Nanoscale fabrication of a three-dimensional stack of graphene layers using a focused ion beam

A top-down nanoscale stack fabrication approach involving the high-precision carving of a stack of graphene layers from a thin graphite flake via focused-ion-beam (FIB) three-dimensional (3D) etching is presented. Using this technology, etching was performed in the c-axis with the height of a few tens of nanometres. By reducing the stack height to 50 nm, a 3D stack of graphene layers coupled in a stacked manner was fabricated. The transport characteristics of the stack in the c-axis were studied and compared with the transport characteristics of the stack with a larger in-plane area and stack height value. The observed conductivity of the nanostack with a 50 nm height was one order smaller than the conductivity of the stack with a larger in-plane area and stack height value. Nonlinear current-voltage (I-V) characteristics were observed in all the studied temperatures, but the stack with a larger in-plane area and stack height value showed nonlinear characteristics only at lower temperatures. The observation of these temperature-dependent I-V characteristics was discussed in detail, and the tunneling characteristics were investigated using the Fowler-Nordheim tunneling model, which showed the best fit to the experiment data in this study.     

Fabrication and characteristics of submicron stacked-junctions on thin graphite flakes

We report on the fabrication and transport characteristics of submicron-size stacks along c-axis of thin graphite flakes. The stacks were fabricated using a three-dimensional focused-ion-beam (FIB) etching technique. The stack with in-plane area A of 0.5 microm2 showed nonlinear concave-like I-V characteristics even at 300 K; however the stack with A of > 0.5 microm2 were shown an ohmic-like I-V characteristic at 300 K for both low and high-current biasing. It turned into nonlinear characteristics when the temperature goes down. The in-plane area dependence of stack capacitance were discussed and the observed capacitance of stack with A of 0.5 microm2 is smaller than the capacitance of stack with A of 1 microm2 which causes the nonlinear I-V characteristics in stack with A of 0.5 microm2 even at 300 K.     

Production and characterization of glycolipid biosurfactant from Streptomyces enissocaesilis HRB1 and its evaluation for biomedical and bioremediation applications

The aim of this investigation is to produce and characterize biosurfactant from Streptomyces sp. HRB1 and to evaluate its biomedical and bioremediation potential. Biosurfactant producing property of Streptomyces sp. HRB1 isolated from petroleum contaminated soil was confirmed by hemolytic and oil spread assays. Based on the results of FT-IR spectral and GC–MS analysis, the biosurfactant was confirmed as glycolipid type. Biosurfactant from Streptomyces sp. HRB1 exhibited 71% inhibition against Pseudomonas aeruginosa biofilm formation, 77.33% quorum sensing inhibition property against Chromobacterium violeceum MTCC 2656, more than 80% inhibition in antioxidant assays namely, DPPH, ABTS, and metal chelation, promising anti-proliferative activity against leukemia and myeloma cells with low IC₅₀ values, 96% decolorization of malachite green within 48 h of reaction time, and minimal toxicity against normal cell lines in dose-dependent manner. The taxonomic position of the potential strain HRB1 was further confirmed as Streptomyces enissocaesilis HRB1 based on their phenotypic and molecular characteristics. To conclude, Streptomyces enissocaesilis HRB1 isolated from petroleum-contaminated soil is a promising source for low-cost production of glycolipid biosurfactant with potential biomedical and environmental applications such as antiphytofungal, antibiofilm, anti-quorum sensing, antioxidant, anticancer, and dye degradation properties.     

Calculation of thermodynamic parameters of U–Pu–N system with carbon and oxygen impurities

Mixed nitride fuels are being considered for advanced FBR, but very little is known about the thermodynamic properties of these fuels. For an overall composition of the nitride fuel with small amounts of oxygen and carbon impurities, thermodynamic properties, e.g. carbon activity and partial pressures of nitrogen, carbon-monoxide, plutonium and uranium, were calculated in present work. These calculations were based on standard Gibbs free energies of the binary compounds, present in this multi-component system (U,Pu)–C–N–O. For an over all composition of the fuel, stable phase-field was determined by minimization of the Gibbs free energy of the system. The fabrication experiences of various workers, reported in literature, have shown that depending on the impurity content, nitride fuel can exist in two phase fields, mono-nitride phase in equilibrium with sesquinitride phase or mono-nitride phase in equilibrium with dioxide phase. Therefore, in present calculations special attention was given to the thermodynamic behavior of these two phase-fields. A comparison of calculated thermodynamic properties indicated that nitride fuel with dioxide as second phase will be superior to the one with sesquinitride.     

