Circ_0081054 facilitates melanoma development via sponging miR-637 and regulating RAB9A.

BACKGROUND: Accumulating evidence announces that aberrantly expressed circRNAs were closely related to the development of human cancers. However, the role and mechanism of multiple circRNAs remain unclear. Our work aimed to disclose the functional role and mechanism of circ_0081054 in melanoma. METHODS: Quantitative real-time polymerase chain reaction assay was utilized to detect circ_0081054, microRNA-637 (miR-637) and RAB9A (member RAS oncogene family) mRNA expression. Cell proliferative ability was evaluated via Cell Counting Kit-8 and colony formation assay. Cell invasion was assessed by using wound healing assay. RESULTS: The significant upregulation of circ_0081054 was detected in melanoma tissues and cells. The proliferation, migration, glycolytic metabolism, and angiogenesis in melanoma cells were suppressed, while apoptosis was promoted following the silence of circ_0081054. In addition, circ_0081054 could target miR-637, and miR-637 inhibitor could reverse the effects of circ_0081054 deficiency. Furthermore, RAB9A was a target gene for miR-637 and RAB9A overexpression could reverse the effects of miR-637 overexpression. In addition, the deficiency of circ_0081054 hampered tumor growth in vivo. Moreover, circ_0081054 could regulate RAB9A expression by sponging miR-637. CONCLUSION: All results indicated that circ_0081054 promoted the malignant behaviors of melanoma cells partly by regulating the miR-637/RAB9A molecular axis.

Pressure-induced stability and superconductivity in LuH12 polyhydrides.

The phase stability and superconductivity of lutetium polyhydrides under pressure were systematically explored via particle swarm optimization. Several lutetium hydrides, such as LuH, LuH3, LuH4, LuH6, LuH8, and LuH12, were found to be dynamically and thermodynamically stable. Combined with the electronic properties, there are a large number of H-s states and low density of Lu-f states at the Fermi level, leading to superconductivity. The phonon spectrum and electron-phonon coupling interaction are considered to calculate the superconducting critical temperature (Tc) of stable lutetium hydrides at high pressure. The new predicted cubic LuH12 has the highest Tc value of 187.2 K at 400 GPa in all the stable LuHn compounds, which was estimated by directly solving the Eliashberg equation. The calculated results provide insights into the design of new superconducting hydrides under pressure.

Effects of Kangfuxinye on NF-κB and Inflammatory Cytokines in Gingival Crevicular Fluid of Patients with Orthodontic Gingivitis Caused by Orthodontic Treatment.

Explore the Kangfuxinye effection on the expressions of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and inflammatory cytokines (IC) in the gingival crevicular fluid of patients with orthodontic gingivitis caused by orthodontic treatment. 98 patients with orthodontic gingivitis in Qingdao Stomatological Hospital caused by orthodontic treatment were divided into two groups, namely, the control treatment group and the Kangfuxinye treatment group. In this study, the expressions of those proteins and IC in gingival crevicular fluid before and after treatment were analyzed at first, and the correlations of the NF-κB p65 expression with IC were explored. Then the differences in the expressions of those proteins and IC and the efficacy between the control treatment group and the Kangfuxinye treatment group were analyzed. Compared with those before treatment, the expressions of NF-κB-related proteins and IC interleukin-1ß (IL-1ß), tumor necrosis factor-alpha (TNF-α) and vascular endothelial growth factor (VEGF)] were significantly decreased after treatment (p<0.05). After treatment, the expression of NF-κB p65 was positively correlated with IL-1ß, TNF-α and VEGF, but negatively related to IL-4 and IL-10. In addition, compared with the control treatment, Kangfuxinye significantly reduced the expressions of those proteins and their messenger ribonucleic acids (mRNAs) (p<0.05), decreased the expressions of IL-1ß, TNF-α and VEGF (p<0.05) but improved the total effective rate of treatment. Kangfuxinye can reduce the NF-κB expressions and IC in the gingival crevicular fluid of patients with orthodontic gingivitis caused by orthodontic treatment and enhance the efficacy.

Predicted the structural diversity and electronic properties of Pt-N compounds under high pressure.

