Mode In Air Research Articles

Fractal Features and Surface Micromorphology of Unworn Surfaces of Rigid Gas Permeable Contact Lenses

ABSTRACTPurpose: The aim of this exploratory study was to investigate the micromorphology of surfaces of rigid gas permeable (RGP) contact lenses (CLs) using atomic force microscopy (AFM) followed by fractal analysis.Materials and methods: In order to characterize in a quantitative manner the micromorphology of surfaces of new and unworn RGP CLs made of twelve different materials, AFM was taken and then analyzed using fractal methods. Surface topography was sampled in an intermittent-contact mode in air, on square areas of 5 × 5 µm2 (MultiMode with Nanoscope V (Bruker). Spatial characteristics of 3-D surface texture were obtained using parameters defined in ISO 25178-2: 2012 norm.Results: The surface texture turned out to have complex 3-D nanoscale geometry. For quantitative characterization of the properties of surface geometry at nanometer level of CL on the global scale, a series of fractal parameters was used.Conclusions: Statistical and fractal parameters of 3-D surfaces can be used by manufacturers to assess the micromorphology of CLs in order to improve their 3-D surface texture characteristics. These parameters can also be used in an elastic–plastic finite element model with contact elements to simulate the friction, wear and micro-elastohydrodynamic lubrication at a nanometer scale between the CL with the corneal surface.

Air and water oxidation of aluminum flake particles

The article deals with the oxidation of aluminum flake particles with specific surface area ranged from 0.37m2/g to 0.73m2/g. The investigated powders which consisted of the above mentioned flake particles contained metal aluminum in high values (95–98 mass %). The powders possess a high hydrogen release rate (up to 27cm3/min) by the interaction with calcium hydroxide water solution. The powders under study revealed a high reactivity while oxidized in a non-isothermal mode in air. The reactivity parameter values for aluminum flake particles can be compared to those of aluminum spherical nanoparticles. The application of these aluminum flake particles were possible in two directions due to their high metal content in combination with low specific surface area and high reactivity: pyrotechnics and cellular concrete production.

Application of PAP-2 aluminum powder to produce powdered composite materials: The features of technology, structure, and physicomechanical properties of composites. Part I. Process approaches providing the formation of composite materials and applied procedures for determining their physicomechanical properties

Composites Al/Al2O3 (lamellar cermet matrix)–filler (discrete metallic fibers, duralumin chips, graphite particles, fused corundum grains, and technical alumina spherulites) are fabricated. To form the lamellar cermet matrix, industrially produced PAP-2 aluminum powder was used. This powder consists of scaled particles with stearin coating (the specific surface of the powder is 4.1322 m2/g, and its particle size varies from 0.03 to 10 μm). In order to form the composites, the following main process operations were used: heat treatment of the PAP-2 powder in air to burn out stearin from the particle surface and replace it with a passivating alumina film, mixing of the thus formed powder product with a filler, and compaction and reaction sintering of powder billets in the filtration burning mode in air. To fabricate the Al/Al2O3–C composite, a new approach based on the saponification chemical reaction of stearin is proposed. This reaction runs between stearin on the surface of aluminum particles and caustic soda, which is the product of hydrolysis of the diluted liquid glass introduced into initial powder. The reaction products (sodium stearate and glycerol) are decomposed during the subsequent heat treatment in air with the formation of a coke residue on the particle surface. The physicochemical properties of the composites were determined using standard and conventional procedures.

Modification of polysulfone porous hollow fiber membranes by air plasma treatment

Air plasma treatment was used to enhance the surface hydrophilic properties of the polysulfone porous hollow fiber membranes prepared via a dry-wet phase invertion technique in the free spinning mode in air. Membranes prepared had porous asymmetric structure with macroporous support on the shell side and fine-porous selective layer on the lumen side. The wettability of the inner membrane surfaces were checked by contact angle measurements and FTIR was used to compare the surfaces before and after plasma treatment. Membrane morphology was examined with confocal scanning laser microscopy (CSLM). Contact angle measurements confirm that air plasma treatment affords improvement in the wettability of polysulfone membranes and FTIR results show that air plasmas chemically modify the lumen side membrane surface, however, there is no significant change in membranes chemical structure after modification. CSLM data obtained, as well as gas permeability (He and CO2) measurements show that after plasma treatment pore etching occurs.

