34,644 research outputs found
New nickel-base wrought superalloy with applications up to 1253 K (1800 F)
Alloy possesses combination of high tensile strength at low and intermediate temperatures to 1033 K with good rupture strength at high temperatures to 1255 K. Alloy has promise for turbine disk application in future gas turbine engines and for wrought integrally bladed turbine wheel; thickness and weight of disk portion of wheel could be reduced
Feasibility study of the ultraviolet spectral analysis of the lunar surface
Ultraviolet spectral analysis of granite, gabbro, and serpentinite samples to determine feasibility of mapping surface composition of moo
The common nodulation genes of Astragalus sinicus rhizobia are conserved despite chromosomal diversity
The nodulation genes of Mesorhizobium sp. (Astragalus sinicus) strain 7653R were cloned by functional complementation of Sinorhizobium meliloti nod mutants. The common nod genes, nodD, nodA, and nodBC, were identified by heterologous hybridization and sequence analysis. The nodA gene was found to be separated from nodBC by approximately 22 kb and was divergently transcribed. The 2.0-kb nodDBC region was amplified by PCR from 24 rhizobial strains nodulating A. sinicus, which represented different chromosomal genotypes and geographic origins. No polymorphism was found in the size of PCR products, suggesting that the separation of nodA from nodBC is a common feature of A. sinicus rhizobia. Sequence analysis of the PCR-amplified nodA gene indicated that seven strains representing different 16S and 23S ribosomal DNA genotypes had identical nodA sequences. These data indicate that, whereas microsymbionts of A. sinicus exhibit chromosomal diversity, their nodulation genes are conserved, supporting the hypothesis of horizontal transfer of nod genes among diverse recipient bacteria
Fracture mechanics approach to design analysis of notches, steps and internal cut-outs in planar components
A new approach to the assessment and optimization of geometric stress-concentrating features is proposed on the basis of the correspondence between sharp crack or corner stressfield intensity factors and conventional elastic stress concentration factors (SCFs) for radiused transitions. This approach complements the application of finite element analysis (FEA) and the use of standard SCF data from the literature. The method makes it possible to develop closed-form solutions for SCFs in cases where corresponding solutions for the sharp crack geometries exist. This is helpful in the context of design optimization. The analytical basis of the correspondence is shown, together with the limits on applicability where stress-free boundaries near the stress concentrating feature are present or adjacent features interact. Examples are given which compare parametric results derived from FEA with closed-form solutions based on the proposed method. New information is given on the stress state at a 90° corner or width step, where the magnitude of the stress field intensity is related to that of the corresponding crack geometry. This correspondence enables the user to extend further the application of crack-tip stress-field intensity information to square-cornered steps, external U-grooves, and internal cut-outs
Nine percent nickel steel heavy forging weld repair study
The feasibility of making weld repairs on heavy section 9% nickel steel forgings such as those being manufactured for the National Transonic Facility fan disk and fan drive shaft components was evaluated. Results indicate that 9% nickel steel in heavy forgings has very good weldability characteristics for the particular weld rod and weld procedures used. A comparison of data for known similar work is included
Static properties of the dissipative random quantum Ising ferromagnetic chain
We study the zero temperature static properties of dissipative ensembles of
quantum Ising spins arranged on periodic one dimensional finite clusters and on
an infinite chain. The spins interact ferro-magnetically with nearest-neighbour
pure and random couplings. They are subject to a transverse field and coupled
to an Ohmic bath of quantum harmonic oscillators. We analyze the coupled system
using Monte Carlo simulations of the classical two-dimensional counterpart
model. The coupling to the bath enhances the extent of the ordered phase, as
found in mean-field spin-glasses. In the case of finite clusters we show that a
generalization of the Caldeira-Leggett localization transition exists. In the
case of the infinite random chain we study the effect of dissipation on the
transition and the Griffiths phase.Comment: 21 pages, 10 figure
A new 1.6-micron map of Titan’s surface
We present a new map of Titan's surface obtained in the spectral 'window' at ∼1.6 μm between strong methane absorption. This pre-Cassini view of Titan's surface was created from images obtained using adaptive optics on the W.M. Keck II telescope and is the highest resolution map yet made of Titan's surface. Numerous surface features down to the limits of the spatial resolution (∼200–300 km) are apparent. No features are easily identifiable in terms of their geologic origin, although several are likely craters
Nonlinear feedback oscillations in resonant tunneling through double barriers
We analyze the dynamical evolution of the resonant tunneling of an ensemble
of electrons through a double barrier in the presence of the self-consistent
potential created by the charge accumulation in the well.
The intrinsic nonlinearity of the transmission process is shown to lead to
oscillations of the stored charge and of the transmitted and reflected fluxes.
The dependence on the electrostatic feedback induced by the self-consistent
potential and on the energy width of the incident distribution is discussed.Comment: 10 pages, TeX, 5 Postscript figure
A quantum measure of coherence and incompatibility
The well-known two-slit interference is understood as a special relation
between observable (localization at the slits) and state (being on both slits).
Relation between an observable and a quantum state is investigated in the
general case. It is assumed that the amount of ceherence equals that of
incompatibility between observable and state. On ground of this, an argument is
peresented that leads to a natural quantum measure of coherence, called
"coherence or incompatibility information". Its properties are studied in
detail making use of 'the mixing property of relative entropy' derived in this
article. A precise relation between the measure of coherence of an observable
and that of its coarsening is obtained and discussed from the intutitive point
of view. Convexity of the measure is proved, and thus the fact that it is an
information entity is established. A few more detailed properties of coherence
information are derived with a view to investigate final-state entanglement in
general repeatable measurement, and, more importantly, general bipartite
entanglement in follow ups of this study.Comment: 19 GS pages; supercedes quant-ph/030921
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