hygroscopicity of unsoftened film and of the pure softeners at the same concentrations. The difference in water content assumed to be caused by interaction between softener and cellulose was calculated in moles of water per mole of softener and per mole of cellulose. A quantitative measure of softener‐cellulose interaction at low and high relative humidities is thus obtained. Ethylene carbonate shows a negative interaction and seems to function only as an inert cushion between cellulose chains, while glycerol interacts with cellulose. This interaction increases with decreasing moisture content (at lower relative humidities) and with increased softener concentration. The softener‐cellulose interaction is a necessary condition for proper softening.
The crosslinking of plasticized poly(methyl methacrylate) by ionizing radiation
Authors: Pinner S. H. , Wycherley V. 
Published: April 2003

AbstractPoly(methyl methacrylate) (PMMA) normally undergoes random main‐chain fracture when exposed to ionizing radiation. In the presence of radical traps, partial protection against degradation may occur, but no crosslinking reactions have hitherto been observed. In this work, diallyl sebacate has been incorporated into PMMA prior to exposure to ionizing radiation (2 m.e.v. electrons). The plasticized PMMA had a low softening point, which was increased by irradiation due to polymerization of the diallyl ester. At the same time, the PMMA was rendered insoluble. With methylene chloride as solvent, the gel fraction greatly exceeded the fraction of diallyl ester present, proving that the PMMA had become crosslinked or incorporated into the allyl network. Beyond a certain dose, however, which varied with the diallyl sebacate weight fraction, continued irradiation led to increased sol fractions and reduced transition temperatures. Spectroscopic measurements showed the disappearance of allyl unsaturation per unit radiation dose to be identical, within experimental error, in the presence of PMMA as in the pure diallyl sebacate. A semiquantitative examination of the gel/dose curve and dynamic energy absorption curves for a sample containing 16% diallyl sebacate has pointed to radicals produced by radiation on the PMMA chains to be the principal initiating species, these becoming junction points to the allyl network. When the gel is depleted of allyl monomer, further radiation causes degradation of the PMMA segments.
Recrystallization of polyethylene during annealing
Authors: Statton W. O. , Geil P. H. 
Published: April 2003

AbstractThe thickness of single crystal lamellae of polyethylene, crystallized from solution, is found to increase greatly during annealing at temperatures above 110°C. The change is observed with small‐angle x‐ray diffraction and electron microscopy. The increase in thickness of the lamellae takes place at the expense of their lateral perfection; holes develop within the lamellae. All evidence indicates that a major refolding of the molecules occurs; this emphasizes the need for a new concept of the amount of motion and freedom that polymer molecules can have in the solid state. A similar process apparently occurs during the annealing of bulk samples crystallized from the melt.
Catalysis of the reaction of urea–formaldehyde precondensates on cellulose
Authors: Steele Richard 
Published: April 2003

AbstractThe reaction of dimethylol urea on cotton cellulose at 150°C. has been studied with NH4Cl and Na2CO3 as catalysts. With the ammonium salt, 0.2 mmole/g. precondensate was required to attain the maximum level of fixed resin, while maximum resistance to hydrolysis by dilute acid required 0.3–0.4 mmole/g. The acid resistance is attributed to the crosslinking of the fiber, which is primarily responsible for the changes produced in resilience and other physical properties. The application of monomethylol urea with NH4Cl does not lead to changes in acid resistance or physical properties such as are attributed to crosslinking. Catalysis with Na2CO3 does not appear to lead to crosslinking with dimethylol urea, since the treated cellulose remains soluble in cuprammonium hydroxide. There is very little difference in the effectiveness of monomethyl and dimethylol ureas for changing physical properties when they are applied with the alkaline catalyst. It is suggested that the curing step with Na2CO3 leads to further condensation through methylene ether linkages rather than to reaction with the cellulose substrate.
Studies on chlorinated polyethylenes. I. Infrared spectra of chlorinated polyethylenes
Authors: Nambu Keiichi 
Published: April 2003

