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  • 1
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The surface topography of three cestode parasites from the gut ofSqualus acanthias is described with the aid of scanning electron microscopy (SEM). The cestodes areTrilocularia acanthiaevulgaris, which occurs in both stomach and spiral valve, andPhyllobothrium squali andGilquinia squali, which only appear in the latter. Differences between the stomach and spiral valve forms ofT. acanthiaevulgaris are recorded. The anterior third of the free proglottis of this species is covered by numerous large, backwardly-projecting spines. Bands of similar, though smaller, spines encircle the anterior margins of proglottides still attached to the strobila and grow larger as the proglottides mature. The adherent surface of the bothridia ofP. squali is covered by large numbers of minute “ear-of-corn” projections, in addition to more normal microtriches, whilst that ofG. squali bears numerous flat, plamate structures. The mature and free proglottides ofG. squali possess large numbers of short, rod-like structures around the genital pore and they are surrounded by a ring of hummock-like papillae. The possibilities of these microtopographical features being used in a sensory and/or attachment role are considered. The value of SEM as a taxonomic aid in cestode systematics is briefly discussed.
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  • 2
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Differences in the internal anatomy and ultrastructure ofTrilocularia acanthiaevulgaris from the stomach and spiral valve of the spiny dogfish are described with the aid of electron microscopy and light microscope histochemistry. Worms from the stomach rarely exceed 7 mm in length and do not exhibit signs of segmentation. In contrast, spiral valve worms are segmented, reach a length of some 30 mm and release free proglottides which mature whilst detached from the strobila. Numerous calcareous corpuscles and large glycogen-filled vacuolations occur throughout the body of stomach worms, but are almost totally absent from spiral valve worms. The neck region of spiral valve worms is packed with many germinative cells. The distal tegumental cytoplasm of the stomach worm contains many electron-lucid vesicles, mitochondria and forming microtriches. Microtriches on the tegumental surface are scant, and those present are directed posteriorly. The distal tegumental cytoplasm of the spiral valve worm contains few electron-lucid vesicles and mitochondria but has many dumb-bell-shaped vesicles. Microtriches are longer and more numerous than those of stomach worms. The differences suggest thatT. acanthiaevulgaris worms from the stomach are juveniles which migrate to the spiral valve where they develop into the adult.
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  • 3
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Mature calcareous corpuscles in the juvenile (stomach) worms of Trilocularia acanthiaevulgaris comprise a number of concentric lamellae interspersed with areas of flocculent material. Each lamella is composed of a pair of membranous rings to which amorphous, non-crystalline material is attached. The process of corpuscle formation is intracellular, beginning with the autophagic breakdown of the cytoplasm to produce a central vacuole within a parenchymal cell. The vacuole enlarges until only a thin layer of cytoplasm remains at the periphery and the nucleus is displaced to one end of the cell. Paired, concentrically arranged membranes are laid down beneath the peripheral cytoplasmic layer and eventually occlude the central vacuole. X-ray analysis of the corpuscles indicates the presence of calcium, phosphorus, sulphur, zinc and molybdenum, with the major peaks representing calcium, phosphorus and sulphur. Calcium appears to be bound to the lamellae rather than associated with the material between lamellae. The possible functions of the corpuscles are discussed in relation to the biology of T. acanthiaevulgaris and its developmental sequence in the dogfish gut.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The kinetics of the production and dark-decay of index gratings in chromium-doped bismuth germanium oxide Bi12GeO20 (BGO) and undoped BGO were investigated as a function of temperature from room temperature to about 500 K. During the write process in undoped BGO the gratings show a fast leading edge peak, which drops quickly to a steady saturated value. The leading-edge peak does not change significantly at the higher temperatures. Grating production was much slower in the BGO:Cr samples and the gratings grew monotonically throughout the 0.5 s write interval. At room temperature the gratings in BGO:Cr are highly persistent. A grating written at room temperature retains 70% of its initial strength after 24 h when it was read only once an hour. Optical erasure plays a major role in the decay of such gratings; reading the grating every 6 min reduced its strength to 48% of its initial value after 24 h. The grating written at room temperature and monitored as the sample was heated decayed within the same 10 K temperature range as the photochromic absorption bands. As expected, undoped BGO shows a rapid dark decay at room temperature that becomes faster at higher temperatures. © 2001 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6017-6021 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Doping the photorefractive material bismuth germanium oxide Bi12GeO20(BGO) with chromium significantly affects its optical properties. An absorption spectrum taken at 300 K shows that the introduction of chromium produces a strong unresolved band which overlaps the absorption cutoff of BGO and a series of smaller overlapping bands between 650 and 1100 nm. Cooling BGO:Cr to 10 K sharpens the small bands and resolves the strong band into a peak near 510 nm. This peak is responsible for the reddish-brown color of BGO:Cr. Excitation at room temperature with visible light increases the bands in the 650–1100 nm range. The production of this additional room temperature photochromic absorption is most efficient with excitation near 490 nm but extends throughout the visible. Chromium occupies the tetrahedral germanium site in BGO; and the observed spectra are consistent with a Cr4+ tetrahedral state. During crystal growth some of the chromium gives up an electron to the antisite bismuth native defect and becomes Cr5+. Exposing the sample to light returns the electron to the chromium and increases the Cr4+ absorption. The photoinduced absorption is thermally stable for temperatures up to about 425 K. This stability suggests that doping BGO with Cr should lead to room temperature persistent photorefractive gratings. © 2001 American Institute of Physics.
