Mechanical analysis of heterogeneous materials with higher-order parameters

Even though heterogeneous porous materials are widely used in a variety of engineering and scientific fields, such as aerospace, energy-storage technology, and bio-engineering, the relationship between effective material properties of porous materials and their underlying morphology is still not fully understood. To contribute to this knowledge gap, this paper adopts a higher-order asymptotic homogenization method to numerically investigate the effect of complex micropore morphology on the effective mechanical properties of a porous system. Specifically, we use the second-order scheme that is an extension of the first-order computational homogenization framework, where a generalized continuum enables us to introduce length scale into the material constitutive law and capture both pore size and pore distribution. Through several numerical case studies with different combinations of porosity, pore shapes, and distributions, we systematically studied the relationship between the underlying morphology and effective mechanical properties. The results highlight the necessity of higher-order homogenization in understanding the mechanical properties and reveal that higher-order parameters are required to capture the role of realistic pore morphologies on effective mechanical properties. Furthermore, for specific pore shapes, higher-order parameters exhibit dominant influence over the first-order continuum.

FUNCTIONAL MATERIALS FROM WASTE PAPER. III. COMPARATIVE STUDY OF MORPHOLOGY OF POWDER CELLULOSES AND CELLULOSE HYDROGELS

The morphology of hydrogels regenerated from solutions of waste paper and cardboard in DMAс/LiCl was studied for the first time in comparison with the morphology of pristine samples and powder celluloses isolated from waste paper. Two sets consisted every of them from 4 samples, pristine waste paper or cardboard, powder cellulose, swollen hydrogel and freeze-dried hydrogel, were examined with a SEM. As revealed by SEM, the freeze-dried hydrogels are porous systems with a variety of through pores in a wide range of sizes. The number, shape, and size of pores, as well as their availability, differed markedly. The pore sizes in freeze-dried hydrogels obtained from the waste paper are mostly ranged at 30-50 nm. The smallest pores in the waste cardboard are 30-40 nm in size, the largest ones are up to 4 μm. According to the results of the study, these samples will have satisfactory sorption properties but, due to the different morphology of the porous system, the availability of each sample is likely to vary significantly.

Nanofluidic thermal-fluid transport in a split-driven porous system working under a magnetic environment

Purpose This study aims to focus on a thermo-fluid flow in a partially driven cavity (PDC) using Cu-water nanoliquid, magnetic field and porous substance. The cooling and sliding motion are applied on the upper half of the vertical walls and the bottom wall is heated. Thermal characteristics are explored to understand magnetohydrodynamic convection in a nanoliquid filled porous system from a fundamental viewpoint. The governing parameters involved to cater to the moving speed of the sidewalls and partial translation direction are the relative strength of thermal buoyancy, porous substance permeability, magnetic field intensity, nanoparticle suspension and orientation of the cavity. Design/methodology/approach The coupled transport equations of the problem are solved using an in-house developed finite volume-based computing code. The staggered nonuniform grids along the x and y directions are used. The SIMPLE algorithm technique is considered for the iterative solution of the discretized equations with the convergence check of the continuity mass defect below 10–10. Findings The present study unveils that the heat transfer enhances at higher Ri with the increasing value of Re, irrespective of the presence of a porous substance or magnetic field or the concentration of nanofluid. Apart from different flow controlling parameters, the wall motions have a significant contribution to the formation of flow vortices and corresponding heat transfer. Orientation of the cavity significantly alters the transport process within the cavity. The upward wall velocity for both the sidewalls could be a better choice to enhance the high heat transfer (approximately 88.39% at Richardson and Reynolds numbers, respectively, 0.1 and 200). Research limitations/implications Considering other multi-physical scenarios like porous layers, conducting block, microorganisms and the present investigation could be further extended to analyze a problem of complex flow physics. Practical implications In this study, the concept of partially driven wall motion has been adopted under the Cu-water nanoliquid, magnetic field, porous substance and oblique enclosure. All the involved flow-controlling parameters have been experimented with under a wide parametric range and associated thermo-flow physics are analyzed in detail. This outcome of this study can be very significant for designing as well as controlling thermal devices. Originality/value The convective process in a partially driven cavity (PDC) with the porous medium has not been investigated in detail considering the multi-physical scenarios. Thus, the present effort is motivated to explore the thermal convection in such an oblique enclosure. The enclosure is heated at its bottom and has partially moving-wall cold walls. It consists of various multi-physical conditions like porous structure, magnetic field, Cu–H2O nanoliquid, etc. The system performance is addressed under different significant variables such as Richardson number, Reynolds number, Darcy number, Hartmann number, nanoliquid concentration and orientation of cavity.

