13,822 research outputs found
Neural-network selection of high-redshift radio quasars, and the luminosity function at z~4
We obtain a sample of 87 radio-loud QSOs in the redshift range 3.6<z<4.4 by
cross-correlating sources in the FIRST radio survey S{1.4GHz} > 1 mJy with
star-like objects having r <20.2 in SDSS Data Release 7. Of these 87 QSOs, 80
are spectroscopically classified in previous work (mainly SDSS), and form the
training set for a search for additional such sources. We apply our selection
to 2,916 FIRST-DR7 pairs and find 15 likely candidates. Seven of these are
confirmed as high-redshift quasars, bringing the total to 87. The candidates
were selected using a neural-network, which yields 97% completeness (fraction
of actual high-z QSOs selected as such) and an efficiency (fraction of
candidates which are high-z QSOs) in the range of 47 to 60%. We use this sample
to estimate the binned optical luminosity function of radio-loud QSOs at , and also the LF of the total QSO population and its comoving density. Our
results suggest that the radio-loud fraction (RLF) at high z is similar to that
at low-z and that other authors may be underestimating the fraction at high-z.
Finally, we determine the slope of the optical luminosity function and obtain
results consistent with previous studies of radio-loud QSOs and of the whole
population of QSOs. The evolution of the luminosity function with redshift was
for many years interpreted as a flattening of the bright end slope, but has
recently been re-interpreted as strong evolution of the break luminosity for
high-z QSOs, and our results, for the radio-loud population, are consistent
with this.Comment: 20 pages. Accepted for publication in MNRAS on 3 March 201
Use of neural networks for the identification of new z>=3.6 QSOs from FIRST-SDSS DR5
We aim to obtain a complete sample of redshift > 3.6 radio QSOs from FIRST
sources having star-like counterparts in the SDSS DR5 photometric survey
(r<=20.2). We found that simple supervised neural networks, trained on sources
with SDSS spectra, and using optical photometry and radio data, are very
effective for identifying high-z QSOs without spectra. The technique yields a
completeness of 96 per cent and an efficiency of 62 per cent. Applying the
trained networks to 4415 sources without DR5 spectra we found 58 z>=3.6 QSO
candidates. We obtained spectra of 27 of them, and 17 are confirmed as high-z
QSOs. Spectra of 13 additional candidates from the literature and from SDSS DR6
revealed 7 more z>=3.6 QSOs, giving and overall efficiency of 60 per cent. None
of the non-candidates with spectra from NED or DR6 is a z>=3.6 QSO,
consistently with a high completeness. The initial sample of z>=3.6 QSOs is
increased from 52 to 76, i.e. by a factor 1.46. From the new identifications
and candidates we estimate an incompleteness of SDSS for the spectroscopic
classification of FIRST 3.6<=z<=4.6 QSOs of 15 percent for r<=20.2.Comment: 16 pages, 9 figures accepted for publication in MNRA
CONDITIONING FACTORS THAT INFLUENCE THE SPONTANEOUS VOLTAGE GRADIENT AND THE TRANSEPITHELIAL RESISTENCE IN DIVERSE IN VITRO MAMMALIANS AND AMPHIBIANS EPITHELIA
An experimental study about spontaneous voltage gradient, total transepithelial resistance and short-circuit current is made on different amphibian and mammalian epithelia. The dissected tissue is placed between two cubic chambers. The biological membrane divides two electrolytic oxigenated-solutions at 20°C and pH 7.4 conditions. A multimeter measures the voltage difference between the solutions, then 6 for transepithelial resistance calculation. Thereafter a 9 – 56 V outer electromotive force and a potential divider are placed in series with the tissue to adjust and maintain zero potential, in order to measure the short-circuit current. Significant differences with 0.01level confidence were found in the electric epithelial parameters of the frog skin and urinary bladder and in the rabbit and rat proximal colon, urinary bladder and gallbladder. While [Na+] decrease from 107 to 0.375 mM minimized the short-circuit current in the frog skin, 100 mU/ml vasopressin in the serosal solution significantly increased it by 62%. The frog urinary bladder