An in vitro thermal analysis during different light-activated hydrogen peroxide bleaching

This study measured the critical temperature reaching time and also the variation of temperature in the surface of the cervical region and within the pulp chamber of human teeth submitted to dental bleaching using 35% hydrogen peroxide gel activated by three different light sources. The samples were randomly divided into 3 groups (n = 15), according to the catalyst light source: Halogen Light (HL), High Intensity Diode Laser (DL), and Light Emmited Diode (LED). The results of temperature variation were submitted to the analysis of variance and Tukey test with p < 0.05. The temperature increase (mean value and standard deviation) inside the pulp chamber for the HL group was 6.8 ± 2.8°C; for the DL group was 15.3 ± 8.8°C; and for the LED group was 1.9 ± 1.0°C for. The temperature variation (mean value and standard deviation) on the tooth surface, for the group irradiated with HL was 9.1 ± 2.2°C; for the group irradiated with DL were 25.7 ± 18.9°C; and for the group irradiated with LED were 2.6 ± 1.4°C. The mean temperature increase values were significantly higher for the group irradiated with DL when compared with groups irradiated with HL and LED (p < 0.05). When applying the inferior limits of the interval of confidence of 95%, an application time of 38.7 s was found for HL group, and 4.4 s for DL group. The LED group did not achieve the critical temperatures for pulp or the periodontal, even when irradiated for 360 s. The HL and DL light sources may be used for dental bleaching for a short period of time. The LED source did not heat the target tissues significantly within the parameters used in this study.     

A flexible 9-channel coil array for fast 3D MR thermometry in MR-guided high-intensity focused ultrasound (HIFU) studies on rabbits at 3 T

Signal-to-noise ratio (SNR) is a critical factor in MR-guided high-intensity focused ultrasound (HIFU) for local heating, which can affect the accuracy of temperature measurement. In order to achieve high SNR and higher temporal resolution, dedicated coil arrays for MR-guided HIFU applications need to be developed. In this work, a flexible 9-channel coil array was designed, and constructed at 3 T to achieve fast temperature mapping for MR-guided HIFU applications on rabbit leg muscle. Coil performance was evaluated for SNR, and parallel imaging capability by in-vivo studies. Compared to a commercially available 4-channel flexible coil array, the dedicated 9-channel coil array has a much higher SNR, with at least a 2.6-fold increment in the region of interest (ROI). The inverse g-factors maps demonstrated that the dedicated 9-channel coil array has a better parallel imaging capability than the Flex Small 4. With accelerations normal to the array direction, both coil arrays showed much higher g-factors than those of accelerations along the array direction. Room temperature mapping was implemented to evaluate the temperature measurement accuracy by in-vivo experiments. The precisions of the 9-channel coil, ±0.18 °C for un-acceleration and ± 0.56 °C for acceleration at R = 2 × 2, both improved by an order of magnitude than these of the 4-channel coil, which were ± 1.45 °C for un-acceleration and ± 3.52 °C for acceleration at R = 2 × 2. In the fast temperature imaging on the rabbit leg muscle with heating, a high temporal resolution of 3.3 s with a temperature measurement precision of ±0.56 °C has been achieved using the dedicated 9-channel coil. This study demonstrates that the dedicated 9-channel coil array for rabbit leg imaging provides improved performance in SNR, parallel imaging capability, and the accuracy of temperature measurement compared to a commercial 4-channel coil, and it also achieves fast temperature mapping in practical MR-guided HIFU applications.     

Preparation of ZnO nanoparticles in amphiphilic gel network

Nanosized zinc oxide (ZnO) particles were prepared in an amphiphilic N,N-dimethylacrylamide (DMAA) gel composed of a three-dimensional network with an effective pore size of the order of nanometers. The procedures consist of two major steps: (1) preparation of a precursor and (2) hydrolysis of the precursor to form nanoparticles. First, the plate-type dry gel was swollen in ethanol containing zinc acetate (ZnAc) in order to diffuse ZnAc molecules into the gel. Then, the ethanolic solution containing the gel was heated to ∼80°C to prepare the precursor. In the hydrolysis of the precursor, lithium hydroxide was added as the catalyst to the precursor solution containing the gel, and the solution was placed in an ultrasonic bath. Although the DMAA gel containing ZnO particles was completely transparent, it exhibited a yellow-green luminescence when irradiated with UV light. The ZnO nanoparticles stably dispersed in the gel network without growing, aggregating, or flowing out for over several months at a relatively high temperature of 50°C. The particle size depended on the effective pore size of the gel network, which could be controlled by the synthesis composition of the gel, that is, by the concentrations of DMAA as the primary monomer and N,N′-methylenebisacrylamide (MBAA) as the cross-linker used for synthesizing the gel. This implies that the particle size can be controlled at the nanosized level by the synthesis composition of the gel.     

