bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Caustic Addition in Epoxy Polymerization Process: A Single and Multi‐Objective Evolutionary Approach
Authors: Raha Sasanka , Majumdar Saptarshi , Mitra Kishalay
Published: March 2004

Summary: An epoxy polymerization process is studied in semi‐batch mode. Caustic has a very critical influence on epoxy polymerization process, which is modeled as a set of highly nonlinear coupled ODE's (ordinary differential equations). Owing to the highly complicated, nonlinear domain of analysis, “Differential Evolution (DE)” and “Genetic Algorithm (GA)” are used as optimization tools to identify the $\overline M _{\rm n}$‐PDI Pareto set and study the best operating strategy with respect to NaOH addition. The moment of various oligomeric components during the semi‐batch polymerization is also presented for a better understanding of the process. This study demonstrates the potential of evolutionary optimization algorithm to identify various operating philosophies of a semi‐batch epoxy reactor for a targeted product quality.

Pareto plot for epoxy polymerization process with intermediate NaOH addition varying from 0.0 to 1.0 kmol · m−3.

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Pareto plot for epoxy polymerization process with intermediate NaOH addition varying from 0.0 to 1.0 kmol · m−3.
Modeling of Ethylene Polymerization Kinetics over Supported Chromium Oxide Catalysts
Authors: Choi Kyu Yong , Tang Shihua , Yoon Won Jung
Published: March 2004

Summary: Silica supported chromium oxide catalysts have been used for many years to manufacture polyethylene and they still account for more than 50% of world production of high‐density polyethylene. Along with its commercial success, the catalytic mechanism and polymerization kinetics of silica supported chromium oxide catalysts have been the subject of intense research. However, there is a lack of modeling effort for the quantitative prediction of polymerization rate and polymer molecular weight properties. The chromium oxide catalyzed ethylene polymerization is often characterized by the presence of an induction period followed by a steady increase in polymerization rate. The molecular weight distribution is also quite broad. In this paper, a two‐site kinetic model is developed for the modeling of ethylene polymerization over supported chromium oxide catalyst. To model the induction period, it is proposed that divalent chromium sites are deactivated by catalyst poison and the reactivation of the deactivated chromium sites is slow and rate controlling. To model the molecular weight distribution broadening, each active chromium site is assumed to have different monomer chain transfer ability. The experimental data of semibatch liquid slurry polymerization of ethylene is compared with the model simulations and a quite satisfactory agreement has been obtained for the polymerization conditions employed.

Polymerization rates at different reaction temperatures: symbols – data, lines – model simulations.

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Polymerization rates at different reaction temperatures: symbols – data, lines – model simulations.
Cover Picture: Macromol. Theory Simul. 2/2004
Authors: Meier Robert J. , Koglin Eckhard
Published: March 2004

Cover: The picture on the cover shows a theoretician, noting that different computational methods yield very different results, asking himself what result to believe, and in particular for what reason. It illustrates a dilemma when studying families of real‐life catalytic systems by quantum calculations, for which high‐level calculations are computationally prohibitive. The experimental chemist is awaiting the prediction by the theoretician.

Further details can be found in the Full Paper by R. J. Meier* and E. Koglin on page 133.
Lack of mutations in DJ‐1 in a cohort of Taiwanese ethnic Chinese with early‐onset parkinsonism
Authors: Lockhart Paul J. , Bounds Rebecca , Hulihan Mary , Kachergus Jennifer , Lincoln Sarah , Lin Chin‐Hsien , Wu Ruey‐Meei , Farrer Matthew J.
Published: March 2004

Recently, mutations in DJ‐1 (PARK7) were described as a novel cause of early‐onset parkinsonism. We analysed the DJ‐1 gene in a cohort of patients originating from Taiwan with early‐onset Parkinson's disease; 41 subjects were clinically and genetically examined. These patients were evaluated previously for the presence of parkin mutations (PARK2) and were found to be negative. The entire DJ‐1 open‐reading frame was amplified from cDNA, analysed for size alterations indicative of mutations affecting splice motifs, and sequenced to identify coding variants. In addition, we developed quantitative polymerase chain reaction assays to examine the genomic copy number of DJ‐1 exons. No potential splice site mutations, coding sequence alterations, or exon deletion/duplications were detected. Our results and previous studies suggest that alterations to DJ‐1 are not a common cause of early‐onset Parkinson's disease and other causes, genetic and/or environmental, remain to be identified. © 2004 Movement Disorder Society
A complete 1H and 13C NMR data assignment for the diterpene methyl (−)‐zanzibarate by 2D spectroscopy and NOE experiments
Authors: Imamura P. M. , Miranda P. C. M. L. , Giacomini R. A.
Published: March 2004

The 1H and 13C NMR spectra of methyl (−)‐zanzibarate (1), an ent‐labdanic diterpene isolated from the epicarp of Hymenaea courbaril var. altissima (Leguminosaea, Cesalpinoideae, Detariae), was fully assigned by COSY experiments, 13C/1H shift correlation diagrams and NOE experiments. Copyright © 2004 John Wiley & Sons, Ltd.
Structural properties of perfluorinated linear alkanes: a 19F and 13C NMR study of perfluorononane
Authors: Schwarz Roman , Seelig Joachim , Künnecke Basil
Published: March 2004

