Fast Orbital-Free Full-Potential Calculations for Large Nano Objects: C, Al and Ti

In the context of a full-potential orbital-free approach for the modeling of multi-atomic systems we investigated the dependence of the cohesive energies and bulk elastic modules of the large nanosystems Cn (n is up to 4096 atoms), Aln (n is up to 23,328 atoms) and tin (n is up to 2160 atoms). It was shown that the cohesive energies and elastic modules tend towards bulk crystal values at n ≈ 3000 for Cn systems, at n ≈ 1500 for Tin and at n ≈ 20,000 for Aln. The execution time for one energy iteration for Ti23328 was only 23 min.

Benefits of Using Fluorescence Induced Theragnosis in Fixed Orthodontic Therapy: Status, Technology and Future Trends

Dental biofilm is often found to be the source of bacteria that releases toxins, peptides, lipopolysaccharides as well as organic acids, which lead to gingival inflammation and tooth caries. Further, the persistent plaque may result in the continued destruction of the surrounding soft and hard tissues. During fixed orthodontic therapy, arch-wires, brackets, and elastic modules have been shown to be sites of significant plaque accumulation, making it difficult for a patient to maintain proper oral hygiene. The problem most dentists face is that they cannot visualize this biofilm completely to be able to carry out efficient plaque removal. Visual assessment is, to date, the most common method for plaque visualization, and various indexes have been demonstrated to be sufficient for quantification of the amount of plaque present. However, the problem is that visual assessments are inconsistent, operator dependent and often subjective, which can lead to inconsistency in results. Fluorescence is one such method that can be explored for its use in effective plaque identification and removal. Literature has it that dentists and patients find it particularly useful for monitoring oral hygiene status during treatment. Fluorescence has the capability of offering clinical orthodontists and researchers a new method of detection of demineralization during orthodontic treatment, furthermore, for efficient removal of orthodontic adhesive cements, fluorescent light may be used in conjunction with high-speed burs to deliver fast, less time consuming, and safer results. The benefit of direct visual treatment using fluorescence enhanced theragnosis is that the patient receives controlled and guided therapy. It has multiple benefits, such as early diagnosis of caries, biofilm identification, and even helps to achieve improved treatment outcomes by better resin selection for esthetic procedures.

Stressed state of two-layer strip when interacting with rigid base

Relevance. In the calculation of multilayer bases, when the material of one or several layers has a pronounced anisotropy, the nature of the distribution of displacements and stresses depends on the direction of the anisotropy axes in each layer. Therefore, it is necessary to have an evaluation of the influence of this factor in the design and analysis of the operation of multilayer media. The aim of the work - to research the stress state in a strip composed of two anisotropic plane-parallel layers with different physical characteristics, lying without friction on a rigid base. Methods. The integration of the equations of the plane problem of the theory of elasticity of an anisotropic body is carried out by the symbolic method in combination with the method of initial functions. The initial functions on the contact line of the strip and the base are determined from the conditions of tight adhesion between the layers, the conditions of tight contact and the absence of friction between the strip and the base, the nature of the load applied to the upper plane of the strip. After transformations, the functions of displacements and stresses in each layer are written through the normal surface load in the form of improper integrals. Results. Plots of changes in stresses in the strip from the values of the characteristics of anisotropic materials, layer thicknesses are given. The maximum stresses on the interface line of the layers and on the line of contact with the base, depending on the direction of the anisotropy axes in each layer, are presented in the tables and shown in graphs. The effect of the elastic modules of materials on the nature of the stress distribution in a strip composed of two isotropic materials is estimated.

COMPARATIVE ANALYSIS OF RESULTS OF NUMERICAL MODELING OF MECHANICAL BEHAVIOR OF GRAPHENE AND SILICENE IN THE FRAMES OF COMMON HARMONIC FIELD

В статье представлены результаты применения модели общего гармонического поля для численного моделирования механических свойств близких по геометрической форме образцов наноструктур графена и силицена. Проведён расчёт коэффициентов жёсткости элементов для этой модели на основе жёсткостей пары базовых через собственные частоты колебаний трёхузловых фрагментов. Приведены зависимости упругих модулей от линейных размеров. В обоих случаях наблюдается рост модуля продольной упругости с выходом на асимптоту при увеличении длины образца и очень слабая зависимость от его ширины. Коэффициент поперечной деформации уменьшается с ростом ширины. Увеличение длины даёт у графена рост данного показателя, а у силицена - его снижение. The article presents the results of application of the general harmonic field model for numerical modeling of mechanical properties of samples of graphene and silicene nanostructures similar in geometric form. A calculation of the stiffness coefficients of the elements for this model was made based on the stiffness of a pair of basic ones through the natural frequencies of oscillations of three-node fragments. Dependencies of elastic modules on linear dimensions for examined samples are given. In both cases, there is an increase in the modulus of longitudinal elasticity with an increase in asymptote with an increase in the length of the sample and a very weak dependence on its width. The coefficient of transverse strain decreases as the width increases. Increasing the length gives graphene an increase in this indicator, and in silicene - its decrease.

