Lamellar Formation Research Articles

Numerical Treatment of the Interface in Two Phase Flows Using a Compressible Framework in OpenFOAM: Demonstration on a High Velocity Droplet Impact Case

The ability to accurately predict the dynamics of fast moving and deforming interfaces is of interest to a number of applications including ink printing, drug delivery and fuel injection. In the current work we present a new compressible framework within OpenFOAM which incorporates mitigation strategies for the well known issue of spurious currents. The framework incorporates the compressible algebraic Volume-of-Fluid (VoF) method with additional interfacial treatment techniques including volume fraction smoothing and sharpening (for the calculation of the interface geometries and surface tension force, respectively) as well as filtering of the capillary forces. The framework is tested against different benchmarks: A 2D stationary droplet, a high velocity impact droplet case (500 m/s impact velocity) against a dry substrate and, with the same impact conditions, against a liquid film. For the 2D static droplet case, our results are consistent with what is observed in the literature when these strategies are implemented within incompressible frameworks. For the high impact droplet cases we find that accounting for both compressibility and correct representation of the interface is very important in numerical simulations, since pressure waves develop and propagate within the droplet interacting with the interface. While the implemented strategies do not alter the dynamics of the impact and the droplet shape, they have a considerable effect on the lamella formation. Our numerical method, although currently implemented for droplet cases, can also be used for any fast moving interface with or without considering the impact on a surface.

Microstructural observations of high temperature creep processes in hardmetals

ABSTRACT High-temperature properties of hardmetals are critical to their use in many applications but a challenge to measure accurately. Creep behaviour is not well understood so this work has studied uniaxial tensile testing of small simple geometry samples to look at how modifications to the microstructure can affect creep behaviour at temperatures between 800 and 900°C. In particular, a carbon-ladder series with high, medium and low carbon contents in the 10wt-%Co binder has been investigated. Significant differences between the stress–strain curves of the different carbon contents have been observed, but the underlying microstructural mechanisms appear to be similar in detailed large area examination of samples after failure. Penetration of Co along WC-WC boundaries with ‘precipitation’ of discrete islands is seen as well as the formation of continuous thin lamellae while void formation tends to occur at WC-Co boundaries. EBSD mapping suggests Co penetration varies as a function of WC-WC misorientation.

Role of Si on lamellar formation and mechanical response of two SPS Ti–15Al–15Si and Ti–10Al–20Si intermetallic alloys

Two TiAlSi intermetallic compounds produced by Spark Plasma Sintering (SPS) adding different Si content were tested by nanoindentation, toughness and wear resistance. Microstructure differences between the two alloys were characterized by TEM and a strengthening model was proposed. The microstructure-based strengthening model well agreed with alloys stress obtained from the nanoindentation hardness. It resulted that as Si content increases, the TiAl phase started to form lamellar structure and inter-lamellar twinning. Al reduction in favour of an equal amount of Si was found to slightly promote Ti5Si3 silicide formation and eventually a TiAl phase coarsening. Ti–15Al–15Si alloy showed submicrometric equiaxed TiAl grains. On the other hand, Ti–10Al–20Si alloy was characterized by a lamellar TiAl phase which was identified as responsible for the different mechanical responses of the two alloys.

Age-related increase of let-7 family microRNA in rat retina and vitreous

Vitreous alterations occur from early stages and continue through the normal aging, with gradual lamellae formation and the appearance of liquefied spaces, which eventually leads to complications, such as retinal tear, retinal detachment, and intravitreal hemorrhage. The aim of the present study was to investigate the expression of let-7 miRNA family in the vitreous and retina in newborn (1-3- day-old), young adult (2-month-old), and aging (12-month-old) rats, as well as their role as regulators of vitreous components. MicroRNAs are small, non-coding RNAs that post-transcriptionally regulate gene expression. Our results showed detection of all investigated let-7 isoforms (let-7a, let-7b, let-7c, let-7d, let-7e, let-7f and let-7i) in the retina and vitreous. Although most let-7 members were significantly upregulated in the vitreous during development, only let-7b, let-7c, and let-7e followed this same expression pattern in the retina. Let-7b and -7c increased in aging vitreous as well, and were expressed in vitro by Müller glial cells and their extracellular vesicles. Moreover, let-7 targeted hyaluronan synthase 2 (Has2) mRNA, a synthesizing enzyme of hyaluronan. These observations indicate that let-7 function is important during retina and vitreous development, and that isoforms of let-7 increased with aging, potentially modulating hyaluronan content.

