Surface Protrusions Research Articles

Simulation of pre-breakdown discharges in high-pressure air: II. Effect of surface protrusions

Analysis of deviations from the similarity law, observed at high and very high pressures in experiments on discharge ignition and breakdown in corona-like configurations, can serve as a useful, albeit inevitably indirect, source of information about microprotrusions on the surface of the electrodes. In this work, such analysis was performed by means of 2D numerical modelling. Conical or cylindrical protrusions on the surface of the inner electrode were studied and the kinetic scheme includes the electrons, one species of positive ions, and negative ions , , and . It is shown that the deviations from the similarity law, observed in the experiment, may indeed be attributed to enhanced ionization of air molecules in regions of amplified electric field near the microprotrusions. A qualitative agreement with the experiment in all the cases is achieved for protrusion heights of the order of 50 µm. Such values may appear rather high, however there is no other explanation in sight at present. The enhancement of the field electron emission from the surface of the negative electrode due to the amplification of the electric field on the microprotrusion was estimated and found insignificant in the range of values of the protrusion aspect ratio where the enhanced ionization in the gas phase is already appreciable.

Improvements in the static/dynamic strength of porcelain fused to metal dental crowns with surface protrusions produced by selective laser melting

Porcelain fused to metal dental crowns (PFMDC) are widely used in dental applications. Although the dental crowns are usually produced by the conventional casting method, additive manufacturing (AM) has recently gained an increased interest in dentistry due to its easy and rapid fabrication. Additive manufacturing is also a very advantageous method in patient-specific dental designs. In addition, through this method, it is possible to obtain products with geometries that cannot be obtained by classical methods. It is important to increase the lifetime of products in dental applications for lower costs and improved patient psychology. By increasing the strength of metal–ceramic interfaces, the total strength of dental crowns can be increased. For that reason, metal crowns with different numbers of protrusions and different locations on their surface edges were designed and produced by the selective laser melting method which is one of the additive manufacturing methods. These crowns were tested under both static and dynamic loading conditions and they mechanical performance was compared with the crowns produced by conventional methods. It was found that the crowns, which had different numbers of protrusions and different locations on the surface edge, showed more resistance under both static and dynamic load conditions. It was found that a metal substructure with dense protrusions that was produced at a thickness of 0.3 mm showed the highest strength under both static and dynamic loads.

Sites responsible for infectivity and antigenicity on nervous necrosis virus (NNV) appear to be distinct

Nervous necrosis virus (NNV) is a pathogenic fish-virus belonging to the genus Betanodavirus (Nodaviridae). Surface protrusions on NNV particles play a crucial role in both antigenicity and infectivity. We exposed purified NNV particles to different physicochemical conditions to investigate the effects on antigenicity and infectivity, in order to reveal information regarding the conformational stability and spatial relationships of NNV neutralizing-antibody binding sites and cell receptor binding sites. Treatment with PBS at 37 °C, drastically reduced NNV antigenicity by 66–79% on day one, whereas its infectivity declined gradually from 107.6 to 105.8 TCID50/ml over 10 days. When NNV was treated with carbonate/bicarbonate buffers at different pHs, both antigenicity and infectivity of NNV declined due to higher pH. However, the rate of decline with respect to antigenicity was more moderate than for infectivity. NNV antigenicity declined 75–84% after treatment with 2.0 M urea, however, there was no reduction observed in infectivity. The antibodies used in antigenicity experiments have high NNV-neutralizing titers and recognize conformational epitopes on surface protrusions. The maintenance of NNV infectivity means that receptor binding sites are functionally preserved. Therefore, it seems highly likely that NNV neutralizing-antibody binding sites and receptor binding sites are independently located on surface protrusions.

Self-Pillared Ultramicroporous Carbon Nanoplates for Selective Separation of CH4 /N2.

There is growing evidence that pillaring up a densely packed ultramicroporous two-dimensional (2D) structure is an effective strategy to reduce their internal diffusion. Reliable pillaring paradigms, however, is rather challenging. Here we report a one-pot multi-component sequential assembly method for the preparation of a new self-pillared 2D polymer and ultramicroporous carbon with integrated surface protrusions. The molecular level pillaring process is surprisingly fast, that is, in 10 min. The thickness of nanoplate edge and the density (roughness), angle as well as height of protrusions can be precisely tuned. Exemplified in coal bed methane purification/separation, this unique pillared 2D carbons exhibit a CH4 /N2 selectivity up to 24 at a low CH4 partial pressure and two orders of magnitude faster CH4 diffusion kinetics than the commercial carbon molecular sieves. This solution synthesis methodology is generalizable for creation and fine tuning of pillared 2D heterostructures.

