Wall-like Structures Research Articles

Microstructure of the silk fibroin-based hydrogel scaffolds derived from the orb-web spider Trichonephila clavata

Due to the unique properties of the silk fibroin (SF) made from silkworm, SF-based hydrogels have recently received significant attention for various biomedical applications. However, research on the SF-based hydrogels isolated from spider silks has been rtricted due to the limited collection and preparation of naïve silk materials. Therefore, this study focused on the microstructural characteristics of hydrogel scaffolds derived from two types of woven silk glands: the major ampullate gland (MAG) and the tubuliform gland (TG), in the orb-web spider Trichonephila clavate. We compared these spider glands with those of the silk fibroin (SF) hydrogel scaffold extracted from the cocoon of the insect silkworm Bombyx mori. Our FESEM analysis revealed that the SF hydrogel has high porosity, translucency, and a loose upper structure, with attached SF fibers providing stability. The MAG hydrogel displayed even higher porosity, as well as elongated fibrous structures, and improved mechanical properties: while the TG hydrogel showed increased porosity, ridge-like or wall-like structures, and stable biocapacity formed by physical crosslinking. Due to their powerful and versatile microstructural characteristics, the MAG and TG hydrogels can become tailored substrates, very effective for tissue engineering and regenerative medicine applications.

Computing thickness of irregularly-shaped thin walls using a locally semi-implicit scheme with extrapolation to solve the Laplace equation: Application to the right ventricle

Cardiac Magnetic Resonance (CMR) Imaging is currently considered the gold standard imaging modality in cardiology. However, it is accompanied by a tradeoff between spatial resolution and acquisition time. Providing accurate measures of thin walls relative to the image resolution may prove challenging. One such anatomical structure is the cardiac right ventricle. Methods for measuring thickness of wall-like anatomical structures often rely on the Laplace equation to provide point-to-point correspondences between both boundaries. This work presents limex, a novel method to solve the Laplace equation using ghost nodes and providing extrapolated values, which is tested on three different datasets: a mathematical phantom, a set of biventricular segmentations from CMR images of ten pigs and the database used at the RV Segmentation Challenge held at MICCAI’12. Thickness measurements using the proposed methodology are more accurate than state-of-the-art methods, especially with the coarsest image resolutions, yielding mean L1 norms of the error between 43.28% and 86.52% lower than the second-best methods on the different test datasets. It is also computationally affordable. Limex has outperformed other state-of-the-art methods in classifying RV myocardial segments by their thickness.

Development of Rectangular Vibration Isolators with Double Core Systems for Structures

One of the best techniques for isolating structures from the ground is the seismic isolation technique. Nowadays, square and circular base isolators are the most frequently employed shapes. Nevertheless, these configurations are not applicable for the wall-like structures; since the applied loads are not distributed in a way that provides a uniform support condition along the shear walls. To address this issue, attempts were made to develop novel rectangular isolators with lead/rubber cores. A total of five large-scale rectangular isolators were experimentally tested and subsequently subjected to finite element analysis. A rectangular seismic isolator having double lead cores was proposed to improve its effectiveness. Exposure to lead-containing materials has been shown to have poisonous effects on both the human health and environment. To avoid this, an isolator having double rubber cores was developed. Moreover, the rubber cores are wrapped with one layer of CFRP sheet and stainless steel tube to enhance the damping ratio of the rectangular isolators. Thereafter, the novel isolators were implemented in a 10-storey tunnel-form building using nonlinear dynamic analyses. The seismic performance of the buildings was then studied by conducting Incremental Dynamic Analyses. The experimental outcomes demonstrated that confining the rubber cores by stainless steel tube and CFRP sheet increased the energy absorption along the length of the isolators by 15 and 7%, respectively. Moreover, the damping ratios of the rectangular isolator with double lead cores have also increased by 36 and 47% along its length and width, respectively.

