Ultrastructural changes in the cemento‐enamel junction caused by acidic beverages: An in vitro study

The present in vitro study was aimed at evaluating the morphological changes in the cemento‐enamel junction (CEJ) after exposure to acidic beverages using the scanning electron microscopy (SEM). The initial pH and titratable acidity (TA) was analyzed from follow groups: (I) Coca cola, (II) orange juice, (III) Cedevita, (IV) Red Bull, (V) Somersby cider, and (VI) white wine. The CEJ samples (n = 64), obtained from unerupted third molars, were allocated to one control (artificial saliva, n = 16) and six experimental groups (n = 8). The experimental samples were immersed in beverages (50 ml) for 15 min, three times daily, 10 days, and in artificial saliva between immersions. SEM analysis was performed in a blind manner, according to scoring scale. One‐way ANOVA and Tukey's post hoc tests, as well as Kruskal–Wallis and Mann–Whitney U test used for statistical analysis. The pH values of the acidic beverages ranged from 2.65 (Coca cola) to 3.73 (orange juice), and TA ranged from 1.90 ml (Coca cola) to 5.70 ml (orange juice) of NaOH to reach pH 7.0. The SEM analysis indicated statistically significant differences between the control samples and those immersed in acidic beverages. The Groups IV, I, and II, showed the highest CEJ damage grade while those of the Group VI were the lowest. All the tested acidic beverages caused morphological changes in the CEJ with a smaller or larger exposure of dentine surface, and were not always related to the pH or TA of acidic beverages.     

Influence of Rare-Earth Dopants on Barium Titanate Ceramics Microstructure and Corresponding Electrical Properties

In this article, ytterbium and erbium oxides are used as doping materials for barium titanate (BaTiO₃) materials. The amphoteric behavior of these rare-earth ions leads to the increase of dielectric permittivity and decrease of dielectric losses. BaTiO₃ ceramics doped with 0.01–0.5 wt% of Yb₂O₃ and Er₂O₃ were prepared by conventional solid-state procedure and sintered at 1320°C for 4 h. In BaTiO₃ doped with a low content of rare-earth ions (0.01 wt%) the grain size ranged between 10 and 25 μm. With the higher dopant concentration of 0.5 wt%, the abnormal grain growth is inhibited and the grain size ranged between 2 and 10 μm. The measurements of capacitance and dielectric losses as a function of frequency and temperature have been carried out in order to correlate the microstructure and dielectric properties of doped BaTiO₃ ceramics. The temperature dependence of the dielectric constant as a function of dopant amount has been investigated.     

Reliability of AlN substrates and their solder joints in IGBT power modules

The reliability of IGBT modules was investigated with respect to the metallized ceramic (substrate) and the solder layer between the substrate and copper baseplate. Thermal cycles were performed between −55°C and +150°C on substrates based on different technologies and from various manufacturers. An incipient delamination of the metallization could be predicted from the mechanical resonance frequency. The warping of the substrates after cycling due to crack propagation and the adhesion of the metallization were determined. Thermal and active-power cycles were performed on 1200 A / 3.3 kV IGBT power modules to investigate the reliability of the solder joint between substrate and baseplate.     

Sliding mode-based minimum variance and generalized minimum variance controls with O( T 2) and O( T 3) accuracy

The paper deals with the discrete-time sliding mode control with O(T ²) and O(T ³) accuracy, based only on input/output measurements. The linear parts of the control algorithms, recognized as the traditional minimum variance and the generalized minimum variance controls, enable the implementation of the sliding mode control on minimum and non-minimum phase plants. The chattering phenomenon is suppressed by filtering the high-frequency control signal of the sliding mode component through the discrete-time integrator.     

