Self-sustaining Structure Research Articles

A mesoscale non-dimensional lattice Boltzmann model for self-sustained structures of swimming microbial suspensions

A new mesoscale two-phase flow non-dimensional lattice Boltzmann model (NDLBM) is developed for dynamical simulations of emergence and dispersion of self-sustained vortex and energy structures in microbial suspensions. Microbial fluids are treated as two-phase fluids with interaction forces between the biofluid phase and the base fluid phase, and the bioforces are based on transient local relative velocities. Microbial concentrations, sizes, shapes, densities, viscosities, surface tensions, active indexes, self repelling coefficients, and the nonlinear drag between the two phases are included in the present model. Base fluid properties and temperatures are also included. Both macroscopic and mesoscopic governing parameters are expressed with physical means for each coefficient. Compared to previous single-phase fluid mixture absolute velocity based models, the present two-phase fluid model based on the relative velocity shows faster convergence and more stable results. Parametric studies have been performed for intensities and group sizes of active flow structures in wide ranges of physical properties and governing parameters. Vorticity and energy structure patterns and scales are illustrated to show the underlying mechanism.

Fire safe and sustainable lightweight materials based on Layer-by-Layer coated keratin fibers from tannery wastes

The increasing consciousness about the depletion of natural resources and the sustainability agenda are the major driving forces to try to reuse and recycle organic materials such as agri-food and industrial wastes. In this context, keratin fibers, as a waste from the tannery industry, represent a great opportunity for the development of green functional materials. In this paper, keratin fibers were surface functionalized using the Layer-by-Layer (LbL) deposition technique and then freeze-dried in order to obtain a lightweight, fire-resistant, and sustainable material. The LbL coating, made with chitosan and carboxymethylated cellulose nanofibers, is fundamental in enabling the formation of a self-sustained structure after freeze-drying. The prepared porous fiber networks (density 100 kg m–3) display a keratin fiber content greater than 95 wt% and can easily self-extinguish the flame during a flammability test in a vertical configuration. In addition, during forced combustion tests (50 kW m–2) the samples exhibited a reduction of 37 % in heat release rate and a reduction of 75 % in smoke production if compared with a commercial polyurethane foam. The results obtained represent an excellent opportunity for the development of fire-safe sustainable materials based on fiber wastes.

Numerical and Experimental Analysis of Quilling-Inspired Metamaterials

In the current paper is presented the behaviour of a quilling-inspired metamaterial with a nonlinear response to deformation loads. The art of paper quilling relates on curved shapes, circles and spirals that generate 3D multi-layered structures that have the ability to auto-sustain. The study started with models of self-sustaining structures created through paper quilling techniques, further serving as base models for generating 3D metamaterials that resulted in spiral shape layers. These structures have demonstrated the capacity to withstand substantial loads, resulting in high deformation rates and instant shape recovery. The samples of metamaterial have been subjected to compressive loads and the results have been collected through three different methods: experimental testing, digital image correlation and numerical analysis. The purpose of this approach was to find a methodology to investigate the mechanical behaviour of these structures, namely the initial stiffness of the metamaterial. Using these methods of data collection and validation of the results, offers the possibility to research in detail the metamaterial inner structure and to predict the nonlinear displacement generated inside each cell of the layer.

코로나19 청년들의 사회적 지지에 따른 유형화 연구

This study conducted categorization according to social support of young people using latent class analysis (LCA), and confirmed participation in the labor market and social activities by type characteristics. Based on the analysis results, a total of five types were derived: social support type, social isolation type, emotional support type, corona-isolated type and corona-vulnerable type. In addition, as a result of analyzing labor market and social activity participation by type, it was found that the socially isolated social isolation type and corona isolation type labor market and social activity participation was low. These results suggest the following policy implications. First, it is necessary to conduct a survey on the social support and isolation of young people and to provide policy support suitable for the characteristics of each type. Second, the social isolation of young people can be effectively resolved if a local self-sustaining structure is prepared using local governments and local private organizations.

