Numerical investigation of water dynamics in a novel wettability gradient anode flow channel for proton exchange membrane fuel cells

The effective removal and transport of water in flow channels play an important role in the water management of proton exchange membrane fuel cells (PEMFCs). In this paper, a novel design of anode serpentine flow channel with the wettability gradient wall is discussed and numerically investigated by utilizing the volume-of-fluid (VOF) method. The effects of the contact angle and the wettability gradient of channel walls, as well as hydrogen flow velocity and water droplet size, on the droplet dynamic behavior are studied. The results indicate that compared with the conventional flow channel, the water droplet can be more effectively removed from the turning part in the wettability gradient flow channel. And the water removal ability in the turning part is improved with the increase of the wettability gradient. Moreover, the wettability gradient flow channel can also improve the water removal performance for the cases with different hydrogen flow velocities and water droplet sizes. This study provides ideas for guiding the design of flow channel to effectively enhance anode water management.     

小城镇厨卫间空气污染及其主要来源

厨卫间是人们在室内活动的重要场所。这些场所的空气污染不仅影响其本身环境的空气质量,也影响室内其他环境的空气质量,对人体造成危害。其污染源主要是燃料的燃烧和人们生活活动所产生的。在我国城市和中小城镇居民生活用燃料主要有煤及其制品、煤气、天然气、液化石油气等等。燃煤污染目前,我国的主要能源为煤。煤及其制品在一些大、中、小城市的老城区及乡镇使用比较普遍。其燃烧过程中产生并排放颗粒物、SO2、CO、NO2、甲醛等有害成分。研究表明,每公斤蜂窝煤可产生SO2306.3mg,NO2385mg和CO4105mg,并可产生颗粒物20.4mg,其中对人体…     

Morphology and magnetic properties of Sm2Co7/α-Fe nanocomposite magnets produced by high energy ball milling and spark plasma sintering

In this article,the Sm₂Co₇/α-Fe nanocomposite magnets were prepared by high energy ball milling and spark plasma sintering method.The effect of soft phase content on the magnetic properties was studied.Up to 30 wt% α-Fe was added into Sm₂Co₇ matrix without the decrease of remanence.Optimal energy product(BH)max of 9.2 MGOe was obtained with 20 wt% α-Fe.TEM observation shows that the grain size of α-Fe is 20-50 nm which ensures a good coupling effect between soft and hard phase.One more thing needs to be mentioned is that there exists inter-diffusion between Sm-Co phase and α-Fe phase.Moreover,our results can also illustrate that the Sm₂Co₇/α-Fe nanocomposite magnets are able to acquire better magnetic properties than the SmCo₅/α-Fe magnets prepared by the same process due to the large domain width of Sm₂Co₇ phase.     

Integration of scheduling and control for batch processes using multi‐parametric model predictive control

Integration of scheduling and control results in Mixed Integer Nonlinear Programming (MINLP) which is computationally expensive. The online implementation of integrated scheduling and control requires repetitively solving the resulting MINLP at each time interval. (Zhuge and Ierapetritou, Ind Eng Chem Res. 2012;51:8550–8565) To address the online computation burden, we incorporare multi‐parametric Model Predictive Control (mp‐MPC) in the integration of scheduling and control. The proposed methodology involves the development of an integrated model using continuous‐time event‐point formulation for the scheduling level and the derived constraints from explicit MPC for the control level. Results of case studies of batch processes prove that the proposed approach guarantees efficient computation and thus facilitates the online implementation. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3169–3183, 2014     

Graph-based algorithms for ranking researchers: not all swans are white!

Scientific importance ranking has long been an important research topic in scientometrics. Many indices based on citation counts have been proposed. In recent years, several graph-based ranking algorithms have been studied and claimed to be reasonable and effective. However, most current researches fall short of a concrete view of what these graph-based ranking algorithms bring to bibliometric analysis. In this paper, we make a comparative study of state-of-the-art graph-based algorithms using the APS (American Physical Society) dataset. We focus on ranking researchers. Some interesting findings are made. Firstly, simple citation-based indices like citation count can return surprisingly better results than many cutting-edge graph-based ranking algorithms. Secondly, how we define researcher importance may have tremendous impacts on ranking performance. Thirdly, some ranking methods which at the first glance are totally different have high rank correlations. Finally, the data of which time period are chosen for ranking greatly influence ranking performance but still remains open for further study. We also try to give explanations to a large part of the above findings. The results of this study open a third eye on the current research status of bibliometric analysis.     

