bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular reorientation of CD4in gas‐phase mixtures
Authors: ter Horst Marc A. , Jameson Cynthia J. , Jameson A. Keith 
Published: February 2006

AbstractSpin‐lattice relaxation times were measured for the deuterons in CD4in pure gas and in mixtures with the following buffer gases: Ar, Kr, Xe, HCl, N2, CO, CO2, CF4, and SF6. Effective collision cross sections σθ, 2for the molecular reorientation of CD4in collisions with these ten molecules are obtained as a function of temperature. These cross sections are compared with the corresponding cross sections σJobtained from1H spin‐rotation relaxation in mixtures of CH4with the same set of buffer gases. Various classical reorientation models typically applied in liquids predict different ratios of the reduced correlation times for the reorientation of spherical tops. The Langevin model comes closest to predicting the magnitude of the σθ, 2/σJratio that we obtain for CD4. Copyright © 2006 John Wiley & Sons, Ltd.
Carbon‐13 chemical shift anisotropy in DNA bases from field dependence of solution NMR relaxation rates
Authors: Ying Jinfa , Grishaev Alexander , Bax Ad 
Published: February 2006

AbstractKnowledge of 13C chemical shift anisotropy (CSA) in nucleotide bases is important for the interpretation of solution‐state NMR relaxation data in terms of local dynamic properties of DNA and RNA. Accurate knowledge of the CSA becomes particularly important at high magnetic fields, prerequisite for adequate spectral resolution in larger oligonucleotides. Measurement of 13C relaxation rates of protonated carbons in the bases of the so‐called Dickerson dodecamer, d(CGCGAATTCGCG)2, at 500 and 800 MHz 1H frequency, together with the previously characterized structure and diffusion tensor yields CSA values for C5 in C, C6 in C and T, C8 in A and G, and C2 in A that are closest to values previously reported on the basis of solid‐state FIREMAT NMR measurements, and mostly larger than values obtained by in vacuo DFT calculations. Owing to the noncollinearity of dipolar and CSA interactions, interpretation of the NMR relaxation rates is particularly sensitive to anisotropy of rotational diffusion, and use of isotropic diffusion models can result in considerable errors. Copyright © 2006 John Wiley & Sons, Ltd.
Comparison of the performance of round and rectangular wire in small solenoids for high‐field NMR
Authors: Li Yu , Webb Andrew G. , Saha Saikat , Brey William W. , Zachariah Cherian , Edison Arthur S. 
Published: February 2006

AbstractThis paper considers the effects of conductor geometry on the performance of small solenoidal coils for high‐field NMR. First, a simple analytical model is presented for investigating the effects of conductor geometry on the current distribution in such coils. The model was used to derive optimum parameters for coils constructed from wire with either rectangular or circular cross‐sections as a function of the length‐to‐diameter ratio. Second, a commercial software package utilizing full three‐dimensional finite‐element solutions to Maxwell's equations was used to confirm the basic findings of the simple analytical model, and also to compare simulated S/N estimations with experimental NMR spectra acquired with 2.5 mm and 1.0 mm‐diameter solenoid coils: reasonable agreement was found. Third, as a demonstration of the usefulness of such coils for mass‐limited samples, multidimensional experiments were performed at 750 MHz on ∼4.7 nmol (41 µg) of PF1061, a protein from Pyrococcus furiosus. Copyright © 2006 John Wiley & Sons, Ltd.
Solid‐state NMR and computational studies of 4‐methyl‐2‐nitroacetanilide
Authors: Harris Robin K. , Ghi Phuong Y. , Hammond Robert B. , Ma Cai Yun , Roberts Kevin J. , Yates Jonathan R. , Pickard Chris J. 
Published: February 2006

AbstractStudies on the solid‐state structure of two polymorphs of 4‐methyl‐2‐nitroacetanilide (MNA) were conducted using magic‐angle spinning 13C, 15N and 1H NMR spectroscopy, together with first‐principles computations of NMR shielding (including use of a program that takes explicit account of the translational symmetry inherent in crystalline structures). The effects on 13C chemical shifts of side‐chain rotations have been explored. Information derived from these studies was then incorporated within a systematic space‐search methodology for elucidation of trial crystallographic structures from powder XRD. Copyright © 2006 John Wiley & Sons, Ltd.
Stability constants: comparative study of fitting methods. Determination of second‐order complexation constants by23Na and7Li NMR chemical shift titration
Authors: Masiker Marilyn C. , Mayne Charles L. , Eyring Edward M. 
Published: February 2006

