Dental Enamel Quality and Black Tooth Stain: A New Approach and Explanation by using Raman and AFM Techniques

This contribution takes in account investigation of dental enamel regarding “quality” of hydroxyapatite material involved in the mineralization process. Areas damaged by black stain were investigated in order to evaluate changes in chemical composition as compared to those of healthy dental enamel.

Different sectors on tooth surfaces were analyzed using micro-Raman spectroscopy. The integral areas of ν₁ (960 cm^?1) phosphate peak as well as of B-type carbonate peak ν₂ (1070 cm^?1) were obtained to investigate structural differences between the specimens (healthy/unhealthy enamel tooth and different sectors on unhealthy surface tooth). A complete list of chemical specimens involved in chemical processes on dental enamel surface was obtained by Energy Dispersive x-rays (EDX) investigation.

It was noticed that mineralized carbonate peak at 1070 cm^?1 decreased significantly for unhealthy tooth enamel or spots areas (as fluorite groups), suggesting that carbonate ions are easily dissolved in the presence of fluoride.

The present study is confirming an organic origin for the dental “black stain.” The “black stain” is the result of a complex generation process from the damaged enamel, thus explaining their reappearance after the mechanical removing. A possible model for the “black stain” generation process is advanced.     

Engineering preliminaries to obtain reproducible mixtures of atelocollagen and polysaccharides

The critical stage in producing blends of biomacromolecules consists in the mixing of component solutions to generate homogenous diluted colloidal systems. Simple experimental investigations allow the establishment of the design rules of recipes and the procedures for preparing homogenous and compositionally reproducible mixtures. Starting from purified solutions of atelocollagen, hyaluronan and native gellan, having as low as possible inorganic salts content, initial binary and ternary mixtures can be prepared up to a total dry matter content of 0.150 g/dL, in no co-precipitating conditions. Two pH manipulation ways are feasible for homogenous mixing: (i) unbuffered prior correction at pH 5.5, and (ii) “rigid” buffering at pH 9.0, using organic species. Atelocollagen including co-precipitates can be obtained in the presence of one or both polysaccharides, preferably in pH domains far from the isoelectric point of scleroprotein. A critical behavior has been observed in mixtures containing gellan, due to its macromolecular dissimilarities compared with atelocollagen. In optimal binary mixtures, the coordinates of threshold points on the phase diagrams are 0.028% w/w atelocollagen/0.025% w/w hyaluronan, and 0.022% w/w atelocollagen/0.020% w/w gellan. Uni- or bi-phasic ternary systems having equilibrated ratios of co-precipitated components can be prepared starting from initial mixtures containing up to 0.032 g/dL atelocollagen, associated with, for example, 0.040 g/dL hyaluronan and 0.008 g/dL gellan, following the first pH manipulation way.     

Assessment of ventilation efficiency for emergency situations in subway systems by CFD modeling

The ventilation system is the strategic component of the subway systems when incidents involving heavy smoke occur in tunnels. Consequently, the purpose of this study is to investigate the ventilation efficiency in one of the most severe emergency scenario: train on fire (maximum heat release rate reaching 30 MW due to an ultra-fast fire) and stopped in the tunnel, the incident requiring passenger evacuation. Two ventilation strategies are taken into account: tunnel ventilation fan system (mid-tunnel fan plant located in separate construction) in conjunction with stations mechanical ventilation and end-of-station fan plants in conjunction with stations mechanical ventilation. The analysis is performed using computational fluid dynamics (CFD) modeling. The numerical model proposes an original approach based on the introduction of source terms in conservation equations for energy, carbon monoxide (CO) and carbon dioxide (CO₂), in order to deal with the heat, CO, and CO₂ due to fire. Equations expressing the conservation of CO and CO₂ are specially added to the basic equations governing a turbulent non-isothermal airflow in the CFD model. This method allowed achieving values of velocity, temperature, CO and CO₂ concentrations all over the computational domain. In addition, the modeling and simulation methodology complies faithfully to the real operation of the ventilation systems investigated in normal and emergency (fire) conditions. The results show that both ventilation alternatives taken into account lead to the secure evacuation of passengers all over the simulation time. The evacuation process toward the nearest station is not at all disturbed by too high air velocities, high temperatures or critical CO or CO₂ concentrations.     

Bound excitons in metallic single-walled carbon nanotubes

We extend previous ab initio calculations on excitonic effects in metallic single-walled carbon nanotubes to more experimentally realizable larger diameter tubes. Our calculations predict bound exciton states in both the (10,10) and (12,0) tubes with binding energies of approximately 50 meV providing experimentally verifiable changes to the absorption line shape in each case. The second and third van Hove singularities in the joint density of states also give rise to a single optically active bound or resonant excitonic state.     

