A system to geometrically rectify and map airborne scanner imagery and to estimate ground area

A system of computer programs were developed which performs geometric rectification and line-by-line mapping of airborne multispectral scanner data to ground coordinates and estimates ground area. The system requires aircraft attitude and positional information furnished by ancillary aircraft equipment, as well as ground control points. The geometric correction and mapping procedure locates the scan lines, or the pixels on each line, in terms of map grid coordinates. The area estimation procedure gives ground area for each pixel or for a predesignated parcel specified in map grid coordinates. The results of exercising the system with simulated data showed the uncorrected video and corrected imagery and produced area estimates accurate to better than 99.7%

Minimising biases in Full Configuration Interaction Quantum Monte Carlo

We show that Full Configuration Interaction Quantum Monte Carlo (FCIQMC) is a Markov Chain in its present form. We construct the Markov matrix of FCIQMC for a two determinant system and hence compute the stationary distribution. These solutions are used to quantify the dependence of the population dynamics on the parameters defining the Markov chain. Despite the simplicity of a system with only two determinants, it still reveals a population control bias inherent to the FCIQMC algorithm. We investigate the effect of simulation parameters on the population control bias for the neon atom and suggest simulation setups to in general minimise the bias. We show a reweighting scheme to remove the bias caused by population control commonly used in Diffusion Monte Carlo [J. Chem. Phys. 99, 2865 (1993)] is effective and recommend its use as a post processing step.Comment: Supplementary material available as 'Ancillary Files

Projections of Australian obstetricians ceasing practice and the reasons

The document attached has been archived with permission from the editor of the Medical Journal of Australia (10 January 2008). An external link to the publisher’s copy is included.Objectives: To assess the intentions of Australia's specialist obstetricians to cease practice and their reasons for abandoning this specialty. Design: A structured questionnaire posted to Fellows of the Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG), issued 11 July 2001 with a return date of 31 July 2001 (in practice, responses were accepted up to 31 August 2001). Participants: Australian specialists holding a Fellowship of the RANZCOG. Main outcome measures: Demographic data (eg, age, sex); type and location of practice; past, current and intended future obstetric practice; reasons for stopping practice; cost of indemnity premiums; experience of litigation and its influence on practice; and experience in giving medicolegal opinion. Results: The response rate was 74% (829/1116), with 826 responses fulfilling our selection criteria. The median number of years since admission as a Fellow was 17 (range, 1–47 years), and 19% (158/817) of respondents were women (9 people did not specify their sex). Of the 826 respondents, 596 (72%) were currently practising obstetrics, 548 (66%) intended to still be practising after one year, 365 (44%) intended to be practising after five years, and 196 (24%) intended to be practising after 10 years. The median indemnity premium in 2001–02 was $35 515 (range, nil to$156 000) for practising obstetricians. The main reasons given for ceasing obstetrics were intention to specialise in gynaecology, fear of litigation, high indemnity costs, family disruption, and long working hours. About two-thirds of respondents (557/818) had experienced the threat of litigation, and almost all (768/803) desired some type of "no-fault" indemnity scheme. Thirty-three of the 314 respondents who had given medicolegal opinions accounted for 71% of the total number of opinions. Many of these were non-practising obstetricians who were not accredited RANZCOG expert witnesses. Conclusion: There will soon be a shortage of experienced practising obstetricians in Australia.Alastair H MacLennan and Michael K Spence

Model of surface instabilities induced by stress

We propose a model based on a Ginzburg-Landau approach to study a strain relief mechanism at a free interface of a non-hydrostatically stressed solid, commonly observed in thin-film growth. The evolving instability, known as the Grinfeld instability, is studied numerically in two and three dimensions. Inherent in the description is the proper treatment of nonlinearities. We find these nonlinearities can lead to competitive coarsening of interfacial structures, corresponding to different wavenumbers, as strain is relieved. We suggest ways to experimentally measure this coarsening.Comment: 4 pages (3 figures included

A Robust Numerical Method for Integration of Point-Vortex Trajectories in Two Dimensions

The venerable 2D point-vortex model plays an important role as a simplified version of many disparate physical systems, including superfluids, Bose-Einstein condensates, certain plasma configurations, and inviscid turbulence. This system is also a veritable mathematical playground, touching upon many different disciplines from topology to dynamic systems theory. Point-vortex dynamics are described by a relatively simple system of nonlinear ODEs which can easily be integrated numerically using an appropriate adaptive time stepping method. As the separation between a pair of vortices relative to all other inter-vortex length scales decreases, however, the computational time required diverges. Accuracy is usually the most discouraging casualty when trying to account for such vortex motion, though the varying energy of this ostensibly Hamiltonian system is a potentially more serious problem. We solve these problems by a series of coordinate transformations: We first transform to action-angle coordinates, which, to lowest order, treat the close pair as a single vortex amongst all others with an internal degree of freedom. We next, and most importantly, apply Lie transform perturbation theory to remove the higher-order correction terms in succession. The overall transformation drastically increases the numerical efficiency and ensures that the total energy remains constant to high accuracy.Comment: 21 pages, 4 figure