517 research outputs found
On Recurrent Reachability for Continuous Linear Dynamical Systems
The continuous evolution of a wide variety of systems, including
continuous-time Markov chains and linear hybrid automata, can be described in
terms of linear differential equations. In this paper we study the decision
problem of whether the solution of a system of linear
differential equations reaches a target
halfspace infinitely often. This recurrent reachability problem can
equivalently be formulated as the following Infinite Zeros Problem: does a
real-valued function satisfying a
given linear differential equation have infinitely many zeros? Our main
decidability result is that if the differential equation has order at most ,
then the Infinite Zeros Problem is decidable. On the other hand, we show that a
decision procedure for the Infinite Zeros Problem at order (and above)
would entail a major breakthrough in Diophantine Approximation, specifically an
algorithm for computing the Lagrange constants of arbitrary real algebraic
numbers to arbitrary precision.Comment: Full version of paper at LICS'1
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Regulating Homeopathic Drugs: Pragmatic Solutions for the Food and Drug Administration
Despite the growth of both the use of homeopathic drugs and the homeopathic drug industry, the Food and Drug Administration (FDA) has not altered its regulatory scheme for homeopathic drugs. As a result, homeopathic drugs are allowed on the market without any evidence that they are either safe or effective. The growing use of homeopathic drugs suggests that the FDA should reconsider its stance on homeopathic drugs so as to ensure consumer safety but yet preserve consumer choice
Flexible Resolution of Authorisation Conflicts in Distributed Systems
Flexible Resolution of Authorisation Conflicts in Distributed System
Counterexample Guided Abstraction Refinement Algorithm for Propositional Circumscription
Circumscription is a representative example of a nonmonotonic reasoning
inference technique. Circumscription has often been studied for first order
theories, but its propositional version has also been the subject of extensive
research, having been shown equivalent to extended closed world assumption
(ECWA). Moreover, entailment in propositional circumscription is a well-known
example of a decision problem in the second level of the polynomial hierarchy.
This paper proposes a new Boolean Satisfiability (SAT)-based algorithm for
entailment in propositional circumscription that explores the relationship of
propositional circumscription to minimal models. The new algorithm is inspired
by ideas commonly used in SAT-based model checking, namely counterexample
guided abstraction refinement. In addition, the new algorithm is refined to
compute the theory closure for generalized close world assumption (GCWA).
Experimental results show that the new algorithm can solve problem instances
that other solutions are unable to solve
Surface Instabilities and Magnetic Soft Matter
We report on the formation of surface instabilities in a layer of
thermoreversible ferrogel when exposed to a vertical magnetic field. Both
static and time dependent magnetic fields are employed. Under variations of
temperature, the viscoelastic properties of our soft magnetic matter can be
tuned. Stress relaxation experiments unveil a stretched exponential scaling of
the shear modulus, with an exponent of beta=1/3. The resulting magnetic
threshold for the formation of Rosensweig-cusps is measured for different
temperatures, and compared with theoretical predictions by Bohlius et. al. in
J. Phys.: Condens. Matter., 2006, 18, 2671-2684.Comment: accepted to Soft Matte
Holography, Unfolding and Higher-Spin Theory
Holographic duality is argued to relate classes of models that have
equivalent unfolded formulation, hence exhibiting different space-time
visualizations for the same theory. This general phenomenon is illustrated by
the higher-spin gauge theory shown to be dual to the theory of 3d
conformal currents of all spins interacting with 3d conformal higher-spin
fields of Chern-Simons type. Generally, the resulting 3d boundary conformal
theory is nonlinear, providing an interacting version of the 3d boundary sigma
model conjectured by Klebanov and Polyakov to be dual to the HS theory
in the large limit. Being a gauge theory it escapes the conditions of the
theorem of Maldacena and Zhiboedov, which force a 3d boundary conformal theory
to be free. Two reductions of particular higher-spin gauge theories where
boundary higher-spin gauge fields decouple from the currents and which have
free boundary duals are identified. Higher-spin holographic duality is also
discussed for the cases of and duality between higher-spin
theories and nonrelativistic quantum mechanics. In the latter case it is shown
in particular that () geometry in the higher-spin setup is dual to
the (inverted) harmonic potential in the quantum-mechanical setup.Comment: 57 pages, V2: Acknowledgements, references, comments, clarifications
and new section on reductions of particular HS theories associated with free
boundary theories are added. Typos corrected, V3. Minor corrections:
clarification in section 9 is added and typos correcte
Conditional Planning with External Functions
Abstract. We introduce the logic-based planning language Kc as an extension of K [5]. Kc has two advantages upon K. First, the introduction of external func-tion calls in the rules of a planning description allows the knowledge engineer to describe certain planning domains, e.g. involving complex action effects, in a more intuitive fashion then is possible in K. Secondly, in contrast to the confor-mant planning framework K, Kc is formalized as a conditional planning system, which enables Kc to solve planning problems that are impossible to express in K, e.g. involving sensing actions. A prototype implementation of conditional plan-ning with Kc is build on top of the DLVKsystem, and we illustrate its use by some small examples.
Answer Set Programming for Non-Stationary Markov Decision Processes
Non-stationary domains, where unforeseen changes happen, present a challenge
for agents to find an optimal policy for a sequential decision making problem.
This work investigates a solution to this problem that combines Markov Decision
Processes (MDP) and Reinforcement Learning (RL) with Answer Set Programming
(ASP) in a method we call ASP(RL). In this method, Answer Set Programming is
used to find the possible trajectories of an MDP, from where Reinforcement
Learning is applied to learn the optimal policy of the problem. Results show
that ASP(RL) is capable of efficiently finding the optimal solution of an MDP
representing non-stationary domains
Asymptotics of Selberg-like integrals: The unitary case and Newton's interpolation formula
We investigate the asymptotic behavior of the Selberg-like integral ,
as for different scalings of the parameters and with .
Integrals of this type arise in the random matrix theory of electronic
scattering in chaotic cavities supporting channels in the two attached
leads. Making use of Newton's interpolation formula, we show that an asymptotic
limit exists and we compute it explicitly
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