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991.
Epstein SA Shemesh D Tran VT Nizkorodov SA Gerber RB 《The journal of physical chemistry. A》2012,116(24):6068-6077
Methyl peroxide (CH(3)OOH) is commonly found in atmospheric waters and ices in significant concentrations. It is the simplest organic peroxide and an important precursor to hydroxyl radical. Many studies have examined the photochemical behavior of gaseous CH(3)OOH; however, the photochemistry of liquid and frozen water solutions is poorly understood. We present a series of experiments and theoretical calculations designed to elucidate the photochemical behavior of CH(3)OOH dissolved in liquid water and ice over a range of temperatures. The molar extinction coefficients of aqueous CH(3)OOH are different from the gas phase, and they do not change upon freezing. Between -12 and 43 °C, the quantum yield of CH(3)OOH photolysis is described by the following equation: Φ(T) = exp((-2175 ± 448)1/T) + 7.66 ± 1.56). We use on-the-fly ab initio molecular dynamics simulations to model structures and absorption spectra of a bare CH(3)OOH molecule and a CH(3)OOH molecule immersed inside 20 water molecules at 50, 200, and 220 K. The simulations predict large sensitivity in the absorption spectrum of CH(3)OOH to temperature, with the spectrum narrowing and shifting to the blue under cryogenic conditions because of constrained dihedral motion around the O-O bond. The shift in the absorption spectrum is not observed in the experiment when the CH(3)OOH solution is frozen suggesting that CH(3)OOH remains in a liquid layer between the ice grains. Using the extinction coefficients and photolysis quantum yields obtained in this work, we show that under conditions with low temperatures, in the presence of clouds with a high liquid-water content and large solar zenith angles, the loss of CH(3)OOH by aqueous photolysis is responsible for up to 20% of the total loss of CH(3)OOH due to photolysis. Gas phase photolysis of CH(3)OOH dominates under all other conditions. 相似文献
992.
Stephen W. C. Chung Jeff C. H. Tran W. W. Wong 《Accreditation and quality assurance》2012,17(1):35-44
A proficiency test (PT) to assess the capabilities of laboratories to determine nutrients in a biscuit sample was carried
out in September 2009. The need for such interlaboratory comparison arose from an increasing nutrition labeling requirements
of different countries around the world. Forty-eight laboratories worldwide participated in this PT program for the determination
of total lipids, saturated fat, trans-fat, protein, sugars, total dietary fiber (TDF), ash and sodium in food. This program
was organized under the auspices of the Asia-Pacific Laboratory Accreditation Cooperation (APLAC). APLAC considers PT programs
as one of the objective means of assessing the performance of the accredited laboratories. The program is one of the APLAC
PT series whose primary purposes are to establish mutual agreement on the equivalence of the operation of APLAC member laboratories
and to provide an opportunity to identify testing deficiency so that corrective actions can be taken, if necessary. The results
of this program indicated that the consensus mean values estimated by robust statistics were in good agreement with the corresponding
values obtained in the homogeneity tests except for trans-fat and TDF. The relative standard deviations of participant results
for trans-fat and TDF were also found to be higher (19 and 24%, respectively) than the other test parameters. The relative
standard deviations for other test parameters were less than 10%. One-half of the laboratories obtained satisfactory z-scores
(| z | < 3) (\left| z \right| < 3) for all their reported results. Although participants were instructed to provide the measurement uncertainties of their reported
results, only 27.5% of them had done so. Albeit many of the measurement uncertainties appear to be reasonable, some of them
were found to vary widely, indicating that some laboratories still have difficulties in estimating measurement uncertainties.
Although the overall measurement capability can be considered to be satisfactory, there is still room for improvement of analytical
procedures. 相似文献
993.
