2,166 research outputs found
On the Nonlocal Equations and Nonlocal Charges Associated with the Harry Dym Hierarchy
A large class of nonlocal equations and nonlocal charges for the Harry Dym
hierarchy is exhibited. They are obtained from nonlocal Casimirs associated
with its bi-Hamiltonian structure. The Lax representation for some of these
equations is also given.Comment: to appear in Journal of Mathematical Physics, 17 pages, Late
Deformed Harry Dym and Hunter-Zheng Equations
We study the deformed Harry Dym and Hunter-Zheng equations with two arbitrary
deformation parameters. These reduce to various other known models in
appropriate limits. We show that both these systems are bi-Hamiltonian with the
same Hamiltonian structures. They are integrable and belong to the same
hierarchy corresponding to positive and negative flows. We present the Lax pair
description for both the systems and construct the conserved charges of
negative order from the Lax operator. For the deformed Harry Dym equation, we
construct the non-standard Lax representation for two special classes of values
of the deformation parameters. In general, we argue that a non-standard
description will involve a pseudo-differential operator of infinite order.Comment: Latex file, 15 page
<sup>210</sup>Pb- <sup>226</sup>Ra chronology reveals rapid growth rate of Madrepora oculata and Lophelia pertusa on world's largest cold-water coral reef
Here we show the use of the 210Pb- 226Ra excess method to determine the growth rate of two corals from the world's largest known cold-water coral reef, Røst Reef, north of the Arctic circle off Norway. Colonies of each of the two species that build the reef, Lophelia pertusa and Madrepora oculata, were collected alive at 350 m depth using a submersible. Pb and Ra isotopes were measured along the major growth axis of both specimens using low level alpha and gamma spectrometry and trace element compositions were studied. 210Pb and 226Ra differ in the way they are incorporated into coral skeletons. Hence, to assess growth rates, we considered the exponential decrease of initially incorporated 210Pb, as well as the increase in 210Pb from the decay of 226Ra and contamination with 210Pb associated with Mn-Fe coatings that we were unable to remove completely from the oldest parts of the skeletons. 226Ra activity was similar in both coral species, so, assuming constant uptake of 210Pb through time, we used the 210Pb- 226Ra chronology to calculate growth rates. The 45.5 cm long branch of M. oculata was 31 yr with an average linear growth rate of 14.4 ± 1.1 mm yr -1 (2.6 polyps per year). Despite cleaning, a correction for Mn-Fe oxide contamination was required for the oldest part of the colony; this correction corroborated our radiocarbon date of 40 yr and a mean growth rate of 2 polyps yr -1. This rate is similar to the one obtained in aquarium experiments under optimal growth conditions. For the 80 cm-long L. pertusa colony, metal-oxide contamination remained in both the middle and basal part of the coral skeleton despite cleaning, inhibiting similar age and growth rate estimates. The youngest part of the colony was free of metal oxides and this 15 cm section had an estimated a growth rate of 8 mm yr -1, with high uncertainty (∼1 polyp every two to three years). We are less certain of this 210Pb growth rate estimate which is within the lowermost ranges of previous growth rate estimates. We show that 210Pb- 226Ra dating can be successfully applied to determine the age and growth rate of framework-forming cold-water corals if Mn-Fe oxide deposits can be removed. Where metal oxides can be removed, large M. oculata and L. pertusa skeletons provide archives for studies of intermediate water masses with an up to annual time resolution and spanning over many decades. © 2012 Author(s)
Use of specific Green's functions for solving direct problems involving a heterogeneous rigid frame porous medium slab solicited by acoustic waves
A domain integral method employing a specific Green's function (i.e.,
incorporating some features of the global problem of wave propagation in an
inhomogeneous medium) is developed for solving direct and inverse scattering
problems relative to slab-like macroscopically inhomogeneous porous obstacles.
