1,256 research outputs found
On the possible values of the orbit distance between a near-Earth asteroid and the Earth
No full textWe consider all the possible trajectories of a near-Earth asteroid (NEA), corresponding to the whole set of heliocentric orbital elements with perihelion distance q ≤ 1.3 au and eccentricity e ≤ 1 (NEA class). For these hypothetical trajectories, we study the range of the values of the distance from the trajectory of the Earth (assumed on a circular orbit) as a function of selected orbital elements of the asteroid. The results of this geometric approach are useful to explain some aspects of the orbital distribution of the known NEAs. We also show that the maximal orbit distance between an object in the NEA class and the Earth is attained by a parabolic orbit, with apsidal line orthogonal to the ecliptic plane. It turns out that the threshold value of q for the NEA class (qmax = 1.3 au) is very close to a critical value, below which the above result is not valid
Low solar elongation searches for NEO: a deep sky test and its implications for survey strategies
No full textThe distribution of energy perturbations at planetary close encounters
No full textOpik’s theory of close encounters allows us to deduce an analytic expression for the distribution of energy perturbations at close encounters between small bodies and planets. The derivation of this expression highlights a simple geometric structure in the plane containing the planet and
perpendicular to the unperturbed planetocentric velocity vector. The analytic formulation reproduces
well the results of the numerical integrations that first pointed out the asymmetries in the distribution of energy perturbations
The Gaugamela battle eclipse: An archaeoastronomical analysis
No full textA total lunar eclipse occurred during the night preceding the decisive Battle of Gaugamela (20th September 331 BCE), when the Macedonian army, led by Alexander the Great, finally defeated the Persian king Darius and his army. This astronomical event, well known to historians, had a relevant role on the battle outcome. The eclipse was described in detail by Babylonian astronomers, though, unfortunately, the text of their report has only partially been preserved. We have reconstructed the evolution of the phenomenon as it appeared to the observer in Babylonia, by using the positional astronomy code "Planetario V2.0". On the base of this reconstruction we suggest a number of integrations to the lost part of the text, allowing a finer astrological interpretation of the eclipse and of its influence on the mood of the armies that set against each other on the following morning. Copyright © 2008 MAA
Resonant returns to close approaches: analytical theory
No full textWe extend Öpik's theory of close encounters of a small body
(either an asteroid or a comet) by explicitly
introducing the nodal distance and a time coordinate. Assuming that
the heliocentric motion between consecutive close encounters is
Keplerian, or given by an explicit propagator, we can compute
the initial conditions
for an encounter as functions of the outcomes of a previous one; in
this way it is possible to obtain a completely analytical theory of
resonant returns. It is found that the initial conditions of a
close encounter that lead to a resonant return must lie close to
easily computable circles on the b-plane of the first encounter.
By further assuming that the nodal distance varies uniformly with
time, due to secular perturbations, and considering the derivatives
of the coordinates on the b-plane of the second encounter with
respect to those on the b-plane of the first encounter, we compute
in the latter the location, shape and size of collision keyholes
A dynamical definition of the sphere of influence of the Earth
No full textThe concept of sphere of influence of a planet is useful in both the context of impact monitoring of asteroids with the Earth and of the design of interplanetary trajectories for spacecraft. After reviewing the classical results, we propose a new definition of the sphere which is suitable for the classical patched-conic method: the new definition depends on the position and velocity of the small body for given values C of the Jacobi constant. Here, we compare the orbit of the small body, obtained in the framework of the circular restricted three-body problem, with orbits computed by patching two -body solutions. Our definition is based on an optimisation process, minimising a suitable target function with respect to the assumed radius of the sphere of influence. For different values C we represent the results in the planar case: we show the values of the selected radius as a function of two angles characterising the orbit. In this case, we also produce a database of radii of the sphere of influence for several initial conditions, allowing an interpolation
Dei fondamenti della religione e dei fonti dell'empieta libri tre
No full textMarca tip. xil. en portSign. : [a]\p3\s, b\p6\s, A-Z\p4\s, 2A-H\p4\s, 2I\p6\
Branching fraction and CP asymmetry of the decays B+→K0Sπ+ and B+→K0SK+
No full textAn analysis of B+ → K0
Sπ+ and B+ → K0
S K+ decays is performed with the LHCb experiment. The pp
collision data used correspond to integrated luminosities of 1 fb−1 and 2 fb−1 collected at centre-ofmass
energies of
√
s = 7 TeV and
√
s = 8 TeV, respectively. The ratio of branching fractions and the
direct CP asymmetries are measured to be B(B+ → K0
S K+
)/B(B+ → K0
Sπ+
) = 0.064 ± 0.009 (stat.) ±
0.004 (syst.), ACP(B+ → K0
Sπ+
) = −0.022 ± 0.025 (stat.) ± 0.010 (syst.) and ACP(B+ → K0
S K+
) =
−0.21 ± 0.14 (stat.) ± 0.01 (syst.). The data sample taken at
√
s = 7 TeV is used to search for
B+
c
→ K0
S K+ decays and results in the upper limit ( fc · B(B+
c
→ K0
S K+
))/( fu · B(B+ → K0
Sπ+
)) <
5.8 × 10−2 at 90% confidence level, where fc and fu denote the hadronisation fractions of a ¯b
quark
into a B+
c or a B+ meson, respectively
LA COLLEZIONE DI DIPINTI DI GIOVANNI TRECCANI DEGLI ALFIERI.
