Tracing the star stream through M31 using planetary nebula kinematics     

H. R. Merrett  K. Kuijken  M. R. Merrifield  A. J. Romanowsky  N. G. Douglas  N. R. Napolitano  M. Arnaboldi  M. Capaccioli  K. C. Freeman  O. Gerhard  N. W. Evans  M. I. Wilkinson  C. Halliday  T. J. Bridges  D. Carter 《Monthly notices of the Royal Astronomical Society》2003,346(4):L62-L66

We present a possible orbit for the Southern Stream of stars in M31, which connects it to the Northern Spur. Support for this model comes from the dynamics of planetary nebulae (PNe) in the disc of M31: analysis of a new sample of 2611 PNe obtained using the Planetary Nebula Spectrograph reveals ∼20 objects with kinematics inconsistent with the normal components of the galaxy, but which lie at the right positions and velocities to connect the two photometric features via this orbit. The satellite galaxy M32 is coincident with the stream both in position and velocity, adding weight to the hypothesis that the stream comprises its tidal debris.  相似文献   

The proton temperature and the total hourly variance of the magnetic field components in different solar wind speed regions     

Chuan-Yi Tu  John W. Freeman  R. E. Lopez 《Solar physics》1989,119(1):197-206

A comparison has been made between the predictions of the theory for radial variations of both Alfvénic fluctuations and solar wind proton temperatures proposed by Tu (1987, 1988) and the statistical results of hourly averaged plasma and magnetic field data observed by Helios 1 and 2 from launch through 1980 for different solar wind speed regimes. The comparison shows that for speed ranges between 500–800 km s^-1, the radial variation of the proton temperature between 0.3 and 1 AU can be explained by heating from the cascade energy determined by the radial variation of the total variance of magnetic field vector. The explanation of the radial variations of both temperature and the total variance of magnetic fields for speed ranges less than 400 km s ^-1 is less clear.This project was supported by National Natural Science Foundation of China for Tu's part of the work.  相似文献   

Effects of PCB's in Atlantic cod (Gadus morhua)     

H.C. Freeman  J.F. Uthe 《Marine pollution bulletin》1979,10(1):3-4

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Stacking for the frequencies and Qs of ₀S₀ and ₁S₀     

Mark A. Riedesel  Duncan Agnew  Jon Berger  Freeman Gilbert 《Geophysical Journal International》1980,62(2):457-471

Summary. Using nine IDA records for the Indonesian earthquake of 1977 August 19, we have formed an optimal linear combination of the records and have measured the frequency and Q of ₀ S ₀ and ₁ S ₀. The frequency was measured using the moment ratio method. The attenuation was measured by the minimum width method and by the time-lapse method. The frequency and attenuation were measured simultaneously by varying them to obtain a best fit to the data. A 2000-hr stack, the sum of nine individual records, for ₀ S ₀ gave a frequency of 0.814664 mHz±4 ppm. The values for the Q of ₀ S ₀ for the three different methods of measurement were 5600,5833 and 5700, respectively. The error in the estimates of Q ^-1 is about 5 per cent for the minimum power method. For ₁ S ₀ a 300-hr stack yielded a frequency of 1.63151 mHz±30 ppm. The values of Q for this mode were 1960, 1800 and 1850, respectively, with an error in Q ^-1 of about 12 per cent for the minimum power method.  相似文献   

Ocean and environmental information: The theory,policy, and practice of knowledge management     

Robert R. Freeman 《Marine Policy》1977,1(3):215-229

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Grid resolution study of ground water flow and transport     

Bower KM  Gable CW  Zyvoloski GA 《Ground water》2005,43(1):122-132

Three-dimensional grids representing a heterogeneous, ground water system are generated at 10 different resolutions in support of a site-scale flow and transport modeling effort. These grids represent hydrostratigraphy near Yucca Mountain, Nevada, consisting of 18 stratigraphic units with contrasting fluid flow and transport properties. The grid generation method allows the stratigraphy to be modeled by numerical grids of different resolution so that comparison studies can be performed to test for grid quality and determine the resolution required to resolve geologic structure and physical processes such as fluid flow and solute transport. The process of generating numerical grids with appropriate property distributions from geologic conceptual models is automated, thus making the entire process easy to implement with fewer user-induced errors. The series of grids of various resolutions are used to assess the level at which increasing resolution no longer influences the flow and solute transport results. Grid resolution is found to be a critical issue for ground water flow and solute transport. The resolution required in a particular instance is a function of the feature size of the model, the intrinsic properties of materials, the specific physics of the problem, and boundary conditions. The asymptotic nature of results related to flow and transport indicate that for a hydrologic model of the heterogeneous hydrostratigraphy under Yucca Mountain, a horizontal grid spacing of 600 m and vertical grid spacing of 40 m resolve the hydrostratigraphic model with sufficient precision to accurately model the hypothetical flow and solute transport to within 5% of the value that would be obtained with much higher resolution.  相似文献   

Blooms of the cyanobacterium Lyngbya majuscula in coastal Queensland, Australia: disparate sites, common factors     

Albert S  O'Neil JM  Udy JW  Ahern KS  O'Sullivan CM  Dennison WC 《Marine pollution bulletin》2005,51(1-4):428-437

During the last decade there has been a significant rise in observations of blooms of the toxic cyanobacterium Lyngbya majuscula along the east coast of Queensland, Australia. Whether the increase in cyanobacterial abundance is a biological indicator of widespread water quality degradation or also a function of other environmental change is unknown. A bioassay approach was used to assesses the potential for runoff from various land uses to stimulate productivity of L. majuscula. In Moreton Bay, L. majuscula productivity was significantly (p<0.05) stimulated by soil extracts, which were high in phosphorus, iron and organic carbon. Productivity of L. majuscula from the Great Barrier Reef was also significantly (p<0.05) elevated by iron and phosphorus rich extracts, in this case seabird guano adjacent to the bloom site. Hence, it is possible that other L. majuscula blooms are a result of similar stimulating factors (iron, phosphorus and organic carbon), delivered through different mechanisms.  相似文献   

A New Datum for use in the Body Wave Travel Time Inverse Problem     

Leonard E. Johnson  Freeman Gilbert 《Geophysical Journal International》1972,30(4):373-380

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Improved resolution of complex eigenfrequencies in analytically continued seismic spectra     

Ray Buland  Freeman Gilbert 《Geophysical Journal International》1978,52(3):457-470

Summary. The response of the Earth to an earthquake is a transient that is effectively zero several days after the event. A recording of the event, of finite duration in time, has a Fourier spectrum that is an entire, or integral, analytic function of frequency. We present a very simple procedure for computing the Fourier spectrum as a function of complex frequency; the analytically continued spectrum. By investigating the properties of the analytically continued spectrum we show how to extract high- Q modes, how to estimate Q either from the amplitude or from the width of a resonance function, and how to improve the resolution of splitting to the theoretical maximum. Examples of these procedures, using observed data, are presented.  相似文献   

Grazing incidence spectra of the sun     

F. F. Freeman  B. B. Jones 《Solar physics》1970,15(2):288-308

Intensity calibrated grazing incidence spectrographs have been flown on three Skylark sounding rockets to record the solar soft X-ray and XUV spectra over a wide wavelength range. This paper describes the instrumentation and calibration procedures, and presents wavelength and intensity data, for each of the flights.  相似文献