Increase In Altitude Research Articles

The balance between spectral and spatial information to estimate straw cereal plant density at early growth stages from optical sensors

Estimating straw cereal plant density at early stages is important for field crop management and phenotyping. Usual plant density estimation methods include manual counting and image-based counting, both of which have limited throughput, due to the need for high spatial resolution images. In this study, we explored the potential of high-throughput estimations with spectral information. A large and diverse dataset was collected on micro plot field experiments, encompassing six sites, three leaf stages, and four species of straw cereals. Canopy spectral reflectance was acquired with a spectrometer, both in 0° or 45° view zenith angle, perpendicularly to the row direction. Two reflectance-based approaches were then tested. In the direct approach, density was directly estimated from reflectance using Gaussian process regression (GPR) and spectral bands selected based on Akaike’s information criterion. In the indirect approach, the green fraction derived from high spatial resolution RGB images (GF_rgb) was first estimated from reflectance using GPR and selected bands, and then linearly related to density. These reflectance-based methods were compared to a classical image-based baseline method, which estimates density directly from GF_rgb.An ablation study firstly showed the superiority of 45° observations, and the necessity to calibrate one model for each site, growth stage, and species. The band selection process recommended using no more than four bands as inputs to the GPR models. The resulting direct and indirect estimations had an overall relative error of 30 %. The image-based baseline method had a lower error of 22 % for submillimeter spatial resolutions, but it performed worse than reflectance-based methods when degrading the spatial resolution to more than 1 to 2 mm to mimic an increase in sensor altitude. These results showed that spectral information can compensate for spatial information and that spectral methods can potentially provide high-throughput and reasonably accurate estimates of straw cereal plant density.

What determines the information update rate in echolocating bats

The rate of sensory update is one of the most important parameters of any sensory system. The acquisition rate of most sensory systems is fixed and has been optimized by evolution to the needs of the animal. Echolocating bats have the ability to adjust their sensory update rate which is determined by the intervals between emissions - the inter-pulse intervals (IPI). The IPI is routinely adjusted, but the exact factors driving its regulation are unknown. We use on-board audio recordings to determine how four species of echolocating bats with different foraging strategies regulate their sensory update rate during commute flights. We reveal strong correlations between the IPI and various echolocation and movement parameters. Specifically, the update rate increases when the signals’ peak-energy frequency and intensity increases while the update rate decreases when flight speed and altitude increases. We suggest that bats control their information update rate according to the behavioral mode they are engaged in, while always maintaining sensory continuity. Specifically, we suggest that bats apply two modes of attention during commute flights. Our data moreover suggests that bats emit echolocation signals at accurate intervals without the need for external feedback.

Leaf phenotypic variation and its response to environmental factors in natural populations of Eucommia ulmoides

BackgroundEucommia ulmoides leaves have high medicinal and economic value as a dual-purpose substance for medicine and food. Employing leaves from 13 natural populations of Eucommia ulmoides as research objects, this study reveals the variation patterns of intra-specific and inter-specific trait variation and explores the response of leaf characteristics to geographical and climatic changes, aiming to provide a scientific basis for the efficient utilization of leaf resources and the breeding of superior varieties.ResultsDescriptive statistical analysis and nested analysis of variance showed significant differences in 11 leaf traits of Eucommia ulmoides inter-populations and intra-populations, with an average coefficient of variation of 17.45%. The coefficient of variation for average leaf phenotypic traits is 20.77%, and the leaf phenotypic variation is mainly from the variation intra-populations. Principal component analysis reveals that the cumulative contribution rate of the top three principal components which mainly contributed to the phenotypic variation of Eucommia ulmoides leaves reached 74.98%, which could be sorted into size traits (34.57%), color traits (25.82%) and shape traits (14.58%). In addition, correlation analysis expresses there is a specific co-variation pattern among leaf traits, with a strong connection between shape, size, and color traits. Geographic and climatic distances are significantly correlated, and mantel test and correlation analysis indicate that leaf traits of Eucommia ulmoides are mainly influenced by altitude. With the increase of altitude, the leaves become smaller. Partial correlation analysis shows that after controlling climate factors, the correlation between some characters and geographical factors disappears significantly. Temperature and precipitation have a great influence on the variation of leaf phenotypic traits, and the larger the leaves are in areas with high temperature and heavy rainfall.ConclusionsThese findings contribute to a further understanding of the leaf morphological characteristics of Eucommia ulmoides and the extent to which the environment influences leaf trait variation. They can provide a scientific basis for the protection and application of Eucommia ulmoides leaf resources in the future.

