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991.
Fausto Barazza Petra Malisan Roberto Carniel 《Communications in Nonlinear Science & Numerical Simulation》2009,14(1):182-193
In this work we investigate the application of the rotation of the coordinate system before applying denoising techniques aimed at improving the H/V spectral ratio for seismic site effects estimation. By this rotation, one can detect the direction of maximum and minimum matching between any couple of orthogonal H/V ratios. The direction of minimum matching should represent the direction of maximum anisotropy of the surface layer or a directional noise. To further improve the method, singular spectrum analysis and WASEE techniques are then applied. 相似文献
992.
993.
Mirka Safarikova Petra Lunackova Karel Komarek Tomas Hubka Ivo Safarik 《Journal of magnetism and magnetic materials》2007
Magnetic solid phase extraction (MSPE) is proposed as a simple and fast method for the preconcentration of free middle oxyethylated nonylphenols (NPs) from water. Middle oxyethylated NPs were extracted by MSPE from different water samples (10 and 500 ml samples of distilled, potable, well, river and pond water in concentrations of 30 and 0.6 μg ml−1) using magnetically modified polyphenyleneoxide, Tenax TA and Tenax GR as magnetic adsorbents. Recoveries were 80–100% and relative standard deviations were less than 10%. 相似文献
994.
Detailed understanding of femtosecond-scale photochemical processes requires dynamical simulations that are complementary to interpretations based on transitions between energy surfaces. For cis to trans photoisomerization of azobenzene following a 100 fs laser pulse, we find that the mechanism is rotation about the central NN bond, and the process is complete in less than 1 ps. The initial excitation and subsequent de-excitation are each achieved via multiple steps, with the molecule always in a superposition of electronic states, as the 3N nuclear degrees of freedom are excited by the laser pulse. 相似文献
995.
Ludk Toman Miroslav Janata Jií Spv
ek Petr Vl
ek Petra Ltalov Bohumil Masa Antonín Sikora 《Journal of polymer science. Part A, Polymer chemistry》2004,42(23):6098-6108
ABCBA‐type pentablock copolymers of methyl methacrylate (MMA), styrene (S), and isobutylene (IB) were prepared by a three‐step synthesis, which included atom transfer radical polymerization (ATRP) and cationic polymerization: (1) poly(methyl methacrylate) (PMMA) with terminal chlorine atoms was prepared by ATRP initiated with an aromatic difunctional initiator bearing two trichloromethyl groups under CuCl/2,2′‐bipyridine catalysis; (2) PMMA with the same catalyst was used for ATRP of styrene, which produced a poly(S‐b‐MMA‐b‐S) triblock copolymer; and (3) IB was polymerized cationically in the presence of the aforementioned triblock copolymer and BCl3, and this produced a poly(IB‐b‐S‐b‐MMA‐b‐S‐b‐IB) pentablock copolymer. The reaction temperature, varied from ?78 to ?25 °C, significantly affected the IB content in the product; the highest was obtained at ?25 °C. The formation of a pentablock copolymer with a narrow molecular weight distribution provided direct evidence of the presence of active chlorine at the ends of the poly(S‐b‐MMA‐b‐S) triblock copolymer, capable of the initiation of the cationic polymerization of IB in the presence of BCl3. A differential scanning calorimetry trace of the pentablock copolymer (20.1 mol % IB) showed the glass‐transition temperatures of three segregated domains, that is, polyisobutylene (?87.4 °C), polystyrene (95.6 °C), and PMMA (103.7 °C) blocks. One glass‐transition temperature (104.5 °C) was observed for the aforementioned triblock copolymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6098–6108, 2004 相似文献
996.
Žaneta Mesíková Petra Šulcová M. Trojan 《Journal of Thermal Analysis and Calorimetry》2007,88(1):103-106
Phosphates belong to the extensive group
of inorganic pigments that are very often used in industry of plastics and
anticorrosive paints. Also, the powders of newberyite MgHPO4·3H2O
and α-pyrophosphate Mg2P2O7
can find the usage in this field. Thus, these compounds were the centre of
our attention. Newberyite and α-pyrophosphate were synthesized by the
method of gelling. Impact of various ways of synthesis, especially reaction
conditions, on the structural, thermal, physical and optical properties was
investigated. α-pyrophosphate was synthesized by the thermal decomposition
of newberyite at temperature around 500°C. Both powders are white color,
but the newberyite is the whitest one. The reaction pH particularly affected
the particle size distribution and optical properties. 相似文献
997.
998.
Peter Sartori Nikolai Ignat'ev Claudia Jünger Ralf Jüschke Petra Rieland 《Journal of Solid State Electrochemistry》1998,2(2):110-116
The electrochemical fluorination of alkanedisulfonyl fluorides, alkanesulfonyl amides and alkanedisulfonyl amides is described.
Detailed analysis of the products and the electrolyte and new information on higher nickel fluorides have led to a new insight
into the mechanism of electrochemical fluorination.
Received: 27 May 1997 / Accepted: 22 October 1997 相似文献
999.
Natacha Malecki Raymond Houssin Jean‐Pierre Hanichart Daniel Couturier Ferdinand Petra Laurent Legentil Benoîct Rigo 《Journal of heterocyclic chemistry》2003,40(1):45-50
Dimethyl 7‐methoxycarbonylmethyl‐5‐oxo‐1,2,3,5‐tetrahydro‐indolizine‐3,8‐dicarboxylate was synthesized starting from methyl pyroglutamate. A study was made of the reactions of this highly functionalized pyridone with ethyl iodide, selenium oxide, isoamyl nitrite and formaldehyde. Literature reports that reaction of 4‐(1‐carbomethoxypropyl)‐5‐carbomethoxy‐1,6‐cyclopentano‐2‐pyridone with formaldehyde lead to a 95% yield of a monolactone (26) precursor of camptothecin. Our experiments resulted in 15 % of this monolactone and 40% of a new dilactone (27) . 相似文献