bluuebunny/crossref_metadata_2025_split huggingface dataset:
Integral representations in elastostatics and their application to an alternative boundary element method
Authors: Turteltaub Sergio , Turteltaub Matías 
Published: June 2004

AbstractWe obtain a new representation for derivatives and anti‐derivatives of any order of the displacement and stress fields for elastostatics problems when the boundary data is given in terms of polynomials of arbitrary degree. The result includes, as a special case, Somigliana's theorem. Based on this identity, we propose an alternative algorithm for the boundary element method that uses polynomial approximations of arbitrary order. The method provides accurate results for two‐dimensional elastostatics boundary value problems and has the advantage that it is easy to implement. The formula can also be used to accurately compute stresses and strains. For domains bounded by polygons, we provide closed‐form analytical expressions for the terms that appear in the stiffness matrix and the load vector for polynomials of arbitrary degree, thus avoiding numerical integration. We analyse the accuracy of the numerical solution as a function of the degree of the polynomial approximation by solving a representative boundary value problem. Copyright © 2004 John Wiley & Sons, Ltd.
A simple estimation method for aggregate government outsourcing
Authors: Minicucci Stephen , Donahue John D. 
Published: June 2004

AbstractThe scholarly and popular debate on the delegation to the private sector of governmental tasks rests on an inadequate empirical foundation, as no systematic data are collected on direct versus indirect service delivery. We offer a simple method for approximating levels of service outsourcing, based on relatively straightforward combinations of and adjustments to standard statistical series, primarily the National Income and Product Account and the Government Finances series produced by the Department of Commerce. The method permits us to separately estimate state and local from federal service outsourcing and (within the federal government) to distinguish between defense and non‐defense services. Alternative estimates, both including and excluding Medicare and Medicaid, are included, as are estimates of outsourcing from 1959 through 2000. The method confirms the general view that the privately provided share of public services has increased, particularly in the last two decades of the past century. But this increase has been shallower than many observers suggest, and as of 2000 more than two‐thirds of the government's service budget was still devoted to employee compensation. © 2004 by the Association for Public Policy Analysis and Management.
The effect of bicycle helmet legislation on bicycling fatalities
Authors: Grant Darren , Rutner Stephen M. 
Published: June 2004

AbstractA number of states passed legislation in the 1990s requiring youths to wear helmets when riding bicycles. The effect of this legislation on bicycling fatalities is examined by subjecting data from the Fatality Analysis Reporting System to a panel analysis, using a control‐group methodology. A helmet law reduces fatalities by about 15 percent in the long run, less in the short run. There is no evidence of spillover effects (to adults) or substitution effects (youths choosing other methods of transportation) associated with implementation of a helmet law. Through 2000, existing helmet laws have saved 130 lives. If all states had adopted helmet laws in 1975, more than 1500 lives would have been saved. © 2004 by the Association for Public Policy Analysis and Management.
Preprocessing of two‐dimensional gel electrophoresis images
Authors: Kaczmarek Krzysztof , Walczak Beata , de Jong Sijmen , Vandeginste Bernard G. M. 
Published: June 2004

AbstractProteomics produces a huge amount of two‐dimensional gel electrophoresis images. Their analysis can yield a lot of information concerning proteins responsible for different diseases or new unidentified proteins. However, an automatic analysis of such images requires an efficient tool for reducing noise in images. This allows proper detection of the spots' borders, which is important in protein quantification (as the spots' areas are used to determine the amounts of protein present in an analyzed mixture). Also in the feature‐based matching methods the detected features (spots) can be described by additional attributes, such as area or shape. In our study, a comparison of different methods of noise reduction is performed in order to find out a method best suited for reducing noise in gel images. Among the compared methods there are the classical methods of linear filtering,e.g., the mean and Gaussian filtering, the nonlinear method,i.e., median filtering, and also the methods better suited for processing of nonstationary signals, such as spatially adaptive linear filtering and filtering in the wavelet domain. The best results are obtained by filtering of gel images in the wavelet domain, using the BayesThresh method of threshold value determination.
Structure–property correlations of sulfonated polyimides. I. Effect of bridging groups on membrane properties
Authors: Lee Choonkeun , Sundar Saimani , Kwon Jinuk , Han Haksoo 
Published: June 2004

