63 research outputs found

    Establishing the carrier scattering phase diagram for ZrNiSn-based half-Heusler thermoelectric materials

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    Chemical doping is one of the most important strategies for tuning electrical properties of semiconductors, particularly thermoelectric materials. Generally, the main role of chemical doping lies in optimizing the carrier concentration, but there can potentially be other important effects. Here, we show that chemical doping plays multiple roles for both electron and phonon transport properties in half-Heusler thermoelectric materials. With ZrNiSn-based half-Heusler materials as an example, we use high-quality single and polycrystalline crystals, various probes, including electrical transport measurements, inelastic neutron scattering measurement, and first-principles calculations, to investigate the underlying electron-phonon interaction. We find that chemical doping brings strong screening effects to ionized impurities, grain boundary, and polar optical phonon scattering, but has negligible influence on lattice thermal conductivity. Furthermore, it is possible to establish a carrier scattering phase diagram, which can be used to select reasonable strategies for optimization of the thermoelectric performance.Comment: 21 pages, 5 figure

    Cracks, microcracks and fracture in polymer structures: Formation, detection, autonomic repair

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    The first author would like to acknowledge the financial support from the European Union under the FP7 COFUND Marie Curie Action. N.M.P. is supported by the European Research Council (ERC StG Ideas 2011 n. 279985 BIHSNAM, ERC PoC 2015 n. 693670 SILKENE), and by the EU under the FET Graphene Flagship (WP 14 “Polymer nano-composites” n. 696656)

    Effects of the Forage Type and Chop Length of Ramie Silage on the Composition of Ruminal Microbiota in Black Goats

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    The aim of this study was to investigate the effects of the forage type and chop length of ramie (Boehmeria nivea (L.) Gaud.) silage on rumen fermentation and ruminal microbiota in black goats. Sixteen Liuyang black goats (22.35 ± 2.16 kg) were fed with the roughage of corn silage or ramie silage at chop lengths of 1, 2, or 3 cm. The Chao 1 index and the observed number of microbial species differed significantly between the corn and ramie silage groups (p < 0.05); however, Firmicutes (relative proportion: 34.99–56.68%), Bacteroidetes (27.41–47.73%), and Proteobacteria (1.44–3.92%) were the predominant phyla in both groups. The relative abundance of Verrucomicrobia (0.32–0.82%) was lowest for the 2 and 3 cm chop lengths (p < 0.05) and was negatively correlated with rumen pH and propionic acid concentration (p < 0.05), but positively correlated with the ratio of acetic acid to propionic acid (p < 0.05). The ramie silage fermentation quality was highest for the 1 cm chop length, suggesting that moderate chopping produces optimal quality silage

    The Impact Mechanism of Digital Transformation on the Risk-Taking Level of Chinese Listed Companies

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    As the core engine of the digital economy, the digital transformation can make modern enterprises survive and develop better now. By the sample data of listed companies in the years from 2015 to 2020, this paper identifies the degree of enterprise digital transformation through text analysis, empirically examines the impact mechanism of digital transformation on corporate risk-taking, and fully considers the heterogeneity problems. The findings are as follows: (1) Digital transformation can improve the level of enterprise risk taking, especially the improvement of enterprise financial stability and strategic risk taking; (2) in terms of enterprise attribute structure, digital transformation can significantly enhance the risk-taking level of non-state-owned enterprises and high-tech enterprises; (3) the mechanism identification test finds that innovation-driven and enterprise value enhancement play a strengthening role in the role of digital transformation in promoting enterprise risk-taking level, and resource allocation efficiency as a mediating path weakens the role of digital transformation on enterprise risk-taking level. This study provides a basis for promoting the improvement of enterprises risk-taking: digital transformation can help enterprises maintain financial stability, improve innovation output capacity, enterprise value level, enterprise risk-taking capacity and sustainable development. At the same time, the Chinese government should take measures to further stimulate the willingness of state-owned enterprises to digital transformation

