On the existence and origin of sluggish diffusion in chemically disordered concentrated alloys

Concentrated single phase solid solutions, including medium- and high-entropy alloys, represent a new class of materials that have recently attracted significant interest due to exceptional functional and structural properties. Their fascinating properties are mainly attributed to the sluggish atomic-level diffusion and transport, but its controlling mechanisms are largely unknown and there is certain skepticism about its very existence. By using microsecond-scale molecular dynamics, on-the-fly and conventional kinetic Monte Carlo, we reveal the governing role of percolation effects and composition dependence of the vacancy migration energy in diffusion. Surprisingly, an increase of concentration of faster species (Fe) in face-centered cubic Ni-Fe alloy may decrease the overall atomic diffusion. Consequently, the composition dependence of tracer diffusion coefficient has a minimum near the site percolation threshold, ～20?at.%Fe. We argue that this coupled percolation and composition-dependent barriers for vacancy jumps within different subsystems in medium- and high-entropy alloys leads, indeed, to the sluggish diffusion. A fast method for preselecting materials with potentially desired properties is suggested.     

Stable controlled growth of 3D CuO/Cu nanoflowers by surfactant-free method for non-enzymatic hydrogen peroxide detection

Sensitive, convenient and rapid detection of hydrogen peroxide(H_2 O_2) is highly desirable in fields like fundamental biological research, food industries, and clinical environmental analysis. Herein, a hierarchical porous CuO/Cu flower-like active electrode material for non-enzymatic H_2 O_2 sensor was synthesized via a low-cost and one-step chemical oxidation of Cu powder in water bath without surfactants. In order to discuss the growth mechanism of the product, products with different growth time length were fabricated. The electro-catalysis of all products were first exhibited by cyclic-voltammetry,and the product under 6 h reaction shows the best result. The detailed electro-catalytic behaviors of the best product(under 6 h reaction) are characterized by cyclic-voltammetry and amperometry under alkaline conditions. The materials have high sensitivity of 103 μA mM~(-1) cm~(-2)(R~2= 0.9979), low detection limit of 2 μmol/L and wide concentration range(from 2 μmol/L to 19.4 mmol/L). Large specific surface area and stabled nanostructure enabled good features, such as stability and sensitivity for the H_2 O_2 determination.     

Activation mechanisms of apatite by purifying reagent polyacrylamide for backwater from mineral processing in flotation of rare earths

This study revealed activation mechanisms of apatite by polyacrylamide (PAM) during flotation of rare earth minerals in Bayan Obo Ore. This activation leads to high phosphorus content in rare earth concentrate. Ultraviolet (UV) absorption measurements show that adsorption of PAM on the surfaces of apatite and rare earths follows a pseudo-second-order reaction kinetic model. The isothermal adsorption process follows the Freundlich adsorption model, indicating that the adsorption of PAM on apatite is a multi-layer, non-uniform process, that is, physical and chemical adsorption occurs simultaneously. The measured zeta potential shows that under weakly alkaline conditions, amide groups with a negative charge are adsorbed on the surface of apatite, increasing the electronegativity, so that the potential is shifted negatively; however, the negative shift of the potential on the surface of rare earths is insignificant. Fourier transform infrared (FT-IR) test and X-ray photoelectron spectroscopy (XPS) results imply that PAM is chemically adsorbed on the surface of apatite, while 506E undergoes stronger chemical adsorption than PAM on the surface of rare earth minerals. It is found that multi-layer, non-uniform adsorption of PAM combining physical and chemical adsorption occurs on the surface of apatite and the process is dominated by physical adsorption: the adsorption of PAM on surfaces of apatite is stronger than that on the surface of rare earth minerals. Such adsorption activates the apatite, causing it to float during the flotation of rare earths, which is the reason for the high phosphorus content in the rare earth concentrate.     

