It is discovered that complexes of DNA and hydrophobically modified polyelectrolytes form a rigid network of threadlike or fibrous aggregates at the liquid–gas interface whose morphology can ...dramatically affect the mechanical properties. While mixed solutions of DNA and poly(N,N-diallyl-N,N-dimethylammonium chloride) (PDADMAC) exhibit no notable surface activity, the complexes formed from DNA with poly(N,N-diallyl-N-butyl-N-methylammonium chloride) are surface-active, in contrast to either of the separate components. Further, complexes of DNA and poly(N,N-diallyl-N-hexyl-N-methylammonium chloride) (PDAHMAC) with its longer hydrophobic side chains exhibit pronounced surface activity with values of surface pressures up to 16 mN/m and dynamic surface elasticity up to 58 mN/m. If the PDAHMAC nitrogen to DNA phosphate molar ratio, N/P, is between 0.6 and 3, abrupt compression of the adsorption layer leads unexpectedly to a noticeable decrease of the surface elasticity. The application of imaging techniques reveals that this effect is a consequence of the destruction of a rigid network of threadlike DNA/polyelectrolyte aggregates at the interface. The toroidal aggregates, which are typical for the bulk phase of DNA/PDADMAC solutions in this range of N/P ratios, are not observed in the surface layer. The observed link between the mechanical properties and interfacial morphology of surface-active complexes formed from DNA with hydrophobically modified polyelectrolytes indicates that tuning polyelectrolyte hydrophobicity in these systems may be a means to develop their use in applications ranging from nonviral gene-delivery vehicles to conductive nanowires.
Abstract The electrocoalescence of a water drop at the water-oil interface was numerically analyzed using the finite element method by solving a set of equations including hydrodynamics and ...electrostatics. The simulation was performed using COMSOL Multiphysics software, the interface movement was implemented using an arbitrary Lagrangian-Eulerian method (also called the moving-mesh method). The influence of the initial distance from the drop to the layer, as well as the size of the entire domain on the outcome of the process was studied. The electrical coalescence and non-coalescence of a single uncharged droplet with a layer under the action of the DC field were calculated in a wide range of electric field strength. The created computer model makes it possible to calculate the voltage dependence of the detached droplet volume and charge. Also, it can help to determine features of non-coalescence, including the stretching of the droplet along the interelectrode gap and spraying.
The results of the calculation of the flow on the plate under the influence of synthetic jets using the RANS and URANS methods are presented. The dependence of the parameters of synthetic jets on the ...distribution of heat flux into the wall on the plate is shown.
Abstract
In case of disconnection of generator from the network and failure of the governor, the rotational speed of the rotor rapidly increases and achieves maximum value, called the runaway speed. ...This value depends on the turbine type, the operating condition, the turbine flow passage and the runner geometry, and for Kaplan turbines might 2.5 times surpass the nominal rotational speed of the runner. The runaway speed is important for evaluation of mechanical resistance of the generator rotor. The value of runaway speed is determined based on the results of the model tests upon completion of the design works related to the runner. Therefore, accurate computation of the runaway speed will improve the design process for the runner and the whole turbine unit. Given in this paper is the numerical computation of the runaway speed for a Kaplan turbine of 40 m head. Calculations were carried out for a series of steady-state operating conditions with different runner speeds and the speed at which the torque on the runner shaft is equal to zero was determined. Two approaches for numerical simulation were compared. In the first one, the flow in the turbine was simulated using 3-D RANS equations of incompressible fluid using
k-ε
model of the turbulence. In the second approach, cavitation phenomena were taken into account using two-phase Zwart-Gerber-Belamri (ZGB) cavitation model. Steady-state computations were carried out in computational domain that included one guide vane channel, one runner channel, the whole draft tube, and the clearances between the runner blade and the hub as well as between the blade and the runner chamber. When setting the boundary conditions, the turbine head, being the difference of energies in the inlet and outlet cross-sections, is pre-set as a constant value, while the discharge and the runner torque are determined in the process of computation. The computed runaway speed is compared to that obtained in the model tests. It is shown that the numerical prediction of the runaway speed using the cavitation model achieves better matching with the experimental data.
Electrohydrodynamic (EHD) devices show many advantages over classical ones and have found wide application in various fields of engineering, in particular, for the heat transfer enhancement. The ...paper studies numerically the flow-type electroconvective heat exchanger that bases on both EHD pumping and mixing near the heater. The problem of the computer simulation of a realistic EHD heat exchanger is resolved by virtue of reduced model resource intensity—a technique for 3D/2D model substitution for a novel streamlined electrode configuration is proposed. The integral characteristics of EHD heat exchanger at hand are presented.
