bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enzymatic Polymerization towards Biodegradable Polyester Nanoparticles
Authors: Taden Andreas , Antonietti Markus , Landfester Katharina 
Published: June 2003

AbstractThe direct enzymatic polymerization of miniemulsions consisting of lactone nanodroplets represents a new and convenient pathway for the synthesis of biodegradable polymer nanoparticles, where the chemical composition and molecular weight can be varied in a certain range. Oligoesters completely end‐capped with an alkene or diene group can also be prepared by this technique. These building blocks extend polyester application as they allow to impart improved biodegradability to both siloxane and resin chemistry.TEM image of the polyester particles obtained by enzymatic polymerization in miniemulsion.magnified imageTEM image of the polyester particles obtained by enzymatic polymerization in miniemulsion.
Silyl‐Substituted Poly(thienylenevinylene) via Heteroaromatic Dehydrohalogenation Polymerization
Authors: Lee Yeong‐Beom , Shim Hong‐Ku , Ko Seung‐Won 
Published: June 2003

AbstractA long alkylsilyl group was attached to a thiophene ring system to overcome the instability of 2,5‐bis(halomethyl)thiophene monomers, by imparting steric hindrance and electronic delocalization. The resulting stable monomer could be used directly to prepare low‐band‐gap poly(thienylenevinylene) (1.57 eV) through heteroaromatic dehydrohalogenation polymerization.
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Cyclodextrins in Polymer Synthesis: Crosslinking Water‐Soluble Unsaturated Polyester Resins Using a Cyclodextrin/Styrene Complex in Aqueous Medium
Authors: Alupei Iulian C. , Alupei Valentina , Ritter Helmut 
Published: June 2003

AbstractA new method was developed to crosslink water‐soluble unsaturated polyester resins prepared from maleic anhydride and poly(ethylene glycol) in water as the solvent. Crosslinking was carried out with various molar ratios of the host‐guest complex consisting of styrene as the guest and methylated β‐cyclodextrin as the host. Polymerizations were performed in water with K2S2O8/Na2S2O5 as free radical initiator at 25 °C. Thermal properties of the networks obtained depend on the amount of styrene incorporated into the polymer.Acceleration effect of me‐β‐CD during crosslinking of an unsaturated polyester with styrene in water: (a) monomer complexed with me‐β‐CD, and (b) with uncomplexed monomer.magnified imageAcceleration effect of me‐β‐CD during crosslinking of an unsaturated polyester with styrene in water: (a) monomer complexed with me‐β‐CD, and (b) with uncomplexed monomer.
Preliminary design optimization of stiffened panels using approximate analysis models
Authors: Lamberti Luciano , Venkataraman Satchi , Haftka Raphael T. , Johnson Theodore F. 
Published: June 2003

AbstractPreliminary sizing of structural components in the conceptual design phase of new aerospace vehicles requires a large number of structural optimizations. Use of detailed finite element models for global optimization of stiffened shell structures is not affordable. Designers have to compromise between the complexity in the structural analysis model (e.g. small models or linear analysis) and that of the optimization method (local versus global optimization). When designing new concepts where good initial designs are not available, global design optimization needs to be performed, and this is not currently possible with complex models. In this paper, we discuss the use of simple analysis methods for performing global optimization of stiffened shell structures. We demonstrate the efficiency of using approximate analysis models by using PANDA2 for a practical design trade‐study. Often approximate models are based on assumptions that are not satisfied throughout the design space. Hence, such models require constraints that will keep the designs in regions where the analysis assumptions are valid. We illustrate with examples situations where such design constraints result in sub‐optimal designs. We conclude that performing global optimization using approximate methods can permit a greater exploration of the design space than the use of local optimization with complex models. Copyright © 2003 John Wiley & Sons, Ltd.
An element removal and reintroduction strategy for the topology optimization of structures and compliant mechanisms
Authors: Bruns T. E. , Tortorelli D. A. 
Published: June 2003