Investigating the Energy-Efficient Structures Using Building Energy Performance Simulations: A Case Study

The use of energy efficient structures in the local construction industry assists in promoting green building concepts, leading to economical and eco-friendly solutions for self-sustained structures. The main aim of this study was to examine and compare the energy performance of various local buildings. Detailed 3D building models (house, office, and warehouse buildings) were constructed and investigated for their cost and energy savings using building energy simulation tools (green building studio and insight). Moreover, the effects of various building materials for walls, window panels, and roof construction were explored, and a life-cycle cost analysis was performed. It was observed that the effect of the window-to-wall ratio was less severe in term of energy use in office buildings compared to normal houses due to the larger amount of space available for air circulation. Furthermore, the most efficient location for windows was found to be at the middle of the wall in comparison with the top and bottom positions. The effect of the orientation mainly depended on the symmetry of the building. More symmetric buildings, i.e., tested warehouse buildings (rectangular structure), showed an energy use difference of around 7 MJ/m2/year for a 360° orientation change. Tested house buildings exhibited an energy use difference of up to 25 MJ/m2/year. Three-pane glass windows also showed major improvements, and the total energy consumption for houses was reduced to 14%. Furthermore, wood walls showed comparable energy performance with brick walls without the use of insulation. According to US-LEED guidelines, the tested house, office, and warehouse buildings achieved 79, 89, and 88 points, respectively. The cost recovery period for house, office, and warehouse buildings was estimated to 54, 13, and 14 years, respectively, including running and maintenance costs. It can be argued that the Insight and Green Building Studio packages can assist construction stakeholders to determine the energy efficiency of the modeled building as well as to help in the selection of materials for optimized and improved design.

DEVELOPMENT OF IDEAS OF STRUCTURALISM AND POSTSTRUCTURALISM IN SOCIAL PHILOSOPHY OF THE XX CENTURY

The article presents a brief analysis of the ideas of the 20th century thinkers M. Foucault and J. Derrida in relation to the ideas of structuralism and poststructuralism, their similarity, difference and development of the discourse of structuralism as the main direction of socio-philosophical thought in Europe of the 20th century. Researchers identify several major milestones in connection with the development of structuralist thought, as well as the key authors of this direction of thought.
 Purpose: to consider structuralism and poststructuralism from the standpoint of the development of socio-philosophical discourse, as well as changing the concept of structure and the role of the subject and his place in the concept of structure.
 Method and methodology of the work: historical, phenomenological and dialectical research methods were used.
 Results: structuralism proclaims decentralization and deautonomization of both the structure itself and the subjects included in it, noting that the person of society is not a structure with a certain center, they are structures of structures. This is the main difference in the definition of the meaning of being of self-sustaining structures both in society and in the person himself between structuralist and poststructuralist discourse.
 Field of application of the results: the results obtained can be used in the study of modern social and cultural processes.

Rockburst Occurrence Mechanism Based on the Self-Sustaining Time-Varying Structure of Surrounding Rock

Rockburst is one of the major disasters that threaten the safety of personnel and equipment underground and affect the normal production of the system. At present, there are many kinds of research on rockburst occurrence mechanisms, but most of them are based on statics and do not consider the time-varying effect of surrounding rock state. Regarding the stress state and characteristics changing with time of the surrounding rock support structure and the internal parameters after the tunnel excavation is analyzed qualitatively in this paper, the concept of the “self-sustaining time-varying structure of the surrounding rock” is put forward. The “self-sustaining time-varying structure of the surrounding rock” is regarded as a nonperiodic time-varying system with a single degree of freedom, then its dynamic characteristics are analyzed by using the momentum theorem of the particle system. The results show that when the mass of the self-sustaining time-varying structure changes with time and d m / d t < 0 , the rockburst may be induced by the free vibration with increasing amplitude. The faster the d m / d t changes, the more violent the rockburst is. This explains the rockburst occurrence mechanism from a new angle and explains the phenomenon that most rockburst occurs when σ θ was lower than σ c better.

