Hollow Geometry Research Articles

Monolithic Integration and Analysis of Vertical, Partially Encapsulated Nanoelectrode Arrays

This study reports on the development of vertical, partially encapsulated nanoelectrodes for electrically contacting the interior of electrogenic cells with microelectronics. Intracellular electrical stimulation and recording with single cell resolution enables new insights into the electrophysiology of cells embedded in a complex multicellular network, providing detailed understanding of fundamental processes affecting cell to cell communication and thereby paving the way for novel applications including pharmacological studies and other neuromodulation techniques like focused ultrasound and electroceuticals. In order to minimize the influence of the measurement system, an approach based on nano-sized hollow electrodes, achieving an adhesion based intracellular access, is used. The focus of the presented work is on the novel fabrication technology and the characterization of the resulting nanoelectrodes. In CMOS compatible processes, the hollow geometry is achieved using a sacrificial layer technique combining deep reactive ion etching and atomic layer deposition of Ru. For decoupling the extracellular milieu, a partial passivation of the nanoelectrodes by Ta2O5 is realized. The monolithic integration allows an application specific fine-tuning of geometry and placement of the nanoelectrodes. A discrete microelectrode array was designed to electrically and electrochemically characterize the nanoelectrodes. Resistance measurements, cyclic voltammetry and electrochemical impedance spectroscopy show the feasibility of the developed electrodes as an electronic interface to electrochemical fluids. Specifically, an electrode resistance of 2.92 $\text{k}\Omega $ and charge delivery capacitance of $748.13~\frac {\mu \text {C}}{\text {cm}^{2}}$ were observed. Confocal microscopy analyses of neural cells interfaced with the nanoelectrodes indicate an adhesion based intracellular access as well as biostability and biocompatibility. [2020-0224]

Theoretical Study of the Effect of Magnetic Field Sweep Rate and Temperature on Shielding Efficiency in a Bulk Tube-Shaped HTS

In this paper, we have studied the shielding properties of a high temperature superconducting (HTS) bulk tube-shaped cylinder in varying magnetic fields. Within this scope, we have simulated the hollow cylinder geometry in axis-symmetric finite element method (FEM) in which the electromagnetic properties of a HTS are described by a nonlinear electric field-current density (E − J) power law including a critical current density depending on magnetic field. In the first stage, we have analyzed temperature dependence of shielding factor (SF), which is described as the ratio of the applied magnetic field to the magnetic field in the center of the hollow cylinder. In the second stage, the effect of magnetic field’s sweep rate (dBapp/dt) on the magnetic shielding was numerically examined. In the final stage, using the certain lines over the superconducting tube, we have worked out the shielding field (Bsz) of the HTS tube by subtracting the z-component of magnetic field (Bz) from applied magnetic field (Bapp). Our numerical investigations indicate that the superconducting tube can provide field and temperature-controlled magnetic shielding.

Modeling of spiral wound membranes for gas separations. Part I: An iterative 2D permeation model

Membranes are excellent alternatives for gas separations due to their low installation and maintenance costs. In industrial environment, membranes are usually organized in modules with spiral-wound or hollow fiber geometries. Because of their wide range of applications, the development of reliable mathematical models for industrial membrane operations is encouraged. In the present work, a mathematical model is proposed to describe gas separations in spiral-wound membranes, based on a phenomenological approach. The proposed model was validated in four case studies of common separations: (i) ammonia; (ii) hydrogen; (iii) CO2 from natural gas and (iv) CO2 from flue gas. It is shown that the proposed model is able to represent the analyzed phenomena accurately. The robustness and good performance of the model for several operation conditions were evaluated through sensitivity analyses. In addition, a novel numerical approach is proposed to solve the analyzed mathematical model. The proposed procedure presents good efficiency and accuracy and is faster and more efficient than the well-known shooting method, largely employed to perform membrane simulations, allowing the use of the model in real time applications.

