Thin Shell Research Articles

Dynamic response of twin parallel tunnels in unsaturated soil under metro train loadings

The dynamic response of twin parallel tunnels in unsaturated soil under metro train loadings was investigated using analytical methods. In the analysis, the tunnel was simulated as a linear elastic thin cylindrical shell, while the surrounding soil was treated as an unsaturated porous medium containing two cylindrical cavities. The analytical generalized solutions were deduced by solving the governing equations for the coupled tunnel-soil system using the separation of variables method and the Helmholtz decomposition method combined with the Fourier transform technique. Mixed boundary conditions were applied to determine unknown coefficients in the general solutions, yielding closed-form analytical solutions for dynamic displacement fields, as well as pore water/air pressure fields of the tunnel linings and soil. The validity and correctness of the proposed method were confirmed by comparisons with existing theoretical solutions. The parameter sensitivity analysis revealed that the presence of pore fluids (water/air) significantly affects the dynamic response of tunnels and surrounding soil. Increasing the tunnel spacing can effectively reduce the dynamic coupling effect between parallel tunnels. The traditional elastic or saturated medium models, which don’t consider the gas phase and the liquid phase, have a significant bias in the prediction of the dynamic interaction of the tunnel-soil system. The study reveals that variations in saturation degree significantly influence the displacement responses and pore pressure distributions of double-line parallel tunnels. Near-field displacement responses induced by saturated soils are substantially larger than those in unsaturated soils, whereas far-field displacements in saturated soils are smaller compared to unsaturated soils with higher saturation degrees. Moreover, a decrease in saturation degree leads to a rapid reduction in the bulk modulus of pore fluids, thereby amplifying the influence of the second tunnel on pore pressure. Analyzing the dynamic responses of double-line parallel tunnels under arbitrary saturation conditions facilitates more accurate prediction of metro train loading effects on soil behavior and provides critical guidance for tunnel design optimization.

Optical Absorption in Hexagonal-Diamond Si and Ge Nanowires: Insights from STEM-EELS Experiments and Ab Initio Theory.

Hexagonal-diamond (2H) group IV nanowires are key for advancing group IV-based lasers, quantum electronics, and photonics. Understanding their dielectric response is crucial for performance optimization, but their optical absorption properties remain unexplored. We present the first comprehensive study of optical absorption in 2H-Si and 2H-Ge nanowires combining high-resolution STEM, monochromated EELS, and ab initio simulations. The nanowires, grown in situ in a TEM as nanobranches on GaAs stems, show excellent structural quality: single crystalline, strain-free, minimal defects, and no substrate contamination, enabling access to intrinsic dielectric response. 2H-Si exhibits enhanced absorption in the visible range compared to cubic Si, with a marked onset above 2.5 eV. 2H-Ge shows absorption near 1 eV but no clear features at the direct bandgap, as predicted by ab initio simulations. A peak at around 2 eV in aloof-beam spectra is attributed to a thin 3C-Ge shell. These findings clarify the structure-optical response relationships in 2H materials.

Dynamical Formation of Regular Black Holes

We study dynamical gravitational collapse in a theory with an infinite tower of higher-derivative corrections to the Einstein-Hilbert action and we show that, under very general conditions, it leads to the formation of regular black holes. Our results are facilitated by the use of a class of theories that possess second-order equations on spherically symmetric metrics, but which are general enough to provide a basis for the gravitational effective action in any D≥5. We analytically solve the collapse of a thin shell of dust and show that it inevitably experiences a bounce at small radius and that its motion can be extended to arbitrary proper time. The collapse of the shell always gives rise to a singularity-free, geodesically complete spacetime that contains horizons if the total mass is above a critical value. In that case, the shell bounces into a new universe through a white hole explosion. Our construction provides, to the best of our knowledge, the first fully dynamical description of formation of regular black holes, and it suggests that higher-derivative corrections may be the most natural way to resolve the singularities of Einstein’s theory. Published by the American Physical Society 2025

