Average Mole Fraction Research Articles

Day/Night Differences in Molecular Oxygen in the Martian Upper Atmosphere

AbstractWe use the extensive stellar occultation data set of the Imaging Ultraviolet Spectrograph aboard the Mars Atmosphere and Volatile EvolutioN spacecraft to determine the first quantification of vertical variation in O2 mole fraction separately for day and night in the ∼90–130 km altitude range. The upper atmospheric O2 variation is expected to be due to the interplay between diffusion and advection because of its long photochemical lifetime. It is therefore a useful tracer of the state of atmospheric mixing and circulation. The altitude‐averaged mixing ratio is measured to be 2.69(±0.03) × 10−3 for the nightside and 2.05(±0.03) × 10−3 for the dayside. The average O2 mole fraction for day and night are nearly identical below 105 km, consistent with the value of 1.61 × 10−3 derived from the Mars Curiosity Rover/Sample Analysis at Mars near‐surface measurements. At higher altitudes, dominated by molecular diffusive separation, the measured O2 mole fraction demonstrates a vertical gradient with a local time dependence. The nightside mole fraction is a factor of 1.37 ± 0.04 larger than the dayside value at ∼125 km. This nightside enhancement is explained in terms of the relative role of solar‐driven rapid horizontal winds at high altitudes and slower vertical diffusion, resulting in a nightside (dayside) downward (upward) diffusive flux. Using the 1‐D diffusion model, the measured profiles correspond to a vertical eddy diffusion coefficient K = 3.5(±1.5) × 106 cm2/s. The Mars Climate Database predicts comparable but lower day‐night differences in oxygen mole fraction due to an overestimated K = 7.0(±1.0) × 106 cm2/s, which affects atmospheric mixing as well as the rate of atmospheric escape to space.

Evaluating the Model Representation of Asian Summer Monsoon Upper Troposphere and Lower Stratosphere Transport and Composition Using Airborne In Situ Observations

AbstractChemistry Climate Models (CCMs) are essential tools for characterizing and predicting the role of atmospheric composition and chemistry in Earth's climate system. This study demonstrates the use of airborne in situ observations to diagnose the representation of chemical composition and transport by CCMs. Process‐based diagnostics using dynamical and chemical coordinates are presented which minimize the spatial and temporal sampling differences between airborne in situ measurements and CCM grid points. The chosen process is the chemical impact of the Asian summer monsoon (ASM), where deep convection serves as a rapid transport pathway for surface emissions to reach the upper troposphere and lower stratosphere (UTLS). We examine two CCM configurations for their representation of the ASM UTLS using a set of airborne observations from south Asia. The diagnostics reveal good model performance at representing tropospheric tracer distribution throughout the troposphere and lower stratosphere, and excellent representation of chemical aging in the lower stratosphere when chemical loss is dominated by photolysis. Identified model limitations include the use of zonally averaged mole fraction boundary conditions for species with sufficiently short tropospheric lifetimes, which may obscure enhanced regional emissions sources. Overall, the diagnostics underscore the skill of current‐generation models at representing pollution transport from the boundary layer to the stratosphere via the ASM mechanism, and demonstrate the strength of airborne in situ observations toward characterizing this representation.

Computational Particle Fluid Dynamics Simulation on Combustion Characteristics of Blended Fuels of Coal, Biomass, and Oil Sludge in a 130 t h−1 Circulating Fluidized Bed Boiler

