CRYSTALLOGRAPHIC LEAST SQUARES REFINEMENT PROGRAM FOR THE IBM 704

OR XLS 1-5 is a program for structure factor calculation and for the least squares refinement of crystal structures using x-ray or neutron diffraction data. The code is divided into five segments, and the purpose of each is briefly described. (W.D.M.

A FORTRAN PROGRAM FOR CALCULATING SINGLE CRYSTAL ABSORPTION CORRECTIONS

A Fortran program is described for calculating the absorption correction for application to single crystal x ray or neutron intensity measurements. The program is available in the form of symbolic punched cards. InstrucPions are included. (J.R.D.

Experience with the Oak Ridge automatic three-circle neutron diffractometer

The Oak Ridge automatic three-circle neutron diffractometer is a punched paper tape controlled device with paper tape output. It has been in operation since June 1961 and is capable of measuring the intensities of 120 single-crystal reflections per day. The instrument and computer programs associated with it will be described briefly. Methods of crystal orientation will be discussed, and some of the difficulties encountered will be mentioned.Le diffractomètre automatique à neutrons « trois cercles » d'Oak Ridge est un dispositif programmeur à bande perforée (papier) avec déroulement de la bande de papier. Il a été mis en service en juin 1961 et il est capable de mesurer les intensités de 120 réflexions d'un monocristal par jour. L'appareil et les programmes de calcul qui lui sont adjoints seront brièvement décrits. Les méthodes d'orientation du cristal seront discutées et quelques difficultés rencontrées seront mentionnées

Quantification of neighbourhood-dependent plant growth by Bayesian hierarchical modelling

1. The effects of neighbours on the growth of individual plants are fundamental to dynamics in plant populations and can be described by means of mathematical functions, so-called competition kernels, in formal spatiotemporal models. Little is known about the form and components such functions should have. 2. We evaluate some properties of kernel functions using data on the growth of Arabidopsis thaliana plants in replicated, even-aged stands of many individuals. Because of the essential non-independence of plant growth in stands, we employed a Bayesian hierarchical modelling approach to estimate values and uncertainties of kernel parameters in location-dependent models of interacting plants. 3. During the experiment plant size and a simple measure of neighbourhood crowding became strongly correlated, plants tending to be small where local crowding was intense, indicating that local competition was an important process in the growth of the plants. 4. Competitive interactions between plants of different sizes were strongly asymmetric, the larger individual acquiring a disproportionately greater share of resources. Competition increased with plant size and attenuated rapidly at distances of a few centimetres, but the exact shape of the attenuation function was less important. 5. Kernel functions with the same kind of structural features were similar in their predictive ability. However, a simple zone-of-influence model, based on overlap of pairs of individuals, with competition favouring the larger individual, was arguably the most parsimonious. 6. Neighbourhood competition in stands of even-aged plants may be successfully captured with relatively simple kernel functions. The results should inform and enhance the formal theory of spatiotemporal plant population and community dynamics. Bayesian hierarchical modelling is a powerful tool with which to analyse complex, spatially dependent data, and has potential as a widely applicable statistical approach for plant ecology