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Sarah R. Sattin,Cory C. Cleveland,Eran Hood,Sasha C. Reed,Andrew J. King,Steven K. Schmidt,Michael S. Robeson,Nataly Ascarrunz,Diana R. Nemergut 한국미생물학회 2009 The journal of microbiology Vol.47 No.6
Past work in recently deglaciated soils demonstrates that microbial communities undergo shifts prior to plant colonization. To date, most studies have focused on relatively ‘long’ chronosequences with the ability to sample plant-free sites over at least 50 years of development. However, some recently deglaciated soils feature rapid plant colonization and questions remain about the relative rate of change in the microbial community in the unvegetated soils of these chronosequences. Thus, we investigated the forelands of the Mendenhall Glacier near Juneau, AK, USA, where plants rapidly establish. We collected unvegetated samples representing soils that had been ice-free for 0, 1, 4, and 8 years. Total nitrogen (N) ranged from 0.00~0.14 mg/g soil, soil organic carbon pools ranged from 0.6~2.3 mg/g soil, and both decreased in concentration between the 0 and 4 yr soils. Biologically available phosphorus (P) and pH underwent similar dynamics. However, both pH and available P increased in the 8 yr soils. Nitrogen fixation was nearly undetectable in the most recently exposed soils, and increased in the 8 yr soils to ~5 ng N fixed/cm2/h, a trend that was matched by the activity of the soil N-cycling enzymes urease and β-1,4-N-acetyl-glucosaminidase. 16S rRNA gene clone libraries revealed no significant differences between the 0 and 8 yr soils; however, 8 yr soils featured the presence of cyanobacteria, a division wholly absent from the 0 yr soils. Taken together, our results suggest that microbes are consuming allochtonous organic matter sources in the most recently exposed soils. Once this carbon source is depleted, a competitive advantage may be ceded to microbes not reliant on in situ nutrient sources.
Jin S. Kang,Jeffery T. King,Christopher R. Anderson,Michael H. Sanders 한국항공우주학회 2022 International Journal of Aeronautical and Space Sc Vol.23 No.4
As CubeSats have become hugely popular in the recent years, the demand on their capability has also increased. As the missions and functionalities become more complex, coupled with the popular VHF and UHF bands becoming less accessible, CubeSats have been getting pushed into using higher frequency bands. For more capable CubeSats such as NASA and military satellites, utilization of S- and X-band communication have become a common place. While S- and X-band communication provide much higher data rate for the mission, the power and attitude control demand has also increased. Meeting this increased cost and demand on resources may not be feasible for university-level projects as attitude control systems can often cost more than the rest of the CubeSat. This research revisits passive magnetic pointing as an option for providing antenna pointing capability for CubeSats, enabling S- and X-band communication without requiring an active attitude control system. CubeSats can make contact with ground stations located at higher latitude to establish data link with directional antennas. The analyses shows that a higher data throughput can be achieved using S- and X-band communication over the traditional 9600 bps link with the proposed setup, without requiring active attitude control or deployable solar panels. The study characterizes the expected communication link performance for a typical 3U CubeSat when implementing the proposed communication architecture using a S- or X-band patch antenna taking into consideration the expected pointing performance and power generation capability of a 3U CubeSat.