Disk Orientation Research Articles

Experimental investigation of magnetic anisotropy in spin vortex discs

We present experimental 2D vector vibrating sample magnetometer measurements to demonstrate the shape anisotropy effects occurring in micrometer-diameter supermalloy spin vortex discs. Measurements made for different disc sizes and orientations confirm the out-of-plane susceptibility is several orders of magnitude smaller than the in-plane susceptibility. These results validate with a high certitude that spin vortices with high diameter to thickness ratio retain in-plane-only magnetization, even when subjected to fields in the out-of-plane direction. These results contribute to further computational simulations of the dynamics of spin vortex structures in colloidal suspensions where external fields may be applied in any arbitrary direction.

VLA AND CARMA OBSERVATIONS OF PROTOSTARS IN THE CEPHEUS CLOUDS: SUB-ARCSECOND PROTO-BINARIES FORMED VIA DISK FRAGMENTATION

We present observations of three Class 0/I protostars (L1157-mm, CB230 IRS1, and L1165-SMM1) using the Karl G. Jansky Very Large Array (VLA) and observations of two (L1165-SMM1 and CB230 IRS1) with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The VLA observations were taken at wavelengths of $\lambda = 7.3$ mm, 1.4 cm, 3.3 cm, 4.0 cm, and 6.5 cm with a best resolution of $\sim$0\farcs06 (18 AU) at 7.3 mm. The L1165-SMM1 CARMA observations were taken at $\lambda = 1.3$ mm with a best resolution of $\sim0\farcs3$ (100 AU), and the CB230 IRS1 observations were taken at $\lambda = 3.4$ mm with a best resolution of $\sim$3\arcsec\ (900 AU). We find that L1165-SMM1 and CB230 IRS1 have probable binary companions at separations of $\sim$0\farcs3 (100 AU) from detections of secondary peaks at multiple wavelengths. The position angles of these companions are nearly orthogonal to the direction of the observed bipolar outflows, consistent with the expected protostellar disk orientations. We suggest that these companions may have formed from disk fragmentation; turbulent fragmentation would not preferentially arrange the binary companions to be orthogonal to the outflow direction. For L1165-SMM1, both the 7.3 mm and 1.3 mm emission show evidence of a large (R $>$ 100 AU) disk. For the L1165-SMM1 primary protostar and the CB230 IRS1 secondary protostar, the 7.3 mm emission is resolved into structures consistent with $\sim20$ AU radius disks. For the other protostars, including L1157-mm, the emission is unresolved, suggesting disks with radii $< 20$ AU.

Magnetic-field-induced enhancement of crystallinity and field-effect mobilities in phthalocyanine thin films

Organic semiconductor thin films were fabricated by thermal deposition of free-base and metal phthalocyanines under a static magnetic field. A vertical magnetic field enhanced the crystallinity of the edge-on orientation of the phthalocyanine discs, whereas a horizontal magnetic field had a minimal effect on the crystallinity. The major factor for the orientation change is attributed to the diamagnetic anisotropies of π-electrons in the phthalocyanine macrocycles. Field-effect transistors of phthalocyanine films fabricated under a vertical magnetic field exhibited better hole mobilities and on-current values with smaller threshold voltages than those of phthalocyanine films fabricated without a magnetic field.

