5,659 research outputs found
Wetland restoration and nitrate reduction: the example of the periurban wetland of Vitoria-Gasteiz (Basque Country, North Spain)
Changes in land use and agricultural intensification caused wetlands on the quaternary aquifer of Vitoria-Gasteiz (Basque Country) to disappear some years ago and nitrate concentration in groundwaters increased very quickly. The Basque Government recently declared the East Sector of this aquifer a Vulnerable Zone according to the 91/676/CEE European Directive. Recently, the wetlands have been restored through the closure of the main drainage ditches, the consequent elevation of the water table and the abondonment of agricultural practices near the wetlands. This is the case of the Zurbano wetland. Restoration has allowed the recovery of its biogeochemical function, which has reduced nitrate concentrations in waters. Nitrate concentrations which exceed 50 mg l–1 in groundwaters entering into the wetland are less than 10 mg l–1 at the outlet. Conditions in the wetland are conducive to the loss of nitrates: organic matter rich wetted soils, clay presence allowing a local semiconfined flow and very low hydraulic gradient. Water quality monitoring at several points around the wetland showed the processes involved in nitrate loss, although some aspects still remain unresolved. However, during storm events, the wetland effectively reduces the nitrate concentration entering the Alegria River, the most important river on the quaternary aquifer
Experimental Quantum Cloning of Single Photons
Although perfect copying of unknown quantum systems is forbidden by the laws
of quantum mechanics, approximate cloning is possible. A natural way of
realizing quantum cloning of photons is by stimulated emission. In this context
the fundamental quantum limit to the quality of the clones is imposed by the
unavoidable presence of spontaneous emission. In our experiment a single input
photon stimulates the emission of additional photons from a source based on
parametric down-conversion. This leads to the production of quantum clones with
near optimal fidelity. We also demonstrate universality of the copying
procedure by showing that the same fidelity is achieved for arbitrary input
states.Comment: 4 pages, 2 figure
DISTRIBUTION OF PIGMENT CELLS IN THE HEART OF THE RABBITFISH, CHIMAERA MONSTROSA (CONDRICHTHYES: HOLOCEPHALI)
El resumen aparece en el Program & Abstracts of the 10th International Congress of Vertebrate Morphology, Barcelona 2013. Anatomical Record, Volume 296, Special Feature — 1: P-076.The study of extracutaneous cells producing and storing melanin is of interest because it
may provide valuable information about the presence of neural crest elements in internal
organs and tissues. Here we report, for the first time, the presence and distribution of
melanophores in the heart of a chondrichthyan species, the rabbitfish, Chimaera
monstrosa. Pigment cells were found in all of 20 hearts examined. Pigment cells occur
mainly in the cardiac outflow tract, which consists of two anatomical components, the
proximal, myocardial conus arteriosus and the distal, non-myocardial bulbus arteriosus.
A few groups of dark pigmented cells were found in the apex of the ventricle of one
specimen and in the atrium of two specimens. In all instances, the melanophores were
located in the subepicardial space, where they could be well recognized in both
unstained and stained histological sections. The distribution and intensity of the
pigmentation in the cardiac outflow tract varies markedly between individuals. In all
cases, however, the pigmented area is larger on the dorsal than on the ventral surface.
Dorsally, the size of the pigmented area ranges from a fringe that includes the bulbus
and the distal part of the conus to the whole surface of the outflow tract. Ventrally, the
pigmented area does not cover the entire conus arteriosus. The intensity of the
pigmentation also varies widely; in general, it is highest at the distal portion of the conus.
