576 research outputs found
Anomalous population of He states in reactions with Li
Structure with the lowest energy observed in the He spectrum populated
in the proton knockout reaction with Li beam has a peak at
MeV. This peak is usually interpreted as a resonant ground state of
He. Our theoretical calculations indicate that this peak is likely to be
a pileup of , , and excitations with very similar shapes. %We
predict a very specific nature of the excitation in He. Moreover,
the ``soft'' excitation appears to be the lowest one in energy. Such an
anomalous continuum response is traced to the halo structure of Li
providing extreme low energy shift to all the expected continuum excitations.
Competitions of the initial state structure (ISS) and the final state
interaction (FSI) effects on the spectrum and three-body correlations in
He are discussed. Analogous effect of the extreme low-energy shift could
also be expected in other cases of emitters populated in reactions with
halo nuclei. Simplified example of the He spectrum in knockout
from Be, is given. We also discuss limits on the properties of He
stemming from the observed He spectrum.Comment: 10 pages, 13 figure
Scattering theory with finite-gap backgrounds: Transformation operators and characteristic properties of scattering data
We develop direct and inverse scattering theory for Jacobi operators (doubly
infinite second order difference operators) with steplike coefficients which
are asymptotically close to different finite-gap quasi-periodic coefficients on
different sides. We give necessary and sufficient conditions for the scattering
data in the case of perturbations with finite second (or higher) moment.Comment: 23 page
Spectrum of cosmic rays, produced in supernova remnants
Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova
remnants is employed to calculate CR spectra. The magnetic field in SNRs is
assumed to be significantly amplified by the efficiently accelerating nuclear
CR component. It is shown that the calculated CR spectra agree in a
satisfactory way with the existing measurements up to the energy eV.
The power law spectrum of protons extends up to the energy eV
with a subsequent exponential cutoff. It gives a natural explanation for the
observed knee in the Galactic CR spectrum. The maximum energy of the
accelerated nuclei is proportional to their charge number . Therefore the
break in the Galactic CR spectrum is the result of the contribution of
progressively heavier species in the overall CR spectrum so that at
eV the CR spectrum is dominated by iron group nuclei. It is shown that this
component plus a suitably chosen extragalactic CR component can give a
consistent description for the entire Galactic CR spectrum.Comment: 4 pages with emulateapj, 3 figures, accepted for publication in the
Astrophysical Journal Letter
Long-Time Asymptotics of Perturbed Finite-Gap Korteweg-de Vries Solutions
We apply the method of nonlinear steepest descent to compute the long-time
asymptotics of solutions of the Korteweg--de Vries equation which are decaying
perturbations of a quasi-periodic finite-gap background solution. We compute a
nonlinear dispersion relation and show that the plane splits into
soliton regions which are interlaced by oscillatory regions, where
is the number of spectral gaps.
In the soliton regions the solution is asymptotically given by a number of
solitons travelling on top of finite-gap solutions which are in the same
isospectral class as the background solution. In the oscillatory region the
solution can be described by a modulated finite-gap solution plus a decaying
dispersive tail. The modulation is given by phase transition on the isospectral
torus and is, together with the dispersive tail, explicitly characterized in
terms of Abelian integrals on the underlying hyperelliptic curve.Comment: 45 pages. arXiv admin note: substantial text overlap with
arXiv:0705.034
Spatial beam self-cleaning and supercontinuum generation with Yb-doped multimode graded-index fiber taper based on accelerating self-imaging and dissipative landscape
We experimentally demonstrate spatial beam self-cleaning and supercontinuum generation in a tapered Ytterbium-doped multimode optical fiber with parabolic core refractive index profile when 1064 nm pulsed beams propagate from wider (122 µm) into smaller (37 µm) diameter. In the passive mode, increasing the input beam peak power above 20 kW leads to a bell-shaped output beam profile. In the active configuration, gain from the pump laser diode permits to combine beam self-cleaning with supercontinuum generation between 520-2600 nm. By taper cut-back, we observed that the dissipative landscape, i.e., a non-monotonic variation of the average beam power along the MMF, leads to modal transitions of self-cleaned beams along the taper length
Genetic resources of narrow-leaved lupine (Lupinus angustifolius L.) and their role in its domestication and breeding
