Comments on the paper by G.W. Timco titled “On the structural integrity of dolos units under dynamic loading conditions”     

Hans F. Burcharth 《Coastal Engineering》1983,7(1):97-101

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Asteroids in cometary orbits     

Gerhard Hahn  Hans Rickman 《Icarus》1985,61(3):417-442

Orbital integrations are presented for a total of 14 asteroids with perihelia inside 1.7 AU and with aphelion distances in excess of 4 AU, 10 of which were discovered in 1979–1984. The integrations were normally extended over approximately ±1000 years in a three-body model (Sun-Jupiter-asteroid). The effects of uncertainties of starting orbits are not treated in this work, and as far as the real asteroids are concerned, the results should be regarded mostly as preliminary indications. A wide variety of orbital evolutions is found, and some of them evidently belong to the cometary, chaotic type. Three such cases are identified with certainty (1983 SA, 1983 XF, and 1984 BC) and two or three more with various degrees of likelihood. An asteroidal motion is found for the well-observed object 1979 VA. A stable libration around the $\text{2}\text{1}$ resonance is found for 1981 FD, which obviously adds to the Griqua group. A long-lasting libration around the $\text{5}\text{3}$ resonance performed by 1982 YA is probably unstable. Temporary librations are also found for 1983 SA ($\text{4}\text{3}$ resonance) and 1983 XF ($\text{2}\text{1}$ resonance), but these objects appear to transit into irregular motions with close approaches to Jupiter (less than 0.01 AU for 1983 XF). A very rapid large-amplitude ω libration around 90° is found in the future motion of 1983 VA. If this will indeed occur for the real asteroid, the object will oscillate with a period of only 750 years between a main-belt orbit of very high inclination and a low-inclination Apollo-type orbit.  相似文献   

Determination Of The Surface Drag Coefficient   总被引：1，自引：0，他引：1  

L. Mahrt  Dean Vickers  Jielun Sun  Niels Otto Jensen  Hans Jørgensen  Eric Pardyjak  Harindra Fernando 《Boundary-Layer Meteorology》2001,99(2):249-276

This study examines the dependence of the surface drag coefficienton stability, wind speed, mesoscale modulation of the turbulent flux and method of calculation of the drag coefficient. Data sets over grassland, sparse grass, heather and two forest sites are analyzed. For significantly unstable conditions, the drag coefficient does not depend systematically on z/L but decreases with wind speed for fixed intervals of z/L, where L is the Obukhov length. Even though the drag coefficient for weak wind conditions is sensitive to the exact method of calculation and choice of averaging time, the decrease of the drag coefficient with wind speed occurs for all of the calculation methods. A classification of flux calculation methods is constructed, which unifies the most common previous approaches.The roughness length corresponding to the usual Monin–Obukhovstability functions decreases with increasing wind speed. This dependence on wind speed cannot be eliminated by adjusting the stability functions. If physical, the decrease of the roughness length with increasing wind speed might be due to the decreasing role of viscous effectsand streamlining of the vegetation, although these effects cannot be isolated from existing atmospheric data.For weak winds, both the mean flow and the stress vector often meander significantly in response to mesoscale motions. The relationship between meandering of the stress and wind vectors is examined. For weak winds, the drag coefficient can be sensitive to the method of calculation, partly due to meandering of the stress vector.  相似文献   

Population Belongs on the Johannesburg Agenda     

Wolfgang Lutz  Mahendra Shah  Richard E. Bilsborrow  John Bon-gaarts  Partha DasGupta  Barbara Entwisle  Günther Fischer  Brigida Garcia  Daniel J. Hogan  Arne Jernelöv  Zhenghua Jiang  Robert W. Kates  Sanjaya Lall  F. Landis MacKellar  P.K. Makinwa-Adebusoye  Anthony J. McMichael  Vinod Mishra  Norman Myers  Nebojsa Nakicenovic  Sten Nilsson  Brian C. O'Neill  Xizhe Peng  Harriet B. Presser  Nafis Sadik  Warren C. Sanderson  Gita Sen  Barbara Torrey  Dirk van de Kaa  Hans J.A. van Ginkel  Brenda Yeoh  Huda Zurayk 《Global Change & Human Health》2002,3(1):33-35

The forthcoming World Summit on Sustainable Development (WSSD) in Johannesburg (August 26-September 4, 2002) has been set by the United Nations to consider strategies toward sustainable development in all its dimensions. Hence, its mandate is broader than that of the Rio 1992 United Nations Conference on Environment and Development (UNCED). Population issues have so far been discussed in a separate series of World Population Conferences (Bucharest 1974, Mexico City 1984, Cairo 1994). With no new World Population Conference scheduled for 2004 and Johannesburg having a mandate that is stated to explicitly include social and economic aspects, population as a key component of sustainable development should figure prominently on the Johannesburg agenda. Yet, after the third of four preparatory meetings for Johannesburg (which ended in New York on April 5th), consideration of population is completely absent. The reasons for this are not entirely clear. We assume that they have to do with the fear of entering into political controversies over abortion. We are concerned that, despite its broader mandate, in most countries inputs to Johannesburg are being prepared mainly by environment ministries who have little experience in dealing with population questions. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Modelling of convective turbulence with a two-equation k-ɛ turbulence closure scheme     

