Atlas-based segmentation of pathological MR brain images using a model of lesion growth

We propose a method for brain atlas deformation in the presence of large space-occupying tumors, based on an a priori model of lesion growth that assumes radial expansion of the lesion from its starting point. Our approach involves three steps. First, an affine registration brings the atlas and the patient into global correspondence. Then, the seeding of a synthetic tumor into the brain atlas provides a template for the lesion. The last step is the deformation of the seeded atlas, combining a method derived from optical flow principles and a model of lesion growth. Results show that a good registration is performed and that the method can be applied to automatic segmentation of structures and substructures in brains with gross deformation, with important medical applications in neurosurgery, radiosurgery, and radiotherapy.     

Learning eigenfunctions links spectral embedding and kernel PCA

In this letter, we show a direct relation between spectral embedding methods and kernel principal components analysis and how both are special cases of a more general learning problem: learning the principal eigenfunctions of an operator defined from a kernel and the unknown data-generating density. Whereas spectral embedding methods provided only coordinates for the training points, the analysis justifies a simple extension to out-of-sample examples (the Nystr?m formula) for multidimensional scaling (MDS), spectral clustering, Laplacian eigenmaps, locally linear embedding (LLE), and Isomap. The analysis provides, for all such spectral embedding methods, the definition of a loss function, whose empirical average is minimized by the traditional algorithms. The asymptotic expected value of that loss defines a generalization performance and clarifies what these algorithms are trying to learn. Experiments with LLE, Isomap, spectral clustering, and MDS show that this out-of-sample embedding formula generalizes well, with a level of error comparable to the effect of small perturbations of the training set on the embedding.     

Dimensioning IP access links carrying data traffic

This paper proposes simple dimensioning rules for high speedip access links carrying data traffic. Assuming a finite source population and fair bandwidth sharing among user flows, we derive formulas relating capacity, demand and performance. These formulas allow link dimensioning for a target quality of service expressed in terms of useful per-flow throughput. They constitute a data traffic model equivalent of the Engset model for telephone access networks. Performance is shown to be largely independent of detailed traffic characteristics such as the statistical distributions of flow size and think time. Simple approximations are derived for two distinct performance regimes corresponding to transparency and saturation, respectively. Extensions to the basic model account for a heterogeneous user demand, unfair bandwidth sharing or different access rate classes. In any case, the key parameter for dimensioning is the offered traffic, defined as the average data rate a user would generate in the absence of congestion.     

Correction of inner filter effect in mirror coating cells for trace level fluorescence measurements

The sensitivity of the spectrofluorometric technique can be improved by a factor of about 3.6 using a mirror coating cell. In the case of a large working range, the nonlinear relationship due to the absorbance of solutions between concentration of the analyte of interest and fluorescence intensity (called inner filter effect) must be corrected. This paper suggests a universal inner filter correction equation based on the physical absorbance phenomenon of a mirror coating cell that only depends on the solution absorbance spectra and the cell parameters. These parameters are determined with rhodamine b standard solutions and a simplex method-based mathematical fitting. The methodology has been successfully applied to the correction of classical and synchronous spectra in absorbent media. The partial least squares (PLS) quantification of a mixture of trace levels (approximately 1-10 microg L(-1)) of six polycyclic aromatic hydrocarbons (PAHs) by synchronous fluorescence is possible, even in an absorbent matrix. This simple method allows extension of the analytical field of fluorescence quantification to a large working range in absorbent solutions.     

Verification of cardiac tissue electrophysiology simulators using an N-version benchmark

Ongoing developments in cardiac modelling have resulted, in particular, in the development of advanced and increasingly complex computational frameworks for simulating cardiac tissue electrophysiology. The goal of these simulations is often to represent the detailed physiology and pathologies of the heart using codes that exploit the computational potential of high-performance computing architectures. These developments have rapidly progressed the simulation capacity of cardiac virtual physiological human style models; however, they have also made it increasingly challenging to verify that a given code provides a faithful representation of the purported governing equations and corresponding solution techniques. This study provides the first cardiac tissue electrophysiology simulation benchmark to allow these codes to be verified. The benchmark was successfully evaluated on 11 simulation platforms to generate a consensus gold-standard converged solution. The benchmark definition in combination with the gold-standard solution can now be used to verify new simulation codes and numerical methods in the future.     

