1,482 research outputs found

    Techniques for the Microanalysis of Higher Plants with Particular Reference to Silicon in Cryofixed Wheat Tissues

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    The applications of x-ray microanalysis in research into silicon in higher plants are reviewed, recent developments are assessed, and new data are presented. Conventionally prepared material [air or freeze drying for scanning electron microscopy (SEM), and glutaraldehyde/osmium tetroxide fixation for transmission electron microscopy (TEM)) has been studied using both wavelength and energy dispersive microanalysis. These techniques are reliable provided that the deposited form of silica is the major focus of investigation. Recently, studies concerning the soluble, mobile forms of silica, and the ionic environment at deposition sites have been initiated. In these investigations x -ray microanalysis has been carried out on the cold stage of an SEM, or after freeze substitution on sections in TEM. Two other developments which are considered are the use of proton induced x-ray emission, and electron energy loss spectroscopy. To illustrate the most recent developments in this field we present new observations on mineral distribution in the culm and awn of wheat using microanalysis of frozen hydrated material in SEM, and in the wheat leaf using freeze substitution and TE M and scanning transmission electron microscopy

    The Multifragmentation Freeze--Out Volume in Heavy Ion Collisions

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    The reduced velocity correlation function for fragments from the reaction Fe + Au at 100 A~MeV bombarding energy is investigated using the dynamical--statistical approach QMD+SMM and compared to experimental data to extract the Freeze--Out volume assuming simultaneous multifragmentation.Comment: 8 pages; 3 uuencoded figures available with figures command, LateX, UCRL-J-1157

    Generation of Intrinsic Vibrational Gap Modes in Three-Dimensional Ionic Crystals

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    The existence of anharmonic localization of lattice vibrations in a perfect 3-D diatomic ionic crystal is established for the rigid-ion model by molecular dynamics simulations. For a realistic set of NaI potential parameters, an intrinsic localized gap mode vibrating in the [111] direction is observed for fcc and zinc blende lattices. An axial elastic distortion is an integral feature of this mode which forms more readily for the zinc blende than for the fcc structure. Molecular dynamics simulations verify that in each structure this localized mode may be stable for at least 200 cycles.Comment: 5 pages, 4 figures, RevTeX, using epsf.sty. To be published in Phys. Rev. B. Also available at http://www.msc.cornell.edu/~kiselev

    The generation of influenza-specific humoral responses is impaired in ST6Gal I-deficient mice.

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    Posttranslational modification of proteins, such as glycosylation, can impact cell signaling and function. ST6Gal I, a glycosyltransferase expressed by B cells, catalyzes the addition of alpha-2,6 sialic acid to galactose, a modification found on N-linked glycoproteins such as CD22, a negative regulator of B cell activation. We show that SNA lectin, which binds alpha-2,6 sialic acid linked to galactose, shows high binding on plasma blasts and germinal center B cells following viral infection, suggesting ST6Gal I expression remains high on activated B cells in vivo. To understand the relevance of this modification on the antiviral B cell immune response, we infected ST6Gal I(-/-) mice with influenza A/HKx31. We demonstrate that the loss of ST6Gal I expression results in similar influenza infectivity in the lung, but significantly reduced early influenza-specific IgM and IgG levels in the serum, as well as significantly reduced numbers of early viral-specific Ab-secreting cells. At later memory time points, ST6Gal I(-/-) mice show comparable numbers of IgG influenza-specific memory B cells and long-lived plasma cells, with similarly high antiviral IgG titers, with the exception of IgG2c. Finally, we adoptively transfer purified B cells from wild-type or ST6Gal I(-/-) mice into B cell-deficient (microMT(-/-)) mice. Recipient mice that received ST6Gal I(-/-) B cells demonstrated reduced influenza-specific IgM levels, but similar levels of influenza-specific IgG, compared with mice that received wild-type B cells. These data suggest that a B cell intrinsic defect partially contributes to the impaired antiviral humoral response

    An Early CD4+ T Cell–dependent Immunoglobulin A Response to Influenza Infection in the Absence of Key Cognate T–B Interactions

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    Contact-mediated interactions between CD4+ T cells and B cells are considered crucial for T cell–dependent B cell responses. To investigate the ability of activated CD4+ T cells to drive in vivo B cell responses in the absence of key cognate T–B interactions, we constructed radiation bone marrow chimeras in which CD4+ T cells would be activated by wild-type (WT) dendritic cells, but would interact with B cells that lacked expression of either major histocompatibility complex class II (MHC II) or CD40. B cell responses were assessed after influenza virus infection of the respiratory tract, which elicits a vigorous, CD4+ T cell–dependent antibody response in WT mice. The influenza-specific antibody response was strongly reduced in MHC II knockout and CD40 knockout mice. MHC II–deficient and CD40-deficient B cells in the chimera environment also produced little virus-specific immunoglobulin (Ig)M and IgG, but generated a strong virus-specific IgA response with virus-neutralizing activity. The IgA response was entirely influenza specific, in contrast to the IgG2a response, which had a substantial nonvirus-specific component. Our study demonstrates a CD4+ T cell–dependent, antiviral IgA response that is generated in the absence of B cell signaling via MHC II or CD40, and is restricted exclusively to virus-specific B cells

    The use of the 1 mm laparoscope to assist in port insertion in pelvic oncological surgery

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    BACKGROUND: A 1 mm minilaparoscope (Lifeline Biotechnoligies, Florida, USA) was assessed for aiding port site insertions. METHODS: Ten consecutive patients having laparoscopic procedures in a gynaecological oncology unit were included. Minilaparoscopy was feasible in all cases and was used to insert the umbilical port under direct vision in all patients. In one case, a thick band of abdominal adhesions was identified and a further lateral port site was inserted to aid their dissection. RESULTS: The minilaparoscope correctly identified all 10 patients with peritoneal disease and identified all patients who were suitable for debulking procedures. CONCLUSION: Minilaparoscopy with the 1 mm endoscope appears to be safe and accurate and we feel that it has a place in helping the surgeon identify adhesions and peritoneal disease as well as assisting further port site insertion safely and with minimal complications

    Correspondences and Quantum Description of Aharonov-Bohm and Aharonov-Casher Effects

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    We establish systematic consolidation of the Aharonov-Bohm and Aharonov-Casher effects including their scalar counterparts. Their formal correspondences in acquiring topological phases are revealed on the basis of the gauge symmetry in non-simply connected spaces and the adiabatic condition for the state of magnetic dipoles. In addition, investigation of basic two-body interactions between an electric charge and a magnetic dipole clarifies their appropriate relative motions and discloses physical interrelations between the effects. Based on the two-body interaction, we also construct an exact microscopic description of the Aharonov-Bohm effect, where all the elements are treated on equal footing, i.e., magnetic dipoles are described quantum-mechanically and electromagnetic fields are quantized. This microscopic analysis not only confirms the conventional (semiclassical) results and the topological nature but also allows one to explore the fluctuation effects due to the precession of the magnetic dipoles with the adiabatic condition relaxed
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