2,201 research outputs found
A Note on Frame Dragging
The measurement of spin effects in general relativity has recently taken
centre stage with the successfully launched Gravity Probe B experiment coming
toward an end, coupled with recently reported measurements using laser ranging.
Many accounts of these experiments have been in terms of frame-dragging. We
point out that this terminology has given rise to much confusion and that a
better description is in terms of spin-orbit and spin-spin effects. In
particular, we point out that the de Sitter precession (which has been mesured
to a high accuracy) is also a frame-dragging effect and provides an accurate
benchmark measurement of spin-orbit effects which GPB needs to emulate
Radio and X-ray images of SNR G18.8+0.3 interacting with molecular clouds
New HI images from the VLA Galactic Plane Survey (VGPS) show clear absorption
features associated with the supernova remnant (SNR) G18.8+0.3. High-resolution
CO images reveal that molecular clouds overlap the radio filaments of
G18.8+0.3. The CO emission spectrum over the full velocity range in the
direction of G18.8+0.3 shows two molecular components with high
brightness-temperatureand three molecular components with low
brightness-temperature, all with respective HI absorption. This implies that
these clouds are in front of G18.8+0.3. In the HI images, the highest velocity
absorption feature seen against the continuum image of G18.8+0.3 is at 129 km
s, which corresponds to the tangent point in this direction. This yields
a lower distance limit of 6.9 kpc for G18.8+0.3. Absence of absorption at
negative velocities gives an upper distance limit of 15 kpc. The broadened
profile at 205 km s in the CO emission spectra is a strong
indicator of a possible SNR/CO cloud interaction. Thus, G18.8+0.3 is likely to
be at the distance of about 12 kpc. The upper mass limit and mean density of
the giant CO cloud at 205 km s are \sim 6 \times 10^{5} M_{\odot}
and \sim 2 \times 10^{2} cm^{-3}. We find an atomic hydrogen column density in
front of G18.8+0.3 of \sim 2 \times 10^{22} cm^{-2}. The ROSAT PSPC
observations show a diffuse X-ray enhancement apparently associated with part
of the radio shell of G18.8+0.3. Assuming an association, the unabsorbed flux
is 2.2 \times10^{-12} erg cm^{-2} s^{-1}, suggesting an intrinsic luminosity of
3.6 \times 10^{34} erg s^{-1} for G18.8+0.3.Comment: 8 pages, 6 figures, two tables, accepted by A&
Toward closure of upwelling radiance in coastal waters
We present three methods for deriving water-leaving radiance Lw(λ) and remote-sensing reflectance using a hyperspectral tethered spectral radiometer buoy (HyperTSRB), profiled spectroradiometers, and Hydrolight simulations. Average agreement for 53 comparisons between HyperTSRB and spectroradiometric determinations of Lw(λ) was 26%, 13%, and 17% at blue, green, and red wavelengths, respectively. Comparisons of HyperTSRB (and spectroradiometric) Lw(λ) with Hydrolight simulations yielded percent differences of 17% (18%), 17% (18%), and 13% (20%) for blue, green, and red wavelengths, respectively. The differences can be accounted for by uncertainties in model assumptions and model input data (chlorophyll fluorescence quantum efficiency and the spectral chlorophyll-specific absorption coefficient for the red wavelengths, and scattering corrections for input ac-9 absorption data and volume scattering function measurements for blue wavelengths) as well as radiance measurement inaccuracies [largely differences in the depth of the Lu(λ, z) sensor on the HyperTSRB]. © 2003 Optical Society of America
An Evaluation of the Proposals in the FCC\u27s Intercarrier Compensation Reform Docket Related to Tandem Transit Services
As part of its Intercarrier Compensation Reform Docket, the Federal Communications Commission (FCC) has received many proposals advocating for the adoption of regulations relating to tandem transit services. As transiting affects virtually every carrier in the telecommunications industry, including traditional CLECs, cable telephony providers, wireless carriers, and even traditional ILECs, the industry is sharply divided over which, if any, of those proposals should be adopted. This Article provides an in-depth look at the issues dividing the industry, and the various proposals before the FCC. The Authors then hypothesize that the FCC should follow the lead of several state commissions who have addressed this exact issue and adopt a nationwide policy that would facilitate the continued growth of competition in the tandem transiting market, as this result would best serve consumers, telecommunications providers, and the industry as a whole