Liquid perfluorocarbons exhibit unique physical–chemical characteristics such as extraordinary stability, combined hydrophobia and lipophobia, low surface tension and a capacity to carry large quantities of gas. They have found widespread use in industry, medicine and biology even though the molecular origin of these properties is not fully understood. The objective of the present work was to elucidate the physical behavior of perfluorinated linear alkanes by investigating their intramolecular electronic environment using 13C and 19F NMR techniques in combination with theoretical calculations of molecular orbitals. Particular advantage was taken of 19F–19F through‐space couplings, which led us to propose a molecular model in which delocalized p‐electrons of the fluorines cover the entire surface of the molecule in two pairs of intertwined helices. Experimental data are presented for n‐perfluorononane and supported by corresponding measurements with shorter and longer perfluorinated alkanes. Copyright © 2004 John Wiley & Sons, Ltd.
Competition STD NMR for the detection of high‐affinity ligands and NMR‐based screening
Authors: Wang Yu‐Sen , Liu Dingjiang , Wyss Daniel F.
Published: March 2004

The reported competition STD NMR method combines saturation transfer difference (STD) NMR with competition binding experiments to allow the detection of high‐affinity ligands that undergo slow chemical exchange on the NMR time‐scale. With this technique, the presence of a competing high‐affinity ligand in the compound mixture can be detected by the disappearance or reduction of the STD signals of a low‐affinity indicator ligand. This is demonstrated on a BACE1 (β‐site amyloid precursor protein cleaving enzyme 1) protein–inhibitor system. This method can also be used to derive an approximate value, or a lower limit, for the dissociation constant of the potential ligand based on the reduction of the signal intensity of the STD indicator, which is illustrated on an HSA (human serum albumin) model system. This leads to important applications of the competition STD NMR method for lead discovery: it can be used (i) for compound library screening against a broad range of drug targets to identify both high‐ and low‐affinity ligands and (ii) to rank order analogs rapidly and derive structure–activity relationships, which are used to optimize these NMR hits into viable drug leads. Copyright © 2004 John Wiley & Sons, Ltd.
Dynamic NMR spectroscopy of hyperpolarized 129Xe in human brain analyzed by an uptake model
Authors: Kilian Wolfgang , Seifert Frank , Rinneberg Herbert
Published: March 2004

Hyperpolarized 129Xe (HpXe) NMR not only holds promise for functional lung imaging, but for measurements of tissue perfusion as well. To investigate human brain perfusion, several time‐series of 129Xe MR spectra were recorded from one healthy volunteer after HpXe inhalation. The time‐dependent amplitudes of the MR spectra were analyzed by using a compartment model for xenon uptake modified to account for the loss of 129Xe polarization due to RF‐excitation and for the breathhold technique used in the experiments. This analysis suggests that the resonances detected at 196.5 ± 1 ppm and 193 ± 1 ppm originate from HpXe dissolved in gray and white matter, respectively, and that T1 relaxation times of HpXe are different in gray and white matter (T1g > T1w). Magn Reson Med 51:843–847, 2004. © 2004 Wiley‐Liss, Inc.
Complementary displacement‐encoded MRI for contrast‐enhanced infarct detection and quantification of myocardial function in mice
Authors: Gilson Wesley D. , Yang Zequan , French Brent A. , Epstein Frederick H.
Published: March 2004

MRI is emerging as an important modality for assessing myocardial function in transgenic and knockout mouse models of cardiovascular disease, including myocardial infarction (MI). Displacement encoding with stimulated echoes (DENSE) measures myocardial motion at high spatial resolution using phase‐reconstructed images. The current DENSE technique uses inversion recovery (IR) to suppress T1‐relaxation artifacts; however, IR is ill‐suited for contrast‐enhanced infarct imaging in the heart, where multiple T1 values are observed. We have developed a modified DENSE method employing complementary acquisitions for T1‐independent artifact suppression. With this technique, displacement and strain are measured in phase‐reconstructed images, and contrast‐enhanced regions of infarction are depicted in perfectly coregistered magnitude‐reconstructed images. The displacement measurements and T1‐weighted image contrast were validated with the use of a rotating phantom. Modified DENSE was performed in mice (N = 9) before and after MI. Circumferential (Ecc) and radial (Err) strain were measured, and contrast‐enhanced infarcted myocardium was detected by DENSE. At baseline, Ecc was −0.16 ± 0.01 and Err was 0.39 ± 0.07. After MI, Ecc was 0.04 ± 0.02 and Err was 0.03 ± 0.04 in infarcted regions, whereas Ecc was −0.12 ± 0.02 and Err was 0.38 ± 0.09 in noninfarcted regions. In vivo Ecc as determined by DENSE correlated well with Ecc obtained by conventional tag analysis (R = 0.90). Magn Reson Med 51:744–752, 2004. © 2004 Wiley‐Liss, Inc.
Evaluation of a pneumatically driven tactile stimulator device for vision substitution during fMRI studies
Authors: Zappe Anne‐Catherin , Maucher Thorsten , Meier Karlheinz , Scheiber Christian
Published: March 2004

