Effect of power densities and irradiation times on the degree of conversion and temperature increase of a microhybrid dental composite resin

The different parameters used for the photoactivation process provide changes in the degree of conversion (DC%) and temperature rise (TR) of the composite resins. Thus, the purpose of this study was to evaluate the DC (%) and TR of the microhybrid composite resin photoactivated by a new generation LED. For the KBr pellet technique, the composite resin was placed into a metallic mould (1-mm thickness and 4-mm diameter) and photoactivated as follows: continuous LED LCU with different power density values (50-1000 mW/cm(2)). The measurements for the DC (%) were made in a FTIR Spectrometer Bomen (model MB-102, Quebec-Canada). The spectroscopy (FTIR) spectra for both uncured and cured samples were analyzed using an accessory for the diffuse reflectance. The measurements were recorded in the absorbance operating under the following conditions: 32 scans, 4-cm(-1) resolution, and a 300 to 4000-cm(-1) wavelength. The percentage of unreacted carbon-carbon double bonds (% C=C) was determined from the ratio of the absorbance intensities of aliphatic C=C (peak at 1638 cm(-1)) against an internal standard before and after the curing of the specimen: aromatic C-C (peak at 1608 cm-1). For the TR, the samples were made in a metallic mould (2-mm thickness and 4-mm diameter) and photoactivated during 5, 10, and 20 s. The thermocouple was attached to the multimeter to allow the temperature readings. The DC (%) and TR were calculated by the standard technique and submitted to ANOVA and Tukey`s test (p < 0.05). The degree of conversion values varied from 35.0 (+/- 1.3) to 45.0 (+/- 2.4) for 5 s, 45.0 (+/- 1.3) to 55.0 (+/- 2.4) for 10 s, and 47.0 (+/- 1.3) to 52.0 (+/- 2.4) for 20 s. For the TR, the values ranged from 0.3 (+/- 0.01) to 5.4 (+/- 0.11)degrees C for 5 s, from 0.5 (+/- 0.02) to 9.3 (+/- 0.28)degrees C for 10 s, and from 1.0 (+/- 0.06) to 15.0 (+/- 0.95)degrees C for 20 s. The power densities and irradiation times showed a significant effect on the degree of conversion and temperature rise.

Influence of light guide tip used in the photo-activation on degree of conversion and hardness of one nanofilled dental composite

The aim of this study was to evaluate the degree of conversion and hardness of a dental composite resin Filtek (TM) Z-350 (3M ESPE, Dental Products St. Paul, MN) photo-activated for 20 s of irradiation time with two different light guide tips, metal and polymer, coupled on blue LED Ultraled LCU (Dabi Atlante, SP, Brazil). With the metal light tip, power density was of 352 and with the polymer was of 456 mW/cm(2), respectively. Five samples (4 mm in diameter and 2mm in thickness-ISO 4049), were made for each Group evaluated. The measurements for DC (%) were made in a Nexus-470 FT-IR, Thermo Nicolet, E.U.A. Spectroscopy (FTIR). Spectra for both uncured and cured samples were analyzed using an accessory of reflectance diffuse. The measurements were recorded in absorbance operating under the following conditions: 32 scans, 4 cm(-1) resolution, 300-4000 cm(-1) wavelength. The percentage of unreacted carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1637 cm(-1)) against internal standard before and after curing of the sample: aromatic C-C (peak at 1610 cm(-1)). The Vickers hardness measurements (top and bottom surfaces) were performed in a universal testing machine (Buehler MMT-3 digital microhardness tester Lake Bluff, Illinois USA). A 50 gf load was used and the indenter with a dwell time of 30 s. The data were submitted to the test t Student at significance level of 5%. The mean values of degree of conversion for the polymer and metal light guide tip no were statistically different (p = 0.8389). The hardness mean values were no statistically significant different among the light guide tips (p = 0.6244), however, there was difference between top and bottom surfaces (p < 0.001). The results show that so much the polymer light tip as the metal light tip can be used for the photo-activation, probably for the low quality of the light guide tip metal.

