bluuebunny/crossref_metadata_2025_split huggingface dataset:
Succinoylation of wheat straw hemicelluloses in N,N‐dimethylformamide/lithium chloride systems
Authors: Sun Runcang , Sun X F , Zhang F Y 
Published: September 2002

AbstractThe chemical modification of native wheat straw hemicelluloses with succinic anhydride using N,N‐dimethylformamide/lithium chloride system as solvent and pyridine and/or 4‐dimethyaminopyridine as catalyst has been examined. In particular, the progress of the succinoylation reaction is studied as a function of the molar ratio of succinic anhydride/anhydroxylose unit in native hemicelluloses from 1:1 to 5:1, DMAP concentration 0.025–0.20 g, reaction temperature 40–140 °C, and reaction time 2–12 h with succinic anhydride. The degree of substitution of succinylated hemicelluloses ranges between 0.4 and 1.5 depending on the experimental conditions. FTIR and 1H NMR spectroscopic characterization of the esterified polymers indicates a monoester substitution. The thermal stability of the esterified polymer decreases slightly upon chemical modification, but no significant further decrease in thermal stability is observed for DS ≥ 0.7.© 2001 Society of Chemical Industry
Lead–yeast hexokinase interaction: modifications to protein structure caused by the metal
Authors: Teijón C , Olmo R , Socorro J M , Blanco M D , Romero A , Teijón J M 
Published: September 2002

AbstractThe interaction between lead and yeast hexokinase has been studied. Lead provokes a large variation in the aggregation state of the protein, forming bigger structures of high molecular mass. This phenomenon is characterized by a small modification in the tridimensional structure and a great variation in the secondary structure. There is a loss in α‐helix which is compensated by an enhancement in β‐sheet. The polypeptide chain is more stable in the β‐sheet structure corresponding to the aggregate forms. During this change the enzyme maintains a high level of activity in the monomer and also in the aggregate form. This implies that the enzyme function is not greatly affected by the change, and active sites are retained without important modifications. According to kinetic measurements the ATP site is more affected than the glucose site. There is a mixed type inhibition with a main competitive component when glucose acts as a variable substrate.© 2001 Society of Chemical Industry
Characteristics of bifacial solar cells under bifacial illumination with various intensity levels
Authors: Ohtsuka H. , Sakamoto M. , Koyama M. , Tsutsui K. , Uematsu T. , Yazawa Y. 
Published: September 2002

AbstractThe characteristics of bifacial solar cells with different rear structures were investigated under front, rear and bifacial illumination with an intensity of 0.4–4.2 suns. Five kinds of solar cells, rear flat local‐BSF cells, rear textured local‐BSF cells (textured RLB cells), rear total‐BSF cells, rear floating‐emitter cells, and triode cells with double‐sided junctions, were tested. The I–V characteristics of the cells under bifacial illumination were measured with a newly designed measurement system that simultaneously illuminated both surfaces of the cells. In the short‐circuit current (JSC) and the saturation current evaluations, the bifacial illumination effect, which means that the power output of the cell is intrinsically improved by adding rear illumination, was not observed. Although the RLB cells showed a nonlinear increase inJSCand enhancedVOC, these increases did not make a practical contribution to extra output because of the low levels of these characteristics. When we evaluated the maximum output power, the bifacial illumination effect was only observed in the triode cell. A triode cell can decrease resistive loss by introducing light from both surfaces, compared with a conventional cell with one junction. Copyright © 2001 John Wiley & Sons, Ltd.
Manufacturing tolerances of terrestrial concentrator p‐on‐n GaAs solar cells
Authors: Algora Carlos , Díaz Vicente 
Published: September 2002

AbstractThe increasing interest in the manufacturing of terrestrial concentrator GaAs solar cells calls for the need to establish the guidelines, assessments and tolerances of the production process. Accordingly, this paper analyses, for the first time, the tolerances of this process. The influence of the entire solar cell (antireflecting coatings, semiconductor structure and series resistance) is considered. More specifically, the parameters analysed are: the thickness of the double antireflecting coating, window thickness, emitter thickness, base thickness, emitter doping level, base doping level, shadowing factor and specific front contact resistance. The results are presented in the form of iso‐efficiency plots as a function of the aforementioned parameters. Therefore, besides the conclusions extracted in this paper, numerous others may be formed according to particular necessities. Copyright © 2001 John Wiley & Sons, Ltd.
Limiting efficiency for current‐constrained two‐terminal tandem cell stacks
Authors: Brown Andrew S. , Green Martin A. 
Published: September 2002

