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Tooth resorption can occur either physiologically or pathologically and can be classified as internal or external. The term "external invasive resorption" (EIR) has been used to describe lesions originating from any surface defect exposing dentin. The absence of bacterial contamination, an intact pulp space, and a lesion consisting mainly of fibrovascular tissue characterize EIR. This study presents three cases of invasive resorption in unerupted teeth, emphasizing the importance of cone-beam computed tomography (CBCT). In two cases, the primary defect localized on the enamel surface, while in the third case, the focal point of the defect was not clear. CBCT provided detailed visualization of the resorption lesion's size and its relationship with surrounding structures, enhancing the diagnosis of EIR. Histological analysis of the third case confirmed the initial diagnosis. Invasive resorption can occur due to any surface defect in the case of unerupted teeth. Further research and correlation between radiographic and histological analysis are essential for the detection and classification systems in unerupted teeth. [ABSTRACT FROM AUTHOR]

• The formation of vacancy depends on the indentation directions. • Atoms displace in a symmetrical manner on basal plane during indentation. • Least effort required and damage done during indentation on the basal plane. • Formation of symmetrical Voronoi polyhedrons. The present study investigates the effect of nanoindentation on single-crystal magnesium specimens using the embedded-atom method potential in molecular dynamics simulation. Analyses are done under dynamic loading where the load-bearing capacity and change in the structural configuration are studied on the basal (Z–direction) and two prismatic planes (X– and Y–directions) with varying indenter velocities. The investigation of structural evolution is done using atomic displacement analyses to measure the net magnitude of displacement, atomic strain analyses to evaluate the shear strain developed in the process, and Wigner – Seitz defect analyses to calculate the total vacancies at varied timesteps. Furthermore, Voronoi analyses are done when indented on the basal plane to identify the cluster distribution at different planar depths of the specimen. From the analyses, it has been observed that the load-bearing capacity of the specimen varies with the indentation velocity and the direction of indentation on the specimen. Additionally, it is seen that the observed shear and total atomic displacement in the Z–direction is the least in comparison to the other two axes. The partial dislocation 1/3<-12-10> is seen to be majorly present and the population of dislocation loops is more abundant for lower indenter velocities. Furthermore, clusters <0, 4, 4, 6> and <0, 6, 0, 8> are the major indices developed during nanoindentation on the basal plane where they exhibit symmetrical distribution as observed from the Z–direction. [ABSTRACT FROM AUTHOR]

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[Display omitted] • According to the principle of electrical neutrality, a defect cluster model of [Si P ' + Mg K• ] was constructed. • The defect clusters was corrected using the FNV method with DFT and the PBE-GGA exchange-correlation functional, and the band gap was adjusted using the HSE correction. • Detailed analysis encompasses lattice distortions, electronic structures, and optical properties of defect clusters. In this study, the defect formation energies, lattice distortions, electronic structures and optical properties for the KDP crystal with defect cluster [Mg K + Si P ] have been obtained by first-principles methods. The accurate defect formation energies have been obtained by corrected with FNV method. The lattice distortion indicate that the appearance of defect clusters causes Si and P atoms to surround magnesium, resulting in a lattice distortion as high as 34.2 %. Furthermore, an silicate structure emerges, possibly leading to a reduction in the crystal damage threshold. The electronic structures reveal that the emergence of new defect states in the band gap of the crystal with [Mg K + Si P ]' structure. These defect states cause the bottom of the conduction band to shift downwards, resulting in a decrease in the band gap. This is primarily attributed to the contributions from Mg-3 s and O-2p orbitals. This is self-consistent with the larger distortion around Mg in the lattice distortion. This is also a possible factor contributing to the decrease in the crystal damage threshold. The calculated optical spectra demonstrate that absorption peak values at 3.5 eV, 4.53 eV, 5.54 eV, 5.70 eV, and 5.81 eV, originating from defect clusters [Mg K + Si P ]. Therefore, it is conjectured that the presence of impurities magnesium and silicon may be one of the reasons for the reduction in the crystal damage threshold. [ABSTRACT FROM AUTHOR]

