8,267 research outputs found
A decidable subclass of finitary programs
Answer set programming - the most popular problem solving paradigm based on
logic programs - has been recently extended to support uninterpreted function
symbols. All of these approaches have some limitation. In this paper we propose
a class of programs called FP2 that enjoys a different trade-off between
expressiveness and complexity. FP2 programs enjoy the following unique
combination of properties: (i) the ability of expressing predicates with
infinite extensions; (ii) full support for predicates with arbitrary arity;
(iii) decidability of FP2 membership checking; (iv) decidability of skeptical
and credulous stable model reasoning for call-safe queries. Odd cycles are
supported by composing FP2 programs with argument restricted programs
Partial Preferences for Mediated Bargaining
In this work we generalize standard Decision Theory by assuming that two
outcomes can also be incomparable. Two motivating scenarios show how
incomparability may be helpful to represent those situations where, due to lack
of information, the decision maker would like to maintain different options
alive and defer the final decision. In particular, a new axiomatization is
given which turns out to be a weakening of the classical set of axioms used in
Decision Theory. Preliminary results show how preferences involving complex
distributions are related to judgments on single alternatives.Comment: In Proceedings SR 2014, arXiv:1404.041
On finitely recursive programs
Disjunctive finitary programs are a class of logic programs admitting
function symbols and hence infinite domains. They have very good computational
properties, for example ground queries are decidable while in the general case
the stable model semantics is highly undecidable. In this paper we prove that a
larger class of programs, called finitely recursive programs, preserves most of
the good properties of finitary programs under the stable model semantics,
namely: (i) finitely recursive programs enjoy a compactness property; (ii)
inconsistency checking and skeptical reasoning are semidecidable; (iii)
skeptical resolution is complete for normal finitely recursive programs.
Moreover, we show how to check inconsistency and answer skeptical queries using
finite subsets of the ground program instantiation. We achieve this by
extending the splitting sequence theorem by Lifschitz and Turner: We prove that
if the input program P is finitely recursive, then the partial stable models
determined by any smooth splitting omega-sequence converge to a stable model of
P.Comment: 26 pages, Preliminary version in Proc. of ICLP 2007, Best paper awar
Probing defects and correlations in the hydrogen-bond network of ab initio water
The hydrogen-bond network of water is characterized by the presence of
coordination defects relative to the ideal tetrahedral network of ice, whose
fluctuations determine the static and time-dependent properties of the liquid.
Because of topological constraints, such defects do not come alone, but are
highly correlated coming in a plethora of different pairs. Here we discuss in
detail such correlations in the case of ab initio water models and show that
they have interesting similarities to regular and defective solid phases of
water. Although defect correlations involve deviations from idealized
tetrahedrality, they can still be regarded as weaker hydrogen bonds that retain
a high degree of directionality. We also investigate how the structure and
population of coordination defects is affected by approximations to the
inter-atomic potential, finding that in most cases, the qualitative features of
the hydrogen bond network are remarkably robust
Clustering and collision of inertial particles in random velocity fields
The influence of clustering on the collision rate of inertial particles in a
smooth random velocity field, mimicking the smaller scales of a turbulent flow,
is analyzed. For small values of the the ratio between the relaxation time of
the particle velocity and the characteristic time of the field, the effect of
clusters is to make more energetic collisions less likely. The result is
independent of the flow dimensionality and is due only to the origin of
collisions in the process of caustic formation.Comment: 4 pages, 3 figures, revtex
Did Going North Give Us Migraine? An Evolutionary Approach on Understanding Latitudinal Differences in Migraine Epidemiology
This commentary discusses a recent publication by evolutionary biologists with strong implications for migraine experts. The Authors showed that a gene polymorphism associated with migraine gave our ancestors an evolutionary advantage when colonizing northern, and thus colder, territories. They then highlight that the prevalence of migraine may differ among countries because of climatic adaptation. These results may prove useful in planning both epidemiological and physiological studies in the field of migraine
Charged rotating noncommutative black holes
In this paper we complete the program of the noncomutative geometry inspired
black holes, providing the richest possible solution, endowed with mass, charge
and angular momentum. After providing a prescription for employing the
Newman-Janis algorithm in the case of nonvanishing stress tensors, we find
regular axisymmetric charged black holes in the presence of a minimal length.
We study also the new thermodynamics and we determine the corresponding
higher-dimensional solutions. As a conclusion we make some consideration about
possible applications.Comment: 13 pages, 3 figures, correction of a typesetting inattention, updated
reference list, version accepted for publication on Physical Review
Managerial Hedging and Portfolio Monitoring
Incentive compensation induces correlation between the portfolio of managers and the cash flow of the firms they manage. This correlation exposes managers to risk and hence gives them an incentive to hedge against the poor performance of their firms. We study the agency problem between shareholders and a manager when the manager can hedge his incentive compensation using financial markets and shareholders cannot perfectly monitor the manager’s portfolio in order to keep him from hedging the risk in his compensation. In particular, shareholders can monitor the manager’s portfolio stochastically, and since monitoring is costly governance is imperfect. If managerial hedging is detected, shareholders can seize the payoffs of the manager’s trades. We show that at the optimal contract: (i) the manager’s portfolio is monitored only when the firm performs poorly, (ii) the more costly monitoring is, the more sensitive is the manager’s compensation to firm performance, and (iii)conditional on the firm’s performance, the manager’s compensation is lower when his portfolio is monitored, even if no hedging is revealed by monitoring.executive compensation, incentives, monitoring, corporate governance.
Spectral dimension of a quantum universe
In this paper, we calculate in a transparent way the spectral dimension of a
quantum spacetime, considering a diffusion process propagating on a fluctuating
manifold. To describe the erratic path of the diffusion, we implement a minimal
length by averaging the graininess of the quantum manifold in the flat space
case. As a result we obtain that, for large diffusion times, the quantum
spacetime behaves like a smooth differential manifold of discrete dimension. On
the other hand, for smaller diffusion times, the spacetime looks like a fractal
surface with a reduced effective dimension. For the specific case in which the
diffusion time has the size of the minimal length, the spacetime turns out to
have a spectral dimension equal to 2, suggesting a possible renormalizable
character of gravity in this regime. For smaller diffusion times, the spectral
dimension approaches zero, making any physical interpretation less reliable in
this extreme regime. We extend our result to the presence of a background field
and curvature. We show that in this case the spectral dimension has a more
complicated relation with the diffusion time, and conclusions about the
renormalizable character of gravity become less straightforward with respect to
what we found with the flat space analysis.Comment: 5 pages, 1 figure, references added, typos corrected, title changed,
final version published in Physical Review
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