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Nanoscale capillary wetting studied with dissipative particle dynamic  [PDF]
C. Cupelli,B. Henrich,M. Moseler,M. Santer
Physics , 2005,
Abstract: We demonstrate that Multi-Body Dissipative Particle Dynamics (MDPD) can be used as an efficient computational tool for the investigation of nanoscale capillary impregnation of confined geometries. As an essential prerequisite, a novel model for a solid-liquid interface in the framework of MDPD is introduced, with tunable wetting behaviour and thermal roughening to reduce artificial density- and temperature oscillations. Within this model, the impregnation dynamics of a water-like fluid into a nanoscale slit pore has been studied. Despite the coarse graining implied with the model fluid, a sufficient amount of non-equilibrium averaging can be achieved allowing for the extraction of useful information even from transient simulations, such as the dynamic apparent contact angle. Although it is found to determine the capillary driving completely, it cannot be intepreted as a simple function of the capillary number.
Fragmentation and bond strength of airborne diesel soot agglomerates
Sonja Rothenbacher, Armin Messerer, Gerhard Kasper
Particle and Fibre Toxicology , 2008, DOI: 10.1186/1743-8977-5-9
Abstract: It was found that the primary soot agglomerates emitted directly from the engine could not be fragmented at all. Soot agglomerates permitted to grow additionally by Brownian coagulation of the primary emitted particles could be fragmented to a maximum of 75% and 60% respectively, depending on whether adsorbates were removed from their surface prior to aging or not. At most, these aged agglomerates could be broken down to roughly the size of the agglomerates from the primary emission. The energy required for a 50% fragmentation probability of all bonds within an agglomerate was reduced by roughly a factor of 2 when aging "dry" agglomerates. Average bond energies derived from the data were 0.52*10-16 and 1.2*10-16 J, respectively. This is about 2 orders of magnitude higher than estimates for pure van-der-Waals agglomerates, but agrees quite well with other observations.Although direct conclusions regarding the behavior of inhaled diesel aerosol in contact with body fluids cannot be drawn from such measurements, the results imply that highly agglomerated soot aerosol particles are unlikely to break up into units smaller than roughly the size distribution emitted as tail pipe soot.Diesel soot aerosol particles are usually agglomerated to varying degrees, depending on whether they have freshly emerged from the tailpipe, or whether they are aged (i.e. have undergone collisional growth) as in the case of prolonged residence times in a street tunnel. The mechanical stability of soot agglomerate particles is of considerable interest. When used as dye, easy disintegration of "lamp-black" in liquid suspension is usually a desired property; as a reinforcement in automobile tires it is generally not. Shear flow induced soot reentrainment in diesel particulate filters has a strong influence on the over-all system performance [1]. In conjunction with the assessment of health risks posed by inhaled diesel soot in contact with tissue and body fluids, the potential for breaking up la
Cloud condensation nuclei (CCN) from fresh and aged air pollution in the megacity region of Beijing
S. S. Gunthe, D. Rose, H. Su, R. M. Garland, P. Achtert, A. Nowak, A. Wiedensohler, M. Kuwata, N. Takegawa, Y. Kondo, M. Hu, M. Shao, T. Zhu, M. O. Andreae,U. P schl
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2011,
Abstract: Atmospheric aerosol particles serving as cloud condensation nuclei (CCN) are key elements of the hydrological cycle and climate. CCN properties were measured and characterized during the CAREBeijing-2006 campaign at a regional site south of the megacity of Beijing, China. Size-resolved CCN efficiency spectra recorded for a supersaturation range of S=0.07% to 0.86% yielded average activation diameters in the range of 190 nm to 45 nm. The corresponding effective hygroscopicity parameters (κ) exhibited a strong size dependence ranging from ~0.25 in the Aitken size range to ~0.45 in the accumulation size range. The campaign average value (κ =0.3 ± 0.1) was similar to the values observed and modeled for other populated continental regions. The hygroscopicity parameters derived from the CCN measurements were consistent with chemical composition data recorded by an aerosol mass spectrometer (AMS) and thermo-optical measurements of apparent elemental and organic carbon (EC and OC). The CCN hygroscopicity and its size dependence could be parameterized as a function of only AMS based organic and inorganic mass fractions (forg, finorg) using the simple mixing rule κp ≈ 0.1 · forg + 0.7 · finorg. When the measured air masses originated from the north and passed rapidly over the center of Beijing (fresh city pollution), the average particle hygroscopicity was reduced (κ = 0.2 ± 0.1), which is consistent with enhanced mass fractions of organic compounds (~50%) and EC (~30%) in the fine particulate matter (PM1). Moreover, substantial fractions of externally mixed weakly CCN-active particles were observed at low supersaturation (S=0.07%), which can be explained by the presence of freshly emitted soot particles with very low hygroscopicity (κ < 0.1). Particles in stagnant air from the industrialized region south of Beijing (aged regional pollution) were on average larger and more hygroscopic, which is consistent with enhanced mass fractions (~60%) of soluble inorganic ions (mostly sulfate, ammonium, and nitrate). Accordingly, the number concentration of CCN in aged air from the megacity region was higher than in fresh city outflow ((2.5–9.9) × 103 cm 3 vs. (0.4–8.3) × 103 cm 3 for S=0.07–0.86%) although the total aerosol particle number concentration was lower (1.2 × 104 cm 3 vs. 2.3 × 104 cm 3). A comparison with related studies suggests that the fresh outflow from Chinese urban centers generally may contain more, but smaller and less hygroscopic aerosol particles and thus fewer CCN than the aged outflow from megacity regions.
Modification of CeO2-ZrO2 catalyst by potassium for NOx-assisted soot oxidation

