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21.
R. Ignacio Madrid Herre Van Oostendorp Mari Carmen Puerta Melguizo 《Computers in human behavior》2009
Problems in learning with hypertext systems have been claimed to be caused by high levels of disorientation and cognitive load. This was recognized by DeStefano and LeFevre [DeStefano, D., & LeFevre, J. -A., (2007). Cognitive load in hypertext reading: A review. Computers in Human Behavior, 23(3), 1616–1641.] who predicted an increase of cognitive load and impairment of learning for hypertexts with a higher number of links per page. From a practical perspective, several navigation support techniques, such as providing link suggestions, have been proposed for guiding learners and reducing cognitive overload. In an experiment, we tested DeStefano and LeFevre’s predictions as well as the usefulness of link suggestions. Participants used different versions of a hypertext, either with 3-links or 8-links per page, presenting link suggestions or not. We tested their cognitive load and learning outcomes. Results showed that there was a benefit of using link suggestions for learning, but no effect of number of links on learning was found. Moreover, the effects of our manipulations on cognitive load were mediated by the reading order that participants selected. Implications for research and the design of navigation support systems are discussed. 相似文献
22.
Vibhor Agrawal Christopher O'Toole Ignacio A. Gaunaurd Robert S. Gailey 《Ergonomics》2016,59(1):121-129
Current methods of quantifying the stand-to-sit activity (StTS) are resource intensive and have not been applied to unilateral transtibial amputees (TTAs). The purpose of this study is to define five phases of arm-rest assisted and unassisted StTS using simple instrumentation and implement this method for assessing TTA movement patterns. Twelve TTAs and 12 age-matched non-amputees performed StTS with and without arm-rest support. Symmetry of weight distribution between lower limbs was calculated for five StTS phases: Descent Initiation; Descent Deceleration; Seat-Contact; Stabilisation and Sitting. TTAs demonstrated an asymmetrical weight distribution pattern and a tendency to transfer weight to the intact limb during the course of the activity. Non-amputees had relatively higher symmetry and did not exhibit substantial weight shifts during the activity. Symmetry indices were similar for assisted and unassisted sitting in both subject groups. These results highlight a need for therapeutic interventions in TTAs for reducing loading asymmetries and associated co-morbidities. 相似文献
23.
Ignacio Peñarrocha Daniel Dolz Julio Ariel Romero Roberto Sanchis 《International journal of systems science》2016,47(2):283-299
This work presents a strategy to minimise the network usage and the energy consumption of wireless battery-powered sensors in the observer problem over networks. The sensor nodes implement a periodic send-on-delta approach, sending new measurements when a measure deviates considerably from the previous sent one. The estimator node implements a jump observer whose gains are computed offline and depend on the combination of available new measurements. We bound the estimator performance as a function of the sending policies and then state the design procedure of the observer under fixed sending thresholds as a semidefinite programming problem. We address this problem first in a deterministic way and, to reduce conservativeness, in a stochastic one after obtaining bounds on the probabilities of having new measurements and applying robust optimisation problem over the possible probabilities using sum of squares decomposition. We relate the network usage with the sending thresholds and propose an iterative procedure for the design of those thresholds, minimising the network usage while guaranteeing a prescribed estimation performance. Simulation results and experimental analysis show the validity of the proposal and the reduction of network resources that can be achieved with the stochastic approach. 相似文献
24.
Alfonso Fuentes Jose L. Iserte Ignacio Gonzalez-Perez Francisco T. Sanchez-Marin 《Computer Methods in Applied Mechanics and Engineering》2011,200(29-32):2363-2377
The computerized design of advanced straight and skew bevel gears produced by precision forging is proposed. Modifications of the tooth surfaces of one of the members of the gear set are proposed in order to localize the bearing contact and predesign a favorable function of transmission errors. The proposed modifications of the tooth surfaces will be computed by using a modified imaginary crown-gear and applied in manufacturing through the use of the proper die geometry. The geometry of the die is obtained for each member of the gear set from their theoretical geometry obtained considering its generation by the corresponding imaginary crown-gear. Two types of surface modification, whole and partial crowning, are investigated in order to get the more effective way of surface modification of skew and straight bevel gears. A favorable function of transmission errors is predesigned to allow low levels of noise and vibration of the gear drive. Numerical examples of design of both skew and straight bevel gear drives are included to illustrate the advantages of the proposed geometry. 相似文献
25.
A comparison of finite elements for nonlinear beams: the absolute nodal coordinate and geometrically exact formulations 总被引:2,自引:2,他引:0
Ignacio Romero 《Multibody System Dynamics》2008,20(1):51-68
Two of the most popular finite element formulations for solving nonlinear beams are the absolute nodal coordinate and the
geometrically exact approaches. Both can be applied to problems with very large deformations and strains, but they differ
substantially at the continuous and the discrete levels. In addition, implementation and run-time computational costs also
vary significantly. In the current work, we summarize the main features of the two formulations, highlighting their differences
and similarities, and perform numerical benchmarks to assess their accuracy and robustness. The article concludes with recommendations
for the choice of one formulation over the other. 相似文献
26.