Combustion characteristics of primary reference fuel (PRF) droplets: Single stage high temperature combustion to multistage “Cool Flame” behavior

We report experiments and detailed numerical modeling of mixtures of primary reference fuel (PRF) droplets consisting of n-heptane and iso-octane with initial droplet diameters of 0.5 and 3.51mm. The results show a quasi-steady, low temperature (or “Cool Flame” (CF)) droplet burning mode that stems from a varying two-stage chemical kinetic behavior of the combustion chemistry. The simulations further illustrate, that the CF droplet burning mode in 1atm air is dependent upon the iso-octane fraction and droplet size. CF droplet burning is predicted to be absent for large diameter droplets containing more than 50% (by volume) iso-octane (>PRF50), and for all droplet diameters that exhibit hot flame burning without radiative extinction. The model predictions are in agreement with new, large diameter PRF50 experiments reported here, as well as previous ground-based PRF50 sub-millimeter diameter experiments. The effects of PRF mixture fraction are further analyzed numerically. Additional simulations show that replacing small amounts of inert (nitrogen) with ozone can sufficiently modify the low temperature kinetic activity of PRF50 droplets to promote CF droplet burning, even for sub-millimeter droplet diameters (with no hot flame transition). The implications are that with proper experimental configurations, CF droplet burning might be studied in ground-based, sub-millimeter diameter, isolated droplet burning experiments.

Variations of fine particle physiochemical properties during a heavy haze episode in the winter of Beijing

Chemical composition, morphology, size and mixture of fine particles were measured in a heavy haze and the post-haze air in Beijing in January 2012. With the occurrence of haze, the concentrations of gaseous and particulate pollutants including organics, sulfate, nitrate, and ammonium grew gradually. The hourly averaged PM2.5 concentration increased from 118μgm−3 to 402μgm−3 within 12h. In contrast, it was less than 10μgm−3 in the post-haze air. Occupying approximately 46% in mass, organics were the major component of PM1 in both the haze and post-haze air.Analysis of individual particles in the size range of 0.2–1.1μm revealed that secondary-like particles and soot particles were always the majority, and most soot particles had a core-shell structure. The number ratio of secondary-like particles to soot particles in accumulation mode in the haze air was about 2:1, and that in the post-haze air was 8:1. These results indicate both secondary particle formation and primary emission contributed substantially to the haze. The mode size of the haze particles was about 0.7μm, and the mode size of the post-haze particles was 0.4μm, indicating the remarkable growth of particles in haze. However, the ratios of the core size to shell size of core-shell structure soot particles in the haze were similar to those in the post-haze air, suggesting a quick aging of soot particles in either the haze air or the post-haze air.

Hydroxyl Radicals and Hydrogen Peroxide Formation at Nonthermal Plasma–Water Interface

This paper investigated hydroxyl radicals and hydrogen peroxide formation under a needle-plate electrode configuration using positive-polarity dc discharges generated in air, nitrogen, and helium. The discharge mode in air and nitrogen was found to change above ultrapure water; initially, a nanosecond pulse discharge was observed, transitioning to a diffuse discharge due to the increasing conductivity of the water. The discharge in helium was a nanosecond pulse discharge and the repetition rate increased with increasing water conductivity. It was found that hydroxyl radicals contribute to 7%, 78%, and 70% of hydrogen peroxide formation when using the ultrapure water in air, nitrogen, and helium, respectively. It is suggested that hydroxyl radicals are formed by water reactions with energetic positive ions and the neutral particles, such as N2+, He+, O, H, and HO2. Part of hydrogen peroxide is directly formed from atoms and radical reactions with water in nitrogen and helium, while oxygen reactions are heavily involved for hydrogen peroxide formation in air. A fluorophotometry method, using terephthalic acid, was used to directly quantify the formation of hydroxyl radicals and compared with the tert-butanol method.

