Atomic resolution imaging of electrode surfaces in solutions containing reversible redox species

Procedures are described for insulating metal scanning tunneling microscope (STM) tips with either glass or polymer coatings. In solutions containing 0.10 M of a reversible redox couple, Fe(CN) - 3/-46 , the faradaic limiting current to polymer coated tips was 200–500 pA and that for glass coated tips was <10 pA. For polymer insulated tips, steady-state currents of 10–100 pA were observed at tip-sample displacements less than 0.3 µm. The suppression of faradaic current achieved by these coating procedures enabled the collection of the first atomic resolution STM images of highly ordered pyrolytic graphite electrodes in contact with redox-active electrolytes. Preliminary data for the in situ electrochemical characterization of these tips are also discussed

Design of a scanning tunneling microscope for electrochemical applications

A design for a scanning tunneling microscope that is well suited for electrochemical investigations is presented. The construction of the microscope ensures that only the tunneling tip and the sample participate in electrochemical reactions. The design also allows rapid replacement of the tip or sample, and enables facile introduction of auxiliary electrodes for use in electrochemical experiments. The microscope utilizes stepper motor driven approach mechanics in order to achieve fully remote operation and to allow reproducible coarse control of tip/sample spacings for electrochemical experiments. Highly ordered pyrolytic graphite images at atomic resolution in air and aqueous solutions can be obtained with this microscope

Enhancing Oxygen Uptake Efficiency Through Nasal Breathing in Aerobic Exercise

An individual’s ability to use oxygen to sustain aerobic performance, as denoted by the oxygen uptake efficiency (OUE), is calculated by dividing oxygen uptake (VO2) by ventilation (VE). Whether nasal breathing (NB) during exercise would improve OUE more significantly compared to combined breathing (CB) remains uncertain. PURPOSE: To determine the effects of utilizing NB during exercise on OUE. METHODS: Fourteen males (age: 20.57 ± 1.22 yrs; BMI: 26.03 ± 3.16 kg/m2) were randomly assigned to the NB (n = 8) or CB (n = 6) group for a 4-week supervised aerobic exercise intervention conducted four times per week for 30 minutes at moderate intensity (70% maximal heart rate). VO2max tests were performed during the pre- (week 0) and post-study (week 4) periods on a recumbent bike to determine the change in OUE, VO2, and VE at varying intensities (40%, 55%, 70%, 85%, and 100% of VO2max). The OUE was calculated as VO2 (L) ÷ VE (L). A one-way ANCOVA, controlling for OUE, VO2, and VE at pre-study, was utilized to examine if NB elicited cardiorespiratory adaptations that were superior to the CB training at post-study. A paired-sample t-test examined changes in OUE, VO2, and VE throughout the GXT from week 0 to week 4. Data are presented as mean ± standard error. RESULTS: The NB group demonstrated significantly greater [F(1,11) = 7.213, p = 0.021] OUE (0.048 ± 0.002) at 85% of VO2max than the CB (0.037 ± 0.003) group. Similarly, the NB group had a significantly greater (p = 0.014) OUE (0.025 ± 0.001) at 100% of VO2max than the CB (0.021 ± 0.001) group. Only the NB group experienced significant improvements after exercise training in VO2 at 40% ( p = 0.003, 12.02 ± 0.50 to 13.72 ± 0.59 mL·kg·min-1], 55% (p = 0.006, 16.68 ± 0.71 to 18.87 ± 0.81 mL·kg·min-1), 70% (p = 0.005, 21.16 ± 0.93 to 24.00 ± 1.01 mL·kg·min-1), 85% (p = 0.004, 25.81 ± 1.11 to 29.03 ± 1.23 mL·kg·min-1), and 100% VO2max (p = 0.005, 30.31 ± 1.30 to 34.18 ± 1.48 mL·kg·min-1). While not statistically significant, the NB group displayed a trend of reduced VE compared to the CB group. CONCLUSION: The integration of NB during aerobic exercise enhanced the OUE, particularly at higher intensities, compared to CB. This adaptation is noteworthy, as the NB group achieved a comparable range of VO2 as the CB group while maintaining a lower VE after just 1-month of training. This denotes that NB could promote enhanced oxygen movement. Future studies are warranted to investigate additional health adaptations resulting from such training benefits

Authenticity of the Ratio of Inorganic Phosphate to Phosphocreatine as a Marker for Respiratory Stress During a Maximal Aerobic Exercise

