Expansion Of Fibers Research Articles

Requirement of Pitx2 for skeletal muscle homeostasis

Skeletal muscle is generated by the successive incorporation of primary (embryonic), secondary (fetal), and tertiary (adult) fibers into muscle. Conditional excision of Pitx2 function by an MCKCre driver resulted in animals with histological and ultrastructural defects in P30 muscles and fibers, respectively. Mutant muscle showed severe reduction in mitochondria and FoxO3-mediated mitophagy. Both oxidative and glycolytic energy metabolism were reduced. Conditional excision was limited to fetal muscle fibers after the G1-G0 transition and resulted in altered MHC, Rac1, MEF2a, and alpha-tubulin expression within these fibers. The onset of excision, monitored by a nuclear reporter gene, was observed as early as E16. Muscle at this stage was already severely malformed, but appeared to recover by P30 by the expansion of adjoining larger fibers. Our studies demonstrate that the homeodomain transcription factor Pitx2 has a postmitotic role in maintaining skeletal muscle integrity and energy homeostasis in fetal muscle fibers.

Analysis the temperature effect on the output polarization degree of the fiber Lyot depolarizer

First, the temperature effect on the output polarization degree of the fiber Lyot depolarizer was analyzed in this paper theoretically, which shows that when the environment temperature changes from −40℃ to 80℃, the degree of the output light polarization (DOP) of the fiber Lyot depolarizer will increase until about 70℃, then DOP begin to decrease. The further numerical simulations indicate that this result was caused together by thermally induced group birefringence and thermal coefficient of expansion of the polarization fiber. Using our made fiber Lyot depolarizer (DOP≤0.3% when the environment temperature is 20℃), DOP of the fiber Lyot depolarizer was studied at the condition of a variable temperature experimentally, the results are in agreement with the related theoretically results basically, at last, the difference between theoretical and experimental results is discussed, the possible methods to reduce the influence of the temperature on the output DOP of fiber Lyot depolarizer is presented in this paper. It is a good guiding significance to improve the depolarization performance of the fiber Lyot depolarizer in the fields of fiber sensor, fiber gyroscope, fiber Raman amplifier and so on as we believe.

Micromechanics based multi-level model for predicting the coefficients of thermal expansion of hybrid fiber reinforced concrete

This study is involved with presenting a multi-level micromechanical model for predicting the coefficients of thermal expansion (CTE) of randomly distributed and oriented short hybrid fiber reinforced concrete (HFRC), which includes the cement paste level, concrete level, and HFRC level. In this micromechanical model, the inner products (IP), outer products (OP), calcium hydroxide (CH), unhydrated clinker, sands, aggregates and hybrid fibers are comprehensively considered. A substepping homogenization framework is presented to realize the upscaling from the microstructure to macro HFRC, based on which the overall CTE of HFRC is determined. In addition, the volume fractions of phases at each level are also presented to facilitate the prediction of CTE. Comparisons with experimental data from previous studies are implemented level by level. Subsequently, the influences of the water-cement ratio, the hydration degree, the aggregate property and the fiber property on the CTE are discussed carefully.

Measurement of Material Deformation with Fiber Bragg Gratings (Summarization)

Fiber sensing elements based on Bragg gratings (FBG) are a prospective basis of sensors for detecting deformations in measuring systems, in particular, for integrated control of various structures. The possibility of their application in the structure of polymer composite material for aerospace construction elements is examined. The FBG operating principle is based on change in the period of the grating—the periodic structure of the refractive index of an optical fiber core. Change in the period can cause either thermal expansion or compression of an optical fiber. Therefore, to solve integrated control problems, one has to understand the cause of optical fiber deformation in the area of location of FBG—with change in mechanical loading applied to it or thermal operating conditions. Proposed approaches to the allowance for temperature change when measuring deformation with FBG are systemized and the results of works in this field are presented. Possible implementations of each approach are described. Measurement accuracy of deformation and temperature is determined. The structural scheme of sensing elements is described.

