Space-time multiresolution approach to atomistic visualization

Time-varying three-dimensional positional atomistic data are rich in spatial and temporal information. The problem is to understand them. This work offers multiple approaches that enable such understanding. An interactive atomistic visualization system is developed integrating complex analyses with visualization to present the data on space-time multiresolution basis facilitating the information extraction and generate understanding. This work also shows the usefulness of such an integrated approach. The information obtained from the analyses represents the system at multiple length and time scales. Radial distribution function (RDF) provides a complete average spatial map of the distribution of the atoms in the system which is probed to explore the system at different length scales. Coordination environments and cluster structures are visualized to look at the short range structures. Rings are visualized to understand the medium range structure. Displacement data and covariance matrices are visualized to understand the dynamical behaviors. Combinations of rendering techniques including animation, color map, sphere, polygonal and ellipsoid representations, pathlines and glyphs are used during the visualization process. The three-dimensional atomic configurations are reproduced accurately during rendering because of their physical significance while attributes such as coordination number, coordination stability and atomic species lack direct physical relevance and provide additional flexibilities in rendering. The performance results show interactive frame rates are achievable for systems consisting upto a thousand atoms. Such systems are typical of the systems simulated using first principles molecular dynamics simulations. The effectiveness and the usefulness of this work are justified for complex material systems using silicate and oxide liquids for visual analyses. The exploratory approach taken here has not been reported anywhere else before. The major contributions of this works are: 1. A new approach to the atomistic visualization advocating a formal integration of data analyses into the visualization system to improve the effectiveness and also present an implementation of the exploratory atomistic visualization system with integrated spatio-temporal analytical techniques. 2. The modeling of coordination environments, stability of the coordination environments, clusters, ring structures and diffusion for individual atoms. 3. The use of the visualization system for visual analysis of various liquid mineral systems of geophysical relevance

Virtual Inertia: Current Trends and Future Directions

The modern power system is progressing from a synchronous machine-based system towards an inverter-dominated system, with large-scale penetration of renewable energy sources (RESs) like wind and photovoltaics. RES units today represent a major share of the generation, and the traditional approach of integrating them as grid following units can lead to frequency instability. Many researchers have pointed towards using inverters with virtual inertia control algorithms so that they appear as synchronous generators to the grid, maintaining and enhancing system stability. This paper presents a literature review of the current state-of-the-art of virtual inertia implementation techniques, and explores potential research directions and challenges. The major virtual inertia topologies are compared and classified. Through literature review and simulations of some selected topologies it has been shown that similar inertial response can be achieved by relating the parameters of these topologies through time constants and inertia constants, although the exact frequency dynamics may vary slightly. The suitability of a topology depends on system control architecture and desired level of detail in replication of the dynamics of synchronous generators. A discussion on the challenges and research directions points out several research needs, especially for systems level integration of virtual inertia systems

Probing the Inner Jet of the Quasar PKS 1510-089 with Multi-waveband Monitoring during Strong Gamma-ray Activity

We present results from monitoring the multi-waveband flux, linear polarization, and parsec-scale structure of the quasar PKS 1510-089, concentrating on eight major gamma-ray flares that occurred during the interval 2009.0-2009.5. The gamma-ray peaks were essentially simultaneous with maxima at optical wavelengths, although the flux ratio of the two wavebands varied by an order of magnitude. The optical polarization vector rotated by 720 degrees during a 5-day period encompassing six of these flares. This culminated in a very bright, roughly 1 day, optical and gamma-ray flare as a bright knot of emission passed through the highest-intensity, stationary feature (the "core") seen in 43 GHz Very Long Baseline Array images. The knot continued to propagate down the jet at an apparent speed of 22c and emit strongly at gamma-ray energies as a months-long X-ray/radio outburst intensified. We interpret these events as the result of the knot following a spiral path through a mainly toroidal magnetic field pattern in the acceleration and collimation zone of the jet, after which it passes through a standing shock in the 43 GHz core and then continues downstream. In this picture, the rapid gamma-ray flares result from scattering of infrared seed photons from a relatively slow sheath of the jet as well as from optical synchrotron radiation in the faster spine. The 2006-2009.7 radio and X-ray flux variations are correlated at very high significance; we conclude that the X-rays are mainly from inverse Compton scattering of infrared seed photons by 20-40 MeV electrons.Comment: 10 pages of text + 5 figures, to be published in Astrophysical Journal Letters in 201

Misinformation About COVID-19 in Sub-Saharan Africa: Evidence from a Cross-Sectional Survey

Misinformation about coronavirus disease 2019 (COVID-19) is a significant threat to global public health because it can inadvertently exacerbate public health challenges by promoting spread of the disease. This study used a convenience sampling technique to examine factors associated with misinformation about COVID-19 in sub-Saharan Africa using an online cross-sectional survey. A link to the online self-administered questionnaire was distributed to 1,969 participants through social media platforms and the authors' email networks. Four false statements—informed by results from a pilot study—were included in the survey. The participants' responses were classified as “Agree,” “Neutral,” and “Disagree.” A multinomial logistic regression was used to examine associated factors. Among those who responded to the survey, 19.3% believed that COVID-19 was designed to reduce world population, 22.2% thought the ability to hold your breath for 10 seconds meant that you do not have COVID-19, 27.8% believed drinking hot water flushes down the virus, and 13.9% thought that COVID-19 had little effect on Blacks compared with Whites. An average of 33.7% were unsure whether the 4 false statements were true. Multivariate analysis revealed that those who thought COVID-19 was unlikely to continue in their countries reported higher odds of believing in these 4 false statements. Other significant factors associated with belief in misinformation were age (older adults), employment status (unemployed), gender (female), education (bachelor's degree), and knowledge about the main clinical symptoms of COVID-19. Strategies to reduce the spread of false information about COVID-19 and other future pandemics should target these subpopulations, especially those with limited education. This will also enhance compliance with public health measures to reduce spread of further outbreaks

Application of Bessel beams in the human eye

Bessel light beams have spread-resistant and self-reconstruction properties. These beams were compared with conventional light beams for ophthalmic applications. The Bessel beams increased the strength of reflections used to determine ocular lens parameters, improved fixation stability, and decreased light loss during imaging of the retina. These findings indicate that Bessel beams have application in clinical ophthalmic instruments

Visualization of Atomistic Simulation Data for Spatio-Temporal Information

We have proposed a scheme to support interactive visualization at space-time multiresolution of the atomistic simulation data. In this scheme we have adopted two perspectives that differ in their purposes and in the way they process and render the data. First, the complete or nearly complete dataset is rendered using animation, particle-pathline and color-mapped-dimension techniques to achieve an overall idea of the spatio-temporal behavior of the atomic system under consideration. Second, additional data are generated on the fly and analyzed/visualized using a combined graph-theoretic and statistical approach to gain better and more detailed insight into the desired spatio-temporal information. It is also shown that the proposed approach can greatly assist us to better understand various important atomistic (molecular) properties and processes including bondbreaking/ reconstruction, radial distribution, atomic coordination, clustering, structural stability, defects and diffusion

Atomistic visualization: On-the-fly data extraction and rendering

In this paper, we present an approach involving on-the-fly data extraction and rendering to achieve a real-time integration between analysis and visualization of atomistic simulation data. The integration is demonstrated along two directions: The first direction is to explore coordination environments by rendering spatial variation and temporal stability of the coordination states computed for each atom, and the second direction is to explore the aggregate atomic movement by computing ellipsoids. Ellipsoids are computed from covariance matrices of the time-varying positional data. The proposed approach is applied to visualize the data from first-principles molecular dynamics simulations. © Copyright 2007 ACM