Space Information Network (SIN) has significant benefits of providing communication anywhere at any time. This feature offers an innovative way for conventional wireless customers to access enhanced ...internet services by using SIN. However, SIN's characteristics, such as naked links and maximum signal latency, make it difficult to design efficient security and routing protocols, etc. Similarly, existing SIN authentication techniques can't satisfy all of the essentials for secure communication, such as privacy leaks or rising authentication latency. The article aims to develop a novel blockchain-based access authentication mechanism for SIN. The proposed scheme uses a blockchain application, which has offered anonymity to mobile users while considering the satellites' limited processing capacity. The proposed scheme uses a blockchain application, which offers anonymity to mobile users while considering the satellites' limited processing capacity. The SIN gains the likelihood of far greater computational capacity devices as technology evolves. Since authenticating in SIN, the technique comprises three entities: low Earth orbit, mobile user, and network control centre. The proposed mutual authentication mechanism avoids the requirement of a ground station, resulting in less latency and overhead during mobile user authentication. Finally, the new blockchain-based authentication approach is being evaluated with AVISPA, a formal security tool. The simulation and performance study results illustrate that the proposed technique delivers efficient security characteristics such as low authentication latency, minimal signal overhead and less computational cost with group authentication.
Over the past 60 years, satellite technology has demonstrated its usefulness successfully. However, this usefulness is at stake from a future point of view, due to the well-admitted orbital/space ...debris threat. This article thoroughly reviews all aspects of space debris issue including causes, amount and sizes of orbital debris, potential threats, counter-strategies with their latest status and related legal issues to highlight the criticality and urgency of the problem. This review elaborates the fact that despite all the worries and threats, the efforts to confront this challenge are considerably insufficient until today. This bitter reality demands for at-least curtailing the number of future launches to ensure the long-term sustainability of space, until the improvement in debris situation. However, contradictory to this necessity, large satellite constellations have been proposed that can drastically increase the existing orbital population in coming years. This approach will certainly not help in improving the space environment in the future; instead, it can worsen the space environment situation as recent studies shows. Also, space resources (i.e. orbital slots and frequencies) are limited to accommodate many more satellite projects from commercial and government organization in the future. So, there is a serious question of how the space industry can move forward to maintain a balance in controlling the future number of the satellite while accommodating many commercial or government space entities. This article also identifies two optimized approaches as a way forward for future satellite projects that can also enhance the effectiveness of space technology in the future.
Although nanostructured Cu alloys prepared show great advantages in performance, the excellent properties have not been achieved at present primarily due to a single strengthening method or the Fe ...contamination introduced during mechanical alloying. In the present work, an appropriate amount of Zr was added to adjust the milling process and Fe contamination in the Cu matrix. Then the effects of Zr on the morphologies, crystallite sizes, lattice strain, composition and properties were analyzed. When the added Zr content was 0.1 wt%, it could promote the work hardening of Cu powders, resulting in smaller crystallite sizes, larger internal strain. And a slightly higher Fe content was introduced. However, with the increase of the Zr content, the Fe contamination was reduced obviously and the crystallite size began to increase again. Even so, the average crystallite sizes of nanostructured Cu alloys were still less than 20 nm. The results also showed that MA could increase the solid solubility of Zr in Cu. In a word, the properties of the nanostructured Cu alloys were improved by the refinement strengthening of matrix, solid solution and dispersion strengthening of Fe and Zr. The optimum properties were achieved by Cu-0.1 wt% Zr with electrical conductivity of 75.19% IACS and tensile strength of 526 MPa. The study provided a new route for overcoming Fe contamination in the metal matrix, and further improving the properties of Cu alloys through various strengthening methods.
•Nanostructured Cu alloys with crystallite size of nearly 15 nm were prepared.•Addition of 0.1 wt% Zr improved the work hardening of Cu powders during milling.•Fe content doped into the Cu matrix was reduced with above 0.1 wt% Zr added.•High performance Cu alloys were prepared through multiple strengthening methods.
