Fiber Axis Research Articles

Transferring heat accumulated by asphalt pavement from inside to outside through carbon fibers

On the Qinghai-Tibet Plateau, intense solar irradiation will cause serious heat accumulation in asphalt pavement. Downward heat transfer will disturb the permafrost under subgrade, thus leading to a series of subgrade and pavement diseases. This makes construction of asphalt pavement in the permafrost regions of the Qinghai-Tibet Plateau a world-class challenge. This paper proposes for the first time a transversal heat transfer channel in asphalt pavement, which can quickly transfer heat accumulated in pavement to road shoulders. Finite element software ABAQUS was used to simulate the rutting plate with high axial thermal conductivity carbon fibers inserted transversely. Under the constant heat load of 500 W/m2, the heat flux near the carbon fibers showed the characteristic of convergence. The maximum transverse heat flux in the carbon fibers reached 4.97×107W/m2, which was 14 times that in the asphalt mixture. Meanwhile, the maximum vertical heat flux in the carbon fibers reduced to 2.62×106W/m2, which was 12 % less than the asphalt mixture. The effective thermal conductivity of composite specimens with different carbon fiber parameters was studied through control experiments. When the axial thermal conductivity, volume fraction and number of carbon fiber bundles increased to 100 W/m·°C, 10.72 % and 4 bundles respectively, the transverse ETC of composite specimens increased to 4.05 W/m·°C, 7.09 W/m·°C and 16.18 W/m·°C respectively. They were 3.12 times, 5.45 times and 12.45 times of the control group. The radial thermal conductivity of carbon fibers has a significant effect on the vertical ETC. When it decreased to 0.2 W/m·°C, the vertical ETC decreased by 6.15 % compared with the control group. The temperature variation trend of specimens were measured by a laboratory irradiation experiment. The maximum temperature difference between the control group and the experimental group at 0 mm was 5.81 °C, and the average temperature difference within 2 h was 5.14 °C. The maximum temperature difference at 50 mm was 3.84 °C and the average temperature difference within 2 h was 3.24 °C. The results showed that the transverse heat transfer channel can reduce downward heat transfer. The application of the channels will enhance transverse heat release and relieve heat accumulation of asphalt pavement. This can create a low temperature state for pavement structure and has a positive effect on maintaining the stability of the permafrost regions on the Qinghai-Tibet Plateau.

Effect of temperature profiles on Yb3+-doped fiber amplifiers

We present a numerical analysis of the thermal effect of an Yb3+-doped fiber segment subjected to different temperature variation profiles, with the intention of determining the best energy conversion efficiency. The analysis is carried-out using different pump schemes and singular temperature profiles in Yb3+-doped fibers. The study indicates that a temperature distribution, with a concave parabolic profile along the fiber axis, shows higher stability in a fiber amplifier scheme, and it therefore becomes steadier at higher pump power level. Additionally, we find that for a constant temperature profile of 20 °C, the highest energy conversion efficiency occurs with a fiber segment of approximately 1.8 m, while for a constant temperature of 200 °C the maximum conversion occurs for a fiber span approximately 2.31 m. This makes it useful for using it as a sensor, at a temperature in a range of 20 °C to 200 °C. These results can be employed as a tool for optimization in the design of fiber lasers and amplifiers as sensors.

A Long-Term Monitoring Method of Corrosion Damage of Prestressed Anchor Cable

Based on high-stress characteristics of prestressed anchor cables, this paper develops an axial-distributed testing method to test corrosion damage of prestressed anchor cables. The positioning accuracy and corrosion range of an axial-distributed optical fiber sensor is studied, and its mathematical model between corrosion mass loss and axial fiber strain is established. The experimental results show that the fiber strain from an axial-distributed sensor enables one to reflect the corrosion rate along a prestressed anchor. Moreover, it has a greater sensitivity when an anchored cable has a higher stress. The mathematical model between corrosion mass loss and axial fiber strain is determined to be ε=4723.64ρ+2592.95. The corrosion location along the anchor cable is characterized by axial fiber strain. Therefore, this work provides an insight for cable corrosion.

Whispering gallery mode microsphere resonator based on cylindrical air cavity coupling.

