Zweiphasige Mischungen aus Polyamid 6 und Polyäthylen

Polymer blends of polyamide 6 and polyethylene are obtained by application of high shearing forces to the two component polymer melt. No formation of block and of graft copolymers occurs. The polymer blend consists of two separate and mutually incompatible phases of both components, determining its bulk properties. To improve the compatibility of both polymers, experiments were performed to graft polyamide 6 onto polyethylene. It could be shown that polyethylene modified with maleic anhydride was especially suited for this purpose. Polyamide 6 chains could be grafted onto this modified polyethylene by anionic polymerization. The mechanical properties of a mixture of the graft copolymer with polyamide 6 are significantly better than those of a mere polyamide-6-polyethylene blend. This improvement is attributed to a greater homogenity of the two phase mixture if the graft copolymer is added.     

Theoretical calculations and performance results of a PZT thin film actuator

High piezoelectric coupling coefficients of PZT-based material systems can be employed for actuator functions in micro-electro-mechanical systems (MEMS) offering displacements and forces which outperform standard solutions. This paper presents simulation, fabrication, and development results of a stress-compensated, PZT-coated cantilever concept in which a silicon bulk micromachining process is used in combination with a chemical solution deposition (CSD) technique. Due to an analytical approach and a finite element method (FEM) simulation for a tip displacement of 10 /spl mu/m, the actuator was designed with a cantilever length of 300 /spl mu/m to 1000 /spl mu/m. Special attention was given to the Zr/Ti ratio of the PZT thin films to obtain a high piezoelectric coefficient. For first characterizations X-ray diffraction (XRD), scanning electron microscopy (SEM), hysteresis-, current-voltage I(V)and capacitance-voltage C(V)-measurements were carried out.     

Indirect measuring of crack growth by means of a key-curve-method in pre-cracked Charpy specimens made of nodular cast iron

The determination of dynamic crack resistance curves from single specimen fracture tests requires information about the crack advance during the experiment. Here, attention is focused on crack resistance curves for nodular cast iron based on experimental data from instrumented Charpy tests. In order to estimate the actual crack length a key curve method (KCM) is employed. On the other hand, the Charpy impact tests were realized numerically using finite element calculations in conjunction with a continuum damage model (CDM) to simulate ductile crack growth. The parameters of the CDM model were determined from the experimental data of single specimen fracture tests. Equivalence between the experimental and the numerical realization of a fracture test was ensured by validating the predictions of the numerical simulations by means of low blow fracture tests. Comparison between the crack advance predicted by the numerical simulations and the results obtained using the proposed KCM shows a sufficiently well agreement with the actual crack length. Furthermore, crack resistance curves obtained from single specimen tests using either standard estimation schemes in conjunction with the KCM or numerical simulations are compared with the predictions based on low blow fracture tests.     

Systematic pattern selection using pattern language grammars and design space analysis

Software patterns provide reusable solutions to recurring design problems in a particular context. The software architect or designer must find the relevant patterns and pattern languages that need to be considered, and select the appropriate patterns, as well as the best order to apply them. If the patterns and pattern languages are written by multiple pattern authors, it might be necessary to identify interdependencies and overlaps between these patterns and pattern languages first. Out of the possible multitude of patterns and pattern combinations that might provide a solution to a particular design problem, one fitting solution must be selected. This can only be mastered with a sufficient expertise for both the relevant patterns and the domain in which they are applied. To remedy these issues we provide an approach to support the selection of patterns based on desired quality attributes and systematic design decisions based on patterns. We propose to formalize the pattern relationships in a pattern language grammar and to annotate the grammar with effects on quality goals. In a second step, complex design decisions are analyzed further using the design spaces covered by a set of related software patterns. This approach helps to systematically find and categorize the appropriate software patterns—possibly even from different sources. As a case study of our approach, we analyze patterns from a pattern language for distributed object middleware. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of temporal aggregation on multiple time series in the frequency domain

The effect of temporal aggregation on bivariate spectral measures is investigated. First, the low‐frequency regression coefficient turns out to be invariant under aggregation irrespective of differencing, with the exception of when the aggregation of flow and stock variables is combined. Second, the long‐run squared coherency is invariant with respect to aggregation irrespective of differencing. Third, for frequencies different from zero, limiting results for a growing aggregation level m are obtained equal to those at frequency 0 of the underlying basic series. Hence, all frequency domain information is distorted by aggregation apart from the long‐run one. This also holds true for the phase angle that always approaches zero with growing aggregation level m. The sole exception to these findings is the case of the skip sampling stationary series. Moreover, for finite aggregation level, one may exactly quantify the aggregational effect on each cycle of interest. Numerical examples illustrate our results.     

Fabrication of vertically aligned single-walled carbon nanotubes in atmospheric pressure non-thermal plasma CVD

A fabrication technique of high-purity vertically aligned single-walled carbon nanotubes (VA-SWCNTs) using atmospheric pressure plasma enhanced chemical vapor deposition is presented. Although densely mono-dispersed Fe-Co catalysts of a few nanometers is primarily responsible for VA-SWCNT growth, carbon precipitation was virtually absent in the thermal CVD regime at 700 °C. On the other hand, high-purity VA-SWCNTs without measurable defects were grown at 4 μm min⁻¹ by applying atmospheric pressure radio-frequency discharge (APRFD) which has been previously developed for this purpose. The results proved that cathodic ion sheath adjacent to the substrates, where a large potential drop exists, also plays an essential role for the controlled growth of SWCNTs, while ion damage to the VA-SWCNTs is inherently avoided due to high collision frequency among molecules in atmospheric pressure. Operation regime of APRFD and tentative reaction mechanisms for VA-SWCNT growth are discussed along with optical emission spectroscopy of near substrate region.