Ontogenic Development Of Gills In Pre To Post-Flexion Stages Larvae Of Himalayan Snow Trout Schizothorax Plagiostomus (Heckel)

The ontogenic development of gills, including gill arch, gill filaments, and gill rakers in pre to postflexion stages larvae of Himalayan Snow Trout Schizothorax plagiostomus were studied with the objectives that this study could serve as a base for further studies about the early embryonic development and organogenesis in various fish species inhabiting hill stream environments. To obtain the pre to post-flexion stages larvae, an artificial breeding experiment was conducted during September- October on the bank of snow-fed river Alaknanda by stripping method. Further, the development of the gill apparatus was studied histologically, using light microscopy. Hatchling takes place 124-130 hours after fertilization at the incubation temperature of 19-200C. On second dph (day post-hatching), gill arches, gill filaments, and branchiostegal membrane began to differentiate. By the third dph, blood channels were observed in gill filaments as well as in pseudobranch. Formation of secondary lamellae, branchial arteries, elongation of the gill cover, cartilaginous rod formation in the gill arch, and the branchiostegal membrane was discernible by fourth-fifth dph. Pillar cells and afferent and efferent arteries with RBCs in primary and secondary lamellae were observed on the seventh dph. Around the onset of exclusive exogenous feeding (twelfth dph), gill rakers and a group of pillar cells with blood channels were recognizable. Well-organized and functional gill structures with increased number and size of secondary gill lamellae were present among the fifteenth-seventeenth dph larvae. The general pattern of structural and functional development of both the natural site and laboratory-reared larvae was similar, except a large amount of mucous and clustered epithelial cells among the laboratory-reared larvae, which may be due to the physiological as well as environmental stress posed by the adverse physicochemical conditions.

Структурно-фазовые состояния и свойства поверхности катания рельсов при экстремально длительной эксплуатации

Using the methods of modern physical material science the investigations of structure-phase states and properties at different depth from tread surface of differentially quenched rails at extremely long-term operation (passed tonnage 1411 mln t) are carried out. The hardness decrease from 37.1 to 35.8 HRC at the depth 2 and 10 mm and microhardness from 1481 to 1210 MPa, respectively is revealed. The established multiple transformation of tread surface structure concludes in: fracture of lamellar pearlite structure and subgrain structure formation of submicronsizes (100-150 nm); precipitation of carbide phase nanoparticles (30-55 nm)along the boundaries and in the volume ofsubgrains; growth of microdistorsions and α-Fe crystal lattice parameter; growth of scalar and excess dislocation density. The suggestions about the possible reasons of observable regularities are made.

1. Molecular mechanisms of Casparian strip and suberin lamella formation and their function in nutrient transport in roots

1. Molecular mechanisms of Casparian strip and suberin lamella formation and their function in nutrient transport in roots

Molecular dynamics simulation of extension-induced crystallization of branched bimodal HDPE: Unraveling the effects of short-chain branches.

Bimodal HDPE models were designed for extension-induced crystallization imitating the architecture of industrial bimodal HDPE copolymerized with ethylene and 1-butene, 1-hexene, or 1-octene. Crystallites of bimodal HDPE experienced the emergence of precursors, shish nuclei, and lamellae. The compact conformation of branched polymers impeded the rolling-over, deposition, and folding of chains on the substrate, and thus the formation of nuclei and lamella. Moreover, this retardation was intensified with the rising branch density and length, causing a depression of crystallinity and an increment of tie-chains concentration. Besides, when branches were all located on long chains, the compact conformation enlarged the resistance to the disentanglement of main chains, thus relatively fewer branched long chains were involved in the precursors or nuclei, resulting in the attenuation of lamella formation. Furthermore, for ethyl branched polymers, the coexistent orthorhombic and monoclinic crystallites were built up, and a few expanded monoclinic cells occurred for butyl branches because of the larger butyl reeling into lamella, while hexagonal crystals were created for ethyl/1-hexyl copolymers because of cocrystallization. Additionally, relative to ethyl, larger butyl and hexyl were preferential to be repelled outside crystals to form tie-chains, and hexyl branched polymers acquired relatively fewer tie-chains because of hexagonal eutectoid.

