bluuebunny/crossref_metadata_2025_split huggingface dataset:
Practical considerations in the gas chromatography/combustion/isotope ratio monitoring mass spectrometry of 13C‐enriched compounds: detection limits and carryover effects
Authors: Mottram Hazel R. , Evershed Richard P. 
Published: December 2003

AbstractThis paper describes a methodological investigation of the use of gas chromatography/combustion/isotope ratio monitoring mass spectrometry (GC/C/IRMS) for the compound‐specific stable isotope analysis of 13C‐enriched compounds. Analysis of two 13C‐enriched fatty acid methyl esters, possessing δ13C values of ∼500‰, at a range of concentrations, demonstrated that detectable responses, i.e. chromatographic peaks, could be observed in the 45/44 output even when the compound was present in such low abundance that no peak was observed in the m/z 44 ion chromatogram. A limit of detection, defined as the point at which the signal‐to‐background ratio was equal to 3, was calculated for two compounds and for both ion chromatograms. The limit of detection in the 45/44 chromatogram was found to be ca. 30 pg injected for methyl 13C‐hexadecanoate and ca. 20 pg injected for methyl 13C‐octadecanoate, whilst, in the m/z 44 ion chromatogram, detection limits were ∼180 and ∼200 pg, respectively. The δ13C value recorded for the analytes was found to be both inaccurate and imprecise below 5 ng of each component injected, although this would not represent a significant drawback in qualitative tracer‐type experiments. In a further study of co‐injected mixtures of labelled (∼500‰) and unlabelled (natural abundance, −20 to −30‰) fatty acid methyl esters a significant within‐run carryover effect was observed, where the isotope values recorded for compounds eluting immediately after enriched components were significantly affected. Whilst this would not affect qualitative results, quantitative data for mixtures containing enriched compounds should be considered with caution. The standards employed in this investigation were enriched to ∼500‰ in 13C; however, these effects would probably be accentuated at higher levels of labelling and with other elements. The limit of detection work demonstrated the potential of GC/C/IRMS as a highly sensitive and selective detector with many possible applications. Copyright © 2003 John Wiley & Sons, Ltd.
Discrimination against 13C during degradation of simple and complex substrates by two white rot fungi
Authors: Fernandez Irene , Cadisch Georg 
Published: December 2003

AbstractChanges in isotopic 13C signatures of CO2‐C evolved during decomposition of a sugar (glucose), a fatty acid (palmitic acid), a protein (albumin), a structural biopolymer (lignin) and bulk plant tissue (aerial shoots from Lolium perenne) were monitored over a period of 76 days. All materials were sterilized and inoculated with either of two different species of white rot fungi, Phanerochaete chrysosporium or Coriolus versicolor, and incubated in sealed bottles at 28°C. The CO2 concentration in the jars was periodically determined using an infrared gas analyzer and its isotopic (13C) signature was assessed using a trace gas (ANCA TGII) module coupled to an isotope ratio mass spectrometer (IRMS, Europa 20‐20). L. perenne material inoculated with C. versicolor showed the highest C mineralization activity with approximately 70% of total C evolved as CO2 after 76 days of incubation, followed by glucose. Substrates inoculated with C. versicolor generally decomposed faster than when degraded by P. chrysosporium, except for lignin, where no significant differences between the two fungi types were found and CO2‐C released was less than 2% of the initial C. Considerable 13C isotopic fractionation during the degradation of plant tissue and of pure biochemical compounds was revealed as well as progressive shifts in cumulative CO2‐13C isotopic signatures over time. During the first stages of decomposition, the CO2‐C released was usually depleted in 13C as compared with the initial solid substrate, but with ongoing decomposition the CO2‐C evolved became progressively more enriched in 13C. P. chrysosporium usually showed a slightly higher 13C fractionation than C. versicolor during the first decomposition phase. At posterior decomposition stages isotopic discrimination was often stronger by C. versicolor. These findings on isotopic 13C discrimination during microbial degradation both of simple biochemical compounds and of complex vegetal tissue confirmed not only the existence of significant 13C isotopic fractionation during plant residue decomposition, but also the existence of non‐random isotopic distribution within substrates. They also demonstrated the ability of microorganisms to selectively discriminate against 13C even when degrading an isolated simple substrate. Copyright © 2003 John Wiley & Sons, Ltd.
Automated analysis of 13C/12C ratios in CO2 and dissolved inorganic carbon for ecological and environmental applications
Authors: Torn Margaret S. , Davis Simon , Bird Jeffrey A. , Shaw M. Rebecca , Conrad Mark E. 
Published: December 2003

