Chemical Characterization of Flowing Polydisperse Aerosols by Raman Spectroscopy

We have applied Raman spectroscopy to the in-situ measurement of chemical composition of polydisperse flowing aerosols. Monodisperse and polydisperse aerosols in the size range 0.3 to 1.8 w m, composed of diethylsebacate (DES) and ammonium sulfate, were generated. The particles were irradiated with 514.5 nm laser light and Raman spectra were collected. The Raman intensities of DES at 2935 cm -1 and ammonium sulfate at 981 cm -1 , normalized by the nitrogen carrier gas Raman intensity at 2313 cm -1 , were approximately proportional to the aerosol mass loading over the particle size range studied. Calculations based on previous theoretical studies support this observation. The mass loading ranged from 0.17 to 12.8 g/m 3 for DES and 20 to 138 mg/m 3 for ammonium sulfate. The method was applied to mixing aerosol streams containing DES and ammonium sulfate in a turbulent jet. The Raman system, with a sensitive volume of 0.02 mm 3 , was used to measure radial and axial concentration profiles in the mixing region. The results compared well with turbulent mixing theory. The primary limitation for application of the method is the low signal to noise ratio.     

Adhesion-Delamination Mechanics of a Prestressed Circular Film Adhered onto a Rigid Substrate

A thin circular film clamped at the periphery is adhered to the planar surface of a rigid cylindrical punch. An external tensile load is applied to the punch, causing the film to delaminate from the substrate and the circular contact edge to contract. The film spontaneously separates from the punch, or pulls off, when the contact radius reduces to a range between 0.1758 and 0.3651 of the film radius, depending on the magnitude of the residual membrane stress. The mechanical delamination process is derived by a thermodynamic energy balance based on a coupled interfacial adhesion and residual membrane stress. The theoretical model has significant implications in nanoforce measurement, microelectromechanical systems (MEMS) comprising active moveable films, and biological cell adhesion.     

Selective plasma‐induced grafting of polystyrene onto polyolefin blends

Plasma pretreatment has been used to generate reactive radicals and oxygenated groups on polymer surfaces for graft polymerization. The polymer substrates studied were composed of a polypropylene–polyethylene (PP–PE) copolymer, which was predominantly PP, and also contained blended ethylene–propylene rubber (EPR) as either about 15 or about 60 mol %. A pure PP substrate was also studied for comparison. The grafted polymer was polystyrene (PS). Raman microspectroscopic 2‐dimensional mapping was used to elucidate the role of crystallinity and EPR in the plasma treatment and graft polymerization process. It was found that the plasma pretreatment favored the EPR component of the substrate and the graft yield was related to the EPR content. Crystallinity seemed to have a much less significant effect on the grafting reaction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1643–1652, 2003     

Stress Development During Drying of Aqueous Zirconia Based Tape Casting Slurries Measured by Transparent Substrate Deflection Method

During drying of water-based tape casting slurries, high stresses can occur, which lead to crack formation. Under the variety of different techniques to measure the drying stresses, the deflect measurement technique is very common. Due to the nontransparent substrate, this technique has the disadvantage, that a direct observation of the changes in the drying regions during the drying process is not possible. Thus, it cannot be ensured that homogeneous drying occurs, which is the prerequisite for the validity of the Corcoran's equation. Nonuniform drying causes cracks and might lead to errors in data interpretation, if nonuniformity of drying is not visible. To make drying uniformity visible, the deflect measurement technique was improved by the usage of a transparent substrate. The benefit of the new technique is the direct observation of saturation uniformity during drying. The differentiation of nonuniform drying and uniform drying, which is characterized by an optimum permeation of the solvent to the surface, is ensured. The advantage of the method is demonstrated by the characterization of the drying behavior of water-based stabilized zirconia slurries in the presence of dispersants and latex binders. Particularly with regard to slurries containing latex particles as a binder, progress was achieved in understanding drying. Measures to decrease drying stresses are summarized.     

