一米望远镜低色散光谱仪试验     

岑学奋  贾桂斌  曹曙 《中国天文和天体物理学报》1989,(2)

本文介绍了云南天文台一米望远镜附属的一台低色散光谱仪实验装置,介绍了该装置的设计原理、系统结构参数及试观测情况,并讨论了存在的问题和解决问题的设想。我们已用该装置观测到19m左右的具有大红移的类星体光谱。该类低色散光谱仪,将为我国星系研究工作者提供实测条件。  相似文献   

Crustal structure in the Society and Tuamotu Islands, French Polynesia     

Jacques Talandier  Emile A. Okal 《Geophysical Journal International》1987,88(3):499-528

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Pulsar observations at decametric wavelengths using a swept-frequency dedisperser     

A. A. Deshpande  V. Radhakrishnan 《Journal of Astrophysics and Astronomy》1994,15(3):329-341

In this paper, we describe pulsar observations at decametric wavelengths using the Gauribidanur Radio Telescope made subsequent to our earlier measurements (Deshpande & Radhakrishnan 1992). To improve the time-resolution in our measurements of pulse profiles, we have used the ‘swept-frequency dedispersion’ method with some modifications to suit its application at such low radio frequencies. We also present a new scheme that simplifies the calibration of the receiver gain characteristics. We present average profiles on four pulsars from these improved measurements at 34.5 MHz.  相似文献   

Crustal structure and possible anisotropy in Turkey from seismic surface wave dispersion   总被引：2，自引：0，他引：2  

Oznur Y. Mindevalli  Brian J. Mitchell 《Geophysical Journal International》1989,98(1):93-106

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Reduction of deep layers in surface wave computation     

S. N. Bhattacharya 《Geophysical Journal International》1987,88(1):97-109

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Heavy metals in a contaminated Australian estuary—Dispersion and accumulation trend     

P.S. Roy  E.A. Crawford 《Estuarine, Coastal and Shelf Science》1984,19(3):341-358

Very high concentrations of Zn, Pb, Cu and Cd occur in the muddy bottom sediments of Lake Macquarie, a saline coastal lagoon in southeastern Australia. The trace metals emanate from industrial sources, especially a lead-zinc smelter, at the northern end of the lake. Individual metal concentrations decrease progressively away from the source area but at differing rates; Zn is most mobile and Cd appears to be deposited first. They approach natural background levels in the southern part of the lake. Mn shows a reverse trend but Ni, Co, Ag and Fe rarely rise above background levels.Shallow cores in the lake bed penetrated a metal enriched surface zone 15–35 cm thick underlain by uncontaminated sediments with natural (background) metal concentrations. Sedimentation rates determined from radiocarbon ages on shells in the cores mainly range between 0·15 and 0·5 mm yr^?1. Over the 85 years since industrialization commenced, less than 5 cm of mud has accumulated on the lake bed. Bioturbation is invoked to account for the depth to which the sediment has been enriched in heavy metals.  相似文献   

A study of the kinematics of the local dark clouds     

B. Ramesh 《Journal of Astrophysics and Astronomy》1994,15(4):415-443

Lack of reliable estimates of distances to most of the local dark clouds has, so far, prevented a quantitative study of their kinematics. Using a statistical approach, we have been able to extract the average spatial distribution as well as the kinematical behaviour of the local dark clouds from their measured radial velocities. For this purpose, we have obtained radial velocities for 115 southern clouds and used the data from the literature for the northern ones. In this paper we present this new data, analyse the combined data and compare our results with those arrived at by earlier studies. The local clouds are found to be expanding at a speed of ∼ 4 kms^-1 which is in general agreement with the estimates from optical and HI studies. However, it is found that the kinematics of the local clouds is not described by the model proposed for the local HI gas where a ring of gas expanding from a point gets sheared by the galactic rotation. Rather, the observed distribution of their radial velocities is best understood in terms of a model in which the local clouds are participating in circular rotation appropriate to their present positions with a small expansion also superimposed. This possibly implies that cloud-cloud collisions are important. The spatial distribution of clouds derived using such a model is in good agreement with the local dust distribution obtained from measurements of reddening and extinction towards nearby stars. In particular, a region of size ∼ 350 pc in diameter enclosing the Sun is found to be devoid of clouds. Intriguingly, most clouds in the longitude range 100‡ to 145‡ appear to have negative radial velocities implying that they are approaching us. Carried out under the auspices of the Joint Astronomy Program, Department of Physics, Indian Institute of Science, Bangalore in partial fulfillment of the requirements for the Degree of Doctor of Philosophy.  相似文献   

On the predictability of the ¹³⁷Cs distribution in the Severn Estuary     

Maurice Rattray  R.J. Uncles 《Estuarine, Coastal and Shelf Science》1983,16(5):475-487

The observed distribution of ¹³⁷Cs resulting from known sources in the Severn Estuary permits the testing of simple predictive models for the one-dimensional distribution of non-conservative substances in an estuary. These models either use a known distribution of salinity to infer corresponding ones for other substances, or else directly solve mass balance equations utilizing previously determined dispersion coefficients. Both methods are shown to previously determined dispersion coefficients. Both methods are shown to provide results comparing favorably with observations.Stokes drift plays an important role in the circulation of the Severn. A modified densimetric Froude number, including this drift, is therefore used to estimate the circulation and stratification of the estuary.A new equation is used for calculating the ¹³⁷Cs distribution from the observed salinity distribution. It generalizes previous formulations to permit variation of the net runoff with position along the estuary.  相似文献   

A dispersion relation for open spiral galaxies     

G. Contopoulos 《Journal of Astrophysics and Astronomy》1980,1(1):79-95

The Lin-Shu dispersion relation is applicable in the (asymptotic) case of tight spirals (large wave numberk _R). Here we reconsider the various steps leading to the Lin-Shu dispersion relation in higher approximation, under the assumption that the wave numberk _R is not large [(k _Rr) =O(1)], and derive a new dispersion relation. This is valid for open spiral waves and bars. We prove that this dispersion relation is the appropriate limit of the nonlinear self-consistency condition in the case where the linear theory is applicable.  相似文献   

Seasonal variability of physico-chemical characteristics of the Haldia channel of Hooghly estuary, India     

Y. Sadhuram  V. V. Sarma  T. V. Ramana Murthy  B. Prabhakara Rao 《Journal of Earth System Science》2005,114(1):37-49

Physical and chemical characteristics of the Hooghly estuary during winter (December 1997–January 1998), summer (May 1998) and post-monsoon (November 1998) seasons have been studied. Salinity varied spatially and temporally and seasonally during ebb and flood tide conditions. Water temperature showed a difference of 10‡C in winter to summer. Temperature did not vary much vertically as it is a well-mixed estuary. Strong currents exceeding 100 cm S^-1 were observed during peak ebb and flood tide conditions irrespective of the season. Longitudinal eddy diffusion coefficient (K _x ) was estimated as 757m S^-1 and 811m² S^-1 during summer and post-monsoon seasons, respectively. The vertical eddy diffusion coefficient (ε_v) was estimated as 0.0337 m² S^-1 during post-monsoon season. The salinity and current observations are compared with those obtained from models reported earlier. Values of pH, Dissolved Oxygen and Biological Oxygen Demand are within the threshold limits of the estuarine environment. Nutrients show seasonal variation in the estuarine environment. High values (160-2686 mg l^-1) of total suspended matter were noticed both at surface and bottom in the study region showing the impact of fresh water and sediment transportation.  相似文献