ISOTROPIC HEATING OF GALAXY CLUSTER CORES VIA RAPIDLY REORIENTING ACTIVE GALACTIC NUCLEUS JETS

AGN jets carry more than sufficient energy to stave off catastrophic cooling of the intracluster medium (ICM) in the cores of cool-core clusters. However, in order to prevent catastrophic cooling, the ICM must be heated in a near-isotropic fashion and narrow bipolar jets with $P_{\rm jet}=10^{44-45}$ ergs/s, typical of radio AGNs at cluster centres, are inefficient at heating the gas in the transverse direction to the jets. We argue that due to existent conditions in cluster cores, the SMBHs will, in addition to accreting gas via radiatively inefficient flows, experience short stochastic episodes of enhanced accretion via thin discs. In general, the orientation of these accretion discs will be misaligned with the spin axis of the black holes and the ensuing torques will cause the black hole's spin axis (and therefore, the jet axis) to slew and rapidly change direction. This model not only explains recent observations showing successive generations of jet-lobes-bubbles in individual cool-core clusters that are offset from each other in the angular direction with respect to the cluster center, but also shows that AGN jets {\it can} heat the cluster core nearly isotropically on the gas cooling timescale. Our model {\it does} require that the SMBHs at the centers of cool-core clusters be spinning relatively slowly. Torques from individual misaligned discs are ineffective at tilting rapidly spinning black holes by more than a few degrees. Additionally, since SMBHs that host thin accretion discs will manifest as quasars, we predict that roughly 1--2 rich clusters within $z<0.5$ should have quasars at their centers.

Aggressive Diamond Characterization and Wear Analysis During Chemical Mechanical Planarization

In this study, a 3M A3700 diamond disc was used to condition a Cabot Microelectronics Corporation D100 pad for 30 hours, and wear on its aggressive diamonds was analyzed. The top 20 aggressive diamonds for two perpendicular disc orientations were identified before wafer polishing, as well as after 15-hour and 30-hour polishing. Results showed that the original top 20 aggressive diamonds identified before polishing were subjected to wear after the first 15-hour polishing as the furrow surface area that they generated decreased dramatically by 47%. As these original aggressive diamonds were worn, seven new aggressive diamonds were “born” and joined the new top 20 list for both disc orientations. After the second 15-hour wafer polishing, the furrow surface area of these new top 20 aggressive diamonds did not change significantly. The furrow surface area created by all the active diamonds exhibited the same trend as the top 20 aggressive diamonds, confirming that most pad conditioning work was performed by these aggressive diamonds and that the disc lost its aggressiveness in the first 15 hours of polishing and then maintained its aggressiveness during the second 15 hours.

Interaction between massive planets on inclined orbits and circumstellar discs

We study the interaction between massive planets and a gas disc with a mass in the range expected for protoplanetary discs. We use SPH simulations to study the orbital evolution of a massive planet as well as the dynamical response of the disc for planet masses between 1 and $6\ \rmn{M_J}$ and the full range of initial relative orbital inclinations. Gap formation can occur for planets in inclined orbits. For given planet mass, a threshold relative orbital inclination exists under which a gap forms. At high relative inclinations, the inclination decay rate increases for increasing planet mass and decreasing initial relative inclination. For an initial semi-major axis of 5 AU and relative inclination of $i_0=80^\circ,$ the times required for the inclination to decay by $10^\circ$ is $\sim10^{6}\ \rmn{yr}$ and $\sim10^{5}\ \rmn{yr}$ for $1\ \rmn{M_J}$ and $6\ \rmn{M_J}$. Planets on inclined orbits warp the disc by an extent that is negligible for $1\ \rmn{M_J}$ but increases with increasing mass becoming quite significant for a planet of mass $6\ \rmn{M_J}$. We also find a solid body precession of both the total disc angular momentum vector and the planet orbital momentum vector about the total angular momentum vector. Our results illustrate that the influence of an inclined massive planet on a protoplanetary disc can lead to significant changes of the disc structure and orientation which can in turn affect the orbital evolution of the planet significantly.

Aggressive Diamond Characterization and Wear Analysis during Chemical Mechanical Planarization

A 3M A3700 diamond disk was used to condition a Cabot Microelectronics Corporation D100 pad for 30 hours, and wear on its aggressive diamonds was analyzed. The top 20 aggressive diamonds for two perpendicular disk orientations were identified before wafer polishing, as well as after 15-hour and 30-hour polishing. Results showed that the original top 20 aggressive diamonds identified before polishing were subjected to wear after the first 15-hour polishing as the furrow surface area that they generated decreased dramatically by 47%. As these original aggressive diamonds were worn, seven new aggressive diamonds were “born” and joined the new top 20 list for both disk orientations. After the second 15-hour wafer polishing, the furrow surface area of these new top 20 aggressive diamonds did not change significantly. The furrow surface area created by all the active diamonds exhibited the same trend as the top 20 aggressive diamonds, confirming that most pad conditioning work was performed by these aggressive diamonds and that the disk lost its aggressiveness in the first 15 hours of polishing and then maintained its aggressiveness during the second 15 hours.

