Geosynchronous Network Grid Addressing for Integrated Space-Terrestrial Networks

The launch of the StarLink Project has recently stimulated a new wave of research on integrating Low Earth Orbit (LEO) satellite networks with the terrestrial Internet infrastructure. In this context, one distinct technical challenge to be tackled is the frequent topology change caused by the constellation behaviour of LEO satellites. Frequent change of the peering IP connection between the space and terrestrial Autonomous Systems (ASes) inevitably disrupts the Border Gateway Protocol (BGP) routing stability at the network boundaries which can be further propagated into the internal routing infrastructures within ASes. To tackle this problem, we introduce the Geosynchronous Network Grid Addressing (GNGA) scheme by decoupling IP addresses from physical network elements such as a LEO satellite. Specifically, according to the density of LEO satellites on the orbits, the IP addresses are allocated to a number of stationary "grids" in the sky and dynamically bound to the interfaces of the specific satellites moving into the grids along time. Such a scheme allows static peering connection between a terrestrial BGP speaker and a fixed external BGP (e-BGP) peer in the space, and hence is able to circumvent the exposure of routing disruptions to the legacy terrestrial ASes. This work-in-progress specifically addresses a number of fundamental technical issues pertaining to the design of the GNGA scheme

Development and research of a SS-level universal double-beam assembled bridge barrier

Abstract A wide variety of bridge barriers are used on highways. The bearing capacities of different types of deck slabs are measured in this study by applying the yield line theory to determine the worst-case scenario. An improved configuration for the worst-case barrier base and deck slab is developed, namely the universal double-beam assembled bridge barrier, which can enhance the safety performance of exiting concrete-base bridge barriers. According to the simulated impact test results, the new barrier meets SS-level requirements in terms of containment, redirective, and buffering performance as specified in the Standard for Safety Performance Evaluation of Highway Barriers (JTG B05-01-2013). The barrier structure’s compatibility with various bases is also analyzed. SS-level impact tests are conducted on real vehicles, including cars, buss, and trucks. The results show that the safety performance of the new barrier configuration reaches SS-level, and the barrier is universally compatible with concrete bases with a height of 63 cm and above

Parallel Pseudo Arc-Length Moving Mesh Schemes for Multidimensional Detonation

We have discussed the multidimensional parallel computation for pseudo arc-length moving mesh schemes, and the schemes can be used to capture the strong discontinuity for multidimensional detonations. Different from the traditional Euler numerical schemes, the problems of parallel schemes for pseudo arc-length moving mesh schemes include diagonal processor communications and mesh point communications, which are illustrated by the schematic diagram and key pseudocodes. Finally, the numerical examples are given to show that the pseudo arc-length moving mesh schemes are second-order convergent and can successfully capture the strong numerical strong discontinuity of the detonation wave. In addition, our parallel methods are proved effectively and the computational time is obviously decreased

Projections of land use/cover change and habitat quality in the model area of Yellow River delta by coupling land subsidence and sea level rise

Accurately assessing future land use/cover change (LUCC) and habitat quality (HQ) is vital for ensuring sustainable use of coastal ecosystem services, but most studies ignore the effects of seawater inundation. This study developed a framework based on the PLUS model and InVEST-HQ model that considers seawater inundation due to sea level rise (SLR) and land subsidence. We used this framework to simulate future LUCC and HQ under different scenarios in the Yellow River Delta (YRD). The results showed: (1) From 1991 to 2020, natural wetlands decreased by 39.87 %, non-wetlands decreased by 3.06 %, and artificial wetlands increased by 730.71 %. The overall HQ showed a decreasing trend, with the largest decrease in non-wetlands. (2) Land subsidence occurred in 93.26 % of the YRD, with a subsidence rate of −36.55 mm/year. Underground brine mining is the most important driving factor. About 6.81 %∼11.16 % of the area will be inundated in 2035, and about 9.39 %∼19.27 % of the area will be inundated in 2050. (3) Future multi-scenario simulations show that the Ecological-Protection scenario can minimize the ecological losses caused by seawater inundation. The simulation of future HQ will be underestimated when seawater inundation is not considered. Our study shows that seawater inundation caused by land subsidence and SLR must be taken into account when simulating LUCC and HQ in coastal areas

