bluuebunny/crossref_metadata_2025 huggingface dataset:
New Insights into Nickel(II), Iron(II), and Cobalt(II) Bis‐Complex‐Based Metallo‐Supramolecular Polymers
Authors: Chiper Manuela , Meier Michael A. R. , Kranenburg Johannes M. , Schubert Ulrich S.
Published: April 2007

One of the most important characterization methods for macromolecules is SEC. The main difficulty for this type of measurements concerning metallo‐supramolecular polymers based on terpyridines is related to the interaction between the charged supramolecular species and the SEC column material. In this paper, we report new studies on the characterization and the stability of supramolecular polymers based on terpyridine metal complexes utilizing SEC. The main aspects concerning the equilibrium between complexed and uncomplexed species are discussed in detail. The present study reveals a strong relationship between the binding strength of the metal ion used and the stability of the terpyridine metal complex during the SEC measurements, which is in agreement with previously published results regarding the stability of small terpyridine metal complexes in solution. These results can lead to improved analytic possibilities and to a better fundamental understanding of the mentioned metallo‐supramolecular polymers. Furthermore, the prepared chain‐extended supramolecular‐polymer was analyzed by depth‐sensing indentation proving an increase in elastic modulus in comparison with the starting material.

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Effect of Structure of Large Aromatic Molecules Grafted onto Cellulose on Hydrolysis of the Glycosidic Linkages
Authors: Karst David , Yang Yiqi
Published: April 2007

Molecular modeling is used to explain how grafting various molecules that contain large aromatic structures and different reactive groups onto cellulose dramatically increases the hydrolysis of the glycosidic linkages of cellulose. Hydrolysis is found to increase with the increasing size of the molecule grafted to cellulose, and experiments support this finding. A larger substituent on cellulose increases hydrolysis by causing the hydrolyzed cellulose structure to be more stable compared to hydrolyzed cellulose grafted to a smaller substituent. A larger substituent forms stronger interactions with cellulose and has a greater ability to reduce the mobility of the cleaved cellulose chain to which it is bonded, which allows the cleaved cellulose to form stronger cellulose‐cellulose interactions after hydrolysis. A substituent on the C6 position of cellulose increases hydrolysis to a greater extent than does the same substituent on the C3 or C2 position.

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Chromatin changes on the GSTP1 promoter associated with its inactivation in prostate cancer
Authors: Okino Steven T. , Pookot Deepa , Majid Shahana , Zhao Hong , Li Long‐Cheng , Place Robert F. , Dahiya Rajvir
Published: April 2007

Glutathione‐S‐transferases (GSTs) are metabolic enzymes that help detoxify and eliminate harmful chemicals. In prostate tumors, expression of GST π (encoded by GSTP1) is frequently lost because of promoter hypermethylation. Here we analyze the native GSTP1 promoter in cancerous and noncancerous human prostate cells to identify structural features associated with its cancer‐related transcriptional silencing. We find that in noncancerous prostate cells (RWPE‐1 and PWR‐1E) GSTP1 is constitutively expressed, not methylated, highly accessible, bound by transcription factors and associated with histones with activating modifications (histone H3 methylated at lysine 4 and acetylated histones H3 and H4). In contrast, in cancerous prostate cells (LNCaP) GSTP1 is not expressed, extensively methylated, inaccessible, lacks bound transcription factors and is not associated with histones with activating modifications. We do not detect significant levels of histones with repressive modifications (histone H3 methylated at lysine 9 or 27) on GSTP1 in any cell line indicating that they are not associated with cancer‐related GSTP1 silencing. Treatment of LNCaP cells with 5‐azacytidine restores activating histone modifications on GSTP1 and reactivates transcription. We conclude that, in the process of prostate carcinogenesis, activating histone modifications on GSTP1 are lost and the DNA becomes methylated and inaccessible resulting in transcriptional silencing. © 2007 Wiley‐Liss, Inc.
Construction and validation of a Parkinson's disease mutation genotyping array for the Parkin gene
Authors: Clark Lorraine N. , Haamer Eneli , Mejia‐Santana Helen , Harris Juliette , Lesage Suzanne , Durr Alexandra , Bs Sabine Janin , Hedrich Katja , Louis Elan D. , Cote Lucien J. , Andrews Howard , Fahn Stanley , Waters Cheryl , Ford Blair , Frucht Steven , Scott William , Klein Christine , Brice Alexis , Roomere Hanno , Ottman Ruth , Marder Karen
Published: April 2007

Parkin mutations account for the majority of familial and sporadic early onset Parkinson's disease (EOPD) cases with a known genetic association. More than 100 mutations have been described in the Parkin gene that includes homozygous, compound heterozygous, and single heterozygous mutations. We have designed a Parkin mutation genotyping array (gene chip) that includes published Parkin sequence variants and allows their simultaneous detection. The chip was validated by screening 85 PD cases and 47 controls previously tested for Parkin mutations. Similar genotyping microarrays have been developed for other genetically heterogeneous diseases including age‐related macular degeneration. Here, we show the utility of a genotyping array for Parkinson's disease by analysis of 60 subjects from the Genetic Epidemiology of Parkinson Disease (GEPD) study that includes 15 early‐onset PD case probands and 45 relatives. © 2007 Movement Disorder Society
Abnormality of motor cortex excitability in peripherally induced dystonia
Authors: Bohlhalter Stephan , Leon‐Sarmiento Fidias E. , Hallett Mark
Published: April 2007

