Influence of initial conditions on absolute and relative dispersion in semi-enclosed basins

Absolute and relative dispersion are fundamental quantities employed in order to assess the mixing strength of a basin. There exists a time scale called Lagrangian Integral Scale associated to absolute dispersion that highlights the occurrence of the transition from a quadratic dependence on time to a linear dependence on time. Such a time scale is commonly adopted as an indicator of the duration needed to lose the influence of the initial conditions. This work aims to show that in a semi-enclosed basin the choice of the formulation in order to calculate the absolute dispersion can lead to different results. Moreover, the influence of initial conditions can persist beyond the Lagrangian Integral Scale. Such an influence can be appreciated by evaluating absolute and relative dispersion recursively by changing the initial conditions. Furthermore, finite-size Lyapunov exponents characterize the different regimes of the basin

Incidence and prognosis of ventilator-associated pneumonia in critically ill patients with covid-19: A multicenter study

The primary objective of this multicenter, observational, retrospective study was to assess the incidence rate of ventilator-associated pneumonia (VAP) in coronavirus disease 2019 (COVID-19) patients in intensive care units (ICU). The secondary objective was to assess predictors of 30-day case-fatality of VAP. From 15 February to 15 May 2020, 586 COVID-19 patients were admitted to the participating ICU. Of them, 171 developed VAP (29%) and were included in the study. The incidence rate of VAP was of 18 events per 1000 ventilator days (95% confidence intervals [CI] 16–21). Deep respiratory cultures were available and positive in 77/171 patients (45%). The most frequent organisms were Pseudomonas aeruginosa (27/77, 35%) and Staphylococcus aureus (18/77, 23%). The 30-day case-fatality of VAP was 46% (78/171). In multivariable analysis, septic shock at VAP onset (odds ratio [OR] 3.30, 95% CI 1.43–7.61, p = 0.005) and acute respiratory distress syndrome at VAP onset (OR 13.21, 95% CI 3.05–57.26, p < 0.001) were associated with fatality. In conclusion, VAP is frequent in critically ill COVID-19 patients. The related high fatality is likely the sum of the unfavorable prognostic impacts of the underlying viral and the superimposed bacterial diseases

Memoria del Mapa Geológico de España, Escala 1:50.000, 2ª Serie, 1ª Edición, (MAGNA), Hoja Nº 198, Osorno

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Eulerian spectrum of finite-time Lyapunov exponents in compound channels

Fluid flows reveal a wealth of structures, such as vortices and barriers to transport. Usually, either an Eulerian or a Lagrangian frame of reference is employed in order to detect such features of the flow. However, the two frameworks detect structures that have different properties. Indeed, common Eulerian diagnostics (Hua-Klein and Okubo-Weiss criterion) employed in order to detect vortices do not always agree with Lagrangian diagnostics such as finite-time Lyapunov exponents. Besides, the former are Galilean-invariant whereas the latter is objective. However, both the Lagrangian and the Eulerian approaches to coherent structure detection must show some links under any inertial-frame. Compound channels flows have been accurately studied in the past, both from a Lagrangian and an Eulerian point of view. The features detected do not superimpose: Eulerian vortices do not coincide with barriers to transport. The missing link between the two approaches is here recovered thanks to a spectral analysis

Hydrostatic vs. non-hydrostatic modelling of density currents developing two dimensionally on steep and mild slopes

