Risk-based grouping for checked baggage screening systems

With millions of bags checked at over 7000 baggage screening locations in US daily, the checked baggage screening system may be exploited by the terrorists to do harm to the homeland security. Due to such a huge amount of luggage, how to improve the effectiveness and efficiency of the screening system becomes a challenging task. In this paper, we propose a risk-based cost-effectiveness model where checked bags are classified into several risk classes according to their risk characteristics. According to their risk levels, bags from different classes may go through different device combinations sequentially. For a multiple-device screening system, we determine the optimal sequence of the screening devices and the separate grouping strategies for bags from different risk classes with the objective of minimizing the expected cost per bag. Based on a detailed numerical study, we compare our model with three other cost-effectiveness models (the first model assumes that there is only one risk class, the second model assumes that there is only one group for each risk class, and the third model assumes that all devices in a device combination need to be gone through). Our major conclusions are that our proposed model is beneficial compared with other three models and moreover, the relative benefit becomes larger when the authority commands a stricter upper bound for the probability of false clear.     

一般反失效率脆弱模型的年龄性质和随机比较

反失效脆弱模型被广泛应用于医疗、工业与保险等众多领域的研究中,关于反失效脆弱模型的随机比较和年龄性质的研究近年来引起了大家的普遍关注,并取得了一系列丰硕的成果.本文通过进一步讨论一般反失效脆弱模型中的随机比较与年龄性质的手段,为了更好的应用模型对系统进行可靠性刻画,得到了一些年龄性质,给出了一些随机序关系.     

Corrosion behavior of Zn?Ni?Al2O3 nanocomposite coatings obtained by electrodeposition from alkaline electrolytes

The aim of this work was to investigate the anti‐corrosive properties of nanocomposite Zn? Ni coatings containing Al₂O₃ nanoparticles, prepared from alkaline commercial electrolytes (pH 13), (PERFORMA 280.5, COVENTYA S.A.S, France), by electrodeposition on carbon steel (OL37). The corrosion resistance of the coatings prepared with different concentrations of Al₂O₃ (5, 10, and 15 g/L) was evaluated in 0.2 g/L Na₂SO₄ solution (pH 5) by open circuit potential (OCP) measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. The results of electrochemical measurements were corroborated with those obtained by using X‐ray diffraction analysis. The obtained results show that the introduction of Al₂O₃ nanoparticles in the plating bath generally brings an increase in corrosion resistance of Zn? Ni layers and put in evidence the existence of an optimal Al₂O₃ concentration. Under the examined conditions, the optimal concentration determined from polarization measurements was proven to be 5 g/L Al₂O₃. The highest value of the polarization resistance, R_p, obtained from impedance measurements corresponds also to Zn? Ni with 5 g/L Al₂O₃, which is in agreement with the results obtained from polarization and XRD measurements.     

Operation of a horizontal subsurface flow constructed wetland – Microbial fuel cell treating wastewater under different organic loading rates

The aim of the present work is to determine whether a horizontal subsurface flow constructed wetland treating wastewater could act simultaneously as a microbial fuel cell (MFC). Specifically, and as the main variable under study, different organic loading rates were used, and the response of the system was monitored. The installation consisted of a synthetic domestic wastewater-feeding system and a pilot-scale constructed wetland for wastewater treatment, which also included coupled devices necessary to function as an MFC. The wetland worked under continuous operation for 180 d, treating three types of synthetic wastewater with increasing organic loading rates: 13.9 g COD m⁻² d⁻¹, 31.1 g COD m⁻² d⁻¹, and 61.1 g COD m⁻² d⁻¹. The COD removal efficiencies and the cell voltage generation were continuously monitored. The wetland worked simultaneously as an MFC generating electric power. Under low organic loading rates, the wastewater organic matter was completely oxidised in the lower anaerobic compartment, and there were slight aerobic conditions in the upper cathodic compartment, thus causing an electrical current. Under high organic loading rates, the organic matter could not be completely oxidised in the anodic compartment and flowed to the cathodic one, which entered into anaerobic conditions and caused the MFC to stop working. The system developed in this work offered similar cell voltage, power density, and current density values compared with the ones obtained in previous studies using photosynthetic MFCs, sediment-type MFCs, and plant-type MFCs. The light/darkness changes caused voltage fluctuations due to the photosynthetic activity of the macrophytes used (Phragmites australis), which affected the conditions in the cathodic compartment.     

互感器准确级选择

介绍电流、电压互感器的准确级,并给出了不同级次的误差限值并结合DL/T448-2000《电力计量装置技术管理规程》对互感器的准确级选择提供了参考意见。     

Synthesis, characterization and electrochemical properties of 4.8 V LiNi0.5Mn1.5O4 cathode material in lithium-ion batteries

In this work the synthesis of a nickel doped cubic manganese spinel has been studied for application as cathode material in secondary lithium batteries. Six different experimental approaches have been tested in order to carry out a screening of the various possible synthetic routes. The used synthetic strategies were wet chemistry (WC), solid state (SS), combustion synthesis (CS), cellulose-based sol-gel synthesis (SG-C), ascorbic acid-based sol-gel synthesis (SG-AA) and resorcinol/formaldehyde-based sol-gel synthesis (SG-RF). The goal of our study is to obtain insights about how the synthesis conditions can be modified in order to achieve a material with improved electrochemical performances in such devices, especially in high current operating regimes. The synthesized materials have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), atomic absorption, inductively coupled plasma (ICP-MS) atomic emission spectroscopy, surface area measurements and tested as high voltage cathodes in Li-ion electrochemical devices.     

井下远距离供电电压降的计算方法

目前煤矿工作面供电距离长,电压降幅度较大,为改善供电质量,保证井下远距离供电安全,提出了对电压降的几种计算方法,结合余吾煤业公司S1202综采工作面现状,验证了该方法的可行性。     

Influence of nano-CeO2 on coating structure and properties of electrodeposited Al/α-PbO2/β-PbO2

Al/α-PbO₂/β-PbO₂ composite electrodes doped with rare earth oxide (CeO₂) were prepared by anodic oxidation method investigate the influence of nano-CeO₂ dopants on the properties of Al/α-PbO₂/β-PbO₂-CeO₂electrodes and the impact of α-PbO₂ as the intermediate layer. The results show that using α-PbO₂ as the intermediate layer will benefit the crystallization of β-PbO₂ and β-PbO₂ is more suitable as the surface layer than α-PbO₂. CeO₂ dopants change the crystallite size and crystal structure, enhance the catalytic activity, and even change the deposition mechanism of PbO₂. The doping of CeO₂ in the PbO₂ electrodes can enhance the electro-catalytic activity, which is helpful for oxygen evolution, and therefore reduce the cell voltage.     

井下绳类落物打捞工艺技术应用现状分析

井下绳类落物打捞工艺技术是石油井下工程事故处理工艺的重要组成部分。由于绳类落物具有细长、柔软、易滑脱、容易收缩变形的特点，因此在打捞中不易捞获，看似简单，实际打捞还有相当的难度，还有一定的技巧。本文就绳类落物打捞工艺技术进行探讨分析。