756 research outputs found
Planning When Goals Change: A Moving Target Search Approach
International audienceDevising intelligent robots or agents that interact with humans is a major challenge for artificial intelligence. In such contexts, agents must constantly adapt their decisions according to human activities and modify their goals. In this paper, we tackle this problem by introducing a novel planning approach, called Moving Goal Planning (MGP), to adapt plans to goal evolutions. This planning algorithm draws inspiration from Moving Target Search (MTS) algorithms. In order to limit the number of search iterations and to improve its efficiency, MGP delays as much as possible triggering new searches when the goal changes over time. To this purpose, MGP uses two strategies: Open Check (OC) that checks if the new goal is still in the current search tree and Plan Follow (PF) that estimates whether executing actions of the current plan brings MGP closer to the new goal. Moreover, MGP uses a parsimonious strategy to update incrementally the search tree at each new search that reduces the number of calls to the heuristic function and speeds up the search. Finally, we show evaluation results that demonstrate the effectiveness of our approach
On the Complexity of Case-Based Planning
We analyze the computational complexity of problems related to case-based
planning: planning when a plan for a similar instance is known, and planning
from a library of plans. We prove that planning from a single case has the same
complexity than generative planning (i.e., planning "from scratch"); using an
extended definition of cases, complexity is reduced if the domain stored in the
case is similar to the one to search plans for. Planning from a library of
cases is shown to have the same complexity. In both cases, the complexity of
planning remains, in the worst case, PSPACE-complete
Evidence of sub-arc mantle oxidation by sulphur and carbon
The oxygen fugacity (ÆO2) of the Earthâs mantle at subduction zones exerts a primary control on the genesis of mineral deposits in the overlying magmatic arcs and on speciation of volcanic gases emitted into the atmosphere. However, the processes governing mantle ÆO2 such as the introduction of oxidised material by subduction are still unresolved. Here, we present evidence for the reduction of oxidised fluid-borne sulphur and carbon during alteration of depleted mantle by slab fluids at ultra-high pressure in the Bardane peridotite (Western Gneiss Region, Norway). Elevated ferric iron in metasomatic garnet, determined using synchrotron X-ray absorption near edge structure (XANES) spectroscopy, indicates that this process drove oxidation of the silicate assemblage. Our finding indicates that subduction oxidises the Earthâs mantle by cycling of sulphur and carbon.This research was funded by a Monash Research
Accelerator Grant to A. Tomkins and by a Society of Economic Geologists (SEG)
student research grant to A. Rielli. O. Nebel was supported through an ARC
DECRA fellowship (DE120100513)
Measurement of the CMS Magnetic Field
The measurement of the magnetic field in the tracking volume inside the
superconducting coil of the Compact Muon Solenoid (CMS) detector under
construction at CERN is done with a fieldmapper designed and produced at
Fermilab. The fieldmapper uses 10 3-D B-sensors (Hall probes) developed at
NIKHEF and calibrated at CERN to precision 0.05% for a nominal 4 T field. The
precise fieldmapper measurements are done in 33840 points inside a cylinder of
1.724 m radius and 7 m long at central fields of 2, 3, 3.5, 3.8, and 4 T. Three
components of the magnetic flux density at the CMS coil maximum excitation and
the remanent fields on the steel-air interface after discharge of the coil are
measured in check-points with 95 3-D B-sensors located near the magnetic flux
return yoke elements. Voltages induced in 22 flux-loops made of 405-turn
installed on selected segments of the yoke are sampled online during the entire
fast discharge (190 s time-constant) of the CMS coil and integrated offline to
provide a measurement of the initial magnetic flux density in steel at the
maximum field to an accuracy of a few percent. The results of the measurements
made at 4 T are reported and compared with a three-dimensional model of the CMS
magnet system calculated with TOSCA.Comment: 4 pages, 5 figures, 15 reference
Modal Logics of Topological Relations
Logical formalisms for reasoning about relations between spatial regions play
a fundamental role in geographical information systems, spatial and constraint
databases, and spatial reasoning in AI. In analogy with Halpern and Shoham's
modal logic of time intervals based on the Allen relations, we introduce a
