bluuebunny/crossref_metadata_2025_split huggingface dataset:
SNR improvement for multiinjection time‐resolved high‐resolution CE‐MRA of the peripheral vasculature
Authors: Du J. , Carroll T.J. , Block W.F. , Fain S.B. , Korosec F.R. , Grist T.M. , Mistretta C.A. 
Published: April 2003

AbstractPeripheral MR angiography (MRA) should ideally provide images over a large field of view with high spatial resolution and adequate temporal resolution to accommodate differences in regional filling times. Image subtraction is usually used to remove background signals. In examination protocols involving multiple injections at multiple sites, previously injected contrast present in the mask image provides a substantial decrease in the subtraction image signal. Bolus chase methods avoid this problem but provide limited time for acquisition of high‐resolution images at each station. We present here a technique applied to peripheral angiography that provides high spatial and temporal resolution while maintaining high SNR in multiple injection examinations. Undersampled projection imaging was used to increase spatial resolution relative to a previously reported technique using a Cartesian acquisition technique. Late acquisition of high spatial frequencies and temporal matched‐filtering were used to increase spatial resolution and SNR, respectively. Temporal correlation analysis was applied to permit multistation examinations without mask subtraction, thus providing an additional gain in SNR relative to multistation subtraction methods. Quantitative analysis is provided to evaluate the signal and noise behavior in the matched‐filtering process due to multiinjection and mask subtraction. Magn Reson Med 49:909–917, 2003. © 2003 Wiley‐Liss, Inc.
Water diffusion measurements in perfused human hippocampal slices undergoing tonicity changes
Authors: Shepherd Timothy M. , Wirth Edward D. , Thelwall Peter E. , Chen Huan‐Xin , Roper Steven N. , Blackband Stephen J. 
Published: April 2003

AbstractDiffusion MRI has the potential to probe the compartmental origins of MR signals acquired from human nervous tissue. However, current experiments in human subjects require long diffusion times, which may confound data interpretation due to the effects of compartmental exchange. To investigate human nervous tissue at shorter diffusion times, and to determine the relevance of previous diffusion studies in rat hippocampal slices, water diffusion in 20 perfused human hippocampal slices was measured using a wide‐bore 17.6‐T magnet equipped with 1000‐mT/m gradients. These slices were procured from five patients undergoing temporal lobectomy for epilepsy. Tissue viability was confirmed with electrophysiological measurements. Diffusion‐weighted water signal attenuation in the slices was well‐described by a biexponential function (R2 > 0.99). The mean diffusion parameters for slices before osmotic perturbation were 0.686 ± 0.082 for the fraction of fast diffusing water (Ffast), 1.22 ± 0.22 × 10−3 mm2/s for the fast apparent diffusion coefficient (ADC), and 0.06 ± 0.02 × 10−3 mm2/s for the slow ADC. Slice perturbations with 20% hypotonic and 20% hypertonic artificial cerebrospinal fluid led to changes in Ffast of −8.2% and +10.1%, respectively (ANOVA, P < 0.001). These data agree with previous diffusion studies of rat brain slices and human brain in vivo, and should aid the development of working models of water diffusion in nervous tissue, and thus increase the clinical utility of diffusion MRI. Magn Reson Med 49:856–863, 2003. © 2003 Wiley‐Liss, Inc.
Separating arterial and venous components from 3D dynamic contrast‐enhanced MRI studies using factor analysis
Authors: Martel Anne L. , Fraser Doug , Delay G. Steve , Morgan Paul S. , Moody Alan R. 
Published: April 2003

