bluuebunny/crossref_metadata_2025_split huggingface dataset:
Iterative tandem catalysis of racemic AB monomers
Authors: Kanca üMit , Van Buijtenen Jeroen , Van As Bart A. C. , Korevaar Peter A. , Vekemans Jef A. J. M. , Palmans Anja R. A. , Meijer E. W. 
Published: March 2008

AbstractRacemic AB monomers encompassing a secondary hydroxy group and a methyl ester moiety were synthesized and converted to chiral polyesters by iterative tandem catalysis (ITC). The concurrent action of an enantioselective acylation catalyst (Novozym 435) and a racemization catalyst (Ru(Shvo)) results in the high conversion of the racemic monomers to enantio‐enriched polymers. Several factors are important for attaining high ee's and high molecular weights. The enantioselectivities observed for the novel AB monomers by Novozym 435 are high enough at 70 °C (E ratio ≥ 200) for the monomers to be useful for ITC. ITC of methyl 6‐hydroxyheptanoate showed that a catalyst loading of ∼1.4 mol % Ru(Shvo), 25 mg Novozym 435/mmol AB monomer, and 0.5 mmol DMP/mmol monomer employing a monomer concentration of 1 mol/L gave a monomer conversion of 94%, an ee of 91%, and an Mp of 6.0 kg/mol. Application of these conditions to the other AB monomers revealed the sensitivity of the system. Reduced enantioselectivities were observed when longer reaction times were required for attaining high conversions. These long reaction times were necessary due to the slow (or absent) racemization activity of the Ru(Shvo) catalyst as a result of catalyst deactivation. Since quantitative conversions are crucial to attain high molecular weight polymers in polycondensation reactions, we could significantly improve the system by switching to isopropyl esters of the AB monomers and/or by strict exclusion of oxygen during the ITC. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2721–2733, 2008
Synthesis, characterization, and fluorescence of pyrene‐containing eight‐arm star‐shaped dendrimer‐like copolymer with pentaerythritol core
Authors: Yuan Weizhong , Yuan Jinying , Zhou Mi , Pan Caiyuan 
Published: March 2008

AbstractNovel and well‐defined pyrene‐containing eight‐arm star‐shaped dendrimer‐like copolymers were successfully achieved by combination of esterification, atom transfer radical polymerization (ATRP), divergent reaction, ring‐opening polymerization (ROP), and coupling reaction on the basis of pentaerythritol. The reaction of pentaerythritol with 2‐bromopropionyl bromide permitted ATRP of styrene (St) to form four‐arm star‐shaped polymer (PSt‐Br)4. The molecular weights of these polymers could be adjusted by the variation of monomer conversion. Eight‐hydroxyl star‐shaped polymer (PSt‐(OH)2)4 was produced by the divergent reaction of (PSt‐Br)4 with diethanolamine. (PSt‐(OH)2)4 was used as the initiator for ROP of ε‐caprolactone (CL) to produce eight‐arm star‐shaped dendrimer‐like copolymer (PSt‐b‐(PCL)2)4. The molecular weights of (PSt‐b‐(PCL)2)4 increased linearly with the increase of monomer. After the coupling reaction of hydroxyl‐terminated (PSt‐b‐(PCL)2)4 with 1‐pyrenebutyric acid, pyrene‐containing eight‐arm star‐shaped dendrimer‐like copolymer (PSt‐b‐(PCL‐pyrene)2)4 was obtained. The eight‐arm star‐shaped dendrimer‐like copolymers presented unique thermal properties and crystalline morphologies, which were different from those of linear poly(ε‐caprolactone) (PCL). Fluorescence analysis indicated that (PSt‐b‐(PCL‐pyrene)2)4 presented slightly stronger fluorescence intensity than 1‐pyrenebutyric acid when the pyrene concentration of them was the same. The obtained pyrene‐containing eight‐arm star‐shaped dendrimer‐like copolymer has potential applications in biological fluorescent probe, photodynamic therapy, and optoelectronic devices. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2788–2798, 2008
Structure and properties of poly(ethylene terephthalate)/Na+‐montmorillonite nanocomposites prepared by solid state shear milling (S3M) method
Authors: Wang Guoli , Chen Yinghong , Wang Qi 
Published: March 2008

