1,021 research outputs found
Application of the aerodynamic energy concept to flutter suppression and gust alleviation by use of active controls
The effects of active controls on flutter suppression and gust alleviation of the Arava twin turboprop STOL transport and the Westwind twinjet business transport are investigated. The active control surfaces are introduced in pairs which include, in any chosen wing strip, a 20-percent chord leading-edge control and a 20-percent chord trailing-edge control. Each control surface is driven by a combined linear-rotational sensor system located on the activated strip. The control law is based on the concept of aerodynamic energy and utilizes previously optimized control law parameters based on two-dimensional aerodynamic theory. The best locations of the activated system along the span of the wing are determined for bending-moment alleviation, reduction in fuselage accelerations, and flutter suppression. The effectiveness of the activated system over a wide range of maximum control deflections is also determined. Two control laws are investigated. The first control law utilizes both rigid-body and elastic contributions of the motion. The second control law employs primarily the elastic contribution of the wing and leads to large increases in the activated control effectiveness as compared with the basic control law. The results indicate that flutter speed can be significantly increased (over 70 percent increase) and that the bending moment due to gust loading can be almost totally eliminated by a control system of about 10 to 20 percent span with reasonable control-surface rotations
How many Ultra High Energy Cosmic Rays could we expect from Centaurus A?
The Pierre Auger Observatory has associated a few ultra high energy cosmic
rays with the direction of Centaurus A. This source has been deeply studied in
radio, infrared, X-ray and -rays (MeV-TeV) because it is the nearest
radio-loud active galactic nuclei.
Its spectral energy distribution or spectrum shows two main peaks, the low
energy peak, at an energy of eV, and the high energy peak, at about
150 keV.
There is also a faint very high energy (E 100 GeV) -ray
emission fully detected by the High Energy Stereoscopic System experiment. In
this work we describe the entire spectrum, the two main peaks with a
Synchrotron/Self-Synchrotron Compton model and, the Very High Energy emission
with a hadronic model. We consider p and interactions. For the
p interaction, we assume that the target photons are those produced at
150 keV in the leptonic processes. On the other hand, for the pp interaction we
consider as targets the thermal particle densities in the lobes. Requiring a
satisfactory description of the spectra at very high energies with p
interaction we obtain an excessive luminosity in ultra high energy cosmic rays
(even exceeding the Eddington luminosity). However, when considering pp
interaction to describe the -spectrum, the obtained number of ultra
high energy cosmic rays are in agreement with Pierre Auger observations.
Moreover, we calculate the possible neutrino signal from pp interactions on a
Km neutrino telescope using Monte Carlo simulations.Comment: Accepted in Ap
X-ray/gamma-ray flux correlations in the BL Lacs Mrk 421 and 501 using HAWC data
The HAWC gamma ray observatory is located at the Sierra Negra Volcano in
Puebla, Mexico, at an altitude of 4,100 meters. HAWC is a wide field of view
array of 300 water Cherenkov detectors that are continuously surveying ~ 2sr of
the sky, operating since March 2015. The large collected data sample allows
HAWC to perform an unbiased monitoring of the BL Lac Mrk 421. This is the
closest and brightest known extragalactic high-synchrotron-peaked BL Lac in the
gamma-ray/X- ray bands and is extensively monitored by the Large Area Telescope
(LAT) on-board the Fermi satellite, and the BAT and XRT instruments of the
Swift satellite. In this work, we use 25 months of HAWC data together with
Swift-XRT data to characterize potential correlations between both wavelengths.
