Close-coupling Research Articles

生态系统服务与贫困关联视角下生态扶贫策略的实施路径

生态文明建设与脱贫攻坚均是重要的国家战略。由于贫困与生态环境问题存在紧密耦合关系，在生态保护修复中探索生态扶贫措施的实施路径可获得生态环境改善与社会经济发展的双赢。构建生态系统服务-贫困关联分析模型，以山水林田湖草生态保护修复试点的山西省宁武县和静乐县为例，通过村级多维贫困指数（VPI）评价贫困程度，并结合生态系统服务识别出生态修复与生态系统服务提升的重点地区，最后在这些区域布局合适的生态扶贫措施。结果表明处于高贫困的区域占研究区总面积的41%，中贫困所占面积比例为47%，低贫困所占面积比例为12%，地形条件、劳动力状况、生活水平的差异构成了宁武县和静乐县贫困的空间分布格局。研究区水源涵养、土壤保持、食物供给等生态系统服务计算结果分别与贫困程度叠加出九种类型，并根据叠加结果将研究区划分为低贫困修复区、低贫困保护区、中贫困修复区、高贫困修复区和高贫困保护区五个区域，提出在高贫困保护区、低贫困保护区实施以保护为主的扶贫措施，在低贫困修复区、中贫困修复区、高贫困修复区要利用生态修复的契机解决乡镇的主要致贫因素。研究为贫困或欠发达的农村区域生态保护修复与生态扶贫的结合提供借鉴参考。;The ecological civilization and poverty alleviation are both important national strategies. Because there is a close coupling relationship between poverty and eco-environmental problems, exploring the implementation path of ecological poverty alleviation measures in ecological protection and restoration can achieve a win-win situation between ecological environment improvement and socio-economic development. In this paper, an analysis model of correlation between ecosystem service and poverty was constructed. Ningwu and Jingle counties in Shanxi Province was taken as the case area, where there are pilot projects of ecological protection and restoration of mountain-water-forests-cropland-lakes-grasses. The village-level multidimensional poverty indicators (VPI) is used to evaluate the poverty level and identify key areas for ecological restoration in conjunction with ecosystem services, and layout appropriate ecological poverty alleviation measures. The results show that high poverty areas account for 41% of the study area, middle poverty areas account for 47%, and low poverty areas account for 12%. Differences in terrain conditions, labor conditions, and living standards have formed the different spatial distribution pattern of poverty in Ningwu and Jingle County. The calculation results of ecosystem services such as water conservation, soil conservation, food supply in the study area were superimposed on the poverty level for each of the nine types. Based on the superimposed results, the study area is divided into five types of zones:low-poverty restoration area, low-poverty protection area, middle-poverty restoration area, high-poverty restoration area, and high-poverty protection area. The protection-oriented poverty alleviation measures will be implemented at the low-poverty protection area and high-poverty protection area. It shall use the opportunity of ecological restoration to solve the main poor factors at low-poverty restoration area, middle-poverty restoration area and high-poverty restoration area. This study provides a reference for the combination of ecological protection and restoration with ecological poverty alleviation in poor and underdeveloped rural areas.

ISBA-MEB (SURFEX v8.1): model snow evaluation for local-scale forest sites

Abstract. Accurate modeling of the effect of snow cover on the surface energy and mass fluxes is required from land surface models. The Interactions between Soil–Biosphere–Atmosphere (ISBA) model uses a composite soil–vegetation approach that has limitations when representing snow and soil phase change processes in areas of high vegetation cover since it does not explicitly represent the snowpack lying on the ground below the canopy. In particular, previous studies using ISBA have pointed out that the snowpack ablation tends to occur to early in the season in forest regions in the Northern Hemisphere. The multi-energy balance (MEB) version of ISBA has been developed recently, to a large degree, to address this issue. A vegetation layer, which is distinct from the soil, has been added to ISBA and new processes are now explicitly represented, such as snow interception and an understory litter layer. To evaluate the behavior of this new scheme in a cold forested region, long-term offline simulations have been performed for the three BERMS forest sites located in Saskatchewan, Canada. It is shown that the new scheme leads to an improved energy budget representation, especially in terms of the ground and sensible heat fluxes, with decreases in root-mean-square error (RMSE) of 77 % and 18 %, respectively. A positive impact for soil temperatures, consistent with the improvement of the ground heat flux, is obtained, particularly in terms of bias, which is reduced from −6.2 to −0.1 K at a 10 cm soil depth on average for the three sites and 12 studied years. The impact of using MEB on the snowpack simulation is a better agreement with observations during the snow season, especially concerning the last day of snow in the season: errors are on the order of 1 d averaged over the three sites and all of the years using MEB, which represents a reduction in error of 20 d compared to the composite scheme. The analysis shows that this improvement is mostly caused by the ability of MEB to represent a snowpack that nearly completely covers the soil below the canopy and that decouples the soil from the atmosphere, while keeping a close coupling between the vegetation and the atmosphere.

