871 research outputs found
Detection of the onset of nanocrystallization by calorimetric and magnetic measurements
It is generally accepted that measurements of the magnetic properties are more sensitive than measurements of the enthalpy changes in the detection of the onset of crystallization of ferromagnetic phases emerging from a paramagnetic amorphous alloy. In this work, it is shown that the formation of a very fine nanocrystalline microstructure can make this assumption incorrect. Under some circumstances, the nanocrystallization onset temperature obtained from magnetic techniques is higher than the one obtained from enthalpy changes. The phenomenon is explained in terms of the superparamagnetic behavior of the uncoupled nanocrystals at the very early stages of nanocrystallizatio
Evidence for intermediate-age stellar populations in early-type galaxies from K-band spectroscopy
The study of stellar populations in early-type galaxies in different
environments is a powerful tool for constraining their star formation
histories. This study has been traditionally restricted to the optical range,
where dwarfs around the turn-off and stars at the base of the RGB dominate the
integrated light at all ages. The near-infrared spectral range is especially
interesting since in the presence of an intermediate-age population, AGB stars
are the main contributors. In this letter, we measure the near-infrared indices
NaI and D for a sample of 12 early-type galaxies in low density
environments and compare them with the Fornax galaxy sample presented by Silva
et al. (2008). The analysis of these indices in combination with Lick/IDS
indices in the optical range reveals i) the NaI index is a metallicity
indicator as good as C4668 in the optical range, and ii) D is a
tracer of intermediate-age stellar populations. We find that low-mass galaxies
in low density environments show higher NaI and D than those located
in Fornax cluster, which points towards a late stage of star formation for the
galaxies in less dense environments, in agreement with results from other
studies using independent methods.Comment: 7 pages, 3 figures, accepted for publication in ApJ
Influence of Ge addition on the magnetocaloric effect of a Co-containing Nanopermtype alloy.
The influence of the partial substitution of B by Ge on the magnetocaloric response of
Fe78Co5Zr6B10Cu1 is studied. Ge addition produces a reduction in the temperature at which the peak
entropy change takes place, as well as a slight decrease in the magnitude of the peak, SM
pk . The
refrigerant capacity, RC, and its field dependence is also analyzed: although Ge addition increases
RC of the Co-containing alloy, the largest RC value corresponds to the Co- and Ge-free alloy. This
will be discussed on the basis of the recently proposed universal curve for the magnetic entropy
change, which is also followed by the FeZrBCu Co,Ge alloy series
Field dependence of the magnetocaloric effect in materials with a second order phase transition: A master curve for the magnetic entropy change
The field dependence of the magnetic entropy change can be expressed as SM Hn. For soft
magnetic amorphous alloys n=1 well below the Curie temperature TC , n=2 in the paramagnetic
range, and n 0.75 for T=TC. The first value can be explained with simple arguments, n=2 is a
consequence of the Curie-Weiss law, but n TC deviates from mean field predictions. From the
Arrott-Noakes equation of state, a relation between n TC and the critical exponents has been
obtained, showing remarkable agreement with experimental data for an example alloy, predicted
n=0.72 versus experimental n=0.73 . A master curve behavior for the temperature dependence of
SM measured for different maximum fields is proposed
Thermomagnetic detection of recrystallization in FeCoNbBCu nanocrystalline alloys
The recrystallization process in FeCoNbBCu nanocrystallinealloys is evidenced from thermomagnetic results as a significant decrease in magnetization at the second crystallization stage. The lowering in the volume fraction of α-FeCo crystals indicates that some of these crystals contribute to the boride phases formed. Electron microscopy images reveal that the final microstructure consists of large crystals (∼500 nm) of a fcc (FeCo)23B6(FeCo)23B6 phase and small crystals (∼20 nm) of bcc α-FeCo and of some boride phases as such (FeCo)2B
Evidence of ongoing radial migration in NGC 6754: Azimuthal variations of the gas properties
Understanding the nature of spiral structure in disk galaxies is one of the
main, and still unsolved questions in galactic astronomy. However, theoretical
works are proposing new testable predictions whose detection is becoming
feasible with recent development in instrumentation. In particular, streaming
motions along spiral arms are expected to induce azimuthal variations in the
chemical composition of a galaxy at a given galactic radius. In this letter we
analyse the gas content in NGC 6754 with VLT/MUSE data to characterise its 2D
chemical composition and H line-of-sight velocity distribution. We find
that the trailing (leading) edge of the NGC 6754 spiral arms show signatures of
tangentially-slower, radially-outward (tangentially-faster, radially-inward)
streaming motions of metal-rich (poor) gas over a large range of radii. These
results show direct evidence of gas radial migration for the first time. We
compare our results with the gas behaviour in a -body disk simulation
showing spiral morphological features rotating with a similar speed as the gas
at every radius, in good agreement with the observed trend. This indicates that
the spiral arm features in NGC 6754 may be transient and rotate similarly as
the gas does at a large range of radii.Comment: 8 pages, 4 figures, accepted for publication in ApJL 2016 September
2
Soft magnetic properties of high-temperature nanocrystalline alloys: Permeability and magnetoimpedance.
