262,578 research outputs found

    Coordination-driven magnetic-to-nonmagnetic transition in manganese doped silicon clusters

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    The interaction of a single manganese impurity with silicon is analyzed in a combined experimental and theoretical study of the electronic, magnetic, and structural properties of manganese-doped silicon clusters. The structural transition from exohedral to endohedral doping coincides with a quenching of high-spin states. For all geometric structures investigated, we find a similar dependence of the magnetic moment on the manganese coordination number and nearest neighbor distance. This observation can be generalized to manganese point defects in bulk silicon, whose magnetic moments fall within the observed magnetic-to-nonmagnetic transition, and which therefore react very sensitively to changes in the local geometry. The results indicate that high spin states in manganese-doped silicon could be stabilized by an appropriate lattice expansion

    A Mechanism for Photoinduced Effects In Tetracyanoethylene-Based Organic Magnets

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    The photoinduced magnetism in manganese-tetracyanoethylene (Mn-TCNE) molecule-based magnets is ascribed to charge-transfer excitations from manganese to TCNE. Charge-transfer energies are calculated using Density Functional Theory; photoinduced magnetization is described using a model Hamiltonian based on a double-exchange mechanism. Photoexciting electrons from the manganese core spin into the lowest unoccupied orbital of TCNE with photon energies around 3 eV increases the magnetization through a reduction of the canting angle of the manganese core spins for an average electron density on TCNE less than one. When photoexciting with a smaller energy, divalent TCNE molecules are formed. The delocalization of the excited electron causes a local spin flip of a manganese core spin.Comment: 4 pages, 4 figure

    Complete Offloading Cushion for Wheelchair Bound Patients

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    Mobility compromised patients are at risk of developing pressure ulcers due to non-ideal interactions with the surfaces they are resting upon. This project aims to mitigate the onset and development of pressure ulcers in wheelchair bound patients. A cushion capable of controlling surface pressure was developed. The cushion detects local pressure magnitude through pressure sensors distributed on its surface and inflates/deflates to alleviate damaging levels of pressure to the patient’s skin. Pressure exerted on the body should be no more than 80 mmHg. Foam was chosen to reduce friction. A micro air-pump was chosen to distribute air into and inflatable bladder altering its volume, this in return impacts the surface pressure. A custom program and circuit controls all elements of the system. By controlling the effect of shear and pressure on patients’ skin we will be able to reduce damaging effects and the risk of pressure ulcer development

    Study of high performance alloy electroforming

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    Nickel-manganese electroformed specimens and nickel-cobalt-manganese samples were heat treated at 343 C (650 F) for comparison of room temperature ductility with that observed for alloys heat treated at 315.6C (600 F). All heat treatments were for 24 hours. This heat treatment temperature increase generally did not result in significant improvements in ductility. However, increases in yield strength - with slight decreases in tensile strengths - were noted for the nickel-manganese and nickel-cobalt-manganese alloys. For the case of employing fairly high manganese contents in the electrolyte and countering ensuing high tensile stress in the alloy by saccharin additions to the bath, it was noted that nickel-manganese alloys with over 0.4% by weight manganese retained high ultimate and yield strengths after the 343 C (650 F) heat treatment for 24 hours. Elongations were still lower than desired. For alloys with less than 0.4% by weight manganese this heat treatment provided excellent ductility, but very significant reductions in ultimate and yield strengths were noted

    Treading in Mortimer's footsteps: the geochemical cycling of iron and manganese in Esthwaite water

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    A study of the geochemical cycling of iron and manganese in a seasonally stratified lake, Esthwaite water is described. This work is based on speculative ideas on environmental redox chemistry of iron which were proposed by C.H. Mortimer in the 1940's. These observations have been verified and some speculations confirmed, along with a new understanding of the manganese cycle, and detailed information on the particulate forms of both iron and manganese. Details on the mechanisms and transformations of iron have also emerged

    Manganese abundances in mercury-manganese stars

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    We use exact curve-of-growth analysis and spectral synthesis to deduce the abundance of Mn from high signal-to-noise ratio visible-region echelle spectra of selected Mn i and MnII lines in 24 HgMn stars. The results are compared with the Mn abundances derived from UV resonance lines by Smith & Dworetsky. We find excellent agreement for several unblended Mn lines and confirm the temperature dependence of the Mn abundance found by Smith & Dworetsky. The MnII lines at λλ 4206 and 4326 are much stronger than one would predict from the mean Mn abundances. The lack of agreement is greatest for stars with the strongest MnII lines. Using ad hoc multicomponent fits to the profiles of sharp-lined stars, we show that most of the discrepancies can be explained by hyperfine structure that desaturates the lines, with full widths of the order of 0.06--0.09 Å

    High-field (high-frequency) EPR spectroscopy and structural characterization of a novel manganese(III) corrole

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    The X-ray structure, magnetic susceptibility, and high-field (high-frequency) EPR spectrum of manganese 5,10,15-tris(pentafluorophenyl) corrole unambiguously establish that the complex contains an isolated, slightly rhombic, manganese(III) center

    Manganese-56 coincidence-counting facility precisely measures neutron-source strength

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    Precise measurement of neutron-source strength is provided by a manganese 56 coincidence-counting facility using the manganese-bath technique. This facility combines nuclear instrumentation with coincidence-counting techniques to handle a wide variety of radioisotope-counting requirements

    Ab initio molecular dynamics study of manganese porphine hydration and interaction with nitric oxide

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    The authors use ab initio molecular dynamics and the density functional theory+U (DFT+U) method to compute the hydration environment of the manganese ion in manganese (II) and manganese (III) porphines (MnP) dispersed in liquid water. These are intended as simple models for more complex water soluble porphyrins, which have important physiological and electrochemical applications. The manganese ion in Mn(II)P exhibits significant out-of-porphine plane displacement and binds strongly to a single H2O molecule in liquid water. The Mn in Mn(III)P is on average coplanar with the porphine plane and forms a stable complex with two H2O molecules. The residence times of these water molecules exceed 15 ps. The DFT+U method correctly predicts that water displaces NO from Mn(III)P-NO, but yields an ambiguous spin state for the MnP(II)-NO complex.Comment: 10 pages, 6 figure

    Weld microfissuring in Inconel 718 minimized by minor elements

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    Manganese, silicon, and magnesium markedly reduce the tendency of Inconel 718 to weld microfissuring. By combining a manganese, 0.20 percent by content, with silicon, greater than 0.25 percent content, or by adding 20 ppm of magnesium, the weld microfissuring decreased in the standard alloy
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