Edge Of Disk Research Articles

A rapidly spinning supermassive black hole at the centre of NGC 1365

Broad X-ray emission lines from neutral and partially ionized iron observed in active galaxies have been interpreted as fluorescence produced by the reflection of hard X-rays off the inner edge of an accretion disk. In this model, line broadening and distortion result from rapid rotation and relativistic effects near the black hole, the line shape being sensitive to its spin. Alternative models in which the distortions result from absorption by intervening structures provide an equally good description of the data, and there has been no general agreement on which is correct. Recent claims that the black hole (2 × 10(6) solar masses) at the centre of the galaxy NGC 1365 is rotating at close to its maximum possible speed rest on the assumption of relativistic reflection. Here we report X-ray observations of NGC 1365 that reveal the relativistic disk features through broadened Fe-line emission and an associated Compton scattering excess of 10-30 kiloelectronvolts. Using temporal and spectral analyses, we disentangle continuum changes due to time-variable absorption from reflection, which we find arises from a region within 2.5 gravitational radii of the rapidly spinning black hole. Absorption-dominated models that do not include relativistic disk reflection can be ruled out both statistically and on physical grounds.

BUILDING TATOOINE: SUPPRESSION OF THE DIRECT SECULAR EXCITATION IN KEPLER CIRCUMBINARY PLANET FORMATION

Circumbinary planetary systems recently discovered by Kepler represent an important testbed for planet formation theories. Planetesimal growth in disks around binaries has been expected to be inhibited interior to ~10 AU by secular excitation of high relative velocities between planetesimals, leading to their collisional destruction (rather than agglomeration). Here we show that gravity of the gaseous circumbinary disk in which planets form drives fast precession of both the planetesimal and binary orbits, resulting in strong suppression of planetesimal eccentricities beyond 2-3 AU and making possible growth of 1-100 km objects in this region. The precise location of the boundary of accretion-friendly region depends on the size of the inner disk cavity cleared by the binary torques and on the disk mass (even 0.01 M_Sun disk strongly suppresses planetesimal excitation), among other things. Precession of the orbit of the central binary, enhanced by the mass concentration naturally present at the inner edge of a circumbinary disk, plays key role in this suppression, which is a feature specific to the circumbinary planet formation.

EXPERIMENTAL INVESTIGATION OF DYNAMICS AND ATOMIZATION OF A LIQUID FILM FLOWING OVER A SPINNING DISK

One of the most commonly used methods of liquid atomization is the rotary atomization. In this process a radially spreading thin liquid film is created on a surface of a rotating disk, due to centrifugal forces. The liquid flows over the disk edge and disintegrates. The liquid film is mostly wavy. The radially propagating waves induce fluctuations resulting in an expansion of the drop size distribution after atomization. An experimental apparatus has been built to investigate the effect of the film dynamics on the atomization process. A water jet is impinging at the center of a rotating disk made of stainless steel. The local instantaneous film thickness is measured using a confocal chromatic sensoring technique. The drop sizes are determined using the shadowgraphy method. The film flow on the rotating disk has been investigated in a wide range of parameters. The strongly wavy structure of the film flow has been observed for all sets of parameters. The development of waves depends on the nozzle-to-disk distance. The radial distribution of the time-averaged film thickness over the disk surface agrees fairly well with the correlations found in the literature. First results of the drop size distribution show a bimodal distribution for low liquid mass flow rates.

Effect of Disk Edge Profile on Scattering Characteristics of Liquid Droplets Splashed from Spinning Disk

Effects of disk edge profile on scattering characteristics of liquid droplets splashed from a rotating disk edge are experimentally investigated. In the present research, aluminum disks are utilized and purified water is employed for liquid. Scattering phenomena of the droplets are captured by the high-speed digital camera. Distribution of the droplet diameter is evaluated from these images and distributions of horizontal flying velocity component and angle of the droplets are measured by human visual observation of images. Liquid filaments are stretched outward from the stagnant liquid layer on lateral surface of disk edge by centrifugal force. Two main peaks appear in the distribution of the scattered droplet diameter and they are originated from large terminal droplets and small droplets generated from filamentwise breakup. Most of the scattered droplets fly slightly inside of the tangential direction of the disk edge. The water droplets splashed from the disk scatters with regularity compared with ethanol droplets.

