Showing papers by "Trinity College, Dublin published in 1985"

Computer generation of structural models of amorphous Si and Ge.

Abstract: We have developed and applied a computer algorithm that generates realistic random-network models of $a$-Si with periodic boundary conditions. These are the first models to have correlation functions that show no serious discrepancy with experiment. The algorithm provides a much-needed systematic approach to model construction that can be used to generate models of a large class of amorphous materials.

A model for high-order Markov chains

Abstract: On introduit un modele pour des chaines de Markov du leme ordre qui comporte seulement un parametre additionnel pour chaque retard

Mechanisms of Dissolution of Fast Release Solid Dispersions

Abstract: Drug dissolution from a solid dispersion is dependent on the technology employed to prepare the dispersion and on the proportion and properties of the carrier used. The diffusion models describing dissolution from multi-component solids seem to adequately describe drug release from non-disintegrating systems in the weight fraction range where the drug phase is expected to control dissolution. When solid dispersions have higher dissolution rates than corresponding mechanical mixtures, solid state changes during the formation of the dispersion are indicated. These increases in rate may result from the formation of higher energy phases of either component or from interactions between the components. The carrier may play an important role in the formation of these phases and in stabilizing them during subsequent dissolution. When a large relative solubility difference exists between the carrier and the drug, deviations from theory can be expected to occur at high carrier weight fractions. The model fa...

On drawing analogies when solving problems: A theory and test of solution generation in an analogical problem-solving task

Abstract: Three criticisms are made of present theories of analogy: (a) that they fail to model the process of object identification; (b) that, in the case of story analogues, the solution statement part may be accessed directly using schematic knowledge; (c) that they fail to model the role of goals. A theory of solution generation by analogy is proposed which takes these criticisms into account, and two aspects of the theory are tested. Experiment 1 supported the second criticism, in finding that the provision of an analogous solution statement is sufficient to influence significantly the production of a specific solution to Duncker's ‘radiation problem’. Experiment 2 tested a specific aspect of the theory, namely, the prediction that ‘functionally relevant attributes’ (FRAs) significantly influence the generation of solutions by analogy. The results confirmed this prediction but, contrary to pre-experimental predictions, this influence seems mainly attributable to facilitation by FRAs of relational transfer.

Responses of the lower limb to load carrying in walking man

Abstract: Muscle activity patterns of several lower limb muscles were examined in the left leg of normal human subjects walking at comfortable speed on a treadmill. In addition knee angular changes and the durations of the swing and stance phases of the step cycle were recorded. Data were collected during a period of normal control walking and when the subject carried a load, either in his right or left hand or on his back. Load (up to 20% of body weight) carried in either hand caused minimal changes in the kinematic parameters investigated but evoked significant prolongation of the normal ongoing electromyographic activity in the contralateral Gluteus medius and in the ipsilateral Gastrocnemius, Vastus lateralis and Semimembranosus. Load (up to 50% of body weight) carried on the back significantly shortened the swing phase and prolonged the ongoing electromyographic activity of the Vastus lateralis. These findings would seem to indicate that the activity of the leg musculature during walking is so tightly controlled that deviation from the normal kinematic pattern of the legs is largely prevented even when body posture and balance are disturbed by carrying substantial additional load.

Vancomycin toxicity: a prospective study

Abstract: A prospective study of 34 patients treated with 39 courses of intravenous vancomycin, was undertaken in order to assess toxicity. Six patients received vancomycin alone and 27 courses were associated with aminoglycoside administration either concurrently or within two weeks of the first dose of vancomycin. Hearing loss was slight and uncommon; patients were unaware of its occurrence. Tinnitus and dizziness was noted by two patients and resolved on withdrawal of vancomycin. Diminution of renal function was seen both during (7%) and after (9%) vancomycin therapy. A striking feature of these patients with renal deterioration was the severity of their underlying disease. No evidence of synergistic toxicity between vancomycin and aminoglycosides was seen.

