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At least 451 records · Page 25

String Phenomenology 2017 (Conference)

The sixteenth annual International conference in the String Phenomenology series was held at Virginia Tech, Blacksburg on July 3rd - 7th 2017. String Phenomenology 2017 was organized by Professor Lara Anderson and Professor James Gray, with help from two postdoctoral fellows, Seung-Joo Lee and Xin Gao and Professors Eric Sharpe and Djordje Minic. The scientific program was chosen broadly from within the discipline of string phenomenology and related areas of mathematics and physics. Thus, the conference brought together researchers from a wide variety of related fields in order to discuss progress in relating string compactifications to low energy physics and stimulate future developments in such directions. This report summarizes the outcome of the conference.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Mixed gases in compressed cylinders: some popular misconceptions and explanations

Many industrial applications and scientific investigations require gaseous premixes. These are generally available in compressed gas cylinders from commercial vendors. Despite many decades of working knowledge with compressed premixed gases, various individuals from the production plants have expressed concerns regarding the ability of the gases to remain mixed in storage and delivery. In this brief tutorial, we show the mathematics and physics that underwrite our confidence in the use of premixed gases as we explain the following: The conditions in which separation of gases due to gravity is of practical concern; The conditions for preferential extraction of lighter gases from premixed gas tank; The time length necessary for homogeneous mixing of gases by molecular kinetics.

36 MATERIALS SCIENCE↗

Data-Driven Specification of Earth's Magnetic Field

As our society is increasingly dependent on technologies in space, predicting space weather becomes ever more important. We have come to rely on technologies such as cellphones, GPS, the Internet, and other commercial and military assets. In order to protect these systems a high priority is to develop better understanding of the harmful conditions of space weather encountered in the near-Earth radiation environment which are mostly dictated by the dynamics of energetic charged particles. The main objective of our proposal was to improve the specification and forecast of the particle distribution in the Earth’s inner magnetosphere using data assimilation together with machine learning (ML) algorithms in our ring current-atmosphere interactions model with self-consistent magnetic and electric fields (RAM-SCBE). Specifically, we explored the application of machine learning algorithms to emulate and improve, through infusion of observational data, the magnetic field (SCBE) of our ring current model. Our work advanced towards the characterization of the RAM-SCBE particle flux field and its potentially different simulation scenarios. We explored how the model behaves in a number of simulation scenarios in order to better understand how the model reacts to perturbations in the solar wind. We were able to capture this behavior through the simulation of an ensemble of RAM-SCB model solutions. The ensemble showed the important correlations between the particle fluxes and the magnetic field. We were able to start the training of a neural network (Autoencoder) to identify the dominant features of the magnetic field, and the main correlations (linear and non-linear) between the particle fluxes and the magnetic field. Our next steps consists of training a neural network to capture the time evolution of the dominant features and obtain a consistent surrogate model for the RAM-SCB.

42 ENGINEERING↗

Radiation Belt Remediation: A Complex Engineered System (RBR-ACES) (Institutional Computing Report)

We have performed the simulation campaigns in support of LDRD-DR project Radiation Belt Remediation: A Complex Engineered System (RBR-ACES). This project involves modeling wave generation and wave propagation in plasma environment and studying the effect of waves on the distribution of high energy electrons with the focus on electrons appeared after a high-altitude nuclear explosion (HANE). One of the major goal of this research is strong validation of the numerical models with laboratory experiments and space-based experiments and observations.

42 ENGINEERING↗

Sun's Series via Cyclotomic Multiple Zeta Values

We prove and generalize several recent conjectures of Z.-W. Sun surrounding binomial coefficients and harmonic numbers. We show that Sun's series and their analogs can be represented as cyclotomic multiple zeta values of levels N ϵ {4,8,12,16,24} , namely Goncharov's multiple polylogarithms evaluated at N -th roots of unity.

97 MATHEMATICS AND COMPUTING↗

ANALYTIC PROPERTIES OF FORCE-FREE JETS IN THE KERR SPACETIME—II

We reinvestigate the structure of a steady axisymmetric force-free magnetosphere around a Kerr black hole (BH). The BH magnetosphere structure is governed by a second-order differential equation of A{sub ϕ} depending on two “free” functions Ω and I, where A{sub ϕ} is the ϕ component of the vector potential of the electromagnetic field, Ω is the angular velocity of the magnetic field lines, and I is the poloidal electric current. While the two functions Ω and I are not arbitrarily given, they do need to be self-consistently determined along with the differential equation. Based on the perturbation approach we proposed in paper I, in this paper, we self-consistently sort out two boundary conditions governing Ω and I, and interpret these conditions mathematically and physically. Making use of the boundary conditions, we prove that all magnetic field lines crossing the infinite-redshift surface also penetrate the event horizon. Furthermore, we argue that the BH Meissner effect does not work in a force-free magnetosphere due to the perfect conductivity.

79 ASTRONOMY AND ASTROPHYSICS↗

Super-localisation of a point-like emitter in a resonant environment: Correction of the mirage effect

In this paper, we show that it is possible to overcome one of the fundamental limitations of super-resolution microscopy: the necessity to be in an optically homogeneous environment. Using recent modal approximation results from [ 10 , 7 ], we show, as a proof of concept, that it is possible to recover the position of a single point-like emitter in a known resonant environment from far-field measurements, with a precision two orders of magnitude below the classical Rayleigh limit. The procedure does not involve solving any partial differential equation, is computationally light (optimisation in \begin{document}$ \mathbb{R}^d $\end{document} with \begin{document}$ d $\end{document} of the order of \begin{document}$ 10 $\end{document} ) and is therefore suited for the recovery of a very large number of single emitters.

Mathematics↗

Topological symmetry in quantum field theory

We introduce a definition and framework for internal topological symmetries in quantum field theory, including “noninvertible symmetries” and “categorical symmetries”. We outline a calculus of topological defects which takes advantage of well-developed theorems and techniques in topological field theory. Our discussion focuses on finite symmetries, and we give indications for a generalization to other symmetries. We treat quotients and quotient defects (often called “gauging” and “condensation defects”), finite electromagnetic duality, and duality defects, among other topics. We include an appendix on finite homotopy theories, which are often used to encode finite symmetries and for which computations can be carried out using methods of algebraic topology. Throughout we emphasize exposition and examples over a detailed technical treatment.

Mathematics↗

Quark Model of Leptons

Model in which leptons are deeply bound states of combinations of quarks and quirks

LEPTON↗