In a radial bed, the uniformity of the pressure drop distribution is investigated by Euler single-phase flow and porous media models under different operating mode (CF-U/Z, CP-U/Z), gas flow rate ...(120–240 m
3
/h), particle diameter ((0.5–3)exp-3 m) and bed voidage (0.3–0.6). According to the nonuniform index
η
, the uniformity relates to these parameters and improves with increasing total pressure drop of particle bed Δp
s
(sum of the pressure drops of particle bed and gas perforation) or decreasing main channel pressure drop Δp
g
. Comparing the flow fields with/without particles, Δp
s
is approximately equal to the pressure drop of the particle bed with high-porosity Johnson net, which is well calculated by the Ergun equation. Δp
g
can be calculated by the modified momentum equation containing k. After changing the wall shear stress and gas-solid axial resistance, it is found that the internal generation factors for k include the influence of gas perforation on boundary layer and the existence of gas axial velocity after perforation. Besides, the global/local k hardly changes with the investigated parameters. The local k is a function of axial position or velocity ratio, which changes obviously at the end of the main channel for the existence of a gas stagnation zone.
As an emerging business model, live broadcast e-commerce is growing rapidly in China in recent years and prompts the emergence of network anchors, attracting the customers to buy a variety of goods ...in their live broadcasts. In this paper, we take Li Jiaqi, one of most popular live streaming anchors in China as example, collect and transcribe his speech data of live broadcasts to build live broadcast speech-text corpus, and then conduct corpus-based analysis on linguistic characteristics from the aspects of phonetic, usage of various language units, and rhetoric ways, by using the methods and tools from Phonetics, Natural Language Processing, and Corpus Linguistics. Based on the linguistic analysis, we propose the hypothesis that features in the live broadcasts can have some effects on purchase intention of customers, and testify it with questionnaire survey.
Doubly fed induction generators (DFIG) find extensive application in variable-speed wind power plants, providing notable advantages such as cost-effectiveness, operational flexibility across varying ...speeds, and enhanced power quality. This research focuses on the control of DFIGs employed in variable-speed wind turbine configurations. A suitable mathematical model is chosen for representative systems following a comprehensive review of contemporary research. Subsequent analysis reveals the instability of the open-loop time response of the system. To address this instability, the initial approach involves the implementation of the conventional model predictive controller (MPC). However, the outcomes indicate that this controller falls short of delivering satisfactory performance despite the enhanced stability. In the subsequent phase, efforts are made to mitigate the impact of wind input variability by utilizing the Kalman filter, given its effectiveness in handling high variability. Following this, a novel methodology is introduced, which combines nonlinear MPC with the Lyapunov function. This method is based on the nonlinear model of the system. By using the Lyapunov function in the nonlinear MPC structure, the stability of the designed controller is guaranteed. To validate the proposed control approach, the results are compared with PID based controller in MATLAB/Simulink. The simulation results showed that the output variables of the modeled DFIG system achieve stability within a reasonable timeframe applying the input.
In order to reveal the pollution characteristics and sources of heavy metals in surface soil of the region around the Qinghai Lake in Tibet Plateau, improve the prevention awareness and measures of ...local residents and urge the local government to implement necessary prevention and control measures, nine heavy metals (As, Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn) in the surface soil samples of the region around the Qinghai Lake have been collected and analyzed. The methods such as statistic method, geo-accumulation index method, Nemerow index method, potential ecological risk index method, human health risk evaluation method and positive matrix factor analysis model (PMF) have been used to evaluate pollution characteristics and potential risks and analyze the sources of heavy metals. The results are shown below. First, the average contents of heavy metals (As, Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn) in soil are 11.73 ± 3.78, 0.62 ± 1.40, 12.38 ± 3.68, 41.35 ± 13.01, 19.33 ± 8.92, 546.96 ± 159.28, 21.18 ± 7.04, 21.86 ± 6.61 and 63.51 ± 19.71 mg·kg−1, respectively. Compared with the background values of the soil environment in Qinghai Province, it can be seen that there is an accumulation of these heavy metals to varying degrees, which is the most serious in Cd, Co and Pb. Second, the analysis of the geo-accumulation index and Nemerow index indicates that the heavy metals in the surface soil of the region around the Qinghai Lake have reached the level of heavy pollution, mainly polluted by Cd, and the accumulation of heavy metal pollution in the north, south, southwest and southeast of the study area is more serious. Third, the results of potential ecological risk evaluation show that the study area as a whole is classified as an area with high ecological risk, and Cd contributes the most to the overall risk. In fact, the heavy metals in the soil of the study area produce no noncarcinogenic and carcinogenic health risks to human health, and children and adults may be exposed to these risks by the mouth. Finally, the PMF results reveal that the sources of heavy metals in the study area include the sources of agricultural production, the nature, coal burning and transportation, with a contribution rate of 43.10%, 25.34%, 19.67% and 11.89%, respectively.
