Showing papers by "University of Lisbon published in 1992"
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TL;DR: A review of the present understanding of the global climate system, consisting of the atmosphere, hydrosphere, cryosphere, lithosphere and biosphere, and their complex interactions and feedbacks is given from the point of view of a physicist as mentioned in this paper.
Abstract: A review of our present understanding of the global climate system, consisting of the atmosphere, hydrosphere, cryosphere, lithosphere, and biosphere, and their complex interactions and feedbacks is given from the point of view of a physicist. This understanding is based both on real observations and on the results from numerical simulations. The main emphasis in this review is on the atmosphere and oceans. First, balance equations describing the large-scale climate and its evolution in time are derived from the basic thermohydrodynamic laws of classical physics. The observed atmosphere-ocean system is then described by showing how the balances of radiation, mass, angular momentum, water, and energy are maintained during present climatic conditions. Next, a hierarchy of mathematical models that successfully simulate various aspects of the climate is discussed, and examples are given of how three-dimensional general circulation models are being used to increase our understanding of the global climate "machine." Finally, the possible impact of human activities on climate is discussed, with main emphasis on likely future heating due to the release of carbon dioxide in the atmosphere.
2,358 citations
171 citations
TL;DR: The principles of [Ca2+]i imaging and measurement using fluorescent dyes, the equipment required to do it, the problems with botanical material and how they are being overcome, future developments for this approach in plant cell biology, and an entirely different strategy for the imaging and measurements involving genetic transformation with the aequorin gene are described.
Abstract: SUMMARY
Calcium plays a central role as a second messenger in plant and fungal cells and as such is involved in controlling numerous biological processes. Direct demonstration of signal-response coupling via Ca2+ requires the measurement and localization of changes in cytosolic free Ca2+, [Ca2+]i, during these processes in living cells. In recent years this has become possible with the introduction of a range of fluorescent dyes (e.g. Indo-1 Fura-2 and Fluo-3) which have a high affinity and selectivity for free Ca2+. When used with recently developed microscope technologies (e.g. fluorescence ratio imaging or confocal scanning laser microscopy), subcellular localization and precise quantification of [Ca2+]i dynamics in single cells can be achieved. This review describes the principles of [Ca2+]i imaging and measurement using fluorescent dyes, the equipment required to do it, the problems with botanical material and how they are being overcome, future developments for this approach in plant cell biology, and an entirely different strategy for the imaging and measurement of [Ca2+]i involving genetic transformation with the aequorin gene.
129 citations
TL;DR: A case control study of transient global amnesia (TGA), transient ischaemic attacks (TIA) and normal controls is described in this paper, where 51 TGA patients, selected between January 1985 and March 1990, were compared with four controls (two TIAs and two normals) for the presence of vascular risk factors (hypertension, diabetes, smoking habits, cholesterol, triglycerides and haematocrit levels, heart disease, previous stroke), previous TGA, migraine, psychiatric illness and recent head trauma).
Abstract: A case control study of transient global amnesia (TGA), transient ischaemic attacks (TIA) and normal controls is described. Each of the 51 TGA patients, selected between January 1985 and March 1990, was compared with four controls (two TIAs and two normals) for the presence of vascular risk factors (hypertension, diabetes, smoking habits, cholesterol, triglycerides and haematocrit levels, heart disease, previous stroke), previous TGA, migraine, psychiatric illness and recent head trauma. Patients with TGA had less diabetes, hypercholesterolaemia and hypertriglyceridaemia than TIA. TGA subjects had significantly more hypertension (odds ratio = 3.31) and migraine (odds ratio = 8.67) than normal controls. During a mean of 17.4 mths of follow-up (range 1–96 mths), three subjects had recurrent TGA, one sustained a TIA and a minor stroke, but none had seizures. Thrombo-embolism and epilepsy are unlikely to be the cause of this benign disorder. The role is stressed of appropriate precipitants, including haemodynamic changes, and of individual susceptibility (of which migraine is probably a marker) in the genesis of TGA.
89 citations
TL;DR: Daily and annual courses of leaf transpiration, stomatal conductance and shoot water potential of four Quercus suber individuals were compared in a semi-natural stand in southwest Portugal from spring 1989 to early summer 1990.
Abstract: Daily and annual courses of leaf transpiration, stomatal conductance and shoot water potential of four Quercus suber individuals were compared in a semi-natural stand in southwest Portugal, from spring 1989 to early summer 1990.
58 citations
TL;DR: In this paper, the authors investigated the difficulties students encounter in problem solving in the area of sciences and found that a strong relation between social class and specific coding orientation to problem solving was found for race and weaker for gender.
Abstract: This study investigates the difficulties students encounter in problem solving in the area of sciences. Contrary to usual approaches of a fundamental psychological basis, the research takes into account the sociological processes of learning and transmission in both the family and the school. The aim of the study is to see the extent to which the students have recognition and realisation rules in the micro‐context of problem solving (specific coding orientation) and to find out the reasons which may underlie their difficulties. Thus the data obtained are related to social class, race and gender and also to pedagogic practices (differing in power and control relations) and school science achievement in high level cognitive competencies. They are also related to children's cognitive level. The results show a strong relation between social class and specific coding orientation to problem solving. The relation is also strong for race and weaker for gender. Specific coding orientation is also strongly related ...
