Theoretical development and characterisation of a Josephson Traveling Wave Parametric Amplifier for very low power microwave signals

L'abstract è presente nell'allegato / the abstract is in the attachmen

Ride Sharing with a Vehicle of Unlimited Capacity

A ride sharing problem is considered where we are given a graph, whose edges are equipped with a travel cost, plus a set of objects, each associated with a transportation request given by a pair of origin and destination nodes. A vehicle travels through the graph, carrying each object from its origin to its destination without any bound on the number of objects that can be simultaneously transported. The vehicle starts and terminates its ride at given nodes, and the goal is to compute a minimum-cost ride satisfying all requests. This ride sharing problem is shown to be tractable on paths by designing a O(h*log(h)+n) algorithm, with h being the number of distinct requests and with n being the number of nodes in the path. The algorithm is then used as a subroutine to efficiently solve instances defined over cycles, hence covering all graphs with maximum degree 2. This traces the frontier of tractability, since NP-hard instances are exhibited over trees whose maximum degree is 3

A coupled thermal and electrochemical study of lithium-ion battery cooled by paraffin/porous-graphite-matrix composite

Lithium-ion (Li-ion) battery cooling using a phase change material (PCM)/compressed expanded natural graphite (CENG) composite is investigated, for a cylindrical battery cell and for a battery module scale. An electrochemistry model (average model) is coupled to the thermal model, with the addition of a one-dimensional model for the solution and solid diffusion using the nodal network method. The analysis of the temperature distribution of the battery module scale has shown that a two-dimensional model is sufficient to describe the transient temperature rise. In consequence, a two-dimensional cell-centred finite volume code for unstructured meshes is developed with additions of the electrochemistry and phase change. This two-dimensional thermal model is used to investigate a new and usual battery module configurations cooled by PCM/CENG at different discharge rates. The comparison of both configurations with a constant source term and heat generation based on the electrochemistry model showed the superiority of the new design. In this study, comparisons between the predictions from different analytical and computational tools as well as open-source packages were carried out, and close agreements have been observed

Josephson diode effect in monolithic dc-SQUIDs based on 3D Dayem nanobridges

It was recently experimentally proved that the superconducting counterpart of a diode, i.e., a device that realizes nonreciprocal Cooper pairs transport, can be realized by breaking the spatial and time-reversal symmetry of a system simultaneously. Here we report the theory, fabrication, and operation of a monolithic dc superconducting quantum interference device (dc-SQUID) that embedding three-dimensional (3D) Dayem nanobridges as weak links realizes an efficient and magnetic flux-tunable supercurrent diode. The device is entirely realized in Al and achieves a maximum rectification efficiency of $\sim 20\%$, which stems from the high harmonic content of its current-to-phase relation only without the need of any sizable screening current caused by a finite loop inductance. Our interferometer can be easily integrated with state-of-the-art superconducting electronics, and since it does not require a finite loop inductance to provide large rectification its downsizing is not limited by the geometrical constraints of the superconducting ring

Two-Phase Depth-Integrated Model for Unsteady River Flow

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Graphene membrane as suspended mask for lithography

Thanks to its excellent mechanical properties, graphene is particularly suited for the realization of suspended membranes. The present paper deals with one possible application of such membranes that is the realization of suspended lithographic masks for shadow evaporation onto a substrate. This technique, which is largely used for realizing mesoscopic devices, where the quality requirements for the junctions prevent the exposure to ambient air and the occurrence of quantum phenomena requires highly defined structures, can be improved by the use of pure 2-dimensional masks, like graphene ones. Advantages and differences of this material with respect to commonly employed polymers are presented and discussed

Superconducting Josephson-Based Metamaterials for Quantum-Limited Parametric Amplification: A Review

In the last few years, several groups have proposed and developed their own platforms demonstrating quantum-limited linear parametric amplification, with evident applications in quantum information and computation, electrical and optical metrology, radio astronomy, and basic physics concerning axion detection. Here, we propose a short review on the physics behind parametric amplification via metamaterials composed by coplanar waveguides embedding several Josephson junctions. We present and compare different schemes that exploit the nonlinearity of the Josephson current-phase relation to mix the so-called signal, idler, and pump tones. The chapter then presents and compares three different theoretical models, developed in the last few years, to predict the dynamics of these nonlinear systems in the particular case of a 4-wave mixing process and under the degenerate undepleted pump assumption. We will demonstrate that, under the same assumption, all the results are comparable in terms of amplification of the output fields