With the increasing development of low-permeability reservoirs, the significance of conformance control treatment has risen considerably. To address the conflict between injectability and plugging ...performance, as well as to enhance the deep migration capacity of conformance control agents, preformed submicron crosslinked polymer coils (SCPCs) have been manufactured using aqueous solution dispersion polymerization. Fourier transform infrared and scanning electron microscopy were employed to examine the chemical structure and micromorphology, while particle size distribution, zeta potential, rheological, and filtration properties were analyzed. The effectiveness of conformance control was confirmed through the parallel core displacement. The effective particle size of SCPCs was at a submicron level (500~800 nm). SCPCs exhibit a transitional threshold concentration between gel and sol states (0.25 wt%~0.5 wt%). SCPCs can efficiently block the 1.2 μm microporous filter membrane. The filtration time is up to 67.8 min. SCPCs can improve the water absorption rate of lower permeability cores from 21.21% to 57.89% with a permeability difference of 5. Therefore, SCPCs have good injectability, plugging performance, and deep migration capacity and can be used for conformance control in low-permeability reservoirs.
The influence of hydraulic retention times (HRTs) reduction from 25 days to 15 days on the enhancement effects of two pretreatments (thermal pretreatment and alkaline-thermal pretreatment) on the ...continuous anaerobic digestion (AD) of sewage sludge was studied in a long-term experiment (196 days). The operation of the semi-continuous AD fed with raw sludge or pretreated sludge was stable at the three HRTs. The methane production increased from 70.6 to 165.8 ml/L·d to 75.2–172.6 ml/L·d and the methane yield decreased from 98.9 to 234.9 ml/g added volatile solid to 65.6–144.9 ml/g added volatile solid when the HRT reduced from 25 days to 15 days. The two pretreatments reduced the HRT of raw sludge AD by over 40%, and the effects of the alkaline-thermal pretreatment were greater than those of the thermal pretreatment. The reduction of HRT from 25 days to 15 days increased the enhancement effects of the two pretreatments on the removal of organic matter (4.7–15.9% for volatile solid), average hydrolysis ratio (36.9–116.4%), and specific hydrolysis rate (44.1–155.6%) but decreased the enhancement effects of the pretreatments on the methane production (0.9–4.6%) and yield (4.0–15.8%), average reaction ratios (0.4–8.2%), and specific rates of the last three AD steps (0.1–13.9%). The influence of HRT reduction on the enhancement effects of the alkaline-thermal pretreatment for sludge AD was slightly greater than on the enhancement effects of the thermal pretreatment.
•Thermal and alkaline-thermal pretreatments can enhance AD of sludge at three HRTs.•The enhancement effects of the latter were higher than those of the former.•Their enhancement effects on organic matter removals increased with HRT reduction.•Their enhancement effects on methane yield decreased with HRT reduction by 4.0–15.8%.•The influences of HRT reduction on the enhancement effect of the latter were higher.
Growing carbon nanotubes (CNT) on the surface of high performance carbon fibers (CF) provides a means to tailor the thermal, electrical and mechanical properties of the fiber–resin interface of a ...composite. However, many CNT growth processes require pretreatment of the fiber, deposition of an intermediate layer, or harsh growth conditions which can degrade tensile properties and limit the conduction between the fiber and the nanotubes. In this study, high density multi-wall carbon nanotubes were grown directly on two different polyacrylonitrile (PAN)-based carbon fibers (T650 and IM-7) using thermal Chemical Vapor Deposition (CVD). The influence of CVD growth conditions on the single-fiber tensile properties and CNT morphology was investigated. The mechanical properties of the resultant hybrid fibers were shown to depend on the carbon fiber used, the presence of a sizing (coating), the CNT growth temperature, growth time, and atmospheric conditions within the CVD chamber. The CNT density and alignment morphology was varied with growth temperature and precursor flow rate. Overall, it was concluded that a hybrid fiber with a well-adhered array of dense MWCNTs could be grown on the unsized T650 fiber with no significant degradation in tensile properties.
