Evolutionary Stability of Ecological Hierarchy

A self-similar hierarchical solution that is both dynamically and evolutionarily stable is found to the multi dimensional Lotka-Volterra equation with a single chain of prey-predator relations. This gives a simple and natural explanation to the key features of hierarchical ecosystems, such as its ubiquity, pyramidal population distribution, and higher aggressiveness among higher trophic levels. pacs{87.23.Kg, 89.75.Da, 05.45.-a} keywords{Lotka-Volterra equation, Trophic pyramid, Self-similarity}Comment: 4 Pages RevTeX4, 1 Fig, 1 Table, shortened by publishers reques

Hyphomycètes aquatiques : importance dans la décomposition des litières

Les auteurs comparent les communautés d'hyphomycètes aquatiques récoltés dans l'écume de 7 cours d'eau du Béarn et des Landes. L'abondance de spores observées dans les deux régions diffère considérablement (174-1175 spores/µl en Béarn et 2-57 spores/µl dans les Landes) tandis que les variations de richesse spécifique apparaissent faibles. L'influence de la végétation riveraine et du pH de l'eau est discutée.Des expériences de dégradation in vitro montrent que des souches isolées de Tetracladium marchalianum, Heliscus lugdunensis et dans une moindre mesure Anguillospora longissima présentent une activité cellulolytique. T. marchalianum et H. lugdunensis, participent activement à la décomposition de litière de saule blanc, avec respectivement 21,7 et 18,2 % de dégradation après 5 semaines à 18°C.Aquatic hyphomycete communities from the foam of seven streams in the Bearn and Landes regions of France were compared at four different dates. The total number of species was similar in the two regions, but common species (> 5 spores/µl) in the Bearn were twice as abundant as in the Landes. Mean spore concentrations in the Bearn and Landes streams were in a ratio of 10 : 1. In the Bearn, spore concentration and the number of fungal species increased considerably in autumn, subsequent to the fall of leaf litter into the streams. Analysis of variance of spore concentrations (original or transformed data) in the two regions showed that date, station and the interaction of these two factors were highly significant parameters (P ANOVA < 0.0001). Alatospora acuminate was the commonest species both in the Bearn (77 % annual mean) and in the Landes (41 %). After A. acuminata, Clavatospora stellata (7 %) and Tetracladium marchalianum (4 %,) in the Bearn, Flagellospora curvula (28 %) and Clavastospora longibrachiata (20 %) in the Landes were the dominant species of the mycoflora. Five species new to France were noted : Actinospora megalospora Ingold, Camposporium pellucidum (Grave) Hugues, Diplocladiella scalaroides Arnaud, Flabellospora acuminata Descals and Triscelophorus monosporus Ingold. The difference in fungal richness between the two regions was suggested to be due to the composition of the riparian vegetation, the phenology of the litter fall, the presence (or absence) of plant matter accumulation in the stream, and the pH of the stream water. Litter deposits in the Landes streams were rare and made up exclusivey of pine needles, the few deciduous leaves which fall being exported to surrounding lakes and to the ocean. Water pH was always low (5.0-5.5). The riparian vegetation of the Bearn streams, on the contrary, was abundant and varied Cash, common locust-tree, alder, willow, oak, chestnut, poplar). Moreover the neutral or weakly acid pH of the Bearn streams (6.3-7.0) seemed to favour fungal diversity (cf. BÄRLOCHER and ROSSET, 1981; WOOD-EGGENSCHWILLER and BARLOCHER, 1983).Single spore isolates of Anguillospora langissima (de Wild.) Ingold, Heliscus lugdunensis Saccardo et Therry and Tetraclacium marchalianum De Wild were obtained from decomposing leaf litter in the Bearn streams. In laboratory experiments, the degradation activity of each species was tested both on sterilized paper cellulose and white willow leaf litter. The cellutolytic activity of fungal cultures was significant when compared with controls (t test). After 5 weeks at 18 °C, mass loss was 8.6 % for A.longissima and 10.0 % for H.lugdunensis and T.marchalianum. Aeration stimulated cellulose degradation for T.marchalianum (16.6 %) only. With willow leaves as substrate, degradation was greater for T.marchalianum (22.7 %) than for N. lugdunensis (11.8 %) and A. longissima (6.2 %, non-significant)

Particular processing of pro-opiomelanocortin in Xenopus laevis intermediate pituitary Sequencing of α- and β-melanocyte-stimulating hormones

