737 research outputs found
Optimization of the Collection Efficiency of a Hexagonal Light Collector using Quadratic and Cubic B\'ezier Curves
Reflective light collectors with hexagonal entrance and exit apertures are
frequently used in front of the focal-plane camera of a very-high-energy
gamma-ray telescope to increase the collection efficiency of atmospheric
Cherenkov photons and reduce the night-sky background entering at large
incident angles. The shape of a hexagonal light collector is usually based on
Winston's design, which is optimized for only two-dimensional optical systems.
However, it is not known whether a hexagonal Winston cone is optimal for the
real three-dimensional optical systems of gamma-ray telescopes. For the first
time we optimize the shape of a hexagonal light collector using quadratic and
cubic B\'ezier curves. We demonstrate that our optimized designs simultaneously
achieve a higher collection efficiency and background reduction rate than
traditional designs.Comment: 9 pages, 9 figure
Fast Isogeometric Boundary Element Method based on Independent Field Approximation
An isogeometric boundary element method for problems in elasticity is
presented, which is based on an independent approximation for the geometry,
traction and displacement field. This enables a flexible choice of refinement
strategies, permits an efficient evaluation of geometry related information, a
mixed collocation scheme which deals with discontinuous tractions along
non-smooth boundaries and a significant reduction of the right hand side of the
system of equations for common boundary conditions. All these benefits are
achieved without any loss of accuracy compared to conventional isogeometric
formulations. The system matrices are approximated by means of hierarchical
matrices to reduce the computational complexity for large scale analysis. For
the required geometrical bisection of the domain, a strategy for the evaluation
of bounding boxes containing the supports of NURBS basis functions is
presented. The versatility and accuracy of the proposed methodology is
demonstrated by convergence studies showing optimal rates and real world
examples in two and three dimensions.Comment: 32 pages, 27 figure
Curves with rational chord-length parametrization
It has been recently proved that rational quadratic circles in standard Bezier form are parameterized by chord-length. If we consider that standard circles coincide with the isoparametric curves in a system of bipolar coordinates, this property comes as a straightforward consequence. General curves with chord-length parametrization are simply the analogue in bipolar coordinates of nonparametric curves. This interpretation furnishes a compact explicit expression for all planar curves with rational chord-length parametrization. In addition to straight lines and circles in standard form, they include remarkable curves, such as the equilateral hyperbola, Lemniscate of Bernoulli and Limacon of Pascal. The extension to 3D rational curves is also tackled
Prototyping Hexagonal Light Concentrators Using High-Reflectance Specular Films for the Large-Sized Telescopes of the Cherenkov Telescope Array
We have developed a prototype hexagonal light concentrator for the
Large-Sized Telescopes of the Cherenkov Telescope Array. To maximize the
photodetection efficiency of the focal-plane camera pixels for atmospheric
Cherenkov photons and to lower the energy threshold, a specular film with a
very high reflectance of 92-99% has been developed to cover the inner surfaces
of the light concentrators. The prototype has a relative anode sensitivity
(which can be roughly regarded as collection efficiency) of about 95 to 105% at
the most important angles of incidence. The design, simulation, production
procedure, and performance measurements of the light-concentrator prototype are
reported.Comment: 21 pages, 14 figures, accepted for publication in JINS
Flexibility of approximation in pies applied for solving elastoplastic boundary problems
The paper presents the flexibility of approximation in PIES applied for solving elastoplastic boundary value problems. Three various approaches to approximation of plastic strains have been tested. The first one bases on the globally applied Lagrange polynomial. The two remaining are local: inverse distance weighting (IDW) method and approximation in different zones by locally applied Lagrange polynomials. Some examples are solved and results obtained are compared with analytical solutions. Conclusions on the effectiveness of presented approaches have been drawn
Discontinuities in numerical radiative transfer
Observations and magnetohydrodynamic simulations of solar and stellar
atmospheres reveal an intermittent behavior or steep gradients in physical
parameters, such as magnetic field, temperature, and bulk velocities. The
numerical solution of the stationary radiative transfer equation is
particularly challenging in such situations, because standard numerical methods
may perform very inefficiently in the absence of local smoothness. However, a
rigorous investigation of the numerical treatment of the radiative transfer
equation in discontinuous media is still lacking. The aim of this work is to
expose the limitations of standard convergence analyses for this problem and to
identify the relevant issues. Moreover, specific numerical tests are performed.
These show that discontinuities in the atmospheric physical parameters
effectively induce first-order discontinuities in the radiative transfer
equation, reducing the accuracy of the solution and thwarting high-order
convergence. In addition, a survey of the existing numerical schemes for
discontinuous ordinary differential systems and interpolation techniques for
discontinuous discrete data is given, evaluating their applicability to the
radiative transfer problem
Accurate and efficient spin integration for particle accelerators
Accurate spin tracking is a valuable tool for understanding spin dynamics in
particle accelerators and can help improve the performance of an accelerator.
In this paper, we present a detailed discussion of the integrators in the spin
tracking code gpuSpinTrack. We have implemented orbital integrators based on
drift-kick, bend-kick, and matrix-kick splits. On top of the orbital
integrators, we have implemented various integrators for the spin motion. These
integrators use quaternions and Romberg quadratures to accelerate both the
computation and the convergence of spin rotations. We evaluate their
performance and accuracy in quantitative detail for individual elements as well
as for the entire RHIC lattice. We exploit the inherently data-parallel nature
of spin tracking to accelerate our algorithms on graphics processing units.Comment: 43 pages, 17 figure
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