The nitrogen-rich transition metal nitrides have attracted considerable attention due to their potential application as high energy density materials. Here, a systematic theoretical study of PtNxcompounds has been performed by combining first-principles calculations and particle swarm-optimized structure search method at high pressure. The results indicate that several unconventional stoichiometries of PtN2, PtN4, PtN5, and Pt3N4compounds are stabilized at moderate pressure of 50 GPa. Moreover, some of these structures are dynamically stable even when the pressure release to ambient pressure. TheP1-phase of PtN4and theP1-phase of PtN5can release about 1.23 kJ g-1and 1.71 kJ g-1, respectively, upon the decomposition into elemental Pt and N2. The electronic structure analysis shows that all crystal structures are indirect band gap semiconductors, except for the metallic Pt3N4withPcphase, and the metallic Pt3N4is a superconductor with estimated critical temperatureTcvalues of 3.6 K at 50 GPa. These findings not only enrich the understanding of transition metal platinum nitrides, but also provide valuable insights for the experimental exploration of multifunctional polynitrogen compounds.

Ubiquitin-specific protease 34 in macrophages limits CD8 T cell-mediated onset of vitiligo in mice.

As an autoimmune disorder, vitiligo is characterized by depigmented skin macules. CD8+T cells and macrophages enrichment promote the onset of vitiligo, while the role of macrophages to CD8+T is not well deciphered. To develop a mouse model of vitiligo with prominent epidermal depigmentation, Krt14-Kitl* transgenic mice containing an elevated number of melanocytes in the epidermis with membrane-bound Kit ligand (Kitl*) were adoptively transferred with premelanosome protein (PMEL) CD8+ T cells. On the other hand, Krt14-Kitl* mice were mated with ubiquitin-specific protease 34 (USP34)MKO mice to decipher the role of USP34 in vitiligo. Vitiligo scores and PMEL CD8+ T cell enrichment were detected with flow cytometry. Human peripheral blood mononuclear cells (PBMCs) or mice bone marrow-derived macrophages (BMDMs) were incubated with lipopolysaccharide (LPS), CpG, or co-incubated with KU-55933, an ataxia telangiectasia-mutated (ATM) inhibitor. Chemokine (C-C motif) ligand 2 (CCL2), Ccl5, and interleukin (Il)-12α expression was assayed with real-time PCR, and p-IKKα/ß was assayed with Western blots. USP34 was up-regulated in the PBMCs of vitiligo patients and LPS-stimulated BMDMs. USP34 deficiency did not affect the differentiation of CD11b+F4/80+ macrophages in the bone marrow. Immunoprecipitation demonstrated the interaction between USP34 and ATM. USP34 deficiency or KU-55933 administration promoted the induction of Ccl2, Ccl5, Il12α, and p-IKKα/ß in LPS or CpG stimulated BMDMs; KU-55933 administration could not affect the expression of the above molecules in USP34 deficient BMDMs. It further revealed that USP34 deficiency promoted the development of vitiligo with increased PMEL CD8+ T cell enrichment, which was not affected by KU-55933 administration. USP34 deficiency in macrophages promotes the onset of vitiligo with increased PMEL CD8+ T cell enrichment, and USP34/ATM complex can be considered as a therapy target.

Stable multifunctional aluminum phosphides at high pressures.

Phosphides have been used in a wide range of applications due to their excellent optical, mechanical, and catalytic properties. Using an effective unbiased structure searching method combined with first-principles calculations, the phase diagram and physical and chemical properties of aluminum phosphides have been determined at high pressures. The results reveal that the unconventional stoichiometries of Al2P, AlP2, and AlP3 remain stable above 66, 91, and 116 GPa, respectively. Interestingly, the analysis of the phonon spectrum suggests that AlP2 with P21 symmetry can be dynamically stable at atmospheric pressure. In addition, the band gap of 1.51 eV at the HSE06 level and the estimated Vickers hardness of ∼10.54 GPa make P21-AlP2 a hard photoelectric material. Moreover, our electronic properties show that AlP3 with Immm symmetry and AlP2 with I4/mmm structure are metallic at high pressures and further electron-phonon coupling calculations indicate Immm-AlP3 and I4/mmm-AlP2 are superconductors with estimated Tc values of 3.9 K at 150 GPa and 10.2 K at 100 GPa, respectively. Our work provides significant inputs toward understanding novel chemical bonding in aluminum phosphides and gives a direction for the experimental synthesis of multifunctional materials at high pressures.

