Distribution of Stream Macroalgae in Four High Arctic Drainage Basins

Eighty-three stream reaches were sampled from four drainage basins in the central portions of Axel Heiberg and Ellesmere Islands. The stream included small snowmelt tributaries, those flowing through wetlands, pond outflows, glacial meltwaters, and large trunk rivers, some of which had become braided in their lower portions. Larger channels tended to be quite turbid, and macroscopic algae were negligible in these reaches because they lack adequate light and hard substrata for attachment. The overall stream macroalgal flora was relatively small (15 species) compared to that of other regions of the North American tundra. Cyanobacteria and Chlorophyta accounted for all but one species. The most widespread species was the colonial cyanobacterium, Nostoc commune. Only Scytonema mirabile (Cyanophyta) was a new addition to the stream macroalgal flora of arctic North America. The numbers of species per stream reach ranged from 0 to 5, with a mean of 1.3. The amount of stream bottom covered by macroalgae was 0 to 75%, with an average of ca. 5%. Both species number and percent cover per reach are relatively low.On a procédé à des échantillonnages de 83 tronçons de cours d'eau situés dans quatre bassins de drainage au centre de l'île Axel Heiberg et de l'île d'Ellesmere. Les cours d'eau comprenaient de petits affluents alimentés par la fusion nivale, ceux qui traversaient des terres humides, des émissaires d'étangs, des eaux de fonte glaciaires et d'importants cours d'eau principaux, dont certains étaient devenus anastomosés en aval. Les chenaux larges avaient tendance à être relativement troubles et on ne trouvait que peu d'algues macroscopiques dans ces tronçons en raison du manque de lumière adéquat et des substrats de soutien. La flore macroalgale globale des cours d'eau était assez réduite (15 espèces) par rapport à celle d'autres régions de la toundra nord-américaine. Toutes les espèces sauf une appartenaient aux cyanobactéries et aux chlorophycées. L'espèce la plus répandue était la cyanobactérie coloniale, Nostoc commune. Seule Scytonema mirabile (cyanophycée) était une nouveauté dans la flore macroalgale de l'Arctique nord-américain. Le nombre d'espèces par cours d'eau allait de 0 à 5, avec une moyenne de 1,3. De 0 à 75 p. cent de la superficie du fond des cours d'eau était couverte par les macroalgues, avec une moyenne d'environ 5 p. cent. Le nombre d'espèces comme le pourcentage de leur couverture par tronçon étaient relativement bas

A Note on Tachyons in the D3+D3ˉD3+{\bar {D3}} System

The periodic bounce of Born-Infeld theory of $D3$-branes is derived, and the BPS limit of infinite period is discussed as an example of tachyon condensation. The explicit bounce solution to the Born--Infeld action is interpreted as an unstable fundamental string stretched between the brane and its antibrane.Comment: 10 pages, 2 figures. v2: minor changes, acknowledgement added; v3: explanations and references added. Final version to appear in Mod. Phys. Lett.

A condition for first order phase transitions in quantum mechanical tunneling models

A criterion is derived for the determination of parameter domains of first order phase transitions in quantum mechanical tunneling models. The criterion is tested by application to various models, in particular to some which have been used recently to explore spin tunneling in macroscopic particles. In each case agreement is found with previously heuristically determined domains.Comment: 13 pages, 5 figure

Insights into the evolutionary origins of clostridial neurotoxins from analysis of the Clostridium botulinum strain A neurotoxin gene cluster

<p>Abstract</p> <p>Background</p> <p>Clostridial neurotoxins (CNTs) are the most deadly toxins known and causal agents of botulism and tetanus neuroparalytic diseases. Despite considerable progress in understanding CNT structure and function, the evolutionary origins of CNTs remain a mystery as they are unique to <it>Clostridium </it>and possess a sequence and structural architecture distinct from other protein families. Uncovering the origins of CNTs would be a significant contribution to our understanding of how pathogens evolve and generate novel toxin families.</p> <p>Results</p> <p>The <it>C. botulinum </it>strain A genome was examined for potential homologues of CNTs. A key link was identified between the neurotoxin and the flagellin gene (CBO0798) located immediately upstream of the BoNT/A neurotoxin gene cluster. This flagellin sequence displayed the strongest sequence similarity to the neurotoxin and NTNH homologue out of all proteins encoded within <it>C. botulinum </it>strain A. The CBO0798 gene contains a unique hypervariable region, which in closely related flagellins encodes a collagenase-like domain. Remarkably, these collagenase-containing flagellins were found to possess the characteristic HEXXH zinc-protease motif responsible for the neurotoxin's endopeptidase activity. Additional links to collagenase-related sequences and functions were detected by further analysis of CNTs and surrounding genes, including sequence similarities to collagen-adhesion domains and collagenases. Furthermore, the neurotoxin's HCRn domain was found to exhibit both structural and sequence similarity to eukaryotic collagen jelly-roll domains.</p> <p>Conclusion</p> <p>Multiple lines of evidence suggest that the neurotoxin and adjacent genes evolved from an ancestral collagenase-like gene cluster, linking CNTs to another major family of clostridial proteolytic toxins. Duplication, reshuffling and assembly of neighboring genes within the BoNT/A neurotoxin gene cluster may have lead to the neurotoxin's unique architecture. This work provides new insights into the evolution of <it>C. botulinum </it>neurotoxins and the evolutionary mechanisms underlying the origins of virulent genes.</p

