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2020-09-28
|
Intrusion of MeV-TeV Cosmic-Rays into Molecular Clouds Studied by Ionization, the Neutral Iron Line, and Gamma-Rays
|
Low-energy (~MeV) cosmic rays (CRs) ionize molecular clouds and create the
neutral iron line (Fe I K\alpha) at 6.4 keV. On the other hand, high-energy (>~
GeV) CRs interact with the dense cloud gas and produce gamma rays. Based on a
one-dimensional model, we study the spatial correlation among ionization rates
of gas, 6.4 keV line fluxes, and gamma-ray emissions from a molecular cloud
illuminated by CRs accelerated at an adjacent supernova remnant. We find that
the spatial distributions of these three observables depend on how CRs intrude
the cloud and on the internal structure of the cloud. If the intrusion is
represented by slow diffusion, the 6.4 keV line should be detected around the
cloud edge where ionization rates are high. On the other hand, if CRs freely
stream in the cloud, the 6.4 keV line should be observed where gamma rays are
emitted. In the former, the cooling time of the CRs responsible for the 6.4 keV
line is shorter than their cloud crossing time, and it is opposite in the
latter. Although we compare the results with observations, we cannot conclude
whether the diffusion or the free-streaming is dominantly realized. Our
predictions can be checked in more detail with future X-ray missions such as
XRISM and Athena and by observations of ionization rates that cover wider
fields.
|
2009.13524v3
|
2020-10-02
|
Singular magnetic anisotropy in the nematic phase of FeSe
|
FeSe is arguably the simplest, yet the most enigmatic, iron-based
superconductor. Its nematic but non-magnetic ground state is unprecedented in
this class of materials and stands out as a current puzzle. Here, our NMR
measurements in the nematic state of mechanically detwinned FeSe reveal that
both the Knight shift and the spin-lattice relaxation rate 1/T_1 possess an
in-plane anisotropy opposite to that of the iron pnictides LaFeAsO and
BaFe2As2. Using a microscopic electron model that includes spin-orbit coupling,
our calculations show that an opposite quasiparticle weight ratio between the
d_xz and d_yz orbitals leads to an opposite anisotropy of the orbital magnetic
susceptibility, which explains our Knight shift results. We attribute this
property to a different nature of nematic order in the two compounds,
predominantly bond-type in FeSe and onsite ferro-orbital in pnictides. The T_1
anisotropy is found to be inconsistent with existing neutron scattering data in
FeSe, showing that the spin fluctuation spectrum reveals surprises at low
energy, possibly from fluctuations that do not break C_4 symmetry. Therefore,
our results reveal that important information is hidden in these anisotropies
and they place stringent constraints on the low-energy spin correlations as
well as on the nature of nematicity in FeSe.
|
2010.01020v1
|
2020-10-05
|
Magnetic Iron Nanocubes Effectively Capture Epithelial and Mesenchymal Cancer Cells
|
Current methods for capturing circulating tumor cells (CTCs) are based on the
overexpression of cytokeratin (CK) or epithelial cell-adhesion molecule (EpCAM)
on cancer cells. However, during the process of metastasis, tumor cells undergo
epithelial to mesenchymal transition (EMT) that can lead to the loss of
CK/EpCAM expression. Therefore, it is vital to develop a capturing technique
independent of CK/EpCAM expression on the cancer cell. To develop this
technique, it is important to identify common secondary oncogenic markers
overexpressed on tumor cells before and after EMT. We analyzed the biomarker
expression levels in tumor cells, before and after EMT, and found two common
proteins human epidermal growth factor receptor 2 (Her2) and epidermal growth
factor receptor (EGFR) whose levels remained unaffected. So, we synthesized
immunomagnetic iron nanocubes covalently conjugated with antibodies of Her2 or
EGFR to capture cancer cells irrespective of the EMT status. The nanocubes
showed high specificity (6 to 9 fold) in isolating the cancer cells of interest
from a mixture of cells spiked in serum. We characterized the captured cells
for identifying their EMT status. Thus, we believe the results presented here
would help in the development of novel strategies for capturing both primary
and metastatic cancer cells from patients blood to develop an effective
treatment plan.
|
2010.02129v1
|
2020-10-14
|
An extremely metal-deficient globular cluster in the Andromeda Galaxy
|
Globular clusters (GCs) are dense, gravitationally bound systems of thousands
to millions of stars. They are preferentially associated with the oldest
components of galaxies, and measurements of their composition can therefore
provide insight into the build-up of the chemical elements in galaxies in the
early Universe. We report a massive GC in the Andromeda Galaxy (M31) that is
extremely depleted in heavy elements. Its iron abundance is about 800 times
lower than that of the Sun, and about three times lower than in the most
iron-poor GCs previously known. It is also strongly depleted in magnesium.
These measurements challenge the notion of a metallicity floor for GCs and
theoretical expectations that massive GCs could not have formed at such low
metallicities.
|
2010.07395v1
|
2020-11-20
|
Photoionization Models for High Density Gas
|
Relativistically broadened and redshifted 6.4 -- 6.9 keV iron K lines are
observed from many accretion powered objects, including X-ray binaries and
active galactic nuclei (AGN). Existence of gas close to the central engine
implies large radiation intensities and correspondingly large gas densities if
the gas is to remain partially ionized. Simple estimates indicate that high gas
densities are needed to allow survival of iron against ionization. These are
high enough that rates for many atomic processes are affected by mechanisms
related to interactions with nearby ions and electrons. Radiation intensities
are high enough that stimulated processes can be important. Most models
currently in use for interpreting relativistic lines use atomic rate
coefficients designed for use at low densities and neglect stimulated
processes. In our work so far we have presented atomic structure calculations
with the goal of providing physically appropriate models at densities
consistent with line-emitting gas near compact objects. In this paper we apply
these rates to photoionization calculations, and produce ionization balance
curves and X-ray emissivities and opacities which are appropriate for high
densities and high radiation intensities. The final step in our program will be
presented in a subsequent paper: Model atmosphere calculations which
incorporate these rates into synthetic spectra.
|
2011.10603v2
|
2020-12-18
|
Observation of d-wave Pomeranchuk nematic order in floating monolayer FeSe on FeSe/STO
|
As a foundation of condensed matter physics, the normal states of most metals
are successfully described by Landau Fermi liquid theory with quasi-particles
and their Fermi surfaces (FSs). The FSs sometimes become deformed or gapped at
low temperatures owing to quasi-particle interactions, known as FS
instabilities. A notable example of a FS deformation that breaks only the
rotation symmetry, namely Pomeranchuk instability, is the d-wave FS distortion,
which is also proposed as one possible origin of electron nematicity in
iron-based superconductors. However, no clear evidence has been made for its
existence, mostly owing to the mixture of multiple orders. Here we report an
unequivocally observation of the Pomeranchuk nematic order in floating
monolayer (ML) FeSe on 1 ML-FeSe/SrTiO3 substrate. By using angle-resolve
photoemission spectroscopy, we find remarkably that the dxz and dyz bands are
degenerate at the Brillouin zone center (Gamma point), while their splitting is
even larger at zone corner (M point), in stark contrast to that in bulk FeSe.
Our detailed analysis show that the momentum-dependent nematic order in
floating monolayer FeSe is coming from the d-wave Pomeranchuk instability at M
point, shedding light on the origin of the ubiquitous nematicity in iron-based
superconductors. Our results establish the single-layer high-Tc superconductors
as an excellent material platform for investigating emergent quantum physics
under complex intertwinement.
|
2012.10136v1
|
2020-12-19
|
Majorana bound states in vortex lattices on iron-based superconductors
|
Majorana quasi-particles may arise as zero-energy bound states in vortices on
the surface of a topological insulator that is proximitized by a conventional
superconductor. Such a system finds its natural realization in the iron-based
superconductor FeTe$_{0.55}$Se$_{0.45}$ that combines bulk $s$-wave pairing
with spin helical Dirac surface states, and which thus comprises the
ingredients for Majorana modes in absence of an additional proximitizing
superconductor. In this work, we investigate the emergence of Majorana vortex
modes and lattices in such materials depending on parameters like the magnetic
field strength and vortex lattice disorder. A simple 2D square lattice model
here allows us to capture the basic physics of the underlying materials system.
To address the problem of disordered vortex lattice, which occurs in real
systems, we adopt the technique of the singular gauge transformation which we
modify such that it can be used in a system with periodic boundary conditions.
This approach allows us to go to larger vortex lattices than otherwise
accessible, and is successful in replicating several experimental observations
of Majorana vortex bound states in the FeTe$_{0.55}$Se$_{0.45}$ platform.
Finally it can be related to a simple disordered Majorana lattice model that
should be useful for further investigations on the role of interactions, and
towards topological quantum computation.
|
2012.10588v2
|
2020-12-29
|
Supernova neutrino detection through neutron emission by nuclei
|
Neutrinos from core collapse supernovae can excite nuclei of some detector
materials beyond their neutron emission thresholds. Detection of these neutrons
can give valuable information about the supernova explosion mechanism and
possibly also throw light on neutrino properties. In this article, we give a
brief review of the basic physics of neutrino induced neutron emission and
describe the results of some recent calculations of supernova neutrino induced
neutrons for some specific target detector materials due to charged current
(CC) interactions of the electron flavored neutrinos and antineutrinos as well
as due to neutral current (NC) interactions of neutrinos and antineutrinos of
all flavors with the detector nuclei. We highlight the fact that a detector
material such as lead with a relatively large neutron excess produces neutrons
dominantly through the CC interaction of the $\nu_e$s, whereas a material such
as iron with small neutron excess produces neutrons dominantly through the
combined NC interaction of all the six neutrino and antineutrino species. This
raises the interesting possibility of probing the fraction of mu- and tau
flavored neutrinos (which interact only through NC interaction) in the
supernova neutrino flux by means of simultaneous detection of a supernova in a
lead and an iron detector, for example.
|
2012.14888v1
|
2021-01-07
|
An injectable, self-healing and MMP-inhibiting hyaluronic acid gel via iron coordination
|
Regulating the activity of matrix metalloproteinases (MMPs) is a potential
strategy for osteoarthritis (OA) therapy, although delivering this effect in a
spatially and temporally localised fashion remains a challenge. Here, we report
an injectable and self-healing hydrogel enabling factor-free MMP regulation and
biomechanical competence in situ. The hydrogel is realised within one minute
upon room temperature coordination between hyaluronic acid (HA) and a
cell-friendly iron-glutathione complex in aqueous environment. The resultant
gel displayed up to 300% in shear strain and tolerance towards ATDC 5
chondrocytes, in line with the elasticity and biocompatibility requirements for
connective tissue application. Significantly enhanced inhibition of MMP-13
activity was achieved after 12 hours in vitro, compared with a commercial HA
injection (OSTENIL PLUS). Noteworthy, 24-hour incubation of a clinical synovial
fluid sample collected from a late-stage OA patient with the reported hydrogel
was still shown to downregulate synovial fluid MMP activity (100.0 +/- 17.6 %
--> 81.0 +/- 7.5 %), with at least comparable extent to the case of the OSTENIL
PLUS-treated SF group (100.0 +/- 17.6 % --> 92.3 +/- 27.3 %). These results
therefore open up new possibilities in the use of HA as both
mechanically-competent hydrogel as well as a mediator of MMP regulation for OA
therapy.
|
2101.02414v1
|
2021-01-26
|
Superconductivity at 40 K in lithiation-processed [(Fe,Al)(OH)2][FeSe]1.2 with a layered structure
|
Exploration of new superconductors has always been one of the research
directions in condensed matter physics. We report here a new layered
heterostructure of [(Fe,Al)(OH)2][FeSe]1.2, which is synthesized by the
hydrothermal ion-exchange technique. The structure is suggested by a
combination of X-ray powder diffraction and the electron diffraction (ED).
[(Fe,Al)(OH)2][FeSe]1.2 is composed of the alternating stacking of tetragonal
FeSe layer and hexagonal (Fe,Al)(OH)2 layer. In [(Fe,Al)(OH)2][FeSe]1.2, there
exists mismatch between the FeSe sub-layer and (Fe,Al)(OH)2 sub-layer, and the
lattice of the layered heterostructure is quasi-commensurate. The
as-synthesized [(Fe,Al)(OH)2][FeSe]1.2 is non-superconducting due to the Fe
vacancies in the FeSe layer. The superconductivity with a Tc of 40 K can be
achieved after a lithiation process, which is due to the elimination of the Fe
vacancies in the FeSe layer. The Tc is nearly the same as that of (Li,Fe)OHFeSe
although the structure of [(Fe,Al)(OH)2][FeSe]1.2 is quite different from that
of (Li,Fe)OHFeSe. The new layered heterostructure of [(Fe,Al)(OH)2][FeSe]1.2
contains an iron selenium tetragonal lattice interleaved with a hexagonal metal
hydroxide lattice. These results indicate that the superconductivity is very
robust for FeSe-based superconductors. It opens a path for exploring
super-conductivity in iron-base superconductors.
|
2101.10641v1
|
2021-04-08
|
The EOS/Resolution Conspiracy: Convergence in Proto-Planetary Collision Simulations
|
We investigate how the choice of equation of state (EOS) and resolution
conspire to affect the outcomes of giant impact (GI) simulations. We focus on
the simple case of equal mass collisions of two Earth-like $0.5\,M_\oplus$
proto-planets showing that the choice of EOS has a profound impact on the
outcome of such collisions as well as on the numerical convergence with
resolution. In simulations where the Tillotson EOS is used, impacts generate an
excess amount of vapour due to the lack of a thermodynamically consistent
treatment of phase transitions and mixtures. In oblique collisions this
enhances the artificial angular momentum (AM) transport from the planet to the
circum-planetary disc reducing the planet's rotation period over time. Even at
a resolution of $1.3 \times 10^6$ particles the result is not converged. In
head-on collisions the lack of a proper treatment of the solid/liquid-vapour
phase transition allows the bound material to expand to very low densities
which in turn results in very slow numerical convergence of the critical
specific impact energy for catastrophic disruption $Q_{RD}^*$ with increasing
resolution as reported in prior work. The simulations where ANEOS is used for
oblique impacts are already converged at a modest resolution of $10^5$
particles, while head-on collisions converge when they evidence the post-shock
formation of a dense iron-rich ring, which promotes gravitational
re-accumulation of material. Once sufficient resolution is reached to resolve
the liquid-vapour phase transition of iron in the ANEOS case, and this ring is
resolved, the value of $Q_{RD}^*$ has then converged.
|
2104.03559v2
|
2021-04-22
|
Chemical composition of stars with massive planets
|
Stellar parameters of 25 planet-hosting stars and abundances of Li, C, O, Na,
Mg, Al, S, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Zn, Y, Zr, Ba, Ce, Pr, Nd, Sm and
Eu, were studied based on homogeneous high resolution spectra and uniform
techniques. The iron abundance [Fe/H] and key elements (Li, C, O, Mg, Si)
indicative of the planet formation, as well as the dependencies of [El/Fe] on
$T_{cond}$, were analyzed. The iron abundances determined in our sample stars
with detected massive planets range within -0.3<[Fe/H]<0.4. The behaviour of
[C/Fe], [O/Fe], [Mg/Fe] and [Si/Fe] relative to [Fe/H] is consistent with the
Galactic Chemical Evolution trends. The mean values of C/O and [C/O] are <C/O>=
0.48 +/-0.07 and <[C/O]>=-0.07 +/-0.07, which are slightly lower than solar
ones. The Mg/Si ratios range from 0.83 to 0.95 for four stars in our sample and
from 1.0 to 1.86 for the remaining 21 stars. Various slopes of [El/Fe] vs.
