bluuebunny/crossref_metadata_2025_split huggingface dataset:
Computer simulation of conic‐shaped patterns on fracture surfaces of polymers
Authors: Wenbo Luo , Tingqing Yang 
Published: May 2003

AbstractFractographic analysis, using scanning electron microscopy, is an important method to study polymer fracture behavior. There are several distinctive patterns on fracture surfaces, such as radial striations, regularly spaced ‘rib’ markings, and conic‐shaped patterns. The conic‐shaped pattern is the intersection locus of a moving planar crack front and a radially growing circular craze or secondary crack front. In this paper, the effects of the ratio of crack velocity to growing craze or secondary crack velocity on the shape of intersection loci are discussed using computer simulations. It is shown that when the ratio of crack velocity to craze or secondary crack velocity ($\dot{a}/\dot{c}$) increases progressively, the fracture surface pattern changes from a parabola or a prolate parabola to an ellipse and finally to an approximate circle. Therefore, the crack growth velocity can be estimated based on the fracture surface morphology and then related to the fracture processes as well as to the ductile–brittle transition or toughening mechanism of brittle polymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1722–1725, 2003
Electrochemical synthesis of poly(2‐iodoaniline) and poly(aniline‐co‐2‐iodoaniline) in acetonitrile
Authors: Şahin Yücel , Perçin Sabriye , Alsancak Güleren Özkan 
Published: May 2003

AbstractPoly(2‐iodoaniline) (PIANI) and poly(aniline‐co‐2‐iodoaniline) [P(An‐co‐2‐IAn)] were synthesized by electrochemical methods in acetonitrile solution containing tetrabutylammonium perchlorate (TBAP) and perchloric acid (HClO4). The voltametry of the copolymer shows characteristics similar to those of conventional polyaniline (PANI), and it exhibits higher dry electrical conductivity than PIANI and lower than PANI. The observed decrease in the conductivity of the copolymer relative to PANI is attributed to the incorporation of the iodine moieties into the PANI chain. The structure and properties of these conducting films were characterized by FTIR and UV‐Vis spectroscopy and by an electrochemical method (cyclic voltametry). Conductivity values, FTIR and UV‐Vis spectra of the PIANI and copolymer were compared with those of PANI and the relative solubility of the PIANI and the copolymer powders was determined in various organic solvents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1652–1658, 2003
Synthesis, structure, and olefin polymerization catalysis of a novel vanadium(III) 1,1′‐bi‐2‐naphtholate complex
Authors: Sato Yoshinori , Nakayama Yuushou , Yasuda Hajime 
Published: May 2003

AbstractThe reaction of VCl3 with (S)‐(–)‐Na2 (binol) (binol = 1,1′‐bi‐2‐naphtholate) gave a new vanadium(III) complex, [Na(OEt2)]3[V(binol)3] (Fig. 1). The X‐ray crystallographic structure of this complex (Complex 1) in Figure 1 reveals its propeller‐like structure, which is similar to those of the reported rare earth analogues. The complex showed moderate catalytic activities for ethylene polymerization upon activation with modified methylaluminoxane (MMAO) and with diethylaluminum chloride (DEAC). The Complex 1/DEAC system also catalyzed the polymerization of propylene to give atactic polypropylene with low activity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1659–1662, 2003
Complex 1magnified image

1. Molecular structure of [Na(OEt2)]3[V(binol)3] (Complex 1).image1. Molecular structure of [Na(OEt2)]3[V(binol)3] (Complex 1).
Studies on the silicone resins cured with polymethylsilazanes at ambient temperature
Authors: Zhang Yuemei , Huang Ying , Liu Xiangluan , Yu Yunzhao 
Published: May 2003

AbstractPolymethylsilazanes (PMS) were synthesized and used to cure silicone resins at ambient temperature. The curing degree of the silicone resins depends on the structure of PMS and its concentration in the resin. Silicone resins of different structure and different silanol content can be cured to a satisfactory degree, if the concentration of the PMS is high enough. Silicone resins cured with PMS showed improved thermal stability in nitrogen, compared with that of the heat‐cured counterparts. The mechanism of thermal decomposition of the silicone resins is discussed. The improvement of heat resistance using PMS as the curing agent is accounted for by diminished thermal rearrangement and degradation of the polysiloxane network initiated by silanol groups in the resins. © 2003 Wiley Periodicals, J Appl Polym Sci 89: 1702–1707, 2003
Effect of molecular weight and branch content on the creep behavior of oriented polyethylene
Authors: O'Connell P. A. , Bonner M. J. , Duckett R. A. , Ward I. M. 
Published: May 2003

