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The effect of green (514 nm) and ultraviolet (257 nm) pulsed laser light on Ba0.8Sr0.2TiO3/LaMnO3 heterostructure electrical resistance was studied. In 80 ÷ 200 K range illumination induced a trans...

A study of the electrical and photoelectric properties of the heterostructure of barium strontium titanate film on a silicon substrate was performed. The conductivity of the heterostructure signifi...

YVO4:Yb,Er upconversion nanoparticles (UCNPs) are synthesized to study the possibility of using them as nanoprobes to solve biological problems. Aqueous colloidal solutions of UCNPs are injected into the bodies of grape snails. When preparations from animal organs are irradiated with a continuous wave (CW) laser at a wavelength of 980 nm, luminescence is observed in the region of 520–560 nm, due to radiative transitions in Er3+ ions. A comparative analysis of the behavioral activity of animals with injected nanoparticles and control animals with no nanoparticles reveals no signs of toxicity. The nanoparticles are promising as luminescence nanoprobes in biological problems.

Nanoparticles of YVO4 doped with Yb3+ and Er3+ ions, which exhibit upconversion luminescence upon cw laser excitation at 980 nm, are synthesized according to the familiar hydrothermal procedure. Physical and structural features of intermediate products obtained at different technological stages of creating upconversion nanoparticles are established via electron microscopy, Raman spectroscopy, and luminescence microscopy.

Hybrid materials designed for the regeneration of bone defects and consisting of a resorbable ceramic base (tricalcium phosphate, TCP) coated with a layer of hydrophilic biodegradable polymer have been developed. Biocompatibility of the ceramics was evaluated through in vitro tests using cultures of human skin fibroblasts. To increase the therapeutic potential, the created model structures were saturated with the antitumor drug doxorubicin within the composition of the coating of UV-polymerizable hydrogel based on polyacrylamide/polyethylene glycol diacrylate (PAA/PEGDA). The kinetics of drug release was studied by spectrophotometry using saline. The studied hybrid constructs had low cytotoxicity. Saturation of the structures with the antitumor drug resulted in its prolonged release. The results demonstrate the technological feasibility of creating osteoconductive implants based on calcium phosphates suitable for local delivery of antitumor drugs.

We investigate the effect of electric field on the properties of quasi-two-dimensional electron gas at the interface between ferroelectric oxide and insulating oxide in Ba0.8Sr0.2TiO3/LaMnO3 (BSTO/...

A study is performed of the effect irradiation with a series of ultrafast laser pulses at wavelengths of 514 and 257 nm has on the electrical resistivity of Ba0.8Sr0.2TiO3/LaMnO3 heterostructures. In the range of temperatures between 80 and 200 K, irradiation results in a reversible increase in the resistivity of the structure. The characteristic time of resistivity variation is about 10 s.

The results from a comparative analysis of the emission spectra of upconversion YVO4:Yb, Er nanoparticles synthesized in sizes ranging from 10 nm to 1 μm are used to discuss the contribution from high-energy oscillators on the surfaces of nanoparticles to the nonradiative energy transfer between Er3+ ion levels, and to the formation of the red emission band at 660 nm.

We present the results of structural, electronic, and optical properties calculations of BaTiO3/LaMnO3 heterostructure composed of varying number of layers based on first-principles calcula...

The signal of the ultrafast optical Kerr effect (OKE) in liquids, including toluene C7H8, nitrobenzene C6H5NO2, and acetonitrile C2H3N is analyzed. It is shown that considering the correlation between the orientational and librational responses allows us to determine the rise time of the orientational response associated with the inertial nature of molecular rotations over a time interval of 300–500 fs after the impact of a laser pulse, and to increase the accuracy of determining the form of the Raman spectral density function.

Significance In molecular modeling the motion of nuclei, especially hydrogen, cannot be described using the laws of classical mechanics. The importance of nuclear quantum effects has long been appreciated by the ab initio molecular dynamics and by the water simulation communities. However, the vast majority of simulations of biological systems performed at ambient conditions treat atomic motion classically. Even in the new-generation force fields parameterized from quantum mechanics these effects are thought to be minor compared with other inaccuracies at room temperature and pressure. We show that a force field in excellent agreement with quantum mechanical energies and forces will not produce acceptably inaccurate predictions at ambient conditions unless the nuclear motion and interaction are accounted for in the simulation., In many important processes in chemistry, physics, and biology the nuclear degrees of freedom cannot be described using the laws of classical mechanics. At the same time, the vast majority of molecular simulations that employ wide-coverage force fields treat atomic motion classically. In light of the increasing desire for and accelerated development of quantum mechanics (QM)-parameterized interaction models, we reexamine whether the classical treatment is sufficient for a simple but crucial chemical species: alkanes. We show that when using an interaction model or force field in excellent agreement with the “gold standard” QM data, even very basic simulated properties of liquid alkanes, such as densities and heats of vaporization, deviate significantly from experimental values. Inclusion of nuclear quantum effects via techniques that treat nuclear degrees of freedom using the laws of classical mechanics brings the simulated properties much closer to reality.