Non-invasive temperature mapping using MRI: comparison of two methods based on chemical shift and T1-relaxation

Purpose: To implement and evaluate the accuracy of non-invasive temperature mapping using MRI methods based on the chemical shift (CS) and T₁ relaxation in media of various heterogeneity during focal (laser) and external thermal energy deposition.Materials and Methods: All measurements were performed on a 1.5 T superconducting clinical scanner using the temperature dependence of the water proton chemical shift and the T₁ relaxation time. Homogeneous gel and heterogeneous muscle phantoms were heated focally with a fiberoptic laser probe and externally of varying degree ex vivo by water circulating in a temperature range of 20–50°C. Magnetic resonance imaging data were compared to simultaneously recorded fiberoptic temperature readings.Results: Both methods provided accurate results in homogeneous media (turkey) with better accuracy for the chemical shift method (CS: ±1.5°C, T₁: ±2.0°C). In gel, the accuracy with the CS method was ±0.6°C. The accuracy decreased in heterogeneous media containing fat (T₁: ±3.5°C, CS: +5°C). In focal heating of turkey muscle, the accuracy was within 1.5°C with the T₁ method.Conclusion: Temperature monitoring with the chemical shift provides better results in homogeneous media containing no fat. In fat tissue, the temperature calculation proved to be difficult.     

TDPAC studies of Hf doped YBCO

Time differential perturbed angular correlation measurements of the 133–482 keVγ-γ cascade of¹⁸¹Ta in Hf-doped YBa₂Cu₃O_7−x are presented. The¹⁸¹Hf precurser nuclei are incorporated into the sample by thermal neutron irradiation. Two quadrupole interaction frequencies are observed in the as-irradiated sample:v _Q1=161±10 MHz with intensityf ₁=75%, asymmetry parameterη ₁=0.32 and damping parameter Λ₁=0.42, andv _Q2=1108±40 MHz withf ₂=25%,η ₂=0.62, and Λ₂=0.60. On annealing the sample in air at various temperaturesT _a and quenching to room temperature,f ₁ remained nearly constant forT _a<600°C andv _Q1 for all annealing temperatures indicating that these are insensitive to oxygen stoichiometry. This frequency is interpreted to be due to¹⁸¹Hf substitutingY sites. BeyondT _a=600°C,f ₁ increased and reached a constant value of 90% forT _a=800°C. The value ofv _Q2 showed a slight variation between 1086 and 1160 MHz, whilef ₂ remained nearly constant at 25% forT _a<600°C. This component is identified to be due to¹⁸¹Hf substituting Cu 1 sites in the Cu-O chains of YBCO. Above 600°Cv _Q2 decreased and reached a value of 808 MHz beyond 750°C.     

Influence of substrate temperature on the electrical behaviour of zinc stannate thin films deposited by electron beam evaporation technique

Summary  A series of zinc stannate (Zn₂ SnO₄) thin films were prepared at four different substrate temperatures; namely, room-temperature (25°C), 50°C, 100°C and 200°C. Direct-current resistivity measurements were performed on these samples in the temperature range from room temperature (∼290 K) up to about 500 K. A phase transition (of positive temperature coefficient (PTC) of resistance) was observed in the thin film grown at room temperature at about 385 K. Other investigated samples showed a semiconducting behaviour of three distinct conduction mechanisms extending from intrinsic to thermal freeze-out conduction. The width of the band gapE _g was found to depend on the substrate temperature and was discussed in terms of a formation of a band tailing. Thermal freeze-out was dominant at the lower temperature region. On leave from Department of Physics, Faculty of Science, Alexandria University, Alexandria, Egypt.     

Thermographic diagnosis system and imaging algorithm by distributed thermal data using single infrared sensor

An infrared diagnosis device provides two-dimensional images and patient-oriented results that can be easily understood by the inspection target by using infrared cameras. However, this device has disadvantages such as large size, high price, and inconvenient maintenance. In this regard, this study has proposed a small diagnosis device for body heat using a single infrared sensor and implementing an infrared detection system using a single infrared sensor and an algorithm that represents thermography using the obtained data on the temperature of the point source. The developed system had a temperature resolution of 0.1 °C and reproducibility of ±0.1 °C. The accuracy was 90.39% at the error bound of ±0 °C and 99.98% at that of ±0.1 °C. To evaluate the proposed algorithm and system, the infrared images of the camera method were compared. To verify the device’s clinical applicability, thermal images with clinical meaning were obtained from a patient who had lesions.     