AbstractThe infrared absorption spectra of chlorinated polyethylenes with various amounts of combined chlorine have been investigated, and some data on the mechanism of addition of chlorine to the polyethylene molecule has been studied. When polyethylene is chlorinated in carbon tetrachloride solution at 70°C. by chlorine gas, CH2CHCl and the CHClCHCl units are formed in the main carbon chain, but formation of the CCl2 units could not be detected by the present infrared spectral study.
An apparatus for the determination of the minimum film temperature of polymer emulsions
Authors: Protzman Thomas F. , Brown George L. 
Published: April 2003

AbstractAn apparatus has been constructed for measurement of the minimum filming temperature (MFT) of a polymer emulsion. The apparatus consists of a metal bar along which a temperature gradient may be maintained. Recessed channels are provided in which emulsion samples are spread and allowed to dry. Eight thermocouple stations along the bar are connected to a continuous recorder. Following drying of the film, the minimum temperature at which a continuous film is formed is determined. Testing of the apparatus on one emulsion examined under a variety of conditions and on samples of varying composition has demonstrated the reliability, versatility, and utility of the apparatus.
Mechanical degradation of high polymers
Authors: Bueche F. 
Published: April 2003

AbstractA theory for the shear degradation of high polymers is presented. It assumes the molecules to exist in the rubbery or liquid state and does not include the effects of chemical reactions which might occur subsequent to chain rupture. The computation shows that the entanglements along the chains play a major part in the rupture process. Expressions for the rate of chain rupture are obtained in terms of the melt viscosity, shear rate, and molecular weight. Other factors enter also, but the sensitive variables are those listed. The variation of molecular weight distribution with shear degradation is considered. It is pointed out why oxidative scission during shear is not a random process. In general, the theoretical result agrees with the limited experimental data available.
Molecular basis for the mullins effect
Authors: Bueche F. 
Published: April 2003

AbstractA molecular theory for the softening of filled rubbers which is caused by prestressing is presented. It is based upon the assumption that the centers of the filler particles are displaced in an affine manner during deformation of the rubber. Those network chains which are fastened at both ends to filler particles will break when the filler particles have separated enough to stretch the chains to near full elongation. The loss of these chains causes a prestressed rubber to exhibit a much lower modulus than did the original rubber. Equations are derived to describe this phenomena and are tested by comparing with data for black filled synthetic rubber. Good agreement is found if the filler surface area per chain attachment is taken as 44 A.2 and if the strength of the chain is 2 × 10−4 dynes. It is shown that the chains break loose from the filler particle rather than breaking at C C bonds along the chain. The theory appears to offer a convenient tool for systematic studies of rubber–filler interactions.
The determination of the relative isotactic content of polypropylene by extraction
Authors: Russell Charles A. 
Published: April 2003

AbstractAttention is called to the variables effecting the extraction of polypropylene. Under controlled conditions, the extraction of polypropylene with first diethyl ether and then n‐heptane will give reproducible results. It is necessary to extract with heptane in an atmosphere of nitrogen. The values obtained by the extraction procedure described are regarded as relative measures of the amounts of isotactic, stereoblock and atactic material present in a sample. Extraction with n‐heptane alone by this procedure also gives the same value of relative isotacticity. Infrared studies showed that the ether soluble fractions were essentially atactic, while the n‐heptane‐soluble or stereoblock material possessed a degree of order corresponding to 20–40% isotactic polypropylene.
A study of polymer film brittleness
Authors: Amborski L. E. , Mecca T. D. 
Published: April 2003

AbstractThe inability of polymer chains to deform the required amount within the time allowed by a stress‐to‐failure event results in brittle failure. Factors related to brittle behavior of films were investigated. By both conventional and novel testing techniques, stress–time–temperature relationships were studied to determine the brittle point. From high‐speed tensile tests at strain rates up to 106%/min., the critical strain rate (incipient brittleness as indicated by failure accompanied by a marked decrease in ductility) was determined for representative films. High‐speed motion pictures (6,000 frames/sec.) of film failure in rice bag drop tests, were used to ascertain the time of deformation to be related to brittleness. Deformation rates were calculated to be of the order of 130 to 230 × 103%/min.
Viscous flow of molten polyethylene resins
Authors: Schott Hans , Kaghan W. S. 
Published: April 2003

