Model Of Membrane Structure Research Articles

Vibration control of membrane structures by piezoelectric actuators considering piezoelectric nonlinearity under strong electric fields

Membrane structures, which are widely used in aerospace and civil engineering, are susceptible to large amplitude vibrations due to their low structural damping and high flexibility, leading to the degradation of their working performance. Strong electric fields are commonly needed for piezoelectric actuators to control larger amplitude vibration of membrane structures. However, the effect of piezoelectric nonlinearity due to strong electric fields on the control performance of membrane structures is still underexplored. Given the importance of piezoelectric nonlinearity due to strong electric fields, the present study aims to investigate the vibration control performance of piezoelectric actuators for membrane structures. First, based on the piezoelectric nonlinear constitutive equation, the actuation equation of the piezoelectric actuator is generated. Then, following D′Alembert's principle, a nonlinear dynamic control model of membrane structure containing actuation force is derived. Finally, active vibration control based on velocity feedback algorithms is realized. The results show that the predicted strain without considering the piezoelectric nonlinearity is 80 % smaller than the finite element structure at 500 V. Meanwhile, the errors of Root Mean Squared (RMS) control displacement without considering the piezoelectric nonlinearity are more than 24 % when vibration amplitudes achieve 10 % of the membrane thickness. The developed model provides theoretical implications for active vibration control of flexible structures with piezoelectric actuators in strong electric field environments.

Predicting virus filter performance using an advanced membrane structural model

Virus filters are essential in bioprocessing for safe therapeutic protein production. Understanding the correlation between virus filter structure and performance is important for efficient process design. By applying a multilayer structural model comprised of theoretical layers having pore size distributions, to published visualization data, we demonstrate in the present study that virus removal performance and filtration behavior can be quantitatively calculated. Virus filter structure can be classified into asymmetric high porosity, symmetric high density and laminated structure types. All types exhibit sufficient virus removal properties when used in normal processes. Laminated structure filters show extremely high virus particle removal performance, achieving the most robust virus removal even in filtration with process pauses, although flux decay tends to occur during filtration of solutions containing even very small amounts of aggregate. Conversely, asymmetric high porosity filters may show lower virus removal in processes involving multiple pauses that exceed practical conditions but shows stable filtration behavior with lower increase in pressure and lower flux decay even for the filtration of solutions containing aggregates. Such filtration behavior and virus removal properties can be quantitatively expressed and predicted by numerical calculations using a model based on the theoretical multilayer structure.

Experimental and numerical investigation on dynamic responses of the umbrella membrane structure excited by heavy rainfall

In this study, dynamic response of a typical umbrella membrane structure under heavy rainfall load is studied by experimental and numerical methods. In the experiment, heavy rainfalls of three rainfall intensities are applied to a typical umbrella membrane structure under five different tensile force levels. The dynamic responses of feature points and tensile force of cables are monitored by laser displacement sensors and digital tensimeters, respectively, during the experiment. In the numerical simulation, the membrane structural model is established in ANSYS by form-finding analysis, and the rainfall load that is calculated by the analytical formula is applied to dynamic analysis. The results of the numerical simulation and the experiment are in good agreement. According to the research results, the dynamic response laws of the umbrella membrane structure under rainstorm were obtained, and the influence of rainstorm load on the umbrella membrane structure was analyzed. Suggestions for safety and structural stability of the membrane structure are proposed.

Membrane Structures with Half-Costa Surface in YZ-Plane

This paper presents the computational form-finding analysis of half-Costa tensioned membrane structure model in YZ-plane with different boundaries. The computational form-finding analysis is carried out based on nonlinear analysis method. The tensioned membrane structure in the form of half-Costa models in YZ-plane with different geometry have been found to converge with least square error of total warp and fill stress deviation. The outcome of this paper can serve as a reference in selecting satisfactory parameters to allow the performance increase of tensioned membrane structure in the form of half-Costa in YZ-plane respected to their boundary condition. These models will be selective forms of tensioned membrane structure for design engineers and architect to ponder on as it is a resource efficient structure hence preventing further damage to the environment.

