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11.
Johannes Georgi 《Ocean Dynamics》1958,11(6):225-239
Zusammenfassung Das soeben beendete dritte Internationale Geophysikalische Jahr, bisheriger Höhepunkt in der Erforschung der uns zugänglichen Hydro- und Atmosphäre der Erde, führt notwendigerweise zu der Frage nach der Vorgeschichte unserer heutigen geophysikalischen Erkenntnisse und Arbeitsmethoden. Als repräsentativ für die erste Hälfte des 19. Jahrhunderts dürfen wir den englischen Forscher Sir Edward Sabine ansehen, der als erster moderner All-round-Geophysiker gravimetrisch in den Tropen und in der Arktis tätig war, besonders hochgeschätzt von A. v. Humboldt, dessen erdmagnetisches Werk er ausbaute; auch durch wertvolle ozeanographische und meteorologische Untersuchungen rühmlich bekannt.
Edward Sabine, a great geophysicist of the nineteenth century
Summary The past third International Geophysical Year, up to now culminating point in the research for the hydrosphere and the atmosphere of the earth, makes us, necessarily, desirous to learn something about the early development of to-day's geophysical knowledge and working methods. As representative of the first half of the nineteenth century we may regard the English explorer and scientist Sir Edward Sabine, who as the first all-round geophysicist in the modern sense of the word carried out gravimetric measurements in the tropics and in the arctic regions. Alexander von Humboldt whose geomagnetic work he has been developing, held him in high esteem; besides, he is famous for his research work in the oceanographic and meteorological fields.
Edward Sabine, grand géophysicien au dix-neuvième siècle
Résumé La troisième Année géophysique internationale écoulée, jusqu'ici point culminant des recherches sur l'hydrosphère et l'atmosphère de la terre, fait nécessairement naître en nous le désir d'étendre nos connaissances du développement primaire de la science et des méthodes de travail de la géophysique actuelle. Nous sommes tenus de considérer l'explorateur et le savant anglais Sir Edward Sabine comme le représentant de la première moitié du dix-neuvième siècle. Il fut le premier à effectuer des mesures gravimétriques dans les tropiques et dans les zones arctiques en qualité de géophysicien universel au sens moderne de ce mot. Il jouissait de l'estime profond d'Alexander von Humboldt, dont il a développé l'uvre géomagnétique. De plus, Sabine est fameux pour ses études dans les domaines de l'océanographie et de la météorologie.相似文献
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We carried out 16 collision experiments in the drop tower in Bremen, Germany. Dust projectiles and solid projectiles of several mm in size impacted a dust target 5 cm in depth and width at velocities between 3.5 and 21.5 m/s. For solid impactors we found significant mass loss on the front (impact) side of the target. Mass loss depended on the impact velocity and projectile type (solid sphere or dust) and was up to 35 times the projectile mass for targets of the lowest tensile strength. Typical fragment velocities on the front side of the target ranged from 3 to 12 cm/s. The ejecta velocity was independent of the impact velocity but it increased with projectile mass. On the back side of the target (opposite to the impact side) mass was ejected from the target above a certain threshold impact velocity. Ejection velocity on the back side increased with impact velocity and is larger for solid projectiles than for dust projectiles. In one case a slightly stronger target gained mass in a slow dust-dust collision. We verified that collisions of dust projectiles with compact, very strong dust targets lead to a more massive target accreting part of the projectile. Applied to planetesimal formation, the experiments suggest that the maximum possible ejecta velocity from a body of several cm in size after a collision is small. Ejecta were slow enough that they were reaccreted by means of gas flow if large pores were part of the body's morphology. While very weak bodies cannot grow in the primary collision at the given velocities, this can lead to growth by secondary collisions. Slight compression, which could result from preceding collisions, might lead to immediate growth of a body in slow collisions by adding projectile mass. 相似文献
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Dr. J. Georgi 《Pure and Applied Geophysics》1951,20(1):62-66
Zusammenfassung Aus einer einfachen Zeichnung ergibt sich die Grösse und optimale Neigung eines Schirmes zum Abblenden der Sonne von einem Pyranometer.
Summary From a drawing one finds the size and dip of a screen to protect a pyranometer against the sun.相似文献
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Dr. J. Georgi 《Pure and Applied Geophysics》1951,20(1):86-86
Ohne Zusammenfassung 相似文献
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Coastal and bank erosion along the St. Lawrence River Waterway in Quebec, Canada, represents a hazard to local communities
living along the river banks, as well as to the local fauna habitat. The purpose of this study is to assess the potential
impact of the waves generated by long containerships on riverbank erosion and recession at critical sites along the St. Lawrence
River Waterway, which have already experienced significant damage. A field study was carried out to investigate the ship-generated
hydrodynamics and the various driving mechanisms of the erosion process induced by ship waves. The field measurements provided
an assessment of the influence of the length of large vessels by comparing the characteristics of the hydrodynamics fields
induced by the passage of two containerships of different lengths. The potential for bank erosion and recession is assessed
in terms of the wake erosive energy incident to the shoreline. The field data are compared against analytical results predicted
by an empirical model, as well as against a ship-generated hydrodynamics model. Several numerical simulations for quantifying
the ship’s drawdown and its effects are also presented. 相似文献
19.
Georgi Pavlovski Michael D. Smith Mordecai–Mark Mac Low Alexander Rosen 《Astrophysics and Space Science》2004,292(1-4):69-75
Here we present results from simulations of turbulence in star forming environments obtained by coupling three-dimensional hydrodynamical models with appropriate chemical processes. We investigate regimes of decaying high-speed molecular turbulence. Here we analyse PDFs of density for the volume, mass, molecular mass and the energy distribution over the range of scales. We compare our results to those previously obtained for isothermal turbulence and suggest possible explanations. 相似文献
20.
We study central collisions between millimeter-sized dust projectiles and centimeter-sized dust targets in impact experiments. Target and projectile are dust aggregates consisting of micrometer-sized SiO2 particles. Collision velocities range up to 25 m/s. The general outcome of a collision strongly depends on the impact velocity. For collisions below 13 m/s rebound and a small degree of fragmentation occur. However, at higher collision velocities up to 25 m/s approximately 50% of the mass of the projectile rigidly sticks to the target after the collision. Thus, net growth of a body is possible in high speed collisions. This supports the idea that planetesimal formation via collisional growth is a viable mechanism at higher impact velocities. Within our set of parameters the experiments even suggest that higher impact velocities might be preferable for growth in collisions between dusty bodies. For the highest impact velocities most of the ejecta is within small dust aggregates about 500 μm in size. In detail the size distribution of ejected dust aggregates is flat for very small particles smaller than 500 μm and follows a power law for larger ejected dust aggregates with a power of −5.6±0.2. There is a sharp upper cut-off at about 1 mm in size with only a few particles being slightly larger. The ejection angle is smaller than 3° with respect to the target surface. These fast ejecta move with 40±10% of the impact velocity. 相似文献