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排序方式: 共有547条查询结果,搜索用时 15 毫秒
51.
Nasser E. Bastani Thomas E. Gundersen Rune Blomhoff 《Rapid communications in mass spectrometry : RCM》2009,23(18):2885-2890
F2‐isoprostanes are a family of prostaglandin F2‐like compounds that are formed by free‐radical‐catalyzed peroxidation of arachidonic acid. Several F2‐isoprostanes, but in particular 8‐epi PGF2α, are widely used as oxidative stress biomarkers. An analytical method based on liquid chromatography with negative electrospray ionization (ESI) coupled to tandem mass spectrometric detection (LC/MS/MS) was developed for the determination of 8‐epi PGF2α concentrations in human plasma, whole blood, erythrocytes and urine. 8‐epi PGF2α‐d4, a stable isotope derivative of 8‐epi PGF2α, was used as an internal standard (IS). A 50 µL sample was focused on‐column and separated on two 3 µm particle size SUPELCOSIL? ABZ+Plus HPLC columns (15 cm × 4.6 mm and 7.5 cm × 4.6 mm) connected in series. An Applied Biosystems 4000 Q TRAP LC/MS/MS system with ESI was operated in multiple reaction monitoring (MRM) mode with the precursor‐to‐product ion transitions m/z 353.4 → 193.1 (8‐epi PGF2α), 357.4 → 197.1 (8‐epi PGF2α‐d4), used for quantification. The assay was fully validated and found to have adequate accuracy, precision, linearity, sensitivity and selectivity. The mass limit of detection (mLOD) was 1 pg of analyte eluting from the column. The assay has been successfully applied to the analysis of human plasma, whole blood, erythrocytes and urine samples. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
52.
A facile and convenient synthesis of bis(2-(1H-benzo[d]imidazol-2(3H)-ylidene)-3-oxopropanenitrile), bis((3-amino-5-(methylthio)-1H-pyrazol-4-yl)methanone) and bis(2-thioxo-1,2-dihydropyrimidine-5-carbonitrile) derivatives incorporating a thieno- [2,3-b]thiophene moiety via versatile, readily accessible diethyl 3,4-dimethylthieno-[2,3-b]thiophene-2,5-dicarboxylate is described. 相似文献
53.
In the current study we report on the unusual results obtained in the framework of the atom-phonon coupling model: two metastables states at low temperatures. These results can explain the experimental results reported by Ould Moussa et al. [9] and Matsumoto et al. [10]. This type of SCO behavior is due to the competition between the Light-Induced Excited Spin State Trapping (LIESST) effect, the elastic interaction between the molecules and the thermal activation. In order to determine the stability of the states founded at low temperature, the free energy F is presented for the case of the two step spin transition of a SCO compound. 相似文献
54.
H. El-Ghandoor Ibraheem Nasser M. A. Abd-El Rahman R. Hassan 《Optics & Laser Technology》2000,32(4):281
A new technique (El-Ghandoor et al., Opt. Laser Technol. 31(7) (1999) 481–488) has been applied to study the shape of transverse interference fringes, instead of multiple beam Fizeau fringes (Marhic, Stein, Appl. Phys. Lett. 35 (1975) 1678–1682), from a GRIN optical fiber. In this technique, a laser light sheet is used to illuminate and pass directly through the optical fiber. Theoretical expressions are derived for the optical path differences of three groups of interference beams. The first one passes through the cladding, the core, and then the cladding once again; the second passes through the cladding only, and the third passes through the surrounding air. Theoretical expressions for the shape of transverse interference fringes formed across isotropic non-absorbing optical fibers are also calculated. 相似文献
55.
Nasser–eddine Tatar 《Mediterranean Journal of Mathematics》2013,10(1):213-226
A new assumption on the relaxation in a viscoelastic problem ensuring uniform stability in an arbitrary rate is established. This assumption replaces a usual condition and allows for a much wider class of kernels. As consequences several earlier results are extended and improved. 相似文献
56.
