Hollow Space Research Articles

Atomistic Insight into the Role of Porous Structure in Accommodating the Volume Expansion of Silicon Anodes for Lithium-Ion Batteries

Despite possessing high theoretical gravimetric capacity, the practical utilization of silicon anodes for lithium-ion batteries is still challenging because of poor capacity retention caused by massive volume expansion upon lithium insertion. The use of porosity to tackle this issue has widely been scrutinized, and porous silicon materials have been experimentally shown to have improved cycling stability. To provide a fundamental understanding of the structural and chemical evolution, here, we investigate the atomistic behaviors of porous silicon nanowires during lithiation and delithiation by means of a reactive molecular dynamics method. The simulations show that although the porous nanomaterials undergo a large intrinsic volume expansion similar to the non-porous ones, the hollow space available inside the materials can be exploited for lowering the external expansion via the local structure relaxation in the vicinity of the pore. Due to such relaxation, a small pore undergoes structural collapse during the first charge, suggesting that a relatively large pore diameter and a thin wall thickness are required to maintain the porous structural integrity. The simulations also unveil the evolution of the local stresses generated during lithium migration into and out of the materials, which emphasizes the role of porosity in alleviating the induced stresses.

Entropy generation on magnetohydrodynamic conjugate free convection with Joule heating of heat-generating liquid and solid element inside a chamber

This study presents the entropy production of MHD conjugate free convective flow within a square chamber infused with water encasing a heat-generating and conducting square solid element. The chamber’s vertical side is exposed to an external magnetism effect. The flowing fluid circulating inside the hollow space of the chamber produces a volumetric heat generation rate. The finite element approach is used to solve the model equations for mass, momentum, and heat energy conservations, which are affected by a number of variables, including the Rayleigh number (Ra), Hartmann number (Ha), Joule heating parameter, and internal heat generation parameter (Δ), and the area ratio of the solid element (Ab). By systematically varying those parameters (e.g., 103 ≤ Ra ≤ 106, 0 ≤ Ha ≤ 20, 0 ≤ Δ ≤ 10, 0.1 ≤ Ab ≤ 0.3), variations of hydro-thermal properties are observed and analyzed through streamline, isotherm, Nusselt number, entropy generation, thermal performance criterion, and mean fluid temperature of the system. It can be declared that convective heat transport increases as the area ratio of the solid element and the internal heat generation decrease. However, the minimum thermodynamic irreversibility is obtained for the highest area ratio and lowest heat generation parameter. The study shows a 48.37% increase in convective heat transfer as Ab decreases from 0.3 to 0.1. Similarly, reducing Ha and Δ to zero leads to an 8.76% and 526% reduction in TPC, respectively.

Colloidal tubular microrobots for cargo transport and compression

Microrobot swarms have seen increased interest in recent years due to their potentials for in vivo delivery and imaging with cooperative propulsion modes and enhanced imaging signals. Yet most swarms developed so far are limited to dense particle aggregates, far simpler than complicated three-dimensional assemblies of anisotropic particles. Here, we show via assembly path design that complex hollow tubular structures can be assembled from simple isotropic colloidal spheres and those complicated, metastable, microtubes can be formed from simple, energetically favorable colloidal membranes. The assembled microtubes can remain intact and roll under a precessing magnetic field, with propulsion directions and velocities precisely controlled by field components. The hollow spaces inside enable these tubular microrobots to grab, transport, and release cargos on command. We also demonstrate unique compressing and uncompressing capabilities with our tubular microrobots, making them effective microtweezers. Our work shows that complicated microrobots can be transformed from simple assemblies, providing an insight on building micromachines.

Assembly of Metal-Phenolic Networks onto Microbubbles for One-Step Generation of Functional Microcapsules.

