The evaluation of evidence for exponentially distributed data

At present, likelihood ratios for two-level models are determined with the use of a normal kernel estimation procedure when the between-group distribution is thought to be non-normal. An extension is described here for a two-level model in which the between-group distribution is very positively skewed and an exponential distribution may be thought to represent a good model. The theoretical likelihood ratio is derived. A likelihood ratio based on a biweight kernel with an adaptation at the boundary is developed. The performance of this kernel is compared alongside those of normal kernels and normal and exponential parametric models. A comparison of performance is made for simulated data where results may be compared with those of theory, using the theoretical model, as the true parameter values for the models are known. There is also a comparison for forensic data, using the concentration of aluminium in glass as an exemplar. Performance is assessed by determining the numbers of occasions on which the likelihood ratios for sets of fragments from the same group are supportive of the proposition that they are from different groups and the numbers of occasions on which the likelihood ratios for sets of fragments from different group are supportive of the proposition that they are from the same group

Invasive crayfish impacts on native fish diet and growth vary with fish life stage

Assessing the impacts of invasive organisms is a major challenge in ecology. Some widespread invasive species such as crayfish are potential competitors and reciprocal predators of ecologically and recreationally important native fish species. Here, we examine the effects of signal crayfish (Pacifastacus leniusculus) on the growth, diet, and trophic position of the chub (Squalius cephalus) in four rivers in Britain. Growth rates of 0+ chub were typically lower in sympatric populations with signal crayfish compared with allopatric populations, and this effect could be traced through to 2+ chub in one river. However, growth rates of older chub (5+ to 6+) were typically higher in the presence of crayfish. Sympatry with crayfish resulted in lower chub length-at-age and mass-at-age in half of the rivers sampled, with no change detected in the other rivers. Stable isotope analyses (δ13C and δ15N) revealed that both chub and crayfish were omnivorous, feeding at multiple trophic levels and occupying similar trophic positions. We found some evidence that chub trophic position was greater at invaded sites on one river, with no difference detected on a second river. Mixing models suggested crayfish were important food items for both small and large chub at invaded sites. This study provides evidence that invasive species can have both positive and negative effects on different life stages of a native species, with the net impact likely to depend on responses at the population level

Probing the Evolution of the Galaxy Interaction/Merger Rate Using Collisional Ring Galaxies

We present the results from our program to determine the evolution of the galaxy interaction/merger rate with redshift using the unique star-forming characteristics of collisional ring galaxies. We have identified 25 distant collisional ring galaxy candidates (CRGCs) in a total of 162 deep Hubble Space Telescope Wide Field/Planetary Camera-2 images obtained from the HST Archives. Based on measured and estimated redshifts, these 25 CRGCs all lie in the redshift interval of 0.1 < z < 1. Using the local collisional ring galaxy volume density and the new ``standard'' cosmology, we find that in order to account for the number of identified CRGCs in our surveyed fields, the galaxy interaction/merger rate, parameterized as (1 + z)^m, must increase steeply with redshift.We determine a minimum value of m = 5.2 $\pm$ 0.7, though m could be as high as 7 or 8. We can rule out a non-evolving (m = 0) and weakly evolving (m = 1-2) galaxy interaction/merger rate at greater than the 4 sigma level of confidence.Comment: Accepted in the Astrophysical Journal (11 pages, 4 figures). Higher resolution version of the figures is available at http://www.astro.cornell.edu/~vassilis/papers

Dealing with mobility: Understanding access anytime, anywhere

The rapid and accelerating move towards the adoption and use of mobile technologies has increasingly provided people and organisations with the ability to work away from the office and on the move. The new ways of working afforded by these technologies are often characterised in terms of access to information and people ‘anytime, anywhere’. This paper presents a study of mobile workers that highlights different facets of access to remote people and information, and different facets of anytime, anywhere. Four key factors in mobile work are identified from the study: the role of planning, working in ‘dead time’, accessing remote technological and informational resources, and monitoring the activities of remote colleagues. By reflecting on these issues, we can better understand the role of technology and artefact use in mobile work and identify the opportunities for the development of appropriate technological solutions to support mobile workers

N-Acetylation phenotype and genotype and risk of bladder cancer in benzidine-exposed workers

Several studies in subjects occupationally exposed to arylamine carcinogens have shown increased risks for bladder cancer associated with the slow acetylator phenotype. To follow up these reports, a case-control study of N-acetylation and bladder cancer risk was carried out among subjects occupationally exposed to benzidine, in benzidine dye production and use facilities in China. Thirty-eight bladder cancer cases and 43 controls from these factories were included for study of acetylation phenotype, by dapsone administration, and for polymorphisms in the NAT2 gene, by a polymerase chain reaction (PCR)-based test. In contrast to previous studies, no increase in bladder cancer risk was found for the slow N-acetylation phenotype (OR= 0.3; 95% CI = 0.1-1.3) or for slow N-acetylation-associated double mutations in NAT2 (OR = 0.5; 95% CI = 0.1-1.8). Examination of specific mutations and adjustment for age, weight, city and tobacco use did not alter the results. When examined by level of benzidine exposure in the cases, the bladder cancer risks associated with low (OR = 0.3, 95% CI = 0.0-2.2), medium (OR = 0.7, 95% CI = 0.1-4.5) and high (OR = 0.6, 95% CI = 0.1-3.5) exposure showed no interaction between genotype and benzidine exposure, within the range of exposures experienced by subjects in this study. This study, which is the first to incorporate phenotypic and genotypic analyses, provides evidence that the NAT2-related slow N-acetylation polymorphism is not associated with an increased risk of bladder cancer in workers exposed to benzidine, and may have a protective effec