Efficiency optimization for Atomic Frequency Comb storage

We study the efficiency of the Atomic Frequency Comb storage protocol. We show that for a given optical depth, the preparation procedure can be optimize to significantly improve the retrieval. Our prediction is well supported by the experimental implementation of the protocol in a \TMYAG crystal. We observe a net gain in efficiency from 10% to 17% by applying the optimized preparation procedure. In the perspective of high bandwidth storage, we investigate the protocol under different magnetic fields. We analyze the effect of the Zeeman and superhyperfine interaction

Noncommutativity in the analysis of piecewise discrete-time dynamical systems

In this paper, we present a new method for the analysis of piecewise dynamical systems that are similar to the Collatz conjecture in regard to certain properties of the commutator of their sub-functions. We use the fact that the commutator of polynomials $E(n)=n/2$ and $O(n)=(3n+1)/2$ is constant to study rearrangements of compositions of $E(n)$ and $O(n)$. Our main result is that for any positive rational number $n$, if $(E^{e_1} \circ O^{o_1} \circ E^{e_2} \circ \dotsb \circ O^{o_l} \circ E^{e_{l+1}})(n)=1$, then $(E^{e_1} \circ O^{o_1} \circ E^{e_2} \circ \dotsb \circ O^{o_l} \circ E^{e_{l+1}})(n) = \lceil(E^{e_1 + \dotsb + e_{l+1}} \circ O^{o_1 + \dotsb + o_{l}})(n)\rceil$, where exponentiation is used to denote repeated composition and $e_i$ and $o_i$ are positive integers. Composition sequences of this form have significance in the context of the Collatz conjecture. The techniques used to derive this result can be used to produce similar results for a wide variety of repeatedly composed piecewise functions.Comment: 7 page

A post-Keplerian parameter to test gravito-magnetic effects in binary pulsar systems

We study the pulsar timing, focusing on the time delay induced by the gravitational field of the binary systems. In particular, we study the gravito-magnetic correction to the Shapiro time delay in terms of Keplerian and post-Keplerian parameters, and we introduce a new post-Keplerian parameter which is related to the intrinsic angular momentum of the stars. Furthermore, we evaluate the magnitude of these effects for the binary pulsar systems known so far. The expected magnitude is indeed small, but the effect is important per se.Comment: 6 pages, RevTeX, 1 eps figure, accepted for publication in Physical Review D; references adde

Chaotic Accretion in a Non-Stationary Electromagnetic Field of a Slowly Rotating Compact Star

We investigate charge accretion in vicinity of a slowly rotating compact star with a non-stationary electromagnetic field. Exact solutions to the general relativistic Maxwell equations are obtained for a star formed of a highly degenerate plasma with a gravitational field given by the linearized Kerr metric. These solutions are used to formulate and then to study numerically the equations of motion for a charged particle in star's vicinity using the gravitoelectromagnetic force law. The analysis shows that close to the star charge accretion does not always remain ordered. It is found that the magnetic field plays the dominant role in the onset of chaos near the star's surface.Comment: 9 pages, 4 figure

Transient evolution of warm cloud - clear air interface and its impact on cloud droplet evolution

Three dimensional Direct Numerical Simulation (DNS) using pseudo-spectral Fourier Galerkin method is used for simulating Warm Cloud – Clear Air interfaces [1,2]. Transient evolution of transport of energy, water vapour, temperature and Lagrangian tracking of droplets are simulated for decaying turbulent atmospheric flow, where initial turbulent kinetic energy (TKE) in the simulation domain decays with time [1,2]. Simulation results shows anisotropy and high intermittency across the interface (from high TKE region of cloud side to low TKE region of clear air side), which influenced the transient evolution of passive scalar transport [3]. Cloud droplets are observed to be affected by the small scale turbulence, and they preferentially concentrated away from the regions of high vorticity. Transient evolution of various microphysical properties, such as, droplet sedimentation, condensation/evaporation, droplet inertia, droplet collision and coalescence are investigated to understand the role of turbulence in interfacial transient. Supersaturation and preferential concentration resulted in condensational growth of the droplets and increased local droplet collision rate. As a result, droplet size distribution grew with time, in contrary to the saturated case (Fig 1

A stochastic-hydrodynamic model of halo formation in charged particle beams

The formation of the beam halo in charged particle accelerators is studied in the framework of a stochastic-hydrodynamic model for the collective motion of the particle beam. In such a stochastic-hydrodynamic theory the density and the phase of the charged beam obey a set of coupled nonlinear hydrodynamic equations with explicit time-reversal invariance. This leads to a linearized theory that describes the collective dynamics of the beam in terms of a classical Schr\"odinger equation. Taking into account space-charge effects, we derive a set of coupled nonlinear hydrodynamic equations. These equations define a collective dynamics of self-interacting systems much in the same spirit as in the Gross-Pitaevskii and Landau-Ginzburg theories of the collective dynamics for interacting quantum many-body systems. Self-consistent solutions of the dynamical equations lead to quasi-stationary beam configurations with enhanced transverse dispersion and transverse emittance growth. In the limit of a frozen space-charge core it is then possible to determine and study the properties of stationary, stable core-plus-halo beam distributions. In this scheme the possible reproduction of the halo after its elimination is a consequence of the stationarity of the transverse distribution which plays the role of an attractor for every other distribution.Comment: 18 pages, 20 figures, submitted to Phys. Rev. ST A