Browsing by Subject "LIGHT-SCATTERING"

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  • Pandolfi, Marco; Alados-Arboledas, Lucas; Alastuey, Andres; Andrade, Marcos; Angelov, Christo; Artinano, Begona; Backman, John; Baltensperger, Urs; Bonasoni, Paolo; Bukowiecki, Nicolas; Coen, Martine Collaud; Conil, Sebastien; Coz, Esther; Crenn, Vincent; Dudoitis, Vadimas; Ealo, Marina; Eleftheriadis, Kostas; Favez, Olivier; Fetfatzis, Prodromos; Fiebig, Markus; Flentje, Harald; Ginot, Patrick; Gysel, Martin; Henzing, Bas; Hoffer, Andras; Smejkalova, Adela Holubova; Kalapov, Ivo; Kalivitis, Nikos; Kouvarakis, Giorgos; Kristensson, Adam; Kulmala, Markku; Lihavainen, Heikki; Lunder, Chris; Luoma, Krista; Lyamani, Hassan; Marinoni, Angela; Mihalopoulos, Nikos; Moerman, Marcel; Nicolas, Jose; O'Dowd, Colin; Petäjä, Tuukka; Petit, Jean-Eudes; Pichon, Jean Marc; Prokopciuk, Nina; Putaud, Jean-Philippe; Rodriguez, Sergio; Sciare, Jean; Sellegri, Karine; Swietlicki, Erik; Titos, Gloria; Tuch, Thomas; Tunved, Peter; Ulevicius, Vidmantas; Vaishya, Aditya; Vana, Milan; Virkkula, Aki; Vratolis, Stergios; Weingartner, Ernest; Wiedensohler, Alfred; Laj, Paolo (2018)
    This paper presents the light-scattering properties of atmospheric aerosol particles measured over the past decade at 28 ACTRIS observatories, which are located mainly in Europe. The data include particle light scattering (sigma(sp)) and hemispheric backscattering (sigma(bsp)) coefficients, scattering Angstrom exponent (SAE), backscatter fraction (BF) and asymmetry parameter (g). An increasing gradient of sigma(sp) is observed when moving from remote environments (arctic/mountain) to regional and to urban environments. At a regional level in Europe, sigma(sp) also increases when moving from Nordic and Baltic countries and from western Europe to central/eastern Europe, whereas no clear spatial gradient is observed for other station environments. The SAE does not show a clear gradient as a function of the placement of the station. However, a west-to-east-increasing gradient is observed for both regional and mountain placements, suggesting a lower fraction of fine-mode particle in western/south-western Europe compared to central and eastern Europe, where the fine-mode particles dominate the scattering. The g does not show any clear gradient by station placement or geographical location reflecting the complex relationship of this parameter with the physical properties of the aerosol particles. Both the station placement and the geographical location are important factors affecting the intraannual variability. At mountain sites, higher sigma(sp) and SAE values are measured in the summer due to the enhanced boundary layer influence and/or new particle-formation episodes. Conversely, the lower horizontal and vertical dispersion during winter leads to higher sigma(sp) values at all low-altitude sites in central and eastern Europe compared to summer. These sites also show SAE maxima in the summer (with corresponding g minima). At all sites, both SAE and g show a strong variation with aerosol particle loading. The lowest values of g are always observed together with low sigma(sp) values, indicating a larger contribution from particles in the smaller accumulation mode. During periods of high sigma(sp) values, the variation of g is less pronounced, whereas the SAE increases or decreases, suggesting changes mostly in the coarse aerosol particle mode rather than in the fine mode. Statistically significant decreasing trends of sigma(sp) are observed at 5 out of the 13 stations included in the trend analyses. The total reductions of sigma(sp) are consistent with those reported for PM2.5 and PM10 mass concentrations over similar periods across Europe.
