bluuebunny/crossref_metadata_2025_split huggingface dataset:
Changes in superstructure and mechanical properties of poly(ethylene‐2,6‐naphthalate) fibers with critical necking tension
Authors: Suzuki Akihiro , Kawada Takashi , Hasegawa Toshinori 
Published: October 2004

AbstractPoly(ethylene‐2,6‐naphthalate) fibers were zone‐drawn under a critical necking tension (σc) defined as the minimum tension needed to generate a necking at a given drawing temperature (Td). In the zone drawing under σc, the neck was observed from 110 to 160 °C. The superstructure in a neck zone induced at each Td was studied. The σc value decreased exponentially with increasing Td and dropped to a low level at a higher Td. The draw ratio increased rapidly with Td increasing above 90 °C, but the birefringence and degree of crystallinity decreased gradually. To study the molecular orientation in the neck zone, we measured a dichroic ratio (A‖/A⟂) of a CO band at 1256 cm−1 along a drawing direction in the neck zone with a Fourier transform infrared microscope. A‖/A⟂ at Td = 110 °C increased rapidly in the narrow neck zone, and that at Td = 140 °C increased in the edge of the wide neck zone. Wide‐angle X‐ray diffraction patterns of the fibers obtained at Td = 130 °C and lower showed three reflections due to an α form, but those at Td = 140 and 150 °C had reflections due to the α form and a β form. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1629–1637, 2001
Confirmation of universality of time–humidity superposition principle for various water‐absorbable polymers through dynamic viscoelastic measurements under controlled conditions of relative humidity and temperature
Authors: Zhou S.‐M. , Tashiro K. , Ii T. 
Published: October 2004

AbstractDynamic viscoelastic measurements were made for storage (E′) and loss (E″) tensile moduli of water‐absorbable polymers such as nylon‐6, nylon‐66, poly(vinyl alcohol), ethylene–vinyl alcohol copolymers, and regenerated cellulose under the control of stepwise scanned relative humidity at constant temperature by changes in the strain frequency over a wide range. Smooth master curves of log(E′) and log(E″) plotted against log(frequency) were successfully obtained for all samples. The evaluated shift factors changed with the relative humidity and could be interpreted well on the basis of a concept of free volume in the amorphous region. The free volume was affected sensitively, depending on the heat‐treatment condition and the types of polymers used. For nylon‐66 film, the dynamic viscoelastic measurements were made at different humidities and temperatures, from which one smooth master curve was obtained. This experimental result is important in realizing the similar effect of relative humidity and temperature on the expansion of free volume of the amorphous phase: the shift factor change induced by the relative humidity change of about 30% was equivalent to the shift factor change induced by the temperature change of about 30 °C. That is, the time–humidity superposition principle and the time–temperature superposition principle were applicable as equivalent contributors to the mechanical property of water‐absorbable polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1638–1650, 2001
Screening effects in blends of a hyperbranched, dendrimer‐like polyester with poly(4‐vinyl phenol)
Authors: Pruthtikul Rittirong , Coleman Michael M. , Painter Paul C. , Beck Tan Nora 
Published: October 2004

AbstractWe previously reported self‐association and interassociation equilibrium constant values describing hydrogen bonding in solutions of a hyperbranched polyester. These allow us to estimate the extent of intramolecular screening and the fraction of same‐chain contacts in this system as a function of generation number. In this article, we use a similar method to evaluate the degree of intramolecular screening in polymer blends. The calculated values reported here are consistent with those previously reported in our solution study, confirming the validity of the calculation procedures we used to evaluate the accessibility of functional groups in these highly branched systems. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1651–1658, 2001
Effect of residual water and free volume on the glass‐transition temperature and heat capacity in polystyrene/poly(vinyl acetate‐co‐butyl acrylate) structured latex films
Authors: Song M. , Hourston D. J. , Silva G. G. , Machado J. C. 
Published: October 2004

