The Effectiveness of the Commercial Driver Medical Examination in Screening for Hypertension

The Commercial Driver Medical Examination (CDME) is used to assess the medical fitness of a driver to safely operate a commercial motor vehicle. Hypertension is a disease that has been shown in prior research to cause reduced driving safety performance when not properly managed, and it is therefore important that medical examiners be able to consistently identify it in drivers. However, the CDME has historically been ineffective at screening drivers with safety-related diseases. For example, a report from the US Government Accountability Office showed the existence of a substantial number of drivers who were deemed eligible by the federal government for full disability benefits and yet also passed their CDME’s. To address these issues, the Federal Motor Carrier Safety Administration (FMCSA) instituted the Medical Examiner Registry and mandatory training programs for examiners. This project uses data from before these reforms to establish a baseline for comparison to the new version of the CDME. We compare hypertension as captured in CDME records to hypertension as captured in medical insurance claims data on the same drivers. Our initial results indicate that of the 1,320 drivers who were determined from the insurance data to have hypertension, medical examiners were able to correctly identify 74% of them as having the condition. This suggests that while the CDME was moderately successful in screening for hypertension even before the reforms, there was room for improvement.https://digitalcommons.morris.umn.edu/urs_2018/1000/thumbnail.jp

Observer-based Leader-following Consensus for Positive Multi-agent Systems Over Time-varying Graphs

This paper addresses the leader-following consensus problem for discrete-time positive multi-agent systems over time-varying graphs. We assume that the followers may have mutually different positive dynamics which can also be different from the leader. Compared with most existing positive consensus works for homogeneous multi-agent systems, the formulated problem is more general and challenging due to the interplay between the positivity requirement and high-order heterogeneous dynamics. To solve the problem, we present an extended version of existing observer-based design for positive multi-agent systems. By virtue of the common quadratic Lyapunov function technique, we show the followers will maintain their state variables in the positive orthant and finally achieve an output consensus specified by the leader. A numerical example is used to verify the efficacy of our algorithms

Electronic and plasmonic band structure engineering of graphene using superlattices

Patterning graphene with a spatially periodic potential provides a powerful means to modify its electronic properties. In particular, in twisted bilayers, coupling to the resulting moiré superlattice yields an isolated flat band that hosts correlated many-body phases. However, both the symmetry and strength of the effective moiré potential are constrained by the constituent crystals, limiting its tunability. Here, we have exploited the technique of dielectric patterning⁶ to subject graphene to a one-dimensional electrostatic superlattice (SL). We observed the emergence of multiple Dirac cones and found evidence that with increasing SL potential the main and satellite Dirac cones are sequentially flattened in the direction parallel to the SL basis vector, behavior resulting from the interaction between the one-dimensional SL electric potential and the massless Dirac fermions hosted by graphene. Our results demonstrate the ability to induce tunable anisotropy in high-mobility two-dimensional materials, a long-desired property for novel electronic and optical applications. Moreover, these findings offer a new approach to engineering flat energy bands where electron interactions can lead to emergent properties. The photon analog of electronic superlattice is photonic crystals. Efficient control of photons is enabled by hybridizing light with matter. The resulting light-matter quasi-particles can be readily programmed by manipulating either their photonic or matter constituents. Here, we hybridized infrared photons with graphene Dirac electrons to form surface plasmon polaritons (SPPs) and uncovered a previously unexplored means to control SPPs in structures with periodically modulated carrier density. In these photonic crystal structures, common SPPs with continuous dispersion are transformed into Bloch polaritons with attendant discrete bands separated by bandgaps. We explored directional Bloch polaritons and steered their propagation by dialing the proper gate voltage. Fourier analysis of the near-field images corroborates that this on-demand nano-optics functionality is rooted in the polaritonic band structure. Our programmable polaritonic platform paves the way for the much-sought benefits of on-the-chip photonic circuits

Accounting Conservatism and the Consequences of Covenant Violations

Recent studies document that covenant violations intensify the conflicts of interest between lenders and borrowers, and lead to greater restrictions on borrowing firms’ financing and investment activities (Chava and Roberts, 2008; Roberts and Sufi, 2009b). Motivated by this literature, I investigate whether accounting conservatism, specifically conditional conservatism, mitigates the adverse consequences of debt covenant violations. I argue that conservative reporting can potentially ameliorate the conflicts of interest between lenders and borrowers. Therefore, I predict that accounting conservatism reduces the adverse impact of covenant violations on borrowers’ financing and investing activities and exhibits a positive association with operating and stock market performance after covenant violations. I obtain a sample of 312 violating and 5,327 non-violating firm-quarters observations from U.S. non-financial public firms during the period of 1998 – 2007 to test my hypotheses. Using three measures of conditional conservatism and a composite measure of the three individual measures, I find that the degree of increase in borrowing firms’ conservative reporting between loan initiation and covenant violation is associated with smaller reductions in firms’ financing and investing activities in the post-violation period. Furthermore, my analyses provide some evidence that firms that increase conservative reporting exhibit better stock market performance, implying that conservative reporting is beneficial for shareholders after covenant violations. I find no evidence that increased accounting conservatism affects operating performance after covenant violations. My results continue to hold after controlling for pre-contracting unconditional and conditional conservatism. Overall, my dissertation provides evidence that conservative accounting practices followed by borrowing firms ease the adverse consequences of debt covenant violations. My dissertation contributes to the emerging literature on the effects of accounting quality on re-contracting outcomes after covenant violations