OBJECTIVE To assess the risk to human health of the plant bracken (Pteridium sp). DESIGN An evaluation of studies of human and animal populations exposed to bracken, together with a review of expert reports and advice to the public. MAIN RESULTS Bracken induced disease has been demonstrated in animals in both laboratory and field studies. Depending on the species, diseases in animals associ...

We study a phenomenon occuring in various areas of quantum physics, in which an observable density (such as an energy density) which is classically pointwise nonnegative may assume arbitrarily negative expectation values after quantisation, even though the spatially integrated density remains nonnegative. Two prominent examples which have previously been studied are the energy density (in quant...

A Metis design is one for which v = r + k + 1. This paper deals with Metis designs that are quasi-residual. The parameters of such designs and the corresponding symmetric designs can be expressed by Fibonacci numbers. Although the question of existence seems intractable because of the size of the designs, the nonexistence of corresponding di¤erence sets can be dealt with in a substantive way. W...

Urinary bladder tumours in cattle are caused by chronic ingestion of bracken fern and BPV-1/2 infection. The objective of the present study was to assess if BPV-2 was present in urinary bladder lesions from cattle with chronic enzootic haematuria (CEH) from the Azores archipelago (Portugal), in order to gain further information regarding the epidemiologic distribution of this virus. Samples wer...

We discuss a recent model of a Quantum Mechanical Black Hole (QMBH) which describes the most fundamental known particles the leptons and approximately the quarks in terms of the Kerr-Newman Black Hole with a naked singularity shielded by Zitterbewegung effects. This goes beyond the Zitterbewegung and self interaction models of Barut and Bracken, Hestenes, Chacko and others and provides a unifie...