Littérature scientifique sur le sujet « Soft matters »

Photodynamic therapy is a powerful tool in photomedicine. Hydrogels represent very promising candidates to overcome current limitations of this therapeutic technique, such as drug solubility and targeting, and unleash its full potential.

Safe mining is the premise and guarantee of sustainable development of coal energy. Due to the combination of excellent properties of polymers and traditional soft matters, polymer-containing soft matters are playing an increasingly important role in mine disaster and hazard control. To summarize the valuable work in recent years and provide reference and inspiration for researchers in this field, this paper reviewed the recent research progress in polymer-containing soft matters with respect to mine dust control, mine fire control, mine gas control and mine roadway support. From the perspective role of polymers in a material system, we classify mine polymer-containing soft matters into two categories. The first is polymer additive materials, in which polymers are used as additives to modify fluid-like soft matters, such as dust-reducing agents (surfactant solution) and dust-suppressing foams. The second is polymer-based materials, in which polymers are used as a main component to form high performance solid-like soft matters, such as fire prevention gels, foam gels, gas hole sealing material and resin anchorage agent. The preparation principle, properties and application of these soft matters are comprehensively reviewed. Furthermore, future research directions are also suggested.

The evolution of nature created delicate structures and organisms. With the advancement of technology, especially the rise of additive manufacturing, bionics has gradually become a popular research field. Recently, researchers have concentrated on soft robotics, which can mimic the complex movements of animals by allowing continuous and often responsive local deformations. These properties give soft robots advantages in terms of integration and control with human tissue. The rise of additive manufacturing technologies and soft matters makes the fabrication of soft robots with complex functions such as bending, twisting, intricate 3D motion, grasping, and stretching possible. In this paper, the advantages and disadvantages of the additive manufacturing process, including fused deposition modeling, direct ink writing, inkjet printing, stereolithography, and selective laser sintering, are discussed. The applications of 3D printed soft matter in bionics, soft robotics, flexible electronics, and biomedical engineering are reviewed.

The issue is devoted to theoretical, computer and experimental studies of internal heterogeneous patterns, their morphology and evolution in various soft physical systems—organic and inorganic materials (e.g. alloys, polymers, cell cultures, biological tissues as well as metastable and composite materials). The importance of these studies is determined by the significant role of internal structures on the macroscopic properties and behaviour of natural and manufactured tissues and materials. Modern methods of computer modelling, statistical physics, heat and mass transfer, statistical hydrodynamics, nonlinear dynamics and experimental methods are presented and discussed. Non-equilibrium patterns which appear during macroscopic transport and hydrodynamic flow, chemical reactions, external physical fields (magnetic, electrical, thermal and hydrodynamic) and the impact of external noise on pattern evolution are the foci of this issue. Special attention is paid to pattern formation in biological systems (such as drug transport, hydrodynamic patterns in blood and pattern dynamics in protein and insulin crystals) and to the development of a scientific background for progressive methods of cancer and insult therapy (magnetic hyperthermia for cancer therapy; magnetically induced drug delivery in thrombosed blood vessels). The present issue includes works on pattern growth and their evolution in systems with complex internal structures, including stochastic dynamics, and the influence of internal structures on the external static, dynamic magnetic and mechanical properties of these systems. This article is part of the theme issue ‘Patterns in soft and biological matters’.

Abstract. Today, citizens have the possibility to use many different types of news media and participate politically in various ways. This study examines how use of different news types (hard and soft TV news as well as printed and online versions of broadsheet and tabloid newspapers) indirectly affects changes in offline and online political participation through current affairs knowledge and internal efficacy during nonelection and election time. We use a four-wave national panel survey from Denmark (N = 2,649) and show that use of hard TV news and broadsheets as well as online tabloids positively affects changes in both offline and online political participation through current affairs knowledge and internal efficacy. Use of soft TV news and printed tabloids has a negative indirect effect. These results are more pronounced for online political participation and during election time. However, use of soft TV news also has a positive direct effect on changes in political participation, which suggests a positive impact via other processes.

