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Multilayered plate elements with node-dependent kinematics for electro-mechanical problems
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Superconductivity on the Verge of a Pressure-Induced Lifshitz Transition in CaFe2As2: an Interpretation Within the Eliashberg Theory
No full textIn a recent paper, we presented the first directional point-contact Andreev reflection spectroscopy (PCARS) measurements on CaFe2As2 crystals under quasi-hydrostatic pressure and discussed the pressure dependence of the gaps and the critical temperature. While Tc exhibits a well-known smooth dependence and a broad maximum at about 0.6 GPa, both gaps increase very sharply in a small pressure range between 0.5 and 0.6 GPa, leading to a doubling of the ratio 2D2/kBTc and a quadruplication of the ratio 2D1/kBTc, D1 and D2 being the small and large gap, respectively. This peculiar behavior is likely to be related to a sharp change in the lattice structure that, in turn, produces a 2D-3D topological transition in the hole-like Fermi surface sheet. In this work, we show that, within an effective three-band Eliashberg theory for the electron-spin fluctuation coupling (s± symmetry), these results can be rationalized as being due to a large increase of the electron-boson coupling, which mimics the effects of a boost mechanism for the coupling related to the underlying Lifshitz transition
Energy Systems Integration: from building scale to urban scale
No full textThe research activity presented in this thesis focuses on the heating energy demand assessment of a small urban district with buildings connected to the local District Heating Network (DHN). The main goal of the work consisted in determining effective actions that could be applied on both the heating system and on the envelope of five case study buildings in order to reduce the morning peak of the heating system and reduce also the overall energy demand for space heating. The outcomes of this research may be useful to assess the impact of the proposed improvements on the operation of a urban district heating network. A further goal of the work carried out was to develop an Artificial Neural Network useful to forecast, at short term, the indoor temperature of rooms once the weather conditions and the thermal energy supplied by the District Heating Network are known
Development and assessment of a solar home system to cover cooking and lighting needs in developing regions as a better alternative for existing practices
No full textAn estimated 1.2 billion people around the world don't have access to electricity, while many more suffer from supply that is of poor quality. Domestic energy poverty is most severe in the rural areas of South Asia, South East Asia and Sub-Saharan Africa. Basic energy needs, such as cooking and lighting, are covered using traditional biomass and fossil fuels. These are consumed inefficiently in fire stoves and flame lamps. This situation hampers economic growth and social development and implies severe stress on resources and the environment. Photovoltaics could play a major role in overcoming domestic energy poverty, especially as most of the affected regions are within the Earth's Sunbelt. This paper provides such a solution in the form of a solar home system with lithium-ion battery in combination with an energy efficient multicooker and LED lamps to cover the needs for cooking and lighting for one family. A solar home system layout is provided and assessed in terms of its cost and benefits in contrast with the existing practices for cooking and lighting in developing regions. Thereby, evolutionary aspects are taken into account to capture the incremental cost advantage of the solar home system technology over time, and with that support the idea of projecting large-scale implementation in developing regions
A numerical study on backfilling of the tail void with two-component grout based on laboratory tests
No full textIn mechanized tunneling the annular gap between the segmental lining and the surrounding soil caused by tunnel driving must be backfilled instantaneously with an adequate mortar. The annular gap is caused due to the conical shape, overcut and design of the shield. The soft ground tunneling has a prime focus on the settlement control and optimization of the parameters involved. The backfilling is a key component to reduce the surface settlements and deformations after the passage of the TBM. The main functions of backfilling are to 1. lock the segmental lining in position avoiding movements due to self-weight of the lining and other forces present; 2. To bear the loads transmitted by TBM backup weight; 3. Provide a uniform contact between the lining and surrounding soil and 4. Waterproofing the tunnel. Recent developments in the field of backfilling have led to the development of a state-of-the-art two-component grouting system. A two-component grout consists of two components, Component A (Bentonite, water, cement and a retarder), component B (Sodium silicate based accelerator and water). When these two components are mixed just behind the annular gap, the grout starts to attain plasticity in a very quick time and thus, is able to transfer the load to the segmental lining in a very short time after its injection to the annular gap. For a good backfilling grout it is important to satisfy certain engineering aspects (Fluidity, binding and gelling time, mechanical strength). The aim of this research is to understand the behavior of a two component grout in its fresh and hardened state and implement those obtained parameters in a numerical code. A series of laboratory tests are to perform on the two-component grout to determine its physical and mechanical behaviour. Bleeding, Marsh cone and gelling time tests are conducted on the fresh grout sample to test its chemical binding, viscosity and time taken to achieve plastic strain. A series of uniaxial compressive strength (UCS) tests are conducted on the grout sample to obtain its elastic modulus in its early days of setting (up to 28 days). In order to obtain and examine the state and strength of the grout in long term, a