Maintenance of implication integrity constraints under updates to constraints

Semantic integrity constraints are used for enforcing the integrity of the database as well as for improving the efficiency of the database utilization. Although semantic integrity constraints are usually much more static as compared to the data itself, changes in the data semantics may necessitate corresponding changes in the constraint base. In this paper we address the problems related with maintaining a consistent and non-redundant set of constraints satisfied by the database in the case of updates to the constraint base. We consider implication constraints as semantic integrity constraints. The constraints are represented as conjunctions of inequalities. We present a methodology to determine whether a constraint is redundant or contradictory with respect to a set of constraints. The methodology is based on the partitioning of the constraint base which improves the efficiency of algorithms that check whether a constraint is redundant or contradictory with respect to a constraint base. Received August 19, 1993 / Accepted July 7, 1997     

Nonlinear viscoelastic contact and deformation of freeform virtual surfaces

This article is concerned with the haptic deformation display of discrete viscoelastic surfaces by means of a human fingertip. The virtual surface of a deformable quadrilateral mesh is interactively deformed by a Kelvin–Voigt soft fingertip model attached to the end-effector of a haptic interface device. In achieving this task, a nonlinear constitutive model approximating experimental data from literature is developed for determining the contact point deformations. By employing a new kernel weighting function, the deformations are distributed dependently on the discrete surface topology based on a nonlinear spring–damper net around the contact location. For illustration and evaluation of the proposed approach, a parallel robotic device with a constraint-based controller is adopted. The grip of the device is moved by the user to feel a sense of touch as the soft fingertip deforms the mesh surface of an ex vivo porcine liver tissue. Experimental data indicates stable realistic interactions thorough mechanical coupling between the soft fingertip and the deforming liver tissue. Dynamic response data of liver show rate-dependent hysteretic deformations and match closely with experimental indentation data from literature. A thorough analysis of mesh node count on the sample rate and the rendering quality is also presented.     

The development, validity and reliability of TPACK-deep: A technological pedagogical content knowledge scale

The purpose of this study is to develop a TPACK (technological pedagogical content knowledge) scale based on the centered component of TPACK framework in order to measure preservice teachers’ TPACK. A systematic and step-by-step approach was followed for the development of the scale. The validity and reliability studies of the scale were carried out with 995 Turkish preservice teachers. The sample was split into two subsamples on random basis (n1 = 498, n2 = 497). The first sample was used for Exploratory Factor Analysis (EFA) and the second sample for Confirmatory Factor Analysis (CFA). After the EFA, the TPACK-deep scale included 33 items and had four factors. These factors were design, exertion, ethics and proficiency. The Cronbach’s alpha coefficient for the whole scale was found to be .95, whereas the values of Cronbach’s alpha coefficient for individual factors of the scale ranged between .85 and .92. The CFA was conducted within the scope of the validity study of the scale. In this way, this structure of the 4-factor scale was confirmed. In addition, the test-retest reliability coefficient of the scale was calculated as .80. The findings revealed that the TPACK-deep scale was a valid and reliable instrument for measuring TPACK. Consequently, various suggestions were put forward regarding the use the TPACK-deep scale for applied research and for future studies.     

Epipolar Geometry and Linear Subspace Methods: A New Approach to Weak Calibration

This paper addresses the problem of estimating the epipolar geometry from point correspondences between two images taken by uncalibrated perspective cameras. It is shown that Jepson's and Heeger's linear subspace technique for infinitesimal motion estimation can be generalized to the finite motion case by choosing an appropriate basis for projective space. This yields a linear method for weak calibration. The proposed algorithm has been implemented and tested on both real and synthetic images, and it is compared to other linear and non-linear approaches to weak calibration.     

Neural network based approach for determining the shear strength of circular reinforced concrete columns

The objective of this study is to investigate the adequacy of neural networks (NN) as a quicker, more secure and more robust method to determine the shear strength of circular reinforced concrete columns. In the application of the NN model, a multilayer perceptron (MLP) with a back-propagation (BP) algorithm is employed using a scaled conjugate gradient. NN model is developed, trained and tested through a based MATLAB program. The data used for training and testing NN model are gathered from literature. NN based model outputs are compared with ACI, ATC-32, ASCE and CALTRANS codes outcomes on the basis of the experimental results. This comparison demonstrated that the NN based model is highly successful to determine the shear strength of circular reinforced concrete columns.     

A new method for determination of fine particle breakage

Material characterization plays a crucial role by means of equipments efficiency and overall circuit performance. Material properties such as grindability, breakage, crushability, mineralogy can easily be determined by laboratory studies. These parameters are required for modeling and simulation works.Breakage behaviour of material is important for size reduction equipments and it is defined by breakage distribution function. Commonly, single particle breakage method is used to determine breakage behaviour of materials which assumes that breakage is not size dependent. As new surfaces formed material behaviour changes so particle size effect should also be introduced into the grinding model structure. Determination of fine particle breakage becomes important. This will make models more reliable. With this aim a bed breakage method was developed for determination of fine particle breakage. In this study new breakage model is presented and effects of different breakage distribution functions on breakage rate and discharge function is investigated. The bed breakage test results are compared with single size drop-weight test results in the aspect of modeling. It was observed that, the breakage rate and discharge function variation by size indicates a characteristic change at fine size ranges compared to regular curve.