Simulated Process Research Articles

Effects of Lactic Acid Bacteria Fermentation and In Vitro Simulated Digestion on the Bioactivities of Purple Sweet Potato Juice

The effects of lactic acid bacteria fermentation and in vitro simulated digestion on phenolic bioavailability, phenolic bioavailability, and antioxidant activity of purple sweet potato juice (PSPJ) were investigated. The PSPJ was fermented by Lactobacillus rhamnosus and Streptococcus thermophilus. The viable bacterial count, phenolic components, antioxidant activity, phenolic bioaccessibility, and phenolic bioavailability of PSPJ were analyzed during the simulated digestion process in vitro. The data displayed that lactic acid bacteria fermentation increased total α-glucosidase inhibition, total flavonoid content, and ratephenolic content. The antioxidant activities were improved after in vitro simulated digestion due to the biotransformation of phenolic substances by lactic acid bacteria fermentation. The bioaccessibility and bioavailability of phenols in PSPJ were improved with fermentation of lactic acid bacteria. Furthermore, the viable bacteria count of the two strains was significantly improved (>7 log CFU/mL) after simulated digestion in vitro.

Study on zinc removal behavior in simulated pre-reduction sintering process

In this study, blast furnace dust and iron concentrate were used as raw materials and graphite as reducing agent for mixed compacts. The briquettes were roasted in a high temperature tube furnace at 1200°C and kept for a certain time to simulate the pre-reduction sintering dezincification process. The reduced briquettes were characterized by X-ray diffraction, scanning electron microscopy, Energy Dispersive Spectroscopy and flame atomic absorption spectrometry. The effects of C/O molar ratio, basicity and pre-reduction time on the zinc removal rate and pre-reduction degree of the pre-reduction sintered products were studied, and the removal mechanism of zinc was further investigated. The results show that the pre-reduction sintering process can effectively achieve the zinc volatility removal while meeting the requirements of subsequent blast furnace production. The zinc removal rate of pre-reduced sintered products increased with the prolongation of pre-reduction time, increased first and then decreased with the increase of C/O molar ratio and basicity. The pre-reduction degree and Zn removal rate showed the same variation pattern. When the briquettes with C/O molar ratio of 1.0 and basicity of 1.9 were reduced for 20 min, the zinc removal rate and pre-reduction degree could reach 90.40% and 87.74%, respectively, indicating that a large amount of zinc was removed and most of the metallic iron had been reduced. The research results can provide some theoretical basis for industrial production.

From anatomy to surgery: Effectiveness of virtual simulation adjuvant to traditional methods in the preclinical training of apicoectomy.

Anatomy forms the foundation for the training and execution of routine surgical procedures. However, a gap persists in effectively bridging anatomical knowledge with the confident performance of procedures. Virtual simulation (VS) techniques, based on experiential and situated learning theory, hold promise in addressing this challenge. Apicoectomy, a procedure involving root apex resection to preserve a tooth, requires a blend of regional and dental anatomy knowledge, making it an ideal model for assessing the effectiveness of VS. This prospective cohort study evaluated primarily the enhancement of incorporating VS training in the preclinical skill training of apicoectomy for undergraduate dental students, compared to relying solely on traditional methods. VS training includes the simulated dissection process, patient examination, and apicoectomy based on graphically synthesized virtual models. Secondly, the study investigated the influence of exposure to VS training on students' confidence and satisfaction. The training was divided into three progressive levels aligned with students' cognitive processes, employing Miller's competence learning framework. Participants were categorized into the control group (CG) (n = 214) and VS training group (VSTG) (n = 220) based on their classes. The results demonstrated that VSTG showed significantly greater training enhancement (VSTG: 7.14 ± 1.74; CG: 6.57 ± 2.02, p = 0.002) and higher confidence levels (VSTG: 2.94 ± 0.13; CG: 2.69 ± 0.13, p < 0.001), along with greater satisfaction with the training compared to the CG (VSTG: 3.70 ± 0.18; CG: 3.20 ± 0.17, p < 0.001). In conclusion, VS proves to be a valuable adjunct for enhancing procedural skill training in surgical procedures.

