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A PhOLED with lower operating voltage and power efficiency was demonstrated by combining an np-type C60/MoO3 hole-injecting layer with a doping-free ultrathin phosphorescent emitter based on an interfacial exciplex strategy.

Co–Cu ferrite is a promising functional material in many practical applications, and its physical properties can be tailored by changing its composition. In this work, Co1−xCuxFe2O4 (0 ≤ x ≤ 0.3) nanoparticles (NPs) embedded in a SiO2 matrix were prepared by a sol–gel method. The effect of a small Cu2+ doping content on their microstructure and magnetic properties was studied using XRD, TEM, Mossbauer spectroscopy, and VSM. It was found that single cubic Co1−xCuxFe2O4 ferrite was formed in amorphous SiO2 matrix. The average crystallite size of Co1−xCuxFe2O4 increased from 18 to 36 nm as Cu2+ doping content x increased from 0 to 0.3. Mossbauer spectroscopy indicated that the occupancy of Cu2+ ions at the octahedral B sites led to a slight deformation of octahedral symmetry, and Cu2+doping resulted in cation migration between octahedral A and tetrahedral B sites. With Cu2+ content increasing, the saturation magnetization (Ms) first increased, then tended to decrease, while the coercivity (Hc) decreased continuously, which was associated with the cation migration. The results suggest that the Cu2+ doping content in Co1−xCuxFe2O4 NPs plays an important role in its magnetic properties.

Background The outbreak of Coronavirus Disease is causing considerable acute risk to public health and might also have an unanticipated impact on the mental health of children and adolescents in the long run. This study collected data during the national lockdown period in China and aims to understand whether there is a clinically significant difference in anxiety, depression, and parental rearing style when comparing adolescents from Wuhan and other cities in China. This study also intends to examine whether gender, grade in school, single child status, online learning participation, parents’ involvement in COVID-19 related work, and parents being quarantined or infected due to the disease would lead to clinically significant differences in anxiety and depression. Beyond that, this study explored the pathways among the different variables in order to better understand how these factors play a part in impacting adolescents’ mental health condition. Results Results showed that there was a statistically significant difference in anxiety symptoms between participants who were from Wuhan compared to other urban areas, but not in depressive symptoms. In addition, participants’ grade level, gender, relative being infected, and study online have direct positive predictive value for depressive and anxiety symptoms, whereas location and sibling status have indirect predictive value. Having relatives who participated in COVID-19 related work only had positive direct predictive value toward depression, but not anxiety. Conclusions This study discovered several risk factors for adolescents’ depression and anxiety during the pandemic. It also called for a greater awareness of Wuhan parents’ mental wellbeing and recommended a systematic approach for mental health prevention and intervention.

Co-Cu ferrite is a promising functional material in many practical applications, and its physical properties can be tailored by changing its composition. In this work, Co

The internal convective heat transfer characteristics of n-decane at supercritical pressure in a vertical square tube with a hydraulic diameter of 1.8 mm were experimentally investigated. The external wall temperatures of the square tube were measured with welded thermocouples whereas the internal wall temperatures were calculated with space marching method. In this experiment, the operating pressure ranged from 3 to 5 MPa and the heat flux from 100 to 500 kW/m2. Besides, the flow direction in the vertical tube was also switched in order to examine the effects of buoyancy. Moreover, the circumferential uniformity of heat transfer was also discussed. The results showed that the effects of buoyancy on the heat transfer were negligible once the local buoyancy number was less than a threshold. After the threshold, the buoyancy promoted the heat transfer in the downward flow configuration, but weakened the heat transfer in the upward flow one. The reason could be inferred that the buoyancy would influence the intensity of turbulent kinetic energy and the heat transfer near the wall. Finally, new heat transfer correlations for vertical upward and downward flow in square tubes were proposed.

In modern turbine blade designs, a large number of internal cooling technologies have been developed and blade curvature is one of the most important factors. This paper numerically simulates the heat transfer process of the internal cooling channel with flat plate and wall curvature at the trailing edge and analyses Nu distribution and deviation between these two structures. The results show that due to the disruptive and reorganising effects of blade curvature on the vortex structure, blade curvature strengthens the heat transfer. There are significant heat transfer differences at the individual surface of each path.

