Low cycle fatigue of MAR-M 200 single crystals at 760 and 870 deg C

Fully reversed low cycle fatigue tests were conducted on single crystals of the nickel-base superalloys Mar-M 200 at 760 C and 870 C. At 760 C, planar slip (octahedral) lead to orientation-dependent strain hardening and cyclic lives. Multiple slip crystals strain hardened the most, resulting in relatively high stress ranges and low lives. Single slip crystals strain hardened the least, resulting in relatively low stress ranges and higher lives. A preferential crack initiation site which was related to slip plane geometry was observed in single slip orientated crystals. At 870 C, the trends were quite different, and the slip character was much more homogeneous. As the tensile axis orientation deviated from 001 , the stress ranges increased and the cyclic lives decreased. Two possible mechanisms were proposed to explain the behavior: one is based on Takeuchi and Kuramoto's cube cross-slip model, and the other is based on orientation-dependent creep rates

ARBAC Policy for a Large Multi-National Bank

Administrative role-based access control (ARBAC) is the first comprehensive administrative model proposed for role-based access control (RBAC). ARBAC has several features for designing highly expressive policies, but current work has not highlighted the utility of these expressive policies. In this report, we present a case study of designing an ARBAC policy for a bank comprising 18 branches. Using this case study we provide an assessment about the features of ARBAC that are likely to be used in realistic policies

Anisotropic constitutive modeling for nickel base single crystal superalloy Rene N4 at 982 C

A back stress/drag stress constitutive model based on a crystallographic approach to model single crystal anisotropy is presented. Experimental results demonstrated the need for the back stress variable in the inelastic flow equations. Experimental findings suggested that back stress is orientation dependent and controls both strain hardening and recovery characteristics. Due to the observed stable fatigue loops at 1800 F, drag stress is considered constant for this temperature. The constitutive model operated with constraints determined only from tensile data was extensively tested from simple tensile and fatigue to complicated strain hold tests. The model predicted very well under those conditions

Construction and Reactivity Screening of a Surface Composition Gradient for Combinatorial Discovery of Electro-Oxidation Catalysts

Materials possessing gradients in composition or structure are of interest for a range of applications, including the construction of functionally graded structural materials, as novel sensor and actuator platforms, and to control the site-specific binding of proteins and cells on surfaces. Gradients can also be used as sample libraries for combinatorial materials discovery that present an extremely dense sample set

The structure and optical behaviour of iridescent agate

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A Multi-electrode Electrochemical and Scanning Differential Electrochemical Mass Spectrometry Study of Methanol Oxidation on Electrodeposited PtxRuy

Methanol electro-oxidation was studied on a series of electrodeposited PtxRuy catalysts constructed as multielement band electrodes. A combination of electrochemical and scanning differential electrochemical mass spectrometry measurements were performed to evaluate the composition-dependence of methanol oxidation, methanol decomposition, CO2 current efficiency, and the product distribution at 25 and 50 °C. At 25 °C, cyclic voltammetry revealed that the presence of Ru led to enhanced methanol oxidation rates over that of pure Pt. Methanol decomposition showed a similar composition-dependence. Mass spectrometry measurements revealed the evolution of HCOOH and CO2 during methanol oxidation and allowed indirect determination of H2CO produced. Notably, these products were not observed during methanol decomposition. The most active electrode compositions and the highest instantaneous current efficiencies for the formation of CO2 were found to depend on several factors. At 25 °C, the maximum activity was 10% Ru, while at 50 °C the most active composition increased to 25% Ru. Pure Pt had the highest instantaneous current efficiency for CO2 at both temperatures. The product distribution reflected high CO2 evolution for Pt, with an increasing fraction of the product emerging as H2CO at higher Ru content. Increasing the temperature improved the CO2 current efficiency for all electrode compositions. These results confirm that methanol oxidation occurs though a parallel reaction pathway on PtxRuy electrodes. In addition, the balance between the different reaction pathways depends on several factors, including Ru composition and temperature

Developments and achievements in atmospheric sciences and space meteorology in India

Space research in India began in the early sixties, with the establishment of the Thumba Equatorial Rocket Launching Station. Indigenously developed rocket payloads were carried in foreign rockets and flown for studying various atmospheric parameters, which are unique to the tropics. In the seventies, Indian-made rockets became available. Since then, there has been rapid progress in the technical advancement, which helped the atmospheric scientists in taking up more challenging and contemporary problems, related to mesospheric winds, ionospheric irregularities, stratospheric ozone, role of aerosols in atmospheric radiative transfer, etc. India entered into the satellite era in 1975, with the development of the Aryabhatta satellite, the first Indian experimental satellite, followed by Bhaskara-1 in 1979, which carried a microwave radio meter for retrieval of atmospheric water vapour and cloud liquid water contents. Since then, there have been several satellites, such as the INSAT series for meteorology and communication, Indian Remote Sensing (IRS) satellite series, and Stretched Rohini Satellite System (SROSS) for in situ observation of the ionosphere, which are all built in India and launched from Indian soil. High quality data being obtained from these satellite missions are helping scientists in taking up problems that are of regional and global scales and in studying the changes that are taking place in the earth atmosphere system, in a more holistic way. This paper attempts to provide an overview of the scientific developments and highlights some results

Detection of Sugar-Lectin Interactions by Multivalent Dendritic Sugar Functionalized Single-Walled Carbon Nanotubes

We show that single walled carbon nanotubes (SWNT) decorated with sugar functionalized poly (propyl ether imine) (PETIM) dendrimer is a very sensitive platform to quantitatively detect carbohydrate recognizing proteins, namely, lectins. The changes in electrical conductivity of SWNT in field effect transistor device due to carbohydrate - protein interactions form the basis of present study. The mannose sugar attached PETIM dendrimers undergo charge - transfer interactions with the SWNT. The changes in the conductance of the dendritic sugar functionalized SWNT after addition of lectins in varying concentrations were found to follow the Langmuir type isotherm, giving the concanavalin A (Con A) - mannose affinity constant to be 8.5 x 106 M-1. The increase in the device conductance observed after adding 10 nM of Con A is same as after adding 20 \muM of a non - specific lectin peanut agglutinin, showing the high specificity of the Con A - mannose interactions. The specificity of sugar-lectin interactions was characterized further by observing significant shifts in Raman modes of the SWNT.Comment: 12 pages, 3 figure

Experimental and theoretical evidence for molecular forces driving surface segregation in photonic colloidal assemblies

Surface segregation in binary colloidal mixtures offers a simple way to control both surface and bulk properties without affecting their bulk composition. Here, we combine experiments and coarse-grained molecular dynamics (CG-MD) simulations to delineate the effects of particle chemistry and size on surface segregation in photonic colloidal assemblies from binary mixtures of melanin and silica particles of size ratio (Dlarge/Dsmall) ranging from 1.0 to similar to 2.2. We find that melanin and/or smaller particles segregate at the surface of micrometer-sized colloidal assemblies (supraballs) prepared by an emulsion process. Conversely, no such surface segregation occurs in films prepared by evaporative assembly. CG-MD simulations explain the experimental observations by showing that particles with the larger contact angle (melanin) are enriched at the supraball surface regardless of the relative strength of particle-interface interactions, a result with implications for the broad understanding and design of colloidal particle assemblies