Mixing Rate Research Articles

Trends of Key Greenhouse Gases as Measured in 2009–2022 at the FTIR Station of St. Petersburg State University

Key long-lived greenhouse gases (CO2, CH4, and N2O) are perhaps among the best-studied components of the Earth’s atmosphere today; however, attempts to predict or explain trends or even shorter-term variations of these trace gases are not always successful. Infrared spectroscopy is a recognized technique for the ground-based long-term monitoring of the gaseous composition of the atmosphere. The current paper is focused on the analysis of new data on CO2, CH4, and N2O total columns (TCs) retrieved from high resolution IR solar spectra acquired during 2009–2022 at the NDACC atmospheric monitoring station of St. Petersburg State University (STP station, 59.88°N, 29.83°E, 20 m asl.). The paper provides information on the FTIR system (Fourier-transform infrared) installed at the STP station, and an overview of techniques used for the CO2, CH4, and N2O retrievals. Trends of key greenhouse gases and their confidence levels were evaluated using an original approach which combines the Lomb–Scargle method with the cross-validation and bootstrapping techniques. As a result, the following fourteen-year (2009–2022) trends of TCs have been revealed: (0.56 ± 0.01) % yr−1 for CO2; (0.46 ± 0.02) % yr−1 for CH4; (0.28 ± 0.01) % yr−1 for N2O. A comparison with trends based on the EMAC numerical modeling data was carried out. The trends of greenhouse gases observed at the STP site are consistent with the results of the in situ monitoring performed at the same geographical location, and with the independent estimates of the global volume mixing ratio growth rates obtained by the GAW network and the NOAA Global Monitoring Laboratory. There is reasonable agreement between the CH4 and N2O TC trends for 2009–2019, which have been derived from FTIR measurements at three locations: the STP site, Izaña Observatory and the University of Toronto Atmospheric Observatory.

Homophily and social mixing in a small community: Implications for infectious disease transmission.

Community mixing patterns by sociodemographic traits can inform the risk of epidemic spread among groups, and the balance of in- and out-group mixing affects epidemic potential. Understanding mixing patterns can provide insight about potential transmission pathways throughout a community. We used a snowball sampling design to enroll people recently diagnosed with SARS-CoV-2 in an ethnically and racially diverse county and asked them to describe their close contacts and recruit some contacts to enroll in the study. We constructed egocentric networks of the participants and their contacts and assessed age-mixing, ethnic/racial homophily, and gender homophily. The total size of the egocentric networks was 2,544 people (n = 384 index cases + n = 2,160 recruited peers or other contacts). We observed high rates of in-group mixing among ethnic/racial groups compared to the ethnic/racial proportions of the background population. Black or African-American respondents interacted with a wider range of ages than other ethnic/racial groups, largely due to familial relationships. The egocentric networks of non-binary contacts had little age diversity. Black or African-American respondents in particular reported mixing with older or younger family members, which could increase the risk of transmission to vulnerable age groups. Understanding community mixing patterns can inform infectious disease risk, support analyses to predict epidemic size, or be used to design campaigns such as vaccination strategies so that community members who have vulnerable contacts are prioritized.

A call for increased surveillance: monitoring the use of hydroxychloroquine to prevent retinopathy

