Organic field-effect transistors as high performance humidity sensors with rapid response,recovery time and remarkable ambient stability

The stability of organic field-effect transistors (OFETs) under very high humidity condition has been the bottleneck in many applications. In this work, remarkable enhancement in ambient stability and performance of CuPc based OFETs are observed by exploiting the polarization of hydroxyl groups in Poly (vinyl alcohol) (PVA) dielectric layer, which is sandwiched between Al₂O₃ and Poly (methyl methacrylate) (PMMA) layer. The devices are used to fabricate OFETs based humidity sensors, which show exceptional ambient stability and rapid response to the water molecules in moisture. In a controlled experiment, the sensors demonstrate 0.73 s as response time and 0.52 s as recovery time. Such results are the fastest responses observed on humidity sensors fabricated based on OFETs. The enhanced responses of the sensors are due to the systematic polarization of the hydroxyl groups present in PVA layer by the additional dipole field arising from the adsorbed water molecules, which are also polarized under gate-field. The devices show no variation in threshold voltage as well as field-effect carrier mobility, measured throughout a year under ambient exposure. The specific design of the sensors with tri-layer dielectric system plays crucial role in enhancing the stability and moisture sensitivity, which can make the devices technologically very relevant.     

Slow sand filters effectively reduce Phytophthora after a pathogen switch from Fusarium and a simulated pump failure

Slow sand filtration has been shown to effectively reduce Phytophthora zoospores in irrigation water. This experiment tested the reduction of Phytophthora colony forming units (CFUs) by slow sand filtration systems after switching the pathogen contaminating plant leachate from Fusarium to Phytophthora and the resilience of the system to a short period without water, as might be caused by a pump failure. The slow sand filtration system greatly reduced Phytophthora CFUs and transmission after switching the pathogens. In addition, Phytophthora reduction by the slow sand filter was equally effective before and after the simulated pump failure. Reduction of Fusarium was not seen by the SSFs, before or after the simulated pump failure. The results suggest that slow sand filters are effective at reducing larger organisms, such as Phytophthora zoospores, even after a pump failure or a change in pathogens.     

采用E2CN拥塞控制的TCP连接时延模型分析

建立了当边缘路由器采用E^2CN拥塞控制的机制时TCP连接时延的数学模型。在理论上分析了运用这种机制能够降低连接时延的原理,给出了拥塞机制中参数对TCP连接时延的影响。通过仿真表明,提出的新的时延模型相当精确,为能更好设计出符合,IP QoS要求的TCP协议应用提供了理论依据。     

使用缓燃推进剂的小型点火器点火技术研究

为可靠点燃某运载火箭芯级发动机的主装药(缓燃双基推进剂),并满足低温(-40℃)可靠点火和高温(50℃)点火压力峰值不高的设计要求,通过设计点火方式、选择点火药、设计点火药盒结构及试验,确定了点火药为高能药与双基药片,点火方式为逐级点火,点火药盒结构采用多个排气孔的设计方案。经验证表明,该方案满足技术要求。     

Application of Quasi Steady-State Model to Slow Mode Periodic Pulsation of the Liquid in Trickle Bed Reactors

Many published studies show the benefits of forced pulsation of the liquid flow rate in a trickle bed reactor, especially when mass transfer phenomena are rate controlling. Two types of periodic liquid pulsation, the slow and fast mode, are examined in the literature, depending on the period of the pulsation.

The aim of this work is to show that, when slow mode pulsation occurs, the quasi steady-state model can be applied. The model assumes that the mean conversion rate in pulsed mode is the weighted mean of the two steady conversion rates at the minimum and maximum liquid flow rates. In fact, the period of the liquid pulsation is long enough to allow the reactor to reach the quasi steady-state conditions at every level of the liquid flow rate. The validity of the model is checked with experimental data concerning α-methylstyrene hydrogenation to cumene.     

