bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bulk and compound‐specific isotopic characterisation of illicit heroin and cling film
Authors: Idoine Fay A. , Carter James F. , Sleeman Richard 
Published: October 2005

AbstractComparative analysis involves various but complementary methods and can be used for forensic intelligence purposes to group seizures of heroin into batches. Much forensic analysis now combines expertise in the traditional area of drugs investigation with a detailed understanding of supply, packaging, distribution, and drugs intelligence. It was the intention of this research to determine whether illicit heroin seizures and packaging material can be grouped according to isotopic compositions, and to explore factors that affect the isotopic compositions. In order to achieve these aims, 14 samples of seized heroin, thirteen provided by Avon and Somerset Constabulary (UK), were analysed by elemental analysis/isotope ratio mass spectrometry (EA/IRMS) and gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) for carbon and hydrogen isotopes. These tests elucidated that a combination of theδ13C,δ15N,δ18O andδ2H results from EA/IRMS is able to distinguish between most samples of bulk heroin. We speculate that theδ13C values of the alkaloids, obtained by GC/C/IRMS, give indications of different geographical or temporal origins of some of the heroin samples. GC/C/IRMS of the cutting agent, caffeine, provides a means to link dilution events. Fifteen retail cling film samples and seven cling film samples from heroin seizures were analysed by EA/IRMS. A multivariate comparison of the carbon, hydrogen and oxygen isotope ratios was able to distinguish between most of the samples. This technique enabled the cling films from the heroin to be grouped according to seizure. Three solvents were tested on two samples of cling film of known composition. Methanol and chloroform were both found to extract material from PVC and from non‐PVC cling films. Water‐treated PVC was indistinguishable from the untreated PVC and thus water was found to be the most suitable solvent when washing cling film prior to IRMS analysis. Copyright © 2005 John Wiley & Sons, Ltd.
The natural abundance of 13C, 15N, 34S and 14C in archived (1923–2000) plant and soil samples from the Askov long‐term experiments on animal manure and mineral fertilizer
Authors: Bol Roland , Eriksen Jorgen , Smith Pete , Garnett Mark H. , Coleman Kevin , Christensen Bent T. 
Published: October 2005

AbstractThe Askov field experiment (Denmark), established in 1894, provides a unique opportunity to examine long‐term effects of animal manure and mineral fertilizer on soil organic matter quality and turnover. This sandy loam soil is classified as Alfisol (Typic Hapludalf). Soil C, N, S, 13C, 15N, 34S and 14C contents were measured in a selection of archived soil samples (1923, 1938, 1945, 1953, 1964, 1976, 1985, 1996 and 2000) from unfertilized (O), animal manure (1 AM) and mineral fertilizer (1 NPK) treatments. These treatments are imbedded in a four‐course crop rotation of winter cereals, root crops, spring cereals and a clover/grass mixture. The contents of C, N, S, 13C, 15N and 34S in selected crop samples (1953–1996) and in contemporary samples of animal feed and manure were also determined. Temporal soil nutrient and isotope trends between fertilizer treatments were significantly different, except for S content in 1 AM and 1 NPK. The total soil C and S was higher in 1 AM and 1 NPK than in the O treatment. The total soil N content (1 AM > 1 NPK > O) and the δ15N content (1 AM > 1 NPK and O) were also different. Analyses of plant, animal feed and manures confirmed that differences in soil 15N values were related to δ15N values of added source inputs. Soil and crop δ13C values were similar, but manures had slightly lower values. The variation of soil δ34S (and total S) from 1923 to 1996 was larger in the O than 1 AM and 1 NPK plots reflecting changes in atmospheric S inputs. The total contents of soil C, N and S were significantly correlated, but their isotopic signatures were not, suggesting that the C, N, S turnovers in soil are subject to different controls. The 14C content was generally higher in the 1 AM than 1 NPK and O, with bomb‐14C incorporation modelling indicating that mean residence time (MRT) was ca. 170 years in the 1 AM, but closer to 250–290 years in the 1 NPK and O treatments. The measured trends in soil C and 14C during 1923–1996 were successfully modelled using the RothC model. The OM accumulation in the Askov soils was generally dominated by microbial decomposition products rather than by recalcitrant components of the various inputs. Copyright © 2005 John Wiley & Sons, Ltd.
Determination of steroid hormones, hormone conjugates and macrolide antibiotics in influents and effluents of sewage treatment plants utilising high‐performance liquid chromatography/tandem mass spectrometry with electrospray and atmospheric pressure chemical ionisation
Authors: Schlüsener Michael P. , Bester Kai 
Published: October 2005

