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In this study, an innovative hollow-core cross-laminated timber (HC-CLT) system was examined in terms of its human-induced vibration performance. Three types of HC-CLT floors were selected as the research objects, namely 3-ply HC-CLT, 5-ply HC-CLT with hollow cores along the transverse direction, and 5-ply HC-CLT with hollow cores along the longitudinal direction. By theoretical analysis, it was found that the hollow cores had a slight impact on the static bending stiffness, and HC-CLT floors had a good potential for structural applications. The HC-CLT floors were then modelled using OpenSees software to assess its dynamic performance, and experimental testing results have validated the modelling method. The HC-CLT floors were excited by single-person, two-person, and five-person slow walking, fast walking, and running. Based on the recorded acceleration at the centroid of the floor, it was realised that the vibration dose values (VDV) of the 5-ply HC-CLT floor with hollow cores along the transverse direction were not larger than those of the solid CLT floor under walking excitations. It indicated that the hollow cores were more effective to distribute along the transverse direction to assure the comfort level. However, the vibration response of the HC-CLT floor under running excitations was larger. By enhancing the beam supporting condition from the two-side to the four-side support, the vibration response of the HC-CLT floor can be effectively reduced.

This paper provides an experimental investigation to study the effect of using different types of reinforcement on the flexural behavior of ferrocement thin hollow core slabs with embedded PVC pipes. Twelve slabs of 1100 × 400 × 55 mm dimensions were casted and tested till failure. The effect of four different types of reinforcement was investigated in this study including; steel wire mesh, macro and micro steel fibers or a combination of both, steel bars and CFRP bars. The results showed that the slab reinforced with only macro steel fibers provided the highest flexural strength, while that reinforced with steel bars showed the highest stiffness and lowest deflection among all tested slabs. Also, the dry design density for all the hollow core slabs was determined to be below 2000 kg/m3 which is within the requirements of light weight concrete as set by most codes of practice.

We propose a highly sensitive hollow core photonic crystal fiber (HCPCF) for liquid sensing in the terahertz (THz) region. Asymmetrical rectangular shaped air holes in the cladding region along with Topas glass as a background material is used to get high sensitivity and low confinement loss. The full vector finite element method (FEM) is used to calculate relative sensitivity and other parameters of the proposed liquid sensor where frequency range is taken from 1 THz to 2 THz. The strut distance variations are also studied in this study to find out minimum strut length to make the proposed sensor fabrication friendly. Numerical analysis shows the maximum relative sensitivity of 91.42% for water, 92.55% for acetic acid and 94.03% for chloroform at optimal conditions along with the minimum confinement loss of 1.06 × 10−9cm−1 for water, 2.02 × 10−10cm−1 for acetic acid and 1.39 × 10−11cm−1 for chloroform. To the best of our knowledge, the proposed HCPCF sensor shows maximum relative sensitivity for liquid.

The use of industrialized elements results in the speed of execution, it avoids waste of materials, and it meets sustainability requirements. The steel profiles and hollow core slabs are included in this scope. The hollow core slab presents superior quality than cast in-situ structural elements, and it is produced in specific environments with technological control and monitoring. In general, a concrete topping is made for smooth and uniform finishing. Studies addressing the structural behavior of steel-concrete composite beams with hollow core slabs with concrete topping are scarce. The present work aims to investigate the behavior of steel-concrete composite beams with hollow core slabs with concrete topping, considering full and partial interaction. Geometric nonlinear analyses are performed based on experimental tests. The steel-concrete composite beams with hollow core slabs with concrete topping are simply supported and subjected to two points loads symmetrically spaced. The influence of concrete topping (50 mm of thickness), the in situ concrete strength (25 MPa, 30 MPa and 40 MPa), the transverse reinforcement diameter (10 mm, 12.5 mm and 16 mm), the interaction degree (shear connectors spaced at 120 mm, 175 mm and 225 mm), and the steel cross section (W360 × 51, W460 × 74 and W530 × 72) are the parameters investigated. The results are discussed, considering these parameters. It was concluded that the concrete topping increased the strength of the composite beams with precast hollow core slabs, the lower the degree of interaction, the greater the ductile behavior of the composite element as a whole. The in-situ infill concrete strength was directly influenced by the steel cross-sectional area, transverse reinforcement rate and interaction degree. The resistance of steel-concrete composite beams with precast hollow core slabs may vary depending on the transverse reinforcement rate and interaction degree. Ductile behavior was observed for all situations, considering partial interaction.

High-voltage LiNi0.5Mn1.5O4 hollow microspheres are synthesized through a static co-precipitation method. The LiNi0.5Mn1.5O4 microspheres are composed of the spherical micron-sized particles with hollow core, and it has a cubic spinel structure with a space group of Fd3m. Electrochemical results demonstrate that the prepared LiNi0.5Mn1.5O4 exhibit excellent cycle stability and rate capability. The LiNi0.5Mn1.5O4 materials with hollow microsphere structure and excellent electrochemical properties are expected to be used in high energy density lithium-ion batteries.