Functional magnetic resonance imaging (fMRI) experiments on tactile perception are difficult to perform because the special characteristics of an MRI environment restrict the experimental setup. Although recently developed actuators have made it possible to apply vibrotactile stimuli to the skin during an fMRI experiment, the projection of spatially extended patterns is still precluded. In order to examine the processing of tactile perception, a new pneumatically‐driven tactile device (PTD) has been built. This device is capable of stimulating the skin, using arbitrary time sequences that consist of 2D tactile images up to 64 pixels. It is shown how the device is implemented in a 2 T fMRI environment, and show that it operates without generating artifacts. Dedicated software allows the generation of complex paradigms and provides a user‐friendly interface to other brain mapping systems, as well as automated operation. This paper describes the PTD elucidates its features, and demonstrate its reliability by reporting results from an fMRI study based on an event‐related protocol involving six subjects. Magn Reson Med 51:828–834, 2004. © 2004 Wiley‐Liss, Inc.
Normal cerebral perfusion measurements using arterial spin labeling: Reproducibility, stability, and age and gender effects
Authors: Parkes Laura M. , Rashid Waqar , Chard Declan T. , Tofts Paul S.
Published: March 2004

Before meaningful conclusions can be drawn from clinical measures of cerebral blood perfusion, the precision of the measurement must be determined and set in the context of inter‐ and intrasubject sources of variability. This work establishes the reproducibility of perfusion measurements using the noninvasive MRI technique of continuous arterial spin labeling (CASL). Perfusion was measured in 34 healthy normal subjects. Intersubject variability was assessed, and age and gender contributions were estimated. Intersubject variation was found to be large, with up to 100% perfusion difference for subjects of the same age and gender. Repeated measurements in one subject showed that perfusion remains remarkably stable in the short term when compared with intersubject variation and the large capacity for perfusion change in the brain. A significant decrease in the ratio of gray‐matter to white‐matter perfusion was found with increasing age (0.79% per year (P < 0.0005)). This appears to be due mainly to a reduction in gray‐matter perfusion, which was found to decrease by 0.45% per year (P = 0.04). Regional analysis suggested that the gray‐matter age‐related changes were predominantly localized in the frontal cortex. Whole‐brain perfusion was 13% higher (P = 0.02) in females compared to males. Magn Reson Med 51:736–743, 2004. © 2004 Wiley‐Liss, Inc.
Inflow correction of hepatic perfusion measurements using T1‐weighted, fast gradient‐echo, contrast‐enhanced MRI
Authors: Peeters Frank , Annet Laurence , Hermoye Laurent , Van Beers Bernard E.
Published: March 2004

Inflow effects were studied for T1‐weighted, fast gradient‐echo, contrast‐enhanced MRI. This was done on the basis of realistic simulations (e.g., taking slice profiles into account) for unsteady flow. The area under the point spread function (PSF) was used to estimate the flow‐related enhancement. A simple analytical model that accurately describes the inflow effects was derived and validated. This model was used to correct the experimental perfusion calibration curves (signal intensity vs. relaxation rate) for inflow effects. Hepatic perfusion measurements, performed on patients, were analyzed in terms of a dual‐input, first‐order linear model. It was shown that inflow causes incorrect perfusion input functions. The resulting estimated perfusion parameters displayed a systematic error of typically 30–40%. By performing two extra time‐resolved flow measurements during the examination, one can correct the input functions. Magn Reson Med 51:710–717, 2004. © 2004 Wiley‐Liss, Inc.
Reduced field of view and undersampled PR combined for interventional imaging of a fully dynamic field of view
Authors: Peters Dana C. , Guttman Michael A. , Dick Alexander J. , Raman Venkatesh K. , Lederman Robert J. , McVeigh Elliot R.
Published: March 2004

Active catheter imaging was investigated using real‐time undersampled projection reconstruction (PR) combined with the temporal filtering technique of reduced field of view (rFOV). Real‐time rFOV processing was interactively enabled during highly undersampled catheter imaging, resulting in improved artifact suppression with better temporal resolution than that obtained by view‐sharing. Imaging with 64 to 32 projections provided a resolution of 2 × 2 × 8 mm, and four to eight true frames per second. Image artifacts were reduced when rFOV processing was applied to the undersampled images. A comparison with Cartesian rFOV showed that PR image quality is less susceptible to aliasing that results from rFOV imaging with a wholly dynamic outer FOV. Simulations and MRI experiments demonstrated that PR rFOV provides significant artifact suppression, even for a fully dynamic FOV. The near doubling of temporal resolution that is possible with PR rFOV permits accurate monitoring of highly dynamic events, such as catheter movements, and arrhythmias, such as ventricular ectopy. Magn Reson Med 51:761–767, 2004. © 2004 Wiley‐Liss, Inc.
Glucose production pathways by 2H and 13C NMR in patients with HIV‐associated lipoatrophy
Authors: Weis Brian C. , Margolis David , Burgess Shawn C. , Merritt Matthew E. , Wise Holly , Sherry A. Dean , Malloy Craig R.
Published: March 2004