AbstractA method is developed to systematically remove and reintroduce low density elements from and into the finite element mesh on which the structural topology optimization problem is defined. The material density field which defines the topology and the local ‘stiffness’ of the structure is optimally distributed via non‐linear programming techniques. To prevent elements from having zero stiffness, an arbitrarily small lower bound on the material density is typically imposed to ensure that the global stiffness matrix does not become singular. While this approach works well for most minimum compliance problems, the presence of low density elements can cause computational problems, particularly in structures that exhibit geometric non‐linearities, e.g. in compliant mechanisms. To resolve this problem, a systematic approach for removing and reintroducing low density elements is presented, and the substantial performance improvements both in design and computational efficiency of the method over current methods are discussed. Several structures and compliant mechanisms are designed to demonstrate the method. Copyright © 2003 John Wiley & Sons, Ltd.
Adjoint state method for shape sensitivity analysis in non‐steady forming applications
Authors: Chung S. H. , Fourment L. , Chenot J. L. , Hwang S. M. 
Published: June 2003

AbstractThis paper introduces the adjoint state method in non‐steady‐state forming processes, such as forging, whereas this method is more frequently used for steady‐state problems. Some practical details for an efficient implementation are given. The emphasis is put on the accuracy of the sensitivity analysis for problems with remeshings and transfers of variables. The precision of the calculated derivatives is verified by comparing its results with the direct differentiation method. The adjoint state method is then applied to shape optimization problems. Copyright © 2003 John Wiley & Sons, Ltd.
Adaptive algorithms for optimal control of time‐dependent partial differential‐algebraic equation systems
Authors: Serban Radu , Li Shengtai , Petzold Linda R. 
Published: June 2003

AbstractThis paper describes an adaptive algorithm for optimal control of time‐dependent partial differential‐algebraic equation (PDAE) systems. A direct method based on a modified multiple shooting type technique and sequential quadratic programming (SQP) is used for solving the optimal control problem, while an adaptive mesh refinement (AMR) algorithm is employed to dynamically adapt the spatial integration mesh. Issues of coupling the AMR solver to the optimization algorithm are addressed. For time‐dependent PDAEs which can benefit from the use of an adaptive mesh, the resulting method is shown to be highly efficient. Copyright © 2003 John Wiley & Sons, Ltd.
Topology optimization of 2D‐frame structures with path‐dependent response
Authors: Pedersen Claus B. W. 
Published: June 2003

AbstractThis paper deals with topology stiffness optimization of a ground structure consisting of rectangular 2D‐beam elements with path‐dependent response. The objective of the optimization is to minimize the compliance of the structure when the mass is prescribed. The path‐dependent response of the structure is due to the plastic hinges at the ends of the beam elements. The plastic hinges are modelled through yield surfaces giving the interaction between the stress resultants when the cross‐section is fully plastified. In combination with the yield surface a simple hardening rule is applied. The geometrical non‐linearities are also included, so the beam elements can perform large rigid body rotations. The finite element solution is obtained with an implicit backward Euler algorithm. From the finite element solution the analytical sensitivities are computed using the direct method. Copyright © 2003 John Wiley & Sons, Ltd.
Fabrication of porous collagen/chitosan scaffolds with controlling microstructure for dermal equivalent
Authors: Gao Chang‐you , Wang Deng‐yong , Shen Jia‐cong 
Published: June 2003

AbstractTwo sets of homemade apparatus have been utilized to fabricate collagen/chitosan porous membranes by quenching its acetic solution and subsequently extracting the solvent with ethanol. The influence of chitosan concentration on the surface morphology of the collagen/chitosan membranes was studied using a quenching cold plate (apparatus 1). The pore size was enlarged along with an increase in the chitosan content, accompanied with the emergence of a sheet‐like microstructure. Due to the large thermal conductivity of the membrane‐forming platform (stainless steel), collagen/chitosan membranes prepared using apparatus 1 at freezing temperature between −60 to −20 °C present similar pore size (2–4 nm) and surface morphology. However, a large difference in pore size is generated using apparatus 2 (membrane preparation in a cold ethanol bath) and using a membrane‐forming platform of poor thermal conductivity (polymethylmethacrylate), e.g. ∼10 to 20 μm at freezing temperature of −60 to −40 °C, and 265 μm at −20 °C accompanied with the transformation from fiber‐ to sheet‐dominated morphology. The spongy collagen/chitosan membranes with pore sizes ranging from tens to hundreds of micrometers and porosity higher than 95%, which could be used as dermal regeneration template, have thus been fabricated. Copyright © 2003 John Wiley & Sons, Ltd.
Comparative mechanical property characterization of three indirect composite resin materials compared with two direct composites
Authors: Demirel Figen , Saygılı Gülbin , Şahmalı Sevil 
Published: June 2003

