Showing papers by "University of the Algarve published in 2000"

Initial energy density of gluons produced in very-high-energy nuclear collisions

Abstract: In very-high-energy nuclear collisions, the initial energy of produced gluons per unit area per unit rapidity, $(\mathrm{dE}/{L}^{2})/d\ensuremath{\eta}$, is equal to $f({g}^{2}\ensuremath{\mu}L)({g}^{2}\ensuremath{\mu}{)}^{3}/{g}^{2}$, where ${\ensuremath{\mu}}^{2}$ is proportional to the gluon density per unit area of the colliding nuclei. For an SU(2) gauge theory, a nonperturbative computation of $f({g}^{2}\ensuremath{\mu}L)$ shows that it varies rapidly for small ${g}^{2}\ensuremath{\mu}L$ but varies only by $\ensuremath{\sim}25%$, from $0.208\ifmmode\pm\else\textpm\fi{}0.004$ to $0.257\ifmmode\pm\else\textpm\fi{}0.005$, for a wide range $35.36$-- $296.98$ in ${g}^{2}\ensuremath{\mu}L$. This includes the range relevant for collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). Extrapolating to SU(3), we estimate $dE/d\ensuremath{\eta}$ for Au-Au collisions in the central region at RHIC and LHC.

Free Amino Acids Are Absorbed Faster and Assimilated More Efficiently than Protein in Postlarval Senegal Sole (Solea senegalensis)

Abstract: To improve the formulation of diets for the early stages of marine fish, assimilation rates of free amino acids (FAA) and protein in postlarval Senegal sole (Solea senegalensis) were determined. Fish (2.45 +/- 0.87 mg dry weight) were tube fed 36 nL of a diet of FAA containing L-[(35)S] methionine (FAA diet) or bovine serum albumin, containing L-[methylated-(14)C]bovine serum albumin (Prot-diet), both at a concentration of 4.08 g/L. A time series was performed, and the amounts of label in incubation water, liver, gut and body carcass were quantified. The FAA diet was absorbed with a 3.5-times-higher transfer rate (P < 0.001) from the gut into the larval body tissues compared with the Prot-diet. The FAA diet also was assimilated with greater efficiency than the Prot-diet (80% versus 58%, P: = 0.001). If we assume that the label present in the gut represents amino acids incorporated into the intestinal tissue, the assimilation efficiencies for the two diets were 89 and 64%. Therefore, FAA seems to be superior to protein as a dietary source of amino acids in Senegal sole postlarvae. However, because the absorption dynamics of protein and FAA differ, care should be taken when using the sources together to avoid amino acid imbalance.

The infralittoral prograding wedge: a new large-scale progradational sedimentary body in shallow marine environments.

Abstract: A progradational sedimentary body, the infralittoral prograding wedge (IPW), has been developing from the mean fair-weather wave-base level to the storm wave-base level between the onshore (beach) and the offshore (inner continental shelf) depositional zones along the Spanish coast during the Late Holocene. The main sedimentary body is composed of large inclined master beds which prograde seawards parallel to the shoreline, formed by sediments swept offshore by waves from shallow-water littoral environments. The inclined beds downlap onto finer-grained offshore sediments and, in turn, are overlain by shoreface deposits. The IPW is generated by downwelling storm currents and associated seaward transport of sediment. It represents a new depositional model for clastic wave-dominated coasts, and its identification requires a new subdivision of the nearshore environment.

Two estrogen receptors expressed in the teleost fish, Sparus aurata: cDNA cloning, characterization and tissue distribution.

Abstract: Estrogen is an essential hormone for many reproductive and non-reproductive functions. The function of estrogen in the reproductive cycle of seabream (Sparus aurata), a protandrous hermaphrodite teleost fish, is complex but it is understood to be involved in sex inversion, a process that occurs in some individuals during the second reproductive season. Estrogen action is mediated by two estrogen receptor (ER) subtypes designated alpha and beta. As a step to understanding the mechanisms of estrogen action during natural and induced sex reversal in seabream, we have isolated two cDNAs encoding distinct forms of ER homologous to mammalian ER and ER. The seabream ER clone (sbER1), which was truncated in the A/B domain, corresponded to a variant differing in five amino acids from another recently cloned sbER. The ER clone (sbER) encoded a protein 559 amino acids long and showed only 40% identity to sbER. Northern blot analysis of liver and ovary mRNA indicated the presence of several transcripts of the two receptor subtypes. PCR analysis showed that the two receptors differed in their expression pattern. sbER had a more restricted distribution, occurring mainly in testis, liver and heart, and sbER was present in most tissues, being more abundant in ovary, testis, liver, intestine and kidney. The presence in seabream of two ERs with several ER transcripts and their pattern of distribution are consistent with the widespread effects of estrogen in different tissues.