Evaluation of sensitivity of modified star protocol microbiological method for beta-lactame antibiotics detection in raw cow milk

Antibiotic residues when present in animal tissues, through food chain, can enter human body, causing allergic reactions or facilitating the development of resistant bacterial strains. In order to determine the presence of antibiotics in animal tissues, it is appropriate to use convenient, reliable and sensitive methods. Microbiological methods applied for the detection of antibiotic residues in primary products of animal origin are based on the sensitivity of specific bacterial strains to a particular group of antibiotics. Regulatives on the amount of pesticides, metals and metalloids and other toxic substances, chemotherapeutics, anabolics and other substances which can be found in food ("Off. Gazette", No. 5/92, 11/92 - corr. and 32/02), state that milk and milk products can be used in commercial purposes only if not contain antibiotics in quantities that can be detected by reference methods. The applied method is modified STAR (Screening test for detection of antibiotics) protocol, regulated by the CRL (Community Reference Laboratory) Fougeres, France, in which the initial validation of the method had been carried out. In accordance with the demands of Regulative Commission EC No657/2002, the sensitivity of modified STAR protocol for beta lactam antibiotics group was examined , that is, there was carried out a contracted validation of the method, which initial validation had been performed at CRL. In a couple of series of experiments, 20 blank samples of raw cow milk originating from animals not treated by antibiotics, had been examined. By the beginning of the experiment samples were stored in a freezer at -20?C. Samples of raw cow milk enriched by working solutions of seven beta-lactam antibiotics, in order to obtain concentrations at the level of 0.5, 1 and 1.5 MRL (Maximmum Residue Limit) for each given antibiotic (Commission Regulation EC No. 37/2010). For detection of beta-lactam antibiotics, there was used Kundrat agar test with previously inoculated G.stearothermophilus ATCC 10149 strain. Aliquots of 30 _l of working solution at 0.5, 1 and 1.5 MRL concentration level, for each antibiotic, were inflicted on two paper disks placed on inoculated Kundrat agar surface. Petri plates with Kundrat agar previously inoculated with G.stearothermophilus , on which the samples were deposited, were incubated for 12-15h at 55oC. The obtained width of microorganisms growth inhibition zone, that is supposed to be at least 2.0 mm, measured from the disc edge, demonstrated the capability to detect all the tested 7 antibiotics from the beta lactam group at a level below the MRLs. Consequently, this proves that use of this method it is possible to meet the demands of Regulative Commission EC No. 37/2010.

Optic Disc Pit with Sectorial Retinitis Pigmentosa

Sectorial retinitis pigmentosa (RP) and optic disc pit (ODP) are rare clinical conditions. We present a 40-year-old woman with a history of mild night blindness and decreased vision in the right eye for about 5 years. Fundus examination revealed retinal pigmentary changes in the superior and inferotemporal sectors covering the macula and reduced arterial calibre and ODP at the temporal edge of the optic disc. In addition, fundus autofluorescence, spectral-domain optical coherence tomography, fluorescein angiography, and multifocal electroretinogram scans confirmed these clinical findings. Visual acuity was decreased due to an atrophic-appearing foveal lesion. No intervention was suggested because of the poor visual potential. To the best of our knowledge, the present study is the first to describe coexistent optic disc pit and sectorial RP in the superior and inferotemporal sectors covering the macula in the same eye with figures.