Localization of electrical-insulation and partial-dischargefailures of IGBT modules

The partial discharge (PD) and insulation resistance is very important in view of the increasing operating voltages of insulated gate bipolar transistor modules. PD spectroscopy showed that the PDs from metallization edges and interfaces in silicone gel were the main sources of PD at high voltages. It also allows these types of PDs to be clearly distinguished. As the PDs from interfaces in silicone gel increase strongly at high voltages, it is especially important for the silicone gel to adhere well to the ceramic     

Monte Carlo simulations and laser Doppler flow measurements with high penetration depth in biological tissuelike head phantoms

Laser Doppler flow measurements on biological tissuelike phantoms have shown that penetration depths of 30 mm could be obtained, thus exceeding the penetration depth of commercial instruments for the measurement of skin perfusion by more than an order of magnitude. Monte Carlo simulations were performed and compared with measurement results obtained on a headlike tissue model to quantify the influence of perfusion of the scalp on the cortex perfusion results. We found Doppler frequency spectra to be independent of the mean scattering angle and could be fitted with a sum of Gaussian functions, using a simple analytical model.     

The contribution of fractal nature to BaTiO3-ceramics microstructure analysis

The structure of BaTiO₃ based materials can be controlled by using different technological parameters and different additives. In this paper, microstructure and dielectrical properties of Er₂O₃ doped BaTiO₃-ceramics, sintered from 1320 °C to 1380 °C have been investigated. Microstructural investigations were carried out using scanning electron microscope equipped with energy dispersive spectrometer. Grain size distribution was determined by quantitative metallography method.The new correlation between microstructure and dielectric properties of doped BaTiO₃-ceramics, based on fractal geometry and contact surface probability, has been developed. Using the fractals and statistics of the grains contact surface, a reconstruction of microstructure configurations, as grains shapes or intergranular contacts, has been successfully done. Obtained results indicated that fractal analysis and statistics model for contact surfaces of different shapes were very important for the prognosis of BaTiO₃-ceramics microstructure and dielectric properties.The morphology of ceramics grains pointed out the validity of developing new structure analytical methods, based on different grains’ shape geometries. The grains contact model based on ellipsoidal geometry is presented as new modeling tool for structure research of BaTiO₃-ceramics materials. The directions of possible materials properties prognosis are determined according to the correlations synthesis-structure-property.The statistical approach to the investigation of BaTiO₃-ceramic grains concerning the relationship between the temperature and the area of the contact surface is also introduced.     

Acceleration of Anti‐Markovnikov Hydroamination in the Synthesis of an Active Pharmaceutical Ingredient

Slow chemical reactions are a big challenge in the modern pharmaceutical industry. Their accelerations together with the introduction of continuous manufacturing modes are major drivers for future development. One example reaction is hydroamination, a reaction between unsaturated hydrocarbons and amines. Such a reaction type is the main focus of this work. More precisely, the anti‐Markovnikov hydroamination reaction between cis/trans 9H‐thioxanthene‐2‐chloro‐9‐(2‐propenylidene)‐(9CI) and 1‐(2‐hydroxyethyl)piperazine (HEP) is investigated in detail. It has been traditionally performed in toluene with a huge excess of HEP and reaction times of up to 24 h. Acceleration of the reaction from 24 down to 4 h is achieved by switching from batch operation mode in toluene to either solvent‐free batch mode or microwave‐assisted hydroamination with tetrahydrofuran as a solvent.     

Bias spectroscopy and simultaneous single-electron transistor charge state detection of Si:P double dots

We report a detailed study of low-temperature (mK) transport properties of a silicon double-dot system fabricated by phosphorous ion implantation. The device under study consists of two phosphorous nanoscale islands doped to above the metal-insulator transition, separated from each other and the source and drain reservoirs by nominally undoped (intrinsic) silicon tunnel barriers. Metallic control gates, together with an Al-AlO(x) single-electron transistor (SET), were positioned on the substrate surface, capacitively coupled to the buried dots. The individual double-dot charge states were probed using source-drain bias spectroscopy combined with non-invasive SET charge sensing. The system was measured in linear (source-drain DC bias V(SD) = 0) and non-linear (V(SD) ≠ 0) regimes, allowing calculations of the relevant capacitances. Simultaneous detection using both SET sensing and source-drain current measurements was demonstrated, providing a valuable combination for the analysis of the system. Evolution of the triple points with applied bias was observed using both charge and current sensing. Coulomb diamonds, showing the interplay between the Coulomb charging effects of the two dots, were measured using simultaneous detection and compared with numerical simulations.