Properties of Graphene: A Theoretical Perspective

In this review, we provide an in-depth description of the physics of monolayer and bilayer graphene from a theorist's perspective. We discuss the physical properties of graphene in an external magnetic field, reflecting the chiral nature of the quasiparticles near the Dirac point with a Landau level at zero energy. We address the unique integer quantum Hall effects, the role of electron correlations, and the recent observation of the fractional quantum Hall effect in the monolayer graphene. The quantum Hall effect in bilayer graphene is fundamentally different from that of a monolayer, reflecting the unique band structure of this system. The theory of transport in the absence of an external magnetic field is discussed in detail, along with the role of disorder studied in various theoretical models. We highlight the differences and similarities between monolayer and bilayer graphene, and focus on thermodynamic properties such as the compressibility, the plasmon spectra, the weak localization correction, quantum Hall effect, and optical properties. Confinement of electrons in graphene is nontrivial due to Klein tunneling. We review various theoretical and experimental studies of quantum confined structures made from graphene. The band structure of graphene nanoribbons and the role of the sublattice symmetry, edge geometry and the size of the nanoribbon on the electronic and magnetic properties are very active areas of research, and a detailed review of these topics is presented. Also, the effects of substrate interactions, adsorbed atoms, lattice defects and doping on the band structure of finite-sized graphene systems are discussed. We also include a brief description of graphane -- gapped material obtained from graphene by attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic

Incremental Health Care Burden of Bleeding Among Patients with Venous Thromboembolism in the United States

BACKGROUND: The health care and economic burden of venous thromboembolism (VTE) has been evaluated in regard to acute VTE, VTE recurrence, and some VTE complications, such as postthrombotic syndrome, but the cost burden attributed to bleedings is not well understood. OBJECTIVE: To evaluate health care resource utilization and costs associated with major bleeding (MB) and clinically relevant nonmajor bleeding (CRNMB) among a large U.S. commercially and Medicare-insured population with VTE. METHODS: Patients (≥ 18 years of age, continuously insured) with a diagnosis of VTE between January 1, 2008, and December 31, 2011, were identified from the Truven Health Analytics Commercial and Medicare MarketScan databases. Patients who did not have any bleedings during the study period were grouped into a no-bleedings cohort and a random date after VTE diagnosis was selected as the index date. VTE patients who experienced MB within 1 year of the initial VTE diagnosis were grouped into a MB cohort, and patients without MB but with CRNMB were grouped into a CRNMB cohort. Baseline patient demographics and clinical characteristics were determined for study cohorts. All-cause and bleeding-related health care resource utilization and costs (inflation adjusted to 2013 level) during a 12-month follow-up period after the index date of the initial bleeding event were measured and compared. Descriptive statistics were used to evaluate differences in demographics, clinical characteristics, and unadjusted health care resource utilization and costs of patient cohorts. Multivariable generalized linear models were used to evaluate incremental health care costs of bleedings after adjusting for key patient characteristics.   RESULTS: Among the 112,885 patients identified with a VTE diagnosis, 14% (n = 15,897) had MB and 14% (n = 15,842) had CRNMB; 72% (n = 81,146) had neither of these events occur during the study period. The mean ages of the MB and CRNMB cohorts were both 63.6 years, while the mean age of the no-bleedings cohort was significantly lower at 59.6 years (P  less than  0.001). Mean Charlson Comorbidity Index scores were highest for the MB cohort (3.2), followed by those of the CRNMB cohort (2.5) and the no-bleedings cohort (1.6). The MB cohort had the greatest proportion of patients with an initial VTE event of pulmonary embolism only (23.5%), followed by that of the CRNMB cohort (20.2%), and the no-bleedings cohort (16.7%). For MB and CRNMB cohorts, the total mean bleeding-related inpatient and outpatient costs during the follow-up period were $49,779 (SE =$820) and $2,187 ($89), respectively. After adjustment for key patient characteristics, the estimated mean differences in total bleeding-related medical costs were $45,367 ($1,853) for patients with MB and $2,140 ($88) for patients with CRNMB versus patients with no bleedings. CONCLUSIONS: Among patients with VTE diagnosis in the United States, approximately 28% have a bleeding event within 1 year of VTE diagnosis, and about half of these patients experience MB. Patients with MB have greatly elevated health care costs