A Pressure-Based Model for Two-Phase Flows Under Generic Equations of State

We present a diffuse interface method for a pressure-based Baer-Nunziato type model for compressible two-phase flows, which allows the use of generic equations of state to describe each phase. The model is made dimensionless by means of a special pressure scaling that recovers the correct scaling of the discrete governing equations in the zero Mach limit, and overcomes the difficulties related to the lack of a clear notion of reference speed of sound in non-equilibrium two-phase flows. The model is equipped with pressure and velocity relaxation terms to impose the mechanical equilibrium between phases after their independent evolution. Two different finite volume schemes are presented. First, a 1D semi-implicit staggered scheme is introduced to show the capability of the model to work with the Peng-Robinson EOS when each phase evolves close to the saturation curve. Then, a preliminary 2D explicit scheme, which does not include the relaxation terms, is presented as a first step toward the development of an unstructured 2D scheme for compressible two-phase flows at all Mach numbers. The validity of the preliminary 2D monolithic implementation of the hyperbolic operator is illustrated through the simulation of a shock-bubble interaction with air and helium. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG

Local seismic response studies in the north-western portion of the August 24th, 2016 Mw 6.0 earthquake affected area. The case of Visso village (Central Apennines).

In this work, we investigate the possible causes of the differential damaging observed in Visso village (Central Apennines, about 28 km north from the August 24th, 2016 Mw 6.0 earthquake epicenter). Following insights from the available geological cartography at 1:10.000 scale, a preliminary geophysical survey has been performed in the damaged area in order to constrain geometries and extent of the subsoil lithotypes. Then, these results have been used to retrieve a Vs profile close to the most heavily damaged buildings. This latter has been used as input for a numerical analysis aimed at deriving the motion at the ground level in the study area. In particular, a linear equivalent simulation has been performed by means of EERA code and the waveform has been obtained convolving the time history recorded during the August 24th, 2016 mainshock at Spoleto Monteluco (SPM) site. Our preliminary results indicate a possible correlation of damaging to the thickness and shape of the geological units. Nevertheless, further analyses are necessary to highlight any 2D basin and / non- linear soil behaviour effects in order to compare them to the intrinsic buildings vulnerability, according to the EMS98 guidelines

Poly-Dispersed Eulerian-Lagrangian Particle Tracking for In-Flight Icing Applications

The objective of this work is to present a three-dimensional Euler-Euler finite volume poly-dispersed (multi-bin) droplet tracker for in-flight icing purposes, with an additional Lagrangian re-injection step. This step has been added to increase the accuracy of the collection efficiency prediction in multi-element 2D and 3D cases where splashed and rebounding droplets re-impinge on aft surfaces, particularly in SLD conditions. Results show local increases in accuracy of up to 4% in a 3D single element case and up to 100% on flaps in 2D multi-element airfoil cases. The Lagrangian re-impingement correction improves significantly when using multi-bin, while also being more efficient than the standard approaches. Lastly, a simple bin to bin initialization strategy allows for up to 65% less computational time in the Eulerian droplet tracking step when running multi-bin simulations

Touch Versus Tech: When Technology Functions as a Barrier or a Benefit to Service Encounters

Interpersonal exchanges between customers and frontline service employees increasingly involve the use of technology, such as point-of-sale terminals, tablets, and kiosks. The present research draws on role and script theories to demonstrate that customer reactions to technology-infused service exchanges depend on the presence of employee rapport. When rapport is present during the exchange, the use of technology functions as an interpersonal barrier preventing the customer from responding in kind to employee rapport-building efforts, thereby decreasing service encounter evaluations. However, during service encounters in which employees are not engaging in rapport building, technology functions as an interpersonal barrier, enabling customers to retreat from the relatively unpleasant service interaction, thereby increasing service encounter evaluations. Two analyses using J.D. Power Guest Satisfaction Index data support the barrier and beneficial effects of technology use during service encounters with and without rapport, respectively. A follow-up experiment replicates this data pattern and identifies psychological discomfort as a key process that governs the effect. For managers, the results demonstrate the inherent incompatibility of initiatives designed to encourage employee–customer rapport with those that introduce technology into frontline service exchanges

