13,060 research outputs found

    Mesoscale Calculations of the Dynamic Behavior of a Granular Ceramic

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    Mesoscale calculations have been conducted in order to gain further insight into the dynamic compaction characteristics of granular ceramics. The primary goals of this work are to numerically determine the shock response of granular tungsten carbide and to assess the feasibility of using these results to construct the bulk material Hugoniot. Secondary goals include describing the averaged compaction wave behavior as well as characterizing wave front behavior such as the strain rate versus stress relationship and statistically describing the laterally induced velocity distribution. The mesoscale calculations were able to accurately reproduce the experimentally determined Hugoniot slope but under predicted the zero pressure shock speed by 12%. The averaged compaction wave demonstrated an initial transient stress followed by asymptotic behavior as a function of grain bed distance. The wave front dynamics demonstrate non-Gaussian compaction dynamics in the lateral velocity distribution and a power-law strain rate–stress relationship

    Change in fluoride content of Maltese tapwaters : implications for oral health

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    Dietary intake of fluoride is believed to be largely derived from drinking water. In Malta, tap water presently contains less fluoride than is found in naturally occurring ground water obtained from aquifers. Over 55% of water production comes from reverse osmosis and such water is practically fluoride-free. Before the introduction of reverse osmosis water into the water budget, fluoride levels measured from 10 different tap waters averaged 0.51 ppm F-. Now, fluoride content measured from 19 tap water sources averaged 0.21 ppm F- and more than a third of these sources are practically fluoride-free. The incidence of dental caries in Malta has so far been low according to the international standards. We suggest that the lowering of the fluoride level in the water supplies may favour an escalation in the incidence of tooth decay in the future.peer-reviewe

    An annotated catalogue of the Lepidoptera collection of Guido Lanfranco at the National Museum of Natural History in Malta

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    An annotated list of the lepidoptera in the Lanfranco collection donated to the National Museum of Natural History of Mdina in Malta is included. Where relevant, comments on particular species or specimens are provided.peer-reviewe

    Study of cosmic dust particles on board LDEF: The FRECOPA experiments AO138-1 and AO138-2

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    Two experiments, within the French Cooperative Payload (FRECOPA) and devoted to the detection of cosmic dust, were flown on the LDEF. A variety of sensors and collecting devices have made possible the study of impact processes on materials of technological interest. Preliminary examination of hypervelocity impact features gives valuable data on size distribution and nature of interplanetary dust particles in low earth orbit, within the 0.5 to 300 micrometer size range. Most of the events detected on the trailing face of LDEF are expected to be the result of impacts of meteoritic particles only. So far, chemical analysis of craters by EDS clearly shows evidence of elements (Na, Mg, Si, S, Ca, and Fe) consistent with cosmic origin. Systematic occurrence of C and O in crater residues is an important result, to be compared with the existence of CHON particles detected in P-Halley comet nucleus. Crater size distribution is in good agreement with results from other dust experiments flown on LDEF. However, no crater smaller than 1.5 micron was observed, thus suggesting a cutoff in the near earth particle distribution. Possible origin and orbital evolution of micrometeoroids is discussed

    First record of Xenopsylla gratiosa Jordan & Rothschild, 1923 from the Maltese Islands (Siphonaptera: Pulicidae)

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    Xenopsylla gratiosa is reported for the first time from the Maltese Islands. The species was found in an abandoned nest of a Cory’s Shearwater, Calonectris diomedea on the island of Filfla. Brief notes are included on previous records of fleas from the Maltese Islands and taxonomic, distributional and ecological notes are provided for Xenopsylla gratiosapeer-reviewe

    Preliminary notes on the early stages of Isturgia pulinda (Walker, 1860) (Lepidoptera: Geometridae)

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    The early stages, larval hostplant and voltism of Isturgia pulinda in the Maltese Islands are documentedpeer-reviewe

    Validation of a Polymerase Chain Reaction technique for Kidd blood group genotyping

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    The Kidd blood group antigens, Jkª and Jkᵇ , are two of the main surface markers which are found on the membrane of red blood cells. The determination of whether a donor or a recipient has the Jkª and/or the Jkᵇ antigens is crucially important to have a successful transfusion without the development of adverse incompatibility-related reactions. In Malta, routine serological-based tests are applied with the purpose of differentiating between homozygous and heterozygous states for the Jk antigens respectively. Although these tests are highly specific and sensitive, there are particular clinical scenarios where haemagglutination assays are not suitable for determining the individual’s Kidd blood group status. Additionally, the alternative genotyping procedure has never been applied in Malta within the context of blood grouping. The current study was therefore carried out to determine whether a molecular-based technique such as Polymerase Chain Reaction – Restriction Fragment Length Polymorphism analysis (PCR-RFLP) is a suitable alternative procedure for distinguishing amongst the three different Kidd phenotypes. After extracting deoxyribonucleic acid (DNA) from 50 blood samples obtained from serologically-tested healthy blood donors who expressed at least one of the Kidd antigens, PCR-RFLP analyses were carried out. The results of the latter were then compared with those previously obtained with haemagglutination and a complete match was observed between the two. Therefore, this PCR-RFLP method was confirmed as a suitable alternative laboratory technique that can be used to determine efficiently the Kidd blood group of both donors and recipients, in an accurate manner without subjectivity as encountered in the case of haemagglutination. This research further facilitates the introduction of molecular-based techniques in molecular blood transfusion.peer-reviewe

    Population ecology of Phaleria acuminata (Coleoptera : Tenebrionidae) from sandy beaches in the Maltese Islands

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    Populations of the beetle Phaleria acuminata fromfour beaches on the Maltese Islands were sampled for six consecutive seasons to investigate changes in population size, sex ratio, reproductive state and distribution on the shore. The populations on all the beaches showed a small decrease in numbers from spring to summer and a pronounced drop from summer to autumn, with a dramatic increase between winter and spring. Male to female sex ratio varied between 1:1 and 1:1.5. Females of all reproductive stages occurred throughout the year. There were little seasonal differences in distribution of beetles in the wet and dry zones.peer-reviewe

    The influence of inter-atomic transitions in Auger valence band spectroscopy: oxygen on Si(001)2x1

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    In this paper we will show that the description of an Auger process in terms of a process confined to one atom is in general not adequate and the Mulliken population is only in very specific cases a good alternative in evaluating the strength of inter-atomic transitions. The ionicity of the chemical bond cannot be used as a direct measure of the contribution of inter-atomic Auger transitions, as will be demonstrated in the case of the oxygen KVV Auger transitions in gaseous molecular oxygen and oxygen chemisorbed on the Si(001) surface. A full evaluation of inter-atomic transition rates shows that their strength depends on the inter-atomic distance as well as on the screening of the initial core hole
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