bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anisotropy in the electrical behavior of immiscible polypropylene/nylon/carbon black blends processed slightly below the melting temperature of the nylon
Authors: Zoldan J. , Siegmann A. , Narkis M. 
Published: July 2006

AbstractCarbon black (CB) containing polypropylene/nylon (PP/Ny) blends, processed slightly below the melting temperature (Tm) of the dispersed Ny phase, leads to formation of fibrillar Ny phase and electrically anisotropic systems. CB containing PP/Ny blends were compounded (twin screw extruder) and processed (injection molding) slightly below the Tm of dispersed Ny phase at different blending sequences. To establish structure–property relationships scanning electron microscopy, high resolution scanning electron microscopy, differential scanning calorimeter were used and electrical properties were also studied. Addition of CB to binary PP/Ny blends, processed below the Ny Tm, altered the Ny fibrillation process forming an irregular continuous phase, containing the CB particles, rather than the fibrils formed in the PP/Ny blends. Yet, upon changing the processing sequence, i.e., compounding PP and CB and then adding Ny in the injection molding stage, Ny fibrils were attained, maintaining phase continuity, oriented in the flow direction and CB particles preferentially located on their surfaces. Blends exhibiting a fibrillar Ny network covered by CB particles exhibited electrical anisotropy. The Ny fibrils exhibited an additional higher crystalline melting peak and molecular orientation. The composites are conductive in the Ny fibril direction, while insulating in the perpendicular direction. Once the CB is located within both, the Ny and the PP matrix the electrical behavior is isotropic. POLYM. ENG. SCI., 46:1250–1262, 2006. © 2006 Society of Plastics Engineers
Curing behavior and structure of an epoxy/clay nanocomposite system
Authors: Seo Kang Sick , Kim Dae Su 
Published: July 2006

AbstractThe curing behavior of an epoxy/clay nanocomposite system composed of a bifunctional epoxy resin with an aromatic amine curing agent and an organically modified clay was investigated. Differential scanning calorimetry (DSC) was used to investigate the curing behavior of the epoxy/clay nanocomposite system. The curing rate of the nanocomposite system increased with increasing clay content. A kinetic equation, considering an autocatalytic reaction mechanism, could describe fairly well the curing behavior of the epoxy/clay nanocomposite system. The reaction kinetic parameters of the kinetic equation were determined by fitting DSC conversion data to the kinetic equation, using a nonlinear numerical method. Dynamic mechanical analysis was used to investigate the thermomechanical properties of the epoxy/clay nanocomposite system. The glass transition temperature of the epoxy/clay nanocomposite system increased slightly with increasing clay content. The structure of the nanocomposite system was characterized by X‐ray diffraction analysis and transmission electron microscope imaging. The formation of intercalated structures was observed dominantly in the epoxy/clay nanocomposites, together with some exfoliated structures. POLYM. ENG. SCI., 46:1318–1325, 2006. © 2006 Society of Plastics Engineers
Alternating copolymerization of propylene oxide and carbon dioxide with highly efficient and selective (salen)Co(III) catalysts: Effect of ligand and cocatalyst variation
Authors: Cohen Claire T. , Coates Geoffrey W. 
Published: July 2006

AbstractSynthetic routes to a series of new (salen)CoX (salen = N,N′‐bis(salicylidene)‐1,2‐diaminoalkane; X = Br or pentafluorobenzoate (OBzF5)) species are described. Several of these complexes are active for the copolymerization of propylene oxide (PO) and CO2, yielding regioregular poly(propylene carbonate) (PPC) without the generation of propylene carbonate byproduct. Variation of the salen ligand, as well as the inclusion of organic‐based ionic or Lewis basic cocatalysts, has dramatic effects on the resultant (salen) CoX catalytic activity. Highly active (R,R)‐(salen‐1)CoOBzF5 (salen‐1 = N,N′‐bis(3,5‐ di‐tert‐butylsalicylidene)‐1,2‐diaminocyclohexane) catalysts with [Ph4P]Cl or [PPN]Y ([PPN] = bis(triphenylphosphine)iminium; Y = Cl or OBzF5) cocatalysts exhibited turnover frequencies up to 720 h−1 for rac‐PO/CO2 copolymerization, yielding PPC with greater than 90% head‐to‐tail connectivity. Additionally, the (R,R)‐(salen‐1)CoOBzF5/[PPN]Cl catalyst system demonstrated a krel of 9.7 for the enchainment of (S)‐ over (R)‐PO when the copolymerization was carried out at low temperatures. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5182–5191, 2006
Synergetic activation of carbon dioxide molecule using phenylazomethine dendrimers as a catalyst
Authors: Imaoka Takane , Tanaka Reiko , Yamamoto Kimihisa 
Published: July 2006

