21 research outputs found
Search for shower's duplicates at the IAU MDC. Methods and general results
Observers submit both new and known meteor shower parameters to the database
of the IAU Meteor Data Center (MDC). It may happen that a new observation of an
already known meteor shower is submitted as a discovery of a new shower. Then,
a duplicate shower appears in the MDC. On the other hand, the observers may
provide data which, in their opinion, is another set of parameters of an
already existing shower. However, if this is not true, we can talk about a
shower that is a false-duplicate of a known meteor shower.
We aim to develop a method for objective detection of duplicates among meteor
showers and apply it to the MDC. The method will also enable us to verify
whether various sets of parameters of the same shower are compatible and, thus,
reveal the false-duplicates. We suggest two methods based on cluster analyses
and two similarity functions among geocentric and heliocentric shower
parameters collected in the MDC. 8 new showers represented by two or more
parameter sets were discovered. 31 times there was full agreement between our
results and those reported in the MDC. 23 times the same duplicates as given in
the MDC, were found only by one method. We found 27 multi-solution showers for
which the number of the same duplicates found by both method is close to the
corresponding number in the MDC database. However for 60 multi-solution showers
listed in the MDC no duplicates were found by any of the applied methods.
The obtained results confirmed the effectiveness of the proposed approach of
identifying duplicates. We have shown that in order to detect and verify
duplicate meteor showers, it is possible to apply the objective proposal
instead of the subjective approach used so far
An Optical Survey for mm-Sized Interstellar Meteoroids
We report high resolution multi-station observations of meteors by the
Canadian Automated Meteor Observatory (CAMO) recorded from June 2009 to August
2010. Our survey has a limiting detection magnitude of +5 mag in R-band,
equivalent to a limiting meteoroid mass of ~2*E-7 kg. The high metric
trajectory accuracy (of the order of 30 m perpendicular to the solution and 200
m along-track) allows us to determine velocities with average uncertainty of <
1.5% in speed and ~0.4 degr in radiant direction. A total of 1739 meteors had
measured orbits. The data has been searched for meteors in hyperbolic orbits,
which are potentially of interstellar origin. We found 22 potential hyperbolic
meteors among our sample, with only two of them having a speed at least three
sigma above the hyperbolic limit. For our one year survey we find no clear
evidence of interstellar meteoroids at mm-sizes in a weighted time-area product
of ~1*E4 km^2*h. Backward integrations performed for these 22 potentially
hyperbolic meteors to check for close encounters with planets show no
considerable changes in their orbits. Detailed examination leads us to conclude
that our few identified events are most likely the result of measurement error.
We find an upper limit of f_ISP < 2*E-4/(km^2*h) for the flux of interstellar
meteoroids at Earth with a limiting mass of m > 2*E-7 kg.Comment: 15 pages, 2 figures, accepted by Ap
Showers with both northern and southern solutions
Meteoroids of a low-inclination stream hit the Earth arriving from a
direction near the ecliptic. The radiant area of stream like this is often
divided into two parts: one is situated northward and the other southward of
the ecliptic. In other words, two showers are caused by such a stream.
Well-known examples of such showers are the Northern Taurids, #17, and Southern
Taurids, #2, or the Northern -Aquariids, #26, and Southern
-Aquariids, #5. While the meteoroids of the northern shower collide
with the Earth in the descending node, those of the southern shower collide
with our planet in the ascending node of their orbits. Because of this
circumstance and tradition, the northern and southern showers must be
distinguished. Unfortunately, this is not always the case with meteor showers
listed in the IAU Meteor Data Center (MDC). For the same shower, some authors
reported a set of its mean parameters corresponding to the northern shower and
other authors to the southern shower. We found eleven such cases in the MDC. In
this paper, we propose corrections of these mis-identifications.Comment: Submitted: Planetary and Space Scienc
Matching Dynamics with Constraints
We study uncoordinated matching markets with additional local constraints
that capture, e.g., restricted information, visibility, or externalities in
markets. Each agent is a node in a fixed matching network and strives to be
matched to another agent. Each agent has a complete preference list over all
other agents it can be matched with. However, depending on the constraints and
the current state of the game, not all possible partners are available for
matching at all times. For correlated preferences, we propose and study a
general class of hedonic coalition formation games that we call coalition
formation games with constraints. This class includes and extends many recently
studied variants of stable matching, such as locally stable matching, socially
stable matching, or friendship matching. Perhaps surprisingly, we show that all
these variants are encompassed in a class of "consistent" instances that always
allow a polynomial improvement sequence to a stable state. In addition, we show
that for consistent instances there always exists a polynomial sequence to
every reachable state. Our characterization is tight in the sense that we
provide exponential lower bounds when each of the requirements for consistency
is violated. We also analyze matching with uncorrelated preferences, where we
obtain a larger variety of results. While socially stable matching always
allows a polynomial sequence to a stable state, for other classes different
additional assumptions are sufficient to guarantee the same results. For the
problem of reaching a given stable state, we show NP-hardness in almost all
considered classes of matching games.Comment: Conference Version in WINE 201
A study to improve the past orbit of comet C/1917 F1 (Mellish) on the basis of its observed meteor showers
International audienc
Social networks and their importance in job searching of college students
At present, in every sphere of human activity, using modern ICT is considered as a matter of course. Several human resources management institutions are aware of the potential of social networks in estabilishing and building relationships with their target groups. It is a trend to create job portals in social networks. These are currently an integrated part of communication with target audience and therefore also an objects of attention and reflexions. It is also the topic of this paper. The goal of this research is to determine the level of use of social networks by college students in Slovakia. Part of the research is also to discover the effect of social networks on job searching of a selected sample of students. The research was conducted on a sample of 407 slovak students. A questioning method in form of an online questionnaire was used. The obtained results were processed using methods of descriptive and test statistics. We studied the significance of gender on the frequency of using the internet to search for job opportunities via social networks, as well as the ability to apprehend the importance of personal presentation on social networks. The statistical testing did not prove any significant difference between men and women in the question of frequency of using internet to search for job opportunities, nor in the ability to apprehend the importance of personal presentation on social networks. A statistically significant difference in gender was proven only in case of using social networks in job searching. Women tend to use social networks to find jobs more often than men. These statements are proved by the results of tests of significance of mean changes at the 5% significance level, which means that they are valid with 95% probability