bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation and characterization of lead monoxide filled unsaturated polyester based polymer composites for gamma radiation shielding applications
Authors: Harish V. , Nagaiah N. , Prabhu T. Niranjana , Varughese K. T. 
Published: February 2009

AbstractParticulate polymer composites of Isophthalate based unsaturated polyester resin filled with different concentrations of lead monoxide were prepared. These composites were investigated for physical, thermal, mechanical, and gamma radiation shielding characteristics. The results of density evaluation, microscopic studies, and the radiation shielding properties for gamma rays of energy 0.662 MeV from Cs‐137 point source have been presented in this article. The results show that, the density of the composites was observed to increase with filler loading. The morphological analysis of the composites made using the scanning electron microscope showed that, the lead monoxide particles were observed to disperse uniformly in the polymer matrix with an average inter particle distance of about 10 μm and an average size of about 5.36 μm. The linear attenuation coefficient of the composites was found to increase with increased filler content in the composites. The highest value of 0.206 cm−1was found for 50 wt % of lead monoxide. These composites were observed to exhibit excellent % of heaviness and Half value layer in comparison with other conventional materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Crystallization kinetics of isotactic polypropylene nucleated with organic dicarboxylic acid salts
Authors: Zhao Shicheng , Xin Zhong 
Published: February 2009

AbstractBicyclo[2.2.1]hept‐5‐ene‐2,3‐dicarboxylate salts (BCHED) were synthesized by hydrothermal method. The crystallization kinetics of isotactic polypropylene (iPP) and nucleated iPP with BCHED were investigated by differential scanning calorimeter (DSC) under isothermal and nonisothermal conditions. Isothermal crystallization kinetics was described by Avrami equation and the fold surface free energy (σe) of iPP was calculated by Hoffman theory. The results showed Avrami exponents of nucleated iPP become smaller, the values of t1/2 dramatically decrease, the crystallization rate constants Z(T) greatly increase and the fold surface free energy (σe) of iPP decrease with the addition of the nucleating agents. Under nonisothermal condition the Caze method was applied to deal with the crystallization kinetics of iPP and the crystallization active energy of iPP was determined by Kissinger method. The results showed the crystallization peak temperatures (Tcp) of nucleated iPP greatly increase, but Avrami exponents of iPP were slightly influenced and the crystallization active energy of iPP increases by the addition of BCHED. It can be concluded that BCHED act as nucleating agents and BCHE11 shows the best nucleating effect. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
A Note on the Use of Unbiased Estimating Equations to Estimate Correlation in Analysis of Longitudinal Trials
Authors: Sun Wenguang , Shults Justine , Leonard Mary 
Published: February 2009

AbstractLongitudinal trials can yield outcomes that are continuous, binary (yes/no), or are realizations of counts. In this setting we compare three approaches that have been proposed for estimation of the correlation in the framework of generalized estimating equations (GEE): quasi‐least squares (QLS), pseudo‐likelihood (PL), and an approach we refer to as Wang–Carey (WC). We prove that WC and QLS are identical for the first‐order autoregressive AR(1) correlation structure. Using simulations, we then develop guidelines for selection of an appropriate method for analysis of data from a longitudinal trial. In particular, we argue that no method is uniformly superior for analysis of unbalanced and unequally spaced data with a Markov correlation structure. Choice of the best approach will depend on the degree of imbalance and variability in the temporal spacing of measurements, value of the correlation, and type of outcome, e.g. binary or continuous. Finally, we contrast the methods in analysis of a longitudinal study of obesity following renal transplantation in children (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Likelihood Methods for Regression Models with Expensive Variables Missing by Design
Authors: Zhao Yang , Lawless Jerald F. , McLeish Donald L. 
Published: February 2009

AbstractIn some applications involving regression the values of certain variables are missing by design for some individuals. For example, in two‐stage studies (Zhao and Lipsitz, 1992), data on “cheaper” variables are collected on a random sample of individuals in stage I, and then “expensive” variables are measured for a subsample of these in stage II. So the “expensive” variables are missing by design at stage I. Both estimating function and likelihood methods have been proposed for cases where either covariates or responses are missing. We extend the semiparametric maximum likelihood (SPML) method for missing covariate problems (e.g. Chen, 2004; Ibrahim et al., 2005; Zhang and Rockette, 2005, 2007) to deal with more general cases where covariates and/or responses are missing by design, and show that profile likelihood ratio tests and interval estimation are easily implemented. Simulation studies are provided to examine the performance of the likelihood methods and to compare their efficiencies with estimating function methods for problems involving (a) a missing covariate and (b) a missing response variable. We illustrate the ease of implementation of SPML and demonstrate its high efficiency (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some Methods of Propensity‐Score Matching had Superior Performance to Others: Results of an Empirical Investigation and Monte Carlo simulations
Authors: Austin Peter C. 
Published: February 2009

