Large Zero Autocorrelation Zone of Golay Sequences and 4q4^q-QAM Golay Complementary Sequences

Sequences with good correlation properties have been widely adopted in modern communications, radar and sonar applications. In this paper, we present our new findings on some constructions of single $H$-ary Golay sequence and $4^q$-QAM Golay complementary sequence with a large zero autocorrelation zone, where $H\ge 2$ is an arbitrary even integer and $q\ge 2$ is an arbitrary integer. Those new results on Golay sequences and QAM Golay complementary sequences can be explored during synchronization and detection at the receiver end and thus improve the performance of the communication system

Physical Layer Securities in Wireless Communication Systems

Due to the tremendous advancement in the semiconductor and microelectronics technologies, wireless technologies have blossomed in the recent decades. The large scale deployment of wireless networks have revolutionized the way people live. They bring a great deal of convenience and enjoyment to us. Undoubtedly, we have become more and more dependent on these wireless technologies. These include cellular and radio frequency identification (RFID) technologies. However, with great technologies also come great risks and threats. Unlike wired transmissions, the nature of wireless transmissions result in the transmitted signals over the channel can be easily intercepted and eavesdropped by malicious adversaries. Therefore, security and privacy of the employed wireless communication system are easily compromised compared to the wired communication system. Consequently, securing wireless network has attracted a lot of attention in the recent years and it has huge practical implications. Securing wireless networks can be and indeed are performed at all layers of a network protocol stack. These include application, network, data link and physical (PHY) layers. The primary focus of our research is on the PHY layer approaches for securing and attacking wireless networks. In this thesis, we identify three research topics and present our results. They are: 1) PHY layer phase encryption (P-Enc) vs XOR encryption (XOR-Enc); 2) PHY layer signaling scheme to ensure the confidentiality of the transmitted messages from the tag to the reader in RFID systems. 3) Active eavesdropping attack framework under frequency hopping spread spectrum (FHSS) RFID systems. In the first work, we introduce a new OFDM encryption scheme which we call OFDM-Enc, different from convectional XOR-Enc, OFDM-Enc encrypts data by multiplying each of in-phase and quadrature component of the time domain OFDM symbol by a keystream bit. We then perform an initial investigation on the security of OFDM-Enc. We show it is secure against all attacks that are considered in this work. Moreover, depending on the modulation type, OFDM would potentially reduce the keystream size required for encryption, while still achieving the required security level. We also conduct simulations to compare OFDM-Enc with conventional XOR-Enc. We show indeed OFDM-Enc is viable and can achieve good performances. Then we extend OFDM-Enc to general communication systems. Since the encryption is essentially done by changing the phase of the data constellations, we just adopt the term P-Enc. In addition, we form mathematical formulations in order to compare between P-Enc and XOR-Enc in terms of efficiency, security and hardware complexity. Furthermore, we show P-Enc at the PHY layer can prevent traffic analysis attack, which cannot be prevented with the upper layer encryptions. Finally, simulations are conducted again to compare the performance of P-Enc and XOR-Enc. In the second work, we are interested in protecting tag's data from leaking or being compromised to malicious adversaries. As discussed earlier, due to the nature of wireless channels, communications between the tag and the reader is susceptible to eavesdropping. The conventional method uses encryption for confidentiality protection of transmitted messages. However, this requires to pre-share keys between the reader and the tag. As a result, a key management and distribution system needs to be put in place. This introduces heavy system overhead. In this work, we first propose a new PHY layer RFID privacy protection method which requires no pre-shared keys and would achieve the same goal. We also perform theoretical analysis to first validate of our proposed scheme. Finally, we conduct experiments to further verify the feasibility our proposed scheme under the passive eavesdropping attack model. In the third work, we present a new attack on the FHSS RFID system called active eavesdropping attack. In most semi-passive and passive RFID systems, tag to reader communications are accomplished via backscattering modulation. This implies the tag is not required to identify the frequency of the legitimate reader's transmitted signal, it simply responds to a reader's query by setting its impedance in the circuitry to low and high to represent bit 1 and 0. The attacker exploits this design weakness of the tag and broadcasts his own continuous wave (CW) at a different frequency. Consequently, the eavesdropper receives two copies of responses: one from his own broadcasted CW and one from reader's CW. We perform theoretical analysis to show the optimal strategy for the attacker in terms of the decoding error probability. Finally, we conduct simulations and experiments to verify with our theoretical results

