113 research outputs found
Discovery of a new branch of the Taurid meteoroid stream as a real source of potentially hazardous bodies
Taurid meteor shower produces prolonged but usually low activity every
October and November. In some years, however, the activity is significantly
enhanced. Previous studies based on long-term activity statistics concluded
that the enhancement is caused by a swarm of meteoroids locked in 7:2 resonance
with Jupiter. Here we present precise data on 144 Taurid fireballs observed by
new digital cameras of the European Fireball Network in the enhanced activity
year 2015. Orbits of 113 fireballs show common characteristics and form
together a well defined orbital structure, which we call new branch. We found
that this branch is characterized by longitudes of perihelia lying between
155.9-160o and latitudes of perihelia between 4.2-5.7o. Semimajor axes are
between 2.23-2.28 AU and indeed overlap with the 7:2 resonance. Eccentricities
are in wide range 0.80-0.90. The orbits form a concentric ring in the inner
solar system. The masses of the observed meteoroids were in a wide range from
0.1 g to more than 1000 kg. We found that all meteoroids larger than 300 g were
very fragile, while those smaller than 30 g were much more compact. Based on
orbital characteristics, we argue that asteroids 2015 TX24 and 2005 UR, both of
diameters 200-300 meters, are direct members of the new branch. It is therefore
very likely that the new branch contains also numerous still not discovered
objects of decameter or even larger size. Since asteroids of sizes of tens to
hundreds meters pose a treat to the ground even if they are intrinsically weak,
impact hazard increases significantly when the Earth encounters the Taurid new
branch every few years. Further studies leading to better description of this
real source of potentially hazardous objects, which can be large enough to
cause significant regional or even continental damage on the Earth, are
therefore extremely important.Comment: 24 pages, 22 figures, 5 tables. Accepted in Astronomy and
Astrophysic
On quantification of weak sequential completeness
We consider several quantities related to weak sequential completeness of a
Banach space and prove some of their properties in general and in -embedded
Banach spaces, improving in particular an inequality of G. Godefroy, N. Kalton
and D. Li. We show some examples witnessing natural limits of our positive
results, in particular, we construct a separable Banach space with the
Schur property that cannot be renormed to have a certain quantitative form of
weak sequential completeness, thus providing a partial answer to a question of
G. Godefroy.Comment: 9 page
Dedekind order completion of C(X) by Hausdorff continuous functions
The concept of Hausdorff continuous interval valued functions, developed
within the theory of Hausdorff approximations and originaly defined for
interval valued functions of one real variable is extended to interval valued
functions defined on a topological space X. The main result is that the set of
all finite Hausdorff continuous functions on any topological space X is
Dedekind order complete. Hence it contains the Dedekind order completion of the
set C(X) of all continuous real functions defined on X as well as the Dedekind
order completion of the set C_b(X) of all bounded continuous functions on X.
Under some general assumptions about the topological space X the Dedekind order
completions of both C(X) and C_b(X) are characterised as subsets of the set of
all Hausdorff continuous functions. This solves a long outstanding open problem
about the Dedekind order completion of C(X). In addition, it has major
applications to the regularity of solutions of large classes of nonlinear PDEs
Heavy Metal Contamination of the Loučka River Water Ecosystem
Heavy metal contamination of the Loučka River water ecosystem was assessed in July 2005. We analyzed concentrations of T-Hg (total mercury), Cd, Pb, Cr, Cu, Zn, and Ni in water, sediments, zoobenthos, and in the brown trout (Salmo trutta m. fario) muscle and liver tissues (a total of 28 individuals) at four sampling sites. The highest Pb and Ni concentrations (4.634-12.050 and 0.689-24.980 mg kg-1) were found in sediments. The zoobenthos was most contaminated by Zn and Cu (0.556-1.505 and 2.925-74.300 mg kg-1). The heavy metal contamination of river water was highest in Ni and Cr (0.1-6.8 and 0.5-10.0 mg l-1). Concentrations of heavy metals in the brown trout muscle were following (in mg kg-1): Pb 0.108 ± 0.073 - 1.010 ± 0.506, Cd 0.003 ± 0.002 - 0.026 ± 0.022, Zn 3.956 ± 0.371 - 5.801 ± 1.718, Ni 0.058 ± 0.018 - 0.102 ± 0.046, Cr 0.028 ± 0.005 - 0.073 ± 0.039, Cu 0.329 ± 0.079 - 0.437 ± 0.064 and Hg 0.065 ± 0.008 - 0.106 ± 0.047. Statistical differences (P -1). Humans of 60 kg body mass may consume 1.5 kg of brown trout muscle from the Loučka River weekly without any risk. Adverse influence of the Uniglas distillery on the Loučka River environment contamination by heavy metals was not confirmed
Tidal disruption of NEAs - a case of P\v{r}\'ibram
This work studies the dynamical evolution of a possible meteor stream along
the orbit of the P\v{r}\'{i}bram meteorite, which originated in the tidal
disruption of the putative rubble-pile-like parent body during a close approach
to the Earth. We assumed the disruption at the time when the ascending or
descending node of the parent orbit was close to the Earth's orbit. In the last
5000 years, the P\v{r}\'{i}bram orbit has crossed the Earth orbit twice. It
happened about 4200 years and 3300 years ago. In both cases, we modeled the
release of particles from the simplified model of rotating asteroid, and traced
their individual orbital evolution to the current date. It takes several
hundred years to spread released meteoroids along the entire orbit of the
parent body. Even today, the stream would be relatively narrow.
