Simulated High-altitude Conditions Research Articles

Effects of temperature and light on quality-related metabolites in tea [Camellia sinensis (L.) Kuntze] leaves

In China, the environmental conditions in mountainous regions are suitable for producing high-quality tea, but the underlying mechanism is unknown. Analyses of published data revealed tea leaves harvested at high altitudes are associated with high-quality tea, possibly because of the effects of light and temperature. This was confirmed by simulating the changes induced by temperature and light at different altitudes. Catechin biosynthesis was inhibited by high altitudes, whereas free amino acid contents increased, leading to a decrease in polyphenol to amino acids ratio. Under simulated high-altitude conditions, increases in the abundance of l-theanine and other amino acids were due to the increase in precursor contents and chloroplast protein hydrolysis, respectively. In addition, some aroma compound contents increased in fresh or wounded leaves because of up-regulated expression of key structural genes. Overall, tea taste and aroma were enhanced by simulated high-altitude conditions. This study provides the basis for enhancing low-quality tea raw materials.

Insulation Materials and Systems for More- and All-Electric Aircraft: A Review Identifying Challenges and Future Research Needs

In recent decades, extensive research has been conducted on the electrification of commercial aircraft to reduce the dependence on mechanical, hydraulic, and pneumatic systems and replace them with electrical systems. A primary goal of this path is to make the power density of the more-/all-electric aircraft (MEA/AEA) closer to that of conventional aircraft. While current commercial aircraft operate at voltages below 1 kV, it is widely accepted that higher operating voltage is necessary for MEA/AEA. NASA has envisaged a voltage level of at least 6 kV for MEA. In the language of electrical insulation technology, higher voltage levels translate into higher electric tension on the insulation system. A serious challenge stems from the fact that, at high altitudes, high-voltage insulation design strategies are not necessarily as efficient as at sea level due to differences in environmental conditions, including lower pressure, higher moisture level, microgravity, and plasma radiation. In this article, challenges associated with the electrical insulation design of future aircraft are reviewed. These challenges extend to almost any part of the electric power system in an aircraft, such as electric machines, power converters, cables, and printed circuit boards (PCBs). An overview of the aging factors, such as internal discharges, arc tracking, and thermal degradation, is accompanied by a discussion of the potential of novel insulating material and the ways to reinforce the current commercial dielectric materials. Finally, considerations for testing at simulated high-altitude conditions and the existing standards and their deficits are investigated.

Dihydromyricetin Improves Physical Performance under Simulated High Altitude

Dihydromyricetin (DHM) is the major bioactive constituent of rattan tea. Our aim was to investigate the possible mechanism and the effect of DHM in counteracting hypobaric hypoxia (HH)-induced exercise intolerance. Male Sprague-Dawley rats were pretreated with three doses of DHM (50, 75, and 100 mg · kg(-1)) for 7 d and subjected to simulated high-altitude conditions (5000 m with 10.9% oxygen). Physical performance was assessed with the run-to-fatigue model. Mitochondrial morphology in the gastrocnemius muscle was observed by transmission electron microscopy. Protein expression was detected by western blotting. The activity of mitochondrial electron transport chain was analyzed by enzyme-linked immunosorbent assay. DHM administration prolonged the run-to-fatigue time in a dose-dependent manner compared with the control (22.9 ± 2.2, 46.1 ± 4.4, 61.3 ± 3.1 vs 18.4 ± 1.7 min, which represented 50, 75, 100 mg · kg(-1), and the control groups, respectively). DHM also reduced serum blood urea nitrogen, lactate dehydrogenase, and creatine kinase activity levels. HH-induced mitochondrial injuries, including morphological changes, reduction in mitochondrial density and mitochondrial DNA content, and decrease in respiratory chain complex (I, II, IV, and V) activities were effectively attenuated by DHM. Protein expression of mitochondrial biogenesis markers, including peroxisome proliferator-activated receptor-γ coactivator 1α, sirtuin 1, nuclear respiratory factor 1, mitochondrial transcription factor A, AMP-activated protein kinase, and AMP-activated protein kinase phosphorylation, was significantly downregulated in HH, whereas DHM pretreatment significantly restored expression levels. DHM also modulated mitochondrial dynamics of fusion and fission by increasing mitofusins 1 and 2, while decreasing fission-related, dynamin-related protein 1 and mitochondrial fission 1. DHM improves physical performance under simulated high-altitude conditions via protecting mitochondrial biogenesis and modulating mitochondrial dynamics in skeletal muscle cells.

