Absorption density-matrix treatment

Many apparent anomalies in the spectra produced by double resonance experiments can be resolved by a density matrix treatment. Thus in A- X experiments with a reduced amplitude of the irradiated field the normal effect of the NOE upon the intensities of the transitions may be severely modified and both emission and absorption may be observed. (58) It turns out that the overall behaviour depends upon... 

A Density-Matrix Treatment of Absorption of Weak, Continuous Light... 

The coherence transfer provides cross peaks which are antiphase for the various 7//-split components. The antiphase nature of the cross peaks then leads to partial or total cancellation of the cross peaks themselves, especially if they are phased in the absorption mode. This behavior can be simulated (Fig. 8.15) using appropriate treatments of the time evolution of the spin system, for instance using the density matrix formalism [17,18]. It is quite common that signals in paramagnetic systems... 

A numerical matrix correction technique is used to linearise fluorescent X-ray intensities from plant material in order to permit quantitation of the measurable trace elements. Percentage accuracies achieved on a standard sample were 13% for sulfur and phosphorus and better than 10% for heavier elements. The calculation employs all of the elemental X-ray intensities from the sample, relative X-ray production probabilities of the elements determined from thin film standards, elemental X-ray attenuation coefficients, and the areal density of the sample cm2. The mathematical treatment accounts for the matrix absorption effects of pure cellulose and deviations in the matrix effect caused by the measured elements. Ten elements are typically calculated simultaneously phosphorus, sulfur, chlorine, potassium, calcium, manganese, iron, copper, zinc and bromine. Detection limits obtained using a rhodium X-ray tube and an energy-dispersive X-ray fluorescence spectrometer are in the low ppm range for the elements manganese to strontium. 

This important relation allows us to replace the matrix element and the combined density of states in the spontaneous emission rate by the absorption coefficient a(fkj) and makes this treatment applicable to real materials once the absorption coefficient is known ... 

Effect of fiber treatments Alkali treatment of fibers slightly increased the density of composites as a result of low void content indicating better interfacial adhesion between matrix and fiber [39]. AlkaH treatment considerably reduced the porosity, indicating better fiber-matrix adhesion. The principal cause of increase in porosity in composites is the presence of voids in the fiber-matrix interface due to lack of compatibility. Study on water absorption characteristics of OPF-LLDPE composites [53] indicated alkali treatment on fibers reduced water absorption at higher fiber loadings of 40 and 50 percent. Composites made from alkaH-treated fibers exhibited more swelling compared to untreated fiber composites except at 50% fiber loading. Alkali treatment caused more linear expansion. 

The low density of these fibres - about 0.97 g cm - means that in terms of specific stress and specific modulus (i.e. on a mass per unit length basis) they rank very highly. However, they are limited in composites by their low melting temperatures (about 140°C), tendency to creep, and the need for special surface-activation processes, such as corona discharge treatment, to develop adhesion to matrix polymers. They are sometimes used alone, but more often in hybrid yam and fabric stmctures with glass or carbon fibres in an epoxy or unsaturated polyester resin matrix to improve the impact resistance and energy absorption. Curing temperatures should not exceed 125°C. 

---