1,856 research outputs found
Electroelasticity of Charged Black Branes
We present the first-order corrected dynamics of fluid branes carrying
higher-form charge by obtaining the general form of their equations of motion
to pole-dipole order. Assuming linear response theory, we characterize the
corresponding effective theory of stationary bent charged (an)isotropic fluid
branes in terms of two sets of response coefficients, the Young modulus and the
piezoelectric moduli. We subsequently find large classes of examples in gravity
of this effective theory, by constructing stationary strained charged black
brane solutions to first order in a derivative expansion. Using solution
generating techniques and bent neutral black branes as a seed solution, we
obtain a class of charged black brane geometries carrying smeared Maxwell
charge in Einstein-Maxwell-dilaton gravity. In the specific case of
ten-dimensional space-time we furthermore use T-duality to generate bent black
branes with higher-form charge, including smeared D-branes of type II string
theory. By subsequently measuring the bending moment and the electric dipole
moment which these geometries acquire due to the strain, we uncover that their
form is captured by classical electroelasticity theory. In particular, we find
that the Young modulus and the piezoelectric moduli of our strained charged
black brane solutions are parameterized by a total of 4 response coefficients,
both for the isotropic as well as anisotropic cases.Comment: v2: 40pp; typos fixe
Extremal Black Hole Horizons
Using the blackfold effective theory applied to extremal Kerr branes we
provide evidence for the existence of new stationary extremal black hole
solutions in asymptotically flat spacetime with both single and multiple
disconnected horizons. These include extremal doubly-spinning black rings,
black saturns, di-rings and bi-rings in five spacetime dimensions as well as
extremal Myers-Perry black holes and black saturns in dimensions greater than
five. Some of these constructions constitute the first examples of black hole
solutions with extremal disconnected horizons in vacuum Einstein gravity.Comment: v2: 30pp, 12 figures; comments and reference added; comparison
between approximate and analytic black ring and Myers-Perry solutions added;
to be published in JHE
Null-Wave Giant Gravitons from Thermal Spinning Brane Probes
We construct and analyze thermal spinning giant gravitons in type II/M-theory
based on spherically wrapped black branes, using the method of thermal probe
branes originating from the blackfold approach. These solutions generalize in
different directions recent work in which the case of thermal (non-spinning)
D3-brane giant gravitons was considered, and reveal a rich phase structure with
various new properties. First of all, we extend the construction to M-theory,
by constructing thermal giant graviton solutions using spherically wrapped M2-
and M5-branes. More importantly, we switch on new quantum numbers, namely
internal spins on the sphere, which are not present in the usual extremal limit
for which the brane world volume stress tensor is Lorentz invariant. We examine
the effect of this new type of excitation and in particular analyze the
physical quantities in various regimes, including that of small temperatures as
well as low/high spin. As a byproduct we find new stationary dipole-charged
black hole solutions in AdS_m X S^n backgrounds of type II/M-theory. We finally
show, via a double scaling extremal limit, that our spinning thermal giant
graviton solutions lead to a novel null-wave zero-temperature giant graviton
solution with a BPS spectrum, which does not have an analogue in terms of the
conventional weakly coupled world volume theory.Comment: v1: 31p
The Young Modulus of Black Strings and the Fine Structure of Blackfolds
We explore corrections in the blackfold approach, which is a worldvolume
theory capturing the dynamics of thin black branes. The corrections probe the
fine structure of the branes, going beyond the approximation in which they are
infinitely thin, and account for the dipole moment of worldvolume stress-energy
as well as the internal spin degrees of freedom. We show that the dipole
correction is induced elastically by bending a black brane. We argue that the
long-wavelength linear response coefficient capturing this effect is a
relativistic generalization of the Young modulus of elastic materials and we
compute it analytically. Using this we draw predictions for black rings in
dimensions greater than six. Furthermore, we employ our corrected blackfold
equations to various multi-spinning black hole configurations in the blackfold
limit, finding perfect agreement with known analytic solutions.Comment: v1: 28 pages + appendices. v2: Important sign corrections in sec. 3.
