4,202 research outputs found
VHE gamma-ray observations of the young synchrotron-dominated SNRs G1.9+0.3 and G330.2+1.0 with H.E.S.S
Supernova remnants (SNRs) are widely considered to be accelerators of cosmic
rays (CR). They are also expected to produce very-high-energy (VHE;
GeV) gamma rays through interactions of high-energy particles with the
surrounding medium and photon fields. They are, therefore, promising targets
for observations with ground-based imaging atmospheric Cherenkov telescopes
like the H.E.S.S. telescope array. VHE gamma-ray emission has already been
discovered from a number of SNRs, establishing them as a prominent source class
in the VHE domain. Of particular interest are the handful of SNRs whose X-ray
spectra are dominated by non-thermal synchrotron emission, such as the VHE
gamma-ray emitters RX J0852.0-4622 (Vela Jr.) and RX J1713-3946. The shell-type
SNRs G1.9+0.3 and G330.2+1.0 also belong to this subclass and are further
notable for their young ages ( kyr), especially G1.9+0.3, which was
recently determined to be the youngest SNR in the Galaxy ( yr). These
unique characteristics motivated investigations with H.E.S.S. to search for VHE
gamma rays. The results of the H.E.S.S. observations and analyses are
presented, along with implications for potential particle acceleration
scenarios.Comment: ICRC 2011 proceedings, 4 pages, 2 figures, 3 table
Enhanced Optical Dichroism of Graphene Nanoribbons
The optical conductivity of graphene nanoribbons is analytical and exactly
derived. It is shown that the absence of translation invariance along the
transverse direction allows considerable intra-band absorption in a narrow
frequency window that varies with the ribbon width, and lies in the THz range
domain for ribbons 10-100nm wide. In this spectral region the absorption
anisotropy can be as high as two orders of magnitude, which renders the medium
strongly dichroic, and allows for a very high degree of polarization (up to
~85) with just a single layer of graphene. The effect is resilient to level
broadening of the ribbon spectrum potentially induced by disorder. Using a
cavity for impedance enhancement, or a stack of few layer nanoribbons, these
values can reach almost 100%. This opens a potential prospect of employing
graphene ribbon structures as efficient polarizers in the far IR and THz
frequencies.Comment: Revised version. 10 pages, 7 figure
Avaliação de cultivares de alface crespa sob cultivo protegido no município de Iranduba/AM.
O objetivo deste trabalho foi avaliar o desempenho de cultivares de alface crespa sob cultivo protegido no município de Iranduba/AM.Suplemento. Trabalho apresentado no 52. Congresso Brasileiro de Olericultura, Salvador, 2012
Produção de sementes de coentro em função dos tipos de adubação.
O objetivo deste trabalho foi avaliar a influência de tipos de adubo na produção de sementes de coentro (Coriandrum sativum L.) nas condições de Botucatu-SP. Utilizou-se sementes Aglofora S.A, cv. Português
Atividade antihelmintica in vitro do óleo essencial de Lippia alba no controle de monogenóides de tambaqui (Colossoma macropomum).
O objetivo deste estudo foi avaliar a atividade antihelmíntica in vitro do óleo essencial de Lippia alba no controle de monogenóides de tambaqui (Colossoma macropomum)
The first Frontier Fields cluster: 4.5{\mu}m excess in a z~8 galaxy candidate in Abell 2744
We present in this letter the first analysis of a z~8 galaxy candidate found
in the Hubble and Spitzer imaging data of Abell 2744, as part of the Hubble
Frontier Fields legacy program. We applied the most commonly-used methods to
select exceptionally high-z galaxies by combining non-detection and
color-criteria using seven HST bands. We used GALFIT on IRAC images for fitting
and subtracting contamination of bright nearby sources. The physical properties
have been inferred from SED-fitting using templates with and without nebular
emission. This letter is focussed on the brightest candidate we found
(m=26.2) over the 4.9 arcmin field of view covered by the WFC3.
It shows a non-detection in the ACS bands and at 3.6{\mu}m whereas it is
clearly detected at 4.5{\mu}m with rather similar depths. This break in the
IRAC data could be explained by strong [OIII]+H{\beta} lines at z~8 which
contribute to the 4.5{\mu}m photometry. The best photo-z is found at
z~8.0, although solutions at low-redshift (z~1.9) cannot be
completely excluded, but they are strongly disfavoured by the SED-fitting work.
The amplification factor is relatively small at {\mu}=1.490.02. The Star
Formation Rate in this object is ranging from 8 to 60 Mo/yr, the stellar mass
is in the order of M=(2.5-10) x 10Mo and the size is
r~0.350.15 kpc. This object is one of the first z~8 LBG candidates showing
a clear break between 3.6{\mu}m and 4.5{\mu}m which is consistent with the IRAC
properties of the first spectroscopically confirmed galaxy at a similar
redshift. Due to its brightness, the redshift of this object could potentially
be confirmed by near infrared spectroscopy with current 8-10m telescopes. The
nature of this candidate will be revealed in the coming months with the arrival
of new ACS and Spitzer data, increasing the depth at optical and near-IR
wavelengths.Comment: 4 pages, 2 figures, Accepted for publication in Astronomy and
Astrophysics Letter
Efeito da palhada sobre a temperatura do solo, em cultivo protegido de pimentão nas condições do Amazonas.
O objetivo desse trabalho foi avaliar se o uso da palhada, em cultivo protegido de pimentão nas condições de altas temperaturas do Amazonas, auxilia na redução da temperatura do solo
Anderson localization of light in disordered superlattices containing graphene layers
We theoretically investigate light propagation and Anderson localization in
one-dimensional disordered superlattices composed of dielectric stacks with
graphene sheets in between. Disorder is introduced either on graphene material
parameters ({\it e.g.} Fermi energy) or on the widths of the dielectric stacks.
We derive an analytic expression for the localization length , and compare
it to numerical simulations using transfer matrix technique; a very good
agreement is found. We demonstrate that the presence of graphene may strongly
attenuate the anomalously delocalised Breswter modes, and is at the origin of a
periodic dependence of on frequency, in contrast to the usual asymptotic
decay, . By unveiling the effects of graphene on
Anderson localization of light, we pave the way for new applications of
graphene-based, disordered photonic devices in the THz spectral range.We thank W. Kort-Kamp for useful discussions. A.
J. Chaves acknowledge the scholarship from the Brazilian
agency CNPq (Conselho Nacional de Desenvolvimento
Científico e Tecnológico). N.M.R.P. acknowledges financial
support from the Graphene Flagship Project (Contract No.
CNECT-ICT-604391). F.A.P. thanks the Optoelectronics Research Centre and Centre for Photonic Metamaterials, University
of Southampton, for the hospitality, and CAPES for
funding his visit (Grant No. BEX 1497/14-6). F.A.P. also acknowledges
CNPq (Grant No. 303286/2013-0) for financial
support
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