A Framework for Service Differentiation and Optimization in Multi-hop Wireless Networks

In resource-constrained networks such as multi-hop wireless networks (MHWNs), service differentiation algorithms designed to address end users' interests (e.g. user satisfaction, QoS, etc.) should also consider efficient utilization of the scarce network resources in order to maximize the network's interests (e.g. revenue). For this very reason, service differentiation in MHWNs is quite different from the wired network scenario. We propose a service differentiation tool called the ``Investment Function'', which essentially captures the network's cumulative resource investment in a given packet at a given time. This investment value can be used by the network algorithm to implement specific service differentiation principles. As proof-of-concept, we use the investment function to improve fairness among simultaneous flows that traverse varying number of hops in a MHWN (multihop flow fairness). However, to attain the optimal value of a specific service differentiation objective, optimal service differentiation and investment function parameters may need to be computed. The optimal parameters can be computed by casting the service differentiation problem as a network flow problem in MHWNs, with the goal of optimizing the service differentiation objective. The capacity constraints for these problems require knowledge of the adjacent-node interference values, and constructing these constraints could be very expensive based on the transmission scheduling scheme used. As a result, even formulating the optimization problem may take unacceptable computational effort or memory or both. Under optimal scheduling, the adjacent node interference values (and thus the capacity constraints) are not only very expensive to compute, but also cannot be expressed in polynomial form. Therefore, existing optimization techniques cannot be directly applied to solve optimization problems in MHWNs. To develop an efficient optimization framework, we first model the MHWN as a Unit Disk Graph (UDG). The optimal transmission schedule in the MHWN is related to the chromatic number of the UDG, which is very expensive to compute. However, the clique number, which is a lower bound on the chromatic number, can be computed in polynomial time in UDGs. Through an empirical study, we obtain tighter bounds on the ratio of the chromatic number to clique number in UDGs, which enables us to leverage existing polynomial time clique-discovery algorithms to compute very close approximations to the chromatic number value. This approximation not only allows us to quickly formulate the capacity constraints in polynomial form, but also allows us to significantly deviate from the traditional approach of discovering all or most of the constraints \textit{a priori}; instead, we can discover the constraints as needed. We have integrated this approach of constraint-discovery into an active-set optimization algorithm (Gradient Projection method) to solve network flow problems in multi-hop wireless networks. Our results show significant memory and computational savings when compared to existing methods

Carrier Transport and Electrical Conduction in Alloy-Mediated Graphene on Silicon

University of Technology Sydney. Faculty of Engineering and Information Technology.The possibility of graphene-based micro- and nanoelectronic devices that exploit the extraordinary electronic properties of graphene is the biggest inspiration behind the accelerated development of graphene science and technology. Although the remarkable efforts for establishing graphene as a new electronic material began over 15 years ago, the actual realisation of graphene devices on a large-scale remains elusive, mainly due to feasibility, cost-effectiveness and compatibility issues with the existing semiconductor technology and processes. Significant advancements have been achieved in the synthesis and establishment of transport properties of epitaxial graphene (EG) on 4H- and 6H-SiC, while equivalent progress using silicon (Si) as a platform (via a thin film of 3C-SiC) with reliable electrical transport measurements has not been elucidated to date, due to limitations such as non-uniform coverage of graphene on 3C-SiC/Si and high density of defects within the 3C-SiC. In this work, we first show that the heteroepitaxial 3C-SiC on Si as the substrate should be carefully approached, as the 3C-SiC/Si heterojunction is electrically unstable and prone to severe leakage or parallel conduction. Subsequently, we find that the interface instability is due to the diffusion of carbon into the silicon matrix during the 3C-SiC growth, creating electrically active interstitial carbon. We overcome these challenges using 3C-SiC on a highly-resistive silicon substrate. By addressing the parallel conduction issue of the 3C-SiC/Si heteroepitaxial system, in this work, we isolate the charge transport properties of epitaxial graphene (EG) grown directly on 3C-SiC over large areas via an alloy-mediated method and present corresponding physical ab-initio models. Here, we study the properties of EG synthesised on 3C-SiC(100) and 3C-SiC(111). The transport properties of EG on 3C-SiC follow a similar power-law dependence of sheet carrier concentration and mobility and comparable sheet resistance values with the EG on bulk-SiC – although the grain sizes for both are vastly different. Furthermore, we find that the transport properties of graphene within the observed regime are dominated by the substrate interaction, resulting in a large p-type doping, especially for the graphene on 3C-SiC(100). In the case of EG on 3C-SiC(111), the presence of buffer layer reduces the substrate interaction and the charge transfer up to an extent. This work demonstrates a more compelling need to focus on the engineering of the graphene-substrate interface as opposed to graphene grain sizes in order to tune the charge transport properties of the epitaxial graphene for the integration of 2D materials in functional nanosystems

