Einstein supergravity amplitudes from twistor-string theory

This paper gives a twistor-string formulation for all tree amplitudes of Einstein (super-)gravities for N=0 and 4. Formulae are given with and without cosmological constant and with various possibilities for the gauging. The formulae are justified by use of Maldacena's observation that conformal gravity tree amplitudes with Einstein wave functions and non-zero cosmological constant will correctly give the Einstein tree amplitudes. This justifies the construction of Einstein gravity amplitudes at N=0 from twistor-string theory and is extended to N=4 by requiring the standard relation between the MHV-degree and the degree of the rational curve for Yang-Mills; this systematically excludes the spurious conformal supergravity gravity contributions. For comparison, BCFW recursion is used to obtain twistor-string-like formulae at degree zero and one (anti-MHV and MHV) for amplitudes with N=8 supersymmetry with and without cosmological constant.Comment: 20 pages. v2: minor corrections & clarification of relation to formulae of Maldacena & Pimentel and Raju; v3: appendix on BCFW recursion added, published version. v4: Full derivation for 3 point MHV amplitude now include

Fast, accurate, and transferable many-body interatomic potentials by symbolic regression

The length and time scales of atomistic simulations are limited by the computational cost of the methods used to predict material properties. In recent years there has been great progress in the use of machine learning algorithms to develop fast and accurate interatomic potential models, but it remains a challenge to develop models that generalize well and are fast enough to be used at extreme time and length scales. To address this challenge, we have developed a machine learning algorithm based on symbolic regression in the form of genetic programming that is capable of discovering accurate, computationally efficient manybody potential models. The key to our approach is to explore a hypothesis space of models based on fundamental physical principles and select models within this hypothesis space based on their accuracy, speed, and simplicity. The focus on simplicity reduces the risk of overfitting the training data and increases the chances of discovering a model that generalizes well. Our algorithm was validated by rediscovering an exact Lennard-Jones potential and a Sutton Chen embedded atom method potential from training data generated using these models. By using training data generated from density functional theory calculations, we found potential models for elemental copper that are simple, as fast as embedded atom models, and capable of accurately predicting properties outside of their training set. Our approach requires relatively small sets of training data, making it possible to generate training data using highly accurate methods at a reasonable computational cost. We present our approach, the forms of the discovered models, and assessments of their transferability, accuracy and speed

Tidal and marine energy in the uk– identifying the future challenges for supply chain development

The purpose of this paper is to investigate the current technical and operational supply chain issues surrounding the development of tidal and marine energy production in the UK. The paper outlines the market and growth potential of tidal energy production in the UK before identifying the key supply chain themes surrounding tidal energy production including an analysis of the portability and transferability of current supply chain thinking and development from other renewable energy systems such as wind turbine technology towards the development of tidal energy supply chain systems. The paper closes by identifying the major challenges that the UK supply chain must overcome in order to develop a comprehensive and robust supply chain system

The development of marine energy extraction

Accompanied with an increase in world population there is a growing demand for energy from both the industrial and domestic sectors [...

Celestial amplitudes and conformal soft theorems

Scattering amplitudes in $d+2$ dimensions can be expressed in terms of a conformal basis, for which the S-matrix behaves as a CFT correlation function on the celestial $d$-sphere. We explain how compact expressions for the full tree-level S-matrix of gauge theory, gravity and other QFTs extend to this conformal basis, and are easily derived from ambitwistor strings. Using these formulae and their worldsheet origins, we prove various tree-level 'conformal soft theorems' in gauge theory and gravity in any dimension; these arise from limits where the scaling dimension of an external state in the scattering process takes special values. These conformally soft limits are obscure from standard methods, but they are easily derived with ambitwistor strings. Additionally, we make an identification between the residues of conformally soft vertex operator insertions in ambitwistor strings and charges generating asymptotic symmetries.Comment: 18+6 pages, no figures. v2: typos corrected; v3: published versio

MHV scattering of gluons and gravitons in chiral strong fields

We present all-multiplicity formulae for the tree-level scattering of gluons and gravitons in the maximal helicity violating (MHV) helicity configuration, calculated in certain chiral strong fields. The strong backgrounds we consider are self-dual plane waves in gauge theory and general relativity, which are treated exactly and admit a well-defined S-matrix. The gauge theory background-coupled MHV amplitude is simply a dressed analogue of the familiar Parke-Taylor formula, but the gravitational version has non-trivial new structures due to graviton tails. Both formulae have just one residual integral rather than the $n-2$ expected at $n$-points from space-time perturbation theory; this simplification arises from the integrability of self-dual backgrounds and their corresponding twistor description. The resulting formulae pass several consistency checks and limit to the well-known expressions for MHV scattering of gluons and gravitons when the background becomes trivial.Comment: 7 pages, no figures. v2: published versio

The Evolution of Chinese Shopping Mall: An exploration on socio-spatial changes in Chinese shopping malls over 20 years

The rapid development of China has led to a transformation of its economic culture from traditional production to consumption. As the carrier of consumer behaviour, shopping malls present a rising trend in containing social activities in modern Chinese society, which see a functional evaluation towards mega, complex and clustering. This study focuses on the dynamic changes in the socio-spatial characteristics of Chinese shopping malls with a time-based reference, asking: what are the differences between the spatial layouts and behavioural patterns of shopping malls built in different periods? To what extent do these differences reflect the Chinese cultural and economic transformation? Does the spatial design make a difference to how the malls adapt to the contemporary consumer environment? The aim of this paper is to provide an evidence-based reference for the future spatial design of Chinese shopping malls. Based in Changsha, a Chinese central-south provincial city, this study investigates three shopping malls located in the city’s central business district (CBD) that are built in different periods from 1998 to 2016. These are Heiwado Mall, Hisense Plaza and ID Mall. Building on the graph theory in the field of retail research, this study conducts cross-comparison between the chosen malls to systemically examine the spatial/cultural changes over 20 years, including the analysis of spatial layout and on-site observation. The study suggests that understanding the target customer group and accordingly balancing the relationship between space and content are important factors for the successful operation of Chinese shopping malls. The conflict between spatial design and consumer orientation is argued to reduce the commercial value of shopping malls regardless of their advanced spatial design

Application Virtualization utilizing Microsoft System Center Configuration Manager (SCCM)

The National Air and Space Intelligence Center (NASIC) is the Department of Defense’s (DOD) primary source for intelligence on foreign air and space threats. Supporting the NASIC mission is the Communications & Information (SC) directorate. To continue to support the mission, SC has made the decision to explore virtual applications to create a more dynamic and flexible application deployment model that focuses on delivering end users applications quicker and more efficiently. To better understand the benefits of virtual applications the team established a Proof of Concept (PoC) and implemented Microsoft\u27s Application Virtualization (App-V) solution, as well as, reviewed the integration of App-V with the current software deployment solution, Microsoft System Center Configuration Manager (SCCM)