3,352 research outputs found
Rationale for windshield glass system specification requirements for shuttle orbiter
A preliminary procurement specification for the space shuttle orbiter windshield pane, and some of the design considerations and rationale leading to its development are presented. The windshield designer is given the necessary methods and procedures for assuring glass pane structural integrity by proof test. These methods and procedures are fully developed for annealed and thermally tempered aluminosilicate, borosilicate, and soda lime glass and for annealed fused silica. Application of the method to chemically tempered glass is considered. Other considerations are vision requirements, protection against bird impact, hail, frost, rain, and meteoroids. The functional requirements of the windshield system during landing, ferrying, boost, space flight, and entry are included
The Galactic Center as a point source of neutrons at EeV energies
The central region of our Galaxy is a very peculiar environment, containing
magnetic fields in excess of 100 mG and gas densities reaching ~ 10^4cm^-3.
This region was observed as a strong source of GeV and TeVs gammas, what
suggests that a mechanism of proton-neutron conversion could be taking place
therein. We propose that the Galactic Center must also be a source of EeV
neutrons due to the conversion of ultra high energy cosmic ray protons into
neutrons via p-p interactions inside this region. This scenario should be
falsifiable by the Pierre Auger Observatory after a few years of full exposure
Core structure of EAS in 10(15) to 10(17) eV
With the use of Akeno calorimeter, the attenuation of particles in concrete is analyzed as the function of the shower size of 10 to the 5th power to 10 to the 7th power. The attenuation length does not depend much on the shower size but depends a little on the shower age. The average value is approx. 150 g/sq cm for s = 0.5 to 0.85 and approx. 40 g/sq cm for s = 0.85 to 1.15. These values and their fluctuations are consistent with the equi-intensity curves of extensive air showers (EAS)
A numerical code to study the variability of Blazar emission
We present a numerical code, written in C, which can be used to simulate or
to analyze the emission of Blazars over the entire electromagnetic spectrum.
Our code can reproduce the following features: synchrotron emission, inverse
Compton emission (Thomson Klein-Nishina regime) external Compton emission,
accretion disk variability using a Cellular Automata algorithm, temporal
evolution of the emitting plasma energy distribution, flaring phenomena, light
curves in the rest and in the observer frame (taking account for time crossing
effects). In this paper we will show mainly the accretion disk simulation, and
the implications in the External Compton scenario.Comment: 4 pages, 2 eps figures. Poster to "The Physics of Relativistic Jets
in the CHANDRA and XMM Era" (Bologna CNR). Proceedings to be published in New
Astronomy Review
Measurement of energy muons in EAS at energy region larger thean 10(17) eV
A measurement of low energy muons in extensive air showers (EAS) (threshold energies are 0.25, 0.5, 0.75 and 1.38 GeV) was carried out. The density under the concrete shielding equivalent to 0.25 GeV at core distance less than 500 m and 0.5 GeV less than 150 m suffers contamination of electromagnetic components. Therefore the thickness of concrete shielding for muon detectors for the giant air shower array is determined to be 0.5 GeV equivalence. Effects of photoproduced muons are found to be negligible in the examined ranges of shower sizes and core distances. The fluctuation of the muon density in 90 sq m is at most 25% between 200 m and 600 m from the core around 10 to the 17th power eV
Exogenously added naphthols induce three glucosyltransferases, and are accumulated as glucosides in tobacco cells
Plants detoxify and accumulate several compounds as glucosides. In this work, detoxification of the exogenously added harmful compound naphthol in tobacco cells (Nicotiana tabacum L. Bright Yellow) was studied. When 250 μM of 1-naphthol or 2-naphthol was added to the tobacco cells, most of the naphthol was accumulated in the cell as glucosides and in further modified forms. The glucosylation activities against naphthols were increased in proportion to the concentration of naphthols in the culture medium. Addition of 1 mM naphthols caused cell death. Three glucosyltransferase genes, namely NtGT1a, NtGT1b and NtGT3 were isolated and characterized. The recombinant enzymes encoded by these genes showed glucosylation activity against naphthols and other phenolic compounds. It was also shown that these genes were induced following the addition of naphthols to the tobacco cells. These results suggest that naphthols are metabolized by glucosyltransferases whose production is inducible by naphthol itself.ArticlePlant Science. 164(2):231-240 (2003)journal articl
Implications of a Possible Clustering of Highest Energy Cosmic Rays
Very recently, a possible clustering of a subset of observed ultrahigh energy
cosmic rays above about 40EeV (4x10^19eV) in pairs near the supergalactic plane
was reported. We show that a confirmation of this effect would provide
information on origin and nature of these events and, in case of charged
primaries, imply interesting constraints on the extragalactic magnetic field.
