Structure,mechanical and thermal properties of Y-doped CrAlN coatings

CrAlYN coatings with different Y contents (0, 5 and 12 at.%) were deposited by cathodic arc evaporation to investigate the influence of Y-addition on the structure, mechanical and thermal properties of CrAlN coatings by using X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, thermal gravimetric analysis and nanoindentation. The structural transformation of single phase cubic Cr_0.42Al_0.58N and Cr_0.39Al_0.56Y_0.05N coatings to cubic–wurtzite mixed Cr_0.32Al_0.56Y_0.12N coating leads to a drop in hardness from (30.2±0.7) GPa of Cr_0.42Al_0.58N and (32.0±1.0) GPa of Cr_0.39Al_0.56Y_0.05N to (25.2±0.7) GPa of Cr_0.32Al_0.56Y_0.12N. The incorporation of 5 at.% Y retards the thermal decomposition of CrAlN, verified by the postponed precipitation of w-AlN and N-loss upon annealing. Correspondingly, Cr_0.39Al_0.56Y_0.05N coating consistently exhibits the highest hardness value during thermal annealing. Nevertheless, alloying with Y exerts an adverse effect on the oxidation resistance of CrAlN.     

Effect of wind condition on unintended hydrogen release in a hydrogen refueling station

Ambient condition, especially the wind condition, is an important factor to determine the behavior of hydrogen diffusion during hydrogen release. However, only few studies aim at the quantitative study of the hydrogen diffusion in a wind-exist condition. And very little researches aiming at the variable wind condition have been done. In this paper, the hydrogen diffusion in different wind condition which including the constant wind velocity and the variable wind velocity is investigated numerically. When considering the variable wind velocity, the UDF (user defined function) is compiled. Characteristics of the FGC (flammable gas cloud) and the HMF (hydrogen mass fraction) are analyzed in different wind condition and comparisons are made with the no-wind condition. Results indicate that the constant wind velocity and the variable wind velocity have totally different effect for the determination of hydrogen diffusion. Comparisons between the constant wind velocity and the variable wind velocity indicate that the variable wind velocity may cause a more dangerous situation since there has a larger FGC volume. More importantly, the wind condition has a non-negligible effect when considering the HMF along the radial direction. As the wind velocity increases, the distribution of the HMF along the radial direction is not Gaussian anymore when the distance between the release hole and the observation line exceeds to a critical value. This work can be a supplement of the research on the hydrogen release and diffusion and a valuable reference for the researchers.     

Oceanic-Atmospheric Variability Influences on Baseflows in the Continental United States

Water Resources Management - Baseflows are one of the important components of streamflows and the influences of climate change and variability on changes in baseflows in space and time can aid in...     

Challenges in the CO2 emissions of the Turkish power sector: Evidence from a two-level decomposition approach

Decarbonization of the energy system is urgent to avert the disruptions in the climate. Considering its share, the low carbon transition of the power sector is pivotal. Growing electricity demand poses unique challenges for Turkey to enact deep decarbonization. It is vital to uncover the contributing causes of emissions to provide strategic oversight for carbon management activities. This study investigates key drivers of CO₂ emissions from the power sector using the Logarithmic Mean Divisia Index decomposition method. While efficiency improvement contributes to sustainable yet minor mitigation, changes in the fossil-fuel share indicate a cycling but significant overall impact.     

环评与排污许可相互衔接和促进的思考

近年来,世界范围内的工业化和城市化进程明显加快,环境污染是全球性的危机。在我国的环保工作开展中,环境影响评价和排污许可是有效的环保工作手段,这两种手段的有效配合,分别从准入和运营的角度来实现了污染的有效控制,虽然环境影响评价在我国实施的时间非常长,但是,排污许可却是近年来才出现的,出现时间的不一致导致二者在衔接和促进的过程中面临着较大的困境。因此,针对这一情况,本文充分探析了环评和排污许可相互衔接和促进的策略。     

Bond characteristics,vibrational spectrum and optimized microwave dielectric properties of chemically substituted NdNbO4

Coordination chemistry, bond state and vibrational spectrum of co-substituted microwave dielectric NdNb_1-x(Zr_0.5W_0.5)_xO₄ ceramics (x = 0.01∼0.05) were investigated. Raman spectra and XRD refinement showed a solid solution was formed. The compressed and elongated chemical bonds are responsible for the variations of crystal parameters and cell volume. Calculated chemical bond parameters indicated bond covalency, lattice energy and Nb-site bond energy act on the fluctuations of the permittivity, quality factor and temperature coefficient, respectively. Meanwhile, the infrared vibrational spectrum is fitted to quantify the contributions of observed IR mode to the intrinsic loss. Compact ceramic possesses excellent properties: ε_r ∼ 19.2, Q × f ∼ 55282 GHz and τ_f ∼ -11.36 ppm/°C with x = 0.04, at 1250°C.     

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.     

The prevalence of asthma and severe asthma in children influenced by transportation factors: Evidence from spatial analysis in Seoul,Korea

Although the causes of asthma are inconclusive, it is fairly known that exposure to outdoor air pollutants can cause asthma, especially children's asthma morbidity. Whereas transportation is one of the major sectors that generate air pollutants, previous research that investigates the correlation between transportation and asthma narrowly focuses on the contribution of automobile traffic to children's asthma. Developing three spatial regression models (a spatial lag (SL) model, a spatial error (SE) model, and a general spatial (SAC) model), this paper investigates the roles of a variety of transportation factors in two distinct stages of children's asthma morbidity; asthma and severe asthma. With consideration to asthma-related socio-economic factors in the City of Seoul, the SE (R² = 0.31) and SAC (R² = 0.34) models consistently indicate that three out of four transportation factors associate with children's severe asthma at statistically significant level. They include the negative influence of bus transit and dense intersections, and the positive influence of active transportation activities on children's asthma severity. Interestingly, however, no significant contribution of transportation factors to children's asthma morbidity was identified by the SE (R² = 0.29) and SAC (R² = 0.28) models. Shedding more light on the complexity of children's asthma morbidity and severity, this paper proposes collaborative partnerships not only among multi- dimensional agencies, but also among multi-level government organizations.