It is widely accepted that peripheral trauma such as soft tissue injuries can trigger dystonia, although little is known about the underlying mechanism. Because peripheral injury only rarely appears to elicit dystonia, a predisposing vulnerability in cortical motor areas might play a role. Using single and paired‐pulse pulse transcranial magnetic stimulation, we evaluated motor cortex excitability of a hand muscle in a patient with peripherally induced foot dystonia, in her brother with craniocervical dystonia, and in her unaffected sister, and compared their results to those from a group of normal subjects. In the patient with peripherally induced dystonia, we found a paradoxical intracortical facilitation at short interstimulus intervals of 3 and 5 milliseconds, at which regular intracortical inhibition (ICI) occurred in healthy subjects. These findings suggest that the foot dystonia may have been precipitated as the result of a preexisting abnormality of motor cortex excitability. Furthermore, the abnormality of ICI in her brother and sister indicates that altered motor excitability may be a hereditary predisposition. The study demonstrates that the paired‐pulse technique is a useful tool to assess individual vulnerability, which can be particularly relevant when the causal association between trauma and dystonia is less evident. © 2007 Movement Disorder Society
Rate of clinical progression in Parkinson's disease. A prospective study
Authors: Schrag Anette , Dodel Richard , Spottke Annika , Bornschein Bernhard , Siebert Uwe , Quinn Niall P.
Published: April 2007

Few prospective data on the clinical progression of Parkinson's disease (PD) in patient groups outside treatment trials in selected patients are available, and controversy exists on the rate of clinical disease progression with advancing disease. In this study, we investigated the rate of clinical progression of PD in a clinic‐based sample of 145 patients over 1 year and in a community‐based sample of 124 patients over 4 years. Depending on the sample and clinical scale used, mean deterioration of motor and disability scores ranged from 2.4 to 7.4% of the maximum possible score per year, and standard deviations indicated that there was considerable variability of progression rates between individuals. The progression of motor scores decreased with follow‐up over 4 years and significantly decreased in more advanced disease stages. Deterioration of disability scores did not differ between disease stages; this may reflect the increasing rate of disease complications, which contribute to increasing disability in addition to motor impairment alone, in more advanced disease. Thus, motor fluctuations, hallucinations, depression, memory problems, and bladder symptoms were all reported more often at follow‐up in the community‐based sample (all P < 0.01), and dyskinesias, motor fluctuations, falls, and hallucinations were more common and cognitive and depression scores worse in higher disease stages in the clinic‐based sample (all P < 0.001). We conclude that progression of motor scores in PD decreases with advancing disease in PD. However, disability continues to deteriorate with advancing disease and with the development of disease complications that are likely to be related to additional extrastriatal pathology. © 2007 Movement Disorder Society
Dielectric Response of Commercial Polycarbonate
Authors: Pratt Graeme J. , Smith Michael J. A.
Published: April 2007

Contour maps of complex relative permittivity within the range ‐ 175°C to 195°C and 0.1 Hz to 3 MHz are presented for basic and ultraviolet resistant grades of a commercial poly(dian carbonate). Several dispersion regions common to both materials are identified, together with an additional region at high temperatures in the ultraviolet resistant material. Comparisons are made with earlier investigations, and possible sources are suggested for each dispersion.
The Effect of Uncertainties in the Kuhn‐Mark‐Houwink‐Sakurada Constants on the Quantitative Analysis by Gel Permeation Chromatography
Authors: Deniz Veli , Güven Olgun
Published: April 2007

The effect of uncertainties in Kuhn‐Mark‐Houwink‐Sakurada (KMHS) constants on weight average and number average molecular weights and molecular weight distributions of some poly(ethyl methacrylate) samples have been investigated. Parameters were computed by the Weiss and Cohn‐Ginsberg method. Whereas errors introduced in Mw, Mn and HI values due to uncertainty in the K value are insignificant, uncertainties in the KMHS exponent present a serious problem. Deviations of ± 3% around a particular a value cause a ± 20% error in Mw and ± 15% error in Mn, values. The effect of deviations in the KMHS exponent on the HI values is dependent on the polydisperity of the sample investigated.
Chemical Evidence for Remnant cis Bonds in ‘trans’‐Polyacetylene
Authors: Gibson Harry W. , Weagley Ronald J. , Mosher Ralph A. , Kaplan Samuel , Prest William M. , Epstein Arthur J.
Published: April 2007

Residual 740 cm−1 absorption, a signature of the cis isomer, is always observed to the extent of ± 5% in ‘trans’‐polyacetylene prepared thermally from the Shirawaka cis isomer, regardless of the temperature or duration of treatment. The view that a significant fraction of the ‘remnant cis bonds’ is in the form of or can be converted to cisoid single bonds is supported by the results of a Diels‐Alder trapping experiment with maleic anhydride. The presence of the remnant cis linkages leads to simple rationalisation of free radical (soliton) generation and diffusion, conjugation lengths determined by Raman spectroscopy, x‐ray structural evolution and electrical conductivity.
Dichlorocarbene Modified Natural Rubber
Authors: Howard Bradbury J. , Senake Perera M. C.
Published: April 2007

Natural rubber dissolved in chloroform was reacted with aqueous NaOH using a phase transfer reagent or with solid NaOH to produce dichlorocarbene modified natural rubber. The 13C n.m.r. spectrum of the 100% modified natural rubber showed the presence of diastereoisomers due to two modes of addition of dichlorocarbene units as previously observed in epoxidation. There was no evidence of cis‐trans iso‐merisation, occurrence of other side reactions or of chain scission (shown by measurements of intrinsic viscosity). Partially dichlorocarbene modified natural rubber gave rise to a complex 13C n.m.r. spectrum that was assigned in terms of triad structures (for methylene carbon atoms)and pentad structures (for olefinic carbon atoms). Using 13C n.m.r. and measurements of glass transition temperature, it was found that reaction with aqueous NaOH and with solid NaOH both gave a random distribution of dichlorocarbene units, as compared with a block copolymer structure observed by previous workers with dichlorocarbene modified polybutadiene. The thermal stability of natural rubber is intermediate between that of the more stable 100% dichlorocarbene modified rubber and the less stable partially modified rubber.
13C Nuclear Magnetic Resonance Studies of Phenol‐Formaldehyde Resins 1 ‐ Model Compounds
Authors: Pethrick Richard A. , Thomson Barry
Published: April 2007