AbstractStable carbon isotope ratios (13C/12C) are a valuable tool for studying a wide range of environmental processes, including carbon cycling and subsurface microbial activity. Recent advances in automated analysis provide the opportunity to increase greatly the ease and consistency of isotopic analysis. This study evaluated an automated headspace sampler linked to a commercially available CO2 preconcentration system and continuous flow isotope ratio mass spectrometer. Field sampling and analysis methods are illustrated for δ13C of soil respired CO2, from both tracer and natural abundance experiments, and dissolved inorganic carbon from contaminated groundwater. The automated system demonstrated accuracy, precision, and linearity, with standard errors below 0.1‰ for replicate gas standards run at concentrations varying five‐fold. It measured 40 samples per 10‐hour run, with concentrations ranging from ppb to percentage levels. In the field, gas samples were injected into nitrogen‐filled autosampler vials, thereby allowing use of small sample volumes, control of analyte concentration, and direct analysis by the automated system with no further preparation. A significant linear relationship between standard concentrations and peak area allows for accurate estimates of sample CO2 concentration from the mass spectrometric data. The ability to analyze multiple small‐volume samples with minimal off‐line preparation should enhance the application of isotopes to well‐replicated field experiments for process‐level studies and spatial and temporal scaling. Copyright © 2003 John Wiley & Sons, Ltd.
Use of liquid chromatography/time‐of‐flight mass spectrometry and multivariate statistical analysis shows promise for the detection of drug metabolites in biological fluids
Authors: Plumb Robert S. , Stumpf Chris L. , Granger Jennifer H. , Castro‐Perez Jose , Haselden John N. , Dear Gordon J. 
Published: December 2003

AbstractThe process of metabolite identification is essential to the drug discovery and development process; this is usually achieved by liquid chromatography/tandem mass spectrometry (LC/MS/MS) or a combination of liquid chromatography/mass spectrometry (LC/MS) and nuclear magnetic resonance (NMR) spectroscopy. Metabolite identification is, however, a time‐consuming process requiring an experienced skilled scientist. Multivariate statistical analysis has been used in the field of metabonomics to elucidate differences in endogenous biological profiling due to a toxic effect or a disease state. In this paper we show how a combination of liquid chromatography/time‐of‐flight mass spectrometry (LC/TOFMS) and multivariate statistical analysis can be used to detect drug metabolites in a biological fluid with no prior knowledge of the compound administered. Copyright © 2003 John Wiley & Sons, Ltd.
Measurement of the13C/12C ratio of soil‐plant individual sugars by gas chromatography/combustion/isotope‐ratio mass spectrometry of silylated derivatives
Authors: Derrien Delphine , Balesdent Jérôme , Marol Christine , Santaella Catherine 
Published: December 2003

AbstractCarbohydrate is an important pool in the terrestrial carbon cycle. The potential offered by natural and artificial13C‐labelling techniques should therefore be applied to the investigation of the dynamics of individual sugars in soils. For this reason, we evaluated the method of13C sugar analysis by gas chromatography/combustion/isotope‐ratio mass spectrometry (GC/C/IRMS) after hydrolysis and direct trimethylsilylation. Trimethylsilylation involved the addition of several carbon atoms per sugar. These atoms have to be taken into account in the estimation of the carbon isotope ratio. The analysis of standard and natural pentoses and hexoses of known13C enrichments revealed that the number of analysed added carbon atoms was less than expected from stoichiometry. This was attributed to incomplete derivatization and/or incomplete oxidation of methylsilyl carbon before IRMS. Using a calibration of the number of analysed added carbon atoms, the isotope excess of enriched samples could be determined with a relative error close to 5%. Concerning the determination of natural abundances by GC/C/IRMS, we could measure the delta13C of standard C3‐ and C4‐derived sugars with an accuracy of ±1.5‰ using the previous calibration. We were able to apply this technique to plant‐soil systems labelled by pulse‐chase of13CO2, revealing the nature and dynamics of sugars in the plant rhizosphere. Copyright © 2003 John Wiley & Sons, Ltd.
Randomization helps to perform independent tasks reliably
Authors: Chlebus Bogdan S. , Kowalski Dariusz R. 
Published: December 2003

