Microstructure and wear characteristics of ATZ ceramic particle reinforced gray iron matrix surface composites

The alumina toughened zirconia(ATZ) ceramic particle reinforced gray iron matrix surface composite was successfully manufactured by pressureless infi ltration. The porous preform played a key role in the infi ltrating progress. The microstructure was observed by scanning electron microscopy(SEM); the phase constitutions was analyzed by X-ray diffraction(XRD); and the hardness and wear resistance of selected specimens were tested by hardness testing machine and abrasion testing machine, respectively. The addition of high carbon ferrochromium powders leads to the formation of white iron during solidifi cation. The wear volume loss rates of ATZ ceramic particle reinforced gray iron matrix surface composite decreases fi rst, and then tends to be stable. The wear resistance of the composite is 2.7 times higher than that of gray iron matrix. The reason is a combination of the surface hardness increase of gray iron matrix and ATZ ceramic particles and alloy carbides protecting effect on gray iron matrix.

Simulation and Analysis of Outdoor Microcellular Radio Propagation Characteristics Based on the Method of SBR/Image

In this paper, the outdoor microcellular radio propagation characteristics at 3.5 GHz are simulated and analyzed by the method of SBR/Image (Shooting and bouncing ray tracing/Image). A good agreement is achieved between the results simulated and the results given in published literature. So the correctness of the method has been validated. Some simulated propagation parameters of LOS (Line-of-sight) and NLOS (None-line-of-sight) have been compared. The analysis of the above results provides the foundation for the coverage of outdoor microcellular systems.

金属Ni和Co氧化物与N掺杂的碳球协同作用用于电解水析氧反应

电解水制氢被认为是理想的清洁制氢技术,然而,阴阳两极过电位的存在,特别是阳极析氧反应涉及复杂的四电子转移过程,阳极过电位较高,严重制约了电解水制氢效率的提高.因此,研究发现高效且成本低的析氧反应电催化剂具有重要意义.因此,本课题组利用温和的浸渍-热解策略合成了具有高效析氧活性的Ni/Co3O4与N掺杂的碳复合电催化剂(Ni/Co3O4@NC).其中,第一步浸渍过程将无机Ni与Co源浸渍到聚合物纳米球结构中,可以有效地保证热解过程中产生均匀分散的极细Ni和Co3O4纳米颗粒;此外,高温热解过程形成的N掺杂的碳基质可以有效地阻止活性组分的团聚和交联,调控其电子结构.由于Ni, Co3O4和NC的协同作用,制备得到的Ni/Co3O4@NC电催化剂在碱性溶液中均展现了比由单一金属组成的Co3O4@NC和Ni@NC更优异的析氧活性和稳定性,当电流密度为10 m Acm-2时,所需要的过电位仅为350 m V, Tafel斜率低至52.27 m Vdec-1,电荷转移阻抗极小,双电层电容高达25.53 m Fcm-2.本文采用扫描电镜(SEM),高分辨透射电镜(HRTEM), X射线衍射(XRD)和X射线光电子能谱(XPS)等手段研究了Ni/Co3O4@NC电催化剂的微观结构、元素组成和价态,分析了复合Ni/Co3O4@NC电催化剂具有优异析氧性能的原因.SEM结果表明, Ni/Co3O4@NC电催化剂在经历浸渍-热解过程后,完整地继承了聚合物的纳米球状形貌,只是平均粒径由100 nm缩聚为90 nm左右, SEM mapping显示各元素均匀分散在每一个纳米球结构中.HRTEM结果显示,紧密耦合的Ni和Co3O4超细纳米颗粒均匀分散于纳米球结构中,且碳基质有效地限制了这些颗粒的过度生长及团聚.XRD和XPS结果再次印证Ni/Co3O4@NC是由Ni和Co3O4两种晶体结构构成,此外, XPS结果显示N原子成功掺杂到碳基质中,富电子的N原子掺杂到碳基质中可以有效地调控Ni/Co3O4@NC的电子结构,提高本征电催化活性.相应的催化反应结果表明, Ni/Co3O4@NC相较于单一的Co3O4@NC和Ni@NC析氧活性更高,这是由于Ni与Co3O4协同作用,使Co3O4的Co2+/3+氧化还原峰向阳极偏移,从而增加了Co3O4的本征活性;此外高导电性的Ni掺杂到Ni/Co3O4@NC复合物结构中,提高了催化剂的导电性,加快了电子传输能力;杂原子N的掺杂有效地调控了催化剂的电子结构,提高了催化剂的本征活性.总之, Ni、Co3O4和NC的协同作用使Ni/Co3O4@NC复合物在碱性溶液中具有高效催化析氧性能.该策略为制备杂原子掺杂的负载于高导电碳载体的氧化物基催化剂提供了有益参考.

