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Valve is widely used in the various industry areas to adjust and control the flow. Cavitation frequently takes place and sometimes is inevitable in various types of valve to cause the erosion damage. Therefore, how to control and minimize the effect of cavitation is still an important topic. This study numerically investigates the cavitating flow in a control valve with a perforated cage. The effects of some parameters on the cavitation are discussed. It also discusses to use the throttling steps to govern the cavitating flow. The results show that the opening degree of valve and the length of downstream divergent connection both influence the cavitation. The increase of the divergent length reinforces the cavitation. And the larger the opening of valve is, the intenser the cavitation is and the more vapor is present. The more throttling steps are helpful to decrease the cavitation.

Graphene has great application prospects in the field of optoelectronics. We investigate a field effect transistor with a graphene channel. Carrier density and chemical potential of the channel can be spatially modified by topping the channel with dielectric structures consisting of pure and lithium enriched SU-8 layers. As an example, we demonstrate that application of a single-gate voltage can induce a P–N junction to a channel with an appropriate dielectric architecture. Electronic and photoelectric properties of the junction are studied. The photocurrent mapping is investigated, which clearly shows the origin of the photocurrent from the P–N junction. The proposed technology makes fabrication of graphene-based photodetectors simple and flexible, and may also be interesting for the development of future optoelectronic components using other two-dimensional materials.

Many plasmon-induced transparency (PIT) metamaterials previously reported had limited functions. Their tunabilities were realized by complex discrete structures, which greatly increased the difficulty and cost of device fabrication and adversely affected their resonance characteristics. It is an open question to adjust the Fermi levels of many graphene patterns with only a few in-plane electrodes. We propose and numerically study a novel electrically tunable and multifunctional trigate graphene metamaterial (TGGM) based on the concept of “Lakes of Wada”. Benefiting from the trigate regulation, our proposed TGGM turns out to exhibit excellent characteristics, that can not only be used for terahertz band-stop filter, terahertz refractive index sensor, near-field optical switch, slow-light device, but also for double PIT window metamaterial with broad transparency windows and large tunable frequency range.