3D borehole-to-surface and surface electromagnetic modeling and inversion in the presence of steel infrastructure

The borehole-to-surface electromagnetic (EM) method is a viable imaging and monitoring tool for energy reservoirs, geologic storage, geothermal exploration, fault zones, and other subsurface targets. Data interpretation typically requires considering steel-casing effects, but it is difficult and impractical to directly discretize arbitrarily oriented hollow steel-cased wells in a 3D reservoir-scale earth model because of their extremely high electrical conductivity and long hollow geometry. We have considered a borehole-to-surface EM configuration in which an electric dipole source is placed below the bottom of a steel-cased well. To practically simulate the casing effects on EM measurements, we develop a novel 3D finite-element EM algorithm using an unstructured tetrahedral mesh. To avoid excessive use of fine grids for modeling a steel-cased well, the well is replaced with the combination of a short solid conductive prism and a long linewise perfect electric conductor. We find that this combined structure can approximate casing effects at a small fraction of the computational cost required for modeling a complete hollow casing because the linewise structure is volumeless and does not require an excessive number of small elements. We also find that steel-cased wells distant from sources and receivers can be modeled as simple linewise perfect electric conductors, further improving the computational efficiency. Using this approximation, the 3D EM algorithm presented here is well-suited to modeling many arbitrarily oriented steel-cased wells. After verifying the accuracy and efficiency of this approach using various examples, we performed a 3D borehole-to-surface/surface-to-borehole and surface EM inversion and determine that the inversion can image a deep localized target in the presence of steel infrastructure.

Enhanced reversible hydrogen storage in palladium hollow spheres

Palladium has long been used as a hydrogen sponge because of its ability to store hydrogen under ambient conditions (room temperature and 1 bar pressure). However, Pd suffers from a low storage capacity. The current investigation pertains to the enhancement in the reversible hydrogen storage capacity of Pd, by using hollow sphere geometry. Additional storage is achieved in molecular form; thus utilizing a recently developed multi-mode storage strategy. Hollow spheres, which can be viewed as nanocontainers, have been synthesized using a chemical reduction method (outer diameter of ∼300 nm and shell thickness ∼20 nm). Pressure-composition-isotherms have been used to characterize the hydrogen storage capacity and to establish the reversibility of the process. A 54% enhancement in the reversible storage capacity (25 °C and 140 bar) is observed in the case of Pd hollow spheres as compared to that of bulk Pd and 70% with respect to that of nanoporous Pd. The outer and inner surfaces of the hollow sphere play contrasting catalytic roles in the absorption and desorption process.

Use of Multi-Hollow Polyester Particles as Opacifying Agent for Injection-Molded Polyethylene.

Titanium dioxide is considered the most efficient white pigment for opacification of thermoplastics. However, its high cost, combined with strong price oscillations due to production bottlenecks, has been driving the industry towards alternatives that might allow reducing the titanium dioxide content, while maintaining the product’s opacity. A strategy commonly used in waterborne paints consists in adding hollow polymer particles to the formulation, therefore achieving opacification due to light refraction at the air/polymer interface. In the current work, we show preliminary results that indicate that a similar strategy can be followed for thermoplastics opacification, as long as thermoset particles are used, in order to ensure preservation of the hollow geometry during melt-processing. Multi-vesiculated crosslinked styrene–polyester particles, produced by a single-step double emulsion process, are used. Evidence of synergic interaction between the multi-hollow particles and titanium dioxide has been found.

In situ construction of amorphous hierarchical iron oxyhydroxide nanotubes via selective dissolution-regrowth strategy for enhanced lithium storage

