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Showing papers by "University of Lisbon published in 1999"



Journal ArticleDOI
01 Dec 1999-Brain
TL;DR: PET was used to measure regional cerebral activity during tasks requiring reading of concrete and abstract nouns and verbs for lexical decision and indicated that abstract word processing was associated with selective activations, which is compatible with the view that lexical-semantic processing of words is mediated by an extensive, predominantly left hemispheric network of brain structures.
Abstract: The hypothesis that categorical information, distinguishing among word classes, such as nouns, verbs, etc., is an organizational principle of lexical knowledge in the brain, is supported by the observation of aphasic subjects who are selectively impaired in the processing of nouns and verbs. The study of lesion location in these patients has suggested that the left temporal lobe plays a crucial role in processing nouns, while the left frontal lobe is necessary for verbs. To delineate the brain areas involved in the processing of different word classes, we used PET to measure regional cerebral activity during tasks requiring reading of concrete and abstract nouns and verbs for lexical decision. These tasks activated an extensive network of brain areas, mostly in the left frontal and temporal cortex, which represents the neural correlate of single word processing. Some left hemispheric areas, including the dorsolateral frontal and lateral temporal cortex, were activated only by verbs, while there were no brain areas more active in response to nouns. Furthermore, the comparison of abstract and concrete words indicated that abstract word processing was associated with selective activations (right temporal pole and amygdala, bilateral inferior frontal cortex), while no brain areas were more active in response to concrete words. There were no significant interaction effects between word class and concreteness. Taken together, these findings are compatible with the view that lexical-semantic processing of words is mediated by an extensive, predominantly left hemispheric network of brain structures. Additional brain activations appear to be related to specific semantic content, or, in the case of verbs, may be associated with the automatic access of syntactic information.

468 citations


Journal ArticleDOI
TL;DR: This paper presents further international comparisons of progressivity of health care financing systems, modifying the methodology used there and achieving a higher degree of cross-country comparability in variable definitions, and updating and extending the cross-section of countries.

461 citations


Journal ArticleDOI
TL;DR: The results suggest that fluctuating population sizes during the late Pleistocene have left a genetic signature on levels of variation in both species, and a statistical parsimony analysis indicates local genetic structure that suggests recent restricted gene flow.
Abstract: The grey wolf (Canis lupus) and coyote (C. latrans) are highly mobile carnivores that disperse over great distances in search of territories and mates. Previous genetic studies have shown little geographical structure in either species. However, populatio

331 citations


Journal ArticleDOI
TL;DR: In this article, the authors argue that the nature of situated learning and cognition cannot be fully understood by focusing only on social, cultural and contextual factors, and use conceptual metaphor theory to show how embodied cognition, while providing grounding for situatedness, also gives fruitful results in analyzing the cognitive difficulties underlying the understanding of continuity.
Abstract: In this paper we analyze, from the perspective of 'Embodied Cognition', why learning and cognition are situated and context-dependent. We argue that the nature of situated learning and cognition cannot be fully understood by focusing only on social, cultural and contextual factors. These factors are themselves further situated and made comprehensible by the shared biology and fundamental bodily experiences of human beings. Thus cognition itself is embodied, and the bodily-grounded nature of cognition provides a foundation for social situatedness, entails a reconceptualization of cognition and mathematics itself, and has important consequences for mathematics education. After framing some theoretical notions of embodied cognition in the perspective of modern cognitive science, we analyze a case study – continuity of functions. We use conceptual metaphor theory to show how embodied cognition, while providing grounding for situatedness, also gives fruitful results in analyzing the cognitive difficulties underlying the understanding of continuity.