Validation of reanalysis Southern Ocean atmosphere trends using sea ice data

Abstract. Reanalysis products are an invaluable tool for representing variability and long-term trends in regions with limited in situ data, and especially the Antarctic. A comparison of eight different reanalysis products shows large differences in sea level pressure and surface air temperature trends over the high-latitude Southern Ocean, with implications for studies of the atmosphere's role in driving ocean–sea ice changes. In this study, we use the established close coupling between sea ice cover and surface temperature to evaluate these reanalysis trends using the independent, 30-year sea ice record from 1980 to 2010. We demonstrate that sea ice trends are a reliable validation tool for most months of the year, although the sea ice–surface temperature coupling is weakest in summer when the surface energy budget is dominated by atmosphere-to-ocean heat fluxes. Based on our analysis, we find that surface air temperature trends in JRA55 are most consistent with satellite-observed sea ice trends over the polar waters of the Southern Ocean.

Long-term sulfide input enhances chemoautotrophic denitrification rather than DNRA in freshwater lake sediments

Partitioning between nitrate reduction pathways, denitrification and dissimilatory nitrate reduction to ammonium (DNRA) determines the fate of nitrate removal and thus it is of great ecological importance. Sulfide (S2-) is a potentially important factor that influences the role of denitrification and DNRA. However, information on the impact of microbial mechanisms for S2- on the partitioning of nitrate reduction pathways in freshwater environments is still lacking. This study investigated the effects of long-term (108d) S2- addition on nitrate reduction pathways and microbial communities in the sediments of two different freshwater lakes. The results show that the increasing S2- addition enhanced the coupling of S2- oxidation with denitrification instead of DNRA. The sulfide-oxidizing denitrifier, Thiobacillus, was significantly enriched in the incubations of both lake samples with S2- addition, which indicates that it may be the key genus driving sulfide-oxidizing denitrification in the lake sediments. During S2- incubation of the Hongze Lake sample, which had lower inherent organic carbon (C) and sulfate (SO42-), Thiobacillus was more enriched and played a dominant role in the microbial community; while during that of the Nansi Lake sample, which had higher inherent organic C and SO42-, Thiobacillus was less enriched, but increasing abundances of sulfate reducing bacteria (Desulfomicrobium, Desulfatitalea and Geothermobacter) were observed. Moreover, sulfide-oxidizing denitrifiers and sulfate reducers were enriched in the Nansi Lake control treatment without external S2- input, which suggests that internal sulfate release may promote the cooperation between sulfide-oxidizing denitrifiers and sulfate reducers. This study highlights the importance of sulfide-driven denitrification and the close coupling between the N and S cycles in freshwater environments, which are factors that have often been overlooked.

New Frontiers in IoT: Networking, Systems, Reliability, and Security Challenges

The field of IoT has blossomed and is positively influencing many application domains. In this paper, we bring out the unique challenges this field poses to research in computer systems and networking. The unique challenges arise from the unique characteristics of IoT systems such as the diversity of application domains where they are used and the increasingly demanding protocols they are being called upon to run (such as, video and LIDAR processing) on constrained resources (on-node and network). We show how these open challenges can benefit from foundations laid in other areas, such as, 5G cellular protocols, ML model reduction, and device-edge-cloud offloading. We then discuss the unique challenges for reliability, security, and privacy posed by IoT systems due to their salient characteristics which include heterogeneity of devices and protocols, dependence on the physical environment, and the close coupling with humans. We again show how the open research challenges benefit from reliability, security, and privacy advancements in other areas. We conclude by providing a vision for a desirable end state for IoT systems.

