A parallel algorithm for Hamiltonian matrix construction in electron-molecule collision calculations: MPI-SCATCI

Construction and diagonalization of the Hamiltonian matrix is the rate-limiting step in most low-energy electron -- molecule collision calculations. Tennyson (J Phys B, 29 (1996) 1817) implemented a novel algorithm for Hamiltonian construction which took advantage of the structure of the wavefunction in such calculations. This algorithm is re-engineered to make use of modern computer architectures and the use of appropriate diagonalizers is considered. Test calculations demonstrate that significant speed-ups can be gained using multiple CPUs. This opens the way to calculations which consider higher collision energies, larger molecules and / or more target states. The methodology, which is implemented as part of the UK molecular R-matrix codes (UKRMol and UKRMol+) can also be used for studies of bound molecular Rydberg states, photoionisation and positron-molecule collisions.Comment: Write up of a computer program MPI-SCATCI Computer Physics Communications, in pres

Exceptional Point of Degeneracy in Linear-Beam Tubes for High Power Backward-Wave Oscillators

Abstract An exceptional point of degeneracy (EPD) is induced in a system made of an electron beam interacting with an electromagnetic (EM) guided mode. This enables a degenerate synchronous regime in backward wave oscillators (BWOs) where the electron beams provides distributed gain to the EM mode with distributed power extraction. Current particle-in-cell simulation results demonstrate that BWOs operating at an EPD have a starting-oscillation current that scales quadratically to a non-vanishing value for long interaction lengths and therefore have higher power conversion efficiency at arbitrarily higher level of power generation compared to standard BWOs

Vortex-scalar element calculations of a diffusion flame stabilized on a plane mixing layer

The vortex-scalar element method, a scheme which utilizes vortex elements to discretize the region of high vorticity and scalar elements to represent species or temperature fields, is utilized in the numerical simulations of a two-dimensional reacting mixing layer. Computations are performed for a diffusion flame at high Reynolds and Peclet numbers without resorting to turbulence models. In the nonreacting flow, the mean and fluctuation profiles of a conserved scalar show good agreement with experimental measurements. Results for the reacting flow indicate that for temperature independent kinetics, the chemical reaction begins immediately downstream of the splitter plate where mixing starts. Results for the reacting flow with Arrhenius kinetics show an ignition delay, which depends on reactant temperature, before significant chemical reaction occurs. Harmonic forcing changes the structure of the layer, and concomitantly the rates of mixing and reaction, in accordance with experimental results. Strong stretch within the braids in the nonequilibrium kinetics case causes local flame quenching due to the temperature drop associated with the large convective fluxes

Contractual Forms in Islamic Finance Law and Islamic Inv. Co. of the Gulf (Bahamas) Ltd. v. Symphony Gems N.V. & Ors.: A First Impression of Islamic Finance

This Article focuses on the case of Islamic Investment Company of the Gulf (Bahamas) Ltd. v. Symphony Gems N.V. & Others (“Symphony Gems”). Symphony Gems is the first instance where a Western court of law ruled on an Islamic financial transaction. Symphony Gems illuminates the challenges and tensions within the industrial complex of Islamic finance as it seeks to exist and thrive in a commercial reality where the regulatory framework and its associated assumptions (both theoretical as well as those of commercial practice) differ markedly from those of Islamic law and the contemporary Islamic financial industry. The resulting transactions often deviate from the classical modes or forms upon which they are supposed to be based. From a conventional finance perspective, Islamic transactions can be criticized as being anomalous, inefficiently structured and obliquely documented. Symphony Gems arose out of the applicability of an Islamic financial contract known as a murabahah. This Article will explain both the conceptual basis and the contemporary usage of the murabahah contract and, more generally, the challenges of integrating Islamic financial concepts into the Anglo-American legal system that predominates the modern global economy. Murabahah contracts, simply stated, involve the sale of an item, through a middleman, in which the ultimate buyer is aware of the middleman\u27s costs in obtaining the item. As discussed later in this Article, murabahah contracts in contemporary practice closely approximate conventional financing mechanisms, particularly the economics underlying a similarly-profiled conventional commercial financing. This is why murabahah contracts are so popular. Therefore, it is not surprising that the first instance in which a Western court of law has examined and opined upon an Islamic financial contract involves a murabahah sale