AbstractThis article reported a novel technology, solid state shear milling (S3M), to prepare poly(ethylene terephthalate)/Na+‐montmorillonite nanocomposites using the pristine Na+‐MMT without organic modification so as to avoid the problem that the organic modifiers, used for MMT treatment will decompose at high processing temperature of PET, and the structure and properties of the obtained samples were investigated. XRD and TEM analyses showed that Na+‐MMT layers were partially delaminated and intercalated, and uniformly dispersed in the PET matrix when suffering from the strong three dimensional shearing forces of pan‐milling. DSC analysis showed that Na+‐MMT serves as a nucleating agent, increasing the crystallization rate as well as the crystallization temperature of PET. The properties such as thermal stability and tensile strength of the PET/Na+‐MMT nanocomposites prepared by S3M got remarkably improved. Solid state shear milling (S3M) method was a simple and efficient method to get polymer/Na+‐MMT nanocomposites with pretty good performances without organic modification of pristine Na+‐MMT. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 807–817, 2008
Development of a process safety culture of chemical engineers
Authors: Mckay Maxime , Lacoursière J.P. 
Published: March 2008

AbstractChemical engineers are frequently responsible for designing and operating process facilities. These facilities could cause major accidents with consequences on site and off site. Equilibrium has to be maintained between production pressure and safety requirements. This equilibrium can only be achieved if the people involved with the process plant develop and maintain a strong process safety culture. Lessons from the Challenger, Columbia, BP Texas City accidents, etc. indicate that there are five important key organization culture themes that need to be taken into account:
Maintain sense of vulnerability
Establish an imperative for safety
Perform valid/timely hazard/risk assessments
Ensure open and frank communications
Learn and advance the culture
This paper will describe how a chemical engineer can integrate these as a safety roadmap. © 2008 American Institute of Chemical Engineers Process Saf Prog, 2008
Facile synthesis of large scale Er‐doped ZnO flower‐like structures with enhanced 1.54 μm infrared emission
Authors: Yang Wei‐Chieh , Wang Chun‐Wen , He Jr‐Hau , Chang Yu‐Cheng , Wang Jen‐Cheng , Chen Lih‐Juann , Chen Hung‐Ying , Gwo Shangir 
Published: March 2008

AbstractA new strategy to introduce metallic dopant into ZnO structures by a wet chemical reaction is presented. Single‐crystal Er‐doped ZnO flower‐like structures have been synthesized on ZnO‐coated silicon substrate by a low temperature hydrothermal process. The Er‐doped ZnO structures exhibit promising 1.54 μm photoluminescence emission for optoelectronic communication. The successful doping has been confirmed by the X‐ray diffraction, transmission electron microscopy, X‐ray photoemission spectroscopy and photoluminescence measurements. The achievement to introduce Er dopants into ZnO flower‐like structures by the time‐ and cost‐effective wet chemical reaction at low temperature for the first time has vast potential to scale up for possible applications. The photoluminescence properties are significantly improved compared to that reported in the literature for the Er‐doped nanowires and thin films and shall be much more applicable in optical and communication devices. The flower‐like structures are expected to be advantageous in serving as a multi‐directional infrared emitters and/or detectors. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Introducing crystalline rare‐earth oxides into Si technologies
Authors: Osten H. J. , Laha A. , Czernohorsky M. , Bugiel E. , Dargis R. , Fissel A. 
Published: March 2008

AbstractThe ability to integrate crystalline metal oxide dielectric barrier layers into silicon structures can open the way for a variety of novel applications which enhances the functionality and flexibility ranging from high‐K replacements in future MOS devices to oxide/silicon/oxide heterostructures for nanoelectronic application in quantum‐effect devices. We present results for crystalline gadolinium oxides on silicon in the cubic bixbyite structure grown by solid source molecular beam epitaxy. Additional oxygen supply during growth improves the dielectric properties significantly. Experimental results for Gd2O3‐based MOS capacitors grown under optimized conditions show that these layers are excellent candidates for application as very thin high‐K materials replacing SiO2 in future MOS devices. Epitaxial growth of lanthanide oxides on silicon without any interfacial layer has the advantage of enabling defined interfaces engineering. We will show that the electrical properties of epitaxial Gd2O3 thin films on Si substrates can further be improved significantly by an atomic control of interfacial structures. Finally, we will present a new approach for nanostructure formation which is based on solid‐phase epitaxy of the Si quantum‐well combined with simultaneous vapor‐phase epitaxy of the insulator on top of the quantum‐well. Ultra‐thin single‐crystalline Si buried in a single‐crystalline insulator matrix with sharp interfaces was obtained by this approach on Si(111). In addition, structures consisting of a single‐crystalline oxide layer with embedded Si nanoclusters for memory applications will also be demonstrated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tunneling phenomena in carbon nanotube field‐effect transistors
Authors: Knoch Joachim , Appenzeller Joerg 
Published: March 2008

