Laser development for LISA

The two most promising configurations for the LISA laser are a stand-alone diode-pumped nonplanar ring oscillator (NPRO) or a fibre amplifier seeded by a low-power NPRO. The stand-alone laser was stabilized in frequency to a ULE cavity and in power to an electronic reference. For the first time the LISA requirement of relative power noise below 2 × 10-4/Hz1/2 was fulfilled in the whole frequency range from 0.1 mHz to 1 Hz. The LISA goal of frequency noise below 30 Hz/Hz1/2 was achieved for frequencies above 3 mHz. As a first step in the characterization of an oscillator-amplifier system, the excess frequency noise of an ytterbium-doped fibre amplifier was measured. For frequencies between 0.1 mHz and 1 Hz the excess noise was measured to be below 0.1 Hz/Hz1/2, which is significantly below the free-running frequency noise of NPROs

Nonlinear acousto-electric transport in a two-dimensional electron system

We study both theoretically and experimentally the nonlinear interaction between an intense surface acoustic wave and a two-dimensional electron plasma in semiconductor-piezocrystal hybrid structures. The experiments on hybrid systems exhibit strongly nonlinear acousto-electric effects. The plasma turns into moving electron stripes, the acousto-electric current reaches its maximum, and the sound absorption strongly decreases. To describe the nonlinear phenomena, we develop a coupled-amplitude method for a two-dimensional system in the strongly nonlinear regime of interaction. At low electron densities the absorption coefficient decreases with increasing sound intensity, whereas at high electron density the absorption coefficient is not a monotonous function of the sound intensity. High-harmonic generation coefficients as a function of the sound intensity have a nontrivial behavior. Theory and experiment are found to be in a good agreement.Comment: 27 pages, 6 figure

Selected issues of brake design

W artykule przedstawione zostały zagadnienia związane z projektowaniem hamulców. Metodykę projektowania hamulców, jak również proces konstrukcyjny. Różne czynniki brane pod uwagę przy projektowaniu oraz także te wpływające na konstrukcje hamulców lotniczych i samochodowych.This article presents selected issues related to the design of the brakes. Brakes design methodology as well as the construction process. Other factors which are important in the design process and also affect airplane and automotive brake design

Testing friction brakes in Landing Gear Laboratory

W momencie, gdy powstanie nowa prototypowa konstrukcja hamulca po jego wykonaniu zakładzie produkcyjnym trzeba jeszcze przeprowadzić badania, aby sprawdzić, czy przyjęte założenia konstrukcyjne są spełnione. Hamulce pojazdów mechanicznych ze względu na rolę, jaką spełniają podlegają restrykcyjnym badaniom. Badania te są prowadzone na poziomie wdrożenia nowej konstrukcji do użytkowania oraz w trakcie trwania eksploatacji. W artykule opisane zostały badania jakie przeprowadza się na prototypowych konstrukcjach hamulców w Laboratorium Podwozi Lotniczych Instytutu Lotnictwa.Nowadays when brake prototype is created the company responsible for it needs to do the laboratory tests to check if the construction is designed well and works correctly. Mechanical brakes due to their important role must be test very carefully. These tests are done when the new construction is implemented and also during vehicle maintenance. This article describes procedure of laboratory testing, which is performed in Landing Gear Department Institution of Aviation for all of the brake systems and friction materials evaluated for aviation and road vehicles

Wear of non-metal slides under very high load

The tests described in the article are related to the project of a high-altitude scientific rocket, which is expected to be built in the Institute of Aviation. The unguided rocket will be launched from a platform with a relatively long start beam and will be supported by slides at the start. Because of the relatively high rocket mass and nearly horizontal start needed for initial rocket tests, its slides will be under extremely high load defined as a combination of pressure and sliding velocity. In addition to the mechanical load, the slides will be also loaded thermally because of the friction in a pair: slide-guide rail (made of hard-anodized aluminium alloy). This leads to rapid wear of the slides. The aim of the tests was to establish what the friction coefficient between the slide and the guide rail is (as function of mechanical load) and how big slide-wear in a single work cycle (simulation of a single rocket launch) is. The tests were performed for few material samples: two modern plastics used in so-called “linear systems” (offered by a firm, which is one of the leaders on this market), samples made of well-known and widely used materials like cotton-phenolic textolite and well-known samples of material called Teflon (PTFE – polytetrafluoroethylene) with 15% addition of graphite. Results show that the temperature resistant plastic used in general linear systems at our condition are on the verge of wear according to our model. Textolite and Teflon with graphite addition have better characteristics of wear. They can be safely used as material of slides