16 research outputs found
An anisotropic distribution of spin vectors in asteroid families
Current amount of ~500 asteroid models derived from the disk-integrated
photometry by the lightcurve inversion method allows us to study not only the
spin-vector properties of the whole population of MBAs, but also of several
individual collisional families. We create a data set of 152 asteroids that
were identified by the HCM method as members of ten collisional families, among
them are 31 newly derived unique models and 24 new models with well-constrained
pole-ecliptic latitudes of the spin axes. The remaining models are adopted from
the DAMIT database or the literature. We revise the preliminary family
membership identification by the HCM method according to several additional
criteria - taxonomic type, color, albedo, maximum Yarkovsky semi-major axis
drift and the consistency with the size-frequency distribution of each family,
and consequently we remove interlopers. We then present the spin-vector
distributions for eight asteroidal families. We use a combined orbital- and
spin-evolution model to explain the observed spin-vector properties of objects
among collisional families. In general, we observe for studied families similar
trends in the (a_p, \beta) space: (i) larger asteroids are situated in the
proximity of the center of the family; (ii) asteroids with \beta>0{\deg} are
usually found to the right from the family center; (iii) on the other hand,
asteroids with \beta<0{\deg} to the left from the center; (iv) majority of
asteroids have large pole-ecliptic latitudes (|\beta|\gtrsim 30{\deg}); and
finally (v) some families have a statistically significant excess of asteroids
with \beta>0{\deg} or \beta<0{\deg}. Our numerical simulation of the long-term
evolution of a collisional family is capable of reproducing well the observed
spin-vector properties. Using this simulation, we also independently constrain
the age of families Flora (1.0\pm0.5 Gyr) and Koronis (2.5-4 Gyr).Comment: Accepted for publication in A&A (September 16, 2013
Structured models of cell migration incorporating molecular binding processes
The dynamic interplay between collective cell movement and the various
molecules involved in the accompanying cell signalling mechanisms plays a
crucial role in many biological processes including normal tissue development
and pathological scenarios such as wound healing and cancer. Information about
the various structures embedded within these processes allows a detailed
exploration of the binding of molecular species to cell-surface receptors
within the evolving cell population. In this paper we establish a general
spatio-temporal-structural framework that enables the description of molecular
binding to cell membranes coupled with the cell population dynamics. We first
provide a general theoretical description for this approach and then illustrate
it with two examples arising from cancer invasion
Pseudo-three-dimensional maps of the diffuse interstellar band at 862 nm
The diffuse interstellar bands (DIBs) are absorption lines observed in visual and near-infrared spectra of stars. Understanding their origin in the interstellar medium is one of the oldest problems in astronomical spectroscopy, as DIBs have been known since 1922. In a completely new approach to understanding DIBs, we combined information from nearly 500,000 stellar spectra obtained by the massive spectroscopic survey RAVE (Radial Velocity Experiment) to produce the first pseudo–three-dimensional map of the strength of the DIB at 8620 angstroms covering the nearest 3 kiloparsecs from the Sun, and show that it follows our independently constructed spatial distribution of extinction by interstellar dust along the Galactic plane. Despite having a similar distribution in the Galactic plane, the DIB 8620 carrier has a significantly larger vertical scale height than the dust. Even if one DIB may not represent the general DIB population, our observations outline the future direction of DIB research