Dear Sir / Madam. Hydroxychloroquine (HCQ) and chloroquine (CQ) are the main drugs used in the control and treatment of malaria. Although the toxicity of these drugs is rare, it has been reported in high-dose ingestions or chronic intravenous administration. Of these retinal manifestations are one of the most common following the poisoning of CQ. A recent study by Melles et al. found that the overall risk of hydroxychloroquine retinopathy is 8.6% after chronic use with higher dose of HCQ dose being associated with a progressively greater risk for incident retinopathy (1). Retinopathy can lead to serious complications in patients; in fact in most patient’s vision loss. In Melles et al’s study, it mostly led to complaints like reading difficulties, diminished vision, missing center vision, glare, hazy vision, light flashes, and metamorphopsia, while some patients were asymptomatic. The majority of patients exhibited a fundoscopic bull's-eye sign. Other signs include paracentral, central, and peripheral visual field loss, which were present in almost all patients. In the early stages of retinopathy, color vision is typically unaffected, but it too begins to be compromised in the later stages. (2) Malaria is endemic in Pakistan. In 2023 pooled malaria prevalence in Pakistan was found to be 23.3%, with Plasmodium vivax, Plasmodium falciparum, and mixed infection rates of 79.13%, 16.29%, and 3.98%, respectively. According to the World Health Organization (WHO), Pakistan is one of the seven countries in the Eastern Mediterranean Region that account for 98% of the total malaria burden in the region. Around 217 million people in Pakistan are at moderate risk of malaria and 63 million are at high risk. Approximately 0.47 million malaria cases and 800 deaths have been reported in 2020(3). The recent rise in climate change-induced flooding and other weather changes, waterborne diseases such as malaria, are also rising leading to higher HCQ use. Furthermore, CQ and HCQ are also being used in treating covid 19(4). This, combined with factors such as lack of surveillance, self-medication practises, and rampant over-the-counter use in Pakistan greatly increase the risk of patients taking improperly high doses of HCQ or CQ and, consequently, suffering from retinopathy. To prevent the HCQ-associated retinal toxicity proper surveillance methods should be employed, and the prescription and distribution of these drugs should be monitored. Patients and physicians prescribing HCQ should be aware of its toxicity risks (5). ---Continue

Analysis of Distribution and Drug Susceptibility Test Results of Pathogenic Bacteria in Diabetic Foot Ulcers.

This study aimed to determine the pathogen distribution and drug susceptibility of diabetic foot wound secretions in a tertiary hospital in a coastal area of southeastern China to guide clinical antibiotic selection. A retrospective analysis was conducted on 212 patients with diabetic foot hospitalized at Xiamen Third Hospital from 2018 to 2023, and foot wound secretions were collected for microbial culture and drug susceptibility testing. Among 212 cases of patients with diabetic foot wound secretions, 163 cases (76.9%) were cultured with pathogenic bacteria, and a total of 207 strains of pathogenic bacteria were cultured, including 75 strains (36.23%) of Gram-positive (G+) bacteria, 118 strains of Gram-negative (G-) bacteria (57.00%), 14 strains of fungi (6.76%), 120 cases of single microorganism infection (73.62%), 43 cases of mixed infection (26.38%), and 15 strains of multidrug-resistant bacteria (7.25%). The top three pathogenic bacteria were Staphylococcus aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa. G+ bacteria were dominated by S.aureus. Drug susceptibility results showed that G+ bacteria were highly susceptible to vancomycin, linezolid, tigecycline, quinupristin/dalfopristin, rifampicin, and furotoxin, and somewhat resistant to penicillin, erythromycin, clindamycin, and cefoxitin. Among G- bacterial infections, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli, and Proteus were the major species. Drug susceptibility testing indicated that carbapenems such as imipenem and ertapenem were the most effective antibacterial drugs against G- strains, followed by amikacin, piperacillin, and tazabactams to which these bacteria were also relatively sensitive, while resistance to penicillins and first-generation cephalosporins increased significantly. We isolated one strain of pathogenic bacteria from a Wagner grade1 ulcer, which was G+ bacteria. In Wagner grade2 ulcers, the distribution of pathogenic bacteria was mainly G+ bacteria. In Wagner grade3 and 4 ulcers, the distribution of pathogenic bacteria was mainly G- bacteria, and the increased rate of mixed infection was mainly due to mixed infection of G+ and G-. Two strains of pathogenic bacteria were isolated at Wagner grade5, which were mixed infections of G+ and G-. Pathogenic bacteria in diabetic foot wounds are predominantly G- bacteria, followed by G+ bacteria. As the Wagner ulcer grade increases, the distribution of pathogenic bacteria changes from G+ bacteria to G- bacteria, and the mixed infection rate increases. G+ bacteria are highly susceptible to vancomycin, linezolid, tigecycline, quinupristin/dalfopristin, rifampicin, and furotoxin, and somewhat resistant to penicillin, erythromycin, clindamycin, and cefoxitin. G- bacteria are more sensitive to the antimicrobial drugs ertapenem, imipenem, amikacin, piperacillin tazobactam, and have high resistance to penicillin and first-generation cephalosporins.

