bluuebunny/crossref_metadata_2025 huggingface dataset:
Hyaluronic acid grafting mitigates calcification of glutaraldehyde‐fixed bovine pericardium
Authors: Ohri Rachit , Hahn Sei K. , Hoffman Allan S. , Stayton Patrick S. , Giachelli Cecilia M.
Published: June 2004

Pathologic calcification is the leading cause of the clinical failure of glutaraldehyde‐fixed bovine pericardium used in bioprosthetic valves. A novel surface modification of glutaraldehyde fixed bovine pericardium was carried out with high molecular weight hyaluronic acid (HA). HA was chemically modified with adipic dihydrazide (ADH) to introduce hydrazide functional groups onto the HA backbone. Glutaraldehyde‐fixed bovine pericardium (GFBP) was modified by grafting this HA to the free aldehyde groups on the tissue via the hydrazide groups. Following a 2‐week subcutaneous implantation in osteopontin (OPN)‐null mice, the calcification of HA‐modified bovine pericardium was drastically reduced (by 84.5%) compared to positive controls (tissue without HA‐modification) (p = 0.005). The calcification‐mitigating effect of HA surface modification was also confirmed by microscopic analysis of explanted tissue stained with Alizarin Red S for calcium. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 70A: 328–334, 2004
Redox regulation of glial inflammatory response to lipopolysaccharide and interferonγ
Authors: Pawate Siddharama , Shen Qin , Fan Fan , Bhat Narayan R.
Published: June 2004

Astrocytes and microglia, the two immune‐regulatory cells of the central nervous system (CNS), are activated by a variety of pathogens and cytokines to elicit rapid transcriptional responses. This program of activation is initiated by a set of intracellular signaling cascades that includes mitogen‐activated protein kinase (MAPK), nuclear factor (NF) κB, and Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathways. This study defines the critical role that NADPH oxidase(Phox)‐derived reactive oxygen species (ROS) play in lipopolysaccharide (LPS)‐ and interferon (IFN)γ‐induced signaling cascades leading to gene expression in glial cells. Treatment of rat microglia and astrocytes with LPS and IFNγ resulted in a rapid activation of Phox and the release of ROS followed by an induction of inducible nitric oxide synthase (iNOS) expression. iNOS induction was blocked by inhibitors of Phox, i.e., diphenylene iodonium chloride (DPI) and 4‐(2‐aminoethyl) benzenesulfonylfluoride (AEBSF), suggesting an involvement of ROS signaling in iNOS gene expression. Exogenous catalase but not superoxide dismutase suppressed the basal activity and completely blocked induced levels of NO/iNOS, suggesting that hydrogen peroxide is the ROS involved. Phox inhibitors and catalase also suppressed LPS/IFNγ‐induced expression of cytokines, i.e., interleukin (IL)‐1, IL‐6, and tumor necrosis factor (TNF)α and blocked LPS activation of MAP kinases (i.e., p38 MAPK, c‐Jun N‐terminal kinase and extracellular signal‐regulated kinase), NFκB, and IFNγ‐induced STAT1 phosphorylation. A microglial cell line stably transfected with a mutant form of Phox subunit, i.e., p47phox W(193)R, and primary astrocytes derived from Phox‐deficient mice showed attenuated ROS production and induction of iNOS in response to LPS/IFNγ, further strengthening the notion that Phox‐derived ROS are crucial for proinflammatory gene expression in glial cells. © 2004 Wiley‐Liss, Inc.
The impact of winter ice retreat on Antarctic winter sea‐ice extent and links to the atmospheric meridional circulation
Authors: Harangozo S. A.
Published: June 2004

15 years of weekly Antarctic ice extent and 10 m winds from numerical meteorological reanalyses have been used to test the hypothesis that the Antarctic final winter ice extent (FWE) is brought about by ice retreats as much as by advances, and that both are strongly affected by the meridional (north–south) component of the atmospheric circulation. This hypothesis is found to be correct and it is shown that extensive FWE fails to occur when total winter retreat is anomalously large. This is the case even in the coldest Antarctic regions. Retreats reduce the time available for advance, notably when they are substantial, with the ice cover taking up to several weeks to recover. Systematic changes in the meridional winds between retreats and advance are also detected in all regions; retreats are consistently associated with northerly winds supporting ice compaction and ice drift. The results agree with Antarctic case studies.

