Term structure hypotheses

As befits a subject that has been extensively researched, the term structure of interest rates has given rise to a number of hypotheses about how maturity terms are related to spot and forward rates and why it assumes certain shapes. This section briefly reviews the hypotheses. 

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The segmented markets hypothesis, first described in Culbertson (1957), seeks to explain the shape of the yield curve. It states that different types of market participants, with different requirements, invest in different parts of the term structure. For instance, the banking sector needs short-dated bonds, while pension funds require longer-term ones. Regulatory reasons may also affect preferences for particular maturity investments. 

The recovery of molecular structure in terms of the topology of the same physical field that defines the quantum boundary condition of the atom reinforces this identification of the chemical atom with a proper open system of quantum mechanics and reinforces the obvious, that the unquestioned success of the molecular structure hypothesis demands that it be firmly rooted in physics. 

While it is sometimes convenient to categorize the polyenoic fatty acids which predominate in the phospholipids of animals and heterotropic protists as belonging to the co 6 group this can be misleading. The association of function with the structure of these fatty acids originates with the 6,9 term hypothesis of Thomasson (1953) applied to animals. The 6,9 term structure occurs in all the so-called essential fatty acids these include 18 2(9,12), 18 3(6,9,12), 20 3(8,11,14), and 20 4(5,8,11,14). Conversion of the first three to arachidonic acid has been demonstrated (Klenk and Pfluger, 1963 Stoffel, 1963), and it is thought that in mammals such as rat, the essential fatty acids other than arachidonic acid are important only inasmuch as they are arachidonic precursors the arachidonic acid is specifically required for functional phospholipids (Howard, 1964). It appears that mammals are incapable of carboxyl-directed desaturation (Wakil, 1964). It is presumably because of this that all the essential fatty acids have the 6,9 term structure in common. 

The acidity dependences of V(V) oxidations are significant. That of pinacol , which undergoes 100% C-C cleavage, is a+bh ). The first (acid-independent) term is rare in V(V) oxidations and implies that V02 is the active oxidant the second term implies, on the basis of the Zucker-Hammett hypothesis, that the transition state has the structure (J5), the mechanism being... 

The next update of the null hypothesis would incorporate a zero-order description of bonding, in terms of a prior prejudice of standard chemical groups. The MaxEnt map then will tell us about the subtle differences induced in formally equivalent chemical bonds by conjugation, stacking, and other intra- and intermolecular interactions. To achieve this degree of accuracy, the refinement of structural parameters... 

From a structural point of view Bruno s hypothesis is sound. In chemical terms the hydrolysis proceeds with the formation of hydroxide bridges up to the formation of the trimer. Then at high concentrations trimeric units are fused together to form the higher aggregates, that can be seen as precursors to the structure adopted by Be(OH)2 in the solid state. (See Section IV, C, precipitation equilibria). Speciation diagrams for Bruno s model are shown in Fig. 3. Two points are noteworthy in these diagrams. In the first place the concentrations of the... 

As a result, the limited ability of unit processes to create a viable niche for themselves within chemical engineering must ultimately be understood in terms which also involve unit operations. Although the historical resilience of unit processes turned out to be less than that of unit operations, it was no different in its essential elements. Studying the uneasy and ultimately unsuccessful career of unit processes can therefore be easily justified as a way to shed light on the far more successful career of unit operations. In particular, the career of unit processes raises a hypothesis about the evolution of unit operations. The staying power of unit operations was not so much because of the structural coherence of its conceptual elements as its essential links with social and, more specifically, professional groups. As a theoretical entity, unit operations appears far less stable and, in fact, appears quickly threatened by notions which rest on fewer and more fundamental scientific concepts. Ultimately, this threat came to be realized with the advent of transport phenomena, but this is another story. In effect, unit processes can be interpreted as both the attempt to extend the reach of unit operations and a symptom of their conceptual fragility. 

In conclusion, under the hypothesis that the reaction has no barrier in excess of its endoergicity, Att/°j(0) = 0, the enthalpy of reaction 3.10 is given by the Arrhenius activation energy for the forward reaction minus a heat capacity term. This term can be estimated by using statistical mechanics, provided that a structure for the activated complex is available. It is often found that T A Cjj > is fairly small, ca. — 1 kJmol-1 at 298.15 K [60], and therefore, the alternative assumption of a,i Ar//" is commonly accepted if T is not too high. Finally, note that either 3,1 Ar//." or Atf/°j(0) = 0 are not equivalent (see equation 3.22) to another current (but probably less reliable) postulate, Ea- = 0. 

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