Informal intergovernmental organizations have become a prominent feature of the global landscape. Yet it remains unclear why states create informal organizations in some instances and formal organizations in others. Thus far, scholars have argued that states choose to create informal organizations when they offer an “efficient” solution to certain kinds of cross-border cooperation problems. However, such functionalist arguments are underspecified and rest on weak evidence at present. Existing research suggests that functionalist theories can indeed explain certain cases, but numerous anomalies arise when we look at others. This dissertation argues that this is because functionalists do not take into account how domestic politics, distributional conflict and state power can decisively influence the kinds of organizations that are likely to appear. It offers an alternative account of the emergence of informal organizations that incorporates these variables. The theory advanced emphasizes how domestic politics and institutions structure state preferences over organizational form, and how the distribution of preferences and state power then shape the organizations that subsequently emerge. Specifically, it argues that informal organizations arise when either a) policymakers in powerful states face significant domestic constraints, or b) autonomous bureaucrats are given responsibility for “leading” cooperation on the behalf of powerful states. In order to test this theory, a variety of methods are used. First, the theory is evaluated quantitatively through a statistical analysis of an original dataset of formal and informal organizations. Second, the theory is evaluated qualitatively through process tracing of the “emergence” of the International Monetary Fund, the General Agreement on Tariffs and Trade and the International Competition Network. Overall, the analysis provides powerful support for the central thesis of this dissertation: while certain aspects of the cooperation problems states face do play a role, domestic politics and state power are the most important determinants of organizational form. The dissertation’s findings are argued to have implications for theories of rational design in the field of International Relations, for our understanding of the overall rise of informal organizations in the global system, as well as for policy debates about the desirability of this new breed of international institution.
Arts, Faculty of
Political Science, Department of
Graduate

In the last few decades, an increasing number of physicists specialized in soft matter, including polymers, have turned their attention to biologically relevant materials. The properties of various molecules and fibres, such as DNA, RNA, proteins, and filaments of all sorts, are studied to better understand their behaviours and functions. Self-assembled biological membranes, or lipid bilayers, are also the focus of much attention as many life processes depend on these. Small lipid bilayers vesicles dubbed liposomes are also frequently used in the pharmaceutical and cosmetic industries. In this thesis, work is presented on both the elastic properties of polymers and the response of lipid bilayer vesicles to extrusion in narrow-channels. These two areas of research may seem disconnected but they both concern deformed soft materials. The thesis contains four articles: the first presenting a fundamental study of the entropic elasticity of circular chains; the second, a simple universal description of the effect of sequence on the elasticity of linear polymers such as DNA; the third, a model of the symmetric thermophoretic stretch of a nano-confined polymer; the fourth, a model that predicts the final sizes of vesicles obtained by pressure extrusion. These articles are preceded by an extensive introduction that covers all of the essential concepts and theories necessary to understand the work that has been done.

The term “soft matter” applies to a variety of physical systems, such as liquids, colloids, polymers, foams, gels, and granular materials. The most fascinating aspect of soft matter lies in the fact that they are not atomic or molecular in nature. They are instead macromolecular aggregates, whose spatial extent lies in the domain 1 nm to 1 ¹m. Some of the most important examples of soft matter are polymers, which exhibit intriguing and useful physical properties. In this work, the adsorption and self assembly of linear and star polymers on smooth surfaces are studied using coarse-grained, bead-springmolecular models and Langevin dynamics computer simulations. The aim is to gain insight on atomic-forcemicroscopy images of polymer films on mica surfaces, adsorbed from dilute solution following a good solvent-to-bad solvent quenching procedure. In the case of linear polymers, under certain experimental conditions, a bimodal cluster distribution is observed. It is demonstrated that this type of distribution can be reproduced in the simulations, and rationalized on the basis of the polymer structures prior to the quench. In addition to providing insight on experimental observations, the simulation results support a number of predicted scaling laws such as the decay of the monomer density as a function of distance from the surface, and the scaling of the filmheight with the strength of the polymer-surface interactions. Star polymers represent a special class of polymers, in which one end of each linear chain is tethered to a small central core to forma single particle. The discovery of these molecules led to the synthesis of a wide range of new materials. Their structures are effectively considered as intermediate between those of colloids and linear polymers. We explore the behaviour of the star polymers (which are like “soft colloids”) in the proximity of a surface, using Langevin dynamics simulations. A number of different measurements such as the height, radius of gyration, and asphericity of adsorbed stars with different number of arms, are shown to provide valuable insights on experimental findings. The simplest soft matter systems consist of spherical, rigid colloidal particles. Examples of such particles are chemically synthesized polystyrene or silica particles. We investigated the neighbour distribution in a two-dimensional polydisperse harddisk fluid, corresponding physically to a colloidal monolayer. The disk diameter distribution was defined by a power-law with the aim of realizing a scale-free nearneighbour network. Scale-free (power-law) behaviour is found in many important networks, for example, in transportation systems, biochemical reactions, scientific and movie-actor collaborations, and sexual contacts. We have provided the first example of a scale-free network in amodel condensed-matter system. Finally, we use genetic algorithms, a method for efficiently searching for minima on energy landscapes, to investigate the ordered equilibrium structures formed by binary mixtures of anisotropic dipolar particles confined on a plane, under the presence of an external magnetic field. The anisotropy of the interparticle forces is controlled by tilting the external magnetic field with respect to the plane. Initially, as the field is tilted the structures are only slightly perturbed, but once the anisotropy exceeds a critical value, completely new structures emerge.

