357 research outputs found
Solar Chameleons
We analyse the creation of chameleons deep inside the sun and their
subsequent conversion to photons near the magnetised surface of the sun. We
find that the spectrum of the regenerated photons lies in the soft X-ray
region, hence addressing the solar corona problem. Moreover, these
back-converted photons originating from chameleons have an intrinsic difference
with regenerated photons from axions: their relative polarisations are mutually
orthogonal before Compton interacting with the surrounding plasma. Depending on
the photon-chameleon coupling and working in the strong coupling regime of the
chameleons to matter, we find that the induced photon flux, when regenerated
resonantly with the surrounding plasma, coincides with the solar flux within
the soft X-ray energy range. Moreover, using the soft X-ray solar flux as a
prior, we find that with a strong enough photon-chameleon coupling the
chameleons emitted by the sun could lead to a regenerated photon flux in the
CAST pipes, which could be within the reach of CAST with upgraded detector
performance. Then, axion helioscopes have thus the potential to detect and
identify particles candidates for the ubiquitous dark energy in the universe.Comment: 16 pages, 6 figures
Kinematics of Tycho-2 Red Giant Clump Stars
Based on the Ogorodnikov-Milne model, we analyze the proper motions of 95 633
red giant clump (RGC) stars from the Tycho-2 Catalogue. The following Oort
constants have been found: A = 15.9+-0.2 km/s/kpc and B = -12.0+-0.2 km/s/kpc.
Using 3632 RGC stars with known proper motions, radial velocities, and
photometric distances, we show that, apart from the star centroid velocity
components relative to the Sun, only the model parameters that describe the
stellar motions in the XY plane differ significantly from zero. We have studied
the contraction (a negative K-effect) of the system of RGC stars as a function
of their heliocentric distance and elevation above the Galactic plane. For a
sample of distant (500--1000 pc) RGC stars located near the Galactic plane
(|Z|<200 pc) with an average distance of d=0.7 kpc, the contraction velocity is
shown to be Kd= -3.5+-0.9 km/s; a noticeable vertex deviation, lxy = 9.1+-0.5
degrees, is also observed for them. For stars located well above the Galactic
plane (|Z|>=200 pc), these effects are less pronounced, Kd = -1.7+-0.5 km/s and
lxy = 4.9+-0.6 degrees. Using RGC stars, we have found a rotation around the
Galactic X axis directed toward the Galactic center with an angular velocity of
-2.5+-0.3 km/s/kpc, which we associate with the warp of the Galactic
stellar-gaseous disk.Comment: 23 pages, 7 figures, 4 table
Design and performance of the ADMX SQUID-based microwave receiver
The Axion Dark Matter eXperiment (ADMX) was designed to detect ultra-weakly
interacting relic axion particles by searching for their conversion to
microwave photons in a resonant cavity positioned in a strong magnetic field.
Given the extremely low expected axion-photon conversion power we have
designed, built and operated a microwave receiver based on a Superconducting
QUantum Interference Device (SQUID). We describe the ADMX receiver in detail as
well as the analysis of narrow band microwave signals. We demonstrate the
sustained use of a SQUID amplifier operating between 812 and 860 MHz with a
noise temperature of 1 K. The receiver has a noise equivalent power of
1.1x10^-24 W/sqrt(Hz) in the band of operation for an integration time of
1.8x10^3 s.Comment: 8 pages, 12 figures, Submitted to Nuclear Inst. and Methods in
Physics Research,
A Search for Scalar Chameleons with ADMX
Scalar fields with a "chameleon" property, in which the effective particle
mass is a function of its local environment, are common to many theories beyond
the standard model and could be responsible for dark energy. If these fields
couple weakly to the photon, they could be detectable through the "afterglow"
effect of photon-chameleon-photon transitions. The ADMX experiment was used in
the first chameleon search with a microwave cavity to set a new limit on scalar
chameleon-photon coupling excluding values between 2*10^9 and 5*10^14 for
effective chameleon masses between 1.9510 and 1.9525 micro-eV.Comment: 4 pages, 3 figure
Desenvolvimento e aceitação de barra de cereal sabor umbu (Spondias tuberosa).
