Impact of Many-Body Effects on Landau Levels in Graphene

We present magneto-Raman spectroscopy measurements on suspended graphene to investigate the charge carrier density-dependent electron-electron interaction in the presence of Landau levels. Utilizing gate-tunable magneto-phonon resonances, we extract the charge carrier density dependence of the Landau level transition energies and the associated effective Fermi velocity $v_\mathrm{F}$. In contrast to the logarithmic divergence of $v_\mathrm{F}$ at zero magnetic field, we find a piecewise linear scaling of $v_\mathrm{F}$ as a function of charge carrier density, due to a magnetic field-induced suppression of the long-range Coulomb interaction. We quantitatively confirm our experimental findings by performing tight-binding calculations on the level of the Hartree-Fock approximation, which also allow us to estimate an excitonic binding energy of $\approx$ 6 meV contained in the experimentally extracted Landau level transitions energies.Comment: 10 pages, 6 figure

Where is Population II?

The use of roman numerals for stellar populations represents a classification approach to galaxy formation which is now well behind us. Nevertheless, the concept of a pristine generation of stars, followed by a protogalactic era, and finally the mainstream stellar population is a plausible starting point for testing our physical understanding of early star formation. This will be observationally driven as never before in the coming decade. In this paper, we search out observational tests of an idealized coeval and homogeneous distribution of population II stars. We examine the spatial distribution of quasars, globular clusters, and the integrated free electron density of the intergalactic medium, in order to test the assumption of homogeneity. Any $real$ inhomogeneity implies a population II that is not coeval.Comment: for publication in PAS

Native myocardial T1 time can predict development of subsequent anthracycline-induced cardiomyopathy

Aims: This study aims to assess subclinical changes in functional and morphological myocardial magnetic resonance parameters very early into an anthracycline treatment, which may predict subsequent development of anthracycline-induced cardiomyopathy (aCMP). Methods and results: Thirty sarcoma patients with planned anthracycline-based chemotherapy (360-400 mg/m doxorubicin-equivalent) were recruited. Median treatment time was 19.1 ± 2.1 weeks. Enrolled individuals received three cardiovascular magnetic resonance studies (before treatment, 48 h after first anthracycline treatment, and upon completion of treatment). Native T1 mapping (modified Look-Locker inversion recovery 5s(3s)3s), T2 mapping, and extracellular volume maps were acquired in addition to a conventional cardiovascular magnetic resonance with steady-state free precession cine imaging at 1.5 T. Patients were given 0.2 mmol/kg gadoteridol for extracellular volume quantification and late gadolinium enhancement imaging. Development of relevant aCMP was defined as drop of left ventricular ejection fraction (LVEF) by >10%. For analysis, 23 complete data sets were available. Nine patients developed aCMP with LVEF reduction >10% until end of chemotherapy. Baseline LVEF was not different between patients with and without subsequent aCMP. When assessed 48 h after first dose of antracyclines, patients with subsequent aCMP had significantly lower native myocardial T1 times compared with before therapy (1002.0 ± 37.9 vs. 956.5 ± 29.2 ms, P  0.05). Patients with aCMP had decreased left ventricular mass upon completion of therapy (86.9 ± 24.5 vs. 81.1 ± 22.3 g; P = 0.02), while patients without aCMP did not show a change in left ventricular mass (81.8 ± 21.0 vs. 79.2 ± 18.1 g; P > 0.05). No patient developed new myocardial scars or compact myocardial fibrosis under chemotherapy. Conclusions: Early decrease of T1 times 48 h after first treatment with anthracyclines can predict the development of subsequent aCMP after completion of chemotherapy

Single-qubit unitary gates by graph scattering

We consider the effects of plane-wave states scattering off finite graphs, as an approach to implementing single-qubit unitary operations within the continuous-time quantum walk framework of universal quantum computation. Four semi-infinite tails are attached at arbitrary points of a given graph, representing the input and output registers of a single qubit. For a range of momentum eigenstates, we enumerate all of the graphs with up to $n=9$ vertices for which the scattering implements a single-qubit gate. As $n$ increases, the number of new unitary operations increases exponentially, and for $n>6$ the majority correspond to rotations about axes distributed roughly uniformly across the Bloch sphere. Rotations by both rational and irrational multiples of $\pi$ are found.Comment: 8 pages, 7 figure

Entangling flux qubits with a bipolar dynamic inductance

We propose a scheme to implement variable coupling between two flux qubits using the screening current response of a dc Superconducting QUantum Interference Device (SQUID). The coupling strength is adjusted by the current bias applied to the SQUID and can be varied continuously from positive to negative values, allowing cancellation of the direct mutual inductance between the qubits. We show that this variable coupling scheme permits efficient realization of universal quantum logic. The same SQUID can be used to determine the flux states of the qubits.Comment: 4 pages, 4 figure

