bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the cure reaction of carbon nanotubes/epoxy resin composites through thermal analysis and Raman spectroscopy
Authors: Puglia D. , Valentini L. , Kenny J. M.
Published: February 2003

The effect of the incorporation of single‐walled carbon nanotubes (SWNTs) onto a diglycidyl ether of bisphenol A‐based (DGEBA) epoxy resin cure reaction was investigated by thermal analysis and Raman spectroscopy. The results of the investigation show that SWNTs act as a strong catalyst. A shift of the exothermic reaction peak to lower temperatures is, in fact, observed in the presence of SWNTs. Moreover, these effects are already noticeable at the lowest SWNT content investigated (5%) with slight further effects at higher concentrations, suggesting a saturation of the catalyzing action at the higher concentrations studied. The curves obtained under isothermal conditions confirm the results obtained in nonisothermal tests showing that the cure reaction takes less time with respect to the neat epoxy. The thermal degradation of cured DGEBA and DGEBA/SWNT composites was examined by thermogravimetry, showing a faster thermal degradation for DGEBA–SWNT composites. Raman spectroscopy was successfully applied to demonstrate that the observed changes in the cure reaction of the composites lead to a different residual strain on the SWNT bundles following a different intercalation of the epoxy matrix. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 452–458, 2003
Ethylene polymerization with a silica‐supported iron‐based diimine catalyst
Authors: Ma Zhi , Ke Yucai , Wang Hang , Guo Cunyue , Zhang Mingge , Sun Wen‐Hua , Hu Youliang
Published: February 2003

A supported iron‐based diimine catalyst (SC) was prepared by immobilization of 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine iron chloride (I) on silica and employed in ethylene polymerization. The kinetic behavior of ethylene polymerization with SC was studied. The effects of the Al/Fe molar ratio, reaction temperature, and cocatalyst on the catalytic activity as well as the melting temperature, molecular weight, and morphology of the polymers obtained were also investigated. The results showed that good catalytic activities can be obtained even with a small amount of the cocatalyst methylaluminoxane (MAO) or triethylaluminum (AlEt3). The polyethylenes obtained with a supported catalyst had higher molecular weight, higher melting temperature, and better morphology than those obtained with a homogeneous catalyst. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 466–469, 2003
Iron(II)‐based catalysts for ethene oligomerization
Authors: Schmidt Roland , Hammon Ulrich , Gottfried Stefan , Welch M. Bruce , Alt Helmut G.
Published: February 2003

The synthesis of iron(II) complexes with various tridentate di(imino)pyridine ligands and their potential as ethene oligomerization catalysts are described. The ligands are characterized by 1H‐ and 13C‐NMR spectroscopy and the complexes only by mass spectrometry due to their paramagnetism. After activation either with methylalumoxane (MAO) or with a heterogeneous cocatalyst consisting of partially hydrolyzed trimethylaluminum and silica gel, the prepared complexes proved to be good catalysts for the oligomerization of ethene. 1‐Octene, 1‐hexene, and 1‐decene were the major products, formed in very high isomeric purity (99.9 %). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 476–482, 2003
Structural properties of CrF3‐ and MnCl2‐filled poly(vinylalcohol) films
Authors: Zidan H. M.
Published: February 2003

Poly(vinylalcohol) (PVA) films filled with different filling levels of CrF3 and MnCl2 have been prepared by the casting method. Differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) analysis were used to study the changes in structure properties that occur due to filling. The changes occurring in the measured parameters with increasing the filler content was been interpreted in terms of the structural modification of the PVA matrix. It was found that all studied samples had the main melting temperature due to the main crystalline phase of PVA. The intensity and position of this peak depended on the filling level. On the other hand, the samples of CrF3‐filled PVA films with filling level W ≥ 10 wt % revealed another melting temperature, indicating the presence of a new crystalline phase besides the main crystalline phase. Changes occurring in the degree of crystallinity of the studied samples were discussed. The calculated degree of crystallinity was formulated numerically to be an exponential function of filling level. The X‐ray diffraction patterns of the studied samples confirmed the DSC results. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 516–521, 2003
Surface modification of polybutadiene facilitated by supercritical carbon dioxide
Authors: Ngo Truc T. , McCarney Jonathan , Brown James S. , Lazzaroni Michael J. , Counts Karl , Liotta Charles L. , Eckert Charles A.
Published: February 2003

The hydrophilicity of polymers can be improved through surface modification, traditionally done with conventional organic solvents, but these may cause the deterioration of polymer bulk properties due to irreversible polymer swelling. However, supercritical carbon dioxide (scCO2) not only swells the polymer reversibly, but also acts as a convenient transport medium for monomeric solutes, which may be subsequently polymerized. Thus we are able to modify the polymer surface without affecting its bulk strength and durability. Here we report scCO2 surface modification of polybutadiene using ultraviolet‐visible (UV/Vis) and Fourier transform infrared (FTIR) spectroscopy. Monomers such as 3‐vinylbenzoic acid and crotonic acid are used to study the effects of pressure, solute structure, and reaction mechanism on the diffusion rates and partitioning of monomers between the fluid phase and the polymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 522–530, 2003
Effects of dynamic strength training on physical function, Valpar 9 work sample test, and working capacity in patients with recent‐onset rheumatoid arthritis
Authors: Häkkinen Arja , Sokka Tuulikki , Lietsalmi Anna‐Maria , Kautiainen Hannu , Hannonen Pekka
Published: February 2003

Objective

To study the impact of 24 months of strength training on the physical function of patients with early rheumatoid arthritis (RA).

