449 research outputs found
Direct neutron capture of 48Ca at kT = 52 keV
The neutron capture cross section of 48Ca was measured relative to the known
gold cross section at kT = 52 keV using the fast cyclic activation technique.
The experiment was performed at the Van-de-Graaff accelerator, Universitaet
Tuebingen. The new experimental result is in good agreement with a calculation
using the direct capture model. The 1/v behaviour of the capture cross section
at thermonuclear energies is confirmed, and the adopted reaction rate which is
based on several previous experimental investigations remains unchanged.Comment: 9 pages (uses Revtex), 2 postscript figures, accepted for publication
as Brief Report in Phys. Rev.
Can a PCR assay of aphids caught inâcrop on yellow sticky traps inform field level barley yellow dwarf virus ( BYDV ) risk assessment?
Infection with barley yellow dwarf virus (BYDV), caused by strains of virus belonging to the family Luteovirideae including BYDVâPAV, can result in significant yield losses in autumn sown cereals following transmission by aphid vectors such as Rhopalosiphum padi (Homoptera: Aphididae) and Sitobion avenae (Homoptera: Aphididae). Spatial and temporal variance in the infectivity of alate populations influences risk to crops from the disease, which is greatest on infection at early crop growth stages. A decision support system (DSS) to guide optimised integration of crop protection strategies through risk assessment would help avoid unnecessary application of synthetic insecticides. This study contributes to the development of a DSS by exploring the viability and relevance of a methodology to detect virus levels in individual aphids trapped inâcrop using yellow sticky traps. Using a reverse transcription polymerase chain reaction (RTâPCR) assay, the detectability of virus from a BYDVâPAVâpositive control colony was found not to be reduced by the process of trapping, extraction and cold storage, but did drop significantly after between three and seven days of exposure on trap. This method has potential to contribute to localised risk assessment and guide optimisation of crop protection strategies
Close-coupling calculations of low-energy inelastic and elastic processes in He collisions with H: A comparative study of two potential energy surfaces
The two most recently published potential energy surfaces (PESs) for the
HeH complex, the so-called MR (Muchnick and Russek) and BMP (Boothroyd,
Martin, and Peterson) surfaces, are quantitatively evaluated and compared
through the investigation of atom-diatom collision processes. The BMP surface
is expected to be an improvement, approaching chemical accuracy, over all
conformations of the PES compared to that of the MR surface. We found
significant differences in inelastic rovibrational cross sections computed on
the two surfaces for processes dominated by large changes in target rotational
angular momentum. In particular, the H() total quenching cross
section computed using the BMP potential was found to be a factor of 1000
larger than that obtained with the MR surface.Comment: 26 pages, 11 figure
A bimodal spacecraft bus based on a cermet fueled heat pipe reactor
Bimodal space reactor systems provide both thermal propulsion for the spacecraft orbital transfer and electrical power to the spacecraft bus once it is on station. These systems have the potential to increase both the available payload in high energy orbits and the available power to that payload. These increased mass and power capabilities can be used to either reduce mission cost by permitting the use of smaller launch vehicles or to provide increased mission performance from the current launch vehicle. A major barrier to the deployment of these bimodal systems has been the cost associated with their development. This paper describes a bimodal spacecraft bus with performance potential to permit more than 70% of the instrumented payload of the Titan IV/Centaur to be launched from the Atlas IIAS. The development cost is minimized by basing the design on existing component technologies
From bi-layer to tri-layer Fe nanoislands on Cu3Au(001)
Self assembly on suitably chosen substrates is a well exploited root to
control the structure and morphology, hence magnetization, of metal films. In
particular, the Cu3Au(001) surface has been recently singled out as a good
template to grow high spin Fe phases, due to the close matching between the
Cu3Au lattice constant (3.75 Angstrom) and the equilibrium lattice constant for
fcc ferromagnetic Fe (3.65 Angstrom). Growth proceeds almost layer by layer at
room temperature, with a small amount of Au segregation in the early stage of
deposition. Islands of 1-2 nm lateral size and double layer height are formed
when 1 monolayer of Fe is deposited on Cu3Au(001) at low temperature. We used
the PhotoElectron Diffraction technique to investigate the atomic structure and
chemical composition of these nanoislands just after the deposition at 140 K
and after annealing at 400 K. We show that only bi-layer islands are formed at
low temperature, without any surface segregation. After annealing, the Fe atoms
are re-aggregated to form mainly tri-layer islands. Surface segregation is
shown to be inhibited also after the annealing process. The implications for
the film magnetic properties and the growth model are discussed.Comment: Revtex, 5 pages with 4 eps figure
Compactlight design study
H2020 CompactLight Project aims at designing the next generation of compact hard X-Rays Free-Electron Lasers, relying on very high accelerating gradients and on novel undulator concepts. CompactLight intends to design a compact Hard X-ray FEL facility based on very high-gradient acceleration in the X band of frequencies, on a very bright photo injector, and on short-period/superconductive undulators to enable smaller electron beam energy. If compared to existing facilities, the proposed facility will benefit from a lower electron beam energy, due to the enhanced undulators performance, be significantly more compact, as a consequence both of the lower energy and of the high-gradient X-band structures, have lower electrical power demand and a smaller footprint. CompactLight is a consortium of 24 institutes (21 European + 3 extra Europeans), gathering the world-leading experts both in the domains of X-band acceleration and undulator design
Dynamics of Molecular Evolution and Phylogeography of Barley yellow dwarf virus-PAV
Barley yellow dwarf virus (BYDV) species PAV occurs frequently in irrigated wheat fields worldwide and can be efficiently transmitted by aphids. Isolates of BYDV-PAV from different countries show great divergence both in genomic sequences and pathogenicity. Despite its economical importance, the genetic structure of natural BYDV-PAV populations, as well as of the mechanisms maintaining its high diversity, remain poorly explored. In this study, we investigate the dynamics of BYDV-PAV genome evolution utilizing time-structured data sets of complete genomic sequences from 58 isolates from different hosts obtained worldwide. First, we observed that BYDV-PAV exhibits a high frequency of homologous recombination. Second, our analysis revealed that BYDV-PAV genome evolves under purifying selection and at a substitution rate similar to other RNA viruses (3.158Ă10â4 nucleotide substitutions/site/year). Phylogeography analyses show that the diversification of BYDV-PAV can be explained by local geographic adaptation as well as by host-driven adaptation. These results increase our understanding of the diversity, molecular evolutionary characteristics and epidemiological properties of an economically important plant RNA virus
Management of trichobezoar: case report and literature review
Trichobezoars (hair ball) are usually located in the stomach, but may extend through the pylorus into the duodenum and small bowel (Rapunzel syndrome). They are almost always associated with trichotillomania and trichophagia or other psychiatric disorders. In the literature several treatment options are proposed, including removal by conventional laparotomy, laparoscopy and endoscopy. We present our experience with four patients and provide a review of the recent literature. According to our experience and in line with the published results, conventional laparotomy is still the treatment of choice. In addition, psychiatric consultation is necessary to prevent relapses
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