2,537 research outputs found
A tree of linearisable second-order evolution equations by generalised hodograph transformations
We present a list of (1+1)-dimensional second-order evolution equations all
connected via a proposed generalised hodograph transformation, resulting in a
tree of equations transformable to the linear second-order autonomous evolution
equation. The list includes autonomous and nonautonomous equations.Comment: arXiv version is already officia
Florística e fitossociologia em áreas de manejo de açaizais no estuário amazônico.
Este estudo teve como objetivo analisar a composição florística e a fitossociologia em três regiões do estuário amazônico em que é praticado o manejo de açaizais nativos. Nas regiões foram instaladas 30 parcelas de 0,5 ha e amostradas todas as espécies arbóreas e palmeiras com DAP ? 5 cm, mediu-se também a circunferência a altura do peito (CAP) com fita métrica de precisão de 1mm. Foram inventariados 10821 indivíduos, representados por 114 espécies, 96 gêneros e 33 famílias. As famílias mais representativas foram Arecaceae (9 espécies e 8007 indivíduos), seguida por Rubiaceae (2 espécies e 522 indivíduos),Myristicaceae (1 espécie e 268 indivíduos), Malvaceae (10 espécies e 264 indivíduos) e Euphorbiaceae (4 espécies e 247 indivíduos). Constatou-se que a riqueza nas áreas de manejo inventariadas permaneceu alta apesar da pressão antrópica que essas áreas sofrem
Viking navigation
A comprehensive description of the navigation of the Viking spacecraft throughout their flight from Earth launch to Mars landing is given. The flight path design, actual inflight control, and postflight reconstruction are discussed in detail. The preflight analyses upon which the operational strategies and performance predictions were based are discussed. The inflight results are then discussed and compared with the preflight predictions and, finally, the results of any postflight analyses are presented
Revisiting Access to Cultural Heritage in the Public Domain: EU and International Developments
This is the final version. Available on open access from Springer via the DOI in this recordIn the past year, a number of legal developments have accelerated discussions around whether intellectual property rights can be claimed in materials generated during the reproduction of public domain works. This article analyses those developments, focusing on the 2018 German Federal Supreme Court decision Museumsfotos, Art. 14 of the 2019 Copyright and Related Rights in the Digital Single Market Directive, and relevant provisions of the 2019 Open Data and the Re-use of Public Sector Information Directive. It reveals that despite the growing consensus for protecting the public domain, there is a lack of practical guidance throughout the EU in legislation, jurisprudence, and literature on what reproduction media might attract new intellectual property rights, from scans to photography to 3D data. This leaves ample room for copyright to be claimed in reproduction materials produced by new technologies. Moreover, owners remain able to impose other restrictive measures around public domain works and data, like onsite photography bans, website terms and conditions, and exclusive arrangements with third parties. This article maps out these various legal gaps. It argues the pro-open culture spirit of the EU Directives should be embraced and provides guidance for Member States and heritage institutions around national implementation
A nonlocal connection between certain linear and nonlinear ordinary differential equations/oscillators
We explore a nonlocal connection between certain linear and nonlinear
ordinary differential equations (ODEs), representing physically important
oscillator systems, and identify a class of integrable nonlinear ODEs of any
order. We also devise a method to derive explicit general solutions of the
nonlinear ODEs. Interestingly, many well known integrable models can be
accommodated into our scheme and our procedure thereby provides further
understanding of these models.Comment: 12 pages. J. Phys. A: Math. Gen. 39 (2006) in pres
Supergoop Dynamics
We initiate a systematic study of the dynamics of multi-particle systems with
supersymmetric Van der Waals and electron-monopole type interactions. The
static interaction allows a complex continuum of ground state configurations,
while the Lorentz interaction tends to counteract this configurational fluidity
by magnetic trapping, thus producing an exotic low temperature phase of matter
aptly named supergoop. Such systems arise naturally in gauge
theories as monopole-dyon mixtures, and in string theory as collections of
particles or black holes obtained by wrapping D-branes on internal space
cycles. After discussing the general system and its relation to quiver quantum
mechanics, we focus on the case of three particles. We give an exhaustive
enumeration of the classical and quantum ground states of a probe in an
arbitrary background with two fixed centers. We uncover a hidden conserved
charge and show that the dynamics of the probe is classically integrable. In
contrast, the dynamics of one heavy and two light particles moving on a line
shows a nontrivial transition to chaos, which we exhibit by studying the
Poincar\'e sections. Finally we explore the complex dynamics of a probe
particle in a background with a large number of centers, observing hints of
ergodicity breaking. We conclude by discussing possible implications in a
holographic context.Comment: 35 pages,11 figures. v2: updated references to include a previous
proof of classical integrability, exchanged a figure for a prettier versio
Grandparental Child Care in Europe : Evidence for Preferential Investment in More Certain Kin
Peer reviewe
Euler configurations and quasi-polynomial systems
In the Newtonian 3-body problem, for any choice of the three masses, there
are exactly three Euler configurations (also known as the three Euler points).
In Helmholtz' problem of 3 point vortices in the plane, there are at most three
collinear relative equilibria. The "at most three" part is common to both
statements, but the respective arguments for it are usually so different that
one could think of a casual coincidence. By proving a statement on a
quasi-polynomial system, we show that the "at most three" holds in a general
context which includes both cases. We indicate some hard conjectures about the
configurations of relative equilibrium and suggest they could be attacked
within the quasi-polynomial framework.Comment: 21 pages, 6 figure
About the connection between vacuum birefringence and the light-light scattering amplitude
Birefringence phenomena stemming from vacuum polarization are revisited in
the framework of coherent scattering. Based on photon-photon scattering, our
analysis brings out the direct connection between this process and vacuum
birefringence. We show how this procedure can be extended to the Kerr and the
Cotton-Mouton birefringences in vacuum, thus providing a unified treatment of
various polarization schemes, including those involving static fields
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