  • Lampi, Mirka; Oksanen, Hanna M.; Meier, Florian; Moldenhauer, Evelin; Poranen, Minna M.; Bamford, Dennis H.; Eskelin, Katri (2018)
    Basic and applied virus research requires specimens that are purified to high homogeneity. Thus, there is much interest in the efficient production and purification of viruses and their subassemblies. Advances in the production steps have shifted the bottle neck of the process to the purification. Nonetheless, the development of purification techniques for different viruses is challenging due to the complex biological nature of the infected cell cultures as well as the biophysical and -chemical differences in the virus particles. We used bacteriophage phi 6 as a model virus in our attempts to provide a new purification method for enveloped viruses. We compared asymmetrical flow field-flow fractionation (AF4)-based virus purification method to the well-established ultracentrifugation-based purification of phi 6. In addition, binding of phi 6 virions to monolithic anion exchange columns was tested to evaluate their applicability in concentrating the AF4 purified specimens. Our results show that AF4 enables one-hour purification of infectious enveloped viruses with specific infectivity of similar to 1 x 10(13) PFU/mg of protein and similar to 65-95% yields. Obtained purity was comparable with that obtained using ultracentrifugation, but the yields from AF4 purification were 2-3-fold higher. Importantly, high quality virus preparations could be obtained directly from crude cell lysates. Furthermore, when used in combination with inline light scattering detectors, AF4 purification could be coupled to simultaneous quality control of obtained virus specimen.
  • Eskelin, Katri Johanna; Poranen, Minna Marjetta (2018)
    Viruses protect their genomes by enclosing them into protein capsids that sometimes contain lipid bilayers that either reside above or below the protein layer. Controlled dissociation of virions provides important information on virion composition, interactions, and stoichiometry of virion components, as well as their possible role in virus life cycles. Dissociation of viruses can be achieved by using various chemicals, enzymatic treatments, and incubation conditions. Asymmetrical flow field-flow fractionation (AF4) is a gentle method where the separation is based on size. Here, we applied AF4 for controlled dissociation of enveloped bacteriophage phi 6. Our results indicate that AF4 can be used to assay the efficiency of the dissociation process and to purify functional subviral particles.
  • Frattin, E.; Munoz, O.; Moreno, F.; Nava, J.; Escobar-Cerezo, J.; Gomez Martin, J. C.; Guirado, D.; Cellino, A.; Coll, P.; Raulin, F.; Bertini, I.; Cremonese, G.; Lazzarin, M.; Naletto, G.; La Forgia, F. (2019)
    We present experimental phase function and degree of linear polarization curves for seven samples of cometary dust analogues namely: ground pieces of Allende, DaG521, FRO95002, and FRO99040 meteorites, Mg-rich olivine and pyroxene, and a sample of organic tholins. The experimental curves have been obtained at the IAA Cosmic Dust Laboratory at a wavelength of 520 nm covering a phase angle range from 3 degrees to 175 degrees. We also provide values of the backscattering enhancement for our cometary analogue samples. The final goal of this work is to compare our experimental curves with observational data of comets and asteroids to better constrain the nature of cometary and asteroidal dust grains. All measured phase functions present the typical behaviour for mu m-sized cosmic dust grains. Direct comparison with data provided by the OSIRIS/Rosetta camera for comet 67P/Churyumov-Gerasimenko reveals significant differences and supports the idea of a coma dominated by big chunks, larger than one micrometer. The polarization curves are qualitatively similar to ground-based observations of comets and asteroids. The position of the inversion polarization angle seems to be dependent on the composition of the grains. We find opposite dependence of the maximum of the polarization curve for grains sizes in the Rayleigh-resonance and geometric optics domains, respectively.
