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Wang, C.

Publications and source records attributed to Wang, C..

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Corrosion Monitoring in an Irradiated/Used Fuel Dry Storage Container - 19193

A corrosion monitoring system was developed to monitor the corrosion behaviour of steel components embedded in the high density concrete of a Dry Storage Container (DSC). The DSC is a free-standing reinforced concrete container, with an inner carbon-steel liner and an outer carbon-steel shell, for the storage, on-site transfer and off-site transportation of irradiated Candu fuel. Normally, uncontaminated concrete is benign with regards to embedded steel components because high alkalinity in the concrete leads to formation of a passive film on the steel surface, which prevents excessive metal loss. However, corrosion of steel in concrete may be promoted by one or more of local concentration of chloride ions or local loss of alkalinity. For the DSC, it is recognized that the above mechanism(s) are unlikely, however, if any did exist, the corrosion mechanisms that could then occur would include corrosion of carbon steel components and stress corrosion cracking of 304L stainless steel components. In order to confirm that these unlikely events are not occurring, Ontario Power Generation has undertaken a project to investigate the corrosion behaviour of metallic components embedded in the DSC's high density concrete. A corrosion monitoring system that can be installed within the concrete space of a DSC was designed and installed to monitor changes in temperature, corrosion potential, corrosion rate, and electrochemical noise. The corrosion monitoring system was commissioned in July 2012, followed by the commencement of monitoring and measurements. The corrosion data, collected for the three years from year 2012 to 2015, were analyzed. It was concluded that the corrosion rates of both carbon steel and stainless steel within the DSC are very low and consistent with the intended minimum operational life of the DSC. The monitoring system as a whole has allowed a systematic and long term judgement regarding the conditions within the DSCs. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS2019

Contribution of ULF Wave Activity to the Global Recovery of the Outer Radiation Belt During the Passage of a High‐Speed Solar Wind Stream Observed in September 2014

Energy coupling between the solar wind and the Earth's magnetosphere can affect the electron population in the outer radiation belt. However, the precise role of different internal and external mechanisms that leads to changes of the relativistic electron population is not entirely known. This paper describes how ultralow frequency (ULF) wave activity during the passage of Alfvenic solar wind streams contributes to the global recovery of the relativistic electron population in the outer radiation belt. To investigate the contribution of the ULF waves, we searched the Van Allen Probes data for a period in which we can clearly distinguish the enhancement of electron fluxes from the background. We found that the global recovery that started on 22 September 2014, which coincides with the corotating interaction region preceding a high‐speed stream and the occurrence of persistent substorm activity, provides an excellent scenario to explore the contribution of ULF waves. To support our analyses, we employed ground‐ and space‐based observational data and global magnetohydrodynamic simulations and calculated the ULF wave radial diffusion coefficients employing an empirical model. Observations show a gradual increase of electron fluxes in the outer radiation belt and a concomitant enhancement of ULF activity that spreads from higher to lower L‐shells. Magnetohydrodynamic simulation results agree with observed ULF wave activity in the magnetotail, which leads to both fast and Alfven modes in the magnetospheric nightside sector. The observations agree with the empirical model and are confirmed by phase space density calculations for this global recovery period.

Silva, L. A. Da↗
DOE OSTI2018

Luminescence regulation mechanism of single layer NaYF4: Yb3+, Er3+@NaYF4 nanocrystals on Au nanolayer supported by anodic aluminum oxide template

Highlights: • Hybrid structure of AAO or Au sputtered AAO covered by single layer NCs was prepared. • By cavity quantum optics theory, luminescence regulation mechanism was proposed. • A novel idea for SPR induced luminescence regulation exploration has been presented. - Abstract: A kind of novel hybrid nanostructure of anodic aluminum oxide (AAO) template or Au sputtered AAO template covered by a single layer NaYF{sub 4}: Yb{sup 3+}, Er{sup 3+}@NaYF{sub 4} nanocrystals (NCs) was prepared by a facile strategy. Two kinds of available models that include with and without Au nanolayer were suggested for simulations. Significant downconversion luminescence (DCL) enhancement was observed when the supported template changed from single AAO to Au nanolayer covered AAO. A formula for luminescence enhancement factor based on the cavity quantum optics theory was constructed. With luminescence dynamics analyses, the DCL enhancement was ascribe to the main positive influence of excitation enhancement, besides the minor negative impact of the competition among the nonradiative loss of resonant cavity, the higher order mode loss of Purcell factor, and the increase of radiative transition rate. It proposed a new idea for surface plasmon (SP) induced luminescence regulation mechanism exploration.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

