Enhancing reactive species generation upon photo-activation of CdTe quantum dots for the chemiluminometric determination of unreacted reagent in UV/S2O8(2-) drug degradation process.

A new chemiluminescence (CL) flow method for persulfate determination was developed based on luminol oxidation by in-line generated radicals. Reactive oxygen species (ROS) generated by CdTe quantum dots (QDs) under a low energetic radiation (visible light emitted by LEDs) promoted the decomposition of persulfate ion (S2O8(2-)) into sulfate radical (SO4(∙-)), leading to subsequent radical chain reactions that yield the emission of light. Due to the inherent radical short lifetimes and the transient behavior of CL phenomena an automated multi-pumping flow system (MPFS) was proposed to improve sample manipulation and reaction zone implementation ensuring reproducible analysis time and high sampling rate. The developed approach allowed up to 60 determinations per hour and determine S2O8(2-) concentrations between 0.1 and 1 mmol with good linearity (R=0.9999). The method has shown good repeatability with relative standard deviations below 2.5% (n=3) for different persulfate concentrations (0.1 and 0.625 mmol L(-1)). Limits of detection (3σ) and quantification (10σ) were 2.7 and 9.1 µmol L(-1), respectively. The MPFS system was applied to persulfate determination in bench scale UV/S2O8(2-) drug degradation processes of model samples showing good versatility and providing real time information on the persulfate consumption in photo-chemical degradation methodologies.

Quantification of the amount of blue light passing through monolithic zirconia with respect to thickness and polymerization conditions.

STATEMENT OF PROBLEM: Dual-polymerized luting composite resin cements would benefit from enhanced irradiance transmitted through a ceramic restoration. A quantification of the amount of transmitted light through translucent zirconia is lacking. PURPOSE: The purpose of this study was to evaluate the amount of light (360 to 540 nm) passing through translucent and conventional zirconia and a glass ceramic with respect to material thickness and different polymerizing modes. MATERIAL AND METHODS: Six translucent and a conventional zirconia (negative control) and a glass ceramic (positive control) were considered. Ten specimens of each material and thickness (.5, 1, 1.5, 2, 2.5, 3 mm) were fabricated (n=480). Zirconia materials were sintered according to manufacturers' instructions. The irradiance passing the different ceramics and thicknesses was measured with a violet-blue LED polymerizing unit in 3 polymerizing modes (plasma, high, and standard power mode) with a USB4000 Spectrometer. The polymerizing unit was placed directly on the specimen's surface. Data were analyzed with one and multivariate analysis and the Pearson correlation analysis (α=.05). RESULTS: In all materials, the translucency and its rate decreased exponentially according to the specimen thickness. The highest influence on the measured irradiance passing through translucent zirconia was exerted by ceramic thickness (P<.05, partial eta squared [ηP²]=.998), closely followed by polymerizing mode (ηP²=.973), while the effect of the material (P=.03, ηP²=.06) and mean grain size (P=.029, ηP²=.027) was significant but low. CONCLUSIONS: Zirconia was less translucent than the glass ceramic, but the translucency decreased more slowly with material thickness, thus approaching the translucency of glass ceramics at a specimen thicknesses of 2.5 to 3 mm.

Effects of γ-ray irradiation on optical absorption and laser damage performance of KDP crystals containing arsenic impurities.

The effects of γ-irradiation on potassium dihydrogen phosphate crystals containing arsenic impurities are investigated with different optical diagnostics, including UV-VIS absorption spectroscopy, photo-thermal common-path interferometer and photoluminescence spectroscopy. The optical absorption spectra indicate that a new broad absorption band near 260 nm appears after γ-irradiation. It is found that the intensity of absorption band increases with the increasing irradiation dose and arsenic impurity concentration. The simulation of radiation defects show that this absorption is assigned to the formation of AsO44⁻ centers due to arsenic ions substituting for phosphorus ions. Laser-induced damage threshold test is conducted by using 355 nm nanosecond laser pulses. The correlations between arsenic impurity concentration and laser induced damage threshold are presented. The results indicate that the damage performance of the material decreases with the increasing arsenic impurity concentration. Possible mechanisms of the irradiation-induced defects formation under γ-irradiation of KDP crystals are discussed.

Sonochemistry: a good, fast and clean method to promote the synthesis of 5-arylidene-2,4-thiazolidinediones.

The efficient synthesis of sixteen 5-arylidene-2,4-thiazolidinediones by aldol condensation reaction of 2,4-thiazolidinedione, mono- and di-substituted arenealdehydes and KOH using ultrasound irradiation is reported. The desired compounds were obtained in a few min (10-30 min) with moderate to good yields (25-81%).

Quantification of the amount of light passing through zirconia: the effect of material shade, thickness, and curing conditions.

