Comparative analysis of automotive paints by laser induced breakdown spectroscopy and nonparametric permutation tests

Laser-induced breakdown spectroscopy (LIBS) has been investigated for the discrimination of automobile paint samples. Paint samples from automobiles of different makes, models, and years were collected and separated into sets based on the color, presence or absence of effect pigments and the number of paint layers. Twelve LIBS spectra were obtained for each paint sample, each an average of a five single shot “drill down” spectra from consecutive laser ablations in the same spot on the sample. Analyses by a nonparametric permutation test and a parametric Wald test were performed to determine the extent of discrimination within each set of paint samples. The discrimination power and Type I error were assessed for each data analysis method. Conversion of the spectral intensity to a log-scale (base 10) resulted in a higher overall discrimination power while observing the same significance level. Working on the log-scale, the nonparametric permutation tests gave an overall 89.83% discrimination power with a size of Type I error being 4.44% at the nominal significance level of 5%. White paint samples, as a group, were the most difficult to differentiate with the power being only 86.56% followed by 95.83% for black paint samples. Parametric analysis of the data set produced lower discrimination (85.17%) with 3.33% Type I errors, which is not recommended for both theoretical and practical considerations. The nonparametric testing method is applicable across many analytical comparisons, with the specific application described here being the pairwise comparison of automotive paint samples.     

Non‐parametric permutation test for the discrimination of float glass samples based on LIBS spectra

Laser‐induced breakdown spectroscopy (LIBS) coupled with non‐parametric permutation based hypothesis testing is demonstrated to have good performance in discriminating float glass samples. This type of pairwise sample comparison is important in manufacturing process quality control, forensic science and other applications where determination of a match probability between two samples is required. Analysis of the pairwise comparisons between multiple LIBS spectra from a single glass sample shows that some assumptions required by parametric methods may not hold in practice, motivating the adoption of a non‐parametric permutation test. Without rigid distributional assumptions, the permutation test exhibits excellent discriminating power while holding the actual size of Type I error at the nominal level. Copyright © 2010 John Wiley & Sons, Ltd.     

Studies on syntheses and dynamic swelling of pH-sensitive macroporous poly(N-isopropylacrylamide-co-acrylic acid) hydrogels

A series of macroporous poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAm-AA) hydrogels with different composition were synthesized by free-radical copolymerization in the presence of silica particles as a pore generating agent. The equilibrium swelling ratio, half swelling time and dynamic swelling kinetics of the copolymers previously soaked in different acidic buffer solutions were investigated at pH 7 at 25°C. Experimental results revealed that the swelling rate of the macroporous hydrogels was greatly increased compared to conventional hydrogels due to existence of the macroporous structures. It was found that the swelling history of previously putting in acidic solutions copolymers had strong influence on their dynamic swelling kinetics especially for the samples ranging in composition between 30 and 70 mol % of NIPAAm, whereas the swelling history had little influence on the equilibrium swelling ratio of copolymers. The swelling pattern exhibits sigmoid swelling curves. This is explained by an autocatalytic mechanism. The hydrogen bonding dissociation plays an important role in the dynamic swelling behavior.     

Electrochemical Oxidation of Epinephrine and Uric Acid at a Layered Double Hydroxide Film Modified Glassy Carbon Electrode and Its Application

Increasing attention has been paid to layered double hydroxide (LDH) film modified electrode attributing to its desirable properties for fabrication of electrochemical sensor. In this paper, the Zn‐Al LDH film modified glassy carbon electrode was characterized by electrochemical methods. The enhanced electrocatalytic currents and well‐separated potentials for epinephrine (EP) and uric acid (UA) were observed at the as‐prepared electrode. Under selected condition, the differential pulse voltammetry response of the modified electrode to EP (or UA) shows a linear concentration range of 0.5 μM to 0.3 mM (or 2 μM to 0.4 mM) in the presence of 10.0 μM UA (or 20.0 μM EP). At a signal‐to‐noise ratio of 3, the calculated limits of detection are 0.13 μM and 0.66 μM, respectively. The proposed method has been performed to successfully detect EP and UA in analysis of real samples, such as in EP injection solution and human urine samples.     

Empirical regularities of opening call auction in Chinese stock market

We study the statistical regularities of an opening call auction using the ultra-high-frequency data of 22 liquid stocks traded on the Shenzhen Stock Exchange in 2003. The distribution of the relative price, defined as the relative difference between the order price in the opening call auction and the closing price on the last trading day, is asymmetric and that the distribution displays a sharp peak at the zero relative price and a relatively wide peak at the negative relative price. The detrended fluctuation analysis (DFA) method is adopted to investigate the long-term memory of relative order prices. We further study the statistical regularities of order sizes in the opening call auction, and observe a phenomenon of number preference, known as order size clustering. The probability density function (PDF) of order sizes could be well fitted by a q-Gamma function, and the long-term memory also exists in order sizes. In addition, both the average volume and the average number of orders decrease exponentially with the price level away from the best bid or ask price level in the limit-order book (LOB) established immediately after the opening call auction, and a price clustering phenomenon is observed.     