The functions of caspase in whitefly Bemisia tabaci apoptosis in response to ultraviolet irradiation

Abstract Whiteflies ( Bemisia tabaci ) are phloem feeders, and some invasive species are composed of cryptic species complexes that cause extensive crop damage, particularly via the direct transmission of plant viruses. Apoptosis is a type of programmed cell death essential for organismal development and tissue homeostasis. The caspases belong to a family of cysteine proteases that play a central role in the initiation of apoptosis in many organisms. Here, we employed a comprehensive genomics approach to identity caspases in B. tabaci Middle East Asia Minor 1 (MEAM1), an invasive whitefly that carries a cryptic species complex that is devastating to crops. Four caspase genes were identified, and their motif compositions were predicted. Structures were relatively conserved in both putative effector and initiator caspases. Expression patterns of caspase genes differed across insect developmental stages. Three caspase genes were induced immediately after ultraviolet (UV) treatment. Expression levels of Bt‐caspase‐1 and Bt‐caspase‐3b increased in the midgut and salivary glands during apoptosis induced by UV treatments, whereas silencing of both genes reduced UV‐triggered apoptosis. Our study demonstrates that Bt‐caspase‐1 and Bt‐caspase‐3b, respectively, act as putative initiator and effector apoptotic caspases in the MEAM1 whitefly.

Wang, X. ‐R.↗
DOE OSTI2018

Phases of a phenomenological model of twisted bilayer graphene

In this study, we propose a lattice-scale two-band generalized Hubbard model as a caricature of the electronic structure of twisted bilayer graphene. Various possible broken-symmetry phases can arise, including a nematic phase (which is a form of orbital ferromagnet) and an orbital-triplet spin-singlet superconducting phase. Lastly, concerning the mechanism of superconductivity, we propose an analogy with superconductivity in alkali-doped C 60 in which a violation of Hund's first rule plays a central role.

36 MATERIALS SCIENCE↗
DOE OSTI2018

ADAPTIVE SURROGATES WITHIN THE RAVEN FRAMEWORK FOR DYNAMIC PROBABILISTIC RISK ASSESSMENT ANALYSIS

The RAVEN code has been under development at the Idaho National Laboratory since 2012. Its main goal is to create a multi-purpose platform for the deploying of all the capabilities needed for Probabilistic Risk Assessment (PRA), Uncertainty Quantification (UQ), data mining analysis and optimization studies. RAVEN has demonstrated a good level of maturity in terms of state-of-art and advanced analysis methodologies. In the past year the RAVEN code has been released as open-source project and is available to download (raven.inl.gov) free of charge. The main subject of this paper is to present a new system within the RAVEN framework to drastically accelerate PRA and UQ analysis using acceleration schemes based on surrogate modeling. This system is based on the heavy usage of surrogate modeling and artificial intelligence algorithms, able to emulate the response of a physical system in closed domains (domains where the surrogate models have been constructed from). The aim of this paper is to show to the community how the employment of surrogate modeling techniques can be a viable solution for the current and future challenges in terms of PRA, UQ and Safety Margins characterizations. In addition, in this manuscript it is presented the construction of a RAVEN new entity named “HybridModel” that is aimed to switch between a high-fidelity code and its linked surrogate, accelerating the PRA and UQ processes without largely reducing the accuracy of the results of the analyses. All these new capabilities will be shown with an application example about a Station Black Out scenario for a prototypical Pressurized Water Reactor (modeled with RELAP5-3D).

