1,721,113 research outputs found
The MEGaN project II. Gravitational waves from intermediate-mass and binary black holes around a supermassive black hole
No full textWe investigate the evolution of intermediate-mass (IMBHs), stellar (BHs), and binary black holes (BHBs), deposited near a supermassive black hole (SMBH) by a population of massive star clusters. Stellar BHs rapidly segregate around the SMBH, driving the formation of extreme-mass ratio inspirals that coalesce at a rate Γ = 0.02-0.2 yr-1 Gpc-3 at redshift z = 0. A few IMBHs orbiting the SMBH favour the formation of massive pairs that coalescence within a Hubble time, being the merger rate for this channel Γ = 0.03 yr-1 Gpc-3. Recoiling kicks post-merger can eject the remnant from the galaxy centre, especially in dwarf galaxies. Our results suggest that this mechanism can lead to up to 105 ejected SMBH within 1 Gpc. An IMBH co-existing with a few single and binary BHs in the same cluster can affect significantly their evolution, either driving binary disruption, yielding to intermediate-mass ratio inspirals (merger rate Γ = 9.5 yr-1 Gpc-3), or boosting BHBs coalescence (Γ = 2-8 yr-1 Gpc-3). In a few simulations, the SMBH boosts BHBs coalescence, leading this process to a merger rate Γ = 1 yr-1 Gpc-3. We note that BHBs experiencing a merger in a galactic nucleus can be erroneously estimated {̃ } 30{{ per cent}} heavier than it really is because of the Doppler shift of the wave frequency as caused by the rapid motion around the SMBH. All our simulations are carried out using an N-body code tailored to treat close encounters and post-Newtonian dynamics, that includes also the galaxy field and dynamical friction in the particles equation of motion
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Effect of storage time on the accuracy of casts made from different irreversible hydrocolloids
No full textAIM: Several new irreversible hydrocolloid formulations have recently become available with claims of an improved dimensional stability by the manufacturers. The aim of this study was to evaluate the accuracy of casts made from alginate impression materials poured immediately and after specific storage periods.
METHODS AND MATERIALS: Five alginates were tested: CA 37 (Cavex); Jeltrate (Dentsply Caulk); Jeltrate Plus (Dentsply Latin America); Hydrogum 5 (Zhermack); and Alginoplast (Heraeus Kulzer). A master model was mounted on a special device and used to obtain the impressions. These impressions were stored at 23 degrees C and 100% relative humidity, then poured with gypsum immediately, and again after 24, 72 and 120 hours. The casts were measured and the data were analyzed by one way analysis of variance (ANOVA) and Tukey test at p<0.05.
RESULTS: The dimensional stability of the alginate impressions was both material and time dependent (p<0.05). After 24 hours of storage, only Alginoplast and Hydrogum 5 comply with the master model (p>0.05). After 72 and 120 hours, only Hydrogum 5 was dimensionally stable (p>0.05).
CONCLUSION: The dimensional stability of the alginate impressions is influenced by the selected material and the storage time.
CLINICAL SIGNIFICANCE: Alginate impressions should generally be poured immediately. However, some new types of alginate may have the pouring delayed
Influence of polymerization cycle on the flexural strength of four different PMMA-based heat-polymerized denture base RESIN
No full textPurpose: PMMA-based heat-polymerized acrylic resins used in the fabrication of denture bases may be cured in
different ways. As the polymerization cycle length affects fabrication costs and time, a fast cycle is more
advantageous. However, polymerization cycles may influence mechanical properties.
Objective: The purpose of this study was to evaluate the influence of the polymerization cycle on the flexural
strength of four types of PMMA-based heat-polymerized resins used as denture base materials.
Materials and methods: The ISO Standard 1567:1999 (Dentistry - Denture base material) was followed in
specimen preparation and flexural strength testing of four types of PMMA-based heat-curing resins: Characterized
Lucitone (Dentsply-DeTrey); Paladon 65 (Heraeus Kulzer); ProBase Hot (Ivoclar-Vivadent); Prothyl Hot (Zhermack).
Resin specimens were obtained following different curing cycles: Standard and Slow for Lucitone; Fast, Standard,
and Slow for Paladon 65; the five variants defined by the manufacturer for ProBase Hot; the Standard cycle for
Prothyl Hot. For each polymerization cycle six specimens (64 ± 1) mm in length, (10 ± 0,2) mm in width, and (3,3
± 0,2) mm in height, were prepared. For flexural strength measurements each specimen was loaded until failure
with a new testing device (Flexural Test Rig), developed following the indications of ISO 1567:1999. The flexural
strength was calculated in MPa and the values were compared with ANOVA and Tukey’s test for post-hoc
(p = 0.05).
Results: The polymerization cycle has no or minimal influence on the flexural strength of the tested resins. Lucitone
exhibited relatively low resistance to flexural loads as when compared with the other resins (Group 7: 78,467 ±
5,623 MPa; Group 8: 71,198 ± 3,775 MPa).
Conclusion: With regard to flexural strength, a slow curing cycle does not appear to be justified for the either
Lucitone or ProBase Hot, whereas slow polymerization may be advisable for Paladon 65 tested resins, whereas the
fast curing cycle V3 was the most favourable to achieve the optimal flexural strength for ProBase Hot
Valutazione della resistenza alla frattura di frammenti incisali riattaccati con diversi materiali e metodiche
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