Modelling the Distribution of Ischaemic Stroke-Specific Survival Time Using an EM-based Mixture Approach with Random Effects Adjustment

A two-component survival mixture model is proposed to analyse a set of ischaemic stroke-specific mortality data. The survival experience of stroke patients after index stroke may be described by a subpopulation of patients in the acute condition and another subpopulation of patients in the chronic phase. To adjust for the inherent correlation of observations due to random hospital effects, a mixture model of two survival functions with random effects is formulated. Assuming a Weibull hazard in both components, an EM algorithm is developed for the estimation of fixed effect parameters and variance components. A simulation study is conducted to assess the performance of the two-component survival mixture model estimators. Simulation results confirm the applicability of the proposed model in a small sample setting. Copyright (C) 2004 John Wiley Sons, Ltd.

The states, diffusion, and concentration distribution of water in radiation-formed PVA/PVP hydrogels

Hydrogels with various compositions of polyvinyl alcohol (PVA) and poly(1-vinyl-2-pyrrolidinone) (PVP) were prepared by irradiating mixtures of PVA and PVP in aqueous solutions with gamma-rays from Co-60 sources at room temperature. The states of water in the hydrogels were characterized using DSC and NMR T-2 relaxation measurements and the kinetics of water diffusion in the hydrogels were studied by sorption experiments and NMR imaging. The DSC endothermic peaks in the temperature range -10 to +10 degrees C implied that there are at least two kinds of freezable water present in the matrix. The difference between the total water content and the freezable water content was refer-red to as bound water, which is not freezable. The weight fraction of water at which only nonfreezable water is present in a hydrogel with F-VP = 0.19 has been estimated to be g(H2O)/g(Polymer) = 0.375. From water sorption experiments, it was demonstrated that the early stage of the diffusion of water into the hydrogels was Fickian. A curve-fit of the early-stage experimental data to the Fickian model allowed determination of the water diffusion coefficient, which was found to lie between 1.5 x 10(-11) m(2) s(-1) and 4.5 x 10(-11) m(2) s(-1), depending on the polymer composition, the cross-link density, and the temperature. It was also found that the energy barrier for diffusion of water molecules into PVA/PVP hydrogels was approximate to 24 kJ mol(-1). Additionally, the diffusion coefficients determined from NMR imaging of the volumetric swelling of the gels agreed well with the results obtained by the mass sorption method.

Incidence and distribution of viruses of Taro (Colocasia esculenta) in Pacific Island countries

Four viruses have been reported from taro; Dasheen mosaic virus (DsMV), Taro bacilliform virus (TaBV) and two putative rhabdoviruses, Colocasia bobone disease virus (CBDV) and Taro vein chlorosis virus (TaVCV). A fifth virus, tentatively named Taro reovirus (TaRV), has also been recently identified. The distribution of these viruses throughout the Pacific Islands, and the symptoms associated with their infection, are unknown in many cases due to a lack of sensitive diagnostic tests. We have used recently developed PCR-based diagnostic tests to survey taro growing in 11 Pacific Island countries for the presence of known viruses. DsMV and TaBV were widespread, whereas TaVCV and TaRV were more restricted in their distribution. CBDV was restricted to PNG and Solomon Islands and was always associated with the two most serious viral diseases of taro; alomae disease and bobone disease, but the causal agent of these two diseases remains unclear.

Distribution of an asymmetrical copepod, Hatschekia plectropomi, on the gills of Plectropomus leopardus

Hatschekia plectropomi, an ectoparasitic copepod found on the gills, infected Plectropomus leopardus from Heron Island Reef with 100% prevalence (n = 32) and a mean +/- S.E. infection intensity of 131.9 +/- 22.1. The distribution of 4222 adult female parasites across 32 individual host fish was investigated at several organizational levels ranging from the level of holobranch pairs to that of individual filaments. Parasites demonstrated a site preference for the two central holobranchs (2 and 3). Along the lengths of hemibranchs, filaments near the dorsal and ventral ends and those in the proximity of the bend region were rarely occupied. The probability of coming into contact with a suitable attachment site and the ability to withstand ventilation forces at that site were proposed as the major factors affecting distribution. Two H. plectropomi morphotypes were identified based on the direction of body curvature. Regardless of morphotype, 99.9% of individuals were attached such that the convex side of the body was oriented towards the oncoming ventilating water currents. Further, 93.3% of individuals attached to the posterior faces of filaments, leading to a predictable pattern of attachment for this species. It is suggested that the direction of body curvature develops in response to the direction of the ventilating water currents. (c) 2006 The Fisheries Society of the British Isles.

Privacy and security enhanced offline oblivious transfer for massive data distribution

Unauthorized accesses to digital contents are serious threats to international security and informatics. We propose an offline oblivious data distribution framework that preserves the sender's security and the receiver's privacy using tamper-proof smart cards. This framework provides persistent content protections from digital piracy and promises private content consumption.

