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Taha Toros Arşivi, Dosya No: 71-Çelik Gülersoyİstanbul Kalkınma Ajansı (TR10/14/YEN/0033) İstanbul Development Agency (TR10/14/YEN/0033

TEACHING SCIENCE: WHO AM I? WHAT DO I PLAN?

Achievement in the primary school science lesson has always been the subject of attention by researchers in Turkey and different countries. For this reason, they carry out studies on science teaching at the primary school level. This study aimed to reveal the strengths and weaknesses of pre- and in-service classroom teachers in science teaching. In addition, to improve their weaknesses, the features of the science classroom that they imagined were revealed. Seventy-seven juniors, 78 seniors, and 87 in-service teachers participated in the study. We obtained the data through an opinion form called “I Teach Science” and consisting of four questions. Findings were revealed because of the descriptive analysis. We found the most frequently uttered strengths as being able to do/design experiments, adopting activity-based science teaching, having, and applying different methods/technical knowledge, having science process skills, and having an interest in/attitude towards the science. The most common weaknesses were the lack of field knowledge, lack of self-confidence, inability to do experiments, lack of laboratory knowledge, inability to design/use materials, and lack of interest in and attitude towards science. The most common ways they would apply to improve their weaknesses were found as doing research, reviewing resources, obtaining help from experts or colleagues, designing experiments, researching/learning different methods, utilizing different resources, and developing planning skills. While describing a dream science classroom, the participants considered general characteristics of students and teachers and general/physical features of the classroom

Determination of Multi-performance Characteristics in Electric Discharge Machining of DIN 1.2767 Steel Using Grey Relational Analysis

   Electric discharge machining (EDM) is one of the most important unconventional machining processes, which can cut hard materials and complex shapes that are difficult to machine by conventional machining processes easily and with high accuracy. In this study, L18 orthogonal array combined with gray relational analysis (GRA) is implemented to investigate the multiple performances characteristics in EDM of DIN 1.2767 Tool Steel. Machining process parameters selected were discharge current (Ip), pulse-on time (Ton), pulse-off time (Toff), and electrode material (copper alloys [NSS and B2]). The investigated performances characteristics were tool wear rate (TWR) and material removal rate (MRR). Analysis of variance (ANOVA) and Taguchi’s signal-to-noise ratio with the help of Minitab-17 software were used to analysis the effect of the process parameters on TWR and MRR. The experimental results and data analysis reveal that TWR and MRR are more affected by Ip and Ton. The minimum TWR was obtained at parametric combination Ip (6A), Ton (800 μs), and Toff (800 μs) and the maximum MRR attained at Ip (25A), Ton (800 μs), Toff (200 μs), and NSS electrode. After applying GRA, the optimal parametric combination for MRR and TWR was determined as Ip (25A), Ton (800 μs), Toff (200 μs), and NSS electrode. The study also exhibited the occurrence of an interaction between the variables on the responses. In addition, scanning electron microscopy images showed that the metal surface was affected with the increase in Ton and Toff

Symbolic Supervisory Control of Distributed Systems with Communications

We consider the control of distributed systems composed of subsystems communicating asynchronously; the aim is to build local controllers that restrict the behavior of a distributed system in order to satisfy a global state avoidance property. We model distributed systems as \emph{communicating finite state machines} with reliable unbounded FIFO queues between subsystems. Local controllers can only observe the behavior of their proper subsystem and do not see the queue contents. To refine their control policy, controllers can use the FIFO queues to communicate by piggy-backing extra information (some timestamps and their state estimates) to the messages sent by the subsystems. We provide an algorithm that computes, for each local subsystem (and thus for each controller), during the execution of the system, an estimate of the current global state of the distributed system. We then define a synthesis algorithm to compute local controllers. Our method relies on the computation of (co-)reachable states. Since the reachability problem is undecidable in our model, we use abstract interpretation techniques to obtain overapproximations of (co-)reachable states. An implementation of our algorithms provides an empirical evaluation of our method

