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.     

Evaluation of Activation Energies for Pairwise and Non-Pairwise Hydrogen Addition to Propyne Over Pd/Aluminosilicate Fiberglass Catalyst by Parahydrogen-Induced Polarization (PHIP)

Hydrogenation of propyne to propene over Pd/aluminosilicate fiberglass catalyst in the temperature range 175–350 °C was investigated with the use of parahydrogen-induced polarization (PHIP) technique. Activation energies for both pairwise and non-pairwise H₂ addition routes were estimated. It was found that at 175–275 °C the activation energies for hydrogen addition to the triple bond of propyne have similar values (about 60–70 kJ/mol) for both routes of hydrogen addition. At higher temperatures (275–350 °C), the rate constant for pairwise hydrogen addition reaches a maximum value while the rate constant for non-pairwise hydrogen addition continues to increase with increasing temperature.     

Thermodynamic analysis of nanoparticle size effect on kinetics in Fischer–Tropsch synthesis by lanthanum promoted iron catalyst

The kinetic parameters of the Fischer–Tropsch synthesis (FTS) on iron catalyst are analyzed by size-dependent thermodynamic method. A Langmuir–Hinshelwood kinetic equation is considered for evaluation of catalytic activity of lanthanum promoted iron catalyst. A series of unsupported iron catalysts with different particle sizes were prepared via microemulsion method. The experimental results showed that catalyst activity pass from a maximum value by increasing the iron particle size. Also, data presented that iron particle size has considerable effects on adsorption parameters and FTS rates. The ratio of surface tension (σ) to nanoparticle radius (r) is important in FTS reaction on iron catalyst. Finally, the results showed that by increasing of iron particle size from 18 to 45 nm the activation energies of catalysts and heats of adsorption of catalysts as two main parameters of FTS reaction increased from 89 to 114 kJ/mol and from 51 to 71 kJ/mol, respectively.     

Thermal Degradation Kinetics of Plasticized Poly (Vinyl Chloride) with Six Different Plasticizers

Plasticized PVC formulated with different kinds of normally used plasticizers, including bis(2-ethylhexyl) phthalate (DOP), dioctyl terephthalate (DOTP), acetyl tri-n-butyl citrate (ATBC), acetyl trioctyl citrate (ATOC), trioctyl trimellitate (TOTM), and a new vegetable devived plasticizer, isosorbide ester (ID-37), were prepared by a melt blending method. The effect of plasticizer on the thermal degradation behavior of plasticized PVC was investigated by thermal gravimetric analysis (TGA). The activation energies were calculated by three well known methods, developed by Flynn-Wall-Ozawa (FWO), Friedman and Kissinger, respectively. The TGA conducted in N₂ atmosphere showed that the type of plasticizer had an obvious influence on the thermal stability of plasticized PVC. It was found that the peak temperatures (T_P) of the thermal degradation processes shifted to higher temperature with the increase of the heating rate, with two processes being shown. The activation energy of the first thermal decomposition process (E₁), calculated by the Kissinger method, was between 118 and 130 kJ/mol, while the activation energy of the second thermal decomposition process (E₂) was between 261 and 305 kJ/mol, except 499 kJ/mol for the PVC/TOTM formulation. The corresponding values of E₁ and E₂ obtained by the Flynn-Wall-Ozawa method were similar to the above data. E of the sample with TOTM also showed a higher value than the others; the results demonstrated that the PVC plasticized with TOTM was more thermally stable than with the others. The activation energies for certain conversion degrees were calculated by the Friedman method and the FWO method. The value of activation energy for 20%, 50%, and 80% conversion calculated by the Friedman method, exhibited an apparent difference from that calculated by the Flynn-Wall-Ozawa method; the results showed that the value of E obtained by the Friedman method was much more reasonable than that obtained by the Flynn-Wall-Ozawa method.     

