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We report on the synthesis of Pb[ChCN]2 (Ch = O, S, Se) and Pb[SeCN][OH] and their hitherto unknown crystal structures. All products were fully characterized by single-crystal and powder X-ray diffraction. Bulk analysis was performed by Rietveld refinement, elemental analysis, differential scanning calorimetry– thermogravimetric analysis (DSC–TGA), and solid-state Raman spectroscopy. Quantum-mechanical calculations based on the density functional theory allowed optimization of the structural parameters of these lead-based compounds, as well as assessment of their electronic structures and detailed assignment and interpretation of the vibrational spectra. In addition, the origin of bands related to difficulties in assigning the exact position of H atoms in the structures was resolved. [ABSTRACT FROM AUTHOR]

[Display omitted] • "High-temperature carbonate" as descriptor for Cu-Zn-Al catalysts has been studied. • A well-defined Cu-Zn-Al hydrotalcite was employed as a model structure. • Strong carbonate interaction revealed by IR and activation energy analysis. • Comprehensive DFT study evidenced that such carbonates bind CuO and ZnO. • A model for the carbonate's role in retarding CuO/ZnO sintering is proposed. A descriptor of active CuO-ZnO(Al 2 O 3) methanol-synthesis and water–gas-shift catalysts is the presence of high-temperature carbonates (HT-CO 3) in the oxidic catalyst precursor. Previous reports have shown that such HT-CO 3 lead to an appropriate interaction between the oxides; as a result, a high Cu surface area (or Cu-Zn or Cu/ZnO interphase areas) can be achieved. Yet, their nature is not well understood. In this study, the nature of these carbonates was investigated by experimental and theoretical methods in the oxidic precatalyst. A calcined Cu-Zn-Al hydrotalcite model compound revealed to have well-dispersed ZnO and CuO phases, together with highly stable HT-CO 3. It was hypothesized that these HT-CO 3 groups may be placed at critical locations at nano-scale as a glue, thus avoiding the growth of the oxide crystallites during calcination. This is an excellent pre-condition to achieve a high Cu surface area (or Cu-Zn or Cu/ZnO interphase areas) upon reduction, and therefore a high activity. To prove that, first-principles calculations were carried out based on the density functional theory (DFT); alumina was not considered in the model as the experimental data showed it to be amorphous but it may still have an effect. Comprehensive calculations provided evidence that such carbonate groups favourably bind the CuO and ZnO together at the interface, rather than being isolated on the individual oxide surfaces. The results strongly suggest that the HT-CO 3 groups are part of the structure, in the calcined precatalyst, where they would prevent thermal sintering through a bonding mechanism between CuO and ZnO particles, which is a novel interpretation of this important catalyst descriptor. [ABSTRACT FROM AUTHOR]

Raman spectroscopy is widely used to examine the carbonate content within bone apatite, but Raman spectra are also sensitive to orientation effects between the polarisation of the incoming laser light and the sample orientation. This may lead to discrepancies when using Raman spectroscopy to evaluate the carbonate content as the extent of crystal organisation can change depending on the type of bone, age, and presence of mineralisation disorders in the organism. It is experimentally very challenging to evaluate the effect of orientation using individual bone crystals. Therefore, we have used density functional theory to examine the effect of orientation in apatitic materials. We examined hydroxyapatite and three different types of carbonated apatite: A‐type where the carbonate ion substitutes the two OH groups in the unit cell, B‐type where co‐substitution occurs between carbonate in a phosphate position and Na+ for Ca2+ to maintain charge balance, and AB‐type where carbonate sits in both A‐site and B‐site. Our simulations show that the OH group in hydroxyapatite has a strong orientation dependence, consistent with previous literature. In addition, the phosphate and carbonate bands of the apatitic structures are predicted to be orientation dependent, where the maximum scattering efficiency occurs in configurations in which the laser polarisation is parallel to the crystallographic axes of the material. The intensity changes of the phosphate and carbonate bands are not consistent upon changing orientations and thus may lead to an underestimation of carbonate contents if insufficient sampling points are used during bone analysis. [ABSTRACT FROM AUTHOR]

