Showing papers by "École Polytechnique Fédérale de Lausanne published in 1981"
TL;DR: In this article, the decolorization of indigo trisulfonate (600 nm, pH below 4) was used to determine the concentration of aqueous ozone in the range 0.005 −30 mg 1−1.
1,991 citations
TL;DR: In this article, a general framework is proposed to relate tip radius, interface undercooling and primary arm spacing in alloy dendrite growth, and all the growth morphologies developed between the limiting morphology at low and at high velocity are described to a first approximation, using an ellipsoid of revolution.
899 citations
TL;DR: An automatic threshold selection method for picture segmentation based on the definition of an anisotropy coefficient, related to the asymmetry of the grey-level histogram, which has been successfully applied to images having various kinds of histograms.
475 citations
TL;DR: In this article, the authors performed tension tests on re-healed and welded glassy polymers (PMMA-PMMA, SAN-SAN and PMMA-SAN) and found that the facture toughness in the interface increased with contact time, asKIi ∝t 1/4 as predicted by a diffusion model.
Abstract: Compact tension tests have been performed on re-healed and welded glassy polymers (PMMA-PMMA, SAN-SAN and PMMA-SAN). At temperatures above the glass transition temperature,Tg, it was observed that the facture toughness,KIi, in the interface increased with contact time,t, asKIi ∝t1/4 as predicted by a diffusion model. The self-diffusion constantD(Tg + 15 K) of chains of molecular weight 1.2×105 can be estimated as 1×10−21sec−1 with an activation energy of 274 kJ mol−1. For full material resistance, the depth of interdiffusion, 〈Δx2〉1/2, was calculated to be between 2 and 3 nm. Vacuum drying of the specimens, as well as polishing the interfaces, decreases the speed of interdiffusion.
467 citations
TL;DR: In this paper, a modified version of the Brody and Flemings analysis is presented to describe the solidification behavior of two steels solidifying over a range of cooling rates and the results indicate that such systems will in many cases be quite close to thermodynamic equilibrium with respect to carbon redistribution.
Abstract: Unidimensional solute redistribution during freezing is modelled for the important case of complete diffusion in the liquid and incomplete back-diffusion in the solid by the Brody and Flemings analysis. The treatment, however, does not conserve solute and leads to predictions which are incorrect unless solid state diffusion is very limited. This paper outlines the origin of this effect and presents a modification to the model in which the predicted behavior is quantitatively correct in the important limits. Application of the modified analysis is shown to be simple and to lead to realistic descriptions of the solidification behavior in mushy freezing alloys. As an example, the model is applied to two steels solidifying over a range of cooling rates and the results indicate that such systems will in many cases be quite close to thermodynamic equilibrium with respect to carbon redistribution.
467 citations
TL;DR: In all cases where the acute toxicity testing is mainly concerned with the evaluation of toxicological potential of the test substances, the symptomatology following acute overdosing, and the knowledge of target organs of toxicity, the classical LD50-test should be replaced by a more comprehensive short term test that can be done with small numbers of animals.
