Proposed Correlation Function Research Articles

A Spatial Correlation Model for Visual Information in Wireless Multimedia Sensor Networks

Wireless multimedia sensor networks (WMSNs) are interconnected devices that allow retrieving video and audio streams, still images, and scalar data from the environment. In a densely deployed WMSN, there exists correlation among the visual information observed by cameras with overlapped field of views. This paper proposes a novel spatial correlation model for visual information in WMSNs. By studying the sensing model and deployments of cameras, a spatial correlation function is derived to describe the correlation characteristics of visual information observed by cameras with overlapped field of views. The joint effect of multiple correlated cameras is also studied. An entropy-based analytical framework is developed to measure the amount of visual information provided by multiple cameras in the network. Furthermore, according to the proposed correlation function and entropy-based framework, a correlation-based camera selection algorithm is designed. Experimental results show that the proposed spatial correlation function can model the correlation characteristics of visual information in WMSNs through low computation and communication costs. Further simulations show that, given a distortion bound at the sink, the correlation-based camera selection algorithm requires fewer cameras to report to the sink than the random selection algorithm.

Interpretation of Backscattering Mechanisms from Non-gaussian Correlated Randomly Rough Surfaces

In this study we analyzed backscattering mechanism using a non-Gaussian correlation function, called exponential-like, for rough surface. The corresponding surface spectrum properties were investigated. It contains an excessive amount of high frequency spectral components. But unlike exponential one, it has rms slopes and allows to obtain the desired rms slopes. New insight into the physical implications of mechanism behind the backscattering behavior was obtained using the advanced integral equation model (AIEM). It is known that backscattering at large incident angles is proportional to the presence of small scale roughness or the high-frequency spectral components of the surface spectrum. Similarly, the peaking at near normal incidence is proportional to the large scale roughness or the low frequency spectral components of the surface spectrum. However, by increasing frequency while keeping the small roughness scale, scattering cannot approach the geometric optics at large angles of incidence where small roughness scales dominate scattering. There is condition where VV tends to HH returns without approaching the geometric optics limit. This is where we increase the surface rms slope. In fact, the presence of roughness scales, small or comparable to the incident wavelength, implies that the geometric optics condition is not satisfied. When there is a significant amount of backscattering in the large incident angle region, it indicates presence of high frequency spectral components in the surface spectrum. To demonstrate the applicability of the proposed correlation function, comparison of backscattering coefficients between model predictions and insitu measurements was made. Well match was obtained in terms of level and angular trend.

Calculation of NMR Relaxation Times for Quadrupolar Nuclei in the Presence of Chemical Exchange

The correlation function for a quadrupolar nucleus which may exchange its environment between two kinds of sites in solution has been calculated from an appropriate joint conditional probability for changes in site and in electric field gradient direction with time. In the extreme narrowing limit, the resultant NMR linewidth depends both on the exchange lifetimes and also on the correlation times for rotation at each site; the NMR linewidth may thus be used to obtain information about any of these quantities. The results bear directly on the use of quadrupolar nuclei in the presence of chemical exchange of nuclei between suitable sites to obtain motional information about macromolecules in dilute solution. In particular, the proposed correlation function may account for anaomalously small calculated rotational-correlation times for large molecules previously obtained from such studies. A precise criterion for applicability of McConnell-modified Bloch equations is proposed. Other applications of the correlation function derived in this paper are discussed.