The use of PAP-2 aluminum dust to fabricate powder composite materials: the features of technology, structure and physicomechanical composites. Part 1. Manufacturing approaches that provide the creation of composite materials and applied procedures for de

Composites Al/Al2O3 (lamellar cermet matrix)–filling agent (discrete metallic filaments, duralumin chips, graphite particles, fused corundum grains, kaolin filaments, and technical alumina spherolites) are fabricated. Industrially produced PAP-2 aluminum powder, which consists of scaled particles with stearin coating (specific surface of the powder is 4,1322 m2/g, its particle sizes vary from 0,03 to 10 μm), was used to form the lamellar cermet matrix. In order to form the composites, the following production operations were used: heat treatment of PAP-2 powder in air to burn-out stearin from the particle surface and substitute it by alumina film, mixing the formed powder product with the filling agent, pressing, and reaction sintering the powder billets in a filtration burning mode in air. A new approach based on the chemical reaction of stearin saponification is proposed to fabricate the Al/Al2O3 composite. In this reaction, stearin on the surface of aluminum particles reacts with caustic soda resulted from the hydrolysis of diluted liquid glass introduced into initial powder. The reaction products (sodium stearate and glycerin) decompose during subsequent heat treatment in air with the formation of coke residue on the particle surface. Physicochemical properties of composites were determined using standard and generally accepted procedures.

Sildenafil citrate (Viagra) reduces surface roughness of human erythrocytes: Atomic-force-microscopic study

Sildenafil citrate (Viagra) is used to treat erectile dysfunction and pulmonary arterial hypertension. The objective of this study was to analyze the action of sildenafil citrate on normal human erythrocytes in vitro at a concentration (2.5mg/mL) higher than the prescribed for clinical conditions. Imaging of drug-treated erythrocytes was done using an atomic-force microscope in contact mode in air. Data analysis was performed using the scanning-probe-microscopy software WSxM. The study revealed that the drug causes hemolysis of erythrocytes at high concentration in vitro at room temperature. The ghosts (membranes) of erythrocytes with reduced cell size and deformed shape were observed using atomic-force-microscope imaging at low magnification. In addition, the high-magnification images revealed alterations in the nanostructural features of the erythrocyte membrane. There was a complete loss of characteristic membrane-architecture pattern. The root-mean-square surface roughness of the cell membrane after drug treatment was measured and found to be significantly less than that of erythrocytes in the native state. Sildenafil citrate causes hemolysis of erythrocytes in vitro at high concentration with significant alterations in morphometric properties, like change in cell shape, reduction in cell dimension, and disruption of membrane cytoarchitecture, along with a severe drop in membrane root-mean-square surface roughness.

Wear behaviors of Fe-based amorphous composite coatings reinforced by Al2O3 particles in air and in NaCl solution

Abstract In this paper, the influence of the addition of Al2O3 particles on the microstructure and wear properties of Fe-based amorphous coatings prepared by high velocity oxygen fuel (HVOF) has been studied. The wear behaviors of the composite coatings were evaluated against Si3N4 in a pin-on-disk mode in air and in 3.5 wt.% NaCl solution. It was found that the Al2O3 particles were homogenously distributed in the amorphous matrix and the composite coatings exhibited improved wear resistance and reduced coefficient of friction (COF) in both air and wet conditions as compared to the monolithic amorphous coating. The composite coating reinforced with 20 wt.% Al2O3 particles exhibit the best wear performance, which, for example, has extremely low COF (