Within this paper is described an analytical model for the analysis of quasistatic load distribution in four contact ball bearings. The quasistatic model was developed on the basis of the static model, applying Hertz's theory of contact and John-Harris's load distribution on ball. In this paper, the model is extended by introducing parameters such as positive/negative clearances into static equilibrium equations. Behavior analysis of the four point contact ball bearing (FKL LSQFR 308) was performed for different operating conditions. Within certain analyzes, the analysis of the influence of conceptual parameters (positive/negative clearances) on the operational characteristics of bearings was performed. The change in external load also varied. Verification of the static behavior of the ball bearing LSQFR 308 was performed by comparing the results obtained by quasistatic modeling and the results obtained using the finite element method. [ABSTRACT FROM AUTHOR]

Hybrid density functional theory has been used to study the phase stability and formation of native point defects in Cu4O3. This intermediate copper oxide compound, also known as paramelaconite, was observed to be difficult to synthesize due to stabilization issues between mixed-valence Cu1+ and Cu2+ ions. The stability range of Cu4O3 was investigated and shown to be realized in an extremely narrow region of phase space, with Cu2O and CuO forming readily as competing impurity phases. The origin of p-type conductivity is confirmed to arise from specific intrinsic copper vacancies occurring on the 1+ site. Away from the outlined stability region, the dominant charge carriers become oxygen interstitials, impairing the conductivity by creating deep acceptor states in the electronic band gap region and driving the formation of alternative phases. This study further demonstrates the inadequacy of native defects as a source of n-type conductivity and complements existing experimental findings. [ABSTRACT FROM AUTHOR]

A four-point contact ball bearing makes it easy to simplify machine designs that have a combination of radial, axial and moment loads because it can handle all three simultaneously. They are primarily used for slow to moderate-speed applications, or where oscillatory movement is predominant such as agricultural mechanization. Four-point contact ball bearing in this paper is single row angular contact ball bearing with raceways that is designed to support axial loads in both directions. The centre points of curvature raceways on the inner and outer ring are offset relative to each other in such a way that the balls are in contact with the bearing rings at four points under radial load. For a given axial load, a radial load is also considered. This paper presents numerical model (finite element model) for computing the behavior of statically loaded ball bearings with four-point contact, for agricultural mechanization. The numerical model has to predict an influence of axial and radial load on the stress level, and elastic deformation in the explanation condition. The results show that the contact loads of four-point contact ball bearing increase with the value of clearances, small changes of the clearance have a great influence on the contact pressure. [ABSTRACT FROM AUTHOR]

Using quantum theoretical simulations based on density functional and density functional perturbation theory we illuminate the nature of the phase transition occurring in magnesium fluoride (MgF 2 ) at high pressure. At atmospheric pressure it is stable in the rutile structure. It was predicted by theory and later confirmed by experiments that a phonon soft mode driven phase transition transforms MgF 2 to a CaCl 2 -type structure. The phase transition was connected with an optic phonon mode B 1 g . By simulating the behavior of phonons at and near the Γ point we prove that a lattice dynamical instability originates in an unstable acoustic phonon mode. The calculation of the elastic constants shows that the phase transition is a proper ferroelastic phase transition occurring under a homogenous deformation of the crystal lattice. These results further illustrate the behavior of fluoride materials under extreme conditions, such as pressure. [ABSTRACT FROM AUTHOR]

