Effects of axial conduction in laminar tube flow with convective boundaries

Heat transfer in laminar tube flow with convective boundary conditions and axial heat conduction in the fluid is solved exactly. The effects of the external Biot numbers and the axial conduction in fluid on the temperature distribution and the local Nusselt number are determined for both the upstream and the downstream regions. In order to illustrate the effects of velocity profile, the results for the slug flow and the parabolic velocity profiles are plotted simultaneously. The heat transfer characteristics of the flow are found to be rather sensitive to the Péclét number, the external Biot numbers and the velocity profile in the thermal entrance region.     

Effects of shear stresses and antioxidant concentrations on the production of reactive oxygen species in lung cancer cells

Reactive oxygen species (ROS) are known to be a key factor in the development of cancer, and many exogenous sources are supposed to be related to the formation of ROS. In this paper, a microfluidic chip was developed for studying the production of ROS in lung cancer cells under different chemical and physical stimuli. This chip has two unique features: (1) five relative concentrations of 0, 1/8, 1/2, 7/8, and 1 are achieved in the culture regions; (2) a shear stress gradient is produced inside each of the five culture areas. Lung cancer cells were seeded inside this biocompatible chip for investigating their response to different concentrations of H₂O₂, a chemical stimulus known to increase the production of ROS. Then the effect of shear stress, a physical stimulus, on lung cancer cells was examined, showing that the production of ROS was increased in response to a larger shear stress. Finally, two antioxidants, α-tocopherol and ferulic acid, were used to study their effects on reducing ROS. It was found that high-dose α-tocopherol was not able to effectively eliminate the ROS produced inside cells. This counter effect was not observed in cells cultured in a traditional chamber slide, where no shear stress was present. This result suggests that the current microfluidic chip provides an in vitro platform best mimicking the physiological condition where cells are under circulating conditions.     

Effect of geometry on the performance of MEMS aluminum nitride trampoline resonators in longitudinal resonance

The performance of a microscale aluminum nitride piezoelectric resonator in the shape of a trampoline is analyzed using three-dimensional finite element simulations. The air-suspended resonator is supported by beams and is designed to respond to longitudinal through-thickness vibrations. The device is targeted to operate at UHF frequencies (3 GHz) suitable for wireless filtering applications. Energy loss due to material damping is accounted for in the model. Other sources of damping are considered. We analyze if and how the material thickness, number of beams and beam length affect the resonator performance. This is intended to provide useful information at the design stages and eliminate the high costs associated with manufacturing a filter with poor performance. Performance is evaluated by means of the electromechanical coupling coefficient (K²) and the quality factor (Q) calculated from the electrical impedance frequency response plots. The results indicate that (i) K² is insensitive to geometry (K²～6.5%), (ii) Q increases linearly with the AlN thickness attaining Q～1900 for a 1.7 μm thick resonator and (iii) a trampoline resonator with three beams has a better performance capability than the resonator with four or eight beams with a figure of merit K²Q～120 and resonating at a higher frequency value than its counterparts resonators, peaking at 3.21 GHz. The performance figures agree well with those predicted by a one dimensional theory. The value of K² also agrees well with test data but that of Q is higher than the one recorded in the lab.     

轴向进给量对车铣表面微观几何形貌的研究

文章建立球头铣刀正交车铣加工件表面微观几何形貌的数学模型,研究不同的轴向进给量对加工表面微观几何形貌的影响,为在车铣加工中其他的切削用量参数加工的表面微观几何形貌提供一定的参考评价机制。     

苦参总碱中残留溶剂三氯甲烷测定

目的：建立苦参总碱中三氯甲烷残留的检测方法：方法：采用气相色谱顶空进样法。以DB-WAX（或极性相近）为固定液;起始温度为60℃,维持6分钟,再以每分钟15℃的速率升温至180℃,维持5min;进样口温度为220℃,检测器温度为250℃。结果：各个峰的分离效果好,三氯甲烷浓度在12.2~1217.6 ug·mL-1的范围内呈良好的线性关系（r=0.9978）,平均回收率为98.16%。结果与结论：采用本法分离度较好,灵敏度高、重现性好,可以作为苦参总碱中三氯甲烷残留的检测方法。     

浅析焊接残余应力的控制与消除

文章通过分析焊接残余应力产生的原因及其对焊接结构产生的影响,提出了控制焊接残余应力的措施及消除焊接残余应力的方法,明确了控制与消除焊接残余应力对焊接构件的重要性。     

对开采老窿矿山边残矿体的一些看法

对于资源枯竭或经济濒危的老窿矿山,研究边残矿体的回采利用问题,对提高矿产资源利用率,延长矿山寿命,提高经济增长点,是一项有显著的现实意义和长远意义的工作,已被越来越多的矿山所重视。     

基于能量簇头选举算法中选举系数的研究

无线传感器网络中基于节点剩余能量簇头选举算法(MLEACH)是在LEACH协议基础上得到的改进算法,能有效地延长网络的生存时间,改善了网络性能.本算法的关键是设置合理可行的选举系数,它决定了簇头选举时间和轮数.本文提出了选举系数的确立方法,并进行了模拟仿真,试验结果表明:选举系数与节点数目、簇成员节点能量消耗成正比,与簇头节点能量消耗成反比.     