Abstractα- and β-melanocyte-stimulating hormones (α-MSH and β-MSH) have been isolated from Xenopus laevis neurointermediate pituitary and microsequenced. Intracellular α-MSH is not N-acetylated after proteolytic processing of pro-opiomelanocortin in contrast to mammalian α-MSHs. There is a high preservation of the melanotropic amino acid sequence common to all MSHs although in Xenopus β-MSH a histidine residue replaces the glutamic acid residue found in position 8 of mammalian β-MSHs

Neurohypophysial hormones of the 1-month-old bovine fetus: Absence of vasotocin during mammal development

AbstractThe neurohypophysial hormones of the 1-month-old bovine fetus have been identified by their positions in ion-exchange chromatography and their retention times in high-pressure reverse-phase partition chromatography. Arginine vasopressin and oxytocin have been recognized. The molar ratio vasopressin/oxytocin in neurohypophysis is about 6 in the 1-month-old fetus compared with 4 in the 3-month-old fetus, 2.7 in the 7-month-old fetus and 1 in the adult. Vasotocin is virtually absent even in the early fetus (less than 0.1% of arginine vasopressin). The occurrence of a vasotocin gene expressed in the fetus but silent in the adult appears unlikely

Optical study of the anisotropic erbium spin flip-flop dynamics

We investigate the erbium flip-flop dynamics as a limiting factor of the electron spin lifetime and more generally as an indirect source of decoherence in rare-earth doped insulators. Despite the random isotropic arrangement of dopants in the host crystal, the dipolar interaction strongly depends on the magnetic field orientation following the strong anisotropy of the $g$-factor. In Er$^{3+}$:Y$_2$SiO$_5$, we observe by transient optical spectroscopy a three orders of magnitude variation of the erbium flip-flop rate (10ppm dopant concentration). The measurements in two different samples, with 10ppm and 50ppm concentrations, are well-supported by our analytic modeling of the dipolar coupling between identical spins with an anisotropic $g$-tensor. The model can be applied to other rare-earth doped materials. We extrapolate the calculation to Er$^{3+}$:CaWO$_4$, Er$^{3+}$:LiNbO$_3$ and Nd$^{3+}$:Y$_2$SiO$_5$ at different concentrations

Isotropization of Bianchi-Type Cosmological Solutions in Brans-Dicke Theory

The cosmic, general analitic solutions of the Brans--Dicke Theory for the flat space of homogeneous and isotropic models containing perfect, barotropic, fluids are seen to belong to a wider class of solutions --which includes cosmological models with the open and the closed spaces of the Friedmann--Robertson--Walker metric, as well as solutions for models with homogeneous but anisotropic spaces corresponding to the Bianchi--Type metric clasification-- when all these solutions are expressed in terms of reduced variables. The existence of such a class lies in the fact that the scalar field, $\phi$, times a function of the mean scale factor or ``volume element'', $a^3 = a_1 a_2 a_3$, which depends on time and on the barotropic index of the equation of state used, can be written as a function of a ``cosmic time'' reduced in terms of another function of the mean scale factor depending itself again on the barotropic index but independent of the metrics here employed. This reduction procedure permites one to analyze if explicitly given anisotropic cosmological solutions ``isotropize'' in the course of their time evolution. For if so can happen, it could be claimed that there exists a subclass of solutions that is stable under anisotropic perturbations.Comment: 15 pages, Late

Locking Local Oscillator Phase to the Atomic Phase via Weak Measurement

We propose a new method to reduce the frequency noise of a Local Oscillator (LO) to the level of white phase noise by maintaining (not destroying by projective measurement) the coherence of the ensemble pseudo-spin of atoms over many measurement cycles. This scheme uses weak measurement to monitor the phase in Ramsey method and repeat the cycle without initialization of phase and we call, "atomic phase lock (APL)" in this paper. APL will achieve white phase noise as long as the noise accumulated during dead time and the decoherence are smaller than the measurement noise. A numerical simulation confirms that with APL, Allan deviation is averaged down at a maximum rate that is proportional to the inverse of total measurement time, tau^-1. In contrast, the current atomic clocks that use projection measurement suppress the noise only down to the level of white frequency, in which case Allan deviation scales as tau^-1/2. Faraday rotation is one of the possible ways to realize weak measurement for APL. We evaluate the strength of Faraday rotation with 171Yb+ ions trapped in a linear rf-trap and discuss the performance of APL. The main source of the decoherence is a spontaneous emission induced by the probe beam for Faraday rotation measurement. One can repeat the Faraday rotation measurement until the decoherence become comparable to the SNR of measurement. We estimate this number of cycles to be ~100 cycles for a realistic experimental parameter.Comment: 18 pages, 7 figures, submitted to New Journal of Physic