Targeting GRP78 in Cancer with Nucleic Acid Bioconjugates

Nucleic acid bioconjugates have gained widespread use in medicinal chemistry research programs aimed at fighting human malignancies such as cancer, diabetes, genetic and infectious diseases. Their popularity stems from their ability to accelerate the drug development process by conjugating chemical functionality that may improve the pharmacology of a bioactive nucleoside. Moreover, this strategy has been proven to be effective with small molecule nucleoside analogs and those derived from lengthy oligonucleotide sequences. Considering these fruitful applications, my research and this thesis aims to explore the synthesis, characterization and therapeutic potential of novel classes of nucleic acid bioconjugates. These are based on, aminoacyl nucleolipids, from which a simple, versatile and efficient synthesis strategy has been developed for this new class of DNA binding molecules as described in Chapter 2 of this thesis. This bioconjugate exhibited GRP78 oncogene binding affinity (KD: 0.25 mM) as characterized by PAGE gel shift assays. Its binding affinity towards the GRP78 oncogene was also confirmed using circular dichorism spectroscopy, and thermal denaturation experiments. Moreover, dynamic light scattering experiments also demonstrated increases in particle sizes after binding of this molecule to the GRP78 oncogene. In a single dose (10 µM) screen against a panel of 60 cancer cell lines, the aminoacyl nucleolipid demonstrated selective anti-leukemic activity, highlighting its potential in anti-cancer research programs. In Chapter 3, the synthesis, biophysical properties and GRP78 DNA cleavage activity of a phthalocyanine-linked oligonucleotide will be highlighted for photodynamic oncogene therapy applications. The synthesis and characterization of cancer-targeting oligonucleotide (CTO) and its bio-conjugation to a chemically resilient photosensitizer, a carboxy-derived perfluorophthalocyanine (Pc), enabled the production of a unique bioconjugate for potential anti-cancer applications. In this study, the Pc-CTO demonstrated the ability to hybridize to complementary GRP78 DNA and mRNA oncogenes. In a photochemical oxidative cleavage assay, the Pc-CTO triggered significant degradation of the GRP78 oncogenes underscoring its potential in GRP78-targeting photodynamic therapy. In Chapter 4, a study into the design, synthesis and structure-function relationships of a new class of nucleic acid bioconjugates is presented. The diacylhydrazine-linked dinucleosides represent a novel class of nucleic acid bioconjugates that are proposed to improve the structural stability of turn conformations in DNA or RNA hairpin secondary structures. My advances in the synthesis, structure elucidation and biological evaluation of these putative hairpin mimics will be described. In sum, this thesis will serve to highlight my contributions to the flourishing field of nucleic acid bioconjugation for GRP78-targeting for anti-cancer applications