AbstractIn this study we present a high‐performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) method which has been elaborated to analyse steroid hormones, hormone conjugates, oral contraceptives and macrolide antibiotics unchanged in unfiltered influents and effluents of sewage treatment plants (STPs). HPLC separation of the steroid hormones was achieved in 35 min, as well as those of the antibiotics. The analytes were extracted by solid‐phase extraction, followed by clean‐up using size exclusion chromatography (SEC). For the final quantification HPLC/MS/MS was used. The two ionisation modes, electrospray ionisation (ESI) and atmospheric pressure chemical ionisation (APCI), in HPLC/MS/MS were compared for the analysis of steroid hormones. For quantitative results drastic matrix effects were observed while using ESI. These effects were less pronounced while using APCI. These pitfalls were additionally reduced by clean‐up using SEC as well as isotope dilution. Additionally, two multiple reaction monitoring (MRM) transitions per compound were used to prevent false positive results. Recovery experiments with spiked tap water with concentrations varying from 1 to 1000 ng/L gave constant recovery rates: The recovery rates for the hormones and conjugates ranged from 58 to 107%, those of the contraceptives ranged from 83 to 109%. The relative standard deviation was found to be 7 to 24% and the limits of detection were 0.1 to 4.5 ng/L. The recovery rates of the macrolide antibiotics ranged from 76 to 103%, while the relative standard deviation was found to be 7 to 14% and the limits of detection ranged from 0.6 to 1.8 ng/L. The maximum concentrations found in influents of a STP was 470 ng/L for estriol and 1200 ng/L for erythromycin. Copyright © 2005 John Wiley & Sons, Ltd.
A novel dual‐isotope labelling method for distinguishing between soil sources of N2O
Authors: Wrage N. , Groenigen J. W. van , Oenema O. , Baggs E. M. 
Published: October 2005

AbstractWe present a novel 18O‐15N‐enrichment method for the distinction between nitrous oxide (N2O) from nitrification, nitrifier denitrification and denitrification based on a method with single‐ and double‐15N‐labelled ammonium nitrate. We added a new treatment with 18O‐labelled water to quantify N2O from nitrifier denitrification. The theory behind this is that ammonia oxidisers use oxygen (O2) from soil air for the oxidation of ammonia (NH3), but use H2O for the oxidation of the resulting hydroxylamine (NH2OH) to nitrite (NO). Thus, N2O from nitrification would therefore be expected to reflect the 18O signature of soil O2, whereas the 18O signature of N2O from nitrifier denitrification would reflect that of both soil O2 and H2O. It was assumed that (a) there would be no preferential removal of 18O or 16O during nitrifier denitrification or denitrification, (b) the 18O signature of the applied 18O‐labelled water would remain constant over the experimental period, and (c) any O exchange between H218O and NO would be negligible under the chosen experimental conditions. These assumptions were tested and validated for a silt loam soil at 50% water‐filled pore space (WFPS) following application of 400 mg N kg−1 dry soil. We compared the results of our new method with those of a conventional inhibition method using 0.02% v/v acetylene (C2H2) and 80% v/v O2 in helium. Both the 18O‐15N‐enrichment and inhibitor methods identified nitrifier denitrification to be a major source of N2O, accounting for 44 and 40%, respectively, of N2O production over 24 h. However, compared to our 18O‐15N‐method, the inhibitor method overestimated the contribution from nitrification at the expense of denitrification, probably due to incomplete inhibition of nitrifier denitrification and denitrification by large concentrations of O2 and a negative effect of C2H2 on denitrification. We consider our new 18O‐15N‐enrichment method to be more reliable than the use of inhibitors; it enables the distinction between more soil sources of N2O than was previously possible and has provided the first direct evidence of the significance of nitrifier denitrification as a source of N2O in fertilised arable soil. Copyright © 2005 John Wiley & Sons, Ltd.
The effect of growth rate on tissue‐diet isotopic spacing in rapidly growing animals. An experimental study with Atlantic salmon (Salmo salar)
Authors: Trueman Clive N. , McGill Rona A. R. , Guyard Philippe H. 
Published: October 2005

