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1.
Measurement of (231)Pa-(235)U disequilibrium in Tonga-Kermadec island arc lavas (north of New Zealand) permits discrimination of the time scales and mechanisms of fluid addition and partial melting. For Tonga lavas, the ((231)Pa/(235)U) ratios are less than 1 and can be explained by fluid addition from the subducting plate around 60,000 years ago. In contrast, the effects of partial melting overprinted those of fluid addition in the Kermadec lavas resulting in ((231)Pa/(235)U) ratios greater than 1.  相似文献   

2.
In proto-historic Hawaii (1500-1795 A.D.), as in many other evolving polities, temples functioned as centers for control over production and the extraction of surplus food and goods. Thorium-230 dates (uncertainty +/- approximately 10 years) on branch coral dedicatory offerings from temples in the Kahikinui district (Maui) indicate that its temple system was constructed within 60 years, far more rapidly than indicated by radiocarbon dating. Introduction of the temple system in 1580-1640 A.D. coincided with predatory expansion and consolidation of the Maui polity to form an incipient archaic state.  相似文献   

3.
试验对位于山东省无棣县北部的黄河三角洲贝壳堤岛,逐月进行分层(上、中、下3层)取样研究该区跳虫群落结构,共获得各类跳虫标本7461头,隶属于弹尾纲4目7科17属.结果表明,优势类群为棘跳属(Onychiurus)和符跳属(Folsomia)两者之和占总捕获个体数量的79.25%;常见类群为球角跳属(Hypogastru...  相似文献   

4.
Paired carbon-14 ((14)C) and thorium-230((230)Th) ages were determined on fossil corals from the Huon Peninsula, Papua New Guinea. The ages were used to calibrate part of the (14)C time scale and to estimate rates of sea-level rise during the last deglaciation. An abrupt offset between the (14)C and (230)Th ages suggests that the atmospheric (14)C/(12)C ratio dropped by 15 percent during the latter part of and after the Younger Dryas (YD). This prominent drop coincides with greatly reduced rates of sea-level rise. Reduction of melting because of cooler conditions during the YD may have caused an increase in the rate of ocean ventilation, which caused the atmospheric (14)C/(12)C ratio to fall. The record of sea-level rise also shows that globally averaged rates of melting were relatively high at the beginning of the YD. Thus, these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the Mississippi to the St. Lawrence River triggered the YD event.  相似文献   

5.
6.
Temporal evolution of depleted mantle thorium-uranium-niobium systematics constrain the amount of continental crust present through Earth's history (through the niobium/thorium ratio) and date formation of a globally oxidizing atmosphere and hydrosphere at approximately 2.0 billion years ago (through the niobium/uranium ratio). Increase in the niobium/thorium ratio shows involvement of hydrated lithosphere in differentiation of Earth since approximately 3.8 billion years ago. After approximately 2.0 billion years ago, the decreasing mantle thorium/uranium ratio portrays mainly preferential recycling of uranium in an oxidizing atmosphere and hydrosphere. Net growth rate of continental crust has varied over time, and continents are still growing today.  相似文献   

7.
选用生产上推广的4份海岛棉为材料,研究了不同生育期的超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)、抗坏血酸氧化酶(AAO)和多酚氧化酶(PPO)活性的变化规律。结果表明,供试的5种酶各有自身的变化规律,也各有其评价的关键时期。  相似文献   

8.
Moore JG  Moore GW 《Science (New York, N.Y.)》1984,226(4680):1312-1315
Limestone-bearing gravel, the newly named Hulopoe Gravel, blankets the coastal slopes on Lanai. The deposit, which reaches a maximum altitude of 326 meters, formerly was believed to have been deposited along several different ancient marine strandlines, but dated submerged coral reefs and tide-gauge measurements indicate that the southeastern Hawaiian Islands sink so fast that former worldwide high stands of the sea now lie beneath local sea level. Evidence indicates that the Hulopoe Gravel and similar deposits on nearby islands were deposited during the Pleistocene by a giant wave generated by a submarine landslide on a sea scarp south of Lanai.  相似文献   

