1,696 research outputs found
High Order QED Corrections in Physics of Positronium
High-order perturbative corrections to positronium decays and hyperfine
splitting are briefly reviewed. Theoretical predictions are compared to the
most recent experimental data. Perspectives of future calculations are
discussed.Comment: 8 pages, LaTeX, talk given at Workshop on Positronium Physics, ETH
Honggerberg, Zurich, May 30-31, 2003, a misprint in Eq. (1) correcte
VLA Observations of the "Eye of the Tornado"- the High Velocity \HII Region G357.63-0.06
The unusual supernova remnant candidate G357.7-0.1 and the compact source
G357.63-0.06 have been observed with the Very Large Array at 1.4 and 8.3 GHz.
The H92 line (8.3 GHz) was detected from the compact source with a
surprising velocity of about -210 km/s indicating that this source is an \HII
region, is most likely located at the Galactic center, and is unrelated to the
SNR. The \HI absorption line (1.4 GHz) data toward these sources supports this
picture and suggests that G357.7-0.1 lies farther away than the Galactic
center.Comment: Latex, 14 pages including 4 figures. Accepted to A
Value of cost accounting in commercial laboratories
The basic elements of cost are three in number: prime cost, direct expense, and indirect expense. I have found it a great help in any cost system to keep these three great divisions clearly in mind. They of course can be subdivided in various ways, but we should never lose sight of the main divisions. The prime cost is made up of raw materials and direct labor only. Now in a commercial laboratory we have no raw material to deal with; therefore, let us eliminate it from the cost system, which leaves for the prime cost only direct labor; chemicals and apparatus form the direct expense, and overhead or burden the indirect expense. Now certainly with these three elements of prime cost, direct expense and indirect expense, we have something upon which to work, and we can build from this firm foundation a cost system which can be applied directly to any individual laboratory, no matter how large nor how small. In a commercial laboratory where the work is being done for outside clients, what you are really seeking is the cost of your services, that is, the cost of the salaries of the chemists who are working in the laboratory. Thus the prime cost, or the man\u27s time, plus the direct expense of chemicals and apparatus is the direct cost of the work. To this direct cost must be added indirect expense, such as rent, depreciation, taxes, insurance, light, heat, etc., and also the indirect cost of management and supervision, which may be classed as overhead, in order to arrive at the total cost. Once the total cost of the work is ascertained, the next step is the percentage of profit which is reasonable for the work done, and the final figure is the charge to the client, or selling price
Revealing the obscured supernova remnant Kes 32 with Chandra
I report here on the analysis and interpretation of a Chandra observation of
the supernova remnant Kes 32. Kes 32 is rather weak in X-rays due to a large
interstellar absorption, which is found to be ~4E22 cm^-2, larger than
previously reported. Spectral analysis indicates that the ionization age of
this object is very young, with n_e t ~ 4E9 cm^-3s, and a temperature of kT_e ~
1 keV. The X-ray emission peaks at a smaller radius than in the radio. The low
ionization age suggests that Kes 32 is a young remnant. However, a young age is
in contradiction with the relatively large apparent size, which indicates an
age of several thousand years, instead of a few hundred years. This problem is
discussed in connection with Kes 32's unknown distance and its possible
association with the Norma galactic arm.Comment: Accepted for publication in the Astrophysical Journal. 7 pages, 7
figure
What could be learnt from Positronium for Quarkonium?
