Natural Ventilation Characterization in a Classroom under Different Scenarios

The COVID-19 pandemic has pointed to the need to increase our knowledge in fields related to human breathing. In the present study, temperature, relative humidity, carbon dioxide (CO2) concentration, and median particle size diameter measurements were taken into account. These parameters were analyzed in a computer classroom with 15 subjects during a normal 90-minute class; all the subjects wore surgical masks. For measurements, Arduino YUN, Arduino UNO, and APS-3321 devices were used. Natural ventilation efficiency was checked in two different ventilation scenarios: only windows open and windows and doors open. The results show how ventilation affects the temperature, CO2 concentration, and median particle diameter size parameters. By contrast, the relative humidity depends more on the outdoor meteorological conditions. Both ventilation scenarios tend to create the same room conditions in terms of temperature, humidity, CO2 concentration, and particle size. Additionally, the evolution of CO2 concentration as well as the particle size distribution along the time was studied. Finally, the particulate matter (PM2.5) was investigated together with particle concentration. Both parameters showed a similar trend during the time of the experiments.

Experimental Study on Hydraulic Conductivity and Resistance in Silty Sediments

Hydraulic conductivity k as a function of void ratio e and particle diameter for silty sediment was experimentally investigated, and an empirical formula for the estimation of hydraulic conductivity was proposed. Seepage resistance for flow in silty sediment was deliberated. Based on the findings of the study, it was concluded that hydraulic conductivity k could be expressed as an exponential function of void ratio e and median particle diameter d50 {3.1 μm < d50 < 87 μm and 0.26 < e < 4}. It was further found that the formula of seepage resistance factor (?), a form of friction factor, varies linearly with Reynolds number (Re) for silty sediments. A family of such λ-Re curves for various particle diameter d50 is presented.

Deformation of Tianjin soft clay and corresponding micromechanism under cyclic loading

The deformation of soft clays under cyclic loading is controlled by microfabric changes. Cyclic triaxial tests, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) were conducted to investigate the deformation and the corresponding micromechanism under cyclic loading. The correlations between the microparameters and deformation of Tianjin soft clay are discussed. The deformation increases linearly in the initial compression stage (number of cycles, N < 500), at a decreasing rate in the later shearing stage (N < 5000), and eventually stabilizes when the cyclic stress ratio (CSR) is 0.30. The probability entropy of both the soil particles and pores have a weak correlation with the deformation on the whole, reflecting a fluctuation within a small range in the initial compression stage. The correlations between the median pore diameter, median particle diameter, and specific surface area and the deformation are validated by using the gray correlation method. More specifically, the specific surface area and the deformation are highly correlated in the initial compression deformation stage. The median pore diameter and median particle diameter are highly correlated with deformation in the later shearing deformation stage.

Patterns of suspended particulate matter across the continental margin in the Canadian Beaufort Sea

The particulate beam attenuation coefficient at 660 nm, cp(660), was measured in conjunction with properties of suspended particle assemblages in August 2009 within the Canadian Beaufort Sea continental margin, a region heavily influenced by sediment discharge from the Mackenzie River. The suspended particulate matter mass concentration (SPM) ranged from 0.04 to 140 g m−3, its composition varied from mineral to organic-dominated, and the median particle diameter ranged determined over the range 0.7–120 μm varied from 0.78 to 9.45 μm, with the fraction of particles

An expert system with radial basis function neural network based on decision trees for predicting sediment transport in sewers

In this study, an expert system with a radial basis function neural network (RBF-NN) based on decision trees (DT) is designed to predict sediment transport in sewer pipes at the limit of deposition. First, sensitivity analysis is carried out to investigate the effect of each parameter on predicting the densimetric Froude number (Fr). The results indicate that utilizing the ratio of the median particle diameter to pipe diameter (d/D), ratio of median particle diameter to hydraulic radius (d/R) and volumetric sediment concentration (CV) as the input combination leads to the best Fr prediction. Subsequently, the new hybrid DT-RBF method is presented. The results of DT-RBF are compared with RBF and RBF-particle swarm optimization (PSO), which uses PSO for RBF training. It appears that DT-RBF is more accurate (R2 = 0.934, MARE = 0.103, RMSE = 0.527, SI = 0.13, BIAS = −0.071) than the two other RBF methods. Moreover, the proposed DT-RBF model offers explicit expressions for use by practicing engineers.

