72 research outputs found
Gold(I)-Catalyzed Reactivity of Furan-ynes with N-Oxides: Synthesis of Substituted Dihydropyridinones and Pyranones
[Image: see text] The reactivity of “furan-ynes” in combination with pyridine and quinoline N-oxides in the presence of a Au(I) catalyst, has been studied, enabling the synthesis of three different heterocyclic scaffolds. Selective access to two out of the three possible products, a dihydropyridinone and a furan enone, has been achieved through the fine-tuning of the reaction conditions. The reactions proceed smoothly at room temperature and open-air, and were further extended to a broad substrate scope, thus affording functionalized dihydropyridinones and pyranones
Hall Effect of La2/3(Ca,Pb)1/3MnO3 Single Crystals near the Critical Temperature
The Hall resistivity rho_{xy} of a La_{2/3}(Ca,Pb)_{1/3}MnO_3 single crystal
has been measured as a function of temperature and field. The overall behavior
is similar to that observed previously in thin-films. At 5 K, rho_{xy} is
positive and linear in field, indicating that the anomalous contribution
is negligible. However, the effective carrier density in a free electron model
is n_{eff}=2.4 holes/Mn, even larger than the 0.85-1.9 holes/Mn reported for
thin-films and far larger than the 0.33 holes/Mn expected from the doping
level. As temperature increases, a strong, negative contribution to rho_{xy}
appears, that we ascribe to R_S. Using detailed magnetization data, we separate
the ordinary (\propto B) and anomalous (\propto M) contributions. Below T_C,
R_S \propto rho_{xx}, indicating that magnetic skew scattering is the dominant
mechanism in the metallic ferromagnetic regime. At and above the
resistivity-peak temperature, we find that rho_{xy}/rho_{xx}M is a constant,
independent of temperature and field. This implies that the anomalous Hall
coefficient is proportional to the magnetoresistance. A different explanation
based on two fluid model is also presented.Comment: revtex, 11 pages, 4 figure
Chirality driven anomalous Hall effect in weak coupling regime
Anomalous Hall effect arising from non-trivial spin configuration (chirality)
is studied based on the - model. Considering a weak coupling case, the
interaction is treated perturbatively. Scattering by normal impurities is
included. Chirality is shown to drive locally Hall current and leads to overall
Hall effect if there is a finite uniform chirality. This contribution is
independent of the conventional spin-orbit contribution and shows distinct low
temperature behavior. In mesoscopic spin glasses, chirality-induced anomalous
Hall effect is expected below the spin-glass transition temperature.
Measurement of Hall coefficient would be useful in experimentally confirming
the chirality ordering
Anomalous Hall Effect in Ferromagnetic Metals: Role of Phonons at Finite Temperature
The anomalous Hall effect in a multiband tight-binding model is numerically
studied taking into account both elastic scattering by disorder and inelastic
scattering by the electron-phonon interaction. The Hall conductivity is
obtained as a function of temperature , inelastic scattering rate ,
chemical potential , and impurity concentration . We find
that the new scaling law holds over a wide range of these parameters;
, with () being the
conductivity tensor (with only elastic scattering), which corresponds to the
recent experimental observation [Phys. Rev. Lett. {\bf 103} (2009) 087206]. The
condition of this scaling is examined. Also, it is found that the intrinsic
mechanism depends on temperature under a resonance condition.Comment: 5 figure
Large Anomalous Hall effect in a silicon-based magnetic semiconductor
Magnetic semiconductors are attracting high interest because of their
potential use for spintronics, a new technology which merges electronics and
manipulation of conduction electron spins. (GaMn)As and (GaMn)N have recently
emerged as the most popular materials for this new technology. While Curie
temperatures are rising towards room temperature, these materials can only be
fabricated in thin film form, are heavily defective, and are not obviously
compatible with Si. We show here that it is productive to consider transition
metal monosilicides as potential alternatives. In particular, we report the
discovery that the bulk metallic magnets derived from doping the narrow gap
insulator FeSi with Co share the very high anomalous Hall conductance of
(GaMn)As, while displaying Curie temperatures as high as 53 K. Our work opens
up a new arena for spintronics, involving a bulk material based only on
transition metals and Si, and which we have proven to display a variety of
large magnetic field effects on easily measured electrical properties.Comment: 19 pages with 5 figure
