Simulated Fluxes Research Articles

Enhancement of fatty acid degradation pathway promoted glucoamylase synthesis in Aspergillus niger

BackgroundOur recent multi-omics analyses of glucoamylase biosynthesis in Aspergillus niger (A. niger) suggested that lipid catabolism was significantly up-regulated during high-yield period under oxygen limitation. Since the catabolism of fatty acids can provide energy compounds such as ATP and important precursors such as acetyl-CoA, we speculated that enhancement of this pathway might be beneficial to glucoamylase overproduction.ResultsBased on previous transcriptome data, we selected and individually overexpressed five candidate genes involved in fatty acid degradation under the control of the Tet-on gene switch in A. niger. Overexpression of the fadE, fadA and cyp genes increased the final specific enzyme activity and total secreted protein on shake flask by 21.3 ~ 31.3% and 16.0 ~ 24.2%, respectively. And a better inducible effect by doxycycline was obtained from early logarithmic growth phase (18 h) than stationary phase (42 h). Similar with flask-level results, the glucoamylase content and total extracellular protein in engineered strains OE-fadE (overexpressing fadE) and OE-fadA (overexpressing fadA) on maltose-limited chemostat cultivation were improved by 31.2 ~ 34.1% and 35.1 ~ 38.8% compared to parental strain B36. Meanwhile, intracellular free fatty acids were correspondingly decreased by 41.6 ~ 44.6%. The metabolomic analysis demonstrated intracellular amino acids pools increased 24.86% and 18.49% in two engineered strains OE-fadE and OE-fadA compared to B36. Flux simulation revealed that increased ATP, acetyl-CoA and NADH was supplied into TCA cycle to improve amino acids synthesis for glucoamylase overproduction.ConclusionThis study suggested for the first time that glucoamylase production was significantly improved in A. niger by overexpression of genes fadE and fadA involved in fatty acids degradation pathway. Harnessing the intracellular fatty acids could be a strategy to improve enzyme production in Aspergillus niger cell factory.

Simulation of forest carbon fluxes by integrating remote sensing data into biome-BGC model

The accurate quantification and monitoring of intra- and inter-annual variability of long-term forest carbon fluxes are imperative to understand the changes in the forest ecosystems in response to the changing climate. The present study aims to simulate forest carbon fluxes in two major plant functional types (PFTs) of northwest Himalayan (NWH) foothills of India by integrating time-series remote sensing (RS) data into Biome-Biogeochemical Cycle (Biome-BGC), a process-based model, and to study the spatio-temporal variability of carbon fluxes. The parameterization of the Biome-BGC model was carried out using the data from two Eddy covariance (EC) flux tower sites located in the NWH foothills of India. An analysis was carried out to identify the sensitive parameters and their calibration was performed. The calibrated Biome-BGC model with a higher coefficient of determination (R2) and%RMSE for moist deciduous (R2 = 0.80, %RMSE = 13.24) and dry deciduous (R2 = 0.79, %RMSE = 13.85) PFTs was used to estimate the gross primary productivity (GPP) from 2001 to 2018. However, the range of model-simulated leaf area index (LAI) was found to be lower than the field observed LAI. Integrating satellite-based Global Land Surface Satellite (GLASS) LAI into the Biome-BGC model led to substantial improvement in GPP estimates of moist deciduous (R2 = 0.87, %RMSE = 11.12) and dry deciduous PFTs (R2 = 0.86, %RMSE = 10.38) when compared to EC tower-based GPP for the year 2018. Based upon the accuracy, GLASS LAI integrated Biome-BGC model was used to map the spatio-temporal variability of forest carbon fluxes. The study highlighted that integration of RS data into calibrated process-based model increased the accuracy of model-simulated forest carbon fluxes.