The relationship between porosity and strength for porous concrete

As for many porous media, the strength of porous concrete is significantly affected by the porosity of its internal structure. This paper describes the development of a mathematical model to characterize the relationship between compressive strength and porosity for porous concrete by analyzing empirical results and theoretical derivations. The suitability of existing equations for porous concrete is assessed and a new model is then proposed. The new model, which was derived from Griffith’s theory, presents a better agreement with the experimental data for porous concrete. It is demonstrated that the proposed model could provide a better prediction of porous concrete compressive strength based on the material porosity.     

High-Performance Si Nanowire Transistors on Fully Si Bulk Substrate From Top-Down Approach: Simulation and Fabrication

A new method to fabricate high-performance gate-all-around silicon (Si) nanowire transistors (SNWTs) based on fully Si bulk (FSB) substrate is proposed and demonstrated by both simulation and experiments in this paper. Due to the large fan-out and deep junction of Si source/drain (S/D) region connecting with the bulk substrate, the FSB SNWTs can effectively alleviate the self-heating effects with technology scaling. Thermal behavior of multiwire SNWTs is investigated and FSB SNWTs show superior self-heating immunity to SNWTs based on Si-on-insulator (SOI) substrate (SOI SNWTs). In addition, the bottom parasitic transistor can be well suppressed in this structure. Although FSB SNWTs have larger gate parasitic capacitance, the CV/ $I$ is found to be comparable to the SOI SNWTs. With self-aligned, fully epi-free compatible CMOS processes, this new architecture was successfully fabricated, which exhibit high on–off current ratio of $hbox{2.6} times hbox{10}^{8}$ due to better heat dissipation and low S/D resistance realized in this structure.      

Structural and magnetic properties of transition metal doped ZnO films

Structural and magnetic properties have been studied for polycrystalline Zn_1 − xTM_xO films where transition metal (TM) = Fe, Cr. The Zn_1 − xTM_xO films were prepared by the radio frequency magnetron sputtering technique on Al₂O₃ (001) substrates. The microstructures of the films are characterized by X-ray diffraction and X-ray photoelectron spectroscopy. TM in the films exists mainly in the form of TM²⁺, and the TM²⁺ ions have substituted for the Zn²⁺ ions bonded in TM-O in the ZnO lattice and do not change the wurtzite structure of ZnO. The result of magnetic measurement shows that the Zn_1 − xTM_xO films are ferromagnetic at 5 K and 300 K respectively. Subsequently, we discuss the origin of the ferromagnetism in the films.     

色谱监测氢气异常的分析与讨论

根据色谱监测变压器H2含量异常的几种可能原因，对廊坊供电公司一起110kV主变单-H2组分严重超标的非典型故障进行了分析，找出了问题所在。     

陶瓷绘画的具象与抽象

在陶瓷绘画中,尤其是在釉下彩、颜色釉等综合装饰绘画中,具有意象基础的抽象绘画抽象味越浓,意象性更大,给予观众的创意空间更为广阔,当然,其中有一点具象的影子更好。但是,陶瓷绘画的无论何种形式不能损害和掩盖陶瓷本身的自然属性,天然的物理化学之美和人工技艺运乎其中之美,此为陶瓷之大美,而陶瓷绘画只是此大美之附丽、发展而非掩盖,陶瓷绘画不能不顾陶瓷之整体美而独唱主角,尤其是陶瓷装饰中的具象绘画更宜注意。陶瓷艺术的本质属性决定,是具象还是抽象,还是两者之间,各有不同,但笔者倾向于两者之间,并喜爱哪些更有抽象味的陶瓷装饰。