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排序方式: 共有136条查询结果,搜索用时 26 毫秒
61.
Pekka Keski‐Rahkonen Kaisa Huhtinen Reena Desai D. Tim Harwood David J. Handelsman Matti Poutanen Seppo Auriola 《Journal of mass spectrometry : JMS》2013,48(9):1050-1058
Accurate measurement of estradiol (E2) is important in clinical diagnostics and research. High sensitivity methods are critical for specimens with E2 concentrations at low picomolar levels, such as serum of men, postmenopausal women and children. Achieving the required assay performance with LC–MS is challenging due to the non‐polar structure and low proton affinity of E2. Previous studies suggest that ionization has a major role for the performance of E2 measurement, but comparisons of different ionization techniques for the analysis of clinical samples are not available. In this study, female serum and endometrium tissue samples were used to compare electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) in both polarities. APPI was found to have the most potential for E2 analysis, with a quantification limit of 1 fmol on‐column. APCI and ESI could be employed in negative polarity, although being slightly less sensitive than APPI. In the presence of biological background, ESI was found to be highly susceptible to ion suppression, while APCI and APPI were largely unaffected by the sample matrix. Irrespective of the ionization technique, background interferences were observed when using the multiple reaction monitoring transitions commonly employed for E2 (m/z 271 > 159; m/z 255 > 145). These unidentified interferences were most severe in serum samples, varied in intensity between ionization techniques and required efficient chromatographic separation in order to achieve specificity for E2. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
62.
Estimation of the uncertainty of microbiological viable counts by the statistical analysis of series of observations is impractical because the observed value, the number of colonies, usually determines a large share of the uncertainty. Every test result, therefore, has a unique uncertainty and no general method-specific values exist. The most practical ways to estimate the uncertainty are based on mathematical models and assumed statistical distributions where the observed value is a significant parameter. The article describes the traditional solution based on the Poisson distribution and more advanced models based on the negative binomial distribution. The latter model is capable of combining technical and procedural components of uncertainty with the inevitable random scatter of microbial suspensions. The additional uncertainty due to subsampling in the confirmation of presumptive positives is estimated with the help of a binomial model. Traceability issues are discussed.Presented at the Metro Trade Workshop on Traceability and Measurement Uncertainty in Testing, 30–31 January 2003, Berlin, Germany 相似文献
63.
Structure of cellulose and microcrystalline cellulose from various wood species, cotton and flax studied by X-ray scattering 总被引:2,自引:1,他引:1
Kirsi Leppänen Seppo Andersson Mika Torkkeli Matti Knaapila Nina Kotelnikova Ritva Serimaa 《Cellulose (London, England)》2009,16(6):999-1015
The structure of microcrystalline cellulose (MCC) made by mild acid hydrolysis from cotton linter, flax fibres and sulphite
or kraft cooked wood pulp was studied and compared with the structure of the starting materials. Crystallinities and the length
and the width of the cellulose crystallites were determined by wide-angle X-ray scattering and the packing and the cross-sectional
shape of the microfibrils were determined by small-angle X-ray scattering. The morphological differences were studied by scanning
electron microscopy. A model for the changes in microfibrillar structure between native materials, pulp and MCC samples was
proposed. The results indicated that from softwood or hardwood pulp, flax cellulose and cotton linter MCC with very similar
nanostructures were obtained with small changes in reaction conditions. The crystallinity of MCC samples was 54–65%. The width
and the length of the cellulose crystallites increased when MCC was made. For example, between cotton and cotton MCC the width
increased from 7.1 nm to 8.8 nm and the length increased from 17.7 nm to 30.4 nm. However, the longest crystallites were found
in native spruce wood (35–36 nm). 相似文献
64.
Merja R. Häkkinen Tuomo A. Keinänen Seppo Auriola Leena Alhonen Jouko Vepsäläinen 《Tetrahedron》2009,65(2):547-5748
Novel di-, tetra- and octadeuterated derivatives of mono-N-alkylated diaminopropanes, spermidines, spermines, symmetrically bis-N-alkylated spermines and unsymmetrically bis-N-alkylated spermines were synthesized. Deuterium labels were introduced into the RHNCH2CH2CN intermediate either by exchanging the protons next to the nitrile group under basic conditions with D2O-EtOD mixture or/and by reducing the nitrile group to a CD2-NH2 fragment with LiAlD4. 相似文献
65.