Tcond were found. The dependencies of the planetary mass on metallicity, the
lithium abundance, the C/O and Mg/Si ratios, and also on the [El/Fe]-Tcond
slopes were considered.
|
2104.10894v1
|
2021-05-02
|
High-energy magnetic excitations from heavy quasiparticles in CeCu$_2$Si$_2$
|
Magnetic fluctuations is the leading candidate for pairing in cuprate,
iron-based and heavy fermion superconductors. This view is challenged by the
recent discovery of nodeless superconductivity in CeCu$_2$Si$_2$, and calls for
a detailed understanding of the corresponding magnetic fluctuations. Here, we
mapped out the magnetic excitations in \ys{superconducting (S-type)}
CeCu$_2$Si$_2$ using inelastic neutron scattering, finding a strongly
asymmetric dispersion for $E\lesssim1.5$~meV, which at higher energies evolve
into broad columnar magnetic excitations that extend to $E\gtrsim 5$ meV. While
low-energy magnetic excitations exhibit marked three-dimensional
characteristics, the high-energy magnetic excitations in CeCu$_2$Si$_2$ are
almost two-dimensional, reminiscent of paramagnons found in cuprate and
iron-based superconductors. By comparing our experimental findings with
calculations in the random-phase approximation,we find that the magnetic
excitations in CeCu$_2$Si$_2$ arise from quasiparticles associated with its
heavy electron band, which are also responsible for superconductivity. Our
results provide a basis for understanding magnetism and superconductivity in
CeCu$_2$Si$_2$, and demonstrate the utility of neutron scattering in probing
band renormalization in heavy fermion metals.
|
2105.00387v1
|
2021-05-19
|
An examination of local strain fields evolution in ductile cast iron through micromechanical simulations based on 3D imaging
|
Microscopic digital volume correlation (DVC) and finite element
precoalescence strain evaluations are compared for two nodular cast iron
specimens. Displacement fields from \textit{in-situ} 3D synchrotron
laminography images are obtained by DVC. Subsequently the microstructure is
explicitely meshed from the images considering nodules as voids. Boundary
conditions are applied from the DVC measurement. Image segmentation-related
uncertainties are taken into account and observed to be negligible with respect
to the differences between strain levels. Macroscopic as well as local strain
levels in coalescing ligaments between voids nucleated at large graphite
nodules are compared. Macroscopic strain levels are consistently predicted. A
very good agreement is observed for one of the specimens, while the strain
levels for the second specimen presents some discrepancies. Limitations of the
modeling and numerical framework are discussed in light of these differences. A
discussion of the use of strain as coalescence indicator is initiated.
|
2105.09859v3
|
2021-05-24
|
The Surface of (16) Psyche from Thermal Emission and Polarization Mapping
|
The asteroid (16) Psyche is the largest of the M-type asteroids, which have
been hypothesized to be the cores of disrupted planetesimals and the parent
bodies of the iron meteorites. While recent evidence has collected against a
pure metal composition for Psyche, its spectrum and radar properties remain
anomalous. We observed (16) Psyche in thermal emission with the Atacama Large
(sub-)Millimeter Array (ALMA) at a resolution of 30 km over 2/3 of its
rotation. The diurnal temperature variations are at the $\sim$10 K level over
most of the surface and are best fit by a smooth surface with a thermal inertia
of 280$\pm$100 J m$^{-2}$ K$^{-1}$ s$^{-1/2}$. We measure a millimeter
emissivity of 0.61$\pm$0.02, which we interpret via a model that treats the
surface as a porous mixture of silicates and metals, where the latter may take
the form of iron sulfides/oxides or alternatively as conducting metallic
inclusions. The emissivity indicates a metal content of no less than 20\% and
potentially much higher, but the polarized emission that should be present for
a surface with $\geq$20\% metal content is almost completely absent. This
requires a highly scattering surface, which may be due to the presence of
reflective metallic inclusions. If such is the case, a consequence is that
metal-rich asteroids may produce less polarized emission than metal-poor
asteroids, exactly the opposite prediction from standard theory, arising from
the dominance of scattering over the bulk material properties.
|
2105.11372v1
|
2021-08-03
|
Spectroscopy and structural investigation of iron phosphorus trisulfide -- FePS$_3$
|
Lamellar structures of transition metal phosphorus trisulfides possess strong
intralayer bonding, albeit adjacent layers are held by weak van der Waals
interactions. Those compounds received enormous interest due to their unique
combination of optical and long-range magnetic properties. Among them, iron
phosphorus trisulfide (FePS$_3$) gathered special attention for being a
semiconductor with an absorption edge in the near-infrared, as well as showing
an Ising-like anti-ferromagnetism. We report a successful growth of centimeter
size bulk FePS$_3$ crystals with a chemical yield above 70%, whose
crystallographic structure and composition were carefully identified by
advanced electron microscopy methodologies, including atomic resolution
elemental mapping, along with photoelectron spectroscopy. The knowledge on the
optical activity of FePS$_3$ is extended utilizing temperature-dependent
absorption and photoacoustic spectroscopies, while measurements were
corroborated with density-functional theory calculations. Temperature-dependent
experiments showed a small and monotonic band-edge energy shift down to 115 K
and exposed the interconnected importance of electron-phonon coupling. Most of
all, the correlation between the optical behavior and the magnetic phase
transition is revealed, which shows the practical utilization of
temperature-dependent optical absorption to investigate magnetic interactions.
|
2108.01742v3
|
2021-08-08
|
V488 Per revisited: no strong mid-infrared emission features and no evidence for stellar/sub-stellar companions
|
We present characterization of the planetary system architecture for V488
Per, the dustiest main sequence star known with a fractional infrared
luminosity of ~16%. Far-infrared imaging photometry confirms the existence of
an outer planetary system dust population with blackbody-fit temperature of
~130 K. Mid-infrared spectroscopy probing the previously-identified ~800 K
inner planetary system dust population does not detect any obvious solid-state
emission features, suggesting either large grain sizes that mute such emission
and/or grain compositions dominated by species like amorphous carbon and
metallic iron which do not produce such features. In the latter case, the
presence of significant quantities of iron-rich material could be indicative of
the active formation of a Mercury-like planet around V488 Per. In any event,
the absence of solid-state emission features is very unusual among main
sequence stars with copious amounts of warm orbiting dust particles; we know of
no other such star whose mid-infrared spectrum lacks such features. Combined
radial velocity monitoring and adaptive optics imaging find no evidence for
stellar/sub-stellar companions within several hundred AU of V488 Per.
|
2108.03700v1
|
2021-08-20
|
Orbital-dependent modulation of the superconducting gap in uniaxially strained Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$
|
Pairing symmetry which characterizes the superconducting pairing mechanism is
normally determined by measuring the superconducting gap structure
($|\Delta_k|$). Here, we report the measurement of a strain-induced gap
modulation ($\partial|\Delta_k|$) in uniaxially strained
Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ utilizing angle-resolved photoemission
spectroscopy and $in$-$situ$ strain-tuning. We found that the uniaxial strain
drives Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ into a nematic superconducting state
which breaks the four-fold rotational symmetry of the superconducting pairing.
The superconducting gap increases on the $d_{yz}$ electron and hole pockets
while it decreases on the $d_{xz}$ counterparts. Such orbital selectivity
indicates that orbital-selective pairing exists intrinsically in non-nematic
iron-based superconductors. The $d_{xz}$ and $d_{yz}$ pairing channels are
balanced originally in the pristine superconducting state, but become
imbalanced under uniaxial strain. Our results highlight the important role of
intra-orbital scattering in mediating the superconducting pairing in iron-based
superconductors. It also highlights the measurement of $\partial|\Delta_k|$ as
an effective way to characterize the superconducting pairing from a
perturbation perspective.
|
2108.08986v1
|
2021-08-25
|
Synthesis of a High-Capacity α-Fe2O3@C Conversion Anode and a High-Voltage LiNi0.5Mn1.5O4 Spinel Cathode and Their Combination in a Li-Ion Battery
|
A Li-conversion alpha-Fe2O3@C nanocomposite anode and a high-voltage
LiNi0.5Mn1.5O4 cathode are synthesized in parallel, characterized, and combined
in a Li-ion battery. alpha-Fe2O3@C is prepared via annealing of maghemite iron
oxide and sucrose under an argon atmosphere and subsequent oxidation in air.
The nanocomposite exhibits a satisfactory electrochemical response in a lithium
half-cell, delivering almost 900 mA h g-1, as well as a significantly longer
cycle life and higher rate capability compared to the bare iron oxide
precursor. The LiNi0.5Mn1.5O4 cathode, achieved using a modified
co-precipitation approach, reveals a well-defined spinel structure without
impurities, a sub-micrometrical morphology, and a reversible capacity of ca.
120 mA h g-1 in a lithium half-cell with an operating voltage of 4.8 V. Hence,
a lithium-ion battery is assembled by coupling the alpha-Fe2O3@C anode with the
LiNi0.5Mn1.5O4 cathode. This cell operates at about 3.2 V, delivering a stable
capacity of 110 mA h g-1 (referred to the cathode mass) with a Coulombic
efficiency exceeding 97%. Therefore, this cell is suggested as a promising
energy storage system with expected low economic and environmental impacts.
|
2108.11314v1
|
2021-08-25
|
Magnetic properties of BiFeO$_3$-BaTiO$_3$ ceramics in the morphotropic phase boundary: a role of crystal structure and structural parameters
|
A correlation between the crystal structure and magnetic properties of system
(1-x)BiFeO$_3$-(x)BaTiO$_3$ with compounds across the morphotropic phase
boundary was studied using X-ray and neutron diffraction, magnetometry, and
Mossbauer spectroscopy measurements. Increase in the dopants content leads to
the structural transition from the rhombohedral phase to the cubic phase via a
formation of the two-phase region (0.2 < x < 0.33), wherein the magnetic
structure changes from the modulated G-type antiferromagnetic to the collinear
antiferromagnetic via a stabilization of the non-collinear antiferromagnetic
phase with non-zero remanent magnetization. The value of magnetic moment
calculated per iron ion based on the Mossbauer and neutron diffraction data
decreases from m = 4.4 mB for the compound with x=0.25 to m=3.2 mB for the
compound with x=0.35 testifying a dominance of 3+ oxidation state of the iron
ions. Increase in the amount of the cubic phase leads to a reduction in the
remanent magnetization from 0.02 emu.g for the compounds with the dominant
rhombohedral phase (x < 0.27) down to about 0.001 emu/g for the compounds with
dominant cubic structure (x >= 0.27). Rapid decrease in the remanent
magnetization observed in the compounds across the phase coexistence region
points at no direct correlation between the type of structural distortion and
non-zero remanent magnetization, while the oxygen octahedra tilting is the key
factor determining the presence of non-zero remanent magnetization.
|
2108.11447v1
|
2021-08-30
|
Thermodynamic Signatures of Diagonal Nematicity in RbFe$_2$As$_2$ Superconductor
|
Electronic nematic states with broken rotational symmetry often emerge in
correlated materials. In most iron-based superconductors, the nematic
anisotropy is oriented in the Fe-Fe direction of the iron square lattice.
Recently, a novel type of nematicity along the diagonal Fe-As direction has
been suggested in heavily hole-doped $A$Fe$_2$As$_2$ ($A=$ Rb or Cs). However,
the transport studies focusing on the fluctuations of such nematicity have
provided controversial results regarding the presence of diagonal nematic
order. Here we report high-resolution heat capacity measurements under in-plane
field rotation in RbFe$_2$As$_2$. While the temperature dependence of specific
heat shows no discernible anomaly associated with the nematic transition, the
field-angle dependence of specific heat near the superconducting transition (at
$\sim 2.8$ K) reveals clear two-fold oscillations within the plane, providing
thermodynamic evidence for the diagonal nematicity. Moreover, we find that
M\"ossbauer spectroscopy sensitively probes the nematic transition at $\sim 50$
K with no evidence of static magnetism. These results imply that the diagonal
nematicity in RbFe$_2$As$_2$ has a unique mechanism involving charge degrees of
freedom, having unusual thermodynamic properties of the transition.
|
2108.13081v1
|
2021-09-03
|
A stellar census in globular clusters with MUSE. A new perspective on the multiple main sequences of $ω$ Centauri
|
$\omega$ Cen is a rare example of a globular cluster where the iron abundance
of the stars spans more than one order of magnitude. Many spectroscopic
investigations of its red-giant- and sub-giant- branches have revealed multiple
peaks in the iron abundance distribution. The metallicity distribution of
main-sequence (MS) stars is not well characterized yet, due to the faintness of
the stars and lack of data. So far, almost all studies of MS stars are based on
photometric measurements. Our goal is to investigate the metallicity
distribution of a statistically significant sample of MS stars in $\omega$ Cen.
In particular, we aim at revisiting the metallicity difference between the red
and blue MS of the cluster. We used MUSE spectra obtained for the central
region of $\omega$ Cen to derive metallicities for $\approx$4200 MS stars. We
find that blue MS stars are on average $\approx$0.1 dex more metal-rich than
their red counterparts. On the basis of this new estimate, we find that the two
sequences can be fit on the Hubble Space Telescope color-magnitude diagram with
two isochrones having the same global metallicity and age but a higher helium
abundance for the blue MS, that is $\Delta Y \lesssim$ 0.1. Furthermore, we
determine the average metallicity of the five main populations along $\omega$
Cen MS and these estimates are consistent with expectations from previous
photometric studies.
|
2109.01540v2
|
2021-09-09
|
Collisional mixing between inner and outer solar system planetesimals inferred from the Nedagolla iron meteorite
|
The ungrouped iron meteorite Nedagolla is the first meteorite with bulk Mo,
Ru, and Ni isotopic compositions that are intermediate between those of the
non-carbonaceous (NC) and carbonaceous (CC) meteorite reservoirs. The Hf-W
chronology of Nedagolla indicates that this mixed NC-CC isotopic composition
was established relatively late, more than 7 million years after Solar System
formation. The mixed NC-CC isotopic composition is consistent with the chemical
composition of Nedagolla, which combines signatures of metal segregation under
more oxidizing conditions (relative depletions in Mo and W), characteristic for
CC bodies, and more reducing conditions (high Si and Cr contents),
characteristic for some NC bodies, in a single sample. These data combined
suggest that Nedagolla formed as the result of collisional mixing of NC and CC
core material, which partially re-equilibrated with silicate mantle material
that predominantly derives from the NC body. These mixing processes might have
occurred during a hit-and-run collision between two differentiated bodies,
which also provides a possible pathway for Nedagolla's extreme volatile element
depletion. As such, Nedagolla provides the first isotopic evidence for early
collisional mixing of NC and CC bodies that is expected as a result of
Jupiter's growth.
|
2109.04224v1
|
2021-09-11
|
NuSTAR monitoring of MAXI J1348-630: evidence of high density disc reflection
|
We present the broadband spectral analysis of all the six hard, intermediate
and soft state NuSTAR observations of the recently discovered transient black
hole X-ray binary MAXI J1348-630 during its first outburst in 2019. We first
model the data with a combination of a multi-colour disc and a relativistic
blurred reflection, and, whenever needed, a distant reflection. We find that
this simple model scheme is inadequate in explaining the spectra, resulting in
a very high iron abundance. We, therefore, explore the possibility of
reflection from a high-density disc. We use two different sets of models to
describe the high-density disc reflection: relxill-based reflection models, and
reflionx-based ones. The reflionx-based high-density disc reflection models
bring down the iron abundance to around the solar value, while the density is
found to be $10^{20.3-21.4} \rm cm^{-3}$. We also find evidence of a
high-velocity outflow in the form of $\sim$7.3 keV absorption lines. The
consistency between the best-fit parameters for different epochs and the
statistical significance of the corresponding model indicates the existence of
high-density disc reflection in MAXI J1348-630.
|
2109.05380v1
|
2021-09-14
|
Ultrafast Optical Spectroscopy Evidence of Pseudogap and Electron-Phonon Coupling in an Iron-Based Superconductor KCa$_2$Fe$_4$As$_4$F$_2$
|
We use ultrafast optical spectroscopy to study the nonequilibrium
quasiparticle relaxation dynamics of the iron-based superconductor
KCa$_2$Fe$_4$As$_4$F$_2$ with $T_c=33.5$ K. Our results reveal a possible
pseudogap ($\Delta_{PG}$ = 2.4 $\pm$ 0.1 meV) below $T^*\approx 50$ K but prior
to the opening of a superconducting gap ($\Delta_{SC}$(0) $\approx$ 4.3 $\pm$
0.1 meV). Measurements under high pump fluence real two distinct, coherent
phonon oscillations with 1.95 and 5.51 THz frequencies, respectively. The
high-frequency $A_{1g}$(2) mode corresponds to the $c-$axis polarized
vibrations of FeAs planes with a nominal electron-phonon coupling constant
$\lambda_{A_{1g}(2)}$ = 0.194 $\pm$ 0.02. Our findings suggest that the
pseudogap is likely a precursor of superconductivity, and the electron-phonon
coupling may play an essential role in the superconducting pairing in
KCa$_2$Fe$_4$As$_4$F$_2$.
|
2109.06460v2
|
2021-09-27
|
The Three-Dimensional Electronic Structure of LiFeAs: Strong-coupling Superconductivity and Topology in the Iron Pnictides
|
Amongst the iron-based superconductors, LiFeAs is unrivalled in the
simplicity of its crystal structure and phase diagram. However, our
understanding of this canonical compound suffers from conflict between mutually
incompatible descriptions of the material's electronic structure, as derived
from contradictory interpretations of the photoemission record. Here, we
explore the challenge of interpretation in such experiments. By combining
comprehensive photon energy- and polarization- dependent angle-resolved
photoemission spectroscopy (ARPES) measurements with numerical simulations, we
establish the providence of several contradictions in the present understanding
of this and related materials. We identify a confluence of surface-related
issues which have precluded unambiguous identification of both the number and
dimensionality of the Fermi surface sheets. Ultimately, we arrive at a scenario
which supports indications of topologically non-trivial states, while also
being incompatible with superconductivity as a spin-fluctuation driven Fermi
surface instability.
