High-density Layer Research Articles

Sulfidization mechanism in the flotation of cerussite: A heterogeneous solid-liquid reaction that yields PbCO3/PbS core-shell particles

Sulfidizationfollowed byxanthateflotation is an extensively used method for recovering the lead oxide minerals. However, there is a debate about the sulfidization mechanism of cerussite. In this work, the sulfidization mechanism was investigated using optical microscopy (OM), scanning electron microscopy and energy dispersive spectrometry (SEM-EDS), atomic force microscopy (AFM), X-ray diffraction (XRD) and electron probe microanalysis (EPMA). The OM, SEM-EDS and AFM results indicated that many microspheres grew on the cerussite particle surfaces to form a high-density sulfidization product layer after sulfidization, which changed the color, optic character, electrical conductivity and surface morphology of cerussite particles. The XRD results for the sulfidized cerussite samples showed that the sulfidization product layer was too thin to be detected. By the selective solvent action of acetic acid, the sulfidization product was extractedfrom the sulfidized cerussite particles. The XRD pattern interpreted that the sulfidization product were galena (PbS) phase, which provided the strongest proof for the generation of PbS on the cerussite surfaces. Moreover, the crystallite size of PbS calculated by the Scherer formula was in nanoscale. The EPMA analysis showed that the oxygen element was localized in the interior section, whereas the sulphur element was occurred in the outer surfaces of the particle. The aforementioned results demonstrated that after cerussite sulfidization, the mineral particles have a lead carbonate (PbCO3) core and a lead sulfide (PbS) shell. These findings also demonstrated that the sulfidization reaction is a heterogeneous reaction of solid phase (cerussite particles) with an aqueous solution (sodium sulfide solution) in which the solid reaction product adheres to the cerussite surface. From another point of view, the sulfidization process is a crystallization process including the heterogeneous nucleation and growth of PbS.

Surface Ligands as Permeation Barrier in the Growth and Assembly of Anisotropic Semiconductor Nanocrystals.

Because of the large surface-to-volume ratio of colloidal nanocrystals (NCs), surfactant molecules grafted at the NC surface play an important role in NC growth, interparticle interaction, processing, and application. For this reason, much progress has been made in understanding the surface chemistry of NCs along with the organic ligand shell, particularly in terms of grafted polar groups. However, most explanations of aliphatic counterparts are based on spherical NCs that usually have a dilute ligand layer. In anisotropic NCs such as nanorods and nanoplatelets, the linearly extended dimension results in a high-density aliphatic layer on the NC surface. Unlike spherical NCs, the compact organic shell could serve as a permeation membrane, effectively impeding a penetration of foreign molecules toward the NC surface. In this Perspective, we highlight the effects of ligand configuration on the properties of anisotropic NCs by exploring morphologies, assembled superstructures, and surface reaction of anisotropic NCs.

High hardness and fatigue resistance of CoCrFeMnNi high entropy alloy films with ultrahigh-density nanotwins

Development of film materials has been limited by the hardness-fatigue resistance trade-off. The purpose of the present study was to obtain films with a combination of both high hardness and strong fatigue resistance. To achieve this, CoCrFeMnNi high entropy alloy films (HEAFs) were fabricated with three different structures: amorphous, high-density nanotwinned crystal structure with twin spacings of 2.2–5.6 nm, and ultrahigh-density nanotwinned columnar grains with twin spacings of 1.2–2.5 nm. Nanoindentation with dynamic mechanical analysis was used to measure the hardness and perform the fatigue tests. While higher twin densities could dissipate more energy by detwinning during fatigue loading to enhance the fatigue resistance, twin spacings larger than and small than 2 nm could, respectively, result in hardening and softening. Our results showed a high hardness of ~9 GPa and fair fatigue resistance (~104 cycles) for both amorphous and high-density nanotwinned crystalline layers. For the ultrahigh-density nanotwinned columnar grain structure, a high hardness of ~8.5 GPa and an excellent fatigue resistance (~106 cycles) were obtained. The outstanding fatigue resistance and high hardness were attributed to the synergistic effect of strain hardening and detwinning of ultrahigh-density nanotwins. The results not only enable CoCrFeMnNi HEAFs with a predominant combination of hardness and fatigue resistance, but also shed light on a new perspective for overcoming the conflict between hardness and fatigue resistance in film materials for microelectromechanical applications.

