Tensile Fracture Toughness Measurements in Ceramics

A novel procedure is outlined whereby fracture toughness values for ceramics can be measured under uniaxial tension (mode I) in specimens containing a fatigue crack. Circumferentially notched rods of rapolycrystalline aluminum oxide were precracked in cyclic compression to introduce a fatigue crack at room temperature, following the technique proposed by Suresh and co-workers.^7,10,11 Subsequently, the precracked rods were fractured in pure tension. Highly reproducible values of fracture toughness were obtained using this method.     

Compressed Multiresolution Hierarchies for High‐Quality Precomputed Shadows

The quality of shadow mapping is traditionally limited by texture resolution. We present a novel lossless compression scheme for high‐resolution shadow maps based on precomputed multiresolution hierarchies. Traditional multiresolution trees can compactly represent homogeneous regions of shadow maps at coarser levels, but require many nodes for fine details. By conservatively adapting the depth map, we can significantly reduce the tree complexity. Our proposed method offers high compression rates, avoids quantization errors, exploits coherency along all data dimensions, and is well‐suited for GPU architectures. Our approach can be applied for coherent shadow maps as well, enabling several applications, including high‐quality soft shadows and dynamic lights moving on fixed‐trajectories.     

Clip art rendering of smooth isosurfaces

Clip art is a simplified illustration form consisting of layered filled polygons or closed curves used to convey 3D shape information in a 2D vector graphics format. This paper focuses on the problem of direct conversion of smooth surfaces, ranging from the free-form shapes of art and design to the mathematical structures of geometry and topology, into a clip art form suitable for illustration use in books, papers and presentations.We show how to represent silhouette, shadow, gleam and other surface feature curves as the intersection of implicit surfaces, and derive equations for their efficient interrogation via particle chains. We further describe how to sort, orient, identify and fill the closed regions that overlay to form clip art. We demonstrate the results with numerous renderings used to illustrate the paper itself.     

Strength properties and density of SO2 polluted spruce wood

2 pollution during approximately 1935 and 1992 respectively, was studied as to its mechanical properties (fracture toughness, acoustic emission (AE)) as well as its density and annual ring width changes. Earlywood and latewood width and density were measured with X-ray densitometry equipment. The mechanical tests were performed with specimens taken from the same trees using the wedge splitting technique. Using notched, rectangularly shaped specimens, the experiments allowed to determine the notch-tensile strength σ_NTS of each yearring in RL orientation separately by differentiating earlywood and latewood. The results show clear correlations between earlywood density and notch-tensile strength, good, inverse correlation to some extent between ring width and σ_NTS and also between AE emission activity and earlywood width for the less polluted trees. Data scattering with resulting less pronounced trends was found for all parameters measured for the more severely polluted trees. The results and correlations allow assuming that σ_NTS is influenced by the SO₂ pollution to some extent via treering growth (ring width) and density. The results point to a more pronounced influence of SO₂ pollution between approximately 1970 and 1985 than before that time, and a subsequent recovery of the tested wood properties in the trees that had survived this period.

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2 -belastet war, wurde auf seine mechanischen Eigenschaften und auf seine Dichte und Jahrringbreite hin untersucht. Früh- und Sp?tholzbreite und Dichte wurden mittels R?ntgendensitometrie, die mechanischen Eigenschaften mittels Keilspaltverfahren bestimmt. Durch die Verwendung von rechteckigen, gekerbten Proben lie? sich die Kerbzugfestigkeit σ_NTS jedes Jahrrings in RL-Orientierung bestimmen. Die Resultate zeigen einen klaren Zusammenhang zwischen Frühholzdichte und Kerbzugfestigkeit sowie einen gewissen inversen Zusammenhang zwischen Jahrringbreite und Kerbzugfestigkeit bzw. Schallemissionsaktivit?t und Frühholzbreite für die wenig gesch?digten B?ume. Bei den st?rker gesch?digten B?umen war die Streuung der Me?werte deutlich h?her und die Abh?ngigkeiten schw?cher ausgepr?gt. Die Resultate und Zusammenh?nge deuten darauf hin, da? die Kerbzugfestigkeit durch die SO₂ Belastung über den Jahrringwuchs (Jahrringbreite) und die Dichte beeinflu?t wird. Die Resultate zeigen einen st?rkeren Einflu? der SO₂ Belastung zwischen 1970 und 1985 und deuten auf eine Erholung in den Holzeigenschaften bei jenen B?umen, die diese Periode überlebt haben, hin.

     

A Difference Reference Voltage Buffer for ΔΣ-Converters

An open loop architecture for a reference voltage buffer in -converters is presented to achieve fast-settling, since the settling time of the references plays an important role in the global performance of sampled data converters. This design has been tested on a 2-1 -converter with an on-chip bandgap reference increasing the input related dynamic range up to 93.4 dB for a bandwidth of 99 kHz.     

Fluid-Induced Seismicity: Theory, Modeling, and Applications

Operations including borehole fluid injections are typical for exploration and development of hydrocarbon or geothermic reservoirs. Microseismicity occurring during such operations has a large potential for understanding physics of the seismogenic process as well as in obtaining detailed information about reservoirs at locations as far as several kilometers from boreholes. We propose that the phenomenon of microseismicity triggering by borehole fluid injections is related to the process of the Frenkel–Biot slow wave propagation. In the low-frequency range (hours or days of fluid injection durations) this process reduces to the pore-pressure diffusion. We search for diffusion-related features of induced microseismicity. Two types of such signatures are considered. The first one is related to the geometry of microseismic clouds. Another type of signature is related to the probability of microearthquakes. On this basis we introduce a concept for interpretation of microseismic data which provides a possibility to infer information about hydraulic properties of rocks. Such information can be of significant importance for industrial applications and for understanding physical properties of geological structures.     

Wear Mechanisms of Chromia Refractories in Slagging Gasifiers

The hot-face refractory lining is a key component of gasification systems. The refractory liner protects the gasification system from the high-temperature corrosive gaseous and from the molten slag environment associated with the conversion of carbon feedstocks. This paper will discuss the effect of gasifier operating conditions and carbon feedstock slag/ash chemistry on the refractory service life. Particular attention is focused on the wear mechanism of chromia refractories, determined through postmortem analysis of spent refractory bricks from service in gasifiers. Also presented is the behavior of a phosphate-containing chromia refractory with improved resistance to structural spalling.