ECS: Efficient Communication Scheduling for Underwater Sensor Networks

TDMA protocols have attracted a lot of attention for underwater acoustic sensor networks (UWSNs), because of the unique characteristics of acoustic signal propagation such as great energy consumption in transmission, long propagation delay and long communication range. Previous TDMA protocols all allocated transmission time to nodes based on discrete time slots. This paper proposes an efficient continuous time scheduling TDMA protocol (ECS) for UWSNs, including the continuous time based and sender oriented conflict analysis model, the transmission moment allocation algorithm and the distributed topology maintenance algorithm. Simulation results confirm that ECS improves network throughput by 20% on average, compared to existing MAC protocols

Ranging in an Underwater Medium with Multiple Isogradient Sound Speed Profile Layers

In this paper, we analyze the problem of acoustic ranging between sensor nodes in an underwater environment. The underwater medium is assumed to be composed of multiple isogradient sound speed profile (SSP) layers where in each layer the sound speed is linearly related to the depth. Furthermore, each sensor node is able to measure its depth and can exchange this information with other nodes. Under these assumptions, we first show how the problem of underwater localization can be converted to the traditional range-based terrestrial localization problem when the depth information of the nodes is known a priori. Second, we relate the pair-wise time of flight (ToF) measurements between the nodes to their positions. Next, based on this relation, we propose a novel ranging algorithm for an underwater medium. The proposed ranging algorithm considers reflections from the seabed and sea surface. We will show that even without any reflections, the transmitted signal may travel through more than one path between two given nodes. The proposed algorithm analyzes them and selects the fastest one (first arrival path) based on the measured ToF and the nodes’ depth measurements. Finally, in order to evaluate the performance of the proposed algorithm we run several simulations and compare the results with other existing algorithms

A Reverse Localization Scheme for Underwater Acoustic Sensor Networks

Underwater Wireless Sensor Networks (UWSNs) provide new opportunities to observe and predict the behavior of aquatic environments. In some applications like target tracking or disaster prevention, sensed data is meaningless without location information. In this paper, we propose a novel 3D centralized, localization scheme for mobile underwater wireless sensor network, named Reverse Localization Scheme or RLS in short. RLS is an event-driven localization method triggered by detector sensors for launching localization process. RLS is suitable for surveillance applications that require very fast reactions to events and could report the location of the occurrence. In this method, mobile sensor nodes report the event toward the surface anchors as soon as they detect it. They do not require waiting to receive location information from anchors. Simulation results confirm that the proposed scheme improves the energy efficiency and reduces significantly localization response time with a proper level of accuracy in terms of mobility model of water currents. Major contributions of this method lie on reducing the numbers of message exchange for localization, saving the energy and decreasing the average localization response time

Localization Algorithms of Underwater Wireless Sensor Networks: A Survey

In Underwater Wireless Sensor Networks (UWSNs), localization is one of most important technologies since it plays a critical role in many applications. Motivated by widespread adoption of localization, in this paper, we present a comprehensive survey of localization algorithms. First, we classify localization algorithms into three categories based on sensor nodes’ mobility: stationary localization algorithms, mobile localization algorithms and hybrid localization algorithms. Moreover, we compare the localization algorithms in detail and analyze future research directions of localization algorithms in UWSNs

Extracellular expression of alkaline phytase in Pichia pastoris and Development of Nuclear Magnetic Resonance spectroscopy methods for structural investigation of inositol polyphosphates

Acid phytases from fungal sources are used as animal feed supplements to alleviate the environmental contamination and nutritional issues associated with the high concentration of phytic acid in seeds (5-8% of the dry cell weight). Acid phytases function optimally at acidic pH values, however there is need for phytases that operate over a broader pH range. Additionally, there are concerns about potential allergic responses to the incorporation of fungal proteins into the diets of animals for human consumption. A variety of phytases with a range of catalytic and thermal stability properties is needed to be effective in different animals. Our lab has isolated an alkaline phytase from Lilium longiflorum and expressed it in Pichia pastoris. This dissertation describes the: (1) enhancement of the intracellular expression yield of alkaline phytase by employing a constitutive promoter, (2) establishment of extracellular expression of alkaline phytase by employing different secretion signals, (3) delineation of structure-activity relationships of mutant alkaline phytase, (4) development of colorimetric assays to rapidly screen for alkaline phytase activity in a large number of clones, and (5) development of NMR methods for the structural investigation of inositol pyrophosphates. The intracellular yield of alkaline phytase was investigated using two different promoters: the tightly-regulated promoter of the alcohol oxidase 1 gene (PAOX1) and the constitutive promoter from the glyceraldehyde-3-phosphate dehydrogenase gene (PGAP). Employing PGAP resulted in a four-fold increase in intracellular expression (100-120 mg/L) over the use of PAOXI. Extracellular expression constructs with various mutant forms of the rLlAlp2 gene downstream of either the alpha-mating factor secretion signal (α-MF) or the chicken lysozyme (CL) secretion signal were generated and extracellular expression levels investigated. The data suggest that with α-MF-driven secretion, deletion of both N- and C-termini native signal peptides (m2-rLlALP2) enhanced extracellular expression eight- to ten-fold with the constitutive promoter PGAP (80-100 mg/L) compared to PAOXI (~10 mg/L). To delineate structure-activity relationships, the catalytic activity of m2-rLlALP2 was compared to the wt-phytase. Catalytic activity over a broad pH range is important to the feed industry as this enables the enzyme to efficiently digest phytic acid during passage through the GI tracts of different animals. Thermal stability is also important because the enzyme is exposed to approximately 80 °C for 10 min during the feed pelleting process. At pH 9.0 and 6.0, m2-rLlALP2 retained 90% and 40% activity, respectively, compared to 50% and 10% retained by wt-phytase. At 60 °C and 55 °C, m2-rLlALP2 retained 35% and 70% activity, respectively, compared to 15% and 50% retained by wt-phytase. Thus, the improved activity over a broad pH range and temperature profile suggest that the deletion of amino acids at the N- and C-terminal domains resulted in beneficial catalytic properties. Mutagenesis can be used to change the catalytic properties of enzymes. Mutagenesis experiments generate hundreds of clones so a rapid assay to screen for phytase activity in clones is critical. The current standard assay involves many steps and is time-consuming (requires 24 h). Colorimetric assays were developed using the substrates 5-bromo-4-chloro-3-indolyl phosphate (BCIP) and para-nitrophenyl phosphate (p-NPP). These assays yield colored products visible to the eye and can be completed in less than one hour after cell collection. Although inositol phosphates have been investigated for over a hundred years, inositol pyrophosphates have been discovered only recently. The low abundance and facile hydrolysis of the unstable pyrophosphate bond make structural analysis of these highly polar compounds challenging. NMR spectroscopy provides unambiguous structural information when sufficient quantities (1-5 mg) of compounds are available. Pyrophosphorylation resulted in significant (δ 8.0-12.0) upfield shifts of both the Pα and Pβ resonances in 31P-NMR. However, 1H-NMR of 4-InsP7 and 1,5-InsP8 revealed small (δ 0.01-0.20) upfield shifts in the 1H resonances geminal, vicinal, and two carbons removed from the pyrophosphate moiety. Thus, 31P-NMR provides clear evidence for pyrophosphorylation. The two-dimensional NMR methods Total Correlation Spectroscopy (TOCSY) and Heteronuclear Multiple Quantum Coherence (HMQC) were modified to enable conclusive structural assignment of pyrophosphorylated compounds. The results show that the pyrophosphate moiety may be used as a handle to identify all 1H resonances on an individual inositol polyphosphate in a complex spectrum