Three-phase micromechanical analysis of residual stresses in reinforced fiber by carbon nanotubes

In this study, circular disk model and cylinder theory for two dimension (2D) and three dimension (3D), respectively, have been used to determine residual stresses in three-phase representative volume element. The representative volume element is consisting of three phases: carbon fiber, carbon nanotubes, and polymer matrix, that carbon fiber is reinforced by carbon nanotube using electrophoresis method. Initially, the residual stresses analysis of two-phase representative volume element has been implemented. The two-phase representative volume element has been divided to carbon fiber and matrix phases with different volume fractions. In the three-phase representative volume element, although the volume fraction of carbon fiber is constant and equal to 60%, the volume fractions of carbon nanotubes for various cases are different as 0%, 1%, 2%, 3%, 4%, and 5%. Also, there are two different methods to reinforce the fiber according to different coefficients of thermal expansion of the carbon fiber and carbon nanotube in two longitudinal and transverse directions; carbon nanotubes are placed on carbon fiber either parallel or around it like a ring. Subsequently, finite element method and circular disk model have been used for analyzing micromechanic of the residual stresses for 2D and then the results of stress invariant obtained by the finite element method have been compared with the circular disk model. Moreover, for 3D model, the finite element method and cylinder theory have been utilized for micromechanical analysis of the residual stresses and the results of stress invariant obtained by them, have been compared with each other. Results of the finite element method and analytical model have good agreement in 2D and 3D models.

(Invited) SiC Growth Parameter Evolution Utilizing Infrared Thermal Imaging Towards Realization of Extremely Low Dislocation Bulk SiC

The NASA Glenn Research Center (GRC) has employed infrared thermal imaging technology in a hot wall chemical vapor deposition (CVD) system for thermal measurement of silicon carbide (SiC) crystals mounted vertically in the gas stream. The use of infrared thermal imaging technology revealed deficiencies in growth parameters that had previously not been observable utilizing traditional noncontact monitoring techniques. GRC has been investigating the lateral expansion (⊥ to (0001)) of pseudo SiC fiber seed crystals using a custom designed horizontal flow hot wall CVD system in proof of concept research, for a radically new bulk growth process. This bulk growth process would, ideally produce SiC boules with just one single centrally located screw dislocation (SD). Dislocations in general have a negative impact on SiC devices and device fabrication. Current commercially available SiC substrates have a dislocation density of ~1000 cm2. A key requirement of this process is the lateral homoepitaxial growth expansion of a SiC fiber without the introduction of additional defects. This requires maintaining growth temperatures along the length of the SiC fiber. In the absence of purpose grown fiber like seed crystals, pseudo seed crystals were created by mechanically dicing thin slivers from a-plane and m-plane oriented boule slices. The slivers (~17000 x 2000 x 400) µm’s were subsequently subjected to gaseous etching in hydrogen to produce needle like seed crystals with fiber like dimensions with a width of ~100 µm’s. The seed crystals were oriented vertically in a gas stream of the horizontal CVD system. Traditional optical pyrometry coupled with a small CCTV aligned along the horizontal axis was used to be provide real time thermal and optical data of the CVD. Due to the extremely small cross-sectional area of the seed crystals, the thermal radiation was insufficient to be measured with optical pyrometry and was ineffective in resolving the temperature of the vertical slivers. Only the temperature of the carrier holding the seed crystals could be resolved. A commercially available infrared thermal imaging system equipped with an extra-long working distance (530mm) lens replaced the pyrometer and CCTV. The thermal imager requires that the target be only 3 x 3 pixels to obtain accurate temperatures. When coupled with long working distance optics the temperature of the seed crystals could be resolved. A thermal gradient that was previously unobserved was now viewable. Growth parameters were adjusted to compensate for the gradient preventing nucleation of 3C-SiC at the tip of the seed crystal. A growth rate (⊥ to (0001)) of ~80 μm/hr was achieved. Total lateral growth was > 3.5mm. Initial analysis by synchrotron white beam x-ray topography (SWBXT) confirms, that the fiber growth was homoepitaxial, matching the polytype of the respective underlying region of the seed sliver. Although the as grown SiC contained a high density of basal plane dislocations (BPD’s) it appears that the BPD’s originated in the pseudo seed crystal without additional BPD’s introduced during the growth.

Residual Tensile Property of Plain Woven Jute Fiber/Poly(Lactic Acid) Green Composites during Thermal Cycling.

