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  • 1
    ISSN: 1615-6102
    Keywords: Flagellar apparatus ; Green algae ; Rhizoplast ; Rootlets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The ultrastructure of the flagellar apparatus of the marine quadriflagellate green algaTetraselmis subcordiformis is described in detail. Special consideration is given to the functional significance of the contractile rhizoplast and also to a complex structure which anchors the flagellar apparatus to the cell membrane and theca. The flagellar apparatus lies at the base of a deep apical depression. Four basal bodies lie in a zigzag row with their long axes nearly parallel. Outer adjacent pairs of basal bodies are structurally linked by a Z-shaped, ribbon-like structure. A striated fiber (transfiber) connects each outer basal body with the inner basal body of the opposite, mirror image pair. A complex system of four laminated oval discs (rhizanchora), microtubule rootlets and fibrous material anchor the flagellar apparatus and rhizoplasts to the plasma membrane and theca. A 4-2-4-2 arrangement of microtubule rootlets is present. Rhizoplasts, which are contractile organelles, branch into five distinct arms and associate with the near outer basal body and each of the four rhizanchora. Rhizoplast contraction is thought to be linked to flagellar activity and may act to alter the direction of motion of the cell.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1615-6102
    Keywords: Flagellar apparatus ; Green algae ; Phylogeny ; Striated fiber ; Symmetry ; Ulothrix
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The anterior end of the zoospore ofUlothrix belkae has been examined in detail and is compared toStigeoclonium and other filamentous green algae. The nature of the symmetry of green algal motile cells is discussed and the term, 180° rotational symmetry, is proposed to describe the type of arrangement of anterior end components seen inU. belkae, including the four basal bodies, rootlets and striated fibers. The four microtubular rootlets are cruciately arranged. A striated microtubule-associated component (SMAC) has a periodicity of 6.4 nm and extends with each 2-membered rootlet posteriorly into the cell. One 5-membered rootlet passes very near the eyespot. Phylogeny in green algal motile cells is discussed.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4209-4214 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermal emission of charges has been studied in Si3N4-GaAs structures which were prepared using direct plasma-enhanced chemical-vapor deposition. A comparison has been made of the effects of predeposition plasma treatments using hydrogen, argon, and a mixture of the two. Channel current transient spectroscopy was used in the temperature range 77–350 K. All of the samples exhibited electron emission from an interface-state continuum with energies that were consistent with the interface-state-band model proposed by Hasegawa. When argon and hydrogen were used together two extra processes were observed. One of these was due to an electron trap with an activation energy of 0.05 eV; this response was from states at the remote edge of the depletion region several thousand angstroms from the interface. The necessity for argon and hydrogen suggests that argon had created structural damage permitting the entry of hydrogen atoms to form electrically active complexes in the damaged region. The second process which had an activation energy of 0.05 eV resembled hole emission but, because hole injection was an unlikely process, this observation has been attributed to an interfacial polarization process exhibiting thermally activated relaxation. The corresponding dipole moment per unit area was 1.0×1011 C m. Since this mechanism also required the action of argon and hydrogen it was concluded that this was damage related, with electrical activity produced by the hydrogen atoms.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5793-5801 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The static and dynamic properties of interface states between silicon nitride and n-GaAs have been studied. Comparisons have been made between interfaces that were untreated and ones which were plasma pretreated with Ar, N2, H2, and NH3. With the exception of hydrogen the pretreatments did not significantly alter the quiescent surface Fermi level position or the shape of the interface state distribution in the metal-insulator-semiconductor field effect transistor test structures. In all of the samples it required about 10 μs to complete the transfer of the induced charge from the bulk edge of the depletion region to the interface. Charge which had reached the interface equilibrated there within 100 ns. This charge gave rise to a relatively slow emission transient and had a thermal emission energy consistent with emission from the surface Fermi energy to the lower edge of an interface state band, in accord with the interface state band model. The extent in energy of this band depended on the surface treatment. The insensitivity of the emission time constant to both filling time and insulator electric field suggests that irrespective of the treatment the equilibrated charge remained at the interface and did not tunnel into the insulator. © 1995 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7011-7013 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optoelectronic modulation spectroscopy has been applied to field effect transistors. Spectra include responses from bulk levels as well as from the continuum of states at the insulator-semiconductor interface. States that are energetically deep in a continuum can be probed but would not be accessible to the Fermi level in an electrical measurement.