OBJECTIVE: This study aimed to evaluate the amount of light (360-540 nm) passing through shaded zirconia with respect to material thickness, exposure distance, and different curing modes. METHODS: The specimens were divided into groups according to thickness as follows: 0.5, 1, 1.5, 2, 2.5, and 3 mm. Thirty-five zirconia and seven glass-ceramic (control group) specimens were fabricated for each group (N=252). Zirconia was divided into five subgroups (n=7) and stained to the following shades: CL1, CL2, CL3, and CL4. One zirconia group remained unstained (CL0). Irradiance passing through the different specimens was measured using a violet-blue LED curing unit in three curing modes (Xtra-power, high-power, and standard-power mode) with a fibre-optic USB4000 spectrometer. Irradiance was measured at varying exposure distances, ranging from direct contact of the curing unit with the surface to a distance of 7 mm from the surface, increasing in 1 mm steps. Data were analyzed using a multivariate analysis and linear mixed models (p<0.05). RESULTS: The control group, the glass-ceramics, transmitted the highest irradiance values, followed by CL0 (unshaded zirconia), CL1 (~A1/B1), CL2 (~A3/A3.5/A4/B3/B4), and CL3 (~A3.5/B3/B4/C3/D3), respectively. The highest transmitted irradiance was measured at a specimen thickness of 0.5 mm for all materials, decreasing exponentially with increased ceramic thickness. Within one type of ceramic, one thickness, and one polymerization mode, a decrease in transmitted irradiance with increased exposure distance could be observed only at a distance of 3 mm and above. CONCLUSIONS: Unshaded zirconia was significantly less translucent compared with the glass-ceramic, but the translucency decreased slower with material thickness. The Beer-Lambert law describes well the decrease of transmitted irradiance with an increase of the specimens' thickness for all materials. Except for dark ceramics, this would allow for calculating the transmitted irradiance through any material thickness and any initial irradiance. CLINICAL SIGNIFICANCE: The amount of light passing through ceramics is an important aspect for an adhesive cementation, since many dual-cured luting materials reveal a high sensitivity to additional occurrence of blue light. For restorations thicker than 1.5 mm in light-shaded zirconia and 0.5 mm in darker-shaded zirconia the use of less-light-sensitive dual-cured cements are recommended.

Fabrication of spherical mitigation pit on KH2PO4 crystal by micro-milling and modeling of its induced light intensification.

Micro-machining is the most promising method for KH(2)PO(4) crystal to mitigate the surface damage growth in high power laser system. In this work, spherical mitigation pit is fabricated by micro-milling with an efficient machining procedure. The light intensification caused by rear surface features before and after mitigation is numerically modeled based on the finite-difference time-domain method. The results indicate that the occurrence of total internal reflections should be responsible for the largest light intensification inside the crystal. For spherical pits after mitigation, the light intensification can be greatly alleviated by preventing the occurrence of total internal reflections. The light intensification caused by spherical mitigation pit is strongly dependent on the width-depth ratio and it is suggested that the width-depth ratio of spherical mitigation pit must be devised to be larger than 5.0 to achieve the minimal light intensification for the mitigation of surface damage growth. Laser damage tests for KH(2)PO(4) crystal validate that the laser damage resistance of initially damaged surface can be retrieved to near the level of ideal surface by replacing initial damage site with predesigned mitigation pit.

Effect of various surface treatments on the bond strength of porcelain repair.

This study evaluated the effect of surface treatments on the repair strength of composite resin on a feldspathic ceramic. Ninety ceramic specimens were divided into six groups. In the experimental groups, 4% hydrofluoric acid etching, Er:YAG laser irradiation, CO2 laser irradiation, airborne-particle abrasion, and silica coating were used as surface treatments. After the application of a porcelain repair kit, composite resin was placed on the treated surfaces. After a shear bond strength test, data were statistically analyzed (α = .05). Surface treatments increased the repair bond strength values (P < .05). Airborne particle abrasion and silica coating were found to be the most effective. CO2 laser showed higher repair strength values than Er:YAG laser.

Shear bond strength of orthodontic brackets bonded to porcelain following etching with Er:YAG laser versus hydrofluoric acid.

