Main Parameters Of Interest Research Articles

A Bayesian Approach for Incorporating Variable Rates of Heterogeneity in Linkage Analysis

A widely used approach for dealing with locus heterogeneity in linkage analysis is based on mixture likelihood, in which a single mixing (heterogeneity) parameter represents the probability that each family is of linked type. However, in general, different types of families exhibit different heterogeneity levels. To incorporate this variability, we propose a new approach wherein each family has its own heterogeneity parameter representing the probability that it is of linked type. These parameters are nuisance parameters, whereas the main parameter of interest is the location of the disease gene, if there is any. We model the problem in the Bayesian framework and implement it using the Markov chain Monte Carlo (MCMC) methodology. In particular, we use the reversible-jump MCMC sampler to move between the two models: linkage and no linkage. We first estimate the posterior probability of linkage on a chromosome and the corresponding Bayes factor. If linkage is inferred, then the location of the disease gene along with its credible set is estimated. The asymptotic joint distribution of the estimators is derived. We show that this approach is more powerful than the currently used approach in detecting linkage, whereas the two approaches have comparable false-positive rates. The proposed method was applied to a lung cancer dataset of Genetic Epidemiology of Lung Cancer Consortium and an asthma dataset consisting of three samples from Genetic Analysis Workshop 12. Since both lung cancer and asthma are complex traits with heterogeneous genetic predisposition, they provide suitable applications for the proposed method.

RF Radiation Properties of Printed-Circuits Boards in a GTEM Cell

The behavior of reradiated fields from printed-circuits boards (PCBs), with the radar cross section being the main parameter of interest, is investigated in this paper. A rigorous approach to predict radiation from PCBs in a gigahertz transverse electromagnetic cell is presented. The analysis is based upon the use of the reciprocity theorem in combination with the method of moment applied to the scattered field, thus yielding a generalized impedance matrix, whose determinant represents the characteristic polynomial of the scattering system. The effectiveness of the method is demonstrated by investigating some canonical circuit configurations and structures illustrating sources of fundamental electromagnetic interference mechanism. The validity and the accuracy of the analysis becomes obvious in view of the one-to-one correlation with measurements

Investigation on the influence of cell shape anisotropy on the mechanical performance of closed cell aluminium foams using micro-computed tomography

The mechanical behaviour of closed-cell aluminium foams made by both powder metallurgy (LKR) and liquid state (Hydro) processes is investigated. Hydro foams exhibit a significant anisotropy in their mechanical behaviour. The transverse direction stands out as the most favourable one in terms of strength. In contrast, LKR foams show an almost isotropic compressive behaviour. Both foams perform at a level far below the theoretical predictions. The reduced values are a result of imperfections and defects in the cellular microstructure. X-ray microfocus computed tomography (μCT) is therefore used for internal investigation of the foam cell structure. 2D and 3D quantitative image analyses have been performed on μCT images to characterise the morphometric parameters of the foams. The main parameters of interest are cell size, cell size distribution and cell features information. A preferred cell orientation in Hydro foams is observed along the normal and the transverse directions of the specimen. This cell shape anisotropy is quantified using the dimensions of the three axes of the equivalent ellipsoids. The orientation of the cells is well characterised by pole figures of the three axes of equivalent ellipsoids. The influence of this geometrical anisotropy on the mechanical behaviour of the foam is discussed.

Less invasive stabilization of complex tibial plateau fractures: a biomechanical evaluation of a unilateral locked screw plate and double plating.

