On the 4 by 4 Irreducible Sign Pattern Matrices that Require Four Distinct Eigenvalues

A sign pattern matrix is a matrix whose entries are from the set {+,-,0}. For a real matrix B, sgn(B) is the sign pattern matrix obtained by replacing each positive(respectively, negative, zero) entry of B by + (respectively, -, 0). For a sign pattern matrix A, the sign pattern class of A, denoted Q(A), is defined as {B: sgn(B) = A}. An n by n sign pattern matrix A requires all distinct eigenvalues if every real matrix whose sign pattern is represented by A has n distinct eigenvalues. In this thesis, a number of sufficient and/or necessary conditions for a sign pattern to reuiqre all distinct eigenvalues are reviewed. In addition, for n=2 and 3, the n by n sign patterns that require all distinct eigenvalues are surveyed. We determine most of the 4 by 4 irreducible sign patterns that require four distinct eigenvalues

Character of the structural and magnetic phase transitions in the parent and electron doped BaFe2As2 compounds

We present a combined high-resolution x-ray diffraction and x-ray resonant magnetic scattering (XRMS) study of as-grown BaFe2As2. The structural/magnetic transitions must be described as a two-step process. At T_S = 134.5 K we observe the onset of a second-order structural transition from the high-temperature paramagnetic tetragonal structure to a paramagnetic orthorhombic phase, followed by a discontinuous step in the structural order parameter that is coincident with a first-order antiferromagnetic (AFM) transition at T_N = 133.75 K. These data, together with detailed high-resolution x-ray studies of the structural transition in lightly doped Ba(Fe{1-x}Co{x})2As2 and Ba(Fe{1-x}Rh{x})2As2 compounds, show that the structural and AFM transitions do, in fact, occur at slightly different temperatures in the parent BaFe2As2 compound, and evolve towards split secondorder transitions as the doping concentration is increased. We estimate the composition for the tricritical point for Co-doping and employ a mean-field approach to show that our measurements can be explained by the inclusion of an anharmonic term in the elastic free energy and magneto-elastic coupling in the form of an emergent Ising-nematic degree of freedom.Comment: 10 pages, 11 figures; accepted for publication in Phys. Rev.

Tumor Biology and Racial Disparities in Reconstruction After Mastectomy: A SEER Database Analysis

Introduction: Significant disparities in immediate breast reconstruction after mastectomy have persisted, and may even be increasing, despite large-scale efforts to minimize them, such as the Women’s Health and Cancer Rights Act of 1998. Immediate breast reconstruction has been shown to lead to higher rates of surgical satisfaction, minimize delay in post-operative cancer treatment, and improve the quality of life and overall well-being of mastectomy patients. However only 25-40% of eligible women in the United States receive reconstruction. The rate of reconstruction is even lower in African American and Hispanic women compared to White women. To better understand this disparity, this study uses national population-based data to examine how demographic factors, socioeconomic factors, and disease characteristics interact and affect the rate of immediate breast reconstruction (IBR) after mastectomy. Methods: Women with AJCC7 Stage 0-III breast cancer who underwent mastectomy from 2010 to 2012 were identified in the Surveillance, Epidemiology and End Results Program (SEER) database. Race, Hispanic ethnicity, age, marital status, insurance status, tumor grade, AJCC7 stage and hormone receptor/ Her2Neu profile were compared between women undergoing mastectomy with IBR and mastectomy alone using univariate and multivariate analysis. Results: We identified 51,115 women who underwent mastectomy for Stage 0-III breast cancer from 2010-2012, of whom 15,389 (30.1%) received IBR. On multivariate analysis, age (p Conclusion: The decision to undergo reconstruction after mastectomy is influenced by many factors. Our results show that even after adjusting for tumor characteristics, socioeconomic factors are independently associated with receiving IBR after mastectomy. Further research is needed to elucidate the factors that influence the decision to undergo IBR in order to eliminate these persistent disparities