A simple dynamic model for polymer electrolyte membrane fuel cell (PEMFC) power modules: Parameter estimation and model prediction

A simple dynamic model was proposed to describe the transient output characteristics of polymer electrolyte membrane fuel cells (PEMFCs). Physical parameters for the proposed model were estimated based on the steady and transient results experimentally obtained using a commercial PEMFC (1.2 kW Nexa power module, Ballard Power Systems Inc.). In the transient experiments, the load current was varied according to the high–low current step and the high–low current sweep schedules. The practical applicability of the proposed dynamic model was demonstrated by comparing the measured and the predicted output behaviors of the Nexa PEMFC power module for prescribed load current schedules.     

Axial symmetric rotation of a partially immersed body in a liquid with a surfactant layer

This paper gives a simple integral formula to evaluate the torque on a slowly rotating symmetric body partially immersed in a viscous liquid covered by an adsorbed surface film. Besides the results known earlier, new results have also been derived for small values of the surface shear viscosity parameter κ. It is seen that the effect of κ in all cases is to increase the torque.     

Accelerated natural fault diagnosis in slow speed bearings with Acoustic Emission

Rolling element bearings are the most common cause of rotating machinery failure. Over the past 20 years, Acoustic Emission (AE) technology has evolved as a significant opportunity to monitor and diagnose the mechanical integrity of rolling element bearings. This paper presents results of an investigation to assess the potential of the Acoustic Emission (AE) technology for detecting and locating natural defects in rolling element bearings. To undertake this task a special purpose test-rig was built that allowed for accelerated natural degradation of a bearing race. It is concluded that sub-surface initiation and subsequent crack propagation can be detected using a range of data analysis techniques on AE’s generated from natural degrading bearings. The paper also investigates the source characterisation of AE signals associated with a defective bearing whilst in operation. This study also attempted to identify the size of a natural defect on bearings using AE technology. In conclusion, the results from this investigation show that whilst measurements on operational bearings cannot be achieved as described in this paper, the method of identifying the onset of crack propagation can be employed as a quality control tool for bearing manufacturers particularly for testing bearing material homogeneity.     

Performance enhancement of fuel cells using bipolar plate duct indentations

In this paper, a method called “bipolar plate duct indentation” is introduced, in which some partial blocks (indents) are recommended to be placed along the fluid delivery channels being machined in bipolar plates (BPPs) of fuel cells (FCs). The indents are to enhance the over-rib convections and the kinetics of reactions in catalyst layers to improve the cell performance. As an initial step to numerically model this problem, a partially porous channel of BPP of a Direct Methanol FC (DMFC) is taken as the model geometry, and the level of heat exchange enhancement due to channel indentation is examined in this geometry. The performed parametric studies show that channel indentation enhances the heat exchange by 40%; with some minor increases in fluid delivery pumping power. From the analogy between the heat and mass transfer problems in dynamically similar problems, it is believed that the mass exchanges between the core channel and the catalyst layer in FC will enhance the same order as that in the pure heat transfer problem. The present work provides helpful guidelines to the bipolar plate manufactures of low-temperature FCs to considerably alleviate the losses on the side(s) of slow reaction electrodes.     

Numerical study of the conical shaped charge for space debris impact

This paper proposes numerical analysis methods to simulate the 6 to 7 km/s class aluminum conical shaped charge (CSC), in order to calibrate the wide-range ballistic limit data obtained by the CSC with the solid spherical projectiles' data. Two kinds of numerical methods are demonstrated by performing a number of numerical analyses with a coupled hydrocode: AUTODYN™-2D for both the non-inhibited and inhibited CSC: one method is a purely numerical approach and the other is a half-numerical approach combined with a jetting theory. The final purpose of the present study is to assess the orbital space debris impact on the spacecraft in the low earth orbit (LEO), so that aluminum should be adopted as a liner, and the inhibitor should be also equipped. Consequently, the jet ought to have a hollow shape and be vaporized partially. The merits and demerits of two methods are investigated through the numerical analyses, especially the limitations of the half-numerical approach will be made clear when we apply it to the inhibited CSC, while the process of jetting and trapping in the inhibited CSC will be successfully demonstrated by the pure-numerical approach.