9.
该文以干旱区绿洲-荒漠交错带为研究对象,以质量守恒原理与能量平衡原理为基础,建立了潜水-土壤-植被-大气系统中水分与热量传输模式,并提出了求解潜水-土壤-植被 大气系统的数值模拟分解 协调新方法,用天山北麓三工河流域绿洲-荒漠交错带的实测资料验证了水热传输模型的可靠性.结果表明,植被冠层蒸腾量模拟值与实测值比较接近,其最大误差为11.3%,土壤含水率的模拟值与实测值的最大误差仅为5.9%,土壤温度模拟值与实测值的最大误差为8.3%,用该模型模拟绿洲-荒漠交错带潜水-土壤-植被-大气连续体水热动态传输过程、植被蒸腾量、地表蒸发量和植被的根系吸水率具有较高的精度.   相似文献   

10.
自汉至清,历代封建王朝不仅继承了原始宗教教义,而且也继承了以诗事神的古老传统。他们信奉"感天地,动鬼神,莫近乎诗"的古训,坚持"放郑近雅",以《诗经》雅颂为典范,大力创制与使用儒教祭祀乐章,旨在借助诗歌"感鬼神而通教化"的作用,为国家统治服务。在儒者看来,诗歌的主要作用是祀奉神祗,教化民众。认为祭祀诗歌是中国古代最重要的诗歌,也是最有价值的文学作品。  相似文献   

11.
海南岛北部玄武岩发育而成的土壤粘土矿物研究   总被引:2,自引:0,他引:2  
对海南岛北部玄武岩上发育的成土年代系列土壤的研究表明,土壤中高岭石含量随风化成土年代的增加而逐渐增高,至富铁土时含量已达最高,之后含量下降。三水铝石含量逐渐增加。赤铁矿含量和结晶程度也随风化成土年代增加而增高。磁赤铁矿也有增加的趋势。  相似文献   

12.
B Kachar 《Science (New York, N.Y.)》1985,227(4692):1355-1357
A system has been developed in which organelle transport can be studied without the influence of an organized cellular cytoplasm. Binding and continuous unidirectional movement of organelles along isolated cellular transport cables were directly visualized by video light microscopy after the dissociation of the cytoplasm of characean algae cells in a Ca2+-free buffer containing adenosine triphosphate. Individual organelles had more than one attachment site and moved at mean rates of 11.2 or 62.1 micrometers per second along multiple parallel pathways on each cable. Electron microscopy of these cables after direct freezing demonstrated that they consist of compact bundles of actin filaments. Under these conditions, characteristics of organelle movement should reflect directly the underlying molecular processes of binding and force generation.  相似文献   

13.
富英杰  宋刚  陈迪云  冯颖思 《安徽农业科学》2011,39(30):18582-18584
[目的]为了调查土壤中天然放射性核素的水平和分布。[方法]利用高纯锗γ谱仪,调查珠三角区域内采集的796个土壤样品的天然放射性水平。[结果]土壤放射性核素238U、226Ra、232Th和40K的平均含量分别为142.4、135.9、196.9、670.2 Bq/kg。[结论]珠三角土壤中主要天然放射性核素含量高于全国背景含量,主要表现为土壤铀、钍含量较高。  相似文献   

14.
A conceptual framework influenced bythe concept of moral ecology is developed andused to analyze the transition fromtechnological (green revolution) to ecological(organic) rice farming by resource poor farmersfrom the Philippine island of Bohol. This MoralEcology Framework (MEF) focuses on theepistemology of the two farming systems and howthis influences management principles andpractice. The orienting concepts of systemic understanding, exchange betweensociety and the environment, local versusextra-local exchange and scope areintegral to this analysis. The case studydemonstrates how the ostracism of nature underthe green revolution coupled with itsinflexible production options affected thesustainability of some local rice farmingsystems. Whereas the transition to organicfarming and the concomitant incorporation ofecological processes and more flexibleproduction options has allowed local farmers toenhance the sustainability of their farmingsystems by altering the exchange processeswithin the socio-ecological system.  相似文献   

