Changes on degree of conversion of dual-cure luting light-cured with blue LED

The indirect adhesive procedures constitute recently a substantial portion of contemporary esthetic restorative treatments. The resin cements have been used to bond tooth substrate and restorative materials. Due to recently introduction of the self-bonding resin luting cement based on a new monomer, filler and initiation technology has become important to study the degree of conversion of these new materials. In the present work the polymerization reaction and the filler content of dual-cured dental resin cements were studied by means of infra-red spectroscopy (FT-IR) and thermogravimetry (TG). Twenty specimens were made in a metallic mold (8 mm diameter x 1 mm thick) from each of 2 cements, PanaviaA (R) F2.0 (Kuraray) and RelyX (TM) Unicem Applicap (3M/ESPE). Each specimen was cured with blue LED with power density of 500 mW/cm(2) for 30 s. Immediately after curing, 24 and 48 h, and 7 days DC was determined. For each time interval 5 specimens were pulverized, pressed with KBr and analyzed with FT-IR. The TG measurements were performed in Netzsch TG 209 under oxygen atmosphere and heating rate of 10A degrees C/min from 25 to 700A degrees C. A two-way ANOVA showed DC (%) mean values statistically significance differences between two cements (p < 0.05). The Tukey`s test showed no significant difference only for the 24 and 48 h after light irradiation for both resin cements (p > 0.05). The Relx-Y (TM) Unicem mean values were significantly higher than PanaviaA (R) F 2.0. The degree of conversion means values increasing with the storage time and the filler content showed similar for both resin cements.

Degree of Conversion and Temperature Increase of a Composite Resin Light Cured with an Argon Laser and Blue LED

Different light sources and power densities used on the photoactivation process may provide changes in the degree of conversion (DC%) and temperature ( T) of the composite resins. Thus, the purpose of this study was to evaluate the DC (%) and T (degrees C) of the microhybrid composite resin (Filtek (TM) Z-250, 3M/ESPE) photoactivated with one argon laser and one LED (light-emitting diode) with different power densities. For the KBr pellet technique, the composite resin was placed into a metallic mould (2-mm thickness, 4-mm diameter) and photoactivated as follows: a continuous argon laser (CW) and LED LCUs with power density values of 100, 400, 700, and 1000 mW/cm(2) for 20 s. The measurements for DC (%) were made in a FTIR spectrometer Bomen ( model MB 102, Quebec, Canada). Spectroscopy ( FTIR) spectra for both uncured and cured samples were analyzed using an accessory of the reflectance diffusion. The measurements were recorded in absorbance operating under the following conditions: 32 scans, 4 cm(-1) resolution, 300 to 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 1638 cm(-1)) against an internal standard before and after the curing of the specimen: aromatic C-C (peak at 1608 cm(-1)). For T (degrees C), the samples were created in a metallic mould (2-mm thickness, 4-mm diameter) and photoactivated for 20 s. The thermocouple was attached to the multimeter allowing temperature readings. The DC (%) and T (degrees C) were submitted to ANOVA and Tukey`s test (p < 0.05). The degree of conversion values varied from 35.0 to 50.0% ( 100 to 1000 mW/cm(2)) for an argon laser and from 41.0 to 49% (100 to 1000 mW/cm(2)) for an LED. The temperature change values varied from 1.1 to 13.1 degrees C (100 to 1000 mW/cm(2)) for an argon laser and from 1.9 to 15.0 degrees C (100 to 1000 mW/cm(2)) for an LED. The power densities showed a significant effect on the degree of conversion and changes the temperature for both light-curing units.

First principles calculations on the origin of violet-blue and green light photoluminescence emission in SrZrO3 and SrTiO3 perovskites

