Physical Sciences and Mathematics Commons^™

Selective Complexation And Reactivity Of Metallic Nitride And Oxometallic Fullerenes With Lewis Acids And Use As An Effective Purification Method, Steven Stevenson, Mary A. Mackey, Jane E. Pickens, Melissa A. Stuart, Bridget S. Confait, J. Paige Phillips

Faculty Publications

Metallic nitride fullerenes (MNFs) and oxometallic fullerenes (OMFs) react quickly with an array of Lewis acids. Empty-cage fullerenes are largely unreactive under conditions used in this study. The reactivity order is Sc₄O₂@I_h-C₈₀ > Sc₃N@C₇₈ > Sc₃N@C₆₈ > Sc₃N@D_5h-C₈₀ > Sc₃N@I_h-C₈₀. Manipulations of Lewis acids, molar ratios, and kinetic differences within the family of OMF and MNF metallofullerenes are demonstrated in a selective precipitation scheme, which can be used either alone for purifying Sc₃N@I_{h …}

Identification And Structural Analysis Of A Novel Carboxysome Shell Protein With Implications For Metabolite Transport, Michael G. Klein, Peter Zwart, Sarah C. Bag By, Fei Cai, Sallie W. Chisolm, Sabine Heinhorst, Gordon C. Cannon, Cheryl A. Kerfeld

Faculty Publications

Bacterial microcompartments (BMCs) are polyhedral bodies, composed entirely of proteins, that function as organelles in bacteria; they promote subcellular processes by encapsulating and co-localizing targeted enzymes with their substrates. The best-characterized BMC is the carboxysome, a central part of the carbon-concentrating mechanism that greatly enhances carbon fixation in cyanobacteria and some chemoautotrophs. Here we report the first structural insights into the carboxysome of Prochlorococcus, the numerically dominant cyanobacterium in the world's oligotrophic oceans. Bioinformatic methods, substantiated by analysis of gene expression data, were used to identify a new carboxysome shell component, CsoS1D, in the genome of Prochlorococcus strain MED4; …

A Spectral Time-Domain Method For Computational Electrodynamics, James V. Lambers

Faculty Publications

We present a new approach to the numerical solution of Maxwell’s equations in the case of spatially‐varying electric permittivity and/or magnetic permeability, based on Krylov subspace spectral (KSS) methods. KSS methods for scalar equations compute each Fourier coefficient of the solution using techniques developed by Gene Golub and Gérard Meurant for approximating elements of functions of matrices by Gaussian quadrature in the spectral, rather than physical, domain. We show how they can be generalized to coupled systems of equations, such as Maxwell’s equations, by choosing appropriate basis functions that, while induced by this coupling, still allow efficient and robust computation …

Interface Slippage Study Between Polyamide 12 And Ethylene Butene Copolymer Melt In Capillary Extrusion, Jinhai Yang, James L. White

Faculty Publications

Extrusion of a polyamide 12 (PA12) material through a capillary die coated with an ethylene butene copolymer (EBM) was studied. The EBM coated die significantly increased the flow rates of the PA12 melt compared to a clean die at the same extrusion pressure. Introducing a maleic anhydride grafted ethylene-octene copolymer (EOM-g-MAH) into the EBM suppressed the effect. This behavior seems only explained by significant interface slippage between PA12 and EBM melts, which could be eliminated by introducing covalent chemical bonds across the interface. A mathematical analysis was carried out to calculate the interface slippage. The shear stress where slippage began …

On Immunotherapies And Cancer Vaccination Protocols: A Mathematical Modelling Approach, Badal Joshi, Xueying Wang, Sayanti Banerjee, Haiyan Y. Tian, Anastasios Matzavinos, Mark A.J. Chaplain

Faculty Publications

In this paper we develop a new mathematical model of immunotherapy and cancer vaccination, focusing on the role of antigen presentation and co-stimulatory signaling pathways in cancer immunology. We investigate the effect of different cancer vaccination protocols on the well-documented phenomena of cancer dormancy and recurrence, and we provide a possible explanation of why adoptive (i.e. passive) immunotherapy protocols can sometimes actually promote tumour growth instead of inhibiting it (a phenomenon called immunostimulation), as opposed to active vaccination protocols based on tumour-antigen pulsed dendritic cells. Significantly, the results of our computational simulations suggest that elevated numbers of professional antigen presenting …

The Binding Number Of A Graph And Its Cliques, Jeremy Lyle, Wayne Goddard

Faculty Publications

We consider the binding numbers of K(r)-free graphs, and improve the upper bounds on the binding number which force a graph to contain a clique of order r. For the case r = 4, we provide a construction for K(4)-free graphs which have a larger binding number than the previously known constructions. This leads to a counterexample to a conjecture by Caro regarding the neighborhoods of independent sets. (C) 2009 Elsevier B.V. All rights reserved.

