61,666 research outputs found
Computer-derived management information in a special library
Not the least of the benefits of automating libraries and information
centers is the enhanced ability to monitor processes and services, to collect,
structure, analyze, and report critical or useful data hitherto largely
unavailable or excessively difficult and costly to obtain. Good management
of information requires good management information
information that is as cogent, correct, current, clear, concise, and complete
as cost effectiveness and enlightened decision-making demand. Computeraided
information systems offer not only opportunities to gain new
insights into the services they support; they challenge the systems designer
to build in the feedback necessary to control and improve the systems
themselves.
The focus of this paper is computer-supplied management information
in the special library environment. The particular context is that of an
extensively computerized, corporate library network in a large research
and development organization Bell Laboratories.published or submitted for publicatio
Graphite as a structural material in conditions of high thermal flux: a survey of existing knowledge and an assessment of current research and development
The state of fundamental knowledge on the subject of graphite and
the graphitisation process is reviewed. The principle methods of
manufacture may be considered to include (1) conventional graphitisation
of a coke filler-binder mix, (2) the compaction at high pressure and
temperatures of natural or artificial graphite particles without a binder,
(3) pyrolytic graphites derived from gaseous deposition, and (4)
conventional graphites impregnated by liquid or gas and re-graphitised.
The present state of development of these processes is examined. The
erosion of graphite by high velocity gases at high temperatures is due
primarily to oxidation effects which occur preferentially at crystallite
boundaries. Coatings of carbides and nitrides improve the resistance
at temperatures below about 1700 degrees C, but above this, pyrolytic coatings
are more successful. The addition of vapourising compounds, iodides and
fluorides, or the addition of carbides and nitrides to the graphite
mix, are both beneficial, but of little value at very high temperatures.
The development of new graphites, either the impregnated type, or those produced by pressure baking, may offer a margin of improvement, as the
best surface structure at temperatures of 3000 degrees C and above appears to
be simply graphite. Additions may do little to improve the mechanism
of erosion, but they may usefully lower the surface temperature.
Considerations relating to thermal shock, creep and fabrication are
surveyed. Some of the conclusions are: that graphite is of singular
importance to high temperature technology; that commercial issues
cannot be allowed to impede vigorous development towards more resistant
forms; that much is to be gained by viewing graphite from a metals
standpoint; that the fundamental theory of the basic crystal mechanics
is undeveloped; that the present wide variability in properties should
not be regarded overseriously; that non-destructive assessment by
damping measurements needs development, that coatings and impregnants
are of high priority, and that, of all factors, oxidation is the most
serious limitation to use at the present time
The ALEPH Search for the Standard Model Higgs Boson
A search has been performed for the Standard Model Higgs boson in the data
collected with the ALEPH detector in 2000. An excess of 3 sigma above the
background expectation is found. The observed excess is consistent with the
production of the Higgs boson with a mass close to 114 GeV/c2.Comment: 5 pages, 5 figure
Oscillations of atomic fermions in a one dimensional optical lattice
A semiclassical model is used to investigate oscillations of atomic fermions
in a combined magnetic trap and one dimensional optical lattice potential
following axial displacement of the trap. The oscillations are shown to have a
characteristic small amplitude, damped behavior in the collisionless regime.
The presence of a separatrix in the semiclassical Brillouin zone phase space is
predicted and shown to produce a strongly asymmetric phase space distribution
function.Comment: 6 pages, 6 figure
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
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