Self‐Pillared Ultramicroporous Carbon Nanoplates for Selective Separation of CH4/N2

AbstractThere is growing evidence that pillaring up a densely packed ultramicroporous two‐dimensional (2D) structure is an effective strategy to reduce their internal diffusion. Reliable pillaring paradigms, however, is rather challenging. Here we report a one‐pot multi‐component sequential assembly method for the preparation of a new self‐pillared 2D polymer and ultramicroporous carbon with integrated surface protrusions. The molecular level pillaring process is surprisingly fast, that is, in 10 min. The thickness of nanoplate edge and the density (roughness), angle as well as height of protrusions can be precisely tuned. Exemplified in coal bed methane purification/separation, this unique pillared 2D carbons exhibit a CH4/N2 selectivity up to 24 at a low CH4 partial pressure and two orders of magnitude faster CH4 diffusion kinetics than the commercial carbon molecular sieves. This solution synthesis methodology is generalizable for creation and fine tuning of pillared 2D heterostructures.

Mitotic Spindle Positioning (MISP) is an Actin Bundler that Selectively Stabilizes the Rootlets of Epithelial Microvilli

Microvilli are conserved actin-based surface protrusions that have been repurposed throughout evolution to fulfill diverse cell functions. In the case of transporting epithelia, microvilli are supported by a core of actin filaments bundled in parallel by villin, fimbrin, and espin. Remarkably, microvilli biogenesis persists in mice lacking all three of these factors, suggesting the existence of unknown bundlers. We identified Mitotic Spindle Positioning (MISP) as an actin binding factor that localizes specifically to the rootlet end of the microvillus. MISP promotes rootlet elongation in cells, and purified MISP exhibits potent filament bundling activity in vitro. MISP-bundled filaments also recruit fimbrin, which further elongates and stabilizes bundles. MISP confinement to the rootlet is enforced by ezrin, which prevents decoration of the membrane-wrapped distal end of the core bundle. These discoveries reveal how epithelial cells optimize apical membrane surface area and offer insight on the remarkable robustness of microvilli biogenesis.

Modification of Olive Leaves’ Surface by Ultrasound Cavitation. Correlation with Polyphenol Extraction Enhancement

We investigated the impact of ultrasound at 20 kHz on olive leaves to understand how acoustic cavitation could increase polyphenol extraction. Application of ultrasound to whole leaf from 5 to 60 min enabled us to increase extraction from 6.96 to 48.75 µg eq. oleuropein/mL of extract. These results were correlated with Environmental Scanning Electron Microscopy, allowing for leaf surface observation and optical microscopy of treated leaf cross sections to understand histochemical modifications. Our observations suggest that the effectiveness of ultrasound applied to extraction is highly dependent on plant structure and on how this material will react when subjected to acoustic cavitation. Ultrasound seems to impact the leaves by two mechanisms: cuticle erosion, and fragmentation of olive leaf surface protrusions (hairs), which are both polyphenol-rich structures.

EFFECTIVENESS OF ECO-RETROFITS IN REDUCING WAVE OVERTOPPING ON SEAWALLS

Terms such as 'nature-based', 'living shoreline', 'green infrastructure' and 'ecological engineering' are increasingly being used to reflect biomimicry-based engineering measures in coastal defences. Innovative interventions for nature-based sea defences have included the retrofitting of man-made water filled depressions or 'vertipools' to existing seawalls (Hall et al., 2019; Naylor et al., 2017) and the addition of artificial drill-cored rock pools to intertidal breakwaters (Evans et al., 2016). Through their capacity to retain water, such measures serve to enhance biodiversity in the built environment (Browne and Chapman, 2014). Evans et al. (2016) for example, experimentally demonstrated that the introduction of artificial rock pools to an intertidal granite breakwater enhanced the levels of species richness compared to those observed on plain surfaces of the breakwater. Notwithstanding these biological benefits, the impetus for incorporation of ecologically friendly measures to existing defences remains low (Salauddin et al., 2020a). This situation could potentially change should it be shown that the addition of 'green' measures to sea defences could enhance wave attenuation and reduce wave overtopping as well as wave pressures on the coastal defence structures. This paper describes small-scale physical modelling investigations of seawalls and explores reductions in wave overtopping that could be realised by retrofitting sea defences with 'green' features (such as 'vertipools'). Surface protrusions of varying scale and density are used in the physical modelling to mimic 'green' features and the results from measurements of overtopping are benchmarked to reference conditions determined from tests on a plain seawall.

