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171.
Abstract— A methodology for the determination of chemiluminescence quenching terms is given. By using the oxidation of tetrakis(dimethylamino)ethylene as an example, it is shown how the nature and magnitude of the quenching terms help to elucidate the reaction mechanism, or how ignoring them can lead to false impressions. It is shown that chemiluminescence quenching effects need not be the same as those for photoluminescence of the same electronically excited species. 相似文献
172.
Robert E. Linder Günter Barth Edward Bunnenberg Carl Djerassi Lloyd Seamans Albert Moscowitz 《Chemical physics letters》1974,28(4):490-493
The MCD spectrum of formaldehyde in the vapor phase has been measured and analyzed. Triplet bands occur with unusually high ellipticity, allowing identification of several new singlet-triplet bands. Also, an additional singlet progression, based on two quanta of the out-of-plane band and a single quantum of the antisymmetric CH stretch, has been identified. 相似文献
173.
Vincent T’kindt Karima Bouibede-Hocine Carl Esswein 《4OR: A Quarterly Journal of Operations Research》2005,3(1):1-21
In this paper we tackle an important point of combinatorial optimisation: that of complexity theory when dealing with the counting or enumeration of optimal solutions. Complexity theory has been initially designed for decision problems and evolved over the years, for instance, to tackle particular features in optimisation problems. It has also evolved, more or less recently, towards the complexity of counting and enumeration problems and several complexity classes, which we review in this paper, have emerged in the literature. This kind of problems makes sense, notably, in the case of multicriteria optimisation where the aim is often to enumerate the set of the so-called Pareto optima. In the second part of this paper we review the complexity of multicriteria scheduling problems in the light of the previous complexity results.Received: November 2004 / Received version: March 2005MSC classification:
90B40, 90C29, 68Q15 相似文献
174.
Ground-state hyperfine splittings in hydrogen and muonium are very well measured. Their difference, after correcting for magnetic moment and reduced mass effects, is due solely to proton structure-the large QED contributions for a pointlike nucleus essentially cancel. The rescaled hyperfine difference depends on the Zemach radius, a fundamental measure of the proton, computed as an integral over a product of electric and magnetic proton form factors. The determination of the Zemach radius, (1.019+/-0.016) fm, from atomic physics tightly constrains fits to accelerator measurements of proton form factors. Conversely, we can use muonium data to extract an experimental value for QED corrections to hydrogenic hyperfine data. There is a significant discrepancy between measurement and theory, in the same direction as a corresponding discrepancy in positronium. 相似文献
175.
176.
Busacca CA Grossbach D Campbell SJ Dong Y Eriksson MC Harris RE Jones PJ Kim JY Lorenz JC McKellop KB O'Brien EM Qiu F Simpson RD Smith L So RC Spinelli EM Vitous J Zavattaro C 《The Journal of organic chemistry》2004,69(16):5187-5195
The Boehringer-Ingelheim phosphinoimidazoline (BIPI) ligands were applied to the formation of chiral quaternary centers in the asymmetric Heck reaction. Several different substrates were examined in detail, using more than 70 members of this new ligand class. Hammett relationships were determined through systematic variation of the ligand electronics. All substrates showed essentially the same Hammett behavior, where enantioselectivity increased as the ligands were made more electron-deficient. Ligand optimization has led to catalysts which give the highest enantioselectivities reported to date for these difficult systems. 相似文献
177.
Simpson HJ Houston BH Liskey SW Frank PA Berdoz AR Kraus LA Frederickson CK Stanic S 《The Journal of the Acoustical Society of America》2003,114(3):1281-1290
Acoustic bottom penetration experiments were carried out in a medium-grain sandy bottom at a site in St. Andrews Bay, Florida. These investigations used a new buried, vertical, one-dimensional synthetic array system where a small hydrophone was water-jetted into the sediment to a depth of approximately 2 m. Once buried, this hydrophone was mounted to a vertical robotics stage that translated the hydrophone upward in 1-cm increments. A broadband (3 to 80 kHz) spherical source, positioned 50 cm above the sediment-water interface, was used to insonify the sediment. Measurements were made with insonification angles above and below the critical angle by changing the horizontal distance of the source relative to the insertion point. This new measurement system is detailed, and results are presented that include temporal, frequency, and wavenumber analysis for natural and roughened interfaces. The measured compressional sound speed and attenuation are shown to be self-consistent using the Kramers-Kronig relation. Furthermore, only a single fast compressional wave was observed. There was no observation of a second slower compressional wave as predicted by some applications of the Biot model to unconsolidated water-saturated porous media. 相似文献
178.
Studer A Amrein S Matsubara H Schiesser CH Doi T Kawamura T Fukuyama T Ryu I 《Chemical communications (Cambridge, England)》2003,(10):1190-1191
4-[(Trimethylstannyl)diphenylsilyl]butanoyl radical, arising from the corresponding 3-(stannylsilyl)propyl radical and CO, undergoes an SHi reaction at Si with extrusion of trimethyltin radical to give silacyclopentanone. The parent 3-(stannylsilyl)propyl radical was also found to isomerize to (3-stannylpropyl)silyl radical via a 1,4-Sn shift from Si to C with a rate constant of 9.3 x 10(4) s-1 at 80 degrees C. Ab initio and DFT MO calculations support a front-side attack mechanism. 相似文献
179.
Using a multistep state-selective excitation scheme, fluorescence-dip spectra of carbon monoxide have been recorded in the energy region between 106 100 and 112 200 cm(-1). Prominent groups of bands were tentatively identified as transitions into the 6f em leader10f (v=0) and 9psigma em leader11psigma (v=0) triplet Rydberg series. For the f complex states, molecular constants have been calculated. The triplet f levels show an unusually large rotational constant and are located at higher energies than their singlet counterparts. Copyright 2001 Academic Press. 相似文献
180.
This paper deals with quasilinear elliptic differential inclusions defined in all of N and governed in general by a nonpotential quasilinear elliptic operator of the Leray–Lions type and a multivalued term in form of a (nonmonotone) state-dependent subdifferential. We prove the existence of entire extremal solutions within a sector of an ordered pair of appropriately defined upper and lower solutions without imposing any condition at infinity. Therefore, standard variational methods cannot be applied here. Furthermore, due to the unboundedness of the domain and due to lack of monotonicity of the operators involved, no comparison results are available such that the problem under consideration becomes even more difficult. 相似文献