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  • 6
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 7 (1951), S. 261-276 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The intrinsic viscosity of cellulose xanthate solutions was studied as a function of the electrolyte content of the solvent, and found to decrease sharply with increase in electrolyte concentration. All electrolytes tested except sodium and lithium hydroxides produced essentially the same reduction in intrinsic viscosity for solutions of equivalent ionic strenghts, indicating that the effect was largely one of interaction between the solvent ions and the charged xanthate groups. Hydroxides induced a greater viscosity reduction. The reason for this was not fully resolved; however, indications were obtained that the hydroxides, in addition to behaving as electrolytes toward the charged xanthate groups, also interact with the hydroxyl groups on the parent cellulose chain.Light scattering measurements, as well as data on the variation of the intrinsic viscosity with molecular weight in various solvents, showed that the change in intrinsic viscosity with electrolyte concentration could be accounted for by a change in configuration, or degree of coiling of the molecule. Calculations indicated that in pure water cellulose xanthate should approach a rigid rod configuration whereas in 6% caustic coiling occurs and the molecule resembles more a random configuration.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Auger sputter profiles of thin AI films on InP are presented and shown to be susceptible to an unusual type of ion beam induced interfacial distortion. It is found that recoil implantation and atomic mixing produce a differential broadening of the In and P at the interface which can seriously affect the integrity of the Auger profile. Energy shifts in the AI Auger peak indicate that this distortion is associated with AIP formation to a depth dictated by the ion beam energy and species. Experimental requirements for the reduction of interfacial distortion are discussed. We also consider the influence of the ion beam on the topography and morphology of the InP surface in relation to interfacial distortion.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 9
    ISSN: 1572-9699
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Pilus+ “wild-type” gonococci (Gc) frequently display gene conversion of their expressed complete pilin gene (CPG); a copy of DNA derived from one of the Gc genome's multiple silent partial pilin genes (PPG) is recombinationally-inserted into the CPG's central and 3′ portions with formation of a new, chimeric CPG. Expression of that new CPG leads to either 1) retention of pilus+ phenotype but change in pilin primary structure/antigenicity, or 2) phase change to pilus− phenotype capable of reverting. This study utilizes pilus revertants of P− rp±Gc and P+ colony morphotye variants spawned by P++ Gc to examine pilin gene conversion in strain MS11mk Gc in greater detail. Each revertant's and variant's expressed pilin gene's sequence (as pilin mRNA) was defined to learn whether their differences are due to gene conversion by different PPGs, or by varying stretches from the same PPG, or both. Gene conversion by PPG pilS1 copy 2 has been documented in Gc recovered from a human voluteer's urethra previously inoculated with pilus Gc (strain MS11). The pilus+ Gc isolated expressed structurally/antigenically distinct pilins.
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  • 10
    ISSN: 1432-2218
    Keywords: Ultrasound ; Localization ; Adhesions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Laparoscopic candidates with abdominal scars may have adhesions that result in visceral injury during trocar insertion. The purpose of this study was to evaluate the use of preoperative ultrasound mapping of abdominal wall adhesions, to provide safe initial laparoscopic access, and to guide the placement of subsequent trocars, facilitating adhesolysis when necessary. Thirty consecutive patients with previous abdominal surgery who were scheduled for laparoscopy underwent a preoperative ultrasonic examination of the abdominal wall using a 7-MHz linear ultrasound probe. Spontaneous viscera slide was measured during longitudinal scanning (normal=2–5 cm) and induced viscera slide was evaluated during longitudinal and transverse scanning (normal=1 cm or more) over the existing abdominal scar, the peri-umbilical region, and the remaining abdominal quadrants. Sixteen (53%) of 30 patients had adhesions under their scar and only four patients (25%) had umbilical adhesions. The 12 patients without umbilical adhesions all had successful closed cannulation while open cannulation at alternate sites was successful in the four individuals with umbilical adhesions. Blind umbilical needle cannulation was successfully done in all of the remaining 14 patients (47%) without visceral injury, including three patients (21%) with upper abdominal scars who were adhesion-free elsewhere. No adhesions were encountered that had not been preoperatively predicted by ultrasound. We conclude that examination of the abdominal wall with spontaneous and induced viscera slide, using ultrasound scanning, can reliably detect intraabdominal adhesions. The examination is best done on a highly selective basis by the operating surgeon to guide the location for initial trocar insertion and determine the type of abdominal wall cannulation in those individuals with previous abdominal scars.
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