873 research outputs found
Industrial capability to chem-mill aluminum alloy 2219 in T-37 and T-87
Procedures and chemical baths were developed for chem-milling aluminum alloy 2219. Using a series of sample etchings, it was found that good etching results could be obtained by using 'white plastic for porcelain repair (toluol, xylol, and petroleum distillates)' on top of cellosolve acetate as resist coatings and ferric chloride as on etchant
Tribological properties of diamond-like-carbon coating doped with tungsten
This paper presents the tribological properties of diamond-like-carbon coatings (DLC) doped with tungsten. The hardness of the DLC coating was determined using a micro-hardness tester. Friction tests were carried out on a tribometer in rotational motion in a 100Cr6 steel ball-disk association with a-C-H:W tungsten doped hydrogenated DLC coating. Tests were carried out with loads of 10 N, 25 N and 50 N under technically dry friction conditions. Using a scanning electron microscopy (SEM), the surface morphology was observed, and with a confocal microscope, the geometric structure of the surface was observed before and after the friction tests. The wetting angle of the samples was examined on an optical tensiometer for distilled water and diiodomethane. The results indicated that DLC coatings of the a-C:H:W type obtained by the PVD technique can be used in unlubricated high-load tribological systems
Wess-Zumino sigma models with non-Kahlerian geometry
Supersymmetry of the Wess-Zumino (N=1, D=4) multiplet allows field equations
that determine a larger class of geometries than the familiar Kahler manifolds,
in which covariantly holomorphic vectors rather than a scalar superpotential
determine the forces. Indeed, relaxing the requirement that the field equations
be derivable from an action leads to complex flat geometry. The
Batalin-Vilkovisky formalism is used to show that if one requires that the
field equations be derivable from an action, we once again recover the
restriction to Kahler geometry, with forces derived from a scalar
superpotential.Comment: 13 pages, Late
An inertia 'paradox' for incompressible stratified Euler fluids
The interplay between incompressibility and stratification can lead to
non-conservation of horizontal momentum in the dynamics of a stably stratified
incompressible Euler fluid filling an infinite horizontal channel between rigid
upper and lower plates. Lack of conservation occurs even though in this
configuration only vertical external forces act on the system. This apparent
paradox was seemingly first noticed by Benjamin (J. Fluid Mech., vol. 165,
1986, pp. 445-474) in his classification of the invariants by symmetry groups
with the Hamiltonian structure of the Euler equations in two dimensional
settings, but it appears to have been largely ignored since. By working
directly with the motion equations, the paradox is shown here to be a
consequence of the rigid lid constraint coupling through incompressibility with
the infinite inertia of the far ends of the channel, assumed to be at rest in
hydrostatic equilibrium. Accordingly, when inertia is removed by eliminating
the stratification, or, remarkably, by using the Boussinesq approximation of
uniform density for the inertia terms, horizontal momentum conservation is
recovered. This interplay between constraints,action at a distance by
incompressibility, and inertia is illustrated by layer-averaged exact results,
two-layer long-wave models, and direct numerical simulations of the
incompressible Euler equations with smooth stratification
Superform formulation for vector-tensor multiplets in conformal supergravity
The recent papers arXiv:1110.0971 and arXiv:1201.5431 have provided a
superfield description for vector-tensor multiplets and their Chern-Simons
couplings in 4D N = 2 conformal supergravity. Here we develop a superform
formulation for these theories. Furthermore an alternative means of gauging the
central charge is given, making use of a deformed vector multiplet, which may
be thought of as a variant vector-tensor multiplet. Its Chern-Simons couplings
to additional vector multiplets are also constructed. This multiplet together
with its Chern-Simons couplings are new results not considered by de Wit et al.
in hep-th/9710212.Comment: 28 pages. V2: Typos corrected and references updated; V3: References
updated and typo correcte
Using Metaphors in Dynamic Social Stratification Visualizations
We present three information visualizations for studying social stratification. Each Web-based applet uses a different metaphor to display U.S. Census income data along with the categories of race, marital status, and profession. Each system is completely dynamic, affording the user the choice of categorical variable to compare, as well as the choice of categories within each visualization. Two different user interfaces have also been implemented. The systems are described, compared, and their respective merits and deficiencies discussed
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