Implications of asteroid composition for the geochemistry of the ancient terrestrial projectile flux

The discovery of enhanced siderophile abundances at the Cretaceous/Tertiary boundary has provoked many searches for geochemical signatures which could reveal other catastrophic impacts in Earth's history. These searches implicitly assume that most large impactors are of chondritic, iron, or stony-iron composition, with a greatly enhanced abundance of siderophile elements. Impactors composed of asteroidal crust or mantle rocks analogous to the achondritic meteorites would not leave a distinct geochemical trace since their siderophile abundances are grossly similar to those of the Earth's crust. In recent years studies of the mineralogical composition of the current asteroid belt have suggested that the composition of impacting projectiles may be highly variable with both projectile size and time. In particular it seems possible that in the distant past projectiles derived from asteroid mantle material may have caused a large fraction of the cratering events on Earth. Such impacts would be missed by any geochemical search relying on iridium or any other siderophile element. The questions of the effect of size and time variations on projectile composition and the significance of hidden impacts missing in current geochemical searches are examined

Infrared spectral studies of asteroids

The research objective was to improve the understanding of the surface mineralogy of asteroids and to link the vast existing body of meteorite geochemical data with specific astronomical objects which may be the targets of future NASA missions. The methodology used is as follow: (1) to use advanced astronomical instrumentation to obtain reflection spectra in the 0.3 to 5.2 micron wavelength range of selected asteroids; (2) to compare the asteroid data with similar data on simulated asteroid regoliths of various compositions to determine the surface mineralogy and meteoritic affinities of asteroid spectral classes and specific asteroids; (3) to integrate the mineralogical information with other astronomical data, orbital dynamics studies, and meteoritic geochemistry data to reconstruct the condensational, thermal, and collisional history of the present asteroids and their parent planetesimals; and (4) to use the information obtained to assist planning of future NASA asteroid missions such as Galileo and CRAF

Will Galileo resolve the S-asteroid controversy?

The longest running argument in asteroid science concerns mineral composition and meteoritic association of the asteroids assigned to taxonomic type S. The approaching flyby of the S-type asteroid Gaspra by the Galileo spacecraft will drag an even larger section of the space science community into this argument. The basics of this problem are presented and discussed. The various proposed S asteroid compositions are presented and summarized in roughly the order in which they appeared

3x+13x+1 inverse orbit generating functions almost always have natural boundaries

The $3x+k$ function $T_{k}(n)$ sends $n$ to $(3n+k)/2$ resp. $n/2,$ according as $n$ is odd, resp. even, where $k \equiv \pm 1~(\bmod \, 6)$. The map $T_k(\cdot)$ sends integers to integers, and for $m \ge 1$ let $n \rightarrow m$ mean that $m$ is in the forward orbit of $n$ under iteration of $T_k(\cdot).$ We consider the generating functions $f_{k,m}(z) = \sum_{n>0, n \rightarrow m} z^{n},$ which are holomorphic in the unit disk. We give sufficient conditions on $(k,m)$ for the functions $f_{k, m}(z)$ have the unit circle $\{|z|=1\}$ as a natural boundary to analytic continuation. For the $3x+1$ function these conditions hold for all $m \ge 1$ to show that $f_{1,m}(z)$ has the unit circle as a natural boundary except possibly for $m= 1, 2, 4$ and $8$. The $3x+1$ Conjecture is equivalent to the assertion that $f_{1, m}(z)$ is a rational function of $z$ for the remaining values $m=1,2, 4, 8$.Comment: 15 page

Assessing Patterns in the Conversion of Rural Lands to Residential Use

Land Economics/Use,

Nonlinear Instabilities in Chemical and Electrochemical Systems

This dissertation focuses on designing and manipulating nonlinear chemical and electrochemical reactions, with the aim of discovering new behaviors as well as gaining insights into their underlying mechanisms. In Chapter 2 the nonlinear behavior of the 4-aminophenol – bromate photoreaction was investigated from two directions. First, a second autocatalytic cycle was introduced through the incorporation of the metal catalyst cerium (IV). It was found that once the autocatalytic cycles were effectively balanced, complexity in the form of mixed mode oscillations was observed in a closed reactor. This dynamic behavior was successfully simulated using a modified model, which qualitatively reproduced the experimental results. It was also found that the precipitate which forms at the onset of the reaction of 4-aminophenol with bromate, N-bromo-1,4-benzoquinone-4-imine, could form a new bromate-based photochemical oscillator. In Chapter 3, the autocatalytic oxidation of 2-methyl-1,4-hydroquinone by acidic bromate lead to the discovery of a new photochemical oscillator. The system was found to be very sensitive to the intensity of illumination supplied, and complexity in the form of sequential oscillations was discovered using either ferroin or cerium (IV) as catalysts. Interestingly, cerium (IV) had a much more profound effect on the dynamical behavior, substantially lengthening the oscillatory period as well as being capable of inducing mixed-mode oscillations. Chapter 4 reports findings on the photosensitive 4-nitrophenol - bromate reaction. Extreme photo-inhibition was found to occur when illumination was supplied to the system whether in a stirred reactor or when being studied in a spatially extended system. Reaction diffusion experiments showed that under certain conditions long lasting complexity in the form of propagation failures took place. In Chapter 5, oscillations in both current density and potential were observed during the electro-oxidation of bromide ions. Interestingly, mechanistic findings suggest that the oscillations occurring during the oxidation of bromide ions on a platinum electrode belong to the type of oscillator referred to as Capacitance Mediated Positive Differential Resistance oscillator, and is the first solution based system to fit this class. In Chapter 6, the electro-oxidation of two sulfur compounds was seen to display nonlinear behavior. First, the oxidation of hydroxymethanesulfinate leads to oscillations in both current and potential on platinum or gold electrodes. The formation of an inhibiting layer was seen to have a substantial influence on the systems’ ability to support sustained oscillatory behavior. Electrochemical Impedance Spectroscopy showed that the oxidation of hydroxymethanesulfinate fits the class of an HN-NDR type oscillator. The oxidation of methionine only displayed nonlinear behavior on a gold surface, and only when operated under potentiostatic conditions. The oscillations were accompanied by gold dissolution and it was found that the electro-oxidation of methionine belongs to the N-NDR class. Two novel examples of utilizing nonlinear reactions towards application-based research is shown in Chapter 7. Here, the 4-nitrophenol – bromate oscillator is used to fabricate platinum nanoparticles, exploiting the dynamic bromide ion concentration to guide the growth of the noble metal nanocrystals. As an example of using an electrochemical nonlinear reaction, the gold dissolution occurring during the oxidation of methionine was found to lead to the fabrication of a Au nanoparticle modified electrode. This modified electrode was found to be capable of simultaneously detecting both hydroquinone and pyrocatechol in solutions containing both isomers, which is a significant improvement over regular Au electrodes