Etanercept alleviates psoriasis by reducing the Th17/Treg ratio and promoting M2 polarization of macrophages.

INTRODUCTION: This study aimed to investigate the effect of etanercept in psoriasis and its underlying mechanism. METHODS: Female mice were treated with imiquimod (IMQ) to induce psoriasis, and intraperitoneally administered etanercept (0.1-0.4 mg/ml). The RAW264.7 cells were treated with LPS and IFN-γ to polarize to M1, and were treated with IL-13 and IL-4 to polarize to M2. RESULTS: In our study, Etanercept markedly reduced the psoriasis area and severity index scores, and epidermal thickness of mice induced by IMQ. In addition, etanercept reduced the levels of TNF-α and IL-6/12/23, and enhanced the levels of IL-4/10, reduced Th17/Treg ratio and facilitated the polarization of macrophages to M2 in psoriasis model mice. Furthermore, etanercept inhibited the JAK/STAT3 pathway and increased the protein levels of SOCS1 and SOCS3. CONCLUSIONS: In conclusion, our findings indicated that etanercept could inhibit the JAK/STAT3 pathway to reduce Th17/Treg ratio and promote M2 polarization, thereby alleviating psoriasis of mice.

The crystal structures, phase stabilities, electronic structures and bonding features of iridium borides from first-principles calculations.

We present results of an unbiased structure search for the lowest energy crystalline structures of various stoichiometric iridium borides, using first-principles calculations combined with particle swarm optimization algorithms. As a result, besides three stable phases of C2/m-Ir3B2, Fmm2-Ir4B3, and Cm-Ir4B5, three promising metastable phases, namely, P21/m-Ir2B, P21/m-IrB, and Pnma-Ir3B4, whose energies are within 20 meV per atom above the convex hull curve, are also identified at ambient pressure. The high bulk modulus of 301 GPa, highest shear modulus of 148 GPa, and smallest Poisson's ratio of 0.29 for C2/m-Ir3B2 make it a promising low compressible material. C2/m-Ir3B2 is predicted to possess the highest Vickers hardnesses, with a Vickers hardness of 13.1 GPa and 19.4 GPa based on Chen's model and Mazhnik-Oganov's model respectively, and a high fracture toughness of 5.17 MPa m0.5. The anisotropic indexes and the three-dimensional surface constructions of Young's modulus indicate that Ir-B compounds are anisotropic with the sequence of the elastic anisotropy of Ir2B > IrB > Ir4B5 > Ir3B4 > Ir4B3 > Ir3B2. Remarkably, these iridium borides are all ductile. We further find that the four Ir-B phases of P21/m-Ir2B, C2/m-Ir3B2, P21/m-IrB, and Fmm2-Ir4B3 possess dominant Ir-B covalent bonding character, while strong B-B and Ir-B covalent bonds are present in Cm-Ir4B5 and Pnma-Ir3B4, which are responsible for their excellent mechanical properties.

Comparison of clinical and imaging features between pulmonary tuberculosis complicated with lung cancer and simple pulmonary tuberculosis: a systematic review and meta-analysis.

This review aimed to compare the clinical features and CT imaging features between patients with pulmonary tuberculosis (PTB) and lung cancer and patients with PTB alone. That would help to analyse the differences between the two and consequently providing a theoretical basis for the clinical diagnosis and treatment for the patients. Relevant case-control studies focusing on the clinical and CT imaging characteristics between PTB with lung cancer and PTB alone were systematically searched from five electronic databases. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for comparison. As of 2021-07-06, a total of 1735 articles were retrieved. But only 15 articles were finally included for meta-analysis. The results showed a higher proportion of irritable cough, haemorrhagic pleural effusion and lower proportion of night sweating in PTB patients with lung cancer than in PTB patients, and the differences were statistically significant (irritable cough: OR 2.43, 95% CI 1.43-4.11; haemorrhagic pleural effusion: OR 5.73, 95% CI 1.63-20.12; night sweating: OR 0.56, 95% CI 0.36-0.87). In addition, there are many differences in the imaging characteristics of the two types of patients. In conclusion, this review summarises the similarities and differences in clinical symptoms and imaging features between patients with PTB and lung cancer and patients with PTB alone, suggesting that we should be alert to the occurrence of lung cancer in patients with obsolete PTB relapse.