Exact coherent states of attached eddies in channel flow

A new set of exact coherent states in the form of a travelling wave is reported in plane channel flow. They are continued over a range in $Re$ from approximately $2600$ up to $30\,000$, an order of magnitude higher than those discovered in the transitional regime. This particular type of exact coherent states is found to be gradually more localised in the near-wall region on increasing the Reynolds number. As larger spanwise sizes $L_{z}^{+}$ are considered, these exact coherent states appear via a saddle-node bifurcation with a spanwise size of $L_{z}^{+}\simeq 50$ and their phase speed is found to be $c^{+}\simeq 11$ at all the Reynolds numbers considered. Computation of the eigenspectra shows that the time scale of the exact coherent states is given by $h/U_{cl}$ in channel flow at all Reynolds numbers, and it becomes equivalent to the viscous inner time scale for the exact coherent states in the limit of $Re\rightarrow \infty$. The exact coherent states at several different spanwise sizes are further continued to a higher Reynolds number, $Re=55\,000$, using the eddy-viscosity approach (Hwang & Cossu, Phys. Rev. Lett., vol. 105, 2010, 044505). It is found that the continued exact coherent states at different sizes are self-similar at the given Reynolds number. These observations suggest that, on increasing Reynolds number, new sets of self-sustaining coherent structures are born in the near-wall region. Near this onset, these structures scale in inner units, forming the near-wall self-sustaining structures. With further increase of Reynolds number, the structures that emerged at lower Reynolds numbers subsequently evolve into the self-sustaining structures in the logarithmic region at different length scales, forming a hierarchy of self-similar coherent structures as hypothesised by Townsend (i.e. attached eddy hypothesis). Finally, the energetics of turbulent flow is discussed for a consistent extension of these dynamical systems notions to high Reynolds numbers.

Localised streak solutions for a Blasius boundary layer

Streaks are a common feature of disturbed boundary-layer flows. They play a central role in transient growth mechanisms and are a building block of self-sustained structures. Most theoretical work has focused on streaks that are periodic in the spanwise direction, but in this work we consider a single spatially localised streak embedded into a Blasius boundary layer. For small streak amplitudes, we show the perturbation can be described in terms of a set of eigenmodes that correspond to an isolated streak/roll structure. These modes are new, and arise from a bi-global eigenvalue calculation; they decay algebraically downstream and may be viewed as the natural three-dimensional extension of the classical two-dimensional Libby & Fox (J. Fluid Mech., vol. 17 (3), 1963, pp. 433–449) solutions. Despite their bi-global nature, we show that a subset of these eigenmodes (including the slowest decaying) is fundamentally related to the solutions first presented by Luchini (J. Fluid Mech., vol. 327, 1996, pp. 101–116), as derived for spanwise-periodic disturbances (at small spanwise wavenumber). This surprising connection is made by an analysis of the far-field decay of the bi-global state. We also address the fully non-parallel downstream development of nonlinear streaks, confirming that the aforementioned eigenmodes are recovered as the streak/roll decays downstream. Encouraging comparisons are made with available experimental data.

Lecithin and phytosterols-based mixtures as hybrid structuring agents in different organic phases

In this study the effect of lecithin (L) addition and solvent quality in a well-established oleogel system formed by β-sitosterol and γ-oryzanol (BG) was investigated. Medium chain triglycerides (MCT) and sunflower oil (SFO) were used as triglycerides and hexadecane (HEX) as a model of linear hydrocarbon. Lecithin was proposed due to its natural and versatile properties, showing different functionalities such as emulsifier and co-oleogelator. A study based on hierarchical organization of structured oil was performed applying techniques for bulk, meso and nanoscale. Self-sustained structures could no longer be observed after 40 wt% of BG replacement by lecithin. Small-angle X-ray scattering showed that the formed nanostructures (building blocks) were dependent on type of solvent and BG:L ratio in the mixture of oleogelators. Differential scanning calorimetry showed that stability against temperature was improved decreasing the polarity of the oil, and a time-dependent self-assembly of hybrid systems was observed from thermal and rheological measurements. Microscopy images exhibited changes on typical fibril aggregation of BG as lecithin was added, which promoted to a certain extent the suppression of ribbons. Oscillatory shear and uniaxial compression measurements were influenced by BG:L ratio and solvent mainly at higher lecithin amount. The combination of BG and MCT appeared to be the most affected by lecithin incorporation whereas SFO rendered harder oleogels. These results could contribute to understand the role of both lecithin and solvent type influencing the host oleogelator structure. It was hypothesized that intermolecular BG complex formation is hindered by lecithin, besides this phospholipid also might coexist as a different phase, causing structural changes in the gel network. Addressing the role of co-oleogelator it can provide the opportunity to tune soft materials with adjusted properties.

