432 research outputs found
Quantitative analysis of wide-field specular microscopy. II. Precision of sampling from the central corneal endothelium
The precision of the measurement of mean endothelial cell area obtained by sampling with small-field and wide-field specular microscopy from the central 4 mm of human corneal endothelium was studied by comparing endothelial cell parameters from individual specular micrographs in vivo to the results obtained by montaging the micrographs from the entire central 4 mm of the same corneas. The small samples were at least 10% from the true mean cell size of all cells of the central 4 mm in any endothelium other than that with the most homogeneous pattern. A new algorithm for sampling with these two specular microscopes will need to be derived to permit a more precise measure of the mean area of endothelial cells in the central 4 mm of the human corneal endothelium
Infrasound initiates directional fast-start escape responses in juvenile roach Rutilus rutilus
Acoustic stimuli within the sonic range are effective triggers of C-type escape behaviours in fish. We have previously shown that fish have an acute sensitivity to infrasound also, with acceleration thresholds in the range of 10(-5) m s(-2). In addition, infrasound at high intensities around 10(-2) m s(-2) elicits strong and sustained avoidance responses in several fish species. In the present study, the possible triggering of C-escapes by infrasonic single-cycle vibrations was examined in juvenile roach Rutilus rutilus. The fish were accelerated in a controlled and quantifiable manner using a swing system. The applied stimuli simulated essential components of the accelerations that a small fish would encounter in the hydrodynamic flow field produced by a predatory fish. Typical C- and S-type escape responses were induced by accelerations within the infrasonic range with a threshold of 0.023 m s(-2) for an initial acceleration at 6.7 Hz. Response trajectories were on average in the same direction as the initial acceleration. Unexpectedly, startle behaviours mainly occurred in the trailing half of the test chamber, in which the fish were subjected to linear acceleration in combination with compression, i.e. the expected stimuli produced by an approaching predator. Very few responses were observed in the leading half of the test chamber, where the fish were subjected to acceleration and rarefaction, i.e. the stimuli expected from a suction type of predator. We conclude that particle acceleration is essential for the directionality of the startle response to infrasound, and that the response is triggered by the synergistic effects of acceleration and compression
Integrability of the N=2 boundary sine-Gordon model
We construct a boundary Lagrangian for the N=2 supersymmetric sine-Gordon
model which preserves (B-type) supersymmetry and integrability to all orders in
the bulk coupling constant g. The supersymmetry constraint is expressed in
terms of matrix factorisations.Comment: LaTeX, 19 pages, no figures; v2: title changed, minor improvements,
refs added, to appear in J. Phys. A: Math. Ge
Fractional two-branes, toric orbifolds and the quantum McKay correspondence
We systematically study and obtain the large-volume analogues of fractional
two-branes on resolutions of orbifolds C^3/Z_n. We study a generalisation of
the McKay correspondence proposed in hep-th/0504164 called the quantum McKay
correspondence by constructing duals to the fractional two-branes. Details are
explicitly worked out for two examples -- the crepant resolutions of C^3/Z_3
and C^3/Z_5.Comment: 34 pages, 2 figures, LaTeX (JHEP3 style); (v2) typos corrected; (v3)
sec 3 reorganise
Matrix Factorizations, D-Branes and their Deformations
We review in elementary, non-technical terms the description of topological
B-type of D-branes in terms of boundary Landau-Ginzburg theory, as well as some
applications.Comment: 20p, 5 figs, Proceedings of Cargese school on string theory, 200
Moduli Webs and Superpotentials for Five-Branes
We investigate the one-parameter Calabi-Yau models and identify families of
D5-branes which are associated to lines embedded in these manifolds. The moduli
spaces are given by sets of Riemann curves, which form a web whose intersection
points are described by permutation branes. We arrive at a geometric
interpretation for bulk-boundary correlators as holomorphic differentials on
the moduli space and use this to compute effective open-closed superpotentials
to all orders in the open string couplings. The fixed points of D5-brane moduli
under bulk deformations are determined.Comment: 41 pages, 1 figur
D-brane superpotentials and RG flows on the quintic
The behaviour of D2-branes on the quintic under complex structure
deformations is analysed by combining Landau-Ginzburg techniques with methods
from conformal field theory. It is shown that the boundary renormalisation
group flow induced by the bulk deformations is realised as a gradient flow of
the effective space time superpotential which is calculated explicitly to all
orders in the boundary coupling constant.Comment: 24 pages, 1 figure, v2:Typo in (3.14) correcte
Permutation branes and linear matrix factorisations
All the known rational boundary states for Gepner models can be regarded as
permutation branes. On general grounds, one expects that topological branes in
Gepner models can be encoded as matrix factorisations of the corresponding
Landau-Ginzburg potentials. In this paper we identify the matrix factorisations
associated to arbitrary B-type permutation branes.Comment: 43 pages. v2: References adde
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Efficient importance sampling in low dimensions using affine arithmetic
Despite the development of sophisticated techniques such as sequential Monte Carlo, importance sampling (IS) remains an important Monte Carlo method for low dimensional target distributions. This paper describes a new technique for constructing proposal distributions for IS, using affine arithmetic. This work builds on the Moore rejection sampler to which we provide a comparison
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