Massless Particles in Arbitrary Dimensions

Various properties of two kinds of massless representations of the n-conformal (or (n+1)-De Sitter) group $\tilde{G}_n=\widetilde{SO}_0(2,n)$ are investigated for $n\ge2$. It is found that, for space-time dimensions $n\ge3$, the situation is quite similar to the one of the n=4 case for $S_n$-massless representations of the n-De Sitter group $\widetilde{SO}_0(2,n-1)$. These representations are the restrictions of the singletons of $\tilde{G}_n$. The main difference is that they are not contained in the tensor product of two UIRs with the same sign of energy when n>4, whereas it is the case for another kind of massless representation. Finally some examples of Gupta-Bleuler triplets are given for arbitrary spin and $n\ge3$.Comment: 33 pages, LaTeX2e. To be published in Reviews in Math. Phy

Magnetic flux transfer in the 5 April 2010 Galaxy 15 substorm: an unprecedented observation

At approximately 08:25 UT on 5 April 2010, a CME-driven shock compressed Earth's magnetosphere and applied about 15 nT of southward IMF for nearly an hour. A substorm growth phase and localized dipolarization at 08:47 UT were followed by large dipolarizations at 09:03 UT and 09:08 UT, observed by GOES West (11) in the midnight sector, and by three THEMIS spacecraft near X=−11, Y=−2 RE. A large electric field at the THEMIS spacecraft indicates so much flux transfer to the inner magnetosphere that "overdipolarization" took place at GOES 11. This transfer is consistent with the ground and space magnetic signature of the substorm current wedge. Significant particle injections were also observed. The ensemble of extreme geophysical conditions, never previously observed, is consistent with the Near-Earth Neutral Line interpretation of substorms, and subjected the Galaxy 15 geosynchronous satellite to space weather conditions which appear to have induced a major operational anomaly

Modelling Virtual Sensors for Indoor Environments with Machine Learning

Virtual Sensors model the sensing operation of physical sensors deployed in an area of interest by generating sensory data with accuracy and precision close to those collected by physical sensors. Their use in applications such as augmenting the infrastructure of IoT facilities and test beds, monitoring and calibrating the operation of physical sensors, and developing Digital Twins of physical systems have led virtual sensors to attract research attention. Machine learning provides methods for modelling patterns in complex and big data generated by IoT sensing devices, allowing to model the behaviour of these devices. In this work, we investigate ML methods as means of implementation for virtual sensors. In particular, we evaluate the performance of six ML methods in terms of their effectiveness, accuracy and precision in generating sensory data based on data from physical sensors. In our study, we use a multi-modal dataset comprising IoT sensory data for temperature, humidity and illumination collected over a period of two years in an office space at University of Geneva. Our results show that the best performing model at predicting an output of a missing sensor is the Random Forest method, achieving MAPE error below 3%, 5% and 18% respectively for temperature, humidity and illuminance. The worst performing models were the linear radial basis function neural network and linear regression. In future research, we plan to deploy the best performing models natively on IoT devices, making use of tinyML and extreme edge computing methods

On the formation of tilted flux ropes in the Earth's magnetotail observed with ARTEMIS

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95540/1/jgra21806.pd

Inter-social-networking: Accounting for multiple identities

We argue that the current approaches to online social networking give rise to numerous challenges regarding the management of the multiple facets of people’s digital identities within and around social networking sites (SNS). We propose an architecture for enabling people to better manage their SNS identities that is informed by the way the core Internet protocols developed to support interoperation of proprietary network protocols, and based on the idea of Separation of Concerns [1]. This does not require modification of existing services but is predicated on providing a connecting layer over them, both as a mechanism to address problems of privacy and identity, and to create opportunities to open up online social networking to a much richer set of possible interactions and applications.This work is supported by Horizon Digital Economy Research, RCUK grant EP/G065802/1; and by CREATe, the Centre for Copyright and New Business Models, RCUK grant AH/K000179/1. Packages and source are available under open source licenses at github.com/CREATe-centre/.This is the author accepted manuscript. The final version is available from Springer via http://dx.doi.org/10.1007/978-3-319-20367-6_2

Matter effects in the D0-D0bar system

We discuss the impact of matter effects in the D0-D0bar system. We show that such effects could, in principle, be measured, but that they cannot be used to probe the mass difference x_D or the lifetime difference y_D. This occurs because the mixing effects and the matter effects decouple at short times. We also comment briefly on the B systems.Comment: 6 pages, RevTe

Anti de Sitter Holography via Sekiguchi Decomposition

In the present paper we start consideration of anti de Sitter holography in the general case of the (q+1)-dimensional anti de Sitter bulk with boundary q-dimensional Minkowski space-time. We present the group-theoretic foundations that are necessary in our approach. Comparing what is done for q=3 the new element in the present paper is the presentation of the bulk space as the homogeneous space G/H = SO(q,2)/SO(q,1), which homogeneous space was studied by Sekiguchi.Comment: 10 pages, to appear in the Proceedings of the XI International Workshop "Lie Theory and Its Applications in Physics", (Varna, Bulgaria, June 2015