Spatial distribution of pink wax scale, Ceroplastes rubens Maskell (Hemiptera: Coccidae), on umbrella trees in south-eastern Queensland: The pattern of outbreaks

The spatial pattern of outbreaks of pink wax scale, Ceroplastes rubens Maskell, within and among umbrella trees, Schefflera actinophylla (Endl.), in southeastern Queensland was investigated. Pink wax scale was common on S. actinophylla, with approximately 84% of trees positive for scale and 14% of bees recording outbreak densities exceeding 0.4 adults per leaflet. Highly aggregated distributions of C. rubens occur within and among umbrella trees. Clumped distributions within trees appear to result from variable birth and death rates and limited movement of first instar crawlers. The patchy distribution of pink wax scale among trees is probably a consequence of variation in dispersal success of scale, host and environmental suitability for establishment and rates of biological control. Pink wax scale was more prevalent on trees in roadside positions and in exposed situations, indicating that such trees are more suitable and/or susceptible to scale colonisation.

Modelling the distribution of stamp paper thickness via finite normal mixtures: The 1872 Hidalgo stamp issue of Mexico revisited

Izenman and Sommer (1988) used a non-parametric Kernel density estimation technique to fit a seven-component model to the paper thickness of the 1872 Hidalgo stamp issue of Mexico. They observed an apparent conflict when fitting a normal mixture model with three components with unequal variances. This conflict is examined further by investigating the most appropriate number of components when fitting a normal mixture of components with equal variances.

Melphalan dosing regimens for management of recurrent melanoma by isolated limb perfusion: Application of a physiological pharmacokinetic model based on melphalan distribution in the isolated perfused rat hindlimb

The optimal dosing schedule for melphalan therapy of recurrent malignant melanoma in isolated limb perfusions has been examined using a physiological pharmacokinetic model with data from isolated rat hindlimb perfusions (IRHP), The study included a comparison of melphalan distribution in IRHP under hyperthermia and normothermia conditions. Rat hindlimbs were perfused with Krebs-Henseleit buffer containing 4.7% bovine serum albumin at 37 or 41.5 degrees C at a flow rate of 4 ml/min. Concentrations of melphalan in perfusate and tissues were determined by high performance liquid chromatography with fluorescence detection, The concentration of melphalan in perfusate and tissues was linearly related to the input concentration. The rate and amount of melphalan uptake into the different tissues was higher at 41.5 degrees C than at 37 degrees C. A physiological pharmacokinetic model was validated from the tissue and perfusate time course of melphalan after melphalan perfusion. Application of the model involved the amount of melphalan exposure in the muscle, skin and fat in a recirculation system was related to the method of melphalan administration: single bolus > divided bolus > infusion, The peak concentration of melphalan in the perfusate was also related to the method of administration in the same order, Infusing the total dose of melphalan over 20 min during a 60 min perfusion optimized the exposure of tissues to melphalan whilst minimizing the peak perfusate concentration of melphalan. It is suggested that this method of melphalan administration may be preferable to other methods in terms of optimizing the efficacy of melphalan whilst minimizing the limb toxicity associated with its use in isolated limb perfusion.

The effects of perfusion conditions on melphalan distribution in the isolated perfused rat hindlimb bearing a human melanoma xenograft

An isolated rat hindlimb perfusion model carrying xenografts of the human melanoma cell line MM96 was used to study the effects of perfusion conditions on melphalan distribution. Krebs-Henseleit buffer and Hartmann's solution containing 4.7% bovine serum albumin (BSA) or 2.8% dextran 40 were used as perfusates. Melphalan concentrations in perfusate, tumour nodules and normal tissues were measured using high-performance liquid chromatography (HPLC). Increasing the perfusion flow rates (from 4 to 8 mi min(-1)) resulted in higher tissue blood flow (determined with Cr-51-labelled microspheres) and melphalan uptake by tumour and normal tissues. me distribution of melphalan within tumour nodules and normal tissues was similar for both Krebs-Henseleit buffer and Hartmann's solution; however, tissue concentrations of melphalan were significantly higher for a perfusate containing 2.8% dextran 40 than for one containing 4.7% BSA. The melphalan concentration in the tumour was one-third of that found in the skin if the perfusate contained 4.7% BSA. In conclusion, this study has shown that a high perfusion flow enhances the delivery of melphalan into implanted tumour nodules and normal tissues, and a perfusate with low melphalan binding (no albumin) is preferred for maximum uptake of drug by the tumour.

The distribution of naloxone to heroin users

Overdose deaths are a manor contributor to excess mortality among heroin users. It has been proposed that opioid overdose morbidity and mortality could be reduced substantially by distributing the opioid antagonist naloxone to heroin users. The ethical issues raised by this proposal are evaluated from a utilitarian perspective. The potential advantages of naloxone distribution include the increased chance of comatose opioid users being quickly resuscitated by others present at the time of an overdose, naloxone's safety and its lack of abuse potential. The main problems raised by the proposal are: the medico-legal complications of medical practitioners prescribing a drug that is most likely to be administered to and by people other than the one for whom it is prescribed; the economic costs of distributing naloxone sufficiently widely to have an impact on overdose morbidity and mortality; and the potentially greater cost-effectiveness of simpler educational interventions. Given the possible benefits of naloxone distribution, it may be worthwhile considering a controlled trial of naloxone distribution to high-risk heroin users.