Induced higher-derivative massive gravity on a 2-brane in 4D Minkowski space

In this paper we revisit the problem of localizing gravity in a 2-brane embedded in a 4D Minkowski space to address induction of high derivative massive gravity. We explore the structure of propagators to find well-behaved higher-derivative massive gravity induced on the brane. Exploring a special case in the generalized mass term of the graviton propagator we find a model of consistent higher order gravity with an additional unitary massive spin-2 particle and two massless particles: one spin-0 particle and one spin-1 particle. The condition for the absence of tachyons is satisfied for both `right' and `wrong' signs of the Einstein-Hilbert term on the 2-brane. We also find the Pauli-Fierz mass term added to the new massive gravity in three dimensions and recover the low dimensional DGP model.Comment: Latex, 12 pages, no figure; refs added, version to appear in PL

Low Rank Vector Bundles on the Grassmannian G(1,4)

Here we define the concept of $L$-regularity for coherent sheaves on the Grassmannian G(1,4) as a generalization of Castelnuovo-Mumford regularity on ${\bf{P}^n}$. In this setting we prove analogs of some classical properties. We use our notion of $L$-regularity in order to prove a splitting criterion for rank 2 vector bundles with only a finite number of vanishing conditions. In the second part we give the classification of rank 2 and rank 3 vector bundles without "inner" cohomology (i.e. H^i_*(E)=H^i(E\otimes\Q)=0 for any $i=2,3,4$) on G(1,4) by studying the associated monads.Comment: 11 pages, no figure

Gemini spectra of 12000K white dwarf stars

We report signal-to-noise ratio SNR ~ 100 optical spectra for four DA white dwarf stars acquired with the GMOS spectrograph of the 8m Gemini north telescope. These stars have 18<g<19 and are around Teff ~ 12000 K, were the hydrogen lines are close to maximum. Our purpose is to test if the effective temperatures and surface gravities derived from the relatively low signal-to-noise ratio ( ~ 21) optical spectra acquired by the Sloan Digital Sky Survey through model atmosphere fitting are trustworthy. Our spectra range from 3800A to 6000A, therefore including H beta to H9. The H8 line was only marginally present in the SDSS spectra, but is crucial to determine the gravity. When we compare the values published by Kleinman et al. (2004) and Eisenstein et al. (2006) with our line-profile (LPT) fits, the average differences are: Delta Teff ~ 320 K, systematically lower in SDSS, and Delta log g ~ 0.24 dex, systematically larger in SDSS. The correlation between gravity and effective temperature can only be broken at wavelengths bluer than 3800 A. The uncertainties in Teff are 60% larger, and in log g larger by a factor of 4, than the Kleinman et al. (2004) and Eisenstein et al. (2006) internal uncertainties.Comment: 11 pages and 8 figure

HST Observations of the Central-Cusp Globular Cluster NGC 6752. The Effect of Binary Stars on the Luminosity Function in the Core

We consider the effect of binary stars on the main-sequence luminosity functions observed in the core of globular clusters, with specific reference to NGC 6752. We find that mass segregation results in an increased binary fraction at fainter magnitudes along the main-sequence. If this effect is not taken into account when analyzing luminosity functions, erroneous conclusions can be drawn regarding the distribution of single stars, and the dynamical state of the cluster. In the core of NGC 6752, our HST data reveal a flat luminosity function, in agreement with previous results. However, when we correct for the increasing binary fraction at faint magnitudes, the LF begins to fall immediately below the turn-off. This effect appears to be confined to the inner core radius of the cluster.Comment: 10 pages, 3 figures Accepted to ApJ Lett Vol 513 Number

