Sialic Acid Mutarotation Is Catalyzed by the Escherichia coli β-Propeller Protein YjhT

The acquisition of host-derived sialic acid is an important virulence factor for some bacterial pathogens, but in vivo this sugar acid is sequestered in sialoconjugates as the {alpha}-anomer. In solution, however, sialic acid is present mainly as the β-anomer, formed by a slow spontaneous mutarotation. We studied the Escherichia coli protein YjhT as a member of a family of uncharacterized proteins present in many sialic acid-utilizing pathogens. This protein is able to accelerate the equilibration of the {alpha}- and β-anomers of the sialic acid N-acetylneuraminic acid, thus describing a novel sialic acid mutarotase activity. The structure of this periplasmic protein, solved to 1.5Å resolution, reveals a dimeric 6-bladed unclosed β-propeller, the first of a bacterial Kelch domain protein. Mutagenesis of conserved residues in YjhT demonstrated an important role for Glu-209 and Arg-215 in mutarotase activity. We also present data suggesting that the ability to utilize {alpha}-N-acetylneuraminic acid released from complex sialoconjugates in vivo provides a physiological advantage to bacteria containing YjhT

Influence of external flows on crystal growth: numerical investigation

We use a combined phase-field/lattice-Boltzmann scheme [D. Medvedev, K. Kassner, Phys. Rev. E {\bf 72}, 056703 (2005)] to simulate non-facetted crystal growth from an undercooled melt in external flows. Selected growth parameters are determined numerically. For growth patterns at moderate to high undercooling and relatively large anisotropy, the values of the tip radius and selection parameter plotted as a function of the Peclet number fall approximately on single curves. Hence, it may be argued that a parallel flow changes the selected tip radius and growth velocity solely by modifying (increasing) the Peclet number. This has interesting implications for the availability of current selection theories as predictors of growth characteristics under flow. At smaller anisotropy, a modification of the morphology diagram in the plane undercooling versus anisotropy is observed. The transition line from dendrites to doublons is shifted in favour of dendritic patterns, which become faster than doublons as the flow speed is increased, thus rendering the basin of attraction of dendritic structures larger. For small anisotropy and Prandtl number, we find oscillations of the tip velocity in the presence of flow. On increasing the fluid viscosity or decreasing the flow velocity, we observe a reduction in the amplitude of these oscillations.Comment: 10 pages, 7 figures, accepted for Physical Review E; size of some images had to be substantially reduced in comparison to original, resulting in low qualit

Rotational spectra of isotopic species of methyl cyanide, CH3_3CN, in their ground vibrational states up to terahertz frequencies

Methyl cyanide is an important trace molecule in star-forming regions. It is one of the more common molecules used to derive kinetic temperatures in such sources. As preparatory work for Herschel, SOFIA, and in particular ALMA we want to improve the rest frequencies of the main as well as minor isotopologs of methyl cyanide. The laboratory rotational spectrum of methyl cyanide in natural isotopic composition has been recorded up to 1.63 THz. Transitions with good signal-to-noise ratio could be identified for CH$_3$CN, $^{13}$CH$_3$CN, CH$_3^{13}$CN, CH$_3$C$^{15}$N, CH$_2$DCN, and $^{13}$CH$_3^{13}$CN in their ground vibrational states up to about 1.2 THz. The main isotopic species could be identified even in the highest frequency spectral recordings around 1.6 THz. The highest $J'$ quantum numbers included in the fit are 64 for $^{13}$CH$_3^{13}$CN and 89 for the main isotopic species. Greatly improved spectroscopic parameters have been obtained by fitting the present data together with previously reported transition frequencies. The present data will be helpful to identify isotopologs of methyl cyanide in the higher frequency bands of instruments such as the recently launched Herschel satellite, the upcoming airplane mission SOFIA or the radio telescope array ALMA.Comment: 13 pages, 2 figures, article appeared; CDMS links update

