Direct current (DC) potential is an objective measure of the functional state of the human organism. It is a sensitive and accurate indicator of short- and long-term adaptations to stress, adaptive capacities, and it is an important marker of athlete readiness. Sleep is posited to be the most efficacious strategy for improving recovery to enhance sport performance, and adequate sleep is considered vital to normal psycho-physiological function. Thus, optimal sleep may enhance the functional state, in turn enhancing an athlete’s adaptability to training stress. However, little is known about the relationship between sleep and DC potential. Therefore, the purpose of this study was to examine the effect of acute (one-night) and extended (two-night) sleep quantity and quality on DC potentials in collegiate American football players. Twenty-four Division 1 American football players (Age: 20.6 ± 1.30 yr; Height: 183.4 ± 6.40 cm; Body mass: 114.40 ± 24.60 kg) wore a wrist-worn actigraphy band seven days per week over the course of 136 days, which spanned the pre-season training camp and competitive season, to measure sleep quantity and quality. DC potential was assessed six days per week using the Omegawave Ltd (Espoo, Finland) athlete monitoring system either 30 minutes upon waking or 75-120 minutes prior to the onset of the football training session. Sleep quantity was stratified into duration categories and sleep quality was stratified within sleep latency, number of awakenings, and sleep efficiency variables. Sleep quantity and quality were evaluated using acute (one night) and extended (rolling average of two consecutive nights) sleep outcomes. Within subject comparisons of DC potential were made across sleep quantity and quality categories using repeated-measures analysis of variance to examine the influence of acute and extended sleep quantity and quality on DC potential outcomes. The level of significance was set at p ≤ 0.025. Statistically significant main effects were identified for acute sleep (F3,16 = 4.68, p < .02, η2p = 0.47) and extended sleep durations (F2,17 = 7.71, p < 0.005, η2p = 0.48). Specifically, for acute sleep durations, there was a 17.1% increase in DC potentials (3.59, p < 0.01, Cohen’s d = 0.52, SE 1.18) for sleep durations ≥ 7 hours to < 9 hours, compared to sleeping < 6. For extended sleep, there was a 20% increase in DC potentials (4.53, p < 0.002, Cohen’s d = 0.68, SE = 1.13) when recording a two-day sleep average of ≥ 7.5 hours and < 9 hours, compared to an extended sleep duration of < 6 hours. A statistically significant main effect was also identified for extended wake episodes (F2,19 = 4.5, p = 0.025, η2p = 0.32). For extended sleep periods with > 4 wake episodes there was a 12% increase in DC potentials (2.57 ± 2.24mV, p < 0.25, Cohen’s d = 0.34) compared to extended sleep periods with 2-3 wake episodes. There was not a significant effect of acute (p ≥ 0.20) sleep quality or extended latency (p > 0.18) and efficiency (p > 0.08) on DC potentials. These findings suggest that sleep quantity affects DC bio-potentials and thus the functional state of the athlete. Specifically, sleep durations between 7.00/7.50 to 9 hours correspond with higher measures of DC potentials compared to lesser durations. Given the effect of sleep quantity on biological markers for training adaptability, practitioners should prioritize sleep in the training process and educate athletes on proper sleep hygiene and sleep quantity to enhance their readiness to train.

In the present work, the effect of variation in specimen orientation and heat treatment on the Stress Corrosion Cracking (SCC) susceptibility of 7050 aluminum alloy was investigated in 3,5% NaCl solution and under freely corroding conditions. For this purpose, Constant Extension Rate Tests (CERT) was performed on precracked Compact Tension (CT) specimens and the Direct Current Potential Drop technique was applied to measure the crack lengths. In addition to crack length versus time curves, the relationship between the crack growth rate and the stress intensity factor was determined. Fractographic analysis was utilized extensively to support the findings related with basic mechanisms of cracking. The alloy was found to be in the most susceptible state in the SL orientation, in which the crack propagation direction is parallel to the rolling direction. The resistance to SCC is higher in the TS but at maximum in LT orientation where the loading direction is parallel to the rolling direction. In the peak aging treatment, T651, alloy is susceptible to SCC in SL orientation. When the over aging treatment, T7651, is applied the resistance is increased and the two step over aging treatment, T73651, has resulted in an additional improvement in this orientation. On the other hand, the alloy showed higher resistance to SCC in TS and LT orientations in T651 condition compared to the T7651 and T73651 treatments. In these orientations, the alloy is less susceptible in T73651 condition than in T7651 treatment.

The main goal of this thesis is to get an insight into a field of non-destructive testing using potential drop techniques that have nowadays become the standard not only in the fatigue and loading tests but also in the industry. These methods can serve to non-destructively and continuously measure material specimens, thickness, corrosion losses, deformations, spectroscopy and detection and analysis of crack geometry. They can help to identify materials and measure material changes over time. The second part of this thesis deals with designing the aperture for detection of cracks in steam and product piping using potential drop technique modified by Ing. Ladislav Korec, CSc. Last part deals with extensive testing, experimenting and evaluation of the aperture.