61,694 research outputs found
Propagation of exciton pulses in semiconductors
Using a toy model, we examine the propagation of excitons in CuO, 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 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
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