75,667 research outputs found
Photon Stars
We discuss numerical solutions of Einstein's field equation describing
static, spherically symmetric conglomerations of a photon gas. These equations
imply a back reaction of the metric on the energy density of the photon gas
according to Tolman's equation. The 3-fold of solutions corresponds to a class
of physically different solutions which is parameterized by only two
quantities, e.g. mass and surface temperature. The energy density is typically
concentrated on a shell because the center contains a repelling singularity,
which can, however, not be reached by timelike or null geodesics. The physical
relevance of these solutions is completely open, although their existence may
raise some doubts w.r. to the stability of black holes.Comment: 10 pages, 5 figures, talk at the DPG Spring Meeting 199
Forming aluminum for solar energy concentrators Quarterly progress report no. 2, 1 Jan. - 31 Mar. 1964
Electroformed aluminum solar reflector
Theory of magnetization plateaux in the Shastry-Sutherland model
Using perturbative continuous unitary transformations, we determine the
long-range interactions between triplets in the Shastry-Sutherland model, and
we show that an unexpected structure develops at low magnetization with
plateaux progressively appearing at 2/9, 1/6, 1/9 and 2/15 upon increasing the
inter-dimer coupling. A critical comparison with previous approaches is
included. Implications for the compound SrCu(BO) are also
discussed: we reproduce the magnetization profile around localized triplets
revealed by NMR, we predict the presence of a 1/6 plateau, and we suggest that
residual interactions beyond the Shastry-Sutherland model are responsible for
the other plateaux below 1/3.Comment: 5 pages, 6 figure
Redesign and cascade tests of a supercritical controlled diffusion stator blade-section
A supercritical stator blade section, previously tested in cascade, and characterized by a flat-roof-top suction surface Mach number distribution, has been redesigned and retested. At near design conditions, the losses and air turning were improved over the original blade by 50 percent and 7 percent respectively. The key element in the improved performance was a small blade reshaping. This produced a continuous flow acceleration over the first one-third chord of the suction surface which successfully prevented a premature laminar separation bubble. Several recently available inviscid analysis and one fully viscous (Navier-Stokes) analysis code were used in the redesign process. The validity of these codes was enhanced by the test results
Reduced basis method for computational lithography
A bottleneck for computational lithography and optical metrology are long
computational times for near field simulations. For design, optimization, and
inverse scatterometry usually the same basic layout has to be simulated
multiple times for different values of geometrical parameters. The reduced
basis method allows to split up the solution process of a parameterized model
into an expensive offline and a cheap online part. After constructing the
reduced basis offline, the reduced model can be solved online very fast in the
order of seconds or below. Error estimators assure the reliability of the
reduced basis solution and are used for self adaptive construction of the
reduced system. We explain the idea of reduced basis and use the finite element
solver JCMsuite constructing the reduced basis system. We present a 3D
optimization application from optical proximity correction (OPC).Comment: BACUS Photomask Technology 200
Differential analysis for the turbulent boundary layer on a compressor blade element (including boundary-layer separation)
A two-dimensional differential analysis is developed to approximate the turbulent boundary layer on a compressor blade element with strong adverse pressure gradients, including the separated region with reverse flow. The predicted turbulent boundary layer thicknesses and velocity profiles are in good agreement with experimental data for a cascade blade, even in the separated region
Navigation and guidance analysis for a Mars mission Interim study report
Error propagation program simulating earth based tracking for navigation and guidance analysis of Mars missio
Performance with and without inlet radial distortion of a transonic fan stage designed for reduced loading in the tip region
A transonic compressor stage designed for a reduced loading in the tip region of the rotor blades was tested with and without inlet radial distortion. The rotor was 50 cm in diameter and designed for an operating tip speed of 420 m/sec. Although the rotor blade loading in the tip region was reduced to provide additional operating range, analysis of the data indicates that the flow around the damper appears to be critical and limited the stable operating range of this stage. For all levels of tip and hub radial distortion, there was a large reduction in the rotor stall margin
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