AbstractThis paper is about algorithms that schedule tasks to be performed in a distributed failure‐prone environment, when processors communicate by message‐passing, and when tasks are independent and of unit length. The processors work under synchrony and may fail by crashing. Failure patterns are imposed by adversaries. Linearly‐bounded adversaries may fail up to a constant fraction of the processors. Weakly‐adaptive adversaries have to select, prior to the start of an execution, a subset of processors to be failure‐prone, and then may fail only the selected processors, at arbitrary steps, in the course of the execution. Strongly adaptive adversaries have a total number of failures as the only restriction on failure patterns. The measures of complexity are work, measured as the available processor steps, and communication, measured as the number of point‐to‐point messages. A randomized algorithm is developed, that attains both 𝒪(nlog*n) expected work and 𝒪(nlog*n) expected communication, against weakly‐adaptive linearly‐bounded adversaries, in the case when the numbers of tasks and processors are both equal ton. This is in contrast with performance of algorithms against strongly‐adaptive linearly‐bounded adversaries, which has to be Ω(nlogn/log logn) in terms of work. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 2004
Coloring uniform hypergraphs with few colors
Authors: Kostochka Alexandr 
Published: December 2003

AbstractLet m(r, k) denote the minimum number of edges in an r‐uniform hypergraph that is not k‐colorable. We give a new lower bound on m(r, k) for fixed k and large r. Namely, we prove that if k ≥ 2n, then m(r, k) ≥ ϵ(k)kr(r/ln r)n/(n+1). © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 2004
Impact of avoidance angle mitigation techniques on the interference produced by non‐GSO systems in a multiple non‐GSO interference environment
Authors: Fortes José Mauro P. , Sampaio‐Neto Raimundo 
Published: December 2003

AbstractThis paper adresses the impact of avoidance angle mitigation techniques on the interference produced by non‐GSO systems in a multiple non‐GSO interference environment. It considers a situation involving a victim LEO system and two other non‐GSO interfering systems (one MEO and another LEO) that mitigate around (and only around) the victim LEO system. Interference statistics are obtained using the so called Analytical Method for non‐GSO interference computations. The methodology described, including the interference model adopted, and the type of result obtained in Section 3, that shows the variation of the percentage of the total time allowance used by the interference as a function of the Earth station‐based and the satellite‐based avoidance angles, are very helpful in the process of selecting adequate values for these angles. The burden imposed on the mitigating systems by the use of avoidance angle strategies was evaluated through its impact on the coverage capability of the mitigating systems. Copyright © 2003 John Wiley & Sons, Ltd.
Median regression for longitudinal data
Authors: He Xuming , Fu Bo , Fung Wing K. 
Published: December 2003

AbstractWe review and compare three estimators of median regression in linear models with longitudinal data. The estimators are constructed based on well‐known ideas of weighting, decorrelating, and the working assumption of independence. Both asymptotic efficiency calculations and finite‐sample Monte Carlo studies are used to assess the performance of these estimators. We find that their relative performances depend on the nature of covariates. The estimator under the working assumption of independence is computationally simple and yet has good relative performance when the covariates are invariant over time or when the within‐subject correlations are small. Its relative performance in finite samples is also found to be more favourable than suggested by the asymptotic comparisons. Copyright © 2003 John Wiley & Sons, Ltd.
Comparing Cox and parametric models in clinical studies
Authors: Nardi Alessandra , Schemper Michael 
Published: December 2003

