Defensive Weapons and Star Wars: A Supergame with Optimal Punishments

We model the perspective faced by nuclear powers involved in a supergame where nuclear deterrence is used to stabilise peace. This setting allows us to investigate the bearings of defensive weapons on the effectiveness of deterrence and peace stability, relying on one-shot optimal punishments. We find that the sustainability of peace is unaffected by defensive shields if both countries have them, while a unilateral endowment of such weapons has destabilising consequences.

Wetting hysteresis induced by nanodefects

Wetting of actual surfaces involves diverse hysteretic phenomena stemming from ever-present imperfections. Here, we clarify the origin of wetting hysteresis for a liquid front advancing or receding across an isolated defect of nanometric size. Various kinds of chemical and topographical nanodefects, which represent salient features of actual heterogeneous surfaces, are investigated. The most probable wetting path across surface heterogeneities is identified by combining, within an innovative approach, microscopic classical density functional theory and the string method devised for the study of rare events. The computed rugged free-energy landscape demonstrates that hysteresis emerges as a consequence of metastable pinning of the liquid front at the defects; the barriers for thermally activated defect crossing, the pinning force, and hysteresis are quantified and related to the geometry and chemistry of the defects allowing for the occurrence of nanoscopic effects. The main result of our calculations is that even weak nanoscale defects, which are difficult to characterize in generic microfluidic experiments, can be the source of a plethora of hysteretical phenomena, including the pinning of nanobubbles

Vapor nucleation paths in lyophobic nanopores

Abstract.: In recent years, technologies revolving around the use of lyophobic nanopores gained considerable attention in both fundamental and applied research. Owing to the enormous internal surface area, heterogeneous lyophobic systems (HLS), constituted by a nanoporous lyophobic material and a non-wetting liquid, are promising candidates for the efficient storage or dissipation of mechanical energy. These diverse applications both rely on the forced intrusion and extrusion of the non-wetting liquid inside the pores; the behavior of HLS for storage or dissipation depends on the hysteresis between these two processes, which, in turn, are determined by the microscopic details of the system. It is easy to understand that molecular simulations provide an unmatched tool for understanding phenomena at these scales. In this contribution we use advanced atomistic simulation techniques in order to study the nucleation of vapor bubbles inside lyophobic mesopores. The use of the string method in collective variables allows us to overcome the computational challenges associated with the activated nature of the phenomenon, rendering a detailed picture of nucleation in confinement. In particular, this rare event method efficiently searches for the most probable nucleation path(s) in otherwise intractable, high-dimensional free-energy landscapes. Results reveal the existence of several independent nucleation paths associated with different free-energy barriers. In particular, there is a family of asymmetric transition paths, in which a bubble forms at one of the walls; the other family involves the formation of axisymmetric bubbles with an annulus shape. The computed free-energy profiles reveal that the asymmetric path is significantly more probable than the symmetric one, while the exact position where the asymmetric bubble forms is less relevant for the free energetics of the process. A comparison of the atomistic results with continuum models is also presented, showing how, for simple liquids in mesoporous materials of characteristic size of ca. 4nm, the nanoscale effects reported for smaller pores have a minor role. The atomistic estimates for the nucleation free-energy barrier are in qualitative accord with those that can be obtained using a macroscopic, capillary-based nucleation theory. Graphical abstract: [Figure not available: see fulltext.]

Recovering superhydrophobicity in nanoscale and macroscale surface textures

Here, we investigate complete drying of hydrophobic cavities in order to elucidate its dependence on the size of confinement, its geometry, and the degree of hydrophobicity. Two complementary theoretical approaches are adopted: a macroscopic one based on classical capillarity and a microscopic classical density functional theory. This combination allows us to pinpoint unique drying mechanisms at the nanoscale and to clearly differentiate them from the mechanisms operational at the macroscale. Nanoscale hydrophobic cavities allow the thermodynamic destabilization of the confined liquid phase over an unexpectedly broad range of conditions, including pressures as large as 10 MPa and contact angles close to 90°. On the other hand, for cavities on the micron scale, such destabilization occurs only for much larger contact angles and close to liquid-vapor coexistence. These scale-dependent drying mechanisms are used to propose design criteria for hierarchical superhydrophobic surfaces capable of spontaneous self recovery over a broad range of operating conditions. In particular, we detail the requirements under which it is possible to realize perpetual superhydrophobicity at positive pressures on surfaces with micron-sized textures by exploiting drying, facilitated by nanoscale coatings. Concerning the issue of superhydrophobicity, these findings indicate a promising direction both for surface fabrication and for the experimental characterization of perpetual surperhydrophobicity. From a more basic perspective, the present results have an echo on a wealth of biological problems in which hydrophobic confinement induces drying, such as in protein folding, molecular recognition, and hydrophobic gating

