bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of nematic coupling on the phase behaviour of nematogen mixtures
Authors: Benmouna Farida , Maschke Ulrich , Coqueret Xavier , Benmouna Mustapha 
Published: August 2002

AbstractThe phase behaviour of binary nematogen mixtures of side‐chain liquid crystal crosslinked polymers and low molecular weight liquid crystals is investigated with particular emphasis on the effects of nematic coupling. The cross nematic quadrupole parameter ν12is assumed to be proportional to the geometric average of ν11and ν22characteristic of single nematogens. In the weak coupling limit, the proportionality constant is lower than 1, and the phase diagram exhibits a reduced miscibility of the nematogens. In the case of strong coupling, the proportionality constant exceeds 1 resulting in higher miscibility. This is characterized by a nematic order that extends to temperatures above the upper nematic–isotropic transition temperature. A wide region of miscibility emerges showing a single nematic phase. Nematogens having similar nematic–isotropic transition temperatures exhibit different phase properties from systems with widely separated transition temperatures. Effects of the polymer volume fraction at crosslinking, rubber elasticity parameters of the network, and the Flory–Huggins interaction parameter on the equilibrium phase diagram of these systems are discussed.© 2001 Society of Chemical Industry
Surface characterization and study of Langmuir films of poly(4‐vinylpyridine) quaternized with n‐alkylbromide
Authors: Gargallo Ligia , Miranda Beatriz , Ríos Hernán , González‐Nilo Fernando , Radić Deodato 
Published: August 2002

AbstractThe surface behaviour of poly(4‐vinylpyridine)s (P4VP) quaternized with four different alkyl chains (pentyl, hexyl, octyl and decy bromide) were studied. Surface pressure–area isotherms (π–A) at the air–water interface were determined. Depending on the length of the side‐chains, the π–A isotherms show a plateau region. An extensive plateau is observed for n > 6. The plateau pressures are similar for n  = 8 and n  = 10. The monolayers are stable and exhibit hysteresis phenomena. Brewster angle microscopy (BAM) is used to monitor the monolayer topography of the polymer on water subphase. To obtain information about the surface energy (SE) and the degree of hydrophobicity of these systems, we have estimated the critical surface tension, γc, and the dispersion force and polar contributions to SE, γD and γP, respectively, by measurements of the contact angle (CA) of water and bromobenzene on the polymer surface. The results obtained are depend on the length of the alkyl lateral chain of the functionalized polymers.© 2001 Society of Chemical Industry
Dielectric monitoring of curing of liquid oligomer‐modified epoxy matrices
Authors: Kortaberria G , Arruti P , Mondragon I 
Published: August 2002

AbstractDielectric measurements were performed in ‘real‐time’ at several temperatures to follow polymerization reactions on blends of a diglycidyl ether of bisphenol A (DGEBA) epoxy resin with 4, 4′‐diaminodiphenylmethane (DDM) hardener and different amounts of polyoxypropylenetriamine (POPTA) oligomer. These systems exhibit phase separation induced by molar mass increasing through curing of the resin. Monitoring of phase separation and vitrification (related to the α‐relaxation) was performed by this technique. The results are compared with those for the unmodified resin–hardener mixture. The change of the main α‐relaxation with cure time, cure temperature, and amount of modifier was measured for the mixtures. This change of the main relaxation through curing in the frequency domain was indicative of the cure reaction advancement, because of its dependence on the viscosity of the medium. The change of the ionic conductivity during curing was also analysed, showing its dependence upon cure temperature.© 2001 Society of Chemical Industry
Rheology of polyurethane solutions with different solvents
Authors: de Vasconcelos C L , Martins R R , Ferreira M O , Pereira M R , Fonseca J L C 
Published: August 2002

AbstractHard segment hydrogen bonding interactions in a particular polyurethane segmented copolymer have been analysed through a viscometric approach to determine the behaviour of polyurethane solutions with different solvent compositions. Analysis of log ηspversus log c[η] master curves (solely comprising dilute and semidilute regimes) showed that these systems could be differentiated by the slope of the first part of the curve (dilute regime), the characteristic reduced concentration c*[η], and the slope of the second part of the curve (semidilute regime), differences which were related to a possible occurrence of polymer aggregates. Experiments with solutions in the concentrated regime, at different temperatures, were used to relate non‐Newtonian behaviour to hydrogen bonding.© 2001 Society of Chemical Industry
Altering educational environments through positive peer reporting: Prevention and remediation of social problems associated with behavior disorders
Authors: Skinner Christopher H. , Neddenriep Christine E. , Robinson Sheri L. , Ervin Ruth , Jones Kevin 
Published: August 2002

