Large-scale Vortices in Protoplanetary Disks: On the observability of possible early stages of planet formation

We investigate the possibility of mapping large-scale anti-cyclonic vortices, resulting from a global baroclinic instability, as pre-cursors of planet formation in proto-planetary disks with the planned Atacama Large Millimeter Array (ALMA). On the basis of three-dimensional radiative transfer simulations, images of a hydrodynamically calculated disk are derived which provide the basis for the simulation of ALMA. We find that ALMA will be able to trace the theoretically predicted large-scale anti-cyclonic vortex and will therefore allow testing of existing models of this very early stage of planet formation in circumstellar disks.Comment: Accepted by ApJ (Letters section). A preprint version with high-quality figures can be downloaded from http://spider.ipac.caltech.edu/staff/swolf/homepage/public/preprints/ vortex.ps.g

Twistor theory and the K.P. equations

In this thesis, we discuss a geometric construction analogous to the Ward correspondence for the KP equations. We propose a Dirac operator based on the inverse scattering transform for the KP-II equation and discuss the similarities and differences to the Ward correspondence. We also consider the KP-I equation, describing a geometric construction for a certain class of solutions. We also discuss the general inverse scattering of the equation, how this is related to the KP-II equation and the problems with describing a single geometric construction that incorporates both equations. We also consider the Davey-Stewartson equations, which have a similar behaviour. We demonstrate explicitly the problems of localising the theory with generic boundary conditions. We also present a reformulation of the Dirac operator and demonstrate a duality between the Dirac operator and the first Lax operator for the DS-II equations. We then proceed to generalise the Dirac operator construction to generate other integrable systems. These include the mKP and Ishimori equations, and an extension to the KP and mKP hierarchies

KH15D: a star eclipsed by a large scale dusty vortex?

We propose that the large photometric variations of KH15D are due to an eclipsing swarm of solid particles trapped in giant gaseous vortex rotating at \~0.2 AU from the star. The efficiency of the capture-in-vortex mechanism easily explains the observed large optical depth. The weaker opacity at mid-eclipse is consistent with a size segregation of the particles toward the center of the vortex. This dusty structure must extend over ~1/3 of an orbit to account for the long eclipse duration. The estimated size of the trapped particles is found to range from 1 to 10cm, consistent with the gray extinction of the star. The observations of KH15D support the idea that giant vortices can grow in circumstellar disks and play a central role in planet formation.Comment: Accepted in ApJ Letters - 4 pages - 2 figure

Protoplanetary Disk Turbulence Driven by the Streaming Instability: Non-Linear Saturation and Particle Concentration

We present simulations of the non-linear evolution of streaming instabilities in protoplanetary disks. The two components of the disk, gas treated with grid hydrodynamics and solids treated as superparticles, are mutually coupled by drag forces. We find that the initially laminar equilibrium flow spontaneously develops into turbulence in our unstratified local model. Marginally coupled solids (that couple to the gas on a Keplerian time-scale) trigger an upward cascade to large particle clumps with peak overdensities above 100. The clumps evolve dynamically by losing material downstream to the radial drift flow while receiving recycled material from upstream. Smaller, more tightly coupled solids produce weaker turbulence with more transient overdensities on smaller length scales. The net inward radial drift is decreased for marginally coupled particles, whereas the tightly coupled particles migrate faster in the saturated turbulent state. The turbulent diffusion of solid particles, measured by their random walk, depends strongly on their stopping time and on the solids-to-gas ratio of the background state, but diffusion is generally modest, particularly for tightly coupled solids. Angular momentum transport is too weak and of the wrong sign to influence stellar accretion. Self-gravity and collisions will be needed to determine the relevance of particle overdensities for planetesimal formation.Comment: Accepted for publication in ApJ (17 pages). Movies of the simulations can be downloaded at http://www.mpia.de/~johansen/research_en.ph

Formation of Giant Planets by Concurrent Accretion of Solids and Gas inside an Anti-Cyclonic Vortex

