The annual cycle in scintillation time-scale of PMN J1726+0639

PKS B1322-110 is a radio quasar that is located only 8.5' in angular separation from the bright B star Spica. It exhibits intra-day variability in its flux density at GHz frequencies attributed to scintillations from plasma inhomogeneities. We have tracked the rate of scintillation of this source for over a year with the Australia Telescope Compact Array, recording a strong annual cycle that includes a near-standstill in August and another in December. The cycle is consistent with scattering by highly anisotropic plasma microstructure, and we fit our data to that model in order to determine the kinematic parameters of the plasma. Because of the low ecliptic latitude of PKS B1322-110, the orientation of the plasma microstructure is poorly constrained. Nonetheless at each possible orientation our data single out a narrow range of the corresponding velocity component, leading to a one-dimensional constraint in a two-dimensional parameter space. The constrained region is consistent with a published model in which the scattering material is associated with Spica and consists of filaments that are radially oriented around the star. This result has a 1% probability of arising by chance.

A small number of quasars exhibit interstellar scintillation on time-scales less than an hour; their scintillation patterns are all known to be anisotropic. Here, we consider a totally anisotropic model in which the scintillation pattern is effectively one-dimensional. For the persistent rapid scintillator J1819+3845, we show that this model offers a good description of the two-station time-delay measurements and the annual cycle in the scintillation time-scale. Generalizing the model to finite anisotropy yields a better match to the data but the improvement is not significant and the two additional parameters which are required to describe this model are not justified by the existing data. In contrast, our data for the persistent rapid scintillator PKS1257−326 are significantly better fit by a two-dimensional model with a major-to-minor axis ratio of 6 for the scintillation pattern. For J1819+3845, the totally anisotropic model predicts that the particular radio flux variations seen between mid-July and late August should repeat between late August and mid-November, and then again between mid-November and late December as the Earth twice changes its direction of motion across the scintillation pattern. If this effect can be observed then the minor-axis velocity component of the screen and the orientation of that axis can both be precisely determined. In reality, the axis ratio is finite, albeit large and spatial decorrelation of the flux pattern along the major axis may be observable via differences in the pairwise fluxes within this overlap region; in this case, we can also constrain both the major-axis velocity component of the screen and the magnitude of the anisotropy.

We report the discovery of a very H i-massive disk galaxy, HIZOA J0836{43, at a velocity of vhel = 10689 km s 1 , corresponding to a distance of 148 Mpc (assuming H0 = 75 km s 1 Mpc 1 ). It was found during the course of a systematic H i survey of the southern Zone of Avoidance (jbj 5 ) with the multibeam system at the 64 m Parkes radio telescope. Follow-up observations with the Australia Telescope Compact Array (ATCA) reveal an extended H i disk. We derive an H i mass of 7:5 10 10 M . Using the H i radius, we estimate a total dynamical mass of 1:4 10 12 M , similar to the most massive known disk galaxies such as Malin 1. HIZOA J0836{43 lies deep in the Zone of Avoidance (‘; b = 262: 48; 1: 64) where the optical extinction is very high, AB = 9: m 8. However, in the near-infrared wavebands, where the extinction is considerably lower, HIZOA J0836{43 is clearly detected by both DENIS and 2MASS. Deep AAT near-infrared (Ks and H-band) images show that HIZOA J0836{43 is an inclined disk galaxy with a prominent bulge (scale length 2.5 00 or 1.7 kpc), and an extended disk (scale length 7 00 or 4.7 kpc) which can be traced along the major axis out to a radius of 20 00 or 13.4 kpc (at 20 mag arcsec 2 in Ks). The H i disk is much more extended, having a radius of 66 kpc at 1 M pc 2 . Detections in the radio continuum at 1.4 GHz and at 60 m (IRAS) are consistent with HIZOA J0836{43 forming stars at a rate of 35 M yr 1 . We compare the properties of HIZOA J0836{43 with those of the most H i-massive galaxies currently known, UGC 4288, UGC 1752 and Malin 1, all of which are classied as giant low surface brightness galaxies.

