Numerische Simulation von Temperaturgradienten und thermisch induzierten Eigenspannungen in Natursteinplatten infolge von Sonneneinstrahlung

The interaction between micro-organisms and natural stone surfaces has been studied in great detail in the past. The destructive mechanisms of micro-organisms can be roughly subdivided into (a) chemical attack and (b) physical attack. Microorganisms may physically destroy the structure of stones by creating an inter-granular swelling pressure. Recently, it has been shown experimentally that black spots formed by yeast-like fungi lead to a local temperature increase by selective absorption of solar radiation. The maximum temperature observed for clean marble surfaces remained below the maximum temperature observed on inoculated surfaces. As a consequence, thermal dilatation of inoculated marble was shown to be more important. Destruction of the heated stone occurs predominantly if there exists a thermal gradient. In this paper, temperature distribution in clean and stained marble plates have been simulated numerically. Thermal eigenstresses have been determined. It is shown that tensile stresses of up to 5 N/mm2 can be expected. This may cause damage in weak zones of the surface. A sudden driving rain leads to much higher stresses. Cyclic thermal loading may eventually destroy the surface by fatigu

Energy levels and decoherence properties of single electron and nuclear spins in a defect center in diamond

The coherent behavior of the single electron and single nuclear spins of a defect center in diamond and a 13C nucleus in its vicinity, respectively, are investigated. The energy levels associated with the hyperfine coupling of the electron spin of the defect center to the 13C nuclear spin are analyzed. Methods of magnetic resonance together with optical readout of single defect centers have been applied in order to observe the coherent dynamics of the electron and nuclear spins. Long coherence times, in the order of microseconds for electron spins and tens of microseconds for nuclear spins, recommend the studied system as a good experimental approach for implementing a 2-qubit gate.Comment: 4 pages, 4 figure

Reinventing College Physics for Biologists: Explicating an epistemological curriculum

The University of Maryland Physics Education Research Group (UMd-PERG) carried out a five-year research project to rethink, observe, and reform introductory algebra-based (college) physics. This class is one of the Maryland Physics Department's large service courses, serving primarily life-science majors. After consultation with biologists, we re-focused the class on helping the students learn to think scientifically -- to build coherence, think in terms of mechanism, and to follow the implications of assumptions. We designed the course to tap into students' productive conceptual and epistemological resources, based on a theoretical framework from research on learning. The reformed class retains its traditional structure in terms of time and instructional personnel, but we modified existing best-practices curricular materials, including Peer Instruction, Interactive Lecture Demonstrations, and Tutorials. We provided class-controlled spaces for student collaboration, which allowed us to observe and record students learning directly. We also scanned all written homework and examinations, and we administered pre-post conceptual and epistemological surveys. The reformed class enhanced the strong gains on pre-post conceptual tests produced by the best-practices materials while obtaining unprecedented pre-post gains on epistemological surveys instead of the traditional losses.Comment: 35 pages including a 15 page appendix of supplementary material

Failure of Dam concrete subjected to seismic Loading Conditions

e numerical simulation of concrete dams subjected to earthquake loading requires realistic material laws which take into account seismic loading conditions. Dynamic tests were performed in order to examine the effect of initially applied compressive loading on material properties of a dam concrete at high tensile deformation rates. The test results show that no important fracture property is reduced at high deformation rates; the tensile strength and the specific fracture energy GF show a high rate sensitivity. However, dynamic compressive pre-loading leads to a reduction of the fracture properties at both quasi-static and high deformation rates