Numerical simulation of the surface flux of an alpine grassland in the source region of the Yellow River by the land surface model

The simulation performance of the land surface model Community Land Model 5.0 (CLM5.0) is tested by using the eddy correlation system and micrometeorological tower observational data at the Maqu observation field in 2016. The results show that the CLM5.0 model has a good simulation effect on the soil temperature and can well reflect the seasonal variation characteristics of soil temperature. In addition, the model can well simulate the seasonal variation in shallow soil moisture (5 cm and 10 cm). However, the deviations between the simulated and observed values are large. CLM5.0 cannot simulate the water holding capacity of shallow soil well, resulting in its underestimation. The simulation performance of the upward longwave radiation and net radiation is substantially better than that of the upward shortwave radiation due to the change in surface albedo caused by precipitation from March to July. CLM5.0 can also well reproduce the variation trend of the latent heat flux and 5 cm soil heat flux (heat exchange of soil at 5 cm). When the leaf area index (LAI) and Medlyn slope values are changed to 10%, 20%, and 50% of the default values, the simulation effects of soil moisture at depths of 5 cm and 10 cm are significantly improved, and the best simulation effects are achieved at 0.5 times the default values. This result indicates that lower LAI and Medlyn slope values are more suitable for simulating shallow soil moisture.

Understanding wind-driven melt of patchy snow cover

Abstract. The representation of snow processes in most large-scale hydrological and climate models is known to introduce considerable uncertainty into the predictions and projections of water availability. During the critical snowmelt period, the main challenge in snow modeling is that net radiation is spatially highly variable for a patchy snow cover, resulting in large horizontal differences in temperatures and heat fluxes. When a wind blows over such a system, these differences can drive advection of sensible and latent heat from the snow-free areas to the snow patches, potentially enhancing the melt rates at the leading edge and increasing the variability of subgrid melt rates. To get more insight into these processes, we examine the melt along the upwind and downwind edges of a 50 m long snow patch in the Finseelvi catchment, Norway, and try to explain the observed behavior with idealized simulations of heat fluxes and air movement over patchy snow. The melt of the snow patch was monitored from 11 June until 15 June 2019 by making use of height maps obtained through the photogrammetric structure-from-motion principle. A vertical melt of 23 ± 2.0 cm was observed at the upwind edge over the course of the field campaign, whereas the downwind edge melted only 3 ± 0.4 cm. When comparing this with meteorological measurements, we estimate the turbulent heat fluxes to be responsible for 60 % to 80 % of the upwind melt, of which a significant part is caused by the latent heat flux. The melt at the downwind edge approximately matches the melt occurring due to net radiation. To better understand the dominant processes, we represented this behavior in idealized direct numerical simulations, which are based on the measurements on a single snow patch by Harder et al. (2017) and resemble a flat, patchy snow cover with typical snow patch sizes of 15, 30, and 60 m. Using these simulations, we found that the reduction of the vertical temperature gradient over the snow patch was the main cause of the reductions in vertical sensible heat flux over distance from the leading edge, independent of the typical snow patch size. Moreover, we observed that the sensible heat fluxes at the leading edge and the decay over distance were independent of snow patch size as well, which resulted in a 15 % and 25 % reduction in average snowmelt for, respectively, a doubling and quadrupling of the typical snow patch size. These findings lay out pathways to include the effect of highly variable turbulent heat fluxes based on the typical snow patch size in large-scale hydrological and climate models to improve snowmelt modeling.

Numerical simulation on critical heat flux of downward-facing surface with modified wall boiling model

In this work, a modified wall boiling model was developed based on the prevailing Rensselaer Polytechnic Institute (RPI) wall boiling model, the wall heat flux was divided into four parts: sliding heat flux, evaporative heat flux, convective heat flux, and quenching heat flux. Based on the modified model, numerical simulations of the critical heat flux (CHF) of the downward-facing surface with different dimensions and scales were carried out. The CHFs at five angles of 30°, 45°, 60°, 75°, and 85° toward the heating surface under the 2-D model were calculated. Compared with the experimental data, the deviations are all within ±20%, which is better than the RPI model. In the wall flux distribution, the sliding heat flux at the CHF position accounts for more than 30%, and the proportion increases with the increase of angle, which indicates that bubble sliding has a great influence on the downward-facing surface. The influences of dimension and scale were analyzed based on the 1:1, 1:5, and 1:10 3-D numerical simulations. Compared with the 2-D model, the outlet area of the 3-D model is significantly increased, resulting in a 42% decrease in the maximum velocity in the 3-D flow channel under the same inlet velocity. Due to the decrease in flowability, the CHF of 3-D is lower than 2-D under the same condition. By comparing the results of the 1:1, 1:5, and 1:10 models, it can be found the trends of void fraction and wall temperature are similar. With the decrease of scale, the velocity at the critical point increases gradually, and the CHF also increases gradually.