This article discusses the blast response of reinforced concrete hollow core slabs (RCHCS) with a topping layer subjected to a close distance explosion and investigates the efficiency of carbon fiber reinforced polymer (CFRP) as externally bonded reinforcement (EBR) in order to improve the blast resistance of the slabs. Three simply supported RCHCS with a topping layer are subjected to an explosion of 1.5 kg of C4 suspended at mid-span, underneath the slabs at a standoff distance of 0.5 m. One of the slabs is used as a reference specimen and the two remaining ones are retrofitted with different amounts of CFRP. A numerical analysis is also carried out using the finite element (FE) software LS-DYNA to complement the experimental results of the blast campaign. The results indicate that bonding CFRP strips on the surface opposite to the explosion is an effective way to reduce the mid-span deflections and to limit the damage levels in the slabs. A reduction of 16% and 30% in the maximum deflection is recorded for the RCHCS retrofitted with 2 strips and 4 strips, respectively. Longitudinal cracks between the voids are observed on the lateral sides of the slabs due to the propagation of the blast wave through the concrete. These longitudinal cracks, extending with a vertical crack, trigger local debonding between the CFRP strips and the concrete during the explosion. Maximum deflections and crack distribution predicted by the numerical analysis are in a good agreement with the experimental results.

In this study, a low-loss hollow-core photonic bandgap fiber (HC-PBF) with an isolated anti-resonance layer is proposed. The fiber cladding structure is the same as that of conventional HC-PBF, while the fiber core is surrounded and formed by an isolated anti-resonance layer which separates the core from the cladding. Simulation results show that the overlap between the fundamental mode and silica-air interfaces is dramatically reduced owing to introduction of the isolated anti-resonance layer, and the fiber loss lower than 3.5 dB/km can be achieved with only ∼ 13- μ m core diameter and ∼ 8- μ m mode field diameter at 1550 nm

Spectral broadening of a radially polarized (RP) pulse in a gas-filled hollow-core fiber (HCF) is experimentally studied. Broad spectrum covering from 540 nm to 1070 nm is obtained. It is found that the output spectrum preserves the RP state after nonlinear propagation in HCF, both for the components in the input pulse and for the newly generated spectral portion. This method shows great potential in generating RP sources with unprecedented spectral width, and may also be extended to other kinds of cylindrical vector beams.

The Dirac mode in the hollow core photonic crystal fibers (HC-PCFs) traditionally rely on high refractive index glasses with a high air-filling factor. In this paper, the Dirac mode was observed in the modified honeycomb lattice HC-PCFs, which breaks the constraint of refractive index, and can be realized in pure silica glasses for the first time. The band structure of the modified honeycomb lattice was calculated to elaborate the formation process of the Dirac point. The Dirac mode in the HC-PCFs was established at the Dirac frequency outside the bandgaps. In addition, the relationship between the Dirac frequency and the air-filling fraction and the refractive index were also analyzed. This design provides a modified honeycomb lattice HC-PCFs with substantially reduced fabrication effort and expands the application of Dirac mode in the conventional silica-based optical fiber devices.

The Ti3+ self-doping B-TiO2/g-C3N4 hollow core-shell nano-heterojunction is synthesized via the continuous hydrothermal deposition and sculpture-reduction processes. The results of SEM, XRD, TEM, XPS and FT-IR imply that the B-TiO2/g-C3N4 hollow core-shell nanospheres have been prepared successfully. The photocatalytic activity of the B-TiO2/g-C3N4 nano-heterojunctions remarkably exhibits an enhancement of 18 times and 65 times than that of normal TiO2 and g-C3N4, respectively. Further, the photocatalytic process and the mechanism of the photocatalytic hydrogen production enhancement have been studied, which could be ascribed to the Ov-Ti3+ in the B-TiO2 and interface nano-heterojunction, that have been proved by the transient photocurrent, PL, EIS and Mott-Schottky plots.

We propose polarization-maintaining few-mode elliptical hollow-core optical fibers with simple triple-layer structure toward space-division-multiplexing based high-capacity optical communication systems. The proposed fibers include a central elliptical air hole, a concentric elliptical ring core and a circular cladding. The structure-dependent polarization-maintaining performance is comprehensively investigated via numerical simulations. With appropriate structural parameters, 10 distinct polarization-maintaining modes can be guided in this fiber. The effective refractive index differences (Δneff) between all adjacent modes are beyond 1.93 × 10−4 at 1550 nm, and the values are higher than 1.8 × 10−4 over 1510–1630 nm. The modal chromatic dispersions are analyzed subsequently. Furthermore, the number of guided polarization-maintaining modes can be expanded to 14 with modified structural parameters meanwhile keeping all Δneff values no less than 1.33 × 10−4 in range of 1510–1630 nm.

Fragmentation characteristics are the key parameters to assess the damage efficiency, as well as the risks in potential accidents, of a warhead with a hollow core. However, limited work has been conducted to predict the fragment distributions along the axis of novel warheads with hollow cores. In the present work, the fragment distributions and fragment velocity distributions of warheads with different sizes of hollow cores were determined by the processing of witness plates and a flash-radiography method respectively. It was found that the variation of fragment velocity along the axis of cylindrical casing near the detonation end decreased and the fragmentation along the axis of cylindrical casing near the detonation end became more uniform with the increase of the diameter of cylindrical hollow core. The variation of fragment velocity along the axis of cylindrical casing near the non-detonation end slightly increased, and then decreased with the increase of the diameter of cylindrical hollow core. The fragmentation near the non-detonation end did not change significantly because of the short effect distance of the rarefaction wave from the non-detonation end along the axis of the casing. Based on the fragment velocities along the axis, a modified formula including the effects of the rarefaction waves from the hollow core and the ends of explosive charge was established and validated experimentally and numerically. The results indicate that the proposed formula is accurate and reliable in predicting the fragment velocity distribution along the axis of novel warheads filled with hollow-charge and detonated at one end.

