A substantial body of experimental evidence has demonstrated that labels have an impact on infant categorization processes. Yet little is known regarding the nature of the mechanisms by which this effect is achieved. We distinguish between two competing accounts: supervised name‐based categorization and unsupervised feature‐based categorization. We describe a neurocomputational model of infant visual categorization, based on self‐organizing maps, that implements the unsupervised feature‐based approach. The model successfully reproduces experiments demonstrating the impact of labeling on infant visual categorization reported in (...) Plunkett, Hu, and Cohen (2008). It mimics infant behavior in both the familiarization and testing phases of the procedure, using a training regime that involves only single presentations of each stimulus and using just 24 participant networks per experiment. The model predicts that the observed behavior in infants is due to a transient form of learning that might lead to the emergence of hierarchically organized categorical structure and that the impact of labels on categorization is influenced by the perceived similarity and the sequence in which the objects are presented. The results suggest that early in development, say before 12 months old, labels need not act as invitations to form categories nor highlight the commonalities between objects, but they may play a more mundane but nevertheless powerful role as additional features that are processed in the same fashion as other features that characterize objects and object categories. (shrink)

Ocean biology helps regulate global climate by fixing atmospheric CO2 and exporting it to deep waters as sinking detrital particles. New observations demonstrate that particle fragmentation is the principal factor controlling the depth to which these particles penetrate the ocean's interior, and hence how long the constituent carbon is sequestered from the atmosphere. The underlying cause is, however, poorly understood. We speculate that small, particle‐associated copepods, which intercept and inadvertently break up sinking particles as they search for attached protistan prey, (...) are the principle agents of fragmentation in the ocean. We explore this idea using a new marine ecosystem model. Results indicate that explicitly representing particle fragmentation by copepods in biogeochemical models offers a step change in our ability to understand the future evolution of biologically‐mediated ocean carbon storage. Our findings highlight the need for improved understanding of the distribution, abundance, ecology and physiology of particle‐associated copepods. (shrink)

Sinking organic particles transfer ∼10 gigatonnes of carbon into the deep ocean each year, keeping the atmospheric CO2 concentration significantly lower than would otherwise be the case. The exact size of this effect is strongly influenced by biological activity in the ocean's twilight zone (∼50–1,000 m beneath the surface). Recent work suggests that the resident zooplankton fragment, rather than ingest, the majority of encountered organic particles, thereby stimulating bacterial proliferation and the deep‐ocean microbial food web. Here we speculate that this (...) apparently counterintuitive behaviour is an example of ‘microbial gardening’, a strategy that exploits the enzymatic and biosynthetic capabilities of microorganisms to facilitate the ‘gardener's’ access to a suite of otherwise unavailable compounds that are essential for metazoan life. We demonstrate the potential gains that zooplankton stand to make from microbial gardening using a simple steady state model, and we suggest avenues for future research. (shrink)

By considering the irreducible representations of the Lorentz group, an analysis of the different spin-2 waves is presented. In particular, the question of the helicity is discussed. It is concluded that, although from the point of view of representation theory there are no compelling reasons to choose between spin-2 waves with helicity σ=±1 or σ=±2, consistency arguments of the ensuing field theories favor waves with helicity σ=±1.

First published in 1881, as part of the Pitt Press Series, this book presents a guide to classical philosophy aimed at undergraduates and those studying the works of Cicero, Plato or Aristotle. All quotations are in the original Greek and Latin. This book will be of value to anyone with an interest in the history of philosophy and perspectives on classical thought.

Deborah is a thirty-three-year-old who presented to labor and delivery at thirty-seven weeks gestation with complaints of contractions. Upon arrival, she explained that her fetus, Nathan, had been diagnosed with a “lethal” condition by her primary obstetrician. At twenty-two weeks gestation, an amniocentesis confirmed trisomy 13, a chromosomal abnormality leading to miscarriage or stillbirth in nearly one-half of affected pregnancies. During the admission process, Deborah voices the worry that due to Nathan's brain and heart structure, vaginal delivery could be traumatic (...) and cause him to suffer. Deborah wishes for him to have as painless and as dignified a death as possible; cesarean section, she feels, will achieve this. Yet with her history of three prior vaginal deliveries, normally progressing labor, and poor fetal prognosis that is unlikely to improve with cesarean delivery, there is no maternal or fetal indication for a cesarean section. Should the obstetrician proceed with a cesarean delivery despite knowing that it would expose the mother to surgical risks with little or no corresponding fetal or neonatal benefit? (shrink)