General shells and generalized functions

Abstract In this work, standard methods of the mixed thin-shell formalism are refined using the framework of Colombeau’s theory of generalized functions. To this end, systematic use is made of smooth generalized functions, in particular regularizations of the Heaviside step function and the delta distribution, instead of working directly with the corresponding Schwartz distributions. Based on this change of method, the resulting extended thin shell formalism is shown to offer a decisive advantage over traditional approaches to the subject: it avoids dealing with ill-defined products of distributions in the calculation of nonlinear curvature expressions, thereby allowing for the treatment of problems that prove intractable with the ‘conventional’ thin-shell formalism. This includes, in particular, the problem of matching singular spacetimes with distributional metrics (containing a delta distribution term) across a joint boundary hypersurface in spacetime, the problem of setting up the dominant energy condition for thin shells, and the problem of defining reasonably rigorously nonlinear distribution-valued curvature invariants needed in higher-derivative theories of gravity. Eventually, as a further application, close links to Penrose’s cut-and-paste method are established by proving that results of said method can be re-derived using the generalized formalism presented.

Analytical analysis of traveling wave vibration for rotating bi-directional dual-functionally graded carbon nanotube reinforced composite stepped thin cylindrical shells

Analytical analysis of traveling wave vibration for rotating bi-directional dual-functionally graded carbon nanotube reinforced composite stepped thin cylindrical shells

Isotropic and anisotropic radiating gravastars with various matter types of thin shell and interior

Isotropic and anisotropic radiating gravastars with various matter types of thin shell and interior

Controlled assembly engineering of Co@Co9S8-Glass micro-nano composite hollow microspheres towards microwave absorption improvement

Controlled assembly engineering of Co@Co9S8-Glass micro-nano composite hollow microspheres towards microwave absorption improvement

Primary and secondary resonance analysis of hyperelastic thin cylindrical shell under radial harmonic excitation

Primary and secondary resonance analysis of hyperelastic thin cylindrical shell under radial harmonic excitation

Full shell surface coupling along a line with non-conforming meshes

Abstract In intricate, large-scale metal structures, the modelling efficiency and flexibility are substantially limited by the requirements of finite element size, shape, edge orientation compliance and nodal alignment throughout the domain. Such limitations often necessitate the use of complex transitional meshes in intersection regions of plated components, thereby resulting in complex global mesh configurations and significantly increased computational demands. Within this backdrop, this paper presents an original and systematic methodology for translational and rotational coupling of thin plate and shell surfaces along an arbitrary 1D interface, which provides a systematic framework for: (i) geometric modelling of weld lines; (ii) coupling of regions with different mesh densities or element types within a system; and (iii) domain partitioning problems with computationally heterogeneous partitions. The methodology is based upon novel coupling element formulations, which employ principles of the mortar method for interface discretisation and an augmented Lagrangian Multiplier approach for constraint enforcement, and have been implemented for application with co-rotational Reissner–Mindlin shell elements. A series of numerical examples demonstrates the accuracy, versatility, and substantial computational and practical benefits of the developed framework for surface coupling along a line in large-scale metal structures.

Analysis of three-dimensional coupled vibration of thin shallow spherical shells using modified Kirchhoff-Love thin shell theory

Analysis of three-dimensional coupled vibration of thin shallow spherical shells using modified Kirchhoff-Love thin shell theory

Behaviour of gravastar model in mimetic gravity

Abstract In this paper, we have constructed a unique gravastar model proposed by Mazur and Mottola in the spherically symmetric stellar system under the mimetic gravitational framework with the presence of isotropic fluid source. The gravastar consists of three regions namely the interior, the shell and the exterior. In the interior region, the gravastar follows the equation of state(EoS) p = −ρ. Here we have found the non-singular solutions. The next region is a thin shell of ultra-relativistic stiff fluid having EoS p = ρ in which we have investigated several physical properties such as the proper length, energy and entropy and it is observed that all these properties are increasing with the increase in thickness of the shell. The exterior of the gravastar has been described as the Schwarzschild type. We found the matching between the surfaces of interior and exterior of the gravastar. Using the junction conditions, we have obtained the surface energy density and surface pressure which are found to be decreasing with the thickness of the shell. Moreover our gravastar model is found to be stable as we observe from the speed of sound and the entropy maximization technique. Our derived model is in accordance with the works also. Finally we have developed a stable gravastar model without singularities and devoid of any incompleteness in classical black hole theory.