The low-cost and high-capacity metal oxides/oxyhydroxides possess great merits as anodes for lithium-ion batteries (LIBs) with high energy density. However, their commercialization is greatly hindered by insufficient rate capability and cyclability. Rational regulations of metal oxides/oxyhydroxides with hollow geometry and disordered atomic frameworks represent efficient ways to improve their electrochemical properties. Herein, we propose a fast alkalietching method to realize the in-situ fabrication of iron oxyhydroxide with one-dimensional (1D) hierarchical hollow nanostructure and amorphous atomic structure from the iron vanadate nanowires. Benefiting from the improved electron/ ion kinetics and efficient buffer ability for the volumetric change during the electro-cycles both in nanoscale and atomic level, the graphene-modified amorphous hierarchical FeOOH nanotubes (FeOOH-NTs) display high rate capability (~650 mA h g−1 at 2000 mA g−1) and superior long-term cycling stability (463 mA h g−1 after 1800 cycles), which represents the best cycling performance among the reported FeOOH-based materials. More importantly, the selective dissolutionregrowth mechanism is demonstrated based on the time tracking of the whole transition process, in which the dissolution of FeVO4 and the in-situ selective re-nucleation of FeOOH during the formation of FeOOH-NTs play the key roles. The present strategy is also a general method to prepare various metal (such as Fe, Mn, Co, and Cu) oxides/oxyhydroxides with 1D hierarchical nanostructures.

Aquaporin-Containing Proteopolymersomes in Polyelectrolyte Multilayer Membranes.

The field of membranes saw huge developments in the last decades with the introduction of both polyelectrolyte multilayer (PEM)-based membranes and biomimetic membranes. In this work, we combine these two promising systems and demonstrate that proteopolymersomes (PP+) with the incorporated aquaporin protein can be distributed in a controlled fashion using PEMs, even on the inner surface of a hollow fiber membrane. In this way, various proteopolymersome multilayers (PPMs) are fabricated using PP+ as the positively charged species in combination with the polyanions poly(styrene 4-sulfonate) (PSS) and poly(acrylic acid) (PAA). It is shown by reflectometry through alternately adsorbing the polyanions and PP+ that, for both PAA and PSS, a good layer growth is possible. However, when the multilayers are imaged by SEM, the PAA-based PPMs show dewetting, whereas vesicular structures can only be clearly observed in and on the PSS-based PPMs. In addition, membrane permeability decreases upon coating the PPMs to 2.6 L∙m−2∙h−1∙bar−1 for PAA/PP+ and 7.7 L∙m−2∙h−1∙bar−1 for PSS/PP+. Salt retentions show that PAA/PP+ layers are defective (salt retentions <10% and high molecular weight cut-off (MWCO)), in line with the observed dewetting behavior, while PPMs based on PSS show 80% MgSO4 retention in combination with a low MWCO. The PSS/PP+ membranes show a Donnan-exclusion behavior with moderate MgCl2 retention (50%–55%) and high Na2SO4 retention (85%–90%) indicating a high amount of negative charge present within the PPMs. The corresponding PEMs, on the other hand, are predominately positively charged with MgCl2 retention of 97%–98% and Na2SO4 retention of 57%–80%. This means that the charge inside the multilayer and, thus, its separation behavior can be changed when PP+ is used instead of a polycation. When comparing the PPM membranes to the literature, similar performances are observed with other biomimetic membranes that are not based on interfacial polymerization, but these are the only ones prepared using a desired hollow fiber geometry. Combining PEMs and biomimetic approaches can, thus, lead to relevant membranes, especially adding to the versatility of both systems.

Wetting behavior of textured silicon surfaces- an experimental study

The behavior of a liquid on a solid surface has shown great interest in a variety of applications related to surfaces and its interfaces. In this paper, the wetting behavior of DI water on micropatterned silicon surfaces fabricated through photolithography and deep reactive ion etching (DRIE) is investigated. Micro pillars of both solid and hollow geometries at a varying pitch and its arrangement in an array has been examined with static contact angle measurement. However, the results concluded that the arrangement of pillars in an array plays an important role as hollow geometries in the case of chain type arrangement provide both hydrophilic and hydrophobic surface properties, while the same hollow geometries in case of zig-zag orientation experiences only hydrophobicity at a varying pitch. Decreased WCA with increased pitch has been observed in the case of a zig-zag arrangement, due to the effect of capillary and gravitation forces. Also the existence of air pockets at sharp corner in the case of hollow square assists in providing maximum contact angle (WCA = 144°) as compared to hollow circle and solid geometries; thus a non-sticky behavior would be possible between the droplet and the patterned surface, due to less adhesion force.

