The stability of a rising droplet: an inertialess nonmodal growth mechanism

Prior modal stability analysis (Kojima et al., Phys. Fluids, vol. 27, 1984) predicted that a rising or sedimenting droplet in a viscous fluid is stable in the presence of surface tension no matter how small, in contrast to experimental and numerical results. By performing a non-modal stability analysis, we demonstrate the potential for transient growth of the interfacial energy of a rising droplet in the limit of inertialess Stokes equations. The predicted critical capillary numbers for transient growth agree well with those for unstable shape evolution of droplets found in the direct numerical simulations of Koh & Leal (Phys. Fluids, vol. 1, 1989). Boundary integral simulations are used to delineate the critical amplitude of the most destabilizing perturbations. The critical amplitude is negatively correlated with the linear optimal energy growth, implying that the transient growth is responsible for reducing the necessary perturbation amplitude required to escape the basin of attraction of the spherical solution.Comment: 11pages, 7 figure

Edge states control droplet break-up in sub-critical extensional flows

A fluid droplet suspended in an extensional flow of moderate intensity may break into pieces, depending on the amplitude of the initial droplet deformation. In subcritical uniaxial extensional flow the non-breaking base state is linearly stable, implying that only a finite amplitude perturbation can trigger break-up. Consequently, the stable base solution is surrounded by its finite basin of attraction. The basin boundary, which separates initial droplet shapes returning to the non-breaking base state from those becoming unstable and breaking up, is characterized using edge tracking techniques. We numerically construct the edge state, a dynamically unstable equilibrium whose stable manifold forms the basin boundary. The edge state equilibrium controls if the droplet breaks and selects a unique path towards break-up. This path physically corresponds to the well-known end-pinching mechanism. Our results thereby rationalize the dynamics observed experimentally [Stone & Leal, J. Fluid Mech. 206, 223 (1989)

When droplets deform, break up and propel microswimmers

This thesis investigates the motion and breakup of droplets in low-Reynolds-number flows, focusing on two aspects. In the first part, we study the breakup of droplets in subcritical flow conditions, when there exists a linearly stable solution for the droplet shape, but a finite amplitude perturbation might trigger instabilities. Thus, there exists a finite basin of attraction of the stable solution, whose boundary separates droplets that break from those recovering the stable shape. Our effort is mostly devoted to the exploration of the state space in which the basin boundary is defined. To this end, we proceed by adapting theories initially developed to study laminar-turbulent transition, namely nonmodal analysis and edge tracking. We study the influence of non-normal effects in the breakup of a rising droplet, showing that the optimal shapes found with nonmodal analysis are more efficient in triggering breakup than initially ellipsoids droplets. Afterwards, we investigate the relevance of edge state in the breakup of droplet in uni-axial extensional flows, finding that edge states select the path toward breakup. The exploration of the bifurcation diagram reveals a similar situation for bi-axial extensional flows, where droplets are squeezed along the axis instead of being extended. In the second part we develop a joint chemical-hydrodynamics model to study the motion of bubble-propelled conical microswimmers. We conclude that the chemistry and the hydrodynamics partially decouple. In fact, chemistry dictates the time scale at which the microswimmer moves while the hydrodynamics governs the attained displacement. We furthermore find the geometrical and chemical parameters that optimize the swimming velocity. The effects of bubble deformability are then included. In this case, the swimming velocity is optimal for small cone opening angles. Furthermore, we find that the swimming efficiency, measured in displacement attained per fuel consumption, decreases when the bubble is more deformable. Finally, we study the motion of a sphere inflating close to a wall, which is relevant to the study of conical microswimmers and allows us to revisit the classical settling sphere problem. We find that depending on the boundary conditions imposed on the sphere, whether it is a rigid shell or a perfect free-shear bubble, the sphere-wall gap will close or open in time

The Hydrodynamics of a Micro-Rocket Propelled by a Deformable Bubble

We perform simulations to study the hydrodynamics of a conical-shaped swimming micro-robot that ejects catalytically produced bubbles from its inside. We underline the nontrivial dependency of the swimming velocity on the bubble deformability and on the geometry of the swimmer. We identify three distinct phases during the bubble evolution: immediately after nucleation the bubble is spherical and its inflation barely affects the swimming speed; then the bubble starts to deform due to the confinement gradient generating a force that propels the swimmer; while in the last phase, the bubble exits the cone, resulting in an increase in the swimmer velocity. Our results shed light on the fundamental hydrodynamics of the propulsion of catalytic conical swimmers and may help to improve the efficiency of these micro-machines

