703 research outputs found
Light Deflection, Lensing, and Time Delays from Gravitational Potentials and Fermat's Principle in the Presence of a Cosmological Constant
The contribution of the cosmological constant to the deflection angle and the
time delays are derived from the integration of the gravitational potential as
well as from Fermat's Principle. The findings are in agreement with recent
results using exact solutions to Einstein's equations and reproduce precisely
the new -term in the bending angle and the lens equation. The
consequences on time delay expressions are explored. While it is known that
contributes to the gravitational time delay, it is shown here that a
new -term appears in the geometrical time delay as well. Although
these newly derived terms are perhaps small for current observations, they do
not cancel out as previously claimed. Moreover, as shown before, at galaxy
cluster scale, the contribution can be larger than the second-order
term in the Einstein deflection angle for several cluster lens systems.Comment: 6 pages, 1 figure, matches version published in PR
The Contribution of the Cosmological Constant to the Relativistic Bending of Light Revisited
We study the effect of the cosmological constant on the bending of
light by a concentrated spherically symmetric mass. Contrarily to previous
claims, we show that when the Schwarzschild-de Sitter geometry is taken into
account, does indeed contribute to the bending.Comment: 5 pages, 2 figure
Reactive processing of maleic anhydride-grafted poly(butylene succinate) and the compatibilizing effect on poly(butylene succinate) nanocomposites
In this study, maleic anhydride-grafted poly(butylene succinate) (PBS-g-MA) was synthesized via reactive meltgrafting process using different initiator contents. The grafting efficiency was increased with the initiator content, manifested by the higher degree of grafting in PBS-g-MA. The grafting reaction was confirmed through Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. Then, PBS-g-MA was incorporated into organo-montmorillonite (OMMT) filled poly(butylene succinate) (PBS) nanocomposites as compatibilizer. Mechanical properties of PBS nanocomposites were enhanced after compatibilized with PBS-g-MA, due to the better dispersion of OMMT in PBS matrix and the improved filler-matrix interfacial interactions. This was verifiable through X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) showed that the degree of crystallinity and melting temperature increased after addition of PBS-g-MA. However, the presence of PBS-g-MA did not favor the thermal stability of the nanocomposites, as reported in the thermogravimetry (TGA)
Stability of Transparent Spherically Symmetric Thin Shells and Wormholes
The stability of transparent spherically symmetric thin shells (and
wormholes) to linearized spherically symmetric perturbations about static
equilibrium is examined. This work generalizes and systematizes previous
studies and explores the consequences of including the cosmological constant.
The approach shows how the existence (or not) of a domain wall dominates the
landscape of possible equilibrium configurations.Comment: 12 pages, 7 figures, revtex. Final form to appear in Phys. Rev.
Effect Of Organoclay Modification On The Mechanical, Morphology, And Thermal Properties Of Injection Molded Polyamide 6/Polypropylene/Montmorillonite Nanocomposites.
