1,442 research outputs found
OAM mode selection for high-speed optical communications : a bit loading approach
Occupying more channels increases transmission
rate, however, crosstalk increases to an unacceptable level long
before all 24 channels can be exploited. The crosstalk is not
uniform between modes, hence occupying different subsets of
channels leads to vastly different achievable transmission capacities. In addition to optimizing occupied subsets of channels, we
adopt a bit loading approach.
We examine several resource allocation strategies in a coherent
detection system, starting with typical OAM mode group granularity (all channels in a group occupied) and ending with single
channel granularity. By exhaustive search at mode group granularity, we find a bit load increasing the total capacity by ∼15%
compared to a minimax solution for mode group allocation.
Single channel granularity imposes great computational effort
to optimize bit loading. We propose search algorithms that are
computationally tractable and improve capacity by ∼30% vis-à vis the minimax solution for mode groups. Finally, we examine the
impact of signal-to-noise ratio (SNR) and receiver digital signal
processing (DSP) complexity on the overall capacity. We include
a discussion of DSP with limited or with no multi-input, multioutput (MIMO) processing.Our algorithms could be applied to
any mode multiplexing fiber, as it only relies on knowledge of
the crosstalk matrix across modes
The motivating operation and negatively reinforced problem behavior. A systematic review.
The concept of motivational operations exerts an increasing influence on the understanding and assessment of problem behavior in people with intellectual and developmental disability. In this systematic review of 59 methodologically robust studies of the influence of motivational operations in negative reinforcement paradigms in this population, we identify themes related to situational and biological variables that have implications for assessment, intervention, and further research. There is now good evidence that motivational operations of differing origins influence negatively reinforced problem behavior, and that these might be subject to manipulation to facilitate favorable outcomes. There is also good evidence that some biological variables warrant consideration in assessment procedures as they predispose the person's behavior to be influenced by specific motivational operations. The implications for assessment and intervention are made explicit with reference to variables that are open to manipulation or that require further research and conceptualization within causal models
Bose-Einstein condensation in a stiff TOP trap with adjustable geometry
We report on the realisation of a stiff magnetic trap with independently
adjustable trap frequencies, and , in the axial and radial
directions respectively. This has been achieved by applying an axial modulation
to a Time-averaged Orbiting Potential (TOP) trap. The frequency ratio of the
trap, , can be decreased continuously from the original
TOP trap value of 2.83 down to 1.6. We have transferred a Bose-Einstein
condensate (BEC) into this trap and obtained very good agreement between its
observed anisotropic expansion and the hydrodynamic predictions. Our method can
be extended to obtain a spherical trapping potential, which has a geometry of
particular theoretical interest.Comment: 4 pages, 3 figure
Robust optical FFH-CDMA communications: coding in place of frequency and temperature controls
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