DFT/TDDFT Investigation of Electronic,Magnetic, and Optical Properties of Graphene Containing Different Values of Se Impurity

Physics of the Solid State - The electronic, magnetic, and optical properties of graphene (gr) containing selenium impurities of 2, 3, 5.5, and 12.5% were calculated by DFT. By increasing the...     

Cetyl‐alcohol‐reinforced hollow fiber solid/liquid‐phase microextraction and HPLC–DAD analysis of ezetimibe and simvastatin in human plasma and urine

A new cetyl‐alcohol‐reinforced hollow fiber solid/liquid‐phase microextraction (CA–HF–SLPME) followed by high‐performance liquid chromatography–diode array detection (HPLC–DAD) method was developed for simultaneous determination of ezetimibe and simvastatin in human plasma and urine samples. To prepare the CA–HF–SLPME device, the cetyl‐alcohol was immobilized into the pores of a 2.5 cm hollow fiber micro‐tube and the lumen of the micro‐tube was filled with 1‐octanol with the two ends sealed. Afterwards, the prepared device was introduced into 10 mL of the sample solution containing the analytes with agitation. Under optimized conditions, calibration curves plotted in spiked plasma and urine samples were linear in the ranges of 0.363–25/0.49–25 μg L^?1 for ezetimibe/simvastatin and 0.193–25/0.312–25 μg L^?1 for ezetimibe/simvastatin in plasma and urine samples, respectively. The limit of detection was 0.109/0.174 μg L^?1 for ezetimibe/simvastatin in plasma and 0.058/0.093 μg L^?1 for ezetimibe/simvastatin in urine. As a potential application, the proposed method was applied to determine the concentration of selected analytes in patient plasma and urine samples after medication and satisfactory results were achieved. In comparison with reference methods, the CA–HF–SLPME–HPLC–DAD method demonstrates considerable potential in the biopharmaceutical analysis of selected drugs.     

Role of sodium decoration on the methane storage properties of BC3 nanosheet

First-principles calculations including dispersion correction are carried out to investigate pristine and Na-decorated graphene-like BC₃ (h-BC₃) for their application as methane storage materials. Structural optimization shows that the methane is physisorbed on the pristine sheet via van der Waals forces with adsorption energy of ?2.7 kcal/mol. It was found that unlike the pristine graphene, sodium decorated sheet can effectively interact with the CH₄ molecule, so that each metal atom bound on sheet may adsorb up to four CH₄. Furthermore, no bond dissociation was observed for the adsorption of CH₄ on Na-decorated h-BC₃, which means that decorated sheet can act as a storage device for methane safety storage. The results indicate that decoration of the Na atom on surface of sheet induces significant changes in electronic properties of the sheet and its E _g is unchanged after adsorption of CH₄ molecules. Theoretical methane storage capacity of Na-decorated BC₃ nanosheet could approach 18.1 wt%.     

MWCNTs@NHBut/PTA: New efficient solid acid catalyst for solvent free synthesis of benzochromenopyrimidines

In this study, a novel and eco‐friendly synthesis of benzochromenopyrimidines catalyzed by phosphotugstic acid immobilized on aminated multiwalled carbon nanotubes (MWCNTs@NHBut/PTA) is reported. New solid acid catalyst was prepared through a simple process with good percentage of organo metallic groups and characterized with FTIR, TEM, SEM, EDX and TGA techniques. Reusable catalytic system provides a convenient, safe and green pathway to generate a variety of benzochromenopyrimidines under mild conditions.     

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...     

聚多巴胺功能化硅胶沉积单分散Pd纳米粒子的简易原位合成及用作醇需氧氧化反应的多相可循环使用的纳米催化剂（英文）

本文报道了一种不使用任何稳定剂或还原剂,原位合成硅胶/聚多巴胺复合物(SiO_2/PDA)负载的Pd纳米颗粒(Pd NPs)的简易方法.该方法先将PDA涂覆的SiO_2颗粒浸在Pd镀液中,然后利用PDA中含N基团的还原能力将Pd物种原位还原为纳米簇合物.并采用高分辨透射电镜、前场扫描电镜、能量散射谱、X射线衍射、X射线光电子能谱、诱导耦合等离子体和红外光谱等手段对所得纳米复合物的结构、形貌和物化性质进行了表征.被PDA基团锚合的Pd NPs具有显著的小颗粒(30–40 nm)特性.作为一个可循环使用的纳米催化剂,SiO_2/PDA/Pd NPs在醇的需氧氧化反应中表现出高活性.另外,催化剂经回收和多次重复使用时未出现明显的失活.     

Electrochemical Investigation of Activated Carbon Electrode Supercapacitors

Supercapacitors, also called as ultracapacitors, are electrochemical energy-storage devices that exploit the electrostatic interaction between high-surface-area nanoporous electrodes and electrolyte ions, combining properties of conventional batteries and conventional capacitors. A symmetrical activated carbon (AC) electrode supercapacitor has been fabricated in a simple and inexpensive manner. The AC has been synthesized from Charcoal, has activated in a furnace at high temperatures. The electrode was fabricated by casting slurry made of AC and blended in a polymer solution on the counter electrode (current collector), appeared to have high mechanical strength. The electrochemical performance of the prepared samples was tested in 1 M KCl solution by cyclic voltammetry (CV), galvanostatic charge discharge technique, and impedance spectroscopy. The surface and cross-section of electrode was observed with SEM. Capacitance of fabricated supercapacitor has a favorable capacitance in the range of 65–70 F/g with low resistance. The AC electrode supercapacitor has excellent electro chemical reversibility, good cycle stability with a low fading rate of specific capacitance even after 500 cycles, which is promising for energy storage applications.     

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.