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

Changes on degree of conversion of dual-cure luting light-cured with blue LED

The indirect adhesive procedures constitute recently a substantial portion of contemporary esthetic restorative treatments. The resin cements have been used to bond tooth substrate and restorative materials. Due to recently introduction of the self-bonding resin luting cement based on a new monomer, filler and initiation technology has become important to study the degree of conversion of these new materials. In the present work the polymerization reaction and the filler content of dual-cured dental resin cements were studied by means of infra-red spectroscopy (FT-IR) and thermogravimetry (TG). Twenty specimens were made in a metallic mold (8 mm diameter × 1 mm thick) from each of 2 cements, Panavia® F2.0 (Kuraray) and RelyX™ Unicem Applicap (3M/ESPE). Each specimen was cured with blue LED with power density of 500 mW/cm 2 for 30 s. Immediately after curing, 24 and 48 h, and 7 days DC was determined. For each time interval 5 specimens were pulverized, pressed with KBr and analyzed with FT-IR. The TG measurements were performed in Netzsch TG 209 under oxygen atmosphere and heating rate of 10°C/min from 25 to 700°C. A two-way ANOVA showed DC (%) mean values statistically significance differences between two cements (p < 0.05). The Tukey's test showed no significant difference only for the 24 and 48 h after light irradiation for both resin cements (p > 0.05). The Relx-Y™ Unicem mean values were significantly higher than Panavia® F 2.0. The degree of conversion means values increasing with the storage time and the filler content showed similar for both resin cements. © 2009 Pleiades Publishing, Ltd.

Degree of conversion and hardness of two different systems of the vitrebond™ glass ionomer cement light cured with blue LED

This study investigated the physicochemical properties of the new formulation of the glass ionomer cements through hardness test and degree of conversion by infrared spectroscopy (FTIR). Forty specimens (n = 40) were made in a metallic mold (4 mm diameter × 2 mm thickness) with two resin-modified glass ionomer cements, Vitrebond™ and Vitrebond™ Plus (3M/ ESPE). Each specimen was light cured with blue LED with power density of 500 mW/cm2during 30 s. Immediately after light curing, 24h, 48h and 7 days the hardness and degree of conversion was determined. The Vickers hardness was performed by the MMT-3 microhardness tester using load of 50 gm force for 30 seconds. For degree of conversion, the specimens were pulverized, pressed with KBr and analyzed with FT-IR (Nexus 470). The statistical analysis of the data by ANOVA showed that the Vitrebond™ and Vitrebond™ Plus were no difference significant between the same storage times (p > 0.05). For degree of conversion, the Vitrebond™ and Vitrebond™ Plus were statistically different in all storage times after light curing. The Vitrebond™ showed higher values than Vitrebond™ Plus (p < 0.05). The performance of Vitrebond™ had greater results for degree of conversion than Vitrebond™ Plus. The correlation between hardness and degree of conversion was no evidence in this study.

Thermal and structural properties of commercial dental resins light-cured with blue emitting diodes (LEDs)

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

Light-Emitting-Diodes based on ordered InGaN nanocolumns emitting in the blue, green and yellow spectral range

The growth of ordered arrays of InGaN/GaN nanocolumnar light emitting diodes by molecular beam epitaxy, emitting in the blue (441 nm), green (502 nm), and yellow (568 nm) spectral range is reported. The device active region, consisting of a nanocolumnar InGaN section of nominally constant composition and 250 to 500 nm length, is free of extended defects, which is in strong contrast to InGaN layers (planar) of similar composition and thickness. The devices are driven under pulsed operation up to 1300 A/cm2 without traces of efficiency droop. Electroluminescence spectra show a very small blue shift with increasing current, (almost negligible in the yellow device) and line widths slightly broader than those of state-of-the-art InGaN quantum wells.

The Light blue: a Cambridge University magazine.

Mode of access: Internet.

Temperature-dependent internal quantum efficiency of blue high-brightness light-emitting diodes

Internal quantum efficiency (IQE) of a blue high-brightness InGaN/GaN light-emitting diode (LED) was evaluated from the external quantum efficiency measured as a function of current at various temperatures ranged between 13 and 440 K. Processing the data with a novel evaluation procedure based on the ABC-model, we have determined the temperature-dependent IQE of the LED structure and light extraction efficiency of the LED chip. Separate evaluation of these parameters is helpful for further optimization of the heterostructure and chip designs. The data obtained enable making a guess on the temperature dependence of the radiative and Auger recombination coefficients, which may be important for identification of dominant mechanisms responsible for the efficiency droop in III-nitride LEDs. Thermal degradation of the LED performance in terms of the emission efficiency is also considered.

The Game is On! The Adventure of the Girl with the Light Blue Hair

The Game is On! is a series of short animated films that put copyright and creativity under the magnifying glass of Sherlock Holmes, providing a unique, research-led and open access resource for school-aged learners and other creative users of copyright. Drawing inspiration from well-known copyright and public domain work, as well as recent copyright litigation, these films provide a springboard for exploring key principles and ideas underpinning copyright law, creativity, and the limits of lawful appropriation and reuse.

