Symmetries of the Einstein Equations

Generalized symmetries of the Einstein equations are infinitesimal transformations of the spacetime metric that formally map solutions of the Einstein equations to other solutions. The infinitesimal generators of these symmetries are assumed to be local, \ie at a given spacetime point they are functions of the metric and an arbitrary but finite number of derivatives of the metric at the point. We classify all generalized symmetries of the vacuum Einstein equations in four spacetime dimensions and find that the only generalized symmetry transformations consist of: (i) constant scalings of the metric (ii) the infinitesimal action of generalized spacetime diffeomorphisms. Our results rule out a large class of possible ``observables'' for the gravitational field, and suggest that the vacuum Einstein equations are not integrable.Comment: 15 pages, FTG-114-USU, Plain Te

Keynote talk: Augmented, adaptive, accessible, and inclusive things

In this new age of the Internet of Things (IoT) people and things are increasingly immersed in a computing environment that is aimed to simplify and improve daily activities. The Web of Things (WoT) is near to become a W3C Recommendation with the aim to support semantic interoperability across IoT platforms by providing a common interaction model independent of the underlying protocols. In this talk, I will illustrate the main principles of the WoT paradigm and then I will discuss the issue of Accessibility. Following on from the WoT concept of Things as virtual representations of physical digital things and also non-digital things, I will introduce an approach where we envision an Adaptive Web of Things as a mean to increase accessibility and usability of real world objects. The idea is that through the virtualization of physical objects, even objects which are not natively accessible can be augmented to become accessible and inclusive if proper adaptations are performed in order to fit the user\u2019s needs

New Symbolic Tools for Differential Geometry, Gravitation, and Field Theory

DifferentialGeometry is a Maple software package which symbolically performs fundamental operations of calculus on manifolds, differential geometry, tensor calculus, Lie algebras, Lie groups, transformation groups, jet spaces, and the variational calculus. These capabilities, combined with dramatic recent improvements in symbolic approaches to solving algebraic and differential equations, have allowed for development of powerful new tools for solving research problems in gravitation and field theory. The purpose of this paper is to describe some of these new tools and present some advanced applications involving: Killing vector fields and isometry groups, Killing tensors and other tensorial invariants, algebraic classification of curvature, and symmetry reduction of field equations.Comment: 42 page

The origins of the Acheulean: past and present perspectives on a major transition in human evolution

The emergence of the Acheulean from the earlier Oldowan constitutes a major transition in human evolution, the theme of this special issue. This paper discusses the evidence for the origins of the Acheulean, a cornerstone in the history of human technology, from two perspectives; firstly, a review of the history of investigations on Acheulean research is presented. This approach introduces the evolution of theories throughout the development of the discipline, and reviews the way in which cumulative knowledge led to the prevalent explanatory framework for the emergence of the Acheulean. The second part presents the current state of the art in Acheulean origins research, and reviews the hard evidence for the appearance of this technology in Africa around 1.7 Ma, and its significance for the evolutionary history of Homo erectus. This article is part of the themed issue ‘Major transitions in human evolution’

Video augmentation to support video-based learning

Multimedia content and video-based learning are expected to take a central role in the post-pandemic world. Thus, providing new advanced interfaces and services that further exploit their potential becomes of paramount importance. A challenging area deals with developing intelligent visual interfaces that integrate the knowledge extracted from multimedia materials into educational applications. In this respect, we designed a web-based video player that is aimed to support video consumption by exploiting the knowledge extracted from the video in terms of concepts explained in the video and prerequisite relations between them. This knowledge is used to augment the video lesson through visual feedback methods. Specifically, in this paper we investigate the use of two types of visual feedback, i.e. an augmented transcript and a dynamic concept map (map of concept's flow), to improve video comprehension in the first-watch learning context. Our preliminary findings suggest that both the methods help the learner to focus on the relevant concepts and their related contents. The augmented transcript has an higher impact on immediate comprehension compared to the map of concepts' flow, even though the latter is expected to be more powerful to support other tasks such as exploration and in-depth analysis of the concepts in the video

SARS-CoV-2 in pets of infected family groups in a severely affected region in Spain

Purpose The COVID-19 pandemic has caused an unprecedented health crisis with devastating effects. Current evidence suggests that SARS-CoV-2 could have an animal origin. Many uncertainties about the behaviour of the virus still persist, and understanding all the keys of this epidemic requires an interdisciplinary One Health approach spanning the human and animal health sectors. The closest coexistence between people and animals occurs in large cities. This study aims to identify the epidemiology (infection rate, risk habits, etc...) and evolution of the disease in pets that have coexisted during the confinement with family groups affected by the disease in areas of high population density and high disease incidence, i.e. Madrid. Methods & Materials A network of veterinary clinics was created to provide sampling points for the pets. The family groups included both health workers from the collaborating hospitals and affected pet owners informed through the network of clinics. Results Epidemiological and clinical data were collected from 60 family groups and their pets. An epidemiological questionnaire and sample collection (oral and nasal swabs, faeces and blood) were carried out on each pet. The samples were analyzed by RRT-PCR and ELISA. Of the 55 pets analysed (17 cats and 38 dogs), 5 cats presented antibodies. This seroprevalence is in agreement with that shown by Patterson et al, 2020 in cats in Italy in highly affected areas. Conclusion This study intends to extend the knowledge of the epidemiology and evolution of the disease in pets

No New Symmetries of the Vacuum Einstein Equations

In this note we examine some recently proposed solutions of the linearized vacuum Einstein equations. We show that such solutions are {\it not} symmetries of the Einstein equations, because of a crucial integrability condition.Comment: 9 pages, Te