379 research outputs found
Enhancing the Pierre Auger Observatory to the 10^{17} to 10^{18.5} eV Range: Capabilities of an Infill Surface Array
The Pierre Auger Observatory has been designed to study the highest-energy
cosmic rays in nature (E > 10^{18.5} eV). The determination of their arrival
direction, energy and composition is performed by the analysis of the
atmospheric showers they produce. The Auger Surface Array will consist of 1600
water Cerenkov detectors placed in an equilateral triangular grid of 1.5 km
spacing. The aim of this paper is to show that the addition of a "small" area
of surface detectors at half or less the above mentioned spacing would allow a
dramatic increase of the physical scope of this Observatory, reaching lower
energies at which the transition from galactic to extragalactic sources is
expected.Comment: 21 pages, 5 figures, accepted for publication in Nucl. Instr. & Meth.
in Phys. Res.
Algunos factores que afectan las colonizaciones de Caquetá y Putumayo en Colombia.
Maestría en CienciasMaestrí
Monitoring the reproductive status of resident and migrant Atlantic bluefin tuna in the Strait of Gibraltar
Two distinct contingents of Atlantic bluefin tuna (ABFT), migrants and residents,
occur in the Strait of Gibraltar (SoG). Long-term residents are commercially exploited all year
round using hook and line gears, whereas migrants are caught by traps in springtime as they
pass through the SoG towards Mediterranean spawning grounds. While reproductive features of
migrants have been widely studied, the life history of residents remains poorly investigated. The
relative contribution of this subpopulation to ABFT eastern stock productivity is therefore un -
known. Reproductive traits of resident ABFT were monitored throughout the year, and were com pared with those of migrants crossing the SoG in spring. To assess maturation timing, gonads
were classified into maturation stages based on histological features. Our results indicate bio -
metric and reproductive differences between SoG residents and migrants. ABFT caught by hook
and line gears were smaller on average than those collected from traps. The females sampled from
the hook and line fishery in May and early June showed, on average, significantly lower GSI val ues than those caught by trap. In contrast, the GSI values of males sampled in May were not sig nificantly different between gears. Histological analyses showed a more advanced reproductive
condition in trap-caught migrants. Delayed maturation schedules of residents in comparison to
migrants would result in less egg production and poorer larval survival rates. The present findings
encourage further investigation of reproductive schedules in unstudied subpopulations for a
better understanding of ABFT dynamics.En prensa2,48
Effect of multiple reusing of simulated air showers in detector simulations
The study of high energy cosmic rays requires detailed Monte Carlo
simulations of both, extensive air showers and the detectors involved in their
detection. In particular, the energy calibration of several experiments is
obtained from simulations. Also, in composition studies simulations play a
fundamental role because the primary mass is determined by comparing
experimental with simulated data. At the highest energies the detailed
simulation of air showers is very costly in processing time and disk space due
to the large number of secondary particles generated in interactions with the
atmosphere. Therefore, in order to increase the statistics, it is quite common
to recycle single showers many times to simulate the detector response. As a
result, the events of the Monte Carlo samples generated in this way are not
fully independent. In this work we study the artificial effects introduced by
the multiple use of single air showers for the detector simulations. In
particular, we study in detail the effects introduced by the repetitions in the
kernel density estimators which are frequently used in composition studies.Comment: 15 pages and 4 figure
Neutrino initiated cascades at mid and high altitudes in the atmosphere
High energy neutrinos play a very important role for the understanding of the
origin and propagation of ultra high energy cosmic rays (UHECR). They can be
produced as a consequence of the hadronic interactions suffered by the cosmic
rays in the acceleration regions, as by products of the propagation of the
UHECR in the radiation background and as a main product of the decay of super
heavy relic particles. A new era of very large exposure space observatories, of
which the JEM-EUSO mission is a prime example, is on the horizon which opens
the possibility of neutrino detection in the highest energy region of the
spectrum. In the present work we use a combination of the PYTHIA interaction
code with the CONEX shower simulation package in order to produce fast
one-dimensional simulations of neutrino initiated showers in air. We make a
detail study of the structure of the corresponding longitudinal profiles, but
focus our physical analysis mainly on the development of showers at mid and
high altitudes, where they can be an interesting target for space fluorescence
observatories.Comment: To appear in Astroparticle Physic
Abordaje transvasto mínimamente invasivo versus abordaje parapatelar medial convencional en la artroplastia total de rodilla en pacientes con gonartrosis: estudio prospectivo comparativo no randomizado
Objetivos: valorar y comparar los resultados a corto plazo de la artroplastia total de rodilla realizada
mediante dos vías de abordaje. Material y métodos: estudio prospectivo comparativo que compara abordaje
parapatelar medial (24 pacientes) y transvasto mínimamente invasivo (25 pacientes) en artroplastia total de rodilla.
Se incluyeron pacientes con gonartrosis grado IV de la clasificación de Kellgren-Lawrence y se excluyeron
aquellos menores de 50 años, deformidad en varo (> 15º) o valgo (> 10º), artrosis postraumática, artritis reumatoide,
cirugías de revisión, osteotomías correctoras previas, IMC > 40 kg/m2, infección activa local o sistémica
y/o deterioro mental. Resultados: se encontraron diferencias estadísticamente significativas en dolor del primer y
segundo día postoperatorios a favor del abordaje mínimamente invasivo (1º día: 3,8 ± 2,5 vs. 6,7 ± 2,1; p< 0,001.
