Fast maximum likelihood estimation of signal parameters using theshape of the compressed likelihood function

A computationally efficient fast maximum-likelihood (FML) estimation scheme, which makes use of the shape of the surface of the compressed likelihood function (CLF), is proposed. The scheme uses only multiple one-dimensional searches oriented along appropriate ridges on the surface of the CLF. Simulations indicate that the performances of the proposed estimators match those of the corresponding maximum-likelihood estimators with very high probability. The approach is demonstrated by applying it to two different problems. The first problem involves the estimation of time of arrival and Doppler compression of a wideband hyperbolic frequency modulated (HFM) active sonar signal buried in reverberation. The second problem deals with estimating the frequencies of sinusoids. A threshold analysis of the proposed scheme is carried out to predict the signal-to-noise ratio (SNR) at which large estimation errors begin to occur, i.e., the threshold SNR, and its computational complexity is discussed     

On the ability to estimate narrow-band signal parameters usingtowed arrays

Using the Cramer-Rao lower bound (CRLB) as an indicator of potential performance, the limits on the estimation and resolution capabilities of a towed line array of uniformly spaced hydrophones to provide frequency and bearing information about narrowband signals are examined. It is assumed that a monochromatic plane wave arrives at the array for each source. Several versions of the bounds are computed using different assumptions about which parameters have known values and about the way in which the samples are taken in space and in time. It is shown that the CRLB values for different situations can be compared to provide information about the effective use of a moving aperture for estimation of the parameters of narrowband signals arriving at the array. It is also shown that adding at least one hydrophone occupying a fixed position in space can improve the bearing estimates of a towed array by supplying additional frequency information if both the bearings and frequencies of the sources are unknown     

The respiratory physiology of anadromous vertebrates: A comparison of blood gas transport in lampreys and salmonids

Much of our understanding of the respiratory physiology of lower vertebrates has been derived from studies of salmonids. With regard to blood gas transport, investigators recently have documented a number of important features that may be helpful to the animal under stressful conditions. Several studies examining the respiratory physiology of agnathans have also revealed that striking differences in the strategy of blood gas transport may exist among the lower vertebrates inhabiting the estuary. This paper describes the characteristics of blood gas transport in both salmonids and lampreys and attempts to compare the respiratory strategy of each.     

The Rotation of Europa

Theoretical predictions of non-synchronous rotation and of polar wander on Europa have been tested by comparing tectonic features observed in Voyager and Galileo spacecraft images with tidal stresses. Evidence for non-synchronous rotation comes from studying changes in global scale lineaments formed over time, from the character of strike-slip faults, and from comparison of distinctively shaped cycloidal cracks with the longitudes at which such shapes should have formed, in theory. The study of cycloids constrains the rotation period (relative to the direction of Jupiter) to less than 250 000 years, while direct comparison of the orientation of Europa in Voyager and Galileo images shows the rotation is slow, with a period of >12 000 years. Comparison of strike-slip faults with their theoretical locations of formation provides evidence for substantial polar wander, supported by the distribution of various thermally produced features.     

Labouring geography: Negotiating scales, strategies and future directions

In our editorial introduction to this themed issue on labour geography, we outline some important on-going debates in the relatively young field of labour geography and suggest future directions for research. First, there is the key question of labour as an active agent in the production of economic landscapes. The agency of labour will likely remain a defining feature of labour geography, but perhaps it is not as important to construct theoretical analytical boundaries as it is to define labour geography as a political project. Second, debates continue surrounding the production of scale and the multiscalarity of organized labour. Third, labour geographers have yet to engage in any sustained fashion with unpacking the complex identities of workers and the way in which those identities simultaneously are shaped by and shape the economic and cultural landscape. Fourth, there is some debate on the costs and benefits of a ‘normative’ labour geography which emphasizes what workers and their organizations ‘could’ or even ‘should’ do. Lastly, we challenge the assumption that labour geographers have not yet asserted themselves as activists in their own right. We conclude the editorial by introducing the articles included in the issue. While these articles may not address every gap in the literature, they do contribute in significant ways to move the labour geography project forward.