313 citations


Journal ArticleDOI
TL;DR: These studies not only demonstrate that proton gradients exist, but that they may be intimately associated with polarized pollen tube growth.
Abstract: Using both the proton selective vibrating electrode to probe the extracellular currents and ratiometric wide-field fluorescence microscopy with the indicator 2′,7′-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF)-dextran to image the intracellular pH, we have examined the distribution and activity of protons (H+) associated with pollen tube growth. The intracellular images reveal that lily pollen tubes possess a constitutive alkaline band at the base of the clear zone and an acidic domain at the extreme apex. The extracellular observations, in close agreement, show a proton influx at the extreme apex of the pollen tube and an efflux in the region that corresponds to the position of the alkaline band. The ability to detect the intracellular pH gradient is strongly dependent on the concentration of exogenous buffers in the cytoplasm. Thus, even the indicator dye, if introduced at levels estimated to be of 1.0 μM or greater, will dissipate the gradient, possibly through shuttle buffering. The apical acidic domain correlates closely with the process of growth, and thus may play a direct role, possibly in facilitating vesicle movement and exocytosis. The alkaline band correlates with the position of the reverse fountain streaming at the base of the clear zone, and may participate in the regulation of actin filament formation through the modulation of pH-sensitive actin binding proteins. These studies not only demonstrate that proton gradients exist, but that they may be intimately associated with polarized pollen tube growth.

297 citations


Journal ArticleDOI
TL;DR: Data indicate that Dbp5 is a conserved RNA‐dependent ATPase which is recruited to the cytoplasmic fibrils of the NPC where it participates in the export of mRNAs out of the nucleus.
Abstract: Dbp5 is a DEAD‐box protein essential for mRNA export from the nucleus in yeast. Here we report the isolation of a cDNA encoding human Dbp5 (hDbp5) which is 46% identical to yDbp5p. Like its yeast homologue, hDbp5 is localized within the cytoplasm and at the nuclear rim. By immunoelectron microscopy, the nuclear envelope‐bound fraction of Dbp5 has been localized to the cytoplasmic fibrils of the nuclear pore complex (NPC). Consistent with this localization, we show that both the human and yeast proteins directly interact with an N‐terminal region of the nucleoporins CAN/Nup159p. In a conditional yeast strain in which Nup159p is degraded when shifted to the nonpermissive temperature, yDbp5p dissociates from the NPC and localizes to the cytoplasm. Thus, Dbp5 is recruited to the NPC via a conserved interaction with CAN/Nup159p. To investigate its function, we generated defective hDbp5 mutants and analysed their effects in RNA export by microinjection in Xenopus oocytes. A mutant protein containing a Glu→Gln change in the conserved DEAD‐box inhibited the nuclear exit of mRNAs. Together, our data indicate that Dbp5 is a conserved RNA‐dependent ATPase which is recruited to the cytoplasmic fibrils of the NPC where it participates in the export of mRNAs out of the nucleus.

283 citations


Journal ArticleDOI
TL;DR: The site of retention within the nucleus of pre‐mRNA processing mutants unable to be exported to the cytoplasm is described, and 3′ end processing and splicing appear to be rate limiting for release of mRNA from the site of transcription.
Abstract: We describe here for the first time the site of retention within the nucleus of pre-mRNA processing mutants unable to be exported to the cytoplasm. Fluorescence in situ hybridization was used to detect transcripts from human beta-globin genes that are either normal or defective in splicing or 3' end formation. Nuclear transcripts of both wild-type and mutant RNAs are detected only as intranuclear foci that colocalize with the template gene locus. The kinetics of transcript release from the site of transcription was assessed by treatment of cells with the transcriptional inhibitors actinomycin D, alpha-amanitin and DRB. These drugs induce the rapid disappearance of nuclear foci corresponding to wild-type human beta-globin RNA. In contrast, pre-mRNA mutants defective in either splicing or 3' end formation and which fail to be transported to the cytoplasm, are retained at the site of transcription. Therefore, 3' end processing and splicing appear to be rate limiting for release of mRNA from the site of transcription.