FROM PLANETESIMALS TO DUST: LOW-GRAVITY EXPERIMENTS ON RECYCLING SOLIDS AT THE INNER EDGES OF PROTOPLANETARY DISKS

Transporting solids of different sizes is an essential process in the evolution of protoplanetary disks and planet formation. Large solids are supposed to drift inward; high-temperature minerals found in comets are assumed to have been transported outward. From low-gravity experiments on parabolic flights we studied the light-induced erosion of dusty bodies caused by a solid-state greenhouse effect and photophoresis within a dust bed's upper layers. The gravity levels studied were 0.16g, 0.38g, 1g, and 1.7g. The light flux during the experiments was 12 +/- 2 kW/m^2 and the ambient pressure was 6 +/- 0.9 mbar. Light-induced erosion is strongly gravity dependent, which is in agreement with a developed model. In particular for small dusty bodies ((sub)-planetesimals), efficient erosion is possible at the optically thin inner edges of protoplanetary disks. Light-induced erosion prevents significant parts of a larger body from moving too close to the host star and be being subsequently accreted. The small dust produced continues to be subject to photophoresis and is partially transported upward and outward over the surface of the disk; the resulting small dust particles observed over the disk's lifetime. The fraction of eroded dust participates in subsequent cycles of growth during planetesimal formation. Another fraction of dust might be collected by a body of planetary size if this body is already present close to the disk edge. Either way, light induced erosion is an efficient recycling process in protoplanetary disks.

High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A

Abstract We present $ H$-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk object, with a gap structure separating its inner and outer disks. Our imagery taken with the 0$ \rlap{\hskip1pt .}''$ 15 (21 AU) radius coronagraphic mask has revealed a strongly polarized circumstellar disk surrounding UX Tau A, which extends to 120 AU, at a spatial resolution of 0$ \rlap{\hskip1pt .}''$ 1 (14 AU). It is inclined by 46$ ^{\circ}$$ \pm$ 2$ ^{\circ}$ , since the west side is nearest. Although SED modeling and sub-millimeter imagery have suggested the presence of a gap in the disk, with the inner edge of the outer disk estimated to be located at 25–30 AU, we detect no evidence of a gap at the limit of our inner working angle (23 AU) at the near-infrared wavelength. We attribute the observed strong polarization (up to 66%) to light scattering by dust grains in the disk. However, neither polarization models of the circumstellar disk based on Rayleigh-scattering nor Mie-scattering approximations were consistent with the observed azimuthal profile of the polarization degrees of the disk. Instead, a geometric optics model of the disk with nonspherical grains with radii of 30 $ \mu$ m is consistent with the observed profile. We suggest that the dust grains have experienced frequent collisional coagulations, and have grown in the circumstellar disk of UX Tau A.

A classic temporal optic disc pit showing progression in the corresponding optic nerve fiber and visual field defects

We report a rare case with a classic temporal optic disc pit (ODP) showing the progression of an associated nerve fiber layer defect (NFLD) with the corresponding visual field defect (VFD). We describe the patient's medical records and review the pertinent literature. A 54-year-old woman had a temporal ODP, which was considered to be congenital, associated with both NFLD expanded to both the upper and lower sides of the horizontal line and corresponding VFD and a small ODP-like excavation at the 6.5 o'clock position on the disc edge with a narrow NFLD OD. During the 5-year follow-up period, both the NFLD and VFD associated with the temporal pit progressed without serous retinal detachment. The small ODP-like excavation located at the 6.5 o'clock position also showed progressive NFLD in the temporal lower quadrant with advanced VFD, which suggested that the excavation might be associated with glaucoma. Based on the observation that the VFD occupied the two temporal quadrants with no step, an NFLD with corresponding VFD associated with a classic temporal ODP, although not considered to be related to glaucoma, can progress.

