1. The time evolution of the surface detector of the Pierre Auger ObservatoryOrazio Zapparrata, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, objavljeni znanstveni prispevek na konferenci Opis: The surface detector array of the Pierre Auger Observatory, consisting of 1660 water Cherenkov tanks, has been in operation for nearly 20 years. During this long period of data acquisition, ageing
effects in the detector response have been observed. The temporal evolution of the signals recorded by the surface detector is mostly compensated by continuous calibration with atmospheric muons;
however, effects persist in the signal rise time and in high-level data analysis using neural networks. We have implemented a detailed description of the time evolution of the detector response and of
the uptimes of individual stations in GEANT4-based detector simulations. These new simulations reproduce the observed time dependencies in the data. Using air-shower simulations that take
into account the evolution of individual stations, we show that the reconstructed energy is stable at the sub-percent level, and its resolution is affected by less than 5% in 15 years. For a few
specific stations, the collected light produced by muons has decreased to the point where it is difficult to distinguish it from the electromagnetic background in the calibration histograms. The
upgrade of the Observatory with scintillator detectors mitigates this problem: by requiring a coincidence between the water-Cherenkov and scintillator detectors, we can enhance the muon relative contribution to the calibration histogram. We present the impact and performance of this coincidence calibration method.
Ključne besede: surface detector, Pierre Auger Observatory, neural networks, air-shower simulations
Objavljeno v RUNG: 22.01.2024; Ogledov: 2173; Prenosov: 5
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2. Numerical simulations of nozzles with gas and liquid focusing for production of micro-jets : dissertationGrega Belšak, 2022, doktorska disertacija Ključne besede: numerical simulations, OpenFOAM, liquid sheets, micro-jets, multiphase flow, converging nozzles, double flow focusing nozzle, gas compressibility, vacuum conditions, atmospheric conditions, operational parameters, liquid properties, dissertations
Objavljeno v RUNG: 07.12.2022; Ogledov: 3364; Prenosov: 52
Celotno besedilo (21,26 MB) |
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4. Testing the predictions of axisymmetric distribution functions of galactic dark matter with hydrodynamical simulationsMihael Petač, Julien Lavalle, Arturo Núñez-Castiñeyra, Emmanuel Nezri, 2021, izvirni znanstveni članek Opis: Signal predictions for galactic dark matter (DM) searches often rely on assumptions regarding the DM phase-space distribution function (DF) in halos. This applies to both particle (e.g. p-wave suppressed or Sommerfeld-enhanced annihilation, scattering off atoms, etc.) and macroscopic DM candidates (e.g. microlensing of primordial black holes). As experiments and observations improve in precision, better assessing theoretical uncertainties becomes pressing in the prospect of deriving reliable constraints on DM candidates or trustworthy hints for detection. Most reliable predictions of DFs in halos are based on solving the steady-state collisionless Boltzmann equation (e.g. Eddington-like inversions, action-angle methods, etc.) consistently with observational constraints. One can do so starting from maximal symmetries and a minimal set of degrees of freedom, and then increasing complexity. Key issues are then whether adding complexity, which is computationally costy, improves predictions, and if so where to stop. Clues can be obtained by making predictions for zoomed-in hydrodynamical cosmological simulations in which one can access the true (coarse-grained) phase-space information. Here, we test an axisymmetric extension of the Eddington inversion to predict the full DM DF from its density profile and the total gravitational potential of the system. This permits to go beyond spherical symmetry, and is a priori well suited for spiral galaxies. We show that axisymmetry does not necessarily improve over spherical symmetry because the (observationally unconstrained) angular momentum of the DM halo is not generically aligned with the baryonic one. Theoretical errors are similar to those of the Eddington inversion though, at the 10-20% level for velocity-dependent predictions related to particle DM searches in spiral galaxies. We extensively describe the approach and comment on the results.
