The geometry of L^p-spaces over atomless measure spaces and the Daugavet property

We show that $L^p$-spaces over atomless measure spaces can be characterized in terms of a $p$-concavity type geometric property that is related with the Daugavet property

Multifunctional nanocomposites for the conservation of marine archaeological wood

Marine archaeological wood often suffers from acidification processes that lead to the degradation of the fibres, threatening the integrity of archaeological artefacts. Iron ions originating from corroded fixtures, nails, or other objects diffuse into the structure of waterlogged wooden artefacts over time, playing a key role in their degradation. The presence of iron ions and oxidised sulfur species in marine archaeological wood has been linked to the formation of sulfur-based acids and to the oxidative degradation of cellulose and hemicellulose.[1,2] These processes have deleterious effects on the structural integrity of wooden artefacts and pose a major challenge in the long-term conservation of marine archaeological wood.[3] This thesis describes the design, synthesis, characterisation, and preliminary tests of a series of conservation treatments aiming for the sequestration and complete removal of harmful iron species present in waterlogged wood, thus preventing the formation of acidic species. These treatments consist of magnetic nanocomposites which contain iron chelating agents and are encapsulated in a polyethylene glycol-based, thermoresponsive polymer for a safe and controlled application. The iron sequestering capability of the nanocomposites range between 39 and 80 % when tested in aqueous solution. Far IR spectroscopy studies on preliminary treatments on artificial archaeological oak and Mary Rose wood samples indicate that iron ions are successfully removed from the wood by the nanocomposite-laden polymer. These conservation treatments are capable of removing harmful iron ions from marine archaeological wood, and a number of parameters in their preparation can be adjusted to meet the requirements of different artefacts to be treated. The combined magnetic and thermoresponsive properties of these materials allow for a safe and controlled application of the treatments and opens new possibilities in the design of novel non-invasive conservation strategies. While previous conservation treatments aimed to remove the iron ions or to neutralise the acidic species present in the wood, the approach presented here manages to physically remove iron ions from not only the surface, but also from the wood structure. Due to the high tunability of the systems developed, these can be applied for the conservation of many other materials such as stone, paintings, fabric, or leather. [1] G. Almkvist and I. Persson, Holzforschung, 2008, 62, 694–703. [2] K. M. Wetherall, R. M. Moss, A. M. Jones, A. D. Smith, T. Skinner, D. M. Pickup, S. W. Goatham, A. V. Chadwick and R. J. Newport, J. Archaeol. Sci., 2008, 35, 1317–1328. [3] M. Sandström, F. Jalilehvand, I. Persson, U. Gelius, P. Frank and I. Hall-Roth, Nature, 2002, 415, 893–897

Total reflection X-ray fluorescence analysis using polycapillaries. A comparison with conventional setups

The possibility of producing parallel X-ray beams with low divergence by means of half monolithic polycapillaries gives the impression to be useful in total reflection X-ray fluorescence (TXRF) experiments. On one hand, the use of polycapillaries facilitates the alignment and the setup of the experiment. As expected, the spectra registered in the experiment shown low background and good signal-noise ratio. On the other hand, the intensity of photons on the samples when polycapillaries are employed is lower than in other configurations, which produces a loss of efficiency for the excitation of the sample mainly for light elements. In this work, different TXRF experiments were carried out and the minimum detection limits attained were compared with the ones obtained from TXRF using polycapillaries. The results indicate that the decrease of intensity produced by polycapillaries is imposing when detection limits are analyzed. Nevertheless, detection limits are better than conventional XRF. The possibility of employing non-symmetrical polycapillaries could eventually improve the detection limits so as to be equivalent to the conventional TXRF setups. © 2010 Elsevier B.V.Fil: Sanchez, Hector Jorge. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Perez, Roberto Daniel. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Carvalho, Maria Luisa. Universidad de Lisboa; PortugalFil: Rubio, Marcelo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Crucial aspects of the initial mass function (II): The inference of total quantities from partial information on a cluster

In a probabilistic framework of the interpretation of the initial mass function (IMF), the IMF cannot be arbitrarily normalized to the total mass, M, or number of stars, N, of the system. Hence, the inference of M and N when partial information about the studied system is available must be revised. (i.e., the contribution to the total quantity cannot be obtained by simple algebraic manipulations of the IMF). We study how to include constraints in the IMF to make inferences about different quantities characterizing stellar systems. It is expected that including any particular piece of information about a system would constrain the range of possible solutions. However, different pieces of information might be irrelevant depending on the quantity to be inferred. In this work we want to characterize the relevance of the priors in the possible inferences. Assuming that the IMF is a probability distribution function, we derive the sampling distributions of M and N of the system constrained to different types of information available. We show that the value of M that would be inferred must be described as a probability distribution Phi[M; m_a, N_a, Phi(N)] that depends on the completeness limit of the data, m_a, the number of stars observed down to this limit, N_a, and the prior hypothesis made on the distribution of the total number of stars in clusters, Phi(N).Comment: Accepted by A&A; 9 page

Crucial aspects of the initial mass function (I): The statistical correlation between the total mass of an ensemble of stars and its most massive star

Our understanding of stellar systems depends on the adopted interpretation of the IMF, phi(m). Unfortunately, there is not a common interpretation of the IMF, which leads to different methodologies and diverging analysis of observational data.We study the correlation between the most massive star that a cluster would host, mmax, and its total mass into stars, M, as an example where different views of the IMF lead to different results. We assume that the IMF is a probability distribution function and analyze the mmax-M correlation within this context. We also examine the meaning of the equation used to derive a theoretical M-char_mmax relationship, N x int[Char_mmax-mup] phi(m) dm = 1 with N the total number of stars in the system, according to different interpretations of the IMF. We find that only a probabilistic interpretation of the IMF, where stellar masses are identically independent distributed random variables, provides a self-consistent result. Neither M nor N, can be used as IMF scaling factors. In addition, Char_mmax is a characteristic maximum stellar mass in the cluster, but not the actual maximum stellar mass. A -Char_mmax correlation is a natural result of a probabilistic interpretation of the IMF; however, the distribution of observational data in the N (or M)-cmmax plane includes a dependence on the distribution of the total number of stars, N (and M), in the system, Phi(N), which is not usually taken into consideration. We conclude that a random sampling IMF is not in contradiction to a possible mmax-M physical law. However, such a law cannot be obtained from IMF algebraic manipulation or included analytically in the IMF functional form. The possible physical information that would be obtained from the N (or M)-mmax correlation is closely linked with the Phi(M) and Phi(N) distributions; hence it depends on the star formation process and the assumed.Comment: Accepted by A&A; 16 pages, 10 figure

The Fractal Dimension of Projected Clouds

The interstellar medium seems to have an underlying fractal structure which can be characterized through its fractal dimension. However, interstellar clouds are observed as projected two-dimensional images, and the projection of a tri-dimensional fractal distorts its measured properties. Here we use simulated fractal clouds to study the relationship between the tri-dimensional fractal dimension (D_f) of modeled clouds and the dimension resulting from their projected images. We analyze different fractal dimension estimators: the correlation and mass dimensions of the clouds, and the perimeter-based dimension of their boundaries (D_per). We find the functional forms relating D_f with the projected fractal dimensions, as well as the dependence on the image resolution, which allow to estimatethe "real" D_f value of a cloud from its projection. The application of these results to Orion A indicates in a self-consistent way that 2.5 < D_f < 2.7 for this molecular cloud, a value higher than the result D_per+1 = 2.3 some times assumed in literature for interstellar clouds.Comment: 27 pages, 13 figures, 1 table. Accepted for publication in ApJ. Minor change