异常网络流量中的相变理论研究

基于网络相变理论对网络异常流量的本质进行了研究,提出了基于Hurst参数反馈的动态拥塞缓解机制,理论分析和仿真结果验证了该方法的可行性和相对于传统方法的优越性,为异常流量的检测、控制研究做出了有益的探索。     

A new ZVT–ZCT quasi-resonant DC link for soft switching inverters

In this article, the new ZVT–ZCT Quasi-Resonant DC Link, which ensures zero crossings at any time required for soft switching (SS) and provides zero voltage transition (ZVT) turn-on and zero current transition (ZCT) turn-off together for the main switch of active snubber cell in pulse width modulated or space vector modulated operation of inverter is presented. The new circuit combines the most desirable features of the circuits presented previously and overcomes most drawbacks of these circuits by using only one auxiliary switch with fewer other components. Consequently, new ZVT–ZCT Quasi-Resonant DC Link, which is verified by a prototype of a 1.2 kW and 50 kHz circuit, is analysed in detail. All semiconductor devices operate under SS, the main switch is subjected to no additional voltage and current stresses, and the stress on the auxiliary switch is very low in the proposed new inverter.     

有线数字电视整体转换的技术支撑

从前端机房建设、传输平台建设、光缆干线网、互动业务平台、现场技术服务、接入网整改几个方面介绍了如何做好有线数字电视整体转换的技术支撑工作,保障数字电视整体转换的顺利进行。     

Recent Observations on Tin Pest Formation in Solder Alloys

The most recent observations of the response of bulk samples of several lead-free solder alloys, exposed to temperatures below the allotropic transition for tin for extended periods, are reported. Tin pest has been observed in Sn-0.5Cu, Sn-3.5Ag, Sn-3.8Ag-0.7Cu, and Sn-3.0Ag-0.5Cu alloys at both −18°C and −40°C. The process is slow and inconsistent, usually requiring several years, but may eventually result in complete disintegration of the sample. No tin pest was detected in Sn-Zn-3Bi or in the traditional Sn-37Pb solder alloy after exposure for up to 4 and 10 years, respectively. It is suggested that nucleation is affected by local composition and that extremely small amounts of either intentional solute or impurity are influential. Growth of tin pest is accompanied by a large volume change, and it is likely that stress relaxation ahead of the expanding grey tin front is a controlling factor. A stronger matrix would be more resistant in this case, and at the temperatures of exposure Sn-37Pb is stronger than either Sn-3.5Ag or Sn-0.5Cu. The absence of tin pest, to date, on actual joints is attributed to their restricted free surface area and the greater strength associated with very small samples.     

Charge Photogeneration in Few‐Layer MoS2

The 2D semiconductor MoS₂ in its mono‐ and few‐layer form is expected to have a significant exciton binding energy of several 100 meV, suggesting excitons as the primary photoexcited species. Nevertheless, even single layers show a strong photovoltaic effect and work as the active material in high sensitivity photodetectors, thus indicating efficient charge carrier photogeneration. Here, modulation spectroscopy in the sub‐ps and ms time scales is used to study the photoexcitation dynamics in few‐layer MoS₂. The results suggest that the primary photoexcitations are excitons that efficiently dissociate into charges with a characteristic time of 700 fs. Based on these findings, simple suggestions for the design of efficient MoS₂ photovoltaic and photodetector devices are made.     

Synthesis of an aromatic amine derivative with novel double spirobifluorene core and its application as a hole transport material

A synthetic method to prepare a novel double spirobifluorene core structure was developed and a hole transport type exciton blocking material with the double spirobifluorene core was synthesized. A two step ring closing method was used to synthesize the double spirobifluorene core. The double spirobifluorene core based hole transport material showed high glass transition temperature due to rigid structure, and high quantum efficiency in green phosphorescent organic light emitting diodes because of efficient hole injection and triplet exciton blocking properties.     

Ultraflexible and Malleable Fe/BaTiO3 Multiferroic Heterostructures for Functional Devices

The high demand for flexible spintronics based on multiferroic heterostructures makes growing high-quality flexible, functional oxides urgently, in which needs to be deposited on lattice-matched substrates. In this paper, ultraflexible and malleable iron (Fe)/BaTiO₃ (BTO) multiferroic heterostructures are demonstrated, showing a perfect crystallinity and hetero-epitaxial growth. In terms of performance, they indicate good multiferroic properties and excellent bending tunability, as well as obvious magnetoelectric (ME) coupling effect. During the phase transformation from the rhombohedral phase to the orthorhombic phase of BTO layers in the heating process, a large ME coupling coefficient of 120 Oe  ° C⁻¹ along the out-of-plane direction is obtained. This value keeps consistent in the phase-field simulation of magnetic domain evolution, in which the biaxial compressive strain induced-magnetoelastic anisotropy facilitates the magnetic easy axis of Fe layers to the [110] or [–1–10] direction. Besides, ultraflexible Fe/BTO heterostructures are found to have a 690 Oe ferromagnetic resonance (FMR) field shift along the out-of-plane direction under the flexible tuning (R  = 5 mm). This work should pave a way toward flexible spintronic and functional devices with fast speed, portability, and low energy consumption.     

网络流量行为分析的一维元胞自动机模型

提出了一种网络流量的一维元胞自动机模型。制定了节点吞吐量和分组队列长度的更新规则,引入了减速概率来模拟节点发送分组的随机行为。数值仿真结果表明,该模型能较好的描述了网络中从自由流相到拥塞相的相变行为。     

Long transition analysis for digital video sequences

Video indexing is a technique used to extract objects within a video sequence and index them so that they can be used for future retrieval. In many video sequences, special effects such as fade and wipe are incorporated, and in some cases, it is desirable to be able to include objects within such effects for indexing. In this paper, we introduce an automatic process that determines the type of transition and extracts information from it, so that this information can be used in object extraction. Such a process consists of four stages: shot boundary refinement, shot type determination, frame reconstruction for soft transitions, and shot classification for hard transitions. In this paper, we will give the implementation, timing, and performance analysis for each stage. Long transition analysis bridges the gap between shot boundary detection and object tracking and smoothes the process of automatic video indexing for video databases.     

Synthesis and Characterization of 2D Molybdenum Carbide (MXene)

Large scale synthesis and delamination of 2D Mo₂CT _x (where T is a surface termination group) has been achieved by selectively etching gallium from the recently discovered nanolaminated, ternary transition metal carbide Mo₂Ga₂C. Different synthesis and delamination routes result in different flake morphologies. The resistivity of free‐standing Mo₂CT _x films increases by an order of magnitude as the temperature is reduced from 300 to 10 K, suggesting semiconductor‐like behavior of this MXene, in contrast to Ti₃C₂T _x which exhibits metallic behavior. At 10 K, the magnetoresistance is positive. Additionally, changes in electronic transport are observed upon annealing of the films. When 2 μm thick films are tested as electrodes in supercapacitors, capacitances as high as 700 F cm^?3 in a 1 m sulfuric acid electrolyte and high capacity retention for at least 10,000 cycles at 10 A g^?1 are obtained. Free‐standing Mo₂CT _x films, with ≈8 wt% carbon nanotubes, perform well when tested as an electrode material for Li‐ions, especially at high rates. At 20 and 131 C cycling rates, stable reversible capacities of 250 and 76 mAh g^?1, respectively, are achieved for over 1000 cycles.