21 research outputs found
Dynamical Dark Energy simulations: high accuracy Power Spectra at high redshift
Accurate predictions on non--linear power spectra, at various redshift z,
will be a basic tool to interpret cosmological data from next generation mass
probes, so obtaining key information on Dark Energy nature. This calls for high
precision simulations, covering the whole functional space of w(z) state
equations and taking also into account the admitted ranges of other
cosmological parameters; surely a difficult task. A procedure was however
suggested, able to match the spectra at z=0, up to k~3, hMpc^{-1}, in
cosmologies with an (almost) arbitrary w(z), by making recourse to the results
of N-body simulations with w = const. In this paper we extend such procedure to
high redshift and test our approach through a series of N-body gravitational
simulations of various models, including a model closely fitting WMAP5 and
complementary data. Our approach detects w= const. models, whose spectra meet
the requirement within 1% at z=0 and perform even better at higher redshift,
where they are close to a permil precision. Available Halofit expressions,
extended to (constant) w \neq -1 are unfortunately unsuitable to fit the
spectra of the physical models considered here. Their extension to cover the
desired range should be however feasible, and this will enable us to match
spectra from any DE state equation.Comment: method definitely improved in semplicity and efficacy,accepted for
publication on JCA
Semi-empirical catalog of early-type galaxy-halo systems: dark matter density profiles, halo contraction and dark matter annihilation strength
With SDSS galaxy data and halo data from up-to-date N-body simulations we
construct a semi-empirical catalog (SEC) of early-type systems by making a
self-consistent bivariate statistical match of stellar mass (M_star) and
velocity dispersion (sigma) with halo virial mass (M_vir). We then assign
stellar mass profile and velocity dispersion profile parameters to each system
in the SEC using their observed correlations with M_star and sigma.
Simultaneously, we solve for dark matter density profile of each halo using the
spherical Jeans equation. The resulting dark matter density profiles deviate in
general from the dissipationless profile of NFW or Einasto and their mean inner
density slope and concentration vary systematically with M_vir. Statistical
tests of the distribution of profiles at fixed M_vir rule out the null
hypothesis that it follows the distribution predicted by N-body simulations for
M_vir ~< 10^{13.5-14.5} M_solar. These dark matter profiles imply that dark
matter density is, on average, enhanced significantly in the inner region of
halos with M_vir ~< 10^{13.5-14.5} M_solar supporting halo contraction. The
main characteristics of halo contraction are: (1) the mean dark matter density
within the effective radius has increased by a factor varying systematically up
to ~ 3-4 at M_vir = 10^{12} M_solar, and (2) the inner density slope has a mean
of ~ 1.3 with rho(r) ~ r^{-alpha} and a halo-to-halo rms scatter of
rms(alpha) ~ 0.4-0.5 for 10^{12} M_solar ~< M_vir ~< 10^{13-14} M_solar steeper
than the NFW profile (alpha=1). Based on our results we predict that halos of
nearby elliptical and lenticular galaxies can, in principle, be promising
targets for gamma-ray emission from dark matter annihilation.Comment: 43 pages, 20 figures, JCAP, revised and accepted versio
Progress towards materials science above 1000 GPa (10 Mbar) on the NIF laser
Solid state dynamics experiments at extreme pressures, P > 1000 GPa (10 Mbar), and ultrahigh strain rates (106–108 s−1) are being developed for the National Ignition Facility (NIF) laser. These experiments will open up exploration of new regimes of materials science at an order of magnitude higher pressures than have been possible to date. Such extreme, solid state conditions can be accessed with a ramped pressure drive. The experimental, computational, and theoretical techniques are being developed and tested on the Omega laser. Constitutive models for solid state strength under these conditions are tested by comparing simulations with experiments measuring perturbation growth from the Rayleigh–Taylor instability in solid state samples of vanadium. Radiography techniques using synchronized bursts of x-rays have been developed to diagnose this perturbation growth. Velocity interferometer measurements (VISAR) establish the high pressure conditions generated by the ramped drive. Experiments on Omega measuring dynamic material strength at peak pressures of ~1 Mbar will be discussed. The time resolved observation of foil cracking and void formation show the need for tamped samples and a planar drive
Pines
Pinus is the most important genus within the Family Pinaceae and also within the gymnosperms by the number of species (109 species recognized by Farjon 2001) and by its contribution to forest ecosystems. All pine species are evergreen trees or shrubs. They are widely distributed in the northern hemisphere, from tropical areas to northern areas in America and Eurasia. Their natural range reaches the equator only in Southeast Asia. In Africa, natural occurrences are confined to the Mediterranean basin. Pines grow at various elevations from sea level (not usual in tropical areas) to highlands. Two main regions of diversity are recorded, the most important one in Central America (43 species found in Mexico) and a secondary one in China. Some species have a very wide natural range (e.g., P. ponderosa, P. sylvestris). Pines are adapted to a wide range of ecological conditions: from tropical (e.g., P. merkusii, P. kesiya, P. tropicalis), temperate (e.g., P. pungens, P. thunbergii), and subalpine (e.g., P. albicaulis, P. cembra) to boreal (e.g., P. pumila) climates (Richardson and Rundel 1998, Burdon 2002). They can grow in quite pure stands or in mixed forest with other conifers or broadleaved trees. Some species are especially adapted to forest fires, e.g., P. banksiana, in which fire is virtually essential for cone opening and seed dispersal. They can grow in arid conditions, on alluvial plain soils, on sandy soils, on rocky soils, or on marsh soils. Trees of some species can have a very long life as in P. longaeva (more than 3,000 years)