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The kinetics of production and dark decay of index gratings in Bismuth Silicon Oxide was investigated as a function of write-beam intensity at 300 K and of temperature over the 20–300 K temperature range. At 300 K and an intensity of about 200 mW/cm2 the gratings show a fast leading-edge peak which drops to a steady saturated value. At lower intensities the peak slows and broaden, but the grating strength at saturation remains the same. As the temperature is lowered the gratings grow more slowly, and the peak disappears at about 200 K. The slowing and disappearance of the peak are probably related to the large decrease in electron mobility in this temperature range. Below 225 K the grating strength at the end of the 500 ms write time grows significantly and reaches a maximum in the 125–150 K temperature region. The dark decays disappear quickly for temperatures down to about 180 K. At lower temperatures the decays become much slower and become persistent below 60 K. The largest change appears between 150 and 123 K. A persistent grating was written at 20 K, and its strength was measured as the sample warmed. The persistent grating annealed out between 110 and 150 K. The slowing of the dark decays and the anneal of the persistent grating correlate with the reported recovery of Fe3+. © 2001 American Institute of Physics.
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  • 7
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The ultrastructure of the scolex glands ofTrilocularia acanthiaevulgaris is described with the aid of transmission electron microscopy. The syncytial scolex gland cells exhibit an ultrastructure which is typical of secretory cells, in that they contain extensive and distended cisternae of granular endoplasmic reticulum (GER), numerous Golgi complexes and secretory vesicles. The vesicles are transported via microtubule-lined ducts to the apex of the scolex where they are released from the tegumental surface by an eccrine process. The secretion is often accumulated in reservoirs created by a lateral swelling of the ducts. Cytochemical studies show that the secretion has a glycoprotein nature. It is suggested that the secretion probably acts as an adhesive, aiding attachment of the worm to the host mucosa. This may be more important in juvenile worms which have less well-developed scoleces.
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  • 8
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The localisation and distribution of the cholinergic and serotoninergic components of the nervous system in the plerocercoid, adult and free proglottis stages of the tetraphyllidean tapewormTrilocularia acanthiaevulgaris were determined by enzyme histochemical and immunocytochemical techniques. The central nerve ring (CNR) in the scolex contains two lateral ganglia and gives rise to five pairs of longitudinal nerve cords (LNC's; three lateral, two median). The nerve cords run posteriorly throughout the bodies of the plerocercoid and adult worms and the free proglottis. Nerves from the CNR and accessory lateral LNC's pass to the bothridia, where they give rise to extensive nerve plexuses. As the individual proglottides develop along the strobila, a small nerve ring forms at the anterior end of each proglottis; within the nerve ring, distinct bilateral ganglia develop prior to the release of the proglottis. All ten LNC's are present in the free proglottis. The genital atrium and cirrus sac are innervated by cholinergic and serotoninergic elements. The cholinergic nervous system predominates in the CNS within the scolex, whereas there is a larger population of 5-HT-immunoreactive nerve cells associated with the LNC's and segmental ganglia along the strobila and within the free proglottis.
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  • 9
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The fine structure of the excretory system in the juvenile (plerocercoid-like) form ofTrilocularia acanthiaevulgaris is described. The flame cell bears a bunch of 50–70 cilia, which are anchored in the cytoplasm by means of basal bodies possessing striated rootlets. All the cilia in the “flame” are aligned in the same direction. The flame and duct cells are connected by interdigitating ribs of cytoplasm separated by a fibrous sheet. Both internal and external leptotriches are also present. The lumen of the excretory ducts is intracellular in origin. The apical surface of the cytoplasm lining the duct is convoluted and its surface area is further amplified by means of microvilli. The fine structure of the excretory system in this primitive tapeworm is compared with that described for other parasitic and free-living flatworms.
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  • 10
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Phosphorus is one of several dopants that electronically compensate the native deep donor responsible for the yellow coloration observed in bismuth silicon oxide (BSO). Low-temperature optical absorption measurements of a series of Czochralski-grown P-doped BSO crystals show that ∼0.1–0.15 at. % P is needed in the sample to fully remove the yellow coloration. The absorption cutoff in the fully compensated P-doped sample was at 3.2 eV while compensated Al- and Ga-doped samples cutoff at 3.35 eV. Excitation at 10–15 K with near band-edge light produces photochromic absorption bands. In the lightly-doped (partially bleached) samples these bands were identical to those observed in undoped BSO. In the fully bleached sample a new spectrum was observed. Its major contribution was a band centered near 1.8 eV with a weaker absorption in the blue-green. By comparison with the spectra observed in undoped and in Al-doped material before and after photoexcitation it is believed that the 1.8 eV band is due to the [PO4]− center and that the broad 2.45 eV band observed in Al- and Ga-doped BSO is due to the [BiO4]0 center. © 1995 American Institute of Physics.
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