AbstractThe dynamic heat capacity and glass‐transition temperature of polystyrene (PS)/poly(vinyl acetate‐co‐butyl acrylate) (VAc–BA) (50:50 w/w) structured latex films as a function of annealing time at 70, 77, and 85 °C were examined with modulated‐temperature differential scanning calorimetry. The PS and poly(vinyl acetate‐co‐n‐butyl acrylate) components were considered to be the cores and shells, respectively, in the structured latex. The dynamic heat capacity decreased with time. The glass‐transition temperatures of the PS and VAc–BA phases shifted to higher values after annealing. The results of thermogravimetry showed that there existed about 1.8% residual water in the films. The mean free volume and relative concentration of holes at room temperature (before and after annealing) and 85 °C, as a function of time, were obtained with positron annihilation lifetime spectroscopy (PALS). The PALS results indicated no significant change in free volume during annealing. It is believed that the loss, by diffusion, of residual water mainly caused a decrease in heat capacity and an increase in the glass‐transition temperatures. As little as 1.8% residual water in the structured latex films had a significant influence on the thermal properties. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1659–1664, 2001
Attenuated total reflectance/fourier transform infrared studies on the phase‐separation process of aqueous solutions of poly(n‐isopropylacrylamide)
Authors: Ramon Ory , Kesselman Ellina , Berkovici Ronen , Cohen Yachin , Paz Yaron 
Published: October 2004

AbstractTemperature‐induced phase separation of poly(N‐isopropylacrylamide) in aqueous solutions was studied by attenuated total reflectance (ATR)/Fourier transform infrared spectroscopy. The main objectives of the study were to understand, on a molecular level, the role of hydrogen bonding and hydrophobic effects below and above the phase‐separation temperature and to derive the scenario leading to this process. Understanding the behavior of this particular system could be quite relevant to many biological phenomena, such as protein denaturation. The temperature‐induced phase transition was easily detected by the ATR method. A sharp increase in the peaks of both hydrophobic and hydrophilic groups of the polymer and a decrease in the water‐related signals could be explained in terms of the formation of a polymer‐enriched film near the ATR crystal. Deconvolution of the amide I and amide II peaks and the OH stretch envelope of water revealed that the phase‐separation scenario could be divided, below the phase‐separation temperature, into two steps. The first step consisted of the breaking of intermolecular hydrogen bonds between the amide groups of the polymer and the solvent and the formation of free amide groups, and the second step consisted of an increase in intramolecular hydrogen bonding, which induced a coil–globule transition. No changes in the hydrophobic signals below the separation temperature could be observed, suggesting that hydrophobic interactions played a dominant role during the aggregation of the collapsed chains but not before. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1665–1677, 2001
Molecular motion in nanocomposites of poly(ethylene oxide) and montmorillonite
Authors: Kwiatkowski Johann , Whittaker Andrew K. 
Published: October 2004

AbstractMotion of chains of poly(ethylene oxide) within the interlayer spacing of 2:1 phyllosilicate/montmorillonite was studied with 1H and 13C NMR spectroscopy. Measurements of the 1H NMR line widths and relaxation times across a large temperature range were used to determine the effect of bulk thermal transitions on polymer chain motion within the nanocomposites. The results were consistent with previous reports of low apparent activation energies of motion. Details of the frequency and geometry of motion were obtained from a comparison of the 13C cross‐polarity/magic‐angle spinning spectra and relaxation times of the nanocomposite with those of the pure polymer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1678–1685, 2001
Effect of crosslinking on the photoinduced orientation of azo groups in thin polymer films
Authors: Takase Hideaki , Natansohn Almeria , Rochon Paul 
Published: October 2004

AbstractA series of amorphous copolymers containing disperse red 1 and crosslinkable acrylic groups were prepared. The crosslinked polymers were prepared in thin films by thermal polymerization of the acrylic groups in the copolymers. The orientation induced by irradiation with a linearly polarized laser was measured as birefringence at several temperatures, and the effect of crosslinking on the photoinduced orientation was investigated. Crosslinking enhanced the stability of the photoinduced birefringence. In particular, crosslinking helped to maintain the birefringence both at high temperatures and after the linearly polarized laser was turned off. The birefringence dynamics was analyzed with biexponential curve fitting. Crosslinking influenced not only the birefringence levels but also its rate of growth. The growth rate of the photoinduced birefringence decreased by crosslinking, whereas the relaxation was not significantly affected. Although crosslinking restrained the mobility of the azo chromophores, a certain fraction could orient or move randomly even in highly crosslinked polymer networks. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1686–1696, 2001
Organic light‐emitting device dark spot growth behavior analysis by diffusion reaction theory
Authors: Ke Lin , Lim Shuang Fang , Chua Soo Jin 
Published: October 2004