AbstractTypical classroom management procedures designed to reduce instances of inappropriate social behavior (i.e., tattling and punishment systems) may adversely impact the social development and social relations of students with behavior and/or social emotional disorders. Two alternative procedures where students are encouraged to monitor and report incidental prosocial behaviors are described and research supporting their effectiveness in remedying and preventing social interaction problems within classroom environments are reviewed. Recommendations for future research on altering classroom environments so that peers encourage and support classmates' incidental prosocial behavior are provided. © 2002 Wiley Periodicals, Inc.
Self‐modeling as an effective intervention for students with serious emotional disturbance: Are we modifying children's memories?
Authors: Kehle Thomas J. , Bray Melissa A. , Margiano Suzanne G. , Theodore Lea A. , Zhou Zheng 
Published: August 2002

AbstractThe intent of this article is to consider similarities between the research on the alteration of memory, and that on the modification of behavior through viewing edited self‐modeling videotapes that depict exemplary behavior. A considerable number of studies unequivocally show that memory can be altered through several mechanisms, including visual techniques. However, there is limited research indicating that alteration of memory results in valued and adaptive behavioral change. This article explores a tenable explanation for the research finding that self‐modeling is an effective intervention for students with behavior disorders. It was hypothesized that when participants view a change in their behavior, their memories and self‐beliefs subsequently change to be in concert with that shown on the edited videotape. Perhaps as the individuals repeatedly view the videotapes, they alter their memory of engagement in past maladaptive behavior, with an adaptive memory of exemplary behavior. Further, they may come to believe that they were always capable of exhibiting such behavior. © 2002 Wiley Periodicals, Inc.
Identifying and promoting social competence with African American preschool children: Developmental and contextual considerations
Authors: Mendez Julia L. , McDermott Paul , Fantuzzo John 
Published: August 2002

AbstractSchool psychologists and teachers are frequently asked to assess the level of social competence of preschool children as one indicator of their academic readiness. However, many assessment instruments available to psychologists working in early childhood settings fail to consider important contexts where children acquire social competencies. This study presents a comprehensive picture of multiple constructs that play a role in understanding African American preschool children's social competence. Domains of temperament, language, self‐regulation, and peer play were assessed within a classroom context for a sample of 139 low‐income African American children attending Head Start. Findings support the importance of considering both children's developmental stage and their gender when evaluating aspects of social competence, particularly temperament and interactive peer play abilities. As a group, younger boys experienced the greatest difficulties with initiating and sustaining play activities with classmates. Language abilities and self‐regulation were significantly greater among older preschool children. Implications for school psychologists conducting preschool assessment, intervention, and outreach to parents and teachers within early childhood settings are discussed. © 2002 John Wiley & Sons, Inc.
Fragmentation of cyclobutoxychlorocarbene: the cyclopropylcarbinyl/cyclobutyl cations revisited
Authors: Moss Robert A. , Zheng Fengmei , Johnson Lauren A. , Sauers Ronald R. 
Published: August 2002

AbstractFragmentations of cyclobutoxychlorocarbene (13, kfrag = 7.1 × 105 s−1) and cyclopropylmethoxychlorocarbene (14, kfrag = 7.6 × 105 s−1) in MeCN proceed to tight and distinct [R+ OC Cl−] ion pairs, which collapse to different distributions of cyclopropylcarbinyl, cyclobutyl and allylcarbinyl chlorides. B3LYP/6–31G* calculations support these conclusions, affording computed fragmentation activation energies of 6.4 (13) and 3.0 (14) kcal mol−1. Copyright © 2001 John Wiley & Sons, Ltd.
Kinetics of free‐radical graft polymerization of 1‐vinyl‐2‐pyrrolidone onto silica
Authors: Nguyen Van , Yoshida Wayne , Jou Jeng‐Dung , Cohen Yoram 
Published: August 2002

