The Complicated Evolution of the ACIS Contamination Layer over the Mission Life of the Chandra X-ray Observatory

The Chandra X-ray Observatory was launched almost 19 years ago and has been delivering spectacular science over the course of its mission. The Advanced CCD Imager Spectrometer is the prime instrument on the satellite, conducting over 90% of the observations. The CCDs operate at a temperature of -120 C and the optical blocking filter in front of the CCDs is at a temperature of approximately -60C. The surface of the OBF has accumulated a layer of contamination over the course of the mission. We have been characterizing the thickness, chemical composition, and spatial distribution of the contamination layer as a function of time over the mission. All three have exhibited significant changes with time. There has been a dramatic decrease in the accumulation rate of the contaminant starting in 2017. The lower accumulation rate may be due to a decrease in the deposition rate or an increase in the vaporization rate or a combination of the two. We show that the current calibration file which models the additional absorption of the contamination layer is significantly overestimating that additional absorption by using the standard model spectrum for the supernova remnant 1E 0102.2-7219 developed by the International Astronomical Consortium for High Energy Calibration. In addition, spectral data from the cluster of galaxies known as Abell 1795 and the Blazar Markarian 421 are used to generate a model of the absorption produced by the contamination layer. The Chandra X-ray Center calibration team is preparing a revised calibration file that more accurately represents the complex time dependence of the accumulation rate, the spatial dependence, and the chemical composition of the contaminant. Given the rapid changes in the contamination layer over the past year, future calibration observations at a higher cadence will be necessary to more accurately monitor such changes.Comment: 15 pages, 10 figures, SPIE Astronomical Instruments and Telescopes 2018, Conference Series, 1069

Effective behavior of nematic elastomer membranes

We derive the effective energy density of thin membranes of liquid crystal elastomers as the Gamma-limit of a widely used bulk model. These membranes can display fine-scale features both due to wrinkling that one expects in thin elastic membranes and due to oscillations in the nematic director that one expects in liquid crystal elastomers. We provide an explicit characterization of the effective energy density of membranes and the effective state of stress as a function of the planar deformation gradient. We also provide a characterization of the fine-scale features. We show the existence of four regimes: one where wrinkling and microstructure reduces the effective membrane energy and stress to zero, a second where wrinkling leads to uniaxial tension, a third where nematic oscillations lead to equi-biaxial tension and a fourth with no fine scale features and biaxial tension. Importantly, we find a region where one has shear strain but no shear stress and all the fine-scale features are in-plane with no wrinkling

Programming complex shapes in thin nematic elastomer and glass sheets

Nematic elastomers and glasses are solids that display spontaneous distortion under external stimuli. Recent advances in the synthesis of sheets with controlled heterogeneities have enabled their actuation into non-trivial shapes with unprecedented energy density. Thus, these have emerged as powerful candidates for soft actuators. To further this potential, we introduce the key metric constraint which governs shape changing actuation in these sheets. We then highlight the richness of shapes amenable to this constraint through two broad classes of examples which we term nonisometric origami and lifted surfaces. Finally, we comment on the derivation of the metric constraint, which arises from energy minimization in the interplay of stretching, bending and heterogeneity in these sheets

Patterning nonisometric origami in nematic elastomer sheets

Nematic elastomers dramatically change their shape in response to diverse stimuli including light and heat. In this paper, we provide a systematic framework for the design of complex three dimensional shapes through the actuation of heterogeneously patterned nematic elastomer sheets. These sheets are composed of \textit{nonisometric origami} building blocks which, when appropriately linked together, can actuate into a diverse array of three dimensional faceted shapes. We demonstrate both theoretically and experimentally that: 1) the nonisometric origami building blocks actuate in the predicted manner, 2) the integration of multiple building blocks leads to complex multi-stable, yet predictable, shapes, 3) we can bias the actuation experimentally to obtain a desired complex shape amongst the multi-stable shapes. We then show that this experimentally realized functionality enables a rich possible design landscape for actuation using nematic elastomers. We highlight this landscape through theoretical examples, which utilize large arrays of these building blocks to realize a desired three dimensional origami shape. In combination, these results amount to an engineering design principle, which we hope will provide a template for the application of nematic elastomers to emerging technologies