内皮祖细胞在急性肺损伤中应用的研究进展

急性肺损伤是由各种肺内外因素导致的进行性呼吸困难和难治性低氧血症,其病理特征包括炎症反应及肺泡-毛细血管屏障功能破坏,微循环血管内皮损伤是主要标志。内皮祖细胞可以从骨髓动员迁移到损伤部位,分化为成熟内皮细胞发挥直接修复作用,并通过间接免疫调节作用改善微环境。此外内皮祖细胞还可以分泌细胞因子以自分泌或旁分泌方式促进新生血管生成从而减少器官功能障碍。文章旨在综述内皮祖细胞在急性肺损伤中的应用,从而为治疗急性肺损伤提供新思路。

一款含鲜奶面霜对面部皮肤细菌多样性的影响研究

利用高通量测序技术研究使用一款含鲜奶面霜后对皮肤细菌多样性的影响。通过随机抽取10名使用含鲜奶面霜的受试者(女性,平均年龄24.1±0.9岁)并用棉拭子采集面颊皮肤样本,提取DNA及PCR扩增后,进行16S rRNA高通量测序,并根据97%的相似度对序列进行OTU聚类和物种分类注释,分析比较使用样品前后皮肤细菌群落组成、多样性和差异菌群。研究发现使用含鲜奶面霜后脸颊皮肤细菌的多样性降低,但受试者面颊皮肤的细菌种类及相对丰度较为相似,同时受试者皮肤菌群中的厚壁菌门和放线菌门比例明显升高,这主要是由厚壁菌门中的葡萄球菌属和放线菌门中的丙酸杆菌属比例升高导致的。结果表明此款含鲜奶面霜对皮肤菌群微生态发挥一定的调节作用,且具有滋润保湿的效果,可以作为日常护肤中的保湿产品使用。

Effects of luteinizing hormone and androgen on the development of rat progenitor Leydig cells in vitro and in vivo

Progenitor Leydig cells are derived from stem cells. The proliferation and differentiation of progenitor Leydig cells significantly contributes to Leydig cell number during puberty. However, the regulation of these processes remains unclear. The objective of the present study was to determine whether luteinizing hormone （LH） or androgen contributes to the proliferation and differentiation of progenitor Leydig cells. Fourteen-day-old male Sprague-Dawley rats were treated for 7 days with NalGlu, which is a gonadotropin- releasing hormone antagonist, to reduce the secretion of LH in the pituitary and thus, androgen in the testis. Rats were co-administered with LH or 7a-methyl-nortestosterone （MENT）, which is an androgen resistant to metabolism by 5a-reductase 1 in progenitor Leydig cells, and the subsequent effects of LH or androgen were measured. 3H-Thymidine was also intravenously injected into rats to study thymidine incorporation in progenitor Leydig cells. Progenitor Leydig cells were examined. NalGlu administration reduced progenitor Leydig cell proliferation by 83%. In addition, LH or MENT treatment restored Leydig cell proliferative capacity to 73% or 50% of control, respectively. The messenger RNA levels of proliferation-related genes were measured using real-time PCR. The expression levels of Igfl, Lifr, Pdgfra, Bcl2, Ccnd3and Pcnawere upregulated by MENT, and those of Pdgfra, Ccnd3and Pcnawere upregulated by LH. Both LH and MENT stimulated the differentiation of progenitor Leydig cells in vitro. We concluded that both LH and MENT were involved in regulating the development of progenitor Leydig cells.

Synthesis of refrigeration system based on generalized disjunctive programming model

Refrigeration system holds an important role in process industries. The optimal synthesis cannot only reduce the energy consumption, but also save the production costs. In this study, a general methodology is developed for the optimal design of refrigeration cycle and heat exchanger network(HEN) simultaneously. Taking the heat integration between the external heat sources/sinks and the refrigeration cycle into consideration, a superstructure with sub-coolers is developed. Through defining logical variables that indicate the relative temperature positions of refrigerant streams after sub-coolers, the synthesis is formulated as a Generalized Disjunctive Programming(GDP) problem based on LP transshipment model, with the target of minimizing the total compressor shaft work in the refrigeration system. The GDP model is then reformulated as a Mixed Integer Nonlinear Programming(MINLP) problem with the aid of binary variables and Big-M Constraint Method. The efficacy of the process synthesis model is demonstrated by a case study of ethylene refrigeration system. The result shows that the optimization can significantly reduce the exergy loss as well as the total compression shaft work.

Electrochemical derusting in molten Na_(2)CO_(3)–K_(2)CO_(3)

The formation of a rust layer on iron and steels surfaces accelerates their degradation and eventually causes material failure.In addition to fabricating a protective layer or using a sacrificial anode, repairing or removing the rust layer is another way to reduce the corrosion rate and extend the lifespans of iron and steels.Herein, an electrochemical healing approach was employed to repair the rust layer in molten Na_(2)CO_(3)-K_(2)CO_(3).The rusty layers on iron rods and screws were electrochemically converted to iron in only several minutes and a metallic luster appeared.Scanning electron microscopy(SEM) and energy dispersive X-ray spectroscopy(EDS) analyses showed that the structures of the rust layer after healing were slightly porous and the oxygen content reached a very low level.Thus, high-temperature molten-salt electrolysis may be an effective way to metalize iron rust of various shapes and structures in a short time, and could be used in the repair of cultural relics and even preparing a three-dimensional porous structures for other applications.

