Showing papers by "University of Coimbra published in 1985"
TL;DR: In this article, the incorporation of chlorine in trioctahedral biotite-like micas, belonging to the series phlogopite-annite, KCo3AlSi3O10(OH)2 and phlogopsite-KNi3AlSiam3O 10(OH), was investigated at 600°C and 2 kbars, with a duration of two weeks.
172 citations
TL;DR: In this article, the Hartree-Fock and correlation energy components of the many-body expansion of the molecular potential energy are separated from accurate SCF calculations while the correlation components are obtained semiempirically from the dispersion energy coefficients for various separate and united atom limits and those also known for the equilibrium geometries of the subsystems.
Abstract: This paper is concerned with recent theoretical progresses on the determination of potentials for use in spectroscopic and gas phase scattering calculations. Emphasis is placed on the global representation of the potential surface by using the many-body expansion of the molecular potential energy. Novel developments which allow further flexibility and reliability to this method while conveying generality both for chemically stable and van der Waals molecules are described. The essential feature of the new method is to separate the (extended-) Hartree-Fock and correlation energy components of the terms of the many-body expansion. In this double many-body expansion of the molecular energy the Hartree-Fock components are, in principle, obtained from accurate SCF calculations while the correlation components are obtained semiempirically from the dispersion energy coefficients for the various separate and united atom limits and those also known for the equilibrium geometries of the subsystems. Examples are given to illustrate the method.
97 citations
TL;DR: In this paper, the protonation constants of the triazacyclononane triacetic acid (NOTA) have been measured by potentiometry, and the proptonation sequence of the various amino and carboxylate groups of NOTA has been studied in DzO as a function of pD from the chemical shifts of the nonlabile protons.
Abstract: The protonation constants of the macrocyclic ligand 1,4,7-triazacyclononane-N,N’,N”-triacetic acid (NOTA) have been measured by potentiometry, and the protonation sequence of the various amino and carboxylate groups of NOTA has been studied in DzO as a function of pD from the chemical shifts of the nonlabile protons. Shielding constants for protonation of the amino groups were determined in a NMR study of the triaza macrocyclic amine, its trimethylated analogue, and NOTA and compared with values reported for linear polyamino polycarboxylates and cyclic tetraaza tetracarboxylate ligands. The results indicate that two nitrogens of NOTA are protonated at higher pH than the carboxylate groups. The last nitrogen is protonated only at very low pH. The sequence of protonation of NOTA supports the formation of hydrogen bonds between two protonated nitrogens and the adjacent two nonprotonated carboxylates. The ‘H and I3C spectra of the La(N0TA) and Lu(N0TA) species were studied as a function of pH and temperature. The aqueous complexes show spectra characteristic of flexible triaza macrocycles, displaying fast interconversion between the two staggered 6 and X conformations of the ethylenediamine rings even at room temperature. Above pH 9.5, the La(N0TA) and Lu(N0TA) hydroxo complexes start to form and their spectra show evidence of greater rigidity as at room temperature the 6 /X ethylenediamine ring conformational interconversions in the Lu(N0TA) hydroxo complex are slow on the NMR time scale.
79 citations
TL;DR: The clinical study showed that only the posterior vitreous concentration of fluorescein is relevant in the evaluation of the blood-retinal barrier.
Abstract: We compared insulin-dependent diabetic patients with minimal (16 eyes of 9 patients) or no retinopathy (45 eyes of 27 patients) to normal volunteers (20 eyes of 12 subjects) using a commercial vitreous fluorophotometer and different procedures for artifact correction. The influence of background autofluorescence was minimized through the use of a software program that subtracted a fluorophotometric scan obtained before administration of fluorescein from that obtained after its injection. We also compared two programs designed to minimize the contribution of the chorioretinal peak spread function to the readings in the vitreous. The fluorescein concentration in the posterior vitreous was then averaged within two different regions. We then assessed the influence of these data-processing methods on the spread of the results of the different groups. The clinical study showed that only the posterior vitreous concentration of fluorescein is relevant in the evaluation of the blood-retinal barrier. However, since there is a gradient of fluorescein concentration in the posterior vitreous, one needs a scanning device so that one can measure at a precise location in front of the retina. The posterior vitreous concentration of fluorescein was significantly increased in diabetic subjects with one or no aneurysms as compared with normals. Moreover, the eyes with minimal retinopathy, as judged by the presence of microaneurysms, had higher values than those without retinopathy. The clear differences among these three groups were not present when the midvitreous values were used. Finally, the concentrations of fluorescein in the anterior chamber were higher in the diabetic subjects with retinopathy than in the normals, but not in the diabetic subjects without retinopathy.
