Showing papers by "University of Coimbra published in 1998"

An overview of the role and diversity of compatible solutes in Bacteria and Archaea

Abstract: The accumulation of compatible solutes is a prerequisite for the adaptation of microorganisms to osmotic stress imposed by salt or organic solutes Two types of strategies exist to cope with high external solute concentrations; one strategy is found in the extremely halophilic Archaea of the family Halobacteriaceae and the Bacteria of the order Haloanaerobiales involving the accumulation of inorganic ions The other strategy of osmoadaptation involves the accumulation of specific organic solutes and is found in the vast majority of microorganisms The organic osmolytes range from sugars, polyols, amino acids and their respective derivatives, ectoines and betaines The diversity of these organic solutes has increased in the past few years as more organisms, especially thermophilic and hyperthermophilic Bacteria and Archaea, have been examined The term compatible solute can also be applied to solutes that protect macromolecules and cells against stresses such as high temperature, desiccation and freezing The mechanisms by whihh compatible solutes protect enzymes, cell components and cells are still a long way from being thoroughly elucidated, but there is a growing interest in the utilization of these solutes to protect macromolecules and cells from heating, freezing and desiccation

Xception: a technique for the experimental evaluation of dependability in modern computers

Abstract: An important step in the development of dependable systems is the validation of their fault tolerance properties Fault injection has been widely used for this purpose, however with the rapid increase in processor complexity, traditional techniques are also increasingly more difficult to apply This paper presents a new software-implemented fault injection and monitoring environment, called Xception, which is targeted at modern and complex processors Xception uses the advanced debugging and performance monitoring features existing in most modern processors to inject quite realistic faults by software, and to monitor the activation of the faults and their impact on the target system behavior in detail Faults are injected with minimum interference with the target application The target application is not modified, no software traps are inserted, and it is not necessary to execute the target application in special trace mode (the application is executed at full speed) Xception provides a comprehensive set of fault triggers, including spatial and temporal fault triggers, and triggers related to the manipulation of data in memory Faults injected by Xception can affect any process running on the target system (including the kernel), and it is possible to inject faults in applications for which the source code is not available Experimental, results are presented to demonstrate the accuracy and potential of Xception in the evaluation of the dependability properties of the complex computer systems available nowadays

Vesicle Formation and General Phase Behavior in the Catanionic Mixture SDS−DDAB−Water. The Cationic-Rich Side

Abstract: The phase behavior in the cationic-rich side of the phase diagram of the mixed system sodium dodecyl sulfate (SDS)−didodecyldimethylammonium bromide (DDAB)−water at 25 °C is presented. DDAB is a double-chained surfactant and thus it tends to self-assemble in water into bilayer structures−vesicles and lamellar phases. The phase diagram of the binary system DDAB−water has been studied, and some features of the diluted region as revealed by surfactant NMR self-diffusion and light microscopy are shown. The structural and phase behavior effects resulting from the addition of SDS are then investigated by complementary microscopy and NMR methods. Upon adding SDS to DDAB dispersions, the area for which a single phase of vesicles occurs is largely extended and a lobe is defined in the phase diagram. The DDAB-rich vesicles are essentially unilamellar and characterized by large sizes (range 0.1−5 μm) and high polydispersity, as probed by combined cryo-TEM and light microscopy. Self-diffusion measurements show a nonm...

Should the use of inhibition of cholinesterases as a specific biomarker for organophosphate and carbamate pesticides be questioned

Abstract: Recently there has been evidence that contaminants other than organophosphate and carbamate pesticides may inhibit the activity of the enzyme acetylcholinesterase (AChE) both under in vitro and in vivo conditions. In this study we investigated the in vitro effect of three detergents \[dodecyl benzyl sulphonate (DBS), sodium dodecyl sulphate (SDS) and a mixture commonly used as domestic detergent (X)] and three metals \[molybdenum, barium and chromium (VI)] on AChE activity of Mytilus galloprovincialis haemolymph. All the detergents tested significantly inhibited the activity of the enzyme. The lowest observed effect concentrations were equal to 12 5 for DBS and 50 mg l-1 for SDS and X. Among the metals, molybdenum and barium had no effect on AChE activity, whereas chromium (VI) significantly depressed the activity of the enzyme at concentrations equal to or higher than 25 mg l-1. These results suggest that the use of AChE as a specific biomarker for organophosphate and carbamate pesticides should be quest...

