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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 88 (1984), S. 508-519 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 24 (1968), S. 168-174 
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 22 (1967), S. 899-906 
    ISSN: 0001-5520
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 21 (1966), S. 406-412 
    ISSN: 0001-5520
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 23 (1967), S. 448-455 
    ISSN: 0001-5520
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Acta biotheoretica 25 (1976), S. 1-43 
    ISSN: 1572-8358
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A simple model, illustrating the transition from a population of free swimming, solitary cells (Chlamydomonas-type) to one consisting of small colonies (Gonium-type) serves as a basis to discuss the evolution of the cooperative group. The transition is the result of a mutation of the dynamics of cell division, delayed cell separation leads to colonies of four cells. With this mutation cooperative features appear, such as synchronised cell divisions within colonies and coordinated flagellar function which enables the colony to swim in definite directions. The selective advantages under given, environmental conditions are defined and the periods necessary for complete allelic replacement in small populations are calculated for asexual and sexual reproduction. The assumption of a steady-state population during allelic substitution is critically considered, particularly under conditions of competition. It is shown that density-dependent population control must operate in the process of selection. Sexual reproduction slows down the rate of selection even though all cells dre haploid. This phenomenon can be explained in general terms of `organizational dominance', where individual units coordinate the function of their neighbours which may be of a different allelotype. Cooperativity is pointed out as an a priori systemic feature which resides in the sub-units of systems, group formation and coordination appears thus as an almost inevitable event. A particular type of system described as ‘closed cycle of positive fitness interaction’ is discussed in more detail. It has the remarkable feature that its members cannot compete with each other; selection takes place between whole cycles (in analogy to Eigen's 1971 model). Gonium has a wide spectrum of `somatic plasticity' which enables it to assume various colonial configurations depending on physiological and environmental conditions. This feature can be explained as the result of dynamic flexibilities on the macro-molecular level. The particular relationship between the vast, molecular complexity and the relative simple dynamics of the cell cycle must lead eventually to the genetic fixation of an environmentally induced phenotype.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1572-8358
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The dynamics of populations of self-replicating, hierarchically structured individuals, exposedto accidents which destroy their sub-units, is analyzed mathematically, specifically with regardto the roles of redundancy and sexual repair. The following points emerge from this analysis:0 1. A population of individuals with redundant sub-structure has no intrinsic steady-statepoint; it tends to either zero or infinity depending on a critical accident rate α c . 2. Increased redundancy renders populations less accident prone initially, but populationdecline is steeper if a is greater than a fixed value α d . 3. Periodic, sexual repair at system-specific intervals prevents continuous decline and stabilizesthe population insofar as it will now oscillate between two fixed population levels. 4. The stabilizing sexual interval increases with increased complexity provided this is accom-panied by appropriate levels of redundancy. 5. The model closely simulates the dynamics of heterosis effects. 6. Repair fitness is a population fitness: the chance of an individual being repaired is a functionof the statistical make-up of the population as a whole at that particular period. Populationsliving at α 〉 α c either engage in sexual repair at the appropriate time or they die out. 7. The mathematical properties of the model illustrate mechanisms which possibly played arole in the evolution of a mortal soma in relation to sexual reproduction.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of applied electrochemistry 20 (1990), S. 357-364 
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In order to circumvent the corrosion problems prevalent in many existing electrochemical couples using the Na/β″-alumina half cell, a new class of high energy density organic materials was studied as cathode materials. In particular, one material tetracyanoethylene (TCNE), has favourable electrochemical characteristics with a potential 〉3.0 V against Na+/Na and energy density ∼620 Wh kg−1. Adopting a cell designed to permit sealing the anode half cell, the performance of TCNE was evaluated under various experimental conditions, that is, at different concentrations of TCNE in the catholyte and with different current collectors. The electrochemical behaviour of the TCNE cathode and the kinetics of TCNE reduction were examined. The kinetic parameters, exchange current density and diffusion coefficient, were determined from different a.c. and d.c. electrochemical techniques and evaluated with respect to the changes in TCNE concentrations in the catholyte. A chemical transformation occurring in the cell operating conditions which does not reduce the electrochemical activity of TCNE was identified from FTIR spectra. Finally, possible approaches to the use of TCNE or other organic materials in sodium or lithium rechargeable batteries are outlined.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Columnar, porous, magnetron-sputtered molybdenum and tungsten films show optinum performance as AMTEC electrodes at thicknesses less than 1.0 μm when used with molybdenum or nickel current collector grids. Power densities of 0.40 W cm−2 for 0.5 μm molybdenum films at 1200 K and 0.35 W cm−2 for 0.5 μm tungsten films at 1180 K were obtained at electrode maturity after 40–90 h. Sheet resistances of magnetron sputter deposited films on sodium beta″-alumina solid electrolyte (BASE) substrates were found to increase very steeply as thickness is decreased below about 0.3–0.4 μm. The a.c. impedance data for these electrodes have been interpreted in terms of contributions from the bulk BASE and the porous electrode/BASE interface. Voltage profiles of operating electrodes show that the total electrode area, of electrodes with thickness 〈2.0 μm, is not utilized efficiently unless a fairly fine (∼1×1mm) current collector grid is employed.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 21 (1984), S. 371-381 
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss the quantization of Regge's discrete description of Einstein's theory of gravitation. We show how the continuum theory emerges in the weak field long wavelength limit. We also discuss reparametrizations and conformal transformations.
    Type of Medium: Electronic Resource
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