Background: The outbreak of Coronavirus Disease is causing considerable acute risk to public health and might have an unanticipated impact on the mental health of children and adolescents in the long run. This study aims to understand whether there is a clinically significant difference in anxiety, depression, and parental rearing style when comparing adolescents from Wuhan and other cities in China. This study also intends to examine whether gender, grade in school, single child status, online learning participation, parents' involvement in COVID-19 related work, and parents being quarantined or infected due to the disease would lead to clinically significant differences in anxiety and depression. Beyond that, this study explored the pathways among the different variables in order to better understand how these factors play a part in impacting adolescents' mental health condition. Results: Results showed that there was a statistically significant difference in anxiety symptoms between participants who were from Wuhan compared to other areas, but not in depressive symptoms. In addition, participants’ grade level, gender, relative being infected, and study online have direct positive predictive value for depressive and anxiety symptoms, whereas location and sibling status have indirect predictive value. Having relatives who participated in COVID-19 related work had positive direct predictive value only toward depression, but not anxiety.Conclusions: This study discovered several risk factors for adolescents’ depression and anxiety during the pandemic. It also called for a greater awareness of Wuhan parents’ mental wellbeing and recommended a systematic approach for mental health prevention and intervention.

Accepted for publication in a forthcoming issue of International Journal of Heat and Mass Transfer.

At supercritical pressure, due to the drastic change of thermophysical property near the pseudo-critical temperature, the density fluctuation and density variation, along with buoyancy, play an important role in supercritical turbulence modelling. Based on the original LS (Launder–Sharma) low-Reynolds number turbulence model, the buoyancy modification, the density fluctuation modification, the density variation modification and the empirical coefficients modification are considered and the corresponding correction terms are derived and applied in the governing equations. Numerical simulation of heat transfer to hydrocarbon fuel flowing through the uniformly heated round pipe at supercritical pressure has been performed by the modified LS turbulence model incorporated into the in-house numerical code. Inlet temperature varied from 373 K to 473 K, with heat flux varying from 241 kW/m2 to 470 kW/m2. Inlet mass flux was 736 kg/(m2⋅s) and operating pressure was 4 MPa. The flow directions included upflow and downflow. Compared with the original LS turbulence model, the modified LS turbulence model leads to the better agreement with the experimental results, with 41.16% improvement in computation accuracy in the current study. The consideration of density fluctuation and density variation effects makes the turbulence model more suitable for thermophysical property variation at supercritical pressure.

This article presented a numerical investigation of supercritical heat transfer of the hydrocarbon fuel in a series of horizontal tubes with different diameters. The Reynolds averaging equations of mass, momentum and energy with the LS low-Reynolds number turbulence model have been solved using the pressure-based segregated solver based on the finite volume method. For the purpose of comparison, a four-species surrogate model and a ten-species surrogate model of the aviation kerosene RP-3 (Rocket Propellant 3) were tested against the published experimental data. In the current study, the tube diameter varied from 2 mm to 10 mm and the pressure was 3 MPa with heat flux to mass flux ratios ranging from 0.25 to 0.71 kJ/kg. It was found that the buoyancy has significant effect on the wall temperature non-uniformity in the horizontal tube. With the increase of the diameter, the buoyancy effect enhances and the thermal-induced acceleration effect reduces. The buoyancy effect makes wall temperature at the top and bottom generatrices of the horizontal tube increase and decrease, respectively. Due to the coupled effect of the buoyancy and thermal-induced acceleration caused by the significant change of the properties, as the diameter increases, the heat transfer deteriorates dramatically at the top generatrix but remains almost unchanged at the bottom generatrix at high heat flux to mass flux ratio. Heat transfer enhancement is observed at low heat flux to mass flux ratio when the tube diameter is less than 6 mm. Moreover, the safety analysis has been performed in order to optimally design the supercritical cooling system.

Pyrolysis and pyrolytic coking of hydrocarbon fuel have significant influences on the regenerative cooling process. In this article, a three-dimensional (3D) model is developed for numerically investigating the flow and heat transfer of pyrolytically reacted n-decane with pyrolytic coking in the engine cooling tube under supercritical pressure. The one-step global pyrolytic reaction mechanism and the kinetic coking model are incorporated into the numerical model to simulate the pyrolysis and pyrolytic coking process of n-decane. The numerical method is validated based on the good agreement between the current predictions and the experimental data. Numerical studies of the characteristics of pyrolysis and surface coking rate at the start time under various outer wall heat fluxes from 1.2 to 1.8 MW/m2 have been conducted under 5 MPa. Results reveal that heat flux has huge effects on the pyrolytic reaction and the distribution of pyrolytic coking rate. In order to better understand the complicated unsteady p...

