Multilayered Wall Research Articles

Optimized infrared-assisted extraction to obtain total lipid from microalgae Scenedesmus obliquus: a green approach

Abstract Microalgae oil has great potential to address the growing energy demand and dependence on fossil fuels. However, the multilayered cell walls of microalgae hinder efficient extraction and enhanced lipid recovery. In this study, we develop a novel protocol based on near infrared-assisted extraction (NIRAE) technology to extract efficiently total lipids from Scenedesmus obliquus. Under a greener solvent extraction approach, the effect of nine non-polar/polar solvent systems in various ratios on lipid yield was tested, and the results were compared with Soxhlet, Folch, and Bligh–Dyer methods. The highest oil yields were NIRAE 15.43%, and Soxhlet 22.24%, using AcoEt/MeOH (1:2 v/v). For Folch and Bligh–Dyer, 9.11 and 10%, respectively. The optimized NIRAE conditions obtained using response surface methodology (RSM): 43.8 min, solvent/biomass 129.90:1 (m/v), and AcOEt/MeOH 0.57:2.43 (v/v) increased the oil yield significantly to 24.20%. In contrast to conventional methods, the overall optimized NIRAE process satisfied the requirements of a green extraction because of the simple and safe operation, less solvent toxicity, lower extraction time, and solvent and energy consumption.

Construction of discontinuous enrichment functions for enriched or generalized FEM’s for interface elliptic problems in 1D

We introduce an enriched unfitted finite element method to solve 1D elliptic interface problems with discontinuous solutions, including those having implicit or Robin-type interface jump conditions. We present a novel approach to construct a one-parameter family of discontinuous enrichment functions by finding an optimal order interpolating function to the discontinuous solutions. In the literature, an enrichment function is usually given beforehand, not related to the construction step of an interpolation operator. Furthermore, we recover the well-known continuous enrichment function when the parameter is set to zero. To prove its efficiency, the enriched linear and quadratic elements are applied to a multi-layer wall model for drug-eluting stents in which zero-flux jump conditions and implicit concentration interface conditions are both present.

Experimental investigation of multi-layered strong wood-frame shear walls with nonstructural Type X gypsum wallboard layers under cyclic load

A fundamental premise for the design of resilient light frame timber buildings in areas of high seismic activity consists of achieving strong shear walls while keeping nonstructural damage to a minimum, especially by preventing the brittle failure of Type X gypsum wallboard (GWB) finish layers. Under this premise, it has been commonly thought that the stronger the shear wall the lesser the structural contribution of the finishes, and therefore the effect of GWB finishes in strong timber shear walls has been typically ignored by design codes and mechanical models. In the research reported in this paper, the influence of nonstructural finishes on the structural characteristics of a strong light frame shear wall was experimentally and numerically investigated. The wall evaluated in this paper, denoted here Multi-Layered Strong Shear Wall (MLSSW), is representative of walls located at the 1st story of a 7-story building located in Chile, a country where the level of seismic activity is high. The MLSSW has a continuous rod system, double OSB sheathing, robust timber framing, closely spaced nails to attach the OSB sheathing layers to wood-frame members, and is covered at both sides by two layers of screwed Type X GWB. The characteristics of the MLSSW, particularly the quantity and type of nonstructural finishes, are different from those of typical light frame timber walls. Full-scale connection-level tests, both monotonic and cyclic, are reported first, followed by descriptions of the full-scale cyclic assembly-level tests. For comparison purposes, a bare strong wall (i.e., without the GWB layers) was tested as well. The structural response of the MLSSW was evaluated in terms of stiffness, strength, energy dissipation and plastic deformation characteristics. The applicability of the SDPWS analytical model was also evaluated, as well as the applicability of existing numerical models to predict the cyclic behavior of the MLSSW.

Development of a white-box dynamic building thermal model integrated with a heating system

Development of a simplified building model can effectively mimic the transient building thermal behaviour which essentially depends on the weather profile and the building architecture under various operational strategies and occupant behaviour. This work presents the mathematical solution procedure based on the white-box physical building thermal model using resistance and capacitance network (i.e. lumped capacitance). The work takes into account the dynamic behaviour of radiator, and its heat flow adjustment via a thermostatic radiator valve, the solar heat gain (function of the time and location), the infiltration heat loss together with building model having multi-zone with multi-layer wall structure. The case study reveals that the integrated behaviour of the building components under a given control strategy paves the way for simulating different control strategies when large-scale district heating systems are considered.

