2,888 research outputs found
EvoL: The new Padova T-SPH parallel code for cosmological simulations - I. Basic code: gravity and hydrodynamics
We present EvoL, the new release of the Padova N-body code for cosmological
simulations of galaxy formation and evolution. In this paper, the basic Tree +
SPH code is presented and analysed, together with an overview on the software
architectures. EvoL is a flexible parallel Fortran95 code, specifically
designed for simulations of cosmological structure formation on cluster,
galactic and sub-galactic scales. EvoL is a fully Lagrangian self-adaptive
code, based on the classical Oct-tree and on the Smoothed Particle
Hydrodynamics algorithm. It includes special features such as adaptive
softening lengths with correcting extra-terms, and modern formulations of SPH
and artificial viscosity. It is designed to be run in parallel on multiple CPUs
to optimize the performance and save computational time. We describe the code
in detail, and present the results of a number of standard hydrodynamical
tests.Comment: 33 pages, 49 figures, accepted on A&
Angular Signatures of Annihilating Dark Matter in the Cosmic Gamma-Ray Background
The extragalactic cosmic gamma-ray background (CGB) is an interesting channel
to look for signatures of dark matter annihilation. In particular, besides the
imprint in the energy spectrum, peculiar anisotropy patterns are expected
compared to the case of a pure astrophysical origin of the CGB. We take into
account the uncertainties in the dark matter clustering properties on
sub-galactic scales, deriving two possible anisotropy scenarios. A clear dark
matter angular signature is achieved when the annihilation signal receives only
a moderate contribution from sub-galactic clumps and/or cuspy haloes.
Experimentally, if galactic foregrounds systematics are efficiently kept under
control, the angular differences are detectable with the forthcoming GLAST
observatory, provided that the annihilation signal contributes to the CGB for a
fraction >10-20%. If, instead, sub-galactic structures have a more prominent
role, the astrophysical and dark matter anisotropies become degenerate,
correspondingly diluting the DM signature. As complementary observables we also
introduce the cross-correlation between surveys of galaxies and the CGB and the
cross-correlation between different energy bands of the CGB and we find that
they provide a further sensitive tool to detect the dark matter angular
signatures.Comment: 13 pages, 8 figures; improved discussion; matches published versio
Fight to Win! Tools for Confronting Capital
activism anarchism capital as power political-economic disruption campaigns (PEDCs)Anarchists have generally rejected the idea that there is or ought to be a pure or inherently revolutionary strategy or tactic. In this chapter we make use of the capital-as-power theory of value and capital in a way that informs and supports the ad hoc perspective on struggle and fighting to win. Our primary purpose is to propose a method based on this theory as a means for social justice activists to assess political-economic disruption campaigns (PEDCs). Such an analysis is a needed component of an anarchist economics
Magnetic field structure due to the global velocity field in spiral galaxies
We present a set of global, self-consistent N-body/SPH simulations of the
dynamic evolution of galactic discs with gas and including magnetic fields. We
have implemented a description to follow the evolution of magnetic fields with
the ideal induction equation in the SPH part of the Vine code. Results from a
direct implementation of the field equations are compared to a representation
by Euler potentials, which pose a div(B)-free description, an constraint not
fulfilled for the direct implementation. All simulations are compared to an
implementation of magnetic fields in the Gadget code which includes also
cleaning methods for div(B).
Starting with a homogeneous seed field we find that by differential rotation
and spiral structure formation of the disc the field is amplified by one order
of magnitude within five rotation periods of the disc. The amplification is
stronger for higher numerical resolution. Moreover, we find a tight connection
of the magnetic field structure to the density pattern of the galaxy in our
simulations, with the magnetic field lines being aligned with the developing
spiral pattern of the gas. Our simulations clearly show the importance of
non-axisymmetry for the evolution of the magnetic field.Comment: 17 pages, 18 figure
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The Optimal Behaviour of a Split Model of Word Recognition Resembles Observed Fixation Behaviour
We expand upon the case for believing that the initial precise splitting of the foveal projection to the visual cortex fundamentally conditions the whole process of visual word recognition. We explore the optimal behaviour of a split architecture that attempts to divide its processing load equally between its two halves. We successfully model three aspects of fixation behaviour in human readers: (a) the positioning of the optimal viewing position to the left of the midpoint of the word, (b) a displaced Gaussian curve of letter-report accuracy resembling an RVF advantage, (c) the tendency for shorter words not to be directly fixated
Devonian and Carboniferous stratigraphical correlation and interpretation in the Central North Sea, Quadrants 25 – 44
This report details the stratigraphy and palaeogeography of Devonian and Carboniferous rocks of the UK Central North Sea for the 21CXRM Palaeozoic project. The 21CXRM Palaeozoic project results are delivered as a series of reports and digital datasets for each area.
This report describes the stratigraphical correlation of Devonian and Carboniferous strata south of, and over, the Mid North Sea High (Quadrants 25-44) using both well and seismic data. It builds on the work of Cameron (1993a) and others, and uses lithostratigraphy to understand how facies vary across the area. A major outcome of this work is the detailed description of the Cleveland Group, the basinal correlative of the Scremerston, Yoredale and Millstone Grit formations within the offshore extension of the Cleveland Basin
SPHS: Smoothed Particle Hydrodynamics with a higher order dissipation switch
We present a novel implementation of Smoothed Particle Hydrodynamics (SPHS)
that uses the spatial derivative of the velocity divergence as a higher order
dissipation switch. Our switch -- which is second order accurate -- detects
flow convergence before it occurs. If particle trajectories are going to cross,
we switch on the usual SPH artificial viscosity, as well as conservative
dissipation in all advected fluid quantities (for example, the entropy). The
viscosity and dissipation terms (that are numerical errors) are designed to
ensure that all fluid quantities remain single-valued as particles approach one
another, to respect conservation laws, and to vanish on a given physical scale
as the resolution is increased. SPHS alleviates a number of known problems with
`classic' SPH, successfully resolving mixing, and recovering numerical
convergence with increasing resolution. An additional key advantage is that --
treating the particle mass similarly to the entropy -- we are able to use
multimass particles, giving significantly improved control over the refinement
strategy. We present a wide range of code tests including the Sod shock tube,
Sedov-Taylor blast wave, Kelvin-Helmholtz Instability, the `blob test', and
some convergence tests. Our method performs well on all tests, giving good
agreement with analytic expectations.Comment: 21 pages; 15 Figures. Submitted to MNRAS. Comments welcom
Resolving Cosmic Neutrino Structure: A Hybrid Neutrino N-body Scheme
We present the first simulation capable of resolving the structure of
neutrino clustering on Mpc scales. The method combines grid- and particle-based
methods and achieves very good accuracy on both small and large scales, while
keeping CPU consumption under control. Such simulations are not only ideal for
calculating the non-linear matter power spectrum but also particularly relevant
for studies of how neutrinos cluster in galaxy- or cluster-sized halos. We
perform the largest neutrino N-body simulation to date, effectively containing
10 different neutrino hot dark matter components with different thermal
properties.Comment: 13 pages, 6 figure
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