Patients with HIV taking protease inhibitors were selected for the presence (five subjects) or absence (five subjects) of lipoatrophy. Following an overnight fast, subjects were given oral 2H2O in divided doses (5 mL/kg body water), [U‐13C3] propionate (10 mg/kg), and acetaminophen (1000 mg). Glucose (from plasma) or acetaminophen glucuronide (from urine) were converted to monoacetone glucose for 2H NMR and 13C NMR analysis. The fraction of plasma glucose derived from gluconeogenesis was not significantly different between groups. However, flux from glycerol into gluconeogenesis relative to glucose production was increased from 0.20 ± 0.13 among subjects without lipoatrophy to 0.42 ± 0.12 (P < 0.05) among subjects with lipoatrophy, and the TCA cycle contribution was reduced. Lipoatrophy was associated with an abnormal profile of glucose production as assessed by 13C and 2H NMR of plasma and urine. Magn Reson Med 51:649–654, 2004. Published 2004 Wiley‐Liss, Inc.
Improved accuracy for the Helmholtz equation in unbounded domains
Authors: Turkel Eli , Farhat Charbel , Hetmaniuk Ulrich
Published: March 2004

Based on properties of the Helmholtz equation, we derive a new equation for an auxiliary variable. This reduces much of the oscillations of the solution leading to more accurate numerical approximations to the original unknown. Computations confirm the improved accuracy of the new models in both two and three dimensions. This also improves the accuracy when one wants the solution at neighbouring wavenumbers by using an expansion in k. We examine the accuracy for both waveguide and scattering problems as a function of k, h and the forcing mode l. The use of local absorbing boundary conditions is also examined as well as the location of the outer surface as functions of k. Connections with parabolic approximations are analysed. Copyright © 2004 John Wiley & Sons, Ltd.
A recipe to detect the error in discretization schemes
Authors: Lapenta Giovanni
Published: March 2004

The necessity for a reliable measure of the discretization error arises in adaptive mesh refinement and in moving mesh adaptation. The present work discusses a detector of the discretization error based on the interpolation reconstruction of the operators. The technique presented here is named operator recovery error source detector (ORESD). Its main features are: First, the technique is based on the operators being discretized and does not require any user intervention or any a priori knowledge of the solution or its properties. Second, the ORESD is an a posteriori error indicator, but it is shown to be consistent with the a priori error provided by the modified equation approach. Third, the technique is based on the operators being solved and is tailored to the specific problem at hand. Four, the technique is simple and is based on a small stencil, resulting in a very inexpensive error detection.

In the present work, the ORESD is derived and applied to two tutorial examples: divergence and gradient. With the aid of the two examples and using the general derivation, the ORESD is then applied to the gas dynamics equations. Two benchmarks are used to test the performance. First, a shock tube problem is solved (Sod's benchmark) in a Lagrangian and in a Eulerian frame. Second, the Colella's wedge problem is solved using CLAWPACK. Finally, the ORESD is applied to the 2D Poisson equation on a uniform and on a non‐uniform grid to test the application to elliptic problems. In all examples the operator recovery error source detector succeeds in detecting the real sources of error. Copyright © 2004 John Wiley & Sons, Ltd.
Removal of proteins from natural rubber with urea
Authors: Kawahara Seiichi , Klinklai Warunee , Kuroda Hirofumi , Isono Yoshinobu
Published: March 2004

Removal of proteins from natural rubber was achieved by incubation of the rubber latex with urea in the presence of a surfactant to prevent the latex‐allergy caused with thin film products. Temperature, pH and time for the incubation were investigated to remove the proteins effectively, in which nitrogen content of the rubber was reduced to 0.02 from 0.38 wt% under the optimum condition. To remove further the proteins, deproteinization of natural rubber was made by incubation of the latex with proteolytic enzyme in the presence of a surfactant followed by incubation with urea. Amount of allergen decreased through the procedure to less than 0.7 μg/ml, which is a small amount of allergen compared to that for the commercial, deproteinized natural rubber. Copyright © 2004 John Wiley & Sons, Ltd.
Theoretical analysis of fiber motion and loads during flow
Authors: Hernandez J. P. , Raush T. , Rios A. , Strauss S. , Osswald T. A.
Published: March 2004

A pseudo‐analytical model for the forces exerted on fibers during flow that lead to fiber damage is proposed and solved. The fundamental derivations for the forces on fibers moving in suspensions developed by Burgers (1938) were used as a comparison. The cases of the motion of a fiber along its axis and perpendicular to its axis and in shear flow at a −45 degree‐angle were investigated for aspect ratios between 10 and 300. The values for the overall forces on the fiber were in good agreement with the results found earlier by Burgers and others. However, the force distribution along the fiber was found to be significantly different from the constant distribution assumed by Burgers. Because of the higher forces on the fiber from the exact solution, the criterion for the onset of buckling in shear flow was revised. The pseudo‐analytical solution was also compared to numerical results done with the boundary element method (BEM); the results were in good agreement.
Mechanical properties of polypropylene matrix composites reinforced with natural fibers: A statistical approach
Authors: Biagiotti J. , Fiori S. , Torre L. , López‐Manchado M. A. , Kenny J. M.
Published: March 2004

