435 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
Cell shape recognition by colloidal cell imprints: Energy of the cell-imprint interaction
The results presented in this study are aimed at the theoretical estimate of the interactions between a spherical microbial cell and the colloidal cell imprints in terms of the Derjaguin, Landau, Vervey, and Overbeek (DLVO) surface forces. We adapted the Derjaguin approximation to take into account the geometry factor in the colloidal interaction between a spherical target particle and a hemispherical shell at two different orientations with respect to each other. We took into account only classical DLVO surface forces, i.e., the van der Waals and the electric double layer forces, in the interaction of a spherical target cell and a hemispherical shell as a function of their size ratio, mutual orientation, distance between their surfaces, their respective surface potentials, and the ionic strength of the aqueous solution. We found that the calculated interaction energies are several orders higher when match and recognition between the target cell and the target cell imprint is achieved. Our analysis revealed that the recognition effect of the hemispherical shell towards the target microsphere comes from the greatly increased surface contact area when a full match of their size and shape is produced. When the interaction between the surfaces of the hemishell and the target cell is attractive, the recognition greatly amplifies the attraction and this increases the likelihood of them to bind strongly. However, if the surface interaction between the cell and the imprint is repulsive, the shape and size match makes this interaction even more repulsive and thus decreases the likelihood of binding. These results show that the surface chemistry of the target cells and their colloidal imprints is very important in controlling the outcome of the interaction, while the shape recognition only amplifies the interaction. In the case of nonmonotonous surface-to-surface interaction we discovered some interesting interplay between the effects of shape match and surface chemistry which is discussed in the paper. The results from this study establish the theoretical basis of cell shape recognition by colloidal cell imprints which, combined with cell killing strategies, could lead to an alternative class of cell shape selective antimicrobials, antiviral, and potentially anticancer therapies
Photographic Observations of the Hayabusa Re-entry
We analyzed photographic observations of the re-entry of the Hayabusa
spacecraft and capsule over Southern Australia on June 13, 2010, 13:52 UT.
Radiometric measurements of the brightness of the associated fireball were
obtained as well. We derived the trajectories and velocities of the spacecraft,
its four fragments and the capsule. The capsule trajectory was within a few
hundred meters of the trajectory predicted by JAXA prior the re-entry. The
spacecraft trajectory was about 1 km higher than the capsule trajectory. Two
major fragments separated from the spacecraft at a height of about 62 km with
mutual lateral velocity of 250 m/s. The maximum absolute magnitude of the
fireball of -12.6 was reached at a height of 67 km. The dynamic pressures
acting on the spacecraft at the fragmentation points were only 1 - 50 kPa. No
spacecraft fragment was seen to survive below the height of 47 km. The integral
luminous efficiency of the event was 1.3%. As expected, the capsule had a very
low luminous efficiency and very low ablation coefficient. The ablation
coefficients and masses of the major spacecraft fragments are discussed.Comment: Accepted for publication in PASJ, 16 pages, 8 figures, 5 table
Risk Price Dynamics
We present a novel approach to depicting asset pricing dynamics by characterizing shock exposures and prices for alternative investment horizons. We quantify the shock exposures in terms of elasticities that measure the impact of a current shock on future cash-flow growth. The elasticities are designed to accommodate nonlinearities in the stochastic evolution modeled as a Markov process. Stochastic growth in the underlying macroeconomy and stochastic discounting in the representation of asset values are central ingredients in our investigation. We provide elasticity calculations in a series of examples featuring consumption externalities, recursive utility, and jump risk.
Application of an Equilibrium Vaporization Model to the Ablation of Chondritic and Achondritic Meteoroids
We modeled equilibrium vaporization of chondritic and achondritic materials
using the MAGMA code. We calculated both instantaneous and integrated element
abundances of Na, Mg, Ca, Al, Fe, Si, Ti, and K in chondritic and achondritic
meteors. Our results are qualitatively consistent with observations of meteor
spectra.Comment: 8 pages, 4 figures; in press, Earth, Moon, and Planets, Meteoroids
2004 conference proceeding
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