Effect of BaF2 powder addition on the synthesis of YAG phosphor by mechanical method

Here, we report on the effect of BaF₂ powder addition on the mechanical synthesis of Ce³⁺-doped Y₃Al₅O₁₂ (Y_2.97Al₅O₁₂:Ce_0.03³⁺, YAG:Ce³⁺) phosphors for white light emitting diodes. The YAG phosphors were synthesized by the mechanical method using an attrition-type mill. When BaF₂ was added at 6 wt% to the raw powder materials and milled, the synthesis of YAG:Ce³⁺ was favorably achieved at the vessel temperature of 255 °C, which was about 1200 °C lower than the YAG phosphor synthesis temperature by solid-state reaction. The synthesized YAG:Ce³⁺ phosphor revealed the maximum internal quantum yield of 57%.     

Investigation of a double shrouded probe for particle sampling in high velocity airflows

An accurate forecast of the concentration of fine dust in the atmosphere is critical because of the negative public health impacts associated with high concentrations of particulate matter. To achieve an accurate forecast, large volumes of data need to be collected over a wide range of regions to act as forecast model boundary conditions. Therefore, the concentration of fine particles should be measured at both fixed observatories and from a range of moving monitoring stations, including cars, trains, and aviation vehicles. To accurately record particulate concentrations at flow velocities up to 200?km?h^?1, this study proposed a double-shrouded probe design based on the widely used single-shrouded probe. Using the double-shrouded probe, isokinetic sampling for PM_2.5 was achieved at velocities up to 200?km?h^?1, and for PM₁₀ at velocities up to 75?km?h^?1. When flow velocities exceeded these values and particle sizes increased, particulate concentrations were overestimated. However, as compared to the single-shrouded probe, the double-shrouded probe reduced the level of overestimation markedly.     

Investigation of MHD Go-water nanofluid flow and heat transfer in a porous channel in the presence of thermal radiation effect

In this paper, flow and heat transfer of MHD Go-water nanofluid between two parallel flat plates in the presence of thermal radiation are studied. One of plates is externally heated and cooled by coolant injection through the other plate, which also expands or contracts with time. A similarity transformation is used to transmute the governing momentum and energy equations into non-linear ordinary differential equations with the appropriate boundary conditions. The obtained non-linear ordinary differential equations are solved by Duan–Rach Approach (DRA). This method allows us to find a solution without using numerical methods to evaluate the undetermined coefficients. This method modifies the standard Adomian Decomposition Method by evaluating the inverse operators at the boundary conditions directly. The impacts of various parameters such as the Reynolds number, the expansion ratio, the magnetic parameter, the power law index, the solid volume fraction and the radiation parameter are investigated on the velocity and temperature. Furthermore, the value of the Nusselt number is calculated and presented through figures. The results indicate that the temperature profile and the Nusselt number have a direct relationship with the solid volume fraction and have an inverse relationship with the radiation parameter. In addition, the limiting cases are gained and found to be in an excellent agreement with the previous works.     

Thermodynamic criteria for the removal of impurities from end-of-life magnesium alloys by evaporation and flux treatment

Abstract

In this paper, the possibility of removing impurities during magnesium recycling with pyrometallurgical techniques has been evaluated by using a thermodynamic analysis. For 25 different elements that are likely to be contained in industrial magnesium alloys, the equilibrium distribution ratios between the metal, slag and gas phases in the magnesium remelting process were calculated assuming binary systems of magnesium and an impurity element. It was found that calcium, gadolinium, lithium, ytterbium and yttrium can be removed from the remelted end-of-life (EoL) magnesium products by oxidization. Calcium, cerium, gadolinium, lanthanum, lithium, plutonium, sodium, strontium and yttrium can be removed by chlorination with a salt flux. However, the other elements contained in magnesium alloy scrap are scarcely removed and this may contribute toward future contamination problems. The third technological option for the recycling of EoL magnesium products is magnesium recovery by a distillation process. Based on thermodynamic considerations, it is predicted that high-purity magnesium can be recovered through distillation because of its high vapor pressure, yet there is a limit on recoverability that depends on the equilibrium vapor pressure of the alloying elements and the large energy consumption. Therefore, the sustainable recycling of EoL magnesium products should be an important consideration in the design of advanced magnesium alloys or the development of new refining processes.     

