Energy-efficiency based downlink multi-user hybrid beamforming for millimeter wave massive MIMO system

The fifth generation mobile communication(5G) systems can provide Gbit/s data rates from massive multiple-input multiple-output(MIMO) combined with the emerging use of millimeter wavelengths in small heterogeneous cells. This paper develops an energy-efficiency based multi-user hybrid beamforming for downlink millimeter wave(mm Wave) massive MIMO systems. To make better use of directivity gains of the analog beamforming and flexible baseband processing of the digital beamforming, this paper proposes the analog beamforming to select the optimal beam which can maximize the power of the objective user and minimize the interference to all other users. In addition, the digital beamforming maximizes the energy efficiency of the objective user with zero-gradient-based approach. Simulation results show the proposed algorithm provide better bit error rate(BER) performance compared with the traditional hybrid beamforming and obviously improved the sum rate with the increase in the number of users. It is proved that multi-user MIMO(MU-MIMO) can be a perfect candidate for mm Wave massive MIMO communication system. Furthermore, the analog beamforming can mitigate the inter-user interference more effectively with the selection of the optimal beam and the digital beamforming can greatly improve the system performance through flexible baseband processing.     

美国研制出新型银纳米粒子墨水

据海外媒体报道,美国伊利诺伊大学厄本那-香槟分校(UIUC)的研究人员研制出一种由银纳米粒子构成的新型墨水,可应用于电子和光电等领域,创造出能经受反复的弯曲和伸展、跨度较大的微电极,实现信号从一个电路元件到另一个电路元件的传递。     

民营企业家在构建企业文化时应注意四点

民营企业家是企业文化的最佳提炼者。民营企业文化的形成过程实质上就是企业家在挖掘深藏在员工心灵深处的观念体系,结合企业的战略目标和企业的利益共同点提炼出企业的经营哲学、价值观、特色和     

An elastic-viscous-plastic model for overconsolidated clays

The influences of time on clays are discussed first,and the concept of the instant normal compression line is proposed by analyzing the existing theories and experimental results.Based on the creep law,the relationship between the aging time and the overconsolidation parameter is built.With the reloading equation of the UH model(unified hardening model for overconsolidated clays) used to calculate the instant compression deformation,a one-dimensional stress-strain-time relationship is proposed.Furthermore,the evolution of this relationship is analyzed,and the characteristic rate that is a function of the overconsolidation parameter is defined.Then a three-dimensional elastic-viscous-plastic constitutive model is suggested by incorporating equivalent time into the current yield function of the UH model.The new model can describe not only creep,rate effect and other viscous phenomena,but also shear dilatancy,strain softening and other behaviors of overconsolidated clays.Besides,compared with the modified Cam-clay model it requires only one additional parameter(the coefficient of secondary compression) to consider the creep law.Finally,because the proposed model can be changed into the UH model under instantaneous loading,the elastic-plastic and elastic-viscous-plastic frameworks are unified.     

Preparation of dendritic bismuth film electrodes and their application for detection of trace Pb(Ⅱ)and Cd(Ⅱ)

In this paper,dendritic Bi film electrodes with porous structure had successfully been prepared on glassy carbon electrode using a constant current electrolysis method based on hydrogen bubble dynamic templates.The electrode prepared using a large applied current density showed an increased internal electroactive area and a significantly improved electrochemical performance.The analytical utility of the prepared dendritic Bi film electrodes for the determination of Pb(Ⅱ)and Cd(Ⅱ)in the range of 5–50 μg·L~(-1)were presented in combination with square wave stripping voltammetry in model solution.Compared with non-porous Bi film electrode,the dendritic Bi film electrode exhibited higher sensitivity and lower detection limit.The prepared Bi film electrode with dendritic structure was also successfully applied to real water sample analysis.     

Thermal behavior analysis of a pouch type Li[Ni<Subscript>0.7</Subscript>Co<Subscript>0.15</Subscript>Mn<Subscript>0.15</Subscript>]O<Subscript>2</Subscript>-based lithium-ion battery

Since lithium-ion battery with high energy density is the key component for next-generation electrical vehicles,a full understanding of its thermal behaviors at different discharge rates is quite important for the design and thermal management of lithium-ion batteries（LIBs）pack/module.In this work,a 25 Ah pouch type Li[Ni_0.7Co_0.15Mn_0.15]O₂/graphite LIBs with specific energy of200 Wh kg^-1were designed to investigate their thermal behaviors,including temperature distribution,heat generation rate,heat capacity and heat transfer coefficient with environment.Results show that the temperature increment of the charged pouch batteries strongly depends on the discharge rate and depth of discharge.The heat generation rate is mainly influenced by the irreversible heat effect,while the reversible heat is important at all discharge rates and contributes much to the middle evolution of the temperature during discharge,especially at low rate.Subsequently,a prediction model with lumped parameters was used to estimate the temperature evolution at different discharge rates of LIBs.The predicted results match well with the experimental results at all discharge rates.Therefore,the thermal model is suitable to predict the average temperature for the large-scale batteries under normal operating conditions.     

