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Background Modern industrial facilities urgently need effective wireless communication technology to monitor instruments and equipment, but electromagnetic interference and physical shielding often exist in these fields, thereby preventing traditional communication methods from working correctly. Objective As a special wireless optical communication technology, X-ray communication (XCOM) is expected to solve the problem of signal transmission under this extreme condition. Our goal was to prove the feasibility of XCOM for signal transmission under metal barrier condition. Methods The Monte Carlo method was used to simulate the transmission characteristics of X-ray beam under metal barrier conditions, and the communication performance of XCOM was evaluated. Moreover, the experimental demonstration system of XCOM was developed to test the penetration and communication performance of XCOM under metal shield. Results X-ray with energy above 150 keV could achieve a bit error rate of less than 10-4 after passing through a 20 mm iron, whereas X-ray with energy above 250 keV could maintain excellent communication performance after passing through a 30 mm iron. The experimental test results were consistent with the theoretical calculation. Conclusions As a new wireless optical communication technology, X-ray communication is expected to solve the problem of signal transmission under physical shielding conditions.

Contingency plans is growing in quantity and gains higher quality in recent years. Contingency plan management has become a public service and affects our society. In this paper, we proposed a formal model of contingency plans and designed the three-layer architecture of the contingency plan management system. First, we give the formal representation of basic attributes, contents and the task model respectively. We have three layer in proposed contingency plan management system. The storage layer is designed to adapt to various types of data, such as XML and relational. The formal-model layer provides interfaces for accessing contingency plans based on formal representation. The application layer use the interfaces for different applications.

Nowadays, automatic scoring is an important way of teaching and examinations. However, there is no existing research on automatic scoring for subjective item of database domain both at home and abroad. According to the characteristics of database domain, we construct database domain synonyms ontology and proposed a text similarity calculation algorithm based on Hamming distance. Then we implement the automatic scoring for subjective item of database domain on the basis of ontology. In addition, in order to verify the accuracy and rationality of the algorithm, we take a specific subject as an example. The experiment results further illustrate the accuracy and efficiency of the proposed automatic scoring algorithm.

X-ray communication (XCOM) is a novel method that exploits X-rays as a carrier for data transmission. The high penetration of X-rays enables XCOM to avoid radio blackout during the atmospheric re-entry into Earth. To guarantee stable and robust XCOM, this study provides a power budget for XCOM. The Monte Carlo method was used to evaluate the transmission properties of X-ray beams in near-earth space, and a link model in the re-entry blackout region were established. Moreover, we established a noise model for the X-ray detector and evaluated the mathematical relationship between the transmitting power, and the bit-error-rate (BER). Results indicated that the X-rays with energies of 30–50 keV are highly suitable at an altitude of 35 km, and that robust communication performance could be obtained by using soft X-rays in the upper atmosphere. Adopting optimal X-ray energies according to different altitudes of spacecraft re-entry is, thus, of great significance. We calculated the minimum transmitting power of the X-ray source for a targeted BER and found that, when the link distance is 295 km and the X-ray energy is 50 keV, the power consumption of the X-ray source must be 140 W to achieve BER of less than 10−6 level.

The core of exam management system is how to generate test paper automatically. The existing algorithmic is difficult to simultaneously achieve the requirements with efficient, random, flexible and expansive performance. In this paper, we introduce the maximum flow algorithm of the upper and lower bounds in the graph theory, create a test paper generation model based on constraint conditions, and implement the test paper generation under complex constraints. In addition, to illustrate the success rate and efficiency, the system generated automatically test papers on proposition needs. In turn, it verifies the correctness and rationality of the model. The algorithm proposed in this paper will provide theoretical and technical support for other systems, and it further promotes the development of the exam management system.

DO-Swoosh algorithm maps the input data to domain ontology and count the amount of data for each leaf node. Then define the distance between nodes according to the hierarchical relationships reflected by domain ontology and propose a node merging algorithm based on the principles of data balance and nearest merge. At last, perform entity resolution for each group according to the node merging result. DO-Swoosh still keeps the good generality and gets better performance and scalability with the aid of MapReduce.

Domain ontology, which is widely used in knowledge engineering, artificial intelligence and semantic Web domain, describes concepts of the entities and mutual relationships between them. However, there is no existing research on construction of database domain ontology. Domain ontology of database will help to optimize associative knowledge learning in teaching and develop the intelligent tutoring system. It can also maximize domain knowledge sharing and reusing. In this paper, database domain ontology is constructed, and then we achieve the visualization. Finally we also implement the persistent storage of ontology and query.

Recent advances in wireless mobile computing, digital library, and distributed multimedia technologies are stimulating the development of mobile multimedia digital library systems (M2DLS) that allow mobile clients to access multimedia material anywhere and anytime over a cellular radio network. This paper addresses the problem of providing synchronized multimedia retrieval in these systems. An efficient inter-media synchronization scheme called wireless prioritized feedback (WPF) for mobile multimedia on-demand retrieval in digital library systems over CDMA cellular radio networks in the absence of synchronized clocks is presented. In the WPF scheme, base stations use preferential lightweight message called feedback units transmitted by mobile mediaphones to detect and correct asynchronies. The algorithm is described with pseudo code, and experiments are described to demonstrate the efficiency of WPF.

Most of the proposed concurrency control protocols for real-time database systems are based on serializability theorem. Owing to the unique characteristics of real-time database applications and the importance of satisfying the timing constraints of transactions, serializability is too strong as a correctness criterion and not suitable for real-time databases in most cases. On the other hand, relaxed serializability including epsilon-serializability and similarity-serializability can allow more real-time transactions to satisfy their timing constraints, but database consistency may be sacrificed to some extent. We thus propose the use of weak serializability(WSR) that is more relaxed than conflicting serializability while database consistency is maintained. In this paper, we first formally define the new notion of correctness called weak serializability. After the necessary and sufficient conditions for weak serializability are shown, corresponding concurrency control protocol WDHP(weak serializable distributed high priority protocol) is outlined for distributed real-time databases, where a new lock mode called mask lock mode is proposed for simplifying the condition of global consistency. Finally, through a series of simulation studies, it is shown that using the new concurrency control protocol the performance of distributed real-time databases can be greatly improved.