AbstractIn the present article we will discuss the electronic trans‐ port properties of carbon nanotube field‐effect transistors (CNFETs). Three different device concepts will be studied in more detail: Schottky‐barrier CNFETs with metallic source and drain contacts, conventional‐type CNFETs with doped nanotube segments as source and drain electrodes and finally a new concept, the tunneling CNFET. As it turns out, tunneling phenomena play a prominent role in all three CNFET designs and determine their electrical behavior to a large extend. In addition, the one‐dimensionality of the electronic transport makes them ideally suited for novel device architecture such as the tunneling CNFET. Analytical as well as simulation results will be given and compared with each other and with experimental data in order to explain the different influences on the electronic transport in CNFETs and thus on the device behavior. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of the free charge carrier properties at the ZnO‐sapphire interface in a‐plane ZnO films studied by generalized infrared ellipsometry
Authors: Sturm C. , Chavdarov T. , Schmidt‐Grund R. , Rheinländer B. , Bundesmann C. , Hochmuth H. , Lorenz M. , Schubert M. , Grundmann M. 
Published: March 2008

AbstractThe free charge carrier properties at the film‐substrate interface of non‐polar ZnO films were investigated by generalized infrared spectroscopic ellipsometry in dependence on film thickness and annealing time. For all samples a highly‐conductive film‐substrate interface layer was found. It was observed that the charge density at the interface increases with increasing film thickness and decreases with increasing annealing time. Possible explanations could be the diffusion of Al from the substrate into the ZnO film, the formation of zinc aluminate, or structural changes, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Immunodetection using computer screen photo‐assisted ellipsometry
Authors: Bakker J. W. P. , Arwin H. , Lundström I. , Filippini D. 
Published: March 2008

AbstractDetection of antibody‐antigen reactions is demonstrated by measuring changes in reflectance of light polarized parallel to the plane of incidence, using a computer screen as light source and a web camera as detector, giving results similar to traditional off‐null ellipsometry and in accordance with a simplified theoretical model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of ion track and shapes with damage simulations on the base of ellipsometric and backscattering spectrometric measurements
Authors: Polgár O. , Fried M. , Khanh N. , Petrik P. , Bársony I. 
Published: March 2008

AbstractOn the base of geometrical and statistical considerations a damage simulator was created in order to determine the ion track‐radius and ‐shape of ion‐implantation caused damage in single‐crystalline Si. Damage vs. dose curves calculated by spectroscopic ellipsometry (SE) and Rutherford backscattering/channeling spectrometry (RBS/C) measurements, using different doses of 100 keV Xe implantation, gave information about the damage profile in depth. Both methods are required, because of dose‐dependent discrepancies of SE compared with RBS/C [Fried et al., Thin Solid Films 455/456, 404 (2004)]. Different kinds of damage models were investigated to calculate the ion track‐radius and to describe the damages in depth and the shape of ion track. Comparing directly the simulated and the measured damage vs. dose curves, the damage function and the other simulation parameters were optimized and hence the ion track size and even the shape can be determined. The dose dependent mean size of the unchanged crystalline regions, obtained from the simulation was correlated with the complex dielectric functions, obtained from the SE analysis. The results clearly show the effect of decreasing size of the unchanged crystalline regions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural and optical properties of ZrO2 and Al2O3 thin films and Bragg reflectors grown by pulsed laser deposition
Authors: Sellmann J. , Sturm Ch. , Schmidt‐Grund R. , Czekalla Ch. , Lenzner J. , Hochmuth H. , Rheinländer B. , Lorenz M. , Grundmann M. 
Published: March 2008