The technological applicability of FeCoNbBCu alloys is suggested in terms of measurements of
room temperature magnetoimpedance and temperature dependence of magnetic permeability
m
r
.
Results for the Fe
78-
x
Co
x
Nb
6
B
15
Cu
1
alloy series show that room temperature soft magnetic
properties are enhanced in the lowest Co containing alloy (
m
r
;
10 500 and magnetoimpedance ratio
;
60% at 1 MHz
!
. However, permeability exhibits a smoother thermal dependence in the alloys with
medium and high Co content. A tradeoff between magnetic softness and its thermal stability reveals
the alloy with 39 at. % Co as the most suitable composition among those studied, characterized by
a temperature coefficient of
;
0.02%/K from room temperature up to 900 K. This value is 1 order
of magnitude smaller than those observed for FeSiBCuNb
~
FINEMET-type
!
alloys and Mn ferrites
and extended over a much wider temperature range than in these materials
Universal relations for quasinormal modes of neutron stars in gravity
We construct quasinormal modes for neutron stars in gravity in the
Einstein frame, considering scalar masses in the sub-neV range. In particular,
we investigate the fundamental quadrupole fluid f-modes and the dipole fluid
F-modes. Employing six equations of state covering matter content with
nucleons, hyperons, and quarks, we then propose universal relations for the
quadrupole f-modes and dipole F-modes. The dipole F-modes are ultra-long lived
and, for the lower scalar masses, their frequencies are inversely proportional
to the corresponding Compton wavelength.Comment: 25 pages, 23 figures; Some figures update
Thermomechanical relaxation and different water states in cottonseed protein derived bioplastics
Thermomechanical relaxation events and different water states in cottonseed protein bioplastics are presented whilst investigating the effects of aldehyde cross-linking agents. Thermomechanical relaxation of cottonseed protein bioplastics associated with protein denaturation, moisture absorption and broad glass transitions (Tg) were observed from DSC and DMA measurements. It was shown that variation of the aldehyde influences the storage modulus at very low temperature (below Tg). From measurements of the water fusion point, enthalpy, vaporisation, and weight loss, three water states in the water-absorbed bioplastics are suggested; namely strongly-bound-to-polymer, weakly-bound-to-polymer and bulk-like water. The water content and unreacted cross-linking agents are influential factors in controlling formation of the different water states, whilst the selection of different aldehydes was found to be negligible. These results could be valuable for adjusting the thermomechanical relaxations of protein based bioplastics, and tailoring their properties in wet environments
Census of HII regions in NGC 6754 derived with MUSE: Constraints on the metal mixing scale
We present a study of the HII regions in the galaxy NGC 6754 from a two
pointing mosaic comprising 197,637 individual spectra, using Integral Field
Spectrocopy (IFS) recently acquired with the MUSE instrument during its Science
Verification program. The data cover the entire galaxy out to ~2 effective
radii (re ), sampling its morphological structures with unprecedented spatial
resolution for a wide-field IFU. A complete census of the H ii regions limited
by the atmospheric seeing conditions was derived, comprising 396 individual
ionized sources. This is one of the largest and most complete catalogue of H ii
regions with spectroscopic information in a single galaxy. We use this
catalogue to derive the radial abundance gradient in this SBb galaxy, finding a
negative gradient with a slope consistent with the characteristic value for
disk galaxies recently reported. The large number of H ii regions allow us to
estimate the typical mixing scale-length (rmix ~0.4 re ), which sets strong
constraints on the proposed mechanisms for metal mixing in disk galaxies, like
radial movements associated with bars and spiral arms, when comparing with
simulations. We found evidence for an azimuthal variation of the oxygen
abundance, that may be related with the radial migration. These results
illustrate the unique capabilities of MUSE for the study of the enrichment
mechanisms in Local Universe galaxies.Comment: 13 pages, 7 Figurs, accepted for publishing in A&
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