AbstractPropensity‐score matching is increasingly being used to reduce the impact of treatment‐selection bias when estimating causal treatment effects using observational data. Several propensity‐score matching methods are currently employed in the medical literature: matching on the logit of the propensity score using calipers of width either 0.2 or 0.6 of the standard deviation of the logit of the propensity score; matching on the propensity score using calipers of 0.005, 0.01, 0.02, 0.03, and 0.1; and 5 → 1 digit matching on the propensity score. We conducted empirical investigations and Monte Carlo simulations to investigate the relative performance of these competing methods. Using a large sample of patients hospitalized with a heart attack and with exposure being receipt of a statin prescription at hospital discharge, we found that the 8 different methods produced propensity‐score matched samples in which qualitatively equivalent balance in measured baseline variables was achieved between treated and untreated subjects. Seven of the 8 propensity‐score matched samples resulted in qualitatively similar estimates of the reduction in mortality due to statin exposure. 5 → 1 digit matching resulted in a qualitatively different estimate of relative risk reduction compared to the other 7 methods. Using Monte Carlo simulations, we found that matching using calipers of width of 0.2 of the standard deviation of the logit of the propensity score and the use of calipers of width 0.02 and 0.03 tended to have superior performance for estimating treatment effects (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal Response‐Adaptive Designs for Normal Responses
Authors: Biswas Atanu , Bhattacharya Rahul 
Published: February 2009

AbstractMost of the available response‐adaptive designs in phase III clinical trial set up are not from any optimal consideration. An optimal design for binary responses is given by Rosenberger et al. (2001) and an optimal design for continuous responses is provided by Biswas and Mandal (2004). Recently, Zhang and Rosenberger (2006) [ZR] provided another design for normal responses. Biswas, Bhattacharya and Zhang (2007) pointed out that the design of ZR is not suitable for normally distributed responses, or any distribution having the possibility of negative mean, in general. But they only indicated the problem and bypassed the original problem and set up. In the present paper, we first start with the drawback of ZR. We then provide the appropriate optimal response‐adaptive design for normal or continuous distributions which provides the necessary correction for the ZR problem. The proposed methods are illustrated using some real data (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hypoxia and stem cell‐based engineering of mesenchymal tissues
Authors: Ma Teng , Grayson Warren L. , Fröhlich Mirjam , Vunjak‐Novakovic Gordana 
Published: February 2009

AbstractStem cells have the ability for prolonged self‐renewal and differentiation into mature cells of various lineages, which makes them important cell sources for tissue engineering applications. Their remarkable ability to replenish and differentiate in vivo is regulated by both intrinsic and extrinsic cellular mechanisms. The anatomical location where the stem cells reside, known as the “stem cell niche or microenvironment,” provides signals conducive to the maintenance of definitive stem cell properties. Physiological condition including oxygen tension is an important component of the stem cell microenvironment and has been shown to play a role in regulating both embryonic and adult stem cells. This review focuses on oxygen as a signaling molecule and the way it regulates the stem cells' development into mesenchymal tissues in vitro. The physiological relevance of low oxygen tension as an environmental parameter that uniquely benefits stem cells' expansion and maintenance is described along with recent findings on the regulatory effects of oxygen on embryonic stem cells and adult mesenchymal stem cells. The relevance to tissue engineering is discussed in the context of the need to specifically regulate the oxygen content in the cellular microenvironment in order to optimize in vitro tissue development. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009
Vulnerable young people and substance misuse: expanding on the risk and protection‐focused approach using social psychology
Authors: Scaife Victoria , O'Brien Margaret , McEune Rhona , Notley Caitlin , Millings Abigail , Biggart Laura 
Published: February 2009

