Profiles of Mathematics Anxiety Among 15-Year-Old Students: A Cross-Cultural Study Using Multi-Group Latent Profile Analysis

Using PISA 2012 data, the present study explored profiles of mathematics anxiety (MA) among 15-year old students from Finland, Korea, and the United States to determine the similarities and differences of MA across the three national samples by applying a multi-group latent profile analysis (LPA). The major findings were that (a) three MA profiles were found in all three national samples, i.e., Low MA, Mid MA, and High MA profile, and (b) the percentages of students classified into each of the three MA profiles differed across the Finnish, Korean, and American samples, with United States having the highest prevalence of High MA, and Finland the lowest. Multi-group LPA also provided clear and useful latent profile separation. The High MA profile demonstrated significant poorer mathematics performance and lower mathematics interest, self-efficacy, and self-concept than the Mid and Low MA profiles. Same differences appeared between the Mid and Low MA profiles. The implications of the findings seem clear: (1) it is possible that there is some relative level of universality in MA among 15-year old students which is independent of cultural context; and (2) multi-group LPA could be a useful analytic tool for research on the study of classification and cultural differences of MA

A multi-wavelength mid-IR laser based on BaGa4Se7 optical parametric oscillators

A multi-wavelength mid-IR laser consisting of 3.05 μm, 4.25 μm, and 5.47 μm BaGa4Se7(BGSe)optical parametric oscillators (OPOs) switched by DKDP electro-optic switches with one 10 Hz/7.6 ns pumping wave is demonstrated. Maximum energies at 3.05 μm, 4.25 μm, and 5.47 μm are 1.35 mJ, 1.03 mJ, and 0.56 mJ, respectively, corresponding to optical-to-optical conversion efficiencies of 9.4%, 7.6%, and 4.2%. To the best of our knowledge, this study is the first of generation of three mid-IR wavelength lasers using electro-optic switches. Furthermore, this study provides a viable solution for a high-energy or high-power, compact, or even portable multi-wavelength mid-IR laser device that employs a single pumping wave

Strain hardenability of a gradient metallic alloy under high-strain-rate compressive loading

Subjected to an impact loading, metallic alloys usually display strain softening due to the highly localized shear deformation accompanied by temperature rise, which causes the decrease of resistance to an applied loading and even catastrophic failure. In this work, strain hardening under high-rate compressive loading is firstly achieved in a developed metallic alloy with the gradient microstructure of both phases and grain sizes. Mechanical responses at different compressive loading rates all show a unique strain hardening. Rate dependencies of yielding and strain hardening are revealed and illustrated by a modified Johnson-Cook constitutive model. Dynamic deformation and fracture are characterized as macroscopic shear with the shielded cracks. The inherent toughening mechanisms are indicated as gradient straining with phase transformation, twinning and dislocation tangling. This work demonstrates that the highly localized shear deformation accompanied by temperature rise can be prevented by the gradient microstructure with martensitic transformations, twinnings and dislocations. It is full of interest to create a feasible route of developing the strain hardenable metallic alloys under impact loadings via architecturing the gradient microstructure. (C) 2019 The Authors. Published by Elsevier Ltd

Experimental Study on Flotation of Jianshan Iron Using DDA Assisted with Kerosene

In this study, a comparison of traditional cationic collector dodecylamine (DDA) and miscible DDA-Kerosene to the flotation performance of Jianshan ore was discussed based on the concept of reagent combination that kerosene was used as the auxiliary collector and partly replaced expensive DDA. To explore the relationship between DDA-Kerosene composition and mineral flotation performance on the reverse flotation of Jianshan ore, the characteristics of the flotation product were analyzed. The results showed that the floatability of the floating material increased with the DDA consumption increased. Specifically, during the flotation process, the fine quartz (-0.074 mm fraction) would selectively float with DDA-Kerosene. The results showed that the optimal ratio of dodecylamine was 40%, and kerosene had the most obvious effect. The addition of kerosene significantly increased the recovery of fine -0.038 mm quartz. Through the closed-circuit process test, using dodecylamine and kerosene as the collector, the iron concentrate with TFe grade of 68.57% recovery rate of 96.72% can be obtained. DDA-Kerosene with the characteristic of better selectivity and economy had a good application value in the future

Design of automatic shunt control system in dense-medium separation process

In view of problems of poor accuracy and high medium consumption of manual control of shunt in dense-medium separation process , an automatic shunt control system in dense-medium separation process was designed, and opening prediction model of the shunt valve based on the least squares support vector machines was established. The parameters including suspension density, coal slime content, qualified medium tank level and opening degree of water supply valve are collected by sensors, which are used as input variables of opening prediction model of the shunt valve. Output value of opening degree of the shunt valve is calculated by the model and then is sent to PLC, so as to control operation of the shunt valve and realize automatic shunt control. The application results show that the density fluctuation of suspension liquid can be controlled in the range of ±0.005 g/cm3, and the ton coal dense-medium consumption is reduced by 0.216 kg