AbstractCreep studies were carried out on a range of homopolymers and copolymers of polyethylene with well‐defined molecular weight and branch content. The creep data were analyzed in terms of two thermally activated processes acting in parallel and the effects of molecular weight and branch content are discussed. It is shown that increasing either the number‐average molecular weight or the weight‐average molecular weight gives improved creep behavior at all stress levels. The introduction of butyl branches leads to lower creep at low‐stress levels but can give rise to higher creep at high stress. Plots of the equilibrium log10(strain rate) versus stress at fixed draw ratio (strain) can be used to define sections through a unique true stress/true strain/strain rate surface for each material. These creep results have an additional value in terms of the link between slow crack propagation (SCG) in polyethylene and fibril creep, confirming the proposal made elsewhere that SCG can be quantified in terms of creep to failure across the true stress/true strain/strain rate surface. © 2003 Wiley Periodicals, J Appl Polym Sci 89: 1663–1670, 2003
Hemodialysis membrane prepared from cellulose/N‐methylmorpholine‐N‐oxide solution. III. The relationship between the drying condition of the membrane and its permeation behavior
Authors: Abe Yoshihiko , Mochizuki Akira 
Published: May 2003

AbstractThe effects of drying condition on the performance (ultrafiltration rate, diffusive solute permeability, and sieving) of hemodialysis membranes prepared from cellulose/N‐methylmorpholine‐N‐oxide (NMMO) solution (NMMO membrane) and cellulose/cuprammonium solution (cuprammonium membrane; the referential membrane) were studied. The drying condition investigated was the glycerin concentration of the solution, which was used to substitute glycerin for the water in the membrane before the membrane was dried. A lower glycerin concentration in the solution brought about a lower reswelling degree (water content) in the dried membrane in pure water, which resulted in a drop in the performance of the as‐cast membrane. The NMMO membrane had a high water content and a high membrane performance compared with the cuprammonium membrane when both the membranes were treated under the same drying condition. The differences in the performance between both membrane series is discussed on the basis of the results of the observation of the membrane morphology by scanning electron microscopy, the observation of the crystallinity of the membranes by wide‐angle X‐ray diffraction, and the estimation of the pore structure of the membranes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1671–1681, 2003
Searching for complex CA rules with GAs
Authors: Bilotta Eleonora , Lafusa Antonio , Pantano Pietro 
Published: May 2003

AbstractAn important problem in the theory of cellular automata (CA) is the research of complex rules, the parameterization of the rule space, and the description of the CA dynamic behavior. In this article, the authors used evolutionary techniques in the search of CA with specific characteristics, in order to understand how their data are related to the previous findings in this sector. Using as fitness function, the variance of the input‐entropy, a genetic algorithm was built to search complex rules for multistate CA. The algorithm used is efficient and many complex rules have been found. Many of these rules present interesting characteristics. Gliders with large period and large spatial dimensions may be observed. The experiments performed show that complex rules have several λ values, which do not reside in a sharply defined region; on the contrary, these values are extended on very large regions of the λ parameter. The results provide also a view of the CA rule space. © 2003 Wiley Periodicals, Inc.
Quantifying the complexity of flow networks: How many roles are there?
Authors: Zorach Alexander C. , Ulanowicz Robert E. 
Published: May 2003

AbstractWeighted flow networks are structures that arise naturally when analyzing complex systems. The countable properties of unweighted networks are not easily generalized to weighted networks. One candidate measure of complexity is the number of roles, or specialized functions in a network. It is easy to identify the number of roles in a linear or cyclic unweighted network. There is only one logically consistent way to generalize the measures of nodes, flows, connectivity, and roles into weighted networks, and these generalizations are equivalent to indices derived from information theory and used by ecologists since the late seventies. Data from ecosystem networks suggests that ecosystems inhabit a narrow window of the parameter space defined by these measures. © 2003 Wiley Periodicals, Inc.
Agent‐based model for economic impact of free software
Authors: Khalak Asif 
Published: May 2003

AbstractThis article describes the potential impact that free (i.e., open source) software can have on an existing commercial software market. A model for the software market is constructed in terms of autonomous agents, which represent the users, the companies, and the free software providers. The model specifies a reservation price for each user agent and develops a gradient learning strategy for revenue‐maximizing company agents. Simulations explore parameters such as the demand distribution, and the relative importance of market share, advertising and random effects in product visibility. Results from the case without free software show a prevalence of monopolies, which is consistent with other studies of high‐technology market economics. The effects of free software are not uniform, but are highly parameter dependent. A “capture region” is found in which free software eventually dominates the market. © 2003 Wiley Periodicals, Inc.
Recent developments in the field of A3 adenosine receptor antagonists
Authors: Baraldi Pier Giovanni , Tabrizi Mojgan Aghazadeh , Fruttarolo Francesca , Bovero Andrea , Avitabile Barbara , Preti Delia , Romagnoli Romeo , Merighi Stefania , Gessi Stefania , Varani Katia , Borea Pier Andrea 
Published: May 2003

