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
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
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
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
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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