With unique electronic and optical attributes and dangling-bond-free surface, two-dimensional (2D) materials have broadened the functionalities of photodetectors. Here, we report a quadratically nonlinear photodetector (QNPD) composed of a van der Waals (vdW) stacked GaSe/InSe heterostructure. Compared with the reported 2D material-based photodetectors, the extra second-harmonic generation (SHG) process in GaSe/InSe leads to the quadratically nonlinear function between photocurrent and optical intensity, extending the photodetection wavelength from 900 to 1750 nm. The QNPD is highly sensitive to the variation of optical intensity with improved spatial resolution. With the light−light interaction in SHG converted into electrical signal directly, we also demonstrate the QNPD as an autocorrelator for measuring ultrafast pulse widths and an optoelectronic mixer of two modulated pulses for signal processings. The simultaneous involvement of light−light interaction and photoelectric conversion in the vdW stacked QNPD promises its potential to simplify the optoelectronic systems.
Many extensions of Petri nets have been proposed to model the behaviors and time relations of embedded system, yet these models are all based on some assumptions about the behaviors of embedded systems. Especially they all do not have the actual ability to model interrupt mechanism of embedded system. A new net which is called Extended High Level Timed Petri Nets (EHLTPN) is introduced in this study. It shows how to extend High Level Petri Nets (HLPN) with time, actions and interrupt mechanism. Interruptible subnets corresponding to different interruptible resources are introduced to model the behaviors and time relations of distributed embedded real-time systems. Each interruptible subnet realizes interrupt mechanism by an Interrupt Switch Transition and a set of Resuming Transitions. We give an informal description of this new model and show how this model be formally defined. A transform rule presented shows that each subnet corresponding to an interruptible resource in EHLTPN can be transformed into a behaviorally equivalent subnet of HLTPN AT with priority. This model makes it possible to create the compact and comprehensive models for distributed embedded real-time systems.
Parallel data transmission based on multi-copy can enhance transmission speed and ensure the QoS of data grid greatly. The status of network and replica node, the distance of replica node, the time and bandwidth of service requester will directly affect service cost. How to take the above factors into account, so as to provide basis for node selection and bandwidth allocation, guarantee the time constraint of service requestor and optimize service cost is a key problem need to be solved urgently. Based on ‘0-1’ integer programming and linear programming methods, respectively, a minimum transfer time model, minimum cost model and comprehensive optimization model are proposed to solve the above problem. Simulative experiments show that the models are correct and effective
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