Advanced Electrolyte and Electrode Enabling High Energy Lithium Sulfur Batteries

Currently, sulfur encapsulation in high surface area, nanoporous conducting carbon is the most widely studied approach to improve the cycling stability of Li-S batteries. However, the relatively large amount of high surface area carbon results in two fundamental problems with this approach. First, a large amount of electrolyte volume to sulfur (E/S) ratio (typically > 20 mlE/gs) is needed to fully wet the porous sulfur cathode. Second, the large amount use of high surface area carbon greatly decreases the overall energy density in the system, especially for volumetric energy density, and makes it difficult to compete with other battery technologies. Here, we found the E/S ratio plays a critical role in the cycling stability of Li-S batteries. Owing to the insulating nature of S/Li2S, lowering E/S ratio increases the charge carrier transfer resistance on the interface, causing poor rechargeability and sustainability of sulfur cathode. An ammonium-based electrolyte additive is identified to effectively address the passivation issue of Li2S under low E/S ratio. To further solve the critical passivation issue of cathode especially under lean electrolyte condition, we proposed a new approach that does not depend on the conventional sulfur encapsulation with high surface area carbon was proposed to reduce electrolyte absorption. The new approach generates a large spherical porous agglomerated particles with self-sustaining structures to avoid cathode passivation, leading ~100% sulfur utilization with good cycling (Nature Energy 2, 813, 2017).

On the development of Antenna feed array for space applications by additive manufacturing technique

Space agencies are looking for advanced technologies to build light weight and stiff payload components to bear space environment and launch loads. Additive manufacturing (AM) techniques like Direct Metal Laser Sintering (DMLS) is one of the suitable option which can be explored for space applications. This paper highlights the development process of Antenna Feed Array (AFA) using DMLS as an Additive Manufacturing (AM) technique. A high efficiency horn element is used in the array. Such horns are preferred for this development as they are the prime choice for feed elements in High Throughput satellites (HTS) that employ Multibeam Antennas. A brief description of Multibeam antennas along with the RF design process for the high efficiency horn is presented. In the development process, certain design rules of AM are adopted based on consideration to produce self-sustaining structures. AFA realized by DMLS is evaluated by functional testing, vibration testing for space qualification test levels. Test results shows its structural intactness which proves its space worthiness. Procedures are very well established for further development of space payload components.

The Hormesis of Thinking: A Deeper Quantum Thermodynamic Perspective?

We are able to read this because of quantum and thermodynamic principles that via an inorganic proton gradient, possibly generated 4.2 billion years ago, gave rise to a system that has an awareness of time and space by using energy to integrate information. Life can be described as a dissipative system driven by an energy gradient that uses information to positively reinforce its self-sustaining structure, which in turn increases its non-linear decisional capacity. Key in the evolution of life has been stress coupled to natural selection, which usually meant an increased demand for energy. As hormesis describes the adaptive response to stress, we propose that hormesis embraces not only the evolution of life, but that of intelligence itself, as natural selection would favour systems that enhances its efficiency. A component of the hormetic response in eukaryotes is the mitochondrion, which itself relies on quantum effects such as tunnelling. This suggests that quantum effects control the stability of individual cells as well as long-lived cellular networks. Hormesis, which can be anti-inflammatory, is therefore key in maintaining the functional stability of complex systems, including the brain. In contrast, a lack of classical hormetic factors, such as physical activity, plant polyphenols, or calorie restriction, will lead to accelerated cognitive decline, which is associated with increased inflammation. However, there may be another previously unidentified factor that could also be considered hormetic, and that is thinking itself. Here we propose that the process of “thinking”, and managing complex movement, induces “stress” in the neuronal system and is therefore in itself part of maintaining cognitive health and reserve throughout life. In effect, the right amount of thinking and information processing can beneficially induce adaptation, and this itself could be explainable by quantum thermodynamics.

Overview of Cellulose Nanomaterials, Their Capabilities and Applications

Cellulose nanomaterials (CNs) are a new class of cellulose particles with properties and functionalities distinct from molecular cellulose and wood pulp, and as a result, they are being developed for applications that were once thought impossible for cellulosic materials. Momentum is growing in CN research and development, and commercialization in this field is happening because of the unique combination of characteristics (e.g., high mechanical properties, sustainability, and large-scale production potential) and utility across a broad spectrum of material applications (e.g. as an additive, self-sustaining structures, and template structures) that CNs offer. Despite the challenges typical for materials development, CN and near-CN production is ramping up with pilot scale to industry demonstration trials, and the first commercial products are starting to hit the marketplace. This review provides a broad overview of CNs and their capabilities that are enabling new application areas for cellulose-based materials.

