836 research outputs found
Analysis of cancellation in two-dimensional magnetohydrodynamic turbulence
A signed measure analysis of two-dimensional intermittent magnetohydrodynamic
turbulence is presented. This kind of analysis is performed to characterize the
scaling behavior of the sign-oscillating flow structures, and their geometrical
properties. In particular, it is observed that cancellations between positive
and negative contributions of the field inside structures, are inhibited for
scales smaller than the Taylor microscale, and stop near the dissipative scale.
Moreover, from a simple geometrical argument, the relationship between the
cancellation exponent and the typical fractal dimension of the structures in
the flow is obtained.Comment: 21 pages, 5 figures (3 .jpg not included in the latex file
Differences in the Severity of General Aviation Accidents by Age: A Preliminary Examination
This research utilized the NTSB aviation accident and incident database system from 1982 to 2014 to examine differences in the severity of accidents by age for aviation accidents. Accidents were separated by commercial and general aviation (GA). There were 74,686 entries, after excluding home built aircraft, helicopters, and gliders, consisting of 7,203 commercial and 61,363 GA accidents. For commercial, male pilots made up 97.4%, (mean age = 41.75, (SD=10.88). Female pilots (2.6%), had a mean age of 43.51 (SD=9.71). Ages were significantly different, t(7009)=8.76, pSD=14.63).
Damage to the aircraft and injury of crew/passengers as a function of pilot age was examined separately using ANOVA for commercial and GA. For commercial operation, damage levels of none, minor, substantial, and destroyed produced a significant difference by age, F(3, 7197)=40.558, pF(3,60302)=4.06, p=.007. There were significant differences between no damage and substantial (p=.001) and destroyed (p=.005) but no other levels.
This study indicated that there are differences in the degree of damage related to aviation accidents based on age. Additional examination of the causes of accidents, and at what age the increase is observed, is needed to ensure aviation safety for aging pilots
Macro-habitat preferences by the African manatee and crocodiles – ecological and conservation implications
African manatees (<i>Trichechus senegalensis</i>) and crocodiles are threatened species in parts of their range. In West Africa, crocodiles may constitute the main predators for manatees apart from humans. Here, we explore the macro-habitat selection of manatees and two species of crocodiles (West African crocodiles <i>Crocodylus suchus</i> and dwarf crocodile <i>Osteolaemus tetraspis</i>) in the Niger Delta (Nigeria), testing the hypotheses that (i) manatees may avoid crocodiles in order to minimize risks of predation, and (ii) the two crocodile species do compete. The study was carried out between 1994 and 2010 with a suite of different field techniques. We observed that the main macro-habitat types were freshwater rivers and coastal lagoons for manatees, mangroves for West African crocodiles, and rivers and creeks for dwarf crocodiles, with (i) the three species differing significantly in terms of their macro-habitat type selection, and (ii) significant seasonal influence on habitat selection of each species. Null models for niche overlap showed a significantly lower overlap in macro-habitat type use between manatee and crocodiles, whereas the two crocodiles were relatively similar. Null model analyses did not indicate any competitive interactions between crocodiles. On the other hand, manatees avoided macro-habitats where crocodiles, and especially West African crocodiles, are abundant
Macro-habitat preferences by the African manatee and crocodiles – ecological and conservation implications
Abstract. African manatees (Trichechus senegalensis) and crocodiles are threatened species in parts of their range. In West Africa, crocodiles may constitute the main predators for manatees apart from humans. Here, we explore the macro-habitat selection of manatees and two species of crocodiles (West African crocodiles Crocodylus suchus and dwarf crocodile Osteolaemus tetraspis) in the Niger Delta (Nigeria), testing the hypotheses that (i) manatees may avoid crocodiles in order to minimize risks of predation, and (ii) the two crocodile species do compete. The study was carried out between 1994 and 2010 with a suite of different field techniques. We observed that the main macro-habitat types were freshwater rivers and coastal lagoons for manatees, mangroves for West African crocodiles, and rivers and creeks for dwarf crocodiles, with (i) the three species differing significantly in terms of their macro-habitat type selection, and (ii) significant seasonal influence on habitat selection of each species. Null models for niche overlap showed a significantly lower overlap in macro-habitat type use between manatee and crocodiles, whereas the two crocodiles were relatively similar. Null model analyses did not indicate any competitive interactions between crocodiles. On the other hand, manatees avoided macro-habitats where crocodiles, and especially West African crocodiles, are abundant
Quantitative characterization of amyloid deposits in murine models of alzheimer disease by phase-contrast x-ray imaging
Alzheimer's is a neurodegenerative disease that is the most common form of
dementia, but there is still no definitive cure for this disease. The
