Horizontal Correlation of Long-Range Bottom Reverberation in Shallow Sloping Seabed

The performance of active sonar detection systems is seriously affected by the reverberation at the bottom of the waveguide in shallow water. In order to improve the performance of active sonar detection, it is necessary to understand the horizontal correlation of shallow-water bottom reverberation in active towed-array processing technology. However, the current research on the spatial correlation of reverberation is mainly based on vertical correlation, little work has been done on the horizontal correlation characteristics of long-distance seabed reverberation, and there is no support from sea test data. In this paper, the coupled mode reverberation model is applied to the horizontal correlation, and is studied according to the receiving position, time, and frequency. The simulation results show that, for the long-range bottom reverberation, the lateral correlation is greater than the longitudinal correlation in the horizontal space. By introducing the adiabatic mode solution, the mathematical model of horizontal correlation in the range-dependent waveguide with depth is derived. The numerical results show that the influence of the seabed dip angle on the horizontal correlation should be considered and that the horizontal correlation is affected obviously by the propagation effects of the sloped sea floor. Finally, the experimental data processing and analysis are given and verify the correctness of the algorithm.

Generalized Estimating Equation Modeling on Correlated Microbiome Sequencing Data with Longitudinal Measures

Background Existing models for assessing microbiome sequencing such as operational taxonomic units (OTUs) can only test predictors' effects on OTUs. There is limited work on how to estimate the correlations between multiple OTUs and incorporate such relationship into models to evaluate longitudinal OTU measures.Results We propose a novel approach to estimate OTU correlations based on their taxonomic structure, and apply such correlation structure in Generalized Estimating Equations (GEE) models to estimate both predictors' effects and OTU correlations. We develop a two-part Microbiome Taxonomic Longitudinal Correlation (MTLC) model for multivariate zero-inflated OTU outcomes based on the GEE framework. In addition, longitudinal and other types of repeated OTU measures are integrated in the MTLC model.Conclusions Extensive simulations have been conducted to evaluate the performance of the MTLC method. Compared with the existing methods, the MTLC method shows robust and consistent estimation, and improved statistical power for testing predictors' effects. Lastly we demonstrate our proposed method by implementing it into a human microbiome study to evaluate the obesity on twins.

Transport of intense beams with current-dependent initial conditions in linearly tapered solenoid channels

In electron beams where space charge plays an important role in the beam transport, the beams’ transverse and longitudinal properties will become coupled. One example of this is the transverse–longitudinal correlation produced in a current-modulated beam generated in a DC electron gun, formed through the competition between the time-dependent radial space charge force and the time-independent radial focusing force. This correlation will cause both the slice radius and divergence of the beam extracted from the gun to depend on the slice current. Here we consider the transport of such a beam in a linearly tapered solenoid focusing channel. Transport performance was generally improved with longer taper lengths, minimal initial correlation between slice divergence and slice current, and moderate degrees of initial correlation between initial slice radius and slice current. Performance was also generally improved with lower slice emittances, although surprisingly transport was improved by slightly increasing the assumed slice emittance in certain limited circumstances.