On a model of multiphase flow

We consider a hyperbolic system of three conservation laws in one space variable. The system is a model for fluid flow allowing phase transitions; in this case the state variables are the specific volume, the velocity and the mass density fraction of the vapor in the fluid. For a class of initial data having large total variation we prove the global existence of solutions to the Cauchy problem.Comment: 32 pages. Revised and corrected versio

The reflection of an ionized shock wave

In a previous paper we studied the thermodynamic and kinetic theory for an ionized gas, in one space dimension; in this paper we provide an application of those results to the reflection of a shock wave in an electromagnetic shock tube. Under some reasonable limitations, which fully agree with experimental data, we prove that both the incident and the reflected shock waves satisfy the Lax entropy conditions; this result holds even outside genuinely nonlinear regions, which are present in the model. We show that the temperature increases in a significant way behind the incident shock front but the degree of ionization does not undergo a similar growth. On the contrary, the degree of ionization increases substantially behind the reflected shock front. We explain these phenomena by means of the concavity of the Hugoniot loci. Therefore, our results not only fit perfectly but explain what was remarked in experiments.Comment: 16 page

Global existence of solutions for a multi-phase flow: a drop in a gas-tube

In this paper we study the flow of an inviscid fluid composed by three different phases. The model is a simple hyperbolic system of three conservation laws, in Lagrangian coordinates, where the phase interfaces are stationary. Our main result concerns the global existence of weak entropic solutions to the initial-value problem for large initial data

Global weak solutions for a model of two-phase flow with a single interface

We consider a simple nonlinear hyperbolic system modeling the flow of an inviscid fluid. The model includes as state variable the mass density fraction of the vapor in the fluid and then phase transitions can be taken into consideration; moreover, phase interfaces are contact discontinuities for the system. We focus on the special case of initial data consisting of two different phases separated by an interface. We find explicit bounds on the (possibly large) initial data in order that weak entropic solutions exist for all times. The proof exploits a carefully tailored version of the front tracking scheme

Global existence of solutions for a multi-phase flow: a bubble in a liquid tube and related cases

In this paper we study the problem of the global existence (in time) of weak, entropic solutions to a system of three hyperbolic conservation laws, in one space dimension, for large initial data. The system models the dynamics of phase transitions in an isothermal fluid; in Lagrangian coordinates, the phase interfaces are represented as stationary contact discontinuities. We focus on the persistence of solutions consisting in three bulk phases separated by two interfaces. Under some stability conditions on the phase configuration and by a suitable front tracking algorithm we show that, if the BV-norm of the initial data is less than an explicit (large) threshold, then the Cauchy problem has global solutions

Coupling conditions for isothermal gas flow and applications to valves

We consider an isothermal gas flowing through a straight pipe and study the effects of a two-way electronic valve on the flow. The valve is either open or closed according to the pressure gradient and is assumed to act without any time or reaction delay. We first give a notion of coupling solution for the corresponding Riemann problem; then, we highlight and investigate several important properties for the solver, such as coherence, consistence, continuity on initial data and invariant domains. In particular, the notion of coherence introduced here is new and related to commuting behaviors of valves. We provide explicit conditions on the initial data in order that each of these properties is satisfied. The modeling we propose can be easily extended to a very wide class of valves

Prosocial Behaviour in Palliative Nurses: Psychometric Evaluation of the Prosociality Scale

Aim: The aim of this study was to examine the psychometric properties of a prosociality scale within the palliative nursing context, and then examine the impact of prosocial behaviour in relation to job and educational satisfaction among palliative nurses. Methods: An online cross-sectional survey was conducted in 25 Italian palliative care centres, with a total of 107 nurses completing the prosociality scale by Caprara et al (2005). Exploratory and confirmatory factor analyses were examined to evaluate a multidimensional model of prosociality. Results: A three-factor solution with a second order factor fitted the data well. The three dimensions extracted were labelled as helping, empathy, and sharing. Participants reported high levels of prosociality. In addition, prosociality was positively associated with job and educational satisfaction. Conclusions: The prosociality scale was valid and reliable when tested with palliative nurses. Although prosociality may be embedded in nurses’ personalities, this quality should be actively promoted to expand and improve the culture and the ethics of nursing

