The effect of surface inorganic−organic interactions on magnetic and structural properties of iron oxide magnetic nanoparticles functionalized by lipophilic stilbene molecules has been investigated. ...The molecules have been grafted through either phosphonate or carboxylate coupling agents. Mössbauer spectra recorded at 300 and 77K suggest a global composition of Fe2.82O4 for the two types of functionalization. Complementary in-field Mössbauer and SQUID measurements have demonstrated that the nanoparticles consist in a magnetite core surrounded by an oxidized layer. The oxidized shell exhibits a spin canting in the carboxylate case leading to a decrease of the net magnetization of the oxide nanoparticle. No canting occurs in the phosphonate case, and the magnetic properties are therefore preserved. The magnetic properties thus depend on the coupling agent, e.g., surface interactions. This result is of primary importance to tune the magnetic properties of functionalized nanoparticles for biomedical and high density storage media applications.
We report a 5.4sigma detection of pulsed gamma rays from PSR B1821-24 in the globular cluster M28 using ~44 months of Fermi Large Area Telescope (LAT) data that have been reprocessed with improved ...instrument calibration constants. We constructed a phase-coherent ephemeris, with post-fit residual rms of 3 mu s, using radio data spanning ~23.2 yr, enabling measurements of the multi-wavelength light-curve properties of PSR B1821-24 at the milliperiod level. We fold RXTE observations of PSR B1821-24 from 1996 to 2007 and discuss implications on the emission zones. The gamma-ray light curve consists of two peaks separated by 0.41 + or - 0.02 in phase, with the first gamma-ray peak lagging behind the first radio peak by 0.05 + or - 0.02 in phase, consistent with the phase of giant radio pulses. We observe significant emission in the off-peak interval of PSR B1821-24 with a best-fit LAT position inconsistent with the core of M28. We do not detect significant gamma-ray pulsations at the spin or orbital periods from any other known pulsar in M28, and we place limits on the number of energetic pulsars in the cluster. The derived gamma-ray efficiency, ~2%, is typical of other gamma-ray pulsars with comparable spin-down power, suggesting that the measured spin-down rate (2.2 x 10 super(36) erg s super(-1)) is not appreciably distorted by acceleration in the cluster potential. This confirms PSR B1821-24 as the second very energetic millisecond pulsar in a globular cluster and raises the question of whether these represent a separate class of objects that only form in regions of very high stellar density.
To understand the retention of As on a natural manganese sand, the structural, textural and chemical properties of the solid were first investigated by combining scanning electron microscopy (SEM), ...transmission electron microscopy (TEM), electron-energy-loss spectroscopy (EELS), X-ray diffraction (XRD), BET N
2 gas adsorption, diffuse reflectance Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis. Manganese sand could be mainly described as a mixture of a phyllomanganate, lithiophorite (Al,Li)MnO
2(OH)
2, and pyrolusite (MnO
2). Iron particle, kaolinite and gibbsite type-phases were also observed. Particles organization led to the presence of a mesoporosity with pore diameters ranging from 100 to 200 Å and a specific surface area of 23 m
2 g
−1. Contact with an As(V) solution (0.67 mmol L
−1) led to an average fractional surface coverage of 0.4. Both As (V) and (III) were present on the surface of the sand in a 1:1 ratio. As(V) was sorbed on lithiophorite-type particles through surface complexation type reaction. As(III) was thought to result from As(V) reduction mechanism on iron particles.
The fine control of iron oxide nanocrystal sizes within the nanometre scale (diameters range from 2.5 to 14 nm) allows us to investigate accurately the size-dependence of their structural and ...magnetic properties. A study of the growth conditions of these nanocrystals obtained by thermal decomposition of an iron oleate precursor in high-boiling point solvents has been carried out. Both the type of solvent used and the ligand/precursor ratio have been systematically varied, and were found to be the key parameters to control the growth process. The lattice parameters of all the nanocrystals deduced from X-ray diffraction measurements are consistent with a structure of the type Fe3-xO4, i.e. intermediate between magnetite and maghemite, which evolves toward the maghemite structure for the smallest sizes (x=1/3). The evolution of the magnetic behavior with nanoparticle sizes emphasizes clearly the influence of the surface, especially on the saturation magnetization Ms and the magneto-crystalline anisotropy K. Dipolar interactions and thermal dependence have been also taken into account in the study on the nanoscale size-effect of magnetic properties.
Magnetite nanoparticles of 40 nm in size have been phosphated in orthophosphoric acid. Large phosphatation rates, equivalent to goethite capacity, have been pointed out, and the possibility of ...phosphatation−dephosphatation cycles has been proved. Phosphatation occurs rapidly, inhibits the dissolution of magnetite and does not modify the structure and the magnetization of magnetite. IR spectroscopy, X-ray photoelectron spectroscopy (XPS) analysis, and Mössbauer spectrometry have shown that phosphatation occurs by interaction with both positively charged groups and hydroxyl sites at the surface of magnetite and more precisely with Fe3+ in octahedral sites. The main surface species would be a protonated binuclear species and the top layer would be in the (111) plane. The chemical stability of magnetite during cycling and its magnetic macroscopic moment allowing an easy recycling are promising for technological uses.
Magnetite particles with an average size of 39 nm and good monodispersity have been synthesized by coprecipitation at 70 °C from ferrous Fe2+ and ferric Fe3+ ions by a (N(CH3)4OH) solution, followed ...by hydrothermal treatment at 250 °C. The magnetite nanoparticles before the hydrothermal step display an average size of 12 nm and are highly oxidized when they are in contact with air. Complementary microstructural and magnetic characterizations of nanoparticles after hydrothermal treatment show unambiguously that they consist of magnetite with only a slight deviation from stoichiometry (δ ≈ 0.05), leading to Fe2.95O4.
When I say … lived curriculum Khachadoorian‐Elia, Holly R.; Bush, Lynn Wein; Rider, Elizabeth A. ...
Medical education,
July 2023, 2023-07-00, 20230701, Volume:
57, Issue:
7
Journal Article
Peer reviewed
In the latest “When I Say…” the authors describe the “lived curriculum” as an evolution from the hidden curriculum through the incorporation of humanism, empathy, and the growth mindset.
We report on the optical identification of the companion star to the eclipsing millisecond pulsar (MSP) PSR J1824--2452H in the galactic globular cluster M28 (NGC 6626). This star is at only 02 from ...the nominal position of the pulsar and it shows optical variability (~0.25 mag) that nicely correlates with the pulsar orbital period. It is located on the blue side of the cluster main sequence, ~1.5 mag fainter than the turnoff point. The observed light curve shows two distinct and asymmetric minima, suggesting that the companion star is suffering tidal distortion from the pulsar. This discovery increases the number of non-degenerate MSP companions optically identified so far in globular clusters (four out of seven), suggesting that these systems could be a common outcome of the pulsar recycling process, at least in dense environments where they can be originated by exchange interactions.
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