474 research outputs found
Population-Specific Vital Rate Contributions Influence Management of an Endangered Ungulate
To develop effective management strategies for the recovery of threatened and endangered species, it is critical to identify those vital rates (survival and reproductive parameters) responsible for poor population performance and those whose increase will most efficiently change a population\u27s trajectory. In actual application, however, approaches identifying key vital rates are often limited by inadequate demographic data, by unrealistic assumptions of asymptotic population dynamics, and of equal, infinitesimal changes in mean vital rates. We evaluated the consequences of these limitations in an analysis of vital rates most important in the dynamics of federally endangered Sierra Nevada bighorn sheep (Ovis canadensis sierrae). Based on data collected from 1980 to 2007, we estimated vital rates in three isolated populations, accounting for sampling error, variance, and covariance. We used analytical sensitivity analysis, life-stage simulation analysis, and a novel non-asymptotic simulation approach to (1) identify vital rates that should be targeted for subspecies recovery; (2) assess vital rate patterns of endangered bighorn sheep relative to other ungulate populations; (3) evaluate the performance of asymptotic vs. non-asymptotic models for meeting short-term management objectives; and (4) simulate management scenarios for boosting bighorn sheep population growth rates. We found wide spatial and temporal variation in bighorn sheep vital rates, causing rates to vary in their importance to different populations. As a result, Sierra Nevada bighorn sheep exhibited population-specific dynamics that did not follow theoretical expectations or those observed in other ungulates. Our study suggests that vital rate inferences from large, increasing, or healthy populations may not be applicable to those that are small, declining, or endangered. We also found that, while asymptotic approaches were generally applicable to bighorn sheep conservation planning, our non-asymptotic population models yielded unexpected results of importance to managers. Finally, extreme differences in the dynamics of individual bighorn sheep populations imply that effective management strategies for endangered species recovery may often need to be population-specific
Unsteady effects during resistance tests on a ship model in a towing tank
It is known that there are oscillations in the wave resistance during the constantvelocity phase of a towing-tank resistance test on a ship model. In this work, the unsteady thin-ship resistance theory has been applied to this case. The results have been compared with experiment data obtained using a towing carriage the velocity history of which can be programmed. It is demonstrated here that generally excellent correlation exists between the theory and the experiments. In particular, one can predict the influence of Froude number, rate of acceleration, and type of smoothing of the acceleration on the characteristics of the oscillations. These characteristics include the amplitude, rate of decay, frequency, and phasing of the oscillations in the curve of wave resistance versus time
Three-dimensional gravity-capillary solitary waves in water of finite depth and related problems
Dissipative Boussinesq System of Equations in the B\'enard-Marangoni Phenomenon
By using the long-wave approximation, a system of coupled evolution equations
for the bulk velocity and the surface perturbations of a B\'enard-Marangoni
system is obtained. It includes nonlinearity, dispersion and dissipation, and
it can be interpreted as a dissipative generalization of the usual Boussinesq
system of equations. As a particular case, a strictly dissipative version of
the Boussinesq system is obtained. Finnaly, some speculations are made on the
nature of the physical phenomena described by this system of equations.Comment: 15 Pages, REVTEX (Version 3.0), no figure
Processes controlling the geochemical composition of the South China Sea sediments during the last climatic cycle
Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Chemical Geology 257 (2008): 240-246, doi:10.1016/j.chemgeo.2008.10.002.Sediments of the upper 28.2 meters of Ocean Drilling Program (ODP) Site 1145 from
the northern South China Sea (SCS) were analyzed for their geochemical composition. Most
of the major and trace elements exhibit significant fluctuations at glacial-interglacial scales,
implying a close relation with regional and global climate change. Al-normalized elemental
ratios can be subdivided into three principal components (PC). PC1 (e.g., Ca/Al, Ba/Al, Sr/Al)
displays significant glacial-interglacial variation and is related to paleoproductivity in the
northern SCS. PC2 (e.g., K/Al, Mg/Al, Rb/Al) is associated with the degree of chemical
weathering in the source regions and shows little glacial-interglacial variation. PC3 (e.g.,
Ti/Al, Zr/Al) reflects the relative contribution of coarse- and fine-grained materials in the
terrigenous components of the SCS sediments, likely associated with changes in sea level and
monsoon-induced fluvial input. Spectral analyses indicate that paleoproductivity (i.e., Ba/Al)
in the South China Sea lags Hulu/Sanbao speleothem δ18O record (a indicator of annual
average meteoric precipitation) by 102° and Indian summer monsoon (multi-proxy stack) by
23° at the precession band, indicating a close relationship with the Indian summer monsoon.