AbstractPhenylazomethine dendrimers bearing a cobalt porphyrin core act as catalysts for CO2 reduction in the presence of a strong Lewis acid such as lanthanide trifluoromethanesulfonate (Ln(OTf)3). We investigated the catalytic activity using electrochemical measurements (cyclic voltammetry) on a glassy carbon electrode in a DMF solution. Dissolving CO2 gas into the solution, the cyclic voltammograms displayed an irreversible increase of the cathodic current. This result suggests the catalytic reduction of CO2. The redox potential (–1.3 V versus Fc/Fc+) at which the catalytic behavior was observed is 1.1 V higher than that catalyzed by cobalt tetraphenylporphyrin (CoTPP). The generation number (n) dependence of the dendrimer catalysts showed the maximum activity at n = 3. A significant decrease of the activity for the largest dendrimer (n = 4) indicates a steric effect, which prevents transmission of the substrate (CO2 molecule) and electrons to the catalytic center (cobalt porphyrin core). For more efficient catalysis, a novel open‐shell dendrimer having a pocket on one side of the molecule was designed and synthesized. Because the accessibility to the core in the opened shell improved, this dendrimer exhibited the highest catalytic activity. These results suggest that tuning of the local domain around the cobalt porphyrin center would lead to a decisive solution for further activation of the CO2 molecule. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5229–5236, 2006
Effect of Zn doping in Bi(Pb)‐2212 superconducting ceramics
Authors: Bouaïcha F. , Mosbah M.‐F. , Amira A. , Ait‐Kaki A. , Boussouf N. 
Published: July 2006

AbstractThe subject of substitution in the high‐Tc superconductors has received a great deal of interest. Substitution of bismuth by lead stabilizes and purifies the superconducting phase in Bi2223 and enhances Tc in Bi2212 [1–5]. The substitution of Cu by magnetic or non magnetic element such as Fe, Ni, Co or Zn degrades significantly Tc [6, 7]. The substitution by Zn is difficult because the amount that can be dissolved is limited. Samples of Bi1.6Pb0.4Sr2CaCu2‐yZnyO8+d (0 ≤ y ≤ 0.06) were prepared by a solid‐state reaction method. The samples have been characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM) and AC susceptibility versus temperature measurements. Structural analysis shows that the obtained crystalline structure is mainly tetragonal with a c‐axis lattice parameter decreasing with Zn content. AC susceptibility measurements show that the Zn doping decreases the superconducting volume fraction in the samples. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Deficiency effects upon the physical properties of Pr0.8Sr0.2MnO3 manganite oxide
Authors: Cheikh‐Rouhou Koubaa W. , Koubaa M. , Boujelben W. , Cheikhrouhou A. , Haghiri‐Gosnet A. M. , Renard J.‐P. 
Published: July 2006

AbstractThe effects of deficiency in praseodymium and in strontium upon the magnetic and magneto‐transport properties of lacunar Pr0.8–x□xSr0.2MnO3 and Pr0.8Sr0.2–x□x MnO3 oxides have been investigated. Our synthesized samples have been elaborated using the conventional solid state reaction at high temperature. Crystallographic studies show that all our samples are single phase and crystallize in the orthorhombic system with Pnma space group. The praseodymium deficient samples Pr0.8–x□xSr0.2MnO3 exhibit three different regimes in the resistivity variation as a function of praseodymium deficiency amount: (i) at low concentration (0 ≤ x ≤ 0.1), a semiconductor behaviour is observed in the whole temperature range, (ii) at an intermediate amount (x = 0.15), a semiconductor‐metallic transition is followed by a metallic‐semiconductor one with decreasing temperature, and finally (iii) at x = 0.2 and 0.25, a metallic behaviour is observed below TC, whereas all the strontium deficient samples exhibit a semiconductor behaviour in the whole temperature range. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
UV light resistance of biocides for PVC/wood fiber composites
Authors: Grossman Richard F. 
Published: July 2006