73 citations
TL;DR: In this paper, the Rothemund meso-tetraalkylporphyrin was trapped as an intermediate in the Rothemenylphlorin synthesis.
50 citations
TL;DR: In this article, the tetra-n-butylammonium picrate-1 -chloroheptane (TNB-1) was shown to have a critical point at 0.50 with no detectable departure near the critical point, although the present experiments were designed for a very precise test of the last topic.
Abstract: Liquid-liquid phase separation and a critical point have been observed for a system involving a fused salt. Specifically the system is tetra-n-butylammonium picrate-1 -chloroheptane for which T/sub c/ = 414.4 K, chi/sub c/ = 0.08/sub 5/ mole fraction picrate, and V/sub c/ = 2300 cm/sup 3/ x mol/sup -1/ picrate. The critical mole fraction of picrate is very small, and the phase diagram is very asymmetric. The critical exponent shows the mean field value of 0.50 with no detectable departure near the critical point, although the present experiments were not designed for a very precise test of the last topic. 5 references, 2 figures, 1 table.
48 citations
TL;DR: In this article, a variational derivation of the Liouville-von Neumann equation of quantum-statistical mechanics is presented, in order to formulate mean-field approximations appropriate to mixed states.
29 citations
TL;DR: In this paper, the variational derivation of nuclear fluid dynamics is extended to include distortions of the local density which are independent of distortions of local momentum distribution, and the severe constraint implied by the scaling approach is relaxed and one obtains the possibility to describe also lowlying collective modes in a fluid-dynamical formalism.
20 citations
TL;DR: The Mobius function of the poset A = A: A ⊆ E, A O is acyclic and in a special case its homotopy type are computed and the matroidal properties of a finite set of points in R d are precisely the properties which can be formulated in non-Radon partitions terms.
19 citations
TL;DR: The following theorem is proved: ‘For every orientation ϑ of the uniform matroid U 2 r -1, r with r ⩾ 3, there is an acyclic reorientation Ā ϑ, such that all points are extreme points’.
18 citations
TL;DR: Using the cloudy-bag hamiltonian the nucleon is described by means of a variational quantum field theoretical approach (VQF) involving a coherent state of pions.
TL;DR: In this article, the Albrecht method was used to compute stress intensity factors in non-load carrying fillet welds subjected to tension and cantilever bending for cracks growing from the tip of the weld toe through the plate thickness.
TL;DR: The results indicate that diffusion alone does not account for the outward flow of fluorescein in the vitreous, and the possible underlying factors and significance of these findings are discussed.
Abstract: Vitreous fluorophotometry was performed on eight normal subjects to compare the outward and inward permeabilities of fluorescein into the vitreous. The results indicate that diffusion alone does not account for the outward flow of fluorescein in the vitreous. The possible underlying factors and significance of these findings are discussed.
TL;DR: In this article, the hedgehog baryon arises as a variational solution of the linear σ-model, if this is restricted to the chiral circle and if the boson Fock-states are described by coherent states and the valence quarks by a product of three identical wave functions.
TL;DR: Kinetic vitreous fluorophotometry showed an alteration of the blood-retinal barrier (BRB) in patients with retinitis pigmentosa, even in those who had minimal fundoscopic abnormalities and only minor changes on the electroretinogram.
