Confinement Configuration Research Articles

Direct Exfoliation of Nanoribbons from Bulk van der Waals Crystals.

Confinement of monolayers into quasi-1D atomically thin nanoribbons could lead to novel quantum phenomena beyond those achieved in their bulk and monolayer counterparts. However, current experimental availability of nanoribbon species beyond graphene is limited to bottom-up synthesis or lithographic patterning. In this study, a versatile and direct approach is introduced to exfoliate bulk van der Waals crystals as nanoribbons. Akin to the Scotch tape exfoliation method for producing monolayers, this technique provides convenient access to a wide range of nanoribbons derived from their corresponding bulk crystals, including MoS2, WS2, MoSe2, WSe2, MoTe2, WTe2, ReS2, and hBN. The nanoribbons are predominantly monolayer, single-crystalline, parallel-aligned, flat, andexhibit high aspect ratios. The role of confinement, strain, and edge configuration of these nanoribbons is observed in their electrical, magnetic, and optical properties. This versatile exfoliation technique provides a universal route for producing a variety of nanoribbon materials and supports the study of their fundamental properties and potential applications.

On the ignition of H11B fusion fuel

We have revisited recent results on the ideal ignition of H11B fuel, in the light of the latest available reactivity, an alternative self-consistent calculation of the electron temperature, an increased extent of the suprathermal effects and the impact of plasma density. At high density, we find that the ideal ignition temperature is appreciably relaxed (e.g., Ti≃150 keV for ni∼1026 cm−3 and an optimal 11B/H concentration ε=0.15) and burn becomes substantial. We have then investigated central hot-spot ignition in both isobaric and isochoric inertial confinement configurations. Although implosion-driven ignition appears to be unfeasible, the isochoric self-heating conditions foster favourable preliminary conclusions on the utilization of proton fast ignition. In the isochoric case, we find a broad minimum in the ignition energy at ρR≃8.5 g/cm2 and 220≲Ti≲340 keV (80 ≲Te≲95 keV), for ε=0.15.

An alternative modeling approach to incorporate bond-slip effects in fiber-based elements

Fiber-based elements can provide accurate estimates of the global and local inelastic response of RC members subjected to reversed cyclic loads. However, fiber-based elements per se do not account for the localized deformations that arise from strain penetration or bond-slip effects at the member ends. To account for bond-slip effects, some researchers have suggested the use of modified properties for the steel reinforcement fibers, or that a zero-length element be attached at the element ends. In this study, a modified modeling procedure is proposed to include anchorage-slip effects in reinforced concrete frame members modeled with fiber-based beam-column elements. The proposed modeling approach is based on local bond-slip laws that can be implemented in general-purpose fiber-element software, and it differs from existing approaches in that it does not require the use of a zero-length element (though it could be used), and that it can be used with any local bond-slip relationship representative of a variety of bar embedment conditions. As such, the model can be used to simulate the effects of bond-slip of short or long embedment lengths in confined or unconfined concrete. The proposed modeling procedure is validated by comparing the calculated response with experimental data from four independent investigations. The test data included three columns and two beam specimens with various confinement and reinforcement configurations and included members reinforced with conventional and high-strength steel reinforcement. The results from the analyses show that the proposed modeling procedure provides a very good estimate of both the global and the local responses (anchorage-slip rotation) of the specimens.

Review and Assessment of Material, Method, and Predictive Modeling for Fiber-Reinforced Polymer (FRP) Partially Confined Concrete Columns.

The repairing and strengthening of concrete structures using external and internal partial confinements are inevitable in the construction industry due to the new standards and rapid developments. The conventional materials and methods of confinement are unable to meet modern safety and functional standards. The fiber-reinforced polymer (FRP) enhances the strength and ductility of deteriorating and new concrete columns by reducing lateral confinement pressure and resistance against seismic shocks. The precise methods of partial confinement are inevitable for effective FRP-concrete bonding, durability, and cost-effectiveness under different loading conditions and to cope with external environmental factors. Predictive modeling and simulation techniques are pivotal for the optimization of confinement materials and methods by investigating the FRP-concrete novel confinement configurations, stress-strain responses, and failure modes. The novel materials and methods for concrete columns' partial confinement lack high compressive strength, ductility, chemical attack resistivity, and different fiber orientation impacts. This review provides an overview of recent confinement materials, novel methods, and advanced modeling and simulation techniques with a critical analysis of the research gaps for partial FRP confinement of concrete columns. The current challenges and future prospects are also presented.