Chandra observation of the Galactic supernova remnant CTB 109 (G109.1-1.0)

Context: We study the X-ray emission of the Galactic supernova remnant (SNR) CTB 109 (G109.1-1.0), which is well-known for its enigmatic half-shell morphology both in radio and in X-rays and is associated with the anomalous X-ray pulsar (AXP) 1E2259+586. Aims: We want to understand the origin of the X-ray bright feature inside the SNR called the Lobe and the details of the interaction of the SNR shock wave with the ambient interstellar medium (ISM). Methods: The Lobe and the northeastern part of the SNR were observed with Chandra ACIS-I. We analysed the spectrum of the X-ray emission by dividing the entire observed emission into small regions. The X-ray emission is best reproduced with one-component or two-component non-equilibrium ionisation models depending on the position. In the two-component model one emission component represents the shocked ISM and the other the shocked ejecta. Results: We detect enhanced element abundances, in particular for Si and Fe, in and around the Lobe. There is one particular region next to the Lobe with a high Si abundance of 3.3 (2.6 - 4.0) times the solar value. This is the first, unequivocal detection of ejecta in CTB 109. Conclusions: The new Chandra data confirm that the Lobe was created by the interaction of the SNR shock and the supernova ejecta with dense and inhomogeneous medium in the environment of SNR CTB 109. The newly calculated age of the SNR is t ~ 1.4 x 10^4 yr.Comment: Accepted for publication in A&A. 9 pages, 10 figure

The Biophysical Characterization of Caveolin-1

The main topic of this doctoral dissertation is the biophysical characterization of caveolin-1. Caveolin-1 is an integral membrane protein that has been shown to be essential for the formation of caveolae. Caveolae are 50-100 nm invaginations in the plasma membrane that have a plethora of cellular functions including signal transduction, relieving mechano-stresses on the cell, and endocytosis. Caveolin-1 is at the center of all of the functions of caveolae and has been shown to play a predominant role in disease states. However, while there are a large number of biological studies on caveolin-1, there are few biophysical studies, leading to a lack of understanding of the structure, topology and oligomerization of caveolin-1. The progress made in these three main areas of caveolin-1 research as well as introducing a novel in vitro functional assay for caveolin-1 and a broadly applicable membrane protein isolation technique are introduced. In chapter 1, background and general information about caveolin-1 and the biophysical techniques that were utilized for its characterization are discussed. Chapter 2 discusses the structural characterization of a caveolin-1 construct containing residues 62-136 using NMR spectroscopy revealing that the N-terminal residues (62-85) were dynamic and caveolin-1 contains a helix-break-helix motif with two approximately equal length helices. Chapter 3 discusses the structural characterization of caveolin-1 residues (62-178) using NMR spectroscopy. Caveolin-1(62-178) is the longest construct of caveolin-1 to be structurally characterized and encompasses the previously uncharacterized C-terminal domain which formed a long helix. Additionally, caveolin-1 contains a helix-break-helix-break-helix motif. In chapter 4, alanine and phenylalanine scanning mutagenesis of caveolin-1 82-136, was utilized to identify key structural residues within both helix-1 and helix-2. In chapter 5, the efforts to establish an in vitro functional assay for caveolin-1 utilizing the inhibition of endothelial nitric oxide synthase is presented. In chapter 6, cysteine scanning mutagenesis was utilized to evaluate the exposure of single residues in the caveolin-1 scaffolding domain to determine the topology of caveolin-1. Additionally, an evaluation of several different maleimide probes is presented. In chapter 7, a novel method to measure membrane protein oligomerization utilizing homo-FRET in liposomes is presented. Finally, in chapter 8 a purification method utilizing perfluorooctanoic acid (PFOA) to solubilize inclusion bodies is presented. This method has a three-fold advantage over conventional solubilization methods because: 1) PFOA can completely solubilize inclusion bodies, 2) PFOA is compatible with Ni-NTA chromatography and 3) PFOA is easily removed by detergent dialysis. Overall, this work represents significant advancements in understanding of the caveolin-1 protein