S-Scheme CdS/Co₃S₄ Double-Shelled Hollow Nanoboxes for Enhanced Photocatalytic Hydrogen Evolution.

Developing S-scheme systems with high photocatalytic performance is crucial for long-term solar-to-hydrogen conversion. In this study, hollow cobalt tetrasulfide (Co3S4) nanoboxes (NBs), synthesized via sulfurization using zeolitic imidazolate framework (ZIF-67) as a template, are combined with cadmium sulfide (CdS) nanoparticles (NPs) to construct heterojunction photocatalysts under mild conditions. The optimized CdS/Co3S4 double-shelled nanoboxes (DSNBs) achieved a superior photocatalytic hydrogen production rate of 23.45mmol h-1 g-1 under visible light, approximately 24 times greater than that of pure CdS NPs. The apparent quantum efficiency (AQE) of CdS/Co3S4 DSNBs is 18.5 %. The distinctive hollow structure enhances visible-light-harvesting by exposing active sites, enabling multiple light reflections, and allowing the thin shells to shorten the transport distance for charge carriers, effectively minimizing charge recombination. The improved photoactivity results from the synergistic effects of the aligned bandgap structures, strong visible-light absorption, and interfacial interactions driven by the inherent electric field (IEF). The findings offer insights into designing efficient S-scheme heterojunction catalysts for sustainable hydrogen evolution through photocatalytic water splitting.

Tides and traversability in gravastars and other related geometries

Tidal effects related to the traversability across thin shells are examined in spherically symmetric geometries. We focus mainly on shells separating inner from outer regions of gravastars (de Sitter — i.e. [Formula: see text] — interior and Schwarzschild exterior of mass parameter M), but we also examine other related geometries by including the possibility of a negative cosmological constant and, besides, nontrivial topologies where the shell separates two outer regions. The analysis is developed for radially traversing objects and for tides in both radial and transverse directions, which present difficulties of somewhat different nature. Transverse tides across shells which satisfy the flare-out condition are the most troublesome, while shells in trivial topologies, i.e. geometries with one asymptotic region, are more indulgent with the issue of large tides. Besides, contradicting other cases analyzed in the previous works, we find that large radial tides cannot be avoided when traveling across the shell in the gravastar solution, but in nontrivial topologies they can. We study with special attention the traversability in practice of the transition layer in the thin-shell gravastar solution. In particular, a finite object which traverses radially the shell in a gravastar with [Formula: see text] undergoes a compression effect in both the transverse and the radial directions due to the tides associated to the thin layer. The results are interpreted in terms of the total momentum transfer obtained by integrating the travel time of the object.

Searching for the classical version of Hawking radiation and screening of Coulomb field by the horizon

Abstract We investigate the possibility of the existence of a classical version of Hawking radiation - solutions to classical field equations that consist solely of outgoing waves, in the spacetime of a collapsing black hole. The non-static nature of the corresponding metric results in the absence of energy conservation for matter, which could otherwise a priori prohibit such solutions. A specific and simple scenario is considered: a black hole formation as a result of the collapse of a thin shell, which is not necessarily dust-like. In the corresponding spacetime, we study solutions of the equations for a real massless scalar field that take the form of purely outgoing waves. In addition to the homogeneous equation, we also examine the case of a constant point source of the field located at the symmetry center. The general solution outside the shell is expressed in terms of the confluent Heun function, while the equations inside the shell and the matching conditions at its surface are formulated as an integral equation. The analysis of various solution asymptotics enables the reduction of the integral equation to a matrix equation, which is subsequently solved numerically.

Room-Temperature Efficient Single-Photon Generation from CdSe/ZnS Nanoplatelets.

