Opening Reionization: Quantitative Morphology of the Epoch of Reionization and Its Connection to the Cosmic Density Field

We introduce a versatile and spatially resolved morphological characterisation of binary fields, rooted in the opening transform of mathematical morphology. We subsequently apply it to the thresholded ionization field in simulations of cosmic reionization and study the morphology of ionized regions. We find that an ionized volume element typically resides in an ionized region with radius $\sim8\,h^{-1}\mathrm{cMpc}$ at the midpoint of reionization ($z\approx7.5$) and follow the bubble size distribution even beyond the overlap phase. We find that percolation of the fully ionized component sets in when 25% of the universe is ionized and that the resulting infinite cluster incorporates all ionized regions above $\sim8\,h^{-1}\mathrm{cMpc}$. We also quantify the clustering of ionized regions of varying radius with respect to matter and on small scales detect the formation of superbubbles in the overlap phase. On large scales we quantify the bias values of the centres of ionized and neutral regions of different sizes and not only show that the largest ones at the high-point of reionization can reach $b\approx 30$, but also that early small ionized regions are positively correlated with matter and large neutral regions and late small ionized regions are heavily anti-biased with respect to matter, down to $b\lesssim-20$.Comment: 18 pages, 15 figure, as accepted for publication by MNRA

AutoGraff: towards a computational understanding of graffiti writing and related art forms.

The aim of this thesis is to develop a system that generates letters and pictures with a style that is immediately recognizable as graffiti art or calligraphy. The proposed system can be used similarly to, and in tight integration with, conventional computer-aided geometric design tools and can be used to generate synthetic graffiti content for urban environments in games and in movies, and to guide robotic or fabrication systems that can materialise the output of the system with physical drawing media. The thesis is divided into two main parts. The first part describes a set of stroke primitives, building blocks that can be combined to generate different designs that resemble graffiti or calligraphy. These primitives mimic the process typically used to design graffiti letters and exploit well known principles of motor control to model the way in which an artist moves when incrementally tracing stylised letter forms. The second part demonstrates how these stroke primitives can be automatically recovered from input geometry defined in vector form, such as the digitised traces of writing made by a user, or the glyph outlines in a font. This procedure converts the input geometry into a seed that can be transformed into a variety of calligraphic and graffiti stylisations, which depend on parametric variations of the strokes

The SINS Survey: SINFONI Integral Field Spectroscopy of z ~ 2 Star-forming Galaxies

We present the Spectroscopic Imaging survey in the near-infrared (near-IR) with SINFONI (SINS) of high-redshift galaxies. With 80 objects observed and 63 detected in at least one rest-frame optical nebular emission line, mainly Hα, SINS represents the largest survey of spatially resolved gas kinematics, morphologies, and physical properties of star-forming galaxies at z ~ 1-3. We describe the selection of the targets, the observations, and the data reduction. We then focus on the "SINS Hα sample," consisting of 62 rest-UV/optically selected sources at 1.3 < z < 2.6 for which we targeted primarily the Hα and [N II] emission lines. Only ≈30% of this sample had previous near-IR spectroscopic observations. The galaxies were drawn from various imaging surveys with different photometric criteria; as a whole, the SINS Hα sample covers a reasonable representation of massive M_* ≳ 10^(10) M_☉ star-forming galaxies at z ≈ 1.5-2.5, with some bias toward bluer systems compared to pure K-selected samples due to the requirement of secure optical redshift. The sample spans 2 orders of magnitude in stellar mass and in absolute and specific star formation rates, with median values ≈3 × 10^(10) M_☉, ≈70 M_☉ yr^(–1), and ≈3 Gyr^(–1). The ionized gas distribution and kinematics are spatially resolved on scales ranging from ≈1.5 kpc for adaptive optics assisted observations to typically ≈4-5 kpc for seeing-limited data. The Hα morphologies tend to be irregular and/or clumpy. About one-third of the SINS Hα sample galaxies are rotation-dominated yet turbulent disks, another one-third comprises compact and velocity dispersion-dominated objects, and the remaining galaxies are clear interacting/merging systems; the fraction of rotation-dominated systems increases among the more massive part of the sample. The Hα luminosities and equivalent widths suggest on average roughly twice higher dust attenuation toward the H II regions relative to the bulk of the stars, and comparable current and past-averaged star formation rates

Census of HII regions in NGC 6754 derived with MUSE: Constraints on the metal mixing scale