YVO4:Yb,Er luminescent nanoparticles (NPs) with sizes of 10–700 nm are produced. The use of laser excitation wavelengths of 980 and 257 nm results in the emission of Er3+ ions in the spectral region of 527 and 555 nm. No spectral line of Er3+ ions is recorded at 660 nm, which is indirect evidence of the low efficiency of nonradiative multiphonon intra-ion transitions and the insensitivity of NPs to luminescence quenchers in an aqueous solution.

Spectroscopic data are presented for the motion of molecules in a liquid during double-pulse excitation and registration of the ultrafast optical Kerr effect (OKE). It is shown that selective spectroscopy of individual molecular motions can be achieved by choosing certain parameters of the double-pulse sequence.

Results from the nonresonance spectroscopy of CdS/CdSe quantum dots (composites of CdSe–CdS nanoparticles (core–shell)) are presented. The nonlinear optical properties of CdS/CdSe QDs in PMMA are studied with fs pulses at 1053 nm using the transient lens technique. QDs generate rapidly oscillating signals with amplitude rise times of around 200 fs and decay times of around 500 fs, while pure PMMA polymer only generates an oscillating signal whose envelope coincides with its autocorrelation function.

The quantum size effects of colloid water-organic media synthesized nanocomposites (CdSe–CdS core–shell) in toluene solution is studied. Femtosecond fluorescence up-conversion spectroscopy is used to establish that quantum dots are characterized by a biexponential decay of luminescence kinetics: the decay times are 1.8 and 26.8 ps for nanoparticles with average sizes of 2 nm and 4.5, and 68 ps for nanoparticles with an average size of 2.9 nm.

We present the performance of blind predictions of water-cyclohexane distribution coefficients for 53 drug-like compounds in the SAMPL5 challenge by three methods currently in use within our group. Two of them utilize QMPFF3 and ARROW, polarizable force-fields of varying complexity, and the third uses the General Amber Force-Field (GAFF). The polarizable FF's are implemented in an in-house MD package, Arbalest. We find that when we had time to parametrize the functional groups with care (batch 0), the polarizable force-fields outperformed the non-polarizable one. Conversely, on the full set of 53 compounds, GAFF performed better than both QMPFF3 and ARROW. We also describe the torsion-restrain method we used to improve sampling of molecular conformational space and thus the overall accuracy of prediction. The SAMPL5 challenge highlighted several drawbacks of our force-fields, such as our significant systematic over-estimation of hydrophobic interactions, specifically for alkanes and aromatic rings.

The reported study was supported of the Russian Foundation for Basic Research, research project No. 18-42-160005. The work is partially performed according to the Russian Government Program of Competitive Growth of Kazan Federal University. A.S. Elshin thanks the Russian Foundation for Basic Research for financial support, project No. 17-32-50047.

Using the hydrothermal method, we synthesized water soluble YVO4: Yb, Er nanoparticles with a size less than 10 nm. Nanoparticles exhibit intense luminescence in the green region due to Er3+ ions when excited by laser radiation at a wavelength of 980 nm as a result of the up-conversion process. Bright and stable luminescence also persists in an aqueous solution of nanoparticles. Based on experimental data, it can be argued that the objects obtained are promising in biological applications, as well as up-conversion phosphors.

The standard approach to calculating the dielectric constant from molecular dynamics (MD) simulations employs a variant of the Kirkwood-Fröhlich methodology. Many popular nonpolarizable models of water, such as TIPnP, give a reasonable agreement with the experimental value of 78. However, it has been argued in the literature that the dipole moments of these models are effective, being smaller than the real dipole of a liquid water molecule by about a factor of [Formula: see text], or roughly [Formula: see text]. If the total or corrected dipole moment is used in calculations, the dielectric constant comes out nearly twice as large, i.e., in the range of 160, which is twice as high as the experimental value. Here we discuss possible reasons for such a discrepancy. One approach takes into account dynamic corrections due to the dependence of the dielectric response of the medium producing the reaction field on the time scale of dipole fluctuations computed in the Kirkwood-Fröhlich method. When dynamic corrections are incorporated into the computational scheme, a much better agreement with the experimental value of the dielectric constant is found when the corrected (real) dipole moment of liquid water is used. However, a formal analysis indicates that the static properties, such as dielectric constant, should not depend on dynamics. We discuss the resulting conundrum and related issues of simulations of electrostatic interactions using periodic boundary conditions in the context of our findings.

