1,349 research outputs found
Origin of non-keplerian motions of masers in NGC 1068
We demonstrate that the ``sub-keplerian'' rotation curve of maser spots in
NGC 1068 can be explained by the gravitational attraction of the disc orbiting
the central black hole. Possible parameters matching observations are: black
hole mass of 12 million solar masses, disc outer edge > 1.3 pc, aspect ratio in
the range 0.003 to 0.3, surface density varying approximately as 1/R, and disc
mass of about 9.4 million solar masses. The physical conditions required for
the excitation of masers are fulfilled, and the outer disc would stand in a
gravitationally marginally stable state.Comment: 4 pages; accepted in A&A Letter
Nonuniqueness in a minimal model for cell motility
Twoâphase flow models have been used previously to model cell motility, however these have rapidly become very complicated, including many physical processes, and are opaque. Here we demonstrate that even the simplest oneâdimensional, twoâphase, poroviscous, reactive flow model displays a number of behaviours relevant to cell crawling. We present stability analyses that show that an asymmetric perturbation is required to cause a spatially uniform, stationary strip of cytoplasm to move, which is relevant to cell polarization. Our numerical simulations identify qualitatively distinct families of travellingâwave solution that coâexist at certain parameter values. Within each family, the crawling speed of the strip has a bellâshaped dependence on the adhesion strength. The model captures the experimentally observed behaviour that cells crawl quickest at intermediate adhesion strengths, when the substrate is neither too sticky nor too slippy
Recommended from our members
Characterizing an extractive electrospray ionization (EESI) source for the online mass spectrometry analysis of organic aerosols.
Organic compounds comprise a major fraction of tropospheric aerosol and understanding their chemical complexity is a key factor for determining their climate and health effects. We present and characterize here a new online technique for measuring the detailed chemical composition of organic aerosols, namely extractive electrospray ionization mass spectrometry (EESI-MS). Aerosol particles composed of soluble organic compounds were extracted into and ionized by a solvent electrospray, producing molecular ions from the aerosol with minimal fragmentation. We demonstrate here that the technique has a time resolution of seconds and is capable of making stable measurements over several hours. The ion signal in the MS was linearly correlated with the mass of aerosol delivered to the EESI source over the range tested (3-600 ÎŒg/m(3)) and was independent of particle size and liquid water content, suggesting that the entire particle bulk is extracted for analysis. Tandem MS measurements enabled detection of known analytes in the sub-ÎŒg/m(3) range. Proof-of-principle measurements of the ozonolysis of oleic acid aerosol (20 ÎŒg/m(3)) revealed the formation of a variety of oxidation products in good agreement with previous offline studies. This demonstrates the technique's potential for studying the product-resolved kinetics of aerosol-phase chemistry at a molecular level with high sensitivity and time resolution.This is the author's accepted manuscript. The final version is published by ACS in Environmental Science and Technology and can be found here: http://pubs.acs.org/doi/abs/10.1021/es305199h?prevSearch=%255BContrib%253A%2Bgallimore%252C%2Bp.%2Bj.%255D&searchHistoryKey=
Cooperating Agents for 3D Scientific Data Interpretation
Many organizations collect vast quantities of three-dimensional (3-D) scientific data in volumetric form for a range of purposes, including resource exploration, market forecasting, and process modelling. Traditionally, these data have been interpreted by human experts with only minimal software assistance. However, such manual interpretation is a painstakingly slow and tedious process. Moreover, since interpretation involves subjective judgements and each interpreter has different scientific knowledge and experience, formulation of an effective interpretation often requires the cooperation of numerous such experts. Hence, there is a pressing need for a software system in which individual interpretations can be generated automatically and then refined through the use of cooperative reasoning and information sharing. To this end, a prototype system, SurfaceMapper, has been developed in which a community of cooperating software agents automatically locate and display interpretations in a volume of 3-D scientific data. The challenges and experiences in designing and building such a system are discussed. Particular emphasis is given to the agents' interactions and an empirical evaluation of the effectiveness of different cooperation strategies is presented
Structural development of laminar flow control aircraft chordwise wing joint designs
For laminar flow to be achieved, any protuberances on the surface must be small enough to avoid transition to turbulent flow. However, the surface must have joints between the structural components to allow assembly or replacement of damaged parts, although large continuous surfaces can be utilized to minimize the number the number of joints. Aircraft structural joints usually have many countersunk bolts or rivets on the outer surface. To maintain no mismatch on outer surfaces, it is desirable to attach the components from the inner surface. It is also desirable for the panels to be interchangeable, without the need for shims at the joint, to avoid surface discontinuities that could cause turbulence. Fabricating components while pressing their outer surfaces against an accurate mold helps to ensure surface smoothness and continuity at joints. These items were considered in evaluating the advantages and disadvantages of the joint design concepts. After evaluating six design concepts, two of the leading candidates were fabricated and tested using many small test panels. One joint concept was also built and tested using large panels. The small and large test panel deflections for the leading candidate designs at load factors up to +1.5 g's were well within the step and waviness requirements for avoiding transition.The small panels were designed and tested for compression and tension at -65 F, at ambient conditions, and at 160 F. The small panel results for the three-rib and the sliding-joint concepts indicated that they were both acceptable. The three-rib concept, with tapered splice plates, was considered to be the most practical. A modified three-rib joint that combined the best attributes of previous candidates was designed, developed, and tested. This improved joint met all of the structural strength, surface smoothness, and waviness criteria for laminar flow control (LFC). The design eliminated all disadvantages of the initial three-rib concept except for unavoidable eccentricity, which was reduced and reacted satisfactorily by the rib supports. It should also result in a relatively simple low-cost installation, and makes it easy to replace any panels damaged in the field
The effect of an auxiliary discharge on anode sheath potentials in a transverse discharge
A novel scheme that employs the use of an auxiliary discharge has been shown to reduce markedly anode sheath potentials in a transverse discharge. An 8.8 A low-pressure argon discharge in the presence of a transverse magnetic field was used as the plasma source in this study. In such discharges, the transverse flux that is collected by the anode is severely limited due to marked reductions in the transverse diffusion coefficient. Findings of this study indicate that the local electron number density and the transverse flux increase when the auxiliary discharge is operated. Changes in these parameters are reflected in the measured anode sheath voltage. Anode sheath potentials, estimated by using Langmuir probes, were shown to be reduced by over 33% when the auxiliary discharge is operated. These reductions in anode sheath potentials translated into significant reductions in anode power flux as measured using water calorimeter techniques. The reductions in anode power flux also correlate well with changes in the electron transverse flux. Finally, techniques implementing these positive effects in real plasma accelerators are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71328/2/JAPIAU-81-8-3422-1.pd
A Flaring Megamaser in Mrk 348
We report new observations of the H2O megamaser in the Seyfert 2 galaxy Mrk
348. Following our initial detection in 2000 March using the Effelsberg 100 m
telescope, re-analysis of previous data on this source indicates that the maser
was present but only marginally detectable in late 1997. Monitoring through
late 2000 shows that the maser has again decreased to its original level. The
H2O line is redshifted by ~130 km/s with respect to the systemic velocity, is
extremely broad, with a FWHM of 130 km/s, and has no detectable high velocity
components within 1500 km/s on either side of the strong line. Followup VLBA
observations show that the maser emission emanates entirely from a region >0.25
pc in extent, toward the base of the radio jet.Comment: 4 pages, 2 figures, to appear in Cosmic Masers: from Protostars to
Black Holes, IAU 206, Eds. V. Migenes et al., ASP Conference Serie
- âŠ