Hubble Frontier Fields : the geometry and dynamics of the massive galaxy cluster merger MACSJ0416.1−2403

We use a joint optical/X-ray analysis to constrain the geometry and history of the ongoing merging event in the massive galaxy cluster MACSJ0416.1-2403 (z=0.397). Our investigation of cluster substructure rests primarily on a combined strong- and weak-lensing mass reconstruction based on the deep, high-resolution images obtained for the Hubble Frontier Fields initiative. To reveal the system's dynamics, we complement this lensing analysis with a study of the intra-cluster gas using shallow Chandra data, and a three-dimensional model of the distribution and motions of cluster galaxies derived from over 100 spectroscopic redshifts. The multi-scale grid model obtained from our combined lensing analysis extends the high-precision strong-lensing mass reconstruction recently performed to cluster-centric distances of almost 1 Mpc. Our analysis detects the two well known mass concentrations in the cluster core. A pronounced offset between collisional and collisionless matter is only observed for the SW cluster component, while excellent alignment is found for the NE cluster. Both the lensing analysis and the distribution of cluster light strongly suggest the presence of a third massive structure, almost 2 arcmin SW of the cluster centre. Since no X-ray emission is detected in this region, we conclude that this structure is non-virialised and speculate that it might be part of a large-scale filament almost aligned with our line of sight. Combining all evidence from the distribution of dark and luminous matter, we propose two alternative scenarios for the trajectories of the components of MACSJ0416.1-2403. Upcoming deep X-ray observations that allow the detection of shock fronts, cold cores, and sloshing gas (all key diagnostics for studies of cluster collisions) will allow us to test, and distinguish between these two scenarios

Tomographic imaging of combustion zones using tunable diode laser absorption spectroscopy (TDLAS)

This work concentrates on enabling the usage of a specific variant of tunable diode laser absorption spectroscopy (abbr. TDLAS) for tomogaphically reconstructing spatially varying temperature and concentrations of gases with as few reconstruction artifacts as possible. The specific variant of TDLAS used here is known as wavelength modulation with second harmonic detection (abbr. WMS-2f) which uses the wavelength dependent absorbance information of two different spectroscopic transitions to determine temperature and concentration values. Traditionally, WMS-2f has generally been applied to domains where temperature although unknown, was spatially largely invariant while concentration was constant and known to a reasonable approximation (_x0006_+/- 10% ). In case of unknown temperatures and concentrations with large variations in space such techniques do not hold good since TDLAS is a “line-of-sight” (LOS) technique. To alleviate this problem, computer tomographic methods were developed and used to convert LOS projection data measured using WMS-2f TDLAS into spatially resolved local measurements. These locally reconstructed measurements have been used to determine temperature and concentration of points inside the flame following a new temperature and concentration determination strategy for WMS-2f that was also developed for this work. Specifically, the vibrational transitions (in the 1.39 microns to 1.44 microns range) of water vapor (H2O) in an axi-symmetric laminar flame issuing from a standard flat flame burner (McKenna burner) was probed using telecom grade diode lasers. The temperature and concentration of water vapor inside this flame was reconstructed using axi-symmetric Abel de-convolution method. The two different sources of errors in Abel’s deconvolution - regularization errors and perturbation errors, were analyzed and strategies for their mitigation were discussed. Numerical studies also revealed the existence of a third kind of error - tomographic TDLAS artifact. For 2D tomography, studies showing the required number of views, number of rays per view, orientation of the view and the best possible algorithm were conducted. Finally, data from 1D tomography was extrapolated to 2D and reconstructions were benchmarked with the results of 1D tomography

Measuring and Modeling the Interplay between Planetary Orbits, Interiors, Surfaces, and Atmospheres

