Fiber Growth Rate Research Articles

Novel membranes from conducting polymers

The first part of this paper presents the preparation and morphological studies of high surface area polypyrrole with fibrillar morphology. Mode of fibre growth within host membrane pores has been examined by ultra-microtome techniques. The rate of fibre growth in different solvents has been determined. The second part of this paper describes the formation of conducting composite membranes of polypyrrole with in-house prepared and commercial (“Biotran”) microporous polyamides. The conducting polymer was chemically polymerized using several techniques in association with the membranes in these studies. Surface and cross-sectional membrane morphology was studied by high-resolution field emission scanning electron microscopy, optical microscopy and transmission electron microscopy. Environmental stability of composite membranes has been examined by measuring the conductivity as a function of time.

Novel Carbon Fibers by Laser Assisted Chemical Vapor Deposition (Lcvd)

ABSTRACTChemically pure carbon fibers with small fiber diameters and high growth rates were obtained by laser assisted chemical vapor deposition (LCVD) using high reactor pressures and a unique rate control mechanism. Depending upon growth conditions and gases, these fibers were either flexible (elastic), brittle (thickened) or graphitic (strong). The elastic carbon fibers were uniform and appear to represent a novel form of carbon. The reactants were acetylene, ethylene or methane, and the reaction pressures ranged from 1.9 to 7.5 bar. The highest fiber growth rate was 0.33 mrn/s, and the lowest fiber diameter was 10 μm.

Hemoglobin S Polymerization and Gelation Under Shear II. The Joint Concentration and Shear Dependence of Kinetics

Abstract The kinetics of hemoglobin S gelation are critical in sickle disease because microvascular obstruction can be avoided if red blood cells pass these vessels during the delay time, before polymerization and gelation occur in sufficient degree to rigidify the cells. Kinetics, including the delay time and the closely related exponential progress rate, are highly sensitive to hemoglobin concentration and degree of deoxygenation. Kinetics are also greatly accelerated by shear, an effect that may contribute to pathogenesis, since red blood cells deform and can undergo shear in vivo. Here we examine the joint dependence of kinetics on shear and hemoglobin concentration. As shear rate increases, the concentration dependence of the exponential progress rate decreases. The large decrease in concentration dependence supports the conclusion that acceleration of gelation by shear is due to breakage and not to enhancement of heterogeneous nucleation. Under shear, new fibers are created by breakage of existing ones, as well as by heterogeneous nucleation. At high shear, the rate of new fiber creation by breakage is very great and dominates that by heterogeneous nucleation. Therefore, if breakage depended only on shear rate and were independent of the concentration of hemoglobin in solution, the concentration dependence of kinetics should vanish. Although it decreases, it does not disappear. The concentration dependence that remains at high shear arises from (1) the direct contribution of fiber growth rate to the exponential progress rate, (2) the dependence of breakage rate on fiber growth rate, and (3) the dependence of solution viscosity on hemoglobin concentration.

Hemoglobin S polymerization and gelation under shear II. The joint concentration and shear dependence of kinetics

The kinetics of hemoglobin S gelation are critical in sickle disease because microvascular obstruction can be avoided if red blood cells pass these vessels during the delay time, before polymerization and gelation occur in sufficient degree to rigidify the cells. Kinetics, including the delay time and the closely related exponential progress rate, are highly sensitive to hemoglobin concentration and degree of deoxygenation. Kinetics are also greatly accelerated by shear, an effect that may contribute to pathogenesis, since red blood cells deform and can undergo shear in vivo. Here we examine the joint dependence of kinetics on shear and hemoglobin concentration. As shear rate increases, the concentration dependence of the exponential progress rate decreases. The large decrease in concentration dependence supports the conclusion that acceleration of gelation by shear is due to breakage and not to enhancement of heterogeneous nucleation. Under shear, new fibers are created by breakage of existing ones, as well as by heterogeneous nucleation. At high shear, the rate of new fiber creation by breakage is very great and dominates that by heterogeneous nucleation. Therefore, if breakage depended only on shear rate and were independent of the concentration of hemoglobin in solution, the concentration dependence of kinetics should vanish. Although it decreases, it does not disappear. The concentration dependence that remains at high shear arises from (1) the direct contribution of fiber growth rate to the exponential progress rate, (2) the dependence of breakage rate on fiber growth rate, and (3) the dependence of solution viscosity on hemoglobin concentration.

