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  • Springer  (147)
  • American Institute of Physics  (22)
  • Oxford University Press  (11)
  • 1990-1994  (180)
  • 1
    Electronic Resource
    Electronic Resource
    Photocontrol of seed germination in Impatiens wallerana Hook. f. (1994)
    Springer
    Plant growth regulation 14 (1994), S. 249-256 
    Details
    ISSN: 1573-5087
    Keywords: Impatiens wallerana ; photocontrol ; seed germination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract General characteristics of light sensitivity of Impatients wallerana seeds were investigated. Germination was absolutely dependent on light, irrespective of temperature. High percentages of germination were obtained by exposure to long periods of illumination or, alternatively, to several repeated short irradiations with red light. In this case, responsiveness to light was not altered by increasing either the initial incubation period in darkness or the dark intervals between short exposures. Effects of red light were reversed by far-red light, thus demonstrating the involvement of phytochrome. Evidence was presented for an interactive effect, of unknown physiological nature between red and far-red light on the germination of the seeds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00024800
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  • 2
    Electronic Resource
    Electronic Resource
    Portuguese emigration 1958–1985: Some empirical evidence (1994)
    Springer
    Empirical economics 19 (1994), S. 647-657 
    Details
    ISSN: 1435-8921
    Keywords: J61 ; F22
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract Supplying work in the home country or abroad must be seen as the result of the same decisional process. If that is true, the same set of variables should be used to explain the participation in the labor market and the emigration rates. Based upon empirical results, we discuss some of the traditional conclusions of the economic literature. Our empirical results, for example, show that: 1) there is a strong support for considering home wages and the wages in the country of destination asymmetrically, 2) imperfections in the capital markets seem to play an important role when workers must pay for their moving expenses and 3) there is a differential in coefficients between the period before 1974 and after that date, as 1974 is the year most of the Central European countries changed their immigration policies. The results also point to the existence of a large stock of potential emigrants in Portugal. The actual emigration will depend to a great extent on expectations regarding the evolution of real wages in Portugal and in the EC partners. If workers do not expect a rapid growth at home, we will see a large outflow due to the differential of wage levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01205821
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  • 3
    Electronic Resource
    Electronic Resource
    Properties of polyaniline formed at tin dioxide electrodes in weak acid solution: effect of the counterion (1993)
    Springer
    Journal of applied electrochemistry 23 (1993), S. 332-338 
    Details
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Polyaniline films have been formed at tin dioxide electrodes in aqueous 0.4m acetate buffer solutions of pH between 3.5 and 5.5 with added nitrate, perchlorate or halide electrolyte, in order to study the effect of the counterion on the structure and electrochemical properties of the polyaniline film. The films were characterized electrochemically by cyclic voltammetry and by impedance, and morphologically by scanning electron microscopy. Marked differences between the films are found, the highest conductivity and electrochemical response being with nitrate counterion. The films formed are generally flat and porous, with evidence of some small irregular growths. These results are compared to those obtained in sulphuric acid solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00296688
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  • 4
    Electronic Resource
    Electronic Resource
    A constraint generation scheme to probabilistic linear problems with an application to power system expansion planning (1994)
    Springer
    Annals of operations research 50 (1994), S. 367-385 
    Details
    ISSN: 1572-9338
    Keywords: Peak expansion ; hydrothermal systems ; reliability ; constraint generation ; Benders decomposition ; cutting planes ; Monte Carlo simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract In this paper, we first describe a constraint generation scheme for probabilistic mixed integer programming problems. Next, we present a decomposition approach to the peak capacity expansion planning of interconnected hydrothermal generating systems, with bounds on the transmission capacity between the regions. The objective is to minimize investments in generating units and interconnection links, subject to constraints on supply reliability. The problem is formulated as a stochastic integer program. The constraint generation scheme, which is similar to Benders decomposition, is applied in the solution of the peak capacity expansion problem. The master problem in this decomposition scheme is an integer program, solved by implicit enumeration. The operating subproblem corresponds to a stochastic network flow problem, and is solved by a maximum flow algorithm and Monte Carlo simulation. The approach is illustrated through a case study involving the expansion of the system of the Brazilian Southeastern region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02085648
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  • 5
    Electronic Resource
    Electronic Resource
    Mechanisms of shear failure in artificial fractures of sandstone and their implication for models of hydromechanical coupling (1993)
    Springer
    Rock mechanics and rock engineering 26 (1993), S. 195-214 
    Details
    ISSN: 1434-453X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Summary Direct shear tests, in which the behaviour of the rock surfaces during shear could be continuously observed, were used to study the shear failure of a profiled and clean discontinuity artificially prepared from natural sandstone. Displacement transducers were used to measure the normal and shear displacements. A series of strain gauges glued on the sides of the upper block provided information on the change of the stress field occurring close to the discontinuities whilst shear displacement increased, and these changes were then compared with the behaviour of the profiled surface. The results of the laboratory tests, the sequence of photographs taken for most of them, and the results conducted with a sample of similar shape made from the same rock material and tested in a rotary shear machine, allowed several stages and mechanisms of failure to be defined: static friction and mobilization of initial shear stiffness; mobilization of sliding; mobilization of brittle fracture; post-peak failure of the teeth; descent of the teeth; gliding and ploughing; commencement of second cycle of shearing. In many respects these stages are similar to those occurring between sliding surfaces of metal and suggest that the analyses developed in tribology may be relevant to the development of constitutive models for predicting the hydromechanical coupled behaviour of a discontinuity with shear displacement. Such models will have to consider these different stages of shear, because the original discontinuity changes its geometry with displacement and is filled with gouge which changes its grain size with displacement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01040115