AbstractVarious new indirect composite materials have been developed with required advantages. In this study three indirect composite material (Artglass, Belleglass HP, Targis) were tested for flexural strength, fracture toughness, wear resistance and hardness against Filtek P60 and Z‐100.Five specimens of each material were fabricated according to the manufacturer's directions. The flexural strength and fracture toughness was measured using the bending test. The wear test was performed to accelerated wear in a toothbrushing apparatus. Vickers hardness was measured for each of the tested materials. The statistical tests used for flexural strength, fracture toughness, wear and hardness were One‐way ANOVA and Kruskal–Wallis test. The level of statistical significance chosen was p = 0.05.Results of the study showed that Filtek P60 was superior to the other composites in all tests. Significant differences were found among the materials. The differences in flexural strength, fracture toughnes, wear and hardness may have been due to differences in chemistry or method of polymerization of the composites. Copyright © 2003 John Wiley & Sons, Ltd.
The interactions of tooth colored dental restorative materials with aqueous lactic acid
Authors: Şahmalı Sevil , Demirel Figen , Saygılı Gülbin 
Published: June 2003

AbstractIn this study, the interaction of packable composite and ormocer with aqueous lactic acid solutions were determined and changes compared with those for a polyacid modified resin composite and a glass ionomer.For each material, namely Solitaire, Z‐100, Definite, Dyract AP and Vitremer, eight cylindrical specimens of 6 mm diameter and 12 mm height were prepared and weighed. They were stored individually in 20 cm3 0.02 mol−1 lactic acid solution for 1 week, then the pH was determined and the specimens reweighed. This was repeated at 1 week intervals until the specimens were 6 weeks old.The results of this study showed that; polyacid modified resin composites and resin‐modified glass‐ionomers were capable of increasing the pH of lactic acid solutions. The same groups showed an increase in mass during the first week. Composite resins and ormocer showed less increase in mass than the others. Copyright © 2003 John Wiley & Sons, Ltd.
Superabsorbent hydrogel composites
Authors: Kabiri Kourosh , Zohuriaan‐Mehr M. J. 
Published: June 2003

AbstractA new cost‐effective approach to enhance gel strength of superabsorbent hydrogels was invented. Superabsorbent hydrogel composites (SHCs) were prepared through an optimized rapid solution polymerization of concentrated partially neutralized acrylic acid in the presence of a crosslinking agent under normal atmospheric conditions. Kaolin was used as an inorganic component in the polymerization process to strengthen the hydrogel products. FT‐IR spectroscopy was used to confirm grafting of acrylic chains on to the surface of kaolin particles. Morphology of the products was studied by scanning electron microscopy (SEM). Compared with the kaolin‐free hydrogel (control), kaolin caused a reduced equilibrium swelling and swelling rate as low as 17–31% and 19–29%, respectively. Kaolin, however, resulted in enhanced gel strength as high as 21–35% compared to the control. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study thermal properties of the composites. The SHCs exhibited higher thermal stability than the control. Meanwhile, changes in certain thermal transitions reconfirmed the chemical interaction of the acrylic chain with kaolin. These thermostabilized strengthened superabsorbent hydrogels may be considered as good candidates for agricultural application to retain more water under soil pressure. Copyright © 2003 John Wiley & Sons, Ltd.
Predictive mechanical performance evaluation of consumer food cans using stereolithography models
Authors: Karalekas D. , Kakoudakis J. 
Published: June 2003

AbstractThe development of new metal food containers can be a technologically challenging and costly process. Understanding the interplay between the major design characteristics and requirements affecting the product's final structural capability is paramount to achieving an optimum design proposition. As a result, computer‐based simulation has been employed by industry to assess a container's performance under a variety of load conditions, including axial load and panelling of cans. In this paper, the feasibility of a new approach for addressing the effects of design parameters on the structural performance of containers under development is investigated. The evaluation methodology is based on structural testing of stereolithography‐built physical prototypes of a rigid metal container used for coffee packaging. It is shown that the experimentally obtained findings are in accordance to those resulting from computational simulation. This method can be used to support the development of existing and new metal containers. Copyright ©2003 John Wiley & Sons, Ltd.
Resonances and pseudoresonances in a potential with attractive coulomb tail: A study using analytic‐continuation techniques
Authors: Müller Imke B. , Santra Robin , Cederbaum Lorenz S. 
Published: June 2003

