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A quantity of Romano-British material was found in the course of excavation and although most of this was from disturbed contexts an attempt was made to define the nature and period of occupation which it represents.
The principal features dated to this period by material from primary positions are a number of long straight ditches, F138, F225, F225a and F255, running roughly north-east to south-west, and an irregular D-shaped enclosure, F170 (Fig 12). It is suggested that the ditches form the boundaries of a fairly large-scale layout of fields. From the discrepancies of alignment in ditches lying close together it appears that the boundaries silted and were re-cut without much exactitude. Very little stratified pottery could be associated with these ditches: a Flavian sherd from F138 and late Roman wares from F255.
In recent years, a malaria infection of humans in South East Asia, originally diagnosed as a known human-infecting species, Plasmodium malariae, has been identified as a simian parasite, Plasmodium knowlesi. This species had been subject to considerable investigation in monkeys since the 1930s. With the development of continuous culture of the erythrocytic stages of the human malarial parasite, Plasmodium falciparum in 1976, the emphasis in research shifted away from knowlesi. However, its importance as a human pathogen has provoked a renewed interest in P. knowlesi, not least because it too can be maintained in continuous culture and thus provides an experimental model. In fact, this parasite species has a long history in malaria research, and the purpose of this chapter is to outline approximately the first 50 years of this history.
Existing observations of the Magellanic Clouds suggest substantially different star-forming histories for the two systems. The reliability of this conclusion is discussed in the context of the uncertainties and age resolutions of various empirical methods of studying galaxy evolution. An attempt is also made to relate likely evolutionary scenarios for the Clouds to the histories of other Local Group systems, to the evolution seen in galaxies at high redshift, and to possible histories determined by interaction with the Galaxy.
The idea for a Working Group (WG) on “Future Large Scale Facilities in Astronomy” grew from a discussion held on 20 August, 1994, during the IAU General Assembly in The Hague. The IAU Executive Committee approved its formation in August, 1995, and its composition in October, 1995. The WG will remain active at least until the XXIIIrd General Assembly in Kyoto in 1997. Members are: H. Butcher (Chairman), R. Ekers, B. Fort, N. Kardashev, M. Longair, F. Pacini, L. Rodriguez, G. Swarup, Y. Tanaka, H. Tananbaun, and L. Woltjer (ex officio). The WG carries out its work mostly by email and FAX.
The idea for a Working Group (WG) on “Future Large Scale Facilities in Astronomy” grew from the Joint Discussion on this topic held on 20 August 1994, during the IAU General Assembly in The Hague. The IAU Executive Committee approved its formation in August, 1995, and Harvey Butcher was chair until the XXIIIrd General Assembly in Kyoto in 1997.
As the night sky near Canberra grows brighter each year, many of the traditional areas of investigation at Mount Stromlo are suffering, and work in these fields is shifting to Siding Spring Mountain, near Coonabarabran, N.S.W. One of several projects designed to ensure the continued productivity of the 74-inch reflector at Mount Stromlo as conditions change has been the installation of an échelle grating system in the coudé focus of the telescope. This will allow very high dispersion work on bright stars, and should be littles affected by nearby city lights.
Five cases of STEC O157 phage type (PT) 21/28 reported consumption of raw cows' drinking milk (RDM) produced at a dairy farm in the South West of England. STEC O157 PT21/28 was isolated from faecal specimens from milking cows on the implicated farm. Whole genome sequencing (WGS) showed that human and cattle isolates were the same strain. Further analysis of WGS data confirmed that sequences of isolates from an additional four cases (who did not report consumption of RDM when first questioned) fell within the same five single nucleotide polymorphism cluster as the initial five cases epidemiologically linked to the consumption of RDM. These four additional cases identified by WGS were investigated further and were, ultimately, associated with the implicated farm. The RDM outbreak strain encoded stx2a, which is associated with increased pathogenicity and severity of symptoms. Further epidemiological analysis showed that 70% of isolates within a wider cluster containing the outbreak strain were from cases residing in, or linked to, the same geographical region of England. During this RDM outbreak, use of WGS improved case ascertainment and provided insights into the evolution of a highly pathogenic clade of STEC O157 PT21/28 stx2a associated with the South West of England.
New data on the colors of galaxies in distant, rich clusters of galaxies are presented. Of seven clusters examined having z<0.20, all exhibit color distributions indicating that a significant proportion of the member galaxies are undergoing star formation. The one cluster studied with z<0.20 clearly shows a reduced fraction of such galaxies.
The partial excavation under rescue conditions in 1961–63 of the ditches and
interior of an enclosure of the earlier neolithic period is described. The
enclosure, covering a total area of approximately 2.4 ha, was defined by
double concentric interrupted ditches, which were for the most part
naturally filled. There were many traces of activity within the interior,
presumed to be contemporary with the ditches, including pits, gullies, post-
and stake-holes, and varying concentrations of struck and burnt flint and
pottery. Human burials were found. There is a little Ebbsfleet pottery in
secondary contexts and there are later prehistoric, Roman and medieval
finds. It is probably not possible to ascribe a single or specific role to
the site, which may have been important as a place where several activities
were concentrated, including occupation, subsistence, exchange, enclosure or
defence, burial and ritual.