In this Letter, an optical fiber whispering gallery mode microsphere resonator based on cylindrical air cavity coupling is proposed and demonstrated. The cylindrical air cavity is vertical to the axis of a single-mode fiber and in touch with the fiber core, fabricated by using femtosecond laser micromachining together with hydrofluoric acid etching. A microsphere is inserted into the cylindrical air cavity and in tangential contact with the inner cavity wall, which is in touch with or inside the fiber core. The light traveling in the fiber core is coupled into the microsphere via an evanescent wave when the light path is tangential to the contacting point of the microsphere and the inner cavity wall, resulting in whispering gallery mode resonance when the phase-matching condition is satisfied. Such a device is highly integrated, robust in structure, low in cost, stable in operation, and has a good quality factor (Q) of 1.44 × 104.

Ternary selenides nanosheets constituting coaxial structural electrode for flexible supercapacitors

For flexible supercapacitors (FSCs), the structural collapse and performance degradation are still bottlenecks that need to be addressed. Herein, Ni-Co selenides (NCS) nanosheets are fabricated into "sponge" grown in situ on flexible conductive nickel-plated carbon cloth (NPCC), constructing the coaxial electrode structure, consisting of NCS nanosheets “sponge layer” (SL), Ni-plated layer (NL) and carbon fiber axis (CFA). The NC0.25S0.5-5/NPCC coaxial electrode shows a high areal capacitance of 6.47 F cm−2 at the 6 mA cm−2 (Hg/HgO reference electrode, 1 M KOH electrolyte) and excellent structural stability with no cracking or fracture after 5000 bending cycles. With the good electronic conductivity, the intermediate NL binds the SL active material and the flexible CFA substrate together to avoid breakage under mechanical deformation. A developed FSC device using the NC0.25S0.5-5/NPCC electrode shows the maximum energy density of 58.4 Wh kg−1. Besides, the excellent flexibility and coaxial structural stability endow the FCS with 90.5% retention of capacitance after 6000 cycles of electrochemical testing and negligible attenuation of electrochemical performance under bending at 180 ° in the last 1000 cycles.

Fiber Orientation Reconstruction from SEM Images of Fiber-Reinforced Composites

The orientation of fibers in composites reinforced with short fibers can provide insight into the microstructure of the material and considerably affect its macroscopic characteristics. However, the present standard techniques for detecting fiber orientation and length based on microscopic image processing have faults in practical applications, including high effort, low efficiency, and unreliable measurement results. In this study, a method for measuring fiber orientation based on 3D reconstructions of scanning electron microscope (SEM) images is provided. The geodesic active contour (GAC) model is applied to segment the fibers in the SEM images. Matching the fiber contours with the scale-invariant feature transformation (SIFT) algorithm successfully extracts 3D orientation information from the fiber contours. The unit vector of the fiber axis is fitted from the extracted point cloud using the ordinary least squares (OLS) method. With a maximum deviation of 3.83° and an average deviation of 1.50°, the measurement findings of this method are substantially comparable to those of the image-measuring instrument. This paper offers a quantitative approach to studying the microstructure of short fiber-reinforced composites, thereby furnishing objective evidence to support the development and research of such materials.

Fabrication of Silane-Grafted Cellulose Nanocrystals and Their Effects on the Structural, Thermal, Mechanical, and Hysteretic Behavior of Thermoplastic Polyurethane.

Reinforcement of polymer nanocomposites can be achieved by the selection of the appropriate fabrication method, surface modification, and orientation of the filler. Herein, we present a nonsolvent-induced phase separation method with ternary solvents to prepare thermoplastic polyurethane (TPU) composite films with excellent mechanical properties using 3-Glycidyloxypropyltrimethoxysilane-modified cellulose nanocrystals (GLCNCs). ATR-IR and SEM analyses of the GLCNCs confirmed that GL was successfully coated on the surface of the nanocrystals. The incorporation of GLCNCs in TPU resulted in the enhancement of the tensile strain and toughness of pure TPU owing to the enhanced interfacial interactions between them. The GLCNC-TPU composite film had tensile strain and toughness values of 1740.42% and 90.01 MJ/m3, respectively. Additionally, GLCNC-TPU exhibited a good elastic recovery rate. CNCs were readily aligned along the fiber axis after the spinning and drawing of the composites into fibers, which further improved the mechanical properties of the composites. The stress, strain, and toughness of the GLCNC-TPU composite fiber increased by 72.60%, 10.25%, and 103.61%, respectively, compared to those of the pure TPU film. This study demonstrates a facile and effective strategy for fabricating mechanically enhanced TPU composites.