Typically, we only have access to observations that directly probe the instantaneous state of a planet. However, these instantaneous properties are often set by the long-term interplay between several aspects of the planet. I thus use quantitative models of the interactions between the orbital, interior, surface, and atmospheric evolution in the case of three planetary bodies (Mars, Pluto, and the extrasolar planet HAT-P-13b) to gain insight into the underlying physical processes that govern the evolution of planets. In chapter 2, the interplay between the interior structure and orbital evolution of the gas giant exoplanet HAT-P-13b allows measurements of its orbit to reveal its interior structure. I use telescopic observations of HAT-P-13b to measure its orbit and thus determine its core mass. In chapter 3, cell-shaped landforms on Sputnik Planitia, the surface of a vast deposit of nitrogen ice covering 5% of Pluto’s surface, are the surface expression of convection within the nitrogen ice that is driven by heat flow from Pluto’s interior. The cells have sublimation pits on them, with smaller pits near their centers and larger pits near their edges. Using a simple model, I calculate the sublimation rate of these pits, which allows the determination of a size-age relationship. I then use the spatial size distribution of pits on cells to calculate their convection rate, which constrains the plutonian heat flow and thus the interior properties of Pluto. In chapter 4, the interplay of condensation and sublimation between the surface and atmosphere of Mars create a baffling array of uniquely martian morphologies carved into the martian residual south polar CO2 cap (RSPC). Using a multi-year baseline of high-resolution observations to track the evolution of these morphologies, I build a self-consistent conceptual framework capable of explaining the basic mechanisms that give rise to the diversity of landforms that make up the RSPC. In chapter 5, the secular evolution of Mars' orbit drives the evolution of the equilibrium relationship between the martian atmospheric pressure and the large CO2 ice deposit on the martian south polar cap. I construct the first self-consistent conceptual framework capable of predicting the existence and form of the martian residual south polar cap and the buried CO2 deposit. I then use this framework to compute the secular pressure history of Mars. Together, the results of these investigations provide new perspective into the fundamental processes driving the formation and evolution of planetary bodies.</p

New Applications of the Nearest-Neighbor Chain Algorithm

The nearest-neighbor chain algorithm was proposed in the eighties as a way to speed up certain hierarchical clustering algorithms. In the first part of the dissertation, we show that its application is not limited to clustering. We apply it to a variety of geometric and combinatorial problems. In each case, we show that the nearest-neighbor chain algorithm finds the same solution as a preexistent greedy algorithm, but often with an improved runtime. We obtain speedups over greedy algorithms for Euclidean TSP, Steiner TSP in planar graphs, straight skeletons, a geometric coverage problem, and three stable matching models. In the second part, we study the stable-matching Voronoi diagram, a type of plane partition which combines properties of stable matchings and Voronoi diagrams. We propose political redistricting as an application. We also show that it is impossible to compute this diagram in an algebraic model of computation, and give three algorithmic approaches to overcome this obstacle. One of them is based on the nearest-neighbor chain algorithm, linking the two parts together

Wholetoning: Synthesizing Abstract Black-and-White Illustrations

Black-and-white imagery is a popular and interesting depiction technique in the visual arts, in which varying tints and shades of a single colour are used. Within the realm of black-and-white images, there is a set of black-and-white illustrations that only depict salient features by ignoring details, and reduce colour to pure black and white, with no intermediate tones. These illustrations hold tremendous potential to enrich decoration, human communication and entertainment. Producing abstract black-and-white illustrations by hand relies on a time consuming and difficult process that requires both artistic talent and technical expertise. Previous work has not explored this style of illustration in much depth, and simple approaches such as thresholding are insufficient for stylization and artistic control. I use the word wholetoning to refer to illustrations that feature a high degree of shape and tone abstraction. In this thesis, I explore computer algorithms for generating wholetoned illustrations. First, I offer a general-purpose framework, “artistic thresholding”, to control the generation of wholetoned illustrations in an intuitive way. The basic artistic thresholding algorithm is an optimization framework based on simulated annealing to get the final bi-level result. I design an extensible objective function from our observations of a lot of wholetoned images. The objective function is a weighted sum over terms that encode features common to wholetoned illustrations. Based on the framework, I then explore two specific wholetoned styles: papercutting and representational calligraphy. I define a paper-cut design as a wholetoned image with connectivity constraints that ensure that it can be cut out from only one piece of paper. My computer generated papercutting technique can convert an original wholetoned image into a paper-cut design. It can also synthesize stylized and geometric patterns often found in traditional designs. Representational calligraphy is defined as a wholetoned image with the constraint that all depiction elements must be letters. The procedure of generating representational calligraphy designs is formalized as a “calligraphic packing” problem. I provide a semi-automatic technique that can warp a sequence of letters to fit a shape while preserving their readability

Development of a light-sheet fluorescence microscope employing an ALPAO deformable mirror to achieve video-rate remote refocusing and volumetric imaging.