Optimized tilted c-axis AlN films for improved operation of shear mode resonators

Biosensors based on AlN bulk acoustic wave resonators require shear mode operation to avoid acoustic losses upon analysing liquid samples. To generate shear modes, the microcrystals of the AlN thin film must be uniformly tilted with respect to the normal, yet keeping good piezoelectric properties. In this paper, we demonstrate AlN solidly mounted resonators displaying simultaneously material electromechanical coupling of 3.5% and quality factor (QS) of 250 for the shear mode in air. Upon testing the devices in liquid, QS factor drops to 150, which is still large enough for biosensing applications. We deposit the AlN film with tilted microcrystals using a two-stage off-axis sputtering process that involves the use of a seed layer and an active piezoelectric layer. We have studied the parameters involved in each stage of the deposition and identified the factors that are key to achieve reproducible high-quality films. By comparing this method to off-axis deposition of AlN on randomly rough substrates, we conclude that the latter produces hardly reproducible and lower quality AlN thin films.

Nano-Optomechanical Resonators in Microfluidics.

Operation of nanomechanical devices in liquid has been challenging due to the strong viscous damping that greatly impedes the mechanical motion. Here we demonstrate an optomechanical microwheel resonator integrated in microfluidic system that supports low-loss optical resonances at near-visible wavelength with quality factor up to 1.5 million, which allows the observation of the thermal Brownian motion of the mechanical mode in both air and water environment with high signal-to-background ratio. A numerical model is developed to calculate the hydrodynamic effect on the device due to the surrounding water, which agrees well with the experimental results. With its very high resonance frequency (170 MHz) and small loaded mass (75 pg), the present device has an estimated mass sensitivity at the attogram level in water.

One-Year-Long Continuous and Synchronous Data Set of Fossil Carbon in Atmospheric PM2.5 and Carbon Dioxide in Debrecen, Hungary

Radiocarbon investigation of atmospheric PM2.5 aerosol synchronized with 14CO2 observations began in Debrecen in the winter of 2010. The aim of the study was to determine the contemporary and fossil carbon fractions in the aerosol and to set them against the fossil CO2 excess data referring to the same period. The mass of the collected PM2.5 mode on prebaked quartz filters was determined gravimetrically, while its total carbon mass was calculated from the pressure of CO2 gas produced after the combustion of the filters. As a result of the applied sampling and preparation method, the stable, nonvolatile carbon forms were principally studied. 14C measurements of the tiny aerosol bulk samples were performed using the EnvironMICADAS accelerator mass spectrometer at ATOMKI. The sample preparation method was tested using several blanks, standards, and real samples. Test results showed good reproducibility for the applied aerosol sample preparation and accelerator mass spectrometry (AMS) 14C analyses. Atmospheric fossil CO2 excess data were calculated according Levin et al. (2003), using the 14C results of collected CO2 samples measured by the gas proportional counting system at ATOMKI. Mass concentration of PM10 involving the PM2.5 mode in the city air exceeded the daily average of 50 μg/m3 (24-hr limit value in the EU) several times in 2011, mainly during the winter. The results showed that recently derived carbon most likely from domestic wood burning was causing the elevated carbon mass concentration of PM2.5 in Debrecen at the time. In the course of the 1-yr-long continuous and systematic comparison of fossil carbon mass concentration of PM2.5 mode and mole fraction of fossil excess of atmospheric CO2, similar and synchronous trends were observed during the studied period in Debrecen.

Series Circuit Resistance as Factor of DBD Mode in Air at Different Barrier Materials

This paper deals with the realization of a diffuse dielectric barrier discharge in air at atmospheric pressure using a high-voltage pulse generator operating in a single-pulse mode and at frequencies of tens of hertz. This paper is focused on the effects of the series resistor and dielectric materials. It is shown that the parameters of the external circuit strongly influence the discharge mode.