La fracture des matériaux, omniprésente aussi bien en science des matériaux qu’en géologie, implique souvent des événements soudains et imprévisibles, sans précurseurs détectables macroscopiquement. Une compréhension approfondie des mécanismes microscopiques conduisant in fine à la rupture est requise, mais les expériences restent rares. La détection de la dynamique microscopique dans les échantillons cisaillés est expérimentalement très difficile, car elle nécessite de combiner sensibilité mécanique, qualité optique et exigences strictes sur l’encombrement. Dans ce travail, nous présentons l'une des premières tentatives réussies de mesure des précurseurs microscopiques de fracture dans des matériaux mous modèles, grâce à des mesures de la plasticité microscopique à l'aide d'un nouvel instrument, couplant une cellule de cisaillement à contrainte contrôlée à un appareil de diffusion de lumière statique et dynamique (DLS) à petits angles. Dans un premier temps, nous montrons théoriquement, numériquement et expérimentalement comment la DLS, une technique très puissante difficile à utiliser pour un échantillon sous cisaillement, peut être utilisée comme outil de mesure de la dynamique microscopique dans les systèmes mous sous cisaillement. Pour un solide parfait et un fluide visqueux simple, le champ de déplacement résultant d'une déformation de cisaillement est purement affine. Nous montrons comment les déplacements affines et non affines, qui sont présents dans de nombreuses situations d’intérêt (matériaux élastiquement hétérogènes ou en raison de réarrangements plastiques) peuvent être évalués séparément par DLS et discutons de l'effet des non-idéalités dans des expériences typiques.Ce travail est centré sur un gel colloïdal fractal modèle, dont nous caractérisons la rhéologie linéaire en loi de puissance. Nous montrons que celle-ci est décrite par un modèle phénoménologique Fractional Maxwell (FMM), et discutons la relation possible entre FMM et la structure microscopique du gel.Sous une contrainte de cisaillement constante (expérience de fluage), le gel colloïdal présente une déformation rapide élastique suivie d'un fluage lent en loi de puissance, puis, après plusieurs heures par une accélération du taux de cisaillement, entraînant la rupture retardée du gel. Nos expériences montrent que le premier régime en loi de puissance, bien décrit par la viscoélasticité linéaire, correspond à l'échelle microscopique à une dynamique partiellement nonaffine, mais entièrement réversible. Lorsque la viscoélasticité dévie de la linéarité, une accélération nette, localisée dans le temps de la dynamique non-affine, est observée. Ces réarrangements rapides précèdent la fracture macroscopique du gel de plusieurs heures: ce sont des précurseurs dynamiques de la fracture qui permettent de prédire l’évolution du gel bien avant toute mesure rhéologique.Pour obtenir une image plus complète de la fracture, nous étudions l'apparition de l'irréversibilité lors d’une perturbation cyclique répétée plusieurs fois (expérience de fatigue). En suivant l'évolution stroboscopique du système en fonction de la déformation cumulée, on constate que, au-delà du régime linéaire, le taux de relaxation augmente brusquement, signature de plasticité. Si la contrainte appliquée est suffisamment grande, le gel à long terme montre une rupture retardée, en analogie avec celle observée en fluage. Les différences et similitudes entre les deux mécanismes de fracture sont discutées.Enfin, la généralité des résultats obtenus sur les gels colloïdaux est vérifiée en étudiant comme second système modèle un verre colloïdal, dont la mise en écoulement sous contrainte oscillante est un processus progressif, pour lequel deux modes de relaxation contribuent à la dynamique observée. Les analogies qualitatives trouvées avec des systèmes similaires (par ex. des émulsions concentrées) suggèrent qu'une image unifiée pourrait être obtenue, motivant des recherches futures
Material failure is ubiquitous, with implications from geology to everyday life and material science. It often involves sudden, unpredictable events, with little or no macroscopically detectable precursors. A deeper understanding of the microscopic mechanisms eventually leading to failure is clearly required, but experiments remain scarce. The detection of microscopic dynamics in samples under shear is experimentally very challenging, because it requires to combine the highest mechanical sensitivity to strict requirements on the geometry of the whole setup and on the quality of the optical interfaces. In this work we present one of the first successful attempts to measure microscopic failure precursors in model soft solids. Here, microscopic plasticity under shear is observed using a novel setup, coupling a custom-made stress controlled shear cell to small angle static and dynamic light scattering (DLS).DLS is a very powerful technique, but its application to materials under shear is not trivial. In a first step we show a theoretical, numerical and experimental investigation of how DLS may be used as a tool to measure the microscopic dynamics in soft systems under shear. In ideal solids and simple viscous fluids, the displacement field resulting from an applied shear deformation is purely affine. Additional non-affine displacements arise in many situations of great interest, for example in elastically heterogeneous materials or due to plastic rearrangements. We show how affine and non-affine displacements can be separately resolved by DLS, and discuss the effect of several non-idealities in typical experiments.As a model system, this work mainly focuses on a fractal colloidal gel. We thoroughly characterize the linear power-law rheology of the gel, we show that it is very accurately described by the phenomenological Fractional Maxwell (FM) model, and we discuss the possible relationship between the FM model and the microscopic structure of the gel.Under a constant shear stress (creep experiment), the colloidal gel exhibits a fast, elastic deformation followed by a slow sublinear power-law creep, which is eventually interrupted after several hours by an upturn in the shear rate, leading to the delayed failure of the material. Our experiments show that the first power-law regime, nicely described by linear viscoelasticity, corresponds at the microscopic scale to partially nonaffine, yet fully reversible dynamics. Upon deviation from the linear viscoelasticity, a sharp acceleration, localized in time of the nonaffine dynamics is observed. These faster rearrangements precede the macroscopic failure of the gel by thousands of seconds: they thus are dynamic precursors of failure that allow one to predict the fate of the gel well before any rheological measurement.To obtain a more comprehensive picture of material failure, we next address the onset of irreversibility under a cyclic perturbation repeated many times (fatigue experiment). By following the stroboscopic evolution of the system as a function of the cumulated deformation, we observe that as soon as the shear amplitude is increased beyond the linear regime the relaxation rate increases abruptly, indicating that irreversible plasticity is at play. If a large enough stress amplitude is applied, the system on the long run displays delayed fatigue failure, with reminiscences of the one observed in creep. Differences and similarities between the two failure mechanisms are discussed.Finally, the generality of the results obtained on colloidal gels is checked by investigating as second model system a soft colloidal glass. In this case, our experiments indicate that oscillatory yielding is a gradual process, where two relaxation modes contribute to the observed dynamics. Qualitative analogies found with similar systems (e.g. concentrated emulsions) suggest that a general picture might be obtained with our study, which motivates ongoing and future investigations