Perpetual superhydrophobicity

A liquid droplet placed on a geometrically textured surface may take on a “suspended” state, in which the liquid wets only the top of the surface structure, while the remaining geometrical features are occupied by vapor. This superhydrophobic Cassie–Baxter state is characterized by its composite interface which is intrinsically fragile and, if subjected to certain external perturbations, may collapse into the fully wet, so-called Wenzel state. Restoring the superhydrophobic Cassie–Baxter state requires a supply of free energy to the system in order to again nucleate the vapor. Here, we use microscopic classical density functional theory in order to study the Cassie–Baxter to Wenzel and the reverse transition in widely spaced, parallel arrays of rectangular nanogrooves patterned on a hydrophobic flat surface. We demonstrate that if the width of the grooves falls below a threshold value of ca. 7 nm, which depends on the surface chemistry, the Wenzel state becomes thermodynamically unstable even at very large positive pressures, thus realizing a “perpetual” superhydrophobic Cassie–Baxter state by passive means. Building upon this finding, we demonstrate that hierarchical structures can achieve perpetual superhydrophobicity even for micron-sized geometrical textures

Metabolic alteration of circulating monocytes during neuroinflammation: method development and in vitro studies in Alzheimer’s disease and multiple sclerosis

This thesis focuses on the study of the reprogramming of the immunometabolism of infiltrating monocytes during neuroinflammation. Three main results have been achieved. First, the development and validation of a method for analysing changes in the major metabolic pathways of cells. To do so, the analytical challenges presented by the high polarity of the targeted metabolites and the chelating properties of citrate and phosphates have been addressed and overcome. The developed method allows the simultaneous analysis of key-role metabolites with HPLC-ESI-QQQ-MS. It is a suitable tool for future studies to quickly, reliably, and reproducibly investigate the metabolism of cells in different conditions or under various stimulations. The proof of concept of this method is shown by the results of the following two points. Second, in vitro elucidation of monocyte metabolic alterations when infiltrating into the CSF from the bloodstream. These results provide an insight on the immunometabolism rewiring from the production of amino acids (serine and glycine) in normal conditions towards a more active TCA cycle and production of glutamine when stimulated with CSF. This knowledge gives a valuable overview of the effects caused by the compartment change of monocytes and provides the basis for understanding the metabolic adaptation of infiltrating immune cells under different conditions. Third, the display of the significant variations in the metabolism reprogramming of infiltrating monocytes in three study cases: in healthy individuals, in patients with AD and with MScl. These outcomes elucidate how a healthy donor CSF affects monocytes compared to that of patients. Moreover, it distinguishes the alterations caused by a disease more correlated to neurodegeneration, such as AD, from those caused by a disease primarily neuroinflammatory like MScl. The results presented in this thesis are of relevance for a more in-depth understanding of the metabolic fate of monocytes in CSF and to build solid bases for further studies of their role in neuroinflammation. It is one step forward in elucidating the complexity of alterations that occur in our CNS in the case of neurodegenerative or neuroinflammatory diseases.Diese Arbeit konzentriert sich auf die Untersuchung der Umprogrammierung des Immunstoffwechsels von infiltrierenden Monozyten während einer Neuroinflammation. Es wurden drei Hauptergebnisse erzielt. Erstens, die Entwicklung und Validierung einer Methode zur Untersuchung von Veränderungen in den wichtigsten Stoffwechselwegen von Zellen. Zu diesem Zweck wurden die analytischen Herausforderungen, die sich aus der hohen Polarität der Zielmetaboliten und den chelatbildenden Eigenschaften von Citrat und Phosphaten ergeben, angegangen und überwunden. Die entwickelte Methode ermöglicht die gleichzeitige Analyse von essentiellen Metaboliten mittels HPLC-ESI-QQQ-MS. Diese ist ein geeignetes Werkzeug für zukünftige Studien, um schnell, zuverlässig und reproduzierbar den Stoffwechsel von Zellen unter verschiedenen Bedingungen oder Stimuli zu untersuchen. Der Beweis für die Wirksamkeit dieser Methode wird durch die Ergebnisse der folgenden zwei Punkte erbracht. Zweitens, in-vitro-Aufklärung der metabolischen Veränderungen von Monozyten, die aus dem Blutkreislauf in den Liquor eindringen. Die Ergebnisse geben einen Einblick in die Umstellung des Immunstoffwechsels von der Produktion von Aminosäuren (Serin und Glycin) unter normalen Bedingungen auf einen aktivierten Tricarbonsäurezyklus und die Produktion von Glutamin, wenn die Zellen mit Liquor stimuliert werden. Diese Erkenntnisse geben einen wertvollen Überblick über die Auswirkungen des Übergang der Monozyten in ein anderes Kompartiment und bilden die Grundlage für das Verständnis der metabolischen Anpassung von infiltrierenden Immunzellen unter verschiedenen Bedingungen. Drittens, die Darstellung der signifikanten Unterschiede in der Reprogrammierung des Stoffwechsels der infiltrierenden Monozyten in drei Studienfällen: bei gesunden Personen, bei Patienten mit Alzheimer und mit Multiple Sklerose. Diese Ergebnisse geben Aufschluss darüber, wie sich der Liquor eines gesunden Spenders auf die Monozyten auswirkt, im Vergleich zu demjenigen von Patienten. Darüber hinaus wird zwischen den Veränderungen unterschieden, die durch eine Krankheit verursacht werden, die eher mit Neurodegeneration korreliert, wie z.B. Alzheimer, und denen, die durch eine primär neuroinflammatorische Krankheit wie MScl verursacht werden. Die in dieser Arbeit vorgestellten Ergebnisse sind für ein tieferes Verständnis des metabolischen Schicksals der Monozyten im Liquor von Bedeutung und bilden eine solide Grundlage für weitere Studien über ihre Rolle bei Neuroinflammationen. Somit sind diese Erkenntnisse ein weiterer Schritt zur Aufklärung der komplexen Veränderungen, die in unserem zentralen Nervensystem bei neurodegenerativen oder neuroinflammatorischen Erkrankungen auftreten

