Core Diameter Research Articles

Significant changes in the physicochemical properties of BC-containing particles during the cold season in Beijing

The ambient air quality has improved significantly under strict emission controls in Beijing, China over the last decade. Black carbon (BC), as a short-lived climate forcer in ambient aerosols, profoundly impacts the air quality and climate. Previous studies have demonstrated a decline in the mass concentration of BC. In this study, we characterized the chemical compositions and size distributions of BC-containing particles during the cold season of 2022 in Beijing using state-of-the-art instruments capable of exclusively measuring BC-containing particles. The optical properties of BC-containing particles were further calculated based on the Mie theory. Moreover, we compared the properties of BC-containing particles in 2022 with the results of previous studies. The results showed that the diameters of BC cores became larger while the coating thickness of BC-containing particles became thinner in 2022. For the coating materials, the mass fraction of nitrate increased obviously, and even replaced organic matter as the dominant component during the peak of the pollution period. Variations in chemical compositions and size distributions resulted in lower mass absorption cross-sections (MAC) of BC-containing particles from 10.5 ± 1.1 m2/g in 2016 to 7.3 ± 0.8 m2/g in 2022, reduced by 30.5%. Our results demonstrate the synergistic benefits of air pollution control in improving air quality and mitigating climate change. Therefore, the MAC of BC adopted in climate models should vary with the changing air pollution levels. This study emphasizes that it is imperative to conduct long-term observations of BC-containing particles to better estimate BC's climate effects.

Impact of thermal lensing on the TMI threshold powers in rod-type Yb-doped fiber amplifiers

The impact of thermal lensing (TL) on the transverse mode instability (TMI) threshold power in rod-type fiber amplifiers is investigated. Simulations are conducted with a 3D coupled mode analysis on a set of five scaled large pitch fiber (LPF) amplifiers. The LPF fibers are represented by surrogate step-index fibers (SIFs) with scaled cladding diameters, core diameters, and numerical apertures for a fixed normalized frequency V equal to 3.0 and scaled modal field overlap integrals with the core and cladding. It is found that thermal lensing decreases the TMI threshold powers due to increases in the TMI nonlinear gain. This gain increase is attributed to an increase in the nonlinear gain overlap integrals that occurs with the reduction in the fundamental mode effective area. Estimates for the TMI threshold power are in good agreement with measurements; however, the simulations overestimate the mode shrinkage factor. This discrepancy is tentatively attributed to the representation of the LPF by an effective SIF. These results may offer opportunities for fiber designs that increase the TMI threshold powers.

Low-loss and compact photonic lantern based on a step-index double cladding fiber.

The fulfilment of the adiabatic criterion is indispensable for the realization of a low-loss photonic lantern (PL), concurrently imposing a stringent restriction on the taper transition length of the PL. Here, by relaxing the adiabatic criterion, a low-loss and compact PL based on a step-index double cladding fiber (SI-DCF) is theoretically proposed and experimentally demonstrated. The use of SI-DCF can reduce the mode field diameter (MFD) expansion ratio during the tapering processing and greatly decrease the taper transition length required for adiabatic tapering. We initially evaluate the variation of both MFD and effective refractive index (RI) along the fiber tapering based on three types of fiber structures, including the modified standard single-mode fiber (SSMF), the graded-index fiber (GIF), and the proposed SI-DCF. In comparison with the commonly used fiber geometry, the SI-DCF can reduce the MFD expansion ratio from 77.73% to 38.81%, leading to more than half reduction of the tapering length for both 3-mode and 6-mode PLs. Then, two kinds of SI-DCF with different core diameters are fabricated to realize a 3-mode PL. The fabricated PL possesses a 1.5 cm tapering length and less than 0.2 dB insertion loss (IL). After splicing with the commercial few-mode fiber, the PL has an average IL of 0.6 dB and more than 13 dB LP11 mode purity over the C-band. Finally, a transfer matrix measurement indicates that the fabricated PLs have a mode coupling of less than -10 dB at 1550 nm.

