Performance analysis of FSO using relays and spatial diversity under log-normal fading channel

The performance analysis of free space optical communication (FSO) system using relays and spatial diversity at the source is studied in this paper. The effect of atmospheric turbulence and attenuation, caused by different weather conditions and geometric losses, has also been considered for analysis. The exact closed-form expressions are presented for bit error rate (BER) of M-ary quadrature amplitude modulation (M-QAM) technique for multi-hop multiple-input single-output (MISO) FSO system under log-normal fading channel. Furthermore, the link performance of multi-hop MISO and multi-hop single-input and single-output (SISO) FSO systems are compared to the different systems using on-off keying (OOK), repetition codes (RCs) and M-ary pulse amplitude modulation (M-PAM) techniques. A significant performance enhancement in terms of BER analysis and SNR gains is shown for multi-hop MISO and multi-hop SISO FSO systems with M-QAM over other existing systems with different modulation schemes. Moreover, Monte-Carlo simulations are used to validate the accuracy and consistency of the derived analytical results. Numerical results show that M-QAM modulated multi-hop MISO and multi-hop SISO FSO system with relays and spatial diversity outperforms other systems while having the same spectral efficiency of each system.Comment: 4 pages, 4 figures, 4th International Conference on Electrical Energy Systems (ICEES), Feb. 7-9, 2018, SSNCE, Chennai, TN, INDI

Leveling transparency via situated intermediary learning objectives (SILOs)

When designers set out to create a mathematics learning activity, they have a fair sense of its objectives: students will understand a concept and master relevant procedural skills. In reform-oriented activities, students first engage in concrete situations, wherein they achieve situated, intermediary learning objectives (SILOs), and only then they rearticulate their solutions formally. We define SILOs as heuristics learners devise to accommodate contingencies in an evolving problem space, e.g., monitoring and repairing manipulable structures so that they model with fidelity a source situation. Students achieve SILOs through problem-solving with media, instructors orient toward SILOs via discursive solicitation, and designers articulate SILOs via analyzing implementation data. We describe the emergence of three SILOs in developing the activity Giant Steps for Algebra. Whereas the notion of SILOs emerged spontaneously as a framework to organize a system of practice, i.e. our collaborative design, it aligns with phenomenological theory of knowledge as instrumented action

Sturdier DNA nanotubes via ligation

DNA nanotubes are crystalline self-assemblies of DNA tiles ~10 nm in diameter that readily grow tens of micrometers in length. Easy assembly, programmability, and stiffness make them interesting for many applications, but DNA nanotubes begin to melt at temperatures below 40 °C, break open when deposited on mica or scanned by AFM, and disintegrate in deionized water. These weaknesses can be traced to the presence of discontinuities in the phosphate backbone, called nicks. The nanotubes studied here have five nicks, one in the core of a tile and one at each corner. We report the successful ligation of all four corner nicks by T4 DNA ligase. Although ligation does not change the nanotubes’ stiffness, ligated nanotubes withstand temperatures over 70 °C, resist breaking during AFM, and are stable in pure water for over a month. Ligated DNA nanotubes are thus physically and chemically sturdy enough to withstand the manipulations necessary for many technological applications