451 research outputs found
Effects of reduced glutathione and catalase on the kinematics and membrane functionality of sperm during liquid storage of ram semen
AbstractThe objective of this study was to evaluate the effects of reduced glutathione (GSH) and catalase (CAT) supplementation on the kinematics and membrane functionality of sperm during the liquid storage of ram semen, cooled at 5°C, for up to 24h. Semen samples from four rams were pooled, diluted with Tris-egg yolk extender without antioxidants (control) or supplemented with either CAT (100, 200, and 400U/mL) or GSH (100, 200, and 400mM) at a final concentration of 50Ă106sperm/mL. Sperm kinematics, which was analyzed by computer-assisted sperm analysis (CASA), and membrane functionality, which was analyzed using the hypo-osmotic swelling test (HOST), were determined after the addition of the semen samples at different processing times (fresh/diluted, 1.5, 6, 12, and 24h, at 5°C). No significant differences were recorded in the kinematics or membrane functionality between treatments at different times. The supplementation of diluents with 100 and 200U/mL of CAT prevented the harmful effects of cooling on total sperm motility. No significant differences were observed in progressive sperm motility throughout processing, regardless of the treatment and time of evaluation. Supplementation with 400mM GSH resulted in an earlier reduction (P<0.05) of total sperm motility, a decrease in rapid sperm rate and a reduction in curvilinear velocity during incubation, at 5°C. The cooling induced a reduction (P<0.05) in the percentage of sperm with a functional plasma membrane (HOST), especially after 1.5h of incubation. Based on the results of the present study, the addition of CAT (100 and 200U/mL) reduced the deleterious effects of cooling on total motility in ram sperm maintained at 5°C for 24h, although it did not affect the functionality of the sperm membranes. However, the addition of 400mM GSH caused negative effects on the velocity parameters of the sperm
Exact Casimir-Polder potential between a particle and an ideal metal cylindrical shell and the proximity force approximation
We derive the exact Casimir-Polder potential for a polarizable microparticle
inside an ideal metal cylindrical shell using the Green function method. The
exact Casimir-Polder potential for a particle outside a shell, obtained
recently by using the Hamiltonian approach, is rederived and confirmed. The
exact quantum field theoretical result is compared with that obtained using the
proximity force approximation and a very good agreement is demonstrated at
separations below 0.1, where is the radius of the cylinder. The
developed methods are applicable in the theory of topological defects.Comment: 8 pages, 4 figures, Accepted for publication in Eur. Phys. J.
The MIDAS experiment: A prototype for the microwave emission of Ultra-High Energy Cosmic Rays
Recent measurements suggest that extensive air showers initiated by
ultra-high energy cosmic rays (UHECR) emit signals in the microwave band of the
electromagnetic spectrum caused by the collisions of the free-electrons with
the atmospheric neutral molecules in the plasma produced by the passage of the
shower. Such emission is isotropic and could allow the detection of air showers
with 100% duty cycle and a calorimetric-like energy measurement, a significant
improvement over current detection techniques. We have built MIDAS (MIcrowave
Detection of Air Showers), a prototype of microwave detector, which consists of
a 4.5 m diameter antenna with a cluster of 53 feed-horns in the 4 GHz range.
The details of the prototype and first results will be presented.Comment: To appear in the proceedings of 12th Topical Seminar on Innovative
Particle and Radiation Detectors (IPRD10), Siena, Italy, 7 - 10 June 201
Towards a holographic dual of large-N_c QCD
We study N_f D6-brane probes in the supergravity background dual to N_c
D4-branes compactified on a circle with supersymmetry-breaking boundary
conditions. In the limit in which the resulting Kaluza--Klein modes decouple,
the gauge theory reduces to non-supersymmetric, four-dimensional QCD with N_c
colours and N_f << N_c flavours. As expected, this decoupling is not fully
realised within the supergravity/Born--Infeld approximation. For N_f = 1 and
massless quarks, m_q = 0, we exhibit spontaneous chiral symmetry breaking by a
quark condensate, \neq 0, and find the associated massless
`pion' in the spectrum. The latter becomes massive for m_q > 0, obeying the
Gell-Mann--Oakes--Renner relation: M_pi^2= - m_q / \f_pi^2. In
the case N_f > 1 we provide a holographic version of the Vafa--Witten theorem,
which states that the U(N_f) flavour symmetry cannot be spontaneously broken.
