scholarly journals 1-D Air-snowpack modeling of atmospheric nitrous acid at South Pole during ANTCI 2003

2008 ◽  
Vol 8 (23) ◽  
pp. 7087-7099 ◽  
Author(s):  
W. Liao ◽  
D. Tan
Keyword(s):  
Liquid Layer ◽  
Molecular Diffusion ◽  
Volume Ratio ◽  
Critical Factor ◽  
Snow Surface ◽  
High Concentration ◽  
Nitrite Concentration ◽  
Mechanical Dispersion ◽  
Quasi Liquid Layer ◽  
D Model

Abstract. A 1-D air-snowpack model of HONO has been developed and constrained by observed chemistry and meteorology data. The 1-D model includes molecular diffusion and mechanical dispersion, windpumping in snow, gas phase to quasi-liquid layer phase HONO transfer and quasi-liquid layer nitrate and interstitial air HONO photolysis. Photolysis of nitrate is important as a dominant HONO source inside the snowpack, however, the observed HONO emission from the snowpack was triggered mainly by the equilibrium between quasi liquid layer nitrite and firn air HONO deep down the snow surface (i.e. 30 cm below snow surface). The high concentration of HONO in the firn air is subsequently transported above the snowpack by diffusion and windpumping. The model uncertainties come mainly from lack of measurements and the interpretation of the QLL properties based on the bulk snow measurements. One critical factor is the ionic strength of QLL nitrite, which is estimated here by the bulk snow pH, nitrite concentration, and QLL to bulk snow volume ratio.

scholarly journals 1-D air-snowpack modeling of atmospheric nitrous acid at South Pole during ANTCI 2003

2008 ◽  
Vol 8 (3) ◽  
pp. 9731-9759
Author(s):  
◽  
D. Tan
Keyword(s):  
Liquid Layer ◽  
Molecular Diffusion ◽  
Volume Ratio ◽  
Critical Factor ◽  
Snow Surface ◽  
High Concentration ◽  
Nitrite Concentration ◽  
Mechanical Dispersion ◽  
Quasi Liquid Layer ◽  
D Model

Abstract. A 1-D air-snowpack model of HONO has been developed and constrained by observed chemistry and meteorology data. The 1-D model includes molecular diffusion and mechanical dispersion, windpumping in snow, gas phase to quasi-liquid layer phase HONO transfer and quasi-liquid layer nitrate and interstitial air HONO photolysis. Photolysis of nitrate is important as a dominant HONO source inside the snowpack, however, the observed HONO emission from the snowpack was triggered mainly by the equilibrium between quasi liquid layer nitrite and firn air HONO deep down the snow surface (i.e. 30 cm below snow surface). The high concentration of HONO in the firn air is subsequently transported above the snowpack by diffusion and windpumping. The model uncertainties come mainly from lack of measurements and the interpretation of the QLL properties based on the bulk snow measurements. One critical factor is the ionic strength of QLL nitrite, which is estimated here by the bulk snow pH, nitrite concentration, and QLL to bulk snow volume ratio.

scholarly journals Multiphase modeling of nitrate photochemistry in the quasi-liquid layer (QLL): implications for NO<sub>x</sub> release from the Arctic and coastal Antarctic snowpack

2008 ◽  
Vol 8 (16) ◽  
pp. 4855-4864 ◽  
Author(s):  
C. S. Boxe ◽  
A. Saiz-Lopez
Keyword(s):  
Gas Phase ◽  
Liquid Layer ◽  
Solar Spectrum ◽  
The Arctic ◽  
Transfer Model ◽  
Multiphase Model ◽  
Gas Phase Reactions ◽  
One Dimensional ◽  
Quasi Liquid Layer ◽  
Summer Range

Abstract. We utilize a multiphase model, CON-AIR (Condensed Phase to Air Transfer Model), to show that the photochemistry of nitrate (NO3−) in and on ice and snow surfaces, specifically the quasi-liquid layer (QLL), can account for NOx volume fluxes, concentrations, and [NO]/[NO2] (γ=[NO]/[NO2]) measured just above the Arctic and coastal Antarctic snowpack. Maximum gas phase NOx volume fluxes, concentrations and γ simulated for spring and summer range from 5.0×104 to 6.4×105 molecules cm−3 s−1, 5.7×108 to 4.8×109 molecules cm−3, and ~0.8 to 2.2, respectively, which are comparable to gas phase NOx volume fluxes, concentrations and γ measured in the field. The model incorporates the appropriate actinic solar spectrum, thereby properly weighting the different rates of photolysis of NO3− and NO2−. This is important since the immediate precursor for NO, for example, NO2−, absorbs at wavelengths longer than nitrate itself. Finally, one-dimensional model simulations indicate that both gas phase boundary layer NO and NO2 exhibit a negative concentration gradient as a function of height although [NO]/[NO2] are approximately constant. This gradient is primarily attributed to gas phase reactions of NOx with halogens oxides (i.e. as BrO and IO), HOx, and hydrocarbons, such as CH3O2.