Research in structures, structural dynamics and materials, 1989

Topics addressed include: composite plates; buckling predictions; missile launch tube modeling; structural/control systems design; optimization of nonlinear R/C frames; error analysis for semi-analytic displacement; crack acoustic emission; and structural dynamics

Combatant recruitment and the outcome of war

Why do some civil wars terminate soon, with victory of one party over theother? What determines if the winner is the incumbent or the rebel group?Why do other conflicts last longer? We propose a simple model in whichthe power of each armed group depends on the number of combatants itis able to recruit. This is in turn a function of the relative 'distance' between group leaderships and potential recruits. We emphasize the moralhazard problem of recruitment: fighting is costly and risky so combatantshave the incentive to defect from their task. They can also desert alto-gether and join the enemy. This incentive is stronger the farther away thefighter is from the principal, since monitoring becomes increasingly costly.Bigger armies have more power but less monitoring capacity to preventdefection and desertion. This general framework allows a variety of interpretations of what type of proximity matters for building strong cohesivearmies ranging from ethnic distance to geographic dispersion. Di¤erentassumptions about the distribution of potential fighters along the relevantdimension of conflict lead to di¤erent equilibria. We characterize these,discuss the implied outcome in terms of who wins the war, and illustratewith historical and contemporaneous case studies.

Scanning ultrafast electron microscopy

Progress has been made in the development of four-dimensional ultrafast electron microscopy, which enables space-time imaging of structural dynamics in the condensed phase. In ultrafast electron microscopy, the electrons are accelerated, typically to 200 keV, and the microscope operates in the transmission mode. Here, we report the development of scanning ultrafast electron microscopy using a field-emission-source configuration. Scanning of pulses is made in the single-electron mode, for which the pulse contains at most one or a few electrons, thus achieving imaging without the space-charge effect between electrons, and still in ten(s) of seconds. For imaging, the secondary electrons from surface structures are detected, as demonstrated here for material surfaces and biological specimens. By recording backscattered electrons, diffraction patterns from single crystals were also obtained. Scanning pulsed-electron microscopy with the acquired spatiotemporal resolutions, and its efficient heat-dissipation feature, is now poised to provide in situ 4D imaging and with environmental capability

Measurement Errors in Recall Food Expenditure Data

Household expenditure data is an important input into the study of consumption and savings behaviour and of living standards and inequality. Because it is collected in many surveys, food expenditure data has formed the basis of much work in these areas. Recently, there has been considerable interest in properties of different ways of collecting expenditure information. It has also been suggested that measurement error in expenditure data seriously affects empirical work based on such data. The Canadian Food Expenditure Survey asks respondents to first estimate their household's food expenditures and then record food expenditures in a diary for two weeks. This unique experiment allows us to compare recall and diary based expenditure data collected from the same individuals. Under the assumption that the diary measures are "true" food consumption, this allows us to observe errors in measures of recall food consumption directly, and to study the properties of those errors. Under this assumption, measurement errors in recall food consumption data appear to be substantial, and they do not have many of the properties of classical measurement error. In particular, they are neither uncorrelated with true consumption nor conditionally homoscedastic. In addition, they are not well approximated by either a normal or log normal distribution. We also show evidence that diary measures are themselves imperfect, suffering for example, from "diary exhaustion". This suggests alternative interpretations for the differences between recall and diary consumption measures. Finally, we compare estimates of income and household size elasticities of per capita food consumption based on the two kinds of expenditure data and, in contrast to some previous work, find little difference between the two.expenditure, consumption, surveys