The anatomy of transcriptionally active chromatin loops in Drosophila primary spermatocytes using super-resolution microscopy.

While the biochemistry of gene transcription has been well studied, our understanding of how this process is organised in 3D within the intact nucleus is less well understood. Here we investigate the structure of actively transcribed chromatin and the architecture of its interaction with active RNA polymerase. For this analysis, we have used super-resolution microscopy to image the Drosophila melanogaster Y loops which represent huge, several megabases long, single transcription units. The Y loops provide a particularly amenable model system for transcriptionally active chromatin. We find that, although these transcribed loops are decondensed they are not organised as extended 10nm fibres, but rather they largely consist of chains of nucleosome clusters. The average width of each cluster is around 50nm. We find that foci of active RNA polymerase are generally located off the main fibre axis on the periphery of the nucleosome clusters. Foci of RNA polymerase and nascent transcripts are distributed around the Y loops rather than being clustered in individual transcription factories. However, as the RNA polymerase foci are considerably less prevalent than the nucleosome clusters, the organisation of this active chromatin into chains of nucleosome clusters is unlikely to be determined by the activity of the polymerases transcribing the Y loops. These results provide a foundation for understanding the topological relationship between chromatin and the process of gene transcription.

Melt Electrowriting of Liquid Crystal Elastomer Scaffolds with Programmed Mechanical Response.

Recently, significant advances have been achieved to precisely program the response of liquid crystal elastomers (LCEs) through extrusion-based additive manufacturing techniques; however, important challenges remain, especially when well-defined scaffolds based on ultrafine fibers are required. Here the melt electrowriting of reactive liquid crystalline inks, leading, after ultraviolet-light-induced crosslinking, to digitally positioned uniform LCE fibers with diameters ranging from hundreds of nanometers to tens of micrometers is presented, whichishardly accessible with conventional extrusion-based printing techniques. The electrowriting process induces the preferential alignment of the mesogens parallel to the fiber's axis. Such an alignment, defined by the printing path, determines the mechanical response of the crosslinked material upon stimulation. This manufacturing platform allows the preparation of open square lattice scaffolds with ultrafine fibers (afew micrometers in diameter), periods as small as 90µm, and well-defined morphology. Additionally, the combination of accurate fiber stacking (up to 50 layers) and fiber fusion between layers leads to unprecedented microstructures composed of high-aspect-ratio LCE thin walls. The possibility of digitally controlling the printing of fibers allows the preparation complex fiber-based scaffolds with programmed and reversible shape-morphing, thus opening new avenues to prepare miniaturized actuators and smart structures for soft robotics and biomedical applications.

Cross-axis Bragg gratings in few-mode fibers inscribed with a femtosecond laser point-by-point technique

Point-by-point (PbP) cross-axis Bragg gratings in a step-index two-mode fiber are fabricated by tightly focused femtosecond laser pulses. The grating is formed by inscribing a line of periodic damage points crossing the fiber axis at a certain tilting angle. We experimentally show that the cross-axis structure can introduce multiple mainband resonances associated with the higher-order modes, with wavelength spacing proportional to the tilting angle. We also develop a numerical model for the PbP-inscribed gratings based on pulse-wave approximation and the standard coupled-mode theory, the resulting simulation exhibits a good agreement with the experimental findings. This work suggests the higher-order fiber modes, synergizing with the PbP technique, has the potential to add a new dimension to designing gratings with desired spectral spacing; such an inverse problem of PbP gratings can be assisted by the numerical modal we developed.