Synthesis of Communicating Controllers for Distributed Systems

International audienceWe consider the control of distributed systems composed of subsystems communicating asynchronously; the aim is to build local controllers that restrict the behavior of a distributed system in order to satisfy a global state avoidance property. We model our distributed systems as communicating finite state machines with reliable unbounded FIFO queues between subsystems. Local controllers can only observe their proper local subsystems and do not observe the queues. To refine their control policy, they can use the FIFO queues to communicate by piggybacking extra information to the messages sent by the subsystems. We define synthesis algorithms allowing to compute the local controllers. We explain how we can ensure the termination of this control algorithm by using abstract interpretation techniques, to overapproximate queue contents by regular languages. An implementation of our algorithms provides an empirical evaluation of our method

Response of polycaprolactone bone scaffolds with -hydroxyapatite and tricalcium phosphate to elevated loading frequencies

Introduction: Recent studies have implied that bone cells respond more favorably to low amplitude loading at higher frequencies in contrast to high amplitude loading at low frequencies. However, the mechanical response associated with bone scaffolds at elevated frequency loading is unknown. The goal of this study was to evaluate the performance of polycaprolactone (PCL) bone scaffold materials with hydroxyapatite (HA) and tricalcium phosphate (TCP) under various loading frequencies. Materials and Methods: Compression molded scaffolds containing polycaprolactone scaffolds with 14% hydroxyapatite (HA) or 14% tricalcium phosphate (TCP) were fabricated. Scaffolds were subjected to cyclic compressive loading from –0.5 N to –2 N for 535 loading cycles at 1 Hz (N = 12HA, N = 12TCP), 2.5 Hz (N = 12HA, N = 12TCP), 5 Hz (N = 6HA, N = 6TCP), and 7.5 Hz (N=12 HA, N=12 TCP). Compressive loads were applied using a 1-mm diameter indentor mounted to the actuator of a materials testing machine. Load versus deformation data were acquired at cycle 10 and at 25 cycle intervals thereafter. For each scaffold type, deformation changes over the applied loading cycles were calculated for each test site and subjected to nonlinear exponential regression. The resulting exponential parameters included Y0 (initial deformation) and K (rate of deformation change per cycle) and were analyzed using a one-way ANOVA with a Tukey posthoc test for differences between scaffold types and loading frequency. Results and Discussion: Statistically significant differences in the initial deformation, Y0, were found across both material type (HA versus TCP) and loading frequency. (P \u3c 0.05 for all comparisons). For a given frequency, with the exception of 7.5 Hz, TCP scaffolds displayed significantly elevated initial deformation when compared with HA, indicative of a decreased modulus relative to HA. For the K values, statistically significant increases in K value were found for both HA and TCP scaffolds when loaded at 7.5 Hzwhen compared with all other frequencies (P \u3c 0.05). The results of elevated frequency loading can provide insight into the long-term use of scaffolds suitable for bone tissue engineering. In this study, loading at an elevated frequency of 7.5 Hz increased the initial deformation (Y0) for both HA and TCP scaffolds. Such an observation is indicative of an increase in the modulus as the loading frequency increases. For both HA and TCP, 1 Hz, 2.5 Hz, and 7.5 Hz loading frequencies resulted in reduced K values indicative of a frequency dependence to loading rate. The decreased K values indicate an increased number of cycles prior to mechanical compromise,and hence improved mechanical resistance under fatigue loading. However, it is the significant increase in the K value noted at the 7.5-Hz loading frequency that is of interest, as it is indicative of increased energy transfer and a greater response of the HA and TCP scaffolds when compared with the other frequencies. Conclusions: The stiffening of the scaffolds at elevated frequencies may be of mechanical advantage when one considers the long-term physiological and cyclic loading and these devices are to sustain under clinical applications. Scaffold response should also be considered within the concepts of stress shielding and modulus matching to surrounding environments