The effects of simulated inflammatory conditions on the corrosion and fretting corrosion of CoCrMo alloy

In vivo corrosion of CoCrMo alloy and its potential adverse effects on the body have been recognized as major concerns in recent years. While the underlying concepts of general and mechanically-assisted corrosion have been well documented, recent report of inflammatory cell-induced corrosion (ICIC) of CoCrMo alloy challenged traditional understanding of the relationship between biology and corrosion of hip implants. To better understand the role biology may play in the corrosion of CoCrMo-based implants, this study explored the mechanism of ICIC on CoCrMo alloy and investigated how simulated inflammatory (SI) conditions affected the electrochemistry, oxide film and fretting corrosion behavior of CoCrMo alloy. A range of SI solutions, based on phosphate buffered saline with H2O2, HCl, HClO and Fe3+ additions, were investigated. Results of electrochemistry tests (open circuit potential, polarization and electrochemistry impedance spectroscopy) indicated the corrosion susceptibility of CoCrMo alloy can be significantly increased by SI solutions, increasing the oxidizing power and decreasing the passivity of the oxide film. Physiologically possible potential of CoCrMo alloy has been found to be as positive as 0.9 V, a much higher level than previously thought. Inflammatory cell-based chemicals such as H2O2, HClO, acid and Fenton reaction (H2O2 and Fe3+) were able to facilitate the corrosion of CoCrMo alloy and demonstrated part of the mechanism of inflammatory cell induced corrosion. The effect of inflammatory species hydrogen peroxide and voltage on the passive oxide film of CoCrMo alloy was studied by Electrochemical Atomic Force Microscopy (ECAFM). The results showed that simulated inflammatory condition (H2O2) and potential significantly altered oxide film behavior (surface roughness, topography, corrosion resistance). Variation of surface roughness, corrosion resistance were related with potential and time-dependent oxide film topography. Fretting corrosion behavior of CoCrMo/CoCrMo alloy combinations was significantly affected by SI conditions and potential. Presence of Fenton reaction resulted in less stable oxide film and increased oxidizing ability of solution, altering the fretting corrosion behavior of CoCrMo alloy. Additionally, a fundamental study was conducted to investigate the effect of electrode area on the cathodic voltage excursion of metallic biomaterials due to fretting corrosion. This work linked the area-dependent impedance characteristics to the time dependent voltage changes observed during fretting corrosion. Results showed that voltage shifts decreased as the exposed area increased and that this behavior was described well using the impedance-based theory model

Unveiling hidden stellar aggregates in the Milky Way: 1656 new star clusters found in Gaia EDR3

We report 1,656 new star clusters found in the Galactic disk (|b|<20 degrees) beyond 1.2 kpc, using Gaia EDR3 data. Based on an unsupervised machine learning algorithm, DBSCAN, and followed our previous studies, we utilized a unique method to do the data preparation and obtained the clustering coefficients, which proved to be an effective way to search blindly for star clusters. We tabulated the physical parameters and member stars of the new clusters, and presented some interesting examples, including a globular cluster candidate. The cluster parameters and member stars are available at CDS via anonymous ftp to https://cdsarc.cds.unistra.fr/ftp/vizier.submit//he22c. We examined the new discoveries and discussed their statistical properties. The proper motion dispersions and radii of the new clusters were the same as the previously reported ones. The new star clusters beyond 1.2 kpc were older than those in the solar neighborhood, and the new objects found in the third Galactic quadrant presented the lowest line-of-sight extinctions. Combined with our previous results, the total population of new clusters detected through our method was 2,541, corresponding to 55% of all newly published clusters in the Gaia era. The number of cataloged Gaia star clusters was also increased to nearly six thousand. In the near future, it is necessary to make a unified confirmation and member star determination for all reported clusters.Comment: 16 pages, 11 figures, 3 tables with full clusters/members data link in CDS, accepted for publication in ApJ

Mechanism and Growth of Flexible ZnO Nanostructure Arrays in a Facile Controlled Way

Nanostructure arrays-based flexible devices have revolutionary impacts on the application of traditional semiconductor devices. Here, a one-step method to synthesize flexible ZnO nanostructure arrays on Zn-plated flexible substrate in Zn(NO3)2/NH3⋅H2O solution system at 70–90∘C was developed. We found out that the decomposition of Zn(OH)2 precipitations, formed in lower NH3⋅H2O concentration, in the bulk solution facilitates the formation of flower-like structure. In higher temperature, 90∘C, ZnO nanoplate arrays were synthesized by the hydrolysis of zinc hydroxide. Highly dense ZnO nanoparticale layer formed by the reaction of NH3⋅H2O with Zn plating layer in the initial self-seed process could improve the vertical alignment of the nanowires arrays. The diameter of ZnO nanowire arrays, from 200 nm to 60 nm, could be effectively controlled by changing the stability of Zn(NH3)42+ complex ions by varying the ratio of Zn(NO3)2 to NH3⋅H2O which further influence the release rate of Zn2+ ions. This is also conformed by different amounts of the Zn vacancy as determined by different UV emissions of the PL spectra in the range of 380–403 nm

Birthrates and delay times of Type Ia supernovae

Type Ia supernovae (SNe Ia) play an important role in diverse areas of astrophysics, from the chemical evolution of galaxies to observational cosmology. However, the nature of the progenitors of SNe Ia is still unclear. In this paper, according to a detailed binary population synthesis study, we obtained SN Ia birthrates and delay times from different progenitor models, and compared them with observations. We find that the Galactic SN Ia birthrate from the double-degenerate (DD) model is close to those inferred from observations, while the birthrate from the single-degenerate (SD) model accounts for only about 1/2-2/3 of the observations. If a single starburst is assumed, the distribution of the delay times of SNe Ia from the SD model is a weak bimodality, where the WD + He channel contributes to the SNe Ia with delay times shorter than 100Myr, and the WD + MS and WD + RG channels to those with age longer than 1Gyr.Comment: 11 pages, 2 figures, accepted by Science in China Series G (Dec.30, 2009

Structural factors controlling the spin-spin exchange coupling: EPR spectroscopic studies of highly asymmetric trityl-nitroxide biradicals

Highly asymmetric exchange-coupled biradicals, like the trityl-nitroxides (TN), possess particular magnetic properties opening new possibilities for their application in biophysical, physicochemical and biological studies. In the present work, we investigated the effect of the linker length on the spin-spin coupling interaction in TN biradicals using the newly synthesized biradicals CT02-GT, CT02-AT, CT02-VT and CT02-PPT as well as the previously reported biradicals TNN14 and TN1. Results show that the magnitude of the spin-spin interaction (J) can be easily tuned from ~ 4 G (conformer 1 in CT02-PPT) to over 1200 G (in TNN14) using various linkers separating the two radical moieties and with varying temperature. Computer simulation of EPR spectra was carried out to directly estimate J values of the TN biradicals. In addition to the spin-spin coupling interaction of TN biradicals, their g, hyperfine splitting and zero-field splitting interactions were explored at low temperature (220 K). Our present study clearly shows that the spin-spin interaction variation as a function of linker distance and temperature provides an effective strategy to develop new TN biradicals which can find wide applications in relevant fields