Unveiling the effects of landscape-fire interactions on functional diversity in a Southern European mountain.

Climate and land-use changes are contributing to impacts on global ecosystem functioning. These effects are particularly severe in areas undergoing land abandonment and extreme wildfire events, such as the Mediterranean regions of the Iberian Peninsula. Previous studies have evaluated the impacts of land management on fire mitigation and biodiversity (species distribution and species richness), but how such strategies influence functional diversity remains unexplored. This study investigates how alternative land-fire management strategies may affect functional diversity. We modeled for 2050 for the Transboundary Biosphere Reserve Gerês-Xurés (Portugal-Spain). Land-use scenarios simulated processes of land abandonment ("business-as-usual"-BAU) and the implementation of EU rural policies ("high nature value farmlands"-HNVf), and were combined with three fire suppression levels. Species distribution models (102 vertebrates) were projected to each scenario, and functional diversity indices were consequently calculated. The highest functional richness was predicted for BAU scenarios, probably representing the benefits to unique species that deliver singular functions. The HNVf scenarios provided the highest functional divergence, probably indicating a high niche differentiation and low resource competition amongst agricultural communities. HNVf was the most beneficial scenario for ecosystem functioning, while fire suppression did not affect functional diversity. Despite the proneness to burn of our study area and the effects of firefighting on its fire regime, land-use policies are expected to have greater influence than fire suppression effects on functional diversity. These findings suggest that different facets of functional diversity will be unevenly influenced by fire-landscape dynamics driven by the land-use policies to be implemented in the upcoming decades.

Avoiding decoherence with giant atoms in a two-dimensional structured environment

Giant atoms are quantum emitters that can couple to light at multiple discrete points. Such atoms have been shown to interact without decohering via a one-dimensional waveguide. Here, we study how giant atoms behave when coupled to a two-dimensional square lattice of coupled cavities, an environment characterized by a finite-energy band and band gaps. In particular, we describe the role that bound states in the continuum (BICs) play in how giant atoms avoid decoherence. By developing numerical methods, we are able to investigate the dynamics of the system and show the appearance of interfering BICs within a single giant atom, as well as oscillating BICs between many giant atoms. In this way, we find the geometric arrangements of atomic coupling points that yield protection from decoherence in the two-dimensional lattice. These results on engineering the interaction between light and matter may find applications in quantum simulation and quantum information processing. Published by the American Physical Society 2024

A system of trading in the foreign exchange market based on multi-criteria optimization under Belief-Plausibility uncertainty

A new Forex multi-criteria trading model based on the Belief-Plausibility (Bel−Pl) extension is developed and validated. The Bel−Pl approach is, in fact, a meta-theory in relation to the classical theory of fuzzy sets FST and the intuitionistic theory of fuzzy sets (IFST). This allows us to use more available information about the simulated process than these theories. The developed model consists of two interconnected, but different parts combined in the automated trading system (ATS). The first part of the Forex trading model is responsible for generating multi-indicator trading signals based on a set of new proposed technical analysis indicators that have been extended in the framework of the Bel−Pl approach. The second part of the model is a multiple-criteria Bel−Pl extended hierarchical trading model estimation. These two parts of the model are combined into the developed ATS, which implements the appropriate optimization procedure at the optimization stages and the simulation of the trading process at the testing or real trading stages. The advantages of the developed model and ATS were shown by comparing their results with the results obtained using fuzzy multi-criteria models and a single-criterion model. All studies were conducted over the past two years (2022-2023) for the H1 and H4 timeframes and three currency pairs EURUSD, USDJPY and GBPUSD.

