2,531 research outputs found
Locking device for turbine rotor blades Patent
Locking device for retaining turbine rotor blades on turbine whee
Mass fluxes and isofluxes of methane (CH4) at a New Hampshire fen measured by a continuous wave quantum cascade laser spectrometer
We have developed a midâinfrared continuousâwave quantum cascade laser directâabsorption spectrometer (QCLS) capable of high frequency (â„1 Hz) measurements of 12CH4 and 13CH4 isotopologues of methane (CH4) with in situ 1âs RMS image precision of 1.5 â° and Allanâminimum precision of 0.2 â°. We deployed this QCLS in a wellâstudied New Hampshire fen to compare measurements of CH4 isoflux by eddy covariance (EC) to Keeling regressions of data from automated flux chamber sampling. Mean CH4 fluxes of 6.5 ± 0.7 mg CH4 mâ2 hrâ1 over two days of EC sampling in July, 2009 were indistinguishable from mean autochamber CH4 fluxes (6.6 ± 0.8 mgCH4 mâ2 hrâ1) over the same period. Mean image composition of emitted CH4 calculated using EC isoflux methods was â71 ± 8 â° (95% C.I.) while Keeling regressions of 332 chamber closing events over 8 days yielded a corresponding value of â64.5 ± 0.8 â°. Ebullitive fluxes, representing âŒ10% of total CH4 fluxes at this site, were on average 1.2 â° enriched in 13C compared to diffusive fluxes. CH4 isoflux time series have the potential to improve processâbased understanding of methanogenesis, fully characterize source isotopic distributions, and serve as additional constraints for both regional and global CH4 modeling analysis
Charged-Particle Motion in Electromagnetic Fields Having at Least One Ignorable Spatial Coordinate
We give a rigorous derivation of a theorem showing that charged particles in
an arbitrary electromagnetic field with at least one ignorable spatial
coordinate remain forever tied to a given magnetic-field line. Such a situation
contrasts the significant motions normal to the magnetic field that are
expected in most real three-dimensional systems. It is pointed out that, while
the significance of the theorem has not been widely appreciated, it has
important consequences for a number of problems and is of particular relevance
for the acceleration of cosmic rays by shocks.Comment: 7 pages, emulateapj format, including 1 eps figure, to appear in The
Astrophysical Journal, Dec. 10 1998 issu
Gas Dynamics in the LINER Galaxy NGC 5005: Episodic Fueling of a Nuclear Disk
We report high-resolution CO(1-0) observations in the central 6 kpc of the
LINER galaxy NGC 5005 with the Owens Valley Radio Observatory millimeter array.
Molecular gas is distributed in three components - a ring at a radius of about
3 kpc, a strong central condensation, and a stream to the northwest of the
nucleus but inside the 3 kpc ring. The central condensation is a disk of about
1 kpc radius with a molecular gas mass of 2 x 10^9 M_sun. The stream between
the 3 kpc ring and the nuclear disk lies on a straight dust lane seen in the
optical. If this material moves in the plane of the galaxy, it has a velocity
offset by up to ~ 150 km/s from galactic rotation. We suggest that an optically
inconspicuous stellar bar lying within the 3 kpc ring can explain the observed
gas dynamics. This bar is expected to connect the nuclear disk and the ring
along the position angle of the northwest stream. A position-velocity cut in
this direction reveals features which match the characteristic motions of gas
in a barred potential. Our model indicates that gas in the northwest stream is
on an x_1 orbit at the bar's leading edge; it is falling into the nucleus with
a large noncircular velocity, and will eventually contribute about 2 x 10^8
M_sun to the nuclear disk. If most of this material merges with the disk on its
first passage of pericenter, the gas accretion rate during the collision will
be 50 M_sun/yr. We associate the nuclear disk with an inner 2:1 Lindblad
resonance, and the 3 kpc ring with an inner 4:1 Lindblad resonance. The high
rate of bar-driven inflow and the irregular appearance of the northwest stream
suggest that a major fueling event is in progress in NGC 5005. Such episodic
(rather than continuous) gas supply can regulate the triggering of starburst
and accretion activity in galactic nuclei. (abridged)Comment: 26 pages, 12 figures, AASTeX, ApJ in press (Feb. 10, 2000). For
full-resolution figures, see
http://www.ovro.caltech.edu/mm/science/science.htm
