Investigation of high pt_{t} events in Nucleus-Nucleus collisions using the Hijing event generator

In recent years lot of interest has been observed in the nucleus-nucleus collisions at RHIC energies in phenomena related to high $p_{t}$ physics \cite{ref1}. The suppression of high $p_{t}$ particles and disappearance of back-to-back jets compared to the scaling with number of binary nucleon-nucleon collisions indicates that a nearly perfect liquid is produced in these collisions. Results on self shadowing of high $p_{t}$ events are presented using hadron multiplicity associated to high $p_{t}$ and unbiased events in nucleus-nucleus collisions \cite{ref2} obtained from the hijing event generator.Comment: 4 pages, 3 figures, Proceedings of the poster presented at Quark Matter 200

Fusion of strings vs. percolation and the transition to the quark-gluon plasma

In most of the models of hadronic collisions the number of exchanged colour strings grows with energy and atomic numbers of the projectile and target. At high string densities interaction between them should melt them into the quark-gluon plasma state. It is shown that under certain assumptions about the the string interaction, a phase transition to the quark gluon plasma indeed takes place in the system of many colour strings. It may be of the first or second order (percolation), depending on the particular mechanism of the interaction. The critical string density is about unity in both cases. The critical density may have been already reached in central Pb-Pb collisions at 158 A GeV.Comment: 16 pages, 3 Postscript figure

Percolation Effects in Very High Energy Cosmic Rays

Most QCD models of high energy collisions predict that the inelasticity $K$ is an increasing function of the energy. We argue that, due to percolation of strings, this behaviour will change and, at $\sqrt{s} \simeq 10^4$ GeV, the inelasticity will start to decrease with the energy. This has straightforward consequences in high energy cosmic ray physics: 1) the relative depth of the shower maximum $\bar{X}$ grows faster with energy above the knee; 2) the energy measurements of ground array experiments at GZK energies could be overestimated.Comment: Correction of equation (19) and figures 3 and 4. 4 pages, 4 figure

Global ionospheric monitoring and navigation systems

Postprint (published version

Componentes de la corteza del olmo y su posible influencia en la alimentación de los escolítidos

In order to better understand the chemical factors involved in the host feeding selectivity by Scolytus, components were extracted from elm bark and studied. Sampled trees were located in an elm stand that survived the Dutch twig elm disease pandemia, and from elm clones from throughout the Iberian Peninsula. The main samples studied were from Ulmus minor, and the other samples from U. pumila, U. laevis and several hybrids. The main compounds in the extracts obtained from current-year twigs were aliphatic hydrocarbons (particularly heptacosane and nonacosane) and from 2- to 4-year-old stems were triterpenes. Three of the triterpenes were identified for the first time in Ulmus (lupenol, alnulin, and ilexol) and two in Ulmaceae (moretenol and betulin). Differences occurred in the compounds isolated from U. minor from the two locations, and between species.Se analizaron los componentes de la corteza de ramillas de olmos, a fin de determinar los factores químicos involucrados en la selección, por parte de los escolítidos del olmo (Scolytus), de árboles para su alimentación. Las muestras fueron recogidas en árboles de una olmeda que ha sobrevivido a la pandemia de grafiosis y de ejemplares de distintas procedencias de la península Ibérica en un banco clonal. La principal especie estudiada fue Ulmus minor. Se tomaron además muestras de U. pumila, U. laevis y diversos híbridos. Los compuestos más abundantes en los extractos obtenidos de ramillas del año en curso fueron hidrocarburos alifáticos (principalmente heptacosano y nonacosano) y en las ramillas de 2º a 4º año triterpenos pentacíclicos. Tres de los triterpenos (lupenol, alnulina e ilexol) fueron identificados por primera vez en Ulmus y dos (moretenol y betulina) en Ulmaceae. Se observaron diferencias en los compuestos detectados en U. minor de las dos localizaciones así como entre especies

Respuestas de alimentación de Scolytus scolytus a extractos del floema de ramillas de olmo

Feeding responses by Scolytus scolytus were tested using elm twig bark extracts in a laboratory bioassay. One to 4- years-old elm twigs or small branches were sampled in spring and their bark extracted separately with methanol and with a mixture of petroleum ether and diethyl ether (1:1) as solvents. Bark extracts were tested in a two choice feeding bioassay consisting of two polyurethane discs placed in a 10 cm diameter Petri dish. Extracts were applied onto the discs and the amount of disc eaten by ten freshly emerged S. scolytus adults was recorded after 24 hours. Ten U. minor, two U. laevis, six U. glabra, three Dutch hybrids (European x Asiatic) and one U. pumila trees were tested in several comparisons. Discs with extracts from both U. laevis trees were significantly less eaten than those from U. pumila or from U. minor trees in two choice tests. Similarly, extracts from all U. glabra trees received less feeding than those from U. minor. On the contrary, S. scolytus showed no difference in feeding between U. pumila and U. minor extracts, and similarly for Dutch hybrids in comparison with two U. minor clones. Again, beetles preferred to feed on Dutch hybrid extracts better than in those from U. laevis. Significant intraspecific differences in feeding were obtained in U. minor. One of the U. minor clones resulted less chosen when compared to other four trees. Extracts from a dying U. minor tree received more feeding than those from a healthy tree. Comparisons were also made between bark extracts from 2-to 4-year-old vs. current-year twigs within the same trees. In one of the four U. minor tested, a significant preference for the older twig extracts was recorded.Se estudió la respuesta de alimentación de S. scolytus a extractos del floema de ramillas de olmo en bioensayos de laboratorio. Se muestrearon en primavera ramillas de olmo de uno a cuatro años de edad y su floema fue extraído independientemente con metanol o con una mezcla de eter de petróleo y eter dietílico (1:1). Los extractos del floema se evaluaron en un bioensayo de doble elección consistente en dos discos de poliuretano dispuestos en una placa Petri de 10 cm de diámetro. Se aplicaron los extractos a los discos y se midió la superficie de disco comida por diez adultos recién emergidos de S. scolytus durante 24 h. Se ensayaron diez U. minor, dos U. laevis, seis U. glabra, tres híbridos holandeses (europeo x asiático) y un U. pumila en diversas comparaciones. Los discos con extractos de ambos U. laevis fueron significativamente menos comidos que aquéllos con los de U. pumila o de U. minor. Igualmente, los extractos de todos los U. glabra recibieron menor alimentación que aquéllos de U. minor. Por el contrario, S. scolytus no mostró preferencias entre los extractos de U. minor y de U. pumila, e igualmente, entre los de U. minor y los de híbridos holandeses. Nuevamente, los escolítidos prefirieron alimentarse menos de los extractos de U. laevis que de los híbridos holandeses. Se encontraron diferencias intraespecíficas significativas en U. minor. Uno de los clones de U. minor resultó menos preferido cuando se le comparó con otros cuatro árboles. Los extractos de un U. minor moribundo recibieron mayor alimentación que los de un árbol sano. Se realizaron comparaciones entre los extractos del floema de ramillas de 2 a 4 años de edad y de ramillas del año en curso de un mismo árbol. En uno de cuatro U. minor ensayados se observó una preferencia significativa por los extractos de las ramillas más viejas