Energy load prediction on structures and buildings-Effect of numerical model complexity on simulation of heat fluxes across the structure/environment interface

Civil structures, including buildings, constantly exchange heat fluxes with the environment. This includes heat exchange through conduction, convection, radiation and latent heat. A detailed description of the heat fluxes and corresponding transport processes is essential to estimate cooling and heating requirements and inhibit extreme local strains. Moreover, the temperature distribution inside a structure can be predicted by assessing the thermal loads of the environment with respect to the particular material properties of the structure. This is especially substantial for massive structures as thermal stresses can cause cracking. However, in the design of low-energy and passive houses, knowledge about the incoming and outgoing heat fluxes is also of great importance. Considering the numerous meteorological impacts on civil structures, the exact determination of the heat fluxes is quite complex. Most of the studies from literature on heat exchange of civil structures with the environment rely on multiple, not well-founded hypotheses to compensate for the lack of precise data. Therefore, this work aims to improve the understanding and quantification of the heat fluxes between a civil structure and the environment. Various measurement devices have been installed on a gravity dam to capture spatially distributed environmental impacts as well as the temperature distribution inside the structure. This data is used as input to model, quantify and evaluate the governing heat fluxes and thermal transport processes. It can be shown that the temperature fields in civil structures can be modelled even under complex environmental conditions with high accuracy when all essential key processes are incorporated. Furthermore, it is concluded that some simplified models can also yield a good fit even when the modelling parameters are extended beyond their actual definition.

Atmospheric Cold Pools in the Bay of Bengal

Abstract Atmospheric cold pools, generated by evaporative downdrafts from precipitating clouds, are ubiquitous in the Bay of Bengal. We use data from three moorings near 18°N to characterize a total of 465 cold pools. The cold pools are all dry, with a typical temperature drop of 2°C (max. 5°C) and specific humidity drop of 1 g/kg (max. 6 g/kg). Most cold pools last 1.5-3.5 hours (max. 14 hours). Cold pools occur almost every day in the North Bay from April to November, principally in the late morning, associated with intense precipitation that accounts for 80% of total rain. They increase the latent heat flux to the atmosphere by about 32 W/m2(median), although the instantaneous enhancement of latent heat flux for individual cold pools reaches 150 W/m2 . During the rainiest month (July), the cold pools occur 21% of the time and contribute nearly 14% to the mean evaporation. A composite analysis of all cold pools shows that the temperature and specific humidity anomalies are responsible for ~90% of the enhancement of sensible and latent heat flux, while variations in wind speed are responsible for the remainder. Depending on their gust front speed, the estimated height of the cold pools primarily ranges from 850 to 3200 m, with taller fronts more likely to occur during the summer monsoon season (Jun-Sep). Our results indicate that the realistic representation of cold pools in climate models is likely to be important for improved simulation of air-sea fluxes and monsoon rainfall.

Mathematical Modelling of Diffusion Flows in Two-Phase Stratified Bodies with Randomly Disposed Layers of Stochastically Set Thickness

The work is dedicated to mathematical modelling of random diffusion flows of admixture particles in a two-phase stratified strip with stochastic disposition of phases and random thickness of inclusion-layers. The study of such models are especially important during the creation of composite layered materials, in the research of the transmission properties of filters, and in the prediction of the spread of pollutants in the environment. Within the model we consider one case of uniform distribution of coordinates of upper boundaries of the layers of which the body is made up and two more cases, i.e., of uniform and triangular distributions of the inclusion thickness. The initial-boundary value problems of diffusion are formulated for flux functions; the boundary conditions at one of the body’s surfaces are set for flux and, at the other boundary, the conditions are given for admixture concentration; the initial condition being concerned with zero and non-zero constant initial concentrations. An equivalent integro-differential equation is constructed. Its solution is found in terms of Neumann series. For the first time it was obtained calculation formulae for diffusion flux averaged over the ensemble of phase configurations and over the inclusion thickness. It allowed to investigate the dependence of averaged diffusion fluxes on the medium’s characteristics on the basis of the developed software. The simulation of averaged fluxes of admixture in multilayered Fe−Cu and αFe−Ni materials is made. Comparative analysis of solutions, depending on the stage of averaging procedure over thickness, is carried out. It is shown that for some values of parameters the stage of averaging procedure over thickness has almost no effect on the diffusion flow value.

