Modeling and active control of chatter vibrations of piezoelectric stacked machining arm in micro-turning process

Self-excited vibrations known as chatter are considered as the most detrimental issue in micro-turning processes. Occurring unpredictably, they adversely affect the tool life, productivity rate and surface quality of the machining processes. In this paper, a novel machining arm is modeled as a piezoelectric stacked rod which is subjected to a chatter force in the orthogonal micro-turning process. Due to the fact that machining processes are affected by various sources of uncertainties, H_∞ robust control approach is used to suppress the chatter vibrations of the machining arm in the presence of tool wear and dynamic model parameter variations. Also, input control force of the system is provided by exciting the input voltage of piezoelectric layers of the rod. In order to be certain that the designed controller succeeds in suppressing vibrations of the effective structural modes, behavior of the first three modes of vibrations are considered in the final response of the machining arm. In the following, performance of the robust H_∞ controller is compared with a modified PID controller. Simulation results show that the H_∞ controller improves the robustness and performance of the system against uncertainties. The PID controller extends the stability region of the sharp tool and fails to achieve this purpose for the worn tool although its performance is acceptable in suppressing chatter vibrations.

     

Investigation of the effect of the added mass fluctuation and lateral vibration absorbers on the vertical nonlinear vibrations of the offshore wind turbine

Nonlinear Dynamics - In this article, the effects of the changes in the mass of the floating wind turbine (as a multi-body system) on its nonlinear vertical vibrations are investigated. The...     

Ultrasound-promoted green synthesis of 1,4-dihydropyridines using fuctionalized MWCNTs as a highly efficient heterogeneous catalyst

A new method for multi-component synthesis of 1,4-dihydropyridine derivatives (1,4-DHPs) in the presence of meglumine supported on multiwalled carbon nanotubes (MWCNTs@meglumine) as a new heterogeneous, highly efficient and reusable catalyst was investigated. The reaction was performed under ultrasonic irradiation in EtOH at room temperature. A new, highly efficient heterogeneous catalyst, short reaction times, high to excellent yield of products, and safe and clean conditions are the advantages of the presented method.     

Extraction and separation of zirconium from hafnium by using nano-structured supramolecular solvent microextraction method

In the present study, a simple versatile extraction method based on supramolecular solvent microextraction followed by inductively coupled plasma atomic emission spectrometry was developed for the extraction, separation and determination of zirconium (Zr) from hafnium (Hf). Zr and Hf were complexed with bis(2,4,4-trimethylpentyl) phosphinic acid, to obtain hydrophobic complex, and extracted into supramolecular solvent phase. The effective parameters on the supramolecular solvent microextraction efficiency were studied and optimized by using two different optimization methods: one variable at a time and central composite design. Under the optimum conditions, the linear range of 0.3–200.0 and 2.0–200.0 µg L^?1, detection limits (S/N = 3) of 0.1 and 0.6 µg L^?1, and precisions (n = 5) of 3.2–4.9% and 3.0–5.1% were obtained for Zr and Hf, respectively. Finally, the proposed method has been successfully applied for the extraction and separation of these cations in zirconium ore sample.     

A novel inorganic–organic nanohybrid material SBA-15@triazine/H<Subscript>5</Subscript>PW<Subscript>10</Subscript>V<Subscript>2</Subscript>O<Subscript>40</Subscript> as efficient catalyst for the one-pot multicomponent synthesis of multisubstituted pyridines