Other minor correction
Black Branes as Piezoelectrics
We find a realization of linear electroelasticity theory in gravitational
physics by uncovering a new response coefficient of charged black branes,
exhibiting their piezoelectric behavior. Taking charged dilatonic black strings
as an example and using the blackfold approach we measure their elastic and
piezolectric moduli. We also use our results to draw predictions about the
equilibrium condition of charged dilatonic black rings in dimensions higher
than six.Comment: v2: 9 pages; important sign corrections in section 3 and other minor
corrections; published in PR
Uncertainties in the solar photospheric oxygen abundance
The purpose of this work is to better understand the confidence limits of the
photospheric solar oxygen abundance derived from three-dimensional models using
the forbidden [OI] line at 6300 \AA , including correlations with other
parameters involved. We worked with a three-dimensional empirical model and two
solar intensity atlases. We employed Bayesian inference as a tool to determine
the most probable value for the solar oxygen abundance given the model chosen.
We considered a number of error sources, such as uncertainties in the continuum
derivation, in the wavelength calibration and in the abundance/strength of Ni.
Our results shows correlations between the effects of several parameters
employed in the derivation. The Bayesian analysis provides robust confidence
limits taking into account all of these factors in a rigorous manner. We obtain
that, given the empirical three-dimensional model and the atlas observations
employed here, the most probable value for the solar oxygen abundance is
. However, we note that this uncertainty does
not consider possible sources of systematic errors due to the model choice.Comment: Accepted for publication in Astronomy and Astrophysic
Blackfolds in (Anti)-de Sitter Backgrounds
We construct different neutral blackfold solutions in Anti-de Sitter and de
Sitter background spacetimes in the limit where the cosmological scale is taken
to be much larger than the transverse horizon size. This includes a class of
blackfolds with horizons that are products of odd-spheres times a transverse
sphere, for which the thermodynamic stability is also studied. Moreover, we
exhibit a specific case in which the same blackfold solution can describe
different limiting black hole spacetimes therefore illustrating the geometric
character of the blackfold approach. Furthermore, we show that the
higher-dimensional Kerr-(Anti)-de Sitter black hole allows for ultra-spinning
regimes in the relevant limit of large cosmological scale, and demonstrate that
this is correctly described by a pancaked blackfold geometry. We also give
evidence for the possibility of saturating the rigidity theorem in these
backgrounds.Comment: v1: 1+29 pages, latex. v2: cosmetic changes. v3: .pdf file correcte
Influence of High Aspect Ratio Nanoparticle Filler Addition on Piezoelectric Nanocomposites
Piezoelectric nanogenerators (PNGs) are a new class of energy harvesting materials that show potential as a direct energy source for low powered electronics. Recently, piezoelectric polymers have been utilized for PNG technology due to low toxicity, high flexibility, and facile solution processing which provide manufacturing opportunities such as screen printing. Throughout the last decade, countless projects have focused on how to enhance the energy harvesting capabilities of these PNGs through the incorporation of nanoparticle fillers, which have been reported to enhance the piezoelectric properties of the film either directly through their intrinsic piezoelectric properties or through acting as surfaces for the interfacial nucleation of piezoelectric polymer crystals.
Herein, two systems of PNGs formed from piezoelectric copolymers poly(vinylidene fluoride-co-hexafluropropylene) or poly(vinylidene fluoride-co-trifluoroethylene) mixed with high aspect ratio zinc oxide nanowires, hydroxyl functionalized multi-walled carbon nanotubes, or carboxylic acid functionalized single walled carbon nanotubes were investigated. Variations of filler type and loading are tested to determine influences on film morphology and piezoelectric properties. Power harvesting tests are conducted to directly determine the effect of nanoparticle addition on the output power of the non-poled devices. Both copolymer systems are found to exhibit a non-linear increase in output power with the increase of nanoparticle filler loading. The crystal polymorph properties of both systems are investigated by Fourier transform infrared spectroscopy. The microstructure of the poly(vinylidene fluoride-co-trifluoroethylene) films are further examined using X-ray diffraction, differential scanning calorimetry, polarized optical microscopy, and atomic force microscopy to determine the mechanism behind the increased power harvesting capabilities. As well, explanations for perceived output power from “self-poled” films are briefly explored
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