Galactic structure from the Two Micron Galactic Survey     

F. Garzón  P. L. Hammersley  T. Mahoney  X. Calbet  M. J. Selby 《Astrophysics and Space Science》1994,217(1-2):177-180

The Two Micron Galactic Survey (TMGS) is the most sensitive large scale point source near infrared survey of the Galactic Plane yet attempted. The Galactic plane has been drift-scanned in several regions over the areas -5° <l < 30°, |b | 15° and 30° <l < 180°, |b | 5°. The survey is complete in the areas covered to magnitudem _k = +9.8. So far, a total area of 255 square degrees has been mapped and 500000 objects have been detected, the majority of these in the Galactic plane and with no visible counterparts. In this contribution we use data from the TMGS to probe the star distribution within the Galactic disk.  相似文献   

运用生态地球化学调查成果指导农业生产管理——彭州市土壤缺硼针对施肥实验   总被引：1，自引：1，他引：1  

刘应平  张淼  刘应发  严向军 《物探化探计算技术》2007,29(3):253-255

论述了硼的地球化学特征及其分布状况,硼在土壤中的存在形式,以及在土壤中有效硼的影响因素。并以彭州市平坝区为例,论述了在缺硼的蔬菜种植区内,针对喷施硼肥,有效地提高了农作物的产量。特别需要强调的是:利用生态地球化学调查成果指导农业生产管理,可以获得良好的社会经济效益。  相似文献   

高密度电法的发展与应用   总被引：115，自引：0，他引：115  

董浩斌  王传雷 《地学前缘》2003,10(1):171-176

文中从电极排列、反演处理方法、仪器等几个方面 ,介绍了高密度电法的发展 ,说明了所有电极排列方式是从对称四极、单极偶极和单极单极发展而来。在反演方法软件方面 ,介绍了基于圆滑约束最小二乘法及计算机反演快速计算程序。同时 ,提出供电时间、极化补偿和电极转换开关是高密度电法仪器发展的关键技术。文中列举了高密度电法在多个领域的应用简况 ,最后提出了高密度电法在今后发展的趋势为高密度激发极化法、三维高密度电阻率法。  相似文献   

The Portland Hills Fault: uncovering a hidden fault in Portland, Oregon using high-resolution geophysical methods   总被引：3，自引：0，他引：3  

Lee M. Liberty  Mark A. Hemphill-Haley  Ian P. Madin   《Tectonophysics》2003,368(1-4):89

The Portland metropolitan area historically is the most seismically active region in Oregon. At least three potentially active faults are located in the immediate vicinity of downtown Portland, with the Portland Hills Fault (PHF) extending directly beneath downtown Portland. The faults are poorly understood, and the surface geologic record does not provide the information required to assess the seismic hazards associated with them. The limited geologic information stems from a surface topography that has not maintained a cumulative geologic record of faulting, in part, due to rapid erosion and deposition from late Pleistocene catastrophic flood events and a possible strike-slip component of the faults. We integrated multiple high-resolution geophysical techniques, including seismic reflection, ground penetrating radar (GPR), and magnetic methods, with regional geological and geophysical surveys to determine that the Portland Hills Fault is presently active with a zone of deformation that extends at least 400 m. The style of deformation is consistent with at least two major earthquakes in the last 12–15 ka, as confirmed by a sidehill excavation trench. High-resolution geophysical methods provide detailed images of the upper 100 m across the active fault zone. The geophysical images are critical to characterizing the structural style within the zone of deformation, and when integrated with a paleoseismic trench, can accurately record the seismic history of a region with little surface geologic exposure.  相似文献   

The Parkes Southern Pulsar Survey — II. Final results and population analysis     

A. G. Lyne  R. N. Manchester  D. R. Lorimer  M. Bailes  N. D'Amico  T. M. Tauris  S. Johnston  J. F. Bell  & L. Nicastro 《Monthly notices of the Royal Astronomical Society》1998,295(4):743-755

