Ultrasonic-Assisted Dry Creep-Feed Up-Grinding of Superalloy Inconel738LC

Among many machining methods, grinding is the most applicable one for cutting hard-to-cut materials such as superalloys. In this research, effects of longitudinal ultrasonic vibration of workpiece (Inconel738LC) in dry creep-feed up-grinding process were investigated. Mechanism of abrasive grain and workpiece surface interaction and the consequences have been analyzed both analytically and numerically. Then, the results have been compared with experimental findings. Analytical calculations showed that there is a multiple and discontinuous cutting along the contact zone of grinding wheel and the workpiece when longitudinal ultrasonic vibration is used. Two-dimensional finite element modeling in commercial MSC.Superform software, showed the same behavior and results. Grinding forces are one of the major output parameters for evaluations. It was observed that, application of ultrasonic vibration can decrease grinding forces. A practical decrease of up to 27% of vertical grinding forces and up to 22% of horizontal grinding forces has been achieved when using ultrasonic vibration. Finite-Element analysis has shown a reduction of about 40% of grinding forces compared with ordinary grinding. Probable lower risks of thermal damage even for working under dry conditions can be a big advantage of using ultrasonic with grinding.     

Generic tropical initial ideals of Cohen-Macaulay algebras

We study the generic tropical initial ideals of a positively graded Cohen-Macaulay algebra R over an algebraically closed field k. Building on work of Römer and Schmitz, we give a formula for each initial ideal, and we express the associated quasivaluations in terms of certain I-adic filtrations. As a corollary, we show that in the case that R is a domain, every initial ideal coming from the codimension 1 skeleton of the tropical variety is prime, so “generic presentations of Cohen-Macaulay domains are well-poised in codimension 1.”     

Surfactant-Free Hydrothermal Synthesis of Mesoporous Niobia Samples and Their Photoinduced Decomposition of Terephthalic Acid (TPA)

This study introduces a low temperature surfactant-free hydrothermal method to synthesize mesoporous Nb₂O₅ photocatalysts using NbCl₅ and H₂O₂ as precursors that are subsequently calcinated at 300, 400 and 450 °C and are assigned as mNb₂O₅-300, mNb₂O₅-400 and mNb₂O₅-450, respectively. Commercial niobia sample was used as reference sample for comparison purpose. All of materials were characterized by XRD, SEM, UV–Vis DRS, FTIR, TG/DTG and BET techniques. The synthesized Nb₂O₅ particles especially mNb₂O₅-300 sample shows a high surface area (240 m²/g), a large pore volume (0.21 cm³/g) and an identifying morphology of these features. Photocatalytic decomposition of terephthalic acid was evaluated using UV–Vis spectrophotometer. The photocatalytic reactions followed pseudo-first-order kinetics with an apparent rate constant of k = 105 × 10^?3 min^?1 for mNb₂O₅-300 sample with the highest activity among all samples at natural pH (pH = 6). Meanwhile, it was observed that optimum pH of 4 resulted in fast photocatalytic reaction for mNb₂O₅-300 sample.     

Theoretical investigation of the nature and strength of simultaneous interactions of π–π stacking and halogen bond including NMR,SAPT, AIM and NBO analysis

Ab initio MP2/aug-cc-pVDZ calculations were performed to investigate mutual effect between π–π stacking and halogen bond interactions in X-ben||pyr···Cl–F complexes (X = CN, F, Cl, Br, CH₃, OH and H where || and ··· denote π–π stacking and halogen bonds). The results indicate the cooperativity of π–π stacking and halogen bonds in these complexes. This effect was discussed in terms of the energetic, geometrical parameters and charge-transfer properties of the complexes. To explore on the two-bonded spin–spin coupling constant ^2X J(N–F) across ¹⁵N···³⁵Cl–¹⁹F halogen bond in X-ben||pyr···Cl–F complexes, NMR calculations were performed at PBE0/aug-cc-pVDZ levels of theory. To get more insight into the physical nature of the binding energies, Symmetry Adapted Perturbation Theory calculations were carried out. Energy decomposition indicates that the percentage of the electrostatic term in the halogen bonding system constitutes approximately half of the total attractive binding energies, while the percentage of the dispersion term in the π–π stacking complexes constitutes approximately half of the attractive binding energies. In addition, atoms in molecules, natural bond orbital and molecular electrostatic potential were also used to probe the π–π stacking interactions and halogen bonding strengths.     

