Peter J. Edwards

Benthic algae in polluted estuaries

Abstract Three estuaries in north-eastern England provide a natural experiment. The Wear is relatively unpolluted, the Tyne receives a large volume of untreated sewage and the Tees mixed industrial wastes. The algal flora of these estuaries is compared to reveal the effects of different kinds of contamination.

A CULTURE STUDY OF SALINITY RESPONSES IN ECOTYPES OF TWO ESTUARINE RED ALGAE

Laboratory culture studies on the euryhalinity of Bostrychia radicans Montagne and Caloglossa leprieurii (Montagne) J. Agardh from the mouth and head of the Mullica River estuary, New Jersey, revealed both species probably have ecotypes whose growth patterns correlate with the salinity regime of their habitat in nature. Significant growth differences of tetrasporelings were determined in response to four salinities (5, 15, 25, 35%c) even after acclimation periods of the tetrasporophytes from 6 mo–2 yr in laboratory culture. However, one isolate of Bostrychia and both isolates of Caloglossa also demonstrated some capability for physiological adaptation to salinity changes although this was less significant statistically than their ecotypic response. It thus appears that certain euryhaline algae may consist of ecotypes, each of which has some capacity for physiological adaptation to salinity variations.

350 GeV gamma rays from AE Aqr

Abstract We report here the results of VHE γ-ray observations made during 1990 and 1991 using the Durham University Mark III and IV VHE γ-ray telescopes at Narrabri, N.S.W., Australia. There are 4 separate datasets, each obtained from observations over typically 10 days during a lunar dark period. The dataset from October 1990 exhibits periodicity at a chance probability of 1 × 10 -4 , and a similar effect is noted in the dataset from August 1991 at 1.6 × 10 −2 . In both cases, most of the power is in the second harmonic; the period is constant over at least 10 days and similar to that seen at optical wavelengths. No significant signal was detected in the September 1991 and October 1991 datasets. In addition, a strong and highly significant outburst lasting about 1 minute on 13 October 1990 and detected by two independent telescopes is reported. This outburst shows the 33 s periodic pulse structure and the pulses are in phase with those observed during the strongest sustained periodic signal in our data, from an observation lasting 3 h and taken 48 h previously. A second, weaker burst was also observed during August 1991.

Cultured red alga to measure pollution

Abstract The red alga Callithamnion grew equally well in seawater samples from unpolluted and polluted localities. The species was insensitive to nitrate and phosphate levels of the medium and thus cannot be used as an indicator of eutrophication. Relatively small copper concentrations depressed the growth of the species. No difference in copper tolerance was demonstrated between isolates from unpolluted north-east Scotland and polluted County Durham, but the isolate from unpolluted south-west England was apparently less resistant to copper.

Evidence for a relationship between the genera Rosenvingiella and Prasiola (Chlorophyta)

Naturally occurring transitional stages between Rosenvingiella polyrhiza (Rosenv.) Silva and Prasiola from Co. Durham indicate that the former may not be an autonomous species. The Prasiola conforms to the description of P. calophylla (Carmich.) Menegh. which may be an aerial ecophene of P. stipitata Suhr in Jessen. Since the former specific epithet has priority, the name P. stipitata may be invalid. A pluriseriate form of Rosenvingiella is described also, with putative male and female gamete-forming cells.

Measurement of sky clarity using MIR radiometers as an adjunct to atmospheric Čerenkov radiation measurements

A technique for detecting the presence of cloud in the field of view of an atmospheric Čerenkov telescope using a mid infra red radiometer is described. Models for the radiative emission from clear and cloudy skies are tested and found to represent the measurements.

The effect of the geomagnetic field on TeV gamma -ray detection

Very high energy (VHE) gamma -ray astronomy using the ground based atmospheric Cerenkov technique is an important new field of high energy astrophysics and a range of VHE gamma -ray sources has been detected at various levels of significance by a number of experimental groups. Outstanding evidence for gamma -rays from the Crab Nebula was obtained by the Whipple collaboration. This involved the use of a sophisticated technique based on computer simulations to select gamma -ray-like events from the proton induced background When this same technique was applied to data from other sources detected using an earlier version of the Whipple telescope, the evidence for a gamma -ray signal disappeared. The inability to reconcile the Whipple result from the Crab Nebula with both the failure of the Whipple camera to detect other objects and the detections made with other non-imaging telescopes has caused some concern at a critical time in the evolution of this branch of high energy astrophysics. In an attempt to reconcile these results, the authors have made a detailed study of the effects of the geomagnetic field on the electron-photon cascades. They have simulated the Cerenkov light produced by individual protons and gamma -rays at different orientations in the atmosphere, and made measurements of the sensitivity of the observations to the geomagnetic field. Indications are that these geomagnetic effects may be a cause of the differing results.

A dark day for dinosaurs

On average, 91 people are killed by asteroids each year. In her book Dark Matter and the Dinosaurs, theoretical physicist Lisa Randall focuses on a novel question: how did a dinosaur-killing asteroid end up on its collision course with Earth in the first place?

TeV gamma rays from millisecond pulsars

We summarize here the results of the VHE gamma ray study of millisecond pulsars made over seven years by the Durham group. In addition to reporting observations made recently with the Mark III and IV telescopes at Narrabri, Australia, we consider the application of new analysis techniques to earlier data taken using telescopes at Dugway, USA. Pulsed VHE γ‐rays have been detected from three of the eight millisecond pulsars observed; we compare our results with the predictions of a theory of VHE emission from millisecond pulsars.

Bringing light to a dark Universe

One of the biggest challenges facing cosmologists today is to explain how the Universe came to look the way it does. To appreciate the size of this task, consider our local star, the Sun. This is just one of the many billions that form the vast collection we call the Milky Way Galaxy. As we look up into the night sky we know there are at least as many galaxies as there are stars in the Milky Way. Galaxies are the building blocks of the Universe. The key to understanding how the Universe evolved into the beautiful place we see today is being able to explain how galaxies are born and how they change with time. A number of questions spring to mind immediately: Why do galaxies come in a range of sizes and brightness’s, with different abundances? Why do galaxies have a variety of shapes? Did galaxies all begin to form at the same time in the past, or is the formation process more complicated than this? Do galaxies change their appearance over time, perhaps as the result of close encounters or even collisions with other galaxies? The basic recipe for making a galaxy is deceptively simple; take a huge cloud of gas, mix in the force due to gravity and wait. Despite the simplicity of this scheme the physics of galaxy formation remains poorly understood. This is because the processes thought to be important in the formation of galaxies, such as the cooling of gas and the formation of stars from the cold gas, are complex. A further difficulty is that galaxies are very big, very remote and have probably evolved over billions of years: unlike other scientific disciplines, astronomers cannot set up a simple experiment in the laboratory to test their ideas about galaxy formation. Moreover, we cannot go to a neighbouring galaxy to poke and prod at it to see how it is put together. Instead, a new way of doing physics, using mathematical algorithms for computer simulations, is required (Fig. 1). Here a prescription for building a