Small deformations of extreme Kerr black hole initial data

We prove the existence of a family of initial data for Einstein equations which represent small deformations of the extreme Kerr black hole initial data. The data in this family have the same asymptotic geometry as extreme Kerr. In particular, the deformations preserve the angular momentum and the area of the cylindrical end.Comment: 26 pages, 4 figure

Extremal black hole initial data deformations

We study deformations of axially symmetric initial data for Einstein-Maxwell equations satisfying the time-rotation ($t$-$\phi$) symmetry and containing one asymptotically cylindrical end and one asymptotically flat end. We find that the $t$-$\phi$ symmetry implies the existence of a family of deformed data having the same horizon structure. This result allows us to measure how close solutions to Lichnerowicz equation are when arising from nearby free data.Comment: 21 pages, no figures, final versio

Expression and refolding of the protective antigen of Bacillus anthracis: A model for high-throughput screening of antigenic recombinant protein refolding

Bacillus anthracis protective antigen (PA) is a well known and relevant immunogenicprotein that is the basis for both anthrax vaccines and diagnostic methods. Properly foldedantigenic PA is necessary for these applications. In this study a high level of PA was obtained inrecombinant Escherichia coli. The protein was initially accumulated in inclusion bodies, whichfacilitated its efficient purification by simple washing steps; however, it could not be recognizedby specific antibodies. Refolding conditions were subsequently analyzed in a high-throughputmanner that enabled nearly a hundred different conditions to be tested simultaneously. Therecovery of the ability of PA to be recognized by antibodies was screened by dot blot usinga coefficient that provided a measure of properly refolded protein levels with a high degreeof discrimination. The best refolding conditions resulted in a tenfold increase in the intensityof the dot blot compared to the control. The only refolding additive that consistently yieldedgood results was L-arginine. The statistical analysis identified both cooperative and negativeinteractions between the different refolding additives. The high-throughput approach describedin this study that enabled overproduction, purification and refolding of PA in a simple andstraightforward manner, can be potentially useful for the rapid screening of adequate refoldingconditions for other overexpressed antigenic proteins.Fil: Pavan, María Elisa. Biochemiq; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Biológica; ArgentinaFil: Pavan, Esteban E.. Politecnico di Milano; ItaliaFil: Cairo, Fabian Martin. Biochemiq; ArgentinaFil: Pettinari, María Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentin

Non-thermal processes in bowshocks of runaway stars. Application to Zeta Oph

Runaway massive stars are O- and B-type stars with high spatial velocities with respect to the interstellar medium. These stars can produce bowshocks in the surrounding gas. Bowshocks develop as arc-shaped structures, with bows pointing to the same direction as the stellar velocity, while the star moves supersonically through the interstellar gas. The piled-up shocked matter emits thermal radiation and a population of locally accelerated relativistic particles is expected to produce non-thermal emission over a wide range of energies. We aim to model the non-thermal radiation produced in these sources. Under some assumptions, we computed the non-thermal emission produced by the relativistic particles and the thermal radiation caused by free-free interactions, for O4I and O9I stars. We applied our model to Zeta Oph (HD 149757), an intensively studied massive star seen from the northern hemisphere. This star has spectral type O9.5V and is a well-known runaway. Spectral energy distributions of massive runaways are predicted for the whole electromagnetic spectrum. We conclude that the non-thermal radiation might be detectable at various energy bands for relatively nearby runaway stars, especially at high-energy gamma rays. Inverse Compton scattering with photons from the heated dust gives the most important contribution to the high-energy spectrum. This emission approaches Fermi sensitivities in the case of Zeta Oph.Comment: 11 pages, 11 figures.- Accepted for publication in A&A

The role of pressure on the magnetism of bilayer graphene

We study the effect of pressure on the localized magnetic moments induced by vacancies in bilayer graphene in the presence of topological defects breaking the bipartite nature of the lattice. By using a mean-field Hubbard model we address the two inequivalent types of vacancies that appear in the Bernal stacking bilayer graphene. We find that by applying pressure in the direction perpendicular to the layers the critical value of the Hubbard interaction needed to polarize the system decreases. The effect is particularly enhanced for one type of vacancies, and admits straightforward generalization to multilayer graphene in Bernal stacking and graphite. The present results clearly demonstrate that the magnetic behavior of multilayer graphene can be affected by mechanical transverse deformation

Horizon area--angular momentum inequality for a class of axially symmetric black holes

We prove an inequality between horizon area and angular momentum for a class of axially symmetric black holes. This class includes initial conditions with an isometry which leaves fixed a two-surface. These initial conditions have been extensively used in the numerical evolution of rotating black holes. They can describe highly distorted black holes, not necessarily near equilibrium. We also prove the inequality on extreme throat initial data, extending previous results.Comment: 23 pages, 5 figures. We improved the hypothesis of the main theore

Maximum approximate entropy and r threshold: A new approach for regularity changes detection

Approximate entropy (ApEn) has been widely used as an estimator of regularity in many scientific fields. It has proved to be a useful tool because of its ability to distinguish different system's dynamics when there is only available short-length noisy data. Incorrect parameter selection (embedding dimension $m$, threshold $r$ and data length $N$) and the presence of noise in the signal can undermine the ApEn discrimination capacity. In this work we show that $r_{max}$ ($ApEn(m,r_{max},N)=ApEn_{max}$) can also be used as a feature to discern between dynamics. Moreover, the combined use of $ApEn_{max}$ and $r_{max}$ allows a better discrimination capacity to be accomplished, even in the presence of noise. We conducted our studies using real physiological time series and simulated signals corresponding to both low- and high-dimensional systems. When $ApEn_{max}$ is incapable of discerning between different dynamics because of the noise presence, our results suggest that $r_{max}$ provides additional information that can be useful for classification purposes. Based on cross-validation tests, we conclude that, for short length noisy signals, the joint use of $ApEn_{max}$ and $r_{max}$ can significantly decrease the misclassification rate of a linear classifier in comparison with their isolated use