56,989 research outputs found

    Factors determining gender ratio in the Maltese population

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    Introduction: The Male/Female ratio at birth has been described to favour the male conceptus, a situation that persists throughout most of childhood and into the reproductive phase of life. The reasons behind this preferential male-favouring remain elusive. Methodology: The various relevant obstetric and population national registers kept by the Department of Health information and the National Statistics Office of the Maltese Islands were reviewed to elucidate the age-related M/F ratios differences in the population starting with the third trimester of the antenatal period. In addition, third trimester M/F ratios in women with specific metabolic-related disorders were assessed and compared to the on-affected individuals. The role of foetal congenital malformations was also investigated. Results: It would appear that the M/F ratio starts favouring the male conceptus as early as the third trimester of the antenatal period. It remains favoured right through the reproductive age reaching par after the age of 45 years when it shifts to favour the female. This relationship was significantly altered during the 1930s as a result of the emigration patters prevalent during that period. The results further show that the maternal nutritional and biochemical milieu may influence the M/F ratio at the beginning of the third trimester with women suffering from adiposity, diabetes and thyroid disease having higher M/R ratios. In spite of this preference to the male conceptus, malts have a higher mortality throughout life with mortality rates being higher for males from the third trimester up to the age of 75 years. On the other hand, female foetuses with malformations appear to have a higher mortality during intrauterine life than corresponding male foetuses. Conclusion: The M/F ratio appears to favour the male conceptus during antenatal life and is definitely evident by the beginning of the third trimester of pregnancy, the selection mechanism possibly being a greater predisposition of female foetal loss in the presence of malformations. These biological observations may present advantages within the breath of human reproductive ecology, ensuring a healthy reproductive female individual who has the option of choosing her mate from a competing male community.peer-reviewe

    Structure analysis of biologically important prokaryotic glycopolymers

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    Of the many post-translational modifications organisms can undertake, glycosylation is the most prevalent and the most diverse. The research in this thesis focuses on the structural characterisation of glycosylation in two classes of glycopolymer (lipopolysaccharide (LPS) and glycoprotein) in two domains of life (bacteria and archaea). The common theme linking these subprojects is the development and application of high sensitivity analytical techniques, primarily mass spectrometry (MS), for studying prokaryotic glycosylation. Many prokaryotes produce glycan arrangements with extraordinary variety in composition and structure. A further challenge is posed by additional functionalities such as lipids whose characterisation is not always straightforward. Glycosylation in prokaryotes has a variety of different biological functions, including their important roles in the mediation of interactions between pathogens and hosts. Thus enhanced knowledge of bacterial glycosylation may be of therapeutic value, whilst a better understanding of archaeal protein glycosylation will provide further targets for industrial applications, as well as insight into this post- translational modification across evolution and protein processing under extreme conditions. The first sub-project focused on the S-layer glycoprotein of the halophilic archeaon Haloferax volcanii, which has been reported to be modified by both glycans and lipids. Glycoproteomic and associated MS technologies were employed to characterise the N- and O-linked glycosylation and to explore putative lipid modifications. Approximately 90% of the S-layer was mapped and N-glycans were identified at all the mapped consensus sites, decorated with a pentasaccharide consisting of two hexoses, two hexuronic acids and a methylated hexuronic acid. The O-glycans are homogeneously identified as a disaccharide consisting of galactose and glucose. Unexpectedly it was found that membrane-derived lipids were present in the S- layer samples despite extensive purification, calling into question the predicted presence of covalently linked lipid. The H. volcanii N-glycosylation is mediated by the products of the agl gene cluster and the functional characterisation of members of the agl gene cluster was investigated by MS analysis of agl-mutant strains of the S-layer. Burkholderia pseudomallei is the causative agent of melioidosis, a serious and often fatal disease in humans which is endemic in South-East Asia and other equatorial regions. Its LPS is vital for serum resistance and the O-antigen repeat structures are of interest as vaccine targets. B. pseudomallei is reported to produce several polysaccharides, amongst which the already characterised ‘typical’ O-antigen of K96243 represents 97% of the strains. The serologically distinct ‘atypical’ strain 576 produces a different LPS, whose characterisation is the subject of this research project. MS strategies coupled with various hydrolytic and chemical derivatisation methodologies were employed to define the composition and potential sequences of the O-antigen repeat unit. These MS strategies were complemented by a novel NMR technique involving embedding of the LPS into micelles. Taken together the MS and NMR data have revealed a highly unusual O-antigen structure for atypical LPS which is remarkably different from the typical O-antigen. The development of structural analysis tools in MS and NMR applicable to the illustrated types of glycosylation in these prokaryotes will give a more consistent approach to sugar characterisation and their modifications thus providing more informative results for pathogenicity and immunological studies as well as pathway comparisons.Open Acces