In the search to understand the interaction between cells and their underlying substrates, life sciences are beginning to incorporate micro and nano-technology based tools to probe, measure and improve cellular behavior. In this frame, patterned surfaces provide a platform for highly defined cellular interactions and, in perspective, they offer unique advantages for artificial implants. For these reasons, functionalized materials have recently become a central topic in tissue engineering. Nanotechnology, with its rich toolbox of techniques, can be the leading actor in the materials patterning field. Laser assisted methods, conventional and un-conventional lithography and other patterning techniques, allow the fabrication of functional supports with tunable properties, either physically, or topographically and chemically. Among them, soft lithography provides an effective (and low cost) strategy for manufacturing micro and nanostructures. The main focus of this work is the use of different fabrication approaches aiming at a precise control of cell behavior, adhesion, proliferation and differentiation, through chemically and spatially designed surfaces.

In the search to understand the interaction between cells and their underlying substrates, life sciences are beginning to incorporate micro and nano-technology based tools to probe, measure and improve cellular behavior. In this frame, patterned surfaces provide a platform for highly defined cellular interactions and, in perspective, they offer unique advantages for artificial implants. For these reasons, functionalized materials have recently become a central topic in tissue engineering. Nanotechnology, with its rich toolbox of techniques, can be the leading actor in the materials patterning field. Laser assisted methods, conventional and un-conventional lithography and other patterning techniques, allow the fabrication of functional supports with tunable properties, either physically, or topographically and chemically. Among them, soft lithography provides an effective (and low cost) strategy for manufacturing micro and nanostructures. The main focus of this work is the use of different fabrication approaches aiming at a precise control of cell behavior, adhesion, proliferation and differentiation, through chemically and spatially designed surfaces.

