Ice buildup on structures leads to problems that include reduced performance, structural damage and power outages. It is therefore important to limit the energy required for removal of ice from substrates to minimize buildup. Understanding the mechanism of ice adhesion and its dependence on variables like coating thickness, stiffness, surface free energy and morphology is critical for minimizing adhesion. Despite several developments in “icephobic” coatings, which are those that have low ice adhesion, it is important to understand adhesion on the fundamental level to make way for advanced coatings. To do so, a study has been carried out that explores key variables affecting ice adhesion using a commercially available silicone, Sylgard 184®. Sylgard 184 is a two-part, platinum cured silicone elastomer available from Dow Corning with good physical and chemical stability and is used in widely diverse research studies. The thermodynamic work of ice adhesion is related to the receding contact angle θ_r of water by Equation 1. wa≈ γ_w (1+cos⁡ θ_r) Eq 1. where γ_w is the surface tension of water. Considering an elastomeric substrate and ice as a rigid cylindrical adherent, the Kendall modelcan be adapted to relate peak removal force (Pc) with work of adhesion (wa), modulus (K), thickness (t), and radius (a) according to Equation 2. Pc ∝ πa^2 ((2wa K)/t)^(1⁄2) Eq. 2 Considering these relationships, hydrophobic materials with low surface energies and high receding contact angles are generally predicted to show low adhesion. To begin to understand details, the force required to remove an ice cylinder from the silicone elastomer Sylgard 184 was investigated by focusing on three variables: coating thickness, modulus and cure temperature. “Cure” refers to the network formation or crosslinking within the material. The Wynne research group has previously established a surprising dependence of qR on Sylgard 184 cure temperature.In this thesis, the relationship among variables noted above was examined by measuring Pc for Sylgard coatings. Additionally, effects of test temperature on ice adhesion strength was studied. Surface characterization methods including ATR-IR (attenuated total reflectance infrared spectroscopy), DCA (Wilhelmy plate dynamic contact angles) and AFM (atomic force microscopy) were employed. In summary, defined processing conditions were found optimum for minimizing ice adhesion to Sylgard coatings.

Classical theory cannot provide a satisfying scenario for a unitary thermodynamic evolution of black holes. To preserve information one requires quantum mechanical effects on scales reaching beyond the traditional horizon radius. Therefore, common to many of the theories attempting to resolve the paradox is the existence of exotic horizon structures. The recent advent of gravitational wave astronomy provides a possible means for detecting the existence of such structures through gravitational wave emission in the ringdown phase of binary black hole mergers. Such emission is described by quasinormal modes (QNMs) in which the gravitational waves originates outside the black hole, in the vicinity of the photon spheres. Requiring reflective properties of the horizon structure results in the existence of gravitational echoes that may be detected by facilities such as LIGO etc.. This thesis studies geodesic motion of such echoes in the equatorial plane of a rotating black hole. Depending on the extent of the horizon structure, and the particular mode of emission, one can expect different timescales for the echoes. For a horizon structure extending <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5CLambda%20r%20=" /> <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?10%5E%7B-12%7D" /> <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?M" /> outside the traditional horizon of a  <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?M%20=%2022.6%20M_%7B%5Codot%7D" />, <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?a%20=%200.74%20M" /> black hole one would ideally find echoes appearing as integer multiples of <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5CDelta%20t_%7Becho%7D" /><img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?=%200.0204%20s" /> after the primary signal. The time delay is expected to increase by at least an order of magnitude if one lets <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5CDelta%20r%20%5Csim%2010%5E%7B-80%7D%20M" />. The expected echo timescales for gravitational waves emitted from any point around the black hole, in arbitrary modes, is an interesting further study.