Structural evolution and phase transition mechanism of [Formula: see text] under high pressure.

[Formula: see text] is a layered transition-metal dichalcogenide (TMD) with outstanding electronic and optical properties, which is widely used in field-effect transistor (FET). Here the structural evolution and phase transition of [Formula: see text] under high pressure are systematically studied by CALYPSO structural search method and first-principles calculations. The structural evolutions of [Formula: see text] show that the ground state structure under ambient pressure is the experimentally observed P6[Formula: see text]/mmc phase, which transfers to R3m phase at 1.9 GPa. The trigonal R3m phase of [Formula: see text] is stable up to 72.1 GPa, then, it transforms into a new P6[Formula: see text]/mmc phase with different atomic coordinates of Se atoms. This phase is extremely robust under ultrahigh pressure and finally changes to another trigonal R-3m phase under 491.1 GPa. The elastic constants and phonon dispersion curves indicate that the ambient pressure phase and three new high-pressure phases are all stable. The electronic band structure and projected density of states analyses reveal a pressure induced semiconducting to metallic transition under 72.1 GPa. These results offer a detailed structural evolution and phase diagram of [Formula: see text] under high pressure, which may also provide insights for exploration other TMDs under ultrahigh pressure.

The Impact of the Interactivity of Internet Celebrity Anchors on Consumers' Purchase Intention.

The current study focuses on a novel and recently popular internet phenomenon - celebrity livestreaming marketing. As one of the primary advantages of livestreaming marketing by Internet celebrities, we propose that the timely interactivity of Internet celebrities plays an important role in consumers' purchase intention. Based on stimulus-organism-response theory, this paper further identifies social presence and flow experience as mediators and the consistency of Internet celebrities' image and product image as a moderator and constructs an influence model of Internet celebrities' interactivity on consumers' purchase intention. The responses of a sample of 277 participants were collected by a questionnaire survey. SPSS and Amos were used to analyse the data. The results show that consumers' social presence and flow experience mediate the positive impact of the interactivity of Internet celebrity anchors on influencing consumers' purchase intention. However, there is no significant moderating effect of the consistency of Internet celebrities' image and product image on the relationship between social presence or flow experience and purchase intention. A discussion and implications are offered.

CCL17-CCR4 axis contributes to the onset of vitiligo in mice.

BACKGROUND: Destruction of melanocytes mediated by autoimmunity is currently believed as the main cause of vitiligo. This article aims to identify the role of CC chemokine ligand 17 (CCL17)-CC chemokine receptor 4 (CCR4) axis in vitiligo and provide new possibilities for the clinical treatment of vitiligo. METHODS: A total of 30 patients with vitiligo from Affiliated Huaian No. 1 People's Hospital of Nanjing Medical University were recruited based on the inclusion and exclusion criteria. Trephine was used to obtain skin samples from the lesion area and its surrounding normal areas, and the expression levels of CCL17, CCR4, Tbx21, Eomes, and Blimp1 were determined by quantitative reverse transcription polymerase chain reaction. Vitiligo mouse model was established by adoptively transferring CFP-PMEL CD8+ T cells into sublethally irradiated Krt14-Kitl* mice. Recipient mice received intraperitoneal injection of 1 × 106 plaque-forming units of rVV-hPMEL on the same day of transfer. The degree of depigmentation was scored blindly by one observer 5 weeks after vitiligo induction. CFP-PMEL CD8+ T cells migration to skin, draining lymph nodes, spleen, and blood were detected by flow cytometry. CCR4 blockade was performed by intraperitoneal injection of neutralizing antibody. RESULTS: The expression levels of CCL17, CCR4, Tbx21, Eomes, and Blimp1 in skin lesions were significantly increased compared with that in surrounding normal areas. CCL17-/- and CCR4-/- mice exhibited significantly lower disease scores than WT mice. The CFP-PMEL CD8+ T cells accumulation was significantly decreased in the skin of CCL17-/- and CCR4-/- mice, but was not changed in draining lymph nodes, spleen, and blood. Administration of CCR4 neutralizing antibody decreased the degree of depigmentation and the recruitment of CFP-PMEL CD8+ T cells to the skin, while keeping the number of T cells in draining lymph nodes unchanged. CONCLUSION: Targeting CCL17-CCR4 axis might inhibit T cell migrating to skin and alleviate vitiligo progression.