A long pollen record from Laghi di Monticchio, southern Italy: a preiminary account

Abstract: A pollen diagram from Lake Monticchio, a volcanic crater lake in S Central Italy east of Naples, shows a long vegetation record for the Holocene and the later portion of the Last (Weichselian) Glacial Period. The upper 735 cm of a 2550-cm core is assigned to the Holocene. It begins with expansion of Betula (birch) and Quercus (oak), followed by Fagus (beech), Tilia (lime) and other mesic trees. In the next phase the flora is dominated by oak with an increase in herb pollen. In the later Holocene the flora is again diversified by the appearance of Abies (fir), Curpinus (hornbeam) and other trees. In the latest Pleistocene portion of the core the vegetation is dominated by grasses, Artemisia (sage-brush) and chenopods, indicating a treeless environment. The base of the core shows continued dominance by steppe-like vegetation with 9interstadial9 episodes in which trees, especially oak, beech and fir, were abundant. The climatic interpretation is that the late Pleistocene was very dry, at least in the summer growing season, and probably, although not necessarily, colder than now. In the Holocene increased precipitation favoured expansion of tree populations. For a brief period there was a return of water stress in the growing season marked by a loss of tree species diversity and an increase in herbs. In the later Holocene a progressive diversification of tree species indicates a return to a more humid and perhaps cooler climate. The vegetation history and climatic inferences are closely similar to records available from Greece. The available radiocarbon dates, which show a consistent pattern, indicate that the core is much older than 40000 years at the base but not old enough to include the major post-Eemian interstadials. The 9Holocene9 birch expansion began nearly 20000 years ago. These dates appear to be systematically too old in the light of present knowledge. The preliminary character of the study is emphasized. Further radiocarbon dates, especially of the 9Holocene9 section, are needed, as are more detailed studies of sedimentation processes and tephra occurrences.

Selection pressures on codon usage in the complete genome of bacteriophage-t7

Abstract: We searched the complete 39,936 base DNA sequence of bacteriophage T7 for nonrandomness that might be attributed to natural selection. Codon usage in the 50 genes of T7 is nonrandom, both over the whole code and among groups of synonymous codons. There is a great excess of purineany base-pyrimidine (RNY) codons. Codon usage varies between genes, but from the pooled data for the whole genome (12,145 codons) certain putative selective constraints can be identified. Codon usage appears to be influenced by host tRNA abundance (particularly in highly expressed genes), tRNA-mRNA interactions (one such interaction being perhaps responsible for maintaining the excess of RNY codons) and a lack of short palindromes. This last constraint is probably due to selection against host restriction enzyme recognition sites; this is the first report of an effect of this kind on codon usage. Selection against susceptibility to mutational damage does not appear to have been involved.

Physicochemical Properties of Indomethacin and Related Compounds Co-Spray Dried with Polyvinylpyrrolidone

Abstract: The spray drying of indomethacin produced a viscous liquid phase which then solidified to an amorphous glassy solid mass. This amorphous phase was physically unstable and converted on storage to crystalline indomethacin forms II and I. Co -spray drying indomethacin with up to 20% PVP also gave a fused amorphous solid. Apparent solubility and dissolution studies illustrated the higher energy of indomethacin in these systems. The presence of PVP in the solid retarded conversion of indomethacin to a crystalline phase, the effect increasing with increasing PVP content. Scanning electron microscopy revealed the growth, with time, of needle-like whiskers on the surface of the amorphous products. Co-spray drying indomethacin with more than 20% PVP resulted firstly in products composed of a fused network of spherical particles, then partially coalesced spheres and ultimately, above 25% PVP, in individual agglomerated microspherical particles. The spray drying of either naproxen, ketoprofen or ibuprofen di...

Time of deformation in the Caledonide Orogen of Britain and Ireland

Abstract: Considerable problems attach to any attempt to define precisely the timing of such geological events as deformation. The biostratigraphical evidence may be imperfect or lacking, the isotopic evidence may be imprecise or conflicting, and where both lines of evidence are available, disagreement over definition of the Geological time scale creates problems of wider correlation. The last situation is exempslified by the English Lake District wherein the biostratigraphical and isotopic data appear to be reliable and compatible but the isotopic data conflict with some recently published time scales. Of particular importance to the present study are disagreements over the ages of the Lower Palaeozoic period boundaries. Estimates for the Devonian-Silurian boundary vary from 400 to 412 Ma (Odin 1982, cf McKerrowetal. in press); the Silurian-Ordovician boundary 418 to 438 Ma (Odin 1982, cf Harland et al. 1982); the Ordovician-Cambrian boundary 495 to 513 Ma (Odin 1982, cf McKerrow et al. in press); and the Camsbrian-Vendian boundary 530 to 590 Ma (Odin 1982, cf Harland et al . 1982). Such differences evidently become critical where comparisons of timing based only on biostratigraphic evidence are made with those based solely on isotopic data. Particular difficulties also arise from the problems involved in determining the biostratigraphic base of the Devonian within rocks of Old Red Sandstone facies. Throughout this work reference has been made to the Special Reports of the Geological Society of London numbers 1, 2, 3, 6, 7, 8 and 10, which provide summaries of the lithostratigraphic and biostratigraphic record in Britain and

