1,751 research outputs found
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 dimensions can be expressed in terms of a
conformal basis, for which the S-matrix behaves as a CFT correlation function
on the celestial -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 expected at -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
Changing modalities in international development and research in education:Conceptual and ethical issues
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)
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