We present a theoretical and experimental investigation of the effects of a magnetic field on quasi-twodimensional excitons. We calculate the internal structures and dispersion relations of spatially direct and indirect excitons in single and coupled quantum wells in a magnetic field perpendicular to the well plane. We find a sharp transition from a hydrogenlike exciton to a magnetoexciton with increasing the center-of-mass momentum at fixed weak field. At that transition the mean electron-hole separation increases sharply and becomes ϰ P/B Ќ , where P is the magnetoexciton center-of-mass momentum and B Ќ is the magnetic field perpendicular to the quantum well plane. The transition resembles a first-order phase transition. The magneticfield-exciton momentum phase diagram describing the transition is constructed. We measure the magnetoexciton dispersion relations and effective masses in GaAs/Al 0.33 Ga 0.67 As coupled quantum wells using tilted magnetic fields. The calculated dispersion relations and effective masses are in agreement with the experimental data. We discuss the impact of magnetic field and sample geometry on the condition for observing exciton condensation.

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Even when radiographs are taken in a busy National Health Service radiography department, measurement of JSW from the MTP view is more reproducible than from the SEV view, the MTP view gives a slightly lower measurement of JSW, and there is no advantage in using either view in recording osteophyte grade. We recommend the wider adoption of the MTP method.