This thesis describes technical and scientific aspects of new types of composite films/coatings for corrosion protection of carbon steel, composite films with nanometer thickness consisting of mussel adhesive protein (Mefp‐1) and ceria nanoparticles, and polymeric composite coatings with micrometre thickness consisting of conducting polymer and ceria nanoparticles in a UV‐curing polyester acrylate (PEA) resin. The influence of microstructure on corrosion behaviour was studied for a Fe‐Cr‐V‐N alloy containing micro‐sized nitrides with different chemical composition spread in martensitic alloy matrix. The Volta potential mapping suggested higher relative nobility for the nitride particles than the alloy matrix, and the nitrides with higher amounts of nitrogen and vanadium exhibited higher nobility. Potentiodynamic polarization measurements in a 0.1 M NaCl solution at neutral pH and ambient temperature showed passivity breakdown with initiation of localized corrosion which started in the boundary region surrounding the nitride particles, especially the ones enriched in Cr and Mo. Mefp‐1/ceria nanocomposite films were formed on silica and metal substrates by layer‐by‐layer immersion deposition. The film formation process was studied in situ using a Quartz Crystal Microbalance with Dissipation (QCM‐D). The film grows linearly with increasing number of immersions. Increasing Mefp‐1 concentration or using Mefp‐1 with larger size leads to more Mefp‐1 being deposited. Peak Force Quantitative Nanomechanical Mapping (Peak Force QNM) of the composite films in air indicated that the elastic modulus of the film increased when the film deposited had a higher Mefp‐1 concentration. It was also noted that the nature of the outermost layer can affect bulk morphology and surface mechanical properties of the film. The QCM‐D study of Mefp‐1 on an iron substrate showed that Mefp‐1 adsorbs at a high rate and changes its conformation with increasing adsorption time. The QCM‐D and in situ Peak Force QNM measurements showed that the addition of Fe3+ ions causes a transition in the single Mefp‐1 layer from an extended and soft layer to a denser and stiffer layer. In situ ATR‐FTIR and Confocal Raman Microscopy (CRM) analyses revealed complex formation between Fe3+ and catechol groups in Mefp‐1. Moreover, optical microscopy, SEM and AFM characterization of the Mefp‐1/ceria composite film formed on carbon steel showed micron‐size aggregates rich in Mefp‐1 and ceria, and a nanostructure of well dispersed ceria particles in the film. The CRM analysis confirmed the presence of Mefp‐1/Fe complexes in the film. Electrochemical impedance microscopy and potentiodynamic polarization measurements showed that the Mefp‐1/ceria composite film can provide corrosion protection for carbon steel, and that the protection efficiency increases with exposure time. Composite coatings of 10 μm thickness composed of a UV‐curing PEA resin and a small amount of conductive polymer and ceria nanoparticles were coated on carbon steel. The conductive polymer (PAni) was synthesized with phosphoric acid (PA) as the dopant by chemical oxidative polymerization. The ATR‐FTIR and SEM analyses confirmed that the added particles were well dispersed in the coatings. Electrochemical measurements during long exposure in 0.1 M NaCl solution, including open circuit potential (OCP) and EIS, were performed to investigate the protective performance of the coatings. The results showed that adding ceria nanoparticles can improve the barrier properties of the coating, and adding PAni‐PA can lead to active protection of the coating. Adding PAni‐PA and ceria nanoparticles simultaneously in the coating can improve the protection and stability of the composite coating, providing excellent corrosion protection for carbon steel. / <p>QC 20131024</p>

Virtualisation is one of the underlying technologies that led to the success of cloud computing platforms (CCPs). The technology, along with other features such as multitenancy allows delivering of computing resources in the form of service through efficient sharing of physical resources. As these resources are provided through virtualisation, a robust agreement is outlined for both the quantity and quality-of-service (QoS) in a service level agreement (SLA) documents. QoS is one of the essential components of SLA, where performance is one of its primary aspects. As the technology is progressively maturing and receiving massive acceptance, researchers from industry and academia continue to carry out novel theoretical and practical studies of various essential aspects of CCPs with significant levels of success. This thesis starts with the assessment of the current level of knowledge in the literature of cloud computing in general and CCPs in particular. In this context, a substantive