We have used the Australia Telescope Compact Array (ATCA) to search for polarized emission from the Circinus galaxy H2O megamasers. No linear or circular polarized emission was detected with 3σ upper limits of 24 and 39 mJy, respectively, corresponding to fractional polarizations of 0.6 and 0.9 per cent for the strongest line. These results allow us to place upper limits on the strength of the nuclear magnetic field of 150 mG near the outer edge of the masing disc and 360 mG at the inner edge. Rapid variability, thought to be due to interstellar scintillation, is a well-known feature of the Circinus H2O megamasers. Our Stokes-I data show evidence for changes in the shape of the maser line spectral profiles, as well as their intensity. In addition to the rapid variations, the maser light curves also exhibit variations with a time-scale of the order of days (although our observations are too short to characterize this well). These behaviours support the hypothesis that the Circinus H2O megamasers undergo diffractive interstellar scintillation, which has previously only been observed in pulsars and in one active galactic nucleus.

We report on high spatial resolution observations, using the Australia Telescope Compact Array (ATCA), of ground-state OH masers. These observations were carried out toward 196 pointing centers previously identified in the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH) pilot region, between Galactic longitudes of 334° and 344° and Galactic latitudes of −2° and +2°. Supplementing our data with data from the MAGMO (Mapping the Galactic Magnetic field through OH masers) survey, we find maser emission toward 175 of the 196 target fields. We conclude that about half of the 21 nondetections were due to intrinsic variability. Due to the superior sensitivity of the followup ATCA observations, and the ability to resolve nearby sources into separate sites, we have identified 215 OH maser sites toward the 175 fields with detections. Among these 215 OH maser sites, 111 are new detections. After comparing the positions of these 215 maser sites to the literature, we identify 122 (57%) sites associated with evolved stars (one of which is a planetary nebula), 64 (30%) with star formation, two sites with supernova remnants, and 27 (13%) of unknown origin. The infrared colors of evolved star sites with symmetric maser profiles tend to be redder than those of evolved star sites with asymmetric maser profiles, which may indicate that symmetric sources are generally at an earlier evolutionary stage.

We present high spatial resolution observations of ground-state OH masers achieved using the Australia Telescope Compact Array (ATCA). These observations were conducted toward 171 pointing centers where OH maser candidates were identified previously in the Southern Parkes Large-Area Survey in Hydroxyl toward the Galactic center region between Galactic longitudes of 355◦ and 5◦ and Galactic latitudes of −2° and +2°. We detect maser emission toward 162 target fields and suggest that six out of nine nondetections are due to intrinsic variability. Due to the superior spatial resolution of the follow-up ATCA observations, we have identified 356 OH maser sites in the 162 target fields with maser detections. Almost half (161 of 356) of these maser sites have been detected for the first time in these observations. After comparing the positions of these 356 maser sites to the literature, we find that 269 (76%) sites are associated with evolved stars (two of which are PNe), 31 (9%) are associated with star formation, and four are associated with supernova remnants; we were unable to determine the origin of the remaining 52 (15%) sites. Unlike the pilot region, the infrared colors of evolved star sites with symmetric maser profiles in the 1612 MHz transition do not show obvious differences compared with those of evolved star sites with asymmetric maser profiles.

Atmospheric monitoring stations are operated at Barrow, Alaska; Mauna Loa, Hawaii; American Samoa; and South Pole by the Geophysical Monitoring for Climatic Change program to measure the characteristics of gaseous and aerosol species under background conditions. A nearly continuous record of light‐scattering coefficient and condensation nuclei concentration measurements is available for Barrow since 1971, Mauna Loa since 1974, Samoa since 1977, and South Pole since 1974. The Barrow light‐scattering data exhibit a strong annual cycle with a maximum in winter and spring (the Arctic haze) and a minimum in summer. The Barrow condensation nuclei data exhibit a strong semiannual cycle with a maximum coinciding with that of light scattering and an additional maximum about August. The Mauna Loa light‐scattering data show a strong annual cycle with a maximum in April or May caused by long‐range transport of Asian desert dust. The Mauna Loa condensation nuclei data show no significant annual cycle. The Samoa light‐scattering and condensation nuclei data are representative of a clean marine atmosphere and exhibit no significant annual or diurnal cycle. The South Pole light‐scattering data show a complicated annual cycle with a maximum in the austral summer and a minimum about April. The austral winter is dominated by events most likely caused by the transport of sea salt in the troposphere from the coastal regions to the interior of the Antarctic continent. The South Pole condensation nuclei data show a repeatable annual cycle with a maximum in the austral summer and a minimum in the austral winter. Linear least squares trend analyses show no significant trend compared to the standard error about the regression line at any station.