Protonic batteries based on chemically synthesized MnO2

Synthesis temperature, during air-oxidation of manganese hydroxide, of γ-MnO₂ influences performance of the protonic solid-state battery. X-ray powder diffraction analyses reveal a high degree of De Wolff disorder in samples synthesized at 40 and 60 °C, resulting in poor battery performance. The discharge profile of cell with proton-conducting solid electrolyte and composite zinc as anode, recorded at a constant load condition, indicates proton intercalation. MnO₂ synthesized at 80 °C exhibits improved battery performance.     

The system Na2CO3–MgCO3 at 3 GPa

It was suggested that Na–Mg carbonates might play a substantial role in mantle metasomatic processes through lowering melting temperatures of mantle peridotites. Taking into account that natrite, Na₂CO₃, eitelite, Na₂Mg(CO₃)₂, and magnesite, MgCO₃, have been recently reported from xenoliths of shallow mantle (110–115?km) origin, we performed experiments on phase relations in the system Na₂CO₃–MgCO₃ at 3?GPa and 800–1250°C. We found that the subsolidus assemblages comprise the stability fields of Na-carbonate?+?eitelite and eitelite?+?magnesite with the transition boundary at 50?mol% Na₂CO₃. The Na-carbonate–eitelite eutectic was established at 900°C and 69?mol% Na₂CO₃. Eitelite melts incongruently to magnesite and a liquid containing about 55?mol% Na₂CO₃ at 925?±?25 °C. At 1050 °C, the liquid, coexisting with Na-carbonate, contains 86–88?mol% Na₂CO₃. Melting point of Na₂CO₃ was established at 1175?±?25 °C. The Na₂CO₃ content in the liquid coexisting with magnesite decreases to 31?mol% as temperature increases to 1250°C. According to our data, the Na- and Mg-rich carbonate melt, which is more alkaline than eitelite, can be stable at the P–T conditions of the shallow lithospheric mantle with thermal gradient of 45?mW/m² corresponding to temperature of 900 °C at 3?GPa.     

In situ confocal micro‐Raman spectroscopic investigation of rearrangement kinetics and phase evolution of UHMWPE during annealing

Ultrahigh molecular weight polyethylene was investigated using in situ confocal micro‐Raman spectroscopy during annealing at 110.0 °C. Based on the Raman spectra, crystalline, amorphous, and all‐trans noncrystalline fractions were recognized to evaluate rearrangement kinetics during isothermal annealing at 110.0 °C and phase evolution during cooling from 110.0 to 30.0 °C. For the crystalline fraction, a substantial increase from 0.600 ± 0.001 to 0.639 ± 0.008 was observed during the first 24.2 min of annealing; a very gradual increase from 0.639 ± 0.001 to 0.679 ± 0.001 occurred during the following 114.6 min. For the amorphous phase fraction, conversely, a sharp decrease from 0.240 ± 0.000 to 0.213 ± 0.004 was exhibited during the first 24.2 min of annealing, and then, a flat decrease happened from 0.213 ± 0.004 to 0.192 ± 0.001 as time expanded to 138.8 min. For the all‐tans noncrystalline fraction, a gradual decrease was shown from 0.160 ± 0.000 at 0.0 min to 0.128 ± 0.001 at 138.8 min. The rearrangement rate constant K was obtained to be 0.632 by an Avrami equation. During cooling from 110.0 to 30.0 °C, there were two phase evolution regions: region 1 from 110.0 to 90.0 °C and region 2 from 90.0 to 30.0 °C. The crystal lamella thickened faster in region 1 than in region 2. The amorphous layer continually decreased in content in the combined region of 1 and 2. The all‐trans noncrystalline phase obviously decreased in region 1 and then almost maintained a constant level in region 2. Copyright © 2014 John Wiley & Sons, Ltd.     

Structural evolution of ZrO2–mullite nanocomposites from the Si–Al–Zr–O amorphous bulk

ZrO₂–mullite nanocomposites were fabricated by in-situ-controlled crystallization of Si–Al–Zr–O amorphous bulk at 800–1250°C. The structural evolution of the Si–Al–Zr–O amorphous, annealed at different temperatures, was studied by X-ray diffraction, infrared, Laser Raman spectroscopy, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. The materials consisted of an amorphous phase up to 920°C at which phase separation of Si-rich and Al, Zr-rich clusters occurred. The crystalline phases of t-ZrO₂ and mullite were observed at 950°C and 1000°C, respectively. Mullite with a tetragonal structure, formed by the reaction between Al–Si spinel and amorphous silica at low temperature, changed into an orthorhombic structure with the increase of temperature. It was the phase segregation that improved crystallization of the Si–Al–Zr–O amorphous bulk. The anisotropic growth of mullite was observed and the phase transformation from t-ZrO₂ to m-ZrO₂ occurred when the temperature was higher than 1100°C.     