AbstractNMR chemical shift titration has been widely used as a method for the determination of stability constants. Systems involving metal‐ligand complexation have been investigated using a number of methodologies. There are significant differences in the values reported for stability constants obtained by different experimental methods, such as calorimetry and ion selective electrode (ISE) titrations; nor has NMR chemical shift titration always yielded consistent results. Different researchers have obtained different results for the same system with results differing by as much as an order of magnitude. The chemical shift data are generally plotted against the concentration ratio of the metal and ligand for a set of solutions. A nonlinear least squares fitting method using an analytical solution of the cubic equation for the equilibrium concentration of the free ligand is used in this study and compared with methods used in the literature. Second‐order association constants for the LiClO4:12‐crown‐4 system in acetonitrile and the NaClO4:12‐crown‐4 system in methanol are reported. Formation of both 1:1 and 1:2 metal‐ligand complexes are considered. The LiClO4:12‐crown‐4 acetonitrile system had been investigated previously by NMR titration but only 1:1 complexation was considered in that study. This study provides convincing evidence that both 1:1 and 1:2 complexes are important, at least, in the lithium system. A Monte Carlo investigation of the propagation of errors from the chemical shifts to the stability constants shows that the choice of data analysis methods may, in part, contribute to discrepancies and that the nonlinear nature of the model can dramatically affect the error limits on the stability constants. Copyright © 2006 John Wiley & Sons, Ltd.
A broad‐spectrum fluorescence‐based peptide library for the rapid identification of protease substrates
Authors: Thomas Daniel A. , Francis Peter , Smith Carla , Ratcliffe Steven , Ede Nicholas J. , Kay Corinne , Wayne Gareth , Martin Steve L. , Moore Keith , Amour Augustin , Hooper Nigel M. 
Published: February 2006

AbstractIdentification of peptide substrates for proteases can be a major undertaking. To overcome issues such as feasibility and deconvolution, associated with large peptide libraries, a ‘small but smart’ generic fluorescence resonance energy transfer rapid endopeptidase profiling library (REPLi) was synthesised as a tool for rapidly identifying protease substrates. Within a tripeptide core, flanked by Gly residues, similar amino acids were paired giving rise to a relatively small library of 3375 peptides divided into 512 distinct pools each containing only 8 peptides. The REPLi was validated with trypsin, pepsin, the matrix metalloprotease (MMP)‐12 and MMP‐13 and calpains‐1 and ‐2. In the case of calpain‐2, a single iteration step involving LC‐MS, provided the definitive residue specificity from which a highly sensitive fluorogenic substrate, (FAM)‐Gly‐Gly‐Gly‐Gln‐Leu‐Tyr‐Gly‐Gly‐DPA‐Arg‐Arg‐Lys‐(TAMRA), was then designed. The thorough validation of this ‘small but smart’ peptide library with representatives from each of the four mechanistic protease classes indicates that the REPLi will be useful for the rapid identification of substrates for multiple proteases.
Is significant cystic fibrosis‐related liver disease a risk factor in the development of bone mineralization abnormalities?
Authors: Alex George , Catto‐Smith Anthony G. , Ditchfield Michael , Roseby Robert , Robinson Philip J. , Cameron Fergus J. , Oliver Mark R. 
Published: February 2006