Each episode comes accompanied by a number of related Case Files: supplementary educational materials aimed at suggesting points of discussion about copyright for teachers and students.

Superior color rendering with a phosphor-converted blue-cyan monolithic light-emitting diode

The future generation of modern illumination should not only be cheap and highly efficient, but also demonstrate high quality of light, light which allows better color differentiation and fidelity. Here we are presenting a novel approach to create a white solid-state light source providing ultimate color rendition necessary for a number of applications. The proposed semi-hybrid device combines a monolithic blue-cyan light emitting diode (MBC LED) with a green-red phosphor mixture. It has shown a superior color rendering index (CRI), 98.6, at correlated color temperature of around 3400 K. The MBC LED epi-structure did not suffer from the efficiency reduction typical for monolithic multi-color emitters and was implemented in the two most popular chip designs: “epi-up” and “flip-chip”. Redistribution of the blue and cyan band amplitudes in the white-light emission spectrum, using the operating current, is found to be an effective tool for fine tuning the color characteristics. (Figure presented.).

Integrating efficient filtration and visible-light photocatalysis by loading Ag-doped zeolite Y particles on aluminia nanofiber membrane

Filtration membrane technology has already been employed to remove various organic effluents produced from the textile, paper, plastic, leather, food and mineral processing industries. To improve membrane efficiency and alleviate membrane fouling, an integrated approach is adopted that combines membrane filtration and photocatalysis technology. In this study, alumina nanofiber (AF) membranes with pore size of about 10 nm (determined by the liquid-liquid displacement method) have been synthesized through an in situ hydrothermal reaction, which permitted a large flux and achieved high selectivity. Silver nanoparticles (Ag NPs) are subsequently doped on the nanofibers of the membranes. Silver nanoparticles can strongly absorb visible light due to the surface plasmon resonance (SPR) effect, and thus induce photocatalytic degradation of organic dyes, including anionic, cationic and neutral dyes, under visible light irradiation. In this integrated system, the dyes are retained on the membrane surface, their concentration in the vicinity of the Ag NPs are high and thus can be efficiently decomposed. Meanwhile, the usual flux deterioration caused by the accumulation of the filtered dyes in the passage pores can be avoided. For example, when an aqueous solution containing methylene blue is processed using an integrated membrane, a large flux of 200 L m-2 h-1 and a stable permeating selectivity of 85% were achieved. The combined photocatalysis and filtration function leads to superior performance of the integrated membranes, which have a potential to be used for the removal of organic pollutants in drinking water.

