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- Computational modeling of In vitro swelling of mitochondria: A biophysical approachPublication . Makarov, Vladimir I.; Khmelinskii, Igor; Javadov, SabzaliSwelling of mitochondria plays an important role in the pathogenesis of human diseases by stimulating mitochondria-mediated cell death through apoptosis, necrosis, and autophagy. Changes in the permeability of the inner mitochondrial membrane (IMM) of ions and other substances induce an increase in the colloid osmotic pressure, leading to matrix swelling. Modeling of mitochondrial swelling is important for simulation and prediction of in vivo events in the cell during oxidative and energy stress. In the present study, we developed a computational model that describes the mechanism of mitochondrial swelling based on osmosis, the rigidity of the IMM, and dynamics of ionic/neutral species. The model describes a new biophysical approach to swelling dynamics, where osmotic pressure created in the matrix is compensated for by the rigidity of the IMM, i.e., osmotic pressure induces membrane deformation, which compensates for the osmotic pressure effect. Thus, the effect is linear and reversible at small membrane deformations, allowing the membrane to restore its normal form. On the other hand, the membrane rigidity drops to zero at large deformations, and the swelling becomes irreversible. As a result, an increased number of dysfunctional mitochondria can activate mitophagy and initiate cell death. Numerical modeling analysis produced results that reasonably describe the experimental data reported earlier.
- External control of the Drosophila melanogaster egg to imago development period by specific combinations of 3D low-frequency electric and magnetic fieldsPublication . Makarov, Vladimir I.; Khmelinskii, IgorWe report that the duration of the egg-to-imago development period of the Drosophila melanogaster, and the imago longevity, are both controllable by combinations of external 3-dimensional (3D) low-frequency electric and magnetic fields (LFEMFs). Both these periods may be reduced or increased by applying an appropriate configuration of external 3D LFEMFs. We report that the longevity of D. melanogaster imagoes correlates with the duration of the egg-to-imago development period of the respective eggs. We infer that metabolic processes in both eggs and imago are either accelerated (resulting in reduced time periods) or slowed down (resulting in increased time periods). We propose that external 3D LFEMFs induce electric currents in live systems as well as mechanical vibrations on sub-cell, whole-cell and cell-group levels. These external fields induce media polarization due to ionic motion and orientation of electric dipoles that could moderate the observed effects. We found that the longevity of D. melanogaster imagoes is affected by action of 3D LFEMFs on the respective eggs in the embryonic development period (EDP). We interpret this effect as resulting from changes in the regulation mechanism of metabolic processes in D. melanogaster eggs, inherited by the resulting imagoes. We also tested separate effects of either 3D electric or 3D magnetic fields, which were significantly weaker.
- Quantum spin polarization effect in multi-nanolayer structuresPublication . Makarov, Vladimir I.; Khmelinskii, IgorWe studied the spin-polarized state transport in Fe-SnO2-Ag and Fe-BeO-Ag three-nanolayer sandwich structures. The exchange-resonance spectra of these sandwich structures are quite specific and different from those observed earlier in other three-nanolayer structures. The presently recorded spectra comprise a set of discrete lines, their width increasing with the sample temperature and also with the Ag layer thickness, for both samples. The linewidth dependences on temperature and Ag layer thickness were studied in detail. The effect of thickness of the intermediate nanolayers of SnO2 and BeO on the linewidth was also explored. To explain the observed line broadening effects, we proposed and developed the spin-orbit (SO) coupling mechanism of the electron spin relaxation. In the frameworks of this mechanism, we assumed that the electron spin of a bonding electron in one of the layers of the sandwich system is coupled by SO interaction with the other layers. We found that the change in phonon densities affects the linewidths of the exchange resonance spectra. We estimated the values of the model parameters from the analysis of the experimental data. To that end, we continue further development of our earlier theoretical model, using it to interpret the current experimental results, including ab initio calculations of the electronic structure. The exchange resonance spectra were simulated using phenomenological model, where the anisotropy of the g-factor was introduced. We performed ab initio simulations of the exchange resonance spectra and their linewidths, using Gaussian-2000 and a homemade FORTRAN code.
- Quantum confinement in semiconductor nanofilms: Optical spectra and multiple exciton generationPublication . Khmelinskii, Igor; Makarov, Vladimir I.We report optical absorption and photoluminescence (PL) spectra of Si and SnO2 nanocrystalline films in the UV-vis-NIR range, featuring discrete bands resulting from transverse quantum confinement, observed in the optical spectra of nanofilms for the first time ever. The film thickness ranged from 3.9 to 12.2 nm, depending on the material. The results are interpreted within the particle-in-a-box model, with infinite walls. The calculated values of the effective electron mass are independent on the film thickness and equal to 0.17m(o) (Si) and 0.21m(o) (SnO2), with m(o) the mass of the free electron. The second calculated model parameter, the quantum number n of the HOMO (valence band), was also thickness-independent: 8.00 (Si) and 7.00 (SnO2). The transitions observed in absorption all start at the level n and correspond to Delta n =1, 2, 3,.... The photoluminescence bands exhibit large Stokes shifts, shifting to higher energies with increased excitation energy. In effect, nanolayers of Si, an indirect-gap semiconductor, behave as a direct-gap semiconductor, as regards the transverse-quantized level system. A prototype Si-SnO2 nanofilm photovoltaic cell demonstrated photoelectron quantum yields achieving 2.5, showing clear evidence of multiple exciton generation, for the first time ever in a working nanofilm device. (C) 2016 Elsevier B.V. All rights reserved.