Relationship between the disrupted topological efficiency of the structural brain connectome and glucose hypometabolism in normal aging

Normal aging is accompanied by structural degeneration and glucose hypometabolism in the human brain. However, the relationship between structural network disconnections and hypometabolism in normal aging remains largely unknown. In the present study, by combining MRI and PET techniques, we investigated the metabolic mechanism of the structural brain connectome and its relationship with normal aging in a cross-sectional, community-based cohort of 42 cognitively normal elderly individuals aged 57–84 years. The structural connectome was constructed based on diffusion MRI tractography, and the network efficiency metrics were quantified using graph theory analyses. FDG-PET scanning was performed to evaluate the glucose metabolic level in the cortical regions of the individuals. The results of this study demonstrated that both network efficiency and cortical metabolism decrease with age (both p < 0.05). In the subregions of the bilateral thalamus, significant correlations between nodal efficiency and cortical metabolism could be observed across subjects. Individual-level analyses indicated that brain regions with higher nodal efficiency tend to exhibit higher metabolic levels, implying a tight coupling between nodal efficiency and glucose metabolism (r = 0.56, p = 1.15 × 10−21). Moreover, efficiency-metabolism coupling coefficient significantly increased with age (r = 0.44, p = 0.0046). Finally, the main findings were also reproducible in the ADNI dataset. Together, our results demonstrate a close coupling between structural brain connectivity and cortical metabolism in normal elderly individuals and provide new insight that improve the present understanding of the metabolic mechanisms of structural brain disconnections in normal aging.

Quenching and morphological evolution due to circumgalactic gas expulsion in a simulated galaxy with a controlled assembly history

ABSTRACT We examine the influence of dark matter halo assembly on the evolution of a simulated ∼L⋆ galaxy. Starting from a zoom-in simulation of a star-forming galaxy evolved with the EAGLE galaxy formation model, we use the genetic modification technique to create a pair of complementary assembly histories: one in which the halo assembles later than in the unmodified case, and one in which it assembles earlier. Delayed assembly leads to the galaxy exhibiting a greater present-day star formation rate than its unmodified counterpart, while in the accelerated case the galaxy quenches at z ≃ 1, and becomes spheroidal. We simulate each assembly history nine times, adopting different seeds for the random number generator used by EAGLE’s stochastic subgrid implementations of star formation and feedback. The systematic changes driven by differences in assembly history are significantly stronger than the random scatter induced by this stochasticity. The sensitivity of ∼L⋆ galaxy evolution to dark matter halo assembly follows from the close coupling of the growth histories of the central black hole (BH) and the halo, such that earlier assembly fosters the formation of a more massive BH, and more efficient expulsion of circumgalactic gas. In response to this expulsion, the circumgalactic medium reconfigures at a lower density, extending its cooling time and thus inhibiting the replenishment of the interstellar medium. Our results indicate that halo assembly history significantly influences the evolution of ∼L⋆ central galaxies, and that the expulsion of circumgalactic gas is a crucial step in quenching them.

Tree-ring based minimum temperature reconstruction on the southeastern Tibetan Plateau

Increases in the annual minimum temperature (Tmin) has been more obvious than the increase in the annual mean temperature in the southeastern Tibetan Plateau (TP) over the past few decades; however, annual Tmin variability over the long-term in the southeastern TP has received scant attention. Here, we present a 413-year long tree-ring width chronology (TRW), which is composed of 22 site chronologies at high altitudes at the Hengduan Mountains on the southeastern TP. Climate–tree growth relationship analysis revealed that annual Tmin was the climatic factor that influenced radial tree growth in the area the most (R = 0.74, P < 0.001). Accordingly, we reconstructed the annual Tmin over the 1600–2012 AD period on the southeastern TP. The linear regression model between TRW chronology and annual Tmin accounted for 54.3% of the total variance in actual Tmin during the common period, 1960–2012. The close coupling of warm and cold episodes with other temperature reconstructions from surrounding regions indicated the reliability of our reconstruction. In addition, the comparison of reconstructed series with Climate Research Unit gridded data demonstrated that our reconstruction could represent the large-scale variability in annual Tmin on the TP. Furthermore, the Tmin variability exhibited similar trends with the temperature reconstructions from the TP, Asia, and northern hemisphere during the common period (1600–2012), indicating that the thermal variation in southeastern TP was consistent with the continental and hemispheric scale climate system variabilities. Atlantic Multi-Decadal Oscillation (AMO) and solar activity were observed to be key factors influencing annual Tmin variation over the southeastern TP. The results of the moving correlation analyses implied that the radial forest growth at high altitudes on the southeastern TP remained consistent with regional Tmin variation, and the decrease in precipitation has not yet limited forest growth.

