Calcium carbonate solubility: a reappraisal of scale formation and inhibition.

Considerable disparity exists in the published thermodynamic data for selected species in the Ca(2+) /CO(2)/H(2)O system near 25 degrees C and 1 atm pressure. Some authors doubt the significance of CaCO(3)(0)aq) complexes although there is experimental evidence of their occurrence. Evaluation of all the published experimental and estimated data for aqueous calcium carbonate species confirms that the consistent set of constants given by Plummer and Busenberg in 1982 is the best available, and suggests a formation constant log beta = 3.22 for CaCO(3)(0)(aq). This value was confirmed by additional experimental data and calculations using a specially developed computer program. The solubility s and solubility product K(s) are critically evaluated for each solid polymorph (amorphous CaCO(3), ikaite, vaterite, aragonite and calcite) using a hydrated ion pair model and we give coherent explanations for the calcium carbonate precipitation/dissolution process and the existence of supersaturated waters. The practical cases of scale formation and its inhibition by phosphonate-type compounds are discussed and explained with the same model, taking into account the CaCO(3)(0)(aq) species.

Observations on in situ degradation of forage cell components in alfalfa and Italian ryegrass.

The rate and extent of degradation of forage feed fractions contained in alfalfa and Italian ryegrass hays were determined. Nylon bags filled with 4 g of each forage were suspended in the rumen of two cannulated cows immediately before feeding and incubated for 10 different times (0, 2, 4, 8, 12, 24, 48, 72, 120, and 168 h). The alfalfa hay, which had lower NDF, showed a lower extent, but a higher rate, of NDF degradation than the Italian ryegrass (41.1 vs. 59.8% and 4.64 vs. 2.91%/h, respectively). Alfalfa cell walls were degraded more rapidly than Italian ryegrass even though their lignin content was higher. The hemicellulose fermentation of alfalfa showed a longer lag time (13 h) and an undegradable fraction nearly twice that for Italian ryegrass (63.3 vs. 37.1%). Cellulose from alfalfa was degraded at a higher rate than NDF or ADF, indicating that cellulose may be the primary site of hydrolysis of the cell wall in the rumen. Calculations based on in situ degradability indicate that alfalfa can have a higher inclusion than Italian ryegrass in diets for dairy cows because of lower NDF and greater availability of cell contents.

A questäo social no Brasil / The social question in Brazil

Faz um balanço e revisão da questão social no Brasil, tal como ela se configurou nas últimas duas décadas, não de forma isolada, mas articulada com o próprio processo de desenvolvimento. Procura verificar se o Brasil é realmente uma anomalia, no mundo, com uma situação social muito pior do que a situação econômica. Faz a análise quantificada das dimensões reais da problemática social brasileira e sua base demográfica. Discute os problemas da pobreza, da desigualdade de renda e da situação demográfica. Constata o grande avanço, não só econômico como também social, ocorrido nos anos 70, com redução nos desníveis sociais, grande aumento de emprego e redução nos níveis de pobreza absoluta. Relata que nos anos 80 houve uma tendência à estagnação econômica socialmente truncada. Explica que, enquanto a renda "per capita" ficou virtualmente estagnada, a continuação da melhoria social passou a limitar-se a alguns aspectos, e a pobreza absoluta regrediu a níveis anteriores à década de 70. Analisa dois temas especiais: a educação básica e a política habitacional.

Study of luteal function.

On studying various parameters of luteal function, the authors demonstrated that BTT does not permit the evaluation of luteal phase defects, whereas the E.I. and prolactin levels, as well as the endometrial biopsy, may be considered valid parameters. The TRH test is more efficient than basal prolactin evaluation in this respect. Progesterone should be evaluated in various moments of the luteal phase and not by a single determination. The authors conclude that the abnormal luteal phase is the result of an abnormal follicular maturation and that the central origin of this mechanism may be affirmed.