Problem-Centered Approach in a Numerical Methods Course

This paper is an illustration of using a problem-centered approach in an undergraduate course in numerical methods. The problem used in the course was first encountered in a research project that related to the assembly procedure of the fulcrum of bascule bridges. It involved the study of the fulcrum assembly procedure where a trunnion cooled in a dry-ice/alcohol mixture for shrink fitting became stuck halfway in the hub before full insertion could take place. The solution of the problem and its implementation involved numerical solutions of mathematical procedures taught in a typical numerical methods course. The effect of the problem-centered approach in the classroom was quantitatively and qualitatively surveyed over a two-semester period. The results indicate very high student satisfaction in helping them: acquire basic knowledge and skills; reinforce information presented in class, reading assignments, and problem sets; learn to clearly formulate a specific problem and then work it through to completion; develop generic higher-order thinking and problem solving skills; and develop a sense of competence and confidence and see the relevance of the course material to their major.     

Automated Quality Characterization for Composites Using Hybrid Ultrasonic Imaging Techniques

An enhanced technique using image processing has been developed for automated ultrasonic inspection of composite materials, such as glass/carbon-fibre-reinforced polymer (GFRP or CFRP), to ascertain their structural healthiness. The proposed technique is capable of identifying the abnormality features buried in the composite by image filtering and segmentation applied to ultrasonic C-Scan images. This work presents results performed on two composite samples with simulated delamination defects. A local gating scheme is applied to raw A-Scan data for improved contrast between defective and healthy regions in the produced C-Scan image. In this test campaign, different filtering and thresholding algorithms are evaluated and compared in terms of their effectiveness on defect identification. The accuracies of less than 3 mm and 1.11 mm were attained for the defect size and depth, respectively. The results demonstrates the applicability of the proposed technique for accurate defect localization and characterization of composite materials.     

An optimal and a heuristic algorithm for the single-item retrieval problem in puzzle-based storage systems with multiple escorts

Puzzle-based storage systems consist of densely stored unit loads on a square grid. The problem addressed in this paper is to retrieve a stored unit load from a puzzle-based storage using the minimum number of item moves. While previous research contributed optimal algorithms for only up to two empty locations (escorts), our approach solves configurations where multiple empty locations are arbitrarily positioned in the grid. The problem is formulated as a state space problem and solved to optimality using an exact search algorithm. To reduce the search space, we derive bounds on the number of eligible empty locations and develop several search-guiding estimate functions. Furthermore, we present a heuristic variant of the search algorithm to solve larger problem instances. We evaluate both solution algorithms on a large set of problem instances. Our computational results show that the algorithms clearly outperform existing approaches where they are applicate and solve more general configurations, which could not be solved to optimality before. The heuristic variant efficiently yields high-quality solutions for significantly larger instances of practically relevant size.     

Renal artery embolization in severe nephrotic syndrome

Introduction Severe nephrotic syndrome is associated with increased morbidity and mortality. Renal artery embolization (RAE) has been used in a number of renal diseases such as renal tumors, arteriovenous fistulas etc. However, data regarding benefits of RAE in patients with symptomatic severe proteinuria is limited. We decided to evaluate role of RAE in the setting of severe symptomatic nephrotic syndrome. Methods Eight patients who had undergone transcatheter renal artery embolization with polyvinyl alcohol (PVA) were included. Clinico‐demographic characteristics as well as baseline laboratory data including level of proteinuria, serum albumin, C‐reactive protein and LDL cholesterol levels were recorded for each patient. After RAE, outpatient clinic control laboratory values were also assessed. Findings All patients except one underwent bilateral RAE (four simultaneous or three sequential). Two patients experienced postembolization syndrome characterized by flank pain, fever, and leukocytosis, which was self‐limited and responded to analgesics in all patients. There was no technical complications associated with RAE procedure. All patients became anuric except one. Serum albumin levels increased and serum LDL‐cholesterol levels decreased considerably in treated patients. Discussion Renal artery embolization with the purpose of amelioration in nephrotic syndrome complications was effective and free of major technical complications in our patients.     

A software for simulating steady-state properties of passive dendrites based on the cable theory

In this study, a computer software, CableTeo, is introduced for simulating the steady-state electrical properties of passive dendrite based on the cable theory. The cable theory for dendritic neurons addresses to current-voltage relations in a continuous passive dendritic tree. It is briefly summarized that the cable theory related to passive cables and dendrites, which is a useful approximation and an important reference for excitable cases. The proposed software can be used to construct user-defined dendritic tree model. The user can define the model in detail, display the constructed dendritic tree, and examine the basic electrical properties of the dendritic tree using transfer impedance approach. The software addresses to ones who want to run simple simulations of the cable theory without need to any programming language skills or expensive software. It can also be used for educational purposes.     

