Effects of environment on microhardness of magnesium oxide

Micro-Vickers hardness measurements of magnesium oxide single crystals were conducted in various environments. These environments included air, nitrogen gas, water, mineral oil with or without various additives, and aqueous solutions with various pH values. Indentations were made on the (100) plane with the diagonals of the indentation in the (100) direction. The results indicate that a sulfur containing additve in mineral oil increased hardness, a chlorine containing additive in mineral oil decreased hardness, and aqueous solutions of hydrogen chloride decreased hardness. Other environments were found to have little effect on hardness. Mechanically polished surfaces showed larger indentation creep than did as-cleaved surfaces

Influence of corrosive solutions on microhardness and chemistry of magnesium oxide /001/ surfaces

X-ray photoelectron spectroscopy analyses and hardness experiments were conducted on cleaved magnesium oxide /001/ surfaces. The magnesium oxide bulk crystals were cleaved to specimen size along the /001/ surface, and indentations were made on the cleaved surface in corrosive solutions containing HCl, NaOH, or HNO3 and in water without exposing the specimen to any other environment. The results indicated that chloride (such as MgCl2) and sodium films are formed on the magnesium oxide surface as a result of interactions between an HCl-containing solution and a cleaved magnesium oxide surface. The chloride films soften the magnesium oxide surface. In this case microhardness is strongly influenced by the pH value of the solution. The lower the pH, the lower the microhardness. Sodium films, which are formed on the magnesium oxide surface exposed to an NaOH containing solution, do not soften the magnesium oxide surface

Surface effects of corrosive media on hardness, friction, and wear of materials

Hardness, friction, and wear experiments were conducted with magnesium oxide exposed to various corrosive media and also with elemental iron and nickel exposed to water and NaOH. Chlorides such as MgCl2 and sodium containing films were formed on cleaved magnesium oxide surfaces. The MgCl2 films softened the magnesium oxide surfaces and caused high friction and great deformation. Hardness was strongly influenced by the pH value of the HCl-containing solution. The lower the pH, the lower the microhardness. Neither the pH value of nor the immersion time in NaOH containing, NaCl containing, and HNO3 containing solutions influenced the microhardness of magnesium oxide. NaOH formed a protective and low friction film on iron surfaces. The coefficient of friction and the wear for iron were low at concentrations of NaOH higher than 0.01 N. An increase in NaOH concentration resulted in a decrease in the concentration of ferric oxide on the iron surface. It took less NaOH to form a protective, low friction film on nickel than on iron

Spatially Resolved Spectroscopy of Passive Spiral Galaxies

Passive spiral galaxies, despite their spiral morphological appearance, do not have any emission lines indicative of ongoing star formation in their optical spectra. Previous studies have suggested that passive spiral galaxies preferentially exist in infall regions of galaxy clusters, suggesting that the cluster environment is likely to be responsible for creating these galaxies. By carrying out spatially resolved long-slit spectroscopy on four nearby passive spiral galaxies with the Apache Point Observatory 3.5-m telescope, we investigated the stellar populations of passive spiral galaxies separately for their inner and outer regions. In the two unambiguously passive spiral galaxies among the four observed galaxies, H$\delta$ absorption lines are more prominent in the outer regions of the galaxies, whereas the 4000-{\AA} breaks (D$_{4000}$) are strongest in the inner regions of the galaxies. A comparison with a simple stellar population model for the two passive spiral galaxies indicates that the outer regions of the galaxies tend to harbour younger populations of stars. The strong H$\delta$ absorption observed in the outer regions of the sample galaxies is consistent with that of galaxies whose star formation ceased a few Gyrs ago. Because of the large uncertainty in the absorption indices in our samples, further observations are needed in order to place constraints on the mechanisms that quench star formation in passive spiral galaxies.Comment: MNRAS,382,27

