22 GHz Water Maser Search in 37 Nearby Galaxies - Four New Water Megamasers in Seyfert 2 and OH Maser/Absorber Galaxies

We report four new 22 GHz water masers found in a Green Bank Telescope search toward 37 nearby objects. Our goal was to find new maser galaxies, AGN disk-masers, and objects where both hydroxyl and water maser species coexist. We observed 37 sources within 250 Mpc that were selected by high X-ray luminosity (L_X > 10^40 W) and high absorbing column density (N_H ~ 10^22 cm^-2). Sources also included dual or triple AGN and interacting systems. We further included objects detected in hydroxyl (OH). The selection consisted of 16 new sources, 13 previous non-detections to follow up with a factor ten higher sensitivity, 10 OH masers and one deep OH absorber, of which 37 were observed. Water megamasers were detected towards the Sy 2 galaxy 2MFGC 13581 (a disk-maser), towards the 6 GHz OH absorber NGC 4261 (3C 270 with a twin-jet and dusty torus; broad water maser emission), and towards the two 1.6 GHz OH maser sources IRAS 17526+3253 and IRAS 20550+1656 (possible star formation water masers). We set upper limits on 33 non-detections. The search increased the number of known "dual-species" objects containing both OH and H2O masers to eight. The detection rate was 25 % in OH galaxies and 11 % overall. Combined with other searches, a total of 95 objects have now been searched for both OH and H2O masers. We found the overall dual-species detection rate (8 in 95) to be of the order of the joint probability of both species independently occurring in the same object (1 % lower bound). However, this needs to be verified by a more detailed analysis of selection criteria. Lastly, we see a lack of H2O kilomasers in OH megamaser objects already noted by Tarchi et al. (2011). This may be due to sensitivity bias rather than astrophysical reasons.Comment: 8 pages, 2 figures, accepted and to be published in A&

Spurious velocities in lattice Boltzmann

Stationary droplets simulated by multi-phase lattice Boltzmann methods lead to spurious velocities around them. In this article I report the origin of these spurious velocities for one example and show how they can be avoided.Comment: 4 pages, 1 figure, to be presented at the 11th international conference on discrete fluid dynamics (2002

Thermodynamic consistency of liquid-gas lattice Boltzmann simulations

Lattice Boltzmann simulations have been very successful in simulating liquid-gas and other multi-phase fluid systems. However, the underlying second order analysis of the equation of motion has long been known to be insufficient to consistently derive the fourth order terms that are necessary to represent an extended interface. These same terms are also responsible for thermodynamic consistency, i.e. to obtain a true equilibrium solution with both a constant chemical potential and a constant pressure. In this article we present an equilibrium analysis of non-ideal lattice Boltzmann methods of sufficient order to identify those higher order terms that lead to a lack of thermodynamic consistency. We then introduce a thermodynamically consistent forcing method.Comment: 12 pages, 8 figure

Classes of confining gauge field configurations

We present a numerical method to compute path integrals in effective SU(2) Yang-Mills theories. The basic idea is to approximate the Yang-Mills path integral by summing over all gauge field configurations, which can be represented as a linear superposition of a small number of localized building blocks. With a suitable choice of building blocks many essential features of SU(2) Yang-Mills theory can be reproduced, particularly confinement. The analysis of our results leads to the conclusion that topological charge as well as extended structures are essential elements of confining gauge field configurations.Comment: 18 pages, 16 figures, several sections adde

X-ray measurements of stresses and defects in EFG and large grained polycrystalline silicon ribbons

The Bond method was employed to measure the lattice parameter in an area of 0.4 mm in diameter of EFG Si-ribbons to an accuracy of + or - 0.00008 A. A Bond goniometer was built which included a goniostat with a special specimen holder to mount ribbons 1 m in length and 75 mm in width which could be rotated about two orthogonal axes, and a Leitz microscope for precision alignment of a particular area into the center of the goniostat and the small primary X-ray beam. The (321) planes were found to be parallel to the surface of the ribbons with an angular spread of about 15 deg. The poles of the (111) planes clustered about an angle of 25 deg away from the surface normal, again with a spread of 10 deg. The lattice parameter of a small piece of ribbon material was found to be a sub o = 5.43075 A. A maximum stress of 115 MPa was observed in a fractured ribbon which corresponded to the fracture stress of single crystals of Si

Effect of shear on droplets in a binary mixture

In this article we use a lattice-Boltzmann simulation to examine the effects of shear flow on a equilibrium droplet in a phase separated binary mixture. We find that large drops break up as the shear is increased but small drops dissolve. We also show how the tip-streaming, observed for deformed drops, leads to a state of dynamic equilibrium.Comment: 10 pages, LaTex, to appear in International Journal of Physics