Asymptotic normality for two-stage sampling from a finite population

Summary In this paper we consider two-stage sampling from a finite population, and associated estimators of the population total, in a general setting which includes most two-stage procedures in the literature. The main result gives general conditions for asymptotic normality of the estimators. The proof is based on a martingale central limit theorem. It is indicated how the result can be extended to multi-stage procedures.     

Conformational studies on phenyl thioglycosides: a remote effect on disaccharide linkage by phenyl aglycons attenuates recognition of galabiosides by a bacterial adhesin

Phenyl S-galabiosides display altered conformational properties, as compared to phenyl O-galabiosides, characterised by a remote effect on the galabiose intersaccharidic glycoside bond by the phenyl aglycon, resulting in significantly lowered affinity for the PapG class II adhesin of uropathogenic E. coli.     

Structure-activity relationships of galabioside derivatives as inhibitors of E. coli and S. suis adhesins: nanomolar inhibitors of S. suis adhesins

Four collections of Gal alpha1-4Gal derivatives were synthesised and evaluated as inhibitors of the PapG class II adhesin of uropathogenic Escherichia coli and of the P(N) and P(O) adhesins of Streptococcus suis strains. Galabiosides carrying aromatic structures at C1, methoxyphenyl O-galabiosides in particular, were identified as potent inhibitors of the PapG adhesin. Phenylurea derivatisation at C3' and methoxymethylation at O2' of galabiose provided inhibitors of the S. suis strains type P(N) adhesin with remarkably high affinities (30 and 50 nM, respectively). In addition, quantitative structure-activity relationship models for E. coli PapG adhesin and S. suis adhesin type P(O) were developed using multivariate data analysis. The inhibitory lead structures constitute an advancement towards high-affinity inhibitors as potential anti-adhesion therapeutic agents targeting bacterial infections.     

Determination of the 15N/14N ratio of ammonium and ammonia in aqueous solutions by equilibrium headspace-gas chromatography-combustion-isotope ratio mass spectrometry

A method for determination of the 15N/14N ratio of total ammoniacal nitrogen (TAN; ammonium and ammonia) in aqueous solutions was developed, primarily intended for use with soil extracts, which have a high TAN level, e.g. from recently fertilised agricultural soils. Ammonium was converted to ammonia by addition of NaOH, followed by nitrogen isotopic analysis of the headspace by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) where complete separation of TAN from the matrix was not necessary. The ammonia concentration in the gas phase was maximised by increasing the temperature and salt concentration and by decreasing the gas liquid ratio in the headspace vials. Isotopic equilibrium was reached after less than 1 h at 80 degrees C. The measured isotopic ratio was constant for solutions containing 30-200 mM NH4-N, corresponding to 950-7000 ng NH3-N detected with the IRMS. The integrated area response at m/z 28 increased linearly with the ammonium ion concentration in the interval 10-200 mM NH4-N. The fractionation factor between the liquid and gas phases was 1.0054 +/- 0.0007 within the linear range, which is in agreement with values reported in the literature, but with a higher precision. Changes in temperature, gas:liquid ratio or salt concentration did not affect the measured ratio, demonstrating the robustness of the developed method.     

2-Bromoethyl glycosides for synthesis of glycoconjugates on solid support

2-Bromoethyl glycosides can easily and in high yields be transformed into sulfones by treatment with a suitable thiol followed by oxidation with mCPBA. The observation that the so formed sulfones were cleaved by treatment with NaOMe/MeOH was used to design a new safety catch linker for synthesis of glycoconjugates on solid support.     

Evidence for reversible attack of a carbanion on an η6 -arenetricarbonylchromium(0) complex

The regioselectivity of the reaction between 2-lithio-2-methylpropionitrile and η⁶-1-methyl-1,2,3,4-tetrahydroquinolinetricarbonylchromium(0) was found to be time- and temperature-dependent. Reaction at ?70° C yielded initially three regioisomers in the ratio 35/64/1. On prolonged reaction time or warming, equilibration gave the same three isomers but in the ratio 2/96/1.     

The one-year non-life insurance risk

A major part of the literature on non-life insurance reserve risk has been devoted to the ultimo risk, the risk in the full run-off of the liabilities. This is in contrast to the short time horizon in internal risk models at insurance companies, and the one-year risk perspective taken in the Solvency II project of the European Community.This paper aims at clarifying the one-year risk concept and describing simulation approaches, in particular for the one-year reserve risk. We also discuss the one-year premium risk and its relation to the premium reserve.Finally, we initiate a discussion on the role of risk margins and discounting for the reserve and premium risk, with focus on the Cost-of-Capital method. We show that risk margins do not affect the reserve risk and show how reserve duration can be used for easy calculation of risk margins. ¹     

Reduction of bias in static closed chamber measurement of δ13C in soil CO2 efflux

The ¹³C/¹²C ratio of soil CO₂ efflux (δ_e) is an important parameter in studies of ecosystem C dynamics, where the accuracy of estimated C flux rates depends on the measurement uncertainty of δ_e. The static closed chamber method is frequently used in the determination of δ_e, where the soil CO₂ efflux is accumulated in the headspace of a chamber placed on top of the soil surface. However, it has recently been shown that the estimate of δ_e obtained by using this method could be significantly biased, which potentially diminish the usefulness of δ_e for field applications. Here, analytical and numerical models were used to express the bias in δ_e as mathematical functions of three system parameters: chamber height (H), chamber radius (R_c), and soil air‐filled porosity (θ). These expressions allow optimization of chamber size to yield a bias, which is at a level suitable for each particular application of the method. The numerical model was further used to quantify the effects on the δ_e bias from (i) various designs for sealing of the chamber to ground, and (ii) inclusion of the commonly used purging step for reduction of the initial headspace CO₂ concentration. The present modeling work provided insights into the effects on the δ_e bias from retardation and partial chamber bypass of the soil CO₂ efflux. The results presented here supported the continued use of the static closed chamber method for the determination of δ_e, with improved control of the bias component of its measurement uncertainty. Copyright © 2009 John Wiley & Sons, Ltd.     

Prevalence of voice symptoms and risk factors in teacher students

Teacher students seem to have low awareness of the vocal demands in their future professions, and students with vocal symptoms are at risk for developing voice disorders during their professional careers. The purpose of the present study was to determine the prevalence of voice problems in teacher students at the very beginning of their education at the university. Of 1636 students approached in the first couple of days, 1250 (76%) answered two questionnaires about voice symptoms, Screen6 and Swedish Voice Handicap Index (Sw-VHI), and one questionnaire about potential risk factors. A majority of the students were women, and their mean age was 23 years (range, 18-52 years). The results showed that 208 of 1250 students (17%) had voice problems, defined as at least two symptoms weekly or more often in Screen6. The proportion of women was larger in the group with voice problems than in the group without voice problems. Significant risk factors for voice problems were vocal fold problems in childhood and adulthood, frequent throat infections, airborne allergy, smoking, hearing problems, previous work as teacher or leader, voice demanding hobbies, and previous speech therapy or voice training. There was a clear association between the number of potential vocal risk factors and the number of voice symptoms. There was also a strong association between the scores of the two questionnaires, the Sw-VHI and the Screen6. Students with voice problems according to Screen6 scored 23.1 (mean Sw-VHI) compared with 7.8 for students without voice problems.