AbstractA series of six‐membered sulfonated polyimides were synthesized using 1,4,5,8‐naphthalenetetracarboxylic dianhydride, 4,4′‐diaminobiphenyl 2,2′‐disulfonic acid as the sulfonated diamine, and various nonsulfonated diamine monomers having different bridging groups. These bulky bridging groups have the capacity to increase hydrolytic stability and proton conductivity. Polyimides with bulky bridging groups showed increased solubility but exhibited lower thermal stability. The ion exchange capacity and water uptake reduced with increase in the bulkiness of the bridging group. This was attributed to the increase in the molecular weight of the repeating unit and hence effectively reduced the sulfonic acid content. In low temperatures, the conductivity was lower than Nafion®115 and, with increase in temperature, the conductivity rapidly increased and exhibited better conductivity than Nafion®115. Polyimides with bulky bridging groups 4‐amino phenyl sulfone, and 2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane showed higher conductivity than other polyimides and Nafion®115 despite low ion exchange capacity. The hydrolytic stability of the polyimides with bulky bridging groups was higher than the polyimides with less bulky atoms because of the imparted flexibility. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3612–3620, 2004
Structure–property correlations of sulfonated polyimides. II. Effect of substituent groups on membrane properties
Authors: Lee Choonkeun , Sundar Saimani , Kwon Jinuk , Han Haksoo 
Published: June 2004

AbstractA series of sulfonated polyimides with increasing alkyl substituents in the o‐position to diamine were synthesized from 4,4′‐methylene dianiline, 4,4′‐diamine‐3,3′‐dimethyl‐diphenylmethane, and 4,4′‐diamine‐3,5,3′,5′‐tetraethyl‐diphenylmethane using 1,4,5,8‐naphthalenetetracarboxylic dianhydride and perylenetetracarboxylic dianhydride by chemical imidization method. 4,4′‐Diaminobiphenyl 2,2′‐disulfonic acid was used as sulfonated diamine. The variation in the membrane properties with increase in substitution was analyzed. Solubility increased with substitution whereas the thermal stability decreased with increase in substitution. Ion exchange capacity and water uptake reduced with increase in substitution because of the low sulfonic acid content at a particular weight due to the increased molecular weight of the repeating unit. The conductivity of the substituted diamines was higher than the unsubstituted diamines at higher temperature regardless of low ion exchange capacity and water uptake. The increase in conductivity with increase in temperature was more rapid in polyimides than in Nafion®115. Hydrolytic stability of the polyimides with substitution is more than the unsubstituted diamines. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3621–3630, 2004
Energy‐damping behaviors of poly(methyl acrylate‐co‐divinylbenzene) microspheres coated with a porous nickel–phosphorus layer
Authors: Ng Yeap Hung , Hong Liang 
Published: June 2004

AbstractHybrid microspheres of poly(methyl acrylate‐co‐divinylbenzene) (PMADVB) with a thin and porous nickel–phosphorus (Ni–P) alloy layer were prepared via suspension polymerization and electroless nickel plating. The characterization of pristine and nickel‐coated microspheres was carried out with a differential scanning calorimeter and a scanning electron spectroscope equipped with an energy‐dispersive system. The glass‐transition range of Ni–P‐coated PMADVB was broadened and extended in the higher temperature direction. This effect allowed the PMADVB network to embrace more diversified energy states of the segment motion, this being a desired feature for damping sound waves. The low‐frequency (100–1000‐Hz) sound absorption behavior of the microspheres was tested with a sound attenuation kit. Besides the testing of their low‐frequency damping performance, an investigation into the ultrasonic‐wave (∼35 kHz) absorption feature of the microspheres was conducted through chemical means; that is, the attenuation to the ultrasonic wave with respect to the unprotective situation was assessed through the chemisorption extent of copper ions on a biomass adsorbent. The Ni–P deposition layer was found to augment the damping capacity of the polymer network. The alloy layer was determined to cause an expansion of the glass‐transition range of PMADVB and its wave‐scattering capability because this layer was made up of submicrometer metallic grains. In this work, the particulars of the metal–polymer interactions were associated with a core–shell structure. The metal outer layer was thought to create a spherical temperature field inside the PMADVB network, and concerted motions of the polymer segments resulted. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2710–2723, 2004
Structure and formation mechanism of melt‐drawn highly oriented polymer fibers
Authors: Wang Jijun , Kuang Xun , Yan Shouke 
Published: June 2004