The effect of food deprivation and refeeding on the liver, thyroid hormones and transthyretin in sea bream

Abstract: There was a significant reduction in body weight of sea bream Sparus aurata and the hepatosomatic index after 3 weeks food deprivation. Liver biochemical indices and morphology were altered by food deprivation, there was a loss of eosin staining in hepatocyte cytoplasm and the appearance of large depleted vacuoles. Cell and nuclear area were significantly reduced (P<0.001) and did not return to control values after 1 week of refeeding. The water, lipid, glycogen and protein content of the liver was significantly reduced by 3 weeks fasting but recovered rapidly after 1 week refeeding. Food restriction also had a marked effect on circulating thyroid hormones and the concentration of plasma T 3 (33.98 ± 12.47 ng ml -1 ) and T 4 (16.54 ± 9.5 ng ml -1 ) was significantly (P<0.001) lower than the control (66.52 ± 13.4 and 56.83 ± 7.3, respectively). Refeeding for 1 week restored circulating T 3 (P<0.05) close to control levels but did not significantly affect the concentration of T 4 . Northern blotting with an homologous probe for transthyretin (TTR) demonstrated clearly the expression of a single mRNA transcript of 0.7 kb for this protein in the liver. The level of TTR message was substantially reduced below control levels in the liver of fasted fish and I week refeeding failed to restore expression.

The Upper Palaeolithic settlement of Iberia: first-generation maps

Abstract: Modelling of Upper Palaeolithic occupation in Iberia (one of the most important refugia of the last Ice Age) has enabled mapping of human occupation against an improving chronology of absolute dates. Important patterns emerge from the still uneven data of Iberia, providing a basis for new hypotheses.

Effect of Aluminum Competition on Lead and Cadmium Binding to Humic Acids at Variable Ionic Strength

Abstract: Complexation of Al3+ by NOM will change the speciation of Al and influence its toxicity. Competitive binding data between Al and metal ions to humic acids are needed to understand changes in specia...

Assessment of genetic relationships among Pyrus species and cultivars using AFLP and RAPD markers

Abstract: Twenty-five Pyrus communis L. cultivars including eight traditional Portuguese pears, and four commercial Pyrus pyrifolia (Burm.) Nak. (Japanese pear or `nashi') cultivars were analysed by RAPD and AFLP techniques focusing on their molecular discrimination and the assessment of their genetic relatedness. Twenty-five primers generated 324 RAPD markers, among which 271 (84%) were polymorphic. The AFLP technique, using seven primer combinations, revealed a similar level of molecular polymorphisms (87%), representing 418 polymorphic bands among a total of 478 scored in autoradiographs. The high reproducibility of RAPD and AFLP techniques was confirmed comparing DNA samples from different extractions and different digestions of DNA from the same plant. Three genetic similarity matrices and respective dendrograms were elaborated on using RAPD, AFLP or joint RAPD and AFLP data. Both molecular marker techniques proved their reliability to assess genetic relationships among pear cultivars. P. pyrifolia cultivars exhibit a closer genetic relatedness, clustering apart from P. communis cultivars. Within P. communis, `William's', as well as `Doyenne du Comice', cluster close to their hybrids. Most of the Portuguese cultivars tend to cluster together, indicating to constitute a relatively independent genetic pool, which can be of interest in pear breeding programs.

