123 research outputs found
Ferromagnetism and large negative magnetoresistance in Pb doped Bi-Sr-Co-O misfit-layer compound
Ferromagnetism and accompanying large negative magnetoresistance in
Pb-substituted Bi-Sr-Co-O misfit-layer compound are investigated in detail.
Recent structural analysis of (Bi,Pb)SrCoO, which has
been believed to be a Co analogue of
BiSrCaCuO, revealed that it has a more complex
structure including a CoO hexagonal layer [T. Yamamoto {\it et al.}, Jpn.
J. Appl. Phys. {\bf 39} (2000) L747]. Pb substitution for Bi not only
introduces holes into the conducting CoO layers but also creates a
certain amount of localized spins. Ferromagnetic transition appears at =
3.2 K with small spontaneous magnetization along the axis, and around the
transition temperature large and anisotropic negative magnetoresistance was
observed. This compound is the first example which shows ferromagnetic
long-range order in a two-dimensional metallic hexagnonal CoO layer.Comment: 8 pages including eps figures. To be published in J. Phys. Soc. Jp
Electronic and magnetic states in doped LaCoO_3
The electronic and magnetic states in doped perovskite cobaltites, (La,
Sr)CoO_3, are studied in the numerically exact diagonalization method on
Co_2O_{11} clusters. For realistic parameter values, it is shown that a high
spin state and an intermediate spin state coexist in one-hole doped clusters
due to strong p-d mixing. The magnetic states in the doped cobaltites obtained
in the calculation explain various experimental results.Comment: 4 pages, 2 figures, epsfj.st
Evidence for a Low-Spin to Intermediate-Spin State Transition in LaCoO3
We present measurements of the magnetic susceptibility and of the thermal
expansion of a LaCoO single crystal. Both quantities show a strongly
anomalous temperature dependence. Our data are consistently described in terms
of a spin-state transition of the Co ions with increasing temperature
from a low-spin ground state to an intermediate-spin state without (100K -
500K) and with (>500K) orbital degeneracy. We attribute the lack of orbital
degeneracy up to 500K to (probably local) Jahn-Teller distortions of the
CoO octahedra. A strong reduction or disappearance of the Jahn-Teller
distortions seems to arise from the insulator-to-metal transition around 500 K.Comment: an error in the scaling factor of Eq.(4) and consequently 2 values of
table I have been corrected. The conclusions of the paper remain unchanged.
See also: C. Zobel et al. Phys. Rev. B 71, 019902 (2005) and J. Baier et al.
Phys. Rev. B 71, 014443 (2005
Ferromagnetism and Superconductivity in the multi-orbital Hubbard Model: Hund's Rule Coupling versus Crystal-Field Splitting
The multi-orbital Hubbard model in one dimension is studied using the
numerical diagonalization method. Due to the effect of the crystal-field
splitting , the fully polarized ferromagnetism which is observed in the
strong coupling regime becomes unstable against the partially polarized
ferromagnetism when the Hund's rule coupling is smaller than a certain
critical value of order of . In the vicinity of the partially polarized
ferromagnetism, the orbital fluctuation develops due to the competition between
the Hund's rule coupling and the crystal-field splitting. The superconducting
phase with the Luttinger liquid parameter is observed for the
singlet ground state in this region.Comment: 4 pages,5 figures,submitted to J.Phys.Soc.Jp
Thermopower of the Correlated Narrow Gap Semiconductor FeSi and Comparison to RuSi
Iron based narrow gap semiconductors such as FeSi, FeSb2, or FeGa3 have
received a lot of attention because they exhibit a large thermopower, as well
as striking similarities to heavy fermion Kondo insulators. Many proposals have
been advanced, however, lacking quantitative methodologies applied to this
problem, a consensus remained elusive to date. Here, we employ realistic
many-body calculations to elucidate the impact of electronic correlation
effects on FeSi. Our methodology accounts for all substantial anomalies
observed in FeSi: the metallization, the lack of conservation of spectral
weight in optical spectroscopy, and the Curie susceptibility. In particular we
find a very good agreement for the anomalous thermoelectric power. Validated by
this congruence with experiment, we further discuss a new physical picture of
the microscopic nature of the insulator-to-metal crossover. Indeed, we find the
suppression of the Seebeck coefficient to be driven by correlation induced
incoherence. Finally, we compare FeSi to its iso-structural and iso-electronic
homologue RuSi, and predict that partially substituted Fe(1-x)Ru(x)Si will
exhibit an increased thermopower at intermediate temperatures.Comment: 14 pages. Proceedings of the Hvar 2011 Workshop on 'New materials for
thermoelectric applications: theory and experiment
Synchronization of multi-phase oscillators: An Axelrod-inspired model
Inspired by Axelrod's model of culture dissemination, we introduce and
analyze a model for a population of coupled oscillators where different levels