Insights into the Structures and Bonding of Medium-Sized Cerium-Doped Boron Clusters.

Since the discovery of metal-doped boron clusters attracted great significance to create a new class of materials, research interests have been directed to chemical bonding and structural evolution of lanthanide boride clusters. Here, we perform an extensive ground-state structure search for the CeBn and CeBn- clusters in the size range from 9 to 18 using the Crystal structure AnaLYsis by Particle Swarm Optimization method and density functional theory optimization. It is found that the ground-state structures in both neutral and anionic series possess half-sandwich geometry. The host boron moiety in neutral series has a tendency to form borophene-like geometry. The pentagonal and hexagonal holes are more common in the larger anionic CeBn- series. The theoretical photoelectron spectroscopy has been simulated by applying time-dependent density functional theory calculations. The neutral CeB14 cluster is identified as a magic cluster on the basis of its robust relative stability with respect to its neighbors. Electronic structure and chemical bonding analyses reveal that the CeB14 cluster possesses a large HOMO-LUMO gap and enhanced stability with strong delocalized π and δ bonding via interactions between the Ce 5d- and B 2p-AOs.

CircRNA circ_0067772 aggravates the malignant progression of cutaneous squamous cell carcinoma by regulating miR-1238-3p/FOXG1 axis.

BACKGROUND: Cutaneous squamous cell carcinoma (CSCC) is a severe malignancy derived from skin. Dysregulated circular RNAs (circRNAs) might play vital roles in tumor development. OBJECTIVE: Here, we aimed to explore the function of a novel circRNA circ_0067772 in CSCC. METHODS: Quantitative real-time PCR (qRT-PCR) or Western blot assay was performed to determine the expression of circ_0067772, microRNA (miR)-1238-3p and forkhead box protein G1 (FOXG1). Cell proliferation was assessed by Cell Counting Kit-8 (CCK-8) assay and colony formation assay. Transwell assay and wound healing assay were employed to examine cell metastasis. Flow cytometry was employed to monitor cell cycle and apoptosis. The target association between miR-1238-3p and circ_0067772 or FOXG1 was validated by dual-luciferase reporter assay. Moreover, role of circ_0067772 in vivo was investigated via xenograft model in nude mice. RESULTS: Circ_0067772 and FOXG1 were upregulated, while miR-1238-3p was downregulated in CSCC tissues and cells. Circ_0067772 knockdown conferred inhibitory effects on cell proliferation, migration and invasion of CSCC cells. MiR-1238-3p served as a target of circ_0067772, whose silencing could reverse circ_0067772 knockdown-induced inhibitory impact on the malignant cellular behaviors. Circ_0067772 positively regulated FOXG1 expression by antagonizing miR-1238-3p. Additionally, miR-1238-3p could repress CSCC cell proliferation, migration and invasion by targeting FOXG1. Also, circ_0067772 knockdown hindered CSCC tumor growth in vivo. CONCLUSION: Our study identified a novel oncogenic circRNA and the involvement of circ_0067772/miR-1238-3p/FOXG1 axis in CSCC development, providing a target for CSCC therapy.

A20 deficiency in myeloid cells deteriorates the onset of vitiligo in mice.

