Godzilla from a Zoological Perspective     

Per Christiansen 《Mathematical Geology》2000,32(2):231-245

The 1998 TriStar movie Godzilla proved to be a major blockbuster, although not the financial success that was initially anticipated and movie critics have been rather unforgiving. Apart from a radically different external morphology compared to the classic Japanese movie monster, the new Godzilla character apparently was made different from the old version on a number of key points to make him more biologically probable. However, calculations show that his limbs and limb muscles must have been severely undersized to move his huge bulk around at even a leisurely pace, and most other biological problems with the old Godzilla, e.g., growth rates and reptilian physiology at such a massive size, have remained unaltered. The old Godzilla was actually the more plausible from a biomechanical point of view.  相似文献   

Sputtering in the outflows of cool stars     

Carl Covatto  Per A. Aannestad 《Monthly notices of the Royal Astronomical Society》2000,318(1):67-72

Radiation pressure acts to accelerate dust grains and, by transfer of momentum through collisions with the gas, drives the outflows of late-type stars. Some of these dust–gas collisions may be energetic enough to remove atoms from the dust grains. From an assumed initial size distribution for the dust grains, the method of Krüger et al. is used to study the evolution of a sample of spherical amorphous carbon grains under conditions typical of a late-type star. The size distribution of dust grains is presented for various sets of model parameters. One set of models assumes an initial Mathis, Rumpl & Nordsieck (MRN) distribution for the dust grains. The high-luminosity ( L ∗), high-effective temperature ( T _eff) set of parameters has a terminal velocity ( v _term) that is near, but above , the upper limit of observed outflow velocities for carbon stars (∼30 km s⁻¹ for the assumed ̇ of 5×10⁻⁶ M_⊙ yr⁻¹). The low L ∗, T _eff model has a v _term that lies near, but below , the upper limit of observed velocities. A significant amount of sputtering occurs in the high L ∗, T _eff model with ∼40 per cent of the grain mass sputtered. About ∼1 per cent of the dust mass is sputtered in the low L ∗, T _eff. Another set of models assumes that the dust forms with a log-normal distribution. Here, v _term is nearly the same for the high L ∗, T _eff model as for the low L ∗, T _eff model. This is a result of the large amount of dust mass loss (∼75 per cent) by sputtering in the high L ∗, T _eff model.  相似文献   

Simulation of nonlinear wave run-up with a high-order Boussinesq model   总被引：2，自引：0，他引：2  

David R. Fuhrman  Per A. Madsen 《Coastal Engineering》2008

This paper considers the numerical simulation of nonlinear wave run-up within a highly accurate Boussinesq-type model. Moving wet–dry boundary algorithms based on so-called extrapolating boundary techniques are utilized, and a new variant of this approach is proposed in two horizontal dimensions. As validation, computed results involving the nonlinear run-up of periodic as well as transient waves on a sloping beach are considered in a single horizontal dimension, demonstrating excellent agreement with analytical solutions for both the free surface and horizontal velocity. In two horizontal dimensions cases involving long wave resonance in a parabolic basin, solitary wave evolution in a triangular channel, and solitary wave run-up on a circular conical island are considered. In each case the computed results compare well against available analytical solutions or experimental measurements. The ability to accurately simulate a moving wet–dry boundary is of considerable practical importance within coastal engineering, and the extension described in this work significantly improves the nearshore versatility of the present high-order Boussinesq approach.  相似文献   