A redundant hydraulic function of root hairs in barley plants grown in hydroponics.

The root hair-less brb of Hordeum vulgare L. (bald root barley) mutant was used to assess the significance that root hairs have for the hydraulic properties of roots and response to a limited supply of mineral nutrients in plants grown on hydroponics. The barley brb mutant and its parent wild-type (H. vulgare cv. Pallas) were grown under nutrient sufficient control conditions, and under conditions of low supply of P and N. Plants were analysed when they were 14-18 days old. Root hydraulic conductivity (Lp) was determined for excised root systems and intact transpiring plants, and cell Lp was determined through cell pressure probe measurements. The formation of Casparian bands and suberin lamellae was followed through staining of cross-sections. The presence or absence of root hairs had no effect on the overall hydraulic response of plants to nutritional treatments. Root and cell Lp did not differ between the two genotypes. The most apparent difference between brb and wild-type plants was the consistently reduced formation of apoplastic barriers in brb plants. Any hydraulic function of root hairs can be redundant in barley, at least under the hydroponic conditions tested.

Grain size effects in donor doped lead zirconate titanate ceramics

The ferroelectric, ferroelastic, and dielectric properties as well as the crystal structure were investigated for polycrystalline donor doped lead zirconate titanate (PZT) with grain sizes ranging from 0.25 to 5 μm, which were prepared using a novel zirconium titanium hydrate precursor (ZTH) with a specific surface area of 310 m2/g. Piezoforce microscopy was used to investigate the change in the domain structure, revealing a change in the domain configuration from a complex 3D structure to a simple lamellar domain formation at a 1 μm grain size that corresponded to a rapidly increasing internal mechanical stress observed with in situ synchrotron x-ray experiments. The correlation between the change in domain configuration, increasing internal stresses, effects of poling on the crystal structure, and the macroscopic ferroelectric and ferroelastic properties are discussed in detail, allowing a deeper understanding of size effects in polycrystalline donor doped PZT ceramics.

Histopathology of osteogenesis imperfecta bone. Supramolecular assessment of cells and matrices in the context of woven and lamellar bone formation using light, polarization and ultrastructural microscopy