  • Marwah, Megha; Magarkar, Aniket; Ray, Debes; Aswal, Vinod; Bunker, Alex; Nagarsenker, Mangal (2018)
    Glyceryl monostearate (GMS) is a single-tailed lipidic monoglyceride commonly used as a nontoxic food additive. In this study, we have investigated GMS, specifically its self-assembling properties and subsequent application in drug delivery. Results from in silico modeling, corroborated by complementary small-angle neutron scattering, demonstrated vesicle formation; associated phase transitions were analyzed using differential scanning calorimetry; dynamic light scattering revealed particle size alterations that occurred in the transition region. Spherical morphology of unilamellar vesicles was visualized using transmission electron microscopy imaging. Further, hydrophilic and hydrophobic drug loading in GMS vesicles and their amenability to surface modification for hepatic targeting have, in this study, been both predicted through molecular simulation study and demonstrated experimentally. The influence of hepatotropic ligands on the stability of drug-loaded GMS vesicles vis-a-vis cholesterol has also been investigated; the resulting GMS-based drug delivery vehicle, its properties enhanced through surface decoration, is envisaged to achieve targeted delivery of its payload to hepatocytes.
  • Xu, Guanglang (2020)
    Fast, accurate, and stable computation of the Clebsch-Gordan (C-G) coefficients is always desirable, for example, in light scattering simulations, the translation of the multipole fields, quantum physics and chemistry. Current recursive methods for computing the C-G coefficients are often unstable for large quantum numbers due to numerical overflow or underflow. In this paper, we present an improved method, called the sign-exponent recurrence, for the recursive computation of C-G coefficients. The result shows that the proposed method can significantly improve the stability of the computation without losing its efficiency, producing accurate values for the C-G coefficients even with very large quantum numbers. (C) 2020 The Author. Published by Elsevier Ltd.
  • Ballance, Simon; Lu, Yudong; Zobel, Hanne; Rieder, Anne; Knutsen, Svein Halvor; Dinu, Vlad T.; Christensen, Bjorn E.; Ulset, Ann-Sissel; Schmid, Marius; Maina, Ndegwa; Potthast, Antje; Schiehser, Sonja; Ellis, Peter R.; Harding, Stephen E. (2022)
    In an interlaboratory study we compare different methods to determine the weight-average molecular weight (Mw) and molecular weight distribution of six cereal beta-glucan isolates of nutritional importance. Size exclusion chromatography (SEC) with multi-angle light scattering (MALS), capillary viscometry, sedimentation velocity analytical ultracentrifugation and one asymmetric flow field-flow fractionation (AF4)-MALS method all yielded similar Mw values for mostly individual chains of dissolved beta-glucan molecules. SEC with post-column calcofluor detection underestimated the Mw of beta-glucan > 500 x 10(3) g/mol. The beta-glucan molecules analysed by these methods were primarily in a random coil conformation as evidenced from individual MarkHouwink-Kuhn-Sakurada (MHKS) scaling coefficients between 0.5 and 0.6 and Wales-Van Holde ratios between 1.4 and 1.7. In contrast, a second AF4-MALS method yielded much larger Mw values for these same samples indicating the presence and detection of beta-glucan aggregates. Storage of the six beta-glucan solutions in the dark at 4 C for 4 years revealed them to be stable. This suggests an absence of storage-induced irreversible aggregation phenomena or chain-scission. Shear forces in SEC and the viscometer capillary and hydrostatic pressure in analytical ultracentrifugation probably led to the reversable dissociation of beta-glucan aggregates into molecularly dissolved species. Thus, all these methods yield true weight-average molecular weight values not biased by the presence of aggregates as was the case in one of the AF4 based methods employed.