Solar radiation and heat sink impact on fluctuating mixed convective flow and heat rate of Darcian nanofluid: Applications in electronic cooling systems

One of the most effective techniques for electronic-cooling devices involves the use of nanofluid, a substance known for its superior heat transfer capabilities. The main challenge in modern production engineering lies in the efficient cooling of electronic devices. Nanofluids have attracted widespread interest in various technical fields due to their exceptional characteristics, which enable effective cooling of electronic devices while improving energy efficiency. In the field of electronic systems, engineers are exploring the potential of nanofluids in a range of applications and phenomena. Choosing the right heat transfer fluid to dissipate heat is crucial in managing electronic component temperatures. This study examines the effects of heat sinks and thermal radiation on the flow of Darcy-Forchheimer nanofluid over a vertical plate, with the aim of enhancing the thermal durability of electronic components. The governing mathematical model has been refined to accurately represent the physical coefficients. To develop a relevant algorithm in the FORTRAN environment, primitive variables are employed in steady-state and oscillatory models, nanomaterial and heat sink. Outputs are presented numerically and graphically using Tecplot 360, revealing that an increase in heat sink capacity leads to a reduction in surface temperature due to the heat sink's ability to absorb excess thermal energy. The use of porous Darcy-Forchheimer material is shown to lower the fluid temperature. The study also shows that the heat transfer rate decreases with an increase in the heat sink coefficient, and the oscillatory frequency of heat transfer reduces with a decrease in the Prandtl number. Decreasing behavior of heat transfer is depicted for maximum thermophoretic factor due to heat sink impact.

Combustor shape optimization and NO emission characteristics for premixed NH3-CH4 turbulent swirling flame towards sustainable combustion

Ammonia is considered an attractive carbon-free fuel for energy generation in aerospace gas turbine engines. However, ammonia is often used with methane fuel blend due to its low combustion limits. The formation of nitrogen oxides (NOx) during the combustion of ammonia-methane fuel blend is a fundamental problem of interest in the scientific community. To date, there have been several studies of ammonia-methane fuel blend, but none of them have considered the effect of combustor shape on NO emission. In this work, large eddy simulations (LES) are carried out at stoichiometric condition to analyze the flame structure and NO emission characteristics of the ammonia-methane premixed turbulent swirling flame in box and cylindrical shaped combustors. The fuel blend used in this study is 70% ammonia and 30% methane by volume. The LES solver employs a dynamic thickened flame (DTF) combustion model along with Okafor's reduced mechanism, which consists of 43 species and 130 elementary reactions. The flame shape and stabilization are discussed for both combustors, along with the effects of flowfield on the flame. The characteristics of the swirl stabilized flame are illustrated using several time-averaged and instantaneous contours of parameters, including heat release rate, local equivalence ratio, axial velocity, and NO emission. The effect of mixing and reaction rate distribution in the premixed configuration is studied quantitatively, subsequently identifying several flame regions. It is identified from the LES results that the NO emission is 1.6 times higher in the cylindrical combustor compared to the box combustor. While a typical V-shape flame is observed for both combustors, a flame tail also co-exits for the cylindrical combustor. The heat release rate in the flame tail is about 33% higher than the main flame which reignites the unburnt gases for a secondary combustion and generates NO. Thus, a box combustion chamber design is beneficial to minimize the NO emission. The residence time is also analyzed in both combustor to understand the oxidation process and identify the key reaction pathways for NH3/CH4 premixed flames.

Thermal radiation and soret/dufour effects on amplitude and oscillating frequency of darcian mixed convective heat and mass rate of nanofluid along porous plate

