Tropical Africa: Problem Child of the 60\u27s

The cold war has focused the attention of United States and world leaders on the strategic position, vast mineral wealth, and newly acquired political power of Africa. Recent events in the Congo, Ghana, and Guinea have forced Americans to reflect on the advantages of a friendly Africa or even a neutral Africa as contrasted with a communist-oriented Africa

Handbook for Learning-centred evaluation of Computer-facilitated learning projects in higher education

This handbook supports a project funded by the Australian Government Committee for University Teaching and Staff Development (CUTSD). The amended project title is “Staff Development in Evaluation of Technology-based Teaching Development Projects: An Action Inquiry Approach”. The project is hosted by Murdoch University on behalf of the Australasian Society for Computers in Learning in Tertiary Education (ASCILITE), as a consortium of 11 universities. The rationale of the project is to guide a group of university staff through the evaluation of a Computer-facilitated Learning (CFL1) project by a process of action inquiry and mentoring, supported by the practical and theoretical material contained in this handbook

Simulating the diffusion of technological innovation with an integrated hybrid agent-based system dynamics model

The potential of hybrid models to enhance simulations of the real world is explored. While the scope for design of such models is large, the focus here brings together agent-based (AB) and system dynamics (SD) modelling within a defined architectural framework. Comprising a number of modules, each of which is implemented in a single modelling paradigm, the design of hybrid models looks to exploit the potential from a range of approaches and tools. Coded within a single programming environment, the international diffusion of technological innovation is used as a case study to highlight hybrid simulation model design and implementation. An integrated hybrid simulation design that incorporates feedback between modules in a continuous, fluid, process is employed to develop a model comprising two SD modules and one AB module. The predictions from the hybrid model are compared to known outcomes regarding the national adoption of mobile telephony, fixed internet and fixed broadband. We conclude with some thoughts on the design of hybrid simulation models

Comparing a simulation model with various analytic models of the international diffusion of consumer technology

In this paper we propose and evaluate a method for studying technology adoption at the national level using hybrid simulation. A hybrid simulation model is developed which combines elements of system dynamics and agent-based modelling, and treats nations as adopting agents. International diffusion is modelled as a social system where the adoption of an innovation, or even just growing pressure to adopt an innovation, in one nation can then influence its adoption in others. The model is used to investigate nine different technological innovations for which sufficient international data are available. Using the available empirical data, the method of differential evolution is used to configure the model which allows the parameter space to be explored in an efficient manner, without bias or subjective disagreement. Good agreement is found between the parameters derived in this way and those reported to configure analytic models. For each of the nine innovations, we report the rank order correlation between the actual order of adoption of the innovations by nations and the order predicted by the simulation model. We also report the rank order correlations between the actual order and the order predicted by a much simpler statistical model. Improvements in the rank order correlation are shown when some form of social influence between nations is included, although there is no significant difference in results between the four different types of social influence considered by the simulation. The nine technologies investigated also appear to fall into two groups with significantly different uptake speeds. Advantages and limitations of the approach are discussed along with suggested implications for practice

Oxygen Isotopes of Al-Rich Chondrules from Unequilibrated Ordinary Chondrites

Al-rich chondrules (ARCs) are a rare constituent of chondrites. They have relatively high bulk Al_2O_3 content (> 10 wt%), which is due to the presence of Al-rich phases, such as plagioclase, spinel, Al-rich glass etc. [1]. ARCs share some chemical and petrologic characteristics with Ca, Al-rich inclusions (CAis), and may represent a genetic link between ferromagnesian chondrules and CAis

The Radio Afterglow and Host Galaxy of the Dark GRB 020819

Of the fourteen gamma-ray bursts (GRBs) localized to better than 2' radius with the SXC on HETE-2, only two lack optical afterglow detections, and the high recovery rate among this sample has been used to argue that the fraction of truly dark bursts is ~10%. While a large fraction of earlier dark bursts can be explained by the failure of ground-based searches to reach appropriate limiting magnitudes, suppression of the optical light of these SXC dark bursts seems likely. Here we report the discovery and observation of the radio afterglow of GRB 020819, an SXC dark burst, which enables us to identify the likely host galaxy (probability of 99.2%) and hence the redshift (z=0.41) of the GRB. The radio light curve is qualitatively similar to that of several other radio afterglows, and may include an early-time contribution from the emission of the reverse shock. The proposed host is a bright R = 19.5 mag barred spiral galaxy, with a faint R ~ 24.0 mag "blob'' of emission, 3" from the galaxy core (16 kpc in projection), that is coincident with the radio afterglow. Optical photometry of the galaxy and blob, beginning 3 hours after the burst and extending over more than 100 days, establishes strong upper limits to the optical brightness of any afterglow or associated supernova. Combining the afterglow radio fluxes and our earliest R-band limit, we find that the most likely afterglow model invokes a spherical expansion into a constant-density (rather than stellar wind-like) external environment; within the context of this model, a modest local extinction of A_V ~ 1 mag is sufficient to suppress the optical flux below our limits.Comment: 7 pages, 2 figures. ApJ, in press. For more info on dark bursts, see http://www.astro.ku.dk/~pallja/dark.htm

Examining Visual Field Loss in Patients in Glaucoma Clinics During Their Predicted Remaining Lifetime

Purpose.: To evaluate the proportion of patients in glaucoma clinics progressing at rates that would result in visual disability within their expected lifetime. Methods.: This retrospective study used visual field (VF) series of at least 3 years’ duration from 3790 UK patients in glaucoma clinics calculating rates of loss for each eye using linear regression of mean deviation (MD) over time. Residual life expectancies derived from the UK Office of National Statistics actuarial tables for each patient were combined with these rates to estimate predicted MDs at end of expected lifetime. The proportion of patients projected to progress to visual impairment (MD: −14 dB or worse) or statutory blindness (MD: −22 dB or worse) in both eyes before end of expected lifetime was calculated. Results.: Only 3.0% (95% confidence interval [CI] 2.7%–3.4%) of patient eyes progressed at faster than −1.5 dB/year (n = 7149 eyes). Of those patients with both eyes followed, 5.2% (CI 4.5%–6.0%) were predicted to progress to statutory blindness, with a further 10.4% (CI 9.4%–11.4%) reaching visual impairment in their lifetime. More than 90% (CI 85.7%–94.3%) of patients predicted to progress to statutory blindness, had an MD worse than −6 dB in at least one eye at presentation. Conclusions.: This modeling exercise indicates that most patients in glaucoma clinics are not at high risk of progressing to statutory blindness. The likelihood of patients suffering impairment in their lifetimes is linked to VF loss at presentation, which illuminates the importance of reliably detecting significant VF defects in primary care

Electronic Structure of Few-Layer Graphene: Experimental Demonstration of Strong Dependence on Stacking Sequence

The electronic structure of few-layer graphene (FLG) samples with crystalline order was investigated experimentally by infrared absorption spectroscopy for photon energies ranging from 0.2 - 1 eV. Distinct optical conductivity spectra were observed for different samples having precisely the same number of layers. The different spectra arise from the existence of two stable polytypes of FLG, namely, Bernal (AB) stacking and rhombohedral (ABC) stacking. The observed absorption features, reflecting the underlying symmetry of the two polytypes and the nature of the associated van Hone singularities, were reproduced by explicit calculations within a tight-binding model. The findings demonstrate the pronounced effect of stacking order on the electronic structure of FLG.Comment: 13 pages, 3 figure