Accretional series

The accretional series is a series of stmctures in which the type(s) of building blocks (rods, layers) and the principles that define their mutual relationships remain preserved but the size of these blocks varies incrementally by varying the number of fundamental coordination polyhedra in them. The order of a homologue in this type of series can be defined by the number of coordination polyhedra (polyhedral layers) across a suitably defined diameter of the buiiding block (rod, layer). The ratio of atoms on the block surfaces (interfaces) to those inside the blocks varies with as also does the overall M/S ratio. 

An estimate of the iron core mass before collapse is found as follows. We need 1.6 to 1.7 M0 to explain the 12 second signal and a few tenths of a solar mass for the accretion phase luminosity. From a series of stellar evolution calculations of stars producing different iron core masses by Weaver and Woosley (private communication), we find that for models with iron core masses less than 1.5 M0 the density exterior to the core falls so rapidly with radius that appreciable accretion could occur not in a few seconds. For high mass iron cores the density doesn t fall off... 

Modeling a disk by solving the full three-dimensional Navier-Stokes equations is a complicated task. Moreover, it is still not fully understood what is the cause of frictional forces in the disk. Molecular viscosity is by orders of magnitude too small to cause any appreciable accretion. Instead, the most widely accepted view is that instabilities within the disk drive turbulence that increases the effective viscosity of the gas (see Section 3.2.5). A powerful simplification of the problem is (a) to assume a parameterization of the viscosity, the so-called a-viscosity (Shakura Syunyaev 1973) ((3-viscosity in the case of shear instabilities, Richard Zahn 1999) and (b) to split the disk into annuli, each of which constitutes an independent one-dimensional (ID) vertical disk structure problem. This then constitutes a 1+1D model a series of ID vertical models glued together in radial direction. Many models go even one step further in the simplification by considering only the vertically integrated or representative quantities such as the surface density X(r) = p(r, z.)dz... 

In the solid Earth, production of nucleogenic Ne is coupled to that of radiogenic " He. This is because production of Ne is directly proportional to the a-particle production ratio from the uranium and thorium series. The Ne/ He production ratio is constant and has been estimated at a value of 4.5 X 10 (Yatsevich and Honda, 1997). In this way, if the Earth accreted with solar helium and neon and initial ratios were modified by production of Ne and " He in a fixed proportion then the present-day He/ He and Ne/ Ne ratios in the mantle should be correlated. Honda et al. (1993) noted a strong correlation between OIB helium and neon isotopes such that steeper trajectories in three-isotope neon space were characterized by samples with high He/ He ratios. Indeed, they showed that it was possible to estimate the He/ He ratio of a suite of OIBs based solely on measurements of the neon isotope composition. 

The Japanese islands are essentially composed of a series of terranes that have been accreted to the continental margin of the Eurasian plate during the past 400 Myr. These terranes consist of trench-hlling terrigenous sediments with variable quantities of accreted oceanic crust that are intruded and partly overlain by the products of subsequent subduction-related volcanism. Within Japan the ages of the accreted complexes become younger from north to south and from west to east (Kimura et ai, 1994). However, relatively little is known about the trace element chemistry of these oceanic accreted terranes. 

It was found that the sand-mud transition zone could be adequately represented by allowing the sedimentary processes to proceed at constant rates. When this was done, the calculated sand flux agrees well with the sand flux that has been measured over the sand-wave field in the eastern Sound. Since the tides and the estuarine circulation control the sand fluxes, the resulting distribution of sand approaches a steady state very quickly. It is likely that the sand-mud transition was established soon after the Sound became an arm of the sea and has persisted unchanged to the present day. As a corollary to this hypothesis, it would seem that Mattituck Sill has been accreting over the lifetime of the Sound. Small variations in the sand content preserved in short cores are probably due to the perturbation of the sand distribution by a series of winter storms rather than individual storm events. 

A series of diversion projects have been implemented to reintroduce freshwater and sediment from the Mississippi River into Louisiana coastal wetlands (Figure 18.9). A recent study examined the impact of Mississippi River freshwater diversion on enhancing vertical marsh accretion (mineral and organic matter accumulation) in Breton Sound estuary, a coastal wetland experiencing marsh deterioration as a result of subsidence and saltwater intrusion (DeLaune et al., 2003). The Caernarvon diversion has positively impacted marsh accretion in Brenton Sound estuary helping to slow or reverse wetland loss. Several hundred hectares of new marsh have been created by the introduction of Mississippi River water into the system (Villarrubia, 1998). 

ABSTRACT. Crystal structures of many complex sulfides can be obtained by recombination of fragments of archetypal structures by the action of various structure-building operators. Chemical categories, coordination polyhedra, archetypes and recombination operators for these structures are described in the paper. These structures often occur as members of accretional or variable-fit homologous series or as homologous pairs of various kinds. Three case studies supplemented by exercises are described in some detail the lillianite homologous series, the misfit layer structures and those structures that represent combination of the accretional and variable-fit principles. 

A large number of sulfosalts and other complex sulfides represent members of homologous series. There are two principal types of homologous series which the present author defined as the accretional and the variable-fit series, respectively (Makovicky, 1989). 

When the Earth and other planets accreted aroxmd 4.5-4.6 billion years ago, the mixture of elements remaining reflected the cosmic abundances. Through a series of complex chemical reactions the Earth warmed up and differentiation of the constituent elements took place. 

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