This thesis describes digital television transition in the United States. Its goal is to introduce the way how digital television broadcasting in the United States was formed and analog broadcasting was switched off, and how these changes affected American television market and usage of broadcasting spectrum. In the first part I explain a context in which American television market has been formed and has developed until the beginning of 1990s, when the debate about digital television broadcasting commenced. Reason for a development of the new television norm was a desire to broadcast in high definition. Establishment of ATSC norm is explained in 4th chapter. Following chapter describes how digital television coverage grew and what the expenses were for viewers. The thesis then describes spectrum auctions and changes in the television market which digital television transition brought. When the transition ended need for a new debate about television emerged because current norm is becoming obsolete and did not allow broadcasting in ultra high definition. This lead to the development of ATSC 3.0 norm which allows broadcasting more programs in terrestrial television broadcasting and allows expanding terrestrial broadcasting to other mobile devices.

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This thesis concerns the mathematical modelling of phase transformations with a special emphasis on martensitic phase transformations and their application to the modelling of steels. In Chapter 1, we develop a framework that determines the optimal transformation strain between any two Bravais lattices and use it to give a rigorous proof of a conjecture by E.C. Bain in 1924 on the optimality of the so-called Bain strain. In Chapter 2, we review the Ball-James model and related concepts. We present some simplification of existing results. In Chapter 3, we pose a conjecture for the explicit form of the quasiconvex hull of the three tetragonal wells, known as the three-well problem. We present a new approach to finding inner and outer bounds. In Chapter 4, we focus on highly compatible, so called self-accommodating, martensitic structures and present new results on their fine properties such as estimates on their minimum complexity and bounds on the relative proportion of each martensitic variant in them. In Chapter 5, we investigate the contrary situation when self-accommodating microstructures do not exist. We determine, whether in this situation, it is still energetically favourable to nucleate martensite within austenite. By constructing different types of inclusions, we find that the optimal shape of an inclusion is flat and thin which is in agreement with experimental observation. In Chapter 6, we introduce a mechanism that identifies transformation strains with orientation relationships. This mechanism allows us to develop a simpler, strain-based approach to phase transformation models in steels. One novelty of this approach is the derivation of an explicit dependence of the orientation relationships on the ratio of tetragonality of the product phase. In Chapter 7, we establish a correspondence between common phenomenological models for steels and the Ball-James model. This correspondence is then used to develop a new theory for the (5 5 7) lath transformation in low-carbon steels. Compared to existing theories, this new approach requires a significantly smaller number of input parameters. Furthermore, it predicts a microstructure morphology which differs from what is conventionally believed.