温态超声冲击强化对AA6061-T6空蚀行为的影响

目的 进一步提高超声冲击处理对AA6061-T6抗空蚀性能的强化效果。方法 通过不同温度（RT、50、100和150℃）温态超声冲击强化处理,结合冲击强化与动态应变时效（DSA）的优点,获得应变速率更高、密度位错更高的塑性变形强化层,以提高其抗空蚀性能。利用X射线衍射技术（XRD）、金相显微镜研究了强化层的微观组织。利用显微硬度仪研究了强化层深度方向的硬度分布。利用超声振动空蚀平台、扫描电子显微镜（SEM）和激光共聚焦显微镜,研究了强化试样的空蚀性能及空蚀机理。结果 随温度的升高,强化后的铝合金近表层分别形成30、50、70、90μm的晶粒细化层,表面择优取向由（200）转变为（111）;强化温度为50℃时的表面显微硬度最高,较原始试样提高了108.2%;经300 min空化腐蚀后,常温、50、100、150℃条件下处理的超声冲击试样的抗空蚀性能分别是未处理试样的1.77、2.03、1.49和1.38倍;温态冲击强化后,试样的空化腐蚀损伤机制不仅包括初始的韧性断裂破坏,还增加了脆性及疲劳损伤形式。结论 经过温态超声冲击强化处理后,AA6061-T6的抗空蚀性能随温度的升高呈先增后减的趋...     

Enhancing laccase stability and activity for dyes decolorization using ZIF-8@MWCNT nanocomposite

The continuous use of chemical dyes in various industries, and their discharge into industrial effluents, results in severe problems to human life and water pollution. Laccases have the ability to decolorize dyes and toxic chemicals in industrial effluents as green biocatalysts. Their possible industrial applications have been limited by poor reusability, low stability, and loss of free laccase action. In this research, laccase was immobilized on zeolitic imidazolate framework coated multi-walled carbon nanotubes (Laccase@ZIF-8@MWCNTs) via metal affinity adsorption to develop an easy separable and stable enzyme. The optimum reaction conditions for immobilized laccase are at a pH of 3.0 and a temperature of 60?℃. The immobilized laccase was enhanced in storage and thermal stability. The results indicated that Laccase@ZIF-8@MWCNTs still maintained 68% of its original activity after 10 times of repeated use. Most importantly, the biocatalytic system was applied for decolorization of different dyes (20?mg·L^?1) without a mediator, and up to 97.4% for Eriochrome black T and 95.6% Acid red 88 was achieved in 25 min. Biocatalysts with these properties may be used in a variety of environmental and industrial applications.     

Platinum on nitrogen doped graphene and tungsten carbide supports for ammonia electro-oxidation reaction

Ammonia electrooxidation reaction involving multistep electron-proton transfer is a significant reaction for fuel cells, hydrogen production and understanding nitrogen cycle. Platinum has been established as the best electrocatalyst for ammonia oxidation in aqueous alkaline media. In this study, Pt/nitrogen-doped graphene (NDG) and Pt/tungsten monocarbide (WC)/NDG are synthesized by a wet chemistry method and their ammonia oxidation activities are compared to commercial Pt/C. Pt/NDG exhibits a specific activity of 0.472 mA∙cm^–2, which is 44% higher than commercial Pt/C, thus establishing NDG as a more effective support than carbon black. Moreover, it is demonstrated that WC as a support also impacts the activity with further 30% increase in comparison to NDG. Surface modification with Ir resulted in the best electrocatalytic activity with Pt-Ir/WC/NDG having almost thrice the current density of commercial Pt/C. This work adds insights regarding the role of NDG and WC as efficient supports along with significant impact of Ir surface modification.     

Refractory Ceramic Fiber and the Products GB/T 3003-2006

正GB/T 3003-20061 Scope This standard specifies the terms,definitions,classifications,brands,technical requirements,test methods,quality appraisal procedure,packing,marking,transportation,storage and quality certificate of