Close similarities are found between several Antarctic and sub‐Arctic regions in terms of the prevalence of retreat in some winters, its impact on the FWE and its relationship to the meridional atmospheric circulation. The study also reveals a more complex picture of the atmospheric circulation during sub‐monthly ice retreats and advances. In particular, retreats in some Pacific regions are, on average, associated with anomalous anticyclonic circulations. This helps to explain why evidence of strong cyclone–ice extent relationships has not been found previously. A meteorological explanation is also sought for total retreat in winter being small in a winter of limited ice extent in the Bellingshausen Sea despite this being the mildest Antarctic region. In such cases, limited winter ice extent is attended by reduced advance caused by ice compaction due to northerly winds and waves and also anomalously high air temperatures. Reduced advance then limits opportunities for retreat to take place compared with winters with more advance and sea ice reaching lower latitudes. Overall, the results point to sub‐monthly ice–atmospheric circulation interactions largely determining the winter ice extent throughout much of the Antarctic. Copyright © 2004 Royal Meteorological Society
North Atlantic oscillation influence on precipitation, river flow and water resources in the Iberian Peninsula
Authors: Trigo Ricardo M. , Pozo‐Vázquez David , Osborn Timothy J. , Castro‐Díez Yolanda , Gámiz‐Fortis Sonia , Esteban‐Parra María Jesus
Published: June 2004

The Iberian Peninsula precipitation and river flow regimes are characterized by large values of inter‐annual variability, with large disparities between wet and dry years, especially in southern Iberia. This situation is a major problem for water resources management in general, and for the production of hydroelectricity in particular. Hydroelectric production represents, in an average year of precipitation, 20% of the total Spanish electricity production (and 35% for Portuguese production). Its absolute value, however, can vary by a factor of three between wet and dry years. We have assessed the impact of the North Atlantic oscillation (NAO) on winter precipitation and river flow regimes for the three main international Iberian river basins, namely the Douro (north), the Tejo (centre) and the Guadiana (south). Results show that the large inter‐annual variability in the flows of these three rivers is largely modulated by the NAO phenomenon. Throughout most of the 20th century, the January‐to‐March river flow is better correlated with the December to February (DJF) NAO index than is the simultaneous (DJF) river flow. Correlation values for the period 1973–98 are highly significant (−0.76 for Douro, −0.77 for Tejo and −0.79 for Guadiana), being consistently of higher magnitude than those obtained over previous decades. This impact of the NAO on winter river flow was quantified in terms of total Spanish potential hydroelectricity production. The important control exerted by the NAO and the recent positive trend in the NAO index contribute to a significant decrease in the available flow. This reduction represents an important hazard for the two Iberian economies because of its negative impact on water‐dependent resources, such as intensive agriculture and hydroelectric power production. Copyright © 2004 Royal Meteorological Society
Climate signature of solar irradiance variations: analysis of long‐term instrumental, historical, and proxy data
Authors: Lohmann Gerrit , Rimbu Norel , Dima Mihai
Published: June 2004

The signature of solar irradiance variations on decadal‐to‐centennial climate variability is analysed by means of statistical analysis of long‐term instrumental, historical, and proxy data sets. Solar variations associated with the Schwabe, Hale, and Gleissberg cycles are detected by their spatial patterns in sea‐surface temperature and sea‐level pressure. Different statistical methods for instrumental and proxy data show that the mode related to solar irradiance fluctuations on multi‐decadal time scales (Gleissberg cycle) is distinct from the Atlantic multi‐decadal mode associated with ocean circulation changes. From this, one can infer the degree to which solar variability has contributed to long‐term temperature variations during the instrumental and pre‐instrumental era. Copyright © 2004 Royal Meteorological Society
Energy transfer effects during the multichannel decomposition of ethanol
Authors: Tsang Wing
Published: June 2004