Duan Weng,Jia Li,Xiaodong Wu,Zhichun Si,

环境科学学报(英文版) , 2011,
Abstract: Potassium-modified ceria-zirconia catalyst was synthesized by wetness impregnation method. The ageing treatment was performed in static air at 800°C for 20 hr to evaluate the thermal stability of the catalyst. The catalysts were characterized by X-ray di raction, BET surface area, oxygen storage capacity, NOx-temperature programmed desorption and soot-temperature programmed oxidation measurements. By introduction of potassium, the maximum soot oxidation rate temperature (Tm) of the ceria-zirconia based catalyst decreased from 525 to 428°C in the presence of NO under a loose contact mode. The shift of Tm of the K-modified catalyst after ageing is only 15°C. The enhanced activity of the aged catalyst mainly lies in the promotional e ect of potassium on the NOx/oxygen storage capacity as well as the soot-catalyst contact.
Cloud condensation nuclei activity of fresh primary and aged biomass burning aerosol
G. J. Engelhart, C. J. Hennigan, M. A. Miracolo, A. L. Robinson,S. N. Pandis
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012,
Abstract: We quantify the hygroscopic properties of particles freshly emitted from biomass burning and after several hours of photochemical aging in a smog chamber. Values of the hygroscopicity parameter, κ, were calculated from cloud condensation nuclei (CCN) measurements of emissions from combustion of 12 biomass fuels commonly burned in North American wildfires. Prior to photochemical aging, the κ of the fresh primary aerosol varied widely, between 0.06 (weakly hygroscopic) and 0.6 (highly hygroscopic). The hygroscopicity of the primary aerosol was positively correlated with the inorganic mass fraction of the particles. Photochemical processing reduced the range of κ values to between 0.08 and 0.3. The changes in κ were driven by the photochemical production of secondary organic aerosol (SOA). SOA also contributed to growth of particles formed during nucleation events. Analysis of the nucleation mode particles enabled the first direct quantification of the hygroscopicity parameter κ for biomass burning SOA, which was on average 0.11, similar to values observed for biogenic SOA. Although initial CCN activity of biomass burning aerosol emissions are highly variable, after a few hours of photochemical processing κ converges to a value of 0.2 ± 0.1. Therefore, photochemical aging reduces the variability of biomass burning CCN κ, which should simplify analysis of the potential effects of biomass burning aerosol on climate.
Cloud condensation nuclei activity of fresh primary and aged biomass burning aerosol  [PDF]
G. J. Engelhart,C. J. Hennigan,M. A. Miracolo,A. L. Robinson
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012, DOI: 10.5194/acp-12-7285-2012
Abstract: We quantify the hygroscopic properties of particles freshly emitted from biomass burning and after several hours of photochemical aging in a smog chamber. Values of the hygroscopicity parameter, κ, were calculated from cloud condensation nuclei (CCN) measurements of emissions from combustion of 12 biomass fuels commonly burned in North American wildfires. Prior to photochemical aging, the κ of the fresh primary aerosol varied widely, between 0.06 (weakly hygroscopic) and 0.6 (highly hygroscopic). The hygroscopicity of the primary aerosol was positively correlated with the inorganic mass fraction of the particles. Photochemical processing reduced the range of κ values to between 0.08 and 0.3. The changes in κ were driven by the photochemical production of secondary organic aerosol (SOA). SOA also contributed to growth of particles formed during nucleation events. Analysis of the nucleation mode particles enabled the first direct quantification of the hygroscopicity parameter κ for biomass burning SOA, which was on average 0.11, similar to values observed for biogenic SOA. Although initial CCN activity of biomass burning aerosol emissions are highly variable, after a few hours of photochemical processing κ converges to a value of 0.2 ± 0.1. Therefore, photochemical aging reduces the variability of biomass burning CCN κ, which should simplify analysis of the potential effects of biomass burning aerosol on climate.
Depolarization Currents in Fresh and Aged Corona Poled P(VDF-TFE) Films  [PDF]
S. N. Fedosov,A. E. Sergeeva,A. F. Butenko
Physics , 2007,
Abstract: Using short circuit and open circuit modifications of the thermally stimulated depolarization current technique, relaxation currents have been measured in corona poled copolymer of vinylidene fluoride with tetrafluoroethylene in samples stored after poling for either 1 day, or 16 month. Two well structured peaks observed in aged samples were attributed to relaxation of electret and ferroelectric components of the remnant polarization. In fresh samples the two components were mixed forming one broad peak. Relaxation of the space charge caused inversion of the current in the open circuit mode both in fresh and in aged samples. Space charge peaks extracted from the total current by appropriate calculations have shown that the trapped charges were more stable than the polarization. It was suggested that both the electret and the ferroelectric components of the remnant polarization were accompanied by either space, or surface charges.
Non-UV germicidal activity of fresh TiO2 and Ag/TiO2

