Chamber Simulation Research Articles

Life history parameters of Bemisia tabaci MED (Hemiptera: Aleyrodidae) in the present and future climate of central Europe, predicted by physically realistic climatic chamber simulation.

Whiteflies of the Bemisia tabaci species complex are among the most damaging insect pests in agriculture worldwide, causing damage by feeding on crop plants and by vectoring plant viruses. The species complex consists of over 35 cryptic species that differ in many aspects of their biology including the optimal environment, geographic distribution, and host range. Global warming and associated climate change resulting from human activities is expected to contribute to biological invasions. Bemisia tabaci species show fast adaptability to changes in agroecosystems and have a long record of biological invasions. Climate change driven increase in B. tabaci importance in agricultural systems of Europe has been predicted, but so far not experimentally tested. The present study evaluates the development of B. tabaci MED (=Mediterranean) in a climatic chamber simulation of the future climate in Luxembourg, chosen as a representative region for the Central Europe. Future climate predictions for the period 2061-2070 were derived from a multimodel ensemble of physically consistent regional climatic models. Results show a 40% shorter development time of this important pest in future climatic conditions, with an increase in fecundity by a third, and insignificant difference in mortality. Accelerated development, combined with its already established year-round presence in European greenhouses and predicted northward expansion of outdoor tomato production in Europe, means faster population build-up at the beginning of the outdoor cropping season with the potential of reaching economic importance. Benefits of simulating hourly diurnal cycle of physically consistent meteorological variables versus previous experiments are discussed.

Effect of gas injection holes on mixing and combustion in solid propellant ducted rockets

Combustion efficiency is an important parameter of the combustion chamber. Gas injection holes have an important influence on the mixing and combustion in solid propellant ducted rockets, but there is currently little research on gas injection holes. This paper describes numerical simulations of solid propellant ducted rocket combustion chambers, with the numerical method verified through a direct-connected experiment. We investigate the effect of adding injection holes to the gas generator nozzle on the mixing and combustion performance, and examine the mixing degree, combustion efficiency, and flow field characteristics. This paper focuses on the number and the position of the gas injection holes. The results show that, when the total mass flow rate is constant, the mixing effect becomes better as the dispersion degree of gas injection increases and the mass flow rate of each hole decreases. For this study, the 5-hole scheme has the best performance, and when the total mass flow rate and the number of injection holes are fixed, a smaller mass flow rate of gas injected toward the outlet of each air inlet is more conducive to better mixing and combustion effects. When the total mass flow rate is constant and the shape of the injection holes are complete circles, increasing the number of holes is more effective than decreasing the mass flow rate of gas injected toward the outlet of the air inlets in improving combustion efficiency.

Concurrent dominant pathways of multifunctional products formed from nocturnal isoprene oxidation

Determination of dominant chemical pathways toward the formation of nocturnal secondary organic aerosols (SOA) remains ambiguous by which nitrogen oxides (NOx) always affect oxidation of volatile alkenes. Here, comprehensive chamber simulations on dark isoprene ozonolysis were conducted under different nitrogen dioxides (NO2) mixing ratios to exam multiple functionalized isoprene oxidation products. Aside from that the oxidation processes were concurrently driven by nitrogen radical (NO3) and small hydroxyl radicals (OH), ozone (O3) cycloaddition at isoprene was launched initially regardless of NO2 to rapidly form first-generation oxidation products, i.e., carbonyls and Criegee intermediates (CI) referred to carbonyl oxides. They could further undergo complicated self- and cross-reactions to produce alkylperoxy radicals (RO2). Corresponding to yields of the C5H10O3 tracer, weak OH pathway at night was credited to ozonolysis of isoprene but suppressed by unique NO3 chemistry. Following the ozonolysis of isoprene, NO3 played a crucial supplementary role in nighttime SOA formation. The ensuing production of gas-phase nitrooxy carbonyls (the first-generation nitrates) became dominant in the production of a sizeable pool of organic nitrates (RO2NO2). By contrast, isoprene dihydroxy dinitrates (C5H10N2O8) were outstanding with the elevated NO2, related to typical second-generation nitrates. As such, the yielding number concentrations of dark SOA were promoted to approximately 1.8 × 104 cm−3 but presented a nonlinear relation with excess high-NO2 condition. This study provides valuable insights into importance of multifunctional organic compounds from alkene oxidation to constitute nighttime SOA.