55 citations
TL;DR: In this article, the authors reported thermal conductivity measurements for the alternative refrigerant 1,1, 1,2-tetrafluoroethane (R134a) over the temperature range from 200 to 390 K at pressures to 70 MPa.
54 citations
TL;DR: In this paper, it was demonstrated that the Taylor dispersion method can be used to measure the mutual diffusivity of liquid mixtures near a critical point of mixing, and the results were in agreement with the theoretically predicted behavior of the diffusivities near the critical point.
Abstract: It is demonstrated that the Taylor dispersion method can be used to measure the mutual diffusivity of liquid mixtures near a critical mixing point. For this purpose we have measured the mutual diffusivity of a liquid mixture of n-hexane and nitrobenzene at the critical composition at temperatures from 16 K down to 1 K above the critical temperature. The results are in agreement with the theoretically predicted behavior of the diffusivity near a critical point of mixing.
45 citations
TL;DR: In this article, it is proposed that adsorption isotherms of water vapor determined on non-porous carbons can be classified into four distinct types, and that a certain level of polarity and distribution of polar sites is associated with each.
35 citations
TL;DR: In this paper, a mathematical model for the concentration profile of TiCl4 at the top surface of an Incoloy 800H substrate placed inside a laser chemical vapor deposition (LCVD) reactor is developed by using the three-dimensional transient mass diffusion equation.
Abstract: A mathematical model for the concentration profile of TiCl4 at the top surface of an Incoloy 800H substrate placed inside a laser chemical vapor deposition (LCVD) reactor is developed by using the three‐dimensional transient mass diffusion equation. The model is used for studying the spatial variation of the thickness of TiN dots deposited by LCVD, using a CO2 laser and a reactive atmosphere consisting of TiCl4, N2, and H2. By assuming that the chemical reaction is first‐order with respect to TiCl4, and that the sticking coefficient of TiN at the substrate surface is temperature dependent, the deposited TiN film is found to have a volcanic profile under certain conditions, which is in good agreement with experimental results.
35 citations
TL;DR: Two new meroterpenes, usneoidols Z and E, have been isolated from the brown seaweed Cystoseira usneoides and exhibit antitumoural and antiviral activities.
TL;DR: In this paper, preliminary measurements of the dielectric constant of toluene and benzene have been performed along the saturation line, up to 100°C, using a capacitance bridge operating with a three terminal arrangement.
TL;DR: In this article, the use of a dc polarization voltage applied between the hot wires and the cell wall greatly reduces this uncertainty for polar liquids and enables existing transient hot-wire instruments with bare wires to study the thermal conductivity of moderately polar liquids with confidence.
01 Jan 1992
TL;DR: This paper presents a method developed for the multiple traveling salesman problem (m-TSP), which is a generalization of the well known TSP.
Abstract: This paper presents a method developed for the multiple traveling salesman problem (m-TSP), which is a generalization of the well known TSP [6]. In the m-TSP, there are m salesmen who are required to visit n customers in such a way that all customers are visited exactly once by exactly one of the salesmen. Hence, each salesman leaves from and returns to the same point, the depot, and each one of them completes a tour visiting a subset of the customers.
TL;DR: The Dubna quark confinement model is applied to the study of electromagnetic polarizabilities of the \ensuremath{\pi} and K mesons and finds the electric polarizability considerably larger than the chiral prediction.
Abstract: The Dubna quark confinement model is applied to the study of electromagnetic polarizabilities of the \ensuremath{\pi} and K mesons. Within this model it is found that the effect of quark confinement reduces the value of the pion polarizability from that obtained in such approaches as chiral quark loop and linear \ensuremath{\sigma} models. In the chiral limit our result coincides with the one found in chiral perturbation theory. For the charged kaon we find the electric polarizability considerably larger than the chiral prediction. This is due to the strong meson-mass dependence not expected from the pointlike interaction in effective meson Lagrangian approaches.
TL;DR: Two new meroterpenes have been isolated from the brown seaweed Cystoseira usneoides usneoidone E and usneoidsone Z and exhibit antitumoural and antiviral activities.
TL;DR: In this paper, the lattice location of several transition metal (Hf, Ta) and rare earth (Nd, Eu) impurities has been investigated in LiNbO3 by ion-beam channeling methods, including Rutherford backscattering and the 7Li(p, α)4 He nuclear reaction.
Abstract: The lattice location of several transition metal (Hf, Ta) and rare-earth (Nd, Eu) impurities has been investigated in LiNbO3 by ion-beam channeling methods, including Rutherford backscattering and the 7Li(p, α)4 He nuclear reaction. From the detailed analysis of the angular scans near crystallographic axes and planes and the comparison between the two methods, it has been concluded that Hf lies at a Li site, but Ta at a Nb site, whereas Eu and Nd present double occupancy. By using additional results on other impurities, a wider picture of location behavior is described and possible physical mechanisms are discussed.