Influence of light guide tip used in the photo-activation on degree of conversion and hardness of one nanofilled dental composite

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Degree of conversion of nanofilled and microhybrid composite resins photo-activated by different generations of LEDs

Objective: This study aimed at evaluating the degree of conversion (DC) of four composite resins, being one nanofilled and 3 microhybrid resins, photo-activated with second- and third-generation light-emitting diodes (LEDs). Material and methods: Filtek (TM) Z350 nanofilled composite resins and Amelogen (R) Plus, Vit-l-escence (TM) and Opallis microhybrid resins were photo-activated with two second-generation LEDs (Radii-cal and Elipar Free Light (TM) 2) and one third-generation LED (Ultra-Lume LED 5) by continuous light mode, and a quartz halogen-tungsten bulb (QHT, control). After 24 h of storage, the samples were pulverized into fine powder and 5 mg of each material were mixed with 100 mg of potassium bromide (KBr). After homogenization, they were pressed, which resulted in a pellet that was evaluated using an infrared spectromer (Nexus 470, Thermo Nicolet) equipped with TGS detector using diffuse reflectance (32 scans, resolution of 4 cm(-1)) coupled to a computer. The percentage of unreacted carbon-carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1637 cm-1) against internal standard before and after curing of the specimen: aromatic C-C (peak at 1610 cm-1). Results: The ANOVA showed a significant effect on the interaction between the light-curing units (LCUs) and the composite resins (p<0.001). The Tukey's test showed that the nanofilled resin (Filtek (TM) Z350) and Opallis when photo-activated by the halogen lamp (QTH) had the lowest DC compared with the other microhybrid composite resins. The DC of the nanofilled resin (Filtek (TM) Z350) was also lower using LEDs. The highest degrees of conversion were obtained using the third-generation LED and one of second-generation LEDs (Elipar Free Light (TM) 2). Conclusions: The nanofilled resin showed the lowest DC, and the Vit-l-escence (TM) microhybrid composite resin showed the highest DC. Among the LCUs, it was not possible to establish an order, even though the second-generation LED Radii-cal provided the lowest DC.

Estudio de viabilidad tecnico-economica para la conversion de hornos electricos en hornos a gas natural

Technical and economic feasibility of using natural gas as a non-polluting energy source was studied. Conversion of electric ovens to gas-fired ovens for the preparation of aluminum plates for laminations was used as an example of this application. Four cases were evaluated for the use of heat derived from residual gases following combustion of the natural gas. Additionally, two possibilities are included for the use of systems of co-generation; one using an internal combustion engine, and second using a gas turbine. Results suggested that it was technically and economically feasible to convert the electric ovens considered to natural gas-operated ovens.

Evaluation of degree of conversion and hardness of dental composites photoactivated with different light guide tips

Objective: The aim of this study was to evaluate the degree of conversion and hardness of different composite resins, photo-activated for 40 s with two different light guide tips, fiber optic and polymer. Methods: Five specimens were made for each group evaluated. The percentage of unreacted carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1637 cm-1) against internal standard before and after curing of the specimen: aromatic C-C (peak at 1610 cm-1. The Vickers hardness measurements were performed in a universal testing machine. A 50 gf load was used and the indenter with a dwell time of 30 seconds. The degree of conversion and hardness mean values were analyzed separately by ANOVA and Tukey's test, with a significance level set at 5%. Results: The mean values of degree of conversion for the polymer and fiber optic light guide tip were statistically different (P<.001). The hardness mean values were statistically different among the light guide tips (P<.001), but also there was difference between top and bottom surfaces (P<.001). Conclusions: The results showed that the resins photo-activated with the fiber optic light guide tip promoted higher values for degree of conversion and hardness.

