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The mud film thickness on the outer surface of casing and its distribution laws are important factors affecting the cementation quality at casing–cement interfaces. So far, however, the distribution laws of mud film thickness on the outer surface of casing at different inclinations and its effect on the interfacial cementing strength have never been reported in literatures. In this paper, the mud film thickness at different parts on the outer surface of simulated casing (steel pipe) was measured at the inclination of 0°, 30°, 60° and 86°, respectively, using the independently designed experimental device. Then, the distribution law of mud film thickness on the outer surface of casing and its effect on the interfacial cementing strength were summarized. And the following research results were obtained. First, when the inclination increases from 0° to 86°, the mud film thickness changes from uniform distribution to thin-and-thick distribution, and the area proportions of thinner and thicker mud films both increase. And especially at the inclination of 86°, the mud film thickness on the upper surface is very large, and there are large exposed areas on the left and right surfaces of the steel pipe. Second, the cementing strength at the casing–cement interface of the exposed casing is much higher than that at the interface with mud film. And with the increase of inclination, the interfacial cementing strength with mud film tends to increase. Third, with the increase of inclination, the interfacial cementing strength increases successively, which is closely related to the area proportion of the exposed steel pipe to the solid mud film on the outer surface. In conclusion, the exposed area of the simulated casing on the outer surface is a key factor affecting its interfacial cementing strength. Keywords: Casing–cement interface, Inclination, Mud film thickness, Distribution law, Cementing strength, Exposed outer surface of casing

In this paper, the structural, electronic and optical properties of (N, P), (N, S), (C, P) and (C, S) co-doped CeO2 are studied by using the method of density functional theory (DFT) + U method. The calculated lattice constant, the charge, the bond order, the cell volume and the bond length of CeO2 are consistent with previous experimental and theoretical results. For co-doped CeO2 systems, the calculated results show that the lattice constants, the bond order of Ce O as well as the cell volume increase, while the charge of Ce decrease. Due to co-doping, the energy gap (Eg) between valence band and conduction band becomes narrower than that of pure CeO2. Meanwhile, the electron structures of the co-doped CeO2 are changed, which may lead to transformation of optical properties. Nonmetallic atomic orbital (C 2p, N 2p, P 3p, S 3p) and metal atomic orbital (Ce 4f and 5d) are hybridized, except for the hybridization between Ce (4f and 5d) and O (2p). Compared with CeO2, Eg between Ce 4f and Ce 5d becomes smaller. Further, the optical absorption, refractive index and reflectivity of them are investigated. The calculated results reveal that their absorption edges have a red shift. Co-doping enhances visible light photocatalytic activity, which is related to the transition of valence band → conduction band, and Ce 4f → Ce 5d. The co-doped CeO2 has high refractive index and reflectivity. Therefore they may be becoming an important materials in single (or multilayered) optical coatings and optical reflective pigments.

Two-dimensional metal-semiconductor heterostructures with tunable Schottky barriers are currently attracting extensive interests, owing to their novel properties and potential applications in nanodevices. Here, heterostructures of semiconducting monolayer gold sulfides and graphene (Gr) with tunable Schottky barriers and contact types are reported based on first-principles calculations. α-, β-Au2S/Gr are n-type Schottky contacts with Φ n = 0.14 eV and 1.24 eV, respectively. They could be transformed into p-type Schottky contacts via applying vertically compressive strain. α-, β-, γ-AuS/Gr are ohmic, p-type and n-type Schottky contacts with Φ n = −0.34 eV, Φ p = 0.22 eV, Φ n = 0.22 eV, respectively. The ohmic contact of α-AuS/Gr evolves to a n-type Schottky contact with increasing vertically compressive strain, while the p-type Schottky contact of β-AuS/Gr changes to an ohmic contact. Furthermore, the mechanism of Schottky-barrier modulation via vertical strain underlies that the relative Dirac-cone position of Gr in heterostructures can be tuned by adjusting interfacial charge rearrangement. Benefitting from the tunable Schottky barriers and contact types, heterostructures of semiconducting monolayer gold sulfides and Gr are promising candidates for future-generation nano-devices.

