A light-cone gauge for black-hole perturbation theory

The geometrical meaning of the Eddington-Finkelstein coordinates of Schwarzschild spacetime is well understood: (i) the advanced-time coordinate v is constant on incoming light cones that converge toward r=0, (ii) the angles theta and phi are constant on the null generators of each light cone, (iii) the radial coordinate r is an affine-parameter distance along each generator, and (iv) r is an areal radius, in the sense that 4 pi r^2 is the area of each two-surface (v,r) = constant. The light-cone gauge of black-hole perturbation theory, which is formulated in this paper, places conditions on a perturbation of the Schwarzschild metric that ensure that properties (i)--(iii) of the coordinates are preserved in the perturbed spacetime. Property (iv) is lost in general, but it is retained in exceptional situations that are identified in this paper. Unlike other popular choices of gauge, the light-cone gauge produces a perturbed metric that is expressed in a meaningful coordinate system; this is a considerable asset that greatly facilitates the task of extracting physical consequences. We illustrate the use of the light-cone gauge by calculating the metric of a black hole immersed in a uniform magnetic field. We construct a three-parameter family of solutions to the perturbative Einstein-Maxwell equations and argue that it is applicable to a broader range of physical situations than the exact, two-parameter Schwarzschild-Melvin family.Comment: 12 page

Light-cone coordinates based at a geodesic world line

Continuing work initiated in an earlier publication [Phys. Rev. D 69, 084007 (2004)], we construct a system of light-cone coordinates based at a geodesic world line of an arbitrary curved spacetime. The construction involves (i) an advanced-time or a retarded-time coordinate that labels past or future light cones centered on the world line, (ii) a radial coordinate that is an affine parameter on the null generators of these light cones, and (iii) angular coordinates that are constant on each generator. The spacetime metric is calculated in the light-cone coordinates, and it is expressed as an expansion in powers of the radial coordinate in terms of the irreducible components of the Riemann tensor evaluated on the world line. The formalism is illustrated in two simple applications, the first involving a comoving world line of a spatially-flat cosmology, the other featuring an observer placed on the axis of symmetry of Melvin's magnetic universe.Comment: 11 pages, 1 figur

Speakur : leveraging web components for composable applications

textThis report is a case study of applying abstraction, encapsulation, and composition techniques to web application architecture with the use of Web Components, a proposed extension to the HTML5 Document Object Model. I created Speakur, a real-time social discussion plugin for the mobile and desktop web, to show how Web Components can help realize software engineering principles and design patterns, including the composition of applications from components sourced from diverse authors and frameworks. Web authors can add a Speakur discussion to their page by inserting a simple HTML element at the desired spot to give the page a real-time discussion or feedback system. Speakur uses the Polymer framework's implementation of the draft Web Components standard to achieve the encapsulation of its internal implementation details from the containing page behind a simplified, well defined interface. Web Components are a proposed W3C standard for writing custom HTML tags that take advantage of new browser technologies like Shadow DOM, package importing, CSS Flexboxes and data-bound templates. This report reviews Web Components and related technologies and provides a case study for structuring a real-world WC applet that is embedded in a larger app or system. The major research question is whether Web Components offer a viable path towards the encapsulation and composition principles that have largely eluded web engineers thus far. In other words, are components really the future of the web? Subsidiary topics include assessing the maturity and performance of current Web Components technologies, and methods of synchronization between user interface components and local and remote data models. My analysis shows that Web Components successfully address many of the key structural and organizational problems faced by web software engineers.Electrical and Computer Engineerin

Your Journey to First-Year Success: A K-State First Companion Textbook

This textbook companion is a resource to help students successfully navigate through their first year at Kansas State University. It serves as part of the K-State First mission to create an outstanding university experience for every first-year student by helping with the transition to college-level learning and college life. The textbook helps improve chances for student success by focusing on fostering campus community, offering resources for diverse activities, highlighting academic expectations, and empowering students with personal responsibility and social agency. Instructors are encouraged to use the textbook in their K-State First classes, and it is also offered as a direct resource for students. In any university setting there are often unwritten rules that students are expected to understand, and this guide addresses and answers those questions directly. Ultimately, this guide encourages students to be engaged learners and to enjoy all facets of education, both inside and outside the classroom.https://newprairiepress.org/ebooks/1019/thumbnail.jp

Blogging about Family Building (Infertility, Pregnancy Loss, Adoption, Pregnancy, Trying to Conceive): Content and Blogging Motivations

To better understand the content and process of family building blogging, two interrelated studies took place. First, blogs with posts during a designated week were analyzed for content. Then, hosts of active blogs were invited to complete a survey on their blog content and reasons for blogging. Results of both content analysis and survey indicated a variety of content appearing in such blogs, with children, pregnancy, attempts to conceive, and negative emotional experiences related to those emerging as popular topics. To identify motivations for blogging about such content, a principal components analysis (PCA) suggested seven different blogging motivations: gaining attention, benefitting others, becoming a career blogger, entertaining others, documenting life events, self-expression, and forming an online social support network. To further explore blogging motivations, subgroups of bloggers (those having experienced infertility, those having experienced pregnancy loss, and those already parenting) were compared on their ratings of the seven blogging motivations with multivariate analysis of variance (MANOVA). While results mostly supported consistency across subgroups in motivations, there was a significant effect for infertility experience on ratings for educating others and self-expression. This investigation represents the first known attempt to capture what information is included in the growing subgenre of family building blogs and what reasons inspire bloggers to create and maintain them

