bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of composition on the solution rheology of stearyl methacrylate‐co‐styrene‐co‐vinyl pyrrolidinone in paraffinic base oil
Authors: Torres Edgar , Dutta Naba , Choudhury Namita Roy , Matisons Janis 
Published: May 2004

AbstractThe rheological behavior of dilute and semi‐dilute solutions of stearyl methacrylate‐co‐styrene‐co‐vinyl pyrrolidinone copolymers (SMA‐S‐VP) was investigated over a wide range of temperatures (20–140°C) under steady shear (0.1–5000 s−1) and dynamic conditions (0.01–500 rad/s). The solvent used was polyalpha olefin, PAO4 (C20‐C40 fraction), a fully synthetic paraffinic oil normally used as base oil for lubricant oil formulations. The investigation focuses on the effect of the polar comonomer segment content, of the copolymer, on the viscosity‐temperature relationship of the solution. This information provides insight into the effect of polymer microstructure on the viscosity index (VI) behavior of the lubricant. Copolymers with different ratios of stearyl methacrylate, styrene and vinyl pyrrolidinone were synthesized by solution radical polymerization. The microstructure and molecular weight of the copolymers were evaluated by nuclear magnetic resonance spectroscopy (NMR). The molecular weight and polydispersity of the polymers were determined using GPC. The polymer solutions exhibit non‐Newtonian behavior, which is more evident at lower temperatures and higher concentrations. The temperature‐concentration superposition principle developed by Ferry (1) was applied to steady shear data and the resulting master curve was fitted to the Carreau model. A modified Fedors equation for intrinsic viscosity calculation, at low and moderate polymer solution concentrations, was used. The results confirm that the viscosity index improver properties (VII) of the copolymer are superior when the VP content is low. The polymer‐solvent interactions and solvency power of PAO4 were analyzed using an Arrhenius expression. The results show that at low VP content, PAO4 is a better solvent for the copolymer. Polym. Eng. Sci. 44:736–748, 2004. © 2004 Society of Plastics Engineers.
Vibration welding of nylon 6 to nylon 66
Authors: Bates P. J. , Dyck C. , Osti M. 
Published: May 2004

AbstractVibration welding of dissimilar nylons is a promising technique for assembling complex components made of different polymers. The effects of pressure and meltdown on the tensile strength of nylon 6 (PA 6) to nylon 66 (PA 66) vibration welds were determined in this study using an experimental design and three weld geometries. Weld strengths were generally improved by increasing meltdown and decreasing weld pressure. The weld strength was also shown to vary with the position of the lower melting material for T‐welds. Using differential scanning calorimentry and fracture surface analyses, it is concluded that for all geometries, higher weld strengths can be achieved when both materials are melted. Polym. Eng. Sci. 44:760–771, 2004. © 2004 Society of Plastics Engineers.
Study of particle trajectories, residence times and flow behavior in kneading discs of intermeshing co‐rotating twin‐screw extruders
Authors: Bravo V. L. , Hrymak A. N. , Wright J. D. 
Published: May 2004

AbstractA three‐dimensional finite element model was implemented for the solution of mass and momentum conservation equations in the kneading disc section of an intermeshing co‐rotating twin‐screw extruder. The polymer melt was modeled with a Carreau constitutive equation. The particle tracking technique was used to obtain residence times and analyze distributive mixing for different length to diameter ratios (L/D) of kneading discs. Previous studies from Kalyon et al. (1) and Cheng and Manas‐Zloczower (2) have shown that the mixing performance of intermeshing co‐rotating twin‐screw extruders is highly dependent on the combination of screw configuration and operating conditions. The complexity of the geometry and the transient character of the flow demand powerful computational tools to characterize the flow and to develop a prediction tool for the analysis of relative performance between different configurations. Difficulties arise in the particle tracking technique because of the time discretization and the presence of moving boundaries. Results show the importance of particle history on the evaluation of the relative performance of different configurations of kneading blocks and suggest a reevaluation of the use of average flow characteristics for the analysis of mixing. Results also confirm the importance of an accurate description of the geometry and clearances in order to obtain information about relative mixing performance. Polym. Eng. Sci. 44:779–793, 2004. © 2004 Society of Plastics Engineers.
Improved properties of blends of ultrasonically treated unfilled polyurethane rubber
Authors: Ghose Sayata , Isayev A. I. 
Published: May 2004