This work presents a systematic and statistical approach to evaluate and predict the properties of random discontinuous natural fiber reinforced composites. Different composites based on polypropylene and reinforced with natural fibers were produced and their mechanical properties are measured together with the distribution of the fiber size and the fiber diameter. The values obtained were related to the theoretical predictions, using a combination of the Griffith theory for the effective properties of the natural fibers and the Halpin‐Tsai equation for the elastic modulus of the composites. The relationships between experimental results and theoretical predictions were statistically analyzed using a probability density function estimation approach based on neural networks. The results show a more accurate expected value with respect to the traditional statistical function estimation approach. In order to point out the particular features of natural fibers, the same proposed method is also applied to PP–glass fiber composites.
Damage behavior in multi‐stage fatigue testing of glass‐fiber‐reinforced polyamide 66
Authors: Katoh Atsushi , Handa Kouichi , Narisawa Ikuo
Published: March 2004

With plastics being increasingly applied to moving parts today, predictions of continuous fatigue life under identical conditions (ambient temperature, frequency and load stress) are not sufficient. Rather, there is an urgent need to develop a method of predicting fatigue life under multi‐stage loading involving intermittently changing conditions.

In this study, by applying a temperature‐ and frequency‐superposition method to fatigue life prediction of plastics, it was found that an exponential type of cumulative damage law could be applied to a two‐stage fatigue process. Specifically, when fatigue conditions (interval time, ambient temperature, frequency and load stress) are changed between several stages, the resulting damage behavior follows an exponential law representing the ratio of the number of cycles in each stage to the continuous fatigue life under those conditions. It is shown here that the exponent m has a single value and consists of the product of the independent functions of the factors of the fatigue conditions. It is also shown that the use of this exponential law reproduces very well the damage behavior in a two‐stage fatigue test in which each fatigue condition is changed and in three‐ and four‐stage fatigue tests in which the interval time is varied.
Practical diabetes international: past, present and future
Authors: Connor H
Published: March 2004

The 20th Anniversary of Practical Diabetes International is an opportunity to review the content of the journal over two decades. During this time there has been a marked change in emphasis from papers on type 1 diabetes, microvascular complications and devices for insulin injection and home blood glucose monitoring in the earlier issues, towards articles on type 2 diabetes, macrovascular disease and hypertension in more recent numbers. There has also been a change in emphasis from papers on education towards articles on quality and audit. Although the journal has a wide circulation among representatives of all of the professions who provide diabetes care, the non‐medical professions (nursing, dietetic and podiatric) and patients remain under‐represented as contributors. Copyright © 2004 John Wiley & Sons, Ltd.
An overview of diabetes education in the United Kingdom: past, present and future
Authors: Lucas S , Walker R
Published: March 2004

This paper examines the evolution of diabetes education from a time when it was viewed as an ad hoc event or even as an optional extra to one when it is now accepted as essential and central to successful self‐management. During the last 20 years there has been a transition from didactic teaching practices towards problem‐solving models which are based on modern principles of adult learning, and from one‐to‐one teaching towards group learning. The evolving role of the diabetes nurse specialist over the last two decades has been crucial in enabling these changes. The evidence base for different educational models needs further strengthening, but structured programmes for life‐long learning are now being developed. Important decisions are still needed on the provision and content of the training programmes for educators and on the mechanisms for the provision of quality assurance. Copyright © 2004 John Wiley & Sons, Ltd.
Diabetic dyslipidaemia: past, present and future
Authors: Betteridge DJ
Published: March 2004

Prevention of cardiovascular disease (CVD) in diabetes remains a major challenge for both physicians and patients. Diabetic dyslipidaemia is a major risk factor for CVD and is open to therapeutic intervention. Information now available from randomised, controlled, clinical trials (principally with statins) confirms highly significant benefits in terms of CVD reduction for diabetic patients with and without symptomatic CVD. This evidence base has moved treatment of dyslipidaemia to centre stage in CVD prevention. Important European and American guidelines point to the high CVD risk in type 2 diabetes and type 1 diabetes with albuminuria and advocate aggressive lipid management for primary as well as secondary CVD prevention. Currently there is evidence of sub‐optimal uptake of appropriate lipid‐lowering therapy and guidelines need to be fully implemented in clinical practice for the benefit of individual patients. In the future it is likely that more combination therapy will be used to treat diabetic dyslipidaemia in order to achieve better overall lipid control. Copyright © 2004 John Wiley & Sons, Ltd.
Polyaniline/carbon nanotube composite Schottky contacts
Authors: Ramamurthy Praveen C. , Harrell William R. , Gregory Richard V. , Sadanadan Bindu , Rao Apparao M.
Published: March 2004

Schottky contacts were fabricated on composites of high molecular weight polyaniline and pristine multiwalled carbon nanotubes. Physical and electrical characteristics of these organic composite materials were studied by using atomic force microscopy (AFM), scanning electron microscopy (SEM), and electrical measurements. The RMS surface roughness of the composite films was found to be 4 nm. From the IV characteristics of these composite devices, it appears that the current follows Ohm's law at lower voltages and Child's law at higher voltages, indicating a space‐charge‐limited emission mechanism in the presence of a distribution of shallow traps.
Mechanical properties, water swelling behavior, and morphology of swellable rubber compatibilized by PVA‐g‐PBA
Authors: Zhang Zhihao , Zhang Guo , Zhang Yue , Wang Zhigang , Yu Donghong , Hu Xiangqing , Hu Chaoquan , Tang Xinyi
Published: March 2004