The iron mineral changes occurring in lignite coal during gasification

Representative lignite and gasified material samples were retrieved form a cooled down gasifier. The samples were taken at various heights in the gasifier that operated on lignite, under stable conditions. The proximate analyses, ash composition and temperature in the gasifier were determined according to standard procedures. The main minerals found in the present investigation were bassanite, illite, quartz, kaolinite, calcite and the only iron bearing mineral was found to be pyrite. The trend in the estimated particle surface temperature profile shows an increase in the drying, pyrolysis, gasification and combustion zones from about 300 °C to just over 900 °C. About 1/3 down the gasifier, an average particle temperature of about 400 °C and particle surface temperature of about 600 °C was measured where pyrite conversion started. About 2/3 down the gasifier, where an average temperature of about 700 °C and particle surface temperature of about 900 °C was measured, all the pyrite was converted and in the bottom part of the gasifier, oxidation of the iron started to play a role and hematite and an iron containing glass formed at an average temperature of > 800 °C and surface temperature of 900 °C.     

Melting of Naphthalene Confined in Mesoporous Silica MCM-41

The ²H nuclear magnetic resonance (NMR) solid-echo spectra of naphthalene molecules as guests in the mesopores of neat MCM-41 with a pore width of 3.3 nm were measured in the temperature regime from 180 to 250 K. A strong reduction of the melting point of the naphthalene molecules by 152 K is observed. The line shape changes in the melting region were simulated with two different models, namely, the model of a narrow distribution of activation energies, which is typical for a crystal-like phase, and a two-phase model. Both models indicate a relatively narrow distribution of melting points of the naphthalene molecules inside the pores, indicative of a rather well-defined structure of the naphthalene molecules inside the pores. This finding supports the proposal of a plastic crystalline phase previously proposed by other groups.     

Kinetics of high-temperature deformation of polycrystalline OFHC copper and the role of dislocation core diffusion

The mechanisms of the high-temperature deformation of oxygen-free high-conductivity (OFHC) copper have been evaluated over a wide temperature (300–950°C) and strain rate (0.001–100?s^?1) regime. The stress–strain behaviour in hot compression is typical of the occurrence of dynamic recrystallization with an initial peak in the flow stress followed by a steady state, preceded by oscillations at lower strain rates and higher temperatures. The results are analysed using the kinetic rate equation involving a hyperbolic sine relation of the steady-state flow stress with the strain rate. In the temperature and strain rate range covering 500–950°C and 0.001–10?s^?1, a stress exponent of 5 and an apparent activation energy of 145?kJ/mol were evaluated from this analysis. The power law relationship also yielded similar values (5.18 and 152?kJ/mol, respectively). On the basis of these parameters, the rate-controlling mechanism is suggested to be dislocation core diffusion. The flow stress for the OFHC copper data reported by earlier investigators for different oxygen contents is consistent with the above analysis and revealed that an oxygen content of less than about 40?ppm does not have any significant effect on the core diffusion since it is too low to ‘clog’ the dislocation pipes. At strain rates greater than 10?s^?1 and in the temperature range 750–950°C, the stress exponent is about 3.5 and the apparent activation energy is 78?kJ/mol, which suggests that the plastic flow is controlled by grain boundary diffusion.     

Kinetics,mechanism and thermodynamics of reactions of CH3NHNH2 with OOH

Reactions between CH₃NHNH₂ and OOH radical were studied using computational methods. The activation energies (E_a) and Gibbs free energies of activation (ΔG^#) were calculated at the MP2 and B3LYP levels of theory. The calculated activation energies of the hydrogen abstraction reactions were less than 100 kJ/mol and those for the substitution reactions were about 150–250 kJ/mol. The calculated activation energies for the intra-molecular hydrogen transfer reactions in CH₃NHNH, CH₂NNH₂ and CH₃NN molecules were 210–250 kJ/mol. Catalytic effect of the water molecule on the intra-molecular hydrogen transfer reactions was studied. It was found that the water molecule decreases the activation energies by about 70–100 kJ/mol. Rate constants of the reactions were calculated using transition state theory in the temperature range of 298–2000 K. Consecutive hydrogen abstraction reactions from CH₃NHNH₂ led to the formation of CH₂NN, which was a very stable molecule.     