AbstractThe aim of this investigation is to improve the properties of the polyurethane rubber that has been devulcanized using the coaxial ultrasonic reactor. After devulcanization of the cured rubber under varying gap sizes and amplitudes, blends of the devulcanized and virgin rubber at different ratios are prepared. Rheological and mechanical properties, hardness as well as gel fraction and crosslink density of the vulcanized blends have been investigated. Results show that compared to the vulcanizates of the devulcanized samples, the vulcanizates of the blends show a remarkable improvement in properties, which are sometimes comparable to or even better than the virgin vulcanizate. Blends have also prepared using different proportions of ground samples and virgin rubber, and a comparison of properties between these blends and the blends of the devulcanized rubber has been carried out. The results show that compared to the ground samples, the blends of the devulcanized samples are easier to mix and exhibit enhanced and more uniform properties. Polym. Eng. Sci. 44:794–804, 2004. © 2004 Society of Plastics Engineers.
Equilibrium adsorption model of anions onto a novel synthesized chelating fiber under various pHs and Fourier transform infrared study of these adsorptions
Authors: Ko Young Gun , Choi Ung Su , Woo Je Wan , Park Yong Sung 
Published: May 2004

AbstractIn this article, we present a new adsorption model of anion particles onto a chelating fiber. Nonideal H+ adsorption on the chelating fiber can be described adequately by the use of the heterogeneity factor β and the parameter Φ indicates the geometric factor of effective concentration in this model. The best fits of amines adsorption data were obtained by means of the developed model using two factors. Poly(acrylo‐amidino diethylene diamine) was synthesized as a chelating polymer through the coupling of diethylene triamine with polyacrylonitrile fiber in the presence of AlCl3 · 6H2O addition. Chromate ion and phosphate ion adsorption data on the synthesized poly(acrylo‐amidino diethylene diamine) were obtained. Fourier transform infrared studies of these adsorptions were also performed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2430–2440, 2004
Influence of conservation on calculations of amino acid covariance in multiple sequence alignments
Authors: Fodor Anthony A. , Aldrich Richard W. 
Published: May 2004

AbstractIt has long been argued that algorithms that find correlated mutations in multiple sequence alignments can be used to find structurally or functionally important residues in proteins. We examined the properties of four different methods for detecting these correlated mutations. On both simple, artificial alignments and real alignments from the Pfam database, we found a surprising lack of agreement between the four correlated mutation methods. We argue that these differences are caused in part by differing sensitivities to background conservation. Correlated mutation algorithms can be envisioned as “filters” of background conservation with each algorithm searching for correlated mutations that occur at a different background conservation frequency. Proteins 2004. © 2004 Wiley‐Liss, Inc.
Change in protein flexibility upon complex formation: Analysis of Ras‐Raf using molecular dynamics and a molecular framework approach
Authors: Gohlke Holger , Kuhn Leslie A. , Case David A. 
Published: May 2004

AbstractChanges in flexibility upon protein–protein complex formation of H‐Ras and the Ras‐binding domain of C‐Raf1 have been investigated using the molecular framework approach FIRST (Floppy Inclusion and Rigid Substructure Topology) and molecular dynamics simulations (MD) of in total ∼35 ns length. In a computational time of about one second, FIRST identifies flexible and rigid regions in a single, static three‐dimensional molecular framework, whose vertices represent protein atoms and whose edges represent covalent and non‐covalent (hydrogen bond and hydrophobic) constraints and fixed bond angles within the protein. The two methods show a very good agreement with respect to the identification of changes in flexibility in both binding partners on a local scale. This implies that flexibility can be successfully predicted by identifying which bonds limit motion within a molecule and how they are coupled. In particular, as identified by MD, the β‐sheet in Raf shows considerably more pronounced orientational correlations in the bound state compared to the unbound state. Similarly, FIRST assigns the β‐sheet to the largest rigid cluster of the complex. Interestingly, FIRST allows us to identify that interactions across the interface (but not conformational changes upon complex formation) result in the observed rigidification. Since regions of the β‐sheet of Raf that do not interact directly with Ras become rigidified, this also demonstrates the long‐range aspect to rigidity percolation. Possible implications of the change of flexibility of the Ras‐binding domain of Raf on the activation of Raf upon complex formation are discussed. Finally, the sensitivity of FIRST results with respect to the representation of non‐covalent interactions used as constraints is probed. Proteins 2004. © 2004 Wiley‐Liss, Inc.
Quantum descriptors for biological macromolecules from linear‐scaling electronic structure methods
Authors: Khandogin Jana , York Darrin M. 
Published: May 2004

