Onur Yilmaz

Shortest hop multipath algorithm for wireless sensor networks

Shortest hop or distance path is one of the most common methods used for relaying messages in a wide variety of networks. It provides an efficient message relaying to destination in terms of energy and time. There are many algorithms for constructing shortest hop or distance path. However, according to our knowledge, no algorithm for constructing a shortest hop multipath for wireless sensor networks (WSNs) has yet been proposed in the literature. In this paper, we propose a novel distributed shortest hop multipath algorithm for WSNs in order to generate energy efficient paths for data dissemination or routing. The proposed algorithm generates shortest hop braided multipath to be used for fault-tolerance or load-balancing. It guarantees the BFS tree and generates near optimal paths in O(V.D+V) message complexity and O(D^2) time complexity regarding the communication costs towards the sink after termination of algorithm.

Poly(vinyl alcohol)/chitosan/montmorillonite nanocomposites for food packaging applications Influence of montmorillonite content

Poly(vinyl alcohol) (PVA)/chitosan (CS)/montmorillonite (C30B) materials for food packaging applications were prepared by using a noninvasive and low-cost freeze/thawing method. Cloisite 30B nanoclay content in PVA/CS gels was varied in order to establish optimum amount to obtain improved properties. The structural, morphological, rheological aspects, thermal stability, and antimicrobial activity were investigated using various techniques as Fourier transform infrared, scanning electron microscopy, rheology, thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical thermal analysis, and antibacterial tests. It was noticed that the obtained materials show an intercalated structure with specific interactions between components and nanoclay incorporation led to an increased thermal stability, mechanical properties, and excellent antimicrobial activity against Escherichia coli, Listeria monocytogenes, and Salmonella typhimurium due to synergistic action of CS and nanoclay.

Localization-free and energy-efficient hole bypassing techniques for fault-tolerant sensor networks

Nowadays, since wireless sensor networks (WSNs) are increasingly being used in challenged environments such as underground mines, tunnels, oceans and the outer space, fault-tolerance need has become a major requirement for routing protocols. So far, the proposed fault-tolerance methods or algorithms aim to recover the isolated failures which occur at different parts of the network in different times. However, there is another type of failure for WSNs which is more destructive for the applications. By collapsing sensor nodes as a group at the same time, a hole can appear at the network which may cut the data delivery drastically. In the literature, previous studies for bypassing holes are based on localization which may have significant energy and economic costs. In this paper, two localization-free and energy-efficient algorithms are proposed for bypassing the holes formed by group collapse. We realized that when holes are modeled with clusters, hole bypassing can be solved by cluster bypassing. Our algorithms, intra-cluster bypass and inter-cluster bypass, aim to heal the corrupted communication links in the presence of holes. We show the operation of the algorithms, analyze them and provide extensive simulation results in an ns-2 environment. We compare our proposed algorithms with the other approaches and show that our algorithms significantly improve the fault recovery percentages while consuming a reasonable amount of energy even in the presence of high collapse ratio.

Comparison of different tanning agents on the stabilization of collagen via differential scanning calorimetry

Leather is composed of a three-dimensional weave of collagen fiber bundles. Collagen is a fibrous protein well organized in the formation of skin as building blocks. Leather production involves serial operations where the tanning plays the major role in improving the durability of leather products by stabilizing the triple helical structure of collagen matrix. In the leather-making industry, different tanning agents are used to produce different kind of leather goods. These tanning agents have varied efficiency on the stabilization of collagen. In this study, thermal stability of the leathers tanned with most commonly used tanning agents was evaluated by conventional shrinking test (CST) and differential scanning calorimetry (DSC) methods. The results showed that the thermal stability of leathers varied by the type of tanning agent which were in accordance with theoretical approaches. A distinct correlation was also observed between CST and DSC results of the tanned leathers.

Distributed Weighted Node Shortest Path Routing for Wireless Sensor Networks

Routing in Wireless Sensor Networks contains challenges, including limited energy constraints, network density, wireless channel errors. Different approaches exist in literature to overcome these challenges, such as data centric, location based and hierarchical routing. Most routing protocols in Wireless Sensor Networks are dealing with energy efficiency and network lifetime. In this paper, we present a shortest path routing algorithm based on Chandy-Misra’s distributed shortest path algorithm regarding both node weight and edge weight. X percent of edge’s weight and (100 - X) percent of node’s weight form a total cost between neighbor and source node which is used in order to generate the shortest paths and construct a spanning tree. Variation of X percent, node weight and edge weight provide resilience for shaping needed paths and change the spanning tree’s structure. When at least one node is close to critical energy level or a fault occurs, the routing algorithm is re-executed and new paths are generated. In order to obtain energy efficient paths, high network lifetime and finding out the overheads, we analyze the simulation results by assigning the battery level to node weight, communication cost to edge weight and %10, %30, %60 and %80 to X separately.