Hollow core slabs are widely used in prefabricated buildings either as slab elements or bridge decks because of their economic benefits. However, little attention has been given to developing strengthening techniques that are especially suitable for hollow core slabs to recover or improve the original serviceability and load carrying capacity. In this study, two novel techniques for strengthening hollow core slabs with mounted steel bars and prestressed steel wire ropes (P-SWRs) were proposed. Six slab specimens were tested to failure under a four-point bending configuration, and the strengthening effects of the mounted steel bars and P-SWRs on the hollow core slab performance were studied. The experimental results indicated that the steel bars mounted in the cores were capable of enhancing the flexural performance of the hollow slabs. The prestressing technique and anchorages developed in this paper could be used to feasibly and easily prestress the steel wire ropes. P-SWRs were found to be more efficient in improving cracking load than mounted steel bars because of the prestress in P-SWRs. External P-SWRs were better at improving the cracking load, yield load and precracking stiffness compared with internal P-SWRs. The simultaneous use of both internal and external P-SWRs obtained the highest flexural capacity. A three-dimensional finite element (FE) model was developed incorporating the smeared-crack model for concrete and elastic-linear strain hardening model for steel. The validity of the FE model was verified through comparisons with experimental results. Thus, this study provides both experimental evidence and finite element model for the application of the proposed strengthening techniques for hollow core slabs.

A hollow-core fiber with nested anti-resonant node-free cladding tubes suitable for broadband THz guidance with low transmission losses is proposed. It is shown that the tube separation and tube thickness of the inner elements have a significant effect on the confinement loss and effective material loss of the fiber in the THz band. Using TOPAS copolymer, the proposed fiber was optimized for operation at 1 THz and it is predicted from numerical simulations that loss can be reduced to as low as 0.05 dB/m with a 0.6 THz wide dispersion flattened bandwidth. 426 477 482

An experimental investigation on developing prestressed hollow core slabs (HCS) using self-compacting concrete (SCC) has been conducted at King Saud University with the collaboration of industrial partner. The investigation includes short and long term behavior of the developed SCC-HCS. This paper presents the long term deflection of the developed slabs. Six full-scale HCS were manufactured and tested. Four of the slabs were produced using SCC while the remaining two slabs were produced using the dry cast concrete (DCC) technique for the sake of comparison and verification. The HCS were tested under sustained uniform load for a period of 730 days. The study was carried out on two slab sizes: 300 mm and 470 mm thickness. The long term deflection of the slabs was compared with the predictions of the effective modulus approach considering the creep and shrinkage models prescribed by ACI 209 Committee. SCC-HCS units showed comparable long term deflection behavior to that of DCC-HCS units. The effective modulus approach along with ACI 209 creep and shrinkage coefficients were found to reasonably predict the additional long term deflection of the slabs.

In this work, we present the first demonstration of a gas sensor utilizing the Wavelength Modulation Spectroscopy technique and a mid-IR guiding Antiresonant Hollow-Core Fiber with a record length of 30 m. The self-fabricated ARHCF was used as an air-tight, low-volume absorption cell delivering an extended laser-gas molecules interaction path within the sensor’s setup, which enabled it to efficiently detect ethane at 2996.88 cm−1. Benefiting from the unique guidance properties of the ARHCF, the sensor reached a minimum detection limit of 670 parts-per-trillion by volume for 14 s integration time, which is at a level comparable to the bulk optics-based systems utilizing more complex detection techniques or multipass cells with tens of meters long optical path lengths. The obtained results confirm that ARHCF-based gas sensors can successfully compete with or even outperform bulk optics-based mid-IR gas sensor configurations. The obtained results show the potential for the development of novel, low-volume, compact, and reliable types of gas detectors allowing precise analysis of various gaseous substances at their trace concentration level.

Core-shell semiconductor nanostructures can be suitable for high-performance gas sensors due to their unique structural features. In this study, In2O3@ MoO3 core-shell hollow spheres were synthesized by a facile two-step solvo-thermal method, followed by post-heat treatment. The synthesis results in 20-nm thick MoO3 shells coated on In2O3 hollow spheres (200-nm diameter). The effects of the morphology and composition on gas sensing performance were systematically investigated by adjusting the molar ratio of In to Mo. The sensing tests suggest that the core-shell structure with the In to Mo molar ratio of 1:1 exhibits the highest sensing response (28.1) towards 100-ppm n-butylamine at the optimized working temperature of 300°C. This response is two times higher than that of the In2O3 & MoO3 binary mixture (11.1) and five times than that of the pristine In2O3 hollow spheres (4.8). The sensing performance is a result of the unique core-shell structures including both the catalytic reaction mechanism of MoO3 and the co-catalytic properties of the In2O3 hollow spheres. This study may shed light on the design of practical, high-performance amine gas sensors in the future.

