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

Health Effects of Medical Radiation on Cardiologists Who Perform Cardiac Catheterization

We investigated the health effects of low-dose radiation on cardiologists exposed to scattered radiation while performing cardiac catheterization (CC) in a hospital setting from 2003 to 2006. Methods: We performed a 4-year retrospective study on 2, 292 medical doctors, using claims data from all contracted hospitals of the Bureau of National Health Insurance, Taiwan. We gathered statistical data regarding radiation-related diseases using the International Classification of Diseases, 9th Revision, Clinical Modification record numbers of each doctor. Results: Of the 2,292 doctors evaluated, 1,721 were aged 35–50 years and the remaining 571 were aged 51–65 years. There were 892 cardiologists who performed CC (experimental group), and the majority of these (733/892, 82.17%) were aged 35–50 years. There were 1,400 medical doctors who performed no CC from 2003 to 2006 (control group). A total of 988 of these belonged to the 35–50 years age group and 412 to the 51–65 years group. In the 35–50 years group, the controls had significantly more medical visits for hematological and thyroid cancer (p <0.05), skin disease (p <0.001), and acute upper respiratory tract infection (p <0.001) compared with the experimental group. In contrast, cardiologists who performed catheterization had more cataracts compared with the control group, but this difference was not significant. Conclusion: Doctors who did not perform CC had more visits for radiation-related diseases than those who performed catheterization. In the experimental group, cardiologists aged 35–50 years who were exposed to radiation during CC had more visits for cataracts than the control group. We recommend that radiation protection concepts be emphasized to cardiologists, and that hospital managers be obligated to upgrade angiography equipment because the newer models have less scattered radiation

Independent Component Analysis for Magnetic Resonance Image Analysis

Independent component analysis (ICA) has recently received considerable interest in applications of magnetic resonance (MR) image analysis. However, unlike its applications to functional magnetic resonance imaging (fMRI) where the number of data samples is greater than the number of signal sources to be separated, a dilemma encountered in MR image analysis is that the number of MR images is usually less than the number of signal sources to be blindly separated. As a result, at least two or more brain tissue substances are forced into a single independent component (IC) in which none of these brain tissue substances can be discriminated from another. In addition, since the ICA is generally initialized by random initial conditions, the final generated ICs are different. In order to resolve this issue, this paper presents an approach which implements the over-complete ICA in conjunction with spatial domain-based classification so as to achieve better classification in each of ICA-demixed ICs. In order to demonstrate the proposed over-complete ICA, (OC-ICA) experiments are conducted for performance analysis and evaluation. Results show that the OC-ICA implemented with classification can be very effective, provided the training samples are judiciously selected