Zur statistik des einbaus einer als regler in polyamid 12 verwendeten aliphatischen dicarbonsäure

As hard blocks in polyether block amides, polyamides are used whose length is intensively regulated by dicarboxylic acids. Since, with regard to melting and crystallization behaviour, this acid constitutes an interfering structural unit in the chain, and in the case of a completely converted product each chain contains one acid molecule, it is essential to know where in the chain incorporation will occur. As opposed to monofunctional chain regulators which always form a chain end, a bifunctional chain regulator can a priori also be randomly incorporated into the inner part of the chain. This leads to a far greater interference than occurs if the chain regulator molecule and the chain end, which acts as an interfering unit in any case, coincide with each other. By means of adipic acid-regulated oligoamides based on lauryl lactam, the incorporation of the chain regulator was examined by NMR spectroscopy and compared with model calculations. This resulted in a close match only if it was presupposed that the incorporation was carried out randomly with the same degree of probability at any point whatsoever between two lauryl lactam structural units or at the chain end. Further calculations illustrate the effects of the incorporation of the chain regulator on the size of the amorphous portion.     

Effect of friction,strain hardening,and strain rate hardening on the metal flow in rod extrusion

The metal flow in a rod extrusion is theoretically discussed in relation to a frictional condition, strain hardening and strain rate hardening. An existing rigid plastic FEM-program was modified in order to take a rate sensitivity of a material into consideration through a constitutive equation of the form. An interfatial friction was incorporated by a constant Coulomb-frictional coefficient. When the frictional coefficient is smaller than 0.1, a large effect of the friction does not appear. The larger the n-value is, the stronger the distortion of the grid in a billet becomes even under small frictional resistance. The effect of the m-value is similar qualitatively to that of the n-value. When the rate sensitive material is extruded at very low punch speed under large frictional resistance, the material is strained very irregularly all over the billet at an early stage.     

A Version Space Approach to Learning Context-free Grammars

In principle, the version space approach can be applied to any induction problem. However, in some cases the representation language for generalizations is so powerful that (1) some of the update functions for the version space are not effectively computable, and (2) the version space contains infinitely many generalizations. The class of context-free grammars is a simple representation that exhibits these problems. This paper presents an algorithm that solves both problems for this domain. Given a sequence of strings, the algorithm incrementally constructs a data structure that has nearly all the beneficial properties of a version space. The algorithm is fast enough to solve small induction problems completely, and it serves as a framework for biases that permit the solution of larger problems heuristically. The same basic approach may be applied to representations that include context-free grammars as special cases, such as And-Or graphs, production systems, and Horn clauses.     

A monotonic projective algorithm for fractional linear programming

We demonstrate that Karmarkar's projective algorithm is fundamentally an algorithm for fractional linear programming on the simplex. Convergence for the latter problem is established assuming only an initial lower bound on the optimal objective value. We also show that the algorithm can be easily modified so as to assure monotonicity of the true objective values, while retaining all global convergence properties. Finally, we show how the monotonic algorithm can be used to obtain an initial lower bound when none is otherwise available.     

Stabilization of polyacetals

A brief introduction describes the main differences between homo, and copolymer polyacetals and their main degradation mechanisms. A short overview describes the importance of stabilization and the necessity of using antioxidants and costabilizers during manufacturing, processing and end use of polyoxymethylene(polyacetals). Various stabilizer systems are presented and studies on the interaction of antioxidants with costabilizers added. The criteria for testing the performance of these additives are discussed and demonstrated by many examples. In a second part the increasing importance of light stabilized polyacetal is mentioned and investigations on the performance of light stabilizer systems are highlighted.     

Isotropic Constitutive Model for Sintering Particle Packings

This paper presents an isotropic model for the effective viscosities of sintering particle packings. The relationship between the macroscopic stress and deformation rate is based on the behavior of individual interparticle contacts, represented by contact viscosities, and the statistics of the packing. The contact viscosities depend on the contact area, which is the primary variable used to describe the state of the packing. A direct consequence of this choice of state variable is that the effective viscosities are identically zero for an undeformed and unsintered packing. Specific results are presented for the case of Newtonian viscous materials. The model is compared with existing models for porous Newtonian viscous materials. Experiments conducted with spherical glass powder packings show good agreement with the model. Finite-element simulations using the model have been used to study forging of a pellet.     

Construction and test of a cryocooler-cooled low-Tc SQUID gradiometer system

A cryocooler-cooled low-Tc SQUID gradiometer system was designed and constructed. It is based on a 4 K GM-cooler that is positioned several meters from the measuring head containing the SQUID sensors. The cooling power is transported by means of a circulating helium flow. Thus, there are three main components: the cooler vessel, the measuring head and the connecting flow-line.In stable operation, the SQUID and gradiometric pick-up loop are about 4.3 K. The overall heat loads to the cooler 1st and 2nd stages are estimated at 17 W and 0.3 W, respectively. The overall system noise was about 10 fT/√Hz although a number of peaks were observed in the spectrum. As an example, an adult heart beat was recorded.