6,669 research outputs found
3-D Kinematics of the HH 110 jet
We present new results on the kinematics of the jet HH 110. New proper motion
measurements have been calculated from [SII] CCD images obtained with a time
baseline of nearly fifteen years. HH 110 proper motions show a strong asymmetry
with respect to the outflow axis, with a general trend of pointing towards the
west of the axis direction. Spatial velocities have been obtained by combining
the proper motions and radial velocities from Fabry-Perot data. Velocities
decrease by a factor ~3 over a distance of ~10 cm, much shorter than the
distances expected for the braking caused by the jet/environment interaction.
Our results show evidence of an anomalously strong interaction between the
outflow and the surrounding environment, and are compatible with the scenario
in which HH 110 emerges from a deflection in a jet/cloud collision.Comment: (1)Universitat de Barcelona; (2)UNAM; (3)UPC; (4)University of
Hawaii; (5)Southern Astrophysical Research Telescope. 9 pages; 7 Figures
Accepted by A&
RV POSEIDON Cruise Report POS420 COWACSS Biological observation and sampling of cold-water corals to investigate impacts on climate change
Trondheim â (Kristiansund) â Kiel
08. â (25.) â 30.09.201
Rapid physical and biological particle mixing on an intertidal sandflat
Sediment mixing processes were investigated using inert tracer experiments, benthic macrofaunal community analysis, and surveys of ray feeding pits to quantify the relative rates and controls of physical and biological reworking on Debidue Flat, an intertidal sandflat in South Carolina. Sediment reworking on Debidue Flat was rapid, with both advective and biodiffusive mixing operating over different vertical spatial scales. Physical reworking by tidal currents dominated initial transport of the tracer in the top 5-10 cm on timescales of ~30 days. Although the exact mechanism of tracer transport is unclear, it is most likely due to active fluidization of surface sediments during stages of the tide followed by a density-driven settling of tracer resulting in a steady downward transport to the depth of bedform reworking. Biodiffusive mixing was evident throughout the sampled interval (~30 cm) and dominated reworking at depths greater than 10 cm. Estimated biodiffusive mixing coefficients (Db) were high all year (0.15-0.28 cm2d-1), and were comparable to values reported for coastal bioturbated muds. The haustoriid amphipod Pseudohaustorius caroliniensis was most likely responsible for tracer dispersal in the 10 -30 cm interval based on its distribution, abundance, size, and observed burrow structures. Ray pit excavation and infilling were seasonal disturbances that contributed ~12-22% to spatially averaged advective transport rates but were locally intense and capable alone of turning over the entire upper ~15 cm of the flat in ~100 -1000 d. We propose that the mixing processes on Debidue Flat promote an unconstricted, open sediment matrix that maintains the high permeability required for the rapid porewater exchange to 25 cm noted for this system. Thus, in addition to redistributing organic substrates, physical and biological particle mixing play important roles in controlling permeability of flat deposits and quantification of these processes is important to understand controls on permeability and biogeochemical cycling of solutes in sandy systems
The pathophysiology of distal renal tubular acidosis
The kidneys have a central role in the control of acid-base homeostasis owing to bicarbonate reabsorption and production of ammonia and ammonium in the proximal tubule and active acid secretion along the collecting duct. Impaired acid excretion by the collecting duct system causes distal renal tubular acidosis (dRTA), which is characterized by the failure to acidify urine below pH 5.5. This defect originates from reduced function of acid-secretory type A intercalated cells. Inherited forms of dRTA are caused by variants in SLC4A1, ATP6V1B1, ATP6V0A4, FOXI1, WDR72 and probably in other genes that are yet to be discovered. Inheritance of dRTA follows autosomal-dominant and -recessive patterns. Acquired forms of dRTA are caused by various types of autoimmune diseases or adverse effects of some drugs. Incomplete dRTA is frequently found in patients with and without kidney stone disease. These patients fail to appropriately acidify their urine when challenged, suggesting that incomplete dRTA may represent an intermediate state in the spectrum of the ability to excrete acids. Unrecognized or insufficiently treated dRTA can cause rickets and failure to thrive in children, osteomalacia in adults, nephrolithiasis and nephrocalcinosis. Electrolyte disorders are also often present and poorly controlled dRTA can increase the risk of developing chronic kidney disease
Proper Motions of the Jets in the Region of HH 30 and HL/XZ Tau. Evidence for a Binary Exciting Source of the HH 30 Jet
We present [SII] images of the HH 30 and HL/XZ Tau region obtained at two
epochs, as well as long-slit optical spectroscopy of the HH 30 jet. We measured
proper motions of about 100-300 km/s for the HH 30 jet and counterjet, and of
about 120 km/s for the HL Tau jet. Inclination angles with respect to the plane
of the sky are 0-40 deg for the HH 30 jet and 60 deg for the HL Tau jet.
