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The ocean quahog, Arctica islandica, is a commercially important bivalve in the eastern USA but very little is known about the recruitment frequency and rebuilding capacity of this species. As the longest-living bivalve on Earth, A. islandica can achieve lifespans in excess of 200 y; however, age determinations are difficult to estimate and age variability at size is extreme. Objectives for this study included the creation of an extremely large age-composition dataset to constrain age at length variability, development of reliable age-length keys (ALK), and descriptions of sex-based population dynamics for the quasi-virgin A. islandica population at Georges Bank (GB) within the greater US Mid-Atlantic stock. Sexually dimorphic characteristics are clearly present, as females are larger than males within age classes and males tend to dominate the oldest age classes. A male represented the maximum age of 261 years and is older than the maximum age previously documented for this region. Sex-specific ALKs were robust and reliable but not interchangeable. This population had higher estimated natural mortality rates than presumed for other regions in the Mid-Atlantic, and females have the highest mortality rate. However, recruitment expansion was also occurring which would affect the age-frequency data used to derive mortality estimates and result in higher mortality. Age frequencies at GB suggest effective recruitment to the population each year since 1867 CE. Reduced recruitment periods are documented and likely attributed to fluctuating environmental conditions. Sex-based demographics are clearly divergent in regard to growth rate, maximum size, longevity and mortality rates.
It is pertinent to the safety case for geological disposal in the UK that the behaviour of vitrified wastes in proximity to cementitious materials is understood. In this study, vitrified simulant intermediate level nuclear waste (ILW) was subject to dissolution in a synthetic cement water solution to simulate disposal conditions. Results show that the presence of alkali / alkaline earth elements in the cementitious solution can be favourable, at least in the short-term, leading to lower dissolution rates associated with incorporation of these elements into the altered layer of the glass.
We examine the relationship of biomass B and length L in the eastern oyster Crassostrea virginica by focusing on the scaling exponent b in the allometric equation B = aLb using four datasets: Delaware Bay, Chesapeake Bay, Galveston Bay and a regionally extensive compilation from the NOAA Mussel Watch Program. The average value of the scaling exponent in Delaware Bay and Chesapeake Bay is about 2. For Galveston Bay, the value is distinctly higher, near 2.6. Over all Mussel Watch sites, the value is again near 2. Within Delaware Bay, the salinity gradient exerts an important effect. Shells are longer for their meat weight at lower salinities. The range of scaling exponents revealed by Mussel Watch data is exceedingly large (b < 1 to >3). Scaling exponents below 2.5 are unusual in bivalves. Among bivalves, only other oyster taxa have comparably low scaling exponents averaging near 2. We propose that oyster biomass routinely scales nearer the square of the length rather than the cube and that this is a constraint imposed by the exigency of carbonate production for reef maintenance and accretion in the face of high rates of taphonomic degradation. The adaptation as a reef builder requires the formation of carbonate that rapidly breaks down, thus requiring that carbonate produced be maximized. A biomass-to-length scaling exponent of 2 provides a mechanism to maximize shell production relative to biomass, while at the same time providing maximum surface area for the all-important settling of oyster spat to maintain the population.
Contrary to Vaesen's argument that humans are unique with respect to nine cognitive capacities essential for tool use, we suggest that although such cognitive processes contribute to variation in tool use, it does not follow that these capacities are necessary for tool use, nor that tool use shaped cognition per se, given the available data in cognitive neuroscience and behavioral biology.
Oyster population reproductive capacity and dynamics are controlled at the most basic level by the observed sex-ratios. Since oysters are sequential, protandric hermaphrodites the population sex-ratio is related to the demographics (shell length, age, and biomass). Oysters were collected from June through to August 2008 at twelve bars in the James, Rappahannock and Great Wicomico Rivers, Virginia, USA. Bars were aggregated into five groups on the basis of similar age–length relationships. Sex-ratios (fraction female), age–length, and biomass–length relationships were determined for each group. The fraction female increased within increasing shell length, age, and biomass at all sites. Simultaneous hermaphrodites were rarely observed. Group specific differences in shell length (SL, mm) and age (yr) for the timing of the protandric shift were observed with the earliest shift from male to female occurring at ~60 mm SL and ~1.6 yr. The proportion of females observed in the larger or older individuals was at least 70–80%. Sex-ratios from summer 2008 were used to develop sex–length, sex–age, and sex–biomass keys that were applied to autumn-survey data from 2006, 2007, 2008 and 2009. In these years, sex-ratios by shell length and age were strongly biased towards males while the sex-ratio by biomass was strongly biased towards females. Disease mortality compounds natural and fishing mortality resulting in age/size specific cropping yielding truncated population demographics and an earlier protandric shift in populations on the extremes of the range examined. Regardless of location, market (>76 mm SL) oysters are predominantly female.
Selection designs and futility designs offer investigators a way to screen potential therapies in early phase clinical research with fewer patients than would be required for a traditional phase 3 trial for each candidate. There are some avoidable-pitfalls when planning a futility study. The first is that if the sample size is too small, a rather awkward situation can arise. The last pitfall relates to the use of historical control data in the single-arm design. Selection procedures offer an attractive approach to the problem of screening potentially good treatments. There are many different procedures for general ranking and selection goals such as selection from among more than two treatments, selection of best subsets of treatments, and ranking treatments in order of efficacy. Although selection procedures efficiently achieve their goal of selecting best treatments, the desire to 'test something' with an accompanying statement of statistical significance seems irresistible.
In this paper, we take a detailed look at the performance of components of an idealized
question answering system on two different tasks: the TREC Question Answering task
and a set of reading comprehension exams. We carry out three types of analysis: inherent
properties of the data, feature analysis, and performance bounds. Based on these analyses
we explain some of the performance results of the current generation of Q/A systems and
make predictions on future work. In particular, we present four findings: (1) Q/A system
performance is correlated with answer repetition; (2) relative overlap scores are more effective
than absolute overlap scores; (3) equivalence classes on scoring functions can be used to
quantify performance bounds; and (4) perfect answer typing still leaves a great deal of
ambiguity for a Q/A system because sentences often contain several items of the same type.
One thousand and ten unselected London state schoolgirls were screened by questionnaire to identify an ‘at risk’ cohort displaying abnormal eating attitudes and two control cohorts, one with probable general psychiatric morbidity, one without. Members of all cohorts were assessed at interview for the presence of eating disorder and for putative risk factors implicated in the development of anorexia nervosa. A prevalence rate of 0·99 % was detected for clinical eating disorder and 1·78 % for the partial syndrome of eating disorder. Factors specifically associated with abnormal eating attitudes were identified, in particular, current or past overweight, history of amenorrhoea and perceived stress in school and social life. Some commonly accepted risk factors for eating disorders were discovered to be associations with general psychiatric morbidity. These were perceived parental pressure to eat more, taking exercise to lose weight, perceived stress at home and reporting a family history of anxiety or depression. Other well reported putative risk factors for eating disorder, including social class, birth order, age at menarche, obsessional personality and weight related career choice were not associated specifically with abnormal eating attitudes in schoolgirls. These findings represent cross-sectional data at entry into a prospective epidemiological study.
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