Neighboring Fibers Research Articles

Three-dimensional arrangement of muscle bundles in the outer layers of rodentia vasa deferentia

Three-dimensional arrangement of the smooth muscle bundles of the outer layer of the vas deferens musculature in mammals (guinea-pigs, rats and mice) was examined under the scanning electron microscope (SEM) after removal of fibrous connective tissue elements. Muscle fibers of all examined animals formed bundles. In the guinea-pig, similar sized bundles extended longitudinally along the tubular vas deferens and branched to anastomose with branches of neighboring bundles to create a net which was regular in form. In the rat, longitudinal muscle bundles constituted an outer layer in the form of a net, which was roughly enmeshed with variously-sized, transverse or oblique bundles in anastomosis with underlying longitudinal bundles. In the mouse, longitudinal bundles of irregular thickness branched into many small bundles and anastomosed not only with neighboring bundles to create an irregular net. In both the rat and the mouse there were bundles extending over many other bundles to anastomose with them at a far point. Junctional structures were well developed between neighboring fibers. Myofibrils were represented as thin streaks on muscle fiber surfaces. Varicosed nerve fibers existed between muscle fibers and in narrow cytoplasmic grooves in all the examined animal species. The findings are discussed in correlation with electrophysiological data.

Ordered bundles of infrared-transmitting AgClBr fibers: optical characterization of individual fibers

Silver halide (AgCl(x) Br(1-x)) crystals were extruded to form polycrystalline fibers that are highly transparent in the spectral range 3-30 mum. Ordered bundles consisting of as many as 9000 fibers were fabricated by multiple extrusion steps. The transmission loss of an individual fiber in the 100-fiber bundles was 0.12 dB/cm, and the cross talk between neighboring fibers in the 900-fiber bundles was 25%. Thermal images of bodies at room temperature have been transmitted through the bundles. Such ordered bundles provide a solution for the problem of thermal imaging in regions where there is no line of sight between a thermal camera and a warm object.

Long-term depression of the cerebellar climbing fiber--Purkinje neuron synapse.

In classic Marr-Albus-Ito models of cerebellar function, coactivation of the climbing fiber (CF) synapse, which provides massive, invariant excitation of Purkinje neurons (coding the unconditioned stimulus), together with a graded parallel fiber synaptic array (coding the conditioned stimulus) leads to long-term depression (LTD) of parallel fiber-Purkinje neuron synapses, underlying production of a conditioned response. Here, we show that the supposedly invariant CF synapse can also express LTD. Brief 5 Hz stimulation of the CF resulted in a sustained depression of CF EPSCs that did not spread to neighboring parallel fiber synapses. Like parallel fiber LTD, CF LTD required postsynaptic Ca2+ elevation, activation of group 1 mGluRs, and activation of PKC. CF LTD is potentially relevant for models of cerebellar motor control and learning and the developmental conversion from multiple to single CF innervation of Purkinje neurons.

Weak interface in long fiber composites

The problem of the diffusion of load from a fiber to an embedding matrix is considered in a three dimensional context. It is assumed that the fiber-matrix interface allows sliding, which is assumed to be proportional to the interface tangential stress. The close-form solution is obtained for generic loads applied to the fiber, and the case of a concentrated force is studied in detail. The main effects of the interface stiffness, such as avoiding the stress singularities and increasing the length of the zone of influence, are discussed and illustrated by some numerical examples. Successively, the problem of the broken fiber is considered and solved with the same method as the previous case. Three different situations are discussed: no interaction between fibers, very close neighboring fibers and an intermediate case. It is shown that both problems have the same equations apart from a given function which plays the role of the constitutive equation and which characterizes the considered model. The effect of the neighboring fibers on the interfacial stress is discussed and it is shown that it has a non-monotonic dependence on the distance between the fibers.

