1,639 research outputs found
On the oldest asteroid families in the main belt
Asteroid families are groups of minor bodies produced by high-velocity
collisions. After the initial dispersions of the parent bodies fragments, their
orbits evolve because of several gravitational and non-gravitational
effects,such as diffusion in mean-motion resonances, Yarkovsky and YORP
effects, close encounters of collisions, etc. The subsequent dynamical
evolution of asteroid family members may cause some of the original fragments
to travel beyond the conventional limits of the asteroid family. Eventually,
the whole family will dynamically disperse and no longer be recognizable.
A natural question that may arise concerns the timescales for dispersion of
large families. In particular, what is the oldest still recognizable family in
the main belt? Are there any families that may date from the late stages of the
Late Heavy Bombardment and that could provide clues on our understanding of the
primitive Solar System? In this work, we investigate the dynamical stability of
seven of the allegedly oldest families in the asteroid main belt. Our results
show that none of the seven studied families has a nominally mean estimated age
older than 2.7 Gyr, assuming standard values for the parameters describing the
strength of the Yarkovsky force. Most "paleo-families" that formed between 2.7
and 3.8 Gyr would be characterized by a very shallow size-frequency
distribution, and could be recognizable only if located in a dynamically less
active region (such as that of the Koronis family). V-type asteroids in the
central main belt could be compatible with a formation from a paleo-Eunomia
family.Comment: 9 pages, 5 figures, 5 tables. Accepted for publication in MNRA
A multi-domain approach to asteroid families identification
Previous works have identified families halos by an analysis in proper
elements domains, or by using Sloan Digital Sky Survey-Moving Object Catalog
data, fourth release (SDSS-MOC4) multi-band photometry to infer the asteroid
taxonomy, or by a combination of the two methods. The limited number of
asteroids for which geometric albedo was known until recently discouraged in
the past the extensive use of this additional parameter, which is however of
great importance in identifying an asteroid taxonomy. The new availability of
geometric albedo data from the Wide-field Infrared Survey Explorer (WISE)
mission for about 100,000 asteroids significantly increased the sample of
objects for which such information, with some errors, is now known.
In this work we proposed a new method to identify families halos in a
multi-domain space composed by proper elements, SDSS-MOC4 (a*,i-z) colors, and
WISE geometric albedo for the whole main belt (and the Hungaria and Cybele
orbital regions). Assuming that most families were created by the breakup of an
undifferentiated parent body, they are expected to be homogeneous in colors and
albedo. The new method is quite effective in determining objects belonging to a
family halo, with low percentages of likely interlopers, and results that are
quite consistent in term of taxonomy and geometric albedo of the halo members.Comment: 23 pages, 18 figures, 6 tables. Accepted for publication in MNRA
Dynamical evolution and chronology of the Hygiea asteroid family
The asteroid (10) Hygiea is the fourth largest asteroid of the Main Belt, by
volume and mass, and it is the largest member of its own family. Previous works
investigated the long-term effects of close encounters with (10) Hygiea of
asteroids in the orbital region of the family, and analyzed the taxonomical and
dynamical properties of members of this family. In this paper we apply the
high-quality SDSS-MOC4 taxonomic scheme of DeMeo and Carry (2013) to members of
the Hygiea family core and halo, we obtain an estimate of the minimum time and
number of encounter necessary to obtain a (or 99.7%) compatible
frequency distribution function of changes in proper caused by close
encounters with (10) Hygiea, we study the behavior of asteroids near secular
resonance configurations, in the presence and absence of the Yarkovsky force,
and obtain a first estimate of the age of the family based on orbital diffusion
by the Yarkovsky and YORP effects with two methods.
The Hygiea family is at least 2 Byr old, with an estimated age of Myr and a relatively large initial ejection velocity field,
according to the approach of Vokrouhlick\'{y} et al. (2006a, b). Surprisingly,
we found that the family age can be shortened by 25% if the dynamical
mobility caused by close encounters with (10) Hygiea is also accounted for,
which opens interesting new research lines for the dynamical evolution of
families associated with massive bodies. In our taxonomical analysis of the
Hygiea asteroid family, we also identified a new V-type candidate: the asteroid
(177904) (2005 SV5). If confirmed, this could be the fourth V-type object ever
to be identified in the outer main belt.Comment: 13 page, 15 figures, and 4 table
Dynamical evolution of V-type asteroids in the central main belt
V-type asteroids are associated with basaltic composition, and are supposed
to be fragments of crust of differentiated objects. Most V-type asteroids in
the main belt are found in the inner main belt, and are either current members
of the Vesta dynamical family (Vestoids), or past members that drifted away.
However, several V-type photometric candidates have been recently identified in
the central and outer main belt.
The origin of this large population of V-type objects is not well understood.
Since it seems unlikely that Vestoids crossing the 3J:-1A mean-motion resonance
with Jupiter could account for the whole population of V-type asteroids in the
central and outer main belt, origin from local sources, such as the parent
bodies of the Eunomia, and of the Merxia and Agnia asteroid families, has been
proposed as an alternative mechanism.