Photoacoustic Measurements of Porphyrin Triplet-State Quantum Yields and Singlet-Oxygen Efficiencies

Abstract: Photoacoustic calorimetry was used to measure the quantum yields of singlet molecular oxygen production by the triplet states of tetraphenylporphyrin (TPP), ZnTPP and CuTPP in toluene, yielding values of 0.67 0.14, 0.68 0.19 and 0.03 0.01, respectively. We show that a novel dichlorophenyl derivative of ZnTPP is capable of singlet-oxygen production with a 0.90 0.07 quantum yield. The synthesis and characterisation of a new photostable chlorin with high absorptivity in the red that is capable of singlet-oxygen production with 0.54 0.06 quantum yield is described. Our results suggest that chlorinated chlorins may be interesting new sensitisers for photodynamic therapy.

Gene delivery by negatively charged ternary complexes of DNA, cationic liposomes and transferrin or fusigenic peptides

Abstract: Potential problems with the use of viral vectors for gene therapy necessitate the development of efficient nonviral vectors. The association of transferrin, or the pH-sensitive peptide GALA, with cationic liposomes composed of 1,2-dioleoyl-3-(trimethylammonium) propane and its equimolar mixture with dioleoylphosphatidylethanolamine, under conditions where the liposome/DNA complex is negatively charged, drastically increased luciferase expression from pCMVluc. The percentage of cells transfected, measured by beta-galactosidase expression, was also increased by about 10-fold. The zeta potential of the ternary complexes was lower than that of the liposome/DNA complexes. Transfection activity of positively charged complexes was also enhanced by association with transferrin, GALA or the influenza hemagglutinin N terminal peptide HA-2, but to a smaller extent compared with the negatively charged complexes. The enhancement of gene delivery by transferrin or GALA was not affected significantly by the presence of serum and did not cause significant cytotoxicity. Our results indicate that negatively charged ternary complexes of cationic liposomes, DNA and transferrin, or fusigenic peptides, can facilitate efficient transfection of cultured cells, and that they may alleviate the drawbacks of the use of highly positively charged complexes for gene delivery in vivo.

A meta-analysis and transmission disequilibrium study of association between the dopamine D3 receptor gene and schizophrenia

Abstract: We performed a meta-analysis of over 30 case-control studies of association between schizophrenia and a bi-allelic, Bali polymorphism in exon 1 of the dopamine D3 receptor gene. We observed a significant excess of both forms of homozygote in patients (P = 0.0009, odds ratio (OR) = 1.21, 95% Confidence Interval (CI) = 1.07-1.35) in the combined sample of 5351 individuals. No significant heterogeneity was detected between samples and the effects did not appear to be the product of publishing bias. In addition we undertook an independent, family-based association study of this polymorphism in 57 parent/proband trios, taken from unrelated European multiplex families segregating schizophrenia. A transmission disequilibrium test (TDT) showed a significant excess of homozygotes in schizophrenic patients (P = 0.004, odds ratio (OR) = 2.7, 95% CI = 1.35-5.86). Although no significant allelic association was observed, a significant association was detected with the 1-1 genotype alone (P = 0.02, OR = 2.32, 95% CI = 1.13-4.99). In addition when the results of the family-based association study were included in the meta-analysis, the homozygosity effect increased in significance (P = 0.0002, OR = 1.23, 95% CI = 1.09-1.38). The results of the meta-analysis and family-based association study provide independent support for a relationship between schizophrenia and homozygosity at the Bali polymorphism of the D3 receptor gene, or between a locus in linkage disequilibrium with it.

Surface binding of contaminants by algae: Consequences for lethal toxicity and feeding to Daphnia magna straus

Abstract: Freshwater algae, as with all suspended particulate matter in the water column, exhibit a net negative charge resulting in an affinity for positively charged species, such as toxic metal cations, which will readily adsorb to algal cell surfaces. In this study, the adsorption of a representative toxic metal cadmium cation (Cd{sup 2+}) to a freshwater algal species, Chlorella vulgaris, was investigated using environmentally realistic concentrations of both. A further study of the effects of this particulate adsorption of Cd{sup 2+} on lethal toxicity and feeding in Daphnia magna was conducted. Two apparently contrasting effects were observed. For the D. magna feeding study, cell ingestion was inhibited, leading to reduced growth and reproduction. Experiments comparing the effect of algal-bound cadmium and dissolved forms of cadmium demonstrate that this inhibition is almost entirely due to the surface-bound fraction of ions. However, at concentrations of dissolved cadmium that are lethal to Daphnia, algal cells were found to reduce toxicity. Such findings indicate the importance of food ration in laboratory-based toxicity tests as well as the difficulty in predicting the environmental fate and effect of contaminants using such tests.