AbstractIn order to assess the effects of significant cystic fibrosis‐related liver disease (CFLD) on bone health, we compared the bone mineral status of older children and adolescents with CFLD to those with cystic fibrosis (CF) alone. Thirteen children (age range, 10–19 years) from our clinical CF services were identified with significant CFLD (9 of these 13 patients had clinical and radiological evidence of portal hypertension). This cohort was then matched by age, gender, and anthropometric measurements with equal numbers of patients with CF alone. All patients had a dual‐energy X‐ray absorptiometry (DEXA) scan to determine bone mineral content (BMC), bone area (BA), bone mineral density (BMD), and bone mineral apparent density (BMAD) in the region of the lumbar spine. Blood was drawn to determine serum vitamin A, D, E, and K status and liver function tests. The best forced expired volume in 1 sec (FEV1) for each patient in the 12 months around the time of the scan was also documented. Patients with CFLD had slightly worse FEV1 (82 ± 20% vs. 91 ± 16%, P = 0.05) and significantly higher alanine aminotransferase (65.5 ± 35 IU/l vs. 30 ± 20 IU/l, P = 0.01) than those with CF alone. The mean lumbar spine BA, BMC, BMD, and BMAD were not different between children with CFLD and CF. In conclusion, the presence of significant liver disease in children with CF does not appear to be an additional risk factor for the development of abnormal bone mineralization. Pediatr Pulmonol. © 2006 Wiley‐Liss, Inc.
Factors influencing gender differences in the diagnosis and treatment of asthma in childhood: The Tucson Children's Respiratory Study
Authors: Wright Anne L. , Stern Debra A. , Kauffmann Francine , Martinez Fernando D. 
Published: February 2006

AbstractStudies identified gender differences in diagnosed asthma, but the extent to which they can be attributed to differences in symptom experience and frequency rather than factors influencing diagnosis has not been established. We investigated prevalence of, and consultation for, asthma symptoms, as well as diagnosis and treatment in 533 boys and 556 girls enrolled in the Tucson Children's Respiratory Study, a population‐based birth‐cohort study. Questionnaires regarding respiratory symptoms and diagnoses were obtained at ages 2, 3, 6, 8, 11, 13, 16, and 18 years. Boys were significantly more likely than girls to experience both wheeze and frequent wheeze most years in the first decade of life. However, girls with symptoms were less likely than boys to see a physician (74.1% vs. 83.4%, P < 0.001) and to be labeled as having asthma (43.3% vs. 53.8%, P < 0.009), even after adjusting for symptom frequency. A difference in symptom presentation also appeared to influence diagnosis: nocturnal cough without frequent wheeze was more prevalent among girls, and was associated with reduced diagnosis of asthma. Among subjects who consulted a physician for wheeze, boys were significantly more likely than girls to have taken medication (81.5% vs. 73.5%, P < 0.01). The lag time between age at first wheeze and first use of medication among those consulting a physician for wheeze or asthma was greater for girls, especially among subjects with frequent wheeze (2.8 vs. 1.6 years, P < 0.005). These findings indicate that gender differences in the diagnosis and treatment of asthma cannot be explained completely by differences in symptom prevalence and frequency. Pediatr Pulmonol. © 2006 Wiley‐Liss, Inc.
Automated method for measuring globin adducts of acrylamide and glycidamide at optimized Edman reaction conditions
Authors: Vesper Hubert W. , Ospina Maria , Meyers Tunde , Ingham Leigha , Smith Antoinette , Gray J. Gibson , Myers Gary L. 
Published: February 2006

AbstractThe general population is exposed to acrylamide, a potential human carcinogen, through food and cigarette smoke. The assessment of human exposure to acrylamide is important in the evaluation of health risks associated with this chemical. Hemoglobin adducts of acrylamide (AA‐Hb) and its primary metabolite glycidamide (GA‐Hb) are established biomarkers of acrylamide exposure and methods to measure these biomarkers using modified Edman reaction are described. Only limited information about the optimal Edman reaction conditions such as pH or temperature is available for these adducts and the existing methods do not allow automation needed in biomonitoring studies. In this study, the yield of Edman products of AA‐Hb and GA‐Hb between pH 3–10 and at 35–55°C at different time intervals, and the applicability of liquid‐liquid extraction on diatomaceous earth for analyte extraction, were assessed and results were used in a new optimized method. The applicability of our optimized method was assessed by comparing results obtained with a convenience sample from 96 individuals with a conventional method. Maximum yield of Edman products was obtained between pH 6–7, heating the reaction solution at 55°C for 2 h resulted in the same yields as with conventional conditions, and use of diatomaceous earth was found suitable for automated analyte extraction. Using these conditions, no difference was observed between our optimized and a conventional method. The median globin adduct values in the convenience sample are 129 pmol/g globin (range: 27–453 pmol/g globin) and 97 pmol/g globin (range: 27–240 pmol/g globin) for AA‐Hb and GA‐Hb, respectively. The GA‐Hb/AA‐Hb ratio decreases significantly with increasing AA‐Hb values indicating that measurement of AA‐Hb as well as GA‐Hb are needed to appropriately assess human exposure to acrylamide. Published in 2006 by John Wiley & Sons, Ltd.
Fragmentation study of protonated chalcones by atmospheric pressure chemical ionization and tandem mass spectrometry
Authors: Tai Yuanpo , Pei Saifeng , Wan Jieping , Cao Xiaoji , Pan Yuanjiang 
Published: February 2006

