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Type Expression (type + expression)

Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

Nonisothermal and isothermal crystallization kinetics of nylon-12

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008
Neil L. A. McFerran
Abstract The isothermal and nonisothermal crystallization behavior of Nylon 12 was investigated using differential scanning calorimetry (DSC). An Avrami analysis was used to study the isothermal crystallization kinetics of Nylon 12, the Avrami exponent (n) determined and its relevance to crystal growth discussed and an activation energy for the process evaluated using an Arrhenius type expression. The Lauritzen and Hoffman analysis was used to examine the spherulitic growth process of the primary crystallization stage of Nylon 12. The surface-free energy and work of chain folding were calculated using a procedure reported by Hoffmann and the work of chain folding per molecular fold (,) and chain stiffness of Nylon 12 (q) was calculated and compared to values reported for Nylons 6,6 and 11. The Jeziorny modification of the Avrami analysis, Cazé and Chuah average Avrami parameter methods and Ozawa equation were used in an attempt to model the nonisothermal crystallization kinetics of Nylon 12. A combined Avrami and Ozawa treatment, described by Liu, was used to more accurately model the nonisothermal crystallization kinetics of Nylon 12. The activation energy for nonisothermal crystallization processes was determined using the Kissinger method for Nylon 12 and compared with values reported previously for Nylon 6,6 and Nylon 11. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Gene expression profiling of the human prostate zones

BJU INTERNATIONAL, Issue 4 2006
Leonie Van Der Heul-Nieuwenhuijsen
OBJECTIVE To investigate differences in gene expression in different zones of the prostate by microarray analyses, to better understand why aggressive tumours predominantly occur in the peripheral zone (PZ), whereas benign prostatic hyperplasia (BPH) occurs almost exclusively in the transition zone (TZ). MATERIALS AND METHODS Expression profiling of both prostate zones was done by microarray analysis. Reverse transcription-polymerase chain reaction (RT-PCR) of the top 18 genes confirmed the microarray analyses. RT-PCR with common cell-type markers indicated that the differential expression between the zones was not caused by an unequal distribution of different cell types. Primary stromal and epithelial prostate cells were used to study cell type expression in the 12 highest differentially expressed zonal-specific genes. RESULTS In all, 346 genes were identified as preferentially expressed in the TZ or PZ. A few of the TZ-specific genes, including ASPA, FLJ10970 and COCH, were also stroma-specific. Comparisons with other microarray studies showed that gene expression profiles of prostate cancer and BPH correlate with the expression profiles of the PZ and TZ, respectively. CONCLUSION Gene expression differs between the PZ and TZ of the prostate, and stromal,epithelial interactions might be responsible for the distinct zonal localization of prostate diseases. [source]

Stem cells and gastric cancer: Role of gastric and intestinal mixed intestinal metaplasia

CANCER SCIENCE, Issue 2 2003
Masae Tatematsu
All of the different types of stomach epithelial cells are known to be derived from a single progenitor cell in each gland. Similarly, cancers develop from single cells, based on data from clonality analysis in C3H/HeN , BALB/c chimeric mice. Using gastric and intestinal epithelial cell markers, intestinal metaplasia (IM) can be divided into two major types: a gastric and intestinal (GI) mixed type, and a solely intestinal (I) type. Ectopic expression of Cdx genes and down-regulation of Sox2 in isolated single GI mixed IM glands suggests abnormal differentiation of stem cells that can produce both gastric (G) and I type cells. Similarly, phenotypic expression of gastric cancer cells of each histological type can be clearly classified into G and I type epithelial cells. The heterogeneity of phenotypic expression of gastric cancer cells in individual cancers is assumed to reflect this intrinsic potential for differentiation in two directions. Gastric cancers at early stages, independent of the histological type, mainly consist of G type cells, and phenotypic shift from G to I type expression is clearly observed with progression. The data thus suggest IM may not be a preneoplastic change in gastric carcinoma, but rather that cells of the I type may appear independently in the gastric mucosa in IM and in gastric cancers. Intestinalization of gastric mucosa and cancer cells may represent a kind of homeotic transformation. Whether disturbance of the regulation of Sox2 and Cdx genes may be of importance to the biological behavior of gastric cancers should therefore be clarified in future studies. (Cancer Sci 2003; 94: 135,141) [source]

Transient simulation of a catalytic converter for a dual fuel engine

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2000
Benlin Liu
Abstract An experimental and modelling study was performed for a catalytic converter attached to a natural gas/diesel dual fuel engine. The catalytic converter was a ceramic monolith honeycomb substrate coated with a washcoat of catalyst. A multiple segmented design of converter was used. This paper describes the application of a one-dimensional finite element model for the transient and steady state operation of this converter. The model is a single channel model. The laminar flow was approximated using a dispersed plug flow model. The chemical kinetics were simulated using LHHW type expressions. Comparison of simulated results are made with experimental results for heating and cooling cycles that resulted from speed and load changes on the engine. These comparisons showed a maximum difference between experimental and predicted emission levels of about 10%. On a mené une étude expérimentale et réalisé la modération d'un convertisseur catalytique relié è un moteur è combustible double gaz naturel/diesel. Le convertisseur catalytique est un substrat de monolithes céramique en nid d'abeille enduit d'une couche de catalyseur. Une conception segmentée multiple a étée utilisée pour le convertisseur. On décrit dans cet article l'application d'un modèle d'éléments finis unidimensionnel pour un fonctionnement en régime transitoire et permanent du convertisseur. Ce modèle est un modèle à canal unique. L'écoulement laminaire a été approximé à l'aide d'un modèle à écoulement piston dispersé. La cinétique chimique a été simulée au moyen d'expressions de type LHHW. On effectue une comparaison entre les résultats simulés et les résultats expérimentaux pour les cycles de chauffe et de refroidissement qui résultent des changements de vitesse et de charge sur le moteur. Ces comparaisons montrent une différence maximum entre les taux d'émission expérimentaux et prédits d'environ 10%. [source]