233 citations


Book ChapterDOI
27 Oct 1999
TL;DR: An attempt to present some current definitions and a taxonomy of virtual enterprises and the significance of two key elements: networking and cooperation becomes clear.
Abstract: Among the multiple definitions for the Virtual Enterprise concept, the significance of two key elements: networking and cooperation, becomes clear. The lack of a unified definition is partially resulted by the large diversity in classes of networked organizations, which calls for the establishment of a taxonomy of virtual enterprises. An attempt to present some current definitions and a taxonomy is made. The first step in the analysis of virtual enterprises requires a careful study of various phases of its life cycle and characterization of the roles of various involved actors.

229 citations


Journal ArticleDOI
TL;DR: It is shown that gems are present in a variable but small proportion of rapidly proliferating cells in culture, which suggests that snRNPs flow through the Cajal body during their biogenesis pathway.
Abstract: The spliceosomal snRNAs U1, U2, U4, and U5 are synthesized in the nucleus, exported to the cytoplasm to assemble with Sm proteins, and reimported to the nucleus as ribonucleoprotein particles. Recently, two novel proteins involved in biogenesis of small nuclear ribonucleoproteins (snRNPs) were identified, the Spinal muscular atrophy disease gene product (SMN) and its associated protein SIP1. It was previously reported that in HeLa cells, SMN and SIP1 form discrete foci located next to Cajal (coiled) bodies, the so-called “gemini of coiled bodies” or “gems.” An intriguing feature of gems is that they do not appear to contain snRNPs. Here we show that gems are present in a variable but small proportion of rapidly proliferating cells in culture. In the vast majority of cultured cells and in all primary neurons analyzed, SMN and SIP1 colocalize precisely with snRNPs in the Cajal body. The presence of SMN and SIP1 in Cajal bodies is confirmed by immunoelectron microscopy and by microinjection of antibodies that interfere with the integrity of the structure. The association of SMN with snRNPs and coilin persists during cell division, but at the end of mitosis there is a lag period between assembly of new Cajal bodies in the nucleus and detection of SMN in these structures, suggesting that SMN is targeted to preformed Cajal bodies. Finally, treatment of cells with leptomycin B (a drug that blocks export of U snRNAs to the cytoplasm and consequently import of new snRNPs into the nucleus) is shown to deplete snRNPs (but not SMN or SIP1) from the Cajal body. This suggests that snRNPs flow through the Cajal body during their biogenesis pathway.

229 citations


Journal ArticleDOI
01 Jul 1999-Brain
TL;DR: Cognitive dysfunction in PP and TP multiple sclerosis has a complex and multifactorial aetiology, which is not adequately explained by pathology as demonstrated on conventional MRI.
Abstract: The relative rarity of primary progressive (PP) and transitional progressive (TP) multiple sclerosis has meant that little documentation of cognitive function in such patients is currently available. The aim of this study was to investigate the cognitive skills of patients with PP and TP multiple sclerosis relative to matched healthy controls, and to examine the relationship of this impairment to MRI parameters. Sixty-three patients (43 PP, 20 TP) were individually matched with healthy controls, who undertook the same cognitive tasks as the patient group. The neuropsychological assessment comprised Rao's brief repeatable battery, a reasoning test, and a measure of depression. Patients also underwent T1- and T2-weighted brain MRI. These patients were taken from a larger cohort (158 PP, 33 TP) in whom it had been demonstrated that the re were no significant differences between the mean scores of the PP and TP groups on any of the cognitive variables. The 63 patients were therefore taken as one group for comparison with the healthy controls. These patients performed significantly worse than the controls in tests of verbal memory, attention, verbal fluency and spatial reasoning. An impairment index was constructed and applied to the patient data. This correlated modestly with T2-lesion load ( r = 0.45, P = 0.01), T1-hypointensity load ( r = 0.45, P = 0.01) and cerebral volume ( r = –0.35, P = 0.01). Thus, PP and TP multiple sclerosis patients demonstrate significant cognitive dysfunction when compared with matched healthy controls. The relationship between this impairment and MRI parameters is moderate, suggesting that cognitive dysfunction in PP and TP multiple sclerosis has a complex and multifactorial aetiology, which is not adequately explained by pathology as demonstrated on conventional MRI.