Turbulent states in plane Couette flow with rotation

Shearing and rotational forces in fluids can significantly alter the transport of momentum.A numerical investigation was undertaken to study the role of these forces using plane Couette flow subject to rotation about an axis perpendicular to both wall-normal and streamwise directions. Using a set of progressively higher Reynolds numbers up to Re = 5200, we find that the torque for a given Re is a non-monotonic function of rotation number, Ro. For low-to-moderate turbulent Reynolds numbers we find a maximum that is associated with flow fields that are dominated by downstream vortices and calculations of 2-d vortices capture the maximum also quantitatively. For higher shear Reynolds numbers a second stronger maximum emerges at smaller rotation numbers, closer to non-rotating plane Couette flow. It is carried by flows with a markedly 3-d structure and cannot be captured by 2-d vortex studies. As the Reynolds number increases, this maximum becomes stronger and eventually overtakes the one associated with the 2-d flow state.Comment: 15 pages, 10 figure

Early myocardial oedema can predict subsequent cardiomyopathy in high-dose anthracycline therapy

AIMS: This study aims to assess subclinical changes in functional and morphologic myocardial MR parameters very early into a repetitive high-dose anthracycline treatment (planned cumulative dose >650 mg/m(2)), which may predict subsequent development of anthracycline-induced cardiomyopathy (aCMP). METHODS: Thirty sarcoma patients with previous exposition of 300-360 mg/m(2) doxorubicin-equivalent chemotherapy who were planned for a second treatment of anthracycline-based chemotherapy (360 mg/m(2) doxorubicin-equivalent) were recruited. Enrolled individuals received three CMR studies (before treatment, 48 h after first anthracycline treatment and upon completion of treatment). Native T1 mapping (MOLLI 5s(3s)3s), T2 mapping, and extracellular volume (ECV) maps were acquired in addition to a conventional CMR with SSFP-cine imaging at 1.5 T. Patients were given 0.2 mmol/kg gadoteridol for ECV quantification and LGE imaging. Blood samples for cardiac biomarkers were obtained before each scan. Development of relevant aCMP was defined as drop of left ventricular ejection fraction (LVEF) by >10% compared with baseline. RESULTS: Twenty-three complete datasets were available for analysis. Median treatment time was 20.7 ± 3.0 weeks. Eight patients developed aCMP with LVEF reduction >10% until end of chemotherapy. Baseline LVEF was not different between patients with and without subsequent aCMP. Patients with aCMP had decreased LV mass upon completion of therapy (99.4 ± 26.5 g vs. 90.3 ± 24.8 g; P = 0.02), whereas patients without aCMP did not show a change in LV mass (91.5 ± 20.0 g vs. 89.0 ± 23.6 g; P > 0.05). On strain analysis, GLS (-15.3 ± 1.3 vs. -13.4 ± 1.6; P = 0.02) and GCS (-16.7 ± 2.1 vs. -14.9 ± 2.6; P = 0.04) were decreased in aCMP patients upon completion of therapy, whereas non-aCMP individuals showed no change in GLS (-15.4 ± 3.3 vs. -15.4 ± 3.4; P = 0.97). When assessed 48 h after first dose of anthracyclines, patients with subsequent aCMP had significantly elevated myocardial T2 times compared with before therapy (53.0 ± 2.8 ms vs. 49.3 ± 5.2 ms, P = 0.02) than patients who did not develop aCMP (50.7 ± 5.1 ms vs. 51.1 ± 3.9 ms, P > 0.05). Native T1 times decreased at 48 h after first dose irrespective of development of subsequent aCMP (1020.2 ± 28.4 ms vs. 973.5 ± 40.3 ms). Upon completion of therapy, patients with aCMP had increased native T1 compared with baseline (1050.8 ± 17.9 ms vs. 1022.4 ± 22.0 ms; P = 0.01), whereas non-aCMP patients did not (1034.5 ± 46.6 ms vs. 1018.4 ± 29.7 ms; P = 0.15). No patient developed new myocardial scars or compact myocardial fibrosis under chemotherapy. Cardiac biomarkers were elevated independent of development of aCMP. CONCLUSIONS: With high cumulative anthracycline doses, early increase of T2 times 48 h after first treatment with anthracyclines can predict the development of subsequent aCMP after completion of chemotherapy. Early drop of native T1 times occurs irrespective of development of aCMP in high-dose anthracycline therapy

Neural network and state-space models for studying relationships among soil properties.

O estudo da relação entre as propriedades do solo é de grande importância na área agronômica objetivando um manejo racional dos recursos naturais do meio ambiente e um aumento na produtividade agrícola. Tradicionalmente este estudo tem sido realizado usando modelos de regressão estática os quais não levam em consideração a estrutura espacial envolvida. Este trabalho teve o objetivo de avaliar a relação entre uma variável de determinação mais cara e demorada (por exemplo, nitrogênio total do solo) e outras de mais barata e rápida determinação (p.e., carbono orgânico do solo, pH, etc.). Duas importantes classes de modelos (espaço de estados linear e redes neurais) são usadas para predição e comparadas aos modelos de regressão uni- e multivariados aqui usados como referência. Para tal, em uma área experimental cultivada com aveia, situada em Jaguariúna, SP (22º41? S e 47º00? W), amostras de um solo classificado como Latossolo foram coletadas na camada arável ao longo de uma transeção espacial de 194 m, eqüidistantes de 2 m. Os modelos de rede neural recorrente e de espaço de estados padrão tiveram uma melhor performance preditiva da variável nitrogênio total do solo quando comparados aos modelos de regressão padrão. Entre os modelos de regressão padrão o Autoregressivo Vetorial teve um melhor desempenho preditivo da variável nitrogênio total do solo