Dynamical polarizability of graphene beyond the Dirac cone approximation

We compute the dynamical polarizability of graphene beyond the usual Dirac cone approximation, integrating over the full Brillouin zone. We find deviations at $\hbar\omega=2t$ ($t$ the hopping parameter) which amount to a logarithmic singularity due to the van Hove singularity and derive an approximate analytical expression. Also at low energies, we find deviations from the results obtained from the Dirac cone approximation which manifest themselves in a peak spitting at arbitrary direction of the incoming wave vector \q. Consequences for the plasmon spectrum are discussed.Comment: 8 pages, 6 figure

Age-related changes in trabecular bone microstructures: global and local morphometry

Introduction: A recently developed method allows investigating trabecular bone on an elemental (rod/plate) level. With this method, it is possible to measure local morphometric parameters such as thickness or orientation directly on the extracted rods and plates. Age-related changes of trabecular microarchitecture can thus be investigated on an elemental level, which may help to improve the understanding of age-related bone failure mechanism as well as the effect of pharmaceutical intervention in the prevention of such fractures. Methods: Autopsies from femoral heads (FH) and lumbar spine (LS) were analyzed by global morphometry. Additionally, the trabecular structures were decomposed into rods and plates for the analysis with local morphometry. These morphometric indices were related to age using an analysis of covariance to test for gender differences and linearity with age. Results: In this study, age-related changes showed no gender but site differences. In LS, rods were thinned in aging and finally vanish from the structure, causing a transformation of the trabecular bone structure to longer and, on average, thicker rods. In FH, changes were expressed by a simultaneous thinning and loss of interconnecting trabeculae and perforation of plates leading to new plates and rods. Results were mostly in agreement with earlier findings using descriptive analysis of the aging process. Conclusion: Here we present for the first time preliminary quantitative evidence of changes in the local microstructure, i.e., individual rods and plates. Nevertheless, the number of samples was too small to make for ready conclusions. We conclude that the combination of local and global morphometry is a useful method for a detailed and quantitative description of age-related changes in bone microstructur

Conductivity of suspended and non-suspended graphene at finite gate voltage

We compute the DC and the optical conductivity of graphene for finite values of the chemical potential by taking into account the effect of disorder, due to mid-gap states (unitary scatterers) and charged impurities, and the effect of both optical and acoustic phonons. The disorder due to mid-gap states is treated in the coherent potential approximation (CPA, a self-consistent approach based on the Dyson equation), whereas that due to charged impurities is also treated via the Dyson equation, with the self-energy computed using second order perturbation theory. The effect of the phonons is also included via the Dyson equation, with the self energy computed using first order perturbation theory. The self-energy due to phonons is computed both using the bare electronic Green's function and the full electronic Green's function, although we show that the effect of disorder on the phonon-propagator is negligible. Our results are in qualitative agreement with recent experiments. Quantitative agreement could be obtained if one assumes water molelcules under the graphene substrate. We also comment on the electron-hole asymmetry observed in the DC conductivity of suspended graphene.Comment: 13 pages, 11 figure

Zika virus Concern and Preventative Behaviors During Pregnancy: Analysis of 2017 Georgia Pregnancy Risk Assessment Monitoring System data

Background: Zika virus infection can cause severe health complications in pregnant women such as microcephaly and other congenital anomalies in the developing fetus but it can be prevented. It is imperative to develop an understanding of concern about Zika virus among pregnant women as this can influence their Zika virus preventative behaviors. The purpose of this study was to gain an understanding of Zika virus concern among women in Georgia with live births in 2017 and to examine the frequency of condom use among those who were sexually active during their most recent pregnancy. Methods: This cross- sectional study used secondary data collected by Georgia Pregnancy Risk Assessment Monitoring System in 2017. Descriptive analyses were performed on variables of interest. Chi squared tests examined associations between level of concern about Zika virus and socio-demographic variables. Results: A total of 955 women (age range 18-45) completed the survey. Less than half of the women (n =418,47.4%) reported they were concerned about Zika virus. Consistent use of condoms was not associated with the level of concern of Zika virus. Among the women, those of Hispanic race/ethnicity were more likely to consistently use condoms during their most recent pregnancy (Adjusted Odds Ratio = 11.37; 95%CI: 3.95-32.81) when compared to Non-Hispanic white women, and this association was found to be statistically significant (p\u3c0.0001). Conclusion: Consistent use of condoms by sexually active women in Georgia during pregnancy appears to vary by race/ethnicity for these women. Findings of this study point to opportunities for engagement on Zika virus awareness and help with refining risk messaging for prevention of Zika virus (or other diseases of global concern) to pregnant wome

Transport in a Clean Graphene Sheet at Finite Temperature and Frequency

We calculate the conductivity of a clean graphene sheet at finite temperatures starting from the tight-binding model. We obtain a finite value for the dc-conductivity at zero temperature. For finite temperature, the spontaneous electron-hole creation, responsible for the finite conductivity at zero temperature, is washed out and the dc-conductivity yields zero. Our results are in agreement with calculations based on the field-theoretical model for graphene.Comment: 8 pages, 1 figur

Efficient graphene-based photodetector with two cavities

We present an efficient graphene-based photodetector with two Fabri-P\'erot cavities. It is shown that the absorption can reach almost 100% around a given frequency, which is determined by the two-cavity lengths. It is also shown that hysteresis in the absorbance is possible, with the transmittance amplitude of the mirrors working as an external driving field. The role of non-linear contributions to the optical susceptibility of graphene is discussed.Comment: 10 pages, 8 figures. published version: minor revisio

Flow equations for Hamiltonians: Contrasting different approaches by using a numerically solvable model

To contrast different generators for flow equations for Hamiltonians and to discuss the dependence of physical quantities on unitarily equivalent, but effectively different initial Hamiltonians, a numerically solvable model is considered which is structurally similar to impurity models. By this we discuss the question of optimization for the first time. A general truncation scheme is established that produces good results for the Hamiltonian flow as well as for the operator flow. Nevertheless, it is also pointed out that a systematic and feasible scheme for the operator flow on the operator level is missing. For this, an explicit analysis of the operator flow is given for the first time. We observe that truncation of the series of the observable flow after the linear or bilinear terms does not yield satisfactory results for the entire parameter regime as - especially close to resonances - even high orders of the exact series expansion carry considerable weight.Comment: 25 pages, 10 figure