Commodities: an asset class in their own right?

Investor interest in commodities has risen in recent years in line with the spectacular surge in most commodity prices. Some institutional investors, for instance Dutch or Californian pension funds, have confirmed that they have gained or intend to gain moderate exposure (less than 5% of their assets) to commodities. In parallel, the development of new investment vehicles has enabled individual investors also to gain commodity exposure. Expectations of continued strong economic growth in Asia, which should result in Asian countries’ sustained demand for commodities, may be the driver of the increased appetite for these assets. Interest also seems to be spurred by studies by academics and market analysts that highlight commodities as an effective way of diversifying portfolio risk. This assessment and interpretation suggest that investors are slowly but sustainably including commodities in their portfolios. Can we however assert that commodities constitute an asset class in their own right? This study suggests they do, given that over the long term, returns on commodity-related investments appear to outperform risk-free returns, seem to have a low or negative correlation with other asset classes and can apparently not be replicated with a simple linear combination of assets.

Análisis de la flora vascular endémica y amenazada de los medios salinos de Andalucía (S. España)

Se analiza la flora vascular halófila endémica y amenazada presente en los medios salinos de Andalucía, a partir del catálogo florístico elaborado en el territorio entre los años 2003 y 2008. De un total de 162 especies y subespecies de plantas vasculares que fueron detectados en los ecosistemas halófilos andaluces, 43 taxones son endémicos y 41 taxones están amenazados y/o protegidos por la legislación a un nivel local, regional o nacional.Analysis of endemic and threatened vascular flora in saline environments of Andalusia (S. Spain). An analysis on the endemic and endangered halophyte vascular flora of saline environments of Andalusia is carried out, starting out from the catalog of flora recorded in the territory between the years 2003 and 2008. A total amount of 162 species and subspecies of vascular plants were detected in Andalusian saline environ - ments, 43 of them being endemics and 41 threatened and/or protected by law at different levels: local, regional and nationalConsejería de Economía, Innovación y Ciencia de la Junta de Andalucí

Estudio florístico de los medios húmedos salinos de Andalucía (S. de España). Catálogo y análisis de la flora vascular halófila

El objetivo del presente estudio es el conocimiento de la composición florística de los medios húmedos salinos andaluces. Entre 2003 y 2008 se han inventariado un total de 162 especies y subespecies de plantas vasculares que son propias de los medios salinos andaluces, entre las que se encuentran 41 taxones amenazados y/o protegidos y 6 taxones alóctonos. Para cada uno de los taxones se indica el nombre aceptado, sinónimos más usados, familia a la que pertenece, tipo de vegetación en el que suele aparecer, afinidad fitosociológica, ecología, biotipo, termotipo, distribución general y distribución en el área de estudio por unidades fitogeográficas. Finalmente se indica si la especie es invasora en el territorio o si la especie se considera amenazada.Floristic study of the Andalusian saline wetlands (S. Spain). Checklist and floristic analysis of the halophytic vascular flora. The aim of this study is to contribute to the knowledge of the floristic composition of Andalusian saline wetlands. A total of 162 halophytic vascular plant species and subspecies has been recorded between 2003 and 2008, comprising 41 threatened and/or protected taxa and 6 allochthonous species. For each taxon the accepted name, most usual synonyms, botanic family, vegetation type where it usually appears, phytosociologic affinity, ecology, biotype, termotype, general distribution and phytogeographic distribution in the study area is provided. Finally, it is pointed out whether the species is considered invasive or threatened in the territory.Junta de Andalucía. Consejería de Economía, Innovación y CienciaEmpresa de Gestión Medioambiental (EGMASA

Una nueva asociación de vegetación halófila en el sureste de la península ibérica (España): Limonio Majoris-Sarcocornietum fruticosae

Como resultado del estudio de la vegetación de los humedales salinos en Andalucía, se muestra la descripción y caracterización de una nueva asociación halófila desarrollada en los saladares de la Hoya de Baza (Granada). Se trata de una fitocenosis dominada por Sarcocornia fruticosa (L.) A. J. Scott, junto a otros nanofanerófitos suculentos y hemicriptófitos rosulados entre los que destaca el endemismo local Limonium majus (Boiss.) Erben. La asociación Limonio majoris-Sarcocornietum fruticosae ass. nova es propia del distrito Guadiciano-Bastetano (sector Guadiciano-Bacense, provincia Bética) en el piso bioclimático mesomediterráneo semiárido.A new halophytic vegetation association in southeastern Iberian Peninsula (Spain): Limonio majoris-Sarcocornietum fruticosae. As a result of the research on the vegetation of Andalusian saline wetlands, a new halophytic association in the Baza depression (Granada) is characterized and described. This phytocoenoses is mainly dominated by Sarcocornia fruticosa (L.) A. J. Scott, together with other succulent nanophanerophytes and rosulate hemicryptophytes, highlighting the existence of the local endemic taxon Limonium majus (Boiss.) Erben. The new association is named Limonio majoris-Sarcocornietum fruticosae ass. Nova being exclusive of the Guadician-Bastetan district territories (Guadician-Bacensean sector, Baetic province) and developing in the Mesomediterranean semiarid bioclimatic belt.Junta de Andalucía. Consejería de Economía, Innovación y CienciaJunta de Andalucía. Consejería de Medio Ambient