Modeling and characterization of deeply etched multilayer resonators under partial coherent excitation via multimode optical fibers

Recently, there has been a resurgence of interest in multimode optical fibers illuminated by a white light source. Largely, in anticipation of many integrated applications in the biomedical domain and spectral sensing benefiting from the broad spectral range and high numerical aperture (NA). Along these lines, the output light from these fibers can be captured by the physics of partially coherent sources. While the Gaussian Schell model has provided a framework for studying partial coherence, to our knowledge, its impact on microstructures remains unexplored. As the sheer complexity arising from the interplay between partial coherence and microstructures transfer function has posed fundamental challenges in deciphering their response. In this work, we introduce a comprehensive numerical model paired with experimental validation to assess the performance of multilayer optical resonators, which are meticulously crafted through high aspect ratio silicon etching under the influence of a partially coherent optical source. The model studies the effects of optical fiber NA, Bragg mirror order, cavity length, and surface roughness of the microstructures on the output of the resonator. The results show that the response under standard multimode fiber (MMF, partial coherent source) has lower insertion loss, more asymmetry versus wavelength, and larger full width at half maximum than the standard single mode fiber (full coherent source). A silicon-on-insulator chip is fabricated using 130 µm deep etching of silicon for Bragg mirrors with 2.25, 3, and 3.25 µm silicon layer widths and a different number of layers. The structures are characterized using a MMF of 62.5 µm core diameter illuminated by an infrared white light source. The theoretical results have been compared with the experimental results and a good agreement has been obtained.

3D-printed bioinspired spicules: Strengthening and toughening via stereolithography

Recently, the replication of biological microstructures has garnered significant attention due to their superior flexural strength and toughness, coupled with lightweight structures. Among the most intriguing biological microstructures renowned for their flexural strength are those found in the Euplectella Aspergillum (EA) marine sponges. The remarkable strength of this sponge is attributed to its complex microstructure, which consists of concentric cylindrical layers known as spicules with organic interlayers. These features effectively impede large crack propagation, imparting extraordinary mechanical properties. However, there have been limited studies aimed at mimicking the spicule microstructure. In this study, structures inspired by spicules were designed and fabricated using the stereolithography (SLA) 3D printing technique. The mechanical properties of concentric cylindrical structures (CCSs) inspired by the spicule microstructure were evaluated, considering factors such as the wall thickness of the cylinders, the number of layers, and core diameter, all of which significantly affect the mechanical response. These results were compared with those obtained from solid rods used as solid samples. The findings indicated that CCSs with five layers or fewer exhibited a flexural strength close to or higher than that of solid rods. Particularly, samples with 4 and 5 cylindrical layers displayed architecture similar to natural spicules. Moreover, in all CCSs, the absorbed energy was at least 3–4 times higher than solid rods. Conversely, CCSs with a cylinder wall thickness of 0.65 mm exhibited a more brittle behavior under the 3-point bending test than those with 0.35 mm and 0.5 mm wall thicknesses. CCSs demonstrated greater resistance to failure, displaying different crack propagation patterns and shear stress distributions under the bending test compared to solid rods. These results underscore that replicating the structure of spicules and producing structures with concentric cylindrical layers can transform a brittle structure into a more flexible one, particularly in load-bearing applications.

Multi-mode stable, high peak power Nd:YAG laser device for laser cleaning

High average power and peak power solid-state lasers are of great interest in the field of laser cleaning. In this research, a high peak power laser with over 400 W average power using a multi-mode stable resonator in a diode-pumped Nd:YAG master oscillator power amplifier has been demonstrated. A maximum peak power over 1.08 MW was achieved at a repetition frequency of 5 kHz. Delivery fiber with a 400 µm core diameter was utilized for flexible laser transmission. A prototype of the laser cleaning system was developed and inspiring application effects for paint and mold cleaning were achieved.