This thesis is an attempt to understand ways to improve thermo-mechanical and structural properties of nano-structured materials. A detailed study on computational design and analysis of metallic nanowires is carried out. Molecular dynamic simulation method is applied. In particular, FCC metallic nanowires, NiAl, and CuZr nanowires are studied. Various bottom-up approaches are suggested with improved structural and thermo¬mechanical properties. In the first part of the thesis, Cu nanowires are considered. Existence of a novel and stable pentagonal multi-shell nanobridge structure of Cu under high strain rate tensile loading is reported. Such a structure shows enhanced mechanical properties. A three-fold pseudo-elastic-plastic shape recovery mechanism in such nanowires is established. This study also shows that the length of the pentagonal nanobridge structures can be characterized by its inelastic strain. It is also reported that an initial FCC structure is transformed into a new HCP structure. The evidence of HCP structure is confirmed with the help of experimental data published in the literature. Subsequent to the above study, a novel mechanism involving coupled temperature-stress dependent reorientation in FCC nanowires is investigated. A detailed map is generated for size dependent stress-temperature induced solid-solid reorientation in Cu nanowires. In the second part of the thesis, deformation mechanisms in NiAl based intermetallic nanowires are studied. A novel mechanism of temperature and cross-section dependent pseudo-elastic/pseudo-plastic shape and strain recovery by an initial B2 phase of NiAl nanowire is reported. Such a recoverable strain, which is as high as ~ 30%, can potentially be utilized to realize various types of shape memory and strain sensing phenomena in nano-scale devices. An asymmetry in tensile and compressive yield strength behavior is also observed, which is due to the softening and hardening of the nanowires under tensile and compressive loadings, respectively. Two different deformation mechanisms dominated by twinning under tension and slip under compression are found. Most interestingly, a superplastic behavior with a failure strain of up to 700% in the intermetallic NiAl nanowires is found to exist at a temperature of 0.36Tm. Such superplastic behavior is attributed to the transformation of the nanowire from a crystalline phase to an amorphous phase after yielding of the nanowire. In the last part the work, another type of nanowires having Cu-Zr system is considered. A novel stress induced martensitic phase transformation from an initial B2 phase to BCT phase in a CuZr nanowire under tensile loading is reported. It is further shown that such a stress induced martenistic phase transformation can be achieved under both tensile as well as compressive loadings. Tensile-compressive asymmetry in the stress-strain behavior is observed due to two different phase transformation mechanisms having maximum transformation strains of ~ 5% under compressive loading and ~ 20% under tensile loading. A size and temperature dependent tensile phase transformation in the nanowire is also observed. Small nanowires show a single step tensile phase transformation whereas the nanowires with larger size show a two step deformation mechanism via an intermediate R-phase hardening followed by R-phase yielding. A study of energetic behavior of these nanowires reveals uniform distribution of stress over the nanowire cross-section and such stress distribution can lead to a significant improvement in its thermo-mechanical properties. Similar improvement is demonstrated by designing the nanowires via manipulating the surface configuration of B2-CuZr system. It is found that the CuZr nanowires with Zr atoms at the surface sites are energetically more stable and also give a uniform distribution of stresses across the cross-section. This leads to the improvement in yield strength as well as failure strain. An approach to design energetically stable nano-structured materials via manipulating the surface configurations with improved thermo-mechanical properties is demonstrated which can help in fundamental understanding and development of similar structures with more stability and enhanced structural properties. Further ab-initio and experimental studies on the confirmation of the stability of the nanowires via manipulating the surface site is an open area of research and related future scopes are highlighted in the closure.