AbstractDark spot growth rate tracing experiments performed on an organic light‐emitting device show that moisture entering into the device is relatively properly fitted by Fick's diffusion equation in the substrate/indium tin oxide (ITO)/hole transport layer (HTL)/silver (Ag) structure. It is believed that the moisture is dissolved into the polymer layer, which results in a decrease in the diffusion coefficient in the device with the substrate/ITO/HTL/electroluminescent (EL) polymer/Ag structure. The diffusion and chemical reaction occurring in the cathode layer further decreases the diffusion coefficient in the device with the substrate/ITO/HTL/EL polymer/calcium/Ag structure. Useful parameters, such as diffusion and solubility constants, describing possible mechanisms happening during dark spot growth on organic light‐emitting diode devices are extracted. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1697–1703, 2001
Oxygen‐barrier properties of copolymers based on ethylene terephthalate
Authors: Polyakova A. , Liu R. Y. F. , Schiraldi D. A. , Hiltner A. , Baer E. 
Published: October 2004

AbstractThe oxygen‐barrier properties of amorphous polyethylene terephthalate‐based copolymers with various acid comonomers were examined. The incorporation of increasing amounts of isophthalate, phthalate, or naphthalate gradually reduced the permeability P toward the low values obtained for the corresponding homopolymers. The permeability of poly(ethylene 3,4′‐bibenzoate) homopolymer was only slightly lower than that of polyethylene terephthalate, and the copolymers correspondingly exhibited a very gradual decrease in P as the amount of 3,4′‐bibenzoate (3,4′BB) increased. In contrast, copolymerization with the linear isomer, 4,4′BB, produced a substantial increase in P. Generally, comonomer affected the solubility S less than the diffusivity D, and therefore changes in P reflected primarily changes in D for the polymers studied. The diffusivity and solubility depended on the copolymer composition in accordance with static and dynamic free‐volume concepts of gas permeability in glassy polymers. The solubility S correlated with the amount of free volume as determined by the glass‐transition temperature. Correlation of the diffusivity D with the magnitude of the subambient γ relaxation identified dynamic free volume with thermally activated conformational changes and segmental motions. Correspondence in the activation energy confirmed the relationship. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1889–1899, 2001
Molecular mechanisms of microheterogeneity‐induced defect formation in ferritin crystallization
Authors: Yau S.‐T. , Thomas Bill R. , Galkin Oleg , Gliko Olga , Vekilov Peter G. 
Published: October 2004

AbstractWe apply in situ atomic force microscopy to the crystallization of ferritins from solutions containing ≈5% (w/w) of their inherent molecular dimers. Molecular resolution imaging shows that the dimers consist of two bound monomers. The constituent monomers are likely partially denatured, resulting in increased hydrophobicity of the dimer surface. Correspondingly, the dimers strongly adsorb on the crystal surface. The adsorbed dimers hinder step growth and on incorporation by the crystal initiate stacks of up to 10 triple and single vacancies in the subsequent crystal layers. The molecules around the vacancies are shifted by ≈0.1 molecular dimensions from their crystallographic positions. The shifts strain the lattice and, as a consequence, at crystal sizes > 200 μm, the accumulated strain is resolved by a plastic deformation whereupon the crystal breaks into mosaic blocks 20–50 μm in size. The critical size for the onset of mosaicity is similar for ferritin and apoferritin and close to the value for a third protein, lysozyme; it also agrees with theoretical predictions. Trapped microcrystals in ferritin and apoferritin induce strain with a characteristic length scale equal to that of a single point defect, and, as a consequence, trapping does not contribute to the mosaicity. The sequence of undesired phenomena that include heterogeneity generation, adsorption, incorporation, and the resulting lattice strain and mosaicity in this and other proteins systems, could be avoided by improved methods to separate similar proteins species (microheterogeneity) or by increasing the biochemical stability of the macromolecules against oligomerization. Proteins 2001;43:343–352. © 2001 Wiley‐Liss, Inc.
Significance of aromatic‐backbone amide interactions in protein structure
Authors: Tóth Gergely , Watts Charles R. , Murphy Richard F. , Lovas Sándor 
Published: October 2004