Analyses of the micromechanics of stress transfer in single- and multi-fiber pull-out tests

Analyses have been carried out on the micromechanics of elastic stress transfer taking place across the fiber/matrix interface in both single- and multi-fiber pull-out tests. A two-cylinder model for the single-fiber pull-out test and a three-cylinder model for the multi-fiber pull-out test were employed in order to study the fiber pull-out problems. The difference in the stress transfer between the two models is clearly shown. Moreover, since real multi-fiber composites are inhomogeneous, the local fiber volume fraction would undoubtedly influence the stress transfer between the pulled-out fiber and the neighbouring matrix. The effect of the local fiber volume fraction on the stress transfer is discussed. When the fibers in the composite medium cylinder of the three-cylinder model are short, a fiber length factor for the composite modulus is introduced and its effect on the stress transfer is discussed. Furthermore, special attention is given to how the neighboring and remote fibers affect stress transfer. The results show that the neighboring fibers play a major role in determining the stress transfer while the influence of the remote fibers on the stress transfer is negligible. In addition, the present model for the single-fiber pull-out test is compared with other existing theories.

Effects of debonding and fiber strength distribution on fatigue-damage propagation in carbon fiber-reinforced epoxy

In order to design new fatigue-resistant composites, the underlying fatigue damage mechanisms must be characterized and the controlling microstructural properties should be identified. The fatigue-damage mechanisms of a unidirectional carbon fiber-reinforced epoxy has been studied under tension-tension loading. A ubiquitous form of damage was one or a few planar fiber breaks from which debonds or shear yield zones grew in the longitudinal direction during fatigue cycling. This leads to a change in stress profile of the neighboring fibers, and an increase in failure probability of these fibers. The breakage of fibers in the composite is controlled by the fiber strength distribution. The interaction between the fiber strength distribution and debond propagation leading to further fiber breakage was investigated by a numerical simulation. It was found that a wider distribution of fiber strength and a higher debond rate lead to more distributed damage and a higher fracture toughness. Implications to fatigue life behavior are discussed, with reference to constituent microstructure.

Examination of intrafascicular muscle fiber terminations: implications for tension delivery in series-fibered muscles.

Mammalian skeletal muscles with long fascicle lengths are predominantly composed of short muscle fibers that terminate midbelly with no direct connection to the muscle origin or insertion. The manner in which these short fibers terminate and transmit tension through the muscle to their tendons is poorly understood. We made an extensive morphological study of a series-fibered muscle, the guinea pig sternomastoid, in order to define the full range of structural specializations for tension transmission from short fibers within this muscle. Terminations were examined in single fibers, teased small bundles of fibers, and in sections at both the light and electron microscopic level. In many cases, sites of fiber termination were defined by reactivity for the enzyme acetylcholinesterase, which also marks myotendinous junctions. Additionally, transport of the lipophilic fluorescent dye, DiI, or injection of Lucifer Yellow were used to visualize undisturbed fiber terminations in whole muscles using confocal and fluorescence microscopy. At the light microscopic level, we find that intrafascicularly terminating fibers end about equally often in either a long progressive taper, or in a series of small or larger blunt steps. Combinations of these two morphologies are also seen. However, when analyzed at higher resolution with confocal or electron microscopy, the apparently smooth progressive tapers appear also to be predominantly composed of a series of fine stepped terminations. Stepwise terminations in most cases join face-to-face with complementary endings of neighboring muscle fibers, some via an extended collagenous bridge and others at close interdigitating myomyonal junctions. These muscle-to-muscle junctions show many of the features of myotendinous junctions, including dense subsarcolemmal plaques in regions of myofibrillar termination and we suggest that they serve to pass tension from fiber to fiber along the longitudinal axis of the muscle. In addition, we observe regions of apparent side-to-side adhesion between neighboring fibers at sites where there is no apparent fiber tapering or structural specialization typical of myofibril termination. These sites show acetylcholinesterase reactivity, and large numbers of collagen fibers passing laterally from fiber to fiber. These latter connections seem most likely to be involved in lateral transmission of tension, either from fiber to fiber, or from fiber to endomysium. Overall, our results suggest that tension from intrafascicularly terminating fibers is likely to be passed along the muscle to the tendon using both in-series and in-parallel arrangements. The results are discussed in light of current theories of tension delivery within the series-fibered muscles typical of large, nonprimate mammals.

自動車用カーペット粉砕繊維屑を素材とする断熱板の圧縮成形

The material recyclability of shredder dust of car carpets as insulating boards was investigated by using a compression molding method. The shredder dust used here was mainly composed of nylon 6 (NY 6), and polyester (PET) fibers. The shredder dust was heated in a furnace with infrared heaters such that NY 6, having a lower melting point than PET, was solely melted. After the heating process, the shredder dust was compressed, cooled and easily molded into a porous board with low thermal conductivity. The thermal conductivity and bending strength increased with increasing density of molded board. The thermal conductivity increased suddenly when the melted NY 6 connected the neighboring PET fibers. The results suggest that the compression molding method described here shows promise in contributing toward the material recycle of shredder dust of car carpet as insulating boards.