The Host Galaxy of the Gamma--Ray Burst 971214
We report on Hubble Space Telescope (HST) observations of the host galaxy of
GRB 971214, about four months after the burst. The redshift of the proposed
host galaxy at z=3.418, combined with optical and radio observations of the
burst afterglow, implies the extremely large isotropic energy release from the
burst in gamma-rays of approximately 3x10^53 ergs, some two orders of magnitude
higher than the previously commonly assumed numbers. The positional offset
between the optical transient observed at the Keck telescope and the centroid
of the proposed host galaxy in the HST image is 0.14 -+0.07 arcsec. We find no
evidence in our deep HST image for a chance foreground galaxy superposed along
the line of sight to the proposed host at z=3.418. The morphology and
photometric properties of this galaxy, such as the total flux, morphology,
radial surface profile and scale length, are typical as compared to other,
spectroscopically confirmed z>3 galaxies.Comment: LaTex, 10 pages, 3 figures, accepted to ApJ
Polarized Narrow-Line Emission from the Nucleus of NGC 4258
The detection of polarized continuum and line emission from the nucleus of
NGC 4258 by Wilkes et al. (1995) provides an intriguing application of the
unified model of Seyfert nuclei to a galaxy in which there is known to be an
edge-on, rotating disk of molecular gas surrounding the nucleus. Unlike most
Seyfert nuclei, however, NGC 4258 has strongly polarized narrow emission lines.
To further investigate the origin of the polarized emission, we have obtained
spectropolarimetric observations of the NGC 4258 nucleus at the Keck-II
telescope. The narrow-line polarizations range from 1.0% for [S II] 6716 to
13.9% for the [O II] 7319,7331 blend, and the position angle of polarization is
oriented nearly parallel to the projected plane of the masing disk. A
correlation between critical density and degree of polarization is detected for
the forbidden lines, indicating that the polarized emission arises from
relatively dense (n_e > 10^4 cm^-3) gas. An archival Hubble Space Telescope
narrow-band [O III] image shows that the narrow-line region has a compact,
nearly unresolved core, implying a FWHM size of <2.5 pc. We discuss the
possibility that the polarized emission might arise from the accretion disk
itself and become polarized by scattering within the disk atmosphere. A more
likely scenario is an obscuring torus or strongly warped disk surrounding the
inner portion of a narrow-line region which is strongly stratified in density.
The compact size of the narrow-line region implies that the obscuring structure
must be smaller than ~2.5 pc in diameter.Comment: To appear in the Astronomical Journal. 13 pages, including 1 table
and 4 figures. Uses emulateapj.st
Fermi Surface Properties of Low Concentration CeLaB: dHvA
The de Haas-van Alphen effect is used to study angular dependent extremal
areas of the Fermi Surfaces (FS) and effective masses of CeLaB alloys for between 0 and 0.05. The FS of these alloys was previously
observed to be spin polarized at low Ce concentration ( = 0.05). This work
gives the details of the initial development of the topology and spin
polarization of the FS from that of unpolarized metallic LaB to that of
spin polarized heavy Fermion CeB .Comment: 7 pages, 9 figures, submitted to PR
SN2002kg -- the brightening of LBV V37 in NGC 2403
SN2002kg is a type IIn supernova, detected in October 2002 in the nearby
spiral galaxy NGC 2403. We show that the position of SN2002kg agrees within the
errors with the position of the LBV V37. Ground based and HST ACS images
however show that V37 is still present after the SN2002kg event. We compiled a
lightcurve of V37 which underlines the variablity of the object, and shows that
SN2002kg was the brightening of V37 and not a supernova. The recent brightening
is not a giant eruption, but more likely part of an S Dor phase. V37 shows
strong Halpha +[NII] emission in recent images and in the SN2002kg spectrum,
which we interprete as the signature of the presence of an LBV nebula. A
historic spectrum lacks emission, which may hint that we are witnessing the
formation of an LBV nebula.Comment: 4 pages, 5 figures, accepted in A&A Letter, paper with images in full
resolution at http://www.astro.ruhr-uni-bochum.de/kweis/publications.htm
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