576 research outputs found

    Perbedaan Hasil Belajar Fisika Dengan Menggunakan Model Pembelajaran Kooperatif Tipe Numbered Head Together Berbantu Lembar Kegiatan Siswa Dengan Model Pembelajaran Langsung Pada Materi Pokok Optik Geometri

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    This study aims to determine the differences in physics learningoutcomes using cooperative learning model Numbered Heads Together Sheet-assisted Student Activity with direct instruction model in the subjectmatter Geometric Optics in Class X Semester 2 SMAN 7 T.P. 2012/2013. The population in this study were all students of class X consists of 9 parallelclasses. The study sample comprised 2 classes taken by cluster randomsampling is a class X-3 as a class experiment given cooperative learningmodel Numbered Heads Together Student Activity Sheet assisted and X-9 asa control class with direct instructional model, each of which consists of 40students. Pretest data obtained average value is the experimental class andcontrol class 34.90 is 37.10. After being given a different treatment to thesecond class, the average values obtained posttest for the experimental classwas 73.20 and 66.80 control class. The results of testing hypotheses obtainedt-test = 2.78 and t-table = 1.99 at significance level α = 0.05 and df = 78, ttest>t-table. It showed no significant difference in the learning outcomes of students using cooperative learning model Numbered Heads Together Sheet assisted Student Activity with learning model directly in the subject matterOptical Geometry in class X Semester 2 SMAN 7 T.P. 2012/2013

    The path model and Bott–Samelson manifolds in the context of loop groups

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    We realize the Littelmann path model and the associated root operators on the loop groups of the torus in a compact, simple Lie group. For integral loops - those loops with a good combinatorial description of the root operators - we define a geometric interpolation of the root operators through Bott–Samelson manifolds, whose definition we generalize for this purpose. We embed these manifolds in the loop group of the simple group and give a criterion under which the symplectic structure of the loop group restricts to a symplectic structure of the Bott–Samelson manifold. For loops in dominant direction we compute the image under the moment map. To establish a complex structure we give a diffeomorphism between the Bott–Samelson manifolds and the Bott–Samelson–Demazure–Hansen variety associated to a gallery in the affine building. This map is compatible with the root operators, and we interpret the results of Gaussent and Littelmann in the context of the gallery model anew. By means of this interpretation we define isotopic embeddings of Mirković-Vilonen cycles into the differential-geometric loop group. For this purpose we investigate the behavior of the Bott–Samelson manifold under homotopies of the underlying loop. A consequence of this is another criterion to determine the image of the moment map

    Collective signal processing in cluster chemotaxis: roles of adaptation, amplification, and co-attraction in collective guidance

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    Single eukaryotic cells commonly sense and follow chemical gradients, performing chemotaxis. Recent experiments and theories, however, show that even when single cells do not chemotax, clusters of cells may, if their interactions are regulated by the chemoattractant. We study this general mechanism of "collective guidance" computationally with models that integrate stochastic dynamics for individual cells with biochemical reactions within the cells, and diffusion of chemical signals between the cells. We show that if clusters of cells use the well-known local excitation, global inhibition (LEGI) mechanism to sense chemoattractant gradients, the speed of the cell cluster becomes non-monotonic in the cluster's size - clusters either larger or smaller than an optimal size will have lower speed. We argue that the cell cluster speed is a crucial readout of how the cluster processes chemotactic signal; both amplification and adaptation will alter the behavior of cluster speed as a function of size. We also show that, contrary to the assumptions of earlier theories, collective guidance does not require persistent cell-cell contacts and strong short range adhesion to function. If cell-cell adhesion is absent, and the cluster cohesion is instead provided by a co-attraction mechanism, e.g. chemotaxis toward a secreted molecule, collective guidance may still function. However, new behaviors, such as cluster rotation, may also appear in this case. Together, the combination of co-attraction and adaptation allows for collective guidance that is robust to varying chemoattractant concentrations while not requiring strong cell-cell adhesion.Comment: This article extends some results previously presented in arXiv:1506.0669

    How input fluctuations reshape the dynamics of a biological switching system

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    An important task in quantitative biology is to understand the role of stochasticity in biochemical regulation. Here, as an extension of our recent work [Phys. Rev. Lett. 107, 148101 (2011)], we study how input fluctuations affect the stochastic dynamics of a simple biological switch. In our model, the on transition rate of the switch is directly regulated by a noisy input signal, which is described as a nonnegative mean-reverting diffusion process. This continuous process can be a good approximation of the discrete birth-death process and is much more analytically tractable. Within this new setup, we apply the Feynman-Kac theorem to investigate the statistical features of the output switching dynamics. Consistent with our previous findings, the input noise is found to effectively suppress the input-dependent transitions. We show analytically that this effect becomes significant when the input signal fluctuates greatly in amplitude and reverts slowly to its mean.Comment: 7 pages, 4 figures, submitted to Physical Review
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