Based on the contra-directional coupling, a composite structure consisting of two coupled metal-insulator-metal (MIM) waveguides is proposed to act as an attractive plasmonic reflector. By introducing a defect into one of the MIM waveguides, we show that such a composite structure can be operated as a plasmonic nanocavity with a high quality factor. Both symmetric and anti-symmetric cavity modes are supported in the plasmonic cavity, and their resonance frequencies can be tuned by controlling the defect width. The present structures could have a significant impact for potential applications such as surface plasmon mirrors, filters and solid-state cavity quantum electrodynamics
Composite metal-dielectric-metal (MDM) surface plasmon polariton (SPP) structures are first proposed to realize the ultra-short optical splitters with simplified designs. The operation mechanism is based on the contra-directional coupling achieved in composite plasmonic slot waveguides. In certain cases, the switching function can also be realized. It is further shown that based on the same physical mechanism multi-dielectric-core composite MDM structures could serve as a novel plasmonic waveguide crossover component with low cross talk and high throughput.
Accurate construction of a shale-reservoir fracture network is a prerequisite for optimizing the fracturing methods and determining shale-gas extraction schemes. Considering the influence of geological conditions, stress levels, desorption–adsorption, and fissure characteristics and distribution, establishing a shale-gas reservoir fracture-network model based on a random fracture network is significant. According to the discrete network model and Monte Carlo stochastic theory, the random fracture network of natural and artificial fractures in a shale-gas reservoir stimulation zone was constructed in this study. The porosity and permeability of the stimulation zone were calculated according to the network geometric properties. The fracture network was reconstructed, and the fissure connectivity was characterized. Numerical simulation of the seepage flow was performed for shale-gas reservoirs with different fracking-fracture combinations. The results showed that the local permeability dominated by the main fracture was the main factor that affected the initial shale-gas production efficiency. The total shale-gas productivity was mainly controlled by the effective stimulated volume. The evenly distributed secondary fracture network could effectively improve the effective stimulated volume of the stimulation zone. A 4% increase in the effective stimulated volume could improve the accumulated gas production by approximately 12%. Moreover, when the ratio of the main fracture to the secondary fracture was approximately 1:14, the accumulated gas production was optimized.
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