A Spectral Study of the Interaction Between Chelerythrine Chloride and Adenosine

Abstract

The possible anticancer mechanisms of chelerythrine (CHE) and its interactions with adenosine were investigated by UV‐visible spectrophotometric and spectrofluorimetric measurements and by thermodynamic calculations. The binding of CHE to adenosine could be characterized by the hypochromic and bathochromic effects in the absorption bands and the quenching of fluorescence intensity. The spectral data were fitted by linear analysis, yielding a binding constant of 8.68×10⁴ L · mol^?1 at 25°C of CHE with adenosine, and a van't Hoff enthalpy of 92.8 kJ/mol for the endothermic interactions. In addition, with ΔG=?28.2 kJ/mol and ΔS=406 J/mol · K, the interactions should be entropy‐driven.     

锐钛矿相纳米TiO2晶体生长动力学及生长过程控制

研究了采用溶胶-凝胶法经由前驱物钛酸四异丙酯水解制备纳米TiO₂结构相变及锐钛矿晶体生长动力学过程. 研究结果表明,在酸性条件下水解,由于高压热处理温度的变化导致锐钛矿向金红石相的结构相变,锐钛矿相纳米TiO₂生长活化能在250℃以下和以上分别为(15.8±4.5)kJ/mol和(80.2±1.0)kJ/mol;而在碱性条件下水解的活化能值为(3.5±0.4)kJ/mol. 在不发生结构相变的条件下,酸性水解条件下锐钛矿相纳米TiO₂生长速 关键词： 2')" href="#">纳米TiO₂ 锐钛矿 生长动力学 溶胶-凝胶法     

Weakly interacting molecular clusters of CO with H2O,SO2, and NO+

Intermolecular interactions in three dimers, CO···H₂O, CO···SO₂, and CO···NO⁺, were studied at the CCSD(T) level of theory, using a series of the augmented correlation consistent polarised basis sets. Interaction energy and its components as well as vibrational spectra for local minima were computed using both harmonic and anharmonic approximations. While CO···H₂O and CO···SO₂ are weakly bound with the binding energies ?7.4 and ?6.4 kJ/mol, CO···NO⁺ is much more stable with the binding energy of ?32.8 kJ/mol corresponding to ΔG = ?4.7 kJ/mol at 254 K.     

Thermal Stability and Degradation Kinetics of Poly(Methyl Methacrylate)/Sepiolite Nanocomposites by Direct Melt Compounding

Poly(methyl methacrylate) (PMMA) nanocomposites based on sepiolite modified with trimethyl hydrogenated tallow amine by an adsorption process were prepared by melt compounding using a corotating twin screw extruder. The morphology and dispersion of sepiolite in the PMMA were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermal stability and the activation energies were investigated by thermogravimetric analysis/differential thermogravimetric (TGA/DTG). The XRD and TEM results show that the sepiolite was dispersed homogeneously in the PMMA matrix at a nanometer scale. The TGA analysis revealed that the addition of sepiolite improved the thermal stability of PMMA. The apparent activation energies were calculated by the method of Flynn–Wall–Ozawa in nitrogen at four different heating rates, showing that sepiolite increased the apparent activation energies by about 20 kJ/mol within the degree of conversion (α) of 0.35–0.9, as compared with the reference PMMA sample.     