Metal sulphides constitute cheap, naturally abundant, and environmentally friendly materials for energy storage applications and chemistry. In particular, iron (II) monosulphide (FeS, mackinawite) is a material of relevance in theories of the origin of life and for heterogenous catalytic applications in the conversion of carbon dioxide (CO2) towards small organic molecules. In natural mackinawite, Fe is often substituted by other metals, however, little is known about how such substitutions alter the chemical activity of the material. Herein, the effect of Ni doping on the structural, electronic, and catalytic properties of FeS surfaces is explored via dispersion-corrected density functional theory simulations. Substitutional Ni dopants, introduced on the Fe site, are readily incorporated into the pristine matrix of FeS, in good agreement with experimental measurements. The CO2 molecule was found to undergo deactivation and partial desorption from the doped surfaces, mainly at the Ni site when compared to undoped FeS surfaces. This behaviour is attributed to the energetically lowered d-band centre position of the doped surface, as a consequence of the increased number of paired electrons originating from the Ni dopant. The reaction and activation energies of CO2 dissociation atop the doped surfaces were found to be increased when compared to pristine surfaces, thus helping to further elucidate the role Ni could have played in the reactivity of FeS. It is expected that Ni doping in other Fe-sulphides may have a similar effect, limiting the catalytic activity of these phases when this dopant is present at their surfaces. [ABSTRACT FROM AUTHOR]

The deep groove ball bearing is one of the most important components of the rotary motion system and is the research subject in this paper. After factory assembly, new ball bearings need to pass quality control. The conventional approach relies on measuring the vibration amplitudes for each unit and sorting them into classes according to the vibration level. In this paper, based on experimental research, models are created to predict the vibration class and analyze the dynamic behavior of new ball bearings. The models are based on artificial neural networks. A feedforward multilayer perceptron (MLP) was applied, and a backpropagation learning algorithm was used. A specific method of training groups of artificial neural networks was applied, where each network provided an answer to the input within the group, and the final answer was the mean value of the answers of all networks in the group. The models achieved a prediction accuracy of over 90%. The main aim of the research was to construct models that are able to predict the vibration class of a new ball bearing based on the geometric parameters of the bearing rings. The models are also applied to analyze the influence of surface roughness of the raceways and the internal radial clearance on bearing vibrations. [ABSTRACT FROM AUTHOR]

This paper presents a calculation model the thermal elastic behavior of the cylindrical roller bearing for bearings towed vehicle in railways. The present mathematical model allows to define the value of the moment friction due to lubrication, the friction moment due to the radial and axial loads. Heat generated in the bearing calculated based on the value of previously defined moments. Also, it shows the method of calculating the coefficients of conduction and convection of heat in bearing. Using programming system general purpose analyzed thermal elastic behavior of the cylindrical roller bearing for bearings axle towed vehicle in railways. Finite element method determined by temperature values in the characteristic points of the bearing depending on the speed wheel for different time periods. Also, it determined of displacement in characteristic points of bearing due to the heat load in the steady temperature state, maximal stress and bearing life. [ABSTRACT FROM AUTHOR]

Within the universal motor helical gear reducer, single row deep groove ball bearings are usually used, but for larger driver dimensions and heavily loaded shafts, spherical roller bearings are used. In order to achieve the maximum load capacity of the gearbox, within the same axis height, relatively large single-row ball bearings are necessary. In some cases, due to dimensions constraints, they cannot be installed in the gearbox, so many manufacturers, in certain cases, use somewhat smaller and more expensive single-row cylindrical roller bearings. Though these bearings are not specifically designed to transmit axial forces, they can bear axial loads. The idea of this paper is to point out this problem and the benefits that come from the use of cylindrical roller bearings. [ABSTRACT FROM AUTHOR]