High resolution 13C n.m.r. data are presented for a series of model compounds generated by the acid catalysed reaction of either phenol or cresol with formalin. The pure compounds prepared for this study allow unambiguous identification of features associated with ortho‐ortho, ortho‐para and para‐para linked moieties, and hence allow analysis of the sequence structure in the typical resin. To aid assignment of the spectra a comparison is made between the predictions of the spectra using simple additivity relationships and the experimentally observed shifts. It is found that the differences between theory and experiment vary systematically with structure, and averaged correction factors are presented for various characteristic structures.
Differential Scanning Calorimetry Cure Studies of Tetra‐N‐glycidyldiaminodiphenylmethane Epoxy Resins 3 ‐ Reaction with Dicyandiamide
Authors: Barton John M. , Greenfield David C. L.
Published: April 2007

Continuation of work on the curing characteristics of an epoxy resin which is widely used as a composite matrix is reported. Results are given of study of the cure of the resin with dicyandiamide as hardener and diuron as accelerator, using differential scanning calorimetry to monitor the cure. The effect of diuron on the cure of the resin with an aromatic amine curing agent is also described. Distinctive effects of composition are found and values of the apparent activation energy of the curing reaction are derived.
Structural Versatility of Homo‐peptides from Cα,α‐dialkylated Glycines
Authors: Toniolo Claudio
Published: April 2007

A theoretical and experimental analysis of the preferred conformations of homo‐peptides from Cα,α‐dialkylated glycines revealed that these compounds are characterised by a marked structural versatility. Fully extended (C5‐conformations). folded (of theβ‐bend type), and 310‐helical structures are adopted as a function of side‐chain nature. Dimethylated and cyclic side chains favour folded and helical structures, whereas diethylated and longer acyclic side chains favour the fully extended structure. By means of conformational energy calculations the preferred screw sense of the helical structure of homo‐peptides from a representative chiral acyclic residue is also anticipated.
Direct Mass Spectrometry of Polymers
Authors: Montaudo Giorgio
Published: April 2007

The analysis of polymers by direct mass spectrometry is reviewed, and the principles of the method and some experimental aspects are discussed. Both pyrolysis and desorption methods are described. The mass spectrometric method provides the characterisation of intractable materials and their detection at the submicrogram level; the simultaneous identification and detection of additives or oligomers contained in polymer samples; the identification of components of polymer mixtures, the sequential analysis of copolymers; the identification of the primary thermal fragmentation products of polymers. Direct mass spectrometry has been widely applied to the structural analysis of synthetic and natural polymers. Published work covers nearly all classes of polymers.
Effects of Ultrasonic Vibration on the Electroinitiated Copolymerisation of Styrene and Isoprene
Authors: Akbulut Ural , Toppare Levent , Yurttaş B.
Published: April 2007

Copolymerisation of styrene and isoprene by constant potential electrolysis in dichloromethane was achieved at different polymerisation potentials. Effect of ultrasonic vibration on the rate and the yield of polymerisation has been discussed. The composition of the copolymers was found to be affected by the vibration as well as the polymerisation potential (Epol). At Epol=+3.30 V we found that r1=r2 and mole percents of isoprene and styrene in copolymer were equal to each other. Equality was also observed on reacted monomer concentrations, at that potential, which can be called critical polymerisation potential. At Epol values above or below the critical polymerisation potential none of the above‐mentioned properties were equal. Monomer reactivity ratios were determined by the integrated Lewis‐Mayo equation. Ultrasonic vibration as well as polymerisation potential was found to affect reactivity ratios.
Recent Advances with Glycidylamine Resins
Authors: Thoseby Michael R. , Dobinson Bryan , Bull Christopher H.
Published: April 2007

A new procedure for the glycidylation of aromatic amines has been developed recently, which leads to resins of lower viscosity, longer shelf‐life and higher purity than methods used previously. Resins made by the new process show considerable processing and applications advantages over those made by earlier methods. The new process has also made accessible high purity glycidyl derivatives of amines which have hitherto proved difficult to glycidylate effectively.
Hygrothermal Aging Effects in Cured Epoxies
Authors: Barrie James A. , Rudd Howard , Sagoo Perminder S. , Johncock Peter
Published: April 2007

The effect of relatively severe hygrothermal aging on the sorption and also the diffusion of water at 40°C has been studied for a number of epoxy networks comprising tetraglycidyl 4,4′‐diaminodiphenyl methane, and the curing agent 4,4′‐diaminodiphenyl sulphone, 4,4′‐diaminodiphenyl methane and 2,2′‐dichloro‐4,4′‐diaminodiphenyl methane. Aging at high temperatures is accompanied by a pronounced increase in sorptive capacity at 40°C consistent with a significant expansion of the network. Dry annealing of the aged network at sub‐ Tg temperatures collapses the expanded structure to recover the sorptive capacity of the unaged network. Preliminary studies of the sorption‐desorption kinetics for aged networks indicate that the effective diffusion coefficient is not markedly affected.
A Comparison of the Phase Behaviour of Polystyrene in Cycloalkanes and n‐Alkanes
Authors: Cowie John M. G. , McEwen Iain J.
Published: April 2007