Sinigarra napoense, a new genus and species of labeonin fishes (Teleostei: Cyprinidae) from Guangxi Province, South China

A new garrain genus and species are described from the Zuo-Jiang of the Zhu-Jiang (Pearl River) drainage in GuangxiProvince, South China. Sinigarra, new genus, is characterized by having the lower lip modified into a mental adhesive discposteriorly discontinuous with the mental region. It is distinguished from all other disc-bearing genera, namely Garra,Placocheilus, Discocheilus and Discogobio, by having the anterior edge of the mental adhesive disc not modified to form ananteromedian crescentic fold, an upper lip present, but separated from the upper jaw, and indistinct papillae scarcely scattered over the rostral cap and lower lip or absent.

SPARSE APERTURE MASKING OBSERVATIONS OF THE FL Cha PRE-TRANSITIONAL DISK

We present deep Sparse Aperture Masking (SAM) observations obtained with the ESO Very Large Telescope of the pre-transitional disk object FL Cha (SpT=K8, d=160 pc), the disk of which is known to have a wide optically thin gap separating optically thick inner and outer disk components. We find non-zero closure phases, indicating a significant flux asymmetry in the K-band emission (e.g., a departure from a single point source detection). We also present radiative transfer modeling of the SED of the FL Cha system and find that the gap extends from ~0.06 to ~8.3 AU. We demonstrate that the non-zero closure phases can be explained almost equally well by starlight scattered off the inner edge of the outer disk or by a (sub)stellar companion. Single-epoch, single-wavelength SAM observations of transitional disks with large cavities that could become resolved should thus be interpreted with caution, taking the disk and its properties into consideration. In the context of a binary model, the signal is most consistent with a high-contrast (delta_K ~4.8 mag) source at a ~40 mas (6 AU) projected separation. However, the flux ratio and separation parameters remain highly degenerate and a much brighter source (deta_K ~1 mag) at 15 mas (2.4 AU) can also reproduce the signal. Second-epoch, multi-wavelength observations are needed to establish the nature of the SAM detection in FL Cha.

Expectant management in type II selective intrauterine growth restriction and abnormal chord insertion in monochorionic twins

To assess perinatal outcome in type II monochorionic (MC) diamniotic twin pregnancies (DA) affected by selective intrauterine growth restriction (sIUGR) and abnormal cord insertion managed expectantly. A prospective longitudinal study from June 2008 and July 2011 on 24 MCDA sIUGR twins. sIUGR was defined as estimated fetal weight below the 10th percentile in one twin and was classified into three groups based on umbilical artery (UA) Doppler diastolic flow (I: presence; II: constantly absent/reverse (AEDF/ARED); III: intermittently absent or reverse). Marginal cord insertion was defined as insertion within 2 cm of the placental disc edge, and velamentous insertion as a cord insertion into the fetal membranes. Expectant management was chosen in these twins, and absent or reverse A wave in the ductus venosus (DV) was a criterion for delivery. Neonatal outcome was available for all twins delivered. Pathological examination and vascular cast of placentas were performed in all cases. Fourteen twin pregnancies were type II sIUGR, and ten presented an abnormal umbilical cord insertion. Median gestational age (GA) at diagnosis of sIUGR was 18 weeks' gestation (range 16-20 weeks), and all sIUGR co-twins showed AEDF of UA at a median gestational age of 20 weeks (range 18-22 weeks). Median gestational age at delivery was 30 weeks (range 28-34 weeks) with a median birth weight of 1285 g (range 307-1725 g). pH at birth and base excess (BE) were normal in all IUGR co-twin (pH>7.10, median BE 5.5); Apgar score at 5 min was >7. Perinatal outcome was favorable in all cases. Placental pathological examination confirmed the marginal insertion of the umbilical cord and the absence of anastomosis between the two portions of umbilical insertion. This study highlights that expectant management for sIUGR type II twins with or without an abnormal cord insertion should be a valid option to time delivery for these fetuses as shown by the favorable neonatal outcome.