The one-step assembly of metal-phenolic networks (MPNs) onto particle templates can enable the facile, rapid, and robust construction of hollow microcapsules. However, the required template removal step may affect the refilling of functional species in the hollow interior space or the in situ encapsulation of guest molecules during the formation of the shells. Herein, a simple strategy for the one-step generation of functional MPNs microcapsules is proposed. This method uses bovine serum albumin microbubbles (BSA MBs) as soft templates and carriers, enabling the efficient pre-encapsulation of guest species by leveraging the coordination assembly of tannic acid (TA) and FeIII ions. The addition of TA and FeIII induces a change in the protein conformation of BSA MBs and produces semipermeable capsule shells, which allow gas to escape from the MBs without template removal. The MBs-templated strategy can produce highly biocompatible capsules with controllable structure and size, and it is applicable to produce other MPNs systems like BSA-TA-CuII and BSA-TA-NiII . Finally, those MBs-templated MPNs capsules can be further functionalized or modified for the loading of magnetic nanoparticles and the pre-encapsulation of model molecules through covalence or physical adsorption, exhibiting great promise in biomedical applications.

Combustion Characteristics of a Swirl-Radial-Injection Composite Fuel Grain with Applications in Hybrid Rockets

The combustion characteristics of a swirl-radial-injection composite fuel grain were experimentally and numerically investigated. This composite grain permits swirl-radial oxidizer injection based on three hollow helical blades, each having a constant hollow space allowing uniform oxidizer injection into the main chamber along the axial direction. The oxidizer enters from channel inlets located along a hollow outer wall. This wall, together with the three blades, is fabricated as one piece from acrylonitrile-butadiene-styrene using three-dimensional printing. Paraffin-based fuel is embedded in the spaces between adjacent blades. Firing tests were conducted with gaseous oxygen as the oxidizer, using oxidizer mass flow rates ranging from 7.45 to 30.68 g/s. Paraffin-based fuel grains using conventional fore-end injection were used for comparison. Regression rate boundaries were determined taking into account the erosion of the oxidizer channels. The data show that the regression rate was significantly increased even at the lower limit. Images of the combustion chamber flame and of the exhaust plume were also acquired. The flame was found to be concentrated in the main chamber and a smoky plume was observed, consistent with the high regression rate. A three-dimensional simulation was employed. The present design was found to improve fuel/oxidizer mixing and combustion efficiency compared with a fuel grain using fore-end injection. Both the experimental results and numerical simulations confirmed the potential of this swirl-radial-injection fuel grain.

Dual-template induced interfacial assembly of yolk-shell magnetic mesoporous polydopamine vesicles with tunable cavity for enhanced photothermal antibacterial

Yolk-shell magnetic polymer nanostructures with large cavity, movable magnetic core are attractive carriers for bulk storage, release and transport of guest molecules in various applications. However, it remains great challenge to achieve a controllable transport of guest species into and out from the hollow space in a controlled way due to the lack of tailor-made nanostructures. Herein, a dual-template-induced emulsion interfacial assembly and polymerization method (denoted as de-IAP) was developed to constructyolk-shell magnetic mesoporous polydopamine (YS-MMP) vesicles with magnetic core, large hollow space and uniform mesopores in the soft polymer shell. The obtained YS-MMP vesicles possess tunable cavity size (10–900 nm), flexible mesoporous PDA layer, large pores (21 nm), high surface area (217.4 m2·g−1) and high magnetization saturation (31.0 emu·g−1), thus exhibiting the merits of high loading capacity (29.1%) and encapsulation rates (41.0%) of Curcumin (Cur), and fast magnetic separation speed. Thanks to their superior photothermal effect and magnetic property, the obtained YS-MMP@Cur vesicles exhibit smart on-demand release of Cur and excellent recyclability. With 808 nm laser irradiation, YS-MMP@Cur vesicles show high-efficient photothermal bactericidal effect (>99%) against S. aureus and E. coli, opening up a new avenue for smart cargo delivery, lasting sterilization, and environmental remediation.

