Hollow Core Research Articles

Encapsulation of Uranium Oxide in Multiwall WS2 Nanotubes.

Uranium is a high-value energy element, yet also poses an appreciable environmental burden. The demand for a straightforward, low energy, and environmentally friendly method for encapsulating uranium species can be beneficial for long-term storage of spent uranium fuel and a host of other applications. Leveraging on the low melting point (60°C) of uranyl nitrate hexahydrate and nanocapillary effect, a uranium compound is entrapped in the hollow core of WS2 nanotubes. Followingly, the product is reduced at elevated temperatures in a hydrogen atmosphere. Nanocrystalline UO2 nanoparticles anchor within the WS2 nanotube lumen are obtained through this procedure. Such methodology can find utilization in the processing of spent nuclear fuel or other highly active radionuclides as well as a fuel for deep space missions. Moreover, the low melting temperatures of different heavy metal-nitrate hydrates, pave the way for their encapsulation within the hollow core of the WS2 nanotubes, as demonstrated herein.

Numerical analysis of high-strength centrifugal precast RC hollow pipe columns using grouted corrugated duct connection: Confinement effect and ductility evaluation

High-strength centrifugal precast (HSCP) reinforced concrete (RC) hollow pipe columns using grouted corrugated duct connection (GCDC) is a novel structure form in accelerated bridge construction (ABC). Nevertheless, the confinement effect of the HSCP hollow column core concrete provided by single-layer transverse rebar and its impact on ductility is not clear. Therefore, in this paper, the confinement effect and the ductility of hollow columns is studied using finite element analysis (FEA) method. A modified model is established to evaluate the constitutive relation of the core concrete confined by single layer transverse rebar. Based on the modified model, a simplified fiber model for predicting the hysteric response of HSCP hollow pipe column using GCDC, which considers bond-slip effect in GCDC joint was developed. The results indicate that the confinement effect of HSCP hollow pipe column is sensitive to the wall thickness ratio. When the wall thickness ratio decreases, the ultimate strain of the core concrete significantly decreases, while the effect on strength is not significant. The simplified model which considers confinement effect is more accurate in predicting the ductility of HSCP hollow columns. It proves that the weak confinement effects can lead to early cracking of the inner wall of hollow columns, which leads a significant impact on the ductility of HSCP hollow columns. Based on the parametric analysis, the peak load of the hollow column increases by 16.7% when the wall thickness ratio rises from 0.1 to 0.2, but only slightly changes when the wall thickness ratio is increased beyond 0.2. The wall thickness ratio of HSCP hollow pipe columns should be set above 0.2 to ensure the strength and ductility. In addition, a ductility evaluation method and a design example were developed to guide preliminary ductile design of HSCP hollow columns.

CdS/ZnSnO3 Hollow Core–Shell Nanocubes for Photocatalytic Hydrogen Evolution and Degradation of Ciprofloxacin

CdS/ZnSnO₃ Hollow Core–Shell Nanocubes for Photocatalytic Hydrogen Evolution and Degradation of Ciprofloxacin

Multi-layered cladding based ultra-low loss, single mode antiresonant hollow core fibers

In reality, an efficient platform for high-power laser delivery is highly important, which can be justified by readily available fiber lasers, and hollow-core fiber can be the best platform for guiding high optical power over long distances. The constraints include designing new cladding geometry, which may lead to a higher laser induced damage threshold in the fiber’s structure, having low losses along with a single mode nature. This article reports a new antiresonant fiber that has a hollow core and a triple-layered cladding configuration with only circular tube elements. The effects of multiple layers corresponding to the number of tube rings in the cladding geometry are well explored, which leads to understanding the physical insight of inter-layers. In comparison to double-layered cladding elements fiber, the proposed fiber significantly reduces loss by an order of two and reveals a minimum leakage loss of 5.82 × 10−5 dB/km at the chosen wavelength of 1.06 µm through the proper arrangement of cladding elements. We achieved a maximal higher order mode extinction ratio of about 104 (indicates the excellent single mode properties) and comparatively a little bending-induced loss of 9.00 × 10−4 dB/km, when the radius of bending is 14 cm. As a result, our studies on new multilayer fiber designs are not only useful for delivering high laser power but also serve as guidelines for the experimental realization of future multilayered cladding fibers.