Diaphyseal long bone cortical tissue from 30 patients with lethal perinatal Sillence II and progressively deforming Sillence III osteogenesis imperfecta (OI) has been studied at multiple levels of structural resolution. Interpretation in the context of woven to lamellar bone formation by mesenchymal osteoblasts (MOBLs) and surface osteoblasts (SOBLs) respectively demonstrates lamellar on woven bone synthesis as an obligate self-assembly mechanism and bone synthesis following the normal developmental pattern but showing variable delay in maturation caused by structurally abnormal or insufficient amounts of collagen matrix. The more severe the variant of OI is, the greater the persistence of woven bone and the more immature the structural pattern; the pattern shifts to a structurally stronger lamellar arrangement once a threshold accumulation for an adequate scaffold of woven bone has been reached. Woven bone alone characterizes lethal perinatal variants; variable amounts of woven and lamellar bone occur in progressively deforming variants; and lamellar bone increasingly forms rudimentary and then partially compacted osteons not reaching full compaction. At differing levels of microscopic resolution: lamellar bone is characterized by short, obliquely oriented lamellae with a mosaic appearance in progressively deforming forms; polarization defines tissue conformations and localizes initiation of lamellar formation; ultrastructure of bone forming cells shows markedly dilated rough endoplasmic reticulum (RER) and prominent Golgi bodies with disorganized cisternae and swollen dispersed tubules and vesicles, structural indications of storage disorder/stress responses and mitochondrial swelling in cells with massively dilated RER indicating apoptosis; ultrastructural matrix assessments in woven bone show randomly oriented individual fibrils but also short pericellular bundles of parallel oriented fibrils positioned obliquely and oriented randomly to one another and in lamellar bone show unidirectional fibrils that deviate at slight angles to adjacent bundles and obliquely oriented fibril groups consistent with twisted plywood fibril organization. Histomorphometric indices, designed specifically to document woven and lamellar conformations in normal and OI bone, establish ratios for: i) cell area/total area X 100 indicating the percentage of an area occupied by cells (cellularity index) and ii) total area/number of cells (pericellular matrix domains). Woven bone is more cellular than lamellar bone and OI bone is more cellular than normal bone, but these findings occur in a highly specific fashion with values (high to low) encompassing OI woven, normal woven, OI lamellar and normal lamellar conformations. Conversely, for the total area/number of cells ratio, pericellular matrix accumulations in OI woven are smallest and normal lamellar largest. Since genotype-phenotype correlation is not definitive, interposing histologic/structural analysis allowing for a genotype-histopathologic-phenotype correlation will greatly enhance understanding and clinical management of OI.

Epitaxial Crystallization of Poly(ε-caprolactone) on Reduced Graphene Oxide at a Low Shear Rate by In Situ SAXS/WAXD Methods.

The interfacial interaction between polymers and reinforcements has a positive effect on the properties of polymer nanocomposites, and a further study on the evolution of this interfacial interaction under a shear field is conducive to reasonable regulation of the properties of polymer nanocomposites. For this purpose, epitaxial crystallization of poly(ε-caprolactone) (PCL) on reduced graphene oxide (RGO) is investigated by shearing at the shear rate of 3 s–1 by in situ synchrotron radiation. In situ two-dimensional small-angle X-ray scattering (2D SAXS) results suggest that the imposed shear field promotes the orientation of the polymer chains, resulting in the formation of a large periodic structure of PCL on the RGO surface. In addition, higher shear temperatures facilitate the conformational adjustment of the PCL molecular chain on RGO at the shear rate of 3 s–1, resulting in the formation of thicker lamellae. In situ two-dimensional wide-angle X-ray diffraction (2D WAXD) results show that shear enhances the crystallinity of the PCL/RGO nanocomposite and promotes the oriented growth of epitaxial and bulk crystals. The current findings can improve the understanding of the structural evolution behavior of PCL/RGO nanocomposites after shear and especially enhance dramatically our understanding of the underlying mechanism of influence of shear on interfacial epitaxial crystallization in polymer/graphene nanocomposite systems.

Hydrogen concentration dependence of phase transformation and microstructure modification in metastable titanium alloy β-21S

The present study aims at revealing the relationships between hydrogen concentration and phase structure, as well as microstructure modification in the β-metastable β-21S titanium alloy. The β-bcc phase can accommodate a large number of interstitial atoms, and hydrogenation by means of molecular hydrogen gas was employed in the present work. The phase structure as well as the microstructure of this alloy was found to be strongly dependent on hydrogen concentration. At lower hydrogen concentration (H/M ≤ 0.300), the microstructure consisting of the single β-phase revealed that the interstitially dissolved hydrogen atoms expanded the bcc lattice and inhibited the decomposition of the β phase upon cooling. The introduction of hydrogen beyond H/M = 0.300 was found to generate a large amount of internal stresses in the microstructure inducing the formation of metastable phases α'' in the form of lamellae and ω in the form of nanoparticles. The generation of the nanosized ω-phase was presumed to relax the strain caused by the volume expansion (2.28%) from the hydrogen-containing β phase to the α'' martensite.