2º día: 3 ± 2,1 vs. 6 ± 2; p< 0,001). Conclusiones: no existen diferencias relevantes entre ambos abordajes, por lo
que se recomienda la utilización del abordaje con el que el cirujano se encuentre más cómodo y familiarizadoAim: Assess and compare short-term outcomes of total knee arthroplasty performed using two
surgical approaches. Material and methods: a prospective study with 49 patients comparing medial parapatellar
approach (24 patients) and minimally invasive trans-vastus access (25 patients) in total knee replacement.
The patients included suffered knee osteoarthritis grade IV the Kellgren-Lawrence’s classification. Exclusion
criteria were age under 50 years, large axial deformity (varus deformity > 15° or valgus > 10°), posttraumatic
osteoarthritis, rheumatoid arthritis, revision surgeries, previous osteotomies, BMI> 40 kg/m2 and of course local
or systemic active infection and mental impairment. Results: statistically significant differences were found for
pain in first and second postoperative days for the minimally invasive approach (1st day: 3.8 ± 2.5 vs. 6.7 ± 2.1; p
<0.001. 2nd day: 3 ± 2.1 vs. 6 ± 2; p <0.001). Conclusions: there are not significant differences between mini and
standard approaches in knee replacement, so decision about which access to use in knee reconstruction surgery
depends on surgeon’s preferences
A new composition-sensitive parameter for Ultra-High Energy Cosmic Rays
A new family of parameters intended for composition studies in cosmic ray
surface array detectors is proposed. The application of this technique to
different array layout designs has been analyzed. The parameters make exclusive
use of surface data combining the information from the total signal at each
triggered detector and the array geometry. They are sensitive to the combined
effects of the different muon and electromagnetic components on the lateral
distribution function of proton and iron initiated showers at any given primary
energy. Analytical and numerical studies have been performed in order to assess
the reliability, stability and optimization of these parameters. Experimental
uncertainties, the underestimation of the muon component in the shower
simulation codes, intrinsic fluctuations and reconstruction errors are
considered and discussed in a quantitative way. The potential discrimination
power of these parameters, under realistic experimental conditions, is compared
on a simplified, albeit quantitative way, with that expected from other surface
and fluorescence estimators.Comment: 27 pages, 17 figures. Submitted to a refereed journa
Soft leptogenesis in the inverse seesaw model
We consider leptogenesis induced by soft supersymmetry breaking terms ("soft
leptogenesis"), in the context of the inverse seesaw mechanism. In this model
there are lepton number (L) conserving and L-violating soft
supersymmetry-breaking B-terms involving the singlet sneutrinos which, together
with the -- generically small-- L-violating parameter responsible of the
neutrino mass, give a small mass splitting between the four singlet sneutrino
states of a single generation. In combination with the trilinear soft
supersymmetry breaking terms they also provide new CP violating phases needed
to generate a lepton asymmetry in the singlet sneutrino decays. We obtain that
in this scenario the lepton asymmetry is proportional to the L-conserving soft
supersymmetry-breaking B-term, and it is not suppressed by the L-violating
parameters. Consequently we find that, as in the standard see-saw case, this
mechanism can lead to sucessful leptogenesis only for relatively small value of
the relevant soft bilinear coupling. The right-handed neutrino masses can be
sufficiently low to elude the gravitino problem. Also the corresponding Yukawa
couplings involving the lightest of the right-handed neutrinos are constrained
to be \sum |Y_{1k}|^2\lesssim 10^{-7} which generically implies that the
neutrino mass spectrum has to be strongly hierarchical.Comment: 28 pages, 1 figure; some references added; final version to appear in
JHE
Fatty Acid Methyl Esters as Biosolvents of Epoxy Resins: A Physicochemical Study
The C8 to C18 fatty acid methyl esters (FAME) have been compared as solvents for two epoxy resin pre-polymers, bisphenol A diglycidyl ether (DGEBA) and triglycidyl paminophenol ether (TGPA). It was found that the solubilization limits vary according to the ester and that methyl caprylate is the best solvent of both resins. To explain these solubility performances, physical and chemical properties of FAME were studied, such as the Hansen parameters, viscosity, binary diffusion coefficient and vaporization enthalpy. Determination of the physicochemical parameters of FAME was carried out by laboratory experimentations and by calculation from bibliographic data. The Hansen parameters of FAME and epoxy resins pre-polymers were theoretically and experimentally determined. The FAME chain length showed a long dependence on the binary diffusion parameters and kinematic viscosity, which are mass and momentum transport properties. Moreover, the vaporization enthalpy of these compounds was directly correlated with the solubilization limits
The Higgs mechanism as a cut-off effect
We compute the Coleman-Weinberg potential with a finite cut-off for pure
SU(2) and SU(3) five-dimensional gauge theories compactified on an interval. We
show that besides the expected Coulomb phase located at and in the vicinity of
the free infrared stable or "trivial" fixed point, the theory possesses also a
Higgs phase. We compare the results from the potential computation with lattice
data from simulations.Comment: 22 pages, 5 figures; introduction improved, conclusions added,
published in JHE
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