Abstract: Six patients with various genetic types of retinitis pigmentosa and ten carriers of the X-linked recessive type were studied by vitreous fluorophotometry. Kinetic vitreous fluorophotometry showed an alteration of the blood-retinal barrier (BRB) in patients with retinitis pigmentosa, even in those who had minimal fundoscopic abnormalities and only minor changes on the electroretinogram. Furthermore, an alteration of the BRB could be detected in the carriers of the X-linked recessive form of retinitis pigmentosa. In general, higher concentration of fluorescein in the vitreous correlated topographically with the extent of photoreceptor and retinal pigment epithelial disease, as well as with the presence of leakage from retinal capillaries.
TL;DR: The results of vitreous fluorophotometry in a variety of retinal and systemic diseases are described, particularly in photoreceptor and retinal pigment epithelium dystrophies, in Best dystrophy, and in choriocapillaris atrophy.
Abstract: The results of vitreous fluorophotometry in a variety of retinal and systemic diseases are described, particularly in photoreceptor and retinal pigment epithelium dystrophies, in Best dystrophy, in choriocapillaris atrophy, in choroidemia and in inflammatory conditions, and in cystoid aphakic and non-aphakic macular edema. The patterns involved in breakdown of the blood-retinal barrier are defined for various diseases, and an attempt is made to characterize each disease type by a fluorophotometric "profile."
TL;DR: Results show that many technical problems have been resolved by the Fluorotron Master fluorophotometer and this system can be satisfactory handled by technical personnel after short periods of training.
Abstract: Studies using the Fluorotron Master fluorophotometer in vitro and in vivo are presented. The in vitro tests include lower limit of detection and error of measurement, and the in vivo tests include spread function, axial resolution, and reproducibility. Results show that many technical problems have been resolved by this system. Furthermore, this system can be satisfactory handled by technical personnel after short periods of training.
TL;DR: In this paper, a variational formulation of nuclear fluid dynamics is presented, which is valid both for zero and for finite temperatures, and equations for small-amplitude oscillations around a stationary state are derived.
Abstract: A variational formulation of nuclear fluid dynamics is presented, which is valid both for zero and for finite temperatures The equations for small-amplitude oscillations around a stationary state are derived As an example of the variational approach, a fluid-dynamical calculation which avoids the so-called scaling approximation but takes into account distortions of the Fermi surface is briefly discussed
TL;DR: In this article, the determinant of A + B, where A (B ) is an n × n normal matrix with eigenvalues α 1,...,α n (β 1,...,β n ), was studied.
01 Dec 1985-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: Ionization pulse signals due to 207 Bi conversion electrons were observed in ionization chambers filled with tetramethylsilane which was purified by a simple method in this article, where the pulse height spectra and its variation with the electric field were measured.
Abstract: Ionization pulse signals due to 207 Bi conversion electrons were observed in ionization chambers filled with tetramethylsilane which was purified by a simple method. Pulse height spectra and its variation with the electric field were measured.
TL;DR: In this article, a mechanism based on the observed gain divergence characteris? tics occuring in a gaseous detector at the transition fran the proportional to the self-quenching streamers discharge (SQS), when adquate gas fillings are used and on the role played by photoionization, is proposed to interpret quantitatively the process.
Abstract: Based on the observed gain divergence characteris? tics occuring in a gaseous detector at the transition fran the proportional to the self-quenching streamers discharge (SQS), when adquate gas fillings are used and on the role played by photoionization, a mechanism is proposed to interpret quantitatively the process. The relevant intrinsic parameters, which determine the mechanism, are the number of photons emitted by electron per cm path near the anode, W, the mean free path of VUV radiation, L, the quantum efficiency, ?, geometrical factors, g, which are interrelated. Fran the experimental data some of those parameters are computed for the mixtures argon-isobutane and argon-isobutane-triethylamine.
TL;DR: Results indicate that low concentrations of phenothiazines uncouple the sarcoplasmic reticulum Ca2+ pump without disrupting the membrane and that the drug stimulatory effect on the ATPase is not due to a direct interaction with the enzyme.
TL;DR: No significant differences were found in protein binding among normal volunters and patients with diabetes types I and II, and the best time interval for measurement appeared to be 60 min after the intravenous injection.