In this work we investigated the dynamical evolution of the V-type
photometric candidates in the central main belt, under the effect of
gravitational and non-gravitational forces. Our results show that dynamical
evolution from the parent bodies of the Eunomia and Merxia/Agnia families on
timescales of 2 Byr or more could be responsible for the current orbital
location of most of the low-inclined V-type asteroids.Comment: 16 pages, 10 figures, 3 tables. Accepted for publication in MNRA
Merger trees and the multiplicity function of halos
We present a new method for calculating the merger history of matter halos in
hierarchical clustering cosmologies. The linear density field is smoothed on a
range of scales, these are then ordered in decreasing density and a merger tree
constructed. The method is similar in many respects to the block model of Cole
\& Kaiser but has a number of advantages: (i) it retains information about the
spatial correlations between halos, (ii) it uses a series of overlapping grids
and is thereby much better at finding rare, high-mass halos, (iii) it is not
limited to halos whose mass ratios are powers of two, and (iv) it is based on
an actual realization of the density field and so can be tested against N-body
simulations. The major disadvantages are (i) the minimum halo mass is eight
times the unit cell with a corresponding loss of dynamic range, and (ii)
occasionally the relative location of halos in the tree does not reflect the
correct ordering of their collapse times, as computed from the mean halo
density. We show that our model exhibits the required scaling behaviour when
tested on power-law spectra of density perturbations, but that it predicts far
more massive halos than does the Press-Schechter formalism for flat spectra. We
suggest reasons why this should be so.Comment: plain tex, 10 pages; figures (all Postscript) in a uuencoded
compressed tar file; submitted to M.N.R.A.
On the origin of the extremely different solubilities of polyethers in water
The solubilities of polyethers are surprisingly counter-intuitive. The best-known example is the difference between polyethylene glycol ([–CH2–CH2–O–]n) which is infinitely soluble, and polyoxymethylene ([–CH2–O–]n) which is completely insoluble in water, exactly the opposite of what one expects from the C/O ratios of these molecules. Similar anomalies exist for oligomeric and cyclic polyethers. To solve this apparent mystery, we use femtosecond vibrational and GHz dielectric spectroscopy with complementary ab initio calculations and molecular dynamics simulations. We find that the dynamics of water molecules solvating polyethers is fundamentally different depending on their C/O composition. The ab initio calculations and simulations show that this is not because of steric effects (as is commonly believed), but because the partial charge on the O atoms depends on the number of C atoms by which they are separated. Our results thus show that inductive effects can have a major impact on aqueous solubilities
The XmnI polymorphic site 5’ to the gene Gγ in a Brazilian patient with sickle cell anaemia – fetal haemoglobin concentration, haematology and clinical features
We report a 20-year-old female with sickle cell anaemia and with an HbF concentration of 15.8%. The patient was not using hydroxyurea and was not receiving regular blood transfusions. The patient never had chronic manifestations of sickle cell anaemia, only pain crises of a mild intensity. After laboratory tests, we found that she was homozygous for HbS with the Bantu/atypical haplotype, and was heterozygous for the XmnI site. The influence of the XmnI site on the expression of HbF can explain the amelioration in clinical features in this haplotype association in a case of sickle cell anaemia
Perubahan Fungsi Ruang Domestik di Sekitar Kampus Unpaz (Universidade Da Paz), Dili, Timor Leste
Universidade da Paz (UNPAZ) didirikan oleh Fundação Neon Metin (FNM) pada 9 Maret 2004, dan juga merupakan universitas swasta terbesar yang ada di Timor Leste saat ini. UNPAZ sangat berkembang dari segi pengembangan kampus (infrastruktur) maupun meningkatnya jumlah mahasiswa. Perkembangan kampus ini menyebabkan terjadinya Perubahan fungsi ruang pada Kampus UNPAZ. Selain kampus Perubahan fisik dan fungsi ruang domestik terjadi pada kampung sekitarnya, terutama Kampung Osindo I Manleuana. Kampung Osindo I Manleuana secara geografis terletak di Kelurahan Fatuhada, Kecamatan Dom-Aleixo, Kotamadya Dili, Timor Leste. Kampung ini mula-mula penduduknya bermata pencaharian sebagai petani. Letak kampung dekat jalur akses utama menuju Kampus UNPAZ menyebabkan kegiatan ekonomi penduduk menjadi berubah. Perubahan ini menyebabkan terjadinya Perubahan fungsi ruang domestik pada rumah tinggal maupun halamannya. Untuk meneliti lebih jauh lagi tentang proses Perubahan fungsi ruang domestik dengan kehadirannya Kampus UNPAZ, digunakan pendekatan penelitian kualitatif, dengan teknik pengumpulan data melalui observasi, wawancara, dokumentasi dan pembagian kuesioner pada masyarakat setempat. Perubahan-Perubahan fungsi ruang domestik di atas dianalisis dengan teori-teori yang relevan yaitu Perubahan fisik, ruang, bentuk ruang, dan pola organisasi ruang
Asymptotic integral kernel for ensembles of random normal matrices with radial potentials
We use the steepest descents method to study the integral kernel of a family of normal random matrix ensembles with eigenvalue distribution P_{N}(z_{1},...,z_{N}) = Z_{N}^{-1} e^{-NSigma_{i=1}^{N}V_{alpha}(z_{i})} Pi_{1leqi<jleqN}|z_{i}-z_{j}|^{2} where V_{alpha}(z)=|z|^{alpha}, z in C and alpha in ]0,infty[. Asymptotic analysis with error estimates are obtained. A corollary of this expansion is a scaling limit for the n-point function in terms of the integral kernel for the classical Segal--Bargmann space
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