The baddeleyite-type high pressure phase of Ca(OH)2

Abstract

A phase transition from Ca(OH)₂ I (portlandite) to Ca(OH)₂ II at high pressure and temperature has been confirmed, using in situ x-ray diffraction in a multianvil high pressure device (DIA). The structure was determined at 9.5 GPa and room temperature from data collected after heating the sample at 300°C at 7.2 GPa in a diamond anvil cell. Both the Le Bail fit and preliminary Rietveld refinement suggest that the new phase, which reverts to Ca(OH), I during pressure release, has a structure related to that of baddeleyite (ZrO₁); it is monoclinic (P2₁/c) with a= 4.887(2), b= 5.834(2), c = 5.587(2), β = 99.74(2)°. The coordination number of Ca increases from six to seven (5 + 2) across the transition. At 500°C, the phase boundary is bracketed at 5.7 ± 0.4 GPa by reversal experiments performed in the DIA.     

High pressure X-ray diffraction study on BaWO4-II

BaWO₄-II has been synthesized at 5 GPa and 610°C. Its high pressure behavior was studied by in situ synchrotron X-ray diffraction measurements at room temperature up to 17 GPa. BaWO₄-II retains its monoclinic structure. Bulk and axial moduli determined by fitting a third-order Birch–Murnaghan equation of state to lattice parameters are: K ₀=86.2±1.9 GPa, K ₀(a)=56.0±0.9 GPa, K ₀(b)=85.3±2.4 GPa, and K ₀(c)=146.1±3.2 GPa with a fixed K′=4. Analysis of axial compressible modulus shows that the a-axis is 2.61 times more compressible than the c-axis and 1.71 times more compressible than the b-axis. The beta angle decreases smoothly between room pressure and 17 GPa from 93.78° to 90.90°.     

Gasket temperature: an alternate technique for estimating sample temperature in a multi-anvil apparatus

It is common for sample temperatures to be estimated by the power input to the furnace in multi-anvil experiments in which a thermocouple cannot be used or the thermocouple failed during heating. Uncertainties using this technique are often on the order of ±85°C or larger. This paper describes a new method for estimating sample temperature using a second thermocouple outside all pressure media. Temperatures recorded at this external (gasket) thermocouple trend linearly with the internal (sample) thermocouple temperature. Because of thermal lag, it is necessary to determine the first gasket temperature (T₀) corresponding to the desired sample temperature. Accurate prediction of T₀ for the desired sample temperature can come from relatively few (5–6) gasket-temperature measurements made during the initial temperature ramp over a small temperature range (500–600°C). Using this method and manually ramping to T₀ allows for uncertainties in sample temperature estimation as small as ±20°C.     

Nucleic acid conformation: Crystal and molecular structure of deoxyguanosine (5′) phosphate (disodium salt)—Agauche-trans (gt) conformation about the C(4′)-C(5′) bond and O(1′) puckering of the furanose ring

The crystal structure of deoxyguanosine (5′) phosphate, disodium salt, (5′-dGMP Na₂ 4H₂O) has been determined from three dimensional single crystal x-ray data collected by multiple film, equi-inclination, Weissenberg method using CuK_a radiation. The crystal belongs to the monoclinic space groupP2₁ witha=16.002±0.003 Å,b=10.730±0.003 Å,c=5.575±0.005 Å andβ=101.9°. The structure was solved by symbolic addition method using the program Multan, the reliability index being 0.090. The guanine base is in the usualanti conformation about the C (1′)-N (9) bond withx _CN=52.3°. The structure shows two unique conformational features not observed in any nucleotide structure reported so far. The deoxyribose moiety shows O (1′)endo puckering with respect to the best four atom plane defined by C(1′)-C(2′)-C(3′)-C(4′). The conformation about the C(4′)-C(5′) bond isgauche-trans with ø₀₀=62.5° and ø_oc=174.8°. This is the first nucleotide structure where agt conformer similar to that found in the Watson-Crick double helical DNA model has been experimentally observed. These two conformational features have also direct relevance to the concept of ‘a conformationally rigid nucleotide unit’ developed by Sundaralingam. The nine membered guanine ring is essentially planar. Bases of molecules related by a ‘c’ cell translation tend to overlap, the shortest distance being 3.51 Å between the atoms N (3) and C(8). One of the sodium atoms Na(1) has an octahedral coordination with four water oxygens and O(6) and O(3′) atoms occupying the corners at distances ranging from 2.35 Å to 2.55 Å.     