In this study, the co-combustion of coal and biomass, and the tri-combustion of coal, biomass, and oil sludge in a 130 t h−1 circulating fluidized bed (CFB) boiler are investigated via the computational particle fluid dynamics (CPFD) approach. Furthermore, the effect of biomass feeding position is also comprehensively evaluated. The results show that for the co-combustion of coal and biomass, the O2 mole fraction at the furnace outlet rises from 0.0541 to 0.0640 as the biomass blending ratio enhances from 40% to 100%, while the CO2 mole fraction reduces from 0.1357 to 0.1267. The mole fraction of NOx and SO2 at the furnace outlet decreases from 4.5867 × 10−5 to 3.9096 × 10−5 and 2.8253 × 10−4 to 4.6635 × 10−5, respectively. For the tri-combustion of three fuels, the average NOx mole fraction initially grows quickly and then declines gradually, ranging from 4.1173 × 10−5 to 4.2556 × 10−5. The mole fraction of SO2 at the furnace outlet increases from 3.5176 × 10−4 to 4.7043 × 10−4 when the ratio of oil sludge rises from 10% to 20%. The uniformity of temperature and gas components distribution is “new inlet > secondary air inlet > feed inlet”. As for the three inlet positions, the mole fractions of NOx at the furnace outlet are between 3.9096 × 10−5 and 5.1537 × 10−5, while those for SO2 are between 2.5978 × 10−4 and 2.5278 × 10−4.

Thermodynamics of the van der Waals Dimers of O2, N2 and the Heterodimer (N2)(O2) and Their Presence in Earth's Atmosphere.

The dimerization thermodynamics of N2 and O2, the principal components of Earth's atmosphere, have been determined from the respective second virial coefficients of the bound and metastable dimers calculated using the method of Stogryn and Hirschfelder that utilizes the Lennard-Jones (LJ) potential to account for intermolecular interactions. In addition, the thermodynamic properties of the heterodimer (N2)(O2) have been obtained using the same approach, employing combining rules to construct the LJ potential. Thus, Keq, ΔH, and ΔS for the three dimers are reported between 80-120 K. Over this temperature range, the ranking of Keq is (N2)(O2) > (O2)(O2) > (N2)(N2). The same trend is found for the exoethalpicity of dimer formation. For example, at 100 K, the Keq values are, respectively, 0.0406(14), 0.0215(5), and 0.0181(10), and the corresponding ΔH values are -2401(5), -2344(7), and -2279(1) J/mol. The mole fraction composition of the dimers in the atmosphere was calculated for altitudes up to 20 km. These calculations show that in the troposphere and the lower stratosphere (up to 20 km), the three dimers rank fifth to seventh in abundance, between CO2 and Ne. In this region, the average mole fractions of (N2)(N2), (O2)(O2), and (N2)(O2) are calculated to be 3.4(2) × 10-4, 2.80(9) × 10-5, and 1.95(7) × 10-4, respectively.

Evolution of Atmospheric Carbon Dioxide and Methane Mole Fractions in the Yangtze River Delta, China

As the most economically developed region in China, the Yangtze River Delta (YRD) region contributed to ~17% of the total anthropogenic CO2 emissions from China. However, the studies of atmospheric CO2 and CH4 in this area are relatively sparse and unsystematic. Here, we analyze the changing characters of those gases in different development periods of China, based on the 11-year atmospheric CO2 and CH4 records (from 2010 to 2020) at one of the four Chinese sites participating in the World Meteorological Organization/Global Atmospheric Watch (WMO/GAW) program (Lin’an regional background station), located in the center of YRD region, China. The annual average atmospheric CO2 and CH4 mole fractions at LAN have been increasing continuously, with growth rates of 2.57 ± 0.14 ppm yr−1 and 10.3 ± 1.3 ppb yr−1, respectively. Due to the complex influence of regional sources and sinks, the characteristics of atmospheric CO2 and CH4 varied in different periods: (i) The diurnal and seasonal variations of both CO2 and CH4 in different periods were overall similar, but the amplitudes were different. (ii) The elevated mole fractions in all wind sectors tended to be uniform. (iii) The potential source regions of both gases expanded over time. (iv) The growth rate in recent years (2016–2020) changed significantly less than that in the earlier period (2010–2015). Our results indicated that the CO2 and CH4 mole fractions were mainly correlated to the regional economic development, despite the influence of special events such as the G20 Summit and COVID-19 lockdown.