Mechanism of Lamellar Body Formation by Lung Surfactant Protein B

Breathing depends on pulmonary surfactant, a mixture of phospholipids and proteins, secreted by alveolar type II cells. Surfactant requires lamellar bodies (LBs), organelles containing densely packed concentric membrane layers, for storage and secretion. LB biogenesis remains mysterious but requires surfactant protein B (SP-B), which is synthesized as a precursor (pre-proSP-B) that is cleaved during trafficking into three related proteins. Here, we elucidate the functions and cooperation of these proteins in LB formation. We show that the N-terminal domain of proSP-B is a phospholipid-binding and -transfer protein whose activities are required for proSP-B export from the endoplasmic reticulum (ER) and sorting to LBs, the conversion of proSP-B into lipoprotein particles, and neonatal viability in mice. The C-terminal domain facilitates ER export of proSP-B. The mature middle domain, generated after proteolytic cleavage of proSP-B, generates the striking membrane layers characteristic of LBs. Together, our results lead to a mechanistic model of LB biogenesis.

Internal friction of Ni-Al intermetallic compound formation in sintering process

The Ni-Al intermetallic compounds, as important high-temperature structural materials, have clear target requirements in a number of fields. Powder metallurgy is an important candidate for preparing the Ni-Al intermetallic compounds. Clarifying the formation and transformation process of Ni-Al intermetallic compounds in sintering process and determining the solid diffusion reaction temperature and types of intermetallic compounds are greatly important for tailoring sintering process and optimizing product quality. In this paper, the internal friction behaviors of Ni-Al powder mixture compacts in the sintering process are systematically investigated by the internal friction technique. A typical internal friction peak is observed in the internal friction-temperature spectrum. The peak height decreases with the measuring frequency increasing, but the peak temperature is independent of frequency. Moreover, the internal friction peak shifts toward higher temperature and the peak height increases as the heating rate increases. It is reasonable that the internal friction peak belongs to the typical phase transformation internal friction peak which is associated with the formation of intermetallic compounds NiAl<sub>3</sub> and Ni<sub>2</sub>Al<sub>3</sub> in the heating process. Furthermore, the microstructure of the Ni-Al powder mixture can be tailored by mechanical ball-milling. The internal friction peak shifts toward lower temperature and the peak height decreases with the ball-milling time increasing, which indicates that the solid diffusion reaction can be activated at lower temperature with a slower reaction rate. This decrease is related to the refinement of powder particles, the lamellar formation of powder mixture, the enhancement of solid solution degree and surface energy, and the shortened atomic diffusion distance due to the mechanical ball-milling. It is also indicated that the mechanical ball-milling can effectively reduce the initial temperature of solid diffusion reaction, thus lowering sintering temperature.

Texture and Microstructure Evolution During Single-Point Incremental Forming of Commercially Pure Titanium

In the present investigation, the evolution of texture and microstructure during incremental sheet forming was investigated. Hot-rolled sheets of commercially pure titanium were subjected to single-point incremental forming to obtain truncated pyramid geometries. It was observed from texture measurements that there was splitting of basal poles along the transverse direction. Moreover, a significant number of twins was observed in the deformed microstructure with the fraction of extension twins being highest compared to other variants. The crossing of deformation twins, formation of twin lamellar structure and formation of secondary extension twins within primary contraction twins were additionally observed. The state of deformation in the pyramid walls was analyzed via finite element method which in turn was used as input for carrying out crystallographic texture simulations via visco-plastic self-consistent simulations. It was observed that the state of deformation in the wall regions is plain strain compression plus through-thickness shear.

Nodular Epiretinal Gliosis in the Fovea

Abstract To describe a peculiar hyperreflective optical coherence tomography finding of nodular epiretinal gliosis at the fovea that may be a manifestation of Muller response to retinal injury. The central fovea is stabilized by the Muller cell cone but is at risk of foveal dehiscence due to various insults including vitreomacular traction which can lead to lamellar or full thickness macular hole formation. 1 Degenerative lamellar macular holes can be associated with epiretinal proliferation which has been attributed to activated Muller cells. 2 In this report, we describe a very unusual optical coherence tomography (OCT) finding of nodular epiretinal gliosis which may be the result of Muller cell activation and expansion.