There are numerous situations in microscopy where it is desirable to remotely refocus a microscope employing a high numerical aperture (NA) objective lens. This thesis describes the characterisation, development and implementation of an Alpao membrane deformable mirror-based system to achieve this goal for a light-sheet fluorescence microscope (LSFM). The Alpao deformable mirror (DM) DM97-15 used is this work has 97 actuators and was sufficiently fast to perform refocus sweeps at 25 Hz and faster. However, a known issue with using Alpao deformable mirrors in open-loop mode is that they exhibit viscoelastic creep and temperature- dependent variations in the mirror response. The effect of visco-elastic creep was reduced by ensuring that the mirror profile was on average constant on timescales shorter than the characteristic time of the visco-elastic creep. The thermal effect was managed by ensuring that the electrical power delivered to the actuators was constant prior to optimisation and use. This was achieved by ensuring that the frequency and amplitude of oscillation of the mirror was constant prior to optimisation, so that it reached a thermal steady state, was approximately constant during optimisation and constant during use. The image-based optimisation procedure employed used an estimate of the Strehl ratio of the optical system calculated from an image of an array of 1 μm diameter holes. The optimisation procedure included optimising the amount of high-NA defocus and the Zernike modes from Noll indices 4 to 24. The system was tested at 26.3 refocus sweeps per second over a refocus range of -50 to 50 μm with a 40x/0.85 air objective and a 40x/0.80 water immersion objective. The air objective enabled a mean Strehl metric of more than 0.6 over a lateral field of view of 200x200 microns and for a refocus range of 45 microns. The water objective achieved a mean Strehl metric of more than 0.6 over a lateral field of view of 200x200 microns over a larger refocus range of 77 microns. The DM-based refocusing system was then incorporated into a LSFM setup. The spatial resolution of the system was characterised using fluorescent beads imaged volumetrically at 26.3 volumes per second. The performance of the system was also demonstrated for imaging fluorescence pollen grain samples.Open Acces

Modeling Human Atrial Patho-Electrophysiology from Ion Channels to ECG - Substrates, Pharmacology, Vulnerability, and P-Waves

Half of the patients suffering from atrial fibrillation (AF) cannot be treated adequately, today. This thesis presents multi-scale computational methods to advance our understanding of patho-mechanisms, to improve the diagnosis of patients harboring an arrhythmogenic substrate, and to tailor therapy. The modeling pipeline ranges from ion channels on the subcellular level up to the ECG on the body surface. The tailored therapeutic approaches carry the potential to reduce the burden of AF

Optimizing constrained offset and scaled polygonal annuli

Aicholzer et al. recently presented a new geometric construct called the straight skeleton of a simple polygon and gave several combinatorial bounds for it. Independently, the current authors defined in companion papers a distance function based on the same offsetting function for convex polygons. In particular, we explored the nearest- and furthest- neighbor Voronoi diagrams of this function and presented algorithms for constructing them. In this paper we give solutions to some constrained annulus placement problems for offset polygons. The goal is to find the smallest annulus region of a polygon containing a set of points. We fix the inner (resp.,outer) polygon of the annulus and minimize the annulus region by minimizing the outer offset (resp., maximizing the inner offset. We also solve a a special case of the first problem: finding the smallest translated offset of a polygon containing an entire point set. We extend our results for the standard polygon scaling function as well

LIPIcs, Volume 248, ISAAC 2022, Complete Volume

LIPIcs, Volume 248, ISAAC 2022, Complete Volum