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New Findings What is the central question of this study? What is the effect of three repeated breath‐hold techniques routinely used by freedivers, thought to manipulate arterial partial pressures of O2 and CO2, on the cardiorespiratory and haematological response to breath‐holding during facial immersion? What is the main finding and its importance? All three techniques increased breath‐hold by a similar duration, probably owing to the similar marked increase in end‐tidal O2 and decrease in end‐tidal CO2 observed in all three trials before facial immersion. These were the only cardiorespiratory changes that were consistently manipulated before the maximal breath‐hold. This would suggest that pronounced bradycardia and vasoconstriction of selective vascular beds are probably not obligatory for prolonging breath‐hold duration. Repeated maximal breath‐holds have been demonstrated to induce bradycardia, increase haematocrit and haemoglobin and prolong subsequent breath‐hold duration by 20%. Freedivers use non‐maximal breath‐hold techniques (BHTs) to improve breath‐hold duration. The aim of this study was to investigate the cardiorespiratory and haematological responses to various BHTs. Ten healthy men (34.5 ± 1.9 years) attended five randomized experimental trials and performed a 40 min period of quiet rest or one of three BHTs followed by a maximal breath‐hold challenge during facial immersion in water at 30 or 10°C. Cardiovascular and respiratory parameters were measured continuously using finger plethysmography and breath‐by‐breath gas analysis, respectively, and venous blood samples were collected throughout. Facial immersion in cold water caused marked bradycardia (74.1 vs. 50.2 beats/min after 40 s) but did not increase breath‐hold duration compared with warm water control conditions. Facial immersion breath‐hold duration was 30.8–43.3% greater than the control duration when preceded by BHTs that involved repeated breath‐holds of constant duration (P = 0.021), increasing duration (P < 0.001) or increasing frequency (P < 0.001), with no difference observed between BHTs. The increased duration of apnoea across all three BHT protocols was associated with a 6.8% increase in end‐tidal O2 and a 13.1% decrease in end‐tidal CO2 immediately before facial immersion. There were no differences in blood pressure, cardiac output, heart rate, haematocrit or haemoglobin between each BHT and control conditions (P > 0.05). In conclusion, the duration of apnoea can be extended by manipulating blood gases through repeated prior breath‐holds, but changes in cardiac output and red blood cell mass do not appear essential.

Why do forest productivity and biomass decline with elevation? To address this question, research to date generally has focused on correlative approaches describing changes in woody growth and biomass with elevation. We present a novel, mechanistic approach to this question by quantifying the autotrophic carbon budget in 16 forest plots along a 3300m elevation transect in Peru. Low growth rates at high elevations appear primarily driven by low gross primary productivity (GPP), with little shift in either carbon use efficiency (CUE) or allocation of net primary productivity (NPP) between wood, fine roots and canopy. The lack of trend in CUE implies that the proportion of photosynthate allocated to autotrophic respiration is not sensitive to temperature. Rather than a gradual linear decline in productivity, there is some limited but nonconclusive evidence of a sharp transition in NPP between submontane and montane forests, which may be caused by cloud immersion effects within the cloud forest zone. Leaf-level photosynthetic parameters do not decline with elevation, implying that nutrient limitation does not restrict photosynthesis at high elevations. Our data demonstrate the potential of whole carbon budget perspectives to provide a deeper understanding of controls on ecosystem functioning and carbon cycling.

The western region of China is characterized by abundant coal resources but scarce water resources, and underground reservoir systems have been proposed to mitigate this mismatch. However, during the operation of these reservoirs, fluctuating water levels cause coal pillar dams to be prone to damage due to the combined effects of in-situ stress and water immersion. In this study, cyclic loading-unloading experiments and nuclear magnetic resonance tests were performed on coal samples with varying immersion heights to investigate their mechanical behavior. The results showed that immersion leads to the mechanical properties exhibiting a trend of “short-term strengthening followed by significant weakening”. Unsoaked coal samples exhibited brittle characteristics, while immersed samples showed ductile behavior, with stress fluctuations after reaching peak load. Pore structure analysis revealed that higher immersion heights caused significant damage, with micropores evolving into mesopores and macropores, weakening the mechanical strength of the coal samples. The interaction between water and coal revealed a “compaction strengthening—damage softening” mechanism: at lower immersion heights, water infiltration created micropores that buffered external loads, resulting in compaction strengthening. At higher immersion levels, however, deeper water penetration triggered physicochemical interactions, generating macropores and microcracks that reduced mechanical strength. This study provides both macroscopic deformation-failure analysis and microscopic mechanistic insights into water-induced damage, aiming to enhance the stability and safety of coal pillar dams in underground reservoir systems.