AbstractThe difference in isotopic composition between a consumer's tissues and that of its diet is a critical aspect of the use of stable isotope analyses in ecological and palaeoecological studies. In a controlled feeding experiment with the Atlantic salmon, Salmo salar, we demonstrate for the first time that the value of tissue‐diet isotope spacing in nitrogen in a growing animal is not constant, but varies inversely with growth rate. The value of tissue‐diet isotopic spacing in N reflects N use efficiency. Thus, in salmon, growth rate is accompanied by, or requires, increased N use efficiency. The total range in tissue‐diet isotopic spacing in N seen in the experimental population of 25 fish was 1‰, approximately 50% of the total trophic shift. Mean equilibrium tissue‐diet isotopic spacing (±standard deviation) in salmon averaged 2.3‰ (±0.3‰) and 0.0‰ (±0.3‰) for N in muscle and liver, respectively, and 2.1‰ (±0.1‰) and 1.6‰ (±0.3‰) for C in muscle and liver, respectively. Feeding with a mixed dietary source (wheat and fish‐meal origin) resulted in tissue‐diet isotopic fractionation in both C and N due to the differential digestibility of food components with distinct isotopic composition. The rate of change in isotopic composition of S. salar tissues was dominated by growth, but the estimated contribution of metabolic turnover to change in tissue N was relatively high for an ectothermic animal at ca. 20–40%. The estimated half‐life for metabolic turnover of the tissue N pool was ca. 4 months in both muscle and liver tissue. This is the first study to demonstrate a direct relationship between tissue‐diet isotopic spacing in N and growth rate and adds to the growing list of factors known to influence the level of isotopic separation between a consumer's tissue and that of its diet. Copyright © 2005 John Wiley & Sons, Ltd.
Harnessing the transient signals in atomic force microscopy
Authors: Sahoo Deepak R. , Sebastian Abu , Salapaka Murti V. 
Published: October 2005

AbstractIn the existing dynamic‐mode operation of atomic force microscopes (AFMs) steady‐state signals like amplitude and phase are used for detection and imaging of material. Due to the high quality factor of the cantilever probe the corresponding methods are inherently slow. In this paper, a novel methodology for fast interrogation of material that exploits the transient part of the cantilever motion is developed. This method effectively addresses the perceived fundamental limitation on bandwidth due to high quality factors. It is particularly suited for the detection of small time scale tip–sample interactions. Analysis and experiments show that the method results in significant increase in bandwidth and resolution as compared to the steady‐state‐based methods. This article demonstrates the effectiveness of a systems perspective to the field of imaging at the nano‐scale and for the first time reports realtime experimental results and scanning applications of the transient method. Copyright © 2005 John Wiley & Sons, Ltd.
Statistical properties and inference of the antimicrobial MIC test
Authors: Annis David H. , Craig Bruce A. 
Published: October 2005

AbstractA common method for measuring the drug‐specific minimum inhibitory concentration (MIC) of an antibacterial agent is via a two‐fold broth dilution test known as the MIC test. Because this procedure implicitly rounds data upward, inference based on unadjusted measurements is biased and overestimates bacterial resistance to a drug. We detail this test procedure and its associated bias, which, in many cases, has an expected value of approximately 0.5 on the log2scale. In addition, new bias‐corrected estimates of resistance are proposed. A numeric example is used to illustrate the extent to which the traditional resistance estimate can overestimate the true proportion of resistant strains, a phenomenon which is remedied by using the proposed estimates. Published in 2005 by John Wiley & Sons, Ltd.
An appraisal of methods for the analysis of longitudinal categorical data with MAR drop‐outs
Authors: O'Hara Hines R. J. , Hines W. G. S. 
Published: October 2005