Generalized thermoelastic analysis of thermo-optic switch multi-layer structure

Delaminating failure is the fatal failure mode of Micro Electro Mechanical Systems(MEMS) multi-layer membrane structures and severely affects the reliability of MEMS devices. In this work, a multi-layer membrane structural model of a thermo-optic switch is established under the framework of generalized thermoelastic theory, and the distribution of interlayer temperature, thermal mismatch stress and core refractive index is calculated. The effect of relaxation time on thermal mismatch stress and refractive index is discussed, and numerical results show that the thermal mismatch stress increases with the heating power. When the relaxation time rises to 10−3s magnitude, the thermal mismatch stress decreases, the core layer reaches a high steady-state temperature and the refractive index of the core layer expands. These results provide a new idea for the research and development of new devices; that is, the adoption of core layer materials with long relaxation time can improve the reliability of MEMS devices.

Modeling effects of membrane tension on dynamic stall for thin membrane wings

An approach for predicting time varying aerodynamic loads on a pitching membrane wing due to rotational pitching and steady airflow is presented. The proposed model utilizes potential flow theory for a thin cambered airfoil with finite span, combined with a linearized representation of the membrane physics to predict lift under static conditions. Quasi-steady rotational effects and added mass effects are considered in a classic potential flow approach, modified for a membrane airfoil. A high-fidelity numerical model has been developed as well, coupling a viscous fluid solver and a non-linear membrane structural model, to predict the configuration of the system under static and unsteady loads. Moving Least Squares are used to map the structural and fluid interface kinematics and loads during the fluid–structure co-simulation. The static and dynamic lift predictions of the two models are compared to wind tunnel data, and show reasonable accuracy over a wide range of flow conditions, reduced frequency, and membrane pretension.

Electro-aeromechanical modelling of actuated membrane wings

This paper presents a numerical investigation on the aeromechanical performance of dynamically actuated membrane wings made of dielectric elastomers. They combine the advantages of membrane shape adaptability, which produces increased lift and delayed stall, with the benefits of simple, lightweight but high-authority control mechanism offered by integral actuation. High-fidelity numerical models have been developed to predict their performance and include a fluid solver based on the direct numerical integration of the unsteady Navier–Stokes equations, an electromechanical constitutive material model and a non-linear membrane structural model. Numerical results show that harmonic actuation can either increase or reduce the overall aerodynamic efficiency of the wing, measured as the mean lift-to-drag ratio, depending on the ratio between the actuation frequency and the natural frequency of the membrane. In addition, the definition of a reduced-order model based on POD modes of the complete high-fidelity system provides an insight of the main characteristics of the dynamics of the coupled system.

Thrust augmentation of flapping airfoils in low Reynolds number flow using a flexible membrane

The unsteady aerodynamic thrust and aeroelastic response of a two-dimensional membrane airfoil under prescribed harmonic motion are investigated computationally with a high-order Navier–Stokes solver coupled to a nonlinear membrane structural model. The effects of membrane prestress and elasticity are examined parametrically for selected plunge and pitch–plunge motions at a chord-based Reynolds number of 2500. The importance of inertial membrane loads resulting from the prescribed flapping is also assessed for pure plunging motions. This study compares the period-averaged aerodynamic loads of flexible versus rigid membrane airfoils and highlights the vortex structures and salient fluid–membrane interactions that enable more efficient flapping thrust production in low Reynolds number flows.

