286 research outputs found
Antimicrobial susceptibility patterns of Haemophilus parasuis from pigs in the United Kingdom and Spain
18 p.A total of 30 British and 30 Spanish Haemophilus parasuis isolates were tested
for their susceptibility to 19 of the antimicrobials currently used in swine practice with a
broth microdilution method in order to know the emergence of resistance against these
compounds in this porcine pathogen. All the British isolates were susceptible to penicillin,
ceftiofur, erythromycin, tilmicosin, enrofloxacin, and florfenicol, and most of them were
susceptible to the remaining antimicrobials (the highest resistance rate found was of 20%
to neomycin). In contrast, all the Spanish isolates were susceptible exclusively to
florfenicol, and high proportions of resistance were encountered for penicillin, ampicillin,
oxytetracycline, erythromycin, tilmicosin, tiamulin and trimethoprim +
sulphamethoxazole; in addition, a bimodal or multimodal distribution, or tailing of Spanish
isolates over the MIC range was observed for clindamycin, sulphonamides and tylosine
tartrate, suggesting the development of acquired resistance. In addition, several multiresistance patterns were found among the Spanish isolates, 23.3% of them being
resistant to at least eight antimicrobials, the same rate as that encountered for those being
susceptible to all antimicrobials tested. This study showed that in general British H.
parasuis isolates are susceptible to antimicrobial agents routinely used for treatment of
porcine respiratory diseases; however, the Spanish isolates need a more continuous
surveillance of their susceptibility patternsS
Real time dynamic strain monitoring of optical links using the backreflection of live PSK data
A major cause of faults in optical communication links is related to unintentional
third party intrusions (normally related to civil/agricultural works) causing fiber breaks or
cable damage. These intrusions could be anticipated and avoided by monitoring the dynamic
strain recorded along the cable. In this work, a novel technique is proposed to implement realtime
distributed strain sensing in parallel with an operating optical communication channel.
The technique relies on monitoring the Rayleigh backscattered light from optical
communication data transmitted using standard modulation formats. The system is treated as a
phase-sensitive OTDR (ΦOTDR) using random and non-periodical non-return-to-zero (NRZ)
phase-shift keying (PSK) pulse coding. An I/Q detection unit allows for a full (amplitude,
phase and polarization) characterization of the backscattered optical signal, thus achieving a
fully linear system in terms of ΦOTDR trace coding/decoding. The technique can be used
with different modulation formats, and operation using 4 Gbaud single-polarization dual PSK
and 4 Gbaud dual-polarization quadrature PSK is demonstrated. As a proof of concept,
distributed sensing of dynamic strain with a sampling of 125 kHz and a spatial resolution of
2.5 cm (set by the bit size) over 500 m is demonstrated for applied sinusoidal strain signals of
500 Hz. The limitations and possibilities for improvement of the technique are also discussed.European CommissionMinisterio de Economía y CompetitividadComunidad de Madri
Chaotic exchange of solid material between planetary systems: implications for lithopanspermia
We examine a low energy mechanism for the transfer of meteoroids between two
planetary systems embedded in a star cluster using quasi-parabolic orbits of
minimal energy. Using Monte Carlo simulations, we find that the exchange of
meteoroids could have been significantly more efficient than previously
estimated. Our study is relevant to astrobiology as it addresses whether life
on Earth could have been transferred to other planetary systems in the solar
system's birth cluster and whether life on Earth could have been transferred
here from beyond the solar system. In the solar system, the timescale over
which solid material was delivered to the region from where it could be
transferred via this mechanism likely extended to several hundred million years
(as indicated by the 3.8-4.0 Ga epoch of the Late Heavy Bombardment). This
timescale could have overlapped with the lifetime of the Solar birth cluster
(~100-500 Myr). Therefore, we conclude that lithopanspermia is an open
possibility if life had an early start. Adopting parameters from the minimum
mass solar nebula, considering a range of planetesimal size distributions
derived from observations of asteroids and Kuiper Belt Objects and theoretical
coagulation models, and taking into account Oort Cloud formation models, the
expected number of bodies with mass > 10 kg that could have been transferred
between the Sun and its nearest cluster neighbor could be of the order of
1E14-3E16, with transfer timescales of 10s Myr. We estimate that of the order
of 3E8 x l(km) could potentially be life-bearing, where l(km) is the depth of
