Browsing by Author "Shi, X"

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    10Be in late deglacial climate simulated by ECHAM5-HAM – Part 2: Isolating the solar signal from 10Be deposition
    (Copernicus Publications, 2014-04-01) Heikkilä, UE; Shi, X; Phipps, SJ; Smith, AM
    This study investigates the effect of deglacial climate on the deposition of the solar proxy 10Be globally, and at two specific locations, the GRIP site at Summit, Central Greenland, and the Law Dome site in coastal Antarctica. The deglacial climate is represented by three 30 year time slice simulations of 10 000 BP (years before present = 1950 CE), 11 000 and 12 000 BP, compared with a preindustrial control simulation. The model used is the ECHAM5-HAM atmospheric aerosol–climate model, driven with sea-surface temperatures and sea ice cover simulated using the CSIRO Mk3L coupled climate system model. The focus is on isolating the 10Be production signal, driven by solar variability, from the weather- or climate-driven noise in the 10Be deposition flux during different stages of climate. The production signal varies at lower frequencies, dominated by the 11 year solar cycle within the 30 year timescale of these experiments. The climatic noise is of higher frequencies than 11 years during the 30 year period studied. We first apply empirical orthogonal function (EOF) analysis to global 10Be deposition on the annual scale and find that the first principal component, consisting of the spatial pattern of mean 10Be deposition and the temporally varying solar signal, explains 64% of the variability. The following principal components are closely related to those of precipitation. Then, we apply ensemble empirical decomposition (EEMD) analysis to the time series of 10Be deposition at GRIP and at Law Dome, which is an effective method for adaptively decomposing the time series into different frequency components. The low-frequency components and the long-term trend represent production and have reduced noise compared to the entire frequency spectrum of the deposition. The high-frequency components represent climate-driven noise related to the seasonal cycle of e.g. precipitation and are closely connected to high frequencies of precipitation. These results firstly show that the 10Be atmospheric production signal is preserved in the deposition flux to surface even during climates very different from today's both in global data and at two specific locations. Secondly, noise can be effectively reduced from 10Be deposition data by simply applying the EOF analysis in the case of a reasonably large number of available data sets, or by decomposing the individual data sets to filter out high-frequency fluctuations. © Author(s) 2014.
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    The MUMBA campaign: measurements of urban, marine and biogenic air
    (Copernicus Publications, 2017-06-06) Paton-Walsh, C; Guérette, ÉA; Kubistin, D; Humphries, R; Wilson, SR; Dominick, D; Galbally, IE; Buchholz, R; Bhujel, M; Chambers, SD; Cheng, M; Cope, M; Davy, P; Emmerson, K; Griffith, DWT; Griffiths, AD; Keywood, MD; Lawson, S; Molloy, SB; Rea, G; Selleck, PW; Shi, X; Simmons, J; Velazco, V
    The Measurements of Urban, Marine and Biogenic Air (MUMBA) campaign took place in Wollongong, New South Wales (a small coastal city approximately 80 km south of Sydney, Australia) from 21 December 2012 to 15 February 2013. Like many Australian cities, Wollongong is surrounded by dense eucalyptus forest, so the urban airshed is heavily influenced by biogenic emissions. Instruments were deployed during MUMBA to measure the gaseous and aerosol composition of the atmosphere with the aim of providing a detailed characterisation of the complex environment of the ocean–forest–urban interface that could be used to test the skill of atmospheric models. The gases measured included ozone, oxides of nitrogen, carbon monoxide, carbon dioxide, methane and many of the most abundant volatile organic compounds. The aerosol characterisation included total particle counts above 3 nm, total cloud condensation nuclei counts, mass concentration, number concentration size distribution, aerosol chemical analyses and elemental analysis. The campaign captured varied meteorological conditions, including two extreme heat events, providing a potentially valuable test for models of future air quality in a warmer climate. There was also an episode when the site sampled clean marine air for many hours, providing a useful additional measure of the background concentrations of these trace gases within this poorly sampled region of the globe. In this paper we describe the campaign, the meteorology and the resulting observations of atmospheric composition in general terms in order to equip the reader with a sufficient understanding of the Wollongong regional influences to use the MUMBA datasets as a case study for testing a chemical transport model. © Author(s) 2017.