Panorama of “fuzz” growth on tungsten surface under He irradiation

Nanostructure formation on tungsten (W) surfaces under helium (He) irradiation is a unique and interesting phenomenon that directly impacts the performance and lifetime of W-based materials as plasma-facing materials (PFMs) in nuclear fusion reactors. The evolution of He bubbles beneath the W surface and its effect on surface morphology are essential for understanding the deterioration of the surface properties of PFMs. In this work, the morphology of the W surface under different irradiation conditions was investigated using molecular dynamics in order to extract essential factors that determine the nanostructure of the W surface. The design concerned with investigating the W surface morphology encompassed: (1) the morphology of the W-free surface without He bubbles vs. recoil energy; (2) the morphology of the W surface in the presence of He bubbles vs. recoil energy; and (3) sputtering vs. surface roughness in the absence of He bubbles. A mass of adatoms generated primarily by loop punching of sub-surface He bubbles slightly roughens the surface. Bubble bursting further heightens surface protrusions. In this case, the fiber-like structure of the surface is attributable to two processes involved in He bubble evolution: He diffusion plus aggregation and bubble expansion plus bursting. A high temperature window expedites He diffusion and aggregation beneath the protruded surface. Once the He bubbles burst regardless of spontaneous bursting (when the bubble pressure is beyond the critical value), or bursting due to external irradiation, the protrusions will be further heightened, thus serving as precursors of the fiber-like structure. Continuous aggregation, followed by bursting, should constitute the recursive process of protrusion upgrowth. The panoramic view of the fiber-like structure growth described here is expected to provide a clue for designing tungsten-based materials with high radiation-resistance performance.

Numerical Study of Pool Boiling Heat Transfer From Surface With Protrusions Using Lattice Boltzmann Method

Abstract This paper reports our numerical studies on pool boiling heat transfer from a plane and with protruding surface using single component pseudo-potential phase change model of lattice Boltzmann method. The surface protrusions are assumed to be rectangular in shape with a given height and width. The surface protrusions are seen to promote nucleation of bubbles from the heated surface resulting in significantly higher heat transfer rates compared to the plane surface. Spatial and temporal averaged heat fluxes from all these protruding surfaces are found to be 3–4 times higher than that of a plane surface. The effects of the protrusion height, width, spacing, and associated geometrical parameters on surface heat flux have been investigated in order to arrive at an optimal design for maximum heat transfer.

Functional, Rheological, Morphological, and Micro‐Structural Properties of Extrusion‐Processed Corn and Potato Starches

AbstractThe purpose of this study is to investigate the effect of twin‐screw extrusion conditions on the properties and quality attributes of corn starch (CS) and potato starch (PS). Extrusion processing conditions used are—feed moisture level of 17% and 18%, screw speed level of 414 and 533 rpm, and barrel temperature of 131 and 135 °C for CS and PS, respectively. When compared with native starches, it is demonstrated that extrusion has a positive effect on the functional properties, that is, bulk density decreases, but water absorption index, water solubility index, degree of gelatinization, and in vitro digestibility increase significantly, and transform its native structure to a honeycomb‐like fine meshwork. Extrusion also results in a significant decrease in pasting temperature, peak viscosity, hold viscosity, final viscosity, breakdown viscosity, and setback viscosity of both the starches. In color profile, a decrease in luminosity, but increase in redness and yellowness are observed in extruded starches. Scanning electron microscopy and X‐ray diffractometry studies show that extrusion leads to complete destruction of structure along with reduced crystallinity and formation of V‐type polymorphs in starches. Compared to CS, PS shows more surface protrusions and formation of air cells leading to formation of a much more microporous structure.

Occurrence and characteristics of microplastics in the coral reef, sea grass and near shore habitats of Rameswaram Island, India

This study compares the occurrence and characteristics of microplastics (MPs) and heavy metal contaminants in the water and sediment of three habitats (corals, seagrass-beds and near-shores) of Rameswaram Island, India. The overall mean concentration of MPs varies from 24 ± 9 to 96 ± 57 items/L in water, and from 55 ± 21 to 259 ± 88 items/kg in sediment. The value of abundance is the greatest in the coral reef site CR-1 (96 ± 51 items/L; 259 ± 88 items/kg) followed by the seagrass site SG-2 (94 ± 55 items/L; 203 ± 75 items/kg) and the near-shore site St-15 (95 ± 63 items/L; 193 ± 75 items/kg). PE fiber (<1000 μm) is predominant in water, whereas PP fiber and fragment (between 2000 and 5000 μm) dominate the sediment. The SEM images of MPs reveal features which are characteristic of degradation like surface roughness, cracks, protrusions, and chalking, along with surface precipitates of both chemical and biological origin. EDAX images show the presence of Cr, Fe, Hg, Pb, Cu, As and Cd associated with MP surfaces.