scholarly journals The Hydrodynamic Dispersion Characteristics of Coral Sands

2019 ◽  
Vol 7 (9) ◽  
pp. 291 ◽  
Author(s):  
Xiang Cui ◽  
Changqi Zhu ◽  
Mingjian Hu ◽  
Xinzhi Wang ◽  
Haifeng Liu
Keyword(s):  
Particle Size ◽  
Porous Media ◽  
Flow Velocity ◽  
Molecular Diffusion ◽  
Dispersion Coefficient ◽  
Hydrodynamic Dispersion ◽  
Dispersion Characteristics ◽  
Factors Affecting ◽  
Mechanical Dispersion ◽  
Freshwater Aquifers

Dispersion characteristics are important factors affecting groundwater solute transport in porous media. In marine environments, solute dispersion leads to the formation of freshwater aquifers under islands. In this study, a series of model tests were designed to explore the relationship between the dispersion characteristics of solute in calcareous sands and the particle size, degree of compactness, and gradation of porous media, with a discussion of the types of dispersion mechanisms in coral sands. It was found that the particle size of coral sands was an important parameter affecting the dispersion coefficient, with the dispersion coefficient increasing with particle size. Gradation was also an important factor affecting the dispersion coefficient of coral sands, with the dispersion coefficient increasing with increasing d10. The dispersion coefficient of coral sands decreased approximately linearly with increasing compactness. The rate of decrease was −0.7244 for single-grained coral sands of particle size 0.25–0.5 mm. When the solute concentrations and particle sizes increased, the limiting concentration gradients at equilibrium decreased. In this study, based on the relative weights of molecular diffusion versus mechanical dispersion under different flow velocity conditions, the dispersion mechanisms were classified into five types, and for each type, a corresponding flow velocity limit was derived.

scholarly journals Plasmon-Enhanced Photothermal and Optomechanical Deformations of a Gold Nanoparticle

Nanomaterials ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1881
Author(s):  
Jiunn-Woei Liaw ◽  
Guanting Liu ◽  
Yun-Cheng Ku ◽  
Mao-Kuen Kuo
Keyword(s):  
Gold Nanoparticle ◽  
Liquid Layer ◽  
Viscoelastic Model ◽  
Dynamics Simulation ◽  
Photothermal Effect ◽  
Continuous Heating ◽  
Heating Process ◽  
Elastic Model ◽  
Linearly Polarized ◽  
Quasi Liquid Layer

Plasmon-enhanced photothermal and optomechanical effects on deforming and reshaping a gold nanoparticle (NP) are studied theoretically. A previous paper (Wang and Ding, ACS Nano 13, 32–37, 2019) has shown that a spherical gold nanoparticle (NP) irradiated by a tightly focused laser beam can be deformed into an elongated nanorod (NR) and even chopped in half (a dimer). The mechanism is supposed to be caused by photothermal heating for softening NP associated with optical traction for follow-up deformation. In this paper, our study focuses on deformation induced by Maxwell’s stress provided by a linearly polarized Gaussian beam upon the surface of a thermal-softened NP/NR. We use an elastic model to numerically calculate deformation according to optical traction and a viscoelastic model to theoretically estimate the following creep (elongation) as temperature nears the melting point. Our results indicate that a stretching traction at the two ends of the NP/NR causes elongation and a pinching traction at the middle causes a dent. Hence, a bigger NP can be elongated and then cut into two pieces (a dimer) at the dent due to the optomechanical effect. As the continuous heating process induces premelting of NPs, a quasi-liquid layer is formed first and then an outer liquid layer is induced due to reduction of surface energy, which was predicted by previous works of molecular dynamics simulation. Subsequently, we use the Young–Laplace model to investigate the surface tension effect on the following deformation. This study may provide an insight into utilizing the photothermal effect associated with optomechanical manipulation to tailor gold nanostructures.

