66,217 research outputs found
Temperature effects on material characteristics
Some of the physical properties of the main elements of interest in
high temperature technology are reviewed. Some general trends emerge
when these properties are viewed as a function of melting point, but there
are a few notable exceptions. Titanium, zirconium, niobium and tantalum
all have disappointingly low moduli; chromium is excellent in many ways,
but has a limited ductility at lower temperatures; molybdenum oxidises
catastrophically above about 700° C, and niobium suffers from severe
oxygen embrittlement. Beryllium and carbon (in the graphitic form) both
stand out as exceptional materials, both have very low densities, beryllium
a very high modulus but an unfortunately low ductility, while graphite has
a relatively low strength at the lower temperatures, although at temperatures
of 2000° C and above it emerges as a quite exceptional (and probably as the
ultimate) high temperature material. Some of the fundamental factors
involved in high temperature material development are examined, in the
light, particularly, of past progress with the nickel alloys. If a similar
progress can be achieved with other base elements then a considerable
margin still remains to be exploited. Protection from oxidation at high
temperatures is evidently a factor of major concern, not only with metals,
but with graphite also. Successful coatings are therefore of high importance and the questions they raise, such as bonding, differential thermal expansion,
and so on, represent aspects of an even wider class covered by the term
“composite structures". Such structures appear to offer the only serious
solution to many high temperature requirements, and their design,
construction and utilization has created a whole series of new exercises
in materials assessment. Matters have become so complex, that a very
radical and fundamental reassessment is required if we are to change, in
any very significant way, the wasteful and ad hoc methods which characterise
so much of present-day materials engineering
An overview of SAE ARP 1587: Aircraft gas turbine engine monitoring system guide
A systematic approach to developing an engine monitoring system (EMS) is outlined. An extensive shopping list of EMS capabilities and benefits are included. A team approach to developing an EMS is emphasized with a description of the responsibilities of each team member
New low-mass members of the Octans stellar association and an updated 30-40 Myr lithium age
The Octans association is one of several young stellar moving groups recently
discovered in the Solar neighbourhood, and hence a valuable laboratory for
studies of stellar, circumstellar disc and planetary evolution. However, a lack
of low-mass members or any members with trigonometric parallaxes means the age,
distance and space motion of the group are poorly constrained. To better
determine its membership and age, we present the first spectroscopic survey for
new K and M-type Octans members, resulting in the discovery of 29 UV-bright
K5-M4 stars with kinematics, photometry and distances consistent with existing
members. Nine new members possess strong Li I absorption, which allow us to
estimate a lithium age of 30-40 Myr, similar to that of the Tucana-Horologium
association and bracketed by the firm lithium depletion boundary ages of the
Beta Pictoris (20 Myr) and Argus/IC 2391 (50 Myr) associations. Several stars
also show hints in our medium-resolution spectra of fast rotation or
spectroscopic binarity. More so than other nearby associations, Octans is much
larger than its age and internal velocity dispersion imply. It may be the
dispersing remnant of a sparse, extended structure which includes some younger
members of the foreground Octans-Near association recently proposed by
Zuckerman and collaborators.Comment: Accepted for publication in MNRAS (16 pages, 5 tables
Recommended from our members
A class of algorithms for rational approximation of functions formally defined by power series
Corresponding sequence algorithms are defined and shown to exist for a wide range of corresponding continued fractions. Particular examples of these algorithms are given, including an algorithm for forming Pade approximants, and an error analysis is given in one case
The square root law and structure of finite rings
Let be a finite ring and define the hyperbola . Suppose that for a sequence of finite odd order rings of size tending
to infinity, the following "square root law" bound holds with a constant
for all non-trivial characters on : Then, with a finite number of
exceptions, those rings are fields.
For rings of even order we show that there are other infinite families given
by Boolean rings and Boolean twists which satisfy this square-root law
behavior. We classify the extremal rings, those for which the left hand side of
the expression above satisfies the worst possible estimate. We also describe
applications of our results to problems in graph theory and geometric
combinatorics.
These results provide a quantitative connection between the square root law
in number theory, Salem sets, Kloosterman sums, geometric combinatorics, and
the arithmetic structure of the underlying rings
Laser-actuated mechanical device
Actuator is portable and can be used in high-temperature (over 500 C) environments by incorporating tungsten metal film and quartz window. Actuator can be triggered when it is not directly in laser beam path by utilizing fiber optics. It is advantageous for remotely switching ultra-high voltage systems
Optically actuated two position mechanical mover
An optically actuated mechanical mover adapted to be moved from an ambient position to an active position, is disclosed. The mechanical mover essentially comprises a piston/cylinder arrangement including a piston that is contained within an internal cylindrical chamber of a housing. The cylindrical chamber is configured to permit the piston to be moved for the length of the chamber as a work stroke. A lock pin extending through the piston, and diametrically opposed walls of the chamber housing, retain the piston in the ambient position at one end of the chamber. An actuator for producing a pressure or shock wave that drives the piston is positioned at the end of the chamber corresponding to the piston ambient position
Repeatability, accuracy, portability, and errors of the portable alignment gyrocompass system
Portable alignment gyrocompass system accuracy, repeatability, portability, and error
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