The odd couple: contrasting openness in innovation and science

ABSTRACT Over the last few decades, two domains have undergone seemingly similar transformations: Closed innovation turned into open innovation, closed science into open science. In this essay we engage critically with recent calls for a close coupling of the two domains based on their apparent commonality: openness. Comparing the historically-specific ways in which openness has been defined and mobilised, we find substantial differences between open innovation and open science. While openness in innovation was developed as an analytic concept and redefined quite flexibly over time, openness in science was created as a programmatic concept and its initial definition has been preserved rather rigidly. Contrasting openness in innovation and science helps anticipate some of the unintended consequences that a close coupling of these domains might yield. A close coupling might alienate advocates for change within the academic community, marginalise maintenance-oriented collaborations between science and practice, and increase the dependence of science on profit-oriented platforms. Reflecting upon these unintended consequences can help policy-makers and researchers to fine-tune their concepts for new forms of engagement across the science-practice divide.

Circular Economy potential within the building stock - Mapping the embodied greenhouse gas emissions of four Danish examples

Circular Economy (CE) can help reduce the building industry's immense environmental impact. Life cycle assessment (LCA) can facilitate CE decision-making by identifying the largest environmental impact reduction opportunities throughout a building's life cycle, but it does not suffice in a design situation. Thus, aggregated LCA knowledge is needed. However, existing building LCAs lack transparency, coherence and a closer coupling with the building context. Performing in-depth systematic LCA on four Danish case-study buildings (a school, an office, a residential building and a hospital), this study identifies where the largest embodied greenhouse gas emissions (EG) exist. The study also identifies which building design and construction strategies should be in focus in transitioning the building sector to a CE. The LCA generalisations found that all the buildings exhibited considerable EG originating from production and replacement of floors and ceilings, outer walls, inner walls and roofs. Thus, to come closer to meeting climate goals, a combination of different strategies going across and beyond the life cycles of buildings, components and materials is needed. These strategies include reusing existing buildings, components and materials; avoiding, substituting or reducing the use of EG-intensive and short-lived materials; and enabling future reuse, recycling and/or energy recovery options for materials. Differences between the buildings were also found. Thus, it is suggested to combine generalised learnings with LCA of buildings on a case-to-case basis, and to focus on optimising EG-intensive components and materials based on their different use-contexts and interconnectedness rather than on optimising the entire building.

Soil moisture retrievals using ALOS2-ScanSAR and MODIS synergy over Tibetan Plateau

This paper investigates the soil moisture retrievals over Tibetan Plateau using multi-temporal ALOS2-PALSAR2 data acquired in ScanSAR mode, in contrary to the commonly used StripMap SAR imaging mode. Considering the dual-polarimetry with limited observables, the surface roughness parameters such as the RMS height and auto-correlation length are first estimated by optimizing the semi-empirical Oh2004 model applied to the ALOS2 data acquired under bare soil condition. The vegetation water content corresponding to each ALOS2 acquisition time is derived from an empirical model applied to the temporally interpolated MODIS NDVI data. Then, the obtained roughness and vegetation optical depth are substituted into the Water Cloud Model which we modified by adding a double-bounce component according to the L-band scattering processes to retrieve the effective scattering albedo and soil moisture. The results show that the optimized surface RMS height and the associated slope are negatively related to a dual-angular radar index ΔHH, indicating the feasibility to optimize the relatively stable surface roughness parameters before retrieving the soil moisture dynamics. The obtained vegetation optical depth which is cross-validated against a normalized cross-polarized radar descriptor indicates a significant increase from May to August, in response to the vegetation phenological growth. Furthermore, the time-variable scattering albedo is less than 0.08, and slightly increases with the vegetation development. By accounting for the double-bounce component, the retrieved soil moisture better agrees with the ground measurements with R = 0.89 and RMSE = 0.058 m3/m3, but exhibits an overestimation issue for the soil moisture higher than 0.35 m3/m3 due to the saturation of SAR signal and the relatively strong vegetation cover. A positive correspondence (R = 0.81) between the retrieved soil moisture and the interpolated NDVI was found, verifying their close coupling in the soil-vegetation system. This study deepens the insights in the potential integration between the optical and L-band microwave observations to retrieve soil moisture over vegetated area.

