A four-stage index 2 Diagonally Implicit Runge-Kutta method

High index Differential Algebraic Equations (DAEs) force standard numerical methods to lower order. Implicit Runge-Kutta methods such as RADAU5 handle high index problems but their fully implicit structure creates significant overhead costs for large problems. Singly Diagonally Implicit Runge-Kutta (SDIRK) methods offer lower costs for integration. This paper derives a four-stage, index 2 Explicit Singly Diagonally Implicit Runge-Kutta (ESDIRK) method. By introducing an explicit first stage, the method achieves second order stage calculations. After deriving and solving appropriate order conditions., numerical examples are used to test the proposed method using fixed and variable step size implementations. (C) 2001 IMACS. Published by Elsevier Science B.V. All rights reserved.

Application of a simplified method based on regular regime approach to determine the effective moisture diffusivity of mixture of low molecular weight sugars and maltodextrin during desorption

The binary diffusivities of water in low molecular weight sugars; fructose, sucrose and a high molecular weight carbohydrate; maltodextrin (DE 11) and the effective diffusivities of water in mixtures of these sugars (sucrose, glucose, fructose) and maltodextrin (DE 11) were determined using a simplified procedure based on the Regular Regime Approach. The effective diffusivity of these mixtures exhibited both the concentration and molecular weight dependence. Surface stickiness was observed in all samples during desorption, with fructose exhibiting the highest and maltodextrin the lowest. (C) 2002 Elsevier Science Ltd. All rights reserved.

Comparison of an ELISA and an LC/MS/MS method for measuring tacrolimus concentrations and making dosage decisions in transplant recipients

This study compared an enzyme-linked immunosorbent assay (ELISA) to a liquid chromatography-tandem mass spectrometry (LC/MS/MS) technique for measurement of tacrolimus concentrations in adult kidney and liver transplant recipients, and investigated how assay choice influenced pharmacokinetic parameter estimates and drug dosage decisions. Tacrolimus concentrations measured by both ELISA and LC/MS/MS from 29 kidney (n = 98 samples) and 27 liver (n = 97 samples) transplant recipients were used to evaluate the performance of these methods in the clinical setting. Tacrolimus concentrations measured by the two techniques were compared via regression analysis. Population pharmacokinetic models were developed independently using ELISA and LC/MS/MS data from 76 kidney recipients. Derived kinetic parameters were used to formulate typical dosing regimens for concentration targeting. Dosage recommendations for the two assays were compared. The relation between LC/MS/MS and ELISA measurements was best described by the regression equation ELISA = 1.02 . (LC/MS/MS) + 0.14 in kidney recipients, and ELISA = 1.12 . (LC/MS/MS) - 0.87 in liver recipients. ELISA displayed less accuracy than LC/MS/MS at lower tacrolimus concentrations. Population pharmacokinetic models based on ELISA and LC/MS/MS data were similar with residual random errors of 4.1 ng/mL and 3.7 ng/mL, respectively. Assay choice gave rise to dosage prediction differences ranging from 0% to 30%. ELISA measurements of tacrolimus are not automatically interchangeable with LC/MS/MS values. Assay differences were greatest in adult liver recipients, probably reflecting periods of liver dysfunction and impaired biliary secretion of metabolites. While the majority of data collected in this study suggested assay differences in adult kidney recipients were minimal, findings of ELISA dosage underpredictions of up to 25% in the long term must be investigated further.

Linguistic evaluation method for the environmental assessment of infrastructure projects

A soft linguistic evaluation method is proposed for the environmental assessment of physical infrastructure projects based on fuzzy relations. Infrastructure projects are characterized in terms of linguistic expressions of 'performance' with respect to factors or impacts and the 'importance' of those factors/impacts. A simple example is developed to illustrate the method in the context of three road infrastructure projects assessed against five factors/impacts. In addition, a means to include hard or crisp factors is presented and illustrated with respect to a sixth factor.