AbstractA number of methods for analysing longitudinal ordinal categorical data with missing‐at‐random drop‐outs are considered. Two are maximum‐likelihood methods (MAXLIK) which employ marginal global odds ratios to model associations. The remainder use weighted or unweighted generalized estimating equations (GEE). Two of the GEE use Cholesky‐decomposed standardized residuals to model the association structure, while another three extend methods developed for longitudinal binary data in which the association structures are modelled using either Gaussian estimation, multivariate normal estimating equations or conditional residuals. Simulated data sets were used to discover differences among the methods in terms of biases, variances and convergence rates when the association structure is misspecified. The methods were also applied to a real medical data set. Two of the GEE methods, referred to as Cond and ML‐norm in this paper and by their originators, were found to have relatively good convergence rates and mean squared errors for all sample sizes (80, 120, 300) considered, and one more, referred to as MGEE in this paper and by its originators, worked fairly well for all but the smallest sample size, 80. Copyright © 2005 John Wiley & Sons, Ltd.
Adaptation of multiple logistic regression to a multiple inverse sampling design: application to the Isfahan healthy heart program
Authors: Salehi M. Mohammad , Levy Paul S. , Jamalzadeh Mohammad A. , Chang K.‐C. 
Published: October 2005

AbstractIn observational and experimental studies in the health sciences involving human populations, it is sometimes considered desirable to recruit subjects according to designs that specify a predetermined number of subjects in each of several mutually exclusive classes (generally but not necessarily demographic in nature). This type of adaptive sampling design, now generally referred to as multiple inverse sampling (MIS), has received recent attention, and estimation methods are now available for several sequential MIS sampling designs. In this class of designs, subjects are sampled randomly and sequentially, usually one at a time, until all classes have the pre‐specified number of subjects. In this paper, we extend MIS for finite population sampling to estimation of the parameters in multiple logistic regression under MIS. Using estimated logistic regression parameters and cost components obtained from the Isfahan Healthy Heart Program (IHHP), we report findings from a simulation experiment in which it appears that, at fixed cost, MIS at the last stage of sampling compares favourably to simple random sampling. The IHHP is a large community intervention study for prevention of cardiovascular disease being conducted in Isfahan, Iran and two other cities in Iran. The IHHP identified subjects through a multistage sample survey in which MIS was used at the final stage of sampling. MIS is one of several methods of adaptive sampling that are generating considerable interest and show promise of being useful in a wide variety of applications. Copyright © 2005 John Wiley & Sons, Ltd.
Tutorial in biostatistics: the self‐controlled case series method
Authors: Whitaker Heather J. , Paddy Farrington C. , Spiessens Bart , Musonda Patrick 
Published: October 2005

AbstractThe self‐controlled case series method was developed to investigate associations between acute outcomes and transient exposures, using only data on cases, that is, on individuals who have experienced the outcome of interest. Inference is within individuals, and hence fixed covariates effects are implicitly controlled for within a proportional incidence framework. We describe the origins, assumptions, limitations, and uses of the method. The rationale for the model and the derivation of the likelihood are explained in detail using a worked example on vaccine safety. Code for fitting the model in the statistical package STATA is described. Two further vaccine safety data sets are used to illustrate a range of modelling issues and extensions of the basic model. Some brief pointers on the design of case series studies are provided. The data sets, STATA code, and further implementation details in SAS, GENSTAT and GLIM are available from an associated website. Copyright © 2005 John Wiley & Sons, Ltd.
Constructing intervals for the intracluster correlation coefficient using Bayesian modelling, and application in cluster randomized trials
Authors: Turner Rebecca M. , Omar Rumana Z. , Thompson Simon G. 
Published: October 2005

AbstractStudies in health research are commonly carried out in clustered settings, where the individual response data are correlated within clusters. Estimation and modelling of the extent of between‐cluster variation contributes to understanding of the current study and to design of future studies. It is common to express between‐cluster variation as an intracluster correlation coefficient (ICC), since this measure is directly comparable across outcomes. ICCs are generally reported unaccompanied by confidence intervals. In this paper, we describe a Bayesian modelling approach to interval estimation of the ICC. The flexibility of this framework allows useful extensions which are not easily available in existing methods, for example assumptions other than Normality for continuous outcome data, adjustment for individual‐level covariates and simultaneous interval estimation of several ICCs. There is also the opportunity to incorporate prior beliefs on likely values of the ICC. The methods are exemplified using data from a cluster randomized trial. Copyright © 2005 John Wiley & Sons, Ltd.
The importance of varying the event generation process in simulation studies of statistical methods for recurrent events
Authors: Metcalfe Chris , Thompson Simon G. 
Published: October 2005

