bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of 60Co γ‐rays on the crystal structure, melting and crystallization behavior of poly(butylene succinate)
Authors: Song Jianbin , Ren Minqiao , Song Chunlei , Wang Shuyun , Zhang Hongfang , Mo Zhishen 
Published: July 2004

AbstractThe results obtained for poly(butylene succinate) (PBS) after 60Co γ‐ray irradiation, studied by wide‐angle X‐ray diffraction (WAXD), differential scanning calorimeter (DSC) and polarizing optical microscopy (POM), revealed that the degree of crystallinity, melting temperature and enthalpy decreased with increasing irradiation dose, but that the crystal structure of PBS did not vary when compared to non‐irradiated PBS. By using Scherrer equation, small changes occurred in the crystal sizes of L020, L110 and L111. The spherulitic morphology of PBS was strongly dependent on irradiation dose and changed significantly at higher irradiation dosages. The crystallization kinetics of PBS indicated that the Avrami exponent (n) for irradiated PBS was reduced to 2.3, when compared to non‐irradiated PBS (3.3). Copyright © 2004 Society of Chemical Industry
Green composites of organic materials and recycled post‐consumer polyethylene
Authors: La Mantia FP , Dintcheva N Tzankova , Morreale M , Vaca‐Garcia C 
Published: July 2004

AbstractAddition of organic fillers to post‐consumer recycled plastics can give rise to several advantages. First of all, the cost of these fillers is usually very low, the organic fillers are biodegradable contributing to an improved environmental impact and, last but not least, some mechanical and thermomechanical properties can be enhanced. Organic fillers are not widely used in the plastic industry although their use is increasing. Bad dispersion into the polymer matrix at high‐level content and poor adhesion with the matrix are the more important obstacles to this approach. In this work various organic fillers have been used with a post‐consumer plastic material originating from films for greenhouses. The properties of these green composites have been compared with those of materials filled with a conventional inorganic filler. The organic fillers cause slightly worse processability, due to an increase of viscosity, an enhancement of the rigidity and of the thermomechanical resistance similar to that measured for the inorganic filler, while a reduction of the impact strength is observed. Copyright © 2004 Society of Chemical Industry
Counterintuitive influence of microscopic chirality on helical order in polymers
Authors: Cheon Kap Soo , Selinger Jonathan V. , Green Mark M. 
Published: July 2004

AbstractStudies of copolymers of chiral and achiral units forming a helical array correlate to statistical physical predictions of the influence of the chiral units on the helical sense taken by the array. In the absence of conflict among the chiral units for helical sense control, the sergeants and soldiers experiment, a larger chiral bias leads to increased control. However, when conflict exists among the chiral units for helical sense control, the majority rule experiment, a larger chiral bias leads to decreased control of the helical sense and therefore a smaller optical activity. Changing the achiral units in the majority rule experiment can change the nature of the statistical physics between statistical and thermal randomness. In general, the experiments quantitatively demonstrate that the effect of chirality is not an intrinsic property of the chiral moiety but rather depends on the molecular environment. Copyright © 2004 John Wiley & Sons, Ltd.
Synthesis and photochemistry of a carotene–porphyrin–fullerene model photosynthetic reaction center
Authors: Kodis Gerdenis , Liddell Paul A. , Moore Ana L. , Moore Thomas A. , Gust Devens 
Published: July 2004

AbstractA new photosynthetic reaction center mimic consisting of a porphyrin (P) linked to both a fullerene electron acceptor (C60) and a carotenoid secondary electron donor (C) was synthesized and studied in 2‐methyltetrahydrofuran using transient spectroscopic methods. Excitation of the porphyrin is followed by photoinduced electron transfer to the fullerene (τ = 32 ps) to yield C–P·+–C60·−. Electron transfer from the carotene to the porphyrin radical cation (τ = 125 ps) gives a final C·+–P–C60·− state with an overall yield of 0.95. This state decays to give the carotenoid triplet state with a time constant of 57 ns. The molecular triad is highly soluble in organic solvents and readily synthesized. These qualities make the molecule a useful artificial photosynthetic reaction center for a variety of spectroscopic and photochemical investigations. Copyright © 2004 John Wiley & Sons, Ltd.
Conformational analysis of calixarene derivatives substituted at the methylene bridges
Authors: Simaan Samah , Biali Silvio E. 
Published: July 2004

