Abstract: The goal of this study is to compare surface morphologies on dental implants created by a range of five different surface-modification technologies and, in addition, cell assays to assess the subsequent cell proliferation on each treated surface. In our research, we surface-treated 5 mm-diameter – 2 mm-thick discs, machined from Grade 1 titanium. We treated the surfaces of the discs with chemical etching, electro-polishing, Al2O3 sand-blasting, and surface melting with 1 Joule or 3 Joule impulse-energy laser beam. We carried out quantitative as well as qualitative analyses with stereo and scanning electron microscopes (SEM), confocal and atomic force microscopes (AFM) and goniometer. We examined each surface with cell-testing, as a measure of osseointegration. In tests with fibroblasts, the highest cell proliferation occurred on the Al2O3-roughened surfaces. In the case of osteoblasts, we measured the greatest cell activity on the laser-melted samples with different energy levels.
Keywords: surface modification; surface analyses; surface morphology; cell proliferation
Abstract: Performance modeling and prediction of web-based software systems are important and complicated considerations. The goal of our paper is to establish proper mathematical models in the form of difference equations, by subspace identification, in order to model and predict the performance of web-based software systems. First, simulation models have been provided to simulate the behavior of thread pool and queued requests. Second, analytical models have been proposed in form of state space models using subspace identification. In addition, it has been demonstrated that the proposed models can be applied to performance prediction of web-based software systems. The proposed models have been validated and verified. Furthermore, performance factor identification and performance prediction techniques have been proposed based on subspace identification.
Keywords: web-based software system; subspace identification; performance modeling; performance factor identification; performance prediction
Abstract: This paper presents a theoretical examination of acoustic metamaterials and their application in vibration absorption. Acoustic metamaterials are concerned as analogy to electromagnetic metamaterials which are suitable for refraction and decline of electromagnetic waves at certain frequencies. Due to the analogy with these materials, the acoustic metamaterials is required to have negative effective (dynamic) mass to enable vibration elimination at the certain frequency. The concept of negative effective mass is explained based on the motion of an externally excited mass-in-mass system where the vibration elimination at the certain frequency is due to the mass-spring unit. Using these vibration absorber units, the acoustic metamaterial beams are made. Depending on the way how the units are attached to the beam, the structure may absorb waves in one-direction (for example, longitudinal waves) or waves in two directions (such as, for instance, transversal and longitudinal waves). Moreover, according to the frequency properties of the absorber units the acoustic metamaterial beams may give one, two or multi-frequency gaps. This work provides an overview of the mathematical models of acoustic metamaterial beams and also contains some suggestions for future work.
Keywords: elastic metamaterial; acoustic metamaterial beam; spring-mass systems; negative effective mass
Abstract: A class of cascade filters, orthogonal with respect to a new inner product, is presented in this paper. A sequence of generalized Malmquist orthogonal rational functions is used for design of these filters. In addition, by using these functions Müntz polynomials which are orthogonal in respect to a special inner product were derived. Obtained Müntz polynomials are applied in determination of outputs of the proposed filters. Depending on whether the design of the filters is performed in the s-domain or complex z-domain, we can derive a class of analogue or digital filters, respectively. Outputs from these filters are orthogonal with respect to the two different inner products. Both classes of filters are practically realized and their application in modeling of continuous-time and discrete-time dynamical systems is given. Obtained results show that there are great agreements between the outputs of models and real dynamical systems.
Keywords: orthogonal filters; inner product; dynamical systems modeling; Malmquist functions; Müntz polynomials
Abstract: Stepping motor drives are widely used for positioning applications due to their easy controllability and straightforward connectivity to digital electronics. One of their greatest advantages is the possibility to perform positioning without requiring a closed-loop position control system. Stepping motor drives have special characteristics and therefore are considered as special types of electric drives. In this paper, these special characteristics are presented, along with a new type of classification. This classification is based on both the presented special characteristics (construction, etc.) and a newly derived equation called the fundamental equation of stepping motor drives. It is also shown in this paper that based on the new classification stepping motor drives can be divided into two subcategories: synchronous-type and asynchronous-type steppers. These subcategories are based on their similarities to traditional synchronous- and asynchronous (induction) motor drives. Also, the basic equations of the presented stepping motor drives will be derived from the fundamental equation of stepping motor drives. Therefore, this new type of classification is well applicable for both scientific analysis and educational purposes.
Keywords: stepping motor; stepper motor; step motor; special characteristic; classification; the fundamental equation of stepping motor drives; variable reluctance stepping motor; permanent magnet stepping motor; hybrid stepping motor
Abstract: Cardiovascular diseases are still among the most common causes of death. Online and automated diagnostic solutions are considered as a possible remedy. In this paper, the authors present one such solution, which is based on the Minnesota Code and type-2 fuzzy for identifying cardiovascular diseases. The presented diagnostic system is case studied on various ECG data sets and compared to diagnostic results provided by physicians.