Impact of unintentional Sb in the tensile InAs layer of strain-balanced type-II InAs/InAsSb superlattices grown on GaSb by molecular beam epitaxy

The impact of unintentional incorporation of Sb in the tensile InAs layer of type-II strain-balanced InAs/InAsSb superlattices is investigated. Several coherently strained midwave and longwave superlattices are grown on (100) GaSb substrates by molecular beam epitaxy and examined using x-ray diffraction and temperature-dependent photoluminescence spectroscopy. The zero-order diffraction angle provides the average Sb mole fraction of the strain-balanced superlattice period. Analysis of the higher order diffraction angles, along with the individual layer growth times and strain, provides the InAs and InAsSb layer thicknesses. Analysis of the photoluminescence measurements provides the ground-state bandgap of the superlattice, which along with simulations of the ground-state energies of the electrons and holes using a Kronig–Penney model, specify how the Sb is distributed between the tensile and compressive layers of the period and ultimately the quantity of unintentional Sb in the InAs layer. The unintentional Sb mole fractions observed in the tensile InAs layers are 1.9% for midwave and 1.2% for longwave. When compared to superlattices with the same period and no Sb in the tensile layer, the presence of unintentional Sb blue-shifts the 77 K temperature cutoff wavelength from 6.3 to 5.3 μm for midwave and from 18.8 to 12.0 μm for longwave.

Temporal dynamics and controlling factors of CO2 and CH4 variability in the urban atmosphere of Wroclaw, Poland

Temporal and spatial distribution of both biogenic and anthropogenic components of atmospheric carbon dioxide (CO2) and methane (CH4) is crucial for understanding the environmental impacts of climate change over urban areas. This research focuses on applying stable isotope source-partitioning studies to determine the interactions between biogenic and anthropogenic CO2 and CH4 emissions in an average-sized city environment. Study signifies the weight of instantaneous variability and diurnal averaging as compared with seasonal records of variations of the atmospheric CO2 and CH4 at a variety of typical urban sites in the city of Wroclaw, conducted during a one-year period from June 2017 to August 2018.The findings reveal distinct temporal variations in atmospheric CO2 and CH4 mole fractions and their isotopic composition. The average atmospheric CO2 and CH4 mole fractions during the study period were 416.4 ± 20.5 ppm, and 1.95 ± 0.09 ppm, respectively. The study highlights the high variability of driving forces, including current energy use patterns, natural carbon reservoirs, planetary boundary layer dynamics, and atmospheric transport. Additionally, the relationship between the evolution of the convective boundary layer depth and the CO2 budget was analyzed using the CLASS model with input parameters based on field observations, resulting in insights such as an increase in the range of 25–65 ppm of CO2 during stable nocturnal boundary layers.The observed changes in stable isotopic signatures of air samples allowed for the identification of two main source categories in the city area: fuel combustion and biogenic processes. The δ13C-CO2 values of collected samples suggest that biogenic emissions dominate (up to 60 % of CO2 excess mole fraction) during the growing season, but are reduced by plant photosynthesis during summer afternoons. In contrast, local fossil-fuel CO2 contribution (up to 90 % of excess CO2 mole fraction) from domestic heating, vehicle emissions, and heat and power plants predominantly influence the urban GHG budget during winter. The δ13C-CH4 values indicate anthropogenic sources related to fossil fuel combustion during winter, with values ranging from −44.2 ‰ to −51.4 ‰, while slightly more depleted values, between −47.1 ‰ and −54.2 ‰, reflect a larger input of biological processes in the methane urban budget during summer.Overall, instantaneous and hourly variability of the above-mentioned readings of gas mole fraction and isotopic composition, have shown higher variability than seasonal amplitudes. Hence, respecting this granularity is the key to alignment and understanding significance of such localized atmospheric pollution studies. Additionally, the changing overprint of the system's framework, such as variability of wind and atmospheric layering patterns, weather events, provides context of sampling and data analysis at different frequencies.