To compare the vertical subsidence in a bicondylar tibial plateau fracture model stabilized either by a unilateral locked screw plate (LSP) or by double plating. Biomechanical cadaver study. A 41-C1 fracture model was created in eight pairs of fresh-frozen human cadaver tibiae. Stabilization was performed either by open reduction and internal fixation (ORIF) using a lateral L-buttress plate and a medial four-hole, one-third tubular antiglide-plate or by a lateral LSP. Four load levels (400N, 800N, 1200N, 1600N), each with five cycles, were consecutively applied to the medial plateau. The vertical plastic deformation at the end of each cycle was the main parameter of interest. Statistical analysis was performed with the two-way ANOVA test for repeated measurements. Each individual loading level was analyzed separately using Student t test. In one pair, both fixation techniques failed at the first loading cycle of 1200N. One ORIF fixation failed at the first loading cycle of 1600N. The average plastic vertical subsidence was 0.40 mm (LSP) and 0.25 mm (ORIF) at 400N (P = 0.291), 0.83 mm (LSP) and 0.81 mm (ORIF) at 800N (P = 8.82), 1.06 mm (LSP) and 0.96 mm (ORIF) at 1200N (P = 0.98), and 1.54 mm (LSP) and 1.14 mm (ORIF) at 1600N (P = 0.53). Vertical subsidence depended on the applied load (P = 0.002), but not on the method of fixation (P = 0.236). Both fixation techniques have a high resistance to vertical subsidence even with loads exceeding the average body weight. No statistically significant difference was seen between the two methods of fixation.

Error variation in OSL palaeodose estimates from single aliquots of quartz: a factorial experiment

We use a factorial experiment to study systematic and random differences between measured OSL palaeodoses for a variety of quartz samples. These include samples that have absorbed either a large or small natural or laboratory-induced radiation dose, either with or without prior heating or bleaching. The systematic factors studied are the size of the test dose, the preheat temperature and the number of quartz grains in each multi-grain aliquot. Palaeodoses were estimated using a single-aliquot regenerative-dose protocol. The main parameter of interest is the amount of random variation, over and above that due to photon counting statistics, to be expected between estimates from aliquots that have received the same radiation dose. This over-dispersion is generally larger for natural samples than for artificially bleached ones, and it varies from about 1% in the most favourable cases to about 18% for small aliquots of a sample that had received a natural dose of about 46 Gy . The latter is comparable to the over-dispersion reported for single grains of natural quartz that are thought to have been well-bleached at the time of deposition. The factorial experiment also revealed a number of systematic effects. In particular, measured palaeodoses using a preheat temperature of 260°C were systematically lower than those using 180°C, by up to about 5% in some cases.

Determination of the axial and radial fibre stress distributions for the Broutman test

Composite micromechanics has been a subject of considerable interest over the past 25 years. Most research has been concerned with single-fibre composite specimens and the distribution of axial fibre stress or strain. The main parameter of interest is normally the interfacial shear stress that characterises the conditions for the breakdown of the fibre/matrix interface. Over recent years significant advances have been made through the use of Raman and/or fluorescence microscopy to map the distribution of axial stress and strain along the fibres. This paper reports the development of fluorescence microscopy to enable both axial and radial fibre stresses to be determined in alumina single crystal fibres embedded in epoxy resins. This is demonstrated for the Broutman test in which the fibre/matrix interface is subjected to significant levels of transverse radial stress. The micromechanics of reinforcement by single crystal and polycrystalline alumina fibres is contrasted. Important new insights into the processes that initiate breakdown of the fibre/matrix interface are evaluated.

Anomalous Kinetics of Depletion Zone Growth with One-Dimensional Geometry: Photobleaching Experiments and Simulations

ABSTRACTWe studied the kinetics of a diffusion-limited trapping reaction A + T → T in an effective one-dimensional geometry by experiments, supported by simulation calculations. The experiments are based on the photobleaching reaction of fluorescein dyes. The main parameter of interest is the θ-distance, which is related to the expansion of the depletion zone and can be measured directly from experiment. We found that θ-distance scales with t1/2 asymptotically, as predicted by previous theory. In addition, we found that the θ-distance increases faster than t1/2 inside the trap at early times, which has not been explored previously. Furthermore, there is a third, intermediate regime, with a slow increase of slope. Our experimental results are consistent with our simulation results.

2D and 3D Characterization of Metal Foams Using X-ray Tomography

The aim of this paper is to present a methodology for 2D and 3D characterization of different foams using X-ray microtomography with a resolution of 30 micrometer. 2D and 3D quantitative image analyses have been performed to obtain information about the cells. The main parameters of interest are the cell size, the cell size distribution, morphology of the cells, connectivity of the cells, and fraction of matter at the edges. We use morphological operations such as opening granulometry to separate cells when they are not perfectly closed. This characterization was performed on Alporas, IFAM, and Norsk-Hydro foam.

