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In the social sciences, social structure is the aggregate of patterned social arrangements in society that are both emergent from and determinant of the actions of individuals. Likewise, society is believed to be grouped into structurally related groups or sets of roles, with different functions, meanings, or purposes. Examples of social structure include family, religion, law, economy, and class. It contrasts with "social system", which refers to the parent structure in which these various structures are embedded. Thus, social structures significantly influence larger systems, such as economic systems, legal systems, political systems, cultural systems, etc. Social structure can also be said to be the framework upon which a society is established. It determines the norms and patterns of relations between the various institutions of the society. Since the 1920s, the term has been in general use in social science, especially as a variable whose sub-components needed to be distingui

Numerical characterization and engineering of transport in morphologically complex heterogeneous media

Xiaoyu Dai

A multi-scale numerical methodology for the assessment of radiation and optical characteristics of complex structured soot-contaminated snow layers was investigated first. The methodology accounted for the exact morphology at the various scales and utilizes volume-averaging approaches with the corresponding effective properties to couple the scales. At the continuum level, the volume-averaged coupled radiative transfer equations were solved utilizing i) effective radiative transport properties obtained by direct Monte Carlo simulations at the pore level, and ii) averaged bulk material properties obtained at particle level by discrete dipole approximation calculations. The contribution of soot additives to the radiative forcing was quantitatively estimated by numerical simulation and qualitatively validated with the published experimental data.Additional coupled heat and mass transfer phenomena were then investigated for a two-step solar thermochemical water/carbon dioxide splitting reactor. It was composed of two distinct scales: porous reacting materials at the mesoscale and a batch reactor at the macro-scale. A transient multi-physics volume-averaged model of the reactive porous media undergoing the reduction and oxidation steps was developed. The effective heat and mass transport properties of reticulated porous foams were incorporated through porosity-dependent empirical correlations. Porosity-dependent reduction, oxidation, and cyclic performance for a uniform and homogenous porous structure were assessed and followed by the investigation of diverse structures with non-uniform porosities along the reactor. Subsequently, the effect of structural anisotropy on the system performance was assessed by extending the previous model into 2-dimensions. The porous medium was assumed to exhibit anisotropic transport behaviors in terms of heat transfer (radiation, conduction, convection) and mass transfer. Additionally, two operational configurations were investigated: a conventional concurrent flow configuration of fluid and irradiation and a scenario where the principal flow axis was perpendicular to the irradiation direction. In terms of radiative properties, a structure with a complete forward scattering phase function and low scattering albedo ensured the largest absorption, increasing the production rate. Anisotropic structures with a higher degree of anisotropy in permeability were more favored when the incoming radiation was perpendicular to the fluid flow direction, where the interphase heat convection was enhanced.Lastly, the engineering of the porous structure was explored by establishing a direct relationship between the local morphological characteristics and the reduction performance. This was implemented by direct-pore simulations on the discrete scale that were directly coupled to the volume-averaged finite volume simulations on the continuum scale. A large number of porous structures were artificially generated and its transport characteristics calculated by the pore-levels simulations. These calculated results were used to train a machine-learning algorithm that predicted the oxygen yield solely from based on the morphology. The learning algorithm identified the most significant morphological descriptors for a specific performance target and provided guidelines for the optimal porous structure design.

EPFL2021

Seismic vulnerability assessment of free-standing massive masonry columns by the 3D Discrete Element Method

Jinwoo Kim

Free-standing masonry column is a recurrent typology of built cultural heritage. Usually raised without seismic design, columns are subject to intense rocking and overturning under strong ground motions. In this paper, a strategy to assess their seismic vulnerability using the 3-D Discrete Element Method is proposed. It includes calibrating the elastic parameters (joint stiffness parameters) using ambient vibration test data and developing fragility curves from a large set of time history analysis results. This procedure was verified for four selected water towers, a representative archaeological monument in Pompeii, Italy. Based on preliminary structural analyses, the water towers were modeled as rigid monolithic blocks. The outcomes of modal analysis were used to calibrate the input elastic parameters, starting from a range of values given by analytical calculations derived by literature. Artificial earthquakes with peak ground acceleration levels ranging from 0.167 g to 0.803 g were implemented as ground motions. Collapses and non-collapses configurations were subdivided through a threshold concerning the maximum allowable rotation of the blocks. Fragility curves were statistically developed; these revealed the overturning probabilities of the investigated structures and also enabled to conduct a parametric study of the Rayleigh damping constants.

ELSEVIER SCI LTD2021

Second harmonic scattering of water in a biological context

Tereza Schönfeldová

Water is one of the most abundant molecules in the universe. It forms a hydrogen bond network with unique structure and dynamics. Hydrogen bonding is highly relevant to many biological processes including membrane formation, protein folding, adsorption, and lubrication. However, the underlying molecular interactions within water and between water and membranes are difficult to study and hence not fully understood. In this thesis, we utilize second harmonic scattering (SHS) to investigate inhomogeneities in bulk water, probe structural changes in lipid bilayer membranes, and detect and characterize protein-membrane interactions. Firstly, we explore the structure of bulk water in comparison to a common model liquid, carbon tetrachloride. Combining SHS measurements and molecular dynamics simulations, we report on the nanoscale inhomogeneities in bulk water that occur on femtosecond timescales. We attribute the rise in the coherent second harmonic (SH) intensity to charge density fluctuations with enhanced nanoscale polarizabilities around transient voids. Even though the transient voids also exist in carbon tetrachloride, they do not show polarizability fluctuations and the SH response of carbon tetrachloride thus corresponds to that of a model isotropic liquid. Then, we study the structure of water around large unilamellar vesicles (LUVs), which serve as a model for cell membranes. We focus on the role of water during the lipid melting phase transition. Using SHS, differential scanning calorimetry, and temperature-dependent zeta-potential measurements, we investigate the structural changes of hydration shells around the vesicle membrane. We use lipids with phosphoserine, phosphocholine, and phosphate headgroups and observe different hydration behavior upon the lipid melting transition depending on the membrane composition. Next, we characterize the interface of membranes composed of lipids containing phosphocholine and phosphate headgroups in solutions with different CaCl2 concentrations. We observe that the SH intensity is decreasing with the addition of CaCl2, which we attribute to the formation of a condensed layer of Na+ counterions on the inner leaflet of the LUVs. Additionally, we extract the vesicle surface potential and second-order surface susceptibility from SHS data for membranes with different content of lipids with phosphate headgroups, and observe composition dependent behaviour which suggests structural membrane reorganization. We continue by exploring protein-membrane interactions using water as a contrast agent. We study a pore-forming toxin, perfringolysin O (PFO), known for selective insertion into cholesterol-rich membranes. Combining SHS measurements and cryo-electron microscopy, we compare the interaction between PFO and LUV membranes with a high and low cholesterol content. By obtaining a sub-picomolar insertion constant of PFO, we show that SHS can be used to determine protein-membrane binding constants in concentration ranges not accessible by conventional methods.Finally, we investigate the interaction of protein aerolysin and its mutants with lipid membranes. We observe changes in surface charge in the cap region of membrane-bound aerolysin at different pH of the surrounding solution. By combining SHS with single-channel measurements, we obtain the membrane binding constant of wild-type aerolysin and its mutants, and we dissect their pore-forming mechanism.

EPFL2022