Fiber Growth Rate Research Articles

Assembly of fibrin. A light scattering study.

Using stopped flow light scattering, we show that assembly of fibrin following activation with non-rate-limiting amounts of thrombin or reptilase occurs in two steps, of which the first is end-to-end polymerization of fibrin monomers to protofibrils and the second is lateral association of protofibrils to fibers, in agreement with Ferry's original proposal. Polymerization is found to proceed as a bimolecular association of bifunctional monomers; the overall rate varies as the inverse first power of the concentration; end-to-end association of two monomers, of a monomer and an oligomer, and of two oligomers occurs with the same rate constant. The value of the rate constant is 8.2 C 10(5) M-1 s-1 in 0.5 M NaCl, is three times larger in 0.1 M NaCl (0.05 M Tris, pH 7.4), and is the same following activation by reptilase and by thrombin. The onset of growth of fibers from protofibrils takes 12 times longer in 0.5 than in 0.1 M salt, i.e. thick fibers ("coarse" gels) form from short protofibrils, and thin fibers ("fine" gels) form from longer protofibrils. Jumps of salt concentration at times when protofibrils, but not fibers, have formed result in immediate growth of thick fibers at low salt from long protofibrils formed at high salt. The rate of fiber growth in these experiments varies as the inverse first power of the concentration. 3the instant of gelation (formation of a network of fibers) falls in the later half of the time during which the scattering rises due to fiber growth; the rise of gel rigidity after gelation is found to continue beyond the end of this period. Jumps from low to high salt result in retention of whatever fibers have formed at low salt and a very small additional increase of the scattering due to further fiber growth at high salt. From a variety of evidence, we conclude that the properties of fibrin are determined by kinetics and not equilibria of assembly steps. Results obtained here agree with the following scheme of fibrin assembly: monomers polymerize to protofibrils; long protofibrils associate laterally to fibers; occasionally a long protofibril associates with two different fibers to form an interfiber connection; fiber growth does not reverse to yield stabler, more compact, structures and terminates in formation of a network of fibers. The typical delay of fiber growth is the time during which protofibrils form from monomers. Measurements at rate-limiting concentrations of thrombin have allowed estimation of turnover rates of fibrinopeptides that agree with kinetic parameters obtained with direct assay of fibrinopeptide. Release of fibrinopeptide B causes more rapid fiber formation. Addition of thrombin after activation by reptilase, at a time when protofibrils, but not fibers, have formed, is followed rapidly by fiber formation; this proves that thrombin readily removes fibrinopeptide B from protofibrils. On the basis of these new results and earlier work (in particular, Blombäck, B., Hessel, B., Hogg, D., and Therkildsen, L...

Oriented polymers from solution. I. A novel method for producing polyethylene films

AbstractA novel method for the production of uniaxially oriented polyethylene film is demonstrated, it being an extension of the “surface growth” method for obtaining polyethylene fibers from solution using a Couette apparatus. The film growth is found to be affected by temperature, rotor speed, rotor material, and surface roughness. Together with its possible practical importance, film growth is presented as a useful means of sample preparation and as a way to increased linear fiber growth rates. In addition, its use for studies on solution grown polypropylene fibers is indicated as well as its implications for “surface growth” of polymer crystals in general.

DNA fiber replication of chromosomes of pea root cells terminating S

Autoradiographic analysis of chromosomal DNA fiber replication was used to measure the distance between initiation points of adjacent replicons and the rate of fiber growth during cessation of proliferation that results from carbohydrate starvation of pea root meristem cells. The rate of fiber growth at 23 °C decreased from 34 μm/h/fork at 3 h to less than 2 μm/h/fork at 24 h of starvation. The distance between initiation points, i.e., the average replicon size, was 36–38 μm in starved cells terminating S. Replenishment of carbohydrate was accompanied by an increase in the rate of fiber growth and larger replicons.

