Geometrical Restrictions Research Articles

Synthesis of Ultrathin Film PEGDMA Hydrogels Coated onto Different Surfaces by Atmospheric Pressure Plasma: Characterization and Potential Features for the Biomedical Field

AbstractThe preparation of resistant ultrathin film (utf) hydrogels coated onto different working surfaces (e.g., fabrics) is paying increasing attention as an advantageous strategy for customizing their resultant properties. More specifically, poly(ethylene glycol) (PEG)‐based utf‐hydrogels are relevant for their superior biocompatibility or antibiofouling properties. However, promoting the generation of poly(ethylene glycol) dimethacrylate (PEGDMA) cross‐links ideally without the use of initiators or other cross‐link agents, which might compromise the final bioactivity of the system, is complicated. Moreover, the actual synthesis techniques used for the preparation of such utf‐hydrogels face important drawbacks like high scale‐up costs or important geometrical restrictions, completely hindering its technological transfer. Herein, for the first time and easy and technologically scalable technology is reported for the synthesis and direct deposition of PEGDMA400 utf‐hydrogels onto different substrates based on atmospheric pressure nanosecond pulsed plasma approach. The advantages of the technology are explored and discussed, reporting the ready‐to‐use transparent coating of fabrics. After washing the samples using washing programs of a commercial laundry machine, coatings are still well adhered, showing excellent stability. Finally, the resultant properties of PEGDMA400 utf‐hydrogels are exhaustively characterized using in operando conditions in order to elucidate their potential capabilities in the biomedical field.

A C3‐symmetric like structurally twisted molecular architecture: mechano/fluorochromic behavior and selective multiphase detection of Pd (II)

Triaminoguanidinium (TG)‐based C3‐symmetric‐like molecular architectures with diverse donors and acceptors are well established as organic molecular materials for promising stimuli‐responsive and metal sensing‐based applications. However, the mechanofluorochromic (MFC) response was unremarkable upon applying external mechanical stress. Even though some show MFC features, there was no optical shift under ambient light. In this paper, we developed a novel C3‐symmetric molecule, TAC3, containing the TG core linked with conformationally twisted thiophene‐linked anthracenyl terminals. Three conformationally deformed hands in TAC3 respond against external mechanical stimuli with a redshifted absorption and emission, easily detectable through the naked eye. Although MFC features were reported before for such C3‐symmetric molecules, the change in absorbance was not identified. In addition, TAC3 could selectively detect Pd2+ through extreme emission quenching (green to black). The mechanochromism and sensing outcomes are elucidated by the experimental and theoretical support. Compared to the previous reports, the notable 2:3 (metal: ligand) binding due to geometric restriction creating a specific pocket size for Pd+2 is unusual for this system. The onsite application on Pd2+ detection and measurable MFC features are demonstrated to validate the potential of this C3‐symmetric molecule in advanced optoelectronic applications such as security writing and Pd2+ ion detection.

Effect evaluation of fluid movement and rock properties for artificial seismic activity on hydrocarbons

Despite the effectiveness of seismic stimulation in enhancing oil production from reservoirs, the impact of high-frequency vibrations on oil droplets confined within pore throats has not been adequately investigated. This laboratory-scale experimental study examines the impact of low and high-frequency sinusoidal vibrations in dislodging oil droplets trapped in a specific pore-throat region. Sinusoidal vibrations ranging from 10 to 80 Hz and with maximum displacement amplitudes of 1.2–0.06 mm are applied. By comparing the images captured prior to and after the application of seismic vibrations, the amount of oil recovered is determined. Commercial gasoline and diesel are used as trapped oil samples, and water is used as the injection fluid to bring out the effect of fluid viscosities in seismic dislodgment. While applying vibrations to trapped oil in the pore throat, three different recovery modes are observed: continuous, snap-off, and emulsified. The continuous oil recovery mode is observed in cases with minimal flow resistance through the pore throat, whereas a snap-off or intermittent recovery mode is observed when the flow resistance is high, and the vibration frequencies fall within the midrange of 40-60 Hz. An emulsified oil recovery mode is observed at high vibration frequencies. The amount of recovered oil increases as geometrical restrictions and trapped oil viscosity decrease. Seismic mobilization is observed to be directly proportional to the mobilization velocity and inversely proportional to the entrapped oil viscosity and geometrical restriction factors.