of synchronization can be assimilated to different degrees of cultural
organization. The state of each oscillator is represented by a set of phases,
and the interaction --which occurs between homologous phases-- is weighted by a
decreasing function of the distance between individual states. Both ordered
arrays and random networks are considered. We find that the transition between
synchronization and incoherent behaviour is mediated by a clustering regime
with rich organizational structure, where some of the phases of a given
oscillator can be synchronized to a certain cluster, while its other phases are
synchronized to different clusters.Comment: 6 pages, 5 figure
Monitoring Bacterial Community of Human Gut Microbiota Reveals an Increase in Lactobacillus in Obese Patients and Methanogens in Anorexic Patients
Background: Studies of the bacterial communities of the gut microbiota have revealed a shift in the ratio of Firmicutes and Bacteroidetes in obese patients. Determining the variations of microbial communities in feces may be beneficial for the identification of specific profiles in patients with abnormal weights. The roles of the archaeon Methanobrevibacter smithii and Lactobacillus species have not been described in these studies. Methods and Findings: We developed an efficient and robust real-time PCR tool that includes a plasmid-based internal control and allows for quantification of the bacterial divisions Bacteroidetes, Firmicutes, and Lactobacillus as well as the methanogen M. smithii. We applied this technique to the feces of 20 obese subjects, 9 patients with anorexia nervosa, and 20 normal-weight healthy controls. Our results confirmed a reduction in the Bacteroidetes community in obese patients (p<0.01). We found a significantly higher Lactobacillus species concentration in obese patients than in lean controls (p = 0.0197) or anorexic patients (p = 0.0332). The M. smithii concentration was much higher in anorexic patients than in the lean population (p = 0.0171). Conclusions: Lactobacillus species are widely used as growth promoters in the farm industry and are now linked to obesity in humans. The study of the bacterial flora in anorexic patients revealed an increase in M. smithii. This increase might represent an adaptive use of nutrients in this population
Differential effects of glucagon-like peptide-1 receptor agonists on heart rate
Abstract
While glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are known to increase heart rate (HR), it is insufficiently recognized that the extent varies greatly between the various agonists and is affected by the assessment methods employed. Here we review published data from 24-h time-averaged HR monitoring in healthy individuals and subjects with type 2 diabetes mellitus (T2DM) treated with either short-acting GLP-1 RAs, lixisenatide or exenatide, or long-acting GLP-1 RAs, exenatide LAR, liraglutide, albiglutide, or dulaglutide (N\ua0=\ua01112; active-treatment arms). HR effects observed in two independent head-to-head trials of lixisenatide and liraglutide (N\ua0=\ua0202; active-treatment arms) are also reviewed. Short-acting GLP-1 RAs, exenatide and lixisenatide, are associated with a transient (1\u201312\ua0h) mean placebo- and baseline-adjusted 24-h HR increase of 1\u20133\ua0beats per minute (bpm). Conversely, long-acting GLP-1 RAs are associated with more pronounced increases in mean 24-h HR; the highest seen with liraglutide and albiglutide at 6\u201310\ua0bpm compared with dulaglutide and exenatide LAR at 3\u20134\ua0bpm. For both liraglutide and dulaglutide, HR increases were recorded during both the day and at night. In two head-to-head comparisons, a small, transient mean increase in HR from baseline was observed with lixisenatide; liraglutide induced a substantially greater increase that remained significantly elevated over 24\ua0h. The underlying mechanism for increased HR remains to be elucidated; however, it could be related to a direct effect at the sinus node and/or stimulation of the sympathetic nervous system, with this effect related to the duration of action of the respective GLP-1 RAs. In conclusion, this review indicates that the effects on HR differ within the class of GLP-1 RAs: short-acting GLP-1 RAs are associated with a modest and transient HR increase before returning to baseline levels, while some long-acting GLP-1 RAs are associated with a more pronounced and sustained increase during the day and night. Findings from recently completed trials indicate that a GLP-1 RA-induced increase in HR, regardless of magnitude, does not present an increased cardiovascular risk for subjects with T2DM, although a pronounced increase in HR may be associated with adverse clinical outcomes in those with advanced heart failure
Abstracts of presentations on plant protection issues at the xth international congress of virology: August 11-16, 1996 Binyanei haOoma, Jerusalem Iarael part 3(final part)
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