417 research outputs found
Depth of maximum of extensive air showers and cosmic ray composition above 10**17 eV in the geometrical multichain model of nuclei interactions
The depth of maximum for extensive air showers measured by Fly's Eye and
Yakutsk experiments is analysed. The analysis depends on the hadronic
interaction model that determine cascade development. The novel feature found
in the cascading process for nucleus-nucleus collisions at high energies leads
to a fast increase of the inelasticity in heavy nuclei interactions without
changing the hadron-hadron interaction properties. This effects the development
of the extensive air showers initiated by heavy primaries. The detailed
calculations were performed using the recently developed geometrical multichain
model and the CORSIKA simulation code. The agreement with data on average depth
of shower maxima, the falling slope of the maxima distribution, and these
distribution widths are found for the very heavy cosmic ray mass spectrum
(slightly heavier than expected in the diffusion model at about 3*10**17 eV and
similar to the Fly's Eye composition at this energy).Comment: 11pp (9 eps figures
Twisted supersymmetric 5D Yang-Mills theory and contact geometry
We extend the localization calculation of the 3D Chern-Simons partition
function over Seifert manifolds to an analogous calculation in five dimensions.
We construct a twisted version of N=1 supersymmetric Yang-Mills theory defined
on a circle bundle over a four dimensional symplectic manifold. The notion of
contact geometry plays a crucial role in the construction and we suggest a
generalization of the instanton equations to five dimensional contact
manifolds. Our main result is a calculation of the full perturbative partition
function on a five sphere for the twisted supersymmetric Yang-Mills theory with
different Chern-Simons couplings. The final answer is given in terms of a
matrix model. Our construction admits generalizations to higher dimensional
contact manifolds. This work is inspired by the work of Baulieu-Losev-Nekrasov
from the mid 90's, and in a way it is covariantization of their ideas for a
contact manifold.Comment: 28 pages; v2: minor mistake corrected; v3: matches published versio
Temporal dynamics of aquatic communities and implications for pond conservation
Conservation through the protection of particular habitats is predicated on the assumption that the conservation value of those habitats is stable. We test this assumption for ponds by investigating temporal variation in macroinvertebrate and macrophyte communities over a 10-year period in northwest England. We surveyed 51 ponds in northern England in 1995/6 and again in 2006, identifying all macrophytes (167 species) and all macroinvertebrates (221 species, excluding Diptera) to species. The alpha-diversity, beta-diversity and conservation value of these ponds were compared between surveys. We find that invertebrate species richness increased from an average of 29. 5 species to 39. 8 species between surveys. Invertebrate gamma-diversity also increased between the two surveys from 181 species to 201 species. However, this increase in diversity was accompanied by a decrease in beta-diversity. Plant alpha-, beta and gamma-diversity remained approximately constant between the two periods. However, increased proportions of grass species and a complete loss of charophytes suggests that the communities are undergoing succession. Conservation value was not correlated between sampling periods in either plants or invertebrates. This was confirmed by comparing ponds that had been disturbed with those that had no history of disturbance to demonstrate that levels of correlation between surveys were approximately equal in each group of ponds. This study has three important conservation implications: (i) a pond with high diversity or high conservation value may not remain that way and so it is unwise to base pond conservation measures upon protecting currently-speciose habitats; (ii) maximising pond gamma-diversity requires a combination of late and early succession ponds, especially for invertebrates; and (iii) invertebrate and plant communities in ponds may require different management strategies if succession occurs at varying rates in the two groups
Geometric construction of D-branes in WZW models
The geometric description of D-branes in WZW models is pushed forward. Our
starting point is a gluing condition\, that matches the model's
chiral currents at the worldsheet boundary through a linear map acting on
the WZW Lie algebra. The equivalence of boundary and gluing conditions of this
type is studied in detail. The analysis involves a thorough discussion of
Frobenius integrability, shows that must be an isometry, and applies to
