Approaches to the Monopole-Dynamic Dipole Vacuum Solution Concerning the Structure of its Ernst's Potential on the Symmetry Axis

The FHP algorithm allows to obtain the relativistic multipole moments of a vacuum stationary axisymmetric solution in terms of coefficients which appear in the expansion of its Ernst's potential on the symmetry axis. First of all, we will use this result in order to determine, at a certain approximation degree, the Ernst's potential on the symmetry axis of the metric whose only multipole moments are mass and angular momentum. By using Sibgatullin's method we analyse a series of exacts solutions with the afore mentioned multipole characteristic. Besides, we present an approximate solution whose Ernst's potential is introduced as a power series of a dimensionless parameter. The calculation of its multipole moments allows us to understand the existing differences between both approximations to the proposed pure multipole solution.Comment: 24 pages, plain TeX. To be published in General Relativity and Gravitatio

Buscant Robert H. Merriman

El major Robert H. Merriman, va desaparèixer, els primers dies d’abril del 1938 en les rodalies de Corbera d’Ebre. La XV Brigada Internacional havia quedat encerclada per l’enemic, i grups de soldats intentaven arribar a les línies republicanes. En aquesta retirada potser va caure abatut en combat com també i ha la possibilitat que fos capturat i executat per les forces feixistes. Les especulacions sobre la mort de Merriman, i el lloc on van anar a raure les seves restes, han estat motiu de debat continuat. Fonts orals de Corbera d’Ebre manifestaven que oficials internacionals havien estat tancats en cases del Poble Vell abans de ser executats. Una de les fonts indicava l’emplaçament d’una fossa aïllada on havia estat enterrat un comandament que podia haver estat en Robert H. Meriman. Per tal de verificar la informació un grup d’estudiosos, arqueòlegs i antropòlegs va procedir a excavar el lloc la primavera del 2017, tanmateix no es van trobar indicis de cap enterrament

The temperature and chronology of heavy-element synthesis in low-mass stars

Roughly half of the heavy elements (atomic mass greater than that of iron) are believed to be synthesized in the late evolutionary stages of stars with masses between 0.8 and 8 solar masses. Deep inside the star, nuclei (mainly iron) capture neutrons and progressively build up (through the slow-neutron-capture process, or s-process) heavier elements that are subsequently brought to the stellar surface by convection. Two neutron sources, activated at distinct temperatures, have been proposed: 13C and 22Ne, each releasing one neutron per alpha-particle (4He) captured. To explain the measured stellar abundances, stellar evolution models invoking the 13C neutron source (which operates at temperatures of about one hundred million kelvin) are favoured. Isotopic ratios in primitive meteorites, however, reflecting nucleosynthesis in the previous generations of stars that contributed material to the Solar System, point to higher temperatures (more than three hundred million kelvin), requiring at least a late activation of 22Ne. Here we report a determination of the s-process temperature directly in evolved low-mass giant stars, using zirconium and niobium abundances, independently of stellar evolution models. The derived temperature supports 13C as the s-process neutron source. The radioactive pair 93Zr-93Nb used to estimate the s-process temperature also provides, together with the pair 99Tc-99Ru, chronometric information on the time elapsed since the start of the s-process, which we determine to be one million to three million years.Comment: 30 pages, 10 figure

Unusual case of a myxoma atrial left presenting with recurrent monoparesis

Usually, embolism is described from cardiac or large artery disease. Atrial fibrillation is the most common cause of cardiogenic emboli in stroke. Myxoma is responsible in only a few cases. We describe here a case of a patient who presented with recurrent pure left brachial monoparesis as a manifestation of a cardiac myxoma

Magnetic properties and domain-wall motion in single-crystal BaFe10.2Sn0.74Co0.66O19

The magnetic properties of BaFe12O19 and BaFe10.2Sn0.74Co0.66O19 single crystals have been investigated in the temperature range (1.8 to 320 K) with a varying field from -5 to +5 T applied parallel and perpendicular to the c axis. Low-temperature magnetic relaxation, which is ascribed to the domain-wall motion, was performed between 1.8 and 15 K. The relaxation of magnetization exhibits a linear dependence on logarithmic time. The magnetic viscosity extracted from the relaxation data, decreases linearly as temperature goes down, which may correspond to the thermal depinning of domain walls. Below 2.5 K, the viscosity begins to deviate from the linear dependence on temperature, tending to be temperature independent. The near temperature independence of viscosity suggests the existence of quantum tunneling of antiferromagnetic domain wall in this temperature range