Hierarchical Modeling of the Liver Vascular System

The liver plays a key role in the metabolic homeostasis of the whole organism. To carry out its functions, it is endowed with a peculiar circulatory system, made of three main dendritic flow structures and lobules. Understanding the vascular anatomy of the liver is clinically relevant since various liver pathologies are related to vascular disorders. Here, we develop a novel liver circulation model with a deterministic architecture based on the constructal law of design over the entire scale range (from macrocirculation to microcirculation). In this framework, the liver vascular structure is a combination of superimposed tree-shaped networks and porous system, where the main geometrical features of the dendritic fluid networks and the permeability of the porous medium, are defined from the constructal viewpoint. With this model, we are able to emulate physiological scenarios and to predict changes in blood pressure and flow rates throughout the hepatic vasculature due to resection or thrombosis in certain portions of the organ, simulated as deliberate blockages in the blood supply to these sections. This work sheds light on the critical impact of the vascular network on mechanics-related processes occurring in hepatic diseases, healing and regeneration that involve blood flow redistribution and are at the core of liver resilience.

Magnetic Resonance Pore Imaging, a new tool for porous media research

<p>Porous media are highly prevalent in nature and span a wide range of systems including biological tissues, chemical catalysts or rocks in oil reservoirs. Imaging of the structure of the constituent pores is therefore highly desirable for life sciences and technological applications. This thesis presents the new development and application of a nuclear magnetic resonance (NMR) technique to acquire high resolution images of closed pores. The technique is a further development of diffusive-diffraction Pulsed Gradient Spin Echo (PGSE) NMR, which has been shown to image the pore auto-correlation function averaged over all pores. Until recently it was conventional wisdom that diffusive-diffraction PGSE NMR can only measure the magnitude of the form factor, due to its similarity to diffraction techniques such as x-ray and neutron scattering. In diffraction applications the loss of phase information is commonly referred to as the “phase problem”, which prevents the reconstruction of images of the pore space by inverse Fourier transform. My work is based on a recently suggested modification of the diffusive-diffraction PGSE NMR method, which creates a hybrid between Magnetic Resonance Imaging (MRI) and PGSE NMR. Therefore, we call this approach Magnetic Resonance Pore Imaging (MRPI). We provide experimental confirmation that MRPI does indeed measure the diffractive signal including its phase and thus the “phase problem” is lifted. We suggest a two-dimensional version of MRPI and obtain two-dimensional average pore images of cylindrical and triangular pores with an unprecedented resolution as compared to state of the art MRI. Utilizing a laser machined phantom sample we present images of microscopic pores with triangular shape even in the presence of wall relaxation effects. We therefore show that MRPI is able to reconstruct the pore shape without any prior knowledge or assumption about the porous system under study. Furthermore, we demonstrate that the MRPI approach integrates seamlessly with known MRI concepts. For instance we introduce “MRPI mapping” which acquires the MRPI signal for each pixel in an MRI image. This enables one to resolve pore sizes and shapes spatially, thus expanding the application of MRPI to samples with heterogeneous distributions of pores.</p>

Magnetic Resonance Pore Imaging, a new tool for porous media research

<p>Porous media are highly prevalent in nature and span a wide range of systems including biological tissues, chemical catalysts or rocks in oil reservoirs. Imaging of the structure of the constituent pores is therefore highly desirable for life sciences and technological applications. This thesis presents the new development and application of a nuclear magnetic resonance (NMR) technique to acquire high resolution images of closed pores. The technique is a further development of diffusive-diffraction Pulsed Gradient Spin Echo (PGSE) NMR, which has been shown to image the pore auto-correlation function averaged over all pores. Until recently it was conventional wisdom that diffusive-diffraction PGSE NMR can only measure the magnitude of the form factor, due to its similarity to diffraction techniques such as x-ray and neutron scattering. In diffraction applications the loss of phase information is commonly referred to as the “phase problem”, which prevents the reconstruction of images of the pore space by inverse Fourier transform. My work is based on a recently suggested modification of the diffusive-diffraction PGSE NMR method, which creates a hybrid between Magnetic Resonance Imaging (MRI) and PGSE NMR. Therefore, we call this approach Magnetic Resonance Pore Imaging (MRPI). We provide experimental confirmation that MRPI does indeed measure the diffractive signal including its phase and thus the “phase problem” is lifted. We suggest a two-dimensional version of MRPI and obtain two-dimensional average pore images of cylindrical and triangular pores with an unprecedented resolution as compared to state of the art MRI. Utilizing a laser machined phantom sample we present images of microscopic pores with triangular shape even in the presence of wall relaxation effects. We therefore show that MRPI is able to reconstruct the pore shape without any prior knowledge or assumption about the porous system under study. Furthermore, we demonstrate that the MRPI approach integrates seamlessly with known MRI concepts. For instance we introduce “MRPI mapping” which acquires the MRPI signal for each pixel in an MRI image. This enables one to resolve pore sizes and shapes spatially, thus expanding the application of MRPI to samples with heterogeneous distributions of pores.</p>

Pore pressure coefficient in frozen soils

The Skempton pore pressure coefficient, B, is defined as the variation in pore pressure with the unit change in confining pressure under undrained conditions. The B-parameter is an essential parameter to consider the coupled effects of solid-fluid compressibility and skeleton compressibility in the porous system. It is a key factor in exploring a possible definition of effective stress in frozen soil. However, limited experimental and theoretical research is available in the literature to give insight to the problem. Therefore a series of B tests on frozen clay was conducted in this study. Results from these tests along with tests on Ottawa sand, available in the literature, are analyzed considering the effect of the ice crystallization mode on the skeleton stiffness. The measured B values were lower than expected compared with B-value using models which consider single grain bulk stiffness. However, when the difference in bulk stiffness of ice and of soil grains is considered, even an increase in pore volume, for an increase in fluid pressure, at constant Terzaghi effective stress is possible. The “pore stiffness”, different from the solid phase stiffness, can take a negative value and can be used to explain the low measured B values.

