裂变径迹法测定年轻火山岩年龄中值得重视的几个问题——以长白山天池火山为例

根据用裂变径迹法测试长白山天池火山和腾冲火山年轻火山岩年龄的工作经验，以长白山天池火山为例，说明了裂变径迹法测定年轻火山岩年龄中存在的问题和可能的解决办法，供以后研究工作参考。     

青海地震局青年在青藏高原显露才华

在世界上大陆地震最活跃的地区之一——青藏高原上,一批年轻的地震科研工作者正显示着他们的才华.这两年来,一批文化程度较高、业务能力较强的青年在改革中进入了青海省地震局基层领导岗位和研究机构,他们在地震监测预报、地震地质、工程地质等方面的工作中,发挥了骨干作用.     

消息

▲四川省地震局职工技术学校全体学员,在有关教师带领下,于1981年14月25日,前往乐山,峨眉等地进行为期一周的野外地质实习,以巩固和加深课堂知识、锻炼和培养学员的独立工作能力。     

年轻火山岩氩同位素体系定年技术最新进展及问题

对年轻(第四纪)火山岩K-Ar法、常规40Ar/39Ar法和激光40Ar/39Ar法定年的优缺点进行了评述,回顾了近10年40Ar/39Ar定年技术在该领域的进展,介绍了惰性气体质谱技术的进步及测量自动化对年轻火山岩定年的影响。讨论了快中子照射及40Ar/39Ar标样问题对高精度年轻火山岩定年的影响,分析了国内用于快中子照射的北京49-2反应堆中子通量梯度问题及对高精度定年的影响。结合年轻火山岩定年及数据处理的实际经验,介绍了年轻火山岩定年中的分析误差、主要影响因素及每个影响因子对总误差的贡献,指出36Ar测试精度、系统本底和质量歧视是影响年轻火山岩高精度定年3个主要内部因素,并给出定量化曲线及减小影响的处理方法。最后列举了年轻火山岩定年存在的问题及可能的探索方向。随着技术的发展,40Ar/39Ar法在晚更新世火山岩定年领域将会占有主导地位     

珠江三角洲台网——中国区域数字地震台网的源点

通过对广东省珠江三角洲数字化地震台网筹建过程的概述,回顾台网建设的困难.台网建设的完成,不但大幅度提高了广东省的地震监测能力,而且带动和引领了全国数字地震台网建设,同时也获得了溢出效应.更重要的是广东省地震局的一批年轻技术人员通过台网建设,业务上得到了提升,成为了重要的技术骨干.寄希望于年轻的一代,经过承担大项目,快速...     

洋脊和年轻洋壳俯冲与埃达克岩生成的热模拟

新生代以来 ,环太平洋周边分布的埃达克岩 (Adakite)主要与年轻洋壳俯冲时在 70～ 90km深处的部分熔融有关。利用数值方法 ,模拟了洋壳俯冲的热演化过程并讨论了脱水、熔融对埃达克岩浆活动的影响。结果表明 :仅在活动海岭俯冲前后约 10Ma内 ,年轻的、热的俯冲海洋板片在 75～85km深度范围内 ,温度升高至 82 5～ 10 0 0℃脱水 ,导致年轻洋壳中角闪岩部分熔融 ,形成埃达克岩(Adakite)。而一般洋壳俯冲在 10 0km以下深度才脱水 ,由于脱水区压力较高洋壳自身不能熔融 ,水进入上覆地幔楔状体导致部分熔融 ,形成安山岩 (Andesite     

年轻矿物质表明火星曾有水

《地质学》杂志日前发表的一篇最新研究报告称,研究发现火星上的小洼地含有丰富的矿物质。相比于火星上那些古老的岩石,这些矿物质显得更年轻。这表明在火星相对较近的历史时期曾经有水,也即有生命存在。     

管天管地为人民

我们在党的地震工作方针的指引下,在一九七一年一月张兰中学地震工作现场会议精神鼓舞下,于一九七一年夏季成立了地震测报小组.三年来,我们在毛主席革命路线指引下,在上级党委和本站党支部的领导下,以批林批孔为动力,为地震予报工作积累了连续、及时、准确的气象和土地电等资料,对于气象和地震的关系做了一些初步的探索,对于地震予报也做了一些粗浅的研究.加强领导 提高认识地震工作是一门年轻的科学工作,对我们来说又是一项业余的工作.要做好这项工作必须加强领导,提高对地震群测工作重要意义的认识,否则,这项工作是做不好的.     

