An empirical calibration of star formation rate estimators     

Daniel Rosa&#;González  Elena Terlevich †  Roberto Terlevich ‡ 《Monthly notices of the Royal Astronomical Society》2002,332(2):283-295

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A PRINCIPAL AXIS SHIFT IN THE AMERICAN SPATIAL ECONOMY?*     

Daniel R. Vining  Joseph B. Dobronyi  Mark A. Otness  James E. Schwinn 《The Professional geographer》1982,34(3):270-278

Gottmann in his classic Megalopolis attributes the dominance of the Northeast to its function as the hinge region of the United States. In this paper, we show, via statistics on maritime trade and interregional freight traffic by rail, that Megalopolis is no longer the dominant “hinge” region. We present evidence that the Gulf region may be supplanting it in this function. Finally, we speculate on some of the reasons for the Gulf's rather sudden assumption of this role and its implications for the economic geography of the U.S.  相似文献   

The detection of the donor star in IY UMa     

Daniel J. Rolfe  Timothy M. C. Abbott  Carole A. Haswell 《Monthly notices of the Royal Astronomical Society》2002,334(3):699-704

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The MESSENGER mission to Mercury: scientific objectives and implementation     

Sean C. Solomon  Ralph L. McNutt  Jr.  Robert E. Gold  Mario H. Acua  Daniel N. Baker  William V. Boynton  Clark R. Chapman  Andrew F. Cheng  George Gloeckler  James W. Head III  Stamatios M. Krimigis  William E. McClintock  Scott L. Murchie  Stanton J. Peale  Roger J. Phillips  Mark S. Robinson  James A. Slavin  David E. Smith  Robert G. Strom  Jacob I. Trombka  Maria T. Zuber 《Planetary and Space Science》2001,49(14-15)

Mercury holds answers to several critical questions regarding the formation and evolution of the terrestrial planets. These questions include the origin of Mercury's anomalously high ratio of metal to silicate and its implications for planetary accretion processes, the nature of Mercury's geological evolution and interior cooling history, the mechanism of global magnetic field generation, the state of Mercury's core, and the processes controlling volatile species in Mercury's polar deposits, exosphere, and magnetosphere. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission has been designed to fly by and orbit Mercury to address all of these key questions. After launch by a Delta 2925H-9.5, two flybys of Venus, and two flybys of Mercury, orbit insertion is accomplished at the third Mercury encounter. The instrument payload includes a dual imaging system for wide and narrow fields-of-view, monochrome and color imaging, and stereo; X-ray and combined gamma-ray and neutron spectrometers for surface chemical mapping; a magnetometer; a laser altimeter; a combined ultraviolet–visible and visible-near-infrared spectrometer to survey both exospheric species and surface mineralogy; and an energetic particle and plasma spectrometer to sample charged species in the magnetosphere. During the flybys of Mercury, regions unexplored by Mariner 10 will be seen for the first time, and new data will be gathered on Mercury's exosphere, magnetosphere, and surface composition. During the orbital phase of the mission, one Earth year in duration, MESSENGER will complete global mapping and the detailed characterization of the exosphere, magnetosphere, surface, and interior.  相似文献   

A CAUTIONARY NOTE ON THE USE OF THE ALLOMETRIC FUNCTION TO ESTIMATE URBAN POPULATIONS     

Daniel R. Vining  Stephanus J. H. Louw 《The Professional geographer》1978,30(4):365-370

Use of the allometric function to estimate the number of inhabitants of urban areas, given knowledge of their land areas obtained through satellite photographs, rests as much on the stability of this function over time as on its goodness of fit to a cross section of cities at a single point in time. Using urban land and population data for four countries, the United States, Japan, Sweden, and Norway, this paper demonstrates that the function is not generally stable but rather has been subject to rapid upward shifts over the past 10 to 20 years.  相似文献   

COMPUTER-INTENSIVE SIGNIFICANCE-TESTING PROCEDURES*     

Daniel C. Knudsen 《The Professional geographer》1987,39(2):208-214

The role of statistics in geography is now widely recognized, yet there are continuing suspicions as to the appropriateness of traditional methods. I review three computer-intensive approaches to significance testing of sample data. Using these methods, one can virtually always make some statement about the significance of a measure for comparing samples. Yet each approach also yields slightly different information about the measure. This confusion may be lessened somewhat by adopting standard sets of significance-testing procedures.  相似文献   

On the detectability of H₂S in Jupiter     

Bruno Bézard  André Marten  Jean Paul Baluteau  Daniel Gautier  Jean-Marie Flaud  Claude Camy-Peyret 《Icarus》1983,55(2):259-271

The influence of hydrogen sulfide, a still-undetected key molecule for the Jovian atmospheric chemistry in the infrared spectrum, was investigated. Synthetic spectra including various vertical distribution profiles of H₂S have been computed and compared with observational data for Jupiter in the 2- to 15-cm^?1 and 1160- to 1200-cm^?1 spectral ranges. No firm conclusion about the presence of H₂S can be drawn from the latter spectral region because of large uncertainties in gaseous opacities. In the microwave range, H₂S is found to be a possible candidate to explain the measurements. Constraints to its vertical distribution which would imply a significant supersaturation in the troposphere are derived. Physical and chemical processes involving H₂S in the atmosphere are discussed in the light of this hypothesis.  相似文献   

Cosmological radiative transfer codes comparison project – I. The static density field tests     

