Social-context based routing and security in delay tolerant networks

Delay Tolerant Networks (DTNs) were originally intended for interplanetary communications and have been applied to a series of difficult environments: wireless sensor networks, unmanned aerial vehicles, and short-range personal communications. There is a class of such environments in which nodes follow semi-predictable social patterns, such as wildlife tracking or personal devices. This work introduces a series of algorithms designed to identify the social patterns present in these environments and apply this data to difficult problems, such as efficient message routing and content distribution. Security is also difficult in a mobile environment. This is especially the case in the event that a large portion of the network is unreliable, or simply unknown. As the network size increases nodes have difficulty in securely distributing keys, especially using low powered nodes with limited keyspace. A series of multi-party security algorithms were designed to securely transmit a message in the event that the sender does not have access to the destinations public key. Messages are routed through a series of nodes, each of which partially decrypts the message. By encrypting for several proxies, the message can only be intercepted if all those nodes have been compromised. Even a highly compromised network has increased security using this algorithm, with a trade-off of reduced delivery ratio and increased delivery time -- Abstract, page iv

Dynamics of Di(propylene Glycol) Dibenzoate-d10 in Poly(vinyl Acetate) by Solid-state Deuterium NMR

Deuterium solid-state NMR and temperature-modulated differential scanning calorimetry were used to probe the dynamics of the plasticizer di(propylene glycol) dibenzoate (DPGDB-d10) in mixtures with poly(vinyl acetate) (PVAc). The plasticizer, deuterated in the phenyl rings, was synthesized, and 2H NMR spectra were obtained from PVAc samples with 10, 22, 27, and 37% deuterated plasticizer content as a function of temperature. The dynamics of the plasticizer in the plasticized polymer system were found to be heterogeneous with respect to different plasticizer molecules undergoing different motions. The experimental 2H NMR line shapes were fitted using a set of simulated spectra obtained from the MXQET program. The simulations were based on the superposition of two types of motion: a two-site jump motion, i.e., 180° ring flips, plus isotropic motions. The presence of the polymer allowed more plasticizer molecules to undergo 180° ring flips than in the bulk plasticizer. For the average of the log of the rate constants for the ring flips (〈log k〉) versus 1/temperature was linear with an apparent energy of activation of 75 kJ/mol for ring flips. From both NMR and TMDSC, the reduction in Tg was proportional to the amount of plasticizer added. In addition, the Tgs of DPGDB-d10/PVAc as a function of plasticizer content were found to be similar to those of PVAc-d3/DPGDB as determined by NMR The NMR data for both the polymer and plasticizer and TMDSC data may be fit to a plasticization model of Jenkel and Heusch with an interaction parameter b = -0.53, suggesting that both species were sensitive to the same local environment. © 2012 American Chemical Society