Methods

Seventy patients were assigned to either the strength training (experimental) group (n = 35) or the control group (n = 35). Patients in the experimental group performed strength training for 24 months, and control patients were instructed to perform range of motion exercises. Maximal strength of the knee extensors, trunk flexors, and extensors, as well as grip strength were recorded with dynamometers. Disease activity was assessed by the erythrocyte sedimentation rate and Ritchie's articular index, joint damage was determined by the Larsen x‐ray index, and functional capacity was assessed using the Valpar 9 test and the Stanford Health Assessment Questionnaire (HAQ). The employment status of each patient was recorded.

Results

In the experimental group, strength training led to significant increases (19–59%) in maximal strength of the trained muscles. Such increases in the control group varied from 1% to 31%. There was a clear training effect on muscular strength in favor of the experimental group, but significant improvements in the HAQ indices as well as in the Valpar 9 test were seen also in control patients. Results of the Valpar 9 and the HAQ were statistically significantly better in patients who remained gainfully employed compared with patients who retired preterm during followup. However, compared with patients who remained in the work force, patients who retired were older, and their work was physically more demanding.

Conclusion

As expected, strength training led to increased muscle strength, but this increase did not correlate with improved physical function as assessed by the Valpar 9 work sample test. The increased muscle performance did not prevent a substantial proportion of patients from retiring preterm. The 2 items from the Valpar 9 test that were applied were not sensitive enough to differentiate the patients according to their working status.
The assessment of rheumatoid arthritis and the acceptability of self‐report questionnaires in clinical practice
Authors: Wolfe Frederick , Pincus Theodore , Thompson Ann K. , Doyle Joseph
Published: February 2003

Objective

To assess the acceptability of self‐report questionnaires (SRQ) in clinical practice and to understand the value that rheumatologists give to various assessment methods in rheumatoid arthritis.

Methods

Rheumatologists who completed a training course in the use of SRQ in clinical trials and clinical practice used the SRQ in their practices. Six months later 221 rheumatologists completed a survey regarding their experiences in assessing rheumatoid arthritis and in the use of SRQ.

Results

Prior to the start of the program, 18% of rheumatologists used self‐report questionnaires, 6 months later, 48% were using SRQ in their practices. Rheumatologists who did not use questionnaires placed less value on all assessment methods, and particularly on questionnaire assessments of function and pain. They also were more likely to report that questionnaires were difficult to use, not accepted by staff, were too long, and that they had limited staff. Rheumatologists who used the questionnaires reported none of these difficulties and were satisfied with the benefits provide by SRQ. When assessment measures were ranked, rheumatologist ranked ACR 20, radiography, and erythrocyte sedimentation rate/c‐reactive protein as the least important in both clinical trials and in clinical practice, and they rated swollen and tender joint counts followed by SRQ as the most useful assessment tools.

Conclusion

SRQ are well received by rheumatologists, and following a training program almost 50% continued to use SRQ in their practices. Those who used questionnaires were generally more positive about assessments and had little difficulty in the technical aspects of administration, scoring, and interpretation.
Costs and predictors of costs in rheumatoid arthritis: A prevalence‐based study
Authors: Lajas Cristina , Abasolo Lydia , Bellajdel Boutayeb , Hernández‐García César , Carmona Loreto , Vargas Emilio , Lázaro Pablo , Jover Juan A.
Published: February 2003

Objective

To analyze the annual cost of rheumatoid arthritis (RA) and its predictive factors.

Methods

Data were obtained from a 12‐month retrospective cohort of 201 RA patients, randomly selected from a rheumatology registry, through a structured interview and records of the Central Information System of the hospital. Results were divided into direct, indirect, and total costs in 2001 US dollars. A sensitivity analysis was performed. Multiple linear regression models for the different types of costs were carried out.

Results

The total cost was $2.2 million per year, with a cost attributable to RA of $2.07 million per year. The average cost per patient was $10,419 per year (ranging from $7,914 per patient per year in the best scenario to $12,922 per patient per year in the worst case). Direct costs represent nearly 70% of total costs. We found an average increment in total costs of $11,184 per year per unit of Health Assessment Questionnaire (HAQ) score (P < 0.0001) and an average annual increment of $621 per year of disease (P < 0.0001). After adjustment, the HAQ score, inability to perform housework tasks, and being permanently disabled for work were the only predictors of high costs.

Conclusion

Our data show a remarkable economic impact of RA over society and link the costs of the disease to its consequences in terms of functional disability, work disability, and housework disability.
Preoperative predictors of locomotor ability two months after total knee arthroplasty for severe osteoarthritis
Authors: Parent Éric , Moffet Hélène
Published: February 2003

Objective

To identify preoperative predictors of locomotor ability 2 months after total knee arthroplasty (TKA).

Methods

Sixty‐five participants scheduled for a first TKA were recruited. The dependent variable was the distance covered during the 6‐minute gait test 2 months after TKA. The independent variables, measured before surgery, were grouped into 3 categories: 1) personal; 2) organic system, and 3) capability variables. Multiple regression analyses were conducted to determine the best predictors of the dependent variable. Modified cross‐validation of the model combining predictors from the three categories was obtained with 10 random samples derived from the original cohort by resampling with replacement.

