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1.
关键元素与生命健康:中国耕地缺硒吗?   总被引:1,自引:0,他引:1  
地球上的生命和非生命都是由自然界已发现的92种化学元素组成的,通过全国土壤地球化学基准值与人体血液元素含量对比研究,发现血液中40~50种化学元素平均值与土壤地球化学基准值的分布高度一致,表明这些关键元素与生命息息相关。近年大家持续关注的硒(Se)元素是人体必需的微量元素,缺乏会产生健康风险,但摄入过量也会导致中毒,因此被称为健康窗口元素。过去研究认为,中国耕地缺硒是造成健康危害的原因之一。本文通过对全国3 382个网格化点位土壤采样,获得Se的地球化学基准值和空间分布数据,发现中国贫硒国土面积,按照世界卫生组织推荐值(0.1 mg/kg)和中国规范(0.125 mg/kg)计算,分别占21.1%和31.6%;适宜区(0.125~0.40 mg/kg)面积大约555万km2,占国土面积约57.1%;富硒区(>0.40 mg/kg)面积达110万km2,占国土面积约11.2%。贫硒国土主要分布在青藏高原和内蒙古局部地区,而中国9大平原的粮食主产区耕地总体上不缺硒,其中珠江三角洲平原、广西平原、成都平原、长江中下游平原是富硒区(>0.40 mg/kg),华北平原、东北平原、三江平原、关中平原是硒边缘区-适量区(0.125~0.40 mg/kg),只有河套平原是缺硒区(<0.125 mg/kg)。根据覆盖全国的网格化土壤采样分析结果,发现低硒带呈不连续的片状分布于内蒙古东部至青藏高原一带,与传统认为“低硒带分布于东北三省至西南云贵高原”不完全一致。硒的空间分布模式主要受地质背景、岩石类型、土壤类型和自然地理景观控制。  相似文献   
2.
增强型地热系统(EGS)用于通过人工形成地热储层的方法从深部低渗透性岩体中开采地热能;国际上常采用水力压裂辅以化学刺激的方法改造EGS 储层以提高其渗透率。本文以采自青海共和盆地的花岗闪长岩样品为对象,选用3种不同化学刺激剂(氢氧化钠、盐酸和土酸),在3组不同注入流速条件下开展了系统化学刺激实验。结果表明:注入盐酸和土酸后样品渗透率均有提高,且采用土酸时渗透率提高幅度明显大于盐酸;但注入氢氧化钠后,样品渗透率反而降低。在3类化学刺激剂中,土酸对长石类矿物的溶蚀能力最强,而氢氧化钠溶液对石英的溶蚀能力最强,但氢氧化钠溶液在溶解岩石样品裂隙表面矿物后极易形成非定形态二氧化硅或非定形态铝硅酸盐蚀变矿物并阻塞裂隙,反而对化学刺激效果造成负面影响。总体来看,土酸是青海共和盆地干热岩体的最佳化学刺激剂。在中等注入速度(3 mL·min-1)条件下,土酸对岩石样品的溶蚀程度就可达到最高;在此基础上进一步降低流速,则可能使溶解组分更易从液相中沉淀而充填于样品裂隙,导致样品渗透率有所下降。  相似文献   
3.
张青海 《探矿工程》2019,46(10):53-57
小秦岭北矿带上部覆盖层为第四系沉积物,其厚度700~950 m,钻探施工中经常出现卡钻、埋钻、塌孔等恶性事故,甚至造成钻孔报废,严重制约钻探效率,造成钻探成本过高。针对这些技术难点开展技术分析和研究,通过优化钻孔结构,采用适宜该矿区厚覆盖层的绳索取心钻进方法,合理选择护壁性能好的冲洗液等技术措施解决了厚覆盖层钻进难题,提高了钻探施工效率和质量,降低了工程成本。  相似文献   
4.
在对依兰-伊通断裂通河段晚第四纪活动参数获取的基础上,对该断裂的几何学特征和晚第四纪活动特征及有关拟建铁路地震安全的设防参数进行了探讨.研究结果表明,依兰-伊通断裂通河段总体走向N30-40°E,由3条断层组成,中支最新活动时代为全新世.该断裂未来发生7级地震时的水平位移量可能达2.2m左右,垂直位错量约为1.1m左右.该断裂全新世以来的活动性质表现为右旋走滑为主,兼具逆冲活动.根据探槽结果和野外地震地质调查得出断裂垂直位错约(1.0±0.2)m,右旋位错量约为(2.7±0.1)m,(1730-30)aB.P.以来的垂直滑动速率和水平滑动速率分别约为(0.57±0.11)mrn/a和(1.57±0.06)mm/a.未来100年内若遭遇地震,其最大水平位错量约2.87m,垂直位错值为1.04m.断层影响带宽度约为8m.该研究结果为拟建哈—佳铁路工程可能遭受的断层影响和抗震设防提供了一定的数据基础,也为地震安评中线状工程的抗断评价问题提供了一定的参考.  相似文献   
5.
54个晋冀低山丘陵区人工和人工扰动植被表土花粉样品分析表明:花粉组合以草本植物花粉(74.5%)为主,乔木花粉含量低于20%。人类活动较强的农田以谷物禾本科、蒿属和藜科花粉为主,人类活动较弱的荒地以蒿属、藜科和杂草禾本科花粉为主。人类活动强度不同,指示种不同,孢粉浓度亦不同;农田指示种为谷物禾本科、葡萄科和胡桃科,孢粉浓度约4380粒/g;而蒿属、蓼科和蔷薇科则为荒地指示种,孢粉浓度约10983粒/g。农作物种植方式不同,谷物禾本科花粉含量不同,单一禾本科作物种植区谷物禾本科花粉含量(40.2%)高于多种作物混作区(18.8%)和荒地(3.8%)的含量。谷物禾本科含量的变化可以为利用化石花粉提取和检测人类活动信息提供依据,也可为利用地层中谷物禾本科花粉判断古代农业活动提供依据。  相似文献   
6.