AbstractParametric models are only occasionally used in the analysis of clinical studies of survival although they may offer advantages over Cox's model. In this paper, we report experiences that we have made fitting parametric models to data sets from different clinical trials mainly performed at the Vienna University Medical School. We emphasize the role of residuals for discriminating among candidate models and judging their goodness of fit. The effect of misspecification of the baseline distribution on parameter estimates and testing has been explored. The results from parametric analyses have always been contrasted with those from Cox's model. Copyright © 2003 John Wiley & Sons, Ltd.
Simulating global software evolution processes by combining simple models: an initial study
Authors: Wernick Paul , Hall Tracy 
Published: December 2003

AbstractA number of studies of the long‐term evolution of commercial software products over many releases have established a consistent pattern for growth in the size of the systems examined. This shows a trend towards a progressive slowdown in growth over time. The work described here forms the first step in developing a simulation of the combined effects of the causes of this trend. A number of simple system dynamics simulations, each capturing the causal structure and behaviour of one of a number of causes believed to contribute to the observed behaviour, and its calibration to follow the observed trend, is presented. These models are then combined into a single simulation model reflecting the effect in combination of these causes. Possible causes considered here are: the reduction over time in both the conceptual space which can be searched for new uses of a system and the design spaces constraining developers' ability to modify their systems, the effects of the degradation of the structure of a software system as is it is evolved in unanticipated directions, and the reducing coverage of developers' knowledge of the structure of the system. The combined model incorporates all of these causal mechanisms and introduces a relative weighting for each. The long‐term aim of this work is to produce a simulation embodying those possible causes which are found to be supported by actual evidence. Calibration of this model to reflect the relative importance of each cause in a real‐world situation should then enable it to reproduce the actual software system size trend, so assisting in identifying those causes which affect most significantly the growth trend of that system. Copyright © 2003 John Wiley & Sons, Ltd.
Improved verification of linear‐time properties within fairness: weakly continuation‐closed behaviour abstractions computed from trace reductions
Authors: Ultes‐Nitsche Ulrich , St James Simon 
Published: December 2003

AbstractThe satisfaction of linear‐time temporal properties within fairness introduces an implicit fairness constraint to the verification process. To be applied to practical verification tasks, weakly continuation‐closed abstractions preserve properties satisfied within fairness. Being defined on the complete behaviour of a distributed system, weakly continuation‐closed abstractions require, in principle, an exhaustive state space construction prior to abstraction. Constructing the state space of a practically relevant specification exhaustively, however, is usually not feasible.Based on the notion of traces, i.e. certain equivalence classes of behaviours, trace reductions are defined in this paper. Trace reduction is a particular partial‐order reduction based on the persistent‐set selective search technique. It is shown that a trace reduction can be used on behalf of the complete behaviour of a distributed system in order to compute abstractions as well as to check whether the abstractions are weakly continuation closed. Thus, trace reductions allow one, in the discussed context, to overcome the requirement of an exhaustive state‐space construction prior to abstraction. Copyright © 2003 John Wiley & Sons, Ltd.
Pushing to the edge: Rutgers astrophysics institute motivates talented high school students
Authors: Etkina Eugenia , Matilsky Terry , Lawrence Michael 
Published: December 2003

AbstractThe Rutgers Astrophysics Institute is a program in which gifted high school students learn about contemporary science and its methods, and conduct independent authentic research using real‐time data. The students use the processes of science to acquire knowledge, and serve as cognitive apprentices to an expert astrophysicist. A variety of naturalistic and statistical methods were employed to gather data concerning various changes in the students as a result of their participation in the institute. Specifically, we concluded that students were able to (a) distinguish between observational data and models, devise testing experiments, and reflect on the analysis and the interpretation of X‐ray data; (b) achieve results comparable to those of regular Advanced Placement (AP) students on individual AP exam problems (the students had not taken AP Physics), (c) engage in elements of meaningful authentic research, and (d) change their approaches toward learning science. © 2003 Wiley Periodicals, Inc. J Res Sci Teach 40: 958–985, 2003
Teaching elements of nature of science: A yearlong case study of a fourth‐grade teacher
Authors: Akerson Valarie L. , Abd‐El‐Khalick Fouad 
Published: December 2003

