Estimation of acoustic forces on submicron aerosol particles in a standing wave field

The net acoustic force acting on submicron particles suspended in a gas and exposed to a standing wave field is investigated as a function of particle size, by measuring both the aerosol number density and size distribution in a flow-through resonator. By taking into account all contributions relevant to the net force, this experimental study provides a first estimate for the acoustic radiation force in a size range where molecular effects are expected to be significant. The experiment consists of an electrostatic transducer generating a standing wave in the 50–80 kHz frequency range, with the submicron aerosol particles concentrated at pressure antinodes located across the height of a rectangular channel. A section of the flow is sampled isokinetically and analyzed using a Scanning Mobility Particle Sizer (SMPS), while the nodal patterns are visualized simultaneously using light scattering. The net acoustic force is calculated from their measured displacement along the axis of the 1D standing wave field. The component of this force resulting from radiation pressure is estimated by subtracting contributions from other forces. The results provide the first experimental estimation of the size dependence of the acoustic contrast factor for submicron aerosol particles, demonstrating the possibility of performing acoustic separation for diameters as small as 150 nm.

Copyright © 2018 American Association for Aerosol Research     

Turkish diasporic responses to the Taksim Square protests: Legacy media and social media uses in Belgium,the Netherlands and Germany

Based on an offline and online survey of 967 people of Turkish origin living in these countries, we test how legacy and social media have influenced the participation of the members of the Turkish diaspora in Belgium, Germany and the Netherlands in the mid-2013 protests in Turkey’s social movement referred to as Gezi Park. This study also investigates how living in Europe can influence the behavior and attitudes of the sampled individuals from the Turkish Diaspora of Germany, Belgium and Netherlands during the period when the Gezi Park demonstration took place. Our results make it clear that social media were used by those who supported the protest movement, while those who opposed the protest movement primarily used or followed traditional sources of media, including Turkish and European television. Furthermore, supporters amongst the diaspora for the Gezi-protests were primarily active in accruing social capital through bonding and social networking among those who belong to the Turkish diaspora under the guise of the Gezi Park protests. Finally, a significant number of the supporters of the protests in the three countries took part in several different means of supporting the movement, including: disseminating awareness about the Gezi protests through social media, engaging in meetings, and in some cases, even severing contact with friends and acquaintances who did not share their support for the protest movement.     

Lattice Boltzmann Simulation of Conjugate Heat Transfer from Multiple Heated Obstacles Mounted in a Walled Parallel Plate Channel

In the present study, lattice Boltzmann simulation of conjugate heat transfer from multiple heated obstacles mounted in a walled parallel-plate channel is carried out. The aim is to investigate the effects of the pertinent thermophysical and geometrical parameters on the local Nusselt number around the obstacle's periphery. The result showed that increasing the obstacle to fluid thermal conductivity ratio and decreasing wall-to-obstacle thermal conductivity ratio results in increasing the local Nusselt number around the obstacle's periphery. The results of the present study are compared with those available from the conventional numerical methods, and good agreement is observed.     

Density Functional Theory Study on the Mechanical Properties and Interlayer Interactions of Multi-layer Graphene: Carbonic,Silicon-Carbide and Silicene Graphene-like Structures

Silicon - The main purpose of this study is to calculate the Young’s modulus of carbonic (c-graphene), silicon-carbide (SiC) and silicene graphene-like structures using density functional...     

Global occurrence of aflatoxin M1 in milk with particular reference to Iran

Aflatoxin M₁ (AFM₁) is an hydroxylated derivative of aflatoxin B₁ (AFB₁), which occurs in the milk of lactating animals. The aim of the present study was to determine the concentrations of AFM₁ in raw milk samples collected from 18 dairy farms in Qazvin, Iran, over a period of 1 year and compare them with those found in other countries. Samples (30 per farm) were collected in the four seasons, Spring, Summer, Autumn and Winter occurring between April 2009 and March 2010, giving a total of 2160 samples. They were centrifuged and 100 μl of the resulting skimmed milk were tested for AFM₁ contamination by competitive enzyme immunoassay (EIA). All samples (100 %) were contaminated with AFM₁ with concentrations ranging from 0.04 to 148.01 ng.l^?1 and a mean of 38.82 ng.l^?1. Summer samples with a mean of 64.69 ng.l^?1 and autumn samples with a mean of 0.14 ng.l^?1 had the highest and lowest concentrations, respectively, and differed significantly (P?<?0.05). AFM₁ content in 722 samples (33.4 %) was higher than the maximum tolerance limit of 50 ng.l^?1 accepted by the European Union (EU). As contamination of milk with AFM₁ is a potential risk for human health, raw milk should be monitored for its presence.     