Physical systems composed of a large number of reciprocally interacting constituents provide the natural context for the rise of emergent phenomena. Despite the intrinsic difficulty in providing a mathematical definition of what is meant for ‘emergence’ (see [Baas, in Langton, Alife III, Santa Fe Studies in the Sciences of Complexity, Proc. Volume XVII, Addison-Wesley, (1994)]), the intuitive notion of emergent property is that of a collection of interact- ing objects showing a novel collective behavior, qualitatively different from and not immediately attributable to the behaviors of the individual components. Non-linear interactions among elements of the system, or interactions between the system and the environment, or merely the large number of constituents are usually the motivations addressed to be responsible for emergent behavior. It is important to remark that emergent properties can only be inferred from a comprehension of the collective properties of the microscopic constituents [Kivelson et al, npj Quant. Mater. 1, 16024 (2016)]. In this regard, computer simulations provide a unique tool to support experimental observation, develop abstract models and investigate systems’ properties at a microscopic level. In general, condensed matter, particularly soft matter but also the complex systems studied in Physics, are necessarily described via simplified models, which include the key features of the corresponding real systems. On the one hand, this certainly represents a powerful approach when it finds its roots in the concept of universality, connected with critical phenomena, but this also turns into a limiting factor for the realistic description of the considered phenomena. On the other hand, it makes the properties of such abstract simulated systems calculable and investigable via computer simulations. As a consequence, the simulations assume a key role in complementing the comparison between experiments and theory [Frenkel and Smit, Understanding Molecular Simulations, Academic Press (2002); Allen and Tildesley, Computer simulation of liquids, Oxford University Press (2017)]. In this sense, simulations are often regarded as being computer experiments, in which materials properties and novel phases of matter can be investigated. The present PhD thesis is a collection of the main results coming from four different research lines which I have been involved into in the last 3 years. The topics could appear to be rather diverse but they are all connected by the presence of emergent phenomena which were studied via computer simulations (Molecular Dynamics and Monte Carlo methods, mainly). Three of these four research lines are related to collaborations with as many experimental groups. The first group I started collaborating with is led by dr. R. Grisenti, at the University of Frankfurt (https://www.atom. uni-frankfurt.de/hhng-grisenti/index.html). As reported in Chapter 1 and in a recent paper which I contributed to as first co-author [Schottelius, Mambretti et al., Nat. Mat. (2020)], we studied the crystal growth of supercooled Ar–Kr liquid mixtures by means of a micro–jet experiment, Molecular Dynamics simulation and thermodynamic analysis. The second ongoing collaboration is with the group of prof. P. Milani, which is the leader of the CIMaINa laboratories (http://cimaina.unimi.it/) at the Università degli Studi di Milano. We developed an abstract stochastic model of resistive switching devices that they are characterizing for neuromorphic applications (see Chapter 3). More recently, I started a collaboration with the group led by prof. T. Bellini at the Università degli Studi di Milano (https://sites.google.com/site/unimisoft/), in order to investigate the spinodal decomposition of mixtures of DNA nanostars via light scattering experiments and Monte Carlo simulations, as described in Chapter 4. I will now provide a brief overview of the contents of each Chapter, where each Chapter corresponds to a different research line. Crystal growth from a supercooled melt is of fundamental theoretical and practical importance in many fields, ranging from materials science to the production of phase–change memories. To date, the temperature dependence of the growth rates of many materials, including pure metals, metallic alloys, colloids and many others are still under intense scrutiny (see e.g. Tang et al., Nat. Mat. (2013) and Sun et al., Nat. Mat. (2018)). The majority of systems display a maximum growth rate at a temperature located between the melting point and the glass transition [Orava et al., J. Chem. Phys. (2014)]. Several materials are characterized by a range of many orders of magnitude between this maximum value and the crystal growth rates measured in other regimes. We still lack a deep comprehension of the mechanism underlying this phenomenology, which emerges from experiments and simulations both. Classical models of crystal growth from a melt hypothesize either a diffusion-limited process, or a collision–limited one, but for a lot of materials them both fail to fit the available data. This situation claims for further investigation about the key elements that tune the crystal growth rates from supercooled liquids, extending the current theoretical framework. Jointly with the experimental group of dr. Grisenti (which performed measurements at the EU-XFEL facility https://www.xfel.eu/), we studied the crystallization of supercooled mixtures of argon and krypton via Molecular Dynamics. Our results showed that their crystal growth rates (obtained from the analysis of simulated configurations exploiting Steinhardt angular order parameters) can be reconciled with existing crystal growth models only by explicitly accounting for the non–ideality of the mixtures. Our theoretical and computational contribution aided in highlighting the importance of thermodynamic aspects in describing the crystal growth kinetics, yielding a substantial step towards a more sophisticated theory of crystal growth. A second project concerns the study of soft matter systems in one dimension (1D), detailed in Chapter 2. Soft matter systems are made of particles which can overlap by paying a finite energy cost and they are renowned for being able to display complex emerging phenomena. Some of them, for example, are characterized by the presence of clustering phases [Prestipino, Phys. Rev. E (2014)]. Recently, a surprising quantum phase transition has been revealed in a 1D system composed of bosons interacting via a pairwise soft potential in the continuum. It was shown that the spatial coordinates undergoing two-particle clustering could be mapped into quantum spin variables of a 1D transverse Ising model [Rossotti et al., Phys. Rev. Lett. (2017)]. Extending the description and the results provided in a very recent paper I contributed to as first author [Mambretti et al., Phys. Rev. E (2020)], in the second Chapter we investigate the manifestation of an analogous critical phenomenon in 1D classical fluids of soft particles in the continuum. In particular, we studied the