The synergetic influence of silane-grafting and polar additives （EVA） on the water tree resistance of the low density polyethylene has been investigated. A series of samples obtained before and after hydration have ...The synergetic influence of silane-grafting and polar additives （EVA） on the water tree resistance of the low density polyethylene has been investigated. A series of samples obtained before and after hydration have been characterized by measuring gel content, infrared spectroscopy （FTIR）, differential scanning calorimetry （DSC） and dielectric measurements. The results obtained clearly show that the silane condensation occurred and that the silane-grafting and polar additives have synergetic effects on the water tree resistance of LDPE with little influence on its dielectric properties, e.g. the dielectric breakdown strength, dielectric permittivity and loss tangent.展开更多
To improve the water tree resistance of PE, linear low-density polyethylene （LLDPE） was compounded with sodium acrylate （NaAA） for in situ polymerization, in which NaAA was fbrmed through the neutralization of acr...To improve the water tree resistance of PE, linear low-density polyethylene （LLDPE） was compounded with sodium acrylate （NaAA） for in situ polymerization, in which NaAA was fbrmed through the neutralization of acrylic acid （AA） with sodium hydroxide （NaOH） before adding dicumyl peroxide （DCP） to initiate the in situ graft polymerization and homo polymerization. A series of LLDPE/NaAA compounds were investigated for their water absorption ratio （WAR） measurement, water treeing, mechanical and dielectric properties. The results strongly suggest that NaAA can improve the water tree resistance of LLDPE. In addition, the LLDPE/NaAA compounds possess satisfactory mechanical properties and dielectric properties. Characterization of LLDPE/NaAA compounds by using Fourier transform infrared spectrometry （FTIR） suggests that the neutralization and polymerization reaction could be achieved effectively. Using adequate DCP content is the key factor for controlling the polymerization of NaAA with precise conversion ratio.展开更多
We examined stable isotope signals of precipitation, soil water, and xylem water and ran the multi-source linear mixing model （IsoSource） to determine water uptake depths and estimate proportional contribution of po...We examined stable isotope signals of precipitation, soil water, and xylem water and ran the multi-source linear mixing model （IsoSource） to determine water uptake depths and estimate proportional contribution of possible water pools to the water use of Mongolian pine （Pinus sylvestris var. mongolica） plantation in southeast Horqin Sandy Land. We also examined variations of the water use by Mongolian pine trees before and after a heavy precipitation event. The closeness of isotopic composition between xylem water and potential water pools presented that most of water uptake by the trees occurred in the depth of below 20 cm soil （up to 80 cm in this study）. Estimate from the IsoSource model agrees well with observation, and the model yielded that over 60% of the water was derived from 20–80 cm soil layer under relatively higher soil moisture conditions, contribution from much deeper soil depth may increase when the soil in this layer became dry. The contribution from the groundwater was very low since water table was much deeper than rooting depth of the trees. Isotopic signals of xylem water of Mongolian pine trees before and after a heavy precipitation of 14.4 mm on July 13 in 2009 exhibited that the trees could sense and use recent rain-charged soil water at the upper 20 cm soil layer 36 hours after the rain, and this contribution decreased rapidly in the following 24 hours. The ability of accessing different water pools of Mongolian pine trees under various soil moisture conditions is likely a good indicator of their adaptability to dry habitats in sandy lands.展开更多
Aims Beech(Fagus sylvatica L.)is an important species in natural and managed forests in Europe.This drought-sensitive species dominates even-aged stands as well more natural stands composed of a mixture of tree specie...Aims Beech(Fagus sylvatica L.)is an important species in natural and managed forests in Europe.This drought-sensitive species dominates even-aged stands as well more natural stands composed of a mixture of tree species,age and size classes.This study evaluates the extent that heterogeneity in spacing and tree diameter affect the seasonal availability and use of water.Methods Two stands were evaluated:(i)a heterogeneous forest remnant(NAT)with trees up to;300 years old,a mean top height of 28.4 m and a total of 733 stems ha1with stem diameters averaging 18 cm and(ii)an even-aged 80-year old stand(MAN),with a height of 25 m,and a total of 283 stems ha1 with diameters averaging 38 cm.Stem sap flow,Js(g m2 s1),was continuously measured in 12(MAN)and 13(NAT)trees using 20-mm long heat dissipation sensors.Individual tree measures of sap flow were correlated using non-linear statistical methods with air vapour pressure deficit(D,hPa)and global radiation(Rg,J m2 day1),along with constraints imposed by reductions in soil water content(SWC).SWC was measured as volumetric%using time domain reflectometry.Important Findings The daily integrated Js(Js-sum)for trees growing in the evenly spaced MAN stand and trees in canopy and closed forest positions in NAT stand decreased as the availability of soil moisture was reduced.In the heterogeneous NAT stand,SWC in a recently formed canopy gap remained high throughout the vegetation period.Based on regression models,the predicted relative decrease in Js-sum for dry relative to moist soil water conditions in the closed forest(at mean daily D=10 hPa)was 7–11%for trees near the gap and 39–42%for trees in the closed forest.In MAN,the reduction in Js-sum was 29%in dry relative to moist conditions.Js-sum in the outer 20 mm of the xylem in NAT was lower than that in MAN and the rate of decline in Js with xylem depth was less in NAT than in MAN.In MAN,Js-sum in deep and outer xylem was negatively affected at low soil moisture availability;in NAT,this was the case for only the outer xylem indicating that deep roots could be important in supplying water at times of low soil moisture in the upper soil.展开更多
文摘The synergetic influence of silane-grafting and polar additives （EVA） on the water tree resistance of the low density polyethylene has been investigated. A series of samples obtained before and after hydration have been characterized by measuring gel content, infrared spectroscopy （FTIR）, differential scanning calorimetry （DSC） and dielectric measurements. The results obtained clearly show that the silane condensation occurred and that the silane-grafting and polar additives have synergetic effects on the water tree resistance of LDPE with little influence on its dielectric properties, e.g. the dielectric breakdown strength, dielectric permittivity and loss tangent.
