End Of Fiber Research Articles

Tribological properties and related effects of compressed, thermally modified and wax-impregnated wood

AbstractThis paper develops a process for the preparation of modified wood with low friction and low wear for tribological applications such as self-lubricating bearings. Two types of wood, beech (Fagus sylvatica) and robinia (Robinia pseudoacacia), have been studied and the results compared with naturally lubricated native lignum vitae. The process developed consists of plasticisation followed by compression in a mould, thermal modification and subsequent wax impregnation. Plasticisation was carried out by conditioning the samples to a low equilibrium moisture content of 10%, followed by heating to a sample core temperature of 80 °C. This process protects the internal wood structure from mechanical damage during densification. After plasticisation, the wood was compressed in a press mould. A low springback effect (SBE), resulting in compression of up to 40%, was achieved by unloading the mould without opening it. This step optimises compressive strength and hardness. Subsequent heat treatment reduces thickness swelling by up to 85%. Finally, a wax impregnation was applied to reduce friction. Sliding wear tests on modified beech wood have shown that the lowest wear occurs in the cross-sectional orientation (load perpendicular to the fibre ends; rxt orientation). Sliding friction studies using a steel ball on a ball-on-disc tribometer showed that compressed and thermally modified samples impregnated with rapeseed wax or beeswax exhibited coefficients of friction in a range of 0.08 to 0.09. These values are almost four times lower than those of plain compressed wood and even lower than those of lignum vitae, which was used for plain bearings decades ago. This study clearly demonstrates the high potential of compressed, thermally modified and wax-impregnated wood.

Decreasing propagation rate of interfacial debonding between a single carbon fiber and epoxy matrix under cyclic loading

The interfacial debonding of a single carbon fiber transversely embedded in a dumbbell-shaped epoxy sample was generated under cyclic loading, and images were captured using synchrotron radiation X-ray computed tomography. A fatigue testing machine driven by a piezoelectric actuator placed along the beamline for in situ observation was developed for precise alignment. Interfacial debonding was initially observed under a static tensile load and was confirmed to be almost of the same length at both ends of the carbon fiber, implying negligible bending deformation due to inclination. Cyclic loads were then applied to the sample to capture the progressive debonding. The propagation rate of the interfacial debonding decreased as the number of cycles increased. Another sample with a single carbon fiber aligned parallel to the loading direction was prepared following a single-fiber fragmentation test. Interfacial debonding was clearly observed around the fiber breakage. Cyclic loads were also applied to this sample; however, no progression of the interfacial debonding was evident. Degradation of the interfacial strength between the carbon fiber and epoxy matrix was not confirmed under cyclic loading within the elastic deformation range.

Optical absorption spectrum reveals gaseous chlorine in anti-resonant hollow core fibers

We have observed unexpected spectral attenuation of ultraviolet light in freshly drawn hollow core optical fibers. When the fiber ends are left open to atmosphere, this loss feature dissipates over time. The loss matches the absorption spectrum of gaseous (molecular) chlorine and, given enough time, the transmission spectrum of the fiber recovers to that expected from the morphological structure of the fiber. Our measurements indicate an initial chlorine concentration of 0.45 µmol/cm3 in the hollow core, equivalent to 1.1 mol% Cl2 at atmospheric pressure.

A char removal protocol to visualize fiber cross‐sections of carbon/epoxy composites subjected to flame