low–temperature behavior of three different classical models of 1D soft matter, whose inter–particle interactions allow for cluster- ing. The two–particle cluster phase is largely explored, by simulating the systems at the commensurate density via Monte Carlo and Simulated Annealing methods. The same string variables exploited in the aforementioned quantum case highlight that, at the right commensurate density, the peculiar pairing of neighboring soft particles can be nontrivially mapped onto a 1D discrete classical Ising model. We also observe a related phenomenon, i.e. the presence of an anomalous peak in the low–temperature specific heat, thus indicating the emergence of Schottky phenomenology in a non–magnetic fluid. The third Chapter presents the case of an electrical resistor network featuring novel emergent properties, such as memristivity and the possibility to be used as a self–assembled logic gate; an article on this topic is currently in preparation. The growing difficulties arising in the improvement of the performance of standard computing architectures encouraged the quest for different approaches aiming at reproducing the computational capability and energy efficiency of the human brain, by mimicking neurons and synapses as probabilistic computing units [Markovic et al., Nat. Rev. Phys. 2, 499–510 (2020)]. Networks based on the bottom–up assembling of nanoscale building blocks and characterized by resistive switching (RS) activities are becoming increasingly popular as possible solutions for a straightforward fabrication of complex architectures with neuromorphic features [Wang et al., Nat. Rev. Mat. 5, 173-195 (2020)]. Specifically, it has recently been demonstrated that metallic nanostructured Au films, under certain conditions show a non–ohmic electrical behavior and complex and reproducible resistive switching, which can be exploited for the innovative realization of logic gates. In these devices, the nonlinear dynamic switching behavior resulting from an applied input voltage can be exploited for developing hardware for reservoir computing applications. In Chapter 3, I show how it is possible to simulate a complex model (Stochastic Resistor Network Model, SRNM) able to imi- tate the phenomenology and give hints for the development of experiments ongoing at the CIMaINa research laboratories, regarding the electrical current passage through nanostructured cluster gold films [Mirigliano et al., Nanotechnology, 31, 23, (2020)]. To this purpose, I personally contributed to develop from scratch a C++ code, parallelized via the Armadillo library (http://arma.sourceforge.net/). To study the electrical transport properties of this system, we modeled the experimental sample as a network of interconnected resistors whose effective resistance under a given voltage can be determined using spectral graph theory. The network state evolves stochastically via random physically–inspired update moves, and its effective total resistance (and the related Power Spectral Density) has been analyzed. The structure and the topology of the network were studied via the investigation of the shortest path connecting the source and the sink of the system, thus exploring the possible paths in which the current could flow. Moreover, we also applied Information Theory entropy–based tools to investigate the time evolution of network resistance at a local, coarse–grained, scale. We observed that specific input signals corresponding to 2 logical ‘bits’ pro- duce rich outputs associable to a logical NAND gate, which posses functional completeness. Given that relevant differences could be detected between the behavior of the network at low voltage before and after the so called ‘writing’ step (where the system is under a high applied voltage), memristive effects naturally emerge in the study of network properties. These results encourage further investigations, both experimental and via the innovative SRNM approach we developed, in order to exploit these RS devices in hardware computing applications as self–assembled logic gates. Last, in Chapter 4 I focus on another soft matter system, that I have started to investigate during my PhD research activity, regarding Monte Carlo simulations of low valence DNA–based colloidal particles. This last Chapter is mainly devoted to the description of the simulation method I have been developing during my more recent PhD research activities, while the preliminary results presented obviously need to be confirmed and extended by further studies. Particles with a limited number of attractive spots (patches) on their surface are generally characterized by non–crystalline low energy states; they rather generate a disordered 3D network in which all the sticky sites are engaged in (mutually exclusive) patch–patch bonds [Bianchi et al., Phys. Rev. Lett. (2006)]. One of the most promising experimental realizations of such peculiar colloids is extremely recent: laboratory synthesized DNA nanostars (NS) with fixed valence [Bi et al., PNAS (2013)]. In this field the landmark is represented by our collaborators from the group led by prof. T. Bellini. Recently, they started to investigate the behavior of mixtures of nanostars with leftwise or rightwise chirality of the DNA strands, characterized by a merely repulsive interspecies interaction. To date, our contribution mainly consisted in the development of an abstract model of these DNA nanostars, schematized as limited valence soft patchy particles, whose equilibrium configurations are sampled via a canonical Monte Carlo program. Their different chirality is represented by a mixed interaction which only comprises excluded volume terms. Our goal in this project is twofold: on the one hand, we aim to reconstruct the temperature–density phase diagram of such mixtures, also depending on the mixing ratio. Experiments revealed a critical behavior and a phase separation processes for dilute mono–component DNA solutions; the properties of a mixture of two components, each found in critical conditions, are studied in this work. In this Chapter, after a detailed overview of the experimental, computational and theoretical studies regarding low valence particles, the simulation code is described and it is presented a comparison between the simulation results and the experimental measurements at equilibrium. The peculiar structures found in the patchy particles network claim for further analysis, as well as the interesting behavior near the critical point for mono–component and bi–component systems both. The second perspective of this research regards the unexplored aggregation and cluster growth process of such particles. In this concern, part of the future research effort will be devoted to the transformation of our custom code into a Brownian Monte Carlo in order to unveil the mechanisms underlying the dynamics of such particles during their aggregation stages. The conclusions and further perspectives concerning each of the four topics addressed in this work can be retrieved at the end of each Chapter.