Charge Transport in Manganites: Hopping Conduction, the Anomalous Hall Effect and Universal Scaling
The low-temperature Hall resistivity \rho_{xy} of La_{2/3}A_{1/3}MnO_3 single
crystals (where A stands for Ca, Pb and Ca, or Sr) can be separated into
Ordinary and Anomalous contributions, giving rise to Ordinary and Anomalous
Hall effects, respectively. However, no such decomposition is possible near the
Curie temperature which, in these systems, is close to metal-to-insulator
transition. Rather, for all of these compounds and to a good approximation, the
\rho_{xy} data at various temperatures and magnetic fields collapse (up to an
overall scale), on to a single function of the reduced magnetization
m=M/M_{sat}, the extremum of this function lying at m~0.4. A new mechanism for
the Anomalous Hall Effect in the inelastic hopping regime, which reproduces
these scaling curves, is identified. This mechanism, which is an extension of
Holstein's model for the Ordinary Hall effect in the hopping regime, arises
from the combined effects of the double-exchange-induced quantal phase in
triads of Mn ions and spin-orbit interactions. We identify processes that lead
to the Anomalous Hall Effect for localized carriers and, along the way, analyze
issues of quantum interference in the presence of phonon-assisted hopping. Our
results suggest that, near the ferromagnet-to-paramagnet transition, it is
appropriate to describe transport in manganites in terms of carrier hopping
between states that are localized due to combined effect of magnetic and
non-magnetic disorder. We attribute the qualitative variations in resistivity
characteristics across manganite compounds to the differing strengths of their
carrier self-trapping, and conclude that both disorder-induced localization and
self-trapping effects are important for transport.Comment: 29 pages, 20 figure
Effects of Crystal Structure and the On-Site Coulomb Interactions on the Electronic and Magnetic Structure of Pyrochlores MoO (A= Y, Gd, and Nd)
Being motivated by recent experimental studies, we investigate magnetic
structures of the Mo pyrochlores MoO (= Y, Nd, and Gd) and
their impact on the electronic properties. The latter are closely related with
the behavior of twelve Mo() bands, located near the Fermi level and
well separated from the rest of the spectrum. We use a mean-field Hartree-Fock
approach, which combines fine details of the electronic structure for these
bands, extracted from the conventional calculations in the local-density
approximation, the spin-orbit interaction, and the on-site Coulomb interactions
amongst the Mo(4d) electrons, treated in the most general rotationally
invariant form. The Coulomb repulsion U plays a very important role in the
problem, and the semi-empirical value U1.5-2.5 eV accounts simultaneously
for the metal-insulator (M-I) transition, the ferromagnetic (FM) - spin-glass
(SG) transition, and for the observed enhancement of the anomalous Hall effect
(AHE). The M-I transition is mainly controlled by . The magnetic structure
at the metallic side is nearly collinear FM, due to the double exchange
mechanism. The transition into the insulating state is accompanied by the large
canting of spin and orbital magnetic moments. The sign of exchange interactions
in the insulating state is controlled by the Mo-Mo distances. Smaller distances
favor the antiferromagnetic coupling, which preludes the SG behavior in the
frustrated pyrochlore lattice. Large AHE is expected in the nearly collinear FM
state, near the point of M-I transition, and is related with the unquenched
orbital magnetization at the Mo sites. We also predict large magneto-optical
effect in the same FM compounds.Comment: 26 pages, 17 figures (low resolution is used for Figs. 6, 8, and 9,
please contact directly if you need the originals), 1 tabl
Circulating microRNAs in sera correlate with soluble biomarkers of immune activation but do not predict mortality in ART treated individuals with HIV-1 infection: A case control study
Introduction: The use of anti-retroviral therapy (ART) has dramatically reduced HIV-1 associated morbidity and mortality. However, HIV-1 infected individuals have increased rates of morbidity and mortality compared to the non-HIV-1 infected population and this appears to be related to end-organ diseases collectively referred to as Serious Non-AIDS Events (SNAEs). Circulating miRNAs are reported as promising biomarkers for a number of human disease conditions including those that constitute SNAEs. Our study sought to investigate the potential of selected miRNAs in predicting mortality in HIV-1 infected ART treated individuals. Materials and Methods: A set of miRNAs was chosen based on published associations with