AbstractTandem stacks of solar cells have clearly shown their ability to increase the efficiency of solar energy conversion. In the past, the challenge in making these devices often has been in the materials science area, working around the constraints imposed by different materials to meet requirements imposed by lattice constant and bandgap. However, developments in the field of low‐dimensional structures; particularly superlattices, may allow generic approaches to developing tandem stacks of large numbers of cells. The current flowing through such devices will have to be constrained so that it is the same through all the cells within the stack since separately contacting such large numbers of cells is impractical. The series‐constrained two‐terminal tandem solar cell is compared with the unconstrained tandem solar cell for stacks containing both small and large numbers of cells. As expected, we find that the detailed balance limiting efficiencies for the two‐terminal cell are less than those for the unconstrained device involving the same number of cells, due to the constraint imposed by current matching. However the difference is always less than 1.5% relative under the design spectrum. However, the two‐terminal case shows much greater variation in efficiency if the spectrum varies from that for which the design was optimised. A relationship is derived between the performance of a two‐terminal stack of a finite number of cells and the performance of an unconstrained stack of an infinite number of cells. This shows that the performance of the two‐terminal device approaches that of the unconstrained device as the number of cells in the stack approaches infinity. Copyright © 2002 John Wiley & Sons, Ltd.
Ideal efficiency of monolithic, series‐connected multijunction solar cells
Authors: Tobías I. , Luque A. 
Published: September 2002

AbstractTwo‐terminal, monolithic tandem solar cells represent the most interesting implementation of tThe multijunction photovoltaic array capable of very high efficiency. Radiative coupling among the cells, and between the cells and the substrate, along with series interconnection are features present in this approach. Their effect on efficiency is quantified for arrays with a small number of cells in the radiative limit and compared with the best experimental cells to assess their potential improvement. Finally, it is shown that they do not lower the limiting efficiency of the infinite tandem array, which is determined by the emission losses through the illuminated face. Copyright © 2002 John Wiley & Sons, Ltd.
Synthesis, characterization, and electrical properties of nanostructural polyaniline doped with novel sulfonic acids (4‐{n‐[4‐(4‐nitrophenylazo)phenyloxy]alkyl}aminobenzene sulfonic acid)
Authors: Qiu Hongjin , Wan Meixiang 
Published: September 2002

Abstract4‐{n‐[4‐(4‐Nitrophenylazo)phenyloxy]alkyl}aminobenzene sulfonic acid (Cn‐ABSA, where n = 2, 4, 6, 8, or 10) as a novel dopant for conducting polymers of polyaniline (PANI) was designed and synthesized. The molecular structure of Cn‐ABSA was characterized with 1H NMR, Fourier transform infrared, and secondary‐ion mass spectrometry. Nanostructures (nanotubes or nanorods) of PANI–(Cn‐ABSA) were successfully synthesized with a self‐assembly process in the presence of Cn‐ABSA as the dopant. The morphology (shape and size) and conductivity of the resulting nanostructures strongly depended on the number of alkyl groups (n) and, in particular, the addition of water before polymerization. The formed micelles of aniline/Cn‐ABSA/water were proposed to be templatelike in forming PANI–(Cn‐ABSA) nanostructures on the basis of the emulsion properties measured by dynamic light scattering. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3485–3497, 2001
Graft copolymers from star‐shaped and hyperbranched polystyrene macromonomers
Authors: Al‐Muallem Hasan A. , Knauss Daniel M. 
Published: September 2002