Abstract: The LD50-test was developed in 1927 for the biological standardization of dangerous drugs. Then it was incorporated into the routine toxicological protocol of other classes of chemical compounds and is now part of practically all governmental guidelines which regulate toxicological testing of chemicals. For scientific, economic, and ethical reasons it is necessary to periodically reassess all toxicological test procedures, including the LD50-test. Tests which are not optimal or that have become obsolete because of new scientific knowledge, must be changed or eliminated. The review of the LD50-test shows that the precision of the procedure is dependent on the number of animals used. But even with large numbers of animals there are considerable variations of the test results, because the numerical value of the LD50 is influenced by many factors, such as animal species and strain, age and sex, diet, food deprivation prior to dosing, temperature, caging, season, experimental procedures, etc. Thus, the LD50 value cannot be regarded as a biological constant. Through standardization of the test animals and the experimental conditions the variability of the LD50 determinations can be reduced but never fully eliminated. There are several tests with which an approximate LD50 can be determined. These methods use fewer animals than the classical LD50-test, but their precision and reproducibility are sufficient for most purposes of acute toxicity testing. Through incorporation of physiological, hematological, biochemical, pathological, and histopathological investigations in the simplified test procedures with small numbers of animals, it is possible to markedly increase the informational content of the results with regard to the toxicological spectrum and the target organs of toxicity. Such studies have already replaced the LD50-test in large animals, such as dogs and monkeys. It is also desirable to replace the LD50 in rodents with such a procedure. With pharmacologically inert compounds that have no acute effects with single administration the classical LD50-test does not provide relevant toxicological results. For the prediction of the human lethal dose and for the prediction of the symptomatology of poisoning after acute overdosing in man the LD50-test is of limited usefulness. An acute toxicity test with small numbers of animals combined with comprehensive studies of physiological functions, biochemical and histopathological examinations often provides more important information for emergency physicians and poison control centers. For the selection of doses to be used in subacute and chronic toxicity experiments the LD50-test does not provide consistent and reliable results. A simple pilot experiment with few animals but repeated dosing gives more useful information. For the evaluation of special risks for the human newborn and infant the LD50-test is poorly suited. For the appraisal of pharmacokinetic behavior and bioavailability the LD50-test gives only semi-quantitative, often ambiguous information. In all cases where the acute toxicity testing is mainly concerned with the evaluation of toxicological potential of the test substances, the symptomatology following acute overdosing, and the knowledge of target organs of toxicity, the classical LD50-test should be replaced by a more comprehensive short term test that can be done with small numbers of animals. The classical LD50-test should only be permitted in those rare instances where a high precision of the LD50 determination is indispensable.
291 citations
TL;DR: In this paper, the authors derived a relationship between measured reflection factors and the permittivity of the materials for the open-ended coaxial line propagating the TEM mode, which is used for reflection measurement.
Abstract: Reflection measurement techniques require a way to correlate measured reflection factors with the permittivity of the materials. This relationship is derived for the open-ended coaxial line propagating the TEM mode.
262 citations
TL;DR: Liposomes, in the size range of 40--180 nm, are formed when lipid and additives are solubilized with detergent, yielding defined mixed micelles, and the detergent is subsequently removed by controlled dialysis.
211 citations
TL;DR: In this paper, the effect of the aeration system and surface active agents on the mass transfer coefficient of tetrachloroethylene is studied and the stripping efficiencies of different types of gas-liquid contact devices used in water and waste water treatment are assessed.
183 citations
TL;DR: An electrically neutral hydrogen ion-selective carrier, tri-n-dodecylamine, was used as the active component for liquid-membrane electrodes as mentioned in this paper.
154 citations
TL;DR: The structures of the crystalline lithium enolates derived from 3, 3-dimethyl-2-butanone and from cyclopentanone have been determined by X-ray analysis as mentioned in this paper.
Abstract: The structures of the crystalline lithium enolates derived from 3, 3-dimethyl-2-butanone and from cyclopentanone have been determined by X-ray analysis. Both structures are tetrameric aggregates based on a Li4O4-cube, each Li+-ion being additionally bonded to the O-atom of a tetrahydrofuran solvent molecule.
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TL;DR: In this article, the problem of scheduling the games of a hockey or football league is addressed using a graph theoretical model and some constraints related to the alternating pattern of home-games and away-games.
Abstract: The purpose of this paper is to present the problem of scheduling the games of a hockey or football league. It is shown how a graph theoretical model may be used and how some constraints related to the alternating pattern of home-games and away-games can be handled. Finally some other requirements occurring in practice are also discussed and introduced into the model.
TL;DR: The possibility of using pulsed current in electrochemical machining at low electrolyte flow rate has been investigated in this article, where theoretical aspects of predicting electrolyte heating and limiting rate of mass transport are discussed in terms of simplified models.
TL;DR: In this paper, the overall enantioselective α-alkylation of chiral, non-racemic α-heterosubstituted carboxylic acids (4 → 6) is realized.
Abstract: Dioxolanones 7 and 8a and oxazolinones 9a derived from pivalaldehyde and lactic acid, mandelic acid, and proline, respectively, furnish chiral enolates of type 3 by deprotonation with LDA. Reactions of these enolates with alkyl halides, aldehydes, and ketones (→ 8b, 9b, 11–13) are highly diastereoselective. Thus, the overall enantioselective α-alkylation of chiral, non-racemic α-heterosubstituted carboxylic acids (4 → 6) is realized.
TL;DR: The dependence of the appearance of nucleosomes and chromatin upon its composition and upon the ionic strength of the solvent is demonstrated, which supports the model that an H1 polymer is stabilizing the higher order chromatin structures.
