Showing papers by "Paul Morris published in 1988"

Ammonia Production and Assimilation in Glutamate Synthase Mutants of Arabidopsis thaliana.

Abstract: Ammonia production and assimilation(1) were examined in photorespiratory mutants of Arabidopsis thaliana L lacking ferredoxin-dependent glutamate synthase (Fd-GluS) activity Although photosynthesis was rapidly inhibited in these mutants in normal air, NH(4) (+) continued to accumulate The accumulation of NH(4) (+) was also seen after an initial lag of 30 minutes in 2% O(2), 350 microliters per liter of CO(2) and after 90 minutes in 2% O(2), 900 microliters per liter of CO(2) The accumulation of NH(4) (+) in normal air and low O(2) was also associated with an increase in the total pool of amino acid-N and glutamine, and a decrease in the pools of glutamate, aspartate, alanine, and serine Upon return to dark conditions, or to 21% O(2), 1% CO(2) in the light, the NH(4) (+) which had accumulated in the leaves was reassimilated into amino acids The addition of methionine sulfoximine (MSO) resulted in higher accumulations of NH(4) (+) in glutamate synthase mutants and prevented the reassimilation of NH(4) (+) upon return to the dark The addition of MSO also resulted in the accumulation of NH(4) (+) in glutamate synthase mutants in the light and in 21% O(2), 1% CO(2) These results indicate that glutamine synthetase is essential for the reassimilation of photorespiratory NH(4) (+) and for primary N assimilation in the leaves and strongly suggest that glutamate dehydrogenase plays only a minimal role in the assimilation of ammonia Levels of NADH-dependent glutamate synthase (NADH-GluS) appear to be sufficient to account for the assimilation of NH(4) (+) by a GS/NADH-GluS cycle

Method for representing a directed acyclic graph of worlds using an assumption-based truth maintenance system

Abstract: In artificial intelligence, a method is provided for representing a directed acyclic graph of worlds using an assumption-based truth maintenance system (ATMS) as a tool The invention introduces the concepts of a nondeletion assumption and a deletion nogood, in order to allow deletion of an assertion upon transition between worlds The traditional (de Kleer) ATMS tool is augmented to allow distinction between two kinds of assumptions, namely the nondeletion assumption and the world assumption The nondeletion assumption is the elementary stipulation indicating the presence of an added assertion in a world The world assumption is the elementary stipulation representing existence of a world According to the invention, a method for testing assertions is provided for determining whether an assertion holds in a world The method involves taking into account the presence of deletion nogoods relevant to the tested assertion A deletion nogood is a nogood which indicates the contradiction between a world assumption and a nondeletion assumption which arises from a deletion of an assertion Deletion nogoods are introduced at a world to block any further inheritance of an assertion from an ancestor world The ATMS tool is further modified by replacing the traditional ATMS notion of inconsistency with a concept of inconsistency wherein only world assumptions are blamed for inconsistencies The present invention may be used in connection with planning systems and diagnosis systems as well as with other types of knowledge-based systems

Stable closures, defeasible logic and contradiction tolerant reasoning

Abstract: A solution to the Yale shooting problem has been previously proposed that uses so-called non-normal defaults. This approach produces a single extension. One disadvantage, however, is that new conflicting information causes the extension to collapse. In this paper we propose a new formal counterpart to the intuitive notion of a reasonable set of beliefs. The new formalization reduces to the previous one when there are no conflicts. However, when fresh conflicting information is added, instead of collapsing it produces a revised interpretation similar to that obtained by dependency-directed backtracking in a truth maintenance system. Consideration of the relationship to relevance logic motivates the development of a new formalism for default reasoning, called Defeasible Logic, which behaves like Autoepistemic Logic, but may be more intuitive.