Numerical and analytical modelling of battery thermal management using passive cooling systems

This thesis presents the battery thermal management systems (BTMS) modelling of Li-ions batteries and investigates the design and modelling of different passive cooling management solutions from single battery to module level. A simplified one-dimensional transient computational model of a prismatic lithium-ion battery cell is developed using thermal circuit approach in conjunction with the thermal model of the heat pipe. The proposed model is compared to an analytical solution based on variable separation as well as three-dimensional (3D) computational fluid dynamics (CFD) simulations. The three approaches, i.e. the 1D computational model, analytical solution, and 3D CFD simulations, yielded nearly identical results for the thermal behaviours. Therefore the 1D model is considered to be sufficient to predict the temperature distribution of lithium-ion battery thermal management using heat pipes. Moreover, a maximum temperature of 27.6ºC was predicted for the design of the heat pipe setup in a distributed configuration, while a maximum temperature of 51.5ºC was predicted when forced convection was applied to the same configuration. The higher surface contact of the heat pipes allows a better cooling management compared to forced convection cooling. Accordingly, heat pipes can be used to achieve effective thermal management of a battery pack with confined surface areas. In addition, the thermal management of a cylindrical battery cell by a phase change material (PCM) / compressed expanded natural graphite (CENG) is investigated. The transient thermal behaviour of both the battery and the PCM/CENG is described with a simplified onedimensional model taking into account the physical and phase change properties of the PCM/CENG composite. The 1D analytical/computational model predicted nearly identical results to the three-dimensional simulation results for various cooling strategies. Therefore, the 1D model is sufficient to describe the transient behaviour of the battery cooled by a PCM/CENG composite. Moreover, the maximum temperature reached by the PCM/CENG cooling strategy is much lower than that by the forced convection in the same configuration. In the test case studied, the PCM showed superior transient characteristics to forced convection cooling. The PCM cooling is able to maintain a lower maximum temperature during the melting process and to extend the transient time for temperature rise. Furthermore, the graphite-matrix bulk density is identified as an important parameter for optimising the PCM/CENG cooling strategy. Finally, the lithium-ion battery cooling using a passive cooling material (PCM) / compressed expanded natural graphite (CENG) composite is investigated for the battery module scale. An electrochemistry model (average model) is coupled to the thermal model, with the addition of a one-dimensional model for the solution and solid diffusion using the nodal network method. The analysis of the temperature distribution of the battery module scale has shown that a twodimensional model is sufficient to describe the transient temperature rise. In consequence, a two-dimensional cell-centred finite volume code for unstructured meshes is developed with additions of the electrochemistry and the phase change. This two-dimensional thermal model is used for investigating a new and usual battery module configurations cooled by PCM/CENG at different discharge rates. The comparison of both configurations with a constant source term and heat generation based on the electrochemistry model, showed the superiority of the new design. In this study, comparisons between the predictions from different analytical and computational tools as well as open-source packages were carried out, and close agreements have been observed

Modeling dam break granular flows

River morphodynamics and sediment transportMechanics of sediment transpor

A two-dimensional model of a solid-state regenerator based on combined electrocaloric-elastocaloric effect

Abstract Solid-state refrigeration technologies are considered nowadays emerging alternative to vapor compression refrigeration. In this paper is introduced a two-dimensional model of solid-state refrigerator, which employs materials experiencing a combined electrocaloric-elastocaloric effect and it operates at room temperature. A numerical investigation is performed to explore the energetic performance of the refrigerators. The results reveal that PbTiO 3 as elastocaloric refrigerant confers the best performances in terms of COP; the highest cooling power estimated are proper of combined elastocaloric-electrocaloric effect, with increments around +65% than employing PbTiO 3 in single electrocaloric/elastocaloric refrigeration, on equal operative conditions