How effective is kaolin clay for the creation of a perfect hydraulic interface contact between materials?

Due to interface phenomena such as compaction pores, a mismatch of the pore structure, etc., moisture transfer in multi-layered building elements can deviate from the moisture transfer observed for the combination of the separate materials. Several studies on interface phenomena make use of kaolin clay to provide – as a reference – a perfect hydraulic contact between materials. This paper investigates, based on a series of imbibition experiments, whether kaolin clay truly creates this perfect contact, and thus, whether the hydraulic interface resistance between materials can be nullified by use of kaolin clay. For a low absorptive material or a large distance between the contact interface and the water surface, composite samples put together with kaolin clay show an identical water uptake curve as observed for homogeneous samples. For a material with a high absorptivity and a contact interface closer to the water plain, however, even with kaolin clay a hydraulic interface resistance is observed and estimated to be in the order of 6 000 m/s till 12 000 m/s. If present, such an interface resistance is furthermore shown to have no impact on the water uptake curve for samples composed of low absorptive bricks or with a contact interface further away from the water plain.

Determination of styrene hydrogenation surface kinetics through detailed simulation of the hydrogen uptake curve

The styrene hydrogenation over Pd/C in a three-phase dead-end stirred tank reactor has been simulated without neglecting the mass transfer effects.

Evaluation of sources, doses and application schedules of nitrogen on drip-irrigated tomato

We aimed to establish strategies for nitrogen (N) fertilization on drip-irrigated determinate-growth-habit tomato, under Cerrado conditions of Central Brazil. Three field experiments were carried out in a randomized block design. In experiment I six N doses (0, 80, 160, 240, 320 and 400 kg ha-1 N) were tested, in experiment II six combinations of the N forms (nitric; ammonium; amide; 2/3 nitric + 1/3 ammonium; 2/3 nitric + 1/3 amide; and 1/3 nitric + 2/3 amide) were evaluated, and in experiment III the combination of three soil pre-plant fertilization fractions (0, 20 and 40%) was evaluated with two splitting schemes of the remaining N via fertigation (linear and adjusted N-uptake curve). SPAD chlorophyll index and N content were measured in the leaves of tomato plants on experiment I. The physical and economic yields of tomato crop were maximized for the doses of 287 kg N ha-1 and 270 kg N ha-1, respectively, with doses of 2.1 g and 2.0 g of N per kg of commercial fruit. The yield was maximized for 52 SPAD units. The combinations of forms and the application schedules of N had no significant effect on the yield components of the tomato crop.

A Two-Compartment Mathematical Model of Neuroglial Metabolism Using [1-11C] Acetate

The purpose of this study was to develop a two-compartment metabolic model of brain metabolism to assess oxidative metabolism from [1-11C] acetate radiotracer experiments, using an approach previously applied in 13C magnetic resonance spectroscopy (MRS), and compared with an one-tissue compartment model previously used in brain [1-11C] acetate studies. Compared with 13C MRS studies, 11C radiotracer measurements provide a single uptake curve representing the sum of all labeled metabolites, without chemical differentiation, but with higher temporal resolution. The reliability of the adjusted metabolic fluxes was analyzed with Monte-Carlo simulations using synthetic 11C uptake curves, based on a typical arterial input function and previously published values of the neuroglial fluxes Vtcag, Vx, Vnt, and Vtcan measured in dynamic 13C MRS experiments. Assuming Vxg=10 × Vtcag and Vxn= Vtcan, it was possible to assess the composite glial tricarboxylic acid (TCA) cycle flux Vgtg ( Vgtg= Vxg × Vtcag/( Vxg+ Vtcag)) and the neurotransmission flux Vnt from 11C tissue-activity curves obtained within 30 minutes in the rat cortex with a beta-probe after a bolus infusion of [1-11C] acetate ( n=9), resulting in Vgtg=0.136±0.042 and Vnt=0.170±0.103 μmol/g per minute (mean±s.d. of the group), in good agreement with 13C MRS measurements.