22,881 research outputs found

    The influence of structural defects on intra-granular critical currents of bulk MgB2

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    Bulk MgB2 samples were prepared under different synthesis conditions and analyzed by scanning and transmission electron microscopy. The critical current densities were determined from the magnetization versus magnetic field curves of bulk and powder-dispersed-in-epoxy samples. Results show that through a slow cooling process, the oxygen dissolved in bulk MgB2 at high synthesis temperatures can segregate and form nanometer-sized coherent precipitates of Mg(B,O)2 in the MgB2 matrix. Magnetization measurements indicate that these precipitates act as effective flux pinning centers and therefore significantly improve the intra-grain critical current density and its field dependence.Comment: 4 pages, 4 figures, to be published in IEE Transactions in Applied Superconductivit

    Preview Tracking Control of Linear Periodic Switched Systems with Dwell Time

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    This paper studies the preview tracking control problem for linear discrete-time periodic switched systems. Firstly, an augmented error system is constructed for each subsystem by stabilizing the augmented error systems through the method of optimal preview control, and the tracking problem of the switched system is transformed into the switched stability problem of closed-loop augmented error systems. Secondly, a switched Lyapunov function method is applied to search the minimal dwell time satisfying the switched stability of the closed-loop augmented error systems. Thirdly, the switched preview control input is solved from the controller of the individual augmented error system, and then the sufficient conditions and the preview controller can be obtained to guarantee the solvability of the original periodic switched preview tracking problem. Finally, numerical simulations show the effectiveness of the stabilization design method

    The expression of VFL and VvTFL1 genes in relation to the effects of gibberellins in different organs of “Xiangfei” grapevine

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    The effects of gibberellins (GAs) on plant growth and the expression of VFL and VvTFL1 genes in different organs of “Xiangfei” grapevine (Vitis vinifera L.) were investigated. The endogenous GA content significantly increased in the apical bud, inflorescence and tendril after GA treatment ofgrapevine. The expression of the VFL gene was obviously reduced in the meristem of apical buds, tendrils with florets and small inflorescences after GA treatment, but VFL gene expression was clearly found during the middle and big inflorescence developmental stages. These results suggested that the exogenous GAs delayed floral development of grapevine by inhibiting VFL gene expression at the early stage of inflorescence development. VvTFL1 gene expression was detected in the meristem of apical bud and lateral bud, but not during the process of inflorescence development. After applying GAs on grapevine, VvTFL1 gene expression decreased in the apical bud. These results suggested thatexogenous GA treatments might repress differentiation of the inflorescence meristem primordia by reducing VvTFL1 expression in the apical bud but have no effect on VvTFL1 expression during floraldevelopment

    Composition design and physical properties prediction of mold flux for continuous casting of high Mn–HIGH Al steel

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    The deterioration of CaO-SiO2 based mold flux caused by the reaction of steel -slag interface is a bottleneck restricting the high Mn-Al steel continuous casting production efficiently. Therefore, the development of low-reactivity mold flux has become a research hotspot. In this paper, the scheme of high Al2O3 and low SiO2 was adopted to suppress or reduce the occurrence of steel-slag reaction. Drawing binary phase diagram of mold flux based on the CaO–Al2O3 composition, the influence of different solvents on the melting characteristics of the mold flux were investigated and the reasonable mass ratio of CaO/Al2O3and the content of SiO2, SrO, MgO, Na2O and B2O3 were determined. According to the viscosity and the melting temperature model calculation, the physical property is beneficial for the composition design of low-reactivity mold flux
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