|
2109.13276v1
|
2021-10-12
|
Vortex dynamics and second magnetization peak in the iron-pnictide superconductor Ca$_{0.82}$La$_{0.18}$Fe$_{0.96}$Ni$_{0.04}$As$_2$
|
We report the studies of detailed magnetic relaxation and isothermal
magnetization measurements in the vortex state of the 112-type iron-pnictide
Ca$_{0.82}$La$_{0.18}$Fe$_{0.96}$Ni$_{0.04}$As$_2$ superconductor with $T_c$
$\sim$ 22 K. In the isothermal $M(H)$, a well defined second magnetization peak
(SMP) feature is observed in the entire temperature range below $T_c$ for
measurements with $H$ $\parallel$ $c$-axis. However, for $H$ $\parallel$
$ab$-planes, the SMP feature is suppressed at low temperatures, which might be
due to 2D Josephson vortices forming at low temperatures and high magnetic
fields in such an anisotropic system. A rigorous analysis considering the
magnetic relaxation data for $H$ $\parallel$ $c$-axis suggests an elastic to
plastic pinning crossover across $H_p$, which also seems accompanied with a
possible phase transition in vortex lattice near $H_p$. Moreover, point
disorder and surface defects are likely to be the dominant sources of pinning,
which contribute to the $\delta l$-type of pinning in the sample. A high $J_c$,
in access of 10$^5$ A/cm$^2$ observed could potentially make this material
technologically important.
|
2110.05677v1
|
2021-10-19
|
Generalized estimates for the density of oxide scale in the range from 0 C to 1300 C
|
Oxide scale formed on the surface of steel products during high-teperature
processes is studied as a composite material, the main solid components of
which, in general, are wustite, magnetite, hematite and metallic iron. To
estimate the density of each of these components in the temperature range from
0 C to 1300 C, formulas are proposed that are consistent with the empirical
functions of the coefficient of linear thermal expansion, which the authors
obtained earlier by generaizing data from open sources. The Curie and
polymorphic transformation temperatures are included in these generalized
formulas as variable parameters, which allows one to take into account the
movability of phase transitions due to impurities, crystal lattice defects,
particle sizes, cooling rate, and other factors. When specifying the particular
values of critical temperatures, the other parameters of the formulas are
recalculated automatically. In a particular form, the proposed formulas
correspond to the basic values of critical temperatures. According to the
calculation examples given, the true (not including pores) density of oxide
scale can be about 5200 to 5600 kg/m3, depending on the temperature and
percentage of components, whereby a local density minimum may be observed in
the region of 570 C due to eutectoid decomposition of wustite into magnetite
and iron. The proposed methods are recommended for use in mathematical
simulation of processing of steel products in the presence of oxide scale on
its surface.
|
2110.09791v1
|
2021-10-26
|
Stochastic Low Frequency Variability in 3-Dimensional Radiation Hydrodynamical Models of Massive Star Envelopes
|
Increasing main sequence stellar luminosity with stellar mass leads to the
eventual dominance of radiation pressure in stellar envelope hydrostatic
balance. As the luminosity approaches the Eddington limit, additional
instabilities (beyond conventional convection) can occur. These instabilities
readily manifest in the outer envelopes of OB stars, where the opacity increase
associated with iron yields density and gas pressure inversions in 1D models.
Additionally, recent photometric surveys (e.g. TESS) have detected excess
broadband low frequency variability in power spectra of OB star lightcurves,
called stochastic low frequency variability (SLFV). This motivates our novel 3D
Athena++ radiation hydrodynamical (RHD) simulations of two 35$\,$M$_\odot$ star
envelopes (the outer $\approx$15$\%$ of the stellar radial extent), one on the
zero-age main sequence and the other in the middle of the main sequence. Both
models exhibit turbulent motion far above and below the conventional iron
opacity peak convection zone (FeCZ), obliterating any ``quiet" part of the
near-surface region and leading to velocities at the photosphere of
10-100$\,$km$\,$s$^{-1}$, directly agreeing with spectroscopic data. Surface
turbulence also produces SLFV in model lightcurves with amplitudes and
power-law slopes that are strikingly similar to those of observed stars. The
characteristic frequencies associated with SLFV in our models are comparable to
the thermal time in the FeCZ ($\approx$3-7$\,$days$^{-1}$). These simulations,
which have no free parameters, are directly validated by observations and,
though more models are needed, we remain optimistic that 3D RHD models of main
sequence O star envelopes exhibit SLFV originating from the FeCZ.
|
2110.13944v1
|
2021-12-01
|
Orbital-Selective High-Temperature Cooper Pairing Developed in the Two-Dimensional Limit
|
The orbital multiplicity in multiband superconductors yields orbital
differentiation in normal-state properties, and can lead to orbital-selective
spin-fluctuation Cooper pairing. This phenomenon has become increasingly
pivotal in clarifying the pairing 'enigma' particularly for multiband
high-temperature superconductors. In one-unit-cell (1-UC) FeSe/SrTiO3, the
thinnest and highest-Tc member of iron-based superconductors, the standard
electron-hole Fermi pocket nesting scenario is apparently not applicable since
the Gamma-centered hole pockets are absent, so the actual pairing mechanism is
the subject of intense debate. Here, by measuring high-resolution Bogoliubov
quasiparticle interference, we report observations of highly anisotropic
magnetic Cooper pairing in 1-UC FeSe. From a theoretical point of view, it is
important to incorporate effects of electronic correlations within a
spin-fluctuation pairing calculation, where the dxy orbital becomes
coherence-suppressed. The resulting pairing gap is compatible with the
experimental findings, which suggests that high-Tc Cooper pairing with orbital
selectivity applies to 1-UC FeSe. Our findings imply the general existence of
orbital selectivity in iron-based superconductors and the universal importance
of electron correlations in high-Tc superconductors.
|
2112.00383v1
|
2021-12-05
|
Optical singly-ionized iron emission in radio-quiet and relativistically jetted active galactic nuclei
|
The issue of the difference between optical and UV properties of radio-quiet
and radio-loud (relativistically "jetted") active galactic nuclei (AGN) is a
long standing one, related to the fundamental question of why a minority of
powerful AGN possess strong radio emission due to relativistic ejections. This
paper examines a particular aspect: the singly-ionized iron emission in the
spectral range 4400 -- 5600 A, where the prominent HI H$\beta$ and [OIII] 4959,
5007 lines are also observed. We present a detailed comparison of the relative
intensity of Fe II multiplets in the spectral types of the quasar main sequence
where most jetted sources are found, and afterwards discuss radio-loud
narrow-line Seyfert 1 (NLSy1) nuclei with $\gamma$-ray detection and with
prominent Fe II emission. An Fe II template based on I Zw 1 provides an
accurate representation of the optical Fe II emission for RQ and, with some
caveats, also for RL sources. CLOUDY photoionization simulations indicate that
the observed spectral energy distribution can account for the modest Fe II
emission observed in composite radio-loud spectra. However, spectral energy
differences alone cannot account for the stronger Fe II emission observed in
radio-quiet sources, for similar physical parameters. As for RL NLSy1s, they do
not seem to behave like other RL sources, likely because of their different
physical properties that could be ultimately associated with a higher Eddington
ratio.
|
2112.02632v1
|
2021-12-10
|
Random-strain-induced correlations in materials with intertwined nematic and magnetic orders
|
Electronic nematicity is rarely observed as an isolated instability of a
correlated electron system. Instead, in iron pnictides and in certain cuprates
and heavy-fermion materials, nematicity is intertwined with an underlying
spin-stripe or charge-stripe state. As a result, random strain, ubiquitous in
any real crystal, creates both random-field disorder for the nematic degrees of
freedom and random-bond disorder for the spin or charge ones. Here, we put
forward an Ashkin-Teller model with random Baxter fields to capture the dual
role of random strain in nematic systems for which nematicity is a composite
order arising from a stripe state. Using Monte Carlo to simulate this
$\textit{random Baxter-field model}$, we find not only the expected break-up of
the system into nematic domains, but also the emergence of nontrivial
disorder-promoted magnetic correlations. Such correlations enhance and tie up
the fluctuations associated with the two degenerate magnetic stripe states from
which nematicity arises, leaving characteristic signatures in the spatial
profile of the magnetic domains, in the configurational space of the spin
variables, and in the magnetic noise spectrum. We discuss possible experimental
manifestations of these effects in iron-pnictide superconductors. Our work
establishes the random Baxter-field model as a more complete alternative to the
random-field Ising model to describe complex electronic nematic phenomena in
the presence of disorder.
|
2112.05769v1
|
2021-12-15
|
A Suzaku sample of unabsorbed narrow-line and broad-line Seyfert 1 galaxies: II. Iron emission and absorption
|
A sample of 22 narrow-line Seyfert 1 (NLS1) and 47 broad-line Seyfert 1
(BLS1) galaxies observed with Suzaku is used to examine the Fe K band
properties of each group. Three different models are used to examine the
presence of: narrow neutral Fe Ka line at 6.4 keV and ionised Fe xxv and Fe
xxvi emission lines (model A); a broad emission feature at around 6 - 7 keV
(model B); and an absorption edge at 7.1 keV (model C). In all three models,
the neutral Fe Ka line is weaker (lower luminosity and equivalent width) in
NLS1s than in BLS1s. Model (B) also finds a more significant broad component
(larger equivalent width) in NLS1s than in BLS1s. The feature does not appear
to be an artefact of steeper spectra in NLS1s, but rather an intrinsic property
of these sources. From model (C), the optical depth of the absorption edge
appears comparable between the two samples. When comparing the absorption with
the emission line properties, NLS1s seem to exhibit a lower ratio of
emission-to-absorption of iron than BLS1s, and than expected based on the
fluorescence yield. The observed differences may arise from different torus
geometries (e.g. larger opening angle in NLS1s), and/or additional sources of
Fe K emission and absorption in NLS1s beyond pure fluorescence (e.g.
originating in the disc and broad line region).
|
2112.08127v1
|
2021-12-15
|
Stellar population astrophysics (SPA) with the TNG -- The chemical content of the red supergiant population in the Perseus complex
|
Context. The Perseus complex in the outer disk of the Galaxy hosts a number
of clusters and associations of young stars. Gaia is providing a detailed
characterization of their kinematic structure and evolutionary properties.
Aims. Within the SPA Large Programme at the TNG, we secured HARPS-N and GIANO-B
high-resolution optical and near-infrared (NIR) spectra of the young red
supergiant (RSG) stars in the Perseus complex, in order to obtain accurate
radial velocities, stellar parameters and detailed chemical abundances.
Methods. We used spectral synthesis to best-fit hundreds of atomic and
molecular lines in the spectra of the observed 27 RSGs. We obtained accurate
estimates of the stellar temperature, gravity, micro and macro turbulence
velocities and chemical abundances for 25 different elements. We also measured
the $^{12}$C/$^{13}$C abundance ratio. Results. Our combined optical and NIR
chemical study provides homogeneous half-solar iron with a small dispersion,
about solar-scaled abundance ratios for the iron-peak, alpha and other light
elements and a small enhancement of Na, K and neutron-capture elements,
consistent with the thin disk chemistry traced by older stellar populations at
a similar Galactocentric distance of about 10 kpc. We inferred enhancement of
N, depletion of C and of the $^{12}$C/$^{13}$C isotopic abundance ratio,
consistent with mixing processes in the stellar interiors during the RSG
evolution.
|
2112.08402v1
|
2021-12-28
|
Simulations of globular clusters within their parent galaxies: Metallicity spreads and anomalous precursor populations
|
Recent observations of globular clusters (GCs) suggest that elemental
abundance variations may exist between first-generation (1G) stars. We propose
that metal abundance ('metallicity') spreads within GC forming giant molecular
clouds (GMCs) can influence the iron abundances of future cluster members. To
investigate this, we use original hydrodynamical simulations to model GMC
formation in a high redshift dwarf galaxy. Our simulations self-consistently
model physical processes such as stellar feedback, dust formation and
destruction, and molecular gas formation on dust grains, making them well
suited to the study of GMC formation. We conclude that iron abundance
variations in GMCs are due to the merging of gas clumps and self-enrichment
processes. The metallicity dispersions of GC forming clumps is ~0.1 dex,
reflecting a growing number of studies that claim a non-zero dispersion within
GCs. The galactic gas fraction is a key parameter for the formation of clumps
and the metallicity 'floor' observed for both Galactic and extragalactic GCs
are associated with the parent galaxy's capacity to form massive GMCs. Finally,
we argue that GMCs have the potential to trap surrounding metal-poor galactic
disc stars, which we interpret as a precursor population (0G). These low
metallicity stars are representative of the [Fe/H] value of the host dwarf and
thus the chemistry of this 0G may be a fossilized record of the parent galaxy.
These results depend on the initial metallicity and radial gradient of the
galaxy, the threshold gas density for star formation, and the star formation
prescription.
|
2112.13971v1
|
2022-01-04
|
Reconstruction of Air-Shower Parameters Through the Lateral Distribution Function of Ultra-High Energy Particles
|
In this study, the necessity of the simulation study for exploring the
interactions of ultra-high energy particles cosmic rays was examined. Different
hadronic interaction models such as (SIBYLL, QGSJET, and EPOS) were simulated
by using air showers simulation AIRES system (version 19.04.00). Also, the
charged particle density of Extensive Air Showers (EAS) was calculated by
estimating the lateral distribution function (LDF). Moreover, the LDF
simulation of the two primary particles (proton and iron nuclei) was performed,
taking into account their primary energies effect and the zenith angle of
charged particles that produced in the EAS, within the energy range
(10^17-10^19) eV. At extremely high energies (10^17, 10^18, and 10^19) eV, new
parameters as a function of the primary energy were obtained by fitting the
lateral distribution curves of EAS using Sigmoidal function (Logistic model).
Comparison of the results showed a good agreement between the values obtained
from the parameterized LDF using Sigmoidal function with experimental results
by AGASA EAS observatory for the primaries proton as well iron nuclei, with the
production of (electron positron) pair and the charged muons secondary
particles at high energy about 10^19 eV and (theta = 0 degree).
|
2201.01368v1
|
2022-02-01
|
Optical Properties of C$-$rich ($^{12}$C, SiC and FeC) Dust Layered Structure of Massive Stars
|
The composition and structure of interstellar dust are important and complex
for the study of the evolution of stars and the \textbf{interstellar medium}
(ISM). However, there is a lack of corresponding experimental data and model
theories. By theoretical calculations based on ab-initio method, we have
predicted and geometry optimized the structures of Carbon-rich (C-rich) dusts,
carbon ($^{12}$C), iron carbide (FeC), silicon carbide (SiC), even silicon
($^{28}$Si), iron ($^{56}$Fe), and investigated the optical absorption
coefficients and emission coefficients of these materials in 0D
(zero$-$dimensional), 1D, and 2D nanostructures. Comparing the \textbf{nebular
spectra} of the supernovae (SN) with the coefficient of dust, we find that the
optical absorption coefficient of the 2D $^{12}$C, $^{28}$Si, $^{56}$Fe, SiC
and FeC structure corresponds to the absorption peak displayed in the infrared
band (5$-$8) $\mu$$m$ of the spectrum at 7554 days after the SN1987A explosion.
And it also corresponds to the spectrum of 535 days after the explosion of
SN2018bsz, when the wavelength in the range of (0.2$-$0.8) and (3$-$10)
$\mu$$m$. Nevertheless, 2D SiC and FeC corresponds to the spectrum of 844 days
after the explosion of SN2010jl, when the wavelength is within (0.08$-$10)
$\mu$$m$. Therefore, FeC and SiC may be the second type of dust in SN1987A
corresponding to infrared band (5$-$8) $\mu$$m$ of dust and may be in the
ejecta of SN2010jl and SN2018bsz.
|
2202.00260v1
|
2022-01-30
|
Ultrahigh-Pressure Magnesium Hydrosilicates as Reservoirs of Water in Early Earth
|
The origin of water on the Earth is a long-standing mystery, requiring a
comprehensive search for hydrous compounds, stable at conditions of the deep
Earth and made of Earth-abundant elements. Previous studies usually focused on
the current range of pressure-temperature conditions in the Earth's mantle and
ignored a possible difference in the past, such as the stage of the core-mantle
separation. Here, using ab initio evolutionary structure prediction, we find
that only two magnesium hydrosilicate phases are stable at megabar pressures,
$\alpha$-Mg$_2$SiO$_5$H$_2$ and $\beta$-Mg$_2$SiO$_5$H$_2$, stable at 262-338
GPa and >338 GPa,respectively (all these pressures now lie within the Earth's
iron core). Both are superionic conductors with quasi-one-dimensional proton
diffusion at relevant conditions. In the first 30 million years of Earth's
history, before the Earth's core was formed, these must have existed in the
Earth, hosting much of Earth's water. As dense iron alloys segregated to form
the Earth's core, Mg$_2$SiO$_5$H$_2$ phases decomposed and released water.
Thus, now-extinct Mg$_2$SiO$_5$H$_2$ phases have likely contributed in a major
way to the evolution of our planet.
|
2202.00752v1
|
2022-03-30
|
The Chemical Composition of Extreme-Velocity Stars
|
Little is known about the origin of the fastest stars in the Galaxy. Our
understanding of the Milky Way and surrounding dwarf galaxies chemical
evolution history allows us to use the chemical composition of a star to
investigate its origin, and say whether a star was formed in-situ or was
accreted. However, the fastest stars, the hypervelocity stars, are young and
massive and their chemical composition has not yet been analyzed. Though it is
difficult to analyze the chemical composition of a massive young star, we are
well versed in the analysis of late-type stars. We have used high-resolution
ARCES/3.5m Apache Point Observatory, MIKE/Magellan spectra to study the
chemical details of 15 late-type hypervelocity stars candidates. With Gaia EDR3
astrometry and spectroscopically determined radial velocities we found total
velocities with a range of $274$ - $520$ km s$^{-1}$ and mean value of $381$ km
s$^{-1}$. Therefore, our sample stars are not fast enough to be classified as
Hypervelocity stars, and are what is known as extreme-velocity stars. Our
sample has a wide iron abundance range of $-2.5 \le \mathrm{[Fe/H]} \le -0.9$.