Journal ArticleDOI
TL;DR: In this paper, it was shown that every hyperbolic measure invariant under a C 1+fi difieomorphism of a smooth Riemannian manifold possesses asymptotically "almost" local product structure, i.e., its density can be approximated by the product of the densities on stable and unstable manifolds up to small exponentials.
Abstract: We prove that every hyperbolic measure invariant under a C 1+fi difieomorphism of a smooth Riemannian manifold possesses asymptotically \almost" local product structure, i.e., its density can be approximated by the product of the densities on stable and unstable manifolds up to small exponentials. This has not been known even for measures supported on locally maximal hyperbolic sets. Using this property of hyperbolic measures we prove the long-standing Eckmann-Ruelle conjecture in dimension theory of smooth dynamical systems: the pointwise dimension of every hyperbolic measure invariant under a C 1+fi difieomorphism exists almost everywhere. This implies the crucial fact that virtually all the characteristics of dimension type of the measure (including the Hausdorfi dimension, box dimension, and information dimension) coincide. This provides the rigorous mathematical justiflcation of the concept of fractal dimension for hyperbolic measures.


Journal ArticleDOI
TL;DR: A2A-induced “desensitization” of A1receptors was prevented by the protein kinase C inhibitor, chelerythrine (6 μM), and was not detected in the presence of theprotein kinase...
Abstract: Adenosine modulates synaptic transmission by acting on inhibitory A1 and facilitatory A2A receptors, the densities of which are modified in aged animals. We investigated how A2A receptor activation...

Journal ArticleDOI
TL;DR: The BEAM Monte Carlo code is used to simulate the 60Co beam from an Eldorado 6 radiotherapy unit and to calculate the relative air-kerma output factors as a function of field size, and the results accurately predict the effects of electron contamination from the surface to dose maximum.
Abstract: The BEAM Monte Carlo code is used to simulate the 60Co beam from an Eldorado 6 radiotherapy unit and to calculate the relative air-kerma output factors as a function of field size. The unit is realistically modeled, including source capsule, housing and collimator assembly. The calculated relative air-kerma output factors at SSD=80.5 cm agree to within 0.1% with measured values. It is shown that the variation of the output factor is almost entirely due to scattered photons from the fixed and adjustable collimators and there is no effect of shadowing primary photons. The influence of the geometry of the collimation system on the photon spectra on-axis is shown to be small but finite. The calculated buildup region of a depth-dose curve in a water phantom irradiated by a narrow and a broad 60Co beam is shown to agree with experimental data at the 2% to 3% level. Unlike previous calculations, the results accurately predict the effects of electron contamination from the surface to dose maximum. The variation of electron contamination with field size is also presented, as are spectra as a function of field size.

Journal ArticleDOI
TL;DR: In this paper, the effect of doping and annealing on zinc oxide thin films prepared by spray pyrolysis has been studied and the results show that the way doping influences the electrical and structural properties depends also on the characteristics of the doping element.

Journal ArticleDOI
TL;DR: In this paper, a new pollen-derived method of climatic quantification, based on the mutual climatic range of plant taxa, has been applied to 17 Pliocene pollen sequences in the West Mediterranean area.