Formation and early evolution of circumstellar discs in turbulent molecular cloud cores

We investigate the formation and evolution of circumstellar disks in turbulent cloud cores until several 104 years after protostar formation using smoothed particle hydrodynamics (SPH) calculations. The formation and evolution process of circumstellar disk in turbulent cloud cores differs substantially from that in rigidly rotating cloud cores. In turbulent cloud cores, a filamentary structure appears before the protostar formation and the protostar forms in the filament. If the turbulence is initially sufficiently strong, the remaining filament twists around the protostar and directly becomes a rotation-supported disk. Upon formation, the disk orientation is generally misaligned with the angular momentum of its host cloud core and it dynamically varies during the main accretion phase, even though the turbulence is weak. This is because the angular momentum of the entire cloud core is mainly determined by the large scale velocity field whose wavelength is comparable to the cloud scale, whereas the angular momentum of the disk is determined by the local velocity field where the protostar forms and these two velocity fields do not correlate with each other. In the case of disk evolution in a binary or multiple stars, the disks are misaligned with each other at least during the main accretion phase, because there is no correlation between the velocity fields around the position where each protostar forms. In addition, each disk is also misaligned with the binary orbital plane. Such misalignment can explain the recent observations of misaligned disks and misaligned protostellar outflows.

Idealized models for galactic disc formation and evolution in ‘realistic’ ΛCDM haloes

We study the dynamics of galactic disc formation and evolution in ‘realistic’ Λ cold dark matter haloes with idealized baryonic initial conditions. We add rotating spheres of hot gas at z = 1.3 to two fully cosmological dark-matter-only halo (re)simulations. The gas cools according to an artificial and adjustable cooling function to form a rotationally supported galaxy. The simulations evolve in the full cosmological context until z = 0. We vary the angular momentum and density profiles of the initial gas sphere, the cooling time and the orientation of the angular momentum vector to study the effects on the formation and evolution of the disc. The final discs show exponential radial and (double)-exponential vertical stellar density profiles, and stellar velocity dispersions that increase with age of the stars, as in real disc galaxies. The slower the cooling/accretion processes, the higher the kinematic disc-to-bulge (D/B) ratio of the resulting system. We find that the initial orientation of the baryonic angular momentum with respect to the halo has a major effect on the resulting D/B. The most stable systems result from orientations parallel to the halo minor axis. Despite the spherical and coherently rotating initial gas distribution, the orientation of the central disc and of the outer gas components, and the relative angle between the components can all change by more than 90° over several billion years. Initial orientations perpendicular to the major axis tend to align with the minor axis during their evolution, but the sign of the spin can have a strong effect. Discs can form from initial conditions oriented parallel to the major axis, but there is often strong misalignment between inner and outer material. The more the orientation of the baryonic angular momentum changes during the evolution, the lower the final D/B. The behaviour varies strongly from halo to halo. Even our very simple initial conditions can lead to strong bars, dominant bulges, massive, misaligned rings and counter-rotating components. We discuss how our results may relate to the failure or success of fully cosmological disc formation simulations.

