Porphyroblast inclusion-trail orientation data: eppure non son girate*!     

T. H. BELL  S. E. JOHNSON  B. DAVIS  A. FORDE  N. HAYWARD  C. WILKINS 《Journal of Metamorphic Geology》1992,10(3):295-307

Extensive examination of large numbers of spatially orientated thin sections of orientated samples from orogens of all ages around the world has demonstrated that porphyroblasts do not rotate relative to geographical coordinates during highly non-coaxial ductile deformation of the matrix subsequent to their growth. This has been demonstrated for all tectonic environments so far investigated. The work also has provided new insights and data on metamorphic, structural and tectonic processes including: (1) the intimate control of deformation partitioning on metamorphic reactions; (2) solutions to the lack of correlation between lineations that indicate the direction of movement within thrusts and shear zones, and relative plate motion; and (3) a possible technique for determining the direction of relative plate motion that caused orogenesis in ancient orogens.  相似文献   

A circular passive synthetic array: an inverse problem approach     

Yen  N. 《Oceanic Engineering, IEEE Journal of》1992,17(1):40-47

Based on the general concept of the inverse acoustic radiation problem, the temporal scanning of a stationary acoustic field along a closed contour is used to simplify the measurement approach for obtaining information on source directionality. The mathematical formulation is derived from a model of the two-dimensional acoustic field. The formulation of the inverse problem is also investigated to establish a methodology for improving the angular resolution of the array processing. The fundamental relationship between the sound sources and the circular passive synthetic array is explored, utilizing existing mathematical methods, in order to develop the processing algorithm. Other subjects of practical interest, such as directional ambiguity, effect of Doppler frequency, interference noise, and processing gain are discussed. It is concluded that the results can be used to establish guidelines for engineering design and deployment of this type of synthetic array, and to further exploit the new array signal processing technique  相似文献   

Recent warming in southeastern Zaire (Central Africa) inferred from disturbed geothermal gradients     

M.N. Sebagenzi  G. Vasseur  P. Louis 《Global and Planetary Change》1992,6(2-4)

Several temperature-depth profiles measured in Kasai and in Shaba provinces of Zaire using mining exploration boreholes exhibit a significant negative temperature gradient near the surface. This anomalous curvature which extends to 100–200 m depth could reflect the effect of variations in surface conditions. Applying the theory of heat conduction in a semi-infinite homogeneous medium, these profiles indicate a surface warming by 3–4°C. This warming is related to the effect of the environmental changes associated with the mining exploitation and the urbanization during the last 40–90 years.  相似文献   

A sedimentary record from a deep Quaternary valley in the southern Lillebælt area, Denmark: Eemian and Early Weichselian lithology and chronology at Mommark     

JÓN EIRÍKSSON  PETER H. KRISTENSEN  HOLGER LYKKE-ANDERSEN  KATHRYN BROOKS  REW MURRAY  KAREN LUISE KNUDSEN  CHRISTOPHER GLAISTER 《Boreas: An International Journal of Quaternary Research》2006,35(2):320-331

A unique sequence of Late Saalian, Eemian and Early Weichselian strata is exposed in a coastal outcrop at Mommark in the western Baltic. The sedimentary facies and faunas reflect palaeoenvironmental changes from an initial freshwater lake followed by marine transgression and interglacial deposition in a palaeo-Baltic sea. The upper part of the Eemian marine record indicates regression followed by lacustrine sedimentation and deposition of Early Weichselian aeolian sediments, which are truncated by an erosional unconformity overlain by a till bed. The lower and middle parts of the sequence have previously been correlated with the European glacial-interglacial stratigraphy on the basis of pollen analysis, while the upper part has been dated for the present study using optically stimulated luminescence (OSL) of samples from the aeolian and glacial deposits. A similar complete glacial-interglacial-glacial succession has not previously been recorded from this area. The Mommark sequence of conformable strata has been subjected to lateral compression, evidenced by folding and low-angle reverse faults. Seismic records from the adjacent waters in the western Baltic reveal a system of buried Quaternary valleys in the area. It is suggested that the interglacial deposition took place in a basin within one of these valleys and that a slab constituting the Mommark sequence, originating from the margin of a valley, has been glaciotectonically displaced northwestwards to the present location.  相似文献   

Observing the CMB at high-ℓ using the VSA and AMI     

Angela C. Taylor 《New Astronomy Reviews》2003,47(11-12):925

We discuss two experiments – the Very Small Array (VSA) and the Arcminute MicroKelvin Imager (AMI) – and their prospects for observing the CMB at high angular multipoles. Whilst the VSA is primarily designed to observe primary anisotropies in the CMB, AMI is designed to image secondary anisotropies via the Sunyaev–Zel’dovich effect. The combined ℓ-range of these two instruments is between ℓ=150 and 10,000.  相似文献   

