Accepting its random coil nature allows a partial NMR assignment of the neuronal Tau protein

A combined strategy to obtain a partial NMR assignment of the neuronal Tau protein is presented. Confronted with the extreme spectral degeneracy that the spectrum of this 441 amino acid long unstructured protein presents, we have introduced a graphical procedure based on residue type-specific product planes. Combining this strategy with the search for pairwise motifs, and combining the spectra of different Tau isoforms and even of peptides derived from the native sequence, we arrive at a partial assignment that is sufficient to map the interactions of Tau with its molecular partners. The obtained assignments equally confirm the absence of regular secondary structure in the isolated protein.     

Respiratory motion of the heart from free breathing coronary angiograms

Respiratory motion compensation for cardiac imaging requires knowledge of the heart's motion and deformation during breathing. This paper presents a method for measuring the natural tidal respiratory motion of the heart from free breathing coronary angiograms. A three-dimensional (3-D) deformation field describing the cardiac and respiratory motion of the coronary arteries is recovered from a biplane acquisition. A cardiac respiratory parametric model is formulated and used to decompose the deformation field into cardiac and respiratory components. Angiograms from ten patients were analyzed. A 3-D translation motion model was sufficient for describing the motion of the heart in only two patients. For all patients, the heart translated caudally (mean, 4.9+/-1.9 mm; range, 2.4 to 8.0 mm) and underwent a cranio-dorsal rotation (mean, 1.5 degrees+/-0.9 degrees; range, 0.2 degrees to 3.5 degrees) during inspiration. In eight patients, the heart also translated anteriorly (mean, 1.3+/-1.8 mm; range, -0.4 to 5.1 mm) and rotated in a caudo-dextral direction (mean, 1.2 degrees+/-1.3 degrees; range, -1.9 degrees to 3.2 degrees).     

Atmospheric deposition of polycyclic aromatic hydrocarbons to Atlantic Canada: geographic and temporal distributions and trends 1980-2001

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants. The semivolatile organic compounds may disperse into the atmosphere by direct input from several sources such as the burning of fossil fuels, from motor vehicle emissions, and forest fires. Once in the atmosphere, they may travel great distances before being deposited to the earth's surface by the scavenging action of rain and snow. Up to 14 PAHs were determined in wet precipitation samples collected monthly from five sites in the four Canadian Atlantic Provinces during 1980-2001. The relatively more volatile PAHs (phenanthrene, fluoranthene, naphthalene, and pyrene) were predominant in the samples. Significant (P < 0.05) spatial variations in the deposition of some PAHs were observed among sites, but there were no consistent geographic patterns. Seasonal patterns were discernible with peak deposition for sigma6&14 PAHs occurring during the colder months of the year (December to March) and coinciding with higher energy consumption for heating and transport. The monthly volume weighed mean concentration for sigma6 PAHs has declined steadily since the mid-1980s at Kejimkujik National Park in southwest Nova Scotia, with a calculated half-life of 6.4 +/- 0.3 years. The maximum annual deposition flux of 20 microg m(-2) yr(-1) reached in 1985 for sigma6 PAHs decreased approximately 1 order of magnitude by the year 2000. The decrease in sigma6&14 PAHs for the region was found to be correlated (P < 0.05) with decreasing sulfate ion concentrations in the precipitation. The implementation of air pollution abatement programs in Canada, the United States, and elsewhere, switching to cleaner sources of energy and improved technology during the pastfew decades is most likely responsible for the observed decline.     

Use of correspondence discriminant analysis to predict the subcellular location of bacterial proteins

Correspondence discriminant analysis (CDA) is a multivariate statistical method derived from discriminant analysis which can be used on contingency tables. We have used CDA to separate Gram negative bacteria proteins according to their subcellular location. The high resolution of the discrimination obtained makes this method a good tool to predict subcellular location when this information is not known. The main advantage of this technique is its simplicity. Indeed, by computing two linear formulae on amino acid composition, it is possible to classify a protein into one of the three classes of subcellular location we have defined. The CDA itself can be computed with the ADE-4 software package that can be downloaded, as well as the data set used in this study, from the P?le Bio-Informatique Lyonnais (PBIL) server at http://pbil.univ-lyon1.fr.     