AbstractZrO2‐Al2O3 Bragg reflectors for future application in ZnO based resonators grown by pulsed laser deposition on c‐plane sapphire and silicon substrates show a reflectivity up to 99.8% with a layer pair number of 12.5. Layer thicknesses obtained from standard ellipsometry agree very well with thicknesses observed by transmission scanning electron microscopy. A very smooth surface roughness of Ra = 0.5 nm was observed for these Bragg reflectors. ZnO thin films grown on bulk c‐plane sapphire and on Bragg reflectors revealed comparable high photoluminescence intensity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of heteroepitaxy on nanoscopically roughened (001)Si by real‐time spectroscopic polarimetry
Authors: Liu X. , Kim I.‐K. , Aspnes D. E. 
Published: March 2008

AbstractWe use a real‐time spectroscopic polarimeter integrated with an organometallic chemical vapor deposition system to investigate growth of GaP on Si, and particularly nanoscopically roughened (nr‐)Si. We find nanoroughening is necessary to increase the density of nucleation sites and decrease reactant mobility and thereby grow continuous films instead of widely spaced islands. The nrSi surfaces are more highly reactive to the trimethylgallium precursor than III‐V growth surfaces, leading to the appearance of metallic Ga if standard growth conditions are used in the initial phase of heteroepitaxy. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of ion concentration on refractive indices of fluids measured by the minimum deviation technique
Authors: Berlind T. , Pribil G. K. , Thompson D. , Woollam J. A. , Arwin H. 
Published: March 2008

AbstractThe prism minimum deviation technique has been used to measure the fluid dependence of refractive indices. Fluids with varying ion concentration (0 to 1.0 M) and varying protein concentration (0.01‐10 mg/ml) have been examined and the measurements show that these parameters influence the refractive index values. Also it is shown by simulations that it is important to take the change of refractive index of the fluid into account when evaluating insitu protein adsorption measurements. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Conceptualizations of argumentation from science studies and the learning sciences and their implications for the practices of science education
Authors: Bricker Leah A. , Bell Philip 
Published: March 2008

AbstractArgumentation has become an increasingly recognized focus for science instruction‐‐‐as a learning process, as an outcome associated with the appropriation of scientific discourse, and as a window onto the epistemic work of science. Only a small set of theoretical conceptualizations of argumentation have been deployed and investigated in science education, however, while a plethora of conceptualizations have been developed in the interdisciplinary fields associated with science studies and the learning sciences. This paper attempts to review a range of such theoretical conceptualizations of argumentation and discuss the possible implications for the orchestration of science education; the goal being that the science education research community might consider a broader range of argumentation forms and roles in conjunction with the learning of science. © 2008 Wiley Periodicals, Inc.Sci Ed92:473–493, 2008
Demotivators of software process improvement: an empirical investigation
Authors: Niazi Mahmood , Ali Babar Muhammad , Katugampola Nolin Mark 
Published: March 2008

AbstractWe have conducted an empirical study with 23 Vietnamese software practitioners to determine Software Process Improvement (SPI) demotivators. We have compared the demotivators identified by the Vietnamese practitioners with the demotivators identified by UK practitioners. The main objective of this study is to provide SPI managers with insight into the nature of factors that can hinder the success of a SPI program, so that SPI managers can better manage those demotivators to maximize practitioners' support for an SPI program.We used face‐to‐face questionnaire‐based survey sessions for gathering data. We also asked the participants to rank each identified SPI demotivator on a five‐point scale (high, medium, low, zero or do not know) to determine the perceived importance of each demotivator. From this, we proposed the notion of ‘perceived value’ associated with each identified demotivator.Our findings identify the ‘high’ and ‘medium’ perceived value demotivators that can undermine SPI initiatives. The findings also show that there are differences in SPI demotivators across practitioners' groups (i.e., developers and managers) and across organisational sizes (i.e. large and small‐to‐medium). Moreover, our results reveal the similarities and differences between SPI demotivators as perceived by practitioners in Vietnam and the United Kingdom. The findings are expected to provide SPI managers with insight to design and implement suitable strategies to deal with the identified SPI demotivators. Copyright © 2008 John Wiley & Sons, Ltd.
Effects of 2,4‐dichlorophenol on the expression of vitellogenin and estrogen receptor genes and physiology impairments in Chinese rare minnow (Gobiocypris rarus)
Authors: Zhang Xiaoyan , Zha Jinmiao , Li Wei , Yang Lihua , Wang Zijian 
Published: March 2008

