The Influence of lithophysal porosity on the in-situ stress-strain properties of Topopah Spring Tuff

Numerical analysis and a laboratory testing program were conducted in order to investigate the effect of lithophysal porosity on the elastic stress-strain properties of the lithophysae-rich tuff specimens and to find the locations of cavities in both analog and tuff specimens. In the first part of the study, a finite difference mesh containing circular holes was modeled for varying porosity ranges between 5 and 40% using commercially available software FLAG20\u27 version 3.5. Elastic (Young\u27s) modulus and Poisson\u27s ratio were calculated for each setup and normalized with respect to matrix elastic modulus and Poisson\u27s ratio. The moduli calculated through numerical analysis were compared with those determined by the biaxial testing of urethane cubes containing circular holes extending through the cube that have same sizes and distribution of holes as those numerically analyzed. Correlation between moduli determined through testing and numerical analysis was very good. Secondly, ultrasonic testing was conducted on plaster of Paris specimens containing spherical STYROFOAM® inclusions and tuff specimens to determine the locations of the spherical STYROFOAM® inclusions and lithophysal cavities, respectively. The ultrasonic characterization technique was able to detect numerous inclusions within each plaster and some cavities in most of the tuff specimens. The ultrasound technique could not locate the exact positions and dimensions of STYROFOAM® inclusions in plaster of Paris specimens and cavities in tuff specimens but rather roughly detected such zones in specimens. Thirdly, lithophysal tuff and plaster of Paris specimens containing spherical STYROFOAM® inclusions were tested under uniaxial compression and moduli and compressive strengths were determined. Elastic moduli of plaster specimens were normalized with respect to the matrix modulus of a zero porosity plaster specimen. Similar decreasing trend in modulus with increasing porosity was observed and correlation between each data set was good in most of the porosity values. Fifteen tuff specimens, including five specimens from middle non-lithophysal units, were also tested under uniaxial compression. The compressive strength and elastic modulus values for tuff showed a decreasing trend with increasing porosity. The reason of variations in data is due to heterogeneities and discontinuities within the tuff

Novel regulators of PrPC biosynthesis revealed by genome-wide RNA interference

The cellular prion protein PrPC is necessary for prion replication, and its reduction greatly increases life expectancy in animal models of prion infection. Hence the factors controlling the levels of PrPC may represent therapeutic targets against human prion diseases. Here we performed an arrayed whole-transcriptome RNA interference screen to identify modulators of PrPC expression. We cultured human U251-MG glioblastoma cells in the presence of 64'752 unique siRNAs targeting 21'584 annotated human genes, and measured PrPC using a one-pot fluorescence-resonance energy transfer immunoassay in 51'128 individual microplate wells. This screen yielded 743 candidate regulators of PrPC. When downregulated, 563 of these candidates reduced and 180 enhanced PrPC expression. Recursive candidate attrition through multiple secondary screens yielded 54 novel regulators of PrPC, 9 of which were confirmed by CRISPR interference as robust regulators of PrPC biosynthesis and degradation. The phenotypes of 6 of the 9 candidates were inverted in response to transcriptional activation using CRISPRa. The RNA-binding post-transcriptional repressor Pumilio-1 was identified as a potent limiter of PrPC expression through the degradation of PRNP mRNA. Because of its hypothesis-free design, this comprehensive genetic-perturbation screen delivers an unbiased landscape of the genes regulating PrPC levels in cells, most of which were unanticipated, and some of which may be amenable to pharmacological targeting in the context of antiprion therapies

Structural, thermal and magnetic characterization of nanocrystalline Co65Ti25W5B5 powders prepared by mechanical alloying