Study on Promoting Effect of Carboxylic Acid on Flotation of Low-rank Coal

The surface oxygen content of low rank coal is high and the surface hydrophobicity is poor. It is difficult for diesel oil to adsorb on the coal surface efficiently. The reagent consumption is large and the flotation effect is not ideal. In this paper, diesel oil and carboxylic acid of oleic acid, lauric acid, decanoic acid and octanoic acid were combined to carry out flotation test on Datong Jurassic low rank coal. The results show that the addition of oleic acid, lauric acid and decanoic acid can effectively improve the flotation effect, and oleic acid and lauric acid have the most obvious effect. Compared with diesel oil alone, the oil rate can reach 50%. In addition, the addition of oleic acid and lauric acid can effectively increase the contact angle of coal sample surface and make the coal sample more hydrophobic. The effect of n-decanoic acid is weaker than that of oleic acid and lauric acid. Among the four carboxylic acids with 10% mass fraction and diesel oil, oleic acid has the smallest particle size in slurry, followed by lauric acid; and through XPS analysis, it is found that oleic acid can effectively increase the C-C, C-H hydrophobic oxygen-containing functional groups of coal samples, and reduce the C-O hydrophilic oxygen-containing functional groups. The dispersion of the reagent is improved effectively, and the hydrophilicity of the coal sample is weakened, and the hydrophobicity is enhanced, which improves the flotation effect

General formulas for drag coefficient and settling velocity of sphere based on theoretical law

The settlement of particles is of great importance in many areas. The accurate determination of drag coefficient and settling velocity in wide Reynolds number (Re) range remains a problem. In this paper, a series of new formulas for drag coefficient of spherical particles based on theoretical laws, such as the Stokes law, the Oseen law, and the Goldstein law, were developed and fitted using 480 groups of experimental data (Re < 2 × 105). The results show that the 2nd approximation of a rational function containing only one parameter can describe CD–Re relationship accurately over the whole Re range of 0–2 × 105. The new developed formulas containing five parameters show higher goodness over wide Re range than presently existing equations. The introduction of the Oseen law is helpful for improving the fitting goodness of the empirical formulas. On the basis of one of the Oseen-based CD–Re formulas giving the lowest sum of squared relative errors Q over the whole Re range (Re < 2 × 105), a general formula for settling velocity ut based on dimensionless parameters was proposed showing high goodness. Keywords: Sphere, Drag coefficient, Settling velocity, Reynolds number, Theoretical equatio

Integrated estimation model of clean coal ash content for froth flotation based on model updating and multiple LS-SVMs

Clean coal ash content, a prominent product index describing coal froth flotation, is difficult to be measured online. This constraint leads to a lack of timely guidance during operation and impedes the optimal operation of the coal flotation process. To solve this problem, considering the fluctuation of working conditions, the heterogeneity of raw coal and the variation of feed coal classes, an integrated estimation model of clean coal ash content for coal flotation based on model updating and multiple least squares support vector machines (LS-SVMs) is proposed. First, a single estimation model for a single class of coal based on LS-SVM is built, and the internal parameters are optimized by gravitational search algorithm (GSA). Second, the model updating strategy is designed to solve the problem of the decline in single model accuracy. Furthermore, a multiple LS-SVMs model formed by several single models for different classes of coal is studied along with the model switching mechanism to address the problem of model mismatch. Finally, an industrial experiment and evaluation are conducted. The mean relative error between the estimated and actual values is 3.32%, and the correlation coefficient is 0.9331. The estimation accuracy and adaptability of the integrated model can meet the industrial requirements

Separation and physicochemical properties of residual carbon in gasification slag

Gasification slag is the solid waste produced in the coal gasification process, and its treatment and disposal problems are becoming more and more serious. In this study, the gasification slag produced in a chemical base in northern China and its residual carbon obtained by gravity separation of water medium were taken as the research objects, and their physicochemical properties were analyzed comprehensively. The residual carbon products, ash-rich products and high-ash products were obtained from the gasification slag after gravity separation. Under the optimal structure, the ignition loss of residual carbon products was reduced from 79.80% to 16.84%, and the yield was 11.64%. The high content of amorphous carbon and developed pores in the residual carbon provide the possibility of manufacturing high value-added materials. Raman spectrum showed that the residual carbon had lower aromaticity, higher content of small and medium aromatic ring structures, lower structural stability and easier combustion. Thermogravimetric combustion kinetics showed that the average combustion rate of residual carbon was 0.325(dm/dt)mean/%•min−1, the comprehensive combustion characteristic index was 1.41•10−9%2•min−2•°C−3. It has excellent performance and can be used as a raw material for mixed combustion in a circulating fluidized bed. The analysis of physical and chemical properties of residual carbon is of great significance for follow-up exploration of the resource utilization and high-value utilization of the residual carbon