Coplanar circumbinary debris discs

We present resolved Herschel images of circumbinary debris disks in the alpha CrB (HD139006) and beta Tri (HD13161) systems. We find that both disks are consistent with being aligned with the binary orbital planes. Though secular perturbations from the binary can align the disk, in both cases the alignment time at the distances at which the disk is resolved is greater than the stellar age, so we conclude that the coplanarity was primordial. Neither disk can be modelled as a narrow ring, requiring extended radial distributions. To satisfy both the Herschel and mid-IR images of the alpha CrB disk, we construct a model that extends from 1-300AU, whose radial profile is broadly consistent with a picture where planetesimal collisions are excited by secular perturbations from the binary. However, this model is also consistent with stirring by other mechanisms, such as the formation of Pluto-sized objects. The beta Tri disk model extends from 50-400AU. A model with depleted (rather than empty) inner regions also reproduces the observations and is consistent with binary and other stirring mechanisms. As part of the modelling process, we find that the Herschel PACS beam varies by as much as 10% at 70um and a few % at 100um. The 70um variation can therefore hinder image interpretation, particularly for poorly resolved objects. The number of systems in which circumbinary debris disk orientations have been compared with the binary plane is now four. More systems are needed, but a picture in which disks around very close binaries (alpha CrB, beta Tri, and HD 98800, with periods of a few weeks to a year) are aligned, and disks around wider binaries (99 Her, with a 50 yr period) are misaligned, may be emerging. This picture is qualitatively consistent with the expectation that the protoplanetary disks from which the debris emerged are more likely to be aligned if their binaries have shorter periods.

Elastic and hydrodynamic torques on a colloidal disk within a nematic liquid crystal

The orientationally dependent elastic energy and hydrodynamic behavior of colloidal disks with homeotropic surface anchoring suspended in the nematic liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) have been investigated. In the absence of external torques, the disks align with the normal of the disk face â parallel to the nematic director n[over ^]. When a magnetic field is applied, the disks rotate â by an angle θ so that the magnetic torque and the elastic torque caused by distortion of the nematic director field are balanced. Over a broad range of angles, the elastic torque increases linearly with θ in quantitative agreement with a theoretical prediction based on an electrostatic analogy. When the disks are rotated to angles θ>π/2, the resulting large elastic distortion makes the disk orientation unstable, and the director undergoes a topological transition in which θ→π-θ. In the transition, a defect loop is shed from the disk surface, and the disks spin so that â sweeps through π radians as the loop collapses back onto the disk. Additional measurements of the angular relaxation of disks to θ=0 following removal of the external torque show a quasi-exponential time dependence from which an effective drag viscosity for the nematic can be extracted. The scaling of the angular time dependence with disk radius and observations of disks rotating about â indicate that the disk motion affects the director field at surprisingly modest Ericksen numbers.

RELATIVE ORIENTATION OF PAIRS OF SPIRAL GALAXIES IN THE SLOAN DIGITAL SKY SURVEY

We find, from our study of binary spiral galaxies in the Sloan Digital Sky Survey Data Release 6, that the relative orientation of disks in binary spiral galaxies is consistent with their being drawn from a random distribution of orientations. For 747 isolated pairs of luminous disk galaxies, the distribution of phi, the angle between the major axes of the galaxy images, is consistent with a uniform distribution on the interval [0 degrees, 90 degrees]. With the assumption that the disk galaxies are oblate spheroids, we can compute cos(beta), where beta is the angle between the rotation axes of the disks. In the case that one galaxy in the binary is face-on or edge-on, the tilt ambiguity is resolved, and cos(beta) can be computed unambiguously. For 94 isolated pairs with at least one face-on member, and for 171 isolated pairs with at least one edge-on member, the distribution of cos(beta) is statistically consistent with the distribution of cos(i) for isolated disk galaxies. This result is consistent with random orientations of the disks within pairs.

The position ofβPictoris b position relative to the debris disk

Context. We detected in 2009 a giant, close-by planet orbiting {\beta} Pic, a young star surrounded with a disk, extensively studied for more than 20 years. We showed that if located on an inclined orbit, the planet could explain several peculiarities of {\beta} Pictoris system. However, the available data did not permit to measure the inclination of {\beta} Pic b with respect to the disk, and in particular to establish in which component of the disk - the main, extended disk or the inner inclined component/disk-, the planet was located. Comparison between the observed planet position and the disk orientation measured on previous imaging data was not an option because of potential biases in the measurements. Aims. Our aim is to measure precisely the planet location with respect to the dust disk using a single high resolution image, and correcting for systematics or errors that degrades the precision of the disk and planet relative position measurements. Methods. We gathered new NaCo data at Ks band, with a set-up optimized to derive simultaneously the orientation(s) of the disk(s) and that of the planet. Results. We show that the projected position of {\beta} Pic b is above the midplane of the main disk. With the current data and knowledge on the system, this implies that {\beta} Pic b cannot be located in the main disk. The data rather suggest the planet being located in the inclined component.

