174 research outputs found
Inversion and Interpretation of Magnetic Anomaly in the Presence of Significant Remanence and Self-Demagnetization Based on Magnetic Amplitude
Remanent magnetization and self-demagnetization effects of high-susceptibility body distort the intensity and direction of internal magnetization and hence complicate the inversion and interpretation of magnetic anomaly. The magnitude magnetic anomaly, which is weakly sensitive to the magnetization direction, provides an indirect way to investigate these complex anomalies. We study the sensitivity characteristics of 2D magnitude magnetic anomaly to magnetization direction and source shapes, implement the magnetization intensity inversion, and further estimate the magnetization direction by inverting for the total field data. The magnetic amplitude inversion is tested by the use of synthetic data, which are caused by prism models with strong remanent magnetization and high susceptibility. It is also applied to the field data of an iron-ore deposit in South Australia. The primary advantage of magnitude anomaly inversion is that the magnetization directions are not assumed to parallel the geomagnetic field. The magnetization intensity inversion and magnetization direction estimation make full use of the amplitude and phase information of magnetic anomalies. Magnetic amplitude inversion including other amplitude quantities such as normalized source strength and analytic signal offers an effective approach to investigate and interpret the magnetic anomalies affected by complicated remanence and self-demagnetization
Recent developments on fractal-based approaches to nanofluids and nanoparticle aggregation
This project was supported by the National Natural Science Foundation of China (Nos. 41572116, 51576114, 41630317), the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) (No. CUG160602) and the Natural Science Foundation of Fujian Province of China (No. 2016J01254). The authors of the figures that used in presented review are also highly appreciated.Peer reviewedPostprin
Fractal analysis of the effect of particle aggregation distribution on thermal conductivity of nanofluids
This project was supported by the National Natural Science Foundation of China (No. 41572116), the Fundamental Research Funds for the Central Universities, China University of Geosciences, Wuhan) (No. CUG160602).Peer reviewedPostprin
Achieving Covert Wireless Communications Using a Full-Duplex Receiver
Covert communications hide the transmission of a message from a watchful
adversary while ensuring a certain decoding performance at the receiver. In
this work, a wireless communication system under fading channels is considered
where covertness is achieved by using a full-duplex (FD) receiver. More
precisely, the receiver of covert information generates artificial noise with a
varying power causing uncertainty at the adversary, Willie, regarding the
statistics of the received signals. Given that Willie's optimal detector is a
threshold test on the received power, we derive a closed-form expression for
the optimal detection performance of Willie averaged over the fading channel
realizations. Furthermore, we provide guidelines for the optimal choice of
artificial noise power range, and the optimal transmission probability of
covert information to maximize the detection errors at Willie. Our analysis
shows that the transmission of artificial noise, although causes
self-interference, provides the opportunity of achieving covertness but its
transmit power levels need to be managed carefully. We also demonstrate that
the prior transmission probability of 0.5 is not always the best choice for
achieving the maximum possible covertness, when the covert transmission
probability and artificial noise power can be jointly optimized.Comment: 13 pages, 11 figures, Accepted for publication in IEEE Transactions
on Wireless Communication
Artificial-Noise-Aided Secure Transmission Scheme With Limited Training and Feedback Overhead
We design a novel artificial-noise-aided secure onoff
transmission scheme in a wiretap channel. We consider
a practical scenario where the multi-antenna transmitter only
obtains partial channel knowledge from the single-antenna receiver
through limited training and feedback but has no channel
knowledge about the single-antenna eavesdropper. In the design,
we first propose a three-period block transmission protocol to
capture the practical training and quantization features. We
then characterize the statistics of the received signal-to-noise
ratios (SNRs) at the receiver and the eavesdropper. Under the
secrecy outage constraint, we exploit the on-off scheme to perform
secure transmission and derive a closed-form expression for the
secrecy throughput. Moreover, we investigate the optimization
problem of maximizing the secrecy throughput by proposing an
iterative algorithm to determine the optimal power allocation
between the information signal and artificial noise, as well as the
optimal codeword transmission rate. Furthermore, we define the
net secrecy throughput (NST) which takes the signaling overhead
into account and address the problem of optimally allocating the
block resource to the training and feedback overhead. Numerical
results clearly demonstrate how the optimal signaling overhead
changes with the number of transmit antennas, and there exists
an optimal number of antennas that maximizes the NST.ARC Discovery Projects Grant DP15010390
Secure beamforming transmission with limited training and feedback
We consider the secure beamforming transmission over a quasi-static block fading channel from a multi-antenna transmitter to a desired single-antenna receiver, in the presence of a passive single-antenna eavesdropper. We focus on a practical scenario where the transmitter can only acquire the statistical channel knowledge of the eavesdropper and the partial channel knowledge of the legitimate receiver through a finite amount of signaling overhead. To keep control of the outage events caused by the limited channel knowledge, We firstly propose a strategy to determine the wiretap code parameters under the outage constraints, based on which we establish a necessary transmission condition to guarantee a positive secrecy rate. Aided by this transmission condition, we propose an on-off-based transmission scheme and characterize the secrecy throughput performance of the system. Our designed transmission scheme is beneficial for the deployment of physical layer security in practical frequency division duplex (FDD) systems with limited training and feedback.ARC Discovery Projects Grant DP15010390
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