Blocking streamer development by plane gaseous layers of various densities

Streamer interaction with gaseous layers of various densities is numerically simulated in ambient air on the basis of a two-dimensional fluid model. It is shown that rarefied layers are greater obstacles to streamer propagation in comparison with dense layers. When intersecting a low-density layer, the streamer tends to initiate a radial ionization wave, which screens and weakens the electric field both on the axis in the layer and behind it. As a result, it is difficult to form a secondary streamer behind the low-density gas layer. A streamer interacting with a high-density layer also can initiate a radial ionization wave, which develops in undisturbed air along the outer surface of the layer. The streamer can overcome a high-density layer at not-too-high values of the layer thickness. The effects of the streamer polarity, layer thickness and density on the streamer interaction with the layer are studied. It is shown that the discharge gap with a thin low-density layer behaves like a diode in which streamer discharges of negative polarity can pass through the gap, while discharges of positive polarity are blocked.

Growth ring formation of Dichrostachys cinerea and Senegalia mellifera in arid environments in Namibia

Dichrostachys cinerea and Senegalia mellifera trees are the most widespread invasive encroacher species in Namibia. Understanding their growth performance under arid conditions is key to understanding and managing the arid ecosystems of Namibia. To determine their utility in dendrochronology, we analyzed the formation of growth rings for two species from three sites in Namibia. We applied cross-dating techniques to 69 tree discs, the analysis of which confirmed the formation of annual growth rings. The rings are characterised by alternating layers of low and high vessel density and are separated by bands of marginal parenchyma. D. cinerea shows a well-defined pattern of growth rings, whereas the ring patterns of S. mellifera are more complex. Because aging trees tend to display narrower rings toward the outside of the stem, we applied both ring-width index and basal area increment methods in developing ring-width chronologies for the two species. Descriptive statistics for the chronologies indicate that the average ring chronologies are of good quality and that the trees are responding to common environmental signals. The basal area increment methodology produced better statistics than the ring-width index for these two species. Furthermore, statistical characteristics of the chronologies indicate that D. cinerea has a higher mean sensitivity (MS), expressed population signal (EPS), and signal-to-noise ratio (SNR) than S. mellifera. Thus, we find that both species are suitable for dendrochronological study, with D. cinerea being better than S. mellifera.

Crustal density structure of the northwestern Iranian Plateau

We present a new 2D crustal-scale model of the northwestern Iranian plateau based on gravity–magnetic modeling along the 500 km long China–Iran Geological and Geophysical Survey in the Iranian plateau (CIGSIP) seismic profile across major tectonic provinces of Iran from the Arabian plate into the South Caspian Basin (SCB). The seismic P-wave receiver function (RF) model along the profile is used to constrain major crustal boundaries in the density model. Our 2D crustal model shows significant variation in the sedimentary thickness, Moho depth, and the depth and extent of intra-crustal interfaces. The Main Recent Fault (MRF) between the Arabian crust and the overriding central Iran crust dips at approximately 13° towards the northeast to a depth of about 40 km. The geometry of the MRF suggests about 150 km of underthrusting of the Arabian plate beneath central Iran. Our results indicate the presence of a high-density lower crustal layer beneath Zagros. We identify a new crustal-scale suture beneath the Tarom valley between the South Caspian Basin crust and Central Iran and the Alborz. This suture is associated with sharp variation in Moho depth, topography, and magnetic anomalies, and is underlain by a 20 km thick high-density crustal root at 35–55 km depth. The high-density lower crust in Alborz and Zagros may be related to partial eclogitization of crustal roots below about 40 km depth. The gravity and magnetic models indicate a highly extended continental crust for the SCB crust along the profile. Low observed magnetic susceptibility of the Kermanshah ophiolites likely indicates that the ophiolite rocks only form a thin layer that has been thrust over the sedimentary cover.