Gauge fields in a string-cigar braneworld

In this work we investigate the properties of an Abelian gauge vector field in a thin and in a smoothed string-like braneworld, the so-called string-cigar model. This thick brane scenario satisfies the regularity conditions and it can be regarded as an interior and exterior string-like solution. The source undergoes a geometric Ricci flow which is connected to a variation of the bulk cosmological constant. The Ricci flow changes the width and amplitude of the massless mode at the brane core and recover the usual thin string-like behavior at large distances. By numerical means we obtain the Kaluza-Klein (KK) spectrum for both the thin brane and the string-cigar. It turns out that both models exhibit a mass gap between the massless and the massive modes and between the high and the low mass regimes. The KK modes are smooth near the brane and their amplitude are enhanced by the string-cigar core. The analogue Schr\"odinger potential is also tuned by the geometric flow.Comment: The discussion about the Kaluza-Klein spectrum of the gauge field was improved. Numerical analysis was adapted to the conventional notation on Kaluza-Klein number. Some graphics were modified for considering other notation. Results unchanged. References added. Corrected typos. 17 pages. 6 figures. To match version to appears in Physics Letters

Wavepacket scattering on graphene edges in the presence of a (pseudo) magnetic field

The scattering of a Gaussian wavepacket in armchair and zigzag graphene edges is theoretically investigated by numerically solving the time dependent Schr\"odinger equation for the tight-binding model Hamiltonian. Our theory allows to investigate scattering in reciprocal space, and depending on the type of graphene edge we observe scattering within the same valley, or between different valleys. In the presence of an external magnetic field, the well know skipping orbits are observed. However, our results demonstrate that in the case of a pseudo-magnetic field, induced by non-uniform strain, the scattering by an armchair edge results in a non-propagating edge state.Comment: 8 pages, 7 figure

Efficiency of low versus high airline pressure in stunning cattle with a pneumatically powered penetrating captive bolt gun

The efficiency of stunning cattle was assessed in 443 animals (304 pure Zebu and 139 crossbred cattle), being mainly mature bulls and cows. Cattle were stunned using a Jarvis pneumatically powered penetrating captive bolt gun operating with low (160–175 psi, N = 82) and high (190 psi, N = 363) airline pressure, which was within the manufactures specifications. Signs of brain function and the position of the shots on the heads were recorded after stunning. Velocity of the captive bolt and its physical parameters were calculated. Cattle shot with low pressures showed more rhythmic respiration (27 vs. 8%, P < 0.001), less tongue protrusion (4 vs. 12%, P = 0.03) and less masseter relaxation (22 vs. 48%, P < 0.001). There was an increased frequency of shots in the ideal position when cattle were shot with the low compared to high airline pressures (15.3 vs. 3.1%). Bolt velocity and its physical parameters were significantly (P < 0.01) higher when using high pressure. Airline pressures below 190 psi are inappropriate when shooting adult Zebu beef cattle with pneumatically powered penetrating captive bolt guns

A systematic comparison of supervised classifiers

Pattern recognition techniques have been employed in a myriad of industrial, medical, commercial and academic applications. To tackle such a diversity of data, many techniques have been devised. However, despite the long tradition of pattern recognition research, there is no technique that yields the best classification in all scenarios. Therefore, the consideration of as many as possible techniques presents itself as an fundamental practice in applications aiming at high accuracy. Typical works comparing methods either emphasize the performance of a given algorithm in validation tests or systematically compare various algorithms, assuming that the practical use of these methods is done by experts. In many occasions, however, researchers have to deal with their practical classification tasks without an in-depth knowledge about the underlying mechanisms behind parameters. Actually, the adequate choice of classifiers and parameters alike in such practical circumstances constitutes a long-standing problem and is the subject of the current paper. We carried out a study on the performance of nine well-known classifiers implemented by the Weka framework and compared the dependence of the accuracy with their configuration parameter configurations. The analysis of performance with default parameters revealed that the k-nearest neighbors method exceeds by a large margin the other methods when high dimensional datasets are considered. When other configuration of parameters were allowed, we found that it is possible to improve the quality of SVM in more than 20% even if parameters are set randomly. Taken together, the investigation conducted in this paper suggests that, apart from the SVM implementation, Weka's default configuration of parameters provides an performance close the one achieved with the optimal configuration