Optimal Experiment Design for the estimation of building wall material thermal properties

The estimation of wall thermal properties through an inverse problem procedure enables to increase the reliability of the model predictions for building energy efficiency. Nevertheless, it requires to define an experimental campaign to obtain on-site observations for existing buildings. The design of experiments enables to search for the optimal measurement plan that ensure the highest precision of the parameter estimation. For on-site measurement in buildings, it seeks an answer to several questions such as number and position of sensors, period and duration of the experimental campaign. In this article, the Optimal Experiment Design (OED) methodology is applied for a multi-layer building wall to resolve the aforementioned issues.

Structural insight into mycobacterial cell wall biosynthesis by AftB, a potential anti-TB drug target.

Tuberculosis (TB) is a severe infectious disease caused by Mycobacterium tuberculosis (Mtb) and remains a significant health problem worldwide. The success of Mtb as the leading pathogen can largely be attributed to its atypical multilayered cell wall, which is highly impermeable and confers natural protection against attack from the immune system and many antibiotics. Due to its unique character, the mycobacterial cell wall has become the most widely exploited target of anti-TB drugs. AftB is an arabinofuranosyltransferase that functions in the terminal step of cell wall arabinan biosynthesis, catalyzing the transfer of arabinose from the donor decaprenyl-phosphate-arabinose (DPA) onto the cell wall polysaccharides. AftB is essential for Mtb's survival and is deemed a potential new drug target for TB. Here we report the atomic-resolution structures of AftB obtained by cryo-EM in both apo and donor substrate analog bound forms. The apo structure revealed that AftB contains 11 transmembrane helices belonging to the GT-C glycosyltransferase superfamily and a periplasmic segment of a novel fold which might direct the binding of polysaccharides acceptor. AftB forms a large putative substrate-binding cavity, with one side facing the periplasmic domain and the other facing the lipid bilayer. The substrate-bound structure further unmasked the nature of the active site. Using synthetic AftB donor and acceptor substrates, we recapitulated the enzymatic reaction in vitro. And the functional analysis using AftB variants further proved the importance of the active site revealed from our structures. We proposed that AftB catalyzes the glycosylation reaction by utilizing a conserved aspartate residue as the base catalyst. Collectively, our work provides a structural basis for understanding the molecular mechanism of AftB and a blueprint for developing new drugs to combat the increasing threat caused by Mtb.

Testing the thermal properties of modern ventilated facade fastening systems

The study reported in this paper investigated a set of building fasteners used in ventilated facades. For the building fasteners actually present in the industrial market the values of the effective thermal conductivity were measured experimentally. These values were used next in numerical simulations run with COMSOL Multiphysics software application. The validation of the simulation model was done in specific additional experimental test. The paper presents a method of determining the effective thermal conductivity coefficient for fasteners with a novel design. Temperature distributions and heat fluxes were determined for different variants of multilayer walls with the fasteners. The calculation of the effective thermal conductivity coefficient for a structural profile is based on the heat balance of the measuring stand. The performed tests show not only an expected reduction in the coefficient value for structures in which stainless steel is used. The results also demonstrate that the fasteners with holes cut out in their structures have significantly lower effective thermal conductivity coefficients than those with solid walls. This effect can be justified by the formation of labyrinth-like narrowings extending the conductive heat flow path in the fastener. As a final result of the experimental tests and the COMSOL simulations the application of the effective thermal conductivity as the new indicator of a thermal effectiveness of building fasteners is proposed in industrial practice. Consequently the design of the building fasteners with various shapes of holes is recommended for improving their insulation features.