Investigation on performance of prestressed hollow core slabs exposed to elevated temperatures

PurposeThis study focused on identifying critical factors governing the fire response of prestressed hollow-core slabs. The hollow-core slabs used as flooring units can be subjected to elevated temperatures during a fire. The fire response of prestressed hollow-core slabs is required to develop slabs with greater fire endurance. The present study aims to determine the extent to which the hollow-core slab can sustain load during a fire without undergoing progressive collapse under extreme fire and heating scenarios.Design/methodology/approachA finite element model was generated to predict the fire response of prestressed hollow core slabs under elevated temperatures. The accuracy of the model was predicted by examining thermal and structural responses through coupled temperature displacement analysis. A sensitivity analysis was performed to study the effects of concrete properties on prediction of system response. A parametric study was conducted by varying the thickness of the slab, fire and heating scenarios.FindingsThermal conductivity and specific heat of concrete were determined as sensitive parameters. The thickness of the slab was identified as a critical factor at a higher load level. Asymmetric heating of the slab resulted in higher fire resistance compared with symmetric heating.Originality/valueThis is the first study focused on studying the effect of modeling uncertainties on the system response by sensitivity analysis under elevated temperatures. The developed model with a parametric study helps in identifying critical factors for design purposes.

High sensitivity temperature and gas pressure sensor based on PDMS sealed tapered hollow-core fiber

We use hollow core fiber (HCF) and single mode fiber (SMF) fusion splicing to form a sensor with a “SMF-HCF-SMF” structure. To improve the sensitivity of the sensor, the HCF is tapered and stretched to a waist diameter of 10 μm. Then, in order to further improve the sensitivity of the sensor to temperature and pressure, as well as the mechanical strength of the sensor, we coated a layer of polydimethylsiloxane (PDMS) thin film on the surface of the tapered HCF. When light propagates in the sensor, an anti-resonant reflection optical waveguide (ARROW) mechanism is formed. Due to the excellent thermal sensitivity and elasticity of PDMS, the transmission spectrum of the sensor will significantly drift due to changes in environmental temperature and gas pressure, achieving temperature and pressure measurement. The experimental results show that the maximum temperature and gas pressure sensitivity of the sensor reach −3.2321 nm/℃ and −22.80 nm/MPa, respectively. In addition, the sensor also has good repeatability and stability, as well as short response time. It has certain application prospects in the field of high sensitivity temperature and gas pressure sensing measurement.

Stabilizing Undercoordinated Zn Active Sites through Confinement in CeO2 Nanotubes for Efficient Electrochemical CO2 Reduction

AbstractZn‐based catalysts hold great potential to replace the noble metal‐based ones for CO2 reduction reaction (CO2RR). Undercoordinated Zn (Znδ+) sites may serve as the active sites for enhanced CO production by optimizing the binding energy of *COOH intermediates. However, there is relatively less exploration into the dynamic evolution and stability of Znδ+ sites during CO2 reduction process. Herein, we present ZnO, Znδ+/ZnO and Zn as catalysts by varying the applied reduction potential. Theoretical studies reveal that Znδ+ sites could suppress HER and HCOOH production to induce CO generation. And Znδ+/ZnO presents the highest CO selectivity (FECO 70.9 % at −1.48 V vs. RHE) compared to Zn and ZnO. Furthermore, we propose a CeO2 nanotube with confinement effect and Ce3+/Ce4+ redox to stabilize Znδ+ species. The hollow core–shell structure of the Znδ+/ZnO/CeO2 catalyst enables to extremely expose electrochemically active area while maintaining the Znδ+ sites with long‐time stability. Certainly, the target catalyst affords a FECO of 76.9 % at −1.08 V vs. RHE and no significant decay of CO selectivity in excess of 18 h.

A controllable humidity sensitivity measurement solution based on a pure FPI fiber tip and the harmonic Vernier effect

Hygroscopic films used to enhance the humidity sensitivity of fiber-optic sensors often experience material aging and nonlinear response issues. To address this issue, this study proposes a controllable humidity sensitivity measurement solution that offers a simple and cost-effective fabrication process without requiring humidity-sensitive material sensitization. The solution is based on a Fabry-Perot interferometer (FPI) fiber tip and the harmonic Vernier effect. By employing a cascade structure of single-mode fiber (SMF)-hollow core fiber (HCF)-no core fiber (NCF) with fiber grinding techniques, the FPI-based fiber sensing probe constructed a resonance cavity to detect small variations in air refractive index (RI) induced by humidity. A reference spectrum, which can flexibly control parameters, such as free spectral range (FSR), contrast, phase, and intensity, is superimposed onto the sensing spectrum acquired by the FPI fiber sensing tip. By extracting features from the internal envelope generated by the harmonic Vernier effect, the mapping relationship between the center wavelength of the inner envelope and the humidity is determined. The harmonic Vernier effect amplifies the humidity sensitivity of the fiber-optic FPI sensing tip, with the magnification factor determined by the optical path length (OPL) detuning of the created reference and sensing spectra. For the harmonic order j = 4, a humidity sensitivity of approximately 76.01 pm/% RH@ 24 ℃ was achieved without using hygroscopic material sensitization. The proposed solution offers numerous advantages and enables high-precision and high environmental reliability humidity monitoring.