The Mechanism of Selective Recognition of Lipid Substrate by hDHHC20 Enzyme

S-acylation is a post-translational linkage of long chain fatty acids to cysteines, playing a key role in normal physiology and disease. In human cells, the reaction is catalyzed by a family of 23 membrane DHHC-acyltransferases (carrying an Asp-His-His-Cys catalytic motif) in two stages: (1) acyl-CoA-mediated autoacylation of the enzyme; and (2) further transfer of the acyl chain to a protein substrate. Despite the availability of a 3D-structure of human acyltransferase (hDHHC20), the molecular aspects of lipid selectivity of DHHC-acyltransferases remain unclear. In this paper, using molecular dynamics (MD) simulations, we studied membrane-bound hDHHC20 right before the acylation by C12-, C14-, C16-, C18-, and C20-CoA substrates. We found that: (1) regardless of the chain length, its terminal methyl group always reaches the “ceiling” of the enzyme’s cavity; (2) only for C16, an optimal “reactivity” (assessed by a simple geometric criterion) permits the autoacylation; (3) in MD, some key interactions between an acyl-CoA and a protein differ from those in the reference crystal structure of the C16-CoA-hDHHS20 mutant complex (probably, because this structure corresponds to a non-native dimer). These features of specific recognition of full-size acyl-CoA substrates support our previous hypothesis of “geometric and physicochemical selectivity” derived for simplified acyl-CoA analogues.     

Formation and Growth of the Crack in Bonded Joints Under Mode I Fracture: Substrate Deflection at Crack Vicinity

Adhesive bonding is now commonly used in aircraft, cars, boats, etc. In these applications, thin panels are often bonded. In such thin structures, heterogeneous mechanical loading along the bondline edge (or potential crack front) is likely to arise due to 3D structural effects. The crack front and its vicinity is a special region, in that it is where structural properties of the adherend material meet those of the adhesive (discontinuity). To investigate the stress distribution in this region, we have observed the deflection of a flexible adherend in an asymmetric wedge bonded joint loaded in Mode I. A sensitive laser profilometry technique was used to observe the main vertical beam displacement and curvature along the length, as well as the resulting transverse, or anticlastic effect, due to Poisson's ratio. From this analysis is evaluated the heterogeneous tensile stress distribution in the adhesive in the vicinity of the crack front.     

Formation of Nanometric Yttrium Silicides Layers onto Si (111) Substrate by Ion Implantation

Silicon - Nanometric YSi2 − x yttrium silicides layers have been formed onto a Si(111) single-crystal substrate by implantation at room temperature (RT) of Y ions using an energy...     

Dielectric Properties of Coronene Film Deposited onto Silicon Substrate by Spin Coating for Optoelectronic Applications

Silicon - To determine the electrical modulus, dielectric properties, and ac conductivity of Coronene semiconductor layer, we have produced Al/Coronene/n-Si structure by using the thermally...     

油田自喷井井底流压计算方法研究及应用

在矿场上,井底流压的测试是一种常见的方法,但由于多方面的原因,使得许多井缺乏井底流压数据。因此借用一些计算方法进行井底压力的计算是十分必要的。本文在前人的工作基础上,分析不同流动形态时的空隙率与压降梯度的关系,建立了利用生产数据计算自喷井井底流压的方法,并用实例进行了验证。计算结果与实测值较为接近,能满足工程计算要求。     