Biological matter is driven far from thermodynamic equilibrium by active processes on the molecular scale. These processes are usually driven by the chemical reaction of a fuel and generate spontaneous movements and mechanical stresses in the system, even in the absence of external forces or torques. Moreover these active stresses effectively fluidify the material. The cell cytoskeleton, suspensions of swimming microorganisms or tissues are prominent examples of active fluids. Active processes in biological systems often exhibit chiral asymmetries. Examples are the chirality of cytoskeletal filaments which interact with motor proteins, the chirality of the beat of cilia and flagella as well as the helical trajectories of many biological micro-swimmers. Moreover, large scale chiral flows have been observed in the cell cortex of C. elegans and Xenopus embryos. Active force generation induces force and torque dipoles in the material. If all forces are internal the total force and torque vanish as required by the conservation of momentum and angular momentum. The density of force dipoles is an active stress in the material. In addition, active chiral processes allow for the existence of active torque dipoles which enter the conservation of angular momentum and generate an active antisymmetric stress and active angular momentum fluxes. We developed a generic description of active fluids that takes into account active chiral processes and explicitly keeps track of spin and orbital angular momentum densities. We derived constitutive equations for an active chiral fluid based on identifying the entropy production rate from the rate of change of the free energy and linearly expanding thermodynamic fluxes in terms of thermodynamic forces. We identified four elementary chiral motors that correspond to localized distributions of chiral force and torque dipoles that differ by their symmetry and produce different chiral fluid flows and intrinsic rotation fields. We employ our theory to analyze different active chiral processes. We first show that chiral flows can occur spontaneously in an active fluid even in the absence of chiral processes. For this we investigate the Taylor-Couette motor, that is an active fluid confined between two concentric cylinders. For sufficiently high active stresses the fluid generates spontaneous rotations of the two cylinders with respect to each other thus breaking the chiral symmetry of the system spontaneously. We then investigate cases where active chiral processes on the molecular scale break the chiral symmetry of the whole system. We show that chiral flows occur in films of chiral motors and derive a generic theory for thin films of active fluids. We discuss our results in the context of carpets of beating cilia or E. coli swimming close to a surface. Finally, we discuss chiral flows that are observed in the cellular cortex of the nematode C. elegans at the one cell stage. Two distinct chiral flow events are observed. The first chiral flow event (i) is a screw like chiral rotation of the two cell halves with respect to each other and occurs around 15min after fertilization. This event coincides with the establishment of cortical cell polarity. The second chiral flow event (ii) is a chiral rotation of the entire cell cortex around the anterior posterior axis of the whole cell and occurs around 30min after fertilization. Measuring densities of molecular motors during episode (i) we fit the flow patterns observed using only two fit parameters: the hydrodynamic length and cortical chirality. The flows during (ii) can be understood assuming an increase of the hydrodynamic length. We hypothesize that the cell actively regulates the cortical viscosity and the friction of the cortex with the eggshell and cytosol. We show that active chiral processes in soft biological matter give rise to interesting new physics and are essential to understand the material properties of many biological systems, such as the cell cortex.

