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We report on a chemical way to tune the efficiency of second harmonic generation (SHG) by aminothiophene-based molecular crystals (MCs) of a fixed noncentrosymmetric crystal structure. Through the multistep synthesis of three substituted pyrrolo[1,2-a]thieno[3,2-e]pyrimidines, we design a set of MCs of a similar Pna21 space group, providing stable (over 30 min of continuous generation) SHG in a controlled visible spectral range. Substitution of the donor methyl component of the MC with neutral hydrogen and acceptor chlorine leads to an approximately 400-fold increase in SHG efficiency due to 70% growth of the MC's hyperpolarizability. The reported chemical strategy, thereby, opens the way to design MCs and tune their SHG efficiency, being competitive with commercial nonlinear optical crystals.

Tungsten is widely used as a material capable of withstanding extreme operating conditions and is one of the candidates for use in fusion and Generation IV fission reactors. Atomistic modelling implemented to solve various material science problems is an indispensable approach for improving material properties. This work analyzes the interaction of an edge dislocation with a void in single-crystal tungsten with the help of molecular dynamics simulation. Two different approaches for studying the dynamics of dislocations in tungsten that differ in boundary conditions are compared. Multiple interactions of the dislocation and void at different temperatures are investigated, and based on the obtained stress–strain curves, the dislocation obstacle strength for voids having various diameters is defined. It is shown that when applied to a crystal with small voids, the model with the fixed boundary conditions returns incorrect results. Moreover, the influence of the cell size for the model with periodic boundary conditions is analyzed, and the case of a non-central interaction of a dislocation with a void is considered. The obtained results improve our understanding of the mechanical response of irradiated materials.

Abstract—: The article refines the axiomatic foundation of central place theory (CPT) and identifies the possibilities and limitations of a logical transition in research from real settlement systems to central place (CP) systems. The necessity of relying on the CPT axioms in the following form is determined: (1) the space of a CP system is not infinite, but finite: the basis of each system is formed by an isolated lattice; the theory deals with physical space, not mathematical or geographical; (2) the space is homogeneous and isotropic in all respects, except for the distribution of not only the urban, but also the rural population; (3) a hexagonal lattice corresponds to the equilibrium state of an isolated CP system as an attractor; deviations from a hexagonal shape result only from external impact on the system; (4) CP systems are polymorphic: they can exist in modifications with both the same and different values for all levels of the hierarchy and not necessarily an integer value K∈ (1, 7]. The axiom about a consumer’s “rational” behavior is accepted when establishing the CP hierarchy in terms of the volume of functions performed; when establishing their hierarchy in terms of population, it is redundant. In contrast to the foreign approach to CPT, which presupposes the transfer of properties of an ideal CP system to a real settlement system, in the approach of the Russian school, they are compared. The possibility of the latter is due to the equivalence principle in the relativistic version of the theory, according to which settlement systems form in the geographic space similarly to how CP systems form in the physical space. In both cases, if the gravitational effects are compensated, it is impossible to distinguish a settlement system from a CP system; i.e., a heterogeneous and anisotropic geographical space cannot be distinguished from a homogeneous and isotropic physical one. The immediate consequence of this is equivalence, on the one hand, of the population of settlements and CP, and, on the other, the distances between them in real settlement systems and CP systems.

A combined analytical and molecular dynamics model for the electrocaloric effect in ferroelectric poly(vinylidene difluoride‐co‐trifluoroethylene) copolymer (poly(VDF‐co‐TrFE)) is developed. The model calculates the polymer polarization, P, and temperature change under adiabatic electric field variation, ΔT, as functions of temperature. An analytical component of the model is based on the Landau phenomenological theory adapted for modeling of the first order phase transitions in a polymer crystal from a ferroelectric β phase to a paraelectric conformationally disordered (condis) phase. Parameters of the free energy functional are calibrated through molecular dynamics simulations of poly(VDF‐co‐TrFE) perfect crystal. Random orientation and the scatter of the phase transition temperature for various crystallites in a real amorphous‐crystalline polymer are incorporated into the model. Comparison of the model prediction with experimental data shows good agreement for PTwhile the model overestimates the value of ΔTby approximately 2.5 times. We attribute this discrepancy to the presence of structural defects in real polymer crystallites, which reduces the entropy change under the phase transition compared to the perfect crystal simulated in our molecular dynamics approach. The theoretical limit of ΔTcalculated by the model indicates that ΔTcan be increased up to 3 times compared to the currently observed experimental value of ΔT.