Stress concentrations caused by fiber failure in two-dimensional composites

In the process of fracture of fiber-reinforced composites, the stress concentrations caused by the redistribution of stress from a failed fiber to its intact adjacent neighboring fibers play a substantial role, as they determine the overall failure pattern of the composites. In the present article we propose a new model for the stress concentration factors (SCFs) in two-dimensional unidirectional composites. This model is based on an earlier shear-lag scheme which is here modified in several respects: a new shear-lag constant β N (proposed by Nayfeh) is included (which replaces the classical shear-lag constant of Cox, β C), and the effects of fiber/matrix debonding and fiber/matrix interfacial friction are incorporated. We find that the proposed model is in good agreement with recently published Raman spectroscopy results. When the fibers are in close contact, the SCF is found to possess a maximum value of 1.33, identical with the classical result of Hedgepeth and Van Dyke. However, unlike the scheme of Hedgepeth and Van Dyke, the SCF decreases with increasing interfiber distance, similar to more recent models, but in closer agreement than these models with the micro-Raman spectroscopy data.

Vers une neurogéométrie. Fibrations corticales, structures de contact et contours subjectifs modaux

This work presents some variational models for the cortical algorithms processing Kanizsa modal subjective contours . These models are based on the geometric concepts of fibration and contact structure. The retinoptic structure of the orientation hypercolumns in the visual area V1 is a functionnal architecture which can be mathematically idealized by the fibration having the retinian plane M as base and the projective line P1 as fiber F. The total space E of Pi p is isomorphic to the direct product M x F. The cortico-cortical horizontal connections implement what is called the local triviality of this fibration, and also a Cartan connection defining a parallel transport between neighboring fibers. Then the paper focuses on the geometrical interpretation of the results of Field, Hayes and Hess concerning the association field. It shows that the latter implements what is called the contact structure of the fibration. The association field expresses an integrability condition for the skew curves in E : they have to be a lifting of their projection on the retinian plane M. This model of fibration endowed with a contact structure is then applied to the modal subjective contours and provides a variant of the elastica model developped by B.K.P. Horn and D. Mumford. The key idea is that the lifting of subjective contours satisfy a "geodesic" condition in the cortical fibration E : they have to be of minimal lenght (for an appropriate metrics) among the class of curves satisfying the integrability condition. These "geodesic" models are then reformulated, according to R. Bryant and P. Griffiths, in the more fondamental geometric framework of Lie groups and Cartan's "repère mobile" (Vielbein). Finally, some experimental possibilities are suggested.

Load transfer from broken fibers in continuous fiber Al 2O 3-Al composites and dependence on local volume fraction

The load transfer characteristics of a continuous, high volume fraction alumina (Al 2O 3)fiber reinforced aluminum matrix composite are determined by combining high spatial resolution stress measurements and computational micromechanical modeling. The residual stresses in individual fibers and the redistribution of applied load due to fiber failure have been measured using photostimulated Cr 3+ luminescence based piezospectroscopy. From these measurements, the load transfer profiles along broken fibers and the induced stress concentration profiles on their adjacent neighbors have been determined. They are found to depend on the local inter-fiber spacing. They are compared with fiber stress profiles predicted by a shear-lag stress analysis which accounts for the influences of matrix yielding, called the quadratic influence superpositon (QIS) technique, as well as other shear-lag based multifiber composite models. The current study indicates that fiber breaks are accompanied by matrix yielding extending on the order of fiber diameters and which induce significant stress concentrations on neighboring fibers, dependent on the local fiber spacing and extent of plastic yielding. Additionally, the matrix yield strength is dependent on the local fiber spacing and increases with decreasing local fiber spacing. The implications of the micromechanical load sharing characteristics and composite processing on ultimate tensile strength are discussed.