Abstract Ferromagnetic soft materials (FSM) can generate flexible movement and shift morphology in response to an external magnetic field. They have been engineered to design products in a variety of promising applications, such as soft robots, compliant actuators, or bionic devices, et al. By using different patterns of magnetization in the soft elastomer matrix, ferromagnetic soft matters can achieve various shape changes. Although many magnetic soft robots have been designed and fabricated, they are limited by the designers’ intuition. Topology optimization (TO) is a systematically mathematical method to create innovative structures by optimizing the material layout within a design domain without relying on the designers’ intuition. It can be utilized to architect ferromagnetic soft active structures. Since many of these ‘soft machines’ exist in the form of thin-shell structures, in this paper, the extended level set method (X-LSM) and conformal mapping theory are employed to carry out topology optimization of the ferromagnetic soft actuator on manifolds. The objective function consists of a sub-objective function for the kinematics requirement and a sub-objective function for minimum compliance. Shape sensitivity analysis is derived using the material time derivative and adjoint variable method. Two examples, including a circular shell actuator and a flytrap structure, are studied to demonstrate the effectiveness of the proposed framework.

The Compact Pulsed Hadron Source (CPHS) of Tsinghua University will produce neutrons by the Be(n,p) reaction through bombarding a proton beam with 13MeV/50Hz/1.25mA from a LINAC system on a beryllium target. One of the purposes of this neutron source facility is to provide the neutron scattering capability for characterization of materials, especially soft matters and biological systems. Cold neutrons (wavelength > 4 Å) are essential to characterize the structure of these materials over the length scale of ∼100 nm with good resolution. We discuss the design and optimization of a cold neutron source (CNS) which employs a solid methane moderator for cold neutron generation. The moderator configuration, the associated cryogenic system, and operation conditions will be discussed.

The purpose of this text or dissertation is to throw some basic light on a fundamental problem concerning manhood, namely the question of evil, its main sources, dynamics and importance for human attitudes and behaviour. The perspective behind the analysis itself is that of psychology. Somebody, or many, may feel at bit nervous by the word “evil” itself. It may very well be seen as too connected to religion, myth and even superstition. Yet those who are motivated to lose oneself in the subject retain a deep interest in human destructiveness, malevolence and hate, significant themes pointing at threatening prospects for mankind. The text is organized or divided into four main ordinary chapters, the three first of them organized or divided into continuous and numbered sections. A crucial point or question is of cause how to define evil itself. It can of cause be done both intentional, instrumental and by consequence. Other theorists however have stated that the concept of evil exclusively rests on a myth originated in the Judean-Christian conception of Satan and ultimate evil. This last argument presupposes evil itself as non-existent in the real rational world. It seems however a fact that most people attach certain basic meaning to the concept, mainly that it represents ultimately bad and terrible actions and behaviour directed toward common people for the purpose of bringing upon them ultimate pain and suffer. However, there is no room for essentialism here, meaning that we simply can look “inside” some original matter to get to know what it “really” is. Rather, a phenomenon gets its identity from the constituted meaning operating within a certain human communities and contexts loaded with intentionality and inter-subjective meaning. As mentioned above, the concept of evil can be interpreted both instrumental and intentional, the first being the broadest of them. Here evil stands for behaviour and human deeds having terrifying or fatal consequences for subjects and people or in general, regardless of the intentions behind. The intentional interpretation however, links the concept to certain predispositions, characteristics and even strong motives in subjects, groups and sometimes political systems and nations. I will keep in mind and clear the way for both these perspectives for the discussion in prospect. This essay represents a psychological perspective on evil, but makes it clear that a more or less complete account of such a psychological view also should include a thorough understanding or integration of some basic social and even biological assumptions. However, I consider a social psychological position of significant importance, especially because in my opinion it represents some sort of coordination of knowledge and theoretical perspectives inherent in the subject or problem itself, the main task here being to integrate perspectives of a psychological as well as social and biological kind. Since humans are essential social creatures, the way itself to present knowledge concerning the human condition, must be social of some sort and kind, however not referring to some kind of reductionism where social models of explanation possess or holds monopoly. Social and social psychological perspectives itself represents parts of the whole matter regarding understanding and explanation of human evil. The fact that humans present, or has to represent themselves as humans among other humans, means that basically a social language is required both to explain and describe human manners and ways of being. This then truly represents its own way or, more correctly, level or standard of explanation, which makes social psychology some sort of significant, though not sufficient. More substantial, the vision itself of integrating different ontological and theoretical levels and objects of science for the purpose of manifesting or make real a full-fledged psychological perspective on evil, should be considered or characterized a meta-psychological perspective. The text is partially constructed as a review of existing theories and theorists concerning the matter of evil and logically associated themes such as violence, mass murder, genocide, antisocial behaviour in general, aggression, hate and cruelty. However, the demands of making a theoretical distinction between these themes, although connected, is stressed. Above all, an integral perspective combining different scientific disciplines is aimed at.