In this study, Brazilian splitting tests were conducted on sandstone samples subjected to drying and immersing at water pressures of 0, 1, and 3 MPa (immersion duration of 120 h). Investigation of the immersion effects of pressure water on the tensile characteristics of the samples revealed that their tensile strengths decreased with the immersion water pressure. Relative to a sandstone sample subjected to drying alone, immersing at water pressures of 0, 1, and 3 MPa reduced the tensile strength by 12.96%, 19.03%, and 30.16%, respectively. Although the immersed samples experienced splitting failure indicative of obvious brittle failure characteristics, decreases in the postpeak stress reduction rate with immersion water pressure revealed that the intensity of brittle failure weakened with pressure. Based on the obtained data, the deformation evolution process of the sandstone samples could be divided into five stages: deformation adjustment, formation of local deformation zones, local deformation zone propagation, failure surface formation, and sample failure. The water pressure aggravated the physicochemical reactions between water and the hydrophilic minerals in the sandstone, promoting argillisation, dissolution, and loss of hydrophilic minerals and interparticle cementitious materials. As a result of these immersion micromechanisms, the deterioration of the sandstone samples increased with the immersion water pressure, with the average porosities of the fracture surfaces at 0, 1, and 3 MPa increasing by 142.86%, 368.37%, and 593.88%, respectively, relative to the dried sample. As a result of these morphological changes, the sandstone samples subjected to water pressure immersion failed at small axial stresses with low levels of applied mechanical energy.

Immersion is a useful tool for studying fluid-volume homeostasis. Natriuretic peptides play a vital role in renal, humoral, and cardiovascular regulation under changing environmental conditions. We hypothesized that dry immersion would rapidly induce a new steady state for water and sodium metabolism, and that serum NT-proBNP levels, a proxy measure for brain natriuretic peptide (BNP), would decrease during long-term dry immersion and increase during recovery. Eight healthy young men were studied before, during, and after 7 days of dry immersion. Body weight, water balance, and plasma volume changes were evaluated. Plasma and serum samples were analyzed for active renin, NT-proBNP, aldosterone, electrolytes, osmolality, total protein, and creatinine. Urine samples were analyzed to determine levels of electrolytes, osmolality, creatinine, and free cortisol. A stand test was performed before and after dry immersion to evaluate cardiovascular deconditioning. Long-term dry immersion induced acute changes in water and sodium homeostasis on day 1, followed by a new steady state. Plasma volume decreased significantly during dry immersion. The serum levels of NT-proBNP increased significantly in recovery (10 ± 3 ng/L before dry immersion vs. 26 ± 5 ng/L on the fourth recovery day). Heart rate in the standing position was significantly greater after immersion. Results suggest that chronic dry immersion rapidly induced a new level of water-electrolyte homeostasis. The increase in NT-proBNP levels during the recovery period may be related to greater cardiac work and might reflect the degree of cardiovascular deconditioning.

Polymer-based composite materials are widely used in engineering applications due to their lightweight structure and tunable physical properties. However, exposure to environmental conditions such as moisture and chemical solutions can significantly influence their thermal performance. This study investigates the effect of immersion media and reinforcing materials on the thermal conductivity of epoxy-based composites reinforced with polyethylene fibers. Composite specimens were fabricated using epoxy resin as the matrix material and polyethylene fibers as reinforcement with volume fractions of 15 and 20%. The samples were immersed in tap water and ethanol solutions for different exposure periods. Thermal conductivity measurements were performed before and after immersion to evaluate the influence of chemical absorption on heat transfer behavior. The experimental results revealed that unreinforced epoxy exhibited higher thermal conductivity than fiber-reinforced composites. Furthermore, polyethylene fiber reinforcement significantly reduced thermal conductivity due to increased phonon scattering within the polymer matrix. Water immersion led to a noticeable increase in thermal conductivity, whereas ethanol immersion resulted in a reduction of thermal conductivity values with prolonged exposure time. The findings confirm that polyethylene fibers enhance the resistance of epoxy composites to liquid absorption; however, extended immersion causes microstructural degradation that adversely affects thermal performance. These results provide useful insights for the design of polymer composite materials intended for applications under humid or chemically aggressive environments.

The rapid evolution of technology has created new opportunities for teleoperation, especially with the emergence of affordable Virtual Reality (VR) systems originally designed for entertainment and gaming. Teleoperation in robotics has a long history, however, its integration with VR for controlling robotic systems is currently gaining significant attention. In this study, a novel real-time platform is developed that integrates teleoperation with a VR system, providing immersive control of a biomimetic robotic head. A 3D model of the robotic head was designed and built to mimic the movements of the operator's head in real-time using the operator’s kinematics. The fabricated robotic head is equipped with a pair of cameras and a binaural microphone to provide vision and audio perception. Additionally, two servomotors are employed to track the motion of the operator’s neck. To control the biomimetic robotic head, a game was developed in Unity to deliver 3D visual and stereophonic audio inputs to the headset, which ensures a smooth viewing and listening experience for the operator. The designed platform is operated through a custom-written C + + program that facilitates continuous tracking of the headset and establishes constant communication with the servomotors. High precision in the positional data and accurate tracking of the head-mounted display (HMD), along with efficient communication with the motors, were achieved. The integration of the VR system and teleoperation developed in this study advances VR technology beyond traditional entertainment-oriented applications and makes it applicable in diverse industrial fields, simultaneously elevating teleoperation in human–robot interactions to new levels of productivity.