AbstractDynamic contrast‐enhanced MRI has been used extensively for angiography but in order to generate separate arterial and venous images some form of postprocessing is required. This typically involves the subtraction of one image in a dynamic sequence from another in order to suppress unwanted signal; however, this also has the effect of decreasing the signal‐to‐noise ratio (SNR) of the image. In this study, factor analysis, a technique related to eigenimage filtering, is used to separate arterial and venous components from dynamic contrast‐enhanced images of the legs acquired with a temporal resolution of 30 sec. The SNR of the venous and arterial images extracted from a series of 20 patients using conventional single subtraction, a double subtraction method, and factor analysis were compared. Results show that the use of factor analysis improved the SNR in the venous images by a factor of 2.3 compared with the use of simple subtraction. A subjective comparison of the maximum intensity projection images generated from the venous images was also carried out and showed a significant preference for those generated using factor analysis over those generated using other subtraction methods. Magn Reson Med 49:928–933, 2003. © 2003 Wiley‐Liss, Inc.
Conveners as champions of collaboration in the public sector: a case from South Africa
Authors: Dorado Silvia , Vaz Peter 
Published: April 2003

AbstractThis article analyses the role of conveners in facilitating interorganisational collaboration. Consistent with previous research, the article shows that conveners help overcome the obstacles frequent in interorganisational collaboration processes. It also illustrates further how their effectiveness depends on their credibility among the partners, their familiarity with the collaborative project and their being perceived as unbiased intermediaries. Most interestingly, the article advances our knowledge on conveners by suggesting that their behaviour is consistent with that common among ‘champions’ of innovation. They are likely to assume a leadership role and use influence politics, such as salesmanship, personal appeal and persuasion. These findings build on a case study of successful collaboration between two government agencies in South Africa. We believe, however, that the findings are likely to apply to other types of organisation, private and voluntary, and to other country contexts. Copyright © 2003 John Wiley & Sons, Ltd.
Fighting fiscal corruption: lessons from the Tanzania Revenue Authority
Authors: Fjeldstad Odd‐Helge 
Published: April 2003

AbstractOver the last decade, several African countries have undertaken comprehensive reforms of their tax administrations to increase revenue and curb corruption. This article examines recent experiences in the fight against corruption in the Tanzania Revenue Authority (TRA). Two lessons of broader relevance are highlighted. Firstly, even with relatively high wages and good working conditions, corruption may continue to thrive. In a situation where there is high demand for corrupt services, it is unrealistic to provide tax officers with pay rates that can compensate for the amount gained through bribery. Without extensive and effective monitoring, wage increases may produce not only a highly paid, but also a highly corrupt tax administration. Secondly, hiring and firing procedures may lead to more corruption. Corrupt tax officers often operate in networks, which also include external actors. These corruption networks seem to have been strengthened because many of those fired were recruited to the private sector as ‘tax experts’. This partly explains why the positive process experienced in the initial phase of the new revenue authority was later reversed. Copyright © 2003 John Wiley & Sons, Ltd.
The mechanism of reinforcement. II
Authors: Goldfinger George 
Published: April 2003

AbstractFurther experimental evidence is given which indicates that, when a dilute solution of GR‐S is mixed with carbon black, certain fractions of the rubber are preferentially adsorbed by the black. After removal of the carbon black and the adsorbed fractions by centrifuging, the “treated” GR‐S is obtained by precipitation from the solution. Samples compounded as GR‐S gum stock show increasing modulus with increasing amounts of carbon black used for adsorption treatment. However, when the GR‐S thus treated is compounded with carbon black, then the effect is reversed. The more black used in the treatment and the higher the modulus of the gum stock, the lower the modulus of loaded stock.
Intramolecular reactions in vinyl polymers as a means of investigation of the propagation step
Authors: Merz E. , Alfrey T. , Goldfinger G. 
Published: April 2003

AbstractThe Flory‐Wall expressions for the fraction of substituents remaining on a vinyl copolymer, when substituents are removed at random from adjacent 1,3 positions, are extended to the case of nonrandom copolymerization. A copolymer composition equation is derived for the case in which the type of monomer preceding the active freeradical chain end affects the propagation reaction. The distribution of lengths of sequences in copolymers is discussed.
Preparation, purification, and polymerization of diethyl silicon dichloride
Authors: Alfrey Turner , Honn Francis J. , Mark H. 
Published: April 2003