Detection of Cold Atomic Clouds in the Magellanic Bridge
We report a detection of cold atomic hydrogen in the Magellanic Bridge using
21-cm absorption spectroscopy toward the radio source B0312-770. With a column
density of N_HI=1.2E20 cm^-2, a maximum absorption optical depth of tau=0.10
and a maximum 21-cm emission brightness temperature of 1.4 K, this line of
sight yields a spin temperature, T_s, between 20 K and 40 K. H I 21-cm
absorption and emission spectroscopy toward 7 other low column density
sightlines on the periphery of the LMC and SMC reveal absorption toward one
additional background radio source behind the SMC with tau=0.03. The data have
typical sensitivities of sigma_tau=0.005 to 0.070 in absorption and
sigma_{T_B}=0.03 K in emission. These data demonstrate the presence of a cold
atomic phase which is probably accompanied by molecular condensations in the
tenuous interstellar medium of the Bridge region. Young OB stars observed in
the Magellanic Bridge could form "in situ" from these cold condensations rather
than migrate from regions of active star formation in the main body of the SMC.
The existence of cold condensations and star formation in the Magellanic Bridge
might be understood as a small scale version of the mechanism that produces
star formation in the tidal tails of interacting galaxies.Comment: 25 pages, uses AASTeX and psfig; Accepted for Publication in the
Astronomical Journa
Sensor And Method For Detecting A Superstrate
Method and apparatus are provided for determining a superstrate on or near a sensor, e.g., for detecting the presence of an ice superstrate on an airplane wing or a road. In one preferred embodiment, multiple measurement cells are disposed along a transmission line. While the present invention is operable with different types of transmission lines, construction details for a presently preferred coplanar waveguide and a microstrip waveguide are disclosed. A computer simulation is provided as part of the invention for predicting results of a simulated superstrate detector system. The measurement cells may be physically partitioned, nonphysically partitioned with software or firmware, or include a combination of different types of partitions. In one embodiment, a plurality of transmission lines are utilized wherein each transmission line includes a plurality of measurement cells. The plurality of transmission lines may be multiplexed with the signal from each transmission line being applied to the same phase detector. In one embodiment, an inverse problem method is applied to determine the superstrate dielectric for a transmission line with multiple measurement cells
The VLA Galactic Plane Survey
The VLA Galactic Plane Survey (VGPS) is a survey of HI and 21-cm continuum
emission in the Galactic plane between longitude 18 degrees 67 degr. with
latitude coverage from |b| < 1.3 degr. to |b| < 2.3 degr. The survey area was
observed with the Very Large Array (VLA) in 990 pointings. Short-spacing
information for the HI line emission was obtained by additional observations
with the Green Bank Telescope (GBT). HI spectral line images are presented with
a resolution of 1 arcmin x 1 arcmin x 1.56 km/s (FWHM) and rms noise of 2 K per
0.824 km/s channel. Continuum images made from channels without HI line
emission have 1 arcmin (FWHM) resolution. VGPS images are compared with images
from the Canadian Galactic Plane Survey (CGPS) and the Southern Galactic Plane
Survey (SGPS). In general, the agreement between these surveys is impressive,
considering the differences in instrumentation and image processing techniques
used for each survey. The differences between VGPS and CGPS images are small, <
6 K (rms) in channels where the mean HI brightness temperature in the field
exceeds 80 K. A similar degree of consistency is found between the VGPS and
SGPS. The agreement we find between arcminute resolution surveys of the
Galactic plane is a crucial step towards combining these surveys into a single
uniform dataset which covers 90% of the Galactic disk: the International
Galactic Plane Survey (IGPS). The VGPS data will be made available on the World
Wide Web through the Canadian Astronomy Data Centre (CADC).Comment: Accepted for publication in The Astronomical Journal. 41 pages, 13
figures. For information on data release, colour images etc. see
http://www.ras.ucalgary.ca/VGP
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