Recent studies raised a concern about the compaction quality of concrete of deep hollow core slabs (HCS) during the fabrication process using the dry extrusion method. Due to its specific properties, self-compacting concrete (SCC) can serve as a practical solution to such a problem by producing HCS using SCC. However, the structural behavior of such slabs should be examined and verified before the acceptance of SCC in such an application. This paper investigates the structural behavior of SCC-HCS. In addition to the development of HCS using SCC, the study also included flexural and shear tests on the developed slabs. A total of 8 full-scale HCS including two sizes of 300 mm and 470 mm thickness were constructed and tested up to failure. The slabs comprised 4 specimens fabricated using SCC and 4 specimens using the dry cast concrete (DCC) technique for the sake of comparison and verification. Also, 4 of the specimens were tested in flexure and the other 4 were tested in shear. The outcomes of this investigation showed that the structural behavior of SCC-HCS was comparable to that of DCC-HCS. Furthermore, both flexural and shear capacities of SCC slabs were conservatively predicted by the relevant ACI 318-14 design expressions.

We present a polarization-maintaining photonic bandgap fiber (PBGF) in terahertz (THz) regime, consisting of a quasi-elliptical hollow-core (QEHC) and triangularly arranged hexagonal holes in cladding. Thanks to the specially designed core shape, the QEHC-PBGF can support two stable polarization-maintaining fundamental modes. From numerical simulations, birefringence, confinement loss and group velocity dispersion of the fundamental mode group are 9.4 × 10−4, 3 × 10−3 cm−1 and 0.39 psTHz−1 cm−1 at 0.9 THz, respectively. Moreover, we investigate the fiber fabrication tolerance in the context of polarization-maintaining and confinement performances. The proposed QEHC-PBGF is anticipated to be useful in polarization sensitive THz applications.

Prestressed precast hollow core slabs (PPHCS) are commonly used as floor elements in the precast buildings. These slabs could crack due to various reasons and can affect the overall integrity of the structure. Also, tension stiffening of concrete in PPHCS is not as effective due to the absence of additional reinforcement other than prestressing strands and the transition between a flexurally ‘uncracked’ and flexurally ‘cracked’ section is rapid. Therefore, strengthening of such cracked slabs is essential for ensuring its adequate performance. Effect of FRP strengthening of hollow core slabs is relatively well established. However, the effect of hybrid strengthening on the behavior of pre-cracked hollow core slabs is not fully understood yet. The performance of pre-cracked hollow core slabs strengthened with near surface mounting (NSM) of carbon fiber reinforced polymer (CFRP) laminates, and hybrid strengthening is investigated. Hybrid strengthening includes a combination of concrete bonded overlay in the compression zone and NSM CFRP laminates in the tension zone. A total of eight full-scale hollow core slabs are tested at two different shear span (a) to the depth (d) ratios of 3.75 and 7.50. Before strengthening of the hollow core slabs, the slabs were pre-cracked by applying the load equal to 65% of its ultimate capacity. Strengthening by NSM technique increased the ultimate capacity of the slabs by 50% whereas hybrid strengthening increased the strength by 130% when compared to pre-cracked control specimens. Finite element (FE) models were developed and calibrated to predict the behavior of tested hollow core slabs. Peak load predictions obtained from the finite element analysis had good correlation with the test results.

This paper presents an experimental investigation on the behaviour of hollow core Reactive Powder Concrete (HCRPC) columns confined with a circular Carbon-Fibre-Reinforced polymer (CFRP) tube. Sixteen circular hollow core specimens (206 mm in diameter, 800 mm in height and a 90 mm circular hole) were made with Reactive Powder Concrete (RPC) of 105 MPa compressive strength. These specimens were divided into four groups. The first group was the control group that consisted of four unconfined HCRPC specimens reinforced with conventional longitudinal steel bars and steel helices. The specimens of the second group had the same configuration as the first group except that these specimens were externally confined with CFRP tube. The specimens of the third group were externally confined with a CFRP tube and internally confined with a Polyvinyl chloride (PVC) tube. Finally, the specimens of the fourth group had no steel reinforcement and were only made with an external CFRP tube and an internal steel tube. These specimens were subjected to different loading conditions: concentric, eccentric (25 mm and 50 mm) and four-point bending. It was found that the CFRP tube confinement slightly increased the strength of the HCRPC columns, whereas the ductility was significantly enhanced. In addition, by introducing the PVC tube as internal confinement to the hollow columns the ductility was also improved.

Fiber enhanced Raman spectroscopy (FERS) is a powerful multigas analysis technique. It combines the unmatched analytical prowess of Raman spectroscopy with the enhancement of small signals through the sophisticated use of hollow core optical fibers. Consequently, FERS is highly selective and very sensitive and as an optical technique label-free, non-invasive, and fast. Hollow core photonic crystal fibers and metal coated capillaries provide enhancement based on the confinement of guided light and gas. The technique allows the unambiguous identification and quantification of various gas mixture components, including hydrogen and nitrogen. The resulting versatility opens a broad range of applications for FERS. Several examples of medical gas sensing are reported. Furthermore, FERS gas sensing is applied in industrial and environmental process monitoring. Newly developed optical fibers and further advances in the field might increase sensitivity and stability.

In this report, we present a numerical study of the Stokes amplification in the complex transient regime in gas filled hollow-core photonic crystal fibres (HC-PCFs). The temporal and space evolution of pump, Stokes fields are described in detail. Moreover, the complex process of population inversion and coherence are also insightfully discussed.

