2,784 research outputs found

    Reduced O diffusion through Be doped Pt electrodes

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    Using first principles electronic structure calculations we screen nine elements for their potential to retard oxygen diffusion through poly-crystalline Pt (p-Pt) films. We determine that O diffuses preferentially as interstitial along Pt grain boundaries (GBs). The calculated barriers are compatible with experimental estimates. We find that Be controls O diffusion through p-Pt. Beryllium segregates to Pt GBs at interstitial (i) and substitutional (s) sites. i-Be is slightly less mobile than O and it repels O, thus stuffing the GB. s-Be has a high diffusion barrier and it forms strong bonds to O, trapping O in the GB. Experiments confirm our theoretical predictions.Comment: 3 pages, 2 figure

    Reflectance measurement of two-dimensional photonic crystal nanocavities with embedded quantum dots

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    The spectra of two-dimensional photonic crystal slab nanocavities with embedded InAs quantum dots are measured by photoluminescence and reflectance. In comparing the spectra taken by these two different methods, consistency with the nanocavities' resonant wavelengths is found. Furthermore, it is shown that the reflectance method can measure both active and passive cavities. Q-factors of nanocavities, whose resonant wavelengths range from 1280 to 1620 nm, are measured by the reflectance method in cross polarization. Experimentally, Q-factors decrease for longer wavelengths and the intensity, reflected by the nanocavities on resonance, becomes minimal around 1370 nm. The trend of the Q-factors is explained by the change of the slab thickness relative to the resonant wavelength, showing a good agreement between theory and experiment. The trend of reflected intensity by the nanocavities on resonance can be understood as effects that originate from the PC slab and the underlying air cladding thickness. In addition to three dimensional finite-difference time-domain calculations, an analytical model is introduced that is able to reproduce the wavelength dependence of the reflected intensity observed in the experiment.Comment: 24 pages, 7 figures, corrected+full versio

    Taxonomic status of Bambusaspis miliaris : B. robusta, and B. pseudomiliaris (Hemiptera: Coccoidea: Asterolecaniidae)

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    Based on an assessment of 50 morphological characters from 110 specimens of Bambusaspis miliaris (BoisduvalI869), B. robusta (Green 1908), andB. pseudomiliaris (Green 1922) from different geographic regions around the world, we conclude that these specimens represent the same species. Therefore, the taxa B. robusta and B. pseudomiliaris are considered junior subjective synonyms of B. miliaris

    On optimality of kernels for approximate Bayesian computation using sequential Monte Carlo

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    Approximate Bayesian computation (ABC) has gained popularity over the past few years for the analysis of complex models arising in population genetics, epidemiology and system biology. Sequential Monte Carlo (SMC) approaches have become work-horses in ABC. Here we discuss how to construct the perturbation kernels that are required in ABC SMC approaches, in order to construct a sequence of distributions that start out from a suitably defined prior and converge towards the unknown posterior. We derive optimality criteria for different kernels, which are based on the Kullback-Leibler divergence between a distribution and the distribution of the perturbed particles. We will show that for many complicated posterior distributions, locally adapted kernels tend to show the best performance. We find that the added moderate cost of adapting kernel functions is easily regained in terms of the higher acceptance rate. We demonstrate the computational efficiency gains in a range of toy examples which illustrate some of the challenges faced in real-world applications of ABC, before turning to two demanding parameter inference problems in molecular biology, which highlight the huge increases in efficiency that can be gained from choice of optimal kernels. We conclude with a general discussion of the rational choice of perturbation kernels in ABC SMC settings

    Overcoming Psychologism. Twardowski on Actions and Products

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    This paper is about the topic of psychologism in the work of Kazimierz Twardowski and my aim is to revisit this important issue in light of recent publications from, and on Twardowski’s works. I will first examine the genesis of psychologism in the young Twardowski’s work; secondly, I will examine Twardowski’s picture theory of meaning and Husserl’s criticism in Logical Investigations; the third part is about Twardowski’s recognition and criticism of his psychologism in his lectures on the psychology of thinking; the fourth and fifth parts provide an overview of Twardowski’s paper “Actions and Products” while the sixth part addresses the psychologism issue in the last part of this paper through the delineation of psychology and the humanities. I shall conclude this study with a brief assessment of Twardowski’s solution to psychologism

    A NEW APPROACH TO ANALYSING CERVICAL SPINAL MOTION

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    INTRODUCTION Several investigations on the problem of cervical spine motion describe the difficulties of measuring the movement exactly. Those models have to deal with the difficulties to fixate something at the human head and to track the range of motion in degrees concerning the three directions of movement, flexiodextension, lateral bending and rotation. The only objective method of measuring cervical spine movement and CO/C 1 or C 1lC2 displacements is the functional computer tomogram as described by Dvorak et. al. (1989). The aim of our survey has been to differ between the "normal" and pathologic cervical spine (after whip leash injuries, disc diseases or spondylarthrosis in sport) concerning with the range of movement and angular velocity. l b o Groups of 15 probants have been tested by a new computer-controlled setup. By using a three-dimensional motion-analysis-system special rigid-body software has been developed to calculate the cervical spine motion in all three coordinate directions (Truesdell & Noll, 1965). The first time it is possible to get results about the movement and their time-derivations. These angles and the angular velocities were traced for 15 normal individuals and 15 persons suffering with cervical spine problems. The setup for the tested patients was not more then a small frame like sunglasses which gives us an exact information about the movement in space. This information gives accurate data to calculate the amount of motion concerning the patients personal orientation in space and can be additionally used to compute the coupled motions to the probants reference coordinate system. We found significant differences in the range of motion between normal individuals as reference group and patients with cervical spine problems in all defined directions. CONCLUSIONS One conclusion, was that there were possibilities to measure those differences in cervical spine motion by the presented biomechanical measurement-setup very easily. The setup furthermore is capable of getting exact results about rang of motion, coupled motion end their time-derivations very fast and without any x-ray exposition for the patient. This possibilities and the good results are very important to judge problems after "whip lash injuries" and other cervical spine diseases in sport. REFERENCES Dvorak, A. et. al. (1989): Functional evaluation of the spinal cord by magnetic imaging in patients with rheumatoid arthritis and instability of upper cervical spine, Spine 14 (10); 1057- 1064. Truesdell, C.; W. No11 (1965): The nonlinear field theories of mechanics - Kinematics, in: Handbuch der Physik, von: S. Fliigge, Springer, New York

    Taxonomic Status of \u3ci\u3eBambusaspis miliaris\u3c/i\u3e, \u3ci\u3eB. robusta\u3c/i\u3e, and \u3ci\u3eB. pseudomiliaris\u3c/i\u3e (Hemiptera: Coccoidea: Asterolecaniidae)

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    Based on an assessment of 50 morphological characters from 110 specimens of Bambusaspis miliaris (Boisduval 1869), B. robusta (Green 1908), and B. pseudomiliaris (Green 1922) from different geographic regions around the world, we conclude that these specimens represent the same species. Therefore, the taxa B. robusta and B. pseudomiliaris are considered junior subjective synonyms of B. miliaris
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