Low-frequency oscillations and associated wave motions over Eurasia     

XIAOLAN WANG  JOÃO. CORTE-REAL  XUEBIN ZHANG 《地球，A辑:动力气象学与海洋学》1996,48(2):238-253

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Constraints on the formation of layered tektites from the excavation and analysis of layered tektites from northeast Thailand     

Peter S. Fiske 《Meteoritics & planetary science》1996,31(1):42-45

Abstract— The size, shape, composition, and vesicle content of 6 kg of layered tektite fragments, excavated near the town of Huai Sai, Thailand, place some constraints on the formation of layered tektites. The mass, shape, and distribution of the fragments are not consistent with an origin as a “puddle” of impact melt but suggest that they were derived from a single equant block. The presence of vesicles up to 7 mm in mean diameter within the tektite fragments suggests that the material was too viscous to allow for significant gravity-driven flow. These results suggest that layered tektites may be analogous to lava bombs, which may have been stretched and deformed in flight but underwent little flow after landing. Rather than being a product of “unusual circumstances,” such as multiple impacts, layered tektites may differ from splash-form tektites only in initial temperature of formation, speed of ejection, and small differences in initial composition.  相似文献   

Generating interface waves using a freely falling, instrumentedsource     

Stoll  R.D. Bautista  E.O. Akal  T. 《Oceanic Engineering, IEEE Journal of》1996,21(4):452-457

In recent years, interface waves such as the Scholte wave have become important tools in the study of the geoacoustic properties of near-bottom seafloor sediments. Traditionally, these waves have been generated by explosive or pneumatic sources deployed at or near the seafloor and monitored by ocean-bottom seismographs or geophone arrays. While these sources generate the requisite interface waves, they also produce higher frequency compressional waves in the water and sediment that tend to contaminate the surface wave and make inversion of the data difficult in the near field. In this paper, a new source consisting of a freely falling projectile instrumented with an accelerometer is described. When the projectile impacts the bottom, the exact time history of the vertical force applied to the sediment is known and therefore may be convolved with the transfer function of a sediment geoacoustic model to produce accurate synthetic seismograms. Moreover, the vertical force applied to the seafloor is very efficient in generating surface wave motion while producing very little compressional wave energy so that the near-field signals are much more easily analyzed. An example of the use of the new source is presented including inversion of the received signals to obtain shear-wave velocity and attenuation as a function of depth in the near bottom sediments at a shallow-water site  相似文献   

Studying Hydrodynamic Instability Using Shock-Tube Experiments     

O. Sadot  K. Levy  A. Yosef-Hai  D. Cartoon  Y. Elbaz  Y. Srebro  G. Ben-Dor  D. Shvarts 《Astrophysics and Space Science》2005,298(1-2):305-312

The hydrodynamic instability, which develops on the contact surface between two fluids, has great importance in astrophysical phenomena such as the inhomogeneous density distribution following a supernova event. In this event acceleration waves pass across a material interface and initiate and enhance unstable conditions in which small perturbations grow dramatically. In the present study, an experimental technique aimed at investigating the above-mentioned hydrodynamic instability is presented. The experimental investigation is based on a shock-tube apparatus by which a shock wave is generated and initiates the instability that develops on the contact surface between two gases. The flexibility of the system enables one to vary the initial shape of the contact surface, the shock-wave Mach number, and the density ratio across the contact surface. Three selected sets of shock-tube experiments are presented in order to demonstrate the system capabilities: (1) large-initial amplitudes with low-Mach-number incident shock waves; (2) small-initial amplitudes with moderate-Mach-number incident shock waves; and (3) shock bubble interaction. In the large-amplitude experiments a reduction of the initial velocity with respect to the linear growth prediction was measured. The results were compared to those predicted by a vorticity-deposition model and to previous experiments with moderate- and high-Mach number incident shock waves that were conducted by others. In this case, a reduction of the initial velocity was noted. However, at late times the growth rate had a 1/t behavior as in the small-amplitude low-Mach number case. In the small-amplitude moderate-Mach number shock experiments a reduction from the impulsive theory was noted at the late stages. The passage of a shock wave through a spherical bubble results in the formation of a vortex ring. Simple dimensional analysis shows that the circulation depends linearly on the speed of sound of the surrounding material and on the initial bubble radius.  相似文献   

A Faraday rotation template for the Galactic sky     

Patrick Dineen  Peter Coles 《Monthly notices of the Royal Astronomical Society》2005,362(2):403-410