Co-curing of epoxy resins with aminated lignins: insights into the role of lignin homo crosslinking during lignin amination on the elastic properties

To improve the reactivity of lignin for incorporation into high value polymers, the introduction of amines via Mannich reaction is a commonly used strategy. During this functionalization reaction, intra- as well as intermolecular lignin–lignin crosslinking occurs, which can vastly change the elastic properties of the lignin, and therefore, the properties of the resulting polymer. Therefore, the molecular structure of the amine that is used for such a lignin functionalization may be of great importance. However, the relationship between the molecular structure of the amine and the elastic properties of the lignin-based polymer that is generated thereof, has not been fully understood. Herein, this relationship was investigated in detail and it was observed that the molecular flexibility of the amines plays a predominant role: The use of more flexible amines results in an increase in elasticity and the use of less flexible amines yields more rigid resin material. In addition to the macroscopic 3-point bending flexural tests, the elastic modules of the resins were determined on the nanometer scale by using atomic force microscopy (AFM) in the PeakForce tapping modus. Thus, it could be demonstrated that the intrinsic elasticities of the lignin domains are the main reason for the observed tendency.

Dental Composition Modified with Aryloxyphosphazene Containing Carboxyl Groups

A modifier consisting of the mixture of cyclotriphosphazenes containing 4-allyl-2-methoxyphenoxy and β-carboxyethenylphenoxy moieties was developed for administration with acrylate dental restorative compositions. The synthesized compounds were characterized by 1H and 13C NMR spectroscopy and MALDI-TOF mass spectrometry. The optimal conditions to combine the modifier with the starting dental mixture consisting of bis-GMA and TGM-3 were revealed by differential scanning calorimetry (DSC) method. Properties of the cured modified compositions were evaluated for the compliance with requirements of ISO 4049:2019. It was found that these compositions possess the increased adhesion to dental tissues and cure depth and the decreased water sorption and water solubility. The values of elastic modules, destructive compressive stress and microhardness were also increasing along with the increased content of the modifier in the composition.

Theoretical Preconditions for Determination of the Elastic Modulus of Clt-Panels

Cross laminated timber panels (CLT) are promising building structures that are actively used in the construction of buildings around the world. In Russia the construction is rarely used, despite the existing factories for their manufacturing. In regulatory documents there are no specific data on the elastic modulus for these structures. As a method for determining this calculated characteristic, a numerical experiment in the SCAD Office software package is proposed. During the experiment, panels of various thickness and different numbers of layers are considered. Based on the obtained displacements from the action of the applied load, the values of the elastic modules are determined and summarized in the table. According to the results of the calculation, graphs of dependences of the reduced elastic modules on the thicknesses and the number of layers are constructed and analyzed.

Influence of Class of Concrete on Oscillations of Thin-Wall Cylindrical Reinforced Concrete Shells

Thin-walled cylindrical shell made of reinforced concrete, is widely used in the construction of buildings and structures as coatings and forms of architecture of buildings. Thin-walled shell its shape can give entertainment to the architectural design of buildings, and their rigidity helps to block large spans, creating more closure of the room without additional supports. Another advantage of using cloud forms of structures is the efficiency of this design, since for the manufacture of shell forms of structures less construction material is spent than any other design for coating. The purpose of theoretical calculations and the studied excrement over reinforced concrete shells with different elastic modules, is to ensure reliability in the operation of buildings and structures, and to exclude accidents arising resonance phenomena of free vibrations of the shells from the effects of external forces (loads). On the basis of the laboratories of Komsomolsk-on-Amur state University in the laboratory of building materials and structures, experimental studies were conducted to determine the spectra of forced and free vibrations of the reinforced concrete shell with different elastic modules. The purpose of research on reinforced concrete shells is to determine the oscillation frequencies at different locations of the combined masses. The article deals with the theoretical calculation based on the equation of the theory of flat thin-walled shells, using the Bubnov-Galerkin method, by which we determine how the parameters of the shell affect the process of free oscillation.