A STUDY ON MULTI-MODELING FOR ARTIFACT RESTORATION

Abstract. Restoration is carried out in order to restore damaged antiquities to their original form. Recently, research has been active in obtaining the target three-dimensional (3D) model by optical scanning and X-ray computed tomography (CT), as well as restoring artifacts via modeling. Because the cultural artifacts are restored in a virtual environment without direct contact with the cultural artifacts, secondary damage can be preserved. Furthermore, the restoration results can be used for the physical restoration of cultural artifacts via 3D printing. In this study, multi-digital modeling technology was used to restoration horse-shaped earthenware artifact that still had its missing part. After 3D printing, the restoration part was applied to the artifact. In order to record the shape of the artifact in detail, a high-precision 3D scanner was used to construct the shape of the artifact into a 3D model. Two models were then built as a reference for restoration: The legs of the excavated horse-shaped earthenware are believed to have been bent during burning, but they were reproduced in their entirety for restoration by conducting rigging and keyframe animation. For the restoration of the missing horse body, horse and rider-shaped vessels excavated from the same site were used as references. However, since the decorations on the reference surfaces obscured the horse body, a 3D model of the horse shape was obtained through X-ray CT segmentation modeling. Using the obtained model, the missing 3D horse body was restored. For the hind legs, the leg geometry reconstructed by the rigging was used as a reference. The hollow space inside the artifact and the structures that could be restored were further modeled. The finished model was completed by outputting a mock-up using a material extrusion system 3D printer, conducting a bonding test with actual artifacts, and finally creating the restoration model. Afterward, a photopolymerization system 3D printer is used to output the restoration part, and then it is applied to the artifacts through post-processing. A study for restoration artifacts based on multi-modeling techniques was proposed in this work. In particular, rigging and x-ray CT segmentation modeling were used to restoration the artifacts based on their original form and historical research. As such, multi-modeling techniques are an effective way to not only restore artifacts, but also to build a reference for restoration.

Time-Dependent Controlled Release of Ferulic Acid from Surface-Modified Hollow Nanoporous Silica Particles.

Release of ferulic acid from surface-functionalized hollow nanoporous silica particles (HNSPs) was investigated in deionized water (DI water) and in ethanol. The host material, an HNSP, was synthesized in the presence of polymer and surfactant templates, and the pore as well as the surface were modified with either pentyltriethoxysilane (PTS) or octyltriethoxysilane (OTS) through silane coupling reactions. The inner hollow space occupied a volume of ~45% of the whole HNSP with a 2.54 nm pore channel in the wall. The pore size was estimated to decrease to 1.5 nm and 0.5 nm via the PTS and OTS functionalization, respectively. The encapsulation efficiencies of the HNSP (25 wt%), PTS-functionalized HNSP (PTS-HNSP, 22 wt%) and OTS-functionalized HNSP (OST-HNSP, 25 wt%) toward ferulic acid were similar, while the %release in DI water and ethanol varied following HNSP > PTS-HNSP > OTS-HNSP. Release kinetic analyses with Korsmeyer-Peppas fitting suggested a trade-off relationship between the solvent's ability to access the HNSP and the affinity of ferulic acid to the surface, allowing us to understand the solvent's controlled release rate and mechanism.

Heterologous expression, purification, and characterization of a recombinant Cordyceps militaris lipase from Candida rugosa-like family in Pichia pastoris

Multiple sequence alignments of three lipase isoforms from the filamentous fungus, Cordyceps militaris, have revealed that the deduced protein from their common sequence belongs to the Candida rugosa lipase-like group. To express the protein in its active form, recombinant lipase from C. militaris (rCML) was extra cellularly expressed in Pichia pastoris X-33 after removing its signal peptide. Purified rCML was a stable monomeric protein with a molecular mass of 90 kDa, and was highly N-mannosylated compared to the native protein (69 kDa). The catalytic efficiency (kcat/Km) of rCML was greater than the native protein (1244.35 ± 50.88 and 1067.17 ± 29.07 mM−1·min−1, respectively), yet they had similar optimal pH values and temperatures (40 °C and pH 7.0–7.5), and showed preferences for Tween esters and short-chain triacylglycerols. Despite its monomeric conformation, interfacial activation was not observed for rCML, unlike the classical lipases. From the structural model of rCML, the binding pocket of rCML was predicted as a funnel-like structure consisting of a hollow space and an intramolecular tunnel, which is typical of C. rugosa lipase-like lipases. However, a blockage shortened the tunnel to 12–15 Å, which endows strict short-chain selectivity towards triacylglycerols and a perfect match for tricaproin (C6:0). The limited depth of the tunnel may enable accommodation of triacylglycerols with medium-to-long-chain fatty acids, which differentiates rCML from other C. rugosa lipase-like lipases with broad substrate specificities.