Cyanuric chloride as promoter for the oxidation of sulfides and deoxygenation of sulfoxides

This Letter discusses the use of cyanuric chloride as an efficient promoter for the chemoselective oxidation of sulfides to the corresponding sulfones in the presence of H₂O₂ as the terminal oxidant. Sulfoxides were also found to undergo deoxygenation to sulfides with cyanuric chloride and potassium iodide system. The reaction is broad in scope and easy to perform.     

Novel cationic surfactant ion pair based solid phase microextraction fiber for nano-level analysis of BTEX

Ion pair of cationic surfactant (cetytrimethylammonium bromide) and tungestosilicic acid incorporated in PVC matrix, was used for coating a piece of copper wire as a new high sensitive SPME fiber in extraction and determination of BTEX compounds from the headspace of water samples prior to GC/FID analysis. Under optimum extraction conditions, limits of detection for benzene, toluene, ethylbenzene, p-xylene, m-xylene and o-xylene were found to be 1.18, 5.61, 0.87, 0.29, 0.22 and 0.33 ng L(-1) respectively. Low detection limits, wide linear dynamic ranges, good reproducibility (RSD% 1.48-4.27), high fiber capacity and high mechanical durability are some of the most important advantages of the new fiber.     

A novel approach towards dethioacetalization reactions with H2O2-SOCl2 system

A simple and efficient protocol for the deprotection of dithioacetal,1,3-dithianes and 1,3-dithiolanes has been developed using H₂O₂-SOC1₂ reagent system.In addition to the absence of overoxidation products for oxidation-prone substrates,high chemoselectivity, the low cost and availability of the reagents,simplicity of the method,short reaction times,and excellent yields can also be considered as strong points for this method.     

Application of hollow fiber-supported liquid-phase microextraction coupled with HPLC for the determination of guaifenesin enantiomer-protein binding

A hollow fiber liquid-phase microextraction technique coupled with high-performance liquid chromatography with fluorescence detection was employed for determination and evaluation of the binding characteristics of drugs to bovine serum albumin (BSA). Enantiomers of guaifenesin (an expectorant drug) were investigated as a model system. After optimization of some influencing parameters on microextraction, the proposed method was used for calculation of the target drug distribution coefficient between n-octanol and the buffer solution as well as study of drug-BSA binding in physiological conditions. The developed method shows a new, improved and simple procedure for determination of free drug concentration in biological fluids and the extent of drug-protein binding.     

Numerical study of melting inside concentric and eccentric horizontal annulus

This paper presents numerical investigations on melting of phase change material using N-eicosane inside a cylindrical container. Numerical simulations are performed for symmetric melting of phase change material between two cylinders in concentric and eccentric arrays using the FLUENT software which is sub-cooled initially to 1 °C. Inner cylindrical tube is considered hot wall while outer tube is insulated. Predicted result shows that melting rate is the same approximately for concentric and eccentric array before time of 15 min. After this time, melting rate decreases in concentric array. It is due to the pure conduction between hot tube and cold solid phase change material.     

Kinetic modeling of pyrolysis of scrap tires

The disposal of used tires is a major environmental problem. With increasing interest on recovery of wastes, pyrolysis is considered as an alternative process for recovering some of the value in scrap tires. An accurate kinetic model is required to predict product yields during thermal or catalytic pyrolysis of scrap tires. Pyrolysis products contain a variety of hydrocarbons over a wide boiling range. A common approach for kinetic modeling of such complex systems is lumping where each lump is defined by a boiling point range. Available experimental data for thermal and catalytic pyrolysis of scrap tires from the literature were used to evaluate two types of lumping models; discrete and continuous lumping models. The lumps were described in terms of the boiling point distribution of the reactant mixture. In the discrete model, the conversion of heavier to lighter lumps was described in terms of series and parallel first order reactions. In the continuous model, the normalized boiling point was used to describe the reactant mixture as a continuous mixture. An optimization procedure was implemented for estimation of the model parameters using experimental data reported in the literature. Model predictions with indicated that although the discrete model could reasonably predict the yields of different cuts in the products, predictions of the continuous model were very good, especially in thermal pyrolysis.