Chandra survey in the AKARI North Ecliptic Pole Deep Field. I. X-ray data, point-like source catalog, sensitivity maps, and number counts

We present data products from the 300 ks Chandra survey in the AKARI North Ecliptic Pole (NEP) deep field. This field has a unique set of 9-band infrared photometry covering 2-24 micron from the AKARI Infrared Camera, including mid-infrared (MIR) bands not covered by Spitzer. The survey is one of the deepest ever achieved at ~15 micron, and is by far the widest among those with similar depths in the MIR. This makes this field unique for the MIR-selection of AGN at z~1. We design a source detection procedure, which performs joint Maximum Likelihood PSF fits on all of our 15 mosaicked Chandra pointings covering an area of 0.34 square degree. The procedure has been highly optimized and tested by simulations. We provide a point source catalog with photometry and Bayesian-based 90 per cent confidence upper limits in the 0.5-7, 0.5-2, 2-7, 2-4, and 4-7 keV bands. The catalog contains 457 X-ray sources and the spurious fraction is estimated to be ~1.7 per cent. Sensitivity and 90 per cent confidence upper flux limits maps in all bands are provided as well. We search for optical MIR counterparts in the central 0.25 square degree, where deep Subaru Suprime-Cam multiband images exist. Among the 377 X-ray sources detected there, ~80 per cent have optical counterparts and ~60 per cent also have AKARI mid-IR counterparts. We cross-match our X-ray sources with MIR-selected AGN from Hanami et al. (2012). Around 30 per cent of all AGN that have MID-IR SEDs purely explainable by AGN activity are strong Compton-thick AGN candidates.Comment: 23 pages, 20 figures; catalogs, sensitivity maps, and upper limit flux maps are available from the VizieR Servic

Environmental dependence of 8 μm luminosity functions of galaxies at z ~ 0.8: Comparison between RXJ1716.4+6708 and the AKARI NEP-deep field

Aims. We aim to reveal environmental dependence of infrared luminosity functions (IR LFs) of galaxies at z ~ 0.8 using the AKARI satellite. AKARI’s wide field of view and unique mid-IR filters help us to construct restframe 8 μm LFs directly without relying on SED models. Methods. We construct restframe 8 μm IR LFs in the cluster region RXJ1716.4+6708 at z = 0.81, and compare them with a blank field using the AKARI north ecliptic pole deep field data at the same redshift. AKARI’s wide field of view (10' × 10') is suitable to investigate wide range of galaxy environments. AKARI’s 15 μm filter is advantageous here since it directly probes restframe 8 μm at z ~ 0.8, without relying on a large extrapolation based on a SED fit, which was the largest uncertainty in previous work. Results. We have found that cluster IR LFs at restframe 8 μm have a factor of 2.4 smaller L^∗ and a steeper faint-end slope than that of the field. Confirming this trend, we also found that faint-end slopes of the cluster LFs becomes flatter and flatter with decreasing local galaxy density. These changes in LFs cannot be explained by a simple infall of field galaxy population into a cluster. Physics that can preferentially suppress IR luminous galaxies in high density regions is required to explain the observed results

Ferromagnetic Quantum Critical Fluctuations and Anomalous Coexistence of Ferromagnetism and Superconductivity in UCoGe Revealed by Co-NMR and NQR Studies

