The creeping motion of liquid drops through a circular tube of comparable diameter

The creeping motion through a circular tube of neutrally buoyant Newtonian drops which have an undeformed radius comparable to that of the tube was studied experimentally. Both a Newtonian and a viscoelastic suspending fluid were used in order to determine the influence of viscoelasticity. The extra pressure drop owing to the presence of the suspended drops, the shape and velocity of the drops, and the streamlines of the flow are reported for various viscosity ratios, total flow rates and drop sizes

Migration of rigid spheres in a two-dimensional unidirectional shear flow of a second-order fluid

The lateral migration of a neutrally buoyant rigid sphere suspended in a second-order fluid is studied theoretically for unidirectional two-dimensional flows. The results demonstrate the existence of migration induced by normal stresses whenever there is a lateral variation of the shear rate in the undisturbed flow. The migration occurs in the direction of decreasing absolute shear rate, which is towards the centre-line for a plane Poiseuille flow and towards the outer cylinder wall for Couette flow. The direction of migration agrees with existing experimental data for a viscoelastic suspending fluid, and qualitative agreement is found between the theoretically predicted and experimentally measured sphere trajectories

Circumbinary Molecular Rings Around Young Stars in Orion

We present high angular resolution 1.3 mm continuum, methyl cyanide molecular line, and 7 mm continuum observations made with the Submillimeter Array and the Very Large Array, toward the most highly obscured and southern part of the massive star forming region OMC1S located behind the Orion Nebula. We find two flattened and rotating molecular structures with sizes of a few hundred astronomical units suggestive of circumbinary molecular rings produced by the presence of two stars with very compact circumstellar disks with sizes and separations of about 50 AU, associated with the young stellar objects 139-409 and 134-411. Furthermore, these two circumbinary rotating rings are related to two compact and bright {\it hot molecular cores}. The dynamic mass of the binary systems obtained from our data are $\geq$ 4 M$_\odot$ for 139-409 and $\geq$ 0.5 M$_\odot$ for 134-411. This result supports the idea that intermediate-mass stars will form through {\it circumstellar disks} and jets/outflows, as the low mass stars do. Furthermore, when intermediate-mass stars are in multiple systems they seem to form a circumbinary ring similar to those seen in young, multiple low-mass systems (e.g., GG Tau and UY Aur).Comment: Accepted by Astronomy and Astrophysic

A Tidal Flare Candidate in Abell 1795

As part of our ongoing archival X-ray survey of galaxy clusters for tidal flares, we present evidence of an X-ray transient source within 1 arcmin of the core of Abell 1795. The extreme variability (a factor of nearly 50), luminosity (> 2 x 10^42 erg s^{-1}), long duration (> 5 years) and supersoft X-ray spectrum (< 0.1 keV) are characteristic signatures of a stellar tidal disruption event according to theoretical predictions and to existing X-ray observations, implying a massive >~10^5 M_sun black hole at the centre of that galaxy. The large number of X-ray source counts (~700) and long temporal baseline (~12 years with Chandra and XMM-Newton) make this one of the best-sampled examples of any tidal flare candidate to date. The transient may be the same EUV source originally found contaminating the diffuse ICM observations of Bowyer et al. (1999), which would make it the only tidal flare candidate with reported EUV observations and implies an early source luminosity 1-2 orders of magnitude greater. If the host galaxy is a cluster member then it must be a dwarf galaxy, an order of magnitude less massive than the quiescent galaxy Henize 2-10 which hosts a massive black hole that is difficult to reconcile with its low mass. The unusual faintness of the host galaxy may be explained by tidal stripping in the cluster core.Comment: Accepted by MNRAS 2013 July 23. 27 pages, 10 figure

Self-shadowing Effects of Slim Accretion Disks in Active Galactic Nuclei: Diverse Appearance of the Broad-line Region

