Gravity on a parallelizable manifold. Exact solutions

The wave type field equation \square \vt^a=\la \vt^a, where \vt^a is a coframe field on a space-time, was recently proposed to describe the gravity field. This equation has a unique static, spherical-symmetric, asymptotically-flat solution, which leads to the viable Yilmaz-Rosen metric. We show that the wave type field equation is satisfied by the pseudo-conformal frame if the conformal factor is determined by a scalar 3D-harmonic function. This function can be related to the Newtonian potential of classical gravity. So we obtain a direct relation between the non-relativistic gravity and the relativistic model: every classical exact solution leads to a solution of the field equation. With this result we obtain a wide class of exact, static metrics. We show that the theory of Yilmaz relates to the pseudo-conformal sector of our construction. We derive also a unique cosmological (time dependent) solution of the described type.Comment: Latex, 17 page

An assessment of Evans' unified field theory II

Evans developed a classical unified field theory of gravitation and electromagnetism on the background of a spacetime obeying a Riemann-Cartan geometry. In an accompanying paper I, we analyzed this theory and summarized it in nine equations. We now propose a variational principle for Evans' theory and show that it yields two field equations. The second field equation is algebraic in the torsion and we can resolve it with respect to the torsion. It turns out that for all physical cases the torsion vanishes and the first field equation, together with Evans' unified field theory, collapses to an ordinary Einstein equation.Comment: 11 pages of late

Plane torsion waves in quadratic gravitational theories

The definition of the Riemann-Cartan space of the plane wave type is given. The condition under which the torsion plane waves exist is found. It is expressed in the form of the restriction imposed on the coupling constants of the 10-parametric quadratic gravitational Lagrangian. In the mathematical appendix the formula for commutator of the variation operator and Hodge operator is proved. This formula is applied for the variational procedure when the gravitational field equations are obtained in terms of the exterior differential forms.Comment: 3 May 1998. - 11

On a class of invariant coframe operators with application to gravity

Let a differential 4D-manifold with a smooth coframe field be given. Consider the operators on it that are linear in the second order derivatives or quadratic in the first order derivatives of the coframe, both with coefficients that depend on the coframe variables. The paper exhibits the class of operators that are invariant under a general change of coordinates, and, also, invariant under the global SO(1,3)-transformation of the coframe. A general class of field equations is constructed. We display two subclasses in it. The subclass of field equations that are derivable from action principles by free variations and the subclass of field equations for which spherical-symmetric solutions, Minkowskian at infinity exist. Then, for the spherical-symmetric solutions, the resulting metric is computed. Invoking the Geodesic Postulate, we find all the equations that are experimentally (by the 3 classical tests) indistinguishable from Einstein field equations. This family includes, of course, also Einstein equations. Moreover, it is shown, explicitly, how to exhibit it. The basic tool employed in the paper is an invariant formulation reminiscent of Cartan's structural equations. The article sheds light on the possibilities and limitations of the coframe gravity. It may also serve as a general procedure to derive covariant field equations

The quadratic spinor Lagrangian is equivalent to the teleparallel theory

The quadratic spinor Lagrangian is shown to be equivalent to the teleparallel / tetrad representation of Einstein's theory. An important consequence is that the energy-momentum density obtained from this quadratic spinor Lagrangian is essentially the same as the ``tensor'' proposed by Moller in 1961.Comment: 10 pages, RevTe

Electrodeposition of palladium dotted nickel nanowire networks as a robust self supported methanol electrooxidation catalyst

Mass activity and long term stability are two major issues in current fuel cell catalyst designs. While supported catalysts normally suffer from poor long term stability but show high mass activity, unsupported catalysts tend to perform better in the first point while showing deficits in the latter one. In this study, a facile synthesis route towards self supported metallic electrocatalyst nanoarchitectures with both aspects in mind is outlined. This procedure consists of a palladium seeding step of ion track etched polymer templates followed by a nickel electrodeposition and template dissolution. With this strategy, free standing nickel nanowire networks which contain palladium nanoparticles only in their outer surface are obtained. These networks are tested in anodic half cell measurements for demonstrating their capability of oxidising methanol in alkaline electrolytes. The results from the electrochemical experiments show that this new catalyst is more tolerant towards high methanol concentrations up to 5molL amp; 8722;1 than a commercial carbon supported palladium nanoparticle catalyst and provides a much better long term stability during potential cyclin

First Results on In-Beam gamma Spectroscopy of Neutron-Rich Na and Mg Isotopes at REX-ISOLDE

After the successful commissioning of the radioactive beam experiment at ISOLDE (REX-ISOLDE) - an accelerator for exotic nuclei produced by ISOLDE - first physics experiments using these beams were performed. Initial experiments focused on the region of deformation in the vicinity of the neutron-rich Na and Mg isotopes. Preliminary results show the high potential and physics opportunities offered by the exotic isotope accelerator REX in conjunction with the modern Germanium gamma spectrometer MINIBALL.Comment: 7 pages, RNB6 conference contributio

Embedded Star Clusters in the W51 Giant Molecular Cloud

We present sub-arcsecond (0.35"-0.9"), near-infrared J,H,K band photometric observations of six fields along the W51 Giant Molecular Cloud (W51 GMC). Our observations reveal four new, embedded clusters and provide a new high-resolution (0.35") view of the W51IRS2 (G49.5-0.4) region. The cluster associated with G48.9-0.3 is found to be a double cluster enclosed in a nest of near-infrared nebulosity. We construct stellar surface density maps for four major clusters in the W51 GMC. These unveil the underlying hierarchical structure. Color-color and color-magnitude diagrams for each of these clusters show clear differences in the embedded stellar populations and indicate the relative ages of these clusters. In particular, the clusters associated with the HII regions G48.9-0.3 and G49.0-0.3 are found to have a high fraction of YSOs and are therefore considered the youngest of all the near-infrared clusters in the W51 GMC. The estimated masses of the individual clusters, when summed, yield a total stellar mass of ~10^4 Msun in the W51 GMC, implying a star formation efficiency of 5-10%. These results in comparision with the CO observations of the W51 GMC, suggest for the first time, that star formation in the W51 GMC is likely triggered by a galactic spiral density wave.Comment: 10 pages and 5 figures. 3 figures in jpeg forma

Maternal microchimerism in the livers of patients with Biliary atresia

BACKGROUND: Biliary atresia (BA) is a neonatal cholestatic disease of unknown etiology. It is the leading cause of liver transplantation in children. Many similarities exist between BA and graft versus host disease suggesting engraftment of maternal cells during gestation could result in immune responses that lead to BA. The aim of this study was to determine the presence and extent of maternal microchimerism (MM) in the livers of infants with BA. METHODS: Using fluorescent in situ hybridization (FISH), 11 male BA & 4 male neonatal hepatitis (NH) livers, which served as controls, were analyzed for X and Y-chromosomes. To further investigate MM in BA, 3 patients with BA, and their mothers, were HLA typed. Using immunohistochemical stains, the BA livers were examined for MM. Four additional BA livers underwent analysis by polymerase chain reaction (PCR) for evidence of MM. RESULTS: By FISH, 8 BA and 2 NH livers were interpretable. Seven of eight BA specimens showed evidence of MM. The number of maternal cells ranged from 2–4 maternal cells per biopsy slide. Neither NH specimen showed evidence of MM. In addition, immunohistochemical stains confirmed evidence of MM. Using PCR, a range of 1–142 copies of maternal DNA per 25,000 copies of patients DNA was found. CONCLUSIONS: Maternal microchimerism is present in the livers of patients with BA and may contribute to the pathogenesis of BA