This study investigated the residual tensile properties of plain woven jute fiber reinforced poly(lactic acid) (PLA) during thermal cycling. Temperature ranges of thermal cycling tests were 35–45 °C and 35–55 °C. The maximum number of cycles was 103 cycles. The quasi-static tensile tests of jute fiber, PLA, and composite were conducted after thermal cycling tests. Thermal mechanical analyses of jute fiber and PLA were conducted after thermal cycling tests. Results led to the following conclusions. For temperatures of 35–45 °C, tensile strength of composite at 103 cycles decreased 10% compared to that of composite at 0 cycles. For temperatures of 35–55 °C, tensile strength and Young’s modulus of composite at 103 cycles decreased 15% and 10%, respectively, compared to that of composite at 0 cycles. Tensile properties and the coefficient of linear expansion of PLA and jute fiber remained almost unchanged after thermal cycling tests. From observation of a fracture surface, the length of fiber pull out in the fracture surface of composite at 103 cycles was longer than that of composite at 0 cycles. Therefore, tensile properties of the composite during thermal cycling were decreased, probably because of the decrease of interfacial adhesion between the fiber and resin.

Expansion of mossy fibers and CA3 apical dendritic length accompanies the fall in dendritic spine density after gonadectomy in male, but not female, rats.

Androgen loss is an important clinical concern because of its cognitive and behavioral effects. Changes in androgen levels are also suspected to contribute to neurological disease. However, the available data on the effects of androgen deprivation in areas of the brain that are central to cognition, like the hippocampus, are mixed. In this study, morphological analysis of pyramidal cells was used to investigate if structural changes could potentially contribute to the mixed cognitive effects that have been observed after androgen loss in males. Male Sprague-Dawley rats were orchidectomized or sham-operated. Two months later, their brains were Golgi-impregnated for morphological analysis. Morphological endpoints were studied in areas CA3 and CA1, with comparisons to females either intact or 2months after ovariectomy. CA3 pyramidal neurons of orchidectomized rats exhibited marked increases in apical dendritic arborization. There were increases in mossy fiber afferent density in area CA3, as well as robust enhancements to dendritic structure in area CA3 of orchidectomized males, but not in CA1. Remarkably, apical dendritic length of CA3 pyramidal cells increased, while spine density declined. By contrast, in females overall dendritic structure was minimally affected by ovariectomy, while dendritic spine density was greatly reduced. Sex differences and subfield-specific effects of gonadal hormone deprivation on the hippocampal circuitry may help explain the different behavioral effects reported in males and females after gonadectomy, or other conditions associated with declining gonadal hormone secretion.

Determinants of aponeurosis shape change during muscle contraction

Aponeuroses are sheet-like elastic tendon structures that cover a portion of the muscle belly and act as insertion sites for muscle fibers while free tendons connect muscles to bones. During shortening contractions, free tendons are loaded in tension and lengthen due to the force acting longitudinally along the muscle׳s line of action. In contrast, aponeuroses increase in length and width, suggesting that aponeuroses are loaded in directions along and orthogonal to the muscle׳s line of action. Because muscle fibers are isovolumetric, they must expand radially as they shorten, potentially generating a force that increases aponeurosis width. We hypothesized that increases in aponeurosis width result from radial expansion of shortening muscle fibers. We tested this hypothesis by combining in situ muscle-tendon measurements with high-speed biplanar fluoroscopy measurements of the turkey׳s lateral gastrocnemius (n=6) at varying levels of isotonic muscle contractions. The change in aponeurosis width during periods of constant force depended on both the amount of muscle shortening and the magnitude of force production. At low to intermediate forces, aponeurosis width increased in direct proportion to fiber shortening. At high forces, aponeurosis width increased to a lesser extent or in some cases, decreased slightly during fiber shortening. Our results demonstrate that forces generated from radial expansion of shortening muscle fibers tend to drive increases in aponeurosis width, whereas longitudinal forces tend to decrease aponeurosis width. Ultimately, it is these two opposing forces that drive changes in aponeurosis width and alter series elastic stiffness during a muscle contraction.

Histologic and sonographic features of holmium laser in the treatment of chronic venous disease.

