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PubMed2003

[Temporal-spatial distribution characteristics of microclimate in tropical secondary forest canopy gap in Xishuangbanna].

Based on the data obtained from vertical gradient measurements of microclimatic elements of canopy gap in tropical secondary forest of Xishuangbanna in fog-cool and dry-hot season, the daytime characteristics of temporal-spatial distribution and variation of trunk surface temperature, air temperature, water vapor pressure and relative humidity in canopy gap were discussed. The data showed that gap edge had not only a remarkable thermal effect, but also a significant water vapor effect. These effects resulted in environmental heterogeneity in canopy gap. The results provided a basis for further studying heat and water vapor transport, microclimatic formation, biodiversity, and forest succession in canopy gap.

Climate↗
PubMedDate not supplied

[Microclimate and the respiratory system].

The thermal exchanges between lung and working or living environment constitute a very small amount of the total thermal exchange of the human body. They mainly depend on temperature and humidity gradients between inspired and expired air and on ventilatory levels as well. In spite of the smallness of such exchanges regarding the thermal steady state of the body, the variations of the climate physical parameters can greatly affect the lung either from the subjective or the objective point of view. Air humidity, temperature and ventilation are here considered as causes of respiratory discomfort and as risk factors of respiratory disease. It has been pointed out that the same parameter levels can exert a favourable or unfavourable influence on respiratory tract. For instance low humidity values can support the respiratory infections but usually prevent asthma crisis caused by indoor mite sensitization. Sometimes among the causes of respiratory risk can be involved the artificial systems of ventilation and humidification (air conditioning, humidifiers). It is not possible to set proper limit values for the physical parameters but only ranges where to determine the best combination for each single situation. The width of such ranges as well as the dysfunctioning of the artificial conditioning systems can in particular cases support some conditions of respiratory risk.

Air Conditioning↗
PubMed1986

Intestinal uptake of nicotinic acid as a function of microclimate-pH.

The investigations aimed at clarifying the pH-dependence of 3H-nicotinic acid uptake into isolated strips of rat jejunum. Nicotinic acid is a weak-electrolyte with pKa 4.90. Thus, it was anticipated that the penetration rate of this vitamin into the intestinal epithelial cells is closely related to the amount of the diffusible i.e. non-ionic form which for its part is a function of the "virtual pH" on the mucosal surface. As determined by microelectrodes the surface pH was found to be between 5.41 and 6.80 when the strips were incubated in buffers between pH 4.5 and 9.0. At surface pH 5.83 the unidirectional flux rate was twice as high, at pH 5.41 three times as high as at surface pH values between 5.95 and 6.80. At each pH the unidirectional flux of nicotinic acid was linearly dependent on the substrate concentration in a range between 0.1 microM and 1 mM, indicating simple diffusion as transport mechanism. Accordingly, the uptake rate was not affected by the substrate analogon, isonicotinic acid (5 microM and 250 microM). It can be concluded that the predominant part of the nicotinic acid is transported through the brush border membrane obeying the laws of a non-ionic diffusion. A relatively small portion of this substrate, however, was taken up by the tissue even when the vitamin was entirely dissociated, possibly by ionic diffusion or by binding.

Animals↗