Search

The origin of the ferroelectricity in HfO 2 is considered to be the formation of the non-centrosymmetric polar orthorhombic phase. The double-well energy landscape as a function of the polarization for orthorhombic HfO 2 is obtained using density functional computations. Our calculation shows that the orthorhombic HfO 2 has the remnant polarization of $66.25 \mu \mathrm{C}$ cm $^{-2}$ and a barrier height of 77.4 meV atom $^{-1}$ for polarization switching. Two methods (doping with Zr and applying biaxial strain) are theoretically investigated to adjust the ferroelectricity of the orthorhombic HfO 2 . Moreover, both single- and double-domain HfO 2 structures are calculated and discussed in this work. We found the ferroelectricity of HfO 2 could be stabilized under tensile strain.

Physical layer security (PLS) technologies have attracted much attention in recent years for their potential to provide information-theoretically secure communications. Artificial Noise (AN)-aided transmission, which can realize secure communications against the external passive eavesdropping, is considered one of the most practicable PLS technologies. In this paper, we reveal that the conventional AN scheme has a severe vulnerability when the eavesdropper adopts Independent Component Analysis (ICA)-based attack, by which the AN-aided transmission will be cracked in a high probability even with most transmission power allocated to AN signals. In order to ensure secure communications, we propose a robust AN scheme focused on the ICA's ability of blind source separation. In our proposed scheme, AN signals are generated with the same modulation scheme and a certain correlation to information signals, thus to introduce irremovable correlation to degrade the ICA's separation performance. Furthermore, we derive the optimal correlation factors from the relation between an information-AN correlation and the ICA's performance. Numerical simulation results with the comparison to the conventional AN scheme show that, our proposed scheme can ensure secure communications by degrading eavesdropper's success probability of attack from 96% to lower than 1%.

The reliability of aeroengine compressor blisk is affected by the uncertainty of numerous parameters involving geometer, materials, loads, and so forth. To efficiently and accurately assess the reliability of aeroengine compressor blisk stress, an enhanced weighted regression model (EWRM) was proposed by integrating extremum response surface method (ERSM) and enhanced weighted regression method, in respect of the transient and uncertainty of numerous parameters. For the proposed method, the ERSM is utilized to process the transient problem of dynamic reliability to acquire highly-computational efficiency, and the enhanced weighted regression method is used to find efficient samples with larger weights and smaller errors to enhance calculative accuracy. We firstly elaborated the basic principle of the developed technique in dynamic reliability assessment, and the mathematical model of EWRM was then established, regarding fluid-structure interaction and random inputs (inlet velocity, outlet pressure, angular speed and material density) during time domain [0, T]. Finally, the dynamic probabilistic analysis of compressor blisk stress with the developed EWRM was implemented compared with the direct simulation with Monte-Carlo (MC) method and ERSM from fitting accuracy and simulation performance. We find that the reliability probability and important degrees of influential factors can be regarded guiding the optimization design of compressor blisk stress; the EWRM improves the efficiency and precision of dynamic probabilistic analysis of compressor blisk. It is validated that the EWRM is highly computational precision and efficiency in the dynamic reliability and sensitivity assessment of compressor blisk. The efforts of this work provide a promising technique for the dynamic probabilistic analysis of complex structure with working process.

This paper presents the results of the first ASIC implementation of the authenticated encryption scheme KetjeSR. The design covers the encryption and decryption operation in combination with a handshake protocol for the data transfer. The chip implementation was done in a TSMC 90nm GUTM process. The encryption/decryption module has an area footprint of 12.2kGE. The processor reaches an end-to-end throughput of 2.08 Gbps when running at a clock frequency of 130 MHz. The design was further optimized for low power and consumes 2.421 mW. The optimization is based on the reuse of the permutation function in combination with extensive pipelining. In terms of energy, the encryption operation costs 1.16 pJ/bit.

Based on the traffic conflict technique, this paper analyzes the aerial photography video of the highway interchanges, obtains the survey data, and calibrates the parameters of VISSIM and SSAM. Traffic conflict prediction models for single lane ramp and two-lane ramp are established. The negative binomial distribution model is selected as the single-lane ramp collision prediction model, and the Poisson distribution model is selected for the two-lane ramp collision prediction model. The test results show that the model has high accuracy, and MAPE is 8.41 % and 12.0% respectively. The results show the models can provide a basis for the safety assessment of highway merging area and the decrease of traffic accidents.