Results

Predictors were identified in the 3 categories: 1) gender, number of comorbidities, body mass index, 2) knee pain, flexion and strength, lower limb mechanical power, and 3) preoperative 6‐minute gait distance. When these variables were modeled together only the preoperative 6‐minute gait distance and knee pain and flexion remained significant (adjusted R2= 0.66).

Conclusion

Using variables easily measured before surgery, it is possible to predict with good accuracy locomotor ability 2 months after TKA.
Isometric muscle force measurement for clinicians treating patients with osteoarthritis of the knee
Authors: Fransen Marlene , Crosbie Jack , Edmonds John
Published: February 2003

Objective

To evaluate the discriminant validity and, for clinicians, the test–retest reliability of isometric force in patients with knee osteoarthritis (OA).

Methods

Mean isometric muscle strength data collected for 113 patients with knee OA were compared with published normative data for 131 asymptomatic subjects.

Results

Patients with knee OA, ages 60–79 years, could attain only 40–53% of the knee extensor force and 35–46% of the knee flexor force generated by their age‐ and sex‐matched peers. One‐week test–retest intraclass correlations ranged from 0.79 to 0.95. Random measurement error demonstrated a favorable “signal‐to‐noise” ratio.

Conclusion

The similar decrease in knee extensor and knee flexor strength demonstrated by patients with knee OA compared with their age‐ and sex‐matched asymptomatic peers suggests that strategies should be directed at both muscle groups to optimally limit joint damage. Isometric muscle force measurement can be a useful assessment tool for clinicians.
Use of complementary and alternative medicine by pediatric rheumatology patients
Authors: Hagen Lorrie E. M. , Schneider Rayfel , Stephens Derek , Modrusan Diana , Feldman Brian M.
Published: February 2003

Objective

To assess how often the patients in The Hospital for Sick Children's rheumatology clinic use complementary and alternative medicine (CAM), and the type of CAM used.

Methods

Cross‐sectional descriptive survey study in a tertiary care referral center.

Results

We found that 90 (64%) of 141 respondents used at least 1 form of CAM; 45 (50%) of these 90 used more than 1 form. Duration of illness was positively associated with the use of CAM; the difference in the mean length of illness between users (4.12 ± 3.60 years) and nonusers (2.82 ± 3.23 years) was 1.3 years (P = 0.04). Of the 41 respondents with more than 1 illness, 32 used CAM, compared with 57 of 96 who had only 1 illness (P = 0.036).

Conclusion

Health care providers must be aware of their patients' possible use of CAM, especially those with more than 1 illness.
Gaussian docking functions
Authors: McGann Mark R. , Almond Harold R. , Nicholls Anthony , Grant J. Andrew , Brown Frank K.
Published: February 2003

A shape‐based Gaussian docking function is constructed which uses Gaussian functions to represent the shapes of individual atoms. A set of 20 trypsin ligand–protein complexes are drawn from the Protein Data Bank (PDB), the ligands are separated from the proteins, and then are docked back into the active sites using numerical optimization of this function. It is found that by employing this docking function, quasi‐Newton optimization is capable of moving ligands great distances [on average 7 Å root mean square distance (RMSD)] to locate the correctly docked structure. It is also found that a ligand drawn from one PDB file can be docked into a trypsin structure drawn from any of the trypsin PDB files. This implies that this scoring function is not limited to more accurate x‐ray structures, as is the case for many of the conventional docking methods, but could be extended to homology models. © 2002 Wiley Periodicals, Inc. Biopolymers 68: 76–90, 2003
The relaxed complex method: Accommodating receptor flexibility for drug design with an improved scoring scheme
Authors: Lin Jung‐Hsin , Perryman Alexander L. , Schames Julie R. , McCammon J. Andrew
Published: February 2003

An extension of the new computational methodology for drug design, the “relaxed complex” method (J.‐H. Lin, A. L. Perryman, J. R. Schames, and J. A. McCammon, Journal of the American Chemical Society, 2002, vol. 24, pp. 5632–5633), which accommodates receptor flexibility, is described. This relaxed complex method recognizes that ligand may bind to conformations that occur only rarely in the dynamics of the receptor. We have shown that the ligand–enzyme binding modes are very sensitive to the enzyme conformations, and our approach is capable of finding the best ligand enzyme complexes. Rapid docking serves as an efficient initial filtering method to screen a myriad of docking modes to a limited set, and it is then followed by more accurate scoring with the MM/PBSA (Molecular Mechanics/Poisson Boltzmann Surface Area) approach to find the best ligand–receptor complexes. The MM/PBSA scorings consistently indicate that the calculated binding modes that are most similar to those observed in the x‐ray crystallographic complexes are the ones with the lowest free energies. © 2002 Wiley Periodicals, Inc. Biopolymers 68: 47–62, 2003
Atomistic protein folding simulations on the submillisecond time scale using worldwide distributed computing
Authors: Pande Vijay S. , Baker Ian , Chapman Jarrod , Elmer Sidney P. , Khaliq Siraj , Larson Stefan M. , Rhee Young Min , Shirts Michael R. , Snow Christopher D. , Sorin Eric J. , Zagrovic Bojan
Published: February 2003

