Margaret Wegener

Laser-Beams with Phase Singularities

Phase singularities in an optical field appear as isolated dark spots and can be generated in active laser cavities or by computer generated holograms. Detection and categorization of these singularities can easily be achieved either by interferometry or Fourier transform pattern recognition using a computer generated hologram.

Simultaneous two-wavelength holographic interferometry in a superorbital expansion tube facility

A new variation of holographic interferometry has been utilized to perform simultaneous two-wavelength measurements, allowing quantitative analysis of the heavy particle and electron densities in a superorbital facility. An air test gas accelerated to 12 km/s was passed over a cylindrical model, simulating reentry conditions encountered by a space vehicle on a superorbital mission. Laser beams with two different wavelengths have been overlapped, passed through the test section, and simultaneously recorded on a single holographic plate. Reconstruction of the hologram generated two separate interferograms at different angles from which the quantitative measurements were made. With this technique, a peak electron concentration of (5.5 +/- 0.5) x 10(23) m(-3) was found behind a bow shock on a cylinder.

Student experiences of virtual reality - a case study in learning special relativity

A teaching package has been developed centered around a relativistic virtual reality. It introduces concepts of special relativity to students in a gamelike environment where users experience the effects of traveling at near light speeds. From this perspective, space and time are significantly different from that experienced in everyday life. We explore how students worked with this environment and how they used this experience in their study of special relativity. Students found the simulation to be a positive learning experience and described the subject area as being less abstract after its use. Students were more capable of correctly answering concept questions relating to special relativity, and a small but measurable improvement was observed in the final exam.

Emission and holographic interferometry measurements in a superorbital expansion tube

Free-piston-driven expansion tubes are capable of generating flaw conditions over a wide range of enthalpies ranging from orbital up to superorbital velocities. Initial optical measurements aimed at investigating the flow in such a facility are presented. Emission studies were used to identify impurities in the how and to investigate spectral regions that are accessible by optical techniques. At moderate enthalpies, it was found that significant radiation resulted from metallic contaminants. At high enthalpies, the spectrum consisted of a number of atomic lines together with a broadband background component indicative of the presence of electrons. The presence of this radiation may limit the applicability of optical techniques that require spectral regions free from the influence of atomic transitions or background radiation. Emission spectroscopy (through Stark broadened hydrogen lines) and two-wavelength holographic interferometry were used to measure the electron number density behind a bow shock on a blunt body at conditions where significant ionization was observed. They yielded average concentrations of (3 +/- 1) x 10(17) cm(-3) from the emission measurements and (3.8 +/- 0.6) x 10(17) cm(-3) from the interferometry.

Visualization and analysis of bow shocks in a superorbital expansion tube

Reported here are the first optical measurements of very high enthalpy flows in a superorbital expansion tube. Holographic interferograms have been recorded of air flows at a velocity of 11 kms -1 around a variety of models.The ratios of densities across the shocks have been calculated from measurement of the shock shapes displayed in the interferograms. These results have been compared with predictions based on assumptions of frozen and equilibrium flow.

Teaching physics using virtual reality

We present an investigation of game‐like simulations for physics teaching. We report on the effectiveness of the interactive simulation “Real Time Relativity” for learning special relativity. We argue that the simulation not only enhances traditional learning, but also enables new types of learning that challenge the traditional curriculum. The lessons drawn from this work are being applied to the development of a simulation for enhancing the learning of quantum mechanics.

DIAGNOSTICS OF A RANGE OF HIGHLY SUPERORBITAL CARBON DIOXIDE FLOWS

Expansion tubes are impulse facilities capable of generating highly energetic hyper-sonic flows. This work surveys a broad range of flow conditions produced in the facility X1 with carbon dioxide test gas, for simulation of spacecraft entry into the Martian atmosphere. Conditions with nominal flow speeds of 7, 9, 11 and 13 km/s were tested. The freestream conditions were calibrated using static/Pitot pressure measurements and advanced optical diagnostics. An extensive set of holographic interferometry experiments was performed on flows over wedges for quantitative study of freestream and post-shock densities, and post-shock ionisation. A one-dimensional code with frozen and equilibrium chemistry capabilities was used to estimate the freestream conditions. An equilibrium chemistry model produced a good match to measured freestream quantities at the high enthalpy conditions which are a major aim of this facilitys operation. The freestream in the lower enthalpy conditions was found to be heavily influenced by chemical non-equilibrium. Non-equilibrium in the final unsteady expansion process of flow generation was accounted for by switching from equilibrium to frozen chemistry at a predetermined point. Comparison between the freestream density results of holographic interferometry, pressure measurements and computations shows good agreement.

Dynamic visualization of line integrals of vector fields: a didactic proposal

ABSTRACT In this paper we present two simulations designed with GeoGebra that illustrate dynamically a key concept in Vector Calculus: line integrals of vector fields, along with other associated mathematical properties and applications. Students are not required to know the GeoGebra environment: a user-friendly interface with buttons, functionalities and online help and exemplar problems allows immediate use of the simulations. The goal of the simulations is to enhance student insight, in the spirit of learning by experimentation, by analysing the dynamic representations provided by the simulations and by dragging objects and changing the parameters involved. The numerical results can be confirmed for special cases by standard undergraduate calculations.

Australian update on women in physics in 2014

Australia has had some setbacks for women in physics, where gains reported in earlier years have not been sustained because support has been fragile. There is now recognition of the importance of the country’s culture. Further-more the numbers of girls undertaking science and mathematics subjects in the final years of high school have dropped. There are, however, good initiatives on the horizon.

Optical measurements for a superorbital expansion tube

The flow in a new super-orbital expansion tube, X2, has been investigated using two optical techniques. X2 is capable of generating air flows at around 10 km/s simulating re-entry into Earth’s atmosphere by vehicles on interplanetary missions. Emission measurements identified sources of visible radiation which may influence optical measurements and can also contribute to radiative heat transfer. As well, Stark broadened hydrogen lines were used to measure electron concentrations between the bow shock and the body. Peak levels of around (3.5±0.5)xl016 cm were observed. Two-wavelength holographic interferometry was used to provide two-dimensional density and electron concentration profiles of the flow. The results compared well with the emission measurements. A gradual increase in electron population was observed, reaching a maximum about one quarter of the distance from the body to the shock along the stagnation streamline. Thereafter the concentration decreased due to the influence of the body. Comparisons were also made between flows over different sized cylinders and between air and nitrogen flows.