This study experimentally investigated the behavior of glass fiber-reinforced polymer (GFRP) reinforced hollow-core concrete specimens under concentric axial compression . The effect of the type of concrete (non-fibrous concrete, i.e., normal concrete without the addition of fibers; polypropylene fiber concrete; and glass fiber concrete) and pitches of the GFRP helices on the behavior of GFRP bar-reinforced hollow-core concrete specimens were investigated. The experimental program consisted of seven circular hollow-core specimens with an outer diameter of 214 mm, an inner circular hole diameter of 56 mm, and a height of 850 mm. The failure modes, axial load carrying capacity, and ductility of GFRP bar-reinforced hollow-core concrete specimens were investigated. The experimental results showed that, for a similar amount of reinforcement, the GFRP bar-reinforced hollow-core polypropylene fiber concrete (GFRP–HC–PFC) specimen achieved 2% higher maximum axial load and 19% higher ductility than the GFRP bar-reinforced hollow-core non-fibrous concrete (GFRP–HC–NFC) specimen. For a similar amount of reinforcement, the GFRP bar-reinforced hollow-core glass fiber concrete (GFRP–HC–GFC) specimen achieved 14% lower maximum axial load but 9% higher ductility than the GFRP–HC–NFC specimen. The axial load carrying capacity and ductility of the specimens enhanced with the close pitch of the GFRP helices. A simplified equation was developed for GFRP bar-reinforced hollow-core concrete columns, which predicted the axial load capacity of the specimens with reasonable accuracy.

The unique design of hollow-core photonic crystal fibers (HC-PCFs) has attracted a lot of researchers’ attention. Their hollow-core structure with low transmission loss allow strong light-gas interaction inside the fiber, making HC-PCF a strong candidate as portable gas cells for sensing or spectroscopic purposes. Gas-filled HC-PCFs also have applications in the study of Raman scattering (SRS) transient regime and waveguides research. Considering the design of the cell, it is important to understand the gas flow dynamic, for example, estimate the evacuation or gas filling time for a certain length of fiber. In this paper, the gas dynamics theory and the comparison between single- and double-end pumping in special HC-PCFs is investigated. For two different types of HC-PCFs, our experimental data verified the trend for pressure decrease during the evacuation process was consistent with the theoretical prediction. After adding a correction factor, which represents the hollow-core structure of the fiber, to the existing model, the simulation results matched well with the experimental observation.

Due to their low self-weight and high strength, precast and prestressed hollow core concrete slabs are widely used in construction. However, the combination of low self-weight and long span implies that the slabs are sensitive to vibrations induced by human activities. In this work, experimental tests and numerical analyses are performed in order to understand the dynamic behaviour of hollow core concrete floors. For the experiments, a test floor of dimension 10 m × 7.2 m and consisting of 6 hollow core elements was built. Very good agreements between experimental and numerical results have been obtained. Comprehensive numerical parametric analyses have been performed in order to determine the optimal value of the material parameters.

This study reports tests of prestressed concrete hollow-core slabs strengthened with externally-bonded laminated bamboo plates. The strengthened slabs are provided with varying ratios of externally-bonded laminated bamboo plate reinforcement having different widths and thicknesses. Structural performance is reported and the relationships between flexure and shear failure modes are described allowing guidance for the design of such externally-bonded laminated bamboo-strengthened hollow-core slabs. The low stiffness of the laminated bamboo helps to mitigate debonding, allowing the strength of the laminate to be fully developed. Both the load bearing and deformation capacities of the slabs are improved with strengthening. A value of equivalent steel reinforcing ratio (accounting for both internal prestressing wire and externally bonded bamboo laminates) ρs,eff = 0.0083 was determined to be the threshold between flexure- and shear-dominated failures. Using simple fundamental analysis, the behavior of the strengthened hollow-core slabs was easily and reliably predicted.

A silica microcapillary preform and a hollow-core anti-resonant optical fiber doped with small-size (

The European Corn Borer (ECB), Ostrinia nubilalis, is an agricultural pest which bores small holes in the rind of maize stalks and then proceeds to consume the pith. Because most of the damage to the stalk is internal, it is difficult to quantify the damage to an individual stalk without time-consuming, manual examination. This work focused on determining the feasibility of detecting internal damage using non-destructive, electrical measurements. Laboratory experiments and numerical simulation studies predicted changes in capacitance of stalks due to hollow core ECB damage. A guarded probe device to measure electrical impedance from 500 Hz to 100 kHz was designed and constructed for data collection. A field test with the measurement device was conducted and frequency-swept impedance measurements were taken on field-grown plants with and without ECB damage. Field measurements demonstrated that statistically significant capacitance changes associated with ECB damage could be detected in agreement with numerical simulations of stalk damage. Numerical, laboratory, and field test results all supported the hypothesis that electrical impedance measurements, in particular, capacitance, provide a promising new avenue for ECB damage evaluation. While further research will be needed to further refine this concept, this measurement approach is non-destructive, thus allowing measurements to be performed without sacrificing the infested plants.

A laser beam carrying object information will become a random speckle pattern as it propagates through a hollow core fiber (HCF) of large inner diameter. We propose and experimentally demonstrate a technique that employs the convolutional neural network (CNN), which is one type of deep learning, for image reconstruction from the random speckle pattern. In the experimental demonstration, 4000 speckle images and 4000 corresponding original images are used to train CNN, and 1000 speckle images are used to test the trained CNN. The experimental results demonstrate the possible realization of deep learning for the image reconstruction through the HCF. Furthermore, the influence of the diameter and length of HCF on the fidelity of the image reconstruction is quantitatively investigated by determining the accuracy and Pearson correlation coefficient (PCC).

