疏水石墨烯水相分散液的制备及电化学性能

通过未添加表面活性剂和稳定剂而得到均匀的石墨烯水相分散液的方法,近来来成为研究的一大热点.本工作通过提高水合肼的用量,来替代表面活性剂或者其它稳定剂的作用,得到了良好的均匀的水相石墨烯分散液,可长期稳定存放,6个月内未发生团聚现象.其Zeta电位低于-32.5 mV(pH值为5.89),原子力显微镜和透射电子显微镜图像表明产物为具有褶皱结构的、六方晶系的单层石墨烯结构,厚度为0.38 nm.XPS分析显示这种方法对于除去羟基和环氧基团起到了有效的作用.利用这种分散液所制备的石墨烯-玻碳电极(GE-GCE)在检测抗坏血酸(AA)和尿酸(UA)时,比普通玻碳电极(GCE)显示出更良好的电化学响应.     

3D网络虚拟实验开发中基于组件的模型处理与交互方法

针对微型计算机接口课程的网络虚拟实验提出了基于组件的3D网络虚拟实验实现方法.利用3DMAX的坐标轴变换技术与材质技术实现了组件局部坐标系的调整与模型的材质;利用Java3D的模型导入技术与交互式编程技术解决了导入实验板模型时丢失材质、模型的重装、虚拟场景与实验板的操作等问题.以微型计算机接口课程教学实验中基础的8255并行接口实验作为实例设计了一个虚拟实验,为虚拟实验室的开发与应用提供了实用的案例.     

微生物酶催化制备人参皂苷20(S)-Rg2,20(S)-Rh1和20(S)-PPT

摘要 人参次级皂苷具有较强的抗癌、抗癌转移等药理活性,但由于在人参中含量少或不存在,因此以人参中含量较高的主要人参皂苷制备药效更高的人参次级皂苷不仅有必要,而且很有意义．本文以微生物Microbacterium esteraromaticum GS514的培养液中分离的粗酶为催化剂水解人参皂苷Re和Rg1,并通过1H NMR和13C NMR谱进行了水解产物的结构表征．实验结果表明,反应体系中无机盐NaCl的存在与否直接影响人参皂苷Re,Rg1与粗酶液的反应结果.人参皂苷与粗酶液直接反应,人参皂苷Re不发生反应,人参皂苷Rg1通过C6所连β-D-吡喃葡萄糖的选择性水解转化成人参皂苷F1.如果该反应是在无机盐NaCl存在下进行,人参皂苷Re通过对C20 所连β-D-吡喃葡萄糖的选择性水解定向转化为20(S)-人参皂苷Rg2;人参皂苷Rg1定向转化成20(S)-人参皂苷Rh1以及20(S)-原人参三醇（PPT）.这说明NaCl的加入激活了C20β-D-吡喃葡萄糖苷酶的活性,这对定向合成不同次级人参皂苷具有重要意义.     

混合及流体动力润滑下规则微小凹痕图型表面的摩擦特性研究

采用销-盘摩擦副接触方式在混合及流体动力润滑下,对不同密度的规则微小凹痕图型表而进行石蜡油润滑下的摩擦试验,利用Stribeck曲线分析在不同试验条件下,不同密度的规则微小凹痕图型表面的摩擦特性,利用摩擦系数曲线图解析不同载荷和滑动速度下,不同密度的规则微小凹痕图型表面的摩擦行为.结果表明,当试样表面具有规则微小凹痕图型时,其减摩效果较无微小凹痕图型表而更佳,在不同载荷作用下,规则微小凹痕图型存在着最佳的密度分布,即在载荷为5～30N,规则微小凹痕图型密度为32.4%时的减摩效果最佳.     

