The thyroid and environmental stress in mammals

The effects of hyperoxia at ambient pressure on thyroid function and thyroid hormone metabolism have been assessed. Thyroidal activity was depressed in mice and rats by exposure to hyperoxia, due at least in part to a decrease in the rate of secretion of pituitary thyrotropin. The effects of hyperoxia on the peripheral deiodination of thyroxine were dependent on the concentration of oxygen employed and/or the duration of exposure. When significant changes were observed a reduction in the rate of deiodination and in the deiodinative clearance of T sub 4 occurred. Hyperoxia also resulted in a marked fall in circulating T sub 4 concentration and a decrease in T sub 4-binding activity in serum. Many of these effects of hyperoxia were prevented by the concomitant administration of large amounts of Vitamin E. These decreases in thyroid function and T sub 4 metabolism were associated with a decrease in the rate of whole body oxygen consumption. It was concluded that the deleterious effects of oxygen in the rat were not due to an oxygen induced hyperthyroid state in the peripheral tissues. Thyroxine was shown to be essential for survival during acute cold stress

Discrete Mereotopology

PublishedWhereas mereology, in the strict sense, is concerned solely with the part–whole relation, mereotopology extends mereology by including also the notion of connection, enabling one to distinguish, for example, between internal and peripheral parts, and between contact and separation. Mereotopology has been developed particularly within the Qualitative Spatial Reasoning research community, where it has been applied to, amongst other areas, geographical information science and image analysis. Most research in mereotopology has assumed that the entities being studied may be subdivided without limit, but a number of researchers have investigated mereotopological structures based on discrete spaces in which entities are built up from atomic elements that are not themselves subdivisible. This chapter presents an introductory treatment of mereotopology and its discrete variant, and provides references for readers interested in pursuing this subject in further detail

On generically dependent entities

This is the author accepted manuscript. The final version is available from IOS via the DOI in this record.An entity x is said to be generically dependent on a type F if x cannot exist without at least one entity of type F existing. In this paper several varieties of generic dependence are distinguished, differing in the nature of the relationship between an entity and the instances of a type on which it generically depends, and in the light of this, criteria of identity for generically dependent entities are investigated. These considerations are then illustrated in detail in a series of three case studies, covering shapes, linguistic entities such as letters, words and sentences, and collectives. Each case study examines how far the entities involved have robust identity criteria, and to the extent that they do not it is questioned whether they can be regarded as bona fide examples of generic dependent entities. Finally, in the light of this, a number of possible accounts that may be given of the ontological status of such entities are considered

Prolegomena to an ontology of shape

PublishedConference ProceedingInfluenced by the four-category ontology of Aristotle, many modern ontologies treat shapes as accidental particulars which (a) are specifically dependent on the substantial particulars which act as their bearers, and (b) instantiate accidental universals which are exemplified by those bearers. It is also common to distinguish between, on the one hand, these physical shapes which form part of the empirical world and, on the other, ideal geometrical shapes which belong to the abstract realm of mathematics. Shapes of the former kind are often said to approximate, but never to exactly instantiate, shapes of the latter kind. Following a suggestion of Frege, ideal mathematical shapes can be given precise definitions as equivalence classes under the relation of geometrical similarity. One might, analogously, attempt to define physical shape universals as equivalence classes under a relation of physical similarity, but this fails because physical similarity is not an equivalence relation. In this talk I will examine the implications of this for the ontology of shape and in particular for the relationship between mathematical shapes and the shapes we attribute to physical objects

Artificial development of connections in SHRUTI networks using a multi-objective genetic algorithm

SHRUTI is a model of how first-order logic can be represented and reasoned upon using a network of spiking neurons in an attempt to model the brain’s ability to perform reasoning. This paper extends the biological plausibility of the SHRUTI model by presenting a genotype representation of connections in a SHRUTI network using indirect encoding and showing that networks represented in this way can be generated by an evolutionary process

Evolution of connections in SHRUTI networks

SHRUTI is a model of how predicate relations can be represented and reasoned upon using a network of spiking neurons, attempting to model the brain’s ability to perform reasoning using as biologically plausible a means as possible. This paper extends the biological plausibility of the SHRUTI model by presenting a genotype representation of connections in a SHRUTI network using indirect encoding and showing that working networks represented in this way can be produced through an evolutionary process. A multi-objective algorithm is used to minimise the error and the number of weight changes that take place as a network learn

A scalable genome representation for neural-symbolic networks

Neural networks that are capable of representing symbolic information such as logic programs are said to be neural-symbolic. Because the human mind is composed of interconnected neurons and is capable of storing and processing symbolic information, neural-symbolic networks contribute towards a model of human cognition. Given that natural evolution and development are capable of producing biological networks that are able to process logic, it may be possible to produce their artificial counterparts through evolutionary algorithms that have developmental properties. The first step towards this goal is to design a genome representation of a neural-symbolic network. This paper presents a genome that directs the growth of neural-symbolic networks constructed according to a model known as SHRUTI. The genome is successful in producing SHRUTI networks that learn to represent relations between logical predicates based on observations of sequences of predicate instances. A practical advantage of the genome is that its length is independent of the size of the network it encodes, because rather than explicitly encoding a network topology, it encodes a set of developmental rules. This approach to encoding structure in a genome also has biological grounding

Directing transport by polarized radiation in presence of chaos and dissipation

We study numerically the dynamics of particles on the Galton board of semi-disk scatters in presence of monochromatic radiation and dissipation. It is shown that under certain conditions the radiation leads to appearance of directed transport linked to an underlining strange attractor. The direction of transport can be efficiently changed by radiation polarization. The experimental realization of this effect in asymmetric antidot superlattices is discussed.Comment: revtex, 4 pages, 6 fig