Diverse Intestinal Bacteria Contain Putative Zwitterionic Capsular Polysaccharides with Anti-inflammatory Properties

Zwitterionic capsular polysaccharides (ZPSs) are bacterial products that modulate T cells, including inducing anti-inflammatory IL-10-secreting T regulatory cells (Tregs). However, only a few diverse bacteria are known to modulate the host immune system via ZPS. We present a genomic screen for bacteria encoding ZPS molecules. We identify diverse host-associated bacteria, including commensals and pathogens with known anti-inflammatory properties, with the capacity to produce ZPSs. Human mononuclear cells stimulated with lysates from putative ZPS-producing bacteria induce significantly greater IL-10 production and higher proportions of Tregs than lysates from non-ZPS-encoding relatives or a commensal strain of Bacteroides cellulosilyticus in which a putative ZPS biosynthetic operon was genetically disrupted. Similarly, wild-type B. cellulosilyticus DSM 14838, but not a close relative lacking a putative ZPS, attenuated experimental colitis in mice. Collectively, this screen identifies bacterial strains that may use ZPSs to interact with the host as well as those with potential probiotic properties

Autonomous tracking and sampling of the deep chlorophyll maximum layer in an open-ocean eddy by a long-range autonomous underwater vehicle

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Zhang, Y., Kieft, B., Hobson, B. W., Ryan, J. P., Barone, B., Preston, C. M., Roman, B., Raanan, B., Marin,Roman,,III, O'Reilly, T. C., Rueda, C. A., Pargett, D., Yamahara, K. M., Poulos, S., Romano, A., Foreman, G., Ramm, H., Wilson, S. T., DeLong, E. F., Karl, D. M., Birch, J. M., Bellingham, J. G., & Scholin, C. A. Autonomous tracking and sampling of the deep chlorophyll maximum layer in an open-ocean eddy by a long-range autonomous underwater vehicle. IEEE Journal of Oceanic Engineering, 45(4), (2020): 1308-1321, doi:10.1109/JOE.2019.2920217.Phytoplankton communities residing in the open ocean, the largest habitat on Earth, play a key role in global primary production. Through their influence on nutrient supply to the euphotic zone, open-ocean eddies impact the magnitude of primary production and its spatial and temporal distributions. It is important to gain a deeper understanding of the microbial ecology of marine ecosystems under the influence of eddy physics with the aid of advanced technologies. In March and April 2018, we deployed autonomous underwater and surface vehicles in a cyclonic eddy in the North Pacific Subtropical Gyre to investigate the variability of the microbial community in the deep chlorophyll maximum (DCM) layer. One long-range autonomous underwater vehicle (LRAUV) carrying a third-generation Environmental Sample Processor (3G-ESP) autonomously tracked and sampled the DCM layer for four days without surfacing. The sampling LRAUV's vertical position in the DCM layer was maintained by locking onto the isotherm corresponding to the chlorophyll peak. The vehicle ran on tight circles while drifting with the eddy current. This mode of operation enabled a quasi-Lagrangian time series focused on sampling the temporal variation of the DCM population. A companion LRAUV surveyed a cylindrical volume around the sampling LRAUV to monitor spatial and temporal variation in contextual water column properties. The simultaneous sampling and mapping enabled observation of DCM microbial community in its natural frame of reference.10.13039/501100008982 - National Science Foundation 10.13039/100000936 - Gordon and Betty Moore Foundation 10.13039/100000008 - David and Lucile Packard Foundation 10.13039/100016377 - Schmidt Ocean Institute 10.13039/100000893 - Simons Foundatio

Autonomous Application of Quantitative PCR in the Deep Sea: In Situ Surveys of Aerobic Methanotrophs Using the Deep-Sea Environmental Sample Processor

Recent advances in ocean observing systems and genomic technologies have led to the development of the deep-sea environmental sample processor (D-ESP). The DESP filters particulates from seawater at depths up to 4000 m and applies a variety of molecular assays to the particulates, including quantitative PCR (qPCR), to identify particular organisms and genes in situ. Preserved samples enable laboratory-based validation of in situ results and expanded studies of genomic diversity and gene expression. Tests of the D-ESP at a methane-rich mound in the Santa Monica Basin centered on detection of 16S rRNA and particulate methane monooxygenase (pmoA) genes for two putative aerobic methanotrophs. Comparison of in situ qPCR results with laboratory-based assays of preserved samples demonstrates the D-ESP generated high-quality qPCR data while operating autonomously on the seafloor. Levels of 16S rRNA and pmoA cDNA detected in preserved samples are consistent with an active community of aerobic methanotrophs near the methane-rich mound. These findings are substantiated at low methane sites off Point Conception and in Monterey Bay where target genes are at or below detection limits. Successful deployment of the D-ESP is a major step toward developing autonomous systems to facilitate a wide range of marine microbiological investigations