OPTIMAL GAIN DISTRIBUTION FOR TWO-DIMENSIONAL MODAL TRANSDUCER AND ITS IMPLEMENTATION USING MULTI-LAYERED PVDF FILMS

Using finite element techniques to optimize the spatial gain distribution of PVDF film, we developed a modal transducer for specific modes to perform real-time vibration control of integrated smart structures. This method makes it possible to design the modal transducer for two-dimensional structure with arbitrary geometry and boundary conditions. As a practical means for implementation, the gain distribution was approximated by optimizing electrode patterns, lamination angles, and relative poling directions of the multi-layered PVDF transducer. This corresponds to the approximation of a continuous function using discrete values. A genetic algorithm was used in the optimization of the electrode pattern and lamination angle of each PVDF layer. For this purpose, the continuous value of the lamination angle was encoded into discrete values using binary 5-bit strings. Validity of the proposed concept was demonstrated experimentally. A modal sensor for the first and second modes of cantilevered composite plate was designed using two layers of PVDF films. The experimental results show that spillover signals by residual modes were successfully reduced using the optimized multi-layered PVDF sensor. The actuator was designed also using two layers of PVDF films to minimize the system energy in the control modes. Real-time vibration control system was successfully realized using the optimized sensor, actuator, and a discrete LQG controller. Closed-loop test showed that modal peaks of the first and second modes were reduced by amounts of 13 and 4 dB respectively.     

STUDY OF THE IMPULSE WAVE DISCHARGED FROM THE EXIT OF A RIGHT-ANGLE PIPE BEND

The impulse wave, which is usually generated by a shock wave discharge from the exit of a pipe, almost always leads to undesirable noise and vibration problems. The present study addresses experimental and computational work of the impulse wave discharged from the exit of two kinds of right-angle pipe bends, which are attached to the open end of a simple shock tube. The weak normal shock wave with its magnitude of Mach number from 1·02 to 1·20 is employed to obtain the impulse wave propagating outside the exit of the pipe bends. A Schlieren optical system is employed to visualize the impulse wave discharged from the exit of the pipe bends at an instant. The experimental data of the magnitude of the impulse wave and its propagation directivity are analyzed to characterize the impulse waves discharged from the exit of the pipe bends and compared with those discharged from a straight pipe. Computational analysis using the unsteady, inviscid, compressible equations is complemented to represent the major features of the impulse wave obtained from the shock tube experiments. Computational results well predict the experimented dynamic behaviors of the impulse wave. The results obtained show that a right-angle miter bend considerably reduces the magnitude of the impulse wave and its directivity toward to the pipe axis, compared with the straight pipe. It is believed that the right-angle miter bend pipe can play one role of a passive control against the impulse wave.     

CRACK DETECTION IN BEAM-TYPE STRUCTURES USING FREQUENCY DATA

A practical method to non-destructively locate and estimate size of a crack by using changes in natural frequencies of a structure is presented. First, a crack detection algorithm to locate and size cracks in beam-type structures using a few natural frequencies is outlined. A crack location model and a crack size model are formulated by relating fractional changes in modal energy to changes in natural frequencies due to damage such as cracks or other geometrical changes. Next, the feasibility and practicality of the crack detection scheme are evaluated for several damage scenarios by locating and sizing cracks in test beams for which a few natural frequencies are available. By applying the approach to the test beams, it is observed that crack can be confidently located with a relatively small localization error. It is also observed that crack size can be estimated with a relatively small size error.     

A CONCENTRATED MASS ON THE SPINNING UNCONSTRAINED BEAM SUBJECTED TO A THRUST

The dynamic stability of a spinning unconstrained beam subjected to a pulsating follower forceP₀ +P₁cos Ωt is analyzed. A concentrated mass is located at an arbitrary location on the beam, and the stability of the beam is studied with the mass at various locations. The beam is analyzed using the Timoshenko-type shear deformation theory with the rotary inertia. Hamilton's principle is used to derive the equations of motion, and the spinning speed of the beam with various non-dimensional parameters subjected to a pulsating follower force is investigated. The finite element method is applied to analyze the spinning beam model, and the method of multiple scales is used to investigate the dynamic stability characteristics. A pulsating follower force is applied, and then the stability regions are changed with the transitions of the stability area in many regions. The results show that the concentrated mass increases the dynamic stability of the spinning unconstrained beam subjected to a thrust. As the spinning speed of the beam is increased, the instability regions are reduced, but various slight instability regions are additionally developed.