Einfluß der Erstarrungsgeschwindigkeit auf die Gehalte der Legierungselemente an und vor der Phasengrenze flüssig-fest bei der Kristallisation verschiedener Legierungen der Systeme Kupfer—Mangan und Kupfer—Nickel

Modellvorstellungen zum Kristallisationsverlauf einphasig erstarrender Legierungen. Erörterung der Profile der chemischen Zusammensetzung im Kristall und, in der Schmelze bei zwei Geschwindigkeiten am Beispiel einer Kupfer-Mangan-Legierung. Einfluß der Erstarrungsgeschwindigkeit und des Ausgangsgehaltes auf die Gehalte des Legierungselementes an der Kristallisationsfront im Feststoff und in der Schmelze. Vergleich der eigenen Ergebnisse mit den Erstarrungsmodellen des Schrifttums.     

Labour market regulation, industrial relations and technological regimes: a tale of comparative advantage

In this paper we present comparative evidence from OECD countriesconcerning the impact of labour market institutions and regulationson technological specialization. The interplay between the degreeof labour market flexibility, the system of industrial relationsand the knowledge base of different industries determines theviability of different human resource strategies, thereby shapingthe patterns of comparative advantage. Our empirical resultsshow that countries with coordinated industrial-relations systemsand strict employment protection tend to specialize in industrieswith a cumulative knowledge base. We argue that two mechanismsexplain these patterns. The larger the scope for resorting tointernal labour markets, the lower the adjustment costs imposedby labour market regulation. Furthermore, employment protectionand coordinated industrial-relations regimes, by aligning workers'and firms' bjectives, encourage firm-sponsored training as wellas the accumulation of firm-specific competencies, allowingfirms to fully exploit the potential of the internal labourmarket.     

Modified BCS Mechanism of Cooper Pair Formation in Narrow Energy Bands of Special Symmetry II. Matthias Rule Reconsidered

In part I of this paper a modified BCS mechanism of Cooper pair formation of electrons was proposed. This mechanism is connected with the existence of a narrow, roughly half-filled superconducting energy band of given symmetry. The special symmetry of the superconducting band was interpreted within a nonadiabatic extension of the Heisenberg model of magnetism. Within this nonadiabatic Heisenberg model, the electrons of the superconducting band are constrained to form Cooper pairs at zero temperature because in any normal conducting state the conservation of crystal-spin angular momentum would be violated. Except for this participation of the angular momentum, the pair formation is mediated in the familiar way by phonons. Superconducting bands can be identified even within a free-electron band structure. Therefore, in this paper the band structures of the bcc and hcp solid solution alloys composed of transition elements are approximated by appropriate free-electron band structures with s–d symmetry. From the free-electron bands, the number n of valence electrons per atom related to the maxima of the superconducting transition temperature T _c in these solid solutions is calculated within the nonadiabatic Heisenberg model. The two observed maxima of T _c are reproduced without any adjustable parameter at valence numbers n approximately equal to 4.9 and 6.5 in bcc and 4.7 and 6.7 in hcp solid solutions. This result is in good agreement with the measured values of 4.7 and 6.4 of Hulm and Blaugher. The upper maximum is predicted not to exist in bcc transition elements but to occur in several ordered structures of bcc solid solution alloys.     

Antiferromagnetic, Neutral, and Superconducting Band in La2CuO4

The symmetry of the Bloch functions in the conduction band of tetragonal and orthorhombic La₂CuO₄ is examined for the existence of symmetry-adapted and optimally localizable (usual or spin-dependent) Wannier functions. It turns out that such Wannier functions do not exist in the tetragonal phase. In the orthorhombic phase, on the other hand, the Bloch functions can be unitarily transformed in three different ways into optimally localizable Wannier functions: they can be chosen to be adapted to each of the three phases observed in the pure or doped material, that is, to the antiferromagnetic phase, to the superconducting phase or to the phase evincing neither magnetism nor superconductivity. This group-theoretical result is proposed to be interpreted within a nonadiabatic extension of the Heisenberg model. Within this model, atomic-like states represented by these Wannier functions are responsible for the stability of each of the three phases. However, all the three atomic-like states cannot exist in the tetragonal phase, but are stabilized by the orthorhombic distortion of the crystal. A simple model is proposed which may explain the physical properties of La_2-x Sr _x CuO₄ as a function of the Sr concentration x.     