A novel water swellable rubber (WSR) was prepared by blending chlorohydrin rubber (CHR) with crosslinked polyacrylate (CPA), poly(vinyl alcohol)‐g‐poly(butyl acrylate) (PVA‐g‐PBA), precipitated silica (PSA), and poly(ethylene glycol) (PEG). The amphiphilic graft copolymer PVA‐g‐PBA was incorporated as the compatibilizer between CHR and CPA. Water swellable‐rubber with different grafting percentages and contents of PVA‐g‐PBA was investigated by SEM, mechanical measurement, and water‐swelling tests. The results prove that PVA‐g‐PBA increased interfacial cohesion between CHR and CPA before and after water swelling, decreased percentage loss by weight, and improved water‐swelling behavior. Mechanical properties of WSR were significantly improved by PVA‐g‐PBA, especially for the blends of 5 phr PVA‐g‐PBA with G% = 151.7% before water swelling and that with G% = 340.4% after water swelling.
The synergistic effect of boron nitride particle and die on the capillary extrusion processability of mLDPE
Authors: Lee Sang Myung , Nam Gi Joon , Lee Jae Wook
Published: March 2004

The synergistic effects of boron nitride (BN) powder and die on the rheology and processability of metallocene‐catalyzed low density polyethylene (mLDPE) were investigated. The processability in the extrusion process is closely related to the interfacial properties between the polymer melts and the die wall. BN powder was added to mLDPE to reduce the friction coefficient and surface energy. Adding 0.5 wt% BN powder to mLDPE was very effective in improving the processability and the extrudate appearance. To study the effect of die surface property, three different dies were applied in capillary extrusion. One was conventional tungsten carbide (TC) die, and the others were hot‐pressed BN (hpBN) die and hot‐pressed BN composite (hpBNC) die. The applications of these BN dies were quite effective in delaying surface melt fracture (sharkskin) and postponing gross melt fracture to higher shear rate compared to the TC die. These improvements result from the fact that BN dies reduce the wall shear stress significantly and promote slip. The synergistic effect of processability could be obtained when both BN powder and hpBN die were used together.
Structure and properties of poly(ethylene‐co‐chlorotrifluoroethylene) and polyvinylidene fluoride exposed to water, hydrochloric acid, hydrobromic acid and tetrachloroethylene
Authors: Hedenqvist M. S. , Ritums J. E. , Condé‐Brana M. , Bergman G.
Published: March 2004

The transport of water, hydrochloric acid, hydrobromic acid and tetrachloroethylene in an poly(ethylene‐co‐chlorotrifluoroethylene) and polyvinylidene fluoride were studied at 70°C by the sorption/desorption technique. The effects on the structure and mechanical properties were studied using size‐exclusion chromatography, infrared spectroscopy, differential scanning calorimetry and tensile testing. Solute concentrations in the polymers indicated that both the water and HCl/HBr components diffused into the polymers on exposure to acid solutions. The calculated water contents of the diffusing acids generally differed from the water content in the solution. The ratio of water content in the diffusing acid to that in the surrounding acid solution was generally a function of the relative vapor activity of water and HCl/HBr. It was possible to describe the 35%HCl and 47%HBr desorption data using a two component model. It was here assumed that the water and HCl/HBr diffused separately, each having its own constant diffusion coefficient. The water diffusivity was obtained from the pure water system, and this allowed the HCl/HBr diffusivity to be calculated. It was found that the diffusivity decreased, in a non‐simple way, as a function of solute size. The exposure to solute did not lower the molar mass of the polyvinylidene fluoride. Differential scanning calorimetry indicated the development of low‐melting point polyvinylidene fluoride crystals during the exposure to all solutes. This seemed to be a consequence of the long‐term exposure (175 to 376 days) at 70°C. The long‐term exposure stiffened several of the polyvinylidene fluoride resins and occasionally made them less ductile. The poly(ethylene‐co‐chlorotrifluoroethylene) also became stiffer, but it was otherwise unaffected as far as observation by the other available techniques was concerned.
Peroxide crosslinking of Ziegler‐Natta thermoplastic polyolefins
Authors: Bacci Dino , Marchini Roberta , Scrivani Maria Teresa
Published: March 2004

A range of reactor grade TPO alloys (PP/EPM alloys from Ziegler‐Natta catalysis) were studied in order to evaluate their dynamic cross‐linkability, using a peroxide system. The amount of ethylene content in EPM rubber ranged from 28 to 77 wt%, to investigate the competition between vis‐breaking and cross‐linking during the peroxide reaction. Processing temperature and different peroxide/coagent ratios were the parameters varied in the present work. Cross‐linking degree was evaluated with Compression Set measurements and Dynamic Mechanical Analysis. It was therefore possible to find a correlation between the two analytical techniques. Feasibility of TPV rubbers with Compression Set at about 50% (22 h, 70°C) was demonstrated.
Influence of untreated and novel electron beam modified surface coated silica filler on dynamic mechanical thermal properties of ethylene‐octene copolymer
Authors: Ray Sudip , Bhowmick Anil K.
Published: March 2004