Sequences design for OFDM and CDMA systems

With the emergence of multi-carrier (MC) orthogonal frequency division multiplexing (OFDM) scheme in the current WLAN standards and next generation wireless broadband standards, the necessitation to acquire a method for combating high peak to average power ratio (PMEPR) becomes imminent. In this thesis, we will explore various sequences to determine their PMEPR behaviours, in hopes to find some sequences which could potentially be suitable for PMEPR reduction control under MC system settings. These sequences include $m$ sequences, Sidelnikov sequences, new sequences, Golay sequences, FZC sequences and Legendre sequences. We will also examine the merit factor properties of these sequences, and then we will derive a bound between PMEPR and merit factor. Moreover, in the design of code division multiple access (CDMA) spreading sequence sets, it is critical that each sequence in the set has low autocorrelations and low cross-correlation with other sequences in the same set. In the thesis, we will present a class of GDJ Golay sequences which contains a large zero autocorrelation zone (ZACZ), which could satisfy the low autocorrelation requirement. This class of Golay sequences could potentially be used to construct new CDMA spreading sequence sets

Multi-objective rotor dynamics optimization of the plain bearing-rotor system

The study on rotor dynamics optimization of the plain bearing-rotor system was conducted. In this paper, multi-objective genetic algorithm was used to optimize the weight and stability of a rotor system, so that the stability of the rotor system was improved while the weight was reduced. Compared with single objective optimization, a large number of alternative results could be provided by optimizing one time in the use of the method in this paper. Furthermore, the optimization process can be greatly accelerated with the method, and the method is expected to provide a theoretical basis for improving rotor dynamics optimization of the plain bearing-rotor systems

Optimization of critical speed of double spools with reverse rotation

Under the requirement of high speed, high pressure ratio and high thrust weight ratio, more and more aircraft engines adopt counter rotating technology. In this model, the F135 engine is used to research the dynamic characteristics of a dual rotor system with four supports supported by an intermediary. In this paper, the critical speed of the system is solved by the direct method. Compared with the Campell diagram, the eigenvalue problem of the required solution is greatly reduced. The critical speed is optimized by using genetic algorithm. Moreover, when the constraint of frequency forbidden zone is more severe, the elitist preserving genetic algorithm is used, which greatly reduces the required convergence algebra

A novel methodology based on hidden semi-Markov model for equipment health assessment

As one of the most important aspects of PHM in many application domains, health monitoring and management could maximize the equipment effectiveness within the allowed health ranges. This paper proposes a novel approach to assess the equipment health based on hidden semi-Markov model (HSMM), which is an extension of HMM and does not follow the unrealistic Markov chain assumption to provide more powerful modeling and analysis capability for real problems. With training the standard health state HSMM model by normal state data, the test data is inputted into the trained model in order to calculate the corresponding relative divergence, which is the deviation extent from the standard health state model. Then we can obtain the health index model for the equipment health monitoring and measurement. Moreover, the proposed HSMM based method is applied to the draught fan and showed to be effective

Growth Inhibition and Induction of Apoptosis in SHG-44 Glioma Cells by Chinese Medicine Formula “Pingliu Keli”