Elevational variability in the fractal structure of the root system of Kobresia tibetica in alpine peat swamp

Root fractal structure is the result of the phenotypic plasticity of plant root conformation in response to environmental heterogeneity, which can reflect the adaptation strategy of plants to the external environment. Four altitudinal gradients of 3400 m, 3500 m, 3600 m, and 3700 m were selected as experimental sites in Gahai Wetland on the Ruoerge Plateau. Additionally, the Win-RHIZO root analyzer and the standardized major axis estimation (SMA) method were employed to examine the fractal structure of Kobresia tibetica root system at various elevations in the alpine peat swamp. The results showed that the height, density, aboveground biomass, soil water content of the wetland community, as well as the fractal dimension of Kobresia tibetica root system decreased gradually with the increase of altitude, whereas the fractal abundance of Kobresia tibetica root system gradually grew. Kobresia tibetica root fractal dimension and fractal abundance at the 3400 m and 3700 m sites are in a very significant negative correlation between the sample area (p < 0.01), in the land of 3500 m and 3600 m sample was a significantly negative correlation between (p < 0.05). Meanwhile, there is a “shift” between both trade-off relationships. There were elevational differences in the allometric growth relationship between root fractal dimension and root fractal abundance. At the 3400 m sample location, Kobresia tibetica root fractal structure’s regression equation’s SMA slope was <−1, suggesting that the root fractal dimension’s growth rate was greater than the fractal abundance’s growth rate. The SMA slope of the regression equation for the fractal structure of the root system at the 3700 m sample site was >−1, suggesting that the growth rate of Kobresia tibetica root system’s fractal dimension was slower than that of its fractal abundance. Furthermore, at the 3500 m and 3600 m sites, the development rates of fractal dimension and fractal abundance of Kobresia tibetica roots were similar. As the altitude rises, the root system of Kobresia tibetica changes from “dense” to “diffuse”, illustrating how populations of alpine peat swamp plants have ecologically adapted to habitat stress.

Effect of operating conditions of unmanned aerial vehicle powered by PEMFC on water and heat distributions of cell

ABSTRACT The cell performance of a proton exchange membrane fuel cell (PEMFC)-driven unmanned aerial vehicles (UAV) is affected by environmental changes during high-altitude flights. Therefore, the distribution of water and heat in a PEMFC was investigated. The result showed that the uniformity of temperature distribution on the membrane could be improved by increasing the air stoichiometry ratio, but the temperature difference on the membrane was still large and the minimum temperature difference was 14.6°C. When the temperature distribution is uniform, the temperature on the membrane is too low. Consequently, increasing the inlet temperature to 60°C, 70°C and 80°C resulted in inlet and outlet temperature differences of 3.5°C, 0.5°C and 2.7°C for the membrane respectively. By analyzing the distribution of the water content and temperature on the membranes, 70°C and 20 were considered to be the optimal inlet temperature and air stoichiometry, respectively. Under this condition, as the altitude increases, the temperature and water content on the membrane gradually decrease.

Spatial and Temporal Variation in Water Use Efficiency and Ecosystem Photosynthetic Efficiency in Central Asia