Machine learning approach to predict the strength of concrete confined with sustainable natural FRP composites

Recent earthquakes have highlighted the need to strengthen existing structures with substandard designs. NFRPs provide a sustainable, cost-effective alternative for strengthening, but accurately predicting their performance remains a challenge. This study investigates the use of machine learning algorithms for predicting the compressive strength concrete specimens confined with various NFRPs. Four algorithms were employed: decision tree, random forest, neural network, and gradient boosting regressor. A diverse dataset encompassing various geometries, material properties, and confinement configurations was used to train and evaluate the models. Gradient boosting regressor (GBR) achieved the highest performance, with an average R-squared value of 0.94 and low mean absolute error (MAE) and root mean squared error (RMSE) during training and k-fold cross-validation. Neural network and random forest also demonstrated satisfactory performance, with average R-squared values of 0.88 and 0.86, respectively, during cross-validation. These results suggest that machine learning holds promise for predicting the compressive strength of concrete confined with NFRPs. GBR offers the most accurate predictions, making it a valuable tool for engineers seeking to optimize the design and performance of strengthened structures using sustainable materials.

Nonneutral Weibel model plasma in the non-minimal CPT-odd coupling

Inspired by the extension of the Standard Model, we investigate the effects of the space-time anisotropy caused by Lorentz symmetry violation (LSV) on a plasma column confinement configuration. The model of Plasma taken into account is the z-pinch model that was in the earliest efforts in fusion power research. This model comprises particles in a nonequilibrium cylindrical distribution, which remains stationary in the absence of collisions. We propose a disturbance in the distribution by a Lorentz violation environment. As proposed by Carroll, Field, and Jackiw, in a scenario of (LSV), a background field vector could couple with the electromagnetic field, modifying the classical behavior of the electromagnetic field. As reported here, considering the presence of a background field vector, the intensities of the fields and particle densities would be disturbed by the influence of the LSV. For different values of the background field vector coupling constant, the contribution of the background vector field could modify the intensity of the electromagnetic fields, and concentrate even more the electrons densities in the edge of the plasma column, evidencing a behavior similar to a skin effect in this plasma column.

Constructing the space of quasisymmetric stellarators through near-axis expansion

Abstract A simplified view of the space of optimised stellarators has the potential to guide and aid the design efforts of magnetic confinement configurations suitable for future fusion reactors. We present one such view for the class of quasisymmetric stellarators based on their approximate description near their centre (magnetic axis). The result is a space that captures existing designs and presents new ones, providing a common framework to study them. Such a simplified construction offers a basic topological approach, guided by certain theoretical and physical choices, which this paper presents in detail.

Locally Asymmetric BiOBr for Efficient Exciton Dissociation and Selective O2 Activation toward Oxidative Coupling of Amines.

Two-dimensional (2D) layered photocatalysts with highly ordered out-of-plane symmetry usually display robust excitonic effects, thus being ineffective in driving catalytic reactions that necessitate unchained charge carriers. Herein, taking 2D BiOBr as a prototype model, we implement a superficial asymmetric [Br-Bi-O-Bi] stacking in the out-of-plane direction by selectively stripping off the top-layer Br of BiOBr. This local asymmetry disrupts the diagnostic confinement configuration of BiOBr to urge energetic exciton dissociation into charge carriers and further contributes to the emergence of a surface dipole field that powers the subsequent separation of transient electron-hole pairs. Distinct from the symmetric BiOBr, which activates O2 into 1O2 via an exciton-mediated energy transfer, surface asymmetric BiOBr favors selective O2 activation into ·O2- for a broad range of amine-to-imine conversions. Our work here not only presents a paradigm for asymmetric photocatalyst design but also expands the toolkit available for regulating exciton behaviors in semiconductor photocatalytic systems.

Experimental Analysis of the Mechanical Response of Masonry Columns Partially Confined with PBO FRCM (Fabric Reinforced Cementitious Mortar) Composites.

An experimental investigation on partially PBO (short of Polyparaphenylenebenzobisthiazole) FRCM (Fiber Reinforced Cementitious Mortar) confined clay brick masonry columns has been conducted. Ten small-scale specimens measuring 445 mm high with a square cross-section of the 250 mm side have been tested under monotonic axial loading until collapse. Two columns were unconfined, while the remaining ones were confined with single-layer PBO FRCM jackets varying the geometric configuration along their height. The vertical spacing ratio sf'/sf, being sf' and sf the center-to-center and the net spacings between two consecutive jackets, respectively, was considered as the key parameter of the confinement configuration. The failure modes, stress-strain curves and peak axial stress and strain values are reported. The experimental results have been compared to the predictions of models found in the Italian guidelines CNR DT 215/2018 and the American ACI 549-R20 standards. The main aspects analyzed involved (i) the evaluation of the effectiveness of partial confinement on the mechanical response of columns, (ii) the definition of the mechanical and geometrical parameters that influence the structural response of partially confined columns, and (iii) the development of appropriate analytical models for the prediction of the resisting capacity of masonry columns partially confined with PBO FRCM.