Drought‐Intensity Duration and Frequency Analysis: A Case Study of Western Uganda

AbstractThis paper describes (a) drought occurrences in two selected climatic zones of western Uganda and (b) examines the meteorological aspects of drought where rainfall is the main parameter of interest. Rainfall data from various stations in each climatic zone were checked for consistency using the double mass curve technique, and one representative station from each climatic zone was selected. Two probability distributions: normal and log‐normal were fitted to the data, and the log‐normal distribution provided a better fit in each case. Drought volumes, return periods, intensities, and severity indexes were determined for each climatic zone. The annual potential evapotranspiration was also calculated and plotted against the rainfall to give the soil‐moisture deficit. From the results of the analysis it was observed that droughts of a higher severity occurred in Kasese compared with Mbarara.

High-resolution separation of polychlorinated biphenyls by comprehensive two-dimensional gas chromatography

Comprehensive two-dimensional gas chromatography (GC×GC) with micro electron-capture detection (μECD) has been optimised for the separation of polychlorinated biphenyl congeners with emphasis on the separation of 12 toxic non- and mono- ortho chlorinated biphenyls (CBs), viz. CBs 77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169 and 189. The selection of the first- and second-dimension columns and the temperature programme optimisation were carried out with a mixture of 90 CBs and the results are compared with those of one-dimensional GC. A complete separation of all 12 priority CBs was obtained with two column combinations, HP-1–HT-8 and HP-1–SupelcoWax-10. With the HP-1–HT-8 column set, ordered structures show up in the two-dimensional plane, with the number of chlorine substituents and their position ( ortho vs. non- ortho) being the main parameters of interest. This can help with congener identification. Estimated detection limits are excellent, i.e. about 10 fg. To illustrate the potential and the versatility of GC×GC–μECD, a cod liver extract and a standard mixture of the 17 most toxic polychlorinated dibenzo- p-dioxins and polychlorinated dibenzofurans together with 90 CBs were analysed as an application.

Aggregation Number Determination in Aqueous Solutions of a Hydrophobically Modified Poly(ethylene oxide) by Fluorescence Probe Techniques

In this paper, we report the results of fluorescence probe studies of association in aqueous solution of a model polymer ODU, which is a C18H37 end-capped monodisperse poly(ethylene oxide) with a molecular weight of 35 000 and essentially 100% end group substitution. The main parameter of interest is the end group aggregation number NR, which we determine by the time-resolved fluorescence quenching technique using pyrene as a probe. Aiming to extend this technique to situations where the probe is not solubilized completely by the polymer micelles, which happens when the polymer concentration in a solution becomes very low, we modified the standard Poisson quenching model to account for the emission of the probe in the water phase. ODU solutions undergo phase separation at polymer concentrations between 2.1 g/L and 20 g/L. The aggregation number in a 2.1 g/L solution was found to be 23. For high concentration polymer solutions, from 3 to 17 wt %, we found that the aggregation number tends to increase with ...

Nanoindentation as a tool for characterising the mechanical properties of tribological transfer films

In conventional pin-on-disk testing of the tribological characteristics of two different materials in sliding contact, the main parameters of interest are notably the friction and wear properties of the material pair. However, when two bodies consisting of hard and soft materials, respectively, are subjected to such testing, the appearance of a transfer film, or third body, which can be a composite mixture of the two, is often observed. This layer is formed through mutual transfer and/or by mechanical mixing of the two materials. Until now, the characterisation of transfer films in terms of their mechanical properties has been hampered by their non-homogeneous distribution across a tested surface, their small size, low thickness and the difficulty in accurately positioning a test probe such that the film properties can be measured independently from those of the substrate. This paper investigates the mechanical properties of transfer films created between other material pairs of significant industrial importance, namely hard coatings (TiN, TiCN, TiAlN, CrN) for cutting tool applications and bulk ceramics (Al 2O 3, WC). Results are presented in terms of friction and wear properties, and correlated with mechanical properties.