Rate constants and expressions for the initial processes in the decomposition of ethanol have been derived on the basis of existing experimental and estimated results. Energy transfer effects on the multichannel decomposition processes have been determined through the solution of the master equation and on the basis of exponential‐down and step‐ladder collisional transition models. The predominant (lower threshold) channel is unaffected by the presence of the upper channels and results for the two transition models can be brought into correspondence by using a somewhat higher value for the step‐size down parameter in the step‐ladder model. For the upper channels and with an exponential‐down model, the logarithms of the ratio of the rate constants between perturbed and unperturbed systems can be captured by a sigmoidal shaped curve. In the case of the step‐ladder model, the logarithms of this ratio decreases monotonically. Initially, differences between the two models are small (after adjusting the step‐size down parameter). The results are compared with the recent simulations of Marinov. The order of magnitude differences in rate constants have been traced to the inclusion in the present study of experimental results pertaining to decomposition and the reverse combination processes in addition to the proper treatment of energy transfer effects during multichannel decompositions. Some observations regarding the parameterization of this type of pressure dependent data for use in simulations are presented. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:456–465, 2004.
Unusual kinetic role of a water‐soluble iron(III) porphyrin catalyst in the oxidation of 2,4,6‐trichlorophenol by hydrogen peroxide
Authors: Lente Gábor , Espenson James H.
Published: June 2004

The oxidation of 2,4,6‐trichlorophenol (TCP) to 2,6‐dichloro‐1,4‐benzoquinone (DCQ) by hydrogen peroxide using iron(III) meso‐tetra(4‐sulfonatophenyl) porphine chloride, Fe(TPPS)Cl, as a catalyst was studied with stopped‐flow UV–vis spectrophotometry and potentiometry using a chloride ion selective electrode. The observations are interpreted by a three‐step kinetic model: the initial reaction of the catalyst with the oxidant (Fe(TPPS)+ + H2O2 → Cat′) produces an active intermediate, which oxidizes the substrate (Cat′ + TCP → Fe(TPPS)+ + DCQ + Cl−) in the second step. The third step is the transformation of the catalyst into a much less active form (Cat′ → Cat″) and is responsible for the unusual kinetic phenomena observed in the system. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:449–455, 2004.
Non‐local damage model with evolving internal length
Authors: Pijaudier‐Cabot Gilles , Haidar Khalil , Dubé Jean‐François
Published: June 2004

A modified non‐local damage model with evolving internal length, inspired from micromechanics, is developed. It is shown in particular that the non‐local influence between two points in the damaged material depends on the value of damage at each of these points. The resulting weight function is non‐symmetric and truncated. Finite element results and strain localization analysis on a one‐dimensional problem are presented and compared to those of the original non‐local damage model. It is shown that in the course of damage localization, the incremental strain profiles expand according to the modified non‐local model, instead of shrinking according to the original constitutive relation. Comparisons with experimental data on model materials with controlled porosity are also discussed. Acoustic emission analyses provide results with which the theoretical model is consistent qualitatively. This model also opens the path for durability mechanics analyses, where it has been demonstrated that the internal length in the non‐local model should evolve with environmentally induced damage. Copyright © 2004 John Wiley & Sons, Ltd.
Discrete vs smeared crack models for concrete fracture: bridging the gap
Authors: Borst René de , Remmers Joris J. C. , Needleman Alan , Abellan Marie‐Angèle
Published: June 2004

Discrete and smeared crack models for concrete fracture are discussed in a historical perspective. It is argued that these two computational approaches, originally conceived as very different, can be brought together by exploiting the partition‐of‐unity property of finite element shape functions. The cohesive segments method, which exploits this partition‐of‐unity property, exhibits advantages of both the discrete and smeared crack approaches, and is capable of describing the transition from distributed micro‐cracking to a dominant crack. The versatility of the cohesive methodology is shown by incorporating water diffusion and ion transport into the formulation. Copyright © 2004 John Wiley & Sons, Ltd.
A model updating strategy of non‐linear vibrating structures
Authors: Kerschen G. , Golinval J. C.
Published: June 2004

