Photocatalytic degradation of model organic pollutants on an immobilized particulate TiO2 layer: Roles of adsorption processes and mechanistic complexity

The kinetics of photocatalytic degradation of four different model organic compounds, formic acid (FA), oxalic acid (OA), 4-chlorophenol (4-CP) and the herbicide monuron (3-(4-chlorophenyl)-1,1-dimethylurea) in a self-constructed batch-mode plate photoreactor with a thin flow of contaminated aqueous solution circulating over an illuminated particulate layer of TiO₂ P25 (Degussa) was compared. Both OA and FA were adsorbed on TiO₂ surface; their mineralization, induced by direct transfer of photogenerated holes, proceeded in a single step, without observable intermediates, following approximately zero order kinetics. Numerical simulations were performed using a newly proposed kinetic model based on the photostationary state assumption. The model allowed an explanation of the observed reaction order as well as the comparison of independent with competitive adsorption of organic compound and oxygen on the photocatalyst surface, yielding a better fit for the case of competition. 4-CP and monuron, which were not adsorbed under the conditions used, were degraded through the action of photogenerated hydroxyl radicals. Their degradation proceeded with lower photoefficiency than for the adsorbed compounds (FA and OA). While the mineralization of both 4-CP and monuron followed zero order kinetics, their degradation was close to first order. The different reaction orders were consistently explained using the photostationary state approach.     

Coverage metrics for formal verification

In formal verification, we verify that a system is correct with respect to a specification. Even when the system is proven to be correct, there is still a question of how complete the specification is and whether it really covers all the behaviors of the system. The challenge of making the verification process as exhaustive as possible is even more crucial in simulation-based verification, where the infeasible task of checking all input sequences is replaced by checking a test suite consisting of a finite subset of them. It is very important to measure the exhaustiveness of the test suite, and indeed there has been extensive research in the simulation-based verification community on coverage metrics, which provide such a measure. It turns out that no single measure can be absolute, leading to the development of numerous coverage metrics whose usage is determined by industrial verification methodologies. On the other hand, prior research of coverage in formal verification has focused solely on state-based coverage. In this paper we adapt the work done on coverage in simulation-based verification to the formal-verification setting in order to obtain new coverage metrics. Thus, for each of the metrics used in simulation-based verification, we present a corresponding metric that is suitable for the setting of formal verification and describe an algorithmic way to check it.     

Step-zoom dual-field-of-view infrared telescope

The design of a dual-field-of-view telescope for an 8-12-microm imaging waveband is described. Preliminary calculations are made to determine the first-order parameters of the narrow- and the wide-field modes. To achieve a switchable dual-field-of-view system, one use an optical configuration based on the axial motion of a single lens group along the optical axis. The same lens is also used for focusing at near objects and for athermalization by small axial movement. A total of six lenses with one conic surface are used in the design, making the telescope cost effective and lightweight. The final optical design is presented, along with the aberrations curves and modulation transfer function plots, showing excellent performance in both fields of view.     

Continuous Query Processing of Spatio-Temporal Data Streams in PLACE

The tremendous increase in the use of cellular phones, GPS-like devices, and RFIDs results in highly dynamic environments where objects as well as queries are continuously moving. In this paper, we present a continuous query processor designed specifically for highly dynamic environments (e.g., location-aware environments). We implemented the proposed continuous query processor inside the PLACE server (Pervasive Location-Aware Computing Environments); a scalable location-aware database server developed at Purdue University. The PLACE server extends data streaming management systems to support location-aware environments. These environments are characterized by the wide variety of continuous spatio-temporal queries and the unbounded spatio-temporal streams. The proposed continuous query processor includes: (1) New incremental spatio-temporal operators to support a wide variety of continuous spatio-temporal queries, (2) Extended semantics of sliding window queries to deal with spatial sliding windows as well as temporal sliding windows, and (3) A shared-execution framework for scalable execution of a set of concurrent continuous spatio-temporal queries. Experimental evaluation shows promising performance of the continuous query processor of the PLACE server. This work was supported in part by the National Science Foundation under Grants IIS-0093116, IIS-0209120, and 0010044-CCR.     

