to be done in this area. Face recognition is a problem that scarcely clamoured for attention before the computer age but, having surfaced, has involved a wide range of techniques and has attracted the attention of some fine minds (David Mumford was a Fields Medallist in 1974). This singular application of mathematical modelling to a messy applied problem of obvious utility and importance but with no unique solution is a pretty one to share with students: perhaps, returning to the source of our opening quotation, we may invert Duncan's earlier observation, 'There is an art to find the mind's construction in the face!'.

Linear and nonlinear waves, by G. B. Whitham. Pp.636. £50. 1999. ISBN 0 471 35942 4 (Wiley).

We review current understanding of star formation, outlining an overall theoretical framework and the observations that motivate it. A conception of star formation has emerged in which turbulence plays a dual role, both creating overdensities to initiate gravitational contraction or collapse, and countering the effects of gravity in these overdense regions. The key dynamical processes involved in star formation—turbulence, magnetic fields, and self-gravity— are highly nonlinear and multidimensional. Physical arguments are used to identify and explain the features and scalings involved in star formation, and results from numerical simulations are used to quantify these effects. We divide star formation into large-scale and small-scale regimes and review each in turn. Large scales range from galaxies to giant molecular clouds (GMCs) and their substructures. Important problems include how GMCs form and evolve, what determines the star formation rate (SFR), and what determines the initial mass function (IMF). Small scales range from dense cores to the protostellar systems they beget. We discuss formation of both low- and high-mass stars, including ongoing accretion. The development of winds and outflows is increasingly well understood, as are the mechanisms governing angular momentum transport in disks. Although outstanding questions remain, the framework is now in place to build a comprehensive theory of star formation that will be tested by the next generation of telescopes.

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Theory of Star Formation

Monthly Notices is one of the three largest general primary astronomical research publications. It is an international journal, published by the Royal Astronomical Society. This article 1 describes its publication policy and practice.

Monthly Notices of the Royal Astronomical Society

In the real world, a realistic setting for computer vision or multimedia recognition problems is that we have some classes containing lots of training data and many classes contain a small amount of training data. Therefore, how to use frequent classes to help learning rare classes for which it is harder to collect the training data is an open question. Learning with Shared Information is an emerging topic in machine learning, computer vision and multimedia analysis. There are different level of components that can be shared during concept modeling and machine learning stages, such as sharing generic object parts, sharing attributes, sharing transformations, sharing regularization parameters and sharing training examples, etc. Regarding the specific methods, multi-task learning, transfer learning and deep learning can be seen as using different strategies to share information. These learning with shared information methods are very effective in solving real-world large-scale problems. This special issue aims at gathering the recent advances in learning with shared information methods and their applications in computer vision and multimedia analysis. Both state-of-the-art works, as well as literature reviews, are welcome for submission. Papers addressing interesting real-world computer vision and multimedia applications are especially encouraged. Topics of interest include, but are not limited to:  • Multi-task learning or transfer learning for large-scale computer vision and multimedia analysis • Deep learning for large-scale computer vision and multimedia analysis • Multi-modal approach for large-scale computer vision and multimedia analysis • Different sharing strategies, e.g., sharing generic object parts, sharing attributes, sharing transformations, sharing regularization parameters and sharing training examples, • Real-world computer vision and multimedia applications based on learning with shared information, e.g., event detection, object recognition, object detection, action recognition, human head pose estimation, object tracking, location-based services, semantic indexing. • New datasets and metrics to evaluate the benefit of the proposed sharing ability for the specific computer vision or multimedia problem. • Survey papers regarding the topic of learning with shared information.  Authors who are unsure whether their planned submission is in scope may contact the guest editors prior to the submission deadline with an abstract, in order to receive feedback.

IEEE transactions on pattern analysis and machine intelligence

The projections of the ventral tegmental area and adjacent regions: A combined fluorescent retrograde tracer and immunofluorescence study in the rat

A general theory is presented for the origin and collimation of centrifugally driven, hydromagnetic winds from the surfaces of Keplerian accretion disks that surround central objects such as young stellar objects (YSOs) or black holes. The theory is fully two-dimensional and makes no assumption about self-similarity of the flows. These winds efficiently extract disk angular momentum and convert the gravitational binding energy released in the accretion process into the mechanical energy of the wind. Solutions under the very general assuption the the magnetic flux in the disk scales as a power law in disk radius are investigated

Hydromagnetic Disk Winds in Young Stellar Objects and Active Galactic Nuclei

We compare the angular momentum extracted by a wind from a pre-main-sequence star to the torques arising from the interaction between the star and its Keplerian accretion disk. We find that the wind alone can counteract the spin-up torque from mass accretion, solving the mystery of why accreting pre-main-sequence stars are observed to spin at less than 10% of breakup speed, provided that the mass outflow rate in the stellar winds is ~10% of the accretion rate. We suggest that such massive winds will be driven by some fraction of the accretion power. For observationally constrained typical parameters of classical T Tauri stars, needs to be between a few and a few tens of percent. In this scenario, efficient braking of the star will terminate simultaneously with accretion, as is usually assumed to explain the rotation velocities of stars in young clusters.