Flow structure and characteristics of fluid undergoing a sudden contraction to an annular gap under dynamic boundary

Pipeline transport serves as an effective means to alleviate traffic congestion and reduce carbon emissions from transportation. The hydraulic delivery system, which employs pipeline cars as carriers, addresses the limitations of existing systems. However, its transportation efficiency is affected by variations in the flow structure within the pipelines. During the acceleration of the pipeline car, the sudden contraction flow field from circular to annular gap formed in the vicinity of the end face under dynamic boundary conditions. This study utilized particle image velocimetry (PIV) to visualize and measure the sudden contraction flow field. Based on the obtained experimental results, it investigated the impact of dynamic boundary velocity on the flow structure, velocity characteristics, and energy dissipation of the annular gap. The acceleration process of the dynamic boundary is the conversion of flow energy into the kinetic energy of the annular gap flow and the kinetic energy of the pipeline car. This process is accompanied by phenomena of velocity slip and velocity overshoot. As the velocity of the pipeline car increases, the recirculating vortex within the annular gap dissipates and eventually disappears. The velocity slip gradually decreases, the location of the overshoot point shifts radially, and the magnitude of the overshoot diminishes before ultimately vanishing. From static to steady, the probability density distribution of the slipstream face transitions from a distribution with high skewness and low peak value to a normal distribution with high peak value and low skewness. The irreversible losses that arise in a sudden contraction flow field can be quantified by the increase in entropy. Due to the similarity of the solving processes of large Eddy simulation and PIV, a combined sub-grid stress model is used to solve the flow losses in the flow field. The turbulent dissipation occurs mainly in the recirculation region, shear layer, and high-speed shear regions near the wall.

The mechanism of peanut shell flavonoids inhibiting the oxidation of myofibrillar protein: An elucidation of the antioxidative preservation action of peanut shell flavonoids on chilled pork.

Flavonoids, a significant subclass of polyphenols, possess antioxidant properties and contribute to the preservation of chilled meat. In this paper, a phosphate buffer solution (pH = 6.25, simulated chilled pork) and a Fenton oxidation system (simulated myofibrillar protein oxidation process during storage) were established to explain the antioxidative preservation of chilled pork using peanut shell flavonoids (PSFs). The results indicated that PSFs changed the secondary structure of myofibrillar protein (MP), significantly inhibiting the oxidation of amino acids and the formation of carbonyl groups in MP (P < 0.05). Because PSFs and amino acids in chilled pork were combined to form complex through non-covalent bond in a pH 6.25 environment and covalent bond in a Fenton oxidation system. The antioxidant capacity of the complex was significantly enhanced (P < 0.05). The molecular docking technique predicted the antioxidant binding sites were Cys176, Ala182 and Val 124. This study provides a theoretical foundation for the preservation of chilled pork using PSFs.

Unfolding bovine serum albumin decorated selenium nanoparticles crosslinking with chitosan: Achieve stabilization of Pickering emulsions gel and enhance resveratrol bioaccessibility.

Resveratrol (Res) is a natural polyphenol exhibiting anti-oxidant and anti-inflammatory activity. However, the applications of Res have been limited due to its low stability and water solubility. To enhance the bioaccessibility of Res, unfolding bovine serum albumin-modified selenium nanoparticles (UBSA@SeNPs) encapsulated within chitosan (CS)-coated Pickering emulsions (CS-UBSA@SeNPs-PE) were used to load Res. The results showed that Res-loaded CS(0.06 %)-UBSA@SeNPs-PE has small droplet size (16.13 μm), high gel properties and excellent antioxidant properties. During the simulated digestion process, CS reduced the release rate of Res from Res-loaded CS(0.06 %)-UBSA@SeNPs-PE (42.27 %) to reach a slow release effect. Importantly, Res could quickly release from CS-UBSA@SeNPs-PE within intestinal fluid or in the presence of chitosanase. In simulated absorption experiments, the intestinal permeability of Res in Res-loaded CS(0.06 %)-UBSA@SeNPs-PE were enhanced by 292.31 % compare to Res-loaded CS(0 %)-UBSA@SeNPs-PE. In pharmacokinetic studies, Res-loaded CS(0.06 %)-UBSA@SeNPs-PE had an area under the curve (AUC) up to 3467.99 ± 127.43 ng*h/mL. Furthermore, CS also improved the mucoadhesive nature of UBSA@SeNPs-PE, resulting in a gut-retention time of Res-loaded CS(0.06 %)-UBSA@SeNPs-PE that reached up to 60 h. In conclusion, CS-UBSA@SeNPs-PE can serve as an effective oral delivery system for improving the bioaccessibility of Res.