Study on the reduction of flow-induced noise through the suppression of vortex shedding at rotating disk edge

We conducted a computational analysis to better understand the coherent flow structure that arises when the rotation of a disk drive generates flow-induced noise. We set the flow domain to be similar to the actual shape of the flow in Blu-ray disks and examined the phenomena of vortex generation and shedding at the disk edge, focusing on the source of the noise. Our results showed that disk edge vortex shedding was the primary cause of disk-drive-flow-induced noise; therefore, we investigated the technique of lowering the intensity of a disk edge vortex to reduce this noise. We attached concentric projections onto the cover of the disk to suppress the flow returning to the center of the disk through the gap between the disk and cover. Noise induced by disk rotation was reduced by 2.68 dB at the optimal setting: projections 0.002 m wide and 0.006 m width between the projections (and thus a ratio of 1: 3).

Oxygen isotopic zoning of reversely zoned melilite crystals in a fluffy type A Ca‐Al‐rich inclusions from the Vigarano meteorite

Abstract– The oxygen isotopic microdistributions within melilite measured using in situ secondary ion mass spectrometry correspond to the chemical zoning profiles in single melilite crystals of a fluffy type A Ca‐Al‐rich inclusions (CAIs) of reduced CV3 Vigarano meteorite. The melilite crystals show chemical reverse zoning within an individual single crystal from the åkermanite‐rich core to the åkermanite‐poor rim. The composition changes continuously with the crystal growth. The zoning structures suggest that the melilite grew in a hot nebular gas by condensation with decreasing pressure. The oxygen isotopic composition of melilite also changes continuously from 16O‐poor to 16O‐rich with the crystal growth. These observations suggest that the melilite condensation proceeded with change consistent with an astrophysical setting around the inner edge of a protoplanetary disk where both 16O‐rich solar coronal gas and 16O‐poor dense protoplanetary disk gas could coexist. Fluffy type A CAIs could have been formed around the inner edge of the protoplanetary disk surrounding the early sun.

The growth and hydrodynamic collapse of a protoplanet envelope

We have conducted three-dimensional self-gravitating radiation hydrodynamical models of gas accretion onto high mass cores (15-33 Earth masses) over hundreds of orbits. Of these models, one case accretes more than a third of a Jupiter mass of gas, before eventually undergoing a hydrodynamic collapse. This collapse causes the density near the core to increase by more than an order of magnitude, and the outer envelope to evolve into a circumplanetary disc. A small reduction in the mass within the Hill radius (R_H) accompanies this collapse as a shock propagates outwards. This collapse leads to a new hydrostatic equilibrium for the protoplanetary envelope, at which point 97 per cent of the mass contained within the Hill radius is within the inner 0.03 R_H which had previously contained less than 40 per cent. Following this collapse the protoplanet resumes accretion at its prior rate. The net flow of mass towards this dense protoplanet is predominantly from high latitudes, whilst at the outer edge of the circumplanetary disc there is net outflow of gas along the midplane. We also find a turnover of gas deep within the bound envelope that may be caused by the establishment of convection cells.

In-Plane and Transverse Eigenmodes of High-Speed Rotating Composite Disks

We apply Hamilton's principle and model the coupled in-plane and transverse vibrations of high-speed spinning disks, which are fiber-reinforced circumferentially. We search for eigenmodes in the linear regime using a collocation scheme, and compare the mode shapes of composite and isotropic disks. As the azimuthal wavenumber varies, the radial nodes of in-plane waves are remarkably displaced in isotropic disks while they resist such displacements in composite disks. The reverse of this phenomenon happens for transversal waves and the radial nodes move toward the outer disk edge as the azimuthal wavenumber is increased in composite disks. This result is in accordance with the predictions of Nowinski's theory, and therefore, it is independent of the magnitude of the spinning velocity and the mode frequency. Although there are notable differences between the form of governing equations derived from Hamilton's principle and Nowinski's theory, transverse eigenmodes differ a little in the two approaches. We argue that the application of orthotropic composites as the core material of the next generation of hard disk drives, together with an angular velocity controller, can enhance the data access rate.