In order to fulfill Low's theorem requirements, a new lowest order basis for
bound state decay computations is proposed, in which the binding energy is
treated non-perturbatively. The properties of the method are sketched by
reviewing standard positronium decay processes. Then, it is shown how applying
the method to quarkonia sheds new light on some longstanding puzzles.Comment: 12 pages, 10 figures. Talk given at the ETH Workshop on Positronium
Physics, May 30-31, 2003, Zurich, Switzerlan
The Arecibo Methanol Maser Galactic Plane Survey - II: Statistical and Multi-wavelength Counterpart Analysis
We present an analysis of the properties of the 6.7 GHz methanol maser sample
detected in the Arecibo Methanol Maser Galactic Plane Survey. The distribution
of the masers in the Galaxy, and statistics of their multi-wavelength
counterparts is consistent with the hypothesis of 6.7 GHz maser emission being
associated with massive young stellar objects. Using the detection statistics
of our survey, we estimate the minimum number of methanol masers in the Galaxy
to be 1275. The l-v diagram of the sample shows the tangent point of the
Carina-Sagittarius spiral arm to be around 49.6 degrees, and suggests
occurrence of massive star formation along the extension of the Crux-Scutum
arm. A Gaussian component analysis of the maser spectra shows the mean
line-width to be 0.38 km/s which is more than a factor of two larger than what
has been reported in the literature. We also find no evidence that faint
methanol masers have different properties than those of their bright
counterparts.Comment: Accepted by ApJ; Revised footnote number 3 on page 8 based on private
communicatio
Quantum Hall Effect in Quantum Electrodynamics
We consider the quantum Hall effect in quantum electrodynamics and find a
deviation from the quantum mechanical prediction for the Hall conductivity due
to radiative antiscreening of electric charge in an external magnetic field. A
weak universal dependence of the von Klitzing constant on the magnetic field
strength, which can possibly be observed in a dedicated experiment, is
predicted.Comment: 4 pages, 2 figures, LaTeX, perturbative result correcte
The Distances of SNR W41 and overlapping HII regions
New HI images from the VLA Galactic Plane Survey show prominent absorption
features associated with the supernovae remnant G23.3-0.3 (SNR W41). We
highlight the HI absorption spectra and the CO emission spectra of eight
small regions on the face of W41, including four HII regions, three non-thermal
emission regions and one unclassified region. The maximum velocity of
absorption for W41 is 782 km/s and the CO cloud at radial velocity
955 km/s is behind W41. Because an extended TeV source, a diffuse X-ray
enhancement and a large molecular cloud at radial velocity 775 km/s are
also projected at the center of W41, these yield the kinematic distance of 3.9
to 4.5 kpc for W41. For HII regions, our analyses reveal that both G23.42-0.21
and G23.07+0.25 are at the far kinematic distances (9.9 kpc and
10.6 kpc respectively) of their recombination-line velocities (1030.5 km/s
and 89.62.1 km/s respectively), G23.07-0.37 is at the near kinematic
distance (4.40.3 kpc) of its recombination-line velocity (82.72.0
km/s), and G23.27-0.27 is probably at the near kinematic distance (4.10.3
kpc) of its recombination-line velocity (76.10.6 km/s).Comment: 11 pages, 3 figs., 2 tables, accepted by A
Effects of correlated turbulent velocity fields on the formation of maser lines
The microturbulent approximation of turbulent motions is widely used in
radiative transfer calculations. Mainly motivated by its simple computational
application it is probably in many cases an oversimplified treatment of the
dynamical processes involved. This aspect is in particular important in the
analysis of maser lines, since the strong amplification of radiation leads to a
sensitive dependence of the radiation field on the overall velocity structure.
To demonstrate the influence of large scale motions on the formation of maser
lines we present a simple stochastic model which takes velocity correlations
into account. For a quantitative analysis of correlation effects, we generate
in a Monte Carlo simulation individual realizations of a turbulent velocity
field along a line of sight. Depending on the size of the velocity correlation
length we find huge deviations between the resulting random profiles in respect
of line shape, intensity and position of single spectral components. Finally,
we simulate the emission of extended maser sources. A qualitative comparison
with observed masers associated with star forming regions shows that our model
can reproduce the observed general spectral characteristics. We also
investigate shortly, how the spectra are effected when a systematic velocity
field (simulating expansion) is superposed on the fluctuations. Our results
convincingly demonstrate that hydrodynamical motions are of great importance
for the understanding of cosmic masers.Comment: Accepted for publication in A&A. 8 pages, 8 figure
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