Desertification in the Sahel: a reinterpretation of a reinterpretation

In semiarid regions the ratio of annual net primary production to precipitation, rain-use efficiency (RUE), has been used as an index of desertification. In a recent publication ( Hein & de Ridder, 2006 ) it was proposed that an incorrect understanding of the relationship between RUE and rainfall has led to a misinterpretation of the satellite record of desertification in the African Sahel. Here, we examine this suggestion and show that, contrary to Hein and de Ridder's statement, satellite studies of Sahelian RUE have reported increases, decreases, and constant values since 1981. Furthermore, we find that data do not support their proposal that RUE increases with rainfall, even in nondegraded areas. Hence we reject their corollary, that constant RUE is prima facie evidence of desertification. The fundamental difficulty with the use of RUE for detection of desertification remains, that is the difficulty of estimation of the RUE for nondegraded land at a regional scale.     

On the Feasibility of a Coulomb Explosion in a Micropinch

Plasma Physics Reports - In this paper we present experimental data on the generation of ions with MeV-energy in a Z-pinch discharge in a heavy-element medium. The calculations show that the escape...     

Behavioral effects of the presence of a dog in a classroom

Abstract

To test the idea that dogs have a positive influence on the social behavior of school children, one of three dogs was introduced alternately into a class at an elementary school in Vienna, attended by 24 children (mean age: 6.7 years). Most of the 14 boys and ten girls came from first-generation immigrant families. With parental consent, their behavior was videotaped for two hours every week, during “open teaching situations,” first during a one-month control period in the absence of dogs, followed by an experimental period of similar duration, when a dog was present in the classroom. Frequency and duration of all observable behaviors of individuals and their interactions were coded from these tapes. Although major individual differences were found in the children's interest in the dog and their behavioral responses, the group became socially more homogenous due to decreased behavioral extremes, such as aggressiveness and hyperactivity; also, formerly withdrawn individuals became socially more integrated. Effects were more pronounced in the boys than the girls. Even though the children spent considerable time watching and making contacting with the dog, they also paid more attention to the teacher. We conclude that the presence of a dog in a classroom could positively stimulate social cohesion in children and provide a relatively cheap and easy means of improving teaching conditions.     

Induced indirect defence in a lycaenid-ant association: the regulation of a resource in a mutualism

Indirect defences involve the protection of a host organism by a mutualistic partner. Threat of predation to the host organism may induce the production of rewards and/or signals that attract the mutualistic partner. In laboratory and field experiments we show that threatened lycaenid butterfly larvae (Plebejus acmon) produce more nectar rewards from their gland and were tended by protective ants twice as much as controls. Ant attendance did not affect the leaf consumption or feeding behaviour of larvae in the absence of predators. Inducible nectar production and indirect defence in this system may be a mechanism by which larvae provide rewards for services when they are needed the most. Such a system may stabilize the mutualistic association between lycaenid larvae and ants by preventing exploitation by either partner.     

Change in the dynamics of a spin probe in complement-dependent lysis of a liposome

The mobility of phospholipid chains in membranes of liposomes consisting of egg lecitin, cholesterol, dicetylphosphate, sensitized by the lipopolysaccharide antigen F. tularensis by the action of a homologous antiserum and a rabbit complement preparation was studied using 5- and 16-doxylstearate spin probes. It was shown that, during the immune lysis of liposome membranes, changes in the dynamics of spin probes occur, which correlate with the formation of transmembrane channels and exit of the fluorescent marker from the interior of liposomes. It was found that the ratio of the intensities I1/I2 of two low-field extrema in the ESR spectrum is most sensitive to changes in the liposome membrane that are induced by immune components.     

Relevance of a neutral cue in a two-choice detection task in the rat

Relevance of a neutral cue for performance in a two-choice visuospatial detection task was examined. Nine rats were trained, 5 with short intertrial interval (ITI) and 4 with long ITI, to detect a target (lateral lights) presented after a neutral-cue (central light). The removal of the neutral-cue decreased accuracy and increased response latencies and omissions. These results demonstrate that a neutral-cue, preceding the target, is relevant for the performance, suggesting that rats are highly expectant during the neutral-cue and reallocate attentional resources during ITI. Furthermore, latencies were higher, omissions were lower and the fall of accuracy was greater for rats with long than with short ITI, which could indicate that the neutral-cue was more relevant for the former group.     