No full textWe know that Giovanni Treccani bought and offered to Italy the Borso d’Este Bible in 1923, he financed the 1929-1937 edition of the Enciclopedia Italiana and the 1953-1961 edition of the Storia di Milano but nobody knows his activity as collector of modern and antique pictures which begins about in 1923.
The reconstruction of Treccani collection, now lost, has been based on the autobiography of Treccani himself: Nel cammino della mia vita (1960), printed in very few copies for his daughters and sons; on the article by Antonio Morassi issued in 1930-31 on the magazine “Dedalo” and on the recovery of the correspondence between Giovanni Treccani and Adolfo Venturi who has been consultant for Treccani to the purchases of antique art. In addition to these written sources I have put the photolibrary research of these authors in Venice and Rome, in that of the Milan Council Archivio Fotografico and in other Italian and foreign Photo Libraries. After the reconstruction of the collection I have studied each picture to catalogue them.
To reconstruct the contest in which the collection was born, I have considered first the background of the Milan collectionism world in the first two decades of the twentieth century, especially that of industry people in relationship with Treccani, then I analyzed the presence of the pictures of Treccani in several exhibitions between the 20s and the 50s. The borrowings of works reflect the relationship between the collector with the art historians who organized some exhibitions and allow us to hypothesize the contest in which Treccani purchased some paintings. The personality who emerges in the 20s and the 30s beside Venturi, is Ugo Ojetti. The probable responsible for the entrance in the collection of Francesco Paolo Michetti paintings and Vincenzo Gemito drawings.
In the 40s the work of Treccani is in Milan and is linked to the art historians who work in the city: Costantino Baroni, Gian Alberto dell’Acqua, Fernanda Wittgens.
The exhibitions of this period, some publications and the contribution of these historians for the Storia di Milano testify to this relationship.
The reconstruction of the Treccani collection also has taken account of the issues financed by the entrepreneur: the pages of Enciclopedia, of the Storia di Milano, and of the Enciclopedia del costume allow you to monitor the inputs of a number of paintings in the collection and to backdate the ownership of Treccani.
Finally, the study has also allowed us to identify several new works, among which should be noted a study by Pelizza da Volpedo and a painting by Adolfo Feragutti Visconti and donated by the author to the collector
Nonlinear impact monitoring: line of variation searches for impactors
No full textSUMMARY When a new near Earth asteroid is discovered, it is important to know whether or not there is the possibility of an impact with the Earth in the near future. In this paper, we describe the technical approaches employed by the two operational second-generation asteroid impact monitoring systems, CLOMON2 and Sentry, paying particular attention to the similarities and differences between these independent systems. The detection and characterization of a potential impact requires the propagation of the orbital probability density function from the time of discovery to the time of hypothetical impact. Since the N-body problem is not integrable, this can be done only by sampling the orbital elements space with a finite number of Virtual Asteroids (VAs), the orbit of each one being propagated numerically. Our methods, illustrated in this paper, use the Line Of Variation (LOV), a unidimensional subspace, to perform this sampling. The primary goal is to detect Virtual Impactors (VIs), which are regions in the initial conditions space leading to dynamically distinct collision solutions; then a probability integral needs to be computed on the volume of the VI. An important issue is how to assure completeness of such a search down to some impact probability threshold. This problem cannot be efficiently solved just by computing more VAs, but requires a geometric description of the behavior of the LOV in order to identify the critical segments of this curve. We have studied these behaviors on the Target Plane (TP) through our analytical theory and the output of many numerical tests. Assuming that the geometry is the simplest compatible with the data available from the sampling, we obtain a classification which allows us to use iterative methods, appropriate for each case, to find the closest approach distance possible along the LOV. After an LOV minimum has been identified, it is possible to use a probability density linearized at this point. However, when the cross section of the Earth is not crossed by the LOV, there is no guarantee that nonlinearity would be negligible in the direction on the TP transversal to the LOV. We describe how to test for such nonlinearity, and thus reduce or eliminate the possibility of spurious VIs. In this way, the performance of our impact monitoring systems has been significantly increased in comparison to the earlier and simpler solitary system. These more advanced systems have identified and then eliminated (through additional observations) more than one hundred cases of asteroids with VIs in the years 2002–2003
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