Abstract: Preliminary studies on fluorescein kinetics in the plasma of humans were performed by fluorophotometry and spectrophotometry. Noninsulin diabetics (type II) were similar to normal individuals. Insulin-dependent diabetics (type I), however, had lower plasma concentrations of fluorescein than the other two groups. No significant differences were found in protein binding among normal volunters and patients with diabetes types I and II. The best time interval for measurement appeared to be 60 min after the intravenous injection. The possible reasons for these results are discussed, and the importance of these findings to vitreous fluorophotometry is outlined.
15 Apr 1985-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: A 12-bit analog-to-digital converter (ADC) module, which is part of a computer based multichannel analyser (MCA), is described with emphasis on a new approach to the implementation of the sliding scale method for improvement of the differential linearity.
Abstract: A 12-bit analog-to-digital converter (ADC) module, which is part of a computer based multichannel analyser (MCA), is described with emphasis on a new approach to the implementation of the sliding scale method for improvement of the differential linearity. The performances of the module described are the following: input range 0 to 10 V, conversion time 12 μs, differential linearity better than ±0.2% and integral linearity better than ±0.025%. The interfacing of this module to the computer bus is also discussed.
TL;DR: In this article, the tunnel effect theory has been used to calculate the reactivity of a large number of ketones and good agreement is found between calculated and experimental values, and the results of the present model are compared with those from thermal activation studies, within the approximations of the models, thermal activation rate constants never exceed those for nuclear tunnelling.
TL;DR: In this article, the pseudocontact shifts induced by lanthanide-nota chelates were analyzed for cyclopropanecarboxylic acid (CPCA) binding to nine nota (nota is the axially symmetric macrocyclic triaza ligand 1,4,7-triazacyclonionane-N, N, N ′ N ″-triacetic acid) chelsates.
Abstract: Lanthanide-induced shift data are presented for cyclopropanecarboxylic acid (CPCA) binding to nine lanthanide-nota (nota is the axially symmetric macrocyclic triaza ligand 1,4,7-triazacyclonionane- N , N ′ N ″-triacetic acid) chelates at pH 6, 25 °C and 70 °C. The contact and pseudocontact contributions to the observed proton and carbon shifts have been separated by linear regression analysis. Plots of the data in two linear forms show a break at Dy in the lanthanide series. Possible sources of this break are discussed with the help of measured proton and carbon relaxation rates of CPCA bound to five different lanthanide chelates, and comparison with similar data for CPCA bonding to the lanthanide-ethylenediaminetetraacetate chelates. This work shows that the pseudocontact shifts induced by Ln(nota) chelates in the CPCA 1 H and 13 C nuclei conform to the axial symmetry model, making these chelates potentially very useful as conformational probes in biological systems.
TL;DR: In this paper, the authors considered a C1 immersion f: S1-R2 with period 1.2 and showed that the immersions are always non-injective.
Abstract: 2. Definitions. A closed curve is a C1 immersion f: S1 -> R2. A pair { x, y } of distinct points of S1 is a double point, crossing, or self-intersection of f if f (x) = f (y). We assume that no three distinct points of S1 have the same image and that f is self-transverse. By self-transverse we mean that if { x, y } is a double point, then the tangents to f at x and y are distinct. These restrictions are not very serious. In fact, with a suitable topology for the set of maps g: S1 -> R2, the immersions we are interested in form an open and dense subset. According to [1] and [14], they are called clean immersions and normal curves respectively. In this note the immersions are always non-injective. By composing with g: R -S1 given by g(t) = (cos 27Tt, sin 2 7t), we can consider f to be a periodic map f: R -R2 with period 1. A loop of f is a restriction of f to a closed interval [a, b] such that fI [a, b) is injective and f(a) = f(b). We shall not distinguish between two loops of f with the same image in R2. Let { xi, Yi }, . ., { xn, yn } be the n pairs of points of [0, 1) corresponding to the double points
TL;DR: Use of this approach should optimize the evaluation of fluorophotometry data and maximize the information obtained concerning the status of the blood retinal barrier.
Abstract: Findings during fluorophotometry studies of the normal human vitreous are described. The major landmarks are presented and a system of significant fluorophotometric variables is proposed. Use of this approach should optimize the evaluation of fluorophotometry data and maximize the information obtained concerning the status of the blood retinal barrier.