Journal ArticleDOI
TL;DR: It is shown that most primary HIV-2 isolates can infect either CCR5+ or CXCR4+ cells without CD4, and the use of CD4 enables a wider range of 7TM receptors to be exploited for infection and may assist adaptation or switching to new coreceptors in vivo.
Abstract: Cell surface receptors exploited by human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) for infection are major determinants of tropism. HIV-1 usually requires two receptors to infect cells. Gp120 on HIV-1 virions binds CD4 on the cell surface, triggering conformational rearrangements that create or expose a binding site for a seven-transmembrane (7TM) coreceptor. Although HIV-2 and SIV strains also use CD4, several laboratory-adapted HIV-2 strains infect cells without CD4, via an interaction with the coreceptor CXCR4. Moreover, the envelope glycoproteins of SIV of macaques (SIVMAC) can bind to and initiate infection of CD4− cells via CCR5. Here, we show that most primary HIV-2 isolates can infect either CCR5+ or CXCR4+ cells without CD4. The efficiency of CD4-independent infection by HIV-2 was comparable to that of SIV, but markedly higher than that of HIV-1. CD4-independent HIV-2 strains that could use both CCR5 and CXCR4 to infect CD4+ cells were only able to use one of these receptors in the absence of CD4. Our observations therefore indicate (i) that HIV-2 and SIV envelope glycoproteins form a distinct conformation that enables contact with a 7TM receptor without CD4, and (ii) the use of CD4 enables a wider range of 7TM receptors to be exploited for infection and may assist adaptation or switching to new coreceptors in vivo. Primary CD4− fetal astrocyte cultures expressed CXCR4 and supported replication by the T-cell-line-adapted ROD/B strain. Productive infection by primary X4 strains was only triggered upon treatment of virus with soluble CD4. Thus, many primary HIV-2 strains infect CCR5+ or CXCR4+ cell lines without CD4 in vitro. CD4− cells that express these coreceptors in vivo, however, may still resist HIV-2 entry due to insufficient coreceptor concentration on the cell surface to trigger fusion or their expression in a conformation nonfunctional as a coreceptor. Our study, however, emphasizes that primary HIV-2 strains carry the potential to infect CD4− cells expressing CCR5 or CXCR4 in vivo.

Journal ArticleDOI
TL;DR: In this article, a Gaussian-smoothed extinction map of the dark cloud with an angular resolution of 30'' was constructed using measurements of ~2000 stars and used to construct ordered, uniformly sampled maps of the extinction through this cloud.
Abstract: We report deep near-infrared (HK) imaging observations of the dark cloud associated with IC 5146. With an order of magnitude greater sensitivity, we have imaged roughly half the region of the cloud originally surveyed by Lada and coworkers. Using measurements of ~2000 stars, we have employed techniques previously developed by Lada and coworkers to construct ordered, uniformly sampled maps of the extinction through this cloud. With the improved sensitivity, we detected approximately 5 times as many heavily extincted stars (i.e., A~20-50 mag) as found in the earlier survey of this same cloud area. Moreover, we were able to produce a Gaussian-smoothed extinction map of the cloud with an angular resolution (30'') somewhat more than a factor of 2 higher than achieved in the earlier study. With the increased sensitivity and angular resolution we were also able to measure the average radial column density profile orthogonal to the major axis of this filamentary cloud. Assuming cylindrical symmetry, we modeled this column density gradient and determined that the corresponding volume density profile of the cloud must smoothly fall off as r-2. To investigate the structure of the cloud on size scales smaller than the effective resolution of our maps, we constructed plots of the relation between the derived mean extinction and its measured dispersion for all the pixels in a series of maps made with varying angular resolution. We find, similar to Lada et al., that the dispersion increases linearly with mean AV, independent of the angular resolution of our maps. However, although we quantitatively reproduce the earlier results at the same angular resolution (90''), we find the interesting result that the slope of the σ-A relation decreases in a systematic fashion with increasing angular resolution. We construct synthetic models of the cloud density distribution and use Monte Carlo techniques to produce artificial extinction maps and investigate the origin of the σ-A relations. These models show that both the observed form of the σ-A relation and its variation with angular resolution are the natural consequences of a smooth, radially decreasing volume density gradient in a cylindrically symmetric cloud. For a volume density gradient falling off as r-2, the quantitative agreements between the model predictions and data are excellent. Apparently, these relations can be understood without the need for random fluctuations in the structure of the cloud on small spatial scales.