Prestressed hollow core slabs are widely used in precast construction. The objective of this study is to understand the efficiency of hybrid strengthening technique at different levels of flexure to shear or shear span (a) to depth (d) ratios. Hybrid strengthening technique includes bonded overlay on the compression side and carbon fiber reinforced polymer (CFRP) composites on the tension side. Two different techniques are employed for the application of CFRP composites namely Near Surface Mounted (NSM) or Externally Bonded (EB). Fourteen full scale prestressed precast hollow core slabs were strengthened using different combinations of these techniques and tested at low (a/d = 3.75) and high (a/d = 7.50) shear span to depth ratio. The bonded overlay strengthening increased the peak strength by 59.2% and 89.0% respectively at low and high shear span to depth ratios. The externally bonded strengthening solely increased the peak strength by 16.9% and 87.6% at low and high a/d ratios, respectively. The NSM strengthening increased the peak strength by 49.4% and 68.9% at low and high a/d ratios respectively. Hybrid strengthening resulted in the best performance with highest increase in peak strength at both a/d ratios without a significant reduction in the ultimate displacement.

An original concept of Slimfloor structure made of hollow core slabs with structural concrete topping and post-tensioned delta-shaped beams is given in the paper. The technological assumptions and the results of computational analysis for this solution are also discussed. Multi-span continuous prestressed beam can significantly increase length of the span of the Slimfloor ceiling and at the same time keeps its primary asset - almost flat bottom surface - creating the ideal solution for the demanding projects.

Risk management assists the practitioners in manufacturing industries to determine types of risk and the best way to treat the risk. Source of risk and the uncertain condition following the risk can be predicted, as well as the impacts of risk and the solutions to overcome the risk. Identifying potential failure and the impact of risk are considered as an important fields in research on risk management. This study was focused on identifying strategy to overcome the risk in the fabrication process of hollow core slab using. Failure Mode and Effect Analysis method will be implemented in this study in order to achieve the aim of this study. This study found 23 failure modes and the highest risk priority is the realizing-agent spraying which is not evenly distributed on the mold in mold cleaning process. The strategy to overcome this failure mode risk is to spray the releasing-agent two layers. Meanwhile the most frequent failure mode is the overhead-crane hoist-cable broken off and machine breakdown. The strategy to overcome this failure mode is to employ mechanical engineer to carry out regular inspections and maintenance.

This paper presents an investigation of the deformations and damage modes, which occur in reinforced concrete (RC) or prestressed concrete (PC)hollow core slabs subjected to blast loads. This study focuses on four tests which have been performed on hollow core slabs with a compression layer, simply supported, subjected to explosions with different standoff distances for a constant charge weight. The paper discusses the numerical analysis carried out using the finite element software LS-DYNA. The results indicate that the appearance and growth of flexural cracks in concrete is delayed effectively by using prestressing. Moreover, prestressing decreases the deflection at mid-span of the tested hollow core slab and reduces the oscillation period due to the increase of the flexural stiffness and resistance of the hollow core slabs.

The total weight of the building is greatly influenced by the self-weight of the reinforced concrete. The hollow core slab is one of alternatives to reduce its self-weight. On the other hand, with advancements in the quality of materials, workmanship and new technologies, precast concrete has become popular in the construction industry. This study discusses the flexural behavior of precast hollow core slab with different type of reinforcements. The test specimens consist of a solid slab as a reference slab, a hollow core slab type 1 (using PVC pipe to create the cavities), and a hollow core slab type 2 (using styrofoam to create the cavities). The diameter of steel reinforcements used in this study are 10 mm plain and deformed bars, 12 mm plain bars, and 13 mm deformed bar. The slab thickness was 12 cm. The results showed that hollow core slab type 1 and type 2 can reduce the weight by 24% and 25% as compared to the solid slab. Flexural strength of hollow core slab type 2 is higher than the hollow core slab type 1. However, it is lower than the solid slab with all variations in reinforcement diameter. The value of flexural stiffness of the solid slab is greater than hollow concrete slab type 1 and type 2. Cracks that occur in solid slab are distinguished as flexural crack, while the cracks that occur in the hollow core slab type 1 and type 2 are shear cracks.

High strength fusion splicing hollow core photonic crystal fiber (HC-PCF) and single-mode fiber (SMF) requires sufficient energy, which results in collapse of the air holes inside HC-PCF. Usually the additional splice loss induced by the collapse of air holes is too large. By large offset reheating, the collapse length of HC-PCF is reduced, thus the additional splice loss induced by collapse is effectively suppressed. This method guarantees high-strength fusion splicing between the two types of fiber with a low splice loss. The strength of the splice compares favorably with the strength of HC-PCF itself. This method greatly improves the reliability of splices between HC-PCFs and SMFs.

Nanopipes associated to screw dislocations are studied by transmission electron microscopy in Si-doped GaN films grown on silicon substrates. The observations revealed that dislocations had an empty core and that an AlN interlayer is suited to block their propagation. The termination mechanism is discussed in terms of strain and kinetic growth factors, which may affect the creation and propagation of nanopipes. According to the observations, it is proposed that either step pinning or lateral overgrowth occurring at the proximity of the defect assists in capping the nanopipe.

Gas sensors play an important role in the increasing trend of industrial automation in recent years. Hollow core microstructured optical fibers have become a popular material for gas sensors because of their unique structure and excellent performance. In this paper, the hollow-core microstructured optical fiber gas sensors are divided into two types (interferometric type and absorptive type) according to the sensing principle. The corresponding principles and structures are introduced and discussed respectively. We focus on the research progress and key performance of hollow core microstructured optical fiber based gas sensors reported in the past 10 years to compare and discuss their advantages and disadvantages, as well as their future development prospects.

