No description available.

Wireless sensor networks can enable numerous advanced monitoring and control applications. They are characterized by a need to maximize their efficiency, especially with respect to energy consumption, since the lifetime of a sensor node has a huge impact on the usability of a wireless sensor network. In this thesis, an energy efficient MAC protocol for wireless sensor networks is proposed. The protocol is based on IEEE 802.11, with some modifications to accommodate power efficiency and scalability which are the two main design factors for wireless sensor networks. The proposed Multi-Phase MAC (Φ-MAC) protocol uses periodic listen and sleep modes to save energy. Sensor nodes in Φ-MAC protocol are allocated into different phases so that the listen periods of the different phases are non-overlapping. Distributing the nodes among the phases allows the nodes to sleep longer and conserve battery power. This distribution also effectively reduces the traffic seen by the nodes in each phase, which reduces the probability of collisions and retransmissions. The results of the numerical simulations show that Φ-MAC outperforms other proposed MAC protocols in its efficiency of consuming power.

Sensor technologies are improving fast: sensors are being developed to record more types of phe- nomena in improving precisions, and they are becoming less expensive. The vision is that sensor networks deployed across large spaces, attached to important infrastructure, and embedded in our everyday environments, will become an ubiquitous element of the worlds information infrastruc- ture. The apparent bottleneck in reaching this vision efciently and cost effectively is software development. In this thesis, we discuss an integrated service-oriented architecture for collecting, archiving, analyzing and visualizing sensor network data. The framework has been deployed and evaluated in two applications: SensorGIS and SmartCondo, designed for sensor networks deployed in outdoor and indoor spaces.

The tin oxide thin films were deposited on the Corning 7059 glass by sputtering, chemical mist deposition and spin coating. The influences of different process parameters on the microstructure, electrical-optical and gas-sensing properties were studied to establish their interrelation. During the sputtering, the total pressure, the partial pressure of oxygen and substrate temperature were varied and dense thin films were obtained. The films possess (110) preferred orientation along with {011} twins. As no doping was attempted, transmittance of the films in the range of visible light is > 85 %. The lowest resistivity is ~1.4¡Ñ10-2 £[-cm. Therefore , they can be used as transparent conductive films. On the contrary, these dense films are not suitable for gas-sensor application. Chemical Mist Deposition (CMD) method employs SnCl4¡D5H2O dissolved ethanol as starting solution. The flow rate of carrier gas, substrate temperature and deposition time were varied to obtain films of different features. Below 350¢J of substrate temperature, the deposition films are amorphous, while SnO2 crystalline films are obtained when temperature above 400¢J. As (110) preferred orientation increases with deposition temperature. The films transmittance decrease with increasing thickness as well as porosity and maintains at a level around 85 %. The lowest resistivity of undoped films is 1.2¡Ñ10-2 £[-cm. These characteristic render them as good transparent conductive films. As dense films with negligible porosity, the sensitivity for CO gas detection of these films is less than 2 when thickness is less than 100 nm and can not serve as a decent gas sensor. Porous films were obtained using spin-coating. No preferred orientation is found in these films. As porosity is high, the optical transmittance and electrical conductance are low. SnCl4¡D5H2O dissolve in DI water (with NH3(aq) added for promotion of hydrolysis) was used as starting solution. The starting solution contains large amounts of electrolytes of NH4+ and Cl-, and the resultant films contain large amounts of small cracks with low surface area. The sensitivity of CO gas is 3~4. If the electrolytes are eliminated before deposition, finer cracks are obtained in the films with increased surface area, and the sensitivity for CO gas detection can reach 12.9. Meso-structure precipitates were obtained when the starting solution was mixed with CTAB(aq). The resultant solution yield films of high surface area and sensitivity for CO gas can reach 16.1, rendering them as good gas sensors.

No description available.

Thesis (Ph. D.)--George Mason University, 2007. / Title from PDF t.p. (viewed Jan. 18, 2008). Thesis director: Sanjeev Setia. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Computer Science. Vita: p. 117. Includes bibliographical references (p. 112-116). Also available in print.

Zugl.: Aachen, Techn. Hochsch., Diss., 2006.

Techn. Hochsch., Diss.--Aachen, 2000. / Nebent.: Amperometrischer NOx-Sensor für KFZ. Literaturverz. S. 233 - 244.

Zugl.: Stuttgart, Univ., Habil.-Schr., 2005.

Techn. Univ., Diss.--Ilmenau, 2002. / Parallel als Online-Ausg. erschienen unter der Adresse http://www.db-thueringen.de/servlets/DocumentServlet?id=1170.