Choreographic solution to the general relativistic three-body problem

We revisit the three-body problem in the framework of general relativity. The Newtonian N-body problem admits choreographic solutions, where a solution is called choreographic if every massive particles move periodically in a single closed orbit. One is a stable figure-eight orbit for a three-body system, which was found first by Moore (1993) and re-discovered with its existence proof by Chenciner and Montgomery (2000). In general relativity, however, the periastron shift prohibits a binary system from orbiting in a single closed curve. Therefore, it is unclear whether general relativistic effects admit a choreographic solution such as the figure eight. We carefully examine general relativistic corrections to initial conditions so that an orbit for a three-body system can be closed and a figure eight. This solution is still choreographic. This illustration suggests that the general relativistic N-body problem also may admit a certain class of choreographic solutions.Comment: 10 pages, 4 figures, text improved, accepted for publication in PR

Gravitational wave forms for a three-body system in Lagrange's orbit: parameter determinations and a binary source test

Continuing work initiated in an earlier publication [Torigoe et al. Phys. Rev. Lett. {\bf 102}, 251101 (2009)], gravitational wave forms for a three-body system in Lagrange's orbit are considered especially in an analytic method. First, we derive an expression of the three-body wave forms at the mass quadrupole, octupole and current quadrupole orders. By using the expressions, we solve a gravitational-wave {\it inverse} problem of determining the source parameters to this particular configuration (three masses, a distance of the source to an observer, and the orbital inclination angle to the line of sight) through observations of the gravitational wave forms alone. For this purpose, the chirp mass to a three-body system in the particular configuration is expressed in terms of only the mass ratios by deleting initial angle positions. We discuss also whether and how a binary source can be distinguished from a three-body system in Lagrange's orbit or others.Comment: 21 pages, 3 figures, 1 table; text improved, typos corrected; accepted for publication in PR

Action minimizing orbits in the n-body problem with simple choreography constraint

In 1999 Chenciner and Montgomery found a remarkably simple choreographic motion for the planar 3-body problem (see \cite{CM}). In this solution 3 equal masses travel on a eight shaped planar curve; this orbit is obtained minimizing the action integral on the set of simple planar choreographies with some special symmetry constraints. In this work our aim is to study the problem of $n$ masses moving in \RR^d under an attractive force generated by a potential of the kind $1/r^\alpha$, $\alpha >0$, with the only constraint to be a simple choreography: if $q_1(t),...,q_n(t)$ are the $n$ orbits then we impose the existence of x \in H^1_{2 \pi}(\RR,\RR^d) such that q_i(t)=x(t+(i-1) \tau), i=1,...,n, t \in \RR, where $\tau = 2\pi / n$. In this setting, we first prove that for every d,n \in \NN and $\alpha>0$, the lagrangian action attains its absolute minimum on the planar circle. Next we deal with the problem in a rotating frame and we show a reacher phenomenology: indeed while for some values of the angular velocity minimizers are still circles, for others the minima of the action are not anymore rigid motions.Comment: 24 pages; 4 figures; submitted to Nonlinearit

Collinear solution to the general relativistic three-body problem

The three-body problem is reexamined in the framework of general relativity. The Newtonian three-body problem admits Euler's collinear solution, where three bodies move around the common center of mass with the same orbital period and always line up. The solution is unstable. Hence it is unlikely that such a simple configuration would exist owing to general relativistic forces dependent not only on the masses but also on the velocity of each body. However, we show that the collinear solution remains true with a correction to the spatial separation between masses. Relativistic corrections to the Sun-Jupiter Lagrange points L1, L2 and L3 are also evaluated.Comment: 12 pages, 2 figures, accepted for publication in PR

Uniqueness of collinear solutions for the relativistic three-body problem

Continuing work initiated in an earlier publication [Yamada, Asada, Phys. Rev. D 82, 104019 (2010)], we investigate collinear solutions to the general relativistic three-body problem. We prove the uniqueness of the configuration for given system parameters (the masses and the end-to-end length). First, we show that the equation determining the distance ratio among the three masses, which has been obtained as a seventh-order polynomial in the previous paper, has at most three positive roots, which apparently provide three cases of the distance ratio. It is found, however, that, even for such cases, there exists one physically reasonable root and only one, because the remaining two positive roots do not satisfy the slow motion assumption in the post-Newtonian approximation and are thus discarded. This means that, especially for the restricted three-body problem, exactly three positions of a third body are true even at the post-Newtonian order. They are relativistic counterparts of the Newtonian Lagrange points L1, L2 and L3. We show also that, for the same masses and full length, the angular velocity of the post-Newtonian collinear configuration is smaller than that for the Newtonian case. Provided that the masses and angular rate are fixed, the relativistic end-to-end length is shorter than the Newtonian one.Comment: 18 pages, 1 figure; typos corrected, text improved; accepted by PR