Inkjet Aerosol Generator as Monodisperse Particle Number Standard

The AIST-inkjet aerosol generator (IAG) can generate highly monodisperse solid or liquid aerosol particles in the particle diameter range from 0.3 to 20 μm at precisely known particle generation rates. The device has been developed for evaluating the counting efficiencies of optical and condensation particle counters. Particle generation efficiency of the IAG is defined as the number of aerosol particles generated by one voltage pulse sent to an inkjet head. The 95% confidence interval of the efficiency were 0.998 ± 0.006 within the 0.4 to 10 μm particle diameter range. The efficiencies remained close to unity when the droplet generation rates were within 20–500 s^?1 and 100–900 s^?1 using ultrapure-water and isopropyl alcohol (IPA) as the solvent of the inkjet solution, respectively. The operating aerosol flowrate range of the IAG is currently 0.5 and 1.0 L/min. The coefficients of variations (C.V.) of the size distributions were 2 to 3% indicating the generated particles were highly monodisperse. The generated particle sizes were defined as the volume equivalent diameter, D_ve. The uncertainty analysis on the factors affecting D_ve indicated that 95% confidence interval of the D_ve is expected to be ±5%. The uncertainty of D_ve was entirely caused by the uncertainty of the average mass of a droplet. The reproducibility of particle sizes within 0.5 to 10 μm was evaluated using an aerodynamic particle sizer. The C.V. of the measured particle sizes were less than 6% and 4% when NaCl particles and ionic liquid droplets were generated, respectively.

Copyright 2014 American Association for Aerosol Research     

Improved technique for measuring the size distribution of black carbon particles in liquid water

We developed an improved technique for measuring the size distribution of black carbon (BC) particles suspended in liquid water to facilitate quantitative studies of the wet deposition of BC. The measurement system, which consists of a nebulizer and a single-particle soot photometer, incorporates two improvements into the system that we developed earlier. First, we extended the upper limit of the detectable BC size from 0.9 μm to about 4.0 μm by modifying the photo-detector for measuring the laser-induced incandescence signal. Second, we introduced a pneumatic nebulizer (Marin-5) with a high extraction efficiency (～50.0%) that was independent of particle diameter up to 2.0 μm. For BC mass concentrations less than 70 μg L^?1, we experimentally showed that the diameters of BC particles did not appreciably change during the Marin-5 extraction process, consistent with theoretical calculations. Finally, we demonstrated by laboratory experiments that the size distributions of ambient BC particles changed little during their growth into cloud droplets under supersaturation of water vapor. Using our improved system, we measured the size distributions of BC particles simultaneously in air and rainwater in Tokyo during summer 2014. We observed that the size distributions of BC particles in rainwater shifted to larger sizes compared with those observed in ambient air, indicating that larger BC particles in air were removed more efficiently by precipitation.

Copyright © 2016 American Association for Aerosol Research     

First measurements of the number size distribution of 1–2 nm aerosol particles released from manufacturing processes in a cleanroom environment

This study was conducted to observe a potential formation and/or release of aerosol particles related to manufacturing processes inside a cleanroom. We introduce a novel technique to monitor airborne sub 2 nm particles in the cleanroom and present results from a measurement campaign during which the total particle number concentration (>1 nm and >7 nm) and the size resolved concentration in the 1 to 2 nm size range were measured. Measurements were carried out in locations where atomic layer deposition (ALD), sputtering, and lithography processes were conducted, with a wide variety of starting materials. During our campaign in the clean room, we observed several time periods when the particle number concentration was 10⁵ cm^?3 in the sub 2 nm size range and 10⁴ cm^?3 in the size class larger than 7 nm in one of the sampling locations. The highest concentrations were related to the maintenance processes of the manufacturing machines, which were conducted regularly in that specific location. Our measurements show that around 500 cm^?3 sub 2 nm particles or clusters were in practice always present in this specific cleanroom, while the concentration of particles larger than 2 nm was less than 2 cm^?3. During active processes, the concentrations of sub 2 nm particles could rise to over 10⁵ cm^?3 due to an active new particle formation. The new particle formation was most likely induced by a combination of the supersaturated vapors, released from the machines, and the very low existing condensation sink, leading to pretty high formation rates J_{1.4 nm} = (9 ± 4) cm^?3 s^?1 and growth rates of particles (GR_{1.1–1.3 nm} = (6 ± 3) nm/h and GR_{1.3–1.8 nm} = (14 ± 3) nm/h).