Lagrangian fluid approach for the modeling of peculiarities of the interstellar dust distribution in the astrospheres/heliosphere

Abstract Interstellar dust penetrates into the heliosphere/astrosphere due to relative motion of the Sun and the local interstellar medium (LISM). Inside the heliosphere/astrosphere and at the heliospheric boundaries, where the solar/stellar wind interacts with LISM, distribution of the interstellar dust is modified due to an action of electromagnetic forces, the solar gravitation and radiation pressure. In this paper we show that the distribution of the interstellar dust particles in the heliosphere has peculiarities of high density layers. In order to understand the nature of the peculiarities Osiptsov’s Lagrangian method has been employed and developed for the case when the force acting on the particles has discontinuity as it is for the electromagnetic force at the helioshperic current sheet. In the result of the modeling we demonstrate existence of multiple layers of high density of the interstellar dust located at 0.03 - 10 AU north and south with respect to the heliospheric current sheet.

Development of a Cuvette-Based LSPR Sensor Chip Using a Plasmonically Active Transparent Strip.

This research demonstrates the development of a transmission-mode localized surface plasmon resonance (LSPR) sensor chip using a cuvette cell system for the sensitive detection of a biomolecule marker such as C-reactive protein (CRP). In order to develop a highly sensitive LSPR sensor chip, plasmonically active gold nanoparticles (AuNPs) were decorated onto various transparent substrates in the form of a uniform, high-density single layer using a self-assembly process. The transparent substrate surface was modified with amine functional groups via (3-Aminopropyl)triethoxysilane (APTES) treatment, and the ligand concentration and temperature (0.5% APTES at 60°C) were then optimized to control the binding energy with AuNPs. The optimized plasmonically active strip was subsequently prepared by dipping the amine-functionalized substrate into AuNPs for 8 h. The optimized plasmonic strip functionalized with anti-CRP was transformed into a portable LSPR sensor chip by placing it inside a cuvette cell system, and its detection performance was evaluated using CRP as a model sample. The detection limit for CRP using our LSPR sensor chip was 0.01 μg/mL, and the detection dynamic range was 0.01–10 μg/mL with a %CV of <10%, thus confirming its selectivity and good reproducibility. These findings illustrate that the highly sensitive portable LSPR biosensor developed in this study is expected to be widely used in a diverse range of fields such as diagnosis, medical care, environmental monitoring, and food quality control.

Deep Structure of the Eastern Himalayan Collision Zone: Evidence for Underthrusting and Delamination in the Postcollisional Stage

AbstractBased on broadband seismic data from 102 stations in the eastern Himalayan collision zone, the crustal thickness and Poisson's ratio were determined by using the H‐κ stacking analysis of teleseismic P wave receiver functions. The Moho topography rapidly deepens northward in the northern Lhasa terrane, inferring the northern limit of the Indian plate underthrusting beneath Tibetan Plateau. Our seismic images show that steep subduction of the Indian plate occurs to the west of the Eastern Himalayan Syntaxis while gentle subduction to the east. The variation of subduction geometry of the Indian plate may be one of the causes for the formation of the eastern Himalayan Syntaxis. The 2‐D crustal density modeling of the gravity measurements shows that the average crustal density in the eastern Himalayan collision zone is less dense than the global average continental crust, and our preferred model has 5‐ to 10‐km‐thick, high density layer (2,970–3,000 kg/m3) in the lower crust beneath the eastern Lhasa terrane, consistent with mafic underplating. The attributes of a thickened crust with northward deepening Moho and low‐to‐normal Poisson's ratio might be the geophysical signature of delamination beneath the Lhasa terrane and underthrusting of Indian plate. We hypothesize that the orogenic root of the Lhasa terrane was removed by convective‐driven delamination, followed by northward subduction of the Indian plate. Thus, delamination and continental subduction are the dominant deep processes in the postcollisional stage in the eastern Himalayan collision zone.