亚洲-澳洲-太平洋过渡带的大地构造、地球动力学和地质特征

地球物理、海底采掘及深水钻探资料均指出,亚洲东部边缘海属于晚中生代未补偿的地台,它们于始新世-渐新世时期主要是在不均匀的大陆型基底上形成的,称它们为新地台,以区别于老地台和年轻地台。在类似的基底上多数又自身建起了岛弧和深水海沟。然而,作为地貌结构,边缘海、岛弧和深海沟大约在上新世时期形成。从亚洲到太平洋的过渡带是沉没水下的亚洲大陆的东部边缘。     

“第一届年轻地质年代学学术讨论会”在京召开

第一届年轻地质年代学学术讨论会于1986年12月9日至13日在京召开。到会代表来自我国28个单位,共计82人。提交大会的报告和论文共计33篇。会议涉及的主要年轻地质年代测定方法有~(14)C、TL、FT、K-Ar、U系、ESR、古地磁、~(210)pb、~(10)Be,~3H,孢粉分析、钙质土壤测年法以及石英碎粒显微风貌判断相对地质     

Effects of Salinity and Mangrove Detritus on Desorption of Metals from Brackish Water Desorption of Metals from Brackish Water and Shrimp

Desorption and bioaccumulation of Cd, Zn, and Pb were studied using naturally contaminated sediment from a brackish water pond in the Sunderban Biosphere Reserve in India. Pattern of desorption of the metals from the sediment and bioaccumulation in fingerlings of the teleost Oreochromis mossambicusand postlarvae of the shrimp Penaeus monodon were studied as a function of salinity and loading of detritus of a mangrove plant. Effects of both salinity and loading of detritus on bioaccumulation of the metals were studied under two conditions: either the animals were allowed free access to the sediment or access was denied. Ninety‐six hour experiments showed that desorption of Cd and Pb from sediment into water increased with salinity of the medium while desorption of Zn decreased. Salinity of the medium also had a significant effect on the bioaccumulation of metals by fish; Cd and Pb accumulation decreased in saline medium while the accumulation of Zn increased. Conditions of access to sediment had no effect on the bioaccumulation of metals by fish; effect of interaction between salinity and access condition was also insignificant. The access conditions, however, significantly influenced accumulation of metal by the shrimp postlarvae. The effect of interaction between salinity and access condition was insignificant in influencing the bioaccumulation of all metals except Zn. The accumulation of Zn increased as a function of the salinity of the medium when shrimp postlarvae were allowed access to the sediment. Desorption of metals from sediment to water were below detection limits when detritus of a mangrove plant was added to the medium. Both the level of detritus and the conditions of access influenced accumulation of metals by fish, but the effect of interaction between the two factors were found to be insignificant. Shrimp postlarvae showed net accumulation only of Pb in the presence of detritus and the accumulation of Pb increased when the larvae were separated from the sediment. The results are important in understanding the mobility of metals between solid and aqueous phases in brackish water environments that experience periodic fluctuations in salinity and fluxes of organic load in the form of mangrove detritus.     

完善医学影像设备的管理

随着我国医疗保险制度的全面实施和逐步完善和医疗保障体制改革的深入开展,我国医疗卫生行业必将引进社会主义经济体制下的宏观调控和市场竞争机制,这无疑有利于我国卫生事业的健康发展。面对当今科技进步与医院建设的新形势,对开展医院医疗仪器设备的管理提出了挑战。为此,本文探讨了在医院中,医学影像设备管理的几个问题和解决的方案。     

Trophieindikation in Fließgewässern mit Hilfe des TIM (Trophie‐Index Makrophyten) – Erprobung eines neu entwickelten Index im Inninger Bach

