38,933 research outputs found
2Planning for Contingencies: A Decision-based Approach
A fundamental assumption made by classical AI planners is that there is no
uncertainty in the world: the planner has full knowledge of the conditions
under which the plan will be executed and the outcome of every action is fully
predictable. These planners cannot therefore construct contingency plans, i.e.,
plans in which different actions are performed in different circumstances. In
this paper we discuss some issues that arise in the representation and
construction of contingency plans and describe Cassandra, a partial-order
contingency planner. Cassandra uses explicit decision-steps that enable the
agent executing the plan to decide which plan branch to follow. The
decision-steps in a plan result in subgoals to acquire knowledge, which are
planned for in the same way as any other subgoals. Cassandra thus distinguishes
the process of gathering information from the process of making decisions. The
explicit representation of decisions in Cassandra allows a coherent approach to
the problems of contingent planning, and provides a solid base for extensions
such as the use of different decision-making procedures.Comment: See http://www.jair.org/ for any accompanying file
Permutation Symmetric Critical Phases in Disordered Non-Abelian Anyonic Chains
Topological phases supporting non-abelian anyonic excitations have been
proposed as candidates for topological quantum computation. In this paper, we
study disordered non-abelian anyonic chains based on the quantum groups
, a hierarchy that includes the FQH state and the proposed
Fibonacci state, among others. We find that for odd these
anyonic chains realize infinite randomness critical {\it phases} in the same
universality class as the permutation symmetric multi-critical points of
Damle and Huse (Phys. Rev. Lett. 89, 277203 (2002)). Indeed, we show that the
pertinent subspace of these anyonic chains actually sits inside the symmetric sector of the Damle-Huse model, and this symmetry stabilizes the phase.Comment: 13 page
Fully Unintegrated Parton Correlation Functions and Factorization in Lowest Order Hard Scattering
Motivated by the need to correct the potentially large kinematic errors in
approximations used in the standard formulation of perturbative QCD, we
reformulate deeply inelastic lepton-proton scattering in terms of gauge
invariant, universal parton correlation functions which depend on all
components of parton four-momentum. Currently, different hard QCD processes are
described by very different perturbative formalisms, each relying on its own
set of kinematical approximations. In this paper we show how to set up
formalism that avoids approximations on final-state momenta, and thus has a
very general domain of applicability. The use of exact kinematics introduces a
number of significant conceptual shifts already at leading order, and tightly
constrains the formalism. We show how to define parton correlation functions
that generalize the concepts of parton density, fragmentation function, and
soft factor. After setting up a general subtraction formalism, we obtain a
factorization theorem. To avoid complications with Ward identities the full
derivation is restricted to abelian gauge theories; even so the resulting
structure is highly suggestive of a similar treatment for non-abelian gauge
theories.Comment: 44 pages, 69 figures typos fixed, clarifications and second appendix
adde
Non-Linear Beam Splitter in Bose-Einstein Condensate Interferometers
A beam splitter is an important component of an atomic/optical Mach-Zehnder
interferometer. Here we study a Bose Einstein Condensate beam splitter,
realized with a double well potential of tunable height. We analyze how the
sensitivity of a Mach Zehnder interferometer is degraded by the non-linear
particle-particle interaction during the splitting dynamics. We distinguish
three regimes, Rabi, Josephson and Fock, and associate to them a different
scaling of the phase sensitivity with the total number of particles.Comment: draft, 19 pages, 10 figure
Estimations for the Single Diffractive production of the Higgs boson at the Tevatron and the LHC
The single diffractive production of the standard model Higgs boson is
computed using the diffractive factorization formalism, taking into account a
parametrization for the Pomeron structure function provided by the H1
Collaboration. We compute the cross sections at next-to-leading order accuracy
for the gluon fusion process, which includes QCD and electroweak corrections.
The gap survival probability () is also introduced to account for
the rescattering corrections due to spectator particles present in the
interaction, and to this end we compare two different models for the survival
factor. The diffractive ratios are predicted for proton-proton collisions at
the Tevatron and the LHC for the Higgs boson mass of = 120 GeV.
Therefore, our results provide updated estimations for the diffractive ratios
of the single diffractive production of the Higgs boson in the Tevatron and LHC
kinematical regimes.Comment: 20 pages, 6 figures, 3 table
Tear film thickness variations and the role of the tear meniscus
A mathematical model is developed to investigate the two-dimensional variations in the thickness of tear fluid deposited on the eye surface during a blink. Such variations can become greatly enhanced as the tears evaporate during the interblink period.\ud
The four mechanisms considered are: i) the deposition of the tear film from the upper eyelid meniscus, ii) the flow of tear fluid from under the eyelid as it is retracted and from the lacrimal gland, iii) the flow of tear fluid around the eye within the meniscus and iv) the drainage of tear fluid into the canaliculi through the inferior and superior puncta.\ud
There are two main insights from the modelling. First is that the amount of fluid within the tear meniscus is much greater than previously employed in models and this significantly changes the predicted distribution of tears. Secondly the uniformity of the tear film for a single blink is: i) primarily dictated by the storage in the meniscus, ii) quite sensitive to the speed of the blink and the ratio of the viscosity to the surface tension iii) less sensitive to the precise puncta behaviour, the flow under the eyelids or the specific distribution of fluid along the meniscus at the start of the blink. The modelling briefly examines the flow into the puncta which interact strongly with the meniscus and acts to control the meniscus volume. In addition it considers flow from the lacrimal glands which appears to occurs continue even during the interblink period when the eyelids are stationary
QCD Corrections to Scalar Production via Heavy Quark Fusion at Hadron Colliders
We recently proposed that, due to the top-quark-mass enhanced Yukawa
coupling, the s-channel production of a charged scalar or pseudo-scalar from
heavy quark fusion can be an important new mechanism for discovering
non-standard spin-0 particles. In this work, we present the complete O(alpha_s)
QCD corrections to this s-channel production process at hadron colliders,
including the results of QCD resummation over multiple soft-gluon emission. The
systematic QCD-improved production and decay rates at the FermiLab Tevatron and
the CERN LHC are given for the charged top-pions in the topcolor models and for
the charged Higgs bosons in the generic two Higgs doublet model. The direct
extension to the production of the neutral (pseudo-)scalars via bb\bar fusion
is studied in the minimal supersymmetric standard model (MSSM) with large
tan(beta), and in the topcolor model with large bottom Yukawa coupling.Comment: Version to be published in Phys.Rev.D. Discussion on Rb added plus
minor improvements. Conclusions not changed. Latex2e, 40 pages, 16 figure
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