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Measurement of Absorption Coefficient of Paraformaldehyde and Metaldehyde with Terahertz Spectroscopy

The characteristic absorption spectra of paraformaldehyde and metaldehyde in the terahertz frequency region are obtained by terahertz time-domain spectroscopy (THz-TDS). In order to reduce the absorption of terahertz (THz) wave by water vapor in the air and the background noise, the measurement system was filled with dry air and the measurements were conducted at the temperature of 24°C. Meanwhile, the humidity was controlled within 10% RH. The THz frequency domain spectra of samples and their references from 0 to 2.5 THz were analyzed via Fourier transform. The refractive index and absorption coefficients of the two aldehydes were calculated by the model formulas. From 0.1 to 2.5 THz, there appear two weak absorption peaks at 1.20 and 1.66 THz in the absorption spectra of paraformaldehyde. Only one distinct absorption peak emerges at 1.83 THz for metaldehyde. There are significant differences between the terahertz absorption coefficients of paraformaldehyde and metaldehyde, which can be used as 'fingerprints' to identify these substances. Furthermore, the relationship between the average absorption coefficients and mass concentrations was investigated and the average absorption coefficient–mass concentration diagrams of paraformaldehyde and metaldehyde were shown. For paraformaldehyde, there is a linear relationship between the average absorption coefficient and the natural logarithm of mass concentration. For metaldehyde, there exists a simpler linear relationship between the average absorption coefficient and the mass concentration. Because of the characteristics of THz absorption of paraformaldehyde and metaldehyde, the THz-TDS can be applied to the qualitative and quantitative detection of the two aldehydes to reduce the unpredictable hazards due to these substances.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Magnetic, Mechanical, and Electronic Properties of RhH{sub x} (x = 0, 0.25, 0.75, 1) from First-Principles Calculations

The magnetic, mechanical, and electronic properties of RhH{sub x} (x = 0, 0.25, 0.75, 1) have been investigated by first-principles calculations based on density functional theory. It is shown that RhH{sub x} (x = 0.25, 0.75, 1) in the cubic structure are magnetic except for Rh. The total magnetic moments of RhH{sub x} (x = 0.25, 0.75, 1) decrease with increasing content of H, which mainly results from the change of the Rh moments. The calculated elastic constants indicate that RhH{sub x} (x = 0, 0.25, 0.75, 1) in the cubic structure are mechanically stable. With increasing H content, the bulk modulus, shear modulus, and Young modulus gradually decrease except the bulk modulus of RhH. By means of the values of the B/G ratio, it is concluded that H doping improves the ductile properties of Rh. The strong hybridization between H-s and Rh-d is the origin of magnetism for RhH{sub x} (x = 0.25, 0.75, 1) and decreases with increasing H content.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effects of Voltage on Microstructure and Corrosion Resistance of Micro-arc Oxidation Ceramic Coatings Formed on KBM10 Magnesium Alloy

Micro-arc oxidation (MAO) coatings on KBM10 magnesium alloy were prepared in an electrolyte system with sodium silicate, potassium hydroxide, sodium tungstate, and citric acid. The effects of voltage on the microstructure and corrosion resistance of MAO coatings were studied using stereoscopic microscopy, scanning electron microscopy, x-ray diffraction, scratch tests, potentiodynamic polarization, and electrochemical impedance spectroscopy. The results showed that the roughness of the MAO coatings, diameter, and number of pores increase with the increase in voltage. The coating formed at the voltage of 350 V exhibited the best adhesive strength when evaluated by the automatic scratch tester. The coatings were mainly composed of MgO, MgWO{sub 4}, and Mg{sub 2}SiO{sub 4}, and the content of Mg{sub 2}SiO{sub 4} increased with the increase in voltage. The corrosion resistance of MAO coatings could be improved by changing the applied voltage, and the best corrosion resistance of MAO coating was observed at the voltage of 350 V.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Discovery of Two New Hypervelocity Stars from the LAMOST Spectroscopic Surveys

We report the discovery of two new unbound hypervelocity stars (HVSs) from the LAMOST spectroscopic surveys. They are, respectively, a B2V-type star of ∼7 M {sub ⊙} with a Galactic rest-frame radial velocity of 502 km s{sup −1} at a Galactocentric radius of ∼21 kpc and a B7V-type star of ∼4 M {sub ⊙} with a Galactic rest-frame radial velocity of 408 km s{sup −1} at a Galactocentric radius of ∼30 kpc. The origins of the two HVSs are not clear given their currently poorly measured proper motions. However, the future data releases of Gaia should provide proper motion measurements accurate enough to solve this problem. The ongoing LAMOST spectroscopic surveys are expected to yield more HVSs to form a statistical sample, providing vital constraints on understanding the nature of HVSs and their ejection mechanisms.

79 ASTRONOMY AND ASTROPHYSICS↗