AbstractThis paper critically reviews recent research exploring risk and protective factors for the development of problematic substance use in populations of young people. Specific populations of young people who are most vulnerable to developing problematic patterns of use are identified, and alterations to methods of data collection which would improve the ability of local authorities to monitor these populations and more efficiently target them for early preventative interventions are highlighted. It is argued that social‐psychological research techniques and approaches should be used to complement a risk and protection‐focused approach in order to improve the design and evaluation of interventions, and provide decision‐aids for practitioners when assessing the needs of vulnerable young people. Examples are provided to demonstrate the utility of social psychology in this regard, and the paper concludes with specific recommendations for future research and services. Copyright © 2009 John Wiley & Sons, Ltd.
Impulsive donation decisions during online browsing of charity websites
Authors: Bennett Roger 
Published: February 2009

Abstract

Although online fundraising by charitable organisations is now commonplace, many aspects of effective online fundraising remain unexamined. In particular, little is known about the nature and determinants of impulsive donation decisions taken by browsers of charity websites. This empirical study attempted to help fill this important gap in current knowledge about online fundraising via an investigation of the antecedents of impulsive online giving to a hospice organisation in the south of England. Two hundred and thirty‐nine donors who stated that their gifts had been made impulsively and 223 donors whose online gifts were reported as having been pre‐planned completed a questionnaire that explored, inter alia, a person's socio‐demographic characteristics, level of impulsiveness and attitude towards impulsive behaviour, charity donation history, prior knowledge of hospice issues, subjective norms and personal involvement with charity giving. The main determinants of impulsive donations were identified and the profiles of various types of impulsive giver were established. Relevant matters were investigated in the contexts of two types of web page design: emotive and informative.

Copyright © 2009 John Wiley & Sons, Ltd.
Crystal Structure Analysis and in Silico pKa Calculations Suggest Strong pKa Shifts of Ligands as Driving Force for High‐Affinity Binding to TGT
Authors: Ritschel Tina , Hoertner Simone , Heine Andreas , Diederich François , Klebe Gerhard 
Published: February 2009

AbstractExpanded lin‐benzoguanines exhibit binding affinities to tRNA‐guanine transglycosylase (TGT) in the low‐nanomolar range. A significant pKa shift is observed for the inhibitors moving from aqueous solution to protein environment. The protonation of the inhibitor facilitates a charge‐assisted hydrogen bond in the protein–ligand complex.magnified imageA novel ligand series is presented to inhibit tRNA‐guanine transglycosylase (TGT), a protein with a significant role in the pathogenicity mechanism of Shigella flexneri, the causative agent of Shigellosis. The enzyme exchanges guanine in the wobble position of tRNAAsn,Asp,His,Tyr against a modified base. To prevent the base‐exchange reaction, several series of inhibitors have already been designed, synthesized, and tested. One aim of previous studies was to address a hydrophobic pocket with different side chains attached to the parent skeletons. Disappointingly, no significant increase in binding affinity could be observed that could be explained by the disruption of a conserved water cluster. The ligand series examined in this study are based on the known scaffold lin‐benzoguanine. Different side chains were introduced leading to 2‐amino‐lin‐benzoguanines, which address a different pocket of the protein and avoid disruption of the water cluster. With the introduction of an amino group in the 2‐position, a dramatic increase in binding affinity can be experienced. To explain this significant gain in binding affinity, Poisson–Boltzmann calculations were performed to explore pKa changes of ligand functional groups upon protein binding, they can differ significantly on going from aqueous solution to protein environment. For all complexes, a permanent protonation of the newly designed ligands is suggested, leading to a charge‐assisted hydrogen bond in the protein–ligand complex. This increased strength in hydrogen bonding takes beneficial effect on binding affinity of the ligands, resulting in low‐nanomolar binders. Crystal structures and docking emphasize the importance of the newly created charge‐assisted hydrogen bond. A detailed analysis of the crystal structures in complex with substituted 2‐amino‐lin‐benzoguanines indicate pronounced disorder of the attached side chains addressing the ribose 33 binding pocket. Docking suggests multiple orientations of these side chains. Obviously, an entropic advantage of the residual mobility experienced by these ligands in the bound state is beneficial and reveals an overall improved protein binding.
From Molecular Fragments to Crystals: A UV Raman Spectroscopic Study on the Mechanism of Fe‐ZSM‐5 Synthesis
Authors: Fan Fengtao , Sun Keju , Feng Zhaochi , Xia Haian , Han Bo , Lian Yuxiang , Ying Pinliang , Li Can 
Published: February 2009