In this paper, we propose a novel radio access technology (RAT) selection method that can maximize total throughput by simultaneously selecting optimal RATs for a group of user equipments (UEs). To perform simultaneous selection, we also propose a novel throughput estimation method based on not wireless information collected from the existing network equipment but the accurate estimation of the amount of radio resources available for the UEs. Throughputs of all the UEs are estimated for all RAT selection patterns, by using the estimated available radio resources. The RAT selection method then selects a RAT selection pattern that gives the maximum total throughput. We conduct both simulations with a network simulator and field experiments with a commercially operating LTE network. The field experiments confirm that the proposed throughput estimation method can achieve an average estimation error of about 10%. The simulations confirm that the proposed method with a 10% throughput estimation error can achieve 96% throughput compared to that with perfect estimation. A conventional successive RAT selection method takes 1–10 minutes to achieve the same throughput as the proposed method, while the proposed simultaneous RAT selection method only takes about 1–10 seconds. Moreover, the conventional method achieves only 71% throughput of the proposed method with same processing time as the proposed method.

Increasing use of IEEE 802.11 WLAN specifications has resulted in dense deployment of access points (AP) to provide service to stations (STA). Dynamic sensitivity control (DSC) technology, which adjusts the carrier sense threshold (CST) to encourage more APs and STAs to transmit simultaneously, is considered an effective approach to improve the throughput in densely-deployed WLAN networks. The DSC algorithm should take into account both the increase of transmission opportunity, and the possible transmission rate degradation of related links caused by the consequent interference. Conventional algorithms, which set the CST value to allow simultaneous transmission only when a required signal to interference plus noise ratio (usually for a high transmission rate) can be guaranteed, are too conservative to improve the throughput. In this paper, we propose a novel DSC algorithm that enables simultaneous transmissions which lead to improved system throughput even when the transmission rate is degraded. Since whether system throughput can be improved by simultaneous transmission is different for each communication link, we set different CST values for different links instead of setting just one common CST value. We first formulate the throughput of each downlink as a function of related links' CST, and then search a set of CST values for these links to maximize the system throughput. A heuristic procedure is adopted in our algorithm to reduce calculation complexity. From numerical simulation results, it is shown that our algorithm can improve the system throughput by up to 30% when compared to a conventional algorithm.

Less offspring and aging are global issues that will be a bad news for cleaning work that requires a lot of manpower; the nightly cleaning jobs for large-scale indoor spaces introduce workers' overwork/fatigue problem. This study proposes a robot suitable for night time cleaning, which uses the industrial computer as the software control core, the AVR MCU for the control hardware part, the various obstacles avoidance sensors, and the cleaning mode algorithms. In the section of mechanism design, with a rotating space detection capability, the robot can safely avoid the steering into the corner. Users can utilize the interface for remote control and remote monitoring, allowing users to see the details of the cleaning and handling of goods transportation; remote monitoring can provide the video of robot's cleaning, so that users knows the cleaning status. Large-scale space cleaning robots used in the late night hours manage to transfer the original late-night cleaning manpower to the peak hours, not only solve the problem of late-night work but also solve the problem of lack of manpower during peak hours.

Various radio access technology (RAT) selection methods between LTE and wireless LAN (WLAN) have been proposed, which aim to improve the capacity of the cellular network and to improve user satisfaction through mobile network operators. However, studies from the viewpoint of mobile virtual network operators (MVNOs) have not yet been investigated sufficiently. We propose a novel RAT virtualization system suitable for MVNO composed of a new network-initiated RAT selection method and RAT selection algorithms. The system conceals a change of IPs associated with a change of RATs and offers a context-aware virtualized RAT for the application server and user application. We demonstrate a new RAT selection method by developing a prototype of the proposed RAT selection system. We also evaluate a system-level performance by using a network simulator (NS-3) and show that our proposed algorithm outperforms conventional algorithms in terms of the WLAN usage ratio and user satisfaction.

