scholarly journals Asteroid Families

1994 ◽  
Vol 160 ◽  
pp. 395-414 ◽  
Author(s):  
Vincenzo Zappalà ◽  
Alberto Cellino
Keyword(s):  
Numerical Simulations ◽  
Excellent Agreement ◽  
Present Review ◽  
The Family ◽  
Suitable Technique ◽  
Asteroid Families ◽  
Collisional Evolution

In spite of their widely recognized importance in the framework of the modern understanding of the asteroidal population and its collisional evolution, asteroid dynamical families have long been a puzzling subject of research, due to the disagreement among the family lists published by different authors. In the present review, the definition and meaning of asteroid families are critically discussed, as well as the various problems which have to be faced by any suitable technique of family identification. In this respect, major improvements have been achieved during the last few years. The most recent family searches show an excellent agreement both in the number of reliably identified families, and in their members. Moreover, the overall performances of the most recent techniques of family identification have been tested by means of numerical simulations, with encouraging results. For these reasons, we believe that we are presently at the beginning of an era in which detailed physical studies of families can be attempted, and observational campaigns can be planned on the basis of solid evidence, like in the case of the recent spectacular results obtained for the family associated to the large asteroid 4 Vesta.

Spin clusters inside four young asteroid groups

2020 ◽  
Vol 493 (2) ◽  
pp. 2556-2567
Author(s):  
V Carruba ◽  
L G M Ramos ◽  
F Spoto
Keyword(s):  
Numerical Simulations ◽  
Transition Region ◽  
Semimajor Axis ◽  
Family Members ◽  
Proper Elements ◽  
The Family ◽  
Induced Fission ◽  
Spin Clusters ◽  
Spin Pairs ◽  
Asteroid Families

ABSTRACT Asteroid groups may either form because of collisions or because of spin induced fission. Recently it has been shown that young spin clusters tend to form more frequently in young collisional families than in older groups. Here, we study the occurrence of spin clusters inside four very recently identified asteroid groups: the (525) Adelaide, (2258) Viipuri, (6142) Tantawi, and (18429) (1994 AO1) groups. Using combinations of techniques based on backward numerical simulations, we identify four spin pairs among the family members. All groups have fractions of observed spin clusters well above 5 per cent, so confirming an observed trend for other young asteroid groups. The (2258) Viipuri and (18429) (1994 AO1) groups are compatible with an origin as a spin clusters themselves, and could be other occurrences of cascade spin clusters, as recently detected in other asteroid groups. Finally, the separation between collisional asteroid families and spin clusters in domains of dispersion of proper semimajor axis, σa, versus age seems to be more complex than previously thought. While spin clusters tend to be much more compact in proper elements than collisional families, there appears to be a transition region in σa where both the groups be found.

The common origin of family and non-family asteroids: Implications for meteorites and NEAs

2018 ◽  
Vol 14 (S345) ◽  
pp. 281-282
Author(s):  
Stanley F. Dermott ◽  
Dan Li ◽  
Apostolos A. Christou
Keyword(s):  
Hierarchical Clustering ◽  
Common Origin ◽  
Clustering Method ◽  
Main Belt ◽  
Frequency Distributions ◽  
Size Frequency ◽  
The Family ◽  
The Common ◽  
The Mean ◽  
Asteroid Families

AbstractThe observed size-frequency distributions (SFDs) of the five major asteroid families in the Inner Main Belt (IMB), defined by Nesvorný (2015) using the Hierarchical Clustering Method (Zappala et al. 1990), are distinctly different and deviate significantly from the linear log-log relation described by Dohnanyi (1969). The existence of these differences in the SFDs, and the fact that the precursor bodies of the major families have distinctly different eccentricities and inclinations, provides an explanation for the observations that the mean sizes of both the family and the non-family asteroids are correlated with their mean proper eccentricities and anti-correlated with their mean proper inclinations. We deduce from this, and from the fact that the SFDs of the family and the non-family asteroids are almost identical, that the family and most of the non-family asteroids in the IMB have a common origin (Dermott et al. 2018).