Atomistic simulations of protein folding have the potential to be a great complement to experimental studies, but have been severely limited by the time scales accessible with current computer hardware and algorithms. By employing a worldwide distributed computing network of tens of thousands of PCs and algorithms designed to efficiently utilize this new many‐processor, highly heterogeneous, loosely coupled distributed computing paradigm, we have been able to simulate hundreds of microseconds of atomistic molecular dynamics. This has allowed us to directly simulate the folding mechanism and to accurately predict the folding rate of several fast‐folding proteins and polymers, including a nonbiological helix, polypeptide α‐helices, a β‐hairpin, and a three‐helix bundle protein from the villin headpiece. Our results demonstrate that one can reach the time scales needed to simulate fast folding using distributed computing, and that potential sets used to describe interatomic interactions are sufficiently accurate to reach the folded state with experimentally validated rates, at least for small proteins. © 2002 Wiley Periodicals, Inc. Biopolymers 68: 91–109, 2003
Condensation heat transfer on tubes in actual flue gas (Parametric study for condensation behavior)
Authors: Osakabe Masahiro , Yagi Kiyoyuki , Itoh Tsugue , Ohmasa Kunimitsu
Published: February 2003

In order to improve boiler efficiency, latent heat recovery from the flue gas is a very important concept. Condensation heat transfer on horizontal tubes was investigated experimentally by using flue gas from a natural gas boiler. The parametric studies concerning the effects of tube stages, gas velocities, SO2 in the flue gas, and Teflon‐lined tubes were conducted at a wide range of tube surface temperature. The heat transfer was enhanced at the second stage due to the wake turbulence of the first stage. No significant decrease of the condensation in the second stage due to the condensate falling from the first stage could be observed. Even at the high gas velocity condition, the condensation pattern was similar to that observed in previous low gas velocity experiments. The effect of SO2 in the flue gas on the condensation behavior could not be observed. The heat and mass transfer behaviors on stainless‐steel and Teflon‐lined surfaces were well predicted with the analogy correlation. The above results suggested that the heat and mass transfer were dominated by the convection and diffusion process on the gas side. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(2): 153–166, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10079
Study of thermal characteristics of bubble‐driven heat‐transport device
Authors: Nishio Shigefumi , Nagata Shin‐ichi , Numata Shohei , Shirakashi Ryo
Published: February 2003

In the present paper, we report on heat transport rates and fluid flow patterns of a bubble‐driven heat‐transport device (BD‐HTD) made of glass, obtained with the working fluids water, soapsuds, ethanol, and R141b. In this type of HTD, the cooling and heating sections are connected to each other by a closed loop of tube meandering between them, and the loop is filled to a certain volume fraction with a working fluid. The present BD‐HTD was set vertically and was heated at the bottom by warm water and cooled at the top by cold water. Experimental parameters were the inner diameter of the tube (D = 1.8, 2.4, 5.0 mm), the total temperature difference of heating and cooling water (ΔT = 20 to 60 K), and liquid volume fraction (α = 18 to 98%). The main results are summarized as follows. Heat transfer coefficient of the working fluid at the heating and cooling sections, hfi, is not strongly dependent on α and ΔT. Among the present test liquids, the effective thermal conductivity kef is the highest for R141b, but the heat transfer coefficient hfi is the highest for water. As kef is sufficiently high even for water, the heat transport rate Q is the highest for water. Q of the present BD‐HTD using water can exceed the maximum heat transport rate of conventional heat pipes of the same geometry. For R141b, the BD‐HTD operated for D/λ0 = 1.5 to 4.2 (λ0: the capillary length) and Q is not strongly dependent on the tube diameter. This result indicates that BD‐HTDs are suitable for micro‐HTDs, but the BD‐HTD did not operate with water at D/λ0 = 0.65. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(2): 167–177, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10082
Differentiation of a pair of diastereomeric tertiarybutoxycarbonylprolylproline ethyl esters by collision‐induced dissociation of sodium adduct ions in electrospray ionization mass spectrometry and evidence for chiral recognition by ab initio molecular orbital calculations
Authors: Tsunematsu Hideaki , Ikeda Hirohito , Hanazono Hiroshi , Inagaki Masanori , Isobe Ryuichi , Higuchi Ryuichi , Goto Yoshinobu , Yamamoto Magobei
Published: February 2003

