Giant phonon anomaly associated with superconducting fluctuations in the pseudogap phase of cuprates.

The pseudogap in underdoped cuprates leads to significant changes in the electronic structure, and was later found to be accompanied by anomalous fluctuations of superconductivity and certain lattice phonons. Here we propose that the Fermi surface breakup due to the pseudogap, leads to a breakup of the pairing order into two weakly coupled sub-band amplitudes, and a concomitant low energy Leggett mode due to phase fluctuations between them. This increases the temperature range of superconducting fluctuations containing an overdamped Leggett mode. In this range inter-sub-band phonons show strong damping due to resonant scattering into an intermediate state with a pair of overdamped Leggett modes. In the ordered state, the Leggett mode develops a finite energy, changing the anomalous phonon damping into an anomaly in the dispersion. This proposal explains the intrinsic connection between the anomalous pseudogap phase, enhanced superconducting fluctuations and giant anomalies in the phonon spectra.

Response to treatment following recently acquired hepatitis C virus infection in a multicentre collaborative cohort.

Pegylated interferon therapy is highly effective in recently acquired HCV. The optimal timing of treatment, regimen and influence of host factors remains unclear. We aimed to measure sustained virological response (SVR) during recent HCV infection and identify predictors of response. Data were from five prospective cohorts of high-risk individuals in Australia, Canada, Germany and the United States. Individuals with acute or early chronic HCV who commenced pegylated interferon therapy were included. The main outcome was SVR, and predictors were assessed using logistic regression. Among 516 with documented recent HCV infection, 237 were treated (pegylated interferon n = 161; pegylated interferon/ribavirin n = 76) (30% female, median age 35 years, 56% ever injected drugs, median duration of infection 6.2 months). Sixteen per cent (n = 38) were HIV/HCV co-infected. SVR among those with HCV mono-infection was 64% by intention to treat; SVR was 68% among HCV/HIV co-infection. Independent predictors of SVR in HCV mono-infection were duration of HCV infection (the odds of SVR declined by 8% per month of infection, aOR 0.92, 95% CI 0.85-0.99, P = 0.033), IFNL4 genotype (adjusted OR 2.27, 95% CI 1.13-4.56, P = 0.021), baseline HCV RNA <400 000 IU/mL (aOR 2.06, 95% CI 1.03-4.12, P = 0.041) and age ≥40 years (vs <30: aOR 2.92, 95% CI 1.31-6.49, P = 0.009), with no difference by drug regimen, HCV genotype, symptomatic infection or gender. The effect of infection duration on odds of SVR was greater among genotype-1 infection. Interferon-based HCV treatment is highly effective in recent HCV infection. Duration of infection, IFNL4 genotype and baseline HCV RNA levels can predict virological response and may inform clinical decision-making.

Factors associated with hepatitis C virus RNA levels in early chronic infection: the InC3 study.

Improved understanding of natural history of hepatitis C virus (HCV) RNA levels in chronic infection provides enhanced insights into immunopathogenesis of HCV and has implications for the clinical management of chronic HCV infection. This study assessed factors associated with HCV RNA levels during early chronic infection in a population with well-defined early chronic HCV infection. Data were from an international collaboration of nine prospective cohorts studying acute HCV infection (InC(3) study). Individuals with persistent HCV and detectable HCV RNA during early chronic infection (one year [±4 months] postinfection) were included. Distribution of HCV RNA levels during early chronic infection was compared by selected host and virological factors. A total of 308 individuals were included. Median HCV RNA levels were significantly higher among males (vs females; 5.15 vs 4.74 log IU/mL; P < 0.01) and among individuals with HIV co-infection (vs no HIV; 5.89 vs 4.86; P = 0.02). In adjusted logistic regression, male sex (vs female, adjusted odds ratio [AOR]: 1.93; 95%CI: 1.01, 3.69), interferon lambda 4 (IFNL4) rs12979860 CC genotype (vs TT/CT; AOR: 2.48; 95%CI: 1.42, 4.35), HIV co-infection (vs no HIV; AOR: 3.27; 95%CI: 1.35, 7.93) and HCV genotype G2 (vs G3; AOR: 5.40; 95%CI: 1.63, 17.84) were independently associated with high HCV RNA levels (>5.6 log IU/mL = 400 000 IU/mL). In conclusion, this study demonstrated that IFNL4 rs12979860 CC genotype, male sex, HIV co-infection and HCV genotype G2 are associated with high HCV RNA levels in early chronic infection. These factors exert their role as early as one year following infection.