Numerical Estimation of Bonding Force of EPDM Grommet Parts with Hollow Shaft Geometry

A grommet is a representative component that fixes the position of a cable. It is made from hyper-elastic materials (rubber), such as ethylene propylene diene monomer (EPDM). The grommet and cable are conventionally fixed through bonding; however, this method has numerous disadvantages that can be improved through relevant research. To apply a fixing method using the elastic force of EPDM rubber, this paper presents an empirical equation for approximating the bonding force of EPDM grommet parts with a hollow shaft geometry. First, tensile tests and the inverse method were used to approximate the basic mechanical properties. The physical properties were derived through basic tests; furthermore, bonding force tests and the inverse method were used on a grommet with a hollow shaft structure. In addition, the Box–Behnken design of experiments was used to predict the amount of change in the bonding force according to the geometry variables. Finally, this study was validated by comparing the approximation results derived through the design of experiments with the analysis and bonding force test results.

Engineering anisotropic 3D tubular tissues with flexible thermoresponsive nanofabricated substrates

Tissue engineering aims to capture the structural and functional aspects of diverse tissue types in vitro. However, most approaches are limited in their ability to produce complex 3D geometries that are essential for tissue function. Tissues, such as the vasculature or chambers of the heart, often possess curved surfaces and hollow lumens that are difficult to recapitulate given their anisotropic architecture. Cell-sheet engineering techniques using thermoresponsive substrates provide a means to stack individual layers of cells with spatial control to create dense, scaffold-free tissues. In this study, we developed a novel method to fabricate complex 3D structures by layering multiple sheets of aligned cells onto flexible scaffolds and casting them into hollow tubular geometries using custom molds and gelatin hydrogels. To enable the fabrication of 3D tissues, we adapted our previously developed thermoresponsive nanopatterned cell-sheet technology by applying it to flexible substrates that could be folded as a form of tissue origami. We demonstrated the versatile nature of this platform by casting aligned sheets of smooth and cardiac muscle cells circumferentially around the surfaces of gelatin hydrogel tubes with hollow lumens. Additionally, we patterned skeletal muscle in the same fashion to recapitulate the 3D curvature that is observed in the muscles of the trunk. The circumferential cell patterning in each case was maintained after one week in culture and even encouraged organized skeletal myotube formation. Additionally, with the application of electrical field stimulation, skeletal myotubes began to assemble functional sarcomeres that could contract. Cardiac tubes could spontaneously contract and be paced for up to one month. Our flexible cell-sheet engineering approach provides an adaptable method to recapitulate more complex 3D geometries with tissue specific customization through the addition of different cell types, mold shapes, and hydrogels. By enabling the fabrication of scaled biomimetic models of human tissues, this approach could potentially be used to investigate tissue structure-function relationships, development, and maturation in the dish.

Effect of convective heat transfer coefficient on estimation of effective thermal conductivity of two-phase material

Two-phase materials are involved in applications of day to day life, the reason being it is having discrete properties like firmness, required thermal conductivity, durability as well as good impact properties, etc. Thermal conductivity of two-phase material is a basic property to envision its evaluation in engineering. Distinct geometry for example cylinder, spherical, random size particles are being proposed by researchers for computation of effective thermal conductivity (ETC) of material like two-phase. This paper includes a two-dimensional two-phase system with hollow square geometry which is being considered for mathematically deriving an algebraic equation for computing ETC with the inclusion of the convective heat transfer coefficient. A unit cell approach is considered for deriving the equations. The obtained results are validated with the basic available models for distinctive types of two-phase materials. Hollow square model with Ψ = 0.3 gives approximate reasonable agreement for predicting ETC having a mean percentage error of 5.73% which is acceptable.

