Efficient GTS Allocation Schemes for IEEE 802.15.4

IEEE 802.15.4 is a standard defined for wireless sensor network applications with limited power and relaxed throughput needs. The devices transmit data during two periods: Contention Access Period (CAP) by accessing the channel using CSMA/CA and Contention Free Period (CFP), which consists of Guaranteed Time Slots (GTS) allocated to individual devices by the network coordinator. The GTS is used by devices for cyclic data transmission and the coordinator can allocate GTS to a maximum of only seven devices. In this work, we have proposed two algorithms for an efficient GTS allocation. The first algorithm is focused on improving the bandwidth utilization of devices, while the second algorithm uses traffic arrival information of devices to allow sharing of GTS slots between more than seven devices. The proposed schemes were tested through simulations and the results show that the new GTS allocation schemes perform better than the original IEEE 802.15.4 standard

Resilient IEEE802.15.4MAC Protocol for Multi-Hop Mesh Wireless Sensor Network

The success of a modern power grid system is inevitably based on the integration of a smart data exchange amid several devices in power production, transportation, dispatching and loads. For large coverage data exhange, a distributed multi-hop mesh is structured from low voltage distribution boards to the substations. Thus, being cheap, less power intake, easy set-up and operating in a free licensed spectrum, ZigBee/IEEE802.15.4 makes the most suitable wireless protocol for communicating in power grid systems. Nevertheless, IEEE802.15.4MAC protocol lacks a mechanism to enable a multi-hop mesh network with efficient energy and quality of service (QoS). Hence, in this paper, a Multi-Hop Mesh IEEE802.15.4MAC protocol is designed for a large coverage data exchange. This developed model provides a resilient network with energy efficiency and QoS. Hence, the IEEE802.15.4 super_frame_standard_structure is modified by swapping the contention_free period (CFP) and contention_access_period (CAP) for time sensitive applications. For network resilience, a Reserved_Broadcast Duration_Slot (RB_DS) is introduced in the active super_frame standard_structure as beacon_offset reference time computation. Finally, for the network performance analysis, the developed Markov chain_Model with retry and saturated traffic regime without feedback is run on NS-2 simulator. Here, the hidden terminal problem is not considered since it is assumed that all nodes can "hear" each other. The simulation results are encouraging as the developed IEEE802.15.4MAC protocol is capable of improving the time delivery delay up to 35.7%

Adaptive Channel Access Mechanism for Zigbee (IEEE 802.15.4)

The IEEE 802.15.4 (also known as Zigbee) is a new wireless personal area network (PAN) standard designed for wireless monitoring and control applications. The Zigbee standard is based on CSMA-CA for contention based medium access. In this paper a study of the Adaptive backoff exponent (BE) management of CSMA-CA for 802.15.4 is presented. The BEs determine the number of backoff slots that the device shall wait before accessing the channel. The power consumption requirements make CSMA-CA use fewer BEs which increase the probability of devices choosing identical BEs and as a result, wait for the same number of backoff slots in some cases. This often leads to degradation of system performance at congestion scenarios, due to higher number of collisions. This paper addresses the problem by proposing an adaptive mechanism to the current implementation of the backoff exponent management, based on a decision criterion. As a result of the implementation, potential packet collisions are reduced. The results of NS-2 simulations are presented, indicating an overall improvement in network performance

An Examination of Sustainability Practices Within NCAA Division I Athletic Teams

According to The United States Environmental Protection Agency, in 1960, 7% of US waste was recycled or diverted – today, that is almost 35%. The minimization and eventual elimination of such products will help with issues such as diversion from these products in everyday life and replacing them with reusable alternatives are what makes a difference. Universities nationwide are beginning to understand the importance of the relationships between sustainability personnel and athletic administrators, which then channels into how collegiate teams practice sustainability. There is still much work to be done regarding the implementation of sustainability practices and procedures in college athletics. A working definition of Environmental Sustainability by Robert Goodland suggests “environmental sustainability as the maintenance of natural capital” (Morelli, 2011, 1). Within universities, a new method of sustainability integration has emerged - Green Teams. Green Teams serve to formalize the relationship between institutional partnerships, which allows athletic departments to contribute to the sustainability goals of the university. The purpose of the current in-progress study is to determine whether sustainability practices change based on an individual’s environment and how those behaviors influence others. I will interview staff that hold the title of Director of Operations or conduct operation-like tasks for all NCAA Division I teams. Questions will be prompted to gain knowledge on the individual’s perception of sustainability and how they implement sustainable habits in their daily lives. The goal of these interviews is to understand the relationship between sustainability practices in one’s personal life and how that’s translated into work. After analyzing results, it was clear that there is a strong correlation in the disconnect between athletic and on campus departments regarding environmental sustainability habits. Participants mentioned that although they noticed on-campus ES efforts being enforced, those same practices were not implemented throughout athletic departments. There was also a disconnect between home and work practices, as many participants noticed that it was easier to practice ES on their own compared to at work due to the sheer number of athletes and staff they’re in charge of. Geographic location also played a role in participants’ mindset and ES habits overall

