A separated-electron pair study of the electronic structure of the Li2O molecule

A separated pair calculation of the electronic structure of the Li₂O molecule is described. Rather extensive calculations were made of the potential surface for symmetric configurations of Li₂O using a double zeta Slater orbital basis. A linear configuration with LiO bond length of 1.71 Å is found to be most stable. The electron distribution and correlation effects are discussed.     

Altering surface charge nonuniformity on individual colloidal particles

Charge nonuniformity (sigmazeta) was altered on individual polystyrene latex particles and measured using the novel experimental technique of rotational electrophoresis. It has recently been shown that unaltered sulfated latices often have significant charge nonuniformity (sigmazeta = 100 mV) on individual particles. Here it is shown that anionic polyelectrolytes and surfactants reduce the native charge nonuniformity on negatively charged particles by 80% (sigmazeta = 20 mV), even while leaving the average surface charge density almost unchanged. Reduction of charge uniformity occurs as large domains of nonuniformity are minimized, giving a more random distribution of charge on individual particle surfaces. Targeted reduction of charge nonuniformity opens new opportunities for the dispersion of nanoparticles and the oriented assembly of particles.     

Brownian sampling in an unbounded space

As a particle undergoes translational Brownian motion in an unbounded space, the particle samples the space. Traditionally the sampling in N dimensions is quantified in terms of average squared distance traversed (). However, another quantitative measure of the sampled space is the total number (n) of equispaced regions (of size LN) sampled after a particle moves with a diffusion coefficient (D) for a time (t). Calculations show that the average =a(Dt/L2)b. Results are given for a and b for 1, 2, 3, and 4 dimensions.     

Importance of molecular details in predicting bacterial adhesion to hydrophobic surfaces

Electrostatic and hydrophobic forces are generally recognized as important in bacterial adhesion. Current continuum models for these forces often wrongly predict measurements of bacterial adhesion forces. The hypothesis tested here is that even qualitative guides to bacterial adhesion often require more than continuum information about hydrophobic forces; they require knowledge about molecular details of the bacteria and substrate surface. In this study, four different strains of bacteria were adsorbed to silica surfaces hydrophobized with alkylsilanes. The thickness of the lipopolysaccharide layers varied on the different bacteria, and the lengths of the alkylsilane molecules were varied from experiment to experiment. Bacterial adhesion was assessed using column experiments and atomic force microscopy (AFM) experiments. Results show that hydrophobized surfaces have higher bacterial sticking coefficients and stronger adhesion forces than bare silica surfaces, as expected. However, adhesion decreased as the solution Debye length became longer than the alkylsilane, perhaps since the silane molecules could not "reach" the bacterial surface. Similarly, those bacteria with a long o-antigen layer had decreased adhesion, perhaps since the silane molecules could not reach surface-bound proteins on the bacteria. This study reveals that macroscopic measurements such as contact angle are not able to fully describe bacterial adhesion; rather, additional details such as the molecular length are required to predict adhesion.     

On Convergence Approach Spaces

The extension of two axioms due to Cook and Fischer to the category CAP of convergence approach spaces leads to the study of non-Archimedean approach spaces as well as two versions of regularity appropriate to CAP and related categories.     

Total Syntheses of (−)‐Huperzine Q and (+)‐Lycopladines B and C

Utilizing a late‐stage enamine bromofunctionalization strategy, the twelve‐step total synthesis of (?)‐huperzine Q was accomplished. Furthermore, the first total syntheses of (+)‐lycopladines B and C are described. An unprecedented X‐ray crystal structure of an unusual epoxyamine intermediate is also reported, and the synthetic application of this intermediate in natural product synthesis is demonstrated.     

Fatigue-life prediction using local stress-strain concepts

A cumulative-damage approach for predicting fatigue-crack initiation in engineering structures subjected to random loading is outlined. This procedure is based on the assumption that if the stresses and strains at the critical location in a structure can be related to the cyclic stress-strain properties of smooth laboratory specimens, the crack-initiation life in the structure will be the same as the specimen. A flow diagram, indicating the steps required for implementing this procedure on a high-speed digital computer, is discussed in detail.