Supermassive black holes in active galactic nuclei (AGNs) undergo a wide range of accretion rates, which lead to diversity of appearance. We consider the effects of anisotropic radiation from accretion disks on the broad-line region (BLR), from the Shakura-Sunyaev regime to slim disks with super-Eddington accretion rates. The geometrically thick funnel of the inner region of slim disks produces strong self-shadowing effects that lead to very strong anisotropy of the radiation field. We demonstrate that the degree of anisotropy of the radiation fields grows with increasing accretion rate. As a result of this anisotropy, BLR clouds receive different spectral energy distributions depending on their location relative to the disk, resulting in diverse observational appearance of the BLR. We show that the self-shadowing of the inner parts of the disk naturally produces two dynamically distinct regions of the BLR, depending on accretion rate. These two regions manifest themselves as kinematically distinct components of the broad H$\beta$ line profile with different line widths and fluxes, which jointly account for the Lorentzian profile generally observed in narrow-line Seyfert 1 galaxies. In the time domain, these two components are expected reverberate with different time lags with respect to the varying ionizing continuum, depending on the accretion rate and the viewing angle of the observer. The diverse appearance of the BLR due to the anisotropic ionizing energy source can be tested by reverberation mapping of H$\beta$ and other broad emission lines (e.g., \feii), providing a new tool to diagnose the structure and dynamics of the BLR. Other observational consequences of our model are also explored.Comment: emulatapj style, 15 pages, 6 figures, in pres

VLA Imaging of the Disk Surrounding the Nearby Young Star TW Hya

The TW Hya system is perhaps the closest analog to the early solar nebula. We have used the Very Large Array to image TW Hya at wavelengths of 7mm and 3.6 cm with resolutions 0.1 arcseconds (about 5 AU) and 1.0 arcseconds (about 50 AU), respectively. The 7mm emission is extended and appears dominated by a dusty disk of radius larger than 50 AU surrounding the star. The 3.6 cm emission is unresolved and likely arises from an ionized wind or gyrosynchrotron activity. The dust spectrum and spatially resolved 7mm images of the TW Hya disk are fitted by a simple model with temperature and surface density described by radial power laws, $T(r)\propto r^{-0.5}$ and $\Sigma(r) \propto r^{-1}$. These properties are consistent with an irradiated gaseous accretion disk of mass $\sim0.03~{\rm M_{\odot}}$ with an accretion rate $\sim10^{-8}~{\rm M_{\odot}yr^{-1}}$ and viscosity parameter $\alpha = 0.01$. The estimates of mass and mass accretion rates are uncertain as the gas-to-dust ratio in the TW Hya disk may have evolved from the standard interstellar value.Comment: 13 pages, 3 figures, accepted by ApJ Letter

A halo and a blow-out in NGC 253

We present the discovery of a 'synchrotron halo' in NGC 253. NGC 253 is an inclined, dusty, barred Sc galaxy in the Sculptor Group. It is also one of the prototype nuclear star burst galaxies. Very Large Array observations at 327 MHz and 1.4 GHz have revealed a synchrotron emitting 'halo' extending 9 kpc above and below the plane of NGC 253 (assuming a distance of 4 Mpc). The spectral index for the radio emission steepens from -0.7 in the disk to -1.0 in the halo. The fractional polarization at 1.4 GHz increases from less than or equal to 2 percent in the disk up to 20 percent in the halo, and the magnetic field vectors project parallel to the plane over most of the halo

The design of aircraft brake systems, employing cooling to increase brake life

A research program was initiated to determine the feasibility of using cooling to increase brake life. An air cooling scheme was proposed, constructed and tested with various designs. Straight and curved slotting of the friction material was tested. A water cooling technique, similar to the air cooling procedure, was evaluated on a curved slotted rotor. Also investigated was the possibility of using a phase-change material within the rotor to absorb heat during braking. Various phase-changing materials were tabulated and a 50%, (by weight) LiF - BeF2 mixing was chosen. It was shown that corrosion was not a problem with this mixture. A preliminary design was evaluated on an actual brake. Results showed that significant improvements in lowering the surface temperature of the brake occurred when air or water cooling was used in conjunction with curved slotted rotors