Degree of conversion of different composite resins photo-activated with light-emitting diode and argon ion laser

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Degree of conversion of nanofilled and microhybrid composite resins photo-activated by different generations of LEDs

Objective: This study aimed at evaluating the degree of conversion (DC) of four composite resins, being one nanofilled and 3 microhybrid resins, photo-activated with second- and third-generation light-emitting diodes (LEDs). Material and methods: Filtek (TM) Z350 nanofilled composite resins and Amelogen (R) Plus, Vit-l-escence (TM) and Opallis microhybrid resins were photo-activated with two second-generation LEDs (Radii-cal and Elipar Free Light (TM) 2) and one third-generation LED (Ultra-Lume LED 5) by continuous light mode, and a quartz halogen-tungsten bulb (QHT, control). After 24 h of storage, the samples were pulverized into fine powder and 5 mg of each material were mixed with 100 mg of potassium bromide (KBr). After homogenization, they were pressed, which resulted in a pellet that was evaluated using an infrared spectromer (Nexus 470, Thermo Nicolet) equipped with TGS detector using diffuse reflectance (32 scans, resolution of 4 cm(-1)) coupled to a computer. The percentage of unreacted carbon-carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1637 cm-1) against internal standard before and after curing of the specimen: aromatic C-C (peak at 1610 cm-1). Results: The ANOVA showed a significant effect on the interaction between the light-curing units (LCUs) and the composite resins (p<0.001). The Tukey's test showed that the nanofilled resin (Filtek (TM) Z350) and Opallis when photo-activated by the halogen lamp (QTH) had the lowest DC compared with the other microhybrid composite resins. The DC of the nanofilled resin (Filtek (TM) Z350) was also lower using LEDs. The highest degrees of conversion were obtained using the third-generation LED and one of second-generation LEDs (Elipar Free Light (TM) 2). Conclusions: The nanofilled resin showed the lowest DC, and the Vit-l-escence (TM) microhybrid composite resin showed the highest DC. Among the LCUs, it was not possible to establish an order, even though the second-generation LED Radii-cal provided the lowest DC.

Evaluation of degree of conversion and hardness of dental composites photo-activated with different light guide tips

Objective: The aim of this study was to evaluate the degree of conversion and hardness of different composite resins, photo-activated for 40 s with two different light guide tips, fiber optic and polymer. Methods: Five specimens were made for each group evaluated. The percentage of unreacted carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1637 cm-1) against internal standard before and after curing of the specimen: aromatic C-C (peak at 1610 cm-1). The Vickers hardness measurements were performed in a universal testing machine. A 50 gf load was used and the indenter with a dwell time of 30 seconds. The degree of conversion and hardness mean values were analyzed separately by ANOVA and Tukey's test, with a significance level set at 5%. Results: The mean values of degree of conversion for the polymer and fiber optic light guide tip were statistically different (P<.001). The hardness mean values were statistically different among the light guide tips (P<.001), but also there was difference between top and bottom surfaces (P<.001). Conclusions: The results showed that the resins photo-activated with the fiber optic light guide tip promoted higher values for degree of conversion and hardness.

