Reconstruction from three orthographic views     

Urban Herbert 《Journal of Geodesy》1996,70(5):245-249

Summary As Ullman (1979) showed, an object can be reconstructed uniquely from three orthographic views, if at least four homologous tripels of points are known. If only three homologous tripels of points are observed, the reconstruction problem has a finite number of solutions (cf. Huang and Lee (1989)). In this article the 3-point-problem is reduced to a quadratic problem: If the squares of the sides of the considered triangles are interpreted as coordinates in a three-dimensional parameter space, the reconstruction problem is equivalent to the determination of the intersection of three parallelly shifted cones subject to certain constraints.  相似文献   

Astronomical calibration of the Matuyama-Brunhes boundary: Consequences for magnetic remanence acquisition in marine carbonates and the Asian loess sequences   总被引：4，自引：0，他引：4  

L. Tauxe  T. Herbert  N.J. Shackleton  Y.S. Kok 《Earth and Planetary Science Letters》1996,140(1-4):133-146

We have compiled 19 records from marine carbonate cores in which the Matuyama-Brunhes boundary (MBB) has been reasonably well constrained within the astronomically forced stratigraphic framework using oxygen isotopes. By correlation of the δ¹⁸O data to a timescale based on astronomical forcing, we estimate astronomical ages for each of the MBB horizons. In all but one record the MBB occurs within Stage 19.

Most magnetostratigraphic sections in Asian Loess place the MBB within a loess interval. Since loess deposition is presumed to be associated with glacial intervals, loess horizons should correspond to even-numbered oxygen isotope stages. A glacial age for the MBB is at odds with the results presented here, which firmly place the MBB within interglacial Stage 19. Inconsistency among the many loess sections and between the loess and the marine records suggests that the magnetic interpretation of loess sections may be more complicated than hitherto supposed.

The mean of the Stage 19 age estimates for the MBB is 777.9 ± 1.8 (N = 18). Inclusion of the single Stage 20 age results in a mean of 778.8 ± 2.5 (N = 19). The astronomical age estimate of the MBB compares favorably with an (unweighted) mean of 778.2 ± 3.5 (N = 10) from a compilation of ⁴⁰Ar/39^Ar results of transitional lava flows. Combining the two independent data sets yields a grand mean of 778.0 ± 1.7 (N = 28).

The new compilation shows virtually no trend in placement of the MBB within isotope Stage 19 as a function of sediment accumulation rate. We interpret this to mean that the average depth of remanence acquisition is within a few centimeters of the sediment-water interface.

Separating the cores into two geographic regions (an Indo-Pacific-Caribbean [IPC] Group and an Atlantic Group) results in a significant difference in the position of the mid-point of the reversal with respect to the astronomical time scale. The data presented here suggest a difference of several thousand years between the two regions. This observation could be caused by systematic differences between the two regions in sedimentation rate within the interval of interest, systematic differences in remanence acquisition, or by genuine differences in the timing of the directional changes between the two regions.  相似文献   

The Baltic Sea in 1996 — continuation of stagnation and decreasing phosphate concentrations     

Dr.  habil. Wolfgang Matthäus  Dr.  Prof. Dietwart Nehring  Dr.  habil. Hans Ulrich Lass  Dr. Günther Nausch  Dr. Klaus Nagel  Dr. Herbert Siegel 《Ocean Dynamics》1996,48(2):161-174

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Geodetic determination of crustal deformation across the Strait of Gibraltar     

W. Ian Reilly  Gabriele Fredrich  Günter W Hein  Herbert Landau  J. L. Almazán  J. L. Caturla 《Geophysical Journal International》1992,111(2):391-398

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Experimental and thermodynamic study of heterogeneous and homogeneous equilibria in the system NaAlSiO4-SiO2     

Tanja Waterwiese  Niranjan D. Chatterjee  Ivana Dierdorf  Jörg Göttlicher  Herbert Kroll 《Contributions to Mineralogy and Petrology》1995,121(1):61-73