AbstractSeveral of the biocides most commonly used in PVC compositions were exposed to UV‐A radiation for periods up to 2000 hr in order to determine the effects on their ability to protect various wood fibers from colonization by bacteria and fungi. Three species of bacteria and three fungi, all known to metabolize cellulose, were used. The ability of these species to exist by predation on their competitors also was studied. J. VINYL. ADDIT. TECHNOL. 12:124–126, 2006. © 2006 Society of Plastics Engineers
Synergistic Sedation With Oral Midazolam as a Premedication and Intravenous Propofol Versus Intravenous Propofol Alone in Upper Gastrointestinal Endoscopies in Children
Authors: Paspatis Gregorios A. , Charoniti Ioanna , Manolaraki Maria , Vardas Emmanouil , Papanikolaou Nikolaos , Anastasiadou Almout , Gritzali Aliki 
Published: July 2006

ABSTRACTObjectives:The primary objective of the present study was to compare the required dose of intravenous (IV) propofol between group A (synergistic sedation with an oral dose of midazolam combined with IV propofol) and group B (IV propofol alone), in diagnostic upper gastrointestinal endoscopy (UGIE) in pediatric patients. The secondary objective was to compare the safety, the efficacy, the ease of IV line placement and the ease of separation from parents between the 2 groups.Methods:Fifty‐four consecutive children (aged 3 y or older) who underwent UGIE were randomly assigned to 1 of the 2 medication regimens. Patients in group A (n = 26, mean age: 8.1 y) received midazolam (0.5 mg/kg) orally. Thirty minutes after the midazolam dose was given, repeated IV doses of propofol 0.5 mg/kg were administered titrated to achieve the level of deep sedation. Patients in group B (n = 28, mean age: 9 y) received IV propofol alone with the same methodology and sedation end point.Results:The mean dose (1.8 ± 0.7 mg/kg) of propofol administered in group A patients was remarkably lower compared with that (2.9 ± 0.9 mg/kg) of group B. Multivariate stepwise logistic regression analysis revealed that among sex, age, ASA grade and the type of sedation, the synergistic sedation was the only factor associated with the ease of IV line placement (χ2 = 16.3, P < 0.001) and the ease of separation from parents (χ2 = 41.6, P < 0.001). Additional multivariate stepwise logistic regression analysis revealed that among sex, age, ASA grade and the type of sedation, synergistic sedation was the only factor associated with a higher level of patient comfort (χ2 = 35.5, P < 0.001). The recovery time was significantly shorter in group B patients (7.7 ± 3.6 min) compared with that of group A (25.9 ± 4.1 minutes) (P < 0.01). The 2 regimens were equally safe.Conclusions:Our data suggest that synergistic sedation with an oral dose of midazolam combined with propofol may benefit the children who undergo UGIE with regard to lower mean dose of propofol used, easier IV line placement, easier separation from the parents, less pain induced by the IV line placement and greater patient comfort.
Evaluation of Cardiac Function by Tissue Doppler Imaging in Children With Chronic Hepatitis
Authors: Bora Polat Tugcin , Urganci Nafiye , Yalcin Yalim , Akdeniz Celal , Zeybek Cenap , Erdem Abdullah , Celebi Ahmet 
Published: July 2006

ABSTRACTObjectives:Pathoanatomic changes in cirrhosis result in impaired ventricular filling and diastolic dysfunction and were named as cirrhotic cardiomyopathy. However, cardiac functions have not been studied in patients with chronic hepatitis. We hypothesized that such patients might have subclinical ventricular dysfunction, detectable by tissue Doppler echocardiography and related to the severity of hepatic inflammation and fibrosis.Methods:We studied 63 clinically stable patients, 27 patients with mild chronic hepatitis (group 1), 22 patients with moderate chronic hepatitis (group 2) and 14 patients with severe chronic hepatitis (group 3) according to the scoring system of Knodell, and 36 age‐matched healthy subjects.Results:Patients with severe chronic hepatitis had impaired right ventricular diastolic function. The early diastolic velocity of the tricuspid valve annulus was lower in patients from group 3 than in healthy subjects (P < 0.001). Patients in group 3 had a greater isovolumic relaxation time (P < 0.001), indicating right ventricular diastolic dysfunction. Comparing group 3 with the healthy subjects, the ratio of peak early myocardial tissue velocity and peak late (or atrial) myocardial tissue velocity was significantly decreased (P < 0.001), at 1.4 (0.7) and 1.9 (0.7), respectively. There was also a slightly lower peak early myocardial tissue velocity and peak late (or atrial) myocardial tissue velocity ratio and a slightly longer isovolumic relaxation time in patients from group 2 than in healthy subjects (P < 0.05).Conclusions:We detected subclinical dysfunction of the right ventricle in children with chronic hepatitis in whom hepatic inflammation and fibrosis is prominent. Tissue Doppler echocardiography provides a quantifiable indicator useful for detection and monitoring of disease progression.
Hyaluronic Acid Predicts Hepatic Fibrosis in Children With Hepatic Disease
Authors: Hartley Jane L. , Brown Rachel M. , Tybulewicz Aniela , Hayes Peter , Wilson David C. , Gillett Peter , McKiernan Patrick 
Published: July 2006