We demonstrate an in-line polarization controller for hollow core photonic bandgap fiber made by inserting a length of the fiber into a standard, off-the-shelf, 3-paddle controller as widely used for polarization control using standard single mode fibers. Although the operational principle of this 3-paddle controller is very different when using hollow core photonic bandgap fiber rather than SMF effective polarization control is readily achieved.

In this paper, the noise characteristics of Hollow Core Photonic Crystal Fiber (HC-PCF) Interferometer fiber-optic gyroscope (IFOG) which contains the optical fundamental noise, the electronic circuit noise and the backscattering and back-reflection noise induced by HC-PCF is analyzed. A random walk coefficient model for closed-loop HC-PCF IFOG based on the noise power spectrum density is built. Taking into account the correlation modulation and demodulation method used in closed-loop gyro, for different noise sources, the noise power spectrum density at different frequencies are used in the model. Using the model, the main noise source in HC-PCF IFOG is determined. For a HC-PCF IFOG with RWC equals 6.3 × 10−3°/√h, the RWC induced by backscattering and back-reflection noise is 5.2 × 10−3°/√h, account for 67.8 % of the overall RWC. Moreover, a HC-PCF IFOG parameters optimal method is proposed based on the model, which can decrease the random walk coefficient by a factor of 17 %.

For the first time, herein, we report the theoretical investigation on short and elongated photonic nanojets (PNJs) generated by single solid/hollow core-shell microparticles illuminated with focused Gaussian beams (FGBs). This investigation is carried out using developed analytical equations based on Bromwich formalism. The effect of the beam waist, thickness of shell, size and refractive index of the microparticle on the characteristic parameters of the PNJs such as maximum electric field enhancement, spatial separation between the PNJs, and length of the PNJs is studied in detail. The electric field enhancement values of the PNJs upon FGB illumination are compared to those obtained from the plane wave illumination.

Precast hollow-core concrete (HC) slabs are widely used in construction, especially in Nordic countries. The combination of prestressing and low self-weight due to the voids makes it possible to build long-span floors. However, this also implies that the floors become more sensitive to vibrations from human activities, and consequently a finite element model of the floor is often necessary in order to perform a dynamic analysis. However, there are no guidelines or recommendations to implement such finite element models for HC floors. In this paper, six in-situ dynamic experiments performed in 4 buildings are presented. For each case, several finite element models have been implemented and tested. These analyses show that the orthotropic shell model for the HC floor proposed by the authors in a previous publication gives good results in all the studies. The results also indicate that the concrete walls or the steel beams and columns surrounding the floor should be incorporated in the finite element model in order to get accurate results. Besides, in some cases, the floors below and above must be modelled in order to catch all the eigenmodes. The influence of the non-bearing internal walls is also discussed.

A general design method is provided to predict the load distribution at serviceability condition in hollow-core floors formed by precast units linked together through cast in place reinforced concrete joints. Each panel forming the floor is schematized as a Saint-Venant beam connected to the others by means of rotational hinges. In this way, the only unknowns of the solving system, characterized by an exponential dichotomy, are represented by shear forces transmitted along joints. The model is first validated through comparisons with significant experimental results available in the literature, and subsequently applied to the construction of design charts to be used in current practice. These latter are also compared with the provisions on load distribution effects suggested by European Standard UNI EN 1168, pointing out some limitations of current design procedures and suggesting possible improvements.

Hollow-core masonry block walls and precast concrete slabs can be used for active thermal energy storage to assist space heating and cooling by circulating air through their hollow-core space. This Building-Integrated Thermal Energy Storage (BITES) approach can provide a significant amount of effective mass for relatively fast thermal energy storage and release. Furthermore, it integrates several building functions into one building fabric component. Hence, it can significantly improve buildings’ thermal performance while saving overall cost and room space. This study explains the benefits of using ventilated BITES systems, such as effective use of materials and enhanced thermal performance. The characteristics and thermal performance of three system configurations that have airflow to zone are presented. These three configurations can significantly enhance the thermal coupling between a ventilated BITES and its zone, and hence can enhance the thermal performance of the zone. Qualitative and quantitative comparisons of thermal performances between different configurations with and without airflow to zone are presented. This study also investigates a practical approach for applying ventilated BITES in buildings-using standard hollow-core masonry blocks and precast concrete slabs. The thermal properties of these standard construction units and their potential variations are investigated, and some design considerations are presented. The walls and slabs of interest include structural or non-structural masonry block walls and structural precast concrete slabs.

