Showing papers by "University of Lisbon published in 2001"

Isentropic Compressibilities—Experimental Origin and the Quest for their Rigorous Estimation in Thermodynamically Ideal Liquid Mixtures

Abstract: In this review, attention is initially focused upon the evolution of the Newton-Laplace Equation, that links the measured speed of sound in a fluid in conjunction with its density, to a reliable estimate of its isentropic compressibility κS. Definitions of ideal and excess isentropic quantities are formulated on the premise that the thermodynamic properties of an ideal mixture are mutually related in the same manner as are those of a real mixture or a pure substance. It is shown that both intensive and extensive properties can be derived from the ideal Gibbs energy. Different approaches previously used to calculate ideal isentropic quantities are examined and some subtle errors are identified. The consequences of using conflicting definitions are pointed out. Isentropic pressure derivatives obtained under different conditions and empirical models for estimating the differences between ultrasonic speeds in real and ideal liquid mixtures are discussed.

Apoptosis induced by exposure to a low steady-state concentration of H2O2 is a consequence of lysosomal rupture

Abstract: We have re-examined the lysosomal hypothesis of oxidative-stress-induced apoptosis using a new technique for exposing cells in culture to a low steady-state concentration of H(2)O(2). This steady-state technique mimics the situation in vivo better than the bolus-administration method. A key aspect of H(2)O(2)-induced apoptosis is that the apoptosis is evident only after several hours, although cells may become committed within a few minutes of exposure to this particular reactive oxygen species. In the present work, we were able to show, for the first time, several correlative links between the triggering effect of H(2)O(2) and the later onset of apoptosis: (i) a short (15 min) exposure to H(2)O(2) caused almost immediate, albeit limited, lysosomal rupture; (ii) early lysosomal damage, and later apoptosis, showed a similar dose-related response to H(2)O(2); (iii) both events were inhibited by pre-treatment with iron chelators, including desferrioxamine. This compound is known to be taken up by endocytosis only and thus to become localized in the lysosomal compartment. After exposure to oxidative stress, when cells were again in standard culture conditions, a time-dependent continuous increase in lysosomal rupture was observed, resulting in a considerably lowered number of intact lysosomes in apoptotic cells, whereas non-apoptotic cells from the same batch of oxidative-stress-exposed cells showed mainly intact lysosomes. Taken together, our results reinforce earlier findings and strongly suggest that lysosomal rupture is an early upstream initiating event, and a consequence of intralysosomal iron-catalysed oxidative processes, when apoptosis is induced by oxidative stress.

cAMP acts as a second messenger in pollen tube growth and reorientation.

Abstract: Pollen tube growth and reorientation is a prerequisite for fertilization and seed formation. Here we report imaging of cAMP distribution in living pollen tubes microinjected with the protein kinase A-derived fluorosensor. Growing tubes revealed a uniform distribution of cAMP with a resting concentration of ≈100–150 nM. Modulators of adenylyl cyclase (AC), forskolin, and dideoxyadenosine could alter these values. Transient elevations in the apical region could be correlated with changes in the tube-growth axis, suggesting a role for cAMP in polarized growth. Changes in cAMP arise through the activity of a putative AC identified in pollen. This signaling protein shows homology to functional motifs in fungal AC. Expression of the cDNA in Escherichia coli resulted in cAMP increase and complemented a catabolic defect in the fermentation of carbohydrates caused by the absence of cAMP in a cyaA mutant. Antisense assays performed with oligodeoxynucleotide probes directed against conserved motifs perturbed tip growth, suggesting that modulation of cAMP concentration is vital for tip growth.

It's what you do and the way that you do it: Team task, team size, and innovation-related group processes

Abstract: This article describes a study of the relationships between team inputs (task type and team size) and team processes in 87 cross industry Portuguese teams, some of which had high and some low requirements to innovate. Team processes were measured using the Team Climate Inventory (TCI), which focuses on clarity of and commitment to team objectives, levels of participation, support for innovation, and quality emphases. Three hypotheses were tested. The first proposed that teams carrying out tasks with a high innovation requirement would have high scores on a measure of team processes. This was supported insofar as such teams reported higher levels of participation and support for innovation. The second hypothesis proposed that large teams would have poorer team processes. This hypothesis was confirmed. The third hypothesis concerned the interaction between size and innovation. The results suggested that large teams operating under a relatively high pressure to innovate have poorer team processes than large teams that do not have a high requirement to innovate.

Evolution in action through hybridisation and polyploidy in an Iberian freshwater fish: a genetic review.

