A Non-isothermal Theory for Interpreting Sodium Lines in Transmission Spectra of Exoplanets

We present a theory for interpreting the sodium lines detected in transmission spectra of exoplanetary atmospheres. Previous analyses employed the isothermal approximation and dealt only with the transit radius. By recognising the absorption depth and the transit radius as being independent observables, we develop a theory for jointly interpreting both quantities, which allows us to infer the temperatures and number densities associated with the sodium lines. We are able to treat a non-isothermal situation with a constant temperature gradient. Our novel diagnostics take the form of simple-to-use algebraic formulae and require measurements of the transit radii (and their corresponding absorption depths) at line center and in the line wing for both sodium lines. We apply our diagnostics to the HARPS data of HD 189733b, confirm the upper atmospheric heating reported by Huitson et al. (2012), derive a temperature gradient of $0.4376 \pm 0.0154$ K km$^{-1}$ and find densities $\sim 1$ to $10^4$ cm$^{-3}$.Comment: Accepted by ApJ Letters. 6 pages, 3 figure

Effects of NHC-Backbone Substitution on Efficiency in Ruthenium-Based Olefin Metathesis

series of ruthenium olefin metathesis catalysts bearing N-heterocyclic carbene (NHC) ligands with varying degrees of backbone and N-aryl substitution have been prepared. These complexes show greater resistance to decomposition through C−H activation of the N-aryl group, resulting in increased catalyst lifetimes. This work has utilized robotic technology to examine the activity and stability of each catalyst in metathesis, providing insights into the relationship between ligand architecture and enhanced efficiency. The development of this robotic methodology has also shown that, under optimized conditions, catalyst loadings as low as 25 ppm can lead to 100% conversion in the ring-closing metathesis of diethyl diallylmalonate

Revitalizing Urban Waterway\u27s Community Greenspace: Streams of Environmental Justice

While there are many reports of physical demonstration projects that attempt to restore segments and functions of urban waterways, there is no consensus about what to do and how to do it from a social or environmental justice perspective. We have discovered this during the three years of working on the Onondaga Creek Revitalization Plan in Syracuse, New York, and others have found this to be a major challenge as well. There are also equity issues in terms of who has historically been forced to live in high-risk flood plain or polluted water areas, with marginalized communities being the ones who shoulder the greatest burdens. This paper explores approaches to urban creek and river revitalization, drawing from international case studies from Europe and North America plus the authors’ experience with the Onondaga Creek Revitalization Plan in Syracuse, NY. Given the different waterway objectives for both restoration and /or revitalization, there is a need for a collaborative social process, with attention to social equity, in developing such projects and plans. The authors’ new book ’Revitalizing Urban Waterway Communities: Streams of Environmental Justice’ (Smardon et al. 2018) presents ways of addressing multiple jurisdictions and diverse sets of stakeholders. European and US case studies present challenging environmental justice issues, and so principles and methods for addressing them are needed (Moran 2007, 2010, Perreault et al. 2012, Platt 2006). Drawing on the concepts of collaborative learning models and coproduction of knowledge, the authors developed a process for community input for urban community waterway revitalization

LineStacker: A spectral line stacking tool for interferometric data

LineStacker is a new open access and open source tool for stacking of spectral lines in interferometric data. LineStacker is an ensemble of CASA tasks, and can stack both 3D cubes or already extracted spectra. The algorithm is tested on increasingly complex simulated data sets, mimicking Atacama Large Millimeter/submillimeter Array and Karl G. Jansky Very Large Array observations of [CII] and CO(3-2) emission lines, from $z\sim7$ and $z\sim4$ galaxies respectively. We find that the algorithm is very robust, successfully retrieving the input parameters of the stacked lines in all cases with an accuracy $\gtrsim90$\%. However, we distinguish some specific situations showcasing the intrinsic limitations of the method. Mainly that high uncertainties on the redshifts ($\Delta z > 0.01$) can lead to poor signal to noise ratio improvement, due to lines being stacked on shifted central frequencies. Additionally we give an extensive description of the embedded statistical tools included in LineStacker: mainly bootstrapping, rebinning and subsampling. Velocity rebinning {is applied on the data before stacking and} proves necessary when studying line profiles, in order to avoid artificial spectral features in the stack. Subsampling is useful to sort the stacked sources, allowing to find a subsample maximizing the searched parameters, while bootstrapping allows to detect inhomogeneities in the stacked sample. LineStacker is a useful tool for extracting the most from spectral observations of various types.Comment: Resubmitted to MNRAS after referee repor

Diffractive arrays of gold nanoparticles near an interface: critical role of the substrate

The optical properties of periodic arrays of plasmonic nanoantennas are strongly affected by coherent multiple scattering in the plane of the array, which leads to sharp spectral resonances in both transmission and reflection when the wavelength is commensurate with the period. We demonstrate that the presence of a substrate (i.e., an asymmetric refractive-index environment) can inhibit long-range coupling between the particles and suppress lattice resonances, in agreement with recent experimental results. We find the substrate-to-superstrate index contrast and the distance between the array and the interface to be critical parameters determining the strength of diffractive coupling. Our rigorous electromagnetic simulations are well reproduced by a simple analytical model. These findings are important in the design of periodic structures and in the assessment of their optical resonances for potential use in sensing and other photonic technologies

Duality and ontology

A ‘duality’ is a formal mapping between the spaces of solutions of two empirically equivalent theories. In recent times, dualities have been found to be pervasive in string theory and quantum field theory. Naïvely interpreted, duality-related theories appear to make very different ontological claims about the world—differing in e.g. space-time structure, fundamental ontology, and mereological structure. In light of this, duality-related theories raise questions familiar from discussions of underdetermination in the philosophy of science: in the presence of dual theories, what is one to say about the ontology of the world? In this paper, we undertake a comprehensive and non-technical survey of the landscape of possible ontological interpretations of duality-related theories. We provide a significantly enriched and clarified taxonomy of options—several of which are novel to the literature

Teaching computational reproducibility for neuroimaging

We describe a project-based introduction to reproducible and collaborative neuroimaging analysis. Traditional teaching on neuroimaging usually consists of a series of lectures that emphasize the big picture rather than the foundations on which the techniques are based. The lectures are often paired with practical workshops in which students run imaging analyses using the graphical interface of specific neuroimaging software packages. Our experience suggests that this combination leaves the student with a superficial understanding of the underlying ideas, and an informal, inefficient, and inaccurate approach to analysis. To address these problems, we based our course around a substantial open-ended group project. This allowed us to teach: (a) computational tools to ensure computationally reproducible work, such as the Unix command line, structured code, version control, automated testing, and code review and (b) a clear understanding of the statistical techniques used for a basic analysis of a single run in an MRI scanner. The emphasis we put on the group project showed the importance of standard computational tools for accuracy, efficiency, and collaboration. The projects were broadly successful in engaging students in working reproducibly on real scientific questions. We propose that a course on this model should be the foundation for future programs in neuroimaging. We believe it will also serve as a model for teaching efficient and reproducible research in other fields of computational science