3,445 research outputs found
How rapidly do neutron stars spin at birth? Constaints from archival X-ray observations of extragalactic supernovae
Traditionally, studies aimed at inferring the distribution of birth periods of neutron stars are based on radio surveys. Here we propose an independent method to constrain the pulsar spin periods at birth based on their X-ray luminosities. In particular, the observed luminosity distribution of supernovae (SNe) poses a constraint on the initial rotational energy of the embedded pulsars, via the correlation found for radio pulsars, and under the assumption that this relation continues to hold beyond the observed range. We have extracted X-ray luminosities (or limits) for a large sample of historical SNe observed with Chandra, XMM and Swift, which have been firmly classified as core-collapse SNe. We have then compared these observational limits with the results of Monte Carlo simulations of the pulsar X-ray luminosity distribution for a range of values of the birth parameters. We find that a pulsar population dominated by millisecond periods at birth is ruled out by the data
Hardy's inequalities for monotone functions on partially ordered measure spaces
We characterize the weighted Hardy's inequalities for monotone functions in
In dimension , this recovers the classical theory of
weights. For , the result was only known for the case . In
fact, our main theorem is proved in the more general setting of partially
ordered measure spaces.Comment: 14 page
Fifteen years follow-up of photorefractive keratectomy up to 10 D of myopia: outcomes and analysis of the refractive regression
PURPOSE:
To evaluate outcomes of photorefractive keratectomy up to -10.00 D of myopia and -4.50 of astigmatism and to develop a predictive model for the refractive changes in the long term.
SETTING:
Vissum Corporation and Miguel Hernandez University (Alicante, Spain).
DESIGN:
Retrospective-prospective observational series of cases.
METHODS:
This study included 33 eyes of 33 patients aged 46.79±7.04 years (range 40-57) operated with the VISX 20/20 excimer laser with optical zones of 6 mm. No mitomycin C was used in any of these cases. The minimum follow-up was 15 years. The main outcome measures were: uncorrected and corrected distance visual acuity, manifest refraction and corneal topography. Linear regression models were developed from the observed refractive changes over time.
RESULTS:
Safety and efficacy indexes at 15 years were 1.18 and 0.83, respectively. No statistically significant differences were detected for any keratometric variable during the follow-up (p≥0.103). 15 years after the surgery 54.55% of the eyes were within ±1.00 D of spherical equivalent and 84.85% within ±2.00 D. The uncorrected distance visual acuity at 15 years was 20/25 or better in 60.6% of the eyes and 20/40 or better in 72.73% of the eyes. The correlation between the attempted and the achieved refractions was r=0.948 (p<0.001) at 1 year, and r=0.821 (p<0.001) at 15 years. No corneal ectasia was detected in any case during the follow-up.
CONCLUSIONS:
Photorefractive keratectomy is a safe refractive procedure in the long term within the range of myopia currently considered suitable for its use, although its efficacy decreases with time, especially, in high myopia. The model developed predicts a myopic regression of 2.00 D at 15 years for an ablation depth of 130 µm
The effect of upstream boundary layer conditions on planar wake development
This paper investigates the characteristics of the turbulent wake structure developing from the trailing edge of an elliptical leading edge flat plate using particle image velocimetry. The objective of this present research is to measure the velocity fields in the near and far wake regions of the flat plate to provide insight into the flow mechanisms responsible for the development of the coherent structures within the wake due to the characteristics of the boundary layer at the trailing edge. The effect of two different boundary layers at the trailing edge of the flat plate is investigated – one laminar and one turbulent. In the laminar boundary layer case, the boundary layer is allowed to develop from the elliptic leading edge without disturbance to the trailing edge feeding a laminar boundary layer into the wake. In the turbulent boundary layer case, exactly the same free-stream velocity as the laminar case is used, but the boundary layer is tripped at the leading edge such that a turbulent boundary layer at the trailing edge feeds into the wake
How agriculture, connectivity and water management can affect water quality of a Mediterranean coastal wetland
The Natural Park of Albufera (Valencia, Spain) is an important Mediterranean coastal wetland that suffers continuous environmental effects from human activities and water uses, mainly related to agriculture and urban/industrial sewage discharges. The aim of this research was to assess the water quality of the different aquatic environments of this wetland, taking into account the connection between them, the agricultural impact and the management of irrigation water. The UEWater Framework Directive was followed in order to evaluate the ecological and trophic status of water systems. Spatial approaches were used to integrate physicochemical data into GIS vector layers to map the more problematic points of pollution. The results showed a globally eutrophic system with poor ecological potential. The wetland is nutrient-overloaded during the entire rice cultivation period. Good-quality water inputs are deficient, since the river network already has high levels of nutrients and pollutants, especially in the northern area, where river water is mixed with inappropriate effluents from wastewater treatment plants. Agriculture and water management affected the area intensively up to the Albufera lake, modulating most of the studied variables. The information gathered here can help to optimize the global study and management of the coastal Mediterranean wetlands, which are highly linked to agriculture
Recovery of the Historical SN1957D in X-rays with Chandra
SN1957D, located in one of the spiral arms of M83, is one of the small number
of extragalactic supernovae that has remained detectable at radio and optical
wavelengths during the decades after its explosion. Here we report the first
detection of SN1957D in X-rays, as part of a 729 ks observation of M83 with
\chandra. The X-ray luminosity (0.3 - 8 keV) is 1.7 (+2.4,-0.3) 10**37 ergs/s.
