Can hydraulically redistributed water assist surrounding seedlings during summer drought?

Plant interaction studies provide a good understanding of the roles of key species, which can assist restoration of natural ecosystems. Among the interactions, facilitation and competition are known to affect ecosystem structure and function. We investigated whether a deep-rooted species could positively affect surrounding seedlings through hydraulic redistribution during dry months. We conducted two experiments in which seedlings from two species were growing together or isolated from source plants (field experiment) and where plants were isolated from source plants that were connected to or separated from a water table (glasshouse experiment). Survival, growth, water relations and soil water content were measured. We also applied δ2H enriched water adjacent to, or into, the roots of source plants to track water movement between plants. Soil water content was higher in shallow layers where source plants could interact with seedlings (field) and when accessing water tables (glasshouse). Seedlings from all treatments had an increase in leaf δ2H. Seedlings of Banksia attenuata that were isolated from source plants had the highest survival, growth and stomatal conductance rates. Seedlings of Gompholobium tomentosum presented higher stomatal conductance rates when growing with source plants than when isolated from them during the first months, but this relationship reversed towards the end of summer. These results suggest that source plants and seedlings competed, but the influence of facilitation and competition might change during the year, at least for the shallow-rooted species. Therefore, competition for water and/or other limiting factors must be considered when planning ecological restoration in such areas.

Spontaneous gas bubbling in microporous oxygenators.

During operation of the microporous membrane oxygenators at some conditions, gas microbubbles penetrate into the blood. This effect, so-called spontaneous bubbling, takes place even when the blood pressure is higher than the gas pressure. This phenomenon was confirmed experimentally both in a model cell with hydrophobic microporous hollow fibers being used in the oxygenators and in in vitro tests on the actual microporous hollow fiber oxygenator. We proposed a mechanism of spontaneous gas bubbling into liquid that contains dissolved gases. Because of a partial pressure gradient, the dissolved gases and water vapors are transported from blood into the gas pore. This causes Stefans gas flow directed from the liquid-gas interface. Because of the high hydraulic resistance of the micropores, gas pressure at the meniscus increases up to gas bubbling. A mishandled priming of the oxygenator as well as the blood pressure pulsation caused by the roller pump operation contribute to spontaneous gas bubbling in the microporous oxygenators. The flow and pressure in the hydrophobic pores were calculated for various gases.

[Effects of heterogeneity of gas channels on carbon dioxide output of membrane oxygenators]. / O vliianii neodnorodnosti gazovykh kanalov na proizvoditel'nost' membrannykh oksigenatorov po uglekislomu gazu.

A relationship between the carbon dioxide output of the oxygenators and the value of ventilating gas flow is analyzed. It is shown that a potential inhomogeneity of gas channels may result from the lower efficiency of the oxygenators. The tests of the MOST oxygenators have indicated that the achieved homogeneity of their gas chambers is sufficient for carbon dioxide to be effectively removed.

[Study of the functioning of a membrane oxygenator MOST-122 during artificial circulation with pulsed blood flow]. / Issledovanie raboty membrannogo oksigenatora MOST-122 pri iskusstvennom krovoobrashchenii s pu'lsiruiushchim krovotokom.

Functioning of membrane oxygenator "MOCT-122" in pulsed operation of bypass in treadmil tests and during clinical perfusions was investigated. It was established that the inclusion of the oxygenator into the test line lead to a considerable decrease in parasitic pulsations both of rate and pressure. The pulsatory character of the flow was observed though the transconductance of increase and decrease fronts of the rate (as the result of oxygenator "MOCT-122" installation) demonstrated their satisfactory functioning.

[Transport of carbon dioxide in membrane oxygenators]. / Transport uglekislogo gaza v membrannykh oksigenatorakh.

A study has been made of the process of removing carbon dioxide from blood in the MOST-type membrane oxygenators. An expression was obtained for the carbon dioxide flow near the diffusional border layer and its change in the blood with regard to the permeability of the membrane used, the value of the blood flow rate, the value of the geometric parameters of the oxygenator, and the blood parameters. The value of the rated by carbon dioxide volumetric capacity of the blood has been calculated. The results of the numerical analysis of the input equations of the carbon dioxide transport are compared to the experimental data obtained from the medico-biologic testing of the oxygenators.

[Efficiency of membrane oxygenators of various designs under standard conditions]. / Proizvoditel'nost' membrannykh oksigenatorov razlichnykh konstruktsii v standartnykh usloviiakh.

The article shows the possibility of calculating the output of membrane oxygenators of blood under standard conditions by simple and common formula which includes only important design parameters (the membrane surface and the filled volume). The obtained output expression was used to evaluate the intensity of the mass transfer in membrane oxygenators of different design.

[Calculation of the capacity of a roller pump]. / Raschet proizvoditel'nosti rolikovogo nasosa.

The capacity (G) of the roller pump was calculated for pipes of different rigidity. It was shown that the value G related to the viscosity of the liquid will be determined either by the roller revolution speed or by the pipe elasticity characteristics. Methods of calculation for choosing the optimum pipe type are described.

[Oxygen transport in membrane oxygenators]. / Transport kisloroda v membrannkh oksigenatorakh.

Mass transfer properties of the Soviet membrane oxygenator, MOCT, are tested. The liquid chambers of the oxygenator are made of disk membranes separating the moving blood from gas chambers. Processes of transportation and saturation of the blood film with oxygen are described by the simultaneous solution of the hydrodynamic and diffusion problem that is complicated by the chemical reaction. To derive approximate analytical solution the concept of a spreading front separating the area of the saturated blood layer from the venous area is applied. The expression for the thickness of the saturated layer and the oxygen flow to the blood is deduced as a function of the following parameters: membrane permeability, blood output, hemoglobin concentration, etc. The analytical solution is found to be satisfactory in describing experimental data obtained in the course of laboratory, clinical and biomedical tests.