Cloud point curves for several narrow fractions of polystyrene dissolved in cycloheptane, in cyclooctane and in cyclodecane have been established, and the critical solution temperatures extrapolated to give the respective temperatures. All three cycloalkanes are good solvents for the polymer. A comparison is made between the phase behaviour of polystyrene dissolved in cyclic alkanes and in n‐alkanes using free volume polymer solution theory.
Selective Chlorination of Side‐chains in Friedel‐Crafts Polymers
Authors: Blincow Philip J. , Ghotra Joginder S. , Pritchard Geoffrey
Published: April 2007

Aralkyl polymers with ethyl side‐chains were prepared by Friedel‐Crafts reactions. Ethylbenzene and bis(p‐chloromethyl)benzene (BCMB) were reacted together in the presence of stannic chloride to produce polymers of various molecular weights. A study was then carried out of the chlorination of these polymers, using (a) molecular chlorine, (b) molecular chlorine with a peroxide catalyst and phosphorus pentachloride, (c) sulphuryl chloride. The objective was to determine the best conditions for chlorination to occur selectively at the α‐carbon atom of the ethyl group, with minimal chlorination at either the β‐position or the main‐chain methylene groups. Analysis of 1H nuclear magnetic resonance spectra of the chlorinated polymers suggests that in most cases chlorination occurs extensively both in the side‐chain and in the main‐chain methylene groups. Conditions were found, however, which favour chlorination at the α‐position. The greatest selectivity was achieved when molecular chlorine, a peroxide catalyst and phosphorus pentachloride were used in benzene solvent.
Interpretation of intrinsic viscosity/temperature data for solutions of poly(phenyl acrylate) and poly(ethylene oxide)
Authors: Gregory Peter , Huglin Malcolm B. , Khorasani Mohamad K. H. , Sasia Pedro M.
Published: April 2007

Measured intrinsic viscosities ([η]) at several temperatures (T) within the interval 280–350 K have been found to increase with T for solutions of poly(phenyl acrylate) (PPA) in ethyl lactate. A decrease of [η] with T was observed for aqueous solutions of poly(ethylene oxide) (PEO) at several temperatures within the range 276–358 K. The results have been treated on the basis of eight excluded volume theories, among which the best consistency was afforded by those of Kurata‐Stockmayer‐Roig, Fixman, and Stockmayer (Padé). These yielded values of −3.4 × 10−3 to −4.7 × 10−3 deg−1 and −0.9 × 10−3 to −2.4 × 10−3 deg−1 for the temperatur coefficient of the unperturbed dimensions of PPA and PEO, respectively. The derived θ‐temperatures were 287 K as the upper critical solution temperature for PPA in ethyl lactate and 365–382 K as the lower critical solution temperature for aqueous PEO.
Silicones as biomaterials
Authors: Quinn Karen J. , Courtney James M.
Published: April 2007

Silicon has the ability to form polymeric chains, commonly linear chains of dimethylsiloxane, although other organic groups can be substituted for methyl. In addition, the properties of the resultant silicone polymers can vary with composition and curing procedure. This leads to a wide range of materials known as the silicones. This group of polymers, which have excellent biocompatibility, have been utilised to develop and manufacture a wide range of biomedical products. These range from simple tubing to complex implants, for example those used to replace diseased finger joints. The versatility of these materials has led to silicone products being employed in almost every medical speciality.
Interaction between polyvinylpyrrolidone and surfactant from viscosimetric data
Authors: de Sa Teresa Garcia López , Fernández Luis M. Garrido , Riaño José L. Allende
Published: April 2007

The intrinsic viscosities of solutions of polyvinylpyrrolidone (PVP) in water‐sodium dodecyl sulphate have been measured, for four different molecular weights of PVP, and different concentrations of sodium dodecyl sulphate at temperatures between 20 and 35°C. The exponent a of the Mark‐Houwink‐Sakurada equation has been determined, and the values of the short range interaction parameter Kθ, and expansion factor αη derived. Above a certain concentration the sodium dodecyl sulphate is adsorbed on the polymer by means of hydrophobic attractions, and the consequent repulsion between anionic heads provokes expansion of the macromolecule.
Curing kinetics of epoxy‐anhydride systems using quaternary ammonium guar and hydroxyethyl guar as catalysts
Authors: Patel Shailesh P. , Patel Ranjan G. , Patel Vithal S.
Published: April 2007

The kinetic parameters for the curing reactions of initially uncured and partly cured samples of the diglycidyl ether of bisphenol‐A (DGEBA) with phthalic anhydride and quaternary ammonium compounds of guar gum or quaternary ammonium compounds of hydroxyethyl guar gum as catalyst, with or without n‐butanol as diluent, were determined using the differential scanning calorimetry technique with a dynamic scan. To evaluate the kinetic parameters, four different computational methods were applied. The reaction was found to be first‐order, with activation energy in the range 65‐96 kJ mol−1.
Differential scanning calorimetric study of curing of acrylated epoxy resin with benzoyl peroxide
Authors: Thakkar Jatin R. , Patel Ranjan G. , Patel Vithal S.
Published: April 2007

The curing reaction of the acrylated diglycidyl ether of bisphenol‐A (DGEBA) with benzoyl peroxide has been investigated by differential scanning calorimetry at three different heating rates. The overall cure kinetics were found to be first‐order, with Arrhenius parameters E=83 kJ mol−1 and In A = 16.5 min−1, independent of the scan rate, up to at least 90% conversion.
Polymeric reagents: Part 1. Synthesis of polymer‐anchored amines useful for curing epoxy resins
Authors: Otaigbe John O. E. , Banks R. Eric , Smith Sydney
Published: April 2007

