The Q value variations in the preparing pro－cess of rock rupture

In this paper, the 'spectral amplitude ratio method'(SAR) , 'energy method'(EN) and 'coda wave method'(CW) are used to calculate the Q value variations of gneiss in the preparing rupture process. The obtained results show that the variation state of Q values by SAR features the shape of relative stability gradual increment to the maximum then decrement and final rupture.The variation state of Q values by EN is just contrary to that by SAR,i.e.with the shape of stability decrement increment and final rupture . The varation state of Q values by CW is similar to that by EN, its main frequency features the shape of relatively high value decrement to the minimum increment and final rupture.But to the high frequency (higher than the main frequency),the variation state of Q values features the shape of the stable value increment to the maximum decrement and final rupture.At the same time, the results by coda wave amplitude spectrum show that, when stress reaches 70% of rupture stress, the high frequency component of S wave rapidly reduces( Q c increasing); at the time of impending the main rupture, the main frequency component reduces with a large scale( Q c increasing again), this may be the reason which causes the different variation states of two coda Q values.The result of amplitude spectra of P, S(initial wave) waves also show that with the appearance of microcracks the frequency band of S wave turn to be narrow, the high frequency component is reduced quickly, i.e. the S wave spectra have different variation states with different frequeny components. That is why the Q s obtained by different methods have different variation characteristics.

Degradability evaluation for natural material fibre used on fish aggregation devices(FADs)in tuna purse seine fishery

Purse seiners deploy large amounts of drifting fish aggregation devices(FADs)in all tropical oceans to catch tunas.These FADs are constructed with porous synthetic fibre netting,which are responsible for incidental mortality of sea turtles and sharks through entanglement,and can engage in ghost fishing if they are lost and abandoned.The use of natural or biodegradable materials to build FADs can effectively mitigate marine pollution and bycatch issues,and as such they are currently promoted by fisheries management organizations.This study evaluated the degradability of ropes made of common natural fibres;cotton rope(3-strand,96-thread,twisted,S-lay),jute rope(3-strand,13-thread,twisted,Z-lay)and sisal rope(3-strand,8-thread,twisted,Z-lay).Degradability was evaluated by measuring the breaking strength(cN/dtex)and retention ratio of rupture elongation.Results showed that jute rope and sisal rope experienced rapid reduction of strength which over the first month soaking in the sea fell by 66.8%and 46.9%,respectively.Cotton rope exhibited the most inert degradation behavior,with breaking strength maintained at half of the initial value at 10 months.The retention ratio of rupture elongation for jute ropes and sisal ropes fluctuated considerably in the following months after deployment,compared to the relatively stable change for cotton rope.Results suggested that among these congeners,cotton rope would be most preferable component for Bio-FADs with a 10-month minimum durability that matches the required lifetime of FAD fishing strategies.