Their chemistry indicate that at least 50\% of them are accreted extragalactic
stars, with iron-peak elements consistent with prior sub-Chandrasekhar mass
type Ia supernova enrichment. Without indication of binary companions, their
chemical abundances and orbital parameters are indicative that they are the
accelerated tidal debris of disrupted dwarf galaxies.
|
2203.16364v1
|
2022-04-08
|
Estimation of Nitrogen-to-Iron Abundance Ratios From Low-Resolution Spectra
|
We present a method to determine nitrogen abundance ratios with respect to
iron ([N/Fe]) from molecular CN-band features observed in low-resolution ($R
\sim$ 2000) stellar spectra obtained by the Sloan Digital Sky Survey (SDSS) and
the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Various
tests are carried out to check the systematic and random errors of our
technique, and the impact of signal-to-noise (S/N) ratios of stellar spectra on
the determined [N/Fe]. We find that the uncertainty of our derived [N/Fe] is
less than 0.3 dex for S/N ratios larger than 10 in the ranges $T_{eff}$ =
[4000, 6000] K, log g = [0.0, 3.5], [Fe/H] = [--3.0, 0.0], [C/Fe] = [--1.0,
+4.5], and [N/Fe] = [--1.0, +4.5], the parameter space that we are interested
in to identify N-enhanced stars in the Galactic halo. A star-by-star comparison
with a sample of stars with [N/Fe] estimates available from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) also suggests a similar
level of uncertainty in our measured [N/Fe], after removing its systematic
error. Based on these results, we conclude that our method is able to reproduce
[N/Fe] from low-resolution spectroscopic data, with an uncertainty sufficiently
small to discover N-rich stars that presumably originated from disrupted
Galactic globular clusters.
|
2204.03933v1
|
2022-04-08
|
Possible Implications of Relatively High Levels of Initial $^{60}$Fe in Iron Meteorites for the Non-Carbonaceous -- Carbonaceous Meteorite Dichotomy and Solar Nebula Formation
|
Cook et al. (2021) found that iron meteorites have an initial abundance ratio
of the short-lived isotope $^{60}$Fe to the stable isotope $^{56}$Fe of
$^{60}$Fe/$^{56}$Fe $\sim$ $(6.4 \pm 2.0) \times 10^{-7}$. This appears to
require the injection of live $^{60}$Fe from a Type II supernova (SN II) into
the presolar molecular cloud core, as the observed ratio is over a factor of
ten times higher than would be expected to be found in the ambient interstellar
medium (ISM) as a result of galactic chemical evolution. The supernova
triggering and injection scenario offers a ready explanation for an elevated
initial $^{60}$Fe level, and in addition provides a physical mechanism for
explaining the non-carbonaceous -- carbonaceous (NC-CC) dichotomy of
meteorites. The NC-CC scenario hypothesizes the solar nebula first accreted
material that was enriched in supernova-derived nuclides, and then later
accreted material depleted in supernova-derived nuclides. While the NC-CC
dichotomy refers to stable nuclides, not short-lived isotopes like $^{60}$Fe,
the SN II triggering hypothesis provides an explanation for the otherwise
unexplained change in nuclides being accreted by the solar nebula. Three
dimensional hydrodynamical models of SN II shock-triggered collapse show that
after triggering collapse of the presolar cloud core, the shock front sweeps
away the local ISM while accelerating the resulting protostar/disk to a speed
of several km/s, sufficient for the protostar/disk system to encounter within
$\sim$ 1 Myr the more distant regions of a giant molecular cloud complex that
might be expected to have a depleted inventory of supernova-derived nuclides.
|
2204.04134v1
|
2022-04-21
|
Ferrous Metal Matrix Composites Status Scope and Challenges
|
The present paper is an effort to culminate the status, scopes and challenges
in the development of ferrous metal matrix composites (FMMCs). The FMMCs are
old but less in use than the non-ferrous metal matrix composites (NFMMCs), as
far as literature and actual applications are concerned. Therefore, this
stimulates the exploration of the reasons behind the scarcity of literature and
field applications of the FMMCs, which must be investigated scientifically. The
powder metallurgy route is the most used process for fabricating iron and steel
based FMMCs by reinforcing particulates. At the same time, the in-situ method
has been used for the fabrication and cast iron-based FMMCs. The main
characteristics being considered during the designing and fabrication of FMMCs
are wear resistance and improved specific mechanical properties. To fabricate
cheaper and eco-friendly FMMCs, traditionally used costly reinforcements such
as SiC, WC, TiC, SiO2, TiO2, TiB2 are required to be replaced by inexpensive
industrial wastes like red-mud, fly-ashes and grinding swarf. The data
extracted from the web of science exhibited that the FMMCs have been researched
less than the NFMMCs. The increasing number of research papers on FMMCs
indicates a bright future. FMMCs are going to be a favourite topic among
researchers and manufacturers. Higher strengths, wear resistance, dimensional
stability at elevated temperatures, and, most importantly, the lower cost will
put forward the FMMCs as a stiff competitor of NFMMCs. In developing and mass
production of FMMCs for field applications, challenges like oxidation and
higher weight still require special research efforts.
|
2204.09999v2
|
2022-04-21
|
Detection of CO emission lines in the dayside atmospheres of WASP-33b and WASP-189b with GIANO
|
Ultra-hot Jupiters (UHJs) are expected to possess temperature inversion
layers in their dayside atmospheres. Recent thermal emission observations have
discovered several atomic and molecular species along with temperature
inversions in UHJs. We observed the thermal emission spectra of two UHJs
(WASP-33b and WASP-189b) with the GIANO-B high-resolution near-infrared
spectrograph. Using the cross-correlation technique, we detected carbon
monoxide (CO) in the dayside atmospheres of both planets. The detected CO lines
are in emission, which agrees with previous discoveries of iron emission lines
and temperature inversions in the two planets. This is the first detection of
CO lines in emission with high-resolution spectroscopy. Further retrieval work
combining the CO lines with other spectral features will enable a comprehensive
understanding of the atmospheric properties such as temperature structures and
C/O ratios. The detected CO and iron emission lines of WASP-189b have
redshifted radial velocities of several km/s, which likely originate from a
dayside to nightside wind in its atmosphere. Such a redshifted velocity has not
been detected for the emission lines of WASP-33b, suggesting that the
atmospheric circulation patterns of the two UHJs may be different.
|
2204.10158v1
|
2022-05-17
|
A Disc Reflection Model for Ultra-Soft Narrow-Line Seyfert 1 Galaxies
|
We present a detailed analysis of the XMM-Newton observations of five
narrow-line Seyfert 1 galaxies (NLS1s). They all show very soft continuum
emission in the X-ray band with a photon index of $\Gamma\gtrsim 2.5$.
Therefore, they are referred to as `ultra-soft' NLS1s in this paper. By
modeling their optical/UV-X-ray spectral energy distribution (SED) with a
reflection-based model, we find indications that the disc surface in these
ultra-soft NLS1s is in a higher ionisation state than other typical Seyfert 1
AGN. Our best-fit SED models suggest that these five ultra-soft NLS1s have an
Eddington ratio of $\lambda_{\rm Edd}=1-20$ assuming available black hole mass
measurements. In addition, our models infer that a significant fraction of the
disc energy in these ultra-soft NLS1s is radiated away in the form of
non-thermal emission instead of the thermal emission from the disc. Due to
their extreme properties, X-ray observations of these sources in the iron band
are particularly challenging. Future observations, e.g. from Athena, will
enable us to have a clearer view of the spectral shape in the iron band and
thus distinguish the reflection model from other interpretations of their
broadband spectra.
|
2205.08236v1
|
2022-05-28
|
Spectral Evidence for Unidirectional Charge Density Wave in Detwinned BaNi$_2$As$_2$
|
The emergence of unconventional superconductivity in proximity to intertwined
electronic orders is especially relevant in the case of iron-based
superconductors. Such order consists of an electronic nematic order and a spin
density wave in these systems. BaNi$_2$As$_2$, like its well-known iron-based
analog BaFe$_2$As$_2$, also hosts a symmetry-breaking structural transition
that is coupled to a unidirectional charge density wave (CDW), providing a
novel platform to study intertwined orders. Here, through a systematic
angle-resolved photoemission spectroscopy study combined with a detwinning
$B_1g$ uniaxial strain, we identify distinct spectral evidence of band
evolution due to the structural transition as well as CDW-induced band folding.
In contrast to the nematicity and spin density wave in BaFe$_2$As$_2$, the
structural and CDW order parameters in BaNi$_2$As$_2$ are observed to be
strongly coupled and do not separate in the presence of uniaxial strain. Our
measurements point to a likely lattice origin of the CDW in BaNi$_2$As$_2$.
|
2205.14339v1
|
2022-06-02
|
Lithium detection in red supergiant stars of the Perseus complex
|
We present the first systematic study of lithium abundance in a chemically
homogeneous sample of 27 red supergiants (RSGs) in the young Perseus complex.
For these stars, accurate stellar parameters and detailed chemical abundances
of iron and iron peak, CNO, alpha, light and neutron-capture elements have been
already obtained by means of high resolution optical and near-infrared
spectroscopy. The observed RSGs have half-solar metallicity, 10-30 Myr age,
bolometric luminosities in the 10$^4$-10$^5$ L$_{\odot}$ range and likely mass
progenitors in the 9-14 M$_{\odot}$ range. We detected the optical Li I doublet
in eight out of the 27 observed K and M type RSGs, finding relatively low
A(Li)$<$1.0 dex abundances, while for the remaining 19 RSGs upper limits of
A(Li)$<$-0.2 dex have been set. Warmer and less luminous (i.e. likely less
massive) as well as less mixed (i.e. with lower [C/N] and $^{12}$C/$^{13}$C
depletion) RSGs with Li detection show somewhat higher Li abundances. In order
to explain Li detection in $\sim$30\% of the observed RSGs, we speculate that
some stochasticity and a scenario where Li was not completely destroyed in the
convective atmospheres and/or a secondary production took place during the
post-Main Sequence evolution, should be at work.
|
2206.01218v1
|
2022-06-15
|
Hyperfine fields at $^{66}$Ga, $^{67,69}$Ge implanted into iron and gadolinium hosts at 6 K, and applications to g-factor measurements
|
Isomers in $^{66}$Ga, $^{67}$Ge, and $^{69}$Ge were recoil-implanted into
ferromagnetic hosts of iron and gadolinium at $\approx 6$~K, and the hyperfine
magnetic fields were determined by Time Differential Perturbed Angular
Distribution (TDPAD) measurements. The hyperfine field strengths at $\approx
6$~K are compared to the results of previous higher-temperature measurements
and the amplitudes of the $R(t)$ functions are compared to empirical
expectations. The results show that gadolinium can be a suitable host for
high-precision in-beam $g$-factor measurements. The results of new $g$-factor
measurements for isomers in $^{66}$Ga and $^{67}$Ge are $g(^{66}$Ga$,7^{-}) =
+0.126(4)$, supporting a $[\pi_{f5/2} \otimes \nu g_{9/2}]_{7^-}$ configuration
assignment, and $g(^{67}$Ge$,\frac{9}{2}^{+})=-0.1932(22)$, derived from a new
measurement of the ratio $g(^{67}\mathrm{Ge})/g(^{69}\mathrm{Ge}) = 0.869(9)$.
These values are in agreement with previous results. The $R(t)$ amplitudes
indicate that the nuclear alignment produced in the isomeric states was
significantly lower than the empirically expected $\sigma/I \approx 0.35$.
|
2206.07294v1
|
2022-06-23
|
Size-dependent Failure Behavior of Lithium-Iron Phosphate Battery under Mechanical Abuse
|
Under mechanical abuse conditions, the failure of lithium-ion batteries
occurs in various stages characterized by different force, temperature and
voltage response which require it's in-situ measurements for analysis. Firstly,
four sizes of commercially available lithium-iron phosphate batteries (LFPB)
viz. 18650, 22650, 26650, and 32650 are subjected to quasi static lateral,
longitudinal compression, and nail penetration tests. The failure,
characterized by the voltage drop and temperature rise, at the onset of the
first internal short-circuit (ISC), is identified by Aurdino-based voltage
sensor module and temperature measurement module, respectively. The battery
failure load and peak temperature at the onset of ISC are found to rely on the
battery size strongly. The failure is observed to be delayed for small-sized
18650 batteries during lateral compression, unlike longitudinal compression and
nail penetration test. At the onset of the short circuit, the temperature rise
above the ambient value is different for different LFPBs. It is found to be
maximum (64.4 degree C ) for LFPB 32650 under longitudinal compression and
minimum (29.5 degree C) under lateral compression tests amongst the considered
geometries. Further, LFPB 26650 exhibited a balanced thermal behavior during
the considered abused condition. Such data can be sensed timely for effective
thermal management and improved safety of lithium-ion batteries.
|
2206.11732v2
|
2022-08-03
|
Light-induced dynamics of liquid-crystalline droplets on the surface of iron-doped lithium niobate crystals
|
We investigated the effect of a photovoltaic field generated on the surface
of iron-doped lithium niobate crystals on droplets of a ferroelectric nematic
liquid crystalline and a standard nematic liquid crystalline material deposited
on this surface. When such assembly is illuminated with a laser beam, a wide
range of dynamic phenomena are initiated. Droplets located outside the laser
spot are dragged in the direction of the illuminated area, while droplets
located inside the illuminated region tend to bridge each other and rearrange
into tendril-like structures. In the ferroelectric nematic phase (NF) these
processes take place via the formation of conical spikes evolving into jet
streams, similar to the behavior of droplets of conventional dielectric liquids
exposed to overcritical electric fields. However, in contrast to conventional
liquids, the jet streams of the NF phase exhibit profound branching. In the
nematic phase (N) of both the ferroelectric nematic and the standard nematic
material, dynamic processes occur via smooth-edged continuous features typical
for conventional liquids subjected to under-critical fields. The difference in
dynamic behavior is attributed to the large increase of dielectric permittivity
in the ferroelectric nematic phase with respect to the dielectric permittivity
of the nematic phase.
|
2208.02318v1
|
2022-09-07
|
Transport evidence for the surface state and spin-phonon interaction in FeTe$_{0.5}$Se$_{0.5}$
|
The iron chalcogenides have been proved to be intrinsic topological
superconductors to implement quantum computation because of their unique
electronic structures. The topologically nontrivial surface states of
FeTe$_{0.5}$Se$_{0.5}$ have been predicted by several calculations and then
confirmed by high-resolution photoemission and scanning tunneling experiments.