Broadband ultrafast-laser-absorption spectroscopy for multi-hydrocarbon measurements near 3.3 µm in flames.

This paper presents the development and application of a broadband ultrafast-laser-absorption-spectroscopy (ULAS) technique operating in the mid-infrared for simultaneous measurements of temperature, methane (C H 4), and propane (C 3 H 8) mole fractions. Single-shot measurements targeting the C-H stretch fundamental vibration bands of C H 4 and C 3 H 8 near 3.3µm were acquired in both a heated gas cell up to ≈650K and laminar diffusion flames at 5kHz. The average temperature error is 0.6%. The average species mole fraction errors are 5.4% for C H 4 and 9.9% for C 3 H 8. This demonstrates that ULAS is capable of providing high-fidelity hydrocarbon-based thermometry and simultaneous measurements of both large and small hydrocarbons in combustion gases.

Effects of alumina nanoparticles on evaporation and combustion characteristics of diesel fuel droplets

BackgroundEffects of alumina nanoparticles (Al2O3 − NPs) on the evaporation and combustion characteristics of diesel fuel (C10H22) droplets in a model combustion chamber are numerically investigated. The nanofuel (n-fuel) is resulted from adding Al2O3 − NPs in volume fractions of 0.5 and 1 percent (0.5 and 1 vol%) to the base fuel (C10H22). MethodsTo model the two-phase flow, consisting of fuel droplets and inlet air, the Eulerian-Lagrangian approach is applied. The discrete ordinates (DO) radiation heat transfer model and the diffusion flamelet combustion model are employed in order to investigate the characteristics of the reactive flow. Significant findingsWith the addition of 0.5 and 1 vol% of Al2O3 − NPs, average increases of 0.48% and 0.95% in the heat capacity, as well as 20% and 46% in the latent heat of evaporation, of the base fuel occur, respectively. The maximum temperature of the chamber drops by 30 K and 60 K, consecutively. Further, the average mole fractions of oxides of nitrogen (NOx) at the outlet decrease by 17.6% and 34.3%, respectively. However, the oxides of carbon (CO and CO2) decrease too, as drops of 5.6% and 7.7% in CO2 average mole fraction at the outlet are observed. This can indicate the lower evaporation and burning rate of the n-fuels, as compared with the pure fuel.

Insights From the Last Year’s Atmospheric CO2 Measurements in the Urban Atmosphere and the Natural Ecosystem in Southern Poland

Abstract This article aims to compare the molar fraction of atmospheric CO2 measured in southern Poland, specifically in Gliwice (an urban area), Kraków (an urban area), and Kasprowy Wierch (a mountain environment) from August 2022 to March 2023. The study examines diurnal, monthly and seasonal variations in the molar fraction of CO2. Monthly and diurnal average CO2 air mole fraction data are reported for Gliwice, Kraków, and Kasprowy Wierch during the specified period. The results reveal greater fluctuations in CO2 amplitude in urban areas compared to the mountain environment. Significant differences in diurnal, nocturnal, monthly and seasonal variabilities of atmospheric CO2 are observed in the urban sites. The findings suggest that the biosphere may act as a dominant source of local CO2 in summer and fall, while other local or regional anthropogenic sources could impact CO2 levels during winter and early spring, prior to the vegetation period. Additionally, this paper discusses challenges encountered during the use of a low-cost system (CARBOCAP GMP-343) for measuring CO2 levels in the urban area of Gliwice in 2022.

