Managing the complexity of digital terrain models

Today, the surface of our planet can be sampled extremely accurately. Also, the need for information about the topography within specified regions becomes increasingly important in geographic information systems. Meaning can often only be extracted from certain data in combination with the digital terrain models. In particular, visualization techniques and image mapping methods in geographic information systems require this kind of information. And now there are very densely sampled grids of height data available—too dense in many areas of the terrain, since most sampling techniques are nonadaptive.

We have developed algorithms to cope with the complexity of such digital terrain models. They analyze each given model and reduce the number of points while preserving the accuracy as good as possible. In our research, we compared three basic approaches and implemented methods to minimize emerging errors. This paper describes the necessary steps for reducing regularly sampled height grids or given triangular meshes to meet specified quality or quantity criteria.     

Modelling of the deformation behaviour of FGM by fuzzy-logic

A lot of processes for the manufacture of functionally gradient materials (FGM) have their limitations (simple geometry of components, gradient limited in one dimension). A further treatment by forming processes would extend the field of applications of FGM because it would make it possible to manufacture shaped pieces and to influence the properties of the material.

For this it is necessary to predetermine the deformation behaviour by mathematical models. Conventional equations have only limited applications because many other influences have to be considered.

Therefore a new model based on mathematical methods of fuzzy-logic has been developed which can describe the plasto-mechanical behaviour of FGM during the deformation process. The main advantages are:

• no necessity to represent the mathematical equation between in- and output variables by functions;

• adaptable algorithms;

• almost no restriction of the number of influencing variables;

• simple solution of multi-dimensional approximation problems.

Experiments to determine the deformation behaviour have been carried out on different material systems (Al–Cu, 316L–430L, Al–SiC) by using the hot upsetting test. First results show that this kind of modelling is suitable to describe the deformation behaviour very accurately.     

High-speed phosphor thermometry

Phosphor thermometry is a semi-invasive surface temperature measurement technique utilising the luminescence properties of doped ceramic materials. Typically, these phosphor materials are coated onto the object of interest and are excited by a short UV laser pulse. Up to now, primarily Q-switched laser systems with repetition rates of 10 Hz were employed for excitation. Accordingly, this diagnostic tool was not applicable to resolve correlated temperature transients at time scales shorter than 100 ms. This contribution reports on the first realisation of a high-speed phosphor thermometry system employing a highly repetitive laser in the kHz regime and a fast decaying phosphor. A suitable material was characterised regarding its temperature lifetime characteristic and its measurement precision. Additionally, the influence of laser power on the phosphor coating was investigated in terms of heating effects. A demonstration of this high-speed technique has been conducted inside the thermally highly transient system of an optically accessible internal combustion engine. Temperatures have been measured with a repetition rate of 6 kHz corresponding to one sample per crank angle degree at 1000 rpm.     

Surface modeling and chemical solution deposition of SrO(SrTiO3)n Ruddlesden–Popper phases

Strontium titanate (STO) is a preferred substrate material for functional oxide growth, whose surface properties can be adjusted through the presence of Ruddlesden–Popper (RP) phases. Here, density functional theory (DFT) is used to model the (1 0 0) and (0 0 1) surfaces of SrO(SrTiO₃)_n RP phases. Relaxed surface structures, electronic properties and stability relations have been determined. In contrast to pure STO, the near-surface SrO–OSr stacking fault can be employed to control surface roughness by adjusting SrO and TiO₂ surface rumpling, to stabilize SrO termination in an SrO-rich surrounding or to increase the band gap in the case of TiO₂ termination. RP thin films have been epitaxially grown on (0 0 1) STO substrates by chemical solution deposition. In agreement with DFT results, the fraction of particular RP phases n = 1–3 changes with varying heating rate and molar ratio Sr:Ti. This is discussed in terms of bulk formation energy.     