AbstractThe kinetics of aqueous free‐radical graft polymerization of 1‐vinyl‐2‐pyrrolidone onto silica activated with vinyltrimethoxysilane was studied with a mechanistic polymerization model and experimental data for a temperature range of 70–90 °C. The polymerization was initiated with hydrogen peroxide with initial monomer concentrations ranging from 10 to 40 vol %. The kinetic model, which incorporates the hybrid cage–complex initiation mechanism, describes the experimental polymerization data for which the kinetic order, with respect to the monomer concentration, varies from 1 to . Surface chain growth occurs by both monomer addition and homopolymer grafting, although the latter contribution to the total polymer graft yield is less significant. Increasing the initial monomer concentration enhances both surface polymer density and average grafted chain length. Increasing reaction temperature, however, produces a denser surface layer of shorter polymer chains. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 26–42, 2002
Conductive mechanism of polymer/graphite conducting composites with low percolation threshold
Authors: Zou Jun‐Feng , Yu Zhong‐Zhen , Pan Yu‐Xun , Fang Xiao‐Ping , Ou Yu‐Chun 
Published: August 2002

AbstractPreparation of the conducting composites of polystyrene/expanded graphite via in situ polymerization and investigation of the conductive mechanism were carried out. They are characterized by high conductivity and a low percolation threshold. The electrical conductivity reached 10−2 S/cm with 3.0 vol % expanded graphite content, whereas the percolation threshold was 1.0 vol %. Optical micrographs revealed the heterogeneous distribution of the graphite particles and the formation of a conductive network in the polymer matrix. A model of primary particle was proposed to interpret the conductive phenomena. The primary particle is the basic conductive unit in the composites that comprises three of the following parts: the graphite particle, the compact‐adsorbed layer, and the wrapping shell. Our model was also used to explain the experimental data in our previous studies on nylon‐6/expanded graphite composites. A low percolation threshold of conducting composites can be also explained according to the model of the primary particle. Furthermore, the theoretical line of conductivity versus primary particle content calculated from the revised Flory's theory fits the experimental data well. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 954–963, 2002
Film‐formation property of vinylidene chloride‐methyl methacrylate copolymer latex. II. Effect of latex storage temperature
Authors: Sakai Hideki , Kodani Takahiko , Takayama Atsuko , Nomura Mamoru 
Published: August 2002

AbstractChanges in the minimum film‐formation temperature (MFFT) of 91:9 wt % vinylidene chloride (VDC)‐methyl methacrylate (MMA) latex prepared by the seeded batch process during storage at 5, 20, and 40 °C were investigated. MFFT of the latex rose the fastest at 20 °C. Infrared absorption of fresh and stored latexes and wide‐angle X‐ray diffraction of powder polymers obtained by lyophilization of fresh and stored latexes indicated a much greater increase in polymer crystallinity during latex storage at 20 °C than at 5 and 40 °C. Observed increases in MFFT during latex storage correlated with increases in polymer crystallinity. Infrared absorption of polymer stored at 5–60 °C in the dry state, such as lyophilized polymer and coating film, indicated that a polymer crystallinity increase was greater during storage at higher temperatures. These results showed that crystallization behavior of 91:9 wt% VDC‐MMA copolymer latex differed from that of VDC‐MMA copolymer in the dry state. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 948–953, 2002
Morphology of α‐transcrystalline isotactic polypropylene under tensile stress studied with synchrotron microbeam X‐ray diffraction
Authors: Assouline E. , Grigull S. , Marom G. , Wachtel E. , Wagner H. D. 
Published: August 2002

AbstractThe morphology of transcrystalline isotactic polypropylene under tensile stress was studied with wide‐angle synchrotron X‐ray diffraction. The strain was apparently generated predominantly within the amorphous phase because no change in the crystal structure or in the orientation of the lamellae was detected. The results are interpreted in terms of anchoring of the transcrystalline layer to the fiber surface, and the possible consequences of these morphological features on the mechanical properties of the aramid–polypropylene composite as a whole are discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2016–2021, 2001
Evolutionary analysis of HIV‐1 protease inhibitors: Methods for design of inhibitors that evade resistance
Authors: Stoffler Daniel , Sanner Michel F. , Morris Garrett M. , Olson Arthur J. , Goodsell David S. 
Published: August 2002