Finite Element Investigation of Angle Ring Confinement for Clustered Large-size Stud Shear Connector in Full-Depth Precast Concrete Bridge Deck Panel

Full-Depth Precast Concrete (FDPC) bridge deck panel system, consisting of concrete deck and steel girders, has been used widely for highway and bridge construction due to rapid construction and replacement as well as in terms of economics. This system could integrate with clusters of large size headed-stud shear connectors for more significant connection, although larger composite actions were experienced. Therefore, a new angle steel ring confinement was introduced and tested by push-off samples for the most effective shear transfer. The Finite Element Analysis (FEA) of the push-off model with an in-depth investigation of non-linear concrete properties, boundary parameters, and different geometries of angle ring confinement was developed in this study. The FE models were verified with the push-off test in terms of loads, displacements, and failure stages. Nonlinear concrete material models: Concrete Damage (CD) and Drucker Prager (DP) were identified the different abilities either for predicting initial cracks, or determining maximum resistance and critical failure, respectively. The thickness of the angle and the sizes of hook bars were investigated for the most effective aspects of the angle ring confinement. The results showed comparable stiffness and load resistance for various aspects. However, compatible geometries, either 5 mm thick angles with DB12 hook bars or 10 mm angles with DB25 hook bars, were suggested. The final non-linear FEA model was reliable for comparative studies to FDPC push-off with different confinement configurations.

Confinement and alkali-silica reaction in concrete: Review and numerical investigation

The effect of confinement and Alkali-Silica Reaction (ASR) in concrete is of paramount importance when assessing damage in existing structures. It appears that this effect has been only seldom investigated with respect to the vast literature on free-expanding ASR, especially in its modeling aspect. This paper proposes to address this topical issue. For this purpose, an exhaustive review on the effect of confinement and ASR was first provided. Key features that must be taken into account were discussed and a discrete model equipped with the relevant multi-physics models was proposed. The computational framework which includes models for moisture diffusion, heat transfer, cement hydration and aging, thermal expansion, creep, and shrinkage was validated through a detailed comparison with a recent large experimental campaign for which all model parameters have already been calibrated. After accounting for possible alkali-leaching in the experiments and adjusting three model parameters, the numerical framework was used to simulate expansion curves, crack distribution, and damage evolution in unconfined samples, and drilled cores. Results show that overall, the model is able to well reproduce the transfer of expansion in the transversal unrestrained direction, cracks having a preferential direction in the restrained direction, expansion behaviors in the three spatial directions, and the evolution of mechanical properties in time for different confinement configurations. The important effect of creep and shrinkage was also emphasized. Crack distributions numerically generated were found consistent with Damage Rating Index analysis. One major finding of this study is that the true strength inside concrete subjected to multi-axial confining loads was found unaltered due to ASR in the direction of confinement. This striking result confirms many practitioners’ field experience with core testing and raises the fact that as sophisticated modeling tools become more and more reliable, existing methods of assessment must be improved by incorporating results from numerical modeling.

Finite element modeling of partially-confined concrete and RC columns with embedded hexagonal-FRP strips under axial and horizontal loading

Recently, GFRP-strips partial confinement has demonstrated significant revelations as an effective and economical method of structural rehabilitation and strengthening. In this connection, this paper firstly presents a finite element modeling (FEM) on the behavior of a novel confinement configuration of concrete cylinders with embedded hexagonally designed GFRP strips under axial loading using ABAQUS. The simulation outcomes in terms of stress–strain response and damages were experimentally and analytically validated. The second objective of this paper is to develop a FEM to study a new reinforcement method of large scale partially-confined RC columns subjected to a monotonic horizontal loading. For this purpose, full 3D numerical simulations were carried out taking into account the nonlinear behavior of all used materials. The accuracy of the numerical results was emphasized through a comparison with ones of previous experimental tests. In addition, the effects of various parameters on the failure mode and the ultimate lateral carrying load capacity of the columns were studied on twenty-four numerical models. As main conclusion, the predicted results indicated that the proposed strengthening design with a greater encased-GFRP strip thickness combined with smaller spacing significantly improved the performances of RC columns.