AbstractWell‐separated and parallel aligned fibers of various polymers have been prepared by a simple but effective melt‐drawing procedure, and their structural features have been studied with field‐emission scanning electron microscopy. The results show that the resulting polymer fibers, with diameters ranging from tens of nanometers to hundreds of nanometers, consist of highly oriented lamellar or fibrillar crystals with the molecular chains aligned in the drawing direction. Scanning electron microscopy images of the drawing process indicate that drawing a thin polymer molten layer at temperature far above its melting point leads to the formation of elongated microcracks. The microcracks embedded in the polymer thin film propagate along the drawing direction and result in the formation of polymer microfibers, which split continuously under high instantaneous stresses and produce well‐separated polymer fibers with diameters on the nanometer scale. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2703–2709, 2004
Simple method for determining the critical molecular weight from the loss modulus
Authors: Cho Kwang Soo , Ahn Kyung Hyun , Lee Seung Jong 
Published: June 2004

AbstractThe normal concept is that the critical molecular weight (MC) is about twice as large as the entanglement molecular weight (Me). However, experimental data have shown considerable deviations from MC ≈ 2Me. Furthermore, a determination of MC requires samples with a wide range of molecular weights, including weights lower than MC and higher than MC. In this article, we suggest a simple method for determining MC from the loss moduli of nearly monodisperse linear polymers with M ≫ MC. We consider two characteristic relaxation times, which correspond to the local maximum and minimum of the loss modulus. MC is determined from the intersection of two phenomenological relaxation times as a function of the molecular weight. The method precisely agrees with MC ≈ 2Me, which is not shown by conventional methods. Moreover, our method provides a determination of relaxation time τe, at which chain segments first feel the constraints imposed by the conceptual tube, without the measurement of the tube diameter and the monomeric friction coefficient, which may be determined by complicated procedures with a lot of data. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2724–2729, 2004
Gas‐transport properties of indan‐containing polyimides
Authors: Liu S. L. , Chng M. L. , Chung T. S. , Goto K. , Tamai S. , Pramoda K. P. , Tong Y. J. 
Published: June 2004

AbstractA series of indan‐containing polyimides were synthesized, and their gas‐permeation behavior was characterized. The four polyimides used in this study were synthesized from an indan‐containing diamine [5,7‐diamino‐1,1,4,6‐tetramethylindan (DAI)] with four dianhydrides [3,3′4,4′‐benzophenone tetracarboxylic dianhydride (BTDA), 3,3′4,4′‐oxydiphthalic dianhydride (ODPA), (3,3′4,4′‐biphenyl tetracarboxylic dianhydride (BPDA), and 2,2′‐bis(3,4′‐dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)]. The gas‐permeability coefficients of these four polyimides changed in the following order: DAI–BTDA < DAI–ODPA < DAI–BPDA < DAI–6FDA. This was consistent with the increasing order of the fraction of free volume (FFV). Moreover, the gas‐permeability coefficients were almost doubled from DAI–ODPA to DAI–BPDA and from DAI–BPDA to DAI–6FDA, although the FFV differences between the two polyimides were very small. The gas permeability and diffusivity of these indan‐containing polyimides increased with temperature, whereas the permselectivity and diffusion selectivity decreased. The activation energies for the permeation and diffusion of O2, N2, CH4, and CO2 were estimated. In comparison with the gas‐permeation behavior of other indan‐containing polymers, for these polyimides, very good gas‐permeation performance was found, that is, high gas‐permeability coefficients and reasonably high permselectivity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2769–2779, 2004
Hiral effects of single‐wall carbon nanotube fluorination and hydrogenation
Authors: Lebedev N. G. , Zaporotskova I. V. , Chernozatonskii L. A. 
Published: June 2004