Time complexity of genetic algorithms on exponentially scaled problems

Abstract: This paper gives a theoretical and empirical analysis of the time complexity of genetic algorithms (GAs) on problems with exponentially scaled building blocks It is important to study GA performance on this type of problems because one of the difficulties that GAs are generally faced with is due to the low scaling or low salience of some building blocks The paper is an extension of the model introduced by Thierens, Goldberg, and Pereira (1998) for the case of building blocks rather than single genes, and the main result is that under the assumption of perfect building block mixing, both population size and time to convergence grow linearly with the problem length, giving an overall quadratic time complexity in terms of fitness function evaluations With traditional simple GAs, the assumption of perfect mixing only occurs when the user has knowledge about the structure of the problem (which is usually not true) However, the assumption is well approximated for advanced GAs that are able to automatically learn gene linkage

Off-shell structure of the string sigma model

Abstract: The off-shell structure of the string sigma model is investigated. In the open bosonic string, nonperturbative effects appear to depend crucially on the regularization scheme. A scheme retaining the notion of string width reproduces the structure of Witten's string field theory. (c) 2000 The American Physical Society.

Detection of mineralized structures in early stages of development of marine Teleostei using a modified alcian blue-alizarin red double staining technique for bone and cartilage.

Abstract: We have developed a procedure for staining cartilage and bone in fish larvae as small as 2 mm (notochord length), for which standard alcian blue/alizarin red procedures did not give positive and/or consistent results. Small calcified structures only 100–200 ixm in length can be clearly visualized. The method is suitable for both onto-genic studies during early stages of skeletal development in most marine fishes (e.g., Sporus aurata L., Solea senegalensis Kaup), whose larvae at hatching are often only a few millimeters long and for detecting skeletal abnormalities in small larvae. This procedure can also be used for specimens that have been preserved in 100% ethanol for up to two years.

Recent evolution in Baltic Fucus vesiculosus: reduced tolerance to emersion stresses compared to intertidal (North Sea) populations

Abstract: The Baltic is a young, brackish and non-tidal sea, supporting an impoverished marine flora compared with adjacent open coastal areas. Populations of the normally intertidal brown alga Fucus vesiculosus L. are permanently submerged in the Baltic. We tested the hypothesis that these populations have evolved a reduced ability to withstand water-stresses caused by aerial exposure (desiccation and freezing), relative to adjacent intertidal populations in the North Sea. Desiccation and freezing tolerance were compared using chlorophyll fluorescence to monitor photosynthetic sta- tus during stress and recovery. To control for the influence of growth salinity on stress tolerance, the experimental material consisted of either adult algae cross-acclimated at Baltic and North Sea salin- ities (6.5 and 20 to 24 practical salinity units (psu), respectively), or juveniles from both populations grown in the Baltic from embryos (submersed, 6.5 psu). Baltic algae were less able to recover maxi- mum photochemical yield (Fv/Fm) after freezing at -15°C than North Sea algae, and neither acclima- tion (adults) or growth salinity (juveniles) accounted for between-population differences. During des- iccation at 5°C, differences in the response of variable fluorescence (Fv), as well as in initial fluorescence (F0) and Fv during recovery, indicated that impaired photoprotective processes may con- tribute to the inability of Baltic algae to fully recover Fv/Fm after stress, in contrast to North Sea algae which displayed dynamic and rapidly recoverable reductions of Fv/Fm. Subsequent desiccation experiments during the summer (at 25°C) showed that, relative to North Sea algae, the effective pho- tochemical yield (ΔF/Fm') of Baltic algae started to decline at lower tissue-water content (TWC) and recovered less completely after a return to seawater. A critical TWC of ca 10% for Baltic populations was identified, below which ΔF/Fm' did not fully recover. In addition, Baltic algae were less able to regain initial TWC during recovery. These results indicate that, in ca 7500 yr since the recruitment of the present marine flora to the Baltic, F. vesiculosus has evolved reduced tolerance to emersion stresses compared to adjacent intertidal populations.

