Boiling Liquid Expanding Vapor Explosion of liquid hydrogen

This thesis focuses on the modelling of liquid hydrogen Boiling Liquid Expanding Vapor Explosions (BLEVEs). This terminology identifies a catastrophic release of this unconventional fuel following the loss of its containment. The present work aims to enhance the knowledge on the consequences of such explosions, using the data collected from crucial experiments to validate the simulations. The consequence analysis of the "SH2IFT Project" and the ”Bursting Tank Scenario” experimental BLEVEs is carried out simulating the explosions to verify the reliability of the implemented physical models. To complete the modeling of the catastrophic rupture of liquid hydrogen (LH2) tanks, the combustion process is taken into account to describe the aftermath of the simulated accidents in terms of overpressure and impulse. Furthermore, it is also discussed the possible involvement of the endothermic reaction of the hydrogen para-isomer converting into its ortho-isomer form. In this way, a further validation and confrontation between the models currently used for conventional liquid fuels like propane and liquefied petroleum gas (LPG) is possible, adopting and adapting them to the specific case of a liquid hydrogen catastrophic release. So, it is possible to consider this thesis as divided in three major steps: the first one is the analysis of the physical explosions with the proposed models, the second one is the adaptation of such models to take hydrogen combustion into consideration and the third and last one is an analysis of the para-ortho reaction which may follow the explosion. At the end, a confrontation between the experimental data and the proposed calculations is carried out, underlining the aspects which still require further studies, experiments and documentation

Search for high mass resonances decaying to Higgs pairs in the bbbb final state with the CMS experiment at the LHC

The discovery of the Higgs boson at the LHC in 2012 represents a major step in our understanding of fundamental interactions. Moreover, the newly-discovered particle can be seen as a promising "tool" to look for new phenomena. Specifically, this thesis focuses on high mass resonances decaying to Higgs pairs. The search presented in this thesis aims to be as much as possible model inde- pendent. Nevertheless, the results can be interpreted within several New Physics models. Among those, two possible scenarios are the Randall-Sundrum Radion and massive KK-Graviton productions in Warped Extra Dimensions. Other well motivated scenarios featuring a heavy CP-even scalar decaying to Higgs pairs are the Next-to-Minimal Supersymmetric Standard Model and the Twin Higgs model. The analysis target is a narrow di-Higgs resonance with both Higgs bosons decaying to b quarks, in the highest possible mass range detectable at the LHC (above ∼ 1 TeV). Despite the large QCD multi-jet background, the b ̄ bb ̄ b final state has showed the best sensitivity overall for resonance masses 400 GeV in the LHC Run1 searches, but no evidence of signal. A high mass resonance is expected to produce two energetic Higgs bosons, so that the b quarks produced from their decay are collimated along the direction of motion. As a consequence, the hadronization products of a pair of narrowly separated b quarks can be reconstructed as a single large jet. Boosted Higgs bosons decaying to b-quark pairs can be distinguished from the QCD multi-jet background exploiting the jet substructure and through a dedicated b-tagging algorithm. The transition region between the aforementioned boosted topology and the resolved topology, where four unmerged b-jets are reconstructed, has been studied for the first time in this thesis and it is addressed matching one large Higgs jet to a pair of unmerged b-jets. The analysis has been carried out on 2.7/fb of proton-proton collision data recorded by the CMS experiment at the LHC at a center of mass energy of 13 TeV during 2015. The benchmark signal process used to design the analysis strategy is the spin-2 Bulk Graviton with negligible natural width. A data-driven estimation of the background, which minimizes systematic uncertainties that might arise from poorly-understood QCD multi-jet backgrounds in the simulation, has been employed. As no signal evidence has been detected, upper limits on the production cross section of the benchmark resonance in the mass range 600-3000 GeV are presented. The event reconstruction addressing the transition region has been found to improve the sensitivity of ∼15-20%