ABSTRACTBackground:Hyaluronic acid (HA) is removed by the liver via sinusoidal cell adhesion molecules. This is impeded in fibrosis, leading to a rise in serum HA. As a noninvasive marker of fibrosis, HA may obviate the need for liver biopsy.Objective:To evaluate HA as a marker of hepatic fibrosis, in unselected children undergoing liver biopsy.Methods:Ninety‐three unselected consecutive children (median age, 7.5 years; range, 0.07‐19 years) undergoing a liver biopsy between April 2003 and March 2004 were prospectively recruited. Liver biopsy and fasting HA levels were taken simultaneously. The Ishak score was used to stage fibrosis. Scores of 3 or greater were regarded as significant fibrosis. Hyaluronic acid levels were measured using an enzyme‐linked binding protein assay (2002 Corgenix, Inc) (adult reference range, 0‐75 ng/mL; pediatric reference range, 0‐30 ng/mL).Results:Twenty‐three (25%) of 93 biopsies had significant fibrosis, and HA levels in this group were significantly higher than those with mild fibrosis (Ishak score, <3), (median level, 72 ng/mL vs 30 ng/mL; Mann‐Whitney U test; P < 0.005). Hyaluronic acid level of 50 ng/mL had a positive predictive value 40% and negative predictive value 86% for significant fibrosis. An HA level 200 ng/mL has a sensitivity of 26% and specificity of 90%.Conclusions:Hyaluronic Acid is a valid noninvasive predictor of hepatic fibrosis in unselected children with liver disease. An HA level of 200 ng/mL strongly suggests significant fibrosis. Hyaluronic acid level of less than 50 ng/mL accurately identifies those who do not have significant fibrosis.
Increased mobility in the membrane targeting PX domain induced by phosphatidylinositol 3‐phosphate
Authors: Cheever Matthew L. , Kutateladze Tatiana G. , Overduin Michael 
Published: July 2006

AbstractPhosphoinositides (PIs) are concentrated in specific subcellular membranes in order to recruit and regulate cytosolic proteins responsible for vesicular trafficking, cytoskeletal rearrangement, and eukaryotic cell growth, differentiation, and survival. Phox homology (PX) domains are found in proteins that are integral players in endocytic pathways. For example, Vam7p is targeted by its PX domain to phosphatidylinositol 3‐phosphate [PtdIns(3)P] in the yeast vacuole, where it interacts with other SNARE proteins and GTPases of the vesicular membrane fusion machinery. Although several PX structures have been solved, the role of dynamics in their interactions with membrane lipids is unclear. Here, we present the first detailed characterization of the backbone dynamics of a PX domain, that of Vam7p, in the presence and absence of its ligand. The structure appears to tumble more rapidly in solution upon binding PtdIns(3)P, revealing a conformational change that includes adjustments in the flexible membrane insertion loop (MIL). The flexibilities of the MIL and domain termini are pronounced in both states, while the α1 and α2 helices are rigid. Dynamic effects are spread across the binding pocket, with PtdIns(3)P inducing altered mobility of different residues on multiple timescales, including a shift in the MIL to slower timescale motions. The bound state is more dynamic overall, particularly in the β‐sheet lobe, which packs against the ligand's 3‐phosphate. Thus, the induced dynamic and structural effects are transduced from the buried heart of the binding pocket in the helical lobe through the β‐sheet lobe to the exposed surface of the bilayer‐inserted protein.
The CXXC motif at the N terminus of an α‐helical peptide
Authors: Iqbalsyah Teuku M. , Moutevelis Efrosini , Warwicker Jim , Errington Neil , Doig Andrew J. 
Published: July 2006

