Accurate determination of antenna directivity

The derivation of a formula for accurate estimation of the total radiated power from a transmitting antenna for which the radiated power density is known in a finite number of points on the far-field sphere is presented. The main application of the formula is determination of directivity from power-pattern measurements. The derivation is based on the theory of spherical wave expansion of electromagnetic fields, which also establishes a simple criterion for the required number of samples of the power density. An array antenna consisting of Hertzian dipoles is used to test the accuracy and rate of convergence of the derived formula. Its performance is compared to that of numerical integration using Simpson's formula     

Trapezoidal-shaped electrostatic comb-drive actuator with large displacement and high driving force density

This paper presents a design of a comb finger shape and calculation of a trapezoidal-shaped electrostatic comb-drive actuator (TECA) in order to aim a higher electrostatic force density and larger displacement in comparison with the typical rectangular-shaped electrostatic comb-drive actuator (RECA). Relation between a beam’s stiffness and a driving voltage has been examined to predict a pull-in effect occurring in TECA. Micro fabrication and characterization of TECA and RECA systems are performed by using a standard SOI-MEMS technology. Theoretical and experimental results confirm the strong points of TECA’s structure (similar to the dimensions of RECA) such as a larger number of movable comb finger arrayed at the same length and larger displacement. At driving voltages of 47.9 and 50 (V), the calculation and measurement displacement of TECA are approximately 2.2 and 1.78 times larger than that of RECA, respectively.

     

Unpacking the relationship between existing and new measures of physiological synchrony and collaborative learning: a mixed methods study

International Journal of Computer-Supported Collaborative Learning - Over the last decade, there has been a renewed interest in capturing twenty-first century skills using new data collection...     

Recursive algorithm in radius of curvature measurement

A recursive algorithm is considered for measuring the radius of curvature of spherical surface by means of IZS-7, IZS-11, and 1ZS-12 spherometers. It is found that the algorithm does not converge for some values in the measurement range and that it is insufficient to use only the first step in the iteration to calculate the radius. The convergence conditions for the computational procedures are given.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 29–31, April, 1995.     

Cytoprotective effect of tocopherols in hepatocytes cultured with polyunsaturated fatty acids

When highly unsaturated fatty acids are added to cell cultures, it can become important to include antioxidants in the culture medium to prevent cytotoxic peroxidation. To find an optimal antioxidant for this purpose, the effect of 50 μM α-tocopherol, γ-tocopherol, α-tocopheryl acetate, α-tocopheryl acid succinate, or α-tocopheryl phosphate, or of 1 μMN,N′-diphenyl-1,4-phenylenediamine, was investigated with respect to the agent's ability to prevent lactate dehydrogenase leakage in long-term rat hepatocyte cultures supplemented with 0.5 mM highly unsaturated fatty acids. Formation of thiobarbituric acid reactive substances in the cultures was also measured. α-Tocopheryl acid succinate was found to be the most effective cytoprotective compound, followed byN,N′-diphenyl-1,4-phenylenediamine, α-tocopherol, γ-tocopherol and α-tocopheryl acetate, and α-tocopheryl phosphate was without effect.     

Dynamic aspects of precision linear-displacement measurement

A qualitative analysis is presented for dynamic linear-displacement measurement. When measurements are made with errors in the submicron and nanometer ranges, it may be necessary to correct for dynamic errors whose origin is geometrical.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 23–25, September, 1994.