Creep Behaviour and Fracture Analysis of MoSi2 Based Composites

AbstractMolybdenum disilicide based composites containing different types of additive materials such as SiC and nano SiC particles have been investigated, based on the detailed examination of their microstructures and fracture surfaces after creep. The materials were prepared via powder metallurgy using high temperature controlled reaction sintering (CRS). The creep experiments were carried out in four-point bending mode in air in the temperature range from 1273 to 1673 K, with constant stress of 100 MPa. The creep behaviour and the mechanisms of damage were investigated on fracture surfaces by SEM and the microstructure and its response to high temperature load were investigated by TEM using the thin foil technique.

Nano-hydrogels of methoxy polyethylene glycol-grafted branched polyethyleneimine via biodegradable cross-linking of Zn2+-ionomer micelle template

Soft polymeric nanomaterials were synthesized by the template-assisted method involving self-association of methoxy polyethylene glycol-g-branched polyethyleneimine (mPEG-g-branched PEI) ionomer by transition metal ions such as Zn2+ followed by chemical cross-linking of the polyamine core by dithiopropionic acid. The formation of donor–acceptor complexes of Zn2+ and PEI ionomer was characterized by FT-IR spectroscopy and potentiometric titration. Turbidimetry was performed to study the solution property of the complexes which depended on pH, relative weight fraction of mPEG, and the molar ratio of Zn2+. The cross-linking reaction was studied by TNBS assay, 1H-NMR, and size exclusion chromatography. Upon removal of Zn2+ from cl-mPEG-g-branched PEI/Zn2+ at pH 3 by dialysis, the resulting cross-linked self-assembly represented a uniform, stable, and less positively charged hydrogel-like nanosphere with an intensity-averaged size ranging from 150 to 250 nm as determined by a Zetasizer. Atomic forced microscopy imaging was performed in intermittent contact mode in air that revealed discrete and oval-to-spherically shaped particles with average sizes ranging from 40 to 50 nm depending on the degree of cross-linking. This functional nanocarrier is expected to exhibit some key features such as active encapsulation of negatively charged hydrophilic agents in the swollen core of polyamine network and a hydrophilic mPEG shell which provides an increased solubility and passive targeting of active pharmaceutical agents to impaired tissues. The nano-hydrogels especially at 12 % degrees of cross-link demonstrated excellent biocompatibility determined by different experiments such as albumin aggregation, erythrocyte aggregation, hemolysis, and MTT cytotoxicity assay. Moreover, biodegradability of the cross-links as shown by the Ellman assay can offer a time-dependent degradation and redox-stimulated release of active agents.

Dry cleaning tetrachlorethylene pollution impact on indoor air quality in Paris territory

The Central Laboratory of the Police headquarters (LCPP) is a public department which has the task among others of showing up harmful effects from exterior sources. These effects can be followed by some deteriorations of indoor air quality in close dwellings. The aim of this study is to investigate dry cleaning sources that could cause intoxications and to identify the pollution transfer mode in indoor air (air ventilation, ceiling, sewage network). The air is sampling by using sensor (passive sampling) during 7 days or by using pumps during 1 to 8 hours (active sampling) on charcoal trap and solvent desorption. The identification and quantity determination are realised by Gas Chromatography coupled to a Flame Ionization Detector (GC/FID) or to a Mass Spectrometer (GC/MS). The laboratory is accredited according to ISO 17025 for VOCs measurement on charcoal traps and the uncertainty is estimated to be around 20%. Some important levels of tetrachloroethylene were measured after more than 100 investigations in dwellings resulting from proximity complaints since 2010. The statistics results of these different studies will be discussed here. More than 80 % dwellings located above dry cleaners were polluted by tetrachloroethylene. Levels were clearly higher than the references values provided by the French high council of public health (0.25 mg/m3 for a guide value and 1.25 mg/m3 for a quick action to reduce air pollution). 50% of dwellings have tetrachlorethylene levels higher than 0.25 mg/m3. A maximum value of 120 mg/m3 have been measured in a bedroom just around a dry cleaner. Transfer modes of pollution were identified with simultaneous measures in dwelling, staircase and outdoor nearby home air inlet. The main transfer mode was carried out by ceiling or technical passage. Works of putting in conformity can be prescribed to dry cleaners. Results of studies realized before and after these works will be described. Measurements realized in dwellings above dry cleaners using substitute products of tetrachlorethylene will also been presented.