AbstractAn active site containing a CXXC motif is always found in the thiol‐disulphide oxidoreductase superfamily. A survey of crystal structures revealed that the CXXC motif had a very high local propensity (26.3 ± 6.2) for the N termini of α‐helices. A helical peptide with the sequence CAAC at the N terminus was synthesized to examine the helix‐stabilizing capacity of the CXXC motif. Circular dichroism was used to confirm the helical nature of the peptide and study behavior under titration with various species. With DTT, a redox potential of Eo = −230 mV was measured, indicating that the isolated peptide is reducing in nature and similar to native human thioredoxin. The pKa values of the individual Cys residues could not be separated in the titration of the reduced state, giving a single transition with an apparent pKa of 6.74 (±0.06). In the oxidized state, the N‐terminal pKa is 5.96 (±0.05). Analysis of results with the modified helix‐coil theory indicated that the disulfide bond stabilized the α‐helical structure by 0.5 kcal/mol. Reducing the disulfide destabilizes the helix by 0.9 kcal/mol.
An amino acid “transmembrane tendency” scale that approaches the theoretical limit to accuracy for prediction of transmembrane helices: Relationship to biological hydrophobicity
Authors: Zhao Gang , London Erwin 
Published: July 2006

AbstractHydrophobicity analyses applied to databases of soluble and transmembrane (TM) proteins of known structure were used to resolve total genomic hydrophobicity profiles into (helical) TM sequences and mainly “subhydrophobic” soluble components. This information was used to define a refined “hydrophobicity”‐type TM sequence prediction scale that should approach the theoretical limit of accuracy. The refinement procedure involved adjusting scale values to eliminate differences between the average amino acid composition of populations TM and soluble sequences of equal hydrophobicity, a required property of a scale having maximum accuracy. Application of this procedure to different hydrophobicity scales caused them to collapse to essentially a single TM tendency scale. As expected, when different scales were compared, the TM tendency scale was the most accurate at predicting TM sequences. It was especially highly correlated (r = 0.95) to the biological hydrophobicity scale, derived experimentally from the percent TM conformation formed by artificial sequences passing though the translocon. It was also found that resolution of total genomic sequence data into TM and soluble components could be used to define the percent probability that a sequence with a specific hydrophobicity value forms a TM segment. Application of the TM tendency scale to whole genomic data revealed an overlap of TM and soluble sequences in the “semihydrophobic” range. This raises the possibility that a significant number of proteins have sequences that can switch between TM and non‐TM states. Such proteins may exist in moonlighting forms having properties very different from those of the predominant conformation.
Sediment microbial enzyme activity as an indicator of nutrient limitation in Great Lakes coastal wetlands
Authors: HILL B. H. , ELONEN C. M. , JICHA T. M. , COTTER A. M. , TREBITZ A. S. , DANZ N. P. 
Published: July 2006

Summary1. We compared the extracellular enzyme activity (EEA) of sediment microbial assemblages with sediment and water chemistry, gradients in agricultural nutrient loading (derived from principal component analyses), atmospheric deposition and hydrological turnover time in coastal wetlands of the Laurentian Great Lakes.2. There were distinct increases in nutrient concentrations in the water and in atmospheric N deposition along the gradient from Lake Superior to Lake Ontario, but few differences between lakes in sediment carbon (C), nitrogen (N) or phosphorus (P). Wetland water and sediment chemistry were correlated with the agricultural stress gradient, hydrological turnover time and atmospheric deposition.3. The N : P ratio of wetland waters and sediments indicated that these coastal wetlands were N‐limited. Nutrient stoichiometry was correlated with the agricultural stress gradient, hydrological turnover time and atmospheric deposition.4. Extracellular enzyme activity was correlated with wetland sediment and water chemistry and stoichiometry, atmospheric N deposition, the agricultural stress gradient and the hydrological turnover time. The ratios of glycosidases to peptidases and phosphatases yielded estimates of nutrient limitation that agreed with those based solely on nutrient chemistry.5. This study, the first to link microbial enzyme activities to regional‐scale anthropogenic stressors, suggests that quantities and ratios of microbial enzymes are directly related to the concentrations and ratios of limiting nutrients, and may be sensitive indicators of nutrient dynamics in wetland ecosystems, but further work is needed to elucidate these relationships.