Precise simulation of drift chamber in the CEPC experiment

The Circular Electron Positron Collider (CEPC) is one of the future experiments which aims to precisely study the properties of the Higgs boson and to search for new physics beyond the Standard Model. To achieve that, it puts strict requirements on the particle reconstruction and identification ability of the CEPC detector. In order to obtain better particle identification performance, the drift chamber is chosen for the outer tracking detector which can provide information used by the cluster counting method for getting excellent particle identification performance. To evaluate the performance of the cluster counting method, it is necessary to develop a simulation tool that can be used to precisely simulate the response of the gaseous particle detector. This work proposes a new way to combine Geant4 and Garfield++ at the Geant4 step level for the drift chamber simulation. Due to the extreme time consumption of simulating the avalanche process in Garfield++, a fast signal response simulation method based on a neural network has been developed to replace detailed simulation. It shows the fast simulation can give consistent results with Garfield++ simulation and achieve the speedup by a factor of 200.

Scheme Design and Pressure-Retaining Performance Analysis of Macrobiological Sampler in the Full-Ocean-Depth Operating Environment

AbstractA new full-ocean-depth macroorganisms pressure-retaining sampler (FMPS) was designed to collect pressure-retaining macroorganisms samples from the abyssal seafloor. A mathematical model for pressure compensation in the FMPS recovery process was developed. The effects of FMPS structural parameters, pressure compensator structural parameters, and sampling environment on the pressure retention performance of FMPS were analyzed. Using the developed FMPS engineering prototype, FMPS internal pressure test, high-pressure chamber simulation sampling, and pressure-retaining test was carried out. The test results show that the key components of FMPS can carry 115 MPa pressure, FMPS can complete the sampling action in the high-pressure chamber of 115 MPa, the pressure is maintained at 105.5 MPa, and the pressure drop rate (ratio of pressure drop during FMPS recovery to sampling point pressure) is 9.13%; the experimental results are consistent with the theoretical calculation. The test verified the feasibility of FMPS design and the reliability of pressure retention, providing a theoretical basis and technical support for the design and manufacture of full-ocean-depth sampling devices.

Study on the effect of discharge chamber length on the performance of electron cyclotron resonance ion thruster

Discharge chamber length is one of the factors in optimizing the electron cyclotron resonance ion thruster performance. It adjusts the distance between bulk plasma and grid system to change the plasma density upstream of the screen grid, which will affect the ion beam current and focusing state to achieve optimization purpose. However, new evidence shows the discharge chamber length plays an important role in ionization during ion beam extraction, which means that the effect of discharge chamber length on the performance of electron cyclotron resonance ion thruster should be reexamined. After applying grid voltages, another high electron temperature region located upstream of the screen grid is observed in the integrated simulation using particle-in-cell with Monte Carlo collision method, but it is not observed in the traditional discharge chamber simulation. It is believed in the paper that the high electron temperature region exists objectively, because the Child-Langmuir sheath will repel electrons moving towards screen grid back to magnetic mirrors again. Those electrons will gain energy from microwave, and finally form a high electron temperature region along the Child-Langmuir sheath. This phenomenon implies that discharge chamber length can adjust the high electron temperature distribution upstream of screen grid to affect the plasma generation. Therefore, in this work, the effect of discharge chamber length on discharge and ion beam performance is systematically studied by adopting the integrated simulation. In this paper, three ion thrusters with different discharge chamber lengths are simulated. Under the conditions of same magnetic field and operation parameters, the comparisons of electron energy gain, plasma parameter distributions and ion beam current among the three ion thrusters are conducted. The results show that shorter discharge chamber length has higher electron energy gain, plasma density and voltage, but smaller ion beam current. This abnormal phenomenon can also be seen experimentally. By analyzing the ionization rate inside the chamber, it can be seen that high-temperature electrons upstream of the screen grid have a significant contribution to ionization. And thus, a little bit longer discharge chamber length with lower plasma density inside the chamber has bigger ion beam current for having higher plasma density upstream of the screen grid. According to this phenomenon, an electron heating mode is proposed: electrons gain energy by reciprocating through the electron cyclotron resonance layer between the Child-Langmuir sheath and magnetic mirrors. This heating mode can be used as a supplement to the electronic constraints outside the magnetic mirrors to improve the energy utilization efficiency of the thruster, which can provide a new insight into the electron cyclotron resonance ion thruster design in the future.