Characteristics of a rat model of an open craniocerebral injury at simulated high altitude

To establish a rat model of an open craniocerebral injury at simulated high altitude and to examine the characteristics of this model. Rats were divided randomly into a normobaric group and a high-altitude group and their corresponding control groups. A rat model of an open craniocerebral injury was established with a nail gun shot. Simulated high-altitude conditions were established with a hypobaric chamber at 0.6 ATA to mimic pressure at an altitude of 4000 m. Mortality, brain water content (BWC), Evans blue content, pathology, regional cerebral blood flow (rCBF), partial pressure of brain tissue oxygen (PbtO2), and brainstem auditory-evoked potential were observed after injury. The mortality of the high-altitude group was significantly greater than that of the normobaric group within 72 h after injury (P<0.05). BWC and Evans blue content increased by 48 h after injury (P<0.05); pathological changes in damaged brains were more serious. In contrast, rCBF and PbtO2 had decreased markedly by 72 h (P<0.01); brainstem auditory-evoked potential values were significantly prolonged (P<0.05). Moreover, an inverse correlation between rCBF and BWC and a positive correlation between rCBF and PbtO2 were found. The rat model of an open craniocerebral injury at simulated high altitude can be established successfully using a nail gun shot and a hypobaric chamber. The injury characteristics at high altitude were more serious, rapid, and prolonged than those in the normobaric group.

Performance of a single-cylinder diesel engine using oxygen-enriched intake air at simulated high-altitude conditions

A single-cylinder, naturally aspirated, air-cooled, direct-injected diesel engine was used to study the effects of oxygen enrichment of intake air on engine performance at simulated high altitude conditions. Altitudes up to 5200 m (17,000 ft) were simulated by using a throttle valve to restrict the mass air flow to the engine and reduce intake pressure to represent the atmospheric pressures observed at high altitudes. This altitude ceiling is relevant to current technology UAVs used by the military, such as the RQ-7A/B Shadow 200 and the MQ-1 Predator. The oxygen volume fraction in the combustion air was increased by mixing pure oxygen from gas bottles into the intake air. The response surface methodology (RSM) was used to determine the relationships between fuel injection timing (FIT), engine load, simulated altitude, and oxygen volume fraction to parameters of engine performance, such as power output, brake-specific fuel consumption and fuel conversion efficiency. It was found that power output depended mainly on engine load and was not improved by the use of oxygen-enriched air, but it did not decrease significantly for altitudes up to 2600 m (8500 ft). The use of oxygen-enriched air was also effective to prevent the deterioration in brake-specific fuel consumption when increasing simulated altitude, an effect that was observed on fuel conversion efficiency, peak cylinder pressures and maximum rates of heat release. Peak combustion temperatures were significantly affected by simulated altitude and oxygen volume fraction, but the effect of simulated altitude was of larger magnitude than the effect of oxygen volume fraction.

