24,784 research outputs found
Drilling system design project 1967: final report of frame design committee
This report outlines the recommendations of the Frame
Design Committee for the final design of the machine, each
major part of the structure being considered individually
in the following sections :
1. Worktables
2. Guide and Slideways
3. Drill Head Support Structure
4. Swarf Disposal and Coolant Supply
5. General Constructio
Improved zinc oxide thermal control coatings
Ferricyanide/ferrocyanide couple prevents zinc oxide pigment degradation in thermal control coatings. Chemical couple retards physical optical property changes
Non-Simply-Connected Gauge Groups and Rational Points on Elliptic Curves
We consider the F-theory description of non-simply-connected gauge groups
appearing in the E8 x E8 heterotic string. The analysis is closely tied to the
arithmetic of torsion points on an elliptic curve. The general form of the
corresponding elliptic fibration is given for all finite subgroups of E8 which
are applicable in this context. We also study the closely-related question of
point-like instantons on a K3 surface whose holonomy is a finite group. As an
example we consider the case of the heterotic string on a K3 surface having the
E8 gauge symmetry broken to (E6 x SU(3))/Z3 or SU(9)/Z3 by point-like
instantons with Z3 holonomy.Comment: 15 pages, 2 embedded figures, some spurious U(1)'s remove
Tall sections from non-minimal transformations
In previous work, we have shown that elliptic fibrations with two sections,
or Mordell-Weil rank one, can always be mapped birationally to a Weierstrass
model of a certain form, namely, the Jacobian of a model.
Most constructions of elliptically fibered Calabi-Yau manifolds with two
sections have been carried out assuming that the image of this birational map
was a "minimal" Weierstrass model. In this paper, we show that for some
elliptically fibered Calabi-Yau manifolds with Mordell-Weil rank-one, the
Jacobian of the model is not minimal. Said another way,
starting from a Calabi-Yau Weierstrass model, the total space must be blown up
(thereby destroying the "Calabi-Yau" property) in order to embed the model into
. In particular, we show that the elliptic fibrations studied
recently by Klevers and Taylor fall into this class of models.Comment: 16 page
Development of small bore, high speed tapered roller bearing
The performance of four rolling bearing configurations for use on the input pinion shaft of a proposed commercial helicopter transmission was evaluated. The performance characteristics of a high speed tapered roller bearing operating under conditions comparable to those existing at this input pinion shaft were defined. The tapered roller bearing shaft support configuration was developed for the gearbox using commercially available bearing designings. The configuration was optimized and interactive thermomechanically system analyzed. Automotive pinion quality tapered roller bearings were found to be reliable under load and speed conditions in excess of those anticipated in the helicopter transmission. However, it is indicated that the elastohydrodynamic lubricant films are inadequate
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