Approximating Node Connectivity Problems via Set Covers

Given a graph (directed or undirected) with costs on the edges, and an integer $k$, we consider the problem of finding a $k$-node connected spanning subgraph of minimum cost. For the general instance of the problem (directed or undirected), there is a simple $2k$-approximation algorithm. Better algorithms are known for various ranges of $n,k$. For undirected graphs with metric costs Khuller and Raghavachari gave a $( 2+{2(k-1)}/{n})$-approximation algorithm. We obtain the following results: (i) For arbitrary costs, a $k$-approximation algorithm for undirected graphs and a $(k+1)$-approximation algorithm for directed graphs. (ii) For metric costs, a $(2+({k-1})/{n})$-approximation algorithm for undirected graphs and a $(2+{k}/{n})$-approximation algorithm for directed graphs. For undirected graphs and $k=6,7$, we further improve the approximation ratio from $k$ to $\lceil (k+1)/2 \rceil=4$; previously, $\lceil (k+1)/2 \rceil$-approximation algorithms were known only for $k \leq 5$. We also give a fast $3$-approximation algorithm for $k=4$. The multiroot problem generalizes the min-cost $k$-connected subgraph problem. In the multiroot problem, requirements $k_u$ for every node $u$ are given, and the aim is to find a minimum-cost subgraph that contains $\max\{k_u,k_v\}$ internally disjoint paths between every pair of nodes $u,v$. For the general instance of the problem, the best known algorithm has approximation ratio $2k$, where $k=\max k_u$. For metric costs there is a 3-approximation algorithm. We consider the case of metric costs, and, using our techniques, improve for $k \leq 7$ the approximation guarantee from $3$ to $2+{\lfloor (k-1)/2 \rfloor}/{k} < 2.5$.     

Evaluation of bent-crystal x-ray backlighting and microscopy techniques for the Sandia Z machine

X-ray backlighting and microscopy systems for the 1-10-keV range based on spherically or toroidally bent crystals are discussed. These systems are ideal for use on the Sandia Z machine, a megajoule-class x-ray facility. Near-normal-incidence crystal microscopy systems have been shown to be more efficient than pinhole cameras with the same spatial resolution and magnification [Appl. Opt. 37, 1784 (1998)]. We show that high-resolution (< or = 10 microm) x-ray backlighting systems using bent crystals can be more efficient than analogous point-projection imaging systems. Examples of bent-crystal-backlighting results that demonstrate 10-microm resolution over a 20-mm field of view are presented.     

Three-dimensional point spread functions of an optical heterodyne scanning image processor

We study the three-dimensional (3-D) imaging properties of an optical heterodyne scanning image processor. The image processor is a two-pupil optical system capable of 3-D imaging coherently or incoherently, depending on the detection scheme used. We derive the imaging properties in terms of the two pupils and then show an important 3-D imaging application in scanning holography by deriving its 3-D point spread functions and compare them with conventional 3-D imaging systems.     

On the designing of densely dispersion-managed optical fiber systems for ultrafast optical communication

We present some theoretical and experimental results which suggest the possibility of constructing a non-empirical methodology of designing optical transmission systems with ultra high bit-rate per channel. Theoretically, we present an average dispersion decreasing densely dispersion-managed (A4dm) fiber system, which exhibits many advantages over the densely dispersion-managed fiber system, such as the possibility of transmitting chirp-free Gaussian pulses at 160 Gbit/s per channel over transoceanic distances, with a reduced energy and minimal intra-channel interaction. Experimentally we present generation of a 160-GHz picosecond pulse train at 1550 nm using multiple four-wave mixing temporal compression of an initial dual frequency beat signal in the anomalous-dispersion regime of a non-zero dispersion shifted fiber. A complete intensity and phase characterization of the pulse train by means of a frequency-resolved optical gating technique is achieved, showing generation of transform-limited pedestal-free Gaussian pulses.     

Fiber optic applications of multiple quantum well electroabsorption modulators

Electroabsorption modulators (eam) have proved to be very attractive both as optical sources (monolithically integrated NRZ transmitters andrz pulse generators) as well as for very fast signal processing (demultiplexing, regeneration, wavelength conversion,...). Their design criteria, technology and implementation in future networks are reviewed, and the main issues are discussed.