7,157 research outputs found

    Formation control of nonholonomic mobile robots using implicit polynomials and elliptic Fourier descriptors

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    This paper presents a novel method for the formation control of a group of nonholonomic mobile robots using implicit and parametric descriptions of the desired formation shape. The formation control strategy employs implicit polynomial (IP) representations to generate potential fields for achieving the desired formation and the elliptical Fourier descriptors (EFD) to maintain the formation once achieved. Coordination of the robots is modeled by linear springs between each robot and its two nearest neighbors. Advantages of this new method are increased flexibility in the formation shape, scalability to different swarm sizes and easy implementation. The shape formation control is first developed for point particle robots and then extended to nonholonomic mobile robots. Several simulations with robot groups of different sizes are presented to validate our proposed approach

    Modeling of temperature distribution in orthogonal cutting with dual-zone contact at rake face

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    In this study, an analytical model is developed in order to calculate the temperature distribution in orthogonal cutting with dual-zone contact at the rake face. The study focuses on heat generation at the primary shear zone and at the rake face. The material behavior at the primary shear zone is represented by Johnson-Cook constitutive equation whereas the contact at the rake face is modeled by sticking and sliding friction zones. This new temperature distribution model allows obtaining the maximum temperature at the rake face and helps determining two dimensional temperature distribution in the chip. The simulation results obtained from the developed model are also compared with experimental results where good agreement is observed

    Technology upgrading of middle income economies: A new approach and results

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    We explore issues of measurement for technology upgrading of the economies moving from middle to high-income status. In exploring this issue, we apply theoretically relevant and empirically grounded middle level conceptual and statistical framework based on three dimensions: (i) Intensity (ii) breadth of technological upgrading, and (iii) technology and knowledge exchange. As an outcome, we construct a three-pronged composite indicator of technology upgrading based on 35 indicators which reflect different drivers and patterns of technology upgrading of countries at different income levels. We show that technology upgrading of middle-income economies is distinctively different from that of low and high-income economies. Our results suggest the existence of middle-income trap in technology upgrading - i.e. countries' technology upgrading activities are not reflected in their income levels. Based on the simple statistical analysis we show that the middle-income trap is present in all three aspects of technology upgrading, but their importance varies across different aspects. A trap seems to be higher for 'breadth' of technology upgrading than for 'intensity' of technology upgrading and is by far the highest for the dimension of knowledge and technology interaction with the global economy. Finally, our research shows that technology upgrading is a multidimensional process and that it would be methodologically wrong to aim for an aggregate index

    Formation control of multiple robots using parametric and implicit representations

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    A novel method is presented for formation control of a group of autonomous mobile robots using parametric and implicit descriptions of the desired formation. Shape formation is controlled by using potential fields generated from Implicit Polynomial (IP) representations and the control for keeping the desired shape is designed using Elliptical Fourier Descriptors (EFD). Coordination of the robots is modeled by linear springs between each robot and its nearest two neighbors. This approach offers more flexibility in the formation shape and scales well to different swarm sizes and to heterogeneous systems. The method is simulated on robot groups with different sizes to form various formation shapes

    A Combinatorial Discussion on Finite Dimensional Leavitt Path Algebras

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    Any finite dimensional semisimple algebra A over a field K is isomorphic to a direct sum of finite dimensional full matrix rings over suitable division rings. In this paper we will consider the special case where all division rings are exactly the field K. All such finite dimensional semisimple algebras arise as a finite dimensional Leavitt path algebra. For this specific finite dimensional semisimple algebra A over a field K, we define a uniquely detemined specific graph - which we name as a truncated tree associated with A - whose Leavitt path algebra is isomorphic to A. We define an algebraic invariant {\kappa}(A) for A and count the number of isomorphism classes of Leavitt path algebras with {\kappa}(A)=n. Moreover, we find the maximum and the minimum K-dimensions of the Leavitt path algebras of possible trees with a given number of vertices and determine the number of distinct Leavitt path algebras of a line graph with a given number of vertices.Comment: 10 pages, 5 figure

    Magnetic inversion as a mechanism for the spectral transition of black hole binaries

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    A mechanism for the transition between low/hard, high/soft, and steep power law (SPL) spectral states in black hole X-ray binaries is proposed. The low/hard state is explained by the development of a magnetically arrested accretion disk attributable to the accumulation of a vertical magnetic field in a central bundle. This disk forms powerful jets and consists of thin spiral accretion streams of a dense optically thick plasma surrounded by hot, magnetized, optically thin corona, which emits most of the energy in hard X-rays. State transition occurs because of the quasi-periodic or random inversion of poloidal magnetic fields in the accretion flow supplied by the secondary star. The inward advection of the inverted field results in a temporal disappearance of the central bundle caused by the annihilation of the opposed fields and restoration of the optically thick disk in the innermost region. This disk represents the high/soft state. The SPL state develops at the period of intensive field annihilation and precedes the high/soft state. The continuous supply of the inverted field leads to a new low/hard state because of the formation of another magnetically arrested disk.Comment: 5 plot files are attached separately. Accepted by the ApJ

    Prenatal breastfeeding self efficacy scale: validity and reliability study

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    Aim: To determine the validity and the reliability of the Prenatal Breastfeeding Self-Efficacy Scale. Material and Methods: This was a methodologic study. The sample of the research comprised 200 pregnant women who presented to the outpatient clinic of Gynecology between April and June 2015. An introductory information form and the Prenatal Breast Self-Efficacy Scale were used to collect the data. In the analysis of the data, descriptive statistics, content validity index for coverage validity, exploratory factor analysis, and confirmatory factor analysis for construct validity, and Cronbach-alfa╬▒ for reliability were used. Results: In the explanatory factor analysis of the scale, the Kaiser-Meyer- Olkin floor number was 0.84 and the BarlettÔÇÖs sphericity test results were ¤ç2=1812.608; df=171; p<0.001. The contribution of the factors to total variance was 59.06%. According to confirmatory factor analysis of the scale, the Chi-square test result was as follows: ¤ç2=254.23 (p<0.001, SD=146). The model fit indices were as follows: ¤ç2/SD=1.74, Root Mean Square Error of Approximation=0.06, Comparative Fit Index=0.96, Normed Fit Index=0.92, Non-Normed Fit Index=0.96, Goodness of Fit Index=0.88 and Adjusted Goodness of Fit Index=0.85. The internal consistency reliability coefficient of Prenatal Breastfeeding Self-Efficacy Scale was 0.86. Conclusion: The Prental Breastfeeding Self-Efficacy Scale is a valid and reliable scale which is applicable to Turkish culture and an appropriate tool which can be used by all healthcare workers who wish to design and evaluate interventions to support breastfeeding in the prenatal period. ┬ę 2018 by Turkish Pediatric Association
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