Bacteremia Due to Viridans Streptococcus in Neutropenic Patients with Cancer: Clinical Spectrum and Risk Factors

Between 1988 and 1991, 26 episodes of bacteremia due to viridans streptococci occurred in 25 neutropenic patients undergoing intensive chemotherapy for hematologic malignancies. Complications related to the bacteremia were observed in 10 episodes: unilateral pulmonary infiltrates (4), acute respiratory distress syndrome (ARDS) (4), hypotension (3), and endocarditis (2). All patients with ARDS had received high doses of cytosine arabinoside and had bacteremia due to Streptococcus mitis. Death occurred in three patients (12%) but was possibly related to bacteremia in only one case. Case patients who had received prophylaxis with quinolones were compared with matched control patients who received similar prophylaxis but who did not have bacteremia due to viridans streptococci. Multivariate analysis of predisposing factors showed that high doses of cytosine arabinoside (P = .01), the presence of mucositis (P = .02), and the absence of previous therapy with parenteral antibiotics (P = .01) were independent risk factors for the development of viridans streptococcal bacteremia. Of 259 patients who had received quinolone prophylaxis during the study period, 22 (8.5%) developed an episode of viridans streptococcal bacteremia as compared with three episodes (3.7%) in 82 patients who had received a quinolone and penicillin (P = .07). However, the latter three episodes were caused by strains with decreased susceptibility to penicillin, thus suggesting that resistance to penicillin might limit the use of this antibiotic as a prophylactic agent in the futur

Long range Neel order in the triangular Heisenberg model

We have studied the Heisenberg model on the triangular lattice using several Quantum Monte Carlo (QMC) techniques (up to 144 sites), and exact diagonalization (ED) (up to 36 sites). By studying the spin gap as a function of the system size we have obtained a robust evidence for a gapless spectrum, confirming the existence of long range Neel order. Our best estimate is that in the thermodynamic limit the order parameter m= 0.41 +/- 0.02 is reduced by about 59% from its classical value and the ground state energy per site is e0=-0.5458 +/- 0.0001 in unit of the exchange coupling. We have identified the important ground state correlations at short distance.Comment: 4 pages, RevTeX + 4 encapsulated postscript figure

Microscopic description of d-wave superconductivity by Van Hove nesting in the Hubbard model

We devise a computational approach to the Hubbard model that captures the strong coupling dynamics arising when the Fermi level is at a Van Hove singularity in the density of states. We rely on an approximate degeneracy among the many-body states accounting for the main instabilities of the system (antiferromagnetism, d-wave superconductivity). The Fermi line turns out to be deformed in a manner consistent with the pinning of the Fermi level to the Van Hove singularity. For a doping rate $\delta \sim 0.2$, the ground state is characterized by d-wave symmetry, quasiparticles gapped only at the saddle-points of the band, and a large peak at zero momentum in the d-wave pairing correlations.Comment: 4 pages, 2 Postscript figure

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