noninvasive X-ray Phase Contrast Tomography (XPCT) imaging technique was used
to study brain tissues in mouse models of Alzheimer's disease, AP-PS1 and
APP23. The XPCT technique enabled high-resolution imaging of brain tissues,
distinguishing between different brain structures, such as amyloid deposits and
neuronal cells. In addition, the XPCT technique provided detailed information
on the distribution and morphology of amyloid deposits in AP-PS1 and APP23 mice
putting in evidence the differences between these two models. This work
demonstrates the effectiveness of this technique in supporting Alzheimer's
studies and evaluating new therapeutic strategies.Comment: 14 pages, 8 figure
The Formation of Cataclysmic Variables with Brown Dwarf Secondaries
The present-day formation of cataclysmic variables (CVs) with brown dwarf
(BD) secondaries (0.013 M_sun < M_sec < 0.075 M_sun) is investigated using a
population synthesis technique. Results from the latest, detailed models for
BDs have been incorporated into the population synthesis code. For our models,
we find that ZACVs with BD secondaries have orbital periods in the range 46 min
to 2.5 hrs. We also find that ZACVs with BD secondaries comprise 18% of the
total, present-day ZACV population. In addition, we find that 80% of ZACVs with
BD secondaries have orbital periods < 78 minutes. This implies that 15% of the
present-day ZACV population should have orbital periods shorter than the
observed orbital period minimum for CVs. We also investigate the dependence of
the present-day formation rate of CVs with BD secondaries on the assumed value
of the common envelope efficiency parameter, alpha_CE, for three different
assumed mass ratio distributions in ZAMS binaries. Surprisingly, we find that
the common envelope process must be extremely inefficient (alpha_CE < 0.1) in
order for CVs with BD secondaries not to be formed. Finally, we find that the
progenitor binaries of ZACVs with BD secondaries have ZAMS orbital separations
< 3 AU and ZAMS primary masses between ~1-10 M_sun, with ~75% of the primary
masses less than ~1.6 M_sun. Interestingly, these ranges in orbital separation
and primary mass place the majority of the progenitor binaries within the
so-called ``brown dwarf desert.''Comment: preprint 27 pages 4 figures; to appear in ApJ April 1, 200
Cross-layer reliability evaluation, moving from the hardware architecture to the system level: A CLERECO EU project overview
Advanced computing systems realized in forthcoming technologies hold the promise of a significant increase of computational capabilities. However, the same path that is leading technologies toward these remarkable achievements is also making electronic devices increasingly unreliable. Developing new methods to evaluate the reliability of these systems in an early design stage has the potential to save costs, produce optimized designs and have a positive impact on the product time-to-market.
CLERECO European FP7 research project addresses early reliability evaluation with a cross-layer approach across different computing disciplines, across computing system layers and across computing market segments. The fundamental objective of the project is to investigate in depth a methodology to assess system reliability early in the design cycle of the future systems of the emerging computing continuum. This paper presents a general overview of the CLERECO project focusing on the main tools and models that are being developed that could be of interest for the research community and engineering practice
Production of light (anti)nuclei in pp collisions at √s = 5.02 TeV
The study of the production of nuclei and antinuclei in pp collisions has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic collisions. In this paper, the production of protons, deuterons and He-3 and their charge conjugates at midrapidity is studied as a function of the charged-particle multiplicity in inelastic pp collisions at root s = 5.02 TeV using the ALICE detector. Within the uncertainties, the yields of nuclei in pp collisions at root s = 5.02 TeV are compatible with those in pp collisions at different energies and to those in p-Pb collisions when compared at similar multiplicities. The measurements are compared with the expectations of coalescence and Statistical Hadronisation Models. The results suggest a common formation mechanism behind the production of light nuclei in hadronic interactions and confirm that they do not depend on the collision energy but on the number of produced particles
Surface plasmons at composite surfaces with diffusive charges
Metal surfaces with disorder or with nanostructure modifications are studied,
allowing for a localized charge layer (CL) in addition to continuous charges
(CC) in the bulk, both charges having a compressional or diffusive non-local
response. The notorious problem of "additional boundary conditions" is resolved
with the help of a Boltzmann equation that involves the scattering between the
two charge types. Depending on the strength of this scattering, the oscillating
charges can be dominantly CC or CL; the surface plasmon (SP) resonance acquires
then a relatively small linewidth, in agreement with a large set of data. With
a few parameters our model describes a large variety of SP dispersions
corresponding to observed data.Comment: 6 pages, 2 figure
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