Holonomy and parallel transport for Abelian gerbes

Abstract: In this paper we establish a one-to-one correspondence between $S^1$-gerbes with connections, on the one hand, and their holonomies, for simply connected manifolds, or their parallel transports, in the general case, on the other hand. This result is a higher-order analogue of the familiar equivalence between bundles with connections and their holonomies for connected manifolds. The holonomy of a gerbe with group $S^1$ on a simply connected manifold $M$ is a group morphism from the thin second homotopy group to $S^1$, satisfying a smoothness condition, where a homotopy between maps from $[0,1]^2$ to $M$ is thin when its derivative is of rank $\leq 2$. For the non-simply connected case, holonomy is replaced by a parallel transport functor between two monoidal Lie groupoids. The reconstruction of the gerbe and connection from its holonomy is carried out in detail for the simply connected case. Our approach to abelian gerbes with connections holds out prospects for generalizing to the non-abelian case via the theory of double Lie groupoids.

Single hydrophone source localization

Abstract: The method presented in this paper assumes that the received signal is a linear combination of delayed and attenuated uncorrelated replicas of the source emitted waveform. The set of delays and attenuations, together with the channel environmental conditions, provide sufficient information for determining the source location. If the transmission channel is assumed known, the source location can be estimated by matching the data with the acoustic field predicted by the model conditioned on the estimated delay set. This paper presents alternative techniques that do not directly attempt to estimate time delays from the data but, instead, estimate the subspace spanned by the delayed source signal paths. Source Localization is then done using a family of measures of the distance between that subspace and the subspace spanned by the replicas provided by the model. Results obtained on the INTIMATE'96 data set, in a shallow-water acoustic channel off the coast of Portugal, show that a sound source emitting a 300-800-Hz LFM sweep could effectively be localized in range or depth over an entire day.

The reproductive biology of the two-banded sea bream (Diplodus vulgaris) from the southwest coast of Portugal

Abstract: Summary The study of the reproduction of Diplodus vulgaris (Geoff.) as part of a base-line study of the fishery resources of the south-west coast of Portugal, was based on the analysis of the spawning season, gonad maturation, size at maturity, fecundity and hermaphroditism. The spawning season is relatively long, from December to March, with peaks in January and February. No significant differences were found either in the sex ratio (M : F = 1.01) over the year or by size. The size at first maturity (L50) for all sexes and undetermined individuals combined was 18.33 cm total length (TL), with no significant differences between males and females. The estimated L50 is considerably greater than the minimum legal size in Portugal of 15.0 cm. Mean absolute fecundity (Fa) was 131 127 oocytes, ranging from 31 523 to 250 608. The relationship between absolute fecundity and total length (TL) (Fa = 25 398 TL – 484 426) and somatic weight (SW) (Fa = 878.8SW – 71 416) was of the linear type. The mean number of oocytes per gram of somatic weight was 526, ranging from 194 to 887. The reproductive strategy of this species is characterized by a rudimentary hermaphroditism with possible protandry, as evidenced by the existence of individuals in sexual transition.

Occurrence of Salmonella spp in estuarine and coastal waters of Portugal.

Abstract: The presence of Salmonella and its relationship with indicator organisms of fecal pollution, such as total coliforms, fecal coliforms and fecal streptococci, was studied at two marine zones in Portugal. Seventeen different Salmonella serotypes were isolated and identified, S. virchow was the most frequently isolated (21.6%). In addition, a high percentage (35.1%) was recorded for some Salmonella serotypes of clinical significance, namely S. enteritidis, S. infantis, S. typhimurium and S. virchow. In any of the samples from the two zones Salmonella was not detected in the absence of any of the indicator organisms. However, the incidence of Salmonella as a function of indicator concentration intervals established by the EEC standards was 0, 10 and 19.3% at guide values of total coliforms, fecal coliforms and fecal streptococci, respectively in the Faro samples (south of Portugal). In contrast, Salmonella incidence rates of 37.5, 36.4 and 33.3% were recorded at the corresponding guide values the Caminha samples (north of Portugal). No significant correlations (p>0.005) were obtained between Salmonella and the indicators at the sampling stations; however, total coliforms and fecal streptococci were the indicators most closely related to Salmonella in Caminha and Faro samples, respectively. Survival experiments in Escherichia coli, Enterococcus faecalis and S. typhimurium, using diffusion chambers, were performed to verify whether the lack of correlation between indicators and Salmonella was due to different inactivation rates in seawater. The results indicate that survival percentages of the three microorganisms tested were similar after 48 h of exposure to seawater.