1,983 research outputs found
Coulomb blockade thermometry using a two-dimensional array of tunnel junctions
We have measured current-voltage characteristics of two-dimensional arrays of
small tunnel junctions at temperatures from 1.5 K to 4.2 K. This corresponds to
thermal energies larger than the charging energy. We show that 2D-arrays can be
used as primary thermometers in the same way as 1D-arrays, and even have some
advantages over 1D-arrays. We have carried out Monte Carlo simulations, which
agree with our experimental results.Comment: 4 pages, 4 eps figures. Also available from Journal of Applied
Physics (http://link.aip.org/link/?jap/86/3844
M-grid: Using Ubiquitous Web Technologies to create a Computational Grid
There are many potential users and uses for grid computing. However, the concept of sharing computing resources excites security concerns and, whilst being powerful and flexible, at least for novices, existing systems are complex to install and use. Together these represent a significant barrier to potential users who are interested to see what grid computing can do. This paper describes m-grid, a system for building a computational grid which can accept tasks from any user with access to a web browser and distribute them to almost any machine with access to the internet and manages to do this without the installation of additional software or interfering with existing security arrangements
Morphology of the larvae of Rhantaticus congestus (Klug, 1833) and phylogenetic comparison with other known Aciliini (Coleoptera: Dytiscidae: Dytiscinae)
We describe the second- and third instar larvae of the diving beetle Rhantaticus congestus (Klug, 1833), including detailed morphometric and chaetotaxic analyses of the cephalic capsule, head appendages, legs, terminal abdominal segment and urogomphi in order to discover useful characters for distinguishing Rhantaticus Sharp, 1882 larvae from those of other known Aciliini (Coleoptera: Dytiscidae: Dytiscinae). A parsimony analysis based on 94 larval characteristics of nine Aciliini species in five genera (Acilius Leach, 1817, Graphoderus Dejean, 1833, Rhantaticus, Sandracottus Sharp, 1882, Thermonectus Dejean, 1833) was conducted using the program TNT. Rhantaticus shares with all these genera several larval character states which support its inclusion in the Aciliini. Whereas Rhantaticus larva stands out from other known genera by several unique character states, our parsimony analysis did not recover any clear phylogenetic position of this genus within the Aciliini.Fil: Alarie, Yves. Laurentian University. Department of Biology; CanadáFil: Michat, Mariano Cruz. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental. Laboratorio de Entomología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; ArgentinaFil: Bergsten, J.. No especifíca;Fil: Hájek, Jirí. No especifíca
Taxonomic revision of the Afrotropical Agabus raffrayi species group with the description of four new species (Coleoptera, Dytiscidae)
We revise the Afrotropical Agabus raffrayi species group, motivated by the discovery of new diversity in
Kenya and South Africa. Whilst Agabus is mainly a holarctic genus, the Agabus raffrayi group is restricted
to high altitude regions of eastern Africa and temperate parts of South Africa, from where we describe the
southernmost Agabus in the world. The following new species are introduced: Agabus anguluverpus sp.
nov. from Mount Kenya in central Kenya, Agabus austellus sp. nov. a widespread species in South Africa,
Agabus riberae sp. nov. from the Kamiesberg and northeastern Cederberg ranges in the Northern and
Western Cape Provinces of South Africa and Agabus agulhas sp. nov. from the Agulhas Plain, Western
Cape Province, South Africa. We provide a distribution map, a determination key for males, quantitative measurements of diagnostic characters, habitus photos and detailed photos of male genitalia for all
described species in the group, as well as images of diagnostic characters and habitats. The presence or
absence of an elongated section between the subapical broadening and the base of the apical and subapical teeth of the male aedeagus is a useful novel character, first revealed by our study. In contrast with the most
recent revision of Afrotropical Agabus, we show that Agabus ruwenzoricus Guignot, 1936 is restricted to
eastern Africa; South African records of this species having been based on misidentifications, no species of
the group being common to southern and eastern Africa. We speculate that the raffrayi group may display
phylogenetic niche conservatism, being restricted, as an originally temperate taxon, to higher elevations in
tropical eastern Africa, but occurring at lower altitudes in temperate South Africa
Glucose metabolism and oscillatory behavior of pancreatic islets
A variety of oscillations are observed in pancreatic islets.We establish a
model, incorporating two oscillatory systems of different time scales: One is
the well-known bursting model in pancreatic beta-cells and the other is the
glucose-insulin feedback model which considers direct and indirect feedback of
secreted insulin. These two are coupled to interact with each other in the
combined model, and two basic assumptions are made on the basis of biological
observations: The conductance g_{K(ATP)} for the ATP-dependent potassium
current is a decreasing function of the glucose concentration whereas the
insulin secretion rate is given by a function of the intracellular calcium
concentration. Obtained via extensive numerical simulations are complex
oscillations including clusters of bursts, slow and fast calcium oscillations,
and so on. We also consider how the intracellular glucose concentration depends
upon the extracellular glucose concentration, and examine the inhibitory
