Mikania cordata, an invasive weed is becom- ing a problem in the secondary degraded forests and plantations of Bangladesh, not only competing with but also releasing allelochemicals to cultivated crops. Allelo- pathic...Mikania cordata, an invasive weed is becom- ing a problem in the secondary degraded forests and plantations of Bangladesh, not only competing with but also releasing allelochemicals to cultivated crops. Allelo- pathic effects of the leaves of M. cordata were investigated through an experiment in the green house of the Institute of Forestry and Environmental Sciences, University of Chit- tagong, Bangladesh. Five economically important agricul- tural crops （Oryza sativa L., Triticum aestivum L., Vigna sinensis L., Abelmoschus esculentus L. and Amaranthus tricolor L.） and three forest crops （Acacia auriculiformis A. Cunn. ex Benth. ＆ Hook, Albizia procera （Roxb.） Benth., and Paraserianthes falcataria （L.） Nielson） were used as bioassay species. Experiments were conducted on trays at an average room temperature 27 ~C. The effects of dif- ferent concentrations of leaf extracts were compared to controls. Water soluble allelochemicals of M. cordata inhibited the germination and initial growth of the tested agricultural and forest crops. Germination percent of forest crops declined with increasing concentration of extracts. The inhibitory effect on root elongation of forest crops was pronounced, whereas a stimulatory effect was found on P. falcataria up to a concentration of 25 %. Abelmoschus esculentus showed poor germination （%） and low shoot development （0.5 cm） and no development of taproot or lateral roots at treatment of 100 % concentration. Theinhibitory effect was proportional to the concentrations of the extracts with higher concentrations producing stronger inhibitory effects. Lower concentrations showed some stimulatory effect. The inhibitory effect was pronounced in root and lateral root development rather than germination or shoot development of the crops. Mikania cordata should be eradicated for healthy growth and development of the forest and adjacent agricultural crops.展开更多
Aurivillius type compound BaBi_(4)Ti_(4)O_(15)(BBT)ceramic was prepared by solid state reaction route and its electrical properties were studied.X-ray diffraction(XRD)pattern showed orthorhombic structure with space g...Aurivillius type compound BaBi_(4)Ti_(4)O_(15)(BBT)ceramic was prepared by solid state reaction route and its electrical properties were studied.X-ray diffraction(XRD)pattern showed orthorhombic structure with space group A21am confirming it to be an m=4 member of the Aurivillius oxide.The scanning electron microscope of the sintered pellet showed a plate-like morphology of grains which is a characteristic feature of the Aurivillius compounds.The temperature and frequency dependence dielectric study showed a shifting of transition temperature with frequency indicating relaxor type behavior in the material.The diffuseness parameter(γ)established the relaxor nature and it was attributed to the A-site cationic disorder.The dielectric relaxation obeyed the VogelFulcher(VF)relation and various parameters like activation energy for relaxation,freezing temperature,relaxation frequency were determined after nonlinear curve fitting.The temperature dependence of dielectric constant at temperatures much higher and lower than Tm was analyzed by two exponential functions,which gives an idea about the production of polar clusters at high temperature and the distribution of freezing temperatures at lower temperature.Various other associated parameters were calculated by nonlinear curve fitting and their significance has been explained.展开更多
文摘Mikania cordata, an invasive weed is becom- ing a problem in the secondary degraded forests and plantations of Bangladesh, not only competing with but also releasing allelochemicals to cultivated crops. Allelo- pathic effects of the leaves of M. cordata were investigated through an experiment in the green house of the Institute of Forestry and Environmental Sciences, University of Chit- tagong, Bangladesh. Five economically important agricul- tural crops （Oryza sativa L., Triticum aestivum L., Vigna sinensis L., Abelmoschus esculentus L. and Amaranthus tricolor L.） and three forest crops （Acacia auriculiformis A. Cunn. ex Benth. ＆ Hook, Albizia procera （Roxb.） Benth., and Paraserianthes falcataria （L.） Nielson） were used as bioassay species. Experiments were conducted on trays at an average room temperature 27 ~C. The effects of dif- ferent concentrations of leaf extracts were compared to controls. Water soluble allelochemicals of M. cordata inhibited the germination and initial growth of the tested agricultural and forest crops. Germination percent of forest crops declined with increasing concentration of extracts. The inhibitory effect on root elongation of forest crops was pronounced, whereas a stimulatory effect was found on P. falcataria up to a concentration of 25 %. Abelmoschus esculentus showed poor germination （%） and low shoot development （0.5 cm） and no development of taproot or lateral roots at treatment of 100 % concentration. Theinhibitory effect was proportional to the concentrations of the extracts with higher concentrations producing stronger inhibitory effects. Lower concentrations showed some stimulatory effect. The inhibitory effect was pronounced in root and lateral root development rather than germination or shoot development of the crops. Mikania cordata should be eradicated for healthy growth and development of the forest and adjacent agricultural crops.
文摘Aurivillius type compound BaBi_(4)Ti_(4)O_(15)(BBT)ceramic was prepared by solid state reaction route and its electrical properties were studied.X-ray diffraction(XRD)pattern showed orthorhombic structure with space group A21am confirming it to be an m=4 member of the Aurivillius oxide.The scanning electron microscope of the sintered pellet showed a plate-like morphology of grains which is a characteristic feature of the Aurivillius compounds.The temperature and frequency dependence dielectric study showed a shifting of transition temperature with frequency indicating relaxor type behavior in the material.The diffuseness parameter(γ)established the relaxor nature and it was attributed to the A-site cationic disorder.The dielectric relaxation obeyed the VogelFulcher(VF)relation and various parameters like activation energy for relaxation,freezing temperature,relaxation frequency were determined after nonlinear curve fitting.The temperature dependence of dielectric constant at temperatures much higher and lower than Tm was analyzed by two exponential functions,which gives an idea about the production of polar clusters at high temperature and the distribution of freezing temperatures at lower temperature.Various other associated parameters were calculated by nonlinear curve fitting and their significance has been explained.