TL;DR: The inhibition of the Na+/Ca2+ exchange in isolated dog heart sarcolemma1 vesicles by low concentrations of doxorubicin is reported, the first known specific inhibitor of this exchange system.
TL;DR: The limiting viscosity numbers calculated for the “mannan backbones” of α- D -galactosidase-treated, guar galactomannan having galactose-mannose ratios of 38:62 to 15:85 were the same.
TL;DR: In this article, the authors present a geo-archaeological analysis of Axum, a city that began A.D. 100 as a ceremonial center, growing to over 10,000 people, as a prosperous emporium for international trade.
Abstract: Civilizations represent human ecosystems amenable to systematic geo-archaeological analysis. The civilization of Axum, spanning the first millennium A.D., had its settlement core on the now-denuded, subhumid plateau of northern Ethiopia. Axum, a new city, began A.D. 100 as a ceremonial center, growing to over 10,000 people, as a prosperous emporium for international trade. Intensified land use led to mass movements in slope soils before A.D. 300, but a range of clayey stream deposits also implicates strong periodic floods and seasonally abundant moisture. The paleoclimatic ensemble suggests that stronger and more reliable spring rains allowed two crops yearly without irrigation, compared to only one with modern summer rains. Trade declined after 600 and Axum was essentially landlocked by 715. Intense land pressure and more erratic rainfall favored soil destruction and ecological degradation during the seventh and eighth centuries. Largely abandoned by 800 and pillaged by border tribes. Axum retained only symbolic significance as power shifted to the more fertile lands of humid central Ethiopia. Axum shows how the spatial and temporal variability of resources, and the interactions between a society and its resource base, can be fundamental in the analysis of historical process.
TL;DR: In this article, the IR spectra of methyl formate and methyl acetate have been studied by trapping thermal molecular beams in Ar matrices, and four bands have been assigned to the anti conformer.
TL;DR: In this paper, the authors derived the angular distribution of light emitted into the half-spaces 1 and 2, and derived the dipole radiation patterns for the case in which any numbers of loss-free or absorbing, dielectric or metallic thin films are present between the loss-less layer 0 of arbitrary thickness containing the source and the halfspaces 0 and 2.
Abstract: The emission of light by sources, e.g., by luminescent centers, located in a thin nonabsorbing dielectric layer 0 between two half-spaces 1 and 2 is investigated theoretically. It is assumed that the light is emitted in electric or magnetic dipole transitions. But the theory is given in such a form that it can easily be extended to electric and magnetic quadrupole and higher-order multipole transitions. The electromagnetic boundary-value problem is solved rigorously for sources in layers 0 of arbitrary thickness. The radiation patterns, i.e., the angular distributions of light emitted into the half-spaces 1 and 2, are calculated. The theory takes into account the following effects that strongly influence the radiation patterns: (1) the wide-angle interferences that are a consequence of the coherence of the plane waves emitted into different directions, (2) the multiple-beam interferences that result from the multiple reflections of the plane waves between the interfaces 0/1 and 0/2, and (3) that evanescent waves present in the near field of the source radiate into media 1 and/or 2 if these media are denser than layer 0. This emission process is influenced by evanescent-wave effects analogous to the wide-angle interferences and the multiple-beam interferences of the plane waves. The limiting case of extremely thin layers 0 with optical thickness much smaller than the wavelength is also treated. Explicit analytical expressions are presented for the dipole radiation patterns in this case. Furthermore, the theory is generalized for sources in plane-stratified-layer systems. The dipole radiation patterns are derived for the case in which any numbers of loss-free or absorbing, dielectric or metallic thin films are present between the loss-free layer 0 of arbitrary thickness containing the source and the half-spaces 1 and 2.
TL;DR: In this article, the authors investigated the variation of the transient optical density as a function of the intensity of the exciting laser in homogeneous solutions (1-chloronaphthalene, 1-propanol) and in microemulsion.
Abstract: Triplet state formation (Φisc) and properties (eT-T, τT) of phthalocyanine (HPC) and zinc phthalocyanine (ZnPC) have been characterized in homogeneous solutions (1-chloronaphthalene, 1-propanol) and in microemulsion by investigating the variation of the transient optical density as a function of the intensity of the exciting laser. Experimental results follow the theoretically predicted dependence only for very low intensities of the exciting pulse. At higher intensities, a more complicated scheme of primary reactions has to be taken into account, implicating qualitative restrictions in the application of saturation experiments. The observed transients at high-intensity excitation are interpreted as being perturbed by aggregational phenomena.