Keywords: fuzzy; type-2 fuzzy; interval fuzzy; Minnesota Code
Abstract: Skeletons are widely used shape descriptors which summarize the general form of binary objects. There exist numerous skeletonization techniques that produce various skeleton-like features for the same object. Despite of the fact, that some researchers have made efforts to compare skeletons and evaluate skeletonization algorithms, we propose a new similarity measure that is based on the concept of normalized distance maps. In addition, a novel method for the quantitative comparison of skeletons is also presented. The reported method uses a high resolution dataset containing pairs of elongated objects and their expected skeletons. Our method is validated with the help of generalized morphological skeletons driven by neighborhood sequences. Based on the proposed method, we compared and ranked nineteen existing 2D thinning algorithms.
Keywords: skeleton; comparison of skeletons; generalized morphological skeleton; neighborhood sequences
Abstract: The evaluation and ranking of recycling technologies for each treated waste with respects to many different criteria has important results for the management team of any recycling center. Improvement of business strategy is based on the obtained rank of recycling technologies. It represents a key success factor for a recycling center in dealing with crisis. Uncertainties in: relative importance of evaluation criteria and priority of recycling technologies under each criterion are described by triangular fuzzy numbers. Relative importance of evaluation criteria is stated by fuzzy pair-wise comparison matrices. Determining of elements values of these matrices can be considered as a fuzzy group decision making problem. Aggregation of individual opinions into group consensus is performed by using fuzzy averaging method and Fuzzy Ordered Weighted Aggregation (FOWA,) Operator Fuzzy Analytic Hierarchy Process (FAHP) is used for determination of rank of recycling technologies with respects to evaluation criteria and its weights. Proposed model is tested by example with real life data.
Keywords: waste; recycling technologies; fuzzy set; FAHP
Abstract: This study explores the potential of using creative 3D modeling for the development of spatial abilities. We investigate the efficiency of spatial training programs with a focus on differences in spatial information processing in real and virtual environments. Participants were architecture and civil engineering students in the first and second study year. The standardized Spatial Ability Test by Séra, Kárpáti and Gulyás (2002) was used for the assessment of relevant skill components: spatial perception, visualization and mental manipulation. In order to analyze visuospatial information processing and problem solving, we documented the phases of planning and modeling and revealed problems and motivating factors of the design process through student surveys. We discuss factors influencing the perception and interpretation of space and showed strategies of engineering students in solving spatial problems. The effectiveness of the program was unrelated to gender, specialization, secondary level studies and learning environments (real and virtual spaces). Post-test results of the experimental groups were significantly higher (t=-4.70, p<0.001) and the effect size of the developmental program was d=1.07. Research has proven that an appropriately constructed set of creative problem solving tasks in modeling and construction, results in significant development of spatial skills and are as effective as traditional drawing tasks. Creative modeling is an activity with high motivation value and can be utilized to develop spatial abilities that are basic for the professional development of engineers and architects
Keywords: spatial abilities; creative problem solving; 3D modeling; project pedagogy; virtual learning environment
Abstract: In this paper, the optimum geometry of a journal bearing is calculated for minimum friction coefficient and for maximum load carrying capacity. The optimized versions can be compared, which makes it possible to draw important conclusions concerning the necessary constructional changes in journal bearings if we want to increase the load carrying capacity or to decrease the energy loss due to friction. It is also interesting to see the differences in the load carrying capacity when the friction coefficient is minimal or in the friction coefficient when the load carrying capacity is maximal. During the investigations the basic equation of the THD (Thermo-Hydrodynamic) state of hydrodynamic journal bearings is solved by using the finite difference technique, while for the optimization the RVA (Random Virus Algorithm) is used. As the result of the optimization process, the load carrying capacity can be increased by more than 28% or the friction coefficient in the oil film can be decreased by 29% compared to the starting design.
Keywords: friction coefficient; journal bearing; load bearing capacity; optimization; RVA
Abstract: In the initial stage of the abrasive wear process, the microtopography of steels drastically changes until it reaches a stable state. This stage can be described by the changes of the 3 dimensional roughness parameters. To predict these parameters, a simulation algorithm has been developed which was validated by wear tests. The applied load and the length of the wear path varied in wide interval during the experiments. The 1.1191 steel specimen was worn using an ISO 6344:1998 abrasive paper with a mesh size of 1200. It was found that both the experimental and the simulation results can be modelled in the same manner, meaning that we use a single function involving different parameters, which depends on the problem to be solved.
Keywords: algorithm; surface roughness measurement; wear; abrasion; steel; design of experiment