All-optical switching in a two-channel waveguide with cubic-quintic nonlinearity

We consider dynamics of spatial beams in a dual-channel waveguide with competing cubic and quintic (CQ) nonlinearities. Gradually increasing the power in the input channel, we identify four different regimes of the pulses coupling into the cross channel, which alternate three times between full pass and full stop, thus suggesting three realizations of switching between the channels. As in the case of the Kerr (solely cubic) nonlinearity, the first two regimes are the linear one, and one dominated by the self-focusing nonlinearity, with the beam which, respectively, periodically couples between the channels, or stays in the input channel. Further increase of the power reveals two novel transmission regimes, one characterized by balance between the competing nonlinearities, which again allows full coupling between the channels, and a final regime dominated by the self-defocusing quintic nonlinearity. In the latter case, the situation resembles that known for a self-repulsive Bose-Einstein condensate trapped in a double-well potential, which is characterized by strong symmetry breaking; accordingly, the beam again abides in the input channel, contrary to an intuitive expectation that the self-defocusing nonlinearity would push it into the cross channel. The numerical results are qualitatively explained by a simple analytical model based on the variational approximation.Comment: Journal of Physics B (in press

Temperature dependence of instantons in QCD

We investigate the temperature dependence of the instanton contents of gluon fields, using unquenched lattice QCD and the cooling method. The instanton size parameter deduced from the correlation function decreases from 0.44fm below the phase-transition temperature $T_c$ ($\approx 150$MeV) to 0.33fm at 1.3 $T_c$. The instanton charge distribution is Poissonian above $T_c$, but it deviates from the convoluted Poisson at low temperature. The topological susceptibility decreases rapidly below $T_c$, showing the apparent restoration of the $U(1)_A$ symmetry already at $T \approx T_c$.Comment: 8 pages TEX, 3 Postscript figures available at http://www.krl.caltech.edu/preprints/MAP.htm

Pilot interaction with automated airborne decision making systems

An investigation was made of interaction between a human pilot and automated on-board decision making systems. Research was initiated on the topic of pilot problem solving in automated and semi-automated flight management systems and attempts were made to develop a model of human decision making in a multi-task situation. A study was made of allocation of responsibility between human and computer, and discussed were various pilot performance parameters with varying degrees of automation. Optimal allocation of responsibility between human and computer was considered and some theoretical results found in the literature were presented. The pilot as a problem solver was discussed. Finally the design of displays, controls, procedures, and computer aids for problem solving tasks in automated and semi-automated systems was considered

Holography and Cosmological Singularities

Certain null singularities in ten dimensional supergravity have natural holographic duals in terms of Matrix Theory and generalizations of the AdS/CFT correspondence. In many situations the holographic duals appear to be well defined in regions where the supergravity develops singularities. We describe some recent progress in this area.Comment: Anomaly equation corrected. References adde

Magnetic Helicity in Sphaleron Debris

We develop an analytical technique to evaluate the magnetic helicity in the debris from sphaleron decay. We show that baryon number production leads to left-handed magnetic fields, and that the magnetic helicity is conserved at late times. Our analysis explicitly demonstrates the connection between sphaleron-mediated cosmic baryogenesis and cosmic magnetogenesis.Comment: 9 pages, 1 figure. v2: Minor revisions; matches published version in Physical Review

Probing the role of single defects on the thermodynamics of electric-field induced phase transitions

The kinetics and thermodynamics of first order transitions is universally controlled by defects that act as nucleation sites and pinning centers. Here we demonstrate that defect-domain interactions during polarization reversal processes in ferroelectric materials result in a pronounced fine structure in electromechanical hysteresis loops. Spatially-resolved imaging of a single defect center in multiferroic BiFeO3 thin film is achieved, and the defect size and built-in field are determined self-consistently from the single-point spectroscopic measurements and spatially-resolved images. This methodology is universal and can be applied to other reversible bias-induced transitions including electrochemical reactions.Comment: 34 pages,4 figures, high quality figures are available upon request, submitted to Phys. Rev. Let