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Accretion-powered Stellar Winds as a Solution to the Stellar Angular Momentum Problem

We suggest that bipolar outflows in dense molecular clouds associated with young stellar objects are steady, centrifugally driven, hydromagnetic winds that arise from molecular disks (on scales < or =10/sup 16/ cm) in which the infrared source(s) embedded. A disk of mass approx.100 M/sub sun/ and rotational speed of approx.10/sup 6/ cm s/sup -1/ provides a resevoir of 10/sup 47/ ergs, which could power the most energetic outflows observed. Acceleration to supersonic speeds is accomplished by the magnetic field embedded in the disk (paralllel rotational and magnetic axes) and extending outward beyond the wind region to join the galactic field. The wind carries angular momentum and energy from the disk out to large distances. Our analysis treats the problem of magnetic braking and energy transport in a partially ionized (two-fluid) wind. The basic parameter which is shown to govern the flow is the coupling parameter ..beta.. = T/sub n/-i/T/sub n/, the ratio of the characteristic neutral-ion collision time to flow time. A general analysis of angular momentum and energy transport is given, and the wind equation is solved along flux tubes in the strongly coupled (..beta..<<1) limit. The centrifugally driven wind forms when an embedded protostar begins to ionize themore » disk core region. A disk envelope forms at the wind base at a pressure which adjusts to the wind requirements. Envelope heating may be maintained by magnetic flux loss from the dense core (which has a field approx.10/sup -3/ gauss) that is preferentially along the rotation axis for flattened disks. The structure of the field at the disk core surface is derived. The observational implications are discussed; in particular, we emphasize that such molecular disks with double profiles should be observed.« less

/pdf/centrifugally-driven-winds-from-contracting-molecular-disks-54op5m36us.pdf

Centrifugally driven winds from contracting molecular disks

We study the equilibrium of pressure truncated, filamentary molecular clouds that are threaded by rather general helical magnetic fields. We first apply the virial theorem to filamentary molecular clouds, including the effects of non-thermal motions and the turbulent pressure of the surrounding ISM. When compared with the data, we find that many filamentary clouds have a mass per unit length that is significantly reduced by the effects of external pressure, and that toroidal fields play a significant role in squeezing such clouds.

We also develop exact numerical MHD models of filamentary molecular clouds with more general helical field configurations than have previously been considered. We examine the effects of the equation of state by comparing ‘isothermal’ filaments, with constant total (thermal plus turbulent) velocity dispersion, with equilibria constructed using a logatropic equation of state.

Our theoretical models involve three parameters: two to describe the mass loading of the toroidal and poloidal fields, and a third that describes the radial concentration of the filament. We thoroughly explore our parameter space to determine which choices of parameters result in models that agree with the available observational constraints. We find that both equations of state result in equilibria that agree with the observational results. Moreover, we find that models with helical fields have more realistic density profiles than either unmagnetized models or those with purely poloidal fields; we find that most isothermal models have density distributions that fall off as r−1.8 to r−2, while logatropes have density profiles that range from r−1 to r−1.8. We find that purely poloidal fields produce filaments with steep radial density gradients that are not allowed by the observations.

/pdf/helical-fields-and-filamentary-molecular-clouds-i-2ueqk6zryb.pdf

Helical fields and filamentary molecular clouds — I

We present 2.5-dimensional time-dependent simulations of the evolution of nonrelativistic outflows from Keplerian accretion disks orbiting low-mass protostars or black holes accreting at sub-Eddington rates. The gas is injected at a very small speed (vinj = 10-3vK) from the surface of the disk (a fixed boundary in our simulations) into a cold corona. The corona is in stable equilibrium and is supported by Alfvenic turbulent pressure. The initial magnetic field configuration in the corona is poloidal and is given by a potential field (J${b J}$ --> = 0). This configuration is extended smoothly into the disk where the toroidal magnetic field is taken to scale inversely with the disk radius. We present the analytical and the numerical approaches to our problem, as well as many results for a steady state simulation. We find that the gas is centrifugally accelerated through the Alfven and the fast magnetosonic (FM) surfaces and collimated into cylinders parallel to the disk's axis. The collimation of the outflow is due to the pinch force exerted by the dominant toroidal magnetic field generated by the outflow itself. Beyond the FM surface, we found that a Hubble flow is present; vz z. The velocities achieved in our simulations are of the order of 180 km s-1 for our standard young stellar object (a 0.5 M☉ protostar) and of the order or 105 km s-1 for our standard active galactic nuclei (a 108 M☉ black hole). Our jet solutions, dominated mainly by the poloidal kinetic energy ρv -->2p, are very efficient in magnetically extracting angular momentum and energy from the disk. We find the ratio of the disk accretion rate to the wind mass flux rate to be of the order of ${u{m}{"705F}}$ --> -->a/${u{m}{"705F}}$ --> -->w 6.0. We find that our stationary outflows have many similarities to steady state models of MHD disk winds.

http://iopscience.iop.org/article/10.1086/304170/pdf

Ralph E. Pudritz

Papers

Hydromagnetic Disk Winds in Young Stellar Objects and Active Galactic Nuclei

Accretion-powered Stellar Winds as a Solution to the Stellar Angular Momentum Problem

Centrifugally driven winds from contracting molecular disks

Helical fields and filamentary molecular clouds — I

Numerical Simulations of Astrophysical Jets from Keplerian Disks. I. Stationary Models