Hygrothermal transfers through a bio-based multilayered wall: Modeling study of different wall configurations subjected to various climates and indoor cyclic loads

The hygrothermal behavior of a bio-based multilayered wall has been studied by numerical simulations. The key point of these research investigations was to properly describe the hygrothermal transfers occurring inside the studied wall solution. In previous work, the case of the wall subjected to a given real climate (Wroughton HIVE demonstrator, UK, Feb 2018) has been investigated. The present work, focused on the moisture regulation capacity of the wall, considers an improved kinetics model of sorption, different layer configurations, one additional climate (Bordeaux, FR, Apr 2008) and the effect of indoor cyclic loads. Compared to the classical approach, the local kinetics approach results in prediction of stronger and steeper hygric dynamics with larger relative humidity variations at small time scales. The study of the different wall configurations allows to determine the best one in terms of moisture damping: the vapor control membrane is advantageously removed provided the OSB3 12 mm layer is replaced by an OSB4 18 mm layer. Moreover, the simulations show that the Moisture Buffer Value characteristic of each material layer is not a sufficient criterion to evaluate hygric performance of the wall; strong hygric interactions occur with the layer’s permeability independently of its sorption capacity. Finally, water content hysteresis phenomena are studied and it appears that under usual operating conditions, they can be ignored by adjusting the layers’ permeabilities for adequate fits on the Moisture Buffer Value tests.

Experimental and numerical study of blast resistance of geopolymer based high performance concrete sandwich walls incorporated with metallic tube core

To reduce the disastrous consequences caused by explosion, increasing attention has been paid to the blast mitigation of structures while keeping their adequate functions in recent years. In this study, an innovative multi-layer sandwich wall has been developed to provide blast mitigation for protective structures. Such a multi-layer sandwich wall consists of three layers including two steel wire mesh (SWM) reinforced geopolymer based high performance concrete (G-HPC) layers and a metallic tube core (MTC) layer. The blast behavior of the multi-layer sandwich walls under 1.0 kg contact explosion was investigated experimentally and numerically. A total of five sandwich walls were tested to explore the influence of different factors (including the thickness of the front/rear G-HPC layer and MTC layer) on their performance. Subsequently, a finite element model was developed and validated by comparing the numerical results with the experimental data. The findings indicated that the well-designed sandwich walls exhibited excellent anti-blast performance and the rear G-HPC layer remarkably affected the anti-blast performance. In addition, the numerical results could fairly predict the experimental phenomenon.

Challenges on pumping infra-lightweight concrete based on highly porous aggregates

Infra-lightweight concrete (ILC) is the latest step in the development lightweight concrete mainly for the use in monolithic exterior walls. By optimizing the balance between reduced density, sufficient strength and the lowest possible thermal conductivity, ILC offers a competitive alternative to multilayer wall structures commonly used today. Pumping of fresh concrete is becoming increasingly important owing to further rationalization on the construction site and the increasing use of ready-mix concrete. However, pumping lightweight concretes is often associated with difficulties. This article presents the first study ever on pumpability of a record breaking ILC, using some of the most common concrete pumps. Therefore, an experimental study was carried out to determine whether the pressurization of the fresh concrete in the course of the pumping process influences fresh and hardened ILC properties. Based on the results, it can be concluded that ILC can be pumped. The delivery principle of the pumps has a particular influence on fresh ILC properties, especially in terms of abrasive stress on the porous aggregates and workability. No significant negative influences on hardened concrete properties were detected. Classification of the ILC can be accomplished in the same density and strength class before and after pumping. The study highlights challenges of pumping ILC with highly porous aggregates and provides practical approaches to its realization.

Simulation of LDL permeation into multilayer wall of a coronary bifurcation using WSS-dependent model: effects of hemorheology.