  • Friess, U.; Baltink, H. Klein; Beirle, S.; Clemer, K.; Hendrick, F.; Henzing, B.; Irie, H.; de Leeuw, G.; Li, A.; Moerman, M. M.; van Roozendael, M.; Shaiganfar, R.; Wagner, T.; Wang, Y.; Xie, P.; Yilmaz, S.; Zieger, P. (2016)
    A first direct intercomparison of aerosol vertical profiles from Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations, performed during the Cabauw Intercomparison Campaign of Nitrogen Dioxide measuring Instruments (CINDI) in summer 2009, is presented. Five out of 14 participants of the CINDI campaign reported aerosol extinction profiles and aerosol optical thickness (AOT) as deduced from observations of differential slant column densities of the oxygen collision complex (O-4) at different elevation angles. Aerosol extinction vertical profiles and AOT are compared to backscatter profiles from a ceilometer instrument and to sun photometer measurements, respectively. Furthermore, the near-surface aerosol extinction coefficient is compared to in situ measurements of a humidity-controlled nephelometer and dry aerosol absorption measurements. The participants of this intercomparison exercise use different approaches for the retrieval of aerosol information, including the retrieval of the full vertical profile using optimal estimation and a parametrised approach with a prescribed profile shape. Despite these large conceptual differences, and also differences in the wavelength of the observed O-4 absorption band, good agreement in terms of the vertical structure of aerosols within the boundary layer is achieved between the aerosol extinction profiles retrieved by the different groups and the backscatter profiles observed by the ceilometer instrument. AOTs from MAX-DOAS and sun photometer show a good correlation (R > 0.8), but all participants systematically underestimate the AOT. Substantial differences between the near-surface aerosol extinction from MAX-DOAS and from the humidified nephelometer remain largely unresolved.
  • Markkanen, Johannes; Agarwal, Jessica; Väisänen, Timo; Penttilä, Antti; Muinonen, Karri (2018)
    We show that the scattering phase functions of the coma and the nucleus of the comet 67P/Churyumov-Gerasimenko measured by the Rosetta/Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) instrument can be reproduced by a particle model involving clustered, densely packed submicrometer-sized grains composed of organic material and larger micrometer-sized silicate grains. The simulated and measured coma phase functions suggest that near the nucleus scattering is dominated by large particles, and the size distribution of dust particles varies with time and/or local coma environment. Further, we show that the measured nucleus phase function is consistent with the coma phase function by modeling a nucleus-sized object consisting of the same particles that explain the coma phase functions.
  • Zieger, P.; Aalto, P. P.; Aaltonen, V.; Aijala, M.; Backman, John; Hong, J.; Komppula, M.; Krejci, R.; Laborde, M.; Lampilahti, J.; de Leeuw, G.; Pfuller, A.; Rosati, B.; Tesche, M.; Tunved, P.; Väänänen, R.; Petaja, T. (2015)
    Ambient aerosol particles can take up water and thus change their optical properties depending on the hygroscopicity and the relative humidity (RH) of the surrounding air. Knowledge of the hygroscopicity effect is of crucial importance for radiative forcing calculations and is also needed for the comparison or validation of remote sensing or model results with in situ measurements. Specifically, particle light scattering depends on RH and can be described by the scattering enhancement factor f(RH), which is defined as the particle light scattering coefficient at defined RH divided by its dry value (RH <30-40 %). Here, we present results of an intensive field campaign carried out in summer 2013 at the SMEAR II station at Hyytiala, Finland. Ground-based and airborne measurements of aerosol optical, chemical and microphysical properties were conducted. The f(RH) measured at ground level by a humidified nephelometer is found to be generally lower (e.g. 1.63 +/- 0.22 at RH = 85% and lambda = 525 nm) than observed at other European sites. One reason is the high organic mass fraction of the aerosol encountered at Hyytiala to which f(RH) is clearly anti-correlated (R-2 approximate to 0.8). A simplified parametrization of f(RH) based on the measured chemical mass fraction can therefore be derived for this aerosol type. A trajectory analysis revealed that elevated values of f(RH) and the corresponding elevated inorganic mass fraction are partially caused by transported hygroscopic sea spray particles. An optical closure study shows the consistency of the ground-based in situ measurements. Our measurements allow to determine the ambient particle light extinction coefficient using the measured f(RH). By combining the ground-based measurements with intensive aircraft measurements of the particle number size distribution and ambient RH, columnar values of the particle extinction coefficient are determined and compared to columnar measurements of a co-located AERONET sun photometer. The water uptake is found to be of minor importance for the column-averaged properties due to the low particle hygroscopicity and the low RH during the daytime of the summer months. The in situ derived aerosol optical depths (AOD) clearly correlate with directly measured values of the sun photometer but are substantially lower compared to the directly measured values (factor of similar to 2-3). The comparison degrades for longer wavelengths. The disagreement between in situ derived and directly measured AOD is hypothesized to originate from losses of coarse and fine mode particles through dry deposition within the canopy and losses in the in situ sampling lines. In addition, elevated aerosol layers (above 3 km) from long-range transport were observed using an aerosol lidar at Kuopio, Finland, about 200 km east-northeast of Hyytiala. These elevated layers further explain parts of the disagreement.