增温和光周期变化对东北地区兴安落叶松主要物候期的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 增温和光周期变化对东北地区兴安落叶松主要物候期的影响 DOI: 10.5846/stxb202203230724 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研究计划项目(2018YFA0606103);国家自然科学基金重点项目(42130514) Effects of warming and photoperiod change on main phenological phases of Larix gmelinii in Northeast China Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:兴安落叶松在东北地区森林生态系统的结构与功能中起着重要作用,气候变化背景下东北地区气温增加且光照缩短必将影响兴安落叶松的变化,特别是物候这一气候变化的敏感指标。弄清其物候对气候变化的响应有助于揭示兴安落叶松的变化趋势。但是,当前关于兴安落叶松物候对温度、光周期及其协同作用的响应机制仍不清楚。针对东北地区温度剧增、日照时数减少的特点,2019年4月至11月开展了3年生兴安落叶松幼苗主要物候期响应温度和光周期变化的大型人工气候室模拟控制实验。结果表明:(1)不同程度的增温对兴安落叶松生长周期(展叶始期至完全变色期)无显著影响,但显著缩短生长盛期(展叶盛期至叶变色普期),且增温2.0℃较增温1.5℃对生长盛期影响更大。(2)长光照显著增加兴安落叶松的生长周期(9.25 d),短光照对兴安落叶松生长周期的影响不显著,且长光照和短光照均使兴安落叶松生长盛期缩短,二者对兴安落叶松生长盛期影响表现一致。(3)长光照、短光照分别与增温协同作用均使兴安落叶松生长盛期缩短,其中增温2.0℃与长光照协同作用对生长盛期缩短更显著(34.67 d)。(4)与生长始期(展叶始期)和末期(完全变色期)相比,兴安落叶松生长盛期对温度响应更敏感,除叶变色普期外,兴安落叶松物候温度敏感度均随温度升高而降低。不同增温条件下,光照减少降低叶变色始期的温度敏感度,但增温1.5℃时光照减少降低展叶盛期的温度敏感度,增加叶变色普期的温度敏感度;增温2.0℃则相反。东北地区气候变化不利于兴安落叶松生长,且增温2.0℃较增温1.5℃更为不利。研究结果可为理解东北地区生态系统结构与功能变化提供依据。 Abstract:Larix gmelinii forest plays an important role in the structure and function of forest ecosystem in Northeast China. In the context of climate change, the increase of temperature and the decrease of light in Northeast China will affect the change of Larix gmelinii forest, especially its phenology, a sensitive index of climate change. Understanding the response of phenology to climate change is helpful to reveal the change trend of Larix gmelinii. However, the response mechanism of Larix gmelini phenology to temperature, photoperiod and its synergistic effect is still unclear. According to the fact of increasing temperature and decreasing sunshine duration in Northeast China, a large-scale artificial climate chamber simulation experiment was conducted from April to November 2019 to understand the response of main phenological stages of Larix gmelinii seedlings with 3-year old to the changes of temperature and sunshine duration. The results indicate that: (1) Different degrees of warming had no significant effect on the growth cycle of Larix gmelinii (from the first stage of leaf unfolding to the complete discoloration stage), but significantly shortened the peak growth period (from the peak stage of leaf unfolding to the leaf discoloration in general). The effect of 2.0 ℃ warming on the growth peak was greater than that of 1.5 ℃ warming. (2) The growth cycle of Larix gmelinii significantly increased (9.25 days) with long sunshine duration, but the effect of short sunshine duration on the growth cycle of Larix gmelinii was not significant, and both long and short sunshine duration shortened the peak growth period of Larix gmelinii, and had the same effect on the peak growth period of Larix gmelinii. (3) The interaction between sunshine duration and increasing temperature shortened the peak growth period of Larix gmelinii, and the interaction between 2.0 ℃ warming and long sunshine duration had more significant to shorten the peak period of growth (34.67 days). (4) Compared with the initial growth stage (the first stage of leaf unfolding) and the final growth stage (complete discoloration stage), the peak growth stage of Larix gmelinii was more sensitive to temperature. The temperature sensitivity of phenology of Larix gmelinii decreased with the increase of temperature except the leaf discoloration in general. Under the conditions of different increasing temperatures, the decrease of sunshine duration decreased the temperature sensitivity at the leaf discoloration onset, however, when the temperature increased by 1.5 ℃, the decrease of sunshine duration decreased the temperature sensitivity at the peak stage of leaf unfolding and increased the temperature sensitivity at the leaf discoloration in general, while it was the opposite under 2.0 ℃ warming. This indicates that climate change in Northeast China is not conducive to the growth of Larix gmelinii, and that 2.0 ℃ warming is more unfavorable than 1.5 ℃ warming. The results can provide a basis for understanding the changes of ecosystem structure and function in Northeast China. 参考文献 相似文献 引证文献