Abstract2,4‐Dichlorophenol (2,4‐DCP) is known as a toxicant, but unknown as an environmental endocrine disruptor. In the present work, Chinese rare minnow (Gobiocypris rarus) was exposed to 0.03, 0.3, and 3 mg/L 2,4‐DCP for 3 d and 0.1, 0.3, and 1 mg/L 2,4‐DCP for 21 d, respectively. Endpoints including somatic index, vitellogenin (VTG) mRNA and protein level, estrogen receptor (ER) mRNA and histopathology were measured. In the 3‐d exposure experiment, the effect concentrations were 0.3 mg/L and above, and in 21‐d exposure, the effect concentrations were 0.1 mg/L and above. When exposed to the effect concentrations, GSI was significantly reduced for both male and female, ER mRNA was upregulated in male and downregulated in female. There were no significant variations of VTG mRNA in both male and female in 3‐d exposure and in male in 21‐d exposure. However, VTG mRNA in female in 21‐d exposure was upregulated, corresponding to an increase of VTG protein in serum. Histopathological observation showed that ovaries were degenerated in the effect concentrations, where follicular atresias were more frequently observed. Because the sex hormones related genes and toxicological endpoints were affected in the dose‐dependent manner, the results suggest that 2,4‐DCP could be a potential endocrine disruptor and might cause adverse effects in female sex organs through interruption of ER‐mediated processes. © 2008 Wiley Periodicals, Inc. Environ Toxicol, 2008.
Oxygen decline in biotesting of environmental samples—Is there a need for consideration in the acute zebrafish embryo assay?
Authors: Küster Eberhard , Altenburger Rolf 
Published: March 2008

AbstractEnvironmental samples such as groundwater, sediment pore water, native or freeze dried sediments may be difficult to analyze for toxic effects with organismic aquatic bioassays. These samples might evoke low oxygen concentration or oxygen depletion during the test. The toxicity assessment could thus be confounded by low oxygen concentrations. The acute zebrafish embryo assay was used to analyze the influence of oxygen deficit on the embryonic development in the first 48 h post fertilization. Embryos were exposed to varying oxygen concentrations ranging from <30 to >80% oxygen saturation of water. A clear concentration dependent retardation of fish embryo development was observed. Because of a retarded development toxic thresholds of environmental samples which might include substances slowing down the development will be altered. For the purpose of identification of critical contaminants in complex environmental samples, it is proposed to actively aerate environmental samples which are likely to be oxygen depleted during the duration of the zebrafish embryo bioassay. © 2008 Wiley Periodicals, Inc. Environ Toxicol, 2008.
New charts for ultrasound dating of pregnancy and assessment of fetal growth: longitudinal data from a population‐based cohort study
Authors: Verburg B. O. , Steegers E. A. P. , De Ridder M. , Snijders R. J. M. , Smith E. , Hofman A. , Moll H. A. , Jaddoe V. W. V. , Witteman J. C. M. 
Published: March 2008

AbstractObjectivesCorrect assessment of gestational age and fetal growth is essential for optimal obstetric management. The objectives of this study were, first, to develop charts for ultrasound dating of pregnancy based on crown–rump length and biparietal diameter and, second, to derive reference curves for normal fetal growth based on biparietal diameter, head circumference, transverse cerebellar diameter, abdominal circumference and femur length from 10 weeks of gestational age onwards.MethodsA total of 8313 pregnant women were included for analysis in this population‐based prospective cohort study. All women had repeated ultrasound assessments to examine fetal growth.ResultsCharts for ultrasound dating of pregnancy, based on crown–rump length and biparietal diameter, were derived. Internal validation with the actual date of delivery showed that ultrasound imaging provided reliable gestational age estimates. Up to 92% of deliveries took place within 37–42 weeks of gestation if gestational age was derived from ultrasound data, compared with 87% based on a reliable last menstrual period. The earlier the ultrasound assessment the more accurate the prediction of date of delivery. After 24 weeks of gestation a reliable last menstrual period provided better estimates of gestational age. Reference curves for normal fetal growth from 10 weeks of gestational age onwards were derived.ConclusionsCharts for ultrasound dating of pregnancy and reference curves for fetal biometry are presented. The results indicate that, up to 24 weeks of pregnancy, dating by ultrasound examination provides a better prediction of the date of delivery than does last menstrual period. The earlier the ultrasound assessment in pregnancy, preferably between 10 and 12 weeks, the better the estimate of gestational age. Copyright © 2008 ISUOG. Published by John Wiley & Sons, Ltd.