Eco-Friendly Chitosan-Based Nanocomposites: Chemistry and Applications

The deacetylated chitin derivative, chitosan (CS), as a linear polysaccharide having reactive side amino groups is among the favorite bio-based materials due to its nontoxicity, biodegradability, biocompatibility, antimicrobial properties mucoadhesivity among other advantages. Chitosan as a hydrophilic biopolymer exhibits a variety of physicochemical and biological properties resulting in numerous applications in fields such as pharmaceutical and biopharmaceutical, cosmetics, biomedical engineering, biotechnology, agriculture, textiles, food processing nutrition, etc. The mechanical properties and hardness of CS are frequently not enough to meet some of the biomedical applications requirements. The addition even of a very small amount of nanoparticles leads to obtain materials with improved mechanical, chemical, and antimicrobial properties targeted to particular application. The mechanical, thermal, and antibacterial properties of the nanocomposites as well as their biodegradability and applications are reviewed.

Interference-Aware Dynamic Algorithms for Energy-Efficient Topology Control in Wireless Ad Hoc and Sensor Networks

In wireless ad hoc and sensor networks, energy is a scarce resource and a considerable amount of energy is dissipated due to interference. Therefore, interference is one of the major challenges in wireless ad hoc and sensor networks. It alters or disrupts a message as it is being transmitted along a channel between source and destination. Since the messages are disrupted when the interference occurs, they have to be detected and the interfered messages have to be retransmitted. In this paper, we propose central and distributed heuristic algorithms for reducing average interference in a receiver-centric interference model. In the literature, the minimum spanning tree (MST) algorithm is generally used through the interference coverage graph directly or indirectly in order to generate minimum average interference topology. Our algorithm, dynamic average interference (DAI), however, generates lower average interference as well as more sparse topology than MST. We realized that if the transmission ranges of nodes are taken into consideration at each stage of the topology control algorithm, the interference of links are changed dynamically. This interference changing enables up to 22% more energy saving than the MST algorithm. Thus, DAI provides energy saving by reducing the interference as far as possible in generated topology.

Nanocomposites Based On Montmorillonite/Acrylic Copolymer for Aqueous Coating of Soft Surfaces

Nanocomposites based on layered silicate organically modified montmorillonite (Cloisite 20A) and acrylic comonomers (butyl acrylate and methyl methacrylate) were prepared by simple “in situ” batch emulsion polymerization method. The particle size and zeta potential of the emulsions were analyzed. The structural characterizations of the nanocomposites were performed by FTIR, thermal behaviors of the films were investigated by DSC, mechanical properties of the films were tested by DMA and intercalation success was viewed by XRD. The mechanical properties of the nanocomposites were improved significantly especially at the temperatures above Tg. The ultrasonication process was found to be useful for increasing the homogeneity of the emulsions and intercalation success. The obtained nanocomposite emulsions were applied on garment leathers in a finishing formulation as aqueous binders sharing good film forming ability and elasticity.

Functionalization of chitosan by click chemistry

Chitosan modification represents a challenge nowadays. The variety of compounds which can be obtained with various architectures and different functionalities made it attractive to be used in fields like pharmacy and material science. Presents study deals with the chemical modification of chitosan by using click chemistry technique. The study adopted the approach of clicking azidated chitosan with a synthesized alkyne terminated polymer i.e. poly N isopropylacrylamide with thermoresponsive properties. Structures were confirmed by the FT-IR and HNMR spectra. Thermal characterization was performed showing different thermal behaviour with the chemical modification. The final synthesized graft copolymer can play important role within pharmaceutical formulations carrying drugs for topical or oral treatments.

Bitkisel Tabaklanmış Saraciyelik Derilerde Yağlayıcı Polimerlerin Kullanılabilirliği

The demand on the production of leathers with natural look and touch has shown an increase in recent years. Therefore, the usage of vegetable tannins in leather production has also increased accordingly. However, the leathers tanned or heavily retanned with vegetable tannins show high hydrophilic character. Besides, a light finishing is usually preferred to be applied on leathers in order to obtain the natural look and touch which hinders the resistance of leathers to external factors (water, humidity, light etc.). Lubricating acrylic syntans are well-known auxiliaries in leather industry with their fatliquoring and filling effect in retannage as well as their water-repellent properties. In this research, different percentages of a lubricating acrylic polymer was used in retanning process of vegetable tanned leathers and its effect on water absorption and vapour permeability properties of the leathers were investigated. The results showed that the water absorption properties of the leathers processed with lubricating acrylic syntans were lower than the blank samples. The increase in syntan quantities resulted in decreased water absorption values of the leathers. The water vapour permeability of the samples was also found to be increased with the offer of lubricating acrylic syntans.