AbstractAdenosine is an endogenous modulator of a large variety of physiological functions through the interaction with specific cell membrane G‐protein‐coupled receptors classified as A1, A2A, A2B, and A3. Activation of A3 receptors has been shown to stimulate phospholipase C and to inhibit adenylate cyclase. A3 agonists also cause stimulation of phospholipase D and the release of inflammatory mediators, such as histamine from mast cells, which are responsible for inflammation and hypotension. For these reasons, the clinical use of A3 adenosine receptors antagonists for the treatment of asthma and inflammatory disease has been suggested. Recent studies also indicated a possible employment of these derivatives as antitumor agents. Different classes of polyheterocyclic compounds have been identified as potent A3 antagonists. Herein, we report our past and recent results in the development of tricyclic A3 selective antagonists. The pyrazolo[4,3‐e]‐1,2,4‐triazolo[1,5‐c]pyrimidine nucleus has especially been investigated by our group. Our interests were focused on the effects of substitution of the phenyl ring of the arylcarbamoyl moiety at N5 position and of substituents at C9 and/or at N8 pyrazole nitrogen. These studies allowed us to obtain a large variety of compounds which showed affinities in the nanomolar range with human A3 adenosine receptors with a high degree of selectivity vs. all other receptors subtypes. Thanks to the introduction of alkylating groups at p‐position of the N5‐phenylcarbamoyl chain, we succeeded in realizing potent irreversible A3 adenosine antagonists. Finally, the replacement of the phenyl nucleus of carbamoyl function with a pyridine ring conferred water solubility to the corresponding derivatives, which are also characterized by high levels of A3 affinity and selectivity. Drug Dev. Res. 58:315–329, 2003. © 2003 Wiley‐Liss, Inc.
Engineering of A3 adenosine and P2Y nucleotide receptors and their ligands
Authors: Jacobson Kenneth A. , Kim Hak Sung , Ravi Gnana , Kim Soo‐Kyung , Lee Kyeong , Chen Aishe , Chen Wangzhong , Kim Seong Gon , Barak Dov , Liang Bruce T. , Gao Zhan‐Guo 
Published: May 2003

AbstractModification of the ribose moiety of nucleotides and nucleosides has provided new insights into structural and conformational requirements for ligands at P2Y nucleotide receptors and at adenosine receptors (ARs). Methanocarba derivatives (containing a rigid bicyclic ring system in place of ribose) of adenosine, ATP, ADP, UTP, UDP, and other receptor agonist analogs were synthesized. Biological evaluation led to the conclusion that in general the Northern (N)‐conformation was favored over the Southern (S)‐conformation of the pseudoribose moiety at A1 and A3 ARs and at P2Y1, P2Y2, P2Y4, or P2Y11 receptors, but not P2Y6 receptors. At the hA3 AR a new full agonist, MRS1898, the (N)‐methanocarba equivalent of Cl‐IB‐MECA (2‐chloro‐N6‐(3‐iodobenzyl)‐5'‐N‐methylcarbamoyladenosine), had a Ki value of 1.9 nM in binding to the hA3 AR expressed in CHO cells. Functional assays confirmed the selectivity of MRS1898, although Cl‐IB‐MECA was even more functionally selective for human A3 vs. hA1 and hA2A ARs. Thirty µM MRS1898 did not induce apoptosis in HL‐60 cells, suggesting that some of the proapoptotic effects of Cl‐IB‐MECA may be nonreceptor‐mediated. Manipulation of the sequence of A3 ARs through site‐directed mutagenesis has led to pharmacologically unique constructs: constitutively active receptors and “neoceptors.” Such engineered receptors may later prove to have potential for cardioprotection through gene transfer. Effects of single amino acid replacement were interpreted using a rhodopsin‐based model of ligand‐A3 receptor interactions, leading to the proposal that a movement of the conserved W243 in TM6 may be involved in AR activation. Drug Dev. Res. 58:330–339, 2003. © 2003 Wiley‐Liss, Inc.
Hetero‐oligomerization between adenosine A1 and P2Y1 receptors in living cells: Formation of ATP‐sensitive adenosine receptors
Authors: Nakata Hiroyasu , Yoshioka Kazuaki , Saitoh Osamu 
Published: May 2003

