68 research outputs found
Corrosion behaviors of super austenitic stainless steel weldment by GTAW welding for ships desulfurization system
This study aims to clarify how filler-typed metals which were ERNiCrMo-3 and ERNiCrMo-4 affect corrosion resistance characteristics in the weldment of super austenitic stainless steel joints under the simulated desulfurization environment for ships. The desulfurization environment includes high temperature, chlorides, and acidic conditions, which, inevitably, can cause severe corrosion to great extent. For exact clarification, the variations of microstructure and the composition distribution in the weldment before and after welding was examined by using scanning electron microscope and energy dispersive X-ray spectroscopy. Then, the corrosion resistance characteristics were comparatively evaluated through the cyclic potentiodynamic polarization test together with potential measurement under the desulfurization simulated environments. In addition, the correlation between passive film and corrosion resistance characteristics was investigated after identifying the formed features of the passive film through the X-ray photoelectron spectroscopy analysis. Through these studies, it made certain, ERNiCrMo-4 filler metal with high Mo content is advantageous for the formation of MoO3 oxide on the surface, which belongs to form a stable passive film and maintains the corrosion resistance characteristics under the simulated desulfurization environment
Atomic-scale control of magnetic anisotropy via novel spin-orbit coupling effect in La2/3Sr1/3MnO3/SrIrO3 superlattices
Magnetic anisotropy (MA) is one of the most important material properties for
modern spintronic devices. Conventional manipulation of the intrinsic MA, i.e.
magnetocrystalline anisotropy (MCA), typically depends upon crystal symmetry.
Extrinsic control over the MA is usually achieved by introducing shape
anisotropy or exchange bias from another magnetically ordered material. Here we
demonstrate a pathway to manipulate MA of 3d transition metal oxides (TMOs) by
digitally inserting non-magnetic 5d TMOs with pronounced spin-orbit coupling
(SOC). High quality superlattices comprised of ferromagnetic La2/3Sr1/3MnO3
(LSMO) and paramagnetic SrIrO3 (SIO) are synthesized with the precise control
of thickness at atomic scale. Magnetic easy axis reorientation is observed by
controlling the dimensionality of SIO, mediated through the emergence of a
novel spin-orbit state within the nominally paramagnetic SIO.Comment: Proceedings of the National Academy of Sciences, May 201
Spontaneous orbital polarization in the nematic phase of FeSe
The origin of nematicity in FeSe remains a critical outstanding question
towards understanding unconventional superconductivity in proximity to nematic
order. To understand what drives the nematicity, it is essential to determine
which electronic degree of freedom admits a spontaneous order parameter
independent from the structural distortion. Here, we use X-ray linear dichroism
at the Fe K pre-edge to measure the anisotropy of the 3d orbital occupation as
a function of in situ applied stress and temperature across the nematic
transition. Along with X-ray diffraction to precisely quantify the strain
state, we reveal a lattice-independent, spontaneously-ordered orbital
polarization within the nematic phase, as well as an orbital polarizability
that diverges as the transition is approached from above. These results provide
strong evidence that spontaneous orbital polarization serves as the primary
order parameter of the nematic phase.Comment: Main: 22 pages, 4 figures. Supp: 32 pages, 18 figure
Optimizing Semi-Analytical Algorithms for Estimating Chlorophyll-a and Phycocyanin Concentrations in Inland Waters in Korea
Several semi-analytical algorithms have been developed to estimate the chlorophyll-a (Chl-a) and phycocyanin (PC) concentrations in inland waters. This study aimed at identifying the influence of algorithm parameters on the output variables and searching optimal parameter values. The optimal parameters of seven semi-analytical algorithms were applied to estimate the Chl-a and PC concentrations. The absorption coefficient measurements were coupled with pigment measurements to calibrate the algorithm parameters. For sensitivity analysis, the elementary effect test was conducted to analyze the influence of the algorithm parameters. The sensitivity analysis results showed that the parameters in the Y function and specific absorption coefficient were the most sensitive parameters. Then, the parameters were optimized via a single-objective optimization that involved one objective function being minimized and a multi-objective optimization that contained more than one objective function. The single-objective optimization led to substantial errors in absorption coefficients. In contrast, the multi-objective optimization improved the algorithm performance with respect to both the absorption coefficient estimates and pigment concentration estimates. The optimized parameters of the absorption coefficient reflected the high-particulate content in waters of the Baekje reservoir using an infrared backscattering wavelength and relatively high value of Y. Moreover, the results indicate the value of measuring the site-specific absorption if site-specific optimization of semi-analyical algorithm parameters was envisioned
Strain-Switchable Field-Induced Superconductivity
Field-induced superconductivity is a rare phenomenon where an applied
magnetic field enhances or induces superconductivity. This fascinating effect
arises from a complex interplay between magnetism and superconductivity, and it
offers the tantalizing technological possibility of an infinite
magnetoresistance superconducting spin valve. Here, we demonstrate
field-induced superconductivity at a record-high temperature of T=9K in two
samples of the ferromagnetic superconductor
Eu(FeCo)As. We combine tunable uniaxial stress
and applied magnetic field to shift the temperature range of the
zero-resistance state between 4K and 10K. We use x-ray diffraction and
spectroscopy measurements under stress and field to demonstrate that stress
tuning of the nematic order and field tuning of the ferromagnetism act as
independent tuning knobs of the superconductivity. Finally, DFT calculations
and analysis of the Eu dipole field reveal the electromagnetic mechanism of the
field-induced superconductivity.Comment: Main text: 15 pages, 5 figures; Supplement: 15 pages, 10
supplementary figure
Quasi-2D anomalous Hall Mott insulator of topologically engineered Jeff =1/2 electrons
We investigate an experimental toy-model system of a pseudospin-half
square-lattice Hubbard Hamiltonian in [(SrIrO3)1/(CaTiO3)1] to include both
nontrivial complex hopping and moderate electronic correlation. While the
former induces electronic Berry phases as anticipated from the weak-coupling
limit, the later stabilizes an antiferromagnetic (AFM) Mott insulator ground
state in analogous to the strong-coupling limit. Their combined results in the
real system are found to be an anomalous Hall effect with a non-monotonic
temperature dependence due to the self-competition of the electron-hole pairing
in the Mott state, and an exceptionally large Ising anisotropy that is captured
as a giant magnon gap beyond the superexchange approach. The unusual phenomena
highlight the rich interplay of electronic topology and electronic correlation
in the intermediate-coupling regime that is largely unexplored and challenging
in theoretical modelling.Comment: Accepted by Phys. Rev.
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Monitoring Genetic & Metabolic Potential for In Situ Bioremediation: Mass Spectrometry
A number of DOE sites are contaminated with dense non-aqueous phase liquids (DNAPLs) such as carbon tetrachloride and trichloroethylene. At many of these sites, microbial bioremediation is an attractive strategy for cleanup, since it has the potential to degrade DNAPLs in situ. A rapid screening method to determine the broad range potential of a site's microbial population for contaminant degradation would greatly facilitate assessment for in situ bioremediation, as well as for monitoring ongoing bioremediation treatment. Current laboratory based treatability methods are cumbersome and expensive. In this project, we are developing methods based on matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) for rapid and accurate detection of polymerase chain reaction (PCR) products from microbial genes involved in biodegradation of pollutants. PCR primers are being developed to amplify DNA sequences that are amenable to MALDI-MS detection. This work will lay the foundation for development of a field-portable MS-based technique for rapid on site assessment and monitoring of bioremediation processes
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