A conceptual review of Artavavaha Srotas and its Viddha Lakshan

According to Ayurvedic Samhitas, Srotas is a structural and functional unit of the body. Srotas are the hollow spaces or channels which are responsible for any movement or transformation. There are many types of Srotas mention by Acharyas. Maharshi Charaka explains Srotas as a medicinal aspect and Maharshi Sushruta explains Srotas according to surgical aspect. Artavavaha Srotas is Antarmukh Srotas which are also known as Yogawahi Srotas. It is similar to the female reproductive system in modern medical science. As per Maharshi Sushruta, Artavavaha Srotas are two in number and their Moolsthana is Garbhashaya and Artavavahi Dhamanya. Any trauma to this Srotas causes Bhandhayatva (infertility), Artavanasha (amenorrhea) and Maithuna Asahishnuta (dyspareunia). In this study description of Ayurvedic concept along with discussion regarding the patho-clinical perspective of Artavavaha Srotas and its Viddha Lakshan in light of modern science.

A closed-ended MXene armor on hollow Sn4P3 nanospheres for ultrahigh-rate and stable sodium storage

The development of sodium-ion batteries has been seriously discouraged by the major limitation in the rate capability and the cycle life of the anode materials. Sn4P3 is recognized as a potential anode for sodium -ion batteries owing to its ultrahigh specific capacity and low cost, but the great volumetric change and low intrinsic electrical conductivity severely limit the cycling performance. Herein, we propose a closed-ended MXene and Sn4P3 hybrid consisting of active Sn4P3 porous hollow nanospheres (Sn4P3 HS) armored by a conductive MXene shell. Notably, the outer MXene shell protects Sn4P3 from direct exposure to the electrolyte and only allows the inward expansion of Sn4P3 into the hollow space, resulting in the formation of a thin solid-electrolyte interphase layer of high stability. As predicted, the hybrids can deliver an extraordinarily high capacity of 302.1 mAh g−1 even at an ultrahigh rate of 10 A g−1 and cycle at 1 A g−1 for 1500 cycles with a capacity retention of 94.9%. Moreover, the Sn4P3 HS@MXene//Na3V2(PO4)3/C full cell exhibits an outstanding energy density of 287.8 Wh kg−1 and good cyclic ability (390.5 mAh g−1 at 1A g−1 after 500 cycles), exhibiting a great potential in practical application.

Effects of base material and magnetic field on the dynamic response of MR-laminated composite structures

Stability and vibration control are major challenges for applications in which laminated composite beams are being used. Using composite base materials with higher strength and/or using appropriate layout orientation are the two potential methods to improve the dynamic performance of laminated composite structures. However, using composite materials with higher strength significantly increases the manufacturing cost. Recently, layers/segments of Magnetorheological (MR) fluids have been added to the common laminated beams, the so-called MR-laminated beam, to improve the dynamic characteristics of such structures. The present work investigates the effect of base materials and applied magnetic field on the dynamic response of MR-laminated beams. Different composite materials, including E-glass, carbon fiber, and Kevlar, have been used as base materials to build the sandwich MR-laminated beam. The hollow spaces of the sandwich beam are filled with MR fluid to fabricate a testing sample for experimental purposes. A modified layerwise theory, N-layer, has been used to determine the vibration response of the structures. It is concluded that applying a magnetic field increases the natural frequency of the MR-laminated beam. In fact, applying 1400-Gauss magnetic fields to a low-cost material like E-glass provides the same natural frequency as that of the fiber-carbon without magnetic fields.

Increasing Sedimentation Stability of Cement-Mineral Suspensions by Adding the Hydroxyl-Containing Water-Soluble Polymers

There are the results of studies on increasing the sedimentation stability of cement-mineral suspensions intended to fill hollow spaces in fractured rocky soils and strengthen dispersed soils, as well as to prevent filtration processes in soils.To ensure the sedimentation stability of cement-mineral suspensions, it is proposed to use the water solutions of hydroxyl-containing polymers prone to swelling as a dispersion medium (mixing water): water solutions of polyvinyl alcohol (PVA) in 4% - 8% concentration. The concentration range of polymer solution from 4% to 8% was established in order to prevent coagulation during storage and to ensure the production of polymer films from water PVA solutions.The research results showed that polyvinyl alcohol provides the high kinetic sedimentation stability of cement-mineral systems determined by hydrodynamic factors as follows: the viscosity and density of the water polymer solution. The higher the viscosity and density of the water solution of polyvinyl alcohol (concentration), the higher the sedimentation stability of cement-mineral suspensions.