both metrically degenerate and nondegenerate D-branes. The isometry need
not be a Lie algebra automorphism nor constantly defined over the brane. This
approach, when applied to isometries of the form with a constant Lie
algebra automorphism, validates metrically degenerate -twined conjugacy
classes as D-branes. It also shows that no D-branes exist in semisimple WZW
models for constant\, .Comment: 23 pages, discussion of limitations of the gluing condition approach
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Coping Strategies Used by Female Victims of the Colombian Armed Conflict: The Women in the Colombian Conflict (MUCOCO) Program
The effects of armed conflict on women in post-conflict situations are an area of analysis for social disciplines. This study
will analyze the situation in Colombia, currently involved in a peace restoration process. The aim is to verify the efficacy of a
coping and emotion regulation program analyzing victimization as well as the coping strategies employed in response to these
violent acts. The program focuses on 62 women contacted through the Ruta Pacífica de las Mujeres, a nongovernmental
organization. The program had a positive effect on women, reporting lower levels of posttraumatic stress, more functional
coping strategies, and less use of dysfunctional strategies. All emotional cognitive and social indicators improved. Women
felt emotionally better, perceiving greater social support and more trust in institutions. Survivors had more self-confidence
to achieve their goals and solve their problems. The implications in a context of peace reconstruction and search for social
cohesion are discussed.project (Proyectos CUD 2017) funded by the Oficina de Cooperación al Desarrollo (Development Cooperation Office) of the Universidad del País Vasco/Euskal Herriko Unibertsitatea (University of the Basque Country, Spain) and the University of Burgos funding for the research group SIQoL (Y133GI)
Examination of the role of Mycoplasma bovis in bovine pneumonia and a mathematical model for its evaluation
The authors screened 34 large cattle herds for the presence of Mycoplasma bovis infection by examining slaughtered cattle for macroscopic lung lesions, by culturing M. bovis from lung lesions and at the same time by testing sera for the presence of antibodies against M. bovis. Among the 595 cattle examined, 33.9% had pneumonic lesions, mycoplasmas were isolated from 59.9% of pneumonic lung samples, and 10.9% of sera from those animals contained antibodies to M.bovis. In 25.2% of the cases M. bovis was isolated from lungs with no macroscopic lesions. The proportion of seropositive herds was 64.7%. The average seropositivity rate of individuals was 11.3% but in certain herds it exceeded 50%. A probability model was developed for examining the relationship among the occurrence
of pneumonia, the isolation of M. bovis from the lungs and the presence of M. bovis specific antibodies in sera
On the geometry of quantum indistinguishability
An algebraic approach to the study of quantum mechanics on configuration
spaces with a finite fundamental group is presented. It uses, in an essential
way, the Gelfand-Naimark and Serre-Swan equivalences and thus allows one to
represent geometric properties of such systems in algebraic terms. As an
application, the problem of quantum indistinguishability is reformulated in the
light of the proposed approach. Previous attempts aiming at a proof of the
spin-statistics theorem in non-relativistic quantum mechanics are explicitly
recast in the global language inherent to the presented techniques. This leads
to a critical discussion of single-valuedness of wave functions for systems of
indistinguishable particles. Potential applications of the methods presented in
this paper to problems related to quantization, geometric phases and phase
transitions in spin systems are proposed.Comment: 24 page
First and second variation formulae for the sub-Riemannian area in three-dimensional pseudo-hermitian manifolds
We calculate the first and the second variation formula for the
sub-Riemannian area in three dimensional pseudo-hermitian manifolds. We
consider general variations that can move the singular set of a C^2 surface and
non-singular variation for C_H^2 surfaces. These formulas enable us to
construct a stability operator for non-singular C^2 surfaces and another one
for C2 (eventually singular) surfaces. Then we can obtain a necessary condition
for the stability of a non-singular surface in a pseudo-hermitian 3-manifold in
term of the pseudo-hermitian torsion and the Webster scalar curvature. Finally
we classify complete stable surfaces in the roto-traslation group RT .Comment: 36 pages. Misprints corrected. Statement of Proposition 9.8 slightly
changed and Remark 9.9 adde
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