Achieving targets for bone and mineral metabolism: the impact of cinacalcet HCl in clinical practice

Achieving the K/DOQI targets for bone and mineral metabolism has proven difficult with the use of vitamin D analogues and phosphate binders. The introduction of cinacalcet HCl provided a new tool with a novel therapeutic mechanism of action. The purpose of this study was to evaluate the effect of the introduction of combination algorithm for managing secondary hyperparathyroidism (SHPT) on phosphorus, calcium, and biointact parathyroid hormone (PTH). The 61 patients who dialyzed in the facility from January 2004 (baseline) and who remained in the facility as of April 2005 (follow-up) were included in the study. In the baseline period, 37 (61%) of the patients received paricalcitol at some time during the 3-month observation period. In the follow-up period, 19% or 31% of the patients received cinacalcet HCl. Of those not receiving cinacalcet HCl, 67% had PTH at or below target, 17% were felt to be noncompliant with oral meds, 7% had low calcium, and 10% either could not get the medication or were not switched to the combination pathway. Compared with the baseline period, the percent of patients who met the PTH target increased from 19.7% to 37.7%, p<0.05. The percent of patients meeting all 4 targets increased from 14.8% to 24.6%, although this did not reach statistical significance. The introduction of cinacalcet HCl into a treatment algorithm for management of SHPT resulted in a significant increase in the percentage of patients achieving the PTH target while maintaining the other mineral metabolism targets.     

Theoretical treatment of the Cherenkov emission contribution to biological effects induced by gamma-rays in microorganisms

The contribution of Cherenkov emission in the formation of photoreactivatable damage (pyrimidine dimers) in E. coli cells has been analyzed. The mean quantity of Cherenkov photons in the wavelength range (200–600) nm produced in a suspension volume unit per absorbed dose unit was calculated by a Monte Carlo method for a point isotropic gamma-ray source with energy up to 30 MeV. The Cherenkov emission spectrum and the dose dependence on gamma-ray energy and the linear dimension irradiated suspension volumes were also obtained. On the basis of this data the magnitude of the photoreactivation effect as a function of gamma-ray energy and suspension volume have been predicted and are compared with experimental results. The role of direct electronic excitation of DNA in the formation of photoactivatable damage in E. coli cells is also discussed.     

膜截留分子量对污水分置式好氧膜生物反应器处理性能的影响

不同截留分子量超滤膜的好氧膜生物反应器研究结果表明,膜的截留分子量越大,膜表面越易出现浓差极化现象,清洗周期缩短;截留分子量对越滤膜水通量的影响随运行时间增加而逐渐减少;截留分子量对好氧膜生物反应器有机物去除性能影响较小;膜截留分子量不同,生物反应器内的MLSS浓度也会明显不同,该现象的确切原因则有待于实验研究来进一步确定。     

Proposal for the measurement of backward and total scattering by mineral particles suspended in water

An experimental procedure for the determination of the specific backscattering and total scattering coefficients of mineral particles suspended in water is described. The procedure combines measurements performed on samples of particles retained in glass-fiber filters and suspended in water, using a dual-beam spectrophotometer provided with an integrating-sphere attachment.     

The effect of the diffusive, composite chromium nitride layers produced by a hybrid surface treatment on the corrosion behavior of AZ91D magnesium alloy

The layers based on chromium nitride were produced on the AZ91D magnesium alloy using a hybrid surface treatment. The treatment consists of nitriding of the chromium-precoated magnesium alloy. The proposed treatment yields diffusive, composite gradient-type chromium nitride layers which are diffusion-bonded to the substrate. The effect of these layers on the corrosion behavior of the AZ91D magnesium alloy was investigated by the potentiodynamic and impedance spectrometry methods. It was found that the formation of the diffusive, composite chromium nitride layers on the AZ91D alloy may result in a significant decrease of the corrosion activity measured by the corrosion potential. This effect is correlated with the layer thickness and becomes significant with relatively thin layers (less than 1 μm thick). Moreover, with the thin layers the impedance modulus is the highest and phase angle has a beneficial character.     