Effects of Temperature, Salinity, and Medium Composition on Compatible Solute Accumulation by Thermococcus spp.

Abstract: The effects of salinity and growth temperature on the accumulation of intracellular organic solutes were examined by nuclear magnetic resonance spectroscopy (NMR) in Thermococcus litoralis, Thermococcus celer, Thermococcus stetteri, and Thermococcus zilligii (strain AN1). In addition, the effects of growth stage and composition of the medium were studied in T. litoralis. A novel compound identified as beta-galactopyranosyl-5-hydroxylysine was detected in T. litoralis grown on peptone-containing medium. Besides this newly discovered compound, T. litoralis accumulated mannosylglycerate, aspartate, alpha-glutamate, di-myo-inositol-1,1'(3,3')-phosphate, hydroxyproline, and trehalose. The hydroxyproline and beta-galactopyranosyl-5-hydroxylysine were probably derived from peptone, while the trehalose was derived from yeast extract; none of these three compounds was detected in the other Thermococcus strains examined. Di-myo-inositol-1,1'(3,3')-phosphate, aspartate, and mannosylglycerate were detected in T. celer and T. stetteri, and the latter organism also accumulated alpha-glutamate. The only nonmarine species studied, T. zilligii, accumulated very low levels of alpha-glutamate and aspartate. The levels of mannosylglycerate and aspartate increased in T. litoralis, T. celer, and T. stetteri in response to salt stress, while di-myo-inositol-1,1'(3,3')-phosphate was the major intracellular solute at supraoptimal growth temperatures. The phase of growth had a strong influence on the types and levels of compatible solutes in T. litoralis; mannosylglycerate and aspartate were the major solutes during exponential growth, while di-myo-inositol-1,1'(3,3')-phosphate was the predominant organic solute during the stationary phase of growth. This work revealed an unexpected ability of T. litoralis to scavenge suitable components from the medium and to use them as compatible solutes.

Control of pulsatile 5‐HT/insulin secretion from single mouse pancreatic islets by intracellular calcium dynamics

Abstract: 1Glucose-induced insulin release from single islets of Langerhans is pulsatile. We have investigated the correlation between changes in cytosolic free calcium concentration ([Ca2+]i) and oscillatory insulin secretion from single mouse islets, in particular examining the basis for differences in secretory responses to intermediate and high glucose concentrations. Insulin release was monitored in real time through the amperometric detection of the surrogate insulin marker 5-hydroxytryptamine (5-HT) via carbon fibre microelectrodes. The [Ca2+]i was simultaneously recorded by whole-islet fura-2 microfluorometry. 2In 82 % of the experiments, exposure to 11 mM glucose evoked regular high-frequency (average, 3.4 min−1) synchronous oscillations in amperometric current and [Ca2+]i. In the remaining experiments (18 %), 11 mM glucose induced an oscillatory pattern consisting of high-frequency [Ca2+]i oscillations that were superimposed on low-frequency (average, 0.32 min−1) [Ca2+]i waves. Intermittent high-frequency [Ca2+]i oscillations gave rise to a similar pattern of pulsatile 5-HT release. 3Raising the glucose concentration from 11 to 20 mM increased the duration of the steady-state [Ca2+]i oscillations without increasing their amplitude. In contrast, both the duration and amplitude of the associated 5-HT transients were increased by glucose stimulation. The amount of 5-HT released per secretion cycle was linearly related to the duration of the underlying [Ca2+]i oscillations in both 11 and 20 mM glucose. The slopes of the straight lines were identical, indicating that there is no significant difference between the ability of calcium oscillations to elicit 5-HT/insulin release in 11 and 20 mM glucose. 4In situ 5-HT microamperometry has the potential to resolve the high-frequency oscillatory component of the second phase of glucose-induced insulin secretion. This component appears to reflect primarily the duration of the underlying [Ca2+]i oscillations, suggesting that glucose metabolism and/or access to glucose metabolites is not rate limiting to fast pulsatile insulin release.

Mitochondrial function impairment induced by amyloid beta-peptide on PC12 cells.