AbstractWe explored the possibility of hetero‐oligomerization between Gi/o protein‐coupled A1 adenosine receptor (A1R) and Gq protein‐coupled P2Y1 receptor (P2Y1R) in transfected cultured cells by a new bioluminescence resonance energy transfer technology (BRET2) in addition to indirect biochemical or pharmacological methods. The existence of A1R/P2Y1R hetero‐oligomers in cotransfected HEK293T cells was first shown using coimmunoprecipitation methods. In the same cotransfected cells, ADPβS was able to reduce forskolin‐evoked cAMP accumulation in a pertussis toxin‐ and A1R antagonist‐sensitive manner, indicating that the pharmacology of A1R was significantly modified in the cotransfected cells, i.e., ADPβS binds A1R and inhibits adenylyl cyclase activity via Gi/o proteins. Also, a high degree of A1R and P2Y1R colocalization was demonstrated in cotransfected cells by double immunofluorescence experiments with confocal laser microscopy. Then the BRET2 technique revealed constitutive heteromeric oligomerization between A1R and P2Y1R in living HEK293T cells. The BRET2 signal also increased in a time‐dependent manner upon addition of agonists for both receptors, which was inhibited by pretreatment with the P2Y1R antagonist MRS2179, indicating that this process is promoted by the simultaneous activation of both receptors. These results suggest that the oligomeric association of A1R with P2Y1R generates A1R with P2Y1R‐like agonistic pharmacology and provides a molecular mechanism for an increased diversity of purinergic signaling. Existence of this hybrid purinergic receptor may explain the controversial inhibition of synaptic transmission by adenine nucleotides. Drug Dev. Res. 58:340–349, 2003. © 2003 Wiley‐Liss, Inc.
In vivo studies of the release of adenine 5′‐nucleotides, adenosine, and its metabolites from the rat brain
Authors: Phillis John W. , O'Regan Michael H. 
Published: May 2003

AbstractAdenosine 5′ ‐triphosphate (ATP) and adenosine function as an excitatory neurotransmitter and a neuromodulator, respectively, in the central nervous system. Neuroexcitatory effects of ATP are mediated by P2X receptors: neuromodulator effects of adenosine by A1, A2, or A3 receptors. There is also evidence that ATP, acting a P2Y receptor, is involved in osmoregulatory responses to cell swelling. Studies on the release of ATP and/or adenosine into the interstitial fluid of the brain have served to clarify their roles in cerebral function. ATP release occurs during electrical or K+‐induced depolarization of cerebral tissues. Released ATP is rapidly hydrolyzed by ectonucleotidases, which may be released concurrently, to form adenosine 5′‐diphosphate (ADP) and adenine 5′‐monophosphate (AMP). In addition to synaptic release from neurons, there is evidence of glial release via gap‐junction hemichannels. Hydrolysis of AMP to adenosine initiates a further metabolic cascade with the formation of inosine, hypoxanthine, xanthine, and uric acid by adenosine deaminase, purine nucleoside phosphorylase, and xanthine oxidase. Hypoxanthine can be converted to inosine monophosphate by hypoxanthine phosphoribosyl transferase and thus used to replenish ATP. Cerebral ischemia causes ATP utilization, and adenosine formation. Adenosine can then be transported across the plasma membrane and released into the interstitial space. Hypoxemia‐evoked adenosine release from the cerebral cortex is inhibited by blockers of adenosine transport. Inhibition of purine metabolism by blockers of adenosine deaminase, purine nucleoside phosphorylase, and xanthine oxidase elevates upstream levels of adenosine and its metabolites. Exposure of the in vivo rat cerebral cortex to cerebrospinal fluid containing swelling‐inducing monocarboxylic acids elevated interstitial fluid levels of ADP and AMP, but not of adenosine. Taken together, these studies have led to a greater understanding of the metabolism and release of adenosine and the adenine nucleotides in the normoxic and ischemic brain. Drug Dev. Res. 58:412–419, 2003. © 2003 Wiley‐Liss, Inc.
Renal effects of BG9928, an A1 adenosine receptor antagonist, in rats and nonhuman primates
Authors: Ticho Barry , Whalley Eric , Gill Alan , Lutterodt Frank , Jin Xiaowei , Auchampach John , Smits Glenn 
Published: May 2003