Simulation of solar neutron flux in the Earth's atmosphere for three selected flares

We performed simulations of the solar neutron (ns) flux in the Earth's atmosphere associated with three significant flares (X17 of September 07, 2005, X1.3 of September 07, 2017 and M2.9 of September 08, 2017). The input of the simulations was calculated on the basis of ns signals detected at ground level by the Solar Neutron Telescope of Sierra Negra (SNT-SN), in Mexico, and by the FIB scintillator of the Space Environment Data Acquisition-Attached Payload on board of the International Space Station. Since ns can produce Extensive Air Showers (EAS) in the Earth's atmosphere, we used the CORSIKA code and FLUKA subroutines to simulate the particle fluxes associated with the X17, X1.3 and M2.9 flares. We studied the average longitudinal variations of particle flux and energy loss through the atmosphere to estimate the ns flux impinging on the SNT-SN. The results of the simulated interactions and multiplicities of the particles, as a function of their energy, showed that 11–13% of the ns, released by the X17 flare, could overcome the atmospheric attenuation and propagate from the top of the atmosphere to the SNT-SN (4580 m a.s.l.) without producing EAS. On the other hand, ns associated with the X1.3 and M2.9 flares were lost due to atmospheric attenuation and the production of new particles; therefore, they were not detected at ground level by the SNT- SN. The characterization of these events allowed to develop an automatic tool for the analysis of ns emissions associated with solar flares.

Dynamic simulation of CO2 flux in a hydropower reservoir in Southwest China

• CE-QUAL-W2 is a valid module to research carbon cycle in Wujiangdu Reservoir. • CO 2 flux of reservoir in the cold season was higher than that in the warm season. • CO 2 flux varied much along the reservoir, positively correlated with water flow. • As withdrawal elevation increased 30 m, reservoir’s CO 2 emission increased by 39.31 %. • As withdrawal elevation decreased 30 m, reservoir’s carbon flux increased by 1.44 %. Carbon emissions from aquatic ecosystems, including reservoirs, play an important role in the global carbon budget, while the carbon cycle in reservoirs is still far from clearly understood. In this study, a vertical two-dimensional quality-hydrodynamic model (CE-QUAL-W2) was established to simulate CO 2 fluxes and carbon transport in the Wujiangdu Reservoir in Southwest China, verified by field measurement in 2017. Thanks to overall good accuracy of multi-indicator simulation of the model (mean RRE = 23.4 %, mean NES = 0.67), CE-QUAL-W2 is considered as a valid module to simulate carbon flux in the reservoir. Based on the model, the average CO 2 flux across the air–water interface of the reservoir was 4.37 mmol m −2 d -1 . Temporally, CO 2 fluxes in the cold season were higher than those in the warm season, indicating the important effect of seasonal temperature change on CO 2 flux, as well as the effect of other parameters, such as DO, Chla, TN, TP and pH. Spatially, CO 2 emission fluxes were lower in the water inlet area of the reservoir (2.74 mmol m −2 d -1 ) and in front of the dam (3.40 mmol m −2 d -1 ), but higher in the middle part of the reservoir (highest 5.42 mmol m −2 d -1 at Segment 54). Different discharge elevation scenarios were set up to model the influences of hydrodynamics on CO 2 emission fluxes. When the water discharge elevation increased by 30 m, CO 2 emission increased by 39.31 % and discharged downstream carbon decreased by 1.90 % compared with the actual working condition. Finally, the total mass of carbon released by the reservoir (the combination of carbon diffused into the atmosphere and carbon in released water) decreased by 1.85 % compared with the actual working condition. When the water discharge elevation decreased by 30 m, no obvious change of CO 2 emission happened, but the total mass of carbon released by the reservoir increased by 1.44 %. This research confirmed the validity of CE-QUAL-W2 in simulating carbon flux in reservoirs. Our modelling results shed light on the influence of hydrodynamics on carbon emission in reservoirs, and optimizing water discharge elevation can be helpful to mitigate carbon emission from reservoirs.