Adaptive vibration control of a flexible structure based on hybrid learning controlled active mass damping

Natural disasters such as earthquakes and strong winds will lead to vibrations in ultra-high or high-rise buildings and even the damages of the structures. The traditional approaches resist the destructive effects of natural disasters through enhancing the performance of the structure itself. However, due to the unpredictability of the disaster strength, the traditional approaches are no longer appropriate for earthquake mitigation in building structures. Therefore, designing an effective intelligent control method for suppressing vibrations of the flexible buildings is significant in practice. This paper focuses on a single-floor building-like structure with an active mass damper (AMD) and proposes a hybrid learning control strategy to suppress vibrations caused by unknown time-varying disturbances (earthquake, strong wind, etc.). As the flexible building structure is a distributed parameter system, a novel finite dimension dynamic model is firstly constructed by assumed mode method (AMM) to effectively analyze the complex dynamics of the flexible building stucture. Secondly, an adaptive hybrid learning control based on full-order state observer is designed through back-stepping method for dealing with system uncertainties, unknown disturbances and immeasurable states. Thirdly, semi-globally uniformly ultimate boundedness (SGUUB) of the closed-loop system is guaranteed via Lyapunov’s stability theory. Finally, the experimental investigation on Quanser Active Mass Damper demonstrates the effectiveness of the presented control approach in the field of vibration suppression. The research results will bring new ideas and methods to the field of disaster reduction for the engineering development.     

企业竞争优势的知识合作剩余创造机理

知识是企业的重要资源,知识合作已经成为企业发展的重要战略。本文从合作剩余的概念着手,描述了知识合作剩余更新企业知识的过程,解释了知识合作剩余创造和维持企业竞争优势的机理,为企业采取合作战略发展核心竞争能力提供了依据。     

陕西省农业科技进步贡献率测算分析——基于索罗余值法

在阐明农业科技进步贡献率概念与整理相关数据的基础上,利用索罗余值法对陕西农业科技进步贡献率进行测算分析。针对陕西省耕地面积变动幅度较大的特点,在比较分析常用固定弹性法与变动弹性法后选择变动弹性法,结合SPSS 18.0软件测算出近年来陕西省物质费用弹性系数为0.353,劳动力弹性系数为0.636,耕地弹性系数为0.111;同时,对陕西省农业科技进步贡献率的测算结果首次表明,陕西省的农业科技进步贡献率周期为5年。最后,将测算结果与陕西省实况相结合,给出具体对策建议。     

延长中试装置轴流泵机械密封使用周期的探索

轴流泵是聚丙烯装置的关键设备,机械密封是否正常关系轴流泵的稳定运行。通过对磨损机械密封部件原因分析,对应采取措施,提高了机械密封的使用寿命。     

Distributed formation control of double-integrator fractional-order multi-agent systems with relative damping and nonuniform time-delays

In this paper, distributed formation control problems are studied for double-integrator fractional-order multi-agent systems (DIFOMASs) with relative damping and nonuniform time-delays. The required state deviations of a group of multi-agent systems are achieved through a local state information interaction, which means that this group of multi-agent systems achieves formation control. In the context of this paper, the dynamic model is first established and the formation control protocol is designed for distributed formation control of DIFOMASs with relative damping under symmetric time-delays and asymmetric time-delays. Then, some sufficient conditions for achieving distributed formation control of DIFOMASs are acquired with the help of graph theory, matrix theory, stability theory and frequency-domain theory. In the end, two simulation examples are performed to verify the efficacy of our proposed method.     

Quantum dynamics of two photons in the coherent feedback system composing of two separated resonators coupling to a waveguide

Quantum coherent feedback based on waveguide quantum electrodynamics plays important roles in quantum devices design and quantum information processing. In this paper, we study the coherent dynamics of the quantum network composed of two separated resonators coupling to a waveguide. Using the dynamical feedback equation in Markovian regime, we obtain the analytical solutions to the output states for the two photons incident from the same or different directions of the waveguide. The two- photon scattering properties are analyzed based on the analytical expressions. It is found that the output states of the two photons can be controlled well by the phase induced by the single photon propagating between the two separated resonators. The results given in this paper are helpful in designing quantum devices at few-photon level.