The objective of this paper is to present a model updating strategy of non‐linear vibrating structures. Because modal analysis is no longer helpful in non‐linear structural dynamics, a special attention is devoted to the features extracted from the proper orthogonal decomposition and one of its non‐linear generalizations based on auto‐associative neural networks. The efficiency of the proposed procedure is illustrated using simulated data from a three‐dimensional portal frame. Copyright © 2004 John Wiley & Sons, Ltd.
Gradient method for inverse heat conduction problem in nanoscale
Authors: Kim Sun K. , Daniel Isaac M.
Published: June 2004

An inverse heat conduction problem for nanoscale structures was studied. The conduction phenomenon is modelled using the Boltzmann transport equation. Phonon‐mediated heat conduction in one dimension is considered. One boundary, where temperature observation takes place, is subject to a known boundary condition and the other boundary is exposed to an unknown temperature. The gradient method is employed to solve the described inverse problem. The sensitivity, adjoint and gradient equations are derived. Sample results are presented and discussed. Copyright © 2004 John Wiley & Sons, Ltd.
Numerical analysis of Augmented Lagrangian algorithms in complementary elastoplasticity
Authors: Contrafatto L. , Ventura G.
Published: June 2004

The main subject of the paper is the investigation of Augmented Lagrangian algorithms and update formulas in the solution of elastoplastic problems. A stress rate formulation for elastoplastic models with internal variables and its finite increment form is employed to state the mechanical problem. In this formulation the Augmented Lagrangian is used to enforce the constraint of plastic admissibility directly on the stresses and thermodynamic forces. This is not a limitation of the Augmented Lagrangian approach, and the same framework can be built on more classical displacement formulations as well. The meaning and the derivation of various first and second order Lagrangian multipliers update formulas and iterative schemes is shown. A new diagonal iteration algorithm and the introduction of a scale factor for the Augmented Lagrangian term are proposed. Numerical examples compare the efficiency of several forms of Augmented Lagrangian algorithms and illustrate the influence of the scale factor and of the penalty parameter. Copyright © 2004 John Wiley & Sons, Ltd.
A mesh free approach using radial basis functions and parallel domain decomposition for solving three‐dimensional diffusion equations
Authors: Ingber M. S. , Chen C. S. , Tanski J. A.
Published: June 2004

The analysis of transient heat conduction problems in large, complex computational domains is a problem of interest in many technological applications including electronic cooling, encapsulation using functionally graded composite materials, and cryogenics. In many of these applications, the domains may be multiply connected and contain moving boundaries making it desirable to consider meshless methods of analysis. The method of fundamental solutions along with a parallel domain decomposition method is developed for the solution of three‐dimensional parabolic differential equations. In the current approach, time is discretized using the generalized trapezoidal rule transforming the original parabolic partial differential equation into a sequence of non‐homogeneous modified Helmholtz equations. An approximate particular solution is derived using polyharmonic splines. Interfacial conditions between subdomains are satisfied using a Schwarz Neumann–Neumann iteration scheme. Outside of the first time step where zero initial flux is assumed, the initial estimates for the interfacial flux is given from the converged solution obtained during the previous time step. This significantly reduces the number of iterations required to meet the convergence criterion. The accuracy of the method of fundamental solutions approach is demonstrated through two benchmark problems. The parallel efficiency of the domain decomposition method is evaluated by considering cases with 8, 27, and 64 subdomains. Copyright 2004 © John Wiley & Sons, Ltd.
A geometry projection method for shape optimization
Authors: Norato J. , Haber R. , Tortorelli D. , Bendsøe M. P.
Published: June 2004