The influence of thermal radiations and Soret/Dufour significantly increases the mass and heat transport in material science, geothermal process, chemical rectors and heat exchangers due to temperature and concentration variation of nanoparticles. Main objective is to enhance the amplitude, oscillation and frequency of heat transfer using the Soret and Dufour characteristics in Darcian radiating flow of thermophoretic nanoparticles along vertical porous surface. The dimensionless analysis is performed to develop the convenient form of governing thermodynamic Darcian nanofluid formulation. To develop the programming algorithm in FORTRAN language, the primitive variable formulation is used for both time-dependent and steady models. The numerical and graphical outcomes of primitive type equations under boundary conditions are explored by using implicit finite difference approach with Gaussian elimination scheme. Various pertinent parameters are used to elaborate the steady fluid velocity, surface temperature and steady concentrated nanoparticle volume fraction. Valuable novelty of current research is to use steady results for fluctuating shear stress, fluctuation heating rate and fluctuating mass rate. It is found that the influence of Soret and Dufour parameter enhances the fluid velocity and temperature distribution with maximum variations. It is noticed that the temperature distribution enhances as thermal radiation parameter increases. The oscillation and transient stability of heating rate enhances with prominent variations as thermal radiation and Soret/Dufour parameter increases. It is depicted that amplitude in shear stress and mass rate enhances as Soret and Dufour parameter enhances.

Dynamic contact networks of residents of an urban jail in the era of SARS-CoV-2

BackgroundIn custodial settings such as jails and prisons, infectious disease transmission is heightened by factors such as overcrowding and limited healthcare access. Specific features of social contact networks within these settings have not been sufficiently characterized, especially in the context of a large-scale respiratory infectious disease outbreak. The study aims to quantify contact network dynamics within the Fulton County Jail in Atlanta, Georgia. MethodsJail roster data were utilized to construct social contact networks. Rosters included resident details, cell locations, and demographic information. This analysis involved 6702 male residents over 140,901 person days. Network statistics, including degree, mixing, and dissolution (movement within and out of the jail) rates, were assessed. We compared outcomes for two distinct periods (January 2022 and April 2022) to understand potential responses in network structures during and after the SARS-CoV-2 Omicron variant peak. ResultsWe found high cross-sectional network degree at both cell and block levels. While mean degree increased with age, older residents exhibited lower degree during the Omicron peak. Block-level networks demonstrated higher mean degrees than cell-level networks. Cumulative degree distributions increased from January to April, indicating heightened contacts after the outbreak. Assortative age mixing was strong, especially for younger residents. Dynamic network statistics illustrated increased degrees over time, emphasizing the potential for disease spread. ConclusionsDespite some reduction in network characteristics during the Omicron peak, the contact networks within the Fulton County Jail presented ideal conditions for infectious disease transmission. Age-specific mixing patterns suggested unintentional age segregation, potentially limiting disease spread to older residents. This study underscores the necessity for ongoing monitoring of contact networks in carceral settings and provides valuable insights for epidemic modeling and intervention strategies, including quarantine, depopulation, and vaccination, laying a foundation for understanding disease dynamics in such environments.Top of Form

Multi-objective optimization and energy efficiency improvement for rotor duct in integrated energy recovery-pressure boost device

To reduce the volumetric mixing rate of the integrated energy recovery-pressure boost device, a novel symmetrical duct structure with diversion surface was proposed. The surrogate model-based multi-objective optimization framework was established, and obtained the optimal ducts V1 and V2 combined with computational fluid dynamics simulation. Numerical results indicate that optimized duct structure could promote the formation of plug flow and effectively improve the collision efficiency between high-pressure brine and low-pressure seawater, and the volumetric mixing rate corresponding to the ducts V1 and V2 was reduced by 31.52% and 22.18%, and the duct volume efficiency was increased by 16.04% and 19.56%, respectively. Finally, the performance of optimized device was verified through seawater reverse osmosis desalination system under actual working conditions. Experimental results showed that the mixing rate of optimized ducts had a significant decrease of 30.86% and 20.53% in the applicable range, and the energy recovery efficiency improved at most 5.41% and 7.55%, respectively. The optimized ducts could significantly reduce the specific energy consumption of the desalination system by 26.01% and 18.22%, respectively, and the specific energy consumption reached the lowest level of 3.02 kWh/m3, demonstrating the superiority of the structure and the accuracy and effectiveness of the optimization strategy.

Microscale Chaotic Mixing as a Driver for Chemical Reactions in Porous Media.

