Testing BOI and BOB algorithms for solving the Winner Determination

Eighth International Conference on Hybrid Intelligent Systems, 2008. HIS '08. Barcelona, 10-12 September 2008Combinatorial auctions are a promising auction format for allocating radio spectrum, as well as other goods. An important handicap of combinatorial auctions is determining the winner bids among many options, that is, solving the winner determination problem (WDP). This paper tackles this computational problem using two approaches in a combinatorial first-price sealed bid auction. The first one, is an A* based on items (BOI). The second one, is an A* based on bids (BOB). These two techniques are tested in several scenarios for allocating radio spectrum licenses. The results obtained reveal that the search algorithm A* with the BOB formulation outperforms the other and always finds the optimal solution very quickly

Parabolic curves in a Helmholtz solution for a bowed string

If one is not familiar with the physics of the violin, it is not easy to guess, even for an experimental physicist, that the so-called Helmholtz motion can be obtained as a solution to the one-dimensional wave equation for the motion of a bowed violin string. It is worth visualising this aspect from a graphical perspective without recourse to ordinary Fourier analysis, as has customarily been done. We show in this paper how to obtain the shape of the Helmholtz trajectory, that is, two mirror-symmetric parabolas, in the ideal case of no losses from internal dissipation and no viscous drag from the air and the non-rigid end supports. We also show that the velocity profile of the Helmholtz motion is also a solution of the one-dimensional wave equation. Finally, we again derive the parabolic shape of the Helmholtz trajectory by applying the principle of energy conservation to a violin string

Degradación de rojo congo en un fotorreactor tubular de tecnología excimer. Estudio cinético

Como ampliación al estudio realizado sobre la fotodegradación de rojo congo con lámparas discontinuas de tecnologíaexcimer de XeBr, KrCl y Cl2, en este trabajo se ha estudiado la fotodegradación de dicho colorante mediante un fotorreactor continuo de KrCl, con recirculación, con H2O2 y con reactivo Fenton. Del estudio de la influencia de las condiciones de operación, se han seleccionado los valores de caudal y de concentración inicial de rojo congo óptimos para su degradación. Adicionalmente, se ha comprobado que la degradación de rojo congo mejora al aumentar la cantidad de H2O2 adicionada al medio hasta una relación molar H2O2: rojo congo de 75:1 a partir de la cual ya no aumenta más. Además, la fotodegradación de rojo congo también se ve favorecida al aumentar la concentración de Fe2+ al utilizar el reactivo Fenton.El modelo modificado de pseudo primer orden propuestopreviamente se ha aplicado a este tipo de reactor. Delajuste del modelo, se ha obtenido la tendencia de la constantede velocidad (k), para las diferentes series experimentales.Además, los valores calculados con el modelopara la conversión de rojo congo se han comparado conlos experimentales, obteniéndose un buen ajuste lineal.Finalmente, se ha realizado un análisis ANOVA confirmándosela validez del modelo

Anquilosis de la articulación coxofemoral y alteraciones biomecánicas en un individuo medieval de la necrópolis de la catedral de Sigüenza (Guadalajara)

X Congreso Nacional de Paleopatología. Univesidad Autónoma de Madrid, septiembre de 200

Changes in the trajectory of the radio jet in 0735+178?

We present multi-epoch 8.4 and 43 GHz Very Long Baseline Array images of the BL Lac object 0735+178. The images confirm the presence of a twisted jet with two sharp apparent bends of 90$^{\circ}$ within two milliarcseconds of the core, resembling a helix in projection. The observed twisted geometry could be the result of precession of the jet inlet, but is more likely produced by pressure gradients in the external medium through which the jet propagates. Quasi-stationary components are observed at the locations of the 90$^{\circ}$ bends, possibly produced by differential Doppler boosting. Identification of components across epochs, since the earliest VLBI observations of this source in 1979.2, proves difficult due to the sometimes large time gaps between observations. One possible identification suggests the existence of superluminal components following non--ballistic trajectories with velocities up to $11.6\pm 0.6 h_{65}^{-1} c$. However, in images obtained after mid-1995, components show a remarkable tendency to cluster near several jet positions, suggesting a different scenario in which components have remained nearly stationary in time at least since mid-1995. Comparison with the earlier published data, covering more than 19 years of observations, suggests a striking qualitative change in the jet trajectory sometime between mid-1992 and mid-1995, with the twisted jet structure with stationary components becoming apparent only at the later epochs. This would require a re-evaluation of the physical parameters estimated for 0735+178, such as the observing viewing angle, the plasma bulk Lorentz factor, and those deduced from these.Comment: 18 pages, 5 figures, accepted for publication in MNRA

Fire does not transform shrublands of Echinospartum horridum (Vahl) Rothm. into grasslands in the Pyrenees: Development of community structure and nutritive value after single prescribed burns

Prescribed fire has been extensively used in recent years to control woody encroachment into mountain and other grassland–dominated landscapes. In the Aragon Pyrenees, prescribed burns have been mainly used to remove the native thorny shrub Echinospartum horridum (Vahl) Rothm., whose populations are spreading to the detriment of grasslands. To study the effectiveness of the burning of E. horridum to preserve grasslands for livestock grazing, the vegetation of six sites burned 0.5, 2, 3, 6, 15 and 35 years ago was sampled and compared with that of nearby unburned shrubland (control) and grassland (reference). In addition, the nutritional quality of E. horridum was examined and compared to that of the reference grassland to evaluate to what extent shrub growth can be controlled by herbivores after burning. Initial shrub cover recovered as early as 15 years after fire, with E. horridum being dominant. Plant diversity was greatest at intermediate number of years after fire. Initial floristic composition and life–form spectrum were restored 15–35 years after burning. Echinospartum horridum exhibited early lignification that restricts its availability as a palatable forage for the first two years after burning and makes it unlikely to be consumed thereafter, highlighting the difficulty in controlling the expansion of this species by livestock herbivory. The analysis of the nutrient levels suggested an increased shortage of limiting elements, such as phosphorus or sulfur, in the mid–term after burning due to substantial nutrient losses and exports during and after the burn. Our results question the suitability and sustainability of a single prescribed burn as management tool alone to control the expansion of E. horridum and call for caution in its application for fighting shrub encroachment in the Central Pyrenees