Upconversion nanoparticles: Recent strategies and mechanism based applications

Upconversion nanoparticles (UCNPs) doped with lanthanides can convert near-infrared excitation into UV and visible emissions. Because of their relatively high emission efficiency, UCNPs are appealing materials for use in a variety of sectors. UCNPs are known for low auto-fluorescence, excellent chemical and thermal photo-stability, deep tissue penetration, exceptional biocompatibility, low toxicity, color purity, and ease of surface functionalization. In this review, we explain a few recent strategies to boost the efficiency and luminescence of upconversion nanoparticles and minimize quenching by fabricating them as core/shell, nanofibers, or heavily doped lanthanides. Applications of UCNPs in drug delivery, Photodynamic therapy (PDT), biosensors, bioimaging, and optogenetics are also discussed along with their mechanism of action. Our motivation for this review is to understand the working mechanism of UCNPs and their applications in various fields.     

A mathematical model for open pit mine production scheduling with Grade Engineering® and stockpiling

This paper presents the development and implementation of an innovative mixed integer programming based mathematical model for an open pit mining operation with Grade Engineering framework. Grade Engineering comprises a range of coarse-separation based pre-processing techniques that separate the desirable (i.e. high-grade) and undesirable (i.e. low-grade or uneconomic) materials and ensure the delivery of only selected quantity of high quality (or high-grade) material to energy, water, and cost-intensive processing plant. The model maximizes the net present value under a range of operational and processing constraints. Given that the proposed model is computationally complex, the authors employ a data pre-processing procedure and then evaluate the performance of the model at several practical instances using computation time, optimality gap, and the net present value as valid measures. In addition, a comparison of the proposed and traditional (without Grade Engineering) models reflects that the proposed model outperforms the traditional formulation.     

Recent activities in the field of Nuclear Operational Management and Nuclear Safety Engineering

Recent activities in the field of Nuclear Operational Management and Nuclear Safety Engineering, the studies related to risk analysis methodology, design, and operational management, physical phenomena, and emergency preparedness and nuclear security, have been progressed. Especially, ‘risk analysis methodology’ and ‘design and operational management’ are the main categories of the field, in which more than half of published articles on Journal of Nuclear Science and Technology are related to these categories.     

Advances in statistical mechanics of rock masses and its engineering applications

To efficiently link the continuum mechanics for rocks with the structural statistics of rock masses,a theoretical and methodological system called the statistical mechanics of rock masses(SMRM)was developed in the past three decades.In SMRM,equivalent continuum models of stressestrain relationship,strength and failure probability for jointed rock masses were established,which were based on the geometric probability models characterising the rock mass structure.This follows the statistical physics,the continuum mechanics,the fracture mechanics and the weakest link hypothesis.A general constitutive model and complete stressestrain models under compressive and shear conditions were also developed as the derivatives of the SMRM theory.An SMRM calculation system was then developed to provide fast and precise solutions for parameter estimations of rock masses,such as full-direction rock quality designation(RQD),elastic modulus,Coulomb compressive strength,rock mass quality rating,and Poisson’s ratio and shear strength.The constitutive equations involved in SMRM were integrated into a FLAC3D based numerical module to apply for engineering rock masses.It is also capable of analysing the complete deformation of rock masses and active reinforcement of engineering rock masses.Examples of engineering applications of SMRM were presented,including a rock mass at QBT hydropower station in northwestern China,a dam slope of Zongo II hydropower station in D.R.Congo,an open-pit mine in Dexing,China,an underground powerhouse of Jinping I hydropower station in southwestern China,and a typical circular tunnel in Lanzhou-Chongqing railway,China.These applications verified the reliability of the SMRM and demonstrated its applicability to broad engineering issues associated with jointed rock masses.     

Influence of lanthanum on enhancement of mechanical and electrical properties of Cu-Al_2O_3 composites

Two kinds of Cu-Al_2O_3 composites(with and without La) were prepared via mechanical alloying-spark plasma sintering(MA-SPS) method. Microstructure, mechanical properties and electrical resistivity were investigated systematically using metallography, scanning electron microscopy, transmission electron microscopy, mechanical and electrical properties testing. The results indicate that an appropriate amount of La can homogenize the distribution of Al_2O_3. As such, yield strength, ultimate tensile strength and elongation of Cu-Al_2O_3-La are greatly increased. Some semi-coherent interface between Cu and Al_2O_3 is found, which means a low interface energy. The grain shape of Cu changes to irregular band with the addition of La. This change results in a density decrease of grain boundary and reduces electrical resistance. Lanthanum may exist in the form of La_2O_3.     