Scaling and memory in the non-Poisson process of limit order cancelation

The order submission and cancelation processes are two crucial aspects in the price formation of stocks traded in order-driven markets. We investigate the dynamics of order cancelation by studying the statistical properties of inter-cancelation durations, defined as the waiting times between consecutive order cancelations of 22 liquid stocks traded on the Shenzhen Stock Exchange of China in year 2003. Three types of cancelations are considered, including cancelation of any limit orders, of buy limit orders and of sell limit orders. We find that the distributions of the inter-cancelation durations of individual stocks can be well modeled by Weibulls for each type of cancelation, and the distributions of rescaled durations of each type of cancelations exhibit a scaling behavior for different stocks. Complex intra-day patterns are also unveiled in the inter-cancelation durations. The detrended fluctuation analysis (DFA) and the multifractal DFA show that the inter-cancelation durations possess long-term memory and multifractal nature, which are not influenced by the intra-day patterns. No clear crossover phenomenon is observed in the detrended fluctuation functions with respect to the time scale. These findings indicate that the cancelation of limit orders is a non-Poisson process, which has potential worth in the construction of order-driven market models.     

532nm激光作用下甲基异丙基酮的电离解离研究

在532 nm激光波长下,利用时间飞行质谱(TOF-MS)对甲基异丙基酮的多光子电离解离机制进行了研究.实验结果显示,母体分子首先发生α断裂并且吸收(2+2)个光子到达离子态.主要的质谱峰C_2H_3~+,CH_3COC_3H_7~+,CH_3~+等在质谱图中清晰可见.结合Guassian03,运用HF/3-21G、CIS/3-21G对基态和激发态的构型进行了优化和频率计算,发现激发态的碳氧键变为介于碳氧单键和双键之间特殊键,并用QST2方法找到了其中的过渡态,对三个状态的几何结构参数进行了分析得出了其解离过程是α键断裂和基团构象转化协同进行的结论.     

Sensitive and Facile Determination of Catechol and Hydroquinone Simultaneously Under Coexistence of Resorcinol with a Zn/Al Layered Double Hydroxide Film Modified Glassy Carbon Electrode

A stable dihydroxybenzene sensor was fabricated by electrochemical deposition of Zn/Al layered double hydroxide film on glassy carbon electrode (LDHf/GCE). The sensitive and facile electrochemical method for the simultaneous determination of catechol (CA) and hydroquinone (HQ) under coexistence of resorcinol (RE) has been achieved at the LDHf/GCE in phosphate buffer solution (pH 6.5). Under the optimized conditions, the differential pulse voltammetry response of the modified electrode to CA (or HQ) shows a linear concentration range of 0.6 μM to 6.0 mM (or 3.2 μM to 2.4 mM) with a correlation coefficient of 0.9987 (or 0.9992) and the calculated limit of detection is 0.1 μM (or 1.0 μM) at a signal‐to‐noise ratio of 3. In the presence of 50 μM isomer, the linear concentration ranges for CA and HQ are 3.0 μM to 1.5 mM and 12.0 μM to 0.8 mM, respectively. The detection limits are 1.2 μM and 9.0 μM. Further, the proposed method has been performed to successfully detect dihydroxybenzene isomers in analysis of real samples, such as water and tea.     

Preparation and characterization of microencapsulated ammonium polyphosphate with polyurethane shell by in situ polymerization and its flame retardance in polyurethane

Microencapsulated ammonium polyphosphate (APP) with polyurethane (MCAPP) was prepared by in situ polymerization of pentaerythtritol (PER) and toluene‐2,4‐diisocyanate (TDI) in the presence of added APP. MCAPP was then incorporated into polyurethane (PU) to obtain flame retarded PU/MCAPP. Fourier transform infrared (FT‐IR) and X‐ray photoelectron spectroscopy (XPS) showed that APP was encapsulated by a layer of PU. It found that the optimal reaction time was 8 hr and microencapsulation led to an improvement in water leaching from scanning electron microscopy (SEM) and determination of water resistance. Thermal degradation of flame retarded PU was also investigated by thermogravimetric analysis (TGA). UL‐94 test and SEM were performed before and after water treatment at 75°C for seven days, and the results showed that PU loading of 30% MCAPP can maintain the V‐0 level, due to the shield effect of microencapsulation. Copyright © 2008 John Wiley & Sons, Ltd.     

Simultaneous processes of electricity generation and p-nitrophenol degradation in a microbial fuel cell

This study initially demonstrates that the electricity generated by a microbial fuel cell (MFC) can be used to in situ generate H₂O₂ at a carbon felt cathode. In the presence of scrap iron, H₂O₂ further reacts with Fe²⁺ to produce hydroxyl radicals. Attributed to the oxidation of H₂O₂ and hydroxyl radicals, and the oxidation–reduction of scrap iron, p-nitrophenol was significantly removed in the cathode chamber of the MFC. The p-nitrophenol was completely degraded after 12 h, and about 85% of TOC was removed after 96 h. Simultaneously, a maximum power density (143 mW m^?2) was generated by the MFC. It is concluded that a MFC not only can generate electricity and degrade biodegradable compounds, but also remove bio-refractory pollutants.