AbstractThe nucleation process of iron‐exchanged zeolite Fe‐ZSM‐5, from the assembly of distorted tetrahedrally coordinated iron species and silicate rings in the precursor to the final Fe‐ZSM‐5 crystals, as well as variations in the coordination environment of iron, were studied by UV resonance Raman spectroscopy and complementary techniques.magnified imageThe entire sequence of crystallization events of Fe‐ZSM‐5 was monitored by UV Raman spectroscopy in combination with HRTEM, UV/Vis spectroscopy, X‐ray diffraction patterns, and periodic DFT calculations. Fe‐ZSM‐5 was synthesized by an organic‐free method to avoid signal interference from the organic template in Raman spectra. Framework iron atoms with resonance Raman bands at 516, 1115, and 1165 cm−1, and a Raman band at 1016 cm−1 are detected for Fe‐ZSM‐5. In the early stage of Fe‐ZSM‐5 synthesis, the precursor contains iron atoms in distorted tetrahedral coordination and five‐ and six‐membered silicate rings. Nucleation by aggregation of the precursor species was monitored by UV Raman spectroscopy based on the resonance Raman effect, and confirmed by periodic DFT calculations. Evolution of iron species on the surface and in the bulk phase was monitored by UV Raman spectroscopy with excitation at 244 and 325 nm, as well as HRTEM. Nucleation takes place first in the core of the amorphous particles, and crystalline nuclei with Fe‐ZSM‐5 structure are formed in the core by consuming the amorphous shell. Finally the amorphous particles are completely transformed into Fe‐ZSM‐5 crystals.
Synthesis, X‐ray Single‐Crystal Structure Determination, and Magnetic Properties of [Rb(benzo[18]crown‐6)]+ Salts Containing Well‐Ordered Fulleride Trianions C603−
Authors: Boeddinghaus M. Bele , Salzinger Michael , Fässler Thomas F. 
Published: February 2009

AbstractFinally, a structure with well‐resolved C603− ions and S=1/2 spin system: The two novel title compounds have clearly S=1/2 and not S=3/2 electronic states, as expected for the occupation of the triply degenerate LUMO of C60. These structures with well‐ordered fullerene trianions show that the expected Jahn–Teller distortion is not observable in X‐ray diffraction experiments.magnified imageCrystals of the composition [Rb(benzo[18]crown‐6)]3[η3‐C60](C7H8)(C3H7NO)4.5 (1) and [Rb(benzo[18]crown‐6)]3[C60](C3H7NO)5.33(C4H8O)1.66 (2) were synthesized by reduction of C60 with elemental rubidium in a mixture of dimethylformamide/tetrahydrofuran in the presence of benzo[18]crown‐6. X‐ray single‐crystal structure determinations reveal well‐ordered C60 trianions in both compounds. In contrast to previously reported structures of compounds containing C603− ions the present structure refinements allow the description of the buckyballs with good resolution (R1/wR2 for I>2σ(I) (all data) are 0.030/0.069 (0.051/0.071) and 0.042/0.101 (0.076/0.108) for 1 and 2, respectively). In 1 the C603− unit coordinates in an η3‐fashion to one Rb atom, whose coordination sphere is completed by one benzo[18]crown‐6 and one dimethylformamide molecule. In 2 no coordination of the alkali metal atom to the C60 trianion is observed. Magnetic measurements for 1 reveal a magnetic moment of 1.74 μB, as expected for an isolated S=1/2 spin system. The high‐quality data of the present studies allowed a comparison of structural details of C603− ions with other C60n− units (n=0, 2, 3) and a discussion of the structural Jahn–Teller distortions.
On the Signalling Pathways and CuII‐Mediated Anion Indication of N‐meso‐Substituted Heptamethine Cyanine Dyes
Authors: Descalzo Ana B. , Rurack Knut 
Published: February 2009

