A perturbation theory for Love waves in anelastic media     

G. Madja  R. C. Y. Chin  F. E. Followill 《Geophysical Journal International》1985,80(1):1-34

Summary. We give a systematic formulation and a rigorous justification of a perturbation technique for the computation of the eigenvalues and eigenfunctions of Love waves (and toroidal oscillations by an appropriate change for variables) in an anelastic medium with a constitutive law modelling geophysical media of current interest such as the Kelvin—Voigt Solid, the Maxwell Solid, the Standard Linear Solid, and the Standard Linear Solid with a continuous spectrum of relaxation times. We develop expressions relating the eigenvalues of eigenfunctions for Love waves in a continuously varying vertically stratified anelastic half-space to the corresponding elastic eigenvalues and eigenfunctions. Analytically, our correspondence principle has the form of a regular perturbation expansion in terms of a parameter for both the eigenvalues and eigenfunctions. The identification of ɛ is motivated by the dissipativity principle of viscoelasticity theory. Moreover, we show that our correspondence principle applies respectively only in the high and low frequency range for the Maxwell and Kelvin—Voigt Solids. Outside of the applicable range of frequencies, our correspondence principle yields no useful information. For the family of Standard Linear Solids it is uniformly applicable for all non-zero frequencies.
We also derive an explicit formula to estimate the radius of convergence of our perturbation expansions. This estimate of the radius of convergence for each eigenvalue and eigenfunction is functionally defined by the constitutive model for the anelastic medium. The estimate is frequency dependent and depends on the separation distance between the eigenvalue and the remainder of the spectrum of the corresponding elastic problem.  相似文献   

Volcanic style in the Strand Fiord Formation (Upper Cretaceous), Axel Heiberg Island, Canadian Arctic Archipelago     

B. RICKETTS  K. G. OSADETZ  A. K EMBRY 《Polar research》1985,3(1):107-122

The Strand Fiord Formation is a volcanic unit of early Late Cretaceous age which outcrops on west-central and northwestern Axel Heiberg Island in the Canadian Arctic Archipelago. The formation is part of the thick Sverdrup Basin succession and immediately precedes the final basin foundering event. The Strand Fiord volcanics are encased in marine strata and thin southward from a maximum thickness of 789+ m on northwestern Axel Heiberg to a zero edge near the southern shore of the island. Tholeiitic icelandite flows are the main constituent of the formation with volcaniclastic conglomerates, sandstones, mudrocks and rare coal seams also being present. The lava flows range in thickness from 6 to 60 m and subaerial flows predominate. Both pahoehoe and aa lava types are common and the volcanic pile accumulated mostly by the quiet effusion of lavas. The volcaniclastic lithologies become more common near the southern and eastern edges of the formation and represent lahars and beach to shallow marine reworked deposits. The Strand Fiord volcanics are interpreted to represent the cratonward extension of the Alpha Ridge, a volcanic ridge that was active during the formation of the Amerasian Basin.  相似文献   

Astrometry from space: GAIA and planet detection     

S. Casertano  M. G. Lattanzi  M. A. C. Perryman  A. Spagna 《Astrophysics and Space Science》1996,241(1):89-104

The proposed baseline GAIA mission will be able to detect the astrometric signature of Jupiter-size planets around of the order of a million stars, using either global or narrow-angle astrometry. If the mission can realize the higher astrometric accuracy that photon statistics allows for bright stars, lower-mass planets (from Earth size to ten times larger) can be found around ten to a few hundred stars.  相似文献   

Influence of viscous dissipation on a hydromagnetic field     

Th. I. Lekas  G. A. Georgantopoulos 《Astrophysics and Space Science》1992,191(2):299-305

The effect of a transverse magnetic field and of the viscosity diffusion on the free-convection flow of an electrically-conducting incompressible fluid past a uniformally accelerated vertical plate is discussed. A finite difference method has been used to obtain a numerical solution. The influence of the various parameters on the flow field is discussed.  相似文献   

Radial velocities of the components of Trapezium type multiple stellar systems. II     

G. Sh. Dzhavakhishvili  G. N. Salukvadze 《Astrophysics》1994,37(4):326-328

Translated fromAstrofizika, Vol. 37, No. 4, 1994.  相似文献   

A 20 cm2 CCD mosaic camera for a dark matter search part I : Mechanics,optics and cryogeny     

Arnaud  M.  Aubourg  E.  Bareyre  P.  Br';ehin  S.  Caridroit  R.  de Kat  J.  Dispau  G.  Djidi  K.  Gros  M.  Lachièze-Rey  M.  Laigneau  Y.  Laurent  B.  Lesquoy  E.  Lavocat  Ph.  Magneville  C.  Mazeau  B.  Milsztajn  A.  Moscoso  L.  Pasquaud  J.  Paul  B.  Perrin  P.  Petibon  J.  Piret  Y.  Queinnec  F.  Rich  J.  Spiro  M.  de Trogoff  J.  Vigroux  L.  Zylberajch  S.  Ansari  R.  Cavalier  F.  Moniez  M.  Beaulieu  J. P.  Ferlet  R.  Grison  Ph.  Vidal-Madjar  A.  Adrianzyk  G.  Berger  J. P.  Burnage  R.  Delclite  J. C.  Kohler  D.  Magnan  R.  Richaud  A.  Guibert  J.  Moreau  O.  Tajahmady  F.  Baranne  A.  Maurice  E.  Prévôt  L.  Gry  C. 《Experimental Astronomy》1994,4(3-4):265-278