AbstractDiethyl silicon dichloride was prepared by a Grignard synthesis and purified highly. The material in various stages of purification was hydrolyzed and then polymerized. The properties of the hydrolyzate and of the final polymer depended markedly upon the degree of purification of the dichloride. The reaction of diethylsilicanediol with phosphorous pentoxide was also studied; the predominating reaction appears to involve entrance of the pentoxide into the polymeric structure, rather than a simple acceleration of the polycondensation reaction by the removal of water.
Polymerization of olefins and diolefins in suspension and emulsion. Part I.
Authors: Hohenstein W. P. , Mark H. 
Published: April 2003

AbstractThis and a following article review the literature from 1910–1945 on polymerization of olefins and diolefins in suspension and emulsion, and present a number of new measurements not published to date. The subject is considered mainly from the point of view of scientific information on the mechanism of polymerization in aqueous suspensions and emulsions, but brief mention is also made of the more important disclosures in the patent literature. The new data presented in this article refer to (1) initial rates of polymerization of styrene, methyl methacrylate, vinyl acetate and acrylonitrile in aqueous suspensions and in soap emulsions as a function of catalyst concentration, temperature, and soap concentration; (2) influence of water‐soluble activators, such as sodium bisulfite; (3) influence of initial size of monomer droplets on initial rates of monomer consumption; (4) study, with the aid of the electron microscope, of size of monomer droplets and polymer particles throughout polymerization; and (5) a few experiments on side reactions in the domain of higher conversions. No attempt is made in this paper to review and appraise the very large number of recent patents (from about 1930 on), which protect special procedures on the use of various promoting, regulating, or modifying ingredients. A complete digest of this practice does not exist at present, but reference may be made to the excellent chapter on emulsion polymerization in the book of Talalay and Magat (55), to the very valuable compilation of patents by Hosch in “India Rubber World” (27), and to the enumeration of a selected number of patents in the book of Scheiber (50) on pages 210–213.
Density of cellulose fibers. II. Density and refractivity of model filaments
Authors: Hermans P. H. , Hermans J. J. , Vermaas D. 
Published: April 2003

AbstractAccurate determinations of the density and refractive power of various types of model filaments prepared from viscose in the bone‐dry state were made. The molecular refraction, according to the formula of Gladstone and Dale, was calculated and shown to correspond within three parts per thousand with the refraction calculated from atomic refractions. It is concluded that the liquid used for the density determinations (mixtures of carbon tetrachloride and nitrobenzene) does not penetrate into the fiber substance. The technique of the experiments is described in detail. The immersion liquids used in the optical measurements were standardized mixtures of butyl stearate and tricresyl phosphate; contamination with moisture during the measurements was definitely excluded.
Spectrophotometric determination of the styrene content of butadiene–styrene copolymers
Authors: Meehan E. J. 
Published: April 2003

AbstractThe ultraviolet absorption of polystyrene, with maximum absorption at 262 mμ, is due to the presence of phenyl residues in the polymer. The specific extinction coefficient is constant, i.e., independent of the molecular weight of the polymer. This shows that the extinction of the phenyl residues is additive. On the basis of this fact, it is shown that the styrene content of a butadiene–styrene copolymer (such as GR‐S rubber) can be determined by ultraviolet spectrophotometry. The relative precision of the determination is about 1%, the probable relative accuracy is about 3%.
The photochemical decomposition of cellulose acetate–butyrate
Authors: Tichenor R. L. 
Published: April 2003

AbstractThe chief result of irradiation of cellulose acetate–butyrate with ultraviolet light is cleavage of the cellulose chains so that the average molecular weight is lowered. The exposed material dissolves more slowly in common solvents than the unexposed. The acyl content and carbon and hydrogen contents are not altered appreciably. The rate of the reaction is independent of the type of common mineral impurities, the concentration of expected decomposition products, such as acetic and butyric acids, and the molecular weight of the cellulose ester. Ultraviolet light is necessary for appreciable reaction. Wave lengths shorter than 3500 Å. are most effective; longer wave lenghts are much less active.
Comparison of ultraviolet absorption and chlorine analysis methods for composition of butadiene–p‐chlorostyrene copolymers
Authors: Meehan E. J. , Parks T. D. , Laitinen H. A. 
Published: April 2003

