The electrochemical behaviour of the altenuene mycotoxin and its acidic properties

The electrooxidation of altenuene (ALT), one of the mycotoxins of the Alternaria alternata genus, on a glassy carbon disk electrode is studied for the first time by using cyclic and square wave voltammetry. From the electrochemical responses, a complex reaction mechanism could be inferred. Values of 1.06×10⁻⁵ cm² s⁻¹, 1.116 V and 2 were determined for the diffusion coefficient, the apparent formal potential and the electron number, respectively, for the overall electrode process by convolution analysis of linear scan voltammograms. Square wave voltammetry was used to generate I_p versus c_ALT* calibration curves for this fungal metabolite. A detection limit of 4.0×10⁻⁷ M was determined for a 2:1 signal to noise ratio. The acid dissociation constant for ALT was determined from conventional UV–vis spectrophotometric measurements. Experimental variations of absorbance as a function of pH at a given wavelength were fitted by using the exact equation that describes the system. Good agreement between the experimental absorbance versus pH plots and the curves generated by the fitting process was found.     

偏最小二乘回归方法的局限性及改进算法

提出了偏最小二乘回归中的一类不适用情况,并从理论上分析,实例上验证,给出了针对这种情况的一种改进算法,从而拓宽了偏最小二乘回归的使用范围.     

Smash Products for Secondary Homotopy Groups

We construct a smash product operation on secondary homotopy groups yielding the structure of a lax symmetric monoidal functor. Applications on cup-one products, Toda brackets and Whitehead products are considered. The second author was partially supported by the Spanish Ministry of Education and Science under MEC-FEDER grants MTM2004-01865 and MTM2004-03629, the postdoctoral fellowship EX2004-0616, and a Juan de la Cierva research contract.     

A New Indirect Electroanalytical Method to Monitor the Contamination of Natural Waters with 4‐Nitrophenol Using Multiwall Carbon Nanotubes

The electrochemical detection of the hazardous pollutant 4‐nitrophenol (4‐NP) at low potentials, in order to avoid matrix interferences, is an important research challenge. This study describes the development, electrochemical characterization and utilization of a multiwall carbon nanotube (MWCNT) film electrode for the quantitative determination of 4‐NP in natural water. Electrochemical impedance spectroscopy measurements showed that the modified surface exhibits a decrease of ca. 13 times in the charge transfer resistance when compared with a bare glassy carbon (GC) surface. Voltammetric experiments showed the possibility to oxidize a hydroxylamine layer (produced by the electrochemical reduction of 4‐NP on the GC/MWNCT surface) in a potential region which is approximately 700 mV less positive than that needed to oxidize 4‐NP, thus minimizing the interference of matrix components. The limit of detection for 4‐NP obtained using square‐wave voltammetry (0.12 μmol L^?1) was lower than the value advised by EPA. A natural water sample from a dam located in São Carlos (Brazil) was spiked with 4‐NP and analyzed by the standard addition method using the GC/MWCNT electrode, without any further purification step. The recovery procedure yielded a value of 96.5% for such sample, thus confirming the suitability of the developed method to determine 4‐NP in natural water samples. The electrochemical determination was compared with that obtained by HPLC with UV‐vis detection.     

变折射率方形孔径平面微透镜阵列的聚焦和散焦特性

为提高变折射率平面微透镜阵列的填充率,利用光刻工艺和离子交换技术制备了填充率近达100%的方形孔径平面微透镜阵列,并对其透镜元及相邻透元间间隙构成的角落区域的成像进行了理论和实验研究.根据变折射率介质光线追迹法,利用MATLAB软件模拟,发现在透镜元区域和角落区域成像特性相反.成像系统测试表明:由于透镜元区域和角落区域的折射率分布变化规律不同,透镜元与角落区域对物体分别成倒立实像和正立虚像;透镜阵列可实现聚焦和散焦功能;角落区域得到充分的离子交换使得间隙足够小,形成了从该区域中心向外逐渐增大的新型梯度折射率模型.     

Birefringence,dispersion and loss properties for PCFs with rectangular air-holes

In this paper, the solid-core fiber designs constructed by omitting one air-hole at the center of square-lattice silica photonic crystals with rectangular shaped air-holes have been investigated theoretically and their characteristics have been compared with those of square ones. Using commercial simulation software, birefringence, dispersion, numerical aperture and confinement loss of the fundamental modes are analyzed.     

A novel methodology for online detection of bearing health status for naturally progressing defect

A methodology is proposed for the online detection of health status of rolling element bearing into various damage stages for naturally progressing defect. Various damage identification parameters are derived from processing vibration data in time domain, frequency domain and time–frequency domain. The parameters are fused into a single parameter, Mahalanobis distance, by application of Gram–Schmidt Orthogonalization process. Chebyshev?s inequality is applied to the Mahalanobis distance for online monitoring and damage stage detection. A simulation study is first carried out to show working of the proposed methodology in presence of varying trends of damage identification parameters. The proposed methodology is then validated on experimental data. The first validation is on the vibration data acquired from a bearing having seeded defect. Later, two accelerated life tests are conducted on a specially designed test rig at different load and speed combinations on the bearings for ensuring naturally induced and progressed defects. The methodology is successfully verified on the vibration data acquired from the naturally induced and progressed defect experiments.     

Dispersion-ultra-flattened square-lattice photonic crystal fiber with small effective mode area and low confinement loss

Proposed in this paper is a simple square-lattice photonic crystal fiber (PCF) with nearly zero flattened dispersion (NZFD) over a wide wavelength span. We make a trade-off between the coupling efficiency and the effective mode area in order to obtain relatively low confinement loss and high nonlinearity. Via full-vector finite element method with hybrid edge/node elements, over 1137–1710 nm, the dispersion coefficient is 0.3 ± 0.3 ps/(km nm), the confinement loss is relatively low, in level of 10⁻⁷–10⁻⁴ dB/km and the effective mode area remains 5.88–6.59 μm².     

Experimental investigation on the aerodynamic behavior of square cylinders with rounded corners

The influence of corner shaping on the aerodynamic behavior of square cylinders is studied through wind tunnel tests. Beside the sharp-edge corner condition considered as a benchmark, two different rounded-corner radii (r/b=1/15 and 2/15) are studied. Global forces and surface pressure are simultaneously measured in the Reynolds number range between 1.7×10⁴ and 2.3×10⁵. The measurements are extended to angles of incidence between 0° and 45°, but the analysis and the discussion presented herein is focused on the low angle of incidence range. It is found that the critical angle of incidence, corresponding to the flow reattachment on the lateral face exposed to the flow, decreases as r/b increases and that an intermittent flow condition exists. In the case of turbulent incoming flow, two different aerodynamic regimes governed by the Reynolds number have been recognized.