Calibration of tapping AFM cantilevers and uncertainty estimation: Comparison between different methods

We present a comparative study between three different methods for the spring constant calibration of silicon beam-shaped Atomic Force Microscope (AFM) cantilevers, used in tapping AFM mode in air. The geometries of these levers can be quite different from the standard rectangular cross section. We examine a method that combines the knowledge of cantilever dimensions and eigenfrequencies (Cleveland formula), the Sader method and we build cantilever models based on Finite Element Analysis (FEA). We demonstrate that with accurate measurement of dimensions, resonance frequency and quality factor, the Cleveland formula yields a combined cantilever stiffness uncertainty of approximately ±7% and the Sader method an uncertainty of ±5%. We also use FEA to show that when trying to approximate a realistic trapezoidal 3D tipped geometry, there exists a systematic overestimation in cantilever stiffness of ±2%, compared to when considering a simple rectangular cross section. Our constructed FE models are able to account for inhomogeneities in material properties as well as the influence of the added reflective coating in the cantilever stiffness estimation.

Extractive electrospray ionization mass spectrometry for sensitive detection of gaseous radioactive iodine-129

A rapid method based on extractive electrospray ionization mass spectrometry (EESI-MS) has been developed for quantitative detection of trace radioactive molecular iodine-129 (129I2) in negative ion detection mode in ambient air. For actual air samples, gaseous 129I2 was completely converted into iodine-129 ions (129I−) by an excess of Na2SO3 solution. By adding excess amounts of 127I2 into the solution, the 129I− ions formed triiodide ion complexes (i.e.129+127*2I3−) which were subjected to tandem mass spectrometry experiments to exclude false positives. Quantification of iodine-129 was achieved by quantitatively measuring the characteristic fragment (i.e., 129I−) of the triiodide ion complexes. The calibration curve showed a good linearity within an relatively wide concentration range of 0.01–1000 ppb (R2 = 0.991), a limit of detection (LOD) of 4.5 ppt and a relative standard deviation (RSD) of 4.0–13.1% (n = 5). The spiking recovery of this method was found to be 82.6–110.5%. The method had also been successfully applied to detecting the trace amount of gaseous 129I2 released in a simulated nuclear leakage accident, showing a satisfactory result for the tested gaseous samples. The experimental data demonstrated that EESI-MS was a useful tool for quantitative measurement of radioactive iodine in cases such as nuclear leakage, nuclear explosions and related scenarios.

Thrust measurements and flow field analysis of a piezoelectrically actuated oscillating cantilever

Although not identical to the motion employed by nature’s swimmers and flyers, the simple harmonic oscillations of cantilever-like structures have been shown to provide efficient low-power solutions for applications ranging from thermal management to propulsion. However, in order to quantify their true potential, the resulting flow field and corresponding thrust must be better understood. In this work, a thin, flexible cantilever is actuated via a piezoelectric patch mounted near its base and caused to vibrate in its first resonance mode in air. The flow field is experimentally measured with particle image velocimetry while the thrust produced from the oscillatory motion is quantified using a high-resolution scale. The trends observed in the data are captured using an oscillating Reynolds number, and a clear relationship is defined between the operating parameters and the resulting thrust. Two-dimensional flow fields are extracted from the x–y and y–z planes and are primarily used to motivate future geometry and sidewall configurations that could greatly enhance the thrust capabilities of the cantilever by directing the flow downstream in a more effective manner.