Monitoring of drying kinetics evolution and hygrothermal properties of new earth-based materials using climatic chamber simulation

This study focuses on the drying kinetics of cob and light-earth layers comprising a hybrid walling system. Volumetric water content sensors are immersed and placed at different positions on the walls of a building to measure the drying kinetics. In addition, an experimental analysis of the effect of temperature, relative humidity (RH), and wind velocity variations on thermal conductivity in a climatic chamber under winter and summer conditions was conducted. The analysis of samples in laboratory aims to investigate the hygrothermal properties of cob and light-earth materials, and their dependency on the aforementioned parameters. The in situ drying kinetics of both materials involves water content reduction and stabilization; however, in the laboratory, although the water content of materials decreases, the drying is incomplete. Which may be due to the limited wind speed. The hydrothermal properties show that open porosity affects water vapor permeability and modifies the RH of cob and light-earth. At 23 °C, when the relative humidity (RH) range was 10–30%, the absorbed water vapor of cob and light earth was 0–2%. However, when the RH is 40–90%, the absorbed water vapor of light earth (2–9%) exceeds that of cob (0.5–2%). Moreover, the response to relative humidity (RH) with regard to the mixing law of components and samples differs. The resistance factor to water vapor diffusion values for cob and light-earth are 12.9 and 8.2, respectively. In this study, the thermal conductivity measurements under summer and winter conditions provide the relationship between the thermal conductivity, density, and water content of cob and light-earth materials.

Lee model based numerical scheme for steady vapor chamber simulations

Vapor chamber is a phase-change based heat spreader widely used in thermal management. Steady numerical simulation is a useful practice for vapor chamber design and optimization. In numerical simulations, assuming incompressible flow and isothermal vapor core is common to alleviate the stability issues raised at liquid-vapor interfaces because the mass/energy transfers at such interfaces are sensitive to the fluctuations of pressure, temperature, and density. It is also typical to preset a single kind of phase change behavior at a liquid-vapor interface (either condensation or evaporation). However, these assumptions could no longer be appropriate when input heat flux is high, the ratio of heating area to evaporator area is small, and/or pillars are presented. This paper presents a novel numerical scheme for vapor chamber simulations by accounting for both the flow compressibility and the temperature variations within the vapor core while applying mass/energy source terms to liquid-vapor interfaces based on the Lee model through the ghost fluid method. No preset of the phase change behavior at liquid-vapor interfaces is needed as well. The results show that, under the input heat flux from 5.6 to 38.9 W/cm2, the average temperature errors between the experiments and the simulations range from 3.0% to 5.0% for the heating area, 5.5% to 8.0% for the evaporator, and 1.4% to 3.0% for the condenser. Although these temperature errors are not exceptional, this proposed scheme is numerically stable by exhibiting good grid independence and being able to converge in 128 iterations over four million elements. Furthermore, attributed to fewer assumptions needed, this proposed scheme can simulate flow characteristics that well agree with the sense of phase change behaviors and is also applicable to other two-phase based heat spreaders (such as heat pipes) at various conditions in structure, dimension, heat input, and convergence criteria.

