340 research outputs found
The emerging population of pulsar wind nebulae in hard X-rays
The hard X-ray synchrotron emission from pulsar wind nebulae (PWNe) probes
energetic particles, closely related to the pulsar injection power at the
present time. INTEGRAL has disclosed the yet poorly known population of hard
X-ray pulsar/PWN systems. We summarize the properties of the class, with
emphasys on the first hard X-ray bow-shock (CTB 80 powered by PSR B1951+32),
and highlight some prospects for the study of Pulsar Wind Nebulae with the
Simbol-X mission.Comment: Proceedings of the 2nd Simbol-X Symposium, AIP Conf. Proc. Series,
Eds. P. Ferrando and J. Rodriguez (4 pages, 2 figures
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
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
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&
Contribuição à biologia larval de Hylesia sp. (Lepidoptera: Hemileucidae) em Bracatinga (Mimosa scabrella Benth.).
bitstream/item/101249/1/PA-1983-Iede-ContribuicaoBiologia.pd
Exchange bias in GeMn nanocolumns: the role of surface oxidation
We report on the exchange biasing of self-assembled ferromagnetic GeMn
nanocolumns by GeMn-oxide caps. The x-ray absorption spectroscopy analysis of
this surface oxide shows a multiplet fine structure that is typical of the Mn2+
valence state in MnO. A magnetization hysteresis shift |HE|~100 Oe and a
coercivity enhancement of about 70 Oe have been obtained upon cooling (300-5 K)
in a magnetic field as low as 0.25 T. This exchange bias is attributed to the
interface coupling between the ferromagnetic nanocolumns and the
antiferromagnetic MnO-like caps. The effect enhancement is achieved by
depositing a MnO layer on the GeMn nanocolumns.Comment: 7 pages, 5 figure
Discovery of a highly energetic pulsar associated with IGR J14003-6326 in a young uncataloged Galactic supernova remnant G310.6-1.6
We report the discovery of 31.18 ms pulsations from the INTEGRAL source IGR
J14003-6326 using the Rossi X-ray Timing Explorer (RXTE). This pulsar is most
likely associated with the bright Chandra X-ray point source lying at the
center of G310.6-1.6, a previously unrecognised Galactic composite supernova
remnant with a bright central non-thermal radio and X-ray nebula, taken to be
the pulsar wind nebula (PWN). PSR J1400-6325 is amongst the most energetic
rotation-powered pulsars in the Galaxy, with a spin-down luminosity of Edot =
5.1E+37 erg.s-1. In the rotating dipole model, the surface dipole magnetic
field strength is B_s = 1.1E+12 G and the characteristic age tau_c = P/2Pdot =
12.7 kyr. The high spin-down power is consistent with the hard spectral indices
of the pulsar and the nebula of 1.22 +/- 0.15 and 1.83 +/- 0.08, respectively,
and a 2-10 keV flux ratio F_PWN/F_PSR ~ 8. Follow-up Parkes observations
resulted in the detection of radio emission at 10 and 20 cm from PSR J1400-6325
at a dispersion measure of ~ 560 cm-3 pc, which implies a relatively large
distance of 10 +/- 3 kpc. However, the resulting location off the Galactic
Plane of ~ 280 pc would be much larger than the typical thickness of the
molecular disk, and we argue that G310.6-1.6 lies at a distance of ~ 7 kpc.
There is no gamma-ray counterpart to the nebula or pulsar in the Fermi data
published so far. A multi-wavelength study of this new composite supernova
remnant, from radio to very-high energy gamma-rays, suggests a young (< 1000
yr) system, formed by a sub-energetic (~ 1E+50 ergs), low ejecta mass (M_ej ~ 3
Msun) SN explosion that occurred in a low-density environment (n_0 ~ 0.01
cm-3).Comment: 9 pages, 6 figures, 2 tables. Accepted for publication in ApJ (after
responding to referee's comments, expanded version after the radio detection
of the pulsar
Overexpression of Osmyb4 enhances compatible solute accumulation and increases stress tolerance of arabidopsis thaliana
In this paper, we report the metabolic and molecular changes in response to cold and drought induced in Osmyb4 transgenic Arabidopsis thaliana compared with the wildtype (WT). The rice Osmyb4 gene codes for a transcription factor (Myb4) induced by cold treatment and, in Arabidopsis transgenic plants, improves cold and freezing tolerance [Vannini C, Locatelli F, Bracale M, Magnani E, Marsoni M, Osnato M, Mattana M, Baldoni E, Coraggio I (2004) Plant J 37: 115-127]. Here, we report the ability of Myb4 to induce also drought tolerance in Arabidopsis transgenic plants. By the use of nuclear magnetic resonance (NMR) and enzymatic assays, we showed that several compatible solutes (glucose, fructose, sucrose, proline, glycine betaine and sinapoyl malate) accumulate in higher amount in Osmyb4-overexpressing plants with respect to the WT, both under normal and stress conditions. Considering proline, we also found that in transgenic plants the levels of the mRNAs coding for \u3941- pyrroline-5-carboxylate synthase (EC not assigned) and for \u3941- pyrroline-5-carboxylate dehydrogenase (EC 1.5.1.12) were higher and lower, respectively. The constitutive activation of several stress-inducible pathways and different kinetics in the accumulation of several metabolites, in Myb4 transgenic plants, may represent an advantage to prepare plants to face the stress condition. Moreover, these results taken together suggest that Myb4 integrates the activation of multiple components of stress response
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