Simulation-based evaluation of road transportation logistics in a dry port with topographic challenges

The extension of existing container terminals or the creation of new ones introduces new logistical challenges, including topographic issues and increased distances between the quays and storage yards located several kilometers away from the quay (dry port). These challenges are complex to evaluate analytically and directly impact the acceleration, deceleration, and average speed of a truck which in turn affect the productivity and synchronization of the overall terminal logistics. This paper proposes a transportation simulation model that incorporates detailed descriptions of the topographical and geometrical restrictions. Our simulation model evaluates various scenarios for container transportation logistics, including varying road design terminals and truck fleet size to enhance productivity. A case study from a potential container terminal on Canada’s St. Lawrence River is used to demonstrate the simulation model. Several scenarios with different designs are tested and the simulation provides numerical results for supporting decision makers.

Multi-Variable Optimization to Enhance the Performance of a Cantilevered Piezoelectric Harvester

Over the past decade, various researchers have shown the practicality of extracting electrical energy from vibrating structures. The primary objective of this research was to optimize the parameters of a basic cantilever harvester to maximize the energy production of electricity from surrounding mechanical energy. A distributed parameter model and its modal solution were utilized to determine the design variables via a parametric investigation. It is important to ensure sufficient power generation when there is a wide range of frequencies being excited, without any specific frequency being emphasized. The cost function for the optimization problem was defined as the average power within a specific frequency range, considering geometric and physical restrictions. It was discovered that different parameters’ values can be utilized to generate varying maximum power levels for different frequency ranges. Furthermore, a comparative analysis was performed between the finite element method (FEM) using ANSYS and the current harvesting model. The comparison demonstrated a high level of concordance, enabling the utilization of the finite element method (FEM) for subsequent investigation.

Modeling the selective attenuation of thin film composite membranes: Implementing the mass transfer perspective

Numerous experiments have demonstrated that the porous support layer limits the diffusion behavior and leads to a reduction in permeability of thin film composite (TFC) membranes. Although this geometric restriction has been described using empirical models, it is still rough and unable to describe the effect of support layer on selectivity, an accurate theoretical model to quantitatively calculate the permeation performance of TFC membranes is lacking. In this study, an equivalent theoretical model is proposed to describe the mass transfer process of TFC membrane, by properly handling the tangential diffusion at the interface between the selective layer and the support layer. Both the computational fluid dynamics (CFD) simulations performed in this work and experimental data in some literatures prove the validity of the equivalent model. Analysis of the theoretical model and CFD simulation results show that: Restriction factor Ψ is independent of the solubility coefficients but dependent of the diffusion coefficients and support layers, which would alter the TFC membrane selectivity to the diffusing species with different diffusion coefficients. Tuning the structural parameters of the support layer is an effective way to bring the performance of TFC membranes closer to that of ideal free-standing membranes. Among them, High surface porosity of the support layer is the most critical factor affecting TFC membrane performance, both for permeability and selectivity.

Generalized Hamiltonian systems on subvarieties: constant rank case

For the constraint variety in symplectic manifold, the solvable Hamiltonian vector fields on the constraint are investigated. According to P.A.M. Dirac [3], the space of solvable Hamiltonian systems is determined by the geometric restriction of the symplectic form to the constraint. Solvability condition of the generalized Hamiltonian systems is extended to singular varieties and applied under some assumption on singularities. The constraint being a smooth submanifold in a symplectic space was considered in [6]. In this paper, we investigate the solvability of generalized Hamiltonian systems and the constraint invariants on singular constraints in the constant rank case.

Bound states in bent soft waveguides

The aim of this paper is to show that a two-dimensional Schrödinger operator with the potential in the form of a ‘ditch’ of a fixed profile can have a geometrically induced discrete spectrum. This occurs if such a potential channel has a single or multiple bends, being straight outside a compact. Moreover, under stronger geometric restrictions, the claim remains true in the presence of a potential bias at one of the channel ‘banks.’

Dynamic response of a pipe with geometrical restriction subjected to gas-liquid internal flow