Copyright © 2017 American Association for Aerosol Research     

New Particle Formation and Growth in an Isoprene-Dominated Ozark Forest: From Sub-5 nm to CCN-Active Sizes

Particle Investigations at a Northern Ozarks Tower: NOx, Oxidant, Isoprene Research (PINOT NOIR) were conducted in a Missouri forest dominated by isoprene emissions from May to October 2012. This study presents results of new particle formation (NPF) and the growth of new particles to cloud condensation nuclei (CCN)-active sizes (～100 nm) observed during this field campaign. The measured sub-5 nm particles were up to ～20,000 cm^?3 during a typical NPF event. Nucleation rates J₁ were relatively high (11.0 ± 10.6 cm^?3 s^?1), and one order of magnitude higher than formation rates of 5 nm particles (J₅). Sub-5 nm particle formation events were observed during 64% of measurement days, with a high preference in biogenic volatile organic compounds (BVOCs)- and SO₂-poor northwesterly (90%) air masses than in BVOCs-rich southerly air masses (13%). About 80% of sub-5 nm particle events led to the further growth. While high temperatures and high aerosol loadings in the southerly air masses were not favorable for nucleation, high BVOCs in the southerly air masses facilitated the growth of new particles to CCN-active sizes. In overall, 0.4–9.4% of the sub-5 nm particles grew to CCN-active sizes within each single NPF event. During a regional NPF event period that took place consecutively over several days, concentrations of CCN size particles increased by a factor of 4.7 in average. This enhanced production of CCN particles from new particles was commonly observed during all 13 regional NPF events during the campaign period.

Copyright 2014 American Association for Aerosol Research     

Effect of mechanical and air-particle cleansing protocols of provisional cement on immediate dentin sealing layer and subsequent adhesion of resin composite cement

Immediate dentin sealing (IDS) could avoid contamination of dentin from impression material and provisional cement but prior to final cementation of indirect restorations, removal of the provisional cement may damage the IDS. The objectives of this study were to investigate the effect of mechanical and air-particle cleansing protocols of provisional cement on IDS layer and subsequent adhesion of resin composite cement. The cuspal dentin surfaces of human third molars (N = 21, n_quadrant = 84) were exposed by a low-speed diamond saw under water cooling and conditioned with an adhesive system based on the three-step etch and rinse technique (OptiBond FL). Provisional cement (Freegenol) was applied on each specimen. They were then randomly divided into six subgroups where the provisional cement was removed either by (1) air-borne particle abrasion with 50-μm Al₂O₃ particles at 2 bar (AL2), (2) air-borne particle abrasion with 50-μm Al₂O₃ particles at 3.5 bar (AL3.5), (3) air-borne particle abrasion with 30-μm SiO₂ particles at 2 bar (SL2), (4) air-borne particle abrasion with 30-μm SiO₂ particles at 3.5 bar (SL3.5), (5) prophylaxy paste (Cleanic) (PP) or (6) pumice-water slurry (PW) at 1500 rpm for 15 s. The dentin surface on each tooth was assigned to four quadrants and each quadrant received the cleansing methods in a clockwise sequence. The non-contaminated and non-cleansed teeth acted as the control (C). Two separate teeth, contaminated and cleansed according to six cleansing protocols, were allocated for scanning electron microscopy (SEM) analysis (×2000). The dentin surfaces in each quadrant received resin composite luting cement (Variolink II, Ivoclar Vivadent) incrementally in a polyethylene mould (diameter: 1 mm²; height: 4 mm) and photopolymerized. The specimens were stored in distilled water for 24 h at 37 °C until the testing procedures and then shear force was applied to the adhesive interface until failure occurred in a universal testing machine (0.5 mm/min). Microshear bond (μSBS) was calculated by dividing the maximum load (N) by the bonding surface area of the resin cement. Failure types were analysed using optical microscope and SEM. Data (MPa) were analysed using one-way ANOVA (α = 0.05). Two-parameter Weibull distribution values including the Weibull modulus, scale (m) and shape (₀), values were calculated. Mean μSBS results (MPa) showed a significant difference between the experimental groups (p = 0.011) and were in a descending order as follows: C (8 ± 2.3)^a < AL2 (6.7 ± 2.4)^b < PP (6.9 ± 2)^b < PW (6.5 ± 2.1)^b < AL3.5 (5.8 ± 1.1)^b < SL2 (5.3 ± 1)^b < SL3.5 (5.2 ± 1)^b. Failure types were predominantly mixed failure type between the dentin and the adhesive resin which is a combination of adhesive and cohesive failures in the adhesive resin. Cohesive failure in the dentin was not observed in any of the groups. Weibull distribution presented lower shape (₀) for C (3.9), AL2 (3.2), PP (3.5) and PW (3.6). SEM analysis showed rough surfaces especially in the air-abraded groups whereas mechanical cleansing methods presented smoother surfaces and partially covered by particle remnants all of which occluded the dentin tubuli.     

