Simultaneous and Sequential Photosonolysis of TCE and PCE

Aqueous solutions of trichloroethylene (TCE) and tetrachloroethylene (PCE) were treated in a flow-through reactor equipped with ultrasound and ultraviolet light sources. The reactor was operated as sonolysis (US), photolysis (UV), and simultaneous photosonolysis (UV/US) reactors; then as US, UV, and sequential UV/US reactors with the installation of a partition in the reactor. The reactor without the partition was simulated by using one continuously stirred-tank-reactor (1-CSTR) model, and the reactor with the partition was simulated by using the sequential CSTR model. Through model calibration, the decomposition rate constants and reactor efficiencies for the removal of TCE and PCE were evaluated. The results suggest that the combined effect of UV and US on the decomposition of TCE and PCE is synergistic in both the simultaneous and sequential UV/US modes, that the rate constants of sonolysis and photolysis are greater with the sequential combination than with the simultaneous combination, and that overall efficiency is higher for the reactor with the partition than for the one without it.     

Destruction of Trichloroethylene and Perchloroethylene DNAPLs by Catalyzed H2O2 Propagations

The destruction of trichloroethylene (TCE) and perchloroethylene (PCE) dense nonaqueous phase liquids (DNAPLs) using catalyzed H2O2 propagations (CHP), an in situ chemical oxidation process based on Fenton’s reagent, was investigated in batch, bench scale reactors. TCE and PCE masses were quantified over time in DNAPLs, aqueous phases, and off gasses, and the rate of DNAPL destruction was compared to the corresponding rate of gas purge dissolution. TCE and PCE DNAPLs were rapidly destroyed by CHP at 1.7 and 4.4 times the rate of gas purge dissolution, respectively. Use of reactions in which a single reactive oxygen species was generated demonstrated that both hydroxyl radical and superoxide were involved in TCE and PCE DNAPL destruction, with superoxide having the major role in the destruction of the DNAPLs. These results show that DNAPLs composed of contaminants highly reactive with hydroxyl radical, such as TCE and PCE, are destroyed primarily through reaction with superoxide.     

Evaluation of Granular Surfactant-Modified/Zeolite Zero Valent Iron Pellets As a Reactive Material for Perchloroethylene Reduction

The use of permeable reactive barriers (PRBs) for groundwater remediation is based on two distinct mechanisms: sorption and transformation. With sorption as the main mechanism, contaminants sorb on the PRB materials and are retarded. With transformation as the main mechanism, the contaminants react with the PRB materials and then converted to less toxic or innocuous substances. In this study, we tested surfactant-modified zeolite/zero valent iron (SMZ/ZVI) pellets as a PRB material to retard and degrade perchloroethylene (PCE), utilizing both sorption and transformation processes. Batch PCE kinetic studies showed instantaneous PCE removal from the aqueous phase due to sorption and subsequent removal with time due to reduction. The separation of sorption from reduction can be used to obtain both the PCE distribution coefficient (Kd) and the pseudofirst-order reduction rate constant (μobs) from a single batch experiment. The calculated Kd and μobs values are 3.0 and 0.5?L/kg and 0.14 and 0.05?h?1 for SMZ/ZVI and Z/ZVI pellets, respectively. Column experiments were performed at linear flow velocities of 0.07, 0.14, and 0.20?cm/min. The results were modeled using the one-dimensional advection–dispersion equation with linear sorption and first-order transformation. The Kd values were 2.3±0.4 and 0.5±0.1?L/kg for SMZ/ZVI and Z/ZVI pellets, respectively, in agreement with those of the batch study. The PCE transformation constants varied between 0.077 and 0.199?h?1 for the SMZ/ZVI pellets and between 0.037 and 0.144?h?1 for the Z/ZVI pellets, indicating that an enhanced transformation of PCE occurred with the sorbing SMZ/ZVI pellets. The PCE reduction rates were faster at slower flow rates, indicating that the reduction was not a mass-transfer-limited process.     

普适环境下的一种跨域认证机制

由于普适计算的高度移动性,通信的双方经常位于不同的区域,为了保证服务的合法访问以及消息的安全传输,需要进行跨域认证以及安全会话密钥建立。提出了一种新的跨域认证与密钥建立协议,该协议采用生物加密技术省去了证书管理的负担,合理设计了通信双方及其各自服务器之间的交互,完成了跨域双向认证,并采用签密技术为通信双方派生密钥。对协议进行了安全及性能的分析,并用经典的SVO逻辑证明了其正确性。     

ChinaNet向SDN演进的方法探索

中国电信的ChinaNet是全球最大的Internet之一,承载着全球最大的流量,并且长期呈高速增长,今后也将继续保持高增长态势.超大流量的Internet可持续发展和网络每比特承载成本的降低,是两个关键的问题.从这两个方面出发,利用集中控制的技术优势,探索如何将ChinaNet逐步迁移到SDN,并利用集中控制技术解决ChinaNet面临的问题.     