The current study investigated the combinatorial effect of cyclic strain and electrical stimulation on neural differentiation potential of rat bone marrow-derived mesenchymal stem cells (BMSCs) under ...epidermal growth factor (EGF) and fibroblast growth factor 2 (FGF2) inductions
in vitro
. We developed a prototype device which can provide cyclic strain and electrical signal synchronously. Using this system, we demonstrated that cyclic strain and electrical co-stimulation promote the differentiation of BMCSs into neural cells with more branches and longer neurites than strain or electrical stimulation alone. Strain and electrical co-stimulation can also induce a higher expression of neural markers in terms of transcription and protein level. Neurotrophic factors and the intracellular cyclic AMP (cAMP) are also upregulated with co-stimulation. Importantly, the co-stimulation further enhances the calcium influx of neural differentiated BMSCs when responding to acetylcholine and potassium chloride (KCl). Finally, the phosphorylation of extracellular-signal-regulated kinase (ERK) 1 and 2 and protein kinase B (AKT) was elevated under co-stimulation treatment. The present work suggests a synergistic effect of the combination of cyclic strain and electrical stimulation on BMSC neuronal differentiation and provides an alternative approach to physically manipulate stem cell differentiation into mature and functional neural cells
in vitro
.
To determine the permeability characteristics and the groundwater enrichment conditions of loess and paleosol layers, this article systematically investigated the permeability, magnetic ...susceptibility, porosity, and carbonate mass percentage of representative loess-paleosol layers (L1 to S5) on the Bailu tableland in the Chinese Loess Plateau south. The result of in situ permeability measurements showed that the average time to reach quasi-steady infiltration of loess layers is shorter than that of paleosol layers. In addition, loess layers have higher porosity and better water storage spaces than paleosol layers and were prone to form aquifers. Paleosol layers, on the contrary, are more likely to form aquitards. The difference between loess and paleosol in permeability, porosity and groundwater enrichment conditions is largely attributed to lower intensity pedogenesis of loess, which is in turn ascribed to the colder and drier palaeoclimatic conditions. It is worth mentioning that the CaCO3 concretion layer is a good aquifuge for its compact structure. Generally, the empirical formula of the Koctakob formula is applicable for describing the permeability rule of loess and paleosol layers, and the parameters of the empirical formulas can provide an important reference for hydrological and agricultural departments. In this regard, the Quaternary climatic change theory can contribute to the hydrogeology of the Chinese Loess Plateau, and the regional climatostratigraphy can be regarded as a baseline for local water resource positioning and revegetation in such a semi-arid area, which broadens the application field of Quaternary climatic change theory. Meanwhile, it also provides a reference path for solving water shortages of other loess distribution areas in China and other countries.
•A new compound parallel flow shell and tube heat exchanger is proposed.•The thermal-hydraulic performance of five different configurations is compared.•The effects of geometric parameter on ...thermal-hydraulic performance are discussed.
A new compound parallel flow STHX with CPB and LVG is proposed. Firstly, the turbulent thermal performance and flow structure of STHX with five different configurations of LVG are compared numerically. The effect of serrate, hole and layout on thermal-hydraulic performance is discussed. Secondly, the thermal performance of the selected configuration is further investigated using RSM analysis. The effect of geometric parameters on thermal-hydraulic performance is illustrated. Finally, the obtained results are compared with those of the previous configurations. The results show that the baseline configuration has the best thermal performance; the increase of the LVG height and LVG attack angle can improve the heat transfer performance and overall thermal-hydraulic performance. The LVG pitch has a complicate effect on the thermal performance. The LVG may have a broader application prospect in terms of thermal-hydraulic performance and manufacturing cost compared with the sinusoidal wavy tape and wire coil.
•Analyzing the rotational–perforated static mixer (RPSM) mixing images using three equal parts of the pixel.•Coefficient of variation (CoV) time series is proposed to calculate largest Lyapunov ...exponent (LLE).•Backward installations can enter the chaotic mixing state earlier than forward installations.•The chaotic advective behavior is divided into the isolated mixing area, poor mixing area and good mixing area.
Chaotic advection is an important reason for laminar fluids to enter the chaotic mixing state. The flow images obtained by Planar Laser Induced Fluorescence (PLIF) were calculated as the coefficient of variation (CoV), mixing index, and the largest Lyapunov exponent (LLE) with CoV time series. The effect of the number of spatial periods (P) formed by the rotational–perforated static mixer (RPSM) on the chaotic advection behavior was investigated in combination with grayscale images, and the mixing areas were divided according to the position as well as visually described. The results showed that increasing the number of spatial periods accelerated the formation of chaotic advection. The chaotic mixing effect of backward installation was more pronounced than that of forward installation. The near-wall areas had the deepest degree of chaotic mixing, in which the minimum CoV was 0.043 and the maximum LLE was 1.242, reaching a uniform chaotic mixing state.
•There are rotational flow, flow through one perforation and flow through two perforations in a tridimensional rotational flow sieve tray (TRST).•The main characteristic of the flow through one ...perforation is the conversion between rotational liquid film and perforated liquid column.•The flow through two perforations has a more prominent shear effect on the fluid.•The flow through one perforation in the liquid phase was dominant, and the rotational flow in the gas phase was dominant.•The proportions of rotational flow and flow through perforations in coupled state in the TRST are determined.
Tridimensional rotational flow sieve trays (TRST) have a variety of gas–liquid flow structures, such as rotational flow, flow through one perforation and flow through two perforations, it is important to have a deep understanding of the coupling and distribution laws of rotational flow and flow through perforations for the selection and regulation of actual working conditions. In this study, the flow structures and proportions for the rotational–perforated coupling flow in a TRST were analyzed and predicted using the measured distribution ratio for the three-blade unit. The results showed that the gas phase mainly flowed in a rotational pattern, and its proportion was approximately 62%–83%. The proportion of flow through perforations in the liquid phase was relatively large, and the proportion of flow through one perforation was approximately 51%–57%. The proportion of flow through two perforations was approximately 27%–29%.
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