Membrane formation and aggregation properties of two series of (±) α-tocopherol-based cationic gemini lipids without and with hydroxyl functionalities at the headgroup region (TnS n = 3,4,5,6,8,and 12; THnS n = 4,5,6,8,and 12) with varying polymethylene spacer lengths were investigated extensively while comparing with the corresponding properties of the monomeric counterparts (TM and THM). Liposomal suspensions of each cationic lipid were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), zeta potential measurements, and small-angle X-ray diffraction studies. The length of the spacer and the presence of hydroxyl functionalities at the headgroup region strongly contribute to the aggregation behavior of these gemini lipids in water. The interaction of each tocopherol lipid with a model phospholipid, 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC)-derived vesicles, was thoroughly examined by differential scanning calorimetry (DSC) and 1,6-diphenyl-1,3,5-hexatriene (DPH)-doped fluorescence anisotropy measurements. The binding efficiency of the cationic tocopherol liposomes with plasmid DNA (pDNA) was followed by an ethidium bromide (EB) exclusion assay and zeta potential measurements, whereas negatively charged micellar sodium dodecyl sulfate (SDS)-mediated release of the pDNA from various preformed pDNA−liposomal complexes (lipoplex) was studied by an ethidium bromide (EB) reintercalation assay. The structural transformation of pDNA upon complexation with liposome was characterized using circular dichroism (CD) spectroscopic measurements. Gemini lipid−pDNA interactions depend on both the presence of hydroxyl functionalities at the headgroups and the length of the spacer chain between the headgroups. Succinctly, we performed a detailed physical−chemical characterization of the membranes formed from cationic monomeric and gemini lipids bearing tocopherol as their hydrophobic backbone and describe the role of inserting the −OH group at the headgroup of such lipids.
A promising solution to increasing busty traffic over the Internet can be Optical Burst Switched (OBS) networks with scalable and efficient multicast support. The efficiency of multicasting in OBS networks depends on: the burstification process, the multicasting schemes, tree sharing strategies, construction of shared trees, multicast schemes for dynamic sessions and membership. In this article, the contributions of various researchers are studied thoroughly and compared to survey the various approaches and problems of multicasting in OBS networks and outline several future research directions in terms of applications in business, especially in Business-toBusiness (B2B) and Business-to-Consumer (B2C) Models, through optimal resource utilization of QoS aware multicasting in OBS networks.
General TermsOptical Networks
Performance of existing TCP implementations over Optical Burst Switched (OBS) networks is not satisfactory, as they suffer from false congestion detection. As the contention induced losses are more common than congestion induced losses in OBS, the TCP reduces the congestion window even when there is no congestion. This effect, in turn unnecessarily reduces the TCP throughput. So it is crucial to differentiate the contention induced loss from congestion induced loss in such networks. It has been proposed in this paper, a mechanism that makes use of short-term RTT variation and assembly times' of individual TCP segments to differentiate between congestion and contention induced losses. This mechanism is a cross layer modification of a congestion control scheme called Statistical Additive Increase and Multiplicative Decrease (SAIMD). Our proposed scheme is found to be more efficient than existing one in terms of TCP throughput. The gain in throughput is primarily because of avoidance of misdirection of contention induced loss as congestion induced loss. A throughput-cost study has been conducted based on the throughput metric available from the efficiency analysis of our proposed scheme. The cost model used focuses on initial capital expenditure including switching, routing and amplification cost. An extension of ns2 called nOBS, to support OBS protocol is used for simulation to study the performance.
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