Ecological Benefits Evaluation in Ecological Migration Zone Based on Ecological Green Equivalent: A Case Study of Migration Zone in Yanchi County

With four ecological migration zones in Huamachi Town of Yanchi County in Ningxia Autonomous Region as the object of study,we carry out the evaluation of ecological benefits in ecological migration zone. Using the SPOT satellite remote sensing image in 2008 and UAV aerophotographic image in 2013,we first monitor and analyze the land use change over five years in the study area,and then adopt ecological green equivalent evaluation model for the evaluation of ecological benefits in the ecological migration zone. Studies have shown that:( i) from 2008 to 2013,the ecological green equivalent in the study area was increased and the ecological environment was improved;( ii) the ecological green equivalent in the study area was less than 1 in 2008 and 2013,and ecological environment was still fragile in the migration zone;( iii)the forest coverage rate of the study area was 20% less than the minimum forest coverage rate of the United Nations,but 15% higher than the forest coverage rate of the Ministry of Environmental Protection. There is a large gap between the forest coverage rate based on ecological green equivalent and optimal forest coverage rate,suggesting that the land use still needs to be adjusted in study area,and it is necessary to increase efforts to strengthen ecological restoration and continue to implement forest conservation,returning land for farming to forestry and other measures.

Microstructure and melting properties of Ag–Cu–In intermediate-temperature brazing alloys

The microstructure and melting properties of ternary Ag-Cu-In intermediate-temperature alloys （400-600 ℃） prepared by electric arc melting were investigated in this work. The melting properties, phase compositions, microstructure and hardness were charac- terized by differential scanning calorimetry （DSC）, X-ray diffraction （XRD）, scanning electron microscopy （SEM） and micro-hardness tester, respectively. The results show that the melting properties, phase compositions, microstructure and hardness of Ag-Cu-In brazing alloys are substantially different when adding different levels of indium. Indium element could effectively reduce the melting temperatures of （Ag-Cu28）-xIn alloys, and the melting temperatures of （Ag-Cu28）-25In alloy are located at 497.86 and 617.48 ℃. When the indium content varies from 5 wt% and 10 wt%, the dominant phases in the alloys are Ag-rich and Cu-rich phases, and their granular crystals are smaller than 0.5 ktm. When the indium content is higher than 15 wt%, the phase compositions of the alloy are Ag4In and Cu11In9, and the microstructure exhibits dendritic crystals with a uniform distribution. The hardness of （Ag- Cu28）-xIn alloy decreases first and then increases with the content of indium increasing, and the highest hardness of （Ag-Cu28）-25In alloy is HV 266.0.

High-pressure microwave-assisted synthesis of WS_(x)/Ni_(9)S_(8)/NF hetero-catalyst for efficient oxygen evolution reaction

Designing the specific crystal phase with better intrinsic activity and more active sites is a very promising strategy for earth-abundant electrocatalysts for oxygen evolution reaction(OER).Herein,a facile two-step method including the high-pressure microwave and the hydrothermal sulfurization is adopted to prepare the WS_(x)/Ni_(9)S_(8) hetero-catalyst on nickel foam(WS_(x)/Ni_(9)S_(8)/NF).Firstly,WO3 polyhedrons homogeneously cover the surface of NF through the high-pressure microwave hydrothermal process.Secondly,WS_(x)/Ni_(9)S_(8) nanoparticles on the surface of NF can be synthesized after a hydrothermal sulfurization,which has been confirmed by scanning electron microscopy(SEM) elemental mapping and high-resolution transmission electron microscopy(HRTEM).The amorphous WSx and Ni9 S8 phase may provide the dual active sites for OER.The electrochemical measurements show that WS_(x)/Ni_(9)S_(8)/NF has superior OER activity with a low overpotential of 320 mV at the current density of 100 mA·cm^(-2),better than those of other samples.The enhanced OER performance may be due to the synergistic catalysis from Ni9 S8 phase and high valence of W.Owing to the stable structure of Ni9 S8,the long-term stability of WS_(x)/Ni_(9)S_(8)/NF for at least 10 h can be obtained.This work may provide a new approach for the doped nickel sulfides crystal phase through high-pressure microwave hydrothermal assistance for OER.

Squamous cellpapilloma at the urethral meatus

Dear Editor,Squamous cell papilloma in the urethra is a rare benign tumor and is usually reported in middle-aged and older women.It has never been documented in children.It is difficult to distinguish squamous papilloma from condylomata acuminatum and verrucous carcinoma because of their morphological overlap.?Here,we report a rare case of a young child with squamous papilloma of the urethral meatus.Informed consent was obtained from the patient's parents.