330 research outputs found
A hypothalamic-thalamostriatal circuit that controls approach-avoidance conflict in rats
Survival depends on a balance between seeking rewards and avoiding potential threats, but the neural circuits that regulate this motivational conflict remain largely unknown. Using an approach-food vs. avoid-predator threat conflict test in rats, we identified a subpopulation of neurons in the anterior portion of the paraventricular thalamic nucleus (aPVT) which express corticotrophin-releasing factor (CRF) and are preferentially recruited during conflict. Inactivation of aPVTCRF neurons during conflict biases animal’s response toward food, whereas activation of these cells recapitulates the food-seeking suppression observed during conflict. aPVTCRF neurons project densely to the nucleus accumbens (NAc), and activity in this pathway reduces food seeking and increases avoidance. In addition, we identified the ventromedial hypothalamus (VMH) as a critical input to aPVTCRF neurons, and demonstrated that VMH-aPVT neurons mediate defensive behaviors exclusively during conflict. Together, our findings describe a hypothalamic-thalamostriatal circuit that suppresses reward-seeking behavior under the competing demands of avoiding threats.Fil: Engelke, D. S.. The University of Texas Health Science Center; Estados UnidosFil: Zhang, X. O.. The University of Texas Health Science Center; Estados UnidosFil: O’Malley, J. J.. The University of Texas Health Science Center; Estados UnidosFil: Fernandez Leon, Jose Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. Sede Olavarría del Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aire. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. Sede Olavarría del Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; ArgentinaFil: Li, S.. University of Manitoba; CanadáFil: Kirouac, G. J.. University of Manitoba; CanadáFil: Beierlein, M.. The University of Texas Health Science Center; Estados UnidosFil: Do Monte, F. H.. The University of Texas Health Science Center; Estados Unido
Total carotenoids pumpkin (C. moschata DUCH) of landraces after cooking: a preliminary study.
Total carotenoid content, a-carotene and b-carotene, of landrace pumpkins (Cucurbita moschata Duch): a preliminary study.
Landrace pumpkins occur in nature and their potential as source of pro-vitamin A may be investigated in order to be used in conventional plant breeding or biofortification programs, aiming to increase the total carotenoids and b-carotene contents. The objective of the study was to determine the total carotenoid, a-carotene, b-carotene and its isomers and contents in two landrace samples (A and B) of raw pumpkins (Cucurbita moschata) to verify its seed production potential.High Performance Liquid Chromatography andUV/Visible spectrophotometrywere used to determine a-carotene, b-carotene and its isomers, and total carotenoid contents, respectively. All analyses were carried out in triplicate. The results showedmean total carotenoid contents of 404.98 in sample A, and 234.21 ug/g in sample B. The a-carotene contents varied from 67.06 to 72.99 ug/g in samples A and B, respectively. All E-b-carotene was the most abundant isomer found varying from 244.22 to 141.95 ug/g in samples A and B, respectively. The 9 and 13-Z-b-carotene isomers were still found in lowconcentrations in both analyzed landrace samples. The content of b-carotene inrawsampleAshowed to be promising for the production of seeds for cultivation and consumption
Fermi Large Area Telescope Observations of the Cosmic-Ray Induced gamma-ray Emission of the Earth's Atmosphere
We report on measurements of the cosmic-ray induced gamma-ray emission of
Earth's atmosphere by the Large Area Telescope onboard the Fermi Gamma-ray
Space Telescope. The LAT has observed the Earth during its commissioning phase
and with a dedicated Earth-limb following observation in September 2008. These
measurements yielded 6.4 x 10^6 photons with energies >100MeV and ~250hours
total livetime for the highest quality data selection. This allows the study of
the spatial and spectral distributions of these photons with unprecedented
detail. The spectrum of the emission - often referred to as Earth albedo
gamma-ray emission - has a power-law shape up to 500 GeV with spectral index
Gamma = 2.79+-0.06.Comment: Accepted for publication in PR
Fermi-LAT Study of Gamma-ray Emission in the Direction of Supernova Remnant W49B
We present an analysis of the gamma-ray data obtained with the Large Area
Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the direction of
SNR W49B (G43.3-0.2). A bright unresolved gamma-ray source detected at a
significance of 38 sigma is found to coincide with SNR W49B. The energy
spectrum in the 0.2-200 GeV range gradually steepens toward high energies. The
luminosity is estimated to be 1.5x10^{36} (D/8 kpc)^2 erg s^-1 in this energy
range. There is no indication that the gamma-ray emission comes from a pulsar.