Nanoconfined Expansion Behavior of Hollow MnS@Carbon Anode with Extended Lithiation Cyclic Stability

AbstractThe construction of hollow nanostructure by compositing with carbonaceous materials is generally considered an effective strategy to mitigate the drastic volume expansion of transition metal sulfides (TMSs) with high theoretical specific capacity in the process of lithium storage. However, designing well‐controlled architectures with extended lithiation cyclic stability, and ease the expansion of the electroactive materials into the reserved hollow spaces still needs to be developed. Herein, using MnS as an example, the hollow double‐shell carbon‐coated TMSs architecture is designed to achieve the controllable operation of shell thickness to regulate interfacial stress. The functional architecture enables the high‐capacity MnS to reach reversible capacities and extended lithiation cycling stability at high current densities. In situ transmission electron microscopy, optical observation characterizations and finite elements are used to analyze the nanoconfined expansion behavior of hollow MnS@C anodes. The as‐designed hollow structure with a carbon shell thickness ≈12.5 nm can effectively restrict the drastic expansion of MnS nanoshell into inner voids with compressive stress. This study demonstrates a general strategy to design functional carbon coating metal sulfides with tailored interfacial stress.

Synthesis of Monodispersed Hollow Mesoporous Organosilica and Silica Nanoparticles with Controllable Shell Thickness Using Soft and Hard Templates

Hollow mesoporous nanoparticles with controllable size (less than 100 nm) are desired as drug-delivery carriers. Herein, we report the synthesis of monodispersed hollow mesoporous organosilica (HMOS) and hollow mesoporous silica (HMS) nanoparticles using soft and hard templating methods. HMOS shells, with 1,2-bis(triethoxysilyl)ethane (BTEE) as the precursor and hexadecyltrimethylammonium bromide and sodium dodecyl sulfate (SDS) as the soft templates, were formed on monodispersed silica nanoparticles (SNPs), which were used as the hard templates. HMOS and HMS nanoparticles were obtained by removing the SNPs after three rounds of ammonia dialysis. The hollow size of HMOS can be tuned by changing the size of the SNPs. By using SNPs with a size of 36.5 nm, hollow spaces of approximately 20 nm connected the surface through narrow pores (<5 nm). Mesopores of approximately 12 nm were formed by the surfactant micelles. Additionally, the interparticle space in HMOS and HMS was approximately 12 nm. The shell thicknesses of HMOS and HMS could be tuned in the range of 5-9 nm by changing the BTEE amount. Moreover, the amount of surfactant used varied the porous structure. The HMOS with a thickness of 5 nm exhibited a Brunauer-Emmett-Teller (BET) surface area of 268 m2/g and a total pore volume of 1.14 cm3/g. Meanwhile, HMS demonstrated a BET surface area of 553 m2/g and a total pore volume of 1.82 cm3/g while maintaining a hollow structure. HMOS displayed a high loading capacity for ibuprofen (3009 mg/g), and its drug release system showed a sustained-release property. Therefore, the HMOS preparation using hard and soft templates proposed herein can control the hollow size and shell thickness for drug-delivery applications.

A non-intrusive seismic retrofitting technique for masonry infills based on bed-joint sliding

In recent years, several seismic retrofitting projects of existing buildings have been involving additional measures to improve their energy efficiency, thanks to new regulations aiming at optimizing the buildings overall performance. Significant improvement is usually obtained through radical measures aiming at strengthening the infill panels, typically vulnerable to both out-of-plane overturning and in-plane cracking, and at enhancing their thermal insulation. Measures not disrupting the internal activities are generally favored.Back in 2012, two of the authors proposed a seismic-resistant double-layered infill panel for new buildings endowed with innovative flexible dissipative joints, placed along the horizontal brick interfaces, made from recycled plastic. In this work, those joints are upgraded to be used for retrofitting infill panels made of double-layered bricks and intermediate hollow space, as typical in most existing buildings. Within an existing infill panel, such joints create a system of parallel sliding surfaces along the horizontal bed-joints, after cutting off the mortar layer, thus channeling the in-plane deformation in the joints. On passing, it is noticed that the out-of-plane resistance is ensured by cantilevering elements protruding outwards from the joints surface, which prevent the panel from developing out-of-plane mechanisms. Such system has been preliminarily tested on a real-scale double-layer infill equipped with two joint lines under horizontal force. The experimental results have been compared with analytical models available in the literature for assessing stiffness and strength of the possible failure mechanisms, and a modified equation has been proposed for the mechanism involving bed-joint sliding induced by plastic joints.