TL;DR: A chemically defined medium is described that allows substantial proliferation and subsequent differentiation in primary cultures of cells derived from embryonic chicken breast muscle, and which provides a convenient means for obtaining nearly homogeneous muscle cell cultures.
TL;DR: The tetrameric cubic structure established for lithium enolates in the solid state is used as a model to discuss several facets of enolate chemistry: solubility, effects of cosolvents, addition to aldehyde and acid chloride, influence of mixed aggregates on diastereo- and enantioselectivities.
Abstract: The tetrameric cubic structure established for lithium enolates in the solid state is used as a model to discuss several facets of enolate chemistry: solubility, effects of cosolvents, addition to aldehyde and acid chloride, influence of mixed aggregates on diastereo- and enantioselectivities.
TL;DR: The variation of the sidechain length of n-alkyl-β-D-glucopyranosides and the use of mixtures of these detergents for the preparation of lipid/detergent mixed micelles followed by controlled detergent removal applying defined dialysis rates yields best characterized bilayer liposomes.
TL;DR: In this paper, the authors define the change-of-variance curve (CVC) of location M-estimators in order to investigate the infinitesimal stability of the asymptotic variance.
Abstract: We define the change-of-variance curve (CVC) of location M-estimators in order to investigate the infinitesimal stability of the asymptotic variance. We also construct the so-called hyperbolic tangent estimators, proving their existence and performing certain numerical computations of their defining constants. Their introduction is motivated by a theorem that shows they are the optimally robust redescending M-estimators in the sense of the CVC.
TL;DR: In this article, the characteristic absorption bands of lignin in the ultraviolet range of the spectrum were used for the determination of residual free lignins in broth cultures, and the effects of medium composition, pH, biomass, metabolite production and some lignini-related aromatic compounds were reported.
TL;DR: It is shown that every 2-satisfiable cnf s has an interpretation which satisfies at least h¿length(s) clauses (h=(√5-1)/2∼0.618).
Abstract: A conjunctive-normal-form expression (cnf) is said to be 2-satisfiable if and only if any two of its clauses are simultaneously satisfiable. It is shown that every 2-satisfiable cnf has a truth assignment that satisfies at least the fraction h of its clauses, where \( h = (\sqrt 5 - 1)/2 \sim 0.618 \) (the reciprocal of the “golden ratio”). The proof is constructive in that it provides a polynomial-time algorithm that will find for any 2-satisfiable cnf a truth assignment satisfying at least the fraction h of its clauses. Furthermore, this result is optimal in that the constant h is as large as possible. It is shown that, for any rational h’ > h, the set of all 2-satisfiable cnfs that have truth assignments satisfying at least the fraction h’ of their clauses is an NP-complete set.
TL;DR: In this article, the pit growth rate is not only time dependent but also markedly influenced by the applied potential and the chloride concentration of the electrolyte, and it can be concluded that the potentiostatically determined pitting potentials depend primarily on pit growth rather than on pit initiation.
Abstract: A new method to study the pit growth kinetics is proposed. On metal foils, the perforation time of growing pits is easily measured by an appropriate detecting system on the unexposed side of the specimen. Using metal foils of different thicknesses, the pit growth kinetics can be determined. The results obtained on aluminum show that the pit growth rate is not only time dependent but also markedly influenced by the applied potential and the chloride concentration of the electrolyte. Additions of foreign ions either accelerate or inhibit pit growth depending on the type and concentration of the ions added. The accelerating effect depends directly on the conductivity of the electrolyte. Furthermore, pit growth limiting potentials have been determined, below which pit growth is not possible. From the results obtained on aluminum, it can be concluded that the potentiostatically determined pitting potentials depend primarily on pit growth rather than on pit initiation.
TL;DR: In this article, archeological sediments are analysed from karst cave columns in Cantabrian Spain: Cueva Morin, El Pendo, the Castillo cave complex (including La Flecha, Las Chimeneas, La Pasiega, Las Monedas), Hornos de la Pena and Cobalejos.