杭嘉湖地区淹水稻田氮素径流流失负荷估算

通过大田试验、定点观测等方法对现有的关于长江三角洲平原地区水田降雨径流产生模型进行验证,发现该模型在考虑排水堰的影响之后,基本能够模拟杭嘉湖平原水网区水田降雨径流产生过程,误差在-19.9%～+18.0%之间,同时提出了淹水稻田降雨径流氮素浓度模型（R=0.948）,从而得到了该地区淹水稻田氮素径流流失负荷模型.在此基础上,搜集了该地区水稻田氮肥施用情况、30年逐日降雨量、1∶250000地形图、土地利用现状图和水系图等资,利用GIS技术对该地区淹水稻田氮素的径流流失负荷以及空间分布进行了估算和分析.结果表明,该地区淹水稻田氮素径流流失负荷平均高达35.26 kg N·hm^-2,约占当季水稻氮素施用量的12.69%,而且在空间上存在着明显的差异,安吉、余杭等地区氮素流失负荷和流失率明显高于其它地区,海宁地区的流失情况也较为严重.     

Effects on apoptosis and reactive oxygen species formation by Jurkat cells exposed to 50 Hz electromagnetic fields

The effect of exposure to 50 Hz electromagnetic field on a human T-leukaemia cell line (Jurkat) was investigated by evaluating the reactive oxygen species (ROS) production and apoptosis, both spontaneous and induced by a specific anti Fas/CD95 monoclonal antibody (anti-Fas). Our results suggest that 1 h intermittent (5 min field on/10 min field off) exposure does not affect ROS formation, while a slight but statistically significant decrease of both spontaneous and anti-Fas-induced apoptosis was observed.     

南方稻田活性氮损失途径及其影响因素

基于文献数据,研究了南方不同稻区水稻生长期氧化亚氮排放(N₂O排放)、硝态氮或铵态氮淋洗(N淋洗)、硝态氮或铵态氮径流(N径流)、氨挥发(NH₃挥发)的差异及其影响因素.结果表明: N₂O排放、N淋洗和N径流主要发生在长江流域单季稻区,损失量分别为1.89、6.4和10.4 kg N·hm^-2,损失率分别为0.8%、3.8%和5.3%,较高施氮量和稻田土壤干湿交替可能是主要原因;NH₃挥发主要发生在华南晚稻,损失量和损失率分别为54.9 kg N·hm^-2和35.2%,晚稻生长期较高的温度可能是NH₃挥发较大的主要原因.田间优化管理措施减少某一途径氮损失的同时可能会增加另一种途径氮素损失,实际生产中应综合考虑田间管理措施对各种活性氮损失的影响,活性氮损失量随着水稻产量水平的提高而增加,主要是因为施氮量也在逐渐增加.随着氮肥偏生产力的增加,N₂O排放、N淋洗和N径流损失率逐渐下降,因此,努力减小单位产量的氮损失,是协同提高作物产量和氮肥利用效率的重要途径.     

不同施肥模式下稻田土壤微生物生物量磷对土壤有机碳和磷素变化的响应

通过15年的红壤稻田长期定位试验,研究了不同施肥模式下土壤微生物生物量磷(MB-P)对土壤有机碳和磷素变化的响应.结果表明红壤稻田有机碳源的长期投入和土壤有机碳的逐年升高使土壤微生物生物量碳(MB-C)维持在较高水平(＞800 mg·kg-1),是稻田土壤MB-P(＞16.0 mg·kg-1)提高的主要原因.长期不施磷肥条件下,土壤全磷含量与试验前相比显著降低(P＜0.05),而土壤有机磷含量平均提高了29.3%;土壤亏损的磷形态主要是无机磷(Al-P、Fe-P、Ca-P和O-P),其中Al-P含量处于最低水平(平均0.5 mg·kg-1).另外,长期不施磷肥土壤的MB-P远高于Olsen法提取态磷(Olsen-P)(＜7.0 mg·kg-1),而稻田土壤MB-P与Al-P呈显著相关(P＜0.05),表明土壤微生物对稻田土壤Al-P、Fe-P、Ca-P和O-P的利用是促进其向有效磷方向转化的关键途径.磷肥配合有机养分循环利用不仅提高了土壤磷库的积累,而且通过土壤微生物的活化有效地提高了土壤磷的有效性.     

