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Particulate and gas sampling of prescribed fires in South Georgia, USA
Balachandran, S.,Pachon, J.E.,Lee, S.,Oakes, M.M.,Rastogi, N.,Shi, W.,Tagaris, E.,Yan, B.,Davis, A.,Zhang, X.,Weber, R.J.,Mulholland, J.A.,Bergin, M.H.,Zheng, M.,Russell, A.G. Pergamon Press ; Elsevier [distribution] 2013 Atmospheric environment Vol.81 No.-
Gaseous and particulate species from two prescribed fires were sampled in-situ, to better characterize prescribed burn emissions. Measurements included gaseous and fine particulate matter (PM<SUB>2.5</SUB>) species, particle number concentration, particulate organic carbon (POC) speciation, water-soluble organic carbon (WSOC) and water-soluble iron. Major PM<SUB>2.5</SUB> components included OC (~57%), EC (~10%), chloride (~1.6%), potassium (~0.7%) and nitrate (~0.9%). Major gaseous species include carbon dioxide, carbon monoxide, methane, ethane, methanol and ethylene. Particulate organic tracers of biomass burning, such as levoglucosan, dehydroabietic acid and retene, increased significantly during the burns. Water-soluble organic carbon (WSOC) also increased significantly during the fire and levels are highly correlated with total potassium (K) (R<SUP>2</SUP> = 0.93) and levoglucosan (R<SUP>2</SUP> = 0.98). The average WSOC/OC ratio was 0.51 +/- 0.03 and did not change significantly from background levels. Thus, the WSOC/OC ratio may not be a good indicator of secondary organic aerosol (SOA) in regions that are expected to be impacted by biomass burning. Results using a biomass burning source profile derived from this work further indicate that source apportionment is sensitive to levels of potassium in biomass burning source profiles. This underscores the importance of quantifying local biomass burning source profiles.
The validity of Kirchhoff theory for scattering of elastic waves from rough surfaces
Shi, F.,Choi, W.,Lowe, M. J. S.,Skelton, E. A.,Craster, R. V. The Royal Society 2015 Proceedings, Mathematical, physical, and engineeri Vol.471 No.2178
<P> The Kirchhoff approximation (KA) for elastic wave scattering from two-dimensional (2D) and three-dimensional (3D) rough surfaces is critically examined using finite-element (FE) simulations capable of extracting highly accurate data while retaining a fine-scale rough surface. The FE approach efficiently couples a time domain FE solver with a boundary integration method to compute the scattered signals from specific realizations of rough surfaces. Multiple random rough surfaces whose profiles have Gaussian statistics are studied by both Kirchhoff and FE models and the results are compared; Monte Carlo simulations are used to assess the comparison statistically. The comparison focuses on the averaged peak amplitude of the scattered signals, as it is an important characteristic measured in experiments. Comparisons, in both two dimensions and three dimensions, determine the accuracy of Kirchhoff theory in terms of an empirically estimated parameter <I>σ</I><SUP>2</SUP> /λ 0 ( <I>σ</I> is the RMS value, and λ 0 is the correlation length, of the roughness), being considered accurate when this is less than some upper bound <I>c</I> , ( <I>σ</I><SUP>2</SUP> /λ 0 < <I>c</I> ). The incidence and scattering angles also play important roles in the validity of the Kirchhoff theory and it is found that for modest incidence angles of less than 30°, the accuracy of the KA is improved even when <I>σ</I><SUP>2</SUP> /λ 0 > <I>c</I> . In addition, the evaluation results are compared using 3D isotropic rough surfaces and 2D surfaces with the same surface parameters. </P>
Response of plasma rotation to resonant magnetic perturbations in J-TEXT tokamak
Yan, W,Chen, Z Y,Huang, D W,Hu, Q M,Shi, Y J,Ding, Y H,Cheng, Z F,Yang, Z J,Pan, X M,Lee, S G,Tong, R H,Wei, Y N,Dong, Y B IOP 2018 Plasma physics and controlled fusion Vol.60 No.3
