90,894 research outputs found
When are two Coxeter orbifolds diffeomorphic?
One can define what it means for a compact manifold with corners to be a
"contractible manifold with contractible faces." Two combinatorially
equivalent, contractible manifolds with contractible faces are diffeomorphic if
and only if their 4-dimensional faces are diffeomorphic. It follows that two
simple convex polytopes are combinatorially equivalent if and only if they are
diffeomorphic as manifolds with corners. On the other hand, by a result of
Akbulut, for each n > 3, there are smooth, contractible n-manifolds with
contractible faces which are combinatorially equivalent but not diffeomorphic.
Applications are given to rigidity questions for reflection groups and smooth
torus actions.Comment: 24 page
Geomorphology of Mountainous Deserts
The peculiar land forms of the desert are due largely (1) to the paucity of plant growth, in consequence of which (2) disintegrated rock, produced more by physical than by chemical processes, which (3) vary with rock nature (hence granitic rocks assume forms of special interest), does not remain near its source long enough in the earlier stages of erosion to be reduced to very fine texture before (4) it is carried by stream floods or sheet floods toward or to (5) playa basins of rising base-level; but in an advanced stage of the arid cycle (6) the playa surface may be lowered by the wind, whereupon the rock slopes previously weathered down to sheet-flood grade and buried with sheet-flood waste will be (7) trenched by stream floods with respect to the sinking baselevel, and the buried rock floors will be laid bare until again reduced to sheet-flood grade. But (8) in deserts draining to the ocean these various processes will work with respect to a relatively fixed baselevel; also (9) in deserts where the action of water floods is dominated by wind action, the carving of the surface will be in part independent of any baselevel
Flow equation for porous plug and capillary tube flow restrictors
Development of flow measuring apparatus for determining low flow performance of resistojet thruster is discussed. Diagram of test equipment is presented. Operation of test equipment is described and numerical relationships are explained
Missile rolling tail brake torque system
Apparatus for simulating varying levels of friction in the bearings of a free rolling tail afterbody on a canard-controlled missile to determine friction effects on aerodynamic control characteristics is described. A ring located between the missile body and the afterbody is utilized in a servo system to create varying levels of friction between the missile body and the afterbody to simulate bearing friction
System measures angular displacement without contact
Optic system coupled to an electronic detection and measuring system converts angular movement of reflected light to a direct readout, without any direct contact with the object
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