Magneto-optical behaviors at a 2-D ferromagnetic/organic semiconductor interface for singlet fission

This article reports the magneto-optical effects on the singlet fission of the p-type organic semiconductor, tetracene, from a ferromagnetic/semiconductor interface between thin films of cobalt and tetracene. We experimentally show that this interface has two effects on the thin films of tetracene: spin interactions and electrical polarization. The experimental tools used to study the interface include magnetic field effect photoluminescence (MFE_PL), photoluminescence and absorption. Spin interaction effects are shown by MFE_PL data, where we observe a large increase in the maximum MFE_PL when cobalt is introduced, as well as changes in the hyperfine interactions at low magnetic fields. Electrical polarization is analyzed with photoluminescence and absorption measurements, showing small changes in the energy difference between the HOMO and LUMO levels of tetracene, as well as an increase in the electron-phonon coupling in tetracene. Also, electrical polarization is shown to increase electrical interactions between tetracene molecules. Therefore, we conclude that using spin interactions and electrical polarization from the ferromagnetic/organic semiconductor interface can tune the properties of tetracene, ultimately enhancing singlet fission. This work gives new insight to understand the singlet fission process using a ferromagnetic interface. These changes can be further utilized in photovoltaic applications based on this singlet fission material and be applied to other similar types of singlet fission organic semiconductors.     

A common-gate bootstrapped CMOS rectifier for VHF isolated DC-DC converter

A common-gate bootstrapped CMOS rectifier dedicated for VHF (very high frequency) isolated DC-DC converter is proposed.It uses common-gate bootstrapped technique to compensate the power loss due to the threshold voltage,and to solve the reflux problem in the conventional rectifier circuit.As a result,it improves the power conversion efficiency (PCE) and voltage conversion ratio (VCR).The design saves almost 90% of the area compared to a previously reported double capacitor structure.In addition,we compare the previous rectifier with the proposed common-gate bootstrapped rectifier in the case of the same area;simulation results show that the PCE and VCR of the proposed structure are superior to other structures.The proposed common-gate bootstrapped rectifier was fabricated by using CSMC 0.5 μm BCD process.The measured maximum PCE is 86% and VCR achieves 77% at the operating frequency of 20 MHz.The average PCE is about 79% and average VCR achieves 71% in the frequency range of 30-70 MHz.Measured PCE and VCR have been improved compared to previous results.     

Biodegradation of Tetrachloroethene by Chitin Fermentation Products in a Continuous Flow Column System

The ability of chitin fermentation products to promote tetrachloroethene (PCE) reduction was evaluated in a continuous-flow column system to identify how different electron donors affect reductive dechlorination. Natural chitin fermentation products were initially used to support PCE reduction. Acetate (3.5?mM) was the dominant fermentation product, followed by propionate (0.1?mM), butyrate (0.1?mM), and hydrogen (100?nM). After chlorinated ethene concentration profiles reached pseudo steady state, the ability of individual fermentation products (acetate, acetate+propionate, propionate, or formate) to support PCE reduction was evaluated. None of the fermentation products tested stimulated dechlorination as well as the suite generated from chitin (kPCE = 6.9?day?1); however, acetate-stimulated PCE dechlorination the best (kPCE = 5.3?day?1), followed by formate (kPCE = 2.4?day?1), acetate+propionate (kPCE = 1.8?day?1), and propionate (kPCE = 1.2?day?1). Similar trends were observed for the PCE daughter products trichloroethene and dichloroethene. Free energies of individual fatty acid reactions were calculated and shown to be useful predictors of dechlorination performance, except for the case of acetate+propionate. Hence, acetate is the dominant fatty acid controlling dechlorination in the chitin-enhanced system, propionate appears to have an inhibitory effect when present with acetate alone, and other unidentified nutrients produced during chitin fermentation likely contribute to dechlorination activity as well.     

Photochemical Remediation of Tetrachloroethylene: Reactor Design, Construction, and Preliminary Results

A custom designed pilot-scale photochemical remediation reactor is constructed for remediation of vapor-phase volatile organic halocarbons (VOHs), particularly chlorinated hydrocarbons such as PCE (tetrachloroethylene). Ultraviolet (UV) light, when emitted at an effective absorption frequency, cleaves a VOH’s carbon-chloride bond, transforming harmful contaminants to harmless products. The stainless steel reactor is of tubular-shape with an inner diameter of 32 cm and a length of 105 cm. The net volume of the reactor is approximately 73.7 L. Three stainless steel baffles are welded inside the reactor to create a well-mixed vapor phase and uniform UV contact time. Special low-pressure mercury amalgam UV lamps (Heraeus, Inc., Duluth, Ga.) are used as the photoenergy source. Two independent vapor-phase PCE destruction experiments are conducted using different influent contaminant concentrations. Both experiments show a PCE destruction efficiency of over 99%.