115 research outputs found
Magnetic non-destructive materials characterization of non-ferromagnetic materials using magnetic susceptibility
International audienceAll materials interact with an external magnetic field to some extent quantified by the magnetic susceptibility χ . There is a correlation between local χ value and local anomalies of material composition, deformation and stress, which makes it interesting to explore related sensor principles with a potential for NDT application. This contribution however concerns a modification over the magnetic force based sensor for laterally resolved susceptibility measurement and demonstrates the possible range of NDT applications on different non-ferromagnetic material samples. This sensor however eliminates the use of cantilever to avoid possible vibrations in the industrial environment
Monte Carlo studies of skyrmion stabilization under geometric confinement and uniaxial strain
Geometric confinement (GC) of skyrmions in nanodomains plays a crucial role
in skyrmion stabilization. This confinement effect decreases the magnetic field
necessary for skyrmion formation and is closely related to the applied
mechanical stresses. However, the mechanism of GC is unclear and remains
controversial. Here, we numerically study the effect of GC on skyrmion
stabilization and find that zero Dzyaloshinskii-Moriya interaction (DMI)
coupling constants imposed on the boundary surfaces of small thin plates cause
confinement effects, stabilizing skyrmions in the low-field region. Moreover,
the confined skyrmions are further stabilized by tensile strains parallel to
the plate, and the skyrmion phase extends to the low-temperature region. This
stabilization occurs due to the bulk anisotropic DMI coupling constant caused
by lattice deformations. Our simulation data are qualitatively consistent with
reported experimental data on skyrmion stabilization induced by tensile strains
applied to a thin plate of the chiral magnet .Comment: 33 pages, 16 figure
Characterization of the distribution of the Lly\alpha emitters in the 53W002 field at z = 2.4
We present the results of our wide-field narrow band imaging of the field
around the radio galaxy 53W002 at z = 2.390 with Subaru/Suprime-Cam. A custom
made filter NB413 centered at 4140 \AA\ with the width of 83 \AA\ is used to
observe the 31' x 24' area around the radio galaxy. We detected 204 Ly\alpha
emitters (LAEs) at z = 2.4 with a rest frame equivalent width larger than 25
\AA\ to the depth of 26 AB mag (in NB413). The entire LAE population in the
53W002 field has an average number density and distributions of equivalent
width and size that are similar to those of other fields at z ~ 2. We identify
a significant high density region (53W002F-HDR) that spreads over ~ 5' x 4'
near 53W002 where the LAE number density is nearly four times as large as the
average of the entire field. Using the probability distribution function of
density fluctuation, we evaluate the rareness probability of the 53W002F-HDR to
be 0.9^{+2.4}_{-0.62}%, which corresponds to a moderately rich structure. No
notable environmental dependency at the comoving scale of 10 Mpc is found for
the distributions of the Ly\alpha equivalent width and luminosity in the field.
We also detected 4 Ly\alpha blobs (LABs), one of which is newly discovered.
They are all found to be located in the rims of high density regions. The
biased location and unique morphologies in Ly\alpha suggest that galaxy
interaction play a key role in their formation.Comment: 26 pages, 12 figure
White Lines and 3d-Occupancy for the 3d Transition-Metal Oxides
Electron energy-loss spectrometry was employed to measure the white lines at
the L23 absorption edges of the 3d transition-metal oxides and lithium
transition-metal oxides. The white-line ratio (L3/L2) was found to increase
between d^0 and d^5 and decrease between d^5 and d^10, consistent with previous
results for the transition metals and their oxides. The intensities of the
white lines, normalized to the post-edge background, are linear for the 3d
transition-metal oxides and lithium transition-metal oxides. An empirical
correlation between normalized white-line intensity and 3d occupancy is
established. It provides a method for measuring changes in the 3d-state
occupancy. As an example, this empirical relationship is used to measure
changes in the transition-metal valences of Li_{1-x}Ni_{0.8}Co_{0.2}O_2 in the
range of 0 < x < 0.64. In these experiments the 3d occupancy of the nickel ion
decreased upon lithium deintercalation, while the cobalt valence remained
constant.Comment: 6 pages, 7 figure
MOIRCS Deep Survey IV: Evolution of Galaxy Stellar Mass Function Back to z ~ 3
