bluuebunny/crossref_metadata_2025_split huggingface dataset:
Syntheses and characteristics of polyimides for the applications to alignment film for liquid crystal display
Authors: Lee Sang Jin , Ha Chang‐Sik , Lee Jin Kook 
Published: August 2002

AbstractIn this work, several polyimides (PIs) containing diphenyl ether group were synthesized and characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. The relationship between the surface structures and the molecular chain conformations of the PIs, whether helical or zigzag, was discussed. The effects of the molecular chain conformations of the PIs on the pretilt angles of liquid crystal molecules were systematically investigated. The surface orientations of polyimides whose chains adopt zigzag and planar conformations were less improved by rubbing treatment than those of polyimides whose chains adopt helical and nonplanar conformations, because the polyimide chains of zigzag and planar conformation are easily packed. The polyimides, whose chains adopt helical and nonpolar conformations, gave larger pretilt angles than the polyimides whose chains adopt zigzag and planar conformations. The pretilt angles measured under the condition of rubbing depth of 0.5 mm were smaller than under the condition of rubbing depth of 0.3 mm. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2365–2371, 2001
Analysis of the crosslinking process of a phenolic resin by thermal scanning rheometry
Authors: Laza J. M. , Vilas J. L. , Rodríguez M. , Garay M. T. , Mijangos F. , León L. M. 
Published: August 2002

AbstractThe curing reaction of a phenolic resin (resole type) carried out in the absence of an initiator was studied by thermal scanning rheometry under isothermal conditions at temperatures from 70 to 105°C. The same curing reaction was studied in the presence of an acid as a catalyst in the temperature range of 50–80°C. The gel time, which was defined by several criteria, was found to be a good parameter to determine the apparent activation energy of this process. An empirical model was used to predict the change in complex viscosity with time until the gel time was reached. If first‐order kinetics were assumed, the apparent kinetic constant of the curing reaction could be obtained. Furthermore, the effect that the addition of water and free phenol had on the curing process of this type of resin was studied. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 57–65, 2002
Research anxiety and students' perceptions of research: An experiment. Part II. Content analysis of their writings on two experiences
Authors: Kracker Jacqueline , Wang Peiling 
Published: August 2002

AbstractThis is Part II of an experimental study investigating students' perceptions of research and research paper anxiety. The study integrates quantitative and qualitative designs to collect complimentary data. The participants were students in four sections of an upper division undergraduate course on technical and professional writing during the fall of 1999. A survey instrument used the Critical Incident Technique to solicit writings in students' own words about a memorable past research and writing experience at the beginning of the semester and the current research and writing at the end of the semester. The quantitative part of the survey measured students' perceptions about research using a questionnaire with five‐point Likert scale, and students' anxiety levels using a standard state anxiety test (STAI Y‐1). The first article, Part I, provides a detailed description of the experimental design and reports on quantitative results. This article reports on content analysis of students' writings about their experiences of the two research projects. Analysis of the data confirmed Kuhlthau's Information Search Process (ISP) model and revealed additional affective and cognitive aspects related to research and writing.
Taming the fierce roller: an “enhanced” understanding of cellular differentiation in Volvox
Authors: Miller Stephen M. 
Published: August 2002

AbstractFew organisms offer a better opportunity to explore the mechanisms of cellular differentiation, and their origins, than Volvox. Volvox consists of just two cell types, germ and soma, and is the most complex member of a family of green algae that includes unicellular and multicellular relatives. At the heart of the cell‐fate determination program of Volvox carteri is the regA gene, which encodes a putative transcriptional repressor that prevents somatic cells from expressing reproductive functions. Stark et al.(1) have dissected the regA gene to determine how its expression is restricted to somatic cells. Their results suggest that regA expression is controlled by multiple enhancers, the most important of which prevents transcription in reproductive cells. While these findings shed light on Volvox development, they also raise a new set of questions about the mechanisms that control the germ–soma dichotomy in this organism. BioEssays 24:3–7, 2002. © 2002 John Wiley & Sons, Inc.
Surface‐enhanced Raman and steady fluorescence study of interaction between antitumoral drug 9‐aminoacridine and trypsin‐like protease related to metastasis processes, guanidinobenzoatase
Authors: Murza Adrian , Sánchez‐Cortés Santiago , García‐Ramos José V. 
Published: August 2002