A novel inorganic–organic nanohybrid material SBA-15@triazine/H₅PW₁₀V₂O₄₀ (SBA-15@ADMPT/H₅PW₁₀V₂O₄₀) was prepared and used as an efficient, eco-friendly, and highly recyclable catalyst for the one-pot multicomponent synthesis of multisubstituted pyridines from the reaction of aldehydes, cyclic ketones, malononitrile, and ammonium acetate with good to excellent yields (77–97%). The nanohybrid catalyst was prepared by the chemical anchoring of Keggin heteropolyacid H₅PW₁₀V₂O₄₀ onto the surface of SBA-15 mesoporous silica modified with 2-APTS -4,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1,3,5-triazine (ADMPT) linker. Standard characterization data such as FT-IR, XRD, SEM, TEM, BET, EDX, and DTA-TGA spectroscopy confirmed that the heteropolyacid H₅PW₁₀V₂O₄₀ is well dispersed on the surface of the solid support and its structure is preserved after immobilization on the SBA-15 mesoporous silica modified with ADMPT. Furthermore, the nanocatalyst can be recovered easily and reused five times without considerable loss of catalytic activity. In general, these advantages highlight this protocol as an attractive and useful methodology, among the other methods reported in the literature, for the eco-friendly and rapid synthesis of biologically active multisubstituted pyridines.     

Efficient synthesis of N,N′-dialkyl-N″-dialkylaminocarbothioyl thioureas from cyclic secondary amines, CS2, and N,N′-dialkyl carbodiimides in water

A mild, convenient, and practical one-pot procedure for direct synthesis of N,N′-dialkyl-N″-dialkylaminocarbothioyl thioureas is described via three-component reaction of cyclic secondary amines, CS₂, and N,N′-dialkyl carbodiimides in water at room temperature.     

Effect of Aqueous Ablation Environment on the Characteristics of ZnO Nanoparticles Produced by Laser Ablation

Effect of ablation environment on the nature of ZnO nanoparticles produced by laser ablation method in liquid medium is investigated experimentally. High purity Zn plate was irradiated by the fundamental beam of a Q-switch Nd-YAG laser in cetyltrimethylammonium bromide (CTAB), acetone, sodium dodecyl sulfate and water. Produced nanoparticles were characterized by UV–Vis absorption spectroscopy, transmission electron microscopy, scanning electron microscopy, X-ray diffraction spectrum, and fourier transform infrared spectroscopy. Results show that the highest rate of ablation occurs in CTAB. Largest nanoparticles are produced in acetone, and crystallinity of nanoparticles produced in CTAB is higher than other samples. CTAB surfactant changed the morphology of ZnO nanoparticles.     

Existence of one weak solution for p(x)-biharmonic equations with Navier boundary conditions

We study the existence of at least one weak solution for a class of elliptic Navier boundary value problems involving the p(x)-biharmonic operator. Our technical approach is based on variational methods. In addition, an example to illustrate our results is given.     

Hydration dynamics and time scales of coupled water-protein fluctuations

We report experimental and theoretical studies on water and protein dynamics following photoexcitation of apomyoglobin. Using site-directed mutation and with femtosecond resolution, we experimentally observed relaxation dynamics with a biphasic distribution of time scales, 5 and 87 ps, around the site Trp7. Theoretical studies using both linear response and direct nonequilibrium molecular dynamics (MD) calculations reproduced the biphasic behavior. Further constrained MD simulations with either frozen protein or frozen water revealed the molecular mechanism of slow hydration processes and elucidated the role of protein fluctuations. Observation of slow water dynamics in MD simulations requires protein flexibility, regardless of whether the slow Stokes shift component results from the water or protein contribution. The initial dynamics in a few picoseconds represents fast local motions such as reorientations and translations of hydrating water molecules, followed by slow relaxation involving strongly coupled water-protein motions. We observed a transition from one isomeric protein configuration to another after 10 ns during our 30 ns ground-state simulation. For one isomer, the surface hydration energy dominates the slow component of the total relaxation energy. For the other isomer, the slow component is dominated by protein interactions with the chromophore. In both cases, coupled water-protein motion is shown to be necessary for observation of the slow dynamics. Such biologically important water-protein motions occur on tens of picoseconds. One significant discrepancy exists between theory and experiment, the large inertial relaxation predicted by simulations but clearly absent in experiment. Further improvements required in the theoretical model are discussed.