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  • Chemistry  (2)
  • Klinotaxis  (2)
  • Polymer and Materials Science  (2)
  • Lunar and Planetary Science and Exploration
  • ddc:650
  • 1990-1994  (4)
Collection
Keywords
Publisher
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Scanning motion, ocellar morphology and orientation mechanisms in the phototaxis of the nematode Mermis nigrescens (1990)
    Springer
    Journal of comparative physiology 167 (1990), S. 257-268 
    Details
    ISSN: 1432-1351
    Keywords: Scanning motion ; Shadowing ; Ocellus ; Mechanism ; Orientation ; Phototaxis ; Klinotaxis ; Photomovement ; Transverse phototaxis ; Nematode
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The putative ocellus of Mermis females consists of a hollow cylinder of dense hemoglobin pigmentation located in the anterior tip. The exact location of the photoreceptive nerve endings, however, is unknown. During phototaxis a continual bending or scanning motion of the head (anterior 2 mm) causes the orientation of the tip to swing about the direction of the source. By turning off (shuttering) the light source whenever the tip orientation was to one side of the source direction, the average orientation of the base of the head, and eventually the body orientation, was caused to be biased about 28° to the opposite side. Because the shuttering was synchronized with the scanning motion, the scanning motion must be involved in the maintenance of orientation to light. The direction of the bias rules out a two-signal comparison mechanism of orientation and demonstrates that a deviation of the tip from the source direction must decrease, rather than increase, the illumination of the photoreceptors. These findings, and the ocellar morphology, require that the photoreceptors be located inside the hollow tube of pigmentation where they can be shadowed by the pigment during deviations of the tip. Focusing by the curved anterior end should cause a similar modulation of the illumination at this location. The occasional episodes of transverse phototaxis can be explained by the leakiness of the pigment walls to transverse illumination. Analysis of the motion of the anterior in the presence and absence of shuttering indicates that the orientation of the base of the head, due to the motion of the neck, is controlled by the signals generated during one or more cycles of the scanning motion of the head. The orientation may be regulated by the phase relationship between the photoreceptor signal and putative proprioceptive signals that indicate the bending in the head.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00188118
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  • 2
    Electronic Resource
    Electronic Resource
    Components of phototaxis of the nematode Mermis nigrescens (1990)
    Springer
    Journal of comparative physiology 167 (1990), S. 245-255 
    Details
    ISSN: 1432-1351
    Keywords: Undulatory locomotion ; Scanning motion ; Directed turn ; Orientation ; Phototaxis ; Klinotaxis ; Photomovement ; Nematode
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The gravid females of Mermis are positively phototaxic at the time of their migration to egglaying sites in vegetation on which their grasshopper hosts feed. On a horizontal felt surface, segments of the path traced by the tail are oriented approximately towards a source of monochromatic light in the 350–540 nm region, but are not oriented at longer wavelengths and in the dark. The components of this phototaxis include locomotion by the posterior 4/5 of the body, orientational bending of the neck region while the anterior is held above the substrate, and a scanning motion (bending) of the head region (anterior 2 mm). Like other nematodes and snakes, propulsion is associated with posteriorly propagated body waves, but unlike other animals known, the waves tend to lie perpendicular to a felt surface, and unlike other nematodes, contact with the surface is on the female's ventral surface. The body waves are initiated by the motion of the anterior 1/5 (15 mm) of the body, the average orientation of which determines the path of the following 4/5. During phototaxis, the anterior tip is swung both sideways and vertically about the direction towards the light source. The tip motion is a result of a scanning motion of the head and a slower orientational bending of the neck. The base of the head appears to be actively directed towards the source by the bending of the neck. This behavior can resolve two light sources positioned 120° apart but not 90° apart. The scanning motion of the head is independent of neck orientation and appears to enhance the probability of discovering the direction of a new source. Discovery is followed by a directed turn of the base of the head towards the source which is initiated by the bending of the neck. Locomotion of the body follows the path of the anterior through the turn and phototaxis is thus initiated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00188117
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  • 3
    Electronic Resource
    Electronic Resource
    Water-soluble photoinitiators: Primary processes in hydroxy alkyl phenyl ketones (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 1319-1327 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photopolymerization of acrylamide in water has been investigated in the presence of watersoluble hydroxy alkyl phenyl ketones. The processes involved in the excited states (α-cleavage, electron transfer, monomer quenching) have been studied by time-resolved laserspectroscopy. Substitution at the para position of the phenyl ring changes drastically the reactivity and influences the possibility of synergistic effects when combining these photoinitiators with thioxanthone derivatives.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080290911
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  • 4
    Electronic Resource
    Electronic Resource
    Histomorphometric assessment of the mechanisms for rapid ingrowth of bone to HA/TCP coated implants (1993)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 27 (1993), S. 645-653 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The purpose of this work is to use dynamic histomorphometry to evaluate the basic biological mechanisms by which hydroxyapatite/tricalcium phosphate (HA/TCP) implant coatings accelerate bone formation rates. Twenty-five rabbits had an HA/TCP coated cylindrical titanium fiber metal mesh implant surgically placed in the subchondral bone of the proximal tibia and a noncoated implant placed in the contralateral tibia. Twenty-two of these animals had HA/TCP coated cylindrical solid titanium implants placed in the distal femur and an uncoated implant placed in te contraleteral femur. The animals were double labeled with vital stains, and sacrificed at 3, 6, 16, or 26 weeks after surgery. Histomorphometric analyses were done of the bone implant interfaces. Both static and dynamic histomorphometric parameters indicate that HA/TCP coatings stimulate faster bone ingrowth to coated fiber metal implants through the early production of woven bone and by subsequent rapid lamellar bone formation rates. Coated fiber metal implants demonstrated significantly more bone ingrowth than noncoated implants through 16 weeks postimplatatin, but not by 26 weeks, In solid implants, the differences between coated and noncoated implants are less pronouned and not statistically significant, although there is a trend toward increased bone appostion to the surface of the implants over the first 16 weeks following implantation. The clinical significance of these results is that coated implants may allow earlier return to normal weightbearing. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820270512
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