Could readily silanized silica particles substitute silica coating and silanization in conditioning zirconium dioxide for resin adhesion?

This study investigated the effect of particle types with different morphology and surface properties on the wettability and adhesion of resin cement to zirconia. Zirconia specimens (5 × 5 × 1 mm³) were wet polished. Specimens were randomly assigned to one of the following protocols (N = 36, n = 9 per group): Group CON: Control, no surface conditioning; Group AL: Chairside air-abrasion with aluminium trioxide (50 μm Al₂O₃) + silane; Group SIL: Chairside air-abrasion with alumina particles coated with silica (SIL) (30 μm SiO2, SilJet) + air-drying + silane; Group 4: Chairside air-abrasion with readily silanized silica particles (SILP) (30 μm SiO_2, SilJet Plus). Adhesive resin was applied and resin cement (Variolink II, Ivoclar) was bonded using polyethylene moulds and photo-polymerized and aged (thermocycling, 6.000 cycles, 5–55 °C). Shear bond test was performed using Universal Testing Machine (1 mm/min). Pretest failures were considered 0 MPa. Contact angle measurements were performed (n = 2/group, sessile drop with water). Data (MPa) were analyzed (ANOVA, Tukey’s (α = 0.05). Two-parameter Weibull distribution values including the Weibull modulus, scale (m) and shape (0), values were calculated. Contact angle measurements were in descending order as follows: SIL (74°)^c < CON (60°)^c < AL (51°)^b < SILP (40°)^a. Bond strength (MPa) with SIL (17.2 ± 4)^a and SILP (17.3 ± 1.9)^a demonstrated no significant difference (p > 0.05), being higher than AL (8.4 ± 1.5)^b and CON (0)^c (p < 0.05). Failure types were exclusively adhesive in all groups. Weibull distribution presented the highest shape (0) for SILP (10.8). SILP presented better wettability than AL. SILP provided similar bond strength to SIL. Readily silanized silica particles may substitute for conventional silica coating and silanization.     

Thermophysical properties of laboratory-prepared corn/wheat dried distillers grains and dried distillers solubles dehydrated with superheated steam and hot air

The objective of this study was to dry–wet distillers grains and centrifuged solubles and to examine the effect of two different drying media, superheated steam and hot air, at different drying temperatures (110, 130, and 160°C), moisture contents (5–30% wb), and percentages of solubles’ presence (0 or 100%) on some thermophysical properties of laboratory-prepared corn/wheat dried distillers co-products, including geometric mean diameter (d_g), particle density (ρ_p), bulk density (ρ_b), bulk porosity (?_b), specific heat (C), effective thermal diffusivity (α_eff), and bulk thermal conductivity (λ_b). The values of d_g of corn/wheat dried distillers co-products ranged from 0.358 ± 0.001 to 0.449 ± 0.001 mm. Experimental values of ρ_p, ρ_b, and ?_b varied from 1171 ± 6 to 1269 ± 3 kg m^?3, from 359 ± 7 to 605 ± 5 kg m^?3, and from 0.54 ± 0.01 to 0.71 ± 0.01 kg m^?3, respectively. The values of α_eff were between 0.58 × 10^?7 and 0.93 × 10^?7 m² s^?1. The calculated values of C ranged from 1887 ± 11 to 2599 ± 19 J kg^?1 K^?1, and the values of λ_b of corn/wheat dried distillers co-products ranged from 0.06 ± 0.01 to 0.09 ± 0.01 W m^?1 K^?1. Multiple linear regression prediction models were developed to predict the changes in d_g, ρ_p, ρ_b, ?_b, C, α_eff, and λ_b of laboratory-prepared corn/wheat dried distillers co-products with different operational factors.     

