Investigation of line-of-sight propagation in dense atmosphere, phase 2 Final report, Jun. 1970 - Feb. 1971

Effect of microwave absorption and decimetric radio noise in Jovian atmospheres on radio communication in 1 to 10 GHz frequency ban

Atmospheric turbulence on Venus - Evidence for severe microwave signal fading from Venera 4

Signal fading analysis from Venera 4 data in lower Venusian atmospher

Anomalous Lattice Response at the Mott Transition in a Quasi-2D Organic Conductor

Discontinuous changes of the lattice parameters at the Mott metal-insulator transition are detected by high-resolution dilatometry on deuterated crystals of the layered organic conductor $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br. The uniaxial expansivities uncover a striking and unexpected anisotropy, notably a zero-effect along the in-plane c-axis along which the electronic interactions are relatively strong. A huge thermal expansion anomaly is observed near the end-point of the first-order transition line enabling to explore the critical behavior with very high sensitivity. The analysis yields critical fluctuations with an exponent $\tilde{\alpha} \simeq$ 0.8 $\pm$ 0.15 at odds with the novel criticality recently proposed for these materials [Kagawa \textit{et al.}, Nature \textbf{436}, 534 (2005)]. Our data suggest an intricate role of the lattice degrees of freedom in the Mott transition for the present materials.Comment: 4 pages, 4 figure

On the experimental determination of the one-way speed of light

In this contribution the question of the isotropy of the one-way speed of light from an experimental perspective is addressed. In particular, we analyze two experimental methods commonly used in its determination. The analysis is aimed at clarifying the view that the one-way speed of light cannot be determined by techniques in which physical entities close paths. The procedure employed here will provide epistemological tools such that physicists understand that a direct measurement of the speed not only of light but of any physical entity is by no means trivial. Our results shed light on the physics behind the experiments which may be of interest for both physicists with an elemental knowledge in special relativity and philosophers of science.Comment: 8 pages, 5 figures. To appear in the European Journal of Physic

Lattice Boltzmann models for non-ideal fluids with arrested phase-separation

The effects of mid-range repulsion in Lattice Boltzmann models on the coalescence/breakup behaviour of single-component, non-ideal fluids are investigated. It is found that mid-range repulsive interactions allow the formation of spray-like, multi-droplet configurations, with droplet size directly related to the strength of the repulsive interaction. The simulations show that just a tiny ten-percent of mid-range repulsive pseudo-energy can boost the surface/volume ratio of the phase- separated fluid by nearly two orders of magnitude. Drawing upon a formal analogy with magnetic Ising systems, a pseudo-potential energy is defined, which is found to behave like a quasi-conserved quantity for most of the time-evolution. This offers a useful quantitative indicator of the stability of the various configurations, thus helping the task of their interpretation and classification. The present approach appears to be a promising tool for the computational modelling of complex flow phenomena, such as atomization, spray formation and micro-emulsions, break-up phenomena and possibly glassy-like systems as well.Comment: 12 pages, 9 figure

Pterygoplichthys pardalis (Castelnau, 1855), an introduced species in the Cauca River Basin, Colombia.

Reportamos la introducción de Pterygoplichthys pardalis- una especie íctica de agua dulce de la cuenca del río Amazonas- en la cuenca del río Cauca y en las represas de Salvajina y Calima, Colombia. Alcance: Registramos y evaluamos taxonómicamente a P. pardalis para verificar su identificación, evitando que se eliminen especies nativas morfológicamente similares. Metodología empleada: Se examinó material depositado en algunas colecciones de ictiología, evaluando 35 caracteres morfométricos para su identificación siguiendo las claves de Armbruster. Estos resultados se compararon con la literatura disponible para el género Pterygoplichthys. Conclusiones: Este artículo reporta algunos errores en identificación, principalmente de Pterygoplichthys undecimalis, que en realidad corresponden a ejemplares de P. pardalis. También sugiere dos posibles mecanismos que explican su introducción en cuencas nacionales: i) descuidos durante el comercio de especies ornamentales de peces y por parte de sus compradores y ii) proyectos de acuicultura que pretenden “mejorar” la economía regional sin considerar las características e idoneidad de las especies que buscan fomentar. Finalmente, este artículo alerta sobre la introducción de P. pardalis en cuencas nacionales, y sus posibles efectos sobre especies y ecosistemas nativos.We report Pterygoplichthys pardalis introduction - a freshwater fish species from the Amazon river basin - in the Cauca river basin and in Salvajina and Calima dams, Colombia. Scope: We registered and taxonomically evaluated P. pardalis to verify its identification, seeking to avoid the elimination of native morphologically similar species. Methodology: Material deposited in some ichthyology collections was examined, evaluating 35 morphometric characters for identification following Armbruster’s keys. These results were compared with the available literature for Pterygoplichthys genus. Conclusions: This article reports some identification errors, mainly regarding Pterygoplichthys undecimalis, which actually correspond to P. pardalis. We also suggest two possible mechanisms that explain P. pardalis introduction into national basins: i) oversights during ornamental fish species trade and by their buyers, and ii) aquaculture projects that, seeking to “improve” regional economy, not take into consideration characteristics and suitability of the species they seek to promote. Finally, this article alerts about P. pardalis introduction in national basins and their possible effects on native species and ecosystems

Mid-infrared interferometry of the massive young stellar object NGC3603 - IRS 9A

We present observations and models for one of these MYSO candidates, NGC3603 IRS 9A. Our goal is to investigate with infrared interferometry the structure of IRS 9A on scales as small as 200AU, exploiting the fact that a cluster of O and B stars has blown away much of the obscuring foreground dust and gas. Observations in the N-band were carried out with the MIDI beam combiner attached to the VLTI. Additional interferometric observations which probe the structure of IRS 9A on larger scales were performed with an aperture mask installed in the T-ReCS instrument of Gemini South. The spectral energy distribution (SED) is constrained by the MIDI N-band spectrum and by data from the Spitzer Space Telescope. Our efforts to model the structure and SED of IRS 9A range from simple geometrical models of the brightness distribution to one- and two-dimensional radiative transfer computations. The target is resolved by T-ReCS, with an equivalent (elliptical) Gaussian width of 330mas by 280mas (2300 AU by 2000 AU). Despite this fact, a warm compact unresolved component was detected by MIDI which is possibly associated with the inner regions of a flattened dust distribution. Based on our interferometric data, no sign of multiplicity was found on scales between about 200AU and 700AU projected separation. A geometric model consisting of a warm (1000 K) ring (400 AU diameter) and a cool (140 K) large envelope provides a good fit to the data. No single model fitting all visibility and photometric data could be found, with disk models performing better than spherical models. While the data are clearly inconsistent with a spherical dust distribution they are insufficient to prove the existence of a disk but rather hint at a more complex dust distribution.Comment: 8 pages, 11 figures. Accepted for publication in A&