Using a set of compilations of measurements for extragalactic radio sources, we construct all-sky maps of the Faraday rotation produced by the Galactic magnetic field. In order to generate the maps, we treat the radio source positions as a kind of 'mask' and construct combinations of spherical harmonic modes that are orthogonal on the masked sky. As long as relatively small multipoles are used, the resulting maps are quite stable to changes in the selection criteria for the sources, and show clearly the structure of the local Galactic magnetic field. We also suggest the use of these maps as templates for cosmic microwave background (CMB) foreground analysis, illustrating the idea with a cross-correlation analysis between the Wilkinson Microwave Anisotropy Probe ( WMAP ) data and our maps. We find a significant cross-correlation, indicating the presence of a significant residual contamination.  相似文献   

The Preboreal climate reversal and a subsequent solar‐forced climate shift     

J. van der Plicht  B. van Geel  S. J. P. Bohncke  J. A. A. Bos  M. Blaauw  A. O. M. Speranza  R. Muscheler  S. Bjrck 《第四纪科学杂志》2004,19(3):263-269

Accurate chronologies are essential for linking palaeoclimate archives. Carbon‐14 wiggle‐match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands). Following the Younger Dryas–Preboreal transition, two climatic shifts could be inferred. Around 11 400 cal. yr BP the expansion of birch (Betula) forest was interrupted by a dry continental phase with dominantly open grassland vegetation, coeval with the PBO (Preboreal Oscillation), as observed in the GRIP ice core. At 11 250 cal. yr BP a sudden shift to a humid climate occurred. This second change appears to be contemporaneous with: (i) a sharp increase of atmospheric ¹⁴C; (ii) a temporary decline of atmospheric CO₂; and (iii) an increase in the GRIP ¹⁰Be flux. The close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity, which may have forced the changes in climate and vegetation at around 11 250 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

The Relationship of Green-Line Transients to White-Light Coronal Mass Ejections     

S. P. Plunkett  G. E. Brueckner  K. P. Dere  R. A. Howard  M. J. Koomen  C. M. Korendyke  D. J. Michels  J. D. Moses  N. E. Moulton  S. E. Paswaters  O. C. St. Cyr  D. G. Socker  D. Wang  G. M. Simnett  D. K. Bedford  D. A. Biesecker  C. J. Eyles  S. J. Tappin  R. Schwenn  P. L. Lamy  A. Llebaria 《Solar physics》1997,175(2):699-718

We report observations by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft of three coronal green-line transients that could be clearly associated with coronal mass ejections (CMEs) detected in Thomson-scattered white light. Two of these events, with speeds >25 km s^-1, may be classified as ‘whip-like’ transients. They are associated with the core of the white-light CMEs, identified with erupting prominence material, rather than with the leading edge of the CMEs. The third green-line transient has a markedly different appearance and is more gradual than the other two, with a projected outward speed <10 km s^-1. This event corresponds to the leading edge of a ‘streamer blowout’ type of CME. A dark void is left behind in the emission-line corona following each of the fast eruptions. Both fast emission-line transients start off as a loop structure rising up from close to the solar surface. We suggest that the driving mechanism for these events may be the emergence of new bipolar magnetic regions on the surface of the Sun, which destabilize the ambient corona and cause an eruption. The possible relationship of these events to recent X-ray observations of CMEs is briefly discussed. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004981125702  相似文献   

Some comments on the asymptotic limit of antiproton-proton flux ratio at the top of the atmosphere     

O. C. Allkofer  D. P. Bhattacharyya 《Astrophysics and Space Science》1987,132(1):141-146

Using the leaky-box model the upper limit of the antiproton-proton flux ratio at the top of the atmosphere has been estimated from the latest primary nucleon spectrum and accelerator data on inclusive reactions. The estimated value of flux ratio comes out to be (3.6±0.3)×10^–4 is in accord with the previous results but still far from the measurements.  相似文献   

Reviews     

Ian Alexander  D. S. Houghton  L. D. B. Heenan  Peter Curson  B. R. O'Donnell  D. A. Chisholm 《The Australian geographer》1987,18(1):67-100

OFFICE DEVELOPMENT: A Geographical Analysis by M. Bateman. 14 × 22 cm, xvi and 175 pages. Croom Helm: London 1985 (ISBN 0 7099 0697 8) $A35.95 (cloth).

