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Agricultural plastic film mulching is one of important technologies, but the plastic film pollution has been a serious issue for agri-cultural sustainable development in China. System analysis of this technique and its residue pollution and control ways have vital practicalsignificance for rational application of agricultural plastil film. In this paper, on the basis of our previous work,agricultural plastic filmmulching, its residue pollution and control technologies were concluded. Some important conclusions were found that, the amount of plasticfilm and mulching area had kept increasing with annual increasing rate about 8% since the 80s of the 20th century. From 1991 to 2011, thedensity of plastic film utilized increased 3-10 times, but it has very sharply different spatial pattern in different province. In general, the northand west China has high value, and the increase rate is also huge in the past 20 years. The crops of utilized mulching plastic film have extendedfrom cash crops to grain crops, and the order of crop area is followed by maize, vegetable, cotton, tobacco and peanut. The main functions ofmulching plastic film are keeping soil moisture and increasing soil temperature, against weeds and insect. At the same time, its side effectsappear with continuous utilization. The main problems are residues left in soil to destroy soil structure, impress soil permeability, impede seedgermination as well as water and nutrients uptaking, and block crop root system development. It has very serious pollution for the field utilizedplastic mulching film for long term. The residual amount in soil is about 71.9-259.1 kg·hm-2, and has sharply spatial difference. The residualamount in soil. In Northwest China, is more serious than that in North China and Southwest China. Because of difference of tillage and appli-canon ways, there are great differences on the area and shape of the plastic film piece left in soil. The main types of shapes are flaky, crispat-ural cylindric and spherality existed in soil as horizontal, vertical and incline state. In present, there are machinery harvesting technique, re-ducing plastic film mulching technique, replacing technique with biodegradable plastic film to against this pollution. For plastic film residuespollution countermeasures, it is necessary to revise the standard of plastic film and strive monitoring the quality of plastic film, improve theretrievability of plastic residue; It is also necessary to extend reducing plastic film mulching technique, harvesting techniques and increaseharvesting rate of residue; strength the adaption study and promote the rational utilization of agricultural plastic film.

The crystal structures and magnetic properties of Ni50-xCoxMn39Sn11 (8≤x≤10) Heusler alloys are investigated. As a result, we achieve the magnetic field induced martensitic transformation in Ni42Co8Mn39Sn11. It is found that the saturation magnetic moments of alloys increase with Co content increasing. Moreover, a superspin glass behavior and a large exchange bias effect are also found in samples with Co content being higher than 8. We confirm the coexistence of superspin glass of the martensite and ferromagnetic parent phase, which is the physical origin of the exchange bias effect. On the other hand, we propose that the origin of superspin glass in our NiMnCoSn system is due to the occurence of Mn-Mn cluster as reported by Ma et al. in Heusler Mn2Ni1.6Sn0.4 alloys [Ma L, Wang W H, Liu J B, Li J Q, Zhen M, Hou D L and Wu G H 2011 Appl. Phys. Lett. 99 182507].

The crystal structures and magnetic properties of Mn2CoMxGa1-x and Mn2CoMxAl1-x (M=Cr, Fe, Co) alloys are investigated through experiment and calculation. Due to the covalent effect, the doped Fe and Co atoms preferentially occupy the A sites. It causes that some MnA (-2.1 B) atoms become MnD (3.2 B) and a local ferromagnetic structure of MnB-CoC-MnD is generated in the ferrimagnetic matrix, showing that an increment of molecular moment is as high as 6.18 B. The achievement of the ferromagnetic structure consumes the exchange interaction energy, consequently, reducing the TC in Fe doping alloys. It is found that the toleration for doping Co in Mn2CoAl reaches up to x=0.64, much more than that in Mn2CoGa (x=0.36), and the change from ordered B2 to A2 structures along with the decrease of Al content. These observations reveal the importance of the covalent effect in these intermetallic compounds. The Cr doping shows an abnormal increment of molecular moment of 3.65 B and increases the TC rapidly, which implies that Cr atoms may take an atomic configuration thereby disobeying to the occupation rule.

In this paper, ZnO nanowire (NW) arrays are prepared by the thermal chemical vapor deposition (CVD) method, and the characteristic of field electron emission of ZnO NW arrays under the illumination of ultraviolet light is investigated. It is found that, upon ultraviolet light illumination, the turn-on voltage drops off and emission current increases. A process of field emission coupled with semiconducting properties of ZnO NWs is proposed. Ultraviolet photon-excited electron transition from valence band to conductance band and defect energy levels of ZnO NWs can lead the number of emitting electrons to increase, and the photoemission reduces the effective work function of zinc oxide emitters, which largely enhances the field emission performance. The characteristic of field emission of ZnO NWs under ultraviolet light illumination suggests an approach to tuning field emission of semiconductor emitters, which is promising for the applications in optical sensor, cold-cathode flat panel display and field electron source.

The crystal structure, magnetism and transport properties of a series alloys from Co2CrGa to Cr2CoGa (Co50-xCrx+25Ga25, x=0—25) have been investigated by the experimental and KKR-CPA-LDA calculation methods. Substituting Cr for Co atoms, the crystal structure changes from L21 type to Hg2CuTi structure, which make, the lattice parameters increase about 0.69% linearly. Also, the ferromagnetic coupling turns to anti-ferromagnetic coupling, that makes the magnetic moment linearly decrease from 3.06μB to nearly zero. Through ab initio study of CPA, it has been found that the extraneous Cr atom at the A site couples anti-ferromagnetically with the Cr atom originally situated at B site with a nearly equal magnitude of magnetic moment, and the magnetic moment of Co atoms occupying the C site decreases from 0.60μB to 0.21μB through the whole substituting process. Based on the results of magnetic measurement and calculation, about 20% atomic disorder in the alloy Cr2CoGa has been confirmed, which is consistent with the observation of the X-ray examination. It is interesting that a non-linear "middle component phenomenon" has been observed in the composition dependence of both Curie temperature and the electrical resistivity. The related discussions is based on the magnetic environment change surrounding the magnetic atoms.

The structural and the magnetic properties of Co50Fe50-xSix alloys are investigated by carrying out experimental measurements and electron structure calculation. The alloy series exhibits the highly chemical ordering structure, showing a strong covalent bonding effect. The lattice parameters, molecular moment and Curie temperature linearly decrease with the increase of the Si content. The deviation of the structure is attributed to the atomic size effect. Based on Stearns theories, the decrease of the itinerant 3d (di) electron results in the decrease of Curie temperature due to the substitution of Si for Fe. The change of molecular moment follows the Slater-Pauling rule, but the calculation indicates that the change of the atomic moments is not linear. It implies that the covalent bonding effect is responsible for the magnetic changes. The molecular moment and Curie temperature of Heusler alloy Co2FeSi are measured to be 5.92 B and 777 ℃, respectively. The calculation results also indicate that the half-metallic property of Co2FeSi may not be so perfect as reported, which requires a new design of energy band for the practical application. The investigation also shows that the structural transition and the magnetic structure transition accumulate in a narrow interval of Si content, which may become a good object for studying the interaction between the magnetization and the structure.