How well do radiographic absorptiometry and quantitative ultrasound predict osteoporosis at spine or hip? A cost-effectiveness analysis

Dual energy X-ray absorptiometry (DXA) is widely accepted as the reference method for diagnosis and monitoring of osteoporosis and for assessment of fracture risk, especially at hip. However, axial-DXA is not suitable for mass screening, because it is usually confined to specialized centers. We propose a two-step diagnostic approach to postmenopausal osteoporosis: the first step, using an inexpensive, widely available screening technique, aims at risk stratification in postmenopausal women; the second step, DXA of spine and hip is applied only to potentially osteoporotic women preselected on the basis of the screening measurement. In a group of 110 healthy postmenopausal woman, the capability of various peripheral bone measurement techniques to predict osteoporosis at spine and/or hip (T-score < -2.5SD using DXA) was tested using receiver operating characteristic (ROC) curves: radiographic absorptiometry of phalanges (RA), ultrasonometry at calcaneus (QUS. CALC), tibia (SOS.TIB), and phalanges (SOS.PHAL). Thirty-three women had osteoporosis at spine and/or hip with DXA. Areas under the ROC curves were 0.84 for RA, 0.83 for QUS.CALC, 0.77 for SOS.PHAL (p < 0.04 vs RA) and 0.74 for SOS.TIB (p < 0.02 vs RA and p = 0.05 vs QUS.CALC). For levels of sensitivity of 90%, the respective specificities were 67% (RA), 64% (QUS.CALC), 48% (SOS.PHAL), and 39% (SOS.TIB). In a cost-effective two-step, the price of the first step should not exceed 54% (RA), 51% (QUS.CALC), 42% (SOS.PHAL), and 25% (SOS.TIB). In conclusion, RA, QUS.CALC, SOS.PHAL, and SOS.TIB may be useful to preselect postmenopausal women in whom axial DXA is indicated to confirm/exclude osteoporosis at spine or hip.

A Nonstationary Space-Time Gaussian Process Model for Partially Converged Simulations

In the context of expensive numerical experiments, a promising solution for alleviating the computational costs consists of using partially converged simulations instead of exact solutions. The gain in computational time is at the price of precision in the response. This work addresses the issue of fitting a Gaussian process model to partially converged simulation data for further use in prediction. The main challenge consists of the adequate approximation of the error due to partial convergence, which is correlated in both design variables and time directions. Here, we propose fitting a Gaussian process in the joint space of design parameters and computational time. The model is constructed by building a nonstationary covariance kernel that reflects accurately the actual structure of the error. Practical solutions are proposed for solving parameter estimation issues associated with the proposed model. The method is applied to a computational fluid dynamics test case and shows significant improvement in prediction compared to a classical kriging model.

Beyond biofuels: jatropha’s multiple uses for farmers in East Africa

The jatropha plant produces seeds containing 25–40% oil by weight. This oil can be made into biodiesel. During the recent global fuel crisis, the price of crude oil peaked at over USD 130 per barrel. Jatropha attracted huge interest – it was touted as a wonder crop that could generate biodiesel oil on “marginal lands” in semi-arid areas. Its promise appeared especially great in East Africa. Today, however, jatropha’s value in East Africa appears to lie primarily in its multipurpose use by small-scale farmers, not in large-scale biofuel production.

Collingwood on religious atonement

R. G. Collingwood’s philosophical analysis of religious atonement as a dialectical process of mortal repentance and divine forgiveness is explained and criticized. Collingwood’s Christian concept of atonement, in which Christ TeX the Atonement (and also TeX the Incarnation), is subject in turn to another kind of dialectic, in which some of Collingwood’s leading ideas are first surveyed, and then tested against objections in a philosophical evaluation of their virtues and defects, strengths and weaknesses. Collingwood’s efforts to synthesize objective and subjective aspects of atonement, and his proposal to solve the soteriological problem as to why God becomes flesh, as a dogma of some Christian belief systems, is finally exposed in adversarial exposition as inadequately supported by one of his main arguments, designated here as Collingwood’s Dilemma. The dilemma is that sin is either forgiven or unforgiven by God. If God forgives sin, then God’s justice is lax, whereas if God does not forgive sin, then, also contrary to divine nature, God lacks perfect loving compassion. The dilemma is supposed to drive philosophy toward a concept of atonement in which the sacrifice of Christ is required in order to absolve God of the lax judgment objection. God forgives sin only when the price of sin is paid, in this case, by the suffering and crucifixion of God’s avatar. The dilemma can be resolved in another way than Collingwood considers, undermining his motivation for synthesizing objective and subjective facets of the concept of atonement for the sake of avoiding inconsistency. Collingwood is philosophically important because he asks all the right questions about religious atonement, and points toward reasonable answers, even if he does not always deliver original philosophically satisfactory solutions.

Minimum carbon payment along an aridity gradient for dryland afforestation in non annex I countries with stochastic weather and prices

Recent findings demonstrate that trees in deserts are efficient carbon sinks. It remains however unknown whether the Clean Development Mechanism will accelerate the planting of trees in Non Annex I dryland countries. We estimated the price of carbon at which a farmer would be indifferent between his customary activity and the planting of trees to trade carbon credits, along an aridity gradient. Carbon yields were simulated by means of the CO2FIX v3.1 model for Pinus halepensis with its respective yield classes along the gradient (Arid – 100mm to Dry Sub Humid conditions – 900mm). Wheat and pasture yields were predicted on somewhat similar nitrogen-based quadratic models, using 30 years of weather data to simulate moisture stress. Stochastic production, input and output prices were afterwards simulated on a Monte Carlo matrix. Results show that, despite the high levels of carbon uptake, carbon trading by afforesting is unprofitable anywhere along the gradient. Indeed, the price of carbon would have to raise unrealistically high, and the certification costs would have to drop significantly, to make the Clean Development Mechanism worthwhile for non annex I dryland countries farmers. From a government agency's point of view the Clean Development Mechanism is attractive. However, such agencies will find it difficult to demonstrate “additionality”, even if the rule may be somewhat flexible. Based on these findings, we will further discuss why the Clean Development Mechanism, a supposedly pro-poor instrument, fails to assist farmers in Non Annex I dryland countries living at minimum subsistence level.