Reducing Client-Server Communication for Efficient Real-Time Web Applications: The Use of Adaptive Polling as A Case Study for Multi-User Web Applications

A key challenge of current multi-user web applications is to provide users with interesting events and information in real-time. This research reviews the most common real-time web techniques to identify drawbacks while exploring solutions to improve simplicity, efficiency, and compatibility within a client-server environment. Two solutions are proposed for enhancing the efficiency of real-time web techniques by reducing client-server communication. First, a model of browser monitoring control observes the browser activity and decides if to postpone client-server communication in the case of inactive tabs. This model was implemented and tested with results demonstrating that a significant number of client-server connections can be avoided in the browser background. These results suggest the solution can be optimised for any real-time technique as it benefits from being a developer side technique that works consistently on all browsers. Second, ‘Adaptive Polling’ is a pull-based real-time web technique to overcome bandwidth issues of the reverse AJAX method of ‘Polling’ by controlling the frequency of requesting updates from the server based on the last server response. This approach is implemented and tested with results showing how a significant number of redundant connections can be avoided while the server does not return updates. This solution is a good alternative to other real-time web techniques as it features low latency, the simplicity of implementation, and compatibility with all browsers and servers

New Software Architecture for Mobility and Handoff Management in Mobile IPV6 Networks

This paper addresses the problem of overall network signaling and packet delivery cost in Mobile Internet Protocol (MIP) systems for serving mobility and service management related operations. In MIP, a Mobile Node (MN) interacts with its home agent, when it is connected to a foreign agent to manage the mobility and packet delivery in a bidirectional tunneling mode. This paper proposes new software mobility management service architecture with the goal to handle the heavy burden on the home network and to minimize the cost of network signaling and packet delivery. Under the proposed architecture, a MN creates a Mobile Remote Object (MRO) and transfers it to the router of the hosted network. The MRO registers itself with a naming service server. The MRO handles all services engaged by the MN without relying on centralized traffic

Hydrogen Production in the Cyanobacterium Synechocystis sp. PCC 6803 with Engineered Subunit of the Bidirectional H2-ase

Hydrogenase (H2-ase) enzyme holds great promise as a bio-generator for bio-solar hydrogen (H2) production. Consequently, an oxygen-tolerant H2-ase is needed in a photosynthetic organism.  In this work, a mutant strain of Synechocystis sp. PCC 6803 with modified H2-ase analyzed under various physiological conditions. The growth rate was higher than that of wt strain and cellular capacity to fix carbon was increased, as shown by higher glycogen accumulation. Oxygen evolution by mutant strain in chemostats was higher than by wt cells over a range of pH levels. The mutant displayed significantly higher hydrogen (H2) production than wt cells, especially at high pH. Examinations of electron flow pathways in the presence of various inhibitors indicated that the genetically modified H2-ase apparently behaves similarly to the wt with respect to its electron source. Remarkably, it was consistently observed H2 production under continuous light conditions, in the presence of oxygen (O2), under many circumstances in both chemostat and batch tests. H2 production in the light was improved under alkaline pH in mutant strain than wt. The data suggest that the genetically modified hydrogenase (H2ase) is a functionally active. Several lines of evidence suggest that O2 may be important in draining electrons from the donor side of photosystem I (PSI) in turn increases the linear electron flow and thereby helping to feed the H2ase activity. In conclusion, the bidirectional H2ase in Synechocystis may play a critical role in cell physiology not only under anoxic conditions but also under O2-evolving activity. Keywords: Cyanobacteria, Hydrogen, Hydrogenase, Protein engineering

Place evaluation: a transactional adaptive approach. The case study of Cairo's waterfront

The objective of this research is to determine how Cairenes construe places. The body of study is applied to the context of the waterfront area along the Nile River within Cairo. It is important to stress that the research is not based upon a witnessed well-defined problem but rather built upon a model, based upon a Transactional approach that explores how Cairenes construe places later revealing particular problems. A review of literature initially identifies many paradigms of perception and human behaviour. These paradigms have been used in order to identify a model, which is used to guide the course of the research and is based upon a man in environment perspective. Therefore the study is set out to individually determine aspects of place and human perception, bearing in mind the theoretical reasoning behind the model, which suggests that both entities should holistically be examined.The research is therefore orientated towards determining aspects of change between people and place. From an adaptation approach it is therefore argued that the level of variation existing within the environment determines the amount of change in behaviour and perception that may occur in order to achieve the appropriate balance required between people and place. As the research attempts to determine how Cairenes construe places, and as people's perceptions and the environment are in constant change, thus change in our case relates to how human perception and behaviour are affected by the level of variation existing within the environment. The basis of the model is therefore related to both context and human perception.The case study involves Cairo's waterfront as it is centrally located and considered as a convenient public place. This area is used in order to determine aspects of the context and human perception. Therefore the waterfront is considered as a public place used to examine the objectives of the research. The results reveal that there exists a lack of variation in public spaces along the waterfront and Cairo. It also highlights that the social class of people within a context affects how Cairenes' construe places. Both the contextual and perceptual analysis uncovers segregated patterns of behaviour within the City and is tackled by introducing general design recommendations for public areas situated along Cairo's waterfront and in general within public space.The methodology involves a qualitative analysis of interviews and a further quantitative analysis of a questionnaire. Both analyses attempt to determine dominant aspects of perception and context. It is also important to underline that within the proposed model derived from the Transactional approach, aspects of change are embodied in the level of variation existing within the environment. This is based upon the assumption that higher levels of variation in the context affect people's perceptions