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    Phase transition enhanced thermoelectric performance in Cu2Se
    (Australian Institute of Physics, 2014-02-06) Liu, H; Shi, X; Zhang, W; Chen, L; Danilkin, SA
    Worldwide efforts to searching for good thermoelectric materials are frequently focusing on normal phases in crystalline semiconductors. The material’s thermoelectric performance is described the parameter of figure of merit, zT, which is around unity around room temperature and above 1.5 at high temperatures. In the Cu2Se with anti-fluorite structure above 400K, Se atoms form a rigid face-centred cubic lattice, while the copper ions are highly disordered or moving around the tetrahedral voids with liquid-like mobility, resulting in an extraordinarily low lattice thermal conductivity, which enables zT up to 1.5 at 1,000K. Here, we report significantly enhanced thermoelectric performance during the phase transitions in Cu2Se and iodine doped Cu2Se. It is showed that the critical electron and phonon scattering greatly improve the thermopower and strongly reduce the thermal coductivity, leading to the improvement in the figure of merit more than 3-7 times compared to the normal phases, and achieving zT value of 2.3 at 400K. This mechanism pave a new way to increase the figure of merit of thermoelectric materials, and expend the utility of thermoelectrics in electronic cooling industry.z
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    Temperature effects in lattice dynamics of SnSe
    (International Conference on Neutron Scattering, 2017-07-12) Danilkin, SA; Yu, DH; Deng, GC; Avdeev, M; Kutten, R; Pomjakushina, E; Shi, X; Liu, H
    Tinselenide demonstrates a record high thermoelectric figure of merit [1]. The distinctive feature of this material is very low thermal conductivity directly related to peculiarities of SnSe lattice dynamics. We studied the temperature dependence of the crystal structure, phonon dispersion curves and vibrational density of states (VDOS) of SnSe in the temperature range from 300 to 750 K using neutron scattering instruments at ANSTO. We found that frequencies of longitudinal and transverse phonons in SnSe have remarkably low frequencies, in particular the acoustic phonons propagating along a - axis perpendicular to the b-c layers. The low-energy TOc [100] optic mode polarized along c-axis is highly anharmonic and shows the soft-mode behavior. Measurements of VDOS during heating reveal rather complex modifications of the spectrum showing a significant softening of SnSe phonon frequencies as a function of temperature. The DFT-MD simulation describes softening of phonons at frequencies around 7.5 and 16 meV in agreement with the experiment. By analyzing the displacements of a Sn atom from DFT-MD, the strong anisotropy of thermal parameters was found near the phase transition temperature.
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    Update on the MUMBA campaign: measurements of urban, marine and biogenic air
    (Atmospheric Composition & Chemistry Observations & Modelling Conference, 2014-09-22) Paton-Walsh, C; Guérette, ÉA; Rea, G; Kubistin, D; Humphries, R; Wilson, SR; Griffith, DWT; Buchholz, R; Velazco, V; Shi, X; Galbally, IE; Keywood, MD; Lawson, S; Selleck, PW; Cheng, M; Molloy, SB; Bhujel, M; Griffiths, AD; Chambers, SD; Davy, P
    The Measurements of Urban, Marine and Biogenic Air (MUMBA) campaign took place in Wollongong, New South Wales (a small coastal city approximately 80 km south of Sydney, Australia), from 21st December 2012 to 15th February 2013. Like many Australian cities, Wollongong is surrounded by dense eucalyptus forest and so the urban air-shed is heavily influenced by biogenic emissions. Instruments were deployed during MUMBA to measure the gaseous and aerosol composition of the atmosphere with the aim of providing a detailed characterisation of the complex environment of the ocean/forest/urban interface that could be used to test the skill of atmospheric models. Gases measured included ozone, oxides of nitrogen, carbon monoxide, carbon dioxide, methane and many of the most abundant volatile organic compounds. Aerosol characterisation included total particle counts above 3 nm, total cloud condensation nuclei counts; mass concentration, number concentration size distribution, aerosol chemical analyses and elemental analysis. The campaign captured varied meteorological conditions, including two extreme heat events, providing a potentially valuable test for models of future air quality in a warmer climate. There was also an episode when the site sampled clean marine air for many hours, providing a useful additional measure of background concentrations of these trace gases within this poorly sampled region of the globe. In this paper we describe the campaign, the meteorology and the resulting observations of atmospheric composition in general terms, in order to equip the reader with sufficient understanding of the Wollongong regional influences to use the MUMBA datasets as a case study for testing a chemical transport model. The data is available from PANGAEA (see https://doi.pangaea.de/10.1594/PANGAEA.871982).