Adolf Stips  Hans Burchard  Karsten Bolding  Walter Eifler 《Ocean Dynamics》2002,52(4):153-168

 In this study we aim at comparing turbulence parameters from field observations and model simulations under convective conditions. The comparison is focused on the depth dependence and temporal dynamics of viscous and diffusive dissipation rates ɛ and χ. The near-surface observations were obtained by using a quasi-free-rising profiler which measured small-scale shear and temperature fluctuations to within the vicinity of the water surface. Convective conditions during the experiment are characterized by low wind speeds (between 0 and 4 m s⁻¹) and a typical heat loss of about 150 Wm⁻². We applied a state-of-the-art two-equation k-ɛ turbulence model with an algebraic second-moment closure scheme. The qualitative agreement of the turbulence quantities resulting from observations and simulations is rather good. The temporal dynamics of the temperature field is simulated correctly, whereas in the spatial dynamics some deficiencies of the model due to its local character can be seen. It is concluded that such models realistically reproduce convective turbulence and therefore represent a reasonable compromise between complexity and simplicity, so that they can be used with acceptable costs in large-scale models. Received: 31 October 2001 / Accepted: 20 September 2002 Acknowledgements The whole project was intitiated by Peter Schlittenhardt, who strongly supported the development of the observational technique in uprising mode and encouraged us to undertake the experiment in Lake Maggiore; for which we will thank him most. Performing the measurement campaign was only possible with the help of several colleagues from the Marine Environment Unit at the Joint Research Centre. Thanks to all of them, but especially to Dirk van d. Linde, Ulisse Devisioni, Bjarke Rasmussen and Hartmut Prandke. The Istituto Italiano di Idrobiologia, Verbania Pallanza, provided the boat Livia for the installation and removal of the measurement system; thanks to the master Stefano Maurizio for his engagement. Ute Tschesche provided the data evaluation and presentation software and Judith Challis helped to polish our English. Part of the study was␣supported by the PROVESS project (MAS3-CT97-0159); thanks to our sponsors at the European Commission. We are further grateful to two anonymous referees for their constructive comments. Responsible Editor: Charitha Pattiaratchi  相似文献   

Daily Air Temperature and Pressure Series for Uppsala (1722–1998)     

Hans Bergström  Anders Moberg 《Climatic change》2002,53(1-3):213-252

Daily meteorological observations have been made in Uppsala, Sweden, since 1722, and complete series of air temperature and sea level air pressure have been reconstructed and homogenised for the period 1722–1998. The reconstruction work was based on the hand written registers and printed monthly bulletins before 1985, after which data was directly stored on computers. Methods to determine daily average temperatures from the typically available 2–3 observations per day were developed. Thesemethods take into account observation times and cloud amount. Pressure reductions back to 1840 involved only routine calculations, while earlier pressure data needed major homogenisations. All data were searched for errors by comparisons with previously determined monthly averages and by different plotting techniques, mainly comparing with independently reconstructed data from Stockholm, 65 km south of Uppsala. This comparison also shows that the quality of the data is generally good, although the reliability is lower before the mid-19th century. Results are given illustrating changes in the daily average temperature and pressure climate on a200–250 year time scale.  相似文献   

Deltas in the Abisko area, northern Sweden: the Abiskojokka delta in lake Torneträsk     

Hans Andrén  Christer Jonasson  & Johan Ottosson 《Geografiska Annaler: Series A, Physical Geography》2002,84(3-4):151-156

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Book review: The Territorial Factor; Ploitical Geography in a Globalising World     

Gertjan Dijkink  Hans Knippenberg 《GeoJournal》2002,57(4):345-346

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The effect of fluorine, boron and excess sodium on the critical curve in the albite–H2O system     

John R. Sowerby  Hans Keppler 《Contributions to Mineralogy and Petrology》2002,143(1):32-37

Experiments to define the critical curve for a series of silicate melts in equilibrium with a hydrous fluid were carried out in a hydrothermal diamond anvil cell. Silicate compositions studied were albite with several wt% excess Na₂O, B₂O₃ and F₂O_-1. Complete miscibility between melt and water was observed at lower pressure and temperature conditions compared to pure albite for all compositions. For albite + excess Na₂O, the critical curve had been lowered by 143 and 247 °C at 10 kbar for 5 and 10 wt% excess Na. For albite +5 and 10 wt% F, the difference at 10 kbar was 147 and 246 °C respectively, and for albite +5 and 10 wt% B differences of 168 and 262 °C were found. These results are likely to be additive, with the presence of more than one of the components depressing the critical curve to even lower temperatures and pressures. The results suggest that in complex pegmatitic systems, complete miscibility between melt and fluid may be important in the final stages of crystallisation. The unusual properties of fluid phases under conditions close to the critical curve in a silicate melt-water system may be essential for the enrichment of trace elements in pegmatites as well as for the formation of typical pegmatite textures.  相似文献   

Deltas in the Abisko area, northern Sweden: the Abiskojokka delta in lake Torneträsk     

Hans Andrén  Christer Jonasson  & Johan Ottosson 《Geografiska Annaler: Series A, Physical Geography》2002,84(3&4):151-156

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