基于强化学习的非正交多址接入和移动边缘计算联合系统信息年龄更新

物联网发展对信息时效性的需求越来越高,信息新鲜度变得至关重要。为了维持信息新鲜度,在非正交多址接入(NOMA)和移动边缘计算(MEC)的联合系统中,对多设备单边缘计算服务器的传输场景进行了研究。在该场景中,如何分配卸载任务量和卸载功率以最小化平均更新代价是一个具有挑战性的问题。该文考虑到现实中的信道状态变化情况,基于多代理深度确定性策略梯度(MADDPG)算法,考虑信息新鲜度影响,建立了最小化平均更新代价的优化问题,提出一种寻找最优的卸载因子和卸载功率决策。仿真结果表明,采用部分卸载的方式可以有效地降低平均更新代价,利用MADDPG算法可以进一步优化卸载功率,经比较,MADDPG算法在降低平均更新代价方面优于其他方案,并且适当地减少设备数量在降低平均更新代价方面效果更好。     

Ionic Modulation of Interfacial Magnetism in Light Metal/Ferromagnetic Insulator Layered Nanostructures

Ferromagnetic insulator thin film nanostructures are becoming the key component of the state‐of‐the‐art spintronic devices, for instance, yttrium iron garnet (YIG) with low damping, high Curie temperature, and high resistivity is explored into many spin–orbit interactions related spintronic devices. Voltage modulation of YIG, with great practical/theoretical significance, thus can be widely applied in various YIG‐based spintronics effects. Nevertheless, to manipulate ferromagnetism of YIG through electric field (E‐field), instead of current, in an energy efficient manner is essentially challenging. Here, a YIG/Cu/Pt layered nanostructure with a weak spin–orbit coupling interaction is fabricated, and then the interfacial magnetism of the Cu and YIG is modified via ionic liquid gating method significantly. A record‐high E‐field‐induced ferromagnetic resonance field shift of 1400 Oe is achieved in YIG (17 nm)/Cu (5 nm)/Pt (3 nm)/ionic liquid/Au capacitor layered nanostructures with a small voltage bias of 4.5 V. The giant magnetoelectric tunability comes from voltage‐induced extra ferromagnetic ordering in Cu layer, confirmed by the first‐principle calculation. This E‐field modulation of interfacial magnetism between light metal and magnetic isolator may open a door toward compact, high‐performance, and energy‐efficient spintronic devices.     

A Robust,Freestanding MXene‐Sulfur Conductive Paper for Long‐Lifetime Li–S Batteries

Freestanding, robust electrodes with high capacity and long lifetime are of critical importance to the development of advanced lithium–sulfur (Li–S) batteries for next‐generation electronics, whose potential applications are greatly limited by the lithium polysulfide (LiPS) shuttle effect. Solutions to this issue have mostly focused on the design of cathode hosts with a polar, sulfurphilic, conductive network, or the introduction of an extra layer to suppress LiPS shuttling, which either results in complex fabrication procedures or compromises the mechanical flexibility of the device. A robust Ti₃C₂T_x/S conductive paper combining the excellent conductivity, mechanical strength, and unique chemisorption of LiPSs from MXene nanosheets is reported. Importantly, repeated cycling initiates the in situ formation of a thick sulfate complex layer on the MXene surface, which acts as a protective membrane, effectively suppressing the shuttling of LiPSs and improving the utilization of sulfur. Consequently, the Ti₃C₂T_x/S paper exhibits a high capacity and an ultralow capacity decay rate of 0.014% after 1500 cycles, the lowest value reported for Li–S batteries to date. A robust prototype pouch cell and full cell of Ti₃C₂T_x/S paper // lithium foil and prelithiated germanium are also demonstrated. The preliminary results show that Ti₃C₂T_x/S paper holds great promise for future flexible and wearable electronics.     

TiO_2对BLT微波介质陶瓷结构及介电性能的影响

采用传统固相烧结工艺制备了BaO-La2O3-nTiO2(n为3,4,5和6)微波介质陶瓷,研究了该系陶瓷的相组成、微观形貌和微波介电性能之间的关系。结果表明:该系陶瓷具有较优介电性能的主晶相为斜方晶系BaLa2Ti4O12,并且第二相的存在对其介电性能影响明显。烧结体致密性是Q·f及τf的重要影响因素。当n为4时,获得相对较优的介电性能:εr为139.7,Q·f为1239.0GHz和τf达180.0×10–6℃–1。     