Equilibrium Moisture Content of High Strength Concrete Used in Hollow Core Slabs

The aim of this study was to measure equilibrium moisture content of hollow core slabs on both hygroscopic and capillary ranges. Because of the fabrication method of hollow core slabs, concrete grades and compacting methods used in the production differ from those used with reinforced concrete structures and elements. Test samples were taken from two slabs delivered by different manufacturers. Both slabs had similar geometry and were made of C50/60 grade concrete. Hygroscopic moisture equilibrium values were determined in climate chambers. Thin test specimens were used to perform tests within a reasonable time. Hygroscopic moisture equilibrium was measured at high relative humidities (RH), from 85 to 97 % RH. These measurements could be connected to the measurements of the retention curve done by a pressure plate. Measurements done in climate chambers and by pressure plate provided coherent results within the accuracies of these two methods. The results of two concrete slabs representing two different manufacturers differed significantly from each other, indicating the deviation of hygrothermal material properties even if the studied slabs were almost identical in many respects. Measured data is especially useful in modelling as well as analysing moisture damages.

Coherent Mid-IR Supercontinuum in a Hollow Core Fiber Filled with a Mixture of Deuterium and Nitrogen

Coherent Mid-IR Supercontinuum in a Hollow Core Fiber Filled with a Mixture of Deuterium and Nitrogen

Measurement and modelling of the moisture distribution in early-age concrete in the joint of composite beam and hollow core slab

The building moisture in concrete can damage the surface material if applied too early before the excess moisture has dried out. The composite beam forms an abnormal structure at the joint of the hollow-core slab, in which the thickness of the structural concrete is almost the thickness of the entire slab. For this reason, the joint of the beam and hollow core slab must be taken into account when assessing the adequate drying of concrete structures. The considered composite beams are steel casing beams, which are casted full of concrete. To achieve a composite structure, there are holes in the sides of the casing, through which moisture from the concrete transfers to the surrounding structure. However, the drying of the concrete inside the beam is significantly limited. The level of relative humidity of the concrete inside the beam remains moderately high for a long time, depending on the quality of the concrete and, consequently, the self-desiccation of the concrete. When using concrete with a low water binder ratio, drying occurs at a level of about 85%RH as a result of self-desiccation. In the study, relative humidity in the joint was measured continuously and with instantaneous measurements. The relative humidity in the joint concrete was also monitored after the surface structure layers were installed. In addition, humidity was measured from below the surface material and continued until equilibrium was reached. The structure was simulated as a 3D model and studied using a concrete material model which takes into account the self-desiccation and the thermal dependence of the sorption. A good agreement was found to describe the effect of temperature changes on the relative humidity of concrete that can be observed in continuous measurement. In addition, a suitable prediction of relative humidity below the surface material can be achieved based on modelled relative humidity distribution before the installation of the surface structure.

Double nested dual-core negative curvature fiber polarization beam splitter

In this paper, a polarization beam splitter（PBS） based on double nested dual-core negative-curvature fiber (DNHC-NCF) is designed. Two hollow cores are constructed by eight double nested cladding tubes arranged at certain angles. The influences of structural parameters on the performances of the DNHC-NCF PBS have been studied by using the finite element method (FEM). According to the simulation results, the structure of the proposed DNHC-NCF PBS is optimized. The final results indicate that the length of the proposed DNHC-NCF PBS is 1.38 cm and the extinction ratio (ER) is less than −20 dB in the wavelength range of 1.48–1.80 µm (320 nm, covers S + C + L + U bands). Besides, the higher order mode extinction ratio (HOMER) in the wavelength range of 1.3–1.71 µm is greater than 100, showing good single-mode characteristic as well. It is believed that the proposed double nested dual-core negative curvature fiber polarization beam splitter will have important applications in the fields of optical communication system.

