Prescission neutron multiplicity and fission probability from Langevin dynamics of nuclear fission

A theoretical model of one-body nuclear friction which was developed earlier, namely the chaos-weighted wall formula, is applied to a dynamical description of compound nuclear decay in the framework of the Langevin equation coupled with statistical evaporation of light particles and photons. We have used both the usual wall formula friction and its chaos-weighted version in the Langevin equation to calculate the fission probability and prescission neutron multiplicity for the compound nuclei $^{178}$W, $^{188}$Pt, $^{200}$Pb, $^{213}$Fr, $^{224}$Th, and $^{251}$Es. We have also obtained the contributions of the presaddle and postsaddle neutrons to the total prescission multiplicity. A detailed analysis of our results leads us to conclude that the chaos-weighted wall formula friction can adequately describe the fission dynamics in the presaddle region. This friction, however, turns out to be too weak to describe the postsaddle dynamics properly. This points to the need for a suitable explanation for the enhanced neutron emission in the postsaddle stage of nuclear fission.Comment: RevTex, 14 pages including 5 Postscript figures, results improved by using a different potential, conclusions remain unchanged, to appear in Phys. Rev.

Quasi-fission reactions as a probe of nuclear viscosity

Fission fragment mass and angular distributions were measured from the ^{64}Ni+^{197}Au reaction at 418 MeV and 383 MeV incident energy. A detailed data analysis was performed, using the one-body dissipation theory implemented in the code HICOL. The effect of the window and the wall friction on the experimental observables was investigated. Friction stronger than one-body was also considered. The mass and angular distributions were consistent with one-body dissipation. An evaporation code DIFHEAT coupled to HICOL was developed in order to predict reaction time scales required to describe available data on pre-scission neutron multiplicities. The multiplicity data were again consistent with one-body dissipation. The cross-sections for touch, capture and quasi-fission were also obtained.Comment: 25 pages REVTeX, 3 tables, 13 figures, submitted to Phys. Rev

The Natural History Museum Fossil Porifera Collection

This article provides updated information about the Porifera Collection at The Natural History Museum (NHM), London. With very little information available regarding fossil sponge digitization or any similar initiative, this paper covers the type and figured specimens and drawer label content data of the Porifera Collection and also describes the collection and its research potential. With approximately 71,000 specimens, of which more than 60% are Mesozoic, the NHM holdings offer the best Mesozoic sponge collection in the world and one of the most important due to its breadth and depth. The Porifera Collection covers all stratigraphic periods and all taxonomic groups and includes almost 3000 cited and figured specimens including types. Although most of the specimens come from the British Isles, worldwide samples are also present, with abundant specimens from other Commonwealth countries and from Antarctica.The attached document is the author(’s’) final accepted/submitted version of the journal article. You are advised to consult the publisher’s version if you wish to cite from it

Vanishing wildlife corridors and options for restoration: a case study from Tanzania

Conserving wildlife corridors is increasingly important for maintaining ecological and genetic connectivity in times of unprecedented habitat fragmentation. Documenting connectivity loss, assessing root causes, and exploring restoration options are therefore priority conservation goals. A 2009 nationwide assessment in Tanzania documented 31 major remaining corridors, the majority of which were described as threatened. The corridor between the Udzungwa Mountains and the Selous Game Reserve in south-central Tanzania, a major link between western and southern wildlife communities, especially for the African elephant Loxodonta africana, provides an illuminating case study. A preliminary assessment in 2005 found that connectivity was barely persisting via two remaining routes. Here we present assessments of these two corridors conducted from 2007-2010, using a combination of dung surveys, habitat mapping and questionnaires. We found that both corridor routes have become closed over the last five years. Increased farming and livestock keeping, associated with both local immigration and population growth, were the main reasons for corridor blockage. However, continued attempts by elephants to cross by both routes suggest that connectivity can be restored. This entails a process of harmonizing differing land owners and uses towards a common goal. We provide recommendations for restoring lost connectivity and discuss the prospects for preventing further loss of corridors across the country

Review Section : Nature/Nurture Revisited I

Biologically oriented approaches to the study of human conflict have thus far been limited largely to the study of aggression. A sample of the literature on this topic is reviewed, drawing upon four major approaches: comparative psychology, ethology (including some popularized accounts), evolutionary-based theories, and several areas of human physiology. More sophisticated relationships between so-called "innate" and "acquired" determinants of behavior are discussed, along with the proper relevance of animal behavior studies for human behavior. Unless contained in a comprehensive theory which includes social and psychological variables, biolog ically oriented theories (although often valid within their domain) offer at best severely limited and at worst highly misleading explanations of complex social conflicts. The review concludes with a list of several positive contributions of these biological approaches and suggests that social scientists must become more knowledgeable about them.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68270/2/10.1177_002200277401800206.pd

Should science educators deal with the science/religion issue?

