Characteristics of PM2.5 Episodes Revealed by Semi-Continuous Measurements at the Baltimore Supersite at Ponca St

Highly time-resolved measurements of PM_2.5, its major constituents, particle size distributions (9 nm to 20 μ m), CO, NO/NO₂, and O₃, and meteorological parameters were made from February through November 2002, at the Baltimore Supersite at Ponca St. using commercial and prototype semi-continuous instruments. The average PM_2.5 mass concentration during the study period was 16.9 μ g/m³ and a total of 29 PM_2.5 pollution episodes, each in which 24-h averaged PM_2.5 mass concentrations exceeded 30.0 μ g/m³ for one or more days, were observed. Herein, 6 of the worst episodes are discussed. During these events, PM_2.5 excursions were often largely due to elevations in the concentration of one or two of the major species. In addition, numerous short-term excursions were observed and were generally attributable to local sources. Those in OC, EC, nitrate, CO, and NO_x levels were often observed in the morning traffic hours, particularly before breakdown of nocturnal inversions. Moreover, fresh accumulation aerosols from local stationary combustion sources were observed on several occasions, as evidenced by elevations in elemental markers when winds were aligned with sources resulting in PM_2.5 increments of ～ 17 μ g/m³. Overall, the results described herein show that concentrations of PM_2.5 and its major constituents vary enormously on time scales ranging from < 1 hr to several days, thus imposing a more highly complex pattern of pollutant exposure than can be captured by 24-hr integrated methods, alone. The data suggest that control of a limited number of local sources might achieve compliance with daily and annual PM_2.5 standards.     

Influence of surface characteristics on insect residue adhesion to aircraft leading edge surfaces

Leading edge contamination caused by insects is problematic for modern aircraft utilizing laminar flow aerofoils. The residue of crushed insect bodies adhering to aircraft leading edge surfaces can cause transition of the boundary layer, from laminar to turbulent, resulting in a significant increase in drag and therefore causing an increase in fuel consumption. Consequently, current research is focused on the evaluation of novel low surface energy coatings that will reduce or prevent insect adhesion. Insect residue adhesion tests were conducted on a range of surfaces, from superhydrophobic to hydrophilic. Surface free energy of the investigated substrates was obtained from measured dynamic contact angle values and surface roughness was measured using profilometry. Live insect testing with Drosophila melanogaster and Drosophila hydei was conducted using an insect delivery device inserted into a medium-speed wind tunnel. Tests were conducted at speeds ranging from 90 to 100 m/s (speeds representative of those on take-off and landing of a commercial passenger aircraft). Topography of insect residues was characterized using scanning electron microscopy and confocal laser scanning microscopy. Results obtained indicate that coatings with high surface roughness values and low wettability exhibit good anti-contamination properties.     

Comparison of the corrosion resistance of an Al–Cu alloy and an Al–Cu–Li alloy

ABSTRACT

In this study, the corrosion mechanisms of the AA2024-T3 and the AA2098-T351 were investigated and compared using various electrochemical techniques in 0.005?mol?L^?1 NaCl solution. The severe type of corrosion in the AA2098-T351 was intragranular attack (IGA) although trenching and pitting related to the constituent particles were seen. On the other hand, the AA2024-T3 exhibited severe localised corrosion associated with micrometric constituent particles, and its propagation was via grain boundaries leading to intergranular corrosion (IGC). Electrochemical techniques showed that the corrosion reaction in both alloys was controlled by diffusion. The non-uniform current distribution in both alloys showed that EIS was not a proper technique for comparing the corrosion resistance of the alloys. However, local electrochemical techniques were useful for the evaluation of the corrosion resistance of the alloys.     

Mechanical Alloying of β‐Type Ti–Nb for Biomedical Applications

β‐Type Ti–Nb powders which are needed as precursors for porous implant materials were produced by mechanical alloying of elemental powders. The effect of different fractions of the inorganic milling agent NaCl on the phase reactions during the milling process was investigated by means of X‐ray diffraction and scanning and transmission electron microscopy. It was demonstrated, that addition of ≥2 wt% NaCl during continuous ball milling is efficient for establishing a nanostructured β‐phase alloy and for the achievement of high powder yield.     

Combinatorial On‐Chip Study of Miniaturized 3D Porous Scaffolds Using a Patterned Superhydrophobic Platform

One of the main challenges in tissue engineering (TE) is to obtain optimized products, combining biomaterials, cells and soluble factors able to stimulate tissue regeneration. Multiple combinations may be considered by changing the conditions among these three factors. The unpredictable response of each combination requires time‐consuming tests. High‐throughput methodologies have been proposed to master such complex analyses in TE. Usually, these tests are performed using cells cultured into 2D biomaterials or by dispensing arrays of cell‐loaded hydrogels. For the first time an on‐chip combinatorial study of 3D miniaturized porous scaffolds is proposed, using a patterned bioinspired superhydrophobic platform. Arrays of biomaterials are dispensed and processed in situ as porous scaffolds with distinct composition, surface characteristics, porosity/pore size, and mechanical properties. On‐chip porosity, pore size, and mechanical properties of scaffolds based on chitosan and alginate are assessed by adapting microcomputed tomography equipment and a dynamic mechanical analyzer, as well as cell response after 24 hours. The interactions between cell types of two distinct origins—osteoblast‐like and fibroblasts—and the scaffolds modified with fibronectin are studied and validated by comparison with conventional destructive methods (dsDNA quantification and MTS tests). Physical and biological on‐chip analyses are coherent with the conventional measures, and conclusions about the most favorable conditions for each cell type are taken.     