Mixing-induced reactions play a key role in a large range of biogeochemical and contaminant transport processes in the subsurface. Fluid flow through porous media was recently shown to exhibit chaotic mixing dynamics at the pore scale, enhancing microscale concentration gradients and controlling mixing rates. While this phenomenon is likely ubiquitous in environmental systems, it is not known how it affects chemical reactions. Here, we use refractive index matching and laser-induced fluorescence imaging of a bimolecular redox reaction to investigate the consequence of pore scale chaotic mixing on the reaction rates. The overestimation of measured reaction rates by the classical macrodispersion model highlights the persistence of incomplete mixing on the pore scale. We show that the reaction product formation is controlled by microscale chaotic mixing, which induces an exponential increase of the mixing interface and of the reaction rates. We derive a reactive transport model that captures experimental results and predicts that chaotic mixing has a first order control on reaction rates across a large range of time scales and Péclet and Damköhler numbers. These findings provide a new framework for understanding, assessing, and predicting mixing-induced reactions and their role on the fate and mobility of environmental compounds in natural porous media.

Combined Effects of Banana Peels and Pith as Dual Natural Plant-Based Coagulants for Turbidity Removal

Combined Effects of Banana Peels and Pith as Dual Natural Plant-Based Coagulants for Turbidity Removal

Development and preliminary application of a quadruplex real-time PCR assay for differential detection of porcine circovirus 1-4 in Chengdu, China.

Porcine circovirus (PCV) typically causes severe immune suppression in pigs, leading to mixed clinical infections with various pathogens that can cause significant harm to the pig industry. PCV has four subgenotypes, with PCV4 being an emerging virus that requires investigation due to its potential for epidemic outbreaks. Therefore, there is a need to develop a method that can detect all four PCV strains simultaneously. In this study, four pairs of specific primers and TaqMan probes were designed based on the conserved sequence of the PCV1-4 ORF2 gene to establish a PCV1-4 TaqMan multiplex real-time quantitative PCR method. The novel method was compared to six commercial testing kits for its efficacy. Then, a total of 595 mixed samples of spleen and lymph node collected from 12 districts in Chengdu from July to December 2021 were tested using the novel method. The results showed that the novel PCV1-4 TaqMan multiplex real-time quantitative PCR detection method has satisfied specificity, sensitivity, and repeatability. The positive rates of PCV1, PCV2, and PCV3 in Chengdu were 2.18%, 31.60%, and 15.29%, respectively, while no positive PCV4 was detected. The mixed infection rate of PCV2 and PCV3 was 5.21%. Our novel method may be as a potential method for PCV1-4 detection. Currently, PCV2 is the main epidemic PCV subtype in Chengdu, while the potential threat of PCV4 should also be considered.

The Impact of Varying Mixing Rates in a Surfactant-Free Fuel Emulsion Mixer on the Efficiency and Emissions of a Diesel Engine

The research focuses on water diesel emulsion (WDE), a topic that has captivated researchers for an extended period. While previous studies predominantly employed surfactants to enhance mixing efficiency, their non-economic feasibility in transportation logistics has prompted a shift in recent investigations. This study presents experiments utilizing a cost-effective WDE comprising 15% water and a mixer devoid of surfactants to investigate the impact of mixer blade rotation on engine performance, fuel consumption, and NOx emissions. NOx emission tests were conducted under a constant engine speed of 2,000 rpm and a 75% load (3,23 kW). The optimal brake-specific fuel consumption (BSFC) for the 15% WDE fuel occurred at a blade rotation speed of 3,000 rpm, resulting in a 1% power reduction (from 4,41 kW to 4,38 kW), a 13.3% decrease in BSFC (from 694,98 gr/kW.h to 602,52 gr/kW.h), and a 30% reduction in NOx emissions (from 54 ppm to 38 ppm). This discovery holds promise for future advancements in green energy applications within the transportation sector.

