Istituto Universitario Di Studi Superiori Di Pavia

About: Istituto Universitario Di Studi Superiori Di Pavia is a education organization based out in Pavia, Italy. It is known for research contribution in the topics: Pulsar & Neutron star. The organization has 162 authors who have published 566 publications receiving 22605 citations.

Efficient Probabilistic Tsunami Hazard and Risk Assessment Using a Hybrid Modeling Approach: A Systematic Evaluation

Abstract: The hybrid modelling approach combining machine learning and physics-based simulation has been used in a variety of ways to study tsunami and improve our understanding of this complex natural hazard. They are broadly applied for (1) Tsunami forecasting and early warning systems and (2) Tsunami hazard and risk assessment including sensitivity, analysis uncertainty studies and inverse modelling for estimating the source. Rigorous evaluation of such a hybrid approach is constrained by the limited size of available simulation datasets which is important to guide their usage by practitioners. This study investigates the application of a hybrid tsunami modelling technique (Ragu Ramalingam et al., 2022, Ragu Ramalingam et al., 2022) which offers a computationally efficient approach for hazard assessment where large events-sets must be modelled typical of probabilistic tsunami hazard and risk assessment (PTHA/PTRA). We use a large tsunami simulation dataset for a coastal region of eastern Sicily, Italy and try to address the following question:How to efficiently sample scenarios used to train the ML models? Where and when are such methods accurate?  How do they compare with other traditional modelling methods like Monte Carlo Sampling? Additionally, the effort will deliver an open tsunami benchmarking dataset that can be utilised for further development, baseline comparison of various ML algorithms, and improved hyperparameter tuning.ReferencesRagu Ramalingam, N., Johnson, K., Pagani, M., and Martina, M.: A hybrid ML-physical modelling approach for efficient approximation of tsunami waves at the coast for probabilistic tsunami hazard assessment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5642, https://doi.org/10.5194/egusphere-egu22-5642, 2022.Ragu Ramalingam, N., Rao, A., Johnson, K., Pagani, M. and Martina, M. A hybrid ML-physical modelling approach for efficient probabilistic tsunami hazard and risk assessment, Proceedings of the 19th Annual Meeting of the Asia Oceania Geosciences Society (AOGS 2022), August 1-5, 2022, Virtual.

VLT observations of the two Fermi pulsars PSR J1357-6429 and PSR J1048-5832

Abstract: Optical observations of pulsars are crucial to study the neutron star properties, from the structure and composition of the interior, to the properties and geometry of the magnetosphere Historically, X and gamma-ray observations have paved the way to the pulsar optical identifications The launch of Fermi opened new perspectives in the optical-to-gamma-ray studies of neutron stars, with the detection of more than 80 pulsars Here, we aim to search for optical emission from two Fermi pulsars which are interesting targets on the basis of their spin-down age, energetics, and distance: PSR J1357-6429and PSR J1048-5832 The two pulsars and their pulsar wind nebulae (PWNe) are also detected in X-rays by Chandra and XMM No deep optical observations of these two pulsars have been reported so far We used multi-band optical images (V,R,I) taken with the VLT and available in the European Southern Observatory (ESO) archive to search for, or put tight constraints to, their optical emission We re-assessed the positions of the two pulsars from the analyses of all the available Chandra observations and the comparison with the published radio coordinates For PSR J1357-6429, this yielded a tentative proper motion mu=017+/-0055 "/yr (70+/-15 deg position angle) We did not detect candidate counterparts to PSR J1357-6429 and PSR J1048-5832 down to V~27 and ~276, respectively, although for the former we found a possible evidence for a faint, unresolved object at the Chandra position Our limits imply an efficiency in converting spin-down power into optical luminosity <7x10^{-7} and <6x10^{-6}, respectively, possibly close to that of the Vela pulsar

Algebraic Aspects of Saddle Point Problems

Abstract: The examples of Chap. 1 clearly showed that several formulations typically lead to linear systems of the general form $$\displaystyle{ \left (\begin{array}{lll} &A\quad &{B}^{T} \\ &B\quad &0 \end{array} \right )\left (\begin{array}{l} \mathbf{x}\\ \mathbf{y} \end{array} \right ) = \left (\begin{array}{l} \mathbf{f}\\ \mathbf{g} \end{array} \right ), }$$ (3.0.1) where A and B are linear differential operators from some functional space to another (which often is its dual space).

Three-dimensional pathways of Saharan dust export over the North Atlantic during the CADDIWA field campaign

Abstract: Massive amounts of desert dust uplifted over the Sahara are exported over the North Atlantic. They play a major environmental role over this region, impacting the Earth radiative budget, atmospheric dynamics and thermodynamics, cloud properties, atmospheric composition, and biogeochemistry. These multiple impacts of Saharan dust can also affect the evolution of mesoscale convective systems (MCS) formed over West Africa that may lead to the formation of tropical cyclones over the North Atlantic. A better understanding of these aspects, also influenced by African Easterly waves, is the primary objective of the &#8220;Clouds-Atmospheric Dynamics-Dust Interactions in West Africa - CADDIWA &#8221; field experiment that took place on September 2021.&#160;&#160;The current presentation will provide a comprehensive description of the three-dimensional (3D) distribution of Saharan dust and its pathways of export over the North Atlantic during CADDIWA. This will be analysed with respect to the location and evolution of the MCS travelling over the region. This characterisation will be done using a suite of observations which will be compared with dust simulations. The objective is to analyse the difference in terms of abundance and 3D distribution of dust between the cases where MCSs lead to cyclogenesis and those not evolving that way.The ensemble of datasets describing the Saharan dust distribution will be inter-compared and their consistency verified. Twice-daily satellite thermal infrared hyperspectral measurements from IASI will be used to document the 3D distribution of desert dust for cloud-free conditions using the AEROIASI approach (Cuesta et al., 2015; 2020). Further details will be provided by nadir-pointing lidar measurements from AEOLUS and CALIOP space sensors, and from the RALI airborne instruments, in terms of transects of aerosol profiles and winds. In addition to aerosol backscatter profiles, AEOLUS and LNG-RALI will provide aerosol extinction profiles, provided their high spectral resolution capabilities. Observations from MODIS and VIIRS of aerosol optical depth will inform on the horizontal distribution of desert dust. Airborne in situ measurements of the size distribution and intensive optical properties of desert dust, such as the angstrom exponent, will be compared to those used as a priori properties of dust within the satellite dust retrievals (particularly for IASI). These satellite and airborne measurements will be confronted with simulations from the Meso-NH and WRF-CHIMERE, contributing with an all-sky and hourly 3D description.