Multi-objective shape optimization of a hydraulic turbine runner using efficiency,strength and weight criteria

An approach for multi-discipline automatic optimization of the hydraulic turbine runner shape is presented. The approach accounts hydraulic efficiency, mechanical strength and the weight of the runner. In order to effectively control the strength and weight of the runner, a new parameterization of the blade thickness function is suggested. Turbine efficiency is evaluated through numerical solution of Reynolds-averaged Navier-Stokes equations, while the finite element method is used to evaluate the von Mises stress in the runner. An objective function, being the weighted sum of maximal stress and the blade volume, is suggested to account for both the strength and weight of the runner. Multi-objective genetic algorithm is used to solve the optimization problem. The suggested approach has been applied to automatic design of a Francis turbine runner. Series of three-objective optimization runs have been carried out. The obtained results clearly indicate that simultaneous account of stress and weight objectives accompanied by thickness variation allows obtaining high efficiency, light and durable turbine runners.     

Small RNA F6 Provides Mycobacterium smegmatis Entry into Dormancy

Regulatory small non-coding RNAs play a significant role in bacterial adaptation to changing environmental conditions. Various stresses such as hypoxia and nutrient starvation cause a reduction in the metabolic activity of Mycobacterium smegmatis, leading to entry into dormancy. We investigated the functional role of F6, a small RNA of M. smegmatis, and constructed an F6 deletion strain of M. smegmatis. Using the RNA-seq approach, we demonstrated that gene expression changes that accompany F6 deletion contributed to bacterial resistance against oxidative stress. We also found that F6 directly interacted with 5′-UTR of MSMEG_4640 mRNA encoding RpfE2, a resuscitation-promoting factor, which led to the downregulation of RpfE2 expression. The F6 deletion strain was characterized by the reduced ability to enter into dormancy (non-culturability) in the potassium deficiency model compared to the wild-type strain, indicating that F6 significantly contributes to bacterial adaptation to non-optimal growth conditions.     

Nitrogen and Luminescent Nitrogen‐Vacancy Defects in Detonation Nanodiamond

An efficient method to investigate the microstructure and spatial distribution of nitrogen and nitrogen‐vacancy (N‐V) defects in detonation nanodiamond (DND) with primary particle sizes ranging from approximately 3 to 50 nm is presented. Detailed analysis reveals atomic nitrogen concentrations as high as 3 at% in 50% of diamond primary particles with sizes smaller than 6 nm. A non‐uniform distribution of nitrogen within larger primary DND particles is also presented, indicating a preference for location within the defective central part or at twin boundaries. A photoluminescence (PL) spectrum with well‐pronounced zero‐phonon lines related to the N‐V centers is demonstrated for the first time for electron‐irradiated and annealed DND particles at continuous laser excitation. Combined Raman and PL analysis of DND crystallites dispersed on a Si substrate leads to the conclusion that the observed N‐V luminescence originates from primary particles with sizes exceeding 30 nm. These findings demonstrate that by manipulation of the size/nitrogen content in DND there are prospects for mass production of nanodiamond photoemitters based on bright and stable luminescence from nitrogen‐related defects.     

Efficient photochromic transformation of a new fluorenyl diarylethene: one- and two-photon absorption spectroscopy

Efficient reversible phototransformation of a new diarylethene-fluorene derivative, 1,2-bis(5-(9,9-didecyl-7-nitro-9H-fluoren-2-yl)-2-methylthiophen-3-yl)cyclopent-1-ene (1), was demonstrated in organic media under low-intensity laser excitation. Linear photophysical characterization of 1 was performed at room temperature in solvents of different polarity and viscosity. Significantly, close to unity quantum yield for the cyclization reaction of 1 was shown in nonpolar solutions. The lifetimes of the excited states of the open (OF) and closed (CF) forms of 1 were measured by a femtosecond transient absorption technique, and corresponding values of ～0.7 and ～0.9 ps were shown in dichloromethane (DCM), respectively. Degenerate two-photon absorption (2PA) spectra of the OF and CF of 1 were obtained over a broad spectral range by the open aperture Z-scan method under 1 kHz femtosecond excitation. The values of 2PA cross sections of the OF in DCM (～50-70 GM) were found to increase up to 1 order of magnitude (～600 GM) after cyclization to the CF. The nature of cyclization and cylcoreversion processes were investigated by quantum chemistry with employment of DFT-based methods implemented in the Gaussian'09 program. The potential of 1 for application in optical data storage was shown using poly(methyl methacrylate)-doped films and two-photon fluorescence microscopy readout.     