It is shown how to numerically solve such problems, involving both
spatially-varying density and compressibility, by means of an iterative scheme
initialized with a Born approximation. A numerical solution is obtained for a
canonical problem involving a two-layer slab.Comment: submitted to Math.Meth.Appl.Sc
Action versus Result-Oriented Schemes in a Grassland Agroecosystem: A Dynamic Modelling Approach
Effects of agri-environment schemes (AES) on biodiversity remain controversial. While most AES are action-oriented, result-oriented and habitat-oriented schemes have recently been proposed as a solution to improve AES efficiency. The objective of this study was to compare action-oriented, habitat-oriented and result-oriented schemes in terms of ecological and productive performance as well as in terms of management flexibility. We developed a dynamic modelling approach based on the viable control framework to carry out a long term assessment of the three schemes in a grassland agroecosystem. The model explicitly links grazed grassland dynamics to bird population dynamics. It is applied to lapwing conservation in wet grasslands in France. We ran the model to assess the three AES scenarios. The model revealed the grazing strategies respecting ecological and productive constraints specific to each scheme. Grazing strategies were assessed by both their ecological and productive performance. The viable control approach made it possible to obtain the whole set of viable grazing strategies and therefore to quantify the management flexibility of the grassland agroecosystem. Our results showed that habitat and result-oriented scenarios led to much higher ecological performance than the action-oriented one. Differences in both ecological and productive performance between the habitat and result-oriented scenarios were limited. Flexibility of the grassland agroecosystem in the result-oriented scenario was much higher than in that of habitat-oriented scenario. Our model confirms the higher flexibility as well as the better ecological and productive performance of result-oriented schemes. A larger use of result-oriented schemes in conservation may also allow farmers to adapt their management to local conditions and to climatic variations
Symmetry, Local Linearization, and Gauge Classification of the Doebner-Goldin Equation
For the family of nonlinear Schr\"odinger equations derived by H.-D.~Doebner
and G.A.~Goldin (J.Phys.A 27, 1771) we calculate the complete set of Lie
symmetries. For various subfamilies we find different finite and infinite
dimensional Lie symmetry algebras. Two of the latter lead to a local
transformation linearizing the particular subfamily. One type of these
transformations leaves the whole family of equations invariant, giving rise to
a gauge classification of the family. The Lie symmetry algebras and their
corresponding subalgebras are finally characterized by gauge invariant
parameters.Comment: 17 pages, LaTeX, 1 figure, to appear in Reports on Mathematical
Physic
Telomerase activation cooperates with inactivation of p16 in early head and neck tumorigenesis
Alteration of the p16/pRb pathway may cooperate with telomerase activation during cellular immortalization and tumour progression. We studied p16 expression status by immunohistochemistry and telomerase activity using the TRAP assay in 21 premalignant lesions of the head and neck epithelium as well as 27 squamous-cell carcinomas. We also examined expression of other components of the pathway (cyclin D1 and pRb) as well as presence of human papillomavirus genomes which can target these molecules. 4 of 9 mild dysplastic lesions (44%), 8 of 12 moderate/severe dysplastic lesions (67%), and 25 of 27 squamous-cell carcinomas (92%) demonstrated high telomerase activity (P = 0.009). There was a parallel increase with severity of lesions for the trend in proportions of cases demonstrating p16 inactivation or cyclin D1 overexpression (P = 0.02 and P = 0.01, respectively). For Ki67, a marker of cell proliferation, this trend was not significant (P = 0.08). Human papillomavirus infection was only found in 4 cases among the 48 samples tested (8.3%). In conclusion, progression of disease is accompanied by a parallel and continuous increase in telomerase activity and alterations in cell cycle regulators (p16, cyclin D1), as proposed by in vitro models. © 2001 Cancer Research Campaign http://www.bjcancer.co
Local and non-local equivalent potentials for p-12C scattering
A Newton-Sabatier fixed energy inversion scheme has been used to equate
inherently non-local p-C potentials at a variety of energies to pion
threshold, with exactly phase equivalent local ones. Those energy dependent
local potentials then have been recast in the form of non-local Frahn-Lemmer
interactions.Comment: 15 pages plus 9 figures submitted to Phys. Rev.
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