Abstract: In recent decades, much interest has been shown in nonlinear lattice vibrations because crystalline materials are subjected to high-amplitude impacts in many fields of human activity. One of the effects of nonlinearity in discrete periodic structures is the possibility of existence of spatially localized high-amplitude vibrations, referred to as discrete breathers (DBs), or intrinsic localized modes. The problem of searching for DBs in nonlinear chains (i.e., one-dimensional crystals) can be solved in a fairly simple way, because the variety of possible DBs is small in this case. However, no general approaches to the search for DBs have been developed for high-dimension crystal lattices. Such an approach was derived based on the works by Chechin, Sakhnenko et al., who developed the theory of bushes of nonlinear normal modes, which (as applied to crystals) were later referred to as delocalized nonlinear vibrational modes (DNVMs). It has recently been noted that all known DBs can be obtained by superimposing localizing functions on DNVMs with a frequency beyond the phonon spectrum of the lattice. Since the Chechin and Sakhnenko theory makes it possible to find all possible DNVMs by considering the lattice symmetry, it has become possible to formulate the problem of determining all possible DBs in a given lattice. This approach has recently been applied with success to the search for DBs in a two-dimensional triangular lattice. The purpose of this study is to analyze and describe DBs in a two-dimensional square lattice obtained using a localizing function. As a result, new types of DBs of a square lattice are obtained, including one-dimensional DBs (i.e., those localized only in one of two orthogonal directions) and zero-dimensional DBs (i.e., those localized in two directions).

Abstract: The influence of discrete breathers (DBs) on the macroscopic properties of the Fermi–Pasta–Ulam chain with symmetric and asymmetric single-well potentials is investigated. The ratio of the total energy to the kinetic energy (which determines the specific heat) was monitored during the development of modulation instability of the short-wavelength vibrational mode with the wavenumber at the boundary of the Brillouin zone. Instability leads to the formation of chaotic DBs with subsequent transition to thermal equilibrium when DBs disappear due to the emission of energy in the form of low-amplitude phonons. The localization parameter, the number of DBs in the chain, and the average energy per one DB are given as functions of time. The number of DBs is close to the maximum at the point in time when the energy localization parameter reaches its maximum. It is found that DBs reduce the heat capacity for all considered parameters of the chain potential. This is due to the fact that the chain under consideration has a hard type of anharmonicity, at which the DB frequency increases with an increase in the amplitude. In the energy localization regime, the DB oscillation frequencies increase, which leads to an increase in the particle velocities and, accordingly, in their kinetic energy. An increase in the kinetic energy in the presence of DBs in the chain leads to a decrease in the ratio of total energy to kinetic energy, that is, to a decrease in the specific heat capacity. In chains with soft anharmonicity, the DB frequency decreases with an increase in the amplitude, and the opposite effect is obtained, i.e., DBs increase the heat capacity in this case. The obtained results can be useful for setting up experiments on the identification of discrete breathers in crystals by measuring their macroscopic properties.

The results of an investigation that focused on the development of an adjustable image contrast method are presented. The method was designed to solve the applied problem of measuring the concentration of contamination of recoverable scrap with cutting fluid to enhance the accuracy of visual inspection methods. The currently used control method is based on visual assessment of the degree of contamination of a sheet of paper after its contact with a sample of contaminated material. The proposed method entails the use of a standard image scanner for digitizing visual information in the form of oil imprints on the paper and its subsequent processing by adjusting the image contrast, which makes it possible to obtain quantitative information on the object under investigation. The principal parameters of oil imprint scanning and subsequent processing of the obtained images were determined during the course of the study. Equations for calculating the values of reduction of cutting fluid content in the cleaned samples with respect to its initial concentration were obtained. The main concepts of the proposed method were formulated. Its main advantage is its simplicity and the use of commonly available, inexpensive control and measuring equipment.