Design and analysis of tooth abutment implant

Design and analysis of tooth abutment implant

Light-Emitting-Diode-Based Multispectral Photoacoustic Computed Tomography System.

Photoacoustic computed tomography (PACT) has been widely explored for non-ionizing functional and molecular imaging of humans and small animals. In order for light to penetrate deep inside tissue, a bulky and high-cost tunable laser is typically used. Light-emitting diodes (LEDs) have recently emerged as cost-effective and portable alternative illumination sources for photoacoustic imaging. In this study, we have developed a portable, low-cost, five-dimensional (x, y, z, t, PACT system using multi-wavelength LED excitation to enable similar functional and molecular imaging capabilities as standard tunable lasers. Four LED arrays and a linear ultrasound transducer detector array are housed in a hollow cylindrical geometry that rotates 360 degrees to allow multiple projections through the subject of interest placed inside the cylinder. The structural, functional, and molecular imaging capabilities of the LED–PACT system are validated using various tissue-mimicking phantom studies. The axial, lateral, and elevational resolutions of the system at 2.3 cm depth are estimated as 0.12 mm, 0.3 mm, and 2.1 mm, respectively. Spectrally unmixed photoacoustic contrasts from tubes filled with oxy- and deoxy-hemoglobin, indocyanine green, methylene blue, and melanin molecules demonstrate the multispectral molecular imaging capabilities of the system. Human-finger-mimicking phantoms made of a bone and blood tubes show structural and functional oxygen saturation imaging capabilities. Together, these results demonstrate the potential of the proposed LED-based, low-cost, portable PACT system for pre-clinical and clinical applications.

On application of wobbler in experiments with cylindrical targets

For the experiments with irradiation of cylindrical targets by intense heavy ion beams which are actual for fundamental and applied researches (laboratory astrophysics, heavy ion inertial fusion, ion therapy, industry) it is necessary to shape the driver beam with hollow geometry. The wobbling method is of interest for such experiments. In the paper one of the problems of the method is considered leading to possible symmetry violation. The results of the simulation of the rotated beam dynamics are presented.

A low temperature solid state reaction to produce hollow MnxFe3-xO4 nanoparticles as anode for lithium-ion batteries

Hollow MnxFe3-xO4 nanoparticles (NPs) with an average size of 15 nm are produced from the solid state reaction of Fe3O4–Mn3O4 heterostructures. These heterostructures are synthesized through the seeded-growth of Mn3O4 crystal domains on the surface of hollow Fe3O4 NPs obtained by the nanoscale Kirkendall effect. Fe3O4–Mn3O4 heterostructures are subsequently annealed at 500 °C, enough temperature to promote the interfusion of Fe and Mn ions, but without compromising the hollow geometry. MnxFe3-xO4 nanostructures are tested as anode in lithium-ion batteries (LIBs), delivering large lithium storage capacities and high-rate capabilities of 1054 mAh g−1 at 0.1 A g−1 and 369 mAh g−1 at 5 A g−1. Additionally, hollow MnxFe3-xO4 NPs display long cycling stability, with a capacity up to 887 mAh g−1 at 0.3 A g−1 after 450 cycles. The excellent performance of hollow MnxFe3-xO4 NPs as anode for LIBs is associated with their crystal structure, composition, and the presence of carbonized ligands, which further promote electrical conductivity and buffer the volume changes during cycling. Additionally, the small particle size and hollow morphology improves the lithium kinetics, structural stability and cycling performance.

3D printed thermoplastic polyurethane bladder for manufacturing of fiber reinforced composites

The Bladder Assisted Composite Manufacturing (BACM) technique allows fabrication of complex hollow composite geometries. However, traditional bladder manufacturing methods require multiple steps and a master geometry which increases the cost and the manufacturing time. Hence, additively manufactured bladders are presented as an alternative solution to bladders manufactured through traditional methods. The use of printed bladders is demonstrated by consolidating and curing a composite part made out of an aerospace grade composite prepreg material, IM7/8552. Bladders are additively manufactured using the Fused Deposition Modeling (FDM) technique with Thermoplastic Polyurethane (TPU). Based on the results of a thermomechanical investigation of the TPU, a two-step curing cycle for manufacturing a composite part with IM7/8552 prepreg was designed. The part consolidation achieved with this method was characterized by measuring void content and comparing it to the void content in a sample cured in a standard autoclave process. The low void content achieved with the BACM method demonstrated the potential of this technology for providing bladders for short production runs or prototyping.

