Numerical and analytical calculation of the orthotropic heat transfer properties of fibre reinforced materials

This paper is on the investigation of the orthotropic heat transfer properties of unidirectional fibre reinforced materials. The orthotropic effective thermal conductivity of such composite materials is investigated based on two different approaches: the finite element method as a representative for numerical approximation methods and an analytical method for homogenised models based on the solution of the respective boundary value problem. It is found that fibre reinforced composites possess strong orthotropic heat transfer properties, which are getting more distinctive with increasing deviation of the thermal conductivities of matrix and reinforcements. Furthermore, the effect of small perturbations of the periodic configuration of fibres in the matrix on the thermal conductivity is investigated.     

The impact of young drivers’ lifestyle on their road traffic accident risk in greater Athens area

Young drivers (18–24) both in Greece and elsewhere appear to have high rates of road traffic accidents. Many factors contribute to the creation of these high road traffic accidents rates. It has been suggested that lifestyle is an important one. The main objective of this study is to find out and clarify the (potential) relationship between young drivers’ lifestyle and the road traffic accident risk they face. Moreover, to examine if all the youngsters have the same elevated risk on the road or not. The sample consisted of 241 young Greek drivers of both sexes. The statistical analysis included factor analysis and logistic regression analysis. Through the principal component analysis a ten factor scale was created which included the basic lifestyle traits of young Greek drivers. The logistic regression analysis showed that the young drivers whose dominant lifestyle trait is alcohol consumption or drive without destination have high accident risk, while these whose dominant lifestyle trait is culture, face low accident risk. Furthermore, young drivers who are religious in one way or another seem to have low accident risk. Finally, some preliminary observations on how health promotion should be put into practice are discussed.     

Approximation Algorithms for 3D Orthogonal Knapsack

We study non-overlapping axis-parallel packings of 3D boxes with profits into a dedicated bigger box where rotation is either forbidden or permitted, and we wish to maximize the total profit. Since this optimization problem is NP-hard, we focus on approximation algorithms. We obtain fast and simple algorithms for the non-rotational scenario with approximation ratios 9 ε and 8 ε , as well as an algorithm with approximation ratio 7 ε that uses more sophisticated techniques; these are the smallest approximation ratios known for this problem. Furthermore, we show how the used techniques can be adapted to the case where rotation by 90° either around the z-axis or around all axes is permitted, where we obtain algorithms with approximation ratios 6 ε and 5 ε , respectively. Finally our methods yield a 3D generalization of a packability criterion and a strip packing algorithm with absolute approximation ratio 29/4, improving the previously best known result of 45/4.     

Corrosion of yttria-fully stabilized zirconias in molten fluorides

Yttria-fully stabilized zirconia ceramics were manufactured from home-made and commercially available powders and were sintered under different conditions. The ceramics were immersed in the corrosive environment of molten LiF, NaF, KF (FLINAK) eutectic for up to 360 h from 700–900 °C. The changes caused in the crystal structure were probed with laser Raman spectroscopy and X-ray diffraction. The degree of corrosion (phase transformation) depends on immersion period, FLINAK temperature, and ceramics microstructure. From the tested ceramics, ZrO₂-8 mol % Y₂O₃ with a grain size larger than 8 μm and having zero open porosity, exhibits the best resistance to the corrosive influence of FLINAK.     

Grenzen des Wachstums?

Limits of Growth? Discussions on the environmental politics are dominated by theories on the downfall of the earth, which were proclaimed in the Club of Rome and further elaborated by extremists like Gruhl and others. According to them, the human beings are moving towards calamity, if the highly developed industrial nations do not radically change their economical and living habits at the last moment. The expansion of industry accompanied by stress on the nature, excessive exploitation of unreplacable raw materials and energy sources, explosive increase of world population along with inadequate production of foods are, according to the Club of Rome and its interpreters, the causes of the approaching global catastrophy. Statistical estimates, which are supposed to support these theories, are no longer valid and partly contradicted by other developments. The basis of such estimates is also wrong because they consider the reserve of raw material and agricultural land as constant but represent the utilization in an exponential manner without taking into account the flow of new inventions and regular increase of agricultural production. The theories of the Club of Rome are spiritual armaments of radical environmental protection fanatics who wish to change the existing system. They oppose the principles of free economy and free society.     

Note on the ill-conditioned eigenvalue problem in elastic vibrations

Two cases which could cause ill-conditioning of the lower modes and frequencies of an undamped elastic structure are discussed. The first case is when rigid body motions are connected to a relatively small moment of inertia. The second case is when the stiffness matrix is ill-conditioned with respect to the solution of linear equations. It is shown that the first kind of ill-conditioning is not serious provided that an appropriate method of computation is used. The second kind, which is more common and more serious, is dealt with in more detail. It is shown how the results may be improved in various ways by applying the Natural Factor approach of Argyris and Brönlund and computing singular values and vectors.     

Plane longitudinal waves of small amplitude in a nonlinear viscoelastic material

Summary A study of small amplitude, plane, longitudinal waves in a nonlinear, viscoelastic material is presented. The mechanical behavior of the material is described by the use of state variables and the associated differential equations. In particular, we examine the response of a half-space of viscoelastic material which is subjected to a small constant velocityu(0,t)=, 1 at the surface of the halfspace for timet>0. This behavior is analyzed by the use of matched asymptotic expansions in the plane of characteristic coordinates. With the use of these matched asymptotic expansions, the nature of the waves in the near and far fields are discussed. A particular advantage of this method is that wave velocities in the far field can be corrected to second and higher orders. We show that the far field wave is a steady state wave to first order, but that its higher order behavior is transient.

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Ebene Longitudinalwellen kleiner Amplitude in einem nichtlinearen viskoelastischen Werkstoff

Zusammenfassung Eine Untersuchung der im Titel genannten Wellen wird angegeben. Das mechanische Verhalten des Werkstoffes wird unter Verwendung innerer Zustandsvariablen durch Differentialgleichungen beschrieben. Insbesondere untersucht wird das Verhalten eines Halbraumes aus viskoelastischem Material, dessen Oberfläche sich für Zeitent>0 mit einer kleinen konstanten Geschwindigkeitu(0,t)=, 1, bewegt. Das Verhalten wird untersucht unter Verwendung von asymptotischen Entwicklungen in der Ebene der charakteristischen Koordinaten. Dadurch wird die Art der Wellen im Nah- und Fernfeld erläutert. Eine besonderer Vorteil dieser Methode ist die Möglichkeit von Korrekturen zweiter und höherer Ordnung beim Fernfeld. Gezeigt wird, daß die Fernfeldwelle erster Ordnung stationär ist, nicht jedoch die höherer Ordnung.

     

Widely tunable narrow linewidth erbium doped fibre ring laser

An erbium doped fibre ring laser enabling singlemode operation over a continuous wavelength tuning range of 44 nm (1528 nm-1572 nm) with laser linewidths of less than 10 kHz is reported.<>