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Photoionized gaseous nebulae and magnetized stellar winds: The evolution and shaping of H II regions and planetary nebulae : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)

Franco, José ; García-Segura, Guillermo ; Kurtz, Stan E. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 8 (2001), S. 2432-2438

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ISSN: 1089-7674

Source: AIP Digital Archive

Topics: Physics

Notes: The early evolution of hydrogen+ (H II) regions is controlled by the properties of the star-forming cloud cores. The observed density distributions in some young H II regions indicate that the power-law stratifications can be steeper than r−2. Ionization fronts can overrun these gradients and the ionized outflows are strongly accelerated along these steep density distributions. Thus, photoionized regions can either reach pressure equilibrium inside the inner parts of the high-pressure cores [with sizes and densities similar to those observed in ultra compact (UC) H II regions], or create bright H II regions with extended emission. The density inhomogeneities engulfed within the ionization fronts create corrugations in the front, which in turn drive instabilities in the ionization-shock (I-S) front. These instabilities grow on short time scales and lead to the fragmentation of the dense shells generated by the shock fronts. Thus, new clumps are continuously created from the fragmented shell, and the resulting finger-like structures can explain the existence of elephant trunks and cometary-like globules in most H II regions. In the case of planetary nebulae (PNe), wind asymmetries and magnetic fields from rotating stars, along with precession of the rotation axis, can create the wide range of observed PNe morphologies and collimated outflows (jets). Magnetic collimation and jet formation in PNe become very efficient after the flow has passed through the reverse shock of the PN. © 2001 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1351825

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Binding of the Streptococcus gordonii surface glycoproteins GspB and Hsa to specific carbohydrate structures on platelet membrane glycoprotein Ibα (2005)

Takamatsu, Daisuke ; Bensing, Barbara A. ; Cheng, Hui ; [et al.]

Oxford, UK : Blackwell Science Ltd

Molecular microbiology 58 (2005), S. 0

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ISSN: 1365-2958

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Medicine

Notes: GspB and Hsa are homologous serine-rich surface glycoproteins of Streptococcus gordonii strains M99 and Challis, respectively, that mediate the binding of these organisms to platelet membrane glycoprotein (GP) Ibα. Both GspB and Hsa consist of an N-terminal putative signal peptide, a short serine-rich region, a region (BR) that is rich in basic amino acids, a longer serine-rich region and a C-terminal cell wall anchoring domain. To further assess the mechanisms for GspB and Hsa binding, we investigated the binding of the BRs of GspB and Hsa (expressed as glutathione S-tranferase fusion proteins) to sialylated glycoproteins in vitro. Both fusion proteins showed significant levels of binding to sialylated moieties on fetuin and GPIbα. In contrast, the corresponding region of a GspB homologue of Streptococcus agalactiae, which is acidic rather than basic, showed no binding to either fetuin or GPIbα. As measured by surface plasmon resonance kinetic analysis, GspB- and Hsa-derived fusion proteins had high affinity for GPIbα, but with somewhat different dissociation constants. Dot blot analysis using a panel of synthesized oligosaccharides revealed that the BR of Hsa can bind both α(2-3) sialyllactosamine [NeuAcα(2-3)Galβ(1-4)GlcNAc] and sialyl-T antigen [NeuAcα(2-3)Galβ(1-3)GalNAc], whereas the BR of GspB only bound sialyl-T antigen. Moreover, far Western blotting using platelet membrane proteins revealed that GPIbα is the principal receptor for GspB and Hsa on human platelets. The combined results indicate that the BRs of GspB and Hsa are the binding domains of these adhesins. However, the subsets of carbohydrate structures on GPIbα recognized by the binding domains appear to be different between the two proteins.