Markov Chain Analysis of Self-organizing Mobile Nodes

Self-organization of autonomous mobile nodes using bio-inspired algorithms in mobile ad hoc networks (manets) has been presented in earlier work of the authors. In this paper, the convergence speed of our force-based genetic algorithm (called fga) is provided through analysis using homogeneous Markov chains. The fga is run by each mobile node as a topology control mechanism to decide a corresponding node??s next speed and movement direction so that it guides an autonomous mobile node over an unknown geographical area to obtain a uniform node distribution while only using local information. The stochastic behavior of fga, like all ga-based approaches, makes it difficult to analyze the effects that various manet characteristics have on its convergence speed. Metrically transitive homogeneous Markov chains have been used to analyze the convergence of our fga with respect to various communication ranges of mobile nodes and also the number of nodes in various scenarios. The Dobrushin contraction coefficient of ergodicity is used for measuring convergence speed for Markov chain model of our fga. Two different testbed platforms are presented to illustrate effectiveness of our bio-inspired algorithm in terms of area coverage.     

Identification of common sensory features for the control of CNC milling operations under varying cutting conditions

The main focus of this study is to identify the most influential and common sensory features for the process quality characteristics in CNC milling operations—dimensional accuracy (bore size tolerance) and surface roughness—using three different material types (6061-T6 aluminum, 7075-T6 aluminum, and ANSI-4140 steel). The materials were machined on a vertical CNC mill, retrofitted with multiple sensors and data acquisition systems, to investigate the effects of variations in material types and machining parameters. The sensor data include cutting force measurements, spindle quill vibration, and acoustic emission, each of which further divided into measurable components, such as x, y, and z components in cutting force, x and y spindle quill vibration, DC, AC, and Count Rate for acoustic emission signals. Those components were filtered and analyzed to determine the sensory features that best correlate with process quality characteristics. Tool wear rate and machining characteristics appeared differently, depending on the material types, yet some components of the sensory data were found to be significant with relation to the variations in bore size and surface roughness for all three types of materials. This suggests that even under the varying cutting conditions involving different materials, the identified sensory features can be used for the reliable and accurate control of milling operations.     

How a new realistic mobility model can affect the relative performance of a mobile networking scheme

The validity of the mobility model used to evaluate a cellular network determines the validity of the evaluation. In the literature, unrealistic assumptions on mobility are exercised for the sake of simplicity. In this paper, we present a novel mobility model which is realistic in the sense that it captures the moving‐in‐groups, conscious traveling and inertial behaviours of the subscribers while respecting the non‐pass‐through feature of structures like households and preserving the autonomy of the subscribers. The mobility and call patterns of the subscribers are determined according to the locus of the subscriber over a real map. Thus, our model allows the subscribers to leave home or arrive home, walk or drive in the streets, get on the highways at specific entry points together with numerous hot and blind spots in the terrain, like city centers and lakes. The call pattern of a subscriber is affected by the type of structure he is in. The model can work on real maps to simulate the mobility patterns in real life. We have evaluated the proposed model against the well‐known way point mobility model. We also analyzed the effect of the mobility model on systems with and without guard channels. Copyright © 2004 John Wiley & Sons, Ltd.     

Effects of sodium ascorbate and delayed bonding after bleaching on shear bond strengts of orthodontic brackets

Introduction: The aim of the study was to determine the effects of sodium ascorbate and delaying bonding for 4 weeks after bleaching on SBS of orthodontic brackets.

Methods: Sixty freshly extracted, noncarious, premolars were randomly assigned to 4 groups of 15 each. Orthodontic brackets were bonded with a composite resin and cured with a halogen light. After bonding, the shear bond strengths of the brackets were tested with a universal testing machine. Group I served as the control. In groups II, III, and IV, teeth were bleached with an office bleaching method. In group II, brackets bonded immediately after bleaching. In group III, teeth were immersed in artificial saliva of 4 weeks after bleaching before bonding brackets. In group IV, teeth were treated with 10% sodium ascorbate after bleaching before bonding brackets.

Results: One-way analysis of variance indicated a significant difference between groups (P < .001). The highest values for SBS were measured in group I (11.92 ± 0.81 MPa). The SBS was significantly lower in groups II, III, and IV than in group I (P < .001). There was no statistically significant difference between groups III and IV.

Conclusions: Bleaching significantly reduced the SBS of orthodontic brackets on human enamel. If bleaching is mandatory, teeth should be treated with sodium ascorbate before bonding.