Inverse Stress Relaxation and Viscoelastic Recovery of Multifilament Textile Yarns in Different Test Cycles
The article presents the results of the experimental research of inverse stress relaxation (IR) and viscoelastic recovery (VR) that take place in acetate and polyester multifilament yarns in dependance on the mechanical pre-history. The above-mentioned time-effects are investigated in two different – stress relaxation (R-) and creep (C-) testing cycles. The fact that inverse stress relaxation process takes place in Ctest cycle, i.e. after previous sustaining the specimen at constant load is experimentally confirmed. It is shown that viscoelastic recovery is the slower process than the inverse stress relaxation. At identical elongations of the yarns at the end of loading period the inverse relaxation and viscoelastic recovery processes go on similarly regardless of the character of testing cycle.
Mechanical Properties of Textiles, IV
(Figure 1) consisting of a spring in parallel with a Maxwell element which, in turn, is composed of a spring and a non-Newtonian dashpot in series. The extension of the springs was shown to be related to the uncoiling of the polymer molecules from their random or equilibrium positions against the restoring tendencies of potential energy and entropy; the slipping of the dashpot was explained in terms of the rate process of the slipping of the segments of the molecules past each other. The detailed molecular theory of these unit processes is the subject of previous [1, 2] and future papers. These elements may be characterized by four constants-namely, the force constants of the two springs, and two constants of the non-Newtonian
Genotypic diversity in field isolates of Babesia bovis from cattle with babesiosis after vaccination.
OBJECTIVE
To determine whether particular genotypes of Babesia bovis were common to field isolates obtained from cattle properties in Queensland where the B bovis vaccine had apparently failed.


DESIGN
A comparative study of polymerase chain reaction genotypes in different populations of B bovis.


PROCEDURE
Two polymerase chain reaction assays were applied to analyse DNA extracts of B bovis vaccine (K, T and Dixie strains) and 27 field isolates from 24 properties where disease outbreaks had occurred despite the use of the vaccine. To evaluate the stability of the genotypes identified, 11 of the field isolates were inoculated into experimental cattle that had either been previously vaccinated with T strain or not vaccinated.


RESULTS
No particular genotype of B bovis was responsible for the problems observed in previously vaccinated herds. None of the isolates had genotypes identical to the vaccine strains used. No geographic trends among the genotypes were observed. Isolates that originated from the same property also had different genotypes. Blood passage of the 11 field isolates in either previously vaccinated or nonvaccinated cattle did not alter the original genotype.


CONCLUSION
No particular genotypes identified by the Bv80 and BvVA1 polymerase chain reaction assays could be associated with vaccine failures.