Copyright of Science of Sintering is the property of National Library of Serbia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The growth kinetics of the surface film formed upon the multi-principal element alloy AlTiVCr under anodic polarisation in 0.6 M NaCl was investigated using atomic emission spectroelectrochemistry (AESEC). The AESEC charge balance analysis revealed that thickness of the barrier layer of the passive film upon the alloy: (1) increases linearly with the increase in anodic potential during potentiodynamic polarisation, and (2) increases logarithmically with exposure time during potentiostatic polarisation. This is consistent with the assumptions of the point defect model, despite the film being a multi-oxide film with transpassive dissolution of V and Cr. The X-ray photoelectron spectroscopy (XPS) analysis suggested that the growth of the film was predominantly due to TiO2 during anodic polarisation. The electric field was found to decrease with enrichment of TiO2 in the barrier layer. The Mott-Schottky analysis revealed that the diffusivity of oxygen vacancies increased with the increase in fraction of TiO2 in the film, which subsequently led to the increase in the growth rate of the barrier layer during transpassive dissolution. The present work is a discrete effort towards understanding the growth behaviour of the passive film experiencing complex and competing interfacial electrochemical processes, upon a multi-principal element alloy. [ABSTRACT FROM AUTHOR]

An impedance-based Point Defect Model (PDM) was developed for the potentiostatic, anodic formation of gold oxide at potentials of 1.40–1.70 V vs SHE in H2SO4 (0.1 M and 0.5 M). Film thickness and refractive indices were determined at each oxide formation potential using spectroscopic ellipsometry. The thickness of the oxide increases linearly with increasing potential. Mott-Schottky analysis shows that the oxide exhibits both n-type and p-type character and the dominant defect density is calculated to be in the order of 1021−1022 (1 cm−3). The PDM was optimized upon experimental EIS data to extract values for model parameters and accounts well for the experimental observations in both the steady-state time and frequency domains. [ABSTRACT FROM AUTHOR]

The ion exchange and point defect models are two prominent models describing the role of anions, such as chlorides, in the degradation of passive oxide films. Here the thermodynamic feasibility of critical steps of Cl-induced degradation of ahydroxylated α-Cr2O3 (0001) surface, as proposed by these two models, are studied. Both models begin with Cl substitution of surface OH and H2O, which becomes less favorable with increasing Cl coverage. The initial stages of Cl-induced breakdown of theα-Cr2O3 depend on Cl coverage and the presence of O vacancy near the surface as follows: (1) neither Cl insertion (supporting the ion exchange model) nor Cr vacancy formation (supporting the point defect model) is feasible at low Cl coverages except in the presence of O vacancies near the surface, where Cl insertion is thermody namically feasible even at low coverages, (2) in the absence of O vacancies, Cr vacancy formation becomes feasible from 10/12 ML onwards whereas Cl insertion by exchange with subsurface OH only becomes feasible at full coverage. This implies that at higher coverages Cl-induced degradation first initiates through a vacancy formation mechanism, but both insertion and vacancy formation would be feasible at full coverage. [ABSTRACT FROM AUTHOR]

The early stage of electrochemically-induced Fe(001) passivation is investigated via a sub-second resolution real-time X-ray reflectivity technique. Static measurements clearly demonstrate that the passive layer is composed of two distinct layers comprising a dense inner oxide layer and a loosely packed outer layer. The growth of the inner passive layer is mostly completed within 1 s, while the growth rate in the later process is much slower and is qualitatively consistent with typical growth models such as the high-field model and point defect model. The rate-determining mechanism in the early stage is clearly different from that in the later stage. [ABSTRACT FROM AUTHOR]

[Display omitted] • The catalytic activity of CoN4 was found to be the highest among five different Co- N -B-C graphite structures, including those with single vacancy, double vacancy, and defect point. • The introduction of B atom into the first layer of five configurations resulted in enhanced stability of the electrocatalyst; however, it did not mitigate the adsorption of O intermediate, leading to suboptimal catalytic performance. • By doping the second coordination layer of CoN4 with B, the stability was enhanced and excellent catalytic activity was observed when 4 or 5B atoms were introduced. The performance of single atom catalyst (SAC) is strongly affected by its carrier. Five configurations with single vacancy, double vacancy, and defect site were calculated using density functional theory (DFT), and it was found that the electronic structure and state density were effectively regulated after introducing the B atom. The ORR activity was studied by doping different coordination layers. The results show that when doped with the second coordination layer of Co-DVG-N4 configuration, B can improve the adsorption strength of the central Co atom to the oxygen intermediate and show excellent ORR activity. Co-DVG-N4-B4(12.9 %) and Co-DVG-N4-B5(16.1 %) have relatively low overpotentials of 0.49 V and 0.47 V, providing an effective theoretical basis for rationalizing efficient electrocatalysts based on Co carbon materials. [ABSTRACT FROM AUTHOR]

