8,066 research outputs found
Realization of an all-optical zero to Ï cross-phase modulation jump
We report on the experimental demonstration of an all-optical Ï cross-phase modulation jump. By performing a preselection, an optically induced unitary transformation, and then a postselection on the polarization degree of freedom, the phase of the output beam acquires either a zero or Ï phase shift (with no other possible values). The postselection results in optical loss in the output beam. An input state may be chosen near the resulting phase singularity, yielding a pi phase shift even for weak interaction strengths. The scheme is experimentally demonstrated using a coherently prepared dark state in a warm atomic cesium vapor
Path integral approach to no-Coriolis approximation in heavy-ion collisions
We use the two time influence functional method of the path integral approach
in order to reduce the dimension of the coupled-channels equations for
heavy-ion reactions based on the no-Coriolis approximation. Our method is
superior to other methods in that it easily enables us to study the cases where
the initial spin of the colliding particle is not zero. It can also be easily
applied to the cases where the internal degrees of freedom are not necessarily
collective coordinates. We also clarify the underlying assumptions in our
approach.Comment: 11 pages, Latex, Phys. Rev. C in pres
Entropic Barriers, Frustration and Order: Basic Ingredients in Protein Folding
We solve a model that takes into account entropic barriers, frustration, and
the organization of a protein-like molecule. For a chain of size , there is
an effective folding transition to an ordered structure. Without frustration,
this state is reached in a time that scales as , with
. This scaling is limited by the amount of frustration which
leads to the dynamical selectivity of proteins: foldable proteins are limited
to monomers; and they are stable in {\it one} range of temperatures,
independent of size and structure. These predictions explain generic properties
of {\it in vivo} proteins.Comment: 4 pages, 4 Figures appended as postscript fil
Delineation of the Native Basin in Continuum Models of Proteins
We propose two approaches for determining the native basins in off-lattice
models of proteins. The first of them is based on exploring the saddle points
on selected trajectories emerging from the native state. In the second
approach, the basin size can be determined by monitoring random distortions in
the shape of the protein around the native state. Both techniques yield the
similar results. As a byproduct, a simple method to determine the folding
temperature is obtained.Comment: REVTeX, 6 pages, 5 EPS figure
Voltage Stability Analysis of Grid-Connected Wind Farms with FACTS: Static and Dynamic Analysis
Recently, analysis of some major blackouts and failures of power system shows that voltage instability problem has been one of the main reasons of these disturbances and networks collapse. In this paper, a systematic approach to voltage stability analysis using various techniques for the IEEE 14-bus case study, is presented. Static analysis is used to analyze the voltage stability of the system under study, whilst the dynamic analysis is used to evaluate the performance of compensators. The static techniques used are Power Flow, VâP curve analysis, and QâV modal analysis. In this study, Flexible Alternating Current Transmission system (FACTS) devices- namely, Static Synchronous Compensators (STATCOMs) and Static Var Compensators (SVCs) - are used as reactive power compensators, taking into account maintaining the violated voltage magnitudes of the weak buses within the acceptable limits defined in ANSI C84.1. Simulation results validate that both the STATCOMs and the SVCs can be effectively used to enhance the static voltage stability and increasing network loadability margin. Additionally, based on the dynamic analysis results, it has been shown that STATCOMs have superior performance, in dynamic voltage stability enhancement, compared to SVCs
Gravitomagnetism in Metric Theories: Analysis of Earth Satellites Results, and its Coupling with Spin
Employing the PPN formalism the gravitomagnetic field in different metric
theories is considered in the analysis of the LAGEOS results. It will be shown
that there are several models that predict exactly the same effect that general
relativity comprises. In other words, these Earth satellites results can be
taken as experimental evidence that the orbital angular momentum of a body does
indeed generate space--time geometry, notwithstanding they do not endow general
relativity with an outstanding status among metric theories. Additionally the
coupling spin--gravitomagnetic field is analyzed with the introduction of the
Rabi transitions that this field produces on a quantum system with spin 1/2.
Afterwards, a continuous measurement of the energy of this system is
introduced, and the consequences upon the corresponding probabilities of the
involved gravitomagnetic field will be obtained. Finally, it will be proved
that these proposals allows us, not only to confront against future experiments
the usual assumption of the coupling spin--gravotimagnetism, but also to
measure some PPN parameters and to obtain functional dependences among them.Comment: 10 page
All-Optical Switching Demonstration using Two-Photon Absorption and the Classical Zeno Effect
Low-contrast all-optical Zeno switching has been demonstrated in a silicon
nitride microdisk resonator coupled to a hot atomic vapor. The device is based
on the suppression of the field build-up within a microcavity due to
non-degenerate two-photon absorption. This experiment used one beam in a
resonator and one in free-space due to limitations related to device physics.
These results suggest that a similar scheme with both beams resonant in the
cavity would correspond to input power levels near 20 nW.Comment: 4 pages, 5 figure
Dimensional crossover of a boson gas in multilayers
We obtain the thermodynamic properties for a non-interacting Bose gas
constrained on multilayers modeled by a periodic Kronig-Penney delta potential
in one direction and allowed to be free in the other two directions. We report
Bose-Einstein condensation (BEC) critical temperatures, chemical potential,
internal energy, specific heat, and entropy for different values of a
dimensionless impenetrability between layers. The BEC critical
temperature coincides with the ideal gas BEC critical temperature
when and rapidly goes to zero as increases to infinity for
any finite interlayer separation. The specific heat \textit{vs} for
finite and plane separation exhibits one minimum and one or two maxima
in addition to the BEC, for temperatures larger than which highlights
the effects due to particle confinement. Then we discuss a distinctive
dimensional crossover of the system through the specific heat behavior driven
by the magnitude of . For the crossover is revealed by the change
in the slope of and when , it is evidenced by a broad
minimum in .Comment: Ten pages, nine figure
Space--time fluctuations and the spreading of wavepackets
Using a density matrix description in space we study the evolution of
wavepackets in a fluctuating space-time background. We assume that space-time
fluctuations manifest as classical fluctuations of the metric. From the
non-relativistic limit of a non-minimally coupled Klein-Gordon equation we
derive a Schr\"odinger equation with an additive gaussian random potential.
This is transformed into an effective master equation for the density matrix.
The solutions of this master equation allow to study the dynamics of
wavepackets in a fluctuating space-time, depending on the fluctuation scenario.
We show how different scenarios alter the diffusion properties of wavepackets.Comment: 11 page
Realization of an All-Optical Zero To Cross-Phase Modulation Jump
We report on the experimental demonstration of an all-optical Ï cross-phase modulation jump. By performing a preselection, an optically induced unitary transformation, and then a postselection on the polarization degree of freedom, the phase of the output beam acquires either a zero or Ï phase shift (with no other possible values). The postselection results in optical loss in the output beam. An input state may be chosen near the resulting phase singularity, yielding a Ï phase shift even for weak interaction strengths. The scheme is experimentally demonstrated using a coherently prepared dark state in a warm atomic cesium vapor
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