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This abstract presents the results of screening for allelopathic activity of three pairs “aboriginal-exotic” of comparison species of herbs, including invasive species, systematically related at the level of the genus. It was shown that a 1% leaf extract of Solidago virgaurea and S. canadensis, Pulmonaria obscura and P. saccharata, Veronica serpyllifolia and V. fi liformis had a similar or equal inhibitory eff ect on the germination and growth of test-plant roots in biotests owing to its chemosystematic correlation. Extracts of Solidago and Pulmonaria species slowed down the rate of germination and root growth by 1.5–2 times lower than the control. In the Salidago sp. experiment options the dynamics of the processes developed according to the type of stress-reaction. The absolute rate of root growth at the exponential stage diff ered twice in the Solidago sp. options: 16.8±0.43 and 8.99±0.23 mm/day in native and exotic specie, respectively. The total germination was close to or equal to the control level. In a comparison pair Pulmonaria sp. germination decreased by 58.66 and 43.5%. V. fi liformis extract inhibited germination by 24.4% more than the native species. Extracts 0.05% extracts of Solidago sp. had no eff ect, P. saccharata and V. fi liformis extracts caused the eff ects of hormesis. P. saccharate option produced an – acceleration of the absolute and relative root growth rate of the test-plants by two times, exceeding the total length of the roots by half compared to the control and the native species. In the V. fi liformis option, the rates of germination and root growth was inhibited by 24.7 and 50.2% of the values of the paired species, respectively. The comparative method increases the level of analysis of bioassay data, allows for a deeper study of the specifi cs of test-plants reactions, and allows the evaluation of the modes of action of allelochemics.

Thanks to their low friction, aerostatic pads have important applications in precision positioning systems and linear guides. A simple and cheap solution to increase the static stiffness of aerostatic pads is to add a proper designed pneumatic valve to regulate the air flow supplied to the bearing. However, integrating aerostatic pads with additional devices can reduce its dynamic performance. This paper presents a numerical study on the dynamic behaviour and stability a commercial aerostatic pad controlled by a custom-built diaphragm valve. The bearing performance is studied by means of a lumped parameters model. Air bearing stiffness and damping are analysed in the frequency domain. Subsequently, the lumped model is linearized to investigate the stability of the system by means of Routh-Hurwitz method. The performance of the controlled air pad is compared to that of a simple commercial air pad.

Because of their almost zero friction, cleanness and long life, aerostatic bearings are commonly used in many applications where high precision of positioning is required, e.g. machine tools, measuring machines, semiconductor manufacturing and power board testing. However, air bearings suffer from low relative stiffness and poor damping. Active and passive compensation are two effective methods to enhance the static and dynamic performance of these kinds of bearings. Despite their higher performance, active compensation solutions are too expensive to be used in industrial applications, as a consequence of the costs related to their controllers, actuators and sensors. This paper presents the design and performance of a passive compensation method that exploits a diaphragm valve. Thanks to its ease of integration, satisfactory performance and relatively low cost, this method could be a valuable solution to increasing the stiffness of aerostatic bearings. This work provides a procedure to design diaphragm valves depending on the type of the integrated pad and the desired nominal air gap height. Results demonstrate that, once correctly designed, the diaphragm valve makes it possible to obtain bearings with quasi-static infinite stiffness at the selected air gap height.

Because of their almost zero friction and wear, aerostatic pads are widely used in applications where very precise positioning is required. However, this kind of bearing suffers from poor damping and low specific stiffness. This paper presents a new compensation strategy to increase air pad stiffness. This method exploits a custom-built pneumatic valve which can be easily integrated with any commercial pad. The design and the working principle of the proposed system are described and studied with the aid of a lumped parameter model. The effectiveness of the proposed compensation is numerically and experimentally evaluated. The results demonstrate that the solution represents a good and cost-effective method to enhance the static stiffness of aerostatic pads.

This paper presents a fast method for determining the conductance of gas microfluidic devices with low flow rates and very small pressure drops starting from 30 Pa, corresponding to Re = 0.3. This method is based on discharging a gas-pressurized chamber through the microfluidic device under test. The microfluidic device's conductance can be estimated as a function of inlet pressure and the Reynolds number of the flow by recording the upstream pressure during the discharging process and calculating the time derivative of the gas pressure. The pressurized chamber is considered as an isothermal chamber. Experimental results show that a sufficiently accurate isothermal discharging process up to an upstream-to-downstream pressure ratio of 0.8 can be achieved by immersing the chamber in a thermal bath. The method presented here is very fast, requiring only a few seconds for the acquisition procedure and computerized data processing. [DOI: 10.1115/1.4003089]

In this study, two novel split and recombine (SAR) ‘H-C’ and ‘Y-Y’ micromixers along with a known SAR ‘Chain’ mixer are presented. The efficiency and pressure drop at Reynolds numbers (Re) up to 100 were investigated numerically as well as experimentally. Numerical and experimental values of mixing efficiency and pressure drop coincide considerably, which validate the numerical model. Results show that the mixing efficiency of the Chain mixer is good only at Re≥50 and the pressure drop is relatively high, whereas the H-C and the Y-Y mixers give a mixing efficiency higher than 90% over all the range of Reynolds numbers examined and their energy requirement is less than that of the Chain mixer. Furthermore, numerical residence time distribution (RTD) was explored, which successfully predicts the experimental results.