Atherosclerosis, due to the permeation of low-density lipoprotein (LDL) particles into the arterial wall, is one of the most common and deadly diseases in today's world. Due to its importance, numerous studies have been conducted on the factors affecting this disease. In this study, using numerical simulation, the effects of Wall Shear Stress (WSS), non-Newtonian behavior of blood, different values of hematocrit and blood pressure on LDL permeation into the arterial wall layers are investigated in a 4-layer wall model of a coronary bifurcation. To obtain the velocity and concentration fields in the fluid domain, the Navier-Stokes, Brinkman, and mass transfer equations are numerically solved in the lumen and wall layers. Results show that it is important to consider the effects of WSS on transport properties of endothelium layer in bifurcations and this leads to completely different concentration profiles compared to the constant properties model. Our computations show that a giant accumulation of LDL in the intima layer of the outer wall of the left anterior descending artery, especially in low WSS regions, may lead to atherosclerosis. It is also, necessary to consider the non-Newtonian behavior of blood in bifurcations due to its direct effect on WSS. A pressure-induced increase in the half-width of leaky junctions may be responsible for the higher risk of atherosclerosis in hypertension. In addition, it is shown that the dominant mechanism in LDL permeation into the wall is convection, and also, hypertension increases the effect of mass transfer by convection mechanism more than the diffusion mechanism. Furthermore, our results are consistent with various clinical studies.

The spread of eigen time-values to find the wall heat transfer coefficients dk

It has long been recognised that in evaluation of wall heat transfer coefficients, a series of values with units of time, denoted here by zj (z1 is of order hours), has to be found by search, and that consecutive values are sometimes close and may be missed. This problem is investigated here through two approaches: (i) the zj-related properties are examined of various simplifications of a basic seven-parameter model, so having fewer parameters than those of multilayer building walls; (ii) the series of zj values, found from imposition of zero-temperature boundary conditions are placed in sequence with those found from the other three boundary conditions. Using an appropriate non-dimensional form for zj, the spread of these values has been examined for one of the sets of walls of widely varying construction listed by ASHRAE. The significance of this approach is that the transient thermal behaviour of walls can be visualised and interpreted in terms of the set of eigenfunction temperature profiles associated with its series of zj values. An appendix sketches the broader mathematical framework into which the study fits, and another outlines its use in the present context.

Lightweight Composite Partitions with High Sound Insulation in Hotel Interior Spaces: Design and Application

Sound insulation performance of partitions is one of the key factors contributing to the comfort of the hotel interior spaces. Based on the theory of constrained layer damping, this study proposed the light-weight composite partition structure with high sound insulation, which was composed of gypsum boards of different thicknesses and an isobutylene isoprene rubber board. The normal incidence sound transmission loss of the structure was evaluated through finite element simulations as well as experiments, which were conducted in a standing wave tube. The results show that the simulation and experimental results of two kinds of lightweight high sound insulation multi-layer composite partition walls are closely aligned; the surface density of the optimized partition wall was less than 42 kg/m2, although the normal incidence STL exceeded 51.8 dB at 200 Hz and at 1/3 octave of 1000 Hz with the maximum value of 58.5 dB. The lightweight composite partition wall with high sound insulation has a huge application potential in enhancing the sound environment quality of hotels.

Zygospores of the green alga Spirogyra: new insights from structural and chemical imaging.

Zygnematophyceae, a class of streptophyte green algae and sister group to land plants (Embryophytes) live in aquatic to semi-terrestrial habitats. The transition from aquatic to terrestrial environments requires adaptations in the physiology of vegetative cells and in the structural properties of their cell walls. Sexual reproduction occurs in Zygnematophyceae by conjugation and results in the formation of zygospores, possessing unique multi-layered cell walls, which might have been crucial in terrestrialization. We investigated the structure and chemical composition of field sampled Spirogyra sp. zygospore cell walls by multiple microscopical and spectral imaging techniques: light microscopy, confocal laser scanning microscopy, transmission electron microscopy following high pressure freeze fixation/freeze substitution, Raman spectroscopy and atomic force microscopy. This comprehensive analysis allowed the detection of the subcellular organization and showed three main layers of the zygospore wall, termed endo-, meso- and exospore. The endo- and exospore are composed of polysaccharides with different ultrastructural appearance, whereas the electron dense middle layer contains aromatic compounds as further characterized by Raman spectroscopy. The possible chemical composition remains elusive, but algaenan or a sporopollenin-like material is suggested. Similar compounds with a non-hydrolysable character can be found in moss spores and pollen of higher plants, suggesting a protective function against desiccation stress and high irradiation. While the tripartite differentiation of the zygospore wall is well established in Zygnematopyhceae, Spirogyra showed cellulose fibrils arranged in a helicoidal pattern in the endo- and exospore. Initial incorporation of lipid bodies during early zygospore wall formation was also observed, suggesting a key role of lipids in zygospore wall synthesis. Multimodal imaging revealed that the cell wall of the sexually formed zygospores possess a highly complex internal structure as well as aromatics, likely acting as protective compounds and leading to impregnation. Both, the newly discovered special three-dimensional arrangement of microfibrils and the integration of highly resistant components in the cell wall are not found in the vegetative state. The variety of methods gave a comprehensive view on the intricate zygospore cell wall and its potential key role in the terrestrial colonization and plant evolution is discussed.