Synthesis of carbon nanohoops containing thermally stable cis azobenzene

Cycloparaphenylenes (CPPs) have been praised for their size-tunable HOMO/LUMO gap and associated electronic and optical properties, and have generated significant interest for small-molecule electronics. Another fascinating but less-explored prospect for CPPs involves exploiting their hollow geometry. With a rigid pore of tunable size and high electron density arising from the inward facing π-orbitals, CPPs are ideal for electron-poor guests. [10]CPP in particular has shown very high binding affinity for fullerene C60. The ability to reverse this encapsulation by external stimuli is an important next step. Herein we report the design and synthesis of two CPPs containing thermally stable cis azobenzene moieties in the conjugated framework, their behavior upon irradiation, and computational results evaluating their potential as photoswitchable fullerene hosts.

Electrical swing adsorption on functionalized hollow fibers

Temperature swing adsorption (TSA) is a favorable adsorption technique when applied for capturing CO2 but limited by long cycle times and low concentrations of the recovered adsorbate. Direct heating of the adsorbent can mitigate these drawbacks. Combined with the beneficial mass transfer of a hollow fiber geometry it offers a powerful sorption process. In this study, we combine the advantages of direct heating and the benefits of the hollow fiber geometry in electrically conducting hybrid hollow fibers. Two different solid sorbents are manufactured and characterized: polyethylenimine-impregnated silicon carbide fibers (SiC-PEI) and fibers consisting of a carbon nanotube matrix with dispersed zeolite particles (CNT-zeolite). Both fibers exhibit Joule heating properties and high adsorption capacities. The CO2 uptake, CO2 isotherms, and the kinetic behavior are examined. The maximum CO2 uptakes at 30 °C and 15 vol% CO2 are 8.3 mg/gfiber for SiC-PEI and 102.2 mg/gfiber for CNT-zeolite. A lab-scale module is designed and used to determine the CO2 capacity of a fiber bundle. The energy requirement to heat such a fiber bundle from ambient temperature to 80 °C is 3.1 J/gFiberK (SiC-PEI) and 15.8 J/gFiberK (CNT-zeolite). To investigate the suitability of the fibers for real process applicability, a mathematical model is established and simulation results are presented and discussed. The two different approaches prove to be viable options for CO2 separation. They are not limited to CO2 capture but can be expanded to other gas separation tasks.

Rapid prototyping for hypervelocity impulse facility test models

The X2 expansion tube facility at The University of Queensland is capable of simulating entry into most of the planetary bodies in our solar system, producing test conditions with stagnation enthalpies in excess of 100 MJ/kg. Models used in X2 are typically made from steel and, consequently, manufacture is often constrained to conventional methods, with associated long lead times, and high cost. Through an experimental campaign, the survivability and applicability of Rapid Prototype models was investigated. Three prototyping methods were investigated; Selective Laser Sintering, Stereolithography, and Fused Deposition Modelling, and these were compared to a steel baseline. A computational stress analysis was used to design an internally hollow test model geometry. All models survived the experimental test-time, one was destroyed by the post-experiment flow. It was thought that test-models might ablate during the experimental test time and this was investigated by using filtered imaging to capture Cyanogen radiation occurring in the model's boundary layer. Ablation was seen in all Rapid Prototype models, most strongly observed in the Selective Laser Sintered and Acrilonitrile Butadiene Styrene models. These models may be suitable for the study of non-equilibrium radiative emission just behind the shock wave, or ablation phenomena in a model's boundary layer.