3,494 research outputs found

    Optically probing symmetry breaking in the chiral magnet Cu2OSeO3

    Get PDF
    We report on the linear optical properties of the chiral magnet Cu2OSeO3, specifically associated with the absence of inversion symmetry, the chiral crystallographic structure, and magnetic order. Through spectroscopic ellipsometry, we observe local crystal-field excitations below the charge-transfer gap. These crystal-field excitations are optically allowed due to the lack of inversion symmetry at the Cu sites. Optical polarization rotation measurements were used to study the structural chirality and magnetic order. The temperature dependence of the natural optical rotation, originating in the chiral crystal structure, provides evidence for a finite magneto-electric effect in the helimagnetic phase. We find a large magneto-optical susceptibility on the order of V(540nm)~10^4 rad/(T*m) in the helimagnetic phase and a maximum Faraday rotation of ~165deg/mm in the ferrimagnetic phase. The large value of V can be explained by considering spin cluster formation and the relative ease of domain reorientation in this metamagnetic material. The magneto-optical activity allows us to map the magnetic phase diagram, including the skyrmion lattice phase. In addition to this, we probe and discuss the nature of the various magnetic phase transitions in Cu2OSeO3.Comment: 9 pages, 10 figure

    Optimal Use of Vitamin D When Treating Osteoporosis

    Get PDF
    Inadequate serum 25-hydroxyvitamin D (25[OH]D) concentrations are associated with muscle weakness, decreased physical performance, and increased propensity in falls and fractures. This paper discusses several aspects with regard to vitamin D status and supplementation when treating patients with osteoporosis in relation to risks and prevention of falls and fractures. Based on evidence from literature, adequate supplementation with at least 700 IU of vitamin D, preferably cholecalciferol, is required for improving physical function and prevention of falls and fractures. Additional calcium supplementation may be considered when dietary calcium intake is below 700 mg/day. For optimal bone mineral density response in patients treated with antiresorptive or anabolic therapy, adequate vitamin D and calcium supplementation is also necessary. Monitoring of 25(OH)D levels during follow-up and adjustment of vitamin D supplementation should be considered to reach and maintain adequate serum 25(OH)D levels of at least 50 nmol/L, preferably greater than 75 nmol/L in all patients

    CuAu-type ordering in epitaxial CuInS<sub>2</sub> films

    Get PDF
    Ordering of Cu and In atoms in near-stoichiometric CuInS2 epitaxial films grown on Si (111) by molecular beam epitaxy was studied by transmission electron microscopy. Nonchalcopyrite ordering of the metal atoms in CuInS2 is observed, which is identified as CuAu-type ordering. Sharp spots in electron diffraction patterns reveal the ordered Cu and In atom planes alternating along the [001] direction over a long range. High-resolution electron microscopy confirms this ordering. The CuAu-ordered structure coexists with the chalcopyrite ordered structure, in agreement with theoretical prediction

    Vitamin D and Systemic Lupus Erythematosus: Bones, Muscles, and Joints

    Get PDF
    Vitamin D3, or cholecalciferol, is the naturally occurring form of vitamin D that is converted in the skin and hydroxylated in the liver and kidney to the active form found in humans. The main role for vitamin D is calcium homeostasis, and low levels of vitamin D result in lower gastrointestinal absorption of calcium. Vitamin D is also critical for mineralization of bone tissue, muscle function, and coordination. Recent studies have found prevention of bone mass loss and reduction in falls and fractures in patients supplemented with vitamin D. A high percentage of systemic lupus erythematosus patients are reported to have insufficient or deficient levels of vitamin D. This paper reviews the biology of vitamin D, its role in calcium homeostasis, and how it contributes to the maintenance of bone, muscle, and joint function in older adults and individuals with systemic lupus erythematosus

    The Physics of Crystallization from Globular Cluster White Dwarf Stars in NGC 6397

