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- Chen, Donglei, et al.
(författare)
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Three-dimensional histology of tooth cushions of Lophosteus from the Upper Silurian of Estonia
- 2011
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Ingår i: Abstracts. ; , s. 5-6
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Lophosteus superbus from the Late Silurian of Estonia is one of the oldest and most plesiomorphic osteichthyans described to date. Unfortunately at present it is known only from fragmented dermal microremains. The affinities of Lophosteus are therefore controversial with the taxon placed as either basal to both actinopterygians and sarcopterygians, or ambiguously linked to either placoderms or acanthodians. To confound matters further, the character states diagnosing actinopterygians and sarcopterygians have recently been brought into question, and even monophyly of the traditional placoderm and acanthodian clades has been challenged. As a possible stem osteichthyan, Lophosteus could thus be central to our understanding of early gnathostome evolution and the origin of the osteichthyan body plan. Often the best-preserved, although incompletely documented, elements of Lophosteus are tooth cushions. These tooth-bearing arched ossicles could arguably be homologous with the parasymphysial tooth whorls in chondrichthyans, acanthodians, and sarcopterygians, or even the parasymphysial tooth plates in tetrapodomorphs. High-resolution synchrotron scans of 6 isolated tooth cushions from the Upper Silurian of Estonia has permitted a detailed reconstruction of their three-dimensional architecture. The absence of an enamel layer and the presence of large hollows (bigger than normal osteocytes) in the deepest lamellar layer confirmed assignment of the specimens to Lophosteus. The external surface displays irregularly distributed denticles and there are large parallel vessels running horizontally on the basal bone that feed the denticle rows internally. The odontodes have two distinct generations (with successive odontodes accreted between those of the preceding buried generation) and are organised in a similar manner to those found on Lophosteus scales. This new histological data on vascularization provides insight into early gnathostome tooth patterning and could contribute to future phylogenetic assessments.
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- Grape, Sophie, 1982-, et al.
(författare)
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Partial defect verification using the DCVD : a capability evaluation approach
- 2011
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Digital Cherenkov Viewing Device (DCVD) is a non-intrusive instrument available to theInternational Atomic Energy Agency (IAEA) for verifying spent nuclear fuel in storage pools. It iscurrently used for gross-defect evaluations, i.e. to verify that an item in a storage pool is anirradiated fuel assembly and not a fresh assembly or a dummy. This is done by recording images ofthe Cherenkov light emitted in the water surrounding the fuel. Currently, the instrument’s ability toalso detect partial defects at the 50% level or even lower is under study. Here, experimental work iscomplimented by modeling and simulations due to the limited availability of assemblies with partialdefects.Ideally, an IAEA inspector should be able to use the DCVD at e.g. a fuel storage site andimmediately after scanning obtain information on (1) whether an item is an irradiated fuel assemblyor not, and (2) whether the assembly is intact or suffers from a partial defect. This paper discusses adecision-making methodology intended for the latter purpose with the objective to implement it inthe DCVD software in order to facilitate smooth inspection procedures. Inspectors will thus not berequired to possess any expertise in the decision-making methodology.The paper also describes measurements performed during spring 2011 at the CLAB interim spentfuel storage in Sweden. The measurements were carried out with the objective to optimize theequipment handling and work flow during this type of measurement campaigns and to form a basisfor the evaluation of the DCVD’s ability to detect partial defects.
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- Parcey, Dennis A., et al.
(författare)
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Determination of Cerenkov light absorption by fuel pond water using a calibration light source
- 2011
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Quantitative measurement of Cerenkov light generated by spent fuel assemblies requires anunderstanding of the absorbance characteristics of the spent fuel pond water. The presence ofparticulate or organic material can severely attenuate the transmission of the ultravioletcomponent of the Cerenkov spectrum. This can make the quantitative measurement of theCerenkov light using a digital Cerenkov viewing device difficult or in some cases impossible.A calibration light source that can be inserted into the fuel pond has been constructed. Thissource generates a known ultraviolet light flux. Measurements of this source can be used tocalculate the absorbance of Cerenkov light by the fuel pond water and in turn compensate for theabsorbance when measuring the intensity of a spent fuel assembly. This paper discusses thechallenges of constructing such a device and the results from measurements in two spent fuelponds.
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