    Evolution and chemical yields of AGB stars: effects of low-temperature opacities

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    The studies focused on the Thermally-Pulsing Asymptotic Giant Branch phase experienced by low- and intermediate-mass stars are extremely important in many astrophysical contexts. In particular, a detailed computation of their chemical yields is essential for several issues, ranging from the chemical evolution of galaxies, to the mechanisms behind the formation of globular clusters. Among all the uncertainties affecting the theoretical modelling of this phase, and described in the literature, it remains to be fully clarified which results are severely affected by the use of inadequate low-temperature opacities, that are in most cases calculated on the basis of the original chemical composition of the stars, and do not consider the changes in the surface chemistry due to the occurrence of the third dredge-up and hot-bottom burning. Our investigation is aimed at investigating this point. By means of full evolutionary models including new set of molecular opacities computed specifically with the AESOPUS tool, we highlight which stellar models, among those present in the literature, need a substantial revision, mainly in relation to the predicted chemical yields. The interplay among convection, hot bottom burning and the low-temperature opacity treatment is also discussedComment: 6 pages, 2 figure

    Language and the science curriculum

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    Current interest about which language (Maltese or English) is more suitable for teaching certain subjects in the secondary school touches upon important educational issues (1). Language is not simply the medium of exchange of ideas but, once acquired, it becomes the instrument that the learner can then use to bring order into his/her environment (2). In the absence of a prescribed language policy, many teachers opt for the language which in their judgement best helps pupils to understand the subject and to perform well in tests and examinations. In practice this means that they use a mixture of languages depending on the objectives of their lessons. This article focuses on the language used in science teaching and it is based on research carried out in June 1984 as an off-shoot of an evaluation of the science curriculum in the first two years of the Area Secondary schools (3). At that time, excluding pupils attending Junior Lyceums and private schools, the Area Secondary schools catered for 60 percent of all boys and 66.5 percent of all girls at Form 1 and Form 2 level.peer-reviewe

    Sex differences in science achievement at G.C.E. 'O' level

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    It is usually taken for granted that boys are better than girls in science subjects. A recent study that shows science achievement of males and females separately indicates that this assumption has an empirical basis. Thus the I.E.A. (International Association for the Evaluation of Educational Achievement) study of science education in nineteen countries shows that boys consistently achieve significantly higher than girls in the physical science items at each of the three age levels sampled in every country, and the differences widen with increasing age.peer-reviewe

    A new method for the representation and evolution of three dimensional discontinuity surfaces in XFEM/GFEM

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    The ability of the extended and generalized finite element methods of modeling discontinuities independent of mesh alignment requires a suitable representation for the discontinuity surfaces. In the present paper a method for constructing level set functions based on vector data and geometric operations in three dimensions is presented. In contrast to classical level set methods, the proposed approach does not require the integration of differential evolution equations, resulting in a particularly simple structure and easy implementatio

    Nineteenth-century disciplinary enquiry at Victoria Hospital, Gozo

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    In this article the author presents a report which describes an enquiry into the actions of a junior medical practitioner employed with the public sector in the late nineteenth century, wherein the final intention was in disciplining the officer without attempting to correct the circumstances which led to the incident. An account of the case which provoked the disciplinary enquiry is described in the article.peer-reviewe
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