We present a new method for shape optimization that uses an analytical description of the varying design geometry as the control in the optimization problem. A straightforward filtering technique projects the design geometry onto a fictitious analysis domain to support simplified response and sensitivity analysis. However, the analytical geometry model is referenced directly for all purely geometric calculations. The method thus combines the advantages of direct geometry representations with the simplified analysis procedures that are possible with fictitious domain analysis methods, such as the material distribution methods commonly used in topology optimization. The projected geometry measure converges to the indicator function of the analytical geometry model in the limit of numerical mesh refinement. Consequently, optimal designs obtained with the new method converge to solutions of well‐defined continuum optimization problems in the limit of mesh refinement. This property is confirmed in example computations for minimum compliance design of an elastic structure subject to a volume constraint and for minimum volume design subject to a maximum stress constraint. Copyright © 2004 John Wiley & Sons, Ltd.
Finite element formulation for modelling large deformations in elasto‐viscoplastic polycrystals
Authors: Matouš Karel , Maniatty Antoinette M.
Published: June 2004

Anisotropic, elasto‐viscoplastic behaviour in polycrystalline materials is modelled using a new, updated Lagrangian formulation based on a three‐field form of the Hu‐Washizu variational principle to create a stable finite element method in the context of nearly incompressible behaviour. The meso‐scale is characterized by a representative volume element, which contains grains governed by single crystal behaviour. A new, fully implicit, two‐level, backward Euler integration scheme together with an efficient finite element formulation, including consistent linearization, is presented. The proposed finite element model is capable of predicting non‐homogeneous meso‐fields, which, for example, may impact subsequent recrystallization. Finally, simple deformations involving an aluminium alloy are considered in order to demonstrate the algorithm. Copyright © 2004 John Wiley & Sons, Ltd.
A simple boundary element method for problems of potential in non‐homogeneous media
Authors: Sutradhar Alok , Paulino Glaucio H.
Published: June 2004

A simple boundary element method for solving potential problems in non‐homogeneous media is presented. A physical parameter (e.g. heat conductivity, permeability, permittivity, resistivity, magnetic permeability) has a spatial distribution that varies with one or more co‐ordinates. For certain classes of material variations the non‐homogeneous problem can be transformed to known homogeneous problems such as those governed by the Laplace, Helmholtz and modified Helmholtz equations. A three‐dimensional Galerkin boundary element method implementation is presented for these cases. However, the present development is not restricted to Galerkin schemes and can be readily extended to other boundary integral methods such as standard collocation. A few test examples are given to verify the proposed formulation. The paper is supplemented by an Appendix, which presents an ABAQUS user‐subroutine for graded finite elements. The results from the finite element simulations are used for comparison with the present boundary element solutions. Copyright © 2004 John Wiley & Sons, Ltd.
Integral representations in elastostatics and their application to an alternative boundary element method
Authors: Turteltaub Sergio , Turteltaub Matías
Published: June 2004

We 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

The 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

A 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

Proteomics 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

A 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

A 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

Hybrid 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

Well‐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

The 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

A 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

The 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

A 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

The 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

Resonant 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

We 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

The 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

Progress 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

This 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

This 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.
Use of energy‐space diagrams in free‐electron models of field electron emission
Authors: Forbes Richard G.
Published: June 2004

An improved method is reported for deriving the equations for cold field electron emission from a free‐electron metal. It is shown that the derivation of these equations can be presented as a straightforward double integral in a space where the vertical axis represents the total electron energy, and the horizontal axis represents the component of electron kinetic energy parallel to the emitter surface. A general approach is developed that applies to a tunnelling barrier of any shape. It is shown that the temperature‐correction factor derived by Murphy and Good for emission through an image‐rounded barrier also applies to a more general barrier. For the standard image‐rounded barrier the results coincide with those of Murphy and Good, but the derivation is more straightforward mathematically and the physics involved can be visualized more easily. The method developed here should be a good foundation for developing an improved theory of cold field electron emission from semiconductors: the main object of the paper is to lay this foundation. Copyright © 2004 John Wiley & Sons, Ltd.