CAVITATION PROCESSES IN THE MULTIPORT BALL VALVE SYSTEMS

Valves are essential components of a fluid management system, and their proper functioning is critical to ensuring the system's efficiency and durability. Multiport ball valves are versatile and commonly used in various industries to control fluid flows. These valves have multiple ports or outlets, allowing for different flow paths and configurations. One of the key considerations when using multiport ball valves is the flow characteristics within the valve itself. The flow within multiport ball valves is governed by several factors, including the design of the valve and the pressure drop across it. Understanding the flow behavior in multiport ball valves is crucial for optimizing their performance and ensuring efficient fluid handling. Different flow paths and configurations in multiport ball valves result in varying flow characteristics. For example, in a three-way multiport ball valve, there are typically two inlet ports and one outlet port. The flow can be diverted from one inlet to the outlet, or it can be split between the two outlets. This flow behavior is influenced by the presence of a constant throttling channel in the valve design.The constant throttling channel helps regulate the flow rate through the valve, and its size and shape can impact the flow characteristics. Additionally, the flow behavior in multiport ball valves can be further influenced by factors such as the material properties of the valve and the flow conditions. Furthermore, the overall flow behavior in multiport ball valves can have an impact on mass transfer and chemical reactions in the system. Different flow patterns and configurations within multiport ball valves can affect the mass transfer and transport characteristics in a system. For example, if the flow is not well-distributed or if there are areas of stagnant flow, it can lead to uneven mixing and reaction rates. Keywords: Multiport ball valve, cavitation, fluid characteristics, control of cavitation processes.

Effect of mixing rate on molecular structure parameters of polybutadiene rubber based on rheology

Effect of mixing rate on molecular structure parameters of polybutadiene rubber based on rheology

Effect of fluid properties on intensification of heat transfer process in oil-water droplet flow in a T-shaped microchannel

Droplet-based microfluidics refers to the production and utilization of micrometer-sized droplets. This technology has found widespread applications in drug delivery, biotechnology, disease prevention, chemical analysis, cell research, and functional material synthesis. Cooling of high heat flux electronic systems and hot spots is another application of the droplet flow which is focused by the current work. In this paper, formation and hydrothermal performance of oil droplets in water flow in a T-junction microchannel is studied by a 3D numerical simulation. Effects of different parameters such as surface tension, wettability and heat flux on the droplet size, heat transfer rate and pressure drop are investigated. It is observed that the shear between the discrete and continuous phases results in recirculating zones in both phases which contribute to improved mixing and heat transfer rates. Liquid film thickness adjacent to the heated surface and the droplet velocity are two other factors that positively affect the heat transfer. Decreasing the surface tension is shown to enhance the heat transfer rate. Moreover, an optimum value is found for the contact angle as 135° at which a 23 % heat transfer enhancement is achieved. Results also indicate that droplet size decreases with increase of contact angle while it slightly increases with increase of the surface tension and negligibly varies with the applied heat flux.

Investigating hydrodynamic cavitation as an efficient means for removal of per- and polyfluoroalkyl substances from solution

With nearly five decades of per- and polyfluoroalkyl substances (PFASs) being associated with firefighting and industrial activities, these compounds inevitably accumulate in both ground and surface water. PFAS contamination in water has emerged as a significant environmental and public health concern, particularly perfluorooctanesulfonic acid (PFOS), which is often found in higher concentrations compared to other PFAS and has more pronounced adverse health effects. Addressing PFAS contamination requires treating large volumes of water, making technologies that rapidly separate and concentrate PFASs highly favoured. The strong surface activity of PFAS, such as PFOS, enables them to generate colloidal gas aphrons (CGAs) during high shear mixing of their aqueous solutions, where PFASs can be separated and collected as foam. This study aims to evaluate the effectiveness of high shear mixing in separating PFOS from solution, leveraging its accumulation at air–water interfaces. High shear-assisted PFOS separation was tested by varying parameters like rotational speed (4000 to 10,000 rpm), mixing time (30 s to 30 min), and the effect of electrolytes. Results showed greater PFOS separation in the presence of electrolytes, particularly monovalent cations like Na+, compared to divalent cations such as Ca2+, due to the creation of more stable CGAs with smaller sizes. At a mixing rate of 6000 rpm, 85 % of PFOS was removed in 30 s from a highly contaminated PFOS solution (10 mg/L), with over 95 % separation after 5 mixing cycles. While high-shear mixing was efficient in PFOS separation from highly contaminated solutions it was less efficient for low-level contaminated solutions (less than 1 mg/L). These results suggest that hydrodynamic cavitation induced by high-shear mixing seems promising for enhancing the separation of PFOS from heavily contaminated solutions. This technique could serve as a standalone method or be integrated with other PFAS removal technologies to enhance the overall efficiency of PFAS removal from polluted water sources.

