Chlorotellurium Compounds of Aryl Ethers

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Spectroscopic Evidence for the Localization of Skyrmions near Nu=1 as T->0

Optically pumped nuclear magnetic resonance measurements of Ga-71 spectra were carried out in an n-doped GaAs/Al0.1Ga0.9As multiple quantum well sample near the integer quantum Hall ground state Nu=1. As the temperature is lowered (down to T~0.3 K), a ``tilted plateau'' emerges in the Knight shift data, which is a novel experimental signature of quasiparticle localization. The dependence of the spectra on both T and Nu suggests that the localization is a collective process. The frozen limit spectra appear to rule out a 2D lattice of conventional skyrmions.Comment: 4 pages (REVTEX), 5 eps figures embedded in text, published versio

Optically Pumped NMR Measurements of the Electron Spin Polarization in GaAs Quantum Wells near Landau Level Filling Factor nu=1/3

The Knight shift of Ga-71 nuclei is measured in two different electron-doped multiple quantum well samples using optically pumped NMR. These data are the first direct measurements of the electron spin polarization, P(nu,T)=/max, near nu=1/3. The P(T) data at nu=1/3 probe the neutral spin-flip excitations of a fractional quantum Hall ferromagnet. In addition, the saturated P(nu) drops on either side of nu=1/3, even in a Btot=12 Tesla field. The observed depolarization is quite small, consistent with an average of about 0.1 spin-flips per quasihole (or quasiparticle), a value which does not appear to be explicable by the current theoretical understanding of the FQHE near nu=1/3.Comment: 4 pages (REVTEX), 5 eps figures embedded in text; minor changes, published versio

Observation of a new phase transition between fully and partially polarized quantum Hall states with charge and spin gaps at ν=2/3\nu = 2/3

The average electron spin-polarization $\cal P$ of two-dimensional electron gas confined in $\rm GaAs/GaAlAs$ multiple quantum-wells was measured by nuclear magnetic resonance (NMR) near the fractional quantum Hall state with filling factor $\nu={2/3}$. Above this filling factor (${{2/3}} \leq \nu < 0.85$), a strong depolarization is observed corresponding to two spin flips per additional flux quantum. The most remarkable behavior of the polarization is observed at $\nu ={{2/3}}$, where a quantum phase transition from a partially polarized (${\cal P} \approx {{3/4}}$) to a fully polarized (${\cal P} = 1$) state can be driven by increasing the ratio between the Zeeman and the Coulomb energy above a critical value $\eta_{c} = \frac{\Delta_{Z}}{\Delta_{C}} = 0.0185$.Comment: 4 pages including 4 figure

NMR Determination of 2D Electron Spin Polarization at ν=1/2\nu=1/2

Using a `standard' NMR spin-echo technique we determined the spin polarization of two-dimensional electrons, confined to GaAs quantum wells, from the hyperfine shift of Ga nuclei in the wells. Concentrating on the temperature and magnetic field dependencies of spin polarization at Landau level filling factor $\nu =1/2$, we find that the results are described well by a simple model of non-interacting composite fermions, although some inconsistencies remain when the two-dimensional electron system is tilted in the magnetic field.Comment: 4 pages (REVTEX) AND 4 figures (PS

Threshold meson production and cosmic ray transport

An interesting accident of nature is that the peak of the cosmic ray spectrum, for both protons and heavier nuclei, occurs near the pion production threshold. The Boltzmann transport equation contains a term which is the cosmic ray flux multiplied by the cross section. Therefore when considering pion and kaon production from proton-proton reactions, small cross sections at low energy can be as important as larger cross sections at higher energy. This is also true for subthreshold kaon production in nuclear collisions, but not for subthreshold pion production.Comment: 9 pages, 1 figur

Comparison of cardiovascular health profiles across population surveys from five high- to low-income countries