The Structure of D2-Branes in the Presence of an RR field

A Born--Infeld theory describing a $D2$--brane coupled to a 3--form RR potential is reconsidered and a new type of static solution is obtained which is even stable.Comment: 11 pages, 2 postscript figures, v2 a significantly revised including title, v3 expression of energy for D2 brane is improved, version to appear in JHE

Spectral asymmetry for bag boundary conditions

We give an expression, in terms of boundary spectral functions, for the spectral asymmetry of the Euclidean Dirac operator in two dimensions, when its domain is determined by local boundary conditions, and the manifold is of product type. As an application, we explicitly evaluate the asymmetry in the case of a finite-length cylinder, and check that the outcome is consistent with our general result. Finally, we study the asymmetry in a disk, which is a non-product case, and propose an interpretation.Comment: Some minor changes. To appear in Journal of Physics A: Mathematical and Genera

Macroscopic Quantum Phase Interference in Antiferromagnetic Particles

The tunnel splitting in biaxial antiferromagnetic particles is studied with a magnetic field applied along the hard anisotropy axis. We observe the oscillation of tunnel splitting as a function of the magnetic field due to the quantum phase interference of two tunneling paths of opposite windings. The oscillation is similar to the recent experimental result with Fe}$_8$\textrm{\ molecular clusters.}Comment: 8 pages, 2 postscript figures, to appear in J. Phys.: Condes. Matte

Exact calculation of the skyrmion lifetime in a ferromagnetic Bose condensate

The tunneling rate of a skyrmion in ferromagnetic spin-1/2 Bose condensates through an off-centered potential barrier is calculated exactly with the periodic instanton method. The prefactor is shown to depend on the chemical potential of the core atoms, at which level the atom tunnels. Our results can be readily extended to estimate the lifetime of other topological excitations in the condensate, such as vortices and monopoles.Comment: 16 pages, 4 figures, to appear Phys. Rev.

Yale Global Tic Severity Scale (YGTSS): Psychometric Quality of the Gold Standard for Tic Assessment Based on the Large-Scale EMTICS Study.

The Yale Global Tic Severity Scale (YGTSS) is a clinician-rated instrument considered as the gold standard for assessing tics in patients with Tourette's Syndrome and other tic disorders. Previous psychometric investigations of the YGTSS exhibit different limitations such as small sample sizes and insufficient methods. To overcome these shortcomings, we used a subsample of the large-scale "European Multicentre Tics in Children Study" (EMTICS) including 706 children and adolescents with a chronic tic disorder and investigated convergent, discriminant and factorial validity, as well as internal consistency of the YGTSS. Our results confirm acceptable convergent and good to very good discriminant validity, respectively, indicated by a sufficiently high correlation of the YGTSS total tic score with the Clinical Global Impression Scale for tics (r &lt;sub&gt;s&lt;/sub&gt; = 0.65) and only low to medium correlations with clinical severity ratings of attention deficit/hyperactivity symptoms (r &lt;sub&gt;s&lt;/sub&gt; = 0.24), obsessive-compulsive symptoms (r &lt;sub&gt;s&lt;/sub&gt; = 27) as well as internalizing symptoms (r &lt;sub&gt;s&lt;/sub&gt; = 0.27). Internal consistency was found to be acceptable (Ω = 0.58 for YGTSS total tic score). A confirmatory factor analysis supports the concept of the two factors "motor tics" and "phonic tics," but still demonstrated just a marginal model fit (root mean square error of approximation = 0.09 [0.08; 0.10], comparative fit index = 0.90, and Tucker Lewis index = 0.87). A subsequent analysis of local misspecifications revealed correlated measurement errors, suggesting opportunities for improvement regarding the item wording. In conclusion, our results indicate acceptable psychometric quality of the YGTSS. However, taking the wide use and importance of the YGTSS into account, our results suggest the need for further investigations and improvements of the YGTSS. In addition, our results show limitations of the global severity score as a sum score indicating that the separate use of the total tic score and the impairment rating is more beneficial

Space Symmetries and Quantum Behavior of Finite Energy Configurations in SU(2)-Gauge Theory

The quantum properties of localized finite energy solutions to classical Euler-Lagrange equations are investigated using the method of collective coordinates. The perturbation theory in terms of inverse powers of the coupling constant $g$ is constructed, taking into account the conservation laws of momentum and angular momentum (invariance of the action with respect to the group of motion M(3) of 3-dimensional Euclidean space) rigorously in every order of perturbation theory.Comment: LaTex, 17 pages typos correcte