AbstractA screw extruder and capillary dies of different length radius ratios were used to measure melt flow and end effects for three commercial polyethylene resins, two of low density and one of high density. The apparent melt viscosities of the low density resins decreased faster with increasing shear and temperature than that of the high density resin. Zero shear activation energies for viscous flow were 11.6 and 12.7 kcal./mole for the low density resins and 7.0 for the high density resin. Apparent activation energies at fixed shear stresses were independent of shear stress while apparent activation energies at fixed shear rates decreased with increasing shear rate. End effects and recoverable shear strain were smallest for the high density resin. The differences between the melt flow characteristics of the two types of polyethylene are tentatively correlated with structure.
The estimation of catalytic parameters of metal acetylacetonates in isocyanate polymerization reactions
Authors: Weisfeld L. B. 
Published: April 2003

AbstractThe polyaddition process involving a hydroxy‐terminated linear polyester and an organic diisocyanate in the presence of a series of metal acetylacetonates has been investigated. The method involved kinetic analysis of plasticity build‐up in a Brabender Plastograph. Catalytic orders and relative catalytic constants (kc/k0) were determined for Mn(Aa)3, VO(Aa)2, V(Aa)3, Fe(Aa)3, Cu(Aa)2, Co(Aa)3, and Cr(Aa)3; the constants decrease in that order. Catalytic orders are unity for all complexes save manganese, which is 1.75. No correlation between dissociation potential and catalytic coefficient has been found, and it is believed that catalysis may be associated with the paramagnetic properties of the metal.
Viscoelastic factors in the strength of elastomers under complex stress by a puncture method
Authors: Livingston D. I. , Yeh G. S. , Rohall P. , Gehman S. D. 
Published: April 2003

AbstractInvestigations of the viscoelastic aspects of the mechanical behavior of polymers have been limited almost exclusively to relatively simple conditions of homogeneous stress, that is, to tension or shear loadings. In the present work a study has been made from the viscoelastic standpoint of the response of several elastomers to a much more complex type of stress distribution arising from penetration up to failure by a cylindrical indentor for a range of temperatures and rates of penetration. The failure or “puncture point” was determined by a dip in the recorded curve of load versus depth of penetration. The puncture strength values were reduced to 25°C. by applying the ratio of absolute temperatures and plotted against the logarithm of the reciprocal of the rate of penetration. These curves were then shifted on the time scale to give a master curve after the manner of Tobolsky and of Ferry. The logarithms of the shift factors thus obtained were related to the reciprocal of the absolute temperature over the range studied. The results indicate a broader generality for the viscoelastic principle of time–temperature equivalence than has usually been supposed.
Activated carbon‐loaded rayon monofilaments
Authors: McDowell Robert L. 
Published: April 2003

AbstractRayon monofilaments containing 80% activated carbon were prepared. They are an effective medium for adsorbing noxious odors. High grade gas‐adsorbing carbons are intimately bound in a cellulose matrix by niising the carbon in viscose ‘sodium cellulose xanthate solution’ and extruding the mixture through a special conjugate jet as iiioiiofilaments into a rayon coagulating bath. The special jet permits a backbone of plain viscose to be spun as a spine support for the carbon‐loaded portion of the monofilament to give it added strength. The diameters of the dry, nondusting monofils can be varied greatly. For air cleaning purposes the nonfilanients range from 1/64 to 3/64 in. in diameter. Although imbedded in cellulose, the carbon's capxity to remove malodors remains high. In addition, when made into a filter unit, the resistance to air flow through the unit is low. The novel use of regenerated cellulose as a carrier for large quantities of activated carbon indicatcs that other materials (catalysts, ion exchange resins, etc.) can be similarly bound in cellulose and still retain a high level of their original performance.