Plastic deformation of metals and alloys are invariably accompanied by the development of texture. The origin of texture is attributed to the deformation micro-mechanisms associated with processing. The face-centered cubic (FCC) metals and alloys are known to exhibit two distinct types of textures when subjected to large strain rolling deformation, namely, (i) Cu-type texture, commonly seen in high/medium stacking fault energy (SFE) materials, (ii) Bs-type texture in low SFE materials. The circumstances that could result in the formation of Bs-type texture in low SFE materials still remains an open question and no definite mechanism has been uniquely agreed upon. Apart from the SFE, grain size could also influence the deformation mechanism and hence the deformation texture. It is well known that in materials with grain sizes less than 100 nm (referred to as nano-crystalline materials), the microstructures contain large fraction of grain boundaries. This subsequently introduces a variety of deformation mechanisms in the microstructure involving grain boundary-mediated processes such as grain boundary sliding and grain rotation, in addition to slip and twinning. A clear understanding of texture evolution in nano-crystalline materials, particularly at large strains, is a topic that remains largely unexplored. The present work is an attempt to address the aforementioned issues pertaining to the evolution of deformation texture, namely, (i) the effect of SFE and (ii) the effect of grain size, in FCC metals and alloys. Nickel-cobalt alloys are chosen as the model system for the present investigation. The addition of cobalt to nickel leads to a systematic reduction of SFE as a function of cobalt content. In this thesis, three alloys of Ni-Co system have been considered, namely, nickel – 20 wt.% cobalt, nickel – 40 wt.% cobalt and nickel – 60 wt.% cobalt. For a comparison, pure nickel has also been subjected to similar study. Chapter 1 of the thesis presents a detailed survey of literature pertaining to the evolution of rolling textures in FCC metals and alloys, and chapter 2 includes the details of the experimental techniques and characterization procedures, which are commonly employed for the entire work. Chapter 3 addresses the effect of stacking fault energy on the evolution of rolling texture. The materials subjected to study in this chapter are microcrystalline Ni-Co alloys. The texture evolution in Ni-20Co is very similar to pure Ni, and a characteristic Cu-type rolling texture is observed. The evolution of texture in these materials is primarily attributed to the intense dislocation activity throughout the deformation stages. In Ni-40Co, a medium SFE material, the rolling texture was predominantly Cu-type up to a strain of ε = 3 (95% thickness reduction). However, beyond this strain level, namely at ε = 4 (98%), the texture gets transformed to Bs-type with orientations maxima predominantly close to Goss ({110} <001>) position. Simultaneously, the Cu component which was dominant until 95% reduction has completely disappeared. The analysis of microstructures indicate that deformation is mostly accommodated by dislocation slip up to 95%, however, at ε > 3, Cu-type shear bands get initiated, preferably in the Cu-oriented ({112} <111>) grains. The sub-grains within the shear bands show preferred orientation towards Goss, which indicates that the Cu component should have undergone transformation and resulted in high fraction of Goss component. In Ni-60Co alloy, Bs-type texture forms in the early stages of deformation (ε ~ 0.5) itself and further deformation results in strengthening of the texture with an important difference that the maximum in orientation distribution has been observed at a location close to Goss component, rather than at exact Bs-location. The development of Bs-type texture is accompanied by the complete absence of Cu and S components. Extensive EBSD analyses show that the deformation twinning gets initiated beyond 10% reduction and was found extensively in most of the grains up to 50% reduction. At higher strains, tendency for twinning ceases and extensive shear banding is observed. A non-random distribution of orientations close to Goss orientation was found within the shear bands. The near-Goss component in the Ni-60Co alloy can be explained on the basis of deformation twinning and shear banding. Thus, a reasonable understanding of the deformation texture transition in the extreme SFE range has been developed. In chapter 4, the effect of fine grain size on the evolution of rolling texture has been addressed. Nanocrystalline (nc) nickel-cobalt alloys with a mean grain size of ~20 nm have been prepared by pulse electro-deposition method. For a comparison, nc Nickel (without cobalt) with similar grain size has also been deposited. For all the materials, a weakening of the initial fiber texture is observed in the early stage of room temperature rolling (ε ~ 0.22). A combination of equiaxed grain microstructure and texture weakening suggests grain boundary sliding as an operative mechanism in the early stage of rolling. At large strain (ε = 1.2), Ni-20Co develops a Cu-type texture with high fractions of S and Cu components, similar to pure Ni. The texture evolution in Ni-40Co and Ni-60Co alloys is more towards Bs-type. However, the texture maximum occurs at a location 10° away from the Goss. The evolution of Cu and S components in nc Ni-60Co alloy takes place simultaneously along with the α-fiber components during rolling. Microstructural investigation by TEM indicates deformation twinning to be more active in all the materials up to 40% reduction. However, no correlation could be drawn between the texture evolution and the density of twins. The deformation of nc Ni-20Co alloy, is also accompanied by significant grain growth at all the stages of rolling. The increase in grain size, subsequently, renders the texture to be of Cu-type. However, Ni-40Co and Ni-60Co alloys show high grain stability. The absence of strain heterogeneities such as shear bands, and the lack of significant fraction of deformation twins indicate that the observed Bs-type texture could be due to planar slip. The increase in deformation beyond 70% reduction caused a modest reduction in the intensity of deformation texture. The microstructural observation indicates the occurrence of restoration mechanisms such as recovery/ recrystallization at large strains. The overall findings of the investigation have been summarized in chapter 5. The deformation mechanism maps relating stacking fault energy with amount of strain and with grain size are proposed for micro- and nano- crystalline materials respectively.