An extensive study on dynamic mechanical thermal analysis has been carried out to investigate the effect of filler‐filler and polymer‐filler interaction in cured ethylene‐octene copolymer reinforced by unmodified and modified silica. The silica was treated with trimethylolpropane triacrylate (TMPTA) or triethoxyvinyl silane (TEVS), followed by electron beam irradiation at room temperature. Modification of the silica filler, especially via silanization, significantly reduces filler‐filler networking, as evidenced from the strain sweep tests, and thus helps reduce the Payne effect, particularly at high filler loadings. The effect of modification is quantified with the help of a new mathematical model correlating the storage modulus and the volume fraction of the filler. The enhancement in the storage modulus at high temperatures and changes in the loss tangent at the glass transition temperature suggest definite improvement in the polymer‐filler interaction in the case of these modified fillers. The results obtained from the master curves constructed based on the time‐temperature‐superposition principle further support the findings.
A rheokinetic study of bulk free radical polymerization performed with a helical barrel rheometer
Authors: Cioffi M. , Ganzeveld K. J. , Hoffmann A. C. , Janssen L. P. B. M.
Published: March 2004

The Trommsdorff effect is a non‐linear autoacceleration phenomenon in bulk free radical polymerizations. It is undesired in processes on industrial scale, as is causes hot spots and erratic behavior. In this paper a rheokinetic investigation of the Trommsdorff effect is performed with a helical barrel rheometer. This rheometer can be considered a small‐scale model of large reactors, particularly extruders. The rheokinetic measurements show that the Trommsdorff effect can be reduced when the polymerization is performed at a high rotational velocity of the screw. This confirms a previous study performed with a cone and plate rheometer and is encouraging with a view to designing better‐controlled bulk free radical polymerization processes on industrial scale.
Rheo‐optical studies of the effect of shear flow on the structure of elastomer blends
Authors: Xu Tao , Shaw Montgomery T. , Weiss R. A.
Published: March 2004

The effect of shear flow on the structure of a phase‐separated, near‐critical blend of 50/50 (w/w) poly(styrene‐ran‐butadiene) and polybutadiene was studied with two different custom‐built rheo‐optical instruments that combined polymer melt flow and small‐angle light scattering (SALS). The deformation of the phase domains during shear flow was nonaffine, and the SALS patterns evolved from a spinodal ring (SR) pattern to a squashed SR with two high‐intensity lobes, to an H‐pattern, to a butterfly pattern with a dark streak along the equator, and finally to a steady‐state, elliptical pattern. The SALS patterns were explained in terms of a network model, in which the strands of the network first orient in the flow direction, then extend in this direction, and finally break up into droplets aligned in the flow direction. According to this picture, the strands in the vorticity direction do not deform until relatively high strains, after which the periodicity of the network begins to disappear. Supporting this model was the observation that the transitions between the different SALS patterns corresponded to inflections and/or maxima in the shear stress or first normal stress difference. Increasing the shear rate changed the kinetics of the structure evolution and reduced the size of the phase‐separated droplets in the steady state. No evidence was obtained for flow‐induced miscibility. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1725–1738, 2004
Miscibility, melting, and crystallization of poly(butylene‐2,6‐naphthalate)/poly(ether imide) blends
Authors: Huang Jieh‐Ming
Published: March 2004

We prepared blends of poly(butylene‐2,6‐naphthalate) (PBN) and poly(ether imide) (PEI) by solution‐casting from dichloroacetic acid solutions. The miscibility, crystallization, and melting behavior of the blends were investigated with differential scanning calorimetry (DSC) and dynamic mechanical analysis. PBN was miscible with PEI over the entire range of compositions, as shown by the existence of single composition‐dependent glass‐transition temperatures. In addition, a negative polymer–polymer interaction parameter was calculated, with the Nishi–Wang equation, based on the melting depression of PBN. In nonisothermal crystallization investigations, the depression of the crystallization temperature of PBN depended on the composition of the blend and the cooling rate; the presence of PEI reduced the number of PBN segments migrating to the crystallite/melt interface. Melting, recrystallization, and remelting processes occurring during the DSC heating scan caused the occurrence of multiple melting endotherms for PBN. We explored the effects of various experimental conditions on the melting behavior of PBN/PEI blends. The extent of recrystallization of the PBN component during DSC heating scans decreased as the PEI content, the heating rate, the crystallization temperature, and the crystallization time increased. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1694–1704, 2004
Effect of methyl substitution of the ethylene unit on the physical properties of poly(butylene succinate)
Authors: Chae Han Gi , Park Sun Ho , Kim Byoung Chul , Kim Dong Kook
Published: March 2004

