LTE Baseband Algorithms for Uplink

LTE is a next generation mobile system from the 3GPP with a focus on wireless broadband.The aim of LTE is to achieve high data rates in both uplink & downlink, and to achieve high spectral efficiencies.The main focus of the work is to develop baseband algorithms in the uplink in order to achieve uplinksynchronization between the user and the base station and also for the detection of the control data that is transmitted. For the base station to obtain the knowledge of the presence of the user and also about its position, the user has to transmit synchronization signals to the base station, which are transmitted on the Physical Random Access CHannel (PRACH) in LTE. These signals are used to obtain the uplink timing correction and hence synchronize with the base station. It is very important for the base station to detect the control data that has been transmitted by the user on Physical Uplink Control CHannel (PUCCH). The control data may consist of the response of the UE to the data packets that were transmitted by the base station, request for resource allocation etc.So efficient algorithms are necessary for the accurate detection of the control data at the base station. The current work presents algorithms that are essential for obtaining uplink synchronization and also for efficient detection of the control channel data

Guidance for Materials 4.0 to interact with a digital twin

The rapid development of new infrastructure programmes requires an accelerated deployment of new materials in new environments. Materials 4.0 is crucial to achieve these goals. The application of digital to the field of materials has been at the forefront of research for many years, but there does not exist a unified means to describe a framework for this area creating pockets of development. This is confounded by the broader expectations of a digital twin (DT) as the possible answer to all these problems. The issue being that there is no accepted definition of a component DT, and what information it should contain and how it can be implemented across the product lifecycle exist. Within this position paper, a clear distinction is made between the “manufacturing DT” and the “component DT”; the former being the starting boundary conditions of the latter. In order to achieve this, we also discuss the introduction of a digital thread as a key concept in passing data through manufacturing and into service. The stages of how to define a framework around the development of DTs from a materials perspective is given, which acknowledges the difference between creating new understanding within academia and the application of this knowledge on a per-component basis in industry. A number of challenges are identified to the broad application of a component DT; all lead to uncertainty in properties and locations, resolving these requires judgments to be made in the provision of safety-dependent materials property data

Twin nucleation and variant selection in Mg alloys: An integrated crystal plasticity modelling and experimental approach

Extension twin nucleation and variant selection in magnesium alloy WE43 is investigated in experimentally characterised and deformed microstructures replicated in crystal plasticity models. Total stored (dislocation) energy density is found to identify the experimentally observed locations of twins which are not otherwise explained by global Schmid factors or local resolved shear stress criteria. A critical total stored energy of the order 0.015 Jm-2 is determined below which twin nucleation does not occur. The total stored energy density explains the locations of the observed twins and the absence of twins in parent grains anticipated to be favourable for twin nucleation. Twin variant selection has been shown to be driven by minimising locally stored shear energy density, while the geometric compatibility and strain compatibility factors only aid in partial prediction. All experimentally observed variants were correctly determined

Micromechanics of twin nucleation and growth in magnesium alloys

This thesis presents an integrated experimental and computational study that investigates the mechanistic drivers of twin nucleation, variant selection and twin growth in magnesium alloys. The analyses investigate microstructure sensitivity of twin nucleation in both 2D free surfaces and full 3D microstructures, while twin growth is extensively studied in pseudo-3D microstructures. It is shown that the total stored (dislocation) energy density identifies the experimentally observed locations of both classical (favourably oriented parent grains) and non-classical (unfavourable parent grains) twins. In both the cases, a critical total stored energy density of the order 0.015 Jm-2 is determined below which twin nucleation does not occur. In the case of classical twins, the local twin resolved shear stresses drive the variant selection, while it is the local shear stored energy density (that stored within the twin embryo) in the case of non-classical twins. Once these twins propagate, it is shown that the local deformation characteristics that govern their subsequent growth are influenced mainly by their crystallographic orientations. The experimental observations indicate that the intra-twin geometrically necessary dislocations (GND) density and twin-resolved shear stress (TRSS) differences within twin vary with twin crystallographic orientation, which is characterised in terms of inclination angle (that between the loading direction and twin c-axis). Further, model predictions, where the twin transformation is considered as a sequential process of reorientation followed by shear, and experimental measurements show that intra-twin average GND density increases with inclination angle, and that a reversal in the sign of intra-twin TRSS occurs as the inclination angle increases. This implies that the TRSS (backstress) within a twin is not always negative, which further suggests that the rate of twin growth is influenced by its own crystallographic orientation instead of global Schmid factor (which is based on parent grain orientation).Open Acces