In this paper, we study the difference in stability between two low refractive index interfaces (0 0 1) and (1 1 0) of Fe3Si/GaAs heterostructures, the optimal geometry, adhesion work, interfacial energy, interfacial distance and interface electronic structure were calculated by using density functional theory (DFT). We constructed four different Fe3Si/GaAs heterostructures models by combining different stacking methods with two interfaces. Changes in interfaces and stacking methods can affect adhesion work, interfacial distance, and interfacial energy. The research shows that the hollow-site has a larger adhesion work and smaller interfacial energy than the top-site. Based on the data of the adhesion work and the interfacial energy, the mechanical properties and ductility of the (0 0 1) interface with hollow-site is stronger than others. In order to enhance the stability and fracture toughness of the system, more (0 0 1) interface with hollow-site need to be formed. At the same time, it has the smallest interfacial energy and is easier to form. The electronic structure of the (0 0 1) interface with hollow-site and the contribution of electron orbital hybridization to the formation of covalent bonds at the interface are also discussed. A new covalent bond is formed at the interface, and Fe-As bond is easier to form than Si-As bond.

A dual-level direct dynamics method is employed to study the reaction mechanism of (CH3)2NNH2 (unsymmetrical dimethylhydrazine) with the oxygen (O) atom. The geometries and frequencies of all the stationary points are optimized at the MPW1K/6-311G (d, p) level, and the energy profiles are further refined by the interpolated single-point energies (ISPE) method at the BMC-CCSD level of theory. The rate constants of the O atom with (CH3)2NNH2 are evaluated over a wide temperature range of 200–2000 K by using the canonical variational transition-state theory (CVT) with the small curvature tunneling correction (SCT). The agreement between the theoretical and experimental rate constants is good around room temperature. The channels of H abstraction from the -NH2 position favor temperatures below 1200 K. With increasing temperature, contributions from other channels should be taken into account. The reactivity of N2H4, CH3NHNH2, and (CH3)2NNH2 toward atomic O is compared to explore the methylation effect.

Arborous structure SnO 2 porous films were electrodeposited on Ti substrate using pulse-potential technique. The deposition process of SnO 2 was investigated through cyclic voltammetry, potentiostatic electrolysis and chronoamperometry. It was found that SnO 2 and metallic Sn were codeposited under the low pulse potential (−0.6 V vs . Ag/AgCl). The electrodeposited Sn was anodic oxidized under the subsequent high pulse potential (−0.1 V vs . Ag/AgCl). The formation of SnO 2 possessed an instantaneous nucleation process. Dye-sensitized solar cells were fabricated using the electrodeposited SnO 2 porous films. The photo-electricity conversion efficiency was about 0.47%.

Transport of an inertial Brownian motor moving in an asymmetric periodic potential driven by an external force and correlated noises is investigated. Using the numerical algorithm, the asymptotic mean velocity (AMV) for characterizing directed transport is obtained. The effects of the external driving force f and the correlation λ between the two noises on the AMV are discussed. The results manifest: (1) the external driving force and the correlation between the two noises can lead to the phenomena like current reversal. (2) The competitions among the external driving force and the correlation between the two noises are necessary for current reversal, i.e., f λ > 0 . (3) Different directions of transport are found for different masses of the Brownian particles under the condition f λ > 0 . Therefore a theoretical study is suggested for separating Brownian particles according to their different masses in the ratchet system.

In order to reduce the noise disturbance to ECG signals, ECG front-end signal processing method is proposed in this paper. In this method, the RFI filter is a bridge type differential low-pass filter. The input amplifier is high precision instrument amplifier AD8220 which has JFET input stage characteristic, the low-pass filter is a five order Bessel filter which has the most flat amplitude and phase response, and the right leg driving circuit is precision operational amplifier OP2177 which has low input bias current. The method is characterized with simpleness, easy integration, good stability and high precision. It is significant for the future electrocardiogram instrument.