78,765 research outputs found
REBA: A Refinement-Based Architecture for Knowledge Representation and Reasoning in Robotics
This paper describes an architecture for robots that combines the
complementary strengths of probabilistic graphical models and declarative
programming to represent and reason with logic-based and probabilistic
descriptions of uncertainty and domain knowledge. An action language is
extended to support non-boolean fluents and non-deterministic causal laws. This
action language is used to describe tightly-coupled transition diagrams at two
levels of granularity, with a fine-resolution transition diagram defined as a
refinement of a coarse-resolution transition diagram of the domain. The
coarse-resolution system description, and a history that includes (prioritized)
defaults, are translated into an Answer Set Prolog (ASP) program. For any given
goal, inference in the ASP program provides a plan of abstract actions. To
implement each such abstract action, the robot automatically zooms to the part
of the fine-resolution transition diagram relevant to this action. A
probabilistic representation of the uncertainty in sensing and actuation is
then included in this zoomed fine-resolution system description, and used to
construct a partially observable Markov decision process (POMDP). The policy
obtained by solving the POMDP is invoked repeatedly to implement the abstract
action as a sequence of concrete actions, with the corresponding observations
being recorded in the coarse-resolution history and used for subsequent
reasoning. The architecture is evaluated in simulation and on a mobile robot
moving objects in an indoor domain, to show that it supports reasoning with
violation of defaults, noisy observations and unreliable actions, in complex
domains.Comment: 72 pages, 14 figure
Automatic quantification of the microvascular density on whole slide images, applied to paediatric brain tumours
Angiogenesis is a key phenomenon for tumour progression, diagnosis and
treatment in brain tumours and more generally in oncology. Presently, its
precise, direct quantitative assessment can only be done on whole tissue
sections immunostained to reveal vascular endothelial cells. But this is a
tremendous task for the pathologist and a challenge for the computer since
digitised whole tissue sections, whole slide images (WSI), contain typically
around ten gigapixels.
We define and implement an algorithm that determines automatically, on a WSI
at objective magnification , the regions of tissue, the regions
without blur and the regions of large puddles of red blood cells, and
constructs the mask of blur-free, significant tissue on the WSI. Then it
calibrates automatically the optical density ratios of the immunostaining of
the vessel walls and of the counterstaining, performs a colour deconvolution
inside the regions of blur-free tissue, and finds the vessel walls inside these
regions by selecting, on the image resulting from the colour deconvolution,
zones which satisfy a double-threshold criterion. A mask of vessel wall regions
on the WSI is produced. The density of microvessels is finally computed as the
fraction of the area of significant tissue which is occupied by vessel walls.
We apply this algorithm to a set of 186 WSI of paediatric brain tumours from
World Health Organisation grades I to IV. The segmentations are of very good
quality although the set of slides is very heterogeneous. The computation time
is of the order of a fraction of an hour for each WSI on a modest computer. The
computed microvascular density is found to be robust and strongly correlates
with the tumour grade.
This method requires no training and can easily be applied to other tumour
types and other stainings
GEANT4 : a simulation toolkit
Abstract Geant4 is a toolkit for simulating the passage of particles through matter. It includes a complete range of functionality including tracking, geometry, physics models and hits. The physics processes offered cover a comprehensive range, including electromagnetic, hadronic and optical processes, a large set of long-lived particles, materials and elements, over a wide energy range starting, in some cases, from 250 eV and extending in others to the TeV energy range. It has been designed and constructed to expose the physics models utilised, to handle complex geometries, and to enable its easy adaptation for optimal use in different sets of applications. The toolkit is the result of a worldwide collaboration of physicists and software engineers. It has been created exploiting software engineering and object-oriented technology and implemented in the C++ programming language. It has been used in applications in particle physics, nuclear physics, accelerator design, space engineering and medical physics. PACS: 07.05.Tp; 13; 2
Assessing Visualization Techniques for the Search Process in Digital Libraries
In this paper we present an overview of several visualization techniques to
support the search process in Digital Libraries (DLs). The search process
typically can be separated into three major phases: query formulation and
refinement, browsing through result lists and viewing and interacting with
documents and their properties. We discuss a selection of popular visualization
techniques that have been developed for the different phases to support the
user during the search process. Along prototypes based on the different
techniques we show how the approaches have been implemented. Although various
visualizations have been developed in prototypical systems very few of these
approaches have been adapted into today's DLs. We conclude that this is most
likely due to the fact that most systems are not evaluated intensely in
real-life scenarios with real information seekers and that results of the
interesting visualization techniques are often not comparable. We can say that
many of the assessed systems did not properly address the information need of
cur-rent users.Comment: 23 pages, 14 figures, pre-print to appear in "Wissensorganisation mit
digitalen Technologien" (deGruyter
Telecommunications media for the delivery of educational programming
The technical characteristics of various telecommunications media are examined for incorporation into educational networks. FM radio, AM radio, and VHF and UHF television are considered along with computer-aided instruction. The application of iteration networks to library systems, and microform technology are discussed. The basic principles of the communications theory are outlined, and the operation of the PLATO 4 random access system is described
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