Solidification cracking resistance of high strength aluminum alloys

In Direct chill (DC) casting which is used in the manufacture of high strength aluminum alloys uneven cooling rates at different parts of the ingot cause thermal stresses. Due to these thermal stresses, cracks are initiated at the startup stage which may propagate as the stress elevates. Hence the evaluation of fracture toughness (cracking resistance) at different parts of ingot is very much essential to understand the propagation of cracks in ingots.;The objective of this research was to determine the cracking resistance of Al 2024 (Al-Cu-Mg) and Al 3004 (Al-Mn-Mg) alloys and to illustrate the relation of cooling rate during solidification and alloy composition on the cracking resistance of these alloys. The specimens were obtained from ALCOA and were first precracked and the cracking resistance was determined by quench cracking tests which simulated the propagation of cracks under thermal stresses. The software for these tests was developed at West Virginia University. They were performed on specimens obtained from different locations of directionally solidified ingots that exhibited different solidification rates along their length. The solidification rates were similar to the range of real time cast ingots. After the tests microstructures and fractured surfaces of the specimens were examined by optical microscope, SEM and HISCOPE.;The cracking resistance was observed to increase with the solidification rate (which decreases from surface to center in a real time cast DC ingot) for both the alloys and for a given solidification rate the cracking resistance of 3004 was found to be higher than 2024. The above variations were successfully explained based on the microstructural observation and fracture surfaces of the alloys and the effect of alloy composition and solidification rate on cracking resistance was successfully illustrated

Void Nucleation and Growth from Heterophases and the Exploitation of New Toughening Mechanisms in Metals

Heterophases, such as precipitates, inclusions, second phases, or reinforcement particles, often drive void nucleation due to local incompatibilities in stresses/strains. This results in a significant life-limiting condition, as voids or their coalescence can lead to microcracks that reduce the ductility and fatigue life of engineering components. Continuum-mechanics-based analytical models have historically gained momentum due to their relative ease in predicting failure strain. The momentum of such treatment has far outpaced the development of theories at the atomic and micron scales, resulting in an insufficient understanding of the physical processes of void nucleation and growth. Evidence from the recent developments in void growth theories indicates that the evolution of voids is intrinsically linked to dislocation activity at the void–matrix interface. This physical growth mechanism opens up a new methodology for improving mechanical properties using hydrostatic pressurization. According to the limited literature, with a hydrostatic pressure close to 1 GPa, aluminium matrix composites can be made 70 times more ductile. This significant ductility enhancement arises from the formation of dislocation shells that encapsulate the heterophases and inhibit the void growth and coalescence. With further investigations into the underlying theories and developments of methods for industrial implementations, hydrostatic pressurization has the potential to evolve into an effective new method for improving the ductility and fatigue life of engineering components with further development

Extending the capability of component digital threads using material passports

Nuclear and aerospace applications are critical to safety that demand quality metallic components. The cost of failure in these components far exceed that of repair or replacement. Thus, it is necessary to track the evolution of material properties at critical locations of the component geometry during manufacturing and in-service to avoid premature failures. The digital thread/twin (DTh/DT) paradigm shows promise for its ability to interact with components by monitoring their production. This capability of the DTh can be further extended by generating component specific unique identification document called material passport (MP). In addition to storing the manufacturing history and inspection records, the MP can be used to indicate remaining useful life estimations to guide component recyclability/reusability. The structure of the DTh and the corresponding MP depends on several factors. This article presents an overview of the nature of DThs/DTs for manufacturing based on the lengthscale of material property definitions employed in respective computational framework and the type of material purchase specification system implemented in the industry. Then, the possible structure, significance and challenges of realizing MPs that enable predictive maintenance and circular economy are discussed. The preliminary discussions indicate that the implementation of component specific DThs encompassing all the stages of manufacturing in conjunction with the generation of summary and detailed MPs at every stage improves data storage and accessibility within MPs and predictive maintenance capabilities of DThs. Finally, the landscape of standards used in MPs and DThs is addressed briefly