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  • Articles  (465)
  • American Physical Society  (332)
  • Springer  (133)
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  • Articles  (465)
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  • 1
    ISSN: 1572-879X
    Keywords: microemulsion synthesis ; ruthenium or copper catalysts ; N2O decomposition ; mesopores ; surface area
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Bimetallic Ru–Cu catalysts supported on SiO2 have been synthesized in microemulsions using sodium metasilicate (Na2SiO3), copper nitrate (Cu(NO3)2·3H2O) and ruthenium chloride (RuCl3) at 28 °C. The microemulsion system consists of sodium 1,4‐bis(2‐ethylhexyl) sulfosuccinate (AOT) and sodium dodecyl sulphate (SDS), cyclohexane, and an aqueous solution of sodium metasilicate or metal salts. The catalysts have been characterized by XPS, EDX/SEM with line scanning and they possess a very narrow pore size distribution (around 38 Å) and relatively high specific surface areas (around 400 m2/g). The catalytic results of the N2O decomposition reveal that higher conversions of N2O can be achieved by the catalysts synthesized from the microemulsion process at lower temperatures (around 400 °C).
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 41 (1986), S. 125-129 
    ISSN: 1432-0649
    Keywords: 33 ; 42.55
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper reports the observation and analysis of several different opticalpumping and energy-transfer processes for generating stimulated radiation, including equal or unequal frequency two-step Na2−K and K2−K hybrid resonance. A series of infrared stimulated and cascade stimulated lines by the transitions in atomic potassium were detected.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Applied mathematics & optimization 36 (1997), S. 323-360 
    ISSN: 1432-0606
    Keywords: Key words. Approximations, Constraint qualification, Dirichlet boundary controls, Minimax criterion, Parabolic equations, State constraints, Uncertain disturbances, Variational inequalities. AMS Classification. Primary 49K20, 49K35, Secondary 49J20, 35K50.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract. In this paper we formulate and study a minimax control problem for a class of parabolic systems with controlled Dirichlet boundary conditions and uncertain distributed perturbations under pointwise control and state constraints. We prove an existence theorem for minimax solutions and develop effective penalized procedures to approximate state constraints. Based on a careful variational analysis, we establish convergence results and optimality conditions for approximating problems that allow us to characterize suboptimal solutions to the original minimax problem with hard constraints. Then passing to the limit in approximations, we prove necessary optimality conditions for the minimax problem considered under proper constraint qualification conditions.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Earth, moon and planets 69 (1995), S. 237-247 
    ISSN: 1573-0794
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract First, a sequence of four-zone models for the interior of Venus is constructed under the assumption of hydrostatic equilibrium. While the equation of state for each zone is taken to be the Bullen's relation with its coefficients consistent with the PREM Earth model (Dziewonski and Anderson, 1981), the position of core-mantle boundary is determined by matching solutions of the Emden's equation in different regions. The results of hydrostatic models indicate the presence of a reasonably large molten iron core in Venus, broadly similar to the Earth. It is also found that the position of the core-mantle interface is nearly model-independent. Second, we focus on the question why Venus does not possess a significant global magnetic field and on what we can learn from this fact. Solutions of magnetohydrodynamic equations appropriate for the molten core of Venus are discussed. It is argued that, because the Elsasser number Λ measuring the relative importance of Coriolis and Lorentz forces satisfies Λ ≪ 1, equations for the problem of thermal convection in the Venusian fluid core must be nearly uncoupled with the dynamo equation. The existence of a global magnetic field, though small, then suggests that the size of the magnetic Reynolds numberR m must beR m =O(10), sustaining a dynamo action near its marginal state but not an active dynamo in the Venusian molten core. On the basis of asymptotic relations for finite amplitude convection, a useful constraint on important physical parameters for the liquid core of Venus is derived and discussed.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Earth, moon and planets 73 (1996), S. 221-236 
    ISSN: 1573-0794
    Keywords: Planet ; Jupiter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In the deep interior of the giant planets Jupiter and Saturn, ordinary hydrogen and helium are transformed into a conducting metallic liquid at extremely high pressure. It is likely that the giant planets' observed magnetic field is constantly generated in the metallic fluid core by magnetohydrodynamic processes, converting mechanic energy in the form of convection into magnetic energy. The maximum strength of their magnetic fields is likely to be limited by magnetic field instabilities which convert the magnetic energy back into convection. The parameter which governs the occurrence of magnetic instabilities is the Elsasser number, λ = B 2Σ/2Ωϱ, where B is the field strength, Σ is the electrical conductivity, Ω is the rotation rate and ϱ is the density. Since magnetic instability will be very active when λ exceeds a critical value λ c ∼ 10 (the precise value depending on the magnetic field distribution), this imposes an upper bound on the effective electrical conductivity of the metallic fluid which comprises the bulk of Jupiter's interior and much of Saturn's. Stability calculations including both toroidal (model) and poloidal (observed) components of the magnetic field in a rapidly rotating spherical shell, have been performed. The most stable configuration of the field is when the poloidal component of field is strong and the toroidal field is weak; in this case we obtain an upper bound for electrical conductivity of Σ ∼ 3 × 106 S/m; while the most unstable configuration of the field is when the toroidal and poloidal fields are comparable, giving rise to Σ m ∼ 3 × 105 S/m. The implications of the results for general dynamo theory are also discussed.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Mycopathologia 129 (1995), S. 87-90 
    ISSN: 1573-0832
    Keywords: Phytophthora heveae ; Mainland China
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Phytophthora heveae was isolated from soil in Hainan Island. This is the first report of its occurrence in mainland China. The world literature onP. heveae is also reviewed.
