5,203 research outputs found
Evaluation of machine sewn joints for the flexible heat shield curtain
Feasibility of machine sewing wire reinforced asbestos and silica cloth plies of flexible heat shield curtain assembl
Worldwide flight and ground-based exposure of composite materials
The long-term durability of those advanced composite materials which are applicable to aircraft structures was discussed. The composite components of various military and commercial aircraft and helicopters were reviewed. Both ground exposure and flight service were assessed in terms of their impact upon composite structure durability. The ACEE Program is mentioned briefly
Aberrational Effects for Shadows of Black Holes
In this paper, we discuss how the shadow of a Kerr black hole depends on the
motion of the observer. In particular, we derive an analytical formula for the
boundary curve of the shadow for an observer moving with given four-velocity at
given Boyer--Lindquist coordinates. We visualize the shadow for various values
of parameters.Comment: 12 pages, 3 figures; Proceedings of the 524. WE-Heraeus-Seminar held
at the Physikzentrum, Bad Honnef, Germany, 17.--23.2.201
Measurement and analysis of critical crack tip processes during fatigue crack growth
The mechanics of fatigue crack growth under constant-amplitudes and variable-amplitude loading were examined. Critical loading histories involving relatively simple overload and overload/underload cycles were studied to provide a basic understanding of the underlying physical processes controlling crack growth. The material used for this study was 7091-T7E69, a powder metallurgy aluminum alloy. Local crack-tip parameters were measured at various times before, during, and after the overloads, these include crack-tip opening loads and displacements, and crack-tip strain fields. The latter were useed, in combination with the materials cyclic and monotonic stress-strain properties, to compute crack-tip residual stresses. The experimental results are also compared with analytical predictions obtained using the FAST-2 computer code. The sensitivity of the analytical model to constant-amplitude fatigue crack growth rate properties and to through-thickness constrain are studied
Radiative Models of Sagittarius A* and M87 from Relativistic MHD Simulations
Ongoing millimeter VLBI observations with the Event Horizon Telescope allow
unprecedented study of the innermost portion of black hole accretion flows.
Interpreting the observations requires relativistic, time-dependent physical
modeling. We discuss the comparison of radiative transfer calculations from
general relativistic MHD simulations of Sagittarius A* and M87 with current and
future mm-VLBI observations. This comparison allows estimates of the viewing
geometry and physical conditions of the Sgr A* accretion flow. The viewing
geometry for M87 is already constrained from observations of its large-scale
jet, but, unlike Sgr A*, there is no consensus for its millimeter emission
geometry or electron population. Despite this uncertainty, as long as the
emission region is compact, robust predictions for the size of its jet
launching region can be made. For both sources, the black hole shadow may be
detected with future observations including ALMA and/or the LMT, which would
constitute the first direct evidence for a black hole event horizon.Comment: 8 pages, 2 figures, submitted to the proceedings of AHAR 2011: The
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