AbstractJoin or attack: meso‐Cyclam‐substituted heptamethine cyanine dye 1 responds very differently to the presence of metal ions and protons. Whereas the former are embraced in a host–guest complex, the latter attack the cyanine π system (see picture). In the presence of CuII, 1 selectively forms near‐infrared absorbing aggregates in buffered solution that allow the determination of citrate by using colourimetry.magnified imageThree mid‐chain rigidified heptamethine cyanine dyes substituted with dimethylamino or cyclam groups at the meso position of the polymethine chain have been prepared and studied both experimentally and theoretically with respect to their spectroscopic response toward protons and various metal ions. Despite a potentially rich conformational ground‐state chemistry, the spectroscopic studies revealed that the behaviour of the dyes is in agreement with Kuhn's classic polymethine dye theory. Coordination of metal ions and protonation of the alkyl amino groups in the cyclam moiety accordingly lead to moderate bathochromic shifts in absorption and reduced Stokes shifts. In contrast, protonation of the dimethylamino‐substituted derivatives occurs at the polymethine chain, transforming the heptamethine into a trimethine‐type chromophore with concomitant gigantic spectral blueshifts. In the presence of CuII in buffered aqueous solution, the cyclam‐substituted dye selectively forms near‐infrared absorbing aggregates. The latter allow the determination of citrate under realistic conditions by changes in absorption at wavelengths greater than 800 nm, which results from a disruption of the aggregates when citrate binds to CuII. The copper ions thus act as mediators in a signalling reaction that constitutes a colourimetric displacement assay.
Reactions of Ruthenium Vinylidene and Acetylide Complexes Containing Trichloromethyl Groups: Preparation of a Cyclobutenonyl Complex by Solid‐State Photolysis
Authors: Wu Chung‐Yeh , Chou Hsien‐Hsin , Lin Ying‐Chih , Wang Yu , Liu Yi‐Hung 
Published: February 2009

AbstractSolid‐state route to a cyclobutenone: Ruthenium perchlorocyclobutenonyl complex 2 is obtained by solid‐state photoisomerization of ruthenium trichloroacetyl acetylide complex 1. The four‐membered ring is sufficiently robust that transfer of the intact ligand could be readily achieved in a reaction of 2 with an enyne. Cyclobutenedionyl complex 3 was obtained by hydrolysis of 2 in H2O/THF.magnified imageNew reactions were observed for the cationic γ‐hydroxyvinylidene complex [Ru2]CCHC(OH)(CCl3)2+ (2, [Ru2]=CpRu(PPh3)2). A rare chloroform elimination was observed when 2 was treated with nBu4NOH to give neutral acetylide complex [Ru2]CCC(O)CCl3 (3). Solid‐state photoinduced isomerization of 3 generated ruthenium perchlorocyclobutenonyl complex [Ru2]C4Cl3O (4) in high yield. This transformation was analyzed by DFT calculations, and 4 was found to be 4.22 kcal mol−1 more stable in terms of Gibbs free energy than 3. In the coupling reaction of 4 with 2‐methyl‐1‐buten‐3‐yne the four‐membered cyclic ligand is transferred to the enyne to give substituted η3‐butadienyl complex 5 containing a cyclobutenonyl group. This coupling product could be removed from the metal by HCl. Deprotonation of 2 gave γ‐hydroxyacetylide complex [Ru2]CCC(OH)(CCl3)2 (9). In the photolysis of 9 phosphine dissociation is followed by addition of HCl to give neutral vinylidene complex Cl[Ru1]CCHC(OH)(CCl3)2 (10, [Ru1]=Cp(PPh3)Ru). Complex 4 catalyzed the coupling reaction of dimethyl acetylenedicarboxylate with styrene yielding the diene PhCHCHC(CO2Me)CHCO2Me. Solid‐state structures of 3–6 and 10 were determined by single‐crystal X‐ray diffraction analysis.
CuII–Hydrotalcite as an Efficient Heterogeneous Catalyst for Huisgen [3+2] Cycloaddition
Authors: Namitharan Kayambu , Kumarraja Mayilvasagam , Pitchumani Kasi 
Published: February 2009

AbstractTop Cat! CuII–hydrotalcite (HT) is used as a catalyst for the regioselective synthesis of 1,4‐disubstituted 1,2,3‐triazoles by [3+2] cycloaddition of various azides and alkynes. The catalyst enjoys advantages such as faster reactivity, good stability, reusability, high catalytic activity without any additives at room temperature, and does not require a nitrogen atmosphere for this “click‐chemistry” transformation.magnified image