We use very deep near-infrared (NIR) imaging data obtained in MOIRCS Deep
Survey (MODS) to investigate the evolution of the galaxy stellar mass function
back to z~3. The MODS data reach J=24.2, H=23.1, K=23.1 (5sigma, Vega
magnitude) over 103 arcmin^2 (wide) and J=25.1, H=23.7, K=24.1 over 28 arcmin^2
(deep) in the GOODS-North region. The wide and very deep NIR data allow us to
measure the number density of galaxies down to low stellar mass (10^9-10^10
Msun) even at high redshift with high statistical accuracy. The normalization
of the mass function decreases with redshift and the integrated stellar mass
density becomes ~ 8-18% of the local value at z~2 and ~ 4-9% at z~3, which are
consistent with results of previous studies in general fields. Furthermore, we
found that the low-mass slope becomes steeper with redshift from alpha ~- 1.3
at z~1 to alpha ~- 1.6 at z~3, and that the evolution of the number density of
low-mass (10^9-10^10 Msun) galaxies is weaker than that of M* (~10^11 Msun)
galaxies. This indicates that the contribution of low-mass galaxies to the
total stellar mass density has been significant at high redshift. The
steepening of the low-mass slope with redshift is opposite trend expected from
the stellar mass dependence of the specific star formation rate reported in
previous studies. The present result suggests that the hierarchical merging
process overwhelmed the effect of the stellar mass growth by star formation and
was very important for the stellar mass assembly of these galaxies at 1<~z<~3.Comment: 21 pages, 18 figures, accepted for publication in Ap
MOIRCS Deep Survey. VIII. Evolution of Star Formation Activity as a Function of Stellar Mass in Galaxies since z~3
We study the evolution of star formation activity of galaxies at 0.5<z<3.5 as
a function of stellar mass, using very deep NIR data taken with Multi-Object
Infrared Camera and Spectrograph (MOIRCS) on the Subaru telescope in the
GOODS-North region. The NIR imaging data reach K ~ 23-24 Vega magnitude and
they allow us to construct a nearly stellar mass-limited sample down to ~
10^{9.5-10} Msun even at z~3. We estimated star formation rates (SFRs) of the
sample with two indicators, namely, the Spitzer/MIPS 24um flux and the
rest-frame 2800A luminosity. The SFR distribution at a fixed Mstar shifts to
higher values with increasing redshift at 0.5<z<3.5. More massive galaxies show
stronger evolution of SFR at z>~1. We found galaxies at 2.5<z<3.5 show a
bimodality in their SSFR distribution, which can be divided into two
populations by a constant SSFR of ~2 Gyr^{-1}. Galaxies in the low-SSFR group
have SSFRs of ~ 0.5-1.0 Gyr^{-1}, while the high-SSFR population shows ~10
Gyr^{-1}. The cosmic SFRD is dominated by galaxies with Mstar = 10^{10-11} Msun
at 0.5<z<3.5, while the contribution of massive galaxies with Mstar =
10^{11-11.5} Msun shows a strong evolution at z>1 and becomes significant at
z~3, especially in the case with the SFR based on MIPS 24um. In galaxies with
Mstar = 10^{10-11.5} Msun, those with a relatively narrow range of SSFR (<~1
dex) dominates the cosmic SFRD at 0.5<z<3.5. The SSFR of galaxies which
dominate the SFRD systematically increases with redshift. At 2.5<z<3.5, the
high-SSFR population, which is relatively small in number, dominates the SFRD.
Major star formation in the universe at higher redshift seems to be associated
with a more rapid growth of stellar mass of galaxies.Comment: 16 pages, 13 figures, accepted for publication in Ap
MOIRCS Deep Survey III: Active Galactic Nuclei in Massive Galaxies at z=2-4
We investigate the X-ray properties of the K-band-selected galaxies at
redshift 2 < z < 4 by using our deep near-infrared images obtained in the
MOIRCS Deep Survey project and the published Chandra X-ray source catalog. 61
X-ray sources with the 2-10 keV luminosity L_X = 10^{42}-10^{44} erg/s are
identified with the K-selected galaxies and we found that they are exclusively
(90%) associated with the massive objects with stellar mass larger than
10^{10.5} Msun. Our results are consistent with the idea that the M_BH/M_str
ratio of the galaxies at z=2-4 is similar to the present-day value. On the
other hand, the AGN detection rate among the very massive galaxies with the
stellar mass larger than 10^{11} Msun is high, 33% (26/78). They are active
objects in the sense that the black-hole mass accretion rate is ~ 1-50% of the
Eddington limit if they indeed have similar M_BH/M_str ratio with those
observed in the local universe. The active duration in the AGN duty cycle of
the high-redshift massive galaxies seems large.Comment: 33 pages, 12 figures, accepted for publication in Ap
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