Ilian T. Iliev  Benedetta Ciardi  Marcelo A. Alvarez  Antonella Maselli  rea Ferrara  Nickolay Y. Gnedin  Garrelt Mellema  Taishi Nakamoto  Michael L. Norman  Alexei O. Razoumov  Erik-Jan Rijkhorst  Jelle Ritzerveld  Paul R. Shapiro  Hajime Susa  Masayuki Umemura  Daniel J. Whalen 《Monthly notices of the Royal Astronomical Society》2006,371(3):1057-1086

Radiative transfer (RT) simulations are now at the forefront of numerical astrophysics. They are becoming crucial for an increasing number of astrophysical and cosmological problems; at the same time their computational cost has come within reach of currently available computational power. Further progress is retarded by the considerable number of different algorithms (including various flavours of ray tracing and moment schemes) developed, which makes the selection of the most suitable technique for a given problem a non-trivial task. Assessing the validity ranges, accuracy and performances of these schemes is the main aim of this paper, for which we have compared 11 independent RT codes on five test problems: (0) basic physics; (1) isothermal H  ii region expansion; (2) H  ii region expansion with evolving temperature; (3) I-front trapping and shadowing by a dense clump and (4) multiple sources in a cosmological density field. The outputs of these tests have been compared and differences analysed. The agreement between the various codes is satisfactory although not perfect. The main source of discrepancy appears to reside in the multifrequency treatment approach, resulting in different thicknesses of the ionized-neutral transition regions and the temperature structure. The present results and tests represent the most complete benchmark available for the development of new codes and improvement of existing ones. To further this aim all test inputs and outputs are made publicly available in digital form.  相似文献   

Computer mapping of seismic reflectors in the coastal region of the National Petroleum Reserve in Alaska     

Daniel M. Tetzlaff  John W. Harbaugh 《Mathematical Geology》1985,17(4):455-480

This study deals with detailed mapping of sedimentary features within Torok Formation and Nanushuk Group in the northern part of the National Petroleum Reserve in Alsaka (NPRA). These Cretaceous units correspond to a single depositional regime of a large deltaic system. Seismic reflecting surfaces within the sequence are seen as sigmoidal traces in seismic sections. These horizons can be identified over long distances (up to 160 km) within individual seismic sections and can be correlated between intersecting sections. The study is centered in four different areas in which seismic information is relatively abundant and of good quality. One of the study areas is of special interest because of a large, now-filled ancient submarine canyon, Simpson Canyon. Reflection-time measurements were obtained by digitizing various horizons that were manually traced on seismic sections. Reflection-time measurements have been converted to depth values, corrected for postdepositional tilting, and portrayed as structure contour maps, perspective fish-net diagrams, and isopach maps prepared by computer. Computer mapping procedures are essential to obtain three-dimensional representations of reflecting surfaces. Because the northern NPRA has undergone little tectonic deformation since Cretaceous, horizons that have been mapped provide a close representation of submarine paleotopographic surfaces. A succession of these surfaces reveals progressive changes in the form of deltaic deposits from west to east, suggesting that energy of waves and currents increased as the delta prograded eastward. The succession of surfaces also suggests that Simpson Canyon was affected by at least two events of erosion and refilling.  相似文献   

Radar observations of asteroid 25143 Itokawa (1998 SF36)     

Steven J. OSTRO  Lance A. M. BENNER  Michael C. NOLAN  Christopher MAGRI  Jon D. GIORGINI  Daniel J. SCHEERES  Stephen B. BROSCHART  Mikko KAASALAINEN  David VOKROUHLICKÝ  Steven R. CHESLEY  Jean‐Luc MARGOT  Raymond F. JURGENS  Randy ROSE  Donald K. YEOMANS  Shigeru SUZUKI  Eric M. de JONG 《Meteoritics & planetary science》2004,39(3):407-424

Abstract— We observed 25143 Itokawa, the target of Japan's Hayabusa (MUSES‐C) sample‐return mission, during its 2001 close approach at Arecibo on twelve dates during March 18‐April 9 and at Goldstone on nine dates during March 20‐April 2. We obtained delay‐Doppler images with range resolutions of 100 ns (15 m) at Arecibo and 125 ns (19 m) at Goldstone. Itokawa's average circular polarization ratio at 13 cm, 0.26 ± 0.04, is comparable to that of Eros, so its cm‐to‐m surface roughness probably is comparable to that on Eros. Itokawa's radar reflectivity and polarization properties indicate a near‐surface bulk density within 20% of 2.5 g cm^?3. We present a preliminary estimate of Itokawa's shape, reconstructed from images with rather limited rotation‐phase coverage, using the method of Hudson (1993) and assuming the lightcurve‐derived spin period (12.132 hr) and pole direction (ecliptic long., lat. = 355°, ?84°) of Kaasalainen et al. (2003). The model can be described as a slightly asymmetrical, slightly flattened ellipsoid with extents along its principal axes of 548 times 312 times 276 m ± 10%. Itokawa's topography is very subdued compared to that of other asteroids for which spacecraft images or radar reconstructions are available. Similarly, gravitational slopes on our Itokawa model average only 9° and everywhere are less than 27°. The radar‐refined orbit allows accurate identification of Itokawa's close planetary approaches through 2170. If radar ranging planned for Itokawa's 2004 apparition succeeds, then tracking of Hayabusa during its 2005 rendezvous should reveal Yarkovsky perturbation of the asteroid's orbit.  相似文献