Role distinctions

Electrons, protons and neutrons and all other particles that have s = are known as fennions. Other particles are restricted to s = 0 or 1 and are known as bosons. There are thus profound differences in the quantum-mechanical properties of fennions and bosons, which have important implications in fields ranging from statistical mechanics to spectroscopic selection mles. It can be shown that the spin quantum number S associated with an even number of fennions must be integral, while that for an odd number of them must be half-integral. The resulting composite particles behave collectively like bosons and fennions, respectively, so the wavefunction synnnetry properties associated with bosons can be relevant in chemical physics. One prominent example is the treatment of nuclei, which are typically considered as composite particles rather than interacting protons and neutrons. Nuclei with even atomic number tlierefore behave like individual bosons and those with odd atomic number as fennions, a distinction that plays an important role in rotational spectroscopy of polyatomic molecules. 

The second-order nonlinear susceptibility tensor ( 3> 2, fOj) introduced earlier will, in general, consist of 27 distinct elements, each displaying its own dependence on the frequencies oip cci2 and = oi 012). There are, however, constraints associated with spatial and time-reversal symmetry that may reduce the complexity of for a given material [32, 33 and Ml- Flere we examine the role of spatial synnnetry. 

Prolactin-Like Proteins. A number of prolactin-like proteins (PLPs), which ate distinct from the PLs, have been identified in mminants and rodents (11,23). Several cDNA transcripts coding for PLPs in catde have been identified (23). These transcripts code for proteins which possess about 40% sequence homology with bovine PRL 60% if conservative substitutions ate considered. Three glycosylated PLPs, ie, PLP-A, -B, and -C, ate produced during pregnancy in the rat (11). Two additional prolactin-related molecules have been identified in the mouse (24,25), ie, proliferin [92769-12-5] (PLF) and PLF-related protein [98724-27-7]. These ate not found in other rodents and may be unique to the mouse. The functional roles of PLPs remain to be deterrnined. 

Previous expositions of photochemical laws have distinguished ptominentiy between states of singlet and triplet multiplicity (1). This distinction continues to be important with respect to photophysics of smaH organic molecules, but among inorganic and organometaHic compounds, states of other multiplicities, eg, doublet and quartet states (23), play an important role. Spin conservation characterizes electronic molecular excitations and localized... 

The transport of charged ions in alkali halides and, later on, in (insulating) ceramics is a distinct parepisteme, because electric fields play a key role. This large field is discussed in Schmalzried s 1995 book, already mentioned, and also in a review by one of the pioneers (Nowick 1984). This kind of study in turn led on to the developments of superionic conductors, in which ions and not electrons carry substantial currents (touched on again in Chapter 11, Section 11.3.1.1). 

The role that acid and base catalysts play can be quantitatively studied by kinetic techniques. It is possible to recognize several distinct types of catalysis by acids and bases. The term specie acid catalysis is used when the reaction rate is dependent on the equilibrium for protonation of the reactant. This type of catalysis is independent of the concentration and specific structure of the various proton donors present in solution. Specific acid catalysis is governed by the hydrogen-ion concentration (pH) of the solution. For example, for a series of reactions in an aqueous buffer system, flie rate of flie reaction would be a fimetion of the pH, but not of the concentration or identity of the acidic and basic components of the buffer. The kinetic expression for any such reaction will include a term for hydrogen-ion concentration, [H+]. The term general acid catalysis is used when the nature and concentration of proton donors present in solution affect the reaction rate. The kinetic expression for such a reaction will include a term for each of the potential proton donors that acts as a catalyst. The terms specific base catalysis and general base catalysis apply in the same way to base-catalyzed reactions. 

All this being said, perhaps the most definitive study of the relative roles of electrostatic and van der Waals forces was performed by Gady et al. [86,101,102]. In their studies, they attached a spherical polystyrene particle, having a radius between 3 and 6 p.m, to the cantilever of an atomic force microscope. They then conducted three distinct measurements that allowed them to distinguish between electrostatic and van der Waals forces that attracted the particle to various conducting, smooth substrates. 

Lu and Pizzi [83] showed that lignocellulosic substrates have a distinct influence on the hardening behavior of PF-resins, whereby the activation energy of the hardening process is much lower than for the resin alone [84]. The reason is a catalytic activation of the PF-condensation by carbohydrates like crystalline and amorphous cellulose and hemicellulose. Covalent bonding between the PF-resin and the wood, especially lignin, does not play any role [84]. 

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