Considering a model parent body with physical parameters of the asteroid
Itokawa, the complete disintegration of the object produced 3.8
meteoroid particles with diameter 1\,cm. The meteor activity observed
from the Earth is revealed and justification of follow-up observation during
suggested activity of the shower in the first two weeks of April is discussed.
The Earth's tidal forces would disintegrate a fraction of NEA population into
smaller objects. We evaluate the upper limit of mass of disintegrated asteroids
within the mean NEA lifetime and the contribution of disrupted matter to the
size distribution of the NEA.Comment: 8 pages, 10 figure
Atmospheric trajectories and light curves of shower meteors
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Orbital evolution of P\v{r}\'{i}bram and Neuschwanstein
The orbital evolution of the two meteorites P\v{r}\'{i}bram and
Neuschwanstein on almost identical orbits and also several thousand clones were
studied in the framework of the N-body problem for 5000 years into the past.
The meteorites moved on very similar orbits during the whole investigated
interval. We have also searched for photographic meteors and asteroids moving
on similar orbits. There were 5 meteors found in the IAU MDC database and 6
NEAs with currently similar orbits to P\v{r}\'{i}bram and Neuschwanstein.
However, only one meteor 161E1 and one asteroid 2002 QG46 had a similar orbital
evolution over the last 2000 years.Comment: 7 pages, 2 figures, 3 table
Trajectory and orbit of the unique carbonaceous meteorite Flensburg
Stars and planetary system
Fault-tolerant formation driving mechanism designed for heterogeneous MAVs-UGVs groups
A fault-tolerant method for stabilization and navigation of 3D heterogeneous formations is proposed in this paper. The presented Model Predictive Control (MPC) based approach enables to deploy compact formations of closely cooperating autonomous aerial and ground robots in surveillance scenarios without the necessity of a precise external localization. Instead, the proposed method relies on a top-view visual relative localization provided by the micro aerial vehicles flying above the ground robots and on a simple yet stable visual based navigation using images from an onboard monocular camera. The MPC based schema together with a fault detection and recovery mechanism provide a robust solution applicable in complex environments with static and dynamic obstacles. The core of the proposed leader-follower based formation driving method consists in a representation of the entire 3D formation as a convex hull projected along a desired path that has to be followed by the group. Such an approach provides non-collision solution and respects requirements of the direct visibility between the team members. The uninterrupted visibility is crucial for the employed top-view localization and therefore for the stabilization of the group. The proposed formation driving method and the fault recovery mechanisms are verified by simulations and hardware experiments presented in the paper
The Stubenberg meteorite—An LL6 chondrite fragmental breccia recovered soon after precise prediction of the strewn field
On March 6, 2016 at 21:36:51 UT, extended areas of Upper Austria, Bavaria (Germany) and the southwestern part of the Czech Republic were illuminated by a very bright bolide. This bolide was recorded by instruments in the Czech part of the European Fireball Network and it enabled complex and precise description of this event including prediction of the impact area. So far six meteorites totaling 1473 g have been found in the predicted area. The first pieces were recovered on March 12, 2016 on a field close to the village of Stubenberg (Bavaria). Stubenberg is a weakly shocked (S3) fragmental breccia consisting of abundant highly recrystallized rock fragments embedded in a clastic matrix. The texture, the large grain size of plagioclase, and the homogeneous compositions of olivine (Fa31.4) and pyroxene (Fs25.4) clearly indicate that Stubenberg is an LL6 chondrite breccia. This is consistent with the data on O, Ti, and Cr isotopes. Stubenberg does not contain solar wind-implanted noble gases. Data on the bulk chemistry, IR spectroscopy, cosmogenic nuclides, and organic components also indicate similarities to other metamorphosed LL chondrites. Noble gas studies reveal that the meteorite has a cosmic ray exposure (CRE) age of 36 ± 3 Ma and that most of the cosmogenic gases were produced in a meteoroid with a radius of at least 35 cm. This is larger than the size of the meteoroid which entered the Earth's atmosphere, which is constrained to <20 cm from short-lived radionuclide data. In combination, this might suggest a complex exposure history for Stubenberg.PostprintPeer reviewe
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