Characteristics of the methane (CH4) mole fraction in a typical city and suburban site in the Yangtze River Delta, China

China is the largest emitter of greenhouse gases in the world. However, the atmospheric observation of greenhouse gases is relatively sparse. In this study, surface measurements of CH4 over 5 years at a typical city site (Hangzhou) in an economically developed region in China were conducted to study the temporal variations and the influence of meteorological factors and airmass transport. The CH4 observations from a suburban site (Lin'an station [LAN]) which is a World Meteorological Organization/Global Atmosphere Monitoring Program (WMO/GAW) regional site, were also compared. Our results showed that the atmospheric CH4 mole fraction in Hangzhou was not only affected by meteorological factors and topography, but also by strong local emissions. Although the distance between the two stations was only 50 km, there was a significant difference in the temporal CH4 variations. The strong anthropogenic emissions in the city were responsible for the urban-suburban site difference. The CH4 peaks in the diurnal cycles in Hangzhou corresponded to rush hours, and there were unique variations during special periods (i.e., the National Day holiday, coronavirus disease 2019 [COVID - 19] lock-down). It also led to an annual average CH4 mole fraction at the Hangzhou station (HZ) that was on average 111.1 ± 1.6 ppb higher than that at the LAN from 2016 to 2020. The lock-down measures caused by the outbreak of COVID - 19 decreased the atmospheric CH4 mole fractions by 6.8% in Hangzhou but only 1.9% in Lin'an in 2020 compared to those in 2019. Excluding the data in 2020, the annual growth rate of the CH4 mole fraction was 19.0 ppb yr−1 in Hangzhou. Our results indicated that the CH4 mole fraction in Hangzhou was mainly driven by local anthropogenic emissions, although they were influenced by emissions from surrounding cities such as Nanjing and Ningbo.

Occurrence and Discrepancy of Surface and Column Mole Fractions of CO2 and CH4 at a Desert Site in Dunhuang, Western China

Carbon dioxide (CO2) and methane (CH4) are the two major radiative forcing factors of greenhouse gases. In this study, surface and column mole fractions of CO2 and CH4 were first measured at a desert site in Dunhuang, west China. The average column mole fractions of CO2 (XCO2) and CH4 (XCH4) were 413.00 ± 1.09 ppm and 1876 ± 6 ppb, respectively, which were 0.90 ppm and 72 ppb lower than their surface values. Diurnal XCO2 showed a sinusoidal mode, while XCH4 appeared as a unimodal distribution. Ground observed XCO2 and XCH4 were compared with international satellites, such as GOSAT, GOSAT-2, OCO-2, OCO-3, and Sentinel-5P. The differences between satellites and EM27/SUN observations were 0.26% for XCO2 and −0.38% for XCH4, suggesting a good consistency between different satellites and ground observations in desert regions in China. Hourly XCO2 was close to surface CO2 mole fractions, but XCH4 appeared to have a large gap with CH4, probably because of the additional chemical removals of CH4 in the upper atmosphere. It is necessary to carry out a long-term observation of column mole fractions of greenhouse gases in the future to obtain their temporal distributions as well as the differences between satellites and ground observations.

Thermodynamic re-modelling of the Cu–Nb–Sn system: Integrating the nausite phase

Currently available Cu–Nb–Sn phase diagrams lack the recently discovered nausite phase (Cu,Nb)Sn2, which is an important intermediate in the course of thermal processing of superconducting Nb3Sn wires. Processing decisively determines the resulting microstructure of Nb3Sn and, thus, its superconducting properties. Lack of suitable and complete phase diagrams, however, obstructs rational design of such thermal processing procedures. To close this gap and to obtain valid knowledge of homogeneity and stability range of nausite, various Cu–Nb–Sn samples, which are heat-treated between 300 °C and 500 °C, are investigated. By means of energy-dispersive X-ray spectroscopy (EDX), a temperature-dependent homogeneity range of nausite is observed, which covers average mole fractions of Cu between 0.09 and 0.15. This is correlated with a change in the mean atomic volume and can be seen in the lattice parameters determined by X-ray diffraction (XRD). Additionally performed first-principles calculations on different CuSn2 and NbSn2 model structures confirm this trend. Furthermore, the peritectic decomposition of nausite to NbSn2 and liquid at 586 °C is determined by means of in situ XRD and differential scanning calorimetry (DSC). By using the CALPHAD (CALculation of PHase Diagrams) approach, all these findings are used to extend a previous thermodynamic description of the Cu–Nb–Sn system by including the nausite as an additional phase. With this noteworthy integration, the updated modelling of the Cu–Nb–Sn system can be used for optimizing the multistage heat-treatment steps during processing superconducting Nb3Sn wires.