A range of polymers carrying amino‐functions [NHEt, NHBun, NEt2, NPr, N(CH2CH2CH2NH2)2, NMeCH2CH2CH2NH2 or NEtCH2CH2CH2 NH2] has been synthesised via amination of styrene‐vinylbenzyl chloride copolymers, poly(epichlorohydrin) and poly(2‐chloroethyl vinyl ether), and via homopolymerisation and copolymerisation (with styrene) of (n‐butyl)(vinylbenzyl)‐ammonium chloride. Some of the polymers showed promise as curing agents for epoxy resins.
Synthesis and characterisation of poly(arylene sulphides): Part 10. A comparative evaluation of the thermoanalytical behaviour and curing of poly(1,4‐phenylene sulphide) and copolymers containing 1,4‐phenylene sulphide and 2‐methyl‐1,4‐phenylene sulphide repeat units
Authors: Lovell Peter A. , Still Richard H.
Published: April 2007

Thermogravimetry, differential scanning calorimetry and curing studies were used to assess the viability of random and block copolymers comprising 1,4‐phenylene sulphide and 2‐methyl‐1,4‐phenylene sulphide repeat units as alternatives to poly(1,4‐phenylene sulphide) (PPS). The properties of the copolymers are discussed critically and compared with those of the parent homopolymers PPS and poly(2‐methyl‐1,4‐phenylene sulphide) (PMPS). The results suggest that (a) random copolymers with low PMPS contents would offer the best compromise between PPS and PMPS properties, and (b) more desirable physical properties might be achieved from systems containing a less reactive 2‐substituted‐1,4‐phenylene sulphide comonomer repeat unit.
Synthesis and reactions of polytetrahydrofuran with thiolanium end groups
Authors: D'Haese François , Goethals Eric J.
Published: April 2007

Living polytetrahydrofuran can be terminated with thiolane to form the corresponding thiolanium‐terminated polymers. The thus obtained monotelechelic or ditelechelic polymers are unreactive towards water, but can selectively couple with charged nucleophiles by a nucleophilic ring‐opening reaction of the terminal thiolanium ions. This process has been used to prepare well‐defined homopolymers such as star polymers, segmented polymers or model networks.
Solution properties of polyelectrolytes. III. Effect of sodium polystyrene sulfonate concentration on viscometric and size exclusion chromatographic behavior at different ionic strengths
Authors: Soria Vicente , García Rosa , Campos Agustín , Braco Lorenzo , Abad Concepción
Published: April 2007

The effect of sodium polystyrene sulfonate concentration on the shape of its molecules in aqueous solution at different NaNO3 ionic strengths has been analyzed by viscometry and size‐exclusion chromatography (s.e.c). An equation has been developed which predicts the intrinsic viscosity, [η] p.cp.cs, at finite concentration of both polyion (cp) and electrolyte (cs). The experimental results obtained by both techniques can be accounted for in terms of the theory. Several factors involved in the elution mechanism have been considered and the variation of the slopes of s.e.c. calibration curves with cp and cs has been discussed in terms of polyion conformation changes.
Radical copolymerization of sulphur dioxide and styrene: 4. Intramolecular excimer formation in poly(styrene sulphone)s
Authors: Bae Hun‐Jai , Miyashita Tokuji , Matsuda Minoru
Published: April 2007

Intramolecular excimer formation in poly(styrene sulphone)s with various compositions has been investigated based on the characteristic monomer sequence distributions which were determined experimentally. The fluorescence spectra of the poly(styrene sulphone)s show two emission bands at 285 nm and 330 nm as for polystyrene, corresponding to the monomer and the excimer bands, respectively. The ratio of the excimer to the monomer emission intensities (Ie/Im) is linearly correlated with the mole fraction of styrene. This observation is a consequence of the characteristic sequence distributions in poly(styrene sulphone)s. containing a very small fraction of SMS units (S = SO2; M = styrene). The efficiency of excimer formation in poly(styrene sulphone)s with regular styrene sequences, e.g. dyad sequence only, was calculated from the sequence distribution and empirical Ie/Im. It is concluded that the excimer formation in poly(styrene sulphone)s is very efficient. Energy migration along the copolymer chain was also demonstrated by measuring the degree of polarization as a function of copolymer composition. The efficient excimer formation and the depolarization in poly(styrene sulphone)s suggest that the SO2 unit in poly(styrene sulphone)s does not act as a barrier or trap to energy migration unlike the methyl methacrylate unit.
Rate and product studies in the solvolyses of methanesulfonic anhydride and a comparison with methanesulfonyl chloride solvolyses
Authors: Kevill Dennis N. , Ryu Zoon Ha , Niedermeyer Monica A. , Koyoshi Fumie , D'Souza Malcolm J.
Published: April 2007

The specific rates of solvolysis of methanesulfonic anhydride have been measured conductometrically at −10 °C in 41 solvents. Use of the extended Grunwald–Winstein equation, with the NT scale of solvent nucleophilicity and the YOTs scale of solvent ionizing power, leads to sensitivity to changes in solvent nucleophilicity (ℓ value) of 0.95 and a sensitivity to changes in solvent ionizing power (m value) of 0.61, with a multiple correlation coefficient (R) of 0.973. Product selectivity values (S) in binary hydroxylic solvents favor alcohol attack in EtOH–H2O (a value of 1.2 in 90% EtOH rising to 4.0 in 40% EtOH) and in MeOH–H2O (a value of 3.7 in 90% MeOH rising to 6.0 in 50% MeOH). In 2,2,2,‐trifluoroethanol–H2O, the S values are much lower at about 0.1. Entropy of activation values are appreciably negative. Literature values for the specific rates of solvolysis of methanesulfonyl chloride have been extended to fluoroalcohol‐containing solvents (titrimetric method) and, at 45.0 °C, for an overall 43 solvents values are obtained (using NT and YC1 scales) of 1.20 for ℓ and of 0.52 for m (R = 0.969). It is proposed that both substrates solvolyze by an SN2 pathway. Copyright © 2007 John Wiley & Sons, Ltd.
Investigation of ZnO substrates: effects of high temperature annealing
Authors: Graubner S. , Neumann C. , Krost A. , Bläsing J. , Meyer B. K.
Published: April 2007