Synthesis and evaluation of thermal, electrical, and electrochemical properties of Ba0.5Sr0.5Co0.04Zn0.16Fe0.8O3�C�� as a novel cathode material for IT-SOFC applications

Ba_0.5Sr_0.5[Co_xZn_0.2-x]Fe_0.8O_3?C??, (x?=?0, 0.04, 0.08, 0.12) cathode formulations were successfully synthesized by solid state reactions and the effect of cobalt doping at Zn site of Ba_0.5Sr_0.5Zn_0.2Fe_0.8O_3?C?? (BSZF0.2) on the electrical conductivity, the polarization resistance and electrochemical behavior was evaluated. X-ray diffraction patterns indicate that a single cubic perovskite phase of Ba_0.5Sr_0.4Co_0.8Fe_0.2O_3?C?? oxide is successfully obtained. Ba_0.5Sr_0.5Co_0.04Zn_0.16Fe_0.8O_3?C?? (BSCZF0.16) exhibited a high electrical conductivity of 10 S/cm at 400 °C in comparison to the BSZF0.2 showing 5.5 S/cm. Further, BSCZF0.16 also possess a low polarization resistance as low as 0.22, 0.38, 0.87, and 1.55 ?? cm² at 750, 700, 650, and 600 °C in air, respectively. Accordingly, a low activation energy value of 149.8 kJ/mol for BSCZF0.16 in comparison to 159.4 kJ/mol for BSZF0.2 indicates high catalytic efficiency. Enhancement of desirable properties such as electrical conductivity in combination with low-polarization resistance and low-activation energy values can be attributed to the coexistence of Co and Zn in the B-site of BSCZF0.16 leading to the multivalent states which contributes to the enhanced electron transport properties demonstrating BSCZF0.16 as a better cathode for intermediate temperature solid oxide fuel cells applications.     

Effects of particle size of silica aerogel on its nano-porous structure and thermal behaviors under both ambient and high temperatures

Silica aerogel as the most commonly used aerogel has attracted increasing attention from both academia and industries due to its extraordinary performances and potentials. Through this study, influences of the particle size (38–880 μm) on its nano-porous structure and thermal behaviors were addressed based on a series of experimental tests under both ambient and high temperatures (i.e., 1000 °C). It was known from the experimental results that the fractional densities of samples with particle sizes of 270–880 μm were similar, which were about 40% of the sample with a particle size of 38 μm. The ratio of densification was found decrease to about 10–40% when heating time increased from 10 to 90 min. For those samples with 150 μm or finer particles, SiC crystal with 70.8 nm particles was generated, and the pore shape was slit in the silica aerogel. The Brunauer–Emmett–Teller (BET) surface area, cumulative pore volume, and average pore diameter of those heated samples with over 75 μm diameter were about 40%, 20%, and 50% of those unheated (virgin) samples, respectively. Virgin samples showed 18% lower thermal conductivity for 75 μm particles compared to that of 38 μm, while for the heated samples, 38 μm particles showed a 28% lower thermal conductivity than that with 880 μm. Mixture of silica aerogel and other inorganic material particles are recommended for high-temperature applications, while the silica aerogel with different-sized particles are observed better for applications under ambient temperature.     

Effect of processing on structural features of anodic aluminum oxides

Morphological features of the anodic aluminum oxide (AAO) templates fabricated by electrochemical oxidation under different processing conditions were investigated. The selection of the polishing parameters does not appear to be critical as long as the aluminum substrate is polished adequately prior to the anodization process. AAO layers with a highly ordered pore distribution are obtained after anodizing in 0.6 M oxalic acid at 20 °C under 40 V for 5 minutes suggesting that the desired pore features are attained once an oxide layer develops on the surface. While the pore features are not affected much, the thickness of the AAO template increases with increasing anodization treatment time. Pore features are better and the AAO growth rate is higher at 20 °C than at 5 °C; higher under 45 V than under 40 V; higher with 0.6 M than with 0.3 M oxalic acid.     