However, so far, the shreds of the electrical transport evidence for
topological surface states are still in absence. By carrying out electrical
transport experiments, we observe a topological transition with a nonlinear
Hall conductivity and simultaneous linear magnetoresistance near the
superconducting transition temperature. Furthermore, we observe a sign reversal
of the Hall coefficient accompanied by a concurrently softening of the
${A}_{1g}$ phonon mode at about 40 K, indicating a nematic transition. The
synchronized phonon softening with nematicity manifests an enhanced fluctuation
state through spin-phonon interaction. Our results solidly corroborate the
topological surface states of FeTe$_{0.5}$Se$_{0.5}$ and provide an
understanding of the mechanism of the superconductivity in iron chalcogenides.
|
2209.03267v2
|
2022-09-14
|
Structural peculiarities of $\varepsilon$-Fe$_2$O$_3$ / GaN epitaxial layers unveiled by high-resolution transmission electron microscopy and neutron reflectometry
|
The present paper is dedicated to the structural study of crystallographic
peculiarities appearing in epitaxial films of metastable epsilon iron oxide
($\varepsilon$-Fe$_2$O$_3$) grown by pulsed laser deposition onto a
semiconductor GaN (0001) substrate. The columnar structure of the nanoscale
$\varepsilon$-Fe$_2$O$_3$ films has been for the first time investigated using
high resolution electron microscopy (HRTEM) direct space technique complemented
by reciprocal space methods of high-energy electron diffraction and
color-enhanced HRTEM image Fourier filtering. The study of
$\varepsilon$-Fe$_2$O$_3$ / GaN interface formation has been further expanded
by carrying out a depth resolved analysis of density and chemical composition
by neutron reflectometry and energy-dispersive X-ray spectroscopy. The obtained
results shed light onto the properties and the origin of the enigmatic
few-nanometer thick low density transition layer residing at the
$\varepsilon$-Fe$_2$O$_3$ / GaN interface. A detailed knowledge of the
properties of this layer is believed to be highly important for the development
of $\varepsilon$-Fe$_2$O$_3$ / GaN heterostructures that can potentially become
part of the iron-oxide based ferroic-on-semiconductor devices with room
temperature magneto-electric coupling.
|
2209.06460v1
|
2022-09-15
|
Spin-charge coupling and decoupling in perovskite-type iron oxides (Sr$_{1-x}$Ba$_x$)$_{2/3}$La$_{1/3}$FeO$_3$
|
The perovskite-type iron oxide Sr$_{2/3}$La$_{1/3}$FeO$_3$ is known to show
characteristic spin-charge ordering (SCO), where sixfold collinear spin
ordering and threefold charge ordering are coupled with each other. Here, we
report the discovery of a spin-charge decoupling and an antiferromagnetic (AFM)
state competing with the SCO phase in perovskites
(Sr$_{1-x}$Ba$_x$)$_{2/3}$La$_{1/3}$FeO$_3$. By comprehensive measurements
including neutron diffraction, M$\"{o}$ssbauer spectroscopy, and x-ray
absorption spectroscopy, we found that the isovalent Ba$^{2+}$ substitution
systematically reduces the critical temperature of the SCO phase and
additionally yields the spin-charge decoupling in $x$ > 0.75. Whereas the
ground state remains in the SCO phase in the whole $x$ region, an unexpected
G-type AFM phase with incoherent charge ordering or charge fluctuation appears
as the high-temperature phase in the range of $x$ > 0.75. Reflecting the
competing nature between them, the G-type AFM phase partially exists as a
metastable state in the SCO phase at low temperatures. We discuss the origin of
the spin-charge decoupling and the emergence of the G-type AFM phase with
charge fluctuation in terms of the bandwidth reduction by the Ba substitution.
|
2209.07310v1
|
2022-09-18
|
Revisit the Circumnuclear X-ray Emission of NGC 2992 in a Historically Low State
|
The inner-most region of the Seyfert galaxy NGC 2992 has long been suspected
to be the location of intense AGN-host galaxy interaction, but photon pile-up
in previous high-resolution observations hampered the study of soft X-ray
excess and the interaction near its nucleus. We present an X-ray imaging
spectroscopic analysis of the circumnuclear
($1^{\prime\prime}$--$3^{\prime\prime}$) region of NGC 2992 using the
zeroth-order image of a 135 ks grating observation obtained with Chandra, which
captured the nucleus in a historically low flux state. Extended soft X-ray
emission is detected in the circumnuclear region with observed luminosity
$L_{\rm X} \sim 7 \times 10^{39}\rm\ erg\ s^{-1}$. The majority of previously
puzzling detection of soft excess could be associated with the outflow,
indicated by the morphological correspondences between soft X-ray emission and
figure-eight-shaped radio bubbles. An anomalous narrow emission line with the
centroid energy $\sim4.97$ keV is found. If attributed to redshifted highly
ionized iron emission (e.g., Fe xxv), the required outflow velocity is
$\sim0.23\,c$. An alternative explanation is that this line emission could be
produced by the nuclear spallation of iron. We also find asymmetric extended Fe
K$\alpha$ emission along the galactic disk, which could originate from
reflection by cold gas on $\sim 200$ pc scale.
|
2209.08534v1
|
2022-09-18
|
Efficient photocatalytic nitrogen fixation from air under sunlight via iron-doped WO$_3$
|
Photocatalytic nitrogen fixation from air directly under sunlight can
contribute significantly to carbon neutralization. It is an ideal pathway to
replace the industrial Haber Bosch process in future. A Fe-doped layered WO$_3$
photocatalyst containing oxygen vacancies was developed which can fix nitrogen
from air directly under sunlight at atmospheric pressure. The iron doping
enhances the transport efficiency of photogenerated electrons. The
photocatalytic efficiency is around 4 times higher than that of pure WO$_3$.
The optimum nitrogen fixation conditions were examined by orthogonal
experiments and its nitrogen fixation performance could reach up to 477 $\mu
\text{g} \cdot \text{g}_{\text{cat}}^{-1} \cdot \text{h}^{-1}$ under sunlight.
In addition, the process of nitrogen fixation was detected by situ infrared,
which confirmed the reliability of nitrogen fixation. Also, modelling on the
interactions between light and the photocatalyst was carried out to study the
distribution of surface charge and validate the light absorption of the
photocatalyst. This work provides a simple and cheap strategy for
photocatalytic nitrogen fixation from air under mild conditions.
|
2209.08547v1
|
2022-09-30
|
Charge Transport in Ba$_{1-x}$Rb$_{x}$Fe$_{2}$As$_{2}$ Single Crystals
|
Recent studies in heavily hole-doped iron-based superconductor RbFe$_2$As$_2$
have suggested the emergence of novel electronic nematicity directed along the
Fe-As direction, 45$^\circ$ rotated from the usual nematicity ubiquitously
found in BaFe$_2$As$_2$ and related materials. This motivates us to study the
physical properties of Ba$_{1-x}$Rb$_{x}$Fe$_{2}$As$_{2}$, details of which
remain largely unexplored. Here we report on the normal-state charge transport
in Ba$_{1-x}$Rb$_{x}$Fe$_{2}$As$_{2}$ superconductors by using high-quality
single crystals in the range of Rb concentration $0.14\le x \le 1.00$. From the
systematic measurements of the temperature dependence of electrical resistivity
$\rho(T)$, we find a signature of a deviation from the Fermi liquid behavior
around the optimal composition, which does not seem related to the
antiferromagnetic quantum criticality but has a potential link to hidden
nematic quantum criticality. In addition, electron correlations derived from
the coefficient of $T^2$ resistivity show a marked increase with Rb content
near the heavily hole-doped end, consistent with the putative Mott physics near
the $3d^5$ electron configuration in iron-based superconductors.
|
2209.15526v1
|
2022-10-20
|
Kinetics of transformation, border of metastable miscibility gap in Fe-Cr alloy and limit of Cr solubility in iron at 858 K
|
The study was aimed at determination of the position of the Fe-rich border of
the metastable miscibility gap (MMG) and of the solubility limit of Cr in iron
at 858 K. Towards this end a Fe73.7Cr26.3 alloy was isothermally annealed at
858 K in vacuum up to 8144 hours and M\"ossbauer spectra were recorded at room
temperature after every step of the annealing. Three spectral parameters viz.
the average hyperfine field, <B>, the average isomer shift, <IS>, and the
probability of the atomic configuration with no Cr atoms in the two-shell
vicinity of the probe Fe atoms, P(0,0), gave evidence that the transformation
process takes place in two stages. All three parameters could have been well
described in terms of the Johnson-Mehl-Avrami-Kolmogorov equation, yielding
kinetics parameters. The first stage, associated with the phase decomposition,
proceeded much faster than the second stage, associated with the alpha-to-sigma
phase transformation. The most reliable estimation of the position of the MMG
and that of the value of the Cr solubility limit was obtained from the
annealing time dependence of <B>, namely 24.5 at.% Cr for the former and 20.3
at.% Cr for the latter. A comparison of these figures with the recent phase
diagrams pertinent to Fe-Cr system was done.
|
2210.11550v1
|
2022-11-04
|
Unusual Abundances from Planetary System Material Polluting the White Dwarf G238-44
|
Ultraviolet and optical spectra of the hydrogen-dominated atmosphere white
dwarf star G238-44 obtained with FUSE, Keck/HIRES, HST/COS, and HST/STIS reveal
ten elements heavier than helium: C, N, O, Mg, Al, Si, P, S, Ca, and Fe.
G238-44 is only the third white dwarf with nitrogen detected in its atmosphere
from polluting planetary system material. Keck/HIRES data taken on eleven
nights over 24 years show no evidence for variation in the equivalent width of
measured absorption lines, suggesting stable and continuous accretion from a
circumstellar reservoir. From measured abundances and limits on other elements
we find an anomalous abundance pattern and evidence for the presence of
metallic iron. If the pollution is from a single parent body, then it would
have no known counterpart within the solar system. If we allow for two distinct
parent bodies, then we can reproduce the observed abundances with a mix of
iron-rich Mercury-like material and an analog of an icy Kuiper Belt object with
a respective mass ratio of 1.7:1. Such compositionally disparate objects would
provide chemical evidence for both rocky and icy bodies in an exoplanetary
system and would be indicative of a planetary system so strongly perturbed that
G238-44 is able to capture both asteroid- and Kuiper Belt-analog bodies
near-simultaneously within its $<$100 Myr cooling age.
|
2211.02673v1
|
2022-11-09
|
Asynchronous accretion can mimic diverse white dwarf pollutants I: core and mantle fragments
|
Polluted white dwarfs serve as astrophysical mass spectrometers - their
photospheric abundances are used to infer the composition of planetary objects
that accrete onto them. We show that due to asymmetries in the accretion
process, the composition of the material falling onto a star may vary with time
during the accretion of a single planetary body. Consequently, the
instantaneous photospheric abundances of white dwarfs do not necessarily
reflect the bulk composition of their pollutants, especially when their
diffusion timescales are short. In particular, we predict that when an asteroid
with an iron core tidally disrupts around a white dwarf, a larger share of its
mantle is ejected, and that the core/mantle fraction of the accreting material
varies with time during the event. Crucially, this implies that the core
fraction of differentiated pollutants cannot be determined for white dwarfs
with short diffusion timescales, which sample only brief episodes of longer
accretion processes. The observed population of polluted white dwarfs backs up
the proposed theory. More white dwarfs have accreted material with high Fe/Ca
than low Fe/Ca relative to stellar abundance ratios, indicating the ejection of
mantle material. Additionally, we find tentative evidence that the accretion
rate of iron decreases more rapidly than that of magnesium or calcium, hinting
at variability of the accreted composition. Further corroboration of the
proposed theory will come from the up-coming analysis of large samples of young
white dwarfs.
|
2211.05114v1
|
2022-11-21
|
Discontinuous Shear Thickening (DST) transition with spherical iron particles coated by adsorbed brush polymer
|
In this work we explore the rheology of very concentrated (0.55<$\Phi$<0.67)
suspensions of carbonyl iron (CI) particles coated by a small polymer. A strong
DST is observed in a large range of volume fraction presenting some
specificities relatively to other systems. In particular, in a given range of
volume fraction, the DST transition appears suddenly without being preceded by
shear thickening. The presence of a frictional network of particles is
confirmed by a simultaneous measurement of the electric resistance of the
suspension and of the rheological curve. Using the Wyart-Cates model we show
that, increasing the volume fraction, the fraction of frictional contacts grows
more and more quickly with the stress that disagrees with the prediction of
computer simulations. The same kind of behavior is observed in the presence of
a magnetic field with, in addition, a very strong increase of the viscosity
with the magnetic field before the transition. We interpret this behavior by
the interpenetration of the polymer layer under the effect of the shear
stress-and of the magnetic stress-followed by the expulsion of the polymer out
of the surfaces. Besides we point that, above the DST transition, we do not
observe a jamming in the range of volume fraction whereas it is predicted by
the W-C model. Based on the fact that in the absence of shear flow, the polymer
should come back to the surface and destroy the frictional contacts we can
predict an asymptotic non-zero shear rate and reproduce the experimental
behavior.
|
2211.11807v1
|
2022-12-03
|
Electron correlation in the Iron(II) Porphyrin by NOF approximations
|
The relative stability of the singlet, triplet, and quintet spin states of
Iron(II) porphyrin (FeP) represents a challenging problem for electronic
structure methods. While it is currently accepted that the ground state is a
triplet, multiconfigurational wavefunction-based methods predict a quintet, and
density functional approximations vary between triplet and quintet states,
leading to a prediction that highly depends on the features of the method
employed. The recently proposed Global Natural Orbital Functional (GNOF) aims
to provide a balanced treatment between static and dynamic correlation, and
together with the previous Piris Natural Orbital Functionals (PNOFs), allowed
us to explore the importance of each type of correlation in the stability order
of the states of FeP with a method that conserves the spin of the system. It is
noteworthy that GNOF correlates all electrons in all available orbitals for a
given basis set; in the case of the FeP with a double zeta basis set as used in
this work; this means that GNOF can properly correlate 186 electrons in 465
orbitals, significantly increasing the sizes of systems amenable to
multiconfigurational treatment. Results show that PNOF5, PNOF7s and PNOF7
predict the quintet to have a lower energy than the triplet state; however, the
addition of dynamic correlation via second-order Moller-Plesset corrections
(NOF-MP2) turns the triplet state to be lower than the quintet state, a
prediction also reproduced by GNOF that incorporates much more dynamic
correlation than its predecessors.
|
2212.01640v1
|
2022-12-13
|
Collapse of Metallicity and High-$T_c$ Superconductivity in the High-Pressure phase of FeSe$_{0.89}$S$_{0.11}$
|
We investigate the high-pressure phase of the iron-based superconductor
FeSe$_{0.89}$S$_{0.11}$ using transport and tunnel diode oscillator studies. We
construct detailed pressure-temperature phase diagrams that indicate that
outside of the nematic phase, the superconducting critical temperature reaches
a minimum before it is quickly enhanced towards 40 K above 4 GPa. The
resistivity data reveal signatures of a fan-like structure of non-Fermi liquid
behaviour which could indicate the existence of a putative quantum critical
point buried underneath the superconducting dome around 4.3 GPa. Further
increasing the pressure, the zero-field electrical resistivity develops a
non-metallic temperature dependence and the superconducting transition broadens
significantly. Eventually, the system fails to reach a fully zero-resistance
state despite a continuous finite superconducting transition temperature, and
any remaining resistance at low temperatures becomes strongly
current-dependent. Our results suggest that the high-pressure, high-$T_c$ phase
of iron chalcogenides is very fragile and sensitive to uniaxial effects of the
pressure medium, cell design and sample thickness which can trigger a
first-order transition. These high-pressure regions could be understood
assuming a real-space phase separation caused by concomitant electronic and
structural instabilities.
|
2212.06824v1
|
2022-12-21
|
Post-Synthetic Treatment of Nickel-Iron Layered Double Hydroxides for the Optimum Catalysis of the Oxygen Evolution Reaction
|
Nickel-iron layered double hydroxide (NiFe LDH) platelets with high
morphological regularity and sub-micrometre lateral dimensions were synthesized
using a homogeneous precipitation technique for highly efficient catalysis of
the oxygen evolution reaction (OER). Considering edge sites are the point of
activity, efforts were made to control platelet size within the synthesized
dispersions. The goal is to controllably isolate and characterize size-reduced
NiFe LDH particles. Synthetic approaches for size control of NiFe LDH platelets
have not been transferable based on published work with other LDH materials and
for that reason, we instead use post-synthetic treatment techniques to improve
edge-site density. In the end, size reduced NiFe LDH/single-wall carbon
nanotube (SWCNT) composites allowed to further reduce the OER overpotential to
237 plus/minus 7 mV ( L = 0.16 plus/minus 0.01 micrometres, 20 wt% SWCNT),
which is one of the best values reported to date. This approach as well
improved the long term activity of the catalyst in operating conditions.
|
2212.11378v1
|
2023-01-03
|
Extracting optical parameters of Cu-Mn-Fe spinel oxide nanoparticles for optimizing air-stable, high-efficiency solar selective coatings
|
High-temperature Cu-Mn-Fe spinel-oxide nanoparticle solar selective absorber
coatings are investigated experimentally and theoretically. A reliable, general
approach to evaluate absorption coefficient spectra from the optical
measurements of the nanoparticle-pigmented coatings is developed based on
solving the inverse problem using four-flux-radiative method. The derived
absorption properties of NP materials can be directly applied to predict the
solar absorptance, optimize the nanoparticle-pigmented coatings, and analyze
the thermal degradation, which agree well with the experimental results. The
analysis reveals that the Cu-Mn-Fe spinel oxides are fundamentally indirect
bandgap ranging from 1.7 to 2.1 eV, while iron-free CuMn2O4 is a direct bandgap
material with Eg=1.84 eV. With the same coating thickness and nanoparticle
load, the solar absorptance ranks in the order of Mn2O3 < MnFe2O4 < CuFe2O4 <
CuFeMnO4 < CuMn2O4. The optimized spray-coated iron-free CuMn2O4 NP-pigmented
coating demonstrates a high solar absorptance of 97%, a low emittance of 55%, a
high optical-to-thermal energy conversion efficiency of ~93.5 % under 1000x
solar concentration at 750 degrees C, and long-term endurance upon thermal
cycling between 750{\deg}C and room temperature in air. The optical parameter
analysis approach can be easily extended to other material systems to
facilitate the searching and optimizing high-temperature pigmented-solar
selective coatings.
|
2301.01194v1
|
2023-01-07
|
Orthogonal magnetic structures of Fe4O5:representation analysis and DFT calculations
|
The magnetic and electronic structures of Fe4O5 have been investigated at
ambient and high pressures via a combination of representation analysis,
density functional theory (DFT+U) calculations, and M\"ossbauer spectroscopy. A
few spin configurations corresponding to the different irreducible
representations have been considered. The total-energy calculations reveal that
the magnetic ground state of Fe4O5 corresponds to an orthogonal spin order.