AIM: The purpose of the present study was to evaluate the shear bond strength of orthodontic brackets bonded to porcelain following etching with erbium-doped yttrium aluminum garnet (Er:YAG) laser compared with 9.6% hydrofluoric acid (HF). METHODS: A total of 100 porcelain disk samples were divided into four groups, and after removing their glazed layer, the first group was etched with 9.6% HF, and the other three groups were etched with Er:YAG lasers of 1.6, 2, and 3.2 W, respectively. After application of silane on the disk surfaces, central incisor brackets were bonded with composite on the disks. The disks were mounted on an acrylic stand for measuring the shear bond strengths. The shear bond strengths were measured by a testing machine. RESULTS: The mean shear bond strength in the laser group with power of 1.6 W (7.88 MPa) was more than that of the HF (7.4MPa), 2-W power (7.52 MPa), and 3.2-W power (7.45 MPa) groups, but this difference was not statistically significant. Examination with an electron microscope showed different patterns of etching by HF and laser. Also, etching by laser and HF had not resulted in cracks on the porcelain surface. CONCLUSION: Er:YAG laser can be a suitable method for bonding of orthodontic brackets to porcelain surfaces.

Dynamics of transient absorption in bulk DKDP crystals following laser energy deposition.

The transient changes in the optical properties of bulk DKDP material arising from its exposure to high temperatures and pressures associated with localized laser energy deposition are investigated. Two methods for initiation of laser-induced breakdown are used, intrinsic, involving relatively large energy deposition brought about by focusing of the laser beam to high intensities, and extrinsic, arising from more localized deposition due to the presence of pre-existing absorbing damage initiating defects. Each method leads to a very different volume of material being affected, which provides for different material thermal relaxation times to help better understand the processes involved.

A study of hydrogen peroxide chemistry and photochemistry in tea stain solution with relevance to clinical tooth whitening.

OBJECTIVE: Tooth whitening using hydrogen peroxide is a complex process, and there is still some controversy about the roles of pH, temperature, chemical activators, and the use of light irradiation. In this work the basic interactions between whitening agents and stain molecules are studied in simple solutions, thus avoiding the physics of diffusion and light penetration in the tooth to give clarity on the basic chemistry which is occurring. METHOD: The absorbance of tea stain solution at 450 nm was measured over a period of 40 min, with various compositions of whitening agent added (including hydrogen peroxide, ferrous gluconate and potassium hydroxide) and at the same time the samples were subjected to blue light (465 nm) or infra-red light (850 nm) irradiation, or alternatively they were heated to 37°C. RESULTS: It is shown that the reaction rates between chromogens in the tea solution and hydrogen peroxide can be accelerated significantly using ferrous gluconate activator and blue light irradiation. Infra red irradiation does not increase the reaction rate through photochemistry, it serves only to increase the temperature. Raising the temperature leads to inefficiency through the acceleration of exothermic decomposition reactions which produce only water and oxygen. CONCLUSION: By carrying out work in simple solution it was possible to show that ferrous activators and blue light irradiation significantly enhance the whitening process, whereas infra red irradiation has no significant effect over heating. The importance of controlling the pH within the tooth structure during whitening is also demonstrated.

An assessment of the external radiological impact in granites and pegmatite in central Eastern Desert in Egypt with elevated natural radioactivity.

The contents of natural radionuclides ((226)Ra, (232)Th and (40)K) were measured in investigated samples (granite Gabal Ras Barud, Eastern Desert in Egypt) by using gamma spectrometry (NaI (Tl) 3″×3″). The activities of (226)Ra, (232)Th series and (40)K are between (3.8±0.5 and 172.8±1135.1±56.8 8.6), (2.3±0.3 and 103.8±5.2) and (53.1±2.7 and 1135.1±56.8) Bq kg(-1), respectively. With average total annual dose being only 67.2 µSv y(-1), this value is about 6.72 % of the 1.0 mSv y(-1) recommended by the International Commission on Radiological Protection (ICRP-60, 1990) as the maximum annual dose to members of the public. Geochemical studies revealed that Gabal Ras Barud is formed from a highly fractionated biotite granite, with SiO(2) >75 % and generally enriched in alkali with K/Na >8 %.

Synthesis of glycoluril catalyzed by potassium hydroxide under ultrasound irradiation.

Synthesis of the glycolurils catalyzed by potassium hydroxide was carried out in 17-75% yield at 40 degrees C in EtOH under ultrasound irradiation. Compared to the method using stirring, the main advantage of the present procedure is milder conditions and shorter reaction time.

Laser damage performance of KD2-chiHchiPO4 crystals following X-ray irradiation.

We investigate the laser-induced damage performance of KD(2-chi)H(chi)PO(4) crystals following exposure to X-ray irradiation. Two important issues addressed by our study are i) the performance of the material when operational conditions lead to its exposure to ionizing irradiation and ii) the way the radiation-induced transient defects interact with the pre-existing precursor defects responsible for laser-induced damage. Our results indicate that the damage performance of the material is affected by exposure to X-rays. This behavior is attributed to a change in the physical properties of the precursors which, in turn, affect their ability to initiate damage following interaction with X-ray generated defects.

Numerical simulation of self-compressed second-harmonic generation in type II potassium dihydrogen phosphate with a time predelay for Yb-doped solid-state lasers.