AbstractWeakly polar interactions between aromatic rings of amino acids and hydrogens of backbone amides (Ar‐HN) have been shown to support local structures in proteins. Their role in secondary structures, however, has not been elucidated. To investigate the relationship between Ar‐HN interaction and the stability of local and secondary structures of polypeptides and to improve the prediction of this interaction based on amino acid sequence, the structures of 560 nonhomologous proteins, from the Protein Data Bank, were searched for Ar–HN interactions between the aromatic ring of each Phe, Tyr, and Trp residue at position i and the backbone amide group of any residue, except Pro, at the positions i, i − 1, i − 2, i − 3, i + 1, i + 2, and i + 3. Ar‐HN interactions were identified by calculating the chemical shift of the amide hydrogen caused by the proximal aromatic ring. Ar(i)–HN(i + 1, i + 2 and i + 3) interactions were more common (7.10%, 2.08%, and 0.54%, respectively) than were Ar(i)–HN(i − 1, i − 2, and i − 3) interactions (0.66%, <0.1%, and 0.18%, respectively). The value of the χ1 torsion angle of the aromatic residue in position i depended on the direction of the Ar–HN interaction. The position of the aromatic ring in Ar(i)–HN(i + 1, i + 2, and i + 3) interactions was mostly trans, in Ar(i)–HN(i − 1, i − 2, and i − 3) interactions mainly gauche(−), and in Ar(i)–HN(i) interactions mostly gauche(+). The analyses of the secondary structures of the protein fragments containing Ar–HN interactions showed that Ar–HN interactions were in all types of secondary structures. Search results suggest that Ar–HN interactions have a stabilizing effect on all types of secondary structures. Proteins 2001;43:373–381. © 2001 Wiley‐Liss, Inc.
Mechanism of NAD(P)H:Quinone reductase: Ab initio studies of reduced flavin
Authors: Cavelier German , Amzel L. Mario 
Published: October 2004

AbstractNAD(P)H:quinone oxidoreductase type 1 (QR1, NQO1, formerly DT‐diaphorase; EC 1.6.99.2) is an FAD‐containing enzyme that catalyzes the nicotinamide nucleotide‐dependent reduction of quinones, quinoneimines, azo dyes, and nitro groups. Animal cells are protected by QR1 from the toxic and neoplastic effects of quinones and other electrophiles. Alternatively, in tumor cells QR can activate a number of cancer chemotherapeutic agents such as mitomycins and aziridylbenzoquinones. Thus, the same enzyme that protects the organism from the deleterious effects of quinones can activate cytotoxic chemotherapeutic prodrugs and cause cancer cell death. The catalytic mechanism of QR includes an important initial step in which FAD is reduced by NAD(P)H. The unfavorable charge separation that results must be stabilized by the protein. The details of this charge stabilization step are inaccessible to easy experimental verification but can be studied by quantum chemistry methods. Here we report ab initio quantum mechanical calculations in and around the active site of the enzyme that provide information about the fine details of the contribution of the protein to the stabilization of the reduced flavin. The results show that (1) protein interactions provide approximately 2 kcal/mol to stabilize the planar conformation of the reduced flavin isoalloxazine ring observed in the X‐ray structure; (2) the charge separation present in the reduced planar form of the flavin is stabilized by interactions with groups of the protein; (3) even after stabilization, the reduction potential of the cofactor remains more negative than that of the free flavin, making it a better reductant for a larger variety of quinones; and (4) the more negative reduction potential may also result in faster kinetics for the quinone reduction step. Proteins 2001;43:420–432. © 2001 Wiley‐Liss, Inc.
Intrasubthalamic injection of 6‐hydroxydopamine induces changes in the firing rate and pattern of subthalamic nucleus neurons in the rat
Authors: Ni Zhongge , Bouali‐Benazzouz Rabia , Gao Dongming , Benabid Alim‐Louis , Benazzouz Abdelhamid 
Published: October 2004