Comparison of full fiber coupled interferometer systems under vacuum conditions

Abstract The PTB built a comparator setup for testing length measuring systems under vacuum conditions. The setup is equipped with a linear stage which is operated in a closed loop using the feedback of a 1.5D encoder system with three encoder heads for length and vertical rotation angle and exhibits a movement range of 150 mm. The main measurement system is a heterodyne interferometer with periodic nonlinearities with amplitudes below 10 pm. The comparator setup was characterized using a mirror mounted on the stage reflecting the measurement as well as the reference beams. By these means, the resolution, the stability of the setup as well as the influence of guiding errors on position-dependent measurement deviations of the fully fiber coupled interferometer were investigated. A position-depending error was observed which was resulting from the variation of the performance of the coupling into the multi-mode fibers used to transfer the superposed beams to the photoreceivers. The measured deviations were 1.5 nm or 0.2 nm over 70 mm travel range depending on the core diameter of the multi-mode fibers of 50 µm and 200 µm, respectively. Three different commercial fiber interferometer systems were analysed under vacuum conditions with the comparator setup. All tested systems are working with light sources with a wavelength of approximately 1535 nm but differ in the amplitude of their periodic nonlinearities in the range between 10 pm and 29 nm. The tests of their resolution and stability were limited by vibrations in the comparator setup and the lack of adequate synchronization capabilities of the data acquisition of these systems.

A Micro-Mach–Zehnder Interferometer Temperature Sensing Design Based on a Single Mode–Coreless–Multimode–Coreless–Single Mode Fiber Cascaded Structure

In this paper, a temperature sensing scheme with a miniature MZI structure based on the principle of inter-mode interference is proposed. The sensing structure mainly comprises single mode–coreless–multimode–coreless–single mode fibers (SCMCSs), which have been welded together, with different core diameters. The light beam has been expanded after passing through the coreless optical fiber and is then coupled into a multimode optical fiber. Due to the light passing through the cladding and core mode of the multimode optical fiber with different optical paths, a Mach–Zehnder interferometer is formed. Moreover, due to the thermo-optic and thermal expansion effects of optical fibers, the inter-mode interference spectrum of a multimode fiber shifts when the external temperature changes. Through theoretical analysis, it is found that the change in the length of the sensing fiber during temperature detection has less of an effect on the sensitivity of the sensing structure. During the experiment, temperature changes between 20 and 100 °C are measured at sensing fiber lengths of 1.5 cm, 2.0 cm, 2.5 cm, 3.0 cm, 3.5 cm, and 4.0 cm, respectively, and the corresponding sensitivities are 65.98 pm/°C, 72.70 pm/°C, 67.75 pm/°C, 66.63 pm/°C, 74.80 pm/°C, and 72.07 pm/°C, respectively. All the corresponding correlation coefficients are above 0.9965. The experimental results indicate that in the case of a significant change in the length of the sensing fiber, the sensitivity of the sensing structure changes slightly, which is consistent with the theory that the temperature sensitivity is minimally affected by a change in the length of the sensing fiber. Therefore, the effect of the length on sensitivity in a cascade-based fiber structure is well solved. The sensing scheme has an extensive detection range, small size, good linearity, simple structure, low cost, and high sensitivity. It has a good development prospect in some detection-related application fields.

Research on the preparation of multi-core photonic crystal fiber and the curvature sensing performance of three-core photonic crystal fiber

Two- and three-core photonic crystal fibers are prepared by using the same photonic crystal fiber preform structure. Not only the fiber diameter is reduced to standard size of 125μm, but also the core diameter is reduced to below 4μm. A curvature and temperature sensing system is built, and the curvature and temperature sensing performance of the three-core optical fiber is tested. When the length of three-core optical fiber is 150 mm, the measured curvature sensitivity is −7.27069 nm/m−1 in the range of 0 to 0.990 m−1, and the temperature sensitivity is −34 pm/°C during the temperature reduction from 75 to 45 °C. When the length of three-core photonic crystal fiber is 68 mm, the curvature sensitivity and temperature sensitivity are 2.42419 nm/m−1 and −7 pm/°C, respectively. In a small range of temperature, the sensor is insensitive to temperature, and the cross interference of temperature to curvature is very small.