Effects of different particle deposition parameters on adhesion of resin cement to zirconium dioxide and phase transformation

This study evaluated the effect of air-abrasion parameters such as particle size, distance, and time on adhesion of resin cement to zirconium dioxide (Y-TZP) and t→m phase transformation. Y-TZP blocks (N = 80) (In-Ceram YZ, Vita) (4 mm^3?×?4 mm^3?×?3 mm³) were assigned into eight groups (n = 10): air-abrasion with 30 μm (CoJet Sand, S30) and 110 μm (Rocatec-Plus, S110) silica-coated alumina particles, applied for either for 10–20 s (T = time), from a distance of 10–20 mm (D = distance), composing the following groups: S₃₀T₁₀D₁₀, S₃₀T₁₀D₂₀, S₃₀T₂₀D₁₀, S₃₀T₂₀D₂₀, S₁₁₀T₁₀D₁₀, S₁₁₀T₁₀D₂₀, S₁₁₀T₂₀D₁₀, and S₁₁₀T₂₀D₂₀. Resin composite (RelyX ARC) was bonded to Y-TZP blocks in polyethylene molds. The specimens were aged (10,000 thermal cycles and water storage for 90 days) prior to shear bond test. Failure types were analyzed under stereomicroscope and SEM, and phase transformation was calculated. Data (MPa) were analyzed using 3-way ANOVA and Tukey’s tests. Air-abrasion with 110 μm silica particles (10.96) presented significantly higher bond strength (p = 0.0149) compared to 30 μm (8.96). Time (p = 0.403) and distance (p = 0.179) parameters did not affect the results significantly. Air-abrasion with 110 μm particles (12.3) promoted higher bond strength than that of 30 μm (6.4) when applied for 10 s from a distance of 10 mm (Tukey’s). Failure types were predominantly adhesive. Phase transformation ranged between 30.3 and 35.9% for 30 μm particles and 23.8–43.7% for 110 μm particles. While the size of silica-coated alumina particles were more relevant parameter for resin cement adhesion to Y-TZP, time (up to 20 s) and distance (up to 20 mm) appear to be less pertinent.     

Study of marine bacteria adhesion on sea-immersed 304 and 316 stainless steels: experimental and theoretical investigations

In this study, we investigated the potential adhesion of marine bacteria isolated from seawater in the port of Chmaâla, Morocco, to sea-immersed 304 and 316 stainless steels using thermodynamic approach and the Environmental Scanning Electron Microscopy (ESEM). Furthermore, the physicochemical properties including hydrophobicity and electron donor / electron acceptor (Lewis acid-base) of bacterial isolates and both substrates were evaluated using the contact angle measurements. The molecular identification indicated that the isolated strains were Bacillus thuringiensis and Bacillus amyloliquefascience. Results also showed that both bacterial strains’s cells have a hydrophilic character with Δ_Giwi values of 29.30 and 24.12 mJ m^?2 respectively for Bacillus thuringiensis and Bacillus amyloliquefascience, and are strong electron donating (γ^?) and weakly electron accepting (γ⁺). For substrates surfaces, we found that both sea-immersed stainless steels types were hydrophilic and present strong electron-donor character (γ^? = 49 ± 0.2 mJ m^?2 for 304 and γ^? = 55.07 ± 0.02 mJ m^?2 for 316) and weak electron-acceptor character (γ⁺ = 5.4 ± 0.1 mJ m^?2 for 304 and γ⁺ = 8.3 ± 0.06 mJ m^?2 for 316). The theoretical prediction showed that both tested strains, B. thuringiensis and B. amyloliquefascience, exhibited positive values of ΔG^Total vis-à-vis the two sea-immersed stainless steels types which indicates unfavorable adhesion while the ESEM electro-micrographs show that both strains were able to adhere to both strainless steels surfaces.     

Adhesion of resin composite to enamel and dentin: a methodological assessment

This study compared the impact of four test methods on adhesion of resin composite to enamel and dentin. Human molars (N = 54) were randomly assigned to test the adhesion of resin composite material (Quadrant Universal LC) using one of the following test methods: (a) macroshear test (SBT; n = 16), (b) macrotensile test (TBT; n = 16), (c) microshear test (μSBT; n = 16) and (d) microtensile test (μTBT; n = 6). In a randomized manner, buccal or lingual surfaces of each tooth, were assigned as enamel or dentin substrates. Enamel and dentin surfaces were conditioned using an etch-and-rinse adhesive system (Syntac Classic). After storage (24 h, 37 °C), bond tests were conducted in a Universal Testing Machine (1 mm/min) and failure types were analyzed. Data were analyzed using Univariate and Tukey`s, Bonneferroni tests (α = 0.05). Two-parameter Weibull modulus, scale (m) and shape (0) were calculated. Test method (p < 0.001) and substrate type (p < 0.001) significantly affected the results. When testing adhesion of resin composite to enamel, SBT (25.9 ± 5.7)^a, TBT (17.3 ± 5.1)^a,c and μSBT (27.2 ± 6.6)^a,d test methods showed significantly higher mean bond values compared to μTBT (10.1 ± 4.4)^b (p < 0.05). Adhesion of resin composite to dentin did not show significant difference depending on the test method (12 ± 5.7–20.4 ± 4.8; p > 0.05). Only with SBT, significant difference was observed for bond values between enamel (25.9 ± 5.7) and dentin (12 ± 5.7; p < 0.05). Weibull distribution presented the highest shape values for enamel-μSBT (29.7) and dentin-μSBT (22.2) among substrate-test combinations. Regardless of the test method, cohesive failures in substrate were more frequent in enamel (19.1%) than in dentin (9.8%).     