As indicated by observed X-ray flares,a great amount of energy can be intermittently released from the postburst central engine of gamma-ray bursts(GRBs).As a natural consequence,the GRB’s external shock could be repeatedly energized.With such a multiple energy injection model,we explore the unique X-ray afterglow light curve of GRB 050712,which exhibits four shallow decay plateaus.Together with three early X-ray flares,the central engine of GRB 050712 is believed to have released energy at least seven times after the burst.Furthermore,we find that the energies released during the four plateaus are all on the same order of magnitude,but the luminosity significantly decreased with time.These results may provide some interesting implications for the GRB central engine.  相似文献   
7.
The Yilan‐Yitong Fault Zone (YYFZ) is considered to be the key branch of the Tancheng‐Lujiang Fault Zone (TLFZ) in northeastern China. Although the Mesozoic and early Cenozoic deformation of the YYFZ has been studied intensively over the past century, few estimates of slip rate and recurrence interval of large earthquakes in the late Quaternary, which are the two most important parameters for understanding the potential seismic hazard of this crucial structure, were obtained. Based on integrated interpretations of high resolution satellite images and detailed geologic and geomorphic mapping, linear landforms were identified, including fault scarps and troughs, along the Shangzhi segment of the YYFZ, which exceeds 25 km in length. Synthesized results of trench excavations and differential GPS measurements of terrace surfaces indicate that two events (E1, E2) occurred along the Shangzhi segment during the late Holocene, which resulted in 3.2 ±0.1 m of total vertical co‐seismic displacement with clear features of thrust motion. 14C dating of samples suggests that event E1 occurred between 440 ±30 years BP and 180 ±30 years BP and that event E2 occurred between 4 090 ±30 years BP and 3 880 ±30 years BP, which indicates that the minimum vertical slip rate of the Shangzhi segment of the YYFZ has been approximately 0.8 ±0.03 mm/year during the late Holocene. Constraints from paleo events and the slip rate suggest that the average recurrence interval of major earthquakes on the YYFZ is 3 800 ±200 years. Historical documents in Korea show that event E1 possibly corresponds to the earthquake that occurred in AD 1810 (the Qing Dynasty in Chinese history) in the Ningguta area, which had surface‐wave magnitude (Ms) of 6.8–7.5. Studies of kinematics show that the right‐lateral strike‐slip with a reverse component has been dominant along the YYFZ during the late Holocene.  相似文献   
8.
The optical observations of the type Ic supernova(SN Ic) SN 2012 ap in NGC 1729 are presented. A comparison with other SNe Ic indicates that SN 2012 ap is highly reddened(with E(B- V)host~0.8 mag) and may represent one of the most luminous SNe Ic ever observed, with an absolute V-band peak magnitude of ~-19.3±0.5 mag after extinction correction. The near-maximum-light spectrum shows wide spectral features that are typical of broad-lined SNe Ic. One interesting feature in the spectrum is the appearance of some narrow absorption features that can be attributed to the diffuse interstellar bands, consistent with the large reddening inferred from the photometric method. Based on the light curves and the spectral data, we estimate that SN 2012 ap produced a56 Ni mass of ~ 0.3 ± 0.1M in the explosion, with an ejecta mass of 2.4+0.7-0.7M and a kinetic energy of E5K= 1.1+0.4-0.4× 102 erg. The properties of its progenitor are also briefly discussed.  相似文献   
9.
10.
The association of seasonal timing of stratospheric final warming events(SFWs) in spring and the occurrence of major and minor stratospheric sudden warming events(SSWs) in midwinter were investigated through statistical analysis, parallel comparison, and composite analysis, based on the NCEP-NCAR reanalysis dataset covering 1958–2012. It was found that the intensity and occurrence of winter SSW events can largely affect the timing of spring SFWs. Specifically, the SFW onset dates tend to be later(earlier) after the occurrence(absence) of winter major SSWs. However, the occurrence or absence of minor SSWs does not change the frequency of early and late SFWs. A parallel comparison of the temporal evolution of the anomalous circulation and planetary-waves between major SSW and minor SSW winters indicates that the stratospheric polar vortex(polar jet) will keep being anomalously stronger 30 days after major SSW onset. And the associated significant negative Eliassen-Palm(EP) flux anomalies can persist for as long as 45 days after major SSW events. In contrast, the circulation anomalies around the occurrence of minor SSW events can last only a few days. To further verify the possible influence of the occurrence of major SSWs on the seasonal timing of SFWs, composite analysis was performed respectively for the 21 major-SSW years, 15 minor-SSW years, and the 15 non-SSW years. Generally, planetary-wave activity in the extratropical stratosphere tends to be stronger(weaker) and the westerly polar jet is anomalously weaker(stronger) in major-SSW(non-SSW) winters. But in the following spring, the planetary-wave activity is weaker(stronger) accompanied with an anomalously stronger(weaker) stratospheric polar vortex. In spring after minor-SSW years, however, the stratospheric polar vortex and the westerly polar jet exhibit a state close to climatology with relatively gentle variations.  相似文献   
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