AbstractPost‐crash fires obscure or destroy critical fracture surfaces needed to determine the origin of aircraft structural failures. Our goal is to eliminate combustion residue from carbon fiber‐reinforced polymer composites to enable fractographic examination during aviation accident investigations. In this work, combustion residues were removed from burned Hexcel SGP370‐8H/8552 woven‐fabric carbon/epoxy specimens by nitric/sulfuric acid oxidations. Scanning electron microscopy identified various types of char obscuring the fiber ends. For char removal, the burned specimens were immersed in a nitric acid/sulfuric acid/water solution (0.18 wt.%, 96.25 wt.%, 3.57 wt.%) at elevated temperatures (75–150°C). Higher temperatures enhanced nitric acid decomposition in this highly acidic, low‐water environment, accelerating char oxidation and progressively enhancing the extent of char removal. At lower temperatures (T < 100°C), char deposits were partially oxidized after 60 mins. At 125 and 150°C, the char was removed within 30 mins of immersion. The epoxy matrix both chemically decomposed and oxidized and the char oxidized during these oxidation treatments. Gas evolution and soluble products dissolved in the HNO3/H2SO4 media. The damage morphology created by the sawing action on the fiber ends, created before flame exposure, remained clearly visible after the acid oxidations. This occurs because oxidation rates at the carbon fiber ends are much slower than the char oxidation in these acid treatments. If the acid treatment temperature raised above 185°C, then this sawing‐induced fiber damage morphology will also be destroyed. This preliminary understanding can be applied to develop a comprehensive forensic analysis procedure for post‐crash fire investigations.Highlights Flame exposure of sawed specimen cross‐sections leads to char formation, obscuring fiber damage morphologies. HNO3/H2SO4 oxidations at elevated temperatures (75–150°C) resulted in char removal from fiber ends. Higher temperatures (T = 125 and 150°C) accelerated char oxidation. The sawing of carbon/epoxy composites caused extensive fiber damage and ply delamination. Residual decomposed resin matrix and char oxidized faster than the carbon fibers and the fiber sawing‐induced fiber damage morphologies created before flame exposure and were preserved after char removal.

Study of the effect of interfacial damage and friction on stress transfer in short fiber-reinforced composites

The purpose of this study is to investigate the influence of different stages of different interfaces evolution under external forces on stress transfer within composite materials, which is crucial for analyzing reinforcement mechanisms in composite materials. Analytical solutions are derived to explore the impact of these distinct phases, both at the interfaces along the fiber length direction and at the fiber ends, on the complex stress distribution profiles within composite materials. Furthermore, the frictional effect at the interface serves to impede the debonding process in the composite. Under the same load, the debonding length of the interface decreases as the frictional effect increases. The increase in fiber aspect ratio (AR) effectively reduces the length of the damage and debonding interface and increases the axial fiber stress. Additionally, the theoretical results agree well with numerical simulation and experimental results. In essence, this model provides analytical solutions that are instrumental for analyzing stress transfer in fiber-reinforced composites during different stages of interface evolution.

Residual force enhancement decreases when scaling from the single muscle fiber to joint level in humans

BackgroundResidual force enhancement (rFE), defined as increased isometric force following active lengthening compared to a fixed-end isometric contraction at the same muscle length and level of activation, is present across all scales of muscle. While rFE is always present at the cellular level, often rFE “non-responders” are observed during joint-level voluntary contractions. MethodsWe compared rFE between the joint level and single fiber level (vastus lateralis biopsies) in 16 young males. In vivo voluntary knee-extensor rFE was measured by comparing steady-state isometric torque between a stretch-hold (maximal activation at 150°, stretch to 70°, hold) and a fixed-end isometric contraction, with ultrasonographic recording of vastus lateralis fascicle length (FL). Fixed-end contractions were performed at 67.5°, 70.0°, 72.5°, and 75.0°; the joint angle that most closely matched FL of the stretch-hold contraction's isometric steady-state was used to calculate rFE. The starting and ending FLs of the stretch-hold contraction were expressed as % optimal FL, determined via torque-angle relationship. ResultsIn single fiber experiments, the starting and ending fiber lengths were matched relative to optimal length determined from in vivo testing, yielding an average sarcomere excursion of ∼2.2–3.4µm. There was a greater magnitude of rFE at the single fiber (∼20%) than joint level (∼5%) (p = 0.004), with “non-responders” only observed at the joint level. ConclusionBy comparing rFE across scales within the same participants, we show the development of the rFE non-responder phenomenon is upstream of rFE's cellular mechanisms, with rFE only lost rather than gained when scaling from single fibers to the joint level.