Environmental effects on galaxy luminosity functions: the cluster Abell 496     

F. Durret  C. Adami  C. Lobo 《Astrophysics and Space Science》2003,285(1):185-189

We have derived the galaxy luminosity function in various regions of the cluster of galaxies Abell 496 from a wide field image in the I band. A Schechter function fit in the 17≤ I_AB ≤22(–19.5≤ M_IAB ≤ –14.5) magnitude interval gives a steep power law index, which is somewhat steeper in the outer regions than in the inner zones. This result agrees with previous findings obtained by several teams on the Coma cluster and can be interpreted as due to the fact that faint galaxies are accreted by large ones in the central regions. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The Siberian Solar Radio Telescope: the current state of the instrument,observations, and data   总被引：2，自引：0，他引：2  

Grechnev  V.V.  Lesovoi  S.V.  Smolkov  G. Ya.  Krissinel  B.B.  Zandanov  V.G.  Altyntsev  A.T.  Kardapolova  N.N.  Sergeev  R.Y.  Uralov  A.M.  Maksimov  V.P.  Lubyshev  B.I. 《Solar physics》2003,216(1-2):239-272

The Siberian Solar Radio Telescope (SSRT) is one of the world's largest solar radio heliographs. It commenced operation in 1983, and since then has undergone several upgrades. The operating frequency of the SSRT is 5.7 GHz. Since 1992 the instrument has had the capability to make one-dimensional scans with a high time resolution of 56 ms and an angular resolution of 15 arc sec. Making one of these scans now takes 14 ms. In 1996 the capability was added to make full, two-dimensional images of the solar disk. The SSRT is now capable of obtaining images with an angular resolution of 21 arc sec every 2 min. In this paper we describe the main features and operation of the instrument, particularly emphasizing issues pertaining to the imaging process and factors limiting data quality. Some of the data processing and analysis techniques are discussed. We present examples of full-disk solar images of the quiet Sun, recorded near solar activity minimum, and images of specific structures: plages, coronal bright points, filaments and prominences, and coronal holes. We also present some observations of dynamic phenomena, such as eruptive prominences and solar flares, which illustrate the high-time-resolution observations that can be done with this instrument. We compare SSRT observations at 5.7 GHz, including computed `light curves', both morphologically and quantatively, with observations made in other spectral domains, such as 17 GHz radio images, Hα filtergrams and magnetograms, extreme-ultraviolet and X-ray observations, and dynamic radio spectra.  相似文献   

Towards a free–free template for CMB foregrounds     

C. Dickinson  R. D. Davies  R. J. Davis 《Monthly notices of the Royal Astronomical Society》2003,341(2):369-384

A full-sky template map of the Galactic free–free foreground emission component is increasingly important for high-sensitivity cosmic microwave background (CMB) experiments. We use the recently published Hα data of both the northern and southern skies as the basis for such a template.
The first step is to correct the Hα maps for dust absorption using the 100-μm dust maps of Schlegel, Finkbeiner & Davis. We show that for a range of longitudes, the Galactic latitude distribution of absorption suggests that it is 33 per cent of the full extragalactic absorption. A reliable absorption-corrected Hα map can be produced for ∼95 per cent of the sky; the area for which a template cannot be recovered is the Galactic plane area  | b | < 5°, l = 260°–0°–160°  and some isolated dense dust clouds at intermediate latitudes.
The second step is to convert the dust-corrected Hα data into a predicted radio surface brightness. The free–free emission formula is revised to give an accurate expression (1 per cent) for the radio emission covering the frequency range 100 MHz–100 GHz and the electron temperature range 3000–20 000 K. The main uncertainty when applying this expression is the variation of electron temperature across the sky. The emission formula is verified in several extended H  ii regions using data in the range 408–2326 MHz.
A full-sky free–free template map is presented at 30 GHz; the scaling to other frequencies is given. The Haslam et al. all-sky 408-MHz map of the sky can be corrected for this free–free component, which amounts to a  ≈6  per cent correction at intermediate and high latitudes, to provide a pure synchrotron all-sky template. The implications for CMB experiments are discussed.  相似文献   

The gigantic interacting galaxy NGC 6872     

C. Horellou  B. Koribalski 《Astrophysics and Space Science》2003,284(2):499-502

The luminous barred galaxy NGC 6872 is one of the largest spiral galaxies known. Star formation is traced all along the arms, which extend over more than 100 kpc. The galaxy is likely to be affected by tidal perturbations from the nearby companion IC 4970 passing by on a low-inclination, prograde orbit. We have mapped the large-scale distribution and kinematics of the atomic gas in the NGC 6872/IC 4970 system and carried out N-body simulations. Our aim is to investigate the evolution of gas and stars in such close encounters, examine the influence of a dark matter halo on the length of the tidal tails, and test models of collisionally induced star formation. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Transient‐state groundwater flow in various geometries with wells at arbitrary positions: analytical methods     

M. W. Roth  C. M Wilson  M. Z. Iqbal 《水文研究》2003,17(17):3519-3530

We have developed a method for analytically solving the porous medium flow equation in many different geometries for horizontal (two‐dimensional), homogeneous and isotropic aquifers containing impermeable boundaries and any number of pumping or injection wells located at arbitrary positions within the system. Solutions and results are presented for rectangular and circular aquifers but the method presented here is easily extendible to many geometries. Results are also presented for systems where constant head boundary conditions can be emulated internal to the aquifer boundary. Recommendations for extensions of the present work are briefly discussed. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献