Results 1 - 10 of 58
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[en] Highlights: •Twist grain boundary has lower grain-boundary energy. •Twist grain-boundary has similar electronic structure to that in crystal. •Charge and magnetic-moment fluctuations are large within tilt grain boundary. •Bi-collinear AFM is most stable even with existence of grain boundary. •Insulating Fe-vacancy phase is stable with existence of twist grain boundary. -- Abstract: The electronic and atomic structures of the twist and tilt grain boundaries (GB) of the iron-based superconductor KFe2Se2 are studied based on the simulations of the first principles density functional theory. Our results have clarified that the Σ5[0 0 1] twist grain boundary of KFe2Se2 with layered structure has the lower grain-boundary energy. The local structure and the main features of the basic electronic structure within the [0 0 1] twist grain-boundary region have small differences compared with those in KFe2Se2 crystal. The large fluctuations of the charges and magnetic moments are found in the [0 0 1] tilt grain-boundary regions, especially the former are more prominent. The bi-collinear anti-ferromagnetic order is the most stable magnetic order even with grain boundaries in the bulk. The √(5)a×√(5)a superstructure of Fe-vacancies in K2Fe4Se5 phase is intrinsically related to the coincident-site lattice of Σ5[0 0 1] twist grain boundary
[en] We study the effects of the next-nearest-neighbor hopping and nearest-neighbor interactions on topological phases in a one-dimensional generalized Kitaev model. In the noninteracting case, we define a topological number and calculate exactly the phase diagram of the system. With addition of the next-nearest-neighbor hopping, the change of phase boundary between the topological and trivial regions can be described by an effective shift of the chemical potential. In the interacting case, we obtain the entanglement spectrum, the degeneracies of which correspond to the topological edge modes, by using the infinite time-evolving block decimation method. The results show that the interactions change the phase boundary as adding an effective chemical potential which can be explained by the change of the average number of particles. (paper)
[en] The molecular weights of chlorinated polypropylene in toluene solution at various concentrations were determined. Limiting molecular weight of polymers under ultrasonic irradiation could be obtained by the data fitting technique. The fitting accuracy of common kinetic equations for experimental data of chlorinated polypropylene was evaluated. It was found that the fitting results of these kinetic equations were not satisfactory. In order to fit the experimental data better, a new second order kinetic equation was proposed. This equation described well the experimental data. It was found that the fitting results for available experimental data of other polymers using this new equation were better than when using equations in the literature. Therefore, the equation proposed here is a new supplement to the original kinetic equations for polymers under ultrasonic irradiation. For chlorinated polypropylene, the rate of ultrasonic degradation decreased with increasing concentration while the limiting molecular weights increased with increasing concentration
[en] Local fluctuations and fluctuation-induced transitions in catalytic CO oxidation are studied with field electron microscopy on the (112) facets of a -oriented Pt field emitter tip. The reaction is investigated in the bistable range close to the cusp point (critical point) that terminates the bistability range in pCO, T-parameter space. The amplitude and the spatial coherence of the fluctuations increase on approaching the critical point. The fluctuations are spatially well correlated on each flat (112) facet, but their correlation decays rapidly across stepped regions that terminate the flat facets. On smaller (112) facets, an onset of fluctuation-induced transitions is observed earlier (i.e., further away from the critical point) than for larger (112) facets. The behavior of the reaction system near the cusp point appears to be similar to that of an equilibrium system near the critical point. The observed fluctuations are mimicked in a simple reaction model for CO oxidation on surfaces that incorporates both rapid diffusion of adsorbed CO, and superlattice ordering of adsorbed immobile oxygen. The steady states of the model exhibit a cusp bifurcation, from a regime of bistability to one of monostability. The fluctuations increase near this cusp point, as in experiment. This behavior is analyzed via kinetic Monte Carlo simulations and analytic procedures, focusing on the consequences for fluctuation-induced transitions
[en] A pinch-off phenomenon is discovered in the evolution of 2D wormlike nanoclusters formed in homoepitaxial adlayers. This feature is shown to distinguish mass transport via periphery diffusion from other mechanisms. Continuum modeling of such evolution accurately describes experimental observations, particularly if one incorporates the anisotropy in step-edge line tension