Further we find N_f^2 - 1 unexpectedly light pseudo-scalar mesons in the
spectrum. We argue that these are not (pseudo) Goldstone bosons and speculate
on the string mechanism responsible for their lightness. We then study the
theory at finite temperature and exhibit a phase transition associated with a
discontinuity in the chiral condensate. D6/anti-D6 pairs are also briefly
discussed.Comment: 43 pages, LaTeX; v3: Scalar vs. pseudo-scalar nature of mesons
clarified, references added. v4: Small change in Acknowledgment
The MIDAS telescope for microwave detection of ultra-high energy cosmic rays
We present the design, implementation and data taking performance of the
MIcrowave Detection of Air Showers (MIDAS) experiment, a large field of view
imaging telescope designed to detect microwave radiation from extensive air
showers induced by ultra-high energy cosmic rays. This novel technique may
bring a tenfold increase in detector duty cycle when compared to the standard
fluorescence technique based on detection of ultraviolet photons. The MIDAS
telescope consists of a 4.5 m diameter dish with a 53-pixel receiver camera,
instrumented with feed horns operating in the commercial extended C-Band (3.4
-- 4.2 GHz). A self-trigger capability is implemented in the digital
electronics. The main objectives of this first prototype of the MIDAS telescope
- to validate the telescope design, and to demonstrate a large detector duty
cycle - were successfully accomplished in a dedicated data taking run at the
University of Chicago campus prior to installation at the Pierre Auger
Observatory.Comment: 13 pages, 18 figure
Comparing the egg ultrastructure of three Psorophora ferox (Diptera: Culicidae) populations
Astrobiologically Interesting Stars within 10 parsecs of the Sun
The existence of life based on carbon chemistry and water oceans relies upon
planetary properties, chiefly climate stability, and stellar properties, such
as mass, age, metallicity and Galactic orbits. The latter can be well
constrained with present knowledge. We present a detailed, up-to-date
compilation of the atmospheric parameters, chemical composition, multiplicity
and degree of chromospheric activity for the astrobiologically interesting
solar-type stars within 10 parsecs of the Sun. We determine their state of
evolution, masses, ages and space velocities, and produce an optimized list of
candidates that merit serious scientific consideration by the future
space-based interferometry probes aimed at directly detecting Earth-sized
extrasolar planets and seeking spectroscopic infrared biomarkers as evidence of
photosynthetic life. The initially selected stars number 33 solar-type within
the population of 182 stars (excluding late M-dwarfs) closer than 10 pc. A
comprehensive and detailed data compilation for these objects is still
essentially lacking: a considerable amount of recent data has so far gone
unexplored in this context. We present 13 objects as the nearest "biostars",
after eliminating multiple stars, young, chromospherically active, hard X-ray
emitting stars, and low metallicity objects. Three of these "biostars", HD
1581, 109358 and 115617, closely reproduce most of the solar properties and are
considered as premier targets. We show that approximately 7% of the nearby
stars are optimally interesting targets for exobiology.Comment: 36 pages, recommended for publication in Astrobiolog
Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory
Data from the Pierre Auger Observatory are analyzed to search for
anisotropies near the direction of the Galactic Centre at EeV energies. The
exposure of the surface array in this part of the sky is already significantly
larger than that of the fore-runner experiments. Our results do not support
previous findings of localized excesses in the AGASA and SUGAR data. We set an
upper bound on a point-like flux of cosmic rays arriving from the Galactic
Centre which excludes several scenarios predicting sources of EeV neutrons from
Sagittarius . Also the events detected simultaneously by the surface and
fluorescence detectors (the `hybrid' data set), which have better pointing
accuracy but are less numerous than those of the surface array alone, do not
show any significant localized excess from this direction.Comment: Matches published versio
Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory
Atmospheric parameters, such as pressure (P), temperature (T) and density,
affect the development of extensive air showers initiated by energetic cosmic
rays. We have studied the impact of atmospheric variations on extensive air
showers by means of the surface detector of the Pierre Auger Observatory. The
rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find
that the observed behaviour is explained by a model including the effects
associated with the variations of pressure and density. The former affects the
longitudinal development of air showers while the latter influences the Moliere
radius and hence the lateral distribution of the shower particles. The model is
validated with full simulations of extensive air showers using atmospheric
profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle
Physic
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