Formation of a strong electric field resulting in the excitation of microplasma discharges at the edge of a dielectric film on a metal in a plasma flow

Results are presented from experimental and analytical studies of the processes resulting in the excitation of microplasma discharges (MPDs) on a metal surface partially covered with a thin dielectric film under the action of an external plasma flow in vacuum. It is shown experimentally that MPDs are excited at the interface between the open metal surface and the region covered by the dielectric film. The probability of MPD excitation is investigated as a function of the thickness of the dielectric film deposited on the metal. It is found that, for a film thickness of 1 μm, the probability of MPD excitation is close to unity. As the film thickness decreases below ~10 nm or increases above ~10 μm, the probability of MPD excitation is reduced by more than two orders of magnitude. A two-dimensional kinetic numerical code is developed that allows one to model the processes of Debye sheath formation and generation of a strong electric field near the edge of a finite-thickness dielectric film on a metal surface in a plasma flow for different configurations of the film edge. It is shown that the maximum value of the tangential component of the electric field is reached at the film edge and amounts to E _max ≈ |φ₀|/2d (where φ₀ < 0 is the electric potential applied to the metal and d is the film thickness), which for typical conditions of experiments on the excitation of MPDs on metal surfaces (φ₀ ≈–400 V, d ≈ 1 μm) yields E _max ≈ 2 MV/cm. The results of kinetic simulations confirm the qualitative idea about the mechanism of the formation of a strong electric field resulting in the excitation of MPDs at the edge of a dielectric film on a metal surface in a plasma flow and agree with experimental data.     

Dynamics of a model for the variability of the interspike intervals in a retinal neuron

Recently, a model has been proposed to explain the statistics of the variability of interspike intervals of ganglion cells in the retina of goldfish under steady-state stimulation. In this note, it is shown that the dynamical behaviour of the model, both under steady-state and dynamical stimuli, is characterized by input-invariance of the output random process after a time transformation. This allows to study the signalprocessing properties of the model, and to test its applicability by a more complete experimental analysis.     

A test for a shift in the boundary of the geographical range of a species

One predicted impact of climate change is a poleward shift in the boundaries of species ranges. Existing methods for identifying such a boundary shift based on changes in the observed pattern of occupancy within a grid of cells are sensitive to changes in the overall rate of sightings and their latitudinal distribution that are unconnected to a boundary shift. A formal test for a boundary shift is described that allows for such changes. The test is applied to detect northward shifts in the northern boundary of the Essex skipper (Thymelicus lineola) butterfly and the European goldfinch (Carduelis carduelis) in Great Britain. A shift is detected in the latter case but not in the former. Results from a simulation study are presented showing that the test performs well.     

Needle in a haystack: microdissecting the proteome of a tissue

Summary. Laser-assisted microdissection is a recent technology that enables cells to be harvested from tissue sections. Proteins can be extracted from the dissected cells for molecular analysis. This enables the analysis of proteins in specific cell types in an in vivo system. Although quantities of protein obtained from the dissected material can be small, it is possible to use established methods such as Western Blotting and 2D-PAGE, as well as newer technologies such as SELDI-MS, to analyse the proteins. This review describes the applications and technical considerations for using laser-assisted dissected cells in proteomics research.     

Finding a needle in the virus metagenome haystack--micro-metagenome analysis captures a snapshot of the diversity of a bacteriophage armoire

Viruses are ubiquitous in the oceans and critical components of marine microbial communities, regulating nutrient transfer to higher trophic levels or to the dissolved organic pool through lysis of host cells. Hydrothermal vent systems are oases of biological activity in the deep oceans, for which knowledge of biodiversity and its impact on global ocean biogeochemical cycling is still in its infancy. In order to gain biological insight into viral communities present in hydrothermal vent systems, we developed a method based on deep-sequencing of pulsed field gel electrophoretic bands representing key viral fractions present in seawater within and surrounding a hydrothermal plume derived from Loki's Castle vent field at the Arctic Mid-Ocean Ridge. The reduction in virus community complexity afforded by this novel approach enabled the near-complete reconstruction of a lambda-like phage genome from the virus fraction of the plume. Phylogenetic examination of distinct gene regions in this lambdoid phage genome unveiled diversity at loci encoding superinfection exclusion- and integrase-like proteins. This suggests the importance of fine-tuning lyosgenic conversion as a viral survival strategy, and provides insights into the nature of host-virus and virus-virus interactions, within hydrothermal plumes. By reducing the complexity of the viral community through targeted sequencing of prominent dsDNA viral fractions, this method has selectively mimicked virus dominance approaching that hitherto achieved only through culturing, thus enabling bioinformatic analysis to locate a lambdoid viral "needle" within the greater viral community "haystack". Such targeted analyses have great potential for accelerating the extraction of biological knowledge from diverse and poorly understood environmental viral communities.     

The occurrence of a multilayered structure in the sperm of a pteridophyte

Summary A multilayered structure, previously recorded only in bryophytes, is reported in spermatids of three species of Equisetum. It is interpreted as comprising four layers, recalling the Vierergruppe of Marchantia spermatids. Unlike the multilayered structure of bryophyte spermatids, a rather compact organelle, that of Equisetum forms a thin strip extending almost the whole diameter of the cell. As in bryophytes the upper layer of the Equisetum multilayered structure is composed of parallel microtubules, extending far beyond the underlying layers. The microtubular band is considered equivalent to the similar structure seen in a variety of plant spermatozoids, but in Equisetum it is much longer and composed of many more microtubules than reported from any other plant spermatozoid. The morphology of the multilayered structure is related to the large size and short, broad form of Equisetum spermatozoids.     

The Occurrence of a Gizzard in a Bryozoan of the Order Cheilostomata

Abstract A gizzard is recorded for the first time in a bryozoan, Hippothoa divaricata var. conferta, of the order Cheilostomata.