The Analysis of Pixel Intensity (Myocardial Signal Density) Data: The Quantification of Myocardial Perfusion by Imaging Methods.

This paper described a number of important issues in the analysis of pixel intensity data, as well as approaches for dealing with these. We particularly emphasized the issue of clustering, which may be ubiquitous in studies of pixel intensity data. Clustering can take many forms, e.g., measurements of different sections of a heart or repeated measurements of the same research participant. Clustering typically has the effect of increasing variance estimates. When one fails to account for clustering, variance estimates may be unrealistically small, resulting in spurious significance. We illustrated several possible approaches to account for clustering, including adjusting standard errors for design effects and modeling the covariance structure within clusters using mixed models. These methods offer great flexibility for dealing with a wide variety of research designs and include the capability for adjusting for covariates and different case weights. Similar methods can be used to account for clustering in both superiority and equivalence analyses. In situations where clustering affects the true cluster mean, µ, but not the difference between measures of the mean, it is possible that clustering will have a much greater impact on superiority analyses than on equivalence analyses

Scaling Baroclinic Eddy Fluxes: Vortices and Energy Balance

The eddy heat flux generated by the statistically equilibrated baroclinic instability of a uniform, horizontal temperature gradient is studied using a two-mode f-plane quasigeostrophic model. An overview of the dependence of the eddy diffusivity D on the bottom friction κ, the deformation radius λ, the vertical variation of the large-scale flow U, and the domain size L is provided by numerical simulations at 70 different values of the two nondimensional control parameters κλ/U and L/λ. Strong, axisymmetric, well-separated baroclinic vortices dominate both the barotropic vorticity and the temperature fields. The core radius of a single vortex is significantly larger than λ but smaller than the eddy mixing length ℓ_mix. On the other hand, the typical vortex separation is comparable to ℓ_mix. Anticyclonic vortices are hot, and cyclonic vortices are cold. The motion of a single vortex is due to barotropic advection by other distant vortices, and the eddy heat flux is due to the systematic migration of hot anticyclones northward and cold cyclones southward. These features can be explained by scaling arguments and an analysis of the statistically steady energy balance. These arguments result in a relation between D and ℓ_mix. Earlier scaling theories based on coupled Kolmogorovian cascades do not account for these coherent structures and are shown to be unreliable. All of the major properties of this dilute vortex gas are exponentially sensitive to the strength of the bottom drag. As the bottom drag decreases, both the vortex cores and the vortex separation become larger. Provided that ℓ_mix remains significantly smaller than the domain size, then local mixing length arguments are applicable, and our main empirical result is ℓ_mix ≈ 4λ exp(0.3U/κλ)

Forward (from NDE Education/Training for Engineers )

In 1980 the Materials and Fabrication Committee of the American Society of Engineers, Pressure Vessel and Piping Division, conducted a symposium entitled, Critical Issues in Materials and Mechanical Engineering (1). The purpose of this symposium was to identify those engineering issues which affect the future of ASME and the public at large. One of the critical issues defined and unanimously endorsed by this symposium was the reliability of nondestructive evaluation (NDE). In his statement of the issue, Mordfin pointed out that ... reliable NDE, performed during fabrication and in service, can enhance safety, increase durability, improve performance, and reduce life cycle costs ... He further added that these benefits cannot be achieved without reliable NDE tools, and that reliability itself is a very complex issue that embraces many facets of technology and human skills. Examples of some of the technological facets include the research and development leading to more reliable NDE instrumentation and interpretive signal processing algorithms, the utilization of these advances in the design of NDE systems with predictable and quantifiable performance reliability, and the strong interfacing of NDE with design, materials processing, manufacturing, and maintenance functions that must yet be developed. Human factors that improve reliability are more difficult to define, but certainly include the level of education and training of personnel as well as a number of intangibles that constitute the motivational environment. Burley noted that an important overlying motivational element is management attitude. Reliability in NDE requires an expressed management philosophy that NDE is essential to improved quality and service life of components fabricated from a variety of materials

Action synchronization with biological motion

The ability to predict the actions of other agents is vital for joint action tasks. Recent theory suggests that action prediction relies on an emulator system that permits observers to use information about their own motor dynamics to predict the actions of other agents. If this is the case, then predictions for self-generated actions should be more accurate than predictions for other-generated actions. We tested this hypothesis by employing a self/other synchronization paradigm where prediction accuracy for recording of self-generated movements was compared with prediction accuracy for other-generated movements. As expected, predictions were more accurate when the observer’s movement dynamics matched the movement dynamics of the recording. This is consistent with that idea that the observer’s movement dynamics influence the predictions they generate