Clustering noisy data in a reduced dimension space via multivariate regression trees

Cluster analysis is sensitive to noise variables intrinsically contained within high dimensional data sets. As the size of data sets increases, clustering techniques robust to noise variables must be identified. This investigation gauges the capabilities of recent clustering algorithms applied to two real data sets increasingly perturbed by superfluous noise variables. The recent techniques include mixture models of factor analysers and auto-associative multivariate regression trees. Statistical techniques are integrated to create two approaches useful for clustering noisy data: multivariate regression trees with principal component scores and multivariate regression trees with factor scores. The tree techniques generate the superior clustering results.     

Putting the pieces together: Online argumentation vee diagrams enhance thinking during discussions

We examine the effect of online Argumentation Vee Diagrams (AVDs) on the quality of students’ argumentation during asynchronous, online discussions. With AVDs, students develop arguments on both sides of a controversial issue and then develop an integrated, overall final conclusion. In this study, students used AVDs individually before composing discussion notes, and then—at the end of the discussion—jointly created a group AVD using Wiki technology. Compared to a control group, the experimental intervention was found to significantly enhance the integration of arguments and counterarguments (specifically, compromises) and fostered opinion change. For AVDs to be effective, however, it was found to be necessary to include specific scaffolds on how to evaluate argument strength and/or to provide practice and feedback in using the AVDs.     

Studies of thermally stimulated currents and surface charge in polystyrene thin films

A careful study was undertaken of the initial charge developed on the non-metallized surface and of short-circuit thermally stimulated currents (TSCs) in unilaterally metallized polystyrene (PS) films 25 microm thick. The films had been negatively charged by Townsend breakdown at a voltage of −5 kV at various temperatures ranging from 90 to 130°C. The surface charge densities observed were of the order of 10^-8 C cm^-2, corresponding to full trap densities of the order of 10¹⁴ cm⁻³. The short-circuit TSC spectra of newly charged samples show a single peak at a temperature between 98 and 102°C. The thermal activation energy associated with this peak was found to be 1.2 eV. An analysis of TSCs indicates that electrons are subject to fast retrapping in PS. The ratio of the mean charge depth to the sample thickness is found to increase from 0.069 to 0.12 with the increase in the temperature of polarization, indicating a higher charge accommodation at higher temperatures of polarization. The trap-modulated mobility values for electrons at the TSC peak temperatures are the order of 10⁻¹² cm² V⁻¹s⁻¹. Such low mobility values at peak temperatures are considered to indicate the excellent charge storage properties of PS.     

Fatty Acid Elongation in Non-Alcoholic Steatohepatitis and Hepatocellular Carcinoma

Non-alcoholic steatohepatitis (NASH) represents a risk factor for the development of hepatocellular carcinoma (HCC) and is characterized by quantitative and qualitative changes in hepatic lipids. Since elongation of fatty acids from C16 to C18 has recently been reported to promote both hepatic lipid accumulation and inflammation we aimed to investigate whether a frequently used mouse NASH model reflects this clinically relevant feature and whether C16 to C18 elongation can be observed in HCC development. Feeding mice a methionine and choline deficient diet to model NASH not only increased total hepatic fatty acids and cholesterol, but also distinctly elevated the C18/C16 ratio, which was not changed in a model of simple steatosis (ob/ob mice). Depletion of Kupffer cells abrogated both quantitative and qualitative methionine-and-choline deficient (MCD)-induced alterations in hepatic lipids. Interestingly, mimicking inflammatory events in early hepatocarcinogenesis by diethylnitrosamine-induced carcinogenesis (48 h) increased hepatic lipids and the C18/C16 ratio. Analyses of human liver samples from patients with NASH or NASH-related HCC showed an elevated expression of the elongase ELOVL6, which is responsible for the elongation of C16 fatty acids. Taken together, our findings suggest a detrimental role of an altered fatty acid pattern in the progression of NASH-related liver disease.     

Alicyclobacillus spoilage and isolation--a review

Until recently, acidic products such as fruit juice and fruit based products were generally thought to be susceptible to spoilage by yeasts, mycelia fungi and lactic acid bacteria, as the low pH of these products acts as natural control measures against spoilage by most bacteria. Alicyclobacillus seem to be prevalent in fruit based products as they survive the acidic fruit juice environment, even when they are exposed to pasteurisation temperatures during production. In this review the historical background of the discovery of these bacteria is summarised. The bacterial characteristics and the reported spoilage incidences caused by members of this genus are discussed. As the isolation methods for these bacteria are controversial, this review includes a discussion of the various media that have been reported in the literature for the use in the isolation and enumeration of members of the genus Alicyclobacillus.