Star formation history in the SMC: the case of NGC602

Deep HST/ACS photometry of the young cluster NGC 602, located in the remote low density "wing" of the Small Magellanic Cloud, reveals numerous pre-main sequence stars as well as young stars on the main sequence. The resolved stellar content thus provides a basis for studying the star formation history into recent times and constraining several stellar population properties, such as the present day mass function, the initial mass function and the binary fraction. To better characterize the pre-main sequence population, we present a new set of model stellar evolutionary tracks for this evolutionary phase with metallicity appropriate for the Small Magellanic Cloud (Z = 0.004). We use a stellar population synthesis code, which takes into account a full range of stellar evolution phases to derive our best estimate for the star formation history in the region by comparing observed and synthetic color-magnitude diagrams. The derived present day mass function for NGC 602 is consistent with that resulting from the synthetic diagrams. The star formation rate in the region has increased with time on a scale of tens of Myr, reaching $0.3-0.7 \times 10^{-3} M_\odot yr^{-1}$ in the last 2.5 Myr, comparable to what is found in Galactic OB associations. Star formation is most complete in the main cluster but continues at moderate levels in the gas-rich periphery of the nebula.Comment: 24 pages. Accepted for publication in A

I Zw 18 revisited with HST/ACS and Cepheids: New Distance and Age

We present new V and I-band HST/ACS photometry of I Zw 18, the most metal-poor blue compact dwarf (BCD) galaxy in the nearby universe. It has been argued in the past that I Zw 18 is a very young system that started forming stars only 1 Gyr) red giant branch (RGB) stars may also exist. Our new data, once combined with archival HST/ACS data, provide a deep and uncontaminated optical color-magnitude diagram (CMD) that now strongly indicates an RGB. The RGB tip (TRGB) magnitude yields a distance modulus (m-M)_0 = 31.30 +/- 0.17, i.e., D = 18.2 +/- 1.5 Mpc. The time-series nature of our observations allows us to also detect and characterize for the first time three classical Cepheids in I~Zw~18. The time-averaged Cepheid and magnitudes are compared to the VI reddening-free Wesenheit relation predicted from new non-linear pulsation models specifically calculated at the metallicity of I Zw 18. For the one bona-fide classical Cepheid with a period of 8.63 days this implies a distance modulus (m-M)_0 = 31.42 +/- 0.26. The other two Cepheids have unusually long periods (125.0 and 129.8 d) but are consistent with this distance. The coherent picture that emerges is that I Zw 18 is older and farther away than previously believed. This rules out the possibility that I Zw 18 is a truly primordial galaxy formed recently (z < 0.1) in the local universe.Comment: 12 pages, 3 figures, submitted to ApJ

Past and present star formation in the SMC: NGC 346 and its neighborhood

In the quest of understanding how star formation occurs and propagates in the low metallicity environment of the Small Magellanic Cloud (SMC), we acquired deep F555W (~V), and F814W (~I) HST/ACS images of the young and massive star forming region NGC 346. These images and their photometric analysis provide us with a snapshot of the star formation history of the region. We find evidence for star formation extending from ~10 Gyr in the past until ~150 Myr in the field of the SMC. The youngest stellar population (~3 +/- 1 Myr) is associated with the NGC 346 cluster. It includes a rich component of low mass pre-main sequence stars mainly concentrated in a number of sub-clusters, spatially co- located with CO clumps previously detected by Rubio et al. (2000). Within our analysis uncertainties, these sub-clusters appear coeval with each other. The most massive stars appear concentrated in the central sub-clusters, indicating possible mass segregation. A number of embedded clusters are also observed. This finding, combined with the overall wealth of dust and gas, could imply that star formation is still active. An intermediate age star cluster, BS90, formed ~4.3 +/-0.1 Gyr ago, is also present in the region. Thus, this region of the SMC has supported star formation with varying levels of intensity over much of the cosmic time.Comment: 38 pages, 13 figures, 3 tables; AJ accepte