Abstract: The aim of the present study was to determine whether amyloid beta-peptide (A beta) induces mitochondrial dysfunction. Mitochondrial function was reported to be affected following A beta exposure, as demonstrated by depolarization of the mitochondrial membrane, decrease of oxygen consumption and by the inhibition of complexes I, III and IV of the mitochondrial respiratory chain. A beta25-35 and A beta1-40 peptides also inhibited MTT reduction in a dose-dependent manner in undifferentiated and differentiated PC12 cells. Several antioxidants prevented this inhibitory response, suggesting that oxidative stress is involved in A beta-induced cytotoxicity. These data suggest that mitochondrial dysfunction contributes to amyloid beta-protein cytotoxicity and may play a major role in the abnormalities of energy metabolism observed in Alzheimer's disease.

An Active Set Newton Algorithm for Large-Scale Nonlinear Programs with Box Constraints

Abstract: A new algorithm for large-scale nonlinear programs with box constraints is introduced. The algorithm is based on an efficient identification technique of the active set at the solution and on a nonmonotone stabilization technique. It possesses global and superlinear convergence properties under standard assumptions. A new technique for generating test problems with known characteristics is also introduced. The implementation of the method is described along with computational results for large-scale problems.

Voltage source inverter fault diagnosis in variable speed AC drives, by Park's vector approach

Abstract: This paper presents the use of the Park's vector approach for diagnosing voltage source inverter faults, like output single-phasing and the occurrence of either a short-circuit or an open circuit of the controlled power switches. For this study, a prototype was built, having all the power terminals available for testing, including the ones for every semiconductor. For the short-circuit tests, a 17 /spl Omega/ auxiliary resistor was used, connected in parallel with the power switch to be tested, in order to limit the short-circuit current.

Effect of dietary phenolic compounds on apoptosis of human cultured endothelial cells induced by oxidized LDL

Abstract: 1. Oxidized low density lipoproteins (LDL) are toxic to cultured endothelial cells. Mildly oxidized LDL, characterized by relatively low levels of TBARS and only minor modifications of apoB, were obtained by using 2 experimental model systems of oxidation, namely oxidation by u.v. radiation or ferrylmyoglobin (a two electron oxidation product from the reaction of metmyoglobin with H2O2). 2. Toxic concentrations of mildly oxidized LDL induce apoptosis (programmed cell death) of cultured endothelial cells, as shown by typical morphological features, by the in situ TUNEL procedure and by DNA fragmentation revealed on gel electrophoresis. This apoptosis is calcium-dependent and subsequent to the intense and sustained cytosolic [Ca2+]i peak elicited by oxidized LDL. 3. Five naturally occurring phenolic compounds present in food and beverages were able to prevent, in a concentration-dependent manner, the apoptosis of endothelial cells induced by oxidized LDL. Among the compounds tested, caffeic acid was the most effective. Under the conditions used, the protective effect of caffeic acid (IC50 8.3+/-2.1 micromol l[-1]) in the prevention of apoptosis induced by oxidized LDL was significantly higher than that of the other compounds tested (IC50s were 12.4+/-3.2, 14.1+/-4.1, 20.4+/-4.4 and 72.6+/-9.2 micromol l(-1) for ferulic, protocatechuic, ellagic and p-coumaric acids, respectively). 4. The anti-apoptotic effect of caffeic acid results from the addition of two effects, (i) the antioxidant effect which prevents LDL oxidation and subsequent toxicity ('indirect' protective effect); (ii) a 'direct' cytoprotective effect, acting at the cellular level. 5. Effective concentrations of caffeic acid acted at the cellular level by blocking the intense and sustained cytosolic [Ca2+]i rise elicited by oxidized LDL. 6. In conclusion, phenolic acids (caffeic and ferulic acids being the most potent of the compounds tested under the conditions used) exhibit a potent cytoprotective effect of cultured endothelial cells against oxidized LDL. In addition to antioxidant effect delaying LDL oxidation, caffeic acid acts as a cytoprotective agent, probably by blocking the intracellular signalling triggered by oxidized LDL and culminating in the sustained calcium rise which is involved in oxidized LDL-induced apoptosis.