Using aversive conditioning with near-real-time feedback to shape eye movements during naturalistic viewing.

Strategically shaping patterns of eye movements through training has manifold promising applications, with the potential to improve the speed and efficiency of visual search, improve the ability of humans to extract information from complex displays, and help correct disordered eye movement patterns. However, training how a person moves their eyes when viewing an image or scene is notoriously difficult, with typical approaches relying on explicit instruction and strategy, which have notable limitations. The present study introduces a novel approach to eye movement training using aversive conditioning with near-real-time feedback. Participants viewed indoor scenes (eight scenes presented over 48 trials) with the goal of remembering those scenes for a later memory test. During viewing, saccades meeting specific amplitude and direction criteria probabilistically triggered an aversive electric shock, which was felt within 50 ms after the eliciting eye movement, allowing for a close temporal coupling between an oculomotor behavior and the feedback intended to shape it. Results demonstrate a bias against performing an initial saccade in the direction paired with shock (Experiment 1) or generally of the amplitude paired with shock (Experiment 2), an effect that operates without apparent awareness of the relationship between shocks and saccades, persists into extinction, and generalizes to the viewing of novel images. The present study serves as a proof of concept concerning the implementation of near-real-time feedback in eye movement training.

Low-temperature rate constants and radiative transfer for rotational de-excitation of C5S by collision with He

ABSTRACT The C5S molecule is the largest member of the series of sulphur-containing carbon chains CnS observed in space. Given the lack of data concerning this molecule, we computed rate coefficients of C5S(1Σ+) induced by collision with He. These rates are obtained for thermal temperature below 100 K by mean of a new two-dimensional potential energy surface (PES) calculated with the explicit correlated coupled cluster with single, double, and pertubative triple excitation (ccsd(t)-f12) ab initio approach and the aug-cc-pVTZ basis sets. The C5S–He PES presents three minimums of −59.726, −55.355, and −36.506 cm−1 below its dissociation limit. Using this PES, the integral cross-sections are performed in the close-coupling (CC) and coupled-state (CS) quantum time independent formalisms for $E_\mathrm{ c}\le 500 \, \mathrm{ cm}^{-1}$ and J ≤ 13 (for CC) and J ≤ 50 (for CS). By averaging these cross-sections we obtained the downward rate coefficients. The new collisional data are used to simulate the excitation of C5S in the circumstellar gas. We obtain the excitation and brightness temperatures of the four lines observed towards the IRC+10216 which confirms the necessity of using radiative transfer calculations to accurately determine C5S abundance since the local thermodynamic equilibrium conditions are not fulfilled. The new collisional data should help to estimate the abundance of C5S in several interstellar regions.

Deep Reinforcement Learning for Backscatter-Aided Data Offloading in Mobile Edge Computing

Wireless network optimization has been becoming very challenging as the problem size and complexity increase tremendously, due to close couplings among network entities with heterogeneous service and resource requirements. By continuously interacting with the environment, DRL provides a mechanism for different network entities to build knowledge and make autonomous decisions to improve network performance. In this article, we first review typical DRL approaches and recent enhancements. We then discuss the applications of DRL for mobile edge computing (MEC), which can be used for user devices to offload computation workload to MEC servers. However, for the low-power user devices, for example, wireless sensors, MEC can be costly as data offloading also consumes high power in RF communications. To balance the energy consumption in local computation and data offloading, we propose a novel hybrid offloading model that exploits the complementary operations of active RF communications and low-power backscatter communications. To maximize the energy efficiency in MEC offloading, the DRL framework is customized to learn the optimal transmission scheduling and workload allocation in two communications technologies. Numerical results show that the hybrid offloading scheme can improve the energy efficiency over 20 percent compared to existing schemes.