Infinitely Variable Transmission of Racheting Drive Type Based on One-Way Clutches

2004 ◽  
Vol 126 (4) ◽  
pp. 673-682 ◽  
Author(s):  
F. G. Benitez ◽  
J. M. Madrigal ◽  
J. M. del Castillo
Keyword(s):  
Numerical Simulation ◽  
Dynamic Analysis ◽  
Numerical Simulations ◽  
Mechanical Efficiency ◽  
Testing Equipment ◽  
Epicyclic Gear ◽  
The Family ◽  
Variable Transmission ◽  
Infinitely Variable Transmission ◽  
Oscillatory Character

An infinitely variable transmission (IVT), based on the use of one-way action clutches, belonging to the family of ratcheting drives is described. The mechanical foundations and numerical simulations carried out along this research envisage a plausible approach to its use as gear-box in general mechanical industry and its prospective use in automobiles and self-propelled vehicles. The system includes one-way clutches—free wheels or overrunning clutches—and two epicyclic gear systems. The output velocity, with oscillatory character, common to the ratcheting drives systems, presents a period similar to that produced by alternative combustion motors, making this transmission compatible with automobile applications. The variation of the transmission is linear in all the working range. The kinematics operating principles behind this IVT is described followed by a numerical simulation of the dynamic analysis. A prototype has been constructed and tested to assess its mechanical efficiency for different reduction ratios. The efficiency values predicted by theory agree with those experimentally obtained on a bench-rig testing equipment.

scholarly journals New multi-part collisional model of the main belt: the contribution to near-Earth asteroids

2020 ◽  
Vol 639 ◽  
pp. A9
Author(s):  
P. S. Zain ◽  
G. C. de Elía ◽  
R. P. Di Sisto
Keyword(s):  
Significant Contribution ◽  
Asteroid Belt ◽  
Size Distributions ◽  
Main Belt ◽  
Yarkovsky Effect ◽  
Source Regions ◽  
Main Asteroid Belt ◽  
Near Earth Asteroids ◽  
Asteroid Families ◽  
Collisional Evolution

Aims. We developed a six-part collisional evolution model of the main asteroid belt (MB) and used it to study the contribution of the different regions of the MB to the near-Earth asteroids (NEAs). Methods. We built a statistical code called ACDC that simulates the collisional evolution of the MB split into six regions (namely Inner, Middle, Pristine, Outer, Cybele and High-Inclination belts) according to the positions of the major resonances present there (ν6, 3:1J, 5:2J, 7:3J and 2:1J). We consider the Yarkovsky effect and the mentioned resonances as the main mechanism that removes asteroids from the different regions of the MB and delivers them to the NEA region. We calculated the evolution of the NEAs coming from the different source regions by considering the bodies delivered by the resonances and mean dynamical timescales in the NEA population. Results. Our model is in agreement with the major observational constraints associated with the MB, such as the size distributions of the different regions of the MB and the number of large asteroid families. It is also able to reproduce the observed NEAs with H < 16 and agrees with recent estimations for H < 20, but deviates for smaller sizes. We find that most sources make a significant contribution to the NEAs; however the Inner and Middle belts stand out as the most important source of NEAs followed by the Outer belt. The contributions of the Pristine and Cybele regions are minor. The High-Inclination belt is the source of only a fraction of the actual observed NEAs with high inclination, as there are dynamical processes in that region that enable asteroids to increase and decrease their inclinations.

The small Rho GTPase Rif and actin cytoskeletal remodelling

2012 ◽  
Vol 40 (1) ◽  
pp. 268-272 ◽  
Author(s):  
Lifei Fan ◽  
Harry Mellor
Keyword(s):  
Actin Cytoskeleton ◽  
Rho Gtpase ◽  
Active Form ◽  
Present Review ◽  
Gtpase Domain ◽  
Domain Structures ◽  
Downstream Effectors ◽  
Inactive Form ◽  
The Family ◽  
Recent Addition

The Rif GTPase is a recent addition to small Rho GTPase family; it shares low homology with other members in the family and evolutionarily parallels with the development of vertebrates. Rif has the conserved Rho GTPase domain structures and cycles between a GDP-bound inactive form and a GTP-bound active form. In its active form, Rif signals through multiple downstream effectors. In the present review, our aim is to summarize the current information about the Rif effectors and how Rif remodels actin cytoskeleton in many aspects.