AbstractFragmentation mechanisms of protonated chalcone and its derivatives with different functional groups were investigated by atmospheric pressure chemical ionization with tandem mass spectrometry (MS/MS). The major fragmentation pathways were loss of the phenyl group from the A or B ring, combined with loss of CO. Losses of H2O and CO from the precursor ions of [M+H]+ are proposed to occur via rearrangements. Elimination of water from protonated chalcones was observed in all the title compounds to yield a stable ion but it was difficult to obtain skeletal fragmentation of a precursor ion. Loss of CO was found in the MS/MS spectra of all the compounds except the nitro‐substituted chalcones. When the [M+HCO]+ ion was fragmented in the MS/MS experiments, there were distinctive losses of 15 and 28 Da, as the methyl radical and ethylene, respectively. The ion at m/z 130, found only in the nitro‐substituted chalcones, was assigned as C9H6O by Fourier transform ion cyclotron resonance (FTICR)‐MS/MS; m/z 130 is a common fragment ion in the electron ionization (EI) spectra of chalcones. In order to more easily distinguish the constitutional isomers of these chalcones, breakdown curves were produced and these provided strong support in this study. Copyright © 2006 John Wiley & Sons, Ltd.
Interval estimates for the ratio and difference of two lognormal means
Authors: Chen Yea‐Hung , Zhou Xiao‐Hua 
Published: February 2006

AbstractHealth research often gives rise to data that follow lognormal distributions. In two sample situations, researchers are likely to be interested in estimating the difference or ratio of the population means. Several methods have been proposed for providing confidence intervals for these parameters. However, it is not clear which techniques are most appropriate, or how their performance might vary. Additionally, methods for the difference of means have not been adequately explored. We discuss in the present article five methods of analysis. These include two methods based on the log‐likelihood ratio statistic and a generalized pivotal approach. Additionally, we provide and discuss the results of a series of computer simulations. Finally, the techniques are applied to a real example. Copyright © 2006 John Wiley & Sons, Ltd.
Analysis of repeated bouts of measurements in the framework of generalized estimating equations
Authors: Shults Justine , Mazurick Carissa A. , Richard Landis J. 
Published: February 2006

AbstractWe consider a longitudinal study of interstitial cystitis (IC) in women, in which the time between bouts of repeated measurements is large relative to the within‐bout separation in time. Our outcome of interest is the number of nocturnal voids that we model via quasi‐least squares (QLS) in the framework of generalized estimating equations (GEE). To account for potential intra‐subject correlation, we directly apply a banded Toeplitz correlation structure that previously was only implemented in anad hocapproach using GEE. We describe this structure, its appropriateness for data from the IC study, and the results of our analysis. We then demonstrate that correct specification of the underlying correlation structureversusincorrectly applying a simpler structure can prevent substantial losses in efficiency in estimation of the regression parameter. These comparisons involve the limiting values of the estimates of the correlation parameters, which are not consistent for the misspecification scenarios considered here. We therefore obtain the limiting values of the QLS estimates when the structure is incorrectly specified. Copyright © 2006 John Wiley & Sons, Ltd.
Joint estimation of time‐dependent and non‐linear effects of continuous covariates on survival
Authors: Abrahamowicz Michal , MacKenzie Todd A. 
Published: February 2006