Due to the potential hazard of deepwater oil exploration, the Brazilian industry has an ever-increasing concern for reliability during hydrocarbon production. A major source of concern is mechanical failure in devices, such as safety valves, which can fail without warning, putting both the operation and the environment at risk. A possible reason for malfunction and failure could be the permanent occurrence of vibrations induced by internal two-phase flow during the extraction of fluids from the well. An experimental campaign is proposed to better understand these phenomena. Twenty two-phase flow conditions were tested, with superficial velocities ranging from 0.1 m/s to 2.0 m/s for water, and 0.33 m/s to 7.47 m/s for compressed air. The experiments were carried out in a restricted pipe and a pipe without any restriction to evaluate and compare the vibrations produced by two-phase flow (2-FIV). Three accelerometers positioned downstream of the restriction were used to collect vibrational amplitude spectral density data, 2-D acceleration magnitudes, and RMS values of acceleration. Among the main findings are the roles played by the gas volumetric fraction and the mixture velocity, which strongly influence the vibrational amplitude of both tubes, and the observation that the gas phase is the main responsible for vibrational amplitudes at low frequencies, while the liquid phase acts mainly at high frequencies. Furthermore, the flow pattern is also considered a key feature in determining the vibration level, as 20- and 12-fold increments have been observed for the same volumetric fraction when comparing elongated bubbles and severe slug patterns. Finally, it was demonstrated that the presence of an internal restriction strongly influences the structural response.

3D printing of reversible solid oxide cell stacks for efficient hydrogen production and power generation

Renewable hydrogen offers a promising pathway to address the challenge of large-scale chemical energy storage in the transition to a decarbonized future. The most efficient devices to convert renewable electricity into hydrogen, and vice versa, are reversible solid oxide cells (SOC-s). Despite recent advances in materials performance and durability, conventional ceramic manufacturing technologies strongly limit the huge potential of SOC-s, imposing severe geometrical restrictions that penalize the overall system efficiency. Here we capture the benefits of using previously unexplored complex-shapes by scaling 3D-printed reversible solid oxide cells with improved mechanical properties, higher performance, and embedded functionality. Stacks made of 45 cm2-3D-printed electrolyte-supported solid oxide cells combined with ultrathin flat metallic interconnects were successfully fabricated and operated in fuel cell (SOFC) and electrolysis (SOEC) modes delivering up to 85 L/h of hydrogen production while presenting less than 5 % degradation after more than 500 h of operation. The advances presented here demonstrate the viability of upscaling the process of solid-oxide-cell 3D printing and brings advantageous stack designs aimed for a cost-competitive and customizable hydrogen technologies deployment. In particular, the enhancement by design achieved here provides innovative SOC stacks with volumetric and gravimetric power densities that are three and four times higher, respectively, than their planar counterparts using the same set of materials.

On the Secondary Flow System of an Aggressive Inter Compressor Duct

Abstract In contrast to the highly optimized rotating components, the inter compressor duct (ICD) is offering a high potential for further improvements. Due to a more aggressive design, the length of the whole engine can be reduced. Shorter and thus lighter engines are leading to further fuel savings for the next engine generation. The design of current ICDs is very conservative because of high uncertainties in design space. An extensive test campaign on two highly aggressive ICDs has been conducted at an annular cascade at German Aerospace Center (DLR) Cologne to explore these limitations. The test section consists of low-pressure compressor (LPC)-OGVs, struts, and high-pressure compressor (HPC)-inlet guide vanes (IGVs). To simulate the influence of the last rotor of the LPC and to vary the incidence of the OGV, a moveable swirler is placed in front of the OGV. This simplification results in differences compared to a real rotor outlet flow. Due to geometric constraints, the ability to move the swirler can only be achieved by adding partial gaps in the rear part of the swirler at hub and shroud. These gaps have a huge impact on the secondary flow structure of the swirler outflow and therefore on the inflow of the ICD. In this article, the secondary flow system of an aggressive ICD is analyzed in detail by the means of experimentally validated computational fluid dynamics (CFD) simulations. Special attention is given to the influence of the nonrotating swirler on the secondary flow system. Furthermore, a recommendation for future experimental setups with respect to the described effects is concluded.

Femtosecond Laser Maskless Optical Projection Lithography of Cartilage PCM Inspired 3D Protein Matrix to Chondrocyte Phenotype.

Hydrogels containing chondrocytes have exhibited excellent potential in regenerating hyaline cartilage. However, chondrocytes are vulnerable to dedifferentiation during in vitro culture, leading to fibrosis and mechanical degradation of newly formed cartilage. It is proposed to modulate cartilage formation via the developed chondrocyte pericellular matrix (PCM) -like scaffolds for the first time, in which the S, M, and L-sized scaffolds are fabricated by femtosecond laser maskless optical projection lithography (FL-MOPL) of bovine serum albumin-glyceryl methacrylate hydrogel. Chondrocytes on the M PCM-like scaffold can maintain round morphology and synthesize extracellular matrix (ECM) to induce regeneration of hyaline cartilage microtissues by geometrical restriction. A series of M PCM-like scaffolds is fabricated with different stiffness and those with a high Young's modulus are more effective in maintaining the chondrocyte phenotype. The proposed PCM-like scaffolds are effective in modulating cartilage formation influenced by pore size, depth, and stiffness, which will pave the way for a better understanding of the geometric cues of mechanotransduction interactions in regulating cell fate and open up new avenues for tissue engineering.