Mechanical vibration in “double-wound” magnetic field exposure coils

It has been suggested that “double-wound” (bifilar) exposure coils are capable of producing a sham environment in which hum and vibration will be “similar” to the field-exposed condition. We found by direct measurements in a bifilar coil system that vibration amplitude in sham and exposed conditions differed by a factor of 50 when our test system was driven at B = 10 mT. We also found that the normal laboratory environment can include vibrations of an intensity similar to that produced by the exposure system, although not necessarily of similar spectral distribution. © 1996 Wiley-Liss, Inc.     

Coordinated effects of electromagnetic field exposure on erythropoietin-induced activities of phosphatidylinositol-phospholipase C and phosphatidylinositol 3-kinase

Initial studies with the erythropoietin-sensitive human hematopoietic cell line, TF1, demonstrated both multifarious effects of pulsed electromagnetic field (EMF) exposure on lipid signal transduction and antiproliferative effects of EMF. Stimulation of TF1 cells with erythropoietin resulted in increased phosphatidylinositol 3-kinase activity within 2 min. Addition of wortmannin, an inhibitor of phosphatidylinositol 3-kinase, produced a decrease in cell proliferation as measured by accumulation of cells in the G₀/G₁ phase of the cell cycle and suppression of erythropoietin-induced DNA synthesis. Similar effects on cell proliferation were seen under EMF treatment. Phosphatidylinositol 3-kinase activity in erythropoietin-stimulated TF1 cells, measured in whole-cell extracts, increased 34% within 2 min and remained above basal levels for at least 20 min. EMF decreased erythropoietin-stimulated phosphatidylinositol 3-kinase activity to lower than basal levels. Additionally, translocation of the 85-kDa regulatory subunit (p85) of phosphatidylinositol 3-kinase to the membrane was prevented by EMF. Phosphatidylinositol-specific phospholipase C was activated, as reflected by increases in diacylglycerol and inositol trisphosphate at 15–60 s after EMF treatment. These results provide the first evidence of subtle coordinated changes by EMF associated with loss of phosphatidylinositol 3-kinase activity, inhibition of the translocation of p85 to the membrane, and activation of phosphatidylinositol-phospholipase C.     

耕作方式对紫色水稻土轻组有机碳的影响

以位于西南大学实验农场的长期免耕试验田为研究对象,通过0—60cm分层采集土壤样品的方法,探讨了不同耕作方式———冬水田平作(DP)、水旱轮作(SH)、垄作免耕(LM)及垄作翻耕(LF)对土壤轻组有机碳的影响。结果表明,重组有机碳是土壤总有机碳的主体,约占土壤总有机碳的69.56%—95.66%,在土壤剖面上随土壤深度的增加其分配比例逐渐升高;其次是自由轻组有机碳,约占土壤总有机碳的5.03%—26.43%,从土壤表层向下,其分配比例迅速下降;闭合轻组有机碳最低,仅占土壤总有机碳的1.37%—4.93%,其分配比例随土壤深度的变化不明显。在0—60 cm土壤深度内,不同耕作方式下自由轻组有机碳的平均含量为LM(4.36 g/kg)>DP(2.11 g/kg)>LF(1.74 g/kg)>SH(1.46 g/kg),相应的有机碳分配比例分别为17.1%、14.0%、12.2%和11.3%;闭合轻组有机碳的平均含量为LM(0.82 g/kg)>DP(0.51 g/kg)>LF(0.36 g/kg)>SH(0.34g/kg),相应的有机碳分配比例分别为3.36%、3.45%、2.71%和3.00%。因此,在西南地区紫色水稻土上实行垄作免耕能提高轻组有机碳的含量及其分配比例,从而改善土壤有机碳质量。另外,与土壤总有机碳、重组有机碳及闭合轻组有机碳相比,自由轻组有机碳对耕作方式的变化最敏感,是指示土壤有机碳变化的良好指标。     

Electric field effects on human spinal injury: Is there a basis in the in vitro studies?

