University of Science and Technology Beijing

About: University of Science and Technology Beijing is a education organization based out in Beijing, China. It is known for research contribution in the topics: Microstructure & Alloy. The organization has 41558 authors who have published 44473 publications receiving 623229 citations. The organization is also known as: Beijing Steel and Iron Institute.

A Realistic Energy Consumption Model for TSCH Networks

Abstract: Time slotted channel hopping (TSCH) is the highly reliable and ultra-low power medium access control technology at the heart of the IEEE802.15.4e-2012 amendment to the IEEE802.15.4-2011 standard. TSCH networks are deterministic in nature; the actions that occur at each time slot are well known. This paper presents an energy consumption model of these networks, obtained by slot-based “step-by-step” modeling and experimental validation on real devices running the OpenWSN protocol stack. This model is applied to different network scenarios to understand the potential effects of several network optimization. The model shows the impact of keep-alive and advertisement loads and discusses network configuration choices. Presented results show average current in the order of 570 μA on OpenWSN hardware and duty cycles 1% in network relays in both real and simulated networks. Leaf nodes show 0.46% duty cycle with data rates close to 10 packets per minute. In addition, the model is used to analyze the impact on energy consumption and data rate by overprovisioning slots to compensate for the lossy nature of these networks.

Recent Progress in Chlorinated Organic Photovoltaic Materials.

Abstract: ConspectusOver the past few years, the development of new materials has contributed to rapid increases in the power conversion efficiencies (PCEs) of organic photovoltaic (OPV) cells to over 17%, showing great potential for the commercialization of this technology in the near future. At this stage, designing new materials with superior performance and low cost simultaneously is of crucial importance. Chlorinated materials are emerging as new stars with very high PCEs, creating a molecular design trend to replace the most popular fluorinated materials. For example, by using chlorinated non-fullerene acceptors, we recently got a record PCE of 17% for single-junction OPV cells. Firmly based on recent advances, herein we focus on the topic of chlorinated OPV materials, aiming to provide a guideline for further molecular design.In this Account, first, on the basis of most fundamental features of the Cl atom, we highlight the features of chlorinated materials compared with their fluorinated counterparts: (1) Chlorination is more efficient than fluorination in modulating the optical and electrical properties of OPV materials. In many cases, chlorinated materials show lower energy levels and broader absorption spectra than their fluorinated counterparts, which contribute higher output voltages and current densities in the resulting photovoltaic devices. (2) Cl has a large atomic size than F. On one hand, enhanced overlap of π electrons is beneficial for enhancing the intermolecular packing and crystalline property and thus improving the charge transport. On the other hand, if Cl is introduced inappropriately in the backbone or side chain, this feature will cause a more twisted π plane and larger steric hindrance, having negative impacts on the photovoltaic performance of the corresponding materials. (3) Importantly, chlorination is usually chemically cheaper in synthesis, which has the potential to decrease the material cost of OPV cells. Then, we provide a concise review of chlorinated OPV materials, including polymeric and small-molecule donors and non-fullerene acceptors. The photovoltaic performance in various types of OPV cells using chlorinated materials, such as single-junction, tandem, semitransparent, and indoor-light photovoltaic cells is also discussed. For instance, ultranarrow-band-gap chlorinated acceptors can be used to construct highly efficient color-semitransparent OPV cells, and the wide-band-gap chlorinated materials show great potential for fabricating indoor-light photovoltaic devices. Finally, we briefly discuss current questions related to chlorinated OPV materials and highlight the significance of chlorination in future development.

Degradation Feature Selection for Remaining Useful Life Prediction of Rolling Element Bearings

Abstract: Rolling element bearings are among the most widely used and also vulnerable components in rotating machinery equipment. Recently, prognostics and health management of rolling element bearings is more and more attractive both in academics and industry. However, many studies have been focusing on the prognostic aspect of bearing prognostics and health management and few efforts have been performed in relation to the optimal degradation feature selection issue. For more effective and efficient remaining useful life predictions, three goodness metrics of correlation, monotonicity and robustness are defined and combined for automatically more relevant degradation feature selection in this paper. Effectiveness of the proposed method is verified by rolling element bearing degradation experiments. Copyright © 2015 John Wiley & Sons, Ltd.

Birnessite-type MnO2 Nanowalls and Their Magnetic Properties

Abstract: Birnessite-type MnO2 nanowalls have been fabricated on Si(111) substrate by a facile solution method. The XRD pattern indicates that the sample has the typical feature of turbostratic disorder and prefers to grow in the ab plane. The nanowalls are composed of thin flakes distributing uniformly over the surface of the Si(111) substrate. A magnetic transition temperature of 9.2 K is determined. Prominent magnetic anisotropy with the easy magnetization direction in the ab plane is observed at 5 K.

Preparation, characterization and tribological mechanism of nanofluids

Abstract: A nanofluid is a dispersion of nanoparticles in a base fluid and it has been a hot topic of great interest in recent years primarily due to its potential application in various fields. This review presents an overview of the remarkable progress on nanofluids during the past two decades. Nanoparticles have been investigated intensively as an additive for lubricants due to their special tribological properties. This article is focused on various synthetic methods and characterization techniques of nanofluids. Factors enhancing the stability and lubrication mechanism have been delineated in detail. Although nanofluids are potential candidates for tribological applications, there are still many challenges to overcome. These challenges involve the long term stability of nanofluids and validation of lubrication mechanisms. Especially, nanofluid stability and high costs of production are obstacles for the application of nanofluids. The current review also discusses the problems of nanofluids applied in lubrication.