Assessment of Cyanotoxins Removal Efficiency Using a Simulated Drinking Water Treatment Process for Downstream Source Water of the Nakdong River

Objectives : This study aims to evaluate the removal rates of nine cyanotoxins produced by cyanobacteria using a laboratory-scale simulated drinking water treatment process (DWTP), providing useful data for DWTP operations during algal blooms.Methods : A lab-scale simulated DWTP was used to evaluate the removal rates of nine cyanotoxins under typical operating conditions, including specific chemical dosages and contact times. The study employed chlorine and ozone, as well as powdered activated carbon (PAC) and biological activated carbon (BAC).Results and Discussion : According to the experimental results of removal efficiency for chlorination and ozonation, microcystin-LR (MC-LR), MC-RR, MC-LA, MC-LF, MC-LY, MC-YR, cylindrospermopsin (CYN), and nodularin (NOD) were effectively removed within the typical ranges of pre- and post-chlorine and pre- and post-ozone concentrations in the DWTP. However, anatoxin-a (ANA) exhibited a significantly lower removal efficiency. The evaluation of removal efficiency for PAC treatment indicated that MC-LA, MC-LF, and MC-LY had low removal rates. In contrast, the other six cyanotoxins achieved over 50% removal when PAC concentrations were above 25 mg/L and contact times exceeded 30 minutes. The evaluation of removal rate for BAC treatment showed that under conditions with an empty bed contact time (EBCT) of more than 5 minutes, over 70% of the nine cyanotoxins were removed. When the EBCT exceeded 2 minutes, removal rates reached between 95% and 100%. In the BAC process, the removal of MC-RR was primarily facilitated by the biodegradation, while the removal of CYN was mainly achieved through adsorption.Conclusion : Due to climate change, the bloom periods of various cyanobacteria in domestic water sources are gradually increasing, resulting in a rising trend in both the frequency and concentration of detected cyanotoxins. This study evaluated the removal efficiency of various cyanotoxins in DWTPs, focusing on chlorine/ozone treatment (oxidation), PAC treatment (adsorption), and BAC (adsorption and biodegradation). The different DWTPs at the facility act as multiple barriers, effectively removing cyanotoxins upon their introduction.

Simulating water balance and nutrient losses in a pastoral catchment using the SWAT+ model: added value of isotope data

ABSTRACT New Zealand’s freshwater is under increasing pressure from intensified dairy farming. This study assesses agricultural nitrogen loads from small pastoral catchments contributing to eutrophication and periodic algae blooms in a lake. Using the Soil and Water Assessment Tool (SWAT+), we simulated hydrological processes and nutrient loads, incorporating water (δ2H, δ18O) and nitrate (δ15N, δ18O) isotope data to improve model performance. The SWAT+ model was calibrated and validated with flow and nitrate data, achieving R2 values of 0.65–0.90, Nash-Sutcliffe efficiency (NSE) of 0.46–0.82, and percent bias (PBIAS) between 10.24% and 33.48%. The study demonstrates that stable isotope insights can enhance SWAT+ modelling accuracy and highlight the need for better fertilizer management to reduce nutrient loads.

Research on Energy Efficiency Optimization Control Strategy of Office Space Based on Genetic Simulated Annealing Strategy

Current energy-saving lighting control algorithms often face the dilemma of local optimality, which limits the energy-saving potential and comfort improvement of indoor lighting systems. The control parameters of the lighting system are optimized using a genetic simulated annealing algorithm to achieve the global optimal solution and enhance energy-saving efficacy in indoor lighting. The local search ability of the algorithm is enhanced by simulated annealing processing of excellent individuals after genetic operation. The genetic probability is adaptively adjusted according to the number of iterations and the fitness of the population, so that the algorithm enriches the population diversity in the early stage and avoids the “premature” convergence of the algorithm. A lamp illuminance model based on an artificial neural network and an indoor natural illuminance model based on a workbench are proposed to evaluate the lighting comfort, which provides a basis for constructing the fitness function of the optimization algorithm. Through the simulation experiment, the genetic simulated annealing algorithm is applied to the lighting scene introduced in this paper and compared with the traditional particle swarm optimization algorithm and genetic algorithm, the lighting energy saving performance is significantly improved.