• Synthesis of Cu 2 CdSnS 4 (CCTS) and Cu 2 ZnSnS 4 (CZTS) nanocrystals using low-cost homemade hot-injection method. • First-principles DFT calculated phonon dispersion shows that both CCTS and CZTS are stable at ambient pressure. • Bandgap reduction from 1.51 eV (kesterite- CZTS) to 1.1 eV (stannite-CCTS) is demonstrated. • Fabricated CCTS nanocrystals sensitize solar cell exhibits a power conversion efficiency of 1.1% compared to 0.25% for CZTS. [Display omitted] The Earth-abundant kesterite Cu 2 ZnSnS 4 (CZTS) exhibits outstanding structural, optical, and electronic properties for a wide range of optoelectronic applications. However, the efficiency of CZTS thin-film solar cells is limited due to a range of factors, including electronic disorder, secondary phases, and the presence of anti-site defects, which is a key factor limiting the V oc. The complete substitution of Zn lattice sites in CZTS nanocrystals (NCs) with Cd atoms offers a promising approach to overcome several of these intrinsic limitations. Herein, we investigate the effects of substituting Cd2+ into Zn2+ lattice sites in CZTS NCs through a facile solution-based method. The structural, morphological, optoelectronic, and power conversion efficiencies (PCEs) of the NCs synthesized have been systematically characterized using various experimental techniques, and the results are corroborated by first-principles density functional theory (DFT) calculations. The successful substitution of Zn by Cd is demonstrated to induce a structural transformation from the kesterite phase to the stannite phase, which results in the bandgap reduction from 1.51 eV (kesterite) to 1.1 eV (stannite), which is closer to the optimum bandgap value for outdoor photovoltaic applications. Furthermore, the PCE of the novel Cd-substituted liquid junction solar cell underwent a four-fold increase, reaching 1.1%. These results highlight the importance of substitutional doping strategies in optimizing existing CZTS-based materials to achieve improved device characteristics. [ABSTRACT FROM AUTHOR]

Background/Aim. One of the possible complications after implantation of a cement hip-joint endoprosthesis is fracture in the endoprosthesis body. Fractures arise from overload or material fatigue of which an implant is made. The purpose of this research was to define the intensity of maximum stress and the positions of a critical cross-section in the endoprosthesis body. Methods. Unilaterally changing forces which act on the hip joint during walking as well as the loads result in flexible deformations of the endoprosthesis body. Biomechanical analysis of the forces acting on the hip joint determine their direction and intensity, whereas on the basis of Gruen's classification of the endoprosthesis body loosening the level of fixation is established. The bodies of cement hip joint endoprosthesis are made of cobalt-chromium-molybdenum (CoCrMo) alloy, suitable for vacuum casting, are submitted to the analysis. Analysis of the critical stress in the endoprosthesis body was performed on the endoprosthesis body by means of the finite element method. The experimental verification of the obtained results was carried out on the physical prototype under laboratory conditions. Results. Computer analysis, by means of the finite element method, determined the stress state by calculation of the maximum Von Mises stress and critical cross-sections for different angles of the resultant force action. The results obtained by the computer and experimental method correlate and are comparable to the results of similar analyses conducted on various endoprosthesis types. Conclusion. The analyses described in the paper make the basis for improving the process designing of hip joint endoprostheses and their customization to each individual patient (custom made). [ABSTRACT FROM AUTHOR]

A numerical study of transient three-dimensional heat conduction problem with a moving source is presented. For numerical solution Douglas-Gunn alternating direction implicit method is applied and for the moving heat source flux distribution Gaussian function is used. An influence on numerical solution of input parameters figuring in flux boundary conditions is examined. This include parameters appearing in Gaussian function and heat transfer coefficient from free convection boundaries. Sensitivity of cooling time from 800 to 500 °C with respect to input parameters is also tested. [ABSTRACT FROM AUTHOR]

The friction stir welding (FSW) process starts when the welding tool rotates and plunges into the base material. Significant amount of mechanical energy given to the welding tool is used to overcome resistances in the base material and as a result, this mechanical energy transforms into heat. Experimental studies have shown that extreme values of the resistance forces and maximum engagement of the welding machine power appear during plunging. This leads to the conclusion that the FSW process has to fulfil welding requirements as well as to overcome resistances. Since it is expected that maximal power consumption during FSW appears when the maximum value of heat is generated, the FSW process has to be designed according to this power consumption. An adequate and precise mathematical model for generated heat estimation can be used for the FSW process design. The verification of the mathematical model validity can be done by comparison of the analytical with the experimental values of consumed power. [ABSTRACT FROM AUTHOR]