A survey of the entire southern sky for millisecond and low-luminosity pulsars using the ATNF Parkes radio telescope has now been completed. The survey detected 298 pulsars, of which 101 were previously unknown. The new pulsars include 17 millisecond pulsars. This is the largest sample of both normal and millisecond pulsars detected in any survey. Combining our sample with other recent surveys in the Northern Hemisphere, we present a statistical study of the populations of both normal and millisecond pulsars. We find that the improved statistics allow us to estimate the number and birth-rate of both types of pulsar down to a 400-MHz luminosity limit of 1 mJy kpc². The local surface densities of potentially observable normal pulsars and millisecond pulsars are both about 30 kpc⁻², corresponding to ∼ 30000 potentially observable pulsars of each type in the Galaxy. Once beaming effects are taken into consideration we estimate that the active population of normal pulsars is ∼ 160000. Although there is evidence for flattening of the luminosity function of normal pulsars, this is not evident for millisecond pulsars which probably have a substantial population with luminosities below 1 mJy kpc². After correcting for beaming effects, we estimate that a normal pulsar is born with a luminosity greater than 1 mJy kpc² between once every 60 and 330 yr in the Galaxy. The birth-rate of millisecond pulsars is at least 3 × 10⁻⁶ yr⁻¹ above the same luminosity limit. Modelling the observed transverse speeds of millisecond pulsars using a dynamical simulation, we find their mean birth velocity to be 130 ± 30 km s⁻¹, significantly lower than that of the normal pulsars.  相似文献   

A unifying view of the spectral energy distributions of blazars   总被引：3，自引：0，他引：3  

G. Fossati  L. Maraschi  A. Celotti  A. Comastri  & G. Ghisellini 《Monthly notices of the Royal Astronomical Society》1998,299(2):433-448

We collect data at well-sampled frequencies from the radio to the γ-ray range for the following three complete samples of blazars: the Slew survey, the 1-Jy samples of BL Lacs and the 2-Jy sample of flat-spectrum radio-loud quasars (FSRQs). The fraction of objects detected in γ-rays ( E  ≳ 100 MeV) is ∼ 17, 26 and 40 per cent in the three samples respectively. Except for the Slew survey sample, γ-ray detected sources do not differ either from other sources in each sample, or from all the γ-ray detected sources, in terms of the distributions of redshift, radio and X-ray luminosities or of the broad-band spectral indices (radio to optical and radio to X-ray). We compute average spectral energy distributions (SEDs) from radio to γ-rays for each complete sample and for groups of blazars binned according to radio luminosity, irrespective of the original classification as BL Lac or FSRQ. The resulting SEDs show a remarkable continuity in that (i) the first peak occurs in different frequency ranges for different samples/luminosity classes, with most luminous sources peaking at lower frequencies; (ii) the peak frequency of the γ-ray component correlates with the peak frequency of the lower energy one; (iii) the luminosity ratio between the high and low frequency components increases with bolometric luminosity. The continuity of properties among different classes of sources and the systematic trends of the SEDs as a function of luminosity favour a unified view of the blazar phenomenon: a single parameter, related to luminosity, seems to govern the physical properties and radiation mechanisms in the relativistic jets present in BL Lac objects as well as in FSRQs. The general implications of this unified scheme are discussed while a detailed theoretical analysis, based on fitting continuum models to the individual spectra of most γ-ray blazars, is presented in a separate paper.  相似文献   

The topology of the IRAS Point Source Catalogue Redshift Survey     

A. Canavezes  V. Springel  S. J. Oliver  M. Rowan-Robinson  O. Keeble  S. D. M. White  W. Saunders  G. Efstathiou  C. S. Frenk  R. G. McMahon  S. Maddox  W. Sutherland  & H. Tadros 《Monthly notices of the Royal Astronomical Society》1998,297(3):777-793

