A general stochastic model for sporophytic self-incompatibility

Disentangling the processes leading populations to extinction is a major topic in ecology and conservation biology. The difficulty to find a mate in many species is one of these processes. Here, we investigate the impact of self-incompatibility in flowering plants, where several inter-compatible classes of individuals exist but individuals of the same class cannot mate. We model pollen limitation through different relationships between mate availability and fertilization success. After deriving a general stochastic model, we focus on the simple case of distylous plant species where only two classes of individuals exist. We first study the dynamics of such a species in a large population limit and then, we look for an approximation of the extinction probability in small populations. This leads us to consider inhomogeneous random walks on the positive quadrant. We compare the dynamics of distylous species to self-fertile species with and without inbreeding depression, to obtain the conditions under which self-incompatible species could be less sensitive to extinction while they can suffer more pollen limitation

Ignition characteristics of the nickel-based alloy UNS N07001 in pressurized oxygen

The development of ignition and combustion in pressurized oxygen atmospheres was studied for the nickel-based alloy UNS N07001. Ignition of the alloy was achieved by heating the top surface of a cylindrical specimen with a continuous-wave CO2 laser. Two heating procedures were used. In the first, laser power was adjusted to maintain an approximately linear increase in surface temperature. In the second, laser power was periodically increased until autoheating (self-heating) was established. It was found that the alloy would autoheat to combustion from temperatures below the solidus temperature. In addition, the alloy had a tendency to develop combustion zones (hot spots) at high oxygen pressures when the incremental (step) heating test mode was used. Unique points on the temperature-time curves that describe certain events are defined and the temperatures at which these events occur are given for the oxygen pressure range of 1.72 to 13.8 MPa (250 to 2000 psia)

Narcolepsy: current treatment options and future approaches

The management of narcolepsy is presently at a turning point. Three main avenues are considered in this review: 1) Two tendencies characterize the conventional treatment of narcolepsy. Modafinil has replaced methylphenidate and amphetamine as the first-line treatment of excessive daytime sleepiness (EDS) and sleep attacks, based on randomized, double blind, placebo-controlled clinical trials of modafinil, but on no direct comparison of modafinil versus traditional stimulants. For cataplexy, sleep paralysis, and hypnagogic hallucinations, new antidepressants tend to replace tricyclic antidepressants and selective serotonin reuptake inhibitors (SSRIs) in spite of a lack of randomized, double blind, placebo-controlled clinical trials of these compounds; 2) The conventional treatment of narcolepsy is now challenged by sodium oxybate, the sodium salt of gammahydroxybutyrate, based on a series of randomized, double-blind, placebo-controlled clinical trials and a long-term open label study. This treatment has a fairly good efficacy and is active on all symptoms of narcolepsy. Careful titration up to an adequate level is essential both to obtain positive results and avoid adverse effects; 3) A series of new treatments are currently being tested, either in animal models or in humans, They include novel stimulant and anticataplectic drugs, endocrine therapy, and, more attractively, totally new approaches based on the present state of knowledge of the pathophysiology of narcolepsy with cataplexy, hypocretine-based therapies, and immunotherapy

When tradition becomes trendy : social distinction in Maltese food culture

This article looks at the revival of traditional Maltese food as a medium with which the Maltese represent, and contest, relationships among social classes. The recent revival of traditional Maltese food represents the quest of a young Maltese nation for originality, especially by the elite of that society. I argue that the Maltese elite, by using traditional, picturesque images of themselves, is succumbing to foreign ideals, and accepting the symbolic domination of Europe. Food habits have always been part of one’s everyday passive identity, but the revival of traditional food in Malta is an active and political claim for a desired identity.peer-reviewe

Searching for a national cuisine

As the marketing of national cuisines is spreading at an epidemic rate all around the world and as we witness countless aberrations it is necessary to shed light on the gastronomic search for identity. In this article I will be looking at some common postulates on national food. The discussion will tackle four main issues: are we really what we eat? What makes a cuisine unique? What is the place of tradition in national cuisine and how can food heritage be used to define group identity? Taking Maltese national cuisine as an example, I hope to start an indispensable debate. This article does not intend to define what is national cuisine but exposes the pitfalls and contradictions that are endemic to such definitions.peer-reviewe

Using Fourier Transform Analysis to Extract Information From the Shapes of Folded Layers

Objective methods of fold shape analysis are nessesary to better understand the behavior of folds and the folding process. I examined two methods of analysis, and used a method based on the Fourier Transform to show that the method based on the Fourier Series was insufficient for identifying shape characteristics of aperiodic natural fold trains. I also showed that the Fourier Transform method accessed information that was inaccessable using the Fourier Series method

Using Fourier Transform Analysis to Extract Information From the Shapes of Folded Layers

Objective methods of fold shape analysis are nessesary to better understand the behavior of folds and the folding process. I examined two methods of analysis, and used a method based on the Fourier Transform to show that the method based on the Fourier Series was insufficient for identifying shape characteristics of aperiodic natural fold trains. I also showed that the Fourier Transform method accessed information that was inaccessable using the Fourier Series method

Stochastic dynamics of adaptive trait and neutral marker driven by eco-evolutionary feedbacks

How the neutral diversity is affected by selection and adaptation is investigated in an eco-evolutionary framework. In our model, we study a finite population in continuous time, where each individual is characterized by a trait under selection and a completely linked neutral marker. Population dynamics are driven by births and deaths, mutations at birth, and competition between individuals. Trait values influence ecological processes (demographic events, competition), and competition generates selection on trait variation, thus closing the eco-evolutionary feedback loop. The demographic effects of the trait are also expected to influence the generation and maintenance of neutral variation. We consider a large population limit with rare mutation, under the assumption that the neutral marker mutates faster than the trait under selection. We prove the convergence of the stochastic individual-based process to a new measure-valued diffusive process with jumps that we call Substitution Fleming-Viot Process (SFVP). When restricted to the trait space this process is the Trait Substitution Sequence first introduced by Metz et al. (1996). During the invasion of a favorable mutation, a genetical bottleneck occurs and the marker associated with this favorable mutant is hitchhiked. By rigorously analysing the hitchhiking effect and how the neutral diversity is restored afterwards, we obtain the condition for a time-scale separation; under this condition, we show that the marker distribution is approximated by a Fleming-Viot distribution between two trait substitutions. We discuss the implications of the SFVP for our understanding of the dynamics of neutral variation under eco-evolutionary feedbacks and illustrate the main phenomena with simulations. Our results highlight the joint importance of mutations, ecological parameters, and trait values in the restoration of neutral diversity after a selective sweep.Comment: 29 page

Five dimensional relativity and two times

It is possible that null paths in 5D appear as the timelike paths of massive particles in 4D, where there is an oscillation in the fifth dimension around the hypersurface we call spacetime. A particle in 5D may be regarded as multiply imaged in 4D, and the 4D weak equivalence principle may be regarded as a symmetry of the 5D metric.Comment: 15 pages, in press in Phys. Lett.