Nitric oxide system is involved in hypobaric hypoxia-induced oxidative stress in rat brain

Oxidative stress is involved in memory impairment at high altitude (HA). The aim of the present study was to investigate the involvement of reactive nitrogen species in hippocampus, cortex and striatum of rat brain under simulated HA conditions. Rats were exposed to hypobaric hypoxia (HH) equivalent to 6100 m of HA in an animal decompression chamber for 3, 7, 14 and 21 days. Biochemical estimation of free radicals, nitric oxide (NO) level along with immunoreactivity, reverse transcriptase polymerase chain reaction (RT-PCR) and western blot of neuronal nitric oxide synthase (nNOS), neurodegeneration and DNA fragmentation were studied after HH exposure. The free radicals, NO level, nNOS immunoreactivity (nNOS-IR), nNOS expression, neurodegeneration and DNA fragmentation were increased in hippocampus, cortex and striatum after HH exposure. After 7 and 14 days of HH exposure, the nNOS-IR, nNOS expression, free radical, NO level, neurodegeneration and DNA fragmentation were increased in comparison to 3 or 21 days of HH. The NO system may be involved in increasing oxidative stress and neurodegeneration after HH.

Differential expression of mitochondrial electron transport chain proteins in cardiac tissues of broilers from pulmonary hypertension syndrome-resistant and -susceptible lines

Pulmonary hypertension syndrome (PHS) is a metabolic disease associated with the rapid growth rate of modern broilers. Broilers susceptible to PHS experience sustained elevation of pulmonary arterial pressure leading to right ventricular hypertrophy and ultimately heart failure. Previous studies have shown that mitochondrial function is defective in broilers with PHS; they use oxygen less efficiently than broilers without PHS. In this study mitochondrial electron transport chain (ETC) protein levels were compared in cardiac tissues from PHS resistant and susceptible line broilers using quantitative immunoblots. Seven of 9 anti-mammalian mitochondrial ETC protein antibodies tested exhibited cross-species reactivity. Six ETC proteins were differentially expressed in the right ventricles of broilers raised under simulated high altitude conditions (2,900 m above sea level). Four ETC proteins were present at higher levels in resistant line birds without PHS than in resistant line birds with PHS or in susceptible line birds with or without PHS. One ETC protein was present at higher levels in broilers without PHS than in broilers with PHS in both lines, and one ETC protein was present at lower levels in susceptible line birds without PHS than in susceptible line birds with PHS or in resistant line birds with or without PHS. Interestingly, differential expression of mitochondrial ETC proteins was not observed in the right ventricles of broilers raised at local altitude (390 m above sea level) nor was it observed in the left ventricles of broilers exposed to simulated high altitude. These results suggest that higher levels of mitochondrial ETC proteins in right ventricle cardiac muscle may be correlated with resistance to PHS in broilers.

Modification of the responses of endothelin-1 to exhaustive physical exercise under simulated high-altitude conditions with acute hypoxia

To assess whether acute alveolar hypoxia leads to the release of endothelin-1 (ET) in vivo, ET, cortisol (CORT), and lactate (LA) levels were determined in 15 healthy subjects at rest and during exhaustive incremental cycle ergometry on two separate test days. The subjects were to breathe a gas mixture with reduced O 2 content ([H] fraction of inspired O 2, 0.14) on one day and normal air on the other (N). Modified responses of LA and CORT to exhaustive incremental cycle ergometry on the H day indicated elevated anaerobic tissue metabolism and increased physical stress. With acute alveolar hypoxia, the response of ET to exhaustive physical labor was found to be augmented.

Comment on “Preignition Products from Propellants at Simulated High Altitude Conditions”

Engine pressure spiking restart preignition products, determining hydrazine nitrate and dinitrate presence by spectrum analysis