The Role of Lipid Domains in Bacterial Cell Processes

Membranes are vital structures for cellular life forms. As thin, hydrophobic films, they provide a physical barrier separating the aqueous cytoplasm from the outside world or from the interiors of other cellular compartments. They maintain a selective permeability for the import and export of water-soluble compounds, enabling the living cell to maintain a stable chemical environment for biological processes. Cell membranes are primarily composed of two crucial substances, lipids and proteins. Bacterial membranes can sense environmental changes or communication signals from other cells and they support different cell processes, including cell division, differentiation, protein secretion and supplementary protein functions. The original fluid mosaic model of membrane structure has been recently revised because it has become apparent that domains of different lipid composition are present in both eukaryotic and prokaryotic cell membranes. In this review, we summarize different aspects of phospholipid domain formation in bacterial membranes, mainly in Gram-negative Escherichia coli and Gram-positive Bacillus subtilis. We describe the role of these lipid domains in membrane dynamics and the localization of specific proteins and protein complexes in relation to the regulation of cellular function.

What history tells us XXX. The emergence of the fluid mosaic model of membranes

In 1968, Walther Stoeckenius summarized in Science the conclusions of a meeting held the previous year at Frascati near Rome on ‘membrane modelling and membrane formation’ (Stoeckenius 1968). The diversity of the issues that were raised, and of the methods and models that were used, was such that no consensus could be reached. At that time, even the existence of a cell membrane was not unanimously accepted! Three years later, S Jonathan Singer (1971) proposed the mosaic model of the structure of cell membranes to replace the previously dominant Danielli–Robertson unit membrane model, and one year later he and Garth L Nicolson added the word ‘fluid’ to ‘mosaic’ (Singer and Nicolson 1972). The new model was rapidly and unanimously accepted, and it remained unaltered during the next forty years. This rapid evolution of models of the membrane structure has not been explored by historians. I will show that the emergence of the fluid mosaic model was not as smooth as indicated in the description given by one of its authors (Singer 2004). What happened in the mid-1960s was an unsuccessful attempt to replace the lipid bilayer model, also more precisely named the ‘bimolecular lipid leaflet’ model, by a new model giving proteins a major role in the organization of membranes. The unexpected resistance of the lipid bilayer model, as well as new data demonstrating the rapid displacement of proteins within the membrane plane, led to a progressively elaborated synthesis that was brilliantly outlined by Singer and Nicolson in their famous Science article. 2. The challenges to the lipid bilayer model of membrane structure in the 1960s

High fidelity computational simulation of a membrane wing airfoil

Computations and analysis for a two-dimensional flexible membrane wing airfoil are presented. A well-validated, robust, sixth-order Navier–Stokes solver is employed coupled with a membrane structural model suitable for the highly nonlinear structural response of the membrane. A low Reynolds number, Re=2500, consistent with MAV flight is chosen for the majority of the calculations. The most notable effect of the membrane flexibility is the introduction of a mean camber to the membrane airfoil. A close coupling between unsteady vortex shedding and the dynamic structural response is demonstrated. The dynamic motion of the membrane surface is also shown to significantly alter the unsteady flow over the membrane airfoil at high angles of attack. The coupling of this dynamic effect and the mean camber results in a delay in stall with enhanced lift for higher angles of attack. Exploratory computations investigating the effects of angle of attack, membrane rigidity, membrane pretension and Reynolds number on the membrane airfoil response are also presented.

Application of SMA in Membrane Structure Shape Control

Shape memory alloy (SMA) actuators have found a wide range of applications due to their unique properties such as high force, long stroke, small size, light weight, and silent operation, etc. However, their strong nonlinear properties make them a challenge to achieve accurate actuations. A simple control strategy is presented based on the idea of adjusting the SMA wire temperature as rapidly as possible. This strategy is simple, stable, and requires no hysteresis model or thermal model. The strategy is tested first on tracking displacement outputs, and effects of updating rate and input current on control accuracy are also discussed. It is then used for active shape control of a membrane structure model by adjusting its boundary tensions. Results indicate that under the developed control strategy, SMA wire actuators can offer very good accuracy in tracking displacement outputs and tension outputs. For the membrane structure shape control, the structure shape precision is improved greatly.