Chaotic self-sustaining structure embedded in the turbulent-laminar interface.

An interface structure between turbulence and laminar flow is investigated in two-dimensional channel flow. This spatially localized structure not only sustains itself but also converts the laminar state into turbulence actively. A filtered simulation technique is introduced to understand the invading process as an inhomogeneity-induced self-sustaining coherent structure, which consists of a meandering jet on bulk-region and near-wall vortex pairs. A phenomenological model, called the ejection-jet cycle, reveals the relationship between the spatial inner structure of the interface and the invading speed. This model gives insight on the inner-outer interaction in wall-turbulence.

Self-sustained states at Kolmogorov microscale

It is shown theoretically how the scaling of coherent structures in shear flows changes their asymptotic development at large Reynolds number. Based on the theory a family of nonlinear self-sustained states at Kolmogorov microscale is numerically identified on the laminar–turbulent boundary of shear flows. Theoretically and numerically the states connect to known asymptotic states existing at larger scale. The asymptotically very small amplitude of the new states may explain why strongly sheared, linearly stable laminar flows can cause a turbulent transition by small disturbances. The numerically obtained Kolmogorov-scale solutions can be used to describe the theoretically minimal self-sustained structures appearing in various shear flows.

A wearable thermoelectric generator fabricated on a glass fabric

The conversion of body heat into electrical energy using a thermoelectric (TE) power generator is useful for wearable self-powered mobile electronic systems such as medical sensors or smart watches. We herein demonstrate a glass fabric-based flexible TE generator using a screen printing technique and the self-sustaining structure of a TE device without top and bottom substrates. With this technique it is possible to make the device thin (∼500 μm), lightweight (∼0.13 g cm−2), and flexible. In addition, the developed TE generator achieved an unprecedentedly large output power density which is several tens of times higher than that of flexible TE generators reported to date. The developed TE generator shows an allowable bending radius of as low as 20 mm and no change in performance by repeated bending for 120 cycles. This work can expedite the development of wearable self-powered mobile devices.

Nanowire-based refractive index sensor on the tip of an optical fiber

This letter presents a refractive index sensor created at the tip of an optical fiber that utilizes silica nanowire within a radius of between 225 nm and 600 nm, as a sensing element. Sensitivity in excess of 800 nm/RIU was demonstrated within an aquatic medium, while the entire sensor structure was shorter than 1 mm with a diameter equal to or less than the standard fiber diameter. The presented sensor structure is made entirely from silica and provides the mechanical protection of sensitive nanowire. The proposed sensor is thus a robust and self-sustained structure, which does not require any complex packing.

Traveling self-sustained structures in interstellar clouds with the isentropic instability

The isentropic thermal instability of media with a generalized heat-loss function and negative bulk viscosity condition are discussed. We obtain the nonlinear equation taking into account the nonlinear saturation of the isentropic instability. This equation describes the nonstationary evolution of acoustical waves in media with the isentropic instability. Its stationary solutions are investigated analytically. The most interesting solution is the self-sustained pulse. Using the numerical simulation of the nonlinear acoustical equation and the full system of one-dimensional non-stationary hydrodynamical equations, we showed the disintegration of the initial weak perturbation of compression into sequence of these self-sustained pulses in low-density PDRs.

Zonal Embedded Grids for LES of Self-Sustaining Structures of Wall Turbulence

In this study, a zonal grid refinement method based on the solution of weakly compressible flow equations with large eddy simulation in the finite volume method (FVM) and dynamic subgrid-scale model framework was used to simulate the turbulence structures of a plane-wall flow with Reynolds number Re = U 0 δ/ ν = 10 000. Comparison and analysis were conducted on the distributions of time-averaged velocity and velocity fluctuations, as well as on the actual near-wall structures, to verify the accuracy of the turbulence features that were simulated using the zonal grid refinement method. The results show that the zonal embedded grid is a very efficient way to illustrate the turbulence structures of the near-wall region. The present method is easy to implement and extend to small Mach number flow modeling on a collocated irregular FVM mesh system.