AbstractBranched polystyrene macromonomers were synthesized by the slow addition of a stoichiometric amount of either 4‐(chlorodimethylsilyl)styrene or vinylbenzyl chloride as a coupling agent to living polystyryllithium. Star‐shaped macromonomers were produced by the addition of the coupling agent alone, and hyperbranched macromonomers resulted from the addition of the coupling agent along with styrene monomer. Star and hyperbranched graft copolymers were produced by the copolymerization of the macromonomers with styrene and methyl methacrylate. The copolymers were characterized by gel permeation chromatography coupled with multi‐angle laser light scattering, 1H NMR spectroscopy, and Soxhlet extraction to determine that the macromonomers were incorporated in high yields into the copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3547–3555, 2001
Viscosity effects in cobaloxime‐mediated catalytic chain‐transfer polymerization of methacrylates
Authors: Roberts G. Evan , Davis Thomas P. , Heuts Johan P. A. , Russell Gregory T. 
Published: September 2002

AbstractThe effect of bulk viscosity on the cobaloxime‐mediated catalytic chain‐transfer polymerization of methacrylates at 60 °C was investigated by both the addition of high molecular weight poly(methyl methacrylate) to methyl methacrylate polymerization and the dilution of benzyl methacrylate polymerization by toluene. The results indicate that the bulk viscosity is not directly linked to the chain‐transfer activity. The previously measured relationship between chain‐transfer‐rate coefficient and monomer viscosity therefore probably reflects changes at the molecular level. However, the results in this article do not necessarily disprove a diffusion‐controlled reaction rate because cobaloxime diffusion is expected to scale with the monomer friction coefficient rather than bulk viscosity. Considering the published data, to date we are not able to distinguish between a diffusion‐controlled reaction rate or a mechanism directly affected by the methacrylate substituent. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 782–792, 2002; DOI 10.1002/pola.10152
Discovery of dendrimers and dendritic polymers: A brief historical perspective*
Authors: Tomalia Donald A. , Fréchet Jean M. J. 
Published: September 2002

AbstractA brief historical perspective relating the discovery of dendrimers and other dendritic polymers is presented. Dendritic polymers are recognized as the fourth major class of macromolecular architecture consisting of four sub‐ classes, namely, (1) random hyperbranched, (2) dendrigrafts, (3) dendrons, and (4) dendrimers. The previous literature is reviewed with anecdotal events leading to implications for dendrimers in the emerging science of nanotechnology. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2719–2728, 2002
Polyolefin graft copolymers via living polymerization techniques: Preparation of poly(n‐butyl acrylate)‐graft‐polyethylene through the combination of Pd‐mediated living olefin polymerization and atom transfer radical polymerization
Authors: Hong Sung Chul , Jia Shijun , Teodorescu Mircea , Kowalewski Tomasz , Matyjaszewski Krzysztof , Gottfried Amy C. , Brookhart Maurice 
Published: September 2002

AbstractPoly(n‐butyl acrylate)‐graft‐branched polyethylene was successfully prepared by the combination of two living polymerization techniques. First, a branched polyethylene macromonomer with a methacrylate‐functionalized end group was prepared by Pd‐mediated living olefin polymerization. The macromonomer was then copolymerized with n‐butyl acrylate by atom transfer radical polymerization. Gel permeation chromatography traces of the graft copolymers showed narrow molecular weight distributions indicative of a controlled reaction. At low macromonomer concentrations corresponding to low viscosities, the reactivity ratios of the macromonomer to n‐butyl acrylate were similar to those for methyl methacrylate to n‐butyl acrylate. However, the increased viscosity of the reaction solution resulting from increased macromonomer concentrations caused a lowering of the apparent reactivity ratio of the macromonomer to n‐butyl acrylate, indicating an incompatibility between nonpolar polyethylene segments and a polar poly(n‐butyl acrylate) backbone. The incompatibility was more pronounced in the solid state, exhibiting cylindrical nanoscale morphology as a result of microphase separation, as observed by atomic force microscopy. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2736–2749, 2002
Synthesis and characterization of novel soluble triphenylamine‐containing aromatic polyamides based on N,N′‐bis(4‐aminophenyl)‐N,N′‐diphenyl‐1,4‐phenylenediamine
Authors: Liou Guey‐Sheng , Hsiao Sheng‐Huei , Ishida Mina , Kakimoto Masaaki , Imai Yoshio 
Published: September 2002

