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The results of experimental observations and mathematical modeling of corona formation on the tips of grounded rods are presented as a function of their tip height, curvature radius, the magnitude and polarity of the applied electric field producing corona. The investigations demonstrate that corona current depends on the active volume of zone in which electric field strength exceeds the breakdown criteria for air. The mathematical model was verified with the experimental data, enabling dependence of corona current on rod tip height, tip radius and applied electric field strength to be quantified with the need for a plethora of experiments.

This paper presents the results of an investigation into the influence of corona formation processes at the tips of grounded rod electrodes on the probability of those rods being “struck” by high-voltage discharges. Experiments simulating the final stage of the attachment process were carried out with a composite voltage comprising a simultaneously applied impulse and DC potential of different levels to grounded rod electrodes simulating lightning rods, featuring either a spherical or pointed (conical) tip. The experiments show that corona does not influence the probability of the electrode being struck until a critical electric field (EF) strength is reached.

We report the synthesis and biological evaluation of a ternary copper complex, [Cu(5HTP)(phen)(H2O)](NO3).2H2O, with the antioxidant agent 5-hydroxytryptophan (5-HTP) and phenanthroline (phen, added to improve its lipophilicity and membrane transport). The crystal structure of the complex was determined by X-ray diffraction methods. The complex showed antioxidant, antimicrobial, antitumor and antimetastatic properties with an adequate safety profile. The interaction of the metal with phen promotes cellular copper accumulation and cytotoxicity on human lung A549 cell line (IC50 = 3.6 μM). Furthermore, the viability of the normal human fetal lung fibroblast cell line (MRC-5) is not altered by the complex. An oxidative stress mechanism for the anticancer effect has been determined: cellular increase of reactive oxygen species (ROS), decrease of the glutathione (GSH) and oxidized GSH (GSSG) ratio and alteration of the mitochondrial potential. The complex also displays antimetastatic activities with inhibition of cell adhesion, invasion and migration. It has not mutagenic behavior and no toxicity on Artemia salina indicating its potential to act as an effective and safety antimicrobial and antitumor drug.

Corona discharge measurements made during a thunderstorm on a mountain at an altitude of almost 3300 m above sea level were analyzed for their dependence on the ambient electric field and the local wind speed. The corona current data were taken from an earthed needle point mounted at a height of 3 m above the ground. The coronating point was exposed to natural wind speeds of up to 14 m/s. Comparisons are made with empirical relationships dating back to the mid-1900s and new formulae are provided to describe the effect of wind on the magnitude of corona current measured under natural conditions.

An important consideration in the design of any air termination system is the maximum distance at which the terminations can be placed from the “vulnerable points” on structures, i.e., typically those points that create the highest degree of electric field intensification. This paper extends a previous, preliminary analysis of the problem in three significant ways. Firstly, the height range of the air terminations has been extended by a factor of 4 with a series of additional calculations. Secondly, account is taken of the material of construction of the building on which the air terminations are installed. Thirdly, and most importantly, a field study has been carried out in a high-lightning area as real check on the model results. All of the results are compared and some quantitative guidelines are provided for the maximum distance at which air terminations should be installed from the vulnerable points of structures.

A new methodology, the Collection Volume Method, is given for the placement of lightning rods or “air terminals” for the protection of structures against lightning. Each air terminal is assigned an “attractive radius”, which is calculated as a function of its height, radius of curvature, location on the structure, structure dimensions, and a set of site, atmospheric and lightning-related parameters. In a similar manner, an attractive radius is assigned to all “competing features” on the structure which can also capture a lightning strike, e.g., building edges, corners, parapets, flagpoles, lift motor rooms, etc. The calculations of the attractive radii also depend on the upward leader inception criterion employed, in the present case a critical breakdown field of ∼ 3 MV / m over an effective space charge or corona radius of ∼ 0.3 m , both taken from laboratory experiments of previous investigations. The attractive radius computations involve three-dimensional calculations of the electrostatic field on the surface and immediately around the structure, i.e., the degree of electric field intensification created by the penetration of the structure into the ambient field of the thunderstorm. The structure is regarded as being protected if the combined attractive areas of the various air terminals overlap those of the competing features. The Collection Volume Method is shown to be a new, practical, physically based technique for the efficient placement of air terminals on structures. It can both complement and replace existing placement methods as the need arises.