Artigos em revistas internacionais
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Now showing 1 - 10 of 1920
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- Estimating diet composition from scat analysis in otariid seals (Otariidae): is it reliable?Publication . Dellinger, T.; Trillmich, F.Analysis of teleost sagittal otoliths contained in scats has been widely used to determine the diet of seals. This method is based on the assumption that relative frequencies of otoliths in scats faithfully reflect those of fish in the diet. This assumption has rarely been tested experimentally. We compared the ratios of herring (Clupea harengus) to sprat (Sprattus sprattus) oto liths in faeces (output) of captive California sea lions (Zalophus calijornianus) and South American fur seals (Arctocephalus australis) with the ratios at feeding (input). Sea lions and fur seals showed no consistent differences in recovery rates and partial digestion of otoliths. Output ratios deviated only slightly from input ratios, the smaller sprat otoliths being underrepre sented in the output by 8%. Only about 40% of the otoliths fed to the seals were found in the scats. For both species partial digestion of otoliths led to a 16% underestimation of fish length and a 35% underestimation of fish mass.
- Evolution of the obscura group Drosophila species.: III. phylogenetic relationships in the subobscura cluster based on homologies of chromosome APublication . Brehm, A.; Krimbas, C. B.The Drosophila subobscura cluster comprises D. subobscura, D. madeirensis and D. guanche, species closely related to some interspecific crosses are possible. This paper clarifies definitively the homologies of the segments of the sex chromosome A (= X) among these species and thus permits a phylogenetic seriation of them. This seriation is identical to the one suggested by the study of chromosome O and concordant with similar data for the remaining three rod autosomes (J, U and E), which, however, do not provide qualitative evidence on this subject.
- The basicity of alkali metal methoxides in methanol. The effects of ion association on methoxide additions to activated anisolesPublication . Castilho, Paula C. M. F.; Crampton, Michael R.; Yarwood, JackThe formation of adducts with 1 :2 and 1:3 stoichiometry by methoxide addition to nitro-activated anisoles has been examined spectrophotometrically. For these equilibria the ‘basicity’ of sodium methoxide solutions in methanol is appreciably greater than that of corresponding potassium methoxide solutions. This is in contrast with other measures of basicity and is attributed to the association of the multi-charged adducts with cations which is stronger with sodium than with potassium ions.
- Studies of the species barrier between Drosophila subobscura and D. madeirensis I. The genetics of male hybrid sterilityPublication . Khadem, Mahnaz; Krimbas, Costas B.The genetics of hybrid male sterility between Drosophila subobscura and D. madeirensis were studied with the help of 20 markers in backcross males. A major effect resides in the sex chromo somes: backcross males with the X and Y of different origin (mad X-sub Y or sub X—mad Y) have very small and empty testes. In compatible combinations testes are of normal size but males may be sterile or fertile depending on the genetic constitution of their autosomes. Six autosomal factors affecting hybrid male fertility could be postulated. This estimation is based on the assumption of the absence of interaction between viability and fertility. The presence and the mode of such interaction may modify the number of sterility factors.
- Infrared spectroscopic studies of hydrogen bonding in substituted nitrophenols: substituent and solvent effectsPublication . Castilho, Paula C. M. F.; Crampton, Michael R.; Yarwood, JackA detailed infrared spectroscopic study of the substituted phenols 2-cyano-4,6-dinitrophenol and 4-cyano-2,6-dinitrophenol has been carried out (in several different solvents) in order to investigate the substituent and solvent effects on their intra- and inter-molecular hydrogen bonding properties. In benzene or dichloromethane it is found that both isomers form strong intramolecular hydrogen bonds with the 2-cyano (2CN) isomer having a stronger intramolecular interaction (in accordance with the higher pKa). The 4-cyano (4CN) isomer shows two distinct NO2 groups and exchange between the two possible hydrogen bonding sites is probably slow on the infrared time-scale. In protic solvents such as methanol the intramolecular hydrogen bonds are broken (more easily for the 4CN isomer) by intermolecular hydrogen bonding to the solvent. The differential “reactivity” towards methanol may be associated with steric congestion in the 4CN isomer leading to the forcing of at least one of the NO2 groups out of the aromatic plane. The use of mixed solvents (benzene-methanol) has established that the two hydrogen bonded species are observed together and that a high concentration of methanol is required to drive the equilibrium towards the intermolecular hydrogen bonded species. In dimethyl sulphoxide the behaviour of the two isomers is even more interesting. The 4CN isomer is ionised to produce the corresponding phenolate. However the 2CN isomer remains neutral (but highly solvated). We attribute this difference to the requirement for the 4CN isomer to allow the 2- and 6-NO2 groups to recover planarity with the aromatic ring. The energy compensation involved in this process is clearly sufficient to break a stronger intramolecular hydrogen bond.
- Studies of the species barrier between Drosophila subobscura and D. madeirensis. III. How universal are the rules of speciation?Publication . Khadem, Mahnaz; Krimbas, Costas B.The prevalence of Haldane's rule and the large effect of the X chromosome are examined by analysing the genetics of seven abnormal characters in interspecies hybrids between D. subobscura and D. madeirensis. In two cases Haldane's rule is not obeyed (viability and abnormality of the head). In all characters except the abnormal abdominal tergites, an important effect of the X chromosome is observed. There is an asymmetry in the importance of the effect of the X chromosome. The X of D. madeirensis origin induces abnormality mostly in a mixed background. TheY chromosome plays an important role in determining male sterility.
- The phylogeny of nine species of the Drosophila obscura group inferred by the banding homologies of the chromosomal regions. IV. Element CPublication . Brehm, António; Krimbas, Costas B.Homologies of the sections of the polytene chromosomes of element C, among several species of the obscura group of the genus Drosophila, were established according to the similarity of their banding patterns. The information gathered was used to construct an unrooted phylogenetic tree based on qualitative criteria. This tree is compared to three other similar trees derived from independent information provided by the study of chromosomal elements B, D and E. The general congruence of the patterns of these trees proves the well-foundedness of this approach. A single exception to this congruence is discussed. Finally a consensus tree, encapsulating information from all chromosomal elements, is presented and its topology is compared to those derived from electrophoretic data.
- Identifying vulnerable industries and regions: the proposed European single market and Portuguese manufacturingPublication . Pereira, Pedro Telhado; Seabra, Maria do Carmo
- Portuguese emigration 1958-1985: some empirical evidencePublication . Pereira, Pedro TelhadoSupplying work in the home country or abroad must be seen as the result of the same decisional process. If that is true, the same set of variables should be used to explain the participa tion in the labor market and the emigration rates. Based upon empirical results, we discuss some of the traditional conclusions of the economic literature. Our empirical results, for example, show that: 1) there is a strong support for considering home wages and the wages in the country of destination asymmetrically, 2) imperfections in the capital markets seem to play an important role when workers must pay for their moving expenses and 3) there is a differential in coefficients between the period before 1974 and after that date, as 1974 is the year most of the Central European countries changed their immigration policies. The results also point to the existence of a large stock of potential emigrants in Portugal. The actual emigration will depend to a great extent on expectations regarding the evolution of real wages in Portugal and in the EC partners. If workers do not expect a rapid growth at home, we will see a large outflow due to the differential of wage levels.