Cai Dongqing

Single long-polymer translocation through a long pore

This paper theoretically studies the free energy and conformational entropy of a long polymer threading a long nanopore (n0/N≥0.1) on external electric field. The polymer expanded model is built in this paper, that is, a single long polymer chain with N monomers (each of size a) threading a pore with n0 monomers can be regarded as polymer with N+n0 monomers translocating a 2-dimension hole embedded in membrane. A theoretical approach is presented which explicitly takes into account the nucleation theory. Our calculations imply that, the structure of polymer changes more acutely than other situation, while its leading monomer reaches the second vacuum and its end monomer escapes the first vacuum. And it is also shown that the length scale of polymer and pore play a very important role for polymer translocation dynamics. The present model predicts that the translocation time depends on the chemical potential gradient and the property of the solvent on sides of pore to some extent.

Current status and challenges for potato chemical fertilizer & pesticide reductions in China

Under the pressures from growing population, arable land diminishment, yield limitation of major grain crops, global climatic change, etc, there is a latent crisis in Chinese food security. Potato, as the fourth major crop, plays a vital role in alleviating food problem considering its great nutritive value, high yield and adaptability. Chemical fertilizers and pesticides (CFPs) are implicated in ensuring stable and high yields of potato. Therefore, CFPs were intensively used for boosting up the yield; however, the use intensity of CFPs exceeds the international recognized standard, resulting in negative impacts on environment quality, agri-ecosystem, land productivity and tuber production cost. Consequently, those obstacles mentioned above jeopardized the sustainability of potato industry. In order to solve the dilemma, this article focuses on the analysis of the major reasons for abuse of CFPs, and further identified that the excessive consumption could be attributed to high application intensity, low utilization efficiency and lack of scientific application methods. Furthermore, this article introduces the technological advances and future trends in chemical fertilizer and pesticide reductions (CFPR) of developed countries. Based on the successful CFPR experiences abroad, the article also provides some development strategies for Chinese potato CFPR. (1) Promote legislation curbing application rate of potato CFPs. Several research projects were initiated to investigate the scientific standard of application amount for CFPs. Once the scientific standards were set, they could be gradually legislated into agricultural laws to stipulate the use of CFPs nationwide. (2) Promote the innovation on high-efficient application technology and encourage the use of green alternatives to chemical controls. Efforts on scientific research and education should be strengthen to speed up the innovation/application of advanced CFPR techniques. In addition, recognized reduction techniques abroad could be transferred to improve our application practices in pursuit of chemical contamination decreases. Some chemical fertilizers could be replaced by organic fertilizer, or they could be used in combination with organic fertilizers to enhance use efficiency. Chemical pesticides, to some extent, could be substituted by efficient, low toxicity/residue pesticides, and green prevention techniques could be employed to avoid pesticide abuse. (3) Promote the invention/improvement of intelligent agro-equipment with precision application capabilities. Unlike developed countries, the majority of Chinese potato production entities is still dispersible, small-scale, traditional family farms. Hence, modern fertilizer/pesticide machinery including deep fertilization and accurate spaying should be developed accordingly to meet specific needs of Chinese farmers. However, in the large-scale and intensive potato-growing area of north China, it is reasonable for the large potato enterprise and cooperatives to introduce advanced equipment and management system overseas. (4) Integration of multiple CR technologies to meet diverse regional needs. Combined with traditional reduction techniques such as soil testing, formulated fertilization, drip-fertigation and integrated pest-control, newly developed reduction technology could be integrated into regional “Potato Chemical Fertilizer and Pesticide Reduction” technique systems according to the diverse ecological, climatic and cultivating factors. Through demonstration zones and potato-grower trainings, popularization of reduction techniques would benefit the potato-growing farmers and cooperatives, which would significantly reduce the use of CFPs in China.