Evaluation of antioxidant activity of some plant extracts and their heat,pH and storage stability

In the present study, three plant foods, namely, drumstick leaves (Moringa oleifera), mint leaves (Mentha spicata) and carrot tuber (Daucus carota) were extracted with ethanol and analyzed for their antioxidant activity. The antioxidant activity of extracts was evaluated according to the amount of malonaldehyde (MDA) formed by the FeSO₄-induced oxidation of linoleic acid and a high PUFA oil (sunflower oil) at 37 °C in Trizma-buffer (pH 7.4). At a concentration of 1.5 mg/ml of linoleic acid ,the extracts from drumstick and carrot had a higher antioxidant activity (83% and 80%) than α-tocopherol (72%). In sunflower oil, the extracts from drumstick leaves and mint leaves were found to exhibit a similar activity( 46% and 44%). The extract from drumstick exhibited the highest activity in both lipid systems. In addition, the stability of extracts to pH (4 and 9) and temperature (100 °C, 15 min) was investigated. The antioxidant activity of the extracts from mint leaves and carrot was higher at pH 9 than pH 4, while that of drumstick extract remained the same under both pH conditions. The extract from carrot was more heat-stable than other extracts. The three extracts stored in the dark at 5 and 25 °C after a 15 day period did not show any significant change (p ? 0.05) in their antioxidant activity. These data indicate that selected plant extracts are potential sources of dietary antioxidants.     

In situ photocrosslinkable nanohybrids based on poly(ε-caprolactone fumarate)/polyhedral oligomeric silsesquioxane: synthesis and characterization

Two types of biodegradable, in situ photocrosslinkable macromers were synthesized consisting a linear copolyester i.e., PCLF based on fumaric acid (FA) and poly(ε-caprolactone diol) (PCL diol), and its nanohybrid counterpart (POSS-PCLF) composed of FA, PCL diol and polyhedral oligomeric silsesquioxane (POSS). Chemical structure of the macromers was characterized by ¹HNMR and FTIR spectroscopy. The synthesized macromers were photocrosslinked by visible light irradiation in the presence of camphorquinone and N,N’-dimethylaminoethyl methacrylate as a photoinitiator and accelerator, respectively. Photocrosslinking characteristics of the compositions were investigated as a function of the initial PCL diol molecular weight, presence of POSS nanoparticles or N-vinylpyrrolidone (NVP, as a reactive diluent) by tracing degree of conversion by FTIR spectroscopy, equilibrium swelling studies. Thermal and dynamical properties of the macromers and the resulting networks were studied by TGA, DSC and DMA techniques pre- and post-photocrosslinking. In contrast to the self-crosslinkability of the macromers, the crosslinking reaction was promoted more efficiently in the presence of NVP as a reactive diluent. This scrutiny showed that there is an optimum point for POSS concentration to obtain the maximum improvement in the network properties.     

A novel foam-like silane modified alumina scaffold coated with nano-hydroxyapatite–poly(ε-caprolactone fumarate) composite layer

Although alumina scaffolds with biodegradable polymer coating can overcome the limitations of conventional ceramic bone substitutes, the bioactivity potential of these scaffolds needs to be enhanced. In this study, the macroporous alumina scaffolds with the defined pore-channel interconnectivity were successfully prepared by the foam replication method. The average pore size of the scaffolds was in the range 200–900 μm with around 82% porosity. The average Young's modulus of alumina scaffolds was 2.8 GPa. Coating of nano-hydroxyapatite (nano-HA) in poly(ε-caprolactone fumarate) (PCLF) as a carrier on the surface of alumina scaffold was performed. The nano-HA powder was synthesized successfully by the sol–gel method. The crystallite and particle sizes of HA powders were in nano range and confirmed by the Scherrer equation from X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The PCLF was synthesized and characterized by fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). In order to make a chemical link between the alumina scaffolds and the coating, a silane coupling agent was used. The results showed that using of 1 g Methacryloxypropyl trimethoxysilane in 100 g solvent is sufficient for making a thin interface layer between the scaffold and the polymer. The coating process was performed by immersion of scaffolds in the solutions with different percents of nano-HA. The morphology and chemical structure of the coated scaffolds were investigated by SEM and FTIR. SEM images demonstrated that the scaffolds were constituted of interconnected and homogeneously distributed pores. Also, HA distribution and agglomerates on the surface of scaffolds were enhanced by increasing the nano-HA percent in the coating solutions.     

One polymer,one layer,and two opposite functions: Using a pH-switchable polymer to fabricate a hydrophilic–hydrophobic fibrous membrane

Thanks to their permissibility of vapor transmitting and resistance to water penetration, hydrophilic–hydrophobic membranes (HHMs) are a critical factor in so many applications. Current strategies focus on electrospinning hybrid layers from two different hydrophilic–hydrophobic polymers. Here, we report a new generation of HHMs by electrospinning one layer of pH-switchable polymers followed by a simple post-treatment. In doing so, a hydrophobic poly(methyl methacrylate)-co-poly(N,N-diethylaminoethylmethacrylate) (PMMA-co-PDEAEMA) membrane is fabricated using the electrospinning method. Then, hydrochloric acid (HCl) vapor is used to convert one face of the membrane to a hydrophilic state. Field emission-scanning electron microscopy, drop test, water contact angle (WCA), moisture management test (MMT), t ensile strength, water vapor permeability (WVP), air permeability (AP), and cytotoxicity test were used to characterize the obtained membrane. The results show that by HCl vapor exposure, one side of the membrane gets successfully converted into a hydrophilic state, with the other side still remaining hydrophobic. The drop test and the WCA test showed that the optimal exposure time is only 5 min. This trigger has a small effect on the morphology and, subsequently, on water and air permeability as well as on the mechanical behavior of the membrane. This new generation of membranes can have applications in protective clothing and wound dressing.