AbstractStimulation of A1adenosine receptors in the kidney reduces glomerular filtration rate (GFR) via tubuloglomerular feedback and increases sodium reabsorption. Blocking A1 adenosine receptors would therefore maintain GFR and cause natriuresis. These attributes would be especially beneficial in treating congestive heart failure (CHF). BG9928 is a xanthine derivative that binds with high affinity to A1 adenosine receptors from several species including human and acts as a competitive antagonist at these receptors. This compound is being developed for the treatment of CHF. BG9928 receptor binding across a wide array of human and animal receptors was evaluated in vitro. Oral dose–response was assessed in rats, and oral and iv dose–responses were assessed in monkeys. The functional potency of BG9928 was demonstrated in vivo in rats. The binding affinity (Ki) for the human A1 adenosine receptor is 12.2 nM. BG9928 is orally active, with a dose of 0.3 mg/kg po achieving full natriuretic response in rats and with iv doses as low as 0.03 mg/kg showing activity in nonhuman primates. The renal protective effects of BG9928 were demonstrated by coadministration with the loop diuretic furosemide. In rats, administration of BG9928 effectively attenuated the reductions in GFR that usually occur with the administration of furosemide. Blockade of A1 receptors by BG9928 protects renal function against the adverse effects of loop diuretics and exerts additive natriuretic effects. In CHF patients, this profile may translate into significant clinical benefit by enhancing natriuresis with diminished concern of inducing renal insufficiency. Drug Dev. Res. 58:486–492, 2003. © 2003 Wiley‐Liss, Inc.
Impact of endogenous adenosine on airway hyperreactivity
Authors: Blackburn Michael R. , Young Hays W.J. 
Published: May 2003

AbstractAdenosine signaling has been implicated in the exacerbation of chronic inflammatory lung diseases such as asthma. Challenging the airways with adenosine leads to bronchoconstriction; however, little is known about the role of endogenous adenosine on airway physiology. We examined the consequences of chronic adenosine elevations in mice genetically manipulated to contain low levels of the purine catabolic enzyme adenosine deaminase (ADA), which controls adenosine concentrations in tissues and cells. Examination of airway physiology in these animals revealed an increase in airway responsiveness. This increase in airway responsiveness was dependent on elevated adenosine in that treatment with ADA enzyme therapy reversed increased airway responsiveness in conjunction with lowering lung adenosine levels. Treatment with the broad‐spectrum adenosine receptor antagonist theophylline prevented airway hyperresponsiveness, implicating the involvement of adenosine receptors. Furthermore, transcript levels for the A1, A2B, and A3 adenosine receptors were elevated in the lungs of ADA‐deficient mice. These findings suggest that endogenous increases in lung adenosine concentrations are associated with alterations in airway physiology. Drug Dev. Res. 58:472–478, 2003. © 2003 Wiley‐Liss, Inc.
Evidence of tanscriptional and tanslational components in anti‐ischemic effects of adenosine
Authors: Headrick John P. , Peart Jason , Holmgren Kirsten , Ashton Kevin 
Published: May 2003

AbstractAdenosine protects against myocardial ischemic injury via poorly defined mechanisms. We examined effects of inhibition of gene transcription, mRNA translation, and mitochondrial KATP channels on cardioprotective effects of adenosine in mouse hearts subjected to 20‐min ischemia. Adenosine treatment reduced postischemic lactate dehydrogenase efflux (indicating necrosis) from 24±2 to 9±1 IU/g, and postischemic diastolic contracture from 21±2 to 5±2 mm Hg, and enhanced postischemic ventricular pressure development from 72±3 to 135±4 mm Hg. The antinecrotic response was reduced ≈50% by inhibition of protein translation (10 µM cycloheximide, CHX), unaltered by inhibition of transcription (20 µM actinomycin D, Act‐D), and abrogated by mitochondrial KATP channel inhibition (100 µM 5‐hydroxydecanoate, 5‐HD). In contrast, protection against contractile dysfunction was reduced but not eliminated by CHX, Act‐D, and 5‐HD, and inhibitory effects CHX and Act‐D were not additive with those of 5‐HD, supporting a common mechanistic path. Inhibitory effects of Act‐D were mimicked by 1.5 µM α‐amanitin. These data provide evidence that adenosine limits necrosis in a mito KATP channel‐dependent manner involving protein translation. The translational component is not dependent upon mRNA transcription. Adenosine also substantially reduces contractile dysfunction via a pathway involving mitochondrial KATP channel activation, protein translation, and mRNA transcription. Protection independent of this path was also evident. Thus, distinct signaling pathways appear to be involved in adenosine‐mediated protection against postischemic necrosis and contractile dysfunction. Drug Dev. Res. 58:454–460, 2003. © 2003 Wiley‐Liss, Inc.