Perturbation theory in a framework of iteration methods 总被引:1,自引:0,他引:1
In a previous paper [J. Phys. A 36 (2003) 11807], we introduced the ‘asymptotic iteration method’ for solving second-order homogeneous linear differential equations. In this Letter, we study perturbed problems in quantum mechanics and we use the method to find the coefficients in the perturbation series for the eigenvalues and eigenfunctions directly, without first solving the unperturbed problem. 相似文献
57.
Distributed point source method (DPSM) is gradually gaining popularity in the field of non-destructive evaluation (NDE). DPSM is a semi-analytical technique that can be used to calculate the ultrasonic fields produced by transducers of finite dimension placed in homogeneous or non-homogeneous media. This technique has been already used to model ultrasonic fields in homogeneous and multi-layered fluid structures. In this paper the method is extended to model the ultrasonic fields generated in both fluid and solid media near a fluid-solid interface when the transducer is placed in the fluid half-space near the interface. Most results in this paper are generated by the newly developed DPSM technique that requires matrix inversion. This technique is identified as the matrix inversion based DPSM technique. Some of these results are compared with the results produced by the Rayleigh-Sommerfield integral based DPSM technique. Theory behind both matrix inversion based and Rayleigh-Sommerfield integral based DPSM techniques is presented in this paper. The matrix inversion based DPSM technique is found to be very efficient for computing the ultrasonic field in non-homogeneous materials. One objective of this study is to model ultrasonic fields in both solids and fluids generated by the leaky Rayleigh wave when finite size transducers are inclined at Rayleigh critical angles. This phenomenon has been correctly modelled by the technique. It should be mentioned here that techniques based on paraxial assumptions fail to model the critical reflection phenomenon. Other advantages of the DPSM technique compared to the currently available techniques for transducer radiation modelling are discussed in the paper under Introduction. 相似文献
58.
Olivier Gicque Dominique Thévenin Nasser Darabiha 《Flow, Turbulence and Combustion》2005,73(3-4):307-321
In this paper we wish to investigate the occurrence of super-equilibrium temperature values, observed in many experimental
configurations. We would like to understand the origin of this phenomenon. Previous authors have already shown that differential
diffusion can lead to considerable changes in the temperature field and we would like to build on top of this observation.
We investigate numerically super-equilibrium combustion by considering both laminar counter-flow and turbulent diluted hydrogen/air
diffusion flames. These turbulent flames are computed using direct numerical simulations (DNS). A detailed reaction mechanism
is employed and the transport properties are modeled using multicomponent diffusion velocities, including the Soret effect.
Analyzing these results we introduce three complementary parameters (dilution-free mixture fraction, dilution excess and local
enthalpy) to describe the local combustion conditions. Introducing a measure of dilution separately from the mixture fraction
is necessary for a proper analysis. Using this set of parameters it becomes possible to explain super-equilibrium temperature
levels as a consequence of differential diffusion. 相似文献
59.
Soghra Farzipour Mina Saeedi Mohammad Mahdavi Hossein Yavari Mohammadreza Mirzahekmati Nasser Ghaemi 《合成通讯》2014,44(4):481-487
Clean and easy preparation of quinazolin-4(3H)-one derivatives using 2-aminobenzamides and Vilsmeier reagent is described. 2-Aminobenzamides were converted into the corresponding quinazolinones under mild and efficient conditions, in good yields without undesirable by-products.
[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.] 相似文献
60.
Considering the thermodynamic aspects and reaction pathways of chemical adsorption of NH3 molecule at the open ends of boron nitride nanotubes (BNNTs), theoretically, it was found that the open-ended BNNTs are able
to cleave the N–H bond of NH3 via a one- or two-stepwise mechanism. The N-enriched and B-enriched open-ended BNNTs show a nucleophilic and electrophilic
behavior toward the NH3, respectively. Besides, some effects of this chemical adsorption on the electronic properties of BNNTs were explored. 相似文献