Assuming that the SNR shell is the site of gamma-ray production, the observed
spectrum can be explained either by the decay of neutral pi mesons produced
through the proton-proton collisions or by electron bremsstrahlung. The
calculated energy density of relativistic particles responsible for the LAT
flux is estimated to be remarkably large, U_{e,p}>10^4 eV cm^-3, for either
gamma-ray production mechanism.Comment: 9 pages, 10 figure
Fermi observations of high-energy gamma-ray emission from GRB 090217A
The Fermi observatory is advancing our knowledge of Gamma-Ray Bursts (GRBs)
through pioneering observations at high energies, covering more than 7 decades
in energy with the two on-board detectors, the Large Area Telescope (LAT) and
the Gamma-ray Burst Monitor (GBM). Here we report on the observation of the
long GRB 090217A which triggered the GBM and has been detected by the LAT with
a significance greater than 9 sigma. We present the GBM and LAT observations
and on-ground analyses, including the time-resolved spectra and the study of
the temporal profile from 8 keV up to 1 GeV. All spectra are well reproduced by
a Band model. We compare these observations to the first two LAT-detected, long
bursts GRB 080825C and GRB 080916C. These bursts were found to have
time-dependent spectra and exhibited a delayed onset of the high-energy
emission, which are not observed in the case of GRB 090217A. We discuss some
theoretical implications for the high-energy emission of GRBs.Comment: 17 pages, 4 figures. Contact Authors: Fred, Piron; Sara, Cutini;
Andreas, von Kienli
Fermi Large Area Telescope observations of the Vela-X Pulsar Wind Nebula
We report on gamma-ray observations in the off-pulse window of the Vela
pulsar PSR B0833-45, using 11 months of survey data from the Fermi Large Area
Telescope (LAT). This pulsar is located in the 8 degree diameter Vela supernova
remnant, which contains several regions of non-thermal emission detected in the
radio, X-ray and gamma-ray bands. The gamma-ray emission detected by the LAT
lies within one of these regions, the 2*3 degrees area south of the pulsar
known as Vela-X. The LAT flux is signicantly spatially extended with a best-fit
radius of 0.88 +/- 0.12 degrees for an assumed radially symmetric uniform disk.
The 200 MeV to 20 GeV LAT spectrum of this source is well described by a
power-law with a spectral index of 2.41 +/- 0.09 +/- 0.15 and integral flux
above 100 MeV of (4.73 +/- 0.63 +/- 1.32) * 10^{-7} cm^{-2} s^{-1}. The first
errors represent the statistical error on the fit parameters, while the second
ones are the systematic uncertainties. Detailed morphological and spectral
analyses give strong constraints on the energetics and magnetic field of the
pulsar wind nebula (PWN) system and favor a scenario with two distinct electron
populations.Comment: 21 pages, 5 figures, accepted for publication in Astrophysical
Journa
Fermi LAT Search for Photon Lines from 30 to 200 GeV and Dark Matter Implications
Dark matter (DM) particle annihilation or decay can produce monochromatic
-rays readily distinguishable from astrophysical sources. -ray
line limits from 30 GeV to 200 GeV obtained from 11 months of Fermi Large Area
Space Telescope data from 20-300 GeV are presented using a selection based on
requirements for a -ray line analysis, and integrated over most of the
sky. We obtain -ray line flux upper limits in the range , and give corresponding DM annihilation
cross-section and decay lifetime limits. Theoretical implications are briefly
discussed.Comment: 6 pages, 1 figure. Accepted for publication by The Physical Review
Letter
Constraints on dark matter models from a Fermi LAT search for high-energy cosmic-ray electrons from the Sun
During its first year of data taking, the Large Area Telescope (LAT) onboard
the Fermi Gamma-Ray Space Telescope has collected a large sample of high-energy
cosmic-ray electrons and positrons (CREs). We present the results of a
directional analysis of the CRE events, in which we searched for a flux excess
correlated with the direction of the Sun. Two different and complementary
analysis approaches were implemented, and neither yielded evidence of a
significant CRE flux excess from the Sun. We derive upper limits on the CRE
flux from the Sun's direction, and use these bounds to constrain two classes of
dark matter models which predict a solar CRE flux: (1) models in which dark
matter annihilates to CREs via a light intermediate state, and (2) inelastic
dark matter models in which dark matter annihilates to CREs.Comment: 18 pages, 8 figures, accepted for publication in Physical Review D -
contact authors: Francesco Loparco ([email protected]), M. Nicola Mazziotta
([email protected]) and Jennifer Siegal-Gaskins ([email protected]
Gamma-ray flares from the Crab Nebula
A young and energetic pulsar powers the well-known Crab Nebula. Here we
describe two separate gamma-ray (photon energy >100 MeV) flares from this
source detected by the Large Area Telescope on board the Fermi Gamma-ray Space
Telescope. The first flare occurred in February 2009 and lasted approximately
16 days. The second flare was detected in September 2010 and lasted
approximately 4 days. During these outbursts the gamma-ray flux from the nebula
increased by factors of four and six, respectively. The brevity of the flares
implies that the gamma rays were emitted via synchrotron radiation from PeV
(10^15 eV) electrons in a region smaller than 1.4 10^-2 pc. These are the
highest energy particles that can be associated with a discrete astronomical
source, and they pose challenges to particle acceleration theory.Comment: Contact authors: Rolf Buehler,[email protected]; Stefan
Funk,[email protected]; Roger Blandford,rdb3@stanford ; 16 pages,2
figure
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