[en] MicroRNAs (miRNAs) play significant roles in multiple diseases by regulating the expression of their target genes. Type 2 diabetes mellitus (T2DM) is a chronic endocrine and metabolic disease with complex mechanisms. T2DM can result in diabetic osteoporosis (DO), which is characterized by bone loss, decreased bone mineral density and increased bone fractures. The promotion of osteogenic differentiation of osteoblasts is an effective way to treat osteoporosis. In the present study, high glucose (HG) and free fatty acids (FFA) were employed to mimic T2DM in MC3T3-E1 cells. To induce osteogenic differentiation, MC3T3-E1 cells were cultured in osteogenic medium. The results showed that osteogenic differentiation was significantly suppressed by HG and FFA. We found that miR-132 expression was significantly upregulated and much higher in HG-FFA–induced cells than other selected miRNAs, indicating that miR-132 might play an important role in DO. Furthermore, overexpression of miR-132 markedly inhibited the expression of key markers of osteogenic differentiation and alkaline phosphatase (ALP) activity. Reciprocally, inhibition of miR-132 restored osteogenic differentiation, even under treatment with HG-FFA. We also showed that Sirtuin 1 (Sirt1) was one of the target genes of miR-132, whose expression was controlled by miR-132. Ectopic expression of Sirt1 reversed the decrease in osteogenic differentiation caused by miR-132 and HG-FFA. These results demonstrated the direct role of miR-132 in suppressing osteogenic differentiation through downregulating Sirt1. Moreover, we demonstrated that peroxisome proliferator-activated receptor β/δ (PPARβ/δ) was a downstream molecule of Sirt1, and its knockout by PPARβ/δ siRNA significantly abolished the promotive effects of Sirt1 on osteogenic differentiation, indicating that Sirt1 functioned in a PPARβ/δ–dependent manner. Taken together, we provide crucial evidence that miR-132 plays a key role in regulating osteogenic differentiation through Sirt1 in a PPARβ/δ–dependent manner, indicating that miR-132 and Sirt1-PPARβ/δ may act as potential therapeutic targets for T2DM–induced osteoporosis. - Highlights: • MiR-132 participates in regulating osteogenic differentiation of MC3T3-E1 cells. • Sirt1 is a target gene of miR-132. • Sirt1 is the effector of miR-132 in regulating osteogenic differentiation. • MiR-132-Sirt1 regulates osteogenic differentiation in a PPARβ/δ–dependent manner.
[en] Heat transfer of supercritical water in a 2 × 2 rod bundle with wrapped wire and two channels was investigated experimentally. The non-uniformity of circumferential wall temperature distribution in heating rods was observed. The heat transfer deterioration (HTD) occurred at low G/q in whole rod bundle region while the secondary HTD was observed close to the upstream. The HTD at downstream was restrained due to the disturbance of wrapped wire. The studies show that the heat transfer behavior is similar to that in single tube. The correlation of Bishop et al. (1964) gives the best prediction of Nusselt number. Compared with a 2 × 2 bare rod bundle, the wrapped wire strengthens heat transfer. (authors)
[en] Graphical abstract: A new Eötvös equation, g = B_1(T_c − T), was obtained, where g is the molar surface Gibbs energy; B_1 = s is the molar surface entropy; the product of B_1 with critical temperature, T_c, is the molar surface enthalpy, h, which is a temperature-independent constant. - Highlights: • The new concept of molar surface Gibbs free energy, g, was proposed. • Using g, the traditional Eötvös equation was improved to be a new one. • An equation to predict surface tension of ILs is derived with refractive index and g. - Abstract: Two new amino acid ionic liquids (AAILs) [C_nmim][Thr] (n = 2, 4) (1-alkyl-3-methylimidazolium threonine salt) were prepared and characterized. The values of density, surface tension and refractive index of the ILs were measured at T = (288.15 to 328.15) K and the values of the molar surface Gibbs free energy, g, were calculated. Using the molar surface Gibbs free energy, the traditional Eötvös equation was improved to be a new Eötvös equation. It is found that the slope of the new Eötvös equation is the molar surface entropy of the ILs and the intercept is the molar surface enthalpy which is a temperature-independent constant. With the help of the refractive index and the molar surface Gibbs free energy, an equation to predict surface tension of the ILs was derived. Using this equation, predicted values of surface tension with the corresponding experimental ones are highly correlated and extremely similar. According to a new scale of polarity for ILs, the polarity of ionic liquids [C_nmim][Thr] (n = 2, 4) was estimated.
[en] The reflecting of a single attosecond pulse from a periodic Mo/Si multilayer was investigated. By changing the number of bi-layers, the periodic multilayer showed greatly different spectral and temporal responses of the attosecond pulse reflection, which has been discussed in detail in this paper. The capability of attosecond pulse reflection of the periodic multilayers with different bi-layer numbers has been evaluated using suitable temporal parameters. In addition, the condition for obtaining high-efficiency reflected pulses has been analyzed by comparing the pulse responses of the periodic multilayer with different layers. The transfer-matrix method together with the fast Fourier transform has been used in our simulation
[en] In a beta radioluminescence nuclear battery, the beta energy is converted to light with the phosphor material, and then to electricity via photovoltaic cells. A method to optimize the thickness of phosphor layer is established in this study; the match between the luminescence spectrum and the photovoltaic cell is analyzed. The optimal parameters and output performance of the nuclear battery based on a sandwich-structure 147Pm/ZnS:Cu/photovoltaic cell are determined with the MCNP, transport theory of light, and detailed balance limit of efficiency. The battery prototypes are fabricated and tested, and the experimental optimal thickness matches that of the theoretical result well. (author)