PM2.5-bound toxic metals (TMs) are derived from various sources, and they can cause many adverse health effects on the human body. To effectively reduce the disease burden of TMs by controlling the ...relative sources, an integrated approach of quality-adjusted life years (QALYs) and source-apportionment (positive matrix factorization, PMF) was proposed and applied to some typical diseases induced by TMs in 2017 in Beijing. The estimation included two parts; first, the number of potentially affected people was calculated based on the source mass contribution from PMF and the inhalation unit risk of TMs; second, the QALYs lost per affected person was calculated based on the disease duration, expected years of life lost (EYLL) and quality of life (QoL) for both affected people and the general population. The results showed that QALYs lost per person for renal cancer (17.3 QALYs), pneumonia (14.4 QALYs), lung cancer (14.2 QALYs), skin cancer (12.7 QALYs) and diabetes mellitus (12.6 QALYs) were higher than those for other diseases. Combined with PMF, the source contributions to the overall burden of typical diseases from the TMs followed the order of coal combustion (50.2%) > vehicle emissions (24.4%) > fuel oil combustion (11.4%) > Cr-related industry (10.9%) > resuspended dust (3.0%). The rank was further compared with that assessed for noncancer and cancer risks, and we verified the reasonability of the QALYs method. For seasonal contributions to coal combustion, winter and spring had the highest contributions, which coincided with the fact that coal was the main fuel for heating in Beijing. The QALYs lost attributed to TMs for coal combustion decreased by 49.1% from 2016 to 2017, which may indicate an effective policy associated with coal control. Overall, the integrated approach was successfully employed for estimating the disease burden induced by TMs from each source and was an effective solution to identify the control rank of sources for TM reduction.
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•QALYs and PMF were integrated to quantify the source-attributed disease burden for TMs.•A model of calculating the QALYs lost per person for typical diseases was built.•The ranks of source-attributed QALYs lost from PM2.5-bound TMs were clarified.•Coal burning contribution to the QALYs lost to TMs was the highest but sharply decreased.•More pollutants/toxic effects should be included to determine priority source control.
Quantum hash function is an important area of interest in the field of quantum cryptography. Quantum hash function based on controlled alternate quantum walk is a mainstream branch of quantum hash ...functions by virtue of high efficiency and flexibility. In recent development of this kind of schemes, evolution operators determined by an input message depend on not only coin operators, but also direction-determine transforms, which usually are hard to extend. Moreover, the existing works ignore the fact that improper choice of initial parameters may cause some periodic quantum walks, and further collisions. In this paper, we propose a new quantum hash function scheme based on controlled alternate lively quantum walks with variable hash size and provide the selection criteria for coin operators. Specifically, each bit of an input message determines the magnitude of an additional long-range hop for the lively quantum walks. Statistical analysis results show excellent performance in the aspect of collision resistance, message sensitivity, diffusion and confusion property, and uniform distribution property. Our study demonstrates that a fixed coin operator, along with different shift operators, can effectively work on the design of a quantum hash function based on controlled alternate quantum walks, and shed new light on this field of quantum cryptography.
Estimating the concentration field of effluent mixing and transport is a challenging task because of the complex mechanisms and three‐dimensional (3D) variability, but it is of great importance for ...water quality assessment and water resources management. Sophisticated numerical models based on the 3D computational fluid dynamics (CFD) technique can provide accurate predictions, but they are computationally expensive and require high‐level 3D CFD expertise, impeding their widespread usage. This work primarily develops a Parameter‐based Field Reconstruction convolutional neural network (PFR‐CNN) that can predict the complete concentration field of a target variable using the main influencing parameters, and explores the possibility of employing the proposed network to model the process of effluent mixing and transport. A validated numerical solver, TwoLiquidMixingFoam, was utilized to provide extensive data for multiple vertical buoyant effluents. A PFR‐CNN was developed to estimate the concentration fields based on the densimetric Froude number (F) and normalized port spacing (S/D). The network was developed using the training‐validating dataset from the numerical dataset, and further assessed using additional testing data. A random forest model was also developed, and the results showed that both methods can provide good performance, but the PFR‐CNN method was more robust and required less disk storage space. The results of our study demonstrated that the proposed PFR‐CNN approach is a promising tool for estimating effluent mixing and transport, and can be potentially leveraged to estimate other variables in the field of water resources with the governing parameters.
Key Points
A parameter‐based field reconstruction convolutional neural network (PFR‐CNN) was proposed for effluent concentration field estimation
The performance of the proposed PFR‐CNN method was compared with the random forest approach
Both approaches provided remarkable performance but the PFR‐CNN method was more robust
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