Polyethylene glycol/carboxymethyl cellulose/montmorillonite composite phase change materials for thermal management

The fabrication of composite phase change materials (CPCMs) with excellent shape stability, reasonable thermal conductivity and good mechanical properties using simple process to obtain an effective energy storage and conversion maintains an issue of the utmost importance. In this work, carboxymethylcellulose sodium (CMC)/montmorillonite (MMT) aerogels with various MMT loading is initially prepared by gelation and freeze-drying technique. The prepared CMC/MMT aerogels have a uniformly distributed pore structure, of which the compressive strength can reach 26.4 kPa when the MMT loading content is 40 wt%. When the MMT loading content is 40 wt%, the thermal conductivity of the PEG/CMC/40MMT CPCM can reach up to 0.78 W/m·K, which is 225 % higher than that of pure PEG. In particular, the rigid CMC/MMT composite aerogel is conducive to the storage of PEG, obtaining a maximum loading percentage of 96.8 %, phase change enthalpy of 179.2 J/g, and high enthalpy efficiency of 98.6 % for CMC/40MMT aerogel. The rigid supporting matrix and adsorption capacity of the CMC/MMT framework meliorate the shape stability and cyclic stability during the phase transition, which can also cool the surface temperature of a simulated central processing unit (CPU) from 90 °C to 54.7 °C. In summary, the as-prepared novel PEG/CMC/40MMT CPCM offers a novel strategy for thermal management of next-generation electronic devices.

Changes in the Profile of Phenolic Compounds and in the Antioxidant, Hypoglycemic, and Antidiabetic Activities of a Beverage Based on Sesame By-Product Caused by the Simulated Gastrointestinal Digestion Process

The by-product of extracting oil from sesame has good functional properties for use in the development of new food products. In this study, the effect of simulated gastrointestinal digestion on the bioaccessibility of phenolic compounds, as well as the antioxidant, antidiabetic, and hypoglycemic properties of a beverage from sesame by-products was analyzed. Oral digestion significantly decreased the total phenolic content of the beverage, while the total flavonoid content increased. Both phytochemicals increased after gastric and intestinal digestion. Twenty-five phenolic compounds were characterized in the sesame by-product beverage, including feruloylquinic acid, which was present in all the digestive fractions analyzed. The most abundant free phenolic was quercetin, which was also present in all the digested fractions. On the other hand, the most abundant phenolic in the digested fractions was isorhamnetin. During gastrointestinal digestion, the antioxidant activity and inhibitory effects on the α-glucosidase and DPP-IV of the beverage significantly improved, while the ability to inhibit the α-amylase significantly increased during oral digestion, remaining constant throughout digestion. Correlation analysis indicated that flavonoids, including quercetin, may be the compounds with the greatest effect on the evaluated activities. The results of this study not only improve the understanding of the impact of gastrointestinal digestion on the bioaccessibility of phenolic compounds but also suggest potential applications in formulating functional foods with enhanced antioxidant, hypoglycemic, and antidiabetic properties, contributing to the development of health-promoting food products.