Indoor Sources of Ultrafine and Accumulation Mode Particles: Size Distributions,Size-Resolved Concentrations,and Source Strengths

Ultrafine (< 100 nm) and accumulation mode (0.1–1 μm) particles were monitored in an occupied suburban house at 5-minute intervals for 37 consecutive months between November 21, 1997 and December 31, 2000. Number concentrations for 126 particle sizes from 9.8–947 nm were measured in 259,176 scans. Of 282 separate activities, 18 were chosen for detailed analysis. These included cooking with a gas stove, toasting with electric toasters and toaster ovens, burning candles and incense, and using a gas-powered clothes dryer. Activities leading to increased particle concentrations occurred 17.5% of the time, and accounted for more than half the total concentration of ultrafines and about a quarter of the total accumulation mode particles. The average duration of elevated particle concentrations ranged from 20 minutes to 3 hours. Combustion of natural gas (boiling water, gas clothes dryer) showed number peaks near 10 nm, while the electric toaster and toaster oven had peaks close to 30 nm. More complex cooking (burners plus gas oven) produced peaks in the 35–50 nm range. Burning candles and incense resulted in peaks in the 60-nm range. Finally, outdoor sources peaked at nearly 70 nm, indicating the influence of aging in shifting modes to higher diameters. The highest mean number concentrations were due to complex cooking, producing average number concentrations of 35,000–50,000 cm^{? 3}, compared to 12,000 cm^?3 outdoors and less than 3500 cm^?3 indoors when no sources were observed. A strong contribution of the vented gas-powered clothes dryer was also noted (30,000 cm^{? 3}). Volume concentrations due to these combustion events ranged from < 1 (μm/cm)³ to nearly 100 (μm/cm)³. Source strengths were calculated for three common cooking types (boiling water, deep-frying, oven baking, and broiling) and ranged from 5 × 10 ¹² to 4 × 10 ¹³ particles per cooking event. The detailed concentration and size distribution data collected here may be useful for models of indoor air particle concentrations due to indoor sources and infiltration.     

Chemometric analysis of selective polyphenolic groups in Asparagus racemosus (Shatavar) root extracts by traditional and supercritical fluid (CO2) based extractions

ABSTRACT

Asparagus racemosus root extracts were prepared by supercritical fluid (CO₂), soxhlet, and maceration-based methods also with various pretreatments. Thereafter, these root extracts were analyzed by High-Performance Liquid Chromatography, along with the chemometric study of the disparate phenolic groups. Among these, supercritical fluid (CO₂) based extract has a larger number of polar compounds and the antioxidant activity (98.54 ± 0.22 µM Trolox equivalent mg^?1). It also has the best cell viability (94.37 ± 1.12%) and insulin release (0.82 ± 1.12 ng mL^?1) on β-pancreatic RINm-5F cells whereas, the best extractive yield (75.80 ± 3.44% w/w) was observed for pretreated aqueous soxhlet-based extract.     

A study of compressive strength between zirconia framework and veneering ceramic as a function of thermal expansion coefficient using Shell–Nielsen test method

This study investigated the adhesion between zirconia framework and four veneering ceramic (VC) materials with varying coefficients of thermal expansions (CTE). Zirconia rods (N?=?40) (ICE Zirkon) (diameter: 4 mm, height: 20 mm) were milled and sintered. After firing, the zirconia rods were air-abraded and cleaned. They were randomly assigned to receive four VCs (n?=?10/group), namely (a) Vita VM9 (VZ; 9–9.2?×?10^?6? K^?1), (b) Cerabien ZR (CZ; 9.1?×?10^?6 K^?1), (c) Matchmaker ZR (MM; 9.4?×?10^?6?K^?1), and (d) Ice Zirconia Ceramic (IZ; 9.6?×?10^?6?K^?1). The VCs were then fired onto zirconia rods (height: 2 mm, thickness: 2 mm) circumferentially and were thermocycled for 6000 times (5/55 °C, dwell time: 30?s). Specimens were loaded from the top of the zirconia rods (0.5 mm/min) in a universal testing machine until debonding. Shell–Nielsen bond strength values were calculated (MPa). Failure types were evaluated under SEM. The data were statistically analyzed (one-way ANOVA, Tukey’s; α?=?0.05). Weibull distribution values including the Weibull modulus (m) (0.05) was calculated. The highest mean bond strength (MPa) was obtained for CZ (42.08?±?4.08), followed by VZ (41.77?±?4.92), MM (40.7?±?3.64), and IZ (40.05?±?5.78). While mean bond strength for VZ, MM, and IZ were not significantly different (p?>?0.05), CZ was significantly higher than that of IZ (p?<?0.05). The lowest shape value was for VZ (m?=?16.94) and the highest for MM (m?=?20.16). Mainly, adhesive failures followed by mixed failures were observed. VCs with a greater mismatch of CTE with the zirconia framework exhibited similar Shell–Nielsen bond strength to those with fewer mismatches. CTE mismatch did not affect the results of CZ (9.1?×?10^?6 K^?1) and IZ (9.6?×?10^?6 K^?1).     