Forest Carbon Flux Simulation Using Multi-Source Data and Incorporation of Remotely Sensed Model with Process-Based Model

Forest carbon flux is critical to climate change, and the accurate modeling of forest carbon flux is an extremely challenging task. The remote sensing model (the MODIS MOD_17 gross primary productivity (GPP) model (MOD_17)) has strong practicability and is widely used around the world. The ecological process (the Biome-BioGeochemical Cycles Multilayer Soil Module model (Biome-BGCMuSo)) model can describe most of the vegetation’s environmental and physiological processes on fine time scales. Nevertheless, complex parameters and calibrations pose challenges to the application and development of models. In this study, we optimized all the input parameters of the MOD_17 model for the calibration of the Biome-BGCMuSo model to obtain GPP with continuous spatiality. To determine the contribution of input parameters to the GPP of different forest types, an Extended Fourier Amplitude Sensitivity Test (EFAST) was performed on the Biome-BGCMuSo model firstly. Then, we selected the sample points of each forest type and its different ecological gradients (30 for each type), using the GPP simulation value of the optimized MOD_17 model corresponding to the time and space scale to calibrate the Biome-BGCMuSo model, to drive the calibrated Biome-BGCMuSo, and we simulated the different forest types’ net primary productivity (NPP). According to dendrochronological measurements, the NPP simulation results were verified on the whole regional scale. The results showed that the GPP values of different forest types were highly sensitive to C:Nleaf (C:N of leaf), SLA1 (canopy average specific leaf area in phenological phase 1), and FLNR (fraction of leaf N in Rubisco). The coefficient of determination (R2) between the simulated forest NPP and the measured NPP was 0.64, and the root-mean-square (RMSE) was 26.55 g/C/m2/year. Our study aims to reduce uncertainty in forest carbon fluxes simulated by the Biome-BGCMuSo model, providing feedback for understanding forest ecosystem carbon cycling, vegetation productivity, and climate change.

Simulation of the Isotropic Ultra-High Energy Photon Flux in the Solar Magnetic Field

Both the lack of observation of ultra-high energy (UHE) photons and the limitations of the state-of-the-art methodology being applied for their identification motivate studies on alternative approaches to the relevant simulations and the related observational strategies. One such new approach is proposed in this report and it concerns new observables allowing indirect identification of UHE photons through cosmic ray phenomena composed of many spatially correlated extensive air showers or primary cosmic rays observed at one time. The study is based on simulations of interactions of UHE photons with the magnetic field of the Sun using the PRESHOWER program with some essential modifications. One of the expected results of such interactions is a generation of cosmic ray ensembles (CREs) in the form of very thin and very elongated cascades of secondary photons of energies spanning the whole cosmic ray energy spectrum. Upon entering the Earth’s atmosphere, these cascades or their parts may generate uniquely characteristic walls of spatially correlated extensive air showers, and the effect is expected also in cases when primary UHE photons are not directed towards the Earth. Particle distributions in these multi-primary UHE photon footprints are expected to have thicknesses of the order of meters and elongations reaching even hundreds of millions of kilometers, making them potentially observable with a global, multi-experiment approach, including re-exploring of the historical data, with the expected event rate exceeding the capabilities of even very large cosmic ray observatories. In this report, we introduce for the first time the methods allowing for simulating the isotropic flux of UHE photons in the Sun’s vicinity. Presented methods were verified and optimised in such a way that they would successfully model the cumulative spatial distribution of secondary photons at the top of the atmosphere. The preliminary results of simulations for the UHE photon flux of energy 100 EeV demonstrate the possibility of simulating potentially observable quantities related to CRE induced by UHE photons: densities, energy spectra and geographical orientations of secondary particles at the top of the Earth’s atmosphere. A measurement of at least one of these quantities would be equivalent to a confirmation of the existence of UHE photons, which would give an insight into fundamental physics processes at unprecedentedly high energies, far beyond the reach of man-made accelerators. On the other hand, a lack of such an observation would allow for further constraining of these fundamental processes with the physically new upper limits on UHE photon fluxes after careful analysis of the technical observation ability. The novel advantage of such an approach would lay in the purely electrodynamical character of the underlying simulations which are fully independent on extrapolations of hadronic interaction models by many orders of magnitude. Such extrapolations are necessary in the UHE photon identification methods based on the analyses of properties of individual extensive air showers presently used to determine the UHE photon upper limits.