Understanding molecular aspects of catfish-pathogen interactions

The catfish industry suffers losses primarily due to enteric septicemia of catfish and columnaris disease caused by Edwardsiella ictaluri and Flavobacterium columnare, respectively. Understanding the host-pathogen interactions is vital for prevention and eradication of these diseases. Hence, the overall objective of this study was to analyze whole cell proteomes of these two bacteria, and to determine the changes in E. ictaluri protein expression against in vitro iron-restriction and host serum treatment. High-throughput proteomic analysis of these bacteria was conducted using two-dimensional liquid chromatography followed by electrospray ionization tandem mass spectrometry (2-D LC ESI MS/MS) and two-dimentional gel electrophoresis coupled with matrix-assisted laser desorption/ionization time-oflight mass spectrometry (2-DE MALDI TOF/TOF). Identified proteins were clustered into functional groups using clusters of orthologous groups, and subcellular locations as well as possible functional relationships were determined. A total of 788 unique E. ictaluri and 621 unique F. columnare proteins were identified, which represented 12 and 28 pathways, respectively. Vertebrate hosts tend to chelate free iron of their body and make the environment hostile for bacteria. Hence, reduced availability of iron may cause significant stress for pathogens and is considered a signal that leads to alteration in virulent gene expression. Similarly, E. ictaluri might use the catfish blood stream effectively for quick systemic invasion. Hence, exposure to catfish serum components might reveal the ability of E. ictaluri to protect against host defense mechanisms. Using two-dimensional difference gel electrophoresis, responses of E. ictaluri due to in vitro iron-restriction and host serum treatment were determined. A total of 50 and 19 proteins were identified to be differentially expressed due to in vitro iron-restriction and catfish serum treatment, respectively. Among the differentially expressed proteins, several putative virulent determinants, immunogenic proteins, chaperones, and housekeeping genes were noted. To initiate functional studies, four differentially expressed E. ictaluri genes (lamB, glyS, malE, and sdhA) were mutated by inrame deletion. Results from this study provided experimental evidence for many predicted proteins. In addition, identification of differentially expressed proteins provided targets for further functional analysis, which could help elucidate pathogenic mechanisms of E. ictaluri

Aerocapture Design Reference Missions for Solar System Exploration: from Venus to Neptune

Aerocapture is the technique of using planetary atmospheres to decelerate a spacecraft in a single pass to achieve nearly fuel-free orbit insertion. Aerocapture has been extensively studied since the 1980s but has never been flown yet. The entry conditions encountered during aerocapture are strongly destination dependent, and performance benefit offered by aerocapture is also destination dependent. Aerocapture is applicable to all atmosphere-bearing destinations with the exception of Jupiter and Saturn, whose extreme entry conditions make aerocapture infeasible. A recent study by the NASA Science Mission Directorate highlighted the need for baseline design reference missions, as a starting point for system level architecture studies. The present study uses the Aerocapture Mission Analysis Tool (AMAT) to compile a list of design reference missions at Venus, Earth, Mars, Titan, Uranus, and Neptune. These reference missions can provide an initial assessment of the feasibility of aerocapture for a proposed mission, and provide intial baseline values for more detailed system studies. The reference mission set provides a quick estimate of the entry conditions, control requirements, and aero-thermal loads for architectural level studies.Comment: 12 pages, 7 figure

Comparison of Lift and Drag Modulation Control for Ice Giant Aerocapture Missions

Aerocapture is an orbit insertion technique which uses atmospheric drag from a single pass to decelerate a spacecraft. Compared to conventional propulsive insertion, aerocapture can impart large velocity changes to the spacecraft with almost no propellant. At the far reaches of the outer Solar System, the ice giants remain the last class of planets to be explored using orbiters. Their enormous heliocentric distance presents significant mission design challenges, particularly the large $\Delta$V required for orbit insertion. This makes aerocapture an attractive method of orbit insertion, but also challenging due to the comparatively large navigation and atmospheric uncertainties. The present study performs a comparison of the lift and drag modulation control and their implications for future missions. Lift modulation provides nearly twice the entry corridor width as drag modulation, and can thus accommodate larger uncertainties. Lift modulation offers continuous control throughout the flight enabling it to adjust the trajectory in response to the actual density profile encountered. Drag modulation offers much more benign aero-thermal conditions compared to lift modulation. With drag modulation, there is no control authority after the drag skirt jettison making the vehicle more susceptible to exit state errors from density variations encountered after the jettison event.Comment: 7 pages, 3 figure