Re12C80: A pentagonal hexecontahedron molecule

Based on density-functional theory calculations, a polyhedron molecule, Re12C80 cage, was proposed and showed topological analogy to Catalan pentagonal hexecontahedron. The geometric topology of Re12C80 molecule retains integrity when the effective temperature is up to 782 K. Its electronic structure shows that for the carbon atom there is the feature of sp2-like hybrid orbital, and for the rhenium atom there presents d orbital characteristics. The large hollow space for Re12C80 cage can be useful to encapsulate other atoms or small molecules. The proposal of Re12C80 molecular structure can help to enrich and expand the types of highly symmetric polyhedral molecules.

Highly Porous Carbon Aerogels for High-Performance Supercapacitor Electrodes

In recent years, porous carbon materials with high specific surface area and porosity have been developed to meet the commercial demands of supercapacitor applications. Carbon aerogels (CAs) with three-dimensional porous networks are promising materials for electrochemical energy storage applications. Physical activation using gaseous reagents provides controllable and eco-friendly processes due to homogeneous gas phase reaction and removal of unnecessary residue, whereas chemical activation produced wastes. In this work, we have prepared porous CAs activated by gaseous carbon dioxide, with efficient collisions between the carbon surface and the activating agent. Prepared CAs display botryoidal shapes resulting from aggregation of spherical carbon particles, whereas activated CAs (ACAs) display hollow space and irregular particles from activation reactions. ACAs have high specific surface areas (2503 m2 g-1) and large total pore volumes (1.604 cm3 g-1), which are key factors for achieving a high electrical double-layer capacitance. The present ACAs achieved a specific gravimetric capacitance of up to 89.1 F g-1 at a current density of 1 A g-1, along with a high capacitance retention of 93.2% after 3000 cycles.

Monolithic foam of oriented boron nitride bowl for selective oxidative dehydrogenation of propane and pollutant removal

Bowl-like structures have great potential in the field of catalysis, environmental remediation, energy storage, etc., because of the large surface area, porous structure, and buffer hollow space. Herein, we developed a unique approach to control the opening direction of bowl-like structures via self-assembly strategy at the gas/liquid interface of liquid B2O3 environment foam. BN@BPO4 self-supporting monolithic foam with oriented bowl-like structure was obtained, which is built by numerous oriented bowl-like blocks and shows a double layer structure with face-to-face opening. The opening size can be adjusted by changing the amount of Cu(NO3)2 additives that is beneficial for the production of hexagonal boron nitride (h-BN). We believe the as-generated h-BN can enhance the gas trapping capacity of liquid B2O3 environment foam to precisely control pressure differential between large and small bubbles and thus favors the oriented opening of bowl-like structure. Further, pure h-BN monolithic foam with oriented bowl-like structure prepared at higher temperature possessed multimodal hierarchically porous structure and excellent performance in the catalytic oxidative dehydrogenation of propane into propene and the removal of organic pollutants. This work provides an extended assembly interface strategy of oriented bowl-like structure materials for different applications.

Digital core: modeling the temperature field in the hollow space of the rock

This article considers the problem associated with conducting experiments in computational fluid dynamics, the solution of which is the application of the equations of incompressible fluid flow and the introduction of vortex flow functions.The aim of this work is to simulate the temperature viscous flow with a set Reynolds number inside a porous medium enclosed in the rock material to further describe the thermal front of motion in the form of a system of equations, with the choice of the most likely suitable system with differentiated equations for each segment of the thermal simulation (along the cube axes), the final cross-correlation, spread in the identified physical field of confusers/diffusers. Scientific novelty of the performed work is due to the original approach to the development and interpretation of the results of the algorithm for predicting the temperature field in the textural configuration of the confusers/diffusers of rocks.