The Activation of a Pd/γ-alumina Catalyst During Methane Combustion: Investigation of the Phenomenon and of Potential Causes

Activation phenomena of a Pd/γ-Al₂O₃ catalyst under methane combustion reaction conditions were studied. The activation of the catalyst with time-on-stream is not due to Cl removal from the surface but seems to be related to sintering of the palladium particles. This could induce structural changes in the palladium particle, which would favor the activation of O₂ on the surface of PdO.     

Characterization of the granular packing and percolation threshold of reactive powder concrete

Reactive powder concrete (RPC) is a new cement-based material developed through microstructural engineering. RPC is composed of very fine powders: sand, crushed quartz and silica fume, all with particle sizes comprised between 300 and 0.02 μm, and a low water content, W/C<0.20. A very dense matrix is achieved by optimizing the granular packing of these powders. This compactness confers to RPC ultrahigh strength and durability.

The hydration kinetic of the cementitious matrix using electrical conductivity and isothermal calorimetry is presented. A linear relationship between the logarithm of conductivity ln(σ) and the degree of hydration , has been found:

ln(σ)=A_v−B_v

where A_v depends on the nature and the dosage of the different mineral and organic components, and B_v is an invariant related to the granular packing. From 19 different RPC compositions, an average value of 12.1 with a standard deviation of 1.7 were found for B_v. The capillary porosity percolation threshold was also deduced from this relationship. It has been found that when the degree of hydration is equal to 26%, the capillary pore space is discontinuous. This last result is in agreement with the prediction of the NIST microstructural model by Bentz and Garboczi [D., Bentz, E. Garboczi, Percolation of phases in a three-dimensional cement paste microstructural model, Cem Concr Res 21 (2) (1991) 325–344]. A continuous determination of the degree of hydration based on electrical conductivity is proposed.     

Fatty acid composition of pinaceae as taxonomic markers

Following our previous review on Pinus spp. seed fatty acid (FA) compositions, we recapitulate here the seed FA compositions of Larix (larch), Picea (spruce), and Pseudotsuga (Douglas fir) spp. Numerous seed FA compositions not described earlier are included. Approximately 40% of all Picea taxa and one-third of Larix taxa have been analyzed so far for their seed FA compositions. Qualitatively, the seed FA compositions in the three genera studied here are the same as in Pinus spp., including in particular the same Δ5-olefinic acids. However, they display a considerably lower variability in Larix and Picea spp. than in Pinus spp. An assessment of geographical variations in the seed FA composition of P. abies was made, and intraspecific dissimilarities in this species were found to be of considerably smaller amplitude than interspecific dissimilarities among other Picea species. This observation supports the use of seed FA compositions as chemotaxonomic markers, as they practically do not depend on edaphic or climatic conditions. This also shows that Picea spp. are coherently united as a group by their seed FA compositions. This also holds for Larix spp. Despite a close resemblance between Picea and Larix spp. seed FA compositions, principal component analysis indicates that the minor differences in seed FA compositions between the two genera are sufficient to allow a clear-cut individualization of the two genera. In both cases, the main FA is linoleic acid (slightly less than one-half of total FA), followed by pinolenic (5,9,12-18:3) and oleic acids. A maximum of 34% of total Δ5-olefinic acids is reached in L. sibirica seeds, which appears to be the highest value found in Pinaceae seed FA. This apparent limit is discussed in terms of regio- and stereospecific distribution of Δ5-olefinic acids in seed triacylglycerols. Regarding the single species of Pseudotsuga analyzed so far (P. menziesii), its seed FA composition is quite distinct from that of the other two genera, and in particular, it contains 1.2% of 14-methylhexadecanoic (anteiso-17:0) acid. In the three genera studied here, as well as in most Pinus spp., the C₁₈Δ5-olefinic acids (5,9-18:2 and 5,9,12-18:3 acids) are present in considerably higher amounts than the C₂₀Δ5-olefinic acids (5,11-20:2 and 5,11,14-20:3 acids).