High-cycle fatigue induced twinning in CoCrFeNi high-entropy alloy processed by laser powder bed fusion additive manufacturing

High-cycle fatigue (R=0.1, room temperature) induced microstructural evolution in a laser powder bed fusion (L-PBF) additively manufactured quaternary CoCrFeNi high-entropy alloy (HEA) was studied. The as-built material exhibited a combined < 001 > and < 110 > texture and high proportion of low-angle boundaries. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) revealed that deformation twinning occurred under the high-cycle fatigue of σmax= 450 MPa (Nf=1.06 ×105), but not for the stress level of 300 MPa and 200 MPa. The deformation twins led to the cyclic softening, as manifested by the continuous increase of maximum strain under the stress-controlled fatigue, and the hardness increased by ∼80 HV0.2 in the post-fatigued condition. EBSD revealed that both the < 001 > and < 110 > orientations were favorable for the twin formation. Given that the size of grains with the < 001 > and < 110 > orientations was twice larger than those of the other orientations, the grain size effect on twin formation could play a certain role. High-resolution TEM revealed that the full dislocations, lattice distortion, stacking faults, and partial dislocations were associated with the twin, cellular and labyrinth wall-like dislocation structures. The underlying mechanism for the formation of nano-twins during high-stress fatigue involved the dissociation of 1/2 < 110 > full dislocations to 1/6 < 112 > partial ones. Moreover, the dislocation cell structure as observed in the as-built condition evolved into sub-grains after the high-cycle fatigue loading, with the immensely dense dislocations at the sub-grain boundary.

Damage imaging of concrete wall-like structures using cylindrical concrete implantable module

In this study, an implantable array-based sensing technique for damage imaging of concrete wall-like structures was developed. Unlike conventional concrete damage imaging methods that require several distributive transducers instrumented in the detection structure, the proposed technique integrates a multi-transducer into a cylindrical concrete implantable module (CCIM) that can be directly implanted into the wall-like structures to transmit and receive probe signals based on a sensing array. Implantable designs within integrated sensing elements benefit the management of devices and provide a new transducer-to-structure installation for structural health monitoring (SHM). Furthermore, to analyze the received probe signals and visualize the structural defects, a novel damage-imaging algorithm aimed at a heterogeneous concrete medium was proposed. The algorithm assumed that each point in the detection space was a virtual scatter to simulate a series of signal transceiving processes using a computer. The virtual scattered signals received by the CCIM were projected onto the signals received under real damage conditions to reconstruct an imaging map. The reliability of the developed technique for damage imaging of heterogeneous concrete wall-like structures was studied both numerically and experimentally. The numerical study employed a 2-D mesoscale model considering concrete as a multiphase composite material and revealed the stress-wave propagation law in concrete. In the experiment, two fabricated CCIMs were implanted into a concrete wall-like specimen for signal transmission and reception. The imaging results acquired by simulation and experiment both successfully displayed the damaged area and exhibited excellent prospects for the implantable array-based sensing technique in SHM.

Self-Assembly of Ultrafine Fibers with Micropores via Cryogenic Electrospinning and Its Potential Application in Esophagus Repair.

Electrospinning (e-spinning) has been widely applied to fabricate flat films accumulated by microfibers for tissue engineering. In order to acquire an uneven surface morphology, two methods have been applied traditionally. The first uses a designed receiving substrate, which is stable, but suppresses the flexibility. The second uses dual solvents to achieve bimodal distribution of the fiber diameter. However, the bimodal fiber diameter causes inhomogeneity. To solve these challenges, cryogenic electrospinning, using a flat substrate and a single solvent, was performed in this study to obtain uneven films. By applying a low temperature to the flat receiving substrate, uneven e-spun films with wall-like structures were achieved through the self-assembly of uniform filaments. In addition, the wall-like structures enhanced the mechanical properties of the e-spun films. Moreover, the cryogenic e-spinning produced micropores on the fiber surface, which have the potential to promote esophageal epithelial cell adhesion, proliferation and differentiation.

