Gutzwiller density functional calculations of the electronic structure of FeAs-based superconductors: Evidence for a three-dimensional Fermi surface

The electronic structures of FeAs-compounds strongly depend on the Fe-As bonding, which can not be described successfully by the local density approximation (LDA). Treating the multi-orbital fluctuations from $ab$-$initio$ by LDA+Gutzwiller method, we are now able to predict the correct Fe-As bond-length, and find that Fe-As bonding-strength is 30% weaker, which will explain the observed "soft phonon". The bands are narrowed by a factor of 2, and the $d_{3z^2-r^2}$ orbital is pushed up to cross the Fermi level, forming 3-dimensional Fermi surfaces, which suppress the anisotropy and the ($\pi,\pi$) nesting. The inter-orbital Hund's coupling $J$ rather than $U$ plays crucial roles to obtain these results.Comment: 4 pages, 4 figures, 1 tabl

Selected Topics in Variable Annuities

Variable annuities are long-term insurance products. They have become one of the most popular savings/investment vehicles over the past two decades due to their flexible investment options, stable long-term guarantees, and favorable tax-deferral treatment. The popularity of variable annuities has catalyzed an extensive amount of research papers looking into pricing and hedging of embedded guarantees and attempting to better understand policyholder behavior. This thesis aims to contribute to these two strands of research. While an ample amount of literature has covered various topics in variable annuities, two important market trends/phenomena need further investigation: 1). the variable annuity market has seen decreasing sales ever since the year 2013; 2). there is evident discordance between the theoretical and empirical insurance fees and policyholder behavior. The theme of this thesis is to address these two market phenomena by offering potential remedy or reasonable explanation. Chapter 3 aims to offer an appropriate potential remedy to the declining demand of the variable annuity market. In this chapter, we propose a novel high-water mark fee structure and examine its impact on variable annuity marketability. We apply a mean-variance preference model to evaluate policyholder welfare from holding a variable annuity. By also evaluating policyholder welfare from holding two alternative investments, we introduce a quantitative measure, namely a compatible set of risk aversions, to assess the marketability of the variable annuity under a certain fee structure. We find that the high-water mark fee structure improves the variable annuity’s marketability compared to a constant and a state-dependent fee structure. Chapters 4 and 5 aim to address the aforementioned discordance by investigating the impact of policyholders' uncertainty in discount rates on their welfare and behavior from holding variable annuities. In Chapter 4, we consider policyholders of a variable annuity with guaranteed minimum death and maturity benefits whose subjective discount rates follow a Gamma distribution. We use a constant relative risk aversion utility model to evaluate policyholder welfare and surrender behavior from holding the variable annuity. We also compute an insurer's profit under given insurance fees and policyholder surrender behavior. We find that when sharing the same expected discount rate, Gamma discounting policyholders delay surrender behavior and value the variable annuity more than than exponential discounting policyholders. Moreover, the insurer makes higher profit when policyholders are Gamma discounting than when they are exponential discounting. Chapter 5 considers policyholders of a variable annuity with guaranteed minimum withdrawal benefit whose subjective discount rates follow a Gamma distribution. Policyholder welfare and withdrawal behavior are quantified by the expected present value of variable annuity payouts. Different from the last two chapters, we deal with stochastic optimal control problems in this chapter due to the withdrawal type guarantees. Consistent with Chapter 4, we find that when having the same expected discount rate, Gamma discounting policyholders withdraw less and value the variable annuity more than exponential discounting policyholders. To keep a smooth flow of the thesis, Chapter 1 presents the existing strands of literature and introduces the main motivation of this thesis. Chapter \ref{chapter:mp} presents the core mathematical preliminaries for the latter chapters. Chapter 6 concludes this thesis and proposes potential future research avenues

Dental safety net capacity: An innovative use of existing data to measure dentists’ clinical engagement in state Medicaid programs