effects of insulin.Comment: 11 pages, 16 figure
Checklist of terrestrial Parasitengona mites in Fennoscandia with new species- and distribution records (Acariformes: Prostigmata)
BackgroundThe knowledge of terrestrial Parasitengona in Fennoscandia lies far behind that of their aquatic counterparts, the water mites (Hydrachnidia). Based on new inventories, we provide primary data and an annotated checklist of terrestrial Parasitengona in Fennoscandia including 107 species. Out of these, nineteen species are new findings for the region and five are species potentially new for science. Twenty-three species are new for Norway, fourteen for Finland and eleven for Sweden. The known recorded fauna today of terrestrial Parasitengona is 80 species for Norway, 54 for Sweden and 48 for Finland. Primary data include georeferenced locality data as well as collecting techniques and microhabitat to increase the knowledge on species' habitat requirements
Effects of overstory tree density, site preparation, and ground vegetation on natural Scots pine seedling emergence and survival in northern boreal pine forests
Natural regeneration is a commonly used forest regeneration method in northern Finland. It is not known, however, what would be the optimal overstory density and ground vegetation composition for seedling emergence and survival, and if site preparation is needed to accompany overstory density manipulation. We studied the effects of overstory density (unthinned control and thinning to 50,150, and 250 trees.ha(-1)) and ground vegetation removal (mechanical site preparation with disc trenching) on the number of naturally germinated pine seedlings and survival of individual seedlings over a period of 8 to 11 years. Bare mineral soil was a superior seedbed compared to intact vegetation cover, even though the mortality rate was high on mineral soil. Greater cover of lingonberry, crowberry, and slash had a negative effect on seedling number. Seedling mortality was initially high (60% died during the first 2 years) but decreased throughout the first 5 years. The survival rate of seedlings located in the mineral soil of the upper part of the disc trencher track was twice as high as that of seedlings located in the lower part of the track. High coverage of hair mosses (Polytrichum spp.) was associated with poorer seedling survival. An overstory density of 50-150 trees.ha(-1) with site preparation seems to be an efficient treatment to promote regeneration under these circumstances
No Evidence for More Earth-sized Planets in the Habitable Zone of Kepler's M versus FGK Stars
Reliable detections of Earth-sized planets in the habitable zone remain
elusive in the Kepler sample, even for M dwarfs. The Kepler sample was once
thought to contain a considerable number of M dwarf stars ( K), which hosted enough Earth-sized ( R) planets to
estimate their occurrence rate () in the habitable zone. However,
updated stellar properties from Gaia have shifted many Kepler stars to earlier
spectral type classifications, with most stars (and their planets) now measured
to be larger and hotter than previously believed. Today, only one
partially-reliable Earth-sized candidate remains in the optimistic habitable
zone, and zero in the conservative zone. Here we performed a new investigation
of Kepler's Earth-sized planets orbiting M dwarf stars, using occurrence rate
models with considerations of updated parameters and candidate reliability.
Extrapolating our models to low instellations, we found an occurrence rate of
for the conservative habitable zone
(and for the optimistic), consistent with
previous works when considering the large uncertainties. Comparing these
estimates to those from similarly comprehensive studies of Sun-like stars, we
found that the current Kepler sample does not offer evidence to support an
increase in from FGK to M stars. While the Kepler sample is too
sparse to resolve an occurrence trend between early and mid-to-late M dwarfs
for Earth-sized planets, studies including larger planets and/or data from the
K2 and TESS missions are well-suited to this task.Comment: 22 pages, 11 figures, 2 tables; Accepted for publication in A
Effects of overstory tree density, site preparation, and ground vegetation on natural Scots pine seedling emergence and survival in northern boreal pine forests
Natural regeneration is a commonly used forest regeneration method in northern Finland. It is not known, however, what would be the optimal overstory density and ground vegetation composition for seedling emergence and survival, and if site preparation is needed to accompany overstory density manipulation. We studied the effects of overstory density (unthinned control and thinning to 50,150, and 250 trees.ha(-1)) and ground vegetation removal (mechanical site preparation with disc trenching) on the number of naturally germinated pine seedlings and survival of individual seedlings over a period of 8 to 11 years. Bare mineral soil was a superior seedbed compared to intact vegetation cover, even though the mortality rate was high on mineral soil. Greater cover of lingonberry, crowberry, and slash had a negative effect on seedling number. Seedling mortality was initially high (60% died during the first 2 years) but decreased throughout the first 5 years. The survival rate of seedlings located in the mineral soil of the upper part of the disc trencher track was twice as high as that of seedlings located in the lower part of the track. High coverage of hair mosses (Polytrichum spp.) was associated with poorer seedling survival. An overstory density of 50-150 trees.ha(-1) with site preparation seems to be an efficient treatment to promote regeneration under these circumstances.Peer reviewe
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