Abstract An unceasing scientific challenge to monitor the emissions of toxic and flammable gases in a selective approach is of great importance for safety of human health. As a result, herein, we report on the detailed study of the gas sensing characteristics of ZnO nanostructures prepared at various reaction pH and times. The findings revealed that the variation of synthesis reaction pH and times play a vital role on the morphology and structure. The ZnO-4h@10.5 pH based sensor demonstrated a low response when exposed to reducing gases (CO, CH 4 and NH 3), volatile organic compounds (ethanol, acetone, benzene and toluene) and oxidizing gas (NO 2), while exposed to H 2 S gas unpreceded and reproducible response (i.e. 3 times more than the interfering gases) at low operating temperature of 75 °C was observed. The exceptional response (i.e. resistance ratio) observed at the low operating temperature towards 40 ppm H 2 S was elucidated by the improved gas accessibility and relative concentration of V O induced by structural transformation, which induced change in oxygen adsorption. The high H 2 S gas selectivity was ascribed to the reactivity of H 2 S and low temperature decomposition to participate in a reaction with a ZnO nanoplatelets-based sensor. The fundamental gas-sensing mechanism associated to the ZnO response and point defects at low operating temperature is evaluated in detail. [ABSTRACT FROM AUTHOR]

Highlights • (Ba 1− x Ho x)(Ti 1− x Ho x)O 3 ceramics (BHTH) were prepared using a mixed-oxides method. • Solubility limit of Ho3+ in fine-grained BHTH (0.5 μm) was determined to be x = 0.03. • Ho3+ in BaTiO 3 prefers a self-compensation mode, with a slight Ba-site preference. • The Curie temperature abnormally shifts towards high temperature with increasing x. • Negligible oxygen vacancies are evidenced by EPR, responsible for lower tan δ. Abstract Nominal (Ba 1− x Ho x)(Ti 1− x Ho x)O 3 ceramics (BHTH) were prepared at 1400 °C using a mixed-oxides method. The structure, microstructure, dielectric properties, and point defects of BHTH were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy, electron paramagnetic resonance (EPR), and dielectric measurements. Ho3+ in BaTiO 3 prefers a self-compensation mode with a slight Ba-site preference, and the solubility limit of Ho3+ in the fine-grained BHTH (0.5 μm) was determined by XRD to be x = 0.03. An abnormal phenomenon was observed: the Curie temperature of BHTH shifted towards high temperatures from 128 °C at x = 0.01 to 131 °C at x = 0.03. Ho3+ is inferred to be a potential codopant to achieve X8R specification when BaTiO 3 is doped with Ho3+ and other types of ions. [ABSTRACT FROM AUTHOR]

