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1.
Alexandros A. Skordos Ivana K. Partridge 《Journal of Polymer Science.Polymer Physics》2004,42(1):146-154
This article presents a new methodology for the quantitative determination of the progress of the curing reaction of a thermosetting resin, using the results of electrical impedance spectroscopy. The method is an extension of the use of the imaginary impedance maximum as a reaction progress indicator and is based on the demonstration of a close correlation between the reaction rate, as measured by conventional differential scanning calorimetry, and the rate of change of the value of the imaginary impedance spectrum maximum. Tests on a commercial aerospace epoxy resin under both isothermal and dynamic heating conditions with calorimetry and impedance spectroscopy have demonstrated the validity of the method and set the accuracy limits involved. This technique can be used as a real-time online control tool for thermoset composite manufacturing. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 146–154, 2004 相似文献
2.
M. E. Kompan I. I. Novak V. B. Kulik 《Journal of Experimental and Theoretical Physics》2002,94(4):739-744
Spectra of second-order Raman scattering in porous silicon are investigated. A band shift towards lower energies in second-order spectra is observed, as well as the correlation between the values of band shift in first-and second-order spectra. It is demonstrated that the observed effect cannot be interpreted using the conventional concepts of the mechanisms of scattering in microcrystalline samples. An interpretation of the revealed effect is suggested. 相似文献
3.
The presented work offers new algorithms for phase evaluation in interferometric measurements. Several phase-shifting algorithms with an arbitrary but constant phase-shift between captured intensity frames are proposed. These phase calculation algorithms need to measure five frames of the intensity of the interference field. The algorithms are similarly derived as so called Carré algorithm. The phase evaluation process then does not depend on the linear phase shift errors. Furthermore, the detailed analysis of the algorithms with respect to most important factors, which affect interferometric measurements, is carried out. It is also studied the dependency of the evaluation algorithms on the phase shift values, and the proposed phase calculation algorithms are compared with respect to the resulting phase errors. The influence of most important factors in the measurement and evaluation process was simulated as systematic and random errors using a proposed mathematical model. 相似文献
4.
The stoichiometric reactions of trimethylaluminum with 2,6‐(MeOCH2)2C6H3OH (LH) revealed compounds L3Al ( 1 ) and L2AlMe ( 2 ). On the other hand reaction of 1 equiv. of LH with trimethylaluminum did not lead to the formation of complex LAlMe2 ( 3 ), rather 2 together with Me3Al were observed as a result of a disproportionation of 3 . Compounds 1 and 2 were characterized by elemental analysis, 1H and 13C NMR spectroscopy and in the case of 1 by X‐ray diffraction. Derivative 2 underwent transmetalation with Ph3SnOH, giving LSnPh3 ( 4 ) as the result of a migration of ligand L from the aluminum to the tin atom. The identity of 4 was established by elemental analysis, 1H, 13C and 119Sn NMR spectroscopy and 1H, 119Sn HMBC experiments. The system 2 and B(C6F5)3 in a 1:1 molar ratio was shown to be active in the polymerization of propylene oxide and ε‐caprolactone. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
5.
6.
Erich Novak 《Numerische Mathematik》1986,50(2):245-252
Summary The definition of the average error of numerical methods (by example of a quadrature formula
to approximateS(f)= f d on a function classF) is difficult, because on many important setsF there is no natural probability measure in the sense of an equidistribution. We define the average a posteriori error of an approximation
by an averaging process over the set of possible information, which is used by
(in the example of a quadrature formula,N(F)={(f(a
1), ...,f/fF} is the set of posible information). This approach has the practical advantage that the averaging process is related only to finite dimensional sets and uses only the usual Lebesgue measure. As an application of the theory I consider the numerical integration of functions of the classF={f:[0,1]/f(x)–f(y)||x–y|}. For arbitrary (fixed) knotsa
i
we determine the optimal coefficientsc
i
for the approximation
and compute the resulting average error. The latter is minimal for the knots
. (It is well known that the maximal error is minimal for the knotsa
i
.) Then the adaptive methods for the same problem and methods for seeking the maximum of a Lipschitz function are considered. While adaptive methods are not better when considering the maximal error (this is valid for our examples as well as for many others) this is in general not the case with the average error. 相似文献
7.