An algorithm is proposed for constructing curves of thermal cooling and ordering kinetics with a monotonic decrease in temperature for alloys to stoichiometric composition. Modeling is carried out by the Monte Carlo method in the model of a rigid crystal lattice and pair interatomic interactions. The application of the algorithm is illustrated by the example to a square lattice, taking into account interatomic interactions in the first two coordination spheres for alloys with the composition AB, A3B, and A3B5. The proposed model makes it possible to calculate individual sections of the phase diagrams to the state for binary alloys.

The molecular mechanism of the large electrocaloric effect in ferroelectric vinylidene difluoride-based polymers was proposed. The mechanism involves the electric field-induced phase transition between the ferroelectric β-phase and the paraelectric conformationally disordered (condis) phase. The condis phase is characterized by the absence of a three-dimensional crystallographic order: there is only two-dimensional translational symmetry in the plane perpendicular to the chain direction. Due to conformational disorder, the entropy of the condis phase is higher than that of the β-phase. A high entropy change at the transition from the β to the condis phase causes a large electrocaloric effect. Molecular dynamics simulations of the poly(vinylidene fluoride-co-trifluoroethylene) (poly(VDF-co-TrFE)) copolymer and poly(vinylidene fluoride–ter–trifluoroethylene–ter–chlorofluoroethylene) (poly(VDF-ter-TrFE-ter-CFE)) and poly(vinylidene fluoride-ter-trifluoroethylene-ter-chlorotrifluoroethylene) (poly(VDF-ter-TrFE-ter-CTFE)) terpolymers were performed. The electrocaloric effect was determined from simulations using two techniques: (i) direct calculation of the temperature drop in adiabatic conditions and (ii) calculation of the entropy difference between β and condis phases from the pair histograms of dihedral angles. Both techniques predict similar temperature drops that validate the proposed molecular mechanism.

Abstract: Nanostructured hollow Co3O4spheres are synthesized by ultrasonic spray pyrolysis. Nanocrystals forming the sphere structure have different sizes and packing density, depending on the synthesis conditions. The samples are studied by X-ray diffraction, scanning electron microscopy, low-temperature nitrogen adsorption, vacuum pycnometry, and Raman and X-ray photoelectron spectroscopies. The field and temperature dependences of magnetization show that the magnetic properties and the Néel temperature of Co3O4hollow spheres are determined by the size and packing density of nanocrystals.

The allotropes of a new layered material, phosphorus carbide (PC), have been predicted recently, and a few of these predicted structures have already been successfully fabricated. Herein, by using first-principles calculations, we investigate the effects of rippling an α-PC monolayer, one of the most stable modifications of layered PC, under large compressive strains. Similar to phosphorene, layered PC is found to have the extraordinary ability to bend and form ripples with large curvatures under a sufficiently large strain applied along its armchair direction. The band gap, work function, and Young’s modulus of a rippled α-PC monolayer are predicted to be highly tunable by strain engineering. Moreover, a direct-indirect band gap transition is observed under compressive strains in the range from 6% to 11%. Another important feature of the α-PC monolayer rippled along the armchair direction is the possibility of its rolling to a PC nanotube (PCNT) under an extreme compressive strain. These tubes of different sizes exhibit high thermal stability, possess a comparably high Young’s modulus, and a well tunable band gap which can vary from 0 to 0.95 eV. In addition, for both structures, rippled α-PC and PCNTs, the changes of their properties under compressive strain are explained in terms of the modification of their structural parameters.

