Optical observation of needles in upward lightning flashes.

Why lightning sometimes has multiple discharges to ground is an unanswered question. Recently, the observation of small plasma structures on positive leaders re-ignited the search. These small plasma structures were observed as pulsing radio sources along the positive leader length and were named "needles". Needles may be the missing link in explaining why lightning flickers with multiple discharges, but this requires further confirmation. In this work we present the first optical observations of these intriguing plasma structures. Our high-speed videos show needles blinking in slow motion in a sequential mode. We show that they are formed at unsuccessful leader branches, are as bright as the lightning leaders, and report several other optical characteristics.

On the Triggering Mechanisms of Upward Lightning.

Upward lightning studies took place in Rapid City, South Dakota, USA and S. Paulo, Brazil during the summer thunderstorm seasons from 2011 to 2016. One of the main objectives of these campaigns was to evaluate and characterize the triggering of upward positive leaders from tall objects due to preceding nearby flash activity. 110 upward flashes were observed with a combination of high- and standard-speed video and digital still cameras, electric field meters, fast electric-field antenna systems, and for two seasons, a Lightning Mapping Array. These data were analyzed, along with correlated lightning location system data, to determine the triggering flash type responsible for the initiation of upward leaders from towers. In this paper, we describe the various processes during flash activity that can trigger upward leaders from tall objects in the USA and in Brazil. We conclude that the most effective triggering component is the propagation of the in-cloud negative leader during the continuing current that follows a positive return stroke.

Comparison of force, power, and striking efficiency for a Kung Fu strike performed by novice and experienced practitioners: preliminary analysis.

This paper presents a comparison of force, power, and efficiency values calculated from Kung Fu Yau-Man palm strikes, when performed by 7 experienced and 6 novice men. They performed 5 palm strikes to a freestanding basketball, recorded by high-speed camera at 1000 Hz. Nonparametric comparisons and correlations showed experienced practitioners presented larger values of mean muscle force, mean impact force, mean muscle power, mean impact power, and mean striking efficiency, as is noted in evidence obtained for other martial arts. Also, an interesting result was that for experienced Kung Fu practitioners, muscle power was linearly correlated with impact power (p = .98) but not for the novice practitioners (p = .46).

The role of effective mass and hand speed in the performance of kung fu athletes compared with nonpractitioners.

The main goal of this article is to quantify the contribution of effective mass (me) and handspeed (shi) on the palm strike performance of kung fu athletes (kung fu group) compared with nonpractitioners (control group). All subjects were asked to strike a basketball. Hand and ball speed (sbf) were determined by high-speed video analysis. The value for me was determined by an equation that does not depend upon postimpact measurement of the hand speed. The results show that kung fu athletes had greater shi (6.67 [SD 1.42] m/s), p = 0.042), higher me (2.62 [SD 0.33] kg, p = 0.004), and greater sbf (9.00 [SD 1.89] m/s), p = 0.004) than the nonpractitioners (5.04 [SD 0.57] m/s, 1.33 [SD 0.19] kg, and 5.72 [SD 0.44] m/s, respectively). Comparing the average values obtained for me and hand and forearm mass (m), it was found that for the control group me is statistically equal to m (p = 0.917), whereas for the kung fu group me is significant greater than m (p = 0.003). It is suggested that for impacts against heavier objects, the effective mass would be the main factor to distinguish a martial arts-trained from an untrained subject.