  • Duong, TT; Isomaki, A; Paaver, U; Laidmae, I; Tonisoo, A; Yen, TTH; Kogermann, K; Raal, A; Heinamaki, J; Pham, TMH (2021)
    Berberine (BBR) is a poorly water-soluble quaternary isoquinoline alkaloid of plant origin with potential uses in the drug therapy of hypercholesterolemia. To tackle the limitations associated with the oral therapeutic use of BBR (such as a first-pass metabolism and poor absorption), BBR-loaded liposomes were fabricated by ethanol-injection and thin-film hydration methods. The size and size distribution, polydispersity index (PDI), solid-state properties, entrapment efficiency (EE) and in vitro drug release of liposomes were investigated. The BBR-loaded liposomes prepared by ethanol-injection and thin-film hydration methods presented an average liposome size ranging from 50 nm to 244 nm and from 111 nm to 449 nm, respectively. The PDI values for the liposomes were less than 0.3, suggesting a narrow size distribution. The EE of liposomes ranged from 56% to 92%. Poorly water-soluble BBR was found to accumulate in the bi-layered phospholipid membrane of the liposomes prepared by the thin-film hydration method. The BBR-loaded liposomes generated by both nanofabrication methods presented extended drug release behavior in vitro. In conclusion, both ethanol-injection and thin-film hydration nanofabrication methods are feasible for generating BBR-loaded oral liposomes with a uniform size, high EE and modified drug release behavior in vitro.
  • Ren, Hao; Qiu, Xing-Ping; Shi, Yan; Yang, Peng; Winnik, Francoise M. (2019)
    A series of azopyridine-terminated poly(N-isopropylacrylamide)s (PNIPAM) (C12-PN-AzPy) (similar to 5000 <M-w <20 000 g mol(-1), polydispersity index 1.25 or less) were prepared by reversible addition fragmentation chain-transfer polymerization of NIPAM in the presence of a chain-transfer agent that contains an AzPy group and an n-dodecyl chain. In cold water, the polymers form nanoparticles (5.9 nm <R-h <10.9 nm) that were characterized by light scattering (LS), H-1 NMR diffusion experiments, and high-resolution transmission electron microscopy. We monitored the pH-dependent photoisomerization of C12-PN-AzPy nanoparticles by steady-state and time-resolved UV-vis absorption spectroscopy. Azopyridine is known to undergo a very fast cis-to-trans thermal relaxation when the azopyridine nitrogen is quaternized or bound to a hydrogen bond donor. The cis-to-trans thermal relaxation of the AzPy chromophore in an acidic nanoparticle suspension is very fast with a half-life tau = 2.3 ms at pH 3.0. It slows down slightly for nanoparticles in neutral water (tau = 0.96 s, pH 7.0), and it is very slow for AzPy-PNIPAM particles in alkaline medium (tau > 3600 s, pH 10). The pH-dependent dynamics of the cis-to-trans dark relaxation, supported by Fourier transform infrared spectroscopy, H-1 NMR spectroscopy, and LS analysis, suggest that in acidic medium, the nanoparticles consist of a core of assembled C12 chains surrounded by a shell of hydrated PNIPAM chains with the AzPy(+) end groups preferentially located near the particle/water interface. In neutral medium, the shell surrounding the core contains AzPy groups H-bonded to the amide hydrogen of the PNIPAM chain repeat units. At pH 10.0, the amide hydrogen binds preferentially to the hydroxide anions. The AzPy groups reside preferentially in the vicinity of the C12 core of the nanoparticles. The morphology of the nanoparticles results from the competition between the segregation of the hydrophobic and hydrophilic components and weak attractive interactions, such as H-bonds between the AzPy groups and the amide hydrogen of the PNIPAM repeat units.