Four years of global carbon cycle observed from the Orbiting Carbon Observatory 2 (OCO-2) version 9 and in situ data and comparison to OCO-2 version 7

Abstract. The Orbiting Carbon Observatory 2 (OCO-2) satellite has been providing information to estimate carbon dioxide (CO2) fluxes at global and regional scales since 2014 through the combination of CO2 retrievals with top–down atmospheric inversion methods. Column average CO2 dry-air mole fraction retrievals have been constantly improved. A bias correction has been applied in the OCO-2 version 9 retrievals compared to the previous OCO-2 version 7r improving data accuracy and coverage. We study an ensemble of 10 atmospheric inversions all characterized by different transport models, data assimilation algorithms, and prior fluxes using first OCO-2 v7 in 2015–2016 and then OCO-2 version 9 land observations for the longer period 2015–2018. Inversions assimilating in situ (IS) measurements have also been used to provide a baseline against which the satellite-driven results are compared. The time series at different scales (going from global to regional scales) of the models emissions are analyzed and compared to each experiment using either OCO-2 or IS data. We then evaluate the inversion ensemble based on the dataset from the Total Carbon Column Observing Network (TCCON), aircraft, and in situ observations, all independent from assimilated data. While we find a similar constraint of global total carbon emissions between the ensemble spread using IS and both OCO-2 retrievals, differences between the two retrieval versions appear over regional scales and particularly in tropical Africa. A difference in the carbon budget between v7 and v9 is found over this region, which seems to show the impact of corrections applied in retrievals. However, the lack of data in the tropics limits our conclusions, and the estimation of carbon emissions over tropical Africa require further analysis.

Changes of Atmospheric CO2 in the Tibetan Plateau From 1994 to 2019

AbstractThe importance of carbon neutrality and green development rose sharply in the post‐pandemic era in China. This study investigated the long‐term variability of atmospheric carbon dioxide (CO2) in China using CO2 records from Mount Waliguan (WLG), the only global station of World Meteorological Organization/Global Atmosphere Watch in Eurasia, covering a 26‐year period (1994–2019). Overall, the atmospheric CO2 mole fraction increased continuously and steadily with a growth rate of 2.15 ± 0.01 ppm yr−1 over 1994–2019 at WLG. The average CO2 mole fraction was only 359.9 ± 0.04 ppm in 1994, but reached a historic level of 414.9 ± 0.04 ppm by 2019. The mean growth rates in city sectors (data from the city regions) were slightly higher than that in the Tibetan Plateau. The seasonal amplitude of atmospheric CO2 at WLG was lower than those at adjacent regional stations, such as Lin'an, and Shangdianzi, but larger those at global stations Mauna Loa and Minamitorishima. Potential strong source regions moved from urban areas to the southwest region away from WLG, suggesting the potential emergence of Northern India as a strong CO2 source region. The area of potential CO2 sources at WLG prominently expanded with time, reflecting the effect of more intensifying anthropogenic emissions in recent decades. Although numerous measures for carbon emission reduction have already been implemented, it is clear that much work, e.g., carbon emission estimation, sources/sinks tracing, cleaner energy technologies, remains to be done in order to achieve carbon emission peak and carbon neutrality set by the Chinese government.