Abstract Thermodynamic properties and structural aspects of the nonstoichiometric wüstite Fe 1- z O, and its modifications - the so-called pseudo-phases - as functions of departure z from stoichiometry and of equilibrium temperature are reviewed from 1960 to present. The complexity of the equilibrium phase diagram is described in some details. The first order transition W ⇆ W′ is specified on the iron/wüstite boundary near 1185 K. Transitions correlated to the modifications Wi at T(W) > 1185 K and W'j at T(W′) < 1185 K (i and j = 1,2,3) are re-examined. Structural determinations based on the characterization of point defects stabilization and of their clustering are reviewed. Additionally, the pseudo-phases are examined based on the transformation of defect clusters or of their mode of distribution (i.e., percolation or superstructure) with the inclusion of changes in electronic charge carriers. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The positive vacancy formation energy can be attributed to two competing factors. • Both Ti atoms in the surface and the inner layer see a C 3v crystal field. • It is difficult for Ti vacancy to diffuse from inner Ti layer to surface Ti layer. • A relationship between temperature and equilibrium concentration of vacancy clusters is derived. Abstract Two-dimensional transition metal carbides or nitrides (MXenes) have attracted much research interest and have shown very promising applications. Recently, the Ti vacancies in Ti 3 C 2 were observed in an experiment (Sang et al., 2016) and demonstrated an important influence on the electronic properties of Ti 3 C 2. Based on the first-principles method, this study systemically investigated these issues and found that the formation energy of a single Ti or C vacancy comes from two competing factors. One is the dangling bonds introduced by the vacancies, leading to an increase in the total energy. The other is the splitting of the original degenerate states after the lattice deformation around the vacancies, leading to a decrease in the total energy. Different from a previous study, this report found that both the surface and inner Ti atoms see a C 3v crystal field. The bonding states among Ti 3d orbitals with the same symmetry form a network, which does not break down even around the Ti vacancy, making the system metallic. The diffusion of a single Ti vacancy from the surface Ti layer to the inner Ti layer is more difficult than the path return, whether or not surface functional groups exist. By deriving the relationship between the equilibrium concentration of the vacancy clusters and the temperature, this study found that the formation of vacancy clusters is possible, although their concentration is much lower than that of a single vacancy. The results of this report will enhance the understanding of the relationship between the electronic properties and the native point defects of Ti 3 C 2. [ABSTRACT FROM AUTHOR]

Abstract Czochralski-grown colorless and pink Bi 4 Ge 3 O 12 (BGO) single crystals have been characterized by the X-ray diffraction, X-ray absorption, and luminescence and optical spectroscopy. Additional high-temperature vacuum annealing of the as-grown colorless crystal at 900–950 °C using a special reducing agent leds to the appearance of pink coloration and modification of its properties. The refinement of actual compositions of both BGO crystals showed the distribution of the Bi3+ions over two, tetrahedral and octahedral, sites, the Bi content in the colorless crystal being greater and lower in the octahedral and tetrahedral sites, respectively, compared with the colored crystal. A small amount of Bi5+ions was revealed in the tetrahedral sites of the colorless crystal. Oxygen vacancies, as a part of the color center responsible for the crystal coloration, were found in the structure of pink sample. The pink BGO crystal is characterized by photoluminescence in the near infra-red spectral range. [ABSTRACT FROM AUTHOR]

Highlights • Low temperature synthesized ZnO NPs were used for sun driven photodegradation of Congo red dye. • The sun driven photocatalytic activity is investigated under different pH values. • Higher photodegradation efficiency is found under acidic medium. • Trapping experiments indicated that O H. , a n d O 2. - radicals are responsible for the photodegradiation. • The ZnO NPs showed acceptable degradation efficiency after different usage cycles. Abstract Solar driven photocatalytic processes to remove organic pollutants from wastewater and other aqueous solutions is very important and useful due to its environmental benefits regarding sustainability aspect. In this article, we report a study on the use of bare zinc oxide (ZnO) nanoparticles (NPs) prepared by the chemical low temperature co-precipitation method and used as a catalyst to degrade the Congo red dye from aqueous solution using solar radiation. We performed the photocatalytic experiments for degradation of Congo red dye under solar radiation at different pH values. The results showed that the ZnO NPs are effective under solar radiation for degradation of Congo red dye. Even when the pH was varied down to 4 or raised to 10, the degradation was observed to be slightly improved. This result is due to the excess of radicals species, which enhance the photocatalytic process. In general, the observed degradation efficiency of the ZnO NPs is due to the deep level defects within the band gap that were introduced during the growth process of the ZnO NPs, which enhance the absorption wavelength band towards the visible light region. Recycling of the ZnO NPs for 3 successive runs have indicated the feasibility of reusing the NPs for several times. This implies that by using bare ZnO NPs an efficient approach for degradation of toxic waste can be achieved. Radical scavengers were used to evaluate the role of the radicals in the reaction mechanism. [ABSTRACT FROM AUTHOR]