the Earth crust in km that was ejected as the result of the early bombardment.Comment: Accepted by Astrobiology. Submitted: Sep. 21, 2011. Accepted: May 2,
2012. 39 pages. 21 figures. arXiv admin note: substantial text overlap with
arXiv:0808.326
Observers in an accelerated universe
If the current acceleration of our Universe is due to a cosmological
constant, then a Coleman-De Luccia bubble will nucleate in our Universe. In
this work, we consider that our observations could be likely in this framework,
consisting in two infinite spaces, if a foliation by constant mean curvature
hypersurfaces is taken to count the events in the spacetime. Thus, we obtain
and study a particular foliation, which covers the existence of most observers
in our part of spacetime.Comment: revised version, accepted in EPJ
Anisotropic vortex pinning in superconductors with a square array of rectangular submicron holes
We investigate vortex pinning in thin superconducting films with a square
array of rectangular submicron holes ("antidots"). Two types of antidots are
considered: antidots fully perforating the superconducting film, and "blind
antidots", holes that perforate the film only up to a certain depth. In both
systems, we observe a distinct anisotropy in the pinning properties, reflected
in the critical current Ic, depending on the direction of the applied
electrical current: parallel to the long side of the antidots or perpendicular
to it. Although the mechanism responsible for the effect is very different in
the two systems, they both show a higher critical current and a sharper
IV-transition when the current is applied along the long side of the
rectangular antidots
Electron energy loss and induced photon emission in photonic crystals
The interaction of a fast electron with a photonic crystal is investigated by
solving the Maxwell equations exactly for the external field provided by the
electron in the presence of the crystal. The energy loss is obtained from the
retarding force exerted on the electron by the induced electric field. The
features of the energy loss spectra are shown to be related to the photonic
band structure of the crystal. Two different regimes are discussed: for small
lattice constants relative to the wavelength of the associated electron
excitations , an effective medium theory can be used to describe the
material; however, for the photonic band structure plays an
important role. Special attention is paid to the frequency gap regions in the
latter case.Comment: 12 pages, 7 figure
Ab Initio Calculation of the Lattice Distortions induced by Substitutional Ag- and Cu- Impurities in Alkali Halide Crystals
An ab initio study of the doping of alkali halide crystals (AX: A = Li, Na,
K, Rb; X = F, Cl, Br, I) by ns2 anions (Ag- and Cu-) is presented. Large active
clusters with 179 ions embedded in the surrounding crystalline lattice are
considered in order to describe properly the lattice relaxation induced by the
introduction of substitutional impurities. In all the cases considered, the
lattice distortions imply the concerted movement of several shells of
neighbors. The shell displacements are smaller for the smaller anion Cu-, as
expected. The study of the family of rock-salt alkali halides (excepting CsF)
allows us to extract trends that might be useful at a predictive level in the
study of other impurity systems. Those trends are presented and discussed in
terms of simple geometric arguments.Comment: LaTeX file. 8 pages, 3 EPS pictures. New version contains
calculations of the energy of formation of the defects with model clusters of
different size
Energy radiation of moving cracks
The energy radiated by moving cracks in a discrete background is analyzed.
The energy flow through a given surface is expressed in terms of a generalized
Poynting vector. The velocity of the crack is determined by the radiation by
the crack tip. The radiation becomes more isotropic as the crack velocity
approaches the instability threshold.Comment: 7 pages, embedded figure
The Kuiper Belt and Other Debris Disks
We discuss the current knowledge of the Solar system, focusing on bodies in
the outer regions, on the information they provide concerning Solar system
formation, and on the possible relationships that may exist between our system
and the debris disks of other stars. Beyond the domains of the Terrestrial and
giant planets, the comets in the Kuiper belt and the Oort cloud preserve some
of our most pristine materials. The Kuiper belt, in particular, is a
collisional dust source and a scientific bridge to the dusty "debris disks"
observed around many nearby main-sequence stars. Study of the Solar system
provides a level of detail that we cannot discern in the distant disks while
observations of the disks may help to set the Solar system in proper context.Comment: 50 pages, 25 Figures. To appear in conference proceedings book
"Astrophysics in the Next Decade
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