Excited-state dynamics in donor-acceptor systems for energy conversion

In dieser Arbeit werden die Dynamiken angeregter Zustände in Donor-Akzeptorsystemen für Energieumwandlungsprozesse mit ultraschneller zeitaufgelöster optischer Spektroskopie behandelt. Der Hauptteil dieser Arbeit legt den Fokus auf die Erforschung der Photophysik organischer Solarzellen, deren aktive Schichten aus diketopyrrolopyrrole (DPP) basierten Polymeren mit kleiner Bandlücke als Elektronendonatoren und Fullerenen als Elektronenakzeptoren bestehen. rnEin zweiter Teil widmet sich der Erforschung von künstlichen primären Photosynthesereaktionszentren, basierend auf Porphyrinen, Quinonen und Ferrocenen, die jeweils als Lichtsammeleinheit, Elektronenakzeptor beziehungsweise als Elektronendonatoren eingesetzt werden, um langlebige ladungsgetrennte Zustände zu erzeugen.rnrnZeitaufgelöste Photolumineszenzspektroskopie und transiente Absorptionsspektroskopie haben gezeigt, dass Singulettexzitonenlebenszeiten in den Polymeren PTDPP-TT und PFDPP-TT Polymeren kurz sind (< 20 ps) und dass in Mischungen der Polymere mit PC71BM geminale Rekombination von gebundenen Ladungstransferzuständen ein Hauptverlustkanal ist. Zudem wurde in beiden Systemen schnelle nichtgeminale Rekombination freier Ladungen zu Triplettzuständen auf dem Polymer beobachtet. Für das Donor-Akzeptor System PDPP5T:PC71BM wurde nachgewiesen, dass die Zugabe eines Lösungsmittels mit hohem Siedepunkt, und zwar ortho-Dichlorbenzol, die Morphologie der aktiven Schicht stark beeinflusst und die Solarzelleneffizienz verbessert. Der Grund hierfür ist, dass die Donator- und Akzeptormaterialien besser durchmischt sind und sich Perkolationswege zu den Elektroden ausgebildet haben, was zu einer verbesserten Ladungsträgergeneration und Extraktion führt. Schnelle Bildung des Triplettzustands wurde in beiden PDPP5T:PC71BM Systemen beobachtet, da der Triplettzustand des Polymers über Laungstransferzustände mit Triplettcharakter populiert werden kann. "Multivariate curve resolution" (MCR) Analyse hat eine starke Intensitätsabhängigkeit gezeigt, was auf nichtgeminale Ladungsträgerrekombination in den Triplettzustand hinweist.rnrnIn den künstlichen primären Photosynthesereaktionszentren hat transiente Absorptionsspektroskopie bestätigt, dass photoinduzierter Ladungstransfer in Quinon-Porphyrin (Q-P) und Porphyrin-Ferrocen (P-Fc) Diaden sowie in Quinon-Porphyrin-Ferrocen (Q-P-Fc) Triaden effizient ist. Es wurde jedoch auch gezeigt, dass in den P-Fc unf Q-P-Fc Systemen die ladungsgetrennten Zustände in den Triplettzustand der jeweiligen Porphyrine rekombinieren. Der ladungsgetrennte Zustand konnte in der Q-P Diade durch Zugabe einer Lewissäure signifikant stabilisiert werden.

Ultrafast Relaxation Dynamics of Osmium-Polypyridine Complexes in Solution

We present steady-state absorption and emission spectroscopy and femtosecond broadband photoluminescence up-conversion spectroscopy studies of the electronic relaxation of Os(dmbp)3 (Os1) and Os(bpy)2(dpp) (Os2) in ethanol, where dmbp is 4,4′-dimethyl-2,2′-biypridine, bpy is 2,2′-biypridine, and dpp is 2,3-dipyridyl pyrazine. In both cases, the steady-state phosphorescence is due to the lowest 3MLCT state, whose quantum yield we estimate to be ≤5.0 × 10–3. For Os1, the steady-state phosphorescence lifetime is 25 ns. In both complexes, the photoluminescence excitation spectra map the absorption spectrum, pointing to an excitation wavelength-independent quantum yield. The ultrafast studies revealed a short-lived (≤100 fs) fluorescence, which stems from the lowest singlet metal-to-ligand-charge-transfer (1MLCT) state and decays by intersystem crossing to the manifold of 3MLCT states. In addition, Os1 exhibits a 50 ps lived emission from an intermediate triplet state at an energy 2000 cm–1 above that of the long-lived (25 ns) phosphorescence. In Os2, the 1MLCT–3MLCT intersystem crossing is faster than that in Os1, and no emission from triplet states is observed other than the lowest one. These observations are attributed to a higher density of states or a smaller energy spacing between them compared with Os1. They highlight the importance of the energetics on the rate of intersystem crossing.

Two-way traveltimes of internal layers and ice thickness between Dome C - Vostok - Dome A