ATLAS OF YOUTH UNEMPLOYMENT, 1981: The Geographic Distribution of Youth Unemployment in Australian Cities from the 1981 Census According to Birthplace and Gender by P. Matwijiw with E. Bamford and C. Maher. 21 × 29 cm, 127 pages. Australian Institute of Multicultural Affairs: Melbourne 1985 (ISBN 949890 33 2) $A12.00 (limp).

ENVIRONMENT AND HEALTH by A. J. Rowland and P. Cooper. 23 × 16 cm, vi and 205 pages. Edward Arnold: London 1983 (ISBN 0 7131 2855 0) $A27.95 (limp).

FAMINE AS A GEOGRAPHICAL PHENOMENON edited by B. Currey and G. Hugo. 17 × 24 cm, vi and 202 pages. Reidel: Dordrecht 1984 (ISBN 90 277 1762 1) Dfl 95.00, $US37.00 (cloth).

SOUTH AUSTRALIA'S CHANGING POPULATION (South Australian Geographical Papers No. 1) by G. J. Hugo. 25 × 18 cm, 71 pages. Royal Geographical Society of Australasia (SA Branch): Adelaide 1983 (ISBN 0 909112 05 03) $A4.00 (limp).

DEVELOPMENTS IN POLITICAL GEOGRAPHY edited by M. A. Busteed. 23 × 15 cm, 340 pages. Academic Press: London 1983 (ISBN 0 12 148420 3) $US42.00 (cloth).

NEITHER JUSTICE NOR REASON: A Legal and Anthropological Analysis of Aboriginal Land Rights by M. Gumbert. 22 × 14 cm, xv and 215 pages. University of Queensland Press: St Lucia 1984 (ISBN 0 7022 1746 8) $A20.00 (cloth).

RURAL RESOURCE MANAGEMENT by P. J. Cloke and C. C. Park. 14 × 22 cm, xiii and 473 pages. Croom Helm: London 1985 (ISBN 0 7099 2037 7) $A44.95 (cloth).

FARM POLICY IN AUSTRALIA by R. K. Hefford. 14 × 22 cm, xviii and 415 pages. University of Queensland Press: St Lucia 1985 (ISBN 0 7022 1698 4) $A40.00 (cloth).

TRANSPORT AND COMMUNICATIONS FOR PACIFIC MICROSTATES: Issues in Organisation and Management edited by C. C. Kissling. 14 × 21 cm, 192 pages. Institute of Pacific Studies, University of the South Pacific: Suva 1984. $A10.00 (cloth), $A8.00 (limp).

TIMES OF CRISIS: Epidemics in Sydney 1788–1900 by P. H. Curson. 15 × 25 cm, xii and 195 pages. Sydney University Press: Sydney 1985 (ISBN 0 424 00112 8). $A35.00 (cloth).

PEASANTS, SUBSISTENCE, ECOLOGY AND DEVELOPMENT IN THE HIGHLANDS OF PAPUA NEW GUINEA by L. S. Grossman. 24 × 16 cm, xxi and 302 pages. Princeton University Press: Princeton, NJ 1984 (ISBN 0 691 09406 3) $US45.50.

THE WORLD FOOD PROBLEM 1950–1980 by D. Grigg. 15 × 24 cm, 276 pages. Basil Blackwell: Oxford 1985 (ISBN 0 631 13481 6) $A58.50 (cloth).

POPULATION REDISTRIBUTION AND DEVELOPMENT IN SOUTH ASIA edited by L. A. Kosinski and K. M. Elahi. 17 × 24 cm, 243 pages. Reichel: Dordrecht 1985 (ISBN 90 277 1938 1) Dfl 120.00, $US44.00, £30.50 (cloth).

GEOGRAPHY AND ETHNIC PLURALISM edited by C. Clarke, D. Ley and C. Peach. 15 × 23 cm, xvii and 294 pages. Allen & Unwin: London 1984 (ISBN 0 04 309107 5) $A45.00 (cloth); (ISBN 0 04 309108 3) $A24.95 (limp).

SOCIAL GEOGRAPHY IN INTERNATIONAL PERSPECTIVE edited by J. Eyles. 14 × 22 cm, 295 pages. Croom Helm: London 1986 (ISBN 0 7099 0944 6) $A49.95 (cloth).

THE GENTRIFICATION OF INNER MELBOURNE: A Political Geography of Inner City Housing by W. S. Logan. 14 × 22 cm, xvi and 328 pages. University of Queensland Press: St. Lucia 1985 (ISBN 0 7022 1729 8) $A50.00 (cloth).