AbstractThe characterization of electrostatic and chemical properties at the surface of biological macromolecules is of interest in elucidating the fundamental biological structure‐function relationships as well as in problems of rational drug design. This paper presents a set of macromolecular quantum descriptors for the characterization of biological macromolecules in solution that can be obtained with modest computational cost from linear‐scaling semi‐empirical quantum/solvation methods. The descriptors discussed include: solvent‐polarized electrostatic surface potential maps, equilibrated atomic charges, Fukui reactivity indices, approximate local hardness maps, and relative proton potentials. These properties are applied to study the conformational dependence of the electrostatic surface potential of the solvated phosphate‐binding protein mutant (T141D), the regioselectivity of the zinc finger domains of HIV‐1 nucleocapsid (NC) protein, and the order of pKa values of acidic residues in turkey ovomucoid third domain (OMTKY3) and of the zinc‐binding residues in the carboxyl terminal zinc finger of NC. In all cases, insight beyond that obtainable from purely classical models is gained and can be used to rationalize the experimental observations. The macromolecular quantum descriptors presented here greatly extend the arsenal of tools for macromolecular characterization and offer promise in applications to modern structure‐based drug design. Proteins 2004. © 2004 Wiley‐Liss, Inc.
Profile–profile methods provide improved fold‐recognition: A study of different profile–profile alignment methods
Authors: Ohlson Tomas , Wallner Björn , Elofsson Arne 
Published: May 2004

AbstractTo improve the detection of related proteins, it is often useful to include evolutionary information for both the query and target proteins. One method to include this information is by the use of profile–profile alignments, where a profile from the query protein is compared with the profiles from the target proteins. Profile–profile alignments can be implemented in several fundamentally different ways. The similarity between two positions can be calculated using a dot‐product, a probabilistic model, or an information theoretical measure. Here, we present a large‐scale comparison of different profile–profile alignment methods. We show that the profile–profile methods perform at least 30% better than standard sequence‐profile methods both in their ability to recognize superfamily‐related proteins and in the quality of the obtained alignments. Although the performance of all methods is quite similar, profile–profile methods that use a probabilistic scoring function have an advantage as they can create good alignments and show a good fold recognition capacity using the same gap‐penalties, while the other methods need to use different parameters to obtain comparable performances. Proteins 2004. © 2004 Wiley‐Liss, Inc.
A modified internal lock‐mass method for calibration of the product ions derived from sustained off‐resonance irradiation collision‐induced dissociation using a Fourier transform mass spectrometer
Authors: Duan Lifang , Chan T.‐W. Dominic 
Published: May 2004

AbstractA modified internal lock‐mass calibration method is introduced for improving the mass measurement accuracy of the product ion spectra derived from sustained off‐resonance irradiation collision‐induced dissociation (SORI‐CID) Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. This method involves an initial external calibration of the Fourier transform mass spectrometer to obtain the initial A‐ and B‐terms for the equation (fi = A/(m/z)i + B). The A‐term is adjusted by using an empirical relationship between the up‐shift of the A‐term and the pulse‐gas duration, whereas the B‐term is adjusted by using the mass of the unfragmented precursor ion from the SORI‐CID mass spectrum of the unknown sample as internal lock‐mass. These adjusted A‐ and B‐terms are then used to provide exact mass SORI‐CID calibration for the unknown sample. The modified internal lock‐mass method achieved average mass measurement accuracy of ∼3 ppm which is significantly better than that of the conventional internal lock‐mass calibration (∼9 ppm) and is approaching that of the internal calibration (∼2 ppm) and requires no addition of internal calibrant or instrumental modifications. Copyright © 2004 John Wiley & Sons, Ltd.
Electrospray ionization mass spectrometric analysis of nucleic acids using high‐throughput on‐line desalting
Authors: Fountain Kenneth J. , Gilar Martin , Gebler John C. 
Published: May 2004

