Thermal gradient of in-flight polymer particles during cold spraying

International audienceThe manufacture of polymer coatings via the cold-spray process remains challenging owing to the viscoelastic-viscoplastic behavior exhibited by polymers. One crucial step to improve cold-spray polymer coating is to determine the particles' thermal history during their flight from inside the nozzle to their impact on the substrate. In this study, we propose estimating the velocity and temperature of an isolated polymer particle traveling through a nozzle with a sharp change in its cross-section. The preliminary results show that the geometric discontinuity constricts the flow, thereby increasing the particle velocity. Moreover, a significant thermal gradient is expected inside the particle, which in turn leads to a gradient of mechanical properties of the polymeric particle during impact

Proton Magnetic Resonance Spectroscopy Reveals Neuroprotection by Oral Minocycline in a Nonhuman Primate Model of Accelerated NeuroAIDS

Background: Despite the advent of highly active anti-retroviral therapy (HAART), HIV-associated neurocognitive disorders continue to be a significant problem. In efforts to understand and alleviate neurocognitive deficits associated with HIV, we used an accelerated simian immunodeficiency virus (SIV) macaque model of NeuroAIDS to test whether minocycline is neuroprotective against lentiviral-induced neuronal injury. Methodology/Principal Findings: Eleven rhesus macaques were infected with SIV, depleted of CD8+ lymphocytes, and studied until eight weeks post inoculation (wpi). Seven animals received daily minocycline orally beginning at 4 wpi. Neuronal integrity was monitored in vivo by proton magnetic resonance spectroscopy and post-mortem by immunohistochemistry for synaptophysin (SYN), microtubule-associated protein 2 (MAP2), and neuronal counts. Astrogliosis and microglial activation were quantified by measuring glial fibrillary acidic protein (GFAP) and ionized calcium binding adaptor molecule 1 (IBA-1), respectively. SIV infection followed by CD8+ cell depletion induced a progressive decline in neuronal integrity evidenced by declining N-acetylaspartate/creatine (NAA/Cr), which was arrested with minocycline treatment. The recovery of this ratio was due to increases in NAA, indicating neuronal recovery, and decreases in Cr, likely reflecting downregulation of glial cell activation. SYN, MAP2, and neuronal counts were found to be higher in minocycline-treated animals compared to untreated animals while GFAP and IBA-1 expression were decreased compared to controls. CSF and plasma viral loads were lower in MN-treated animals. Conclusions/Significance: In conclusion, oral minocycline alleviates neuronal damage induced by the AIDS virus

Coexistence of site- and bond-centered electron localization in the high-pressure phase of LuF e₂O₄

International audienceMagnetic-electronic hyperfine interaction parameters of spectral components are obtained from in situ 57Fe Mössbauer spectroscopy pressure studies of the mixed-valence LuFe2O4 multiferroic, up to ∼30GPa and on recovered high-pressure phase samples. Temperature-dependent Mössbauer spectra of the low-pressure phase show that Fe2+ and Fe3+ sites are discernible, consistent with known site-centered charge order in the triangular (frustrated) Fe sublattice network. Magnetic spectra of the high-pressure phase, stabilized in a rectangular Fe sublattice network at P>8GPa, exhibit fingerprints of iron in an intermediate valence state only. Temperature-dependent resistivity pressure studies evidence thermally activated small polaron motion in the high-pressure phase. These experimental signatures, complemented by ab initio calculations of electronic structure, are considered evidence of asymmetric dimer formation Fe(2+Δ+)⇔Fe(3−Δ)+, where the minority-spin electron deconfinement coefficient is Δ=0.3−0.4. Bragg satellites discerned in electron diffraction patterns of the metastable high-pressure phase possibly stem from this admixture of site- and bond-centered localization (intermediate-state charge order) in a magnetic background. This breaks inversion symmetry and potentially renders LuFe2O4 in its high-pressure phase as a new charge order instigated (electronic) ferroelectric