    Slow-Scale Instability of Single-Stage Power-Factor-Correction Power Supplies

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    Abstract—This paper reports slow-scale instability in a single-stage power-factor-correction (PFC) power supply, which is a popular design solution for low power applications. The circuit employs a cascade configuration of a boost converter and a forward converter, which share an active switch and operate in discontinuous-conduction mode (DCM), to provide input PFC and tight output regulation. Main results are given by “exact” cycle-by-cycle circuit simulations. The effect of the slow-scale instability on the attainable power factor is illustrated in terms of total harmonic distortion which can be found by taking the fast Fourier transform of the input current. The slow-scale instability usually manifests itself as local oscillations within a line cycle. Based on the critical condition of DCM for the buck converter, the underlying mechanism of such instability is further investigated. It has been found that border collision is the underlying cause of the phenomenon. Moreover, it has been shown that the border collision observed here is effectively a nonsmooth Neimark–Sacker bifurcation. Finally, experimental results are presented for verification purposes. Index Terms—Power-factor correction (PFC), single-stage PFC power supply, instability, border collision. I

    CONTACT MODELING OF TRAVELING WAVE ULTRASONIC MOTORS

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    ABSTRACT In the pursuit of high areal recording density towards 10 Tb/in 2 , it is necessary to improve the positioning accuracy of the magnetic head in the hard disk drive head-positioning control system. Ultrasonic motors (USMs) are novel electric motors used for positioning controls. Due to the drive characteristic of USMs, wear and fatigue of friction material at the contact friction interface are inevitable. Contact deformation can cause local damage of USMs. Therefore, obtaining the details of the stress distribution in the friction material due to the inelastic deformation is important. In this work, a contact model of traveling wave ultrasonic motor (TWUSM) is proposed. A three dimensional finite element model with cohesive zone elements embedded between friction material and rotor is then developed. Infinite finite elements are incorporated in this modeling as the boundary condition as the model thickness is typically many orders smaller than the longitudinal dimension. The evolution of deformation in friction material and rotor due to the mechanical surface loading is presented. The possible interfacial delamination process between friction material and rotor is numerically studied. And the friction coefficient effect of the friction material on the delamination propagation is also investigated. INTRODUCTION In order to achieve high areal recording density, it is necessary to improve the positioning accuracy of the magnetic head in the hard disk drive (HDD) head-positioning control system. This need has accelerated the exploration of the use of USMs in HDD applications

    A Novel Framework for Automation Technology Based on Machine Vision and Robotics in Electrical Power Inspection Processing

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    As a well-known support, computer vision is a powerful factor to improve the application and development of the electronic system. Whether the power system can operate safely and stably can greatly influence the deduction of providence. All types of electric swinging devices are easily disturbed by various factors during the assistance operation. The ubiquitous power system that operates everywhere becomes extremely small once the electrical equipment is abandoned. For the current complexity system, if the old-fashioned hand-written visual monitoring system is still used, not only will their ability fails to meet the requirements but also the number of cumbersome, important, and financial context will be unsatisfactory. It is natural to reason about some problems. Serious problems are due to incompetent human investigation. Issues are not optimally handled during this period. The application of Coach Ken technology can fully utilize machine vision technology to analyze the salient data and identify dominant devices that support shape vision. Meanwhile, it can truly realize the supervision system of perception and machine control. In view of this, we in this work mainly expound the artifact recognition technology supported by machine vision reproduction. Besides, we disassemble the composition method of the electric power supply recognition system supported by machine vision parallel, in order to enhance the future work

    Characteristics of Metal Magnetic Memory Testing of 35CrMo Steel during Fatigue Loading

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    The fatigue fracture of a drillstring could cause drilling disturbances and some negative impacts (e.g., economic loss) will be brought when restoring the drillstring to functionality. In order to evaluate the effects of the fatigue damage of the drillstring during drilling, a new apparatus, which could monitor the load level in real-time, was built to perform the four-point bending fatigue test on 35CrMo steel, a typical material of drillstrings. Such an apparatus is based on metal magnetic memory (MMM) technology and can acquire the tangential and normal components of MMM signals. Based on the analysis of the change of surface morphology and MMM signals, it was concluded that the variation of MMM signals could be divided into four stages, which are used to accurately describe the fatigue damage process of the drillstring. Additionally, the MMM signal characteristics are introduced to especially evaluate the fatigue damage of the drillstring, including crack initiation. Furthermore, the scanning electron microscopy (SEM) results demonstrated that morphologies of fatigue fracture were related to the variation of MMM signals. Linear fitting results indicated that fatigue crack length had a good linear relationship with the characteristics, so it is feasible to monitor fatigue damage and predict the residual life of a drillstring by using MMM technology
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