  • Asmi, Eija; Neitola, Kimmo; Teinila, Kimmo; Rodriguez, Edith; Virkkula, Aki; Backman, John; Bloss, Matthew; Jokela, Jesse; Lihavainen, Heikki; De Leeuw, Gerrit; Paatero, Jussi; Aaltonen, Veijo; Mei, Miguel; Gambarte, Gonzalo; Copes, Gustavo; Albertini, Marco; Perez Fogwill, German; Ferrara, Jonathan; Elena Barlasina, Maria; Sanchez, Ricardo (2018)
    Aerosol particle optical properties were measured continuously between years 2013-2015 at the Marambio station in the Antarctic Peninsula. Annual cycles of particle scattering and absorption were studied and explained using measured particle chemical composition and the analysis of air mass transport patterns. The particle scattering was found elevated during the winter but the absorption did not show any clear annual cycle. The aerosol single scattering albedo at lambda = 637 nm was on average 0.96 +/- 0.10, with a median of 0.99. Aerosol scattering Angstrom exponent increased during summer, indicating an increasing fraction of fine mode particles. The aerosol was mainly composed of sea salt, sulphate and crustal soil minerals, and most of the particle mass were in the coarse mode. Both the particle absorption and scattering were increased during high wind speeds. This was explained by the dominance of the primary marine sea-spray and wind-blown soil dust sources. In contrast, the back-trajectory analysis suggested that long-range transport has only a minor role as a source of absorbing aerosol at the peninsula.
  • Muinonen, Karri; Tyynela, Jani; Zubko, Evgenij; Videen, Gorden (2010)
  • Escobar-Cerezo, J.; Palmer, C.; Munoz, O.; Moreno, F.; Penttilä, A.; Muinonen, K. (2017)
    The effect of internal inhomogeneities and surface roughness on the scattering behavior of large cosmic dust particles is studied by comparing model simulations with laboratory measurements. The present work shows the results of an attempt to model a dust sample measured in the laboratory with simulations performed by a ray-optics model code. We consider this dust sample as a good analogue for interplanetary and interstellar dust as it shares its refractive index with known materials in these media. Several sensitivity tests have been performed for both structural cases (internal inclusions and surface roughness). Three different samples have been selected to mimic inclusion/coating inhomogeneities: two measured scattering matrices of hematite and white clay, and a simulated matrix for water ice. These three matrices are selected to cover a wide range of imaginary refractive indices. The selection of these materials also seeks to study astrophysical environments of interest such as Mars, where hematite and clays have been detected, and comets. Based on the results of the sensitivity tests shown in this work, we perform calculations for a size distribution of a silicate-type host particle model with inclusions and surface roughness to reproduce the experimental measurements of a dust sample. The model fits the measurements quite well, proving that surface roughness and internal structure play a role in the scattering pattern of irregular cosmic dust particles.