Fiber orientation effects on grinding characteristics and removal mechanism of 2.5D Cf/SiC composites

Carbon fiber reinforced silicon carbide (Cf/SiC) composites are widely used in aerospace for their excellent mechanical properties. However, the quality of the machined surface is poor and unpredictable due to the material heterogeneity induced by complex removal mechanism. To clarify the effects of fiber orientation on the grinding characteristics and removal mechanism, single grit scratch experiments under different fiber orientations are conducted and a three-phase numerical modelling method for 2.5D Cf/SiC composites is proposed. Three fiber cutting modes i.e., transverse, normal and longitudinal, are defined by fiber orientation and three machining directions i.e., MA (longitudinal and normal), MB (longitudinal and transverse) and MC (normal and transverse), are selected to investigate the effect of fiber orientation on grinding force and micro-morphology. Besides, a three-phase cutting model of 2.5D Cf/SiC composites considering the mechanical properties of the matrix, fiber and interface is developed. Corresponding simulations are performed to reveal the micro-mechanism of crack initiation and extension as well as the material removal mechanism under different fiber orientations. The results indicate that the scratching forces fluctuate periodically, and the order of mean forces is MA > MC > MB. Cracks tend to grow along the fiber axis, which results in the largest damage layer for transverse fibers and the smallest for longitudinal fibers. The removal modes of transverse fibers are worn, fracture and peel-off, in which normal fibers are pullout and outcrop and the longitudinal fibers are worn and push-off. Under the stable cutting condition, the change of contact area between fiber and grit leads to different removal modes of fiber in the same cutting mode, and the increase of contact area results in the aggravation of fiber fracture.

Body plan of Dickinsonia, the oldest mobile animals

ABSTRACTMaterials collected on the territory of the southeastern White Sea area, including diversely preserved body imprints, combined body-trace fossils, specimens with signs of intravital damage and regeneration, and extended ontogenetic series, make it possible to significantly widen the data on the body plan and biology of Dickinsonia, the oldest known mobile animal, included in the Late Precambrian taxon of high rank, Proarticulata. A number of reconstructed anatomical features were added to the obvious directly observed features of Dickinsonia, such as a consistent body shape lacking lateral appendages and temporary outgrowths, transverse differentiation, and anterior–posterior polarity. These reconstructed features include dorsoventral polarity, ciliated mucus-secreting epithelium underlain by a basal lamina, two rows of blind food-gathering pockets, absence of a through-gut, nervous system of diffusive type, axial support band and muscle fibres. Such a set of features indicates the affinity of Dickinsonia and Proarticulata as a whole (the only known Ediacaran Metazoa) to Urbilateria, a hypothetical ancestor of bilaterally symmetrical animals.

Synthesis and Characterization of Electrospun Carbon Nanofibers from Polyacrylonitrile and Graphite Nanoplatelets.

Sol-gel electrospinning process was used to prepare electrospun carbon nanofibers (ECNFs) from polyacrylonitrile and graphite nanoplatelets. The nanofibers of as-electrospun carbon were calcinated in argon from room temperature to 500 °C for 1h. Scanning and transmission electron microscopy with energy-dispersive X-ray spectroscopy and X-ray diffractometry (XRD) were used to characterize the synthesized ECNFs. The smooth ECNFs with a diameter of 129 ± 43 nm comprised conical platelets of 30-200 µm length. The plane-layered nanofibers contained crystallites along the long fiber axis and were mainly parallel.

Mechanical anisotropy of hair affected by genetic diseases highlights structural information related to differential crosslinking in keratins.

Previous work with Atomic Force Microscope (AFM) nanoindentation, on longitudinal and cross-sections of the human hair fibre, allowed for the derivation of a model for the mechanical behaviour of human hair, called the Anisotropic Index. Expanding that research further, and by applying this model, the nanomechanical behaviour of hairs from patients with the disease Trichothiodystrophy (TTD) has been examined and structural insights, gained from combining the AFM results with Differential Scanning Calorimetry (DSC) experiments and tensile measurements, suggests that TTD-affected hairs have a relatively increased amount of Keratin Intermediate Filaments, contained in compartments of differing crosslinking extent. The associated calculations of axial and transverse Young's Moduli deliver values in good agreement with the measured fibre mechanics. Furthermore, comparing these findings with the results previously obtained from the study of hairs from patients with the disease Monilethrix, it is shown that the Anisotropic Index correlates well with the known deficiencies in both hair types obtained from such patients and allows for discerning between the Control hair and from those affected by the two diseases. AFM nanoindentation along and across the fibre axis and the Anisotropic Index thus appear to reveal structural details of hair not otherwise acquirable, whilst DSC may offer a quick and simple method for distinguishing between different severities of TTD.