WO3 Films Grown by Spray Pyrolysis for Smart Windows Applications

WO3 nanostructured thin films were grown using spray deposition on FTO coated glass. The effect of the precursor concentration and the solution quantity, which determines the deposition time, on the electrochemical, electrochromic and optical properties of the WO3 films was investigated. The films were found to exhibit a good electrochromic activity with a reasonably good durability of charge exchange and optical modulation under harsh electrochemical cycling in Li-ion-conducting electrolyte. Associated compositional and structural characteristics were probed by several techniques, indicating that the observed improved durability may be due to the unique WO3 thin films’ structuring, the surface of the films consisting of wall-like structures combined with bubble-like islands on a polycrystalline WO3 granular background, that requires further study in greater detail.

Singular spectrum analysis and fuzzy entropy-based damage detection on a thin aluminium plate by using PZTs

In this research, a new method based on singular spectrum analysis (SSA) and fuzzy entropy is developed for damage detection on thin wall-like structures, and the normalized fuzzy entropy is employed as an indicator to identify the severity of the damage. The lead zirconate titanate (PZT) transducers are used in this research to generate and detect the Lamb waves. During the detection, the collected signals from the PZT sensors are firstly decomposed and reconstructed by SSA to extract the feature of the damage, and then the reconstructed signals with the feature of the damage are processed to obtain the normalized fuzzy entropy. An experimental setup of an aluminium plate with added magnets is fabricated to validate the proposed method. The experimental results show that when magnets are attached on the aluminium plate, the normalized fuzzy entropy is smaller than that when there are no magnets. That is because when magnets are placed on the plate, the movement and some vibration modes of Lamb waves are disturbed by the added magnets and this disturbing effect can be enhanced by increasing the number and locations of the added magnets, and eventually the complexity and nonlinearity of the waves are weakened. The experimental results of a single damage with different number of magnets indicate that the normalized fuzzy entropy decreases linearly as the number of the added magnets increases, which demonstrates that the proposed method can be used to detect the severity of the damage. Moreover, the experimental results of multi-damage on different locations indicate that the normalized fuzzy entropy is relevant with both the total number and locations of the added magnets. The normalized fuzzy entropy decreases linearly as the total number of the magnets increases, and the entropy of a single damage is smaller than that of the multi-damage with the same total number of magnets, which demonstrates that the proposed method also can be used for multi-damage detection on a thin plate. This study provides us a new approach to identifying a single or multiple damages on thin wall-like structures.

Geometrical dynamics of edge-driven accretive surface growth

Accretion of mineralized thin wall-like structures via localized growth along their edges is observed in physical and biological systems ranging from molluscan and brachiopod shells to carbonate–silica composite precipitates. To understand the shape of these mineralized structures, we develop a mathematical framework that treats the thin-walled shells as a smooth surface left in the wake of the growth front that can be described as an evolving space curve. Our theory then takes an explicit geometric form for the prescription of the velocity of the growth front curve, along with compatibility relations and a closure equation related to the nature of surface curling. Solutions of these equations capture a range of geometric precipitate patterns seen in abiotic and biotic forms across scales. In addition to providing a framework for the growth and form of these thin-walled morphologies, our theory suggests a new class of dynamical systems involving moving space curves that are compatible with non-Euclidean embeddings of surfaces.

Development of Microstructured Carbon Coatings by Substrate-Catalytic CVD

Carbon nanostructured films were synthesized by chemical vapor deposition (CVD) on H18 stainless steel (AISI 440C) sheets with an H2/CH4/N2 gas mixture at various substrate temperatures. During the synthesis, the iron and chromium oxide layer was formed between the steel and carbonaceous layer. The carbon films exhibited wall-like and spherical morphologies and structures, as characterized by scanning electron microscopy and Raman spectroscopy. It was found that the synthesis temperature affects the microsphere density and, therefore, also in the electrochemical behavior. The electrochemical behavior of nanostructured carbon coatings strongly depends on the CVD deposition conditions. The best corrosion resistance (Rp = 11.8 MΩ·cm2, Icorr = 4.4 nA·cm−2) exhibits a nanostructured carbon sample with a moderate amount of sp2-C-rich carbon microspheres CμSs synthesized at 700 °C. The corrosion resistance of the nanostructured carbon coating is better than raw stainless steel.