A rotary electrostatic micromotor 1×8 optical switch

This paper describes a 1/spl times/8 rotary electrostatic micromotor optical switch fabricated using high-aspect-ratio micromachining technology to produce silicon or nickel components which are subsequently assembled to form a switch. The switch consists of a salient-pole micromotor with 1-mm-diameter 200-/spl mu/m-thick rotor that supports up to a 500-/spl mu/m-tall, 900-/spl mu/m-wide mirror. Typical switches were actuated at 50 V, operated for extended periods in room air, and found to have a rapid rotation with an average optical switching time between two neighboring fiber ports of 18 ms. Optical testing was performed at wavelength of 1310 nm in single- and multimode, and at 850 nm in multimode. The optical beam was propagated in free space with minimal divergence through the use of externally mounted collimating gradient-index lenses. With an aluminum coating, the mirror and external optics exhibited an input to output coupling loss as low as 0.96 dB in multimode and 2.32 dB in single-mode. Interchannel crosstalk was less than -45 dB.

Inelastic contact deformation of metal coated fibers

Metal matrix composites (MMCs) can be synthesized by aligning metal coated ceramic fibers in a shaped container and applying pressure at elevated temperatures. The high stresses created at the contacts between neighboring fibers cause inelastic matrix flow that fills interfiber voids, reduces interfiber separations and results in composite densification. The rate of densification depends on the contact’s resistance to flow. Current contact mechanics models are unable to adequately predict this resistance because they do not account for the effect of the (elastic) fiber. Closed-form solutions for contact stress–displacement rate and contact area–strain relationships are used to describe metal coated fiber blunting as a function of fiber volume fraction, matrix material non-linearity (i.e. creep stress exponent) and fiber packing geometry. The solutions contain two unknown coefficients (c and F) which are evaluated using the finite element method. A simple model for the consolidation of coated SiC fibers is developed in terms of the coefficients, c and F. The model indicates that materials with a low creep stress exponent are more difficult to densify as the fiber volume fraction increases whereas, perfectly plastic materials exhibit a relatively weak dependence on the fiber volume fraction.

Computational micro-mechanics for probabilistic failure of fiber composites in tension

The design of a composite from fiber and matrix properties requires micro-mechanics modeling of strength. The strength of a composite has an inherent variability which is a manifestation of the underlying stochastic failure processes of the constituent fiber and matrix. For fiber-dominated tensile composite failures, the failure process starts with the breaking of weak fibers. The initial failure sites are isolated by micro-redundancy provided by local load-sharing of the neighboring fibers. Higher applied load leads to progressive clustering of fiber breaks which ultimately cause macroscopic failure. Probability modeling of the failure sequences of the fiber breaks and the spatial geometry of the clustering of the sites resulted in the local load-sharing model. This model requires numerical evaluation because it contains an extremely large matrix of the transitional probability of the occurrences of the cluster sites. This paper provides an accessible computational implementation of this model for computer platforms ranging from personal computers to supercomputers. The computational algorithm was made general by a three-section piecewise-linear, tri-modal model for fiber statistics. This tri-modal local load-sharing software numerically computes the cumulative distribution function (CDF) of the composite strength by using a very wide range of fiber statistics as input. This CDF can be used to analyze composite strength data in testing, to predict size effects in design, to monitor processing quality, and to quantify the reliability of composite structures.

Fiber array targets for producing long media of high gain in recombination-pumped soft-x-ray lasers

We demonstrate a target for recombination-pumped soft-x-ray lasers, consisting of an equally spaced array of parallel fibers. This target is capable of producing long media of several centimeters, and can also generate high gain due to the initial two-dimensional expansion of the plasma. Numerical simulations show that amplification occurs after the plasma expansion changes from a cylindrical to a slablike one, as a result of collisions with plasma produced from neighboring fibers. Initial gain measurements using graphite-coated fiber array targets reveal Balmer α gain coefficients of 4.1 cm−1.

Experimental measurement of fiber/fiber interaction using Micro Raman Spectroscopy

Understanding the stress concentrations that develop due to fiber failure in multi-fiber composites is crucial because it dictates the failure mode and toughness of a composite. Composites with strong fiber/fiber interaction (high stress concentrations) are often brittle while those with low fiber/fiber interaction are more ductile. In this study, the effect of fiber failure on neighboring fibers in graphite/epoxy composites was studied using Micro Raman Spectroscopy (MRS). The effect of interphase toughness and strength on the stress concentration factor (SCF) and the radius of the zone of influence, r∞ was studied. It was found that the toughness of the interphase strongly affects SCF and r∞ A brittle interphase was found to reduce r∞ from 30 fiber diameters to 20 and caused SCF to drop more rapidly with inter-fiber distance. The maximum value of SCF was not affected by the toughness of the interphase and was found to be 1.46 ± 0.05. On the other hand, a 50% decrease in the interfacial shear stress (from 40 MPa to 20 MPa) resulted in a further reduction in r∞ down to 10 fiber diameters and a reduction in the maximum SCF to 1.16 ± 0.05. The results are explained and discussed from both micromechanics and energy viewpoints.