A New Formula Describing The Scaffold Structure Of Spiral Galaxies, Harry I. Ringermacher, Lawrence R. Mead

Faculty Publications

We describe a new formula capable of quantitatively characterizing the Hubble sequence of spiral galaxies including grand design and barred spirals. Special shapes such as ring galaxies with inward and outward arms are also described by the analytic continuation of the same formula. The formula is r() = A/log [B tan (/2N)]. This function intrinsically generates a bar in a continuous, fixed relationship relative to an arm of arbitrary winding sweep. A is simply a scale parameter while B, together with N, determines the spiral pitch. Roughly, greater N results in tighter winding. Greater B results in greater arm sweep …

Atomistic Modeling Of Amorphous Silicon Carbide: An Approximate First-Principles Study In Constrained Solution Space, Raymond Atta-Fynn, Parthapratim Biswas

Faculty Publications

Localized basis ab initio molecular dynamics simulation within the density functional framework has been used to generate realistic configurations of amorphous silicon carbide (a-SiC). Our approach consists of constructing a set of smart initial configurations that conform to essential geometrical and structural aspects of the materials obtained from experimental data, which is subsequently driven via a first-principles force field to obtain the best solution in a reduced solution space. A combination of a priori information (primarily structural and topological) along with the ab initio optimization of the total energy makes it possible to model a large system size (1000 atoms) …

Correlated Response In A Driven Flow Of Self-Organizing Particles Around A Slit In Porous Media By Interacting Lattice Gas, Ras B. Pandey, J.F. Gettrust

Faculty Publications

The flow of immiscible particles (A, B) through a porous medium with a vertical slit is studied by an interacting lattice-gas computer simulation on a discrete lattice. The source of the particles is connected to the bottom and particles are driven upward by concentration gradient and a pressure bias against gravity. Distribution of flowing particles around the slit is examined as a function of the slit width and bias at high and low porosity at a steady state. At the low bias, a sharp change in the densities (high in slit to low in adjacent porous media) of both constituents …

Simple Fit Of Data Relating Supermassive Black Hole Mass To Galaxy Pitch Angle, Harry I. Ringermacher, Lawrence R. Mead

Faculty Publications

Seigar et al. have recently demonstrated a new, tight correlation between galactic central supermassive black hole (BH) mass and the pitch angle of the spiral arm in disk galaxies which they attribute to other indirect correlations. They fit a double power law, governed by five parameters, to the BH mass as a function of pitch. Noting the features of their fitted curve, we show that a simple linear proportion of the BH mass to the cotangent of the pitch angle can obtain the same fit, within error. Such a direct, elegant fit may help shed light on the nature of …

Aggregation Of Montmorillonite And Organic Matter In Aqueous Media Containing Artificial Seawater, Yoko Furukawa, Janet L. Watkins, Jinwook Kim, Kenneth J. Curry, Richard H. Bennett

Faculty Publications

Background

The dispersion-aggregation behaviors of suspended colloids in rivers and estuaries are affected by the compositions of suspended materials (i.e., clay minerals vs. organic macromolecules) and salinity. Laboratory experiments were conducted to investigate the dispersion and aggregation mechanisms of suspended particles under simulated river and estuarine conditions. The average hydrodynamic diameters of suspended particles (representing degree of aggregation) and zeta potential (representing the electrokinetic properties of suspended colloids and aggregates) were determined for systems containing suspended montmorillonite, humic acid, and/or chitin at the circumneutral pH over a range of salinity (0 – 7.2 psu).

Results

The montmorillonite-only system increased the …

Hierarchical Modeling: Biogeochemical Processes And Mechanisms That Drive Clay Nano-And Microfabric Development, Kenneth J. Curry, Richard H. Bennett, Paula J. Smithka, Matthew H. Hulbert

Faculty Publications

Conceptual scientific models of clay and clay fabric development can be constructed profitably by considering chemical and physical systems in terms of an ordered hierarchy. We develop here a hierarchical model of early stages of marine sediment development identifying processes and focusing on mechanisms. While the focus of our model is on mechanisms, the physical aspects of the hierarchy are cast in terms of the nanometer (nanofabric) level of organization of sediment fabric. This level is nested below the micrometer (microfabric) level that includes aggregates of clay signatures and is nested above the molecular level that includes edges and faces …