A nonnegative form on a complex linear space is decomposed with respect to another nonnegative form : it has a Lebesgue decomposition into an almost dominated form and a singular form. The part which is almost dominated is the largest form majorized by which is almost dominated by . The construction of the Lebesgue decomposition only involves notions from the complex linear space. An important ingredient in the construction is the new concept of the parallel sum of forms. By means of Hilbert space techniques the almost dominated and the singular parts are identified with the regular and a singular parts of the form. This decomposition addresses a problem posed by B. Simon. The Lebesgue decomposition of a pair of finite measures corresponds to the present decomposition of the forms which are induced by the measures. T. Ando's decomposition of a nonnegative bounded linear operator in a Hilbert space with respect to another nonnegative bounded linear operator is a consequence. It is shown that the decomposition of positive definite kernels involving families of forms also belongs to the present context. The Lebesgue decomposition is an example of a Lebesgue type decomposition, i.e., any decomposition into an almost dominated and a singular part. There is a necessary and sufficient condition for a Lebesgue type decomposition to be unique. This condition is inspired by the work of Ando concerning uniqueness questions. 相似文献
66.
Seppo Aksela 《Journal of Electron Spectroscopy and Related Phenomena》1981,24(1):91-94
The kinetic-energy shifts between atomic and solid-state L3M4,5M4,5 Auger electron spectra of Cu, Zn, Ga, Ge, As, and Se are determined with the aid of semiempirically calculated atomic and experimental solid-state Auger energies. The shift values are calculated by applying the thermochemical model to the Auger process. Good agreement is found between the calculated and experimental values. 相似文献
67.
68.
Seppo Linnainmaa 《BIT Numerical Mathematics》1976,16(2):146-160
The article describes analytic and algorithmic methods for determining the coefficients of the Taylor expansion of an accumulated rounding error with respect to the local rounding errors, and hence determining the influence of the local errors on the accumulated error. Second and higher order coefficients are also discussed, and some possible methods of reducing the extensive storage requirements are analyzed. 相似文献
69.
Markku R. Sundberg Rolf Å. M. Uggla Reijo J. Sillanpää Krzysztof K. Zborowski Angel Sánchez-González Jorma K. T. Matikainen Seppo A. A. Kaltia Tapio A. Hase 《Central European Journal of Chemistry》2010,8(3):486-493
Chromium trioxide forms an adduct with zwitterionic quinolinic acid. The structure of the product was found to be (quinolinium-3-carboxylato-O)trioxidochromium(VI), determined by single-crystal X-ray diffraction methods. To evaluate the bonding properties of the compound,
its structure was optimized at the B3LYP/6-311G* level of theory. The electronic characteristics were investigated by topological
methods applied to the total charge density in various model compounds including the title compound, title compound with a
HF molecule presenting a hydrogen bonding and anionic moiety. Calculated aromaticity indices indicate that the quinolinic
rings tend to conserve their degree of aromaticity against hydrogen bonding. However, when there is hydrogen bonding involving
an N-H bond or when the quinolinium zwitterion is deprotonated, there are clear changes in the interaction between chromium
trioxide and the quinolinic moiety.
相似文献
70.
Antti S?yn?tjoki Benfeng Bai Ari Tervonen Jari Turunen Seppo Honkanen 《Optical Review》2010,17(3):181-186
Optical confinement in slot waveguides with angled sidewalls is studied. Improved vertical optical confinement is observed.
Different mode solvers are compared in the modeling of slot waveguides with varying sidewall angles. The finite element method
was found best suitable for this task. The effect of the slot waveguide geometry on the vertical optical confinement is studied.
The reduced effective mode area is beneficial in all-optical applications due to enhancement of nonlinear effects in the waveguide. 相似文献