A Cross-Layer Approach for Minimizing Interference and Latency of Medium Access in Wireless Sensor Networks

In low power wireless sensor networks, MAC protocols usually employ periodic sleep/wake schedule to reduce idle listening time. Even though this mechanism is simple and efficient, it results in high end-to-end latency and low throughput. On the other hand, the previously proposed CSMA/CA-based MAC protocols have tried to reduce inter-node interference at the cost of increased latency and lower network capacity. In this paper we propose IAMAC, a CSMA/CA sleep/wake MAC protocol that minimizes inter-node interference, while also reduces per-hop delay through cross-layer interactions with the network layer. Furthermore, we show that IAMAC can be integrated into the SP architecture to perform its inter-layer interactions. Through simulation, we have extensively evaluated the performance of IAMAC in terms of different performance metrics. Simulation results confirm that IAMAC reduces energy consumption per node and leads to higher network lifetime compared to S-MAC and Adaptive S-MAC, while it also provides lower latency than S-MAC. Throughout our evaluations we have considered IAMAC in conjunction with two error recovery methods, i.e., ARQ and Seda. It is shown that using Seda as the error recovery mechanism of IAMAC results in higher throughput and lifetime compared to ARQ.Comment: 17 pages, 16 figure

Optimizing the depth and the direction of prospective planning using information values

Evaluating the future consequences of actions is achievable by simulating a mental search tree into the future. Expanding deep trees, however, is computationally taxing. Therefore, machines and humans use a plan-until-habit scheme that simulates the environment up to a limited depth and then exploits habitual values as proxies for consequences that may arise in the future. Two outstanding questions in this scheme are “in which directions the search tree should be expanded?”, and “when should the expansion stop?”. Here we propose a principled solution to these questions based on a speed/accuracy tradeoff: deeper expansion in the appropriate directions leads to more accurate planning, but at the cost of slower decision-making. Our simulation results show how this algorithm expands the search tree effectively and efficiently in a grid-world environment. We further show that our algorithm can explain several behavioral patterns in animals and humans, namely the effect of time-pressure on the depth of planning, the effect of reward magnitudes on the direction of planning, and the gradual shift from goal-directed to habitual behavior over the course of training. The algorithm also provides several predictions testable in animal/human experiments

Hierarchical models of goal-directed and automatic actions

Decision-making processes behind instrumental actions can be divided into two categories: goal-directed actions, and automatic actions. The structure of automatic actions, their interaction with goal-directed actions, and their behavioral and computational properties are the topics of the current thesis. We conceptualize the structure of automatic actions as sequences of actions that form a single response unit and are integrated within goal-directed processes in a hierarchical manner. We represent this hypothesis using the computational framework of reinforcement learning and develop a new normative computational model for the acquisition of action sequences, and their hierarchical interaction with goal-directed processes. We develop a neurally plausible hypothesis for the role of neuromodulator dopamine as a teaching signal for the acquisition of action sequences. We further explore the predictions of the proposed model in a two-stage decision-making task in humans and we show that the proposed model has higher explanatory power than its alternatives. Finally, we translate the two-stage decision-making task to an experimental protocol in rats and show that, similar to humans, rats also use action sequences and engage in hierarchical decision-making. The results provide a new theoretical and experimental paradigm for conceptualizing and measuring the operation and interaction of goal-directed and automatic actions

Characterization and Evaluation of Ground Glass Fiber as a Cementitious Component in Portland Cement and Geopolymer Concrete Mixtures