Optimization of the utilization of phase change materials in planar structures to control and optimize energy flux

The optimal use of phase change materials (PCMs) in multilayer constructions in hot climates is taken into account in this study. PCMs could reduce energy use and improve indoor thermal comfort by being added to the building envelope. To achieve this, an optimization-based numerical model is created to predict the thermal behavior of a multilayer wall of the building in a hot environment. The finite element model is coupled with design exploration tools based on design of experiments methodology and the response surface technique to analyze the relationships between the influencing PCM parameters and the response variable, which is represented by the heat flow into the internal space. Optimization analysis is carried out to identify a set of PCM thermophysical and geometrical parameters which minimize the output variable. The set of input parameters that includes the PCM thickness and location as well as melting temperature and melting zone is implemented in the computational model for a simulation period of 10 days. The achieved results show a decrease in the maximum temperature at the internal wall compared to the original wall without PCM, with <20% of the heat entering the occupant area. The analysis demonstrates the potential utilization of PCMs as an approach to enhance the thermal characteristics of the building and decrease energy use in regions with high temperatures.

Research on 316 stainless steel low-power pulsed laser-induced arc additive manufacturing by different deposition routes

In this paper, a low-power pulsed laser-induced arc heat source is used to complete the wire-filled additive manufacturing of multi-layer multi-pass stainless steel walls. The low-power pulsed laser can induce and compress the arc to achieve the concentration of arc energy. This paper systematically studied the effects of different deposition paths on the microstructure and mechanical properties. The results show that the parallel deposition mainly consists of columnar grains, and the grain size of the fine grain area is about 10 μm. The longitudinal tensile strength of the parallel part can reach 620 Mpa, and that elongation is 46%. The horizontal tensile strength is 590 MPa and the elongation is only 40%. The alternating deposition part is mainly composed of oriented dendrites, and the grain size of the fine crystal area is about 12 μm. While the average tensile strength of the alternate part is 585 MPa, the average elongation is 38%. The parallel deposition part has better anisotropy, and the isotropy of the alternate deposited part is better. A parallel deposition path is recommended to choose if the component is required to serve under the unidirectional stress state. An alternate deposition path should be adopted if the component is required to serve under the multidirectional stress state.

Effect of welding parameters on bead characteristics and mechanical properties of wire and arc additive manufactured inconel 718

In this study, a bi-directional, low-cost, gas metal arc welding (GMAW) based wire arc additive manufacturing (WAAM) setup is used to deposit aerospace-grade super-alloy IN718. The orthogonally designed experiments are carried out to optimize process parameters for bead geometry characteristics. Study result shows that with an increase in heat input, the bead parameters like bead width, reinforcement, dilution, penetration, and weld form factor are increasing, while it has a detrimental effect on weld shape factor and wetting angle. Microstructural examination reveals that at high heat input, coarser grain structure having average grain size of 72.29 µm is obtained while at low heat input, a finer grain structure with average grain size of 32.12 µm along with smaller amount of Laves phases are present. The XRD reveals NbC and TiC phases present in case of low heat input sample which enhances the mechanical properties of deposited material. The multilayer wall structures fabricated at high heat input showed more uniformity in shape with lesser waviness than that fabricated with low heat input. The tensile result of low heat input sample (775.82 MPa) shows higher strength than high heat input sample (741.07 MPa) which is because of smaller grain structure and higher hardness (278.11 HV) as obtained in low heat input sample as compared to high heat input sample (257.26 HV). The EBSD analysis also confirms highly textured surface, more grain boundary lengths and larger grain boundary orientation in low heat input sample imparted better mechanical properties.