Approximate far-field flow description for a nozzle exhausting into a vacuum

References 1 Burch, B. A., of Contamination on Spacecraft Surfaces Exposed to Rocket Exhausts/' AEDC-TR-68-23, April 1968. ARO Inc., Tullahoma, Tenn. 2 Hill, D. W., Jr. and Smith, D. K., and Control of Contamination from a Scaled MOL Altitude Control Thruster in a Tangential Orientation/' AEDC-TR-69-146, Oct. 1969, ARO Inc., Tullahoma, Tenn. 3 Borson, E. N. and Landsbaum, E. M., A Review of Available Rocket Contamination Results, TR-0200(4250-20)-2, Dec. 1969. Aerospace Corp., El Segundo, Calif. 4 Valentine, R. S., Rossi, F. S., and Kromfrey, R. K., Fluid Dynamic Effects on Apollo Engine Pressure Spikes, Journal of Spacecraft and Rockets, Vol. 5, No. 1, Jan. 1968, pp. 31-35. 5 Christos, T. et al., Characteristics of Condensed-Phase Hydrazine-Type Fuels with Nitrogen Tetroxide/' Journal of Spacecraft and Rockets, Vol. 4, No. 9, Sept. 1967, pp. 1224-1229. 6 Per lee, H. E. et al., Preignition Phenomena in Small A-50/NTO Pulsed Rocket Engines, Journal of Spacecraft and Rockets, Vol. 5, No. 2, Feb. 1968, pp. 233-235. 7 Mayer, S. W., Taylor, D., and Schieler, L., Preignition Products from Propellants at Simulated High-Altitude Conditions, Combustion Science and Technology, Vol. 1, 1969, pp. 119-129. 8 Seamans, T. F. and Dawson, B. E., Hyperbolic Ignition at Reduced Pressures, Rept. RMD 5809-Q1, 1966, Thiokol Chemical Corp. 9 Takimoto, H. H. and Denault, G. C., Residues from N2O4-MMH Motors, TR-0066(5210-10)-1, Sept. 1969, Aerospace Corp., El Segundo, Calif.

Preignition Products from Propellants at Simulated High-Altitude Conditions

Abstract In view of the destructive ignitions that occur in hypergolic test firings of attitude-control motors under simulated high-altitude conditions, the preignition behavior of MMH, UDMH, A-50 and N2H4 with N2O4 was examined at low pressures and temperatures in the laboratory. At low NO2 pressures and temperatures, such as those that would be encountered in combustion chambers during starts in space, the ignition of these fuels was significantly delayed. During the preignition period, relatively involatile reaction products were formed between NO2. and the fuels. Infrared spectrophotometry, mass spectrometry, differential thermal analysis, and other techniques were used to examine these preignition residues. The IR absorption curves were consistent with the view that the major component in the MMH residue that could behave as an explosive monopropellant was MMH.nitrate, IR spectra of the preignition residues formed with N2H4 or A-50 suggest that hydrazine nitrate was the major constitutent of these re...

Hatchability of Chicken Embryos under Simulated High Altitude Conditions

High altitude decreases the hatchability of chicken eggs and has some cellular and physiologic effects on young and adult chickens.Francis et al. (1967) observed that the hatchability of eggs from the same strain decreased 10 percent at a 305 m. increase in altitude, 20 percent at a 610 m. increase. These authors also reviewed the earlier literature of altitude effects on hatchability. A significant reduction in hatchability was also reported by Stephens and Ploog (1967), working at a natural altitude of 3,200 m. in Peru. However, Fraps (1945) did not record any significant reduction in the ability of the embryo to hatch until the pressure was reduced to 12.5 mm. of Hg (27,000 m.) for a period of 12 hours per day. Evidently, short term exposure to high altitude is tolerated well. Some physiologic changes in the bloodstream of chick embryos incubated at a 5,490 m. simulated altitude was…

Potential breakdown of small gaps under simulated high-altitude conditions

Potential breakdown of small gaps under simulated high-altitude conditions

Potential Breakdown of Small Gaps Under Simulated High-Altitude Conditions

Concurrent with the present development program of a 400-cycle 208-volt power supply for aircraft, it was deemed advisable to study the effect of high altitudes on the breakdown potential between various conductors at different voltage levels.

Potential breakdown of small gaps under simulated high-altitude conditions

Potential breakdown of small gaps under simulated high-altitude conditions