Dynamics of rod and cone photoreceptor interactions under mesopic light levels

Visual adaptation regulates contrast sensitivity during dynamically changing light conditions (Crawford, 1947; Hecht, Haig & Chase, 1937). These adaptation dynamics are unknown under dim (mesopic) light levels when the rod (R) and long (L), medium (M) and short (S) wavelength cone photoreceptor classes contribute to vision via interactions in shared non-opponent Magnocellular (MC), chromatically opponent Parvocellular (PC) and Koniocellular (KC) visual pathways (Dacey, 2000). This study investigated the time-course of adaptation and post-receptoral pathways mediating receptor specific rod and cone interactions under mesopic illumination. A four-primary photostimulator (Pokorny, Smithson & Quinlan, 2004) was used to independently control the activity of the four photoreceptor classes and their post-receptoral visual athways in human observers. In the first experiment, the contrast sensitivity and time-course of visual adaptation under mesopic illumination were measured for receptoral (L, S, R) and post-receptoral (LMS, LMSR, L-M) stimuli. An incremental (Rapid-ON) sawtooth conditioning pulse biased detection to ON-cells within the visual pathways and sensitivity was assayed relative to pulse onset using a briefly presented incremental probe that did not alter adaptation. Cone.Cone interactions with luminance stimuli (L cone, LMS, LMSR) reduced sensitivity by 15% and the time course of recovery was 25± 5ms-1 (μ ± SEM). PC mediated (+L-M) chromatic stimuli sensitivity loss was less (8%) than for luminance and recovery was slower (μ = 2.95 ± 0.05 ms-1), with KC mediated (S cone) chromatic stimuli showing a high sensitivity loss (38%) and the slowest recovery time (1.6 ± 0.2 ms-1). Rod-Rod interactions increased sensitivity by 20% and the time course of recovery was 0.7 ± 0.2 ms-1 (μ ± SD). Compared to these interaction types, Rod-Cone interactions reduced sensitivity to a lesser degree (5%) and showed the fastest recovery (μ = 43 ± 7 ms-1). In the second experiment, rod contribution to the magnocellular, parvocellular and koniocellular post-receptoral pathways under mesopic illumination was determined as a function of incremental stimulus duration and waveform (rectangular; sawtooth) using a rod colour match procedure (Cao, Pokorny & Smith, 2005; Cao, Pokorny, Smith & Zele, 2008a). For a 30% rod increment, a cone match required a decrease in [L/(L+M)] and an increase in [L+M] and [S/(L+M)], giving a greenish-blue and brighter appearance for probe durations of 75 ms or longer. Probe durations less than 75 ms showed an increase in [L+M] and no change in chromaticity [L/(L+M) or S/(L+M)], uggesting mediation by the MC pathway only for short duration rod stimuli. s We advance previous studies by determining the time-course and nature of photoreceptor specific retinal interactions in the three post-receptoral pathways under mesopic illumination. In the first experiment, the time-course of adaptation for ON cell processing was determined, revealing opponent cell facilitation in chromatic PC and KC pathways. The Rod-Rod and Rod-Cone data identify previously unknown interaction types that act to maintain contrast sensitivity during dynamically changing light conditions and improve the speed of light adaptation under mesopic light levels. The second experiment determined the degree of rod contribution to the inferred post-eceptoral pathways as a function of the temporal properties of the rod signal. r The understanding of the mechanisms underlying interactions between photoreceptors under mesopic illumination has implications for the study of retinal disease. Visual function has been shown to be reduced in persons with age-related maculopathy (ARM) risk genotypes prior to clinical signs of the disease (Feigl, Cao, Morris & Zele, 2011) and disturbances in rod-mediated adaptation have been shown in early phases of ARM (Dimitrov, Guymer, Zele, Anderson & Vingrys, 2008; Feigl, Brown, Lovie-Kitchin & Swann, 2005). Also, the understanding of retinal networks controlling vision enables the development of international lighting standards to optimise visual performance nder dim light levels (e.g. work-place environments, transportation).

Synthetic reevesite-like material as a visible light photocatalyst for the decontamination of water

A synthetic reevesite-like material has been shown to decolorize selected dyes and degrade phenolic contaminants photocatalytically in water when irradiated with visible light. This material can photoactively decolorize dyes such as bromophenol blue, bromocresol green, bromothymol blue, thymol blue and methyl orange in less than 15 min under visible light radiation in the absence of additional oxidizing agents. Conversely, phenolic compounds suc has phenol, p-chlorophenol and p-nitrophenol are photocat- alytically degraded in approximately 3hwith additional H2O2 when irradiated with visible light. These reactions offer potentially energy effective pathways for the removal of recalcitrant organic waste contaminants.

4-hexylbithieno[3,2-b:2′3′-e]pyridine: An efficient electron-accepting unit in fluorene and indenofluorene copolymers for light-emitting devices

4-Hexylbithienopyridine has been prepared as a novel electron-accepting monomer for conjugated polymers. To test its electronic properties, alternating copolymers with fluorene and indenofluorene polymers have been prepared. The copolymers displayed reduction potentials about 0.5 V lower than for the corresponding fluorene and indenofluorene homopolymers, indicating much improved electron-accepting properties. Analysis of the microscopic morphology of thin films of the copolymers by AFM shows that they lack the extensive supramolecular order seen with the homopolymers, which is attributed to the bithienopyridine units disrupting the π-stacking. LEDs using these polymers as the emitting layer produce blue-green emission with low turn-on voltages with aluminum electrodes confirming their improved electron affinity. The indenofluorene copolymer displayed an irreversible red shift in emission at high voltages, which is attributed to oxidation of the indenofluorene units. This red shift occurred at higher potentials than for indenofluorene homopolymers in LEDs, suggesting that the heterocyclic moieties offer some protection against electrically promoted oxidation.