Under the context of assessing the effects of mitochondrial stress on skeletal muscles, consideration for the ratio of inorganic phosphate to phosphocreatine (Pi:PCr) may be used as a surrogate marker. Furthermore, assessing the systemic Pi:PCr, under states of high metabolic and respiratory demands with reduced oxygen supply (VO2), such as strenuous exercise while only using nasal breathing (NB), might provide valuable information regarding respiratory strain to a given exercise bout. PURPOSE: To determine if the systemic assessment of the Pi:PCr ratio can serve as an indicator of respiratory stress. METHODS: Fourteen young males (age = 20.57 ± 1.22 yrs) completed a graded maximal exercise test (GXT) on a recumbent bike using either NB (n = 8) or combined (CB, n = 6) breathing. Plasma Pi and PCr were measured pre- and immediately post-GXT. Pi was analyzed using the malachite green colorimetric method, and PCr was quantified via sandwich enzyme-linked immunosorbent assay. The Pi:PCr was calculated by Pi ÷ PCr. A paired-sample t-test examined the Pi: PCr change following a GXT. A Pearson correlational analysis examined the relationship between the Pi:PCr and the respiratory performance during preset intensities (40%, 55%, 70%, 85%, and 100% VO2max). Data are presented as mean ± SD. RESULTS: The Pi:PCr ratio significantly decreased in the NB group (0.589 ± 0.313 to 0.530 ± 0.304, p = 0.034) mainly due to the elevated PCr (601.68 ± 318.88 mmol/L to 689.40 ± 410.60 mmol/L, p = 0.033). The Pi:PCR ratio was negatively correlated with VO2 only in the NB group throughout all preset intensities of the GXT. After controlling for the pre-GXT Pi:PCr as a covariate, the NB group showed a non-significant (p = 0.340) but higher mean concentration for post-exercise Pi:PCr compared to the CB group [NB: 0.451 ± 0.027 mmol/L versus CB: 0.407 ± 0.320 mmol/L. CONCLUSION: The results from the present study suggest that the assessment of the Pi:PCr ratio could serve as a valuable marker of physical strain pertaining to high respiratory demands. Moreover, the assignment of NB during exercise is becoming a novel method due to its postulated benefits towards respiratory function, which may induce a more significant cellular stress as denoted by an increase in the post-exercise Pi:PCr ratio

Integrating cache-related pre-emption delays into analysis of fixed priority scheduling with pre-emption thresholds

Cache-related pre-emption delays (CRPD) have been integrated into the schedulability analysis of sporadic tasks with constrained deadlines for fixed-priority pre-emptive scheduling (FPPS). This paper generalizes that work by integrating CRPD into the schedulability analysis of tasks with arbitrary deadlines for fixed-priority pre-emption threshold scheduling (FPTS). The analysis is complemented by an optimal threshold assignment algorithm that minimizes CRPD. The paper includes a comparative evaluation of the schedulability ratios of FPPS and FPTS, for constrained-deadline tasks, taking CRPD into account

The Impact of Nasal Breathing During Exercise on Cerebral Blood Flow

Achieving hypercapnic-induced vasodilation while exercising can increase cerebral blood flow (CBF) to a greater extent than during normoxic conditions. Evidence suggests that nasal breathing during a maximal aerobic effort can elicit a hypercapnic condition. PURPOSE: To compare the effect of combined (CB), oral (OB), and nasal (NB) breathing on CBF during a graded maximal exercise test (GXT). METHODS: Six healthy males (age: 21.83 ± 1.00 years) abstained from physical activity and caffeine for 12+ hours prior to a GXT. Three GXTs were performed (48+ hours between each trial) using a different randomized breathing condition (CB, OB, and NB). After a warm-up, participants completed a GXT until volitional fatigue on a semi-recumbent bicycle. Stages lasted 2 minutes and increased by a pre-set wattage at 70 rpm. Respiratory gases were assessed via a metabolic cart. Throughout the GXT, ultrasound sonography (7.5 MHz linear transducer) was utilized to assess the peak systolic velocity (PSV) and vessel diameter of the internal (ICA) and external (ECA) carotid artery on the right side of the neck. A one-way ANCOVA with mean arterial blood pressure and oxygen uptake (VO2) as covariates was utilized to compare the three breathing patterns at 40%, 55%, 70%, 85%, and 100% of VO2max. Data are presented as mean ± SEM. RESULTS: The partial pressure of exhaled CO2 (PECO2) was significantly greater (p = 0.008) during NB (33.16 ± 1.37 mmHg) compared to CB (26.63 ± 1.32 mmHg) and OB (26.72 ± 1.37) at 100% VO2max. While not statistically significant, there was a greater PSV in the ICA during NB (99.72 ± 7.12 cm/s) compared to CB (87.34 ± 9.36 cm/s) and OB (89.63 ± 9.77 cm/s) at 100% VO2max. Similarly, there was a greater PSV in the ICA during NB (102.53 ± 8.07 cm/s) compared to CB (93.13 ± 7.79 cm/s) and OB (81.25 ± 7.80 cm/s) at 85% VO2max. In contrast, there was a significantly greater (p = 0.027) PSV in the ICA during NB (126.12 ± 7.51 cm/s) compared to OB (92.47 ± 7.34 cm/s) but not CB (111.91 ± 7.14 cm/s) at 70% VO2max. There were no significant differences in the PSV of the ECA nor the diameter of the ICA and ECA. CONCLUSION: NB during a GXT increased PSV in the ICA compared to CB and OB, which might be partly related to an increased systemic concentration of CO2. A greater increase in PSV in the ICA represents a greater CBF that might provide greater cognitive health benefits than while exercising with either CB or OB. Studies with a bigger sample size will provide greater statistical power to examine the benefits of increasing the PSV in the ICA and its effect on cognitive health

