Artificial-Noise-Aided Secure Multi-Antenna Transmission with Limited Feedback

We present an optimized secure multi-antenna transmission approach based on artificial-noise-aided beamforming, with limited feedback from a desired single-antenna receiver. To deal with beamformer quantization errors as well as unknown eavesdropper channel characteristics, our approach is aimed at maximizing throughput under dual performance constraints - a connection outage constraint on the desired communication channel and a secrecy outage constraint to guard against eavesdropping. We propose an adaptive transmission strategy that judiciously selects the wiretap coding parameters, as well as the power allocation between the artificial noise and the information signal. This optimized solution reveals several important differences with respect to solutions designed previously under the assumption of perfect feedback. We also investigate the problem of how to most efficiently utilize the feedback bits. The simulation results indicate that a good design strategy is to use approximately 20% of these bits to quantize the channel gain information, with the remainder to quantize the channel direction, and this allocation is largely insensitive to the secrecy outage constraint imposed. In addition, we find that 8 feedback bits per transmit antenna is sufficient to achieve approximately 90% of the throughput attainable with perfect feedback.Comment: to appear in IEEE Transactions on Wireless Communication

Lunar hydrogen: A resource for future use at lunar bases and space activities

Hydrogen abundances were determined for grain size separates of five lunar soils and one soil breccia. The hydrogen abundance studies have provided important baseline information for engineering models undergoing study at the present time. From the studies is appears that there is sufficient hydrogen present in selected lunar materials which could be recovered to support future space activities. It is well known that hydrogen can be extracted from lunar soils by heating between 400 and 800 C. Recovery of hydrogen for regolith materials would involve heating with solar mirrors and collecting the released hydrogen. Current baseline models for the lunar base are requiring the production of 1000 metric tons of oxygen per year. From this requirement it follows that around 117 metric tons per year of hydrogen would be required for the production of water. The ability to obtain hydrogen from the lunar regolith would assist in lowering the operating costs of any lunar base

United Methodist Ministers In South Carolina, 1975

Biographical Sketches and photographs of the ministers and lay pastors serving churches of the South Carolina Conference Southeastern Jurisdiction, The United Methodist Church.https://digitalcommons.wofford.edu/methodistdirectories/1004/thumbnail.jp

The Relationship of L2 Proficiency and L1 Reading Academic Performance Prior to Formal L1 Literacy instruction in Foreign Language Immersion Settings

The purpose of this study is to explore the statistical nature of the linguistic interdependence hypothesis (Cummins, 1976, 2017) in the spring of 2nd grade of students in foreign language immersion programs. Specifically, the interdependent relationship between L2 language proficiency levels and L1 reading academic performance in an environment where L1 is the majority language and L2 is the target language for instruction with students who have yet to receive formal reading instruction in the L1. The Continua Model of Biliteracy was used to frame the existing research on language acquisition. An experimental ex post facto design using archival data from 228 students in a Spanish immersion program in the Midwest was used. A Spearman rank correlation was used to compare L2 proficiency (STAMP 4Se assessment) to L1 reading academic performance (MAP K-2 reading assessment). The findings of this study showed a strong relationship between L1 reading academic performance and L2 composite scores, L2 reading proficiency, and L2 listening proficiency scores, respectively. A moderate correlation between L1 reading academic performance and L2 writing scores was established, as well as a weak correlation between L1 reading academic performance and L2 speaking proficiency. The researcher concluded that programs and teachers can use L2 proficiency composite and interpretive proficiency indicators as a way to make instructional decisions and monitor growth prior to formal L1 instruction and/or between and before L1 reading high stakes assessment periods

Paleolakes and life on early Mars

Two distinct directions have begun to elucidate key parameters in the search for extinct life on Mars. Carbonate sediments, deposited about 10,000 years ago in association with biological activity, have been sampled from the paleolake beds of Lake Vanda and Meirs in the McMurdo Dry Valleys in Antarctica. These samples are being analyzed for simple biological signatures that remain in cold and dry paleolake sediments, namely microfossils, percent carbonate, and total organic carbon. Our second initiative is the study of Colour Lake, in the Canadian Arctic, that periodically maintains a perennial ice cover. Physical measurements started this year will be used to determine one end point for ice covered lake environments and will be compared to continuous measurements from Antarctic lakes started in November 1985. Interestingly, Colour Lake also supports benthic mat communities, but the low pH precludes carbonate deposition. This research will broaden our knowledge base for what conditions are necessary for ice covered lake formation and what biological signatures will remain in paleolake deposits