Statistical 3D morphology characterization of vaterite microspheres produced by engineered Escherichia coli

Hollow vaterite microspheres are important materials for biomedical applications such as drug delivery and regenerative medicine owing to their biocompatibility, high specific surface area, and ability to encapsulate a large number of bioactive molecules and compounds. We demonstrated that hollow vaterite microspheres are produced by an Escherichia coli strain engineered with a urease gene cluster from the ureolytic bacteria Sporosarcina pasteurii in the presence of bovine serum albumin. We characterized the 3D nanoscale morphology of five biogenic hollow vaterite microspheres using 3D high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) tomography. Using automated high-throughput HAADF-STEM imaging across several sample tilt orientations, we show that the microspheres evolved from a smaller more ellipsoidal shape to a larger more spherical shape while the internal hollow core increased in size and remained relatively spherical, indicating that the microspheres produced by this engineered strain likely do not contain the bacteria. The statistical 3D morphology information demonstrates the potential for using biogenic calcium carbonate mineralization to produce hollow vaterite microspheres with controlled morphologies. Statement of significanceThe nanoscale 3D structures of biomaterials determine their physical, chemical, and biological properties, however significant efforts are required to obtain a statistical understanding of the internal 3D morphology of materials without damaging the structures. In this study, we developed a non-destructive, automated technique that allows us to understand the nanoscale 3D morphology of many unique hollow vaterite microspheres beyond the spectroscopy methods that lack local information and microscopy methods that cannot interrogate the full 3D structure. The method allowed us to quantitatively correlate the external diameters and aspect ratios of vaterite microspheres with their hollow internal structures at the nanoscale. This work demonstrates the opportunity to use automated transmission electron microscopy to characterize nanoscale 3D morphologies of many biomaterials and validate the chemical and biological functionality of these materials.

Fire behaviour of hollow core slabs

The objective of our research was to develop an optimum concrete mix for fire resistance, that is usable for hollow core slab prefabrication. Small-scale and full-scale tests were done, and the results were used to calibrate a numerical model that can be used to determine the temperature and load capacity reduction of steel reinforcement. With the help of the calibrated model, the effects of geometric variables were examined. The thickness of the ridge between the cavities has no effect on the change in the maximum temperature of the protected side in the examined 30-minute range, but the minimum temperature decreased.

Deflection prediction of assembly integral steel-concrete floor voided with steel mesh boxes

Steel-concrete assembled hollow core slabs have witnessed widespread adoption in recent years owing to their inherent advantages of reduced self-weight, enhanced rigidity, and superior integrity. Nonetheless, to achieve extended spans and expedite on-site construction, further optimization of the connections and fillers in these assembled slabs is imperative, along with fortifying the overall structural performance. Therefore, this study introduces a novel variant of assembly integral steel-concrete composite floor, incorporating voids filled with steel mesh boxes, which utilizes four prefabricated slabs featuring hidden transverse and longitudinal girders and a steel frame system. Concurrently, a large-scale experiment was conducted to explore its mechanical and deformation recovery performance. The detections indicate that this innovative structure exhibits excellent integrity, as the four prefabricated components transform from individual one-way slabs into a continuous floor, facilitating the efficient transmission of forces in multiple directions. A finite element model was established to provide ideas for the research of scholars in allied domains and a fundamental framework for the subsequent parametric analysis of the structure. Building upon the analog cross-beam method, the deflection of the novel structure is calculated. The resulting discrepancy between the calculated and experimental results is merely 1.87%, attesting to the practical applicability of this method. These findings provide a solid foundation, both experimentally and theoretically, for the future design and engineering application of composite slabs, fostering the advancement of sustainable construction practices.

Design of a magnetic field and temperature fiber sensor based on Fabry–Pérot interferometer and OAM interrogation

We have designed a Fabry–Pérot interferometric fiber sensor based on the principal component analysis (PCA) assisted orbital angular momentum (OAM) interrogation for simultaneous measurement of magnetic field intensity and temperature. A hollow core fiber sandwiched between two segments of single mode fiber serving as the sensing probe, is introduced to the Gaussian interference arm. Encapsulated with magnetic fluid, the intensity and phase of Gaussian beam are highly sensitive to the variations of magnetic field and temperature, exerting a modulation on the intensity and rotation angle of OAM interferograms. A dual-parameter sensing matrix to discrimination the cross-sensitivity could be established via the PCA-assisted OAM interrogation. The minimum sensing resolutions of magnetic field and temperature are calculated as 0.06 G and 0.0079 °C, respectively.