Nonlinear behaviour of corrosion damaged low-strength short reinforced concrete columns under compressive axial cyclic loading

New codes have recently introduced seismic detailing for new structures. However, there are still older reinforced concrete (RC) structures without proper ductile detailing for earthquake resistance in seismic-prone areas. These structures are further impacted by the corrosion of their embedded reinforcing bars, which further reduces the strength and ductility under axial cyclic loading. This paper summarises the results of an experimental investigation performed on low-strength short RC columns, with different confinement configurations, subject to varying degrees of corrosion to investigate their structural responses to axial cyclic loading. The experiment was conducted on 30 short RC columns (square and circular) with three levels of confinement and steel reinforcement corrosion loss ranging from 0% to ∼ 30% subjected to cyclic compressive loading. The test results show that corrosion and inadequate confinements have a significant negative impact on the structural responses of corroded columns.

Modal added-mass matrix of an elongated flexible cylinder immersed in a narrow annular fluid, considering various boundary conditions. New theoretical results and numerical validation

This paper considers the fluid–structure interaction problem of two coaxial cylinders separated by a thin layer of fluid. The flexible inner cylinder is imposed a small amplitude harmonic displacement corresponding to a dry vibration mode of an Euler–Bernoulli beam, while the external cylinder is rigid. A new theoretical formulation based on the assumption of a narrow fluid annulus is derived to estimate the modal added-mass matrix of the vibrating cylinder. This formulation accounts for the finite length of the flexible cylinder, clearly highlights the effect of the aspect ratio of the vibrating cylinder on the structure of the added-mass matrix, and covers all types of classical boundary conditions in the same theory and can easily be implemented in any numerical computing environment. The diagonal coefficients of the added-mass matrix are shown to increase with the confinement, with the aspect ratio of the flexible cylinder, and are sensitive to the wave-number of the vibration mode. Also importantly, we show that the dry vibration modes generate off-diagonal coefficients that vanish for an infinitely long cylinder. Our theoretical observations are corroborated by an extensive set of CFD numerical simulations, covering all types of classical boundary conditions, different confinement configurations, and different aspect ratios of the vibrating cylinder. The results obtained are presented in graphical form, which can be directly applied in engineering applications.

Analysis of CFRP Confined Concrete Cylinders by using ABAQUS Software

The fiber-reinforced polymer (FRP) wrapping is widely used in concrete column strengthening, as it can enhance concrete strength and ductility. This study aims to develop finite element numerical model that can capture the behavior of the short cylinder column confined with CFRP. After validating the proposed finite element models with previous experimental works, a series of parametric studies have been conducted, including, CFRP number of layers, concrete grade, confinement configuration, and size of samples are investigated in terms of stress-strain curves, ductility, and volumetric strain. The results indicate a significant improvement in concrete strength after fully CFRP wrapping. However, the partial confinement records less improvement in concrete strength but considerable ductility. By increasing the specimen’s size and maintaining the same confinement ratio, the strength enhancement was decreased. Based on this observation; it can be concluded that; by increasing the samples sizes, it should be escorted with more confining ratio than that of the small size. Moreover, it was concluded that as the number of layers increases the ductility increases whether it was full or partial confinement configuration. The CFRP confinement can control the specimen’s dilation during the axial compression test thus presenting less volumetric strain. The proposed formula by (Lam & Teng, 2003) that can predict the stress-strain response of FRP full confined concrete cylinder was compared with the corresponding values. The results indicated that; a good matching was noticed only for the samples located in the same area that was studied by (Lam & Teng, 2003).

Effect of curvature on durable ice-phobic surfaces based on buckling metallic plates

Degradation in system performance due to ice accretion on curved surfaces remains a decades-old challenge. We recently reported that Buckling Elastomer-like Anti-icing Metallic Surfaces (BEAMS) exhibit a low ice adhesion strength and extreme durability in realistic icing conditions. BEAMS consist of thin, flat metal sheets suspended on strips or dots of adhesive, and this partial confinement facilitates buckling of the metal sheet, causing ice to dislodge from the surface at a low applied force. The mechanism of ice detachment from curved BEAMS has not been investigated. Here we study how curvature affects the shear ice adhesion strength of BEAMS, using both glaze- and rime-type ice at −20 °C. For glaze, it was observed that increasing the radius of curvature increased the ice adhesion strength regardless of whether the curvature was positive or negative. For rime ice a high radius of curvature, R = 17.3 mm, was used inside an icing wind tunnel. When the compliance of the material used to suspend the metallic sheet was increased, the rime ice adhesion strength was as low as τice≈3 kPa. Further, the confinement configuration of BEAMS was studied to understand its effect on lateral torsional buckling. Lateral torsional buckling altered the radius of curvature of both the suspension material and metal sheet, initiating cracks due to the unchanged curvature of the accreted ice. Accordingly, the extremely low ice adhesion strength of BEAMS, even on curved surfaces, was due to buckling instabilities either within the thin metal plates or the suspension material. Overall, BEAMS would appear to be a durable, low-ice-adhesion candidate material even for complex and curved surface geometries such as the leading edges of aircraft wings, wind turbine blades, or power transmission lines.