Muscle cellularity and postnatal growth in the pig.

Fast-growing strains of pigs and of other animals tend to have more muscle fibers than do slow-growing strains. The relationship between fiber number and growth rate was extended by examining pigs within the same strain. Seven litters of pigs (n = 66) were weighted at monthly intervals from birth to approximately 80 kg. The semitendinosus muscle was removed and an estimation of total fiber number, total primary fiber number, and mean secondary:primary fiber number (S:P) ratio was made for each animal. Pig growth was divided into three approximately linear phases: birth to 6 kg, 6 to 25 kg, and 25 kg to slaughter weight. Average daily gain in the first two phases was correlated with birth weight (r = .3614, P < .05 and r = .5873, P < .001, respectively) but was not correlated with total muscle fiber number. In the third growth phase ADG was correlated with muscle fiber number (r = .4149, P < .001) and was not correlated with birth weight. The gain:feed ratio was also calculated for each pig during the third growth phase and was found to be correlated with fiber number (r = .4191, P < .001). These results suggest that muscle fiber number is an important determinant of postnatal growth such that pig littermates with a high fiber number tend to grow faster and more efficiently than littermates with a lower fiber number.

Synthesis of Conducting Polymer Composite Fibers in Electrochemical Flow Cells

A one‐step electrochemical synthesis of polymer and composite polymer fibers of macroscopic dimensions (>10 cm length and 0.2 mm diam) is reported. Poly(3‐methylthiophene) and polypyrrole fibers are grown from the tip of a Pt microelectrode by oxidation of 3‐methylthiophene and pyrrole, respectively, in a capillary flow cell. Hydrodynamic fields within the capillary cell result in unidirectional growth of the polymer along the axis of the flow cell. High strength, conductive, and flexible composite polymer fibers are synthesized by deposition of poly(3‐methylthiophene) or polypyrrole on a nonconductive Kevlar or polyester string suspended in the solution along the axis of the capillary flow cell. Composite fiber growth rates as large as 30 cm/h are obtained under optimal conditions.

Silicon fibers produced by high-pressure LCVD

Using a unique fiber-growth control mechanism and high-reaction pressures (>1 bar), silicon fibers were grown by laser-assisted chemical vapor deposition (LCVD) from silane near the focal point of a cw Nd:YAG laser beam. Fiber-growth rates ranged from <1 to 500 μm/s and fiber tip temperatures from 525 to 1412° C. At low fibertip temperatures (<600° C) silicon fibers yielding glassy fracture were obtained. Some crystallinity was observed by X-ray diffraction. Polycrystalline silicon fibers were formed at intermediate temperatures, single-crystal silicon fibers at high-laser intensities and high-tip temperatures. The single crystal LCVD silicon fibers were formed by a vapor-liquid-solid (VLS) mechanism. Single-crystal VLS-LCVD silicon fibers were also obtained from liquid silicon-metal alloys by initiating fiber growth from the end of thin palladium, gold and platinum wires.

Biology of fibre growth and possible genetic and non-genetic means of influencing fibre growth in sheep and goats—a review

This paper reviews the biology of wool, mohair and cashmere growth and the options available to sheep and goat farmers to manipulate the quantity and characteristics of fibre produced to meet processors' requirements. The annual pattern of fibre growth in sheep and fibre producing goats is photodependent and regulated by hormone action. In sheep and Angora goats, fibre growth rate is greater in summer than winter with the amplitude varying between breeds. Cashmere-producing goats grow fibre between the longest and shortest day after which it is shed. The large diversity in fleece and fibre characteristics between genotypes of sheep and goats can be used to change characteristics by selection. Fibre characteristics of greatest importance to processors are all of medium to high heritability. Negative genetic correlations between some important characteristics limit overall genetic progress achievable through selection. The principal non-genetic factors affecting fleece and fibre characteristics in both sheep and goats are age, nutrition, physiological status, disease and shearing regime. Further work is required to gain a greater understanding of biological changes occurring within the follicle and fibre during growth to facilitate the production of fibre of specific characteristics through breeding or altering animal management.