Achieving efficient flexible perovskite solar cells with room-temperature processed tungsten oxide electron transport layer

For flexible perovskite solar cells, achieving high power conversion efficiency by using a room-temperature technology to fabricate a compact electron transport layer is one of the best options. Here, we develop an annealing-free, dopant-free, and amorphous tungsten oxide as electron transport layer by vacuum evaporation for flexible perovskite solar cells. The compact amorphous tungsten oxide electron transport layer with different thicknesses (0–50 nm) was directly deposited on flexible PEN/ITO substrate. A model of the improvement mechanism is proposed to understand how the thickness tailoring simultaneously enhances the crystallization and relaxes the trade-off between interface recombination and charge transfer. By optimizing the amorphous tungsten oxide thickness, the high homogeneous, uniform, and dense electron transport layer with a thickness of 30 nm is found to not only decrease the pinhole of the perovskite layer, but also enhance charge transport with reducing resistance. Furthermore, the mechanical bending stability revealed that, the fabricated perovskite solar cells show stable power conversion efficiency up to more than 1000 bending cycles. The room-temperature processed fabrication enables the amorphous tungsten oxide to become a potential electron transport layer candidate for the large-scale flexible perovskite solar cells, which becomes compatible with practical roll-to-roll solar cells manufacturing.

Upper-mantle density structure in the Philippine Sea and adjacent region and its relation to tectonics

SUMMARY The evolution of the Philippine Sea Plate (PSP) since Jurassic is one of the key issues in the dynamics of lithosphere and mantle. The related studies benefited mostly from seismic tomography which provides velocity structures in the upper mantle. However, the upper-mantle structure is not well resolved compared to the continental areas due to the lack of seismic data in the Philippine Sea. We employ a 3-D gravity inversion constrained by an initial model based on the S-wave tomography (SL2013sv; Schaeffer &amp; Lebedev 2013) to image the density structure of the upper mantle of the PSP and adjacent region. The resulting model shows a three-layer pattern of vertical high-low-high density variation in the upper mantle under the PSP. The thin high-density layer evidences for strong oceanic lithosphere in the West Philippine Sea. The relatively low dense mantle located below the PSP possibly originates from the asthenosphere. The PSP differs from the Pacific and the Indian-Australian plates in the whole depth range, while its structure is similar to the eastern Eurasian and Sunda plates. In the depth range, 200–300 km, the relative high-density zone beneath PSP extends to the Sunda Plate and to the eastern Eurasian Plate. We further estimated the conversion factor of our density model and the velocity model (SL2013sv; Schaeffer &amp; Lebedev 2013) in order to locate the changes of compositional effects in the upper mantle. The negative conversion factor indicates that the compositional changes primarily affect the density anomalies beneath the PSP. We, therefore, describe the layered density structures as ‘sandwich’ pattern, which is unique and different from adjacent regions.

Electroosmotic flow in soft microchannels at high grafting densities

This paper reports the results of a theoretical modeling of the fully developed electroosmotic flow in a rectangular microchannel with a high-density polyelectrolyte layer (PEL) attached to the walls. At these conditions, the ions are partitioned between the PEL and the fluid outside the PEL owing to the difference between the permittivities of the two media. It is taken into account that the dynamic viscosity is higher within the PEL because of hydration effects. Solutions are obtained for the electric potential and velocity distributions as well as the mean velocity by making use of a variational approach, applied to the linearized form of the governing equations, which treats the whole area under consideration as a single domain with variable physical properties. The resulting equations are solved using a spectral method. Closed-form analytical expressions are obtained for a slit geometry, representing the case of high aspect ratios. The solutions obtained are validated by comparing to finite-element simulations of the full nonlinear equations. It is shown that the electric potential drop inside the channel increases due to the depletion of the counterions within the PEL caused by the ion partitioning effect. This effect, surprisingly, magnifies the electroosmotic flow rate because of the increase of the space charge outside the PEL. As expected, the hydration effects reduce the flow rate, especially for thick PELs.

Physical Properties of Straw Bales as a Construction Material: A Review

Straw bale buildings provide significant benefits in terms of costs, human health, and environmental sustainability. Several studies in different regions have underlined the remarkable properties of straw bales as insulating and construction material; however, to the authors’ knowledge, there are no reviews published on this topic. The main objective of this paper is to provide a better understanding of straw bale systems, focusing on durability and thermal and acoustic insulation properties. To this end, previous tests and studies on straw bale buildings around the world were reviewed, comparing their results, assessing where research currently stands, and identifying the aspects that need to be further investigated. Results from previous tests have highlighted their ability to achieve excellent living comfort and encouraged their use. Guidelines for the characteristics to be achieved during the baling process are now required. Combining straw bale walls with a render or any type of high-density layer can improve both the thermal and acoustic properties of straw bale constructions. Finally, a quantitative assessment of the most significant properties, such as thermal resistance and acoustic insulation, is necessary to reduce the gap between straw bales and traditional building materials.

