11 research outputs found
A universal velocity distribution of relaxed collisionless structures
Several general trends have been identified for equilibrated,
self-gravitating collisionless systems, such as density or anisotropy profiles.
These are integrated quantities which naturally depend on the underlying
velocity distribution function (VDF) of the system. We study this VDF through a
set of numerical simulations, which allow us to extract both the radial and the
tangential VDF. We find that the shape of the VDF is universal, in the sense
that it depends only on two things namely the dispersion (radial or tangential)
and the local slope of the density. Both the radial and the tangential VDF's
are universal for a collection of simulations, including controlled collisions
with very different initial conditions, radial infall simulation, and
structures formed in cosmological simulations.Comment: 13 pages, 6 figures; oversimplified analysis corrected; changed
abstract and conclusions; significantly extended discussio
The velocity anisotropy - density slope relation
One can solve the Jeans equation analytically for equilibrated dark matter
structures, once given two pieces of input from numerical simulations. These
inputs are 1) a connection between phase-space density and radius, and 2) a
connection between velocity anisotropy and density slope, the \alpha-\beta
relation. The first (phase-space density v.s. radius) has already been analysed
through several different simulations, however the second (\alpha-\beta
relation) has not been quantified yet. We perform a large set of numerical
experiments in order to quantify the slope and zero-point of the \alpha-\beta
relation. We find strong indication that the relation is indeed an attractor.
When combined with the assumption of phase-space being a power-law in radius,
this allows us to conclude that equilibrated dark matter structures indeed have
zero central velocity anisotropy \beta_0 = 0, central density slope of \alpha_0
= -0.8, and outer anisotropy of \beta_\infty = 0.5.Comment: 15 pages, 7 figure
Stellar polytropes and Navarro-Frenk-White halo models: comparison with observations
Motivated by the possible conflict between the Navarro-Frenk-White(NFW) model
predictions for the dark matter contents of galactic systems and its
correlation with baryonic surface density, we will explore an alternative
paradigm for the description of dark matter halos. Such an alternative emerges
from Tsallis' non-extensive thermodynamics applied to self-gravitating systems
and leads to the so-called ``stellar polytrope'' (SP) model. We consider that
this could be a better approach to real structures rather than the isothermal
model, given the fact that the first one takes into account the non-extensivity
of energy and entropy present in these type of systems characterized by
long-range interactions. We compare a halo based on the Navarro-Frenk-White
(NFW) and one which follows the SP description. Analyzing the dark matter
contents estimated by means of global physical parameters of galactic disks,
obtained from a sample of actual galaxies, with the ones of the unobserved dark
matter halos, we conclude that the SP model is favored over the NFW model in
such a comparison.Comment: 21 pages, 4 figures. Accepted for publication in the Journal of
Cosmology and Astroparticle Physic
Hypothetical Hyperbolic Encounters between Venus and Proto-Mercury that Partially Stripped Away Proto-Mercury’s Mantle
DEBIO 1143, an IAP inhibitor, reverses carboplatin resistance in ovarian cancer cells and triggers apoptotic or necroptotic cell death
Mechanism-based mathematical modeling of combined gemcitabine and birinapant in pancreatic cancer cells
Oral contraceptive use and reproductive factors and risk of ovarian cancer in the European Prospective Investigation into Cancer and Nutrition.
BACKGROUND: It is well established that parity and use of oral contraceptives reduce the risk of ovarian cancer, but the associations with other reproductive variables are less clear. METHODS: We examined the associations of oral contraceptive use and reproductive factors with ovarian cancer risk in the European Prospective Investigation into Cancer and Nutrition. Among 327,396 eligible women, 878 developed ovarian cancer over an average of 9 years. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox proportional hazard models stratified by centre and age, and adjusted for smoking status, body mass index, unilateral ovariectomy, simple hysterectomy, menopausal hormone therapy, and mutually adjusted for age at menarche, age at menopause, number of full-term pregnancies and duration of oral contraceptive use. RESULTS: Women who used oral contraceptives for 10 or more years had a significant 45% (HR, 0.55; 95% CI, 0.41-0.75) lower risk compared with users of 1 year or less (P-trend, <0.01). Compared with nulliparous women, parous women had a 29% (HR, 0.71; 95% CI, 0.59-0.87) lower risk, with an 8% reduction in risk for each additional pregnancy. A high age at menopause was associated with a higher risk of ovarian cancer (>52 vs ≤ 45 years: HR, 1.46; 95% CI, 1.06-1.99; P-trend, 0.02). Age at menarche, age at first full-term pregnancy, incomplete pregnancies and breastfeeding were not associated with risk. CONCLUSION: This study shows a strong protective association of oral contraceptives and parity with ovarian cancer risk, a higher risk with a late age at menopause, and no association with other reproductive factors