Ključne besede: galaxy dynamics, dark matter experiments, dark matter simulations, dark matter theory, cosmology, nongalactic astrophysics, astrophysics of galaxies, high energy physics
Objavljeno v RUNG: 01.10.2021; Ogledov: 3398; Prenosov: 69
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5. A structural, functional, and computational analysis suggests pore flexibility as the base for the poor selectivity of CNG channelsLuisa M. R. Napolitano, Ina Bisha, Matteo De March, Arin Marchesi, Manuel Arcangeletti, Nicola Demitri, Monica Mazzolini, Alex Rodriguez, Alessandra Magistrato, Silvia Onesti, 2015, izvirni znanstveni članek Ključne besede: CNG channels, pore flexibility, X-ray crystallography, MD simulations
Objavljeno v RUNG: 03.03.2021; Ogledov: 3454; Prenosov: 0
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9. Bora wind effects on common structures in the Vipava valleyMarija Bervida, 2020, doktorska disertacija Opis: Strong and gusty north-east wind called Bora is common in south-west regions of Slovenia, as well as along the Adriatic coast. Its intermittent behavior, related to variable strength, frequency and duration, has brought out scientific curiosity for decades. Bora affects human life and causes problems for structures built in Bora affected areas. In Slovenia, Bora is the strongest in the Vipava valley. The motivation for this research is the need to evaluate Bora wind effects on structures, commonly found in the Vipava valley region, using a high resolution computational fluid dynamics (CFD) modeling approach. To date, there are several experimental and computational constraints for accurate representation of Bora in a CFD model, therefore, the main aim of this dissertation is to build foundations for Bora wind simulations using CFD and its method of finite
volumes. The dissertation incorporates the analysis of experimental measurements of Bora wind, as well as numerical modeling studies.
Vertical mean wind speed profile characteristics of Bora were analyzed based on experimental measurements at Razdrto just above the Vipava valley. The obtained results contributed to the choice of Bora mean wind profiles applied at the inflow of computational models. Guidelines regarding the choice of the associated wind profile parameters were given and a new relationship between these parameters was found. As orographic barriers to the north of the Vipava valley
are known to give rise to Bora and to define the specific properties of the Bora flow, numerical modeling studies were in the first place focused on the implementation of the real-scale complex terrain into a CFD model. Simulation of wind flow over orographic barrier in Vipava valley was performed using Raynolds averaged Navier-Stokes approach, providing a first estimation of the flow field over a small hill of
Zemono.
As resolving the turbulence characteristics of Bora is very important for the estimation of wind loads on structures, modeling studies converged towards a more appropriate approach - Large eddy simulations (LES). A crucial step in setting up an accurate LES is the generation of appropriate inflow, which was investigated for the case of atmospheric boundary layer (ABL) flow. The synthetic method PRFG^3 for the generation of unsteady inflow was tested and adapted as a source of an ABL flow with desired turbulence flow properties. Based on its performance, in particular on adequate reproduction of target turbulence intensities and length scales, it was found that PRFG^3 method may be used to generate velocity inflow with desired turbulence properties in LES. Finally, simulations of wind flow coming from Bora direction over the Vipava valley were performed with the aim to depict the effects of underlying orography on the flow within and above the valley. Modeling results were found to be comparable with the results of lidar based remote sensing of vertical atmospheric structures within and above the valley.
Ključne besede: Vipava valley, Bora wind, Wind profile, Orography, Atmospheric boundary layer, Computational fluid dynamics, Numerical simulations
Objavljeno v RUNG: 17.06.2020; Ogledov: 8654; Prenosov: 69
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10. The ARCADE Raman Lidar and atmospheric simulations for the Cherenkov Telescope ArrayL. Valore, Christopher Eckner, Gašper Kukec Mezek, Samo Stanič, Serguei Vorobiov, Lili Yang, Gabrijela Zaharijas, Danilo Zavrtanik, Marko Zavrtanik, 2017, objavljeni znanstveni prispevek na konferenci Ključne besede: ARCADE Raman Lidar, CTA, atmospheric simulations
Objavljeno v RUNG: 16.02.2018; Ogledov: 4766; Prenosov: 152
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