296 research outputs found
The world-sheet corrections to dyons in the Heterotic theory
All the linear alpha-prime corrections, however excluding the gravitational
Chern-Simons correction, are studied in the toroidally compactified critical
Heterotic string theory. These corrections are computed to the entropy for a
BPS static spherical four dimensional dyonic black hole which represents a
wrapped fundamental string carrying arbitrary winding and momentum charges
along one cycle in the presence of KK-monopole and H-monopole charges
associated to another cycle. It is verified that after the inclusion of the
gravitational Chern-Simons corrections [hep-th/0608182], all the linear
alpha-prime corrections to the entropy for the supersymmetric dyon can be
reproduced by the inclusion of only the Gauss-Bonnet Lagrangian to the
supergravity approximation of the induced Lagrangian.Comment: JHEP style, 17 Pages; v2: a typo corrected ; v3: The coupling of the
gravitational Chern-Simons terms to the three form field strength taken into
account. The conclusion correcte
Higher Derivative Corrections to Eleven Dimensional Supergravity via Local Supersymmetry
In this paper we derive higher derivative corrections to the eleven
dimensional supergravity by applying the Noether method with respect to the N=1
local supersymmetry. An ansatz for the higher derivative effective action,
which includes quartic terms of the Riemann tensor, is parametrized by 132
parameters. Then we show that by the requirement of the local supersymmetry,
the higher derivative effective action is essentially described by two
parameters. The bosonic parts of these two superinvariants completely match
with the known results obtained by the perturbative calculations in the type
IIA superstring theory. Since the calculations are long and systematic, we
build the computer programming to check the cancellation of the variations
under the local supersymmetry. This is an extended version of our previous
paper hep-th/0508204.Comment: 67 pages, no figure, references added, typos correcte
Incorporation Of Nanocrystals With Different Dimensionalities In Hybrid Tio2/p3ht Solar Cells
We investigate the effect of TiO2 nanoparticles-nanospheres and nanorods-inserted in the poly(3-hexylthiophene) (P3HT) matrix of TiO2?P3HT inverted hybrid solar cells. X-ray diffraction, high-resolution transmission electron microscopy, small-angle x-ray scattering, photoluminescence, and photoelectrochemical experiments were employed to investigate the structure, morphology, and photoactivity of TiO2 nanoparticles modified with 2-thiopheneacetic acid, mixed or not with P3HT. Both TiO2 nanospheres and TiO2 nanorods presented a good dispersion in the polymer matrix. The incorporation of TiO2 nanospheres and nanorods has improved the photocurrent generation, and devices with efficiency values up to 1.35% were obtained. Our results reveal that the nanoscale morphology enables an enhanced interfacial area for exciton dissociation. In particular, the nanospheres contribute with their high specific area, and the nanorods contribute with their high aspect ratio.51Lee, C.-K., Pao, C.-W., Chen, C.-W., Correlation of nanoscale organizations of polymer and nanocrystals in polymer/inorganic nanocrystal bulk heterojunction hybrid solar cells: Insights from multiscale molecular simulations (2013) Energy Environ. Sci., 6, pp. 307-315Huynh, W.U., Dittmer, J.J., Alivisatos, A.P., Hybrid nanorod: Polymer solar cells (2002) Science, 295, pp. 2425-2427Sian, S., Chen, C.-W., Polymer-metal-oxide hybrid solar cells (2013) J. Mater. Chem. A, 1, pp. 10574-10591Das, J., A facile nonaqueous route for fabricating titania nanorods and their viability in quasi-solid-state dye-sensitized solar cells (2010) J. Mater. Chem., 20, pp. 4425-4431Cozzoli, P.D., Kornowski, A., Weller, H., Low-temperature synthesis of soluble and processable organic-capped anatase TiO2 nanorods (2003) J. Am. Chem. Soc., 125, pp. 14539-14548Zeng, T.W., A large interconnecting network within hybrid MEH-PPV/TiO2 nanorod photovoltaic devices (2006) Nanotechnology, 17, p. 5387Yang, P., TiO2 nanowire electron transport pathways inside organic photovoltaics (2013) Phys. Chem. Chem. Phys., 15, pp. 4566-4572Lin, Y., Morphology control in TiO2 nanorod/polythiophene composites for bulk heterojunction solar cells using hydrogen bonding (2012) Macromolecules, 45, pp. 8665-8673Ranjitha, A., Inverted organic solar cells based on Cd-doped TiO2 as an electron extraction layer (2014) Superlattices Microstruct., 74, pp. 114-122Bolognesi, M., The effect of selective contact electrodes on the interfacial charge recombination kinetics and device efficiency of organic polymer solar cells (2011) Phys. Chem. Chem. Phys., 13, pp. 6105-6109Mor, G.K., High efficiency double heterojunction polymer photovoltaic cells using highly ordered TiO2 nanotube arrays (2007) Appl. Phys. Lett., 91, p. 152111Planells, M., Oligothiophene interlayer effect on photocurrent generation for hybrid TiO2/P3HT solar cells (2014) Appl. Mater. Interfaces, 6, pp. 17226-17235Freitas, F.S., Tailoring the interface using thiophene small molecules in TiO2/P3HT hybrid solar cells (2012) Phys. Chem. Chem. Phys., 14, pp. 11990-11993Liu, K., Efficient hybrid plasmonic polymer solar cells with Ag nanoparticle decorated TiO2 nanorods embedded in the active layer (2014) Nanoscale, 6, pp. 6180-6186Lin, Y.