  • Liu, Weiwei; Atherton, Jon; Mõttus, Matti; Gastellu-Etchegorry, Jean-Philippe; Malenovský, Zbyněk; Raumonen, Pasi; Åkerblom, Markku; Mäkipää, Raisa; Porcar-Castell, Albert (2019)
    Solar-induced chlorophyll fluorescence (SIF) has been shown to be a suitable remote sensing proxy of photosynthesis at multiple scales. However, the relationship between fluorescence and photosynthesis observed at the leaf level cannot be directly applied to the interpretation of retrieved SIF due to the impact of canopy structure. We carried out a SIF modelling study for a heterogeneous forest canopy considering the effect of canopy structure in the Discrete Anisotropic Radiative Transfer (DART) model. A 3D forest simulation scene consisting of realistic trees and understory, including multi-scale clumping at branch and canopy level, was constructed from terrestrial laser scanning data using the combined model TreeQSM and FaNNI for woody structure and leaf insertion, respectively. Next, using empirical data and a realistic range of leaf-level biochemical and physiological parameters, we conducted a local sensitivity analysis to demonstrate the potential of the approach for assessing the impact of structural, biochemical and physiological factors on top of canopy (TOC) SIF. The analysis gave insight into the factors that drive the intensity and spectral properties of TOC SIF in heterogeneous boreal forest canopies. DART simulated red TOC fluorescence was found to be less affected by biochemical factors such as chlorophyll and dry matter contents or the senescent factor than far-red fluorescence. In contrast, canopy structural factors such as overstory leaf area index (LAI), leaf angle distribution and fractional cover had a substantial and comparable impact across all SIF wavelengths, with the exception of understory LAI that affected predominantly far-red fluorescence. Finally, variations in the fluorescence quantum efficiency (Fqe) of photosystem II affected all TOC SIF wavelengths. Our results also revealed that not only canopy structural factors but also understory fluorescence should be considered in the interpretation of tower, airborne and satellite SIF datasets, especially when acquired in the (near-) nadir viewing direction and for forests with open canopies. We suggest that the modelling strategy introduced in this study, coupled with the increasing availability of TLS and other 3D data sources, can be applied to resolve the interplay between physiological, biochemical and structural factors affecting SIF across ecosystems and independently of canopy complexity, paving the way for future SIF-based 3D photosynthesis models.
  • Venter, Marcell; Beukes, Johan Paul; van Zyl, Pieter Gideon; Vakkari, Ville; Virkkula, Aki; Josipovic, Miroslav; Kulmala, Markku; Laakso, Lauri (2020)
    Atmospheric aerosols have a significant effect on earth's radiative budget, particularly on regional scales. This paper presents a similar to 6 year, in situ, ground level aerosol scattering and absorption dataset, measured at a background site strategically positioned to enable differentiation of the effect of anthropogenic, population density and open biomass burning activities on a regional scale. Relatively well-defined seasonal and diurnal patterns were observed for all the aerosol optical properties, i.e. scattering coefficient (sigma(SP)), absorption coefficient (sigma(AP)), single scattering albedo (omega(0)) and Angstrom exponent of scattering (sigma(SP)). These patterns were explained by considering southern African specific sources and metrological conditions. Using a receptor modelling method (auto-generated source maps) it was found that air masses that had higher sigma(SP), sigma(AP) and omega(0), and lower alpha(SP), if compared with the relatively clean background, passed over source regions with significant industrial or other anthropogenic activities, higher population density, re-circulation of polluted air masses and higher open biomass burning frequency. To quantify differences, four source regions were defined, i.e. Karoo, Kalahari, anti-cyclonic recirculation pattern and the industrial hub of South Africa. Air masses that had passed over the Karoo source region represented the cleanest regional background conditions, while air masses that had passed either over the industrial hub and/or the anti-cyclonic recirculation pattern represented the most significant anthropogenically impacted, as indicated by the aerosol optical properties. The omega(0) medians of air masses that had passed over the Karoo (0.80-0.86) were 9, 12 and 7% lower than in air masses that had passed over source regions with the highest omega(0) median, in the warmest/wettest, coldest, and driest, peak open biomass burning periods, respectively.