Determination of the runoff threshold for triggering debris flows in the area affected by the Wenchuan Earthquake

We constructed an experiment to determine the critical runoff discharge for debris flow initiation in Wenchuan Earthquake area. A single dimensionless discharge variable was integrated to incorporate influential parameters, including channel width, median particle diameter, and surface flow discharge. The results revealed that relationship with the debris flow density, slope and discharge required. Taking into account the behaviors of debris flow formation corresponding to different ranges of slopes, the critical runoff thresholds for debris flow initiation were calculated for three different scenarios. The thresholds were validated against actual debris flow events, and the use in this study is applicable.

Effects of oxidation reduction potential in the bypass micro-aerobic sludge zone on sludge reduction for a modified oxic–settling–anaerobic process

Batch experiments were conducted to determine the effect of oxidation reduction potential (ORP) on sludge reduction in a bypass micro-aerobic sludge reduction system. The system was composed of a modified oxic–settling–anaerobic process with a sludge holding tank in the sludge recycle loop. The ORPs in the micro-aerobic tanks were set at approximately +350, −90, −150, −200 and −250 mV, by varying the length of aeration time for the tanks. The results show that lower ORP result in greater sludge volume reduction, and the sludge production was reduced by 60% at the lowest ORP. In addition, low ORP caused extracellular polymer substances dissociation and slightly reduced sludge activity. Comparing the sludge backflow characteristics of the micro-aerobic tank's ORP controlled at −250 mV with that of +350 mV, the average soluble chemical oxygen (SCOD), TN and TP increased by 7, 0.4 and 2 times, median particle diameter decreased by 8.5 μm and the specific oxygen uptake rate (SOUR) decreased by 0.0043 milligram O2 per gram suspended solids per minute. For the effluent, SCOD and TN and TP fluctuated around 30, 8.7 and 0.66 mg/L, respectively. Therefore, the effective assignment of ORP in the micro-aerobic tank can remarkably reduce sludge volume and does not affect final effluent quality.

Effect of Reaction Temperature in the Alumina Preparation by Combustion in a Muffle Furnace

The aim of this study is to evaluate the effect of temperature during the synthesis of alumina by combustion in a muffle furnace. The alumina was characterized by X-ray diffraction, particles size distribution and scanning electron microscopy. The results showed that the synthesis temperature of the alumina can affect the structure of the produced samples. The size distribution of the median particle diameter reached higher value for the alumina synthesized at 500°C with 16.07 μm, the range of the total distribution of particles is introduced to the large alumina synthesized 500 and 600°C and close synthesized when 700 and 800°C. The phase of the alumina was identified only after the synthesized sample at 800°C with crystallite size of 22.16 and 6.75 μm synthesized samples 800 and 900°C, respectively. With respect to morphology, increased synthesis temperature was not enough to significantly change.

Development of Conductive and Anticorrosive Paint Dispersed with Carbon Particles for Metal Separators of PEFC

A resin paint dispersed with carbon particles was developed for the purpose of good conductivity and corrosion resistance for metal separators used in Polymer Electrolyte Fuel Cells (PEFC). The use of metal separators, especially Ti separators is a technology which has received much attention for its practical application as it allows for much greater compact stacking, since it is superior in both productivity and strength, in comparison with that of carbon molding separators. However, if pure Ti separators are used in a severe reaction of electricity generation, there is a deterioration in conductivity, because of the formation of a passive film, which subsequently causes electricity generation difficulties after a few hours of use. Through examining the type of resin used for the purpose of controlling the passive state, the grain size of the conductive filler (graphite (Gr) + carbon black (CB)) and the composition combination for the purpose of secure conductivity, it was found that the combination of a scaly graphite-furnaced black mixed powder with a median particle diameter of 4μm and VDF-10%HFP copolymer resin was optimal. As a result of performing a single cell electricity generation evaluation of the Ti separator, which had the above mentioned coating material, the life of 22,000 or more hours was confirmed and an electricity generation evaluation is now being undertaken.

Influences of Microemulsion Cross-linking Reaction and Ball-milling on Particle Size Characteristics of Potato and Maize Starches

In this study, microemulsion cross-linking treatment was used on food grade potato and maize starches for preparing micro starch particles. Laser diffraction technique was introduced to measure the particle size characteristics, including the median particle diameter (d 50), surface area mean diameter D [3, 2], volume mean diameter D [4, 3] and specific surface area of micro potato and maize starch particles. The volume distributions and number distributions were also analyzed using Mastersizer 2000 Software. The d 50, D [3, 2], D [4, 3] of the potato starch granules were reduced significantly (p < 0.05) after the microemulsion cross-linking reaction and ball-milling treatment. However, the microemulsion cross-linking treatment did not produce significant changes in the particle size characteristics of the maize starch samples.