Magnetic field amplification and X-ray emission in galaxy minor mergers

We investigate the magnetic field evolution in a series of galaxy minor mergers using the N-body/smoothed particle hydrodynamics (SPH) code gadget. The simulations include the effects of radiative cooling, star formation and supernova feedback. Magnetohydrodynamics is implemented using the SPH method. We present 32 simulations of binary mergers of disc galaxies with mass ratios of 2:1 up to 100:1, whereby we have additionally varied the initial magnetic field strengths, disc orientations and resolutions. We investigate the amplification of a given initial magnetic field within the galaxies and an ambient intergalactic medium (IGM) during the interaction. We find that the magnetic field strengths of merger remnants with mass ratios up to 10:1 saturate at a common value of several μG. For higher mass ratios, the field strength saturates at lower values. The saturation values correspond to the equipartition value of magnetic and turbulent energy density. The initial magnetization, disc orientation and numerical resolution show only minor effects on the saturation value of the magnetic field. We demonstrate that a higher impact energy of the progenitor galaxies leads to a more efficient magnetic field amplification. The magnetic and turbulent energy densities are higher for larger companion galaxies, consistent with the higher impact energy supplied to the system. We present a detailed study of the evolution of the temperature and the bolometric X-ray luminosity within the merging systems. Thereby we find that magnetic fields cause a more efficient increase of the IGM temperature and the corresponding IGM X-ray luminosity after the first encounter. However, the presence of magnetic fields does not enhance the total X-ray luminosity. Generally, the final value of the X-ray luminosity is even clearly lower for higher initial magnetic fields.

Rheology and processing of suspensions with fiber, disk and magnetic particles

This paper introduces recent development and progress in rheology and processing of suspension materials. In particular, three topics with different suspensions will be discussed, which are relevant in polymer- and powder-based manufacturing industries for various applications. The paper begins with a fundamental study of rheological modeling for short fiber suspension in a viscoelastic liquid. Irreversible thermodynamics based approach is presented to describe the polymer viscoelastic deformation with the fiber anisotropy effect taken into account. Several distinguishing features of the model are presented. Then we turn our attention to more industry-oriented subject of pigment disk orientation in injection molding of aesthetic plastic parts. The major difference between fiber and disk orientation kinematics is briefly discussed using Jeffery model. Experimental and numerical results for the disk orientation and the surface color of the molded part are presented. Finally, we introduce our recent efforts regarding the rheology of magnetic particle suspension, which is an essential part for a development of precision magnetic powder injection molding process. Some rheometer data for stainless steel powder suspensions are presented.

Jet-disk connection in OJ287

AbstractA model for OJ 287 consisting of two orbiting black holes has been constructed using optical light curve data. The model has successfully predicted the occurrence of sharp optical outbursts of OJ 287 for the past 15 years. Here we test if also the variations in the radio jet position angle can be explained within the framework of this same model, which has most of its parameters fixed by the timing of the optical flares. The model applied here has only three free parameters left, the (trivial) zero point of the jet position angle, the time lag between changes in the disk and jet orientations, and the zero point of the viewing angle. Despite its simplicity and the small number of free parameters, the model appears to be able to reproduce the main properties of the observed position angle variations during the past 30 years. The best fits are obtained when the time lag is either ~4 or ~14 years. However, the jet orientation seems to be unrelated to the direction of the spin of the primary black hole. This implies, assuming that the basic model is correct, that the mean orientation of the jet is determined by the orientation of the inner accretion disk, not by the spin axis of the black hole.