Results from studying the effect of ultrashort laser pulses with a wavelength of 514 nm on the electrical resistance of the LAO/STO heterostructure in the temperature range of 80–290 K are discussed. A reversible increase in sample resistance upon irradiation with light over the range of temperature changes is detected.

Bulk SrTiO3 doped by 40 keV Cr+ ions and substrate temperature Timp = 600°C is studied. This sample exhibits supercontinuum generation by amplified femtosecond laser pulses (λ = 800 nm; repetition rate, 3 kHz; pulse duration, 150 fs; pulse energy 4 µJ), recorded by a monochromator with a PMT. The blue edges of the supercontinuum spectra differ, depending on the location of the focused laser beam spot on the sample.

The first experimental results on selective detection of the collective (libration) response in a liquid using a scheme of non-resonance double-pulse spectroscopy based on detecting the ultrafast optical Kerr effect (OKE) in ortho-dichlorobenzene at room temperature are presented. Nonrelevant vibrational and rotational responses are dumped and the relevant libration molecular responses are amplified by varying the duration, delay, and relative intensities of linearly polarized pump pulses.

We report the results of core-shell (CdSe/CdS) quantum dots study. Quantum dots sizes were evaluated as 2.0 and 2.9 nm from absorbance edge position. We suggest two types of traps, predict properties of these traps based on upconversion luminescence data and previous studies of quantum dots (CdSe cores only) and bulk CdS.

In this study, we present a two-range magnetoelectric ME sensor design comprising of permendur (alloy of Fe-Co-V), nickel, and lead zirconate titanate (PZT) laminate composite. A systematic study was conducted to clarify the contribution of magnetostrictive layers variables to the ME response over the applied range of magnetic bias field. The two-range behavior was characterized by opposite sign of the ME response when magnetic dc bias is in different sub-ranges. The ME coefficient as a function of magnetic bias field was found to be dependent on the laminate composite structure.

Although a great number of computational models of water are available today, the majority of current biological simulations are done with simple models, such as TIP3P and SPC, developed almost thirty years ago and only slightly modified since then. The reason is that the non-polarizable force fields that are mostly used to describe proteins and other biological molecules are incompatible with more sophisticated modern polarizable models of water. The issue is electronic polarizability: in liquid state, in protein, and in vacuum the water molecule is polarized differently, and therefore has different properties; thus the only way to describe all these different media with the same model is to use a polarizable water model. However, to be compatible with the force field of the rest of the system, e.g. a protein, the latter should be polarizable as well. Here we describe a novel model of water that is in effect polarizable, and yet compatible with the standard non-polarizable force fields such as AMBER, CHARMM, GROMOS, OPLS, etc. Thus the model resolves the outstanding problem of incompatibility., 38 pages, 5 figures, 2 tables

The issues of electronic polarizability in molecular dynamics simulations are discussed. We argue that the charges of ionized groups in proteins, and charges of ions in conventional non-polarizable force fields such as CHARMM, AMBER, GROMOS, etc should be scaled by a factor about 0.7. Our model explains why a neglect of electronic solvation energy, which typically amounts to about a half of total solvation energy, in non-polarizable simulations with un-scaled charges can produce a correct result; however, the correct solvation energy of ions does not guarantee the correctness of ion-ion pair interactions in many non-polarizable simulations. The inclusion of electronic screening for charged moieties is shown to result in significant changes in protein dynamics and can give rise to new qualitative results compared with the traditional non-polarizable force field simulations. The model also explains the striking difference between the value of water dipole $\mu$~3D reported in recent ab initio and experimental studies with the value $\mu_{eff}$~2.3D typically used in the empirical potentials, such as TIP3P or SPC/E. It is shown that the effective dipole of water can be understood as a scaled value $\mu_{eff}=\mu/\sqrt{\epsilon_{el}}$, where $\epsilon_{el}$=1.78 is the electronic (high-frequency) dielectric constant of water. This simple theoretical framework provides important insights into the nature of the effective parameters, which is crucial when the computational models of liquid water are used for simulations in different environments, such as proteins, or for interaction with solutes., Comment: 53 pages, 6 figures, 3 tables