Search

The performed research presents modeling results for designing microfluidic vortex diodes. These devices rectify fluid flow and can be used in many applications on micro and macro scales. The modeling, utilizing computational fluid dynamics (CFD) with the turbulence model RANS k-ε in COMSOL Multiphysics, has led to optimizing diodicity—the reversed-to-forward flow pressure drop ratio. The goal was to find the best flow-rectifying geometry within the 2D vortex-type design by changing the wall geometry, diode shape, and inflow velocities, identifying significant parameters and dependencies. Improving diodicity can be achieved by increasing the radius r1 of the central channel, increasing the entire diode radius r2, decreasing the width w of the rectangular channel, and reducing its length L. Additionally, changing the circular shape of the diode to an elliptical one can improve diodicity. The significance of this research is evident in the potential applications of these devices in microfluidic setups where fixed-geometry unidirectional flow is required, e.g., mixing, filtration, cell separation, and drug delivery, or on industrial scales, e.g., energy harvesting, wastewater treatment, and water sterilization. [ABSTRACT FROM AUTHOR]

Radical and electrochemical properties of core-shell polydopamine structures (PDA@SiO 2) were studied. We have successfully covered large silica nanoparticles (ca. 960 nm) with a thin layer of polydopamine. The radical's concentration present in PDA is 1.32 × 10 15 spin / mg and after synthesis in PDA@SiO 2 system it is 8.4 × 10 13 spin / mg. The core-shell structure maintained its radical scavenging properties due to a thin layer of PDA covering silica. Cyclic voltammetry (CV) shows a reduction of peak-to-peak potential separation and an increase of anodic and cathodic current with an increase in the scan rate. Electrochemical impedance spectroscopy shows the electrical connection between PDA and SiO 2. PDA@SiO 2 core-shell system is electrochemically non-degradable showing a quasi-reversible electrochemical response, which makes it a promising candidate for sensor applications. • Synthesis of SiO 2 nanoparticles, PDA nanoparticles, PDA@SiO 2 core-shell structure. • Radical scavenging properties are confirmed in PDA system and maintained in core-shell structure. • Additional stabilization effect in CV was observed due to interaction of PDA with SiO 2. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance spectroscopy of conduction electrons, i.e. Conduction Electron Spin Resonance (CESR), is a powerful tool for studies of carbon samples. Conductive samples cause additional effects in CESR spectra that influence the shape and intensity of the signals. In cases where conduction electrons play a dominant role, whilst the influence of localized paramagnetic centres is small or negligible, the effects because of the spins on conduction electrons will dominate the spectra. It has been shown that for some ratios of the bulk sample sizes ( d) to the skin depth ( δ), which depend on the electrical conductivity, additional size effects become visible in the line asymmetry parameter A/| B|, which is the ratio of the maximum to the absolute, minimum value of the resonance signal. To study these effects the electrical direct current-conductivity and CESR measurements are carried out for two amorphous bulk coal samples of anthracite and a higher anthraxolite. The observed effects are described and discussed in terms of the Dyson theory. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A study concerning the image quality in electron paramagnetic resonance imaging in two-dimensional spatial experiments is presented. The aim of the measurements was to improve the signal-to-noise ratio (SNR) of the projections and the reconstructed image by applying modulation amplitude higher than the radical electron paramagnetic resonance linewidth. Data were gathered by applying four constant modulation amplitudes, where one was below 1/3 (Amod = 0.04mT) of the radical linewidth (◢Bpp= 0.14mT). Three other modulation amplitude values were used in this experiment, leading to undermodulated (Amod<1/3 ◢Bpp), partially overmodulated (Amod∼1/3 ◢Bpp) and fully overmodulated (Amod>>1/3 ◢Bpp) projections. The advantages of an applied overmodulation condition were demonstrated in the study performed on a phantom containing four shapes of 1.25mM water solution of 2, 2, 6, 6-tetramethyl-1-piperidinyloxyl. It was shown that even when the overmodulated reference spectrum was used in the deconvolution procedure, as well as the projection itself, the phantom shapes reconstructed as images directly correspond to those obtained in undermodulation conditions. It was shown that the best SNR of the reconstructed images is expected for the modulation amplitude close to 1/3 of the projection linewidth, which is defined as the distance from the first maximum to the last minimum of the gradient-broadened spectrum. For higher modulation amplitude, the SNR of the reconstructed image is decreased, even if the SNR of the measured projection is increased. [ABSTRACT FROM AUTHOR]