A large amount of glass fiber is commercially produced for use in various applications. However, this process generates millions of tons of waste glass fiber annually around the world. This material has an amorphous structure that is rich in silica, alumina and calcium oxides, and if milled into a fine powder, it could potentially be used a supplementary cementitious material (SCM) in portland cement mixtures; or as a source material for production of geopolymer. So, the first objective of this research work, is to evaluate the utilization of ground glass fiber (GGF) as a SCM in portland cement mixtures, and the second objective is to study the mechanical and durability properties of GGF-based geopolymers. To fulfill the first objective, concrete and mortar mixtures containing different dosage of GGF (i.e. 10, 20 and 30% by mass) were prepared. Fresh and hardened properties of these mixtures were tested and compared with two control mixtures, including: (i) a mixture made from 100% portland cement, and (ii) a mixture having 75% portland cement and 25% class F fly ash (by mass). It was observed that utilization of GGF up to 30% (as a cement replacement) did not influence the mechanical properties of the concrete and mortar mixtures significantly compared to control mixtures; however, the use of GGF as SCM resulted in a remarkable improvement in the durability of the mixtures. It was also seen that the utilization of GGF at the 30% replacement level, successfully mitigated the ASR-related expansion of mortar and concrete mixtures containing the crushed glass aggregate. For the second objective, the possibility of producing geopolymer from GGF was investigated. To activate GGF, different dosage and combinations of sodium hydroxide solution (NaOH) and sodium silicate solution were used, and specimens were cured at 60oC for 24 h. Fresh and hardened properties of geopolymer mixtures made from GGF as the precursor, were studied and compared to glass-powder (GLP) and fly ash-based geopolymer mixtures. The effect of change in the Na2O-to-binder ratio (alkali content of the activator solution) and the SiO2/Na2O (silica content of the solution) ratio on the workability of and compressive strength of the mortar mixtures was monitored and compared to the GLP and fly ash-based geopolymers. It was seen that the strength gain in GGF-based geopolymers does not depend on the presence of sodium silicate in the activator solution; and a high compressive strength (as high as 80 MPa) can be achieved in three days, only by using sodium hydroxide solution alone. Furthermore, to better understand parameters affecting the activation of GGF-based geopolymers, effect of temperature (from ambient to 110oC) and duration of heat-curing on the compressive strength and micro-structure of GGF-based geopolymers was studied. The temperature of heat curing was seen to affect the early-age (i.e. 3 to 7 days) compressive strength of the GGF-based samples but had no significant effect on the later-age (i.e. 28 to 56 days) strength. Finally, it was concluded that GGF has a good potential to be used as a precursor to produce high strength geopolymers even at ambient temperature (23oC). Based on the results obtained from the compressive strength experiments, mixtures with the highest compressive strength were selected from each precursor to be used for the durability experiments. Durability aspects of GGF-based geopolymer such as resistance against sodium sulfate solution and magnesium sulfate solution, alkali silica reaction, drying shrinkage and corrosion of steel rebar were investigated and were compared to fly ash and GLP-based geopolymer, and an ordinary portland cement mixture (OPC). Based on this investigation it was found that GGF and fly ash-based geopolymers showed superior performance against ASR-related deterioration in comparison to GLP-based geopolymer and the OPC mixture. It was also observed that despite the fluctuation in properties at early ages, immersion in the sodium sulfate (Na2SO4) solution and magnesium sulfate (MgSO4) solution did not lead to a significant mass or strength loss of GGF-based geopolymer at the later ages. In conclusion, it can be stated that a high compressive strength GGF-based geopolymers could be produced by using an activator solution that is comprised of only NaOH. Durability experiments conducted on GGF-based geopolymer mixtures showed good performance in resisting ASR and sulfate solution exposure. Based on preliminary results it was observed that drying shrinkage of GGF and fly ash-based geopolymer was similar to the OPC mixture while the drying shrinkage of GLP-based geopolymer was significantly higher. Findings from basic experiments conducted in this study showed that factors such as: (i) the low amount of CH in the structure, (ii) low porosity, and (iii) the durable structure of the geopolymer gel in the GGF-based geopolymers, which remains stable under the aggressive conditions such as, exposure to sulfate solutions, are responsible for the superior durability performance of GGF-based geopolymer