Abstract The basic properties, heats of formation, energies of formation, equilibrium concentration of point defects, elastic properties, and electronic structures for point defect structures of B2-NiAl crystal were analyzed by the density functional theory. Compared with B2-NiAl and other B2 intermetallic compounds, purity NiAl has better ductility and bonding strength. According to the calculated heats of formation, energies of formation, and equilibrium concentration of point defects, the Ni antisite and Ni vacancy are primary defects in B2-NiAl crystal. The calculated G / B 0 and Cauchy pressure parameters C 12 - C 44 values confirm that Ni vacancy, Ni antisite, and Al antisite can promote the brittleness of B2-NiAl, in which Ni vacancy is the primary defect, while Al vacancy with a low concentration can improve ductility of B2-NiAl. The density of state confirms that B2-NiAl intermetallic compounds are conductors, and point defects can promote the stability of the system expect Ni antisite defect. [ABSTRACT FROM AUTHOR]

Many optimization methods require accurate partial derivative information in order to ensure efficient, robust, and accurate convergence. In this paper, analytic methods are developed for computing complex partial derivatives of two bounded-impulse trajectory models: the multiple gravity-assist low-thrust and the multiple gravity-assist with n deep-space maneuvers using shooting transcriptions. Particular attention is paid to the match point defect constraint present in these models due to its complex functional dependencies, and the gradient computations presented are extended to allow for the computation of trajectory path constraints. A comet sample return mission design problem is solved that underscores the benefits of implementing analytic gradient equations for these trajectory models. The computational efficiency of the techniques presented is compared against other methods available for computing partial derivative information, including automatic differentiation and the method of finite differences. [ABSTRACT FROM AUTHOR]

This paper presents an application of two-step forming for improvement of the forming limit in rotary nosing with relieved die. Nosing is one of the methods used for reduction of the diameter of a tube tip. "Two-step nosing", in which the working process of nosing is divided into two stages, applies two dies with different shapes at the former and latter stages. The die shapes are determined based on the occurrence tendency of defects in "one-step nosing" which uses only one die through the whole process. In this research, a series of experiments and numerical analyses of one-step nosing were carried out to investigate the mechanism of occurrence of each defect. As a result, it is revealed that the occurrence of defects was highly relevant to the contact area between the die and tube. Two-step nosing was thereafter carried out and attained the improvement of the forming limit, which was 9 % higher than one-step nosing under the optimum condition. Furthermore, additional experiments of forming eccentric tubes were conducted for fabrication of products with complex shapes. [ABSTRACT FROM AUTHOR]

In this section of Resonance, we invite readers to pose questions likely to be raised in a classroom situation. We may suggest strategies for dealing with them, or invite responses, or both. 'Classroom' is equally a forum for raising broader issues and sharing personal experiences and viewpoints on matters related to teaching and learning science. In this series of articles, the authors discuss various phenomena in fluid dynamics, which may be investigated via tabletop experiments using low-cost or home-made instruments. The sixth article in this series explores crystalline defects and motion of dislocations using bubble rafts. Materials [ABSTRACT FROM AUTHOR]

• The effect of C N point defects on the thermoelectric properties of GaN nanowires were investigated. • C N point defects can increase the electrical conductivity of GaN NWs. • GaN NWs containing C N point defects have higher power factor. In this paper, the effects of C N point defects on the thermoelectric properties of GaN nanowires (NWs) were investigated by using first principles calculation. It is found that the C N point defects can increase the electronic density of states (DOS) near the Fermi level of GaN NWs. The calculation results indicate that C N point defects are beneficial for improving the power factor (PF) of GaN NWs. In addition, it was found that C N point defects can increase the electrical conductivity of NWs. At the same time, it also has impact on the thermal conductivity and Seebeck coefficient of NWs. C N point defects will increase the electrical conductivity of GaN NWs from 0.41 × 10 14Wm−1k−1s−1 to 1.15 × 10 14Wm−1k−1s−1 at T = 700 K. In addition, it's also found that as the temperature increases, C N will cause the Seebeck coefficient decreased from 0.001 VK−1 to 0.0008 VK−1 when T = 700 K. It's useful for further understanding the thermoelectric properties of wide bandgap semiconductor materials and improving the performance of thermoelectric devices. [ABSTRACT FROM AUTHOR]