A classical molecular dynamics study of the correlation between the Bredig transition and thermal conductivity of stoichiometric uranium dioxide

Thermophysical properties of uranium dioxide are investigated by classical molecular dynamics for temperatures from 300 K to 3000 K. An increase of specific heat in the temperature range from 1300 K to 2500 K is noted. Comparison with a theoretical model shows that the origin of this behavior is only due to anharmonicity. Such characteristic features of the Bredig transition as the peak in specific heat and high ionic conductivity are investigated. We show that one more important feature was left unnoticed: the rise in the lattice contribution to thermal conductivity at high temperatures. An explanation is provided for this effect which is specific to superionic conductors. Reasonable agreement with experimental data up to 3000 K is obtained for thermal conductivity, even in the absence of electronic excitations.     

Tunable order in colloids of hard magnetic hexaferrite nanoplatelets

Structural ordering in the concentrated magnetic colloids containing 50×5 nm hard magnetic disc-like SrFe₁₂O₁₉ nanoparticles was investigated by cryogenic scanning electron microscopy,optical microscopy,magnetic measurements,and small-angle X-ray scattering.It was revealed that macroscopically homogeneous magnetic liquid consists of dynamic threads of stacked nanoparticles.The threads align into quasiperiodic arrays with the distances between individual threads of a few micrometers.They also can form pseudodomain structures with -90°domain boundaries realized through T-type thread interconnects.The effects of magnetic attraction and electrostatic repulsion on the equilibrium interplatelet distance in the threads were studied.It was demonstrated that this distance can be tuned by the control of the particles charge and electric double layer screening from Stern layer thickness(-1 nm)to tens of nanometers.It was shown that the permanent magnetic field is not able to cause any structural changes in the ordered magnetic liquid phase,while alternating field draws particles apart by their vibrations.External variation of interparticle distance up to 6%was achieved using an alternating magnetic field of low intensity.Experimental data were complemented by the theoretical models of screened electrostatic interactions between spherical and platelike magnetic particles.The last model provides good predictive power and correlates with the experimental data.The stabilization energy of the condensed phase in the order of 1-10 kBT was derived from the model.An approach allows controlling of an equilibrium interparticle distance and interparticle distance distribution by adjusting the magnetization and surface charge of the particles as well as the ionic strength of the solvent.     

Iron Mobilization from Ferritin in Yeast Cell Lysate and Physiological Implications

Most in vitro iron mobilization studies from ferritin have been performed in aqueous buffered solutions using a variety of reducing substances. The kinetics of iron mobilization from ferritin in a medium that resembles the complex milieu of cells could dramatically differ from those in aqueous solutions, and to our knowledge, no such studies have been performed. Here, we have studied the kinetics of iron release from ferritin in fresh yeast cell lysates and examined the effect of cellular metabolites on this process. Our results show that iron release from ferritin in buffer is extremely slow compared to cell lysate under identical experimental conditions, suggesting that certain cellular metabolites present in yeast cell lysate facilitate the reductive release of ferric iron from the ferritin core. Using filtration membranes with different molecular weight cut-offs (3, 10, 30, 50, and 100 kDa), we demonstrate that a cellular component >50 kDa is implicated in the reductive release of iron. When the cell lysate was washed three times with buffer, or when NADPH was omitted from the solution, a dramatic decrease in iron mobilization rates was observed. The addition of physiological concentrations of free flavins, such as FMN, FAD, and riboflavin showed about a two-fold increase in the amount of released iron. Notably, all iron release kinetics occurred while the solution oxygen level was still high. Altogether, our results indicate that in addition to ferritin proteolysis, there exists an auxiliary iron reductive mechanism that involves long-range electron transfer reactions facilitated by the ferritin shell. The physiological implications of such iron reductive mechanisms are discussed.     

Numerical Investigation of Effect of Porosity and Fuel Inlet Velocity on Diffusion Filtration Combustion

Methane-air diffusion filtration combustion in a radiative round-jet burner was numerically investigated in this work.The purpose of this study was focused on t...