AbstractThe conformation of tetrahydroxycalix[4]arene derivatives substituted at two opposite methylene bridges or at a single bridge by an alkyl or aryl group is reviewed. The cone form with an equatorial substituent is the lowest energy conformation of calixarenes possessing one bridge substituted by an alkyl group, whereas both the axial and equatorial conformers are similarly populated if the substituent is an aryl group. In the cone conformation of calixarenes possessing two opposite bridges substituted in trans fashion by a pair of groups, one group must necessarily be located in an axial position. The steric interactions ensuing from the presence of an axial group destabilize the cone conformation, rendering the 1,2‐alternate form the lowest energy conformation in some derivatives. Copyright © 2004 John Wiley & Sons, Ltd.
How quickly do knotty molecules lose their energy as they grow?
Authors: Dhaliwal Manjinder , Weinberg Noham 
Published: July 2004

AbstractThe results of UFF and AM1 calculations for CNH2N hydrocarbon trefoil knots are reported for the range of N from 12 to 59 and used to discuss stabilities of knots and size‐dependent trends in their structural parameters. Other types of molecular knots, including figure‐eight and five‐crossing knots, were identified on MM3 and UFF potential energy surfaces of C30H60 and C50H100. A simple tubular model of molecular knots is discussed and used to identify the minimum size of a knot that has no excess energy due to its topology. Predictions of the tubular model are consistent with UFF and AM1 results. Copyright © 2004 John Wiley & Sons, Ltd.
A p‐benzyne to m‐benzyne conversion through a 1,2‐shift of a phenyl group. Completion of the benzyne cascade
Authors: Polishchuk Alexei L. , Bartlett Kevin L. , Friedman Lee A. , Jones Maitland 
Published: July 2004

AbstractPyrolysis of 1,6‐diphenylhexa‐1,5‐diyne‐cis‐3‐ene at 800–1000°C leads to a mixture of 1‐ and 2‐phenylbiphenylene, along with triphenylene. Formation of the two biphenylenes is taken as strong evidence of the rearrangement of a p‐benzyne into a m‐benzyne through a shift of one of the phenyl groups. Copyright © 2004 John Wiley & Sons, Ltd.
Synthesis and fluorescence properties of a porphyrin–fullerene molecular wire
Authors: Vail Sean A. , Tomé João P. C. , Krawczuk Paul J. , Dourandin Alex , Shafirovich Vladimir , Cavaleiro José A. S. , Schuster David I. 
Published: July 2004

AbstractThe synthesis and photophysical studies of a butadiyne‐linked porphyrin–C60 dyad (ZnP–C60) 6 are described. This is the first porphyrin–[60]fullerene dyad in which the two chromophores are conjugatively linked through a ‘molecular wire’. The UV–visible absorption spectrum for dyad 6 is slightly red shifted relative to the porphyrin precursor 5 whose fluorescence is all but quenched by the attached C60. Copyright © 2004 John Wiley & Sons, Ltd.
Stabilization of benzene versus oligoacetylenes: not another scale for aromaticity
Authors: Baldridge Kim K. , Siegel Jay S. 
Published: July 2004

AbstractThe energies of a number of oligoacetylenes are compared in a homodesmic reaction with benzene. Assessment of the open vs closed form of a conjugated triene is presented along with a perspective on the pursuit of quantitative scales for ‘aromaticity’. Copyright © 2004 John Wiley & Sons, Ltd.
Segmented block copolymers of poly(ethylene glycol) and poly(ethylene terephthalate)
Authors: García‐Gaitán B. , Pérez‐González M. Del P. , Martínez‐Richa A. , Luna‐Bárcenas G. , Nuño‐Donlucas S. M. 
Published: July 2004

AbstractA new series of segmented copolymers were synthesized from poly(ethylene terephthalate) (PET) oligomers and poly(ethylene glycol) (PEG) by a two‐step solution polymerization reaction. PET oligomers were obtained by glycolysis depolymerization. Structural features were defined by infrared and nuclear magnetic resonance (NMR) spectroscopy. The copolymer composition was calculated via 1H NMR spectroscopy. The content of soft PEG segments was higher than that of hard PET segments. A single glass‐transition temperature was detected for all the synthesized segmented copolymers. This observation was found to be independent of the initial PET‐to‐PEG molar ratio. The molar masses of the copolymers were determined by gel permeation chromatography (GPC). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4448–4457, 2004
Study of the conformational change of poly(N‐isopropylacrylamide)‐grafted chains in water with neutron reflection: Molecular weight dependence at high grafting density
Authors: Yim H. , Kent M. S. , Satija S. , Mendez S. , Balamurugan S. S. , Balamurugan S. , Lopez G. P. 
Published: July 2004

