493 research outputs found
Room temperature spin filtering in epitaxial cobalt-ferrite tunnel barriers
We report direct experimental evidence of room temperature spin filtering in
magnetic tunnel junctions (MTJs) containing CoFe2O4 tunnel barriers via
tunneling magnetoresistance (TMR) measurements.
Pt(111)/CoFe2O4(111)/gamma-Al2O3(111)/Co(0001) fully epitaxial MTJs were grown
in order to obtain a high quality system, capable of functioning at room
temperature. Spin polarized transport measurements reveal significant TMR
values of -18% at 2 K and -3% at 290 K. In addition, the TMR ratio follows a
unique bias voltage dependence that has been theoretically predicted to be the
signature of spin filtering in MTJs containing magnetic barriers. CoFe2O4
tunnel barriers therefore provide a model system to investigate spin filtering
in a wide range of temperatures.Comment: 6 pages, 3 figure
In-flight calibration of the INTEGRAL/IBIS mask
Since the release of the INTEGRAL Offline Scientific Analysis (OSA) software
version 9.0, the ghost busters module has been introduced in the INTEGRAL/IBIS
imaging procedure, leading to an improvement of the sensitivity around bright
sources up to a factor of 7. This module excludes in the deconvolution process
the IBIS/ISGRI detector pixels corresponding to the projection of a bright
source through mask elements affected by some defects. These defects are most
likely associated with screws and glue fixing the IBIS mask to its support.
Following these major improvements introduced in OSA 9, a second order
correction is still required to further remove the residual noise, now at a
level of 0.2-1% of the brightest source in the field of view. In order to
improve our knowledge of the IBIS mask transparency, a calibration campaign has
been carried out during 2010-2012. We present here the analysis of these data,
together with archival observations of the Crab and Cyg X-1, that allowed us to
build a composite image of the mask defects and to investigate the origin of
the residual noise in the IBIS/ISGRI images. Thanks to this study, we were able
to point out a simple modification of the ISGRI analysis software that allows
to significantly improve the quality of the images in which bright sources are
detected at the edge of the field of view. Moreover, a refinement of the area
excluded by the ghost busters module is considered, and preliminary results
show improvements to be further tested. Finally, this study indicates further
directions to be investigated for improving the ISGRI sensitivity, such as
taking into account the thickness of the screws in the mask model or studying
the possible discrepancy between the modeled and actual mask element bridges.Comment: accepted for publication in the proceedings of "An INTEGRAL view of
the high-energy sky (the first 10 years)" 9th INTEGRAL Workshop, October
15-19, 2012, Paris, France, in Proceedings of Science (INTEGRAL 2012), Eds.
A. Goldwurm, F. Lebrun and C. Winkler,
(http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=176), id 154; 6 pages, 4
figures, see the PoS website for the full resolution versio
Long-term variability of AGN at hard X-rays
Variability at all observed wavelengths is a distinctive property of AGN.
Hard X-rays provide us with a view of the innermost regions of AGN, mostly
unbiased by absorption along the line of sight. Swift/BAT offers the unique
opportunity to follow, on time scales of days to years and with a regular
sampling, the 14-195 keV emission of the largest AGN sample available up to
date for this kind of investigation. We study the amplitude of the variations,
and their dependence on sub-class and on energy, for a sample of 110 radio
quiet and radio loud AGN selected from the BAT 58-month survey. About 80% of
the AGN in the sample are found to exhibit significant variability on months to
years time scales, radio loud sources being the most variable. The amplitude of
the variations and their energy dependence are incompatible with variability
being driven at hard X-rays by changes of the absorption column density. In
general, the variations in the 14-24 and 35-100 keV bands are well correlated,
suggesting a common origin of the variability across the BAT energy band.
However, radio quiet AGN display on average 10% larger variations at 14-24 keV
than at 35-100 keV and a softer-when-brighter behavior for most of the Seyfert
galaxies with detectable spectral variability on month time scale. In addition,
sources with harder spectra are found to be more variable than softer ones.
