7 research outputs found
Torsion and the Gravitational Interaction
By using a nonholonomous-frame formulation of the general covariance
principle, seen as an active version of the strong equivalence principle, an
analysis of the gravitational coupling prescription in the presence of
curvature and torsion is made. The coupling prescription implied by this
principle is found to be always equivalent with that of general relativity, a
result that reinforces the completeness of this theory, as well as the
teleparallel point of view according to which torsion does not represent
additional degrees of freedom for gravity, but simply an alternative way of
representing the gravitational field.Comment: Version 2: minor presentation changes, a reference added, 11 pages
(IOP style
The gravitational energy-momentum flux
We present a continuity equation for the gravitational energy-momentum, which
is obtained in the framework of the teleparallel equivalent of general
relativity. From this equation it follows a general definition for the
gravitational energy-momentum flux. This definition is investigated in the
context of plane waves and of cylindrical Einstein-Rosen waves. We obtain the
well known value for the energy flux of plane gravitational waves, and conclude
that the latter exhibit features similar to plane electromagnetic waves.Comment: 20 pages, latex file, no figures, two references added, accepted for
publication in Class. Quantum Gravit
UTA versus line emission for EUVL: Studies on xenon emission at the NIST EBIT
Spectra from xenon ions have been recorded at the NIST EBIT and the emission
into a 2% bandwidth at 13.5 nm arising from 4d-5p transitions compared with
that from 4d-4f and 4p-4d transitions in Xe XI and also with that obtained from
the unresolved transition array (UTA) observed to peak just below 11 nm. It was
found that an improvement of a factor of five could be gained in photon yield
using the UTA rather than the 4d-5p emission. The results are compared with
atomic structure calculations and imply that a significant gain in efficiency
should be obtained using tin, in which the emission at 13.5 nm comes from a
similar UTA, rather than xenon as an EUVL source material
Original scientific paper Far-infrared spectroscopy of PbTe doped with iron
Far infrared reflection spectra, at room and liquid nitrogen temperature, of PbTe single crystals doped with iron are presented. Plasma minima were observed at about 160 cm –1 and 180 cm –1 for room and liquid nitrogen temperature, respectively. Using the reflectivity diagrams and their minima, the values of the hole concentrations and their mobility at both temperatures were calculated and compared with galvanomagnetic measurements. All these results indicated that when PbTe is doped with a small concentration of Fe, the hole concentration is reduced by one order of magnitude and the free carrier mobility is larger when compared to pure PbTe
EQUIPARTITION OF SPHERE MEASURES BY HYPERPLANES
AND MARKO S. MILO ˇ SEVIĆ23 Abstract. Measure partition problems are classical problems of geometric combinatorics ([1], [2], [3], [4]) whose solutions often use tools from the equivariant algebraic topology. The potential of the computational obstruction theory approach is partially demonstrated here. In this paper we reprove a result of V.V. Makeev [9] about a 6-equipartition of a measure on S 2 by three planes. The advantage of our approach is that it can be applied on other more complicated questions of the similar nature. 1. Statement of the main result A measure µ is a proper measure if (A) µ([a, b]) = 0 for any circular arc [a, b] ⊂ S 2, and (B) µ(U)> 0 for each nonempty open set U ⊂ S 2. Three planes H1, H2 and H3 in R 3 through the origin are in a fan position if they intersect along the common line. Planes in the fan position cut the sphere S 2 in six parts σ1,.., σ6 which can be naturally oriented up to a cyclic permutation. We are interested in the following measure partition problem. Problem 1. Find all six-tuples (α1,.., α6) ∈ N 6 that for every proper Borel probability measure µ on the sphere S 2 there exist three planes in the fa