Intermittent many-body dynamics at equilibrium.

The equilibrium value of an observable defines a manifold in the phase space of an ergodic and equipartitioned many-body system. A typical trajectory pierces that manifold infinitely often as time goes to infinity. We use these piercings to measure both the relaxation time of the lowest frequency eigenmode of the Fermi-Pasta-Ulam chain, as well as the fluctuations of the subsequent dynamics in equilibrium. The dynamics in equilibrium is characterized by a power-law distribution of excursion times far off equilibrium, with diverging variance. Long excursions arise from sticky dynamics close to q-breathers localized in normal mode space. Measuring the exponent allows one to predict the transition into nonergodic dynamics. We generalize our method to Klein-Gordon lattices where the sticky dynamics is due to discrete breathers localized in real space.

Singularities of the dynamical structure factors of the spin-1/2 XXX chain at finite magnetic field.

We study the longitudinal and transverse spin dynamical structure factors of the spin-1/2 XXX chain at finite magnetic field h, focusing in particular on the singularities at excitation energies in the vicinity of the lower thresholds. While the static properties of the model can be studied within a Fermi-liquid like description in terms of pseudoparticles, our derivation of the dynamical properties relies on the introduction of a form of the 'pseudofermion dynamical theory' (PDT) of the 1D Hubbard model suitably modified for the spin-only XXX chain and other models with two pseudoparticle Fermi points. Specifically, we derive the exact momentum and spin-density dependences of the exponents ζ(τ)(k) controlling the singularities for both the longitudinal (τ = l) and transverse (τ = t) dynamical structure factors for the whole momentum range k ∈ ]0,π[, in the thermodynamic limit. This requires the numerical solution of the integral equations that define the phase shifts in these exponents expressions. We discuss the relation to neutron scattering and suggest new experiments on spin-chain compounds using a carefully oriented crystal to test our predictions.

Oxygen defects in phosphorene.

Surface reactions with oxygen are a fundamental cause of the degradation of phosphorene. Using first-principles calculations, we show that for each oxygen atom adsorbed onto phosphorene there is an energy release of about 2 eV. Although the most stable oxygen adsorbed forms are electrically inactive and lead only to minor distortions of the lattice, there are low energy metastable forms which introduce deep donor and/or acceptor levels in the gap. We also propose a mechanism for phosphorene oxidation involving reactive dangling oxygen atoms and we suggest that dangling oxygen atoms increase the hydrophilicity of phosphorene.

Resonant tunneling in graphene pseudomagnetic quantum dots.

Realistic relaxed configurations of triaxially strained graphene quantum dots are obtained from unbiased atomistic mechanical simulations. The local electronic structure and quantum transport characteristics of y-junctions based on such dots are studied, revealing that the quasi-uniform pseudomagnetic field induced by strain restricts transport to Landau level- and edge state-assisted resonant tunneling. Valley degeneracy is broken in the presence of an external field, allowing the selective filtering of the valley and chirality of the states assisting in the resonant tunneling. Asymmetric strain conditions can be explored to select the exit channel of the y-junction.

Electronic compressibility of a graphene bilayer.

We calculate the electronic compressibility arising from electron-electron interactions for a graphene bilayer within the Hartree-Fock approximation. We show that, due to the chiral nature of the particles in this system, the compressibility is rather different from those of either the two-dimensional electron gas or ordinary semiconductors. We find that an inherent competition between the contributions coming from intraband exchange interactions (dominant at low densities) and interband interactions (dominant at moderate densities) leads to a nonmonotonic behavior of the compressibility as a function of carrier density.

Magnetic excitations of stripes near a quantum critical point.

We calculate the dynamical spin structure factor of spin waves for weakly coupled stripes. At low energy, the spin-wave cone intensity is strongly peaked on the inner branches. As energy is increased, there is a saddlepoint followed by a square-shaped continuum rotated 45 degrees from the low energy peaks. This is reminiscent of recent high energy neutron scattering data on the cuprates. The similarity at high energy between this semiclassical treatment and quantum fluctuations in spin ladders may be attributed to the proximity of a quantum critical point with a small critical exponent eta.

Drug-eluting stents: clinical perspectives on drug and design differences.

Although the introduction of coronary stents has significantly improved the treatment of patients with coronary artery disease, restenosis, due to neointimal proliferation following stent deployment and associated with a return of ischemic symptoms, has remained a critical concern. Recent studies have shown that the use of drug-eluting stents to deliver antiproliferative agents directly to the vessel wall dramatically reduces the rate of restenosis. However, important differences exist among stent designs, drug-delivery vehicles, and choices of pharmacologic agents that can significantly affect the safety and efficacy of each device. Although engineers, vascular biologists, and clinicians all agree that clinical success of drug-eluting stents requires careful integration of the individual system components, the optimal combination remains to be determined.

Optimal stent design for drug delivery.