Thermal/tribological effects of superimposed ultrasonic vibration on viscoelastic responses and mold-filling capacity of optical glass: A comparative study

Ultrasonic-assisted glass molding (UGM) has recently gained a promising start in fast replication of tailored functional structures onto glasses; however, the underlying mechanisms of the unique thermomechanical and micro-filling behaviors of glasses in UGM remain largely unrevealed. This study presents a full demonstration and elucidation of the ultrasonic-induced thermal/tribological effects on viscoelastic responses and filling capacity of the typical optical glass L-BAL42. First, conventional precision glass molding (PGM) and UGM experiments with partial-filling settings are implemented, whereby glass arrays with surface protrusions of varied depths (460–780 μm) are directly formed. Subsequently, the molding force, forming time and filling depth of the glass under varying pressing speeds/loads are comparatively evaluated. Furthermore, experimental quantifications of ultrasonic-induced heat increment and friction reduction are performed to account for the differentiated molding effects in UGM and PGM. The results indicate that compared with PGM, the molding force and forming time in UGM are greatly reduced, while the average filling depth of the UGM-formed glass array is effectively improved. This overall enhancement can be attributed to the ultrasonic-induced thermal softening, friction reduction and stress superposition effects, among which the thermal contribution is dominant. The findings in this study will provide new references for ultrasonic-assisted precision molding of glass-based micro/meso components.

Analysis of conditions of the quartz surface photochemical polishing by way of profile optimization

PurposeThe purpose of this paper is to show the possibility of using the quartz regular surface profile in the form of protrusions and troughs of a triangular shape instead of a random surface profile characterized by a Gaussian correlation function when analyzing the electromagnetic field parameters above the quartz surface to determine the conditions of the effective surface subnano-polishing.Design/methodology/approachThe numerical determination of the evanescent field optimal configuration formed near the quartz rough surface coated with an aqueous solution of calcium hypochlorite when illuminated from the side of the solution has been considered. The finite-element approach is used to solve the Helmholtz two-dimensional vector equation.FindingsConditions of effective photochemical polishing of rough surface with profile in the form of triangular protrusions and troughs to a sub-nanometer level of roughness are found. These optimal conditions are achieved when the light falls normally on the quartz surface and the height of the surface protrusions is small (up to 20 nm).Originality/valueThis paper shows the possibility of simplifying electrodynamic calculations and analyzing an evanescent field near a quartz surface for the purpose of photochemical polishing by replacing the random profile function with a deterministic periodic function. That is, the novelty of this paper, which supplements the works published earlier [Journal of Modern Optics, 67(3) (2020):242–251; Optik, 207 (2020):164438].

Lysophosphatidic acid modulates ovarian cancer multicellular aggregate assembly and metastatic dissemination

Epithelial ovarian cancer (EOC) metastasis occurs by exfoliation of cells and multicellular aggregates (MCAs) from the tumor into the peritoneal cavity, adhesion to and retraction of peritoneal mesothelial cells and subsequent anchoring. Elevated levels of lysophosphatidic acid (LPA) have been linked to aberrant cell proliferation, oncogenesis, and metastasis. LPA disrupts junctional integrity and epithelial cohesion in vitro however, the fate of free-floating cells/MCAs and the response of host peritoneal tissues to LPA remain unclear. EOC MCAs displayed significant LPA-induced changes in surface ultrastructure with the loss of cell surface protrusions and poor aggregation, resulting in increased dissemination of small clusters compared to untreated control MCAs. LPA also diminished the adhesive capacity of EOC single cells and MCAs to murine peritoneal explants and impaired MCA survival and mesothelial clearance competence. Peritoneal tissues from healthy mice injected with LPA exhibited enhanced mesothelial surface microvilli. Ultrastructural alterations were associated with restricted peritoneal susceptibility to metastatic colonization by single cells as well as epithelial-type MCAs. The functional consequence is an LPA-induced dissemination of small mesenchymal-type clusters, promoting a miliary mode of peritoneal seeding that complicates surgical removal and is associated with worse prognosis.