Color flow mapping has become an important clinical tool, for diagnosing a wide range of vascular diseases. Only the velocity component along the ultrasonic beam is estimated, so to find the actual blood velocity, the beam to flow angle has to be known. Because of the unpredictable nature of vascular hemodynamics, the flow angle cannot easily be found as the angle is temporally and spatially variant. Additionally the precision of traditional methods is severely lowered for high flow angles, and they breakdown for a purely transverse flow. To overcome these problems we propose a new method for estimating the transverse velocity component. The method measures the transverse velocity component by estimating the transit time of the blood between two parallel lines beamformed in receive. The method has been investigated using simulations performed with Field II. Using 15 emissions per estimate, a standard deviation of 1.64% and a bias of 1.13% are obtained for a beam to flow angle of 90 degrees. Using the same setup a standard deviation of 2.21% and a bias of 1.07% are obtained for a beam to flow angle of 75 degrees. Using 20 emissions a standard deviation of 3.4% and a bias of 2.06% are obtained at 45 degrees. The method performs stable down to a signal-to-noise ratio of 0 dB, where a standard deviation of 5.5% and a bias of 1.2% is achieved.

Characterisation of transverse turbulent motion in quasi-two-dimensional aerated flow: Application of four-point air-water flow measurements in hydraulic jump

In this paper we investigate numerically the periodic, axisymmetric response of a liquid annulus enclosed in a revolving cylinder and subject to a periodic axial excitation within the range of the natural frequencies. We use a description which employs as solution variables the transverse component of the vorticity vector, the scalar stream function and the transverse velocity component, as well as the position of the free surface. The acceleration due to gravity is neglected, whereas friction and surface tension are taken into account. At the fixed walls the no-slip condition is fulfilled except at points on the contact line. At the contact line the slip condition is applied. The solution of this problem is achieved using the spectral method in the time direction and finite differences in the space direction, whereby surface-adapted coordinates are utilized. Far away from the walls the computational results show good agreement with results obtained from a linearized theory assuming an inviscid liquid, while at the walls boundary layers are generated.

We present a sample of 706, z < 1.5 active galactic nuclei (AGNs) selected from optical photometric variability in three of the Dark Energy Survey (DES) deep fields (E2, C3, and X3) over an area of 4.64 deg2. We construct light curves using difference imaging aperture photometry for resolved sources and non-difference imaging PSF photometry for unresolved sources, respectively, and characterize the variability significance. Our DES light curves have a mean cadence of 7 d, a 6-yr baseline, and a single-epoch imaging depth of up to g ∼ 24.5. Using spectral energy distribution (SED) fitting, we find 26 out of total 706 variable galaxies are consistent with dwarf galaxies with a reliable stellar mass estimate ($M_{\ast }\lt 10^{9.5}\, {\rm M}_\odot$; median photometric redshift of 0.9). We were able to constrain rapid characteristic variability time-scales (∼ weeks) using the DES light curves in 15 dwarf AGN candidates (a subset of our variable AGN candidates) at a median photometric redshift of 0.4. This rapid variability is consistent with their low black hole (BH) masses. We confirm the low-mass AGN nature of one source with a high S/N optical spectrum. We publish our catalogue, optical light curves, and supplementary data, such as X-ray properties and optical spectra, when available. We measure a variable AGN fraction versus stellar mass and compare to results from a forward model. This work demonstrates the feasibility of optical variability to identify AGNs with lower BH masses in deep fields, which may be more ‘pristine’ analogues of supermassive BH seeds.

The respiratory system is characterized by many bifurcations. The bronchi are composed of symmetrical and asymmetrical bifurcations. It is generally considered that the gas mixing during the respiration are induced by the flow through the bronchi. In the present study, the axial and the transverse velocity components have been measured in the asymmetrical bifurcation by LDV. Consequently, the asymmetry of axial flow and the secondary flow around the flow divider have been clarified experimentally.