We report a study which exhibits for the first time the catalytic activity of LiMgPO4in the reaction of hydroquinone oxidation. The samples were synthesized by solid state reaction, glycerol-nitrate method and ultrasonic spray pyrolysis. It was proved that LiMgPO4makes the hydroquinone decomposition possible in the absence of irradiation and accelerates it under the action of light. It was determined that the lager is the specific surface area of the catalyst, the higher is the reaction rate constant. The high catalytic activity of LiMgPO4in the oxidation reaction was explained by the existence of defects on the LiMgPO4surface able to adsorb ions, radicals, etc. The UV–vis spectra clearly indicated the existence of defects. The results of voltammetric and NMR studies confirmed that the defective surface of LiMgPO4easily adsorbs molecular and ionic groups of different nature formed during sorption and electrolysis of water.

Impact of regiodefects in the ferroelectric poly(vinylidene difluoride-co-trifluoroethylene) copolymer [poly(VDF-co-TrFE)] on the electrocaloric effect was studied with use of a developed analytical model and molecular dynamics (MD) simulations. It was shown earlier that the electrocaloric effect in these polymers is caused by the first-order phase transition from the ferroelectric β phase to the paraelectric conformationally disordered (condis) phase. MD simulations performed in the current work show that the presence of regiodefects in polymer chains makes this phase transition more gradual, the second order. The proposed analytical model is based on the Landau phenomenological theory of phase transitions, modified to ensure the correct behavior of polymer polarization at low temperatures. The model calculates the polymer polarization, P, and temperature change under adiabatic electric field variation, ΔT, as functions of temperature, applied electric field, and regiodefect concentration. Parameters of the free energy functional are calibrated through MD simulations of the poly(VDF-co-TrFE) crystal. The obtained results show that presence of regiodefects substantially changes the form of dependencies P(T) and ΔT(T), which significantly shifts them closer to experimental data.

Abstract: The dynamics of a three-component nonlinear delocalized vibrational mode in graphene is studied with molecular dynamics. This mode, being a superposition of a root and two one-component modes, is an exact and symmetrically determined solution of nonlinear equations of motion of carbon atoms. The dependences of a frequency, energy per atom, and average stresses over a period that appeared in graphene are calculated as a function of amplitude of a root mode. We showed that the vibrations become periodic with certain amplitudes of three component modes, and the vibrations of one-component modes are close to periodic one and have a frequency twice the frequency of a root mode, which is noticeably higher than the upper boundary of a spectrum of low-amplitude vibrations of a graphene lattice. The data obtained expand our understanding of nonlinear vibrations of graphene lattice.

Abstract: Using the method of molecular dynamics and taking Ni3Al and Pt3Al as examples, crystals of the A3B composition are considered for the possibility of excitation of soliton-type waves in them. The potentials obtained by the embedded-atom method were used to describe interatomic interactions. It is shown that the harmonic external stimulus can excite waves of the soliton type in a Pt3Al crystal, but not in Ni3Al. Such compression–expansion waves are generated because of excitation of discrete breathers with soft nonlinearity that cannot exist in a Ni3Al crystal near the affected region. The detected waves are capable of propagating to thousands of nanometers along the Pt3Al crystal without losses of integrity and speed. The shape of the obtained wave corresponds to the kink solution of the sine-Gordon equation. The aggregate amount of energy transferred by a wave is determined by the number of rows of atoms involved in fluctuations; this may involve dozens and hundreds of electron volts.

We study two events of structured Pc1 waves (pearls) observed by CARISMA magnetometers during a period of quiet magnetic (Kp~1) and solar wind conditions on 1 August 2008. Bursts of proton precipitations and electromagnetic ion‐cyclotron waves were simultaneously observed by NOAA/POES and GOES satellites at dayside. Apparent correspondence was found between ground pearl pulsations and magnetospheric compressions observed by GOES and THEMIS satellites. We have found the Pc1 wave splitting into very close subfrequencies (within 0.1 Hz) that can be explained by weak magnetospheric compressions. The compressions are caused by pressure pulses originated from transient foreshock and interplanetary magnetic field discontinuities observed upstream of the bow shock by the THEMIS‐C probe. Thus, the observed pearls are compression‐related Pc1 waves generated under transient foreshock conditions. Pc1 pearls at morning and EMIC waves on the dayside are found during quiet timePearls and EMIC waves are associated with weak and transient magnetospheric compressionsMagnetospheric compressions are produced by foreshock pressure pulses