Poor local search capability is a defect of genetic algorithms (GA), which make the GA easily trapped in a local extremum during the later evolution stages. However, as a local optimization method, the Taguchi method has strong local optimizing ability, which could overcome this shortcoming of GA. Therefore, in this paper, a hybrid genetic algorithm (HGA) which combines the GA with the Taguchi method is used to optimize the rotor shape of an IPMSM to obtain lower iron loss and torque ripple as well as higher average torque and efficiency. The optimization results of the HGA design is compared with the initial and GA designs. It is shown that the performance of the IPMSM is effectively improved by employing the GA and HGA, especially by adopting HGA. Moreover, better flux-weakening capability and less mass magnet is also obtained by these methods.

With increase in the use of Wireless LANs in the enterprise area, network systems are often scattered across multiple locations in a wide area. Hence, there may be cases where a network administrator manages multiple locations. When users complain about connectivity issues, network administrators are expected to diagnose these problems without disrupting the normal operation of devices such as wireless stations (STAs) or access points (APs). In such cases, an on-site failure diagnosis is both time-consuming and expensive. Thus, an automated diagnostic technique to identify the cause of failure is important. We propose a method that can automatically identify the cause of the connectivity issues. The proposed method does not introduce any additional monitoring device, or require any functionality to be added in the AP or STA. In our proposed method, we send test packets to all STAs periodically and analyze the distribution of the responses and the RSSIs (received signal strength indicators) of the STAs. This helps to distinguish whether the connectivity issue is being caused by an AP failure, STA failure, or by a coverage-hole, which is a lack of network connectivity in certain areas of a building. The experimental results show that our proposed method is effective for the detection of AP failures, STA failures, and coverage-hole failures. From the detection results of a long experimental trial conducted in an actual office environment, it was observed that the false-detection probability of AP failure was very low. The STA failure was reported to be 0.36%, which was assumed to be because of hardware switch-offs or false detections because STA breakdowns were not reported during the trial. The ratio of the status “AP failure or STA failure” in the total failure detection was about 11%. Therefore, our proposed diagnosis system can suggest the cause of failure with a probability of 89%.

In a wireless convergecast network, load-balancing routing contributes to improving energy-efficiency by eliminating the difference of relaying load among one-hop nodes. Load-balancing algorithms can be operated by centralized and distributed implementation. Centralized implementation needs to collect global neighborhood information, which leads to a large amount of signaling overhead. On the contrary, distributed implementation can overcome such issue. However, it only achieves sub-optimal load-balancing. Thus, it is obscure that which type of implementation is more energy-efficiency. In this paper, a novel distributed implementation for load-balancing routing is proposed. We make a series of analyses of comparing the energy-efficiency between centralized and distributed implementation. The results show that, the overhead for constructing load-balancing routing via distributed implementation is always less than that via centralized implementation. However, the heaviest one-hop node in distributed implementation suffers from more loads so that according to its energy consumption, distributed implementation can maintain energy-efficiency only in the condition that routing update cycle is shorter than a threshold.

Automated interference detection is required for operation and management services in wireless networks as Wireless Local Area Networks (WLANs) based on IEEE 802.11 Standard since co-channel interference from other wireless transmitters occurs irregularly. We propose a new approach for detecting the presence of interference on 802.11 links. Our solution focuses on the Access Point (AP)-initiated monitoring approach without Wireless Station (STA)-initiated additional function and sniffer devices. Our approach uses the geographical distribution of the response delay of the Acknowledgment packet (ACK) to the downlink packet that AP transmitted to STAs. The proposed method consists of a continuous monitoring step and a periodical diagnosis step to measure network statistics by ACK response delay between an AP and STAs and to detect whether and where interference occurs respectively. Comprehensive simulation results show that the proposed approach has a good accuracy and low misdetection ratio for diagnosing the interference existence and location in IEEE 802.11 WLANs.

Recently, wireless networks using ISM band have been attracting a lot of attention. In these systems using carrier sense multiple access with collision avoidance (CSMA/CA), the packet collision and recollision between hidden nodes occur frequently and drastically decrease the network (NW) capacity. In this paper, we propose a packet retransmission protocol to avoid the packet recollision in 1 hop many-to-one network, in which all nodes send their packets to an access point (AP). In our proposed retransmission protocol, hidden nodes whose first transmitted packet is lost control their retransmission timing autonomously to avoid recollision with each other by using time lag between the finish time of their first transmitted packet and the received time of a collision inform signal, which is sent by AP to inform nodes about packet collision. The NW capacity using the proposed retransmission protocol is evaluated by computer simulation. And it is shown that the maximum network capacity of our proposed method is about 1.7 times better than that of the conventional method.