Investigations of deformation of FGM

FGM are marked by a heterogeneous composition changing continuously. Therefore, it must be considered while deformation that different material ranges show different deformation behaviour and that the overall deformation is inhomogeneous. For this reason the graded material was subdivided into a finite number of ranges for the simulation of the deformation behaviour. Homogeneous material behaviour is assumed in these ranges. The yield strengths of the respective homogeneous materials are determined experimentally and then applied as material parameters in the simulation. A simple upsetting of a cylindrical specimen at constant temperature and deformation rate was calculated as an example. The results of the simulation show that, as expected, the material flow is marked differently in various material ranges due to the differing yield strength. This is confirmed by experimental investigations. Differences in the results of simulation and experiments in particular occur in the case of the direct comparison of the geometrical dimensions. This is mainly explained by differing initial microstructures. The comparison of the compression forces shows good agreement between simulation and experiment.     

Geothermal resources in the shallow, unsaturated zone of the Wiesbaden spa district, Germany

The geothermal energy potential of the Wiesbaden spa district continues to be largely untapped. Although the thermal water is being utilized, any other activity liable to disturb the hydraulic regime of the thermal springs is prohibited. The geothermal potential of the unsaturated zone in the spa district has been mapped, although the zone must be regarded as a thermal insulator rather than a good conductor. The results of the mapping revealed the presence of a number of heat anomalies that could be exploited in the future; further economic benefits could be gained from installing the heat transfer units during road works. The modelling studies considered two possible scenarios: direct heating and heat pump usage. The results indicate that heat pumps are the more efficient option, yielding a thermal capacity of approximately 100 W/m².     

A study of the deformation behaviour of veneers resulting from water storage (A methodological approach for determining the swelling characteristic using the example of European beech veneer)

This article discusses the swelling-induced deformation behaviour of veneers. Impregnation tests were performed to assess the influences on the unrestrained deformation of veneers. Among others, the tests focused on a comparison of the swelling-induced deformation in consideration of influences caused by the manufacturing process for different anatomical orientations (tangential or radial veneer). For this, samples of European beech veneer (Fagus sylvatica L.) were measured under a microscope and categorised into groups of tangentially or radially sampled veneers based on the anatomical characteristics. In addition, manufacture-specific damage was documented during the slicing process and also considered for the assessment. As a result of these tests, it was proven that the influence of near-surface damage caused by the manufacture on the unrestrained deformation of veneers was significantly dominant.     

Polyethylene wear particles induce TLR 2 upregulation in the synovial layer of mice

A cellular and receptor mediated response to ultra-high-molecular-weight-polyethylene (UHMWPE) wear particles results in a release of proinflammatory cytokines and induces an inflammatory reaction causing osteolysis in total joint replacement. This investigation offers insight into the toll-like receptor (TLR) mediated activation by polyethylene wear particles in the synovial layer of mice. We hypothesized that, similar to recent in vitro results, UHMWPE particles lead to an upregulation of TLR 1 and 2 and TLR 4 in vivo in the synovial tissue of mice as well. Therefore, UHMWPE particles were generated in a common knee simulator according to the ISO standard, separated by acid digestion and determined by scanning electron microscopy. Endotoxin was removed using a method based on ultracentrifugation. A particle suspension (50 μl; 0.1 vol./vol.%) was injected into the left knee joint of female Balb/c mice (n = 8). In a control group, phosphate-buffered saline was injected into the left knee of Balb/c mice (n = 8). The mice were sacrificed after 7 days. Immunohistochemical staining was performed with TLR 1, 2 and 4 polyclonal antibodies for Balb/c mice and evaluated by light microscopy. The particle-stimulated group showed a thickened synovial layer, an increased cellular infiltration and a TLR 2-upregulation in the synovial layer compared to the control group. An increased expression of TLR 1 and TLR 4 could not be demonstrated. These results indicate a mainly TLR 2-induced inflammation to polyethylene wear debris in the synovial layer of mice.