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- Ulfat, Intikhab, 1966, et al.
(author)
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Estimation of solar energy potential for Islamabad, Pakistan
- 2012
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In: Energy Procedia. - : Elsevier. - 1876-6102. ; 18, s. 1496-1500
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Conference paper (peer-reviewed)abstract
- In order to design a solar energy system with optimized performance a thorough knowledge of solar radiation data for a considerably long period (20-25 years) is a pre-requisite. For developing countries like Pakistan, the need of empirical models to assess the feasibility of solar energy utilization seems inevitable due to the absence and scarcity of trustworthy solar radiation data. We present such models for the capital city of Pakistan, Islamabad to estimate global and diffuse solar radiation. It is found that with the exception of monsoon month, solar energy can be utilized very efficiently throughout the year. The models suggested could be used for most of the north-eastern areas of Pakistan, which are similar to Islamabad with respect to the climate and the availability of solar radiation but lack in the record of solar radiation data.
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| 2. |
- Aksteiner, S., et al.
(author)
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New identities for linearized gravity on the Kerr spacetime
- 2019
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In: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029. ; 99:4
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Journal article (peer-reviewed)abstract
- In this paper we derive a differential identity for linearized gravity on the Kerr spacetime and more generally on vacuum spacetimes of Petrov type D. We show that a linear combination of second derivatives of the linearized Weyl tensor can be formed into a complex symmetric 2-tensor M-ab which solves the linearized Einstein equations. The identity makes this manifest by relating M-ab to two terms solving the linearized Einstein equations by construction. The self-dual Weyl curvature of M-ab gives a covariant version of the Teukolsky-Starobinsky identities for linearized gravity which, in addition to the two classical identities for linearized Weyl scalars with extreme spin weights, includes three additional equations. In particular, they are not consequences of the classical Teukolsky-Starobinsky identities, but are additional integrability conditions for linearized gravity. The result has direct application in the construction of symmetry operators and also yields a set of nontrivial gauge invariants for linearized gravity.
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