A 20cm ² CCD mosaic camera has been especially built to search for dark galactic halo objects by the gravitational microlensing effect. The sensitive area is made of 16 edge-buttable CCDs developped by Thomson-CTS, with 23×23 µm ² pixels. The 35 kg camera housing and mechanical equipment is presented. The associated electronics and data acquisition system are described in a separate paper. The camera resides at the focal plane of a 40 cm, f/10, Ferson reflector. The instrument has been in operation since December 1991 at the La Silla Observatory (ESO).  相似文献   

Purana basins of peninsular India: a review     

Vivek S. Kale  V. G. Phansalkar 《Basin Research》1991,3(1):1-36

Seven supracratonic, Proterozoic basins, occupying more than a fifth of the Precambrian exposures in the Indian Peninsula, comprise the Purana basins. A comprehensive review of the current status of knowledge of these voluminous orthoquartzite-carbonate-shale suites in the context of their contemporary lithostratigraphy, depositional environments and structural disposition is presented. Stromatolite biostratigraphy and available geochronological data are compared, to discern their age limits.
These basins contain perhaps one of the most elaborate records of Middle to Late Proterozoic (Riphean-Vendian) sedimentation preserved in an unmetamorphosed and only slightly deformed state. Further sedimentological and structural studies could lead to a better understanding of the Proterozoic craton-margin processes. Their close association with the Middle Proterozoic Mobile Belt of peninsular India is that of two contrasting tectonic regimes, contemporaneously adjoining each other. The existing lithostratigraphic classifications of many of these sequences may not stand the test of process - response considerations as demonstrated by the recent revisions in the stratigraphy of the Cuddapah and Bhima basins. The prolific stromatolitic, micro-organic and trace-fossil communities preserved in them require much more detailed, but cautious study, and may yield information on the Riphean-Vendian biota. However, these studies must be undertaken in association with elaborate geochronological determinations which are sparse at present.
Inadequacy of the existing knowledge of these basins is highlighted, with the view of inviting the attention of the geological community to these unique basins from peninsular India.  相似文献   

The estimation of the shape of an array using a hidden Markov model     

Quinn  B.G. Barrett  R.F. Kootsookos  P.J. Searle  S.J. 《Oceanic Engineering, IEEE Journal of》1993,18(4):557-564

A hidden Markov model (HMM) technique for the estimation of the shape of a towed array is presented. It is assumed that there is a far-field source radiating sound containing possibly weak spectral lines. The technique uses either the Fourier coefficients at a given frequency computed from a single time block or the maximal eigenvector of a sample spectral covariance matrix. The technique is illustrated using several simulations. The results of these simulations indicate that the HMM technique yields shape and bearing estimates more accurate than those provided by a maximum-likelihood array shape estimation technique  相似文献   

A study of the Equatorial Atlantic currents using historical moored data     

Dr. Alexander B. Polonsky  Dr. Evgeniy G. Nikolaenko  Dr. Sekou Konate  Dr. Toumany Camara 《Ocean Dynamics》1993,45(4):219-254

  相似文献   

Magnetic Field Strengths and Structures from Radio Observations of Solar Active Regions     

Chang－XiZhang  G.B.Gelfreikh 《中国天文和天体物理学报》2002,2(3):266-276

Radio observations of some active regions (ARs) obtained with the Nobeyama radioheliograph at λ=1.76cm are used for estimating the magnetic field strength in the upper chromosphere, based on thermal bremsstrahlung. The results are compared with the magnetic field strength in the photosphere from observations with the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station of Beijing Astronomical Observatory. The difference in the magnetic field strength between the two layers seems reasonable. The solar radio maps of active regions obtained with the Nobeyama radioheliograph, both in total intensity (I-map) and in circular polarizations (V-map), are compared with the optical magnetograms obtained with the SMFT. The comparison between the radio map in circular polarization and the longitudinal photospheric magnetogram of a plage region suggest that the radio map in circular polarization is a kind of magnetogram of the upper chromosphere. The comparison of the radio map in total intensity with the photospheric vector magnetogram of an AR shows that the radio map in total intensity gives indications of magnetic loops in the corona, thus we have a method of defining the coronal magnetic structure from the radio I-maps at λ=1.76 cm. Analysing the I-maps, we identified three components: (a) a compact bright source; (b) a narrow elongated structure connecting two main magnetic islands of opposite polarities (observed in both the optical and radio magnetograms); (c) a wide, diffuse, weak component that corresponds to a wide structure in the solar active region which shows in most cases an S or a reversed S contour, which is probably due to the differential rotation of the Sun. The last two components suggest coronal loops on different spatial scales above the neutral line of the longitudinal photospheric magnetic field.  相似文献