In this paper we discuss the formation of InN on GaN heterostructures. Film growth was accomplished using a new method coined Migration Enhanced Epitaxial Afterglow (MEAglow), an improved form of pulsed delivery Plasma Enhanced Chemical Vapour Deposition (PECVD) . Initial x-ray diffraction (XRD) analysis results indicated that an InGaN alloy layer formed under the InN during growth. No GaN was seen from the original buffer layer. It was postulated that indium metal deposited prior to complete nitridation diffused into the relatively thin GaN layer producing InGaN. To verify the integrity of the insulating GaN layer, a third party GaN substrate was substituted. Results were unchanged. Parameters were then modified to reduce the amount of indium used for the initial metal deposition. XRD results indicated a sharper interface between the semi-insulating GaN and conductive InN layer. Hall Effect measurements are included. We’ve shown that the growth of a device suitable heterostructure is possible using the MEAglow technique.
The highest mobility nitrides ever grown were indium nitride polycrystalline thin films. The original reactive ion sputtering unit used to produce those films is still in existence and has been substantially upgraded. In this paper we describe some of the parameters that are important for high purity indium nitride growth, while providing the most recent results for films grown with the upgraded system. A long lag time (greater than 100 hours of growth time) has been observed before obtaining stable material properties for a given set of growth conditions.
A single crystalline Si1-xGex overlayer on insulator is realised by the implantation of germanium into a SIMOX (Separation by IMplantation of OXygen) substrate. Two SIMOX samples were implanted with 74Ge+ at elevated temperature (≈600°C), and subsequently annealed at different temperatures and anneal ambients. The microstructure, stoichiometry, and conductivity of the Si1-xGex over-layer were studied using transmission electron microscopy, Rutherford backscattering spectrometry/ion channelling and two-probe conductivity measurements. As a result of lattice reordering after final heat treatment, and despite high defect density observed in the XTEM microstructure, the measured conductivity of the over-layer is higher than of the starting SIMOX material. These results suggest a possibility of band-gap engineering by synthesis of Si1-xGex-on-insulator.
The band-gap of indium nitride has long been believed to be about 1.9eV with slight variations due to band-tailing in polycrystalline samples and degenerate doping. Recently, other values as low as 0.7 eV have apparently been observed. We have compared samples spanning this apparent range of band-gap using secondary ion mass spectroscopy (SIMS), X-ray Photoelectron Spectroscopy (XPS) and heavy ion elastic recoil detection analysis (ERDA), in conjunction with spectral optical density measurements. Once structural inhomogeneiteies are taken into account, we show that much of the conflicting data are compatible with direct photoionisation with a threshold energy of about 1.0eV. This feature was first reported in polycrystalline indium nitride over 15 years ago and attributed to a ∣p> like defect state. We ask whether the feature may instead be a direct band-gap.
We present a comparative study of the effects of low power reactive ion etching (RIE) on GaN and InN. This new, highly chemical, dry etching, using CF4 and Ar, has been developed for thin nitride films grown at low temperature in our laboratories. GaN films were grown by remote plasma enhanced-laser induced chemical vapor deposition and InN films were grown by radio-frequency RF reactive sputtering. Commercial GaN samples were also examined. Optical and electrical characteristics of the films are reported before and after removing 100 to 200 nm of the film surface by RIE. We have previously shown that the GaN films, although polycrystalline after growth, may be re-crystallized below the growth temperature. Removal of the surface oxide has been found to be imperative since a polycrystalline residue remains on the surface after re-crystallization.
Water is a necessary component in the production of encapsulated wastes based on hydraulic cements which are widely used for immobilization of intermediate and low level waste (ILW) and (LLW). Apart from providing the fluidity required to readily transport slurry wastes, it plays an essential role in hydrating the cement. Too low a water content prevents homogeneous mixing of the cement binder and waste and does not provide the fluidity needed for effective infilling of solid wastes. The water left after hydration creates a porous network that allows egress of gaseous corrosion/radiolytic degradation products such as hydrogen. A broad envelope (i.e. range) of acceptable water/binder ratios is essential for effective process control, particularly for the encapsulation of slurry wastes which have widely varying water contents.
Nevertheless, the presence of large amounts of free water in the pore system of the hardened matrix allows easy transport of soluble ions such as hydroxide, which can lead to metal corrosion, and the increased permeability of the system increases the leachability. Therefore effective management of the ‘free’ water content of a waste product will allow optimisation of both the encapsulation process and the product quality and durability.
This paper describes a range of innovative approaches to ‘water management’, including the use of alternative hydraulic cements, modification of powder characteristics and use of superplasticised composite OPC grouts and examines the contribution of 1H NMR relaxometry in providing improved understanding of the distribution of water within the pores of the hardened cement matrix.
LOFAR (Low Frequency Array) is an innovative radio telescope optimized for the frequency range 30–240 MHz. The telescope is realized as a phased aperture array without any moving parts. Digital beam forming allows the telescope to point to any part of the sky within a second. Transient buffering makes retrospective imaging of explosive short-term events possible. The scientific focus of LOFAR will initially be on four key science projects (KSPs): (i) Detection of the formation of the very first stars and galaxies in the universe during the so-called epoch of reionization by measuring the power spectrum of the neutral hydrogen 21-cm line (Shaver et al. 1999) on the ∼ 5′ scale; (ii) Low-frequency surveys of the sky with of order 108 expected new sources; (iii) All-sky monitoring and detection of transient radio sources such as γ-ray bursts, X-ray binaries, and exo-planets (Farrell et al. 2004); and (iv) Radio detection of ultra-high energy cosmic rays and neutrinos (Falcke & Gorham 2003) allowing for the first time access to particles beyond 1021 eV (Scholten et al. 2006). Apart from the KSPs open access for smaller projects is also planned. Here we give a brief description of the telescope.