INNER EDGES OF COMPACT DEBRIS DISKS AROUND METAL-RICH WHITE DWARFS

A number of metal-rich white dwarfs (WDs) are known to host compact, dense particle disks, which are thought to be responsible for metal pollution of these stars. In many such systems the inner radii of disks inferred from their spectra are so close to the WD that particles directly exposed to starlight must be heated above 1500 K and are expected to be unstable against sublimation. To reconcile this expectation with observations we explore particle sublimation in H-poor debris disks around WDs. We show that because of the high metal vapor pressure the characteristic sublimation temperature in these disks is 300-400 K higher than in their protoplanetary analogues, allowing particles to survive at higher temperatures. We then look at the structure of the inner edges of debris disks and show that they should generically feature superheated inner rims directly exposed to starlight with temperatures reaching 2500-3500 K. Particles migrating through the rim towards the WD (and rapidly sublimating) shield the disk behind them from strong stellar heating, making the survival of solids possible close to the WD. Our model agrees well with observations of WD+disk systems provided that disk particles are composed of Si-rich material such as olivine, and have sizes in the range ~(0.03-30) cm.

Three-Dimensional Architecture of the Rod Sensory Cilium and Its Disruption in Retinal Neurodegeneration

Defects in primary cilia lead to devastating disease because of their roles in sensation and developmental signaling but much is unknown about ciliary structure and mechanisms of their formation and maintenance. We used cryo-electron tomography to obtain 3D maps of the connecting cilium and adjacent cellular structures of a modified primary cilium, the rod outer segment, from wild-type and genetically defective mice. The results reveal the molecular architecture of the cilium and provide insights into protein functions. They suggest that the ciliary rootlet is involved in cellular transport and stabilizes the axoneme. A defect in the BBSome membrane coat caused defects in vesicle targeting near the base of the cilium. Loss of the proteins encoded by the Cngb1 gene disrupted links between the disk and plasma membranes. The structures of the outer segment membranes support a model for disk morphogenesis in which basal disks are enveloped by the plasma membrane.

Using ball indentation to determine the mechanical properties of an Al-7475 alloy processed by high-pressure torsion

A commercial Al-7475 alloy with an initial grain size of ~40 μm was processed by high-pressure torsion (HPT) for up to 2 turns at room temperature under a pressure of 6.0 GPa. The mechanical properties of the processed materials were evaluated by the ball-indentation technique to give information on the yield strength and the ultimate tensile strength. Following HPT, microhardness measurements revealed a steady increase in the hardness values from the centers of the samples towards the edges. After 2 turns, the ultimate tensile strength was ~1050 MPa at the edge of the disk and the measured grain size was ~70 nm. The results demonstrate the potential for using HPT to achieve excellent grain refinement in the Al-7475 alloy.

Linking accretion flow and particle acceleration in jets – I. New relativistic magnetohydrodynamical jet solutions including gravity

We present a new, approximate method for modelling the acceleration and collimation of relativistic jets in the presence of gravity. This method is self-similar throughout the computational domain where gravitational effects are negligible and, where significant, self-similar within a flux tube. These solutions are applicable to jets launched from a small region (e.g., near the inner edge of an accretion disk). As implied by earlier work, the flow can converge onto the rotation axis, potentially creating a collimation shock. In this first version of the method, we derive the gravitational contribution to the relativistic equations by analogy with non-relativistic flow. This approach captures the relativistic kinetic gravitational mass of the flowing plasma, but not that due to internal thermal and magnetic energies. A more sophisticated treatment, derived from the basic general relativistic magnetohydrodynamical equations, is currently being developed. Here we present an initial exploration of parameter space, describing the effects the model parameters have on flow solutions and the location of the collimation shock. These results provide the groundwork for new, semi-analytic models of relativistic jets which can constrain conditions near the black hole by fitting the jet break seen increasingly in X-ray binaries.