A novel assumed-strain finite element for detecting the elastic behavior of wall-like structures

It is aimed to propose a new triangular plane finite element to improve the accuracy and reduce the computational effort for analysis of plane structures. The suggested element is formulated by assuming an incomplete second-order strain field. It leads to an element free from shear parasitic error with lower sensitivity to the mesh distortion. Satisfying both equilibrium and compatibility equations in the strain field level results in 12 independent strain states. Accordingly, the suggested element has 12 degrees of freedom, which are allocated to six nodes. Although the suggested element has the geometry and number of degrees of freedom same as the well-known linear strain triangular element, but its accuracy and efficiency are much better than many of the available high-performance membrane elements. The selected geometry provides the opportunity to simply include the presented element in the general finite element analysis software. After evaluation of the element performance using basic benchmark problems, to demonstrate the efficiency of the proposed formulation in comparison with widely used finite elements, different shear and retaining wall structures are analyzed by the developed element. The attained results for even coarse meshes prove higher accuracy and efficiency of the developed element in computation of displacements and stresses. Another advantage of the proposed element in comparison with the other available robust finite elements is its simple and straightforward formulation.

A Find of Transoceanic Pottery at Bwejuu Island of the Rufiji Delta and Mafia Island, Tanzania: More Clue to the Elusive Ancient Azania’s Metropolis of Rhapta

The island of Bwejuu is one of the islands of the Mafia archipelago on the central coast of Tanzania. It is only 15 km off the Rufiji Delta and its inhabitants carry out cultivation activities on the delta. The Rufiji delta has been considered by several scholars to be the location of the elusive ancient Azania’s metropolis of Rhapta. Past research on the island established that it was of the 16th–18th centuries post-Swahili civilization. This research has verified that finding although underwater work on the south-east part discovered pottery attributed to ancient transoceanic activities, possibly arriving from either the Mediterranean region or probably Oman or Indian regions. Sites with trade remains from those regions have been discovered on the Delta and Mafia archipelago. Also, an underwater site with wall-like structures believed to be remains of a long-submerged ancient settlement has recently been found in the northwestern waters of Mafia Island. The site has drawn attention of some archaeologists who believe it could be the long-lost metropolis of Rhapta. The new findings from Bwejuu Island may suggest that there are several trading sites in the region of the Mafia archipelago and the Rufiji Delta as outskirts of a large settlement which could be Rhapta. This study collected data through archaeological surveys and test excavations. Data analysis involved pottery attribute analysis and metric dating by thermoluminescence method.

3D investigation shows walls and wall-like structures around human germinal centres, probably regulating T- and B-cell entry and exit.

This study deals with 3D laser investigation on the border between the human lymph node T-zone and germinal centre. Only a few T-cells specific for antigen selected B-cells are allowed to enter germinal centres. This selection process is guided by sinus structures, chemokine gradients and inherent motility of the lymphoid cells. We measured gaps and wall-like structures manually, using IMARIS, a 3D image software for analysis and interpretation of microscopy datasets. In this paper, we describe alpha-actin positive and semipermeable walls and wall-like structures that may hinder T-cells and other cell types from entering germinal centres. Some clearly defined holes or gaps probably regulate lymphoid traffic between T- and B-cell areas. In lymphadenitis, the morphology of this border structure is clearly defined. However, in case of malignant lymphoma, the wall-like structure is disrupted. This has been demonstrated exemplarily in case of angioimmunoblastic T-cell lymphoma. We revealed significant differences of lengths of the wall-like structures in angioimmunoblastic T-cell lymphoma in comparison with wall-like structures in reactive tissue slices. The alterations of morphological structures lead to abnormal and less controlled T- and B-cell distributions probably preventing the immune defence against tumour cells and infectious agents by dysregulating immune homeostasis.