transepithelial resistance increased by means of pH decrease from 7.4 to 6.0 in the serosal solution and also by 10 mM amiloride in the mucosal solution. Neither the total transepithelial resistance nor the shor-circuit current significantly changed in the rabbit urinary bladder exposed to amiloride.Se realiza un estudio experimental sobre el gradiente de voltaje espontáneo, la resistencia transepitelial total y la corriente cortocircuito en algunos epitelios de anfibios y mamÃferos. Se coloca el tejido disecado entre dos hemicámaras cúbicas de acrilato. El tejido separa a dos soluciones electrolÃticas oxigenadas, a 20°C y pH 7.4. Un multÃmetro mide la diferencia de voltaje entre las soluciones y luego se inyecta 6A de corriente para calcular la resistencia transepitelial. Luego se coloca una fuerza electromotriz externa de 9 – 56 V y un resistor variable en serie con el tejido para medir la corriente cortocircuito cuando la diferencia de voltaje es 0 mV. Se encontraron diferencias significativas en los parámetros eléctricos transepiteliales medidos en la piel y vejiga urinaria del sapo, en la vesÃcula biliar, colon y vejiga urinaria del conejo y de la rata, con un nivel de confianza de 0.01. La disminución de la [Na+] de 107 a 0.375 mM disminuyó la corriente cortocircuito en la piel de sapo. La administración de 100 mU/ml de vasopresina en el lado seroso de la piel de sapo aumentó significativamente la corriente en un 62%. La resistencia transepitelial aumentó por efecto de la disminución del pH de 7.4 a 6.0 en la vejiga urinaria del sapo y también cuando se administró 10 mM amilorida en su lado mucoso. Ni la resistencia ni la corriente cortocircuito variaron significativamente en la vejiga urinaria de conejo expuesta a amilorida
From Physical to Cyber: Escalating Protection for Personalized Auto Insurance
Nowadays, auto insurance companies set personalized insurance rate based on
data gathered directly from their customers' cars. In this paper, we show such
a personalized insurance mechanism -- wildly adopted by many auto insurance
companies -- is vulnerable to exploit. In particular, we demonstrate that an
adversary can leverage off-the-shelf hardware to manipulate the data to the
device that collects drivers' habits for insurance rate customization and
obtain a fraudulent insurance discount. In response to this type of attack, we
also propose a defense mechanism that escalates the protection for insurers'
data collection. The main idea of this mechanism is to augment the insurer's
data collection device with the ability to gather unforgeable data acquired
from the physical world, and then leverage these data to identify manipulated
data points. Our defense mechanism leveraged a statistical model built on
unmanipulated data and is robust to manipulation methods that are not foreseen
previously. We have implemented this defense mechanism as a proof-of-concept
prototype and tested its effectiveness in the real world. Our evaluation shows
that our defense mechanism exhibits a false positive rate of 0.032 and a false
negative rate of 0.013.Comment: Appeared in Sensys 201
Current-induced two-level fluctuations in pseudo spin-valves (Co/Cu/Co) nanostructures
Two-level fluctuations of the magnetization state of pseudo spin-valve
pillars Co(10 nm)/Cu(10 nm)/Co(30 nm) embedded in electrodeposited nanowires
(~40 nm in diameter, 6000 nm in length) are triggered by spin-polarized
currents of 10^7 A/cm^2 at room temperature. The statistical properties of the
residence times in the parallel and antiparallel magnetization states reveal
two effects with qualitatively different dependences on current intensity. The
current appears to have the effect of a field determined as the bias field
required to equalize these times. The bias field changes sign when the current
polarity is reversed. At this field, the effect of a current density of 10^7
A/cm^2 is to lower the mean time for switching down to the microsecond range.
This effect is independent of the sign of the current and is interpreted in
terms of an effective temperature for the magnetization.Comment: 4 pages, 5 figures, revised version, to be published in Phys. Rev.
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