Fabrication of nanostructured silicon by metal-assisted etching and its effects on matrix-free laser desorption/ionization mass spectrometry

A matrix-free, high sensitivity, nanostructured silicon surface assisted laser desorption/ionization mass spectrometry (LDI-MS) method fabricated by metal-assisted etching was investigated. Effects of key process parameters, such as etching time, substrate resistance and etchant composition, on the nanostructured silicon formation and its LDI-MS efficiency were studied. The results show that the nanostructured silicon pore depth and size increase with etching time, while MS ion intensity increases with etching time to 300 s then decreases until 600 s for both low resistance (0.001–0.02 Ω cm) and high resistance (1–100 Ω cm) silicon substrates. The nanostructured silicon surface morphologies were found to directly affect the LDI-MS signal ion intensity. By characterizing the nanostructured silicon surface roughness using atomic force microscopy (AFM) and sample absorption efficiency using fluorescence microscopy, it was further demonstrated that the nanostructured silicon surface roughness was highly correlated to the LDI-MS performance.     

Stress-concentration factors for semielliptical notches in beams under pure bending

Elliptical notches in rectangular beams under pure bending are examined photoelastically. Stress-concentration factors due to a single elliptical notch are obtained for wide ranges of 2a/h andd/h, where 2a, d, andh are the width of notch, depth of notch, and depth of beam, respectively. In particular, the geometries of the optimum elliptical notches producing the least stress concentrations are obtained. Almost the whole elliptical boundary of these notches are stressed to the same peak, which indicates that these notches will probably produce the least stress concentrations among all notches, elliptical or nonelliptical. The graphs herein will enable the designers to find the stress-concentration factors of elliptical notches and to pick out the geometry of the optimum notch which will give the least stress concentration for any given values of 2a/h andd/h. Stresses and the stress-concentration factors at the bottom of the beam opposite the notch are also obtained. These stresses, though smaller in magnitude, are of an opposite sign to the peak stress at the notch. For brittle materials, a smaller tensile stress may be more critical than a large compressive stress; therefore, these stress-concentration factors are also given.     

Solid-state fermentation with Aspergillus niger for cellobiase production

Aspergillus niger NRRL3 was cultivated in a moist wheat bran and ground corncob solid medium supplemented with inorganic minerals for the production of cellobiase (β-1,4-glucosidase, EC 3.2.1.21). With this method, A. niger NRRL3 was able to produce a high concentration of cellobiase (215 IU/gofsolid substrate) after 96 h of incubation. Temperature and moisture content affected final cellobiase titers. The best conditions for cell obiase production from solid substrate by A. niger NRRL3 were determined to be 70% moisture and 35°C.     

Photochemistry of ortho, ortho' dialkyl phenyl azides

Phenyl azide, 2,6-diethylphenyl azide, 2,6-diisopropylphenyl azide, and 2,4,6-tri-tert-butylphenyl azide were studied by laser flash photolysis (LFP) methods. LFP (266 nm) of the azides in glassy 3-methylpentane at 77 K produces the transient UV-vis absorption spectra of the corresponding singlet nitrenes. At 77 K, the singlet nitrenes relax to the corresponding triplet nitrenes. The triplet nitrenes are persistent at 77 K and their spectra were recorded. The rate constants of singlet to triplet intersystem crossing were determined at this temperature. LFP of 2,4,6-tri-tert-butyl phenyl azide in pentane at ambient temperature again produces a singlet nitrene, which is too short-lived to detect by nanosecond spectroscopy under these conditions. Unlike the other azides, the first detectable intermediate produced upon LFP of 2,4,6-tri-tert-butyl phenyl azide at ambient temperature is the benzazirine (285 nm) which has a lifetime of 62 ns controlled by ring opening to a didehydroazepine. The results are interpreted with the aid of Density Functional Theoretical and Molecular Orbital Calculations.     

