12,658 research outputs found
Optical sensor to measure the projectile velocity
Displays & Photonics Applications Group (GDAF), belonging to Electronics Technology Department of University Carlos III of Madrid (Spain), has designed and implemented a simple, cost-effective, and robust optoelectronic system to measure online the average velocity of a projectile. This system is able to measure velocities ranged between 100m/s and 1200m/s). Potential applications are focused on experimental impact tests on aircraft and spacecraft structures. We are seeking potential collaborations with international/national research centres and enterprises to extent the range of potential applications
Subordinated Public Participation Loans for Financing Motorway concessions in Spain.
Budgetary constraints are prompting many governments to encourage private financing of transportation infrastructure through concession contracts. The length and complexity of such contracts often force governments to provide fiscal support in order to increase the attractiveness of concessions. This paper deals with a new public support mechanism for concession contracts, called Subordinated Public Participation Loans (SPPLs), which has been implemented in Spain during the last few years. SPPLs are subordinated loans that may be given by the government to the concessionaire if the latter requests them in the tender. SPPLs are defined in such a way that the increase in interest accrued will reflect the traffic level: the larger the traffic the larger will be the SPPL yield. SPPLs have a twofold goal. First, they increase the financial attractiveness, and hence the feasibility, of concessions contracts. And second, they set up a fairer risksharing approach between the public and the private sector. This paper analyzes the implications of SPPLs in motorway concessions by contrasting the theoretical analysis with the empirical results obtained form the tender of five motorway concessions in Spain. Overall we found that the implementation of this mechanism may be considered a success. In spite of that, we propose some measures that may contribute to improving the SPPL performance in the future
Web Acceptance and Usage Model: A Comparison between Goal-directed and Experiential Web Users
In this paper we analyse the Web acceptance and usage between goal-directed users and experiential users, incorporating intrinsic motives to improve the particular and explanatory TAM value –traditionally related to extrinsic motives-. A field study was conducted to validate measures used to operationalize model variables and to test the hypothesised network of relationships. The data analysis method used was Partial Least Squares (PLS).The empirical results provided strong support for the hypotheses, highlighting the roles of flow, ease of use and usefulness in determining the actual use of the Web among experiential and goal-directed users. In contrast with previous research that suggests that flow would be more likely to occur during experiential activities than goal-directed activities, we found clear evidence of flow for goal-directed activities. In particular the study findings indicate that flow might play a powerfulrole in determining the attitude towards usage,intention to useand, in turn,actual Web use among experiential and goal-directed users
OPTIMAL REGULATION AND GROWTH IN A NATURAL-RESOURCE-BASED ECONOMY
This paper develops a two-sector model for a renewable natural resource based economy. Pareto efficient results show the optimal harvesting rate that allows for sustained long-run optimal growth, which is upper-bounded by the biological rate of reproduction. Regulation prevents from resource over-exploitation and exhaustion which arise under open access. The Ramsey policy allowing the competitive economy to reach the first-best solution, leads the government to tax harvesting activity from firms and distribute the receipts among households. In the short-run the tax is variable. In the long-run, the lower the intrinsic rate of reproduction the higher the constant unit tax on the resource use.Natural Resources, Efficiency, Open Access, Ramsey Regulation, Growth.
Self-Modeling Based Diagnosis of Software-Defined Networks
Networks built using SDN (Software-Defined Networks) and NFV (Network
Functions Virtualization) approaches are expected to face several challenges
such as scalability, robustness and resiliency. In this paper, we propose a
self-modeling based diagnosis to enable resilient networks in the context of
SDN and NFV. We focus on solving two major problems: On the one hand, we lack
today of a model or template that describes the managed elements in the context
of SDN and NFV. On the other hand, the highly dynamic networks enabled by the
softwarisation require the generation at runtime of a diagnosis model from
which the root causes can be identified. In this paper, we propose finer
granular templates that do not only model network nodes but also their
sub-components for a more detailed diagnosis suitable in the SDN and NFV
context. In addition, we specify and validate a self-modeling based diagnosis
using Bayesian Networks. This approach differs from the state of the art in the
discovery of network and service dependencies at run-time and the building of
the diagnosis model of any SDN infrastructure using our templates
The bootstrap -A review
The bootstrap, extensively studied during the last decade, has become a powerful tool in different areas of Statistical Inference. In this work, we present the main ideas of bootstrap methodology in several contexts, citing the most relevant contributions and illustrating with examples and simulation studies some interesting aspects
Linearity Testing Against a Fuzzy Rule-based Model
In this paper, we introduce a linearity test for fuzzy rule-based models in the framework of time series modeling. To do so, we explore a family of statistical models, the regime switching autoregressive models, and the relations that link them to the fuzzy rule-based models. From these relations, we derive a Lagrange Multiplier linearity test and some properties of the maximum likelihood estimator needed for it. Finally, an empirical study of the goodness of the test is presented.fuzzy rule-based models, time series, linearity test, statistical inference
Uniqueness of limit cycles for quadratic vector fields
Producción CientíficaThis article deals with the study of the number of limit
cycles surrounding a critical point of a quadratic planar vector field,
which, in normal form, can be written as x
′ = a1x − y − a3x
2 + (2a2 +
a5)xy+a6y
2
, y
′ = x+a1y+a2x
2+(2a3+a4)xy−a2y
2
. In particular, we
study the semi-varieties defined in terms of the parameters a1, a2, . . . , a6
where some classical criteria for the associated Abel equation apply.
The proofs will combine classical ideas with tools from computational
algebraic geometry.Agencia Estatal de Investigación - Fondo Europeo de Desarrollo Regional (grant MTM 2011-22751)Junta de Extremadura (grant GR15055)Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (grant MTM2015-65764-C3-1-P
Magnetic field induced inversion in the effect of particle size on powder cohesiveness
Experimental measurements are reported on the tensile yield stress of magnetofluidized beds of fine
magnetic powders operated in the cross-flow configuration. In the absence of externally applied
magnetic field the yield stress of the powder depends on particle size as expected, i.e., it increases
as bead size is decreased. This trend is however inverted when an external magnetic field is applied.
It is suggested that the average orientation of interparticle contacts relative to the direction of the
field as affected by particle size plays a relevant role on the magnetic yield stress of these
systems.Ministerio de Ciencia y Tecnología de España-FIS2006-0364
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