There is no relationship between the distribution and intensity of the pigmentation and
the sex and age of the animals. The functional role of the pigmented cells is unknown. If
the melanophores in the heart of C. monstrosa are indeed of neural crest origin, it would
suggest a notable contribution of the neural crest cells to the cardiac outflow tract in
holocephalans.Proyecto CGL2010-16417/BOS; Fondos FEDER
BES-2011-04690
The bulbus arteriosus of the holocephalan heart
El resumen aparece en el Program & Abstracts of the 10th International Congress of Vertebrate Morphology, Barcelona 2013.Anatomical Record, Volume 296, Special Feature — 1: P-074.Previous work has shown that the outflow tract of the elasmobranch heart, namely the
cardiac portion intercalated between the ventricle and the ventral aorta, does not consist
of a single component, the conus arteriosus, as has classically been assumed, but two,
the myocardial conus arteriosus and the non-myocardial bulbus arteriosus. From the
evolutionary perspective, knowledge of the anatomy of the cardiac outflow tract of the
holocephali is important, as they are the sister group of elasmobranchs. Our aim is to
describe the cardiac outflow tract of four holocephalan species, two of them, Chimaera
monstrosa and Hydrolagus affinis of the family Chimaeridae, and the other two, Harriotta
raleighana and Rhinochimaera atlantica, of the family Rhinochimaeridae. The cardiac
outflow tract of the four species consisted of a myocardial conus arteriosus, furnished
with valves, and a bulbus arteriosus devoid of cardiac muscle. Both the bulbus and
conus are tubular in shape. The length of the bulbus relative to the total length of the
outflow tract is somewhat smaller in the rhinochimaerids (15%-19%) than in the
chimaerids (19%-23%). The bulbus is covered by epicardium and is crossed by the main
coronary artery trunks. Histologically, the bulbus is mainly composed of elastin and
collagen, and, to a lesser extent, by smooth muscle. This suggests that in
holocephalans, the bulbus actively helps to protect the gill vasculature from exposure to
high-pressure pulses of blood. Our results prove that the bulbus arteriosus is common to
chondrichthyans. In addition, they support the hypothesis that the cardiac outflow tract
consisted of a conus arteriosus and a bulbus arteriosus from the beginning of the jawed
vertebrate radiation, contributing to our understanding of the morphological changes that
have occurred at the arterial pole of the heart in both actinopterygians and
sarcopterygians.Proyecto CGL2010-16417/BOS; Fondos FEDE
Experimental violation of a spin-1 Bell inequality using maximally-entangled four-photon states
We demonstrate the first experimental violation of a spin-1 Bell inequality.
The spin-1 inequality is a calculation based on the Clauser, Horne, Shimony and
Holt formalism. For entangled spin-1 particles the maximum quantum mechanical
prediction is 2.552 as opposed to a maximum of 2, predicted using local hidden
variables. We obtained an experimental value of 2.27 using the
four-photon state generated by pulsed, type-II, stimulated parametric
down-conversion. This is a violation of the spin-1 Bell inequality by more than
13 standard deviations.Comment: 5 pages, 3 figures, Revtex4. Problem with figures resolve
Well-posedness and stability results for the Gardner equation
In this article we present local well-posedness results in the classical
Sobolev space H^s(R) with s > 1/4 for the Cauchy problem of the Gardner
equation, overcoming the problem of the loss of the scaling property of this
equation. We also cover the energy space H^1(R) where global well-posedness
follows from the conservation laws of the system. Moreover, we construct
solitons of the Gardner equation explicitly and prove that, under certain
conditions, this family is orbitally stable in the energy space.Comment: 1 figure. Accepted for publication in Nonlin.Diff Eq.and App
Coupling Between Thermal Oscillations in the Surface of a Micro-Cylinder and Vortex Shedding
his article studies the coupling between prescribed thermal oscillations in the surface of a micro-cylinder and vortex shedding. We deal with the unsteady, laminar, compressible flow regime where the aerodynamics forces have a periodic behavior. It is shown that appropriate spatial and time-dependent temperature oscillations on the surface of the micro-cylinder create a resonance that controls the amplitude and frequency of both lift and drag coefficients. In practice, what we study is a mechanism to modulate the amplitude and frequency of mechanical loads of aerodynamics origin in a micro-structure by using surface temperature fluctuations as the control parameter
Constraining the properties of neutron star crusts with the transient low-mass X-ray binary Aql X-1
Aql X-1 is a prolific transient neutron star low-mass X-ray binary that
exhibits an accretion outburst approximately once every year. Whether the
thermal X-rays detected in intervening quiescent episodes are the result of
cooling of the neutron star or due to continued low-level accretion remains
unclear. In this work we use Swift data obtained after the long and bright 2011
and 2013 outbursts, as well as the short and faint 2015 outburst, to
investigate the hypothesis that cooling of the accretion-heated neutron star
crust dominates the quiescent thermal emission in Aql X-1. We demonstrate that
the X-ray light curves and measured neutron star surface temperatures are
consistent with the expectations of the crust cooling paradigm. By using a
thermal evolution code, we find that ~1.2-3.2 MeV/nucleon of shallow heat
release describes the observational data well, depending on the assumed
mass-accretion rate and temperature of the stellar core. We find no evidence
for varying strengths of this shallow heating after different outbursts, but
this could be due to limitations of the data. We argue that monitoring Aql X-1
for up to ~1 year after future outbursts can be a powerful tool to break model
degeneracies and solve open questions about the magnitude, depth and origin of
shallow heating in neutron star crusts.Comment: 14 pages, 5 figures, 3 tables, accepted to MNRA
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