Salinity and turbidity currents developing two dimensionally on steep and mild slopes are simulated numerically. An application of the process-based model Delft3D-Flow is presented that is able to capture the dynamics of subaqueous dense underflows by solving the two dimensional over the vertical (2DV) Reynolds-averaged Navier\u2013Stokes equations under hydrostatic (H) and non-hydrostatic (NH) pressure assumptions. The development of conservative density currents that plunge in fresh water as a result of an upstream input of denser salty water and turbidity currents flowing down a fixed sandy bed with uniform slope are thoroughly investigated. Down-slope evolution of the modelled density currents is characterised by water entrainment coefficients that fall within the range of laboratory data. Vertical profiles of both velocity and excess density conform with previous experimental measurements. NH solutions, differently from their H counterparts, are shown to capture in detail time-dependent stages of dense undercurrents, such as the dynamics of their fronts, the passage of their heads as well as the development of Kelvin\u2013Helmholtz (KH) instabilities at their interfaces with the ambient fluid resulting in the velocity pulsing of their bodies. Nonetheless, the H application of Delft3D-Flow predicts fairly well the steady state of salty and turbid undercurrents, thus representing a computationally cost-effective alternative for the modelling of field-scale density currents

Barriere Lagrangiane superficiali nel Golfo di Trieste

Un problema di grande importanza nell\u2019Ingegneria Ambientale consiste nella previsione del trasporto e della concentrazione di contaminanti rilasciati all\u2019interno di un corpo idrico, per garantire la conservazione della sua naturalit\ue0 da un punto di vista ecologico (preservazione della risorsa) e naturalistico (conservazione di flora e fauna). Tali problemi di mescolamento si differenziano in funzione delle caratteristiche del moto del fluido stesso (moto laminare o turbolento, presenza di convezione e dispersione) e vengono generalmente affrontati tramite lo schema diffusivo alla Fick. Chiaramente la conoscenza delle velocit\ue0 del campo di moto gioca un ruolo fondamentale nell\u2019impostazione di tali problemi. E\u2019 per\uf2 vero che la conoscenza del campo di velocit\ue0 in ogni punto e in qualsiasi istante temporale risolve effettivamente qualsiasi problema legato al moto di un fluido? In verit\ue0, le informazioni di maggiore interesse, ovvero legate al trasporto di materia nel campo di moto, derivano dalla conoscenza del campo di velocit\ue0, ma non sono contenute gi\ue0 direttamente in esso

Il servizio di posizionamento GNSS della Regione Liguria: prime analisi

Il Servizio di Posizionamento GNSS della Regione Liguria (Sguerso, 2004), ufficialmente attivo dal 21/01/2010, offre servizi per il rilevamento in tempo reale ed in post-processing, con relativo supporto tecnico sia telefonico che per posta elettronica. Gli incontri tecnico-divulgativi che la Regione Liguria, in collaborazione con il gruppo di ricerca del Laboratorio di Geodesia, Geomatica e GIS del Dipartimento di Ingegneria delle Costruzioni, dell'Ambiente e del Territorio (DICAT) dell'Universit\ue0 di Genova, ha organizzato nel corso della primavera, sia nelle sedi delle province del proprio territorio sia presso gli Istituti secondari per geometri aderenti all'iniziativa, costituiscono un primo supporto formativo dedicato all\u2019impiego delle tecnologie GNSS (cfr. www.gnssliguria.it). Durante la fase sperimentale, la cui conclusione \ue8 prevista per fine anno, il Servizio \ue8 disponibile in tutte le sue applicazioni gratuitamente per gli utenti iscritti; ad essi \ue8 stata richiesta collaborazione nell'evidenziare eventuali malfunzionamenti o particolari esigenze; in questo contesto, nei primi mesi di funzionamento del Servizio, il gruppo di ricerca del Laboratorio di Geodesia, Geomatica e GIS ha condotto diversi rilievi GNSS in appoggio a tale Servizio, utilizzando sia i prodotti NRTK (Network Real Time Kinematic) che quelli per il Post-Processamento, coinvolgendo il lavoro di tesi di laurea di alcuni degli autori. Il principale obiettivo delle campagne effettuate \ue8 stato quello di evidenziare l\u2019importanza di un Servizio di Posizionamento GNSS in diverse situazioni rappresentative delle comuni difficolt\ue0 di rilievo cinematico e in condizioni particolarmente critiche da un punto di vista della visibilit\ue0 satellitare