Surface Representation of Pulsed Eddy Current Sensor Signals for Improved Ferromagnetic Material Thickness Quantification

Pulsed eddy current (PEC) sensing is a nondestructive testing and evaluation technique widely used for detecting and quantification of flaws and properties of metallic test pieces. In recent years, the use of the technique for the assessment of ferromagnetic materials, specifically, for the purpose of thickness quantification of ferromagnetic plates, or wall-like structures, has risen. The detector coil-based PEC sensor architecture has been the most commonly used sensor architecture for the purpose. Recent works have demonstrated the effectiveness of the detector coil voltage decay rate for this purpose. The decay rate signal feature has been used to construct a linear functional relationship between thickness and the feature value. This functional relationship has eventually been used for thickness estimation. However, this method has proven to come with a limitation of accuracy in thickness estimates. Therefore, we present in this article a method for surface representation of PEC sensor signals. In this method, the thickness varies as a surface-like function in 3D, relying on two signal feature values provided as independent variables. We demonstrate how the surface representation yields a 2% improvement in accuracy (with respect to correlation coefficient) in previous results (i.e., thickness estimates) through a case-study of quantifying wall thickness of a gray cast iron pipe. Such an improvement in accuracy has significant cost-saving implications in the field of structural health monitoring, especially in managing critical pipes in sectors such as water and energy. Cost savings result by enabling infrastructure managers to optimize rehabilitation and thereby provide improved services.

On the origin of hyolith helens

Helens, the curved lateral spines inserted between the conch and operculum of some hyoliths, are a unique morphological adaptation characterizing the order Hyolithida. These structures are paired, movable and had a mechanical function, probably related to orienting the hyolith conch and lifting its aperture above the sea floor. We show that helens are intimately associated with the hyolith opercula and are structurally comparable to the rod like units that constitute the clavicles, internal wall-like structures of the hyolithid operculum that probably evolved to secure the operculum from lateral displacement in the conch aperture. In some early Cambrian hyolith taxa that lack helens, such as Paramicrocornus, new clavicle rods are added in the gap separating the clavicles from the cardinal processes, the same position where helens are inserted in later hyolithids. We also show that the size of incipient helens at the earliest ontogenetic stage matches the size of the clavicles in associated opercula. We propose that helens are modified clavicle rods that were detached from the operculum and developed into lateral spines through allometric growth during early ontogeny. Further, we suggest a four-step model for the evolution of hyolithid hyoliths from orthothecid ancestors: 1, Externally fitting operculum; 2, Stabilizing, radially arranged structures on the inside of the operculum; 3, Ligula and folded operculum; 4, Detachment of clavicle rods and origin of helens.

The potential of flax shives as reinforcements for injection moulded polypropylene composites

Flax shives (FS) represent approximately 50 % in weight of dry flax stems, making it the main by-product of the flax scutching industry. Being an available and low-added value lignocellulosic resource, flax shives are an interesting candidate for thermoplastic composite reinforcement. In this study, raw flax shives were fragmented by knife milling using two grids of 500 and 250 μm respectively, while a third batch, with a targeted particle size below 50 μm, was obtained by an attrition beads mill. The fragmentation methods used do not modify the biochemical composition of FS but do reduce their crystallinity due to both crystalline cellulose allomorph conversion and amorphization. The poly-(propylene) and 4%-wt maleic anhydride modified poly-(propylene) injection moulded composites produced with these reinforcing materials have a maximum tensile strength that evolves linearly with particle aspect ratio after processing. The tensile Young’s modulus of the composites reinforced by coarser particles is 3268 ± 240 MPa, which is almost 90 % that obtained for a reference 1mm flax fibre reinforced composite. Furthermore, a basic micromechanical model was applied highlighting the reinforcing capacity of cell wall-like small tubular structures (e.g. flax shives). This study underlines the reinforcing potential of low-value by-product flax shives for value-added composite applications.