Internally consistent thermodynamic datasets available at present call for a further improvement of the data for nepheline (Holland and Powell 1988; Berman 1991). Because nepheline is a common rock-forming mineral, an attempt has been made to improve on the present state of knowledge of its thermodynamic properties. To achieve that goal, two heterogeneous reactions involving nepheline, albite, jadeite and a-quartz in the system NaAlSiO₄-SiO₂ have been reversed bylong duration runs in the range 460 ≤ T(°C) ≤ 960 and 10 ≤ P(kbar) ≤ 22. Given sufficiently long run times, thealbite run products approach internal equilibrium with respect to their Al,Si order-disorder states. Using appropriate thermochemical, thermophysical, and volumetric data, Landau expansion for albite, and the relevant reaction reversals, a refined thermodynamic dataset (Δ_fH_i⁰ and S_i⁰) has been derived for nepheline, jadeite, a-quartz, albite, and monalbite. Our refined data agree very well with theircalorimetric counterparts, but have smaller uncertainties. The refined dataset for Δ_fH_i⁰ and S_i⁰, including their uncertainties and correlation, help generate the NaAlSiO₄-SiO₂ phase diagram including 2a confidence interval for eachP-T curve (Fig. 5). Editorial responsibility: W. Schreyer  相似文献   

An experimental study on the effects of phenocrysts on convection in magmas     

Takehiro Koyaguchi  Mark A. Hallworth  Herbert E. Huppert 《Journal of Volcanology and Geothermal Research》1993,55(1-2)

The effect of phenocrysts on convection in magma chambers is investigated experimentally using small heavy particles in convecting fluids. The particles are initially uniformly distributed in a fluid which is either heated from below or cooled from above. The system is allowed to evolve, and temperature and particle concentration profiles are measured as functions of time. When the concentration of particles is sufficiently small, convection is basically unaffected by their presence. When the concentration is above a critical value, however, the convective motion is considerably altered. The effect of particles on the subsequent fluid behaviour is different in the cases of heating from below and cooling from above. In the former case, there are strong convective motions confined to a sedimentary layer of decreasing thickness beneath a clear layer which displays rather weak convective motions. With time, the destabilizing increase of temperature in the lower layer overcomes the stabilizing contribution to the bulk density due to the particles and the layer overturns quite suddenly. In the situation of cooling from above, a critical condition separates a case of continual overturn from a case of no overturn at all, with the sedimentary layer falling unimpeded to the bottom. Theoretical analysis suggests that the critical value is determined primarily by the ratio of the contribution to the bulk density of the suspension due to particles to the change in fluid density due to the thermal effect. The size distribution of the particles can also modify the fluid behaviour. Applying our general results to geological situations, we suggest that the presence of relatively small concentrations of phenocrysts can critically influence the mode of convection in magmas.  相似文献   

Über einige Fortschritte der Sporen- uno Pollenforschung     

Prof. Dr. Herbert Straka 《International Journal of Earth Sciences》1962,51(2):517-530

Ohne ZusammenfassungProf.Gunnar Erdtman, Stockholm, danke ich für die freundliche Überlassung der meisten Abbildungsvorlagen.  相似文献   

Analysing Pumping Tests by Resistance Network Analogue     

Robin Herbert 《Ground water》1968,6(2):12-18

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Forstmeteorologische Untersuchungen an der Wald- und Baumgrenze in den Zentralalpen     

Herbert Aulitzky 《Theoretical and Applied Climatology》1953,4(3):294-310

Zusammenfassung Bei vergleichsweisen Registrierungen der Lufttemperatur und relativen Luftfeuchtigkeit, sowie bei Verdunstungseinzel-messungen, die im Bereiche der jetzigen (künstlichen) Wald- und Baumgrenze 10 km südwestlich von Innsbruck (Tirol) in Seehöhen von 1400 bis 1900 m in Bestand, Horst und Freiland durchgeführt wurden, ergaben sich deutliche Stationsunterschide. Trotz stärkerer Einstrahlung und höheren Windgeschwindigkeiten, wie sie die Höhenlage neben geringerer Bestockungsdichte bedingt, ergab sich im Bestandesinneren ein, gegenüber dem Freiland stark gemäßigtes Klima, das die Aushagerung des Bodens verhindert und vor allem der jungen Holzpflanze eine nicht zu übersehende Feuchtigkeitsreserve bietet. Bei extrem auftretenden Außeneinflüssen erfolgt allerdings eine raschere Angleichung an die Freilandsverhältnisse als in tieferen Lagen. Hoch- und Tieflagen unterscheiden sich demnach nur graduell und soweit, als es die lichtere Bestockung und größere Außenbeeinflussung der Hochlagen bedingen. Der Wirkungsgrad der Außeneinflüsse wurde auch von der Exposition bestimmt, die im Zusammenwirken mit der vorherrschenden Windrichtung das Auftreten der einzelnen Holzarten beeinflußte. Der stärkere Einfluß der Luftbewegung drückt sich auch im unsteten Momentancharakter der relativen Luftfeuchtigkeit aus.Der Einfluß der Vegetationsform auf die lokalen Kleinklimaverhältnisse ergab sich auch aus den Ergebnissen der Verdunstungsmessungen, die ein nach Holzart und Bestockungsform spezifisches Mosaikklima deutlich erkennen lie\en.