A mixing index for uniformly and gap-graded cohesionless particles influenced by mixing rate and diameter of stirring rods

Soil mechanics, sometimes, deals with the mixing of soil such as in deep mixing of soil and mixing of soil in tunnel boring machines, i.e., earth pressure balance (EPB-TBM) shields. The geometry of mixing apparatus such as size of stirring rods plays an important role to achieve higher degree of mixing. Moreover, the effect of gap-graded particles being mixed on degree of mixture should also be evaluated. It is important to estimate the extent of mixing of the soil to confirm the required performance of such phenomenon.This study aims to propose a simple method to quantify the degree of mixture of solid particles stirred by rotation of rods with varying diameters at different mixing rates. Discrete element method (DEM) is used to simulate the stirring process and evaluate the degree of mixture at each rotation based on the spatial distribution of different types of particles. To reduce complexity in the mixing process of particles, this study focuses on monodispersed (i.e., uniformly graded) and bidispersed (i.e., narrowly gap-graded) spherical particles where inter-particle cohesion is not considered. The DEM results reveal spatial variation of the degree of mixture (dm) in the given volume; however, its mean (dm¯) increases with the rotation number of stirring rods. Besides, dm¯ depends on the size of stirring rods whereas the mixing rate is less sensitive to dm¯ for the non-cohesive sandy particles. The dm¯ of narrowly gap-graded particles cases is slightly on the lower side as compared to that of uniformly graded particles. The results of the DEM simulations are validated through the model test.

Changing clinical characteristics of pediatric inpatients with pneumonia during COVID-19 pandamic: a retrospective study

BackgroundThe COVID-19 pandemic have impacts on the prevalence of other pathogens and people’s social lifestyle. This study aimed to compare the pathogen, allergen and micronutrient characteristics of pediatric inpatients with pneumonia prior to and during the COVID-19 pandemic in a large tertiary hospital in Shanghai, China.MethodsPatients with pneumonia admitted to the Department of Pediatric Pulmonology of Xinhua Hospital between March-August 2019 and March-August 2020 were recruited. And clinical characteristics of the patients in 2019 were compared with those in 2020.ResultsHospitalizations for pneumonia decreased by 74% after the COVID-19 pandemic. For pathogens, virus, mycoplasma pneumoniae (MP) and mixed infection rates were all much lower in 2020 than those in 2019 (P < 0.01). Regarding allergens, compared with 2019, the positive rates of house dust mite, shrimp and crab were significantly higher in 2020 (P < 0.01). And for micronutrients, the levels of vitamin B2, B6, C and 25-hydroxyvitamin D (25(OH)D) in 2020 were observed to be significantly lower than those in 2019 (P < 0.05). For all the study participants, longer hospital stay (OR = 1.521, P = 0.000), milk allergy (OR = 6.552, P = 0.033) and calcium (Ca) insufficiency (OR = 12.048, P = 0.019) were identified as high-risk factors for severe pneumonia by multivariate analysis.ConclusionsThe number of children hospitalized with pneumonia and incidence of common pathogen infections were both reduced, and that allergy and micronutrient status in children were also changed after the outbreak of the COVID-19 pandemic.

Direct Numerical Simulation of Mixed Convection Flow in Lid-Driven Cavities

The mixed convection of heat transfer and fluid flow in a - lid drivencubical cavity filled with air is investigated numerically in this study. The computational procedure is based on the finite volume method and a full multigrid acceleration solver. The top wall of the cavity is maintained at a constant high temperature - Th, and it can move with a constant velocity U0. The bottom wall is immobile and maintained at a cold temperature Tc. While, the remaining boundary parts of the cavity are motionless and kept thermally insulated. Several numerical simulations were conducted to investigate mixed convection heat transfer in a sliding cubical cavity for a range of Reynolds numbers from 1000 to 5000 and Richardson numbers from 0.001 to 10. The influence of mixed convection parameters, Reynolds number, Richardson number, and heat transfer rate on the flow behavior was analyzed through parametric studies. The results include flow and heat transfer characteristics, iso-surfaces, and streamlines for the entire range of Richardson numbers and Reynolds numbers investigated. The study shows that as Reynolds number is increased beyond a critical value, the flow becomes unstable and bifurcates.