Investigating the Expression Profiles of Cysteine String Proteins (CSPs) in Cochlear Tissue

ObjectiveThis study aims to explore the expression patterns of cysteine string protein alpha (CSPα) and cysteine string protein beta (CSPβ) in the mammalian inner ear, with an emphasis on their temporal dynamics during the developmental stages of C57BL/6 mice. MethodsWe utilized immunofluorescence staining to assess the localization and distribution of CSPα and CSPβ within the inner ears of C57BL/6 mice and miniature pigs. Additionally, this method facilitated the investigation of their temporal expression profiles. ResultsIn adult C57BL/6 mice and miniature pigs, CSPα and CSPβ were identified in the cytoplasm of inner hair cells and spiral ganglion cells, yet were absent in outer hair cells. Both proteins were found to colocalize with Ctbp2 on the basal side of the cytoplasm in inner hair cells' basilar membrane. Expression of CSPα was observed at the nerve fiber termini at the basilar membrane's base of inner and outer hair cells 10 days postnatally in C57BL/6 mice. Notably, expression of both CSPα and CSPβ in the cytoplasm of inner hair cells emerged on the 12th day post-birth, aligning with the timeline for registering cochlear potentials. The expression levels of both proteins increased with age, but were consistently absent in outer hair cells. Contrastingly, expression of CSPα and CSPβ was present in the cytoplasm of inner hair cells in miniature pigs as early as one day post-birth, yet remained absent in the three rows of outer hair cells. ConclusionCSPα and CSPβ exhibit predominant and specific expression in inner hair cells and spiral ganglion cells. A unique expression pattern was observed for CSPα, which was also present at the nerve fiber endings of both inner and outer hair cells. The developmental expression trajectory of CSPα and CSPβ in mouse inner hair cells is characterized by an initial absence, followed by a gradual increase. Moreover, the timing of expression onset between mice and miniature pigs indicates distinct temporal dynamics, suggesting a potential role in auditory development.

Optimal Design of a Sensor Network for Guided Wave-Based Structural Health Monitoring Using Acoustically Coupled Optical Fibers.

Guided waves (GW) allow fast inspection of a large area and hence have received great interest from the structural health monitoring (SHM) community. Fiber Bragg grating (FBG) sensors offer several advantages but their use has been limited for the GW sensing due to its limited sensitivity. FBG sensors in the edge-filtering configuration have overcome this issue with sensitivity and there is a renewed interest in their use. Unfortunately, the FBG sensors and the equipment needed for interrogation is quite expensive, and hence their number is restricted. In the previous work by the authors, the number and location of the actuators was optimized for developing a SHM system with a single sensor and multiple actuators. But through the use of the phenomenon of acoustic coupling, multiple locations on the structure may be interrogated with a single FBG sensor. As a result, a sensor network with multiple sensing locations and a few actuators is feasible and cost effective. This paper develops a two-step methodology for the optimization of an actuator-sensor network harnessing the acoustic coupling ability of FBG sensors. In the first stage, the actuator-sensor network is optimized based on the application demands (coverage with at least three actuator-sensor pairs) and the cost of the instrumentation. In the second stage, an acoustic coupler network is designed to ensure high-fidelity measurements with minimal interference from other bond locations (overlap of measurements) as well as interference from features in the acoustically coupled circuit (fiber end, coupler, etc.). The non-sorting genetic algorithm (NSGA-II) is implemented for finding the optimal solution for both problems. The analytical implementation of the cost function is validated experimentally. The results show that the optimization does indeed have the potential to improve the quality of SHM while reducing the instrumentation costs significantly.

Monolithic linear array fiber end cap for spectral beam combination

In this study, a fusion splicing system that facilitates the splicing of a monolithic linear array fiber end cap is constructed. The fusion splicing thermal field of the end cap irradiated by a CO2 laser is theoretically simulated using the finite element method. The experimental fusion splicing temperature agrees well with the simulation results. The splicing strength, misalignment, and high-power withstanding capacity of the fusion-spliced monolithic linear 3-fiber end cap are investigated. The use of the fabricated device in a dual-grating spectral beam combination (SBC) is also demonstrated with three-channel laser beams, achieving a combined beam with near-diffraction-limited beam quality M2=1.101. It shows that the development of the monolithic linear array fiber end cap is meaningful for achieving a compact high-brightness SBC system.