Fate of N-15-labelled nitrate in a wet summer under different residue management regimes in young hoop pine plantations

A field study was conducted to investigate the fate of N-15-labelled nitrate applied at 20 kg N ha(-1) in a wet summer to microplots installed in areas under different residue management regimes in second-rotation hoop pine (Araucaria cunninghamii) plantations aged 1-3 years in south-east Queensland, Australia. PVC microplots of 235 mm diameter and 300 mm long were driven into 250 mm soil. There were three replications of each of eight treatments. These were areas just under and between 1-year-old windrows (ca. 2-3 m in width) of harvesting residues spaced 15 m apart, and with and without incorporated foliage residues (20 t DM ha(-1)); the areas just under and between 2- or 3-year-old windrows spaced 10 m apart. Only 7-29% of the added N-15 was recovered from the top 750 mm of the soil profile with the leaching loss estimated to be 70-86% over the 34-day period. The N-15 loss via denitrification was 3.7-6.3% by directly measuring the N-15 gases emitted. The microplots with the incorporated residues at the 1-year-old site had the highest N-15 loss (6.3%) as compared with the other treatments. The N-15 mass balance method together with the use of bromide (Br) tracer applied at 100 kg Br ha(-1) failed to obtain a reliable estimate of the denitrification loss. The microplots at the 1-year-old site had higher N-15 immobilisation rate (7.5-24.7%) compared with those at 2- and 3-year-old sites (2.1-3.6%). Incorporating the residues resulted in an increase in N-15 immobilisation rate (24.5-24.7%) compared with the control without the incorporated residues (8.4-14.3%). These findings suggest that climatic conditions played important roles in controlling the N-15 transformations in the wet summer season and that the residue management regimes could also significantly influence the N-15 transformations. Most of the N-15 loss occurred through leaching, but a considerable amount of the N-15 was lost through denitrification. Bromide proved to be an unsuitable tracer for monitoring the N-15 leaching and movement under the wet summer conditions. (C) 2002 Elsevier Science B.V. All rights reserved.

Assessing clinical reasoning: a method to monitor its development in a PBL curriculum

The aim of this study was to develop and trial a method to monitor the evolution of clinical reasoning in a PBL curriculum that is suitable for use in a large medical school. Termed Clinical Reasoning Problems (CRPs), it is based on the notion that clinical reasoning is dependent on the identification and correct interpretation of certain critical clinical features. Each problem consists of a clinical scenario comprising presentation, history and physical examination. Based on this information, subjects are asked to nominate the two most likely diagnoses and to list the clinical features that they considered in formulating their diagnoses, indicating whether these features supported or opposed the nominated diagnoses. Students at different levels of medical training completed a set of 10 CRPs as well as the Diagnostic Thinking Inventory, a self-reporting questionnaire designed to assess reasoning style. Responses were scored against those of a reference group of general practitioners. Results indicate that the CRPs are an easily administered, reliable and valid assessment of clinical reasoning, able to successfully monitor its development throughout medical training. Consequently, they can be employed to assess clinical reasoning skill in individual students and to evaluate the success of undergraduate medical schools in providing effective tuition in clinical reasoning.

Identification and minisequencing-based discrimination of SHV beta-lactamases in nosocomial infection-associated Klebsiella pneumoniae in Brisbane, Australia

Extended-spectrum beta-lactamases (ESBLs) are active against oxyimino cephalosporins and monobactams. Twenty-one Klebsiella pneumoniae isolates obtained between 1991 and 1995 at the Princess Alexandra Hospital in Brisbane, Australia, were subject to amplification and sequencing of the SHV beta-lactamase-encoding genes. Thirteen strains were phenotypically ESBL positive. Of these, six strains carried the bla(SHV-2a) gene and seven strains carried the bla(SHV-12) gene. Eight strains were phenotypically ESBL negative. Of these, seven strains carried the non-ESBL bla(SHV-11) gene and one strain carried the non-ESBL bla(SHV-1) gene. There was complete correspondence between the ESBL phenotype and the presence or absence of an ESBL-encoding gene(s). In addition, it was determined that of the 13 ESBL-positive strains, at least 4 carried copies of a non-ESBL-encoding gene in addition to the bla(SHV-2a) or bla(SHV12) gene. A minisequencing-based assay was developed to discriminate the different SHV classes. This technique, termed first-nucleotide change, involves the identification of the base added to a primer in a single-nucleotide extension reaction. The assay targeted polymorphisms at the first bases of codons 238 and 240 and reliably discriminated ESBL-positive strains from ESBL-negative strains and also distinguished strains carrying bla(SHV-2a) from strains carrying bla(SHV-12). In addition, this method was used to demonstrated an association between the relative copy numbers of bla(SHV) genes in individual strains and the levels of antibiotic resistance.