Nguyen Van Quy Tran Minh Hung Trinh Quang Thong Le Anh Tuan Tran Quang Huy Nguyen Duc Hoa 《Current Applied Physics》2013,13(8):1581-1588
The controlled synthesis of mesoporous silica and metal oxide nanocomposites with a highly ordered porous structure and large specific surface area for specific applications has been an attractive topic in the field of porous materials. Herein, we introduce a novel method for the fabrication of highly ordered mesoporous structured and large specific surface area Fe2O3/SiO2 nanocomposites, and consider their application in room temperature gas sensors. The mesoporous Fe2O3/SiO2 nanocomposites were synthesised by a two-step method, which combines the hydrothermal growth of Fe2O3 nanoparticles and the microemulsion phase of Brij 56 (C16EO10) surfactant as templates in instantly direct-templating synthesis. This synthesis method enables the fabrication of mesoporous Fe2O3/SiO2 nanocomposites without distortion of the ordered porous structure after calcination at high temperature. The synthesised materials were found to be efficient in a room temperature VOC sensor application, with good recovery. 相似文献
994.
995.
This report analyzes the long time stability of four methods for non-iterative, sub-physics, uncoupling for the evolutionary Stokes–Darcy problem. The four methods uncouple each timestep into separate Stokes and Darcy solves using ideas from splitting methods. Three methods uncouple sequentially while one is a parallel uncoupling method. We prove long time stability of four splitting based partitioned methods under timestep restrictions depending on the problem parameters. The methods include those that are stable uniformly in S0, the storativity coefficient, for moderate kmin, the minimum hydraulic conductivity, uniformly in kmin for moderate S0 and with no coupling between the timestep and the spacial meshwidth. 相似文献
996.
Tran Dan Thu 《Graphs and Combinatorics》2012,28(3):423-432
The Ahlswede–Zhang identity is an elegant sharpening of the famous LYM-inequality. Recently, we have found a parametrised
identity which implies the AZ identity and characterizes deficiencies of other inequalities in combinatorics. In this paper,
we show identities of half-way extraction from AZ-style identities. These identities aim to characterize more clearly terms
participating in AZ identities or LYM-style inequalities. 相似文献
997.
Dual extragradient algorithms extended to equilibrium problems 总被引:1,自引:0,他引:1
In this paper we propose two iterative schemes for solving equilibrium problems which are called dual extragradient algorithms. In contrast with the primal extragradient methods in Quoc et al. (Optimization 57(6):749–776, 2008) which require to solve two general strongly convex programs at each iteration, the dual extragradient algorithms proposed
in this paper only need to solve, at each iteration, one general strongly convex program, one projection problem and one subgradient
calculation. Moreover, we provide the worst case complexity bounds of these algorithms, which have not been done in the primal
extragradient methods yet. An application to Nash-Cournot equilibrium models of electricity markets is presented and implemented
to examine the performance of the proposed algorithms. 相似文献
998.
T. T. Van Tran T. Si Bui S. Turrell B. Capoen P. Roussel M. Bouazaoui M. Ferrari O. Cristini C. Kinowski 《Journal of Raman spectroscopy : JRS》2012,43(7):869-875
Crack‐free (100–x) SiO2–x SnO2 glass‐ceramic monoliths have been prepared by the sol–gel method obtaining for the first time SnO2 concentrations of 20% with annealing at 1100 °C. Heat‐treatment resulted in the formation and growth of SnO2 nanocrystals within the silica matrices. Combined use of Fourier transform–Raman spectroscopy and in situ high‐temperature X‐Ray diffraction shows that SnO2 particles begin to crystallize in the cassiterite‐type phase at 80 °C and that their average apparent size remains around 7 nm, even after annealing at 1100 °C. Nanocrystal sizes and size distributions determined by low‐wavenumber Raman are in good agreement with those obtained from transmission electron microscopy measurements. Results indicate that the formation and the growth of SnO2 nanocrystals impose a residual porosity in the silica matrix. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
999.
1000.
Pham Huu Anh Ngoc Thai Bao Tran Toshiki Naito 《Journal of Difference Equations and Applications》2013,19(1):15-24
We study stability radii of higher order linear difference systems under multi-perturbations. A formula for complex stability radius of higher order linear difference systems under multi-perturbations is given. Then, for the class of positive systems, we prove that the complex stability radius and real stability radius of the system under multi-perturbations coincide and they are computed via a simple formula. These are extensions of corresponding results of Hinrichsen and Son, Hinrichsen et al., Ngoc and Son, and Pappas and Hinrichsen. An example is given to illustrate the obtained results. 相似文献