Compact and efficient high-power mid-infrared supercontinuum fiber laser source based on a noise-like pulse and germania fiber

Here, we demonstrate a compact and efficient high-power mid-infrared supercontinuum (MIR-SC) laser source based on a tunable noise-like pulse (NLP) fiber laser system and a short section of single-mode germania-core fiber (GCF). The NLP all-polarization-maintaining fiber laser system can deliver the maximum output power of ∼30.6 W and a broadband spectrum (∼1.8-2.7 µm) with a compact single-stage fiber amplifier. By directly pumping only ∼6.5 cm-long GCF with a core diameter of ∼3.5 µm, a MIR-SC (spectral coverage of ∼1.5-3.3 µm) with a maximum power of ∼25.2 W and a power conversion efficiency ∼81.2% is obtained, which represent the highest power and efficiency in any single-mode GCF-based MIR-SCs, to the best of our knowledge. Our study contributes to the high-power MIR-SC laser source with compact all-fiber configuration, and will prompt its practical applications.

Practical Methodology for Evaluating Mining Front Stability Based on the Diametrical Core Deformation Technique

The state of stress in a mining front constantly changes with mining activities. In a recent study, the authors developed and verified with laboratory measurements an analytical model for the calculation of mining-induced stresses based on measuring the deformations of a diamond drill rock core extracted perpendicular to the mining front or face. The method is called diametrical core deformation technique (DCDT). In this study, the DCDT is used in combination with 3D numerical modelling to develop a practical methodology for the assessment of mining face stability. To demonstrate the methodology, a diamond drill rock core was retrieved from an access drift face 530 m below the surface of an underground mine in northern Quebec. The state of stress in the mining front is estimated from the DCDT and used to adjust the orientation and principal stress magnitudes in the local area around the access drift in a 3D linear-elastic numerical model using an iterative approach. As the rock core is partially fractured due to previous face advance blasting, the numerical model is further adjusted to model the observed damage zone. The 3D model after adjustments is used to examine the mining front stability with the Hoek–Brown failure criterion. It is postulated that the proposed methodology is suitable for the stability assessment of any mining front with or without an observed damage zone.

Detection of NT-proBNP Using Optical Fiber Back-Reflection Plasmonic Biosensors.

Heart failure (HF) is a clinical entity included in cardiovascular diseases affecting millions of people worldwide, being a leading cause of hospitalization of older adults, and therefore imposing a substantial economic burden on healthcare systems. HF is characterized by dyspnea, fatigue, and edema associated with elevated blood levels of natriuretic peptides, such as N Terminal pro-B-type Natriuretic Peptide (NT-proBNP), for which there is a high demand for point of care testing (POCT) devices. Optical fiber (OF) biosensors offer a promising solution, capable of real-time detection, quantification, and monitoring of NT-proBNP concentrations in serum, saliva, or urine. In this study, immunosensors based on plasmonic uncladded OF tips were developed using OF with different core diameters (200 and 600 µm). The tips were characterized to bulk refractive index (RI), anddetection tests were conducted with NT-proBNP concentrations varying from 0.01 to 100 ng/mL. The 200 µm sensors showed an average total variation of 3.6 ± 2.5 mRIU, an average sensitivity of 50.5 mRIU/ng·mL-1, and a limit of detection (LOD) of 0.15 ng/mL, while the 600 µm sensors had a response of 6.1 ± 4.2 mRIU, a sensitivity of 102.8 mRIU/ng·mL-1, and an LOD of 0.11 ng/mL. Control tests were performed using interferents such as uric acid, glucose, and creatinine. The results show the potential of these sensors for their use in biological fluids.