AbstractThe results of calculations of the electronic and energy characteristics of atomic hydrogen and fluorine adsorption processes on an external surface of single‐wall hiral carbon nanotubes (n,m) are represented. Molecular cluster model within a framework of quantum chemical semiempirical schemes modified neglect of diatomic overlap (MNDO) and parametric method 3 (PM3) has been used. Sorption properties of (4,1), (4,2), (4,3), (5,1), (5,3), (5,4), (6,1), (6,2), (6,3), (6,4), and (6,5) tubes have been considered. Periodical behavior of the chemical bond and activation energies as nanotube diameter functions has been found. It appeared that (4,2), (4,3), and (5,1) nanotubes show more effective adsorption processes and (5,3), (5,4), (6,2), and (6,3) tubes are not advantageous for the chemisorptions. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Improvements in ion signal reproducibility obtained using a homogeneous laser beam for on‐line laser desorption/ionization of single particles
Authors: Wenzel Ryan J. , Prather Kimberly A. 
Published: June 2004

AbstractA major factor limiting on‐line single particle mass spectrometry techniques from becoming more quantitative is the large shot‐to‐shot variability in ion intensities observed in the laser desorption/ionization (LDI) mass spectra.1,2 In previous work, lab‐generated particles showed fluctuations of up to 152% in the absolute ion intensities in averaged spectra of 200–300 ‘identical’ particles.2 Most of these fluctuations were attributed to inhomogeneities in the laser beam profile, leading to significant differences in the power each particle encountered depending on the position in the LDI laser beam where it underwent analysis. The goal of the work presented herein is to determine whether a fiber optic actually reduces the observed variability in single particle LDI mass spectral data. Initial results are presented for individual single component organic particles composed of 2,4‐dihydroxybenzoic acid (2,4‐DHB) analyzed using a low‐power flat‐top laser beam profile created by sending an ultraviolet (266 nm) DI laser through a fiber optic. Relative standard deviations of the total ion intensities for peaks in individual spectra are reduced to 31%. Single particle spectra, compared with and without laser homogenization at the same nominal laser fluence, show a marked enhancement. Specifically, the ion signal patterns of the 2,4‐DHB particle spectra obtained using a homogenous LDI beam look identical to one another (i.e. only one particle type was produced with a commonly used neural network grouping algorithm), whereas without beam homogenization 25 different particle types (based on ion intensity patterns) were obtained. Future publications will explore more particle types and matrices but the initial results described herein are quite encouraging. Copyright © 2004 John Wiley & Sons, Ltd.
Tandem mass spectrometric analysis of distinct fragmentation patterns to [M+Na]/z and [M+H]/z of dendritic Al(III) and Zn(II) quinolates
Authors: Shen Liang , Sha Yaowu , Hong Xiaoyin 
Published: June 2004

AbstractThe synthesis of two novel dendritic aluminum and zinc quinolates, which are soluble in common solvents, was monitored effectively by positive ion electrospray ionization mass spectrometry (ESI‐MS). Through tandem mass spectrometric analysis of the complexes, distinct fragmentation pathways for sodium adduct molecular ion [M+Na]+and protonated molecular ion [M+H]+were observed. Copyright © 2004 John Wiley & Sons, Ltd.
Experimental evidence of resonant field emission from ultrathin amorphous diamond thin film
Authors: She J. C. , Xu N. S. , Deng S. Z. , Chen J. , Li Z. B. , Huq S. E. , Wang L 
Published: June 2004

AbstractResonant field electron emission was observed from amorphous diamond thin film. An ultrathin, i.e. ∼2 nm, amorphous diamond thin film highly localize on a single sharp Si tip apex was used for the experiments. Tip specimens were fabricated by state‐of‐the‐art microfabrication techniques, including high‐resolution electron beam lithography, plasma dry etching and local amorphous diamond deposition on the tip apex. It was observed from current–field (I–E) characteristics that in the applied macro‐field of typically 11–12 MV m−1 there are reversible and relatively strong current peaks, in contrast to the normal current instability phenomenon. The results confirm the effect of resonant tunnelling from amorphous diamond thin films. Copyright © 2004 John Wiley & Sons, Ltd.
Theoretical calculation of spatial variation of the transmission coefficient of closed carbon nanotubes
Authors: Xanthakis J. P. , Kokkorakis G. C. 
Published: June 2004