The fragmentation of the sodium adduct ions for tert‐butoxycarbonyl‐L‐prolyl‐L‐proline ethyl ester (Boc‐L‐Pro‐L‐Pro‐OEt) was compared with that for Boc‐D‐Pro‐L‐Pro‐OEt in positive‐ion electrospray ionization (ESI) mass spectrometry. In the collision‐induced dissociation (CID) mass spectra of the [M + Na]+ ions, the abundance of the [M + Na − C(CH3)3 + H]+ ion, which is due to the loss of a tert‐butyl group from the [M + Na]+ ion for Boc‐D‐Pro‐L‐Pro‐OEt, was about eight times higher than that for Boc‐L‐Pro‐L‐Pro‐OEt. In addition, in the CID spectra of the sodium adduct fragment ion ([M + Na − Boc + H]+), the abundance of the [M + Na − Boc − prolylresidue + H]+ ion, which is due to the loss of prolyl residue from the [M + Na − Boc + H]+ ion for Boc‐L‐Pro‐L‐Pro‐OEt, was about five times higher than that for Boc‐D‐Pro‐L‐Pro‐OEt. These results indicate that Boc‐L‐Pro‐L‐Pro‐OEt was distinguished from Boc‐D‐Pro‐L‐Pro‐OEt by the CID mass spectra of the sodium adduct ions in ESI mass spectrometry. The optimized geometries of the [M + Na]+ and the [M + Na − Boc + H]+ ions calculated by ab initio molecular orbital calculations suggest that the chiral recognition of these diastereomers was due to the difference of the orientation of a sodium ion to the oxygen and nitrogen atoms in dipeptide derivatives, and to the difference of the total energies between them. Copyright © 2003 John Wiley & Sons, Ltd.
Deconvolution of mass spectra measuredwith a non‐uniform detector array to give accurate ion abundances
Authors: Birkinshaw K.
Published: February 2003

Array detectors are under active development since they offer large improvements in the efficiency of mass spectrum measurements. High quality is always a requirement whether array detectors are used for ions, electrons, UV, x‐rays, etc., but in mass spectrometry the very high accuracy frequently needed in ion abundance measurements for isotope ratios is unique. These demands necessitate modelling the measurement process and careful deconvolution of the measured data. A linear model in terms of matrix algebra is presented in which the incident spectrum (unknown) and the measured spectrum are represented by column matrices and the action of the detector array on the incident spectrum is represented by an experimentally measurable square ‘A’ matrix. Residual noise in this matrix can be minimized following a singular value decomposition procedure and its use in ‘forward deconvolution’ of measured spectra is discussed. The random error in the incident ion counts is accounted for after the deconvolution since this is not an error from the perspective of the detector. The microchannel plate electron multiplier gain distribution is an important feature of the deconvolution. Copyright © 2003 John Wiley & Sons, Ltd.
Addressing the metabolic activation potential of new leads in drug discovery: a case study using ion trap mass spectrometry and tritium labeling techniques
Authors: Samuel Koppara , Yin Wenji , Stearns Ralph A. , Tang Yui S. , Chaudhary Ashok G. , Jewell James P. , Lanza Thomas , Lin Linus S. , Hagmann William K. , Evans David C. , Kumar Sanjeev
Published: February 2003

Metabolic activation of drug candidates to electrophilic reactive metabolites that can covalently modify cellular macromolecules may result in acute and/or idiosyncratic immune system‐mediated toxicities in humans. This presents a significant potential liability for the future development of these compounds as safe therapeutic agents. We present here an example of an approach where sites of metabolic activation within a new drug candidate series were rapidly identified using online liquid chromatography/multi‐stage mass spectrometry on an ion trap mass spectrometer. This was accomplished by trapping the reactive intermediates formed upon incubation of compounds with rat and human liver microsomes as their corresponding glutathione conjugates and mass spectral characterization of these thiol adducts. Based on the structures of the GSH adducts identified, potential sites and mechanisms of bioactivation within the chemical structure were proposed. These metabolism studies were interfaced with iterative structural modifications of the chemical series in order to block these bioactivation sites within the molecule. This strategy led to a significant reduction in the propensity of the compounds to undergo metabolic activation as evidenced by reductions in the irreversible binding of radioactivity to liver microsomal material upon incubation of tritium‐labeled compounds with this in vitro system. With the efficiency and throughput achievable with such an approach, it appears feasible to identify and address the metabolic activation potential of new drug leads during routine metabolite identification studies in an early drug discovery setting. Copyright © 2003 John Wiley & Sons, Ltd.
Adiabatic RARE imaging
Authors: de Graaf Robin A. , Rothman Douglas L. , Behar Kevin L.
Published: February 2003

The practical implementation of ultra‐fast spin‐echo, or RARE imaging with adiabatic RF pulses and surface coil transmission at 7 T is described. Despite the large RF inhomogeneities, the adiabatic character of the 180° BIR‐4 refocusing pulses ensures optimal sensitivity and minimal image artifacts. An internal ‘phase‐cycle’ is used to remove spurious unwanted coherences. The short T2 relaxation times in rat brain at 7 T demand a centric, rather than a linear coverage of k‐space in order to avoid excessive signal loss. T2 relaxation during k‐space coverage also leads to image blurring, which can be counteracted by interleaved k‐space sampling. The coverage of k‐space in four acquisitions provides high‐quality anatomical images comparable to conventional spin‐echo images. A two‐scan RARE implementation provides sufficient spatial and temporal resolution for most applications. Quantitative mapping of T1 relaxation and cerebral blood flow changes during forepaw stimulation in the rat are demonstrated. Copyright © 2003 John Wiley & Sons, Ltd.
Trait emotional intelligence: behavioural validation in two studies of emotion recognition and reactivity to mood induction
Authors: Petrides K. V. , Furnham Adrian
Published: February 2003