AbstractFluorescence spectroscopy and surface‐enhanced Raman spectroscopy (SERS) were applied to study the interaction of the antitumoral drug 9‐aminoacridine (9AA) with a trypsin‐like protease guanidinobenzoatase (GB) extracted from a mouse Erlich tumor. As a consequence of this interaction, a strong 9AA exciplex emission was detected in the emission fluorescence spectra at certain drug and enzyme concentrations. A SERS study was accomplished on silver colloids at several excitation wavelengths in order to obtain more information about the interaction mechanism. The results derived from Raman spectroscopy indicated that 9AA in the amino monomeric form may interact with the enzyme by means of two different bonds: an ionic bond with a negatively charged amino acid and a ring stacking interaction with an aromatic residue placed in the catalytic site of GB. This interaction mechanism was responsible for a strong exciplex emission detected at a longer wavelength than the expected value of the normal fluorescence emission. Moreover, the GB concentration dependence of the interaction suggested that the drug was sensitive to the quaternary structure of the enzyme. © 2001 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 85–94, 2001
Dynamics and orientation of transmembrane peptide from bacteriorhodopsin incorporated into lipid bilayer as revealed by solid state 31P and 13C NMR spectroscopy
Authors: Kimura Shigeki , Naito Akira , Tuzi Satoru , Saitô Hazime 
Published: August 2002

Abstract13C and 31P NMR spectra of a transmembrane peptide, [1‐13C]Ala14‐labeled A(6–34), of bacteriorhodopsin incorporated into dimyristoylphosphatidylcholine (DMPC) bilayer were recorded to clarify its dynamics and orientation in the lipid bilayer. This peptide is shown to take an α‐helical form both in liquid crystalline and gel phases, as viewed from the conformation dependent 13C chemical shifts. In addition, this peptide undergoes rapid rigid‐body rotation about the helical axis at ambient temperature as viewed from the axially symmetric 13C chemical shift anisotropy, whereas this symmetric anisotropy is changed to an asymmetric pattern at temperatures below 10°C. We further incorporated the peptide into the spontaneously aligned DMPC bilayer to applied magnetic field, induced by dynorphin (dynorphin:DMPC =1:10), a heptadeca‐opioid peptide with very high affinity to opioid receptor, in order to gain insight into its orientation in the bilayer. This magnetically aligned system turned out to be persistent even at 0°C as viewed from 31P NMR spectra of the lipid bilayer, after this peptide was incorporated into this system [A(6–34): dynorphin: DMPC = 4:10:100]. It was found from the 13C NMR spectra of [1‐13C]Ala14 A(6–34) that the helical axis of A(6–34) is oriented parallel to the bilayer normal irrespective of the presence or absence of reorientation motion about the helical axis at a temperature above the lowered gel to liquid crystalline phase transition. © 2002 John Wiley & Sons, Inc. Biopolymers 63: 122–131, 2002
A biosensor for the detection of triazine and phenylurea herbicides designed using Photosystem II coupled to a screen‐printed electrode
Authors: Koblížek Michal , Malý Jan , Masojídek Jiří , Komenda Josef , Kučera Tomáš , Giardi Maria T. , Mattoo Autar K. , Pilloton Roberto 
Published: August 2002

AbstractA biosensor for the detection of triazine‐ and phenylurea‐type herbicides was constructed using isolated Photosystem II (PS II) complexes as a biosensing element. PSII isolated from the thermophilic cyanobacterium Synechococcus elongatus was immobilized on the surface of a screen‐printed sensor composed of a graphite working electrode and Ag/AgCl reference electrode deposited on a polymeric substrate. The biosensor was mounted in a flow microcell with illumination. The principle of the detection was based on the fact that herbicides selectively block PSII electron transport activity in a concentration‐dependent manner. Changes of the activity were registered amperometrically as the rate of photoreduction of an artificial electron acceptor. The setup resulted in a reusable herbicide biosensor with a good stability (half‐life of 24 h) and limit of detection of approximately 10−9 M for diuron, atrazine and simazine. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 78: 110–116, 2002; DOI 10.1002/bit.10190
Efficiency of embryoid body formation and hematopoietic development from embryonic stem cells in different culture systems
Authors: Dang Stephen M. , Kyba Michael , Perlingeiro Rita , Daley George Q. , Zandstra Peter W. 
Published: August 2002