literature review was carried out focusing on performance modelling, testing, analysis and evaluation of Infrastructure as a Service (IaaS), methodologies. To this end, a systematic mapping study (SMSs) of the literature was conducted. SMS guided the choice and direction of this research. The SMS was followed by the development of a novel open queueing network model (QNM) at equilibrium for the performance modelling and analysis of an OpenStack IaaS CCP. Moreover, it was assumed that an external arrival pattern is Poisson while the queueing stations provided exponentially distributed service times. Based on Jackson’s theorem, the model was exactly decomposed into individual M/M/c (c ≥ 1) stations. Each of these queueing stations was analysed in isolation, and closed-form expressions for key performance metrics, such as mean response time, throughput, server (resource) utilisation as well as bottleneck device were determined. Moreover, the research was extended with a proposed open QNM with a bursty external arrival pattern represented by a Compound Poisson Process (CPP) with geometrically distributed batches, or equivalently, variable Generalised Exponential (GE) interarrival and service times. Each queueing station had c (c ≥ 1) GE-type servers. Based on a generic maximum entropy (ME) product form approximation, the proposed open GE-type QNM was decomposed into individual GE/GE/c queueing stations with GE-type interarrival and service times. The evaluation of the performance metrics and bottleneck analysis of the QNM were determined, which provided vital insights for the capacity planning of existing CCP architectures as well as the design and development of new ones. The results also revealed, due to a significant impact on the burstiness of interarrival and service time processes, resulted in worst-case performance bounds scenarios, as appropriate. Finally, an investigation was carried out into modelling and analysis of performance and security trade-offs for a CCP architecture, based on a proposed generalised stochastic Petri net (GSPN) model with security-detection control model (SDCM). In this context, ‘optimal’ combined performance and security metrics were defined with both M-type or GE-type arrival and service times and the impact of security incidents on performance was assessed. Typical numerical experiments on the GSPN model were conducted and implemented using the Möbius package, and an ‘optimal’ trade-offs were determined between performance and security, which are crucial in the SLA of the cloud computing services. / Petroleum technology development fund (PTDF) of the government of Nigeria Usmanu Danfodiyo University, Sokoto

The present thesis entitled “Design, Synthesis and Characterization of Novel Nanomaterials” is divided into five chapters, staring with a general introduction. The remaining chapters focus on four different areas/projects that I have worked on. Chapter 1: Introduction to nanomaterials This chapter reviews the basic concepts of nanomaterials and their fabrication methods. Nanomaterials are defined as materials whose dimensions (at least one) are below 100 nm. One of the most exciting aspects of nanomaterials is that their properties may differ significantly from those of the corresponding bulk materials. Nanomaterials fabrication methods can be broadly classified according to whether the assembly follows either i) the bottom-up approach or ii) the top-down approach. These methods have been discussed with various examples including the self-assembly of proteins, peptides and small molecules. In the top-down approach synthetic procedures for Graphene Oxide and its application are discussed. All characterization techniques that are used for characterizing the nanomaterials are also described briefly. Chapter 2 Section A: Self-assembly of 1-Hydroxy benzotriazole (HOBT) in water The studies presented in Chapter 2 identifies HOBT as the smallest non-peptide building block that spontaneously self-assembles into hollow micro tubular structures upon evaporation of water. The tubes form under ambient conditions by rolling over of crystalline sheets of HOBT. The packing of HOBT in the tubes seem to be predominantly driven by intermolecular π-stacking interactions between the aromatic rings of HOBT. These structural and packing patterns are similar to those found in nanotubes formed by the self-assembly of peptides and other larger molecules. The cavities of these thermolabile microtubes act as molds for casting gold nanoparticles for the synthesis of gold microrods with monodisperse dimensions. The non-reacting inner surfaces of the cavities have been used to uniquely synthesize R6G-functionalized gold microrods. With these features, HOBT is an important novel non-peptide building block for accessing micro and nanometric materials