15.
Hearing subjects unfamiliar with American Sign Language and deaf native signers made triadic comparisons of movements of the hands and arms isolated from American Sign Language. Clustering and scaling of subjects' judgments revealed different psychological representations of movement form for deaf and hearing observerd. Linguistically relevant dimensions acquired modified salience for users ofa visual-gestural language. The data indicate that the modification of natural perceptual categories after language acquisition is not bound to a particular transmission modality, but rather can be a more general consequence of acquiring a formal linguistic system.  相似文献   

16.
The mean flux of radon-222 atoms from the island of Hawaii is 0.45 atom per square centimeter per second. Lava fields occupy 50 percent of the land area, but their radon flux is only 1 percent of that from deep volcanic soils. The island yields approximately 10 curies of radon-222 per hour to the air surrounding it. The radon-222 contribuition of volcanoes is negligible.  相似文献   

17.
In the presence of antigen presenting cells, a murine T helper (Th) cell specific for murine hemoglobin (Hb) responded to its immunogenic peptide by both cytokine (interleukin-4) secretion and proliferation. An altered Hb peptide with a single amino acid substitution induced only cytokine secretion and did not induce proliferation. Interleukin-1 costimulated and restored the Th proliferative response to normal levels. The altered peptide also supported cognate T cell-B cell interactions indicative of T cell helper function. Thus, this result suggests that the T cell receptor has the capacity of differential signaling.  相似文献   

18.
19.
Employing the case of theredwood Headwaters forest in rural NorthernCalifornia, this paper investigates the extentto which an anti-corporate progressive alliancebetween labor and the environmental movement ispossible in contemporary global capitalism.Progressive alliances between labor and theenvironmental movement have been historicallydifficult. This has been particularly the casein the timber industry, where companies havebeen able to mobilize workers againstenvironmentalists' designs. The caseillustrates the events that led to the purchaseof the Headwaters Forest by the state ofCalifornia and the Federal Government fromPacific Lumber. This is a subsidiary of Maxxam,a corporation with interests in a variety ofeconomic sectors. The objective was to haltMaxxam's rampant deforestation of old growthredwood. Though conflict between labor andenvironmentalists existed, the casedemonstrates that the labor and theenvironmental movement were united againstMaxxam. They, however, were not completelysuccessful in their struggle as Maxxam greatlybenefited from the state-sponsored landpurchase. Maxxam gained economically, was ableto shape the ideological framework throughwhich the purchasing agreement was achieved,and extended its hegemony over the state. Thisoutcome cast doubts on the possibility thatcurrent forms of environmental protection couldtranscend commodified and reductionistpostures. Simultaneously, the existence of acommon anti-corporate consciousness among largesegments of labor and the environmentalmovement makes the environment a contestedterrain and allows for some optimism about thefuture of the struggle for ecologically soundsocial arrangements.  相似文献   

20.
长乐口岸进境粮谷疫情截获情况分析   总被引:2,自引:1,他引:1  
对长乐口岸2014年进境粮谷疫情截获进行统计分析.结果表明,进境粮谷携带大量外来有害生物,截获的有害生物以杂苹为主;不同种类和不同来源国的进境粮谷中截获的主要有害生物存在明显差异,从大豆中截获有害生物种类数最多,油菜籽相对偏少.分析结果还明确了截获频率较高的检疫性有害生物种类,为后续检疫措施的制定提供了依据.同时,分析认为应通过检验检疫、全程监督管理、检疫除害处理和本底调查与疫情监测4个方面加强检验检疫监管工作,防止疫情的传入扩散.  相似文献   

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