I begin by examining the natures of science and religion before looking at the ways in which they relate to one another. I then look at a number of case studies that centre on the relationships between science and religion, including attempts to find mechanisms for divine action in quantum theory and chaos theory, creationism, genetic engineering and the writings of Richard Dawkins. Finally, I consider some of the pedagogical issues that would need to be considered if the science/religion issue is to be addressed in the classroom. I conclude that there are increasing arguments in favour of science educators teaching about the science/religion issue. The principal reason for this is to help students better to learn science. However, such teaching makes greater demands on science educators than has generally been the case. Certain of these demands are identified and some specific suggestions are made as to how a science educator might deal with the science/religion issue. © 2008 Taylor & Francis

Nutrition of the temperate Australian soft coral Capnella gaboensis - II. The role of zooxanthellae and feeding

We examined the ability of Capnella gaboensis Verseveldt, 1977 (Coelenterata: Octocorallia: Alcyonacea: Nephtheidae) to utilize heterotrophic food sources, and the importance of heterotrophic nutrition and photosynthesis in its diet, by using preserved material and histological sections of field-collected specimens and by means of laboratory experiments in which coral branches were fed with 14C-labelled food of different sizes. The study was conducted from April 1982 to August 1984. C. gaboensis receives nutrition from the photosynthesis of its symbiotic zooxanthellae, Symbiodinium sp., and from heterotrophic sources. Up to 10% of the algal photosynthate was translocated to the animal-host tissues. The contribution of translocated carbon from the zooxanthellae to the daily respiratory carbon requirement of the animal was estimated to be well below 50% in all seasons except in the summer of 1983-1984, indicating that the coral must rely on additional sources of nutrition (i.e., heterotrophy) for most, if not all, of the year. Field (Sydney Harbour: 33°50′S; 151°15′E) and laboratory observations and experiments indicated that this coral probably feeds upon zooplankton, small particulate matter and dissolved organic matter

Nutrition of the temperate Australian soft coral Capnella gaboensis - I. Photosynthesis and carbon fixation

Capnella gaboensis Verseveldt, 1977 (Coelenterata: Octocorallia: Alcyonacea: Nephtheidae) is an abundant soft coral in the temperate waters of south-eastern Australia. From 1981 to 1984, using material collected from Sydney Harbour (33°50′S; 151°15′E), we investigated certain aspects of its apparently obligate association with its symbiotic zooxanthellae, Symbiodinium sp. Numbers of zooxanthellae and chlorophyll content were recorded throughout the first year, then net photosynthesis and respiratory rates of the coral as a function of photo-flux densities, temperature and season were measured in later years. The fractions into which photosynthetically fixed carbon was incorporated were also determined. The zooxanthellae contained a mean of 4.1 μg chlorophyll a 10-6 zooxanthellae. Neither the numbers of zooxanthellae in C. gaboensis nor the chlorophyll a content varied on a seasonal basis. Photon-flux densities in the field ranged from 5 to 120 μE m-2 s-1 over the year. The maximum net oxygen-exchange rate recorded for C. gaboensis was 9.4 μmol O2 mg-1 chlorophyll a h-1 at 871 μE m-2 s-1. The maximum carbon fixation rate obtained was 65.6 μmol C mg-1 chlorophyll a h-1 at 100 μE m-2 s-1. Photosynthesis of C. gaboensis was not light-saturated at 871 μE m-2 s-1; the light compensation point was in the range 50 to 90 μE m-2 s-1 and the optimum temperature was 25°C. Photosynthetic rates were highest in populations sampled in summer. Labelling with 14C showed that photosynthetically fixed carbon was initially incorporated into the aqueous-methanol (low molecular weight) fraction of the coral tissues. From 20 to 100 min after the introduction of the 14C label the rate of incorporation was fairly evenly divided between the aqueous methanol-soluble, the chloroform-soluble (lipid) and the insoluble fractions. In the light, little 14C was released as particulate and/or dissolved organic carbon. Translocation of products of photosynthesis represented up to approximately 10% of the total fixation

Breakup and transfer processes in the 9Be+208Pb reaction

α-Particle singles and doubles yields for the reaction of 9Be+208Pb have been measured from below to well above the fusion barrier energy. These yields have been reproduced by calculations including both neutron transfer and inelastic excitation. The calculations predict breakup cross sections to persist to very low energies, where the latter process dominates