Mechanically induced defect in high energy milled Cd 0.3 Zn 0.7 Se nanocrystals was investigated using electron spin resonance (ESR). The broad ESR component with g ∼ 2 was attributed to paramagnetic defects present in the milled powder. The spin density of the center increases linearly from ∼1 × 10 20 spins/g to 7 × 10 20 spins/g with milling time. The most probable induced centers during mechanical milling were (V Zn –Zn i ), V Zn . The best simulations were produced for relative spin concentrations of three paramagnetic defects with ratio 3:6:10 for 5 h and 10 h milled samples. [ABSTRACT FROM AUTHOR]

In this paper, we emphasize on the experimental study of absorption properties of tunable sonic crystal assisted sound absorber regarding replacement of sonic crystal unit with an artificial single and multi local defect element. Nine pieces of Helmholtz resonators was constructed in a three row to form square 3x3 resonators unit sound absorber model. The influence of a single and multiple Helmholtz resonator manipulation on its sound absorption coefficient was investigated. The experimental results show that the artificial defect manipulation gives the promising possibility for researchers to develop tunable sonic crystals assisted sound absorber. The sound absorber shows a higher sound absorption performance on several different frequency bands associated with the local defect placement position in the sonic crystal structure. [ABSTRACT FROM AUTHOR]

Through the imposition of various assumptions that have been validated using numerical analysis, a greatly simplified method has been developed for expressing the impedance of a passive metal upon the basis of the Point Defect Model. The approach has greatly decreased the dimensionality of the problem, by, for example, showing that the relaxation of the barrier layer thickness can be neglected. Clear criteria have been formulated for identifying the circumstances when the faradaic impedance of the barrier layer does not depend on frequency. In many practical systems, the last simplification can be used when the frequency of the applied, modulated voltage is greater than 10-3-102 Hz. Application of the revised model is illustrated by optimization of model parameters based upon experimental EIS data for carbon steel in borate buffer solutions, for nickel in chloride-containing solutions, and for Type 316 SS in H2S and CO2 environment. It is shown that, in the cases of Fe and Ni, the simplest equivalent electrical equivalent circuit (parallel resistance and capacitor) adequately describes the EIS behavior of passive metals, but in the case of Alloy 316 a constant phase element must be used instead of the capacitor in this equivalent circuit. [ABSTRACT FROM AUTHOR]

This paper presents the MSM structure magnetic detector device that normally detects the electromagnetic wave. The device is special design for magnetic field detector and still detects the electromagnetic wave as normal function. The schottky diode with the split contacts structure allows us to reach this target. The device operates with the saturation current and the magnetic response is the current difference between two contacts which is injected from one metal and deflected in semiconductor toward to another metal. From the simulation result by Sentaurus TCAD, the relative sensitivity is 14.19 mT -1 at the current 0.3 μA. This device is the first MSM multi-sensor for magnetic and electromagnetic wave detector. [ABSTRACT FROM AUTHOR]

Linear Abrasive WaterJet Machining (AWJM) tests have been performed on Carbon Fiber Reinforced Plastic (CFRP) in order to have a first reference of the main defects developed onto the machined surface. Delamination has been proved as one of the most critical defects when machining composites or layered materials. In this work this defect and the influence of cutting parameters in its formation have been studied. For this purpose, delamination morphology has been characterized using Scanning Optical Microscope and Scanning Electron Microscope. Additionally, a study of the influence of cutting conditions and material removal mechanisms involved has been achieved. [ABSTRACT FROM AUTHOR]

In the process of constructional steel products operation in conditions of high temperatures, chemical elements segregation occurs, which leads to the surface characteristics changing and influences their operation period. This paper is aimed in developing the model of mass transfer and redistribution of small-sized atoms (carbon, oxygen) in the binary system “steel-coating” after high temperature annealing in air atmosphere. It is estimated, that carbon concentration inside the grain increases up to 2.81%, at the grain boundaries it reaches 0.44%, while oxygen concentration increases in average up to 16%. The main mechanisms, leading to the redistribution of small-sized impurities, are non-equilibrium flows of point defects to the surface and grains boundaries. [ABSTRACT FROM AUTHOR]