Analysis of a 115MW, 3 shaft, helium Brayton cycle

This research theme is originated from a development project that is going on in South Africa, for the design and construction of a closed cycle gas turbine plant using gas-cooled reactor as the heat source to generate 115 MW of electricity. South African Power utility company, Eskom, promotes this developmental work through its subsidiary called PBMR (Pebble Bed Modular Reactor). Some of the attractive features of this plant are the inherent and passive safety features, modular geometry, small evacuation area, small infrastructure requirements for the installation and running of the plant, small construction time, quick starting and stopping and also low operational cost. This exercise is looking at the operational aspects of a closed cycle gas turbine, the finding of which will have a direct input towards the successful development and commissioning of the plant. A thorough understanding of the fluid dynamics in this three-shaft system and its transient performance analysis were the two main objectives of this research work. A computer programme called GTSI, developed by a previous Cranfield University research student, has been used in this as a base programme for the performance analysis. Some modifications were done on this programme to improve its control abilities. The areas covered in the performance analysis are Start-up, Shutdown and Load ramping. A detailed literature survey has been conducted to learn from the helium Turbo machinery experiences, though it is very limited. A critical analysis on the design philosophy of the PBMR is also carried out as part of this research work. The performance analysis has shown the advantage, disadvantage and impact of various power modulation methods suggested for the PBMR. It has tracked the effect of the operations of the various valves included in the PBMR design. The start-up using a hot gas injection has been analysed in detail and a successful start region has been mapped. A start-up procedure is also written based on this. The analysis on the normal and emergency load rejection using various power modulation devices has been done and it stress the importance of more control facilities during full load rejection due to generator faults. A computational fluid dynamics (CFD) analysis, using commercial software, has been carried out on some geometry of the PBMR design to find out whether its flow characteristic will have any serious impact on the performance on the cycle during the load control of the plant. The analysis has demonstrated that there will not be much impact on the performance, during load control using pressure level changes, from this geometry. However, some locations in the geometry have been identified as areas where the flow is experiencing comparatively high pressure losses. Recommendations, which include modification in the physical design, were made to improve this. The CFD analysis has extended to a cascade to compare the flow behaviour of Air and Helium with an objective of using air, being inexpensive, to test the helium flow characteristic in a test rig to simulate the behavioural pattern of helium in the PBMR pressure vessel. The specification of a hypothetical test rig and the necessary scaling parameters has been derived from this exercise. This will be useful for designing test rigs during the developmental and operational stage of the PBMR project

Launch Vehicle High-Energy Performance Dataset

The choice of the launch vehicle is an important consideration during the preliminary planning of interplanetary missions. The launch vehicle must be highly reliable, capable of imparting sufficient energy to the spacecraft to inject it on to an Earth-escape trajectory, and must fit within the cost constraints of the mission. Over the recent past, the most commonly used launchers for interplanetary missions include the Atlas V401, Atlas V551, Delta IVH, and Falcon Heavy expendable version. The NASA Launch Vehicle Performance website maintains a tool to help mission planners evaluate various launch vehicles during mission studies. However, there is no comprehensive dataset which can be used to quickly compare the launch performance and launch cost of various options. The present study compiles a dataset of the high energy performance of existing and planned launchers from open-source data and performs a quantitative comparison of the launch performance and the launch cost per kg. The Falcon Heavy expendable offers the lowest cost-per-kg for high-energy launches, with only $0.075M per kg. The Vulcan Centaur offers comparable performance to the Falcon Heavy. The results indicate Falcon Heavy Expendable and the Vulcan Centaur will be the likely choice for several future missions.Comment: 6 pages, 4 figure