Propagation of exciton pulses in semiconductors

Using a toy model, we examine the propagation of excitons in Cu$_2$O, which form localized pulses under certain experimental conditions. The formation of these waves is attributed to the effect of dispersion, non-linearity and the coupling of the excitons to phonons, which acts as a dissipative mechanism.Comment: 5 pages, 4 ps figures, RevTe

Vortices in Bose-Einstein condensates with anharmonic confinement

We examine an effectively repulsive Bose-Einstein condensate of atoms, that rotates in a quadratic-plus-quartic trapping potential. We investigate the phase diagram of the system as a function of the angular frequency of rotation and of the coupling constant, demonstrating that there are phase transitions between multiply- and singly-quantized vortex states. The derived phase diagram is shown to be universal and exact in the limits of small anharmonicity and weak coupling constant.Comment: 4 pages, 2 ps figures, RevTe

Wind tunnel model and method

The design and development of a wind tunnel model equipped with pressure measuring devices are discussed. The pressure measuring orifices are integrally constructed in the wind tunnel model and do not contribute to distortions of the aerodynamic surface. The construction of a typical model is described and a drawing of the device is included

Finding the Pion in the Chiral Random Matrix Vacuum

The existence of a Goldstone boson is demonstrated in chiral random matrix theory. After determining the effective coupling and calculating the scalar and pseudoscalar propagators, a random phase approximation summation reveals the massless pion and massive sigma modes expected whenever chiral symmetry is spontaneously broken.Comment: 3 pages, 1 figure, revte

Evidence, Mechanisms and Improved Understanding of Controlled Salinity Waterflooding Part 1 : Sandstones

Acknowledgements TOTAL are thanked for partial supporting Jackson through the TOTAL Chairs programme at Imperial College London, for supporting Vinogradov through the TOTAL Laboratory for Reservoir Physics at Imperial College London, and for granting permission to publish this work.Peer reviewedPostprin

Cosmic Superstring Scattering in Backgrounds

We generalize the calculation of cosmic superstring reconnection probability to non-trivial backgrounds. This is done by modeling cosmic strings as wound tachyon modes in the 0B theory, and the spacetime effective action is then used to couple this to background fields. Simple examples are given including trivial and warped compactifications. Generalization to $(p,q)$ strings is discussed.Comment: 12 pages, 2 figures; v2: references adde

Bright solitary waves in a Bose-Einstein condensate and their interactions

We examine the dynamics of two bright solitary waves with a negative nonlinear term. The observed repulsion between two solitary waves -- when these are in an antisymmetric combination -- is attributed to conservation laws. Slight breaking of parity, in combination with weak relaxation of energy, leads the two solitary waves to merge. The effective repulsion between solitary waves requires certain nearly ideal conditions and is thus fragile.Comment: 6 pages, 14 figure

Vehicle Design for Mars Landing and Return to Mars Orbit

This paper briefly describes three modes for accomplishing the Mars landing mission and compares them on a gross basis to indicate their probable order of merit and to identify design requirements placed on the Mars-excursion module (MEM) by the choice of mode. The paper shows that a flyby-rendezvous mode requiring low weight in earth orbit requires the MEM to enter the Mars atmosphere at velocities ranging from 20,000 to 30,000 ft/sec. The MEM for the flyby-rendezvous mode is not covered in this paper but merits further study. The MEM for the other modes of mission accomplishment begins its active operational sequence in Mars orbit and need not be greatly influenced by the method of delivery to Mars orbit. Parametric studies of the entry problem for two vehicles typifying a ballistic-type and a lifting-body-type were conducted to identify the problems associated with design of a MEM to accommodate the extremes of Mars atmospheric density presently predicted. This brief study indicates that: (a) the presently predicted density extremes of the Mars atmosphere present no serious design problems for a MEM which can operate across the entire band of predicted densities; (b) details of operational requirements and mission objectives will control the choice of configuration rather than entry requirements; and (c) the ballistic-type MEM is lighter and simpler but has less operational flexibility than a high L/D MEM