Background The demand for dentists available for state Medicaid populations has long outpaced the supply of such providers. To help understand the workforce dynamics, this study sought to develop a novel approach to measuring dentists’ relative contribution to the dental safety net and, using this new measurement, identify demographic and practice characteristics predictive of dentists’ willingness to participate in Indiana's Medicaid program. Methods We examined Medicaid claims data for 1,023 Indiana dentists. We fit generalized ordered logistic regression models to measure dentists’ level of clinical engagement with Medicaid. Using a partial proportional odds specification model, we estimated proportional adjusted odds ratios for covariates and separate estimates for each contrast of nonproportional covariates. Results Though 75% of Medicaid‐enrolled dentists were active providers, only 27% of them had 800 or more claims during fiscal year 2015. As has been shown in previous studies, our findings from the proportional odds model reinforced certain demographic and practice characteristics to be predictive of dentists’ participation in state Medicaid programs. Conclusions In addition to confirming predictive factors for Medicaid enrollment, this study validated the clinical engagement measure as a reliable method to assess the level of Medicaid participation. Prior studies have been limited by self‐reported data and variations in Medicaid claims reporting

Implementation of Hot Electrons in Hybrid Antenna-Graphene Structures

Graphene, a one-atom-thick sheet of hexagonally packed carbon atoms, is a novel material with high electron mobility due to its unique linear and gapless electronic band structure. Its broadband absorption and unusual doping properties, along with superb mechanical flexibility make graphene of promising application in optoeletronic devices such as solar cell, ultrafast photodetectors, and terahertz modulators. How- ever, the current performance of graphene-based devices is quite unacceptable owning to serious limitations by its inherently small absorption cross section and low quan- tum efficiency. Fortunately, nanoscale optical antennas, consisting of closely spaced, coupled metallic nanoparticles, have fascinating optical response since the collective oscillation of electrons in them, namely surface plasmons, can concentrate light into a subwavelength regime close to the antennas and enhance the corresponding field considerably. Given that optical antenna have been applied in various areas such as subwavelength optics, surface enhanced spectroscopies, and sensing, they are also able to assist graphene to harvest visible and near-infrared light with high efficiency. Moreover, the efficient production of hot electrons due to the decay of the surface plasmons can be further implemented to modulate the properties of graphene. Here we choose plasmonic oligomers to serve as optical antenna since they pos- sess tunable Fano resonances, consisting of a transparency window where scattering is strongly suppressed but absorption is greatly enhanced. By placing them in di- rect contact with graphene sheet, we find the internal quantum efficiency of hybrid antenna-graphene devices achieves up to 20%. Meanwhile, doping effect due to hot electron is also observed in this device, which can be used to optically tune the elec- tronic properties of graphene

Residual Control Chart for Binary Response with Multicollinearity Covariates by Neural Network Model

Quality control studies have dealt with symmetrical data having the same shape with respect to left and right. In this research, we propose the residual (r) control chart for binary asymmetrical (non-symmetric) data with multicollinearity between input variables via combining principal component analysis (PCA), functional PCA (FPCA) and the generalized linear model with probit and logit link functions, and neural network regression model. The motivation in this research is that the proposed control chart method can deal with both high-dimensional correlated multivariate data and high frequency functional multivariate data by neural network model and FPCA. We show that the neural network r control chart is relatively efficient to monitor the simulated and real binary response data with the narrow length of control limits

Research on the reaction of furil with ammonium acetate

The direct reaction of furil with ammonium acetate in refluxing glacial acetic acid under the absence of appropriate aldehydes was systematically studied. The principal product with furan rings and imidazole ring 2,4,5-tri(furan-2-yl)-1H-imidazole (I) was obtained in moderate yield, and two new byproducts containing furan rings were successfully purified by C18 reversed phase column. All compounds were characterized by elemental analysis, MS, IR, 1H and 13C NMR spectroscopy. The structure of I was further confirmed by the 13C-1H COSY spectroscopy. The putative reaction mechanism via stable 1,2-di(furan-2-yl)ethane-1,2-diimine, furan-2-yl-(2,4,5-tri-furan-2-yl-2H-imidazol-2-yl)-methanone and intermediate 5 traced by GC-MS was proposed