Predicting the evolution of texture and grain size during deformation and recrystallization of polycrystals using field fluctuations viscoplastic self-consistent crystal plasticity

This paper advances a recent formulation of a field fluctuations viscoplastic self-consistent (FF-VPSC) crystal plasticity model to predict not only the evolution of texture in polycrystalline metals undergoing deformation and recrystallization but also the evolution of grain size. The model considers stress and lattice rotation rate fluctuations inside grains to calculate intragranular misorientation spreads. The spreads are used for modeling of grain fragmentation during deformation and grain nucleation during recrystallization enabling the predictions of concomitant evolution of texture and grain size distributions. The evolutions of textures and grain size distributions are first simulated for commercially pure Cu undergoing severe plastic deformation (SPD) in high pressure torsion to agree well with corresponding experimental data. Next, the evolution of texture and grain size in an aluminum alloy (AA) 5182-O after simple tension and static recrystallization are predicted and compared with experiments. Finally, the predictions of texture and grain size distributions in a magnesium alloy WE43 undergoing a thermo-mechanical loading in the dynamic recrystallization regime are presented and compared with experiments. After validation, the model is coupled with the implicit finite element method (FEM) via a user-material subroutine (UMAT) in Abaqus to facilitate modeling of complex boundary conditions and geometries. The multilevel approach is referred to as FE-FF-VPSC in which every integration point embeds the FF-VPSC constitutive law, considering texture evolution and the directionality of deformation mechanisms operating at the single crystal level. FE-FF-VPSC is applied to simulate a sequence of rolling, recrystallization, and deep drawing of a circular cup of AA6022-T4. The simulated processing sequence demonstrates the versatility of the simulation framework developed in the present paper in not only predicting texture and grain size evolution and phenomena pertaining to behavior of materials but also geometrical shape changes important for the optimization of metal forming processes. To this end, the effects of initial texture and underlying anisotropy on the formation of earing profiles during deep drawing are simulated and discussed.

Dependencies of Simulated Convective Cell and System Growth Biases on Atmospheric Instability and Model Resolution.

This study evaluates convective cell properties and their relationships with convective and stratiform rainfall within a season-long convection-permitting weather research and forecasting simulation over central Argentina using radar, satellite, and radiosonde measurements from the RELAMPAGO-CACTI field campaign. The simulation slightly underestimates radar-estimated rainfall over the ∼3.5-month evaluation period but underestimates stratiform rainfall by 46% and overestimates convective rainfall by 43%. As convective available potential energy (CAPE) increases, the convective rainfall overestimation decreases, but the stratiform rainfall underestimation increases such that the contribution of convective to total rainfall remains constantly high biased by ∼26%. Overestimated convective rainfall arises from the simulation generating 2.6 times more precipitating convective cells (14,299) than observed by radar (5,662) despite similar observed and simulated cell growth processes, with relatively wide cells contributing mostly to excessive convective rainfall. Relatively shallow cells, typically reaching heights of 4-7km, contribute most to the cell number bias. This cell number bias increases as CAPE decreases, potentially because cells and their updrafts become narrower and more under-resolved as CAPE decreases. The gross overproduction of precipitating shallow cells leads to overly efficient precipitation and inadequate detrainment of ice aloft, thereby diminishing the formation of robust stratiform rainfall regions. Decreasing model horizontal grid spacing from 3 to 1 or 0.333km for low (<300Jkg-1) and high CAPE (>1,000Jkg-1) cases results in minimal change to cell number, depth, and convective-to-stratiform partitioning biases. This suggests that improving prediction of these convective properties depends on factors beyond solely increasing model resolution.

Boxy/peanut shaping of a mature galactic bar in action-angle space

We study vertical resonant trapping and resonant heating of orbits. These two processes both lead to the growth of a boxy/peanut-shaped bulge in a typical $N$-body model. For the first time, we study this by means of the action variables and resonant angles of the actual orbits that compose the model itself. We used the resonant angle instead of the frequency ratio, which allowed us to clearly distinguish between these two processes in numerical simulations. We show that trapping and heating occur simultaneously, at least at the stage of a mature bar, that is, some orbits quickly pass through vertical resonance while at the same time, a substantial number of orbits remains trapped into this stage for a long time. Half of all bar orbits spend more than 2.5 Gyr in vertical resonance over an interval of 4 Gyr. Half of the orbits trapped into the bar over the last 3 Gyr of simulation remain captured in vertical resonance for more than 2 Gyr. We conclude that in the later stages of the bar evolution, the process of vertical trapping dominates in the ongoing process that causes the boxy/peanut shape of a bar in a typical $N$-body model. This contradicts the results of several recent works.