This paper presents two experiments concerning trait emotional intelligence (‘trait EI’). In study 1, ten high and ten low trait EI individuals were selected from a sample of 85 persons to participate in a computerized experiment involving the recognition of morphed emotional expressions. As hypothesized, high trait EI participants were faster at identifying the expressions than their low trait EI counterparts. In study 2, trait EI scores from 102 persons were residualized on the Big Five and subsequently 15 high and 15 low trait EI individuals were selected to participate in a mood induction experiment. As hypothesized, high trait EI participants exhibited greater sensitivity to the mood induction procedure than their low trait EI counterparts. The findings are discussed in terms of the construct validity of trait EI, with particular emphasis on the issue of incremental validity vis‐à‐vis broad personality traits. Copyright © 2002 John Wiley & Sons, Ltd.
Folding in lipid membranes (FILM): A novel method for the prediction of small membrane protein 3D structures
Authors: Pellegrini‐Calace M. , Carotti A. , Jones D. T.
Published: February 2003

We present the results of applying a novel knowledge‐based method (FILM) to the prediction of small membrane protein structures. The basis of the method is the addition of a membrane potential to the energy terms (pairwise, solvation, steric, and hydrogen bonding) of a previously developed ab initio technique for the prediction of tertiary structure of globular proteins (FRAGFOLD). The method is based on the assembly of supersecondary structural fragments taken from a library of highly resolved protein structures using a standard simulated annealing algorithm. The membrane potential has been derived by the statistical analysis of a data set made of 640 transmembrane helices with experimentally defined topology and belonging to 133 proteins extracted from the SWISS‐PROT database. Results obtained by applying the method to small membrane proteins of known 3D structure show that the method is able to predict, at a reasonable accuracy level, both the helix topology and the conformations of these proteins. Proteins 2003;50:537–545. © 2003 Wiley‐Liss, Inc.
A path from primary protein sequence to ligand recognition
Authors: Kho Richard , Baker Brian L. , Newman Joseph V. , Jack Richard M. , Sem Daniel S. , Villar Hugo O. , Hansen Mark R.
Published: February 2003

A novel method to organize protein structural information based solely on sequence is presented. The method clusters proteins into families that correlate with the three‐dimensional protein structure and the conformation of the bound ligands. This procedure was applied to nicotinamide adenine dinucleotide [NAD(P)]‐utilizing enzymes to identify a total of 94 sequence families, 53 of which are structurally characterized. Each of the structurally characterized proteins within a sequence family correlates to a single protein fold and to a common bound conformation of NAD(P). A wide range of structural folds is identified that recognize NAD(P), including Rossmann folds and β/α barrels. The defined sequence families can be used to identify the type and prevalence of NAD(P)‐utilizing enzymes in the proteomes of sequenced organisms. The proteome of Mycobacterium tuberculosis was mined to generate a proteome‐wide profile of NAD(P)‐utilizing enzymes coded by this organism. This enzyme family comprises approximately 6% of the open reading frames, with the largest subgroup being the Rossmann fold, short‐chain dehydrogenases. The preponderance of short‐chain dehydrogenases correlates strongly with the phenotype of M. tuberculosis, which is characterized as having one of the most complex prokaryotic cell walls. Proteins 2003;50:589–599. © 2003 Wiley‐Liss, Inc.
D‐amino acid residues in peptides and proteins
Authors: Mitchell John B.O. , Smith James
Published: February 2003

We have investigated the D‐amino acid residues present in Protein Data Bank (PDB) entries, categorizing them into “real” D‐residues and artifacts. In polypeptide chains of more than 20 residues, only a single instance of a “real” D‐residue, other than those deliberately designed or engineered, was found. This example was the result of a slow chemical epimerization process. Another 12 designed D‐residues were found in these longer polypeptide chains. Smaller peptides of 20 or fewer residues contained 479 “real” D‐residues, the majority in various gramicidin, actinomycin, or cyclosporin structures. We found 148 PDB entries with “real” D‐residues and a further 186, in which all apparent D‐residues are artifacts. Investigating the (ϕ, ψ) preferences of the “real” D‐residues, we found that the region around (−60°, −45°) was almost completely unoccupied, even though it is not formally disallowed. We link the low propensity to occupy this region with the α‐helix destabilizing properties of D‐residues. Proteins 2003;50:563–571. © 2003 Wiley‐Liss, Inc.
A neural network approach to evaluate fold recognition results
Authors: Juan D. , Graña O. , Pazos F. , Fariselli P. , Casadio R. , Valencia A.
Published: February 2003

Fold recognition techniques assist the exploration of protein structures, and web‐based servers are part of the standard set of tools used in the analysis of biochemical problems. Despite their success, current methods are only able to predict the correct fold in a relatively small number of cases. We propose an approach that improves the selection of correct folds from among the results of two methods implemented as web servers (SAMT99 and 3DPSSM). Our approach is based on the training of a system of neural networks with models generated by the servers and a set of associated characteristics such as the quality of the sequence‐structure alignment, distribution of sequence features (sequence‐conserved positions and apolar residues), and compactness of the resulting models. Our results show that it is possible to detect adequate folds to model 80% of the sequences with a high level of confidence. The improvements achieved by taking into account sequence characteristics open the door to future improvements by directly including such factors in the step of model generation. This approach has been implemented as an automatic system LIBELLULA, available as a public web server at http://www.pdg.cnb.uam.es/servers/libellula.html. Proteins 2003;50:600–608. © 2003 Wiley‐Liss, Inc.
Observation of residual dipolar couplings in short peptides
Authors: Ohnishi Satoshi , Shortle David
Published: February 2003