Velocity potential formulations of highly accurate Boussinesq-type models     

Harry B. Bingham  Per A. Madsen  David R. Fuhrman 《Coastal Engineering》2009

The highly accurate Boussinesq-type equations of Madsen et al. (Madsen, P.A., Bingham, H.B., Schäffer, H.A., 2003. Boussinesq-type formulations for fully nonlinear and extremely dispersive water waves: Derivation and analysis. Proc. R. Soc. Lond. A 459, 1075–1104; Madsen, P.A., Fuhrman, D.R., Wang, B., 2006. A Boussinesq-type method for fully nonlinear waves interacting with a rapidly varying bathymetry. Coast. Eng. 53, 487–504); Jamois et al. (Jamois, E., Fuhrman, D.R., Bingham, H.B., Molin, B., 2006. Wave-structure interactions and nonlinear wave processes on the weather side of reflective structures. Coast. Eng. 53, 929–945) are re-derived in a more general framework which establishes the correct relationship between the model in a velocity formulation and a velocity potential formulation. Although most work with this model has used the velocity formulation, the potential formulation is of interest because it reduces the computational effort by approximately a factor of two and facilitates a coupling to other potential flow solvers. A new shoaling enhancement operator is introduced to derive new models (in both formulations) with a velocity profile which is always consistent with the kinematic bottom boundary condition. The true behaviour of the velocity potential formulation with respect to linear shoaling is given for the first time, correcting errors made by Jamois et al. (Jamois, E., Fuhrman, D.R., Bingham, H.B., Molin, B., 2006. Wave-structure interactions and nonlinear wave processes on the weather side of reflective structures. Coast. Eng. 53, 929–945). An exact infinite series solution for the potential is obtained via a Taylor expansion about an arbitrary vertical position z = zˆ. For practical implementation however, the solution is expanded based on a slow variation of zˆ and terms are retained to first-order. With shoaling enhancement, the new models obtain a comparable accuracy in linear shoaling to the original velocity formulation. General consistency relations are also derived which are convenient for verifying that the differential operators satisfy a potential flow and/or conserve mass up to the order of truncation of the model. The performance of the new formulation is validated using computations of linear and nonlinear shoaling problems. The behaviour on a rapidly varying bathymetry is also checked using linear wave reflection from a shelf and Bragg scattering from an undulating bottom. Although the new models perform equally well for Bragg scattering they fail earlier than the existing model for reflection/transmission problems in very deep water.  相似文献   

Tsunami generation,propagation, and run-up with a high-order Boussinesq model   总被引：1，自引：0，他引：1  

David R. Fuhrman  Per A. Madsen 《Coastal Engineering》2009

In this work we extend a high-order Boussinesq-type (finite difference) model, capable of simulating waves out to wavenumber times depth kh < 25, to include a moving sea-bed, for the simulation of earthquake- and landslide-induced tsunamis. The extension is straight forward, requiring only an additional term within the kinematic bottom condition. As first test cases we simulate linear and nonlinear surface waves generated from both positive and negative impulsive bottom movements. The computed results compare well against earlier theoretical, numerical, and experimental values. Additionally, we show that the long-time (fully nonlinear) evolution of waves resulting from an upthrusted bottom can eventually result in true solitary waves, consistent with theoretical predictions. It is stressed, however, that the nonlinearity used far exceeds that typical of geophysical tsunamis in the open ocean. The Boussinesq-type model is then used to simulate numerous tsunami-type events generated from submerged landslides, in both one and two horizontal dimensions. The results again compare well against previous experiments and/or numerical simulations. The new extension compliments recently developed run-up capabilities within this approach, and as demonstrated, the model can therefore treat tsunami events from their initial generation, through their later propagation, and final run-up phases. The developed model is shown to maintain reasonable computational efficiency, and is therefore attractive for the simulation of such events, especially in cases where dispersion is important.  相似文献   

Mangrove expansion and rainfall patterns in Moreton Bay, Southeast Queensland, Australia     

L. Eslami-Andargoli  Per Dale  N. Sipe  J. Chaseling 《Estuarine, Coastal and Shelf Science》2009,85(2):292-298

Changes in rainfall pattern have been suggested as a mechanism for the landward incursion of mangrove into salt marsh. The aim of the research was to assess the relationship between rainfall patterns and the spatial distribution of mangrove forests at study sites in Moreton Bay, Southeast Queensland, Australia, over a 32-year period from 1972 to 2004. To identify periods of relatively consistent rainfall patterns points at which rainfall patterns changed (change-points) were identified using the non-parametric Pettitt–Mann–Whitney-Statistic and the cumulative sum technique. The change-points were then used to define the temporal periods over which changes to mangrove area were assessed. Both mangrove and salt marsh area were measured by digitizing aerial photographs acquired in 1972, 1990 (the year with the most significant change-point), and 2004. The rates of change in mangrove area pre-1990 (a wetter period) and post-1990 (a drier period) were estimated. A significant positive relationship was demonstrated between rainfall variables and landward mangrove expansion, but not for seaward expansion. We concluded that rainfall variability is one of the principal factors influencing the rate of upslope encroachment of mangrove. However, the rate of expansion may vary from site to site due to site-specific geomorphological and hydrological characteristics and the level of disturbance in the catchment.  相似文献   

Circulation on the north central Chukchi Sea shelf   总被引：8，自引：0，他引：8  

Thomas Weingartner  Knut Aagaard  Rebecca Woodgate  Seth Danielson  Yasunori Sasaki  Donald Cavalieri 《Deep Sea Research Part II: Topical Studies in Oceanography》2005,52(24-26):3150