A Hybrid Rogue Access Point Protection Framework for Commodity Wi-Fi Networks

Abstract—We develop a practical and comprehensive hybrid rogue access point (AP) detection framework for commodity Wi-Fi networks. It is the first scheme that combines the distributed wireless media surveillance and the centralized wired end socket level traffic “fingerprinting. ” The former is designed not only to detect various types of rogue APs, but also to discover suspicious activities so as to prevent the adversaries from turning victim APs into rogue devices. Moreover, the socket level traffic fingerprinting helps our frame work to achieve a finer granularity on rogue AP detection among the existing schemes. This framework has the following nice properties: i) it requires neither specialized hardware nor modification to existing standards; ii) the proposed mechanism greatly improves the rogue AP detection probability so that network resilience is improved; iii) it provides a cost-effective solution to Wi-Fi network security enhancement by incorporating free but mature software tools; iv) it can protect the network from adversaries capable of using customized equipment and/or violating the IEEE 802.11 standard; v) its open architecture allows extra features to be easily added on in the future. Our analysis and evaluation demonstrate that this hybri

Extracellular expression of alkaline phytase in Pichia pastoris: Influence of signal peptides, promoters and growth medium

Alkaline phytase isolated from pollen grains of Lilium longiflorum (LlALP) possesses unique catalytic and thermal stability properties that suggest it has the potential to be used as a feed supplement. However, substantial amounts of active enzymes are needed for animal feed studies and endogenous levels of LlALP in lily pollen are too low to provide the required amounts. Active rLlALP2 (coded by LlAlp2, one of two isoforms of alkaline phytase cDNA identified in lily pollen) has been successfully expressed in intracellular compartments of Pichia pastoris, however enzyme yields have been modest (25–30 mg/L) and purification of the enzyme has been challenging. Expression of foreign proteins to the extracellular medium of P. pastoris greatly simplifies protein purification because low levels of endogenous proteins are secreted by the yeast. In this paper, we first describe the generation of P. pastoris strains that will secrete rLlALP2 to the extracellular medium. Data presented here indicates that deletion of native signal peptides at the N- and C-termini of rLlALP2 enhanced α-mating factor (α-MF)-driven secretion by four-fold; chicken egg white lysozyme signal peptide was ineffective in the extracellular secretion of rLlALP2. Second, we describe our efforts to increase expression levels by employing a constitutive promoter from the glyceraldehyde-3-phosphate dehydrogenase gene (PGAP) in place of the strong, tightly controlled promoter of alcohol oxidase 1 gene (PAOX1). PGAP enhanced the extracellular expression levels of rLlALP2 compared to PAOX1. Finally, we report on the optimization of the culture medium to enhance yields of rLlALP2. The strength of PGAP varies depending on the carbon source available for cell growth; secreted expression of rLlALP2 was highest when glycerol was the carbon source. The addition of histidine and Triton X-100 also enhanced extracellular expression. Taken together, the employment of PGAP under optimized culture conditions resulted in approximately eight-fold (75–80 mg/L) increase in extracellular activity compared to PAOXI (8–10 mg/L). The P. pastoris expression system can be employed as a source of active alkaline phytase for animal feed studies

An one-way function based framework for pairwise key establishment in sensor networks

We develop a one-way function based key establishment framework for Wireless Sensor Networks (WSNs). The proposed framework allows sensors to establish pairwise session keys at an arbitrary network operation stage using pre-loaded one-way functions. We also present an efficient instantiation of the proposed framework using Cellular Automata (CA). The analysis based on the CA instantiation indicates that our framework possesses a number of nice properties: • inherent support for rekeying; • quasi-perfect resilience against node compromise; • computational efficiency; • strong cryptographic strength of generated pairwise keys; • a high probability to establish pairwise keys between sensors. © 2008, Inderscience Publishers