SN1987A constraints to BSM models with extra neutral bosons near the trapping regime: U(1)Lμ−Lτ model as an illustrative example

New physics beyond the Standard Model (BSM) with an extra neutral boson can be constrained from the observation of SN1987A, since productions of this neutral boson in a supernova (SN) could accelerate the SN cooling and potentially lead to a period of the neutrino burst incompatible with the observation. The constraint to the model is formulated by the condition LNB≤3×1052 erg/s according to Raffelt with LNB the luminosity of BSM neutral boson. Computing the above luminosity in the large coupling case, the so-called trapping regime, is nontrivial since the luminosity is a competition between the large production rate and the efficient absorption or decay rate of the neutral boson. We illustrate such a subtlety using U(1)Lμ−Lτ model as an example where the Z′ luminosity, LZ′, from the neutrinosphere is calculated. We calculate Z′ production, absorption, and decay rates through pair-coalescence, semi-Compton, loop-bremsstrahlung from proton-neutron scattering, and their inverse processes in a benchmark SN simulation with muons. We point out that, as the coupling constant gZ′ increases, LZ′ shall be approaching to a constant plateau value for a given mZ′ instead of monotonically decreasing down to zero as obtained in the previous literature. We demonstrate that this plateau phenomenon can be understood by physical arguments and justified by numerical calculations. With a different result on LZ′ from the previous one, we discuss impacts on the constraints to U(1)Lμ−Lτ parameter space by SN1987A. The implication of our result to the similar constraint on a generic BSM model with an extra neutral boson is also discussed. Published by the American Physical Society 2024

A novel conceptual model coupling crop growth and soil water-heat-salt processes in arid area

In arid farmland, the soil water, heat, and salt movement tightly couple with crop growth. Accurately expressing the coupling relationships is essential to understanding the complex agricultural hydrological system and enhancing agricultural water productivity. A novel conceptual model coupling crop growth, soil water-heat-salt movement, and energy balance in arid area with shallow groundwater was developed which has potential for use in large heterogeneous irrigation districts. The model can calculate the crop-soil system through the effect of crop canopy and leaf area index (LAI) on potential evapotranspiration and the stress of soil moisture, temperature, and salinity status to root water uptake. The energy balance equation was used for calculating the upper boundary condition for soil temperature. The model was calibrated and validated using four years of field monitoring data for two crops located in a typical arid agricultural area in China. The model performed well in simulated field hydrology and crop growth processes. The model can capture soil water-heat-salt dynamics and model field evapotranspiration with RMSE below 1.14 mm/day, and crop transpiration with R2 of above 0.61. Furthermore, the model can accurately describe crop growth processes with R2 of 0.95 and RMSE of 0.49 for LAI, and R2 of 0.99, RMSE of 12.95 cm for crop height. With few parameters, our work supplies an alternative method for quantifying agricultural hydrological processes. In particular, the model has potential to simulate the regional crop growth and soil water-heat-salt processes for heterogeneous agricultural area. This method is helpful in determining the scientific irrigation management schedule.

Bubbles and crashes: A tale of quantiles

Periodically collapsing bubbles, if they exist, induce asymmetric dynamics in asset prices. In this article, I show that unit root quantile autoregressive models can approximate such dynamics by allowing the largest autoregressive root to take values below unity at low quantiles, which correspond to price crashes, and above unity at upper quantiles, that correspond to bubble expansions. On this basis, I employ two unit root tests based on quantile autoregressions to detect bubbles. Monte Carlo simulations suggest that the two tests have good size and power properties, and can outperform recursive least‐squares‐based tests. The merits of the two tests are further illustrated in three empirical applications that examine Bitcoin, US equity and US housing markets. In the empirical applications, special attention is given to the issue of controlling for economic fundamentals. The estimation results indicate the presence of asymmetric dynamics that closely match those of the simulated bubble processes.