Ecosystem water use efficiency (WUE) and ecosystem photosynthetic efficiency (EPE) are key indicators in studies of the carbon–water cycle in terrestrial ecosystems. Analyses of WUE and EPE can enhance our understanding of the relationship between ecosystem light use efficiency and WUE. Although several studies of individual indexes (i.e., either WUE or EPE) have been conducted, analyses of variation in both WUE and EPE, as well as their relationships, have rarely been conducted. Here, we analyzed spatial and temporal variation in WUE and EPE in Central Asia. Specifically, time trend analysis was conducted to characterize temporal and spatial changes in WUE and EPE in Central Asia from 2001 to 2020 at different altitudes and latitudes. Pearson correlation analysis was used to characterize the effects of precipitation and temperature on WUE and EPE. WUE decreased and EPE increased in Central Asia over the 20-year study period; this might have been due to interannual variations in precipitation and temperature. WUE was highest in August, and EPE was highest in June and July. Substantial spatial heterogeneity in WUE and EPE was observed; WUE was highly variable in Central Asia as well as in western and southern Central Asia. Major changes in EPE were observed in northern, eastern, and southern Central Asia. We also found that both WUE and EPE decreased with the increase in altitude. WUE was positively correlated with temperature and negatively correlated with precipitation, whereas EPE was positively correlated with both temperature and precipitation. The increase in photosynthetic efficiency might be one of the main factors contributing to increases in ecosystem productivity in arid environments. The temporal and spatial variation in WUE and EPE observed in our study will aid ecosystem research, providing a reliable theoretical basis for ecosystem research in areas with scarce large-scale data, integrated water resources management, and ecosystem restoration efforts. Our findings also enhance our understanding of the terrestrial carbon–water cycle and have implications for predicting ecosystem responses to climate change. The results of this study provide insights that will aid studies of the terrestrial carbon–water cycle under the background of climate change. It is of great significance to further study the carbon water cycle in the future.

Study on Temperature Field in Common-rail Diesel Engine Combustion Chamber at Different Altitudes

The plateau covers 26% of China’s land area, the higher altitude, the lower atmospheric pressure, the smaller air density, the lower average temperature. Therefore diesel engine power decreases significantly, fuel consumption increases, starting performance deteriorates, and soot emissions increase. In this paper, virtual simulation and simulation test methods are used to study the temperature field change in the combustion chamber of CA6DL2-35E3R common-rail diesel engine at different altitudes and atmospheric pressures. The results show that the altitude has a great influence on the temperature field in the combustion chamber. The maximum combustion temperature gradually increases with increase of altitude, post-combustion is serious and the exhaust temperature increases.

Explicitly Resolved Cloud Feedbacks in the Radiative‐Convective Equilibrium Model Intercomparison Project

AbstractRadiative‐convective equilibrium (RCE) is particularly well suited for studying tropical deep‐convection, a regime of clouds that contributes some of the highest uncertainties to the estimates of total cloud feedback. In order to perform a comprehensive calculation and decomposition of cloud feedbacks in cloud‐permitting models, previously primarily done in global climate models, the configuration of a satellite simulator for use with offline data was successfully implemented. The resultant total cloud feedback is slightly positive, primarily driven by the longwave effects of increases in cloud altitude. The high‐cloud altitude feedback is robustly positive and has a central value and uncertainty well‐matched with prior estimates. Reductions in high cloud amount drive a tropical anvil cloud area feedback that is on average negative, consistent with prior estimates. However, a subset of models with finer horizontal grid spacing indicate that a positive tropical anvil cloud area feedback cannot be ruled out. Even though RCE is only applicable to tropical deep‐convective clouds, the RCE total cloud feedback is within the range of prior comprehensive estimates of the global total cloud feedback. This emphasizes that the tropics heavily influence the behavior of global cloud feedbacks and that RCE can be exploited to learn more about how processes related to deep convection control cloud feedbacks.

Numerical simulation of atmospheric transmittance between heliostats and heat receiver in Tower-Type solar thermal power station

Based on the Simple Model for Atmospheric Transmission of Sunshine and meteorological observations, a simulation method for atmospheric transmittance between tower solar thermal power heliostats and heat receivers is developed. This method is verified by the vertical radiation observations in Tianjin, China. The results indicate remarkable differences between the simulated global horizontal irradiation (GHI) and the observations under different weather types, and the magnitude of the difference is mainly influenced by near-surface visibility and cloud cover. However, the ratios of the simulated GHI at the altitude of 40 m to that of 200 m are basically consistent with the observations, with deviations of less than 0.02 for more than 97 % of the moments, indicating this method is applicable to simulating the ratio of GHI at different heights. Results show a 20-m increase in altitude leads to an increase of 0.009 % in atmospheric transmittance within 200 m above the ground. Due to the influence of meteorology, the atmospheric transmittance shows obvious diurnal and seasonal variations. Assuming the vertical altitude of a heat receiver is 200 m and its horizontal distance from a heat receiver is 50 m, the average atmospheric transmittance between them is 94.72 %, and the transmittance drops to 76.49 % at the horizontal distance of 1000 m. This method estimates atmospheric transmittance between heliostats and heat receiver, and provides reference for the design of tower type solar thermal power station and the evaluation of the operation status.

