Machining High-Temperature Alloys by Means of Solid Ceramic End Mills

Russian Engineering Research - The cutting of high-temperature alloys is considered. The performance of solid ceramic end mills is assessed by experimental comparison of five different designs with...     

Oscillations of the Electric-Dipole Echo in Glasses in a Magnetic Field

Using a simple diagram technique we derive the electric-dipole echo amplitude from two-level systems with a quadrupole nuclear moment in glasses in an external magnetic field. We show, that due to the quadrupole moment interaction of a tunneling particle with a gradient of an internal electric field, the echo amplitude experiences oscillations in rather weak magnetic fields. With an increase of the magnetic field, when the Zeeman energy becomes larger than the quadrupole energy splitting, the average echo amplitude increases and saturates (for high magnetic fields) at some level which is above the average level of echo oscillations for small magnetic fields. PACS numbers: 77.22.Ch, 61.43.Fs, 76.60.Gv, 76.60.Lz     

Power Dissipation in Spintronic Devices Out of Thermodynamic Equilibrium

Quantum limits of power dissipation in spintronic computing are estimated. A computing element composed of a single electron in a quantum dot is considered. Dynamics of its spin due to external magnetic field and interaction with adjacent dots are described via the Bloch equations. Spin relaxation due to magnetic noise from various sources is described as coupling to a reservoir. Resulting dissipation of energy is calculated and is shown to be much less than the thermal limit, ∼kT per bit, if the rate of spin relaxation is much slower than the switching rate. Clues on how to engineer an energy efficient spintronic device are provided.     

Algorithms and software tools for ordering clone libraries: application to the mapping of the genome of Schizosaccharomyces pombe

A complete set of software tools to aid the physical mapping of a genome has been developed and successfully applied to the genomic mapping of the fission yeast Schizosaccharomyces pombe. Two approaches were used for ordering single-copy hybridisation probes: one was based on the simulated annealing algorithm to order all probes, and another on inferring the minimum-spanning subset of the probes using a heuristic filtering procedure. Both algorithms produced almost identical maps, with minor differences in the order of repetitive probes and those having identical hybridisation patterns. A separate algorithm fitted the clones to the established probe order. Approaches for handling experimental noise and repetitive elements are discussed. In addition to these programs and the database management software, tools for visualizing and editing the data are described. The issues of combining the information from different libraries are addressed. Also, ways of handling multiple-copy probes and non-hybridisation data are discussed.     

Mechanical and Corrosion Properties of ZrB2–SiC Composite Ceramics with Oxide Additions

Powder Metallurgy and Metal Ceramics - Hot pressing was used to produce compact ceramic samples with the following composition (wt.%): 60 ZrB2 + 20 SiC + 20 (Al2O3 + 32 t-ZrO2). The tetragonal...     

Hydrogenolysis of alkanes and olefin polymerization on the silica-supported zirconium hydrides: A comparative DFT study

The model reactions of ethylene polymerization and hydrogenolysis of linear alkanes (propane, n-butane, and n-pentane) on the silica-supported zirconium hydrides (Si–O)₃Zr^IVH, (Si–O)₂Zr^IVH₂, and (Si–O)₂Zr^IIIH were studied using the DFT approach. Catalytic processes under study were shown to occur involving different surface hydrides. The ethylene polymerization was found to proceed at comparable rates on the zirconium monohydrides, (Si–O)₃ZrH, and dihydrides, (Si–O)₂ZrH₂. Cleavage of linear alkanes on the monohydrides (Si–O)₃ZrH is thermodynamically unfavorable; however, the dihydrides (Si–O)₂ZrH₂ can act as catalysts of the process under mild conditions. Hydrides of the trivalent zirconium, (Si–O)₂Zr^IIIH, can also contribute to the hydrogenolysis reaction. A feature of all the systems studied is low regioselectivity of the corresponding processes.     

Influence of hydrogen on the thermoelectric voltage signal in a Pt/WO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/6<Emphasis Type="Italic">H</Emphasis>-SiC/Ni/Pt layered structure

The possibility of detecting H₂ by registering the thermal electromotive force signal, which arises between the surfaces of 6H-SiC plates with a thickness of 400 μm, is established. The working surface of the plates is modified by deposition of a WO _x film and catalytic Pt. An ohmic contact (Ni/Pt) is created on the rear surface of the plate, and this surface is maintained at a stabilized temperature of 350°C. The temperature gradient through the plate thickness arises due to the cooling of the working surface with the air medium. The delivery of H₂ into this medium up to a concentration of 2% gives rise to a 15-fold increase in the electric signal, which considerably exceeds the Pt/WO _x /SiC/Ni/Pt system’s response registered in the usual way by measuring the current–voltage dependence. In this case, an additional power source for the registration of the thermal electromotive force is not required.