Depending on the magnetic propagation vector k two spin ordered phases with
minimal energy differences are realized. The lowest energy magnetic phase is
related to k = (0, 0, 0) and is characterized by the ferromagnetic ordering of
the iron magnetic moments at prismatic sites along the b axis and
antiferromagnetic ordering of iron moments at octahedral sites along the c
axis. For the k = (1/2, 0, 0) phase, the moments in the prisms are
antiferromagnetically ordered along the b axis and the moments in the octahedra
are still antiferromagnetically ordered along the c axis. Under high pressure,
the Fe4O5 exhibits magnetic transitions with corresponding electronic
transitions of the metal-insulator type. At a critical pressure PC ~ 60 GPa the
Fe ions at the octahedral sites undergo a high-spin to low-spin state crossover
with a decrease in the unit-cell volume of ~ 4%, while the Fe ions at the
prismatic sites remain in the high-spin state up to 130 GPa. This
site-dependent magnetic collapse is experimentally observed in the
transformation of M\"ossbauer spectra measured at room temperature and high
pressures.
|
2301.02824v1
|
2023-02-03
|
An empirical relation to estimate host galaxy stellar light from AGN spectra
|
Measurement of black hole mass for low-$z$ ($z\leq 0.8$) Active Galactic
Nuclei (AGNs) is difficult due to the strong contribution from host galaxy
stellar light necessitating detailed spectral decomposition to estimate the AGN
luminosity. Here, we present an empirical relation to estimate host galaxy
stellar luminosity from the optical spectra of AGNs at $z\leq 0.8$. The
spectral data were selected from the fourteenth data release of the Sloan
Digital Sky Survey (SDSS-DR14) quasar catalog having a signal-to-noise ratio at
5100 \AA (SNR$_{5100}$) $>$10 containing 11415 quasars. The median total
luminosity (log ($L_\text{total}$/[erg s$^{-1}$])), stellar luminosity (log
($L_\text{star}$/[erg s$^{-1}$])), and AGN continuum luminosity (log
($L_\text{cont}$/[erg s$^{-1}$])) in our sample are 44.52, 44.06, and 44.30,
respectively. We fit the AGN power-law continuum, host galaxy, and iron blend
contribution, simultaneously over the entire available spectrum. We found the
host galaxy fraction to anti-correlate with continuum luminosity and can be
well-represented by a polynomial function, which can be used to correct the
stellar light contribution from AGN spectra. We also found anti-correlation
between host galaxy fraction and iron strength, Eddington ratio, and redshift.
The empirical relation gives comparable results of host-fraction with the image
decomposition method.
|
2302.01948v2
|
2023-02-13
|
Evolution of phase morphology in dispersed clay systems under the microwave irradiation
|
The results of a study of the effect of microvolume emission (power 700 W,
frequency 2.45 GHz) on the structural changes in natural clay particles are
presented. The influence of the irradiation time (10 and 20 minutes) and the
environment in the microwave chamber (atmospheric air and air saturated with
water vapor) on the structural changes occurring in the particles was traced.
During the first 10 minutes, capillary water is completely removed and
agglomeration is carried out by attaching single dispersed particles (diffusion
limited aggregation model). At the second stage (10-20 minutes), already formed
agglomerates (cluster-cluster aggregation model) are growing. A complex of
independent optical-physical methods was used to analyze weak structural
changes. It includes X-ray phase analysis, colorimetry and wavelet analysis.
This approach has made it possible to increase the information content and
reliability of measurements, quantitatively characterize the structural
responses in disperse clay systems. In the air, the removal of capillary water
is accompanied by agglomerations of particles and polymorphic transformations
of oxides: montmorillonite is completely decomposed, amorphous phases
crystallize. The composition of the environment in the microwave chamber
affects the type of phase transformations in iron compounds: iron-alumina is
formed in air, magnetite appear in the water vapor medium. The studies carried
out using the developed set of experimental methods indicate the possibility of
regulating the processes of structure formation in disperse clay systems by
optimizing the regimes of exposure to microwave radiation.
|
2302.06330v1
|
2023-03-01
|
A Search for Chemical Anomalies of Seven A-types Stars
|
We present a chemical abundance analysis of seven A-type stars with no
detailed chemical abundance measurements in the literature. High-resolution
spectra of the targets HD 2924, HD 4321, HD 26553, HD 125658, HD 137928, HD
154713, and HD 159834 were obtained using the Coude Echelle Spectrograph at the
TUBITAK National Observatory. We determined the atmospheric abundances of the
samples and measured the elemental abundances of C, N, O, Na, Mg, Al, Si, S, K,
Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, Eu,
and Gd. The masses of the stars were estimated based on their evolutionary
tracks, and their ages were calculated using isochrones. We also calculated the
radii of the stars. The abundance patterns of HD 4321, HD 125658, and HD 154713
were found to be in agreement with those of classical Am stars, with
underabundant Ca and Sc, overabundant heavier elements, and moderate
overabundance of iron-peak elements. We found that HD 137928 and HD 159834 have
similar abundance characteristics to marginal Am-type stars. The elemental
distributions of HD 2924 and HD 26553 are consistent with the pattern of normal
A-type stars. The iron, nickel, and zinc abundances of HD 125658 and HD 137928
are significantly higher than other Am stars. These values suggest that they
are among the most metal-rich Am stars
|
2303.00584v1
|
2023-05-29
|
Intertwined charge and pair density orders in a monolayer high-Tc iron-based superconductor
|
Symmetry-breaking electronic phase in unconventional high-temperature
(high-Tc) superconductors is a fascinating issue in condensed-matter physics,
among which the most attractive phases are charge density wave (CDW) phase with
four unit-cell periodicity in cuprates and nematic phase breaking the C4
rotational symmetry in iron-based superconductors (FeSCs). Recently, pair
density wave (PDW), an exotic superconducting phase with non-zero momentum
Cooper pairs, has been observed in high-Tc cuprates and the monolayer FeSC.
However, the interplay between the CDW, PDW and nematic phase remains to be
explored. Here, using scanning tunneling microscopy/spectroscopy, we detected
commensurate CDW and CDW-induced PDW orders with the same period of lambda =
4aFe (aFe is the distance between neighboring Fe atoms) in a monolayer high-Tc
Fe(Te,Se) film grown on SrTiO3(001) substrate. Further analyses demonstrate the
observed CDW is a smectic order, which breaks both translation and C4
rotational symmetry. Moreover, the smecticity of the CDW order is strongest
near the superconducting gap but weakens near defects and in an applied
magnetic field, indicating the interplay between the smectic CDW and PDW
orders. Our works provide a new platform to study the intertwined orders and
their interactions in high-Tc superconductors.
|
2305.17991v1
|
2023-06-22
|
Type Ia Supernova Nucleosynthesis: Metallicity-Dependent Yields
|
Type Ia supernova explosions (SNIa) are fundamental sources of elements for
the chemical evolution of galaxies. They efficiently produce intermediate-mass
(with Z between 11 and 20) and iron group elements - for example, about 70% of
the solar iron is expected to be made by SNIa. In this work, we calculate
complete abundance yields for 39 models of SNIa explosions, based on three
progenitors - a 1.4M deflagration detonation model, a 1.0 double detonation
model and a 0.8 M double detonation model - and 13 metallicities, with 22Ne
mass fractions of 0, 1x10-7, 1x10-6, 1x10-5, 1x10-4, 1x10-3, 2x10-3, 5x10-3,
1x10-2, 1.4x10-2, 5x10-2, and 0.1 respectively. Nucleosynthesis calculations
are done using the NuGrid suite of codes, using a consistent nuclear reaction
network between the models. Complete tables with yields and production factors
are provided online at Zenodo: Yields. We discuss the main properties of our
yields in the light of the present understanding of SNIa nucleosynthesis,
depending on different progenitor mass and composition. Finally, we compare our
results with a number of relevant models from the literature.
|
2306.12885v1
|
2023-06-27
|
Permanent magnet systems to study the interaction between magnetic nanoparticles and cells in microslide channels
|
We optimized designs of permanent magnet systems to study the effect of
magnetic nanoparticles on cell cultures in microslide channels. This produced
two designs, one of which is based on a large cylindrical magnet that applies a
uniform force density of 6 MN/m$^3$ on soft magnetic iron-oxide spherical
nanoparticles at a field strength of over 300 mT. We achieved a force
uniformity of better than 14% over the channel area leading to a concentration
variation that was below our measurement resolution. The second design was
aimed at maximizing the force by using a Halbach array. We indeed increased the
force by more than one order of magnitude at force density values over 400
MN/m$^3$, but at the cost of uniformity. However, the latter system can be used
to trap magnetic nanoparticles efficiently and to create concentration
gradients. We demonstrated both designs by analyzing the effect of magnetic
forces on the cell viability of human hepatoma HepG2 cells in the presence of
bare Fe$_2$O$_3$ and cross-linked dextran iron-oxide cluster-type particles
(MicroMod). Python scripts for magnetic force calculations and particle
trajectory modeling as well as source files for 3D prints have been made
available so these designs can be easily adapted and optimized for other
geometries.
|
2306.15459v2
|
2023-07-10
|
Design and processing as ultrathin films of a sublimable Iron(II) spin crossover material exhibiting efficient and fast light-induced spin transition
|
Materials based on spin crossover (SCO) molecules have centred the attention
in Molecular Magnetism for more than forty years as they provide unique
examples of multifunctional and stimuli-responsive materials, which can be then
integrated into electronic devices to exploit their molecular bistability. This
process often requires the preparation of thermally stable SCO molecules that
can sublime and remain intact in contact with surfaces. However, the number of
robust sublimable SCO molecules is still very scarce. Here we report a novel
example of this kind. It is based on a neutral iron (II) coordination complex
formulated as [FeII(neoim)2], where neoimH is the ionogenic ligand
2-(1H-imidazol-2-yl)-9-methyl-1,10-phenanthroline. In the first part a
comprehensive study, which covers the synthesis and magneto-structural
characterization of the [FeII(neoim)2] complex as a bulk microcrystalline
material, is reported. Then, in the second part we investigate the suitability
of this material to form thin films through high vacuum (HV) sublimation.
Finally, the retainment of all present SCO capabilities in the bulk when the
material is processed is thoroughly studied by means of X-ray absorption
spectroscopy. In particular, a very efficient and fast light-induced spin
transition (LIESST effect) has been observed, even for ultrathin films of 15
nm.
|
2307.04591v1
|
2023-07-17
|
Controlling the Temperature of the Spin-Reorientation Transition In HoFe1-xMnxO3 Orthoferrite Single Crystals
|
HoFe1-xMnxO3 (0 < x < 1) single crystals have been grown by the optical
floating zone technique. A structural transition from the orthorhombic to
hexagonal modification has been established in the crystals in the
concentration range of 0.7-0.8, which has been confirmed by the X-ray
diffraction data. For a series of the rhombic crystals, the room-temperature
Mossbauer study and magnetic measurements in the temperature range of 4.2-1000
K have been carried out. It has been observed that, with an increase in the
manganese content in the samples, the temperature of the spin-reorientation
transition increases significantly: from 60 K in the HoFeO3 compound to room
temperature in HoFe0.6Mn0.4O3. The magnetic measurements have shown that, upon
substitution of manganese for iron, the magnetic orientational type transition
changes from a second-order transition (AxFyGz -> CxGyFz) to first-order one
(AxFyGz -> GxCyAz) with a weak ferromagnetic moment only in the b direction
(for Pnma notation). The growth of the spin-reorientation transition
temperature has been attributed to the change in the value of the indirect
exchange in the iron subsystem under the action of manganese, which has been
found when studying the Mossbauer effect in the HoFe1-xMnxO3 (x < 0.4)
compound.
|
2307.08236v1
|
2023-07-19
|
Origin of Life Molecules in the Atmosphere After Big Impacts on the Early Earth
|
The origin of life on Earth would benefit from a prebiotic atmosphere that
produced nitriles, like HCN, which enable ribonucleotide synthesis. However,
geochemical evidence suggests that Hadean air was relatively oxidizing with
negligible photochemical production of prebiotic molecules. These paradoxes are
resolved by iron-rich asteroid impacts that transiently reduced the entire
atmosphere, allowing nitriles to form in subsequent photochemistry. Here, we
investigate impact-generated reducing atmospheres using new time-dependent,
coupled atmospheric chemistry and climate models, which account for gas-phase
reactions and surface-catalysis. The resulting H$_2$-, CH$_4$- and NH$_3$-rich
atmospheres persist for millions of years, until hydrogen escapes to space. HCN
and HCCCN production and rainout to the surface can reach $10^9$ molecules
cm$^{-2}$ s$^{-1}$ in hazy atmospheres with a mole ratio of $\mathrm{CH_4} /
\mathrm{CO_2} > 0.1$. Smaller $\mathrm{CH_4} / \mathrm{CO_2}$ ratios produce
HCN rainout rates $< 10^5$ molecules cm$^{-2}$ s$^{-1}$, and negligible HCCCN.
The minimum impactor mass that creates atmospheric $\mathrm{CH_4} /
\mathrm{CO_2} > 0.1$ is $4 \times 10^{20}$ to $5 \times 10^{21}$ kg (570 to
1330 km diameter), depending on how efficiently iron reacts with a steam
atmosphere, the extent of atmospheric equilibration with an impact-induced melt
pond, and the surface area of nickel that catalyzes CH$_4$ production.
Alternatively, if steam permeates and deeply oxidizes crust, impactors $\sim
10^{20}$ kg could be effective. Atmospheres with copious nitriles have $> 360$
K surface temperatures, perhaps posing a challenge for RNA longevity, although
cloud albedo can produce cooler climates. Regardless, post-impact cyanide can
be stockpiled and used in prebiotic schemes after hydrogen has escaped to
space.
|
2307.09761v1
|
2023-07-28
|
Structural phase transition, $s_{\pm}$-wave pairing and magnetic stripe order in the bilayered nickelate superconductor La$_3$Ni$_2$O$_7$ under pressure
|
Motivated by the recently discovered high-$T_c$ superconductor
La$_3$Ni$_2$O$_7$, we comprehensively study this system using density
functional theory and random phase approximation calculations. At low
pressures, the Amam phase is stable, containing the Y$^{2-}$ mode distortion
from the Fmmm phase, while the Fmmm phase is unstable. Because of small
differences in enthalpy and a considerable Y$^{2-}$ mode amplitude, the two
phases may coexist in the range between 10.6 and 14 GPa, beyond which the Fmmm
phase dominates. In addition, the magnetic stripe-type spin order with
wavevector ($\pi$, 0) was stable at the intermediate region. Pairing is induced
in the $s_{\pm}$-wave channel due to partial nesting between the {\bf M}=$(\pi,
\pi)$ centered pockets and portions of the Fermi surface centered at the {\bf
X}=$(\pi, 0)$ and {\bf Y}=$(0, \pi)$ points. This resembles results for
iron-based superconductors but has a fundamental difference with iron pnictides
and selenides. Moreover, our present efforts also suggest that
La$_3$Ni$_2$O$_7$ is qualitatively different from infinite-layer nickelates and
cuprate superconductors.
|
2307.15276v4
|
2023-08-01
|
The current state of disk wind observations in BHLMXBs through X-ray absorption lines in the iron band
|
The presence of blueshifted absorption lines in the X-ray spectra of Black
Hole Low Mass X-ray Binaries is the telltale of massive outflows called winds.
These signatures are found almost exclusively in soft states of high-inclined
systems, hinting at equatorial ejections originating from the accretion disk
and deeply intertwined with the evolution of the outburst patterns displayed by
these systems. In the wake of the launch of the new generation of X-ray
spectrometers, studies of wind signatures remain mostly restricted to single
sources and outbursts, with some of the recent detections departing from the
commonly expected behaviors. We thus give an update to the current state of
iron band absorption lines detections, through the analysis of all publicly
available XMM-$Newton$-PN and $Chandra$-HETG exposures of known Black Hole
Low-Mass X-ray Binary candidates. Our results agree with previous studies, with
wind detections exclusively found in dipping, high-inclined sources, and almost
exclusively in bright ($L_{X}>0.01L_{Edd}$) soft ($HR<0.8$) states, with
blueshift values generally restricted to few 100 km s$^{-1}$. The line
parameters indicate similar properties between objects and outbursts of single
sources, and despite more than 20 years of data, very few sources have the HID
sampling necessary to properly study the evolution of the wind during single
outbursts. We provide an online tool with details of the wind signatures and
outburst evolution data for all sources in the sample.
|
2308.00691v1
|
2023-08-07
|
Energy-resolved pulse profiles of accreting pulsars: Diagnostic tools for spectral features
|
We introduce a method for extracting spectral information from
energy-resolved light curves folded at the neutron star spin period (known as
pulse profiles) in accreting X-ray binaries. Spectra of these sources are
sometimes characterized by features superimposed on a smooth continuum, such as
iron emission lines and cyclotron resonant scattering features. We address here
the question on how to derive quantitative constraints on such features from
energy-dependent changes in the pulse profiles. We developed a robust method
for determining in each energy-selected bin the value of the pulsed fraction
using the fast Fourier transform opportunely truncated at the number of
harmonics needed to satisfactorily describe the actual profile. We determined
the uncertainty on this value by sampling through Monte Carlo simulations a
total of 1000 faked profiles. We rebinned the energy-resolved pulse profiles to
have a constant minimum signal-to-noise ratio throughout the whole energy band.
