3,038 research outputs found
Integrating Learning from Examples into the Search for Diagnostic Policies
This paper studies the problem of learning diagnostic policies from training
examples. A diagnostic policy is a complete description of the decision-making
actions of a diagnostician (i.e., tests followed by a diagnostic decision) for
all possible combinations of test results. An optimal diagnostic policy is one
that minimizes the expected total cost, which is the sum of measurement costs
and misdiagnosis costs. In most diagnostic settings, there is a tradeoff
between these two kinds of costs. This paper formalizes diagnostic decision
making as a Markov Decision Process (MDP). The paper introduces a new family of
systematic search algorithms based on the AO* algorithm to solve this MDP. To
make AO* efficient, the paper describes an admissible heuristic that enables
AO* to prune large parts of the search space. The paper also introduces several
greedy algorithms including some improvements over previously-published
methods. The paper then addresses the question of learning diagnostic policies
from examples. When the probabilities of diseases and test results are computed
from training data, there is a great danger of overfitting. To reduce
overfitting, regularizers are integrated into the search algorithms. Finally,
the paper compares the proposed methods on five benchmark diagnostic data sets.
The studies show that in most cases the systematic search methods produce
better diagnostic policies than the greedy methods. In addition, the studies
show that for training sets of realistic size, the systematic search algorithms
are practical on todays desktop computers
PDFS: Practical Data Feed Service for Smart Contracts
Smart contracts are a new paradigm that emerged with the rise of the
blockchain technology. They allow untrusting parties to arrange agreements.
These agreements are encoded as a programming language code and deployed on a
blockchain platform, where all participants execute them and maintain their
state. Smart contracts are promising since they are automated and
decentralized, thus limiting the involvement of third trusted parties, and can
contain monetary transfers. Due to these features, many people believe that
smart contracts will revolutionize the way we think of distributed
applications, information sharing, financial services, and infrastructures.
To release the potential of smart contracts, it is necessary to connect the
contracts with the outside world, such that they can understand and use
information from other infrastructures. For instance, smart contracts would
greatly benefit when they have access to web content. However, there are many
challenges associated with realizing such a system, and despite the existence
of many proposals, no solution is secure, provides easily-parsable data,
introduces small overheads, and is easy to deploy.
In this paper we propose PDFS, a practical system for data feeds that
combines the advantages of the previous schemes and introduces new
functionalities. PDFS extends content providers by including new features for
data transparency and consistency validations. This combination provides
multiple benefits like content which is easy to parse and efficient
authenticity verification without breaking natural trust chains. PDFS keeps
content providers auditable, mitigates their malicious activities (like data
modification or censorship), and allows them to create a new business model. We
show how PDFS is integrated with existing web services, report on a PDFS
implementation and present results from conducted case studies and experiments.Comment: Blockchain; Smart Contracts; Data Authentication; Ethereu
Multigraded Castelnuovo-Mumford Regularity
We develop a multigraded variant of Castelnuovo-Mumford regularity. Motivated
by toric geometry, we work with modules over a polynomial ring graded by a
finitely generated abelian group. As in the standard graded case, our
definition of multigraded regularity involves the vanishing of graded
components of local cohomology. We establish the key properties of regularity:
its connection with the minimal generators of a module and its behavior in
exact sequences. For an ideal sheaf on a simplicial toric variety X, we prove
that its multigraded regularity bounds the equations that cut out the
associated subvariety. We also provide a criterion for testing if an ample line
bundle on X gives a projectively normal embedding.Comment: 30 pages, 5 figure
Optical orientation and alignment of excitons in direct and indirect band gap (In,Al)As/AlAs quantum dots with type-I band alignment
The spin structure and spin dynamics of excitons in an ensemble of
(In,Al)As/AlAs quantum dots (QDs) with type-I band alignment, containing both
direct and indirect band gap dots, are studied. Time-resolved and spectral
selective techniques are used to distinguish between the direct and indirect
QDs. The exciton fine structure is studied by means of optical alignment and
optical orientation techniques in magnetic fields applied in the Faraday or
Voigt geometries. A drastic difference in emission polarization is found for
the excitons in the direct QDs involving a -valley electron and the
excitons in the indirect QDs contributed by an -valley electron. We show
that in the direct QDs the exciton spin dynamics is controlled by the
anisotropic exchange splitting, while in the indirect QDs it is determined by
the hyperfine interaction with nuclear field fluctuations. The anisotropic
exchange splitting is determined for the direct QD excitons and compared with
model calculations
Optical orientation and alignment of excitons in direct and indirect band gap (In,Al)As/AlAs quantum dots with type-I band alignment
The spin structure and spin dynamics of excitons in an ensemble of
(In,Al)As/AlAs quantum dots (QDs) with type-I band alignment, containing both
direct and indirect band gap dots, are studied. Time-resolved and spectral
selective techniques are used to distinguish between the direct and indirect
QDs. The exciton fine structure is studied by means of optical alignment and
optical orientation techniques in magnetic fields applied in the Faraday or
Voigt geometries. A drastic difference in emission polarization is found for
the excitons in the direct QDs involving a -valley electron and the
excitons in the indirect QDs contributed by an -valley electron. We show
that in the direct QDs the exciton spin dynamics is controlled by the
anisotropic exchange splitting, while in the indirect QDs it is determined by
the hyperfine interaction with nuclear field fluctuations. The anisotropic
exchange splitting is determined for the direct QD excitons and compared with
model calculations
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