Biocompatible Glyconanoparticles by Grafting Sophorolipid Monolayers on Monodispersed Iron Oxide Nanoparticles.

This work presents the synthesis and characterization of sophorolipid-coated monodisperse iron oxide nanoparticles. Sophorolipids are biological glycosylated amphiphiles produced by the yeast S. bombicola. In their open acidic form, sophorolipids have been used as a surface stabilizing agent for metal and metal oxide nanoparticles but with a poor control over size and structural properties. In this work, the COOH function of sophorolipids (SL) was modified with nitrodopamine (NDA), a catechol known for its high affinity to iron ions. The resulting new form of sophorolipid-nitrodopamide (SL-NDA) was used as a surface ligand for monodisperse iron oxide nanoparticles. We show by a combination of thermogravimetric analysis and small-angle X-ray and neutron scattering that iron oxide nanoparticles (IONP) are stabilized by a single, high-density SL-NDA layer. This results in excellent colloidal stability under biologically relevant conditions, such as athigh protein and salt concentrations. The IONP grafted with SL-NDA showed a negligible uptake by cellsand no cytotoxicity, which wastested on two representative cell lines. Thus, they reveal the potential of sophorolipids as stable and nontoxic surface coatings for IONP-based biomedical and biotechnological applications.

Modelling of stresses and strains in two-layer combined materials at their formation

Purpose: The aim of the represented study was to model the behaviour of two-layer combined material during its manufacturing. Design/methodology/approach: The model of material layers joining by means of calender method is built in LS-DYNA software on the basis of finite element method. Using the developed model the study of stress and strain condition changes is carried out. Numerical modelling was carried out for two types of two-layer combined materials in similar conditions. First combination was of high-density polyethylene top layer and aluminium foil bottom layer. Second combination was of high-density polyethylene top layer and low- density polyethylene bottom layer. Joining materials had equal thicknesses. Findings: During formation of two-layer combined materials the primary strain always occurs at the bottom plate of the bottom layer. However, the maximum plastic strain will be represented for the layer with lower elastic modulus value. At the point of the highest loading applied to the two-layer combined material the elasticity condition is changed to the plasticity one and the yield process is registered. Practical implications: Multi-layer combined materials are some of the most advanced types of materials. The quality of the joining of the layers, the strains and the stresses arising in their manufacturing process are the main causes of low interlayer strength. It leads to easy exfoliation and destruction of the material. The results of the study may be used to improve the quality of multi-layer combined materials. Originality/value: For the first time the model was developed for the determination of strains and stresses arising during the formation of multi-layer combined materials by means of calendering method. The calculations of the stresses and strains distribution dynamics for two-layer combined materials are represented for polymer-metal and polymer-polymer layers combinations. The results of the study may be of interest to specialists in the field of multi-layer combined materials designing and manufacturing.

Soft-confinement conversion of Co-Salen-organic-frameworks to uniform cobalt nanoparticles embedded within porous carbons as robust trifunctional electrocatalysts

Co nanoparticles with about 10 nm particle size embedded in nitrogen-doped carbons (Co@NC) were successfully synthesized by a soft-confinement conversion strategy. A special Co(II)-Salen-organic framework was prepared as the precursor, which isolated a few Co(II) ions with thick aromatic polymer pore walls. These Co(II) ions were thermally converted into fine Co nanoparticles highly dispersing in porous nitrogen-doped carbons. The as-prepared Co@NCs showed efficient electrocatalytic performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), together with better catalytic durability. In alkaline solution, the optimized Co@NC-800 exhibited a positive ORR half-wave potential (E1/2) of 0.85 V, superior to the benchmark Pt/C (E1/2 = 0.84 V). It also had a low overpotential (Eη) of 0.35 V at a current density of 10 mA cm−2 for OER, close to IrO2 (Eη = 0.36 V) catalysts. It could be also utilized as the outstanding air electrode materials in Zn-air batteries, which exhibited higher peak power density and cycling stability than Pt/C-based counterpart. By this unique soft-confinement conversion of Co(II)-Salen-COFs, the derived Co@NCs possessed the optimized local strcutures (high porosity and graphization degree) and the multiple active sites especially including high-density Co nanoparticle-activitated carbon layers, which contributed to their impressive trifunational electrocatalytic properities.

