The wide variety of dead wood habitats supports a wide variety of specialized fungi, which globally may exceed 100,000 species. Of these the majority of known taxa are Basidiomycota. They exhibit a wide variety of strategies to gain and hold territory within wood, defined by their mode of dispersal, establishment, competitive ability and adaptation to disturbance and stress factors. Many habitat factors affect community composition and development, both exogenous, e.g. microclimatic regime, and endogenous, e.g. interspecific interactions. Initial microenvironmenta[ factors--at one extreme high stress and at the other extreme absence of abiotic stress--are major determinants of the communities that establish. Following initial British Mycological Society Symposia Series Published by Elsevier Ltd. 9 2008 The British Mycological Society All rights reserved.

Basidiomycete community development in temperate angiosperm wood

Asynchronous circuits behave like concurrent programs implemented in hardware logic. The processes in such circuits are synchronised in accordance with the dynamic logical and causal conditions between switching events. The classical paradigm, easily represented in most process-oriented languages for concurrent systems modelling, is AND causality, which is often associated with a rendez-vous synchronisation. In this paper we investigate a different, less known paradigm, called OR causality. This paradigm is however different from the classical MERGE paradigm, which is based on mutually exclusive events. Petri nets and Change Diagrams provide adequate modelling and circuit synthesis tools for the various OR causality types, yet they do not always bring the specifier to a unique decision about which modelling construct must be used for which type. We present a unified descriptive tool, called Causal Logic Net, which is graphically based on Petri net but has an explicit logic causality annotation for transitions. It is aimed as the least possible generalisation of Petri nets and Change Diagrams. The signal-transition interpretation of this tool is analogous to, but more powerful than, the well-known Signal Transition Graph. A number of examples demonstrate the usefulness of this model in the synthesis of asynchronous control circuits. It is shown that the extension of the basic, unconditional, firing rule with the one that depends upon the marking of the transition preconditions increases the descriptive power of the model to that of the Turing Machine model and allows the modelling of non-commutative state transition behaviour in a purely causal form.

On the models for asynchronous circuit behaviour with OR causality

The paper presents asynchronous design solutions to the problem of Priority Arbitration which is defined in the following form. A system consists of multiple, physically concurrent, processes with a shared resource. The discipline of resource allocation is a function of parameters of the active requests, which are assigned to the requests either statically or dynamically. This function can be defined in an (arbitrary) combinatorial way (contrary to conventional, 'topological', mappings, such as that used in a daisy-chain arbiter). The proposed designs are quasi-speed-independent. Furthermore, the priority logic, in the dynamic case, has the following architectural feature: it is a tree structure in which the control flow is maximally decoupled from the data-path by means of an early propagation of the 'valid'-'invalid' signals, concurrently, with processing the priority data. This lends to significant reduction in the overall arbitration delay when the number of active requests is low.

Priority arbiters

The wide variety of dead wood habitats supports a wide variety of specialized fungi, which globally may exceed 100,000 species. Of these the majority of known taxa are Basidiomycota. They exhibit a wide variety of strategies to gain and hold territory within wood, defined by their mode of dispersal, establishment, competitive ability and adaptation to disturbance and stress factors. Many habitat factors affect community composition and development, both exogenous, e.g. microclimatic regime, and endogenous, e.g. interspecific interactions. Initial microenvironmental, factors—at one extreme high stress and at the other extreme absence of abiotic stress—are major determinants of the communities that establish. Following initial establishment, community development is influenced by four main driving forces: stress aggravation (worsening of abiotic environmental conditions), stress alleviation (improvement in abiotic conditions), disturbance and combat (interspecific competition for space rather than directly for nutrients). The ecological strategies adopted by wood decay Basidiomycota, habitat factors influencing community development and community development pathways are discussed in relation to angiosperm wood.

Chapter 12 Basidiomycete community development in temperate angiosperm wood

An asynchronous arbiter dynamically allocates a resource in response to requests from processes. Glitch-free operation when two requests arrive concurrently is possible in MOS technologies. Multiway arbitration using a request-grant-release-acknowledge protocol can be achieved by connecting together two-way arbiters (mutual exclusion and tree arbiter elements). We have devised a fast and compact design for the tree arbiter element which offers eager forward-propagation of requests. It compares favorably with a well-known design in which request propagation must wait for arbitration to complete. Our analysis and simulations also suggest that no performance improvement will be obtained by incorporating eager acknowledgment of releases. All of the designs considered in this paper are speed-independent, a formal property of a network of elements which can be taken as a positive indication of their robustness.

CMOS design of the tree arbiter element

We present an asynchronous circuit for an arbiter cell that can be used to construct cascaded multiway arbitration circuits. The circuit is completely speed-independent. It has a short response delay at the input request-grant handshake link due to both a) the propagation of requests in parallel with starting arbitration and b) the concurrent resetting of request-grant handshakes in different cascades of a request-grant propagation chain. >

A. Petrov

Papers

A low latency asynchronous arbitration circuit

The influence of subzero temperatures on mycelial growth and fruit bodies vitality of some higher xylotrophic basidiomycetes.