Effect of Initial Position and Crystallographic Orientation on Grain Selection Procedure in Z-Form Selector for Ni-Based Single-Crystal Superalloy.

The grain selection process in a Z-form selector for Ni-based single-crystal superalloy was simulated using a macro-scale ProCAST software (2013 version) coupled CAFE module combined with an experiment to investigate the grain selection procedure and mechanism with different grain positions and crystal orientation relationships. A non-stationary solidification process was found in the Z-form selector, and the liquid-solid (L-S) interface was tilted in the same direction as the selector channel during directional solidification. Given that the grain boundary was parallel to the Z-form selector, the overgrowth rate of the bi-crystal in the selector channel was very low. The initial position of the bi-crystal in the selector channel has a greater effect on the overgrowth rate than the effects of primary and secondary orientations. The grain selection was a result of the coupling of the competitive grain growth effect and geometrical restriction effect. Finally, the selection grain mechanism within the Z-form selector was discussed, coalescing the temperature field and the grain competition growth mechanism.

Cucker–Smale type flocking models on a sphere

Cucker–Smale type flocking models on a sphere

Collective motion in a sheet of microswimmers

Self-propelled particles such as bacteria or algae swimming through a fluid are non-equilibrium systems where particle motility breaks microscopic detailed balance, often resulting in large-scale collective motion. Previous theoretical work has identified long-ranged hydrodynamic interactions as the driver of collective motion in unbounded suspensions of rear-actuated (“pusher”) microswimmers. In contrast, most experimental studies of collective motion in microswimmer suspensions have been carried out in restricted geometries where both the swimmers’ motion and their long-range flow fields become altered due to the proximity of a boundary. Here, we study numerically a minimal model of microswimmers in such a restricted geometry, where the particles move in the midplane between two no-slip walls. For pushers, we demonstrate collective motion with short-ranged order, in contrast with the long-ranged flows observed in unbounded systems. For front-actuated (“puller”) microswimmers, we discover a long-wavelength density instability resulting in the formation of dense microswimmer clusters. Both types of collective motion are fundamentally different from their previously studied counterparts in unbounded domains. Our results show that this difference is dictated by the geometrical restriction of the swimmers’ motion, while hydrodynamic screening due to the presence of a wall is subdominant in determining the suspension’s collective state.

Novel approach for strengthening T-beams deficient in shear with near-surface mounted CFRP ropes in form of closed stirrups

Existing reinforced concrete buildings frequently require shear-strengthening to ensure structural integrity, and externally bonded carbon fiber-reinforced polymers (EB-CFRP) have become a wide-applicable approach. However, slabs and geometric restrictions impede wrapping the element, necessitating incomplete U-shaped applications vulnerable to debonding failures. This experimental study introduces a novel approach for shear-strengthening nine full-scale T-beams using near-surface mounted CFRP ropes forming closed stirrups. Their effectiveness as shear reinforcement is investigated compared to an alternative method incorporating EB-CFRP sheets with CFRP rope anchorage. Test results indicate that both techniques enhance the beams’ strength and performance. The load capacity increased 2 times for the reference specimen and 1.4-1.9 times for the strengthened beam with FRP sheets. The displacement at the maximum load increased 5.2-7.8 and 6.6-7.5 times, respectively. The rope stirrup arrangement outperforms the rope anchorage system in mechanical and construction efficiency. A thorough protocol for executing these processes to mitigate construction-related defects is introduced.

Construction and Evaluation of Cheap and Robust Miniature Ag/AgCl Reference Electrodes for Aqueous and Organic Electrolytes