<P>The response of plasma toroidal rotation to the external resonant magnetic perturbations (RMP) has been investigated in Joint Texas Experimental Tokamak (J-TEXT) ohmic heating plasmas. For the J-TEXT’s plasmas without the application of RMP, the core toroidal rotation is in the counter-current direction while the edge rotation is near zero or slightly in the co-current direction. Both static RMP experiments and rotating RMP experiments have been applied to investigate the plasma toroidal rotation. The core toroidal rotation decreases to lower level with static RMP. At the same time, the edge rotation can spin to more than 20 km s<SUP>−1</SUP> in co-current direction. On the other hand, the core plasma rotation can be slowed down or be accelerated with the rotating RMP. When the rotating RMP frequency is higher than mode frequency, the plasma rotation can be accelerated to the rotating RMP frequency. The plasma confinement is improved with high frequency rotating RMP. The plasma rotation is decelerated to the rotating RMP frequency when the rotating RMP frequency is lower than the mode frequency. The plasma confinement also degrades with low frequency rotating RMP.</P>
EPIR effect of Cu2O films by electrochemical deposition
D.W. Shi,C.J. Luo,C.P. Yang,R. Yang,H.B. Xiao,K. Barner,V.V. Marchenkov 한국물리학회 2014 Current Applied Physics Vol.14 No.9
Cuprous oxide (Cu2O) films and Cu/Cu2O/Cu/FTO sandwich structures were prepared by electrochemical deposition on conductive FTO substrates with different pH value conditions but constant deposition potential. The phase composition, crystal structure and microstructure of the Cu2O films were characterized by XRD, SEM and EDS as well as by ElectricePulseeInducedeResistance (EPIR) perturbation. In particular, the switching effects of the Cu/Cu2O/Cu/FTO device are examined in this work. The result shows that the EPIR-effect is large for the Cu/Cu2O/Cu/FTO device at room temperature and strongly related to the pH value of the solution. In both acidic and neutral conditions, for example at pH ¼ 5, 6 and 7, the EPIR effect is significant and decreases with increasing pH value. It disappears when the pH value goes further into the alkaline regime, i.e. pH ¼ 8, 9 and 10. Space charge barriers at the interface of electrode and Cu2O are used to explain the IeV characteristic of the layer structure and the EPIR-effect.
Isostructural metal-insulator transition in VO<sub>2</sub>
Lee, D.,Chung, B.,Shi, Y.,Kim, G.-Y.,Campbell, N.,Xue, F.,Song, K.,Choi, S.-Y.,Podkaminer, J. P.,Kim, T. H.,Ryan, P. J.,Kim, J.-W.,Paudel, T. R.,Kang, J.-H.,Spinuzzi, J. W.,Tenne, D. A.,Tsymbal, E. Y. American Association for the Advancement of Scienc 2018 Science Vol.362 No.6418
<P><B>Separating structure and electrons in VO<SUB>2</SUB></B></P><P>Above 341 kelvin—not far from room temperature—bulk vanadium dioxide (VO<SUB>2</SUB>) is a metal. But as soon as the material is cooled below 341 kelvin, VO<SUB>2</SUB> turns into an insulator and, at the same time, changes its crystal structure from rutile to monoclinic. Lee <I>et al.</I> studied the peculiar behavior of a heterostructure consisting of a layer of VO<SUB>2</SUB> placed underneath a layer of the same material that has a bit less oxygen. In the VO<SUB>2</SUB> layer, the structural transition occurred at a higher temperature than the metal-insulator transition. In between those two temperatures, VO<SUB>2</SUB> was a metal with a monoclinic structure—a combination that does not occur in the absence of the adjoining oxygen-poor layer.</P><P><I>Science</I>, this issue p. 1037</P><P>The metal-insulator transition in correlated materials is usually coupled to a symmetry-lowering structural phase transition. This coupling not only complicates the understanding of the basic mechanism of this phenomenon but also limits the speed and endurance of prospective electronic devices. We demonstrate an isostructural, purely electronically driven metal-insulator transition in epitaxial heterostructures of an archetypal correlated material, vanadium dioxide. A combination of thin-film synthesis, structural and electrical characterizations, and theoretical modeling reveals that an interface interaction suppresses the electronic correlations without changing the crystal structure in this otherwise correlated insulator. This interaction stabilizes a nonequilibrium metallic phase and leads to an isostructural metal-insulator transition. This discovery will provide insights into phase transitions of correlated materials and may aid the design of device functionalities.</P>