Determination of the Local Dark Matter Density in our Galaxy

The rotation curve, the total mass and the gravitational potential of the Galaxy are sensitive measurements of the dark matter halo profile. In this publication cuspy and cored DM halo profiles are analysed with respect to recent astronomical constraints in order to constrain the shape of the Galactic DM halo and the local DM density. All Galactic density components (luminous matter and DM) are parametrized. Then the total density distribution is constrained by astronomical observations: 1) the total mass of the Galaxy, 2) the total matter density at the position of the Sun, 3) the surface density of the visible matter, 4) the surface density of the total matter in the vicinity of the Sun, 5) the rotation speed of the Sun and 6) the shape of the velocity distribution within and above the Galactic disc. The mass model of the Galaxy is mainly constrained by the local matter density (Oort limit), the rotation speed of the Sun and the total mass of the Galaxy from tracer stars in the halo. It is shown from a statistical chi^2 fit to all data that the local DM density is strongly positively (negatively) correlated with the scale length of the DM halo (baryonic disc). Since these scale lengths are poorly constrained the local DM density can vary from 0.2 to 0.4 GeV/cm^3 (0.005 - 0.01 M_sun/pc^3) for a spherical DM halo profile and allowing total Galaxy masses up to 2 * 10^12 M_sun. For oblate DM halos and dark matter discs, as predicted in recent N-body simulations, the local DM density can be increased significantly.Comment: 10 pages, 8 figure

Causation in perspective: are all causal claims equally warranted?

In a paper ‘Causation in Context’ (2007) Peter Menzies has argued that the truth value of causal judgments is perspective-relative (i.e. their truth value does not depend entirely on mind-independent structures). His arguments are confined to causation as difference making (a term he uses to cover probabilistic, counterfactual and regularity views of causation). In this paper we first briefly present Menzies’ arguments. Then we show that perspective-relativity also holds for causation in the sense of process theories. These parts of the paper prepare the ground for the topic we really want to investigate: we want to find out whether this perspective-relativity leads to an epistemic predicament with respect to causal claims. The potential epistemic predicament we consider is that all causal claims would be equally warranted

A Multi-Core Solver for Parity Games

We describe a parallel algorithm for solving parity games,\ud with applications in, e.g., modal mu-calculus model\ud checking with arbitrary alternations, and (branching) bisimulation\ud checking. The algorithm is based on Jurdzinski's Small Progress\ud Measures. Actually, this is a class of algorithms, depending on\ud a selection heuristics.\ud \ud Our algorithm operates lock-free, and mostly wait-free (except for\ud infrequent termination detection), and thus allows maximum\ud parallelism. Additionally, we conserve memory by avoiding storage\ud of predecessor edges for the parity graph through strictly\ud forward-looking heuristics.\ud \ud We evaluate our multi-core implementation's behaviour on parity games\ud obtained from mu-calculus model checking problems for a set of\ud communication protocols, randomly generated problem instances, and\ud parametric problem instances from the literature.\ud \u

Black ravens, white shoes and scientific evidence : the Ravens Paradox and/in scientific practice

1BLACK RAVENS, WHITE SHOES AND SCIENTIFIC EVIDENCE.THE RAVENS PARADOX AND/IN SCIENTIFIC PRACTICEErik Weber, Mathieu Beirlaen&Inge De BalCentre for Logic and Philosophy of ScienceGhent University (UGent)Blandijnberg 2, B-9000 Gent , BelgiumAbstractA well-known consequence of Hempel’s account of confirmation is the RavensParadox. In this paper we discuss this paradox from the viewpointof scientific practice. The main worry, when looking at this paradox from a scientific practiceperspective, is that it seems to lead to problematic methodological advice for scientists: it seems to licence ‘indoor ornithology’. We show that this problematic advice only follows from Hempel’s account if one adoptsa suboptimal viewof what counts as evidence for anhypothesis. We present and defend a more sophisticated viewof what counts as evidence, whichtakesrandom sampling–an important methodological principle in scientific practice–into account. On this sophisticated view, the problematic methodological advice connected tothe RavensParadox is avoided

Boosting Multi-Core Reachability Performance with Shared Hash Tables

This paper focuses on data structures for multi-core reachability, which is a key component in model checking algorithms and other verification methods. A cornerstone of an efficient solution is the storage of visited states. In related work, static partitioning of the state space was combined with thread-local storage and resulted in reasonable speedups, but left open whether improvements are possible. In this paper, we present a scaling solution for shared state storage which is based on a lockless hash table implementation. The solution is specifically designed for the cache architecture of modern CPUs. Because model checking algorithms impose loose requirements on the hash table operations, their design can be streamlined substantially compared to related work on lockless hash tables. Still, an implementation of the hash table presented here has dozens of sensitive performance parameters (bucket size, cache line size, data layout, probing sequence, etc.). We analyzed their impact and compared the resulting speedups with related tools. Our implementation outperforms two state-of-the-art multi-core model checkers (SPIN and DiVinE) by a substantial margin, while placing fewer constraints on the load balancing and search algorithms.Comment: preliminary repor

Indispensability arguments in favour of reductive explanations

Instances of explanatory reduction are often advocated on metaphysical grounds; given that the only real things in the world are subatomic particles and their interaction, we have to try to explain everything in terms of the laws of physics. In this paper, we show that explanatory reduction cannot be defended on metaphysical grounds. Nevertheless, indispensability arguments for reductive explanations can be developed, taking into account actual scientific practice and the role of epistemic interests. Reductive explanations might be indispensable to address some epistemic interest answering a specific explanation-seeking question in the most accurate, adequate and efficient way. Just like explanatory pluralists often advocate the indispensability of higher levels of explanation pointing at the pragmatic value of the explanatory information obtained on these higher levels, we argue that explanatory reduction – traditionally understood as the contender of pluralism – can be defended in a similar way. The pragmatic value reductionist, lower level explanations might have in the biomedical sciences and the social sciences is illustrated by some case studies