2,520 research outputs found
A measurement system for the atmospheric trace gases CH4 and CO
A system for measuring ambient clean air levels of the atmospheric trace gases methane and carbon monoxide is described. The analytical method consists of a gas chromatographic technique that incorporates sample preconcentration with catalytic conversion of CO to CH4 and subsequent flame ionization detection of these gases. The system has sufficient sensitivity and repeatability to make the precise measurements required to establish concentration profiles for CO and CH4 in the planetary boundary layer. A discussion of the bottle sampling program being conducted to obtain the samples for the concentration profiles is also presented
Three field tests of a gas filter correlation radiometer
Test flights to remotely measure nonurban carbon monoxide (CO) concentrations by gas filter correlation radiometry are discussed. The inferred CO concentrations obtained through use of the Gas Filter Correlation Radiometer (GFCR) agreed with independent measurements obtained by gas chromatography air sample bottle analysis to within 20 percent. The equipment flown on board the aircraft, the flight test procedure, the gas chromatograph direct air sampling procedure, and the GFCR data analysis procedure are reported
Coulomb correlation in presence of spin-orbit coupling: application to plutonium
Attempts to go beyond the local density approximation (LDA) of Density
Functional Theory (DFT) have been increasingly based on the incorporation of
more realistic Coulomb interactions. In their earliest implementations, methods
like LDA+, LDA + DMFT (Dynamical Mean Field Theory), and LDA+Gutzwiller used
a simple model interaction . In this article we generalize the solution of
the full Coulomb matrix involving to parameters, which is
usually presented in terms of an basis, into a basis of
the total angular momentum, where we also include spin-orbit coupling; this
type of theory is needed for a reliable description of -state elements like
plutonium, which we use as an example of our theory. Close attention will be
paid to spin-flip terms, which are important in multiplet theory but that have
been usually neglected in these kinds of studies. We find that, in a
density-density approximation, the basis results provide a very good
approximation to the full Coulomb matrix result, in contrast to the much less
accurate results for the more conventional basis
Sub-Milliarcsecond Precision of Pulsar Motions: Using In-Beam Calibrators with the VLBA
We present Very Long Baseline Array phase-referenced measurements of the
parallax and proper motion of two pulsars, B0919+06 and B1857-26.
Sub-milliarcsecond positional accuracy was obtained by simultaneously observing
a weak calibrator source within the 40' field of view of the VLBA at 1.5 GHz.
We discuss the merits of using weak close calibrator sources for VLBI
observations at low frequencies, and outline a method of observation and data
reduction for these type of measurements. For the pulsar B1919+06 we measure a
parallax of 0.31 +/- 0.14 mas. The accuracy of the proper motions is
approximately 0.5 mas, an order of magnitude improvement over most previous
determinations.Comment: 11 pages plus 4 figures. In press, Astronomical Journa
Asymptotic solvers for ordinary differential equations with multiple frequencies
We construct asymptotic expansions for ordinary differential equations with highly oscillatory forcing terms, focusing on the case of multiple, non-commensurate frequencies. We derive an asymptotic expansion in inverse powers of the oscillatory parameter and use its truncation as an exceedingly effective means to discretize the differential equation in question. Numerical examples illustrate the effectiveness of the method
The star catalogues of Ptolemaios and Ulugh Beg: Machine-readable versions and comparison with the modern Hipparcos Catalogue
In late antiquity and throughout the middle ages, the positions of stars on
the celestial sphere were obtained from the star catalogue of Ptolemaios. A
catalogue based on new measurements appeared in 1437, with positions by Ulugh
Beg, and magnitudes from the 10th-century astronomer al-Sufi. We provide
machine-readable versions of these two star catalogues, based on the editions
by Toomer (1998) and Knobel (1917), and determine their accuracies by
comparison with the modern Hipparcos Catalogue. The magnitudes in the
catalogues correlate well with modern visual magnitudes; the indication `faint'
by Ptolemaios is found to correspond to his magnitudes 5 and 6. Gaussian fits
to the error distributions in longitude / latitude give widths sigma ~ 27
arcmin / 23 arcmin in the range |Delta lambda, Delta beta|<50 arcmin for
Ptolemaios and sigma ~ 22 arcmin /18 arcmin in Ulugh Beg. Fits to the range
|Delta lambda, Delta beta|<100 arcmin gives 10-15 per cent larger widths,
showing that the error distributions are broader than gaussians. The fraction
of stars with positions wrong by more than 150 arcmin is about 2 per cent for
Ptolemaios and 0.1 per cent in Ulugh Beg; the numbers of unidentified stars are
1 in Ptolemaios and 3 in Ulugh Beg. These numbers testify to the excellent
quality of both star catalogues (as edited by Toomer and Knobel).Comment: to be published in Astronomy and Astrophysics; 34 pages with 57
Figures. Note changed address and email address of first autho
Estrogen depletion alters mineralization regulation mechanisms in an ovariectomized monkey animal model
Ovariectomized animal models have been extensively used in osteoporosis research due to the resulting loss of bone mass. The purpose of the present study was to test the hypothesis that estrogen depletion alters mineralization regulation mechanisms in an ovariectomized monkey animal model. To achieve this we used Raman microspectroscopy to analyze humeri from monkeys that were either SHAM-operated or ovariectomized (N = 10 for each group). Measurements were made as a function of tissue age and cortical surface (periosteal, osteonal, endosteal) based on the presence of calcein fluorescent double labels.
