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International audience; The increasing demand for sustainable tribology has accelerated the development of environmentally friendly lubrication solutions such as water or water-related lubricants. Earlier works have reported on water-lubricated sliding of silicon nitride (Si3N4) at high speeds, which can result in a superlow friction (m < 0.01) owing to the formation of hydrodynamic water films on hydrophilic surface layers. Here, combined boundary-lubrication experiments at low sliding speeds and atomistic simulations reveal an alternative superlubricity mechanism for glycerol-lubricated Si3N4. X-ray photoelectron and time-of-flight secondary ion mass spectrometry performed inside and outside the wear track as well as high-resolution mass spectroscopy of the used lubricant strongly suggest that sub-nanometer-thick graphene nitride layers form at the very top of Si3N4. In the accompanying atomistic simulations, glycerol molecules undergo tribochemical decomposition and react with surface-bound nitrogen atoms to form carbon nitrides. Further shearing promotes the formation of 2D graphene nitrides that passivate the ceramic surfaces and induce a superlow friction under boundary lubrication. Thus, glycerol-lubricated Si3N4 has a high potential for use in green superlubricity enabled by in situ synthesis of disordered graphene nitride species.

Hydration states are a crucial factor that affect the self-assembly and properties of soft materials and biomolecules. Although previous experiments have revealed that the hydration state strongly depends on the chemical structure of lipid molecules, the mechanisms at the molecular level remain unknown. Classical and density-functional tight-binding (DFTB) molecular dynamics (MD) simulations are employed to determine the mechanisms underlying dissimilar water dynamics between lipid membranes with phosphatidylcholine (PC) and phosphatidylethanolamine (PE) head groups. The classical MD simulation shows that rotational relaxations of water are faster on the PE lipid than on the PC lipid, which is consistent with a previous experimental study using terahertz spectroscopy. Furthermore, DFTB-MD simulation of N(CH3)4+ and NH4+ ions, which correspond to the different head groups in PC and PE, respectively, shows qualitative agreement with the classical MD simulation. Remarkably, the PE lipids and the NH4+ ions break hydrogen bonds between water molecules in the secondary hydration shell. In contrast, the PC lipids and the N(CH3)4+ ions bind water molecules weakly in both the primary and secondary hydration shells and increase hydrogen bonds between water. Our atomistic simulations show that these changes in the hydrogen-bond network of water molecules cause the different rotational relaxation of water molecules between the two lipids.

資料番号: SA1004856000

International audience

Angiomyolipoma (AML), a benign renal tumor, has various clinical forms, and the nature of AML is not sufficiently understood because of few reports of long-term observation. We report a 57-year-old female without tuberous sclerosis who developed multiple pulmonary AML 26 years after a right nephrectomy for renal AML. A computed tomogram demonstrated multifocal round lesions with lipid-like density throughout both lung fields. An open lung biopsy revealed a histological diagnosis of pulmonary AML. An abdominal computed tomogram was also compatible with splenic AML. She has been in good health for 12 years since the lung biopsy over the 38 years since the nephrectomy. This case suggests that multicentric AML can recur at distant organs even after long-term silence in a patient who has a past history of renal AML.

We have carried out a spectral analysis of the Suzaku X-ray data in the 0.4-12 keV range toward the shell-type very-high-energy ��-ray supernova remnant RX J1713.7-3946. The aims of this analysis are to estimate detailed X-rays spectral properties at a high angular resolution up to 2 arcmin, and to compare them with the interstellar gas. The X-ray spectrum is non-thermal and used to calculate absorbing column density, photon index, and absorption-corrected X-ray flux. The photon index varies significantly from 2.1 to 2.9. It is shown that the X-ray intensity is well correlated with the photon index, especially in the west region, with a correlation coefficient of 0.81. The X-ray intensity tends to increase with the averaged interstellar gas density while the dispersion is relatively large. The hardest spectra having the photon index less than 2.4 are found outside of the central 10 arcmin of the SNR, from the north to the southeast (~430 arcmin^2) and from the southwest to the northwest (~150 arcmin^2). The former region shows low interstellar gas density, while the latter high interstellar gas density. We present discussion for possible scenarios which explain the distribution of the photon index and its relationship with the interstellar gas., 11 pages, 9 figures, 1 table, accepted for publication in The Astrophysical Journal

第4回極域科学シンポジウム横断セッション：[IM] 中層大気・熱圏11月14日（木）〜15日（金） 国立極地研究所 2階大会議室前ラウンジ