AbstractA comparison has been made of the ultraviolet spectrophotometric and chlorine analysis methods for the composition of copolymers of butadiene and p‐chlorostyrene. The results of the two methods are in good agreement.
Use of density‐gradient tube in the study of high polymers
Authors: Boyer R. F. , Spencer R. S. , Wiley R. M. 
Published: April 2003

AbstractThe density‐gradient tube is a special glass vessel in which a vertical linear density gradient of almost any desired magnitude can be maintained in a stable condition for prolonged periods by using liquids or solutions of the proper density. This article describes the application of such a device to three typical problems appearing in the field of high polymers: crystallization‐rate data, inhomogeneities in composition of copolymers, and rates of polymerization. Possible application to still other problems is indicated.
Sodium‐catalyzed copolymerization of 1,3‐butadiene and styrene
Authors: Marvel C. S. , Bailey W. J. , Inskeep G. E. 
Published: April 2003

AbstractButadiene and styrene have been copolymerized by the use of sodium sand as a catalyst. The copolymers containing 75 parts of butadiene and 25 parts of styrene and made at 30° and 50° are soluble in benzene and have intrinsic viscosities ranging from 2.5 to 7.5. The copolymers has a very nearly constant composition throughout the course of the polymerization. The amount of butadiene which has entered the chain by 1,2 addition is greater than in the case of the emulsion copolymer.
β‐Aminoethoxyl‐ and β‐cyanoethoxylcellulose acetates
Authors: Gardner Thomas S. 
Published: April 2003

AbstractMixed cellulose acetate‐ethers were prepared which contain basic‐type nitrogen groups whose films were dyed by xylene brilliant blue. β‐Aminoethoxylcellulose acetate was prepared from cellulose diacetate and yarn‐type cellulose acetate–propionate using ethyleneimine. β‐Cyanoethoxylcellulose acetate was prepared from β‐cyanoethoxylcellulose and from cellulose acetate using acrylonitrile with an organic base as catalyst. The solubilities of the mixed ether–esters containing basic type nitrogen groups were less than those of cellulose esters and ethers of comparable degrees of substitution.
Composition of butadiene–styrene copolymers prepared by emulsion polymerization
Authors: Meehan E. J. 
Published: April 2003

AbstractExperimental data are presented on the monomer composition of copolymers of butadiene and styrene prepared by emulsion polymerization at 50°C. The composition of the copolymers is shown to be unaffected by variations in the amount of emulsifier, of mercaptan, and of the nature of the water‐soluble polymerization catalyst. The composition of the copolymers formed from a charge containing 25% styrene (by wt.) can be represented accurately over the entire conversion range by the approximate theory according to which each monomer disappears by a first order reaction with the growing chain of the polymer, without taking into account the fact that the end of the growing chain to which the monomer adds may be a radical derived from either of the two monomer molecules. If the ratio of monomers in the charge is varied within wide limits, however, it is found that the simple theory is not adequate and it is necessary to consider that the chain may end with different radicals. The analysis of the experimental data shows that a butadiene molecule adds more rapidly than a styrene molecule to a radical derived either from a butadience or a styrene molecule.
Dependence of the average transversal on the longitudinal dimensions of statistical coils formed by chain molecules
Authors: Kuhn Werner 
Published: April 2003

AbstractThe transversal dimension of the statistical coil formed by a long‐chain molecule in solution or in bulk rubber is independent of the longitudinal dimension, h1, of the coil as long as h1 is small compared with the length of the stretched molecule. On the other hand, the lateral dimension of a coil whose longitudinal vector, h1, is oriented in the direction of stretch undergoes a forced contraction during the deformation of bulk rubber. The forced contraction of the transversal dimension is therefore supplying an extra contribution to the entropy change. Its amount has been estimated in earlier work and it influences the numerical factor occurring in the formula connecting the strain‐stretch relation for rubber with the molecular weight of the net fragments.
Deformation mechanism of cellulose gels. II. Course of crystallite orientation compared to that required by Kratky's theory
Authors: Hermans P. H. , Hermans J. J. , Vermaas D. , Weidinger A. 
Published: April 2003