Potential anti-icing applications of encapsulated phase change material–embedded coatings; a review

Abstract Icephobic surfaces are highly sought-after materials as there is a need to reduce the catastrophic outcomes of ice formation on outdoor surfaces. Existing anti-icing strategies, including superhydrophobic surfaces (SHPSs) and slippery liquid–infused porous surfaces (SLIPS), are often ineffective against frost formation or have a limited durability. As such, new approaches are required, and the incorporation of phase change materials (PCMs) into polymeric matrices offers a potential means of delaying ice formation and reducing ice adhesion on exposed surfaces. Homogeneously dispersed encapsulated PCMs (EPCMs) of uniform size inside a binder can release high amounts of latent heat and produce local shear stresses on surfaces—due to their volume change—during icing conditions, thereby reducing ice adhesion strength. Furthermore, surface protrusions produced by the EPCMs can also impart hydrophobicity or even superhydophobicity onto a surface to delay ice formation. This contribution reviews recent progress in the development of ECPM-based anti-icing surfaces. We also discuss the advantages and challenges of using PCM materials for anti-icing applications, summarize existing encapsulation methods, and outline the ECPM-based mechanisms that hinder ice formation and lower ice adhesion.

Diaphragm-Micro-Stylus-Based Fiber Bragg Grating Tactile Sensor

We propose a simple and novel circular diaphragm-micro-stylus based single fiber Bragg grating (FBG) tactile sensor for reading Standard English Grade-1 Braille cells. The surface protrusions on the cells are transduced into strain variations on the FBG sensor, bonded along the line of symmetry of the diaphragm, by a free, vertically moving Micro-Stylus (MS). The tension mode of the diaphragm and the mass of the micro-styli are varied to optimize the sensing properties of the system. The maximum sensitivity of 1.786nm/mm is exhibited by the sensor system with the highest mass of the MS (MS-1; 167mg) in the highest tension mode (770μe). The repeatability error and resolution of the sensor in the aforementioned configurations are found to be 0.028nm and 559nm respectively. The proposed sensor system displayed good linearity, repeatability, high resolution, and easily adjustable sensitivity in the present scenario.

Formation of residual droplets upon dip-coating of chemical and topographical surface patterns on partially wettable substrates

We have studied the occurrence of residual liquid induced by the presence of defects during dip-coating of partially wettable surfaces. The defects are either topographical in nature such as surface protrusions or depressions, or chemically defined surface energy heterogeneities. Typically the residual liquid is distributed in a cascade of satellite droplets that arise from capillary break-up and the recession of the coating meniscus, after it is temporarily pinned by the defect. We characterize the volume and position of the largest satellite droplet as a function of the geometrical shape and size of the defect as well as its topographical amplitude or contact angle contrast. Our results are relevant for instance to immersion lithography, where the occurrence of residual droplets is undesirable.

Dependence of nanoscale heat transfer across a closing gap on the substrate material and ambient humidity

We investigate the heat transfer across a closing nanoscale gap between an operational microelectronic device and a static substrate in ambient conditions. The device contains an embedded microheater and a nanoscale metal wire that works as a thermometer. The heater causes a microscale protrusion by thermal expansion such that its surface approaches the substrate until contact occurs. Meanwhile, the metal wire located near the center of the protrusion surface measures the temperature of the protrusion, which is dependent on the size of the gap, the substrate material, and the ambient conditions. We study the nanoscale heat transfer using three different substrates and find that their thermal conductivity plays an essential role. Finally, the experiments are conducted under different relative humidity (RH) conditions. The results show that the ambient humidity can also affect the nanoscale heat transfer when RH &amp;gt; 75%.

Electrodynamic analysis of light-assisted subnano-polishing of a quartz surface under conditions of total internal reflection by using surface profile optimization

The solution of the electrodynamic problem for determining the optimal configuration of the evanescent field formed near the rough quartz surface coated with an aqueous solution of sodium hypochlorite when illuminated from the side of quartz has been considered in order to ensure effective photochemical polishing of this surface to a sub-nanometer level of roughness. It was found that for a quartz surface profile in the form of triangular protrusions and troughs, which periodically repeat, the optimal conditions for photochemical polishing are achieved when the angle of incidence of light is critical and the height of the surface protrusions is small (up to 20 nm). It has been shown that in this case, the incident electromagnetic wave forms significantly higher values of the electric field in the protrusion region than in the trough region, creating optimal conditions for the subnano-polishing of this surface. Criteria are described for the possibility of using a regular profile in the form of protrusions and troughs of a triangular shape instead of a random surface profile characterized by a Gaussian correlation function when determining the optimal field parameters above the quartz surface.