Bir Tarih Araştırması: Selçuklardan Osmanlılara Kadar Alevilik-Bektaşilik

Das Alevitentum-Bektaschitum gehört zu den wichtigen Bewegungen, die im 13. Jahrhundert entstanden ist. Sein Gründer, Hadschi Bektasch Veli zog aus Chorasan, dem Zentrum des Sufismus, nach Anatolien um. Höchstwahrscheinlich war Hadschi Bektasch Veli der Nachfolger von Baba İlyas Horasani, einem geistigen Führer des Babai Aufstandes, welcher in der ersten Hälfte des 13. Jahrhunderts den Seldschuken Staat erschüttert hatte. Schließlich gelang es den Seldschuken diesen Aufstand mit Hilfe der Franken niederzukämpfen. Der Verlust seines Bruders im Krieg (er wurde getötet) war für Hadschi Bektasch Veli ein ausreichender Grund, um weiteren Gefechten mit den Seldschuken aus dem Weg zu gehen. Er blieb aber Zeit seines Lebens den Ideen der Babai treu. Die vorislamischen Glaubensvorstellungen, die weitverbreiteten Vorstellungen über den Sufismus in Anatolien und viele Faktoren wie z.B. das Christentum haben historisch gesehen geistigen Einfluss auf die Bektaschiten ausgeübt. Dabei bildeten kulturelle und religiöse Toleranz das geistige Fundament der Bektaschi-Bewegung, die über viele Anhänger in Anatolien verfügte. In der Osmanischen Zeit avancierte sich der Bektaschi Derwisch-Orden offiziell zu einer Bruderschaft, welche die Janitscharen geistig-seelisch inspiriert hat. Das Alevitentum-Bektaschitum wurde auch von anderen geistigen Faktoren geprägt, wozu auch die Schia-Propaganda der Scheichs der Hurûfi und der Safawiden zählt. Dieser Artikel analysiert die Entstehung der Alevitisch-Bektaschi Bewegung in historischer Perspektive und erläutert die Einflüsse der iranischen und der türkischen Geschichte auf die Aleviten-Bektaschiten und liefert auch Erkenntnisse über den Einfluss der Aleviten-Bektaschiten auf die betreffende Geschichte.Alevi-Bektashi is one of the significant orders which was formed in Anatolia in 13th AD. Haj Bektash Veli, as the founder of the order, migrated to Anatolia from the focal point of Sufism, Khorasan. Probably Haj Bektash Veli was the caliph of Baba Elyas Khorasani, who was the leader of the Baba’i uprising that shook the foundations of the Seljuks in Anatolia in the first half of the 13th century. Eventually, the Seljuks could defeat them by the Frankish forces aid. Loss of his brother in the battle was enough for Haj Bektash to avoid a new military confrontation with the Seljuks, however, followed the intellectual path of the Baba’is in the rest of his life. Many factors such as the religious beliefs of Turks in the pre-Islamic era, the prevailing Sufi thoughts in Anatolia and Christianity affected the Bektashis during their long history. The backbone of the order was the cultural and religious tolerance that found several adherents in Anatolia. In Ottoman era Bektashiya became the official order that spiritually led the Jannissaries. Alevi-Bektashi also was influenced by other streams of thoughts such as Hurufis and the shi’i propaganda of the Safavid sheikhs. This article by historical approach examine the formation of Alevi-Bektashi order and clarifies how they were influenced and then had their impact on the history of Iran and Turkey.Alevilik-Bektaşilik 13. yüzyılda ortaya çıkan önemli hareketlerden biridir. Kurucusu Hacı Bektaş Veli tasavvufun merkez noktası Horasan’dan Anadolu’ya göç etmişti (taşınmıştı). Hacı Bektaş Veli büyük olasılıkla, 13. yüzyılın ilk yarısında Anadolu’daki Selçuklu Devleti’ni sarsmış olan Babai Ayaklanmasının önderi Baba İlyas Horasani’nin halifesiydi. Nihayetinde Selçuklular, Frankların yardımı ile ayaklanmayı bastırabilmişlerdi. Muharebede kardeşini kaybetmesi (öldürülmesi) Hacı Bektaş Selçuklular ile yeni çatışmalardan kaçınmak için yeterli bir sebepti. Ancak hayat boyu Babailerin fikirlerini takip etmişti. İslam öncesi döneme ait Türklerin inançları, Anadolu’da yaygın tasavvufi fikirler ve Hıristiyanlık gibi pek çok unsur uzun tarihi boyunca Bektaşileri etkilemişti. Hareketin temeli Anadolu’da birçok destekçisi bulan kültürel ve dini hoşgörüydü. Osmanlı döneminde Bektaşi tarikatı Yeniçerileri manevi olarak etkileyen resmi tarikat olmuştu. Alevilik-Bektaşilik, Hurufiler ve Safevi şeyhlerinin Şii propagandası gibi diğer fikir akımlarından da etkilemişti. Bu makalede Alevilik-Bektaşilik hareketinin oluşması tarihi yaklaşımla incelenmiş, Iran ve Türkiye tarihinin Alevi-Bektaşiler üzerindeki etkileri ve sonra da onların söz konusu tarihe etkileri açıklanmıştır