Single Fiber Measurements Research Articles

Two Mechanisms for Supercontraction in Nephila Spider Dragline Silk

Supercontraction in dragline silk of Nephila edulis spider is shown to have two distinct components revealed by single fiber measurements using dynamic mechanical thermal analysis. The first component relies on a contraction of maximum 13% and seems to be associated with relaxation processed through the glass transition, T(g), as is induced by increasing temperature and/or humidity. The second component is induced by liquid water to the total contraction of 30%. The T(g)-induced contraction is linearly correlated with the restraining stress on the fiber, and the mechanical properties of the partially contracted silk have mechanical profiles that differ from both native and fully supercontracted fibers. Here we present novel supercontraction data and discuss their structural origins, examining the relaxation of stretched orientation in the different primary structure sequences.

Novel Characterization Procedure for Single Piezoelectric Fibers

The characterization of the ferroelectric properties of piezoelectric ceramic fibers is paramount for optimizing their manufacturing processes, for quality control purposes, and for modeling the response of components and structures. Until now, fibers were generally characterized by measuring the so-called 1-3 composites, fiber arrays embedded in a polymer matrix. The fiber properties can then be extracted, provided the volume fraction and stiffness of each phase, the fiber piezoelectric charge constant as a function of the electrical field strength, and the matrix permittivity are known. This implies a large amount of time and experimental effort. This article presents a comprehensive procedure for the direct characterization of single piezoelectric ceramic fibers in terms of butterfly and polarization loops, as well as their blocking force. The experimental setup is composed of a waveform generator, a high-voltage amplifier, a dynamic mechanical analyzer, a current/charge measuring circuit, and an oscilloscope. The active circuitry used for reliably collecting the charge generated by a single fiber is presented in full detail. The very good repeatability of the measurements showed the proposed procedure to be robust. The comparison between single fiber measurements and the investigation of 1-3 composites revealed both procedures to be equal, at 99.9%, in determining the average strain and polarization properties. In addition, the single fiber measurement provides an estimation of the variation in fiber properties within a single production batch. This information is essential to understand how to optimize processing routes and build robust devices.

Evaluating Single Fiber and Fiber Bundle Tensile Curves

Most research on estimations of fiber bundle tensile curves from single fiber tensile properties is based on knowledge of the frequency density distribution of fiber breaking extension and the linear elastic spring constant. Such research focuses on cotton fibers and fiber bundles. On the other hand, there are few methods to predict the tenacity of single wool fibers from fiber bundle tensile curves. Using characteristics of specific stress-strain curves from both single fiber and fiber bundle tensile testing, new theoretical calculations to estimate the tenacity and breaking extension distribution of single fibers from bundle tensile curves are described in detail for wool fibers. The experimental results show that these algorithms are effective and reliable for such evaluations, the experimental and estimated results obtained from the TENSOR fiber bundle tests and the SIFAN single fiber measurements agree with each other, and single fiber tenacity or even its urve can be evaluated using the tail of the bundle tensile curve.

Predicting the Strength Variation of Wool from Its Diameter Variation

In this study, we have derived and evaluated a simple statistical relationship between the coefficient of variation ( CV) of fiber breaking load and that of minimum fiber diameter. This relationship indicates the CV of fiber breaking load is about twice the CV of fiber minimum diameter. We have made single fiber measurements on a recently developed single fiber analyzer (SIFAN). We test wool fibers for both diameter along the fiber length and fiber breaking load, and use the coefficient of variation of minimum fiber diameters ( CVDmin) to predict the CV of single fiber breaking load ( CVF). The results support the statistically derived relationship between the CV of fiber breaking load and that of minimum fiber diameter. In addition, we modify an equation we derived in a previous study to better relate the fiber diameter variation to fiber strength variation for small fiber samples.

Urinary stress incontinence. A urodynamic and quantitative electromyographic study of the perineal muscles

Neurophysiological techniques are increasingly used in examination of urinary incontinence. The purpose was to measure the activity in the perineal muscles in women with urinary stress incontinence and compare with normal subjects by using quantitative EMG methods. Twenty-four incontinent women and seven normal subjects were evaluated urodynamically and with quantitative EMG analysis of interference pattern and single fiber measurements. The recordings were made in the pubo rectal and the external anal sphincter muscle with empty urinary bladder at rest and maximal voluntary contraction as well as during cystometry. The incontinent women had a denser interference pattern in the anal sphincter at rest but no differences at maximal activation compared to the reference group. No differences in interference pattern were noted between the two groups in the pubo rectal muscle. Fiber density in the external anal sphincter muscle was increased in the patient group (2.01 compared to 1.33, p<0.01). The urethral pressures at rest and activation were higher in the normal subjects (p<0.05). The normal subjects showed a denser interference pattern in the external anal sphincter muscle during cystometry (p<0.05). Quantitative analysis of the interference pattern and fiber density in the perineal muscles in incontinent women showed a denser interference pattern at rest and increased fiber density. Both observations indicate a peripheral nerve lesion. Furthermore, the interference pattern showed signs of reduced central activation in the incontinent women during cystometry.

A Rapid, Direct Measurement of Short Fiber Content

Technology for rapidly determining cotton fiber length distributions using single fiber measurements has been developed jointly by USDA-ARS and Schaffner Tech nologies (now Zellweger Uster, Inc.). The instrument (AFIS) includes a mechanism for mechanically opening a hand-fed ribbon of fibers so that individual fibers can be presented aerodynamically to an electro-optical system for measuring fiber length. Length measurements for 10,000 individual fibers can be obtained in approximately 5 minutes. Although there are measurements for the entire fiber length distribution, measurements of mean length, upper half mean length, and short fiber content are particularly important. Measurements of mean length and upper half mean length can be made rapidly with other instruments, but instruments to rapidly measure short fiber content have not been available until now. Evaluation results show good corre lations between measurements made using conventional laboratory methods and measurements using AFIS.