Competing states in the t-J model: uniform D-wave state versus stripe state.

Variational studies of the t-J model on the square lattice based on infinite projected-entangled pair states confirm an extremely close competition between a uniform d-wave superconducting state and different stripe states. The site-centered stripe with an in-phase d-wave order has an equal or only slightly lower energy than the stripe with antiphase d-wave order. The optimal stripe filling is not constant but increases with J/t. A nematic anisotropy reduces the pairing amplitude and the energies of stripe phases are lowered relative to the uniform state with increasing nematicity.

Spin density wave fluctuations and p-wave pairing in Sr2RuO4.

Recently, a debate has arisen over which of the two distinct parts of the Fermi surface of Sr(2)RuO(4) is the active part for the chiral p-wave superconductivity exhibited. Early theories proposed p-wave pairing on the two-dimensional γ band, whereas a recent proposal focuses on the one-dimensional (α, ß) bands whose nesting pockets are the source of the strong incommensurate spin density wave (SDW) fluctuations. We apply a renormalization group theory to study quasi-one-dimensional repulsive Hubbard chains and explain the form of SDW fluctuations, reconciling the absence of long-range order with their nesting Fermi surface. The mutual exclusion of p-wave pairing and SDW fluctuations in repulsive Hubbard chains favors the assignment of the two-dimensional γ band as the source of p-wave pairing.

A phenomenological theory of the anomalous pseudogap phase in underdoped cuprates.

The theoretical description of the anomalous properties of the pseudogap phase in the underdoped region of the cuprate phase diagram lags behind the progress in spectroscopic and other experiments. A phenomenological ansatz, based on analogies to the approach to Mott localization at weak coupling in lower dimensional systems, has been proposed by Yang et al (2006 Phys. Rev. B 73 174501). This ansatz has had success in describing a range of experiments. The motivation underlying this ansatz is described and the comparisons with experiment are reviewed. Implications for a more microscopic theory are discussed together with the relation to theories that start directly from microscopic strongly coupled Hamiltonians.

Andreev and single-particle tunneling spectra of underdoped cuprate superconductors.

We study tunneling spectroscopy between a normal metal and an underdoped cuprate superconductor modeled by a phenomenological theory in which the pseudogap is a precursor to the undoped Mott insulator. In the low barrier tunneling limit, the spectra are enhanced by Andreev reflection only within a voltage region of the small superconducting energy gap. In the high barrier tunneling limit, the spectra show a large energy pseudogap associated with single particle tunneling. Our theory semiquantitatively describes the two gap behavior observed in tunneling experiments.

The association between booster seat use and risk of death among motor vehicle occupants aged 4-8: a matched cohort study.

OBJECTIVE: To estimate the effectiveness of booster seats and of seatbelts in reducing the risk of child death during traffic collisions and to examine possible effect modification by various collision and vehicle characteristics. METHODS: A matched cohort study was conducted using data from the Fatality Analysis Reporting System. Death risk ratios were estimated with conditional Poisson regression, bootstrapped coefficient standard errors, and multiply imputed missing values using chained equations. RESULTS: Estimated death risk ratios for booster seats used with seatbelts were 0.33 (95% CI 0.28 to 0.40) for children age 4-5 years and 0.45 (0.31 to 0.63) for children aged 6-8 years (Wald test of homogeneity p<0.005). The estimated risk ratios for seatbelt used alone were similar for the two age groups, 0.37 (0.32 to 0.43) and 0.39 (0.34 to 0.44) for ages 4-5 and 6-8, respectively (Wald p = 0.61). Estimated booster seat effectiveness was significantly greater for inbound seating positions (Wald p = 0.05) and during rollovers collisions (Wald p = 0.01). Significant variability in risk ratio estimates was not observed across levels of calendar year, vehicle model year, vehicle type, or land use. CONCLUSIONS: Seatbelts, used with or without booster seats, are highly effective in preventing death among motor vehicle occupants aged 4-8 years. Booster seats do not appear to improve the performance of seatbelts with respect to preventing death (risk ratio 0.92, 95% CI 0.79 to 1.08, comparing seatbelts with boosters to seatbelts alone), but because several studies have found that booster seats reduce non-fatal injury severity, clinicians and injury prevention specialists should continue to recommend the use of boosters to parents of young children.