On the role of microkinetic network structure in the interplay between oxygen evolution reaction and catalyst dissolution

Understanding the pathways of oxygen evolution reaction (OER) and the mechanisms of catalyst degradation is of essential importance for developing efficient and stable OER catalysts. Experimentally, a close coupling between OER and catalyst dissolution on metal oxides is reported. In this work, it is analysed how the microkinetic network structure of a generic electrocatalytic cycle, in which a common intermediate causes catalyst dissolution, governs the interplay between electrocatalytic activity and stability. Model discrimination is possible based on the analysis of incorporated microkinetic network structures and the comparison to experimental data. The derived concept is used to analyse the coupling of OER and catalyst dissolution on rutile and reactively sputtered Iridium oxides. For rutile Iridium oxide, the characteristic activity and stability behaviour can be well described by a mono-nuclear, adsorbate evolution mechanism and the chemical type of both competing dissolution and rate-determining OER-step. For the reactively sputtered Iridium oxide surface, experimentally observed characteristics can be captured by the assumption of an additional path via a low oxidation state intermediate, which explains the observed characteristic increase in OER over dissolution selectivity with potential by the competition between electrochemical re-oxidation and chemical dissolution.

Electron Scattering Cross Sections for Anthracene and Pyrene.

UK molecular R-matrix calculations have been carried out for electron scattering from anthracene and pyrene. These molecules belong to the family of polycyclic hydrocarbons (PAHs) and are found in a nebula known as the Red Rectangle. Static exchange (SE), static exchange plus polarization (SEP), and close coupling (CC) approximations are used for scattering calculations. Different elastic and inelastic cross sections are computed in the present work in the energy range of 0.1-15 eV. Dissociative electron attachment cross sections are also calculated for both the molecules. Various shape, Feshbach/core-excited, and mixed resonances are detected for these molecules below 10 eV. All of the resonances detected in the present study are in agreement with the existing experimental and theoretical results. Due to the complexity of the present targets, electron collision cross sections are essentially unknown and hence most of the results are presented for the first time.

Propagation of perturbations and meandering in a free surface shallow water jet

A shallow water free-surface turbulent jet is investigated at Froude numbers variable between about 0.15 and 0.6 and a Reynolds number equal to 5000, with a jet height-to-width aspect ratio variable from 0.5 to 1.1. In these experimental conditions, the flow is unstable and develops local transverse instabilities, which are amplified to a global meandering motion, forcing the jet to oscillate orthogonally to its axis. Instantaneous and averaged velocity fields are obtained by means of high-density, correlation-based time-resolved Particle Tracking Velocimetry. From the average point of view, the present jet configuration resembles a confined jet condition similar to that of wall jets, but with additional relevant three-dimensional effects, retaining self-similar properties, with a net co-flow and some ambient fluid entrainment. For increasing Froude numbers, such configuration is moved downstream and the jet spreading is delayed. The high resolution in space and time of present measurements allows to locally detect and following perturbed patterns and to derive amplitude and frequency of oscillation of the global meandering motion, the former increasing with axial distance and decreasing with Froude number, the latter doing just the opposite. The velocity of propagation of perturbed patterns is also investigated in comparison to the jet mean velocity, the local celerity of propagation of fluctuating velocity fields being derived. Results indicate that axial fluctuations propagate downstream similarly to transverse fluctuations along the orthogonal direction, thus showing a close coupling among the two motions and the onset of a self-sustained mechanism driven by the mean flow, responsible for the generation of the macroscopic meandering motion. This effect is in agreement with numerical predictions and is emphasised as the Froude number increases.

Polygonal Eyewall Asymmetries During the Rapid Intensification of Hurricane Michael (2018)

AbstractPolygonal eyewall asymmetries of Hurricane Michael (2018) during rapid intensification (RI) are analyzed from ground‐based single Doppler radar. Here, we present the first observational evidence of the evolving wind field of a polygonal eyewall during RI to Category 5 intensity by deducing the axisymmetric and asymmetric winds at 5‐min intervals. Spectral time decomposition of the retrieved tangential wind structure shows quantitative evidence of low (1–4) azimuthal wavenumbers with propagation speeds that are consistent with linear wave theory on a radial vorticity gradient, suggesting the presence of rapidly evolving vortex Rossby waves. Dual‐Doppler winds from the NOAA P‐3 Hurricane Hunter airborne radar provide further evidence of the three‐dimensional vortex structure that supports growth of asymmetries during RI. Both reflectivity and tangential wind fields show polygonal structure and propagate at similar speeds, suggesting a close coupling of the dynamics and the convective organization during the intensification.