Modelling water and energy fluxes with an explicit representation of irrigation under mulch in a maize field

Globally, water-saving irrigation plays a vital role in agricultural ecosystems to achieve sustainable food production under climate change. Irrigation under mulch (IUM) system has been widely used in modern agricultural ecosystems due to its high water use efficiency, but it remains unclear how each component of the water and energy processes responds to this agricultural management practice. Current modeling approaches are inadequate in investigating the impacts of IUM management on water-energy balance, which have shown more complicated than non-mulched management. Therefore, this study provided an explicit simulation of water and energy fluxes in IUM system using a process-oriented ecosystem model—CoupModel and the three years of the eddy covariance (EC) measurements. Based on Monte Carlo and the multiple model performance evaluation criteria, most of the model sensitive parameters were well constrained and 32 potentially important parameters, e.g., iscovevap, the fraction of mulch coverage, were identified to characterize the impacts of plastic mulching on energy balance and water transport. After proper calibration, the coefficient of determination (R2) for measured and simulated soil temperature (T) and soil water content (SWC) was 0.79 and 0.60, respectively, and the R2 for T and SWC during the validation period were 0.91 and 0.71, respectively. Furthermore, we found that there was a strong coupling between the parameters of the water and energy processes, which would restrict the simulation results due to the correlation between the parameters and the evaluation indices. This study presented a systematic model parameters calibration in the agricultural ecosystem implemented with IUM and provided with a more comprehensive understanding of the water and energy balance in cropland. These results would help agricultural model development with more detailed considerations of the water-saving management.

Accumulation characteristic of nitrogen in reservoirs during the ice-covered period under superimposed influence of ice and sediments: A case study of Biliuhe reservoir

Reservoirs located in middle and high latitudes freeze for months in winter, where the accumulation characteristics of pollutants are changed by superimposed influence of salt exclusion from ice on the surface and pollution release from sediments at the bottom. Taking total nitrogen (TN) of Biliuhe reservoir in Northeast China as an example, we developed a model to simulate TN accumulation characteristics influenced by ice and sediments during the freezing period (NACISF), and quantified contributions of TN from ice and sediments. Model parameters of ice and sediments were determined by laboratory freeze-up simulation experiment and sediment release flux simulation experiment, and water quality data were obtained from field investigations. Results showed that the annual average amount of TN input during the ice-covered period from 2015 to 2020 was 220.77 t, the output was 400.11 t, and the accumulated amount was 589.52 t. TN excluded from ice and released from sediments contributed 8.12% and 7.17% of the total TN inputs in winter, respectively. Analysis showed that the TN excluded from ice was positively correlated with ice thickness and initial TN concentration. The maximum ice thickness of Biliuhe reservoir had a 13 year cyclic feature, and the proportion of TN excluded from ice to the total TN inputs in different periods ranged from 10.68% to 17.30% (mean 13.18%). Meanwhile, TN accumulated seasonally as summer > autumn > winter > spring. The TN exclusion effect in 2050 would be weakened when considering the combined effects of climate change and human activities, with a reduction of about 40.85% compared to the current. It is concluded that the NACISF model took into account the influences of both ice and sediments, which provided a detailed understanding of the accumulation characteristics of TN during freezing period, and had important reference significance for water quality management in winter.

Water Vapor Flux‐Profile Relationship in the Stable Boundary Layer Over the Sea Surface

AbstractComprehensive marine atmospheric turbulence observation data, meteorological sounding and sea surface conditions in the South China Sea were employed to analyze and parameterize the vapor profile in the stable marine atmospheric boundary layer. The observations involved a three‐dimensional ultrasonic anemometer, water vapor carbon dioxide analyzer, radiosonde, and buoy. This paper theoretically determined that the water vapor profile function φq differs from the temperature profile function φh and that φq should be independently parameterized. A linear relationship existed between the dimensionless water vapor gradient and stability parameters based on the observation results, and φq was then obtained as φq(z/L) = az/L + b, in which the stability covered the stability range (z/L > 1). This result was applied in the Tropical Ocean‐Global Atmosphere Coupled‐Ocean Atmosphere Response Experiment bulk flux algorithm, and the simulation of the latent heat flux was improved.