Strain Distributions and Over-Stressed Volumes in Unidirectional Composites with Multiple Fiber Breaks

A finite element technique was used for determining the strain distribution around fiber breaks in unidirectional composite monolayers subjected to tensile stress in the fiber direction. Various extents of damage, ranging from a single fiber break to ten adjacent fiber breaks, were considered. Both the fiber and the matrix were considered to be elastic. From the finite element results, the level of overloading in fibers around such damage and the volume of neighboring fibers subjected to overload were determined. To provide a detailed description of the stress distribution, this over-stressed volume was divided into sub-volumes corresponding to various strain levels and presented in the form of a histogram. Over-stressed volume histograms were generated for a variety of composite materials having various combinations of fiber volume fraction and matrix stiffness. In most cases, the stress concentration factor obtained from the finite element analysis was significantly greater than the corresponding value obtained by using the shear-lag model. The overstressed volume histograms are expected to be useful in the strength prediction of composite materials.

The Inferior Collicular Potential in Acoustic and Electrical Stimulation of the Cochlea: An Experimental Study of Guinea Pig

We made experiments of the inferior collicular potentials in acoustic and electrical stimulation for the purpose of studying fundamental issues for cochlear implantation. Guinea pigs with normal Preyer's reflex were used for this study. The results were as follows: (1) in acoustic stimulation relatively wide and large waveforms were gained but in electrical stimulation sharp and narrow ones were gained, (2) in acoustic stimulation the input-output curve of latency and amplitude was biphasic but in electrical stimulation it was monophasic. For this reason, in acoustic stimulation by click, when the intensity is low (under 80 dB SPL) stimulus site would be comparatively low frequency fibers. When the intensity is high (over 80 dB SPL) the stimulus site would shift to high frequency fibers. Therefore, many more neighboring fibers start responding. This results in biphasic input-output curves of latecy and amplitude. By electrical stimulation, however, it would be possible to stimulate only a restricted area among the bipolar electrode. Therefore, as the intensity increases, the response amplitude increases and becomes saturated at a constant level. This results in monophasic input-output curves of latency and amplitude.

Design and Analysis of Fiber Enhanced Viscoelastic Damping Polymers

A new composite damping material is investigated, which consists of a viscoelastic matrix and high elastic modulus fiber inclusions. This fiber enhanced viscoelastic damping polymer is intended to be applied to lightweight flexible structures as a surface treatment for passive vibration control A desirable packing geometry for the composite material is proposed, which is expected to produce maximum shear strain in the viscoelastic damping matrix. Subsequently, a micromechanical model is established in which the effect of fiber segment length and relative motion between neighboring fibers are taken into account. Based on this model, closed form expressions for the effective storage and loss properties of the damping material are developed, and an optimal relation between design parameters, such as the length, diameter, spacing, and Young’s modulus of fibers and the shear modulus of viscoelastic matrix, is derived for achieving maximum damping performance. To address the verification of the development, the theoretical results are compared with NASTRAN finite element results. Upon comparison of an enhanced viscoelastic damping treatment with a conventionally constrained layer damping treatment, it is found that the enhanced polymer provides a significant improvement in damping performance.

Self-Organized Criticality in a Model for Fracture on Fibrous Materials

We investigate the existence of self-organized criticality on a model to describe the failure process in fibrous materials. This model consists of identical parallel fibers which are pulled with constant velocity. The rupture probability of each fiber depends on the elastic energy of the fiber and on the number of unbroken neighboring fibers. In the brittle-ductile transition, we have observed a power law behaviour on the number of cracks versus its size. This indicates that, in this region, the model shows self-organized criticality and the fracture pattern can be a fractal. The power law exponent is not universal, but depends on the temperature and traction velocity.