Deposition of Ultrafine Aerosols in a Human Oral Cast

This paper reports experimental measurements of the total deposition of ultrafine aerosols in a human oral airway cast. A clear polyester resin cast of the upper airways of a normal human adult, including the nasal airways, oral cavity, tongue, nasopharynx, and larynx, was made from a postmortem solid cast. Measured pressure drop in the oral airway was slightly lower than in the nasal airway. The measured oral flow resistance was similar to the values reported for human volunteers breathing through the mouth at rest and for spontaneously opening of the mouth. Aerosol deposition data in the cast for monodisperse NaCl aerosols between 0.2 and 0.005 μm in diameter deposited in the cast were obtained for inspiratory and expiratory flow rates of 4, 20, and 40 L/min. Deposition efficiency increased with decreasing particle size and flow rate indicating that turbulent diffusion was the dominant mechanism for deposition. Higher deposition efficiency was observed for inspiratory flow in the oral airway than for expiratory flow. Oral deposition and nasal deposition for inspiratory flow were similar, but oral deposition was lower for expiratory flow. Deposition efficiency can be expressed as a function of the flow rate and diffusion coefficient of the particle.     

纳米无机粒子选择性分布与迁移对聚合物共混物形态与性能的影响

综述了纳米无机粒子在聚合物合金中选择性分布的影响因素及纳米无机粒子在聚合物中分散的重要性,重点从相行为、相形态、力学性能、电学性能、流变行为、结晶和熔融行为以及光学性能等方面总结了近年来纳米无机粒子在聚合物共混物中的选择性分布与迁移对以聚合物共混物为基体的纳米复合材料的形态和性能的影响。特别强调了如何利用热力学和动力学因素调控纳米无机粒子在聚合物合金中的分布。     

Selective Growth of Vertical-aligned ZnO Nanorod Arrays on Si Substrate by Catalyst-free Thermal Evaporation

By thermal evaporation of pure ZnO powders, high-density vertical-aligned ZnO nanorod arrays with diameter ranged in 80–250 nm were successfully synthesized on Si substrates covered with ZnO seed layers. It was revealed that the morphology, orientation, crystal, and optical quality of the ZnO nanorod arrays highly depend on the crystal quality of ZnO seed layers, which was confirmed by the characterizations of field-emission scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and photoluminescence measurements. For ZnO seed layer with wurtzite structure, the ZnO nanorods grew exactly normal to the substrate with perfect wurtzite structure, strong near-band-edge emission, and neglectable deep-level emission. The nanorods synthesized on the polycrystalline ZnO seed layer presented random orientation, wide diameter, and weak deep-level emission. This article provides a C-free and Au-free method for large-scale synthesis of vertical-aligned ZnO nanorod arrays by controlling the crystal quality of the seed layer.     

Theoretical Modeling of the Nucleation and Growth of Aluminium Films Thermally Evaporated onto Poly(ethylene terephthalate) Substrate

The interface between aluminium and poly(ethylene terephthalate) (PET) has been studied using the density functional theory (DFT) formalism within the local density approximation (LDA). An examination of the charge transfers during Al bonding with the polymer functional groups provides a better understanding of the nucleation of the metallic film. Indeed, when reacting with the doubly-bonded oxygen atom of the ester function, the metal particle induces strong modifications in the highest occupied molecular orbitals (HOMOs) as well as in the lowest unoccupied molecular orbitals (LUMOs) of the PET. The shape of the HOMO, HOMO-3 and HOMO-4 of the Al/PET complex confirms the evolution of the phenyl structure to a quinoid structure. We emphasise the extent to which the reactivity of the PET can be modified after Al interaction with the ester function. After losing their aromaticity, the phenyl rings of the polymer are no longer available for subsequent interactions. Hence, we propose that the Al film will then grow following a compact cubic stacking on top of Al atoms already fixed on the ester functions.     