Measures of quasisymmetry for stellarators

Quasisymmetric stellarators are an attractive class of optimised magnetic confinement configurations. The property of quasisymmetry (QS) is in practice limited to be approximate, and thus the construction requires measures that quantify the deviation from the exact property. In this paper we study three measure candidates used in the literature, placing the focus on their origin and a comparison of their forms. The analysis shows clearly the lack of universality in these measures. As these metrics do not directly correspond to any physical property (except when exactly quasisymmetric), optimisation should employ additional physical metrics for guidance. It is suggested that close to QS minima, one should treat QS metrics through inequality constraints so that additional physics metrics dominate optimisation. The impact of different quasisymmetric measures on optimisation is presented through an example, for which the standard metric that weights the asymmetric Fourier modes of the field magnitude appears to perform best.

Appraisal of visual inspection techniques to understand and describe ASR-induced development under distinct confinement conditions

Conventional visual inspection techniques are generally qualitative and therefore unable to provide accurate information on the extend of alkali-silica reaction (ASR)-induced damage development in concrete. Therefore, improving and finding more accurate visual procedures is extremely important for a better condition assessment and development of management protocols of ASR-deteriorated infrastructure. This work intends to assess ASR-induced damage development on distinct surfaces of thirty-two concrete blocks displaying various confinement configurations (none, 1D and 2D) and incorporating different aggregate types (reactive fine and coarse) through the use of distinct visual and microscopic techniques. Three expansion levels were selected for analysis (0.08%, 0.15% and 0.25%) and once reached, various visual inspection techniques (qualitative, semi-quantitative and quantitative) along with the Damage Rating Index (DRI), a semi-quantitative petrographic analysis, were conducted on the surface of the affected members. Moreover, cores were extracted from the three different directions (longitudinal, transverse, and vertical) of affected blocks at selected expansion levels, and the DRI was performed on those with the aim of comparing the damage on the surface and core of the affected blocks. Results show that the higher the confinement, the higher the surface damage on the affected members. Furthermore, the DRI results obtained from the cores and surfaces of the blocks demonstrate that the surface of the members experienced significantly higher amount of damage than the core specimens. Finally, a qualitative model is proposed to describe ASR-induced surface deterioration in concrete under distinct confinement configurations.

Condition assessment of alkali-silica reaction affected concrete under various confinement conditions incorporating fine and coarse reactive aggregates

The multi-level assessment, combining microscopic (i.e., Damage Rating Index) and mechanical (i.e., Stiffness Damage Test) techniques, has been effectively used to appraise the deterioration cause by alkali-silica reaction (ASR) in unconfined concrete. However, the impact of restrainment on ASR-induced deterioration originated from reactive fine and coarse aggregates has not been fully explored. This study intends to evaluate the effect of the confinement degree and reactive aggregate type on ASR damage development through the multi-level assessment. Twenty-four concrete blocks incorporating two different reactive aggregate types (fine and coarse) and three confinement configurations (unconfined, 1D, and 2D) were produced and monitored over time. Upon reaching the desired expansion levels (0.08% and 0.15%), cores were retrieved from three main directions (vertical, longitudinal and transverse) and the multi-level assessment was performed. Results indicate that ASR-induced expansion and damage are influenced by the reactive aggregate type, confinement configuration and coring direction.

Quasistatic Equilibrium Chemical Vapor Deposition of Graphene

AbstractThis study reviews the majorly used chemical vapor deposition (CVD) with a focus on confined reaction configurations in which quasistatic equilibrium conditions are obtained for the fabrication of graphene with large size and high quality through controlled nucleation density, feedstock flux, and growth rates. The confinement configurations can also be used to tune the thickness, domain size and shape, and stacking order of the synthetic graphene. The confined CVD reaction configurations discussed include enclosure systems, inner‐tube setups, sandwiched substrates, as well as other types of configurations. The advantages and limitations of the different confinement configurations are presented, along ways to optimize the operational parameters for them.