In this work, nanocrystalline Co65Ti25W5B5 (at.%) powders were prepared by mechanical alloying (MA) of the elemental powder mixture under argon gas atmosphere. The powders were milled during different periods (2.5, 5, 10, 20 and 30 h) using a planetary ball-mill (Retsch PM100 CM) at 400 rpm. The structural, morphological, thermal and magnetic properties of the nanocrystalline Co65Ti25W5B5 powders were studied by means of X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX), differential thermal analysis (DTA) and vibrating sample magnetometer (VSM) techniques. Because of its high melting point, hardness and low solubility in the alloy components, a small amount of tungsten remained in the amorphous matrix during MA. By using the Williamson-Hall method, the crystallite size and lattice strain of the tungsten phase were calculated as about 25 nm and 0.48% respectively, for 30 h of milling. The DTA curves of the milled powders demonstrated an exothermic peak at about 600 °C, indicating the crystallization of the amorphous phase. The apparent mean activation energy, 303.5 ± 7 kJ/mol for 20 h milled powders was determined by Kissenger and Ozawa methods. The saturation magnetization (Ms), the coercivity (Hc) and the remanence-to-saturation ratio (Mr/Ms), values were of about 66 emu/g, 11 Oe and 0.012 respectively, after 30 h of milling. © 2015 Elsevier B.V

Characterization and amorphous phase formation of mechanically alloyed Co60Fe5Ni5Ti25B5 powders

In this work, the multicomponent Co60Fe5Ni5Ti25B5 (at.%) alloy powders were synthesized from commercially available pure elemental powders by using a mechanical alloying (MA) process under argon gas atmosphere. The changes in structural, morphological, thermal and magnetic properties of the processed powders during MA were examined by X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX), differential thermal analysis (DTA) and vibrating sample magnetometer (VSM). The results showed that the amorphization occurred after 3.5 h of milling, and the amorphous phase was stable up to 580 °C, where crystallization occurred. The SEM observations indicated that different morphologies were obtained during the MA stages. In addition, the EDX mapping confirmed the uniform distribution of elemental content. Magnetic results indicated that all the samples exhibited soft-ferromagnetic behavior. The evolution of the saturation magnetization (Ms), the coercivity (Hc) and the squareness ratio (Ms/Mr) during milling process were discussed with respect to microstructural changes. The influence of the annealing on magnetic hysteresis was also studied. The Ms, Hc and Ms/Mr values of about 53.4 emu/g, 7.6 Oe and 0.01, respectively was obtained after 7 h of milling. © 2015 Elsevier B.V. All rights reserved

Structural evolutions in Ti and TiO2 powders by ball milling and subsequent heat-treatments

In this study, nanocrystalline Ti and TiO2 powders were synthesized by wet milling of Ti powder within water and reactive milling of Ti powder under oxygen atmosphere, respectively. The wet milling processes were performed at 300 rpm milling speed for different milling durations (6, 12, 24, and 48 h). Subsequent heat-treatments of the as-milled powders were performed at 200-800 °C for 1 h in an air atmosphere. Structural characteristics of the as-milled and the heat-treated powders were investigated by X-ray diffraction (XRD). The crystallite size, lattice strain and lattice parameters of the powders were also calculated. It has been realized that during the wet milling process, elemental Ti powder undergoes an hcp to fcc polymorphic transformation, which is related to grain refinement and plastic strain. In addition, TiO 2 powders are produced after heat-treatments at 600 and 800 °C. Reactive milling of the elemental Ti powder in pressurized oxygen atmosphere leads to nanocrystalline TiO2 powders with an average crystallite size of about 10 nm after 48 h milling time. The subsequent heat-treatments of the as-milled TiO2 powders results in the increase of the crystallite size up to 70-150 nm. In order to understand the thermal behavior of the as-milled powders, thermal analysis (DTA) and thermogravimetric analysis (TGA) were employed. The activation energy of the nanocrystalline TiO2 powders was determined by the Kissinger method is 128±3 kJ/mol. © 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.0901-602006We would like to thank Hacettepe University , Scientific Research and Development Office, through the Grant (no. 0901-602006 ) and TUBITAK-BIDEP postdoctoral research fellowship

Earthquake Surface Rupture: A Brief Survey on Interdisciplinary Research and Practice from Geology to Geotechnical Engineering