for their applications in medicine, biology and molecular biotechnology. Section B: Controlling the orientation of self-assembly of HOBT microtubes The studies presented in this chapter address the self-assembly of HOBT into microtubular structures in different solvents of varying polarities (H2O and DCM:MeOH) to understand the role of solvent volatility and its direction on the orientation of the HOBT microtubes. HOBT self-assembles from DCM:MeOH mixtures in its bipolar canonical form and is coordinated with its water of hydration, similar to its crystals obtained from water. FTIR and TGA data shows that MeOH is also integrated with the microtubes. We observe for the first time that the orientation of microtubular self-assembly is controlled in the direction of evaporation of the solvent. We demonstrate further this feature by controlling the orientation of HOBT self-assembly in exclusively vertical direction through controlled vertical evaporation of the solvent mixture DCM:MeOH (9:1). Additionally, the unique transition between vertical and horizontal orientations for self-assembled HOBT microtubes is achieved by simple change of solvation between aqueous and organic solvents. These results reveal a dynamic relationship between the rate of evaporation of solvent and the rates of formation of different self-assembled morphologies. The rate of evaporation of the solvent primarily governs the rate of formation of the tubes, rather than their orientations in three dimensions. Chapter 3: Chemical origins of debris in Graphene Oxide (GO) This chapter is focused on the investigation of the carbonyl rich fragments arising from GO and provides an understanding of its formation. The fragments are expelled from GO due to an uncontrolled nucleophile driven reaction in aqueous medium leaving the holes on the sheet. These fragments are carbonyl rich small (5 ± 2 nm) nonaromatic molecules that form as by-products of oxidative chemical reactions that occur at the sp3 clusters on the basal surface of GO sheets when they are treated with nucleophilic bases under aqueous conditions. The structure and size of the debris, and hence that of the hole, depend on the size of the sp3 cluster on the sheet. These debris fall out of the GO sheet surface, leading to formation of nanometer sized holes. Formation of debris and hence the holes can be avoided by using anhydrous polar solvents. This work sheds new light on the fundamental structure of GO and the prevention of debris from it during redox reactions enabling better control over functionalization of the GO surface. Chapter 4: Measurement of mechanical properties of polypeptide fragment from Insulin like growth factor binding protein nanotubes by the Peak Force QNM method This chapter describes the discovery of Polypeptide fragment from an IGFBP-2. This fragment self-assembles spontaneously and reversibly into nanotubular structures under oxidizing conditions. These nanotubes were characterized by using Transmission electron microscopy. Notably as compared to the monomer, an increase in intrinsic fluorescence upon self-assembly. The thermal stability of these nanotubes is realized form the fluorescence studies. Peak Force Quantitative Nanomechanical Mapping method of AFM was used to measure the Young’s modulus of the nanotubes. These nanotubes were found to have Young’s modulus value of ~10 Gpa, which is comparable to those of bones presumably due to intermolecular disulphide bonds. These nanotubes will have potential applications in tissue engineering. Chapter 5: Probing the pathways of n→π* interaction in peptides This chapter deals with the theoretical study of n→π* interaction in designed peptidomimetics. The n→π* interaction involves the delocalization of the lone pair of the donor group into the antibonding orbital (π*) of a carbonyl group. However despite beeing extensively studied there exists a debate over the validation of these n→π* interaction which is reminiscent to Bürgi and Dunitz trajectory. This chapter present our findings that peptidomimetics containing the 5,6-dihydro-4H-1,3-oxazine (Oxa) and 5,6-dihydro-4H-1,3-thiazine (Thi) functional groups at the C-terminus of Pro selectively stabilizes the cis conformer by reverse n→πi-1* interaction. These systems have been used to study the n→πi1* interaction using Natural Bond Orbital (NBO) method. Our study reveals that the energetically most favorable trajectory of a nucleophile for a favorable n→π* interaction presumably to facilitate the overlap between the lonepair of the nucleophile and the antibonding orbital of the carbonyl group. The geometrical requirements for the optimum n→π* interaction depends on the relative orientations of the orbitals that are involved. This study has implications for more accurately identifying long distant n→π* interaction.