-Y., Interfacial nanostructuring on the performance of polymer/TiO2 nanorod bulk heterojunction solar cells (2009) J. Am. Chem. Soc., 131, pp. 3644-3649Eom, S.H., Roles of interfacial modifiers in hybrid solar cells: Inorganic/polymer bilayer versus inorganic/polymer: Fullerene bulk heterojunction (2014) Appl. Mater. Interfaces, 6, pp. 803-810Ravirajan, P., Hybrid polymer/zinc oxide photovoltaic devices with vertically oriented ZnO nanorods and an amphiphilic molecular interface layer (2006) J. Phys. Chem. B, 110, pp. 7635-7639Abate, A., Protic ionic liquids as p-dopant for organic hole transporting materials and their application in high efficiency hybrid solar cells (2013) J. Am. Chem. Soc., 135, pp. 13538-13548Beaucage, G., Approximations leading to a unified exponential/power-law approach to small-angle scattering (1995) J. Appl. Cryst., 28, pp. 717-728Beaucage, G., Small-angle scattering from polymeric mass fractals of arbitrary mass-fractal dimension (1996) J. Appl. Cryst., 29, pp. 134-146Beaucage, G., Kammler, H.K., Pratsinis, S.E., Particle size distributions from smallangle scattering using global scattering functions (2004) J. Appl. Cryst., 37, pp. 523-535Khatri, I., Similar device architectures for inverted organic solar cell and laminated solid-state dye-sensitized solar cells (2012) ISRN Electron., 10Choi, H.C., Jung, Y.M., Kim, S.B., Size effects in the Raman spectra of TiO2 nanoparticles (2005) Vib. Spectrosc., 37, pp. 33-38Li, G., Polymer self-organization enhances photovoltaic efficiency (2005) J. Appl. Phys., 98, p. 43704Salim, T., Solvent additives and their effects on blend morphologies of bulk heterojunctions (2011) J. Mater. Chem., 21, pp. 242-250Hwang, I.W., Carrier generation and transport in bulk heterojunction films processed with 1,8-octanedithiol as a processing additive (2008) J. Appl. Phys., 104, p. 033706Nguyen, H.Q., Synthesis and characterization of a polyisoprene-b-polystyrene-b-poly (3-hexylthiophene) triblock copolymer (2013) Polym. Chem., 4, pp. 462-465Prosa, T.J., X-ray structural studies of poly(3-alkylthiophenes): An example of an inverse comb (1992) Macromolecules, 25, p. 4364De Freitas, J.N., Connecting the (quantum) dots: Towards hybrid photovoltaic devices based on chalcogenide gels (2012) Phys. Chem. Chem. Phys., 14, pp. 15180-15184Yang, P., Identifying effects of TiO2 nanowires inside bulk heterojunction organic photovoltaics on charge diffusion and recombination (2014) J. Mater. Chem. C, 2, pp. 4922-4927Grancini, G., Boosting infrared light harvesting by molecular functionalization of metal oxide/polymer interfaces in efficient hybrid solar cells (2012) Adv. Funct. Mater., 22, pp. 2160-2166Liao, H.-C., Diketopyrrolopyrrole-based oligomer modified TiO2 nanorods for airstable and all solution processed poly(3-hexylthiophene): TiO2 bulk heterojunction inverted solar cell (2012) J. Mater. Chem., 22, pp. 10589-1059
Charge and mass effects on the evaporation of higher-dimensional rotating black holes
To study the dynamics of discharge of a brane black hole in TeV gravity
scenarios, we obtain the approximate electromagnetic field due to the charged
black hole, by solving Maxwell's equations perturbatively on the brane. In
addition, arguments are given for brane metric corrections due to backreaction.
We couple brane scalar and brane fermion fields with non-zero mass and charge
to the background, and study the Hawking radiation process using well known low
energy approximations as well as a WKB approximation in the high energy limit.
We argue that contrary to common claims, the initial evaporation is not
dominated by fast Schwinger discharge.Comment: Published version. Minor typos corrected. 29 pages, 5 figure
Heterotic String Compactifications on Half-flat Manifolds II
In this paper, we continue the analysis of heterotic string compactifications
on half-flat mirror manifolds by including the 10-dimensional gauge fields. It
is argued, that the heterotic Bianchi identity is solved by a variant of the
standard embedding. Then, the resulting gauge group in four dimensions is still
E6 despite the fact that the Levi-Civita connection has SO(6) holonomy. We
derive the associated four-dimensional effective theories including matter
field terms for such compactifications. The results are also extended to more
general manifolds with SU(3) structure.Comment: 31 page
Fermion Zero Modes in the Presence of Fluxes and a Non-perturbative Superpotential
We study the effect of background fluxes of general Hodge type on the
supersymmetry conditions and on the fermionic zero modes on the world-volume of
a Euclidean M5/D3-brane in M-theory/type IIB string theory.