Flexible FPI sensor fabricated by fiber end photopolymerization and integration for high sensitivity gas pressure sensing

This work presents a new design framework for highly sensitive fiber gas pressure sensor. We construct a Flexible Fabry–Perot Interferometer (F-FPI), which consists of three polymer pillars and an end cap, on a fiber end face. A unique fiber-end photopolymerization and integration (FEPI) technique is adopted for fabricating the device. The varied gas pressure in the enclosed space not only changes the refractive index (RI) of the gas but also the length of the pillars. Therefore the difference in the optical path length of the FPI is more sensitive to pressure changes. Experimental results indicate that the F-FPI realizes a gas pressure sensitivity up to 79.0 pm/kPa in the range of 0–200 kPa. In addition, the Vernier effect is introduced to amplify the sensitivity to −409.7 pm/kPa. The temperature compensation is achieved by cascading a Fiber Bragg Grating (FBG) behind the F-FPI. Such a design framework provides a new idea for highly sensitivity gas pressure sensing.

The laser screen imaging measurement system based on arrayed fibers

This paper presents a laser screen imaging measurement system (LSIMS) based on arrayed fibers to measure the velocity and dimension of a flying object. A laser diode is connected to the emission module of the laser screen via a single-mode fiber, then the emitted light beam is collimated into a parallel beam with a lens, this structure is arrayed to form the laser screen. The receiving module of the laser screen employs a cylindrical lens array to converge the collimated beams into a focal line. The input ends of the plastic fibers are arrayed along this focal line, while the output ends are imaged on the sensor of a line scan camera (LSC) through a lens. The LSIMS effectively modulates the process of a flying object passing through the laser screen into the light intensity change in the plastic fibers. The velocity and dimension of the flying object are subsequently measured through the analysis of the image obtained by the LSC. The timing accuracy of the LSIMS is verified through experiments. The velocity and diameter of pellets launched by a slingshot are measured and analyzed for errors.

Near-Infrared On-Site Evaluation (NOSE) Examination of EBUS/EUSb Samples-A New Method for Sample Adequacy Evaluation.

Fine-needle aspiration biopsy is crucial for modern diagnostics of endoscopic procedures and thus an efficient and reliable method for increasing biopsy yields is urgently needed. In our study, we address the limited availability and high price of the rapid onsite evaluation (ROSE) technique by introducing the technique of near-infrared on-site evaluation (NOSE) consisting of spectral measurement of near-infrared radiation (NIR) transmitted through the evaluated material. For this purpose, we designed a special optical probe consisting of two fibres, of which one is a source fibre and the second is a detector fibre. The distal ends of both fibres are brought together into one bundle which is, with the help of a special extension, applied to a cuvette with an analysed sample at a defined distance from the cuvette bottom and fixed in place. A portion of the NIR radiation received by the detector fibre after it propagates through the sample then depends on the optical and therefore morphological characteristics of the sample. Based on the measured spectral curve, we can calculate the attenuation coefficient curve and subsequently the parameter of the sample richness and the parameter characterising the autofluorescence peak as well. We found that the value of our introduced parameters is in significant relation to sample richness as well as to sample malignity. NOSE evaluation of EBUS/EUSb (endobronchial/oesophageal ultrasound bronchoscopy) specimens can be considered an easy new technique aiming to improve sampling diagnostic accuracy and to diminish costs related to the presence of a cytopathologist and related instrumentation in the endoscopy suite.

Fiber laser irradiation in chemical solution for micro fabrication: Mechanisms and applications

The laser and electrochemical hybrid machining (LECM) could realize high-efficient and quality processing of difficult-to-cut materials and has become a research topic in microfabrication. However, it was difficult to ensure the stability and efficiency of laser transmission in chemical solutions, and an external voltage and auxiliary cathode should be added. In the present study, a novel fiber laser irradiation in chemical solution (LICS) has been proposed to process microstructures. The surface microstructures and chemical composition of the surfaces processed by LICS, laser irradiation in the ultrapure water, and electrochemical machining were compared. In LICS the materials were removed by laser processing and the following high-temperature gradient induced electrochemical dissolution. The high temperature gradient induced electrochemical dissolution could enhance the MRR and improve the surface quality. LICS can be regarded as a novel LECM process. The machining efficiency of LICS had been improved by 46.2 % compared with that laser irradiation in the ultrapure water, and the proportion of laser-induced electrochemical dissolution was 31.6 % in the LICS process. Further, the effects of laser power, chemical solution concentration, and optical fiber end movement control on the processing of micro grooves were explored, considering the dimension, MRR, and surface roughness. A front gap of smaller than 0.8 mm between the optical fiber end and workpiece was recommended during LICS. The repeated feeding of optical fiber was proposed to improve the depth-to-width ratio of the micro grooves fabricated by LICS. Finally, LICS was used to process microstructures with the controlled profiles on the nickel-based superalloy and titanium alloy workpieces without a recast layer, which holds great potential in surface microfabrication and texturing.