In order to promote growth of ZnO films on ZnO substrates, defects introduced by the surface polishing procedure have to be removed. We investigate the influence of high temperature annealing in O2‐atmosphere on the structural properties of the ZnO substrates by atomic force microscopy. Only at temperatures above 1100 °C atomic steps (terraces) are seen, the remaining defects can be assigned to dislocations in a density between 104 to 105 cm–2. Interestingly the electrical properties also change from high resistive to n‐type conduction, which make the substrates – apart for the homoepitaxial growth on a perfect template – suitable for top‐to‐bottom contacts. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of anisotropic II–VI superlattices
Authors: Schillak P. , Czajkowski G.
Published: April 2007

We show how to compute optical spectra of semiconductor superlattices (SLs) in the region of interband electronic transitions. The method uses the microscopic calculation of superlattice minibands and the macroscopic real density matrix approach to compute the electromagnetic fields and susceptibilities. The Kronig–Penney model is adapted for computing miniband SL parameters. The electron–hole screened Coulomb potential is adapted and the valence band structure is taken into account in the cylindrical approximation, thus separating light‐ and heavy‐hole motions. We calculate the optical functions, including the optical Stokes parameters and ellipsometric functions for the case of oblique incidence. Results are given for Zn1–x Cdx Se/ZnSe SLs and a good agreement with experiments is obtained. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Post‐annealing effect upon phosphorus‐doped ZnTe homoepitaxial layers grown by MOVPE
Authors: Saito Katsuhiko , Fujimoto Kenji , Yamaguchi Kouji , Tanaka Tooru , Nishio Mitsuhiro , Guo Qixin , Ogawa Hiroshi
Published: April 2007

The effect of post‐annealing treatment upon the photoluminescence (PL) spectra of phosphorus‐doped ZnTe homoepitaxial layers grown by metalorganic vapour phase epitaxy using tris‐dimethylaminophosphorus (TDMAP) has been investigated. PL properties at 4 K of the layers are dramatically improved by the post‐annealing in nitrogen flow, i.e. donor–acceptor pair emission vanishes and instead free‐to‐bound transition emission (FB) and broadened acceptor‐related excitonic emission (Ia) appear. PL intensity at room temperature is enhanced remarkably by the treatment. While the post‐annealing treatment in hydrogen flow also gives an increase in PL intensity at room temperature of the layer, PL spectrum at 4 K is almost unchanged. The intensity ratio of FB to broadened Ia for the layer after post‐annealing treatment in nitrogen flow increases and the broadened Ia shifts towards longer wavelength side with increasing TDMAP transport rate. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High temperature electrical properties of CdTe〈Pb〉 crystals under Te saturation
Authors: Fochuk P. , Grill R. , Kadys A. , Jarasiunas K. , Verstraeten D. , Feychuk P. , Parfenyuk O. , Panchuk O.
Published: April 2007

The point defect equilibrium of CdTe〈Pb〉 single crystals under well‐defined Te vapor pressure was investigated up to 1070 K. At 630–900 K these crystals showed p‐type conductivity and at higher temperatures – native n‐type one. During measurements the hole density reached up to ∼2 × 1017 cm–3 at 800 K. The main acceptor dominant species, which determined the electrical properties of crystals, was supposed to be the (Pb$ ^+_{\rm Cd} $V$ ^{2-}_{\rm Cd} $)– associate with its level in the gap located at EV + 0.42–0.45 eV. Above 900 K native electrons began to influence the conductivity type. Three models of point defect structure were used to describe the galvanomagnetic data – (i) frozen defect structure, (ii) defect structure with shallow or deep acceptor levels fixed during thermal cycles and native defects being in three‐phase solid–liquid–gas (SLG) equilibrium, and (iii) defect structure without any fixed energy level and defect densities being determined by the SLG equilibrium. The FWM technique confirmed p‐type photoconductivity at 300 K, but also revealed bipolar carrier generation at high photoexcitation levels with very fast electron trapping. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
In‐doped transparent and conducting cubic magnesium zinc oxide thin films grown by pulsed laser deposition
Authors: Lau C. H. , Zhuang L. , Wong K. H.
Published: April 2007

In‐doped n‐type semiconducting magnesium zinc oxide (MZO) thin films have been fabricated on MgO (100) and LaAlO3 (LAO) (100) substrates under low oxygen ambient by pulse laser deposition (PLD). X‐ray diffraction and HRTEM studies reveal the presence of pure cubic phase MZO (c‐MZO). High quality cube‐on‐cube epitaxy is obtained in films grown on MgO. For films deposit on LAO, they exhibit heteroepitaxial relationship of (100)c‐MZO ‖ (100)LAO and (011)c‐MZO ‖ (010)LAO. All as‐prepared c‐MZO thin films show good optical transmittance over the whole visible spectrum. Samples with In dopant concentration above 8 at% yield an electrical resistivity of less than 10–2 Ω cm and can be used as Transparent Conducing Oxide (TCO). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and properties of Zn1–x –yBex Mny Se crystals
Authors: Firszt F. , Łęgowski S. , Męczyńska H. , Rozpłoch F. , Marasek A. , Strzałkowski K. , Patyk J. , Nowak L.
Published: April 2007