We study the formation of a giant gas planet by the core--accretion gas--capture process, with numerical simulations, under the assumption that the planetary core forms in the center of an anti-cyclonic vortex. The presence of the vortex concentrates particles of centimeter to meter size from the surrounding disk, and speeds up the core formation process. Assuming that a planet of Jupiter mass is forming at 5 AU from the star, the vortex enhancement results in considerably shorter formation times than are found in standard core--accretion gas--capture simulations. Also, formation of a gas giant is possible in a disk with mass comparable to that of the minimum mass solar nebula.Comment: 27 pages, 4 figures, ApJ in pres

The Ingram Conjecture

We prove the Ingram Conjecture, i.e., we show that the inverse limit spaces of ev- ery two tent maps with di®erent slopes in the interval [1; 2] are non-homeomorphic. Based on the structure obtained from the proof, we also show that every self- homeomorphism of the inverse limit space of the tent map is pseudo-isotopic, on the core, to some power of the shift homeomorphism

Dust sedimentation and self-sustained Kelvin-Helmholtz turbulence in protoplanetary disk mid-planes. I. Radially symmetric simulations

We perform numerical simulations of the Kelvin-Helmholtz instability in the mid-plane of a protoplanetary disk. A two-dimensional corotating slice in the azimuthal--vertical plane of the disk is considered where we include the Coriolis force and the radial advection of the Keplerian rotation flow. Dust grains, treated as individual particles, move under the influence of friction with the gas, while the gas is treated as a compressible fluid. The friction force from the dust grains on the gas leads to a vertical shear in the gas rotation velocity. As the particles settle around the mid-plane due to gravity, the shear increases, and eventually the flow becomes unstable to the Kelvin-Helmholtz instability. The Kelvin-Helmholtz turbulence saturates when the vertical settling of the dust is balanced by the turbulent diffusion away from the mid-plane. The azimuthally averaged state of the self-sustained Kelvin-Helmholtz turbulence is found to have a constant Richardson number in the region around the mid-plane where the dust-to-gas ratio is significant. Nevertheless the dust density has a strong non-axisymmetric component. We identify a powerful clumping mechanism, caused by the dependence of the rotation velocity of the dust grains on the dust-to-gas ratio, as the source of the non-axisymmetry. Our simulations confirm recent findings that the critical Richardson number for Kelvin-Helmholtz instability is around unity or larger, rather than the classical value of 1/4Comment: Accepted for publication in ApJ. Some minor changes due to referee report, most notably that the clumping mechanism has been identified as the streaming instability of Youdin & Goodman (2005). Movies of the simulations are still available at http://www.mpia.de/homes/johansen/research_en.ph

Enhancement of mammogram for detection of breast cancer using adaptive median filter

Digital mammogram becomes the most effective technique for early breast cancer detection modality and processing these images requires high computational capabilities. Computer image processing techniques will be applied to enhance images. This paper attempts to study about pre-processing is the most important step in the mammogram analysis due to poor captured mammogram image quality. Pre-processing is very important to correct and adjust the mammogram image for further study and processing. Different types of filtering techniques are available for pre-processing. Filters are used to improve image quality, remove the noise, preserves the edges within an image, enhance and smoothen the image. The experimental results concludes that the adaptive median filter is best for mammogram image noise removal and gives better performance by estimating the PSNR values Keywords: Median filter, Adaptive median filter, Peak Signal to Noise Ratio, Mean Squared Error

More than I expected: a qualitative exploration of participants’ experience of an online adoptive parent-toddler group

The question of how best to support adoptive parents has been attracting increasing attention in recent years. This paper aims to explore participants’ experience of a new online intervention for adoptive parents and toddlers, which was adapted from an existing psychoanalytic Parent-Toddler Group (PTG) model. Participants were recruited from the parents attending the intervention, and four took part in a semi-structured post-intervention interview, aimed at exploring their experience of the PTG. Findings showed that, despite difficulties with the online setting of this intervention, participants overall experienced it positively, and particularly valued the supportive element of the group and the improvements in the parent-child relationship. However, challenges included engaging toddlers in the online setting, and participants’ confusion over the expectations and outcomes of the group. Based on these findings, suggestions were made for further research and adaptations of this model for future adoptive parenting interventions and support