A Square Equal-area Map Projection

A novel square equal-area map projection is proposed. The projection combines closed-form forward and inverse solutions with relatively low angular distortion and minimal cusps, a combination of properties not manifested by any previously published square equal-area projection. Thus, the new projection has lower angular distortion than any previously published square equal-area projection with a closed-form solution. Utilizing a quincuncial arrangement, the new projection places the north pole at the center of the square and divides the south pole between its four corners; the projection can be seamlessly tiled. The existence of closed-form solutions makes the projection suitable for real-time visualization applications, both in cartography and in other areas, such as for the display of panoramic images.Comment: 15 pages, 5 figures, 1 tabl

Stability, Interactions, and Architectures of Colloids with Adsorbed Zwitterionic and Ethylene-Oxide Polymer Coatings

Zwitterionic polymer coatings have recently gained attention as stabilizing materials in drug delivery, diagnostic, and other biomedical applications. However, claims of improved stabilization and antifouling properties over traditional polymer chemistries are somewhat inconsistent, and with an unclear mechanistic link between studies at the molecular (e.g. atomic) and macromolecular (e.g. polymer surface) levels. This thesis uses single-particle, kT-scale measurements of colloidal interactions to probe the mechanics and colloidal stabilization of zwitterionic polymer coatings. Novel amphiphilic block copolymers form dense zwitterionic polymer layers through adsorption onto colloids. Adsorbed copolymers of sufficient repeat units stabilize colloids against deposition and aggregation in high-salt (0-3M NaCl) and physiological media (serum, cell media). Polymers of approximately 2-3 fold reduced contour lengths are needed to stabilize µm-sized colloids when using a common zwitterionic phosphorylcholine polymer (PMPC) than more conventional poly(ethylene oxide) (PEO) copolymers. Colloidal interaction measurements show that, relative to PEO coatings of similar contour lengths, zwitterionic PMPC coatings exert repulsion over a 2-3-fold longer range. This increased repulsion length is a result of increased zwitterionic layer thickness caused by complete chain extension of the PMPC polymer away from the adsorbate surface. Colloids with PEO and PMPC layers of equivalent thicknesses also possess equivalent interactions and stability against a variety of model biomaterial surface chemistries, further demonstrating the importance of layer thickness in stabilizing colloids against aggregation and deposition. The molecular mechanisms for the highly extended zwitterionic brush architectures were studied by using dissolved salt to perturb layer properties and colloidal interactions. Measurements of two contrasting zwitterionic chemistries showed salt-dependent brush extension that is intricately linked to poly-zwitterion solution behavior. Layer architectures result from a balance between attractive dipole-dipole and repulsive solvation and excluded volume molecular interactions. However the relative importance of these attractive and repulsive contributions is dependent on both solution properties (e.g. ion composition) and specific molecular affects (e.g. monomer structure and solvation). Ultimately, this thesis provides guidance regarding the design of effective polymer coatings for the stabilization of colloids. Polymer layers primarily impart stability through nonspecific macromolecular interactions, and must be of sufficient thickness and density to both screen attractive colloidal interactions and mitigate surfaces non-uniformities. Zwitterionic monomer chemistries only indirectly impact layer stability by influencing polymer layer extension. However zwitterionic chemistries may be useful for the engineering of additional layer properties, such as salt or pH - responsive layer thickness and stabilization

Instrumentation and Analysis Miscellanea Regarding the Cosmology Large Angular Scale Surveyor

The Cosmology Large Angular Scale Surveyor (CLASS) is an array of polarization-sensitive millimeter-wave telescopes that observes ~70% of the sky in frequency bands centered near 40 GHz, 90 GHz, 150 GHz, and 220 GHz from a high-altitude site in the Atacama desert of northern Chile. It seeks to measure polarization anisotropy in the cosmic microwave background (CMB), with a particular emphasis on measuring the optical depth due to reionization via large-angular-scale polarization E-modes, as well as searching for primordial polarization B-modes, a detection of which would provide strong evidence for cosmological inflation. This dissertation starts by providing an overview of physical cosmology, before describing the science goals and instrument design of CLASS. It then describes various instrument components that were developed, describes a novel 3D-printed millimeter-wave absorber, and describes the control and systems software used to operate the telescopes. Analysis efforts are then covered, specifically the modeling and detection of atmospheric circular polarization due to Zeeman-splitting of molecular oxygen emission lines in the geomagnetic field and a method of cleaning CMB foregrounds from full-sky maps that utilizes machine learning techniques

Frequency control of photonic crystal membrane resonators by mono-layer deposition

We study the response of GaAs photonic crystal membrane resonators to thin film deposition. Slow spectral shifts of the cavity mode of several nanometers are observed at low temperatures, caused by cryo-gettering of background molecules. Heating the membrane resets the drift and shielding will prevent drift altogether. In order to explore the drift as a tool to detect surface layers, or to intentionally shift the cavity resonance frequency, we studied the effect of self-assembled monolayers of polypeptide molecules attached to the membranes. The 2 nm thick monolayers lead to a discrete step in the resonance frequency and partially passivate the surface.Comment: 3 pages, 4 figures, submitted to Appl. Phys. Let

Sulphur and carbon cycling in the subduction zone mélange

Subduction zones impose an important control on the geochemical cycling between the surficial and internal reservoirs of the Earth. Sulphur and carbon are transferred into Earth’s mantle by subduction of pelagic sediments and altered oceanic lithosphere. Release of oxidizing sulphate- and carbonate-bearing fluids modifies the redox state of the mantle and the chemical budget of subduction zones. Yet, the mechanisms of sulphur and carbon cycling within subduction zones are still unclear, in part because data are typically derived from arc volcanoes where fluid compositions are modified during transport through the mantle wedge. We determined the bulk rock elemental, and sulphur and carbon isotope compositions of exhumed ultramafic and metabasic rocks from Syros, Greece. Comparison of isotopic data with major and trace element compositions indicates seawater alteration and chemical exchange with sediment-derived fluids within the subduction zone channel. We show that small bodies of detached slab material are subject to metasomatic processes during exhumation, in contrast to large sequences of obducted ophiolitic sections that retain their seafloor alteration signatures. In particular, fluids circulating along the plate interface can cause sulphur mobilization during several stages of exhumation within high-pressure rocks. This takes place more pervasively in serpentinites compared to mafic rocks