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

Elucidating the Polymorphism of Xanthone: A Crystallization and Characterization Study

The aim of this work is to shed light on the polymorphism of xanthones, a class of oxygenated molecules well known for their bioactivity, including antioxidant, anticancer, and anti-inflammatory effects. Understanding the polymorphism of xanthones can enable the design of novel solid products for pharmaceutical, nutraceutical, and agrochemical applications. Prior to this work, two entries accounting for different space groups were deposited for 9-xanthone in the Cambridge Structure Database (CSD): an orthorhombic P2(1)2(1)2(1) and a monoclinic P2(1) structure solved at room and low temperatures, respectively. However, the very high similarity between these two structures and the lack of clear differences in their physical properties (e.g., thermal behavior) suggested the possibility of the existence of only one crystal structure. In fact, the differences shown in the literature data might be related to the chosen operating parameters, as well as the instrumental resolution of the single-crystal X-ray diffraction experiments. In the work presented here, the ambiguity in the polymorphism of xanthone is investigated using thermal analysis, powder and synchrotron single-crystal XRD, and optical microscopy. Additionally, a workflow for the correct identification of twinned crystal structures, which can be applied to other polymorphic systems, is presented. Such workflow combines the collection of a large data set of high-resolution diffraction patterns using synchrotron radiation with the use of principal component analysis, a dimensionality reduction technique, for a quick and effective identification of phase transitions happening during the data collection. Crystallization experiments were designed to promote the formation of different crystal structures of xanthone that were recrystallized based on past literature and beyond

It takes two to tango:High Rates of Injury and Concussion in Ball Carriers and Tacklers in High School Boys' Rugby

Objective: To examine injury and concussion rates, mechanisms, locations, and types of injury in Canadian high school male rugby.Design:Prospective cohort study.Setting:High school male rugby.Participants:A total of 429 high school players (2018: n = 225, 2019: n = 256) were recruited from 12 teams in 7 schools in Calgary, Canada.Interventions: None.Main Outcome Measures: Injury surveillance included baseline questionnaires, weekly exposure, and injury reports. Injuries included those requiring medical attention, resulted in time loss and/or inability to complete a session. Concussion was defined as per the fifth Consensus on Concussion in Sport, and all players with a suspected concussion were referred to a study sport medicine physician.Results: A total of 134 injuries were captured, leading to an injury incidence rate (IR) of 57.9/1000 hours [95% confidence intervals (CIs): 45.4-73.8]. Median time loss was 6 days (range: 0-90). Injuries to the head were the most common (40%), followed by shoulder (12%) and ankle (10%). The concussion IR was 22.0/1000 hours (95% CIs: 15.9-30.4), which was the most common injury type (38%), followed by sprain (20%) and strain (15%). Sixty-five percent of injuries occurred in the tackle (ball carrier 35%, tackler 30%) and 76% of concussions (ball carrier 41%, tackler 35%).Conclusions: The rate of injury and concussion in Canadian youth high school male rugby is high, with tackle-related injuries and concussions the most common. Given this, there is a critical need for implementation of prevention strategies, in particular targeting concussion and the tackle event (eg, neuromuscular, tackle training, and law changes).</p

It takes two to tango:High Rates of Injury and Concussion in Ball Carriers and Tacklers in High School Boys' Rugby

Objective: To examine injury and concussion rates, mechanisms, locations, and types of injury in Canadian high school male rugby.Design:Prospective cohort study.Setting:High school male rugby.Participants:A total of 429 high school players (2018: n = 225, 2019: n = 256) were recruited from 12 teams in 7 schools in Calgary, Canada.Interventions: None.Main Outcome Measures: Injury surveillance included baseline questionnaires, weekly exposure, and injury reports. Injuries included those requiring medical attention, resulted in time loss and/or inability to complete a session. Concussion was defined as per the fifth Consensus on Concussion in Sport, and all players with a suspected concussion were referred to a study sport medicine physician.Results: A total of 134 injuries were captured, leading to an injury incidence rate (IR) of 57.9/1000 hours [95% confidence intervals (CIs): 45.4-73.8]. Median time loss was 6 days (range: 0-90). Injuries to the head were the most common (40%), followed by shoulder (12%) and ankle (10%). The concussion IR was 22.0/1000 hours (95% CIs: 15.9-30.4), which was the most common injury type (38%), followed by sprain (20%) and strain (15%). Sixty-five percent of injuries occurred in the tackle (ball carrier 35%, tackler 30%) and 76% of concussions (ball carrier 41%, tackler 35%).Conclusions: The rate of injury and concussion in Canadian youth high school male rugby is high, with tackle-related injuries and concussions the most common. Given this, there is a critical need for implementation of prevention strategies, in particular targeting concussion and the tackle event (eg, neuromuscular, tackle training, and law changes).</p

Injuries and concussions in Female High School Rugby:Prevention is worth a try

Objectives: To describe injury and concussion rates and mechanisms in female high school rugby players.Design:Two-year prospective cohort study.Setting:High school rugby.Participants: Participants included 214 female High school rugby players (year 1) and 207 female High school players (year 2) from the Calgary Senior High School Athletics Association 2018 and 2019 rugby competition.Intervention: None.Main Outcome Measures: Match and training injury and concussion. Injury definition included any injury resulting in time loss, inability to complete a session, and/or requiring medical attention. Details of reported injuries were collected on injury report forms and validated by a certified athletic therapist on a validated online injury surveillance platform. Exposure hours for players were tracked using paper or virtual weekly exposure forms by team designates.Results: A match incidence rate (IR) = 93.7 injuries/1000 match hours (95% confidence intervals (CI): 78.6-11.7) and training IR = 5.3 injuries/1000 training hours (95% CI: 4.0-6.9) were estimated. The tackle accounted for 109 (70%) match and 37 (44%) training injuries. Tackling was the most frequent mechanism of injury (IR = 37.5 injuries/1000 match hours, 95% CI: 27.5-51.8 and 1.2 injuries/1000 training hours, 95% CI: 0.7-2.4). Sixty-two match concussions (IR = 37.5 concussions/1000 match hours, 95% CI: 26.8-52.3) and 16 training concussions (IR = 1.0 concussions/1000 training hours, 95% CI: 0.7-1.4) occurred. Of 78 reported concussions, 78% for match and 56% for training were physician diagnosed. Tackling was the most frequent mechanism of concussion in matches (IR = 18.1 concussions/1000 match hours, 95% CI:11.4-28.6).Conclusions: Injury and concussion rates in female high school rugby are high. The tackle accounted for the highest proportion of injuries. Prevention strategies (eg, tackle policy change, tackle-training programs, and neuromuscular training) should be explored to increase sport safety.</p

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