LSST: from Science Drivers to Reference Design and Anticipated Data Products

(Abridged) We describe here the most ambitious survey currently planned in the optical, the Large Synoptic Survey Telescope (LSST). A vast array of science will be enabled by a single wide-deep-fast sky survey, and LSST will have unique survey capability in the faint time domain. The LSST design is driven by four main science themes: probing dark energy and dark matter, taking an inventory of the Solar System, exploring the transient optical sky, and mapping the Milky Way. LSST will be a wide-field ground-based system sited at Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m effective) primary mirror, a 9.6 deg$^2$ field of view, and a 3.2 Gigapixel camera. The standard observing sequence will consist of pairs of 15-second exposures in a given field, with two such visits in each pointing in a given night. With these repeats, the LSST system is capable of imaging about 10,000 square degrees of sky in a single filter in three nights. The typical 5$\sigma$ point-source depth in a single visit in $r$ will be $\sim 24.5$ (AB). The project is in the construction phase and will begin regular survey operations by 2022. The survey area will be contained within 30,000 deg$^2$ with $\delta<+34.5^\circ$, and will be imaged multiple times in six bands, $ugrizy$, covering the wavelength range 320--1050 nm. About 90\% of the observing time will be devoted to a deep-wide-fast survey mode which will uniformly observe a 18,000 deg$^2$ region about 800 times (summed over all six bands) during the anticipated 10 years of operations, and yield a coadded map to $r\sim27.5$. The remaining 10\% of the observing time will be allocated to projects such as a Very Deep and Fast time domain survey. The goal is to make LSST data products, including a relational database of about 32 trillion observations of 40 billion objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures available from https://www.lsst.org/overvie

Diabetes, periodontitis, and the subgingival microbiota

Both type 1 and type 2 diabetes have been associated with increased severity of periodontal disease for many years. More recently, the impact of periodontal disease on glycaemic control has been investigated. The role of the oral microbiota in this two-way relationship is at this stage unknown. Further studies, of a longitudinal nature and investigating a wider array of bacterial species, are required in order to conclusively determine if there is a difference in the oral microbiota of diabetics and non-diabetics and whether this difference accounts, on the one hand, for the increased severity of periodontal disease and on the other for the poorer glycaemic control seen in diabetics

Spatial and Orientation Control of Cylindrical Nanostructures in ABA Triblock Copolymer Thin Films by Raster Solvent Vapor Annealing

We present a spatially resolved approach for the solvent vapor annealing (SVA) of block copolymer thin films that permits the facile and relatively rapid manipulation of nanoscale ordering and nanostructure orientation. In our method, a localized (point) SVA zone is created through the use of a vapor delivery nozzle. This point annealing zone can be rastered across the thin film using a motorized stage to control the local nanoscale structure and orientation in a cylinder-forming ABA triblock copolymer thin film. At moderate rastering speeds (∼100 μm/s) (<i>i.e.</i>, relatively modest annealing time at a given point), the film displayed ordered cylindrical nanostructures with the cylinders oriented parallel to the substrate surface. As the rastering speed was decreased (∼10 μm/s), the morphology transformed into a surface nanostructure indicative of cylinders oriented perpendicular to the substrate surface. These perpendicular cylinder orientations also were created by rastering multiple times over the same region, and this effect was found when rastering in either retrace (overlapping) or crossed-path (orthogonal) geometries. Similar trends in nanostructure orientation and ordering were obtained from various nozzle diameters by accounting for differences in solvent flux and annealing time, illustrating the universality of this approach. Finally, we note that our “stylus-based” raster solvent vapor annealing technique allows a given point to be solvent annealed approximately 2 orders of magnitude faster than conventional “bell jar” solvent vapor annealing

Switching the Adhesive State of Catecholic Hydrogels using Phototitration

A polyacrylamide hydrogel system that can be liquefied by remote activation using UV irradiation is investigated as a degradable adhesive. The linear polyacrylamide copolymer, formed by conventional free-radical polymerization, contains biomimetic catechol–iron-mediated cross-linkers that are sensitive to pH changes. Hydrogel films and bulk gels are prepared by basic titration of a polymer solution doped with a photoacid generator, diphenyliodonium chloride, generating an ionic cross-linked network via the catechol pendant groups. Irradiation of these hydrogels with UV light affords a viscous liquid solution, demonstrating a gel–sol transition with a subsequent decrease in the adhesive strength of the material. These gels may be prepared in high throughput and require few synthetic steps with commercially available precursors

