Viewing Sea Level by a One-Dimensional Random Function with Long Memory

Sea level fluctuation gains increasing interests in several fields, such as geoscience and ocean dynamics. Recently, the long-range dependence (LRD) or long memory, which is measured by the Hurst parameter, denoted byH, of sea level was reported by Barbosa et al. (2006). However, reports regarding the local roughness of sea level, which is characterized by fractal dimension, denoted byD, of sea level, are rarely seen. Note that a common model describing a random function with LRD is fractional Gaussian noise (fGn), which is the increment process of fractional Brownian motion (fBm) (Beran (1994)). If using the model of fGn,Dof a random function is greater than 1 and less than 2 becauseDis restricted byHwith the restrictionD=2−H. In this paper, we introduce the concept of one-dimensional random functions with LRD based on a specific class of processes called the Cauchy-class (CC) process, towards separately characterizing the local roughness and the long-range persistence of sea level. In order to achieve this goal, we present the power spectrum density (PSD) function of the CC process in the closed form. The case study for modeling real data of sea level collected by the National Data Buoy Center (NDBC) at six stations in the Florida and Eastern Gulf of Mexico demonstrates that the sea level may be one-dimensional but LRD. The case study also implies that the CC process might be a possible model of sea level. In addition to these, this paper also exhibits the yearly multiscale phenomenon of sea level

A New High-Speed Foreign Fiber Detection System with Machine Vision

A new high-speed foreign fiber detection system with machine vision is proposed for removing foreign fibers from raw cotton using optimal hardware components and appropriate algorithms designing. Starting from a specialized lens of 3-charged couple device (CCD) camera, the system applied digital signal processor (DSP) and field-programmable gate array (FPGA) on image acquisition and processing illuminated by ultraviolet light, so as to identify transparent objects such as polyethylene and polypropylene fabric from cotton tuft flow by virtue of the fluorescent effect, until all foreign fibers that have been blown away safely by compressed air quality can be achieved. An image segmentation algorithm based on fast wavelet transform is proposed to identify block-like foreign fibers, and an improved canny detector is also developed to segment wire-like foreign fibers from raw cotton. The procedure naturally provides color image segmentation method with region growing algorithm for better adaptability. Experiments on a variety of images show that the proposed algorithms can effectively segment foreign fibers from test images under various circumstances

Variance Bound of ACF Estimation of One Block of fGn with LRD

This paper discusses the estimation of autocorrelation function (ACF) of fractional Gaussian noise (fGn) with long-range dependence (LRD). A variance bound of ACF estimation of one block of fGn with LRD for a given value of the Hurst parameter (H) is given. The present bound provides a guideline to require the block size to guarantee that the variance of ACF estimation of one block of fGn with LRD for a given H value does not exceed the predetermined variance bound regardless of the start point of the block. In addition, the present result implies that the error of ACF estimation of a block of fGn with LRD depends only on the number of data points within the sample and not on the actual sample length in time. For a given block size, the error is found to be larger for fGn with stronger LRD than that with weaker LRD

Asymptotic Identity in Min-Plus Algebra: A Report on CPNS

Network calculus is a theory initiated primarily in computer communication networks, especially in the aspect of real-time communications, where min-plus algebra plays a role. Cyber-physical networking systems (CPNSs) are recently developing fast and models in data flows as well as systems in CPNS are, accordingly, greatly desired. Though min-plus algebra may be a promising tool to linearize any node in CPNS as can be seen from its applications to the Internet computing, there are tough problems remaining unsolved in this regard. The identity in min-plus algebra is one problem we shall address. We shall point out the confusions about the conventional identity in the min-plus algebra and present an analytical expression of the asymptotic identity that may not cause confusions

Cauchy-Matern Model of Sea Surface Wind Speed at the Lake Worth, Florida

We study the Cauchy-Matern (CM) process with long-range dependence (LRD). The closed form of its power spectrum density (PSD) function is given. We apply it to model the autocovariance function (ACF) and the PSD of the sea surface wind speed (wind speed for short) observed in the Lake Worth, Florida, over the 1984–2006 period. The present results exhibit that the wind speed at the Lake Worth over 1984–2006 is of LRD. The present results exhibit that the CM process may yet be a novel model to fit the wind speed there

Hydrodynamic responses and power efficiency analyses of an oscillating wave surge converter under different simulated PTO strategies

Experimental investigation on the power performance of a bottom hinged oscillating wave surge converters (OWSC) with different power take-off (PTO) damping strategies (provided by a generic PTO simulation platform) are conducted in regular and irregular waves. The hydrodynamic performance of the OWSC under different damping modes, in regular waves and irregular waves, is observed. For regular waves, the effects of the main influential parameters (including the incident wave height, wave frequency, phase difference between the buoy velocity and wave elevation) on the output power were quantitatively studied. Six damping coefficients of the linear PTO damping is examined under constant incident wave height, and increasing wave frequencies and an output power curve along wave frequency are presented for each input gain of the PTO simulation platform in both linear damping mode and nonlinear damping mode. Additionally, the best coefficient or input gain is obtained for both linear or nonlinear PTO damping mode in different wave conditions. The phase difference between the buoy velocity and wave elevation of the OWSC model in irregular waves has the same trend as that in regular waves. The output electricity in the JONSWAP spectrum is found to be (approximately 300%) higher than that in a user-defined spectrum for the same wave parameters. However, nonlinear PTO strategies have no distinct advantage in the amount of electricity output but have better stability and broader damping range