A new holmium laser (HOL) has been introduced to the market. The device is able to reduce the great saphenous vein (GSV) caliber in a tumescence-free procedure, favoring an effective sclerotherapy of large vessels. Aim of the present investigation is to provide the first in vivo data about the effect of HOL on GSV histology. Six chronic venous disease (C2-5, Ep, As, Pr) patients (M:F ratio 1:1; age: 57±8, BMI 24±2 kg/m2) underwent HOL-assisted caliber reduction of the GSV, high-ligation and flush ligation of the incompetent tributaries. Three cm of proximal great saphenous vein not treated by laser and 3 cm of a contiguous segment that was just previously treated by HOL were harvested. Histological assessments were performed. Patent GSV lumen caliber was assessed at the mid-thigh right before, and after the procedure. Periprocedural pain was graded by Visual Analogue Scale. GSV samples after holmium laser therapy showed thickening of the vascular wall with a decreased, yet patent lumen. Immunostaining demonstrated intact endothelial lining in both the treated and not treated segments. Expansion of collagen fibers was observed in the laser-treated segments. Collagen appeared more homogeneous than in controls, with an amorphous appearance. Laser treated veins showed a reduction in elastic fibers with greater fragmentation. Smooth muscle cells appeared swollen. The caliber of the mid-thigh great saphenous vein lumen decreased from 8.1±0.8 mm to 3.9±0.2 mm (P<0.0001). The average periprocedural pain was 1±0.6. HOL significantly reduces the caliber of the GSV. The endothelial lining is spared, while the remaining wall is thickened by a hyalinization-like process.

Exposure to noise in wood chipping operations under the conditions of agro-forestry

An increasing number of agricultural contractors are getting into industrial wood chipping, following the rapid expansion of fiber farms on ex-arable land. Wood chippers are noisy machines and agricultural contractors tend to work long hours, which raises the question about their exposure to noise. The objective of the study was to quantify noise exposure for this occupational group. The Authors selected a representative operation and monitored noise exposure for five full working days, covering the main job types typically encountered in agro-forestry. Noise exposure was highest during chipping time, with 81.8 dB(A). The main source of noise was the powerful diesel engine, followed by the chipper drum: they generated the highest noise levels in the 100–200 Hz and the 20–50 Hz frequency ranges, respectively. Daily noise exposure did not exceed the 80 dB(A) lower action value, and it was similar to the exposure of other workers operating industrial in-wood chippers. However, future optimization measures may lead to increasing the proportion of total time when the machine is under full load, and it generates the highest noise levels. Modeling exposure as a function of efficiency showed that exposure levels may exceed the lower action values, once utilization will increase above 64%. This is a realistic target, which may be achieved in the near future. Fortunately, the problem will materialize only with some specific operation types, which represent a minor component in the wood basket of agro-forestry chipping companies.

Properties of ultra-high performance fiber reinforced cementitious composites made with gypsum-contaminated aggregates and cured at normal and elevated temperatures

Aggregates in many parts of the Middle East are contaminated with gypsum. Therefore, in this study the effects of using gypsum-contaminated natural sand on the compressive strength and expansion of ultra-high performance fiber reinforced cementitious composites (UHPFRCCs) were investigated over a period of one year. Two groups of UHPFRCCs were designed with binary and ternary cementitious blends of Portland cement, silica fume, and/or ground granulated blast furnace slag. Each group consisted of five mixes with different SO3 contents of between 0.11% and 4.5% by weight of natural sand. For each mix, the samples were either water cured or steam cured over a 48h period. The microstructure of the cementitious composites was also studied by the SEM–EDX. Besides, some findings of UHPFRCCs were compared to those of Portland cement mortars. Test results indicated that UHPFRCCs showed a strength gain, particularly under steam curing and an insignificant expansion even in the presence of excess sulfates, in contrast to the mortars.

A 3-Dimensional Anatomic Study of the Distal Biceps Tendon: Implications for Surgical Repair and Reconstruction.