RMetS National Meeting – Arctic prediction in a changing climate: understanding key processes and challenges

RMetS National Meeting – Arctic prediction in a changing climate: understanding key processes and challenges

Design boundary layer structure for improving the particle separation performance of a hydrocyclone

This study aims to address the problem of fine particle entrainment in the underflow of a hydrocyclone. To improve the separation performance of hydrocyclones, we investigated the effect of the boundary layer structure. Several completely cylindrical structures were developed based on the conventional cylindrical-conical structure. By modifying the bottom structure of the completely cylindrical hydrocyclones, the entrainment of fine particles can be reduced, and the separation sharpness can be improved. Ultimately, a W-shaped apex was proposed. A computational fluid dynamics (CFD)-based numerical simulation was conducted to compare the performance of different hydrocyclone structures. The variations of the pressure field, velocity field, air-core shape, density field, and separation performance were investigated, and the results were compared with classical experimental data to verify the accuracy of the numerical simulations. The results show that the total pressure drops and the radial pressure gradients in type B (with a cylindrical section), type C (with a 3° gradient cylindrical section), and type E (with a W-shaped apex) hydrocyclones are lower than those in the type A (a conventional cylindrical-conical-shaped hydrocyclone), which is beneficial for reducing the energy loss and increasing the throughput. In the completely cylindrical hydrocyclones, the axial velocity is reduced, and the residence time of the particles is prolonged, which facilitates the sufficient separation of the particles. In addition, a high-density suspension layer forms near the apex in the completely cylindrical hydrocyclones. This suspension layer causes elutriation and hence reduces the entrainment of fine particles in the underflow. In the completely cylindrical hydrocyclones, the recovery rate and entrainment of fine particles in the underflow are reduced, and the separation sharpness is improved. The type E hydrocyclone has the least entrainment of fine particles and has a separation sharpness that is between those of type A and types B, C, and D (with a 3° gradient cylindrical section and a 150° sloping bottom).

Joint inversion of gravity with cosmic ray muon data at a well-characterized site for shallow subsurface density prediction

SUMMARYEstimating subsurface density is important for imaging various geologic structures such as volcanic edifices, reservoirs and aquifers. Muon tomography has recently been used to complement traditional gravity measurements as a powerful method for probing shallow subsurface density structure beneath volcanoes. Gravity and muon data have markedly different spatial sensitivities and, as a result, the combination is useful for imaging structures on spatial scales that are larger than the area encompassed by crossing muon trajectories. Here we explore and test a joint inversion of gravity and muon data in a study area where there is an independently characterized target anomaly: a regionally extensive, high-density layer beneath Los Alamos, New Mexico, USA. We resolve the nearly flat-lying structure using a unique experimental set-up wherein surface and subsurface gravity and muon measurements are obtained above and below the target volume. Our results show that with minimal geologic (prior) constraints, the joint inversion correctly recovers salient features of the expected density structure. The results of our study illustrate the potential of combining surface and subsurface (e.g. borehole) gravity and muon measurements to invert for shallow geologic structures.

Molecular dynamics simulations of Lennard-Jones systems confined between suspended nanoscale graphene sheets.

The distribution of particles interacting with Lennard-Jones potentials and confined between parallel graphene sheets is investigated by molecular dynamics simulations. For small separation distances, the particles are densely localized in the central region between the graphene sheets. However, two high-density layers appear as the separation distance increases. The particle distribution also depends on the temperature, tensile force of the graphene sheets, and the initial configuration, and various configurations are observed for large separation. For example, an argon cluster initially located between the graphene sheets changes shape, and a bridge between the parallel walls is formed at low temperature. In contrast to the Lennard-Jones system sandwiched between rigid walls, the flexibility of the graphene sheets strongly affects the distribution of particles in the direction perpendicular to the graphene sheets.