MR image-based measurement of rates of change in volumes of brain structures. Part 1: Method and validation

A detailed analysis procedure is described for evaluating rates of volumetric change in brain structures based on structural magnetic resonance (MR) images. In this procedure, a series of image processing tools have been employed to address the problems encountered in measuring rates of change based on structural MR images. These tools include an algorithm for intensity non-uniforniity correction, a robust algorithm for three-dimensional image registration with sub-voxel precision and an algorithm for brain tissue segmentation. However, a unique feature in the procedure is the use of a fractional volume model that has been developed to provide a quantitative measure for the partial volume effect. With this model, the fractional constituent tissue volumes are evaluated for voxels at the tissue boundary that manifest partial volume effect, thus allowing tissue boundaries be defined at a sub-voxel level and in an automated fashion. Validation studies are presented on key algorithms including segmentation and registration. An overall assessment of the method is provided through the evaluation of the rates of brain atrophy in a group of normal elderly subjects for which the rate of brain atrophy due to normal aging is predictably small. An application of the method is given in Part 11 where the rates of brain atrophy in various brain regions are studied in relation to normal aging and Alzheimer's disease. (C) 2002 Elsevier Science Inc. All rights reserved.

A design method for superconducting MRI magnets with ferromagnetic material

The emphasis of this work is on the optimal design of MRI magnets with both superconducting coils and ferromagnetic rings. The work is directed to the automated design of MRI magnet systems containing superconducting wire and both `cold' and `warm' iron. Details of the optimization procedure are given and the results show combined superconducting and iron material MRI magnets with excellent field characteristics. Strong, homogeneous central magnetic fields are produced with little stray or external field leakage. The field calculations are performed using a semi-analytical method for both current coil and iron material sources. Design examples for symmetric, open and asymmetric clinical MRI magnets containing both superconducting coils and ferromagnetic material are presented.

Finite difference time domain (FDTD) method for modeling the effect of switched gradients on the human body in MRI

Numerical modeling of the eddy currents induced in the human body by the pulsed field gradients in MRI presents a difficult computational problem. It requires an efficient and accurate computational method for high spatial resolution analyses with a relatively low input frequency. In this article, a new technique is described which allows the finite difference time domain (FDTD) method to be efficiently applied over a very large frequency range, including low frequencies. This is not the case in conventional FDTD-based methods. A method of implementing streamline gradients in FDTD is presented, as well as comparative analyses which show that the correct source injection in the FDTD simulation plays a crucial rule in obtaining accurate solutions. In particular, making use of the derivative of the input source waveform is shown to provide distinct benefits in accuracy over direct source injection. In the method, no alterations to the properties of either the source or the transmission media are required. The method is essentially frequency independent and the source injection method has been verified against examples with analytical solutions. Results are presented showing the spatial distribution of gradient-induced electric fields and eddy currents in a complete body model.

Study on diffusion and flow of benzene, n-hexane and CCl4 in activated carbon by a differential permeation method

In this paper the diffusion and flow of carbon tetrachloride, benzene and n-hexane through a commercial activated carbon is studied by a differential permeation method. The range of pressure is covered from very low pressure to a pressure range where significant capillary condensation occurs. Helium as a non-adsorbing gas is used to determine the characteristics of the porous medium. For adsorbing gases and vapors, the motion of adsorbed molecules in small pores gives rise to a sharp increase in permeability at very low pressures. The interplay between a decreasing behavior in permeability due to the saturation of small pores with adsorbed molecules and an increasing behavior due to viscous flow in larger pores with pressure could lead to a minimum in the plot of total permeability versus pressure. This phenomenon is observed for n-hexane at 30degreesC. At relative pressure of 0.1-0.8 where the gaseous viscous flow dominates, the permeability is a linear function of pressure. Since activated carbon has a wide pore size distribution, the mobility mechanism of these adsorbed molecules is different from pore to pore. In very small pores where adsorbate molecules fill the pore the permeability decreases with an increase in pressure, while in intermediate pores the permeability of such transport increases with pressure due to the increasing build-up of layers of adsorbed molecules. For even larger pores, the transport is mostly due to diffusion and flow of free molecules, which gives rise to linear permeability with respect to pressure. (C) 2002 Elsevier Science Ltd. All rights reserved.