AbstractThe subthalamic nucleus (STN) receives dopaminergic projections from the substantia nigra pars compacta (SNc). To investigate the role of direct and indirect dopaminergic influences on STN neurons, the spontaneous activity was studied in four groups of animals: normal rats, rats with intrasubthalamic or intranigral injection of 6‐hydroxydopamine (6‐OHDA), and sham STN injection rats by using extracellular recordings 4 weeks postsurgery. After intrasubthalamic injection of 6‐OHDA, the mean firing rate significantly decreased (7.29 ± 0.39 spikes/sec, P < 0.01 vs. 11.13 ± 0.59 spikes/sec in normal or 11.26 ± 0.57 spikes/sec in sham group), and the percentage of STN neurons discharging regularly decreased significantly (81%, P < 0.05 vs. 90% in normal group or P < 0.01 vs. 92% in sham group) and that of bursty cells increased (19%, P < 0.05 vs. 10%; in normal group or P < 0.01 vs. 8% in sham group). In the group of rats with SNc lesion, the firing rate of subthalamic neurons did not show a significant difference (11.61 ± 0.81 spikes/sec) compared with normal group. However, the firing pattern was dramatically changed: 74% of cells exhibited bursty pattern and only 26% of cells discharged regularly or slightly irregularly. Immunohistochemical results showed that intrasubthalamic injection of 6‐OHDA induced a marked degeneration of dopaminergic cells in the lateral part of the ipsilateral SNc, whereas 6‐OHDA injection into the SNc induced a total in situ lesion of dopamine cells. These results suggest that the SNc exerts an excitatory influence on STN neurons and that the loss of this dopaminergic projection could, at least partially, account for the changes in the firing pattern of STN neurons in the 6‐OHDA rat model of parkinsonism. Synapse 40:145–153, 2001. © 2001 Wiley‐Liss, Inc.
Inference of S-system models of genetic networks using a cooperative coevolutionary algorithm
Authors: Kimura Shuhei , Ide Kaori , Kashihara Aiko , Kano Makoto , Hatakeyama Mariko , Masui Ryoji , Nakagawa Noriko , Yokoyama Shigeyuki , Kuramitsu Seiki , Konagaya Akihiko 
Published: October 2004

AbstractMotivation: To resolve the high-dimensionality of the genetic network inference problem in the S-system model, a problem decomposition strategy has been proposed. While this strategy certainly shows promise, it cannot provide a model readily applicable to the computational simulation of the genetic network when the given time-series data contain measurement noise. This is a significant limitation of the problem decomposition, given that our analysis and understanding of the genetic network depend on the computational simulation.Results: We propose a new method for inferring S-system models of large-scale genetic networks. The proposed method is based on the problem decomposition strategy and a cooperative coevolutionary algorithm. As the subproblems divided by the problem decomposition strategy are solved simultaneously using the cooperative coevolutionary algorithm, the proposed method can be used to infer any S-system model ready for computational simulation. To verify the effectiveness of the proposed method, we apply it to two artificial genetic network inference problems. Finally, the proposed method is used to analyze the actual DNA microarray data.Contact: skimura@gsc.riken.jpSupplementary information: See Bioinformatics Online.
Superior feature-set ranking for small samples using bolstered error estimation
Authors: Sima Chao , Braga-Neto Ulisses , Dougherty Edward R. 
Published: October 2004

Abstract
Motivation: Ranking feature sets is a key issue for classification, for instance, phenotype classification based on gene expression. Since ranking is often based on error estimation, and error estimators suffer to differing degrees of imprecision in small-sample settings, it is important to choose a computationally feasible error estimator that yields good feature-set ranking.
Results: This paper examines the feature-ranking performance of several kinds of error estimators: resubstitution, cross-validation, bootstrap and bolstered error estimation. It does so for three classification rules: linear discriminant analysis, three-nearest-neighbor classification and classification trees. Two measures of performance are considered. One counts the number of the truly best feature sets appearing among the best feature sets discovered by the error estimator and the other computes the mean absolute error between the top ranks of the truly best feature sets and their ranks as given by the error estimator. Our results indicate that bolstering is superior to bootstrap, and bootstrap is better than cross-validation, for discovering top-performing feature sets for classification when using small samples. A key issue is that bolstered error estimation is tens of times faster than bootstrap, and faster than cross-validation, and is therefore feasible for feature-set ranking when the number of feature sets is extremely large.
Availability: We provide a companion website, which contains the complete set of tables and plots regarding the simulation study, and a compilation of references on feature-set ranking with applications in Genomics. The companion website can be accessed at the URL http://ee.tamu.edu/~edward/bolster_ranking
Contact: edward@ee.tamu.edu