Review of the influencing factors of secondary organic aerosol formation and aging mechanism based on photochemical smog chamber simulation methods

The formation and aging mechanism of secondary organic aerosol (SOA) and its influencing factors have attracted increasing attention in recent years because of their effects on climate change, atmospheric quality and human health. However, there are still large errors between air quality model simulation results and field observations. The currently undetected components during the formation and aging of SOA due to the limitation of current monitoring techniques and the interactions among multiple SOA formation influencing factors might be the main reasons for the differences. In this paper, we present a detailed review of the complex dynamic physical and chemical processes and the corresponding influencing factors involved in SOA formation and aging. And all these results were mainly based the studies of photochemical smog chamber simulation. Although the properties of precursor volatile organic compounds (VOCs), oxidants (such as OH radicals), and atmospheric environmental factors (such as NOx, SO2, NH3, light intensity, temperature, humidity and seed aerosols) jointly influence the products and yield of SOA, the nucleation and vapor pressure of these products were found to be the most fundamental aspects when interpreting the dynamics of the SOA formation and aging process. The development of techniques for measuring intermediate species in SOA generation processes and the study of SOA generation and aging mechanism in complex systems should be important topics of future SOA research.

Finite-difference diffusion-equation modeling of reverberation chambers in time-domain

Conventional chamber-based methods of random incidence absorbing coefficients overlook the non-diffused sound field in the room acoustics, which decreases accuracy and may even lead to conflicting results. This work applies the diffusion equation model to room-acoustic simulations of standardized reverberation chambers. The simulations can more efficiently capture the chamber's non-diffuse sound field and energy flows than wave-based simulation models. The diffusion equation represents the governing equation of reverberant sound energy densities within the reverberation chamber which is solved using the finite-difference time-domain method. Its computational efficiency of diffusion equation-based modeling lies in a highly sparse domain meshing condition dictated by the mean-free path length rather than wavelengths and still derives a wideband simulation result. This work also dedicates the effort to reexamine the meshing condition, particularly for standardized finite sizes of sound absorbers for measurements of random incidence absorption coefficients. By comparing the outcomes of simulations with measurement data, an a posteriori absorption coefficient is inversely estimated involving Bayesian parameter estimation.

Identification of highly oxygenated organic molecules and their role in aerosol formation in the reaction of limonene with nitrate radical

Abstract. Nighttime NO3-initiated oxidation of biogenic volatile organic compounds (BVOCs) such as monoterpenes is important for the atmospheric formation and growth of secondary organic aerosol (SOA), which has significant impact on climate, air quality, and human health. In such SOA formation and growth, highly oxygenated organic molecules (HOM) may be crucial, but their formation pathways and role in aerosol formation have yet to be clarified. Among monoterpenes, limonene is of particular interest for its high emission globally and high SOA yield. In this work, HOM formation in the reaction of limonene with nitrate radical (NO3) was investigated in the SAPHIR chamber (Simulation of Atmospheric PHotochemistry In a large Reaction chamber). About 280 HOM products were identified, grouped into 19 monomer families, 11 dimer families, and 3 trimer families. Both closed-shell products and open-shell peroxy radicals (RO2⚫) were observed, and many of them have not been reported previously. Monomers and dimers accounted for 47 % and 47 % of HOM concentrations, respectively, with trimers making up the remaining 6 %. In the most abundant monomer families, C10H15−17NO6−14, carbonyl products outnumbered hydroxyl products, indicating the importance of RO2⚫ termination by unimolecular dissociation. Both RO2⚫ autoxidation and alkoxy–peroxy pathways were found to be important processes leading to HOM. Time-dependent concentration profiles of monomer products containing nitrogen showed mainly second-generation formation patterns. Dimers were likely formed via the accretion reaction of two monomer RO2⚫, and HOM-trimers via the accretion reaction between monomer RO2⚫ and dimer RO2⚫. Trimers are suggested to play an important role in new particle formation (NPF) observed in our experiment. A HOM yield of 1.5%-0.7%+1.7% was estimated considering only first-generation products. SOA mass growth could be reasonably explained by HOM condensation on particles assuming irreversible uptake of ultra-low volatility organic compounds (ULVOCs), extremely low volatility organic compounds (ELVOCs), and low volatility organic compounds (LVOCs). This work provides evidence for the important role of HOM formed via the limonene +NO3 reaction in NPF and growth of SOA particles.