Long-term effects of fire on nitrogen cycling in a broad-leaf savanna, Kruger National Park, South Africa

Includes bibliographical references (p. 118-139).Fire with herbivory, climate, and soil properties including nutrients are said to be important in regulating the structure and function of savanna ecosystems. Frequent fire is often held responsible for a decrease in nitrogen pools and availability and the maintenance of low fertility conditions. However, previous research in the Kruger National Park (KNP) and elsewhere found conflicting results for the effects of fire on nitrogen pools and transformation rates. The main aim of this study was to gain a better understanding ofthe long-term effects of fire on nitrogen cycling in the KNP. The KNP provided an ideal opportunity for this study because of the initiation of a fire experiment in 1954. The Experimental Bum Plot (EBP) experiment was initiated in four representative landscapes of the KNP to determine the effects of fire on vegetation structure. I tested the effect of burning on nitrogen cycling and productivity in four fire treatments situated in Pretoriuskop Sour Bushveld (broad-leaf savanna). The fire treatments included a late winter, annual bum (August), late winter and summer triennial bums (August and February) and a fire exclusion treatment. Total soil nitrogen, available nitrogen, woody biomass and herbaceous production were measured. 1 hypothesized that vegetation adapted to low N conditions with low N foliage would be expected to dominate in frequently burnt areas if fire was to decrease N pools and fluxes