Shallow Water Equations in Hydraulics: Modeling, Numerics and Applications

This Special Issue aims to provide a forum for the latest advances in hydraulic modeling based on the use of shallow water and related models as well as their novel application in practical engineering. Original contributions, including those in but not limited to the following areas, will be considered for publication: new conceptual models and applications, flood inundation and routing, sediment transport and morphodynamic modelling, pollutant transport in water, irrigation and drainage modeling, numerical simulation in hydraulics, novel numerical methods for the shallow water equations and extended models, case studies, and high-performance computing

Political economy of climate policy

Die vorliegende Arbeit beschäftigt sich modelltheoretisch, empirisch und experimentell mit dem Thema der Klimapolitik aus einer politökonomischen Perspektive. Der Ansatz der Neuen Politischen Ökonomie versucht, die ökonomischen Modelle um den politischen Prozess zu erweitern. Die Motivation für dieses Vorgehen steht in einem engen Zusammenhang mit der Erkenntnis, dass es unzureichend ist, die ökonomische Analyse auf Probleme des Marktversagens zu reduzieren. Neben Marktversagen können durch den politischen Prozess Probleme generiert werden (sog. Politikversagen). Im Rahmen einer positiven Analyse kann die Neue Politische Ökonomie Erklärungsansätze liefern, die eng mit der Fragestellung verknüpft sind, warum bekannte Ineffizienzen den politischen Prozess überdauern. Dieses Problem lässt sich in vielen Fällen durch Partikularinteressen erklären. Aus einer normativen Perspektive lassen sich die resultierenden Erkenntnisse für Politikempfehlungen heranziehen. Vordergründig sind dabei jene Handlungsalternativen (zum Teil auch Handlungsbeschränkungen z.B. auf konstitutioneller Ebene) die es dem Staat ermöglichen seine Handlungen möglichst unabhängig von Partikularinteressen durchzuführen. Die vorliegende Arbeit gliedert sich in acht Kapitel. Das erste Kapitel dient zur Einleitung. Kapitel zwei bis sieben umfassen den Hauptteil der Arbeit. In Kapitel acht werden die wesentlichen Ergebnisse noch einmal kurz zusammengefasst

Synthesis and evaluation of geometric textures

Two-dimensional geometric textures are the geometric analogues of raster (pixel-based) textures and consist of planar distributions of discrete shapes with an inherent structure. These textures have many potential applications in art, computer graphics, and cartography. Synthesizing large textures by hand is generally a tedious task. In raster-based synthesis, many algorithms have been developed to limit the amount of manual effort required. These algorithms take in a small example as a reference and produce larger similar textures using a wide range of approaches. Recently, an increasing number of example-based geometric synthesis algorithms have been proposed. I refer to them in this dissertation as Geometric Texture Synthesis (GTS) algorithms. Analogous to their raster-based counterparts, GTS algorithms synthesize arrangements that ought to be judged by human viewers as “similar” to the example inputs. However, an absence of conventional evaluation procedures in current attempts demands an inquiry into the visual significance of synthesized results. In this dissertation, I present an investigation into GTS and report on my findings from three projects. I start by offering initial steps towards grounding texture synthesis techniques more firmly with our understanding of visual perception through two psychophysical studies. My observations throughout these studies result in important visual cues used by people when generating and/or comparing similarity of geometric arrangements as well a set of strategies adopted by participants when generating arrangements. Based on one of the generation strategies devised in these studies I develop a new geometric synthesis algorithm that uses a tile-based approach to generate arrangements. Textures synthesized by this algorithm are comparable to the state of the art in GTS and provide an additional reference in subsequent evaluations. To conduct effective evaluations of GTS, I start by collecting a set of representative examples, use them to acquire arrangements from multiple sources, and then gather them into a dataset that acts as a standard for the GTS research community. I then utilize this dataset in a second set of psychophysical studies that define an effective methodology for comparing current and future geometric synthesis algorithms