Complete sources of cluster variation on the risk of under-five malaria in Uganda: a multilevel-weighted mixed effects logistic regression model approach

BackgroundMalaria, a major cause of mortality worldwide is linked to a web of determinants ranging from individual to contextual factors. This calls for examining the magnitude of the effect of clustering within malaria data. Regrettably, researchers usually ignore cluster variation on the risk of malaria and also apply final survey weights in multilevel modelling instead of multilevel weights. This most likely produces biased estimates, misleads inference and lowers study power. The objective of this study was to determine the complete sources of cluster variation on the risk of under-five malaria and risk factors associated with under-five malaria in Uganda.MethodsThis study applied a multilevel-weighted mixed effects logistic regression model to account for both individual and contextual factors.ResultsEvery additional year in a child’s age was positively associated with malaria infection (AOR = 1.42; 95% CI 1.33–1.52). Children whose mothers had at least a secondary school education were less likely to suffer from malaria infection (AOR = 0.53; 95% CI 0.30–0.95) as well as those who dwelled in households in the two highest wealth quintiles (AOR = 0.42; 95% CI 0.27–0.64). An increase in altitude by 1 m was negatively associated with malaria infection (AOR = 0.98; 95% CI 0.97–0.99). About 77% of the total variation in the positive testing for malaria was attributable to differences between enumeration areas (ICC = 0.77; p < 0.001).ConclusionsInterventions towards reducing the burden of under-five malaria should be prioritized to improve individual-level characteristics compared to household-level features. Enumeration area (EA) specific interventions may be more effective compared to household specific interventions.

Exercise in hypoxia: a model from laboratory to on-field studies.

Clinical outcome and quality of life of patients with chronic heart failure (HF) have greatly improved over the last two decades. These results and the availability of modern lifts allow many cardiac patients to spend leisure time at altitude. Heart failure per se does not impede a safe stay at altitude, but exercise at both simulated and real altitudes is associated with a reduction in performance, which is inversely proportional to HF severity. For example, in normal subjects, the reduction in functional capacity is ∼2% every 1000 m altitude increase, whereas it is 4 and 10% in HF patients with normal or slightly diminished exercise capacity and in HF patients with markedly diminished exercise capacity, respectively. Also, the on-field experience with HF patients at altitude confirms safety and shows overall similar data to that reported at simulated altitude. Even 'optimal' HF treatment in patients spending time at altitude or at hypoxic conditions is likely different from optimal treatment at sea level, particularly with regard to the selectivity of β-blockers. Furthermore, high altitude, both simulated and on-field, represents a stimulating model of hypoxia in HF patients and healthy subjects. Our data suggest that spending time at altitude (<3500 m) can be safe even for HF patients, provided that subjects are free from comorbidities that may directly interfere with the adaptation to altitude and are stable. However, HF patients experience a reduction of exercise capacity directly proportional to HF severity and altitude. Finally, HF patients should be tested for functional capacity and must undergo a specific 'hypoxic-tailored treatment' to avoid pharmacological interference with altitude adaptation mechanisms, particularly with regard to the selectivity of β-blockers.

Macroinvertebrates of Altai mountain rivers: factors of their formation and features of distribution within altitudinal gradient

With an increase in altitude, both abiotic and biotic conditions in mountain watercourses change. To assess the features of spatial distribution of macroinvertebrates as well as to identify the driving factors of this dynamics, the data on species richness, abundance and biomass of EPT taxa (mayfly, stonefly, caddisfly) from 21 small mountain rivers of Altai were analyzed. By location, all rivers were divided into 4 groups: the ones running in the low-mountain (&lt;1000 m asl) zone, in the low (1000–1500) and upper (1500–2000) parts of the middle mountains and in the high-mountain (&gt;2000 m asl) zone. A total of 71 EPT macroinvertebrate taxa were recorded in the studied streams. Species richness (according to the average species number per sample) as well as abundance and biomass of macroinvertebrates decreased with an increase in altitude. The maximum variance in structural indicators of communities appeared due to the combined influence of the location of the altitudinal zone and phytoplankton development level (estimated by the content of chlorophyll a). At the same time, categorical predictors (both abiotic and biotic) included in the analysis better explained the variability of diversity-related indicators than that of abundance and biomass. When developing the environmental monitoring programs for mountain watercourses, the identified trends in reduction (with altitude) of species richness of macroinvertebrate taxa responsible for the formation of taxonomically poor and strongly vulnerable communities in high-altitude areas should be taken into account.