An important basis for the clinical application of small DC electric current to mammalian spinal injury is the responses of neurons in culture to applied electric fields. Our recent finding that zebrafish neurons were unresponsive to applied fields prompted us to critically examine previous results. We conclude that compelling evidence for neuronal guidance and directional stimulation of growth toward either the cathode or anode in an electric field exists only for cultured Xenopus neurons, and not for any mammalian neurons. No basis for the reported success in treating spinal injury exists in the in vitro studies, and considerable research will be required if the conditions of field application in mammalian spinal injury are to be optimized.     

Stable isotope and radiocarbon compositions of methane emitted from tropical rice paddies and swamps in Southern Thailand

Stable isotopes (¹³C, D) and radiocarbon weremeasured in methane bubbles emitted from rice paddies and swamps in southernThailand. Methane emitted from the Thai rice paddies was enriched in¹³C (mean ¹³C; –51.5 ±7.1 and–56.5 ± 4.6 for mineral soil and peat soil paddies,respectively)relative to the reported mean value of methane from temperate rice paddies(– 63 ± 5). Large seasonal variation was observed in¹³C(32) in the rice paddies, whereas variationinD was much more smaller (20), indicating that variation in¹³C is due mainly to changes in methane production pathways.Values of ¹³C were lower in swamps (–66.1 ±5.1)than in rice paddies. The calculated contribution of acetate fermentation from¹³C value was greater in rice paddies (mineral soils:62–81%, peat soils: 57–73%) than in swamps (27–42%). Din methane from Thai rice paddies (–324± 7 (n=46)) isrelativelyhigher than those from 14 stations in Japanese rice paddies ranging from–362 ± 5 (Mito: n=2) to –322 ± 8(Okinawa: n=3), due tohigher D in floodwaters. ¹⁴C content in methane produced fromThai rice paddies (127±1 pMC) show higher ¹⁴Cactivity compared with previous work in paddy fields and those from Thai swamps(110±2 pMC).     

Implementation of a dose calculation algorithm based on Monte Carlo simulations for treatment planning towards MRI guided ion beam therapy

Magnetic resonance guidance in particle therapy has the potential to improve the current performance of clinical workflows. However, the presence of magnetic fields challenges the current algorithms for treatment planning. To ensure proper dose calculations, compensation methods are required to guarantee that the maximum deposited energy of deflected beams lies in the target volume. In addition, proper modifications of the intrinsic dose calculation engines, accounting for magnetic fields, are needed. In this work, an algorithm for proton treatment planning in magnetic fields was implemented in a research treatment planning system (TPS), matRad. Setup-specific look up tables were generated using a validated MC model for a clinical proton beamline (62.4 – 215.7 MeV) interacting with a dipole magnet (B = 0–1 T). The algorithm was successfully benchmarked against MC simulations in water, showing gamma index (2%/2mm) global pass rates higher than 96% for different plan configurations. Additionally, absorbed depth doses were compared with experimental measurements in water. Differences within 2% and 3.5% in the Bragg peak and entrance regions, respectively, were found. Finally, treatment plans were generated and optimized for magnetic field strengths of 0 and 1 T to assess the performance of the proposed model. Equivalent treatment plans and dose volume histograms were achieved, independently of the magnetic field strength. Differences lower than 1.5% for plan quality indicators (D_2%, D_50%, D_90%, V_95% and V_105%) in water, a TG119 phantom and an exemplary prostate patient case were obtained. More complex treatment planning studies are foreseen to establish the limits of applicability of the proposed model.