Differential toxicity to Cd, Pb, and Cu in dragonfly larvae (Insecta: Odonata).

Odonate larvae are important organisms in aquatic ecosystems but have been rarely studied in laboratory toxicity tests. Only a few previous studies have been conducted on odonates and their responses to heavy metals. We exposed two species of libellulid larvae (Anisoptera: Libellulidae) to equimolar concentrations of cadmium, lead, or copper in 7-day survival tests. Larvae were tolerant of high concentrations of cadmium and lead, as no significant decrease in survival was observed at exposures as high as 0.893 and 2.232 mM, respectively. In contrast, larvae were more sensitive to copper exposure, demonstrating significantly decreased survival to exposures as low as 2.360 microM. In whole animal samples, larvae accumulated very high concentrations (>1000 microg/g dry weight) of all three metals in an exposure-related manner. Much of this accumulation could probably be attributed to adsorption or accumulation of metal within the exoskeleton, because odonate larvae are known to sequester metals into this material. Our results were generally consistent with previous observations indicating that odonates are tolerant to metal exposures, even in comparison with other aquatic invertebrates. However, there are few studies that have used odonates in toxicity tests and compared these organisms to other aquatic life. Based on their abundance and their simple requirements in the laboratory, we believe that odonate larvae can be useful toxicological model organisms.

Breakdown of Landau theory in overdoped cuprates near the onset of superconductivity.

We use the functional renormalization group to analyze the temperature dependence of the quasiparticle scattering rates in the two-dimensional Hubbard model below half-filling. Using a band structure appropriate to overdoped Tl2Ba2CuO6+x we find a strongly angle-dependent term linearly dependent on temperature which derives from an increasing scattering vertex as the energy scale is lowered. This behavior agrees with recent experiments and confirms earlier conclusions on the origin of the breakdown of the Landau-Fermi liquid near the onset of superconductivity.

Heavy metal levels in ribbon snakes (Thamnophis sauritus) and anuran larvae from the Mobile-Tensaw River Delta, Alabama, USA.

The Mobile-Tensaw River Delta (MTD) drains more than 75% of the state of Alabama and leads into Mobile Bay and the Northern Gulf of Mexico. Although it is a relatively healthy watershed, the MTD is potentially impacted by inputs of contaminants such as heavy metals. The levels of lead, copper, cadmium, and mercury were measured in whole body samples of Eastern Ribbon Snakes (Thamnophis sauritus) collected from the MTD. Lead, copper, and cadmium levels were also measured in anuran larvae (Rana catesbeiana, R. clamitans, and Hyla cinerea). These organisms were chosen because they are abundant in the MTD and are underrepresented in environmental contaminant biomonitoring studies. Ribbon snakes had significantly lower levels of lead, copper, and cadmium compared to whole body levels in anuran larvae, indicating that these metals were not biomagnifying through upper trophic levels. Copper and mercury levels were significantly correlated with age/growth indices in ribbon snakes. Although detectable levels of all metals were found in anuran larvae and ribbon snakes, these levels appear to be less than body burdens that would be associated with toxic effects. Populations of ribbon snakes in our particular collection sites within the MTD appear to be at minimal risk of exposure to toxic levels of metals. However, the MTD contains low- and high-impact areas, and other populations within this watershed could be at higher risk of exposure to heavy metals. We found the Eastern Ribbon Snake to be an excellent snake model for contaminant biomonitoring because of its abundance, reasonable size, and ease of collection.

Role of inelastic tunneling through the insulating barrier in scanning-tunneling-microscope experiments on cuprate superconductors.

The tunneling path between the CuO2 layers in cuprate superconductors and a scanning-tunneling-microscope tip passes through a barrier made from other oxide layers. This opens up the possibility that inelastic processes in the barrier contribute to the tunneling spectra. Such processes cause one or possibly more peaks in the second derivative current-voltage spectra displaced by phonon energies from the density of states singularity associated with superconductivity. Calculations of inelastic processes generated by apical O phonons show good qualitative agreement with recent experiments reported by Lee et al. Further tests to discriminate between these inelastic processes and coupling to planar phonons are proposed.

