A Comparison of the Kubelka-Munk Reflectance with the Exact Reflectance for Isotropic Scattering

The Kubelka-Munk reflectance is compared with the exact reflectance of an isotropically scattering material, under normal experimental conditions, by obtaining estimates of the accuracy of both methods in predicting the colour of mixtures of dyes on textiles. The exact analysis produces results that, on average, are 14% more accurate than those obtained with the Kubelka-Munk analysis.     

The effect of neutron irradiation on the precipitate distribution in adjusted uranium

Precipitates in α-uranium are thought to be very important in controlling the swelling that occurs in the reactor. Cross sections from the 30 mm diameter adjusted uranium fuel bars were cut and heat-treated to give a UAl₂ precipitate distribution peaking at about 30 nm diameter. Alternate sections were irradiated to 500 MWd/te at 673 K. Comparisons before and after irradiation show that a new precipitate population is formed during irradiation. Since new precipitates can form, mechanisms of swelling resistance based on the effects of aluminium in solution are no longer tenable.     

Solubilities of methyl oleate,oleic acid,oleyl glycerols,and oleyl glycerol mixtures in supercritical carbon dioxide

Solubility isotherms for oleic acid and methyl oleate as well as mono-, di-, and trioleylglycerol (MO, DO, and TO) in supercritical fluid CO₂ at 50 and 60°C are reported. Partition coefficients for quaternary (MO-DO-TO-CO₂) mixtures were obtained at 60°C at pressures ranging from 172 to 309 bar. Data indicate that diolein, and especially monoolein, exhibit positive deviation from ideal behavior, possibly due to intermolecular hydrogen bonding. Supercritical fluid CO₂ appears to be a good media for removal of mono- and diacylglycerol by-products from synthetic triglyceride reaction mixtures at moderate temperatures.     

Rheological behaviour and mechanical characterization of injectable poly(propylene fumarate)/single-walled carbon nanotube composites for bone tissue engineering

This work investigated the effects of the use of a surfactant or the functionalization of single-walled carbon nanotubes (SWNTs) on their dispersion in uncrosslinked poly(propylene fumarate) (PPF) and the mechanical reinforcement of crosslinked composites as a function of the SWNT concentration. Rheological measurements showed good dispersion of SWNTs in uncrosslinked PPF at low concentrations of 0.05?wt% and SWNT aggregation for higher concentrations for all formulations examined. Mechanical testing demonstrated significant reinforcement in the compressive and flexural mechanical properties of crosslinked nanocomposites which peaked for low SWNT concentrations of the order of 0.05?wt%. For example, a 74% increase was recorded for the compressive modulus and a 69% increase for the flexural modulus of nanocomposites with functionalized SWNTs at a 0.05?wt% loading. Nevertheless, this reinforcement was not related to the use of a surfactant or the functionalization of the SWNTs tested. Scanning electron microscopy examinations of fractured nanocomposite surfaces revealed the formation of SWNT aggregates at higher concentrations corroborating the rheological and mechanical data. These results suggest that the dispersion of individual SWNTs in a uncrosslinked formulation is pivotal to the development of injectable nanocomposites for bone tissue engineering applications.     

Determination of MeHg in environmental sample matrices using Hg-thiourea complex ion chromatography with on-line cold vapor generation and atomic fluorescence spectrometric detection

A novel system for mercury speciation analysis using high-pressure ion chromatography (IC) has been developed and validated. Its chemistry permits separation of the two most abundant forms of Hg in natural waters, soils, sediments, and biota-monomethyl Hg (CH3Hg+) and mercuric Hg (Hg2+)-on the basis of the difference in charge of their respective thiourea (S=C(NH2)20) complexes. Once separated, both species are converted to Hg0 on-line and quantified by cold-vapor atomic fluorescence spectrometry (CVAFS). A column containing thiol-functionalized silica resin installed in the sample loop of the IC system traps Hg2+ and CH3Hg+ from prepared sample solutions without retaining interfering sample matrix components. The resulting matrix-independent chemistry permits external calibration of the system and a high sample throughput ( approximately 6 samples per hour). The system's accuracy has been validated with environmentally relevant reference materials. Figures of merit for the system, an average precision of approximately 2.5% and an absolute detection limit of <1 pg, are comparable to state-of-the-art gas chromatography approaches for Hg speciation analysis (ethylation/GC-CVAFS) and meet or exceed those of all extant LC systems. Low relative detection limits are attainable through preconcentration onto the thiol resin.     