Abstract: The Iberian minnow Leuciscus alburnoides represents a complex of diploid and polyploid forms with altered modes of reproduction. In the present paper, we review the recent data on the origin, reproductive modes, and inter-relationships of the various forms of the complex, in order to predict its evolutionary potential. The complex follows the hybrid-origin model suggested for most other asexual vertebrates. Diploid and triploid females from the southern river basins exhibit reproductive modes that cannot be conveniently placed into the categories generally recognised for these vertebrate complexes, which imply continuous shifting between forms, where genomes derived from both parental ancestors are cyclically lost, gained or replaced. Replacement of nuclear genomes allow the introduction of novel genetic material, that may compensate for the disadvantages of asexual reproduction. Contrasting with most other vertebrate complexes, L. alburnoides males are fertile and play an important role in the dynamics of the complex. Moreover, diploid hybrid males may have initiated a tetraploidization process, when a diploid clonal sperm fertilised a diploid egg. This direct route to tetraploidy by originating fish with the right constitution for normal meiosis (symmetric), may eventually lead to a new sexually reproducing polyploid species. This case-study reinforces the significance of hybridisation and polyploidy in evolution and diversification of vertebrates.

Appia, a flexible protocol kernel supporting multiple coordinated channels

Abstract: Distributed applications are becoming increasingly complex, often requiring the simultaneous use of several communication channels with different qualities-of-service. This paper presents the Appia system, a protocol kernel that supports applications requiring multiple coordinated channels. Appia offers a clean and elegant way for the application to express inter-channel constraints, such as, for instance, that all channels should provide consistent information about the failures of remote nodes. These constraints can be implemented as protocol layers that can be dynamically combined with other protocol layers.

EEMCO guidance to the in vivo assessment of tensile functional properties of the skin. Part 2: instrumentation and test modes.

Abstract: Tensile functions of the skin and subcutaneous tissues contribute to the appearance of the aged and photodamaged skin and to the effects of various other pathophysiological processes. The assessment of tensile functions of skin can be performed by distinct approaches mainly characterized by the orientation and magnitude of the imposed stress and strain over time. Testing methods are basically grouped into five major classes which include tensile, torsional, indentation, impact and elevation modes. Computed tensile variables are reproducible when the experimental procedure occurs under fully controlled conditions. Consistent and relevant information is yielded when the limitations and pitfalls typical for each test method are taken into consideration.

Alterations in carbon and nitrogen metabolism induced by water deficit in the stems and leaves of Lupinus albus L.

Abstract: Water deficit (WD) in Lupinus albus L. brings about tissue-specific responses that are dependent on stress intensity. Carbohydrate metabolism is very sensitive to changes in plant water status. Six days from withholding water (DAW), sucrose, glucose and fructose levels of the leaf blade had already increased over 5-fold, and the activities of SS and INV A had increased c. 1.5-2 times. From 9 DAW on, when stress intensity was more pronounced, these effects were reversed with fructose and glucose concentrations as well as INV A activity dropping in parallel. The stem (specifically the stele) responded to the stress intensification with striking increases in the concentration of sugars, N and S, and in the induction of thaumatin-like-protein and an increase in chitinase and peroxidase. At 13 DAW, the plants lost most of the leaves but on rewatering they fully recovered. Thus, the observed changes appear to contribute to a general mechanism of survival under drought, the stem playing a key role in that process.

Does the Tagus estuary fish community reflect environmental changes

Abstract: Estuarine fish communities are usually used in an ecological monitoring context to infer the environmental changes ocurring in estuarine environments. In the present paper several analyt- ical tools, namely community analysis indices, species-ranking methods and multivariate ordination techniques, were applied to time series data for the Tagus fish community for 2 periods: 1979 to 1981 and 1995 to 1997. Assessment of the relative importance of anthropogenic versus naturally induced fluctuations is made difficult by the range of natural short-term variations. For the Tagus case study, multivariate ordination techniques, rather than the ranking methods and indices analyzed, provide a good indicator of long-term changes. The major trends in the changes observed in this fish commu- nity were a decrease in abundance for several species that use the estuary as a nursery area and an increase in some resident species, namely Gobius spp. and Halobatrachus didactylus. Several species with southern European affinities have increased their importance within the Tagus estuarine fish community.

Virtual enterprise modeling and support infrastructures: applying multi-agent system approaches

Abstract: Virtual enterprises paradigm represents an important application field for multi-agent approaches, both in terms of modeling and infrastructure development This article summarizes the main challenges in this field and describes several current Multi-Agent System application approaches. A particular emphasis is given to the creation and operation phases of the virtual enterprise life cycle. Several open challenges in this area are also introduced.

The bootstrap methodology in statistics of extremes: Choice of the optimal sample fraction

Abstract: The main objective of statistics of extremes is the prediction of rare events, and its primary problem has been the estimation of the tail index γ, usually performed on the basis of the largest k order statistics in the sample or on the excesses over a high level u. The question that has been often addressed in practical applications of extreme value theory is the choice of either k or u, and an adaptive estimation of γ. We shall be here mainly interested in the use of the bootstrap methodology to estimate γ adaptively, and although the methods provided may be applied, with adequate modifications, to the general domain of attraction of Gγ, γ ∈ ℝ, we shall here illustrate the methods for heavy right tails, i.e. for γ > 0. Special relevance will be given to the use of an auxiliary statistic that is merely the difference of two estimators with the same functional form as the estimator under study, computed at two different levels. We shall also compare, through Monte Carlo simulation, these bootstrap methodologies with other data-driven choices of the optimal sample fraction available in the literature.