Magnetic domain formation in itinerant metamagnets.

We examine the effects of long-range dipolar forces on metamagnetic transitions and generalize the theory of Condon domains to the case of an itinerant electron system undergoing a first-order metamagnetic transition. We demonstrate that, within a finite range of the applied field, dipolar interactions induce a spatial modulation of the magnetization in the form of stripes or bubbles. Our findings are consistent with recent observations in the bilayer ruthenate Sr(3)Ru(2)O(7).

Doped spin liquid: Luttinger sum rule and low temperature order.

We analyze a model of two-leg Hubbard ladders weakly coupled by interladder tunneling. At half filling a semimetallic state with small Fermi pockets is induced beyond a threshold tunneling strength. The sign changes in the single electron Green's function relevant for the Luttinger sum rule now take place at surfaces with both zeros and infinities with important consequences for the interpretation of angle-resolved photoemission spectroscopy experiments. Residual interactions between electron and holelike quasiparticles cause a transition to long range order at low temperatures. The theory can be extended to small doping leading to superconducting order.

Rotational symmetry breaking in the ground state of sodium-doped cuprate superconductors.

We use an extended t-J model to study a single hole bound to a Na+ acceptor in Ca2-xNaxCuO2Cl2. For parameters suitable to cuprates, the ground state has a twofold degeneracy, corresponding to even (odd) reflection symmetry around the x (y) axes. The conductance pattern of the broken symmetry state is anisotropic as the tip of a tunneling microscope scans above the Cu-O-Cu bonds along the x (y) axes. This anisotropy is pronounced at lower voltages but reduced at higher voltages. Our theory agrees qualitatively with recent data of scanning tunneling microscopy showing broken local rotational symmetry.

Orbital-selective mott transitions in the degenerate Hubbard model.

We investigate the Mott transitions in two-band Hubbard models with different bandwidths. Applying dynamical mean field theory, we discuss the stability of itinerant quasiparticle states in each band. We demonstrate that separate Mott transitions occur at different Coulomb interaction strengths in general, which merge to a single transition only under special conditions. This kind of behavior may be relevant for the physics of the single-layer ruthenates, Ca2-xSrxRuO4.

d-Mott phases in one and two dimensions.

We use exact diagonalization to determine the spectrum of reduced Hamiltonians based on renormalization group flows to strong coupling. For the half-filled two-leg Hubbard ladder we reproduce the known insulating d-Mott ground state with spin and charge gaps. For the saddle point regions of the two-dimensional Hubbard model near half filling we find a crossover to a similar strong coupling state, which truncates the Fermi surface near the saddle points. At lower scales d-wave superconductivity appears on the remaining Fermi surface.

Single-particle spectrum in the electron-doped cuprates.

We study the evolution of the single-particle spectrum with electron doping in a scheme which adds multiple exchange of transverse spin excitations to the mean-field antiferromagnetic insulator. Away from half-filling small Fermi surface pockets appear first around the X points, and simultaneously new spectral weight grows in the insulating gap. With further doping the in-gap states develop the character of a renormalized quasiparticle band near the chemical potential. The essential features in momentum-energy space agree well with recent studies using angle-resolved photoemission spectroscopy on electron-doped cuprates. We interpret the origins and the nature of the in-gap states using a simple variational wave function.

Nighttime driving, passenger transport, and injury crash rates of young drivers.

OBJECTIVE: This study examines the association of nighttime driving and the carrying of passengers with the rate of motor vehicle crashes that resulted in severe or fatal injury to young drivers in California before the implementation of a graduated licensing system. METHOD: Passenger vehicle drivers aged 16 or 17 involved in injury crashes in California from 1 January 1993 to 30 June 1998 were identified through a police crash database. An induced exposure method was used to estimate driving exposure. Odds ratios for driver injury crashes were estimated with logistic regression. RESULTS: Driving at night, driving without adult supervision, driving with passengers, using alcohol, being 16, and being male were associated with high rates of driver injury crash. CONCLUSIONS: The injury crash rate for drivers aged 16 or 17 increases during nighttime hours and in the absence of adult supervision, with or without other passengers. Driving between 10 pm and midnight is particularly dangerous for young drivers. Nighttime driving restrictions that begin at 10 pm or earlier and restrictions on carrying passengers at any hour may increase the effectiveness of graduated licensing systems.