Enzyme activity measured in single muscle fibers in partial cytochrome c oxidase deficiency.

Single-fiber analyses using a kinetic microphotometric method were performed on three patients with chronic progressive external ophthalmoplegia and proximal myopathy accompanied by a partial deficiency of cytochrome c oxidase. Two patients had subsarcolemmal accumulation of mitochondria (ragged-red fibers). Qualitative histochemical demonstration of cytochrome c oxidase showed a mosaic of fibers without detectable cytochrome c oxidase activity. Quantitative single fiber measurements in the patients' biopsies showed that the majority of the muscle fibers had decreased cytochrome c oxidase activity without selective involvement of a specific fiber type. Succinate dehydrogenase was measured and the ratio of the activities (succinate dehydrogenase/cytochrome c oxidase) was calculated. Normal muscle showed a ratio of about 2, whereas diseased muscle showed values between 10 and 20, due to a decrease in cytochrome c oxidase activity. Ragged-red fibers showed very low or undetectable cytochrome c oxidase activity.

Computer simulation of action potentials and afterpotentials in mammalian myelinated axons: The case for a lower resistance myelin sheath

Depolarizing afterpotentials, recorded in peripheral nerves [Barrett and Barrett (1982) J. Physiol., Lond. 323, 117–144] and spinal axons [Blight and Someya (1985) Neuroscience 15, 1–12], have been interpreted as representing passive discharge of axolemmal capacitance. This interpretation requires a lower resistance pathway through the myelin sheath than previous measurements have suggested. A computer model was used to examine the contribution of the electrical characteristics of nerve fibers to action potential conduction and afterpotential generation. The model consisted of a resistance-capacitance network representing a chain of 20 internodes. The resistances of node, internode and myelin sheath, deduced from observations in the accompanying paper, [Blight and Someya (1985) Neuroscience, 15] were found to produce suitable length and time constants, and prolonged afterpotentials, when inserted into the model. Similar length and time constants were found using a conventional model of the axon, based on measurements from isolated peripheral fibers, but this did not reproduce the afterpotentials. Action-potential conduction velocity is enhanced by reducing the time constant and increasing the length constant. The problem of minimizing the internodal time constant was met in the conventional model through the low parallel resistance of the node, while in the new model it was met by reducing the resistance of the myelin sheath. The latter strategy required the nodal leakage resistance to be higher than values from single fiber measurements ( ca 250 MΩ rather than ca 50 Mω) in order to maintain the length constant similar to the conventional model. Simulation of the recorded potentials required the resistance of the myelin lamellae to be approx. 100 Ω cm 2. The model quantitatively reproduced the voltage response of the axon to injected current pulses and to propagated action potentials, using Frankenhaeuser-Huxley kinetics. [Frankenhaeuser and Huxley (1964) J. Physiol., Lond. 171, 302–315; Frankenhaeuser and Moore (1963) J. Physiol., Lond. 169, 431–437]. The short duration components of the afterpotential, observed in mammalian recordings were reproduced by assuming a leakage pathway in the myelin sheath, at the impalement site. The calculated lower resistance of the myelin sheath was such that it minimized the effective internodal time constant for a given nodal resistance. This appears to free the myelinated fiber from the alternative requirement for a high nodal leakage conductance. It may also contribute to greater stability of the axon under conditions of prolonged depolarization, by allowing the internodal axolemma to be repolarized more rapidly by voltage-dependent K + currents and making the input resistance of the internode dependent on the permeability of its own axolemma, more than that of the surrounding myelin sheath. In addition the storage of charge at the axolemma following the action potential may be of functional significance in modulating excitability.

Interrelations of Structural and Physical Properties of Untreated Cottons

High correlation is shown to exist between crystallite orientation and tensile proper ties of bundles of cotton fibers. Statistical analyses of bundle data failed to uncover pronounced dependence of bundle tensile properties on reversal frequency. Evidence is given of the influence of heredity on reversal frequency. Data on single cotton fibers are presented to illustrate the relationships or lack of relationships of reversals and x-ray angle to strength and elongation. X-ray angle and reversal frequency are interrelated at a very low level of significance and are shown to be related to single-fiber tenacity, elongation, and decrease in strength with increase in gage length. The tensile properties from bundle and single-fiber measurements are more strongly related to x-ray orientation than to reversal frequency.

Strength Tests of Fiber Arrays

Basic differences between tensile tests of single fibers versus similar fibers in arrays such as yarn, skeins, tow, and staple comhings keep the strength of arrays from exceed ing that of single fibers. The reverse holds true for strain. Moreover, experimental difficulties of achieving simultaneous straining among the fibers in an array further reduce the apparent strength and increase apparent strain, by amounts that depend on the extent of departure from simultaneity, i.e. the strain distribution in the array. Close equivalence of group tests of strength and maximum strain to single fiber measurements can be obtained even for the wide range of slackness observed in some tow, by recourse to a parameter that is not affected by departure from simultaneity of straining, namely, -the energy absorbed in rupture. Strength, maximum strain, and associated measures of variability can be calculated from energy via the tenacity-strain function for the fiber type. Good agreement with single fiber measurements has been obtained for acrylic fibers in the form of tow.