AbstractA rapid on‐line desalting method utilizing ion‐pair reversed‐phase high‐performance liquid chromatography (IP‐RP‐HPLC) was employed in tandem with negative electrospray ionization mass spectrometry (ESI‐MS) for the routine analysis of nucleic acids. Desalting was performed on a short 10 × 2.1 mm guard column packed with 3.5 μm C18 sorbent. The HPLC system was connected in‐line to an orthogonal ESI‐TOF mass spectrometer via a six‐port, two‐position switching valve, allowing desalting followed by mass analysis of nucleic acids. Duty cycle times for the method were as low as 1.5 min per sample. This allowed for the analysis of approximately 950 samples per 24‐h time period, which is suitable for medium‐ to high‐throughput applications. Average mass accuracy was determined to be 80 ppm for oligonucleotides up to 110 mer in length with external calibration. The method was utilized for synthetic oligonucleotide quality control and analysis of DNA genotyping fragments. Copyright © 2004 John Wiley & Sons, Ltd.
Fragmentation of biotinylated cyclic peptides
Authors: Lassman Michael E. , Kulagina Nadia , Taitt Chris Rowe 
Published: May 2004

AbstractElectrospray ionization coupled with tandem mass spectrometry (MS/MS) was used to determine the preferred binding site(s) of biotin NHS ester with a series of cyclic peptides with antibiotic properties. The peptides investigated are polymyxins, cyclic peptides produced by Bacillus polymyxa. In spite of the 1:1 stoichiometry used in the labeling reaction, multiple biotin molecules were incorporated into intact polymyxin peptides. Given the amine specificity of the activated biotin and the large number of amino acids with primary amines in the polymyxins, it was not clear by inspection which binding sites were more reactive than others. MS/MS was used to characterize the structure of the biotinylated peptides. MS/MS spectra of cyclic peptides often lead to ambiguous structure determinations due to the potential for multiple ring openings which result in the generation of multiple ion series. The MS/MS spectra of polymyxin peptides are especially difficult to characterize due to the lack of variety in their amino acids; however, the added complexity of the biotin aided the elucidation of the fragmentation pathways. MS/MS spectra of the species with biotin additions were used to rationalize the preferential binding sites of these molecules. Published in 2004 by John Wiley & Sons, Ltd.
Laparoscopic Cholecystectomy: Its Effect on the Prognosis of Patients with Gallbladder Cancer
Authors: de Aretxabala Xabier A. , Roa Ivan S. , Mora Javier P. , Orellana Juan J , Riedeman Juan P. , Burgos Luis A. , Silva Veronica P. , Cuadra Alvaro J. , Wanebo Harold J. 
Published: May 2004

AbstractNumerous reports suggest more recurrences and a worse prognosis after laparoscopic cholecystectomy (LC) than after open cholecystectomy (OC). The objective of this study was to compare the survival rate of patients undergoing a laparoscopic procedure versus those undergoing an open operation. A series of 24 patients with gallbladder cancer detected after LC were compared with 40 consecutive patients with gallbladder cancer detected after OC. Patients were matched by wall invasion, age, and whether they underwent a reoperation or only cholecystectomy. The series included 2 patients with in situ tumors, 2 with mucosal tumors, 1 with muscular invasion, 13 with subserosal invasion, and 6 with serosal invasion. Recurrences were observed in 4 of the 10 patients with subserosal compromise who underwent reoperation. In contrast, in the OC group of 26 patients with subserosal invasion, 20 of whom were reoperated, only 2 had a recurrence. Of the six patients with serosal infiltration, three in the LC underwent reoperation, all of whom had recurrences that precluded resection. Of the 12 patients in the OC group who presented with serosal invasion, 6 were reoperated and 4 had a recurrence. Overall survival curves did not show differences when patients were compared according to the type of procedure performed. Similarly, the analysis of patients according to the level of wall invasion indicated that there was no significant difference in survival. Although multiple reports have shown a worse prognosis for patients with gallbladder cancer undergoing LC, this study did not show a significant survival difference between the two methods. Although there is a higher but insignificant recurrence rate among the patients who underwent LC, this is not translated into survival.
Usefulness of Radio‐guided Surgery Using Technetium‐99m Methoxyisobutylisonitrile for Primary and Secondary Hyperparathyroidism
Authors: Takeyama Hiroshi , Shioya Hisashi , Mori Yutaka , Ogi Shigeyuki , Yamamoto Hiroyasu , Kato Naohiko , Kinoshita Satoki , Yoshida Kazuhiko , Uchida Ken , Yamazaki Yoji 
Published: May 2004