    Get PDF
    We explore the physics of crystallization in the deep interiors of white dwarf stars using the color-magnitude diagram and luminosity function constructed from proper motion cleaned Hubble Space Telescope photometry of the globular cluster NGC 6397. We demonstrate that the data are consistent with the theory of crystallization of the ions in the interior of white dwarf stars and provide the first empirical evidence that the phase transition is first order: latent heat is released in the process of crystallization as predicted by van Horn (1968). We outline how this data can be used to observationally constrain the value of Gamma = E_{Coulomb}/E_{thermal} near the onset of crystallization, the central carbon/oxygen abundance, and the importance of phase separation.Comment: 5 pages, 5 figures, accepted for publication in the Astrophysical Journal Letter

    'Exacerbation-free time' to assess the impact of exacerbations in patients with chronic obstructive pulmonary disease (COPD):a prospective observational study

    Get PDF
    COPD exacerbations are commonly quantified as rate per year. However, the total amount of time a patient suffers from exacerbations may be stronger related to his or her disease burden than just counting exacerbation episodes. In this study, we examined the relationship between exacerbation frequency and exacerbation-free time, and their associations with baseline characteristics and health-related quality of life. A total of 166 COPD patients reported symptom changes during 12 months. Symptom-defined exacerbation episodes were correlated to the number of exacerbation-free weeks per year. Analysis of covariance was used to examine the effects of baseline characteristics on annual exacerbation frequency and exacerbation-free weeks, Spearman's rank correlations to examine associations between the two methods to express exacerbations and the Chronic Respiratory Questionnaire (CRQ). The correlation between exacerbation frequency and exacerbation-free weeks was -0.71 (p < 0.001). However, among frequent exacerbators (i.e., ≥3 exacerbations/year, n = 113) the correlation was weak (r = -0.25; p < 0.01). Smokers had less exacerbation-free weeks than non-smokers (β = -5.709, p < 0.05). More exacerbation-free weeks were related to better CRQ Total (r = 0.22, p < 0.05), Mastery (r = 0.22, p < 0.05), and Fatigue (r = 0.23, p < 0.05) scores, whereas no significant associations were found between exacerbation frequency and CRQ scores. In COPD patients with frequent exacerbations, there is substantial variation in exacerbation-free time. Exacerbation-free time may better reflect the burden of exacerbations in patients with COPD than exacerbation frequency does

    In matrix derivatization combined with LC-MS/MS results in ultra-sensitive quantification of plasma free metanephrines and catecholamines

    Get PDF
    Plasma-free metanephrines and catecholamines are essential markers in the biochemical diagnosis and follow-up of neuroendocrine tumors and inborn errors of metabolism. However, their low circulating concentrations (in the nanomolar range) and poor fragmentation characteristics hinder facile simultaneous quantification by liquid chromatography and tandem mass spectrometry (LC-MS/MS). Here, we present a sensitive and simple matrix derivatization procedure using propionic anhydride that enables simultaneous quantification of unconjugated l-DOPA, catecholamines, and metanephrines in plasma by LC-MS/MS. Dilution of propionic anhydride 1:4 (v/v) in acetonitrile in combination with 50 μL of plasma resulted in the highest mass spectrometric response. In plasma, derivatization resulted in stable derivatives and increased sensitivity by a factor of 4-30 compared with a previous LC-MS/MS method for measuring plasma metanephrines in our laboratory. Furthermore, propionylation increased specificity, especially for 3-methoxytyramine, by preventing interference from antihypertensive medication (β-blockers). The method was validated according to international guidelines and correlated with a hydrophilic interaction LC-MS/MS method for measuring plasma metanephrines (R2 > 0.99) and high-performance liquid chromatography with an electrochemical detection method for measuring plasma catecholamines (R2 > 0.85). Reference intervals for l-DOPA, catecholamines, and metanephrines in n = 115 healthy individuals were established. Our work shows that analytes in the subnanomolar range in plasma can be derivatized in situ without any preceding sample extraction. The developed method shows improved sensitivity and selectivity over existing methods and enables simultaneous quantification of several classes of amines
    • …
    corecore