Resource location based on precomputed partial random walks in dynamic networks

The problem of finding a resource residing in a network node (the \emph{resource location problem}) is a challenge in complex networks due to aspects as network size, unknown network topology, and network dynamics. The problem is especially difficult if no requirements on the resource placement strategy or the network structure are to be imposed, assuming of course that keeping centralized resource information is not feasible or appropriate. Under these conditions, random algorithms are useful to search the network. A possible strategy for static networks, proposed in previous work, uses short random walks precomputed at each network node as partial walks to construct longer random walks with associated resource information. In this work, we adapt the previous mechanisms to dynamic networks, where resource instances may appear in, and disappear from, network nodes, and the nodes themselves may leave and join the network, resembling realistic scenarios. We analyze the resulting resource location mechanisms, providing expressions that accurately predict average search lengths, which are validated using simulation experiments. Reduction of average search lengths compared to simple random walk searches are found to be very large, even in the face of high network volatility. We also study the cost of the mechanisms, focusing on the overhead implied by the periodic recomputation of partial walks to refresh the information on resources, concluding that the proposed mechanisms behave efficiently and robustly in dynamic networks.Comment: 39 pages, 25 figure

Clima y turismo de interior en la Península Ibérica. Estudios de caos en la Comunidad Autónoma de Castilla-La Mancha

XII Coloquio de Geografía del Turismo, Ocio y Recreación de la Asociación de Geógrafos Españoles. Colmenarejo (Madrid), del 17 al 19 de junio de 2010.Publicad

Reial Societat de Tennis Pompeia, arquitectura e historia

Finalizando la carrera de Ingeniería de la Edificación vimos en la web de la universidad una propuesta hecha por el profesor Benet Meca que consistía en el levantamiento de la sede social y pistas de un club de tenis centenario. En dicho levantamiento deberían constar los planos de proyecto básico y acotados, además de la recopilación de la historia existente del club, como parte de la investigación histórica. En la propuesta se especificaba que era necesario dos personas que dominasen técnicas gráficas de ordenador como: autocad o similares, photoshop o programas parecidos de levantamientos. Como nos pareció interesante decidimos ponernos en contacto con el profesor Benet Meca para hablar sobre la propuesta. La primera reunión fue satisfactoria, ya que el trabajo era exactamente lo que estábamos buscando, mucho trabajo de campo y de despacho con autocad y photoshop. El profesor Benet Meca nos aconsejó que nos acercásemos al club de tenis antes de darle una respuesta, observáramos detenidamente todo el trabajo que había que hacer, hiciéramos un pequeño reportaje fotográfico y una vez estudiado detenidamente le dijéramos si estábamos interesados o no. No hizo falta ver mucho para acabar de convencernos, era exactamente lo que estábamos buscando. Una vez aceptado el proyecto solo quedaba entregar la propuesta y ponerse manos a la obra con el levantamiento de planos. No obstante, antes de empezar con el levantamiento intentamos buscar información gráfica que nos pudiese ayudar en el trabajo, para ello decidimos ir al Archivo Municipal situado en la C/. Bisbe Caçador, 4 de Barcelona, pero en esta primera visita no encontramos ningún plano, así que nos pusimos manos a la obra partiendo desde cero. Poco a poco fuimos entendiendo la composición del edificio y nos dimos cuenta de que se componía por diferentes fases de construcción y que cada una pertenecía a una fecha diferente, gracias a las sucesivas visitas al Archivo Municipal y a la colaboración de los socios y trabajadores del club, en especial, Sr. Antonio Vallecillos Sánchez, actual gerente, pudimos entender las fases a las que éste había estado sometido y entrelazarlas a la historia de la Sociedad

A context vector model for information retrieval

In the vector space model for information retrieval, term vectors are pair-wise orthogonal, that is, terms are assumed to be independent. It is well known that this assumption is too restrictive. In this article, we present our work on an indexing and retrieval method that, based on the vector space model, incorporates term dependencies and thus obtains semantically richer representations of documents. First, we generate term context vectors based on the co-occurrence of terms in the same documents. These vectors are used to calculate context vectors for documents. We present different techniques for estimating the dependencies among terms. We also define term weights that can be employed in the model. Experimental results on four text collections (MED, CRANFIELD, CISI, and CACM) show that the incorporation of term dependencies in the retrieval process performs statistically significantly better than the classical vector space model with IDF weights. We also show that the degree of semantic matching versus direct word matching that performs best varies on the four collections. We conclude that the model performs well for certain types of queries and, generally, for information tasks with high recall requirements. Therefore, we propose the use of the context vector model in combination with other, direct word-matching methods.Publicad

Recent developments in nonbank financing of Spanish firms

Artículo de revistaThe banking sector has traditionally played a key role in the financing of Spanish nonfinancial corporations (NFCs), much more substantial than other alternative sources, such as securities markets or venture capital. The past crisis evidenced that a high degree of dependence on a single source of funding may constitute an element of vulnerability for firms. Against this backdrop, in recent years there has been a process of financial disintermediation, with firms replacing part of their bank loan financing with the issuance of securities (bonds or equity) in official or alternative markets and with equity financing through venture capital entities. Specifically, in the period 2009-2017 NFCs raised funds for an average annual amount of €50 billion through securities markets, compared with an average annual decline of €34 billion through loans. Also, the recently created crowdfunding platforms have become a new alternative channel and although their volumes are marginal for the time being, they could experience stronger growth in the next few years, as has occurred in other European countrie

Critical parameters of the in vitro method of vascular smooth muscle cell calcification

[Background]: Vascular calcification (VC) is primarily studied using cultures of vascular smooth muscle cells. However, the use of very different protocols and extreme conditions can provide findings unrelated to VC. In this work we aimed to determine the critical experimental parameters that affect calcification in vitro and to determine the relevance to calcification in vivo. [Experimental Procedures and Results]: Rat VSMC calcification in vitro was studied using different concentrations of fetal calf serum, calcium, and phosphate, in different types of culture media, and using various volumes and rates of change. The bicarbonate content of the media critically affected pH and resulted in supersaturation, depending on the concentration of Ca2+ and Pi. Such supersaturation is a consequence of the high dependence of bicarbonate buffers on CO2 vapor pressure and bicarbonate concentration at pHs above 7.40. Such buffer systems cause considerable pH variations as a result of minor experimental changes. The variations are more critical for DMEM and are negligible when the bicarbonate concentration is reduced to ¿. Particle nucleation and growth were observed by dynamic light scattering and electron microscopy. Using 2mM Pi, particles of ~200nm were observed at 24 hours in MEM and at 1 hour in DMEM. These nuclei grew over time, were deposited in the cells, and caused osteogene expression or cell death, depending on the precipitation rate. TEM observations showed that the initial precipitate was amorphous calcium phosphate (ACP), which converts into hydroxyapatite over time. In blood, the scenario is different, because supersaturation is avoided by a tightly controlled pH of 7.4, which prevents the formation of PO43--containing ACP. [Conclusions]: The precipitation of ACP in vitro is unrelated to VC in vivo. The model needs to be refined through controlled pH and the use of additional procalcifying agents other than Pi in order to reproduce calcium phosphate deposition in vivo.Funding was provided by a research grant SAF2012-33898 to VS, http://www.mineco.gob.es/portal/site/mineco/idi, Spanish Ministry of Economy and Competitiveness; research grant MAT2014-54975-R to AM, http://www.mineco.gob.es/portal/site/mineco/idi, Spanish Ministry of Economy and Competitiveness.Peer Reviewe

Índice

ÍNDIC

Índice

ÍNDIC