AbstractThe temperature‐dependent conformational change of poly(N‐isopropylacrylamide) (PNIPAM) brushes in D2O was investigated as a function of the molecular weight (M) at a high grafting density with neutron reflection. PNIPAM chains with three different M values were grafted at the same high surface density from a gold surface by atom transfer radical polymerization. A significant change in the segment concentration profile was observed for all three samples as the temperature passed through the lower critical solution temperature (∼30 °C), in contrast to previous results obtained for samples with much lower surface density. Somewhat surprisingly, the fractional change in the first moment of the segment concentration profile (〈z〉) from 20 to 41 °C was weaker with increasing M. This is contrary to the trend for systems involving only van der Waals (VDW) interactions, in which higher M chains experience larger conformational changes with change in solvent quality. Indeed, the M dependence of the first moment of the segment concentration profile for the grafted PNIPAM chains at 20 °C was much weaker than has been reported previously for dense brushes involving only VDW interactions under good solvent conditions. At 20 °C, the form of the segment concentration profile varied systematically with M. A single‐layer profile resulted for the highest M, but the profiles became more bilayer in character with decreasing M. At 41 °C, the profiles for all three samples were adequately described by a single dense layer with a smooth transition region to bulk D2O. The weak dependence of 〈z〉 on M at 20 °C and the trend from a bilayer profile at lower M to a single‐layer profile at higher M appear to be related. These results are interpreted in terms of concentration‐dependent segment–segment interactions that result in a weak attraction for high segment densities at 20 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3302–3310, 2004
Quantum study on the electrocyclic reactions of CH2CHCHCHX (XH, F, Cl)
Authors: Deng Ping , Li Lai‐Cai , Tian An‐Min , Wong Ning‐Bew 
Published: July 2004

AbstractThe microscopic mechanisms of the electrocyclic reactions for cis‐1,3‐butadiene and its monofluoro‐, monochloroderivatives have been studied by density functional theory (DFT), using the B3LYP method and 6‐311++G** basis sets. We optimized the geometric configurations of reactants, transition states, and products; verified all the probable transition states through vibrational analysis; and calculated the relative single‐point energies at the QCISD(T)/6‐311++G**//B3LYP/6‐311++G**. The results show that the monofluoro‐, monochloroderivatives of cis‐1,3‐butadiene both have two conformers; the reactant favors the electrocyclic reaction when one outboard hydrogen atom of the CH2 groups is substituted by the fluorine or chlorine atom. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Quantum analogue of the Kolmogorov–Arnold–Moser transition in different quantum anharmonic oscillators
Authors: Chattaraj P. K. , Maiti B. , Sengupta S. 
Published: July 2004

AbstractThe results of numerical computations are presented for the Bohmian trajectories of the family of different one‐ and two‐dimensional anharmonic oscillators, which exhibit regular or chaotic motion in both classical and quantum domains, depending on the values of the parameters appearing in the respective Hamiltonians. Quantum signatures of the Kolmogorov–Arnold–Moser (KAM) transition from the regular to chaotic classical dynamics of these oscillators are studied using a quantum theory of motion (QTM) as developed by de Broglie and Bohm. A phase space distance function between two initially close Bohmian trajectories, the associated Kolmogorov–Sinai–Lyapunov (KSL) entropy, the phase space volume, the autocorrelation function, the associated power spectrum, and the nearest‐neighbor spacing distribution, clearly differentiate the quantum analogues of the corresponding regular and chaotic motions in the classical domain. These quantum anharmonic oscillators are known to be useful in several diverse branches of science. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Analysis of electron correlation in M2Te (MCu, Ag, Au) systems
Authors: Surong Qi‐Mu , Zhao Yongfang , Jing Xiaogong , Li Xinying , Su Wenhui 
Published: July 2004

AbstractThe electron correlation in M2Te, (MCu, Ag, Au) systems are studied at the HF, MP2, and CCSD(T) levels with pseudopotential. The metallophilic attraction between heavy metal atoms is discussed by introducing a kind of simple model. Nearby the equilibrium point, the attraction is expressed as an angular force and estimated quantitatively by fitting the interaction energy as function of angle θ(MTeM). The behavior of electron correlation in the large distance as function of R(MM) is investigated by extracting the van der Waals coefficients of dispersion. An idea of the metallophilic contribution is given by carrying out a similar calculation on H2Te and being compared with M2Te. The trends of electron correlation and relativistic effects are discussed. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Separability between valence and conduction bands in transition metal clusters
Authors: Aprà Edoardo , Carter Emily A. , Fortunelli Alessandro 
Published: July 2004