An analysis of the interactions between sympathetic nerve fibers and smooth muscle cells in tissue culture

The interactions between sympathetic nerve fibers and smooth muscle cells and fibroblasts from the newborn guinea pig vas deferens were studied in tissue culture with phase contrast microscopy, time-lapse microcinematography, catecholamine fluorescence histochemistry and scanning and transmission electron microscopy. The amount of sympathetic nerve fiber growth, its catecholamine fluorescence reaction and the size of the nerve cell bodies and their nuclei all increased in the presence of vas deferens tissue. Specific growth of nerve fibers to large clumps of vas deferens tissue was seen from distances of up to 2 mm. In contrast, no specific growth from a distance occurred to single cells or small groups of cells. However, random contact with a muscle cell often led to close, extensive, and long-lasting associations. Contact with fibroblasts was always transitory. The rate of sympathetic nerve fiber growth over individual muscle cells was faster than over fibroblasts, which, in turn, was faster than over the collagen-coated surface of the coverslip. Palpation of a muscle cell by a nerve fiber growth cone increased the rate of spontaneous contraction of the muscle cell, the extent of the increase being dependent on the number of nerve fibers involved. Multiple innervation of a smooth muscle cell occurred if nerve fibers reached the cell at about the same time, but not if there was a close association already established. These results are discussed in relation to possible interactions of sympathetic nerve fibers with smooth muscle cells in vivo.

Experimental reorganization of the cerebellar cortex. 3. Regeneration of the external germinal layer and granule cell ectopia.

AbstractThe heads of Long‐Evans hooded rats were irradiated daily from day 3, 4 or 6 onward with schedules of low‐level x‐ray which differentially delayed the regeneration of the subtotally eradicated external germinal layer or prevented its regeneration altogether. Most schedules that permitted regeneration led to the arrest of many granule cells in the molecular layer where they formed an ectopic zone. The dendrites of ectopic granule cells had synapses with mossy fibers located in their vicinity in the molecular layer. The position of the ectopic zone varied in different lobules depending on several factors: the time when regeneration began, the estimated date of descent of granule cells, regional differences in cortical maturation and in the estimated upward growth rate of mossy fibers. Within the same lobule, the longer regeneration was delayed the higher in the molecular layer the differentiating and descending granule cells were captured by the apparently autonomously ascending mossy fibers. If regeneration started early and allowed the descent of granule cells into the granular layer (early irradiation) or if regeneration of granule cells was prevented altogether (late irradiation) an ectopic zone was not formed. The technique was used for estimating the normal growth pattern of mossy fibers in the different lobules.

Lack of toxic effect of guanethidine on nerve cells and small intensely fluorescent cells in cultures of sympathetic ganglia of newborn rats

Pieces of sympathetic ganglia of newborn rats were cultivated in modified Rose chambers in Medium 199 supplemented with serum, insulin, penicillin and glucose. Guanethidine sulphate was added to make the following concentrations in the medium: 0 (controls), 1, 3, 9 or 36 mg/l. The cultures were daily examined using dark ground and phase contrast microscopy. After 6–8 days of culture with guanethidine, the catecholamines were demonstrated with the formaldehyde-induced fluorescent method. There was a clear increase in the number of the small intensely fluorescent cells in cultures with 1 mg/l of guanethidine sulphate, suggesting that it has a direct effect on these cells. Cultures with higher concentrations showed variability in the number of these cells, probably due to depletion of their catecholamine content. Light microscopic appearances of guanethidine-containing cultures did not differ from control cultures in nerve cell structure, nerve fibre growth rate or cellular composition of the outgrowth. It is therefore concluded that guanethidine has no apparent cytotoxic effect on sympathetic nerve cells in vitro.

The Electroforming—Filament Winding Process: A Method of Producing Metal Matrix Composites

SummaryElectroforming coupled with filament winding can be used as a method of producing sophisticated metal matrix composites; this process has a close analogy to that already in use with plastic matrices. The main limitation of the Electroforming—Filament Winding Process (EFW) occurs when structures with a high winding angle are produced. In this case even at relatively low angles the level of porosity in the composites becomes high. The reasons for this and other parameters introducing porosity into the structure are examined, eg the effect of fibre size, composite growth rate, the use of non-conducting fibres and multi-filament tows. It has been found that a change in geometry is produced at the composite-electrolyte interface when any of the above variables is imposed upon the EFW process and this leads to localized alterations in electrodeposition growth behaviour. At high winding angles the resulting increase of porosity has been explained in terms of fibre crossover points which locally increase the radial fibre growth rate. This problem is due to the helical method of filament winding and it is suggested that it may be overcome by using a polar winding method.

Fiber Elongation Rates in Five Varieties of Cotton (Gossypium hirsutum L.) as Influenced by Night Temperature1

Five cotton varieties were grown in the field under four different night temperature regimes (10, 15, 20, and 25 C). The influence of temperature on the rate and extent of fiber elongation was studied. Temperatures below 20 C reduced fiber length; and generally, the reduction was greater in varieties having the longer fibers. Lowering night temperature increased the fiber elongation period and slowed the fiber growth rate. The temperature coefficients of elongation indicated the rate of elongation for all varieties was extremely temperature‐sensitive up to 15 days age. Beyond 15 days age, however, the coefficlents of elongation quickly approached one, indicating temperature independence.