Switching the Adhesive State of Catecholic Hydrogels using Phototitration

A polyacrylamide hydrogel system that can be liquefied by remote activation using UV irradiation is investigated as a degradable adhesive. The linear polyacrylamide copolymer, formed by conventional free-radical polymerization, contains biomimetic catechol–iron-mediated cross-linkers that are sensitive to pH changes. Hydrogel films and bulk gels are prepared by basic titration of a polymer solution doped with a photoacid generator, diphenyliodonium chloride, generating an ionic cross-linked network via the catechol pendant groups. Irradiation of these hydrogels with UV light affords a viscous liquid solution, demonstrating a gel–sol transition with a subsequent decrease in the adhesive strength of the material. These gels may be prepared in high throughput and require few synthetic steps with commercially available precursors

A healable supramolecular polymer blend based on aromatic π-π stacking and hydrogen bonding interactions

An elastomeric, supramolecular healable polymer blend, comprising a chain-folding polyimide and a telechelic polyurethane with pyrenyl endgroups, is compatibilised by aromatic π−π stacking between the π-electron-deficient diimide groups and the π-electron-rich pyrenyl units. This inter-polymer interaction is key to forming a tough, healable, elastomeric material. Variable temperature FTIR analysis of the bulk material also conclusively demonstrates the presence of hydrogen bonding, which complements the π–π stacking interactions. Variable temperature SAXS analysis shows that the healable polymeric blend has a nanophase-separated morphology, and that the X-ray contrast between the two types of domain increases with increasing temperature, a feature that is repeatable over several heating and cooling cycles. A fractured sample of this material reproducibly regains more than 95% of the tensile modulus, 91% of the elongation to break, and 77% of the modulus of toughness of the pristine material

Manipulating Nanoscale Morphologies in Cylinder-Forming Poly(styrene‑<i>b</i>‑isoprene‑<i>b</i>‑styrene) Thin Films Using Film Thickness and Substrate Surface Chemistry Gradients

Controlling the nanostructure of self-assembled block copolymer thin films is critical for applications in nanotemplate design, nanoporous membranes, and organic optoelectronics. In this study, we employed a gradient approach to examine the effects of substrate surface chemistry and film thickness on the self-assembly of cylinder-forming poly­(styrene-<i>b</i>-isoprene-<i>b</i>-styrene) (SIS) thin films. Using gradients in film thickness from 85 to 120 nm (3.1<i>d</i> to 4.4<i>d</i>), we found that the thin films contained parallel cylinders on both bare silicon substrates and benzyldimethylchlorosilane (benzyl silane)-modified substrates regardless of film thickness, while thin films contained surface patterns of hexagonally arranged dots on <i>n</i>-butyldimethylchlorosilane (<i>n</i>-butyl silane)-modified substrates. These surface patterns were further investigated using film etching, cross-sectional transmission electron microscopy (TEM), and grazing-incidence small-angle X-ray scattering (GISAXS) techniques. We determined that the nanostructures represented a hexagonally perforated lamellar (HPL) morphology in which the parallel cylinder layering was preserved during the phase transformation to HPL. Additionally, controlled vapor deposition was used to generate a nearly linear substrate surface chemistry gradient from benzyl silane to <i>n</i>-butyl silane. Examination of SIS thin films on this surface gradient revealed a morphological transformation from parallel cylinders to HPL with changing substrate surface composition. Thus, we demonstrated the combined usage of film thickness and monolayer substrate surface chemistry gradients to manipulate the nanostructure of block copolymer films, such as SIS, that possess moderate differences in surface energy between individual blocks. Our gradients represent a high-throughput and versatile screening tool that facilitates the examination of new materials and furthers the understanding of block copolymer thin film self-assembly