High power Raman second stokes generation in a methane filled hollow core fiber

We demonstrate a multi-watt, picosecond pulse duration laser source by exploiting a cascaded Raman process to the second Stokes signal at a wavelength of 2.58 μm in a methane-filled Nested Anti-Resonant Nodeless fiber from a 1 μm disk laser source. A maximum average power of 2.89 W (14.45 μJ) is produced in a 160 cm length of custom-designed and in-house fabricated fiber filled with methane at a pressure of 2 bar. The impact of gas pressure and propagation distance on the second Stokes signal power are investigated experimentally. The experimental results are simulated by solving the Generalized Nonlinear Schrodinger Equation with the experiment carefully modelled by accounting for the impacts of pressure dependent gas-light interactions along the pressure gradient of the fiber. This work offers a laser source for a variety of applications as well as expanding the modelling space to methane filled fibers including pressure gradients, and nonlinear optical activity in the presence of infrared gas absorption.

Modified genetic algorithm for inverse design of anti-resonant hollow core fiber with low confinement loss

Low-loss anti-resonant hollow core fibers (AR-HCF) are important for optical communication systems, photonics-enabled sensors, and exploring nonlinear dynamics with gas-light interaction. However, the design of AR-HCF that facilitates optical pulse propagation with desirable properties remains highly intricate and time-consuming. In this work, a modified genetic algorithm (MGA) with a small dataset is presented to reduce the confinement loss (CL) of AR-HCF at the telecom wavelength. The algorithm has been modified through a non-uniform mutation process and a simulated binary crossover method to enhance its searching capability and ensure a stable convergence. The inverse design method for AR-HCF, which combines the algorithm with a full vector finite-element method based on a modal solver, can be implemented to search for approximately optimal designs. In our study, MGA is utilized to optimize the tube diameter and thickness of single-ring tubular AR-HCF and nested anti-resonant nodeless fiber (NANF) at 1550 nm. As a result, optimized ratios of 25.4% and 79.8% are achieved for a core diameter of 40 µm, respectively. In addition, MGA also provides the corresponding optimal range of fiber parameters, which is helpful for actual fabrication.

Quasi-periodic layering of linear/nonlinear materials in hollow core Bragg fiber for all-optical diode action

A novel approach to achieving an inline all-optical diode action is presented using a quasi-periodic arrangement of titanium dioxide and polydiacetylene 9-BCMU in cladding region of hollow core Bragg fiber structure. The proposed quasi-periodicity is based on Fibonacci sequences. The reflectance formula and power transmission are derived using the transfer matrix method, and their spectra are plotted for two different Fibonacci sequences. The quasi-periodicity of the structures enables the formation of multiple photonic bandgaps. An optical asymmetry is introduced at both ends of the fiber by splicing two combinations of Bragg fibers. The all-optical diode action is investigated and simulated under two conditions: both spliced Bragg fibers have identical Fibonacci sequences (symmetric combination) and different Fibonacci sequences (asymmetric combination). In the symmetric structure, light propagation is reciprocal for both ends, while the asymmetric structure exhibits non-reciprocal propagation with significantly reduced backward light 92 % less at the output compared to forward propagation. The proposed structure demonstrates a high transmitted contrast over 97 % and exhibits a nonlinear response with increasing incident light intensity at a specific wavelength (λ = 1735 nm). Furthermore, by adjusting the refractive index of the fiber core, the all-optical diode action remains nearly constant. This suggests that the proposed structure can serve as a stable inline all-optical diode in higher wavelength regions with a variable core index.

Effect of hollow structure on solar thermal applications of Au nanodiscs

Plasmonic nanoparticles (PNPs) with hollow structures have shown great potential for enhancing optical absorption. While spheres or cylinders are commonly used for PNPs, the study of hollow PNPs for direct absorption solar collectors is limited. This research investigates the impact of three different hollow structures (cylindrical – Case 1, square – Case 2, and trigonal – Case 3) on the optical absorption properties of Au nanodiscs. The findings demonstrate that the presence of hollow structures significantly enhances the photothermal conversion efficiency of Au nanodiscs. Specifically, Case 1, Case 2, and Case 3 exhibit photothermal conversion efficiencies that are 17.9%, 22.0%, and 16.8% higher, respectively, compared to standard Au nanodiscs. Notably, Case 2 demonstrates the highest optical absorption capacity and photothermal conversion efficiency among the three hollow structures. Through optimization, Case 2 achieves a remarkable photothermal conversion efficiency of 97.6%. Meanwhile, we also investigated the effect of continuously sharpening the hollow edges on the optical absorption properties of the nanodiscs. The continuous sharpening of the hollow core hampers both the enhancement of optical absorption properties and photothermal conversion properties in Au nanodiscs. Therefore, this research provides valuable theoretical insights for utilizing plasmonic nanoparticles with hollow structures to enhance photothermal conversion.