The medium energy X-ray spectrum of the Seyfert galaxy NGC 4151 is characterised by a hard power-law continuum, a variable low-energy cut-off and iron line and edge features. Holt et al. (1980) found the spectral form below 4 keV to be incompatible with absorption in a uniform screen of cold gas and interpreted the apparent soft X-ray excess in terms of a partial covering model. However, recent observations point to a somewhat different description of the X-ray absorbing medium present in the nucleus of this galaxy.

Polymer:fullerene nanoparticles (NPs) offer two key advantages over bulk heterojunction (BHJ) films for organic photovoltaics (OPVs), water-processability and potentially superior morphological control. Once an optimal active layer morphology is reached, maintaining this morphology at OPV operating temperatures is key to the lifetime of a device. Here we study the morphology of the PDPP-TNT (poly{3,6-dithiophene-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-naphthalene}):PC71BM ([6,6]-phenyl C71 butyric acid methyl ester) NP system and then compare the thermal stability of NP and BHJ films to the common poly(3-hexylthiophene) (P3HT): phenyl C61 butyric acid methyl ester (PC61BM) system. We find that material T g plays a key role in the superior thermal stability of the PDPP-TNT:PC71BM system; whereas for the P3HT:PC61BM system, domain structure is critical.

The galaxy identified with the flat-spectrum radio source PKS 2005-489 has a bright stellar nucleus with V ⋍ 13 mag. Optical, UV and X-ray observations indicate variability and power-law continua in each of these wavebands, leading to the conclusion that PKS 2005-489 is one of the brightest BL Lac objects known.

We have investigated the distribution of cool gas within the local interstellar medium (<150 pc) using data derived from both the ROSAT X-ray and EUV all-sky surveys. The EUV/X-ray spectra for a sample of 89 white dwarf stars and 200 active late-type stars have been analysed to give an estimate of the gas column density along each object’s line of sight. In order to extend the sky coverage we have also included in the analysis 190 late-type stars detected only in the X-ray band. The derived NHI measurements confirm the size of the local low density bubble as typically 50-100 pc and also show that in the general direction of Loop I there is a substantial excess of absorption at a range of distances from 10-150 pc.

An overlapping set of ROSAT PSPC observations made in a region of very low Galactic foreground column density, has been used to investigate variations in the soft X-ray background on angular scales of 15′ – 5°. In the ¼ keV band there is a clear inverse correlation of the count-rate with the line-of-sight hydrogen column density. However, after correcting for this absorption effect, strong residual fluctuations remain in the data, with an amplitude which is significantly larger than that due to the counting statistics or the confusion of unresolved discrete sources. In contrast a similar analysis for the ¾ and 1.5 keV ROSAT bands shows no evidence for an excess signal. The most likely origin of the ¼ keV fluctuations would seem to be in a patchy distribution of ~ 106 K gas in the Galactic halo.

Over ninety-seven per cent of Libya's water for agricultural and other uses came from groundwater in 1980 (Pallas). By then it was obvious that the renewable water in the coastal aquifers was seriously depleted and would not be sufficient to sustain the levels of water use implied by the national agricultural development plans. Meanwhile the potential of the southern aquifers had become apparent through their development in Kufrah, Sarir and Fezzan.

The Gefara Plain has always been the major agricultural area of the country and until 1973, both before and after independence, had always attracted the bulk of public and private investment in irrigation. The decline in the level of the coastal groundwater was observed, or predicted, by all hydro-geologists who looked at the Gefara Plain after 1950, although it should be remarked that the observations were made on the basis of imprecise and unrepresentative data. Even by 1980 figures on groundwater recharge (estimated from landuse and assumed pumping levels) were numerous and inconsistent making it difficult for policy makers to determine the economies required and the measures necessary to achieve the optimum management of water resources. Depending upon which estimates of recharge and withdrawal were used, the amount by which withdrawal exceeded recharge varied from three to eight times.

In these circumstances it was obviously prudent to attempt to determine the water balance from the Gefara Plain, and to this end a study was commissioned by FAO, on behalf of the Secretariat of Agriculture in Tripoli, for a study of recent satellite imagery to determine whether this inexpensive system of resources survey could make a contribution to planning water use in north-west Libya. By providing data on the irrigated area. From such data the water use element of the water balance equation could be estimated.