Excitation Frequency Effects on the Stiffness and Damping Coefficients of a Five-Pad Tilting Pad Journal Bearing

An experimental study is performed to investigate the frequency effects of the excitation force on the linear stiffness and damping coefficients of a LOP (load on pad) type five-pad tilting pad journal bearing with the diameter of 300.91 mm and the length of 149.80 mm. The main parameter of interest in the present work is excitation frequency to shake the test hearing. The excitation frequency is controlled independently, using orthogonally mounted hydraulic exciters, as follows: 1) excitation frequency ratio in the x-axis direction νx = 0.5, 2) excitation frequency ratio in the y-axis direction νy = 0.6, 0.7, 0.8, 0.9. The magnitude of the excitation force is controlled to make sure that the test hearing has a linear behavior during the test. The relative movement between the bearing and shaft, and the acceleration of the bearing casing are measured as a function of excitation frequency using the different values of bearing load and shaft speed. Measurements show that the variation of excitation, frequency has quite a little effect on both stiffness and damping coefficients. The stiffness coefficients of the five-pad tilting pad journal bearing slightly decrease as the excitation frequency ratio increases, while the damping coefficients slightly increase with excitation frequency ratio, especially in the case of lower speed and higher load. Both direct stiffness and damping coefficients in the direction of bearing load decrease with an increase of shaft speed, but increase with the bearing load.

Asymptotic properties of some underdiagonal walks generation algorithms

Using classical properties of Random walks and Brownian motion, we derive the asymptotic distribution of some characteristics of an algorithm proposed by Barcucci et al. (1995) to generate underdiagonal walks of size n. The main parameters of interest are the cost of the algorithm (in terms of calls to a random generator), the height of the walk at its last step and the maximum of the walk. We obtain various forms of probability generating functions, Laplace transforms of densities, continuous distribution functions, asymptotic densities and discrete stationary distributions.

Kinetics of absorption atelectasis during anesthesia: a mathematical model.

Recent computed tomography studies show that inspired gas composition affects the development of anesthesia-related atelectasis. This suggests that gas absorption plays an important role in the genesis of the atelectasis. A mathematical model was developed that combined models of gas exchange from an ideal lung compartment, peripheral gas exchange, and gas uptake from a closed collapsible cavity. It was assumed that, initially, the lung functioned as an ideal lung compartment but that, with induction of anesthesia, the airways to dependent areas of lung closed and these areas of lung behaved as a closed collapsible cavity. The main parameter of interest was the time the unventilated area of lung took to collapse; the effects of preoxygenation and of different inspired gas mixtures during anesthesia were examined. Preoxygenation increased the rate of gas uptake from the unventilated area of lung and was the most important determinant of the time to collapse. Increasing the inspired O2 fraction during anesthesia reduced the time to collapse. Which inert gas (N2 or N2O) was breathed during anesthesia had minimal effect on the time to collapse.

Nanoindentation and scanning force microscopy as a novel method for the characterization of tribological transfer films

In conventional pin-on-disk testing of the tribological characteristics of two different materials in sliding contact, the main parameters of interest are notably the friction and wear properties of the material pair. However, when two bodies consisting of hard and soft materials respectively are subjected to such testing, the appearance of a transfer film, or third body, which can be a composite mixture of the two, is often observed. Until now the characterization of transfer films in terms of their mechanical properties has been hampered by their non-homogeneous distribution across a tested surface, their small size, low thickness and the difficulty in accurately positioning a test probe such that the film properties can be measured independently from those of the substrate. In this paper a new method is introduced, consisting of nanoindentation and scanning force microscopy (SFM), which is capable of highly localized indentation testing of a specified sample site with high resolution imaging of the area prior to and after indentation. In this way the hardness and modulus of a transfer film can be obtained, as well as valuable surface topographical information concerning the material response to the indentation. Measurements are presented for the material pair A286/polyimide after testing on a pin-on-disk tribometer in ambient air and liquid nitrogen. Distinct variations in hardness between the transfer films and their contacting bodies have been observed and correlated to the wear behaviour and testing environment.