family of modal logics equipped with eight modal operators that are interpreted
by the Egenhofer-Franzosa (or RCC8) relations between regions in topological
spaces such as the real plane. We investigate the expressive power and
computational complexity of logics obtained in this way. It turns out that our
modal logics have the same expressive power as the two-variable fragment of
first-order logic, but are exponentially less succinct. The complexity ranges
from (undecidable and) recursively enumerable to highly undecidable, where the
recursively enumerable logics are obtained by considering substructures of
structures induced by topological spaces. As our undecidability results also
capture logics based on the real line, they improve upon undecidability results
for interval temporal logics by Halpern and Shoham. We also analyze modal
logics based on the five RCC5 relations, with similar results regarding the
expressive power, but weaker results regarding the complexity
Algebraic Properties of Qualitative Spatio-Temporal Calculi
Qualitative spatial and temporal reasoning is based on so-called qualitative
calculi. Algebraic properties of these calculi have several implications on
reasoning algorithms. But what exactly is a qualitative calculus? And to which
extent do the qualitative calculi proposed meet these demands? The literature
provides various answers to the first question but only few facts about the
second. In this paper we identify the minimal requirements to binary
spatio-temporal calculi and we discuss the relevance of the according axioms
for representation and reasoning. We also analyze existing qualitative calculi
and provide a classification involving different notions of a relation algebra.Comment: COSIT 2013 paper including supplementary materia
Guided assembly of nanoparticles on electrostatically charged nanocrystalline diamond thin films
We apply atomic force microscope for local electrostatic charging of oxygen-terminated nanocrystalline diamond (NCD) thin films deposited on silicon, to induce electrostatically driven self-assembly of colloidal alumina nanoparticles into micro-patterns. Considering possible capacitive, sp2 phase and spatial uniformity factors to charging, we employ films with sub-100 nm thickness and about 60% relative sp2 phase content, probe the spatial material uniformity by Raman and electron microscopy, and repeat experiments at various positions. We demonstrate that electrostatic potential contrast on the NCD films varies between 0.1 and 1.2 V and that the contrast of more than ±1 V (as detected by Kelvin force microscopy) is able to induce self-assembly of the nanoparticles via coulombic and polarization forces. This opens prospects for applications of diamond and its unique set of properties in self-assembly of nano-devices and nano-systems
Insulin Glargine in the Intensive Care Unit: A Model-Based Clinical Trial Design
Online 4 Oct 2012Introduction: Current succesful AGC (Accurate Glycemic Control) protocols require extra clinical effort and are impractical in less acute wards where patients are still susceptible to stress-induced hyperglycemia. Long-acting insulin Glargine has the potential to be used in a low effort controller. However, potential variability in efficacy and length of action, prevent direct in-hospital use in an AGC framework for less acute wards.
Method: Clinically validated virtual trials based on data from stable ICU patients from the SPRINT cohort who would be transferred to such an approach are used to develop a 24-hour AGC protocol robust to different Glargine potencies (1.0x, 1.5x and 2.0x regular insulin) and initial dose sizes (dose = total insulin over prior 12, 18 and 24 hours). Glycemic control in this period is provided only by varying nutritional inputs. Performance is assessed as %BG in the 4.0-8.0mmol/L band and safety by %BG<4.0mmol/L.
Results: The final protocol consisted of Glargine bolus size equal to insulin over the previous 18 hours. Compared to SPRINT there was a 6.9% - 9.5% absolute decrease in mild hypoglycemia (%BG<4.0mmol/L) and up to a 6.2% increase in %BG between 4.0 and 8.0mmol/L. When the efficacy is known (1.5x assumed) there were reductions of: 27% BG measurements, 59% insulin boluses, 67% nutrition changes, and 6.3% absolute in mild hypoglycemia.
Conclusion: A robust 24-48 clinical trial has been designed to safely investigate the efficacy and kinetics of Glargine as a first step towards developing a Glargine-based protocol for less acute wards. Ensuring robustness to variability in Glargine efficacy significantly affects the performance and safety that can be obtained
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