We report numerical results of second-harmonic generation in a type II potassium dihydrogen phosphate crystal with a time predelay for picosecond and/or femtosecond Yb-doped solid-state lasers, and clarify the dependence of the self compression in the second-harmonic laser pulse on the initial frequency chirp, fundamental duration and intensity, and phase-mismatching angle. We also show numerically the generation possibility of a self-compressed second-harmonic laser pulse near 20 fs.

A system to irradiate and measure luminescence at low temperatures.

We have developed a system to irradiate samples and record radioluminescence (RL), optically stimulated luminescence (OSL), and thermoluminescence (TL) at temperatures ranging from -150 degrees C to 200 degrees C. The system consists of a cryostat, an irradiation/stimulation unit fitted with an X-ray tube (40 kV Moxtek) and a quartz window for optical stimulation, and a detection unit that utilises a photomultiplier tube and an interchangeable filter pack. Experiments have been conducted with quartz and albite (a feldspar). TL and OSL experiments show that several optically sensitive trapping states are stable below -50 degrees C. In addition, an increase in OSL is seen as the OSL stimulation temperature is lowered below -50 degrees C, and an increase in RL is apparent as the temperature is lowered during irradiation. This indicates that not only are optically sensitive low temperature traps present but that luminescence becomes more efficient at low temperatures.

A real-time, high-resolution optical fibre dosemeter based on optically stimulated luminescence (OSL) of KBr:Eu, for potential use during the radiotherapy of cancer.

A real-time optically stimulated luminescence (OSL) dosimetry system for potential in vivo use during radiotherapy treatments is proposed. Single-crystal europium-doped KBr samples were grown in a Bridgman furnace, and characterised using optical absorption techniques. An algorithm for the processing of the OSL signal was defined for use in real-time measurements, and its performance was studied on data obtained with a home-built reader, using optical-fibre-coupled dosemeters. OSL dose-response, fading properties and temperature dependence of the signal were investigated in correlation with the concentration of Eu(2+) dopant in the sample.

Progress towards a polymineral single-aliquot OSL dating procedure.

Published single-aliquot regenerative-dose (SAR) procedures for quartz use a 'cutheat' different from the pre-heat. In contrast, previous work has shown that the SAR procedure can be used to correct for sensitivity changes exhibited by feldspars if the cutheat is equal to the pre-heat. In this paper, a procedure that corrects for sensitivity changes in both quartz and feldspar is tested. The results indicate that for sedimentary quartz the cutheat can be equal to the pre-heat. Thus, it may be possible to develop one procedure to measure equivalent doses in a polymineral sample. We also tested several different optical stimulation methods. Using the infrared (IR)-stimulated signal from a post-IR blue-stimulated optically stimulated luminescence sequence extends the potential age range when using feldpathic materials. In addition, since the post-IR blue-stimulated signal from feldspar is much smaller than the blue-stimulated signal from quartz, the possibility exists of extracting a 'quartz signal' from a mixed mineral sample.

Radiation and temperature effects on conductivity properties of PVA-KOH-PC composite.

The aim of this work was to study radiation and the effects of temperature on conductivity properties of polyvinyl alcohol (PVA)-based potassium hydroxide (KOH) and propylene carbonate (PC), where the ionic conduction preferentially occurs in the amorphous phase by free radicals ions through gamma-irradiation. Alkaline composite polymer electrolyte (ACPE) consisting of PVA, KOH and PC of different concentration ratios were prepared by solvent-casting technique. The ACPE were irradiated with different doses from 5 kGy up to 200 kGy. The conductivity properties of the electrolyte films were measured at different frequencies in the range 20 Hz to 1 MHz using LCR meter. The results showed that the conductivity properties were dependent on the radiation dose, temperature and the concentration of the polymer blends.

Optically and thermally stimulated luminescence of KMgF3:Ce3 and NaMgF3:Ce3+.

The potentialities of optically stimulated luminescence (OSL) for personal dosimetry of ionising radiation have stimulated the search for new synthetic materials with good dosimetric properties. The sensitivity of two new OSL materials KMgF3 and NaMgF3 doped with Ce3+ ions has been evaluated and found to be of the same order of magnitude as that of Al2O3:C. Several other characteristics have also been investigated. Promising results for KMgF3:Ce are the high sensitivity and the low fading. However, this material suffers from a high self-dose due to the presence of 40K. NaMgF5:Ce is sensitive as well but shows strong fading. Interesting information on the mechanism has been obtained by correlating the signals of OSL and TL. Furthermore, the different bleachabilities under blue LED illumination of the strongly overlapping glow peaks allowed the extraction of one single peak for KMgF3:Ce3+. The results demonstrate new possibilities offered by the combination of TL and OSL.