Electrocatalytic hydrogen evolution of highly dispersed Pt/NC nanoparticles derived from porphyrin MOFs under acidic and alkaline medium

Platinum (Pt)-based electrocatalysts often exhibit an excellent electrocatalytic activity for hydrogen evolution due to their best hydrogen bonding energy, but materials with high Pt content can easily cause aggregation and reduce their efficiency. In this article, Pt-based electrocatalysts with uniform dispersion and high efficiency were fabricated by a successive hydrothermal and calcination method, and the uniformly distributed Pt nanoparticle was mainly due to the anchoring effect of porphyrin ring in porphyrin MOFs, which made the minimized agglomerations as much as possible in the process of high temperature calcination. The results showed that the optimal Pt/NC-850 could reach current density of 10, 50 and 100 mA cm^?2 with only 17, 82 and 152 mV overpotentials, while the Pt/NC-850 also exhibited a superior stability and durability under acidic medium. Impressively, the Pt/NC-850 also had an excellent activity, good stability and durability under alkaline medium.     

Mesenchymal stem cells and cell-free preparations for treating atopic dermatitis

Atopic dermatitis (AD) is a chronic cutaneous inflammatory disease caused by an interaction between genetic, immune and epidermal barrier factors. Several treatments can be used to treat this disease but there are patients that do not respond to actual drugs. So, there is a need to develop effective therapies for AD. Mesenchymal stem cells (MSCs) are non-hematopoietic multipotent adult progenitor cells with immunomodulatory power and self-regenerating capacity to repair tissue damage, so they could be a potential effective treatment for AD. MSCs-Conditioned Medium (CM) and MSCs-exosomes are cell-free preparation with molecules secreted by stem cells that could be also beneficial for AD. This viewpoint reviews the actual development of MSCs, MSCs-CM and MSCs-exosomes for treating patients with AD.     

Flow field simulation and pressure drop modeling by a porous medium in PEM fuel cells

For proton-exchange membrane fuel cells, the distribution of reactant flow in the stack is critical to the fuel cell's efficiency. The uneven distribution of reactant flow in the stack may cause poor current density, low performance, and material degradation. To understand and accurately predict the flow field in the proton-exchange membrane fuel cell system, the present study aims to develop a simple correlation to analyze the pressure drop in fuel cell stacks. The flow channel in each cell of a stack is treated as a porous medium, and a power-law model is used to approximate the porous medium momentum source term. For the stacks with fewer cell numbers, namely, 1, 5, and 10 cells, the parameters in the power law are established based on the experimental data. Then, a correlation is developed to simulate the flow and predict the pressure drop in the stack with higher cell numbers (ie, 20 and 40 cells). The simulations show that the pressure drop in each cell of a stack is almost invariable, and the average pressure drop decreases with increasing the number of cells. The flow uniformity in the stacks with different cell numbers is evaluated using the dimensionless pressure drop and the pressure drop ratios. It suggests that the lower the cell number, the more uniform the pressure drop. The developed model is conducive to efficiently designing the flow channel for a fuel cell stack with large cell numbers.     

Effects of four multi-compound freezing medium on the quality of red drum (Sciaenops ocellatus) during frozen storage

Taking air freezing (AF) as the reference, the effects of four types of multi-compound freezing medium for cryogenic liquid quick-freezing (immersion freezing, IF) on the freezing rate, quality and myofibrillar protein (MP) denaturation of red drum (Sciaenops ocellatus) fillets during frozen storage (−18°C) from days 0 to 90 were studied. Samples were gathered on days 0, 15, 30, 45, 60 and 90 for analysis. The results showed that IF groups (IF-1: 20% ethanol, 30% propylene glycol, 10% sodium chloride aqueous solution; IF-2: 20% ethanol, 20% propylene glycol, 10% glycerol, 10% sodium chloride aqueous solution; IF-3: 20% ethanol, 20% propylene glycol, 10% polyethylene glycol, 10% sodium chloride aqueous solution; IF-4: 20% ethanol, 20% propylene glycol, 5% glycerol, 5% polyethylene glycol, 10% sodium chloride aqueous solution) significantly shortened the time to cross the formation zone of maximum ice crystals while the freezing rate was 6.13 times higher than the AF group after adding 30% propylene glycol as the freezing medium. Furthermore, compared with the AF group, the IF groups significantly reduced losses in the water-holding capacity, the myofibrillar fragmentation index, microstructure damage, texture characteristics, drip loss and water migration (P < 0.05). In addition, the MP of IF groups had higher maximum transition temperatures (T_max1 and T_max2), total sulfhydryl content, Ca²⁺-ATPase activity and relative α-helix content compared with the AF group. In conclusion, IF could significantly increase the freezing rate of red drum fillets, and slow down quality deterioration and denaturation of MP during frozen storage for 90 days (−18°C). In particular, IF-2 (20% ethanol, 20% propylene glycol, 10% glycerol, 10% sodium chloride aqueous solution) was found to be more suitable for the immersion freezing of marine fish among the four multi-compound freezing medium.     

表面活性剂对电解锌粉形貌的影响

研究氯化铵体系电解制备超细锌粉时,三种典型的表面活性剂对槽电压,锌粉沉积状态和锌粉颗粒大小和形态的影响.结果表明,在锌离子浓度为32g/L.电解液温度为60℃时,非离子表面活性剂吐温-80可以使锌粉颗粒均匀分散,表面活性剂的加入对槽电压影响不大.     

沉积环境分析中地震勘探方法的应用

运用地震勘探方法对地层沉积环境进行了分析 ,对圈定煤田、油汽藏、各类金属非金属矿藏以及地热资源等均具有非常重大的意义 ,并取得了一定的成果     

单体液压支柱制造工艺改进

介绍了化学镀和精密冷拔技术在单体液压支柱制造过程中的应用,用新工艺生产的单体液压支柱通过投放井下试验,证明其性能可靠,效益显著。     

Numerical modeling of hydrofracturing in a multilayer coal seam

The mathematical model of the process for hydrodynamic fracturing in a multilayer coal seam is proposed. The model is based on the equation of continuity and Darcy’s law. The filtration — temperature analogy allows solving the obtained non-linear, non-stationary problem in an axisymmetric statement for the pressure function as the heat-conductivity problem, by the finite-element method. The calculation results yield estimation of the radius of degassing borehole influence zone. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 1, pp. 61–70, January–February, 2006.     

加强管理 降低介耗

重介选矿介子损耗大 ,一直是选煤界难以解决的一个难题 ,现以黑龙江省七台河市桃山和铁东两选煤厂为降低介耗所采取的一系列有效措施为例 ,介绍了介质的质量管理、入料的质量管理到生产工艺改进等方面有效的管理方法 ,分解论述并加以总结。