TL;DR: In this article, a volume integral method is used with the finite element technique as a differential numerical approach to predict the levitating force acting on a E core plate levitator and the results were in good agreement with the experimental measured values.
Abstract: The solution of the electromagnetic field in any electromagnetic device is best appreciated if expressed in terms of the terminal characteristics of the device, namely forces. In this paper expressions for force calculations are derived from the numerical field solutions in terms of \bar{T} -the electric vector potential and Omega(Ω)-the magnetic scalar potential. The volume integral method is used with the finite element technique as a differential numerical approach. The technique was tested to predict the levitating force acting on a E core plate levitator and the results were in good agreement with the experimental measured values.
TL;DR: The introduction of quantitative ocular fluorophotometry was a major breakthrough in this field and further refinements in methodology were introduced subsequently by Waltman and Kaufman (1970) and by my research group in Portugal (Cunha-Vaz et al. 1975).
Abstract: It is for me a great honor and a particular pleasure to address all the participants of this First International Symposium on Ocular Fluorophotometry. It is only befitting that we should recall now all the men who have laid the foundations for ocular fluorophotometry and with their pioneering work made this meeting happen. Ocular fluorophotometry was initiated just a century ago when Ehrlich (1882) described for the first time the use of fluorescein in ophthalmological research. He used it to investigate the mode of origin of the aqueous humor. Ehrlich observed the formation of a vertical fuorescent line in the anterior chamber, after systemic administration of fluorescein, and believed that fluorescein outlined the course of inflowing aqueous humor, a concept soon disproved. Fluorescein, however, became a favorite tool for investigation in ophthalmological research. I consider the milestones in the history of ocular fluorophotometry to have been, since the initial study of Ehrlich, the extensive work on the permeability of the blood-aqueous barrier and the development of a clinical test for its study by Amsler and Huber (1946), the investigations of Goldmann (1950) who laid the technical and mathematical groundwork for the future developments in the study of the dynamics of fluorescein transport in the posterior segment of the eye (Cunha-Vaz and Maurice 1967) and, finally, the development of the first truly quantitative ocular fluorophotometer by Maurice (1963). The introduction of quantitative ocular fluorophotometry was a major breakthrough in this field and further refinements in methodology were introduced subsequently by Waltman and Kaufman (1970) who developed a relatively simple fluorophotometer and by my research group in Portugal (Cunha-Vaz et al. 1975) who initiated the clinical application of fluorophotometry to the study of posterior segment disease (Cunha-Vaz et al. 1975), following previous personal work performed in association with Maurice (1967). The history of ocular fluorophotometry and its clinical application has two phases which have awakened great enthusiasm. The first phase centered on the study of the anterior chamber and aqueous humor was associated with the development by Amsler and Huber of a clinical test to study the permeability of the blood-aqueous barrier (1946). The second, a much more recent phase, which was initiated by our group, focused on the study of the vitreous and the blood retinal barrier. Both should have an important place in the ophthalmological diagnostic armamentarium. But many other applications and diagnostic tests utilizing fluorophotometry are being increasingly used: to name just a few, tear flow studies, corneal permeability, aqueous flow, lens permeability, and intraocular fluid dynamics. Significant contributions to our understanding of the physiology, pharmacology, and pathology of a variety of eye diseases are accepted as a result of the increasing utilization of ocular fluorophotometry. Of special interest is the fact that the application of fluorophotometry to a large number of ophthalmological problems has brought together, under the common denominator of ocular fluorophotometry, specialists on corneal diseases, glaucoma, the vitreous, the retina and neuro-ophthalmology. Finally, what gives me great confidence in the future of ocular fluorophotometry and in its progressively more significant role in ophthalmology is that we are now watching the development of extremely sophisticated new fluorophotometric apparatus that are able to perform fluorophotometric measurements in the eye, noninvasively, and are making these measurements simpler to perform, accurate, and reproducible. We concur with Lugossy (1959) when he wrote in his extensive review on fluorescein and the blood-aqueous barrier: " . . . the modern management of eye diseases cannot dispense with the routine application of fluorophotometry." I believe that this statement will become generally accepted in a not so distant future.