Variation of carbon dioxide mole fraction at a typical urban area in the Yangtze River Delta, China

The observations of atmospheric CO2 mole fraction in urban area in China are relative sparse. Here, we present the first-hand observation of atmospheric CO2 mole fraction from 2016 to 2020 at a city station (Hangzhou, abbreviated as HZ) in the Yangtze River Delta, which is one of the strongest CO2 source regions in China. The CO2 mole fraction at an adjacent World Meteorological Organization / Global Atmospheric Watch (WMO/GAW) programme site (Lin'an, LAN) are also presented and compared. The temporal variations, seasonal variations, and influence of COVID-19 pandemic are analyzed. Our results show that, the variations of CO2 mole fraction in Hangzhou are mainly driven by the local emissions, both atmospheric dilution conditions (i.e., wind speed, visibility) and topography, and the temporal variations are apparently different with the suburb site of LAN, although the distance between the two stations is only 50 km. During the observation period, the CO2 mole fraction at HZ is on average 15.6 ± 0.2 ppm higher than LAN, with two distinct peaks observed at 9:00 and 17:00–18:00, corresponding to traffic rushing hours. The growth rate of atmospheric CO2 mole fraction is 11.2 ± 0.1 ppm yr−1 before the COVID-19 pandemic (from 2016 to 2019), which is much higher than the suburb site of LAN, 5.4 ± 0.1 ppm yr−1. The COVID-19 pandemic has led to a plunge of atmospheric CO2 mole fraction at HZ in 2020, with a value of 15.7 ± 0.7 ppm, corresponding to 3.5% lower than the year of 2019. But at LAN, the annual average CO2 mole fraction in 2020 is 1.5 ± 0.5 ppm higher than the previous year, similar to the trend in the northern hemisphere. The different annual CO2 mole fraction growth rate at HZ indicates that the CO2 mole fraction at Hangzhou may be dominated by local anthropogenic emissions, despite the transport of airmass from the north and southwest.

Light extraction efficiency and internal quantum efficiency of fully UVC-transparent AlGaN based LEDs

The light extraction efficiency (LEE), external quantum efficiency (EQE), and current–voltage characteristics of deep ultraviolet light emitting diodes (DUV-LEDs) with different aluminum mole fractions in the p-AlGaN layers have been investigated. Optimizing the p-AlGaN layer composition requires a tradeoff between reducing the absorption losses and limiting the increases in the p-contact resistance and operation voltage. AlGaN multiple quantum well LEDs emitting around 263 nm with different AlGaN:Mg short period super lattices (p-SPSL) ranging from x = 33% (UV-absorbing) to x = 68% (UV-transparent) average aluminum mole fraction have been explored. DUV-LEDs with different p-contact metals and UV-reflectivities have been characterized by electroluminescence measurements and analyzed by ray-tracing simulations. The comparison shows an increased operating voltage and a five-fold increase of the on-wafer EQE with a maximum value of 3.0% for DUV-LEDs with UV-transparent p-SPSL (x = 68%) and UV-reflective indium contacts in comparison to LEDs with a UV-absorbing p-SPSL (x = 33%). Ray-tracing simulations show that the increase in EQE can be partially ascribed to a 2.5-fold improved LEE in combination with a two-fold increase in internal quantum efficiency.

Surface tensions of biodiesel blends with pentanol and octanol isomers at different conditions: measurement and new correlation

Surface tension is an important biodiesel property, its calculation and prediction are fundamental because high values of surface tension significantly difficult proper atomization, and it can cause a poor engine performance. Surface tensions have been measured for binary liquid blends of pentan-1-ol, pentan-2-ol, 2-methylbutan-1-ol, octan-1-ol, octan-2-ol and 2-ethylhexan-1-ol with biodiesel using a Du Noüy ring tensiometer from (288.15 to 338.15) K at 0.1 MPa over the whole composition range. The measured surface tension data for the pure components shows a good agreement for the six alcohols when it is compared with reported values in the literature, showing an average absolute percentage deviation of 0.93%. Surface tension deviations show positive deviations from the average mole fraction of the pure components and they are correlated using the Redlich-Kister equation over the whole concentration range. Surface entropy and surface enthalpy have been estimated from experimental surface tension values of biodiesel mixtures. A new equation has been developed to correlate the surface tension of biodiesel + alcohols mixtures considering the effects of both temperature and mole fraction. This equation is based upon a quadratic mixing rule for the Gibbs free energy. Our model demonstrates to correlate the surface tension of biodiesel mixtures with an average absolute percentage deviation of 0.4%. The correlative capability of the proposed model is compared with Li et al., Fu et al., Myers and Scott, Wang-Chen, Hoke and Patton, and Jouyban et al. equations.

