Damping of an oscillating scalar field indirectly coupled to a thermal bath

The damping process of a homogeneous oscillating scalar field that indirectly interacts with a thermal bath through a mediator field is investigated over a wide range of model parameters. We consider two types of mediator fields, those that can decay to the thermal bath and those that are individually stable but pair annihilate. The former case has been extensively studied in the literature by treating the damping as a local effect after integrating out the assumed close-to-equilibrium mediator field. The same approach does not apply if the mediator field is stable and freezes out of equilibrium. To account for the latter case, we adopt a non-local description of damping that is only meaningful when we consider full half-oscillations of the field being damped. The damping rates of the oscillating scalar field and the corresponding heating rate of the thermal bath in all bulk parameter regions are calculated in both cases, corroborating previous results in the direct decay case. Using the obtained results, the time it takes for the amplitude of the scalar field to be substantially damped is estimated.Comment: 39 pages, 9 figures, 1 table; typos corrected, references adde

RESOURCE OR NUISANCE? MANAGING AFRICAN ELEPHANTS AS A MULTI-USE SPECIES

Increasing human interference with natural systems causes us to re-think our perception of wildlife species and the economic choices society makes with regards to their management. Accordingly, we generalize existing 'bioeconomic' models by proposing an economically-based classification of species. The theoretical model is applied to the case of African elephant management. We demonstrate that the classification of the steady state population of a species depends on both species' density and economic factors. Our main results are threefold. First, we demonstrate the classification-dependent possibility of multiple equilibria and perverse comparative statics for multi-use species. Second, upon comparing the optimal stock of a multi-use species to the stock under an open access regime, we find that the ranking in terms of abundance is ambiguous. Finally, and consistent with existing literature on resource management in a second-best world, our case study supports the idea that trade measures have ambiguous effects on wildlife abundance under open access.Resource /Energy Economics and Policy,

Dynamics of clade diversification on the morphological hypercube

Understanding the relationship between taxonomic and morphological changes is important in identifying the reasons for accelerated morphological diversification early in the history of animal phyla. Here, a simple general model describing the joint dynamics of taxonomic diversity and morphological disparity is presented and applied to the data on the diversification of blastozoans. I show that the observed patterns of deceleration in clade diversification can be explicable in terms of the geometric structure of the morphospace and the effects of extinction and speciation on morphological disparity without invoking major declines in the size of morphological transitions or taxonomic turnover rates. The model allows testing of hypotheses about patterns of diversification and estimation of rates of morphological evolution. In the case of blastozoans, I find no evidence that major changes in evolutionary rates and mechanisms are responsible for the deceleration of morphological diversification seen during the period of this clade's expansion. At the same time, there is evidence for a moderate decline in overall rates of morphological diversification concordant with a major change (from positive to negative values) in the clade's growth rate.Comment: 8 pages, Latex, 2 postscript figures, submitted to Proc.R.Soc.Lond.

Coevolutionary Investments in Human Speech and Trade

We propose a novel explanation for the emergence of language in modern humans, and the lack thereof in other hominids. A coevolutionary process, where trade facilitates speech and speech facilitates trade, driven by expectations and potentially influenced by geography, gives rise to multiple stable development trajectories. While the trade-speech equilibrium is not an inevitable outcome for modern humans, we do find that it is a relatively likely result given that our species evolved in Africa under climatic conditions supporting relatively high population densities.Institutional and Behavioral Economics,

Competitive Exclusion, Diversification, and the Origins of Agriculture

The beginnings of agriculture, or the agricultural revolution, is now recognized to be the widespread adoption of known practices – a change in behavior – as opposed to a phenomenon of discovery and innovation. In this paper, we combine elements of three theories—climate change, property rights, and competitive exclusion—to create a paleoeconomic model of agriculture and its diffusion. We focus on climate change as a necessary trigger, which combined with group property rights and competitive exclusion processes produced conditions sufficient for the diffusion of early agriculture. In contrast to other models in which farming emerges as technological progress or climate makes it a more productive option than hunting, farming emerges in our model even if farmers are poor hunters and cannot sustain themselves with agriculture alone. Moreover, the strategy of farming can invade the system even if farmers initially generate lower per capita consumption than hunters. The key is that the simple innovation of property rights over an immobile resource can help to insulate farmers from competitive ecological pressures.Farm Management, Research and Development/Tech Change/Emerging Technologies,