Variations in terrestrial oxygen sources under climate change

The terrestrial ecosystem is an important source of atmospheric oxygen, and its changes are closely related to variations in atmospheric oxygen level. However, few studies have focused on the characteristics and driving forces behind terrestrial ecosystem oxygen sources. In this study, based on observations and net carbon flux simulations from the Sixth Coupled Model Intercomparison Project, we investigated temporal and spatial variations in terrestrial oxygen sources. As the largest source of atmospheric oxygen, the terrestrial ecosystem can produce approximately 7.10±0.38 gigatons of oxygen per year, and the tropics are the main oxygen producing regions. Notably, there are many “non-oxygen-producing lands”, where the lands no longer provide oxygen to the atmosphere, located in the high latitudes and around the deserts of Central Asia. Long-term analysis reveals that anthropogenic activities and climate change are responsible for the variations in terrestrial oxygen sources owing to land-use changes and competing effects between net photosynthesis and heterotrophic respiration. By 2100, more oxygen will be produced from the low-middle latitudes, while the high latitudes will serve as a larger oxygen sink due to extreme land-use type changes and drastic increases in soil respiration. Through this study, we supplement the understanding of the modern oxygen cycle and help provide better estimates for future variations in atmospheric oxygen level.

Prediction of crater shape with different heat flux and parametric simulation in electro-chemical discharge machining

Prediction of crater shapes with high accuracy in electrochemical discharge machining plays a significant role in the formation of micro-array on non-conductive materials. In this work, a finite-element method-based thermal model is developed by applying three different heat fluxes such as Gaussian, Constant, and Parabolic to predict the crater shapes on the soda-lime glass substrate. The comparative study of crater shapes reveals that a hemispherical crater is formed with Gaussian and Parabolic heat flux, while the cylindrical crater is formed for Constant heat flux due to the differences in the nature of heat distribution within the glass substrate. Further, material removal rate (MRR) and heat-affected zone (HAZ) are also estimated for Gaussian heat flux as it gives the most suitable crater shape. Parametric simulation is done by considering the supply voltage as a variable parameter and finding that MRR is significantly higher at 60 V compared to 45 V, whereas the increase in HAZ is very small.

Production of the artificial 51Cr neutrino source in the BEST project

The production of the artificial 51Cr neutrino source with activity > 3 MCi for the experiment BEST is presented. This procedure consisted of making a 50Cr target and irradiating it with thermal neutrons in a nuclear reactor SM-3. The production of a target in the form of disks with a thickness of 4 mm and a diameter of 84 and 88 mm included enrichment (to 96.5% in 50Cr) of natural chromium in the form of oxyfluoride by gas centrifugation, electrolytic reduction and refining of metallic chromium, as well as the formation of chromium disks by spark plasma sintering. Simulations of various source geometries, neutron flux and nuclear transmutation were carried out to validate the design of the source, the irradiation device and the transport container, the required chemical purity of the target and the irradiation schedule in the reactor. The calculated activity of the source after 75 effective days of irradiation was 3.55 MCi. The activity of the source was measured by the calorimetric method and amounted to 3.41 MCi at the time of its delivery to the Baksan Neutrino Observatory. This is the most intense chemically pure neutrino source ever produced.

Improved representation of plant physiology in the JULES-vn5.6 land surface model: photosynthesis, stomatal conductance and thermal acclimation