AbstractA new triphenylamine‐containing aromatic diamine, N, N′‐bis(4‐aminophenyl)‐N, N′‐diphenyl‐1,4‐phenylenediamine, was prepared by the condensation of N,N′‐diphenyl‐1,4‐phenylenediamine with 4‐fluoronitrobenzene, followed by catalytic reduction. A series of novel aromatic polyamides with triphenylamine units were prepared from the diamine and various aromatic dicarboxylic acids or their diacid chlorides via the direct phosphorylation polycondensation or low‐temperature solution polycondensation. All the polyamides were amorphous and readily soluble in many organic solvents such as N, N‐dimethylacetamide and N‐methyl‐2‐pyrrolidone. These polymers could be solution cast into transparent, tough, and flexible films with good mechanical properties. They had useful levels of thermal stability associated with relatively high glass‐transition temperatures (257–287 °C), 10% weight‐loss temperatures in excess of 550 °C, and char yields at 800 °C in nitrogen higher than 72%. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2810–2818, 2002
Linear functionalized polyethylene prepared with highly active neutral Ni(II) complexes
Authors: Connor Eric F. , Younkin Todd R. , Henderson Jason I. , Hwang Sonjong , Grubbs Robert H. , Roberts William P. , Litzau Johnathan J. 
Published: September 2002

AbstractNeutral Ni(II) salicylaldimine catalysts (pendant ligand = NCMe or PPh3) were used to copolymerize ethylene with monomers containing esters, alcohols, anhydrides, and amides and yielded linear functionalized polyethylene in a single step. α‐Olefins and polycyclic olefin comonomers carrying functionality were directly incorporated into the polyethylene backbone by the catalysts without any cocatalyst, catalyst initiator, or other disturber compounds. The degree of comonomer incorporation was related to the monomer structure: tricyclononenes > norbornenes > α‐olefins. A wide range of comonomer incorporation, up to 30 mol %, was achieved while a linear polyethylene structure was maintained under mild conditions (40 °C, 100 psi ethylene). Results from the characterization of the copolymers by solution and solid‐state NMR techniques, thermal analysis, and molecular weight demonstrated that the materials contained a relatively pure microstructure for a functionalized polyethylene that was prepared in one step with no catalyst additive. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2842–2854, 2002
Acid chloride‐functionalized hyperbranched polyester for facile and quantitative chain‐end modification: One‐pot synthesis and structure characterization
Authors: Yamaguchi Nori , Wang Jin‐Shan , Hewitt J. Michael , Lenhart William C. , Mourey Thomas H. 
Published: September 2002

AbstractCarboxylic acid chloride end‐functionalized all‐aromatic hyperbranched polyesters were prepared from the bulk polycondensation of the AB2 monomer 5‐(trimethylsiloxy)isophthaloyl dichloride. The acid chloride end functionality of the hyperbranched polyester was modified in situ with methanol and yielded methyl ester ends in a one‐pot process. Chain‐end functionalization and esterification were quantitative according to both potentiometric titration and 1H NMR analysis. The signals of 1H and 13C NMR spectra of the esterified hyperbranched polyester were fully assigned from model compounds of the focal, linear, dendritic, and terminal units. The degree of branching and molecular weight averages measured by 1H and 13C NMR spectroscopy and multidetector size exclusion chromatography increased systematically with increasing polymerization temperatures between 80 and 200 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2855–2867, 2002
Transesterification reaction of the BaSO4‐filled PBT/poly(ethylene terephthalate) blend
Authors: Lee Sang‐Soo , Kim Junkyung , Park Min , Lim Soonho , Choe Chul Rim 
Published: September 2002

AbstractFor the poly(butylene terephthalate) (PBT)/poly(ethylene terephthalate) blend system, the addition of a barium sulfate (BaSO4) particle, the surface of which was modified with a titanate coupling agent, suppressed the transesterification reaction. The polyester chain ends, considered one of the main sites of transesterification reactions, were blocked through a chemical reaction with the surface hydroxyl groups of the BaSO4 particle; a block copolymer‐like architecture was obtained with a BaSO4 linkage. The formation of the block copolymer‐like structure for the polyesters stuck to the BaSO4 particle facilitated crystallization by providing a crystallization nucleus without a significant transesterification reaction, resulting in higher mechanical properties. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2589–2597, 2001
Melt rheology of polypropylene containing small amounts of high molecular weight chain. I. Shear flow
Authors: Sugimoto M. , Masubuchi Y. , Takimoto J. , Koyama K. 
Published: September 2002