Characterization of Encapsulating Materials for Fiber Bragg Grating-Based Temperature Sensors

Abstract

An experimental study has been carried out for the characterization of encapsulating materials for fiber Bragg grating-based temperature sensors to prevent the formation of micro-cracks and devitrification on the fiber surface at elevated temperatures by making use of a rigid probe. The developed sensor probe was configured by encapsulating a type 1 fiber Bragg grating with an aluminum nitride tube and is used to measure temperatures from 20°C to 500°C. The adapted encapsulation technique validated the sensor to achieve linearity of 99.979%, sensitivity of 14.03 ± 0.02 pm/°C, and good repeatability; its practical use in harsh environments is predicted.     

The tricritical point in an ethanediol-nitroethane-cyclohexane-methanol solution

Applying the polythermal method the coexistence region of three liquid phases in an ethanediol-nitroethane-cyclohexane-methanol system has been found for several temperatures. From this the temperature and composition of the tricritical point has been determined as T _TCP = 37.5 ± 1°C and mass fraction :x _ethanediol = 0.09 ± 0.01, x _nitroelhane = 0.45 ± 0.01 x _{cycelohcexane} = 0.40 ± 0.02, x _methanol = 0.060 ± 0.005. The point at which, for a given polytherm, the transition from a two-phase to a three-phase region takes place at the highest temperature is identified as the critical end-point.

Functions of temperature versus heights of menisci separating the individual phases have been determined for selected values of concentration.     

Bound Energy of Water in Hard Dental Tissues

Abstract

Enamel and dentin are composed, respectively, of 3 wt% and 10 wt% of water, which exhibits different features in the tissues: loosely and tightly bound water. The objective of this study is to clarify by infrared spectroscopy, the different features of the water in heated (100–1000°C) hard dental tissues (enamel and dentin). The water band between 3800 cm^?1 and 2500 cm^?1 was analyzed by infrared spectroscopy. The area dependence of the water band with temperature was compared with the Arrhenius equation in two regions (100–400°C and 700–1000°C). The activation energy was determined for these two regions, and similar values were observed for both tissues. For enamel we obtain ?4.1±0.2 kJ/mol at 100–400 °C and ?63±9 kJ/mol at 700–1000°C; for dentin ?4.1±0.2 kJ/mol at 100–400°C and ?60±11 kJ/mol at 700–1000°C. The water loss changes the color of the tissues, hydroxyapatite crystallographic parameters, and produce ESR signals. These changes were discussed and compared with the results observed in this work and after laser irradiation. We conclude that these two activation energies could be assigned to the adsorbed (loosely bound) and trapped (tightly bound) water.     

Optical monitoring of technological parameters in metal-organic vapor-phase epitaxy

The possibility of applying low-coherent tandem interferometry to optical monitoring of the temperature of a semiconductor substrate and the thickness of a deposited layer in metal-organic vapor-phase epitaxy (MOVPE) is demonstrated for the first time. The absolute accuracy in the temperature measurements of Si, GaAs, and sapphire substrates under MOVPE conditions is limited by the calibration accuracy and is ±1°C. The accuracy in the measurement of the deposited layer thickness is 2 nm. A considerable (10–100°C) deviation of the temperature measured by a thermocouple placed inside a susceptor from the actual substrate temperature is found. A significant temperature gradient along the susceptor depending on the gas flow rate and other factors is revealed. It is shown that, owing to the high heating efficiency of sapphire substrates, there is no need to coat their reverse with absorbing layers upon heating up to 300°C or in the presence of hydrogen pressure of higher than 100 mbar.     

Effect of substrate temperature on electrical and magnetic properties of epitaxial La1−x Pb x MnO3 films

Epitaxial La_1−x Pb _x MnO₃ (LPMO) thin films, grown on (100) SrTiO₃ substrates by laser ablation technique at different temperatures between 600 and 850°C, have been characterized for electrical and magnetic properties. The temperature dependence of resistivity showed that the metal-insulator transition temperature (T _MI) decreases with increasing substrate temperature, which has been attributed to decrease in Pb content in the filsm. The YBa₂Cu₃O _x /La_1−x MnO₃ heterostructures, exhibiting both superconductivity and ferromagnetism, have been fabricated.