We compare five lightning return stroke current models that exhibit a simple relationship between the current at the return stroke channel-base and the current along the return stroke channel, namely the Bruce-Golde (BG) model, the transmission line (TL) model, the Master, Uman, Lin, and Standler (MULS) model, the Traveling Current Source (TCS) model, and the Modified Transmission Line (MTL) model, by assuming a common current wave shape at the channel base and then calculating the channel currents and charges and the resultant electric and magnetic fields. There are basically two characteristics that distinguish the models, namely, (1) the treatment of the return stroke wave front and (2) the spatial and temporal distribution of charge removed from the leader channel. The simpler BG model can be used as an excellent approximation to the TCS model. The latter reduces to the former when the current injected downward by the traveling current source has an infinite speed. The MULS model is equivalent to the MTL model when the MULS uniform current is assumed to be zero. The BG and TCS models produce sharper initial field peaks than do the TL, MTL, and MULS models. The ratio of the peak field derivative to the peak current derivative is near the ratio of the peak field to the peak current for the MULS and MTL models and is equal for the TL model, whereas for the BG and TCS models the ratio of the peak derivatives is about twice the ratio of the peak field to peak current. The TL model is unrealistic for long-time field calculations due to the fact that no net charge is removed from the channel. The other four models produce overall fields which are reasonable approximations to measured fields from natural lightning even though, for the assumed channel-base current, the BG and TCS models do not reproduce the observed distant-field zero crossing and the MTL and MULS models do not reproduce the magnetic "hump" observed after the initial field peak at close range. None of the models can reproduce the fine structure observed in the measured fields. 1. 20,395 20,396 NuccI ET AL ' LIGHTNING RETURN STROKE CURRENT MODELS D = 200 km D = •OO km FiB. 2. (a) Typical vertical electric field intensity (leEr column) and horizontal maBnctic flux density (riBht column) Ear first (solid line) and subsequent (dashed line) return strokes and distances oE 1, 2, 5, 10, 15, 50, and 200 kin. The EollowinB characteristic Ecaturcs oE the wave Earms arc identified •or electric field, initial peak, ramp startinB time, romp, and l?0-•s value and zero crossinBs; Ear maBnctic field, initial peak, hump, halE-value. Adopted from Li• • al. [1929].were not correlated by stroke. Willett et al. [1989], in an extension of the previously described experiment, presented simultaneous measurements of channel-base current, current derivative, return stroke speed, electric field at 5 km, and electric field derivative at 5 km. Some data of the type described by Willett et al. [1989], provided by the Centre d'Etudes Nucleaires de Grenoble (CENG), the Centre Na- 13...

A comprehensive study on the effect of a lossy ground on the induced voltages on overhead lines by a nearby lightning is presented. The ground conductivity plays a role in both the evaluation of the lightning radiated fields and of the line parameters. To be calculated by means of a rigorous theory, both fields and line constants need important computation time, which, for the problem of interest, is still prohibitive. The aim of this paper is to discuss and analyze the various simplified approaches and techniques that have been proposed for the calculation of the fields and the line constants when the ground cannot be assumed as a perfectly conducting plane. Regarding the radiated electromagnetic field, it is shown that the horizontal electric field, the component which is most affected by the ground finite conduc~ivity, can be calculated in an accurate way using the Cooray-Rubinstein simplified formula. The presence of an impe~ect~coyn ducting ground is included in the coupling equations by means of two additional terms: the longitudinal ground impedance and the transverse ground admittance, which are both f~equency-dependent. The latter can generally be neglected for typicall overhead lines, due to its small contribution to the overall transverse admittance of the line. Regarding the ground impedance, a comparison between several simplified expressions used in the literature is presented and the validity limits of these expressions are established. It is also shown that for typical overhead lines the wire impedance can be neglected as regard to the ground impedance. We also investigate the time-domain representation of field-to-transmission line coupling equations where the frequency-dependence of the ground is taken into account by the convolution integral. Finally, examples of voltages induced by a typical subsequent return stroke on an overhead l i e are presented, emphasizing the effect of the finitely conducting ground. It is shown that for lines whose length does not exceed a certain ‘critical’ value (typically 2 km), the surge propagation along the line is not appreciably affected by the ground finite conductivity which, therefore, can be neglected in the computation process

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Cannabidiol (CBD) has become a buzzword in many products that have bloomed on the market. The scientific community and some authorities have recently raised concerns on the quality of these products. In particular, the discrepancy between the labelled and the real content of cannabidiol in liquids for e-cigarettes seems to be emerging as a major issue. Furthermore, to-date no studies have been carried out on the chemical stability upon storage of these type of products. The aim of this work was to investigate the accuracy in labelling of thirteen commercially e-liquids containing CBD and the effects of different storage conditions on their quality. The results showed that only 38% of samples were labelled within a ±10% variance from their labels. Stability tests showed a maximum degradation of CBD when samples were stored at 37 °C for 30 days with average values up to 20%. The effect of light was lower but still significant with averages values up to 15% degradation after 30 days. In conclusion, we believe that health authorities should regulate and control this market more stringently to protect customers and their health. Furthermore, our stability tests have shown that if clear indications are provided on the best storage conditions, the quality of these products can be mostly preserved.

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