Polyamide 6/polypropylene (PA6/PP = 70/30 parts) blends containing 4 phr (parts per hundred resin) of organophilic montmorillonite (OMMT) were prepared by melt compounding using co-rotating twin-screw extruder followed by injection molding
All static spherically symmetric perfect fluid solutions of Einstein's Equations
An algorithm based on the choice of a single monotone function (subject to
boundary conditions) is presented which generates all regular static
spherically symmetric perfect fluid solutions of Einstein's equations. For
physically relevant solutions the generating functions must be restricted by
non-trivial integral-differential inequalities. Nonetheless, the algorithm is
demonstrated here by the construction of an infinite number of previously
unknown physically interesting exact solutions.Comment: Final form to appear in Phys Rev D. Includes a number of
clarification
The growth of structure in the Szekeres inhomogeneous cosmological models and the matter-dominated era
This study belongs to a series devoted to using Szekeres inhomogeneous models
to develop a theoretical framework where observations can be investigated with
a wider range of possible interpretations. We look here into the growth of
large-scale structure in the models. The Szekeres models are exact solutions to
Einstein's equations that were originally derived with no symmetries. We use a
formulation of the models that is due to Goode and Wainwright, who considered
the models as exact perturbations of an FLRW background. Using the Raychaudhuri
equation, we write for the two classes of the models, exact growth equations in
terms of the under/overdensity and measurable cosmological parameters. The new
equations in the overdensity split into two informative parts. The first part,
while exact, is identical to the growth equation in the usual linearly
perturbed FLRW models, while the second part constitutes exact non-linear
perturbations. We integrate numerically the full exact growth rate equations
for the flat and curved cases. We find that for the matter-dominated era, the
Szekeres growth rate is up to a factor of three to five stronger than the usual
linearly perturbed FLRW cases, reflecting the effect of exact Szekeres
non-linear perturbations. The growth is also stronger than that of the
non-linear spherical collapse model, and the difference between the two
increases with time. This highlights the distinction when we use general
inhomogeneous models where shear and a tidal gravitational field are present
and contribute to the gravitational clustering. Additionally, it is worth
observing that the enhancement of the growth found in the Szekeres models
during the matter-dominated era could suggest a substitute to the argument that
dark matter is needed when using FLRW models to explain the enhanced growth and
resulting large-scale structures that we observe today (abridged)Comment: 18 pages, 4 figures, matches PRD accepted versio
Mechanical And Thermal Properties Of Hydroxyapatite Filled Poly(Methyl Methacrylate) Composites.
Poly(methyl methacrylate) (PMMA) filled with hydroxyapatite (HA) filler has been widely used in biomaterial
application. Acrylic denture base material was prepared from PMMA filled with HA
A Theoretical Construction of Thin Shell Wormhole from Tidal Charged Black hole
Recently, Dadhich et al [ Phys.Lett.B 487, 1 (2000)] have discovered a black
hole solution localized on a three brane in five dimensional gravity in the
Randall-Sundrum scenario. In this article, we develop a new class of thin shell
wormhole by surgically grafting above two black hole spacetimes. Various
aspects of this thin wormhole are also analyzed.Comment: 14 pages, 6 figures, Accepted in Gen.Rel.Gra
Spatially variable hydrologic impact and biomass production tradeoffs associated with Eucalyptus (E. grandis) cultivation for biofuel production in Entre Rios, Argentina
Climate change and energy security promote using renewable sources of energy such as biofuels. High woody biomass production achieved from short-rotation intensive plantations is a strategy that is increasing in many parts of the world. However, broad expansion of bioenergy feedstock production may have significant environmental consequences. This study investigates the watershed-scale hydrological impacts of Eucalyptus (E. grandis) plantations for energy production in a humid subtropical watershed in Entre Rios province, Argentina. A Soil and Water Assessment Tool (SWAT) model was calibrated and validated for streamflow, leaf area index (LAI), and biomass production cycles. The model was used to simulate various Eucalyptus plantation scenarios that followed physically based rules for land use conversion (in various extents and locations in the watershed) to study hydrological effects, biomass production, and the green water footprint of energy production. SWAT simulations indicated that the most limiting factor for plant growth was shallow soils causing seasonal water stress. This resulted in a wide range of biomass productivity throughout the watershed. An optimization algorithm was developed to find the best location for Eucalyptus development regarding highest productivity with least water impact. E. grandis plantations had higher evapotranspiration rates compared to existing terrestrial land cover classes; therefore, intensive land use conversion to E. grandis caused a decline in streamflow, with January through March being the most affected months. October was the least-affected month hydrologically, since high rainfall rates overcame the canopy interception and higher ET rates of E. grandis in this month. Results indicate that, on average, producing 1 kg of biomass in this region uses 0.8 m of water, and the green water footprint of producing 1 m fuel is approximately 2150 m water, or 57 m water per GJ of energy, which is lower than reported values for wood-based ethanol, sugar cane ethanol, and soybean biodiesel
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