Effects of one-side confinement and current on heat transfer mechanisms over single electrical wire flame spread behaviors

The electrical wire fire often occurs in the confined space, making the flame spread behavior complex and the risk increase. In this paper, experimental and theoretical study on the flame spread over three types of polyethylene (PE) electrical wires under different side-confined distances (0∼40 mm) and currents (0∼60 A) was carried out.The ratios of copper diameter to entire wire diameter were 6mm/10 mm, 8mm/12 mm, and 6mm/12 mm for type I, type II and type III, respectively. The results show that, with the increase of s, the flame width and height, and flame spread rate will firstly increase to the maximum peaks at the position of s = 5 mm with attachment wall effect, and then gradually decrease to the values of the unconfined conditions. And with the increase of current, these parameters will gradually increase to the largest at I = 40 A and then decrease for I = 60 A, as the current effect changes from preheating to dripping acceleration.The firm correlation between preheating length δph and pressure difference ΔP is built, which demonstrates the smallest preheating length is at s = 5 mm with the maximum promotion of heat transfer by gypsum board. On the other hand, the generated Joule heat by the current will enhance the length of preheating, making it proportional to current. Meanwhile, it is found that, the dripping frequency influenced by the dripping mass rate, will increase with the current. The heat transfer components including of the solid conduction heat flux (q˙joule″ and q˙c″), flame heat flux (q˙νf″ and q˙rf″) and gypsum board heat flux (q˙rg″ and q˙νg″) are quantitatively analyzed. Correspondingly, a heat transfer model over flame spread is established, which can well predict the flame spread rate.As the diameter of the wire is relatively small, the controlling heat transfer is the flame convective heat flux q˙νf″ in this research. In addition, it is illustrated that, the heat flux of gypsum board q˙νg″+q˙rg″ will decrease with the increase of copper core diameter from type I of 6 mm to type II of 8 mm.While the solid conduction heat flux of copper q˙c″+q˙joule″ will decrease with the increase of thickness of PE from type I of 2 mm to type III of 3 mm. These findings can well give the understanding of heat transfer of flame spread over electrical wires with the effects of sidewall and current.

Synthesis and characterization of Fe3O4 core nanoparticles coated with TiO2 and ZnO

The room temperature synthesis of the core-shell-shell (CSS) nanoparticles was demonstrated to be green, low-cost, and reproducible. The magnetic core of Fe3O4 nanoparticles was coated with TiO2 and ZnO in two steps. The obtained CSS nanoparticles were extensively characterized by XPS, TEM, XRD, DRS-UV–vis, N2 Physisorption, Electromagnetic, and Raman spectroscopy. XPS analysis revealed that the magnetic core was successfully functionalized with the citric acid. The ratio between the ferric cations (Fe3+) and ferrous (Fe2+) is typically reported to be around two due to the presence of FeO and Fe2O3 to balance the charge in the structure. Nevertheless, XPS results demonstrated that the ratio resulted in higher stability than that of the crystal nominal structure, suggesting that the surface of the CSS is slightly enriched with Fe3+ cations. TEM results indicated an average core diameter of approximately 9±1 nm for Fe3O4 (M-US); the first shell exhibited an average thickness of 3±1 nm, while the ZnO second shell thickness resulted in around 2±1 nm. X-ray diffraction analysis identified inverse spinel, hematite, anatase, and zincite phases in M-US, MT, and MTZ, respectively. Notably, the MTZ sample also contained hematite in addition to inverse spinel. Diffuse Reflectance UV-Vis Spectroscopy results demonstrated a reduction in the band gap as the shell coverage varied. N2 adsorption-desorption isotherms indicated an increase in the surface area as the core nanoparticles were coated with the subsequent shells. Additionally, the coated samples presented a mesoporous structure with a maximum surface area of 110 m2g−1 for the MT material. Raman spectroscopy confirmed the presence of vibrational modes related to TiO2 and ZnO. The core-shell-shell nanoparticles presented suitable electronic properties to potentially be applied in the photodegradation of harmful compounds and azo dyes.