In the present work we focused on osteoid seams (defined as a surface with evident calcein labels, 1 μm distance away from the mineralizing front, and for which the Raman spectra showed the presence of organic matrix but not mineral), as well as the youngest mineralized tissue between the second fluorescent label and the mineralizing front, 1 μm inwards from the front with the phosphate mineral peak evident in the Raman spectra (TA1). The spectroscopically determined parameters of interest were the relative glycosaminoglycan (GAG) and pyridinoline (Pyd) contents in the osteoid, and the mineral content in TA1.
At all three cortical surfaces, significant correlations were evident in the SHAM-operated animals between osteoid GAG (negative) and Pyd content, and mineral content, unlike the OVX animals.
These results suggest that in addition to the well-established effects on turnover rates and bone mass, estrogen depletion alters the regulation of mineralization by GAGs and Pyd
The Spitzer Space Telescope First-Look Survey: Neutral Hydrogen Emission
The Spitzer Space Telescope (formerly SIRTF) extragalactic First-Look Survey
covered about 5 square degrees centered on J2000 17:18 +59:30 in order to
characterize the infrared sky with high sensitivity. We used the 100-m Green
Bank Telescope to image the 21cm Galactic HI emission over a 3x3 degree field
covering this position with an effective angular resolution of 9.8 arcmin and a
velocity resolution of 0.62 km/s. In the central square degree of the image the
average column density is N(HI) = 2.5 x 10^{20} cm-2 with an rms fluctuation of
0.3 x 10^{20}. The Galactic HI in this region has a very interesting structure.
There is a high-velocity cloud, several intermediate-velocity clouds (one of
which is probably part of the Draco nebula), and narrow-line low velocity
filaments. The HI emission shows a strong and detailed correlation with dust.
Except for the high-velocity cloud, all features in the HI map have
counterparts in an E(B-V) map derived from infrared data. Relatively high
E(B-V)/N(HI) ratios in some directions suggest the presence of molecular gas.
The best diagnostic of such regions is the peak HI line brightness temperature,
not the total N(HI): directions where Tb > 12 K have E(B-V)/N(HI) significantly
above the average value. The data corrected for stray radiation have been
released via the Web.Comment: Accepted for publication in the Astronomical Journal, April 2005. 25
pages includes 11 figures. The data and higher resolution figures are
available from http::/www.cv.nrao.edu/fls_gb
Optical Thomas-Reiche-Kuhn sum rules
The Thomas-Reiche-Kuhn sum rule is a fundamental consequence of the position-momentum commutation relation for an atomic electron and it provides an important constraint on the transition matrix elements for an atom. Analogously, the commutation relations for the electromagnetic field operators in a magnetodielectric medium constrain the properties of the dispersion relations for the medium through four sum rules for the allowed phase and group velocities for polaritons propagating through the medium. These rules apply to all bulk media including the metamaterials designed to provide negative refractive indices. An immediate consequence of this is that it is not possible to construct a medium in which all the polariton modes for a given wavelength lie in the negative-index region
Are violations to temporal Bell inequalities there when somebody looks?
The possibility of observing violations of temporal Bell inequalities,
originally proposed by Leggett as a mean of testing the quantum mechanical
delocalization of suitably chosen macroscopic bodies, is discussed by taking
into account the effect of the measurement process. A general criterion
quantifying this possibility is defined and shown not to be fulfilled by the
various experimental configurations proposed so far to test inequalities of
different forms.Comment: 7 pages, 1 eps figure, needs europhys.sty and euromacr.tex, enclosed
in the .tar.gz file; accepted for publication in Europhysics Letter
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