A variational method to avoid locking—independent of the discretization scheme

We present a variational method for problems in solid and structural mechanics that is designed to be intrinsically free from locking when using equal‐order interpolation for all involved fields. The specific feature of the formulation is that it avoids all geometrical locking effects (as opposed to material locking effects, for instance Poisson locking) for any type of structural or solid model, independent of the underlying discretization scheme. The possibility of employing equal‐order interpolation for all involved fields circumvents the task of finding particular function spaces to remove locking and avoid artificial stress oscillations. This is particularly attractive, for instance, for isogeometric analysis using unstructured meshes or T‐splines. Comprehensive numerical tests underline the promising behavior of the proposed method for geometrically linear and nonlinear problems in terms of displacements and stress resultants using standard finite elements, isogeometric finite elements, and a meshless method.     

Exact subthreshold integration with continuous spike times in discrete-time neural network simulations

Very large networks of spiking neurons can be simulated efficiently in parallel under the constraint that spike times are bound to an equidistant time grid. Within this scheme, the subthreshold dynamics of a wide class of integrate-and-fire-type neuron models can be integrated exactly from one grid point to the next. However, the loss in accuracy caused by restricting spike times to the grid can have undesirable consequences, which has led to interest in interpolating spike times between the grid points to retrieve an adequate representation of network dynamics. We demonstrate that the exact integration scheme can be combined naturally with off-grid spike events found by interpolation. We show that by exploiting the existence of a minimal synaptic propagation delay, the need for a central event queue is removed, so that the precision of event-driven simulation on the level of single neurons is combined with the efficiency of time-driven global scheduling. Further, for neuron models with linear subthreshold dynamics, even local event queuing can be avoided, resulting in much greater efficiency on the single-neuron level. These ideas are exemplified by two implementations of a widely used neuron model. We present a measure for the efficiency of network simulations in terms of their integration error and show that for a wide range of input spike rates, the novel techniques we present are both more accurate and faster than standard techniques.     

Preparation of malvalic and sterculic acid methyl esters from Bombax munguba and Sterculia foetida seed oils

A method has been developed for the preparation of highly pure malvalic (cis-8,9-methyleneheptadec-8-enoic) and sterculic (cis-9,10-methyleneoctadec-9-enoic) acid methyl esters starting from Bombax munguba and Sterculia foetida seed oils. The methyl esters of these oils were prepared by sodium methylate-catalyzed transmethylation followed by cooling (6°C) the hexane solution of crude methyl esters and separation of insoluble fatty acid methyl esters by centrifugation in the case of B. munguba and by column chromatography in the case of S. foetida. Subsequently, the saturated straight-chain fatty acid methyl esters were almost quantitatively removed by urea adduct formation. Finally, methyl malvalate and methyl sterculate were separated from the remaining unsaturated fatty acid methyl esters, in particular methyl oleate and methyl linoleate, by preparative high-performance liquid chromatography on C₁₈ reversed-phase using acetonitrile isocratically. Methyl malvalate and methyl sterculate were obtained with purities of 95–97 and 95–98%, respectively.     

砝码件的磁性能检验

砝码件的磁性能检验,推荐采用新的OIML R111规程。所以,应考虑的一些知识是砝码件不再仅仅是几何尺寸方面的要求,而且也应考虑所用砝码材料的密度和表面质量。更确切地说,大量科学试验已证明,必须考虑到砝码件的敏感性与磁化。