4.3 µm high-power amplified spontaneous emission fiber source based on CO2-filled nested hollow-core anti-resonant fiber

We report a 4.3 µm mid-infrared (mid-IR) high-power amplified spontaneous emission (ASE) fiber source based on CO2-filled nested hollow-core anti-resonant fiber (Nested HC-ARF). The pump source is a homemade hundred-watt-level wavelength-tunable 2 µm single-frequency fiber laser. A 5.7 m long 8-tube Nested HC-ARF is used as the gas cell, with a core diameter of 110 µm and cladding diameter of 400 µm, which exhibits transmission loss of 0.1 dB/m at 2 µm and 0.24 dB/m at 4.3 µm respectively. To improve the coupling efficiency of the high-power pump laser and reduce the influence of the thermal effect at the input end of the hollow-core fiber, the fiber is designed for multimode transmission at the pump wavelength. A continuous wave output power of 6.6 W at 4.3 µm is achieved, and the slope efficiency is 17.05%. To the best of our knowledge, it is the highest output power for such gas-filled HC-ARF ASE sources in 4∼5 µm. This work demonstrates the great potential of gas-filled HC-ARF generating high-power mid-IR emission.

Non-invasive FBG-based contact lens for continuous intraocular pressure monitoring

The intraocular pressure (IOP), or pressure inside the eye, is one of the key indicator for glaucoma diagnosis and treatment. The present work shows the design and fabrication of a non-invasive Fiber Bragg Grating (FBG) based contact lens for continuous IOP monitoring. By employing wet etching to reduce the FBG diameter, FBG based contact lens sensitivity and mechanical flexibility are enhanced. The contact lens is made of an optical fiber with a small core diameter that has an inscribed FBG of length 3 mm and is etched for a length of 40 mm to facilitate coiling the eFBG during fabrication. The soft contact lens was fabricated using flexible thin film technology with a transparent and flexible etched Fiber Bragg Grating (eFBG) integrated within flexible polydimethylsiloxane (PDMS) for sensing corneal deformations brought about by IOP variations. Experimental studies on the bionic eyeball model show that the Bragg wavelength shift is highly linear (r2 = 0.9694), with a very good sensitivity of 49.243 pm/mmHg in the IOP pressure range of 0 to 50 mmHg. Due to its ease of fabricating, simplicity of design, and ability to continuously measure pressure with good repeatability and stability, the proposed sensor thus offers a potential solution for IOP monitoring.

Design and fabrication of a tellurite hollow-core anti-resonant fiber for mid-infrared applications

The hollow core anti-resonant fibers (HC-ARFs) based on soft glass are in high demand for 3-6 µm laser delivery. A HC-ARF based on tellurite glass with 6 touching capillaries as cladding was designed and fabricated for the first time, to the best of our knowledge. A relatively low loss of 3.75 dB/m at 4.45 µm was realized in it. The effects of capillary number, core diameter, wall thickness of capillary, and material absorption loss on the loss of the HC-ARF were analyzed by the numerically simulation. The output beam quality was measured and the influence of bending on the fiber loss was discussed. The results of numerical simulation suggested that the theoretical loss of the prepared fiber can be reduced to 0.1 dB/m, indicating that tellurite HC-ARFs have great potential for mid-infrared laser applications.

Aircraft observations of aerosol and BC during the East Asian dust storm event: Vertical profiles, size distribution and mixing state