Progress in quantitative research on the relationship between atmospheric oxidation and air quality

Atmospheric oxidizing capacity (AOC) is an essential driving force of troposphere chemistry and self-cleaning, but the definition of AOC and its quantitative representation remain uncertain. Driven by national demand for air pollution control in recent years, Chinese scholars have carried out studies on theories of atmospheric chemistry and have made considerable progress in AOC research. This paper will give a brief review of these developments. First, AOC indexes were established that represent apparent atmospheric oxidizing ability (AOIe) and potential atmospheric oxidizing ability (AOIp) based on aspects of macrothermodynamics and microdynamics, respectively. A closed study refined the quantitative contributions of heterogeneous chemistry to AOC in Beijing, and these AOC methods were further applied in Beijing-Tianjin-Hebei and key areas across the country. In addition, the detection of ground or vertical profiles for atmospheric OH·, HO2·, NO3· radicals and reservoir molecules can now be obtained with domestic instruments in diverse environments. Moreover, laboratory smoke chamber simulations revealed heterogeneous processes involving reactions of O3 and NO2, which are typical oxidants in the surface/interface atmosphere, and the evolutionary and budgetary implications of atmospheric oxidants reacting under multispecies, multiphase and multi-interface conditions were obtained. Finally, based on the GRAPES-CUACE adjoint model improved by Chinese scholars, simulations of key substances affecting atmospheric oxidation and secondary organic and inorganic aerosol formation have been optimized. Normalized numerical simulations of AOIe and AOIp were performed, and regional coordination of AOC was adjusted. An optimized plan for controlling O3 and PM2.5 was analyzed by scenario simulation.

The effects of extreme high indoor temperature on EEG during a low intensity activity

Climate warming has led to extreme high indoor temperatures above 39 °C in hot and humid areas during the summer, which poses a great risk to work safety. Cognitive impairment is considered to be one of the main causes of work safety accidents under high temperatures. However, there is still no sufficient physiological basis for the damage of high temperature to cognitive performance. EEG is a potential physiological indicator that reflects cognitive performance. Nevertheless, no relevant research on the effects of extreme high indoor temperatures exceeding 35 °C on EEG has been found. In this study, a climate chamber simulation experiment was conducted, and the neutral temperature was set at 26 °C and the extreme high indoor temperature at 39 °C. In the experiment, the subjects completed 6 cognitive tests in the sitting position, and the EEG signals of 14 channels were continuously collected during 25–60 min of the experiment. Based on the analysis of the power of the EEG signals, the effects of extreme high indoor temperature on EEG are investigated in this study. The results showed that, on the one hand, the EEG relative power of δ-band of whole brain increased significantly at 39 °C, while the EEG relative power of β-band of whole brain decreased significantly during certain experimental periods. On the other hand, the accuracy of Overlapping test also decreased significantly at 39 °C. This indicates that the change of δ-band and β-band of EEG signals provides a theoretical basis for the damage of extreme high temperature to cognitive performance from viewpoint of physiology.

Large‐Eddy Simulations of a Convection Cloud Chamber: Sensitivity to Bin Microphysics and Advection

AbstractBin microphysics schemes are useful tools for cloud simulations and are often considered to provide a benchmark for model intercomparison. However, they may experience issues with numerical diffusion, which are not well quantified, and the transport of hydrometeors depends on the choice of advection scheme, which can also change cloud simulation results. Here, an atmospheric large‐eddy simulation model is adapted to simulate a statistically steady‐state cloud in a convection cloud chamber under well‐constrained conditions. Two bin microphysics schemes, a spectral bin method and the method of moments, as well as several advection methods for the transport of the microphysical variables are employed for model intercomparison. Results show that different combinations of microphysics and advection schemes can lead to considerable differences in simulated cloud properties, such as cloud droplet number concentration. We find that simulations using the advection scheme that suffers more from numerical diffusion tends to have a smaller droplet number concentration and liquid water content, while simulation with the microphysics scheme that suffers more from numerical diffusion tends to have a broader size distribution and thus larger mean droplet sizes. Sensitivities of simulations to bin resolution, spatial resolution, and temporal resolution are also tested. We find that refining the microphysical bin resolution leads to a broader cloud droplet size distribution due to the advection of hydrometeors. Our results provide insight for using different advection and microphysics schemes in cloud chamber simulations, which might also help understand the uncertainties of the schemes used in atmospheric cloud simulations.