Indagine conoscitiva sulla violenza verso il maschile

Riassunto La violenza di genere costituisce una tipologia di reato in costante espansione e di continuo interesse da parte della comunità scientifica. Il fenomeno nella sua globalità è complesso da analizzare in quanto gli autori di reato commettono gli episodi perlopiù entro le mura domestiche e ciò comporta, dato il legame spesso di natura intrafamiliare tra autore e vittima, il silenzio di quest’ultima che concorre ad accrescere il cosiddetto “numero oscuro”. Da ciò derivano i limiti dell’analisi di un fenomeno per sua natura sommerso, del quale non è facile tracciare i contorni. Una conoscenza approfondita del fenomeno nel suo insieme, tuttavia, è essenziale per lo sviluppo delle politiche e dei servizi, a partire dalle campagne di sensibilizzazione per arrivare alle contromisure legislative finalizzate a prevenire e/o contenere la violenza. Va rilevato come inchieste, sondaggi e ricerche che analizzano tale comportamento deviante e che vengono proposte con continuità a livello istituzionale e mediatico da diversi decenni, sono solite prendere in considerazione solo l’eventualità che la vittima della violenza di genere sia donna e che l’autore di reato sia uomo. Tale informazione, distorta alla sua origine, passa tramite canali ufficiali (dai media alle campagne di prevenzione) determinando una conseguente sensibilizzazione unidirezionale che relega ad eccezioni - spesso non prese neppure in considerazione - le ipotesi che la violenza possa essere subita e/o agita da appartenenti ad entrambi i sessi. L’indagine presentata in questo articolo è finalizzata a raccogliere elementi di valutazione ancora inesistenti nel nostro Paese, utili a verificare se esista, ed eventualmente in che misura, una realtà diversa da quella fondata esclusivamente su condizionamenti, luoghi comuni e pregiudizi. La violence de genre constitue l’un des crimes qui connaît une forte croissance et qui fait l’objet d’un intérêt certain pour la communauté scientifique. Le phénomène est complexe à analyser dans sa globalité car la plupart des auteurs commettent leurs crimes dans le foyer domestique. Étant donné le lien intrafamilial existant entre l’auteur et la victime, cette dernière reste dans le silence qui contribue à faire augmenter le « chiffre noir ». Par conséquent, l’analyse de ce phénomène, caché à cause de sa propre nature, montre ses limites. Des campagnes de sensibilisation à l’adoption de mesures législatives pour la prévention et répression de la violence, une connaissance approfondie de ce phénomène dans sa globalité est toutefois primordial pour le développement des politiques et des services d’aide aux victimes. Il faut souligner que les enquêtes et les recherches analysant ce comportement déviant et, depuis plusieurs décennies, proposées en permanence à des niveaux institutionnel et médiatique, ont tendance à considérer que la victime de la violence de genre ne peut être qu’une femme et que son auteur, un homme. Cette information, altérée dès le début, passe à travers des chaînes officielles (des médias aux campagnes de prévention) provoquant une sensibilisation unidirectionnelle qui relègue à l’état d’exceptions – qui souvent ne sont même pas prises en considération – les hypothèses que la violence puisse être subie et/ou perpêtrée aussi bien par les hommes que par les femmes. L’enquête présentée dans cet article a pour objectif de collecter des éléments d’évaluation encore inexistants en Italie. Ces données peuvent être utilisées pour vérifier s’il existe une réalité différente de celle qui n’est basée que sur les lieux communs et sur les préjudices et quelle serait sa dimension. Gender-based violence is a constantly increasing crime and continuously attracting a lot of interest in the scientific community. This is a complex phenomenon to analyse as a whole because perpetrators usually commit the acts of violence at home. For this reason, and also due to the intimate relationship between the author and the victim, this latter remains silent, so the dark number increases. Consequently, the analysis of this phenomenon, hidden just because of its nature, has its limits. A deep knowledge of this phenomenon as a whole, however, is important for the development of policies and services, for example sensibilisation campaigns and countermeasures to prevent and combat violence. It is important to point out that surveys and researches studying this deviant behaviour, and continuously proposed at an institutional level and disseminated by mass media, usually consider that the victim of gender-based violence is a woman and the perpetrator a man. This distorted information is transmitted through official channels (for example, mass media and sensibilisation campaigns) producing a consequent unidirectional sensibilisation which relegates as exceptions – often not taken into consideration – hypothesis that violence may be endured and/or committed by both sexes. The purpose of the survey presented in this article is to collect some evaluation data that do not exist yet in our country, data that will be useful in order to verify if it exists in reality, and if yes what extension it has, different from the one based exclusively on common sense and prejudices

Intralesional administration of L19-IL2/L19-TNF in stage III or stage IVM1a melanoma patients: Results of a phase II study

The intratumoral injection of cytokines, in particular IL2, has shown promise for cutaneous melanoma patients with unresectable disease or continuous recurrence despite surgery. We recently reported that the intralesional injection of L19-IL2, an immunocytokine combining IL2 and the human monoclonal antibody fragment L19, resulted in efficient regional control of disease progression, increased time to distant metastasis and evidence of effect on circulating immune cell populations. We have also shown in preclinical models of cancer a remarkable synergistic effect of the combination of L19-IL2 with L19-TNF, a second clinical-stage immunocytokine, based on the same L19 antibody fused to TNF. Here, we describe the results of a phase II clinical trial based on the intralesional administration of L19-IL2 and L19-TNF in patients with stage IIIC and IVM1a metastatic melanoma, who were not candidate to surgery. In 20 efficacy-evaluable patients, 32 melanoma lesions exhibited complete responses upon intralesional administration of the two products, with mild side effects mainly limited to injection site reactions. Importantly, we observed complete responses in 7/13 (53.8 %) non-injected lesions (4 cutaneous, 3 lymph nodes), indicating a systemic activity of the intralesional immunostimulatory treatment. The intralesional administration of L19-IL2 and L19-TNF represents a simple and effective method for the local control of inoperable melanoma lesions, with a potential to eradicate them or make them suitable for a facile surgical removal of the residual mass

Intralesional administration of L19-IL2/L19-TNF in stage III or stage IVM1a melanoma patients: results of a phase II study

ISSN:0340-7004ISSN:1432-085

Sociobiologia possibile. Neodarwinismo e scienze dell'uomo: la ricerca di un'alternativa al determinismo biologico

Un confronto interdisciplinare sulla sociobiologia che cerca di individuare una strada per un confronto costruttivo fra evoluzionismo e scienze sociali oltre il determinismo di molte formulazioni