Anion accumulation by the moss hylocomium splendens: uptake and competition studies involving arsenate, selenate, selenite, phosphate, sulphate and sulphite

Abstract: Summary Arsenic and selenium uptake by the moss Hylocomium splendens (Hedw.) Br. et Sch. from solutions containing arsenate, selenite or selenate ions was investigated. Arsenate and selenite were accumulated only by living shoots. This moss was unable to take up selenate. Arsenate uptake was optimal between pH 3 and 5 whilst selenate uptake was greatest at pH 3. This difference is discussed in terms of speciation of these anions in solution. Uptake of arsenate and selenite displayed saturation kinetics at pH 5 which could be described in terms of Michaelis-Menten parameters with Km values of 418 ± 56 μM and 451±93 μM for arsenate and selenite respectively. Competition studies revealed that pre-incubation of moss shoots in phosphate solutions did not affect the subsequent uptake of either arsenate or selenite. However, the uptake of the latter ions was decreased if phosphate was included in the incubation medium. Phosphate was a competitive inhibitor of arsenate uptake with an inhibition constant (Km phosphate) of 82 μM. Phosphate and arsenate were non-competitive inhibitors of selenite uptake with inhibition constants of 225 and 43 μM for phosphate and arsenate respectively. The results suggest that arsenate and selenite were accumulated via separate transport systems in H. splendens and it is proposed that these systems may normally be responsible, in part, for phosphate uptake by this moss.

Lead and Uranium Uptake by Lichens

Abstract: Interest in the uptake of Pb and U stems from both practical and academic considerations. Lead is currently one of the most widespread environmental contaminants owing to its use as an anti-knock petrol additive. Lead emitted by vehicle exhausts is taken up by both plants and animals and poses a particular health hazard for young children (Richardson, 1982). Uranium is more limited as a pollutant but can be important where this element is mined or refined. Uranium from such operations is accumulated by lichens, mosses and other organisms (Beckett et al., 1982). Monitoring such contamination by using lichens is of value because the environmental impact of U is uncertain but of concern. This element and particularly its decay product, radon, is thought to induce lung cancer in miners (Van Hook, 1979; Band et al., 1982; Gottlieb and Husen 1982).

Specular light scattering from a chiral medium: Unambiguous test of gyrotropic constitutive relations

Abstract: Amplitudes for light reflection from an isotropic chiral medium are derived for both the Condon and Born forms of constitutive relations. Contrary to general belief, the two forms lead to very different physical predictions. The measurement of differential reflection of left and right circularly polarized light provides a decisive experimental test.

The Application of Two Simple Indices to Irish Estuary Pollution Status

Abstract: Two complementary indices of estuarine quality have been developed as a management tool and to facilitate intercomparison of diverse estuarine types. The indices used here have been devised as relatively quick and inexpensive and taking into account both the biological and the environmental information from a systematic survey of the intertidal regions of an estuary.

The case against divination: an examination of Cicero's De Divinatione

Abstract: Ancient divination had something of the status of modern science. Diviners, like scientists, were expected to offer public comment on all manner of subjects, from strange meteorological phenomena to proposals for military campaigns, from shooting stars to Star Wars. In both cases this public responsibility is based upon a supposed expertise in prediction. And the arguments of those ancient philosophers who attempted to justify such a status for divination run in some ways remarkably parallel to those of modern philosophers who have attempted to justify such a status for science. Thus we are told both by Stoics and by modern Scientific Realists that the world forms a single and unitary physical system, with nothing outside it to prevent the course of events from unfolding in accordance with the adamantine regularities which are the laws whereby nature operates. This determinism, and its consequence that the entire future of the world is already prefigured in the current state of things, makes it possible for us now to tell what will happen later. And that possibility is realised. Scientific predictions, we are told, may not be uniformly correct, but they are correct too often for that to be due to chance. The predictions of diviners, one must likewise concede, are not uniformly correct: nonnumquam ea quae praedicta sunt minus eueniunt (Cicero, De Divinatione, 1.24).