AbstractIn order to yield more flexible models, the Cox regression model, λ(t;x) = λ0(t)exp(βx), has been generalized using different non‐parametric model estimation techniques. One generalization is the relaxation of log‐linearity inx, λ(t;x) = λ0(t)exp[r(x)]. Another is the relaxation of the proportional hazards assumption, λ(t;x) = λ0(t)exp[β(t)x]. These generalizations are typically considered independently of each other. We propose the product model, λ(t;x) = λ0(t)exp[β(t)r(x)] which allows for joint estimation of both effects, and investigate its properties. The functions describing the time‐dependent β(t) and non‐linearr(x) effects are modelledsimultaneouslyusing regression splines and estimated by maximum partial likelihood. Likelihood ratio tests are proposed to compare alternative models. Simulations indicate that both the recovery of the shapes of the two functions and the size of the tests are reasonably accurate provided they are based on the correct model. By contrast, type I error rates may be highly inflated, and the estimates considerably biased, if the model is misspecified. Applications in cancer epidemiology illustrate how the product model may yield new insights about the role of prognostic factors. Copyright © 2006 John Wiley & Sons, Ltd.
Monitoring medical procedures by exponential smoothing
Authors: Spliid Henrik 
Published: February 2006

AbstractA new exponentially weighted moving average (EWMA) control chart well suited for ‘online’ routine surveillance of medical procedures is introduced. The chart is based on inter‐event counts for failures recorded when the failures occur. The method can be used for many types of hospital procedures and activities, such as problems or errors in surgery, hospital‐acquired infections, erroneous handling or prescription of medicine, deviations from scheduled treatments causing inconveniences for patients. The construction, the use and the effectiveness of the control chart are demonstrated by two well‐known examples about wound infection in orthopaedic surgery and neonatal arterial switch surgery. The method is easy to implement and apply, it illustrates, estimates and tests the current failure rate. Comparisons with two examples from the literature indicate that its ability to quickly detect an increased failure rate is comparable to that of other well‐established methods. Copyright © 2006 John Wiley & Sons, Ltd.
Key concepts in modeling product development processes
Authors: Browning Tyson R. , Fricke Ernst , Negele Herbert 
Published: February 2006

AbstractThis paper provides a foundation for modeling the set of activities and their relationships by which systems are engineered, or, more broadly, by which products and services are developed. It provides background, motivations, and formal definitions for process modeling in this specialized environment. We treat the process itself as a kind of system that can be engineered. However, while product systems must be created, the process systems for developing complex products must, to a greater extent, be discovered and induced. Then, they tend to be reused, either formally as standard processes, or informally by the workforce. We distinguish and clarify several important concepts in modeling processes, including: product development versus repetitive business processes, descriptive versus prescriptive processes, activities as actions versus deliverables as interactions, standard versus deployed processes, centralized versus decentralized process modeling, “as is” versus “to be” process modeling, and multiple phases in product development. We also present a basically simple yet highly extendable and generalized framework for modeling product development processes. The framework enables building a single model to support a variety of purposes, including project planning (scheduling, budgeting, resource loading, and risk management) and control, and it provides the scaffolding for knowledge management and organizational learning, among numerous other uses. © 2006 Wiley Periodicals, Inc. Syst Eng 9: 104–128, 2006
Efficient Nonparametric Approaches for Estimating the Operating Characteristics of Discrete Item Responses
Authors: Samejima Fumiko 
Published: February 2006

Rationale and the actual procedures of two nonparametric approaches, called Bivariate P.D.F. Approach and Conditional P.D.F. Approach, for estimating the operating characteristic of a discrete item response, or the conditional probability, given latent trait, that the examinee's response be that specific response, are introduced and discussed. These methods are featured by the facts that: (a) estimation is made without assuming any mathematical forms, and (b) it is based upon a relatively small sample of several hundred to a few thousand examinees.Some examples of the results obtained by the Simple Sum Procedure and the Differential Weight Procedure of the Conditional P.D.F. Approach are given, using simulated data. The usefulness of these nonparametric methods is also discussed.