We present a study of the HII regions in the galaxy NGC 6754 from a two pointing mosaic comprising 197,637 individual spectra, using Integral Field Spectrocopy (IFS) recently acquired with the MUSE instrument during its Science Verification program. The data cover the entire galaxy out to ~2 effective radii (re ), sampling its morphological structures with unprecedented spatial resolution for a wide-field IFU. A complete census of the H ii regions limited by the atmospheric seeing conditions was derived, comprising 396 individual ionized sources. This is one of the largest and most complete catalogue of H ii regions with spectroscopic information in a single galaxy. We use this catalogue to derive the radial abundance gradient in this SBb galaxy, finding a negative gradient with a slope consistent with the characteristic value for disk galaxies recently reported. The large number of H ii regions allow us to estimate the typical mixing scale-length (rmix ~0.4 re ), which sets strong constraints on the proposed mechanisms for metal mixing in disk galaxies, like radial movements associated with bars and spiral arms, when comparing with simulations. We found evidence for an azimuthal variation of the oxygen abundance, that may be related with the radial migration. These results illustrate the unique capabilities of MUSE for the study of the enrichment mechanisms in Local Universe galaxies.Comment: 13 pages, 7 Figurs, accepted for publishing in A&

Phototunable block copolymer hydrogels

2017 Fall.Includes bibliographical references.Thermoplastic elastomer (TPE) hydrogel networks, based on swelling of nanostructured blends of amphiphilic, sphere-forming AB diblock and ABA triblock copolymers, provide direct access to thermally processable plastics that exhibit exceptional elastic recovery and fatigue resistance even after hydration. In such two-component systems, the ratio of ABA to AB block copolymer (BCP) is used to control the resultant swelling ratio, system modulus, and overall mechanical response. This dissertation focuses on developing material strategies through which adjustment of such AB/ABA ratios, and thus the resultant properties, can be accomplished using light. The chapters within capture the manipulation of a photoreactive AB diblock copolymer micelle-like spheres to controllably generate ABA triblock copolymer and the network nanostructure in situ, both in the melt state and after dispersal in solution. This was accomplished using efficient photoinduced [4 + 4]cycloaddition (λ = 365 nm) between terminal anthracene units on a ω-anthracenylpolystyrene-b-poly(ethylene oxide) diblock copolymer precursor to produce the desired amount of polystyrene-b-poly(ethylene oxide)-b-polystyrene triblock copolymer. This direct, UV-mediated handle on tethering between adjacent micelles in the BCP matrix was found to be capable of controllably manipulating hydrogel material properties using (1) duration of irradiation, (2) hydration level and consequent micelle spacing upon exposure, and (3) photopatterning strategies to spatially direct swelling and mechanics. This level of control yielded an array of hydrogels, ranging from those irradiated in the dry melt to produce high-modulus, elastic materials suited for fibrocartilage repair and replacement, to moldable or injectable precursor solutions irradiated into soft, conformally shaped TPE hydrogels ideal for use in high contact applications such as wound healing. The development and scope of this versatile new photoactive BCP system is enclosed

Galaxy Disks

The formation and evolution of galactic disks is particularly important for understanding how galaxies form and evolve, and the cause of the variety in which they appear to us. Ongoing large surveys, made possible by new instrumentation at wavelengths from the ultraviolet (GALEX), via optical (HST and large groundbased telescopes) and infrared (Spitzer) to the radio are providing much new information about disk galaxies over a wide range of redshift. Although progress has been made, the dynamics and structure of stellar disks, including their truncations, are still not well understood. We do now have plausible estimates of disk mass-to-light ratios, and estimates of Toomre's $Q$ parameter show that they are just locally stable. Disks are mostly very flat and sometimes very thin, and have a range in surface brightness from canonical disks with a central surface brightness of about 21.5 $B$-mag arcsec$^{-2}$ down to very low surface brightnesses. It appears that galaxy disks are not maximal, except possibly in the largest systems. Their HI layers display warps whenever HI can be detected beyond the stellar disk, with low-level star formation going on out to large radii. Stellar disks display abundance gradients which flatten at larger radii and sometimes even reverse. The existence of a well-defined baryonic Tully-Fisher relation hints at an approximately uniform baryonic to dark matter ratio. Thick disks are common in disk galaxies and their existence appears unrelated to the presence of a bulge component; they are old, but their formation is not yet understood. Disk formation was already advanced at redshifts of $\sim 2$, but at that epoch disks were not yet quiescent and in full rotational equilibrium. Downsizing is now well-established. The formation and history of star formation in S0s is still not fully understood.Comment: This review has been submitted for Annual Reviews of Astronomy & Astrophysics, vol. 49 (2011); the final printed version will have fewer figures and a somewhat shortened text. A pdf-version of this preprint with high-resolution figures is available from http://www.astro.rug.nl/~vdkruit/jea3/homepage/disks-ph.pdf. (table of contents added; 71 pages, 24 figures, 529 references

The stellar structure and outer disk kinematics of high-redshift galaxies from near-infrared observations

