[en] Application status of robot in nuclear power plants in some countries is summarized. The related robots include accident response robot, dismantling and cleaning robot, in-service inspection robot, special-purpose robot and so on. Finally, some key technologies such as the radiation-tolerance and reliability of the robot systems are analyzed in details. (authors)

[en] With the rapid development of nuclear power industry and improving demand for nuclear safety, the demand for developing accident response robot in nuclear power plant is increasingly urgent. Firstly, design analysis for accident response robot is taken with environmental conditions in nuclear power plant. Secondly, development for response robots after Chernobyl, JCO and Fukushima accidents are reviewed, and improvements for commercial mobile robot for use in radioactive environments are summarized. Finally, some key technologies including radiation-tolerance and system reliability are analyzed in details. (authors)

[en] In order to obtain the optimum conditions of LiF-NaF-KF (FLiNaK) molten salt decontaminating by combination of ultrasonic and chemical method, response surface methodology and Box-Behnken design (BBD) are used to establish a polynomial model. The influences of different reaction temperature, ultrasonic wave power, the concentration of aluminum nitrate, and reaction time were explored. The determination coefficient (r²) and adjusted r²_adj of model are 0.9580 and 0.9159, respectively, which indicates the models has good agreements with experimental data. Results indicate that the impacts of factors on removal rate from strong to weak are reaction time, ultrasonic wave power, reaction temperature and the concentration of aluminum nitrate. The model predicts removal rate of molten salt of 99.99% with optimal condition of 60℃ of reaction temperature, 300 W of ultrasonic wave power, 0.1 mol/L of aluminum nitrate concentration and 9 min of reaction time. The experiment is carried out under the predicted optional condition, and the removal rate of 98.74% ± 1.12% (n = 3) is obtained, and the average relative errors is 1.25%. The result can give reference for the next engineering applications. (authors)

[en] With doses simulating those received by spent nuclear fuel (SNF) facilities, gamma-ray (γ-ray) irradiation experiments were conducted on hexagonal zirconium. γ-ray irradiation-induced crystalline defects were observed in the hexagonal zirconium and characterized. Monte Carlo calculations combined with Transmission Electron Microscopy characterizations revealed that the energy of primary knock-on atoms could reach the threshold energy (E_d) of zirconium atoms and result in dislocation loops within the α-zirconium grains. The influence of γ dose on dislocation loop size and number density was also evaluated. (author)

[en] We present a survey of X-ray point sources in the nearest and dynamically young galaxy cluster, Virgo, using archival Chandra observations that sample the vicinity of 80 early-type member galaxies. The X-ray source populations at the outskirts of these galaxies are of particular interest. We detect a total of 1046 point sources (excluding galactic nuclei) out to a projected galactocentric radius of ∼40 kpc and down to a limiting 0.5–8 keV luminosity of $\sim <!--\; ???\; -->2\times <!--\; ??\; -->{10}^{38}\mathrm{e}\mathrm{r}\mathrm{g}{\mathrm{s}}^{-<!--\; ???\; -->1}$. Based on the cumulative spatial and flux distributions of these sources, we statistically identify ∼120 excess sources that are not associated with the main stellar content of the individual galaxies, nor with the cosmic X-ray background. This excess is significant at a 3.5σ level, when Poisson error and cosmic variance are taken into account. On the other hand, no significant excess sources are found at the outskirts of a control sample of field galaxies, suggesting that at least some fraction of the excess sources around the Virgo galaxies are truly intracluster X-ray sources. Assisted with ground-based and HST optical imaging of Virgo, we discuss the origins of these intracluster X-ray sources, in terms of supernova-kicked low-mass X-ray binaries (LMXBs), globular clusters, LMXBs associated with the diffuse intracluster light, stripped nucleated dwarf galaxies and free-floating massive black holes.

[en] We investigate the radial color gradients of galactic disks using a sample of ∼ 20 000 face-on spiral galaxies selected from the fourth data release of the Sloan Digital Sky Survey (SDSS-DR4). We combine galaxies with similar concentrations, sizes and luminosities to construct composite galaxies, and then measure their color profiles by stacking the azimuthally averaged radial color profiles of all the member galaxies. Except for the smallest galaxies (R₅₀ < 3 kpc), almost all galaxies show negative disk color gradients with mean g - r gradient G_gr = -0.006 mag kpc^-1 and r - z gradient G_rz = -0.018 mag kpc^-1. The disk color gradients are independent of the morphological types of galaxies and strongly dependent on the disk surface brightness μ_d, with lower surface brightness galactic disks having steeper color gradients. We quantify the intrinsic correlation between color gradients and surface brightness as G_gr = -0.011 μ_d + 0.233 and G_rz = -0.015 μ_d + 0.324. These quantified correlations provide tight observational constraints on the formation and evolution models of spiral galaxies.