string of UCS tests are carried out on two-component grout samples cured at natural humidity of the soil in long terms (up to 1080 days). In addition to this, permeability and dewatering properties of a two-component are determined in its early state. Furthermore, the stiffness of the hardened grout sample in confined condition is determined by conducting oedometer tests. The oedeometer tests are conducted at various time intervals to obtain a complete time-dependent stiffness of the grout. The research deals with the development of a robust numerical model taking into account all the relevant factors involved in mechanized tunnelling but focusing mainly on the backfilling procedure using FDM software FLAC 3D. The backfilling in the tail grout is modeled as normally applied pressure in a liquid state and later a time-dependent hardening behavior of the grout is initiated. The time-dependent behavior parameters are obtained from the laboratory tests conducted. A new constitutive model (CM) named as Plastic-Hardening (PH) is implemented to model the behavior of the surrounding soil. This CM gives the user a freedom to implement different stiffness for loading and unloading. Since the Mohr-Coulomb (MC) model specifies only one elastic modulus for both loading and unloading, it is unsuitable for cyclic and staged excavation procedures such as mechanized tunnelling itself. The PH CM is validated with the FEM software PLAXIS 3D before implementing it in FLAC 3D. Moreover, Hydro-mechanical coupled analysis is also conducted in the near-field domain of the grouting zones to update the permeability and stiffness of the grout due to consolidation
New techniques for functional testing of microprocessor based systems
No full textElectronic devices may be affected by failures, for example due to physical defects. These defects may be introduced during the manufacturing process, as well as during the normal operating life of the device due to aging. How to detect all these defects is not a trivial task, especially in complex systems such as processor cores. Nevertheless, safety-critical applications do not tolerate failures, this is the reason why testing such devices is needed so to guarantee a correct behavior at any time. Moreover, testing is a key parameter for assessing the quality of a manufactured product. Consolidated testing techniques are based on special Design for Testability (DfT) features added in the original design to facilitate test effectiveness. Design, integration, and usage of the available DfT for testing purposes are fully supported by commercial EDA tools, hence approaches based on DfT are the standard solutions adopted by silicon vendors for testing their devices. Tests exploiting the available DfT such as scan-chains manipulate the internal state of the system, differently to the normal functional mode, passing through unreachable configurations. Alternative solutions that do not violate such functional mode are defined as functional tests. In microprocessor based systems, functional testing techniques include software-based self-test (SBST), i.e., a piece of software (referred to as test program) which is uploaded in the system available memory and executed, with the purpose of exciting a specific part of the system and observing the effects of possible defects affecting it. SBST has been widely-studies by the research community for years, but its adoption by the industry is quite recent. My research activities have been mainly focused on the industrial perspective of SBST. The problem of providing an effective development flow and guidelines for integrating SBST in the available operating systems have been tackled and results have been provided on microprocessor based systems for the automotive domain. Remarkably, new algorithms have been also introduced with respect to state-of-the-art approaches, which can be systematically implemented to enrich SBST suites of test programs for modern microprocessor based systems. The proposed development flow and algorithms are being currently employed in real electronic control units for automotive products. Moreover, a special hardware infrastructure purposely embedded in modern devices for interconnecting the numerous on-board instruments has been interest of my research as well. This solution is known as reconfigurable scan networks (RSNs) and its practical adoption is growing fast as new standards have been created. Test and diagnosis methodologies have been proposed targeting specific RSN features, aimed at checking whether the reconfigurability of such networks has not been corrupted by defects and, in this case, at identifying the defective elements of the network. The contribution of my work in this field has also been included in the first suite of public-domain benchmark networks
EPOXY COUPLING AGENT FOR PLA OR P3HB-3HH-BASED COTTON FABRIC FILM-STACKED COMPOSITES
No full textBio-composites consisting of poly(lactic acid) or Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) matrix were film stacked with cotton twill fabric in multi layer configuration. The flexural properties of these bio-composites were comparable to the ones of particle boards or engineering woods with the advantage to be easily shaped including hollow sections to achieve lightweight structures. The addition of the additive with epoxy reactive sites resulted in the best mechanical properties in PLA but the best increases in the PHB matrix. Furthermore, DMT analyses have showed that the cotton fabric composites caused a consistent increase in the HDT-A in the PHB matrix. The J additive further increased HDT-A of the neat PHB from 70 to 123 °C. Finally, the impact test of PLA and PHB composites reached impact strengths comparable to composites used in automotive applications with a key role exert by the J additive. The J additive probably generated new chemical bonds in the composites between cotton and the polymer and/or between polymer chains. The studied bio-composites are recognized for use in applications such as building, furniture or automotive bringing additional sustainability, recycling and biodegradation properties not owned by common composites