科创中国

搜索引擎是当今人们获取信息的入口,百度指数反映了关键词被搜索的次数,直接衡量着投资者的有限关注.本文实证检验了百度指数和创业板股票市场表现的相关性,在此基础上,验证了投资者有限关注能影响股票的市场交易活动.投资者的有限关注能给股票带来正向的价格压力,而这种压力会很快发生反转.本文还利用百度指数逐日可测的优点,研究发现非交易日的投资者关注将显著影响下一交易日股票集合竞价时的价格跳跃.

The methods of improving the dynamic performance of high speed on/off solenoid valve include increasing the magnetic force of armature and the slew rate of coil current, decreasing the mass and stroke of moving parts. The increase of magnetic force usually leads to the decrease of current slew rate, which could increase the delay time of the dynamic response of solenoid valve. Using a high voltage to drive coil can solve this contradiction, but a high driving voltage can also lead to more cost and a decrease of safety and reliability. In this paper, a new scheme of parallel coils is investigated, in which the single coil of solenoid is replaced by parallel coils with same ampere turns. Based on the mathematic model of high speed solenoid valve, the theoretical formula for the delay time of solenoid valve is deduced. Both the theoretical analysis and the dynamic simulation show that the effect of dividing a single coil into N parallel sub-coils is close to that of driving the single coil with N times of the original driving voltage as far as the delay time of solenoid valve is concerned. A specific test bench is designed to measure the dynamic performance of high speed on/off solenoid valve. The experimental results also prove that both the delay time and switching time of the solenoid valves can be decreased greatly by adopting the parallel coil scheme. This research presents a simple and practical method to improve the dynamic performance of high speed on/off solenoid valve.

在以往的服务管理研究中,服务绩效的影响因素很多,然而没有文献研究员工对服务的概念性界定对服务绩效的影响.基于行为识别理论,文章提出服务认知一行为模式对一线员工的服务绩效存在影响.该研究利用旅行社业和饭店业402名一线服务员工的问卷调查数据,部分验证了所提出的假设,实证结果发现:(1)对顾客理解型服务认知一行为模式具有最高的角色外服务绩效,对工作规范型服务认知一行为模式具有最低的角色外服务绩效;(2)对工作规范型服务认知一行为模式具有最低的角色内服务绩效,对顾客理解型和手段型服务认知一行为模式具有较高的角色内服务绩效.

The transient behavior of centrifugal pumps during transient operating periods,such as startup and stopping,has drawn more and more attention recently because of urgent needs in engineering.Up to now,almost all the existing studies on this behavior are limited to using water as working fluid.The study on the transient behavior related to solid-liquid two-phase flow has not been seen yet.In order to explore the transient characteristics of a high specific-speed centrifugal pump during startup period delivering the pure water and solid-liquid two-phase flow,the transient flows inside the pump are numerically simulated using the dynamic mesh method.The variable rotational speed and flow rate with time obtained from experiment are best fitted as the function of time,and are written into computational fluid dynamics(CFD)code-FLUENT by using a user defined function.The predicted heads are compared with experimental results when pumping pure water.The results show that the difference in the transient performance during startup period is very obvious between water and solid-liquid two-phase flow during the later stage of startup process.Moreover,the time for the solid-liquid two-phase flow to achieve a stable condition is longer than that for water.The solid-liquid two-phase flow results in a higher impeller shaft power,a larger dynamic reaction force,a more violent fluctuation in pressure and a reduced stable pressure rise comparing with water.The research may be useful to understanding on the transient behavior of a centrifugal pump under a solid-liquid two-phase flow during startup period.

物流企业员工绩效考核的内容主要包括员工的态度和能力考核,物流企业员工绩效指标设计的内容分为绩效维度、能力维度、态度维度和个人素质等方面.物流企业员工指标体系设计的考核采用360绩效考核,考核方法主要采用KPI法和AHP法,把绩效考核的结果在报酬运用、工作调整、开发潜能等方面进行运用.

The existing research on improving the hydraulic performance of centrifugal pumps mainly focuses on the design method and the parameter optimization.The traditional design method for centrifugal impellers relies more on experience of engineers that typically only satisfies the continuity equation of the fluid.In this study,on the basis of the direct and inverse iteration design method which simultaneously solves the continuity and motion equations of the fluid and shapes the blade geometry by controlling the wrap angle,three centrifugal pump impellers are designed by altering blade wrap angles while keeping other parameters constant.The three-dimensional flow fields in three centrifugal pumps are numerically simulated,and the simulation results illustrate that the blade with larger wrap angle has more powerful control ability on the flow pattern in impeller.The three pumps have nearly the same pressure distributions at the small flow rate,but the pressure gradient increase in the pump with the largest wrap angle is smoother than the other two pumps at the design and large flow rates.The pump head and efficiency are also influenced by the blade wrap angle.The highest head and efficiency are also observed for the largest angle.An experiment rig is designed and built to test the performance of the pump with the largest wrap angle.The test results show that the wide space of its efficiency area and the stability of its operation ensure the excellent performance of the design method and verify the numerical analysis.The analysis on influence of the blade wrap angle for centrifugal pump performance in this paper can be beneficial to the optimization design of the centrifugal pump.