Observations of thermally induced transformations in amorphous chalcogenide films using transmission electron microscopy

Thermally induced phase transformations in chalcogenide thin films evaporated from the alloy As 36-Te 53-Ge 11 (wt.%) onto glass substrates kept at room temperature were investigated using transmission electron microscopy. Although the as-deposited films showed an amorphous structure, a sudden and very fast transformation to a crystalline phase took place dendritically on electron-beam heating in the microscope. Annealing of thin films outside the microscope in the temperature range 100–170 °C was also found to cause and assist dendritic recrystallization. This formation of dendrites is discussed in terms of the properties of the material.     

Spectrophotometric method for determination of ozone in aqueous solutions

A sensitive spectrophotometric method for determination of ozone in small volumes of water is presented. It was performed in order to meet the requirements of a kinetic study of virus and bacteria inactivation by ozone.The proposed method involves oxidation of a buffered iodine solution and spectrophotometric measurement of the triiodide ion liberated by ozone. Two procedures are used: one for low ozone concentration (0·01–0·30 ppm) and another for higher concentrations (0·30–2·0 ppm). The reproducibility of results is very high when the procedure used corresponds with the ozone level for which it is intended.This spectrophotometric method is compared with the standard volumetric method and the differences are presented and discussed.Some applications of the method for a kinetic study of virus inactivation by ozone are presented.     

Interdiffusion of zircaloy-4 and nickel

Interdiffusion between zircaloy-4 (Zy-4) and nickel was studied using diffusion couples at temperatures of 970 and 1000°C in vacuum. The morphology and composition of the diffusion zone and surrounding regions were examined using metallography, X-ray diffraction and microprobe analysis.The phases formed in the diffusion zone at both temperatures were: Ni₁₀Zr₇, NiZr and NiZr₂. Free Zr was also detected in the diffusion zone. Eutectic melting was observed in couples annealed at 1000°C even for a short time (5 min). X-ray fluorescence analysis showed that Ni diffused long distances in the Zy side. This led to the formation of NiZr₂ precipitates in the Zy side. The diffusion coefficient was found to be very high, $\text{D}{}_{\mathrm{Ni/Zy-4}}\text{= 4.51 × 10}{}^5\text{cm}{}^2\text{/s}$ at 970°C, indicating anomalous diffusion of Ni in β-Zr.The consequences of the interdiffusion of Zy-4 with Ni-bearing alloys (both exist in nuclear fuel assemblies) for nuclear safety are discussed.     

Automated simultaneous monitoring of nitrate and nitrite in surface water by sequential injection analysis

A fully automated procedure based on Sequential Injection Analysis (SIA) methodology for simultaneous monitoring of nitrate and nitrite in surface water samples is described. Nitrite was determined directly using the Griess diazo-coupling reaction and the formed azo dye was measured at 540 nm in the flow cell of the fibre-optic spectrophotometer. Nitrate zone was passed through a reducing mini-column containing copperised-cadmium. After the reduction of nitrate into nitrite the sample was aspirated by flow reversal to the holding coil, treated with the reagent and finally passed through the flow cell. The calibration curve was linear over the range 0.05-1.00 mg N l(-1) of nitrite and 0.50-50.00 mg N l(-1) of nitrate; correlation coefficients were 0.9993 and 0.9988 for nitrite and nitrate, respectively. Detection limits were 0.015 and 0.10 mg N l(-1) for nitrite and nitrate, respectively. The relative standard deviation (RSD) values (n = 3) were 1.10% and 1.32% for nitrite and nitrate, respectively. The total time of one measuring cycle was 250 s, thus the sample throughput was about 14 h(-1). Nitrate and nitrite were determined in the real samples of surface water, and the results have been compared with those obtained by two other flow methods; flow injection analysis based on the same reactions and isotachophoretic determination used in a routine environmental control laboratory.