The universe at redshift 1 < z < 3 represents the peak epoch of rapid galaxy mass assembly and very active star-formation in galaxies, but also poses many observational challenges. This thesis addresses the buildup of galaxy mass as well as the shut-down of star formation in galaxies (referred to as 'quenching') using state-of-the-art spatially resolved observations of galaxies at high redshift from ground- and space based near-infrared (NIR) datasets. The first part of this thesis presents an analysis of the stellar morphology of massive galaxies (M_star > 10^10 M_sun) at 0.5 < z < 2.5 on the basis of the CANDELS dataset, providing deep rest-frame Ultraviolet(UV)-to-NIR imaging from the Hubble Space Telescope (HST) at high angular resolution. This is complemented by grism spectroscopy from the 3D-HST survey used to derive accurate redshift information. Both stellar mass and rest-frame optical light distributions of 6764 galaxies are quantified by performing single Sersic fits as well as bulge-to-disk decompositions. The stellar mass distributions are reconstructed through resolved stellar population modeling on the panchromatic imaging dataset. The results show that quiescent galaxies at high redshift possess increased bulge fractions compared to their star-forming counterparts as seen in their mass distribution, previously only observed in rest-frame optical light. Moreover, the Sersic index and bulge-to-total ratio (B/T) among star- forming galaxies show an increase towards higher stellar masses (with the median B/T reaching 40-50 % above 10^11 M_sun), hinting at significant bulge growth of star-forming galaxies along the main sequence before quenching. The bulge mass of a galaxy appears to be a more reliable predictor of quiescence than total stellar mass or disk mass. These empirical results and a further comparison to state-of-the-art theoretical models support that possible quenching mechanisms are internal to galaxies and closely associated with bulge growth. \\ The second part of this work focuses on the outer disk kinematics of star-forming galaxies at high redshift on the basis of large and deep Integral-Field-Unit (IFU) datasets tracing the resolved ionized gas kinematics from H-alpha. Both the ongoing KMOS-3D survey and the subset of the SINS/zc-SINF survey observed in adaptive optics assisted mode, are exploited to build a sample of ~ 100 massive star forming disk galaxies at 0.7 < z < 2.6. Employing a novel stacking approach, a representative rotation curve reaching out to several effective radii can be robustly constrained. The stacked rotation curve exhibits a significant decrease in rotation velocity beyond the turnover. This result confirms, and extends to a larger sample, the falloff that had so far been observed in a handful of individual high-z disks with best data quality and signal-to-noise ratio. A comparison with models shows that the falling outer rotation curve can be explained by a high mass fraction of baryons in the disk relative to the dark matter halo (m_d = 0.05 -0.1) in combination with a significant level of pressure support in the outer disk (sigma_0 = 35 km/s). These findings confirm the high baryon fractions found by comparing the stellar, gas and dynamical masses of high redshift galaxies independently of assumptions on the light-to-mass conversion and Initial stellar Mass Function (IMF). The rapid falloff of the stacked rotation curve can be explained by pressure gradients, which are significant in the gas-rich, turbulent high-z disks and suggests a possible pressure-driven truncation of the outer disk. \\ Lastly, a derivation of beam smearing corrections is presented that is applicable to high-redshift IFU datasets to recover the intrinsic values of rotation velocity and velocity dispersion. The corrections are based on simulated mock datacubes to mimic real IFU observations for a wide range of various intrinsic galaxy parameters assuming exponential disks. The correction for rotation velocity only depends on the size of the galaxy versus the size of the instrumental spatial point spread function (PSF), and fitting functions for the corrections to be easily applied to large datasets are presented. The corrections for velocity dispersion depend on several additional intrinsic galaxy parameters such as the inclination angle and dynamical mass. Based on the grid of models spanning a wide range in these galaxy parameters, the correction for velocity dispersion can be applied to any observed source

Platinum nanoparticles therapeutic strategy for the prevention of oxidative stress in retinal dystrophies

Neurodegenerations are a complex pool of diseases united by a progressive loss of neuronal cells. Retinal neurodegenerations cause several visual impairment conditions worldwide, burdening the healthcare systems and lowering patients\u2019 quality of life. Several retinal degenerations are associated with reactive oxygen species overproduction, a well-known condition that, in the long term, has a detrimental effect on the degeneration progression. While the neuronal cells loss is irreversible, several therapeutic approaches are currently used to prevent retinal degeneration, with contained and heterogeneous effects depending on both disease and patient. In addition to the preventive therapies available in clinical practice, the scientific community has investigated several therapeutic and preventative solutions, from gene therapy to dietary supplements. Nanomedicine has excellent potential for retinal degeneration prevention. Nanoparticles with ROS scavenging capability, such as gold or cerium-oxide nanoparticles, have been proven effective as neurodegeneration counteractors, leading to intensive research to find more efficient materials for nanoparticles core. Thanks to its high antioxidant activity, solubility and stability, platinum has proven to be a valuable candidate for NPs\u2019 core. Unfortunately, due to different protocols of synthesis, stabilization and coating, platinum nanoparticles display contrasting results in both in vitro and in vivo studies. This controversy induced a slowdown around the research on their applications. In this thesis, we demonstrate that citrate capped platinum nanoparticles, produced by seeded-growth approach and stabilized with an RSA corona, are stable in physiological solution, preserve their catalytic activity, without inducing neuronal death in vitro. Furthermore, in vivo experiments enlightened a preservation effect on retinal electrophysiology, without altering the morphology or the inflammation levels in the retina. These data together suggest that PtNPs are safe to use in vivo and have the potential to be used in medicine