Finally we characterize the dependence of the energy-resolved pulsed fraction
using a phenomenological polynomial model and search for features corresponding
to spectral signatures of iron emission or cyclotron lines using Gaussian line
profiles. We apply our method to a representative sample of NuSTAR observations
of well-known accreting X-ray pulsars. We show that, with this method, it is
possible to characterize the pulsed fraction spectra, and to constrain the
position and widths of such features with a precision comparable with the
spectral results. We also explore how harmonic decomposition, correlation, and
lag spectra might be used as additional probes for detection and
characterization of such features.
|
2308.03395v1
|
2023-08-08
|
Designing optoelectronic properties by on-surface synthesis: formation and electronic structure of an iron-terpyridine macromolecular complex
|
Supramolecular chemistry protocols applied on surfaces offer compelling
avenues for atomic scale control over organic-inorganic interface structures.
In this approach, adsorbate-surface interactions and two-dimensional
confinement can lead to morphologies and properties that differ dramatically
from those achieved via conventional synthetic approaches. Here, we describe
the bottom-up, on-surface synthesis of one-dimensional coordination
nanostructures based on an iron (Fe)-terpyridine (tpy) interaction borrowed
from functional metal-organic complexes used in photovoltaic and catalytic
applications. Thermally activated diffusion of sequentially deposited ligands
and metal atoms, and intra-ligand conformational changes, lead to Fe-tpy
coordination and formation of these nanochains. Low-temperature Scanning
Tunneling Microscopy and Density Functional Theory were used to elucidate the
atomic-scale morphology of the system, providing evidence of a linear tri-Fe
linkage between facing, coplanar tpy groups. Scanning Tunneling Spectroscopy
reveals highest occupied orbitals with dominant contributions from states
located at the Fe node, and ligand states that mostly contribute to the lowest
unoccupied orbitals. This electronic structure yields potential for hosting
photo-induced metal-to-ligand charge transfer in the visible/near-infrared. The
formation of this unusual tpy/tri-Fe/tpy coordination motif has not been
observed for wet chemistry synthesis methods, and is mediated by the bottom-up
on-surface approach used here.
|
2308.04105v1
|
2023-09-05
|
Magnetic and structural properties of the iron silicide superconductor LaFeSiH
|
The magnetic and structural properties of the recently discovered
pnictogen/chalcogen-free superconductor LaFeSiH ($T_c\simeq10$~K) have been
investigated by $^{57}$Fe synchrotron M{\"o}ssbauer source (SMS) spectroscopy,
x-ray and neutron powder diffraction and $^{29}$Si nuclear magnetic resonance
spectroscopy (NMR). No sign of long range magnetic order or local moments has
been detected in any of the measurements and LaFeSiH remains tetragonal down to
2 K. The activated temperature dependence of both the NMR Knight shift and the
relaxation rate $1/T_1$ is analogous to that observed in strongly overdoped
Fe-based superconductors. These results, together with the
temperature-independent NMR linewidth, show that LaFeSiH is an homogeneous
metal, far from any magnetic or nematic instability, and with similar Fermi
surface properties as strongly overdoped iron pnictides. This raises the
prospect of enhancing the $T_c$ of LaFeSiH by reducing its carrier
concentration through appropriate chemical substitutions. Additional SMS
spectroscopy measurements under hydrostatic pressure up to 18.8~GPa found no
measurable hyperfine field.
|
2309.02241v1
|
2023-09-15
|
Superconductivity and vortex structure on Bi$_{2}$Te$_{3}$/FeTe$_{0.55}$Se$_{0.45}$ heterostructures with different thickness of Bi$_{2}$Te$_{3}$ films
|
Using scanning tunnel microscopy (STM), we investigate the superconductivity
and vortex properties in topological insulator Bi$_{2}$Te$_{3}$ thin films
grown on the iron-based superconductor FeTe$_{0.55}$Se$_{0.45}$. The
proximity-induced superconductivity weakens in the Bi$_{2}$Te$_{3}$ film when
the thickness of the film increases. Unlike the elongated shape of vortex cores
observed in the Bi$_{2}$Te$_{3}$ film with 2-quintuple-layer (QL) thickness,
the isolated vortex cores exhibit a star shape with six rays in the 1-QL film,
and the rays are along the crystalline axes of the film. This is consistent
with the sixfold rotational symmetry of the film lattice, and the
proximity-induced superconductivity is still topologically trivial in the 1-QL
film. At a high magnetic field, when the direction between the two nearest
neighbored vortices deviates from that of any crystalline axes, two cores
connect each other by a pair of adjacent rays, forming a new type of electronic
structure of vortex cores. On the 3-QL film, the vortex cores elongate along
one of the crystalline axes of the Bi$_{2}$Te$_{3}$ film, similar to the
results obtained on 2-QL films. The elongated vortex cores indicate a twofold
symmetry of the superconducting gap induced by topological superconductivity
with odd parity. This observation confirms possible topological
superconductivity in heterostructures with a thickness of more than 2 QLs. Our
results provide rich information for the vortex cores and vortex-bound states
on the heterostructures consisting of the topological insulator and the
iron-based superconductor.
|
2309.08246v1
|
2023-09-22
|
Wavelet spectral timing: X-ray reverberation from a dynamic black hole corona hidden beneath ultrafast outflows
|
Spectral timing analyses based upon wavelet transforms provide a new means to
study the variability of the X-ray emission from accreting systems, including
AGN, stellar mass black holes and neutron stars, and can be used to trace the
time variability of X-ray reverberation from the inner accretion disc. The
previously-missing iron K reverberation time lags in the AGN IRAS 13224-3809
and MCG-6-30-15 are detected and found to be transitory in nature.
Reverberation can be hidden during periods in which variability in the iron K
band becomes dominated by ultrafast outflows (UFO). Following the time
evolution of the reverberation lag between the corona and inner accretion disc,
we may observe the short-timescale increase in scale height of the corona as it
is accelerated away from the accretion disc during bright X-ray flares in the
AGN I Zw 1. Measuring the variation of the reverberation lag that corresponds
to the continuous, stochastic variations of the X-ray luminosity sheds new
light on the disc-corona connection around accreting black holes. Hysteresis is
observed between the X-ray count rate and the scale height of the corona, and a
time lag of 10~40ks is observed between the rise in luminosity and the increase
in reverberation lag. This correlation and lag are consistent with viscous
propagation through the inner accretion disc, leading first to an increase in
the flux of seed photons that are Comptonised by the corona, before mass
accretion rate fluctuations reach the inner disc and are able to modulate the
structure of the corona.
|
2309.13107v2
|
2023-10-13
|
Polarized microwave emission from space particles in the upper atmosphere of the Earth
|
Tons of space particles enter the Earth atmosphere every year, being detected
when they produce fireballs, meteor showers, or when they impact the Earth
surface. Particle detection in the showers could also be attempted from space
using satellites in low Earth orbit. Measuring the polarization would provide
extra crucial information on the dominant alignment mechanisms and the
properties of the meteor families. In this article, we evaluate the expected
signal to aid in the design of space probes for this purpose. We have used the
RADMC-3D code to simulate the polarized microwave emission of aligned dust
particles with different compositions: silicates, carbonates and irons. We have
assumed a constant spatial particle density distribution of 0.22 cm$^{-3}$,
based on particle density measurements carried during meteor showers. Four
different grain size distributions with power indices ranging from $-3.5$ to
$-2.0$ and dust particles with radius ranging from 0.01 $\mathrm{\mu}$m to 1 cm
have been considered for the simulations. Silicates and carbonates align their
minor axis with the direction of the solar radiation field; during the flight
time into the Earth atmosphere, iron grains get oriented with the Earth's
magnetic field depending on their size. Alignment direction is reflected in the
$Q$-Stokes parameter and in the polarization variation along the orbit.
Polarization depends on the composition and on the size distribution of the
particles. The simulations show that some specific particle populations might
be detectable even with a small probe equipped with high sensitivity,
photon-counting microwave detectors operating in low Earth orbit.
|
2310.08941v1
|
2023-10-17
|
Towards atomistic understanding of Iron phosphate glass: a first-principles based DFT modeling and study of its physical properties
|
Iron phosphate glasses (IPG) have been proposed as futuristic glass material
for nuclear waste immobilization, anode material for lithium batteries and also
as bioactive glass. In the last decade, there have been attempts to propose
atomistic models of IPG to explain their properties from atomistic viewpoint
and to predict their behavior in radioactive environment. In this paper, we
seek to produce small scale models of IPG that can be handled within the scheme
of Density Functional Theory (DFT) to study the electronic structure of this
material. The starting models generated using Monte Carlo (MC) method [S. Singh
and S. Chandra, Comp. Mat. Sci., 202, 110943, (2022)] were subsequently
annealed (at 1000 K) using ab-initio molecular dynamics (AIMD). This removes
coordination defects present in the MC models. The equilibrated structure at
this temperature was then force-relaxed using conjugate-gradient (CG)
optimization. This hybrid approach (MC + AIMD + 0K DFT-CG optimization)
produced good atomistic models of IPG which can reproduce experimentally
observed electronic band-gap, vibrational density of states (VDOS), magnetic
moment of Fe, the elastic constants as well as optical and dielectric
properties. Computationally expensive melt-quench simulation can be avoided
using present approach allowing the use of DFT for accurate calculations of
properties of complex glass like IPG.
|
2310.11135v1
|
2023-10-25
|
Post-main sequence thermal evolution of planetesimals
|
White dwarfs that have accreted planetary materials provide a powerful tool
to probe the interiors and formation of exoplanets. In particular, the high
Fe/Si ratio of some white dwarf pollutants suggests that they are fragments of
bodies that were heated enough to undergo large-scale melting and iron core
formation. In the solar system, this phenomenon is associated with bodies that
formed early and so had short-lived radionuclides to power their melting,
and/or grew large. However, if the planetary bodies accreted by white dwarfs
formed during the (pre)-main sequence lifetime of the host star, they will have
potentially been exposed to a second era of heating during the star's giant
branches. This work aims to quantify the effect of stellar irradiation during
the giant branches on planetary bodies by coupling stellar evolution to thermal
and orbital evolution of planetesimals. We find that large-scale melting,
sufficient to form an iron core, can be induced by stellar irradiation, but
only in close-in small bodies: planetesimals with radii $\lesssim$ 30 km
originally within $\sim$ 2 AU orbiting a 1$-$3$\,M_{\odot}$ host star with
solar metallicity. Most of the observed white dwarf pollutants are too massive
to be explained by the accretion of these small planetesimals that are melted
during the giant branches. Therefore, we conclude that those white dwarfs that
have accreted large masses of materials with enhanced or reduced Fe/Si remain
an indicator of planetesimal's differentiation shortly after formation,
potentially linked to radiogenic heating.
|
2310.17057v1
|
2023-10-26
|
Honing cross-correlation tools for inference on ultra-high-energy cosmic-ray composition
|
The chemical composition of the highest-energy cosmic rays, namely the atomic
number $Z$ of rays with energies $E\gg1~\text{EeV}$, remains to date largely
unknown. Some information on the composition can be inferred from the
deflections that charged ultra-high-energy cosmic rays experience while they
traverse intervening magnetic fields. Indeed, such deflections distort and
suppress the original anisotropy in the cosmic rays arrival directions; thus, a
measure of the anisotropy is also a measurement of the deflections, which in
turn informs us on the chemical composition. In this work, we show that, by
quantifying ultra-high-energy cosmic ray anisotropies through the angular,
harmonic cross-correlation between cosmic rays and galaxies, we are able to
exclude iron fractions $f_{\rm Fe}\leq{\cal O}(10\%)$ on a fiducial hydrogen
map at $2\sigma$ level, and even smaller fractions in the reverse case of
hydrogen on an iron map, going below $f_{\rm H}\lesssim10\%$ when we mask the
Galactic Centre up to latitudes of $40\,\text{deg}$. This is an improvement of
a factor of a few compared to our previous method, and is mostly ascribable to
a new test statistics which is sensitive to each harmonic multipole
individually. Our method can be applied to real data as an independent test of
the recent claim that current cosmic-ray data can not be reproduced by any
existing model of the Galactic magnetic field, as well as an additional handle
to compare any realistic, competing, data-driven composition models.
|
2310.17699v2
|
2023-10-31
|
Chemical evolution models: the role of type Ia supernovae in the $α$-elements over Iron relative abundances and their variations in time and space
|
The role of type Ia supernovae, mainly the Delay Time Distributions (DTDs)
determined by the binary systems, and the yields of elements created by
different explosion mechanisms, are studied by using the {\sc MulChem} chemical
evolution model, applied to our Galaxy. We explored 15 DTDs, and 12 tables of
elemental yields produced by different SN Ia explosion mechanisms, doing a
total of 180 models. Chemical abundances for $\alpha$-elements (O, Mg, Si, S,
Ca) and Fe derived from these models, are compared with recent observational
data of $\alpha$-elements over Iron relative abundances, [X/Fe]. These data
have been compiled and binned in 13 datasets. By using a $\chi^2$-technique, no
model is able to fit simultaneously these datasets. A model computed with the
13 individual best models is good enough to reproduce them. Thus, a power law
with a logarithmic slope $\sim -1.1$ and a delay in the range $\Delta \tau=40
--350$ Myr is a possible DTD, but a combination of several channels is more
probable. Results of this average model for other disc regions show a high
dispersion, as observed, which might be explained by the stellar migration. The
dispersion might also come from a combination of DTDs or of explosion channels.
The stellar migration joined to a combination of scenarios for SNIa is the
probable cause of the observed dispersion.
|
2311.00076v1
|
2023-11-01
|
Annealing effects on the magnetic and magnetotransport properties of iron oxide nanoparticles self-assemblies
|
In magnetic tunnel junctions based on iron oxide nanoparticles the disorder
and the oxidation state of the surface spin as well as the nanoparticles
functionalization play a crucial role in the magnetotransport properties. In
this work, we report a systematic study of the effects of vacuum annealing on
the structural, magnetic and transport properties of self-assembled ~10 nm
Fe3O4 nanoparticles. The high temperature treatment (from 573 to 873 K)
decomposes the organic coating into amorphous carbon, reducing the electrical
resistivity of the assemblies by 4 orders of magnitude. At the same time, the
3Fe2+/(Fe3++Fe2+) ratio is reduced from 1.11 to 0.13 when the annealing
temperature of the sample increases from 573 to 873 K, indicating an important
surface oxidation. Although the 2 nm physical gap remains unchanged with the
thermal treatment, a monotonous decrease of tunnel barrier width was obtained
from the electron transport measurements when the annealing temperature
increases, indicating an increment in the number of defects and hot-spots in
the gap between the nanoparticles. This is reflected in the reduction of the
spin dependent tunneling, which reduces the interparticle magnetoresistance.
This work shows new insights about influence of the nanoparticle interfacial
composition, as well their the spatial arrangement, on the tunnel transport of
self-assemblies, and evidence the importance of optimizing the nanostructure
fabrication for increasing the tunneling current without degrading the spin
polarized current.
|
2311.00700v1
|
2023-11-10
|
Enhancement of optical absorption in multiferroic (1-x)PZT-xPFN thin films: Experiments and first-principles analysis
|
Multiferroic compounds have gained research attention in the field of
ferroelectric photovoltaics due to the presence of transition-metal d states
from magnetic ions, which tend to reduce the bandgap value. In this work,
0.5Pb(Zr0.52Ti0.48)O3 - 0.5Pb(Fe0.5Nb0.5)O3 PZTFN0.5 thin films were
synthesized using a sol-gel route to investigate the effect of iron doping on
optical and multiferroic properties. For comparative analysis, the end-member
compositions, Pb(Zr0.52Ti0.48)O3 (PZT) and Pb(Fe0.5Nb0.5)O3 (PFN), were also
synthesized under identical conditions. Our results revealed that the presence
of Fe ions, besides inducing multiferroic behavior, effectively enhances the
optical absorption of the material in the visible light region. Optical
transitions at 3.0 eV (2.4 eV) and 2.7 eV (2.2 eV) for the direct (indirect)
bandgap were determined for PZTFN0.5 and PFN, respectively, indicating that the
absorption edges of the iron-containing films result more promising than PZT
(Eg 3.6eV) for photovoltaic applications. Both PZTFN0.5 and PFN thin films
exhibit multiferroic behavior at room temperature, with different electric and
magnetic properties. While PZTFN0.5 presents saturated hysteresis loops with
remanent polarization values around 10 uC/cm2 and magnetization of 1.6 emu/cm2,
PFN displays significantly larger remanence (31 emu/cm2) but poorer
ferroelectric properties due to the presence of leakage. Microscopic insights
into the structural and electronic properties of the PZTFN0.5 solid solution
were provided from first-principles calculations.
|
2311.05855v1
|
2023-11-14
|
Superconductivity with $T_c$ up to 30.7 K in air-annealed CaFeAsF
|
Exploring new unconventional superconductors is of great value for both
fundamental research and practical applications. It is a long-term challenge to
develop and study more hole-doped superconductors in 1111 system of iron-based
superconductors. However, fifteen years after the discovery of iron-based
superconductors, it has become increasingly difficult to discover new members
in this system by conventional means. Here we report the discovery of
superconductivity with the critical transition temperature up to 30.7 K in the
parent compound CaFeAsF by an annealing treatment in air atmosphere. The
superconducting behaviors are verified in both the single-crystalline and
polycrystalline samples by the resistance and magnetization measurements. The
analysis by combining the depth-resolved time-of-flight secondary ion mass
spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) measurements
show that the introduction of oxygen elements and the consequent changing in Fe
valence by the annealing treatment may lead to the hole-type doping, which is
the origin for the occurrence of superconductivity. Our results provide a new
route to induce hole-doped superconductivity in Fe-based superconductors.
|
2311.07943v1
|
2023-12-14
|
X-ray Reflection from the Plunging Region of Black Hole Accretion Disks
|
Accretion around black holes is very often characterized by distinctive X-ray
reflection features (mostly, iron inner-shell transitions), which arise due to
the primary radiation being reprocessed by a dense and relatively colder
medium, such as an accretion disk. Most reflection modeling assume that
emission stops at the inner-most stable circular orbit (ISCO), and that for
smaller radii - in the plunging region - the density drops and the accretion
flow is far too ionized for efficient line production. We investigate the
spectral features of the reflection in the plunging regions of optically-thick
and geometrically-thin accretion disks around black holes. We show that for
cases in which the density profile is considered constant (as expected in
highly magnetized flows), or in cases in which the disk density is high enough
such that the ionization still allows line formation within the ISCO, there is
a significant modification of the observed reflected spectrum. Consistent with
previous studies, we found that the impact of the radiation reprocessed in the
plunging region is stronger the lower the black hole spin, when the plunging
region subtends a larger area. Likewise, as for the case of standard reflection
modeling, the relativistic broadening of the iron line is more pronounced at
low inclination, whereas the blueshift and relativistic beaming effect is
dominant at high inclination. We also tested the effects of various
prescriptions of the stress at the ISCO radius on the reflection spectrum, and
found that several of these cases appear to show line profiles distinct enough
to be distinguishable with reasonably good quality observational data.
|
2312.09210v1
|
2024-01-05
|
Joint analysis of the iron emission in the optical and near-infrared spectrum of I Zw 1
|
Constraining the physical conditions of the ionized media in the vicinity of
an active supermassive black hole (SMBH) is crucial to understanding how these
complex systems operate. Metal emission lines such as iron (Fe) are useful
probes to trace the gaseous media's abundance, activity, and evolution in these
accreting systems. Among these, the FeII emission has been the focus of many
prior studies to investigate the energetics, kinematics, and composition of the
broad-emission line region (BELR) from where these emission lines are produced.
