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 $z\sim 4$, 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

&nbsp;&nbsp;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 mamíferos. Se coloca el tejido disecado entre dos hemicámaras cúbicas de acrilato. El tejido separa a dos soluciones electrolíticas oxigenadas, a 20°C y pH 7.4. Un multímetro 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 vesícula 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. Let