Earthquake source inversion by integrated fiber-optic sensing

We present an earthquake source inversion using a single time series produced by integrated fiber-optic sensing in a phase noise cancellation (PNC) system used for frequency metrology. Operating on a 123 km long fiber between Bern and Basel (Switzerland), the PNC system recorded the Mw3.9 Mulhouse earthquake that occurred on 10 September 2022 around 10 km north-west of the northern fiber end. A generalised least-squares inversion in the 4 - 13 s period band constrains the components of a double-couple moment tensor with an uncertainty that corresponds to around 0.2 moment magnitude units, nearly independent of prior information. Uncertainties for hypocenter location and original time are more variable, ranging between 4 - 20 km and 0.1 - 1 s, respectively, depending on whether injected prior information is realistic or almost absent. This work is a proof of concept that quantifies the resolvability of earthquake source properties under specific conditions using a single-channel stand-alone integrated (non-distributed) fiber-optic measurement. It thereby constitutes a step towards the integration of long-range phase-transmission fiber-optic sensors into existing seismic networks in order to fill significant seismic data gaps, especially in the oceans.

The TRPA1 Ion Channel Mediates Oxidative Stress-Related Migraine Pathogenesis.

Although the introduction of drugs targeting calcitonin gene-related peptide (CGRP) revolutionized migraine treatment, still a substantial proportion of migraine patients do not respond satisfactorily to such a treatment, and new therapeutic targets are needed. Therefore, molecular studies on migraine pathogenesis are justified. Oxidative stress is implicated in migraine pathogenesis, as many migraine triggers are related to the production of reactive oxygen and nitrogen species (RONS). Migraine has been proposed as a superior mechanism of the brain to face oxidative stress resulting from energetic imbalance. However, the precise mechanism behind the link between migraine and oxidative stress is not known. Nociceptive primary afferent nerve fiber endings express ion channel receptors that change harmful stimuli into electric pain signals. Transient receptor potential cation channel subfamily A member 1 (TRPA1) is an ion channel that can be activated by oxidative stress products and stimulate the release of CGRP from nerve endings. It is a transmembrane protein with ankyrin repeats and conserved cysteines in its N-terminus embedded in the cytosol. TRPA1 may be a central element of the signaling pathway from oxidative stress and NO production to CGRP release, which may play a critical role in headache induction. In this narrative review, we present information on the role of oxidative stress in migraine pathogenesis and provide arguments that TRPA1 may be "a missing link" between oxidative stress and migraine and therefore a druggable target in this disease.

Short-length nanosecond pulsed 1.653-μm DBR fiber Raman laser oscillator fabricated by femtosecond laser direct-writing

We demonstrate a nanosecond pulsed 1.653-μm fiber Raman laser (FRL) oscillator in a short-length distributed Bragg reflector (DBR) cavity made by femtosecond laser direct-writing technique. The DBR FRL cavity is composed of commercial ultrahigh NA germanium-doped silica fiber with a short length of 10 m and a pair of fiber Bragg gratings (FBGs). The FBGs were directly inscribed on the ends of the Raman gain fiber, using femtosecond-laser point-by-point (PbP) writing method. A home-made 1.55-μm nanosecond fiber laser source was used as the pump of the FRL. 1.653-μm nanosecond pulsed laser oscillation with maximum average output power of 125 mW (corresponding to peak power of 6.6 W), 3 dB linewidth of ≤ 0.15 nm, and slope efficiency of 48 % was obtained under 1.55-μm pump with optimized repetition rate of 10 MHz. The optical signal-to-noise-ratio (OSNR) of the 1.653-μm narrow-linewidth Raman lasing is above 70 dB. The short-length DBR FRL output exhibits decently high degree of polarization (DOP) and high degree of linear polarization (DOLP) above 80 % in 3-hour period, benefitted from the birefringent FBGs made by femtosecond laser direct-writing method. It is expected that by further reducing the cavity length to < 1 m, the 1.653-μm DBR FRL oscillator made by femtosecond laser direct-writing method is promising as single-frequency narrow-linewidth, highly linearly polarized, high-OSNR laser sources for high-sensitivity CH4 gas detection.