Residual dipolar couplings provide information on the orientation of individual bond vectors with respect to a unique set of molecular axes. We report that short peptides from 2 to 15 amino acids in length of arbitrary sequence exhibit a modest range of residual dipolar couplings when aligned in either strained polyacrylamide gels or alkyl‐PEG bicelles. The absence of significant line broadening in gels suggests peptides align predominantly through steric interactions with the polyacrylamide matrix. However, broadening of NMR lines for a subset of residues aligned in bicelles indicates some peptides bind weakly to these lipid disks, yet a weak negative correlation between the couplings measured in gels and bicelles is consistent with steric hindrance playing a role in both media. The observation of dipolar couplings for peptides of length 10–15 suggests the statistical segment lengths of polypeptide chains must often be >10–15 residues, with data from denatured proteins indicating even larger values. Presumably, local side‐chain backbone interactions severely restrict chain flexibility, with the cumulative effect of many such restrictions giving rise to biases in chain direction that may persist for the entire length of a protein chain. Comparison of experimental dipolar couplings for peptides with couplings calculated for ensembles of conformations generated by molecular dynamics should permit evaluation of the accuracy of molecular mechanics potentials in reproducing sequence‐specific preferences for ϕ and ψ angles. Proteins 2003;50:546–551. © 2003 Wiley‐Liss, Inc.
Real value prediction of solvent accessibility from amino acid sequence
Authors: Ahmad Shandar , Gromiha M. Michael , Sarai Akinori
Published: February 2003

The solvent accessibility of amino acid residues has been predicted in the past by classifying them into exposure states with varying thresholds. This classification provides a wide range of values for the accessible surface area (ASA) within which a residue may fall. Thus far, no attempt has been made to predict real values of ASA from the sequence information without a priori classification into exposure states. Here, we present a new method with which to predict real value ASAs for residues, based on neighborhood information. Our real value prediction neural network could estimate the ASA for four different nonhomologous, nonredundant data sets of varying size, with 18.0–19.5% mean absolute error, defined as per residue absolute difference between the predicted and experimental values of relative ASA. Correlation between the predicted and experimental values ranged from 0.47 to 0.50. It was observed that the ASA of a residue could be predicted within a 23.7% mean absolute error, even when no information about its neighbors is included. Prediction of real values answers the issue of arbitrary choice of ASA state thresholds, and carries more information than category prediction. Prediction error for each residue type strongly correlates with the variability in its experimental ASA values. Proteins 2003;50:629–635. © 2003 Wiley‐Liss, Inc.
Higher accuracy quantum Monte Carlo calculations of the barrier for the H+H2 reaction
Authors: Riley Kevin E. , Anderson James B.
Published: February 2003

We have repeated previous calculations on the potential energy surface for the reaction H+H2→H2+H using Green function diffusion Monte Carlo methods. The barrier height obtained in the new calculations is 9.608±0.001 kcal/mol. Calculations were also made near the Jahn-Teller Cusp and the van der Waals minimum.
Reassessment of the intrinsic carrier density in crystalline silicon in view of band-gap narrowing
Authors: Altermatt Pietro P. , Schenk Andreas , Geelhaar Frank , Heiser Gernot
Published: February 2003

The commonly used value of the intrinsic carrier density of crystalline silicon at 300 K is ni=1.00×1010 cm−3. It was experimentally determined by Sproul and Green, J. Appl. Phys. 70, 846 (1991), using specially designed solar cells. In this article, we demonstrate that the Sproul and Green experiment was influenced by band-gap narrowing, even though the dopant density of their samples was low (1014 to 1016 cm−3). We reinterpret their measurements by numerical simulations with a random-phase approximation model for band-gap narrowing, thereby obtaining ni=9.65×109 cm−3 at 300 K. This value is consistent with results obtained by Misiakos and Tsamakis, J. Appl. Phys. 74, 3293 (1993), using capacitance measurements. In this way, long-prevailing inconsistencies between independent measurement techniques for the determination of ni are resolved.
Electrostatically induced submicron patterning of thin perfect and leaky dielectric films: A generalized linear stability analysis
Authors: Pease Leonard F. , Russel William B.
Published: February 2003

Thin leaky and perfect dielectric films can be driven electrically to form well-ordered patterns typically of pillar arrays. The process, sometimes referred to as lithographically induced self-assembly, begins by spin coating a polymer onto a silicon wafer to generate an initially featureless film. A small gap, filled with air or another polymeric/organic liquid, is left between the first film and a second wafer called the mask, which may be patterned. This configuration is heated above the glass transition temperature of the polymer, upon which flow ensues in response to destabilizing electrical forces. The authors examined the initial stages of pillar formation under a pattern free mask by performing a linear stability analysis under the lubrication approximation [J. Non-Newtonian Fluid Mech. 102, 233 (2002)] and found the quest for smaller pillars to be assisted by the presence of free charge as described by the leaky dielectric. In practice, however, the lubrication approximation may not strictly apply in the situations of greatest interest. Contrasting the linear stability analysis with and without the lubrication approximation shows that the approximation fails where surface tension is small and electric fields are large, typical of experiments with a polymer/organic liquid instead of air in the gap—precisely the conditions that generate the smallest pillar arrays. This general linear stability analysis predicts conditions where pillars/holes pack more tightly, have smaller diameters, greater aspect ratios, and larger growth exponents for both perfect and leaky dielectric films, in which the smallest features reach deep into the submicron length scales. The analysis also highlights two approaches to smaller pillars by either making the polymer film conducting or choosing polymers with high dielectric contrast, with the former being more universally applicable.
Dielectric properties of Li3VO4 single crystals grown by the Czochralski method
Authors: Kim Dong Jin , Jun Byeong Eog , Kim Chung-Sik , Kim Hyung Kook , Kim Jung Nam , Hwang Yoon-Hwae
Published: February 2003

