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排序方式: 共有428条查询结果,搜索用时 15 毫秒
31.
J. Casta R. Gwozdz P. Katrik F. Grass 《Journal of Radioanalytical and Nuclear Chemistry》2000,244(2):349-354
The irradiation of large samples of biological material in a high neutron flux enables the extention of trace element analysis into the ng to pg range, but raises several problems as gamma heating and radiolysis degrade the samples. Gamma heating increases the pressure to a point where either a very large irradiation container is necessary or a container which can endure the high pressure. Several methods to overcome these problems have been published. The irradiation of open samples was performed as an alternative to these methods. Temperature effects on biological material during irradiation in a high and in a low neutron flux were compared. As an example, wheat was irradiated in open containers allowing simultaneous temperature measurement in the sample during irradiation. 相似文献
32.
Juan M. Antelo Florencio Arce Juan Crugeiras Julia Franco Pilar Rodriguez Angel Varela 《国际化学动力学杂志》1990,22(12):1271-1282
This article reports the kinetics of the decomposition of N-bromoserine formed rapidly by bromation of serine by BrO?. The main decomposition products are glycolaldehyde, ammonia, carbon dioxide, and bromide ions at pH < 11.5, and β-hydroxypyruvic acid, ammonia, and bromide ions at pH > 11.5. The reaction is of order one with respect to N-bromoserine, and is independent of ionic strength and excess serine. The rate constant increases with increasing pH at pH > 11 and with decreasing pH at pH < 8, and over the range pH 8–11 has the constant value 1.67 × 10?3 s?1 at 298 K. 相似文献
33.
Daniel Castaño Díez Max Gunzburger Angela Kunoth 《Numerical Methods for Partial Differential Equations》2008,24(6):1388-1404
We extend the multiscale finite element viscosity method for hyperbolic conservation laws developed in terms of hierarchical finite element bases to a (pre‐orthogonal spline‐)wavelet basis. Depending on an appropriate error criterion, the multiscale framework allows for a controlled adaptive resolution of discontinuities of the solution. The nonlinearity in the weak form is treated by solving a least‐squares data fitting problem. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2008 相似文献
34.
35.
V. Torres-Zúñiga O. G. Morales-Saavedra E. Rivera R. Castañeda-Guzmán J. G. Bañuelos R. Ortega-Martínez 《Journal of Sol-Gel Science and Technology》2010,56(1):7-18
SiO2-based bulk and film sol–gel hybrid materials were prepared with a family of novel liquid crystalline (LC) amphiphilic azo-dyes
bearing oligo(ethylene glycol) spacers (named here RED-PEG-n, n = 2, 3, 4, 6). The catalyst-free-sonogel route was implemented to produce optically active hybrid monoliths and spin-coated
films with these materials. Comprehensive morphological, thermal, photo-acoustic and spectroscopic sample characterizations
were performed in order to elucidate the physical properties of these novel compounds within the sonogel environment. Film
samples were also studied via the nonlinear optical (NLO) second harmonic generation (SHG)-Maker fringes technique. Results
show that the chromophores were homogeneously embedded within the highly pure SiO2-sonogel network, showing a clear thermotropic mesogenic behavior. The push–pull structure of the implemented azo-dyes allowed
effective electrically-induced monomeric alignment within the sonogel confinement; thus, stable quadratic NLO-SHG-activity
in the organic–inorganic film samples was achieved despite the lack of glass transition temperature (T
g
) of the guest LC-compounds. 相似文献
36.
I. E. Castañeda J. G. Gonzalez-Rodriguez J. Colin M. A. Neri-Flores 《Journal of Solid State Electrochemistry》2010,14(7):1145-1152
An investigation about the corrosion resistance of Ni-Al-Fe intermetallic alloys in simulated human body fluid environments
has been carried out using electrochemical techniques. Tested alloys included 57 (wt%) Ni-(20 to 30) Al-(12 to 23) Fe using
the Hank's solution because the high corrosion resistance provided by protective Al2O3 external layer. For comparison, AISI 316L type stainless steel has also been used. Electrochemical techniques included potentiodynamic
polarization curves, electrochemical impedance spectroscopy, and electrochemical noise measurements. The different techniques
have shown that these alloys showed a similar or higher corrosion resistance than conventional AISI 316L type stainless steel,
and this corrosion resistance decreased as the Al content in the alloy increased. The alloys were susceptible to pitting type
of corrosion on the interdendritic Ni-rich phases. 相似文献
37.