•A mixing EHD heat exchanger with streamlined electrode configuration improve heat removing without hindering external flow.•The performance of the mixing EHD heat exchanger can be quantified using the proposed 3D/2D model substitution technique.•The technique for 3D/2D model substitution reduces the computation time and computing requirements by a factor of hundreds.
The present study focuses on the investigation of the oxidized cell-free DNA (cfDNA) properties in several experimental models, including cultured cerebellum cells, peripheral blood lymphocytes ...(PBL), plasma, and hippocampus under an acute and chronic unpredictable stress model in rats. Firstly, our study shows that Spectrum Green fluorescence-labeled oxidized cfDNA fragments were transferred into the cytoplasm of 80% of the cerebellum culture cells; meanwhile, the nonoxidized cfDNA fragments do not pass into the cells. Oxidized cfDNA stimulates the antioxidant mechanisms and induction of transcription factor NRF2 expression, followed by an activation of NRF2 signaling pathway genes—rise of Nrf2 and Hmox1 gene expression and consequently NRF2 protein synthesis. Secondly, we showed that stress increases plasma cfDNA concentration in rats corresponding with the duration of the stress exposure. At the same time, our study did not reveal any significant changes of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG) level in PBL of rats under acute or chronic stress, probably due to the significantly increased Nrf2 expression, that we found in such conditions. 8-oxodG is one of the most reliable markers of DNA oxidation. We also found an increased level of 8-oxodG in the hippocampal homogenates and hippocampal dentate gyrus in rats subjected to acute and chronic stress. Taken together, our data shows that oxidized cfDNA may play a significant role in systemic and neuronal physiological mechanisms of stress and adaptation.
Nowadays, the development of multifrequency high-power subterahertz gyrotrons for electron cyclotron (EC) heating and plasma diagnostics is in great demand. The article examines the prospects of ...using a special two-channel quasi-optical converter for the output of radiation at several frequencies through two separate windows. The converter was developed by hybrid synthesis and the MoM/electric field integral equation (EFIE) method. The approach is being investigated for the gyrotron with a frequency of 250 GHz and a power of up to 330 kW. The designed system makes it possible to output radiation at up to five frequencies in the range of 176-250 GHz with efficiency at the level of optimized single-frequency gyrotrons.
Issues related to measuring the radio frequency (RF) power as the main parameter characterizing the intensity of electromagnetic radiation at microwave frequencies in closed transmission paths are ...considered. RF power measurements within the mm-wavelength range are widely used in radio communications, radio navigation, and radiolocation. In order to ensure the uniformity of RF power measurements within the frequency range of 78.33–118.1 GHz, GET 167-2017 State Primary Standard of the unit of power of electromagnetic oscillations in waveguides within the frequency range from 37.5 to 78.33 GHz was improved. To this end, the upper frequency limit of GET 167-2017 was extended by developing a set of bolometric converters in 2.4 × 1.2 and 2.54 × 1.27 mm (WR10) waveguides, as well as calorimeter and comparator systems. A schematic representation, technical characteristics, and results of metrological studies on GET 167-2021 State Primary Standard of the unit of power of electromagnetic oscillations in the frequency range from 37.5 to 118.1 GHz are provided. Taking the effect of the reduced waveguide cross-section into account, procedures for estimating error components associated with realizing and transferring the RF power unit were revised. The study results confirmed the high accuracy of the standard, which now occupies a leading position among similar national standards.
The results of digital simulation of the lithium peroxide formation during the lithium–oxygen battery discharge are presented. The active layer of the positive electrode is described by the simplest ...monoporous model of a porous medium (a set of sinuous homogeneous non-intersecting pores of constant radius). The influence of the active layer thickness on the positive electrode dimensional characteristics during the galvanostatic discharge of the lithium–oxygen battery is investigated. The dependence of the discharge capacity on the positive electrode active layer thickness was shown to have an extreme character. With increase in the positive electrode active layer thickness the initial section of the increase in the calculated capacity is replaced by a section of a decrease in the capacity. It was found that the process of lithium peroxide molecules’ generation mainly occurs within a narrow region where the pore mouths are in contact with the gas phase. The calculations show that the optimal thickness of the positive electrode active layer is very small (of the order of tens of microns).
The paper presents the results of a computer simulation of lithium peroxide formation accompanying the discharge of a lithium-air battery (LAB). Two models (biporous and regular biporous) of the ...structure of the cathode active layer (AL) were compared based on our previous computer simulation of LAB discharge. The use of the regular biporous model was shown to be preferable. The effect of the initial pore radius in the cathode AL on the discharge characteristics was revealed. The discharge characteristics were significantly improved when the initial pore size increased. The use of the regular biporous model together with an attempt to increase the initial pore radius in the cathode AL structure makes it possible to increase the current density and specific capacity of the cathode during LAB discharge by several orders of magnitude.
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