钙离子镁离子共存的纯无机环境中镁方解石介观晶体的形成及其生物学意义

镁方解石介观晶体广泛分布于具有特殊功能的生物矿物中.至今,在排除有机添加剂的参与后合成镁方解石介观晶体仍是一个很大的挑战,同时海洋中镁方解石的形成机理尚不明确.本工作以纯的无定形碳酸钙(ACC)为前驱体,在钙离子镁离子共存的无机环境中控制结晶条件得到了由许多共同结晶取向的纳米晶组成的玉米状镁方解石.在结晶过程中,ACC...     

The gas flux distribution in the XHV chamber of the vacuum primary standard developed by PTB

The ultimate pressure in the XHV calibration chamber of the PTB primary standard CE3, whose operation is based on the continuous expansion of gas, has been reduced by the use of a relatively large orifice area. Thus, the gas density and flux distributions cannot be taken as uniform in the calibration chamber. To eliminate this drawback we examined the gas flux distribution by Direct Simulation using the Monte Carlo method. This paper describes the gas flux distribution over the chamber walls, which was simulated, recorded and related to the idealized conditions. This allows determining the gauge position correction factor K_gi for each of the gauge ports. Using these factors, it is possible to eliminate the systematic deviation of the gas flow parameters from those under the idealized Maxwellian conditions and to improve the uncertainty budget.     

FTIR study of the photocatalytic degradation of gaseous benzene over UV-irradiated TiO2 nanoballs synthesized by hydrothermal treatment in alkaline solution

In this study, photocatalysts of TiO₂ nanoballs were obtained via a hydrothermal treating of commercial P25 in alkaline solution, and then characterized with SEM, XRD, BET and surface photovoltage spectroscopy techniques. The UV-assisted photodegradation of gaseous benzene over P25 and the prepared TiO₂ nanoballs was monitored by an in situ infrared technique. The results demonstrated that the prepared TiO₂ nanoballs in anatase form were more active than commercial P25 in photocatalytic oxidation of gaseous benzene. The promoted activity of the hydrothermal-treated TiO₂ is attributed to the increasing specific surface area and larger band gap induced by the reduced crystallite size. The spectra of FTIR indicated that weakly adsorbed phenol was formed as the reaction progress. Hydroxyl groups on the surface of TiO₂ nanoballs are able to react with photo-produced phenol, which is then retained on the catalyst surface leading to the progressive deactivation of the catalyst in the gas-solid system.     

Electrochemical field effects in biological materials: electro-osmotic dewatering of cancerous tissue as the mechanistic proposal for the electrochemical treatment of tumors

Some recent excellent papers on the electrochemical treatment (ECT) of tumors provide observations for an analysis of this phenomenon from an electrochemical point of view. An attempt is made here to develop the idea that ECT is a case of electro-osmotic dewatering (EOD) of the tumor material with the consequent changes in pH, with the concomitant role of reactions at the electrodes. Some quantitative considerations explaining the role of electrochemical double layers, zeta potential and associated quantities during the electro-osmotic process are outlined. A capsule summary of the factors that may be involved in necrosis of the tumor tissue is given in which the electro-osmotic dewatering at the anode and excess water accumulation at the cathode are the paramount effects, together with the associated pH changes. © 1999 Kluwer Academic Publishers     

The influence of heat treatment on low frequency fatigue crack growth rates for a marine steel tested in air and seawater

A quenched and tempered marine steel has been cooled at different rates after tempering and low frequency fatigue crack growth rates in air and seawater compared. Water quenching was shown to result in significantly lower fatigue crack growth rates compared to furnace cooling. The likely causes and the implications of the results are discussed.