Comparing electrochemical and spectroscopic properties of three cytochrome nanowires from Geobacter sulfurreducens.

The model anaerobic bacterium, Geobacter sulfurreducens, produces filaments that mediate extracellular electron transfer as part of its respiratory metabolism in oxygen-free environments. The physical, biological, and chemical principles supporting conductivity in protein filaments such as those produced by Geobacter have considerable importance for our understanding of biogeochemical cycles, impacts of climate change, and advanced biomedical devices. We have recently discovered that G. sulfurreducens produces at least three such filaments, which structural studies revealed to be polymers of multiheme cytochromes, OmcS, OmcE, and OmcZ. All three filaments are composed of these cytochrome subunits with bis-histidine-coordinated hemes forming a chain along the fiber axis. Our work aims to understand the structure-property relationships in these conductive filaments, including those that directly support long-range electron transport. Our structural studies show that the arrangement of heme in OmcS and OmcE are nearly identical, despite lacking sequence homology. These two filaments also exhibit heme coordinated across the subunit-subunit interface by histidines from neighboring subunits. The structure of OmcZ is distinct in that it lacks this interfacial heme. One heme per subunit is offset from the axial chain and largely exposed to solvent. Moreover, all heme pairs in these filaments, and indeed most heme pairs within multiheme c-type cytochrome structures in the Protein Databank, cluster into common rotation angle and separation distance arrangement, suggesting conserved electron transfer motifs across domains of life. Spectroscopic comparison between OmcS, OmcE, and OmcZ filaments, and their disassembled monomers will be discussed. Additionally, an outline of the biophysical and electrochemical characterizations of cytochrome filaments and their monomeric subunits will be addressed. The new concepts that will be concluded from the investigation of conductive cytochrome filaments in Geobacter will lead to a better understanding of biological structures supporting long-range electronic conductivity.

Microstructure and Crystallographic Characteristics of Stenolaemate Bryozoans (Phylum Bryozoa and Class Stenolaemata)

The bryozoan Cass Stenolaemata is currently represented by the Order Cyclostomata. They produce skeletons made exclusively of calcite crystals assembled into different microstructures. Despite extensive previous research, no appropriate crystallographic techniques have been applied to decipher their crystallographic organization. We present an in-depth crystallographic study of the microstructures of three extant species (Fasciculipora ramosa, Hornera robusta, and Cinctipora elegans) using scanning electron microscopy and associated techniques (energy-dispersive spectroscopy and electron backscatter diffraction), together with atomic force microscopy and micro-computed tomography. We differentiate two microstructures, foliated and tabular calcite, and establish consistent models of their crystallography. Foliated calcite of F. ramosa and C. elegans consists of co-oriented laths arranged with their c-axes parallel to their elongation axis and to their main surfaces, and one a*-axis perpendicular to the latter (sheet texture). Tabular calcite of H. robusta consists of polygonal tablets with the c-axis as fiber axis (axial texture), perpendicular to the tablet surface. The foliated calcite of bryozoans is homeomorph to that of bivalves but has a significantly different crystallography. The tabular calcite of bryozoans lacks the spiral morphology of the tablet-shaped calcite of craniiformis brachiopods and has a different orientation of the c-axis with respect to the constituent tablets.