Study on the Aerothermoelastic Characteristics of a Body Flap Considering the Nozzle–Jet Interference

A body flap/RCS-integrated configuration is often used to achieve pitch trimming and controlled flight in near space for hypersonic vehicles. Under the high temperature and pressure load induced by the expansion wave at the nozzle exit, the body flap is prone to significant structural deformation, which leads to a change in the resulting moment, even comparable to the control ability, and bring additional challenges to the control system. Based on the CFD/CTD/CSD coupling method, the aerothermoelastic effect on the aerodynamic characteristics and structural deformation of the body flap under jet interaction is systematically studied. Numerical results indicate that the pitching moment coefficients show an increasing trend for all the models, rigid, elastic and thermoelastic, while the increment significantly decreases with the increase in trajectory altitudes. With the increase in deflection angle, the pitching moment coefficients of the three models decrease nonlinearly at high altitude, and the aerothermoelastic effect significantly decreases. At a middle-lower altitudes, the pitching moment coefficient is reversed at a lager deflection angle, and the trailing edge of the body flap presents the deformation characteristics of upward bending, which makes the aerothermoelastic phenomenon degenerate into an aeroelastic problem. From the station along the chord and spanwise direction, the change in displacement increment of the thermoelastic model reflects the competitive relationship between normal stress and thermal stress imposed by jet interaction.

Spatiotemporal Variation of Evapotranspiration and Its Driving Factors in the Urumqi River Basin

Evapotranspiration (ET) is a key indicator of arid and semi-arid ecosystem processes and hydrological cycles. The study of basin-scale ET characteristics and drivers can provide a better understanding of regional water balance and energy cycles. This study used the Pixel Information Expert Engine platform based on MODIS (MOD16A2) data to extract the separate spatial and temporal characteristics of interannual and seasonal ET in the Urumqi River Basin in Xinjiang, China, over a 20-year period, from 2000 to 2020, and to analyze the influence of land-use data and altitude on ET in the basin. The average interannual ET in the watershed has had an increasing trend over the past two decades, varying from 126.57 mm to 247.66 mm, with the maximum ET in July and the minimum in December. On the seasonal scale, the ET trend is greatest in summer, followed by spring, and it is the least in winter. Spatially, the surface ET in the Urumqi River Basin is generally high in the upstream area and low in the downstream area, with the average multi-year ET throughout the basin falling within the range of 22.74–479.33 mm. The average ET for each type of land use showed that forest land had the highest ET and unused land the lowest. Analysis found that the effect of altitude on ET was more pronounced, with a significant increase in ET as altitude increases. Analysis of the drivers of ET change from 2000 to 2020 using the Optimal Parameters-based Geographical Detector model (OPGD) showed that the natural factors that had the greatest influence were, in descending order, temperature &gt; vegetation cover &gt; precipitation. Among the interacting factors, vegetation index with temperature, elevation, and precipitation and land use with elevation had a relatively greater influence on ET in the basin, and the effects of interacting factors were all greater than those of single factors.

Effectiveness of hydrogen enrichment strategy for Wankel engines in unmanned aerial vehicle applications at various altitudes