Lipid spirals in Bacillus subtilis and their role in cell division

The fluid mosaic model of membrane structure has been revised in recent years as it has become evident that domains of different lipid composition are present in eukaryotic and prokaryotic cells. Using membrane binding fluorescent dyes, we demonstrate the presence of lipid spirals extending along the long axis of cells of the rod-shaped bacterium Bacillus subtilis. These spiral structures are absent from cells in which the synthesis of phosphatidylglycerol is disrupted, suggesting an enrichment in anionic phospholipids. Green fluorescent protein fusions of the cell division protein MinD also form spiral structures and these were shown by fluorescence resonance energy transfer to be coincident with the lipid spirals. These data indicate a higher level of membrane lipid organization than previously observed and a primary role for lipid spirals in determining the site of cell division in bacterial cells.

Ion mobility in Nafion-117 membranes

Transport phenomena in Nafion-117 perfluorosulphonic membranes have been studied by different techniques. Membrane electric conductivity has been measured under alternative current as a function of the equilibrating concentrations of MCI (M = Li, Na, K) and HCl solutions. Conductivities were found to increase for lithium and sodium membrane forms and decrease for the potassium form with an electrolyte concentration increase. The obtained data were compared with the results of diffusion permeability, ion-exchange kinetics, 7Li and 35Cl NMR measurements. In all cases permeability increased with electrolyte concentration growth. Diffusion coefficients and transport numbers for different counter- and co-ions were determined. The obtained data are discussed with the use of the two-phase membrane structure model. The selectivity of membrane sorption was found to increase with growth of cation radius.

Hypothalamic superoxide dismutase, xanthine oxidase, nitric oxide, and malondialdehyde in rats fed with fish ω-3 fatty acids

Phospholipids located in the cellular membrane play a critical role in the fluid-mosaic model of membrane structure and membrane function. Evidence is mounting for the role of abnormal phospholipid metabolism in some neuropsychiatric disorders including schizophrenia. As an important essential fatty acid (EFA), omega-3 (ω-3) fatty acid series are found in large amounts in fish oil. The aim of this experimental study was to assess the changes of some of the oxidant and antioxidant parameters in the hypothalamus of rats fed with ω-3 EFA diet (0.4 g/kg/day) for 30 days. Eight control rats and nine rats fed with ω-3 were decapitated under ether anesthesia, and hypothalamus was removed immediately. Malondialdehyde (MDA) and nitric oxide (NO) levels as well as superoxide dismutase (SOD) and xanthine oxidase (XO) enzyme activities in the hypothalamus were measured. SOD activity was significantly decreased in ω-3 EFA treated group compared to control group ( p<0.014). Tissue MDA and NO levels were also decreased in ω-3 EFA treated group compared to control rats ( p<0.0001). Xanthine oxidase activity was found to be increased in ω-3 EFA treated rats when compared to the control group ( p<0.0001). Taken together, this preliminary animal study provides strong support for a therapeutic effect of ω-3 EFA in some neuropsychiatric disorders in which reactive oxygen species (ROS) are recently accused to be an important physiopathogenetic factor.

Some early history of membrane molecular biology.

This article is mostly about the beginnings of the molecular biology of membranes, covering the decade 1964-1974. It is difficult to read (or write) this article because of a sense of deja vu. Most of the material in it is considered commonplace today, having been established experimentally since then. But at the time this work was begun, practically nothing was known about the molecular structure and the mechanisms of the functions of membranes. This situation existed because no membrane proteins of the kind I called integral had as yet been isolated in a pure state, and therefore none had had their amino acid sequence determined. The first integral membrane protein to be so characterized was human erythrocyte glycophorin, in 1978. It was the use of the thermodynamic reasoning that had been developed for the study of water-soluble proteins, together with the information from several key experiments carried out in a number of laboratories during the early decade, that led us to the fluid mosaic model of membrane structure in 1972. Without direct evidence to confirm the model in 1971-1972, my colleagues and I nevertheless had the confidence in it to pursue some of the consequences of the model for a new understanding of many membrane functions, which I present here in some detail. Finally, I discuss two recent high-resolution X-ray crystallographic studies of integral proteins to ask how well the structural and functional proposals that we derived from the fluid mosaic model fit these remarkably detailed X-ray results.

