1,523 research outputs found
Energy Distribution of a G\"{o}del-Type Space-Time
We calculate the energy and momentum distributions associated with a
G\"{o}del-type space-time, using the well-known energy-momentum complexes of
Landau and Lifshitz and M{\o}ller. We show that the definitions of Landau and
Lifshitz and M{\o}ller do not furnish a consistent result.Comment: LaTex, no figure
M{\o}ller Energy-Momentum Complex of a Static Axially Symmetric Vacuum Space-Time
The energy and momentum densities associated with the Weyl metric are
calculated using M{\o}ller's energy-momentum complex. These results are
compared with the results obtained by using the energy-momentum complexes of
Einstein, Landau and Lifshitz, Papapetrou and Bergmann. We show that the
aforementioned different prescriptions and that of M{\o}ller do not give the
same energy density, while give the same momentum density.Comment: LATEX, 9 pages, no figures, an improved version, references added,
corrections [Admin note: substantial overlap with gr-qc/0403097,
gr-qc/0404108 , gr-qc/0303009 , hep-th/0311050
M{\o}ller's Energy in the Kantowski-Sachs Space-time
We present a counter example to paper \cite{P71} and show that the result
obtained is correct for a class of metric but not general. We calculate the
total energy of the Kantowski-Sachs space-time by using the energy-momentum
definitions of M{\o}ller in the theory of general relativity and the tetrad
theory of gravity.Comment: 7 pages and no figure
On the Singularities of Reissner-Nordstr\"{o}m Space-Time
It is shown that if two Reissner-Nordstr\"{o}m space-times, both with the
same mass m and charge e, glued together in the singularities, then the light
ray in black hole of the first space-time can go continuously through the
singularity into black hole of the second. The behavior of tidal forces near
the Reissner-Nordstr\"{o}m space-time singularity is examined by considering
what happens between two particles falling freely towards the singularity.Comment: Latex, 4 figures, 11 page
Axially Symmetric Cosmological Mesonic Stiff Fluid Models in Lyra's Geometry
In this paper, we obtained a new class of axially symmetric cosmological
mesonic stiff fluid models in the context of Lyra's geometry. Expressions for
the energy, pressure and the massless scalar field are derived by considering
the time dependent displacement field. We found that the mesonic scalar field
depends on only coordinate. Some physical properties of the obtained models
are discussed.Comment: 13 pages, no figures, typos correcte
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Improving water resources management using different irrigation strategies and water qualities: Field and modelling study
The aim of this study was to investigate the effects of two different irrigation strategies, regulated deficit irrigation, RDI and partial root drying, PRD using surface freshwater (SW) and brackish treated wastewater (TWW) for maize and potato crops. The SALTMED model has been applied using the field measurements of two cropping seasons 2013 and 2014 at the Canale Emiliano Romagnolo, CER’s experimental farm located in Mezzolara di Budrio (Bologna, Italy). In 2013, PRD irrigated potato received 17% less irrigation water than RDI but produced nearly the same yield as under RDI. The water productivity, o naverage, was 11% higher for PRD compared with RDI. For maize 2014 season, the PRD strategy received almost 15% less irrigation water, but produced a yield only 6% lower than that of RDI and gave equal water productivity to RDI. Given that the two strategies received the same amount of rainfall the results favour the PRD over RDI. Had the site not received above average rainfall (258 mm in 2013 and 259 mm during the 2014 growing seasons), PRD might have produced higher yield and water productivity than RDI. In terms of model simulations, overall, the model showed a strong relationship between the observed and the simulated soil moisture and salinity profiles, total dry mater and final yields. This illustrates SALTMED model’s ability to simulate the dry matter and yield of C3 and C4 crops as well as to simulated different water qualities and different water application strategies. Therefore, the model can run with “what if” scenarios depicting several water qualities, crops and irrigation systems and strategies without the need to try them all in the field. This will reduce costs of labour and investment
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