The effect of nonhomogeneous strain caused by two-dimensional objects on single point statistical properties of the turbulent velocity and turbulent scalar (temperature) and their cross moments are investigated experimentally. The heated turbulent flow is produced by means of a biplane array of round rods and a biplane array of heated, thin wires placed downstream of the turbulence producing grid. The experiments are performed for three different ratios of the integral scale, L0, to the object dimension, D, of 0.38, 1.90 and 3.1. Measurements of time resolved temperature and longitudinal and transverse velocity components are obtained using a triple wire probe consisting of a cold wire and two hot wires. Results indicate that, for L0 =1.9 and 3.1, the decay rate of temperature variance is nearly the same in the region of maximum shear stress (mss) and near the centerline. However, the decay rate in these regions is less than the decay rate of the temperature variance outside the cylinder wake. For L0/D = 0.38, the decay rates of temperature variance are the same in the regions of mss, near the centerline and outside the wake. Transverse growth of the wake is found to be either increased or nearly unchanged depending on, respectively, whether the free stream integral scale is larger or less than that of the wake.

Understanding the flow behaviour of synovial fluid is essential for analysing lubrication, nutrient transport, and mechanical functionality within the knee joint. This study presents a mathematical model describing axial and transverse velocity components under pressure driven flow with variable viscosity and porous-like resistance parameters. The governing equations were solved to obtain velocity profiles and volumetric flow rate, enabling a detailed assessment of fluid transport under physiological conditions. The results show that axial velocity follows a smooth parabolic pattern typical of laminar lubrication flow, while transverse velocity is highly sensitive to viscosity ratios and structural resistance, reflecting the influence of synovial membrane permeability. The computed flow rates demonstrate that elevated viscosity and decreased permeability conditions associated with osteoarthritis—significantly reduce fluid transport capacity. The study provides mechanistic insight into synovial fluid dynamics and offers a theoretical basis for improving visco supplementation strategies, developing biomimetic joint lubricants, and informing therapeutic approaches for degenerative knee disorders.

The internal motion through porous chambers generated by wall-normal injection has received considerable attention in the second half of the twentieth century. This may be attributed to its relevance to a large number of phenomenological applications. In actuality, the motion of fluids driven by either wall injection or suction can be used to describe a variety of practical problems that encompass a wide range of industries and research areas. To name a few, these include: paper manufacturing (Taylor, 1956), ablation or sweat cooling (Peng & Yuan, 1965; Yuan & Finkelstein, 1958), boundary layer control (Acrivos, 1962; Libby, 1962; Libby & Pierucci, 1964), peristaltic pumping (Fung & Yih, 1968; Uchida & Aoki, 1977), gaseous diffusion or filtration, isotope separation (Berman, 1953; 1958a;b), irrigation, and the mean flow modeling of both solid (Culick, 1966; Zhou & Majdalani, 2002) and hybrid rockets (Majdalani, 2007a). Wall injected flows are initiated by the injection or suction of a fluid across the boundaries of a ducted region having an arbitrary shape and cross-sectional area. This is illustrated in Figure 1 for the special cases of porous channels and tubes. In general, one is required to solve a reduced-order form of the equations of motion for a bounded fluid in order to retrieve a meaningful solution (Terrill & Thomas, 1969). For a general three dimensional setting, this effort leads to a formidable task that is often intractable. However, when simplifying assumptions are invoked, as in the case of an incompressible stream in a channel or tube with uniform injection or suction, Berman (1953) has shown that the Navier-Stokes equations can be reduced to a fourth order nonlinear ODE that may be susceptible to both analytical and numerical treatment. Berman’s approach is based on a spatial similarity that transforms the Navier-Stokes equations to a more manageable ODE by assuming that the transverse velocity component v is axially invariant; this immediately translates into a streamfunction that varies linearly in the streamwise direction, i.e. ψ(x, y) = xF(y) (Berman, 1953; White, 2005). Then by considering the limiting case of a small suction Reynolds number, Re ∼ e, Berman employs a regular perturbation series in Re to obtain an approximate expansion for the mean flow function F(y). Berman’s Reynolds number, Re = Uwa/ν , is based on the injection speed at the wall, Uw, and the channel half height, a. As for the case of large suction, Berman (1953) first remarks that the limit of the reduced ODE cannot be used to obtain a solution owing to the reduction in order of the governing equation. Later, Sellars (1955) and Terrill (1964) invoke a procedure that permits the extraction of a closed-form analytical approximation for the large Re case by implementing a coordinate transformation that takes into account the spatial relocation of the boundary layer to the sidewall region. Internal Flows Driven by Wall-Normal Injection