Solitons in the Einstein universe

We show that equations of Newtonian hydrodynamics and gravity with Einstein's cosmological constant included admit gravitostatic wave solutions propagating in the background of Einstein's static Universe. In the zero pressure limit these waves exist at an average matter density exceeding that of Einstein's Universe. They have the form of a lattice of integrable density singularities localized at the maxima of the gravitational potential. These singularities are steady-state counterparts of the so-called Zeldovich pancakes (ZP), interim wall-like structures appearing at nonlinear stages of development of gravitational instability. As the average matter density decreases, the period of the ZP lattice increases diverging at the density of Einstein's Universe. Solitary wave solutions are found at exactly the density of Einstein's Universe, and at a slightly larger density the wave may be viewed as a lattice of well-separated ZP solitons.

Dislocation structures and the role of grain boundaries in cyclically deformed Ni micropillars

Transmission electron microscopy and finite element-based dislocation simulations were combined to study the development of dislocation microstructures after cyclic deformation of single crystal and bicrystal Ni micropillars oriented for multi-slip. A direct correlation between large accumulation of plastic strain and the presence of dislocation cell walls in the single crystal micropillars was observed, while the presence of the grain boundary hampered the formation of wall-like structures in agreement with a smaller accumulated plastic strain. Automated crystallographic orientation and nanostrain mapping using transmission electron microscopy revealed the presence of lattice heterogeneities associated to the cell walls including long range elastic strain fields. By combining the nanostrain mapping with an inverse modelling approach, information about dislocation density, line orientation and Burgers vector direction was derived, which is not accessible otherwise in such dense dislocation structures. Simulations showed that the image forces associated with the grain boundary in this specific bicrystal configuration have only a minor influence on dislocation behavior. Thus, the reduced occurrence of “mature” cell walls in the bicrystal can be attributed to the available volume, which is too small to accommodate cell structures.

In situ observation of dewetting-induced deformation of vertically aligned single-walled carbon nanotubes

We investigated dynamical processes of capillary-mediated deformation of vertically aligned single-walled carbon nanotubes (VA-SWCNTs) via in situ observation of their wetting and dewetting behaviors using an environmental scanning electron microscope (ESEM). Three types of wetting behaviors on a VA-SWCNT sample were confirmed, including conical shaped water aggregates, spherical droplets on tips of conical shaped water aggregates, and extensively distributed water layers. While the former two types both resulted in dimples on the VA-SWCNT surface and failed to induce large-scale deformation of VA-SWCNTs, the latter caused the formation of wall-like structures and crack propagation in the VA-SWCNT film during the dewetting process due to directional retraction of vapor-liquid interfaces. This dewetting-induced large-scale deformation that was confirmed by the in situ ESEM observation for the first time represented initial stages of capillary processes, leading to the self-organization of VA-SWCNTs reported in recent literatures. Compared to the previous studies based on ex situ observations of dried samples, our in situ observation successfully captured temporal evolution of the dewetting-induced deformation, facilitating the more precise construction of predictive models of final morphologies of VA-SWCNT films after capillary-mediated densification.

Droplet etching with indium – Intermixing and lattice mismatch

In contrast to Indium droplets the usage of Ga or Al droplets for the local droplet etching (LDE) technique is well established. It has been shown previously that In-droplets or In-alloys can be used for LDE with focus on small hole-depths at low etching temperatures. With our recent experiments we reveal that In-LDE is also well suited for the creation of very deep nanoholes (exceeding 100 nm) and very low densities in the range of 106 cm−2 for large average distances of several micrometers. The unexpected high thermal stability of the etching process itself as well as the formed wall-like structures clearly points to an intermixing between etching and substrate material during the LDE-process. This can be related to the lack of As during LDE. Additional experiments with capping layers also reveal high surface-roughness probably caused by a lattice mismatch, which can be also explained by intermixing. A second LDE step with Al can be applied to avoid roughening effects.