Reduction of homologous blood requirements by blood-pooling at the onset of car to pulmonary bypass

This study was done to investigate whether an intraoperative autologous blood donation (pooling) at the onset of cardiopulmonary bypass can reduce homologous blood requirements during and after operations for myocardial revascularization. Ninety patients were assigned equally to two groups. In group C, serving as the control group, cardiopulmonary bypass was done with a membrane lung primed with 1500 ml of Ringer's solution. The cardiopulmonary bypass flow ranged between 2.4 L/min per square meter in normothermia and 1.5 L/min per square meter in moderate hypothermia of 30 degrees to 32 degrees C. In group P the same devices were used as in group C; however, at the onset of cardiopulmonary bypass 500 to 1000 ml of heparinized blood was "pooled" in a bag and substituted by the same volume of Ringer's solution. The lower hemodilution limit was set to a hematocrit value of 20%. The pooled blood was retransfused after the aorta was decannulated. The main parameter of interest was the total volume of red cell concentrates and fresh frozen plasma required during the operation and the subsequent stay in the hospital. The results were that group C received on average 792 +/- 639 ml and group P 337 ml +/- 382 ml of red cell concentrates. Very small amounts of fresh frozen plasma were used on average: group C, 56 ml; group P, 0 ml. These differences were highly significant (p < 0.001). Remarkably, 44% of patients in group P did not require any homologous blood products compared with 16% in group C. In conclusion, modern oxygenators, which provide sufficient oxygen transport capacity, make it feasible to decrease the hematocrit to 20% by "pooling" blood at the beginning of cardiopulmonary bypass and replacing it with saline solution. This procedure led to a highly significant saving of homologous blood.

Correlational Meta-Analysis: Independent and Nonindependent Cases

The purpose of this study was to determine the effect of the violation of the assumption of independence when combining correlation coefficients in a meta-analysis. In this Monte Carlo simulation the following four parameters were used with the values specified: N-the sample size within a study (20, 50, 100), p-the number of predictors (1, 2, 3, 5), rho( i)-the population intercorrelation among predictors (0, .3, .7), rho( p)-the population correlation between predictors and criterion (0, .3, .7). When cnly one predictor was used or when the intercorrelation among predictors equaled zero, the assumption of independence was not violated. The assumption of independence was violated when more than one predictor with an intercorrelation exceeding zero were used. Therefore, rho( i) the index of nonindependence was the main parameter of interest. For both r's and Fisher's z's, the means, medians, and standard deviations showed no discernible change over levels of rho( i) or p, but the precision of estimation of the expected values improved as N increased. The 90%, 95%, and 99% confidence intervals for both r's and Fisher's z's showed no change over levels of rho( i) or p, but the intervals narrowed as N increased.

Microprocessor-based system for monitoring spinal evoked potentials during surgery.

Recently there has been considerable interest in the use of evoked potentials for monitoring the functional integrity of the spinal cord during surgical procedures such as spinal fusion. This paper describes a signal processing regimen consisting of ensemble averaging and matched filtering, developed to enhance the signal-to-noise ratio of surface-recorded spinal evoked potentials. This system also allows reliable detection of changes in signal latency, amplitude, and waveshape, the main parameters of interest. A microprocessor-based dedicated system for collection and processing of somatosensory evoked potentials data on-line has been designed. Portability, cost effectiveness, and user interaction aresome of the main characteristics of the system design. The performance of the system has been evaluated in the laboratory with simulated data, and data recorded from human subjects. The system performance meets the design expectations. Arrangements are being made to evaluate the system in the clinical environment.

A BOREHOLE MAGNETOMETRIC RESISTIVITY EXPERIMENT*

AbstractA borehole magnetometric resistivity (MMR) experiment is described in which an attempt is made to determine the extent and orientation of zones of fissuring within an otherwise massive sequence of carboniferous limestone. The region under investigation lies beneath a landfill site and the main parameter of interest is the direction of flow of ground water, which will be influenced by the orientation of the faults or fissures within the rock. The MMR method possesses some extremely advantageous features for application to hydro‐geological problems of this kind. The method is sensitive to electrical current channelling within an otherwise relatively resistive medium, and the detection of the magnetic field within the borehole does not depend upon electrical contact of the receiver with the ground. Consequently, the method can be used in dry or plastic‐cased boreholes. A direction of maximum electrical current flow is deduced from the MMR data which coincides with the predominant direction of jointing within the region.We are most grateful to the Water Research Centre, Medmenham, Berkshire, for supporting this research and particularly to Dr M. Fleet and Mr K. Beesley for their help and advice.