用于产生微波信号的分布反馈激光器与Y形波导单片集成器件的研究

设计并制作了一种在Y形波导的两个分支上集成分布反馈(distributed feedback,DFB)激光器的单片集成器件.DFB激光器的布拉格光栅一次曝光形成,具有相同的光栅周期.当注入电流分别单独加载到两段DFB激光器之上时,从Y形波导端输出光波长在1565nm附近,边模抑制比大于30dB.当大于阈值且相差大于20mA的两个电流同时加载到两段DFB激光器上时,从Y形波导端输出的光谱具有双模分布,双模频率的差值可以拍频产生微波频段的信号.通过调节两段DFB的注入电流,微波信号的频率可以在13～42GHz之间快速连续调谐.这种基于Y形波导的两段DFB并联的拍频光源比传统的双段级联DFB器件有较好的光学和电学隔离,可以作为光学拍频源的一种新的实现方法.     

A design framework for hybrid approaches of image noise estimation and its application to noise reduction

Noise estimation is an important process in digital imaging systems. Many noise reduction algorithms require their parameters to be adjusted based on the noise level. Filter-based approaches of image noise estimation usually were more efficient but had difficulty on separating noise from images. Block-based approaches could provide more accurate results but usually required higher computation complexity. In this work, a design framework for combining the strengths of filter-based and block-based approaches is presented. Different homogeneity analyzers for identifying the homogeneous blocks are discussed and their performances are compared. Then, two well-known filters, the bilateral and the non-local mean, are reviewed and their parameter settings are investigated. A new bilateral filter with edge enhancement is proposed. A modified non-local mean filter with much less complexity is also present. Compared to the original non-local mean filter, the complexity is dramatically reduced by 75% and yet the image quality is maintained.     

基于防水墙系统的信息安全与保密解决方案

一、引言防火墙、IDS、内外网隔离以及其它针对外部网络的访问控制系统,可有效防范来自网络外部的进攻,但对于企业内部的信息保密问题,却一直没有好的防范方法:内部人员可以轻松地将计算机中的机密信息通过网络、存储介质和打印等方式泄露出去,一旦这些敏感信息、重要数据、设计图纸等流失到敌对势力、竞争对手手中,将给国家、企、事业单位造成重大损失。特别是军工行业、政府机关、承担国家敏感课题的科研部门,涉及到更多的国家机密,对于涉密信息采取严密的防护措施更是显得尤为必要。目前,国家制定了很多相关规章制度,明确规定,这些企事…     

Micro FET pressure sensor manufactured using CMOS-MEMS technique

The fabrication of a micro field effect transistor (FET) pressure sensor using the commercial 0.35 μm complementary metal oxide semiconductor (CMOS) process and a post-process has been investigated. The pressure sensor is composed of 16 sensing cells in parallel, and each sensing cell includes a suspended membrane and an NMOS. The suspended membrane is the movable gate of the NMOS. The pressure sensor needs a post-process to obtain the suspended membrane after the CMOS process. The post-process employs etchants to etch the sacrificial layers to release the suspended membrane, and then a low-pressure chemical vapor deposition (LPCVD) parylene is used to seal the etching holes in the pressure sensor. The pressure sensor produces a change in current when applying a pressure to the sensing cells. Experimental results show that the pressure sensor has a sensitivity of 0.022 μA/kPa in the pressure range of 0–500 kPa.     

An empirical study on user access to entertainment streaming media

I. Introduction Streaming media has been widely used over the Internet in recent years. However, the growing use in streaming media, which generally has large size, can have a significant impact on the user perceived latency and network congestion. A popular approach to reduce the response time and backbone bandwidth consumption is to deploy proxy caches at the edge of the Internet. Due to the large size and different popularity for different part of the streaming video, it is not practical …     

UWB LNA的增益平坦化及稳定性的反馈技术

从异质结晶体管(HBT)的小信号模型着手,得到了几种不同反馈形式下HBT的S参数解析表达式。通过对比不同反馈形式的仿真结果,分析了各种反馈形式对S参数的影响,并着重研究了反馈技术对电路稳定性以及对超宽带低噪声放大器(UWB LNA)增益平坦度的影响。结果表明,采用串联电阻和电感或并联电阻和电容的电抗性负反馈,可以使S21的幅度随着频率的增大而逐渐上升,从而补偿了晶体管本身高频增益的下降,同时,也提高了整个电路的稳定性。采用这种反馈结构,设计了一款3～10 GHz超宽带低噪声放大器。仿真结果表明,该放大器在整个频带范围内无条件稳定,传输增益较高,增益平坦度较好,噪声系数较低,是一款无条件稳定并有着较好增益平坦度的超宽带低噪声放大器。