In the search for materials for quantum information science applications, colloidal semiconductor nanoplatelets (NPLs) have emerged as a highly promising class of materials due to their interesting optical properties, such as narrow emission line widths and fast photoluminescence (PL) lifetimes at room temperature. So far, only a few works focused on the quantum properties of their emission; however, NPLs, with their atomic-scale thickness and one-dimensional quantum confinement, are promising candidates for single-photon sources. Here, we demonstrate room-temperature single-photon emission from core/shell CdSe/ZnS NPLs, which feature an 8 × 20 nm2 surface area and 1 nm shell. The limited surface area ensures effective Auger nonradiative recombination, resulting in highly efficient single-photon generation with values of photon purity as low as g(2)(0) = 0.04. The observed long-period blinking and bleaching typical of such thin shells can be easily reduced by increasing the shell thickness. This work establishes NPLs as single-photon sources that are very well suited for integration into quantum photonic systems.

Structural Health Monitoring of aerospace thin plate and shell structures using the inverse finite element method (iFEM)

Structural Health Monitoring of aerospace thin plate and shell structures using the inverse finite element method (iFEM)

The deformation mode transition of indented elastic thin shell induced by localized curvature imperfection

The deformation mode transition of indented elastic thin shell induced by localized curvature imperfection

Designing Resilient Thin Shell Structures: A Comprehensive Approach to Extreme Loading Resistance in Building Foundations

This study aims to explore the potential of thin shell structures as large foundations to improve flood resilience and enhance structural robustness. While thin shell structures have shown promise in resisting various loads, their application as foundations for buildings has not been fully investigated. Thus, this study focuses on designing the necessary reinforcement for a proposed thickness of 304mm. The reinforcement design follows Eurocode 2 guidelines, utilizing T32-300 as the main reinforcement rebar of the thin shell and 5T40 and 4T40 rebars for compression and tension of the ring beam, respectively. R12-150 links are incorporated for added strength and connectivity. This optimized design approach extends the application of thin shell structures beyond lightweight usage, making them viable for withstanding hydrodynamic and seismic loads. This advancement expands possibilities for architects and engineers and improves the resilience of buildings in flood-prone areas. Overall, this study presents a comprehensive design procedure for utilizing thin shell structures as large foundations, contributing to the development of resilient buildings capable of withstanding extreme conditions and safeguarding lives and infrastructure.

Retrieval of energy-momentum tensor for self-gravitating and collapsing thin spherical shell

Abstract We prove that the post-Newtonian time-dependent metric of the self-gravitating and collapsing infinitely-thin spherical shell does satisfy Einstein field equations to the corresponding order. Meanwhile, the leading-order components of the thin spherical shell’s energy-momentum tensor are recovered.

Sustainable Pest Management with Hollow Mesoporous Silica Nanoparticles Loaded with β-Cypermethrin

β-cypermethrin (BCP) is a broad-spectrum insecticide known for its rapid efficacy. However, it is highly toxic to non-target organisms such as bees and fish, and its effectiveness is limited by a short duration of action. Improving the release profile of BCP is essential for reducing its environmental toxicity while preserving its effectiveness. In this study, hollow mesoporous silica nanoparticles (HMSNs) were synthesized using a self-templating method, and BCP-loaded HMSNs were prepared through physical adsorption. The structural and physicochemical properties of the nanoparticles were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption–desorption analysis, Fourier transform infrared (FT-IR) spectroscopy, dynamic light scattering (DLS), and thermogravimetric analysis (TGA). The BCP release profile was assessed using the dialysis bag method. The results showed that the synthesized nanoparticles exhibited uniform morphology, thin shells, and large internal cavities. The HMSNs had a pore size of 3.09 nm, a specific surface area of 1318 m2·g−1, a pore volume of 1.52 cm3·g−1, and an average particle size of 183 nm. TEM, FT-IR, and TGA analyses confirmed the successful incorporation of BCP into the HMSNs, achieving a drug loading efficiency of 32.53%. The BCP-loaded nanoparticles exhibited sustained-release properties, with an initial burst followed by gradual release, extending efficacy for 30 days. Safety evaluations revealed minimal toxicity to maize seedlings, confirming the biocompatibility of the nanoparticles. These findings indicate that BCP-loaded HMSNs can enhance the efficacy of BCP while reducing its environmental toxicity, providing a biocompatible and environmentally friendly solution for pest control.