AbstractStatistical methods for the analysis of recurrent events are often evaluated in simulation studies. A factor rarely varied in such studies is the underlying event generation process. If the relative performance of statistical methods differs across generation processes, then studies based upon one process may mislead. This paper describes the simulation of recurrent events data using four models of the generation process: Poisson, mixed Poisson, autoregressive, and Weibull. For each model four commonly used statistical methods for the analysis of recurrent events (Cox's proportional hazards method, the Andersen–Gill method, negative binomial regression, the Prentice–Williams–Peterson method) were applied to 200 simulated data sets, and the mean estimates, standard errors, and confidence intervals obtained. All methods performed well for the Poisson process. Otherwise, negative binomial regression only performed well for the mixed Poisson process, as did the Andersen–Gill method with a robust estimate of the standard error. The Prentice–Williams–Peterson method performed well only for the autoregressive and Weibull processes. So the relative performance of statistical methods depended upon the model of event generation used to simulate data. In conclusion, it is important that simulation studies of statistical methods for recurrent events include simulated data sets based upon a range of models for event generation. Copyright © 2005 John Wiley & Sons, Ltd.
Bivariate isotonic design for dose‐finding with ordered groups
Authors: Ivanova Anastasia , Wang Kai 
Published: October 2005

AbstractWe consider the problem of dose‐finding where subjects can be stratified into two populations with possibly different susceptibility to toxicity. The goal is to find the maximally tolerated dose for each population. We propose a non‐parametric design for this problem. Toxicity is estimated using the bivariate isotonic regression estimator. The new design is compared with the two‐sample continual reassessment method. Copyright © 2005 John Wiley & Sons, Ltd.
Model comparison of generalized linear mixed models
Authors: Song Xin‐Yuan , Lee Sik‐Yum 
Published: October 2005

AbstractGeneralized linear mixed models (GLMMs) have been widely appreciated in biological and medical research. Maximum likelihood estimation has received a great deal of attention. Comparatively, not much has been done on model comparison or hypotheses testing. In this article, we propose a path sampling procedure to compute the observed‐data log‐likelihood function, so that the Bayesian information criterion (BIC) can be applied to model comparison or hypothesis testing. Advantages of the proposed path sampling procedure are discussed. Two medical data sets are analysed for providing illustrative examples of the proposed methodology. Copyright © 2005 John Wiley & Sons, Ltd.
A comparison of propensity score methods: a case‐study estimating the effectiveness of post‐AMI statin use
Authors: Austin Peter C. , Mamdani Muhammad M. 
Published: October 2005

AbstractThere is an increasing interest in the use of propensity score methods to estimate causal effects in observational studies. However, recent systematic reviews have demonstrated that propensity score methods are inconsistently used and frequently poorly applied in the medical literature. In this study, we compared the following propensity score methods for estimating the reduction in all‐cause mortality due to statin therapy for patients hospitalized with acute myocardial infarction: propensity‐score matching, stratification using the propensity score, covariate adjustment using the propensity score, and weighting using the propensity score. We used propensity score methods to estimate both adjusted treated effects and the absolute and relative risk reduction in all‐cause mortality. We also examined the use of statistical hypothesis testing, standardized differences, box plots, non‐parametric density estimates, and quantile–quantile plots to assess residual confounding that remained after stratification or matching on the propensity score. Estimates of the absolute reduction in 3‐year mortality ranged from 2.1 to 4.5 per cent, while estimates of the relative risk reduction ranged from 13.3 to 17.0 per cent. Adjusted estimates of the reduction in the odds of 3‐year death varied from 15 to 24 per cent across the different propensity score methods. Copyright © 2005 John Wiley & Sons, Ltd.