The vertical structure of meteorological elements, black carbon (BC), and aerosols were in situ characterized by the King Air 350 aircraft measurements over the northeast of China during an East Asian dust storm event from April 10 to 13, 2023. The main causes of this dust storm event were the strong winds generated by the Mongolian cyclone, the cold front on the ground provided dynamic conditions, and the unstable atmospheric state provided thermal conditions and less precipitation in the dust source areas led to exposed the ground surface. The number concentrations of BC and aerosol had significant vertical distribution. The number concentration of aerosol in the dust storm (DS) layer increased rapidly with height, while the number and mass concentrations of BC were higher and varied slightly with height. The BC core mass median diameters (MMD) first increased with height, reaching a maximum value of 0.24 μm at 3000 m; and it rapidly decreased to 0.18 μm at 3200 m and then varied slightly with height above 3200 m. BC's bulk relative coating thickness (coated diameter divided by uncoated core diameter Dp/Dc) first decreased with height, reaching a minimum value of 1.16 at 3000 m, then increased with height, reaching a maximum of 1.38 (4250 m). A wind shear layer (7.9 m s−1 at 1850 m) with a sudden drop in temperature (the cooling rate can reach 7.4 °C·(100 m)−1) at 1900 m hinders the transportation of dust particles to the ground, allowing the dust particles to be transported at long-term distances. There were two stratifications in the dust storm layer: DS1 (1700–3000 m, the vertical wind speed was downward, the horizontal wind speed was small) and DS2 (3000–4500 m, the vertical wind speed was upward, the horizontal wind speed was large). The distinct atmospheric flow field conditions between DS1 and DS2 led to different BC and aerosol pollution characteristics. In DS2, the number concentrations of BC and aerosol were higher, the aging ratio of BC particles was higher, and the size of the core particle of BC was smaller. The concentrations of BC, aerosol, Dp/Dc, and MMD in DS2 were 1.1, 59.0, 1.02, and 0.84 times higher than those in DS1, respectively. Dust particles transported over long distances were primarily small. The number concentrations of aerosols at 0.1–0.12 μm and 0.1–0.24 μm were higher in DS1 and DS2, respectively. Still, the number concentration of aerosol at 0.12–0.28 μm in DS1 was lower than in the planetary boundary layer (PBL) and residual layer (RL).

Simulation of heat transport in textiles inspired by polar bear fur

The polar bear and several other Arctic mammals use fur composed of hollow-core fibers to survive in extremely cold environments. Here, we use finite element analysis to elucidate the role that the hollow core plays in regulating thermal transport. Specifically, we establish a three-dimensional model of a textile based on fibers with various core diameters and study transverse heat transport. First, these simulations revealed that textiles based on hollow-core fibers conduct significantly less heat than their solid-core counterparts with fibers with a core-to-fiber diameter ratio of 0.95, reducing thermal transport by 33%. In addition to this decrease in thermal transport, the mass per area of textiles is substantially reduced by making them hollow core. This led us to consider the performance of multi-layer textiles and to find that four-layer hollow-core textiles can exhibit a four-fold decrease in heat flux relative to single-layer solid-core textiles with the same mass per area. Taken together, these simulations show that hollow-core fibers are well suited for thermal insulation applications in which gravimetric thermal insulation is a priority.

Air-lift characteristics of rock core mass in gas–liquid–solid mixed flow

The air-lift reverse circulation drilling method enables efficient and continuous core extraction. However, the flow characteristics of gas–liquid–solid mixtures during core mass transport are complex, and developing a model to predict performance remains challenging. The flow characteristics of gas–liquid–solid mixtures inside the drill pipe are numerically analyzed by calculating the mixing transport of the core during the airlift process. By solving the momentum equations for multiphase flow, the distribution of physical quantities of three phases and pressure along the depth was calculated, and the laws of influence of the operating parameters on the transport characteristics of the core were analyzed. The results show that the drilling performance is related to the geometric parameters of the pipe and core, drilling speed, and depth. When the submergence ratio is increased to 0.9, the maximum liquid-phase superficial velocity is increased by 109% compared with that when the submergence ratio is 0.6. The size of the annular space gap 67 formed between the core and the pipe wall is the key to the core's mechanical properties, and the differential pressure gradient force increases with increasing core diameter. An increase in well depth reduces the fluid flow. In addition, increasing the pipe diameter improves drilling performance due to reduced friction losses, which elevates the air flow rate required for air-lift reverse circulation operation.