25,524 research outputs found
Optofluidic circular grating distributed feedback dye laser
We demonstrate an optically pumped surface emitting optofluidic dye laser using a second-order circular grating distributed feedback resonator. We present a composite bilayer soft lithography technique specifically developed for the fabrication of our dye laser and investigate a hybrid polymer material system [poly(dimethylsiloxane)/perfluoropolyether] to construct high-resolution Bragg gratings. Our lasers emit single frequency light at low lasing thresholds of 6 µJ/mm^2. These optofluidic dye lasers can serve as low-cost and compact coherent light sources that are fully integrated within microfluidic analysis chips and provide an efficient approach to construct compact spectroscopy systems
Technical Assessments of Future European Space Transportation Options
The paper describes some of the most recent activities in Germany in the technical assessment of future European
launcher architecture. In focus is a joint effort of DLR-SART with German launcher industry in the definition of a
next generation upper-medium class expendable TSTO with an initial operational capability after 2020. Involved
companies are EADS astrium and MT Aerospace. This DLR-agency funded study WOTAN investigates fully
cryogenic launchers as well as those with a combination of solid and cryogenic stages, fulfilling a requirement of 5000
kg single payload into GTO. Solid strap-on boosters should allow both versions further payload growth capability.
In its second part the paper analyzes options for new liquid fuel upper stages to be put on the P80 solid first stage of
the Vega small launcher. Versions with storable as well as cryogenic propellants are investigated in a preliminary
launcher system lay-out and their technical viability is critically assessed
Design, fabrication and evaluation of chalcogenide glass Luneburg lenses for LiNbO3 integrated optical devices
Optical waveguide Luneburg lenses of arsenic trisulfide glass are described. The lenses are formed by thermal evaporation of As2S3 through suitably placed masks onto the surface of LiNbO3:Ti indiffused waveguides. The lenses are designed for input apertures up to 1 cm and for speeds of f/5 or better. They are designed to focus the TM sub 0 guided mode of a beam of wavelength, external to the guide, of 633 nm. The refractive index of the As2S3 films and the changes induced in the refractive index by exposure to short wavelength light were measured. Some correlation between film thickness and optical properties was noted. The short wavelength photosensitivity was used to shorten the lens focal length from the as deposited value. Lenses of rectangular shape, as viewed from above the guide, as well as conventional circular Luneburg lenses, were made. Measurements made on the lenses include thickness profile, general optical quality, focal length, quality of focal spot, and effect of ultraviolet irradiation on optical properties
Inverse Mapping of Polarised Optical Emission from Pulsars : Basic Formulation and Determination of Emission Altitude
We present an inverse mapping approach to determining the emission height of
the optical photons from pulsars, which is directly constrained by empirical
data. The model discussed is for the case of the Crab pulsar. Our method, using
the optical Stokes parameters, determines the most likely geometry for emission
including magnetic field inclination angle (), observers line of sight
angle () and emission height. We discuss the computational implementation
of the approach, along with any physical assumptions made. We find that the
most likely emission altitude is at 20% of the light cylinder radius above the
stellar surface, in the open field region. We also present a general treatment
of the expected polarisation from synchrotron source with a truncated power law
spectrum of particles.Comment: 17 pages 16 figures; accepted for publication in MNRA
Development of an integrated BEM approach for hot fluid structure interaction
The progress made toward the development of a boundary element formulation for the study of hot fluid-structure interaction in Earth-to-Orbit engine hot section components is reported. The convective viscous integral formulation was derived and implemented in the general purpose computer program GP-BEST. The new convective kernel functions, in turn, necessitated the development of refined integration techniques. As a result, however, since the physics of the problem is embedded in these kernels, boundary element solutions can now be obtained at very high Reynolds number. Flow around obstacles can be solved approximately with an efficient linearized boundary-only analysis or, more exactly, by including all of the nonlinearities present in the neighborhood of the obstacle. The other major accomplishment was the development of a comprehensive fluid-structure interaction capability within GP-BEST. This new facility is implemented in a completely general manner, so that quite arbitrary geometry, material properties and boundary conditions may be specified. Thus, a single analysis code (GP-BEST) can be used to run structures-only problems, fluids-only problems, or the combined fluid-structure problem. In all three cases, steady or transient conditions can be selected, with or without thermal effects. Nonlinear analyses can be solved via direct iteration or by employing a modified Newton-Raphson approach
Extended Smoothed Boundary Method for Solving Partial Differential Equations with General Boundary Conditions on Complex Boundaries
In this article, we describe an approach for solving partial differential
equations with general boundary conditions imposed on arbitrarily shaped
boundaries. A continuous function, the domain parameter, is used to modify the
original differential equations such that the equations are solved in the
region where a domain parameter takes a specified value while boundary
conditions are imposed on the region where the value of the domain parameter
varies smoothly across a short distance. The mathematical derivations are
straightforward and generically applicable to a wide variety of partial
differential equations. To demonstrate the general applicability of the
approach, we provide four examples herein: (1) the diffusion equation with both
Neumann and Dirichlet boundary conditions; (2) the diffusion equation with both
surface diffusion and reaction; (3) the mechanical equilibrium equation; and
(4) the equation for phase transformation with the presence of additional
boundaries. The solutions for several of these cases are validated against
corresponding analytical and semi-analytical solutions. The potential of the
approach is demonstrated with five applications: surface-reaction-diffusion
kinetics with a complex geometry, Kirkendall-effect-induced deformation,
thermal stress in a complex geometry, phase transformations affected by
substrate surfaces, and a self-propelled droplet.Comment: This document is the revised version of arXiv:0912.1288v
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