589 research outputs found
Genetic variation for nutrient use efficiency in maize under different tillage and fertilization regimes with special emphasis to plant microbe interaction
Conservation tillage (no-till and reduced tillage) brings many benefits with respect to soil fertility and energy use, but it also has drawbacks regarding the need for synthetic fertilizers and herbicides. To promote conversation tillage in organic farming systems, crop rotation, fertilization and weed control have to be optimized. In addition, crop varieties are needed with improved nutrient use efficiency (NUE) and high weed competitiveness or tolerance
Heavy quark flavour dependence of multiparticle production in QCD jets
After inserting the heavy quark mass dependence into QCD partonic evolution
equations, we determine the mean charged hadron multiplicity and second
multiplicity correlators of jets produced in high energy collisions. We thereby
extend the so-called dead cone effect to the phenomenology of multiparticle
production in QCD jets and find that the average multiplicity of heavy-quark
initiated jets decreases significantly as compared to the massless case, even
taking into account the weak decay products of the leading primary quark. We
emphasize the relevance of our study as a complementary check of -tagging
techniques at hadron colliders like the Tevatron and the LHC.Comment: Version revised, accepted for publication in JHEP, 21 pages and 7
figure
Gauged Inflation
We propose a model for cosmic inflation which is based on an effective
description of strongly interacting, nonsupersymmetric matter within the
framework of dynamical Abelian projection and centerization. The underlying
gauge symmetry is assumed to be with . Appealing to a
thermodynamical treatment, the ground-state structure of the model is
classically determined by a potential for the inflaton field (dynamical
monopole condensate) which allows for nontrivially BPS saturated and thereby
stable solutions. For this leads to decoupling of gravity from the
inflaton dynamics. The ground state dynamics implies a heat capacity for the
vacuum leading to inflation for temperatures comparable to the mass scale
of the potential. The dynamics has an attractor property. In contrast to the
usual slow-roll paradigm we have during inflation. As a consequence,
density perturbations generated from the inflaton are irrelevant for the
formation of large-scale structure, and the model has to be supplemented with
an inflaton independent mechanism for the generation of spatial curvature
perturbations. Within a small fraction of the Hubble time inflation is
terminated by a transition of the theory to its center symmetric phase. The
spontaneously broken symmetry stabilizes relic vector bosons in the
epochs following inflation. These heavy relics contribute to the cold dark
matter of the universe and potentially originate the UHECRs beyond the GZK
bound.Comment: 23 pages, 4 figures, subsection added, revision of text, to app. in
PR
Particle emission following Coulomb excitation in ultrarelativistic heavy-ion collisions
We study nuclear reactions induced by virtual photons associated with
Lorentz-boosted Coulomb fields of ultrarelativistic heavy ions. Evaporation,
fission and multifragmentation mechanisms are included in a new RELDIS code,
which describes the deexcitation of residual nuclei formed after single and
double photon absorption in peripheral heavy-ion collisions. Partial cross
sections for different dissociation channels, including the multiple neutron
emission ones, are calculated and compared with data when available. Rapidity
and transverse momentum distributions of nucleons, nuclear fragments and pions,
produced electromagnetically, are also calculated. These results provide
important information for designing large-rapidity detectors and zero-degree
calorimeters at RHIC and LHC. The electromagnetic dissociation of nuclei
imposes some constrains on the investigation of exotic particle production in
gamma-gamma fusion reactions.Comment: 26 LaTeX pages including 8 figures, uses epsf.st
Intra-fraction setup variability: IR optical localization vs. X-ray imaging in a hypofractionated patient population
<p>Abstract</p> <p>Background</p> <p>The purpose of this study is to investigate intra-fraction setup variability in hypo-fractionated cranial and body radiotherapy; this is achieved by means of integrated infrared optical localization and stereoscopic kV X-ray imaging.</p> <p>Method and Materials</p> <p>We analyzed data coming from 87 patients treated with hypo-fractionated radiotherapy at cranial and extra-cranial sites. Patient setup was realized through the ExacTrac X-ray 6D system (BrainLAB, Germany), consisting of 2 infrared TV cameras for external fiducial localization and X-ray imaging in double projection for image registration. Before irradiation, patients were pre-aligned relying on optical marker localization. Patient position was refined through the automatic matching of X-ray images to digitally reconstructed radiographs, providing 6 corrective parameters that were automatically applied using a robotic couch. Infrared patient localization and X-ray imaging were performed at the end of treatment, thus providing independent measures of intra-fraction motion.