基金The project was supported by the Shanghai Committee of Science and Technology (No. 045211024).
文摘To improve the water tree resistance of PE, linear low-density polyethylene （LLDPE） was compounded with sodium acrylate （NaAA） for in situ polymerization, in which NaAA was fbrmed through the neutralization of acrylic acid （AA） with sodium hydroxide （NaOH） before adding dicumyl peroxide （DCP） to initiate the in situ graft polymerization and homo polymerization. A series of LLDPE/NaAA compounds were investigated for their water absorption ratio （WAR） measurement, water treeing, mechanical and dielectric properties. The results strongly suggest that NaAA can improve the water tree resistance of LLDPE. In addition, the LLDPE/NaAA compounds possess satisfactory mechanical properties and dielectric properties. Characterization of LLDPE/NaAA compounds by using Fourier transform infrared spectrometry （FTIR） suggests that the neutralization and polymerization reaction could be achieved effectively. Using adequate DCP content is the key factor for controlling the polymerization of NaAA with precise conversion ratio.
基金the National Science Foundation of China (30770339)
文摘We examined stable isotope signals of precipitation, soil water, and xylem water and ran the multi-source linear mixing model （IsoSource） to determine water uptake depths and estimate proportional contribution of possible water pools to the water use of Mongolian pine （Pinus sylvestris var. mongolica） plantation in southeast Horqin Sandy Land. We also examined variations of the water use by Mongolian pine trees before and after a heavy precipitation event. The closeness of isotopic composition between xylem water and potential water pools presented that most of water uptake by the trees occurred in the depth of below 20 cm soil （up to 80 cm in this study）. Estimate from the IsoSource model agrees well with observation, and the model yielded that over 60% of the water was derived from 20–80 cm soil layer under relatively higher soil moisture conditions, contribution from much deeper soil depth may increase when the soil in this layer became dry. The contribution from the groundwater was very low since water table was much deeper than rooting depth of the trees. Isotopic signals of xylem water of Mongolian pine trees before and after a heavy precipitation of 14.4 mm on July 13 in 2009 exhibited that the trees could sense and use recent rain-charged soil water at the upper 20 cm soil layer 36 hours after the rain, and this contribution decreased rapidly in the following 24 hours. The ability of accessing different water pools of Mongolian pine trees under various soil moisture conditions is likely a good indicator of their adaptability to dry habitats in sandy lands.
文摘Aims Beech(Fagus sylvatica L.)is an important species in natural and managed forests in Europe.This drought-sensitive species dominates even-aged stands as well more natural stands composed of a mixture of tree species,age and size classes.This study evaluates the extent that heterogeneity in spacing and tree diameter affect the seasonal availability and use of water.Methods Two stands were evaluated:(i)a heterogeneous forest remnant(NAT)with trees up to;300 years old,a mean top height of 28.4 m and a total of 733 stems ha1with stem diameters averaging 18 cm and(ii)an even-aged 80-year old stand(MAN),with a height of 25 m,and a total of 283 stems ha1 with diameters averaging 38 cm.Stem sap flow,Js(g m2 s1),was continuously measured in 12(MAN)and 13(NAT)trees using 20-mm long heat dissipation sensors.Individual tree measures of sap flow were correlated using non-linear statistical methods with air vapour pressure deficit(D,hPa)and global radiation(Rg,J m2 day1),along with constraints imposed by reductions in soil water content(SWC).SWC was measured as volumetric%using time domain reflectometry.Important Findings The daily integrated Js(Js-sum)for trees growing in the evenly spaced MAN stand and trees in canopy and closed forest positions in NAT stand decreased as the availability of soil moisture was reduced.In the heterogeneous NAT stand,SWC in a recently formed canopy gap remained high throughout the vegetation period.Based on regression models,the predicted relative decrease in Js-sum for dry relative to moist soil water conditions in the closed forest(at mean daily D=10 hPa)was 7–11%for trees near the gap and 39–42%for trees in the closed forest.In MAN,the reduction in Js-sum was 29%in dry relative to moist conditions.Js-sum in the outer 20 mm of the xylem in NAT was lower than that in MAN and the rate of decline in Js with xylem depth was less in NAT than in MAN.In MAN,Js-sum in deep and outer xylem was negatively affected at low soil moisture availability;in NAT,this was the case for only the outer xylem indicating that deep roots could be important in supplying water at times of low soil moisture in the upper soil.