The observed time correlation would most likely rule out an association of
these events with cosmological gamma ray bursts. If no prominent astrophysical
source candidates such as powerful radiogalaxies can be found, the existence of
a mechanism involving new fundamental physics would be favored.Comment: 10 latex pages, 1 postscript figure, uses aaspp4.sty, submitted to
Astrophysical Journal Letter
Molecular cloning and heterologous expression of novel glucosyltransferases from tobacco cultured cells that have broad substrate specificity and are induced by salicylic acid and auxin.
The definitive version is available at www.blackwell-synergy.com.Scopoletin is one of the phytoalexins in tobacco. Cells of the T-13 cell line (Nicotiana tabacum L. Bright Yellow) accumulate a large amount of scopoletin, also known as 7-hydroxy-6-methoxycoumarin, as a glucoconjugate, scopolin, in vacuoles. We report here the molecular cloning of glucosyltransferases that can catalyze the glucosylation of many kinds of secondary metabolites including scopoletin. Two cDNAs encoding glucosyltransferase (NtGT1a and NtGT1b) were isolated from a cDNA library derived from the tobacco T-13 cell line by screening with heterologous cDNAs as a probe. The deduced amino-acid sequences of NtGT1a and NtGT1b exhibited 92% identity with each other, ≈ 20–50% identities with other reported glucosyltransferases. Heterologous expression of these genes in Escherichia coli showed that the recombinant enzymes had glucosylation activity against both flavonoids and coumarins. They also strongly reacted with 2-naphthol as a substrate. These recombinant enzymes can utilize UDP-glucose as the sugar donor, but they can also utilize UDP-xylose as a weak donor. RNA blot analysis showed that these genes are induced by salicylic acid and auxin, but the time course of the expression was different. This result is similar to the changes in scopoletin glucosylation activity in these tobacco cells after addition of these plant growth regulators. These results might suggest that one of the roles of the products of these genes is scopoletin glucosylation, in response to salicylic acid and/or auxin, together with the other glucosyltransferases in tobacco cells.ArticleEuropean Journal of Biochemistry. 268(14):4086-4094 (2001)journal articl
A Novel Approach in Constraining Electron Spectra in Blazar Jets: The Case of Markarian 421
We report results from the observations of the well studied TeV blazar Mrk
421 with the Swift and the Suzaku satellites in December 2008. During the
observation, Mrk 421 was found in a relatively low activity state, with the
corresponding 2-10 keV flux of erg/s/cm^2. For the purpose
of robust constraining the UV-to-X-ray emission continuum we selected only the
data corresponding to truly simultaneous time intervals between Swift and
Suzaku, allowing us to obtain a good-quality, broad-band spectrum despite a
modest length (0.6 ksec) exposure. We analyzed the spectrum with the parametric
forward-fitting SYNCHROTRON model implemented in XSPEC assuming two different
representations of the underlying electron energy distribution, both well
motivated by the current particle acceleration models: a power-law distribution
above the minimum energy with an exponential cutoff at the
maximum energy , and a modified ultra-relativistic Maxwellian
with an equilibrium energy . We found that the latter implies
unlikely physical conditions within the blazar zone of Mrk 421. On the other
hand, the exponentially moderated power-law electron distribution gives two
possible sets of the model parameters: (i) flat spectrum with low minimum electron energy , and
(ii) steep spectrum with high minimum electron energy
. We discuss different interpretations of
both possibilities in the context of a diffusive acceleration of electrons at
relativistic, sub- or superluminal shocks. We also comment on how exactly the
gamma-ray data can be used to discriminate between the proposed different
scenarios.Comment: 18 pages, 2 figures; accepted for publication in the Astrophysical
Journa
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