Mooring and shipboard data collected between 1992 and 1995 delineate the circulation over the north central Chukchi shelf. Previous studies indicated that Pacific waters crossed the Chukchi shelf through Herald Valley (in the west) and Barrow Canyon (in the east). We find a third branch (through the Central Channel) onto the outer shelf. The Central Channel transport varies seasonally in phase with Bering Strait transport, and is 0.2 Sv on average, although some of this might include water entrained from the outflow through Herald Valley. A portion of the Central Channel outflow moves eastward and converges with the Alaskan Coastal Current at the head of Barrow Canyon. The remainder appears to continue northeastward over the central outer shelf toward the shelfbreak, joined by outflow from Herald Valley. The mean flow opposes the prevailing winds and is primarily forced by the sea-level slope between the Pacific and Arctic oceans. Current variations are mainly wind forced, but baroclinic forcing, associated with upstream dense-water formation in coastal polynyas might occasionally be important.Winter water-mass modification depends crucially on the fall and winter winds, which control seasonal ice development. An extensive fall ice cover delays cooling, limits new ice formation, and results in little salinization. In such years, Bering shelf waters cross the Chukchi shelf with little modification. In contrast, extensive open water in fall leads to early and rapid cooling, and if accompanied by vigorous ice production within coastal polynyas, results in the production of high-salinity (>33) shelf waters. Such interannual variability likely affects slope processes and the transport of Pacific waters into the Arctic Ocean interior.  相似文献   

Sediment-chemistry response to land-use change and pollutant loading in a hypertrophic lake, southern Sweden   总被引：3，自引：0，他引：3  

Siv Olsson  Joachim Regnéll  Anders Persson  Per Sandgren 《Journal of Paleolimnology》1997,17(3):275-294

Responses to recent land-use changes and pollutant loading in the sediment of a hypertrophic lake in southern Sweden were studied by comparison of geochemical, pollen and magnetic records with historical land-use data. A chronology was constructed for the last two centuries by correlating changes in the pollen diagram to major events in the land-use history. Sediment accumulation was low (mean c. 0.2 g cm^-2 yr^-1) prior to 1800 AD, when less than 25% of the catchment was arable land. Reorganization of the agrarian system during the 19th century increased the annually tilled area by 300%, which accelerated soil erosion and substantially increased the accumulation of allochtonous matter in the lake. Since the turn of the century 90% of the catchment has been ploughed every year. The deposition of clastic matter in the lake has, however, decreased due to a gradual rerouting of the drainage system, which has reduced the effective catchment area by c. 85%.Authigenic vivianite (Fe3(PO4)2.8H2O) is a major P phase in the preindustrial non-sulphidic sediments, which suggests that the sediments at that time served as a fairly efficient sink for P. The arable expansion, increased manuring and, eventually, the introduction of artificial fertilizers during the 19th century led to a massive influx of nutrients, which elevated primary production in the lake. Subsequent development of bottom water anoxia around 1900, in combination with an additional pollutant burden of sulphate within the lake basin, led to major alterations of the biogeochemical cycles. The most critical change in the post-1900 sediments involved the cycling of Fe and P. The linkage between the lacustrine P and Fe cycles can explain that FeS formation was paralleled by a release of P from the sedimentary pool. This supply of P to the lake basin must have supplemented the nutrient supply by modern agriculture and contributed to recent hypertrophication. The bacterial sulphate reduction also affected the generation of alkalinity which supported a significant calcite precipitation in the post-1900 sediments.S is enriched 10-fold in the post-1900 sediments compared to preindustrial values. Along with the rise in S, soot particles derived from fossil fuel combustion appear in the sediments for the first time. Therefore, Bussj¨osj¨on is thought to be a good example of how a well-buffered, highly productive lake may respond to the pollution by sulphur from acid rain.  相似文献   

Water-Well Siting in Hard-Rock Areas: Identifying Promising Targets Using a Probabilistic Approach     

Per Sander 《Hydrogeology Journal》1997,5(3):32-43

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Late Holocene tephrochronology of the northern Antarctic Peninsula     

Svante Bjrck  Per Sandgren  Rolf Zale 《Quaternary Research》1991,36(3)

Andesitic and basaltic andesitic tephra layers are abundant in Holocene deposits from the Antarctic Peninsula. Visually discernible tephra horizons occur in three lakes on Livingston Island. Tephra in two other lakes and in a moss bank on Elephant Island, with very low ash concentrations, were detected magnetically. Deception Island is the most likely volcanic source for the tephra. With direct ¹⁴C dating, age/depth curves, and cross-correlations at least 14 tephra horizons dating to between ca. 4700 and 250 yr B.P. were identified and now form the basis for a preliminary regional tephrochronology that will be a valuable dating tool for investigating the Holocene climatic history of Antarctica.  相似文献