Common anesthesia practice for hand surgery combines a preoperative regional anesthetic and intraoperative monitored anesthesia care (MAC). Despite adequate regional anesthesia, patients may receive doses of intraoperative sedatives which can result in oversedation and potentially avoidable complications. VR could prove to be a valuable tool for patients and providers by distracting the mind from processing noxious stimuli resulting in minimized sedative use and reduced risk of oversedation without negatively impacting patient satisfaction. Our hypothesis was that intraoperative VR use reduces sedative dosing during elective hand surgery without detracting from patient satisfaction as compared to a usual care control. Forty adults undergoing hand surgery were randomized to receive either intraoperative VR in addition to MAC, or usual MAC. Patients in both groups received preoperative regional anesthesia at provider discretion. Intraoperatively, the VR group viewed programming of their choice via a head-mounted display. The primary outcome was intraoperative propofol dose per hour (mg · hr.sup.-1). Secondary outcomes included patient reported pain and anxiety, overall satisfaction, functional outcome, and post anesthesia care unit (PACU) length of stay (LOS). Of the 40 enrolled patients, 34 completed the perioperative portion of the trial. VR group patients received significantly less propofol per hour than the control group (Mean (±SD): 125.3 (±296.0) vs 750.6 (±334.6) mg · hr.sup.-1, p<0.001). There were no significant differences between groups in patient reported overall satisfaction, (0-100 scale, Median (IQR) 92 (77-100) vs 100 (100-100), VR vs control, p = 0.087). There were no significant differences between groups in PACU pain scores, perioperative opioid analgesic dose, or in postoperative functional outcome. PACU LOS was significantly decreased in the VR group (53.0 (43.0-72.0) vs 75.0 (57.5-89.0) min, p = 0.018). VR immersion during hand surgery led to significant reductions in intraoperative propofol dose and PACU LOS without negatively impacting key patient reported outcomes.

The circulatory system plays a significant role in the adaptation of the human body to varying environmental conditions and stress factors, such as cold water immersion. The aim of the study was to determine whether a single immersion in cold water below 4 °C, at air temperature of -15 °C constitutes a health risk in young healthy men. For this purpose, the following parameters were determined in the blood samples collected in 13 young males before and after cold water immersion: electrolytes, renal profile, liver profile, lipid profile, glucose, testosterone, thyroid-stimulating hormone, cortisol. After the immersion, a statistically significant decrease was found for Cl – (p ≤ 0.027), mean values of renal profile indicators: urea (p = 0.0019), creatinine (p = 0.0007), and uric acid (p = 0.0293), as well as testosterone (p = 0.000037). In turn, higher values of estimated glomerular filtration rate (p = 0.0425), total bilirubin (p = 0.0033), aspartate transaminase (p = 0.0023), alanine transaminase (p = 0.0053), lactate dehydrogenase (p = 0.0336), creatine kinase (p = 0.0117), CK-MB isoenzyme of creatine kinase (p = 0.0028), and high-density lipoprotein (p = 0.0270) were measured after cold water immersion. No significant changes in other biochemical parameters were observed. Single cold water immersion thus resulted in significant changes of blood parameters within non-pathological limits.

Highlight Research The dose, duration of immersion, and time interval of immersion of the estradiol-17β affect the rate of cannibalism and increase the seed survival of Asian redtail catfish in low treatment in this research. Over optimum treatment increased the incidence of cannibalism at Asian redtail catfish and decrease growth performance. Treatment of estradiol-17β, give the ability of Asian redtail catfish to live on high density The treatment of estradiol-17β, has an effect on concentration plasma of body testosterone and cortisol   Abstract The cannibalistic behavior of Asian redtail catfish greatly hampers the supply of these fish seeds, invoking the need to be controlled. Estradiol is one of the hormones that has been known to reduce cannibalistic behavior on fish. This study aimed to evaluate the effect of estradiol-17β immersion on the incidence of cannibalism in the rearing of post larvae of Asian redtail catfish. Post larvae was treated with a combination of doses of estradiol hormone 0, 1, and 2 ppm and immersion time of two and four hours with immersion intervals of three and six days with a completely randomized design. Each treatment had a fish density of 10 fish L-1, with mean size individual length of 6.73 ± 0.73 mm (three days of age after hatched), with four replications. Fish were fed with tubifex up until satiation point and reared for 30 days. The results showed that the administration of the estradiol-17β through immersion with a dose of 1 ppm for two hours and interval of six days was able to reduce the level of cannibalism and increase the survivability. A further increase in dose, immersion time, and interval had the opposite effect. Estradiol-17β immersion with certain dose, duration, and interval affected the rate of cannibalism, growth rate, and survival. Estradiol-17β immersion at a dose of 1 ppm for two hours and six days interval was the best to reduce the level of cannibalism and normal mortality in post larvae of Asian redtail catfish.