Searching for criteria for the selection of efficient tree species for fallow improvement, with special reference to carbon and nitrogen

Planted fallows are a potential means for regenerating soil fertility in the humid tropics. N-fixing leguminous trees are often recommended for this purpose, but precise criteria for efficient fallow trees do not exist. A combined field and laboratory study was undertaken, including 9 tree species of five years age, of which 6 were N-fixing, and a spontaneous fallow dominated byChromolaena odorata on a Ferralic Cambisol in the Central Côte d'Ivoire. Although the trees differed widely in growth, litterfall and root mass, differences in total soil C and N were small. Soil respiration and N-mineralization were measured by incubating topsoil in the laboratory. The initial CO₂-flush after rewetting differed significantly between species, but non-significant differences afterwards indicated comparable stability and size of the labile C pools of the soils. Total N-mineralization differed significantly between species, with highest values for the control. There was no relationship between the ability of the plants to fix N and N-mineralization or total N-accumulation in the soils. To test the effect of the trees on a subsequent crop, rice was grown in pots filled with topsoil from all plots. Total above-ground dry matter of the rice differed significantly between species and was significantly correlated with N-mineralization in the soil and N-concentration in the rice leaves. N-mineralization was closely related to the amount of litterfall for 7 of the 9 tree species, and to root-mass for the 6 N-fixing tree species. Litterfall and root mass are identified as potential criteria for fallow tree efficiency, but the long-term effect of high N-mineralization rates on available soil-N pools needs further investigation. The importance of soil biological measurements in comparison to chemical soil tests for the assessment of fallow effects is stressed.     

Apolipoprotein B metabolism in hypertriglyceridemic diabetic patients administered either a fish oil- or vegetable oil-enriched diet

The effect on apolipoprotein B kinetics of a diet enriched in either fish oil or safflower oil was investigated in five hypertriglyceridemic (HTG), non-insulin-dependent diabetic subjects. The fish oil diet decreased plasma triglycerides and VLDL-apoB but increased LDL-apoB and LDL-cholesterol. Total plasma apoB concentration did not change, nor did the increased VLDL-apoB secretion present in these HTG subjects, which, accompanied by impaired lipolysis, accounted for their elevated VLDL. The fish oil-induced fall in VLDL resulted from a decrease in secretion without a change in residence time. The IDL fraction, which also contained small VLDL, was the primary site for the secretion of apoB particles in the HTG subjects. On the fish oil diet there was a further, compensatory increase in the secretion of these lipoproteins such that the transport of apoB in IDL remained the same, as did its mass. In the HTG subjects the major portion of IDL lipoproteins was catabolized, with LDL-apoB production comprising the lesser quantity. On the fish oil diet, a shift in the channeling of the lipoprotein output from IDL resulted in a decrease in the catabolic pathway and an increase in conversion to LDL. As the residence time of LDL did not change, this increased input gave rise to the larger mass of LDL-apoB seen in these hypertriglyceridemic subjects when receiving a fish oil diet.     

Simplified versus Detailed Two-Dimensional Approaches to Transient Flow Modeling in Urban Areas

Simplified and detailed two-dimensional modeling approaches to transient flows in urban areas, based on finite-volume solution of the shallow water equations, are compared. Through the example of a dam-break flow in a simplified urban district for which accurate laboratory data exist, various methods are compared: (1) the solution of the two-dimensional shallow water equations with a detailed meshing of each street; (2) the use of a porosity concept to represent the reduction of water-storage and conveyance in the urban area; and (3) the representation of urban areas as zones with higher friction coefficient. Accuracy and adequacy of each method are assessed through comparison with the experiments. Among the simplified models, the porosity approach seems to be the most adequate as head losses at the entrance and the exit of the city are considered.     

Use of organotypical cultures of primary hepatocytes to analyse drug biotransformation in man and animals

1. In conventional single-gel culture systems for primary hepatocytes, rapid loss of drug metabolizing capacities is a common feature and parallels general loss of function. An organotypical (double gel) culture technique for primary hepatocytes is established by enclosing the cells within two layers of extra cellular matrix. This serves to imitate the in vivo microenvironment within the space of Dissé. Using rat hepatocytes, this technique has been shown previously to maintain protein synthetic functions in vitro and to allow more efficient P450A-dependent biotransformation of drugs than a standard single-gel culture system. 2. The aim was to test the capacity of this organotypical culture model for primary rat and human hepatocytes to generate drug metabolites in a typical species-dependent pattern. 3. Urapidil, an antihypertensive drug, was used as a test compound, since it is metabolized in vivo in a species-dependent manner in rat and man. 4. Primary rat and human hepatocytes were cultured within two layers of collagen and exposed to 2.25 micrograms/ml urapidil for periods of 1-24 h at 3 days in culture. Urapidil metabolites were measured using hplc. 5. Metabolite M1 (hydroxylated product) was produced preferentially in human hepatocyte cultures, and metabolites M2/M3 (O-demethylated, N-demethylated product) were preferentially generated in rat cultures. This corresponded to the in vivo pattern found in man and rat, respectively. 6. Since in vitro urapidil metabolism by human and rat hepatocytes cultured in a double-gel system reflects that in vivo, it is suggested that information from such a system may be useful to predict the metabolic pathway of novel xenobiotics and to direct further toxicological evaluation.     

Untersuchung von gefriervorgǎngen in zementstein mit hilfe der DTA.

Freezing phenomena in hardened cement paste (hcp) were investigated by DTA. On cooling at least two phase transitions have been observed in the temperature range betwenn -10°C and -25°C and near -43°C respectively. Also a hysteresis between cooling and heating has been found. The phase transitions are correlated to the radius of the water-filled pores and so to relative humidity and water content. Comparable results were obtained in different kinds of hcp. These findings can be explained by the specific properties of water in porous systems induced by surface interaction.     

Overbank Flow in Symmetrically Narrowing Floodplains

Experimental data are presented for flow in compound channels with symmetrically narrowing floodplains. In such a geometry, the flow behavior presents similarities with the more complex flow in a meandering compound channel, yet without the curvature effects, because of mass transfers between the floodplains and the main channel, and secondary currents induced in the main channel. An estimation of the momentum transfer generated by the mass transfer is found significant compared to the frictional losses. It mainly depends on the geometrical parameters and is practically independent of the friction slope. Free-surface profile computations are performed with the exchange discharge model (EDM) to incorporate the effects of the momentum transfer in terms of an additional head loss. Agreement was found between measured and computed water surfaces, thus validating the EDM approach.