AbstractThe performance of the complex absorbing potential (CAP) and the complex scaling (CS) methods in the detection and calculation of complex Siegert energies is studied using a 1‐D long‐range attractive model potential. This potential is constructed to mimic molecular properties, in particular an attractive Coulombic term, to allow one to draw conclusions on molecular ab initio studies. Analyzing the spectrum of the model potential, one compact bound state embedded in the manifold of Rydberg states is found that shows artificial resonance characteristics when applying the CAP and the CS methods. This pseudoresonance problem is less pronounced in the calculation using the CS method than in that using the CAP method. Despite this deficiency, the CAP method is shown to possess advantages over CS when dealing with physical resonances under conditions that simulate the application of standard basis sets in ab initio calculations. The accuracy of the Siegert energy is shown to be maintained when applying a subspace projection technique to the CAP method. This technique reduces the computational demand significantly and leads to an important improvement of the CAP method, which should be of particular significance in molecular applications. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Simple approach to computing tunneling time: Test cases
Authors: Mondal Chandan Kumar , Maji Kaushik , Bhattacharyya S. P. 
Published: June 2003

AbstractWe suggest a recipe for calculating the time taken by a particle to tunnel out from an initially localized state in one of the wells of symmetrical double‐well potential into the other well. We calculate average velocity 〈v̄〉 of the tunneling particle by solving the Schrödinger equation numerically for Ψ(x, t), then estimating 〈v(t)〉 = (d/dt)〈x(t)〉 and time‐averaging it. The time taken to tunnel is measured by calculating τav = l0/〈v̄〉 where l0 is an idealized estimate of the barrier width. We suggest an approximate partitioning of τav into an intrinsic decay time (τd) and a barrier crossing time (τb), τd being obtained from energy spread of the packet. τav − τd is shown to be close to the Wentzel‐Brillouin‐Kramers estimate of barrier crossing time τsc. The response of τav to an external driving field and nonzero temperatures are tested. We also apply the method to a purely barrier penetration problem as well as to the problem of tunneling through a fluctuating barrier. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Polarization Colors of Lightly Iodine‐stained Maize Starches for Amylose‐Extender and Related Genotypes in the W64A Inbred Line
Authors: Evans Annette , McNish Nayo , Thompson Donald B. 
Published: June 2003

AbstractPrevious qualitative research showed that for some maize endosperm genotype starches the color of variably iodine‐stained starch granules observed by bright field microscopy (BFM) was different from the color of identically stained granules observed by polarized light microscopy (PLM). One objective of the present study was to determine the polarization color for a variety of high‐amylose and other starch genotypes in an identical genetic background. A secondary objective was to determine the iodine concentration dependence of polarization colors for the samples. Starches from the W64A inbred line were obtained from the following genotypes: normal, wx, ae, du, su2, ae wx, ae du, ae su2, and du su2. Starches were stained with iodine solutions ranging from 0.02 to 0.075% and viewed with BFM and PLM, using an auto‐exposure digital camera function. Most starches showed the first appreciable color at about 0.04percnt; I2. Unlike normal and non‐ae‐containing starches, ae starch showed a pink polarization color, despite its blue color in bright field. Heterogeneity in polarization color was observed both within and among granules. Double mutant starches containing ae showed variable effects, depending on the combination. It is suggested that the pink polarization color of ae starch may be due to a lack of symmetrical orientation of iodinecomplexed amylose in these granules
The Effects of Amylose and Starch Phosphate on Starch Gel Retrogradation Studied by Low‐field 1H NMR Relaxometry
Authors: Thygesen Lisbeth G. , Blennow Andreas , Engelsen Søren B. 
Published: June 2003