These properties are generally consistent with a variable power law continuum,
in flux and shape, pivoting at energies >~ 50 keV, to which a constant
reflection component is superposed. When the same time scales are considered,
the timing properties of AGN at hard X-rays are comparable to those at lower
energies, with at least some of the differences possibly ascribable to
components contributing differently in the two energy domains (e.g.,
reflection, absorption).Comment: 17 pages, 11 figures, accepted for publication in A&
Avaliação dos danos de Sibinia spp. (Coleoptera: Curculionidae) em sementes de Bracatinga (Mimosa scabrella Benth.) de três procedências.
bitstream/item/101248/1/PA-1983-Iede-AvaliacaoDanos.pd
Contribuição à biologia larval de Hylesia sp. (Lepidoptera: Hemileucidae) em Bracatinga (Mimosa scabrella Benth.).
bitstream/item/101249/1/PA-1983-Iede-ContribuicaoBiologia.pd
Spin-down rate and inferred dipole magnetic field of the soft gamma-ray repeater SGR 1627-41
Using Chandra data taken on 2008 June, we detected pulsations at 2.59439(4) s
in the soft gamma-ray repeater SGR 1627-41. This is the second measurement of
the source spin period and allows us to derive for the first time a long-term
spin-down rate of (1.9 +/- 0.4)E-11 s/s. From this value we infer for SGR
1627-41 a characteristic age of 2.2 kyr, a spin-down luminosity of 4E+34 erg/s
(one of the highest among sources of the same class), and a surface dipole
magnetic field strength of 2E+14 G. These properties confirm the magnetar
nature of SGR 1627-41; however, they should be considered with caution since
they were derived on the basis of a period derivative measurement made using
two epochs only and magnetar spin-down rates are generally highly variable. The
pulse profile, double-peaked and with a pulsed fraction of (13 +/- 2)% in the
2-10 keV range, closely resembles that observed by XMM-Newton in 2008
September. Having for the first time a timing model for this SGR, we also
searched for a pulsed signal in archival radio data collected with the Parkes
radio telescope nine months after the previous X-ray outburst. No evidence for
radio pulsations was found, down to a luminosity level 10-20 times fainter (for
a 10% duty cycle and a distance of 11 kpc) than the peak luminosity shown by
the known radio magnetars.Comment: 5 pages, 2 figures; accepted for publication in MNRAS Letter
Evaluation of Cytotoxicity and Genotoxicity of Acacia aroma Leaf Extracts
Acacia aroma, native plant from San Luis, Argentina, is commonly used as antiseptic and for healing of wounds. The present study was conducted to investigate the in vitro cytotoxicity and genotoxicity of hot aqueous extract (HAE) and ethanolic extract (EE) of A. aroma. The cytotoxic activity was assayed by neutral red uptake assay on Vero cell. Cell treatment with a range from 100 to 5000 g/mL of HAE and EE showed that 500 g/mL and 100 g/mL were the maximum noncytotoxic concentrations, respectively. The CC50 was 658 g/mL for EE and 1020 g/mL for HAE. The genotoxicity was tested by the single-cell gel electrophoresis comet assay. The results obtained in the evaluation of DNA cellular damage exposed to varied concentrations of the HAE showed no significant genotoxic effect at range of 1–20 mg/mL. The EE at 20 mg/mL showed moderate genotoxic effect related to the increase of the DNA percentage contained in tail of the comet; DNA was classified in category 2. At concentrations below 5 mg/mL, the results of cytotoxicity and genotoxicity of aqueous and ethanolic extracts of Acacia aroma guarantee the safety at cell and genomic level. However further studies are needed for longer periods including animal models to confirm the findings.Fil: Mattana, Claudia Maricel. Universidad Nacional de San Luis. Facultad de QuĂmica, BioquĂmica y Farmacia; ArgentinaFil: Cangiano, Maria de Los Angeles. Universidad Nacional de San Luis. Facultad de QuĂmica, BioquĂmica y Farmacia; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Alcaraz, MarĂa Luciana. Universidad Nacional de San Luis. Facultad de QuĂmica, BioquĂmica y Farmacia; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Sosa, A.. Universidad Nacional de San Luis. Facultad de QuĂmica, BioquĂmica y Farmacia; ArgentinaFil: Escobar, Franco Matias. Universidad Nacional de RĂo Cuarto. Facultad de Ciencias Exactas FisicoquĂmicas y Naturales; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Sabini, C.. Universidad Nacional de RĂo Cuarto. Facultad de Ciencias Exactas FisicoquĂmicas y Naturales; ArgentinaFil: Sabini, Liliana Ines. Universidad Nacional de RĂo Cuarto. Facultad de Ciencias Exactas FisicoquĂmicas y Naturales; ArgentinaFil: Laciar, Analia Liliana. Universidad Nacional de San Luis. Facultad de QuĂmica, BioquĂmica y Farmacia; Argentin
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