Auction-Based Coopetition between LTE Unlicensed and Wi-Fi

Motivated by the recent efforts in extending LTE to the unlicensed spectrum, we propose a novel spectrum sharing framework for the coopetition (i.e., cooperation and competition) between LTE and Wi-Fi in the unlicensed band. Basically, the LTE network can choose to work in one of the two modes: in the competition mode, it randomly accesses an unlicensed channel, and interferes with the Wi-Fi access point using the same channel; in the cooperation mode, it delivers traffic for the Wi-Fi users in exchange for the exclusive access of the corresponding channel. Because the LTE network works in an interference-free manner in the cooperation mode, it can achieve a much larger data rate than that in the competition mode, which allows it to effectively serve both its own users and the Wi-Fi users. We design a second-price reverse auction mechanism, which enables the LTE provider and the Wi-Fi access point owners (APOs) to effectively negotiate the operation mode. Specifically, the LTE provider is the auctioneer (buyer), and the APOs are the bidders (sellers) who compete to sell their channel access opportunities to the LTE provider. In Stage I of the auction, the LTE provider announces a reserve rate. In Stage II of the auction, the APOs submit their bids. We show that the auction involves allocative externalities, i.e., the cooperation between the LTE provider and one APO benefits other APOs who are not directly involved in this cooperation. As a result, a particular APO's willingness to cooperate is affected by its belief about other APOs' willingness to cooperate. This makes our analysis much more challenging than that of the conventional second-price auction, where bidding truthfully is a weakly dominant strategy. We show that the APOs have a unique form of the equilibrium bidding strategies in Stage II, based on which we analyze the LTE provider's optimal reserve rate in Stage I.Comment: 32 page

Proton Exchange Membrane Water Electrolysis as a Promising Technology for Hydrogen Production and Energy Storage

Proton exchange membrane (PEM) electrolysis is industrially important as a green source of high-purity hydrogen, for chemical applications as well as energy storage. Energy capture as hydrogen via water electrolysis has been gaining tremendous interest in Europe and other parts of the world because of the higher renewable penetration on their energy grid. Hydrogen is an appealing storage medium for excess renewable energy because once stored, it can be used in a variety of applications including power generation in periods of increased demand, supplementation of the natural gas grid for increased efficiency, vehicle fueling, or use as a high-value chemical feedstock for green generation of fertilizer and other chemicals. Today, most of the cost and energy use in PEM electrolyzer manufacturing is contributed by the cell stack manufacturing processes. Current state-of-the-art electrolysis technology involves two options: liquid electrolyte and ion exchange membranes. Membrane-based systems overcome many of the disadvantages of alkaline liquid systems, because the carrier fluid is deionized water, and the membrane-based cell design enables differential pressure operation

Engineer flexible loops for improved enzyme thermostability

Enzyme thermostability is a critical factor for its wide applications in industrial fields. Flexible sites are potential targets for engineering the stability of enzymes. Nevertheless, the success rate of the rigidifying flexible sites (RFS) strategy is still low due to a limited understanding of how to determine the best mutation candidates. The stereospecifically controlled carbon-carbon bond forming ability of Escherichia coli transketolase (TK) makes it very promising as a biocatalyst in industry. However, as a mesophilic enzyme, it suffers the limitation of low stability to elevated temperatures and extremes of pH, limiting its current use in industrial processes. In order to improve thermostability of TK, we have applied two parallel strategies to identify mutation candidates within the flexible loops. The first was a “back to consensus mutations” approach, and the second was computational design based on ΔΔG calculations in Rosetta. Forty-nine single variants were generated and characterized experimentally. From these, three single-variants I189H, A282P, D143K were found to be more thermostable than wild-type TK. The combination of A282P with H192P, a variant constructed previously, resulted in the best all-round variant with a 3-fold improved half-life at 60 °C, 5-fold increased specific activity at 65 °C, 1.3-fold improved kcat and a Tm increased by 5 °C above that of wild type. Based on a statistical analysis of the stability changes for all variants, the qualitative prediction accuracy of the Rosetta program reached 65.3%. Furthermore, molecular dynamics (MD) simulations of variants confirmed a good inverse correlation between protein stability and local flexibility which was determined by the magnitude of fluctuations with respect to the average conformations. Both of the two strategies investigated were useful in guiding mutation candidates to flexible loops, and had the potential to be used for other enzyme

Two strategies to engineer flexible loops for improved enzyme thermostability

The stereospecifically controlled carbon-carbon bond forming ability of Escherichia coli transketolase (TK) makes it very promising as a biocatalyst in industry. However, as a mesophilic enzyme the enzyme suffers the limitation of low stability to elevated temperatures and extremes of pH, limiting its current use in industrial processes. Flexible sites are potential targets for engineering the stability of enzymes. Nevertheless, the success rate of the rigidifying flexible sites (RFS) strategy is still low due to a limited understanding of how to determine the best mutation candidates. In this study, two parallel strategies were applied to identify mutation candidates within the flexible loops of TK. The first was a “back to consensus mutations” approach, and the second was computational design based on ΔΔG calculations in Rosetta. Forty-nine single variants were generated and characterised experimentally. From these, three single-variants I189H, A282P, D143K were found to be more thermostable than wild-type TK. The combination of A282P with H192P, a variant constructed previously, resulted in the best all-round variant with a 3-fold improved half-life at 60 °C, 5-fold increased specific activity at 65 °C, 1.3-fold improved kcat and a Tm increased by 5 °C above that of wild type. Based on a statistical analysis of the stability changes for all variants, the qualitative prediction accuracy of the Rosetta program reached 65.3%. Furthermore, molecular dynamics (MD) simulations of variants confirmed a good inverse correlation between protein stability and local flexibility which was determined by the magnitude of fluctuations with respect to the average conformations. Both of the two strategies investigated were useful in guiding mutation candidates to flexible loops, and had the potential to be used for other enzymes