YELLOWCAKE AND CROCODILES: Town Planning, Government and Society in Northern Australia by J. Lea and R. Zehner. 14 × 22 cm, xxvi and 200 pages. Allen & Unwin: Sydney 1986 (ISBN 0 86861 875 6) $A24.95 (cloth); (ISBN 0 86861 843 8) $A 14.95 (limp).

THE BUNGALOW: The Production of a Global Culture by A. D. King. 20 × 25 cm, xii and 310 pages. Routledge & Kegan Paul: London 1984 (ISBN 0 7100 9538 4) $A62.50 (cloth).

THE WEST EUROPEAN CITY: A Social Geography by P. White. 15 × 23 cm, xviii and 269 pages. Longman: London 1984 (ISBN 0 582 30047 9) $A22.95 (limp).

THE SHAPING OF AMERICA: A Geographical Perspective on 500 years of History. Volume 1. Atlantic America, 1492–1800 by D. W. Meinig. 18 × 25 cm, xii and 500 pages. Yale University Press: New Haven 1986 (ISBN 0 300 03548 9) $US35.00 (cloth).

CANBERRA: MYTHS AND MODELS. Forces at Work in the Formation of the Australian Capital by K. F. Fischer. 21 × 30 cm, 166 pages. Institute of Asian Studies: Hamburg 1984 (ISBN 3 88910 009 0).

THE GEOGRAPHY OF PEACE AND WAR edited by D. Pepper and A. Jenkins. 15 × 23 cm, vi and 222 pages. Basil Blackwell: Oxford 1985 (ISBN 0 631 13559 6) $A75.00 (cloth); (ISBN 0 631 14069 7) $A23.95 (limp).

POLITICAL GEOGRAPHY: World‐economy, Nation‐state and Locality by P. J. Taylor. 15 × 23 cm, × and 238 pages. Longman: London 1985 (ISBN 0 582 30088 6) $A24.95 (limp).

THE INDUSTRIAL GEOGRAPHY OF CANADA by A. Blackbourn and R. G. Putnam 14 × 22 cm, 201 pages. Croom Helm: London 1984 (ISBN 0 7099 0622 6) $A42.50 (cloth).

THE FOODMAKERS by S. Sargent. 13 × 20 cm, 296 pages. Penguin: Ringwood 1985 (ISBN 0 14 007359 0) $A8.95 (limp).

LIMITS TO PREDICTION edited by R. B. McKern and G. C. Lowenthal. 13 × 19 cm, xiii and 163 pages. Australian Professional Publications: Sydney 1985 (ISBN 0 949416 029) $A14.95 (limp).

THE KANGAROO KEEPERS edited by H. J. Lavery. 18 × 25 cm, xxvi and 211 pages. University of Queensland Press: St Lucia 1985 (ISBN 0 7022 1875 8).

PRACTICAL ECOLOGY by D. D. Gilbertson, M. Kent and F. B. Pyatt. 15 × 23 cm, 320 pages, Hutchinson: London 1985 (ISBN 0 09 162651 X) £8.95.

BASIC BIOGEOGRAPHY (Second edition) by N. Pears. 15 × 24 cm, × and 358 pages. Longman: London 1985 (ISBN 0 582 30120 3) $A24.95 (limp).

ENVIRONMENTAL CHANGE (Second edition) by A. Goudie. 23 × 15 cm, xi and 258 pages. Oxford University Press: Oxford 1983 (ISBN 0 19 874135 9) A16.00 (limp).

MEGA‐GEOMORPHOLOGY edited by R. Gardner and H. Scoging. 16 × 24 cm, xiii and 240 pages. Oxford University Press: Oxford (ISBN 0 19 823244 6) $A48.00.

GRANITE LANDFORMS by C. R. Twidale. 25 × 17 cm, xxiii and 372 pages. Elsevier: Amsterdam 1982 (ISBN 0 444 42116 5) $A148.25.  相似文献   

IGU commission health and development UGI commission sante et developpement In conjunction with medical geography specialty groups of the AAG,CAG, and IBG     

O. Ransome-Kuti 《GeoJournal》1991,25(4):434-436

The International Geographical Union Reports

IGU commission health and development UGI commission sante et developpement In conjunction with medical geography specialty groups of the AAG, CAG, and IBG International medical geography symposium  相似文献