AbstractStable reference electrodes (REs) are crucial for reliable voltammetry, controlled potential electrosynthesis, or spectro‐electrochemistry. Yet, inferior pseudo‐REs, such as plain Ag wire are often used, because commercial REs are expensive, may degrade or contaminate under required conditions, or don't fit geometric restrictions of custom setups. Addressing such cases, we report construction, benchmarking and utilization of easy to make, cheap (<1 €), and robust miniature REs from pasteur pipettes, molecular sieve beads and Ag wire. Excellent potential precision and accuracy with at least 1 week device stability was obtained for aqueous Ag/AgCl REs with 3 M NaCl in H2O and anhydrous 0.1 M TBACl in MeCN inner‐electrolytes. Even in alkaline 1 M NaOH electrolyte, where initial Ag/AgCl REs quickly convert to Ag/Ag2O (1 M NaOH) REs, perfect potential precision, accuracy, and at least 1 week stability are demonstrated. According to experimental needs, miniature REs can be built with many organic and aqueous electrolytes. For these custom use‐cases, we report guidelines to calibrate absolute RE potential, and to assess device precision, accuracy and stability. Finally, electro‐hydrogenation of styrene on nickel electrodes exemplifies superiority of Ag/AgCl REs over Ag wire pseudo‐REs, affording more reliable electrolysis current, cell potential and potential dependent Faraday efficiency.

Dislodgement of Hydrogen Bubbles in Microchannels with Embedded Pillars: An Analytical, Experimental, and Numerical Study.

Microchannels with integrated pillars have enhanced the production capabilities and performance of various applications due to their high surface-to-volume ratio. However, emerging gas bubbles can become trapped, potentially limiting the functionality or efficiency of the device when scaled down to the low-micrometer scale. Understanding the conditions required to dislodge these bubbles is thus critical for optimizing microfluidic devices with complex physical behaviors. Here an analytical model is presented that outlines the dislodgment conditions and driving forces for such gas-liquid flows. These terms are derived from the gas-liquid interface properties, geometry, and processing parameters. As the density of the pillar arrangement is scaled down, the resistance to bubble dislodgment typically increases. Nevertheless, the bubble is compelled to dislodge at lower pressure loads when critical volumes are reached. This newly discovered effect is particularly noticeable in densely packed arrays and can be explained by the interplay of increased surface tension, geometrical restrictions, and volume-preserving forces. The analytical terms and effects are validated through novel experimental and numerical methods tailored for microchannels in the low-micrometer scale, showing strong agreement.

The effect of a tandem vane crossover diffuser configuration on the performance of a MGT mixed flow compressor

Due to the inherent geometric restrictions of a micro gas turbine (MGT) mixed flow compressor design, diffuser design has a major impact on compressor performance and operating range. Vaned diffusers are often preferred to vaneless diffusers in MGT compressor designs due to better efficiency and pressure recovery, albeit at the expense of operating range. A numeric investigation of the effect of a tandem vane crossover diffuser configuration on the performance and operating range of a MGT mixed flow compressor stage is presented. Three baseline test compressors, covering a wide range of design speeds, mass flow rates and meridional exit angles, are designed with a single vane crossover diffuser. For each of the three baseline compressors, the crossover diffuser design is modified to feature various tandem vane configurations. The tangential shift of the second vane row relative to the first row is evaluated. Additionally, relative first and second vane row lengths are evaluated. The performance (efficiency and pressure ratio) and operating range of the modified diffuser configurations are compared to the baseline configurations. It is shown that a 75% second vane row tangential shift configuration displays the best overall performance, regardless of the relative vane length. It is further shown that an appropriate vane length depends on the design requirement.

Assessing the effects of geometry and non-geometry related factors in work-zone crashes

Objective Work zones are unique in geometry and traffic management, utilizing special traffic signs, standard channelizing devices, appropriate barriers, and pavement markings. These configurations can introduce unexpected driving conditions, potentially posing risks to drivers. This analysis aims to explore potential differences in contributing factors between work-zone crashes where geometry was identified as a factor and those where it was non-geometry factor. To gain insights into driver injury severities in single-vehicle work-zone crashes, this study analyzed work zone crash data from Florida. Method This study employed random parameters logit models, accommodating potential variations in parameter estimates’ means and variances. The dataset encompassed a wide array of factors known to influence driver injury severity, encompassing crash characteristics, vehicle attributes, roadway features, prevailing traffic volume, driver profiles, and spatial and temporal considerations. Results This analysis yielded significantly distinct parameters for work-zone crashes, distinguishing between geometry-related and non-geometry-related factors (primarily the human factors). This distinction suggests a complex interplay between these factors. Notably, the marginal effects of individual parameter estimates exhibited marked differences between these two categories – geometry and non-geometry factors. Conclusion These findings contribute to the growing body of research indicating that geometric restrictions within work zones introduce a distinct set of risk factors compared to non-geometry-related factors. Recognizing the significance of geometric restrictions, beyond typical driving conditions, holds the implications for enhancing safety within various work zone configurations and offers valuable insights for crash scene investigators to pinpoint contributing factors accurately.