Reinvestigation of the Red Sea sponge Suberea mollis afforded two new bromotyrosine-derived alkaloids, subereamollines A (1) and B (2), two new brominated phenolic compounds, subereaphenols B (7) and C (9), and the known compounds aerothionin (3), homoaerothionin (4), 11,19-dideoxyfistularin-3 (5), aeroplysinin-1 (6), and aeroplysinin-2 (8). The structure determination of the isolated compounds was assigned using one- and two-dimensional NMR spectra and HRFABMS data. The antimicrobial and antioxidant activities of the isolated compounds have been evaluated. Aeroplysinin-1 displayed significant antimicrobial activity against S. aureus, P. aerugenosa, and K. pneumoniae. The isolated compounds were examined for their antioxidant activity using a 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) solution-based chemical assay. Among the tested compounds, only subereaphenols B and C displayed a significant effect.

Abstract-We propose a service differentiated peer selection mechanism for peer-to-peer media streaming systems. The mechanism provides flexibility and choice in peer selection to the contributors of the system, resulting in high quality streaming sessions. Free-riders are given limited options in peer selection, if any, and hence receive low quality streaming. The proposed incentive mechanism follows the characteristics of rank-order tournaments theory that considers only the relative performance of the players, and the top prizes are awarded to the winners of the tournament. Using rank-order tournaments, we analyze the behavior of utility maximizing users. Through simulation and wide-area measurement studies, we verify that the proposed incentive mechanism can provide near optimal streaming quality to the cooperative users until the bottleneck shifts from the streaming sources to the network.

We propose a rank-based peer-selection mechanism for peer-to-peer media streaming systems. The mechanism provides incentives for cooperation through service differentiation. Contributors to the system are rewarded with flexibility and choice in peer selection, resulting in high quality streaming sessions. Free-riders are given limited options in peer selection, if any, and hence receive low quality streaming. Through simulation and wide-area measurement studies, we verify that the mechanism can provide near optimal streaming quality to the cooperative users until the bottleneck shifts from the sources to the network.

We present CollectCast, a peer-to-peer (P2P) service for media streaming where a receiver peer is served by multiple sender peers. CollectCast operates at the application level but infers underlying network properties to correlate end-to-end connections between peers. The salient features of CollectCast include: (1) a novel multisender selection method that exploits the performance correlation and dependency among connections between different candidate senders and the receiver, (2) a customization of network tomography techniques and demonstration of improved practicality and efficiency, and (3) an aggregation-based P2P streaming mechanism that sustains receiver-side quality in the presence of sender/network dynamics and degradation. We have performed both real-world (on PlanetLab) and simulation evaluation of CollectCast. Our simulation results show that for a receiver, CollectCast makes better selection of multiple senders than other methods that do not infer underlying network properties. Our PlanetLab experiments are performed using a P2P media streaming application (called PROMISE) which we developed on top of CollectCast. Both packet-level and frame-level performance of MPEG-4 video streaming demonstrates the practicality and effectiveness of CollectCast.