Journal ArticleDOI
TL;DR: The monitoring of disease progression in PPMS is difficult, although measures of atrophy correlate with the EDSS and appear most promising, which increases the understanding of this unique patient group, which will be further expanded with the acquisition of serial data.
Abstract: Background: Ten percent of patients with MS have a progressive course from onset with no history of relapses or remissions. A smaller subgroup follow a similar progressive course but have a single relapse at some point (transitional progressive [TP] MS). To date these patients have been excluded from receiving licensed treatments for MS and from most therapeutic trials. Objective: To document the clinical and MRI characteristics of a large cohort of progressive patients, including 158 with primary progressive (PP) MS and 33 with TPMS. Data from a small reference group of 20 patients with secondary progressive (SP) MS are also presented for reference. Methods: Patients were recruited from six European centers. All underwent a clinical assessment including scoring on the Expanded Disability Status Scale (EDSS) and MRI of the brain and spinal cord. Results: The men-to-women ratio was 81:77 (51% men) in the PP group, 14:19 (42% men) in the TP group, and 5:15 (25% men) in the SP group. The mean age at disease onset was significantly higher in the PP group than it was in the other two groups (PP 40.2 years, TP 34.9 years, SP 28.7 years). On MRI the PP group had lower mean brain T2 and T1 hypointensity lesion loads than the SP group (T2 12.02 versus 27.74 cm 3 , p = 0.001; T1 4.34 versus 7.04 cm 3 , p = 0.015). The SP and TP cohorts had significantly more T2-weighted lesions in the spinal cord than the PP patients, and the SP cohort had the greatest degree of atrophy. There was a correlation in the PP and TP patients between EDSS score and brain and spinal cord atrophy ( r = 0.3, 0.2, p ≤ 0.006) but not with brain lesion load. The PP and TP patients who presented with spinal cord pathology had significantly lower brain T2 and T1 lesion loads than those with non-spinal cord presentations ( p = 0.002). Conclusions: The monitoring of disease progression in PPMS is difficult, although measures of atrophy correlate with the EDSS and appear most promising. This study increases our understanding of this unique patient group, which will be further expanded with the acquisition of serial data.

Journal ArticleDOI
TL;DR: A number of descriptors that relate to the ability of a solute to take part in solute-solvent interactions have been identified, quantified and incorporated into a multiple linear regression equation.
Abstract: A number of solute descriptors that relate to the ability of a solute to take part in solute-solvent interactions have been identified, quantified and incorporated into a multiple linear regression equation. This general solvation equation can then be used for the correlation and prediction of solute effects in transport processes, that is, processes in which the main step is either the equilibrium transfer, or the rate of transfer, of a solute from one phase to another. Examples discussed include the solubility of gases and vapours in water, various water-solvent partitions, blood-brain distribution, brain perfusion, and skin permeability.

Journal ArticleDOI
TL;DR: Seven sites on three tributaries with intermittent flow regimes in the middle reaches of the Guadiana, i.e. Xevora, Caia and Degebe, were sampled and Canonical correspondence analysis (CCA) suggested a simple relationship between the diVerent species and their preferred habitat.
Abstract: Seven sites on three tributaries with intermittent flow regimes in the middle reaches of the Guadiana, i.e. Xevora, Caia and Degebe, were sampled approximately every 3 months from April 1995 to April 1997. The density and biomass of fish were greater in downstream rivers and sites. Along the Xevora River, a series of point abundance samples showed evidence of fish zonation along the river. Canonical correspondence analysis (CCA) suggested a simple relationship between the diVerent species and their preferred habitat. The small-sized Rutilus alburnoides and Leuciscus pyrenaicus used most or all of the habitats with some cover and flowing water. Greater concentrations of larger fish were found in downstream reaches which generally had greater depths as stream width increased: large Barbus microcephalus, B. steindachneri and B. comiza preferred such sites on the Degebe River. Droughts in seasonal Mediterranean streams such as the Guadiana River are a predictable natural disturbance. In the summer, flow ceases and some stretches of river consist of isolated pools. This results in intense aggregations of fish and possible competition for food and/or space. Although some species are well adapted to natural droughts, habitat degradation and possibly the introduction of exotic species contribute to marked variability in species composition. ? 1999 The Fisheries Society of the British Isles

Journal ArticleDOI
TL;DR: An unusual sedimentary horizon, believed to have been deposited by the tsunami associated with the 1755 Lisbon earthquake, has been identified at Boca do Rio in southern Portugal.