A sharp (several orders of magnitude) increase of chain mobility was observed at a certain temperature in molecular dynamics simulation of the polyethylene crystal. Chain mobility as a function of temperature in a polyethylene perfect crystalline structure was studied by applying molecular dynamics simulation with COMPASS and flexible Williams force fields. Three crystallographic crystalline phases of polyethylene were observed in the simulations in both force fields: orthorhombic, monoclinic, and conformationally disordered (condis) phases. There is no three-dimensional crystallographic order in the condis phase—only two-dimensional translational symmetry, which was observed in the plane perpendicular to the chain direction. The simulations show that the chain mobility undergoes a dramatic increase by several orders of magnitude at the transition from monoclinic to condis phase of the crystal. In the condis phase, mobility is almost independent of temperature, which indicates that the diffusion activation energy is less than kT. The calculated mobility in the condis phase is almost the same in both force fields. The calculated kinetic energy of the system per C–C bond at the temperature of the monoclinic → condis transition is approximately equal to the barrier of torsion (trans-eclipsed-trans) around the C–C bond.

Background: Uterine fibroid embolization (UFE) is as an effective alternative to hysterectomy and myomectomy. However, UFE is associated with a wide spectrum of complications including in rare instances thromboembolic events and even pulmonary embolism (PE). Case Presentation: A case of a 36-year-old woman suffering from a symptomatic uterine fibroid is described as follows. The patient underwent UFE and overnight she suddenly collapsed with signs of massive PE. In consequence of cardiopulmonary resuscitation and urgent systemic thrombolytic therapy, cardiac activity was restored successfully. Discussion & Conclusion: This constitutes another report of PE developed following UFE. In the case described here PE occurred 26 hours after the procedure was performed. Before UFE all patients should undergo complete examination for exclusion of pre-existing venous deep thrombosis and coagulopathies.

Drug-drug interaction (DDI) is the phenomenon of alteration of the pharmacological activity of a drug(s) when another drug(s) is co-administered in cases of so-called polypharmacy. There are three types of DDIs: pharmacokinetic (PK), pharmacodynamic, and pharmaceutical. PK is the most frequent type of DDI, which often appears as a result of the inhibition or induction of drug-metabolising enzymes (DME). In this review, we summarise in silico methods that may be applied for the prediction of the inhibition or induction of DMEs and describe appropriate computational methods for DDI prediction, showing the current situation and perspectives of these approaches in medicinal and pharmaceutical chemistry. We review sources of information on DDI, which can be used in pharmaceutical investigations and medicinal practice and/or for the creation of computational models. The problem of the inaccuracy and redundancy of these data are discussed. We provide information on the state-of-the-art physiologically- based pharmacokinetic modelling (PBPK) approaches and DME-based in silico methods. In the section on ligand-based methods, we describe pharmacophore models, molecular field analysis, quantitative structure-activity relationships (QSAR), and similarity analysis applied to the prediction of DDI related to the inhibition or induction of DME. In conclusion, we discuss the problems of DDI severity assessment, mention factors that influence severity, and highlight the issues, perspectives and practical using of in silico methods.

Pressure welding (PW) is an advanced method for obtaining solid phase joints (SPJs). Using physical and finite element modelling (FEM) it is shown that PW under superplasticity conditions provides SPJs between dissimilar cast single-crystal intermetallic and deformed polycrystalline heat-resistant Ni-based superalloys. Special attention is paid to exclude the stagnant zones in the solid phase joining region using surface relief. The results of physical modelling and FEM are in qualitative agreement. It is revealed that the surface relief can decrease the stagnant zone and increase localisation of deformation in the joining region, which helps to improve the joining quality. A monotonous change in microhardness in the joint zone is shown.

