1,020,718 research outputs found
Anti-Structure Problems
The recent success of structured solutions for a class of
information-theoretic network problems, calls for exploring their limits. We
show that sum-product channels resist a solution by structured (as well as
random) codes. We conclude that the structured approach fails whenever the
channel operations do not commute (or for general functional channels, when the
channel function is non decomposable).Comment: a short note, following the Banff meeting on Algebraic structure in
network information theroy, Aug. 14-1
Hash-Tree Anti-Tampering Schemes
Procedures that provide detection, location and correction of tampering in documents are known as anti-tampering schemes. In this paper we describe how to construct an anti-tampering scheme using a pre-computed tree of hashes. The main problems of constructing such a scheme are its computational feasibility and its candidate reduction process. We show how to solve both problems by the use of secondary hashing over a tree structure. Finally, we give brief comments on our ongoing work in this area
Coordinate-free classic geometries
This paper is devoted to a coordinate-free approach to several classic
geometries such as hyperbolic (real, complex, quaternionic), elliptic
(spherical, Fubini-Study), and lorentzian (de Sitter, anti de Sitter) ones.
These geometries carry a certain simple structure that is in some sense
stronger than the riemannian structure. Their basic geometrical objects have
linear nature and provide natural compactifications of classic spaces. The
usual riemannian concepts are easily derivable from the strong structure and
thus gain their coordinate-free form. Many examples illustrate fruitful
features of the approach. The framework introduced here has already been shown
to be adequate for solving problems concerning particular classic spaces.Comment: 20 pages, 2 pictures, 1 table, 32 references. Final versio
Use of apomorphine in Parkinsonian patients with neuropsychiatric complications to oral treatment
Neuropsychiatric side effects often complicate anti-Parkinsonian therapy and pose a significant problem in the optimal management of idiopathic Parkinson's disease. Several publications report a relative lack of neuropsychiatric side effects in Parkinsonian patients treated with subcutaneous apomorphine. To investigate this further, we have used subcutaneous apomorphine to treat 12 non-demented IPD patients with previous oral drug-related neuropsychiatric problems. Treatment with apomorphine allowed alteration of anti-Parkinsonian medication and led to the abolition or reduction of neuropsychiatric complications in all patients. The mechanism remains unclear but may be due, in part, to a reduction in oral medication or a psychotropic action of apomorphine, possibly due to the piperidine moiety in its structure, or both
Fermions in Instanton Anti-Instanton Background
We consider the behaviour of fermions in the background of
instanton-anti\-instanton type configurations. Several different physics
problems, from the high energy electroweak interactions to the study of vacuum
structure of QCD and of large orders of perturbation theory are related to this
problem. The spectrum of the Dirac operator in such a background is studied in
detail. We present an approximation for the fermion correlation function when
the instanton-anti\-instanton separation () is large compared to their sizes
(). The situation when the instanton-anti\-instanton overlap and melt,
is studied through the behaviour of the Chern Simons number as a function of and .
Applying our results to widely discussed cases of fermion-number violation in
the electroweak theory, we conclude that there are no theoretical basis for
expecting anomalous cross sections to become observable at energies in TeV
region.Comment: 36 PAGES, GEF-Th-8/199
Plural Slot Theory
Kit Fine (2000) breaks with tradition, arguing that, pace Russell (e.g., 1903: 228), relations have neither directions nor converses. He considers two ways to conceive of these new "neutral" relations, positionalism and anti-positionalism, and argues that the latter should be preferred to the former. Cody Gilmore (2013) argues for a generalization of positionalism, slot theory, the view that a property or relation is n-adic if and only if there are exactly n slots in it, and (very roughly) that each slot may be occupied by at most one entity. Slot theory (and with it, positionalism) bears the full brunt of Fine's (2000) symmetric completions and conflicting adicities problems. I fully develop an alternative, plural slot theory (or pocket theory), which avoids these problems, key elements of which are first considered by Yi (1999: 168 ff.). Like the slot theorist, the pocket theorist posits entities (pockets) in properties and relations that can be occupied. But unlike the slot theorist, the pocket theorist denies that at most one entity can occupy any one of them. As a result, she must also deny that the adicity of a property or relation is equal to the number of occupiable entities in it. By abandoning these theses, however, the pocket theorist is able to avoid Fine's problems, resulting in a stronger theory about the internal structure of properties and relations. Pocket theory also avoids a serious drawback of anti-positionalism
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