Regularized least-squares migration of simultaneous-source seismic data with adaptive singular spectrum analysis.

Simultaneous-source acquisition has been recognized as an economic and efficient acquisition method, but the direct imaging of the simultaneous-source data produces migration artifacts because of the interference of adjacent sources. To overcome this problem, we propose the regularized least-squares reverse time migration method (RLSRTM) using the singular spectrum analysis technique that imposes sparseness constraints on the inverted model. Additionally, the difference spectrum theory of singular values is presented so that RLSRTM can be implemented adaptively to eliminate the migration artifacts. With numerical tests on a flat layer model and a Marmousi model, we validate the superior imaging quality, efficiency and convergence of RLSRTM compared with LSRTM when dealing with simultaneous-source data, incomplete data and noisy data.

[Interface bond and compatibility between Mark II machining ceramic and vita VM9 veneering porcelain].

OBJECTIVE: To investigate the interface bond and thermal compatibility between Mark II machining ceramic and Vita VM9 veneering porcelain. METHODS: A bar shaped specimen (30 mm x 15 mm x 1 mm in size) of Mark II block was prepared, with 0.5 mm-deep notch (vertical to the long axis of specimen) at the middle of the bottom surface. The upper surface was veneered with 0.3 mm VM9 dentin base porcelain. Then the specimen was fractured from the notching site and the fracture surface was examined under scanning electron microscope (SEM) and electron microprobe analyzer (EMPA) with electron beam of 1 microm in diameter. Another ten specimens (30 mm x 15 mm x 1.5 mm in size) were fabricated and the temperature of thermal shock resistance were tested. RESULTS: SEM observation showed tight bond between these two materials and EMPA results showed penetration of Al element from Mark II block into veneering porcelain and Ca element from veneering porcelain into Mark II block occurred after sintering baking. The average temperature of thermal shock resistance for specimens in this study was (194.0+/-10.3) degrees C. Cracks were mainly distributed in veneering porcelain. CONCLUSION: Chemical bond exists between the Mark II machining ceramic and Vita VM9 veneering porcelain, and there is good thermal compatibility between them.

[Raman spectroscopic analysis of post-cement-root canal dentin interface].

OBJECTIVE: To examine the compositions of those adhesion modes between luting cements and canal dentin, and to evaluate the dentin-cement-post interface by Laser-Ranian spectroscopy. METHODS: Three representative luting cements (zinc phosphate, glass ionomer and resin cements), two kinds of prefabricated posts (titanium and fiber-glass), six extracted intact human maxillary anterior teeth were used canal dentin after endodontic treatment. Laser-Raman spectroscopy measure of cement, post and canal dentin before and after luting together. RESULTS: There are no evident Raman spectra change cross the ZPC/dentin interface and glass ionomer/dentin interface, while cross the resin/dentin interface and resin/glass fiber post interface can be seen special Raman spectra. CONCLUSION: Laser-Raman microspectroscopy is a useful analytical technique for evaluation interface between dentin and luting cements. Resin cement may interact with dentin and glass fiber post.

[The effect of different fabrication methods and luting cements on post retention].

OBJECTIVE: This study was to compare the retention of posts fabricated by different methods and cemented with various cements in order to provide a guidance for clinical choice of post fabrication methods and luting cements. METHODS: Ninety human maxillary anterior teeth were sectioned by the cementoenamel junction and post-holes were prepared. All roots were embedded in the center of plastic cylinders and paralleled with the cylinder. All samples were divided into 9 groups randomly and equally. Posts fabricated with different methods were then cemented with different luting cements. Each sample was placed into a specialized jig and mounted on a tensile testing machine with crosshead speed of 5 mm/min. Constant tensile force was applied until the post was dislodged, and the tensile force required to dislodge the cemented post was recorded. RESULTS: The mean retention force of parapost and direct post demonstrated significantly higher than that of indirect post did (P < 0.05), but there was no significant difference between parapost and direct post(P > 0.05). The mean retention of parapost cement demonstrated significantly higher than that of ZPC and HY-Bond cement did (P < 0.05), but there was no significant difference between ZPC and HY-Bond cement (P > 0.05). CONCLUSION: Different fabrication methods and luting cements significantly affect the retention of posts; and there exists an interaction between different fabricating methods and luting cements.