The efficacy and safety of drug-eluting coronary stents might differ depending on the pharmacologic agents and stent delivery systems used. Recent research has focused on the various constituents of drug-delivery stents, including the stent backbone, materials used as drug-delivery vehicles, and the physicochemical properties of the pharmacotherapeutic agents themselves. Metal stents coated with an outer layer of polymer (bioabsorbable or non-bioabsorbable) can be drug-loaded, thus providing more controlled and sustained drug delivery and allowing more optimal drug-tissue interactions. Among the next generation of drug-eluting stents will be a stent that uses the non-bioabsorbable polymer phosphorylcholine to release the sirolimus analogue ABT-578; another stent will use a highly deliverable cobalt-chromium metal alloy stent platform and, for the first time, a bioabsorbable polymeric coating (thin-film polylactic acid) for drug encapsulation and release.

Vortex liquid crystals in anisotropic type II superconductors.

In an isotropic type II superconductor in a moderate magnetic field, the transition to the normal state occurs by vortex lattice melting. In certain anisotropic cases, the vortices acquire elongated cross sections and interactions. Systems of anisotropic, interacting constituents generally exhibit liquid crystalline phases. We examine the possibility of a two step melting in homogeneous type II superconductors with anisotropic superfluid stiffness from a vortex lattice into first a vortex smectic and then a vortex nematic at high temperature and magnetic field. We find that fluctuations of the ordered phase favor an instability to an intermediate smectic-A in the absence of intrinsic pinning.

No-reflow is an independent predictor of death and myocardial infarction after percutaneous coronary intervention.

BACKGROUND: No-reflow occurring during percutaneous coronary intervention (PCI) has been associated with poor inhospital outcomes. The objectives of this analysis were to evaluate the occurrence of no-reflow as an independent predictor of adverse events and to determine whether treatment with intracoronary vasodilator therapy affected clinical outcomes. METHODS: We prospectively collected data from 4264 consecutive patients undergoing PCI, identifying those with no-reflow, and analyzed their treatments and clinical outcomes. RESULTS: No-reflow was identified in 135 of 4264 patients (3.2%). Baseline demographics were comparable, but patients with no-reflow were more likely to have acute myocardial infarction, unstable angina, and cardiogenic shock and to have undergone saphenous vein graft interventions. No-reflow was highly predictive of postprocedural myocardial infarction (17.7% vs 3.5% in patients without no-reflow, P <.001) and death (7.4% vs 2.0%, P <.001) and remained a strong independent predictor of death or myocardial infarction after multivariate analysis (odds ratio 3.6, P <.001). The administration of intracoronary verapamil, sodium nitroprusside, or both was not associated with a reduction in the rate of death or myocardial infarction (adjusted odds ratio of death or myocardial infarction 1.04, P =.945 for nitroprusside; and adjusted odds ratio of death or myocardial infarction 0.94, P =.91 for verapamil), despite an improvement in angiographic flow rates for patients treated with sodium nitroprusside. CONCLUSIONS: No-reflow is a strong independent predictor of inhospital mortality and postprocedural myocardial infarction. Administration of verapamil or sodium nitroprusside was not associated with improved inhospital outcomes in patients with no-reflow, although anterograde flow rates were improved in patients treated with sodium nitroprusside.

Drug-eluting stents: role of stent design, delivery vehicle, and drug selection.

Increasing focus has recently been directed toward the different parameters of drug-eluting stents-stent design, delivery-vehicle materials, and drug properties-and the manner in which each of these elements may affect the function of the stents. Several specific characteristics of design may affect restenosis, although design optimization often presents a choice between acute procedural success and long-term biological stability. The influence of design parameters such as strut thickness and cell configuration is described. Polymer material has frequently been used to coat drug-eluting stents, although some agents, such as paclitaxel, can be attached directly to the stent's surface, obviating the need for a polymer layer. The properties of agents used in drug-eluting stents and how those properties affect delivery and long-term outcome are discussed, as is the influence of the disease state of the target vessel on stent safety and efficacy.

Re-integerization of fractional charges in the correlated quarter-filled band.

Previous work has demonstrated the existence of soliton defect states with charges +/-e/2 in the limits of zero and infinite on-site Coulomb interactions in the one-dimensional (1D) quarter-filled band. For large but finite on-site Coulomb interaction, the low temperature 2kF bond distortion that occurs within the 4kF bond-distorted phase is accompanied by charge ordering on the sites. We show that a "re-integerization" of the defect charge occurs in this bond-charge-density-wave state due to a "binding" of the fractional charges. We indicate briefly possible implications of this result for mechanisms of organic superconductivity.

Materials processing with CO(2)laser holographic scanner systems.

The complexity of laser material processing can be greatly reduced using computer-generated phase reflection holographic scanners. These scanners direct and focus the beam of a carbon dioxide laser into a spot on the workpiece and then translate this spot over some general 2-D pattern as the scanner undergoes a simple 1-D motion. Procedures for constructing these scanners are presented, and the first-order aberrations introduced by them are analyzed. The primary aberrations cause the diffracted beam to focus to an astigmatic spot on the work surface. The severity of the astigmatism is proportional to the scan rate, scan angle, and f/number. A technique is presented in which the design of the scanner is adjusted so that the astigmatic image is aligned with the scan direction. The resolution perpendicular to the scan direction is the same as that of a scanner without aberrations of the same f/number. Materials processed using these scanners are presented to show their capabilities for carbon dioxide laser material processing. Power densities on the order of 10(6)/cm(2) can be readily obtained using the proposed technique.