Effective Density and Volatility of Particles Emitted from Gasoline Direct Injection Vehicles and Implications for Particle Mass Measurement

The effective density and volatility of particulate emissions from five gasoline direct injection (GDI) passenger vehicles were measured using a tandem differential mobility analyzer (DMA) and centrifugal particle mass analyzer (CPMA) system. The measurements were conducted on a chassis dynamometer at three steady-state operating conditions. A thermodenuder was employed to find the volatility and mixing state of the particles as well as the effective density of nascent and non-volatile particles (defined as particle phase remaining after denuding at 200°C). The mass–mobility exponent ranged between 2.4 and 2.7 for nascent (or undenuded) particles and between 2.5 and 2.7 for non-volatile particles; higher than typical diesel soot. The effective density function was 4278d_m^?0.438 ± 76.3 kg/m³ (for mobility diameter, d_m, in nm) for nascent particles and 3215d_m^?0.395 ± 37.9 kg/m³ for non-volatile particles. The effective density functions of the non-volatile particles were fairly similar for the conditions studied. The uncertainty in using the effective density and mixing state data to determine the mass concentration of the aerosol by integrating mobility size distributions was examined. The uncertainty in mass concentration is minimized when only the non-volatile component is measured. However, the uncertainty in the mass concentration increases substantially if nascent particles are measured due to uncertainties in the particle mixing state and their associated effective densities. Furthermore, transient vehicle operation (cold-starts, accelerations, and decelerations) would likely change the mixing state of the exhaust particles suggesting it is difficult to accurately measure the mass concentration of undenuded GDI exhaust particulate using integrated size distribution methods.

Copyright 2015 American Association for Aerosol Research     

Characterizations of Cloud Droplet Shatter Artifacts in Two Airborne Aerosol Inlets

Aircraft-based aerosol sampling in clouds is complicated by the generation of shatter artifact particles from aerodynamic or impaction breakup of cloud droplets and ice particles in and around the aerosol inlet. Aerodynamic breakup occurs when the Weber number of a droplet, which primarily depends on the droplet size and the magnitude of the relative motion of the droplet and the local air mass, exceeds a critical value. Impaction breakup of a droplet occurs when the droplet's impaction breakup parameter, K, which is a combination of Weber and Ohnesorge numbers, exceeds a critical value. Considering these two mechanisms, the critical breakup diameters are estimated for two aerosol inlets of different designs—a conventional forward-facing solid diffuser inlet (SDI) and a cross-flow sampling sub-micron aerosol inlet (SMAI). From numerical simulations, it is determined that cloud droplets of all sizes will experience impaction breakup in SDI, while only droplets larger than ～16 μm will experience impaction breakup in SMAI. The relatively better in-cloud sampling performance of SMAI is because of its cone design that slows the flow just upstream of the sample tube. The slowing upstream flow, however, causes aerodynamic breakup of drops larger than ～100 μm. The critical breakup diameters determined from analysis of field data largely validate numerical predictions. The cross-flow sampling design of SMAI is seen to ensure that shatter artifacts in the inlet are minimal even when there are a significant number of particles larger that the critical breakup size. The study results, thus, suggest that the SMAI design presents an effective approach to sample interstitial particles from aircraft.