Photoluminescence spectra, photoluminescence‐excitation spectra, Raman and EPR studies were performed in bulk Zn1–x –y Bex Mny Se solid solutions grown by the high pressure Bridgman method in the range of composition 0 < x < 0.2, 0 < y < 0.2. For low Mn content photoluminescence spectra at low temperatures consist of exciton, “edge” and deep levels emission bands. The main yellow band (2.05 eV) is due to internal transition in Mn2+. The exciton energy gap versus Mn content was determined for Zn1–x –y Bex Mny Se samples with Be content x = 0.05. EPR studies show that the g ‐factor is noticeably larger than the gfree value indicating a large exchange interaction. The decreasing of g ‐factor with increasing Mn concentration in the investigated samples can be explained as due to increasing of spin ordering. Applying the DPPH as a standard, the concentration of unpaired spins per unit weight of the crystal was estimated. Measured at room temperature Raman spectra consist of ZnSe‐like, MnSe‐like and BeSe‐like transverse (TO), longitudinal (LO), transverse (TA) and longitudinal (LA) phonon modes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Laser controlled magnetization in bulk Zn1–x Mnx Te
Authors: Khoi Le Van , Avdonin A. , Gałązka R. R. , Lentze M. , Kehl C. , Geurts J. , Eyring M. , Astakhov G. , Ossau W.
Published: April 2007

Zn1–x Mnx Te crystals (0 ≤ x ≤ 0.30) have been grown by the high pressure Bridgman technique. The free exciton energy of Zn1–x Mnx Te was determined from the photoluminescence and reflectance measurements in the temperature range from 1.7 to 270 K. The magneto‐photoluminescence and magneto‐reflectance were studied at T = 1.7 K and in magnetic fields up to 6 T. The magnetization of Zn1–x Mnx Te was calculated from the giant Zeeman effect. It was found that there is an efficient energy transfer channel from the photo‐excited carriers into the Mn2+ ions by spin‐flip scattering processes. It allows one to change the spin temperature of the Mn2+ subsystem and consequently to control its magnetization by tuning laser excitation density. The magnetization of the Zn1–x Mnx Te can be changed by 60% of its maximum value. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study of Al thermal diffusion in ZnTe using secondary ion mass spectroscopy
Authors: Tanaka Tooru , Murata Norihiro , Saito Katsuhiko , Nishio Mitsuhiro , Guo Qixin , Ogawa Hiroshi
Published: April 2007

The thermal diffusion of Al in ZnTe has been studied by using secondary ion mass spectroscopy. The relationships between the diffusion coefficient and the Al concentration were determined from Al depth profiles by a Boltzmann–Matano analysis. The diffusion coefficient depends on the Al concentration and it becomes large at the high doping level, probably due to the increase of Zn vacancy concentration attributed to the self‐compensation effect. As a result of decrease in the diffusion coefficient at low Al concentration, a rapid decrease in the Al concentration was observed at the diffusion front. This would lead to the formation of highly abrupt p–n junctions, resulting in the fabrication of ZnTe light emitting diode with better performance. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Local structure around Mn in Mn containing ZnO nanocrystals
Authors: Koteski V. , Zhou H. , Farangis B. , Hofmann D. M. , Meyer B. K. , Mahnke H.‐E.
Published: April 2007

Among the diluted magnetic semiconductors of current interest, especially ZnO is experiencing a renaissance with the incorporation of Mn because of the recent predictions from theory. We have obtained local structure information from X‐ray Absorption Spectroscopy (XAS) complementing previous electron paramagnetic resonance (EPR) studies on Mn in ZnO nanocrystals and Zn(OH)2. Mn is found to be incorporated substitutionally into the ZnO nanocrystals with a sizeable distortion as compared to the regular ZnO lattice structure. Depending on the preparation of the nanocrystals Mn is found in the ZnO core as well as in a Zn(OH)2 surface shell with a fraction which decreases upon annealing as the shell disintegrates forming additional ZnO. No indications for Mn clusters were found. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The phonon dispersion of wurtzite‐ZnO revisited
Authors: Serrano J. , Manjón F. J. , Romero A. H. , Ivanov A. , Lauck R. , Cardona M. , Krisch M.
Published: April 2007

Inelastic neutron scattering measurements are reported for the optical phonon branches of wurtzite ZnO. The experimental data are in excellent agreement with the ab‐initio calculations for the phonon dispersion relations based on linear response theory. Discrepancies between theory and present data observed for the longitudinal optic branches along the [100] and [001] directions are attributed to an inaccurate description of the dielectric constant of ZnO and, consequently, the crystal‐ and electric‐field splitting. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of underlying layers on the growth of 1D (Mg,Zn)O nanorods
Authors: Kong Bo Hyun , Jun Sang Ouk , Kim Young Yi , Kim Dong Chan , Cho Hyung Koun
Published: April 2007

We grew (Mg,Zn)O nanorods with different morphologies and growth directions on various substrates by the thermal evaporation process using vapor‐solid growth mode. The alignment and growth mode of the nanorods are significantly affected by the underlayer and substrates. By depositing ZnO and (Mg,Zn)O underlayers, the alignment of the (Mg,Zn)O nanorods was changed from random to vertical based on the substrate surface. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of midazolam and its hydroxy metabolites in human plasma and oral fluid by liquid chromatography/electrospray ionization ion trap tandem mass spectrometry
Authors: Link Bettina , Haschke Manuel , Wenk Markus , Krähenbühl Stephan
Published: April 2007