Comparison with previous observations suggests that most of the jet knots
consist of persisting structures. Also, we corroborate that the HH 30-N knots
correspond to the head of the HH 30 jet. The overall HH 30 jet structure can be
well described by a wiggling ballistic jet, arising either by the orbital
motion of the jet source around a primary or by precession of the jet axis
because of the tidal effects of a companion. In the first scenario, the orbital
period would be 53 yr and the total mass 0.25-2 solar masses. In the precession
scenario, the mass of the jet source would be 0.1-1 solar masses, the orbital
period <1 yr, and the mass of the companion less than a few times 0.01 solar
masses, thus being a substellar object or a giant exoplanet. In both scenarios
a binary system with a separation <18 AU (<0.13 arcsec) is required. Since the
radius of the flared disk observed with the HST is about 250 AU, we conclude
that this disk appears to be circumbinary rather than circumstellar, suggesting
that the search for the collimating agent of the HH 30 jet should be carried
out at much smaller scales.Comment: 42 pages, 7 figures, 5 tables. To Appear in The Astronomical Journal,
Vol. 133 No. 6 (June 2007
Integrally Geared Compressor Failure due to excessive pipe strain
Case StudyFollowing a complete overhaul of an integrally geared compressor, the compressor failed upon startup. The compressor ran for 7 seconds before the machinery protection system tripped the machine. During disassembly, it was discovered that three of the four impellers rubber severely against the impeller eye labyrinth seals and the accompanying dry gas seals were destroyed from excessive pipe strain. This case study highlights the failure data, corrective actions taken in investigation and reassembly of the machine
On the origin of radio-loudness in active galactic nuclei using far-infrared polarimetric observations
The dichotomy between radio-loud (RL) and radio-quiet (RQ) active galactic
nuclei (AGN) is thought to be intrinsically related to the radio jet
production. This difference may be explained by the presence of a strong
magnetic field (B-field) that enhances, or is the cause of, the accretion
activity and the jet power. Here, we report the first evidence of an intrinsic
difference in the dust polarized emission cores of four RL and five RQ AGN
using m polarization with HAWC+/SOFIA. We find that the thermal
polarized emission increases with the nuclear radio-loudness, and . The dust emission
cores of RL AGN are measured to be polarized, %, while RQ AGN are
unpolarized, . For RQ AGN, our results are consistent with the observed
region being filled with an unmagnetized or highly turbulent, disk and/or
expanding outflow at scales of pc from the AGN. For RL AGN, the measured
m polarization arises primarily from magnetically aligned dust grains
associated with a pc-scale dusty structure with a toroidal B-field
oriented mostly perpendicular, , to the radio jet orientation.
Our results indicate that the size and strength of the B-fields surrounding the
AGN are intrinsically related to the strength of the jet power -- the stronger
the jet power is, the larger and stronger the toroidal B-field is. The
detection of a pc-scale ordered toroidal B-field suggests that a) the
infalling gas that fuels RL AGN is magnetized, b) there is a
magnetohydrodynamic wind that collimates the jet, and/or c) the jet is able to
magnetize its surroundings.Comment: 22 pages, 6 figures, 7 tables. Summited to ApJ (Comments are welcome
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