© 2013 American Association for Aerosol Research     

Construction and Performance Characteristics of Modified Screen Printed and Modified Carbon Paste Sensors for Selective Determination of Cu(II) Ion in Different Polluted Water Samples

Four new ion-selective electrodes (ISEs), based on N,N′-bis(salicylaldehyde)-p-phenylene diamine (SPD) as ionophore, are constructed for the determination of copper(II) ion. The modified carbon paste (MCPEs; electrodes I and II) and modified screen-printed sensors (MSPEs; electrodes III and IV) exhibit good potentiometric response for Cu(II) over a wide concentration range of 1.0 × 10^?6 – 1.0 × 10^?2 mol L^?1 for electrodes (I and II) and 4.8 × 10^?7–1.0 × 10^?2 mol L^?1 for electrodes (III and IV) with a detection limit of 1.0 × 10^?6 mol L^?1 for electrodes (I and II) and 4.8 × 10^?7 mol L^?1 for electrodes (III and IV), respectively. The slopes of the calibration graphs are 29.62 ± 0.9 and 30.12 ± 0.7 mV decade^?1 for electrode (I) (tricresylphosphate (TCP) plasticizer) and electrode (II) (o-nitrophenyloctylether o-NPOE plasticizer), respectively. Also, the MSPEs showed good potentiometric slopes of 29.91 ± 0.5 and 30.70 ± 0.3 mV decade^?1 for electrode (III) (TCP plasticizer) and electrode (IV) (o-NPOE plasticizer), respectively. The electrodes showed stable and reproducible potentials over a period of 60, 88, 120, and 145 days at the pH range from 3 to 7 for electrodes (II), (III), and (IV) and pH range from 3 to 6 for electrode (I). This method was successfully applied for potentiometric determination of Cu(II) in tap water, river, and formation water samples in addition to pharmaceutical preparation. The results obtained agree with those obtained with the atomic absorption spectrometry (AAS).     

Square wave voltammetric determination of methiocarb insecticide based on multiwall carbon nanotube paste electrode

Cyclic voltammogram of methiocarb in 0.1 M H₂SO₄ exhibited an irreversible anodic peak at about +1285 mV versus Ag/AgCl. Electro-oxidation and determination of methiocarb in spiked soil, river water and agrochemical formulation were realized on a newly prepared carbon-nanotube paste electrode by applying square wave voltammetry (SWV). The dE _p /dpH value indicated that the oxidation mechanism involved the coupling of H⁺ with the oxidation process. The peak signals were linearly related to methiocarb concentration in the range of 1.5–59.1 mgL^?1 with a detection limit of 0.45 mgL^?1. The accuracy and selectivity of the proposed method were shown by calculating the recoveries of methiocarb from soil, river water and pesticide formulation Mesurol^®. The calculated percent recoveries for soil and river water samples spiked with 30.0 μg g^?1 and 40.0 μg mL^?1 levels were 99.3 ± 1.2 and 98.5 ± 0.3 at 95 % confidence limit, respectively.     

Analysis of structural,morphological alterations,wettability characteristics and adhesion to enamel after various surface conditioning methods

Minimal invasive dental reconstructions and orthodontic appliances are bonded to enamel without removing the enamel with rotating instruments but the top layer of enamel may be partially aprismatic and impair adhesion. The objectives of this study were to investigate the effect of mechanical surface conditioning methods for removing enamel on its structural, morphological alterations, wettability characteristics, and adhesion of resin-based cement to the conditioned surfaces. Maxillary human incisors (N = 40, n_quadrant = 160) were obtained and coronal sections were embedded in acrylic with their labial surfaces exposed. The teeth were randomly divided into four groups and the enamel surface of each tooth was divided into four quadrants. The surfaces were conditioned in a clockwise manner by one of the following methods: (1) Non-conditioned enamel acted as the control group (C); (2) Silicone-coated disk (Sof-Lex disc, Black, 3 M ESPE) (SD); (3) Diamond bur at slow speed (DB) and (4) Airborne particle abrasion (50 μm Al₂O₃, 2 bar, 5 s) (AA). Surface roughness was measured at each quadrant using a non-contact digital profilometer and contact angle measurements were performed using a goniometer. Enamel surfaces were then etched with 37% H₃PO₄ for 60 s and roughness and wettability measurements were repeated. The enamel surfaces in each quadrant received resin composite luting cement (Variolink II, Ivoclar Vivadent) incrementally in a polyethylene mold (diameter: 1 mm²; height: 4 mm) and photopolymerized. The specimens were stored in distilled water for 24 h at 37 °C until the testing procedures and then shear force was applied to the adhesive interface until failure occurred in a Universal Testing Machine (0.5 mm/min). Microshear bond (μSBS) was calculated by dividing the maximum load (N) by the bonding surface area of the resin cement. Representative enamel surfaces were analyzed under the scanning electron microscope (SEM) (x5000) to assess the surface morphology. Failure types were analyzed using optical microscope and SEM. Data (MPa) were analyzed using one-way ANOVA and Tukey`s test for each parameter and Linear model for group comparisons (α = 0.05). Surface conditioning method significantly affected the adhesion results (p < 0.001), surface roughness (p = 0.017), and contact angle (p < 0.001). Interaction terms were significant (p > 0.05). AA (338 ± 182) created significantly higher surface roughness compared to SD (308 ± 180) and DB (242 ± 197) (p < 0.05). After etching with 37% H₃PO₄, DB (307 ± 223) resulted in significantly lower roughness than those of SD (385 ± 173) and AA (414 ± 193) (p < 0.05). AA (40 ± 11) delivered significantly lower contact angle compared to those of SD (61 ± 9) and DB (59 ± 10). After etching with 37% H₃PO₄, AA (42 ± 10) and DB (50 ± 10) presented the lowest contact angle (p < 0.05). Mean μSBS results (MPa) showed significant difference between the experimental groups (p = 0.011) and were in descending order as follows: DB (20 ± 8)^a?a b < C (12 ± 5)^b. Failure types were predominantly mixed failure type between the enamel and the resin cement with more than half of the resin remained on the enamel surface (32 to 33 out of 40) in all groups. Cohesive failure in the enamel was not observed in any of the groups. SEM analysis showed that AA group leaves abundant particles on the enamel surface and after DB and AA, etching could not remove the particles completely and expose the enamel prisms.     