Objectives The present study evaluated the long-term dentine bonding effectiveness of five universal adhesives in etch-and-rinse or self-etch mode after 12 months of water-ageing. Methods The adhesives evaluated included All-Bond Universal, Clearfil Universal Bond, Futurabond U Prime&Bond Elect and Scotchbond Universal. Microtensile bond strength and transmission electron microscopy of the resin-dentine interfaces created in human coronal dentine were examined after 24 h or 12 months. Results Microtensile bond strength were significantly affected by bonding strategy (etch-and-rinse vs self-etch) and ageing (24 h vs 12 months). All subgroups showed significantly decreased bond strength after ageing except for Prime&Bond Elect and Scotchbond Universal used in self-etch mode. All five adhesives employed in etch-and-rinse mode exhibited ultrastructural features characteristic of collagen degradation and resin hydrolysis. A previously-unobserved inside-out collagen degradation pattern was identified in hybrid layers created by 10-MDP containing adhesives (All-Bond Universal, Scotchbond Universal and Clearfil Universal Bond) in the etch-and-rinse mode, producing partially degraded collagen fibrils with intact periphery and a hollow core. In the self-etch mode, all adhesives except for Prime&Bond Elect exhibited degradation of the collagen fibrils along the thin hybrid layers. The three 10-MDP containing universal adhesives did not protect surface collagen fibrils from degradation when bonding was performed in the self-etch mode. Conclusions Despite the adjunctive conclusion that bonds created by universal adhesives in the self-etch bonding mode are more resistant to decline in bond strength when compared with those bonds created using the etch-and-rinse mode, bonds created by universal adhesives are generally incapable of defying ageing.

In this article, under investigation is the optical pulse propagation of the transient stimulated Raman scattering (TSRS) system in gas-filled hollow-core crystal fibers. The pump and Stokes breather solutions are constructed via Darboux transformation (DT) method. Novel spatio-temporal propagation patterns of breather waves are observed. The results show that the pump and Stokes breathers not only have rich phase patterns, but also demonstrate certain complementarity.

The curvature condition of power cables is monitored by a fiber sensor based on anti-resonant reflecting guidance mechanism in hollow core optical fibers. The sensor head is simple, which only consists of a section of hollow core fiber fusion spliced between single mode fibers. Multiple transmission dips are observed in the transmission spectrum, which arise from the anti-resonant reflecting effect in the silica ring cladding. The curvature of a power wire can be detected by attaching the fiber sensor to the cable. The transmitted intensity at resonant wavelengths rises as curvature applied on the power cable increases, and a sensitivity of 3.414 dB/m-1 is achieved. The temperature response of the sensor is also investigated, and the results indicate that such a sensor has low temperature cross-sensitivity of 0.002 m−1/oC.

Precast hollow-core slabs (PHSs) are widely used in precast construction due to their relatively low dead weight and easy assemblage. Cast-in-place topping concrete (TC) is utilized to obtain composite sections and to enhance in-plane stiffness of the slab system. Shear transfer between the layers of a composite slab can be provided by the upper face roughness of PHS. However, the roughening process may not be preferred in some plants. This paper evaluates the efficiency of Z-type shear connectors applied in the interface between PHS and TC. Three dissimilar interface conditions (i.e., Z-reinforced, smooth and rough) were studied experimentally in full-scale specimens. Push-off loading was applied to evaluate the interface shear transfer capability of the specimens, and Z-type shear connectors were found to be the most effective when they are applied at each joint between PHSs. The achievements of some code equations to assess interface shear strength were also investigated, and an alteration for the interface shear capacity equation of ACI 318M is proposed.

A Zeonex based loss hollow-core anti-resonant fiber (HC-ARF) for polarization filter (PF) application in the terahertz (THz) spectral range is presented here. The finite element method, a practical and precise computational technique, is used to compute the modal properties of the designed fiber. Simulation results indicate minimum loss of 0.34 dB/m at 1.1 THz, a loss less than 2 dB/m for a large bandwidth of 460 GHz in the horizontal polarization mode (HPM) due to the inclusion of nested tubes in that direction. In addition, a 520 GHz filtering bandwidth with crosstalk higher than 20 dB can be obtained within 1 m of the proposed fiber.

Twelve shear tests were conducted on fiber-reinforced precast/prestressed concrete hollow-core (PCHC) slabs to quantify the effectiveness of polypropylene (pp) and steel fibers (hooked and high-strength/straight types) on shear resistance. Different volume fractions of pp fibers (0.11 and 0.22%) and steel fibers (0.51 and 0.89%) were investigated. The experimental results showed that there were moderate increases in shear strength with the use of pp fibers while substantial increases in shear resistance were observed with the use of steel fibers. In addition, shear strength increased with steel-fiber content. Moreover, with the same steel fiber content of 0.89%, specimens with high-strength/straight fibers exhibited superior performance in shear resistance compared to specimens using hooked steel fibers. In addition, web-shear failure occurred in the majority of specimens. However, as steel fiber content was increased up to 0.89%, in some instances, failure mode shifted from web-shear to flexural-shear failure. In addition, the 2010 fib model code formula for shear strength of steel-fiber-reinforced-concrete (SFRC) members was used to estimate shear capacity of the tested slabs using steel fibers. The calculations showed that the fib model code was overly conservative for shear-strength predictions of SFRC hollow-core slabs reported in this investigation. A semi-empirical formula to calculate shear strength of hollow-core slabs with steel fibers was proposed. It was verified using a database including the 6 shear-test results from this study and another 39 shear-tests on SFRC hollow-core slabs compiled from literature. The formula had a mean value of 1.12 for the ratio of experimental shear strength to calculated shear strength with a coefficient of variation of 0.21. Ministry of National Development (MND) National Research Foundation (NRF) The support of the National University of Civil Engineering (NUCE), Vietnam for granting the first author a sabbatical leave to carry out this research at the Nanyang Technological University, Singapore is highly appreciated. The authors also wish to acknowledge the first author’s scholarship and the funding for testing from the Singapore Ministry of National Development and National Research Foundation under L2 NIC Award No. L2NICCFP1-2013-4.