Melanocyte-specific CD8+ T cells enrichment correlates with the severity of vitiligo, and the role of A20 derived from myeloid cells in the enrichment of pathogenic T cells is unknown. Premelanosome (PMEL)-specific transgenic CD8+ T cells were adoptive transferred into Krt14-Kitl* mice to construct the vitiligo model, which was further mated with A20MKO mice and IKK2fl/fl mice. Bone marrow cells were stimulated with 30% L929 cell-conditioned medium, Fc-human tumor necrosis factor, and lipopolysaccharides to induce bone marrow-derived macrophages (BMDMs). The relative expression of CCL2, CCL5, and IL12A was detected with real-time PCR, and nuclear factor kappa B (NFκB) related molecules were detected with Western blots. Fluorescence-activated cell sorting (FACS) was utilized to assay the percent of innate and adaptive immune cells in the spleen and bone marrow, and CD45+ T in the skin. Down-regulated A20 was detected in the skin biopsies of vitiligo patients. A20 deficiency did not affect the development of T cells, B cells, macrophages, and neutrophils. A20 negatively regulated the induction of proinflammatory chemokines (CCL2, CCL5, and IL12A) and NFκB-related molecule expression in BMDMs, which could be blocked by NFκB knockout. It further revealed that A20 negatively regulated the onset of vitiligo in mice with diminished CD45+ cells enrichment, which could also be reversed by NFκB knockout. A20 deficiency in myeloid cells could deteriorate the onset of vitiligo in mice, and A20 can be considered as a treatment target.

Dissociation of dinitrogen on iron clusters: a detailed study of the Fe16 + N2 case.

The coalescence of two Fe8N as well as the structure of the Fe16N2 cluster were studied using density functional theory with the generalized gradient approximation and a basis set of triple-zeta quality. It was found that the coalescence may proceed without an energy barrier and that the geometrical structures of the resulting clusters depend strongly on the mutual orientations of the initial moieties. The dissociation of N2 is energetically favorable on Fe16, and the nitrogen atoms share the same Fe atom in the lowest energy state of the Fe16N2 species. The attachment of two nitrogen atoms leads to a decrease in the total spin magnetic moment of the ground-state Fe16 host by 6 µB due to the peculiarities of chemical bonding in the magnetic clusters. In order to gain insight into the dependence of properties on charge and to estimate the bonding energies of both N atoms, we performed optimizations of Fe16N and the singly charged ions of both Fe16N2 and Fe16N. It was found that the electronic properties of the Fe16N2 cluster, such as electron affinity and ionization energy, do not appreciably depend on the attachment of nitrogen atoms but that the average binding energy per atom changes significantly. The lowering in total energy due to the attachment of two N atoms was found to be nearly independent of charge. The IR and Raman spectra were simulated for Fe16N2 and its ions, and it was found that the positions of the most intense peaks in the IR spectra strongly depend on charge and therefore present fingerprints of the charged states. The chemical bonding in the ground-state Fe16N20,±1 species was described in terms of the localized molecular orbitals.

Negative Poisson Ratio in Two-Dimensional Tungsten Nitride: Synergistic Effect from Electronic and Structural Properties.

Low-dimensional materials with high stabilities and outstanding mechanical properties are essential for next generation microelectromechanical systems (MEMS). The successful synthesis of two-dimensional (2D) tungsten nitride makes it a promising candidate for the MEMS application. Here, we have confirmed the existence of experimentally synthesized W2N3 and predicted three additional new 2D monolayer tungsten nitrides: WN2, WN4, and W3N based on extensively structural searches by CALYPSO method and first-principle calculations. The calculations indicate that the nitrogen-rich WN4 monolayer possesses large in-plane negative Poisson ratios attributed to the 4-fold-coordinated WN4 νx = -0.103 and νy = -0.113, which are tetrahedron combined with the strong coupling between the 2p orbitals of N and 5d orbitals of W. Our findings not only enrich the family of 2D transition metal nitrides with excellent mechanical properties but also open avenues for design and synthesis of other novel 2D layered materials.

Tuning of Structure Evolution and Electronic Properties through Palladium-Doped Boron Clusters: PdB16 as a Motif for Boron-Based Nanotubes.