Effect of pore morphology on fluid flow and particle deposition on a track-etched polycarbonate membrane

Three-dimensional particles deposition on a filter pore of a track-etched polycarbonate membrane was studied numerically by analyzing forces acting on the depositing particles. The simulation was applied to examine how the morphology of the filter pore affects the deposition of particles on a membrane pore at the initial stage of filtration. The model of membrane structure is a 3D porous surface with circular holes of finite thickness. Both of the effects of constriction and expansion of inner pore geometries on fluid flow and particle deposition are taken into consideration in numerical calculation, and are compared with that of capillary pore. The disturbance of flow field and particle trajectory due to the presence of particles was taken into consideration during each simulation. Simulated results show that the effect of filtration rate, i.e., operating pressure, has a significant influence on the packing morphology of particles on a filter pore.

From proton pump to proteome. Twenty-five years of research on ion transport in higher plants.

To understand just how far research on ion transport has come, it is informative to look first at the status of the field 25 years ago. In the early 1970s, scientists were still struggling to understand the basic structure of the cell membrane. The fluid mosaic model of membrane structure entered

Membrane structure of the hepatitis B virus surface antigen particle.

Expression of S protein, an envelope protein of hepatitis B virus, in the absence of other viral proteins, leads to the secretion of hepatitis B virus surface antigen (HBsAg) particles that are formed by budding from the endoplasmic reticulum membranes. The HBsAg particles produced by mouse fibroblast cells show a unique lipid composition, with 1,2-diacyl glycerophosphocholine being the dominant component. The lipid organization of the HBsAg particles was studied by measuring electron spin resonance (ESR) using various spin-labeled fatty acids, and the results were compared with a parallel study on HVJ (Sendai virus) and vesicles reconstituted with total lipids of the HBsAg particles (HBs-lipid vesicles). HVJ and the HBs-lipid vesicles showed typical ESR spectra of lipids arranged in a lipid bilayer structure. In contrast, the ESR spectra obtained with the HBsAg particles showed that the movement of lipids in the particle is severely restricted and a typical immobilized signal characteristic of tight lipid-protein interactions was also evident. Phosphatidylcholine (PC) in the HBsAg particles was not exchangeable by a PC-specific exchange protein purified from bovine liver, while phospholipase A(2) from Naja naja vemon was able to hydrolyze all the PC in the particles. These analyses suggest that the lipids in the HBsAg particles are not organized in a typical lipid bilayer structure, but are located at the surface of the particles and are in a highly immobilized state. Based on these observations we propose a unique lipid assembly and membrane structure model for HBsAg particles.

Theoretical investigation of water sorption in perfluorinated sulfocationic membranes

A water sorption process in the perfluorinated sulfocationic membranes (PSM) is of interest from the point of view of study of formation of monolayer and multilayer fillings in strongly nonuniform environments and influence of a character of membrane fillings on the diffusion characteristics of their permeability. In the practice tasks the interest to the PSM for the experimental and theoretical investigation is due to unique properties (high chemical and thermal firmness, high permissible density of current). At this work the model of membrane structure is proposed. The interparticle potentials created on the quantum-chemical MNDO calculations are used in the PSM-cation-water system’s potential energy calculation. Influence of the water content of a membrane on character of distribution of molecules of a water is investigated by method of atom–atomic potentials. On analysing of water locations at different water contents in membrane, a lattice structure for water distribution in pore space was created. With lattice-gas model a macroscopic characteristics such as the isotherm and heat of sorption and the coefficient of diffusion of water molecules are calculated. The results are comparing with experimental data and the results of the molecular dynamics simulation method.