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  • 7
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The ability of a photobioreactor to fix CO2 was evaluated with the thermophilic cyanobacterium, Synechocystis aquatilis SI-2. The reactor consisted of three to five flat plates of transparent acrylic plastic standing upright and in parallel and giving a 0.015-m light path. The reactor was 0.8 m high and 1 m long with 9 l working volume. The effects of the orientation of the vertical bioreactor, distance between the plates, and culture temperature on the productivity of biomass were investigated during the summer of 1998 in Kamaishi (39°N, 142°E), Japan. When the illuminated surface reactor was placed in an east–west-facing orientation, the biomass productivity was roughly 1.4-fold higher than that obtained in a north–south-facing orientation, because the former received more solar energy than the latter. The productivity based on the overall land area was the same for plates set either 0.25 m or 0.5 m apart. However, the volumetric productivity of the reactor in which the plates were set 0.25 m apart was lower than that when the plates were set 0.5 m apart, since the former plates received relatively lower solar irradiation because of severe mutual shading. When the culture temperature was maintained in its optimal range (37–43 °C), the productivity was 50% greater than that obtained in a culture at ambient temperature (20–44 °C). The biomass productivity and CO2 fixation rate were investigated under various experimental conditions. The maximum rate of 53 g CO2 m−2 day−1 was achieved in the temperature-regulated culture with the reactor set in an east–west-facing orientation, the distance between plates being 0.25 m.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Electrical engineering 76 (1993), S. 423-426 
    ISSN: 1432-0487
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Description / Table of Contents: Übersicht Die Verteilungen von Potential, Stromdichte und Verlustleistungsdichte in einem kreisförmigen, dünnen Film- bzw. Folienwiderstand werden mittels einer konformen Abbildung berechnet. Das Ergebnis zeigt, daß die Verlustleistungsdichte in der Ecke des Kontakts zwischen der Zuleitung und dem Film (der Folien) des Widerstandes gegen unendlich strebt. Dadurch kann dieser Teil des Widerstandes abbrennen oder schmelzen. Abschließend wird eine geeignete Kontaktform zwischen der Zuleitung und dem Widerstand vorgeschlagen.
    Notes: Contents The potential, current flux and dissipation density distributions in a circular thin film/foil resistor are calculated based on a conformal mapping. The results indicate that the dissipation density at the corner of the contact between the lead and the resistor film/foil reaches infinity. This results in burning down or melting that part of the resistor. Finally, a reasonable contact shape between the lead and the resistor is suggested.
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  • 9
    ISSN: 1432-0487
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Description / Table of Contents: Contents This paper presents a semi-analytical method for the calculation of the electromagnetic field due to a three-dimensional incident field which is screened by an infinitely long circular cylindrical conducting and permeable shell. The resulting threedimensional Helmholtz equations are solved by using the method of the separation of variables together with the Fourier Transform applied to the longitudinal field components. The transformed transversal components are represented in terms of the transformed longitudinal components. With the aid of the DFT (discrete Fourier Transform) the three-dimensional incident field can be expanded into a Fourier series and then be transformed. Finally the inverse DFT yields the solution of the boundary value problem. Calculations using the proposed method are presented.
    Notes: Übersicht Ein semianalytisches Rechenverfahren wird vorgestellt, welches es gestattet, das elektromagnetische Feld eines durch eine unendlich lange, kreiszylindrische, leitfähige und permeable Hülle geschirmten, dreidimensionalen Erregerfeldes zu berechnen. Die dabei auftretenden dreidimensionalen Helmholtz-Gleichungen werden unter Verwendung der longitudinalen Feldkomponenten mit Hilfe der Methode der Separation der Variablen und der Fourier-Transformation gelöst. Die transformierten transversalen Komponenten werden in Abhängigkeit der transformierten longitudinalen Komponenten dargestellt. Unter Zuhilfenahme der DFT (diskrete Fourier-Transformation) wird das dreidimensionale Erregerfeld erst in eine Fourierreihe entwickelt und dann ebenfalls transformiert. Eine abschließende inverse DFT liefert die Lösung des Randwertproblems. Unter Anwendung des vorgeschlagenen Verfahrens werden Rechenergebnisse präsentiert.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Pattern analysis and applications 3 (2000), S. 69-75 
    ISSN: 1433-755X
    Keywords: Keywords: Character recognition; Curve characterisation; Feature extraction; Handwritten text processing; Pattern matching; Signature verification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract. This paper introduces a new approach for point-to-point correspondence finding, which can be used as pre-processing stage of a handwritten signature verification procedure. This approach provides a solid basis for comparing function features of two handwritten signatures. Corner points of the signatures are first extracted based on velocity information. The characteristics of curvilinear velocity and angular velocity are combined successfully by functions based on membership criteria. The signatures to be compared are then segmented at landmarks obtained by corner matching based on similarity measures. In the last step, the corresponding pairs of segments are mapped by a point-to-point matching algorithm, minimising a curve deformation energy. The techniques described were applied to a set of 188 signatures from 19 volunteers. The resulting point-to-point matching of signature pairs was satisfactory in all cases where there was a visual agreement between the signatures.
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