CdSe/CdS semiconductor quantum dots co-sensitized TiO2 nanorod array was fabricated on the transparent conductive fluorine-doped tin oxide (FTO) substrate using the hydrothermal and successive ionic layer adsorption and reaction (SILAR) process. The structural and morphological properties of the samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The results indicate that CdSe/CdS QDs are uniformly coated on the surface of the TiO2 nanorods. The shift of light absorption edge was monitored by taking UV-visible absorption spectra. Compared with the absorption spectra of the TiO2 nanorod array, deposition of CdSe/CdS QDs shifts the absorption edge to the higher wavelength. The enhanced light absorption in the visible-light region of CdSe/CdS/TiO2 nanorod array indicates that CdSe/CdS layers can act as co-sensitizers in quantum dots sensitized solar cells (QDSSCs). By optimizing the CdSe layer deposition cycles, a photocurrent of 5.78 mA/cm2, an open circuit photovoltage of 0.469 V and a conversion efficiency of 1.34 % were obtained under an illumination of 100 mw/cm2.

Traditional model for calculating performance parameters of a fix-pad journal bearing leads to heavy workload,complicated and changeable formulae as it requires deriving various geometric formulae with different bearing types such as circular journal bearing,dislocated bearing and elliptic bearing.Considering different pad preload ratios for non-standard bearing,traditional model not only becomes more complicated but also reduces scalability and promotion of the calculation programs.For the complexly case of traditional model while dealing with various fix-pad journal bearings,unified coordinate system model for performance calculation of fix-pad journal bearing is presented in the paper.A unified coordinate system with the bearing center at the origin is established,and the eccentricity ratio and attitude angle of axis relative to each pad are calculated through the coordinates of journal center and each pad center.Geometric description of fix-pad journal bearing is unified in this model,which can be used for both various standard bearing and non-standard bearing with different pad preload ratios.Validity of this model is verified with an elliptical bearing.Performance of a non-standard four-leaf bearing with different pad preload ratios is calculated based on this model.The calculation result shows that increasing preload ratio of the pad 1 and keeping that of the left three pads constant improves bearing capacity,stiffness and damping coefficients.This research presents a unified coordinate system model unifies performance calculation of fix-pad journal bearings and studied a non-standard four-leaf bearing with different pad preload ratios,the research conclusions provides new methods for performance calculation of fix-pad journal bearings.

目的 调查临床护士情绪智力水平与工作绩效的现状,分析情绪智力与工作绩效的相关性.方法 采用情绪智力量表及工作绩效量表,对378名临床护士进行调查.结果 临床护士情绪智力得分(5.15±0.45)分,工作绩效得分(2.88±0.56)分;情绪智力各维度与工作绩效均呈正相关(P<0.01);情绪智力4个维度均是工作绩效的影响因素.结论 护理管理者应采取适当措施提高临床护士情绪智力,特别是提高临床护士与他人的沟通能力,从而提高工作绩效并建立良好的护患关系.

The current research of machine center accuracy in workspace mainly focuses on the poor geometric error subjected to thermal and gravity load while in operation,however,there are little researches focusing on the effect of machine center elastic deformations on workspace volume.Therefore,a method called pre-deformation for assembly performance is presented.This method is technically based on the characteristics of machine tool assembly and collaborative computer-aided engineering(CAE)analysis.The research goal is to enhance assembly performance,including straightness,positioning,and angular errors,to realize the precision of the machine tool design.A vertical machine center is taken as an example to illustrate the proposed method.The concept of travel error is defined to obtain the law of the guide surface.The machine center assembly performance is analyzed under cold condition and thermal balance condition to establish the function of pre-deformation.Then,the guide surface in normal direction is processed with the pre-deformation function,and the machine tool assembly performance is measured using a laser interferometer.The measuring results show that the straightness deviation of the Z component in the Y-direction is 158.9%of the allowable value primarily because of the gravity of the spindle head,and the straightness of the X and Y components is minimal.When the machine tool is processed in pre-deformation,the straightness of the Z axis moving component is reduced to 91.2%.This research proposes a pre-deformation machine center assembly method which has sufficient capacity to improving assembly accuracy of machine centers.