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Purpose: Underwater divers face several potential neurological hazards when breathing compressed gas mixtures including nitrogen narcosis which can impact diver's safety. Various human studies have clearly demonstrated brain impairment due to nitrogen narcosis in divers at 4 ATA using critical flicker fusion frequency (CFFF) as a cortical performance indicator. However, recently some authors have proposed a probable adaptive phenomenon during repetitive exposure to high nitrogen pressure in rats, where they found a reversal effect on dopamine release.Methods: Sixty experienced divers breathing Air, Trimix or Heliox, were studied during an open water dive to a depth of 6 ATA with a square profile testing CFFF measurement before (T0), during the dive upon arriving at the bottom (6 ATA) (T1), 20 min of bottom time (T2), and at 5 m (1.5 ATA) (T3).Results: CFFF results showed a slight increase in alertness and arousal during the deep dive regardless of the gas mixture breathed. The percent change in CFFF values at T1 and T2 differed among the three groups being lower in the air group than in the other groups. All CFFF values returned to basal values 5 min before the final ascent at 5 m (T3), but the Trimix measurements were still slightly better than those at T0.Conclusions: Our results highlight that nitrogen and oxygen alone and in combination can produce neuronal excitability or depression in a dose-related response. [ABSTRACT FROM AUTHOR]

Purpose: A reduction in ambient pressure or decompression from scuba diving can result in ultrasound-detectable venous gas emboli (VGE). These environmental exposures carry a risk of decompression sickness (DCS) which is mitigated by adherence to decompression schedules; however, bubbles are routinely observed for dives well within these limits and significant inter-personal variability in DCS risk exists. Here, we assess the variability and evolution of VGE for 2 h post-dive using echocardiography, following a standardized pool dive in calm warm conditions.Methods: 14 divers performed either one or two (with a 24 h interval) standardized scuba dives to 33 mfw (400 kPa) for 20 min of immersion time at NEMO 33 in Brussels, Belgium. Measurements were performed at 21, 56, 91 and 126 min post-dive: bubbles were counted for all 68 echocardiography recordings and the average over ten consecutive cardiac cycles taken as the bubble score.Results: Significant inter-personal variability was demonstrated despite all divers following the same protocol in controlled pool conditions: in the detection or not of VGE, in the peak VGE score, as well as time to VGE peak. In addition, intra-personal differences in 2/3 of the consecutive day dives were seen (lower VGE counts or faster clearance).Conclusions: Since VGE evolution post-dive varies between people, more work is clearly needed to isolate contributing factors. In this respect, going toward a more continuous evaluation, or developing new means to detect decompression stress markers, may offer the ability to better assess dynamic correlations to other physiological parameters. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was (1) to further explore the heart rate dynamics and assess a potential cardiovascular risk in response to 4000 m jumps in experienced skydivers; (2) to assess whether there is an impact of such jumps on skydivers' cortical arousal or not, which may impact their decision making processes. Method: 18 experienced skydivers performed successive jumps from a plane at 4000 m of height. Heart rate dynamics and cortical arousal were assessed by the use of heart rate variability and Critical Flicker Fusion Frequency (CFFF), respectively. Results: CFFF did not differ between the three measurement time points ( p > 0.05). Mean heart rate increased during the jump ( p < 0.001) and came back to pre-jump values after the jump ( p < 0.001). Percentage of the differences of successive NN intervals greater than 50 ms (pNN50) decreased during the jump ( p < 0.001) and kept lower values after the jump compared to pre-jump ( p < 0.05). High-frequency power (HF) did not differ during the jump ( p > 0.05) but decreased after the jump compared to both pre-jump ( p < 0.01) and jump ( p < 0.05). Sample entropy decreased during the jump ( p < 0.001) and came back to pre-jump values after the jump ( p > 0.05). Conclusion: These results confirm a vagal input reduction associated with a rise of the sympathetic tone during the jump and suggests that the experienced skydiver is not exposed to a high cardiovascular risk. This study also shows that environmental stresses induced by free fall could not hamper the perceptual vigilance of experienced skydivers. [ABSTRACT FROM AUTHOR]

One of the possible risks incurred while diving is inert gas narcosis (IGN), yet its mechanism of action remains a matter of controversy. Although providing insights in the basic mechanisms of IGN, research has been primarily limited to animal studies. A human study, in real diving conditions, was needed. Twenty volunteers within strict biometrical criteria (male, age 30-40 years, BMI 20-23, non smoker) were selected. They performed a no-decompression dive to a depth of 33 mfw for 20 min and were assessed by the means of critical flicker fusion frequency (CFFF) measurement before the dive, during the dive upon arriving at the bottom, 5 min before the ascent, and 30 min after surfacing. After this late measurement, divers breathed oxygen for 15 min and were assessed a final time. Compared to the pre-dive value the mean value of each measurement was significantly different ( p < 0.001). An increase of CFFF to 104 ± 5.1 % upon arriving to the bottom is followed by a decrease to 93.5 ± 4.3 %. This impairment of CFFF persisted 30 min after surfacing, still decreased to 96.3 ± 8.2 % compared to pre-dive CFFF. Post-dive measures made after 15 min of oxygen were not different from control (without nitrogen supersaturation), 124.4 ± 10.8 versus 124.2 ± 3.9 %. This simple study suggests that IGN (at least partially) depends on gas-protein interactions and that the cerebral impairment persists for at least 30 min after surfacing. This could be an important consideration in situations where precise and accurate judgment or actions are essential. [ABSTRACT FROM AUTHOR]

Two well-separated electron traps with activation energies: E ≊ 0.286 eV and E ≊ 0.433 eV have been consistently detected in the n-type AlGaAs confinement layer of AlGaAs/GaAs single quantum well laser diodes. The physical characteristic parameters for these two traps, including capture cross section, emission time constant, and capture time constant, have been calculated. Reverse-bias pulsed deep level transient spectroscopy (RDLTS) results provide the evidence for the first time that these two traps have strong interaction during emission processes. This allows us to conclude that E and E are indeed both donor-unknown centers. Furthermore, using a temperature-dependent pulse-width method, DLTS signals from E alone can be obtained. The corrected activation energy appears to be a little shallower at E ≊ 0.265 eV. [ABSTRACT FROM AUTHOR]

Non-destructive characterization of III-V compounds has recently received much attention. The demands of efficient use of resources require full wafer processing. Using the fact that semiconductors are semi-transparent at energies below their bandgaps, the theory of thin film interference can be used to measure the thickness of epitaxial layers across the wafer. Ellipsometry and reflection spectroscopy have previously been used for this type of characterization. We have non-destructively measured epitaxial layer thicknesses of the Graded Index Separate Confinement Heterostructure (GRINSCH-SQW) using simple transmission spectroscopy. [ABSTRACT FROM AUTHOR]

The original version of this article unfortunately contained a mistake. [ABSTRACT FROM AUTHOR]