Comparison of methanol/hydrochloric,ferric chloride acid versus tribochemical silica coating for adhesion of resin cement to zirconium dioxide

This study compared air-abrasion and etching regimens on adhesion of resin luting agent to zirconium dioxide. Ceramic specimens (LAVA, 3 M ESPE) (N = 16) were embedded in acrylic resin and exposed surfaces were polished. The specimens were randomly assigned into four groups (n = 12, 3 specimens for each disc): SC: Air-borne particle abrasion (30 μm aluminum oxide particles coated with silica, CoJet, 3 M ESPE); MH: Heated chemical solution (Methanol-800 mL; 37% Hydrochloric Acid-200 mL; Ferric Chloride-2 g) at 100 °C for 30 min, MHP: Primer (Metal/Zirconia Primer, Ivoclar Vivadent) + MH, P: Primer only (Metal/Zirconia Primer). Cylindrical molds (internal diameter: 0.7 mm; height: 1.5 mm) were placed on each conditioned specimen, filled with resin cement (Multilink Automix) and photo-polymerized for 60 s. After 24 h, the molds were removed and the specimens were stored in distilled water at 37 °C for six months). Microshear test was performed in a Universal Testing Machine (1 mm/min). Failures types were classified as adhesive, mixed, or cohesive. In another set of specimens (n = 2 per group) contact angle measurements were recorded. Data were analyzed statistically using Kruskal–Wallis and Dunn’s tests (α = 0.05). The surface conditioning method significantly affected the mean bond strength (MPa) (p < 0.0001): SC(18.3 ± 0.3)^a < P(5.00 ± 0.07)^b < MHP(4.7 ± 0.08)^c < MH(0.84 ± 0.01)^c. While Group SC showed mainly adhesive (58%) and mixed (41.7%) failure types, groups MH, MHP, and P presented exclusively adhesive failures. SC, MHP, and P (29–32°) showed lower contact angle than MH (78.9°). Volume loss was the highest with MHP (9.92 μl) followed by SC (9.67 μl).     

Measurement of Ultrafine Particles: A Comparison of Two Handheld Condensation Particle Counters

The objective of this study was to compare two real-time condensation particle counters for measurement of number concentrations of ultrafine particles (UFPs). The comparison is based on the data from side-by-side measurements conducted in several locations, both indoors and outdoors. CPC 3007 and P-Trak? 8525 manufactured by TSI (instruments A and B, respectively) were used simultaneously. They measure particles in sizes from 0.01 to greater than 1 μ m and 0.02 to greater than 1 μ m, respectively. The results reveal a good correlation between the two instruments. The ratios of measured aerosol concentrations varied from 0.81 to 1.17, which implies that in all data sets the difference between the two instruments was less than ± 20%. About 63% of the results were in the range of ± 10%, and about 44% showed differences less than ± 5%. The maximum particle concentration detected by instrument A was approximately 105,000 particles cm ^{? 3} and the minimum was about 230 particles cm ^{? 3} . Because of the lower particle size threshold for instrument A, it was expected that this instrument should never show concentrations lower than those detected by instrument B. This was the case in most of the measurement series. The results revealed that the concentration of UFPs changes rapidly, especially in the presence of a local UFP source. A sampling interval of 1 min is sufficient to provide substantial information about the change in concentration level.