Interwell relaxation times in p-Si/SiGe asymmetric quantum well structures: the role of interface roughness

We report the direct determination of nonradiative lifetimes in Si∕SiGe asymmetric quantum well structures designed to access spatially indirect (diagonal) interwell transitions between heavy-hole ground states, at photon energies below the optical phonon energy. We show both experimentally and theoretically, using a six-band k∙p model and a time-domain rate equation scheme, that, for the interface quality currently achievable experimentally (with an average step height ⩾1 Å), interface roughness will dominate all other scattering processes up to about 200 K. By comparing our results obtained for two different structures we deduce that in this regime both barrier and well widths play an important role in the determination of the carrier lifetime. Comparison with recently published experimental and theoretical data obtained for mid-infrared GaAs∕AlxGa1−xAs multiple quantum well systems leads us to the conclusion that the dominant role of interface roughness scattering at low temperature is a general feature of a wide range of semiconductor heterostructures not limited to IV-IV material

A3_7 Babylon Gun Revisited

Abstract This paper investigates the Iraqi supergun that was under construction in 1988. The gun was never completed so its performance will be investigated using a model constructed from information about the gun. The maximum range of the gun fired at 33 degrees to the horizontal was investigated and found to be 1406km. Its impact angle was found to be 61 degrees and its impact velocity 2640m/s.Â

A3_4 Babylon Gun

Abstract This paper investigates the Iraqi supergun that was under construction in 1988. The gun was never completed so its performance will be investigated using a model constructed from information about the gun. The maximum height of a projectile fired from the gun was calculated and compared to the project leaders original claims of the weapon. It was found that the projectile would rise to a height of 1046km, which was very close to the 1000km originally predicted

A3_8 Injecting particles into the atmosphere

This paper investigates size restrictions on potential particles that could be injected into the atmosphere to absorb some of the solar spectrum, the purpose in mind being to reverse the effects of the loss of ozone. It finds that, were they above the micron length scale, they would be unlikely to remain in the atmosphere for any considerable length of time

A3_2 Can a Drinking Glass be filled with Water by a Human by exhaling into it?

The following discussion is a brief investigation into whether it is reasonable to expect a human breathing into a glass under normal conditions to be able to fill it with the water from his/her breath. It finds that using this process it takes more than a day to fill a glass and would not be possible without cooling the glass regularly

A3_1 How long for a Ship to sink?

Certain ships take longer to sink than others due to differing masses and other such factors.[1] The determination of the time taken to sink a ship/boat is not straightforward, so we make some simplifying assumptions and use an algorithm to estimate this time taken

A3_5 Possibility of Creating a Star Wars Lightsaber

This papers examines whether or not a lightsaber weapon can possibly be produced and used in the same manner as in the Star Wars film series. It will examine whether the title lightsaber is indeed misleading in terms of describing a mechanism by which such a weapon could possibly be made. The paper considers elements of plasma physics to reach a conclusion, and it turns out that the lightsaber cannot be made (at least with today's technology) akin to that shown in the well-known Star Wars movies

Synthetic Chemistry for Tryptophan Tryptophylquinone like Enzyme Cofactors

This thesis describes studies on the synthesis of model compounds based on the tryptophan tryptophanyl quinone (TTQ) cofactor designed to probe the mechanism by which it catalyses primary amine oxidation and the role of the enzyme in assisting the TTQ-facilitated reaction. This project has begun to explore ways of investigating the mechanistic landscape going from small molecule ortho-quinone catalysis through to the corresponding enzymatic reaction to address the proposal that enzyme environment is directly involved in the catalytic activity of the TTQ moiety by facilitating a process known as quantum tunnelling and to determine at what point does the catalytic mechanism „swap‟ from a classical one to a mechanism involving quantum tunnelling? The principal goal was therefore to establish a synthetic route to novel amino acid building blocks that contained appropriate functionality that could be converted into the key ortho-quinone unit that would mimic TTQ. Such fragments required suitable protecting groups to allow their incorporation into peptide and protein domains. This report describes exploration of two synthetic routes to such molecules, both routes utilising 4-methylphenol that, once modified, incorporates the key ortho-quinone unit. One approach is the synthesis of a novel TTQ-like amino acid that would allow for insertion into a peptide using well documented procedures. This thesis details a variety of different synthetic approaches to the preparation of such a molecule, including problems in coupling the amino acid moiety with the quinone moiety and utilisation of a range of protecting groups in an attempt to overcome these problems. An alternative approach is also explored involving the synthesis of an ortho-quinone cassette that incorporates either alkyne or azide functionality and utilisation of the relatively new field of copper-catalysed click chemistry to insert this unit into an enzyme containing a non-natural amino acid with an alkyne or azide-containing side chain. Again details of a variety of different routes involved in attempting to produce such a molecule are given and although the target molecule was not produced a model system was successfully developed and inserted into an alkyne-containing amino acid