Abstract. Carbon and water cycle dynamics of vegetation are controlled primarily by photosynthesis and stomatal conductance (gs). Our goal is to improve the representation of these key physiological processes within the JULES land surface model, with a particular focus on refining the temperature sensitivity of photosynthesis, impacting modelled carbon, energy and water fluxes. We test (1) an implementation of the Farquhar et al. (1980) photosynthesis scheme and associated plant functional type-dependent photosynthetic temperature response functions, (2) the optimality-based gs scheme from Medlyn et al. (2011) and (3) the Kattge and Knorr (2007) photosynthetic capacity thermal acclimation scheme. New parameters for each model configuration are adopted from recent large observational datasets that synthesise global experimental data. These developments to JULES incorporate current physiological understanding of vegetation behaviour into the model and enable users to derive direct links between model parameters and ongoing measurement campaigns that refine such parameter values. Replacement of the original Collatz et al. (1991) C3 photosynthesis model with the Farquhar scheme results in large changes in GPP for the current day, with ∼ 10 % reduction in seasonal (June–August, JJA, and December–February, DJF) mean GPP in tropical forests and ∼ 20 % increase in the northern high-latitude forests in JJA. The optimality-based gs model decreases the latent heat flux for the present day (∼ 10 %, with an associated increase in sensible heat flux) across regions dominated by needleleaf evergreen forest in the Northern Hemisphere summer. Thermal acclimation of photosynthesis coupled with the Medlyn gs scheme reduced tropical forest GPP by up to 5 % and increased GPP in the high-northern-latitude forests by between 2 % and 5 %. Evaluation of simulated carbon and water fluxes by each model configuration against global data products shows this latter configuration generates improvements in these key areas. Thermal acclimation of photosynthesis coupled with the Medlyn gs scheme improved modelled carbon fluxes in tropical and high-northern-latitude forests in JJA and improved the simulation of evapotranspiration across much of the Northern Hemisphere in JJA. Having established good model performance for the contemporary period, we force this new version of JULES offline with a future climate scenario corresponding to rising atmospheric greenhouse gases (Shared Socioeconomic Pathway (SSP5), Representative Concentration Pathway 8.5 (RCP8.5)). In particular, these calculations allow for understanding of the effects of long-term warming. We find that the impact of thermal acclimation coupled with the optimality-based gs model on simulated fluxes increases latent heat flux (+50 %) by the year 2050 compared to the JULES model configuration without acclimation. This new JULES configuration also projects increased GPP across tropical (+10 %) and northern-latitude regions (+30 %) by 2050. We conclude that thermal acclimation of photosynthesis with the Farquhar photosynthesis scheme and the new optimality-based gs scheme together improve the simulation of carbon and water fluxes for the current day and have a large impact on modelled future carbon cycle dynamics in a warming world.

Two-channel combination methods for count-loss correction in radiation measurements at high rates and with pulsed sources

Pile-up effects due to the overlap of signals within the system dead-time (τ) influence the counting capability of radiation detection devices, necessitating the use of correction algorithms to compensate for the count-losses at high radiation rates. Count-rate linearity is especially critical for clinical applications like X-ray imaging or beam monitoring in particle therapy. In particular, in proton therapy the number of delivered particles must be measured online during the treatment session with a maximum error of 1 % up to an average input beam flux of about 1010cm−2s−1. For a segmented detector used to identify and count the single beam particles, assuming a channel area of 1 mm2 and a dead-time τ=2ns, a maximum counting inefficiency of 1 % is required up to τ.fin=0.2 for each detector channel, where fin represents the input rate. Moreover, the beam is often delivered in bunches with higher instantaneous particle rates, and the saturation model of the detector and electronic chain could not be easily determined. Similar considerations are applicable for pixelated detectors used for photon counting.Two methods are proposed to mitigate counting inefficiencies with radiation sources of variable time-structures. Both methods are based on the collection of logic signals provided by two independent detector channels exposed to the same radiation field after discriminating the detector analog outputs with a fixed threshold, assuming that the duration of the discriminator output signal corresponds to the system dead-time. The correction algorithms employ the measurements of the time durations, the number of signals from the two channels and of their AND/OR combinations. The methods provide count-loss corrections without the need to know the dead-time model.The performances of the proposed algorithms are evaluated by using simulations of ideal boxcar signals of fixed duration τ, distributed randomly in time to emulate the dead-time behavior of the system. Both methods provide an effective count-loss correction with a maximum deviation of 1% for different input rates up to τ.fin=1, assuming a uniform random time distribution of input events for both paralyzable and non-paralyzable systems. The simulations of pulsed radiation fluxes provide the same results as a function of the instantaneous input rates.These results are similar to those obtainable by the standard live-time correction algorithm. However, the latter algorithm can only be applied to continuous particle fluxes, while the proposed algorithms work also for pulsed beams, without any hypothesis on the bunch duration or frequency. The robustness of the algorithms with respect to the resolution of the time measurement is studied and the potential limitations in more realistic systems are discussed.The algorithms can be easily implemented in standard logical circuits with multiple input signals provided by segmented detectors. Even if the methods are intended for real-time correction in beam particle counting, they could be applied in a wider range of applications of radiation measurements.