AbstractDrug‐resistant strains are rapidly selected during AIDS therapy because of the high rate of mutation in HIV. In this report, we present an evolutionary simulation method for analysis of viral mutation and its use for optimization of HIV‐1 protease drugs to improve their robustness in the face of resistance mutation. We first present an analysis of the range of resistant mutants that produce viable viruses by using a volume‐based viral fitness model. Then, we analyze how this range of mutant proteases allows development of resistance to an optimal inhibitor previously designed by computational coevolution techniques. Finally, we evaluate the resistance patterns of commercially available drugs, and we discuss how resistance might be overcome by optimizing the size of specific side‐chains of these inhibitors. Proteins 2002;48:63–74. © 2002 Wiley‐Liss, Inc.
Persistence and performance of esfenvalerate residues on broccoli
Authors: Antonious George F 
Published: August 2002

AbstractThe efficacy of esfenvalerate (84 g litre−1 EC; Asana XL) at 7.0 g AI ha−1 on broccoli was tested against the flea beetle, Phyllotreta cruciferae Goeze (Chrysomelidae: Coleoptera) and the imported cabbage worm, Pieris rapae L (Pieridae: Lepidoptera) under field conditions. Insect populations were monitored before and after treatment. Periodic sweep‐net collections and examination of the leaves in treated and untreated broccoli plots revealed mean reductions of P cruciferae levels of nearly 98% 1 week post‐application compared with untreated plots. The residual toxicity of esfenvalerate was also effective for 2 weeks in reducing population density of P rapae by 69% on broccoli leaves. The impact of esfenvalerate on feeding damage to broccoli leaves was established by counting the number of feeding holes made by P cruciferae on spring broccoli and P rapae on fall broccoli. As the leaf area ingested increased, a linear relationship was seen between the number of holes and number of insects. Results indicated that forage destruction by the two pests was significantly reduced by esfenvalerate application. Esfenvalerate was extracted from broccoli at 1 h and 1, 3, 7, 10, and 14 days post‐application for residue analysis. Residues on spring broccoli were 12.2, 5.2 and 2.9 µg cm−2 on the leaves and 0.13, 0.05 and 0.02 µg g−1 on the heads at 1 h, 1 and 3 days, respectively. Only trace levels (0.001 µg g−1) were detected in/on the heads 14 days after spraying. On the basis of half‐life (T1/2) values, persistence of esfenvalerate on spring broccoli leaves (T1/2 = 1 day) was shorter than on fall broccoli (T1/2 = 1.6 days). T1/2 values were 2.1 and 3.6 days on spring and fall broccoli heads, respectively. The implications of these residue levels on re‐entry times into treated fields are discussed.© 2001 Society of Chemical Industry
A new amino acid derivative with a masked side‐chain aldehyde and its use in peptide synthesis and chemoselective ligation
Authors: Spetzler Jane C. , Hoeg‐Jensen Thomas 
Published: August 2002

AbstractA new amino acid derivative with a diol side‐chain, 𝓁‐2‐amino‐4,5‐dihydroxy‐pentanoic acid (Adi), has been prepared from 𝓁‐allylglycine by suitable protection, for use in peptide synthesis, as Fmoc‐𝓁‐Adi(Trt)2. This building block enables the introduction of a side‐chain aldehyde at any position in a given peptide sequence without use of specialized side‐chain protection schemes. The aldehyde is revealed by mild oxidation with sodium periodate, circumventing the problematic release of reactive peptidic aldehydes in TFA solution. Peptides with aldehyde side‐chains are useful for chemo‐selective ligation, reacting selectively with oxyamines to yield oxime links, while all other peptide functions can be left unprotected. The utility of the new building block has been demonstrated by the synthesis of peptide dimers and a cyclo‐peptide. Copyright © 2001 European Peptide Society and John Wiley & Sons, Ltd.
The structure–activity relationship of flavonoids as scavengers of peroxynitrite
Authors: Choi Jae Sue , Chung Hae Young , Kang Sam Sik , Jung Mee Jung , Kim Jung Won , No Jae Kyung , Jung Hyun Ah 
Published: August 2002