Strong Enhancement of the Critical Current at the Antiferromagnetic Transition in ErNi2B2C Single Crystals

We report on transport and magnetization measurements of the critical current density Jc in ErNi2B2C single crystals that show strongly enhanced vortex pinning at the Neel temperature TN and low applied fields. The height of the observed Jc peak decreases with increasing magnetic field in clear contrast with that of the peak effect found at the upper critical field. We also performed the first angular transport measurements of Jc ever conducted on this compound. They reveal the correlated nature of this pinning enhancement, which we attribute to the formation of antiphase boundaries at TN.Comment: 3 figure

DevA, a GntR-like transcriptional regulator required for development in streptomyces coelicolor

The gram-positive filamentous bacterium Streptomyces coelicolor has a complex developmental cycle with three distinct phases: growth of the substrate mycelium, development of reproductive structures called aerial hyphae, and differentiation of these aerial filaments into long chains of exospores. During a transposon mutagenesis screen, we identified a novel gene (devA) required for proper development. The devA mutant produced only rare aerial hyphae, and those that were produced developed aberrant spore chains that were much shorter than wild-type chains and had misplaced septa. devA encodes a member of the GntR superfamily, a class of transcriptional regulators that typically respond to metabolite effector molecules. devA forms an operon with the downstream gene devB, which encodes a putative hydrolase that is also required for aerial mycelium formation on R5 medium. S1 nuclease protection analysis showed that transcription from the single devA promoter was temporally associated with vegetative growth, and enhanced green fluorescent protein transcriptional fusions showed that transcription was spatially confined to the substrate hyphae in the wild type. In contrast, devAB transcript levels were dramatically upregulated in a devA mutant and the devA promoter was also active in aerial hyphae and spores in this background, suggesting that DevA might negatively regulate its own production. This suggestion was confirmed by gel mobility shift assays that showed that DevA binds its own promoter region in vitro

A surface electrode point Paul trap

We present a model as well as experimental results for a surface electrode radio-frequency Paul trap that has a circular electrode geometry well-suited for trapping of single ions and two-dimensional planar ion crystals. The trap design is compatible with microfabrication and offers a simple method by which the height of the trapped ions above the surface may be changed \emph{in situ}. We demonstrate trapping of single and few Sr+ ions over an ion height range of 200-1000 microns for several hours under Doppler laser cooling, and use these to characterize the trap, finding good agreement with our model.Comment: 10 pages, 11 figures, 1 tabl

Experimental and analytical comparison of flowfields in a 110 N (25 lbf) H2/O2 rocket

A gaseous hydrogen/gaseous oxygen 110 N (25 lbf) rocket was examined through the RPLUS code using the full Navier-Stokes equations with finite rate chemistry. Performance tests were conducted on the rocket in an altitude test facility. Preliminary parametric analyses were performed for a range of mixture ratios and fuel film cooling pcts. It is shown that the computed values of specific impulse and characteristic exhaust velocity follow the trend of the experimental data. Specific impulse computed by the code is lower than the comparable test values by about two to three percent. The computed characteristic exhaust velocity values are lower than the comparable test values by three to four pct. Thrust coefficients computed by the code are found to be within two pct. of the measured values. It is concluded that the discrepancy between computed and experimental performance values could not be attributed to experimental uncertainty

Commensurate antiferromagnetic ordering in Ba(Fe{1-x}Co{x})2As2 determined by x-ray resonant magnetic scattering at the Fe K-edge

We describe x-ray resonant magnetic diffraction measurements at the Fe K-edge of both the parent BaFe2As2 and superconducting Ba(Fe0.953Co0.047)2As2 compounds. From these high-resolution measurements we conclude that the magnetic structure is commensurate for both compositions. The energy spectrum of the resonant scattering is in reasonable agreement with theoretical calculations using the full-potential linear augmented plane wave method with a local density functional.Comment: 5 pages, 3 figures; accepted for publication in Phys. Rev. B Rapid Com