Theoretical Modeling of the Nucleation and Growth of Aluminium Films Thermally Evaporated onto Poly(ethylene terephthalate) Substrate

The interface between aluminium and poly(ethylene terephthalate) (PET) has been studied using the density functional theory (DFT) formalism within the local density approximation (LDA). An examination of the charge transfers during Al bonding with the polymer functional groups provides a better understanding of the nucleation of the metallic film. Indeed, when reacting with the doubly-bonded oxygen atom of the ester function, the metal particle induces strong modifications in the highest occupied molecular orbitals (HOMOs) as well as in the lowest unoccupied molecular orbitals (LUMOs) of the PET. The shape of the HOMO, HOMO-3 and HOMO-4 of the Al/PET complex confirms the evolution of the phenyl structure to a quinoid structure. We emphasise the extent to which the reactivity of the PET can be modified after Al interaction with the ester function. After losing their aromaticity, the phenyl rings of the polymer are no longer available for subsequent interactions. Hence, we propose that the Al film will then grow following a compact cubic stacking on top of Al atoms already fixed on the ester functions.     

Collection and Generation of Sulfuric Acid Aerosols in a Wet Electrostatic Precipitator

Wet electrostatic precipitators (WESPs) are considered to be a possible technology for the control of sulfuric acid mist. The performance of a lab-scale WESP was investigated as a precipitator for sulfuric acid aerosol droplets produced under controlled conditions in a pilot plant. It was found that for higher levels of residual SO₂ in the flue gas, WESP collection efficiencies were greatly reduced due to aerosol formation inside the WESP. Investigations showed a strong correlation of aerosol emission from the WESP with incoming SO₂ concentration and operating voltage. It is suspected that the reactive species produced in the nonthermal plasma of the corona discharge oxidize the SO₂ to SO₃ which forms sulfuric acid. This causes supersaturation with subsequent homogeneous nucleation and thus aerosol formation.

Copyright 2015 American Association for Aerosol Research     

LED陶瓷基板烧成用高温超平板国产化探索研究

随着LED产业的快速发展,解决制约LED寿命的散热陶瓷基板问题也变得尤为重要,因此LED陶瓷基板烧成用高温超平板的国产化研究也迫在眉睫。本工作通过对进口超平板和试制超平板性能进行对比,来探索超平板国产化问题的可能解决方法,为下一步的国产化研究奠定一定的理论基础。凝胶注模成型未来有望成为解决国产超平板问题的新工艺。     

Population Balances of Micron-Sized Aerosols in a Bipolar Ion Environment

The present work re-examines the assumptions that are required for a steady-state charge distribution analysis to be valid. First, the common approximation that there are only 11 charge states available to the distribution is relaxed to allow for 201 charge states to be available to the particle distribution. This is found to have large repercussions on the behavior of the distribution for radii greater than 0.5 μm. The steady-state assumption itself is then re-examined by calculating the time required to reach steady state for many different ion-pair production rates and initial particle charge states as a function of radius. In the steady-state model, the ion populations are often assumed to decouple completely from the aerosol; this is shown to be false throughout the troposphere. Finally, the number of positive and negative charge states needed to accurately model a particle population of a given size is determined.

© 2013 American Association for Aerosol Research     

Simultaneous Production of Two Monodisperse Aerosols Using a Spinning-Top Aerosol Generator

A relatively simple laboratory technique for the simultaneous production of two monodisperse aerosols of different size has been developed and tested. This technique utilizes a standard May spinning-top aerosol generator that has been modified and enclosed under a special dual-cone fractionator. The fractionator efficiently separates the primary and satellite droplets. Illustrative Nacl aerosol generation data, obtained in a series of experiments, show that satellite droplets can provide an important source of the monodisperse aerosol.     

On a Petrov-Galerkin Finite Element Method for Evaporation of Polydisperse Aerosols

A Petrov-Galerkin finite element method is derived for evaporation of polydisperse aerosols. It is demonstrated that this numerical method is accurate and computationally efficient. Together with an appropriate grid system and upwinding factor, this method can reduce spurious oscillations to a negligible level and provide reliable results for a wide range of initial size distributions and evaporation rates. Its performance is superior to the upwind differencing method and the sectional method. It is also shown that analytical solutions are very useful in a priori design of grid systems for simulations of realistic aerosol systems, and evaporative cooling is a significant factor in modeling evaporation of polydisperse volatile aerosols.