AbstractSimplified theories of transition metal electronic structure have been postulated for many decades. We test one such approximation, namely separate treatments of d (valence) and s/p (conduction) electrons in transition metal clusters, within a density functional theory (DFT) formalism. Two different basic approaches are considered: (a) an independent‐band approximation, in which the d‐ and s/p‐bands interact only via the ρ‐dependent components of the Kohn–Sham operator; and (b) a more realistic approximation, in which the lowest‐energy d‐ and s/p‐orbitals (separately derived) are allowed to interact through explicit off‐diagonal coupling matrix elements. The results are presented for the energy differences among three structural forms (icosahedral, cuboctahedral, and truncated decahedral) of 13‐atom Ni and Pt clusters. We demonstrate that an explicit decoupling of the d‐ and s/p‐bands does not produce accurate results for the clusters considered, not even for nickel, i.e., the transition metal for which d–s/p mixing should be at its minimum. By contrast, allowing the lowest‐energy orbitals of the two separate bands to interact improves the results considerably, and ensures a fair description of metal–metal bonding. This finding suggests that simplified models that exclude explicit d–s/p coupling should be employed with caution. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
Implementation of data‐dependent acquisitions in the study of melphalan DNA adducts by miniaturized liquid chromatography coupled to electrospray tandem mass spectrometry
Authors: Van den Driessche Bart , Van Dongen Walter , Lemière Filip , Esmans Eddy L. 
Published: July 2004

AbstractThe study of defects in DNA caused by xenobiotics, more particularly the study of DNA adducts, is an important field in cancer aetiology. The analysis of low abundance DNA adducts formed in vivo both in animals and humans requires the development and implementation of highly sensitive analytical methods. Since only a minute amount of DNA can be isolated (ca. 100 μg) it is evident that the amount of sample consumed per analysis should be as small as possible in order to gather as much analytical information as possible. In this article an example is given of how this problem can be solved by the implementation of data‐dependent acquisitions using capillary liquid chromatography coupled to electrospray tandem mass spectrometry. As a case study the alkylation of DNA by melphalan is presented. Slight modifications of the chromatographic conditions (mobile and stationary phases) can allow the automated analysis of other kinds of DNA adducts. Copyright © 2004 John Wiley & Sons, Ltd.
Simultaneous determination of t,t‐muconic, S‐phenylmercapturic and S‐benzylmercapturic acids in urine by a rapid and sensitive liquid chromatography/electrospray tandem mass spectrometry method
Authors: Barbieri Anna , Sabatini Laura , Accorsi Antonio , Roda Aldo , Violante Francesco Saverio 
Published: July 2004

AbstractWe describe a rapid and sensitive high‐performance liquid chromatography/electrospray tandem mass spectrometry (HPLC/ESI‐MS/MS) method for simultaneous determination of the most relevant metabolites of benzene and toluene, t,t‐muconic acid (t,t‐MA), S‐phenylmercapturic acid (S‐PMA), and S‐benzylmercapturic acid (S‐BMA). Urine samples were purified before analysis by solid‐phase microextraction (SPE) on SAX cartridges with 50 mg sorbent mass. The developed method fulfils all the standard requirements of precision and accuracy. Calibration curves were linear within the concentration range of the standards (0–80 μg/Lurine for t,t‐MA, and 0–25 μg/Lurine for S‐PMA and S‐BMA), and had correlation coefficients ≥0.997. Limits of detection were 6.0 μg/L for t,t‐MA, 0.3 μg/L for S‐PMA, and 0.4 μg/L for S‐BMA. The method was used to determine t,t‐MA, S‐PMA and S‐BMA levels in urine of 31 gasoline‐station workers, with personal monitoring data obtained from radial symmetry passive diffusive samplers. In the context of mean work‐shift exposures of 75.9 μg/m3 (range 9.4–220.2) for benzene and 331.9 μg/m3 (78.2–932.1) for toluene, metabolite concentrations in end‐of‐shift urine samples ranged from 23.5–275.3 μg/gcreatinine for t,t‐MA, non‐detectable to 0.9 μg/gcreatinine for S‐PMA, and 3.8–74.8 μg/gcreatinine for S‐BMA. No significant correlation was found between the environmental concentrations and urinary metabolites (p > 0.05 for all cases); the ratios of benzene metabolites could be influenced by exposure levels and co‐exposure to xylenes and toluene. The high throughput of this procedure should facilitate exploration of the metabolic effects of benzene‐related co‐exposure to toluene and alkylbenzenes in large populations of subjects exposed to gasoline. Copyright © 2004 John Wiley & Sons, Ltd.
Large Kr‐free subgraphs in Ks‐free graphs and some other Ramsey‐type problems
Authors: Sudakov Benny 
Published: July 2004

