1,123 research outputs found
Modified Fowler-Nordheim Field-Emission Formulae from a Nonplanar-Emitter Model
Field emission formulae, current-voltage characteristics and energy
distribution of emitted electrons, are derived analytically for a nonplanar
(hyperboloidal) metallic emitter model. The traditional Fowler-Nordheim
formulae, which are derived from a planar emitter model, are modified, and the
assumption of the planar emitter in the F-N model is reconsidered. Our
analytical calculation also reveals the backgrounds of the previous numerical
discussion by He et al. on the effect of the geometry of emitter on field
emission. The new formulae contain a parameter which characterizes the
sharpness of the hyperboloidal emitter, and experimental data of field
emissions from clean tungsten emitters and nanotip emitters are analyzed by
making use of this feature.Comment: 9 pages, 8 figure
Hidden orders in amorphous structures: extraction of nearest neighbor networks of amorphous Nd-Fe alloys with Gabriel graph analyses
Using the scheme of Delaunay and Gabriel graphs, we analyzed the amorphous
structures of computationally created Nd-Fe alloys for several composition
ratios based on melt quench simulations with finite temperature
first-principles molecular dynamics.By the comparison of the radial
distribution functions of the whole system and those derived from the Delaunay
and Gabriel graphs, it was shown that the Gabriel graphs represent the first
nearest neighbor networks well in the examined amorphous systems. From the
Gabriel graph analyses, we examined the coordination structures of amorphous
Nd-Fe alloys statistically. We found that the ranges of distributions of
coordination numbers vary depending on the composition ratio. The angular
distributions among three adjacent atoms were also analyzed, and it was found
that the angular distributions behave differently in the Nd-rich and Fe-rich
samples. We found that the orders in the amorphous system becomes stronger as
increasing the Nd ratio, which corresponds to the appearance of crystalline
grain boundary phases at high Nd composition ratio [T. T. Sasaki et al., Acta
Mater. 115, 269-277 (2016)].Comment: 9 pages, 9 figure
Induction of cytolytic activity and interferon-gamma production in murine natural killer cells by polymyxins B and E
Natural killer (NK) cells are the primary effector cells of the innate immune system and have well-established roles in tumor rejection and resistance to viruses, bacteria and certain parasites. There is a need for more specific immune modulators of NK cell activity that tack the wide-ranging side effects of NK cell-stimulatory interleukins. The polycationic antibiotic polymyxin B (PMB) has been shown to have a unique ability to enhance activities of some immune cells, independent of its antibiotic properties. Here we report that both PMB and its analog potymyxin E (PME) markedly enhanced the activity of NK cells enriched from the murine spleen. Maximal activation of NK cell activity was obtained after 24 h of incubation with PMB at a dose of 300 mu g/ml. PMB nonapeptide, one of the two PMB domains, and PME methanesulfonate, the negatively charged derivative of PME, had little effect on NK cell activity. PMB induced interferon (IFN)-gamma and tumor necrosis factor-a production in NK cells. Proliferation of NK cells in vitro was significantly stimulated by being incubated with PMB. Administration of PMB to mice for 7 consecutive days stimulated splenic NK cell activity and increased NK cell populations in the spleen. These results suggest that the polycationic antibiotics PMB and PME may up-regulate innate and adaptive immune responses by induction of NK cell activity and IFN-gamma production.</p
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