Yes / This paper describes some underlying principles of multicomponent and high entropy alloys, and gives some examples of these materials. Different types of multicomponent alloy and different methods of accessing multicomponent phase space are discussed. The alloys were manufactured by conventional and high speed solidification techniques, and their macroscopic, microscopic and nanoscale structures were studied by optical, X-ray and electron microscope methods. They exhibit a variety of amorphous, quasicrystalline, dendritic and eutectic structures.

The emergence of Ultra-wideband (UWB) technology application has yielded tremendous and vital impacts in the field of microwave wireless communications. These applications include military radar imaging, security screening, and tumour detection, especially for early detection of breast cancer. These indicators have stimulated and inspired many researchers to make the best use of this promising technology. UWB technology challenges such as antenna design, the problem of imaging reconstruction techniques, challenges of severe signal attenuation and dispersion in high loss material. Others are lengthy computational time demand and large computer memory requirements are prevalent constraints that need to be tackled especially in a large scale and complex computational electromagnetic analysis. In this regard, it is necessary to find out recently developed optimisation techniques that can provide solutions to these problems. In this thesis, designing, optimisation, development, measurement, and analysis of UWB antennas for near-field microwave imaging applications are considered. This technology emulates the same concept of surface penetrating radar operating in various forms of the UWB spectrum. The initial design of UWB monopole antennas, including T-slots, rectangular slots, and hexagonal slots on a circular radiating patch, was explicitly implemented for medical imaging applications to cover the UWB frequency ranging from 3.1 GHz to 10.6 GHz. Based on this concept, a new bow-tie and Vivaldi UWB antennas were designed for a through-the-wall imaging application. The new antennas were designed to cover a spectrum on a lower frequency ranging from 1 GHz - 4 GHz to ease the high wall losses that will be encountered when using a higher frequency range and to guarantee deeper penetration of the electromagnetic wave. Finally, both simulated and calculated results of the designed, optimised antennas indicate excellent agreement with improved performance in terms of return loss, gain, radiation pattern, and fidelity over the entire UWB frequency. These breakthroughs provided reduced computational time and computer memory requirement for useful, efficient, reliable, and compact sensors for imaging applications, including security and breast cancer detection, thereby saving more lives. / Tertiary Education Trust Fund (TET Fund) Supported by the Nigerian Defence Academy (NDA)

The end of the Twentieth Century and the start of the Twenty First Century has been a tumultuous time for the Telecommunications Industry. Even as it moves forward to embrace the new technologies the Industry finds itself embroiled in issues of governance. The Industry finds itself in a dilemma since innovations increase at a rate faster than the laws can be changed and these render its existing laws and policies to be in some cases obsolete and inappropriate for the reality of the present. In the past, the United States of America has relied on vertically integrated top down laws and methods of regulating all the different parts in its Telecommunications Industry. These laws are contained in the different numbered Titles of this Countrys Legal Codes. Since the inception of these laws, emphasis was placed in creating and documenting policies structured by industry, sector and type of content. This form of regulation is usually referred to as the Silo Method. However, in recent years, especially in the regulation of the Telephony industry, the method of law and rule formulation moved from content regulation to one in which the technologies are getting regulated in what has been described as a Layers Method. This paper first considered whether the Silo Method of regulation is in actuality the same as using the Horizontal Layers method and showed that this is the case. Then it determined that Enhanced Services are the same as Basic Services and that Telecommunications Services are the same as Information services and showed that given that the pair sets as noted were the same, it went on to conclude that all these services were essentially the same. While studying to some detail the technologies of VoIP, the paper also showed that VoIP although an Internet technology is similar to traditional telephony, and is both a Telecommunications Service and Information Service based on the definition as given in the law as well as the technologies that are used and that as a result of this, the current regulatory environment for this service with regards to telephony is inconsistent. It concluded that Telecommunications policies though now adequate may need to be modified.

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