Thermally Stable Schiff Base and its Metal Complexes: Molecular Docking and Protein Binding Studies

In this paper, interaction of Schiff base and its metal complexes carrying naphthalene ring in the structure with bovine serum albumin (BSA) were investigated using UV-vis absorption, fluorescence spectroscopies and molecular docking methods. The effect on the binding mechanism and properties of these compounds containing metal-free, iron and copper ions were also investigated. The fluorescence spectroscopy results showed that fluorescence intensity of BSA in the presence of different concentration of ligands was decreased through a static quenching mechanism. Binding constants (KSV, Kbin and Ka) and thermodynamic parameters (ΔG, ΔH and ΔS) for the ligand-protein interactions were also determined. ΔG values of ligand-protein interaction were calculated in the range ? 6.3 to ?5.5 kcal/mol. These negative values showed that binding process is spontaneous and, hydrogen bonding and van der Waals force were main interaction of the protein and ligands. ΔH and ΔS value were also calculated in the range of 1.10 to 1.26 kJ/mol and 0.133 to 0.135 kJ/mol. K, respectively. These positive values indicated that the binding process between ligands and BSA are endothermic and electrostatic interaction, respectively.     

用扩散蒙特卡罗方法研究BH2, B(OH)2, BCl2和BCl的键离解能

采用扩散蒙特卡罗(DMC)方法计算了BH₂, B(OH)₂, BCl₂和BCl的HB-H和HOB-OH的键离解能, 同时也研究了轨道选择和Backflow变换对DMC计算结果的影响． 在Slater-Jastrow DMC(SJ-DMC)计算方法中,当采用B3PW91轨道时得到的HB-H和HOB-OH键离解能分别是359.1±0.12和98.2±0.12 kJ/mol;用B3LYP SJ-DMC计算键离解能得到了与用B3PW91 SJ-DMC方法类似的结果．通过BF-DMC(即在DMC中引入backflow修正)计算得到的HB?H键离解能为369.6±0.12 kJ/mol,也得到了更加接近实验值的HOB-OH键离解能为446.0±1.84 kJ/mol．由DMC的计算结果可以断定HB?H的键离解能的实验值为375.8 kJ/mol．另外还给出了BCl2和BCl的键离解能的计算结果.     

Influence of Al3Ni crystallisation origin particles on hot deformation behaviour of aluminium based alloys

Abstract

Binary Al–Ni, Al–Mg and ternary Al–Mg–Ni alloys containing various dispersions and volume fraction of second-phase particles of crystallisation origin were compressed in a temperature range of 200–500 °C and at strain rates of 0.1, 1, 10, 30 s^?1 using the Gleeble 3800 thermomechanical simulator. Verification of axisymmetric compression tests was made by finite-element modelling. Constitutive models of hot deformation were constructed and effective activation energy of hot deformation was determined. It was found that the flow stress is lowered by decreasing the Al₃Ni particle size in case of a low 0.03 volume fraction of particles in binary Al–Ni alloys. Intensive softening at large strains was achieved in the alloy with a 0.1 volume fraction of fine Al₃Ni particles. Microstructure investigations confirmed that softening is a result of the dynamic restoration processes which were accelerated by fine particles. In contrast, the size of the particles had no influence on the flow stress of ternary Al–Mg–Ni alloy due to significant work hardening of the aluminium solid solution. Atoms of Mg in the aluminium solid solution significantly affect the deformation process and lead to the growth of the effective activation energy from 130–150 kJ/mol in the binary Al–Ni alloys to 170–190 kJ/mol in the ternary Al–Mg–Ni alloy.     

Investigation of the zenith angle dependence of cosmic-ray muons at sea level

Angular distribution of cosmic-ray muons at sea level has been investigated using the Geant4 simulation package. The model used in the simulations was tested by comparing the simulation results with the measurements made using the Berkeley Lab cosmic ray detector. Primary particles’ energy and fluxes were obtained from the experimental measurements. Simulations were run at each zenith angle starting from θ?=?0° up to θ?=?70° with 5° increment. The angular distribution of muons at sea level has been estimated to be in the form I(θ)?=?I(0°) cos ⁿ (θ), where I(0°) is the muon intensity at 0° and n is a function of the muon momentum. The exponent n?=?1.95±0.08 for muons with energies above 1 GeV is in good agreement, within error, with the values reported in the literature.