Crystal growth, structure and thermal properties of noncentrosymmetric single crystals PrCa4O(BO3)3+

Noncentrosymmetric praseodymium calcium oxyborate single crystals, PrCa4O(BO3)3 (PrCOB), were grown by the Czochralski technique. The monoclinic unit cell parameters were found to be a = 8.177 Å, b = 16.157 Å, c = 3.629 Å and Z = 2 with space group Cm. Crystal density was measured using the Archimedes method, being on the order of 3.47 g cm-3. Thermal properties of PrCOB were investigated, where the specific heat was found to be 0.63 J g-1 °C-1 at room temperature, increasing to 0.85 J g-1°C-1 at 700°C. The thermal expansion coefficients were measured to be α11 = 7.99, α22 = 4.90 and α33 = 9.46 (10-6/°C), respectively. In addition, thermal diffusivity λ22 and thermal conductivity κ22 as a function of temperature were studied, where λ22 was observed to decrease from 0.89 to 0.58 mm2 s-1, while κ22 was found to maintain the same value, being ∼1.90 W m-1°C-1 over the temperature range of 20-700°C. 2013 The Royal Society of Chemistry

Crystal growth, structure and thermal properties of noncentrosymmetric single crystals PrCa4O(BO3)3

Noncentrosymmetric praseodymium calcium oxyborate single crystals, PrCa4O(BO3)3 (PrCOB), were grown by the Czochralski technique. The monoclinic unit cell parameters were found to be a = 8.177 Å, b = 16.157 Å, c = 3.629 Å and Z = 2 with space group Cm. Crystal density was measured using the Archimedes method, being on the order of 3.47 g cm-3. Thermal properties of PrCOB were investigated, where the specific heat was found to be 0.63 J g-1 °C-1 at room temperature, increasing to 0.85 J g-1°C-1 at 700°C. The thermal expansion coefficients were measured to be α11 = 7.99, α22 = 4.90 and α33 = 9.46 (10-6/°C), respectively. In addition, thermal diffusivity λ22 and thermal conductivity κ22 as a function of temperature were studied, where λ22 was observed to decrease from 0.89 to 0.58 mm2 s-1, while κ22 was found to maintain the same value, being ∼1.90 W m-1°C-1 over the temperature range of 20-700°C. 2013 The Royal Society of Chemistry

The Effect of Organizational Trust on Turnover Intention of Rural Kindergarten Teachers: The Mediating Role of Teaching Efficacy and Job Satisfaction

Recent studies have focused on turnover among rural kindergarten teachers. However, none of these studies have shown a clear connection between turnover intention and organizational trust, although there are studies in other areas showing that organizational trust can affect turnover intention. Drawing on a sample of 330 kindergarten teachers in rural areas, this study explores the mechanism of influence between organizational trust and turnover intention with teaching efficacy and job satisfaction as mediators. We found that organizational trust negatively impacted teachers’ turnover intention, and this relationship was mediated by a significant chain mediating effect of teaching efficacy and job satisfaction. The findings enrich knowledge about turnover among rural kindergarten teachers and inspire us to create a more supportive organizational environment against the backdrop of the COVID-19 pandemic to improve job satisfaction and alleviate turnover among rural kindergarten teachers

Observer-Based Finite-Time H∞ Control of Singular Markovian Jump Systems

This paper addresses the problem of finite-time H∞ control via observer-based state feedback for a family of singular Markovian jump systems (SMJSs) with time-varying norm-bounded disturbance. Firstly, the concepts of singular stochastic finite-time boundedness and singular stochastic finite-time H∞ stabilization via observer-based state feedback are given. Then an observer-based state feedback controller is designed to ensure singular stochastic finite-time H∞ stabilization via observer-based state feedback of the resulting closed-loop error dynamic SMJS. Sufficient criteria are presented for the solvability of the problem, which can be reduced to a feasibility problem involving linear matrix inequalities with a fixed parameter. As an auxiliary result, we also discuss the problem of finite-time stabilization via observer-based state feedback of a class of SMJSs and give sufficient conditions of singular stochastic finite-time stabilization via observer-based state feedback for the class of SMJSs. Finally, illustrative examples are given to demonstrate the validity of the proposed techniques

Study on Surface-Enhanced Raman Scattering Substrate Based on Titanium Oxide Nanorods Coated with Gold Nanoparticles

A 3D surface-enhanced Raman scattering (SERS) substrate based on titanium oxide nanorods (TiOx-NRs) coated with gold nanoparticles (Au-NPs) was fabricated by a simple hydrothermal, no-template process. The nanostructure of TiOx-NRs influenced by the concentrations of hydrochloric (HCl) acid and sodium chloride (NaCl) was studied in detail. The substrate showed the strongest Raman enhancement, when the diameters of Au-NPs were around 40 nm and the gaps of Au-NPs were in the range of 5 nm to 10 nm. The surface electric field of our substrate was examined by finite-different time-domain (FDTD) solutions. Rhodamine 6G (R6G) was chosen as the probe molecule to study the SERS performance of the substrates. The Raman signal of 10−10 M R6G was detected clearly by the substrate with the enhancement factor of 2.64 × 108. All relative standard deviation (RSD) values of the major peaks for R6G were within the scope of 10.4% to 16.7%. The substrate could work efficiently even after immersed in water for one month

Numerical investigation on multi-stage swirl cooling at mid-chord region of gas turbine blades

Compared with the single-stage one, the multi-stage swirl cooling technique has great potential at the mid-chord region of gas turbine blades. Currently, the effect of the chamber structure at the mid-chord region of the blades on the multi-stage swirl cooling is still unknown. In this study, four kinds of the multi-stage swirl chamber models are built: Case 1 has two swirl nozzles and three chambers, and cases 2-4 have six swirl nozzles and seven chambers. Fluid flow and heat transfer characteristics of the coolant in the swirl cooling configurations are numerically investigated. The standard k-epsilon turbulent model is adopted in current study and the Reynolds number of the coolant varies from 12,000 to 52000. The results show that the long swirl chamber in case 1 has negative effect on the performance of the swirl cooling this is because the swirl velocity along the axial direction is gradually reduced and the Nusselt number is decreased remarkably. For cases 2-4, the chambers are separated into several short ones. Therefore, the swirl velocity could keep high value and so is the Nusselt number. Although more swirl chambers could lead to higher pressure loss coefficient, cases 2-4 show better comprehensive thermal performance as compared to case 1. Among the current cases, the swirl chamber structure in case 4 shows the highest cooling effectiveness and obtains more uniform temperature distributions on the external surface of the blade