AbstractIn this paper we present three Ramsey‐type results, which we derive from a simple and yet powerful lemma, proved using probabilistic arguments. Let 3 ≤ r < s be fixed integers and let G be a graph on n vertices not containing a complete graph Ks on s vertices. More than 40 years ago Erdős and Rogers posed the problem of estimating the maximum size of a subset of G without a copy of the complete graph Kr. Our first result provides a new lower bound for this problem, which improves previous results of various researchers. It also allows us to solve some special cases of a closely related question posed by Erdős. For two graphs G and H, the Ramsey number R(G, H) is the minimum integer N such that any red‐blue coloring of the edges of the complete graph KN, contains either a red copy of G or a blue copy of H. The book with n pages is the graph Bn consisting of n triangles sharing one edge. Here we study the book‐complete graph Ramsey numbers and show that R(Bn, Kn) ≤ O(n3/log3/2n), improving the bound of Li and Rousseau. Finally, motivated by a question of Erdős, Hajnal, Simonovits, Sós, and Szemerédi, we obtain for all 0 < δ < 2/3 an estimate on the number of edges in a K4‐free graph of order n which has no independent set of size n1‐δ. © 2004 Wiley Periodicals, Inc. Random Struct. Alg., 2005
Corrigendum: The complexity of counting graph homomorphisms
Authors: Dyer Martin , Greenhill Catherine 
Published: July 2004

AbstractWe close a gap in the proof of Theorem 4.1 in our paper “The complexity of counting graph homomorphisms” [Random Structures Algorithms 17 (2000), 260–289]. © 2004 Wiley Periodicals, Inc. Random Struct. Alg., 2004
How adolescents construct their future: the effect of loneliness on future orientation
Authors: Seginer Rachel , Lilach Efrat 
Published: July 2004

AbstractThis study examined the effect of loneliness, gender, and two dimensions of prospective life domains on adolescent future orientation. Future orientation was studied in four prospective domains: social relations, marriage and family, higher education and work and career. These domains are described in terms of two dimensions: theme (relational vs. instrumental) and distance (near vs. distant future). Data collected from Israeli Jewish adolescents (11th graders) were analysed by repeated measures ANOVAs and ANCOVAs (covariate: depressive experiences) for seven future orientation variables: value, expectance, control (motivational variables), hopes, fears (cognitive representation variables), exploration, commitment (behavioural variables). As predicted, lonely adolescents scored lower than socially embedded adolescents on future orientation variables applied to the relational and near future domains and lonely boys scored lower than lonely girls. However, effects were found only on the three future orientation motivational variables and not on the cognitive representation and behavioural variables. Contrary to prediction controlling for the effect of depressive experiences did not reduce the effect of loneliness on the future orientation variables, but reduced the tendency of adolescents to score higher on all future orientation variables in the instrumental than in the relational prospective domains. The contribution of these findings to the understanding of adolescent loneliness and future orientation was discussed and directions for future research were suggested.
Pathways to self‐esteem in late adolescence: the role of parent and peer attachment, empathy, and social behaviours
Authors: Laible Deborah J. , Carlo Gustavo , Roesch Scott C. 
Published: July 2004

AbstractThe goal of this study was to examine both the direct and indirect relations of parent and peer attachment with self‐esteem and to examine the potential mediating roles of empathy and social behaviour. 246 college students ( years, ) completed self‐report measures of parent and peer attachment, empathy, social behaviour, and self‐esteem. Structural equation modelling revealed that parental attachment had mostly direct effects on self‐esteem. Among females, the links between peer attachment and self‐esteem, however, were entirely mediated by empathy and prosocial behaviour. The findings from this study suggest that although close supportive relationships with parents and peers are related to adolescent self‐esteem, these links are complex.