Generalized Parton Distributions and Transversity in Nucleons and Nuclei

We present an exploratory study using generalized parton distributions of several observables related to transverse degrees of freedom in hadronic structure -- the nucleon transverse momentum, the transverse radius, or impact parameter, and the momentum transfer, $t$, dependence of the longitudinal variable $x$ -- in both nucleons and nuclei.Comment: 6 pages, 3 figures, Talk presented at "Baryons 04", October 25th-30th, 2004, Palaiseau, Franc

Existence and uniqueness of the integrated density of states for Schr\"odinger operators with magnetic fields and unbounded random potentials

The object of the present study is the integrated density of states of a quantum particle in multi-dimensional Euclidean space which is characterized by a Schr\"odinger operator with a constant magnetic field and a random potential which may be unbounded from above and from below. For an ergodic random potential satisfying a simple moment condition, we give a detailed proof that the infinite-volume limits of spatial eigenvalue concentrations of finite-volume operators with different boundary conditions exist almost surely. Since all these limits are shown to coincide with the expectation of the trace of the spatially localized spectral family of the infinite-volume operator, the integrated density of states is almost surely non-random and independent of the chosen boundary condition. Our proof of the independence of the boundary condition builds on and generalizes certain results by S. Doi, A. Iwatsuka and T. Mine [Math. Z. {\bf 237} (2001) 335-371] and S. Nakamura [J. Funct. Anal. {\bf 173} (2001) 136-152].Comment: This paper is a revised version of the first part of the first version of math-ph/0010013. For a revised version of the second part, see math-ph/0105046. To appear in Reviews in Mathematical Physic

Neglect of the histological diagnostics of onychomycosis – the best would be so easy

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Fast time variations of supernova neutrino signals from 3-dimensional models

We study supernova neutrino flux variations in the IceCube detector, using 3D models based on a simplified neutrino transport scheme. The hemispherically integrated neutrino emission shows significantly smaller variations compared with our previous study of 2D models, largely because of the reduced SASI activity in this set of 3D models which we interpret as a pessimistic extreme. For the studied cases, intrinsic flux variations up to about 100 Hz frequencies could still be detected in a supernova closer than about 2 kpc.Comment: 8 pages, 4 figures. Version accepted for publication in Phys Rev D. Clarifying comments added, results and conclusions are unchange

Non-invasive detection of animal nerve impulses with an atomic magnetometer operating near quantum limited sensitivity

Magnetic fields generated by human and animal organs, such as the heart, brain and nervous system carry information useful for biological and medical purposes. These magnetic fields are most commonly detected using cryogenically-cooled superconducting magnetometers. Here we present the frst detection of action potentials from an animal nerve using an optical atomic magnetometer. Using an optimal design we are able to achieve the sensitivity dominated by the quantum shot noise of light and quantum projection noise of atomic spins. Such sensitivity allows us to measure the nerve impulse with a miniature room-temperature sensor which is a critical advantage for biomedical applications. Positioning the sensor at a distance of a few millimeters from the nerve, corresponding to the distance between the skin and nerves in biological studies, we detect the magnetic field generated by an action potential of a frog sciatic nerve. From the magnetic field measurements we determine the activity of the nerve and the temporal shape of the nerve impulse. This work opens new ways towards implementing optical magnetometers as practical devices for medical diagnostics.Comment: Main text with figures, and methods and supplementary informatio

Hexagons, Kinks and Disorder in Oscillated Granular Layers

Experiments on vertically oscillated granular layers in an evacuated container reveal a sequence of well-defined pattern bifurcations as the container acceleration is increased. Period doublings of the layer center of mass motion and a parametric wave instability interact to produce hexagons and more complicated patterns composed of distinct spatial domains of different relative phase separated by kinks (phase discontinuities). Above a critical acceleration, the layer becomes disordered in both space and time.Comment: 4 pages. The RevTeX file has a macro allowing various styles. The appropriate style is "myprint" which is the defaul