Gongcheng Kexue Yu Jishu/Advanced Engineering Science

In the real world, many problems have the need to conduct relevant operations at a specific time. Timed-release encryption (TRE) is a cryptographic primitive in which the sender specifies the decryption time of the receiver, which can meet the above requirement. To address the problem that the current TRE schemes based on the periodic broadcast time trapdoor of the non-interactive time server cannot meet the user’s arbitrary specified decryption time, and the interactive time server mode meets the arbitrary decryption time but cannot guarantee the user’s identity privacy, a TRE scheme using onion routing network was proposed. In the scheme, when the decryption time approaches, the time trapdoor request was taken as the innermost onion, and the layer by layer encrypted onion was constructed and transmitted to the time server. The time server generates the corresponding time trapdoor and returns it to the receiver according to the original route, so that the user can hide the identity information when making a trapdoor query at any time. Meanwhile, for the node failure problem in the process of onion routing delivery, a method for constructing each layer of onion based on broadcast encryption was proposed, so that each layer of onion node can decrypt that layer of onion. The scheme achieves the trapdoor of successfully querying arbitrary time to the time server while ensuring the anonymity of user’s identity. Security analysis showed that the scheme is secure and robust against possible single-point speculation, monitoring attacks, replay attacks, and collusion attacks. Efficiency analysis showed that compared with the pairing-based onion routing scheme, the proposed scheme reduces the time consumption of solving the node failure problem by about 59%, thus realizing efficient anonymous query

With the development of seismic isolation technology, the service environment of the isolated bridge is becoming increasingly complicated, and the effect of ambient temperature on the seismic performance of isolated bridge should be considered urgently. To reduce the maximum response and residual deformation of the bridge under the action of an earthquake, combining the advantages of the lead rubber bearing (LRB) and shape memory alloy (SMA), a self-resetting SMA–LRB bearing was formed. In view of the temperature sensitivity of rubber and SMA materials, based on a 4–span SMA–LRB seismic isolation continuous girder bridge, the nonlinear dynamic time history analysis of isolated continuous girder bridges under different ambient temperatures was performed to obtain the dynamic response of the key parts of the structure, while the mechanical properties of SMA–LRB bearings at different ambient temperatures were considered. The results showed that the addition of SMA to LRB increased the horizontal rigidity and effectively controls the displacement response of the bearing. At the same time, the self-reset characteristic of SMA made the residual displacement control effective. As the ambient temperature decreases, the peak displacement and residual displacement of the LRB and SMA–LRB bearings would decrease, but the displacement control ability and self-reset ability of the SMA–LRB bearing would decrease compared with normal temperature. The stiffness of the bearing increased with the decrease of the ambient temperature, which caused an increment in the displacement of the top of the pier and the shear force at the bottom of the pier, and the shear force at the bottom of the lower pier was more sensitive to temperature changes. The qualitative evaluation of the influence of ambient temperature on the seismic performance of SMA–LRB isolated bridge can provide reference for the analysis and design of such bridges.

In order to improve the quality of the porous asphalt pavement in seasonal freezing areas and reduce the freeze-thaw damage of the pavement, the modified porous asphalt mixture with glass fiber, diatomite and old asphalt pavement materials are employed to improve the performance. The changes in compressive strength, porosity, and strain of porous asphalt mixtures with different material contents after freeze-thaw cycles are analyzed by considering the influence of different materials and different material contents on the water stability of porous asphalt mixtures. Based on the theory of damage mechanics, the compressive strength is used as an index to represent damage variables, and the evolution of freeze-thaw damage of modified porous asphalt mixtures is also studied. Based on the CT non-destructive testing and digital image processing technology, the changes in the number of air voids and air void area of the glass fiber porous asphalt mixture before and after freezing-thawing are analyzed. The test results show that the compressive strength of the mixture decreases with the increase of the number of freeze-thaw cycles, and the void ratio and strain show an increasing trend. Four porous asphalt mixtures with 0.7% glass fiber content, 15% old asphalt pavement material content, 25% diatomite content and 15% old asphalt pavement material and 20% diatomite content present the best water stability. The modification effect of glass fiber is the best. Mixing glass fiber, 15% diatomite and 15% old asphalt pavement material may reduce the freeze-thaw damage of porous asphalt mixtures. However the recycled porous asphalt mixtures containing diatomite have more serious damage and have higher strength in the early stage of damage, which are more suitable for short-term frozen soil areas. Compared with recycled porous asphalt mixtures containing diatomite, the porous asphalt mixture containing glass fiber, recycled porous asphalt mixture and porous asphalt mixture containing diatomite have a longer rapid damage period, a shorter damage stability period and a shorter damage evolving period. The number of air voids in the sample increases and the average single air void area decreases with a lower glass fiber content, while the sample with a higher glass fiber content has the opposite effect.

River flow is affected by boundary shear stress, and too large boundary shear stress will lead to erosion and reduce the stability of river banks, and cause river morphology changes by affecting sediment deposition and transport. To study the shear stress of river boundary is equivalent to the study of flow characteristics in river. Because there are too many complex factors affecting the boundary shear stress in rivers, a two-dimensional rectangular straight open channel flow model was established by numerical software after removing all factors, and the laboratory experiments were carried out on the rectangular straight open channel model by using similarity theory. Firstly, numerical simulation was carried out for flows in uniform straight channels of 5 different scales. Since the stage-discharge relation obtained from the simulation results is highly consistent with the stage-discharge relation deduced by Manning formula, it can be considered that the parameters simulated by the model are true and reliable. In the case of non-uniform flow, through the concepts of under-uniform flow and super-uniform flow, 9 cases of straight open channels under different discharges were simulated in this paper. The momentum theorem was used to analyze the force at 101 points with the same spacing in the center of the non-uniform straight path. The average value of shear stress was taken between every two points, and then the resistance of all points was summed up to approximate the integral of the river bed resistance, which will greatly reduce the influence of the error caused by uncertain factors such as stage fluctuation. A general formula of bed shear stress was derived, which showed that the bed shear stress could be calculated by the water depth h, flow velocity u and Manning roughness coefficient n, regardless of whether the flow of rectangular open channel is uniform or not. To verify the new formula, the new formula was compared to four existing formulas, and the results showed that the new formula conformed to the momentum theorem and had physical significance. The research result is simpler than the traditional methods and can provide a faster algorithm in required calculations.bm

In order to relieve the alarm fatigue of security analysts and improve the security operation efficiency, an attacker IP analysis system based on the Ensemble-based Local Outlier Factor algorithm (EBLOF) was proposed in this paper. Firstly, normalized network security alarm logs were extracted and merged, and then the feature engineering was constructed from the attribute dimension and attack behavior dimension of attacker IP. Secondly, inspired by the idea of ensemble learning and traditional LOF anomaly detection algorithm, a robust EBLOF algorithm of finding high-threat attacker IP was constructed in the system. Thirdly, a set of online learning architecture was built by the system, aiming to solve the problem that the machine learning model was difficultly updated online. Through the batch real-time learning technology, the learning architectures ensure that the learning model can be updated online from the system architecture level rather than the algorithm level. Finally, the EBLOF algorithm of this paper was trained on the public anomaly detection data set ODD. The experimental results showed a fact that the algorithm has better robustness than the naive LOF algorithm under different data distributions. The system proposed in the paper was applied in real attack and defense scenarios. Its effectiveness and feasibility were verified by comparing with security operation analysts