Intrusion and extrusion of water in hydrophobic nanopores

Heterogeneous systems composed of hydrophobic nanoporous materials and water are capable, depending on their characteristics, of efficiently dissipating (dampers) or storing ("molecular springs") energy. However, it is difficult to predict their properties based on macroscopic theories-classical capillarity for intrusion and classical nucleation theory (CNT) for extrusion-because of the peculiar behavior of water in extreme confinement. Here we use advanced molecular dynamics techniques to shed light on these nonclassical effects, which are often difficult to investigate directly via experiments, owing to the reduced dimensions of the pores. The string method in collective variables is used to simulate, without artifacts, the microscopic mechanism of water intrusion and extrusion in the pores, which are thermally activated, rare events. Simulations reveal three important nonclassical effects: the nucleation free-energy barriers are reduced eightfold compared with CNT, the intrusion pressure is increased due to nanoscale confinement, and the intrusion/extrusion hysteresis is practically suppressed for pores with diameters below 1.2 nm. The frequency and size dependence of hysteresis exposed by the present simulations explains several experimental results on nanoporous materials. Understanding physical phenomena peculiar to nanoconfined water paves the way for a better design of nanoporous materials for energy applications; for instance, by decreasing the size of the nanopores alone, it is possible to change their behavior from dampers to molecular springs

What keeps nanopores boiling

The liquid to vapour transition can occur at unexpected conditions in nanopores, opening the door to fundamental questions and new technologies. The physics of boiling in confinement is progressively introduced, starting from classical nucleation theory, passing through nanoscale effects, and terminating to the material and external parameters which affect the boiling conditions. The relevance of boiling in specific nanoconfined systems is discussed, focusing on heterogeneous lyophobic systems, chromatographic columns, and ion channels. The current level of control of boiling in nanopores enabled by microporous materials, as metal organic frameworks, and biological nanopores paves the way to thrilling theoretical challenges and to new technological opportunities in the fields of energy, neuromorphic computing, and sensing

Collapse of superhydrophobicity on nanopillared surfaces

The mechanism of the collapse of the superhydrophobic state is elucidated for submerged nanoscale textures forming a three-dimensional interconnected vapor domain. This key issue for the design of nanotextures poses significant simulation challenges as it is characterized by diverse time and length scales. State-of-the-art atomistic rare events simulations are applied for overcoming the long time scales connected with the large free energy barriers. In such interconnected surface cavities wetting starts with the formation of a liquid finger between two pillars. This break of symmetry induces a more gentle bend in the rest of the liquid-vapor interface, which triggers the wetting of the neighboring pillars. This collective mechanism, involving the wetting of several pillars at the same time, could not be captured by previous atomistic simulations using surface models comprising a small number of pillars (often just one). Atomistic results are interpreted in terms of a sharp-interface continuum model which suggests that line tension, condensation, and other nanoscale phenomena play a minor role in the simulated conditions