AbstractWe have calculated the spatial (angular) variation of the transmission coefficient of closed carbon nanotubes (CNT). For the evaluation of the local field outside the tip of the CNT we have used the method described in J. Appl. Phys. 2002; 91: 4580. In the present work we require the local field only inside the classically forbidden area, so we have managed to simplify our previous results and obtain an analytical form for the local potential. This potential was then inserted into the method of Das and Mahanty (Phys. Rev. B 1987; 36: 898) to obtain the transmission coefficient T(θ) at an angle θ to the axis of the tube. We have found a substantial angular variation of T(θ), the determining factor being the local field at the surface of the CNT and, to a lesser extent, the radius of the tube. Decreasing the local field increases the directionality of T(θ) but also decreases the current by several orders of magnitude so that a compromise between directionality and value of the current has to be sought. The directionality also increases with decreasing radius of the tube. The ratio of the height to the radius (h/R) of the CNTs per se plays a minor role, i.e. if one compares CNTs with different h/R but the same local field then minor changes are found. Copyright © 2004 John Wiley & Sons, Ltd.
Atomic mechanism of radiation‐induced erosion of field electron emitters
Authors: Mazilova T. I. , Mikhailovskij I. M. 
Published: June 2004

AbstractThe features of erosion of the surface of field electron emitters bombarded by helium and neon ions were studied. Experiments showed that ion bombardment produced tungsten atom transport, the number of atoms transported being proportional to the ion fluence. Analysis of ion bombardment‐induced atomic‐scale surface roughness showed evidence of a non‐dynamic surface atom displacement for primary ion energies below a threshold for stable Frenkel pair formation and cathode sputtering. A quasi‐static mechanism of surface erosion is considered, according to which the process is related to the displacement of metal atoms into low‐coordinated positions upon evolution of the energy of formation of interstitial inert gas atoms. Copyright © 2004 John Wiley & Sons, Ltd.
Physics and chemistry in high electric fields
Authors: Kreuzer H. J. 
Published: June 2004

AbstractProgress is reviewed in our understanding of the effects of high electrostatic fields (of the order of volts per angstrom) on the adsorption and reaction of atoms and molecules on metal surfaces. New results are presented for polymers in high fields, reporting a large electrostriction for oligo(ethylene glycol). The discovery by Block and his collaborators close to two decades ago that polymerized sulphur can be extracted from an adsorbed sulphur multilayer using high electric fields is analysed on the basis of density functional calculations. Copyright © 2004 John Wiley & Sons, Ltd.
Field penetration and field electron emission from HTSC materials
Authors: Uimanov I. V. 
Published: June 2004

AbstractThis paper discusses field penetration into high‐Tc cuprates under field electron emission conditions. A quasi‐classical approximation based on Thomas–Fermi non‐linear screening theory has been used to discuss field penetration into a high‐Tc superconductor (HTSC) emitter, taking into account the HTSC electronic structure. The numerical results obtained are substantially different from the predictions of linear theory. The results show that, for a screening length of several angströms and field strengths typical of field electron emission spectroscopy, the amount of band‐bending can be comparable with the total width of the band. Thus, the effects of field penetration and band‐bending should be taken into account when constructing a theory of field emission from these compounds. Copyright © 2004 John Wiley & Sons, Ltd.
Band structure effects in the field electron emission from HTSC monocrystals
Authors: Uimanov I. V. 
Published: June 2004

AbstractThis paper presents a theoretical approach developed for describing the field emission characteristics of YBa2Cu3O7−y copper oxide high‐Tc superconductors (HTSCs) in the normal state. The approach takes into account both the topological features of the essentially anisotropic band structure of such compounds (using the strong‐bond approximation) and the bending of energy bands induced by field penetration under the conditions of field emission experiments. This field penetration results from the low concentration of mobile charge carriers. Numerical calculations have been performed, and approximate analytical expressions derived, for field emission spectra from the (100) and (010) faces. The theoretical results obtained are able to account for the main ‘abnormal’ experimental characteristics of field emission from the (100) plane of YBa2Cu3O7−y. It has been shown that detailed field emission spectroscopy data for type YBa2Cu3O7−y HTSC emitters make it possible to investigate the main parameters of the band structure of these compounds. Copyright © 2004 John Wiley & Sons, Ltd.