Aims With the greatest burden of cardiovascular disease morbidity and mortality increasingly observed in lower-income countries least prepared for this epidemic, focus is widening from risk factor management alone to primordial prevention to maintain high levels of cardiovascular health (CVH) across the life course. To facilitate this, the American Heart Association (AHA) developed CVH scoring guidelines to evaluate and track CVH. We aimed to compare the prevalence and trajectories of high CVH across the life course using nationally representative adult CVH data from five diverse high- to low-income countries. Methods Surveys with CVH variables (physical activity, cigarette smoking, body mass, blood pressure, blood glucose, and total cholesterol levels) were identified in Ethiopia, Bangladesh, Brazil, England, and the United States (US). Participants were included if they were 18-69y, not pregnant, and had data for these CVH metrics. Comparable data were harmonized and each of the CVH metrics was scored using AHA guidelines as high (2), moderate (1), or low (0) to create total CVH scores with higher scores representing better CVH. High CVH prevalence by age was compared creating country CVH trajectories. Results The analysis included 28,092 adults (Ethiopia n=7686, 55.2% male; Bangladesh n=6731, 48.4% male; Brazil n=7241, 47.9 % male; England n=2691, 49.5% male, and the US n=3743, 50.3% male). As country income level increased, prevalence of high CVH decreased (>90% in Ethiopia, >68% in Bangladesh and under 65% in the remaining countries). This pattern remained using either five or all six CVH metrics and following exclusion of underweight participants. While a decline in CVH with age was observed for all countries, higher income countries showed lower prevalence of high CVH already by age 18y. Excess body weight appeared the main driver of poor CVH in higher income countries, while current smoking was highest in Bangladesh. Conclusion Harmonization of nationally representative survey data on CVH trajectories with age in 5 highly diverse countries supports our hypothesis that CVH decline with age may be universal. Interventions to promote and preserve high CVH throughout the life course are needed in all populations, tailored to country-specific time courses of the decline. In countries where CVH remains relatively high, protection of whole societies from risk factor epidemics may still be feasible.This study was funded with support from the Institute for Global Health, Northwestern University [Catalyzer Award No. 1005]; from the DSI-NRF Centre of Excellence in Human Development hosted at the University of the Witwatersrand in South Africa, and the support of the University of the Witwatersrand research office

Increased Immune-Regulatory Receptor Expression on Effector T Cells as Early Indicators of Relapse Following Autologous Stem Cell Transplantation for Multiple Myeloma

The benefit of autologous stem cell transplantation (ASCT) in newly diagnosed myeloma patients, apart from supporting high dose chemotherapy, may include effects on T cell function in the bone marrow (BM). We report our exploratory findings on marrow infiltrating T cells early post-ASCT (day+100), examining phenotype and T cell receptor (TCR) repertoire, seeking correlations with timing of relapse. Compared to healthy donors (HD), we observed an increase in regulatory T cells (CD4+FoxP3+, Tregs) with reduction in CD4 T cells, leading to lower CD4:8 ratios. Compared to paired pre-treatment marrow, both CD4 and CD8 compartments showed a reduction in naïve, and increase in effector memory subsets, suggestive of a more differentiated phenotype. This was supported by increased levels of several immune-regulatory and activation proteins (ICOS, PD-1, LAG-3, CTLA-4 and GzmB) when compared with HD. Unsupervised analysis identified a patient subgroup with shorter PFS (p=0.031) whose BM contained increased Tregs, and higher immune-regulatory markers (ICOS, PD-1, LAG-3) on effector T cells. Using single feature analysis, higher frequencies of marrow PD-1+ on CD4+FoxP3- cells and Ki67+ on CD8 cells were independently associated with early relapse. Finally, studying paired pre-treatment and post-ASCT BM (n=5), we note reduced abundance of TCR sequences at day+100, with a greater proportion of expanded sequences indicating a more focused persistent TCR repertoire. Our findings indicate that, following induction chemotherapy and ASCT, marrow T cells demonstrate increased activation and differentiation, with TCR repertoire focusing. Pending confirmation in larger series, higher levels of immune-regulatory proteins on T cell effectors at day+100 may indicate early relapse

Temperature dependence of spin polarizations at higher Landau Levels

We report our results on temperature dependence of spin polarizations at $\nu=1$ in the lowest as well as in the next higher Landau level that compare well with recent experimental results. At $\nu=3$, except having a much smaller magnitude the behavior of spin polarization is not much influenced by higher Landau levels. In sharp contrast, for filling factor $\nu=\frac83$ we predict that unlike the case of $\nu=\frac23$ the system remains fully spin polarized even at vanishingly small Zeeman energies.Comment: 4 pages, REVTEX, and 3 .ps files, To be published in Physical Review Letter