Fernando De Andrés Mohammed Zougagh Gregorio Castañeda Angel Ríos 《Analytical and bioanalytical chemistry》2010,397(1):223-231
A rapid and simple method for separation and detection of six heterocyclic aromatic amines (2-amino-1-methyl-6-phenylimidazo
[4,5-b]-pyridine, 2-amino-1-methyl-imidazo [4,5-f]-quinoline, 2-amino-3,8-dimethyl-imidazo [4,5-f]-quinoxaline, 2-amino-3,7,8-trimethyl-imidazo [4,5-f]-quinoxaline, 2-amino-3,4,8-trimethyl-imidazo [4,5-f]-quinoxaline, and 2-amino-3,4-dimethyl-imidazo [4,5-f]-quinoline) in human urine samples is proposed to reflect daily intake and recent HAAs exposure. This method comprises previous
clean-up and preconcentration of the analytes on Strata-X reversed phase extraction cartridges followed by capillary liquid
chromatography (CLC) and evaporative light-scattering detection (ELSD). A mobile phase of acetonitrile and ammonium acetate
35 mM at pH 5.15 through a gradient of composition and a flow rate of 15 μL min−1 resulted in good separations of the analytes. Temperature and gas pressure were optimized for detection. The CLC-ELSD allows
the separation and quantification of HAAs with good resolution, precision, and sensitivity. The usefulness of the proposed
method was demonstrated by the analysis of synthetic and natural human urine samples spiked with different concentration levels
of heterocyclic amines. 相似文献
38.
V. Rodríguez-Lugo L. Ortiz-Velázquez J. Miranda M. Ortiz-Rojas V. M. Castaño 《Journal of Radioanalytical and Nuclear Chemistry》1999,240(2):561-569
The characterization of samples of painted plasters obtained from the archaeological site of Xochicalco, in Central Mexico,
is presented. Elemental concentrations of the painted layers were obtained by using proton induced X-ray emission (PIXE).
The main crystalline structures of the samples are identified with the help of X-ray diffraction (XRD), while the microstructure
is studied by scanning electron microscopy (SEM). The information resulting from the application of these three techniques
is used to achieve more accurate values for the elemental concentrations. Additional data regarding organic components of
the paintings was obtained through Fourier transform infrared spectrometry (FTIR). Although the latter results only provided
reliable data on inorganic components, they help to clarify the results from XRD and confirm those of SEM. 相似文献
39.
Masashi Shiotsuki Atsushi Nakagawa Jesus Rodriguez Castañon Naoya Onishi Tatsurou Kobayashi Fumio Sanda Toshio Masuda 《Journal of polymer science. Part A, Polymer chemistry》2010,48(23):5549-5556
End‐functionalized poly(phenylacetylene)s were synthesized by the polymerization of phenylacetylene (PA) using the well‐defined palladium catalysts represented as [(dppf)PdBr(R)] {dppf = 1,1′‐bis(diphenylphosphino)ferrocene}. The Pd catalysts having a series of R groups such as o‐tolyl, mesityl, C(Ph)?CPh2, C6H4‐o‐CH2OH, C6H4‐p‐CN, and C6H4‐p‐NO2 in conjunction with silver triflate polymerized PA to give end‐functionalized poly(PA)s bearing the corresponding R groups in high yields. The results of IR and NMR spectroscopies and MALDI‐TOF mass analyses proved the introduction of these R groups at one end of each polymer chain. The poly(PA) bearing a hydroxy end group was applied as a macroinitiator to the synthesis of a block copolymer composed of poly(PA) and poly(β‐propiolactone) moieties. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
40.