Fixed priority scheduling with pre-emption thresholds and cache-related pre-emption delays: integrated analysis and evaluation

Commercial off-the-shelf programmable platforms for real-time systems typically contain a cache to bridge the gap between the processor speed and main memory speed. Because cache-related pre-emption delays (CRPD) can have a significant influence on the computation times of tasks, CRPD have been integrated in the response time analysis for fixed-priority pre-emptive scheduling (FPPS). This paper presents CRPD aware response-time analysis of sporadic tasks with arbitrary deadlines for fixed-priority pre-emption threshold scheduling (FPTS), generalizing earlier work. The analysis is complemented by an optimal (pre-emption) threshold assignment algorithm, assuming the priorities of tasks are given. We further improve upon these results by presenting an algorithm that searches for a layout of tasks in memory that makes a task set schedulable. The paper includes an extensive comparative evaluation of the schedulability ratios of FPPS and FPTS, taking CRPD into account. The practical relevance of our work stems from FPTS support in AUTOSAR, a standardized development model for the automotive industry

Evaluation of Body Fat Percentage with Vertical and Longitudinal Skinfolds

Subcutaneous fat content, as well as body fat percentage (BF%), can be effectively assessed using skinfold calipers. While skinfolds (SFs) are practical and easy to attain, their accuracy could be reduced if the SFs are not collected with the ideal fold orientation. PURPOSE: To determine if vertical or longitudinal SFs in the trunk area are better predictors of BF%. METHODS: A pool of thirty-eight male (21.29 ± 4.59 yrs, 15.68 ± 4.82 BF%) and twenty-two female (21.14 ± 4.05 yrs, 26.63 ± 5.34 BF%) participants completed the study. A dual-energy X-ray absorptiometry scan was utilized to assess BF%. Using a Lange caliper, one technician assessed all SFs within the trunk in triplicate using both a vertical pinch and a longitudinal pinch. SFs sites included: 2 cm left, right, superior, and inferior of the umbilicus; left and right anterior mid-axillary line at the level of the navel; 2 cm left and right of the vertebral column at the level of the navel; midsternal line at the slimmest part of the waist and at the level of the xiphoid process. In addition, two commonly assessed diagonal folds (right suprailiac and subscapular) were collected. The relationship between SFs orientation and BF% was assessed utilizing a Pearson correlation. Stepwise linear regression was utilized to predict BF%. Data are presented as mean ± SD. RESULTS: Overall, vertical folds for both males and females had a higher correlation with BF% than longitudinal folds. The right vertical mid-axillary (RVMA) SFs had a significant correlation with BF% for both male (r = 0.864, p \u3c 0.001) and female (r = 0.712, p \u3c 0.001) participants. Similarly, the subscapular (SS) SFs had a significant correlation with BF% for both male (r = 0.851, p \u3c 0.001) and female (r = 0.788, p \u3c 0.001) participants. BF% was successfully predicted [4.142 + (10.154 * Sex) + (0.255 * RVMA) + (0.516 * SS), adjusted R2 = 0.874], where sex (0 = male, 1 = female). The average RVMA SFs were 18.43 ± 7.85 mm for males and 19.91 ± 6.78 mm for females, while the SS SFs were 13.50 ± 4.95 mm for males and 14.05 ± 5.34 mm for females. CONCLUSION: Although RVMA SFs are not commonly utilized to estimate BF%, there is evidence of a high correlation with BF%. The applicability of utilizing the RVMA jointly with the SS SFs as a fast yet reliable method to estimate BF% should be examined in a large and diverse cohort

The Effect on Carbon Dioxide Production During Maximal Exercise with Distinct Breathing Mechanisms

