Browsing by Author "Yang, Lei"

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Decadal Variation in Surface Characteristics over Xinjiang, Western China, from TAP Altimetry Backscatter Coefficients: Evidence of Climate Change
(2013-08-01)
Guo, Jinyun
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Yang, Lei
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Liu, Xin
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Chang, Xiaotao
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Hwang, Cheinway
The backscatter coefficient, known as sigma0, is an important measurement of satellite radar altimetry and a key parameter for land altimetry because of its close relationship with the physical properties and geometric features of land coverage under global/regional climate change effects. Using the TOPEX/Poseidon GDR-M dataset from January 1993 to December 2004, we study the spatial and temporal distribution of sigma at bands Ku and C over Xinjiang, western China. The results show that the sigma0 is influenced by the water distribution over land and the time evolution of sigma0 has clear seasonal changes. River basins or deserts are classified over the spatial distribution based on different sigma0 values. For example, high sigma0 values are found in the Tarim River Basin and low values are found in the Taldimakan Desert. The periodic components of sigma0 time series are determined using the fast Fourier transformation method. The annual variation is the dominating cycle and the semi-annual variation is the secondary signal. The amplitudes of sigma0 time series at bands Ku and C are also given and most areas have quite low amplitudes except for the Tarim River Basin. Several areas including the Tarim River Basin, Tianshan Mountain and Taldimakan Desert are selected for sigma0 time series spacial analysis to discuss the reasons for variations in sigma0. The main factors are precipitation and vegetation growth, which are affected by the global/regional climate change. The correlation between the brightness temperature, which is related to the water-vapor content in the atmosphere measured by TMR at the 21 GHz channel and sigma0 at two bands, is analyzed.
From Ni-YSZ to sulfur-tolerant anode materials for SOFCs: electrochemical behavior, in situ characterization, modeling, and future perspectives
(2011-11-01)
Cheng, Zhe
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Wang, Jeng-Han
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Choi, YongMan
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Yang, Lei
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Lin, M. C.
Solid oxide fuel cells (SOFCs) offer great promise for the most efficient and cost-effective conversion to electricity of a wide variety of fuels such as hydrocarbons, coal gas, and gasified carbonaceous solids. However, the conventional Ni-YSZ (yttria-stabilized zirconia) anode is highly susceptible to deactivation (poisoning) by contaminants commonly encountered in readily available fuels, especially sulfur-containing compounds. Thus, one of the critical challenges facing the realization of fuel-flexible and cost-effective SOFC systems is the development of sulfur-tolerant anode materials. This perspective article aims at providing a comprehensive review of materials that have been studied as anodes for SOFCs, the electrochemical behavior of various anode materials in H(2)S-contaminated fuels, experimental methods for ex situ and in situ characterizations of species and phases formed on anode surfaces upon exposure to H(2)S-containing fuels, mechanisms for the interactions between H(2)S and anode surfaces as predicted from density functional theory (DFT) calculations, and possible strategies of minimizing or eliminating the effect of sulfur poisoning. While significant progress has been made in developing alternative anode materials with better sulfur tolerance, in probing and mapping electrode surface species relevant to sulfur poisoning, and in unraveling the mechanisms of H(2)S-anode interactions using both computational and experimental approaches, many challenges still remain to bridge the gaps between models at different scales or between theoretical predictions and experimental observations. An important new direction for future research is to develop a predictive multiscale (from DFT to continuum) computational framework, through a rigorous validation at each scale by carefully-designed experiments performed under in situ conditions, for rational design of better sulfur-tolerant anode materials and structures for a new generation of SOFCs to be powered by readily available fuels.
Neutrino physics with JUNO
(2016-03)
An, Fengpeng
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An, Guangpeng
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An, Qi
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Antonelli, Vito
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Baussan, Eric
The Jiangmen Underground Neutrino Observatory (JUNO), a 20 kton multipurpose underground liquid scintillator detector, was proposed with the determination of the neutrino mass hierarchy (MH) as a primary physics goal. The excellent energy resolution and the large fiducial volume anticipated for the JUNO detector offer exciting opportunities for addressing many important topics in neutrino and astro-particle physics. In this document, we present the physics motivations and the anticipated performance of the JUNO detector for various proposed measurements. Following an introduction summarizing the current status and open issues in neutrino physics, we discuss how the detection of antineutrinos generated by a cluster of nuclear power plants allows the determination of the neutrino MH at a 3-4 sigma significance with six years of running of JUNO. The measurement of antineutrino spectrum with excellent energy resolution will also lead to the precise determination of the neutrino oscillation parameters sin(2) theta(12), Delta m(21)(2), and vertical bar Delta m(ee)(2)vertical bar to an accuracy of better than 1%, which will play a crucial role in the future unitarity test of the MNSP matrix. The JUNO detector is capable of observing not only antineutrinos from the power plants, but also neutrinos/antineutrinos from terrestrial and extra-terrestrial sources, including supernova burst neutrinos, diffuse supernova neutrino background, geoneutrinos, atmospheric neutrinos, and solar neutrinos. As a result of JUNO\'s large size, excellent energy resolution, and vertex reconstruction capability, interesting new data on these topics can be collected. For example, a neutrino burst from a typical core-collapse supernova at a distance of 10 kpc would lead to similar to 5000 inverse-beta-decay events and similar to 2000 all-flavor neutrino-proton ES events in JUNO, which are of crucial importance for understanding the mechanism of supernova explosion and for exploring novel phenomena such as collective neutrino oscillations. Detection of neutrinos from all past core-collapse supernova explosions in the visible universe with JUNO would further provide valuable information on the cosmic star-formation rate and the average core-collapse neutrino energy spectrum. Antineutrinos originating from the radioactive decay of uranium and thorium in the Earth can be detected in JUNO with a rate of similar to 400 events per year, significantly improving the statistics of existing geoneutrino event samples. Atmospheric neutrino events collected in JUNO can provide independent inputs for determining the MH and the octant of the theta(23) mixing angle. Detection of the Be-7 and B-8 solar neutrino events at JUNO would shed new light on the solar metallicity problem and examine the transition region between the vacuum and matter dominated neutrino oscillations. Regarding light sterile neutrino topics, sterile neutrinos with 10-(5) eV(2) < Delta m(41)(2) < 10(-2) and a sufficiently large mixing angle theta(14) could be identified through a precise measurement of the reactor antineutrino energy spectrum. Meanwhile, JUNO can also provide us excellent opportunities to test the eV-scale sterile neutrino hypothesis, using either the radioactive neutrino sources or a cyclotron-produced neutrino beam. The JUNO detector is also sensitive to several other beyondthe-standard-model physics. Examples include the search for proton decay via the p -> K++ <(v)over bar> decay channel, search for neutrinos resulting from dark-matter annihilation in the Sun, search for violation of Lorentz invariance via the sidereal modulation of the reactor neutrino event rate, and search for the effects of non-standard interactions. The proposed construction of the JUNO detector will provide a unique facility to address many outstanding crucial questions in particle and astrophysics in a timely and cost-effective fashion. It holds the great potential for further advancing our quest to understanding the fundamental properties of neutrinos, one of the building blocks of our Universe.