Steady analysis of transcritical flows in collapsible tubes with discontinuous mechanical properties: implications for arteries and veins

We study the conditions under which discontinuous mechanical properties of a collapsible tube can induce transcritical flows, i.e. the transition through the critical state where the speed index (analogous to the Mach or the Froude numbers for compressible and free surface flows, respectively) is one. Such a critical transition may strongly modify the flow properties, cause a significant reduction in the cross-sectional area of the tube, and limit the flow. General relationships are obtained for a short segment using a one-dimensional model under steady flow conditions. Marginal curves delimiting the transcritical regions are identified in terms of the speed index and the cross-sectional area ratio. Since there are many examples of such flows in physiology and medicine, we also analyse the specific case of prosthesis (graft or stent) implantation in blood vessels. We then compute transcritical conditions for the case of stiffness and reference area variations, considering a collapsible tube characterized by physiological parameters representative of both arteries and veins. The results suggest that variations in mechanical properties may induce transcritical flow in veins but is unrealistic in arterie

Multiple states for flow through a collapsible tube with discontinuities

We study the occurrence of the multiple steady states that flows in a collapsible tube can develop under the effect of: (i)geometrical alterations (e.g.stenosis), (ii)variations of the mechanical properties of the tube wall, or (iii)variations of the external pressure acting on the conduit. Specifically, if the approaching flow is supercritical, two steady flow states are possible in a restricted region of the parameter space: one of these flow states is wholly supercritical while the other produces an elastic jump that is located upstream of the variation. In the latter case the flow undergoes a transition through critical conditions in the modified segment of the conduit. Both states being possible, the actual state is determined by the past history of the system, and the parameter values show a hysteretic behaviour when shifting from one state to the other. First we set up the problem in a theoretical framework assuming stationary conditions, and then we analyse the dynamics numerically in a one-dimensional framework. Theoretical considerations suggest that the existence of multiple states is associated with non-uniqueness of the steady-state solution, which is confirmed by numerical simulations of the fully unsteady proble

Il Museo dell’Osservatorio Vesuviano: dati statistici 2005

Il museo dell'Osservatorio Vesuviano, rinnovato nel 2000, nasce con l’obiettivo di informare la popolazione sui fenomeni vulcanici, sui pericoli connessi e sulla sorveglianza dei vulcani attivi in aree ad alto rischio; è situato nella sede storica dell’Osservatorio Vesuviano, il primo Osservatorio vulcanologico del mondo, attualmente sezione dell’Istituto Nazionale di Geofisica e Vulcanologia. Il percorso museale ha inizio con la presentazione delle diverse tipologie eruttive e dei fenomeni a esse associati e quindi dei pericoli per l’uomo e i manufatti. Si ripercorre la storia eruttiva del Somma-Vesuvio soffermandosi sulle eruzioni più note del 79 d.C. e del 1944, e sulle metodologie adottate dai vulcanologi per ricostruire la storia eruttiva di un vulcano attraverso lo studio dei suoi prodotti. Inoltre, sono esposti i prodotti delle eruzioni effusive ed esplosive, e i minerali che si formano in ambiente vulcanico. Il percorso è arricchito da documenti storici di notevole interesse vulcanologico quali: la carta vulcanologica di Henry James Johnston-Lavis e il volume “Campi Flegrei” di William Hamilton (in visione la riproduzione anastatica). Un altro tema portante della mostra riguarda il monitoraggio dei vulcani attivi. Sono esposti gli strumenti scientifici storici utilizzati per la sorveglianza, tra cui il primo sismografo del mondo costruito nel 1856 da Luigi Palmieri, direttore dell’Osservatorio Vesuviano dal 1855 al 1896. Una sala ospita monitor collegati in tempo reale alla sezione “segnali sismici” del sito web dell’Osservatorio Vesuviano. Si propongono inoltre filmati tratti da modelli fisico-matematici di simulazioni di eruzioni esplosive per la definizione degli scenari attesi in caso di eruzione. Infine, si affronta il problema del rischio mediante pannelli informativi sul piano Nazionale di emergenza al fine di promuovere atteggiamenti adeguati in caso di necessità. Gli strumenti utilizzati sono video, pannelli, webcam, internet. Nel rapporto sono presentati i dati statistici relativi al pubblico del museo nell’anno 2005

Effects of add-on ultramicronized n-palmitol ethanol amide in patients suffering of migraine with aura. a pilot study

