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11.
12.
A mathematical model to calculate the234U/238U activity ratio (AR) in an aqueous phase in contact with rock/soil is presented. The model relies on the supply of238U by dissolution and that of234U by dissolution and preferential release from radiation damaged regions (recoil tracks). The model predicts that values of234U/238U AR>1 in the aqueous phase can be obtained only from weathering “virgin” surfaces. Thus, to account for the observed steady-state supply of234U excess to the oceans by the preferential leaching model, ‘virgin’ rock/soil surfaces would have to be continually exposed and weathered. The238U concentration and234U/238U AR in continental waters allow us to estimate the exposure rates of “virgin” rock/soil surfaces. 相似文献
13.
Hesham M. El-Kaliouby Safwat A. Hussain Abd El-Rahim Bayoumi Essam A.El-diwany Essam A. Hashish 《Geophysical Prospecting》1995,43(5):595-603
The aim of this work is to consider the phenomenon of negative response and its detectability in a polarizable half-space formed of Clay-water mixture which commonly exists in water aquifers and which can be used as a simple indicator of the presence of Underground water. We make use of an analytical treatment for the transient voltage induced in a coincident loop lying on a half-space as a basis for our computations. A Cole-Cole model is used to represent the Clay with appropriate parameters. As saturated Clay is characterized by high conductivity and moderate chargeability, it is hardly detectable relative to the practical noise level. However, there are optimum Clay parameters that offer a maximum negative response. It is also observed that for a very short time constant τ in the Cole-Cole model, the amplitude of the negative response decreases with the decrease of the time constant due to the fast decay of the polarization current. Finally, it is found that there is an optimum value for the loop radius which gives the largest value of the negative response and this loop radius depends on the model parameters. 相似文献
14.
ANALYSIS OF SURFACE AIR TEMPERATURE RECORDED IN LAHORE AND MIANWALI OVER THE PAST THREE DECADES 下载免费PDF全文
Surface air temperatures recorded over the past three decades at the weather stations located in Lahore (anindustrialized and densely populated city) and Mianwali (a small and sparsely populated city) were analyzed in order tostudy their climatic trend.Lahore,where meteorological data are recorded at two weather stations (city station and air-port station) indicates a cooling trend,of about 0.5℃ per record period of 1953—1992,for the airport station (31°31′N,74°24′E) and a slight warming trend,of about 0.2℃,for the city station (31°33′N,74°20′E) for the record period of 1950—1992.The Mianwali weather station (32°33′N,71°31′E) also shows a slight cooling trend,of about 0.4℃ per recordperiod of 1959—1992.The climatic variability at these stations was studied by computing seasonal and annual tempera-ture anomalies.The results are explained in terms of the local environmental conditions. 相似文献
15.
The chemical composition of the Dharwar metavolcanic suite from Chitaldrug is found to be similar to that of early Precambrian metabasalts from Canadian and Australian Shields. Its low K2O content and the similarities in the ferromagnesium trace elements with those of oceanic olivine normative tholeiites indicate a low K2O oceanic type of original magma. It is suggested that a protocontinent having a thin crust approaching basic composition existed during the pre-Dharwar era. 相似文献
16.
Oysters destined for the table in Sydney are alleged to be contaminated with mercury. Analyses performed by the New South Wales Department of Health show that they contain no more mercury than oysters far from sources of pollution. 相似文献
17.
Metaheuristic techniques, which are based on ideas of Artificial Intelligence, are among the best methods for solving computationally the GPS surveying network problem. In this paper, the ant colony optimization metaheuristic, which is inspired by the behavior of real ant colonies, is developed to efficiently provide a general framework for optimizing GPS surveying networks. In this framework, a set of ants co-operate together using an indirect communication procedure to find good GPS observation schedules. A GPS surveying network can be defined as a set of stations, co-ordinated by a series of sessions formed by placing receivers on the stations. The problem is to search for the best order in which to observe these sessions to give the best schedule at minimum cost. Computational results obtained by applying the proposed technique on several networks, with known and unknown optimal schedules, prove the effectiveness of the proposed metaheuristic technique to solve the GPS surveying network problem. 相似文献
18.
N. Hussain N. Bhandari K. R. Ramanathan B. L. K. Somayajulu 《Journal of Earth System Science》1980,89(1):23-29
The miliolite deposits of Saurashtra have been dated by234U,230Th,231Pa and14C methods. Concordant ages of 105 years using the U decay series isotopes are obtained which agree with the ages of the coral reefs of Okha-Dwaraka coast suggesting
a contemporaneous origin for both. The lower14C ages (≤40,000 years) may be due to a recent influx of seawater or ground water. Quartz and clay minerals together constitute
only ≤10% by weight, as such the aeolian characteristics of quartz grains may not be relevant to the origin of the miliolites. 相似文献
19.
Lead levels in the indicator mussel Mytilus edulis, exceeds the WHO food standards in 19 of the 22 locations sampled in Port Phillip Bay, Melbourne. While this seriously reflects contamination of the food chain, LD50 experiments on Mytilus indicate that the lethal effect of lead on this organism is much less severe than excessive doses of mercury, cadmium, copper or zinc. Little is known about the long term effects of lead on Mytilus. 相似文献
20.
刘群 《中国海洋湖沼学报》2015,33(4):966-973
Catch and effort data were analyzed to estimate the maximum sustainable yield(MSY) of King Soldier Bream, Argyrops spinifer(Forssk?l, 1775, Family: Sparidae), and to evaluate the present status of the fish stocks exploited in Pakistani waters. The catch and effort data for the 25-years period 1985–2009 were analyzed using two computer software packages, CEDA(catch and effort data analysis) and ASPIC(a surplus production model incorporating covariates). The maximum catch of 3 458 t was observed in 1988 and the minimum catch of 1 324 t in 2005, while the average annual catch of A. spinifer over the 25 years was 2 500 t. The surplus production models of Fox, Schaefer, and Pella Tomlinson under three error assumptions of normal, log-normal and gamma are in the CEDA package and the two surplus models of Fox and logistic are in the ASPIC package. In CEDA, the MSY was estimated by applying the initial proportion(IP) of 0.8, because the starting catch was approximately 80% of the maximum catch. Except for gamma, because gamma showed maximization failures, the estimated results of MSY using CEDA with the Fox surplus production model and two error assumptions, were 1 692.08 t(R 2 =0.572) and 1 694.09 t( R 2 =0.606), respectively, and from the Schaefer and the Pella Tomlinson models with two error assumptions were 2 390.95 t( R 2 =0.563), and 2 380.06 t( R 2 =0.605), respectively. The MSY estimated by the Fox model was conservatively compared to the Schaefer and Pella Tomlinson models. The MSY values from Schaefer and Pella Tomlinson models were the same. The computed values of MSY using the ASPIC computer software program with the two surplus production models of Fox and logistic were 1 498 t(R 2 =0.917), and 2 488 t( R 2 =0.897) respectively. The estimated values of MSY using CEDA were about 1 700–2 400 t and the values from ASPIC were 1 500–2 500 t. The estimates output by the CEDA and the ASPIC packages indicate that the stock is overfished, and needs some effective management to reduce the fishing effort of the species in Pakistani waters. 相似文献