Smog chamber simulation on heterogeneous reaction of O3 and NO2 on black carbon under various relative humidity conditions

In this study, heterogeneous formation of nitrate from O3 reaction with NO2 on black carbon (BC) and KCl-treated BC surface in the presence of NH3 was simulated under 30–90% RH conditions by using a laboratory smog chamber. We found that O3 and NO2 in the chamber quickly reacted into N2O5 in the gas phase, which subsequently hydrolyzed into HNO3 and further neutralized with NH3 into NH4NO3 on the BC surface, along with a small amount of N2O5 decomposed into NO and NO2 through a reaction with the BC surface active site. Meanwhile, the fractal BC aggregates restructured and condensed to spherical particles during the NH4NO3 coating process. Compared to that during the exposure to NO2 or O3 alone, the presence of strong signals of CH2O+, CH2O2+ and CH4NO+ during the simultaneous exposure to both NO2 and O3 suggested a synergetic oxidizing effect of NO2 and O3, which significantly activated the BC surface by forming carbonyl, carboxylic and nitro groups, promoted the adsorption of water vapor onto the BC surface and enhanced the NH4NO3 formation. Under <75 ± 2% RH conditions the coating process of NH4NO3 on the BC surface consisted of a diffusion of N2O5 onto the surface and a subsequent hydrolysis, due to the limited number of water molecules adsorbed. However, under 90 ± 2% RH conditions N2O5 directly hydrolyzed on the aqueous phase of the BC surface due to the multilayer water molecules adsorbed, which caused an instant NH4NO3 formation on the surface without any delay. The coating rate of NH4NO3 on KCl-treated BC particles was 3–4 times faster than that on the pure BC particles at the initial stage, indicating an increasing formation of NH4NO3, mainly due to an enhanced hygroscopicity of BC by KCl salts.

Technical note: Bremsstrahlung dose in the electron beam at extended distances in total skin electron therapy.

Electron beam from a linear accelerator is commonly used in total skin electron therapy (TSET) at extended distances. Since Das et al (Med Phys 21, p.1733, 1994) reported 5% bremsstrahlung dose for a 6 MeV electron beam at extended distance of 500cm it has been accepted as common knowledge. However, measurements by Chen et al (Int J. Rad Onc Biol Phys 59 p.872, 2004) and Monte Carlo simulations by Ding et al (Phys. Med. Biol. 66, 075010, 2021) were unable to reproduce such high bremsstrahlung dose. As bremsstrahlung dose contributes to whole-body dose, which could produce bone marrow toxicity with serious complications for the outcome of the TSET, it is important to re-evaluate the magnitude of bremsstrahlung dose accurately. The EGSnrc Monte Carlo system is used to investigate bremsstrahlung doses from 6 MeV high dose rate total skin electron (HDTSe) beams from Varian TrueBeam and Clinac Accelerators. The measurements were carried out at a depth of dmax and 5cm in Solid Water and Acrylic phantoms at extended distances using a parallel-plate chamber and a cylindrical ion chamber. We were able to reproduce previously reported high bremsstrahlung dose at extended distances by using a parallel plate ionization chamber. However, both the measurements made by using a cylindrical chamber and Monte Carlo simulations showed an insignificant bremsstrahlung dose (∼1%) even at SSD=500cm. The bremsstrahlung doses of a 6 MeV electron beam are 0.5% to 1% for SSD from 100 to 700cm, although it increases with the increasing extended distance. The common belief of up to 5% bremsstrahlung dose at large extended distances is incorrect. Previously reported high bremsstrahlung doses might be due to poor signal-to-noise ratio of using a parallel plate chamber for measuring very low dose or particular setup.