However, the chemical weathering degree in the source area (PC2) is not sensitive to
monsoon-related changes at the precession band during the last climatic cycle.This study was supported by the NSFC to Y.B. Sun and the US NSF to D.W. Oppo (OCE 0502960) and S.C. Clemens (OCE 0352215)
Practical use of variational principles for modeling water waves
This paper describes a method for deriving approximate equations for
irrotational water waves. The method is based on a 'relaxed' variational
principle, i.e., on a Lagrangian involving as many variables as possible. This
formulation is particularly suitable for the construction of approximate water
wave models, since it allows more freedom while preserving the variational
structure. The advantages of this relaxed formulation are illustrated with
various examples in shallow and deep waters, as well as arbitrary depths. Using
subordinate constraints (e.g., irrotationality or free surface impermeability)
in various combinations, several model equations are derived, some being
well-known, other being new. The models obtained are studied analytically and
exact travelling wave solutions are constructed when possible.Comment: 30 pages, 1 figure, 62 references. Other author's papers can be
downloaded at http://www.denys-dutykh.com
Modeling water waves beyond perturbations
In this chapter, we illustrate the advantage of variational principles for
modeling water waves from an elementary practical viewpoint. The method is
based on a `relaxed' variational principle, i.e., on a Lagrangian involving as
many variables as possible, and imposing some suitable subordinate constraints.
This approach allows the construction of approximations without necessarily
relying on a small parameter. This is illustrated via simple examples, namely
the Serre equations in shallow water, a generalization of the Klein-Gordon
equation in deep water and how to unify these equations in arbitrary depth. The
chapter ends with a discussion and caution on how this approach should be used
in practice.Comment: 15 pages, 1 figure, 39 references. This document is a contributed
chapter to an upcoming volume to be published by Springer in Lecture Notes in
Physics Series. Other author's papers can be downloaded at
http://www.denys-dutykh.com
Static and dynamic response of a fluid-fluid interface to electric point and line charge
We consider the behaviour of a dielectric fluid-fluid interface in the
presence of a strong electric field from a point charge and line charge,
respectively, both statically and, in the latter case, dynamically. The fluid
surface is elevated above its undisturbed level until balance is reached
between the electromagnetic lifting force, gravity and surface tension. We
derive ordinary differential equations for the shape of the fluid-fluid
interface which are solved numerically with standard means, demonstrating how
the elevation depends on field strength and surface tension coefficient. In the
dynamic case of a moving line charge, the surface of an inviscid liquid-liquid
interface is left to oscillate behind the moving charge after it has been
lifted against the force of gravity. We show how the wavelength of the
oscillations depends on the relative strength of the forces of gravity and
inertia, whereas the amplitude of the oscillations is a nontrivial function of
the velocity at which the line charge moves.Comment: 19 pages, 6 figures version accepted for publication in Annals of
Physic
Solar forcing of Nile discharge and sapropel S1 formation in the early to middle Holocene eastern Mediterranean
Wave patterns generated by an axisymmetric obstacle in a two-layer flow
Gravity waves generated by a moving obstacle in a two-layer stratified fluid are investigated. The experimental configuration is three-dimensional with an axisymmetric obstacle which is towed in one of the two layers. The experimental method used in the present study is based on a stereoscopic technique allowing the 3D reconstruction of the interface between the two layers. Investigation into the wave pattern as a function of the Froude number, Fr, based on the relative density of the fluid layers and the velocity of the towed obstacle is presented. Specific attention is paid to the transcritical regime for which Fr is close to one. Potential energy trapped in the wave field patterns is also extracted from the experimental results and is analyzed as a function of both the Froude number, Fr, and the transcritical similarity parameter Γ. In particular, a remarkable increase in the potential energy around Fr = 1 is observed and a scaling allowing to assemble data resulting from different experimental parameters is proposed
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