Oxygen Reduction and Evolution Reactions in Alkaline and Non-aqueous Electrolytes for Li-Air Batteries : RRDE and DEMS Investigations

Due to the worldwide growing energy demand and depletion of fossil fuel resources, sustainable renewable energy conversion and storage systems have to be developed. Among the promising possibilities are the rechargeable batteries. Li-air batteries could be a key technology for automotive applications because of their higher (3-5 times) theoretical capacity than the state-of-the-art Li-ion batteries. However, this technology is facing some critical challenges such as the poor efficiency, high overpotential and electrolyte instability. The current research focuses on two types of Li-Air batteries, namely, aprotic and aqueous electrolyte batteries. Despite the intensive work in the last decade, the fundamental electrochemical reactions such as oxygen reduction reaction (ORR) and oxygen evolution (OER) in aprotic electrolytes are not well understood. Since with aprotic electrolytes the formation of a blocking film of the discharge products limits the capacity, an aqueous Li-air battery is an alternative scenario. In this work, two main issues are addressed: i) development of an efficient carbon-free bifunctional catalyst for the air electrode in alkaline media. ii) mechanistic, kinetic and quantitative investigations of ORR/OER in aprotic electrolytes. After an introduction to the topic, a theoretical background followed by a description of the experimental methods is presented. Subsequently, the results and discussion section consists of 6 chapters. The thesis is then closed with the summary and future perspectives. The results and discussion section starts with chapter 4 (already published, Electrochimica Acta 2015, 151, 332) on the investigation of an efficient bifunctional catalyst based on Ag+Co3O4 for ORR/OER in alkaline media. Interestingly, the combination of both components in one mixture showed superior activity than its single components along with good stability. Ag+Co3O4 mixed catalyst containing 10-20 wt% of Co3O4 is the optimum composition. Rotating ring-disc electrode (RRDE) method revealed negligible formation of peroxide intermediate. Oxygen evolution is also monitored using differential electrochemical mass spectrometry (DEMS). To understand the origin of such synergistic effect between Ag and Co3O4, surface and XPS analyses were conducted (Chapter 5). Further investigations on the activity of Ag+ perovskite catalyst and the role of the support (Ni vs. Ag) are presented in chapter 6. In chapter 7, to better understand the mechanism of OER on Co3O4 and the mixed catalyst, DEMS experiments together with isotope labeling are presented. An oxygen exchange process in the lattice oxygen is inferred. In this part, a new small-volume electrolyte DEMS cell design is developed for application of massive electrodes. The last two chapters are devoted to measurements in aprotic electrolytes for Li-O2 system. RRDE and DEMS were used to characterize the reactions in Tetraglyme G4, DMSO and their mixture. The significant role of the solvent properties (e.g. donor number) on the mechanism is assessed (chapter 8). DEMS enabled us not only to detect the main products and by-products but also the number of electrons transferred per oxygen molecule during discharge and charge. The results showed reversible formation of Li2O2 as the main discharge product despite of the side reactions. The catalytic activity of Co3O4 catalyst in DMSO is reported. In chapter 9, a novel electrolyte based on 1,3-dimethylimidazolidinone solvent is investigated for the first time for Li-O2 battery. Although further research has to be done, this better understanding of the processes could help in the development of strategies for the realization of such Li-air batteries.Sauerstoffreduktion und -entwicklung in alkalischen und nichtwässrigen Elektrolyten für Li-Luft-Batterien : RRDE und DEMS Untersuchungen Aufgrund des weltweit wachsenden Energiebedarfs und der