12,901 research outputs found
Alternative axiomatics and complexity of deliberative STIT theories
We propose two alternatives to Xu's axiomatization of the Chellas STIT. The
first one also provides an alternative axiomatization of the deliberative STIT.
The second one starts from the idea that the historic necessity operator can be
defined as an abbreviation of operators of agency, and can thus be eliminated
from the logic of the Chellas STIT. The second axiomatization also allows us to
establish that the problem of deciding the satisfiability of a STIT formula
without temporal operators is NP-complete in the single-agent case, and is
NEXPTIME-complete in the multiagent case, both for the deliberative and the
Chellas' STIT.Comment: Submitted to the Journal of Philosophical Logic; 13 pages excluding
anne
Fixed-parameter tractability of multicut parameterized by the size of the cutset
Given an undirected graph , a collection of
pairs of vertices, and an integer , the Edge Multicut problem ask if there
is a set of at most edges such that the removal of disconnects
every from the corresponding . Vertex Multicut is the analogous
problem where is a set of at most vertices. Our main result is that
both problems can be solved in time , i.e.,
fixed-parameter tractable parameterized by the size of the cutset in the
solution. By contrast, it is unlikely that an algorithm with running time of
the form exists for the directed version of the problem, as
we show it to be W[1]-hard parameterized by the size of the cutset
Quantum Fluctuations Driven Orientational Disordering: A Finite-Size Scaling Study
The orientational ordering transition is investigated in the quantum
generalization of the anisotropic-planar-rotor model in the low temperature
regime. The phase diagram of the model is first analyzed within the mean-field
approximation. This predicts at a phase transition from the ordered to
the disordered state when the strength of quantum fluctuations, characterized
by the rotational constant , exceeds a critical value . As a function of temperature, mean-field theory predicts a range of
values of where the system develops long-range order upon cooling, but
enters again into a disordered state at sufficiently low temperatures
(reentrance). The model is further studied by means of path integral Monte
Carlo simulations in combination with finite-size scaling techniques,
concentrating on the region of parameter space where reentrance is predicted to
occur. The phase diagram determined from the simulations does not seem to
exhibit reentrant behavior; at intermediate temperatures a pronounced increase
of short-range order is observed rather than a genuine long-range order.Comment: 27 pages, 8 figures, RevTe
The time of the Roma in times of crisis: Where has European neoliberal capitalism failed?
This paper argues that the economic and financial crisis that has ensnared Europe from the late 2000s has been instrumental in reshaping employment and social relations in a detrimental way for the majority of the European people. It argues that the crisis has exacerbated the socio-economic position of most Roma people, immigrants as well as of other vulnerable groups. This development is approached here as an outcome of the widening structural inequalities that underpin the crisis within an increasingly neoliberalised Europe. Through recent policy developments and public discourses from a number of European countries I show how rising inequalities nurture racialised social tensions. My account draws on classic and contemporary theoretical propositions that have been propounded about the nature of capitalism, its contemporary re-articulation as well as its ramification for the future of Europe
Optimality program in segment and string graphs
Planar graphs are known to allow subexponential algorithms running in time
or for most of the paradigmatic
problems, while the brute-force time is very likely to be
asymptotically best on general graphs. Intrigued by an algorithm packing curves
in by Fox and Pach [SODA'11], we investigate which
problems have subexponential algorithms on the intersection graphs of curves
(string graphs) or segments (segment intersection graphs) and which problems
have no such algorithms under the ETH (Exponential Time Hypothesis). Among our
results, we show that, quite surprisingly, 3-Coloring can also be solved in
time on string graphs while an algorithm running
in time for 4-Coloring even on axis-parallel segments (of unbounded
length) would disprove the ETH. For 4-Coloring of unit segments, we show a
weaker ETH lower bound of which exploits the celebrated
Erd\H{o}s-Szekeres theorem. The subexponential running time also carries over
to Min Feedback Vertex Set but not to Min Dominating Set and Min Independent
Dominating Set.Comment: 19 pages, 15 figure
Efficient formalism for large scale ab initio molecular dynamics based on time-dependent density functional theory
A new "on the fly" method to perform Born-Oppenheimer ab initio molecular
dynamics (AIMD) is presented. Inspired by Ehrenfest dynamics in time-dependent
density functional theory, the electronic orbitals are evolved by a
Schroedinger-like equation, where the orbital time derivative is multiplied by
a parameter. This parameter controls the time scale of the fictitious
electronic motion and speeds up the calculations with respect to standard
Ehrenfest dynamics. In contrast to other methods, wave function orthogonality
needs not be imposed as it is automatically preserved, which is of paramount
relevance for large scale AIMD simulations.Comment: 5 pages, 3 color figures, revtex4 packag
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