AbstractPeroxynitrite is a cytotoxic intermediate produced by the reaction between a superoxide anion radical and nitric oxide. The scavenging activities of flavonoids on peroxynitrite were investigated to illustrate the structure–activity relationship. Peroxynitrite was scavenged by the presence of various flavonoids, whose structures seem to be closely related to the degree of scavenging. Of 31 compounds tested, the most active was quercetin, with an IC50 value of 0.93 μM. Others had IC50 values ranging from 0.96 to more than 10 μM. The scavenging activity was postulated to be governed by the position of the hydroxyl group. Ortho‐hydroxyl structures increased the scavenging activity on peroxynitrite. Copyright © 2002 John Wiley & Sons, Ltd.
Interface structure in graphite‐fiber‐reinforced metal–matrix composites
Authors: Rawal Suraj P. 
Published: August 2002

AbstractFiber/matrix interfaces in continuous fiber‐reinforced composites are the regions of imperfections, high dislocation densities and residual stresses that affect the material's properties. The interfacial bond integrity, dislocation substructure and precipitate morphology in the interfiber matrix region in diffusion‐bonded graphite–aluminum (Gr–Al), graphite–magnesium (Gr–Mg) and cast Gr–Mg composites has been examined by transmission electron microscopy. This paper discusses the observations of the typical interface structure in Gr–Al and Gr–Mg composites. The Gr–Al composites exhibit different precipitate morphologies (blocky, lath‐shaped and fine cuboidal of similar chemical composition) and Gr–Mg composites show both spherical and lamellar Mg17Al12 precipitates. A typical interface structure in diffusion‐bonded composites exhibits no voids and reaction compounds, whereas in cast Gr–Mg composites patches of microvoids are observed sporadically near the interface, along with Mg2Si and MgO phases formed due to the chemical interaction between the matrix and SiO2 fiber coating. Adjacent to the interface, both Gr–Al and Gr–Mg exhibit a high density of dislocations that can be attributed to the residual stress state generated because of differential contraction between the fiber and matrix during the fabrication process. Copyright © 2001 John Wiley & Sons, Ltd.
Multiple imputation in public health research
Authors: Zhou Xiao‐Hua , Eckert George J. , Tierney William M. 
Published: August 2002

AbstractMissing data in public health research is a major problem. Mean or median imputation is frequently used because it is easy to implement. Although multiple imputation has good statistical properties, it is not yet used extensively. For two real studies and a real study‐based simulation, we compared the results after using multiple imputation against several simpler imputation methods. All imputation methods showed similar results for both real studies, but somewhat different results were obtained when only complete cases were used. The simulation showed large differences among various multiple imputation methods with a different number of variables for creating the matching metric for multiple imputation. Multiple imputation using only a few covariates in the matching model produced more biased coefficient estimates than using all available covariates in the matching model. The simulation also showed better standard deviation estimates for multiple imputation than for single mean imputation. Copyright © 2001 John Wiley & Sons, Ltd.
Two‐stage methods for the analysis of pooled data
Authors: Stukel Therese A. , Demidenko Eugene , Dykes James , Karagas Margaret R. 
Published: August 2002

AbstractEpidemiologic studies of disease often produce inconclusive or contradictory results due to small sample sizes or regional variations in the disease incidence or the exposures. To clarify these issues, researchers occasionally pool and reanalyse original data from several large studies. In this paper we explore the use of a two‐stage random‐effects model for analysing pooled case‐control studies and undertake a thorough examination of bias in the pooled estimator under various conditions. The two‐stage model analyses each study using the model appropriate to the design with study‐specific confounders, and combines the individual study‐specific adjusted log‐odds ratios using a linear mixed‐effects model; it is computationally simple and can incorporate study‐level covariates and random effects. Simulations indicate that when the individual studies are large, two‐stage methods produce nearly unbiased exposure estimates and standard errors of the exposure estimates from a generalized linear mixed model. By contrast, joint fixed‐effects logistic regression produces attenuated exposure estimates and underestimates the standard error when heterogeneity is present. While bias in the pooled regression coefficient increases with interstudy heterogeneity for both models, it is much smaller using the two‐stage model. In pooled analyses, where covariates may not be uniformly defined and coded across studies, and occasionally not measured in all studies, a joint model is often not feasible. The two‐stage method is shown to be a simple, valid and practical method for the analysis of pooled binary data. The results are applied to a study of reproductive history and cutaneous melanoma risk in women using data from ten large case‐control studies. Copyright © 2001 John Wiley & Sons, Ltd.