No new symmetries of the vacuum Einstein equations
TL;DR: It is shown that some recently proposed solutions of the linearized vacuum Einstein equations are not symmetries of the Einstein equations, because of a crucial integrability condition.
Abstract: We examine some recently proposed solutions of the linearized vacuum Einstein equations. We show that such solutions are not symmetries of the Einstein equations, because of a crucial integrability condition.
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TL;DR: A brief overview on the subject of Supersymmetric Quantum Cosmology (SQC) is presented in this paper, where different approaches are described, all of them being inspired by the search of a square root of (quantum) General Relativity.
Abstract: A brief overview on the subject of Supersymmetric Quantum Cosmology (SQC) is presented here. Different approaches are described, all of them being inspired by the search of a square root of (quantum) General Relativity. Some new ideas in the form of a list of (still!) open problems and an extensive bibliography are included.
7 citations
17 May 2002
TL;DR: In this paper, the emission properties of Al 2 O 3 coated Si field emitters were found to be radically different from any others reported to date, and a tentative explanation in terms of field emission induced secondary electron emission was suggested.
Abstract: The emission properties of Al 2 O 3 coated Si field emitters were found to be radically different from any others reported to date. Silicon field emitter arrays were coated with ultrafine aluminum oxide powders by dielectrophoresis. The emission threshold, corresponding to a current of 10 pA, was 0.25 V/mm. The current–voltage ( I – V ) plots of the Al 2 O 3 coated Si field emitter arrays were steep, with a distinct deviation from Fowler–Nordheim (F–N) behavior. The emission showed a slow but distinct increase or decrease of current with time depending on the magnitude of the current. This behavior could be approximated with an exponential function. We suggest a tentative explanation in terms of “field emission induced secondary electron emission”, i.e. the generation of a secondary electron cascade by the interaction of the field emitted electrons with crystallites comprising the porous aluminum oxide coating.
5 citations
TL;DR: In this article, a matrix integrability theorem is formulated and used to transform the vacuum Einstein equations into a new matrix form, and explicit expressions for the spin-coefficients, satisfying the Bianchi identities, are given.
Abstract: The `post-Bianchi equations', i.e., the extra integrability conditions that arise when a choice of frame is made, provide additional constraints on the mathematical problem of integrating the vacuum Einstein equations. It is shown that these equations give an expression for the divergence of the connection in terms of the Newman - Penrose variables. Explicit expressions for the spin-coefficients, satisfying the Bianchi identities, are also given. A matrix integrability theorem is formulated and used to transform the Einstein equations into a new matrix form.
5 citations
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01 Oct 1984
18 citations
"No new symmetries of the vacuum Ein..." refers background in this paper
...My conventions are the same as in Penrose and Rindler [7] (see also Ref....
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...For the condition that give the other signatures, see [7]....
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