This analysis shows that HAWC and Swift-XRT data are correlated even stronger
than expected for quasi-simultaneous observations.Comment: Presented at the 35th International Cosmic Ray Conference (ICRC2017),
Bexco, Busan, Korea. See arXiv:1708.02572 for all HAWC contribution
Discovery of 21cm absorption in a DLA towards TXS 0311+430: The first low spin temperature absorber at z > 1
We report the detection of HI 21 cm absorption from the damped
Lyman- system (DLA) towards TXS 0311+430, with the Green Bank
Telescope. The 21 cm absorption has a velocity spread (between nulls) of km s and an integrated optical depth of km s. We also present new Giant Metrewave Radio
Telescope 602 MHz imaging of the radio continuum. TXS 0311+430 is unresolved at
this frequency, indicating that the covering factor of the DLA is likely to be
high. Combining the integrated optical depth with the DLA HI column density of
\nhi = \cm, yields a spin temperature of K, assuming a covering factor of unity. This is the first case of
a low spin temperature ( DLA and is among the lowest
ever measured in any DLA. Indeed, the measured for this DLA is similar to
values measured in the Milky Way and local disk galaxies. We also determine a
lower limit (Si/H) solar for the DLA metallicity, amongst the
highest abundances measured in DLAs at any redshift. Based on low redshift
correlations, the low , large 21 cm absorption width and high metallicity
all suggest that the DLA is likely to arise in a massive,
luminous disk galaxy.Comment: 5 pages, 3 figures. Accepted for publication in MNRAS (Letters
The differential contribution of tumour necrosis factor to thermal and mechanical hyperalgesia during chronic inflammation
Therapies directed against tumour necrosis factor (TNF) are effective for the treatment of rheumatoid arthritis and reduce pain scores in this condition. In this study, we sought to explore mechanisms by which TNF contributes to inflammatory pain in an experimental model of arthritis. The effects of an anti-TNF agent, etanercept, on behavioural pain responses arising from rat monoarthritis induced by complete Freund's adjuvant were assessed and compared with expression of TNF receptors (TNFRs) by dorsal root ganglion (DRG) cells at corresponding time points. Etanercept had no effect on evoked pain responses in normal animals but exerted a differential effect on the thermal and mechanical hyperalgesia associated with rat arthritis induced by complete Freund's adjuvant (CFA). Joint inflammation was associated with increased TNFR1 and TNFR2 expression on DRG cells, which was maintained throughout the time course of the model. TNFR1 expression was increased in neuronal cells of the DRG bilaterally after arthritis induction. In contrast, TNFR2 expression occurred exclusively on nonneuronal cells of the macrophage-monocyte lineage, with cell numbers increasing in a TNF-dependent fashion during CFA-induced arthritis. A strong correlation was observed between numbers of macrophages and the development of mechanical hyperalgesia in CFA-induced arthritis. These results highlight the potential for TNF to play a vital role in inflammatory hyperalgesia, both by a direct action on neurons via TNFR1 and by facilitating the accumulation of macrophages in the DRG via a TNFR2-mediated pathway
Do the fundamental constants change with time ?
Comparisons between the redshifts of spectral lines from
cosmologically-distant galaxies can be used to probe temporal changes in
low-energy fundamental constants like the fine structure constant and the
proton-electron mass ratio. In this article, I review the results from, and the
advantages and disadvantages of, the best techniques using this approach,
before focussing on a new method, based on conjugate satellite OH lines, that
appears to be less affected by systematic effects and hence holds much promise
for the future.Comment: 15 pages, 3 figures. This is an electronic version of an invited
review article for Mod. Phys. Lett. A, published as [Mod. Phys. Lett. A, Vol.
23, No. 32, 2008, pp. 2711] (copyright World Scientific Publishing Company;
http://www.worldscientific.com/
Statistical properties of Faraday rotation measure from large-scale magnetic fields in intervening disc galaxies
To constrain the large-scale magnetic field strengths in cosmologically
distant galax- ies, we derive the probability distribution function of Faraday
rotation measure (RM) when random lines of sight pass through a sample of disc
galaxies, with axisymmetric large-scale magnetic fields. We find that the width
of the RM distribution of the galaxy sample is directly related to the mean
large-scale field strength of the galaxy population, provided the dispersion
within the sample is lower than the mean value. In the absence of additional
constraints on parameters describing the magneto-ionic medium of the
intervening galaxies, and in the situation where RMs produced in the
intervening galaxies have already been statistically isolated from other RM
contributions along the lines of sight, our simple model of the magneto-ionic
medium in disc galaxies suggests that the mean large-scale magnetic field of
the population can be measured to within ~ 50% accuracy.Comment: 4 pages, Proceedings of FM8 "New Insights in Extragalactic Magnetic
Fields", XXXth General Assembly of the IAU, Vienna, August 20-31, 201
- …