Formation of vapor-grown carbon fibers in CO-CO 2-H 2 mixtures, II. Influence of catalyst

In order to enhance the growth rate of vapor-grown carbon fibers in a mixture of 77% CO, 19% CO 2 and 4% H 2, the decomposition behavior of ferrocene and the effect of additives, metal acetylacetonates, on the growth rate of fibers were investigated. The decomposition behavior of ferrocene in the CO-CO 2-H 2 mixture was similar to that inpure hydrogen. The addition of acetylacetonates of Fe, Co, and Mn to ferrocene was found to reduce the size of particles and consequently to accelerate the growth rate along with the yield. In particular, the growth rate and the yield of fibers as high as 40 μm/s and 70 wt%, respectively, were obtained in the case of using 80 wt% ferrocene and 20 wt% cobalt acetylacetonate.

Adaptations in skeletal muscle capillarity following changes in oxygen supply and changes in oxygen demands

The effects of changes in oxygen supply and oxygen demands on fiber cross-sectional areas, capillary densities and capillary to fiber ratios were determined in three skeletal muscles of rat. The muscles examined were the vastus lateralis, soleus, and diaphragm. Reduced oxygen supply was produced by subjecting rats to ambient hypoxia, and increased oxygen demands were produced by subjecting rats to low ambient temperatures or treatment with thyroxin. Capillaries were visualized by injecting fluorescent dyes into the circulation. Muscles were quick frozen at resting lengths to preserve normal fiber geometry and were subsequently sectioned on a cryostat. All of the muscles sampled from animals in the experimental groups had elevated capillary densities. However, capillary to fiber ratios were not increased significantly in any muscle, for any experimental condition. Thus, all of the observed differences in capillarity were due to changes in the intrinsic rate of muscle fiber growth. Further, the relations of capillary density and capillary to fiber ratio to fiber area were the same as those obtained during normal maturation, suggesting that capillary growth is closely linked to the intrinsic rate of fiber growth.

Development of transient acetylcholinesterase staining in cells and permanent staining in fibers in cortex of rat brain

The development of the acetylcholinesterase (AChE) texture of the cortex of the rat brain was studied during the first three weeks of life. The Tago technique enables visualization of both AChE+ cells and fibers with both shown in exquisite detail making quantification possible. At each age—0 (birth), 7, 14, 21 and 60 days (adult)—four brain areas were studied (cingulate, dorsal neocortex, lateral neocortex and olfactory) at each of three coronal planes in the brain (anterior, intermediate, posterior). Fiber density reached adult levels by Day 21 in cingulate cortex in intermediate and posterior planes. In other areas fiber density reached adult levels by Day 14 indicating a high rate of fiber growth during the first two weeks of life since at birth rat cortex is innervated only by a sparse AChE+ fiber invasion into neocortex in the anterior plane. Fiber density did not regress after adult levels were reached, however, cell staining showed a different pattern. At birth many lightly stained cells were seen in the olfactory cortex in all three planes, but other areas were devoid of cells. In all areas there was a peak at Day 7 in number of cells stained and in intensity of cells staining with a gradual decline in cell staining until by Day 21 very few stained cells were seen in the cortex (typical adult pattern).

Fibre growth of cashmere-bearing goats given melatonin in late autumn and winter

Abstract At monthly intervals from May to August 1986, groups of 20 reproducing cashmere-bearing does began treatment with continuous-release melatonin implants, with the aim of avoiding winter shearing by prolonging cashmere growth and/or delaying shedding. Treatment groups, plus a group of 20 untreated goats starting in May, were fibre-sampled on the mid-side until 17 November to determine changes in staple fibre length, time of shedding (monthly intervals), and fibre growth rate (bimonthly intervals). Goats treated in May had significantly more cashmere growth on the mid-side than untreated goats in the period July–September, indicating that their cashmere growth rate was higher or that the period of cashmere growth had been prolonged. However, there was no significant increase in total cashmere production or any detectable delay in shedding of cashmere. There was no prolonging of cashmere growth or delaying of shedding in other treatment groups.