The end-Permian mass extinction: A complex, multicausal extinction

The end-Permian mass extinction was the most extensive in the history of life and remains one of the most complex. Understanding its causes is particularly important because it anchors the putative 26-m.y. pattern of periodic extinction. However, there is no good evidence for an impact and this extinction appears to be more complex than others, involving at least three phases. The first began with the onset of a marine regression during the Late Permian and resulting elimination of most marine basins, reduction in habitat area, and increased climatic instability; the first pulse of tetrapod extinctions occurred in South Africa at this time. The second phase involved increased regression in many areas (although apparently not in South China) and heightened climatic instability and environmental degradation. Release of gas hydrates, oxidation of marine carbon, and the eruption of the Siberian flood basalts occurred during this phase. The final phase of the extinction episode began with the earliest Triassic marine regression and destruction of nearshore continental habitats. Some evidence suggests oceanic anoxia may have developed during the final phase of the extinction, although it appears to have been insufficient to the sole cause of the extinction

An Integrated View of Precambrian Eumetazoan Evolution

The eumetazoan clade of modern animals includes cnidarians, acoels, deuterostomes, and protostomes. Stem group eumetazoans evolved in the late Neoproterozoic, possibly before the Marinoan glaciation, according to a variety of different kinds of evidence. Here, we combine this evidence, including paleontological observations, results from molecular and morphological phylogeny, and paleoecological considerations, with deductions from the organization of the gene regulatory networks that underlie development of the bilaterian body plan. Eumetazoan body parts are morphologically complex in detail, and modern knowledge of gene regulatory network structure shows that the control circuitry required for their development is hierarchical and multilayered. Among the consequences is that the kernels of the networks that control the early allocation of spatial developmental fate canalize the possibilities of downstream evolutionary change, a mechanism that can account for the appearance of distinct clades in early animal evolution. We reconstruct preeumetazoan network organization and consider the process by which the eumetazoan regulatory apparatus might have been assembled. A strong conclusion is that the evolutionary process generating the genomic programs responsible for developmental formulation of basic eumetazoan body plans was in many ways very different from the evolutionary changes that can be observed at the species level in modern animals

Comment on "Self-Purification in Semiconductor Nanocrystals"

In a recent Letter [PRL 96, 226802 (2006)], Dalpian and Chelikowsky claimed that formation energies of Mn impurities in CdSe nanocrystals increase as the size of the nanocrystal decreases, and argued that this size dependence leads to "self-purification" of small nanocrystals. They presented density-functional-theory (DFT) calculations showing a strong size dependence for Mn impurity formation energies, and proposed a general explanation. In this Comment we show that several different DFT codes, pseudopotentials, and exchange-correlation functionals give a markedly different result: We find no such size dependence. More generally, we argue that formation energies are not relevant to substitutional doping in most colloidally grown nanocrystals.Comment: 1 page, 1 figur

Overdamped Stress Relaxation in Buckled Rods

We present a comprehensive theoretical analysis of the stress relaxation in a multiply but weakly buckled incompressible rod in a viscous solvent. In the bulk two interesting regimes of generic self--similar intermediate asymptotics are distinguished, which give rise to two classes of approximate and exact power--law solutions, respectively. For the case of open boundary conditions the corresponding non--trivial boundary--layer scenarios are derived by a multiple--scale perturbation (``adiabatic'') method. Our results compare well with -- and provide the theoretical explanation for -- previous results from numerical simulations, and they suggest new directions for further fruitful numerical and experimental investigations.Comment: 20 pages, 12 figure

The Role of Drug-Taking Supervisors and Patient Adherence to Anti Tuberculosis Treatment at Ngawi Health Center, East Java

Background: Treatment adherence is essential for DOTS TB completion and cure. In Ngawi, East Java, DOTS TB treatment coverage has not reached the targeted level of 100%. Some patients did not adhere treatment or even did not complete it. This study aimed to investigate the association between the presence of drug-taking supervisors and patient adherence to DOTS TB treatment at Ngawi Health Center, East Java. Subjects and Method: This was a analytic cross-sectional study conducted at Ngawi community health center, East Java. A sample of 41 patients undertaking TB DOTS treatment were selected for this study. The dependent variable was treatment adherence. The independent variabe was presence of drug-taking supervisor. The data were collected using a set of questionnaire and observation. The data was analyzed using Odds Ratio and Chi Square. Results: There were 25 (94.7%) patients who adhered DOTS treatment and 6 (40%) patients who did not adhere DOTS treatment. Patient adherence to DOTS treatment was associated with the presence of drug-taking supervisor (OR= 16.67; 95% CI= 1.76 to 158.12; p=0.003). Conclusion: Patient adherence to DOTS treatment is associated with the presence of drug-taking supervisor. Keywords: drug-taking supervisor, treatment adherence, tuberculosis, patien