The Wiretap Channel with Feedback: Encryption over the Channel

In this work, the critical role of noisy feedback in enhancing the secrecy capacity of the wiretap channel is established. Unlike previous works, where a noiseless public discussion channel is used for feedback, the feed-forward and feedback signals share the same noisy channel in the present model. Quite interestingly, this noisy feedback model is shown to be more advantageous in the current setting. More specifically, the discrete memoryless modulo-additive channel with a full-duplex destination node is considered first, and it is shown that the judicious use of feedback increases the perfect secrecy capacity to the capacity of the source-destination channel in the absence of the wiretapper. In the achievability scheme, the feedback signal corresponds to a private key, known only to the destination. In the half-duplex scheme, a novel feedback technique that always achieves a positive perfect secrecy rate (even when the source-wiretapper channel is less noisy than the source-destination channel) is proposed. These results hinge on the modulo-additive property of the channel, which is exploited by the destination to perform encryption over the channel without revealing its key to the source. Finally, this scheme is extended to the continuous real valued modulo-$\Lambda$ channel where it is shown that the perfect secrecy capacity with feedback is also equal to the capacity in the absence of the wiretapper.Comment: Submitted to IEEE Transactions on Information Theor

Cognitive Medium Access: Exploration, Exploitation and Competition

This paper establishes the equivalence between cognitive medium access and the competitive multi-armed bandit problem. First, the scenario in which a single cognitive user wishes to opportunistically exploit the availability of empty frequency bands in the spectrum with multiple bands is considered. In this scenario, the availability probability of each channel is unknown to the cognitive user a priori. Hence efficient medium access strategies must strike a balance between exploring the availability of other free channels and exploiting the opportunities identified thus far. By adopting a Bayesian approach for this classical bandit problem, the optimal medium access strategy is derived and its underlying recursive structure is illustrated via examples. To avoid the prohibitive computational complexity of the optimal strategy, a low complexity asymptotically optimal strategy is developed. The proposed strategy does not require any prior statistical knowledge about the traffic pattern on the different channels. Next, the multi-cognitive user scenario is considered and low complexity medium access protocols, which strike the optimal balance between exploration and exploitation in such competitive environments, are developed. Finally, this formalism is extended to the case in which each cognitive user is capable of sensing and using multiple channels simultaneously.Comment: Submitted to IEEE/ACM Trans. on Networking, 14 pages, 2 figure

The Deterministic Capacity of Relay Networks with Relay Private Messages

We study the capacity region of a deterministic 4-node network, where 3 nodes can only communicate via the fourth one. However, the fourth node is not merely a relay since it can exchange private messages with all other nodes. This situation resembles the case where a base station relays messages between users and delivers messages between the backbone system and the users. We assume an asymmetric scenario where the channel between any two nodes is not reciprocal. First, an upper bound on the capacity region is obtained based on the notion of single sided genie. Subsequently, we construct an achievable scheme that achieves this upper bound using a superposition of broadcasting node 4 messages and an achievable "detour" scheme for a reduced 3-user relay network.Comment: 3 figures, accepted at ITW 201

Optimization cultivation of Chlamydomonas reinhardtii in a tubular photobioreactor (2000 Liter) for biomass and green bioenergy (biodiesel) production