In this work, we present the first simultaneous FeII modeling in the optical
and near-infrared (NIR) regions. We use CLOUDY photoionization code to simulate
both spectral regions in the wavelength interval 4000-12000 Angstroms. We
compare our model predictions with the observed line flux ratios for IZw1 - a
prototypical strong FeII-emitting active galactic nuclei (AGN). This allows
putting constraints on the BLR cloud density and metal content that is optimal
for the production of the FeII emission, which can be extended to IZw1-like
sources, by examining a broad parameter space. We demonstrate the salient and
distinct features of the FeII pseudo-continuum in the optical and NIR, giving
special attention to the effect of micro-turbulence on the intensity of the
FeII emission.
|
2401.02936v1
|
2024-01-16
|
Bias-Compensated State of Charge and State of Health Joint Estimation for Lithium Iron Phosphate Batteries
|
Accurate estimation of the state of charge (SOC) and state of health (SOH) is
crucial for the safe and reliable operation of batteries. Voltage measurement
bias highly affects state estimation accuracy, especially in Lithium Iron
Phosphate (LFP) batteries, which are susceptible due to their flat open-circuit
voltage (OCV) curves. This work introduces a bias-compensated algorithm to
reliably estimate the SOC and SOH of LFP batteries under the influence of
voltage measurement bias. Specifically, SOC and SOH are estimated using the
Dual Extended Kalman Filter (DEKF) in the high-slope SOC range, where voltage
measurement bias effects are weak. Besides, the voltage measurement biases
estimated in the low-slope SOC regions are compensated in the following joint
estimation of SOC and SOH to enhance the state estimation accuracy further.
Experimental results indicate that the proposed algorithm significantly
outperforms the traditional method, which does not consider biases under
different temperatures and aging conditions. Additionally, the bias-compensated
algorithm can achieve low estimation errors of below 1.5% for SOC and 2% for
SOH, even with a 30mV voltage measurement bias. Finally, even if the voltage
measurement biases change in operation, the proposed algorithm can remain
robust and keep the estimated errors of states around 2%.
|
2401.08136v2
|
2024-01-19
|
Reflecting on naked singularities: iron line fitting as a probe of the cosmic censorship conjecture
|
We demonstrate that the X-ray iron line fitting technique can be leveraged as
a powerful probe of the cosmic censorship conjecture. We do this by extending
existing emission line models to arbitrary spin parameters of the Kerr metric,
no longer restricted to black hole metrics with $|a_\bullet |< 1$. We show that
the emission lines from naked singularity metrics ($|a_\bullet| > 1$) show
significant differences to their black hole counterparts, even for those
metrics with identical locations of the innermost stable circular orbit, i.e.,
emission line fitting does not suffer from the degeneracy which affects
continuum fitting approaches. These differences are entirely attributable to
the disappearance of the event horizon for $|a_\bullet| > 1$. We highlight some
novel emission line features of naked singularity metrics, such as ``inverted''
emission lines (with sharp red wings and extended blue wings) and ``triple
lines''. The lack of detection of any of these novel features provides support
of the cosmic censorship conjecture. We publicly release {\tt XSPEC} packages
{\tt skline} and {\tt skconv} which can now be used to probe the cosmic
censorship conjecture in Galactic X-ray binaries and Active Galactic Nuclei.
The inclusion of super-extremal spacetimes can be alternatively posed as a way
of stress-testing conventional models of accretion.
|
2401.10565v1
|
2024-01-25
|
Nucleosynthesis in magnetorotational supernovae: impact of the magnetic field configuration
|
The production of heavy elements is one of the main by-products of the
explosive end of massive stars. A long sought goal is finding differentiated
patterns in the nucleosynthesis yields, which could permit identifying a number
of properties of the explosive core. Among them, the traces of the magnetic
field topology are particularly important for \emph{extreme} supernova
explosions, most likely hosted by magnetorotational effects. We investigate the
nucleosynthesis of five state-of-the-art magnetohydrodynamic models with fast
rotation that have been previously calculated in full 3D and that involve an
accurate neutrino transport (M1). One of the models does not contain any
magnetic field and synthesizes elements around the iron group, in agreement
with other CC-SNe models in literature. All other models host a strong magnetic
field of the same intensity, but with different topology. For the first time,
we investigate the nucleosynthesis of MR-SNe models with a quadrupolar magnetic
field and a 90 degree tilted dipole. We obtain a large variety of ejecta
compositions reaching from iron nuclei to nuclei up to the third r-process
peak. We assess the robustness of our results by considering the impact of
different nuclear physics uncertainties such as different nuclear masses,
$\beta^{-}$-decays and $\beta^{-}$-delayed neutron emission probabilities,
neutrino reactions, fission, and a feedback of nuclear energy on the
temperature. We find that the qualitative results do not change with different
nuclear physics input. The properties of the explosion dynamics and the
magnetic field configuration are the dominant factors determining the ejecta
composition.
|
2401.14402v1
|
2024-02-15
|
A variable ionized disk wind in MAXI J1803-298 revealed by NICER
|
We present the results from the NICER observation data of MAXI J1803-298
across the entire 2021 outburst. In the intermediate and soft state, we detect
significant absorption lines at $\sim 7.0$ keV and $\sim 6.7$ keV, arising from
the X-ray disk wind outflowing with a velocity of hundreds of km per second
along our line of sight. The fitting results from photoionized model suggest
that the wind is driven by thermal pressure and the mass-loss rate is low. We
find a clear transition for iron from predominantly H-like to predominantly
He-like during the intermediate-to-soft state transition. Our results indicate
this transition for iron is caused by the evolution of the illuminating
spectrum and the slow change of the geometric properties of the disk wind
together. The coexistence of disk wind and QPOs features in intermediate state
is also reported. Our study makes MAXI J1803-298 the first source in which a
transition from optical wind to X-ray wind is detected, offering new insights
into the evolution of disk winds across an entire outburst and long-term
coupling of accretion disks and mass outflows around accreting black holes.
|
2402.10315v1
|
2024-03-04
|
Interplay between alloying and tramp element effects on temper embrittlement in bcc iron: DFT and thermodynamic insights
|
The details of the temper embrittlement mechanism in steels caused by
impurities are unknown. Especially from an atomistic point of view, there are
still open questions regarding their interactions with alloying elements such
as Ni, Cr, and Mo. Therefore, we used density functional theory to investigate
the segregation and co-segregation behavior and the resulting influence on the
cohesion of three representative tilt grain boundaries in iron. The results are
implemented in a multi-site and multi-component kinetic and thermodynamic model
for grain boundary segregation, to gain insights into the temporal and final
grain boundary coverage. Our results show that the segregation tendency of As,
Sb, and Sn is stronger than that of the alloying elements and significantly
mitigates the grain boundary cohesion. Depending on the GB type, interactions
between Sb and Sn vary from negligible to strongly attractive, which increases
the likelihood of co-segregation. The cohesion-weakening effect is further
amplified when elements such as Sb, Sn, and As co-segregate, compared to their
individual segregation. In contrast, the co-segregation of Ni and Cr does not
significantly increase the enrichment of impurities at grain boundaries, and
their impact on cohesion is found to be negligible. The ability of Mo to
mitigate reversible temper embrittlement is primarily attributed to its
cohesion-enhancing effect and its capability to repel tramp elements from GBs,
rather than scavenging them within the bulk, as suggested by previous
literature.
|
2403.02186v1
|
2024-03-10
|
Conventional Superconductivity in the Doped Kagome Superconductor Cs(V0.86Ta0.14)3Sb5 from Vortex Lattice Studies
|
A hallmark of unconventional superconductors is their complex electronic
phase diagrams where "intertwined orders" of charge-spin-lattice degrees of
freedom compete and coexist as in copper oxides and iron pnictides. While the
electronic phase diagram of kagome lattice superconductor such as CsV3Sb5 also
exhibits complex behavior involving coexisting and competing charge density
wave order and superconductivity, much is unclear about the microscopic origin
of superconductivity. Here, we study the vortex lattice (VL) in superconducting
state of Cs(V0.86Ta0.14)3Sb5, where the Ta-doping suppresses charge order and
enhances superconductivity. Using small-angle neutron scattering, a strictly
bulk probe, we show that the VL exhibits a strikingly conventional behavior.
This includes a triangular VL with a period consistent with 2e-pairing, a field
dependent scattering intensity that follows a London model, and a temperature
dependence consistent with a uniform superconducting gap expected for s-wave
pairing. These results suggest that optimal bulk superconductivity in
Cs(V1-xTax)3Sb5 arises from a conventional Bardeen-Cooper-Schrieffer
electron-lattice coupling, different from spin fluctuation mediated
unconventional copper and iron based superconductors.
|
2403.06046v1
|
2024-03-14
|
An FFT based approach to account for elastic interactions in OkMC: Application to dislocation loops in iron
|
Object kinetic Montecarlo (OkMC) is a fundamental tool for modeling defect
evolution in volumes and times far beyond atomistic models. The elastic
interaction between defects is classically considered using a dipolar
approximation but this approach is limited to simple cases and can be
inaccurate for large and close interacting defects. In this work a novel
framework is proposed to include "exact" elastic interactions between defects
in OkMC valid for any type of defect and anisotropic media. In this method, the
elastic interaction energy of a defect is computed by volume integration of its
elastic strain multiplied by the stress created by all the other defects, being
both fields obtained numerically using a FFT solver. The resulting interaction
energies reproduce analytical elastic solutions and show the limited accuracy
of dipole approaches for close and large defects.
The OkMC framework proposed is used to simulate the evolution in space and
time of self-interstitial atoms and dislocation loops in iron. It is found that
including the anisotropy has a quantitative effect in the evolution of all the
type of defects studied. Regarding dislocation loops, it is observed that using
the "exact" interaction energy result in higher interactions than using the
dipole approximation for close loops.
|
2403.09158v1
|
2024-03-18
|
Primary Defect Production in Doped Iron Grain Boundaries during Low Energy Collision Cascades
|
This study explores the intricate interactions between grain boundaries (GBs)
and irradiation-induced defects in nanocrystalline iron, highlighting the role
of dopants like copper. Utilizing molecular dynamics simulations, the research
delineates how GB properties, such as GB energy and defect formation energies,
influence the formation and evolution of defects in low energy collision
cascades. It reveals that GBs not only augment defect production but also show
a marked preference for interstitials over vacancies, a behavior significantly
modulated by the cascade's proximity to the GB. The presence of dopants is
shown to alter GB properties, affecting both the rate and type of defect
production, thereby underscoring the complex interplay between GB
characteristics, dopant elements, and defect dynamics. Moreover, the
investigation uncovers that the structural characteristics of GBs play a
crucial role in cascade evolution and defect generation, with certain GB
configurations undergoing reconfiguration in response to cascades. For
instance, the reconfiguration of one pure Fe twist GB suggests that GB geometry
can significantly influence defect generation mechanisms. These findings point
to the potential of GB engineering in developing materials with enhanced
radiation tolerance, advocating for a nuanced approach to material design. By
tailoring GB properties and selectively introducing dopant elements, materials
can be optimized to exhibit superior resistance to radiation-induced damage,
offering insights for applications in nuclear reactors and other
radiation-prone environments.
|
2403.12257v1
|
2022-04-02
|
Direct Measurement of the Nickel Spectrum in Cosmic Rays in the Energy Range from 8.8 GeV/n to 240 GeV/n with CALET on the International Space Station
|
The relative abundance of cosmic ray nickel nuclei with respect to iron is by
far larger than for all other trans-iron elements, therefore it provides a
favorable opportunity for a low background measurement of its spectrum. Since
nickel, as well as iron, is one of the most stable nuclei, the nickel energy
spectrum and its relative abundance with respect to iron provide important
information to estimate the abundances at the cosmic ray source and to model
the Galactic propagation of heavy nuclei. However, only a few direct
measurements of cosmic-ray nickel at energy larger than $ \sim$ 3 GeV/n are
available at present in the literature and they are affected by strong
limitations in both energy reach and statistics. In this paper we present a
measurement of the differential energy spectrum of nickel in the energy range
from 8.8 to 240 GeV/n, carried out with unprecedented precision by the
Calorimetric Electron Telescope (CALET) in operation on the International Space
Station since 2015. The CALET instrument can identify individual nuclear
species via a measurement of their electric charge with a dynamic range
extending far beyond iron (up to atomic number $ Z $ = 40). The particle's
energy is measured by a homogeneous calorimeter (1.2 proton interaction
lengths, 27 radiation lengths) preceded by a thin imaging section (3 radiation
lengths) providing tracking and energy sampling. This paper follows our
previous measurement of the iron spectrum [O. Adriani et al., Phys. Rev. Lett.
126, 241101 (2021).], and it extends our investigation on the energy dependence
of the spectral index of heavy elements. It reports the analysis of nickel data
collected from November 2015 to May 2021 and a detailed assessment of the
systematic uncertainties. In the region from 20 to 240 GeV$ /n $ our present
data are compatible within the errors with a single power law with spectral
index $ -2.51 \pm 0.07 $.
|
2204.00845v1
|
2020-12-03
|
On the Use of Field RR Lyrae as Galactic Probes. II. A new $Δ$S calibration to estimate their metallicity
|
We performed the largest and most homogeneous spectroscopic survey of field
RR Lyraes (RRLs). We secured $\approx$6,300 high resolution (HR, R$\sim$35,000)
spectra for 143 RRLs (111 fundamental, RRab; 32 first overtone, RRc). The
atmospheric parameters were estimated by using the traditional approach and the
iron abundances were measured by using an LTE line analysis. The resulting iron
distribution shows a well defined metal-rich tail approaching solar iron
abundance. This suggests that field RRLs experienced a complex chemical
enrichment in the early halo formation. We used these data to develop a new
calibration of the $\Delta$S method. This diagnostic, based on the equivalent
widths of CaII K and three Balmer (H$_{\delta,\gamma,\beta}$) lines, traces the
metallicity of RRLs. For the first time the new empirical calibration: i)
includes spectra collected over the entire pulsation cycle; ii) includes RRc
variables; iii) relies on spectroscopic calibrators covering more than three
dex in iron abundance; iv) provides independent calibrations based on
one/two/three Balmer lines. The new calibrations were applied to both
SEGUE-SDSS and degraded HR spectra totalling 6,451 low resolution (LR,
R$\sim$2,000) spectra for 5,001 RRLs (3,439 RRab, 1,562 RRc). This resulted in
an iron distribution with a median of -1.55$\pm$0.01 and $\sigma$=0.51 dex, in
good agreement with literature values. We also found that RRc are 0.10 dex more
metal-poor than RRab variables, and have a distribution with a smoother
metal-poor tail. This finding supports theoretical prescriptions suggesting a
steady decrease in the RRc number when moving from metal-poor to metal-rich
stellar environments.
|
2012.02284v1
|
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