Fiber and interface fracture in singlecrystal aluminum/SiC fiber composites

Model metal-matrix composite tensile specimens, each containing a single SiC fiber in a single crystal of pure Al, were grown using a modified Bridgman method at two growth rates and with various fiber surface treatments in order to study their effect on fiber and interface strength. Using the load drops in tensile tests, we measured both fiber and interface strengthin situ. Acoustic emission (AE) was monitored to assist in determining the failure mechanisms. Both the fiber surface treatment and growth rate were found to significantly affect the fiber and interface strength. Fibers with carbon-rich outer surfaces had higher fiber strengths but lower interfacial strengths than untreated fibers. These results are discussed in terms of failure mechanisms and interfacial reactions occurring during growth of the composites.

Estimation of Cell Birth Rate in the Wool Follicle Bulb using Colchicine Metaphase Arrest or DNA Labelling with Bromodeoxyuridine

The birth rate of cells in the wool follicle cells (CBR) was measured in two experiments on sheep differing widely in wool growth rate as a consequence of differences in nutritional regime. In Experiment 1, CBR was determined in one sheep on a high and one on a low plane of nutrition by two methods: the colchicine-metaphase arrest method, or from the product of total cell number and cell cycle time (the latter determined by DNA labelling with 5-bromo-2'-deoxyuridine (BrdU) and analysis of the fraction of mitoses labelled curve). CBR by colchicine was 0.73 and 0.56 of that determined using BrdU for the low- and high-plane sheep respectively. Cell cycle times were 26.5 h (low nutrition) to 18.6 h (high nutrition). In Experiment 2, CBR was again measured by the colchicine method, and from the rate of increase in labelled cells following a pulse dose of BrdU, in sheep on two levels of nutrition (n = 4llevel) and with a 3.7-fold difference in wool growth rate. Again, CBR by colchicine was only 0.41 (high nutrition) to 0.74 (low nutrition) of estimates made using the BrdU method, this difference being statistically significant only for sheep on the high plane of nutrition. Nutrition significantly altered CBR determined by colchicine (Pc0.001) and by BrdU (Pc0.034). The rate of fibre growth per follicle measured on two separate occasions was closely related to CBR measured using colchicine (r= 0.83, P&lt; 0.01 and 0.8 1, P c 0.02) or BrdU (r= 0.73, P c 0.04 and 0.64, P&lt; 0.08). It is concluded that CBR is a major determinant of fibre growth, but that colchicine depresses CBR. Previous estimates of mitotic activity in wool follicle bulbs have been made using colchicine and are thus probably underestimated. The technique using BrdU labelling and the subsequent rate of increase in labelled cells appears to be a useful one for estimating follicle cell kinetics.

Growth of barium metaborate (BaB 2O 4) single crystal fibers by the laser-heated pedestal growth method

High optical quality single crystal fibers of β-BaB 2O 4 (BBO), an important new nonlinear optical material, were grown by the laser-heated pedestal growth (LHPG) method. Because the β-phase is the low temperature phase, these fiber crystals were grown from solution to avoid the α-β solid-state phase transformation encountered when crystals are grown directly from the melt. In this study Na 2O and B 2O 3 were found to be the most useful solvents. The effects of solution composition and seed orientation on fiber growth rate and quality were investigated. Inclusions were observed in some fibers and the relationship between the formation of inclusions and supercooling at the growth interface is discussed.