A New Algorithm for Determining the Noise Equivalent Delta Temperature of In-Orbit Microwave Radiometers

The noise equivalent delta temperature (NEDT) determines the radiometric resolution of a radiometer. Determining NEDT is indispensable for assessing the in-orbit radiometer performance and quantifying uncertainty propagation from radiance to climate data records. Agencies of EUMETSAT, UK MetOffice, and National Oceanic and Atmospheric Administration (NOAA) have developed their own algorithms for calculating and monitoring NEDT of in-orbit microwave radiometers. These algorithms are an essential means for monitoring NEDT and hardware health. While remarkable accomplishments have been made, there appears to be room for improvement. The investigation is needed for the NEDT underestimate found at channels like G-band that has pronounced <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1/f$ </tex-math></inline-formula> noise. Also, it is necessary to explain the inconsistency in calculated NEDTs of different algorithms. We have reviewed the theoretical basis for determining NEDT and developed an improved algorithm of clear physics and mathematics. We have developed methods for handling error sources that can result in either negative or positive biases with an overall underestimate of NEDT. We have done comparison and validation with the prelaunch thermal vacuum chamber (TVAC) test, in-orbit data, and simulation. The new algorithm significantly improves the estimate of NEDT, including the G-band and advances the understanding of algorithm structures and physical foundations. It can accurately monitor in-orbit NEDT and facilitate quantifying the associated uncertainty propagation through science products.

Highly Oxygenated Organic Nitrates Formed from NO3 Radical-Initiated Oxidation of β-Pinene.

The reactions of biogenic volatile organic compounds (BVOC) with the nitrate radicals (NO3) are major night-time sources of organic nitrates and secondary organic aerosols (SOA) in regions influenced by BVOC and anthropogenic emissions. In this study, the formation of gas-phase highly oxygenated organic molecules-organic nitrates (HOM-ON) from NO3-initiated oxidation of a representative monoterpene, β-pinene, was investigated in the SAPHIR chamber (Simulation of Atmosphere PHotochemistry In a large Reaction chamber). Six monomer (C = 7-10, N = 1-2, O = 6-16) and five accretion product (C = 17-20, N = 2-4, O = 9-22) families were identified and further classified into first- or second-generation products based on their temporal behavior. The time lag observed in the peak concentrations between peroxy radicals containing odd and even number of oxygen atoms, as well as between radicals and their corresponding termination products, provided constraints on the HOM-ON formation mechanism. The HOM-ON formation can be explained by unimolecular or bimolecular reactions of peroxy radicals. A dominant portion of carbonylnitrates in HOM-ON was detected, highlighting the significance of unimolecular termination reactions by intramolecular H-shift for the formation of HOM-ON. A mean molar yield of HOM-ON was estimated to be 4.8% (-2.6%/+5.6%), suggesting significant HOM-ON contributions to the SOA formation.

Simulation of a GOx-GCH4 Rocket Combustor and the Effect of the GEKO Turbulence Model Coefficients

In this study, a single injector methane-oxygen rocket combustor is numerically studied. The simulations included in this study are based on the hardware and experimental data from the Technical University of Munich. The focus is on the recently developed generalized k–ω turbulence model (GEKO) and the effect of its adjustable coefficients on the pressure and on wall heat flux profiles, which are compared with the experimental data. It was found that the coefficients of ‘jet’, ‘near-wall’, and ‘mixing’ have a major impact, whereas the opposite can be deduced about the ‘separation’ parameter Csep, which highly influences the pressure and wall heat flux distributions due to the changes in the eddy-viscosity field. The simulation results are compared with the standard k–ε model, displaying a qualitatively and quantitatively similar behavior to the GEKO model at a Csep equal to unity. The default GEKO model shows a stable performance for three oxidizer-to-fuel ratios, enhancing the reliability of its use. The simulations are conducted using two chemical kinetic mechanisms: Zhukov and Kong and the more detailed RAMEC. The influence of the combustion model is of the same order as the influence of the turbulence model. In general, the numerical results present a good or satisfactory agreement with the experiment, and both GEKO at Csep = 1 or the standard k–ε model can be recommended for usage in the CFD simulations of rocket combustion chambers, as well as the Zhukov–Kong mechanism in conjunction with the flamelet approach.