AbstractLarge enhancements of the melt strength of polypropylene (PP) were achieved by the introduction of high molecular weight polyethylene (PE) into PP. The viscoelastic properties of the high‐melt‐strength PP melts under shear flow were investigated. It was found that the rheological properties of the high‐melt‐strength PP were distinctly different from those of conventional PP. The elastic response at low frequencies was significantly enhanced in comparison with the conventional PP, implying a presence of a long relaxation time mode that was not revealed in conventional PP. In step‐shear measurements, the fast and slow relaxation processes that characterized the linear viscoelastic properties were observed also for nonlinear relaxation moduli. The dependence of the damping for the slow process of the high‐melt‐strength PP on shear strain was much weaker than that of the fast process. These rheological behaviors characterizing the long relaxation time mode were further enhanced with the increasing concentration of high molecular mass PE. The unusual shear rheological behaviors were discussed in view of the role of high molecular weight PE as a long relaxation time mode within PP. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2692–2704, 2001
Scattering properties of a single semiflexible polyelectrolyte
Authors: Ghosh K. , Muthukumar M. 
Published: September 2002

AbstractThe structure factor of a single semiflexible polyelectrolyte has been calculated as a function of chain length, intrinsic backbone stiffness, and salt concentration. Because of the insignificant coupling of the intrinsic stiffness and electrostatic persistence length, we carry out our calculations in the flexible limit. Within the variational scheme adopted here, we obtain fractal dimensions consistent with our earlier calculations of the configurational properties. As the chain length is increased, the electrostatic interaction is progressively screened, leading to the crossover regions. In the first crossover, the effective fractal dimension, Deff, is as low as 1, and in the second crossover Deff is 5/3, although the radius of gyration exponent is 2/5. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2644–2652, 2001
Sub‐glass‐transition temperature interface formation between an immiscible glass rubber pair
Authors: Forrest J. A. , Dalnoki‐Veress K. 
Published: September 2002

AbstractWe used neutron reflectivity to measure the interfacial width in the immiscible system polystyrene/poly(n‐butyl methacrylate) (PS/PnBMA). Measurements were made on the same samples at temperatures ranging from below the glass‐transition temperature (Tg) of PS to slightly above. We observed significant broadening of the interface at temperatures below the Tg of PS, indicating chain mobility below the bulk Tg value. The interfacial width exhibited a plateau at a value of 20 Å in the temperature range of 365 K < T < 377 K. A control experiment involving hydrogenated and deuterated PS films (hPS/dPS) showed no such broadening over the same temperature region. The results are consistent with a reduction of the Tg of PS in the interfacial region of ∼20 K. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2664–2670, 2001
Why protein R‐factors are so large: A self‐consistent analysis
Authors: Vitkup Dennis , Ringe Dagmar , Karplus Martin , Petsko Gregory A. 
Published: September 2002

AbstractThe R‐factor and R‐free are commonly used to measure the quality of protein models obtained in X‐ray crystallography. Well‐refined protein structures usually have R‐factors in the range of 20–25%, whereas intrinsic errors in the experimental data are usually around 5%. We use molecular dynamics simulations to perform a self‐consistent analysis by which we determine the major factors contributing to large values of protein R‐factors. The analysis shows that significant R‐factor values can arise from the use of isotropic B‐factors to model anisotropic protein motions and from coordinate errors. Even in the absence of coordinate errors, the use of isotropic B‐factors can cause the R‐factors to be around 10%; for coordinate errors smaller than 0.2 Å, the two errors types make similar contributions. The inaccuracy of the energy function used and multistate protein dynamics are unlikely to make significant contributions to the large R‐factors. Proteins 2002;46:345–354. © 2002 Wiley‐Liss, Inc.