AbstractThis study examined and supported the efforts of Tina, an experienced elementary teacher, in helping her fourth graders internalize informed views of the inferential, tentative, and creative nature of science (NOS). Tina held informed views of, and was motivated to teach about, NOS. The study aimed to answer the following question: What specific supports were needed to enable Tina to make the target NOS elements explicit in her teaching? The lead researcher visited Tina's classroom every week and interacted with her on a continuous basis. Data sources included classroom observations and videotapes, teacher NOS questionnaires and associated interviews, teacher–researcher communications, and teacher and researcher logs. Although Tina's understandings and intentions were necessary to enable her to teach about NOS, they were not sufficient. Tina needed support to translate her NOS views and intentions into pedagogically appropriate instructional activities that would make the target NOS aspects accessible to her students. Socially mediated support was needed at the personal level in terms of helping Tina activate her tacit NOS understandings, and at the professional level in terms of modeling explicit NOS instruction in Tina's own classroom by the lead researcher. © 2003 Wiley Periodicals, Inc. J Res Sci Teach 40: 1025–1049, 2003
Progressive inquiry in a computer‐supported biology class
Authors: Hakkarainen Kai 
Published: December 2003

AbstractThe problem addressed in the study was whether 10‐ and 11‐year‐old children, collaborating within a computer‐supported classroom, could engage in progressive inquiry that exhibits an essential principal feature of mature scientific inquiry: namely, engagement in increasingly deep levels of explanation. Technical infrastructure for the study was provided by the Computer‐Supported Intentional Learning Environment (CSILE). The study was carried out by qualitatively analyzing written notes logged by 28 Grade 5/6 students to CSILE's database. Results of the study indicated that with teacher guidance, students were able to produce meaningful intuitive explanations about biological phenomena, guide this process by pursuing their own research questions, and engage in constructive peer interaction that helped them go beyond their intuitive explanations and toward theoretical scientific explanations. Expert evaluations by three widely recognized philosophers of science confirmed the progressive nature of students' inquiry. © 2003 Wiley Periodicals, Inc. J Res Sci Teach 40: 1072–1088, 2003
Prevalence, function, and structure of photographs in high school biology textbooks
Authors: Leivas Pozzer Lilian , Roth Wolff‐Michael 
Published: December 2003

AbstractPhotographs are a major aspect of high school science textbooks, which dominate classroom approaches to teaching and learning. It is thus surprising that the function of photographs and their relation to captions and texts have not been the topic of analysis. The purpose of this study was to investigate the prevalence, function, and structure of photographs in high school science. Our motivating research question was, “What can students learn from textbooks when they study photographs?” To answer this and several subordinate questions, we selected and analyzed four Brazilian biology textbooks. We focus on the use of photographs and the relation among them, various types of texts, and the subject matter presented. Our analysis reveals that the structural elements of text, caption, and photographs and the relations among them differ across the textbooks and at times even within the same book. This, of course, will influence readers' interpretations of the photographs changing their role in the text. The results of our study have implications for textbook authors and textbook readers. We suggest that future studies may focus on students' and teachers' interpretation of photographs in real time. © 2003 Wiley Periodicals, Inc. J Res Sci Teach 40: 1089–1114, 2003
Adapting an immersive virtual reality system for rehabilitation
Authors: Kizony Rachel , Katz Noomi , (Tamar) Weiss Patrice L. 
Published: December 2003

AbstractThe purpose of this paper is to present an overview of the adaptations that have been done to VividGroup's Gesture Xtreme projected VR scenarios in order to facilitate their use in neurological rehabilitation. First, the scenarios and the adaptation (control of the type, speed, location and direction of all stimuli) are briefly described. The advantages and limitations of the adapted VR system as a rehabilitation tool are presented. Next, initial results and two examples of case studies, one a patient following stroke and one who requires balance training as a result of complete spinal cord injury, are used to illustrate applications of this VR system to rehabilitation. Copyright © 2003 John Wiley & Sons, Ltd.