Drilling machinability of engineering ceramics under low-frequency axial vibration processing by sintering/brazing composite diamond trepanning bit

Thin-wall diamond trepanning bits are extensively used for processing hard and brittle materials such as engineering ceramics. However, it is difficult to achieve high-efficiency processing of engineering ceramics at a constant feed speed, because of high dynamic compressive strength, high hardness, and low density of engineering ceramics. In this study, a novel composite diamond bit combining sintering and brazing has been designed, along with the low-frequency axial vibration technology, to realize the continuous hole processing of engineering ceramics. Drilling experiments have been conducted on Al₂O₃ and SiC engineering ceramics with a constant feed speed. The variation of axial force, micromorphology of hole wall surface drilled, as well as the method of removing nesting during the drilling process were analyzed. According to the results, the novel composite diamond bit fabricated by combining sintering and brazing, can achieve the continuous hole processing of engineering ceramics at a constant feed speed, including Al₂O₃ and SiC. Compared to the conventional drilling (CD), the low-frequency axial vibration drilling (LFVD) can significantly reduce the axial force, and produce fewer plastic scratches on the hole wall surface drilled. In particular, the automatic blanking ratio approaches to 100% by LFVD, and only about 73.58% by CD. It can be concluded that LFVD technology can be used to realize continuous hole processing of engineering ceramics. The research results achieved in this study show that the drilling machinability of engineering ceramics by LFVD and novel composite diamond bit is good. Accordingly, this study provides a useful reference for continuous processing or batch production of engineering ceramics at a constant feed speed.     

Development of a void ratio-moisture ratio-net stress framework for the prediction of the volumetric behavior of unsaturated granular materials

Despite extensive research on the behavior of unsaturated fine-grained materials, there is still a lack of understanding of the volumetric behavior of unsaturated granular materials. In this research, a model has been developed to predict the fundamental volumetric behavior of unsaturated granular materials through loading and wetting state paths. In this regard, a loading-wetting surface was developed in a space of void ratio-moisture ratio-net stress. A distinctive feature of the proposed model is the relative simplicity in obtaining the model parameters using conventional geotechnical testing equipment. Two types of recycled granular materials, commonly applied in unbound pavements were used, namely, recycled crushed brick (CB) and excavation waste rock (WR). The uniqueness of the developed surface was evaluated by employing a number of loading and wetting state paths. The results indicate that the developed surface is unique in its loading state paths; however, it only shows uniqueness in its wetting state paths for stress levels greater than 2000 kPa. The proposed model seeks to introduce the application of the unsaturated soil mechanics theory, for predicting the behavior of granular materials in the field, by providing a practical and cost-effective methodology.     

基于GIS技术的工程地质环境系统构建及治理分析

针对传统的工程地质环境系统存在的收集图像与原始图像同向性较低的问题,以下开展了基于GIS技术的工程地质环境系统的构建研究。采用设计对比实验的方式验证该系统在实际应用过程中,可提升收集图像与原始图像的同向程度。     

Owner’s Risk Allocation and Contractor’s Role Behavior in a Project: A Parallel-mediation Model

Risk allocation decisions are of critical importance in project management. The present study proposes an explanation for how risk allocation in a contract motivates a contractor to cooperate with a project owner. Theories of risk allocation and trust were used to motivate the research. Using a survey methodology, we collected data concerning 124 construction projects in China. We found that risk allocation influenced the contractor’s role behavior through the contractor’s feeling of being trusted but not the contractor’s trust in the owner. Feeling of being trusted partially mediated the effect of risk allocation on the contractor’s in-role (i.e., contractual) behavior and fully mediated the effect on extra-role behavior. The study introduces a social and psychological view of the impacts of risk allocation to the project and engineering management literature. We contribute to theory by arguing and demonstrating the mediating effect of trust on the relationship between risk allocation and contractor behavior. From a practical standpoint, we conclude that contractual risk allocation has a significant impact on building a trusting relationship between owners and contractors and that contractors who feel trusted perform both contractually mandated actions and actions external to the contract more diligently, resulting in the likelihood of improved outcomes for both parties.     

Structural-microstructural characterization and optical properties of Eu3+,Tb3+-codoped LaPO4·nH2O and LaPO4 nanorods hydrothermally synthesized with microwaves

Rhabdophane-type Eu³⁺,Tb³⁺-codoped LaPO₄·nH₂O single-crystal nanorods with the compositions La_0.99999-xEu_xTb_0.00001PO₄·nH₂O (x?=?0–0.03), La_0.99999-yTb_yEu_0.00001PO₄·n′H₂O (y?=?0–0.010), and La_0.99999-zTb_zEu_0.000007PO₄·n′′H₂O (z?=?0–0.012) were hydrothermally synthesized with microwaves. It is shown that the Eu³⁺,Tb³⁺ codoping does not affect the thermal stability of these nanorods, which is due to the formation of substitutional solid solutions with both Eu³⁺ and Tb³⁺ replacing La³⁺ in the crystal lattice. Moreover, it is also shown that monazite-type Eu³⁺,Tb³⁺-codoped LaPO₄ single-crystal nanorods can be obtained by calcining their rhabdophane-type Eu³⁺,Tb³⁺-codoped LaPO₄·(n,n′ or n′′)H₂O counterparts at moderate temperature in air, and that they are thermally stable. It is also observed that, for the same Eu³⁺,Tb³⁺-codoping content, the monazite-type Eu³⁺,Tb³⁺-codoped LaPO₄ nanorods exhibit higher photoluminescent efficiency than the rhabdophane-type Eu³⁺,Tb³⁺-codoped LaPO₄· (n,n′ or n′′)H₂O nanorods. Moreover, it is found that the highest photoluminescence emission corresponds to the monazite-type La_0.96999Eu_0.02Tb_0.00001PO₄ nanorods for the La_0.99999-xEu_xTb_0.00001PO₄ system. However, for those compositions energy transfer from Tb³⁺ to Eu³⁺ does not occur. In addition, for an efficient energy transfer to occur, a content of at least 1?mol% Tb³⁺ is needed in all the studied materials.