</p> <p>Results</p> <p>According to optical measurements, the size of intra-fraction motion was (<it>median ± quartile</it>) 0.3 ± 0.3 mm, 0.6 ± 0.6 mm, 0.7 ± 0.6 mm for cranial, abdominal and lung patients, respectively. X-ray image registration estimated larger intra-fraction motion, equal to 0.9 ± 0.8 mm, 1.3 ± 1.2 mm, 1.8 ± 2.2 mm, correspondingly.</p> <p>Conclusion</p> <p>Optical tracking highlighted negligible intra-fraction motion at both cranial and extra-cranial sites. The larger motion detected by X-ray image registration showed significant inter-patient variability, in contrast to infrared optical tracking measurement. Infrared localization is put forward as the optimal strategy to monitor intra-fraction motion, featuring robustness, flexibility and less invasivity with respect to X-ray based techniques.</p
Bayesian analysis of neutrinos observed from supernova SN 1987A
We present a Bayesian analysis of the energies and arrival times of the
neutrinos from supernova SN 1987A detected by the Kamiokande II, IMB, and
Baksan detectors, and find strong evidence for two components in the neutrino
signal: a long time scale component from thermal Kelvin-Helmholtz cooling of
the nascent neutron star, and a brief (~< 1 s), softer component similar to
that expected from emission by accreting material in the delayed supernova
scenario. In the context of this model, we show that the data constrain the
electron antineutrino rest mass to be less than 5.7 eV with 95% probability.
Our analysis takes advantage of significant advances that have occured in the
years since the detections in both our understanding of the supernova mechanism
and our ability to analyze sparse data. As a result there are substantial
differences between our inferences and those found in earlier studies. We find
that two-component models for the neutrino signal make the data >100 times more
probable than single-component models. In addition, the radius and binding
energy of the nascent neutron star implied by single-component models deviates
significantly from the values predicted by current neutron star models, whereas
those implied by models with an accretion component are in complete agreement
with the predictions. As a result, two-component models are hundreds to
thousands of times more probable than single-component models. The neutrino
data thus provide the first direct observational evidence in favor of the
delayed supernova scenario over the prompt scenario. (Abridged abstract)Comment: 46 pages, 12 figures, RevTeX; for submission to Physical Review
Effects of zinc on leaf decomposition by fungi in streams : studies in microcosms
The effect of zinc on leaf decomposition by aquatic fungi was studied in microcosms. Alder leaf disks were precolonized for 15 days at the source of the Este River, and exposed to different zinc concentrations during 25 days. Leaf mass loss, fungal biomass (based on ergosterol concentration), fungal production (rates of [1-14C]acetate incorporation into ergosterol), sporulation rates and species richness of aquatic hyphomycetes were determined. At the source of the Este River decomposition of alder leaves was fast and 50% of the initial mass was lost in 25 days. A total of 18 aquatic hyphomycete species were recorded during 42 days of leaf immersion. Articulospora tetracladia was the dominant species, followed by Lunulospora curvula and two unidentified species with sigmoid conidia. Cluster analysis suggested that zinc concentration and exposure time affected the structure of aquatic hyphomycete assemblages, even though richness had not been severely affected. Both zinc concentration and exposure time significantly affected leaf mass loss, fungal production and sporulation, but not fungal biomass. Zinc exposure reduced leaf mass loss, inhibited fungal production and affected fungal reproduction by either stimulating or inhibiting sporulation rates. The results of this work suggested zinc pollution might depress leaf decomposition in streams due to changes in the structure and activity of aquatic fungi.Fundação para a Ciência e a Tecnologia (FCT) – Programa Operacional “Ciência, Tecnologia, Inovação” (POCTI) - POCTI/34024/BSE/2000
Search for new phenomena in final states with an energetic jet and large missing transverse momentum in pp collisions at √ s = 8 TeV with the ATLAS detector
Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb−1 of √ s = 8 TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with pT > 120 GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between Emiss T > 150 GeV and Emiss T > 700 GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with either large extra spatial dimensions, pair production of weakly interacting dark matter candidates, or production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presente
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