AbstractEmbryonic stem (ES) cells have tremendous potential as a cell source for cell‐based therapies. Realization of that potential will depend on our ability to understand and manipulate the factors that influence cell fate decisions and to develop scalable methods of cell production. We compared four standard ES cell differentiation culture systems by measuring aspects of embryoid body (EB) formation efficiency and cell proliferation, and by tracking development of a specific differentiated tissue type—blood—using functional (colony‐forming cell) and phenotypic (Flk‐1 and CD34 expression) assays. We report that individual murine ES cells form EBs with an efficiency of 42 ± 9%, but this value is rarely obtained because of EB aggregation—a process whereby two or more individual ES cells or EBs fuse to form a single, larger cell aggregate. Regardless of whether EBs were generated from a single ES cell in methylcellulose or liquid suspension culture, or aggregates of ES cells in hanging drop culture, they grew to a similar maximum cell number of 28,000 ± 9,000 cells per EB. Among the three methods for EB generation in suspension culture there were no differences in the kinetics or frequency of hematopoietic development. Thus, initiating EBs with a single ES cell and preventing EB aggregation should allow for maximum yield of differentiated cells in the EB system. EB differentiation cultures were also compared to attached differentiation culture using the same outputs. Attached colonies were not similarly limited in cell number; however, hematopoietic development in attached culture was impaired. The percentage of early Flk‐1 and CD34 expressing cells was dramatically lower than in EBs cultured in suspension, whereas hematopoietic colony formation was almost completely inhibited. These results provide a foundation for development of efficient, scalable bioprocesses for ES cell differentiation, and inform novel methods for the production of hematopoietic tissues. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 78: 442–453, 2002.
A kinetic model for enzyme interfacial activity and stability: pa‐hydroxynitrile lyase at the diisopropyl ether/water interface
Authors: Cascão Pereira Luis G. , Hickel Andrea , Radke Clayton J. , Blanch Harvey W. 
Published: August 2002

AbstractA kinetic framework is developed to describe enzyme activity and stability in two‐phase liquid–liquid systems. In particular, the model is applied to the enzymatic production of benzaldehyde from mandelonitrile by Prunus amygdalus hydroxynitrile lyase (pa‐Hnl) adsorbed at the diisopropyl ether (DIPE)/aqueous buffer interface (pH = 5.5). We quantitatively describe our previously obtained experimental kinetic results (Hickel et al., 1999; 2001), and we successfully account for the aqueous‐phase enzyme concentration dependence of product formation rates and the observed reaction rates at early times. Multilayer growth explains the early time reversibility of enzyme adsorption at the DIPE/buffer interface observed by both enzyme‐activity and dynamic‐interfacial‐tension washout experiments that replace the aqueous enzyme solution with a buffer solution. The postulated explanation for the unusual stability of pa‐Hnl adsorbed at the DIPE/buffer interface is attributed to a two‐layer adsorption mechanism. In the first layer, slow conformational change from the native state leads to irreversible attachment and partial loss of catalytic activity. In the second layer, pa‐Hnl is reversibly adsorbed without loss in catalytic activity. The measured catalytic activity is the combined effect of the deactivation kinetics of the first layer and of the adsorption kinetics of each layer. For the specific case of pa‐Hnl adsorbed at the DIPE/buffer interface, this combined effect is nearly constant for several hours resulting in no apparent loss of catalytic activity. Our proposed kinetic model can be extended to other interfacially active enzymes and other organic solvents. Finally, we indicate how interfacial‐tension lag times provide a powerful tool for rational solvent selection and enzyme engineering. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 78: 595–605, 2002.
Neutral fat hydrolysis and long‐chain fatty acid oxidation during anaerobic digestion of slaughterhouse wastewater
Authors: Masse L. , Massé D. I. , Kennedy K. J. , Chou S. P. 
Published: August 2002