Using the naive susy variation of the modulino fields to determine the number
of zero modes in the presence of a flux of general Hodge type, an inconsistency
appears. This inconsistency is resolved by a modification of the supersymmetry
variation of the modulinos, which captures the back-reaction of the
non-perturbative effects on the background flux and the geometry.Comment: 21 pages, revised version contains a new appendix on dimensional
reduction of spinors and some changes in the spinor equation
High resolution micro arthrography of hard and soft tissues in a murine model
SummaryObjectiveRecent developments on high resolution micro computed tomography (μCT) allow imaging of soft tissues in small animal joints. Nevertheless, μCT images cannot distinguish soft tissues from synovial fluid due to their similar mass density, limiting the 3D assessment of soft tissues volume and thickness. This study aimed to evaluate a lead chromate contrast agent for μCΤ arthrography of rat knee joints ex vivo.DesignIntact tibiofemoral rat joints were injected with the contrast agent at different concentrations and imaged using a μCT at 2.7 μm isotropic voxel size. Cartilage thickness was measured using an automated procedure, validated against histological measurements, and analyzed as a function of μCT image resolution. Changes in hard and soft tissues were also analyzed in tibiofemoral joints 4 weeks after surgical destabilization of the medial meniscus (DMM).ResultsThe contrast agent diffused well throughout the whole knee cavity without penetrating the tissues, therefore providing high contrast at the boundaries between soft tissues and synovial fluid space. Thickness analysis of cartilage demonstrated a high similarity between histology and μ-arthrography approaches (R2 = 0.90). Four weeks after surgical DMM, the development of osteophytes (Oph) and cartilage ulcerations was recognizable with μCT, as well as a slight increase in trabecular bone porosity, and decrease in trabecular thickness.ConclusionsA lead chromate-based contrast agent allowed discriminating the synovial fluid from soft tissues of intact knee joints, and thus made possible both qualitative and quantitative assessment of hard and soft tissues in both intact and DMM tibiofemoral joints using high resolution μCT
Two-charge small black hole entropy: String-loops and multi-strings
We investigate the inclusion of 10-dimensional string loop corrections to the
entropy function of two-charge extremal small black holes of the heterotic
string theory compactified on S^1 x T^5 and show that the entropy is given by
\pi\sqrt{a q_1 q_2+b q_1} where q_1 and q_2 are the charges with q_1 >> q_2 >>
1 and a and b are constants. Incorporating certain multi-string states into the
microstate counting, we show that the new statistical entropy is consistent
with the macroscopic scaling for one and two units of momentum (winding) and
large winding (momentum). We discuss our scaling from the point of view of
related AdS_3 central charge and counting of chiral primaries in superconformal
quantum mechanics as well.Comment: 18 page
Elliptic Calabi-Yau Threefolds with Z_3 x Z_3 Wilson Lines
A torus fibered Calabi-Yau threefold with first homotopy group Z_3 x Z_3 is
constructed as a free quotient of a fiber product of two dP_9 surfaces.
Calabi-Yau threefolds of this type admit Z_3 x Z_3 Wilson lines. In conjunction
with SU(4) holomorphic vector bundles, such vacua lead to anomaly free, three
generation models of particle physics with a right handed neutrino and a
U(1)_{B-L} gauge factor, in addition to the SU(3)_C x SU(2)_L x U(1)_Y standard
model gauge group. This factor helps to naturally suppress nucleon decay. The
moduli space and Dolbeault cohomology of the threefold is also discussed.Comment: 51 pages, 13 figures; v2: references adde
Almost commuting unitary matrices related to time reversal
The behavior of fermionic systems depends on the geometry of the system and
the symmetry class of the Hamiltonian and observables. Almost commuting
matrices arise from band-projected position observables in such systems. One
expects the mathematical behavior of almost commuting Hermitian matrices to
depend on two factors. One factor will be the approximate polynomial relations
satisfied by the matrices. The other factor is what algebra the matrices are
in, either the matrices over A for A the real numbers, A the complex numbers or
A the algebra of quaternions.
There are potential obstructions keeping k-tuples of almost commuting
operators from being close to a commuting k-tuple. We consider two-dimensional
geometries and so this obstruction lives in KO_{-2}(A). This obstruction
corresponds to either the Chern number or spin Chern number in physics. We show
that if this obstruction is the trivial element in K-theory then the
approximation by commuting matrices is possible.Comment: 33 pages, 2 figures. In version 2 some formulas have been corrected
and some proofs have been rewritten to improve the expositio
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