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S. Ó Tuairisg R. F. Butler A. Shearer R. M. Redfern D. Butler A. Penny 《Monthly notices of the Royal Astronomical Society》2003,345(3):960-980
We present the results of TRIFFID simultaneous V - and B -band observations of the cores of the globular clusters M15, M92 and NGC 6712. A variability search of their dense centres was made feasible through performing post-exposure image sharpening on the images, increasing the image resolution by a factor of ∼2. The isis implementation of the image subtraction technique developed by Alard & Lupton was then used to detect flux variations in our image sets. We have obtained periods for all observable variables (in our field of view) in NGC 6712 and we have found two new RR Lyrae variables (an RRab and an RRc). We have confirmed three variables in our field of view of the M92. For M15, we detect 48 variables in our field of view, 23 of which are new discoveries. We obtain periods and amplitudes for all variables and classify new ones based on the light-curve shape, the most significant period and the mean magnitude in the V band. Among the detected RR Lyrae we find 19 RRc, 12 RRab and two RRd types. In the subsequent analysis we find a marked increase in RRc over RRab variables in the core. In a refined procedure to search for fainter objects we find no dwarf novae in our field of view of M15. Simulations performed on the data set to quantify our sensitivity to such objects indicate that an upper limit of 10 dwarf novae (at 92 per cent probability) exist in our field of view. The implications this result has on globular clusters are discussed. 相似文献
3.
非线性中立型时滞微分方程解的振动性 总被引:1,自引:0,他引:1
本文研究几类非线性中立型时滞微分方程解的振动性质 ,利用 Riccati不等式和某个不等式得到了保证方程振动的充分条件 相似文献
4.
二次特征值问题 (QEP)的主要的求解方法之一是转化为广义特征值问题 (GEP) ,然后用求解广义特征值的方法 (比如 QZ方法 )求解。本文研究由此获得的计算解的范数意义下的最佳向后扰动分析 ,所得结果是 Tisseur最近所得结果的加强。 相似文献
5.
Preparation of a geotechnical microzonation model using Geographical Information Systems based on Multicriteria Decision Analysis 总被引:3,自引:0,他引:3
The purpose of this study is to develop a geotechnical microzonation model using Geographical Information Systems (GIS) based on Multicriteria Decision Analysis (MCDA). As study area, the Eski15f;ehir downtown area has been chosen. Eski15f;ehir is one of the most rapidly growing cities in central Turkey. The model inputs include slope, flood susceptibility, soil, depth to groundwater table, swelling potential, and liquefaction potential. The weight and rank values are assigned to the layers and to the classes of each layer respectively. The assignment of the weight/rank values and the analysis are realized by the application of two different decision models, namely Simple Additive Weighting (SAW) and Analytic Hierarchy Process (AHP) methods. The geotechnical microzonation maps prepared as outputs of these methods are found to be consistent with each other and confirmed by the experts within the study area. The geotechnical microzonation map prepared using the AHP method is recommended as the final map of the study. 相似文献
6.
A nitrogen isotope study of soil water and groundwater in southern Indiana, USA, in 1991–1992 demonstrated considerable variations
in nitrate degradation processes compared to an earlier investigation in 1986–1987. Although N-fertilizers were applied in
May 1991, the δ15N values in soil water decreased in February 1992, indicating its delayed release into the system after substantial rainfall.
The δ15N values of groundwater decreased from +12.3‰ in November 1991 to +11.3‰ in February 1992, and to +7.5‰ in March 1992. The
increased residence time of nitrate in the soil resulted in increased denitrification, ammonia volatilization and plant uptake,
and reduced threat to the groundwater quality. The 1986–1987 study in the area reported that excessive rainfall during the
summer rapidly transported the nitrate to deeper horizons and drastically reduced volatilization and microbial reduction of
nitrate, thus increasing the immediate threat to the groundwater quality in the area. The present study demonstrated that
nitrogen isotopic signatures can be used to determine the effects of local soil type, rainfall, and land-use practices on
the fate of nitrate in the subsurface.
Received: 18 February 1997 · Accepted: 17 June 1997 相似文献
7.
Mathematical models of hydrocarbon formation can be used to simulate the natural evolution of different types of organic matter and to make an overall calculation of the amounts of oil and/or gas produced during this evolution. However, such models do not provide any information on the composition of the hydrocarbons formed or on how they evolve during catagenesis.From the kinetic standpoint, the composition of the hydrocarbons formed can be considered to result from the effect of “primary cracking” reactions having a direct effect on kerogen during its evolution as well as from the effect of “secondary cracking” acting on the hydrocarbons formed.This report gives experimental results concerning the “primary cracking” of Types II and III kerogens and their modelling. For this, the hydrocarbons produced have been grouped into four classes (C1, C2–C5, C6–C15 and C15+). Experimental data corresponding to these different classes were obtained by the pyrolysis of kerogens with temperature programming of 4°C/min with continuous analysis, during heating, of the amount of hydrocarbons corresponding to each of these classes.The kinetic parameters of the model were optimized on the basis of the results obtained. This model represents the first step in the creation of a more sophisticated mathematical model to be capable of simulating the formation of different hydrocarbon classes during the thermal history of sediments. The second step being the adjustment of the kinetic parameters of “secondary cracking”. 相似文献
8.
9.
应用ATOVS资料反演大气温湿廓线 总被引:3,自引:2,他引:3
本文用牛顿迭代的方法反演NOAA-15极轨气象卫星ATOVS资料,求解大气温度廓线和水汽廓线,本文利用一阶变分原理从辐射传输方程中得到了大气温度、水汽权重函数的解析形式,并改进了传统使用的线性迭代方法,利用牛顿非线性迭代方法求解大气表层温度,大气温度廓线及大气水汽廓线,并根据大气参量的自相关性,将大气温度廓线、大气水汽廓线用经验正交函数(EOF)的线性组合表示,减少了要反演的参数,提高了反演稳定性和迭代速度。 相似文献
10.
Butler Shearer Redfern Colhoun O'Kane Penny Morris Griffiths & Cullum 《Monthly notices of the Royal Astronomical Society》1998,296(2):379-391
The Galway/DIAS Image Sharpening Camera, TRIFFID, has been used to make observations in two colours of the centre of the post-core-collapse globular cluster M15. We present here our analysis of the photometry in B over two seasons. We have combined the complementary qualities of the HST 's high astrometric precision and TRIFFID's extended coverage and photometric precision, to perform crowded-field photometry in the innermost region of M15. Our technique virtually eliminates the problem of extreme crowding which has hitherto hampered studies of the variable star populations in globular cluster cores, and thereby provides an extension of the HST 's capability. Candidate variables detected with the HST have been confirmed and monitored over longer periods. We show that most of these are RR Lyrae stars, and that one is a short-period Type II Cepheid (the third to be discovered in M15). Our photometric study also produced evidence of a similar number of new variables. These also appear to be RR Lyrae stars, except for a possible eclipsing system. Further data from an upgraded version of TRIFFID have recently been obtained to help to refine the light curves of all these objects. 相似文献