Produto bastante consumido nos dias atuais, a barra de cereal é uma alternativa saudável e prática. Este trabalho teve como objetivo formular barra de cereais contendo umbu, de preparo simples e baixo custo, e avaliar a aceitação do produto pelos consumidores, afim de propor a possÃvel elaboração por pequenas agroindústrias. Foram desenvolvidas três formulações contendo ingredientes em diferentes proporções. A amostra 1 foi composta por xarope de polpa de umbu com sacarose, aveia prensada, coco ralado, castanha de caju, flocos de arroz, uva passa e doce de umbu em corte. A amostra 2 continha xarope de polpa de umbu com glicose, aveia prensada, coco ralado, castanha de caju, flocos de arroz e uva passa; e a amostra 3 foi composta por xarope caramelizado de polpa de umbu com sacarose, aveia prensada, coco ralado, castanha de caju, flocos de arroz e uva passa. Foi realizado teste de aceitação das barrinhas com 50 consumidores que avaliaram o quanto gostaram do produto utilizando escala hedônica de nove pontos (1=desgostei x extremamente; 9=gostei extremamente), além do grau de intenção de compra (1=certamente não compraria; 5=certamente compraria). Para aceitação da aparência, cor e textura as três formulações obtiveram notas sem diferença estatÃstica (p < 0.05) entre si, e acima de 7, equivalente a ?gostei moderadamente? na escala. Para aroma, sabor e impressão global, as amostras 1 e 3 destacaram -se da amostra 2, sendo que a amostra 3 obteve as maiores médias de aceitação. Com relação ao sabor, a amostra 3 obteve média 8, equivalente a ?gostei muito? na escala. Segundo o teste de intenção de compra, 60% dos consumidores responderam que ?certamente comprariam? a amostra 3 caso estivesse a venda. Através desse trabalho pode-se concluir que as formulações testadas apresentaram bons resultados de aceitação, e que a formulação com xarope caramelizado foi a preferida pelos consumidores
A method to localize gamma-ray bursts using POLAR
The hard X-ray polarimeter POLAR aims to measure the linear polarization of
the 50-500 keV photons arriving from the prompt emission of gamma-ray bursts
(GRBs). The position in the sky of the detected GRBs is needed to determine
their level of polarization. We present here a method by which, despite of the
polarimeter incapability of taking images, GRBs can be roughly localized using
POLAR alone. For this purpose scalers are attached to the output of the 25
multi-anode photomultipliers (MAPMs) that collect the light from the POLAR
scintillator target. Each scaler measures how many GRB photons produce at least
one energy deposition above 50 keV in the corresponding MAPM. Simulations show
that the relative outputs of the 25 scalers depend on the GRB position. A
database of very strong GRBs simulated at 10201 positions has been produced.
When a GRB is detected, its location is calculated searching the minimum of the
chi2 obtained in the comparison between the measured scaler pattern and the
database. This GRB localization technique brings enough accuracy so that the
error transmitted to the 100% modulation factor is kept below 10% for GRBs with
fluence Ftot \geq 10^(-5) erg cm^(-2) . The POLAR localization capability will
be useful for those cases where no other instruments are simultaneously
observing the same field of view.Comment: 13 pages, 10 figure
A SQUID-based microwave cavity search for dark-matter axions
Axions in the micro eV mass range are a plausible cold dark matter candidate
and may be detected by their conversion into microwave photons in a resonant
cavity immersed in a static magnetic field. The first result from such an axion
search using a superconducting first-stage amplifier (SQUID) is reported. The
SQUID amplifier, replacing a conventional GaAs field-effect transistor
amplifier, successfully reached axion-photon coupling sensitivity in the band
set by present axion models and sets the stage for a definitive axion search
utilizing near quantum-limited SQUID amplifiers.Comment: 4 pages, 5 figures, submitted to PR
Development of methodology for the determination of organic acids in must, grape juice and wine by high performance liquid chromatography (HPLC).
Development of methodology for the determination of organic acids in must, grape juice and wine by high performance liquid chromatography (HPLC).
Resumo. IUFoST 2012
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