Ammoxidation of 3-picoline over V2O5/TiO2 (anatase) system I. Relationship between ammoxidation activity and oxidation state of vanadium

A series of titania (anatase)-supported vanadia catalysts ranging in V₂O₅ content from 0.4 to 9.9 mol% was prepared by wet impregnation technique, characterized by BET surface area measurement and X-ray diffraction, and evaluated for ammoxidation of 3-picoline. The average oxidation number of vanadium in the fresh and used catalysts was determined by titrimetric methods. The ammoxidation activity and the average oxidation number were observed to increase with vanadia loading up to 3.4 mol% in the catalyst which corresponds to a monolayer coverage. The phase transformation of anatase to rutile after the reaction was observed at a V₂O₅ loading of 5.9 mol%. The slow decrease of ammoxidation activity beyond 3.4 mol% V₂O₅ was attributed to the coverage of active monomeric VO_x species on the support by bulk vanadia and by other oxides, and also to compound formation with ammonia.     

High-temperature deformation behavior of coarse- and fine-grained MoSi<Subscript>2</Subscript> with different silica contents

The elevated-temperature deformation behavior of polycrystalline molybdenum disilicide (MoSi₂), in the range of 1000 °C to 1350 °C at the strain rates of 10⁻³, 5×10⁻⁴, or 10⁻⁴ s⁻¹, has been studied. The yield strength, post-yield flow behavior comprising strain hardening and serrations, as well as some of the deformation microstructures of reaction-hot-pressed (RHP) MoSi₂ samples, processed by hot pressing an elemental Mo + Si powder mixture and having a grain size of 5 μm and oxygen content of 0.06 wt pct, have been compared with those of samples prepared by hot pressing of commercial-grade Starck MoSi₂ powder, with a grain size of 27 μm and oxygen content of 0.89 wt pct. While the fine-grained RHP MoSi₂ samples have shown higher yield strength at relatively lower temperatures and higher strain rates, the coarse-grained Starck MoSi₂ has a higher yield at decreasing strain rates and higher temperatures. The work-hardening or softening characteristics are dependent on grain size, temperature, and strain rate. Enhanced dislocation activity and dynamic recovery, accomplished by arrangement of dislocations in low-angle boundaries, characterize the deformation behavior of fine-grained RHP MoSi₂ at a temperature of 1200 °C and above and are responsible for increased uniform plastic strain with increasing temperature. The silica content appears to be less effective in degrading the high-temperature yield strength if the grain size is coarse, but leads to plastic-flow localization and strain softening in Starck MoSi₂. Serrated plastic flow has also been observed in a large number of samples, mostly when deformed at specific combinations of strain rates and temperatures.     

Hydrogen Diffusion and Trapping Effects in Low and Medium Carbon Steels for Subsurface Reinforcement in the Proposed Yucca Mountain Repository

The electrochemical hydrogen permeation method was used to investigate hydrogen transport, trapping characteristics of low (0.08 pct C) and medium carbon (0.44 pct C) steels proposed for the Yucca Mountain (YM) repository environment. The presence of relatively high amounts of C, Mn, and S increased the density of trapping sites in medium carbon steel. The measured diffusivity of medium carbon steel was lower than that of the low carbon steel due to increased trapping of hydrogen at irreversible sites in the medium carbon steel. Hydrogen concentration values obtained for low carbon steels in YM ground water electrolytes indicate that increased ionic concentration decreases the uptake of hydrogen. The decrease in hydrogen permeation were due the formation of CaCO₃ corrosion products on the surface of steels.     

Coherency identification and equivalents for transient stability studies

This paper presents techniques for identifying coherent generators without conducting a transient stability study and for developing stability equivalents of a group of coherent generators. Identification is based on the property of equal acceleration for coherent machines and it requires only examination of the elements of the Jacobian matrix of the linearized power system model. After the coherent groups have been identified, the stability equivalents are developed on the basis of the power invariance condition at the tie buses and at the internal buses of the coherent generators. These stability equivalents are used in a transient stability study. The techniques are illustrated with a 12-machine system.These techniques greatly improve the efficiency of calculation of coherency based equivalents. They have potential applications in planning studies of large power systems.     

The influence of grain size on the erosion rate of metals

Metallurgical and Materials Transactions A - The objective of this work was to understand the influence of grain size on solid impingement erosion behavior characterized by deformation at high...     

Magnetic resonance imaging features of submitral left ventricular aneurysm

Rotational atherectomy can generate heat from the friction of the burr as it ablates atherosclerotic plaque. The objective of this study is to correlate Rotablator technique and heat generation using two experimental models. First, 2.0 mm burrs were advanced through a lesion model derived from bovine bone implanted with thermal probes. Intermittent ablation with minimal decelerations resulted in a smaller temperature increase than continuous ablation with maximal decelerations (2.6 +/- 1.3 vs. 13.9 +/- 1.0 degrees C, respectively, P < 0.01). The second model used porcine femoral arteries cradled in constricting polyethylene grafts with thermal probes in contact with the adventitia. As the burr advanced through the segment, RPM decreases of 5-7 k resulted in a temperature rise of 4.1 +/- 1.2 degrees C, whereas decelerations of 10-20 k resulted in a 11.3 +/- 6.2 degrees C temperature increase. We conclude that excessive drops in speed and aggressive advancement of the burr are related to significant increases in temperature and potential thermal injury.