  • Kondo, Masaaki; Takahashi, Rintaro; Qiu, Xing-Ping; Winnik, Francoise M.; Terao, Ken; Sato, Takahiro (2017)
    Aqueous solutions of the doubly thermosensitive block copolymer poly(2-isopropyl-2-oxazoline)-b-poly(2-ethyl-2-oxazoline) heated to 50 degrees C underwent a macroscopic liquid/liquid phase separation. The small-angle X-ray scattering intensity recorded from the concentrated phase settled on the bottom of a sample indicated that this phase was in the disordered state without any microphase separation, although the block copolymer was amphiphilic in water at 50 degrees C. It was also confirmed that the contribution to the scattering intensities of individual copolymer chains and their aggregates existing in the coexisting concentrated phase was very small, compared with the total scattering intensity of the phase-separated solution, when the concentrated phase was suspended in the form of colloidal droplets in the lean phase.
  • Fowler, Michael; Duhamel, Jean; Qiu, Xing Ping; Korchagina, Evgeniya; Winnik, Francoise M. (2018)
    Aqueous solutions of a series of monodisperse poly(N-isopropylacrylamide)s end-labeled with n-butyl-1-pyrene at one or both chain ends (Py-n-PNIPAMs with n=1 or 2) were studied by turbidimetry, light scattering, and fluorescence. For a given polymer concentration and heating rate, the cloud point (T-c) of an aqueous Py-n-PNIPAM solution, determined by turbidimetry, was found to increase with the number-average molecular weight (M-n) of the polymer. The steady-state fluorescence spectra and time-resolved fluorescence decays of Py-n-PNIPAM aqueous solutions were analyzed and all parameters retrieved from these analyses were found to be affected as the solution temperature passed through T-c, the solution cloud point, and T-m, the temperature where dehydration of PNIPAM occurred. The trends obtained by fluorescence to characterize the aqueous Py-n-PNIPAM solutions as a function of temperature were found to be consistent with the model proposed for telechelic PNIPAM by Koga et al. in 2006. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 308-318
  • Ren, Hao; Qiu, Xing-Ping; Shi, Yan; Yang, Peng; Winnik, Francoise M. (2020)
    High-sensitivity differential scanning calorimetry (HS-DSC) thermograms of aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions present a sharp unimodal endotherm that signals the heat-induced dehydration/collapse of the PNIPAM chain. Similarly, alpha,omega-di-n-octadecyl-PNIPAM (C18-PN-C18) aqueous solutions exhibit a unimodal endotherm. In contrast, aqueous solutions of alpha,omega-hydrophobically modified PNIPAMs with polycyclic terminal groups, such as pyrenylbutyl (Py-PN-Py), adamantylethyl (Ad-PN-Ad), and azopyridine- (C12-PN-AzPy) moieties, exhibit bimodal thermograms. The origin of the two transitions was probed using microcalorimetry measurements, turbidity tests, variable temperature H-1 NMR (VT-NMR) spectroscopy, and 2-dimensional NOESY experiments with solutions of polymers of molar mass (M-n) from 5 to 20 kDa and polymer concentrations of 0.1 to 3.0 mg/mL. The analysis outcome led us to conclude that the difference of the thermograms reflects the distinct self-assembly structures of the polymers. C18-PN-C18 assembles in water in the form of flower micelles held together by a core of tightly packed n-C18 chains. In contrast, polymers end-tagged with azopyridine, pyrenylbutyl, or adamantylethyl form a loose core that allows chain ends to escape from the micelles, to reinsert in them, or to dangle in surrounding water. The predominant low temperature (T-1) endotherm, which is insensitive to polymer concentration, corresponds to the dehydration/collapse of PNIPAM chains within the micelles, while the higher temperature (T-2) endotherm is attributed to the dehydration of dangling chains and intermicellar bridges. This study of the two phase transitions of telechelic PNIPAM homopolymer highlights the rich variety of morphologies attainable via responsive hydrophobically modified aqueous polymers and may open the way to a variety of practical applications.