scholarly journals Precession-driven flows in non-axisymmetric ellipsoids

2013 ◽  
Vol 737 ◽  
pp. 412-439 ◽  
Author(s):  
J. Noir ◽  
D. Cébron
Keyword(s):  
Theoretical Model ◽  
Numerical Simulations ◽  
Celestial Body ◽  
Excellent Agreement ◽  
Analytical Models ◽  
Forced Flow ◽  
Spheroidal Geometry ◽  
Strong Contrast ◽  
Do So

AbstractWe study the flow forced by precession in rigid non-axisymmetric ellipsoidal containers. To do so, we revisit the inviscid and viscous analytical models that have been previously developed for the spheroidal geometry by, respectively, Poincaré (Bull. Astronomique, vol. XXVIII, 1910, pp. 1–36) and Busse (J. Fluid Mech., vol. 33, 1968, pp. 739–751), and we report the first numerical simulations of flows in such a geometry. In strong contrast with axisymmetric spheroids, where the forced flow is systematically stationary in the precessing frame, we show that the forced flow is unsteady and periodic. Comparisons of the numerical simulations with the proposed theoretical model show excellent agreement for both axisymmetric and non-axisymmetric containers. Finally, since the studied configuration corresponds to a tidally locked celestial body such as the Earth’s Moon, we use our model to investigate the challenging but planetary-relevant limit of very small Ekman numbers and the particular case of our Moon.

scholarly journals The impact crater at the origin of the Julia family detected with VLT/SPHERE?

2018 ◽  
Vol 618 ◽  
pp. A154 ◽  
Author(s):  
P. Vernazza ◽  
M. Brož ◽  
A. Drouard ◽  
J. Hanuš ◽  
M. Viikinkoski ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Adaptive Optics ◽  
Impact Crater ◽  
Large Fraction ◽  
Family Studies ◽  
High Angular Resolution ◽  
Main Belt ◽  
3D Shape ◽  
The Family ◽  
The Impact

Context. The vast majority of the geophysical and geological constraints (e.g., internal structure, cratering history) for main-belt asteroids have so far been obtained via dedicated interplanetary missions (e.g., ESA Rosetta, NASA Dawn). The high angular resolution of SPHERE/ZIMPOL, the new-generation visible adaptive-optics camera at ESO VLT, implies that these science objectives can now be investigated from the ground for a large fraction of D ≥ 100 km main-belt asteroids. The sharp images acquired by this instrument can be used to accurately constrain the shape and thus volume of these bodies (hence density when combined with mass estimates) and to characterize the distribution and topography of D ≥ 30 km craters across their surfaces. Aims. Here, via several complementary approaches, we evaluated the recently proposed hypothesis that the S-type asteroid (89) Julia is the parent body of a small compact asteroid family that formed via a cratering collisional event. Methods. We observed (89) Julia with VLT/SPHERE/ZIMPOL throughout its rotation, derived its 3D shape, and performed a reconnaissance and characterization of the largest craters. We also performed numerical simulations to first confirm the existence of the Julia family and to determine its age and the size of the impact crater at its origin. Finally, we utilized the images/3D shape in an attempt to identify the origin location of the small collisional family. Results. On the one hand, our VLT/SPHERE observations reveal the presence of a large crater (D ~ 75 km) in Julia’s southern hemisphere. On the other hand, our numerical simulations suggest that (89) Julia was impacted 30–120 Myrs ago by a D ~ 8 km asteroid, thereby creating a D ≥ 60 km impact crater at the surface of Julia. Given the small size of the impactor, the obliquity of Julia and the particular orientation of the family in the (a,i) space, the imaged impact crater is likely to be the origin of the family. Conclusions. New doors into ground-based asteroid exploration, namely, geophysics and geology, are being opened thanks to the unique capabilities of VLT/SPHERE. Also, the present work may represent the beginning of a new era of asteroid-family studies. In the fields of geophysics, geology, and asteroid family studies, the future will only get brighter with the forthcoming arrival of 30–40 m class telescopes like ELT, TMT, and GMT.