Ignacio Fernández Manuel Mazo José L. Lázaro Daniel Pizarro Enrique Santiso Pedro Martín Cristina Losada 《Autonomous Robots》2007,23(4):305-324
This paper presents a new proposal for positioning and guiding mobile robots in indoor environments. The proposal is based
on the information provided by static cameras located in the movement environment. This proposal falls within the scope of
what are known as intelligent environments; in this case, the environment is provided with cameras that, once calibrated,
allow the position of the robots to be obtained. Based on this information, control orders for the robots can be generated
using a radio frequency link. In order to facilitate identification of the robots, even under extremely adverse ambient lighting
conditions, a beacon consisting of four circular elements constructed from infrared diodes is mounted on board the robots.
In order to identify the beacon, an edge detection process is carried out. This is followed by a process that, based on the
algebraic distance, obtains the estimated ellipses associated with each element of the beacon. Once the beacon has been identified,
the coordinates of the centroids for the elements that make up the beacon are obtained on the various image planes. Based
on these coordinates, an algorithm is proposed that takes into account the standard deviation of the error produced in the
various cameras in ascertaining the coordinates of the beacon’s elements. An odometric system is also used in guidance that,
in conjunction with a Kalman Filter, allows the position of the robot to be estimated during the time intervals required to
process the visual information provided by the cameras.
相似文献
Cristina LosadaEmail: |
27.
Fernández M Caballero J Fernández L Abreu JI Garriga M 《Journal of molecular graphics & modelling》2007,26(4):748-759
Development of novel computational approaches for modeling protein properties is a main goal in applied Proteomics. In this work, we reported the extension of the radial distribution function (RDF) scores formalism to proteins for encoding 3D structural information with modeling purposes. Protein-RDF (P-RDF) scores measure spherical distributions on protein 3D structure of 48 amino acids/residues properties selected from the AAindex data base. P-RDF scores were tested for building predictive models of the change of thermal unfolding Gibbs free energy change (DeltaDeltaG) of chymotrypsin inhibitor 2 upon mutations. In this sense, an ensemble of Bayesian-Regularized Genetic Neural Networks (BRGNNs) yielded an optimum nonlinear model for the conformational stability. The ensemble predictor described about 84% and 70% variance of the data in training and test sets, respectively. 相似文献
28.
Ricardo Pérez‐Castillo Ignacio García‐Rodríguez de Guzmán Mario Piattini Ángeles S. Places 《Software》2012,42(2):159-189
Business processes have become one of the key assets of organization, since these processes allow them to discover and control what occurs in their environments, with information systems automating most of an organization's processes. Unfortunately, and as a result of uncontrolled maintenance, information systems age over time until it is necessary to replace them with new and modernized systems. However, while systems are aging, meaningful business knowledge that is not present in any of the organization's other assets gradually becomes embedded in them. The preservation of this knowledge through the recovery of the underlying business processes is, therefore, a critical problem. This paper provides, as a solution to the aforementioned problem, a model‐driven procedure for recovering business processes from legacy information systems. The procedure proposes a set of models at different abstraction levels, along with the model transformations between them. The paper also provides a supporting tool, which facilitates its adoption. Moreover, a real‐life case study concerning an e‐government system applies the proposed recovery procedure to validate its effectiveness and efficiency. The case study was carried out by following a formal protocol to improve its rigor and replicability. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
29.
José Ignacio Rojas-Sola Antonio Romero-Manchado 《Expert systems with applications》2012,39(12):11183-11193
Thales’ second theorem can be used for the automatic detection of the vanishing points of an image. This paper explores its reliability and accuracy according to the type of operator used for the detection of edges. An algorithm has been used which processes a photographic image according to the operator selected. The result is a point cloud which is then used to find the desired solution. The comparison between the four discrete gradient operators (Frei-Chen, Prewitt, Roberts and Sobel) has been made taking into account the resolution of the image and the number of vanishing points. The results obtained show that Frei-Chen’s operator shows good performance in determining vanishing points with respect to the spatial X axis, Sobel’s operator is the best for determining the vanishing point with respect to the spatial Y axis, Roberts’ operator gives good results for calculating vanishing points in both spatial axes, and Prewitt’s operator is not appropriate for processing this type of image. 相似文献
30.
Rodríguez José Ignacio Jiménez José Manuel Funes Francisco Javier García de Jalón Javier 《Multibody System Dynamics》2003,10(2):177-199
In this paper a prototype of a computer program for multi-bodysimulation based on the use of CORBA, Java and XML is presented. Thisprototype makes use of a recursive dynamic formalism which outperformsmany implementations based on global formulations. The prototypepresented has been implemented using distributed Object OrientedProgramming techniques. The definition of the multi-body system is donethrough a data file defined using XML (eXtendible Markup Language). Thisprototype implements a `simulation service' on a network of computers,following a client-server scheme. This `simulation service' can operatein two different ways: offering a remote simulation on the server, orproviding a Java compiled code for local simulation on the client. Thepaper describes the practical implementation of such a service. The useof recursive functions and OOP permits the implementation of ageneral-purpose simulation code, which is compact, clear, clean,re-usable and easy to maintain. Once this Java code is compiled, it isstored in less than 125 Kbytes (including the numerical integrators).The Java programming language is used in order to assure compatibilitybetween different platforms. Finally, practical examples which make useof this approach are shown. 相似文献