Narrow-leaved lupine (Lupinus angustifolius L.) is a cultivated multipurpose species with a very short history of domestication. It is used as a green manure, and for feed and food. This crop shows good prospects for use in pharmacology and as a source of fish feeds in aquaculture. However, its genetic potential for the development of productive and adaptable cultivars is far from being realized. For crop species, the genetic base of the cultivated gene pool has repeatedly been shown as being much narrower than that of the wild gene pool. Therefore, efficient utilization of a species’ genetic resources is important for the crop’s further improvement. Analyzing the information on the germplasm collections preserved in national gene banks can help perceive the worldwide diversity of L. angustifolius genetic resources and understand how they are studied and used. In this context, the data on the narrow-leaved lupine collection held by VIR are presented: its size and composition, the breeding status of accessions, methods of studying and disclosing intraspecific differentiation, the classifications used, and the comparison of this information with available data on other collections. It appeared that VIR’s collection of narrow-leaved lupine, ranking as the world’s second largest, differed significantly from others by the prevalence of advanced cultivars and breeding material in it, while wild accessions prevailed in most collections. The importance of the wild gene pool for the narrow-leaved lupine breeding in Australia, the world leader in lupine production, is highlighted. The need to get an insight into the species’ ecogeographic diversity in order to develop cultivars adaptable to certain cultivation conditions is shown. The data on the testing of VIR’s collection for main crop characters valuable for breeders are presented. Special attention is paid to the study of accessions with limited branching as a promising gene pool for cultivation in relatively northern regions of Russia. They demonstrate lower but more stable productivity, and suitability for cultivation in planting patterns, which has a number of agronomic advantages. Analyzing the work with narrow-leaved lupine genetic resources in different national gene banks over the world helps shape the prospects of further activities with VIR’s collection as the only source of promising material for domestic breeding
The passport database of VIR’s bean collection as a tool for systemizing bean genetic diversity, studying the collection’s history, and monitoring the crop’s worldwide breeding (an overview)
The main document attesting the composition of a collection is the passport database (DB), which contains basic information about every accession: its name, status, origin, the year of its placement into the collection, etc. The effort to include every detail of such information into the database opens up a number of possibilities for structuring and exploring the diversity available. For the bean collection, the history of its systemization has had several stages. In 1923, systemic recording of bean accessions that entered the collection started with their registration in special journals, called catalogues. Since the middle of the 1960s, computer aids have been used for data logging and processing. In the 1990s, the DBs thus developed were transferred to personal computers. Today, such data are formatted as a computerized passport database, unified in accordance with modern international standards and consisting of 35 fields. Analysis of the Phaseolus passport database has shown that the bean collection consists of 6586 accessions, registered in the permanent catalogue. These accessions represent four cultivated species of different breeding status from 102 countries of the world. The largest percentage in the collection belongs to the accessions of European origin (61%). The accessions from North and South Americas (over 600 and 460 entries, respectively) make up 17% of the collection, while the gene pool of Asian countries, 16%. The biggest replenishments of VIR’s bean collection in its entire long history happened in the times of the USSR (2129 entries). The passport DB also makes it possible to conduct worldwide monitoring of the breeding work with beans, because it provides a comprehensive overview of the history of bean breeding and its present-day status in foreign countries, the ex-USSR republics and the Russian Federation. The purpose of this article has been to analyze the passport database of VIR’s bean collection and the information stored in it, and produce a retrospective essay on the documentation of the Phaseolus germplasm holdings at VIR
Cosmic Rays: The Second Knee and Beyond
We conduct a review of experimental results on Ultra-High Energy Cosmic Rays
(UHECR's) including measurements of the features of the spectrum, the
composition of the primary particle flux and the search for anisotropy in event
arrival direction. We find that while there is a general consensus on the
features in the spectrum -- the Second Knee, the Ankle, and (to a lesser
extent) the GZK Cutoff -- there is little consensus on the composition of the
primaries that accompany these features. This lack of consensus on the
composition makes interpretation of the agreed upon features problematic. There
is also little direct evidence about potential sources of UHECRs, as early
reports of arrival direction anisotropies have not been confirmed in
independent measurements.Comment: 46 pages, 30 figures. Topical Review to appear in J. Physics
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