ROLE OF SPHINGOLIPID METABOLISM IN MELANOMA PROGRESSION

Gli sfingolipidi sono lipidi polari coinvolti in numerosi processi biologici. Ne consegue che sia gli sfingolipidi che gli enzimi coinvolti nel loro metabolismo, sono importanti per l’omeostasi cellulare e partecipano in numerosi processi fisio-patologici. La mia ricerca mira ad investigare il ruolo degli enzimi GALC e SMPD3 nella progressione del melanoma. SMPD3 codifica per la sfingomielinase neutra di tipo 2 (nSMase2) che promuove la rimozione della testa polare dalla sfingomielina, liberando il ceramide. Studi antecedenti hanno dimostrato che l’espressione di SMPD3 decresce al progredire del melanoma ed è quindi correlata ad una ridotta sopravvivenza. In questo lavoro, SMPD3 è stato sovra-espresso in due linee di melanoma umano, le A2058 e le A375. Livelli aumentati di nSMase2 non hanno inficiato la proliferazione o la migrazione cellulare, tuttavia in un primo saggio di tumorigenesi in vivo hanno compromesso la crescita del tumore, rendendo le lesioni formate da cellule che sovra-esprimono SMPD3 più piccole e meno vascolarizzate, in linea con l’aumento di ceramide, e del suo ruolo protettivo, osservato in queste cellule. GALC è un enzima lisosomiale che rimuove il β-galattosio dal β-galattosilceramide. Mutazioni nel suo gene codificante sono la causa della malattia neurodegenerative di Krabbe. In letteratura sono presenti solo pochi studi sul profilo lipidico di modelli sperimentali o pazienti affetti da Krabbe. Per investigare come GALC modifichi la componente lipidica durante l’embriogenesi, embrioni di zebrafish sono stati trattati con un inibitore irreversibile di GALC. I risultati mostrano un’alterazione significativa della componente lipidica di questi embrioni, fornendo nuove conoscenze sul coinvolgimento della componete lipidica in questa patologia. Belleri et al., hanno mostrato che in campioni di melanoma umano c’è una correlazione inversa tra GALC e SMPD3, dimostrando che GALC esercita un’attività pro-oncogenica sulle cellule di melanoma sia in vitro che in vivo. Partendo da questi presupposti, GALC è stato sovra-espresso nelle cellule di melanoma umano A2058 e A375. I dati indicano che cellule sovra-esprimenti GALC proliferano e migrano di più rispetto al controllo. Inoltre, analisi di proteomica rivelano che GALC modula l’espressione di diverse proteine coinvolte nella regolazione del melanoma, nell’evasione della risposta immunitaria, nella risposta da stress del reticolo endoplasmatico e ossidativo. La progressione del melanoma è strettamente collegata all’angiogenesi. Per tanto il potenziale angiogenetico di queste cellule è stato valutato in un primo esperimento in vivo, dove cellule che sovra-esprimono GALC hanno prodotto lesioni più vascolarizzate. In un contesto tumorale, le cellule secernono fattori pro-angiogenetici volti a innescare il processo di angiogenesi. Si è visto che GALC non promuove la secrezione di tali fattori; tuttavia, viene secreto lui stesso dalle cellule che lo producono. Su queste basi, il terreno condizionato delle cellule che sovra-esprimono GALC è stato utilizzato in saggi di angiogenesi in vitro e in vivo dimostrando per la prima volta che GALC, attraverso la sua attività enzimatica e l’internalizzazione in cellule endoteliali, promuove la risposta angiogenetica. Questo lavoro si propone per tanto di fornire esempi esaustivi sul ruolo degli enzimi del metabolismo degli sfingolipidi nella progressione del melanoma.Sphingolipids and their metabolizing enzymes are involved in a variety of physiological and pathological conditions. During my PhD program I focused my research activity on the role of the sphingolipid metabolizing enzymes nSMase2 and GALC in cutaneous melanoma. nSMase2, encoded by SMPD3, is the enzyme responsible for the breakdown of sphingomyelin into ceramide. Previous studies demonstrated an onco-suppressive role of nMSase2 in melanoma where SMPD3 expression progressively decreases from primary to metastatic melanoma and is associated to short overall survival. Here, I overexpressed SMPD3 in A2058 and A375 human melanoma cell lines to study the role of nSMase2 in this tumor. The upregulation of SMPD3 did not impact their tumorigenic potential in in vitro assays even though preliminary in vivo results suggest an onco-protective role of nSMase2. Accordingly, A2058 nSMase2-overexpressing cells gave origin to smaller and less vascularized tumors in a tumorigenesis assay on the top of the chick embryo chorion allantoid membrane, consistent with the increased amount of ceramide that was observed in a lipidomic analysis on these cell lines. GALC is a lysosomal enzyme that cleaves β-galactose from β-galactosylceramide. Historically, GALC has been studied as a causative gene of the neurodegenerative Krabbe disease. Currently, only a limited information is available about the effect of the modulation of GALC activity on the lipidome. For this purpose, zebrafish embryos were treated with an irreversible GALC inhibitor, leading to significant alterations of the lipidic profile. Belleri et al. showed an inverse correlation between GALC and SMPD3 expression in human melanoma, demonstrating that GALC critically modulates the oncogenic activity of melanoma cells in vitro and in vivo. On this basis, GALC was overexpressed in A2058 and A375 cell lines. Data indicate that GALC upregulation induces a significant increase in the proliferative potential and motility of GALC-overexpressing cells and proteomic analysis reveals that GALC modulates proteins involved in melanoma biology, tumor immune escape, ER stress responses, mitochondrial antioxidant activity, autophagy and/or apoptosis. Melanoma progression strictly relies on angiogenesis. In this frame, previous studies demonstrated that GALC deficient mice have an impaired angio-architecture of brain vessels in post-natal angiogenesis and that their endothelium failed to respond to angiogenic factors, suggesting a role of GALC in neovascularization. Therefore, the angiogenic potential of A2058 and A375 GALC-overexpressing cells was investigate. Indeed, the s.c. grafting of these cells in mice has led to more vascularized tumors compared to controls. By mimicking what happens in tumor microenvironment where GALC is secreted by melanoma cells, the conditioned medium of GALC-overexpressing cells exerted a significant angiogenic activity in vitro and in vivo that was hampered by inhibitors of its enzymatic activity. Finally, the conditioned medium of these cells triggers the phosphorylation of the angiogenic tyrosine kinase VEGF receptor 2 and of various downstream signaling pathways in human endothelial cells. In conclusion, the data pointed out a prominent role of sphingolipid metabolizing enzymes in melanoma progression and angiogenesis