2,784 research outputs found
Microstructural changes of 'rocha' pear following storage under controlled atmosphere
This research effort was aimed at evaluating the influence of storage (for 4 mo at 2°C), under various controlled atmospheres (viz. 1.9 kPa O2 + 4.9 kPa CO2, 1.9 kPa O2 + 0.5 kPa CO2 and 1.9 kPa O2 + 0 kPa CO2), on the microstructure of ′Rocha′ pear. Toward this goal, the morphology of cellular disassembly, as well as the quantity of granules and intercellular space using scanning electron microscopy (SEM), were tentatively correlated with sensory and instrumental firmness, by 1, 6 and 8 d of exposure to air, at room temperature, after storage. A specific methodology, based on panel evaluation of SEM images, was developed and statistically validated. The degree of cellular disassembly increased throughout exposure time to air at room temperature. Pears stored under 1.9 kPa O2 + 0.5 kPa CO2 yielded a degree of cellular disassembly similar to that of the control
First report of Solanum sisymbriifolium and S. americanum as Natural weed hosts of Tomato chlorosis virus (Genus Crinivirus) in South America.
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Entangled-State Lithography: Tailoring any Pattern with a Single State
We demonstrate a systematic approach to Heisenberg-limited lithographic image
formation using four-mode reciprocal binominal states. By controlling the
exposure pattern with a simple bank of birefringent plates, any pixel pattern
on a grid, occupying a square with the side half a
wavelength long, can be generated from a -photon state.Comment: 4 pages, 4 figure
Upper limit for gamma-ray emission above 140 GeV from the dwarf spheroidal galaxy Draco
The nearby dwarf spheroidal galaxy Draco with its high mass to light ratio is
one of the most auspicious targets for indirect dark matter searches.
Annihilation of hypothetical DM particles can result in high-energy gamma-rays,
e.g. from neutralino annihilation in the supersymmetric framework. With the
MAGIC telescope a search for a possible DM signal originating from Draco was
performed during 2007. The analysis of the data results in a flux upper limit
of 1.1x10^-11 photons cm^-2 sec^-1 for photon energies above 140 GeV, assuming
a point like source. Furthermore, a comparison with predictions from
supersymmetric models is given. While our results do not constrain the mSUGRA
phase parameter space, a very high flux enhancement can be ruled out.Comment: Accepted for publication by Astrophysical Journa
Systematic search for VHE gamma-ray emission from X-ray bright high-frequency BL Lac objects
All but three (M87, BL Lac and 3C 279) extragalactic sources detected so far
at very high energy (VHE) gamma-rays belong to the class of high-frequency
peaked BL Lac (HBL) objects. This suggested to us a systematic scan of
candidate sources with the MAGIC telescope, based on the compilation of X-ray
blazars by Donato et al. (2001). The observations took place from December 2004
to March 2006 and cover sources on the northern sky visible under small zenith
distances zd < 30 degrees at culmination. The sensitivity of the search was
planned for detecting X-ray bright F(1 keV) > 2 uJy) sources emitting at least
the same energy flux at 200 GeV as at 1 keV. In order to avoid strong gamma-ray
attenuation close to the energy threshold, the redshift of the sources was
constrained to values z<0.3. Of the fourteen sources observed, 1ES 1218+304 and
1ES 2344+514 have been detected in addition to the known bright TeV blazars Mrk
421 and Mrk 501. A marginal excess of 3.5 sigma from the position of 1ES
1011+496 was observed and has been confirmed as a source of VHE gamma-rays by a
second MAGIC observation triggered by a high optical state (Albert et al.
2007). For the remaining sources, we present here the 99% confidence level
upper limits on the integral flux above ~200 GeV. We characterize the sample of
HBLs (including all HBLs detected at VHE so far) by looking for correlations
between their multi-frequency spectral indices determined from simultaneous
optical, archival X-ray, and radio luminosities, finding that the VHE emitting
HBLs do not seem to constitute a unique subclass. The absorption corrected
gamma-ray luminosities at 200 GeV of the HBLs are generally not higher than
their X-ray luminosities at 1 keV.Comment: 15 pages, 7 figures, 5 tables, submitted to ApJ (revised version
Search for very high energy gamma radiation from the radio bright region DR4 of the SNR G78.2+2.1
Data from the HEGRA air shower array are used to set an upper limit on the emission of gamma-radiation above 25 (18) TeV from the direction of the radio bright region DR4 within the SNR G78.2 + 2.1 of 2.5 (7.1). 10^-13 cm^-2 sec^-1. The shock front of SNR G78.2 + 2.1 probably recently overtook the molecular cloud Gong 8 which then acts as a target for the cosmic rays produced within the SNR, thus leading to the expectation of enhanced gamma-radiation. Using a model of Drury, Aharonian and Völk which assumes that SNRs are the sources of galactic cosmic rays via first order Fermi acceleration, we calculated a theoretical prediction for the gamma-ray flux from the DR4 region and compared it with our experimental flux limit. Our 'best estimate' value for the predicted flux lies a factor of about 18 above the upper limit for gamma-ray energies above 25 TeV. Possible reasons for this discrepancy are discussed
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