Differential selectivity of natural and synthetic aminoglycosides towards the eukaryotic and prokaryotic decoding A sites

The lack of absolute prokaryotic selectivity of natural antibiotics is widespread and is a significant clinical problem. The use of this disadvantage of aminoglycoside antibiotics for the possible treatment of human genetic diseases is extremely challenging. Here, we have used a combination of biochemical and structural analysis to compare and contrast the molecular mechanisms of action and the structure-activity relationships of a new synthetic aminoglycoside, NB33, and a structurally similar natural aminoglycoside apramycin. The data presented herein demonstrate the general molecular principles that determine the decreased selectivity of apramycin for the prokaryotic decoding site, and the increased selectivity of NB33 for the eukaryotic decoding site. These results are therefore extremely beneficial for further research on both the design of new aminoglycoside-based antibiotics with diminished deleterious effects on humans, as well as the design of new aminoglycoside-based structures that selectively target the eukaryotic ribosome.     

Water activity and temperature effects on growth of Aspergillus niger, A. awamori and A. carbonarius isolated from different substrates in Argentina

The objectives of this study were to determine the effect of water activity, temperature, and their interactions on a) mycelial growth rate and b) the lag phase prior to grow of seven isolates of Aspergillus section Nigri isolated from peanuts, maize kernels, dried grapes and coffee cherries from Argentina. Three Aspergillus niger, three A. awamori and one A. carbonarius isolates examined showed optimum a(W) level for growth at 0.97 with optimal temperature of 30 degrees C. for most of the isolates and 25 degrees C for only one (A. awamori RCP176). Minimal a(W) for growth was 0.85 at the highest temperature tested. Overall growth was reduced up to 50% at 0.93 a(W). Growth was also to a large extend inhibited at 0.85 a(W) for most isolates even after 21 days of incubation at temperatures lower than 30 degrees C. The analysis of variance of the effect of single (isolate, a(W) and temperature), two- and three-way interaction showed that all factors alone and all interactions were statistically significant (P<0.001) in relation to growth rates and lag phase for A. niger, A. awamori and A. carbonarius isolates. These data are relevant since these species are isolated in high frequency on numerous substrates for human and animal consumption in Argentina.     

Fibroblast growth factors activate mitogen-activated protein kinase pathways to promote migration in ovine trophoblast cells

Fibroblast growth factors (FGFs) 2 and FGF10 are uterine- and conceptus-derived factors that mediate trophoblast activities in cattle and sheep. To extend our understanding of how FGFs may control peri-implantation development in ruminants, we determined whether FGF2 and FGF10 impact trophoblast cell migration. Transwell inserts containing 8 μm pores were used to examine whether FGF2 or FGF10 supplementation increased oTr1 cell migration. Supplementation with 0.5 ng/ml FGF2 or FGF10 did not affect oTr1 cell migration number, but exposure to 5 or 50 ng/ml FGF2 or FGF10 increased (P<0.05) oTr1 cell migration when compared with controls. The involvement of specific MAP kinase (MAPK) cascades in mediating this FGF response was examined by using pharmacological inhibitors of specific MAPKs. Western blot analysis indicated that FGF2 and FGF10 increased phosphorylation status of MAPKs 1, 3, 8, 9, and 14. Exposure to specific inhibitors blocked FGF induction of each MAPK. Exposure to inhibitors before supplementation with FGF2 or FGF10 prevented FGF induction of cell migration, indicating that each of these signaling molecules was required for FGF effects. A final series of studies examined whether FGF2 and FGF10 also mediated the migration of a bovine trophoblast line (CT1 cell). Increases in migration were detected in each cell line by supplementing 5 or 50 ng/ml FGF2 or FGF10 (P<0.05). In summary, FGF2 and FGF10 regulate migratory activity of ovine trophoblast cells through MAPK-dependent pathways. These outcomes provide further evidence that FGFs function as mediators of peri-implantation conceptus development in cattle and sheep.     

Influence of the support in selective CO oxidation on Pt catalysts for fuel cell applications

One crucial requirement for the proton exchange membrane fuel cells (PEMFC) is to feed clean hydrogen to the anode, which is rapidly poisoned by traces of CO present from the upstream hydrocarbon reforming and water–gas shift processes. The removal of CO can be achieved by using catalysts able to selectively oxidize CO in the presence of excess hydrogen. Herein we report the effect of the support on Pt catalysts for total and selective oxidation (SELOX) of CO. The catalysts supported on ceria and zirconia presented higher activity than alumina and silica supported catalysts in SELOX reaction at low temperatures, but with lower CO conversions.     

Paraquat-loaded alginate/chitosan nanoparticles: preparation, characterization and soil sorption studies

Agrochemicals are amongst the contaminants most widely encountered in surface and subterranean hydrological systems. They comprise a variety of molecules, with properties that confer differing degrees of persistence and mobility in the environment, as well as different toxic, carcinogenic, mutagenic and teratogenic potentials, which can affect non-target organisms including man. In this work, alginate/chitosan nanoparticles were prepared as a carrier system for the herbicide paraquat. The preparation and physico-chemical characterization of the nanoparticles was followed by evaluation of zeta potential, pH, size and polydispersion. The techniques employed included transmission electron microscopy, differential scanning calorimetry and Fourier transform infrared spectroscopy. The formulation presented a size distribution of 635 ± 12 nm, polydispersion of 0.518, zeta potential of -22.8 ± 2.3 mV and association efficiency of 74.2%. There were significant differences between the release profiles of free paraquat and the herbicide associated with the alginate/chitosan nanoparticles. Tests showed that soil sorption of paraquat, either free or associated with the nanoparticles, was dependent on the quantity of organic matter present. The results presented in this work show that association of paraquat with alginate/chitosan nanoparticles alters the release profile of the herbicide, as well as its interaction with the soil, indicating that this system could be an effective means of reducing negative impacts caused by paraquat.