Multiband photometric decomposition of nuclear stellar disks

Small and bright stellar disks with scale lengths of few tens of parsec are known to reside in the center of galaxies. They are believed to have formed in a dissipational process as the end result of star formation in gas either accreted in a merging (or acquisition) event or piled up by the secular evolution of a nuclear bar. Only few of them have been studied in detail to date. Using archival Hubble Space Telescope (HST) imaging, we investigated the photometric parameters of the nuclear stellar disks hosted by three early-type galaxies in the Virgo cluster, NGC 4458, NGC4478, and NGC4570. We aimed at constraining the process of formation of their stars. The central surface brightness, scale length, inclination, and position angle of the nuclear disks were derived by adopting the photometric decomposition method introduced by Scorza & Bender and assuming the disks to be infinitesimally thin and exponential. The location, orientation, and size of the nuclear disks is the same in all the images obtained with the Wide Field Planetary Camera 2 and Advanced Camera for Survey and available in the HST Science Archive. The scale length, inclination, and position angle of each disk are constant within the errors in the observed U, B, V, and I passbands, independently of their values and of the properties of the host spheroid. We interpret the absence of color gradients in the stellar population of the nuclear disks as the signature that star formation homogeneously occurred all through their extension. A inside-out formation scenario is, instead, expected to produce color gradients and therefore is ruled out.

Anisotropic properties of plasmonic nanoparticles: depolarized light scattering, dichroism, and birefringence

The properties of gold and silver nanorods and nanodisks with geometric parameters typical of wet chemical fabrication protocols were investigated. With an extended-precision T-matrix code, a representative set of simulations for extinction, light scattering, and depolarization ratio spectra of randomly oriented particles and for dichroism and birefringence spectra of particles with an arbitrary predominant orientation with respect to incident linearly polarized light were obtained. The appearance of ultra-depolarized light scattering from random ensembles was elucidated by several 3D maps illustrating the dependence of the depolarization ratio on particular orientations of rods and disks. A simple dipole model sufficed to explain the orientation dependence of dichroism and birefringence and the unusual invariant spectral localization of the depolarization ratio maxima. Reasonable agreement was obtained with experimental data on depolarized light scattering from gold nanorods.

Endocytosis and Intracellular Distribution of PLGA Particles in Endothelial Cells: Effect of Particle Geometry

Targeting, internalization, and intracellular trafficking of carriers are key processes in drug delivery to endothelial cells. We synthesized PLGA particles with spherical and elliptical disk geometries and investigated the effect of particle shape on rate of particle endocytosis and their intracellular distribution in endothelial cells. Elliptical disks (aspect ratio of 5) were endocytosed at a slower rate compared to spheres (1.8 µm diameter) of the same volume. However, both particles were eventually internalized and accumulated around the nucleus. We quantified the orientation of elliptical disks and found that disks, on average, oriented tangentially with the nuclear membrane. The non-spherical geometry of elliptical disks brings unique aspects to the kinetics and equilibrium distribution of these particles in cells.

The Warped Disk of Centaurus A from a Radius of 2 to 6500 pc

AbstractWe compile position and inclination angles for tilted ring fits to the warped dusty and gaseous disk of Cen A, spanning a radius of 1.8 to 6500 pc, from recent observations. For radii exterior to 1 kpc, tilted-ring orientations lie on an arc, on a plot of polar-inclination versus position-angle, suggesting that precession following a merger can account for the ring morphology. Three kinks in the ring orientations are seen on the polar plot, the one at radius of about 1.3 kpc we suspect corresponds to the location where self-gravity in the disk affects the ring precession rate. Another at a radius of about 600 pc may be associated with a gap in the gas distribution. A third kink is seen at a radius of 100 pc. A constant inclination tilted disk precessing about the jet axis may describe the disk between 100 and 20 pc but not interior to this. A model with disk orientation matching the molecular circumnuclear disk at 100 pc that decays at smaller radii to an inner flat disk perpendicular to the jet may account for disk orientations within 100 pc. Neither model would account for the cusps or changes in disk orientation at 100 or 600 pc.