Background: Palmitoyl ethanol amide (PEA) is an endogenously produced substance showing anti-nociceptive effect through both receptor and non-receptor mediated effects at the level of different cellular and tissue sites. This study showed the results of a single blind study that was conducted to evaluate both the safety and the efficacy of ultramicronized PEA (umPEA; 1,200 mg/day) for up 90 days in patients suffering of Migraine with Aura (MA) treated with NSAIDs. Methods: A total of 20 patients, 8 male (33-56-years, average 41.4 ± 7.8) and 12 female (19-61-years, average 38.5 ± 11.9) with MA were admitted to our observation and diagnosed according to ICHD-3 criteria, they received umPEA (1,200 mg/day) in combination with NSAIDs for up to 90 days. They were revaluated at 30, 60, and 90 days after treatment. Results: umPEA administration induced a statistically significant and time dependent pain relief. In particular, these effects were evident at 60 days (male P = 0.01189; female P = < 0.01) and they lasted until the end of the study (male P = 0.0066; female P = 0.01473). Conclusion: Although further studies are needed, our findings indicate that in patients suffering of MA treatment with umPEA had good efficacy and safety which candidate this compound as a therapeutic tool in pain migraine management

Assessment of “Carbopeaking” in a hydropeaking-impacted river in the Italian Alpine area

Hydropeaking (i.e., rapid and frequent artificial flow fluctuations caused by reservoir-operated hydropower production) is a much-investigated river stressor, and has been associated, among others, to sudden changes in temperature (“thermopeaking”), underwater soundscape (“soundpeaking”), total dissolved gas saturation (“saturopeaking”). We have recently started investigating the “carbopeaking”, i.e., variations of greenhouse gas (mainly CO2) concentrations and evasion fluxes through the water-air interface associated with hydropeaks. Here we report on the methodology and preliminary results from a field-measurement campaign conducted in a single-thread Alpine river (River Noce, Italy) during multiple hydropeaking events. The analysis of water samples collected in the upstream reservoir showed CO2 oversaturation in the hypolimnion, around the depth of the hydropower intake system. In the Noce reach upstream of the hydropower plant outlet (i.e., in a residual flow stretch), the CO2 concentrations displayed diel fluctuations around the atmospheric equilibrium concentration, likely driven by diurnal primary production. Conversely, water released at the hydropower outlet during hydropeaking were consistently oversaturated in CO2 relative to the atmosphere, in agreement with the concentrations in the reservoir’s hypolimnetic water. As a result, hydropeaking events were associated with an alteration of the sub-daily patterns of CO2 concentration downstream of the hydropower outlet which, combined with higher gas exchange velocities occurring during higher flow rates, can cause periods of enhanced CO2 emissions. The results highlight the potential impact of hydropeaking on greenhouse gas emissions, demonstrating the need to account for sub-daily variations of flow and gas concentration to accurately quantify carbon balances in rivers impacted by hydropower

An ecosystem service approach to license new run of the river hydropower plants

Freshwater ecosystems provide several services (ES) to society. Hydropower production is one of the most relevant ES supported by Alpine rivers, and it is often in conflict with other river uses and services. Recently, the demand by local authorities, public or private agencies for new small hydropower plants have been increasing, and new conflicts have been arousing. We propose an approach to model the alterations of selected ES which integrates hydrological and habitat models and evaluates possible variations of the selected ES under different withdrawal scenarios. The case-study is the Noce River, a gravel-bed river in the Italian Alps (Trentino, North East Italy) which is subject to hydropeaking. We selected four ES: habitat for juvenile and adult marble trout as biodiversity proxy, rafting as recreational services, and small hydropower production as provisioning service. We evaluated the variations of these services for maximum and no hydropower production, chosen as different boundary conditions. Moreover, we simulated the presence of four new different small hydropower plants with increasing withdrawals. Large hydropower is the key driver, affecting all the selected ES. Small hydropower decreases the potential for rafting up to 64%, while it is often negligible for other services

Can the discharge of a hyperconcentrated flow be estimated from paleoflood evidence?

Many flood events involving water and sediments have been characterized using classic hydraulics principles, assuming the existence of critical flow and many other simplifications. In this paper, hyperconcentrated flow discharge was evaluated by using paleoflood reconstructions (based on paleostage indicators [PSI]) combined with a detailed hydraulic analysis of the critical flow assumption. The exact location where this condition occurred was established by iteratively determining the corresponding cross section, so that specific energy is at a minimum. In addition, all of the factors and parameters involved in the process were assessed, especially those related to the momentum equation, existing shear stresses in the wetted perimeter, and nonhydrostatic and hydrostatic pressure distributions. The superelevation of the hyperconcentrated flow, due to the flow elevation curvature, was also estimated and calibrated with the PSI. 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