Digital signal processing is one of many valuable tools for suppressing unwanted signals or inter-ference. Building hardware processing engines seems to be the way to best implement some classes of interference suppression but is, unfortunately, expensive and time-consuming, especially if several miti-gation techniques need to be compared. Simulations can be useful, but are not a substitute for real data. CSIRO’s Australia Telescope National Facility has recently commenced a ‘software radio telescope’ project designed to fill the gap between dedicated hardware processors and pure simulation. In this approach, real telescope data are recorded coherently, then processed offline. This paper summarises the current contents of a freely available database of base band recorded data that can be used to experiment with signal processing solutions. It includes data from the following systems: single dish, multi-feed receiver; single dish with reference antenna; and an array of six 22 m antennas with and without a reference antenna. Astronomical sources such as OH masers, pulsars and continuum sources subject to interfering signals were recorded. The interfering signals include signals from the US Global Positioning System (GPS) and its Russian equivalent (GLONASS), television, microwave links, a low-Earth-orbit satellite, various other transmitters, and signals leaking from local telescope systems with fast clocks. The data are available on compact disk, allowing use in general purpose computers or as input to laboratory hardware prototypes.

Experimental and Modelling studies have been used to investigate the biogeochemical processes occurring at the interface zone between the near-field and far-field of the Drigg Low-Level radioactive Waste (LLW) trenches. These have led to a conceptual model of interface biogeochemistry, which has subsequently been modelled by the BNFL code known as the Generalised Repository Model (GRM). GRM simulations suggest that as organic rich leachate migrates into the far-field, iron III minerals such as iron hydroxide will dissolve, and reduced iron minerals such as siderite will precipitate due to microbial processes. Batch and column experimental studies have verified this conceptual understanding. Some unexpected processes, such as the presence of nitrate enhancing sulphate reduction, were also observed

Eruca vesicaria subsp. sativa (syn. E. sativa) is a cruciferous vegetable and oilseed crop that is high in erucic acid. It occurs throughout the Mediterranean region and western Asia, and has been naturalized elsewhere as a crop/weed escape. It is closely related to subsp. vesicaria and subsp. pinnatifida, which are endemic to Spain and north-western Africa, respectively. This study evaluated patterns and levels of diversity in the three subspecies based on 234 amplified fragment length polymorphisms (AFLP), and evaluated agronomic and seed quality data in a field trial in western Canada. AFLP data revealed three main clusters: ‘Sativa’ (33 accessions of subsp. sativa), ‘Vesicaria’ (nine accessions of subsp. vesicaria) and a ‘Pinnatifida’ cluster (one accession of subsp. pinnatifida and three Moroccan accessions of subsp. sativa). The Sativa cluster separated into Mediterranean and Asian groups, likely reflecting differences in origin (wild versus cultivated) or primary usage, vegetable versus seed oil. The origin of the introduced Mexican population was confirmed as subsp. sativa. The highest levels of diversity were found in the Sativa cluster (88% AFLP polymorphisms) and the least in the Vesicaria (56%) and Pinnatifida (39%) clusters. Extensive variation was observed among the 159 subsp. sativa accessions evaluated in the field trial, and overall findings indicated a favourable agronomic potential.

The central controversy over whether or not ultraluminous X-ray sources (ULXs) contain a new “intermediate-mass” class of black holes (IMBHs) remains essentially unresolved. Indeed, whilst many recent X-ray spectroscopy results find evidence for a cool (100–200 eV) accretion disc – the expected signature of a ${\sim} 1000$ M$_{\odot}$ IMBH – in ULX spectra, most of the circumstantial evidence (a combination of multiwavelength counterparts, theoretical modelling and the behaviour of accreting black holes in our own Galaxy) argues that the black holes underlying ULXs could be substantially less massive. I will present a new analysis of the deepest XMM-Newton observations of ULXs that directly addresses their underlying nature. This includes the results of a new 100-ks observation of the archetypal ULX Holmberg II X-1. Though a slight soft excess in its X-ray spectrum can be fitted by a cool accretion disc model, a rigorous analysis of the temporal data shows that the black hole cannot be larger than ${\sim}100$ M$_{\odot}$. Interestingly, we find evidence that the putative accretion disc corona is cool and optically thick in this source, unlike most Galactic binaries. We have also undertaken a detailed spectral analysis of the next 12 best ULX datasets in the XMM-Newton archive. Using physically self-consistent spectral modelling we show that whilst all the ULXs show possible cool accretion discs, the majority of these ULXs appear dominated by an optically-thick Comptonising medium. I will argue that this is evidence that most (though not necessarily all) ULXs contain black holes that are at most a few tens of solar masses in size.