Origin of aspect ratio decreasing and variant selection for alpha laths in laser directed energy deposited TC11-xB alloys: Spatial inhibition and selective coarsening in thermal cycle

Boron addition is prevalently applied for additively manufactured titanium alloys. The aspect ratio of α laths in titanium alloys tends to decrease with boron addition, while the critical cause is not clear. To reveal the mechanism of this circumstance, Ti-6.5Al-3.5Mo-1.5Zr-0.3Si-xB (x = 0, 0.14, and 0.35) alloys were laser directed energy deposited as multi-layer walls, and the morphology, size, and variant selection of α laths before and after thermal cycle were characterized. It is found that the contribution of heterogeneously nucleated α on TiB to the decrease is limited. The α laths are initially refined due to grain refinement and TiB precipitates from boron addition. However, the layer-by-layer thermal cycle renders the selective coarsening of αp laths, and thus the α laths widen with boron addition. In addition, branching of α also assists to widen the laths. Therefore, spatial inhibition and selective coarsening in thermal cycle predominately account for the aspect ratio decrease of α laths. Boron addition weakens the variant selection in both unstable and stable zones, which assists to prove the mechanism of aspect ratio decrease for α laths.

Efficient utilization of PCM in building envelope in a hot environment condition

The thermal performance of the building envelope must be adjusted to promote sustainability, reduce energy consumption, and reduce greenhouse gas emissions. In this case, the elements' thermal resistance and heat storage capacity are critical. Due to their high energy density and ability to absorb/release heat under nearly isothermal conditions, phase change materials are extremely competitive and have a wide range of applications. The effectiveness of using PCM in the building envelope is studied in this investigation under exceptionally hot climatic conditions. A thermal model is developed based on the nonlinear transient heat conduction equation to predict the time-dependent thermal response of a multilayer building envelope wall. The enthalpy formulation is used to account for the phase change process, and the mathematical model is solved numerically using the finite element method. A typical exterior multilayer wall's thermal performance is studied and utilized as a benchmark. Then, at various points throughout the wall, a PCM layer is incorporated. The effect of the PCM on wall temperature distribution, heat movement into the interior area, and the fraction of molten material in the PCM layer is investigated. Optimization analysis is used to establish the suitable PCM melting temperature interval, with the heat flow at the internal surface of the wall as the objective function to be minimized. The thermal energy flow into the internal space can be reduced by approximately 50% when the PCM settings are improved. The findings of this investigation demonstrate that the suggested computational model is effective in calculating the optimal PCM, resulting in a significant improvement in the external wall's thermal performance. Integrating PCM into the building envelope is a viable technique for the region, as it has the potential to reduce the amount of heat entering the building, hence lowering the air conditioning load and lowering energy consumption.

Influence of WAAM-CMT deposition parameters on wall geometry

The Wire and Arc Additive Manufacturing has called attention due to its potential in allowing the buildup of high integrity metallic parts using the commonly available welding robots in the industry. However, such a technology still presents some challenges, mainly related to obtaining optimal deposition parameters, which result in consistent layer geometry which leads to the robot and the welding power source programming. In this sense, the objective of this work is to analyze the influence of the parameters in bead and multi-layer wall geometries fabricated by the Cold Metal Transfer process to select the configurations that result in the best deposition control. The study was carried out in four steps: (i) deposition of single beads on plate, varying wire feed speed and travel speed that would result in stable and sound beads; (ii) deposition of five layer walls, considering both unidirectional and bidirectional path strategies, with and without stops between layers; (iii) deposition of ten and twenty layer walls, refining deposition parameters; and (iv) deposition of a one hundred layer wall, with the best parameter configuration among the previously tested, with bidirectional continuous strategy. The results showed that the geometry produced with a mean current of 62 A and torch travel speed of 8 mm/s along each layer and 24 mm/s on the transition between layers generated the best results, considering the natural cooling conditions. Also, the bidirectional path deposition presented the most regular geometries, when compared to the unidirectional strategy.