Indicating the Trophic State of Running Waters by Using TIM (Trophic Index of Macrophytes) – Exemplary Implementation of a New Index in the River Inninger Bach The river Inninger Bach represents the outflow of the lake Wörthsee (Bavaria). The mean pH of the calcareous river has a value of ca. 8 during the vegetation period, the mean conductivity is about 350 to 400 μS/cm. The macrophyte vegetation of the river course was mapped and the nutrient concentrations of both the water body and the sediment were measured. In every mapping section the Trophic Index of Macrophytes (TIM) was calculated. By cluster analysis the mapping sections were grouped into three zones which differed in macrophyte vegetation. These differences are not associated with varying nutrient concentrations but are mainly due to differences in the degree of shading. In spite of the characterisation of the lake Wörthsee as oligo‐mesotrophic the river Inninger Bach, which represents the outflow of the lake Wörthsee, is classified as meso‐eutrophic by the Trophic Index of Macrophytes TIM. The increased trophic state of the river compared to the lake is caused by the river Krebsbach, a small tributary flowing into the river Inninger Bach only a short stretch downstream of its outflow of the lake Wörthsee. The river Krebsbach shows a total phosphorus concentration of about 56 μg/L P. The input of diaspores of submerged macrophytes both from the oligo‐mesotrophic lake Wörthsee and the eutrophic river Krebsbach leads to a submerged vegetation comprising species with different optima in regard to the trophic situation. This is one of the main reasons why many values of the TIM have to be labeled as “not sure”.     

THEORETICAL APPROACH TO THE SOLUTION OF THE INFILTRATION PROBLEM

ABSTRACT

The one-dimensional transient downward entry of water in unsaturated soils is investigated theoretically. The mathematical equation describing the infiltration process is derived by combining Darcy's dynamic equation of motion with the continuity and thermodynamic state equations adjusted for the unsaturated flow conditions. The resulting equation together with the corresponding initial and boundary conditions constitues a mathematical initial boundary value problem requiring the solution of a nonlinear partial differential equation of the parabolic type. The volumetric water content is taken as the dependent variable and the time and the position along the vertical direction are taken as the independent variables. The governing equation is of such nature that a solution exists for t > 0 and is uniquely determined if two relationships are defined, together with the specified state of the system, at the initial time t = 0 and at the two boundaries. The two required relations are those of pressure versus permeability and pressure versus volumetric water content.

Since the partial differential equation has strong non-linear terms, a discrete solution is obtained by approximating the derivatives with finite-differences at discrete mesh points in the solution domain and integrated for the corresponding initial and boundary conditions. The use of an implicit difference scheme is employed in order to generate a system of simultaneous non-linear equations that has to be solved for each time increment. For n mesh points the two boundary conditions provide two equations and the repetition of the recurrence formula provides n—2 equations, the total being n equations for each time increment. The solution of the system is obtained by matrix inversion and particularly with a back-substitution technique. The FORTRAN statements used for obtaining the solution with an electronic digital computer (IBM 704) are presented together with the input data.

Analysis of the errors involved in the numerical solution is made and the stability and convergence of the solution of the approximate difference equation to that of the differential equation is investigated. The method applied is that of making a Fourier series expansion of a whole line of errors and then following the progress of the general term of the series expansion and also the behavior of each constituent harmonic. The errors (forming a continuous function of points in an abstract Banach space) are represented by vectors with the Fourier coefficients constituting a second Banach space. The amplification factor of the difference equation is shown to be always less than unity which guarantees the stability of the employed implicit recurrence scheme.

Experiments conducted on a vertical column packed uniformly with very fine sand, show a satisfactory agreement between the theoretically and experimentally obtained values. Many experimental results are shown in an attempt to explain the infiltration phenomenon with emphasis on the shape and movement of the wet front, and the effects of the degree of compaction, initial water content and deaired water on the infiltration rate.     

R. A. BAGNOLD: A BIOGRAPHY AND EXTENDED BIBLIOGRAPHY

1996 is the centenary of the birth of Brigadier Ralph Alger Bagnold, FRS. To mark this important anniversary this paper presents a short biography of Bagnold and an extended bibliography of his published work. The purposes of the paper are firstly, to present a synthesis of the life and significant discoveries made by Brigadier Bagnold, secondly, to communicate something of the character of the man and his work to generations of researchers who have not had the chance to meet him at first hand, and finally, to use this Technical Supplement and Software Bulletin to make summaries of his theories, empirical findings and views on science accessible to students and scholars of physical geography, geomorphology and engineering.     