Interaction between thin conductive fibers and microwave radiation

We study the effect of an anomalously strong interaction of electromagnetic radiation with very thin conducting fibers. Metal, semiconductor or graphite fibers, which diameter is several hundred times smaller than the radiation wavelength, strongly absorb and scatter the electromagnetic waves, which electric vector is parallel to the fiber axis. The efficiency factors of attenuation, absorption, scattering and pressure of radiation for fibers with a diameter of several micrometers in the centimeter and millimeter ranges reach several thousand. We determine the nature of this effect. It occurs when the transverse dimension of the fiber is comparable to the thickness of the skin layer. Then the electric field of the incident wave fills the entire volume of the fiber, and the absorbed power is the highest. We also provide a theoretical analysis of such effect, determine conditions for its existence: the ratio between the radiation wavelength and the diameter of the fiber, the value of conductivity. We also provide an experimental study of the effect, when unfocused radiation beam with a wavelength of 8 mm at the output of waveguide with a \(7.2 \times 3.4\) mm cross section transfers more than 10% of the beam power to a 12 μm diameter graphite fiber. We make an analysis of the mathematical model of the process of heating of graphite fiber by a microwave radiation beam. Then we solve a heat conduction equation and find the temperature distribution along the fiber, which is in agreement with the measured one.

Seasonal temperature and precipitation regimes drive variation in the wood of oak species (Quercus) along a climatic gradient in western Mexico

Summary To achieve optimal balance among wood’s support, storage, and transport functions, tree species present adaptive variation in wood anatomical traits. Oaks (Quercus) are woody plants that are dominant in many ecosystems, possess wide variation in wood traits, and can tolerate water stress in diverse habitats. Mountain regions contain steep climatic gradients that exert strong environmental pressures on wood traits. The aims of this study were: (1) to quantify the anatomical variation in 21 oak species distributed along an environmental gradient and (2) to analyze the interspecific variation among the studied species. Fibres and parenchyma fractions were the most abundant cell types. We found a trade-off between total fibre fraction and total parenchyma fraction modulated by the precipitation during the warmest quarter in which oak species in drier areas invested more in support cells. The 21 oak species studied showed vasicentric tracheids, which could be essential to compensate for the transport system in drier areas. Wood density was negatively correlated with the axial parenchyma fraction and fibre lumen width. Oak species have high interspecific variation in the total vessel fraction and vessel diameter. Anatomical variation in oak species along a climatic gradient showed a broad continuum of fibre characteristics from wide to narrow wall and lumen, abundant to scarce parenchyma, and wide to narrow vessels. These variations imply a diversification of ecological strategies within the genus that includes the vascular design of the stem to define the tolerance and competitiveness of the oak species.

High-sensitivity optical fiber magnetic field sensor based on multimode optical fiber multi Fabry-Perot interference cavities.

A high-sensitivity optical fiber magnetic field sensor based on a multi-Fabry-Perot interference (F-P) cavity in an etched multimode optical fiber (MMF) was proposed. The MMF was etched along the fiber axis and a hole with the length of about 250 µm formed in the MMF. The multi-F-P cavity in the MMF is a sandwich structure, which is composed of UV glue, magnetic fluid and UV glue. The refractive index and effective cavity length of the magnetic fluid cavity change with the changing of the external magnetic field, which will result in changes of the reflection spectra of the multi-F-P. Thus, the external magnetic field could be detected by the changes of spectra. Experimental results showed that the high magnetic field sensitivity of 299.7 pm/mT and 0.164 dB/mT were obtained in the range of 0∼8 mT weak magnetic induction intensity by using the wavelength and intensity demodulations, respectively. The proposed sensor shows the potential applications in the magnetic field measurement in the weak magnetic environment.

Wavelength-switchable L-band fiber laser assisted by random reflectors

A wavelength-switchable L-band erbium-doped fiber laser (EDFL) assisted by an artificially controlled backscattering (ACB) fiber reflector is here presented. This random reflector was inscribed by femtosecond (fs) laser direct writing on the axial axis of a multimode fiber with 50 μm core and 125 μm cladding with a length of 17 mm. This microstructure was placed inside a surgical syringe to be positioned in the center of a high-precision rotation mount to accurately control its angle of rotation. Only by rotating this mount, three different output spectra were obtained: a single wavelength lasing centered at 1574.75 nm, a dual wavelength lasing centered at 1574.75 nm and 1575.75 nm, and a single wavelength lasing centered at 1575.5 nm. All of them showed an optical signal-to-noise ratio (OSNR) of around 60 dB when pumped at 300 mW.