A Novel Synthesis of CaWO4:Eu3+ Flower Like Microcrystals in Ethanol/Water Mixed System and Characterization

2012 ◽  
Vol 531-532 ◽  
pp. 512-518 ◽  
Author(s):  
Ye Qing Chen ◽  
Joo Hyun Lee ◽  
Sung Wook Park ◽  
Byung Kee Moon ◽  
Byung Chun Choi ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Hydrothermal Process ◽  
Volume Ratio ◽  
Mixed System ◽  
Mixed Solution ◽  
Photoluminescence Properties ◽  
X Ray Diffraction ◽  
High Concentration ◽  
X Ray ◽  
Xrd Patterns

In this paper, we report a successful synthesis of CaWO4:Eu3+ phosphor via an ethanol assisted hydrothermal process. X-ray diffraction (XRD) patterns, X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscope (FE-SEM) were used to investigate the growth of the products. The water and ethanol volume ratio is found to have extraordinary effect on the particle size and morphological appearance. Flower like ~ 1µm superstructures can be obtained with mixed solution of w/e of 50/50 at 120 °C hydrothermal sysnthesis for 12 h. High concentration of ethanol in aqueous solution was discovered to have a tendency in limiting the interaction between the small particles for crystallization. Temperature and time experiments were also performed to further investigate the growth mechanism of the ethanol assisted hydrothermal process. The photoluminescence properties of flower like CaWO4:Eu3+ has also been investigated.

Facetting Growth of Low Temperature Polycrystalline Silicon by Ecr-Cvd with Hydrogen Dilution Method

1998 ◽  
Vol 507 ◽  
Author(s):  
H.-L. Hsiao ◽  
A.-B. Yang ◽  
H.-L. Hwang
Keyword(s):  
Free Energy ◽  
Surface Free Energy ◽  
Liquid Layer ◽  
Polycrystalline Silicon ◽  
Diffusion Processes ◽  
Crystalline Silicon ◽  
Dark Field ◽  
Dilution Method ◽  
Hydrogen Dilution ◽  
Quasi Liquid Layer

ABSTRACTThe polycrystalline silicon films with grain size of 1 μ m have been successful deposited on glass substrates using ECR-CVD with hydrogen dilution method at 250°C and without any thermal annealing. The deposited poly-Si films exhibit severe “hill and valley” surface roughness and facets structures. The X-ray diffraction spectra show that the dominant crystal textures are <220> and <111> orientations. The leaf-like two-fold symmetrical grain shape and the corresponding crystallography diffraction pattern indicate the orientation of largest grain is <110>. The dark field TEM image also shows the upside octahedral facets shape. Considering the effect of orientation on deposition rate and symmetry, the possible facets orientation should be <311>. Moreover, the grain sizes of poly-Si thin films deposited on bare Si wafer and on oxidized Si substrates or glass are almost the same. The facetting and textural structures can be attributed to the surface free energy change induced by the adatom quasi-liquid layer which is composed by the radicals and energetic atomic hydrogen. This adatom quasi-liquid layer would dramatically change the surface diffusion processes of adsorbed precursors and surface free energy of low index planes. Therefore, the SiHn radicals and SinHm molecular precursors with enhanced surface mobility would relax to their stable sites and form the crystalline silicon clusters.

Orientation dependence of the quasi-liquid layer on tin and indium crystals

1994 ◽  
Vol 314 (3) ◽  
pp. 341-352 ◽  
Author(s):  
A. Pavlovska ◽  
D. Dobrev ◽  
E. Bauer
Keyword(s):  
Liquid Layer ◽  
Orientation Dependence ◽  
Quasi Liquid Layer

The effects of process variables for GCC pre-flocculation on floc and handsheet properties

2012 ◽  
Vol 27 (2) ◽  
pp. 382-387 ◽  
Author(s):  
Dongil Seo ◽  
Wan Hee Im ◽  
Hye Jung Youn ◽  
Hak Lae Lee
Keyword(s):  
Mechanical Properties ◽  
Particle Size ◽  
Critical Factor ◽  
Process Variables ◽  
Median Particle Size ◽  
High Concentration ◽  
Floc Size ◽  
Turbulent Environments ◽  
Median Particle ◽  
Ground Calcium Carbonate

Abstract Pre-flocculation is a technique that aggregates filler particles by means of polyelectrolytes. The size of the filler flocs is a critical factor affecting the properties of the paper. Process variables including the concentration of the flocculants, the stirring speed, and the dilution of the suspension change the size of the flocculated fillers. Ground calcium carbonate and cationic polyacrylamide were used to investigate the influence of these variables on flocculation. The median particle size and size distribution were examined and the tensile and optical properties influenced by the floc size and ash levels were evaluated. The addition of high concentration C-PAM increased the median particle size. Stirring speeds in the range of 1000 ~ 3000 rpm were used to simulate various turbulent environments, and it was shown that high stirring speeds drastically decreased the floc size. Diluting and low speed stirring the flocculated GCC suspension was effective in keeping the particle size intact without disruption before sheet forming. Larger GCC flocs in the handsheets resulted in better mechanical properties.

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