The biodiesel can be produced from diverse microalgae lipids as alternative and renewable fuel. Thus, the aim of this study was to optimize the Chlamydomonas reinhardtii promising species as biodiesel feedstock for large-scale cultivation in Egypt. To understand some of the triggers required for the metabolic pathway switch to lipid accumulation, the effect of carbon sources and the three elements availability (N, P, S) in C. reinhardtii growth medium was determined. A local microalgae C. reinhardtii was cultured in modified Sueoka medium containing various concentrations of CO2 and bicarbonate (NaHCO3) (in 2-liter flasks) as a carbon source. The optimal source in term biomass, high lipid productivity (10.3 mgL-1d-1) and a higher lipid content (22.76%) were obtained in 6% CO2 culture. Then, the availability of N, P, S (various concentrations of N, P and S) nutrients elements was added to 6% CO2 culture, for produce a highest lipid content and lipid productivity. As expected, under low availability N-1.78 mM; P-0.14mM and S-0.10 mM mediums, C. reinhardtii showed a high accumulation lipid content. Therefore, to improve the economic feasibility of microalgae biofuels production, its concentrations were selected to combine (N+P+S) in order to cultivation of C. reinhardtii in a multi-tubular photobioreactor (400 liter) to produce high lipid contents. Under limited condition, the biomass dry weight, biomass productivity, lipid content and lipid productivity were found to be 3.11 (gL-1), 0.15±0.012 (g-1L-1d-1), 22.76% (w/w %) and 1.9± 0.35 (mg-1L-1d-1), respectively. The extracted lipid was found to have physical and chemical properties similar that plant oils using for biodiesel production. The FAME profiling of prepared biodiesel shows the presence of considerable amount of 36.97% saturated fatty acids (palmitic acid and stearic acid, together) with 27.33% unsaturated (oleic acid and linoleic acid) fatty acids. The FAME had a low iodine value and high CN, which meet with the appropriate of biodiesel standards (EN 14214 and ASTM D6751). Thus, C. reinhardtii appears to be more feasible for high quality biodiesel production

Proučavanje parametara rasprašivanja plazmom velike gustoće u koaksijalnom ubrzivaču plazme

Plasma accelerator was used for the deposition of a material powder placed at a breach. A capacitor bank of 46.26 µF charged to 3 kV (208.17 J) gave a peak current of 8.8 kA after 15 µs. Plasma inductance varied between 3 µH and 1.5 µH while the plasma resistance varied between 5 mΩ and 300 mΩ within one shot, while the electron temperature and plasma density near the substrate measured with a double electric probe was about 3 eV and 2.7 × 1013 cm−3 , respectively. Carbon plasma velocity at the muzzle was 6.0 cm/µs which agrees with calculations. The deposited graphite powder showed mostly a homogeneous distribution of clusters. The total efficiency of the system, considering both the internal and kinetic energy, was found to be 10.9 %.Rabili smo ubrzivač plazme za naparavanje praha postavljenog na otvoru za snop. Sklop kapacitora od 46.26 µF nabijen na 3 kV (208.2 J) davao je vršnu struju 8.8 kA nakon 15 µs. Indukcija plazme mijenjala se između 3 i 1.5 µH, a otpor plazme između 5 i 300 mΩ tijekom pojedinog palenja. Elektronska temperatura i gustoća plazme u blizini podloge, koje smo mjerili dvostrukom električnom sondom, iznose oko 3 eV odn. 2.7 × 1013 cm−3 . Brzina ugljične plazme kod otvora iznosi 6.0 cm/µs, u skladu s izračunatom vrijednošću. Naparen grafitni prah pokazuje većma jednoličnu raspodjelu nakupina. Ukupna učinkovitost sustava, ubrajajući unutarnju i kinetičku energiju, iznosi 10.9 %

Modification of bacterial cell membrane to accelerate decolorization of textile wastewater effluent using microbial fuel cells: role of gamma radiation

The aim of the present work was to increase bacterial adhesion on anode via inducing membrane modifications to enhance textile wastewater treatment in Microbial Fuel Cell (MFC). Real textile wastewater was used in mediator-less MFCs for bacterial enrichment. The enriched bacteria were pre-treated by exposure to 1 KGy gamma radiation and were tested in MFC setup. Bacterial cell membrane permeability and cell membrane charges were measured using noninvasive dielectric spectroscopy measurements. The results show that pre-treatment using gamma radiation resulted in biofilm formation and increased cell permeability and exopolysaccharide production; this was reflected in both MFC performance (average voltage 554.67 mV) and decolorization (96.42%) as compared to 392.77 mV and 60.76% decolorization for non-treated cells. At the end of MFC operation, cytotoxicity test was performed for treated wastewater using a dermal cell line, the results obtained show a decrease in toxicity from 24.8 to 0 (v/v%) when cells were exposed to gamma radiation. Fourier-transform infrared (FTIR) spectroscopy showed an increase in exopolysaccharides in bacterial consortium exposed to increasing doses of gamma radiation suggesting that gamma radiation increased exopolysaccharide production, providing transient media for electron transfer and contributing to accelerating MFC performance. Modification of bacterial membrane prior to MFC operation can be considered highly effective as a pre-treatment tool that accelerates MFC performance