Infrared and Raman spectra of solid magnesium bromide dietherate MgBr22Et2O have been studied at different temperatures between 300 and 90 °K in the 4000 to 30 cm? range. Infrared spectra of this compound at various pressures up to 10 kbar have also been investigated. The MgBr22Et2O crystal has two phases and there is a reversible transition between them. This phase transition concerns primarily the conformational change of (C2Hg5)2O molecules and much less the arrangement of the ligands around the central magnesium atom. At room temperature or low pressure the GG conformation appears to be predominant while at low temperature or high pressure there is only TG (or TT) conformation of ether molecules. The enthalpy difference and transition temperature between the phases have been determined calorimetrically. An assignment of the spectra of both phases is given. The analysis of intramolecular vibrations gives information about the relative contribution of conformational change and coordination effect to the frequency shifts of (C2H5)2O vibrations. The assignment of magnesium-ligand vibrations on the other hand allows us to estimate the Mg-Br and Mg-O force constants. 相似文献
8.
Summary The calculation of the effects of temperature and isotopic composition on the energy weighted moments of the dipole oscillator strength distribution of H2 in the random phase approximation to the polarization propagator are reported. It is seen that the effect of isotopic composition is small, while that of temperature is of an order accessible to experiment. We find that all the mean excitation energiesI
, for =–1, 0, 1, decrease with temperature as does the dipole oscillator strength momentS() for >0, while the opposite is true for <0. These effects are interpreted in terms of the bond length dependence of the excitation energies. 相似文献
9.
Vyskocil S Meca L Tislerová I Císarová I Polásek M Harutyunyan SR Belokon YN Stead RM Farrugia L Lockhart SC Mitchell WL Kocovský P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(20):4633-4648
The title binaphthyls 19 and 26, which are the positional isomers of 2-methoxy-2'-(diphenylphosphino)-1,1'-binaphthyl (MOP, 19) and 2-amino-2'-hydroxy-1,1'-binaphthyl (NOBIN, 26), have been synthesized by Suzuki coupling as the key step (10 + 15-->18), followed by functional group transformations, involving C-P and C-N bond formation (18-->19 and 18-->23). Racemic intermediate 22 was resolved by co-crystallization with N-benzylcinchonidinium chloride and the absolute configuration determined by X-ray crystallography. These novel binaphthyls are configurationally stable and, as such, potentially usable as chiral ligands in asymmetric reactions. Michael addition of the glycine-derived enolate 40 to methyl acrylate, carried out in the presence of (R)-(-)-27 as the chiral phase-transfer catalyst, afforded L-glutamic acid (S)-(+)-43 of 92% ee (after hydrolysis of the primary product). 相似文献
10.
Ivan Němec Zorka Machá?ková Ivana Císa?ová Zdeněk Mi?ka 《Journal of solid state chemistry》2004,177(12):4655-4664
Aminoguanidinium(1+) dihydrogen phosphate was prepared by crystallization from aqueous solution. On the basis of the results of DSC measurements, X-ray structural analysis was carried out at temperatures of 160, 215 and 293 K for three aminoguanidinium(1+) dihydrogen phosphate phases ( |Z=2|non-ferroic |melting point 408 K; II |201-222 K|(2) |Z=2|non-ferroic|-; III |<201 K|(2)|Z=4|non-ferroic|-). The triclinic unit cell dimensions (a=6.8220(2), b=7.1000(2), c=7.4500(2) Å, α=86.925(2)°, β=80.731(2)°, γ=79.630(2)°, V=350.21(2) Å3—phase I) are similar for all three structural phases with the exception of phase III, where doubling of the c-axis length leads to an increase in the volume to 692.34(3) Å3. The crystal structure of all three modifications consists of parallel layers of dihydrogen phosphate anions that are interconnected by aminoguanidinium(1+) cations through hydrogen bonds of the N-H…O type. The planar aminoguanidinium(1+) cations are oriented almost parallel to each other and are perpendicular to the anion layers. The primary differences amongst phases I, II and III lie in the location of the H atom in the short O-H…O bonds connecting the dihydrogen phosphate anions in layers. The FTIR and FT Raman spectra of natural and deuterated compounds were recorded and interpreted. The FTIR spectra were studied down to a temperature of 90 K. 相似文献