Unequal crossover recombination - population screening for PHOX2B gene polyalanine polymorphism using CE

Congenital central hypoventilation syndrome (CCHS) is a rare neurological disorder characterized by abnormal autonomic central nervous system control of breathing during sleep. Mutations in the paired-like homeobox 2B (PHOX2B) gene, including point mutation, frameshift, and polyalanine expansion, are associated with the pathogenesis of CCHS. In this study, PHOX2B mutations were analyzed in seven CCHS patients, their family members, and 1520 healthy individuals from the general population using CE to provide high sensitivity and resolution screening for the PHOX2B polyalanine polymorphism. Seven mutations in the PHOX2B gene, including two frameshift mutations and five polyalanine expansions in the 20-residue polyalanine tract, were identified. The various phenotypes observed in CCHS patients with PHOX2B mutations suggest that the size of the expansion allele is associated with the CCHS risk. In addition, significant differences were found in allele and genotype distributions between the healthy individuals. Alleles (GCN)(20) and (GCN)(15) had the highest population incidence rates of 94.84 and 4.51%, respectively, with the remaining alleles, (GCN)(13) and (GCN)(7), accounting for 0.59 and 0.06%, respectively. Therefore, it has been demonstrated that CE can be used to improve the detection of polyalanine expansions in the PHOX2B gene. The attractive alternative method is a promising tool for the detection of disorders involving trinucleotide repeat tracts.     

Mass spectrometric studies of heterocyclic organophosphorus compounds: 1,3,2-benzodioxaphospholes

The mass spectral behaviour of a new type of organophosphorus compound, 1,3,2-benzodioxaphospholes, under 70 eV electron impact has been studied by means of high and low resolution mass spectrometry as well as by B/E and B²/E linked scans. The influence of different substituents in the molecule (O, S or N) on the mass spectra is investigated. The reason for isomerization between oxygen and sulphur within a molecule studied by mass spectrometry is discussed.     

核磁共振电信号内标法在人体尿液定量分析中的应用

研究了Varian谱仪核磁共振电信号内标法在人体尿液代谢物浓度测定上的应用,通过实验证明了该方法进行定量分析的可靠性.NMR电信号内标法原理上是通过Varian谱仪去耦通道在常规一维谱图上产生一个参考信号,并利用谱仪软件程序来调整该信号在频谱上的强度、频率、衰减速率等参数.避免了代谢组学中NMR定量实验需要添加已知浓度物质(例如TSP)作为内标而引起的内标物与样品相互作用、谱峰重叠、内标物不溶及弛豫时间太长等问题.研究结果表明,Varian谱仪去耦通道产生的电信号稳定可靠(标准偏差0.36%),能够用于定量分析;当样品浓度大于20 mmol/L或小于2 mmol/L时,该方法测定的相对误差分别为1%和5%.通过配制低浓度的尿液模型样品,验证了电信号内标法测量人体尿液代谢物的浓度的可行性,最后使用该方法测量真实的人体尿液中常见代谢物的浓度,测定结果与医院常用生化分析仪器的测定结果相符.     

Public key encryption with filtered equality test revisited

Designs, Codes and Cryptography - Without revealing data in the plain, public key encryption with equality test can achieve the basic cryptographic functionalities required. However, the extended...     

单壁碳纳米管储氢的第一原理分子动力学模拟

本文用第一性原理平面波赝势方法模拟研究了手性单壁碳纳米管与氢分子的相互作用,考察了碳纳米管直径对储氢性能的影响.对单壁碳纳米管储氢的模拟结果表明:(1)物理吸附时,H2可以吸附在空腔内,也可以吸附在管与管之间的空隙中,纳米管内部的氢吸附力均高于管外,而“完好无损”的H2分子不能够穿过管壁而进入管内.(2)化学吸附时,碳纳米管对氢的吸附首先出现在管的边缘附近,碳纳米管局部会发生形变,SWCNTs的张力会随C-H键的增加而增大,系统不稳定.(3)随着直径的增加,纳米管内、外的氢吸附力差异减小.