Kinetic properties of particle-in-cell simulations compromised by Monte Carlo collisions

he particle-in-cell method with Monte Carlo collisions is frequently used when a detailed kinetic simulation of a weakly collisional plasma is required. In such cases, one usually desires, inter alia, an accurate calculation of the particle distribution functions in velocity space. However, velocity space diffusion affects most, perhaps all, kinetic simulations to some degree, leading to numerical thermalization (i.e., relaxation of the velocity distribution toward a Maxwellian), and consequently distortion of the true velocity distribution functions, among other undesirable effects. The rate of such thermalization can be considered a figure of merit for kinetic simulations. This article shows that, contrary to previous assumption, the addition of Monte Carlo collisions to a one-dimensional particle-in-cell simulation seriously degrades certain properties of the simulation. In particular, the thermalization time can be reduced by as much as three orders of magnitude. This effect makes obtaining strictly converged simulation results difficult in many cases of practical interest

3-D seismic exploration for the Victorio Peak treasure

In January of 1994, we conducted an extensive seismic experiment to find caverns under Victorio Peak, a bioherm reef structure located approximately 80 miles northeast of Las Cruces, New Mexico. Within Victorio Peak there is reputed to be an extensive network of caverns, tunnels and fissures that contain a large and varied treasure consisting of gold bars, Spanish armor, jewels, coins, and human skeletons. We used an array of seismic sources that included a sledgehammer on the surface of the mountain, a sledgehammer impacting on the walls of two deep fissures within the mountain, as well as blasting caps located in boreholes drilled into the mountain. Approximately 2,000 source positions were recorded by 120 receiver channels consisting of geophones cemented into fissure walls and hydrophones deployed in a deep horizontal borehole drilled at the base of the mountain. The data analysis consisted of measuring reduced traveltime and amplitude of the direct arrival and isolating those source/receiver pairs that exhibited anomalously large direct arrival traveltimes and/or low amplitudes. We have currently identified and located a major amplitude anomaly under the peak that will be drilled and explored during the summer of 1994

A perspective on circular innovation: Dynamics, strategies, and implications

This is the author accepted manuscript. The final version is available from World Scientific Publishing via the DOI in this record This Letter considers the multifaceted realm of circular innovation, shedding light on its dynamics, strategic implications, and broader significance for sustainable development. By evaluating existing research and exploring examples across sectors, this work contributes to a deeper understanding of the role of circular innovation in transforming industries, economies, and societies. Although the topic has received increased interest in recent years, we find that there are notable gaps. While significant attention has been given to initial adoption and expansion, there is a lack of understanding regarding the enduring impacts on businesses and society. Further research addressing these gaps can enrich our understanding of the challenges and opportunities in this evolving field.University of Exete

Dual Computations of Non-abelian Yang-Mills on the Lattice

In the past several decades there have been a number of proposals for computing with dual forms of non-abelian Yang-Mills theories on the lattice. Motivated by the gauge-invariant, geometric picture offered by dual models and successful applications of duality in the U(1) case, we revisit the question of whether it is practical to perform numerical computation using non-abelian dual models. Specifically, we consider three-dimensional SU(2) pure Yang-Mills as an accessible yet non-trivial case in which the gauge group is non-abelian. Using methods developed recently in the context of spin foam quantum gravity, we derive an algorithm for efficiently computing the dual amplitude and describe Metropolis moves for sampling the dual ensemble. We relate our algorithms to prior work in non-abelian dual computations of Hari Dass and his collaborators, addressing several problems that have been left open. We report results of spin expectation value computations over a range of lattice sizes and couplings that are in agreement with our conventional lattice computations. We conclude with an outlook on further development of dual methods and their application to problems of current interest.Comment: v1: 18 pages, 7 figures, v2: Many changes to appendix, minor changes throughout, references and figures added, v3: minor corrections, 22 page

Exploring the circular economy through coatings in transport

This is the final version. Available on open access from Elsevier via the DOI in this recordCoatings are widely used in a range of aesthetic, protective and durable applications, often leading to extension of the in-service period of many components. There is sizable demand for coatings in the transport sector across road, rail, marine and air. However, the issue of materials circularity with consideration of their surface treatment is an under researched and often overlooked area. The aim of this paper is to explore challenges and enabling factors that can catalyse industrial growth of a new material, technology, or process by investigating coatings within the transport sector. We do this by studying six new or novel approaches that have garnered significant research interest in the last decade, set against system-level drivers and enablers of circularity. Our findings highlight the complications, assumptions and benefits of a circular transition. We conclude that policy and regulation play a key role in supporting or hindering the transition, and further consideration of material ‘lock-in’ is required to understand how materials can be phased out from a design standpoint.Engineering and Physical Sciences Research Council (EPSRC

Lorentzian spin foam amplitudes: graphical calculus and asymptotics

The amplitude for the 4-simplex in a spin foam model for quantum gravity is defined using a graphical calculus for the unitary representations of the Lorentz group. The asymptotics of this amplitude are studied in the limit when the representation parameters are large, for various cases of boundary data. It is shown that for boundary data corresponding to a Lorentzian simplex, the asymptotic formula has two terms, with phase plus or minus the Lorentzian signature Regge action for the 4-simplex geometry, multiplied by an Immirzi parameter. Other cases of boundary data are also considered, including a surprising contribution from Euclidean signature metrics.Comment: 30 pages. v2: references now appear. v3: presentation greatly improved (particularly diagrammatic calculus). Definition of "Regge state" now the same as in previous work; signs change in final formula as a result. v4: two references adde

Coupling of spacetime atoms and spin foam renormalisation from group field theory

We study the issue of coupling among 4-simplices in the context of spin foam models obtained from a group field theory formalism. We construct a generalisation of the Barrett-Crane model in which an additional coupling between the normals to tetrahedra, as defined in different 4-simplices that share them, is present. This is realised through an extension of the usual field over the group manifold to a five argument one. We define a specific model in which this coupling is parametrised by an additional real parameter that allows to tune the degree of locality of the resulting model, interpolating between the usual Barrett-Crane model and a flat BF-type one. Moreover, we define a further extension of the group field theory formalism in which the coupling parameter enters as a new variable of the field, and the action presents derivative terms that lead to modified classical equations of motion. Finally, we discuss the issue of renormalisation of spin foam models, and how the new coupled model can be of help regarding this.Comment: RevTeX, 18 pages, no figure