AbstractThe efficacy of technetium‐99m methoxyisobutylisonitrile (99mTc‐MIBI)‐guided surgery for detecting abnormal parathyroid glands in patients with secondary hyperparathyroidism (2‐HPT) was evaluated and compared with the results from the same examination in patients with primary hyperparathyroidism (1‐HPT). The results were also compared with those found by ultrasonography (US) and preoperative 99mTc‐MIBI scintigraphy was also made. At operation 99mTc‐MIBI accumulated in 64 nodules of 15 cases of 2‐HPT, and all of 60 parathyroid swellings were detected (true‐positives 60, sensitivity 100%, accuracy 94%). In the cases of 1‐HPT, 99mTc‐MIBI revealed 11 hot nodules in 10 cases, and the evaluation was true‐positive 10, sensitivity 100%, and accuracy 91%. US and preoperative 99mTc‐MIBI scintigraphy in patients with 2‐HPT had a sensitivity of 75% and 67% and an accuracy of 70% and 66%, respectively. The usefulness of 99mTc‐MIBI‐guided surgery for detecting abnormal parathyroid tissue in 2‐HPT patients was similar to that in 1‐HPT patients but was superior to US and preoperative 99mTc‐MIBI scintigraphy. Intraoperative 9mTc‐MIBI for patients with 2‐HPT is effective and makes the surgery easier, especially when the parathyroid glands are ectopic or when a few glands are markedly enlarged but the other glands are atrophied.
Combined Assessment of β‐d‐Glucan and Degree of Candida Colonization before Starting Empiric Therapy for Candidiasis in Surgical Patients
Authors: Takesue Yoshio , Kakehashi Masayuki , Ohge Hiroki , Imamura Yuuji , Murakami Yoshiaki , Sasaki Masaru , Morifuji Masahiko , Yokoyama Yujiro , Kouyama Mohei , Yokoyama Takashi , Sueda Taijiro 
Published: May 2004

AbstractThe purpose of the study was to investigate whether examination for plasma β‐d‐glucan, a cell wall constituent of fungi, is useful for selecting surgical patients with Candida colonization who would benefit from empiric antifungal therapy. We administered fluconazole to postoperative patients with Candida colonization who have risk factors for candidemia and complained of persistent fever despite prolonged antibacterial therapy. We then analyzed the clinical outcomes regarding the number of sites colonized with Candida spp. and plasma β‐d‐glucan. Of the 32 patients positive for β‐d‐glucan, 15 (46.9%) responded to the empiric therapy; only 9% of those who were negative responded (p < 0.01). In the multiple logistic regression analysis, being positive for β‐d‐glucan was a significant factor predicting response, with an adjusted odds ratio of 12.9 in patients with Candida colonization [95% confidence interval (CI) 2.07–80.73) (p < 0.01). In addition, the number of sites colonized with Candida spp. was a significant factor predicting response, with an estimated exposure odds ratio of 7.57 for those who were colonized at three or more sites compared with those colonized at one site (95% CI 1.20–47.70) (p = 0.031). In patients with Candida colonization, assessment of β‐d‐glucan was useful for deciding whether to start empiric therapy for suspected candidiasis in surgical patients.