This study investigates the effectiveness of the hydrogen-enrichment strategy on a Wankel engine for unmanned aerial vehicles (UAVs). The primary motivation behind this study is to contribute to the Wankel-type rotary engine designs by revealing the influences of the hydrogen enrichment method on the Wankel engine performance at various altitudes. To achieve these objectives, CFD simulations were conducted by applying a hydrogen enrichment method to a neat gasoline Wankel engine model at sea level, 5000 ft and 15,000 ft altitudes. The hydrogen energy fraction at the intake was gradually increased from 0% to 10%. The decrease in ambient air temperature, pressure, density, and insufficient fresh charge with the increase in altitude leads to the reduced reference chamber temperature and pressure of the Wankel engine. Thus, the combustion worsens, the heat release rate (HRR) and performance decrease, also emissions deteriorate in these colder operating conditions. On the other hand, the unique physicochemical properties of hydrogen such as wide flammability limits, high homogeneity, relatively small quenching distance and high flame speed allow hydrogen-enriched mixture flames to propagate toward the narrower gaps in the combustion chamber and make up for some drawbacks of Wankel engines. As a result, flame propagation is accelerated and fuel burning rate, peak pressure and temperature values in the reference chamber are increased by hydrogen addition. For the cases at sea level with 5% and 10% hydrogen energy fraction, IMEP is increased by 6.59%, 8.50%, and the indicated power is increased by 35.51% and 52.47%. In the cases with the same energy fraction at 15,000 ft, IMEP is increased by 26.61% and 48.75%, and the indicated power is reduced by 26.61% and 48.75%, respectively. It has been proven that a small amount of hydrogen by energy fraction improves combustion efficiency and performance. The findings show that hydrogen has excellent compatibility with Wankel engines and hydrogen enrichment is a very practical concept for the improvement of the performance of these engines for UAVs. Thus, Wankel engines, which are already a very favorable power source for UAVs, become even more favorable by the hydrogen-blending strategy.

High altitudes, population density, and poverty: Unraveling the complexities of COVID-19 in Peru during the years 2020–2022

BackgroundSeveral factors related to hospitalizations, morbidity, and mortality from COVID-19 have been identified. However, limited exploration has been done on geographic and socioeconomic factors that could significantly impact these outcomes. ObjectivesThis study aimed to determine whether altitude, population density, and percentage of population in total poverty are associated with COVID-19 incidence per 1000 inhabitants and COVID-19 case-fatality rate in Peru, from 2020 to 2022. MethodsThis study utilized a multiple group ecological design and relied on secondary databases containing daily records of COVID-19 positive cases and deaths due to COVID-19. An epidemiological analysis was performed, subsequently processed using a random effects model. ResultsAs of August 2022, Peru had recorded a total of 3,838,028 COVID-19 positive cases and 215,023 deaths due to COVID-19. Our analysis revealed a statistically significant negative association between altitude and COVID-19 incidence (aBETA: −0.004; Standard Error: 0.001; p < 0.05). Moreover, we observed a positive association between population density and incidence (aBETA: 0.006; Standard Error: 0.001; p < 0.05). However, we found no significant association between the percentage of population in total poverty and COVID-19 incidence. ConclusionOur study found that an increase in altitude was associated with a decrease in COVID-19 incidence, while an increase in population density was associated with an increase in COVID-19 incidence. High altitude, population density and percentage of population in total poverty does not change case-fatality rate due to COVID-19.

Nutrient content and resorption efficiency of leaves of broad-leaved trees along altitudes in Wuyi Mountains, China.

To reveal the variation of leaf nutrient utilization strategies with altitude gradient in subtropical mountain broadleaved trees, 44 species of broadleaved trees at different altitudes (1400, 1600 and 1800 m) in Wuyi Mountains were selected to measure nutrient content, stoichiometric ratio, and nutrient resorption efficiency of green and senescent leaves, and analyzed their allometric growth relationships. The results showed that nitrogen (N) and phosphorus (P) contents in green leaves were significantly higher than those in senescent leaves, which increased with the increases of altitude. The average values of phosphorus resorption efficiency (PRE) and nitrogen resorption efficiency (NRE) were 48.3% and 34.9%, respectively. PRE was significantly higher than NRE. There was no significant difference in nutrient resorption efficiency with altitude. NRE had positive isokinetic growth with and mature leaf N content at low altitude (1400 m) and negative allometry growth with senescent leaf N content at high altitude (1800 m). PRE and N and P contents of senescent leaves had negative isokinetic growth at low altitude (1400 m) and negative allometry growth at high altitudes (1600 and 1800 m). PRE-NRE allometric growth index was 0.95 at each altitude. The nutrient contents of green and senescent leaves increased with the increases of altitude, but altitude did not affect nutrient resorption efficiency. Plants preferred to re-absorbed P from senescent leaves. Nutrient resorption efficiency of leaves at high altitude affected the nutrient status of senescent leaves.

