Topological phases and phase transitions on the square-octagon lattice

We theoretically investigate a tight binding model of fermions hopping on the square-octagon lattice which consists of a square lattice with plaquette corners themselves decorated by squares. Upon the inclusion of second neighbor spin-orbit coupling or non-Abelian gauge fields, time-reversal symmetric topological Z_2 band insulators are realized. Additional insulating and gapless phases are also realized via the non-Abelian gauge fields. Some of the phase transitions involve topological changes to the Fermi surface. The stability of the topological phases to various symmetry breaking terms is investigated via the entanglement spectrum. Our results enlarge the number of known exactly solvable models of Z_2 band insulators, and are potentially relevant to the realization and identification of topological phases in both the solid state and cold atomic gases.Comment: 12 pages, 9 figure

On the Mixtures of Weibull and Pareto (IV) Distribution: An Alternative to Pareto Distribution

Finite mixture models have provided a reasonable tool to model various types of observed phenomena, specially those which are random in nature. In this article, a finite mixture of Weibull and Pareto (IV) distribution is considered and studied. Some structural properties of the resulting model are discussed including estimation of the model parameters via expectation maximization (EM) algorithm. A real-life data application exhibits the fact that in certain situations, this mixture model might be a better alternative than the rival popular models

Skewed Factor Models Using Selection Mechanisms

Traditional factor models explicitly or implicitly assume that the factors follow a multivariate normal distribution; that is, only moments up to order two are involved. However, it may happen in real data problems that the first two moments cannot explain the factors. Based on this motivation, here we devise three new skewed factor models, the skew-normal, the skew-t, and the generalized skew-normal factor models depending on a selection mechanism on the factors. The ECME algorithms are adopted to estimate related parameters for statistical inference. Monte Carlo simulations validate our new models and we demonstrate the need for skewed factor models using the classic open/closed book exam scores dataset

Towards a simplified description of thermoelectric materials: Accuracy of approximate density functional theory for phonon dispersions

We calculate the phonon-dispersion relations of several two-dimensional materials and diamond using the density-functional based tight-binding approach (DFTB). Our goal is to verify if this numerically efficient method provides sufficiently accurate phonon frequencies and group velocities to compute reliable thermoelectric properties. To this end, the results are compared to available DFT results and experimental data. To quantify the accuracy for a given band, a descriptor is introduced that summarizes contributions to the lattice conductivity that are available already in the harmonic approximation. We find that the DFTB predictions depend strongly on the employed repulsive pair-potentials, which are an important prerequisite of this method. For carbon-based materials, accurate pair-potentials are identified and lead to errors of the descriptor that are of the same order as differences between different local and semi-local DFT approaches

Pseudomonas Aeruginosa Biofilm Formation in Different Environments

poster abstractVarious bacteria, such as the soil microbe Pseudomonas aeruginosa, form into strong structures to defend themselves from antibiotics and other harmful materials. These structures are called biofilms. The goal of this research is to isolate P. aeruginosa from several soil samples and determine whether they are able to form biofilms in those environments. Another goal of this research is to find out how different environmental factors affect the formation of Pseudomonas biofilms. We isolated P. aeruginosa from soil samples using Pseudomonas Isolation Agar plates. The colonies most similar to P. aeruginosa were picked, cultured, and tested by PCR in order to confirm that the strains were actually P. aeruginosa. Using these methods, so far we have collected 12 P. aeruginosa strains and we are collecting more strains from different soil samples. In future studies, we will determine whether these strains form biofilms in soil. We will also demonstrate the effect of magnesium on P. aeruginosa on biofilm formation. These studies will begin to investigate how altering environmental conditions can influence persistence of this bacterial pathogen in the soil. These studies can have broad implications for transmission of the bacterium from the environment to humans during disease