A graph based architectural (Re)configuration language

Abstract: For several different reasons, such as changes in the business or technological environment, the configuration of a system may need to evolve during execution. Support for such evolution can be conceived in terms of a language for specifying the dynamic reconfiguration of systems. In this paper, continuing our work on the development of a formal platform for architectural design, we present a high-level language to describe architectures and for operating changes over a configuration (i.e., an architecture instance), such as adding, removing or substituting components or interconnectons. The language follows an imperative style and builds on a semantic domain established in previous work. Therein, we model architectures through categorical diagrams and dynamic reconfiguration through algebraic graph rewriting.

The persistence of Pliocene populations through the Pleistocene climatic cycles: evidence from the phylogeography of an Iberian lizard.

Abstract: Ancient climatic fluctuations have caused changes in the demography and distribution of many species. The genetic differentiation between populations of the same species and of sister species is often attributed largely to the more recent Pleistocene fluctuations. Recent interpretations, which implicate earlier episodes, have proved controversial. We address the timing of genetic divergence in the Iberian lizard Lacerta schreiberi by studying the phylogeography of the cytochrome b sequence. The species has a remarkable morphological uniformity, yet our evidence suggests that earlier events in the Pliocene initiated the main divergence between populations. This interpretation implies that the different populations survived through the Pleistocene in separate localities. This conclusion is robust to different molecular clock calibrations. The persistence of earlier differentiation through the Pleistocene has wide implications for our understanding of Pleistocene refugia in this species and, by extension, to the biogeography of the whole region.

Leptogenesis via collisions: leaking lepton number to the hidden sector.

Abstract: We propose a leptobaryogenesis mechanism in which the nonzero $B\ensuremath{-}L$ of the Universe is produced in out-of-equilibrium, lepton number and CP-violating scattering processes that convert ordinary particles into particles of some hidden sector. In particular, we consider the processes $l\ensuremath{\varphi}\ensuremath{\rightarrow}{l}^{\ensuremath{'}}{\ensuremath{\varphi}}^{\ensuremath{'}},{\overline{l}}^{\ensuremath{'}}{\overline{\ensuremath{\varphi}}}^{\ensuremath{'}}$ mediated by the heavy Majorana neutrinos $N$ of the seesaw mechanism, where $l$ and $\ensuremath{\varphi}$ are ordinary lepton and Higgs doublets and ${l}^{\ensuremath{'}}$, ${\ensuremath{\varphi}}^{\ensuremath{'}}$ are their hidden counterparts. Such a leptogenesis mechanism is effective even if the reheat temperature is much smaller than the heavy neutrino masses. In particular, it can be as low as ${10}^{9}\phantom{\rule{0ex}{0ex}}\mathrm{GeV}$.

Standards of palliative care for patients with amyotrophic lateral sclerosis: results of a European survey.

Abstract: BACKGROUND: Amyotrophic lateral sclerosis (ALS) may be viewed as a paradigmatic disease for palliative care in neurodegenerative disorders. However, standards of care for ALS are known anecdotally to differ between and even within countries. METHOD: A survey was conducted among the members of the European ALS Study Group on standards of palliative care in the clinical management of patients with ALS and their families, by means of a questionnaire of 111 questions in the following areas: giving the diagnosis, treatment of symptoms, nutrition community services, respiratory support, and terminal care. Of 110 questionnaires sent out, 73 (66%) were completed and returned from 18 countries, including all major ALS centres in Europe. RESULTS: The main areas of consensus included: presenting the diagnosis in the presence of a relative (85%) and offering a short-term follow-up (90%), regular weight checks (82%), availability of percutaneous endoscopic gastrostomy (PEG) (94%), and discussion of respiratory issues ...

Regulation of the ecto-nucleotidase pathway in rat hippocampal nerve terminals.

Abstract: Ecto-nucleotidases play a pivotal role in terminating the signalling via ATP and in producing adenosine, a neuromodulator in the nervous system. We have now investigated the pattern of adenosine formation with different concentrations of extracellular ATP in rat hippocampal nerve terminals. It was found that adenosine formation is delayed with increasing concentrations of ATP. Also, the rate of adenosine formation increased sharply when the extracellular concentrations of ATP + ADP decrease below 5 microM, indicating that ATP/ADP feed-forwardly inhibit ecto-5'-nucleotidase allowing a burst-like formation of adenosine possibly designed to activate facilitatory A2A receptors. Initial rate measurements of ecto-5'-nucleotidase in hippocampal nerve terminals, using IMP as substrate, showed that ATP and ADP are competitive inhibitors (apparent Ki of 14 and 4 microM). In contrast, in hippocampal immunopurified cholinergic nerve terminals, a burst-like formation of adenosine is not apparent, suggesting that channelling processes may overcome the feed-forward inhibition of ecto-5'-nucleotidase, thus favouring A1 receptor activation.