We studied dielectric properties of Li3VO4 single crystals grown by the Czochralski method along the a axis at temperatures ranging from room temperature to 800 °C and frequencies ranging from 100 Hz to 15 MHz. We analyzed the impedance data by introducing an equivalent circuit which consists of two parallel combinations of capacitors and resistors in series. The conductivity and the relaxation time of Li3VO4 are found to show the Arrhenius behavior with two different activation energies which crossed over at temperatures around 400 °C. The observed crossover seems to originate from a dissociation of the Li–O bond at high temperatures.
Formation of face-centered-cubic titanium by mechanical attrition
Authors: Manna I. , Chattopadhyay P. P. , Nandi P. , Banhart F. , Fecht H.-J.
Published: February 2003

This study reports a metastable hcp→fcc polymorphic transformation in elemental titanium induced by high-energy mechanical attrition in a planetary ball mill. The transformation is monitored and verified by x-ray and electron diffraction and high-resolution transmission electron microscopy. The grain size decreases and lattice parameter increases with continued milling. The phase change is gradual and accompanied by about 16% increase in volume per atom. The milling intensity and deformation mode seem crucial for the completion of the change in crystal structure. The extent and influence of both substitutional and interstitial impurities in this transformation have been assessed. It is suggested that structural instability due to negative (from core to boundary) hydrostatic pressure arising out of nanocrystallization or grain refinement, increasing lattice expansion, and plastic strain/strain rate is responsible for this hcp→fcc polymorphic transformation in titanium. Thus, the present transformation is similar in nature and genesis to those in elemental niobium and zirconium earlier reported by us.
CO oxidation on thin Pt crystals: Temperature slaving and the derivation of lumped models
Authors: Cisternas Jaime , Holmes Philip , Kevrekidis Ioannis G. , Li Xiujiang
Published: February 2003

We review the Langmuir–Hinshelwood model for the heterogeneous catalytic oxidation of carbon monoxide on thin (≈3000 Å) platinum catalysts. Our ultimate goal is to model observed thermo-mechano-chemical oscillations on a thin Pt (110) crystal under low pressure/vacuum conditions. Here we consider only the thermochemical aspects. We supplement the reaction-diffusion model of chemical kinetics by a heat balance equation for the catalyst surface, derived from the energetics of the reaction, adsorption, and desorption processes, and including radiation and conduction to the supporting environment. From the resulting distributed system a four-dimensional lumped ordinary differential equation is derived, which we study via dynamical systems theory, making use of time scale separation, and deriving reduced two-dimensional models. We show that key types of dynamics of the isothermal reaction persist, including multiple equilibria and periodic oscillations, but with the varying catalyst temperature “slaved” to the chemistry. We show how the stability of the periodic orbit branch changes as the catalyst’s area and thickness change, we verify that the lumped models capture the dominant dynamics of the distributed system, and we outline the major differences.
Effect of implant temperature on defects created using high fluence of helium in silicon
Authors: David M. L. , Beaufort M. F. , Barbot J. F.
Published: February 2003

Extended defects formed by high-fluence helium implantation in silicon have been studied as a function of the implantation temperature, from room temperature up to 800 °C. Transmission electron microscopy results show that the formation of cavities created by a 50 keV He implantation with a fluence of 5×1016 cm−2 can be divided into three stages. For implantation temperature up to about 300 °C the bubble size is relatively constant but the bubble density decreases due to the increase in dynamic annealing. Above 300 °C, where divacancies are no longer stable and when the helium is mobile, both the density and size of the cavities stay relatively constant. In this stage, helium starts to diffuse out and the cavities become more and more faceted as the temperature increases. Concurrently interstitial-type defects appear: small elongated rod-like defects at relatively low temperatures and large ribbon-like defects at 600 °C. Finally, for implantation at 800 °C, no cavities are formed and only dislocation loops and {113}’s (ribbon-like defects and rod-like defects), are observed depending on the deposited energy profile. At this temperature the defect annealing during implantation becomes efficient to convert ribbon-like defects into dislocation loops.
Studies of surface two-dimensional photonic band-gap structures
Authors: Cross A. W. , Konoplev I. V. , Phelps A. D. R. , Ronald K.
Published: February 2003

Two-dimensional (2D) surface photonic band-gap (SPBG) structures can be obtained by providing a shallow corrugation of the inner surface of a waveguide wall. It can be used as a distributed mirror, a cavity, or a filter in integrated optics or microwave electronics. These structures can also be an alternative to conventional 2D PBG or 1D Bragg structures. In this article, we present the results of theoretical and experimental studies of 2D SPBG structures. Data obtained from experiments are compared with theoretical results and good agreement between theory and experiment is demonstrated. Comparison of a coaxial 2D SPBG structure with a conventional 1D Bragg structure is also presented.