| 1. |
- Ulfat, Intikhab, 1966, et al.
(författare)
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Estimation of solar energy potential for Islamabad, Pakistan
- 2012
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Ingår i: Energy Procedia. - : Elsevier. - 1876-6102. ; 18, s. 1496-1500
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Konferensbidrag (refereegranskat)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. |
- Coley, Alan A., et al.
(författare)
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Spherically symmetric Einstein-aether perfect fluid models
- 2015
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : Institute of Physics (IOP). - 1475-7516. ; :12
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Tidskriftsartikel (refereegranskat)abstract
- We investigate spherically symmetric cosmological models in Einstein-act her theory with a tilted (non-comoving) perfect fluid source. We use a 1+3 frame formalism and adopt the comoving aether gauge to derive the evolution equations, which form a well-posed system of first order partial differential equations in two variables. We then introduce normalized variables. The formalism is particularly well-suited for numerical computations and the study of the qualitative properties of the models, which are also solutions of Horava gravity. We study the local stability of the equilibrium points of the resulting dynamical system corresponding to physically realistic in homogeneous cosmological models and astrophysical objects with values for the parameters which are consistent. with current constraints. In particular, we consider dust models in (beta-) normalized variables and derive a reduced (closed) evolution system and we obtain the general evolution equations for the spatially homogeneous Kantowski-Sachs models using, appropriate bounded normalized variables. We then analyse these models, with special emphasis on the future asymptotic behaviour for different values of the parameters. Finally, we investigate static models for a mixture of a (necessarily non-tilted) perfect fluid with a barotropic equations of state and a scalar field.
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| 3. |
- Aksteiner, S., et al.
(författare)
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New identities for linearized gravity on the Kerr spacetime
- 2019
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Ingår i: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029. ; 99:4
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Alhulaimi, Bassemah, et al.
(författare)
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Anisotropic Einstein-aether cosmological models
- 2013
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Ingår i: Journal of Mathematical Physics. - Melville, USA : American Institute of Physics (AIP). - 0022-2488 .- 1089-7658. ; 54:4
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Tidskriftsartikel (refereegranskat)abstract
- We investigate a class of spatially anisotropic cosmological models in Einstein-aether theory with a scalar field in which the self-interaction potential depends on the timelike aether vector field through the expansion and shear scalars. We derive the evolution equations in terms of expansion-normalized variables, which reduce to a dynamical system. We study the local stability of the equilibrium points of the dynamical system corresponding to physically realistic solutions, and find that there are always ranges of values of the parameters of the models for which there exists an inflationary attractor. © 2013 AIP Publishing LLC.
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| 5. |
- Allasia, D, et al.
(författare)
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Inelastic J ψ production in deep inelastic scattering from hydrogen and deuterium and the gluon distribution of free nucleons
- 1991
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Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 258:3-4, s. 493-498
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Tidskriftsartikel (refereegranskat)abstract
- We present results on inelastic J/PSI-production from muon interactions with hydrogen and deuterium at an incident muon energy of 280 GeV. The measured cross section ratio per nucleon for muon-induced J/PSI-production in deuterium and hydrogen was found to be R(D2/H2) = 1.01 +/- 0.15. The colour singlet model is shown to provide a good description of the observed differential cross section apart from a normalisation factor. The comparison between the observed cross section and the colour singlet model prediction allows the extraction of the gluon structure function G(chi) of the nucleon. The momentum fraction-chi of the nucleon carried by the gluon is measured in the range of chi = [0.02, 0.30]. The normalised gluon distribution of free nucleons thus found can be parametrised as chi-G(chi) = 1/2 (eta + 1)(1 - chi)eta, with eta = 5.1 +/- 0.9 (stat).
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| 6. |
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| 7. |
- Amaudruz, P, et al.
(författare)
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Measurements of Rd-Rp and RCa-Rc in deep inelastic muon scattering
- 1992
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Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 294:1, s. 120-126
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Tidskriftsartikel (refereegranskat)abstract
- Results are presented on the difference in R, the ratio of longitudinally to transversely polarised virtual photon absorption cross sections, for the deuteron and the proton. They are obtained by comparing the ratio of cross sections for the deep inelastic scattering of muons from deuterium and hydrogen targets at 90 and 280 GeV incident energy. The results cover the range x = 0.01 -0.30, at an average Q2 of 9 GeV2. The measured difference R(d)-R(p) shows no significant x dependence and is compatible with zero, as well as with expectations from perturbative QCD. We use the same method to obtain the difference R(Ca)-R(C) from cross section ratios measured on carbon and calcium targets at 90 and 200 GeV incident energy.
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| 8. |
- Amaudruz, P, et al.
(författare)
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Proton and deuteron F2 structure functions in deep inelastic muon scattering
- 1992
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Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 295:1-2, s. 159-168
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Tidskriftsartikel (refereegranskat)abstract
- The structure functions F2p and F2d measured by deep inelastic muon scattering at incident energies of 90 and 280 GeV are presented. These measurements cover a large kinematic range, 0.006 less-than-or-equal-to x less-than-or-equal-to 0.6 and 0.5 less-than-or-equal-to Q2 less-than-or-equal-to 55 GeV2, and include the first precise data at small x, where large scaling violations are observed. The data agree with earlier results from SLAC and BCDMS but exhibit differences with respect to those of EMC-NA2. Extrapolations to small x of recent phenomenological parton distributions are shown to disagree with the present results.
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| 9. |
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| 10. |
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