Coseismic surface ruptures during desctructive earthquakes (1999 Kocaeli–Düzce, Turkey and 1999 Chi-Chi, Taiwan) have caused devastating effects on buildings and infrastructures. Surface rupture remains a complicated phenomenon involving variable movements along near surface traces of both primary and secondary faults. The surface rupture patterns observed in nature, the rupture zone width and the magnitude of the surface rupture displacements, depend on the type of faulting, the earthquake magnitude, the complexities of fault geometry, as well as on the thickness and nature of the materials above bedrock. Surface rupture hazard assessment for determining the width of the surface rupture and rupture displacements magnitudes for civil engineering design needs to be site specific and incorporate various geological and geotechnical investigations. The current research on laboratory and numerical simulations to evaluate the impact of surface rupture on structure foundations is promising. However, it may be misleading to conclude that such models are sufficient to simulate the surface rupture complexities as observed in nature

Porosity dependence of the elastic modulus of lithophysae-rich tuff: Numerical and experimental investigations

The influence of porosity on the mechanical properties of rock has received much research attention. Portions of the Yucca Mountain high-level nuclear waste repository may be placed in tuff units containing lithophysal cavities, which are large, generally noninterconnected cavities that can be considered a form of macroscopic porosity. This paper presents the results of numerical modeling and uniaxial compression testing of analog models and tuff rock, in order to assess the relationships between elastic modulus and porosity. The first part of the paper presents numerical simulation of uniaxial compression testing to calculate the elastic modulus of two-dimensional models containing randomly distributed circular holes in plane strain. The range of porosities investigated is approximately 5–40%. In the second part, the elastic modulus determined from the uniaxial compression testing of analog models and tuff specimens is presented. The analog specimens were made of plaster of Paris containing varying amounts of spherical shaped Styrofoam® inclusions to simulate a cavity structure similar to tuff. The results from the numerical analysis and analog material testing show an exponential decrease in elastic modulus with increasing porosity, whereas the elastic moduli of tuff show a linear decrease. The difference in the two behaviors can be attributed to the nonuniform cavity shapes in the tuff specimens

Nano-sized neodymium hexaboride: Room temperature mechanochemical synthesis

A rapid and easy synthesis of pure neodymium hexaboride, NdB6 nanocrystals was developed, without applying heat treatments at high temperatures. The mechanochemical synthesis of NdB6 powders was performed at room temperature inside a planetary ball mill. The Nd, B2O3 and Mg starting blends were mixed, and subsequently mechanically alloyed to constitute NdB6-MgO as final products. The effect of milling duration on the NdB6 formation mechanism and metallothermic reduction was investigated. Following mechanochemical synthesis, MgO was removed from the system by leaching the powders with CH3COOH solution. The formation of NdB6 phase was monitored by the X-ray diffraction (XRD) analysis. Microstructure and morphology of the synthesized nanocrystals were characterised by using scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDS), and high resolution transmission electron microscopy (HRTEM) techniques. Pure NdB6 nanocrystals with a crystallite size of 18.2 ± 2.0 nm were obtained after 15 h of milling. Microscopic investigations revealed the irregular shape and morphology of NdB6 nanocrystal structures. Rietveld refinements confirm the cubic structure (space group Pm-3m) with a lattice constant of 4.1254 (2) Å and 92 ± 8 nm particle size of NdB6 phase. The Raman active phonons of Pm-3m symmetry were characterised by Raman spectroscopy. © 2019 Elsevier B.V

Compressive strength and failure modes of lithophysae-rich Topopah Spring tuff specimens and analog models containing cavities

The presence of lithophysae in some units of Topopah Spring Tuff at Yucca Mountain, Nevada, the U.S. high level nuclear waste repository, have a detrimental effect on the engineering properties of the rock mass and its performance. The lithophysae were formed by pockets of gas trapped within the falling volcanic ash that formed the tuff units. The porosity associated with the lithophysae is termed macroporosity because of the large pore size as compared with traditional rock pores. In this paper, lithophysae-rich tuff and analog models (both cylindrical and cubic) made of plaster of Paris containing artificially created cavities were tested to assess the effect of macroporosity on both the uniaxial compressive strength and failure modes of the specimens. As expected, compressive strength decreases with increasing porosity due to lithophysae in tuff and cavities in plaster analog specimens. Failure modes of cylindrical specimens were also investigated. The failure modes observed were grouped into four distinct categories: spalling, axial splitting, shear failure and web failure. The failure modes transition from spalling through web failure as the percentage of macroporosity within the specimen increased