29 research outputs found
A search for VHE counterparts of Galactic Fermi bright sources and MeV to TeV spectral characterization
Very high-energy (VHE; E>100 GeV) gamma-rays have been detected from a wide
range of astronomical objects, such as pulsar wind nebulae (PWNe), supernova
remnants (SNRs), giant molecular clouds, gamma-ray binaries, the Galactic
Center, active galactic nuclei (AGN), radio galaxies, starburst galaxies, and
possibly star-forming regions as well. At lower energies, observations using
the Large Area Telescope (LAT) onboard Fermi provide a rich set of data which
can be used to study the behavior of cosmic accelerators in the MeV to TeV
energy bands. In particular, the improved angular resolution of current
telescopes in both bands compared to previous instruments significantly reduces
source confusion and facilitates the identification of associated counterparts
at lower energies. In this paper, a comprehensive search for VHE gamma-ray
sources which are spatially coincident with Galactic Fermi/LAT bright sources
is performed, and the available MeV to TeV spectra of coincident sources are
compared. It is found that bright LAT GeV sources are correlated with TeV
sources, in contrast to previous studies using EGRET data. Moreover, a single
spectral component seems unable to describe the MeV to TeV spectra of many
coincident GeV/TeV sources. It has been suggested that gamma-ray pulsars may be
accompanied by VHE gamma-ray emitting nebulae, a hypothesis that can be tested
with VHE observations of these pulsars.Comment: Astronomy and Astrophysics, in press, 17 pages, 12 figures, 5 table
PSR J1740+1000: A Young Pulsar Well Out Of The Galactic Plane
We discuss PSR J1740+1000, one of five pulsars recently discovered in a
search of 470 square degrees at 430 MHz during the upgrade of the 305-m Arecibo
telescope. The period of 154 ms and period derivative of 2.1 x 10^-14 s/s imply
a spin-down age of 114 kyr that is smaller than 95% of all known pulsars. The
youth and proximity of this pulsar make it a good candidate for detection at
X-ray and gamma-ray energies. Its high Galactic latitude of 20.4 degrees
suggests a very high velocity if the pulsar was born in the midplane of the
Galaxy and if its kinematic age equals its spindown age. Interstellar
scintillations, however, suggest a much lower velocity. We discuss possible
explanations for this discrepancy, taking into account (a) possible birth sites
away from the midplane; (b) contributions from the unmeasured radial velocity;
(c) a kinematic age different from the spin-down age; and (d) biasing of the
scintillation velocity by enhanced scattering from the North Polar Spur.Comment: 27 pages, 9 figures, submitted to Ap
Cassava processing wastewater as a platform for third generation biodiesel production
ABSTRACT This study aimed to evaluate third generation biodiesel production by microalgae Phormidium autumnale using cassava processing wastewater as a platform. Experiments were performed in a heterotrophic bubble column bioreactor. The study focused on the evaluation of the bioreactor (batch and fed-batch) of different operational modes and the analysis of biofuel quality. Results indicate that fed-batch cultivations improved system performance, elevating biomass and oil productions to 12.0 g L−1 and 1.19 g L−1, respectively. The composition of this oil is predominantly saturated (60 %) and monounsaturated (39 %), resulting in a biodiesel that complys with U.S., European and Brazilian standards. The technological route developed indicates potential for sustainable production of bulk oil and biodiesel, through the minimization of water and chemical demands required to support such a process
Gamma-Ray Pulsars
Gamma-ray photons from young pulsars allow the deepest insight into the
properties and interactions of high-energy particles with magnetic and photon
fields in a pulsar magnetosphere. Measurements with the Compton Gamma-Ray
Observatory have led to the detection of nearly ten gamma-ray pulsars. Although
quite a variety of individual signatures is found for these pulsars, some
general characteristics can be summarized: (1) the gamma-ray lightcurves of
most high-energy pulsars show two major peaks with the pulsed emission covering
more than 50% of the rotation, i.e. a wide beam of emission; (2) the gamma-ray
spectra of pulsars are hard (power law index less than 2), often with a
luminosity maximum around 1 GeV. A spectral cutoff above several GeV is found;
(3) the spectra vary with rotational phase indicating different sites of
emission; and (4) the gamma-luminosity scales with the particle flux from the
open regions of the magnetosphere (Goldreich-Julian current).Comment: 9 pages, 9 figures, 2 tables. To appear in the Proceedings of the
270. WE-Heraeus Seminar on Neutron Stars, Pulsars and Supernova Remnants,
Jan. 21-25, 2002, Physikzentrum Bad Honnef, eds W. Becker, H. Lesch & J.
Truemper. Proceedings are available as MPE-Report 27
High-speed video and electromagnetic analysis of two natural bipolar cloud-to-ground lightning flashes
High-speed video records of two bipolar cloud-to-ground flashes were analyzed in detail.\ud
They both began with a single positive return stroke that was followed by more than one subsequent weak\ud
negative stroke. Due to the elevated cloud base height of its parent thunderstorm, the preparatory processes\ud
of each subsequent negative stroke were documented optically below cloud base. In the first event (Case 1) it\ud
was observed that all four subsequent negative strokes were initiated by recoil leaders that retraced one\ud
horizontal channel segment previously ionized by the positive leader. Those recoil leaders connected to the\ud
original vertical channel segment and propagated toward ground, producing four subsequent strokes that\ud
had the same ground contact point as the original positive discharge. The second event (Case 2), in contrast,\ud
presented 15 subsequent strokes that were initiated by recoil leaders that did not reach the original channel\ud
of the positive stroke. They diverged vertically toward ground, making contact approximately 11 km away\ud
from the original positive strike point. These results constitute the first optical evidence that both single- and\ud
multiple-channel bipolar flashes occur as a consequence of recoil leader activity in the branches of the initial\ud
positive return stroke. For both events their total channel length increased continuously at a rate of the order\ud
of 104 m s 1, comparable to speeds reported for typical positive leaders.FAPESP - 08/56711-4, 2010/01742-2FAPESP - CHUVA project - 2009/15235-8UNIVAP - Universidade do Vale do Paraíb
Differential Effects of Aging on Fore– and Hindpaw Maps of Rat Somatosensory Cortex
Getting older is associated with a decline of cognitive and sensorimotor abilities, but it remains elusive whether age-related changes are due to accumulating degenerational processes, rendering them largely irreversible, or whether they reflect plastic, adaptational and presumably compensatory changes. Using aged rats as a model we studied how aging affects neural processing in somatosensory cortex. By multi-unit recordings in the fore- and hindpaw cortical maps we compared the effects of aging on receptive field size and response latencies. While in aged animals response latencies of neurons of both cortical representations were lengthened by approximately the same amount, only RFs of hindpaw neurons showed severe expansion with only little changes of forepaw RFs. To obtain insight into parallel changes of walking behavior, we recorded footprints in young and old animals which revealed a general age-related impairment of walking. In addition we found evidence for a limb-specific deterioration of the hindlimbs that was not observed in the forelimbs. Our results show that age-related changes of somatosensory cortical neurons display a complex pattern of regional specificity and parameter-dependence indicating that aging acts rather selectively on cortical processing of sensory information. The fact that RFs of the fore- and hindpaws do not co-vary in aged animals argues against degenerational processes on a global scale. We therefore conclude that age-related alterations are composed of plastic-adaptive alterations in response to modified use and degenerational changes developing with age. As a consequence, age-related changes need not be irreversible but can be subject to amelioration through training and stimulation