The spectrum is hard and highly self-absorbed compared to most sources in M83
and to other young supernova remnants, suggesting that the system is dominated
at X-ray wavelengths by an energetic pulsar and its pulsar wind nebula. The
high column density may be due to absorption within the SN ejecta. HST WFC3
images resolve the supernova remnant from the surrounding emission and the
local star field. Photometry of stars around SN1957D, using WFC3 images,
indicates an age of less than 10**7 years and a main sequence turnoff mass more
than 17 solar masses. New spectra obtained with Gemini-South show that the
optical spectrum continues to be dominated by broad [O III] emission lines, the
signature of fast-moving SN ejecta. The width of the broad lines has remained
about 2700 km/s (FWHM). The [O III] flux dropped precipitously between 1989 and
1991, but continued monitoring shows the flux has been almost constant since.
In contrast, radio observations over the period 1990-2011 show a decline rate
inf the flux proportional to t**-4, far steeper than the rate observed earlier,
suggesting that the primary shock has overrun the edge of a pre-SN wind.Comment: 28 pages, including 3 tables and 7 figures, accepted for publication
in Ap
A disrupted bulgeless satellite galaxy as counterpart of the ultraluminous X-ray source ESO 243-49 HLX-1
The point-like X-ray source HLX-1, close to the S0 galaxy ESO 243-49, is one the strongest intermediate-mass black hole candidates, but the nature of its counterpart is still puzzling. By means of N-body/smoothed particle hydrodynamics simulations, we investigate the hypothesis that the HLX-1 counterpart is the nucleus of a bulgeless satellite galaxy, which undergoes a minor merger with the S0galaxy.We derived synthetic surface brightness profiles for the simulated counterpart of HLX-1 in six Hubble Space Telescope (HST) filters, ranging from far ultraviolet (FUV) to infrared wavelengths, and we compared them with the observed profiles. Our model matches the emission associated with the HLX-1 counterpart in all considered filters, including the bluer ones, even without requiring the contribution of an irradiated disc. The simulation can also account for an extended FUV emission, which is hinted at by the analysis of the F140LP HST filter. This matching is impossible to achieve by assuming either a bulgy satellite, a young star cluster, or an irradiated disc component
Monitoring of patogen parasites in waste waters of agricultural industries
Las aguas residuales son potenciales
portadoras de enteroparásitos patógenos
para el hombre cuya dosis infectiva puede
ser mínima y prolongado el tiempo de
sobrevivencia de huevos y quistes en el
ambiente. La reglamentación limita la presencia
de huevos de helmintos y, hasta el
año 2000, no proponía una técnica para su
detección. Este trabajo se realizó para caracterizar
parasitológicamente los efluentes
procedentes de agroindustrias.
La capacitación en la identificación microscópica
demandó la confección de fichas
que describen las características de huevos
de helmintos. Se efectuaron ensayos con
muestras de bodegas y aceiteras en los puntos
detectados de contaminación. Los métodos
fueron adaptados a las particularidades
de los efluentes.
Los resultados no señalaron presencia
de helmintos; no obstante, se hallaron
Cyclospora e Isospora, protozoarios que, por
su alto poder infectivo, también constituyen
un riesgo para el hombre. Sin embargo, no
están contemplados por la legislación. Respecto
a helmintos, es necesario un estudio
comparativo de las técnicas de detección
para efluentes agroindustriales, con el fin de
establecer las que optimicen su recuperación.
En cuanto a otras especies es preciso
continuar investigando su presencia para
evaluar la conveniencia de incorporarlas a
la reglamentación.Wastewaters are potential human's
pathogenic parasite carriers which could be
infective in small quantities. Besides, the
eggs and cysts survival time could be
prolonged. Regulation, restricts helminths
eggs presence and, until 2000, did not
propose a detection technique. This research
aims to the parasitological characterization
of waste water from agrarian industries.
Training about microscopical identification
led us to write a helminths eggs
characteristics description. Since the
detection of pollution points, essays were
made with samples from wine vault and olive
oil factories. Techniques were adapted,
according to wastewater peculiarities.
The results did not show helminths
presence, but we found Cyclospora and
Isospora. They are protozoa whose high
infective power makes them a human health
risk. However, they are not included in
current legislation. With respect to helminths,
we concluded that it is important to make a
detection techniques comparative study for
wastewater in order to establish which one
is the best for helminths recovery.
Since other species identification, it is
necessary to investigate their presence in
order to evaluate the convenience of
incorporating them to water regulation.Fil: Enriquez, Verónica L..
Universidad Nacional de Cuyo. Facultad de Ciencias Agrarias. Departamento de Biomatemática y FisicoquímicaFil: Soria, Adriana E..
Universidad Nacional de Cuyo. Facultad de Ciencias Agrarias. Departamento de Biomatemática y FisicoquímicaFil: Salomón, María C..
Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Departamento de Patologí
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