Erschöpfung fossiler Brennstoffe müssen nachhaltige, erneuerbare Energienumwandlungs- und Speichersysteme entwickelt werden. Hierfür stellen wiederaufladbare Batterien vielversprechende Möglichkeiten dar. Insbesondere Li-Luft-Batterien könnten eine Schlüsseltechnologie für Automobilanwendungen sein, weil sie höhere (3-5 mal) theoretische Kapazitäten im Vergleich zu herkömmlichen Li-Ionen-Batterien haben. Diese Technologie steht jedoch vor einigen kritischen Herausforderungen wie schlechte Wiederaufladbarkeit, hohe Überspannung und Elektrolytinstabilität. Die aktuelle Forschung konzentriert sich auf zwei Arten von Li-Luft-Batterien, nämlich aprotische und wässrige Elektrolyt-Batterien. Trotz der intensiven Arbeit im letzten Jahrzehnt sind die grundlegenden elektrochemischen Reaktionen wie Sauerstoffreduktion (ORR) und -entwicklung (OER) in aprotischen Elektrolyten nicht gut verstanden. Da bei aprotischen Elektrolyten die Entladungsprodukte der ORR die Elektrode blockieren und dadurch die Kapazität der Batterie begrenzen, stellen Li-Luft-Batterien mit wässrigen Elektrolyt eine Alternative dar. Die vorliegende Arbeit befasst sich mit zwei Hauptthemen: i) Entwicklung eines effizienten, kohlenstofffreien bifunktionellen Katalysators für die Luftelektrode in alkalischen Elektrolyten. ii) Mechanistische, kinetische und quantitative Untersuchungen von ORR/OER in aprotischen Elektrolyten. Nach einer Einführung in das Thema folgen die theoretische Grundlagen mit einer Beschreibung der experimentellen Methoden. Anschließend werden die Ergebnisse und die Diskussion in 6 Kapiteln dargestellt. Die Arbeit endet mit einer Zusammenfassung und einem Ausblick. Die Ergebnisse und Diskussion beginnen mit Kapitel 4 (schon veröffentlicht, Electrochimica Acta 2015, 151, 332) zur Untersuchung eines effizienten bifunktionellen Katalysators auf der Basis von Ag + Co3O4 für ORR/OER in alkalischen Elektrolyten. Interessanterweise zeigte eine Kombination von beiden Komponenten eine höhere Aktivität als die einzelnen Komponenten und darüber hinaus eine gute Stabilität. Ag + Co3O4-Mischkatalysator, der 10-20 Gew.% Co3O4 enthielt, zeigte die optimale Aktivität. Die rotierende Ringscheibenelektrode (RRDE) zeigte eine vernachlässigbare Bildung des Peroxid-Intermediates. Die Sauerstoffentwicklung wurde mittels differentieller elektrochemischer Massenspektrometrie (DEMS) nachgewiesen. In Kapitel 5 werden Oberflächen- und XPS-Analysen gezeigt, um den Ursprung eines solchen synergistischen Effekts zwischen Ag und Co3O4 zu verstehen. Weitere Untersuchungen über die Aktivität des Ag+Perowskit-Katalysators und die Rolle des Trägers (Ni und Ag) sind in Kapitel 6 dargestellt. Zum besseren Verständnis des Mechanismus der OER auf Co3O4 und Mischkatalysatoren wurden DEMS-Messungen zusammen mit Isotopenmarkierung durchgeführt und der Austausch des Gittersauerstoffs nachgewiesen. Hierfür wurde eine DEMS-Zelle mit kleinem Elektrolytvolumen für die Verwendung von massiven Elektroden entwickelt. Die letzten beiden Kapitel widmen sich Messungen in aprotischen Elektrolyten für das Li-O2-System. RRDE und DEMS wurden verwendet, um die Reaktionen in Tetraglyme G4, DMSO und deren Gemische zu charakterisieren. Die signifikante Rolle der Lösungsmitteleigenschaften (z.B. Donorzahl) auf den Mechanismus wird in Kapitel 8 evaluiert. DEMS ermöglichte es uns, nicht nur die Hauptprodukte und Nebenprodukte zu detektieren, sondern auch die Anzahl der übertragenen Elektronen pro Sauerstoffmolekül während der Entladung und Ladung. Die reversible Bildung von Li2O2 als Hauptentladungspruduct wurde trotz der Nebenreaktionen nachgewiesen. Die katalytische Aktivität des Co3O4 Katalysators in DMSO wird gleichfalls beschrieben. In Kapitel 9 wird ein neuartiger Elektrolyt auf Basis von 1,3-Dimethylimidazolidinon-Lösungsmittel erstmals für Li-O2-Batterien untersucht. Obgleich weitere Forschungen durchgeführt werden müssen, könnte das bessere Verständnis der Prozesse bei der Entwicklung von Strategien für die Realisierung solcher Li-Luft-Batterien helfen