Midazolam (MDZ), a short‐acting benzodiazepine, is a widely accepted probe drug for CYP3A phenotyping. Published methods for its analysis have used either therapeutic doses of MDZ, or, if employing lower doses, were mostly unable to quantify the two hydroxy metabolites. In the present study, a sensitive and specific liquid chromatography/electrospray ionization tandem mass spectrometry method was developed and validated for the quantitative determination of MDZ and two of its metabolites (1′‐hydroxymidazolam (1′‐OHMDZ) and 4‐hydroxymidazolam (4‐OHMDZ)) in human plasma and oral fluid. After liquid‐liquid extraction with hexane/dichloromethane (73:27, v/v), the analytes were separated on a Luna C18(2) (100 × 2.1 mm) analytical column using gradient elution. Detection was achieved using tandem mass spectrometry on an ion trap mass spectrometer. Midazolam‐d6 was used as internal standard for quantification. The calibration curves were linear (R2 >0.998) between 0.05 and 20 ng/mL for MDZ and both metabolites in both matrices. Using 1 mL samples, the limit of detection was 0.025 ng/mL and the limit of quantification was 0.05 ng/mL for MDZ and the hydroxy metabolites in both matrices. Intra‐ and inter‐day accuracies, determined at three different concentrations, were between 92.1 and 102.3% and the corresponding coefficients of variation were <7.3%. The average recoveries were 90.6%, 86.7% and 79.0% for MDZ, 1′‐OHMDZ and 4‐OHMDZ in plasma and 95.3%, 96.6% and 86.8% for MDZ, 1'‐OHMDZ and 4‐OHMDZ, respectively, in oral fluid. The method was successfully applied to a pharmacokinetic study, showing that MDZ and its hydroxy metabolites can be determined precisely in in vivo samples obtained following a single oral or intravenous dose of 2 mg MDZ. The method appears to be useful for CYP3A phenotyping in plasma using sub‐therapeutic MDZ doses, but larger studies are needed to test this assumption. Copyright © 2007 John Wiley & Sons, Ltd.
The challenges of deep impact autonomous navigation
Authors: Kubitschek Daniel G. , Mastrodemos Nickolaos , Werner Robert A. , Synnott Stephen P. , Bhaskaran Shyam , Riedel Joseph E. , Kennedy Brian M. , Null George W. , Vaughan Andrew T.
Published: April 2007

On July 4, 2005 at 05:44:34 UTC the Impactor spacecraft (s/c) impacted comet 9P/Tempel 1 with a relative speed of more than 10 km/s. The Flyby s/c captured the impact event, using both the medium resolution imager and the high resolution imager, and tracked the impact site for the entire observing period following impact. The objective of the Impactor s/c was to impact in an illuminated area viewable from the Flyby s/c and telemeter high‐resolution context images of the impact site prior to impact. The Flyby s/c had two primary objectives: (1) capture the impact event in order to observe the ejecta plume expansion dynamics and (2) track the impact site for at least 800 s to observe the crater formation and capture high‐resolution images of the fully developed crater. All of these objectives were met by estimating the trajectory of each spacecraft relative to 9P/Tempel 1 using the autonomous navigation system, precise attitude information from the attitude determination and control subsystem, and allowing each spacecraft to independently select the same impact site. This paper describes the challenges of targeting and tracking comet 9P/Tempel 1. © 2007 Wiley Periodicals, Inc.
Using dangling bond density to characterize the surface energy of nanomaterials
Authors: Ma Fei , Xu Ke‐Wei
Published: April 2007

Taking f.c.c Ag, Al, Au, Ir, Pd, Pt, Rh and b.c.c Cr, Fe, Mo, Nb, Ta, V, W as examples, the energetic and bonding features of unrelaxed cubic nanoparticles were investigated by the modified embedded atom method. The surface free energy increases almost inversely with the decreasing feature sizes. This is the essential reason for the fantastic microstructures and distinct properties observed at the nanometer scale. According to the analysis on atomic bonding states, we further found that the size‐dependent surface energy is directly associated with the dangling bond density. Summing up these two aspects, the dangling bond density, a microscopic parameter, is believed to be one of the intrinsic physical quantities characterizing the structures and properties of nanomaterials. Copyright © 2007 John Wiley & Sons, Ltd.
Structural control against failure interaction
Authors: Anton M. , Casciati F.
Published: April 2007

Control of structures against environmental loads, such as earthquakes and wind, is generally conceived as the protection of a system with no interaction with the surrounding buildings.

When a large facility is considered, subsystems within it are identified and, in case, controlled. Attention is focused throughout this paper on the interaction of these subsytems in extreme conditions. The new concept of controlling the failure mode arises.

The paper discusses the motivations leading one to adopt such an approach and the guidelines for its design.
Piezoelectric plates with changing thickness
Authors: Nicotra V. , Podio‐Guidugli P.
Published: April 2007

A linear theory of electroelastic plates capable of thickness changes is presented. It is shown that, for transversely isotropic plates, the general boundary‐value problem decouples into a membrane problem and a flexure problem; in each subproblem, piezoelectric and electrostrictive effects are in order, with peculiar forms. An example is studied, where thickness changes in membrane regime are induced either by mechanical loads or by electric loads.
Optimal structural control in the frequency domain: Control in norm H2 and H∞
Authors: Palazzo B. , Petti L.
Published: April 2007

Two different optimal control strategies defined in the frequency domain are discussed in this paper. The general formulation of H2 and H∞ is reorganized in an easy way to be used for mechanical applications. Both the control methodologies are reviewed for general problems and applied to simple systems by showing their main mechanical aspects and differences. The two methods have been numerically compared in controlling the seismic response of a base isolated system equipped with a hybrid mass damper.