4,696 research outputs found

    Gravitation-Wave Emission in Shift-Symmetric Horndeski Theories

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    Gravity theories beyond general relativity typically predict dipolar gravitational emission by compact-star binaries. This emission is sourced by "sensitivity" parameters depending on the stellar compactness. We introduce a general formalism to calculate these parameters, and show that in shift-symmetric Horndeski theories stellar sensitivities and dipolar radiation vanish, provided that the binary's dynamics is perturbative (i.e., the post-Newtonian formalism is applicable) and cosmological-expansion effects can be neglected. This allows one to reproduce the binary-pulsar-observed orbital decay

    Forage Quality, Yield and Palatability of Quackgrass (\u3ci\u3eElytrigia repens\u3c/i\u3e (L.) Nevski)

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    Quackgrass (Elytrigia repens (L.) Nevski) is a competitive perennial invader of pastures and hay meadows which is frequently harvested as forage in mixtures with desired forage species. Field experiments were conducted to compare quackgrass with cool-season perennial grasses grown under the same soil and climatic conditions, in terms of forage quality, productivity, and palatability. The forage quality of the hays was influenced by the grass species. Quackgrass showed forage crude protein (CP) concentration that was equal to those of perennial ryegrass (Lolium perenne), reed canarygrass (Phalaris arundinacea) and Kentucky bluegrass (Poa pratensis), and greater than orchardgrass (Dactylis glomerata). The neutral detergent fiber (NDF) acid detergent fiber (ADF) concentration of the quackgrass was intermediate between those of perennial ryegrass and Kentucky bluegrass. Yields of quackgrass was equal to reed canarygrass, and greater than those of Kentucky bluegrass, orchardgrass and perennial ryegrass. The different hays did not affect the response of animals by feed intake. Quackgrass hay had higher phosphorus (P) and potassium (K) concentration, and lower calcium (Ca), magnesium (Mg) concentrations. Quackgrass was not to be inferior to other cool-season perennial grasses under frequent utilization

    CT dose reduction factors in the thousands using X-ray phase contrast

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    Phase-contrast X-ray imaging can improve the visibility of weakly absorbing objects (e.g. soft tissues) by an order of magnitude or more compared to conventional radiographs. Previously, it has been shown that combining phase retrieval with computed tomography (CT) can increase the signal-to-noise ratio (SNR) by up to two orders of magnitude over conventional CT at the same radiation dose, without loss of image quality. Our experiments reveal that as radiation dose decreases, the relative improvement in SNR increases. We discovered this enhancement can be traded for a reduction in dose greater than the square of the gain in SNR. Upon reducing the dose 300 fold, the phase-retrieved SNR was still almost 10 times larger than the absorption contrast data. This reveals the potential for dose reduction factors in the tens of thousands without loss in image quality, which would have a profound impact on medical and industrial imaging applications

    Investigation of heavy-heavy pseudoscalar mesons in thermal QCD Sum Rules

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    We investigate the mass and decay constant of the heavy-heavy pseudoscalar, BcB_c, ηc\eta_c and ηb\eta_b mesons in the framework of finite temperature QCD sum rules. The annihilation and scattering parts of spectral density are calculated in the lowest order of perturbation theory. Taking into account the additional operators arising at finite temperature, the nonperturbative corrections are also evaluated. The masses and decay constants remain unchanged under T100 MeVT\cong 100 ~MeV, but after this point, they start to diminish with increasing the temperature. At critical or deconfinement temperature, the decay constants reach approximately to 35% of their values in the vacuum, while the masses are decreased about 7%, 12% and 2% for BcB_c, ηc\eta_c and ηb\eta_b states, respectively. The results at zero temperature are in a good consistency with the existing experimental values as well as predictions of the other nonperturbative approaches.Comment: 11 Pages, 2 Tables and 6 Figure

    Slowly Rotating Black Holes in Dynamical Chern-Simons Gravity: Deformation Quadratic in the Spin

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    We derive a stationary and axisymmetric black hole solution to quadratic order in the spin angular momentum. The previously found, linear-in-spin terms modify the odd-parity sector of the metric, while the new corrections appear in the even-parity sector. These corrections modify the quadrupole moment, as well as the (coordinate-dependent) location of the event horizon and the ergoregion. Although the linear-in-spin metric is of Petrov type D, the quadratic order terms render it of type I. The metric does not possess a second-order Killing tensor or a Carter-like constant. The new metric does not possess closed timelike curves or spacetime regions that violate causality outside of the event horizon. The new, even-parity modifications to the Kerr metric decay less rapidly at spatial infinity than the leading-order in spin, odd-parity ones, and thus, the former are more important when considering black holes that are rotating moderately fast. We calculate the modifications to the Hamiltonian, binding energy and Kepler's third law. These modifications are crucial for the construction of gravitational wave templates for black hole binaries, which will enter at second post-Newtonian order, just like dissipative modifications found previously.Comment: 21 pages, 2 figures; Typos correcte

    Meissner effect in honeycomb arrays of multi-walled carbon nanotubes

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    We report Meissner effect for type-II superconductors with a maximum Tc of 19 K, which is the highest value among those in new-carbon related superconductors, found in the honeycomb arrays of multi-walled CNTs (MWNTs). Drastic reduction of ferromagnetic catalyst and efficient growth of MWNTs by deoxidization of catalyst make the finding possible. The weak magnetic anisotropy, superconductive coherence length (- 7 nm), and disappearance of the Meissner effect after dissolving array structure indicate that the graphite structure of an MWNT and those intertube coupling in the honeycomb array are dominant factors for the mechanism.Comment: 6 page

    \Omega-deformation of B-twisted gauge theories and the 3d-3d correspondence

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    We study \Omega-deformation of B-twisted gauge theories in two dimensions. As an application, we construct an \Omega-deformed, topologically twisted five-dimensional maximally supersymmetric Yang-Mills theory on the product of a Riemann surface Σ\Sigma and a three-manifold MM, and show that when Σ\Sigma is a disk, this theory is equivalent to analytically continued Chern-Simons theory on MM. Based on these results, we establish a correspondence between three-dimensional N=2\mathcal{N} = 2 superconformal theories and analytically continued Chern-Simons theory. Furthermore, we argue that there is a mirror symmetry between {\Omega}-deformed two-dimensional theories.Comment: 26 pages. v2: the discussion on the boundary condition for vector multiplet improved, and other minor changes mad
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