Journal ArticleDOI
TL;DR: In this article, the marginal distributions along rotated directions in the ( t, ω ) plane were used to obtain time and frequency information for non-stationary signals, and the rigorous probability interpretation of the marginal distribution avoided all interpretation ambiguities.

Journal ArticleDOI
TL;DR: In this article, the Lisbon principles of sustainable ocean governance (responsibility, scale-matching, precaution, adaptive management, full cost allocation, and participation) are presented as a core set of guidelines for sustainable ocean Governance.

Journal ArticleDOI
TL;DR: In this paper, a chave de leitura do artigo and a logica excesso-pobreza, aplicada ao exame da situacao dos professores, are presented.
Abstract: Este artigo procura analisar a "realidade discursiva" que marca grande parte dos textos sobre educacao neste final de seculo. A chave de leitura do artigo e a logica excesso-pobreza, aplicada ao exame da situacao dos professores: do excesso da retorica politica e dos mass-media a pobreza das politicas educativas; do excesso das linguagens dos especialistas internacionais a pobreza dos programas de formacao de professores; do excesso do discurso cientifico-educacional a pobreza das praticas pedagogicas e do excesso das "vozes" dos professores a pobreza das praticas associativas docentes. Nao recusando um pensamento "utopico", o autor critica as analises "prospectivas" que revelam um "excesso de futuro" que e, ao mesmo tempo, um "defice de presente".

Journal ArticleDOI
TL;DR: The fluorescence parameter Fv/Fm proved to be a good estimator of the survival capacity of R. fastigiata under field conditions and thus a useful parameter in determining the sensitivity of the lichens (photobiont) to Cu pollution.

Journal ArticleDOI
TL;DR: In this article, the authors used a principal components regression (PCR) technique to relate surface pressure patterns to those of the station pressure data, and the relationships were derived over a calibration period (1936-1995) and tested with independent data (the verification period, 1881-1935).
Abstract: Monthly grid-point pressure data are reconstructed from station records of pressure for Europe since 1780. The region encompasses 35-70°N to 30°W-40°E. The reconstructions are based on a principal components regression technique, which relates surface pressure patterns to those of the station pressure data. The relationships are derived over a calibration period (1936-1995) and the results tested with independent data (the verification period, 1881-1935). The reconstructions are of excellent quality, although this is slightly lower for regions with poor station coverage in the early years, particularly during the summer months. The reconstructions are compared with other monthly mean pressure maps produced by Lamb and Johnson (1966) for the years 1780-1872 and by Kington (1980, 1988) for 1781-1785. Both of these map series show systematic biases relative to the present reconstructions.

Journal ArticleDOI
01 Dec 1999-Extremes
TL;DR: In this article, the authors present an adaptive method to choose the number of order statistics involved in an optimal way, balancing variance and bias components, which has been achieved for the similar but some what less involved case of regularly varying tails.
Abstract: Estimators of the extreme-value index are based on a set of upper order statistics. We present an adaptive method to choose the number of order statistics involved in an optimal way, balancing variance and bias components. Recently this has been achieved for the similar but some what less involved case of regularly varying tails (Drees and Kaufmann, 1997); Danielsson et al., 1996). The present paper follows the line of proof of the last mentioned paper.

Journal ArticleDOI
TL;DR: A review of the structural and reactivity aspects of the coordinated indenyl ligand, dealing mainly with the systems theoretically studied by the authors is presented in this paper, where some intermediate distances are found in [(Ind)2Ni] where, formally, the ligand is halfway between η5 and η3.