The present study was carried out to evaluate the effects of the water extract of Chinese medicine “Pingliu Keli” (PK) on human glioma cell viability and apoptosis and to investigate its mechanisms of action in SHG-44 cells. MTT assay showed that PK had a strong cytotoxic effect on SHG-44 cells. The number of live cells was less than 20% after exposure to 90 μg/mL PK for 24 h. PK increased cytotoxicity of SHG-44 cells in a dose-dependent manner. PK caused arrest of SHG-44 cells in G1 phase at low concentration and in G2 phase at high concentration. The percentage of apoptotic cells by flow cytometric analysis of the DNA-stained cells increased to 38% and 52% after treatment with 72 and 108 μg/mL PK, respectively. In addition, PK increased the expression of proapoptotic protein (Bax) and decreased antiapoptotic protein (Bcl-2), with a concomitant increase in the levels of cleaved caspase-3, cleaved caspase-9 and cleaved poly-ADP-ribose polymerase (PARP). These results suggest that PK has a significant apoptosis inducing effect on SHG-44 glioma cells in vitro and caspase-3 may act as a potential mediator in the process

The role of lake heat flux in the growth and melting of ice

For shallow lakes, ice mass balance is largely dominated by thermodynamic processes. The heat flux from lake water plays a critical role for ice growth and melting. In this study, we applied a numerical thermodynamic lake model to investigate the sensitivity of the lake ice mass balance to the lake heat flux during the growth and melting periods. Several groups of modelling experiments forced by simplified climatological weather data have been carried out. Two sites, Lake Wuliangsuhai in Inner Mongolia, China’s arid region and Lake Orajärvi in snowy Finnish Lapland, were investigated. Lake heat flux affects inversely proportional maximum ice thickness followed by ice break-up date. The solar radiation and surface albedo complicate the effect of lake heat flux on lake ice mass balance during melting season. With heavy snowfall, the increase of lake heat flux adds on the formation of granular ice but reduces the formation of columnar ice. Under climatological weather conditions, the ice cover winter seasonal mean lake heat flux were 14 W·m−2 and 4 W·m−2 in Lake Wuliangsuhai and Lake Orajärvi, respectively.Peer reviewe

LGDN: Language-Guided Denoising Network for Video-Language Modeling

Video-language modeling has attracted much attention with the rapid growth of web videos. Most existing methods assume that the video frames and text description are semantically correlated, and focus on video-language modeling at video level. However, this hypothesis often fails for two reasons: (1) With the rich semantics of video contents, it is difficult to cover all frames with a single video-level description; (2) A raw video typically has noisy/meaningless information (e.g., scenery shot, transition or teaser). Although a number of recent works deploy attention mechanism to alleviate this problem, the irrelevant/noisy information still makes it very difficult to address. To overcome such challenge, we thus propose an efficient and effective model, termed Language-Guided Denoising Network (LGDN), for video-language modeling. Different from most existing methods that utilize all extracted video frames, LGDN dynamically filters out the misaligned or redundant frames under the language supervision and obtains only 2--4 salient frames per video for cross-modal token-level alignment. Extensive experiments on five public datasets show that our LGDN outperforms the state-of-the-arts by large margins. We also provide detailed ablation study to reveal the critical importance of solving the noise issue, in hope of inspiring future video-language work.Comment: Accepted by NeurIPS202

Design on the fairwater shape and its influence on the radiation noise of submarines

Firstly, a numerical computation model of submarine radiation noise was established to obtain the radiation noise of the submarine, which was compared with the experimental results, thus verifying the validity of the model. As indicated by the computational result, the submarine fairwater played a significant impact on radiation noise at the front section, whose structure was therefore necessary to be studied. In the paper, there were several different type submarine fairwaters. Large eddy simulation (LES) and boundary element method (BEM) were applied to conduct the numerical computation for the vortex flow field and acoustic characteristics of the original fairwater, the fairwater with fillet and the streamline fairwater. Furthermore, the impact and suppression effect of the fairwater’s type on wall pressure fluctuations and flow-induced noise were analyzed. As shown from the research, the vertical fairwater with fillet or the streamline fairwater can significantly improve the flow quality, thus considerably reducing the pressure fluctuations and flow-induced noise. The paper is conductive to the academic research of flow noise of submarine as well as the new submarine design in the future