2,418 research outputs found
Optical fiber coupling method and apparatus
Systems are described for coupling a pair of optical fibers to pass light between them, which enables a coupler to be easily made, and with simple equipment, while closely controlling the characteristics of the coupler. One method includes mounting a pair of optical fibers on a block having a large hole therein, so the fibers extend across the hole while lying adjacent and parallel to one another. The fibers are immersed in an etchant to reduce the thickness of cladding around the fiber core. The fibers are joined together by applying a liquid polymer so the polymer-air interface moves along the length of the fibers to bring the fibers together in a zipper-like manner, and to progressively lay a thin coating of the polymer on the fibers
Extended OH(1720 MHz) Maser Emission from Supernova Remnants
Compact OH(1720 MHz) masers have proven to be excellent signposts for the
interaction of supernova remnants with adjacent molecular clouds. Less
appreciated has been the weak, extended OH(1720 MHz) emission which accompanies
strong compact maser sources. Recent single-dish and interferometric
observations reveal the majority of maser-emitting supernova remnants have
accompanying regions of extended maser emission. Enhanced OH abundance created
by the passing shock is observed both as maser emission and absorption against
the strong background of the remnant. Modeling the observed OH profiles gives
an estimate of the physical conditions in which weak, extended maser emission
arises. I will discuss how we can realize the utility of this extended maser
emission, particularly the potential to measure the strength of the post-shock
magnetic field via Zeeman splitting over these large-scales.Comment: 5 Pages, 2 Figures, To appear in IAU 242, Astrophysical Masers and
Their Environments, eds. J. Chapman & W. Baa
Ranging system which compares an object reflected component of a light beam to a reference component of the light beam
A system is described for measuring the distance to an object by comparing a first component of a light pulse that is reflected off the object with a second component of the light pulse that passes along a reference path of known length, which provides great accuracy with a relatively simple and rugged design. The reference path can be changed in precise steps so that it has an equivalent length approximately equal to the path length of the light pulse component that is reflected from the object. The resulting small difference in path lengths can be precisely determined by directing the light pulse components into opposite ends of a detector formed of a material that emits a second harmonic light output at the locations where the opposite going pulses past simultaneously across one another
GMRT and VLA observations at 49cm and 20cm of the HII region near l=24.4d, b=0.1d
We report multifrequency radio continuum and hydrogen radio recombination
line observations of HII regions near l=24.8d b=0.1d using the Giant Metrewave
Radio Telescope (GMRT) at 1.28 GHz (n=172), 0.61 GHz (n=220) and the Very Large
Array (VLA) at 1.42 GHz (n=166). The region consists of a large number of
resolved HII regions and a few compact HII regions as seen in our continuum
maps, many of which have associated infrared (IR) point sources. The largest
HII region at l=24.83d and b=0.1d is a few arcmins in size and has a shell-type
morphology. It is a massive HII region enclosing ~ 550 solar mass with a linear
size of 7 pc and an rms electron density of ~ 110 cm^-3 at a kinematic distance
of 6 kpc. The required ionization can be provided by a single star of spectral
type O5.5.
We also report detection of hydrogen recombination lines from the HII region
at l=24.83d and b=0.1d at all observed frequencies near Vlsr=100 km/s. We model
the observed integrated line flux density as arising in the diffuse HII region
and find that the best fitting model has an electron density comparable to that
derived from the continuum. We also report detection of hydrogen recombination
lines from two other HII regions in the field.Comment: 14 pages, 8 Figures. Uses JAA style file. Accepted for publication in
Journal of Astrophysics and Astronomy. High resolution figures (fig 1a, fig
1b and fig 2b) can be downloaded from http://www.ncra.tifr.res.in/~ngk/G2
Linear independence of Gamma values in positive characteristic
We investigate the arithmetic nature of special values of Thakur's function
field Gamma function at rational points. Our main result is that all linear
independence relations over the field of algebraic functions are consequences
of the known relations of Anderson and Thakur arising from the functional
equations of the Gamma function.Comment: 51 page
Use of NOAA-N satellites for land/water discrimination and flood monitoring
A tool for monitoring the extent of major floods was developed using data collected by the NOAA-6 advanced very high resolution radiometer (AVHRR). A basic understanding of the spectral returns in AVHRR channels 1 and 2 for water, soil, and vegetation was reached using a large number of NOAA-6 scenes from different seasons and geographic locations. A look-up table classifier was developed based on analysis of the reflective channel relationships for each surface feature. The classifier automatically separated land from water and produced classification maps which were registered for a number of acquisitions, including coverage of a major flood on the Parana River of Argentina
- …