Nonlinear Quantum Photonics with a Tin-Vacancy Center Coupled to a One-Dimensional Diamond Waveguide.

Color centers integrated with nanophotonic devices have emerged as a compelling platform for quantum science and technology. Here, we integrate tin-vacancy centers in a diamond waveguide and investigate the interaction with light at the single-photon level in both reflection and transmission. We observe single-emitter-induced extinction of the transmitted light up to 25% and measure the nonlinear effect on the photon statistics. Furthermore, we demonstrate fully tunable interference between the reflected single-photon field and laser light backscattered at the fiber end and show the corresponding controlled change between bunched and antibunched photon statistics in the reflected field.

The dialectics of digitalisation: A critique of the modernistic imperative for the development of digital technology

This text discusses today’s digital transformation through the lens of Horkheimer and Adornos’ study of the enlightenment. Policy and public discourse around digitalisation embrace and adhere to the narrow tenets enlightenment thinking; the idea that rationality, individual freedom, and a society free from superstition are necessary and attainable goals. The costs of what has come to be called ‘Modernity’ are many. Through the application of rationality to all spheres of life, married with disruptive technological advancement, humanity has diminished its’ imagination – its ability to seek new directions. To paraphrase Horkheimer and Adorno, Modernism fights against nature, of which we are a part, and thus, paradoxically, sets us in a fight against ourselves. Environmental degradation, the price of progress, being just one example of this – deadening work, consumerism and severed social connections being amongst others. In this framing, digitalisation itself comes to be understood itself as akin to a force of nature – one that we can do little about, other than adjust and adapt or be swept away. But this by no means a foregone conclusion, there is light at the end of the optical fibre. Albeit that recent technical developments around artificial intelligence appears to be pushing policy makers into hasty decisions, the pace of the technical development is not as fast as we believe, and in comparison with the Reformation – we have time. If we can restrain ourselves from the resist, adapt or die responses promoted in popular discourse in face of the shock of large language models and rising threat of automation, then we create room to consider economic, social, and ecological alignment and accord, in the decision making and design of future interactive artefacts and digital services. The article argues that through postdigital aesthetics, technology makers can embrace materiality and the inherent qualities of digital technology to formulate a critique of existing trajectories in digital transformation, with consequences for a more sustainable future.

Акустика кипения с недогревом на лазерном нагревательном элементе

We study acoustic signals arising during cavitation initiated by laser heating of water in the vicinity of the end of an optical fiber immersed in water. It is shown that the growth and collapse of the vapor phase in the vicinity of the end of the optical fiber (laser heating element), along which laser radiation propagates, generate acoustic signals characteristic of the elementary act of boiling, which precede the appearance of large-amplitude signals. It has been established that large amplitude signals are caused by shock waves that arise during the collapse of the main bubble and secondary bubbles - “rebounds”.

Two-photon pumped random lasing in MAPbBr3 with directional output for far-field applications

We investigate the random lasing properties of polycrystalline MAPbBr3 grown in a hollow fiber. Coupling of the random lasing on the inner wall of the hollow fiber into the annular cylinder and guided by the inner surface of hollow cavity enable directional output of the random lasing emission. The polycrystalline MAPbBr3 was grown by the capillary effect, when one end of the hollow fiber was dipped into the precursor solution. A two-photon pumping scheme was employed, where femtosecond pulses centered at about 800 nm was focused onto the MAPbBr3 polycrystals through the side wall of the hollow fiber. Random lasing was achieved due to the strong optical scattering by the interfaces within the polycrystals on the inner wall of the hollow fiber. The random lasing output was re-collimated into a roughly parallel beam with a circular transverse mode, which favors far-field applications of random lasers. Two-photon pumping enables larger penetration depth and larger excitation volume than single-photon pumping, so that strong lasing spot can also be observed in the center area of the output laser beam.