Nasal breathing (NB) may lead to lower maximal oxygen uptake (VO2max) compared to oral breathing (OB) or nasal/oral combined breathing (CB) due to a transient increase in the systemic concentration of carbon dioxide (CO2) that can replicate the effects of a hypoxic environment. The exercise intensity at which NB can elicit this response is poorly understood. PURPOSE: To examine the increase in the fractional rate of exhaled CO2 (FECO2) and FEO2 with different breathing conditions during a graded maximal aerobic exercise test (GXT). METHODS: Eight healthy males (21.88 ± 0.46 years) completed 3 GXTs (separated by 48+ hours of recovery) using a different randomly assigned breathing condition (NB, OB, and CB). Participants exercised on a semi-recumbent bicycle at a pedaling speed of 70 rpm, increasing resistance every 2 minutes until volitional fatigue. Following the GXT, participants had a 2-minute recovery. Expired respiratory gases were collected via a metabolic cart. Six time points (40%, 55%, 70%, 85%, 100% VO2max, and recovery) were compared between NB, OB, and CB. Data are presented as mean ± SD. RESULTS: FECO2 was significantly higher during NB than OB at 70% [4.52 ± 0.37 vs. 4.07 ± 0.26%, p = 0.031 and 85% (4.49 ± 0.43% vs. 3.80 ± 0.32%, p = 0.009) of VO2max. Additionally, FECO2 at 100% of VO2max was significantly higher (p = 0.001) during NB (4.33 ± 0.69%) than OB (3.47 ± 0.29%) and CB (3.55 ± 0.19%). The transient change in FECO2 during exercise rapidly changed after the 2-minute recovery, where NB = 3.75 ± 0.71%, OB = 3.38 ± 0.17%, and CB = 3.30 ± 0.27%. FEO2 was significantly lower during NB than OB at 70% (16.34 ± 0.45% vs. 17.04 ± 0.3%, p = 0.011) and 85% (16.50 ± 0.53% vs. 17.32 ± 0.38%, p = 0.009) of VO2max. FEO2 was significantly lower (p = 0.003) during NB (16.66 ± 0.91%) compared to OB (17.67 ± 0.33%) and CB (17.61 ± 0.26%) at 100% VO2max. The transient change in FEO2 during exercise rapidly changed after the 2-minute recovery, where NB = 17.67 ± 1.00%, OB = 18.03 ± 0.23%, and CB = 18.20 ± 0.17%. CONCLUSION: NB elicits an exercised-induced increase in FECO2 that is analogous to a decrease in FEO2 starting at 70% of VO2max. Given the transient increase in FECO2, NB should be considered as a potential breathing method and further explored to replicate a temporary hypoxic environment that could promote a greater exercise adaptation than CB or OB might do

Relationships Between Anthropometric Variables and the Internal Carotid Blood Flow

Assessment of peak systolic velocity (PSV) of the internal carotid artery (ICA) is utilized to examine stroke-symptomatic individuals for ICA stenosis. While a sedentary lifestyle is a common risk factor for ICA stenosis, a deeper understanding of how body composition affects ICA blood flow could provide insights before symptoms appear. PURPOSE: To examine the relationship between ICA blood flow and body composition variables. METHODS: ICA blood flow was assessed in eight healthy males (21.88 ± 2.25 years) on three different days to control for possible diurnal variability that could affect blood flow. Participants abstained from caffeine and physical activity for a minimum of 12 hours prior to each visit. Dual-energy X-ray absorptiometry was used to assess body fat percentage (BF%) and visceral fat area (VFA). Bioelectrical impedance (BIA) was used to assess body water percentage (BW%), metabolic age (MetA), and visceral fat rating (VFR). Participants rested supine with eyes closed for 5 minutes prior to assessment of ICA. B-mode doppler ultrasound sonography (7.5 MHz linear transducer) was used to measure PSV, end-diastolic velocity (EDV), resistance index (RI), and vessel diameter on the right ICA after 2 minutes of continual scanning with a 60° insonation angle. The relationship between ICA blood flow and body composition variables was examined via Pearson correlation analysis. RESULTS: BF% was positively correlated with ICA EDV (r = 0.669, p \u3c 0.001) and ICA PSV (r = 0.416, p = 0.043) but negatively correlated with ICA diameter (r = -0.424, p = 0.039). VFA was positively correlated with ICA EDV (r = 0.505, p = 0.012). BW% was negatively correlated with ICA PSV (r = -0.417, p = 0.043) and EDV (r = -0.620, p \u3c 0.001). MetA was positively correlated with ICA EDV (r = 0.630, p \u3c 0.001) but negatively correlated with ICA RI (r = -0.509, p = 0.011) and diameter (r = -0.513, p = 0.010). Similarly, VFR was positively correlated with ICA EDV (r = 0.644, p \u3c 0.001) but negatively correlated with ICA RI (r = -0.511, p = 0.011) and diameter (r = -0.496, p = 0.014). CONCLUSION: EDV has a greater correlation with body composition than PSV, suggesting that adiposity-related factors can describe ICA blood flow. Similarly, BIA might offer a solid and easy-to-attain procedure to indirectly assess ICA blood flow that warrants further research