Modeling of terahertz pulse generation from LT-GaAs ultrafast photoconductive switches

The technique of terahertz pulses generated from the photoconductive switches has been applied in the ultrafast electrical pulse metrology recently.A lumped-element theoretical model is established to describe the performance of the LT-GaAs ultrafast photoconductive switch used in the ultrafast pulse standard.The carrier transport processes of the photoexcited semiconductor,the attenuation and dispersion during terahertz pulse propagating are considered in the theoretical model.According to the experimental parameters,the waveforms of the generated terahertz pulses are calculated under optical excitations with different wavelengths of 840 nm and 450 nm,respectively.And comparisons between the theoretical results and the experimental results are carried out.

Ultrafast optoelectronic technology for radio metrology applications

Ultrafast optoelectronic technology has been widely used in terahertz time domain spectrum,terahertz imaging technology,terahertz communication and so on,and great progress has been achieved in the past two decade.Recently,this innovative technology has been applied in radio metrology and supplied a potential and hopeful method to solve the existent challenges of calibration devices and equipments with bandwidth up to 100 GHz.This paper generally summarizes the emerging applications of the ultrafast optoelectronic technology in radio metrology.The main applications of this technology in calibrating broadband sampling oscilloscopes,the high-speed photodiodes and calibrating the electrical pulse generators are emphasized,and the testing of monolithic microwave integrated circuits is also presented.

A review on covalent organic frameworks for rechargeable zinc-ion batteries

In recent years,rechargeable zinc-ion batteries(ZIBs)are considered to be a promising alternative to lithium-ion batteries owing to their high safety and theoretical capacity with low cost.Nevertheless,the in-depth development of rechargeable zinc-ion batteries is restricted by a sequence of issues,such as the dissolution and structure collapse of cathode materials,the formation of by-products,severe anode corrosion,passivation,and the growth of zinc dendrites.The covalent organic frameworks(COFs)can solve the above problems to a certain extent owing to their ideal characteristics,such as rigid structure,insolubility,high porosity,and abundant active sites.COFs,as advanced materials for ZIBs,have attracted researchers'attention.In this review,we systematically summarized the synthesis methods of COFs and discussed the application of several advanced characterization technologies in COFs,which would provide a reference for the in-depth research of COFs.In addition,we elucidated the use of COFs as cathode materials and anode protective layers in rechargeable ZIBs.Finally,we discussed the challenges and solutions in the development of COF materials,which would provide constructive insights into the future direction of COFs.

Effects of protein sources for milk replacers on growth performance and serum biochemical indexes of suckling calves

This study investigated the effects of protein sources for milk replacers on growth performance and serum biochemical indexes of suckling calves. Fifty Chinese Holstein bull calves with similar BW and age were randomly allocated to 5 groups(1 control and 4 treatments) of 10 calves in each group. Five types of milk replacers were designed to have the same level of energy and protein. The protein source for milk replacers of the control group was full milk protein(MP). The protein source of milk replacers of the 4 treatment groups was composed of MP and one vegetable protein(VP)(30 and 70% of total protein). The4 types of VP were soybean protein concentrate(SP), hydrolyzed wheat protein(WP), peanut protein concentrate(PP), and rice protein isolate(RP). Results of the experiment showed: 1) there was no significant difference on average daily gain(ADG) and feed:gain ratio(F:G) among the MP, SP and RP groups(P > 0.05), whereas the ADG and F:G of the WP and PP groups were significantly lower compared with the MP group(P < 0.05); 2) there was not a significant difference in withers height, body length and heart girth among treatment groups compared with the MP group(P > 0.05). Thereby the 4 VP milk replacers had no adverse effects on body size of calves; 3) all groups showed no significant difference in the serum contents of urea nitrogen, total protein, albumin, globulin, β-hydroxybutyrate, growth hormone, insulin-like growth factor-1, and the ratio of albumin to globulin(A:G)(P> 0.05). In conclusion, SP or RP(accounts for 70% of the total protein) as calf milk replacers could substitute MP, whereas wheat gluten and PP had a significant adverse effect on growth performance in this experiment.

GRASSLAND AGRICULTURE IN CHINA--A REVIEW

Interactions between crops and livestock have been at the core of the evolution of many agricultural systems.In this paper,we review the development and characteristics of mixed crop-livestock systems,with a focus on grassland-based systems,as these cover large areas in China,and face several challenges.Following the transition from the original hunting and foraging systems to a sedentary lifestyle with integrated crop-livestock production systems some 8000 years ago,a range of different mixed systems have developed,depending on rainfall,solar radiation and temperature,culture and markets.We describe 5 main types of integrated systems,(1)livestock and rangeland,(2)livestock and grain production,(3)livestock and crop-grassland rotations,(4)livestock,crops and forest(silvo-pasture),and(5)livestock,crops and fish ponds.Next,two of these mixed systems are described in greater detail,i.e.,the mountain-oasis-desert system and its modifications in arid and semi-arid regions,and the integrated crop-livestock production systems on the Loess Plateau.In general,crop-livestock interactions in integrated systems have significant positive effects on crop production,livestock production,energy use efficiency and economic profitability.We conclude that improved integration of crop-livestock production systems is one of the most important ways for achieving a more sustainable development of animal agriculture in China.