3,293,532 research outputs found
Multilayer refractory nozzles produced by plasma-spray process
Multilayer rocket nozzles formed by plasma spraying have good thermal shock resistance and can be reheated in an oxidizing environment without loss of coating adherence. Suggested application of this process are for the production of refractory components, which can be formed as surfaces of revolution
Exponential series without denominators
For a commutative algebra which comes from a Zinbiel algebra the exponential
series can be written without denominators. When lifted to dendriform algebras
this new series satisfies a functional equation analogous to the
Baker-Campbell-Hausdorff formula. We make it explicit by showing that the
obstruction series is the sum of the brace products. In the multilinear case we
show that the role the Eulerian idempotent is played by the iterated pre-Lie
product.Comment: 13
Quantum Group Structure and Local Fields in the Algebraic Approach to 2D Gravity
This review contains a summary of work by J.-L. Gervais and the author on the
operator approach to 2d gravity. Special emphasis is placed on the construction
of local observables -the Liouville exponentials and the Liouville field itself
- and the underlying algebra of chiral vertex operators. The double quantum
group structure arising from the presence of two screening charges is discussed
and the generalized algebra and field operators are derived. In the last part,
we show that our construction gives rise to a natural definition of a quantum
tau function, which is a noncommutative version of the classical
group-theoretic representation of the Liouville fields by Leznov and Saveliev.Comment: 38 pages, LaTex file. Proceedings of the Vth International Conference
on Mathematical Physics, Strings and Quantum gravity, Alushta, Ukraine 199
Computability of the causal boundary by using isocausality
Recently, a new viewpoint on the classical c-boundary in Mathematical
Relativity has been developed, the relations of this boundary with the
conformal one and other classical boundaries have been analyzed, and its
computation in some classes of spacetimes, as the standard stationary ones, has
been carried out.
In the present paper, we consider the notion of isocausality given by
Garc\'ia-Parrado and Senovilla, and introduce a framework to carry out
isocausal comparisons with standard stationary spacetimes. As a consequence,
the qualitative behavior of the c-boundary (at the three levels: point set,
chronology and topology) of a wide class of spacetimes, is obtained.Comment: 44 pages, 5 Figures, latex. Version with minor changes and the
inclusion of Figure
A Layman's guide to SUSY GUTs
The determination of the most straightforward evidence for the existence of
the Superworld requires a guide for non-experts (especially experimental
physicists) for them to make their own judgement on the value of such
predictions. For this purpose we review the most basic results of Super-Grand
unification in a simple and clear way. We focus the attention on two specific
models and their predictions. These two models represent an example of a direct
comparison between a traditional unified-theory and a string-inspired approach
to the solution of the many open problems of the Standard Model. We emphasize
that viable models must satisfy {\em all} available experimental constraints
and be as simple as theoretically possible. The two well defined supergravity
models, and , can be described in terms of only a few
parameters (five and three respectively) instead of the more than twenty needed
in the MSSM model, \ie, the Minimal Supersymmetric extension of the Standard
Model. A case of special interest is the strict no-scale
supergravity where all predictions depend on only one parameter (plus the
top-quark mass). A general consequence of these analyses is that supersymmetric
particles can be at the verge of discovery, lurking around the corner at
present and near future facilities. This review should help anyone distinguish
between well motivated predictions and predictions based on arbitrary choices
of parameters in undefined models.Comment: 25 pages, Latex, 11 figures (not included), CERN-TH.7077/93,
CTP-TAMU-65/93. A complete ps file (1.31MB) with embedded figures is
available by request from [email protected]
A Mechanism Involving Solar Ultraviolet Variations for Modulating the Interannual Climatology of the Middle Atmosphere
In years of low solar activity, free traveling wave modes in the upper stratosphere are dominated by atmospheric normal modes such as the 16-day wave. However, within a 4-year interval centered on the 1980 to 1981 solar maximum, cross-spectral analyses of zonal mean satellite temperature data versus the solar UV flux demonstrate significant power near 27 and 13 days, providing indirect evidence that short-term UV variations were capable of exciting traveling planetary-scale waves in the upper stratosphere. Previous theoretical and observational work has indicated that interference between traveling waves and stationary waves forced from below (and the resulting oscillating latitudinal heat transports) plays a likely role in the initiation of stratospheric warmings. Researchers therefore hypothesize that the initiation of a major stratospheric warming in the upper stratosphere and lower mesosphere may depend to some extent on the amplitude of longer-period 27-day traveling waves in the upper stratosphere. This would represent a new mechanism for solar UV effects on stratospheric climatology that may be relevant to the interpretation of some recent long-term correlative results
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