Applying continuous chaotic modeling to cardiac signal analysis

In the last decade, chaos theory has become a popular method for approaching the analysis of nonlinear data for which most mathematical models produce intractable solutions. The concept of chaos was first introduced with applications in meteorology. Since then, considerable work has been done in the theoretical aspects of chaos. Applications have abounded, especially in medicine and biology. A particularly active area for the application of chaos theory has been cardiology. Many aspects of heart disease have been addressed, including whether chaos represents the healthy or diseased state. Most approaches to chaotic modeling rely on discrete models of continuous problems, which are represented by computer algorithms. Due to the nature of chaotic models, both the discretization and the computer simulation can lead to propagation of errors that may overtake the actual solution. This article describes an approach to chaotic modeling in which a continuous model is developed based on a conjectured solution to the logistic equation. As a result of this approach, two practical methods for quantifying variability in data sets have been derived. The first is a graphical representation obtained by using second-order difference plots of time series data. The second is a central tendency measure (CTM) that quantifies this degree of variability. The CTM can then be used as a parameter in decision models, such as neural networks. It appears that measuring the degree of variability is a more useful measure of chaos, as demonstrated by the application of this work to the analysis of congestive heart failure patients as compared to normal controls     

Elevated transforming growth factor-alpha levels in bronchoalveolar lavage fluid of patients with acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) frequently results in a fibroproliferative response that precludes effective alveolar repair. Transforming growth factor-alpha (TGF-alpha), a potent epithelial and mesenchymal cell mitogen, may modulate the response to lung injury. In this study, we determined whether bronchoalveolar lavage fluid (BALF) concentrations of TGF-alpha are increased during the first 2 wk after the onset of ARDS and, if so, whether increased TGF-alpha levels in lavage fluid are associated with increased levels of procollagen peptide III (PCP III), a biological marker of fibroproliferation, and with increased fatality rates. We enrolled 74 consecutive patients with ARDS prospectively identified on admission to the intensive care unit of a tertiary care hospital, and 11 patients with chronic interstitial lung disease. Thirteen healthy volunteers served as control subjects. TGF-alpha concentrations were measured in BALF recovered on Days 3, 7, and 14 after the onset of ARDS (total of 130 lavage samples). TGF-alpha was detected in the lavage fluid of 90% of patients with ARDS (67 of 74), and in 100% of patients with idiopathic pulmonary fibrosis (IPF) (10 of 10), but in none of 13 normal volunteers. At each day tested, the median lavage TGF-alpha level of patients with ARDS was significantly higher than that of normals. The overall fatality rate was 45% (33 of 74 patients). In a univariate analysis, the median TGF-alpha levels in nonsurvivors were 1.5-fold higher at Day 7 (p = 0.06) and 1.8-fold higher at Day 14 (p = 0.048). The fatality rate was 4 times higher (CI 1.6, 17.5) for patients with both increased lavage TGF-alpha and PCP III concentrations at Day 7 than for patients with low TGF-alpha and PCP III values, indicating a synergistic relationship between TGF-alpha and PCP III. We conclude that increased levels of TGF-alpha in BALF are common in patients with ARDS and that lavage TGF-alpha is associated with a marker of the fibroproliferative response in sustained ARDS.     

Approaches to management of uncertainty in an expert system

The problem of reasoning with uncertainty in expert systems has become an issue of increasing interest. In this article, the development of EMERGE, an expert system for chest pain analysis, is traced. Modifications to the system to utilize new techniques are analyzed. In particular, the incorporation of techniques from approximate reasoning is discussed as applied in the chest pain rule base to take into account degrees of presence of symptoms and unequal contribution of antecedents. Specifically, theoretical results in approximate reasoning by Yager are applied in the EMERGE expert system in an attempt to improve its performance in borderline cases.     

Malaria's Eve: evidence of a recent population bottleneck throughout the world populations of Plasmodium falciparum

We have analyzed DNA sequences from world-wide geographic strains of Plasmodium falciparum and found a complete absence of synonymous DNA polymorphism at 10 gene loci. We hypothesize that all extant world populations of the parasite have recently derived (within several thousand years) from a single ancestral strain. The upper limit of the 95% confidence interval for the time when this most recent common ancestor lived is between 24,500 and 57,500 years ago (depending on different estimates of the nucleotide substitution rate); the actual time is likely to be much more recent. The recent origin of the P. falciparum populations could have resulted from either a demographic sweep (P. falciparum has only recently spread throughout the world from a small geographically confined population) or a selective sweep (one strain favored by natural selection has recently replaced all others). The selective sweep hypothesis requires that populations of P. falciparum be effectively clonal, despite the obligate sexual stage of the parasite life cycle. A demographic sweep that started several thousand years ago is consistent with worldwide climatic changes ensuing the last glaciation, increased anthropophilia of the mosquito vectors, and the spread of agriculture. P. falciparum may have rapidly spread from its African tropical origins to the tropical and subtropical regions of the world only within the last 6,000 years. The recent origin of the world-wide P. falciparum populations may account for its virulence, as the most malignant of human malarial parasites.