BackgroundComplete rupture of the distal biceps tendon from its osseous attachment is most often treated with operative intervention. Knowledge of the overall tendon morphology as well as the orientation of the collagenous fibers throughout the musculotendinous junction are key to intraoperative decision making and surgical technique in both the acute and chronic setting. Unfortunately, there is little information available in the literature.PurposeTo comprehensively describe the morphology of the distal biceps tendon.Study DesignDescriptive laboratory study.MethodsThe distal biceps terminal musculature, musculotendinous junction, and tendon were digitized in 10 cadaveric specimens and data reconstructed using 3-dimensional modeling.ResultsThe average length, width, and thickness of the external distal biceps tendon were found to be 63.0, 6.0, and 3.0 mm, respectively. A unique expansion of the tendon fibers within the distal muscle was characterized, creating a thick collagenous network along the central component between the long and short heads.ConclusionThis study documents the morphologic parameters of the native distal biceps tendon. Reconstruction may be necessary, especially in chronic distal biceps tendon ruptures, if the remaining tendon morphology is significantly compromised compared with the native distal biceps tendon. Knowledge of normal anatomical distal biceps tendon parameters may also guide the selection of a substitute graft with similar morphological characteristics.Clinical RelevanceA thorough description of distal biceps tendon morphology is important to guide intraoperative decision making between primary repair and reconstruction and to better select the most appropriate graft. The detailed description of the tendinous expansion into the muscle may provide insight into better graft-weaving and suture-grasping techniques to maximize proximal graft incorporation.

Direct drawing of gel fibers enabled by twist‐gel spinning process

A new twist‐gel spinning process for ultrahigh molecular weight polyethylene fibers is demonstrated which significantly increases the extraction rate of nonvolatile spin solvent while simultaneously reducing the consumption of extraction solvent by more than 75%. Applying twist to the gel fiber enables it to be directly hot‐drawn, allowing conventional solvent extraction to proceed significantly faster. While solvent extraction effectiveness is largely enhanced, the new process does not show reduced fiber properties. The tensile strength, Young's modulus, surface morphology, and geometry are relatively unaffected when compared to fibers produced using the conventional gel‐spinning process. The new twist‐gel spinning process is expected to improve the processing efficiency of gel‐spun high‐strength fibers, promoting broad expansion of these high performance fibers into applications that were previously prohibitive due to extremely slow production. POLYM. ENG. SCI., 55:1389–1395, 2015. © 2015 Society of Plastics Engineers

Numerical evaluation of the coefficients of thermal expansion of fibers in composite materials using a lamina-scale cost function with quasi-analytical gradients

In this work, the coefficients of thermal expansion (CTEs) of fibers in composite materials that contain microstructures are numerically evaluated using a lamina-scale cost function with quasi-analytical gradients. To consider the effects of fiber arrangements and local defects, such as interface debonding and voids, a variety of representative volume elements are modeled with a number of finite element meshes. Then, the CTEs of fibers are evaluated by minimizing a lamina-scale cost function that represents the difference between the measured CTEs and the computed CTEs by means of a computational homogenization scheme for the composite lamina. The descent direction of the cost function is obtained using quasi-analytical gradients that take partial derivatives from prediction models, such as the Schapery model and Hashin model defined in an explicit manner, which accelerates the minimization procedure. To verify the performance of the proposed scheme in terms of accuracy and efficiency, the CTEs of constituents calculated using the proposed scheme in a unidirectional composite lamina are compared with experimental values reported in the literature. Furthermore, the convergence behavior of the proposed scheme with quasi-analytical gradients is also investigated and compared with other minimization methods.

A Study on Accelerated Thermal Aging of High Modulus Carbon/Epoxy Composite Material

Composite materials have been used increasingly for various space applications due to the favorable characteristic of high modulus to density ratio and potential for near-zero coefficient of thermal expansion. In composite system, depending on the orientation of fibers, strength and stiffness can be changed so that the optimum structure can be accomplished. This is because the coefficient of thermal expansion (CTE) of carbon fibers is negative. For spacecraft and orbiting space structure, which are thermally cycled by moving through the earth' shadow for at least 5 years, it is necessary to investigate the change of properties of the material over time. In this study, thermal aging of epoxy matrix/high modulus carbon fiber composite materials are accelerated to predict the long term creep property. Specimens are tested at various temperatures of 100~140�� with dynamic mechanical analysis to obtain creep compliances that are functions of time and temperature. Using Time Temperature Superposition method, creep compliance curves at each temperature are shifted to the reference temperature by shift factor and a master curve is generated at the reference temperature. This information is useful to predict the long term thermal aging of high modulus composite material for spacecraft application.

