NPLOT: an Interactive Plotting Program for NASTRAN Finite Element Models

The NPLOT (NASTRAN Plot) is an interactive computer graphics program for plotting undeformed and deformed NASTRAN finite element models. Developed at NASA's Goddard Space Flight Center, the program provides flexible element selection and grid point, ASET and SPC degree of freedom labelling. It is easy to use and provides a combination menu and command driven user interface. NPLOT also provides very fast hidden line and haloed line algorithms. The hidden line algorithm in NPLOT proved to be both very accurate and several times faster than other existing hidden line algorithms. A fast spatial bucket sort and horizon edge computation are used to achieve this high level of performance. The hidden line and the haloed line algorithms are the primary features that make NPLOT different from other plotting programs

The moduli space of bilevel-6 abelian surfaces

The moduli space of abelian surfaces with polarisation of type (1,6) and a bilevel structure has positive Kodaira dimension. By contrast, Mukai has shown that the moduli space of bilevel-t abelian sufaces is rational for t=2,3,4,5.Comment: 9 pages, plain TeX. Results improved and extended: an error correcte

Gravitational Acceleration of Spinning Bodies From Lunar Laser Ranging Measurements

The Sun's relativistic gravitational gradient accelerations of Earth and Moon, dependent on the motions of the latter bodies, act upon the system's internal angular momentum. This spin-orbit force (which plays a part in determining the gravity wave signal templates for astrophysical sources) slightly accelerates the Earth-Moon system as a whole, but it more robustly perturbs that system's internal dynamics with a 5 cm, synodically oscillating range contribution which is presently measured to 4 mm precision by more than three decades of lunar laser ranging.Comment: 10 pages, PCTex32.v3.

Four-dimensional gonihedric gauge spin system

We perform Monte Carlo simulations of a four-dimensional gauge invariant spin system which describes random surfaces with gonihedric action. We develop the analogy between the flat-crumpled phase transition of the lattice surface model and the liquid-gas phase transition of non-ideal gases, and identify the self-intersection coupling constant $k$ of the surface model with the pressure $P$. As $k$ increases the system moves to a critical point in complete analogy with the situation for non-ideal gases, where the liquid and the gas phases approach each other with increasing $P$. We measure vacuum expectation values of various operators and the corresponding critical indices.Comment: 12 pages, Late

Optical spectroscopy and X-ray observations of the D-type symbiotic star EF Aql

We performed high-resolution optical spectroscopy and X-ray observations of the recently identified Mira-type symbiotic star EF Aql. Based on high-resolution optical spectroscopy obtained with SALT, we determine the temperature ($\sim$55 000 K) and the luminosity ($\sim$ 5.3 $L_\odot$) of the hot component in the system. The heliocentric radial velocities of the emission lines in the spectra reveal possible stratification of the chemical elements. We also estimate the mass-loss rate of the Mira donor star. Our Swift observation did not detect EF Aql in X-rays. The upper limit of the X-ray observations is 10$^{-12}$ erg cm$^{-2}$ s$^{-1}$, which means that EF Aql is consistent with the faintest X-ray systems detected so far. Otherwise we detected it with the UVOT instrument with an average UVM2 magnitude of 14.05. During the exposure, EF Aql became approximately 0.2 UVM2 magnitudes fainter. The periodogram analysis of the V-band data reveals an improved period of 320.4$\pm$0.3 d caused by the pulsations of the Mira-type donor star. The spectra are available upon request from the authors.Comment: Accepted for publication in MNRA

A D-brane inspired U(3)_CxU(3)_LxU(3)_R model

Motivated by D-brane scenarios, we consider a non-supersymmetric model based on the gauge symmetry U(3)_CxU(3)_LxU(3)_R$ which is equivalent to the SU(3)^3 ``trinification'' model supplemented by three U(1)s. Two U(1) combinations are anomalous while the third U(1)_Z' is anomaly free and contributes to the hypercharge generator. This hypercharge embedding correspods to sin^2\theta_W=6/19 in the case of full gauge coupling unification. The U(3)^3 symmetry is broken down to the Standard Model by vev's of two (1,3,\bar3)- scalar multiplets supplemented by two Higgs fields in (1,3,1) and (1,1,3) representations. The latter break U(1)_Z' and provide heavy masses to the extra lepton doublets. Fermions belong to (3,\bar 3,1)+(\bar 3,1,3)+ (1,3,\bar 3) representations as in the trinification model. The model predicts a natural quark-lepton hierarchy, since quark masses are obtained from tree-level couplings, while charged leptons receive masses from fourth order Yukawa terms, as a consequence of the extra abelian symmetries. Light Majorana neutrino masses are obtained through a see-saw type mechanism operative at the SU(3)_R breaking scale of the order M_R\ge 10^9 GeV.Comment: 10 pages, 2 figure

A Pati-Salam model from branes

We explore the possibility of embedding the Pati-Salam model in the context of Type I brane models. We study a generic model with U(4)_C x U(2)_L x U(2)_R gauge symmetry and matter fields compatible with a Type I brane configuration. Examining the anomaly cancellation conditions of the surplus abelian symmetries we find an alternative hypercharge embedding that is compatible with a low string/brane scale of the order of 5-7 TeV, when the U(4)_C and U(2)_R brane stack couplings are equal. Proton stability is assured as baryon number is associated to a global symmetry remnant of the broken abelian factors. It is also shown that this scenario can accommodate an extra low energy abelian symmetry that can be associated to lepton number. The issue of fermion and especially neutrino masses is also discussed.Comment: 14 pages, 1 figure, final version to be published in Phys. Lett.

Large amplitude gravitational waves

We derive an asymptotic solution of the Einstein field equations which describes the propagation of a thin, large amplitude gravitational wave into a curved space-time. The resulting equations have the same form as the colliding plane wave equations without one of the usual constraint equations