Reduced Fresnel losses in chalcogenide fibers obtained through fiber-end microstructuring

We demonstrate microstructuring of chalcogenide fiber facets in order to obtain enhanced transmission due to the antireflective properties of the microstructured surfaces. A variety of molding approaches have been investigated for As(2)S(3) and As(3)Se(3) fibers. Transmission as high as 97% per facet was obtained in the case of As(2)S(3) fiber, compared to the native, Fresnel-loss limited, transmission of 83%.     

Exploring forces between individual colloidal particles with the atomic force microscope

Forces between individual colloidal particles can be measured with the atomic force microscope (AFM), and this technique permits the study of interactions between surfaces across aqueous solutions in great detail. The most relevant forces are described by the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory, and they include electrostatic double-layer and van der Waals forces. In symmetric systems, the electrostatic forces are repulsive and depend strongly on the type and concentration of the salts present, while van der Waals forces are always attractive. In asymmetric systems, the electrostatic force can become attractive as well, even when involving neutral surfaces, while in rare situations van der Waals forces can become repulsive too. The enormous sensitivity of the double layer forces on additives present is illustrated with oppositely charged polyelectrolytes, which may induce attractions or repulsions depending on their concentrations.     

Long-term assessment of the implant titanium material—artificial saliva interface

This paper studies the long-term (20,000 exposure hours) behavior of titanium and Ti–5Al–4V alloy—Carter–Brugirard saliva interface and the short-term (500 exposure hours) resistance of titanium and Ti–5Al–4V alloy—Tani&Zucchi saliva interface. Potentiodynamic polarization method was applied for the determination of the main electrochemical parameters. Linear polarization measurements for to obtain the corrosion rates were used. Monitoring of the open circuit potentials (E _oc) for long-term have permitted to calculate the potential gradients due to the pH, ΔE _oc(pH) and to the saliva composition ΔE _oc(c) changes which can appear “in vivo” conditions and can generate local corrosion. Atomic force microscopy (AFM) has analyzed the surface roughness. Ion release was studied by atomic absorption spectroscopy (AAS). In Carter–Brugirard saliva both titanium and Ti–5Al–4V alloy present very stable passive films, long-term stability, “very good” resistance, low values of the open circuit potential gradients, which cannot generate local corrosion. In Tani&Zucchi artificial saliva, pitting corrosion and noble pitting protection potentials (which cannot be reached in oral cavity) were registered; titanium ion release is very low; surface roughness increase in time and in the presence of the fluoride ions, denoting some increase in the anodic activity.     

The micro-tube heat transfer and fluid flow of water based Al2O3 nanofluid with viscous dissipation

The numerical modeling of the conjugate heat transfer and fluid flow of Al₂O₃/water nanofluid through the micro-tube was presented in the paper. The laminar flow regime was considered along with viscous dissipation effect. The diameter ratio of the micro-tube was D_i/D_o = 0.1/0.3 mm with a tube length L = 100 mm. The heat transfer rate was fixed to Q = 0.5 W with three different Br = 0.1, 0.5 and 1. The water based Al₂O₃ nanofluid was considered with various volume concentrations of Al₂O₃ particles ? = 1, 4, 6, 9% and two diameters of the particles D_p = 10 nm and 47 nm. The analysis was performed on the results for local heat transfer coefficient.     

Transport and Magnetic Properties of Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6O x /(LiCl) y Superconductors

We investigated the superconducting critical temperature, the intra- and intergranular critical current density, and the thermopower properties of Bi_1.7Pb_0.4Sr_1.5Ca_2.5Cu_3.6O _x /(LiCl) _y samples. All these properties have been compared with those of Bi_1.7Pb_0.4Sr_1.5Ca_2.5Cu_3.6O _x /(LiF) _y specimens. It was found that the critical temperature determined from resistive and AC complex susceptibility measurements show a maximum and the transition width shows a minimum for the intermediate values of y. Powder X-ray diffraction studies and the AC complex susceptibility measurements reveal that in our samples the amount of Bi₂Sr₂Ca₂Cu₃O_{10 + δ} high-temperature superconducting phase is maximum for y ≈ 0.02. The amount of LiCl in Bi_1.7Pb_0.4Sr_1.5Ca_2.5Cu_3.6O _x /(LiCl) _y changes the superconducting properties of the grains as well as of the intergrain matrix. The splitting of the peak in the temperature dependence of the imaginary part of the complex susceptibility, corresponding to the dissipation inside the grains, was also observed.