FFPI-FBG hybrid sensor to measure the thermal expansion and thermo-optical coefficient of a silica-based fiber at cryogenic temperatures

In this Letter, a sensor consisting of a fiber Bragg grating (FBG) and a fiber Fabry–Perot interferometer (FFPI) sensor is developed to measure the coefficient of thermal expansion (CTE) and the thermo-optical coefficient (TOC) of a silica-based optical fiber at cryogenic temperatures. The FFPI is fabricated by welding together two acid-etched fibers. The temperature performance of the FFPI-FBG hybrid sensor is studied in the temperature range of 30–273 K. The CTE and TOC of the optical fiber at cryogenic temperatures are derived analytically and verified by experiments.

Expansion of the dentate mossy fiber–CA3 projection in the brain-derived neurotrophic factor-enriched mouse hippocampus

Structural changes that alter hippocampal functional circuitry are implicated in learning impairments, mood disorders and epilepsy. Reorganization of mossy fiber (MF) axons from dentate granule cells is one such form of plasticity. Increased neurotrophin signaling is proposed to underlie MF plasticity, and there is evidence to support a mechanistic role for brain-derived neurotrophic factor (BDNF) in this process. Transgenic mice overexpressing BDNF in the forebrain under the α-calcium/calmodulin-dependent protein kinase II promoter (TgBDNF mice) exhibit spatial learning deficits at 2–3months of age, followed by the emergence of spontaneous seizures at ∼6months. These behavioral changes suggest that chronic increases in BDNF progressively disrupt hippocampal functional organization. To determine if the dentate MF pathway is structurally altered in this strain, the present study employed Timm staining and design-based stereology to compare MF distribution and projection volumes in transgenic and wild-type mice at 2–3months, and at 6–7months. Mice in the latter age group were assessed for seizure vulnerability with a low dose of pilocarpine given 2h before euthanasia. At 2–3months, TgBDNF mice showed moderate expansion of CA3-projecting MFs (∼20%), with increased volumes measured in the suprapyramidal (SP-MF) and intra/infrapyramidal (IIP-MF) compartments. At 6–7months, a subset of transgenic mice exhibited increased seizure susceptibility, along with an increase in IIP-MF volume (∼30%). No evidence of MF sprouting was seen in the inner molecular layer. Additional stereological analyses demonstrated significant increases in molecular layer (ML) volume in TgBDNF mice at both ages, as well as an increase in granule cell number by 8months of age. Collectively, these results indicate that sustained increases in endogenous BDNF modify dentate structural organization over time, and may thereby contribute to the development of pro-epileptic circuitry.

Young’s modulus, thermal conductivity, electrical resistivity and coefficient of thermal expansion of mesophase pitch-based carbon fibers

Although there are several reported correlations among structural parameters, Young’s modulus (E), thermal conductivity, electrical resistivity and coefficient of thermal expansion of carbon fibers in the longitudinal direction, a single physical model has not yet been established to explain quantitatively these properties. Here a model of continuous defective graphene nanoribbons (dGNR), which are arranged in stacks, is presented to predict a number of properties of mesophase pitch (MPP)-based carbon fibers in a single physical framework. Reported in situ tensile tests and other works support the assumption that, for MPP-based carbon fibers with E>350GPa, slightly misaligned perfect graphene regions of the dGNR are longitudinally in series with defective regions of an approximately constant length δ=3nm. The longitudinal properties of the dGNR depend strongly on the average longitudinal concentration of defective regions (x) of length δ, which can be estimated from the X-ray diffraction in-plane longitudinal coherence length (La‖). The model was applied with success to high- and ultra-high-modulus commercial MPP-based carbon fibers; other fibers were also discussed. The values for the properties of the defective regions were determined and are consistent with the proposed model structure; relative values and scaling factors between properties were discussed.

Fabrication of highly porous interconnected three-dimensional scaffolds with micro-channels

A novel highly porous 3-D poly(ɛ-caprolactone) (PCL) scaffold with micro-channels was fabricated by injection molding and diluent acetic acids leaching technologies. In this study, the chitosan fiber was employed to form the microchannel in PCL matrix. The morphology, porosity and mechanical properties of the scaffolds were studied and calculated. It was found that the larger the content of chitosan fiber is, the higher the porosity would be, due to the volumetric expansion of chitosan fiber in PCL matrix during it being leached. In addition, the less the content of chitosan fiber is, the higher the compressive modulus would be.