The Analysis of the Seasonal,Spatial, and Compositional Distribution of Humic Substances in a Subtropical Shallow Lake

The spatial and temporal distribution of humic substances in aquatic ecosystems can have important effects on ecosystem productivity, negatively impacting primary productivity while positively impacting secondary productivity. In the present investigation, a large shallow lake ecosystem was studied to determine the spatial and seasonal variation of the composition and concentration of humic substances. Concentrations of total dissolved organic matter, humic acid, and fulvic acid were found to display significant spatial distributions (1.3…13.5 mg/L, DOM; 0.1…5.4 mg/L, HA). The distribution is described by using mapping techniques and the analysis of the spatial distribution of the lake. An analysis of the seasonal variations also indicated the dependence of the occurrence of these compounds on meteorological and hydrological conditions. To identify the potential sources of these organic materials, an analysis was made of the ratio of humic and fulvic acid fractions and total DOM. It was found that areas of high DOM concentration coincided with the areas of highest HA percentage of total DOM. Furthermore using the ratio of the normalised concentrations of HA, FA, and residual DOM (< 5000 g/mol) it was found that areas dominated by each are spatially distinct. This confirms the hypothesis that in these shallow lakes, photodegradation and bacterioplankton activity will create a residence time dependent zonation of each component of the total DOM.     

On the Limnology of Deep and Saline Lake Burdur in Turkey

Limnological characteristics of Lake Burdur in Lake District in south‐western Turkey are presented. It is a deep, tectonic (estimated max. depth 100 m), athalassic, highly alkaline, and saline lake. A set of physical and chemical variables was monitored, phyto‐ and zooplankton was sampled from surface layer of the lake during 1997. Physico‐chemical variables indicated that the lake is hyposaline and composed of some hydrochemically different water layers formed by groundwater sources located on the bottom of the lake. The phytoplankton composition of Lake Burdur consisted of Cyanophyta, Chlorophyta, Bacillariophyta, Dinophyta, and Chrysophyta. The abundance and number of species of Chlorophyta and Cyanophyta were higher than the other taxa. The zooplankton composition of the Lake consisted of Rhizopoda, Rotifera, and Crustacea. Number of species of Rotifera was higher than the other taxa. The diversities of the phyto‐ and zooplankton were calculated according to the Shannon‐Weaver diversity index. The diversity of each group was found to be low in the lake.     

Depositional ages and characteristics of Middle–Upper Jurassic and Lower Cretaceous lacustrine deposits in southeastern Mongolia

Lower Cretaceous lacustrine oil shales are widely distributed in southeastern Mongolia. Due to the high organic carbon content of oil shale, many geochemical studies and petroleum exploration have been conducted. Although most of the oil shales are considered to be Early Cretaceous in age, a recent study reveals that some were deposited in the Middle Jurassic. The present study aims at establishing depositional ages and characteristics of the Jurassic and Cretaceous lacustrine deposits in Mongolia. The Lower Cretaceous Shinekhudag Formation is about 250 m thick and composed of alternating beds of shale and dolomite. The Middle Jurassic Eedemt Formation is about 150 m thick and composed of alternating beds of shale, dolomitic marl, and siltstone. The alternations of shale and dolomite in both formations were formed by lake level changes, reflecting precipitation changes. Shales were deposited in the center of a deep lake during highstand, while dolomites were formed by primary precipitation during lowstand. Based on the radiometric age dating, the Shinekhudag Formation was deposited between 123.8 ±2.0 Ma and 118.5 ±0.9 Ma of the early Aptian. The Eedemt Formation was deposited at around 165–158 Ma of Callovian–Oxfordian. The calculated sedimentation rate of the Shinekhudag Formation is between 4.7 ±2.6 cm/ky and 10.0 ±7.6 cm/ky. Shales in the Shinekhudag Formation show micrometer‐scale lamination, consisting of algal organic matter and detrital clay mineral couplets. Given the average thickness of micro‐laminae and calculated sedimentation rate, the micro‐lamination is most likely of varve origin. Both Middle–Upper Jurassic and Lower Cretaceous lacustrine oil shales were deposited in intracontinental basins in the paleo‐Asian continent. Tectonic processes and basin evolution basically controlled the deposition of these oil shales. In addition, enhanced precipitation under humid climate during the early Aptian and the Callovian–Oxfordian was another key factor inducing the widespread oil shale deposition in Mongolia.     

Errors in velocities and displacements deduced from accelerographs: An approach based on the theory of error propagation

Based on the theory of errors, and in particular on the law of error propagation and approximation techniques, we present some simple formulae for random errors of velocities and displacements computed on the basis of numerical integration of accelerometer records. These errors are regarded as function of the characteristic errors of accelerometers and of the duration of the signal for velocities, and of the square of the duration of the signal for displacements. Instabilities in the sampling rate introduce additional noise, which is proportional to the sum of the squares of measurements of acceleration, mostly influenced by high peaks. Because of uneven weighting, however, peaks at early stages of the record are more important than in their later stages.     

A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.