Fragments Generated During Liquid Hydrogen Tank Explosions

Liquid hydrogen (LH2) may be employed to transport large quantities of pure hydrogen or be stored onboard of ships, airplanes and trains fuelled by hydrogen, thanks to its high density compared to gaseous compressed hydrogen. LH2 is a cryogenic fluid with an extremely low boiling point (-253°C at atmospheric pressure) that must be stored in double-walled vacuum insulated tanks to limit the boil-off formation. There is limited knowledge on the consequences of LH2 tanks catastrophic rupture. In fact, the yield of the consequences of an LH2 tank explosion (pressure wave, fragments and fireball) depend on many parameters such as tank dimension, filling degree, and tank internal conditions (temperature and pressure) prior the rupture. Only two accidents provoked by the rupture of an LH2 tank occurred in the past and a couple of experimental campaigns focussed on this type of accident scenario were carried out for LH2. The aim of this study is to analyse one of the LH2 tank explosion consequences namely the fragments. The longest horizontal and vertical ranges of the fragments thrown away from the blast wave are estimated together with the spatial distribution around the tank. Theoretical models are adopted in this work and validated with the experimental results. The proposed models can aid the risk analysis of LH2 storage technologies and provide critical insights to plan a prevention and mitigation strategy and improve the safety of hydrogen applications

Modelling of Fireballs Generated After the Catastrophic Rupture of Hydrogen Tanks

The interest towards hydrogen skyrocketed in the last years. Thanks to its potential as an energy carrier, hydrogen will be soon handled in public and densely populated areas. Therefore, accurate models are necessary to predict the consequences of unwanted scenarios. These new models should be employed in the consequence analysis, a phase of risk assessment, and thus aid the selection, implementation, and optimization of effective risk-reducing measures. This will increase safety of hydrogen technologies and therefore favour their deployment on a larger scale. Hydrogen is known to be an extremely flammable gas with a low radiation flame compared to hydrocarbons. However, luminous fireballs were generated after the rupture of both compressed gaseous and liquid hydrogen tanks in many experiments. Moreover, it was demonstrated that conventional empirical correlations, initially developed for hydrocarbon fuels, underestimate both dimension and duration of hydrogen fireballs recorded during small-scale tests (Ustolin and Paltrinieri, 2020). The aim of this study is to obtain an analysis of hydrogen fireballs to provide new critical insights for consequence analysis. A comparison among different correlations is conducted when predicting fireball characteristics during the simulation of past experiments where both gaseous and liquid hydrogen tanks were intentionally destroyed. All the models employed in this study are compared with the experimental results for validation purposes. Specific models designed for hydrogen can support the design of hydrogen systems and increasing their safety and promote their future distribution

How resistant are levodopa-resistant axial symptoms? Response of freezing, posture and voice to increasing levodopa intestinal infusion rates in Parkinson's disease

Treatment of freezing of gait (FoG) and other Parkinson's disease (PD) axial symptoms is challenging. Systematic assessments of axial symptoms at progressively increasing levodopa doses are lacking. We sought to analyze the resistance to high levodopa doses of FoG, posture, speech, and altered gait features presenting in daily-ON therapeutic condition

Novel 3D Pixel Sensors for the Upgrade of the ATLAS Inner Tracker

The ATLAS experiment will undergo a full replacement of its inner detector to face the challenges posed by the High Luminosity upgrade of the Large Hadron Collider (HL-LHC). The new Inner Tracker (ITk) will have to deal with extreme particle fluences. Due to its superior radiation hardness the 3D silicon sensor technology has been chosen to instrument the innermost pixel layer of ITk, which is the most exposed to radiation damage. Three foundries (CNM, FBK, and SINTEF), have developed and fabricated novel 3D pixel sensors to meet the specifications of the new ITk pixel detector. These are produced in a single-side technology on either Silicon On Insulator (SOI) or Silicon on Silicon (Si-on-Si) bonded wafers by etching both n- and p-type columns from the same side. With respect to previous generations of 3D sensors they feature thinner active substrates and smaller pixel cells of 50 × 50 and 25 × 100 µm2. This paper reviews the main design and technological issues of these novel 3D sensors, and presents their characterization before and after exposure to large radiation doses close to the one expected for the innermost layer of ITk. The performance of pixel modules, where the sensors are interconnected to the recently developed RD53A chip prototype for HL-LHC, has been investigated in the laboratory and at beam tests. The results of these measurements demonstrate the excellent radiation hardness of this new generation of 3D pixel sensors that enabled the project to proceed with the pre-production for the ITk tracker.publishedVersio