A new empirical correlation for upward flowing supercritical aviation kerosene RP-3 in the vertical tubes is proposed. In order to obtain the database, numerical simulation with a four-component surrogate model on RP-3 and LS low Reynolds turbulence model in vertical circular tube has been performed. Tubes of diameter 2mm to 10mm are studied and operating conditions cover pressure from 3MPa to 6MPa. Heat flux is 500KW/m2, mass flow rate is 700kg/(m2·s). The numerical results on wall temperature distribution under various conditions are compared with experimental data and a good agreement is achieved. The existing correlations are summarized and classified into three categories. Three representative correlations of each category are selected out to evaluate the applicability in heat transfer of supercritical RP-3. The result shows that correlations concluded from water and carbon-dioxide do not perform well in predicting heat transfer of hydrocarbon fuel. The mean absolute deviation of them is up to 20% and predict about 80% of the entire database within 30% error bands. So a new correlation which is applicable to different working conditions for supercritical RP-3 is put forward. Gnielinski type has been adapted as the basis of the new correlation for its higher accuracy. In consideration of major influence factors of supercritical heat transfer, correction terms of density and buoyancy effect are added in. The new correlation has a MAD of 9.26%, predicting 90.6% of the entire database within ±15% error bands. The comparisons validate the applicability of the new correlation.

The present study pays attention to the pressure effect and geometric effect on heat transfer deterioration onset to supercritical hydrocarbon fuel. Numerical simulation about heat transfer deterioration of hydrocarbon fuel flowing upward in vertical round tubes with various diameter at supercritical pressure was performed. In the simulation, a four-species surrogate model of RP-3 based on the generalized corresponding states law was used and LS low-Reynolds number eddy viscosity turbulence model was selected. For the boundary conditions, inlet temperature was 623K, pressure ranged from 3 to 4MPa, tube diameter varied from 3 to 9mm, and wall heat flux to mass flux ratio changed from 0.07 to 3.18kJ/kg. Comparative analyses between the predicted results and the experimental data revealed the accuracy of thermophysical property model and numerical method. The results indicated that the operating pressure and tube diameter have significant effect to the heat transfer deterioration onset of supercritical hydrocarbon fuel: heat transfer deterioration aggravates and heat transfer deterioration onset moves upstream when the diameter increases. With the increase of operating pressure, heat transfer deterioration becomes weak and the heat transfer deterioration onset moves downstream. Based on current results, several existing correlations of the heat transfer deterioration onset were reviewed and assessed, showing different prediction performance. A new correlation of the threshold value for the ratio between heat flux and mass flux for determining the boundary for heat transfer deterioration under various tube diameter and operating pressure was obtained. The effect of length to diameter ratio on safety margin was discussed. The present study provides the optimization design of regenerative cooling on reducing heat transfer deterioration.

A variety of turbulence models were used to perform numerical simulations of heat transfer for hydrocarbon fuel flowing upward and downward through uniformly heated vertical pipes at supercritical pressure. Inlet temperatures varied from 373 K to 663 K, with heat flux ranging from 300 kW/m2 to 550 kW/m2. Comparative analyses between predicted and experimental results were used to evaluate the ability of turbulence models to respond to variable thermophysical properties of hydrocarbon fuel at supercritical pressure. It was found that the prediction performance of turbulence models is mainly determined by the damping function, which enables them to respond differently to local flow conditions. Although prediction accuracy for experimental results varied from condition to condition, the shear stress transport (SST) and launder and sharma models performed better than all other models used in the study. For very small buoyancy-influenced runs, the thermal-induced acceleration due to variations in density lead to the impairment of heat transfer occurring in the vicinity of pseudo-critical points, and heat transfer was enhanced at higher temperatures through the combined action of four thermophysical properties: density, viscosity, thermal conductivity and specific heat. For very large buoyancy-influenced runs, the thermal-induced acceleration effect was over predicted by the LS and AB models.