Measurement report: Changing characteristics of atmospheric CH<sub>4</sub> in the Tibetan Plateau: records from 1994 to 2019 at the Mount Waliguan station

Abstract. A 26-year, long-term record of atmospheric methane (CH4) measured in situ at the Mount Waliguan (WLG) station, the only World Meteorological Organization (WMO) and Global Atmosphere Watch (GAW) global station in inland Eurasia, is presented. Overall, a nearly continuous increase in atmospheric CH4 was observed at WLG, with a yearly growth rate of 5.1±0.1 parts per billion (ppb) per year during 1994–2019, except for some particular periods with near-zero or negative values, e.g., 1999–2000 and 2004–2006. The average CH4 mole fraction was only 1799.0±0.4 ppb in 1994 but increased to about 133 ppb and reached a historic level of 1932.0±0.1 ppb in 2019. The case study in the Tibetan Plateau showed that the atmospheric CH4 increased rapidly. During some special periods, it is even larger than that of city regions (e.g., 6.7±0.2 ppb yr−1 in 2003–2007). Generally, the characteristics of CH4 varied in different observing periods as follows: (i) the diurnal cycle has become apparent and the amplitudes of the diurnal or seasonal cycles increased over time; (ii) the wind sectors with elevated CH4 mole fractions switched from ENE-E-ESE-SE-SSE sectors (wind directions) in early periods to NNE-NE-ENE-E sectors in later years; (iii) the area of source regions increased as the years progressed, and strong sources shifted from northeast (city regions) to southwest (northern India); and (iv) the annual growth rates in recent years (e.g., 2008–2019) were significantly larger than those in the early periods (e.g., 1994–2007).

A novel circulated air curtain system to confine the transmission of exhaled contaminants: A numerical and experimental investigation.

Air curtain is an efficient device for cutting off airflow and confining contaminants. Inspired by the ability, a circulated air curtain composed of end-to-end plane jets generated by a relay of air pillars is proposed to confine exhaled contaminants in this study. Furthermore, the optimization study of computational fluid dynamics (CFD) is conducted to explore cutting-off performance and find better design parameters under different conditions, i.e., human-curtain distance, enclosure shape, jet velocity from air pillar, and exhalation modes. The multidirectional blockage and vortex-like rotative transmission routes of exhaled airflow are observed when air curtain exists. Results indicate that contaminants are concentrated around the source. The average mole fraction of exhaled contaminants outside air curtain under different human-curtain distance decreases 4.3%–19.6% compared to mixing ventilation with same flux. Shortening the human-curtain distance can improve the performance of air curtain and may change the direction of exhaled airflow. Moreover, It has better performance when the enclosure shape is close to a circle. Higher jet velocity is better for improving the confinement performance, but the trend is not very obvious as velocity increases. For exhalation modes, it is more challenging to control exhaled contaminants for intense exhalation activity (such as coughing) in steady simulation, but results in transient simulation show better performance when coughing only once. These results can provide a reference for the subsequent design and improvement in applying air curtain in hospital wards or other places, especially during the period of flu outbreak.Electronic Supplementary Material (ESM)Supplementary material is available in the online version of this article at 10.1007/s12273-020-0667-5. The ESM file presents the animation of the droplet trajectory from the droplet birth at 0 s to 8 s