TL;DR: The presence of ionic gradients is not by itself suficient to trigger the polarization of tube growth as the presence of an electric field which drives the ionic currents is essential for this to occur.
Abstract: Agapanthus umbelatus pollen tubes (PTs) display a number of different growth patterns when germinated in an electric field of 750 mV· mm−1. When pollen is germinated near the cathode (82.44% of orientation to the cathode side) or near the anode (55.35% of orientation to the anode), growth is oriented parallel to the applied field but when germinated at an intermediate position, there is random growth. An increase and decrease in the orientation rates as well as reversion of the polarized growth were observed when the growth conditions were systematically altered. These findings reflect the influence of different ionic currents present in the germination medium. These ionic currents induce the formation of ionic gradients, which were monitored by ion-HPLC. The individual omission of Ca2+, K+, Mg2+ and Cl− suppresses or alters the oriented growth pattern. The presence of ionic gradients is not by itself suficient to trigger the polarization of tube growth as the presence of an electric field which drives the ionic currents is essential for this to occur.
TL;DR: In this article, structural and reactivity studies on Mo IV and Mo II alkyl isocyanide complexes of the types [Cp 2 Mo(X)CNR]Y and Cp 2MoCNR (X = H, Me, Et, Cl, I; R = Me, et, t Bu; Y = I, BF 4, PF 6 ) are reported.
TL;DR: In this article, the similarity invariants of a square matrix when prescribed an arbitrary submatrix were studied. And they were shown to be invariant to the number of submatrices.
TL;DR: In this article, the density of the binary mixture 40/60 wt% of monochlorodifluoromethane (HCFC 22) and 1-chloro-1,1-difluoroethane(HCFC 142b) in the liquid phase has been measured between 300 and 370 K and pressures up to 19 MPa, with an oscillating fork densimeter, operating in a relative mode.
02 Feb 1992-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this paper, the 7Li(p, α)4He nuclear reaction has been used for the characterization of the lithium site location in LiNbO crystals, combining results obtained with NRA, PIXE and RBS/channeling.
Abstract: The 7Li(p, α)4He nuclear reaction has been used for the characterization of the lithium site location in LiNbO crystals. Combining results obtained with NRA, PIXE and RBS/channeling, the lattice site locations of Er and Ti introduced during crystal growth in pure LiNbO3, and of Hf in Mg co-doped LiNbO3 are presented and discussed.
TL;DR: Lampreia et al. as discussed by the authors derived partial molar volumes of secondary amines in methanol from density measurements using a vibrating tube densimeter, and discussed the intermolecular interactions in these systems, and in the range of the dilute region studied were obtained by means of excess volumes calculated in terms of Henry's model.
TL;DR: In this paper, the effect of sulphate ions on the anodic behavior of copper in neutral aqueous solutions of various Na2SO4 concentrations was studied by cyclic voltammetry and chronocoulometry.
TL;DR: The shape and the microstructure of the films were analyzed by profilometry and scanning electron microscopy (SEM) as mentioned in this paper, depending on the deposition conditions, different types of profiles and microstructures were observed.
TL;DR: In this paper, the thermal conductivity of 1-chloro-1,1-difluoroethane (HCFC-142b) has been measured in the temperature range 290 to 504 K and pressures up to 20 MPa with a concentric-cylinder apparatus operating in a steady-state mode.
Abstract: The thermal conductivity of 1-chloro-1,1-difluoroethane (HCFC-142b) has been measured in the temperature range 290 to 504 K and pressures up to 20 MPa with a concentric-cylinder apparatus operating in a steady-state mode. These temperature and pressure ranges cover all fluid states. The estimated accuracy of the method is about 2%. The density dependence of the thermal conductivity has been studied in the liquid region.
TL;DR: In this article, the qualitative analysis of a Robertson-Walker geometry non-minimally coupled to a scalar field is summarized, and it is claimed that a divergenceless effective energy-momentum tensor should be used.
TL;DR: The use of quinic acid for the synthesis of linear molecules was demonstrated by an efficient stereoselective synthesis of the antibiotic (+)-negamycin this paper, which was shown to be suitable for linear molecules.
TL;DR: A survey is made covering the pathophysiology, clinical symptoms, diagnosis, management, and results in cases with pyogenic or tuberculous spondylitis, disc space infection, spinal epidural abscess, subdural empyema or intramedullaryAbscess, and parasitic spinal infection.
Abstract: A survey is made covering the pathophysiology, clinical symptoms, diagnosis, management, and results in cases with pyogenic or tuberculous spondylitis, disc space infection, spinal epidural abscess, subdural empyema or intramedullary abscess, and parasitic spinal infection.
TL;DR: In this article, the authors identified the secondary school teachers' conceptions of teaching physics and made an attempt to reach a higher level of synthesis in terms of a typology of physics teaching conceptions.