503 research outputs found
Mechanical and microstructural investigations of tungsten and doped tungsten materials produced via powder injection molding
The physical properties of tungsten such as the high melting point of 3420°C, the high strength and thermal conductivity, the low thermal expansion and low erosion rate make this material attractive as a plasma facing material. However, the manufacturing of such tungsten parts by mechanical machining such as milling and turning is extremely costly and time intensive because this material is very hard and brittle. Powder Injection Molding (PIM) as special process allows the mass production of components, the joining of different materials without brazing and the creation of composite and prototype materials, and is an ideal tool for scientific investigations. This contribution describes the characterization and analyses of prototype materials produced via PIM. The investigation of the pure tungsten and oxide or carbide doped tungsten materials comprises the microstructure examination, element allocation, texture analyses, and mechanical testing via four-point bend (4-PB). Furthermore, the different materials were characterized by high heat flux (HHF) tests applying transient thermal loads at different base temperatures to address thermal shock and thermal fatigue performance. Additionally, HHF investigations provide information about the thermo-mechanical behavior to extreme steady state thermal loading and measurements of the thermal conductivity as well as oxidation tests were done. Post mortem analyses are performed quantifying and qualifying the occurring damage with respect to reference tungsten grades by metallographic and microscopical means
Spin effects in gravitational radiation backreaction II. Finite mass effects
A convenient formalism for averaging the losses produced by gravitational
radiation backreaction over one orbital period was developed in an earlier
paper. In the present paper we generalize this formalism to include the case of
a closed system composed from two bodies of comparable masses, one of them
having the spin S.
We employ the equations of motion given by Barker and O'Connell, where terms
up to linear order in the spin (the spin-orbit interaction terms) are kept. To
obtain the radiative losses up to terms linear in the spin, the equations of
motion are taken to the same order. Then the magnitude L of the angular
momentum L, the angle kappa subtended by S and L and the energy E are
conserved. The analysis of the radial motion leads to a new parametrization of
the orbit.
From the instantaneous gravitational radiation losses computed by Kidder the
leading terms and the spin-orbit terms are taken. Following Apostolatos,
Cutler, Sussman and Thorne, the evolution of the vectors S and L in the
momentary plane spanned by these vectors is separated from the evolution of the
plane in space. The radiation-induced change in the spin is smaller than the
leading-order spin terms in the momentary angular momentum loss. This enables
us to compute the averaged losses in the constants of motion E, L and L_S=L cos
kappa. In the latter, the radiative spin loss terms average to zero. An
alternative description using the orbital elements a,e and kappa is given.
The finite mass effects contribute terms, comparable in magnitude, to the
basic, test-particle spin terms in the averaged losses.Comment: 12 pages, 1 figure, Phys.Rev.D15, March, 199
Post-Newtonian Freely Specifiable Initial Data for Binary Black Holes in Numerical Relativity
Construction of astrophysically realistic initial data remains a central
problem when modelling the merger and eventual coalescence of binary black
holes in numerical relativity. The objective of this paper is to provide
astrophysically realistic freely specifiable initial data for binary black hole
systems in numerical relativity, which are in agreement with post-Newtonian
results. Following the approach taken by Blanchet, we propose a particular
solution to the time-asymmetric constraint equations, which represent a system
of two moving black holes, in the form of the standard conformal decomposition
of the spatial metric and the extrinsic curvature. The solution for the spatial
metric is given in symmetric tracefree form, as well as in Dirac coordinates.
We show that the solution differs from the usual post-Newtonian metric up to
the 2PN order by a coordinate transformation. In addition, the solutions,
defined at every point of space, differ at second post-Newtonian order from the
exact, conformally flat, Bowen-York solution of the constraints.Comment: 41 pages, no figures, accepted for publication in Phys. Rev. D,
significant revision in presentation (including added references and
corrected typos
Gravitational radiation reaction in compact binary systems: Contribution of the quadrupole-monopole interaction
The radiation reaction in compact spinning binaries on eccentric orbits due
to the quadrupole-monopole interaction is studied. This contribution is of
second post-Newtonian order. As result of the precession of spins the magnitude
of the orbital angular momentum is not conserved. Therefore a proper
characterization of the perturbed radial motion is provided by the energy
and angular average . As powerful computing tools, the generalized
true and eccentric anomaly parametrizations are introduced. Then the secular
losses in energy and magnitude of orbital angular momentum together with the
secular evolution of the relative orientations of the orbital angular momentum
and spins are found for eccentric orbits by use of the residue theorem. The
circular orbit limit of the energy loss agrees with Poisson's earlier result.Comment: accepted for publication in Phys. Rev.
Powder injection molding (PIM) - a multi-purpose process for armor part fabrication and materials development
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