Adsorption in slit-like pores of activated carbons: Improvement of the Horvath and Kawazoe method

Anew thermodynamic approach has been developed in this paper to analyze adsorption in slitlike pores. The equilibrium is described by two thermodynamic conditions: the Helmholtz free energy must be minimal, and the grand potential functional at that minimum must be negative. This approach has led to local isotherms that describe adsorption in the form of a single layer or two layers near the pore walls. In narrow pores local isotherms have one step that could be either very sharp but continuous or discontinuous benchlike for a definite range of pore width. The latter reflects a so-called 0 --> 1 monolayer transition. In relatively wide pores, local isotherms have two steps, of which the first step corresponds to the appearance of two layers near the pore walls, while the second step corresponds to the filling of the space between these layers. All features of local isotherms are in agreement with the results obtained from the density functional theory and Monte Carlo simulations. The approach is used for determining pore size distributions of carbon materials. We illustrate this with the benzene adsorption data on activated carbon at 20, 50, and 80 degreesC, argon adsorption on activated carbon Norit ROX at 87.3 K, and nitrogen adsorption on activated carbon Norit R1 at 77.3 K.

Input-driven Language Learning

Input-driven models provide an explicit and readily testable account of language learning. Although we share Ellis's view that the statistical structure of the linguistic environment is a crucial and, until recently, relatively neglected variable in language learning, we also recognize that the approach makes three assumptions about cognition and language learning that are not universally shared. The three assumptions concern (a) the language learner as an intuitive statistician, (b) the constraints on what constitute relevant surface cues, and (c) the redescription problem faced by any system that seeks to derive abstract grammatical relations from the frequency of co-occurring surface forms and functions. These are significant assumptions that must be established if input-driven models are to gain wider acceptance. We comment on these issues and briefly describe a distributed, instance-based approach that retains the key features of the input-driven account advocated by Ellis but that also addresses shortcomings of the current approaches.

Growth hormone regulates osteogenic marker mRNA expression in human periodontal fibroblasts and alveolar bone-derived cells

Background: Growth hormone (GH) is a potent regulator of bone formation. The proposed mechanism of GH action is through the stimulation of osteogenic precursor Cell proliferation and, following clonal expansion of these cells. promotion of differentiation along the osteogenic lineage. Objectives: We tested this hypothesis by studying the effects of GH on primary cell populations of human periodontal ligament cells (PLC) and alveolar bone cells (ABC), which contain a spectrum of osteogenic precursors. Method: The cell populations were assessed for mineralization potential after long-term culture in media containing beta-glycerophosphate and ascorbic acid, by the demonstration of mineral deposition by Von Kossa staining. The proliferative response of the cells to GH was determined over a 48-h period using a crystal violet dye-binding assay. The profile of the cells in terms of osteogcnic marker expression was established using quantitative reverse transcriptase polymerase chain reaction (RT-PCR) for alkaline phosphatase (ALP), osteopontin. osteocalcin, bone sialoprotein (BSP), as well as the bone morphogenetic proteins BMP-2, BMP-4 and BMP-7. Results: As expected, a variety of responses were observed ranging from no mineralization in the PLC populations to dense mineralized deposition observed in one GH-treated ABC population. Over a 48-h period GH was found to be non-mitogenic for all cell populations. Quantitative reverse transcriptase polymerase chain reaction (RT-PCR) BSP mRNA expression correlated well with mineralizing potential of the cells. The change in the mRNA expression of the osteogenic markers was determined following GH treatment of the cells over a 48-h period. GH caused an increase in ALP in most cell populations, and also in BMP expression in some cell populations. However a decrease in BSP. osteocalcin and osteopontin expression in the more highly differentiated cell populations was observed in response to GH. Conclusion: The response of the cells indicates that while long-term treatment with GH may promote mineralization, short-term treatment does not promote proliferation of osteoblast precursors nor induce expression of late osteogenic markers.