AbstractNeutral fat hydrolysis and long‐chain fatty acid (LCFA) oxidation rates were determined during the digestion of slaughterhouse wastewater in anaerobic sequencing batch reactors operated at 25°C. The experimental substrate consisted of filtered slaughterhouse wastewater supplemented with pork fat particles at various average initial sizes (Din) ranging from 60 to 450 μm. At the Din tested, there was no significant particle size effect on the first‐order hydrolysis rate. The neutral fat hydrolysis rate averaged 0.63 ± 0.07 d−1. LCFA oxidation rate was modelled using a Monod‐type equation. The maximum substrate utilization rate (kmax) and the half‐saturation concentration (Ks) averaged 164 ± 37 mg LCFA/L/d and 35 ± 31 mg LCFA/L, respectively. Pork fat particle degradation was mainly controlled by LCFA oxidation rate and, to a lesser extent, by neutral fat hydrolysis rate. Hydrolysis pretreatment of fat‐containing wastewaters and sludges should not substantially accelerate their anaerobic treatment. At a Din of 450 μm, fat particles were found to inhibit methane production during the initial 20 h of digestion. Inhibition of methane production in the early phase of digestion was the only significant effect of fat particle size on anaerobic digestion of pork slaughterhouse wastewater. Soluble COD could not be used to determine the rate of lipid hydrolysis due to LCFA adsorption on the biomass. © 2002 Government of Canada. Exclusive worldwide publication rights in the article have been transferred to Wiley Periodicals, Inc. Biotechnol Bioeng 79: 43–52, 2002.
The metabolic burden of the PGK1 and ADH2 promoter systems for heterologous xylanase production by Saccharomyces cerevisiae in defined medium
Authors: Görgens Johann F. , van Zyl Willem H. , Knoetze Johannes H. , Hahn‐Hägerdal Bärbel 
Published: August 2002

AbstractFive recombinant S. cerevisiae strains were cultivated under identical conditions to quantify the molecular basis of the metabolic burden of heterologous gene expression, and to evaluate mechanisms for the metabolic burden. Two recombinant S. cerevisiae strains, producing Trichoderma reesei xylanase II under control of either the PGK1 or ADH2 promoters, were compared quantitatively with three references strains, where either the heterologous xylanase II (XYN2) gene, or the heterologous gene and the promoter and terminator were omitted from the recombinant plasmid. Neither the replication of multiple copies of the 2‐μm‐based YEp352 plasmid nor the replication the foreign XYN2 gene represented a metabolic burden to the cell, as the growth of the host organism was not affected. The inclusion of a glycolytic promoter on the recombinant plasmid, however, reduced the maximum specific growth rate (12% to 15%), biomass yield on glucose (8% to 11%), and specific glucose consumption rate (6% to 10%) of the recombinant strains. The presence of the heterologous XYN2 gene on the recombinant plasmid caused a further reduction in the maximum specific growth rate (11% to 14%), biomass yield (4%), and specific glucose consumption rate (12%) of the host strain during active gene expression, which was dictated by the regulatory characteristics of the promoter utilized. The metabolic effect of foreign gene expression was disproportionally large, with respect to on the amount of heterologous protein produced. This was most likely due to an increased energetic demand for the expression of a foreign gene and/or a competition for limiting amounts of transcription or translation factors, biosynthetic precursors or metabolic energy. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 73: 238–245, 2001.
A multivariate approach to combine univariate calibration information
Authors: Liao Jason J. Z. 
Published: August 2002

AbstractIt is common practice to calibrate a common value by combining information from different sources, e.g. days, instruments, laboratories, etc. Under each individual source a perfect univariate calibration can be used to calibrate the unknown. Then the common unknown can be estimated by combining the estimates from each source as a weighted mean (Johnson DJ, Krishnamoorthy K. J. Am. Statist. Assoc. 1996; 91: 1707–1715). However, this estimator can be obtained as a special solution directly from a multivariate calibration setting by combining information first and then estimating the common value. Two data sets were analyzed and they showed that the multivariate approach can possibly improve the univariate approach based on the closeness criterion. Copyright © 2001 John Wiley & Sons, Ltd.
Identification of membrane proteins in the hyperthermophilic archaeon Pyrococcus furiosus using proteomics and prediction programs
Authors: Holden James F. , Poole Farris L. , Tollaksen Sandra L. , Giometti Carol S. , Lim Hanjo , Yates John R. , Adams Michael W. W. 
Published: August 2002