Co nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) studies were performed in the recently discovered UCoGe, in which the ferromagnetic and superconducting (SC) transitions were reported to occur at $T_{\rm Curie} \sim 3$ K and $T_S \sim 0.8$ K (N. T. Huy {\it et al.}, Phys. Rev. Lett. {\bf 99} (2007) 067006), in order to investigate the coexistence of ferromagnetism and superconductivity as well as the normal-state and SC properties from a microscopic point of view. From the nuclear spin-lattice relaxation rate $1/T_1$ and Knight-shift measurements, we confirmed that ferromagnetic fluctuations which possess a quantum critical character are present above $T_{\rm Curie}$ and the occurrence of ferromagnetic transition at 2.5 K in our polycrystalline sample. The magnetic fluctuations in the normal state show that UCoGe is an itinerant ferromagnet similar to ZrZn$_2$ and YCo$_2$. The onset SC transition was identified at $T_S \sim 0.7$ K, below which $1/T_1$ of 30 % of the volume fraction starts to decrease due to the opening of the SC gap. This component of $1/T_1$, which follows a $T^3$ dependence in the temperature range of $0.3 - 0.1$ K, coexists with the magnetic components of $1/T_1$ showing a $\sqrt{T}$ dependence below $T_S$. From the NQR measurements in the SC state, we suggest that the self-induced vortex state is realized in UCoGe.Comment: 5 pages, 7 figures. submitted to J. Phys. Soc. Jpn. To appear in J. Phys. Soc. Jp

Searches for New Milky Way Satellites from the First Two Years of Data of the Subaru/Hyper Suprime-Cam Survey: Discovery of Cetus~III

We present the results from a search for new Milky Way (MW) satellites from the first two years of data from the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP) $\sim 300$~deg$^2$ and report the discovery of a highly compelling ultra-faint dwarf galaxy candidate in Cetus. This is the second ultra-faint dwarf we have discovered after Virgo~I reported in our previous paper. This satellite, Cetus~III, has been identified as a statistically significant (10.7$\sigma$) spatial overdensity of star-like objects, which are selected from a relevant isochrone filter designed for a metal-poor and old stellar population. This stellar system is located at a heliocentric distance of 251$^{+24}_{-11}$~kpc with a most likely absolute magnitude of $M_V = -2.4 \pm 0.6$~mag estimated from a Monte Carlo analysis. Cetus~III is extended with a half-light radius of $r_h = 90^{+42}_{-17}$~pc, suggesting that this is a faint dwarf satellite in the MW located beyond the detection limit of the Sloan Digital Sky Survey. Further spectroscopic studies are needed to assess the nature of this stellar system. We also revisit and update the parameters for Virgo~I finding $M_V = -0.33^{+0.75}_{-0.87}$~mag and $r_h = 47^{+19}_{-13}$~pc. Using simulations of $\Lambda$-dominated cold dark matter models, we predict that we should find one or two new MW satellites from $\sim 300$~deg$^2$ HSC-SSP data, in rough agreement with the discovery rate so far. The further survey and completion of HSC-SSP over $\sim 1,400$~deg$^2$ will provide robust insights into the missing satellites problem.Comment: 12 pages, 12 figures, accepted for publication in PASJ special issu

The Infrared Camera (IRC) for AKARI - Design and Imaging Performance

The Infrared Camera (IRC) is one of two focal-plane instruments on the AKARI satellite. It is designed for wide-field deep imaging and low-resolution spectroscopy in the near- to mid-infrared (1.8--26.5um) in the pointed observation mode of AKARI. IRC is also operated in the survey mode to make an all-sky survey at 9 and 18um. It comprises three channels. The NIR channel (1.8--5.5um) employs a 512 x 412 InSb array, whereas both the MIR-S (4.6--13.4um) and MIR-L (12.6--26.5um) channels use 256 x 256 Si:As impurity band conduction arrays. Each of the three channels has a field-of-view of about 10' x 10' and are operated simultaneously. The NIR and MIR-S share the same field-of-view by virtue of a beam splitter. The MIR-L observes the sky about $25' away from the NIR/MIR-S field-of-view. IRC gives us deep insights into the formation and evolution of galaxies, the evolution of planetary disks, the process of star-formation, the properties of interstellar matter under various physical conditions, and the nature and evolution of solar system objects. The in-flight performance of IRC has been confirmed to be in agreement with the pre-flight expectation. This paper summarizes the design and the in-flight operation and imaging performance of IRC.Comment: Publications of the Astronomical Society of Japan, in pres