On Molecular Hydrogen Formation and the Magnetohydrostatic Equilibrium of Sunspots

We have investigated the problem of sunspot magnetohydrostatic equilibrium with comprehensive IR sunspot magnetic field survey observations of the highly sensitive Fe I lines at 15650 \AA\ and nearby OH lines. We have found that some sunspots show isothermal increases in umbral magnetic field strength which cannot be explained by the simplified sunspot model with a single-component ideal gas atmosphere assumed in previous investigations. Large sunspots universally display non-linear increases in magnetic pressure over temperature, while small sunspots and pores display linear behavior. The formation of molecules provides a mechanism for isothermal concentration of the umbral magnetic field, and we propose that this may explain the observed rapid increase in umbral magnetic field strength relative to temperature. Existing multi-component sunspot atmospheric models predict that a significant amount of molecular hydrogen (H2) exists in the sunspot umbra. The formation of H2 can significantly alter the thermodynamic properties of the sunspot atmosphere and may play a significant role in sunspot evolution. In addition to the survey observations, we have performed detailed chemical equilibrium calculations with full consideration of radiative transfer effects to establish OH as a proxy for H2, and demonstrate that a significant population of H2 exists in the coolest regions of large sunspots.Comment: 17 pages, 19 figures, accepted for publication in Ap

Removal of Spectro-Polarimetric Fringes by 2D Pattern Recognition

We present a pattern-recognition based approach to the problem of removal of polarized fringes from spectro-polarimetric data. We demonstrate that 2D Principal Component Analysis can be trained on a given spectro-polarimetric map in order to identify and isolate fringe structures from the spectra. This allows us in principle to reconstruct the data without the fringe component, providing an effective and clean solution to the problem. The results presented in this paper point in the direction of revising the way that science and calibration data should be planned for a typical spectro-polarimetric observing run.Comment: ApJ, in pres

Trilayer Tissue Engineered Heart Valves for Aortic Valve Replacement

Heart valve disease often progresses asymptomatically until valve damage has advanced to the point where replacement is unavoidable. Unfortunately, current valve replacements - including mechanical, bioprosthetic and autografts - have serious drawbacks, which often require replacement surgeries or lifelong anticoagulant therapy. The field of tissue engineering aims to overcome these drawbacks by combining scaffolds, stem cells, and chemical and physical stimuli to produce living tissues. The aortic heart valve has a unique structure composed of three discrete layers – fibrosa, spongiosa, and ventricularis - that work together in concert with the resident valvular interstitial cells to maintain a functioning valve. As a result, current tissue-engineered heart valves miss the mark for successful aortic valve replacement in one of two ways: either by being too weak to endure the stresses of the aortic environment or by being insufficiently recellularized and incapable of self-repair. The primary focus of this research was to create a functional heart valve replicating the unique trilayer structure developed by nature. We showed that valves can be modeled from medical imaging data, 3D printed, and used as molds to create patient-specific heart valves. The valve scaffolds supported cell attachment, growth, and proliferation. Porous, dry scaffolds were effectively glued together to form one cohesive trilayer scaffold. These scaffolds resemble the human valve’s unique histoarchitecture. A meta-analysis of literature defined maximum normal stresses and strains experienced by the native valve; providing a target set of mechanical properties to be replicated by the tissue-engineered valve. Increasing porosity and microneedle rolling treatments produced scaffolds with excellent mechanical strength that were more than strong enough to function in physiological conditions. A novel cell seeding technique was developed to rapidly seed porous and microneedle treated fibrous scaffolds; resulting in full-thickness cell seeding. Functional heart valves were made using a crush-mounting system. This system allowed for rapid and reproducible production of valves for in vitro testing. A comparison between mechanical, bioprosthetic, and trilayer valves revealed outstanding hemodynamic performance of trilayer valves. These valves functioned well for three weeks in a heart valve bioreactor. This research produced functional, tissue-engineered heart valves with excellent mechanical and hemodynamic properties

Molecular absorption in transition region spectral lines

Aims: We present observations from the Interface Region Imaging Spectrograph (IRIS) of absorption features from a multitude of cool atomic and molecular lines within the profiles of Si IV transition region lines. Many of these spectral lines have not previously been detected in solar spectra. Methods: We examined spectra taken from deep exposures of plage on 12 October 2013. We observed unique absorption spectra over a magnetic element which is bright in transition region line emission and the ultraviolet continuum. We compared the absorption spectra with emission spectra that is likely related to fluorescence. Results: The absorption features require a population of sub-5000 K plasma to exist above the transition region. This peculiar stratification is an extreme deviation from the canonical structure of the chromosphere-corona boundary . The cool material is not associated with a filament or discernible coronal rain. This suggests that molecules may form in the upper solar atmosphere on small spatial scales and introduces a new complexity into our understanding of solar thermal structure. It lends credence to previous numerical studies that found evidence for elevated pockets of cool gas in the chromosphere.Comment: accepted by A&A Letter

Learning Generative Models for Multi-Activity Body Pose Estimation

We present a method to simultaneously estimate 3D body pose and action categories from monocular video sequences. Our approach learns a generative model of the relationship of body pose and image appearance using a sparse kernel regressor. Body poses are modelled on a low-dimensional manifold obtained by Locally Linear Embedding dimensionality reduction. In addition, we learn a prior model of likely body poses and a dynamical model in this pose manifold. Sparse kernel regressors capture the nonlinearities of this mapping efficiently. Within a Recursive Bayesian Sampling framework, the potentially multimodal posterior probability distributions can then be inferred. An activity-switching mechanism based on learned transfer functions allows for inference of the performed activity class, along with the estimation of body pose and 2D image location of the subject. Using a rough foreground segmentation, we compare Binary PCA and distance transforms to encode the appearance. As a postprocessing step, the globally optimal trajectory through the entire sequence is estimated, yielding a single pose estimate per frame that is consistent throughout the sequence. We evaluate the algorithm on challenging sequences with subjects that are alternating between running and walking movements. Our experiments show how the dynamical model helps to track through poorly segmented low-resolution image sequences where tracking otherwise fails, while at the same time reliably classifying the activity typ

On some phonologically-null elements in syntax

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Linguistics and Philosophy, 1980.MICROFICHE COPY AVAILABLE IN ARCHIVES AND HUMANITIES.Vita.Bibliography: leaves 314-319.by Osvaldo Adolfo Jaeggli.Ph.D