The wire electrical discharge machining（EDM） of 6061 aluminium alloy in terms of material removal rate,kerf/slit width,surface finish and wear of electrode wire for different pulse on time and wire tension was studi...The wire electrical discharge machining（EDM） of 6061 aluminium alloy in terms of material removal rate,kerf/slit width,surface finish and wear of electrode wire for different pulse on time and wire tension was studied.Eight experiments were carried out in a wire EDM machine by varying pulse on time and wire tension.It is found that the material removal rate increases with the increase of pulse on time though the wire tension does not affect the material removal rate.It seems that the higher wire tension facilitates steady machining process,which generates low wear in wire electrode and better surface finish.The surface roughness does not change notably with the variation of pulse on time.The appearance of the machined surfaces is very similar under all the machining conditions.The machined surface contains solidified molten material,splash of materials and blisters.The increase of the pulse on time increases the wear of wire electrode due to the increase of heat input.The wear of wire electrode generates tapered slot which has higher kerf width at top side than that at bottom side.The higher electrode wear introduces higher taper.展开更多
An evaluation was performed on the influence of mowing height (2.5,5.0 or 7.5 cm) and mowing frequency (weekly or fortnightly) on levels of ergot alkaloids (ergine and ergonovine) formed in drunken horse grass,Achnath...An evaluation was performed on the influence of mowing height (2.5,5.0 or 7.5 cm) and mowing frequency (weekly or fortnightly) on levels of ergot alkaloids (ergine and ergonovine) formed in drunken horse grass,Achnatherum inebrians,grown under greenhouse conditions.Samples were taken monthly and alkaloids were extracted and analyzed by reverse-phase HPLC.Alkaloid levels increased more or less linearly with plant age over the first four months following establishment.Levels were higher in samples cut fortnightly compared to those cut weekly,and were higher when plants were cut at a mowing height of 7.5 cm vs.2.5 cm.In most cases,the highest alkaloid levels observed were almost three times those of the lowest.If plant protection applications are developed for the endophytic fungus,Neotyphodium gansuense,it will be necessary to be aware of the potential role of plant husbandry practices (e.g.,defoliation frequency and intensity) for reducing or enhancing levels of plant alkaloids.Similar husbandry factors may affect alkaloid levels in other Neotyphodium-grass associations,which would be interesting for further study.展开更多
We consider a discrete-time risk model,in which insurance risks and financial risks jointly follow a multivariate Farlie-Gumbel-Morgenstern distribution,and the insurance risks are regularly varying tailed.Explicit as...We consider a discrete-time risk model,in which insurance risks and financial risks jointly follow a multivariate Farlie-Gumbel-Morgenstern distribution,and the insurance risks are regularly varying tailed.Explicit asymptotic formulae are obtained for finite-time and infinite-time ruin probabilities.Some numerical results are also presented to illustrate the accuracy of our asymptotic formulae.展开更多
文摘The wire electrical discharge machining（EDM） of 6061 aluminium alloy in terms of material removal rate,kerf/slit width,surface finish and wear of electrode wire for different pulse on time and wire tension was studied.Eight experiments were carried out in a wire EDM machine by varying pulse on time and wire tension.It is found that the material removal rate increases with the increase of pulse on time though the wire tension does not affect the material removal rate.It seems that the higher wire tension facilitates steady machining process,which generates low wear in wire electrode and better surface finish.The surface roughness does not change notably with the variation of pulse on time.The appearance of the machined surfaces is very similar under all the machining conditions.The machined surface contains solidified molten material,splash of materials and blisters.The increase of the pulse on time increases the wear of wire electrode due to the increase of heat input.The wear of wire electrode generates tapered slot which has higher kerf width at top side than that at bottom side.The higher electrode wear introduces higher taper.
基金supported by the National Basic Research Program of China (Grant No. 2007CB108902)the National Natural Science Foundation of China (Grant No. 30771531)+1 种基金Program for New Century Excellent Talents in University (Grant No. NCET-08-0256)the Fundamental Research Funds for the Central Universities (Grant No. LZUJBKY-2009-156)
文摘An evaluation was performed on the influence of mowing height (2.5,5.0 or 7.5 cm) and mowing frequency (weekly or fortnightly) on levels of ergot alkaloids (ergine and ergonovine) formed in drunken horse grass,Achnatherum inebrians,grown under greenhouse conditions.Samples were taken monthly and alkaloids were extracted and analyzed by reverse-phase HPLC.Alkaloid levels increased more or less linearly with plant age over the first four months following establishment.Levels were higher in samples cut fortnightly compared to those cut weekly,and were higher when plants were cut at a mowing height of 7.5 cm vs.2.5 cm.In most cases,the highest alkaloid levels observed were almost three times those of the lowest.If plant protection applications are developed for the endophytic fungus,Neotyphodium gansuense,it will be necessary to be aware of the potential role of plant husbandry practices (e.g.,defoliation frequency and intensity) for reducing or enhancing levels of plant alkaloids.Similar husbandry factors may affect alkaloid levels in other Neotyphodium-grass associations,which would be interesting for further study.
基金supported by National Natural Science Foundation of China(Grant Nos.10801124 and 11171321)the Fundamental Research Funds for the Central Universities(GrantNo.WK 2040170006)
文摘We consider a discrete-time risk model,in which insurance risks and financial risks jointly follow a multivariate Farlie-Gumbel-Morgenstern distribution,and the insurance risks are regularly varying tailed.Explicit asymptotic formulae are obtained for finite-time and infinite-time ruin probabilities.Some numerical results are also presented to illustrate the accuracy of our asymptotic formulae.
