Yielding of engineering polymers at strain rates of up to 500 s-1

A method is described for measuring the mechanical properties of polymers in compression at strain rates in the range approximately 300-500 s-1. A gravity-driven pendulum is used to load a specimen on the end of an instrumented Hopkinson output bar and the results are processed by a microcomputer. Stress-strain curves up to high strains are presented for polycarbonate, polyethersulphone and high density polyethylene over a range of temperatures. The value of yield stress, for all three polymers, was found to vary linearly with log (strain rate) at strain rates up to 500 s-1. © 1985.

Synthesis and properties of a new series of low-molar-mass organo-siloxane derivatives

Two series of ferroelectric liquid crystalline organo-siloxanes containing a laterally attached halogen on the phenyl ring have been synthesised and characterised to determine the impact of the siloxane group and the halogen on the mesomorphism and electro-optic switching properties. Both monomesogenic and bimesogenic compounds have been studied. The monomesogenic derivatives were found to be ferroelectric with high tilt and Ps. The tilt angle of 45° and the Ps of 95nC/cm2 are almost temperature independent. The bimesogenic bromo substituted derivatives showed mainly ferroelectric phases about 60°C wide. Maximum values for the spontaneous polarisation and the tilt angle were only slightly influenced by the length of the siloxane spacer. Altering the halogen to a fluorine shifted the liquid cystalline phase slightly to higher temperatures whilst maintaining the mesophase range of 60°C.

Ferroelectric liquid crystal mixtures containing chiral ether and ester compounds with the 2-arylidene-p-menthan-3-one skeleton

Some 1R,4R-2-(4-phenylbenzylidene)-p-menthane-3-one derivatives containing the ether or ester linking group between benzene rings of the arylidene fragment have been studied as chiral dopants in ferroelectric liquid crystal systems based on the eutectic mixture (1:1) of two phenylbenzoate derivatives CmH2m+1OC6H4COOC6 H4OCnH2n+1 (n = 6; m = 8, 10). The ferroelectric properties of these compositions (spontaneous polarization, rotation viscosity, smectic tilt angle as well as quantitative characteristics of their concentration dependences) were compared with those for systems including chiral dopants containing no linking group. Ferroelectric parameters of the induced ferroelectric compositions studied have been shown to depend essentially on the presence of the linking group between benzene rings and its nature as well as on the number of the benzene rings in the rigid molecular core of the chiral dopants used. For all ferroelectric liquid crystal systems studied, the influence of the chiral dopants on the thermal stability of N*, SmA and SmC* mesophases has been quantified. The influence of the linking group nature in the dopant molecules on the characteristics of the systems studied is discussed taking into account results of the conformational analysis carried out by the semi-empirical AM1 and PM3 methods.

Construction of a BAC library for Chinese amphioxus Branchiostoma belcheri and identification of clones containing Amphi-pax genes

Amphioxus is a crucial organism for the study of vertebrate evolution. Although a genomic BAC library of Branchiostoma floridae has been constructed, we report here another BAC library construction of its distant relative species Branchiostoma belcheri. The amphioxus BAC library established in present study consists of 45,312 clones arrayed in one hundred and eighteen 384-well plates. The average insert fragment size was 120 kb estimated by Pulsed Field Gel Electrophoresis (PFGE) analysis of 318 randomly selected clones. The representation of the library is about 12 equivalent to the genome, allowing a 99.9995% probability of recovering any specific sequence of interest. We further screened the library with 4 single copied Amphi-Pax genes and identified total of 26 positive clones with average of 6.5 clones for each gene. The result indicates this library is well suited for many applications and should also serve as a useful complemental resource for the scientific community.