Molecular Reorganization during the Formation of the Human Skin Barrier Studied In Situ

In vertebrates, skin upholds homeostasis by preventing body water loss. The skin's permeability barrier is located intercellularly in the stratum corneum and consists of stacked lipid lamellae composed of ceramides, cholesterol, and free fatty acids. We have combined cryo-electron microscopy with molecular dynamics modeling and electron microscopy simulation in our analysis of the lamellae's formation, a maturation process beginning in stratum granulosum and ending in stratum corneum. Previously, we have revealed the lipid lamellae's initial- and end-stage molecular organizations. In this study, we reveal two cryo-electron microscopy patterns representing intermediate stages in the lamellae's maturation process: a single-band pattern with 2.0‒2.5 nm periodicity and a two-band pattern with 5.5‒6.0 nm periodicity, which may be derived from lamellar lipid structures with 4.0‒5.0 nm and 5.5‒6.0 nm periodicity, respectively. On the basis of the analysis of the data now available on the four maturation stages identified, we can present a tentative molecular model for the complete skin barrier formation process.

Could cellular and signaling abnormalities converge to provoke atopic dermatitis?

Diverse inherited and acquired abnormalities in epidermal structural and enzymatic proteins compromise permeability, barrier function and antimicrobial defense in atopic dermatitis (AD). Though several mutations in filaggrin (FLG) predominate, alterations in other S-100, cornified envelope precursor proteins (hornerin [HRNR], filaggrin2 [FLG2], SPRR3, mattrin) which regulate lamellar body formation; SPINK5, which encodes the serine protease inhibitor, LEKTI1, and a fatty acid transporter, FATP4, are all separately associated with an AD phenotype. Exogenous and endogenous stressors, such as prolonged psychological stress, a low environmental humidity, or exposure to basic soaps and surfactants can further compromise barrier function and are often required to trigger disease. In the immunologists' view, the barrier abnormality is relevant only because it allows antigen and pathogen access, while stimulating Th2 cytokine production. These proteins in turn downregulate lipid synthetic enzyme and antimicrobial peptide levels, as well as multiple epidermal structural proteins, including filaggrin. Each inherited and acquired abnormality can independently compromise lamellar body secretion production, resulting in defective lamellar membrane organization and antimicrobial defense. Furthermore, elevated pH of the SC is critical for AD pathogenesis, compromising post-secretory lipid processing, while also enhancing inflammation. There are various therapeutic options that interdict different stages in this pathogenic paradigm.

Formation mechanism of α lamellae during β→α transformation in polycrystalline dual-phase Ti alloys

Phase field simulations incorporating contributions from chemical free energy and anisotropic interfacial energy are presented for the β→α transformation in Ti-6Al-4 V alloy to investigate the growth mechanism of α lamellae of various morphologies from undercooled β matrix. The α colony close to realistic microstructure was generated by coupling the Thermo-Calc thermodynamic parameters of α and β phases with the phase field governing equations. The simulations show that α lamellar side branches with feathery morphology can form under a certain combination of interfacial energy anisotropy and temperature. α lamellae tend to grow slowly at high heat treatment temperature and become wider and thicker as temperature increase from 800 to 900 °C provided that the interfacial energy anisotropy ratio kx: ky was set as 0.1: 0.6. Besides, higher interfacial energy anisotropy can accelerate the formation of α lamellae, and the equilibrium shape of α lamellae changes from rod to plate as the interface energy anisotropy ratio kx: ky vary from 0.1: 0.4 to 0.1: 0.8 under 820 °C. Experiments were conducted to study the α lamellar side branches in Ti-6Al-4 V (Ti-6.01Al-3.98 V, wt.%) and Ti-4211 (Ti-4.02Al-2.52V-1.54Mo-1.03Fe, wt.%) alloys with lamellar microstructure. Electron backscatter diffraction (EBSD) results show that α lamellar side branches and their related lamellae share the same orientation. The predicted temperature range for α lamellar side branches formation under various interfacial energy anisotropy is consistent with experimental results.