AbstractThe paper offers a verification by x‐ray experiments of Kratky's theory of affined transformation (affine Raumverzerrung), aiming at an explanation of the mechanism of deformation of swollen cellulose gels upon stretching. Isotropic model filaments of various degrees of swelling were stretched to various extents and x‐ray photographs were then taken. Following Kratky, the intensity distribution along the sickles of two paratropic planes of the ribbon‐shaped crystallites, the lamellar plane, A0 and the A3 plane (perpendicular to the latter) were measured and the average orientation, expressed in terms of the orientation factor, fx, was calculated. The superposition of the (021) interference on that of the A3 sickle, which had been neglected by Kratky, was accounted for. The experimental results are in conformity with certain characteristic features of the theory; (a) the orientation of the A0 planes advances more rapidly than that of the A3 planes; (b) regardless of the initial degree of swelling of the isotropic filament, the average orientation is actually a univocal function of the elongation, va. On the other hand, the rate of orientation appears to be much greater than that required by theory; the average orientation, expressed in terms of the orientation factor, increases almost twice as rapidly. It is shown, moreover, that, apart from low degrees of orientation, Kratky's theory fails to explain the velocity function of the relative rotation of the crystallites, as derived from the experimental data according to a procedure proposed by Kratky. It is concluded that further work is required to elucidate the mechanism of deformation.
Nature of the carbonyl groups in polyvinyl alcohol
Authors: Clarke John T. , Blout Elkan R. 
Published: April 2003

AbstractMeasurements of the viscosity of polyvinyl alcohol solutions may be correlated with the chemical nature of the polymer. In particular it is shown that polyvinyl alcohol contains carbonyl groups in the polymer chain, which are to some extent present as ketols. The presence of these keto groups has been demonstrated by a combination of spectrophotometric and chemical techniques. The carbonyl groups appear to be randomly distributed along the polymer chain and also seem to be independent of chain length. The presence of keto groups along the chain allows an explanation for the behavior of aqueous polyvinyl alcohol solutions with acid or alkali.
Molecular weight averages obtained from sedimentation velocity and diffusion measurements
Authors: Singer Seymour 
Published: April 2003

AbstractIn using the velocity ultracentrifuge in conjunction with free diffusion measurements for the determination of molecular weights of polymolecular systems, it is desirable to know what average molecular weights are obtainable. These average values are not simple moments of the molecular weight frequency curve, but depend on the methods of experimental observation, and on the hydrodynamic character of the molecules in solution. Most often, however, the average molecular weight falls between the number and weight‐average values.
Dependence of solvation on particle shape
Authors: Jirgensons B. 
Published: April 2003

AbstractThe relationships which exist between the solvation and shape of colloid particles, as well as between solvation and viscosity, are discussed. From the most important experiments on these subjects the following conclusions may be drawn. Solvation is dependent on the size and shape of the particles and on the chemical relationship of the dispersion medium to the dispersed portion. True or chemical solvation is generally very small and there is no reason to speak of a thick and tightly bound solvent layer. The solvation of compactly formed particles of spherocolloids is greater, the smaller the particles (all other conditions being equal). Solvation is greater, the more loosely the particles are formed (for dispersion mediums having similar chemical properties and for similar dispersed or dissolved substances). Solvation increases when a corpuscular particle is transformed into a rodlike or threadlike particle; the viscosity also increases; if the threads are further broken down into smaller fragments, then the viscosity decreases, but a further increase in the chemical solvationis supposed to occur. The stability of many lyophilic sols, especially the proteins, depends very little on the solvation; it is mainly dependent on the chemical characteristics of the atomic groups which are found on the surfaces of the particles; the least stability is found for surfaces which contain heteropolar groups—that is, surfaces which have the same number of positive and negative ions.