ABSTRACTPressure welding (PW) is an advanced method for obtaining solid phase joints (SPJs). Using physical and finite element modelling (FEM) it is shown that PW under superplasticity conditions provides SPJs between dissimilar cast single-crystal intermetallic and deformed polycrystalline heat-resistant Ni-based superalloys. Special attention is paid to exclude the stagnant zones in the solid phase joining region using surface relief. The results of physical modelling and FEM are in qualitative agreement. It is revealed that the surface relief can decrease the stagnant zone and increase localisation of deformation in the joining region, which helps to improve the joining quality. A monotonous change in microhardness in the joint zone is shown.

Collisions of C20and C540fullerenes are studied in a wide range of velocities by means of classical molecular dynamics. The simulations show that the collision scenario strongly depends on the collision velocity of the fullerenes. At low collision energies, the fullerenes are repelled by the van der Waals forces, and after bouncing off a part of the kinetic energy of their translational motion is converted into the energy of cage vibrations. At higher collision energies, the fullerenes overcome the potential barrier of Pauli repulsion with the formation of the new chemical bonds, and a significant change in the geometry of the molecules is observed. At very high collision energies, structure of the molecules is destroyed with the formation of new carbon clusters. Analysis of collisions for fullerenes of significantly different size revealed some new features associated with their asymmetric energy exchange.

Molecular dynamics is applied to study the effect of crystallographic orientation on the plastic deformation mechanisms and mechanical properties of NiAl intermetallic nanofilms subjected to uniaxial tension. It is observed that the deformation mechanisms qualitatively depend on the crystallographic orientation of the nanofilms with respect to the loading direction. Plastic deformation of the nanofilms along [557] crystallographic direction is associated with the edge dislocation sliding in the slip system [001](110). As for the nanofilms stretched along [554] and [111] directions, their deformation occurs first through the dislocation sliding followed by the formation of (112)[11 1] twins. Uniaxial tension of the nanofilms along [559] and [55 11] leads to the nucleation and growth of a martensitic phase followed by their rupture along an interface. The maximum (minimum) strength of 9.9 (7.0) GPa is observed for the nanofilms stretched along the [559] ([554]) crystallographic direction, while the largest (smallest) strain to failure of 27 (15)% is for [559] ([55 11]). Various deformation mechanisms of the nanofilms are explained through computing the Schmid factor for the operational slip system. The results indicate that the crystallographic orientation is among the key parameters controlling the deformation mechanisms and mechanical properties of intermetallic nanofilms.

Sensing with optical whispering gallery modes (WGMs) is a rapidly developing detection method in modern microfluidics research. This method explores the perturbations of spectra of WGMs propagating along the wall of an optical microcapillary to characterize the liquid medium inside it. Here we show that WGMs in a silica microcapillary can be fully localized (rather than perturbed) by evanescent coupling to a water droplet and, thus, form a high-quality-factor microresonator. The spectra of this resonator, measured with a microfiber translated along the capillary, present a hierarchy of resonances that allow us to determine the size of the droplet and variation of its length due to the evaporation. The resolution of our measurements of this variation equal to 4.5 nm is only limited by the resolution of the optical spectrum analyzer used. The discovered phenomenon of complete localization of light in liquid-filled optical microcapillaries suggests a new type of microfluidic photonic device as well as an ultraprecise method for microfluidic characterization.

Fast acting quasi-3D model of proton exchange membrane fuel cell (PEMFC) is developed. The model utilizes multi-scale approach taking advantage of large difference in the spatial scales in the direction along and perpendicular to the gas channels. This allows to decompose the numerical solution of 3D reaction-transport equations on the 2D problem in the plane perpendicular to the gas channels and 1D equations along the channels. The model is formulated in terms of Characteristic Currents (CCs), calibration lumped parameters that characterize the rate of specific processes in the membrane-electrode assembly (MEA). The model calibration through experimental V-I curve using χ2optimization criterion determines the values of CCs for a particular MEA and allows to identify the process that limits performance of this MEA. After calibration, the model allows to predict the PEMFC performance with this particular MEA but arbitrary geometry of bipolar plate. The model predictions are in a good agreement with the literature experimental data.