human disease conditions that constitute SNAEs. This case: control study compared 126 cases (individuals who died whilst on therapy), and 247 matched controls (individuals who remained alive). Cases and controls were ART treated participants of two pivotal HIV-1 trials. The relative abundance of each miRNA in serum was measured, by RTqPCR. Associations with mortality (all-cause, cardiovascular and malignancy) were assessed by logistic regression analysis. Correlations between miRNAs and CD4+ T cell count, hs-CRP, IL-6 and D-dimer were also assessed. Results: None of the selected miRNAs was associated with all-cause, cardiovascular or malignancy mortality. The levels of three miRNAs (miRs -21, -122 and -200a) correlated with IL-6 while miR-21 also correlated with D-dimer. Additionally, the abundance of miRs -31, -150 and -223, correlated with baseline CD4+ T cell count while the same three miRNAs plus miR- 145 correlated with nadir CD4+ T cell count. Discussion: No associations with mortality were found with any circulating miRNA studied. These results cast doubt onto the effectiveness of circulating miRNA as early predictors of mortality or the major underlying diseases that contribute to mortality in participants treated for HIV-1 infection
Development and Validation of a Risk Score for Chronic Kidney Disease in HIV Infection Using Prospective Cohort Data from the D:A:D Study
Ristola M. on työryhmien DAD Study Grp ; Royal Free Hosp Clin Cohort ; INSIGHT Study Grp ; SMART Study Grp ; ESPRIT Study Grp jäsen.Background Chronic kidney disease (CKD) is a major health issue for HIV-positive individuals, associated with increased morbidity and mortality. Development and implementation of a risk score model for CKD would allow comparison of the risks and benefits of adding potentially nephrotoxic antiretrovirals to a treatment regimen and would identify those at greatest risk of CKD. The aims of this study were to develop a simple, externally validated, and widely applicable long-term risk score model for CKD in HIV-positive individuals that can guide decision making in clinical practice. Methods and Findings A total of 17,954 HIV-positive individuals from the Data Collection on Adverse Events of Anti-HIV Drugs (D:A:D) study with >= 3 estimated glomerular filtration rate (eGFR) values after 1 January 2004 were included. Baseline was defined as the first eGFR > 60 ml/min/1.73 m2 after 1 January 2004; individuals with exposure to tenofovir, atazanavir, atazanavir/ritonavir, lopinavir/ritonavir, other boosted protease inhibitors before baseline were excluded. CKD was defined as confirmed (>3 mo apart) eGFR In the D:A:D study, 641 individuals developed CKD during 103,185 person-years of follow-up (PYFU; incidence 6.2/1,000 PYFU, 95% CI 5.7-6.7; median follow-up 6.1 y, range 0.3-9.1 y). Older age, intravenous drug use, hepatitis C coinfection, lower baseline eGFR, female gender, lower CD4 count nadir, hypertension, diabetes, and cardiovascular disease (CVD) predicted CKD. The adjusted incidence rate ratios of these nine categorical variables were scaled and summed to create the risk score. The median risk score at baseline was -2 (interquartile range -4 to 2). There was a 1: 393 chance of developing CKD in the next 5 y in the low risk group (risk score = 5, 505 events), respectively. Number needed to harm (NNTH) at 5 y when starting unboosted atazanavir or lopinavir/ritonavir among those with a low risk score was 1,702 (95% CI 1,166-3,367); NNTH was 202 (95% CI 159-278) and 21 (95% CI 19-23), respectively, for those with a medium and high risk score. NNTH was 739 (95% CI 506-1462), 88 (95% CI 69-121), and 9 (95% CI 8-10) for those with a low, medium, and high risk score, respectively, starting tenofovir, atazanavir/ritonavir, or another boosted protease inhibitor. The Royal Free Hospital Clinic Cohort included 2,548 individuals, of whom 94 individuals developed CKD (3.7%) during 18,376 PYFU (median follow-up 7.4 y, range 0.3-12.7 y). Of 2,013 individuals included from the SMART/ESPRIT control arms, 32 individuals developed CKD (1.6%) during 8,452 PYFU (median follow-up 4.1 y, range 0.6-8.1 y). External validation showed that the risk score predicted well in these cohorts. Limitations of this study included limited data on race and no information on proteinuria. Conclusions Both traditional and HIV-related risk factors were predictive of CKD. These factors were used to develop a risk score for CKD in HIV infection, externally validated, that has direct clinical relevance for patients and clinicians to weigh the benefits of certain antiretrovirals against the risk of CKD and to identify those at greatest risk of CKD.Peer reviewe
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