AbstractCell‐free extracts from the hyperthermophilic archaeon Pyrococcus furiosus were separated into membrane and cytoplasmic fractions and each was analyzed by 2D‐gel electrophoresis. A total of 66 proteins were identified, 32 in the membrane fraction and 34 in the cytoplasmic fraction. Six prediction programs were used to predict the subcellular locations of these proteins. Three were based on signal‐peptides (SignalP, TargetP, and SOSUISignal) and three on transmembrane‐spanning α‐helices (TSEG, SOSUI, and PRED‐TMR2). A consensus of the six programs predicted that 23 of the 32 proteins (72%) from the membrane fraction should be in the membrane and that all of the proteins from the cytoplasmic fraction should be in the cytoplasm. Two membrane‐associated proteins predicted to be cytoplasmic by the programs are also predicted to consist primarily of transmembrane‐spanning β‐sheets using porin protein models, suggesting that they are, in fact, membrane components. An ATPase subunit homolog found in the membrane fraction, although predicted to be cytoplasmic, is most likely complexed with other ATPase subunits in the membrane fraction. An additional three proteins predicted to be cytoplasmic but found in the membrane fraction, may be cytoplasmic contaminants. These include a chaperone homolog that may have attached to denatured membrane proteins during cell fractionation. Omitting these three proteins would boost the membrane‐protein predictability of the models to near 80%. A consensus prediction using all six programs for all 2242 ORFs in the P. furiosus genome estimates that 24% of the ORF products are found in the membrane. However, this is likely to be a minimum value due to the programs' inability to recognize certain membrane‐related proteins, such as subunits associated with membrane complexes and porin‐type proteins. Copyright © 2001 John Wiley & Sons, Ltd.
A genomic approach for the identification and classification of genes involved in cell wall formation and its regulation in Saccharomyces cerevisiae
Authors: de Groot Piet W. J. , Ruiz Cristina , Vázquez de Aldana Carlos R. , Dueňas Encarnación , Cid Víctor J. , Del Rey Francisco , Rodríquez‐Peña José M. , Pérez Pilar , Andel Annemiek , Caubín Julio , Arroyo Javier , García Juan C. , Gil Concha , Molina María , García Luis J. , Nombela César , Klis Frans M. 
Published: August 2002

AbstractUsing a hierarchical approach, 620 non‐essential single‐gene yeast deletants generated by EUROFAN I were systematically screened for cell‐wall‐related phenotypes. By analyzing for altered sensitivity to the presence of Calcofluor white or SDS in the growth medium, altered sensitivity to sonication, or abnormal morphology, 145 (23%) mutants showing at least one cell wall‐related phenotype were selected. These were screened further to identify genes potentially involved in either the biosynthesis, remodeling or coupling of cell wall macromolecules or genes involved in the overall regulation of cell wall construction and to eliminate those genes with a more general, pleiotropic effect. Ninety percent of the mutants selected from the primary tests showed additional cell wall‐related phenotypes. When extrapolated to the entire yeast genome, these data indicate that over 1200 genes may directly or indirectly affect cell wall formation and its regulation. Twenty‐one mutants with altered levels of β1,3‐glucan synthase activity and five Calcofluor white‐resistant mutants with altered levels of chitin synthase activities were found, indicating that the corresponding genes affect β1,3‐glucan or chitin synthesis. By selecting for increased levels of specific cell wall components in the growth medium, we identified 13 genes that are possibly implicated in different steps of cell wall assembly. Furthermore, 14 mutants showed a constitutive activation of the cell wall integrity pathway, suggesting that they participate in the modulation of the pathway either directly acting as signaling components or by triggering the Slt2‐dependent compensatory mechanism. In conclusion, our screening approach represents a comprehensive functional analysis on a genomic scale of gene products involved in various aspects of fungal cell wall formation. Copyright © 2001 John Wiley & Sons, Ltd.