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Summary Distinctly perceptible differences between the stations in thicket and amount of timber as well as in open air resulted from comparing registrations of air temperature and relative humidity, and from measurements of evaporation which were made in range of the present (unnatural) timber line 10 km. south-west of Innsbruck (Tyrol) in altitudes of 1400–1900 m. (4600–6300 ft) above sea-level. In spite of the more intensive insolation and increased wind-velocity—corresponding to altitude and less density of wood—a very temperate climate in comparison with that of open field was evident within amount of timber, preventing impoverishment of soil and-first of all—offering a considerable reserve of moisture to the young tree. Extremely appearing external influences, however, effect a rapid assimilation to the conditions of open field likely to lower levels. The efficacy of the external influences also was fixed by the exposure which influences—together with the prevailing directions of wind—the occurences of the different species of timber. The greater effect of air-movement is also expressed by the unsteady momentary-character of the relative humidity.The influence of different plant communities upon the local climates followed from the results of evaporation measurements (evaporimeter Piche) which made recognizable a tesselated, mosaic-climate specifically to species and formation of timber, unless extreme external influences operated levelling.

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Résumé Des enregistrements comparatifs de la température de l'air et de l'humidité relative ainsi que des mesures d'évaporation effectués à la limite de l'atmosphère forestière ont mis en évidence de nettes différences entre les stations d'essais. Ces expériences ont été faites à 10 km. au sudouest d'Innsbruck (Tirol) dans les bois et la région non boisée, à une altitude de 1400 à 1900 m. Malgré l'insolation plus forte et les vitesses de vent plus grandes, dûes à l'altitude et à la densité plus faible de la forêt, on a constaté à l'intérieur du bois un climat très modéré par opposition à la région non boisée. Ce climat modéré s'oppose au desséchement du sol et assure aux jeunes pousses une humidité suffisante. Si les effets de la température sont extrêmes, l'adaptation aux conditions de la région non boisée est pourtant plus rapide qu'aux altitudes plus basses. Par conséquent les zones supérieures et inférieures ne se distinguent que graduellement, en fonction des forêts moins denses et des influences temporaires plus accusées. Le rôle du climat local est nettement déterminé par l'exposition qui, selon la direction dominante du vent, a une répercussion sur l'apparition des différentes essences de bois. La circulation active de l'air se traduit aussi par la variabilité instantaneé de l'humidité relative de l'air.Les mesures faites avec l'évaporimètre de Piche ont montré l'effet du bioclimat local sur la végétation. Ces travaux font nettement apparaître un climat «mozaïque» spécifique dépendant des différentes essences et de la densité de la population végétale.

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Mit 4 Textabbildungen.  相似文献   

Solar wind induction in Mercury: Constraints on the formation of a magnetosphere     

F. Herbert  M. Wiskerchen  C.P. Sonett  J.K. Chao 《Icarus》1976,28(4):489-500

The discovery of Mercury's magnetosphere by Mariner 10 was surprising since the conventional view of regenerative planetary dynamos had been that the spin requirement would likely have been in excess of the observed spin rate of Mercury. Also internal fluid motions were not expected to be sufficiently large. This paper explores the alternative model of the formation of Mercury's magnetosphere via electromagnetic induction forced by the solar wind. It is shown, however, that the constraints are so severe as to limit severely the applicability of such a model. Although induction is easily observed on the Moon, the modification of the magnetic boundary condition associated with a plasma magnetosphere on Mercury rules out its formation via induction except for interplanetary driving fields which are decreasing in amplitude. That model is explored but retains the difficulty that induced magnetospheres tend to be of small radial and temporal extent compared to that inferred by Ness et al. for Mercury.  相似文献