A series of poly(butylene succinate‐co‐butylene 2‐methyl succinate)s were prepared through variations in the molar fraction of succinic acid to 2‐methyl succinic acid, and the effects of methyl substitution on the shear‐induced crystallization, nonisothermal crystallization behavior, dynamic rheological properties, crystal morphology, and mechanical properties were investigated. Introducing 2‐methyl succinic units reduced the melting temperature and crystallization temperature; this indicated that the substituted units retarded crystallization of the polymer. The Avrami exponents, estimated by modified Avrami plots, ranged from 2.1 to 3.5 and were a little diminished by the substitution. The substitution also reduced the rate of crystallization under shear. However, the effect was diminished with an increasing shear rate because most polymer chains were more regularly arranged at higher shear rates. Dynamic experiments in the solid state revealed that the peak on a plot of the loss tangent against the temperature became sharper at higher contents of the substituted unit, and the peak temperature, the glass‐transition temperature, was reduced as the content of 2‐methyl succinic acid increased. Wide‐angle X‐ray diffraction patterns showed that there was little effect of the 2‐methyl succinic acid unit on the crystal morphology. The toughness of the polymer was abruptly increased up to 350% at the expense of the tensile modulus. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1759–1766, 2004
HP(2–9)‐magainin 2(1–12), a synthetic hybrid peptide, exerts its antifungal effect onCandida albicansby damaging the plasma membrane
Authors: Park Yoonkyung , Lee Dong Gun , Hahm Kyung‐Soo
Published: March 2004

In our previous study, HP(2–9)‐MA(1–12), HP‐MA for short, a hybrid peptide incorporating residues 2–9 ofHelicobacter pyloriribosomal protein L1 (HP) and residues 1–12 of magainin 2 (MA) was shown to have strong antibacterial activity. In this study the antifungal activity of HP‐MA was evaluated using various fungi, and it was shown that the activity was increased when compared with the parent peptides. In order to investigate the fungicidal mechanism(s) of HP‐MA its action against fungal cell membranes was examined by the potassium‐release test, which showed that HP‐MA caused an increase in the amount of K+released from the cells. Furthermore, HP‐MA induced significant morphological changes. These facts suggested that the fungicidal effect of HP‐MA involves damaging the fungal cell membranes. CD investigators suggested that the α‐helical structure of these peptides plays an important role in their antibiotic effect, but that α‐helicity is less directly correlated with the enhanced antibiotic activity of the hybrid. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.
On‐resin head‐to‐tail cyclization of cyclotetrapeptides: optimization of crucial parameters
Authors: Alcaro Maria C. , Sabatino Giuseppina , Uziel Jacques , Chelli Mario , Ginanneschi Mauro , Rovero Paolo , Papini Anna M.
Published: March 2004

Cyclotetrapeptides are constrained cyclic peptides whose synthesis is considered a difficult task. A methodology based on on‐resin head‐to‐tail cyclization by anchoring the side chain of a trifunctional amino acid was investigated. A series of model cyclotetrapeptides containing the RGD sequence cyclo(Xaa‐Arg‐Gly‐Asp) (Xaa = Ala, Phe, Phg, D‐Ala, D‐Phe, D‐Phg) was synthesized with no cyclodimerization by‐products. An evaluation and optimization study of all of the parameters directly involved in the ring closure was performed. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.
Characterizing bathocuproine self‐association and subsequent binding to Alzheimer's disease amyloid β‐peptide by NMR
Authors: Yao Shenggen , Cherny Robert A , Bush Ashley I. , Masters Colin L. , Barnham Kevin J.
Published: March 2004

Aggregated amyloid β‐peptide (Aβ) is the primary constituent of the extracellular plaques and perivascular amyloid deposits associated with Alzheimer's disease (AD). Deposition of the cerebral amyloid plaques is thought to be central to the disease progression. One such molecule that has previously been shown to ‘dissolve’ deposited amyloid in post‐mortem brain tissue is bathocuproine (BC). In this paper 1H NMR chemical shift analysis and pulsed field gradient NMR diffusion measurements were used to study BC self‐association and subsequent binding to Aβ. The results show that BC undergoes self‐association as its concentration increases. The association constant of BC dimerization, Ka, was estimated to be 0.64 mM−1 at 25°C from 1H chemical shift analysis. It was also found that dimerization of BC appeared to be essential for its binding to Aβ. From the self‐association constant of BC, Ka, the fraction of dimeric BC in the complex was obtained and the dissociation constant, Kd, of BC bound to Aβ40 peptide was then determined to be ∼1 mM. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.
Photoaffinity scanning in the mapping of the peptide receptor interface of class II G protein—coupled receptors
Authors: Pham Vi , Sexton Patrick M.
Published: March 2004

The family of G protein‐coupled receptors constitutes about 50% of the therapeutic drug targets used in clinical medicine today, although the mechanisms of ligand binding, activation and signal transduction for G protein‐coupled receptors are not yet well defined. This review discusses ongoing research using the photoaffinity scanning method to map the bimolecular interface between class II G protein‐coupled receptors and their ligands. Furthermore the available computer model of class II peptide ligand docking into the receptor, based on the positional constraints imposed by the photoaffinity scanning analyses, will be discussed briefly. The ultimate goal of these efforts is to understand the molecular basis of receptor binding and therefore to generate a template for rational drug design. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.
Odd electrons and covalent bonding in fullerenes
Authors: Sheka Elena F.
Published: March 2004

The electronic structure of X60 molecules (XC, Si) is considered in terms of 60 odd electrons and the spin‐dependent interaction between them. The conditions for the electrons to be excluded from the covalent pairing are discussed. A computational spin‐polarized quantum‐chemical scheme is suggested to evaluate four parameters (energy of radicalization, exchange integral, atom spin density, and squared spin) to characterize the effect quantitatively. A polyradical character of the species, weak for C60 and strong for Si60, is established. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004