Oxidising alternative species to chromium VI in zinc galvanised steel surface treatment. Part 1—A morphological and chemical study

Abstract: Surface treatment of zinc galvanised steel, using chromate based baths, was extensively used in order to both improve the corrosion resistance and enhance the chemical adhesion of organic coatings Although the detailed formation mechanism of chromium conversion coatings has remained a subject of wide interest for 30 years, it still remains to be completely clarified Meanwhile, as a consequence of recent environmental legislation (US Environmental Protection Agency identified the Metal Finishing Industry as one of the most significant contributors to environmental pollution), a large amount of effort is being made to study alternatives to Cr(VI) baths In the first part of this work, the authors present the main results and conclusions of an experimental and systematic study on zinc conversion layers (ZCLs) based on molybdates, permanganates, vanadates and tungstates, using a good Cr(VI) bath as reference Considering the alternative ZCLs, molybdate-based ones, they showed the best anticorrosive behaviour in salt spray For this reason, they were characterised by scanning electron microscopy with energy X-ray dispersive spectrometry associated (SEM/EDS), X-ray diffraction (XRD) and X-ray photon spectroscopy (XPS), in order to understand their protective mechanisms In a second part of this work, electrochemical ac measurements will be involved in order to complete the study

Identification and proteolytic processing of procardosin A

Abstract: Plant aspartic proteinases contain a plant-specific insert (PSI) of about 100 amino acids of unknown function with no similarity with the other aspartic proteinases but with significant similarity with saposins, animal sphingolipid activator proteins. PSI has remained elusive at the protein level, suggesting that it may be removed during processing. To understand the molecular relevance of PSI, the proteolytic processing of cardosin A, the major aspartic proteinase from the flowers of cardoon (Cynara cardunculus L.) was studied. Procardosin A, a 64-kDa cardosin A precursor containing PSI and the prosegment was identified by immunoblotting using monospecific antibodies against PSI and the prosegment. Procardosin A undergoes proteolytic processing as the flower matures. PSI was found to be removed before the prosegment, indicating that during processing the enzyme acquires a structure typical of mammalian or microbial aspartic proteinase proforms. In vitro studies showed that processing of PSI occurs at pH 3.0 and is inhibited by pepstatin A and at pH 7.0. Sequence analysis allowed the identification of the cleavage sites, revealing that PSI is removed entirely, probably by an aspartic proteinase. Cleavage of the PSI scissile bonds requires, however, a conformation specific to the precursor since isolated cardosins and pistil extracts were unable to hydrolyse synthetic peptides corresponding to the cleavage sites. In view of these results, a model for the proteolytic processing of cardosin A is proposed and the molecular and physiological relevance of PSI in plant aspartic proteinase is discussed.

A Metric for Selection of the Most Promising Rules

Abstract: The process of Knowledge Discovery in Databases pursues the goal of extracting useful knowledge from large amounts of data. It comprises a pre-processing step, application of a data-mining algorithm and post-processing of results. When rule induction is applied for data-mining one must be prepared to deal with the generation of a large number of rules. In these circumstances it is important to have a way of selecting the rules that have the highest predictive power. We propose a metric for selection of the n rules with the highest average distance between them. We defend that applying our metric to select the rules that are more distant improves the system prediction capabilities against other criteria for rule selection. We present an application example and empirical results produced from a synthesized data set on a financial domain.

A multivariable laboratory process with an adjustable zero

Abstract: A novel multivariable laboratory process that consists of four interconnected water tanks is presented. The linearized dynamics of the system have a multivariable zero that is possible to move along the real axis by changing a valve. The zero can be placed in both the left and the right half-plane. In this way the quadruple-tank process is ideal for illustrating many concepts in multivariable control, particularly performance limitations due to multivariable right half-plane zeros. Accurate models are derived from both physical and experimental data and multi-loop control is illustrated.

Forest fire propagation

Abstract: The different phases in the development of forest fires and propagation regimes are characterized, together with the main factors affecting them. The problems of modelling the various fire behaviou...

Litter in a first–order stream of a temperate deciduous forest (Margaraça Forest, central Portugal)

Abstract: To evaluate the importance and fate of organic matter inputs in forested streams, we determined the litterfall inputs and the benthic coarse particulate organic matter (CPOM) in one headwater stream flowing through a mixed deciduous forest, during one year. Both vertical traps and the stream bottom were sampled monthly. The material collected was sorted into four main categories: leaves, fruits and flowers, twigs and debris. Litter production was 715 g m−2 y−1 and seasonal, with 73% of the annual total during October–December (autumn). Leaves comprised the largest litter component. Benthic organic matter was 1880 g m−2 y−1, and was also seasonal. Highest accumulation was attained in spring, and twigs and branches comprised the major component.