Transition metal-doped electronic deficiency boron clusters have led to a vast variety of electronic bonding properties in chemistry and materials science. We have determined the ground state structures of PdBn0/- (n = 10-20) clusters by performing CALYPSO search and density functional theory (DFT) optimization. The identified lowest energy structures for both neutral and anionic Pd-doped boron clusters follow the structure evolution from two dimensional (2D) planar configurations to 3D distorted Pd-centered drum-like or tubular structures. Photoelectron spectra are simulated by time-dependent DFT theoretical calculations, which is a powerful method to validate our obtained ground-state structures. More interestingly, two "magic" number clusters, PdB12 and PdB16, are found with enhanced stability in the middle size regime studied. Subsequently, molecular orbital and adaptive natural density partitioning analyses reveal that the high stability of the PdB16 cluster originates from doubly σ π aromatic and bonding interactions of d-type atomic orbitals of the Pd atom with tubular B16 units. The tubular C8v PdB16 cluster, with robust relative stability, is an ideal embryo for forming finite and infinite nanotube nanomaterials.

The Microstructure and Electronic Properties of Yttrium Oxide Doped With Cerium: A Theoretical Insight.

Trivalent Cerium (Ce3+) doped Yttrium Oxide (Y2O3) host crystal has drawn considerable interest due to its popular optical 5d-4f transition. The outstanding optical properties of Y2O3:Ce system have been demonstrated by previous studies but the microstructures still remain unclear. The lacks of Y2O3:Ce microstructures could constitute a problem to further exploit its potential applications. In this sense, we have comprehensively investigated the structural evolutions of Y2O3:Ce crystals based on the CALYPSO structure search method in conjunction with density functional theory calculations. Our result uncovers a new rhombohedral phase of Y2O3:Ce with R-3 group symmetry. In the host crystal, the Y3+ ion at central site can be naturally replaced by the doped Ce3+, resulting in a perfect cage-like configuration. We find an interesting phase transition that the crystallographic symmetry of Y2O3 changes from cubic to rhombohedral when the impurity Ce3+ is doped into the host crystal. With the nominal concentration of Ce3+ at 3.125%, many metastable structures are also identified due to the different occupying points in the host crystal. The X-ray diffraction patterns of Y2O3:Ce are simulated and the theoretical result is comparable to experimental data, thus demonstrating the validity of the lowest energy structure. The result of phonon dispersions shows that the ground state structure is dynamically stable. The analysis of electronic properties indicate that the Y2O3:Ce possesses a band gap of 4.20 eV which suggests that the incorporation of impurity Ce3+ ion into Y2O3 host crystal leads to an insulator to semiconductor transition. Meanwhile, the strong covalent bonds of O atoms in the crystal, which may greatly contribute to the stability of ground state structure, are evidenced by electron localization function. These obtained results elucidate the structural and bonding characters of Y2O3:Ce and could also provide useful insights for understanding the experimental phenomena.

Mechanical properties of tantalum carbide from high-pressure/high-temperature synthesis and first-principles calculations.

As a member of the refractory metal carbide family of materials, TaC is a promising candidate for ultra-high temperature ceramics (UHTC) with desirable mechanical strength. TaC sample quality and therefore mechanical properties are strongly dependent on synthesis method, and atomistic origins of mechanical failure are difficult to assign. Here, we have successfully synthesized high quality densified TaC samples at 5.5 GPa and 1400 °C using the high pressure and high temperature (HPHT) sintering method, with Vickers hardness determined to be 20.9 GPa. First-principles calculations based on the recently developed strain-stress method show that the ideal indentation strength of TaC is about 23.3 GPa in the (11[combining macron]0)[001] direction, in excellent agreement with experimental results. The detailed indentation shear deformation analysis and structural snapshots from the calculations indicate that the slip dislocations of TaC layers are the main structural deformation mode during the Vickers indentation process, and that the strong directional Ta-C bonds are responsible for the high mechanical strength of TaC. HPHT synthesis is shown to produce TaC samples with superior strength, and together with accurate first-principles calculations offers crucial insights for rational design and synthesis of novel and advanced UHTC materials.