An adsorption-diffusion isotherm and its application to the growth of carbon filaments on iron catalyst particles

Nanometer-sized Fe particles can decompose methane and extrude graphitic filaments which grow as rapidly as millimeters per minute. The filaments are found to lengthen uniformly for a number of minutes at a constant rate until the Fe catalyst particles are deactivated. Steady state carbon surface coverage on these filament-growing particles is determined by the balance between the surface adsorption rate and the rate of diffusion through the solid particle to the filament. A simple isotherm having these characteristics is derived and found to be consistent with observed fiber growth rates. Comparing the experimental lengthening rate data to the model shows that methane forms a gas phase intermediate before adsorption on the Fe particle's surface. The cessation of filament lengthening occurs at a time corresponding to that required to deposit a 2.8 nm layer of carbon on the filaments. This is compatible with the hypothesis that filament growth ceases when the catalytic particle suffers a collision with a reactively condensed viscous hydrocarbon particle.

Changes in hair growth characteristics following the wounding of vibrissa follicles in the hooded rat

The effect on hair growth of wounding the lower region of whisker follicles, and in particular the dermal papilla, with sharply pointed tungsten needles was studied in adult hooded rats. Following injury hair growth ceased, but was subsequently resumed. While it might have been anticipated that follicle wounding would have a negative effect on whisker length, regular postoperative length measurements revealed that in follicles where cellular material was not displaced from the follicle by the original manipulation, 50% of the subsequent hairs produced were longer than their counterparts on the opposite side of the face, with 25% shorter and 25% with their length unchanged. In every case increased hair length was achieved by a prolongation of the growing period of the hair. Growth rate, when altered, was reduced. These results suggest that the factors which control the duration of the hair cycle and fibre growth rate are independent in vibrissa follicles. Since removal of most of the epidermal component by plucking of the hair just prior to injury produced equivalent hair length increases, this implicated the proximal dermal components as being mainly responsible for the observed changes.

Transmitter release during normal and altered growth of identified muscle fibres in the crayfish.

During growth of identified crayfish muscle fibres from a diameter of 20 to 400 micron, the excitatory junctional potential (e.j.p.) amplitude was found to be independent of diameter. Thus, e.j.p. amplitude was maintained during growth in spite of a 21-fold decrease in miniature excitatory junctional potential (m.e.j.p.) amplitude previously reported (Lnenicka & Mellon, 1983). The maintenance of e.j.p. amplitude was found to be partially due to a 5-fold increase in quantal release at 'active sites' during growth. In order to determine whether the increase in transmitter release can be regulated by the rate of muscle fibre growth, the rate of growth was experimentally reduced. By decreasing the resting length of the muscle during growth, the rate of increase in the diameter was reduced by approximately 50% compared with the contralateral control muscle fibres. The input resistance and the m.e.j.p. were appropriately larger in the smaller-diameter experimental fibres. However, e.j.p. amplitude in the experimental fibres was not significantly different from that in the contralateral control fibres. This was apparently due to the significantly smaller quantal release at active sites on the experimental fibres compared with control fibres. Thus, experimental alteration of the rate of muscle fibre growth results in regulation of transmitter release, suggesting that the muscle fibre may control the increase in transmitter release seen during normal growth.

Temperature gradient and growth velocity effects on the irregular monotectic structure

An earlier paper modelling the monotectic interface [Derby and Favier, Acta Met. 31 (1983) 1123] implied that the liquid phase in irregular monotectics will be in advance of the average interface position. Such a geometry suggests a gradient effect on the fibrous irregular structure. Experiments in the Cu-Pb and pseudobinary Al-In-Sn irregular monotectics reveal a growth law of λυ1/2G1/31/3= constant relating fibre spacing (λ), growth rate (ν) and temperature gradient (G). This is compared with the similar laws reported in some facetted/non-facetted eutectics.

Target tissue control of nerve fiber growth rate and periodicity in vitro.

Spinal cord and dorsal root ganglion nerve fibers of tadpoles elongate in vitro at an increased rate in the presence of target tissue or target-conditioned medium. These neurites extend in a cyclic fashion with the period between the occurrence of maximal growth rates being under target influence. Rate parameters may be an important feature in the understanding of directed nerve growth during development and regeneration.