A comparative study of fleece growth in Tasmanian Fine Merino and Wiltshire Horn ewes

1. From repeated fibre samplings and several skin biopsies on six Tasmanian Fine Merinos and eight Wiltshire Horn adult ewes variations in fibre diameter, fibre growth rate, and fibre regeneration or shedding frequency were measured over a period of 15 months. Slight differences were present in the treatment of the two breeds, but from the combined evidence of the live weights and fibre diameters maintained, it was concluded that these were negligible, that both breeds were under closely comparable conditions, and that their performance was at a moderately high and typical level for each breed.2. In the Merinos fibre diameter (ca. 20 µ) fluctuated little during the period of observation, whereas in the Wiltshires it varied over a wide range from less than 40µ in winter to more than 80µ in summer. There were negligible differences between the three body regions, back, side, and belly, in the Merinos, but in the Wiltshires the belly grew markedly coarser fibres than the other two regions.3. The fibre growth rate in the Merinos did not vary greatly from 7 to 8 mm. per 28 days throughout the period of observation or between the body regions. In the Wiltshires, fibre growth rate showed extreme variations from a minimum of about 3 mm. during the winter to a maximum of about 12 mm. per 28 days at the end of summer, with significant differences between the three body regions. However, in spite of these differences in the mode of growth, the total length of fibre grown per annum at the midside was approximately the same (10 cm.). Thus, were it not for fibre shedding, the Wiltshire Horn breed would grow a short-wool fleece.

Mitotic Activity in Wool Follicle Bulbs

The quantitatIve significance of mitosis in wool follicle bulbs in relation to the rate of fibre growth was investigated in 10 major fleece phenotypes (fine .Merino, medium Merino mosaic, strong Merino, Merino lustre mutant, Corriedale carpet-wool, Corriedale mosaic, Southdown, and Border Leicester). Mitotic activity in the follicle bulbs was estimated with the aid of colchicine and the volume rate of fibre growth was inferred from fibre diameter.

Post-natal growth changes in the fibre cortex and medulla of the new zealand romney and N-type sheep

The relationship between cortical area and fibre area has been examined in the N/N, N/ +, + / +, + /nr and nr/nr genotypes of the New Zealand Romney, using skin biopsies taken at birth, 1, 3 and 16 months of age. The presence of the nr gene was shown to reduce significantly the relative cortical area. Within the genotypes there was an increase in relative cortical area with increasing age and in two-tooth ewes of N/N and N/ + there was an increase in relative cortical area in winter compared to summer.Fibre growth rates in length for primaries and for prenatal and post-natal secondaries were found for lambs between 1 and 3 months and for 16-monthold ewes. In N/N, N/+ and nr/nr primary fibre growth tended to be increased and post-natal secondary fibre growth tended to be decreased relative to + / + values.In both cortical area and fibre growth rate the greatest genotypic effect was shown by the primary fibres.Some estimates of cortical volume have been made by combining the information on cortical area and fibre growth rate and the relationship of these factors to follicle density and mean fibre area has been discussed. Finally, an indication has been given of how the associations of all these four factors might be usefully examined in some British breeds.

日本脳炎ウイルスの組織培養に関する研究

As is well known embryonated eggs are used for the culture of all kinds of the virus. With the use of droplet culture the author in the present experiment conducted a series of experiments in order to study influences of the virus of Japanese B encephalitis, the virus which is neurotropic, on the central nervous system of the chick embryo.When the normal brain of chick embryo is cultured under a certain fixed condition, nerve fibers grow almost uniformly.When the Japanese B encephalitis virus is inoculated into the embryonated eggs, the eggs will die on the average of 5 days after the inoculation. However, judging the function of nerve cells by the growth rate of nerve fibers during the culture, it starts to decline on the 3rd day and on the fifth day, the day immediately before death, it is almost lost. Similarly the fnnction of other cells is lost, too. On the other hand, although there is a marked hyperemia in the pathohistological finding, no significant changes as might be expected of the tissue culture findings can be recognized in the nerve cells as well as in other cells. Namely, even where there is no apparent histological abnormalities, the cell functions are actually disturbed to a marked extent.