- Spin-anticrossing effects in Co-SiO2-Fe and ZnO-SiO2-CuO three-nanolayer devicesPublication . Khmelinskii, Igor; Makarov, Vladimir I.Presently we report measurements of the spin-anticrossing spectra in the Co-SiO2-Fe and ZnO-SiO2-CuO three-nanolayer sandwich structures. The spin-anticrossing spectra in these systems are quite specific, differing from those observed earlier in other similar structures built of different materials. The theoretical model developed earlier is extended and used to interpret the available experimental results. A detailed ab initio analysis of the magnetic-field dependence of the output magnetic moment is also performed. The model predicts a spin-anticrossing spectrum comprising a series of peaks, with the spectral structure determined by several factors, discussed in the paper. Published by Elsevier Ltd.
- Quantum confinement in multi-nanolayer sandwich systemsPublication . Khmelinskii, Igor; Makarov, Vladimir I.Presently we explored quantum confinement (QC) in three-nanolayer sandwich systems, composed of Au-SnO2-Fe, Au-SnO2-Si and Au-SnO2-Ag layers. We recorded the absorption spectra of these sandwich systems, all with discrete structure. We recorded the action spectra of the photocurrent for the Au-SnO2-Fe sandwich system, with the photocurrent quantum yields increasing with the photon energy, achieving 3.1 at 4.7 x 10(4) cm(-1). The photocurrent action spectra correlate with high accuracy with optical absorption spectra. We discuss the mechanisms determining the absorption bandwidth value, including surface imperfections, thermal distribution of the vibrational level populations in the electronic ground state, and the diabatic coupling of levels of the excited state to those of a "dark" state. Volt-Ampere (V/A) characteristics were recorded for all three of the sandwich systems, quite similar to those of a Schottky diode. We report the parameter values of the V/A characteristics, found by fitting the experimental data with a theoretical curve. We also report charge density changes in the SnO2 layer caused by low constant voltage applied to the sandwich structure, observed as changes in the absorption band intensity.
- Quantum confinement in metal nanofilms: Optical spectraPublication . Khmelinskii, Igor; Makarov, Vladimir I.We report optical absorption and photoluminescence spectra of Au, Fe, Co and Ni polycrystalline nanofilms in the UV-vis-NIR range, featuring discrete bands resulting from transverse quantum confinement. The film thickness ranged from 1.1 to 15.6 nm, depending on the material. The films were deposited on fused silica substrates by sputtering/thermo-evaporation, with Fe, Co and Ni protected by a SiO2 film deposited on top. The results are interpreted within the particle-in-a-box model, with the box width equal to the mass thickness of the nanofilm. The transverse-quantized energy levels and transition energies scale as the inverse square of the film thickness. The calculated values of the effective electron mass are 0.93 (Au), 0.027 (Fe), 0.21 (Co) and 0.16 (Ni), in units of me - the mass of the free electron, being independent on the film thickness. The uncertainties in the effective mass values are ca. 2.5%, determined by the film thickness calibration. The second calculated model parameter, the quantum number.n of the HOMO, was thickness independent in Au (5.00) and Fe (6.00), and increased with the film thickness in Co (from 7 to 9) and Ni (from 7 to 11). The transitions observed in the absorbance all start at the level n and correspond to Delta n = +1, +2, +3, etc. The photoluminescence bands exhibit large Stokes shifts, shifting to higher energies with the increased excitation energy. The photoluminescence quantum yields grow linearly with the excitation energy, showing evidence of multiple exciton generation. A prototype Fe-SnO2 nanofilm photovoltaic cell demonstrated at least 90% quantum yield of photoelectrons at 77 K. Published by Elsevier Ltd.
- Macroscopic excitation energy transport in a structured Co nanolayerPublication . Khmelinskii, Igor; Makarov, Vladimir I.We report absorption spectra of the 7.3-and 11.3-nm Co nanolayers and emission of a structured Co nanolayer. The structure contains a 7.3-nm Co nanolayer covering a 25 x 25 mm(2) fused silica substrate, with a thicker 11.3-nm Co track in the middle of the substrate. We report that the radiation energy absorbed by the entire Co nanolayer is transferred to the thicker nanotrack. The transferred energy is reemitted by the track, with the emission spectra containing well-defined emission bands, strongly dependent on the excitation wavelength. We report that the bands appearing in the emission spectra of the nanotrack correspond to the transitions from the higher electronic excited states of the nanotrack to its first excited state. We therefore identify the observed emission as the superemission of the Co nanotrack. The superemission quantum yield is dependent on the excitation wavelength, decreasing at higher excitation energies. We propose a theoretical model that explains the results obtained. The model analysis produced estimates of several model parameters.
- Optical properties of ZnO semiconductor nanolayersPublication . Khmelinskii, Igor; Makarov, Vladimir I.Presently we explore absorption and emission spectra of ZnO semiconductor nanolayers 4.1-17.3 nm thick. We report that their absorption spectra have discrete structure, with the transition band density increasing with the nanolayer thickness. The emission spectra recorded at 4.1 and 9.3 nm thickness have resolved band structure, with the bands partially overlapping in the 9.3 nm sample. On the other hand, the emission spectra are strongly overlapped in the 13.1 and 17.3 nm samples. We used our modeling approach that considers electronic states in a one-dimensional infinite potential well, calculating the relative electron mass of 0.205, and the starting quantum number for the absorption transitions of 7, 8, 9 and 9, for the respective samples. We also discuss the present results using the traditional approach of solid-state physics, considering potential surfaces in the linear momentum space.