The Global Variation of Low Ionosphere Under Action of Energetic Electron Precipitation

AbstractThe density in the D region is hard to observe on a large scale, because the density in this region is too low. In addition to solar radiation changes with a sinusoidal period of 24 hr, the energetic electron precipitation (EEP) is the major source for the ionospheric D region. In this study, we utilized observations from NOAA/MetOp satellites to derive the electron density profile from 60 to 150 km under the influence of EEP. It seems that the derived electron profile is roughly consistent with the observed one. Additionally, using above derived method of low ionospheric (D and E regions) electron profile based on the observations of NOAA/MetOp satellites, the actions of EEP on global ionosphere under different level of geomagnetic activity are analyzed. We find that EEP has a significant impact on the electron density in the altitude range from 60 to 90 km in the L ∼ 4.5–8 and MLT ∼ 9–14 regions, particularly during strong geomagnetic activity. A peak in Total Electron Content (TEC) was observed at MLT ∼ 11–12 and L ∼ 5.5–6, exhibiting an enhancement approximately 19.96 times higher than that observed during quiet periods. However, the effects of EEP decrease as altitude increases. The TEC enhancement at altitudes from 90 to 120 km during strong geomagnetic activity is like that at 60–90 km, but only about 2.08 times higher than that during quiet periods. In addition, only a weak increase is detected around midnight at altitudes from 120 to 150 km.

Numerical investigation of the effect of altitude on diesel engine combustion and soot emissions

It is increasing concerned that the plateau environment will potentially increase fuel consumption in engines. Despite this, the current state of research on high altitude engines is still inadequate in providing sufficient and detailed information to counteract the decrease in engine efficiency. In addition, one of the novelty of this study was that the investigated altitudes is up to 4500 m, of which the previous studies was limited. Therefore, this study aims to investigate the effect of altitude on in-cylinder spray, combustion, and soot formation processes in diesel engines. A calibrated three-dimensional (3D) computational fluid dynamics (CFD) model of a single-cylinder, four-strokes, direct injection (DI) compression ignition, intake boost research diesel engine is established. The numerical CFD model used in this study has been validated through comparison with experimental data. It effectively investigates the in-cylinder activities and provides insights into the causes behind combustion and soot emission deterioration. The simulation is operated at altitudes of 0, 1500, 3000, 4500 m with corresponding intake pressure. It has been observed that engine performance and soot emissions deteriorate as altitude increases, and a sharp drop occurs when the altitude exceeds 3000 m, which can be attributed to the dramatic decline in combustion efficiency. The extended spray leads to a decrease in air utilization, which ultimately results in a sudden drop in combustion efficiency at altitudes above 3000 m. Overall, this study has identified that the extended penetration of the spray, caused by reduced pressure and air density, leads to poor air utilization, resulting in decreased performance and increased emissions. Hence, it is recommended that optimization of the combustion chamber geometry and injection strategies of diesel engines operating at high altitudes be undertaken to improve air utilization and combustion quality. This will serve as an avenue for further research in the future.

A new Einstein coefficient method for mesopause-lower thermosphere atmosphere temperature retrieval under a non-local thermal equilibrium situation.

The mesopause-lower thermosphere (MLT) region is an important spatial region in the Earth's atmosphere, making it a valuable area to investigate the temperature variations. Kirchhoff's law fails with the altitude increase due to the non-local thermal equilibrium effect, resulting in an increase in the error of the method to retrieve the atmospheric temperature in the MLT region using the A-band spectral line intensity. In the non-LTE state, the temperature retrieval method based on the Einstein coefficients is proposed to retrieve atmospheric temperature in the 92-140 km height range using the airglow radiation intensity images obtained from the Michelson Interferometer for global high-resolution thermospheric imaging (MIGHTI) measurements. Results show that the temperature deviation of the two-channel combinations does not exceed 15 K in the altitude range of 92-120 km. This deviation increases up to 45 K when the altitude is in the range of 120-140 km due to the influence of the N2 airglow spectrum. The two-channel combinations self-consistency is increased by 85 K compared with the temperature obtained using the spectral line intensity retrieval. Additionally, the comparison of the retrieval results with the spectral line intensity method and the comparison with the atmospheric chemistry experiment Fourier transform spectrometer (ACE-FTS) temperature measurement data shows that the Einstein coefficient method is significantly more rational and accurate than the spectral line intensity method.