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Graphene has been emerging as an ideal mid-infrared saturable absorber (SA) due to its broadband absorption, ultrafast nonlinear optical response, high stability and thermal tolerance. However, the current routes (e.g. chemical vapor deposition and spin coating) for constructing graphene SAs are suffering from the limited flexibility in substrate choice and the introduction of impurities during the transfer process, resulting in poor film quality and unstable laser modulation. Here, we demonstrate a high-quality graphene SA mirror (GSAM) grown directly on calcium fluoride (CaF2) substrate by a low-temperature plasma enhanced chemical vapor deposition (PECVD) method for mid-infrared pulse modulation. The controllable growth of high-quality graphene film on the nickel-modified CaF2 substrate is realized by adjusting the growth time and hydrocarbon ratio during PECVD process. Consequently, the GSAM shows excellent nonlinear optical absorption with the modulation depth of 11.2%. By inserting the GSAM into the Er:ZBLAN fiber laser, a stable passive Q-switched (QS) operation can be achieved with an average output power of 142 mW and a pulse width of 300.2 ns. The slope efficiency of QS laser is up to 17.4% and the peak power is 7.76 W. Our strategy paves the way for developing high quality and modulation stability GSAM towards industrial applications of pulsed mid-infrared lasers.

Diamond, cubic boron nitride (c-BN), silicon (Si), and germanium (Ge), as examples of typical strong covalent materials, have been extensively investigated in recent decades, owing to their fundamental importance in material science and industry. However, an in-depth analysis of the character of these materials' mechanical behaviors under harsh service environments, such as high pressure, has yet to be conducted. Based on several mechanical criteria, the effect of pressure on the mechanical properties of these materials is comprehensively investigated. It is demonstrated that, with respect to their intrinsic brittleness/ductile nature, all these materials exhibit ubiquitous pressure-enhanced ductility. By analyzing the strength variation under uniform deformation, together with the corresponding electronic structures, we reveal for the first time that the pressure-induced mechanical softening/weakening exhibits distinct characteristics between diamond and c-BN, owing to the differences in their abnormal charge-depletion evolution under applied strain, whereas a monotonous weakening phenomenon is observed in Si and Ge. Further investigation into dislocation-mediated plastic resistance indicates that the pressure-induced shuffle-set plane softening in diamond (c-BN), and weakening in Si (Ge), can be attributed to the reduction of antibonding states below the Fermi level, and an enhanced metallization, corresponding to the weakening of the bonds around the slipped plane with increasing pressure, respectively. These findings not only reveal the physical mechanism of pressure-induced softening/weakening in covalent materials, but also highlights the necessity of exploring strain-tunable electronic structures to emphasize the mechanical response in such covalent materials.

In this paper, the causes analysis of the cracking accident at the lead clamp weld-fusion line of transformer in the extra-high voltage substation was conducted. On-site non-destructive detection of weld defects was carried out to determine the size and location of the defects. An anatomical analysis of the clamp sample revealed that there was serious incomplete penetration and incomplete fusion in the internal structure of the weld, which seriously affected the structural strength of the weld. The causes of welding defects were further analyzed, and suggestions for improving product quality and strengthening inspection supervision were put forward.

Let X be a compact metric space and T : X → X be continuous. Let h*(T) be the supremum of sequence entropies of T over all subsequences of and S(X) be the set of h*(T) for all continuous maps T on X. It is known that S(X) {∞, 0, log 2, log 3, ...}. In this paper it is proved that if X is a finite tree or the unit circle S1 then S(X) = {∞, 0, log 2}. Moreover, it is shown that if X = [0, 1] and T has zero topological entropy then the set of sequence entropy pairs is countable and any sequence entropy pair is asymptotic.All the possible sets of S(X) for zero-dimensional spaces X are determined. Moreover, it is shown that for each there is a continuum Xn with dimension n such that S(Xn) = {∞, 0, log 2, log 3, ...}.

In this paper notions of sensitive sets (S-sets) and regionally proximal sets (Q-sets) are introduced. It is shown that a transitive system is sensitive if and only if there is an S-set with Card(S) ≥ 2, and for a transitive system each S-set is a Q-set. Moreover, the converse holds when (X, T) is minimal. It turns out that each transitive (X, T) has a maximal almost equicontinuous factor.According to the cardinalities of the S-sets, transitive systems are divided into several classes. Characterizations and examples are given for this classification both in minimal and transitive non-minimal settings. It is proved that for a transitive system any entropy set is an S-set, and consequently, a transitive system which has no uncountable S-sets has zero topological entropy. Moreover, it is shown that a transitive, non-minimal system with dense set of minimal points has an infinite S-set, and there exists a Devaney chaotic system which has no uncountable S-set. Finally, a non-minimal sensitive E-system is constructed such that each of its S-set has cardinality at most 4.

With the aid of ab initio calculation, the lattice constants and cohesive energies of some ordered metastable Au–W compounds are calculated and used in deriving an n-body Au–W potential under the embedded atom method. On the basis of the proven realistic Au–W potential, molecular dynamics simulations predict the phase selection over the entire composition: the metastable Au100-xWx phase in an fcc structure is more stable than in a bcc structure when 0≤x≤43, whereas the bcc structure becomes energetically favored when 43

The lattice constants and cohesive energies of some possible metastable Cu–W compounds are obtained by ab initio calculation and the formation of a metastable phase at Cu75W25 is predicted for the equilibrium immiscible Cu–W system. The prediction is in agreement with the fact that a metastable hcp phase was indeed observed in the Cu75W25 multilayer films upon ion beam mixing. Furthermore, some of the ab initio calculated properties are used in deriving an n-body Cu–W potential under the embedded atom method. The constructed Cu–W potential is then used to predict the phase stability of the metastable Cu–W phases over the entire composition and the prediction is also supported by some experimental observations.

A new metastable hcp phase was observed by ion mixing Cu–W multilayered films with compositions of Cu75W25 and Cu85W15. In thermodynamic modelling, a Gibbs free-energy diagram was constructed applying Miedema's model, and the calculated results were in good agreement with the experimental observations. Moreover, the restricted kinetic condition involved in ion mixing at far-from-equilibrium is also discussed and a sliding mechanism for growing the hcp phase was proposed and the lattice constants deduced accordingly were in good agreement with the experimental values.

Blue-green electroluminescent diodes utilizing tris (8-quinolinolato)-aluminum doped poly (vinylcarbazole) have been demonstrated. A Schottky-type electroluminescent diode of the polymer film is driven at 20 V and has a peak emission wavelength of 490 nm at room temperature with lifetime up to 4 h.

A phase field dislocation dynamics model that can model widely extended dislocations is presented. Through application of this model, we investigate the dependence of equilibrium stacking fault width (SFW) on the material γ-surface in fcc metals. This phase field model includes a direct energetic dependence on a parametrization of the entire γ-surface, which is directly informed by density functional theory. A wide range of materials are investigated and include both very low stacking fault energy (SFE) materials, such as silver, and high SFE materials, such as palladium. Additionally, analysis shows that by accounting for the unstable stacking fault energy, γU, we can better describe the material dependence of the equilibrium SFW rather than using only the intrinsic SFE, γI. Specifically, we see a direct dependence of the stable SFW between partial dislocations on the energy difference (γU − γI), which describes the energy barrier that partial dislocations must overcome in order to widen the stacking fault.