Thermal and chemical effects of differential diffusion in turbulent non-premixed H2 flames

As a renewable fuel, hydrogen (H2) may play an increasingly important role in the development and control of piston and gas turbine engines to achieve zero carbon emissions. Predictive modeling of H2-fueled combustion processes requires a clear understanding of differential diffusion (DD) due to the high diffusivity of H2. On the assumption that turbulent mixing is a far more dominant process than molecular mixing, DD effects are typically neglected in turbulent combustion simulations to reduce modeling complications. While this assumption is reasonable for hydrocarbon fuels, it is less valid for H2 combustion, where DD is significant. In this work, two three-dimensional direct numerical simulations of temporally evolving turbulent H2 jet flames with and without considering DD are performed and compared with laminar flamelet solutions to assess DD effects under turbulent conditions. The emphasis is placed on assessing the suitability of classical mixture fraction Z and Bilger mixture fraction ZBilger as conditioning variables for non-premixed turbulent combustion modeling through analyzing DD effects on flame structure, chemical reactions, and tangential diffusion (TD). Furthermore, the persistence of DD effects under turbulent conditions and the suitability of a conventional DD parameter are investigated by comparing the turbulent flames to laminar flamelet solutions. It is found that conditioning the thermochemical state on ZBilger helps to capture DD effects and mitigate the relative contribution of TD, which gives ZBilger advantages over Z when employing flamelet modeling. Due to close coupling between DD and local chemical reactions, DD can affect the turbulent/laminar flames in the form of thermal effects due to the change in flame temperature, chemical effects due to the change in chemical reactions, and transport effects due to multiple species with varying diffusivities that could result in the difference between Z and ZBilger. While the transport effects are suppressed, significant chemical and thermal effects of DD still persist under turbulent conditions, which indicates that the DD parameter is probably unsuitable for comprehensively characterizing and assessing DD effects on the structure of turbulent non-premixed flames.

Photoionization features of the ground and excited levels of Cl II and benchmarking with experiment

This report presents i) various characteristic features in photoionization cross sections (σPI) of Cl II + hν → Cl III + e for many fine structure levels of Cl II, 392 in total with n ≤ 10 and l ≤ 9, ii) comparison of features with those observed in an experiment carried out at the Advanced Light Source at Lawrence Berkeley National Lab, and iii) partial photoionization cross sections of the ground level for ionization leaving the core ion in to various excited levels for applications in plasma modeling. The features correspond to resonant structures, the shape of the background, and their interference effect in σPI of this near neutral ion Cl II with 16 electrons. σPI for the 5 levels of the ground configuration 3s23p4(3P0,1,2, 1D2, 1S0) of Cl II show regions of narrow Rydberg resonances at and near threshold energies, and resonant structures at higher energies in contrast to typical smooth decrease in the background. Various other features in σPI of levels of excited equivalent electron states and broad Seaton resonances in single valence electron excited levels are illustrated with examples. Comparison of calculated σPI of the 15 lowest levels with the combined features of the measured photoionization spectrum shows excellent agreement by reproducing and thus identifying them to the levels that they belong to. The calculations were carried out in relativistic Breit-Pauli R-matrix (BPRM) method using a close coupling wave function expansion of 45 levels up to 4s of the core ion Cl III. These levels were optimized using a set of 12 configurations going up to orbital 5s, 3s23p3, 3s3p4, 3p5, 3s23p23d, 3s23p24s, 3s23p24p, 3s23p24d, 3s23p24f, 3s23p25s, 3s3p33d, 3s23p3d2, 3p43d producing 283 levels of Cl III. The autoionizing resonances are delineated with a fine energy mesh to observe the fine structure effects. The present results will provide high precision parameters for various applications involving this less studied ion.