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The behavior of two series of concrete slabs exposed to sulfate-bearing soils was investigated by a numerical model called
STADIUM. In addition to the diffusion of ions and moisture, the model also accounts for the effects of dissolution/precipitation
reactions on the transport mechanisms. The simulations yielded by the model were compared to the actual degradation of the
slabs after 8 years of exposure. The microstructural alterations of concrete resulting from the penetration of magnesium,
chloride and sulfate ions were studied by backscatter mode scanning electron microscope observations and energy-dispersive
X-ray analyses. The comparison of both series of data indicates that the model can reliably predict the various features of
the microstructural alterations of concrete.
Editorial Note Laval University (Canada) is a RILEM Titular Member. Prof. J. Marchand was awarded the 2000 Robert L'Hermite Medal. He is Editor in Chief for Concrete Science and Engineering and Associate Editor for Materials and Structures. He participates in RILEM TC 186-ISA ‘Internal Sulfate attack’. 相似文献
Résumé Le comportement de deux séries de dalles sur sol en béton exposées à des sols chimiquement agressifs a été étudié à l'aide d'un code de calcul numérique appelé STADIUM. Ce modèle permet de décrire le transport couplé de l'eau et des ions dans des matériaux poreux non-saturés en prenant en considération l'influence des réactions chimiques. Les résultats des simultations de la dégradation du béton après huit ans d'exposition à des ions chlore, sulfate et magnésium. Les observations ont été réalisées par microscopie électronique à balayage. Des analyses par dispersion des rayons X ont également été effectuées. Les données démontrent clairement que le modèle perment de prédire avec précision le comportement du béton soumis à différents types d'agression chimique.
Editorial Note Laval University (Canada) is a RILEM Titular Member. Prof. J. Marchand was awarded the 2000 Robert L'Hermite Medal. He is Editor in Chief for Concrete Science and Engineering and Associate Editor for Materials and Structures. He participates in RILEM TC 186-ISA ‘Internal Sulfate attack’. 相似文献
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E Ashihara AM Vannucchi G Migliaccio AR Migliaccio 《Canadian Metallurgical Quarterly》1997,171(3):343-356
The Word Accentuation Test assesses the accentuation of 30 infrequent Spanish words written without the accentuation mark and is an easy-to-use tool for estimating premorbid intelligence of Spanish-speaking people. Its intraobserver (0.97) and interobserver (0.93) reliabilities and its correlation with the Wechsler Adult Intelligence Scale (.837) and Raven's Progressive Matrices (.655) are high, offering a good prediction of general intelligence. It is resistant to mental deterioration; 20 demented and 40 controls matched by sex, age, and education obtained similar scores. The discrepancies between current and predicted scores in Raven's scale can diagnose mild-moderate dementia with 0.79 accuracy (sensitivity, 0.78; specificity, 0.82). 相似文献
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The effect of caseinate and soy protein in the diet on the mutagenicity induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was assessed in-vivo and ex-vivo in the DNA-repair host-mediated assay and liquid suspension assay, respectively. Of the two proteins only casein showed a strong antimutagenic activity over the whole digestive tract, except in the stomach. It is suggested that the molecular structure of a protein determines its protective effect against mutagens: casein lacks secondary and tertiary structure so that amino acids are more readily available for interaction with the mutagen than with the amino acids in soy protein which is a globular protein. 相似文献
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AR Santos JC Nery NC Duppre ME Gallo JT Filho PN Suffys WM Degrave 《Canadian Metallurgical Quarterly》1997,46(2):170-172
A case is described in which a pericardial branch of a nongrafted left internal mammary artery communicated directly with the distal left anterior descending artery, following saphenous vein bypass grafting. This type of collateralization following coronary artery bypass surgery seems to be very rare, and perhaps could protect the myocardium from severe ischemia. 相似文献
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Scattered radiation from within the treatment head can contribute significant dose to all parts of a radiotherapy treatment field. A multileaf collimator may be used to create an arbitrarily shaped field, and may also be used, under dynamic control, to modulate the beam intensity over the field. This method of intensity modulation is effectively a superposition of a large number of fields which have the same beam direction, but different shapes, and some of these shapes may have unusually small dimensions, particularly in the direction of the leaf movement. Two models for predicting the head scatter under these conditions have been investigated. These are a first-order Compton scatter approximation from the flattening filter, and an empirical fit to measured data using an exponential function. The first model only considers scatter from the flattening filter and has been applied to field sizes between 2 cm by 2 cm and 10 cm by 10 cm, where agreements are all within 1%. However it is not satisfactory at larger field sizes where small scatter contributions, from scattering sources other than the flattening filter, are integrated over large areas. The second model uses measured data between 4 cm by 4 cm and 30 cm by 30 cm to optimize the exponential function and is used to calculate the head scatter contribution for all field sizes. In this case good agreement is achieved over the full field size range, and hence this is a more generally applicable model. Results are presented for static irregularly shaped fields and intensity modulated beams created using a Philips multileaf collimator. 相似文献
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KL Gatford TP Fletcher IJ Clarke PC Owens KJ Quinn PE Walton PA Grant BJ Hosking AR Egan EN Ponnampalam 《Canadian Metallurgical Quarterly》1996,74(6):1314-1325
The effects of sex and age on patterns of circulating somatotropin (ST) concentration and plasma IGF-I, IGF-II, insulin, and IGF binding protein-3 (IGFBP-3) were studied in ram, wether, and ewe lambs (n = 7 or 8) sampled at mean ages of 81 (I1) and 158 d (I2). Between 81 and 158 d of age, rams grew more rapidly than wethers (P < .01), and wethers grew more rapidly than ewes (P < .01). The sex differences in growth were reflected in empty body weight at slaughter: rams > wethers > ewes (P < .05). Mean plasma ST concentrations, ST pulse amplitude, and integrated plasma ST concentrations were greater (P < .05) in rams than in ewes at I1 and I2. Characteristics of the ST plasma profile in wethers were generally intermediate between those of rams and ewes. The interpulse interval was greater in ewes than in wethers at I2. The IGF-I and IGFBP-3 concentrations were greater in rams than in ewes at both sampling times. Plasma IGF-II was greater in ewes than in rams at I2. Mean plasma ST was approximately two thirds less at I2 than at I1 regardless of sex. Mean plasma ST and IGF-I at both ages were positively correlated with growth. Mean plasma ST at I2 was negatively correlated with fatness at slaughter. Sex and age significantly affected patterns of circulating ST and concentrations of IGF-I and IGFBP-3 in prepubertal growing lambs, under conditions for which growth rates and composition were also sexually dimorphic. 相似文献