We investigate the topology of the new Point Source Catalogue Redshift Survey (PSCz) of IRAS galaxies by means of the genus statistic. The survey maps the local Universe with approximately 15 000 galaxies over 84.1 per cent of the sky, and provides an unprecedented number of resolution elements for the topological analysis. For comparison with the PSCz data we also examine the genus of large N -body simulations of four variants of the cold dark matter (CDM) cosmogony. The simulations are part of the Virgo project to simulate the formation of structure in the Universe. We assume that the statistical properties of the galaxy distribution can be identified with those of the dark matter particles in the simulations. We extend the standard genus analysis by examining the influence of sampling noise on the genus curve and introducing a statistic able to quantify the amount of phase correlation present in the density field, the amplitude drop of the genus compared to a Gaussian field with identical power spectrum. The results for PSCz are consistent with the hypothesis of random-phase initial conditions. In particular, no strong phase correlation is detected on scales ranging from 10 to 32 h ⁻¹ Mpc, whereas there is a positive detection of phase correlation at smaller scales. Among the simulations, phase correlations are detected in all models at small scales, albeit with different strengths. When scaled to a common normalization, the amplitude drop depends primarily on the shape of the power spectrum. We find that the constant-bias standard CDM model can be ruled out at high significance, because the shape of its power spectrum is not consistent with PSCz. The other CDM models with more large-scale power all fit the PSCz data almost equally well, with a slight preference for a high-density τCDM model.  相似文献   

Aeromagnetic And Aeroradiometric Response To Hydrothermal Alteration     

M.-L. Airo 《Surveys in Geophysics》2002,23(4):273-302

In Precambrian terrains all regional and most localintensive magnetic anomalies areproduced by magnetite. Monoclinic pyrrhotite isresponsible for some local, but oftenintensive, magnetic anomaly patterns. Both magnetiteand pyrrhotite are affected byhydrothermal alteration processes in various ways,resulting in changes either inabundance or in grain fabric. These changes arerecorded in the magnetic properties ofthe altered rock units and reflected in theiraeromagnetic signatures. Hydrothermalalteration in deformed bedrock zones is commonlycontrolled by structural or tectonicfeatures. Regional high-resolution aerogeophysicalsurveys can be utilized, in bothregional and detailed investigations, to map theoverall geological and tectonic settingor to estimate local changes in magnetic mineralogyand the relative abundance ofradionuclides.Magnetite is most commonly destroyed in alterationprocesses, such as biotitization,carbonation, sulfidization and silicification. Theprogressive destruction of magnetitebegins at grain margins and results first in broken and cracked grain texture and smallergrain size, then progresses to total disappearanceof magnetite. Alteration in magnetite-bearing rock units may be recognized by decreasedmagnetic intensity and by thebroken, disrupted magnetic pattern. The abundance ofmonoclinic pyrrhotite isenhanced by reducing hydrothermal fluids, and typicalcrystal anisotropy is developeddue to tectonic stress.The relative contents of radioelements are changedin the same hydrothermal processesand partly for the same reasons as the ferrimagneticminerals. Potassic alteration oftenresults in elevated K radiation particularly formafic rocks, and then anomalous K/Thratios along local shear or fracture zones may beindicative of gold-bearingmineralization. On the other hand, high U/Th ratioswithin metasedimentary units maypoint out prospects for sulphidization. Althoughvariation of U/Th ratios largely reflectsthe environmental conditions during primarydiagenesis or a later deformational phase,mainly the decrease in Th radiation close tosulphide mineralization seems to beresponsible for the elevated U/Th ratios.  相似文献   

Potential representation by independent configurations on a multi-electrode array     

Holger Lehmann 《Geophysical Journal International》1995,120(2):331-338

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Inversion of time-domain electromagnetic data for a horizontally layered Earth   总被引：1，自引：0，他引：1  

C. G. Farquharson  D. W. Oldenburg 《Geophysical Journal International》1993,114(3):433-442

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