MICROSCOPIC CHARACTERISTICS OF STRUCTURAL HETEROGENEITY OF INTACT TOOTH ENAMEL

В нарушении нормального течения обменных процессов, протекающих с участием эмали существенную роль, играют особенности ее структурной неоднородности. Подробная морфологическая микроскопическая характеристика этих структур в литературе отсутствует, что привело к необходимости установления наличия полостей и микрокапиллярной компоненты в системе структурной неоднородности интактной зубной эмали между ее поверхностью и дентином путём применения оптической инвертированной и атомно-силовой микроскопии. Проведено исследование 180 препаратов зубов. Для изучения микро- и ультраструктурного строения эмали предложена методика приготовления препаратов продольного шлифа интактной эмали зуба, включающая финишную ультразвуковую очистку образца. Дана морфологическая оценка структурной неоднородности интактной зубной эмали, обнаруженной при ее оптической инвертированной и атомно-сило-вой микроскопии, которая может быть применена в стоматологии для разработки инновационных методов диагностики, лечения и профилактики заболеваний зубов. Выявленные неоднородности в структуре ткани интактной эмали зуба представлены пустотами (полостями) в твердой фазе вещества эмали, позволяющими характеризовать эмаль как микрокапиллярно-пористую систему. Визуализировалась твердая фаза эмали и система иерархически организованных полостей, протяженных и взаимосвязанных между собой, упорядоченно и равномерно распределённых по всему объёму эмали зуба от ее поверхности до эмалево-дентинного соединения. Наличие таких сообщений указывает на возможность прямого обмена вещества в ткани эмали зуба как с поверхности, так и из корневого канала. Полученные при оптическом инвертированном и атомно-силовом микроскопировании данные создают представление о наличии между поверхностью эмали зуба и границей эмалево-дентинного соединения в эмали полых пространств – пор, сопряжённых с микрокапиллярами, значительно преобладающих над твердой фазой объема эмали. Система полостей в эмали зуба может быть выявлена при рутинном исследовании с использованием оптического инвертированного и атомно-силового микроскопов, что делает доступным изучение объектов, не требующего значительных временных и финансовых затрат. In violation of the normal course of metabolic processes occurring with the participation of enamel, the features of its structural heterogeneity play an essential role. Detailed morphological microscopic characteristics of these structures are not available in the literature, which led to the need to establish the presence of cavities and microcapillary components in the system of structural heterogeneity of intact tooth enamel between its surface and dentin by using optical inverted and atomic force microscopy. A study of 180 dental preparations was conducted. To study the micro- and ultrastructural structure of enamel, a method for preparing preparations of the longitudinal section of intact tooth enamel, including the final ultrasonic cleaning of the sample, is proposed. A morphological assessment of the structural heterogeneity of intact tooth enamel detected by its optical inverted and atomic force microscopy is given, which can be used in dentistry to develop innovative methods for the diagnosis, treatment and prevention of dental diseases. The revealed inhomogeneities in the structure of the intact tooth enamel tissue are represented by voids (cavities) in the solid phase of the enamel substance, which make it possible to characterize the enamel as a microcapillary-porous system. The solid phase of the enamel and a system of hierarchically organized cavities, extended and interconnected, orderly and evenly distributed over the entire volume of tooth enamel from its surface to the enamel-dentine junction were visualized. The presence of such messages indicates the possibility of direct exchange of substances in the tooth enamel tissue both from the surface and from the root canal. The data obtained by optical inverted and atomic force microscopy give an idea of the presence of hollow spaces - pores conjugated with microcapillaries in the enamel between the surface of the tooth enamel and the border of the enamel–dentine junction, significantly prevailing over the solid phase of the enamel volume. The system of cavities in the tooth enamel can be detected during routine examination using optical inverted and atomic force microscopes, which makes it possible to study objects that do not require significant time and financial costs.

Stability Result for a Weakly Nonlinearly Damped Porous System with Distributed Delay

In this paper, we consider a one-dimensional porous system damped with a single weakly nonlinear feedback and distributed delay term. Without imposing any restrictive growth assumption near the origin on the damping term, we establish an explicit and general decay rate, using a multiplier method and some properties of convex functions in case of the same speed of propagation in the two equations of the system. The result is new and opens more research areas into porous-elastic system.