Research on vacuum plume and its effects

AbstractIn vacuum environment, the exhaust flow of attitude control thrusters would expand freely and produce the plume, which possibly causes undesirable contamination, aerodynamic force and heating effects to the spacecraft. Plume work station (PWS) is developed by Beihang University (BUAA) for numerically simulating the vacuum plume and its effects. An approach which combines the direct simulation Monte Carlo (DSMC) method and difference solution of Navier–Stokes (N–S) equations is applied. The internal flows in nozzles are simulated by solving the NS equations. The flow parameters at nozzle exit are used as the inlet boundary condition for the DSMC calculation. Experimental studies are carried out in a supersonic low density wind tunnel which could simulate the 60–80km altitude environment to investigate the plume and its effects. To demonstrate the capability of PWS, numerical simulations are performed for the vacuum plume of several typical attitude control thrusters. The research results are of great help for the engineering design

NetChain: A Blockchain-Enabled Privacy-Preserving Multi-Domain Network Slice Orchestration Architecture

Multi-domain networking slice orchestration is an essential technology for the programmable and cloud-native 5G network. However, existing research solutions are either based on the impractical assumption that operators will reveal all the private network information or time-consuming secure multi-party computation which is only applicable to limited computation scenarios. To provide agile and privacy-preserving end-to-end network slice orchestration services, this paper proposes NetChain, a multi-domain network slice orchestration architecture based on blockchain and trusted execution environment. Correspondingly, we design a novel consensus algorithm CoNet to ensure the strong security, scalability, and information consistency of NetChain. In addition, a bilateral evaluation mechanism based on game theory is proposed to guarantee fairness and Quality of Experience by suppressing the malicious behaviors during multi-domain network slice orchestration. Finally, the prototype of NetChain is implemented and evaluated on the Microsoft Azure Cloud with confidential computing. Experiment results show that NetChain has good performance and security under the premise of privacy-preserving

ROAchain: Securing Route Origin Authorization with Blockchain for Inter-Domain Routing

The inter-domain routing with BGP is highly vulnerable to malicious attacks, due to the lack of a secure means of verifying authenticity and legitimacy of inter-domain routes. Resource Public Key Infrastructure (RPKI) is a new security infrastructure to prevent the most devastating prefix hijacks in BGP by maintaining a Route Origin Authorization (ROA) repository. However, RPKI is a centralized hierarchical architecture that may empower the centralized authorities to unilaterally revoke or compromise any IP prefixes under their control. To eliminate the risks of RPKI, we present ROAchain, a novel BGP security infrastructure based on blockchain. Different from RPKI, ROAchain is a decentralized architecture, in which each AS maintains a globally consistent and tamper-proof ROA repository, authenticating the legitimacy of route origin and preventing BGP prefix hijacks. To ensure the strong consistency, scalability, and security of ROAchain, a novel consensus algorithm is proposed, in which the credence value, collective signing, sharding, and a penalty mechanism are introduced. Moreover, a compatibility design is proposed without changing the current BGP protocol. Finally, ROAchain is implemented in Golang and validated on the Google Cloud

Netchain: A Blockchain-Enabled Privacy-Preserving Multi-Domain Network Slice Orchestration Architecture

Multi-domain networking slice orchestration is an essential technology for the programmable and cloud-native 5G network. However, existing research solutions are either based on the impractical assumption that operators will reveal all the private network information or time-consuming secure multi-party computation which is only applicable to limited computation scenarios. To provide agile and privacy-preserving end-to-end network slice orchestration services, this paper proposes NetChain, a multi-domain network slice orchestration architecture based on blockchain and trusted execution environment. Correspondingly, we design a novel consensus algorithm CoNet to ensure the strong security, scalability, and information consistency of NetChain. In addition, a bilateral evaluation mechanism based on game theory is proposed to guarantee fairness and Quality of Experience by suppressing the malicious behaviors during multi-domain network slice orchestration. Finally, the prototype of NetChain is implemented and evaluated on the Microsoft Azure Cloud with confidential computing. Experiment results show that NetChain has good performance and security under the premise of privacy-preserving

A momentum flux measuring instrument with the variable-range for exhaust plume

A momentum flux measuring instrument (MFMI), which ranges from 1 mN∼300 N, is designed to measure the parameters related to the momentum flux of exhaust plume of attitude and orbit control thrusters covered electric and chemical thrusters. A MFMI with the variable-range provides an efficient and economy way to study the exhaust plume of both electric and chemical thrusters. The flexural pivots, replaceable strain gauge, replaceable target plate, and force arm with the variable length make it possible. The designed MFMI with the non-displacement measurement can reduce the influence of pipelines and test lines, especially the elastic force and friction due to displacement. The designed MFMI system with the range of 0∼100 mN and 0∼15 N was calibrated separately. The target indirect measurement method is a simple and economical option for measuring the thrust of electric thrusters, and is employed to measure the thrust of the LIPS-200 ion thruster using the designed MFMI. Research indicates that the sputtering contributes to the momentum transfer of plasma-surface interactions. In addition, the high-speed charged ions from the thruster will experience a charge-exchange (CEX) collision with the slow neutral background. Therefore, the influence of the sputtering and CEX on target indirect measurement method is derived in detail, and then the measured thrust is corrected. The measured average thrust, which is 40.1 mN, demonstrates that the designed MFMI is effective. The designed MFMI can also be employed as a thrust stand by directly mounting the thrusters on torsional arm, and a maximum of three thrusters can be installed on the MFMI at the same time

Biotransformation of dihydrocapsaicin by human intestinal fungi and the inhibitory effects of metabolites against LSD1

Dihydrocapsaicin is the main bioactive component in Capsicum plants, which is widely used in China and India as a food drug and additive. In this study, the biotransformation of dihydrocapsaicin was performed using four cultivated human intestinal fungal strains in vitro. Eight metabolites, including seven previously undescribed metabolites (1 and 3−8) and one known analog (2), were obtained. Numerous spectroscopic data, such as NMR and HRESIMS, were collected to determine their structures. Based on the structures of the dihydrocapsaicin metabolites, the main biotransformation reactions were revealed to be hydroxylation, alcohol oxidation, and lactylation. In particular, the lactylation of hydroxyl groups is mainly mediated by Rhizopus oryzae R2701. In addition, metabolite 1 showed significant inhibitory effect on lysine-specific demethylase 1 (LSD1) (IC50 1.99 μM). Therefore, the biotransformation of dihydrocapsaicin by intestinal fungi afforded various derivatives, which were important resources for developing LSD1 inhibitors and potential application in cancer treatment