Collisional evolution of asteroids

1999 ◽  
Vol 173 ◽  
pp. 129-144 ◽  
Author(s):  
P. Farinella ◽  
D.R. Davis ◽  
F. Marzari ◽  
D. Vokrouhlický
Keyword(s):  
High Velocity ◽  
Total Mass ◽  
Complex Mixture ◽  
Research Field ◽  
Near Earth Space ◽  
Accretion Process ◽  
High Velocity Impacts ◽  
Near Earth Asteroids ◽  
Asteroid Families ◽  
Collisional Evolution

AbstractWe review the evidence for, and the modelling work devoted to, the substantial collisional evolution which has generated the current asteroid population and continually injects asteroid fragments into dynamicalroutesthrough which they can reach near-Earth space and sometimes hit our planet. The main obstacles to further progress in this research field are theoretical (mainly related to the physics of high-velocity impacts), but better observational data (in particular on the small-size end of the asteroid population) would help. However, in the last decade new insights have been obtained on specific important issues, such as the total mass of the asteroids at the time when the accretion process was stopped (only moderately larger than the current one), the “demography” of asteroid families (how many/how old they are and how they evolve) and the way meteorites and near-Earth asteroids are delivered/transported by a complex mixture of collisional and dynamical mechanisms.

Shock dispersal of dilute particle clouds

2018 ◽  
Vol 841 ◽  
pp. 732-745 ◽  
Author(s):  
Theo G. Theofanous ◽  
Vladimir Mitkin ◽  
Chih-Hao Chang
Keyword(s):  
Numerical Simulations ◽  
Excellent Agreement ◽  
Volume Fraction ◽  
Essential Feature ◽  
Particle Volume Fraction ◽  
Effective Field ◽  
Blast Waves ◽  
Particle Volume ◽  
Report Data ◽  
The Mathematical Model

We present experiments and numerical simulations for an elementary paradigm of disperse multiphase flow: highly dilute, homogeneous, finite-dimension clouds of particles (curtains) hit by shock/blast waves in one dimension. In the experiments (particle volume fraction ${<}1\,\%$) the blasts that follow the shocks vary from low subsonic to supersonic, and we report data on curtain expansions and volume fraction distributions. The particle-resolving numerical simulations, run for the supersonic case, yield excellent agreement with all of these experimental data. We find that the essential feature for these good predictions is a flow choking phenomenon that entails a (particle) dispersive character of the flow down a volume fraction gradient (as at the downstream portions of the curtain). A most basic effective-field model is made to capture this gas dynamics by emulating the wake behind each particle, as seen in the particle-resolving direct Euler simulation (DES). On this basis, standard drag laws yield excellent agreement with the dispersive behaviour found in the experiment/DES, thus revealing a physics-based path to eventual well posedness of the mathematical model.

scholarly journals Families classification including multiopposition asteroids

2015 ◽  
Vol 10 (S318) ◽  
pp. 28-45 ◽  
Author(s):  
Andrea Milani ◽  
Federica Spoto ◽  
Zoran Knežević ◽  
Bojan Novaković ◽  
Georgios Tsirvoulis
Keyword(s):  
Improved Method ◽  
New Classification ◽  
Family Growth ◽  
The Family ◽  
The Future ◽  
Independent Families ◽  
Future Work ◽  
Current List ◽  
Asteroid Families

AbstractIn this paper we present the results of our new classification of asteroid families, upgraded by using catalog with > 500,000 asteroids. We discuss the outcome of the most recent update of the family list and of their membership. We found enough evidence to perform 9 mergers of the previously independent families. By introducing an improved method of estimation of the expected family growth in the less populous regions (e.g. at high inclination) we were able to reliably decide on rejection of one tiny group as a probable statistical fluke. Thus we reduced our current list to 115 families. We also present newly determined ages for 6 families, including complex 135 and 221, improving also our understanding of the dynamical vs. collisional families relationship. We conclude with some recommendations for the future work and for the family name problem.

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