LIU Lifen,John Barford,YEUNG King Lun,

环境科学学报(英文版) , 2009,
Abstract: Fresh TiO2 was found to possess a strong germicidal activity even without UV irradiation. Live Yeast (Saccharomyces cerevisiae) cells in contact with fresh TiO2 were found deformed and dead after 15 min contact. The cause of germicidal activity was discussed from the observed cell deformation, lysis and increased absorption at 1680 cm-1 in FT-IR spectra of the affected cells, which proved the oxidizing effect of fresh TiO2 to cells. The deformation caused by the stretching of cell wall and pressure built-up inside the cell, led to cell burst and release of intracellular materials. The degree of cell deformation was found positively related with the wetting property of TiO2. Cells are negatively charged, for Gram-negative cell (thinner cell wall), a higher germicidal effect was observed than Gram-positive cells. The germicidal effect of TiO2 gradually decreases after exposure to air at room temperature, as the wetting property decreases. This kind of germicidal activity was more effective compared to other germicidal process such as UVA/TiO2 or Ag+. This shed light on designing new germicidal material either maintained by visible light irradiation, or by oxidation effect generated by reactive oxygen species.
Muon spin rotation measurements of the superfluid density in fresh and aged superconducting PuCoGa$_5$  [PDF]
K. Ohishi,R. H. Heffner,G. D. Morris,E. D. Bauer,M. J. Graf,J. -X. Zhu,L. A. Morales,J. L. Sarrao,M. J. Fluss,D. E. MacLaughlin,L. Shu,W. Higemoto,T. U. Ito
Physics , 2007, DOI: 10.1103/PhysRevB.76.064504
Abstract: We have measured the temperature dependence and magnitude of the superfluid density $\rho_{\rm s}(T)$ via the magnetic field penetration depth $\lambda(T)$ in PuCoGa$_5$ (nominal critical temperature $T_{c0} = 18.5$ K) using the muon spin rotation technique in order to investigate the symmetry of the order parameter, and to study the effects of aging on the superconducting properties of a radioactive material. The same single crystals were measured after 25 days ($T_c = 18.25$ K) and 400 days ($T_c = 15.0$ K) of aging at room temperature. The temperature dependence of the superfluid density is well described in both materials by a model using d-wave gap symmetry. The magnitude of the muon spin relaxation rate $\sigma$ in the aged sample, $\sigma\propto 1/\lambda^2\propto\rho_s/m^*$, where $m^*$ is the effective mass, is reduced by about 70% compared to fresh sample. This indicates that the scattering from self-irradiation induced defects is not in the limit of the conventional Abrikosov-Gor'kov pair-breaking theory, but rather in the limit of short coherence length (about 2 nm in PuCoGa$_5$) superconductivity.
Aged Vacuum Packaged Lamb Cuts Are Less Brown than Fresh Muscle Cuts under Simulated Retail Display  [PDF]
Eric N. Ponnampalam, Kym L. Butler, Viv F. Burnett, Matthew B. McDonagh, Joe L. Jacobs, David L. Hopkins
Food and Nutrition Sciences (FNS) , 2013, DOI: 10.4236/fns.2013.48A018
Abstract:

Fifty four, seven month old lambs, that had grazed perennial or annual pasture, were slaughtered and at 24 h post mortem m. longissimus lumborum samples were collected. Half of the fresh muscle section was sliced into three pieces and overwrapped with 15 micron polyvinyl chloride film and displayed under light (Lux = 1500) at 3℃ - 4. The remainder of the muscle section was vacuum packaged and aged for 4 weeks at 3, before slicing and display. Surface brownness and redness were measured over 3 days of simulated retail display. Aging in vacuum packs led to substantially less brownness and greater redness compared with fresh meat, over the entire three days of display. It was concluded that aging in vacuum packs could be a useful strategy for improving consumer acceptability of retail lamb in local markets, even where there is no logistical or transport need to extend the life of the meat.

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