Shear Performance and Damage Characterization of Prefabricated Basalt Fiber Reactive Powder Concrete Capping Beam Formwork Structure

Basalt Fiber Reactive Powder Concrete (BFRPC) semi-prefabricated composite capping beam structures can effectively improve the shortcomings of ordinary concrete capping beams' construction difficulties and insufficient bearing capacity. In this study, with the objective of analyzing the shear damage and damage characteristics of a prefabricated BFRPC capping beam formwork, structural damage tests under different levels of loading were carried out to obtain the mechanical parameters of key nodes. Acoustic emission (AE) and Digital Image Correlation (DIC) techniques were used to acoustically and visually characterize the formwork damage. The research results showed that the damage stage of the capping beam formwork was divided, and an early damage warning method was proposed based on the acoustic parameters. Using the DIC technique to identify the crack width evolution pattern during the shear process, it was found that the cracks expanded steadily as the load increased. Combining the experimental and simulation results as well as the Subdivision Superposition Theory, a half-open stirrup strength discount factor β was introduced and suggested to take a value of 0.79. The formula for calculating the shear capacity of BFRPC capping beam formwork is proposed to provide a theoretical basis for its application in prefabricated assembled structures

Research on dead-time compensation of common DC bus OW-PMSM based on 120°decoupling modulation

To suppress the switching dead-band in the Open-End Winding Permanent Magnet Synchronous Machine with Common DC bus (OW-PMSM-CDCB) drive system, the dual-inverter switch dead-band generates zero-sequence voltage and current during 120°decoupling modulation. The generation mechanism of dead-band voltage is analyzed with the help of Matlab/Simulink and a method to compensate for the zero-sequence voltage resulting from the dead-band of dual-inverter switches is discussed in this study. With the help of current polarity detection, the zero-sequence voltage resulting from the dead-band of the switch is offset by solving the dead-band voltage compensation amount, and an OW-PMSM-CDCB drive system experimental platform is built for experimental verification. Simulation and experimental show that the proposed compensation method can effectively suppress the zero-sequence current of OW-PMSM-CDCB

An Adaptive Controller Based on Interconnection and Damping Assignment Passivity-Based Control for Underactuated Mechanical Systems: Application to the Ball and Beam System

In this paper, an adaptive technology and the interconnection and damping assignment passivity-based control method are combined to solve the stabilization problem for underactuated mechanical systems with uncertainties (including matched and unmatched). These uncertainties include unknown friction coefficients and unknown terms in kinetic energy and potential energy. A novel adaptive interconnection and damping assignment passivity-based control scheme is proposed and an adaptive stabilization controller is designed to make the closed-loop system locally stable. Verification is conducted on the ball and beam system. The locally asymptotic stability is demonstrated using the LaSalle’s invariance principle and approximate linearization. The effectiveness of the proposed control law is verified through numerical simulations

Detection of Cd2+ in Aqueous Solution by the Fluorescent Probe of CdSe/CdS QDs Based on OFF–ON Mode

The detection of heavy metals in aqueous solutions has always attracted much attention from all over the world. A fluorescent probe of CdSe/CdS core-shell quantum dots (QDs) was designed to detect trace Cd2+ in aqueous solutions using the OFF–ON mode rapidly and efficiently, likely based on adsorption and desorption reactions between ethylenediaminetetraacetic acid disodium salt (EDTA) and CdSe/CdS QDs. In the OFF mode, the optical shielding function of EDTA results in fluorescence quenching owing to the strong adsorption ability of EDTA with Cd2+ on the sites of CdSe/CdS QDs surface. In the ON mode, the introduction of Cd2+ promotes the desorption of EDTA from the EDTA-CdSe/CdS QDs and restores the fluorescence intensity. There were two linear response ranges which were 0.1–20 µmol/L and 20–90 µmol/L for the EDTA-CdSe/CdS system to detect Cd2+. The detection limit was 6 nmol/L, and the standard deviation was below 4% for the detection of Cd2+ concentration in tap water