Dirac fermion time-Floquet crystal: manipulating Dirac points

We demonstrate how to control the spectra and current flow of Dirac electrons in both a graphene sheet and a topological insulator by applying either two linearly polarized laser fields with frequencies $\omega$ and $2\omega$ or a monochromatic (one-frequency) laser field together with a spatially periodic static potential(graphene/TI superlattice). Using the Floquet theory and the resonance approximation, we show that a Dirac point in the electron spectrum can be split into several Dirac points whose relative location in momentum space can be efficiently manipulated by changing the characteristics of the laser fields. In addition, the laser-field controlled Dirac fermion band structure -- Dirac fermion time-Floquet crystal -- allows the manipulation of the electron currents in graphene and topological insulators. Furthermore, the generation of dc currents of desirable intensity in a chosen direction occurs when applying the bi-harmonic laser field which can provide a straightforward experimental test of the predicted phenomena.Comment: 9 pages, 7 figures, version that will appear in Phys. Rev.

Inequality and Mobility

Acknowledging that wage inequality and intergenerational mobility are strongly interrelated, this paper presents a model in which both are jointly determined. The model enables us to study how inequality and mobility are affected by exogenous changes and what determines their correlation. A main implication of the model is that differences in the amount of public subsidies to education and educational quality produce cross-country patterns with a negative correlation between inequality and mobility. Differences in the labor market, like differences in skill-biased technology or wage compression instead produce a positive correlation. The predictions of the model are found to be consistent with various empirical observations on mobility and inequality.

Fetal Alcohol Syndrome Affects in Retinal Cell Gene Expression

poster abstractAlcohol exposure during fetal development has many adverse effects on embryonic cells, this is known as fetal alcohol spectrum disorder (FASD). Retinal cells are consistently affected by ethanol exposure in human patients. Zebrafish are an excellent model to use for studying FASD on, due to their similar developmental pathways to humans. This research aims to understand the changes that occur at the gene level to retinal cells during exposure to ethanol. To better understand changes that occur in retinal cells, a project was begun to examine GFP marked Zebrafish embryos exposed to ethanol [100, 150 mM EtOH], from 2-24 hours postfertilization (hpf), and eyes from treated and control zebrafish embryos will be harvested using dissection, dissociated using papain protease digestion, sorted using fluorescence activated cell sorting (FACS). These GFP labeled cells can then be used to isolate retinal cell RNA for gene expression analysis. This research will provide insight into gene expression changes during retinal development is specific cell types after alcohol exposure. Our goal is to understand the genesis of FASD birth defects caused by ethanol exposure, and this research will possibly identify methods to prevent or reverse the damage

Fetal Alcohol Syndrome Affects in Retinal Cell Gene Expression

poster abstractAlcohol exposure during fetal development has many adverse effects, producing birth defects known as fetal alcohol spectrum disorder (FASD). Retinal development is consistently affected by ethanol exposure in human patients. Zebrafish are an excellent model to study FASD, due to their similar developmental pathways to humans. Previous studies show that ethanol exposure caused retinal cell differentiation defects leading to photoreceptor defects similar to those seen in human FASD patients. This research aims to understand the gene expression changes that occur in retinal cells due to ethanol exposure. Zebrafish embryos exposed to ethanol [100, 150 mM], from 2-24 hours post-fertilization (hpf), were grown in regular medium until 72 hpf. Eyes from ethanol treated and control zebrafish embryos were dissected and total RNA was isolated. The RNA was then purified and reverse transcribed into cDNA. Quantitative PCR was then used to analyze the cDNA using gene specific primers to determine relative expression levels of various genes present in the retinal developmental pathway. We examined specific signaling pathways including, Wnt, Notch, pro-neural gene targets, and other specific markers expressed by retinal precursor cell populations that comprise the differentiation pathways. This research provides insight into gene expression changes during retinal development that affects specific cell types after alcohol exposure. Our goal is to understand the genesis of FASD birth defects caused by ethanol exposure, and this research will possibly identify ethanol targets and therapeutic strategies to prevent or reverse the damage

Evaluation of thermal control coatings for use on solar dynamic radiators in low Earth orbit

Thermal control coatings with high thermal emittance and low solar absorptance are needed for Space Station Freedom (SSF) solar dynamic power module radiator (SDR) surfaces for efficient heat rejection. Additionally, these coatings must be durable to low earth orbital (LEO) environmental effects of atomic oxygen, ultraviolet radiation and deep thermal cycles which occur as a result of start-up and shut-down of the solar dynamic power system. Eleven candidate coatings were characterized for their solar absorptance and emittance before and after exposure to ultraviolet (UV) radiation (200 to 400 nm), vacuum UV (VUV) radiation (100 to 200 nm) and atomic oxygen. Results indicated that the most durable and best performing coatings were white paint thermal control coatings Z-93, zinc oxide pigment in potassium silicate binder, and YB-71, zinc orthotitanate pigment in potassium silicate binder. Optical micrographs of these materials exposed to the individual environmental effects of atomic oxygen and vacuum thermal cycling showed that no surface cracking occurred