Chinese scientists will start to drill a deep ice core at Kunlun station near Dome A in the near future. Recent work has predicted that Dome A is a location where ice older than 1 million years can be found. We model flow, temperature and the age of the ice by applying a three-dimensional, thermomechanically coupled full-Stokes model to a 70 × 70 km**2 domain around Kunlun station, using isotropic non-linear rheology and different prescribed anisotropic ice fabrics that vary the evolution from isotropic to single maximum at 1/3 or 2/3 depths. The variation in fabric is about as important as the uncertainties in geothermal heat flux in determining the vertical advection which in consequence controls both the basal temperature and the age profile. We find strongly variable basal ages across the domain since the ice varies greatly in thickness, and any basal melting effectively removes very old ice in the deepest parts of the subglacial valleys. Comparison with dated radar isochrones in the upper one third of the ice sheet cannot sufficiently constrain the age of the deeper ice, with uncertainties as large as 500 000 years in the basal age. We also assess basal age and thermal state sensitivities to geothermal heat flux and surface conditions. Despite expectations of modest changes in surface height over a glacial cycle at Dome A, even small variations in the evolution of surface conditions cause large variation in basal conditions, which is consistent with basal accretion features seen in radar surveys.

Ultrafast diffraction and structural dynamics: The nature of complex molecules far from equilibrium

Studies of molecular structures at or near their equilibrium configurations have long provided information on their geometry in terms of bond distances and angles. Far-from-equilibrium structures are relatively unknown—especially for complex systems—and generally, neither their dynamics nor their average geometries can be extrapolated from equilibrium values. For such nonequilibrium structures, vibrational amplitudes and bond distances play a central role in phenomena such as energy redistribution and chemical reactivity. Ultrafast electron diffraction, which was developed to study transient molecular structures, provides a direct method for probing the nature of complex molecules far from equilibrium. Here we present our ultrafast electron diffraction observations of transient structures for two cyclic hydrocarbons. At high internal energies of ≈4 eV, these molecules display markedly different behavior. For 1,3,5-cycloheptatriene, excitation results in the formation of hot ground-state structures with bond distances similar to those of the initial structure, but with nearly three times the average vibrational amplitude. Energy is redistributed within 5 ps, but with a negative temperature characterizing the nonequilibrium population. In contrast, the ring-opening reaction of 1,3-cyclohexadiene is shown to result in hot structures with a C—C bond distance of over 1.7 Å, which is 0.2 Å away from any expected equilibrium value. Even up to 400 ps, energy remains trapped in large-amplitude motions comprised of torsion and asymmetric stretching. These studies promise a new direction for studying structural dynamics in nonequilibrium complex systems.

Documentation of reticulate evolution in peonies (Paeonia) using internal transcribed spacer sequences of nuclear ribosomal DNA: implications for biogeography and concerted evolution.

The internal transcribed spacers (ITS) of nuclear ribosomal DNA of 33 species of genus Paeonia (Paeoniaceae) were sequenced. In section Paeonia, different patterns of nucleotide additivity were detected in 14 diploid and tetraploid species at sites that are variable in the other 12 species of the section, suggesting that reticulate evolution has occurred. Phylogenetic relationships of species that do not show additivity, and thus ostensibly were not derived through hybridization, were reconstructed by parsimony analysis. The taxa presumably derived through reticulate evolution were then added to the phylogenetic tree according to additivity from putative parents. The study provides an example of successfully using ITS sequences to reconstruct reticulate evolution in plants and further demonstrates that the sequence data could be highly informative and accurate for detecting hybridization. Maintenance of parental sequences in the species of hybrid origin is likely due to slowing of concerted evolution caused by the long generation time of peonies. The partial and uneven homogenization of parental sequences displayed in nine species of putative hybrid origin may have resulted from gradients of gene conversion. The documented hybridizations may have occurred since the Pleistocene glaciations. The species of hybrid origin and their putative parents are now distantly allopatric. Reconstruction of reticulate evolution with sequence data, therefore, provides gene records for distributional histories of some of the parental species.

On the status of conversion in present-day American English: controversial issues and corpus-based study

This paper examines both theoretical and practical issues related to conversion. A quite detailed characterization of the 5329 instances identified in a 300.000-word corpus of American English written in the late 90s is provided. The examples are grouped according to the type of conversion involved. Frequency and the internal structure of words are also considered and compared with the results obtained by earlier scholars. In spite of the limitations that a corpus study imposes, the conclusions obtained seem to suggest that any item, independent of its morphological structure, may undergo conversion and this may happen in any register. Moreover, conversion seems to be an important source of new items in American English nowadays.