Confronting mortality: the Iliad''s androktasiai

This article describes the results of a survey of radiography program directors on positioning competencies for entry-level radiographers. The survey asked program directors to classify projections as essential, important, rarely needed or for reference only. The objective of the study was to rank radiographic projections from most to least important in clinical practice. The data are provided for use by educators and employers in determining which projections are essential entry-level competencies.     

Reliability and validity of the measurement of position sense in women with osteoarthritis of the knee

OBJECTIVE: We examined the test-retest reliability and the construct validity of the measurement of knee position sense for describing the functional weightbearing performance of women with osteoarthritis (OA) of the knee. METHODS: For the purpose of this study, position sense was defined as the error occurring when subjects attempted to reproduce a criterion angle in standing with visual cues eliminated. Five such tests were recorded photographically on 3 different occasions. On each occasion the 10 subjects also completed a self-paced walking test over a 13 m indoor walkway. RESULTS: The photographic measurements were reproducible (r = 0.90) and there was no change in positioning accuracy across sessions. There was a significant (p < 0.05) inverse correlation of 0.70 between the standard deviation of the mean individual measurements of position sense (precision of the test) and those of walking speed. CONCLUSION: Our study demonstrates good measurement reliability and a comparable mean angular error with repeated tests. It also suggests the amplitude of the variability of this error is a strong determinant of an individual OA patient's functional performance in walking.     

Ceramic Composites Fabricated by Selective Laser Sintering

Selective laser sintering (SLS) uses a computer controlled laser beam to create objects directly from the CAD data without part-specific tooling. In this paper, the effect of material and processing parameters on the microstructure and mechanical properties of an alumina/aluminum phosphate composite fabricated by SLS is described. The precursor material is a blend of alumina and ammonium phosphate powder. This paper deals primarily with the effect of alumina particle size and material composition on the strength of the composite. A constitutive equation is also proposed to relate the mechanical properties of the composite to its microstructural characteristics.     

Estimation of the interindividual variability in the one-compartment pharmacokinetic model for methylmercury: implications for the derivation of a reference dose

A critical step in the U.S. EPA's derivation of an Reference Dose (RfD) for methylmercury is conversion of the maternal hair Hg concentration of 11 ppm to average daily intake using the one-compartment pharmacokinetic model. A default uncertainty factor (UF) adjustment of 3 for interindividual variability was then applied to this conversion. A probabilistic (Monte Carlo) analysis is presented estimating the interindividual variability inherent in this dose conversion for women 18-40 years old based on data in the scientific literature. The dose of 1.1 micrograms/kg/day, calculated by the U.S. EPA to correspond to 11 ppm Hg in hair, is estimated in this analysis to be larger than 94-99% of corresponding doses. The application of a UF of 3 to this U.S. EPA value gives a dose which is estimated to be larger than 28-73% of corresponding doses. This analysis suggests that if the dose conversion in the RfD is intended to be inclusive of 95-99% of women 18-40, the daily intake should be set at 0.1-0.3 microgram/kg/day. The RfD of 0.03-0.1 microgram/kg/day, derived from this dose by the U.S. EPA's application of an additional UF of 3 for additional toxicologic concerns, is somewhat smaller than the current RfD of 0.1 microgram/kg/day.     

Treatment of radiation-induced nervous system injury with heparin and warfarin

When radiation is used to treat nervous system cancer, exposure of adjacent normal nervous system tissue is unavoidable, and radiation-induced injury may occur. Acute injury is usually mild and transient, but late forms of radiation-induced nervous system injury are usually progressive and debilitating. Treatment with corticosteroids, surgery, and antioxidants is often ineffective. We treated 11 patients with late radiation-induced nervous system injuries (eight with cerebral radionecrosis, one with a myelopathy, and two with plexopathies, all unresponsive to dexamethasone and prednisone) with full anticoagulation. Some recovery of function occurred in five of the eight patients with cerebral radionecrosis, and all the patients with myelopathy or plexopathy. Anticoagulation was continued for 3 to 6 months. In one patient with cerebral radionecrosis, symptoms recurred after discontinuation of anticoagulation and disappeared again after reinstitution of treatment. We hypothesize that anticoagulation may arrest and reverse small-vessel endothelial injury--the fundamental lesion of radiation necrosis--and produce clinical improvement in some patients.     

Path integral Monte Carlo simulations of the melting of molecular hydrogen surfaces

We have used Path Integral Monte Carlo to study the surface melting of molecular hydrogen. Density profiles perpendicular and parallel to the bare H₂ surface are computed showing the formation of a liquid adlayer at 6 K, less than half the bulk melting temperature of para-hydrogen, 13.8 K. To estimate the onset temperature and depth of H₂ surface melting we determine the static structure factor within the individual H₂-layers for wave vectors in the plane and find no crystalline order down to 3 K in a partially filled H₂ adlayer at the free surface. We find quantum effects amplify the melting point depression at the free H₂ surface compared to bulk by a factor of five over classical Lennard-Jones solids and find that the zero-point fluctuations of molecules at the surface are much enhanced over their bulk values. We see vacancy formation in the solid before melting.     

Convergence of simultaneous perturbation stochastic approximation for nondifferentiable optimization

We consider simultaneous perturbation stochastic approximation for function minimization. The standard assumption for convergence is that the function be three times differentiable, although weaker assumptions have been used for special cases. However, all work that we are aware of at least requires differentiability. We relax the differentiability requirement and prove convergence using convex analysis.