[en] It is believed that massive galaxies have quenched their star formation because of active galactic nucleus feedback. However, recent studies have shown that some massive galaxies are still forming stars. We analyze the morphology of star formation regions for galaxies of stellar masses larger than 10^11.3 M _⊙ at around redshift z _r = 0.5 using u − z color images. We find that about 20% of the massive galaxies are star-forming (SF) galaxies, and most of them (∼85%) have asymmetric structures induced by recent mergers. Moreover, for these asymmetric galaxies, we find that the asymmetry of the SF regions becomes larger for bluer galaxies. Using the Illustris simulation, we can qualitatively reproduce the observed relation between asymmetry parameter and color. Furthermore, using the merger trees in the simulation, we find a correlation between the color of the main branch galaxies at z _r = 0.5 and the sum of the star formation rates of the recently accreted galaxies, which implies that star formation of the accreted galaxies has contributed to the observed star formation of the massive (host) galaxies (ex situ star formation). Furthermore, we find two blue and symmetric galaxies, candidates for massive blue disks, in our observed sample, which indicates that about ∼10% of massive SF galaxies are forming stars in the normal mode of disk star formation (in situ star formation). With the simulation, we find that the disk galaxies at z _r ≈ 0.5 should have experienced few major mergers during the last 4.3 Gyr.

[en] With the intent of correctly restoring the redshifted 21 cm signals emitted by neutral hydrogen during the cosmic reionization processes, we re-examine the separation approaches based on the quadratic polynomial fitting technique in frequency space in order to investigate whether they work satisfactorily with complex foreground by quantitatively evaluating the quality of restored 21 cm signals in terms of sample statistics. We construct the foreground model to characterize both spatial and spectral substructures of the real sky, and use it to simulate the observed radio spectra. By comparing between different separation approaches through statistical analysis of restored 21 cm spectra and corresponding power spectra, as well as their constraints on the mean halo bias b and average ionization fraction x_e of the reionization processes, at z = 8 and the noise level of 60 mK we find that although the complex foreground can be well approximated with quadratic polynomial expansion, a significant part of the Mpc-scale components of the 21 cm signals (75% for ∼> 6 h ^–1 Mpc scales and 34% for ∼> 1 h ^–1 Mpc scales) is lost because it tends to be misidentified as part of the foreground when the single-narrow-segment separation approach is applied. The best restoration of the 21 cm signals and the tightest determination of b and x_e can be obtained with the three-narrow-segment fitting technique as proposed in this paper. Similar results can be obtained at other redshifts.

[en] Low cycle fatigue (LCF) tests, with the total strain amplitude (ΔƐt/2) in the range of ± (0.5–3.0%), were employed at room temperature on Zircaloy-4 (Zr-4) alloy with recrystallized microstructure, aiming to investigate its fatigue life, fatigue crack initiation and propagation mechanisms. Results indicated that the fatigue behavior of Zr-4 alloy followed Coffin-Mason relation with fatigue ductility exponent of 0.2426. Fractographic investigation of all mechanically tested specimens revealed that the fatigue specimen surface is the preferential crack initiation place. SEM observation on the crack propagation regions of fatigue specimens showed that a large number of fatigue striations distributed in the crack propagation regions. Further detailed investigation revealed that micro-crack growth rates can be quantitatively evaluated in terms of strain amplitude.

[en] We use the largest homogeneous sample of globular clusters (GCs), drawn from the ACS Virgo Cluster Survey (ACSVCS) and ACS Fornax Cluster Survey (ACSFCS), to investigate the color gradients of GC systems in 76 early-type galaxies. We find that most GC systems possess an obvious negative gradient in (g-z) color with radius (bluer outward), which is consistent with previous work. For GC systems displaying color bimodality, both metal-rich and metal-poor GC subpopulations present shallower but significant color gradients on average, and the mean color gradients of these two subpopulations are of roughly equal strength. The field of view of ACS mainly restricts us to measuring the inner gradients of the studied GC systems. These gradients, however, can introduce an aperture bias when measuring the mean colors of GC subpopulations from relatively narrow central pointings. Inferred corrections to previous work imply a reduced significance for the relation between the mean color of metal-poor GCs and their host galaxy luminosity. The GC color gradients also show a dependence with host galaxy mass where the gradients are weakest at the ends of the mass spectrum-in massive galaxies and dwarf galaxies-and strongest in galaxies of intermediate mass, around a stellar mass of M_*∼10¹⁰ M_sun. We also measure color gradients for field stars in the host galaxies. We find that GC color gradients are systematically steeper than field star color gradients, but the shape of the gradient-mass relation is the same for both. If gradients are caused by rapid dissipational collapse and weakened by merging, these color gradients support a picture where the inner GC systems of most intermediate-mass and massive galaxies formed early and rapidly with the most massive galaxies having experienced greater merging. The lack of strong gradients in the GC systems of dwarfs, which probably have not experienced many recent major mergers, suggests that low-mass halos were inefficient at retaining and mixing metals during the epoch of GC formation.