AbstractLow‐field Nuclear Magnetic Resonance (23 MHz) was used to study the effects of the degree of phosphorylation, the amylose content and the amylopectin chain length distribution on gel retrogradation for a set of 26 starches, six of which were of crystal polymorph type A, 18 of type B and two of type C. The phosphate content ranged from 0 to 58.8 nmol Glc6P/mg and the amylose content from 0 to 72.1%. The starch pastes (13%, w/w) were measured before and after storage for six days at 35 °C. It was found that Principal Component Analysis (PCA) of the raw Carr‐Purcell‐Meiboom‐Gill (CPMG) relaxation curves from the two measurements (day 1 and day 7) could be used as a simple, illustrative way of describing the retrogradation. Three different behaviours were identified: One group of samples (mostly potato starches) slowly changed from a soft to a more rigid gel from day 1 to 7. A second group (mostly cereal starches) formed a rigid gel already before the first measurement and changed little after that. A third group comprised a few samples containing little or no amylose aged similarly to the first group of samples, but at a much slower rate. For the potato starches, a weak negative correlation (r = ‐0.63) was found between the degree of phosphorylation and the difference between the LF NMR relaxation curves of day 1 and day 7.
Functional characterization of a H+/nucleoside co‐transporter (CaCNT) from Candida albicans, a fungal member of the concentrative nucleoside transporter (CNT) family of membrane proteins
Authors: Loewen Shaun K. , Ng Amy M. L. , Mohabir Nadira N. , Baldwin Stephen A. , Cass Carol E. , Young James D. 
Published: June 2003

AbstractHuman and other mammalian concentrative (Na+‐linked) nucleoside transport proteins belong to a membrane protein family (CNT, TC 2.A.41) that also includes Escherichia coli H+‐dependent nucleoside transport protein NupC. Here, we report the cDNA cloning and functional characterization of a CNT family member from the pathogenic yeast Candida albicans. This 608 amino acid residue H+/nucleoside symporter, designated CaCNT, contains 13 predicted transmembrane domains (TMs), but lacks the exofacial, glycosylated carboxyl‐terminus of its mammalian counterparts. When produced in Xenopus oocytes, CaCNT exhibited transport activity for adenosine, uridine, inosine and guanosine but not cytidine, thymidine or the nucleobase hypoxanthine. Apparent Km values were in the range 16–64 µM, with Vmax : Km ratios of 0.58–1.31. CaCNT also accepted purine and uridine analogue nucleoside drugs as permeants, including cordycepin (3′‐deoxyadenosine), a nucleoside analogue with anti‐fungal activity. Electrophysiological measurements under voltage clamp conditions gave a H+ to [14C]uridine coupling ratio of 1 : 1. CaCNT, obtained from logarithmically growing cells, is the first described cation‐coupled nucleoside transporter in yeast, and the first member of the CNT family of proteins to be characterized from a unicellular eukaryotic organism. Copyright © 2003 John Wiley & Sons, Ltd.
Response to acetaldehyde stress in the yeast Saccharomyces cerevisiae involves a strain‐dependent regulation of several ALD genes and is mediatedby the general stress response pathway
Authors: Aranda Agustín , del Olmo Marcel.lí 
Published: June 2003

AbstractOne of the stress conditions that yeast may encounter is the presence of acetaldehyde. In a previous study we identified that, in response to this stress, several HSP genes are induced that are also involved in the response to other forms of stress. Aldehyde dehydrogenases (ALDH) play an important role in yeast acetaldehyde metabolism (e.g. when cells are growing in ethanol). In this work we analyse the expression of the genes encoding these enzymes (ALD) and also the corresponding enzymatic activities under several growth conditions. We investigate three kinds of yeast strains: laboratory strains, strains involved in the alcoholic fermentation stage of wine production and flor yeasts (responsible for the biological ageing of sherry wines). The latter are very important to consider because they grow in media containing high ethanol concentrations, and produce important amounts of acetaldehyde. Under several growth conditions, further addition of acetaldehyde or ethanol in flor yeasts induced the expression of some ALD genes and led to an increase in ALDH activity. This result is consistent with their need to obtain energy from ethanol during biological ageing processes. Our data also suggest that post‐transcriptional and/or post‐translational mechanisms are involved in regulating the activity of these enzymes. Finally, analyses indicate that the Msn2/4p and Hsf1p transcription factors are necessary for HSP26, ALD2/3 and ALD4 gene expression under acetaldehyde stress, while PKA represses the expression of these genes. Copyright © 2003 John Wiley & Sons, Ltd.