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  • 6
    Electronic Resource
    Electronic Resource
    The conversion of methane to ethylene and ethane with near total selectivity by low temperature (〈 610 ° C) oxydehydrogenation over a calcium-nickel-potassium oxide catalyst (1990)
    Springer
    Catalysis letters 6 (1990), S. 255-262 
    Details
    ISSN: 1572-879X
    Keywords: Total selectivity in methane conversion ; calcium-nickel-potassium oxide catalyst ; methane conversion to ethylene and ethane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The catalytic oxidative coupling of methane to C2, C3 and C4 paraffins and olefins has been accomplished with close to 100% selectivity at methane conversions of about 10% per pass. Essentially no carbon oxides are formed and the mechanism appears to be a surface catalyzed reaction. Temperatures of 〈 600 ° C are used and the presence of steam is important. The catalyst comprises a ternary mixture of calcium, nickel and potassium oxides. Method of preparation and composition of the catalyst are critical for its performance. Presence of a carbidic carbon on the catalyst surface may be important.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00763991
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  • 7
    Electronic Resource
    Electronic Resource
    The catalytic low temperature oxydehydrogenation of methane. Temperature dependence, carbon balance and effects of catalyst composition (1991)
    Springer
    Catalysis letters 9 (1991), S. 395-401 
    Details
    ISSN: 1572-879X
    Keywords: Oxydehydrogenation of methane ; catalytic methane conversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In an earlier publication [1] it has been claimed that oxidative coupling of methane to higher hydrocarbons had been obtained with close to 100% selectivity at 600 ° C and atmospheric pressure in the presence of steam over a CaNiK oxide catalyst. These results have been confirmed in longer runs. Artifacts, such as carbonate formation on the catalyst, have been excluded. The reaction is slightly exothermic. An Arrhenius plot shows that methane oxidation to CO2 predominates at temperatures above 600 ° C and oxidative methane coupling at lower temperatures. The importance of exact catalyst composition is demonstrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00764831
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  • 8
    Electronic Resource
    Electronic Resource
    New FIR laser lines from CD3OD optically pumped by a CO2 waveguide laser (1991)
    Springer
    Applied physics 52 (1991), S. 36-41 
    Details
    ISSN: 1432-0649
    Keywords: 42.55
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this work we report new FIR laser lines from CD3OD optically pumped by a CO2 waveguide laser. The wide tunability of this laser (290 MHz) makes it possible to pump absorption lines with large frequency offset relative to the CO2 laser line center, which are not possible by using conventional CO2 lasers. As a consequence 19 new laser lines have been discovered, ranging from 38.0 μm to 455.2 μm in wavelength. For all lines, precise frequency offset measurements between the CO2 line center and the center of the absorber CD3OD line were performed using the transferred Lamb-dip technique. We also present direct Doppler-free offset measurements of infrared absorption, obtained within the FIR laser cavity itself, using optoacoustic detection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00405684
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  • 9
    Electronic Resource
    Electronic Resource
    Realization of the Einstein-Podolsky-Rosen paradox for continuous variables in nondegenerate parametric amplification (1992)
    Springer
    Applied physics 55 (1992), S. 265-278 
    Details
    ISSN: 1432-0649
    Keywords: 42.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Einstein-Podolsky-Rosen (EPR) paradox is demonstrated experimentally for continuous variables by employing a nondegenerate optical parametric amplifier (NOPA). Such a system is analogous to and under some ideal conditions is in one-to-one correspondence with the original system discussed by EPR. In particular, the quadrature-phase amplitudes for a signal beam are inferred in turn from those of a spatially separated but strongly correlated idler beam, where these optical amplitudes are analogous to canonical position and momentum variables. The variances for the two inferences are measured and their product is observed to be below the limit of unity associated with the Heisenberg uncertainty relation, in apparent contradiction with quantum mechanics according to the argument of EPR. The smallest product of inference variances achieved in the experiment is (0.70±0.01). Various other types of quantum noise for this system are also investigated, and a theory of a narrowband NOPA is presented with losses included. A comparison between experiment and this theory shows relatively good agreement. The question of a local hidden-variables description of the system is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00325015
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  • 10
    Electronic Resource
    Electronic Resource
    IR and FIR spectroscopy of 13CD3OH around the 10P(22) and 10P(24) CO2 laser lines: New FIR laser emissions, frequency measurements and assignments (1992)
    Springer
    Applied physics 54 (1992), S. 24-28 
    Details
    ISSN: 1432-0649
    Keywords: 42.55
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract By using high resolution infrared Fourier transform data on 13CD3OH and the 10P(22) and 10P(24) lines of a waveguide CO2 laser to optically pump this methanol isotope, eight new FIR laser lines were observed. The frequencies of five laser lines were directly measured by heterodyne detection with already known laser lines. Particularly interesting are the lines pumped by the 10P(24) line, since a triade of emissions could be completely assigned.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00331730
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